long-range corrected density: Topics by Science.gov

Sample records for long-range corrected density

Long-range corrected density functional theory with accelerated Hartree-Fock exchange integration using a two-Gaussian operator [LC-ωPBE(2Gau)].

PubMed

Song, Jong-Won; Hirao, Kimihiko

2015-10-14

Since the advent of hybrid functional in 1993, it has become a main quantum chemical tool for the calculation of energies and properties of molecular systems. Following the introduction of long-range corrected hybrid scheme for density functional theory a decade later, the applicability of the hybrid functional has been further amplified due to the resulting increased performance on orbital energy, excitation energy, non-linear optical property, barrier height, and so on. Nevertheless, the high cost associated with the evaluation of Hartree-Fock (HF) exchange integrals remains a bottleneck for the broader and more active applications of hybrid functionals to large molecular and periodic systems. Here, we propose a very simple yet efficient method for the computation of long-range corrected hybrid scheme. It uses a modified two-Gaussian attenuating operator instead of the error function for the long-range HF exchange integral. As a result, the two-Gaussian HF operator, which mimics the shape of the error function operator, reduces computational time dramatically (e.g., about 14 times acceleration in C diamond calculation using periodic boundary condition) and enables lower scaling with system size, while maintaining the improved features of the long-range corrected density functional theory.
Long-range analysis of density fitting in extended systems

NASA Astrophysics Data System (ADS)

Varga, Scarontefan

Density fitting scheme is analyzed for the Coulomb problem in extended systems from the correctness of long-range behavior point of view. We show that for the correct cancellation of divergent long-range Coulomb terms it is crucial for the density fitting scheme to reproduce the overlap matrix exactly. It is demonstrated that from all possible fitting metric choices the Coulomb metric is the only one which inherently preserves the overlap matrix for infinite systems with translational periodicity. Moreover, we show that by a small additional effort any non-Coulomb metric fit can be made overlap-preserving as well. The problem is analyzed for both ordinary and Poisson basis set choices.
Long-range corrected density functional through the density matrix expansion based semilocal exchange hole.

PubMed

Patra, Bikash; Jana, Subrata; Samal, Prasanjit

2018-03-28

The exchange hole, which is one of the principal constituents of the density functional formalism, can be used to design accurate range-separated hybrid functionals in association with appropriate correlation. In this regard, the exchange hole derived from the density matrix expansion has gained attention due to its fulfillment of some of the desired exact constraints. Thus, the new long-range corrected density functional proposed here combines the meta generalized gradient approximation level exchange functional designed from the density matrix expansion based exchange hole coupled with the ab initio Hartree-Fock exchange through the range separation of the Coulomb interaction operator using the standard error function technique. Then, in association with the Lee-Yang-Parr correlation functional, the assessment and benchmarking of the above newly constructed range-separated functional with various well-known test sets shows its reasonable performance for a broad range of molecular properties, such as thermochemistry, non-covalent interaction and barrier heights of the chemical reactions.
Implementation and benchmark of a long-range corrected functional in the density functional based tight-binding method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lutsker, V.; Niehaus, T. A., E-mail: thomas.niehaus@physik.uni-regensburg.de; Aradi, B.

2015-11-14

Bridging the gap between first principles methods and empirical schemes, the density functional based tight-binding method (DFTB) has become a versatile tool in predictive atomistic simulations over the past years. One of the major restrictions of this method is the limitation to local or gradient corrected exchange-correlation functionals. This excludes the important class of hybrid or long-range corrected functionals, which are advantageous in thermochemistry, as well as in the computation of vibrational, photoelectron, and optical spectra. The present work provides a detailed account of the implementation of DFTB for a long-range corrected functional in generalized Kohn-Sham theory. We apply themore » method to a set of organic molecules and compare ionization potentials and electron affinities with the original DFTB method and higher level theory. The new scheme cures the significant overpolarization in electric fields found for local DFTB, which parallels the functional dependence in first principles density functional theory (DFT). At the same time, the computational savings with respect to full DFT calculations are not compromised as evidenced by numerical benchmark data.« less
Long-range-corrected Rung 3.5 density functional approximations

NASA Astrophysics Data System (ADS)

Janesko, Benjamin G.; Proynov, Emil; Scalmani, Giovanni; Frisch, Michael J.

2018-03-01

Rung 3.5 functionals are a new class of approximations for density functional theory. They provide a flexible intermediate between exact (Hartree-Fock, HF) exchange and semilocal approximations for exchange. Existing Rung 3.5 functionals inherit semilocal functionals' limitations in atomic cores and density tails. Here we address those limitations using range-separated admixture of HF exchange. We present three new functionals. LRC-ωΠLDA combines long-range HF exchange with short-range Rung 3.5 ΠLDA exchange. SLC-ΠLDA combines short- and long-range HF exchange with middle-range ΠLDA exchange. LRC-ωΠLDA-AC incorporates a combination of HF, semilocal, and Rung 3.5 exchange in the short range, based on an adiabatic connection. We test these in a new Rung 3.5 implementation including up to analytic fourth derivatives. LRC-ωΠLDA and SLC-ΠLDA improve atomization energies and reaction barriers by a factor of 8 compared to the full-range ΠLDA. LRC-ωΠLDA-AC brings further improvement approaching the accuracy of standard long-range corrected schemes LC-ωPBE and SLC-PBE. The new functionals yield highest occupied orbital energies closer to experimental ionization potentials and describe correctly the weak charge-transfer complex of ethylene and dichlorine and the hole-spin distribution created by an Al defect in quartz. This study provides a framework for more flexible range-separated Rung 3.5 approximations.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Jong-Won; Hirao, Kimihiko, E-mail: hirao@riken.jp

Since the advent of hybrid functional in 1993, it has become a main quantum chemical tool for the calculation of energies and properties of molecular systems. Following the introduction of long-range corrected hybrid scheme for density functional theory a decade later, the applicability of the hybrid functional has been further amplified due to the resulting increased performance on orbital energy, excitation energy, non-linear optical property, barrier height, and so on. Nevertheless, the high cost associated with the evaluation of Hartree-Fock (HF) exchange integrals remains a bottleneck for the broader and more active applications of hybrid functionals to large molecular andmore » periodic systems. Here, we propose a very simple yet efficient method for the computation of long-range corrected hybrid scheme. It uses a modified two-Gaussian attenuating operator instead of the error function for the long-range HF exchange integral. As a result, the two-Gaussian HF operator, which mimics the shape of the error function operator, reduces computational time dramatically (e.g., about 14 times acceleration in C diamond calculation using periodic boundary condition) and enables lower scaling with system size, while maintaining the improved features of the long-range corrected density functional theory.« less
Simple vertex correction improves G W band energies of bulk and two-dimensional crystals

NASA Astrophysics Data System (ADS)

Schmidt, Per S.; Patrick, Christopher E.; Thygesen, Kristian S.

2017-11-01

The G W self-energy method has long been recognized as the gold standard for quasiparticle (QP) calculations of solids in spite of the fact that the neglect of vertex corrections and the use of a density-functional theory starting point lack rigorous justification. In this work we remedy this situation by including a simple vertex correction that is consistent with a local-density approximation starting point. We analyze the effect of the self-energy by splitting it into short-range and long-range terms which are shown to govern, respectively, the center and size of the band gap. The vertex mainly improves the short-range correlations and therefore has a small effect on the band gap, while it shifts the band gap center up in energy by around 0.5 eV, in good agreement with experiments. Our analysis also explains how the relative importance of short- and long-range interactions in structures of different dimensionality is reflected in their QP energies. Inclusion of the vertex comes at practically no extra computational cost and even improves the basis set convergence compared to G W . Taken together, the method provides an efficient and rigorous improvement over the G W approximation.
Beyond BCS pairing in high-density neutron matter

NASA Astrophysics Data System (ADS)

Rios, A.; Ding, D.; Dussan, H.; Dickhoff, W. H.; Witte, S. J.; Polls, A.

2018-01-01

Pairing gaps in neutron matter need to be computed in a wide range of densities to address open questions in neutron star phenomenology. Traditionally, the Bardeen-Cooper-Schrieffer approach has been used to compute gaps from bare nucleon-nucleon interactions. Here, we incorporate the influence of short- and long-range correlations into pairing properties. Short-range correlations are treated including the appropriate fragmentation of single-particle states, and they suppress the gaps substantially. Long-range correlations dress the pairing interaction via density and spin modes, and provide a relatively small correction. We use three different interactions as a starting point to control for any systematic effects. Results are relevant for neutron-star cooling scenarios, in particular in view of the recent observational data on Cassiopeia A.
Dispersion- and Exchange-Corrected Density Functional Theory for Sodium Ion Hydration.

PubMed

Soniat, Marielle; Rogers, David M; Rempe, Susan B

2015-07-14

A challenge in density functional theory is developing functionals that simultaneously describe intermolecular electron correlation and electron delocalization. Recent exchange-correlation functionals address those two issues by adding corrections important at long ranges: an atom-centered pairwise dispersion term to account for correlation and a modified long-range component of the electron exchange term to correct for delocalization. Here we investigate how those corrections influence the accuracy of binding free energy predictions for sodium-water clusters. We find that the dual-corrected ωB97X-D functional gives cluster binding energies closest to high-level ab initio methods (CCSD(T)). Binding energy decomposition shows that the ωB97X-D functional predicts the smallest ion-water (pairwise) interaction energy and larger multibody contributions for a four-water cluster than most other functionals - a trend consistent with CCSD(T) results. Also, ωB97X-D produces the smallest amounts of charge transfer and the least polarizable waters of the density functionals studied, which mimics the lower polarizability of CCSD. When compared with experimental binding free energies, however, the exchange-corrected CAM-B3LYP functional performs best (error <1 kcal/mol), possibly because of its parametrization to experimental formation enthalpies. For clusters containing more than four waters, "split-shell" coordination must be considered to obtain accurate free energies in comparison with experiment.
Compensation of long-range process effects on photomasks by design data correction

NASA Astrophysics Data System (ADS)

Schneider, Jens; Bloecker, Martin; Ballhorn, Gerd; Belic, Nikola; Eisenmann, Hans; Keogan, Danny

2002-12-01

CD requirements for advanced photomasks are getting very demanding for the 100 nm-node and below; the ITRS roadmap requires CD uniformities below 10 nm for the most critical layers. To reach this goal, statistical as well as systematic CD contributions must be minimized. Here, we focus on the reduction of systematic CD variations across the masks that may be caused by process effects, e.g. dry etch loading. We address this topic by compensating such effects via design data correction analogous to proximity correction. Dry etch loading is modeled by gaussian convolution of pattern densities. Data correction is done geometrically by edge shifting. As the effect amplitude has an order of magnitude of 10 nm this can only be done on e-beam writers with small address grids to reduce big CD steps in the design data. We present modeling and correction results for special mask patterns with very strong pattern density variations showing that the compensation method is able to reduce CD uniformity by 50-70% depending on pattern details. The data correction itself is done with a new module developed especially to compensate long-range effects and fits nicely into the common data flow environment.
First-principles supercell calculations of small polarons with proper account for long-range polarization effects

NASA Astrophysics Data System (ADS)

Kokott, Sebastian; Levchenko, Sergey V.; Rinke, Patrick; Scheffler, Matthias

2018-03-01

We present a density functional theory (DFT) based supercell approach for modeling small polarons with proper account for the long-range elastic response of the material. Our analysis of the supercell dependence of the polaron properties (e.g., atomic structure, binding energy, and the polaron level) reveals long-range electrostatic effects and the electron–phonon (el–ph) interaction as the two main contributors. We develop a correction scheme for DFT polaron calculations that significantly reduces the dependence of polaron properties on the DFT exchange-correlation functional and the size of the supercell in the limit of strong el–ph coupling. Using our correction approach, we present accurate all-electron full-potential DFT results for small polarons in rocksalt MgO and rutile TiO2.
A long-range-corrected density functional that performs well for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states.

PubMed

Rohrdanz, Mary A; Martins, Katie M; Herbert, John M

2009-02-07

We introduce a hybrid density functional that asymptotically incorporates full Hartree-Fock exchange, based on the long-range-corrected exchange-hole model of Henderson et al. [J. Chem. Phys. 128, 194105 (2008)]. The performance of this functional, for ground-state properties and for vertical excitation energies within time-dependent density functional theory, is systematically evaluated, and optimal values are determined for the range-separation parameter, omega, and for the fraction of short-range Hartree-Fock exchange. We denote the new functional as LRC-omegaPBEh, since it reduces to the standard PBEh hybrid functional (also known as PBE0 or PBE1PBE) for a certain choice of its two parameters. Upon optimization of these parameters against a set of ground- and excited-state benchmarks, the LRC-omegaPBEh functional fulfills three important requirements: (i) It outperforms the PBEh hybrid functional for ground-state atomization energies and reaction barrier heights; (ii) it yields statistical errors comparable to PBEh for valence excitation energies in both small and medium-sized molecules; and (iii) its performance for charge-transfer excitations is comparable to its performance for valence excitations. LRC-omegaPBEh, with the parameters determined herein, is the first density functional that satisfies all three criteria. Notably, short-range Hartree-Fock exchange appears to be necessary in order to obtain accurate ground-state properties and vertical excitation energies using the same value of omega.
Describing long-range charge-separation processes with subsystem density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solovyeva, Alisa; Neugebauer, Johannes, E-mail: j.neugebauer@uni-muenster.de; Pavanello, Michele, E-mail: m.pavanello@rutgers.edu

2014-04-28

Long-range charge-transfer processes in extended systems are difficult to describe with quantum chemical methods. In particular, cost-effective (non-hybrid) approximations within time-dependent density functional theory (DFT) are not applicable unless special precautions are taken. Here, we show that the efficient subsystem DFT can be employed as a constrained DFT variant to describe the energetics of long-range charge-separation processes. A formal analysis of the energy components in subsystem DFT for such excitation energies is presented, which demonstrates that both the distance dependence and the long-range limit are correctly described. In addition, electronic couplings for these processes as needed for rate constants inmore » Marcus theory can be obtained from this method. It is shown that the electronic structure of charge-separated states constructed by a positively charged subsystem interacting with a negatively charged one is difficult to converge — charge leaking from the negative subsystem to the positive one can occur. This problem is related to the delocalization error in DFT and can be overcome with asymptotically correct exchange–correlation (XC) potentials or XC potentials including a sufficiently large amount of exact exchange. We also outline an approximate way to obtain charge-transfer couplings between locally excited and charge-separated states.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Jong-Won; Hirao, Kimihiko

Long-range corrected density functional theory (LC-DFT) attracts many chemists’ attentions as a quantum chemical method to be applied to large molecular system and its property calculations. However, the expensive time cost to evaluate the long-range HF exchange is a big obstacle to be overcome to be applied to the large molecular systems and the solid state materials. Upon this problem, we propose a linear-scaling method of the HF exchange integration, in particular, for the LC-DFT hybrid functional.
CoFFEE: Corrections For Formation Energy and Eigenvalues for charged defect simulations

NASA Astrophysics Data System (ADS)

Naik, Mit H.; Jain, Manish

2018-05-01

Charged point defects in materials are widely studied using Density Functional Theory (DFT) packages with periodic boundary conditions. The formation energy and defect level computed from these simulations need to be corrected to remove the contributions from the spurious long-range interaction between the defect and its periodic images. To this effect, the CoFFEE code implements the Freysoldt-Neugebauer-Van de Walle (FNV) correction scheme. The corrections can be applied to charged defects in a complete range of material shapes and size: bulk, slab (or two-dimensional), wires and nanoribbons. The code is written in Python and features MPI parallelization and optimizations using the Cython package for slow steps.
Surface calculations with asymptotically long-ranged potentials in the full-potential linearized augmented plane-wave method

NASA Astrophysics Data System (ADS)

Ye, Lin-Hui

2015-09-01

Although the supercell method has been widely used for surface calculations, it only works well with short-ranged potentials, but meets difficulty when the potential decays very slowly into the vacuum. Unfortunately, the exact exchange-correlation potential of the density functional theory is asymptotically long ranged, and therefore is not easily handled by use of supercells. This paper illustrates that the authentic slab geometry, another technique for surface calculations, is not affected by this issue: It works equally well with both short- and long-ranged potentials, with the computational cost and the convergence speed being essentially the same. Using the asymptotically long-ranged Becke-Roussel'89 exchange potential as an example, we have calculated six surfaces of various types. We found that accurate potential values can be obtained even in extremely low density regions of more than 100 Å away from the surface. This high performance allows us to explore the asymptotic region, and prove with clean numerical evidence that the Becke-Roussel'89 potential satisfies the correct asymptotic behavior for slab surfaces, as it does for finite systems. Our finding further implies that the Slater component of the exact exchange optimized effective potential is responsible for the asymptotic behavior, not only for jellium slabs, but for slabs of any type. The Becke-Roussel'89 potential may therefore be used to build asymptotically correct model exchange potentials applicable to both finite systems and slab surfaces.
Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine.

PubMed

Wu, Wei

2014-06-14

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-½) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.
Optical conductivity of an interacting Weyl liquid in the collisionless regime

NASA Astrophysics Data System (ADS)

Roy, Bitan; Juričić, Vladimir

2017-10-01

Optical conductivity (OC) can serve as a measure of correlation effects in a wide range of condensed-matter systems. We show that the long-range tail of the Coulomb interaction yields a universal correction to the OC in a three-dimensional Weyl semimetal σ (Ω ) =σ0(Ω ) [1 +1/N +1 ] , where σ0(Ω ) =N e02Ω /(12 h v ) is the OC in the noninteracting system, with v as the actual (renormalized) Fermi velocity of Weyl quasiparticles at frequency Ω , and e0 is the electron charge in vacuum. Such universal enhancement of OC, which depends only on the number of Weyl nodes near the Fermi level (N ), is a remarkable consequence of an intriguing conspiracy among the quantum-critical nature of an interacting Weyl liquid, marginal irrelevance of the long-range Coulomb interaction, and violation of hyperscaling in three dimensions, and can directly be measured in recently discovered Weyl as well as Dirac materials. By contrast, a local density-density interaction produces a nonuniversal correction to the OC, stemming from the nonrenormalizable nature of the corresponding interacting field theory.
Accuracy of dynamical-decoupling-based spectroscopy of Gaussian noise

NASA Astrophysics Data System (ADS)

Szańkowski, Piotr; Cywiński, Łukasz

2018-03-01

The fundamental assumption of dynamical-decoupling-based noise spectroscopy is that the coherence decay rate of qubit (or qubits) driven with a sequence of many pulses, is well approximated by the environmental noise spectrum spanned on frequency comb defined by the sequence. Here we investigate the precise conditions under which this commonly used spectroscopic approach is quantitatively correct. To this end we focus on two representative examples of spectral densities: the long-tailed Lorentzian, and finite-ranged Gaussian—both expected to be encountered when using the qubit for nanoscale nuclear resonance imaging. We have found that, in contrast to Lorentz spectrum, for which the corrections to the standard spectroscopic formulas can easily be made negligible, the spectra with finite range are more challenging to reconstruct accurately. For Gaussian line shape of environmental spectral density, direct application of the standard dynamical-decoupling-based spectroscopy leads to erroneous attribution of long-tail behavior to the reconstructed spectrum. Fortunately, artifacts such as this, can be completely avoided with the simple extension to standard reconstruction method.
Molecular density functional theory of water describing hydrophobicity at short and long length scales

NASA Astrophysics Data System (ADS)

Jeanmairet, Guillaume; Levesque, Maximilien; Borgis, Daniel

2013-10-01

We present an extension of our recently introduced molecular density functional theory of water [G. Jeanmairet et al., J. Phys. Chem. Lett. 4, 619 (2013)] to the solvation of hydrophobic solutes of various sizes, going from angstroms to nanometers. The theory is based on the quadratic expansion of the excess free energy in terms of two classical density fields: the particle density and the multipolar polarization density. Its implementation requires as input a molecular model of water and three measurable bulk properties, namely, the structure factor and the k-dependent longitudinal and transverse dielectric susceptibilities. The fine three-dimensional water structure around small hydrophobic molecules is found to be well reproduced. In contrast, the computed solvation free-energies appear overestimated and do not exhibit the correct qualitative behavior when the hydrophobic solute is grown in size. These shortcomings are corrected, in the spirit of the Lum-Chandler-Weeks theory, by complementing the functional with a truncated hard-sphere functional acting beyond quadratic order in density, and making the resulting functional compatible with the Van-der-Waals theory of liquid-vapor coexistence at long range. Compared to available molecular simulations, the approach yields reasonable solvation structure and free energy of hard or soft spheres of increasing size, with a correct qualitative transition from a volume-driven to a surface-driven regime at the nanometer scale.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-Ruiz, F. J.; Blas, F. J., E-mail: felipe@uhu.es; Centro de Investigación de Física Teórica y Matemática, Universidad de Huelva, 21071 Huelva

We propose an extension of the improved version of the inhomogeneous long-range corrections of Janeček [J. Phys. Chem. B 110, 6264–6269 (2006)], presented recently by MacDowell and Blas [J. Chem. Phys. 131, 074705 (2009)] to account for the intermolecular potential energy of spherical, rigid, and flexible molecular systems, to deal with the contributions to the microscopic components of the pressure tensor due to the dispersive long-range corrections. We have performed Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of spherical Lennard-Jones molecules with different cutoff distances, r{sub c} = 2.5, 3, 4, and 5σ. In addition,more » we have also considered cutoff distances r{sub c} = 2.5 and 3σ in combination with the inhomogeneous long-range corrections proposed in this work. The normal and tangential microscopic components of the pressure tensor are obtained using the mechanical or virial route in combination with the recipe of Irving and Kirkwood, while the macroscopic components are calculated using the Volume Perturbation thermodynamic route proposed by de Miguel and Jackson [J. Chem. Phys. 125, 164109 (2006)]. The vapour-liquid interfacial tension is evaluated using three different procedures, the Irving-Kirkwood method, the difference between the macroscopic components of the pressure tensor, and the Test-Area methodology. In addition to the pressure tensor and the surface tension, we also obtain density profiles, coexistence densities, vapour pressure, critical temperature and density, and interfacial thickness as functions of temperature, paying particular attention to the effect of the cutoff distance and the long-range corrections on these properties. According to our results, the main effect of increasing the cutoff distance (at fixed temperature) is to sharpen the vapour-liquid interface, to decrease the vapour pressure, and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases, the width of the tangential microscopic component of the pressure tensor profile increases, and the surface tension increases as the cutoff distance is larger. We have also checked the effect of the impulsive contribution to the pressure due to the discontinuity of the intermolecular interaction potential when it is cut. If this contribution is not accounted for in the calculation of the microscopic components of the pressure tensor, incorrect values of both components as well as a wrong structure along the vapour-liquid interface are obtained.« less
Estimation of Ice Surface Scattering and Acoustic Attenuation in Arctic Sediments from Long-Range Propagation Data

DTIC Science & Technology

1984-01-01

frequencies over the calculation at 1 meter. This was corrected by +60 dB to obtain the signature at I meter, and then by -160 dB to obtain the voltage...FFT with appropriate corrections for one-sided energy spectral density re . 1 V2/Hz. The spectrum was then smeared over a 4 Hz band by a running...after correcting the array estimated slownesses for slight bathymetric dip local to the receiving array. A preliminary inversion of this type is given by
Many-body localization in a long range XXZ model with random-field

NASA Astrophysics Data System (ADS)

Li, Bo

2016-12-01

Many-body localization (MBL) in a long range interaction XXZ model with random field are investigated. Using the exact diagonal method, the MBL phase diagram with different tuning parameters and interaction range is obtained. It is found that the phase diagram of finite size results supplies strong evidence to confirm that the threshold interaction exponent α = 2. The tuning parameter Δ can efficiently change the MBL edge in high energy density stats, thus the system can be controlled to transfer from thermal phase to MBL phase by changing Δ. The energy level statistics data are consistent with result of the MBL phase diagram. However energy level statistics data cannot detect the thermal phase correctly in extreme long range case.
The thermochemistry of london dispersion-driven transition metal reactions: getting the 'right answer for the right reason'.

PubMed

Hansen, Andreas; Bannwarth, Christoph; Grimme, Stefan; Petrović, Predrag; Werlé, Christophe; Djukic, Jean-Pierre

2014-10-01

Reliable thermochemical measurements and theoretical predictions for reactions involving large transition metal complexes in which long-range intramolecular London dispersion interactions contribute significantly to their stabilization are still a challenge, particularly for reactions in solution. As an illustrative and chemically important example, two reactions are investigated where a large dipalladium complex is quenched by bulky phosphane ligands (triphenylphosphane and tricyclohexylphosphane). Reaction enthalpies and Gibbs free energies were measured by isotherm titration calorimetry (ITC) and theoretically 'back-corrected' to yield 0 K gas-phase reaction energies (ΔE). It is shown that the Gibbs free solvation energy calculated with continuum models represents the largest source of error in theoretical thermochemistry protocols. The ('back-corrected') experimental reaction energies were used to benchmark (dispersion-corrected) density functional and wave function theory methods. Particularly, we investigated whether the atom-pairwise D3 dispersion correction is also accurate for transition metal chemistry, and how accurately recently developed local coupled-cluster methods describe the important long-range electron correlation contributions. Both, modern dispersion-corrected density functions (e.g., PW6B95-D3(BJ) or B3LYP-NL), as well as the now possible DLPNO-CCSD(T) calculations, are within the 'experimental' gas phase reference value. The remaining uncertainties of 2-3 kcal mol(-1) can be essentially attributed to the solvation models. Hence, the future for accurate theoretical thermochemistry of large transition metal reactions in solution is very promising.
A meta-GGA level screened range-separated hybrid functional by employing short range Hartree-Fock with a long range semilocal functional.

PubMed

Jana, Subrata; Samal, Prasanjit

2018-03-28

The range-separated hybrid density functionals are very successful in describing a wide range of molecular and solid-state properties accurately. In principle, such functionals are designed from spherically averaged or system averaged as well as reverse engineered exchange holes. In the present attempt, the screened range-separated hybrid functional scheme has been applied to the meta-GGA rung by using the density matrix expansion based semilocal exchange hole (or functional). The hybrid functional proposed here utilizes the spherically averaged density matrix expansion based exchange hole in the range separation scheme. For slowly varying density correction the range separation scheme is employed only through the local density approximation based exchange hole coupled with the corresponding fourth order gradient approximate Tao-Mo enhancement factor. The comprehensive testing and performance of the newly constructed functional indicates its applicability in describing several molecular properties. The most appealing feature of this present screened hybrid functional is that it will be practically very useful in describing solid-state properties at the meta-GGA level.
Charge transfer optical absorption and fluorescence emission of 4-(9-acridyl)julolidine from long-range-corrected time dependent density functional theory in polarizable continuum approach.

PubMed

Kityk, A V

2014-07-15

A long-range-corrected time-dependent density functional theory (LC-TDDFT) in combination with polarizable continuum model (PCM) have been applied to study charge transfer (CT) optical absorption and fluorescence emission energies basing on parameterized LC-BLYP xc-potential. The molecule of 4-(9-acridyl)julolidine selected for this study represents typical CT donor-acceptor dye with strongly solvent dependent optical absorption and fluorescence emission spectra. The result of calculations are compared with experimental spectra reported in the literature to derive an optimal value of the model screening parameter ω. The first absorption band appears to be quite well predictable within DFT/TDDFT/PCM with the screening parameter ω to be solvent independent (ω ≈ 0.245 Bohr(-1)) whereas the fluorescence emission exhibits a strong dependence on the range separation with ω-value varying on a rising solvent polarity from about 0.225 to 0.151 Bohr(-1). Dipolar properties of the initial state participating in the electronic transition have crucial impact on the effective screening. Copyright © 2014 Elsevier B.V. All rights reserved.
Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wei, E-mail: wei.wu@ucl.ac.uk

2014-06-14

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-1/2 ) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by themore » long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.« less
Assessing the role of Hartree-Fock exchange, correlation energy and long range corrections in evaluating ionization potential, and electron affinity in density functional theory.

PubMed

Vikramaditya, Talapunur; Lin, Shiang-Tai

2017-06-05

Accurate determination of ionization potentials (IPs), electron affinities (EAs), fundamental gaps (FGs), and HOMO, LUMO energy levels of organic molecules play an important role in modeling and predicting the efficiencies of organic photovoltaics, OLEDs etc. In this work, we investigate the effects of Hartree Fock (HF) Exchange, correlation energy, and long range corrections in predicting IP and EA in Hybrid Functionals. We observe increase in percentage of HF exchange results in increase of IPs and decrease in EAs. Contrary to the general expectations inclusion of both HF exchange and correlation energy (from the second order perturbation theory MP2) leads to poor prediction. Range separated Hybrid Functionals are found to be more reliable among various DFT Functionals investigated. DFT Functionals predict accurate IPs whereas post HF methods predict accurate EAs. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Long Range Materials Research

DTIC Science & Technology

1976-01-01

the "weight In water -weight In air" method. The compact Is first weighed dry and then weighed while Immersed completely In water . The density was...calculated from the following: (Wdry) ^ compact W. - W dry wet (1) where P^-o ^8 ’^ density of water corrected for temperature. The weight wet...PPh9) ’"NXV 2 (4) ’ X CH20TS + EtO e These bonds are easily cleaved by water and alcohols . Thererore, it should be possible to
Critical assessment of density functional theory for computing vibrational (hyper)polarizabilities

NASA Astrophysics Data System (ADS)

Zaleśny, R.; Bulik, I. W.; Mikołajczyk, M.; Bartkowiak, W.; Luis, J. M.; Kirtman, B.; Avramopoulos, A.; Papadopoulos, M. G.

2012-12-01

Despite undisputed success of the density functional theory (DFT) in various branches of chemistry and physics, an application of the DFT for reliable predictions of nonlinear optical properties of molecules has been questioned a decade ago. As it was shown by Champagne, et al. [1, 2, 3] most conventional DFT schemes were unable to qualitatively predict the response of conjugated oligomers to a static electric field. Long-range corrected (LRC) functionals, like LC-BLYP or CAM-B3LYP, have been proposed to alleviate this deficiency. The reliability of LRC functionals for evaluating molecular (hyper)polarizabilities is studied for various groups of organic systems, with a special focus on vibrational corrections to the electric properties.
Molecular Excitation Energies from Time-Dependent Density Functional Theory Employing Random-Phase Approximation Hessians with Exact Exchange.

PubMed

Heßelmann, Andreas

2015-04-14

Molecular excitation energies have been calculated with time-dependent density-functional theory (TDDFT) using random-phase approximation Hessians augmented with exact exchange contributions in various orders. It has been observed that this approach yields fairly accurate local valence excitations if combined with accurate asymptotically corrected exchange-correlation potentials used in the ground-state Kohn-Sham calculations. The inclusion of long-range particle-particle with hole-hole interactions in the kernel leads to errors of 0.14 eV only for the lowest excitations of a selection of three alkene, three carbonyl, and five azabenzene molecules, thus surpassing the accuracy of a number of common TDDFT and even some wave function correlation methods. In the case of long-range charge-transfer excitations, the method typically underestimates accurate reference excitation energies by 8% on average, which is better than with standard hybrid-GGA functionals but worse compared to range-separated functional approximations.
Short-range second order screened exchange correction to RPA correlation energies

NASA Astrophysics Data System (ADS)

Beuerle, Matthias; Ochsenfeld, Christian

2017-11-01

Direct random phase approximation (RPA) correlation energies have become increasingly popular as a post-Kohn-Sham correction, due to significant improvements over DFT calculations for properties such as long-range dispersion effects, which are problematic in conventional density functional theory. On the other hand, RPA still has various weaknesses, such as unsatisfactory results for non-isogyric processes. This can in parts be attributed to the self-correlation present in RPA correlation energies, leading to significant self-interaction errors. Therefore a variety of schemes have been devised to include exchange in the calculation of RPA correlation energies in order to correct this shortcoming. One of the most popular RPA plus exchange schemes is the second order screened exchange (SOSEX) correction. RPA + SOSEX delivers more accurate absolute correlation energies and also improves upon RPA for non-isogyric processes. On the other hand, RPA + SOSEX barrier heights are worse than those obtained from plain RPA calculations. To combine the benefits of RPA correlation energies and the SOSEX correction, we introduce a short-range RPA + SOSEX correction. Proof of concept calculations and benchmarks showing the advantages of our method are presented.
Short-range second order screened exchange correction to RPA correlation energies.

PubMed

Beuerle, Matthias; Ochsenfeld, Christian

2017-11-28

Direct random phase approximation (RPA) correlation energies have become increasingly popular as a post-Kohn-Sham correction, due to significant improvements over DFT calculations for properties such as long-range dispersion effects, which are problematic in conventional density functional theory. On the other hand, RPA still has various weaknesses, such as unsatisfactory results for non-isogyric processes. This can in parts be attributed to the self-correlation present in RPA correlation energies, leading to significant self-interaction errors. Therefore a variety of schemes have been devised to include exchange in the calculation of RPA correlation energies in order to correct this shortcoming. One of the most popular RPA plus exchange schemes is the second order screened exchange (SOSEX) correction. RPA + SOSEX delivers more accurate absolute correlation energies and also improves upon RPA for non-isogyric processes. On the other hand, RPA + SOSEX barrier heights are worse than those obtained from plain RPA calculations. To combine the benefits of RPA correlation energies and the SOSEX correction, we introduce a short-range RPA + SOSEX correction. Proof of concept calculations and benchmarks showing the advantages of our method are presented.
SU-E-T-129: Dosimetric Evaluation of the Impact of Density Correction On Dose Calculation of Breast Cancer Treatment: A Study Based On RTOG 1005 Cases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J; Yu, Y

Purpose: RTOG 1005 requires density correction in the dose calculation of breast cancer radiation treatment. The aim of the study was to evaluate the impact of density correction on the dose calculation. Methods: Eight cases were studied, which were planned on an XiO treatment planning system with pixel-by-pixel density correction using a superposition algorithm, following RTOG 1005 protocol requirements. Four were protocol Arm 1 (standard whole breast irradiation with sequential boost) cases and four were Arm 2 (hypofractionated whole breast irradiation with concurrent boost) cases. The plans were recalculated with the same monitor units without density correction. Dose calculations withmore » and without density correction were compared. Results: Results of Arm 1 and Arm 2 cases showed similar trends in the comparison. The average differences between the calculations with and without density correction (difference = Without - With) among all the cases were: -0.82 Gy (range: -2.65∼−0.18 Gy) in breast PTV Eval D95, −0.75 Gy (range: −1.23∼0.26 Gy) in breast PTV Eval D90, −1.00 Gy (range: −2.46∼−0.29 Gy) in lumpectomy PTV Eval D95, −0.78 Gy (range: −1.30∼0.11 Gy) in lumpectomy PTV Eval D90, −0.43% (range: −0.95∼−0.14%) in ipsilateral lung V20, −0.81% (range: −1.62∼−0.26%) in V16, −1.95% (range: −4.13∼−0.84%) in V10, −2.64% (−5.55∼−1.04%) in V8, −4.19% (range: −6.92∼−1.81%) in V5, and −4.95% (range: −7.49∼−2.01%) in V4, respectively. The differences in other normal tissues were minimal. Conclusion: The effect of density correction was observed in breast target doses (an average increase of ∼1 Gy in D95 and D90, compared to the calculation without density correction) and exposed ipsilateral lung volumes in low dose region (average increases of ∼4% and ∼5% in V5 and V4, respectively)« less
Quantum mechanical/molecular mechanical/continuum style solvation model: time-dependent density functional theory.

PubMed

Thellamurege, Nandun M; Cui, Fengchao; Li, Hui

2013-08-28

A combined quantum mechanical/molecular mechanical/continuum (QM/MMpol/C) style method is developed for time-dependent density functional theory (TDDFT, including long-range corrected TDDFT) method, induced dipole polarizable force field, and induced surface charge continuum model. Induced dipoles and induced charges are included in the TDDFT equations to solve for the transition energies, relaxed density, and transition density. Analytic gradient is derived and implemented for geometry optimization and molecular dynamics simulation. QM/MMpol/C style DFT and TDDFT methods are used to study the hydrogen bonding of the photoactive yellow protein chromopore in ground state and excited state.
Description of plasmon-like band in silver clusters: the importance of the long-range Hartree-Fock exchange in time-dependent density-functional theory simulations.

PubMed

Rabilloud, Franck

2014-10-14

Absorption spectra of Ag20 and Ag55(q) (q = +1, -3) nanoclusters are investigated in the framework of the time-dependent density functional theory in order to analyse the role of the d electrons in plasmon-like band of silver clusters. The description of the plasmon-like band from calculations using density functionals containing an amount of Hartree-Fock exchange at long range, namely, hybrid and range-separated hybrid (RSH) density functionals, is in good agreement with the classical interpretation of the plasmon-like structure as a collective excitation of valence s-electrons. In contrast, using local or semi-local exchange functionals (generalized gradient approximations (GGAs) or meta-GGAs) leads to a strong overestimation of the role of d electrons in the plasmon-like band. The semi-local asymptotically corrected model potentials also describe the plasmon as mainly associated to d electrons, though calculated spectra are in fairly good agreement with those calculated using the RSH scheme. Our analysis shows that a portion of non-local exchange modifies the description of the plasmon-like band.
Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

PubMed

Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

2015-08-11

The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.
Effects of Discrete Charge Clustering in Simulations of Charged Interfaces.

PubMed

Grime, John M A; Khan, Malek O

2010-10-12

A system of counterions between charged surfaces is investigated, with the surfaces represented by uniform charged planes and three different arrangements of discrete surface charges - an equispaced grid and two different clustered arrangements. The behaviors of a series of systems with identical net surface charge density are examined, with particular emphasis placed on the long ranged corrections via the method of "charged slabs" and the effects of the simulation cell size. Marked differences are observed in counterion distributions and the osmotic pressure dependent on the particular representation of the charged surfaces; the uniformly charged surfaces and equispaced grids of discrete charge behave in a broadly similar manner, but the clustered systems display a pronounced decrease in osmotic pressure as the simulation size is increased. The influence of the long ranged correction is shown to be minimal for all but the very smallest of system sizes.
Multiresolution quantum chemistry in multiwavelet bases: excited states from time-dependent Hartree–Fock and density functional theory via linear response

DOE PAGES

Yanai, Takeshi; Fann, George I.; Beylkin, Gregory; ...

2015-02-25

Using the fully numerical method for time-dependent Hartree–Fock and density functional theory (TD-HF/DFT) with the Tamm–Dancoff (TD) approximation we use a multiresolution analysis (MRA) approach to present our findings. From a reformulation with effective use of the density matrix operator, we obtain a general form of the HF/DFT linear response equation in the first quantization formalism. It can be readily rewritten as an integral equation with the bound-state Helmholtz (BSH) kernel for the Green's function. The MRA implementation of the resultant equation permits excited state calculations without virtual orbitals. Moreover, the integral equation is efficiently and adaptively solved using amore » numerical multiresolution solver with multiwavelet bases. Our implementation of the TD-HF/DFT methods is applied for calculating the excitation energies of H 2, Be, N 2, H 2O, and C 2H 4 molecules. The numerical errors of the calculated excitation energies converge in proportion to the residuals of the equation in the molecular orbitals and response functions. The energies of the excited states at a variety of length scales ranging from short-range valence excitations to long-range Rydberg-type ones are consistently accurate. It is shown that the multiresolution calculations yield the correct exponential asymptotic tails for the response functions, whereas those computed with Gaussian basis functions are too diffuse or decay too rapidly. Finally, we introduce a simple asymptotic correction to the local spin-density approximation (LSDA) so that in the TDDFT calculations, the excited states are correctly bound.« less
Auxiliary-fermion approach to critical fluctuations in the two-dimensional quantum antiferromagnetic Heisenberg model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brinckmann, Jan; Woelfle, Peter

2004-11-01

The nearest-neighbor quantum antiferromagnetic (AF) Heisenberg model for spin-1/2 on a two-dimensional square lattice is studied in the auxiliary-fermion representation. Expressing spin operators by canonical fermionic particles requires a constraint on the fermion charge Q{sub i}=1 on each lattice site i, which is imposed approximately through the thermal average. The resulting interacting fermion system is first treated in mean-field theory (MFT), which yields an AF ordered ground state and spin waves in quantitative agreement with conventional spin-wave theory. At finite temperature a self-consistent approximation beyond mean field is required in order to fulfill the Mermin-Wagner theorem. We first discuss amore » fully self-consistent approximation, where fermions are renormalized due to fluctuations of their spin density, in close analogy to FLEX. While static properties like the correlation length, {xi}(T){proportional_to}exp(aJ/T), come out correctly, the dynamical response lacks the magnon-like peaks which would reflect the appearance of short-range order at low T. This drawback, which is caused by overdamping, is overcome in a 'minimal self-consistent approximation' (MSCA), which we derive from the equations of motion. The MSCA features dynamical scaling at small energy and temperature and is qualitatively correct both in the regime of order-parameter relaxation at long wavelengths {lambda}>{xi} and in the short-range-order regime at {lambda}<{xi}. We also discuss the impact of vertex corrections and the problem of pseudo-gap formation in the single-particle density of states due to long-range fluctuations. Finally we show that the (short-range) magnetic order in MFT and MSCA helps to fulfill the constraint on the local fermion occupancy.« less

Residual Defect Density in Random Disks Deposits.

PubMed

Topic, Nikola; Pöschel, Thorsten; Gallas, Jason A C

2015-08-03

We investigate the residual distribution of structural defects in very tall packings of disks deposited randomly in large channels. By performing simulations involving the sedimentation of up to 50 × 10(9) particles we find all deposits to consistently show a non-zero residual density of defects obeying a characteristic power-law as a function of the channel width. This remarkable finding corrects the widespread belief that the density of defects should vanish algebraically with growing height. A non-zero residual density of defects implies a type of long-range spatial order in the packing, as opposed to only local ordering. In addition, we find deposits of particles to involve considerably less randomness than generally presumed.
Long-range correction for tight-binding TD-DFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Humeniuk, Alexander; Mitrić, Roland, E-mail: roland.mitric@uni-wuerzburg.de

2015-10-07

We present two improvements to the tight-binding approximation of time-dependent density functional theory (TD-DFTB): First, we add an exact Hartree-Fock exchange term, which is switched on at large distances, to the ground state Hamiltonian and similarly to the coupling matrix that enters the linear response equations for the calculation of excited electronic states. We show that the excitation energies of charge transfer states are improved relative to the standard approach without the long-range correction by testing the method on a set of molecules from the database in Peach et al. [J. Chem. Phys. 128, 044118 (2008)] which are known tomore » exhibit problematic charge transfer states. The degree of spatial overlap between occupied and virtual orbitals indicates where TD-DFTB and long-range corrected TD-DFTB (lc-TD-DFTB) can be expected to produce large errors. Second, we improve the calculation of oscillator strengths. The transition dipoles are obtained from Slater Koster files for the dipole matrix elements between valence orbitals. In particular, excitations localized on a single atom, which appear dark when using Mulliken transition charges, acquire a more realistic oscillator strength in this way. These extensions pave the way for using lc-TD-DFTB to describe the electronic structure of large chromophoric polymers, where uncorrected TD-DFTB fails to describe the high degree of conjugation and produces spurious low-lying charge transfer states.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Yanai, Takeshi; Fann, George I.; Beylkin, Gregory

Using the fully numerical method for time-dependent Hartree–Fock and density functional theory (TD-HF/DFT) with the Tamm–Dancoff (TD) approximation we use a multiresolution analysis (MRA) approach to present our findings. From a reformulation with effective use of the density matrix operator, we obtain a general form of the HF/DFT linear response equation in the first quantization formalism. It can be readily rewritten as an integral equation with the bound-state Helmholtz (BSH) kernel for the Green's function. The MRA implementation of the resultant equation permits excited state calculations without virtual orbitals. Moreover, the integral equation is efficiently and adaptively solved using amore » numerical multiresolution solver with multiwavelet bases. Our implementation of the TD-HF/DFT methods is applied for calculating the excitation energies of H 2, Be, N 2, H 2O, and C 2H 4 molecules. The numerical errors of the calculated excitation energies converge in proportion to the residuals of the equation in the molecular orbitals and response functions. The energies of the excited states at a variety of length scales ranging from short-range valence excitations to long-range Rydberg-type ones are consistently accurate. It is shown that the multiresolution calculations yield the correct exponential asymptotic tails for the response functions, whereas those computed with Gaussian basis functions are too diffuse or decay too rapidly. Finally, we introduce a simple asymptotic correction to the local spin-density approximation (LSDA) so that in the TDDFT calculations, the excited states are correctly bound.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-Ruiz, F. J.; Blas, F. J., E-mail: felipe@uhu.es; Moreno-Ventas Bravo, A. I.

We determine the interfacial properties of a symmetrical binary mixture of equal-sized spherical Lennard-Jones molecules, σ{sub 11} = σ{sub 22}, with the same dispersive energy between like species, ϵ{sub 11} = ϵ{sub 22}, but different dispersive energies between unlike species low enough to induce phase separation. We use the extensions of the improved version of the inhomogeneous long-range corrections of Janecek [J. Phys. Chem. B 110, 6264 (2006)], presented recently by MacDowell and Blas [J. Chem. Phys. 131, 074705 (2009)] and Martínez-Ruiz et al. [J. Chem. Phys. 141, 184701 (2014)], to deal with the interaction energy and microscopic components ofmore » the pressure tensor. We perform Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of the symmetrical mixture with different cut-off distances r{sub c} and in combination with the inhomogeneous long-range corrections. The pressure tensor is obtained using the mechanical (virial) and thermodynamic route. The liquid-liquid interfacial tension is also evaluated using three different procedures, the Irving-Kirkwood method, the difference between the macroscopic components of the pressure tensor, and the test-area methodology. This allows to check the validity of the recent extensions presented to deal with the contributions due to long-range corrections for intermolecular energy and pressure tensor in the case of binary mixtures that exhibit liquid-liquid immiscibility. In addition to the pressure tensor and the surface tension, we also obtain density profiles and coexistence densities and compositions as functions of pressure, at a given temperature. According to our results, the main effect of increasing the cut-off distance r{sub c} is to sharpen the liquid-liquid interface and to increase the width of the biphasic coexistence region. Particularly interesting is the presence of a relative minimum in the total density profiles of the symmetrical mixture. This minimum is related with a desorption of the molecules at the interface, a direct consequence of a combination of the weak dispersive interactions between unlike species of the symmetrical binary mixture, and the presence of an interfacial region separating the two immiscible liquid phases in coexistence.« less
Combinations of coupled cluster, density functionals, and the random phase approximation for describing static and dynamic correlation, and van der Waals interactions

NASA Astrophysics Data System (ADS)

Garza, Alejandro J.; Bulik, Ireneusz W.; Alencar, Ana G. Sousa; Sun, Jianwei; Perdew, John P.; Scuseria, Gustavo E.

2016-04-01

Contrary to standard coupled cluster doubles (CCD) and Brueckner doubles (BD), singlet-paired analogues of CCD and BD (denoted here as CCD0 and BD0) do not break down when static correlation is present, but neglect substantial amounts of dynamic correlation. In fact, CCD0 and BD0 do not account for any contributions from multielectron excitations involving only same-spin electrons at all. We exploit this feature to add - without introducing double counting, self-interaction, or increase in cost - the missing correlation to these methods via meta-GGA (generalised gradient approximation) density functionals (Tao-Perdew-Staroverov-Scuseria and strongly constrained and appropriately normed). Furthermore, we improve upon these CCD0+DFT blends by invoking range separation: the short- and long-range correlations absent in CCD0/BD0 are evaluated with density functional theory and the direct random phase approximation, respectively. This corrects the description of long-range van der Waals forces. Comprehensive benchmarking shows that the combinations presented here are very accurate for weakly correlated systems, while also providing a reasonable description of strongly correlated problems without resorting to symmetry breaking.
Absorption and fluorescence spectra of heterocyclic isomers from long-range-corrected density functional theory in polarizable continuum approach.

PubMed

Kityk, Andriy V

2012-03-22

Long-range-corrected (LC) DFT/TDDFT methods may provide adequate description of ground and excited state properties; however, accuracy of such an approach depends much on a range separation (exchange screening) representing adjustable model parameter. Its relation to a size or specific of molecular systems has been explored in numerous studies, whereas the effect of solvent environment is usually ignored during the evaluation of state properties. To benchmark and assess the quality of the LC-DFT/TDDFT formalism, we report the optical absorption and fluorescence emission energies of organic heterocyclic isomers, DPIPQ and PTNA, calculated by LC-BLYP DFT/TDDFT method in the polarizable continuum (PCM) approach. The calculations are compared with the optical absorption and fluorescence spectra measured in organic solvents of different polarity. Despite a considerable structural difference, both dyes exhibit quite similar range separations being somewhat different for the optical absorption and fluorescence emission processes. Properly parametrized LC-BLYP xc-potential well reproduces basic features of the optical absorption spectra including the electronic transitions to higher excited states. The DFT/TDDFT/PCM analysis correctly predicts the solvation trends although solvatochromic shifts of the electronic transition energies appear to be evidently underestimated in most cases, especially for the fluorescence emission. Considering the discrepancy between the experiment and theory, evaluated state dipole moments and solvation corrections to the exchange screening are analyzed. The results of the present study emphasize the importance of a solvent-dependent range separation in DFT/TDDFT/PCM calculations for investigating excited state properties. © 2012 American Chemical Society
TD-CI simulation of the electronic optical response of molecules in intense fields II: comparison of DFT functionals and EOM-CCSD.

PubMed

Sonk, Jason A; Schlegel, H Bernhard

2011-10-27

Time-dependent configuration interaction (TD-CI) simulations can be used to simulate molecules in intense laser fields. TD-CI calculations use the excitation energies and transition dipoles calculated in the absence of a field. The EOM-CCSD method provides a good estimate of the field-free excited states but is rather expensive. Linear-response time-dependent density functional theory (TD-DFT) is an inexpensive alternative for computing the field-free excitation energies and transition dipoles needed for TD-CI simulations. Linear-response TD-DFT calculations were carried out with standard functionals (B3LYP, BH&HLYP, HSE2PBE (HSE03), BLYP, PBE, PW91, and TPSS) and long-range corrected functionals (LC-ωPBE, ωB97XD, CAM-B3LYP, LC-BLYP, LC-PBE, LC-PW91, and LC-TPSS). These calculations used the 6-31G(d,p) basis set augmented with three sets of diffuse sp functions on each heavy atom. Butadiene was employed as a test case, and 500 excited states were calculated with each functional. Standard functionals yield average excitation energies that are significantly lower than the EOM-CC, while long-range corrected functionals tend to produce average excitation energies slightly higher. Long-range corrected functionals also yield transition dipoles that are somewhat larger than EOM-CC on average. The TD-CI simulations were carried out with a three-cycle Gaussian pulse (ω = 0.06 au, 760 nm) with intensities up to 1.26 × 10(14) W cm(-2) directed along the vector connecting the end carbons. The nonlinear response as indicated by the residual populations of the excited states after the pulse is far too large with standard functionals, primarily because the excitation energies are too low. The LC-ωPBE, LC-PBE, LC-PW91, and LC-TPSS long-range corrected functionals produce responses comparable to EOM-CC.
Long-term results of conservative surgery and radiotherapy for ductal carcinoma in situ using lung density correction: the University of Michigan experience.

PubMed

Ben-David, Merav A; Sturtz, David E; Griffith, Kent A; Douglas, Kathye R; Hayman, James A; Lichter, Allen S; Pierce, Lori J

2007-01-01

The purpose of the study was to review the treatment outcomes of 198 patients treated with breast-conserving surgery (BCS) and whole breast radiation therapy using lung density correction for ductal carcinoma in situ (DCIS). Between April 1985 and December 2002, 198 patients with 200 lesions diagnosed as DCIS (AJCC stage 0) were treated at the University of Michigan. All underwent BCS and whole breast radiotherapy. Median total follow-up was 6.2 years (range: 0.8-18.2). The 5- and 10-year cumulative rates of in-breast only failure were 5.9% (95% CI: 2.6-9.3%) and 9.8% (95% CI: 5.2-14.4%), respectively. Factors that significantly predicted for an increased risk of local failure were family history of breast cancer, positive or close surgical margins and age
A note on the accuracy of KS-DFT densities

NASA Astrophysics Data System (ADS)

Ranasinghe, Duminda S.; Perera, Ajith; Bartlett, Rodney J.

2017-11-01

The accuracy of the density of wave function methods and Kohn-Sham (KS) density functionals is studied using moments of the density, ⟨rn ⟩ =∫ ρ (r )rnd τ =∫0∞4 π r2ρ (r ) rnd r ,where n =-1 ,-2,0,1,2 ,and 3 provides information about the short- and long-range behavior of the density. Coupled cluster (CC) singles, doubles, and perturbative triples (CCSD(T)) is considered as the reference density. Three test sets are considered: boron through neon neutral atoms, two and four electron cations, and 3d transition metals. The total density and valence only density are distinguished by dropping appropriate core orbitals. Among density functionals tested, CAMQTP00 and ωB97x show the least deviation for boron through neon neutral atoms. They also show accurate eigenvalues for the HOMO indicating that they should have a more correct long-range behavior for the density. For transition metals, some density functional approximations outperform some wave function methods, suggesting that the KS determinant could be a better starting point for some kinds of correlated calculations. By using generalized many-body perturbation theory (MBPT), the convergence of second-, third-, and fourth-order KS-MBPT for the density is addressed as it converges to the infinite-order coupled cluster result. For the transition metal test set, the deviations in the KS density functional theory methods depend on the amount of exact exchange the functional uses. Functionals with exact exchange close to 25% show smaller deviations from the CCSD(T) density.
Parametrization and Benchmark of Long-Range Corrected DFTB2 for Organic Molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vuong, Van Quan; Akkarapattiakal Kuriappan, Jissy; Kubillus, Maximilian

In this paper, we present the parametrization and benchmark of long-range corrected second-order density functional tight binding (DFTB), LC-DFTB2, for organic and biological molecules. The LC-DFTB2 model not only improves fundamental orbital energy gaps but also ameliorates the DFT self-interaction error and overpolarization problem, and further improves charge-transfer excited states significantly. Electronic parameters for the construction of the DFTB2 Hamiltonian as well as repulsive potentials were optimized for molecules containing C, H, N, and O chemical elements. We use a semiautomatic parametrization scheme based on a genetic algorithm. With the new parameters, LC-DFTB2 describes geometries and vibrational frequencies of organicmore » molecules similarly well as third-order DFTB3/3OB, the de facto standard parametrization based on a GGA functional. Finally, LC-DFTB2 performs well also for atomization and reaction energies, however, slightly less satisfactorily than DFTB3/3OB.« less
Parametrization and Benchmark of Long-Range Corrected DFTB2 for Organic Molecules

DOE PAGES

Vuong, Van Quan; Akkarapattiakal Kuriappan, Jissy; Kubillus, Maximilian; ...

2017-12-12

In this paper, we present the parametrization and benchmark of long-range corrected second-order density functional tight binding (DFTB), LC-DFTB2, for organic and biological molecules. The LC-DFTB2 model not only improves fundamental orbital energy gaps but also ameliorates the DFT self-interaction error and overpolarization problem, and further improves charge-transfer excited states significantly. Electronic parameters for the construction of the DFTB2 Hamiltonian as well as repulsive potentials were optimized for molecules containing C, H, N, and O chemical elements. We use a semiautomatic parametrization scheme based on a genetic algorithm. With the new parameters, LC-DFTB2 describes geometries and vibrational frequencies of organicmore » molecules similarly well as third-order DFTB3/3OB, the de facto standard parametrization based on a GGA functional. Finally, LC-DFTB2 performs well also for atomization and reaction energies, however, slightly less satisfactorily than DFTB3/3OB.« less
Modeling the physisorption of graphene on metals

NASA Astrophysics Data System (ADS)

Tao, Jianmin; Tang, Hong; Patra, Abhirup; Bhattarai, Puskar; Perdew, John P.

2018-04-01

Many processes of technological and fundamental importance occur on surfaces. Adsorption is one of these phenomena that has received the most attention. However, it presents a great challenge to conventional density functional theory. Starting with the Lifshitz-Zaremba-Kohn second-order perturbation theory, here we develop a long-range van der Waals (vdW) correction for physisorption of graphene on metals. The model importantly includes quadrupole-surface interaction and screening effects. The results show that, when the vdW correction is combined with the Perdew-Burke-Enzerhof functional, it yields adsorption energies in good agreement with the random-phase approximation, significantly improving upon other vdW methods. We also find that, compared with the leading-order interaction, the higher-order quadrupole-surface correction accounts for about 25 % of the total vdW correction, suggesting the importance of the higher-order term.
A new smoothing function to introduce long-range electrostatic effects in QM/MM calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Dong; Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706; Duke, Robert E.

2015-07-28

A new method to account for long range electrostatic contributions is proposed and implemented for quantum mechanics/molecular mechanics long range electrostatic correction (QM/MM-LREC) calculations. This method involves the use of the minimum image convention under periodic boundary conditions and a new smoothing function for energies and forces at the cutoff boundary for the Coulomb interactions. Compared to conventional QM/MM calculations without long-range electrostatic corrections, the new method effectively includes effects on the MM environment in the primary image from its replicas in the neighborhood. QM/MM-LREC offers three useful features including the avoidance of calculations in reciprocal space (k-space), with themore » concomitant avoidance of having to reproduce (analytically or approximately) the QM charge density in k-space, and the straightforward availability of analytical Hessians. The new method is tested and compared with results from smooth particle mesh Ewald (PME) for three systems including a box of neat water, a double proton transfer reaction, and the geometry optimization of the critical point structures for the rate limiting step of the DNA dealkylase AlkB. As with other smoothing or shifting functions, relatively large cutoffs are necessary to achieve comparable accuracy with PME. For the double-proton transfer reaction, the use of a 22 Å cutoff shows a close reaction energy profile and geometries of stationary structures with QM/MM-LREC compared to conventional QM/MM with no truncation. Geometry optimization of stationary structures for the hydrogen abstraction step by AlkB shows some differences between QM/MM-LREC and the conventional QM/MM. These differences underscore the necessity of the inclusion of the long-range electrostatic contribution.« less
Dispersion corrected hartree-fock and density functional theory for organic crystal structure prediction.

PubMed

Brandenburg, Jan Gerit; Grimme, Stefan

2014-01-01

We present and evaluate dispersion corrected Hartree-Fock (HF) and Density Functional Theory (DFT) based quantum chemical methods for organic crystal structure prediction. The necessity of correcting for missing long-range electron correlation, also known as van der Waals (vdW) interaction, is pointed out and some methodological issues such as inclusion of three-body dispersion terms are discussed. One of the most efficient and widely used methods is the semi-classical dispersion correction D3. Its applicability for the calculation of sublimation energies is investigated for the benchmark set X23 consisting of 23 small organic crystals. For PBE-D3 the mean absolute deviation (MAD) is below the estimated experimental uncertainty of 1.3 kcal/mol. For two larger π-systems, the equilibrium crystal geometry is investigated and very good agreement with experimental data is found. Since these calculations are carried out with huge plane-wave basis sets they are rather time consuming and routinely applicable only to systems with less than about 200 atoms in the unit cell. Aiming at crystal structure prediction, which involves screening of many structures, a pre-sorting with faster methods is mandatory. Small, atom-centered basis sets can speed up the computation significantly but they suffer greatly from basis set errors. We present the recently developed geometrical counterpoise correction gCP. It is a fast semi-empirical method which corrects for most of the inter- and intramolecular basis set superposition error. For HF calculations with nearly minimal basis sets, we additionally correct for short-range basis incompleteness. We combine all three terms in the HF-3c denoted scheme which performs very well for the X23 sublimation energies with an MAD of only 1.5 kcal/mol, which is close to the huge basis set DFT-D3 result.
Analytical nuclear gradients for the range-separated many-body dispersion model of noncovalent interactions.

PubMed

Blood-Forsythe, Martin A; Markovich, Thomas; DiStasio, Robert A; Car, Roberto; Aspuru-Guzik, Alán

2016-03-01

An accurate treatment of the long-range electron correlation energy, including van der Waals (vdW) or dispersion interactions, is essential for describing the structure, dynamics, and function of a wide variety of systems. Among the most accurate models for including dispersion into density functional theory (DFT) is the range-separated many-body dispersion (MBD) method [A. Ambrosetti et al. , J. Chem. Phys. , 2014, 140 , 18A508], in which the correlation energy is modeled at short-range by a semi-local density functional and at long-range by a model system of coupled quantum harmonic oscillators. In this work, we develop analytical gradients of the MBD energy with respect to nuclear coordinates, including all implicit coordinate dependencies arising from the partitioning of the charge density into Hirshfeld effective volumes. To demonstrate the efficiency and accuracy of these MBD gradients for geometry optimizations of systems with intermolecular and intramolecular interactions, we optimized conformers of the benzene dimer and isolated small peptides with aromatic side-chains. We find excellent agreement with the wavefunction theory reference geometries of these systems (at a fraction of the computational cost) and find that MBD consistently outperforms the popular TS and D3(BJ) dispersion corrections. To demonstrate the performance of the MBD model on a larger system with supramolecular interactions, we optimized the C 60 @C 60 H 28 buckyball catcher host-guest complex. In our analysis, we also find that neglecting the implicit nuclear coordinate dependence arising from the charge density partitioning, as has been done in prior numerical treatments, leads to an unacceptable error in the MBD forces, with relative errors of ∼20% (on average) that can extend well beyond 100%.
Basis convergence of range-separated density-functional theory.

PubMed

Franck, Odile; Mussard, Bastien; Luppi, Eleonora; Toulouse, Julien

2015-02-21

Range-separated density-functional theory (DFT) is an alternative approach to Kohn-Sham density-functional theory. The strategy of range-separated density-functional theory consists in separating the Coulomb electron-electron interaction into long-range and short-range components and treating the long-range part by an explicit many-body wave-function method and the short-range part by a density-functional approximation. Among the advantages of using many-body methods for the long-range part of the electron-electron interaction is that they are much less sensitive to the one-electron atomic basis compared to the case of the standard Coulomb interaction. Here, we provide a detailed study of the basis convergence of range-separated density-functional theory. We study the convergence of the partial-wave expansion of the long-range wave function near the electron-electron coalescence. We show that the rate of convergence is exponential with respect to the maximal angular momentum L for the long-range wave function, whereas it is polynomial for the case of the Coulomb interaction. We also study the convergence of the long-range second-order Møller-Plesset correlation energy of four systems (He, Ne, N2, and H2O) with cardinal number X of the Dunning basis sets cc - p(C)V XZ and find that the error in the correlation energy is best fitted by an exponential in X. This leads us to propose a three-point complete-basis-set extrapolation scheme for range-separated density-functional theory based on an exponential formula.
A Technique for Real-Time Ionospheric Ranging Error Correction Based On Radar Dual-Frequency Detection

NASA Astrophysics Data System (ADS)

Lyu, Jiang-Tao; Zhou, Chen

2017-12-01

Ionospheric refraction is one of the principal error sources for limiting the accuracy of radar systems for space target detection. High-accuracy measurement of the ionospheric electron density along the propagation path of radar wave is the most important procedure for the ionospheric refraction correction. Traditionally, the ionospheric model and the ionospheric detection instruments, like ionosonde or GPS receivers, are employed for obtaining the electron density. However, both methods are not capable of satisfying the requirements of correction accuracy for the advanced space target radar system. In this study, we propose a novel technique for ionospheric refraction correction based on radar dual-frequency detection. Radar target range measurements at two adjacent frequencies are utilized for calculating the electron density integral exactly along the propagation path of the radar wave, which can generate accurate ionospheric range correction. The implementation of radar dual-frequency detection is validated by a P band radar located in midlatitude China. The experimental results present that the accuracy of this novel technique is more accurate than the traditional ionospheric model correction. The technique proposed in this study is very promising for the high-accuracy radar detection and tracking of objects in geospace.
Green autofluorescence, a double edged monitoring tool for bacterial growth and activity in micro-plates

NASA Astrophysics Data System (ADS)

Mihalcescu, Irina; Van-Melle Gateau, Mathilde; Chelli, Bernard; Pinel, Corinne; Ravanat, Jean-Luc

2015-12-01

The intrinsic green autofluorescence of an Escherichia coli culture has long been overlooked and empirically corrected in green fluorescent protein (GFP) reporter experiments. We show here, by using complementary methods of fluorescence analysis and HPLC, that this autofluorescence, principally arise from the secreted flavins in the external media. The cells secrete roughly 10 times more than what they keep inside. We show next that the secreted flavin fluorescence can be used as a complementary method in measuring the cell concentration particularly when the classical method, based on optical density measure, starts to fail. We also demonstrate that the same external flavins limit the dynamical range of GFP quantification and can lead to a false interpretation of lower global dynamic range of expression than what really happens. In the end we evaluate different autofluorescence correction methods to extract the real GFP signal.
Scalar relativistic computations of nuclear magnetic shielding and g-shifts with the zeroth-order regular approximation and range-separated hybrid density functionals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aquino, Fredy W.; Govind, Niranjan; Autschbach, Jochen

2011-10-01

Density functional theory (DFT) calculations of NMR chemical shifts and molecular g-tensors with Gaussian-type orbitals are implemented via second-order energy derivatives within the scalar relativistic zeroth order regular approximation (ZORA) framework. Nonhybrid functionals, standard (global) hybrids, and range-separated (Coulomb-attenuated, long-range corrected) hybrid functionals are tested. Origin invariance of the results is ensured by use of gauge-including atomic orbital (GIAO) basis functions. The new implementation in the NWChem quantum chemistry package is verified by calculations of nuclear shielding constants for the heavy atoms in HX (X=F, Cl, Br, I, At) and H2X (X = O, S, Se, Te, Po), and Temore » chemical shifts in a number of tellurium compounds. The basis set and functional dependence of g-shifts is investigated for 14 radicals with light and heavy atoms. The problem of accurately predicting F NMR shielding in UF6-nCln, n = 1 to 6, is revisited. The results are sensitive to approximations in the density functionals, indicating a delicate balance of DFT self-interaction vs. correlation. For the uranium halides, the results with the range-separated functionals are mixed.« less
Basis convergence of range-separated density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franck, Odile, E-mail: odile.franck@etu.upmc.fr; Mussard, Bastien, E-mail: bastien.mussard@upmc.fr; CNRS, UMR 7616, Laboratoire de Chimie Théorique, F-75005 Paris

2015-02-21

Range-separated density-functional theory (DFT) is an alternative approach to Kohn-Sham density-functional theory. The strategy of range-separated density-functional theory consists in separating the Coulomb electron-electron interaction into long-range and short-range components and treating the long-range part by an explicit many-body wave-function method and the short-range part by a density-functional approximation. Among the advantages of using many-body methods for the long-range part of the electron-electron interaction is that they are much less sensitive to the one-electron atomic basis compared to the case of the standard Coulomb interaction. Here, we provide a detailed study of the basis convergence of range-separated density-functional theory. Wemore » study the convergence of the partial-wave expansion of the long-range wave function near the electron-electron coalescence. We show that the rate of convergence is exponential with respect to the maximal angular momentum L for the long-range wave function, whereas it is polynomial for the case of the Coulomb interaction. We also study the convergence of the long-range second-order Møller-Plesset correlation energy of four systems (He, Ne, N{sub 2}, and H{sub 2}O) with cardinal number X of the Dunning basis sets cc − p(C)V XZ and find that the error in the correlation energy is best fitted by an exponential in X. This leads us to propose a three-point complete-basis-set extrapolation scheme for range-separated density-functional theory based on an exponential formula.« less

Density of states and magnetotransport in Weyl semimetals with long-range disorder

NASA Astrophysics Data System (ADS)

Pesin, D. A.; Mishchenko, E. G.; Levchenko, A.

2015-11-01

We study the density of states and magnetotransport properties of disordered Weyl semimetals, focusing on the case of a strong long-range disorder. To calculate the disorder-averaged density of states close to nodal points, we treat exactly the long-range random potential fluctuations produced by charged impurities, while the short-range component of disorder potential is included systematically and controllably with the help of a diagram technique. We find that, for energies close to the degeneracy point, long-range potential fluctuations lead to a finite density of states. In the context of transport, we discuss that a self-consistent theory of screening in magnetic field may conceivably lead to nonmonotonic low-field magnetoresistance.
Effect of modified thermal conductivity on the temperature distribution in the protonosphere.

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Fontheim, E. G.; Mahajan, K. K.

1973-01-01

At typical protonospheric electron densities the electron mean free path is sufficiently long so that the coefficient of thermal conductivity is no longer given by Spitzer's expression. The effect on the temperature profile of using the corrected expression for conductivity is investigated. The corrected thermal conduction coefficient is density-dependent and has a more complicated temperature dependence than the coefficient applicable to higher density plasmas. The results indicate that the effect is not negligible even under quiet conditions and at low latitudes.
A perspective on thirty years of the Webb, Pearman and Leuning density corrections

Treesearch

Xuhui Lee; William J. Massman

2011-01-01

The density correction theory of Webb et al. (1980, Q J Roy Meteorol Soc 106: 85-100, hereafter WPL) is a principle underpinning the experimental investigation of surface fluxes of energy and masses in the atmospheric boundary layer. It has a long-lasting influence in boundary-layer meteorology and micrometeorology, and the year 2010 marks the 30th anniversary of the...
Geometrical correction of the e-beam proximity effect for raster scan systems

NASA Astrophysics Data System (ADS)

Belic, Nikola; Eisenmann, Hans; Hartmann, Hans; Waas, Thomas

1999-06-01

Increasing demands on pattern fidelity and CD accuracy in e- beam lithography require a correction of the e-beam proximity effect. The new needs are mainly coming from OPC at mask level and x-ray lithography. The e-beam proximity limits the achievable resolution and affects neighboring structures causing under- or over-exposion depending on the local pattern densities and process settings. Methods to compensate for this unequilibrated does distribution usually use a dose modulation or multiple passes. In general raster scan systems are not able to apply variable doses in order to compensate for the proximity effect. For system of this kind a geometrical modulation of the original pattern offers a solution for compensation of line edge deviations due to the proximity effect. In this paper a new method for the fast correction of the e-beam proximity effect via geometrical pattern optimization is described. The method consists of two steps. In a first step the pattern dependent dose distribution caused by back scattering is calculated by convolution of the pattern with the long range part of the proximity function. The restriction to the long range part result in a quadratic sped gain in computing time for the transformation. The influence of the short range part coming from forward scattering is not pattern dependent and can therefore be determined separately in a second step. The second calculation yields the dose curve at the border of a written structure. The finite gradient of this curve leads to an edge displacement depending on the amount of underground dosage at the observed position which was previously determined in the pattern dependent step. This unintended edge displacement is corrected by splitting the line into segments and shifting them by multiples of the writers address grid to the opposite direction.
Accurate thermodynamics for short-ranged truncations of Coulomb interactions in site-site molecular models

NASA Astrophysics Data System (ADS)

Rodgers, Jocelyn M.; Weeks, John D.

2009-12-01

Coulomb interactions are present in a wide variety of all-atom force fields. Spherical truncations of these interactions permit fast simulations but are problematic due to their incorrect thermodynamics. Herein we demonstrate that simple analytical corrections for the thermodynamics of uniform truncated systems are possible. In particular, results for the simple point charge/extended (SPC/E) water model treated with spherically truncated Coulomb interactions suggested by local molecular field theory [J. M. Rodgers and J. D. Weeks, Proc. Natl. Acad. Sci. U.S.A. 105, 19136 (2008)] are presented. We extend the results developed by Chandler [J. Chem. Phys. 65, 2925 (1976)] so that we may treat the thermodynamics of mixtures of flexible charged and uncharged molecules simulated with spherical truncations. We show that the energy and pressure of spherically truncated bulk SPC/E water are easily corrected using exact second-moment-like conditions on long-ranged structure. Furthermore, applying the pressure correction as an external pressure removes the density errors observed by other research groups in NPT simulations of spherically truncated bulk species.
Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J.; Staunton, Julie B.; Billinge, Simon J. L.

2016-05-01

We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ˜1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.
Theoretical investigation of local proton conductance in the proton exchange membranes

NASA Astrophysics Data System (ADS)

Singh, Raman K.; Tsuneda, Takao; Miyatake, Kenji; Watanabe, Masahiro

2014-07-01

The hydrated structures of the proton exchange membranes were theoretically investigated using long-range corrected density functional theory to make clear why perfluorinated polymer membrane Nafion is superior to other membranes in the proton conductivity at low humidity. For exploring the possibility of the proton conductance in the vehicle mechanism with low hydration numbers, we examined the relay model of protonated water clusters between the sulfonic acid groups in Nafion and concluded that this relay model may contribute to the high proton conductivity of Nafion with less-hydrated sulfonic acid groups.
Air density correction in ionization dosimetry.

PubMed

Christ, G; Dohm, O S; Schüle, E; Gaupp, S; Martin, M

2004-05-21

Air density must be taken into account when ionization dosimetry is performed with unsealed ionization chambers. The German dosimetry protocol DIN 6800-2 states an air density correction factor for which current barometric pressure and temperature and their reference values must be known. It also states that differences between air density and the attendant reference value, as well as changes in ionization chamber sensitivity, can be determined using a radioactive check source. Both methods have advantages and drawbacks which the paper discusses in detail. Barometric pressure at a given height above sea level can be determined by using a suitable barometer, or data downloaded from airport or weather service internet sites. The main focus of the paper is to show how barometric data from measurement or from the internet are correctly processed. Therefore the paper also provides all the requisite equations and terminological explanations. Computed and measured barometric pressure readings are compared, and long-term experience with air density correction factors obtained using both methods is described.
Combining extrapolation with ghost interaction correction in range-separated ensemble density functional theory for excited states

NASA Astrophysics Data System (ADS)

Alam, Md. Mehboob; Deur, Killian; Knecht, Stefan; Fromager, Emmanuel

2017-11-01

The extrapolation technique of Savin [J. Chem. Phys. 140, 18A509 (2014)], which was initially applied to range-separated ground-state-density-functional Hamiltonians, is adapted in this work to ghost-interaction-corrected (GIC) range-separated ensemble density-functional theory (eDFT) for excited states. While standard extrapolations rely on energies that decay as μ-2 in the large range-separation-parameter μ limit, we show analytically that (approximate) range-separated GIC ensemble energies converge more rapidly (as μ-3) towards their pure wavefunction theory values (μ → +∞ limit), thus requiring a different extrapolation correction. The purpose of such a correction is to further improve on the convergence and, consequently, to obtain more accurate excitation energies for a finite (and, in practice, relatively small) μ value. As a proof of concept, we apply the extrapolation method to He and small molecular systems (viz., H2, HeH+, and LiH), thus considering different types of excitations such as Rydberg, charge transfer, and double excitations. Potential energy profiles of the first three and four singlet Σ+ excitation energies in HeH+ and H2, respectively, are studied with a particular focus on avoided crossings for the latter. Finally, the extraction of individual state energies from the ensemble energy is discussed in the context of range-separated eDFT, as a perspective.
Generalized model screening potentials for Fermi-Dirac plasmas

NASA Astrophysics Data System (ADS)

Akbari-Moghanjoughi, M.

2016-04-01

In this paper, some properties of relativistically degenerate quantum plasmas, such as static ion screening, structure factor, and Thomson scattering cross-section, are studied in the framework of linearized quantum hydrodynamic theory with the newly proposed kinetic γ-correction to Bohm term in low frequency limit. It is found that the correction has a significant effect on the properties of quantum plasmas in all density regimes, ranging from solid-density up to that of white dwarf stars. It is also found that Shukla-Eliasson attractive force exists up to a few times the density of metals, and the ionic correlations are seemingly apparent in the radial distribution function signature. Simplified statically screened attractive and repulsive potentials are presented for zero-temperature Fermi-Dirac plasmas, valid for a wide range of quantum plasma number-density and atomic number values. Moreover, it is observed that crystallization of white dwarfs beyond a critical core number-density persists with this new kinetic correction, but it is shifted to a much higher number-density value of n0 ≃ 1.94 × 1037 cm-3 (1.77 × 1010 gr cm-3), which is nearly four orders of magnitude less than the nuclear density. It is found that the maximal Thomson scattering with the γ-corrected structure factor is a remarkable property of white dwarf stars. However, with the new γ-correction, the maximal scattering shifts to the spectrum region between hard X-ray and low-energy gamma-rays. White dwarfs composed of higher atomic-number ions are observed to maximally Thomson-scatter at slightly higher wavelengths, i.e., they maximally scatter slightly low-energy photons in the presence of correction.
Finding the best density functional approximation to describe interaction energies and structures of ionic liquids in molecular dynamics studies

NASA Astrophysics Data System (ADS)

Perlt, Eva; Ray, Promit; Hansen, Andreas; Malberg, Friedrich; Grimme, Stefan; Kirchner, Barbara

2018-05-01

Ionic liquids raise interesting but complicated questions for theoretical investigations due to the fact that a number of different inter-molecular interactions, e.g., hydrogen bonding, long-range Coulomb interactions, and dispersion interactions, need to be described properly. Here, we present a detailed study on the ionic liquids ethylammonium nitrate and 1-ethyl-3-methylimidazolium acetate, in which we compare different dispersion corrected density functional approximations to accurate local coupled cluster data in static calculations on ionic liquid clusters. The efficient new composite method B97-3c is tested and has been implemented in CP2K for future studies. Furthermore, tight-binding based approaches which may be used in large scale simulations are assessed. Subsequently, ab initio as well as classical molecular dynamics simulations are conducted and structural analyses are presented in order to shed light on the different short- and long-range structural patterns depending on the method and the system size considered in the simulation. Our results indicate the presence of strong hydrogen bonds in ionic liquids as well as the aggregation of alkyl side chains due to dispersion interactions.
Properties of Organic Liquids when Simulated with Long-Range Lennard-Jones Interactions.

PubMed

Fischer, Nina M; van Maaren, Paul J; Ditz, Jonas C; Yildirim, Ahmet; van der Spoel, David

2015-07-14

In order to increase the accuracy of classical computer simulations, existing methodologies may need to be adapted. Hitherto, most force fields employ a truncated potential function to model van der Waals interactions, sometimes augmented with an analytical correction. Although such corrections are accurate for homogeneous systems with a long cutoff, they should not be used in inherently inhomogeneous systems such as biomolecular and interface systems. For such cases, a variant of the particle mesh Ewald algorithm (Lennard-Jones PME) was already proposed 20 years ago (Essmann et al. J. Chem. Phys. 1995, 103, 8577-8593), but it was implemented only recently (Wennberg et al. J. Chem. Theory Comput. 2013, 9, 3527-3537) in a major simulation code (GROMACS). The availability of this method allows surface tensions of liquids as well as bulk properties to be established, such as density and enthalpy of vaporization, without approximations due to truncation. Here, we report on simulations of ≈150 liquids (taken from a force field benchmark: Caleman et al. J. Chem. Theory Comput. 2012, 8, 61-74) using three different force fields and compare simulations with and without explicit long-range van der Waals interactions. We find that the density and enthalpy of vaporization increase for most liquids using the generalized Amber force field (GAFF, Wang et al. J. Comput. Chem. 2004, 25, 1157-1174) and the Charmm generalized force field (CGenFF, Vanommeslaeghe et al. J. Comput. Chem. 2010, 31, 671-690) but less so for OPLS/AA (Jorgensen and Tirado-Rives, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 6665-6670), which was parametrized with an analytical correction to the van der Waals potential. The surface tension increases by ≈10(-2) N/m for all force fields. These results suggest that van der Waals attractions in force fields are too strong, in particular for the GAFF and CGenFF. In addition to the simulation results, we introduce a new version of a web server, http://virtualchemistry.org, aimed at facilitating sharing and reuse of input files for molecular simulations.
Modal density of rectangular structures in a wide frequency range

NASA Astrophysics Data System (ADS)

Parrinello, A.; Ghiringhelli, G. L.

2018-04-01

A novel approach to investigate the modal density of a rectangular structure in a wide frequency range is presented. First, the modal density is derived, in the whole frequency range of interest, on the basis of sound transmission through the infinite counterpart of the structure; then, it is corrected by means of the low-frequency modal behavior of the structure, taking into account actual size and boundary conditions. A statistical analysis reveals the connection between the modal density of the structure and the transmission of sound through its thickness. A transfer matrix approach is used to compute the required acoustic parameters, making it possible to deal with structures having arbitrary stratifications of different layers. A finite element method is applied on coarse grids to derive the first few eigenfrequencies required to correct the modal density. Both the transfer matrix approach and the coarse grids involved in the finite element analysis grant high efficiency. Comparison with alternative formulations demonstrates the effectiveness of the proposed methodology.
Long-Range Adiabatic Corrections to the Ground Molecular State of Alkali-Metal Dimers.

NASA Astrophysics Data System (ADS)

Marinescu, M.; Dalgarno, A.

1997-04-01

The structure of the long-range limit of the diagonal adiabatic corrections to the ground molecular state of diatomic molecules, may be expressed as a series of inverse powers of internuclear distance, R. The coefficients of this expansion are proportional to the inverse of the nuclear mass. Thus, they may be interpreted as a nuclear mass-dependent corrections to the dispersion coefficients. Using perturbation theory we have calculated the long-range coefficients of the diagonal adiabatic corrections up to the order of R-10. The final expressions are in terms of integrals over imaginary frequencies of products of atomic matrix elements involving Green's functions of complex energy. Thus, in our approach the molecular problem is reduced to an atomic one. Numerical evaluations have been done for all alkali-metal dimers. We acknowledge the support of the U.S. Dept. of Energy.
Invited Paper - Density functional theory: coverage of dynamic and non-dynamic electron correlation effects

NASA Astrophysics Data System (ADS)

Cremer, Dieter

The electron correlation effects covered by density functional theory (DFT) can be assessed qualitatively by comparing DFT densities ρ(r) with suitable reference densities obtained with wavefunction theory (WFT) methods that cover typical electron correlation effects. The analysis of difference densities ρ(DFT)-ρ(WFT) reveals that LDA and GGA exchange (X) functionals mimic non-dynamic correlation effects in an unspecified way. It is shown that these long range correlation effects are caused by the self-interaction error (SIE) of standard X functionals. Self-interaction corrected (SIC) DFT exchange gives, similar to exact exchange, for the bonding region a delocalized exchange hole, and does not cover any correlation effects. Hence, the exchange SIE is responsible for the fact that DFT densities often resemble MP4 or MP2 densities. The correlation functional changes X-only DFT densities in a manner observed when higher order coupling effects between lower order N-electron correlation effects are included. Hybrid functionals lead to changes in the density similar to those caused by SICDFT, which simply reflects the fact that hybrid functionals have been developed to cover part of the SIE and its long range correlation effects in a balanced manner. In the case of spin-unrestricted DFT (UDFT), non-dynamic electron correlation effects enter the calculation both via the X functional and via the wavefunction, which may cause a double-counting of correlation effects. The use of UDFT in the form of permuted orbital and broken-symmetry DFT (PO-UDFT, BS-UDFT) can lead to reasonable descriptions of multireference systems provided certain conditions are fulfilled. More reliable, however, is a combination of DFT and WFT methods, which makes the routine description of multireference systems possible. The development of such methods implies a separation of dynamic and non-dynamic correlation effects. Strategies for accomplishing this goal are discussed in general and tested in practice for CAS (complete active space)-DFT.
Thermal properties of nuclear matter in a variational framework with relativistic corrections

NASA Astrophysics Data System (ADS)

Zaryouni, S.; Hassani, M.; Moshfegh, H. R.

2014-01-01

The properties of hot symmetric nuclear matter for a wide range of densities and temperatures are investigated by employing the AV14 potential within the lowest order constrained variational (LOCV) method with the inclusion of a phenomenological three-body force as well as relativistic corrections. The relativistic corrections of many-body kinetic energies as well as the boot interaction corrections are presented for a wide range of densities and temperatures. The free energy, pressure, incompressibility, and other thermodynamic quantities of symmetric nuclear matter are obtained and discussed. The critical temperature is found, and the liquid-gas phase transition is analyzed both with and without the inclusion of three-body forces and relativistic corrections in the LOCV approach. It is shown that the critical temperature is strongly affected by the three-body forces but does not depend on the relativistic corrections. Finally, the results obtained in the present study are compared with other many-body calculations and experimental predictions.
Verification of Anderson Superexchange in MnO via Magnetic Pair Distribution Function Analysis and ab initio Theory.

PubMed

Frandsen, Benjamin A; Brunelli, Michela; Page, Katharine; Uemura, Yasutomo J; Staunton, Julie B; Billinge, Simon J L

2016-05-13

We present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ∼1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.
Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and ab initio theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benjamin A. Frandsen; Brunelli, Michela; Page, Katharine

Here, we present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominatedmore » by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. Furthermore, the Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.« less
Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and ab initio theory

DOE PAGES

Benjamin A. Frandsen; Brunelli, Michela; Page, Katharine; ...

2016-05-11

Here, we present a temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a ~1 nm length scale that differ substantially from the low-temperature long-range spin arrangement. Ab initio calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominatedmore » by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. Furthermore, the Anderson superexchange model for MnO is thus verified by experimentation and confirmed by ab initio theory.« less
Vibrational spectra of halide-water dimers: Insights on ion hydration from full-dimensional quantum calculations on many-body potential energy surfaces

NASA Astrophysics Data System (ADS)

Bajaj, Pushp; Wang, Xiao-Gang; Carrington, Tucker; Paesani, Francesco

2018-03-01

Full-dimensional vibrational spectra are calculated for both X-(H2O) and X-(D2O) dimers (X = F, Cl, Br, I) at the quantum-mechanical level. The calculations are carried out on two sets of recently developed potential energy functions (PEFs), namely, Thole-type model energy (TTM-nrg) and many-body energy (MB-nrg), using the symmetry-adapted Lanczos algorithm with a product basis set including all six vibrational coordinates. Although both TTM-nrg and MB-nrg PEFs are derived from coupled-cluster single double triple-F12 data obtained in the complete basis set limit, they differ in how many-body effects are represented at short range. Specifically, while both models describe long-range interactions through the combination of two-body dispersion and many-body classical electrostatics, the relatively simple Born-Mayer functions employed in the TTM-nrg PEFs to represent short-range interactions are replaced in the MB-nrg PEFs by permutationally invariant polynomials to achieve chemical accuracy. For all dimers, the MB-nrg vibrational spectra are in close agreement with the available experimental data, correctly reproducing anharmonic and nuclear quantum effects. In contrast, the vibrational frequencies calculated with the TTM-nrg PEFs exhibit significant deviations from the experimental values. The comparison between the TTM-nrg and MB-nrg results thus reinforces the notion that an accurate representation of both short-range interactions associated with electron density overlap and long-range many-body electrostatic interactions is necessary for a correct description of hydration phenomena at the molecular level.

Chronic pharmacological mGlu5 inhibition corrects fragile X in adult mice.

PubMed

Michalon, Aubin; Sidorov, Michael; Ballard, Theresa M; Ozmen, Laurence; Spooren, Will; Wettstein, Joseph G; Jaeschke, Georg; Bear, Mark F; Lindemann, Lothar

2012-04-12

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. Previous studies have implicated mGlu5 in the pathogenesis of the disease, but a crucial unanswered question is whether pharmacological mGlu5 inhibition is able to reverse an already established FXS phenotype in mammals. Here we have used the novel, potent, and selective mGlu5 inhibitor CTEP to address this issue in the Fmr1 knockout mouse. Acute CTEP treatment corrects elevated hippocampal long-term depression, protein synthesis, and audiogenic seizures. Chronic treatment that inhibits mGlu5 within a receptor occupancy range of 81% ± 4% rescues cognitive deficits, auditory hypersensitivity, aberrant dendritic spine density, overactive ERK and mTOR signaling, and partially corrects macroorchidism. This study shows that a comprehensive phenotype correction in FXS is possible with pharmacological intervention starting in young adulthood, after development of the phenotype. It is of great interest how these findings may translate into ongoing clinical research testing mGlu5 inhibitors in FXS patients. Copyright © 2012 Elsevier Inc. All rights reserved.
Optical properties of body-centered tetragonal C4: Insights from many-body perturbation and time-dependent density functional theories

NASA Astrophysics Data System (ADS)

Tarighi Ahmadpour, Mahdi; Rostamnejadi, Ali; Hashemifar, S. Javad

2018-04-01

We study the electronic structure and optical properties of a body-centered tetragonal phase of carbon (bct-C4) within the framework of time-dependent density functional theory and Bethe-Salpeter equation. The results indicate that the optical properties of bct-C4 are strongly affected by the electron-hole interaction. It is demonstrated that the long-range corrected exchange-correlation kernels could fairly reproduce the Bethe-Salpeter equation results. The effective carrier number reveals that at energies above 30 eV, the excitonic effects are not dominant any more and that the optical transitions originate mainly from electronic excitations. The emerged peaks in the calculated electron energy loss spectra are discussed in terms of plasmon excitations and interband transitions. The results of the research indicate that bct-C4 is an indirect wide-band-gap semiconductor, which is transparent in the visible region and opaque in the ultraviolet spectral range.
Hybrid density functional theory band structure engineering in hematite

NASA Astrophysics Data System (ADS)

Pozun, Zachary D.; Henkelman, Graeme

2011-06-01

We present a hybrid density functional theory (DFT) study of doping effects in α-Fe2O3, hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that using a screened functional that smoothly transitions from 12% exact exchange at short ranges to standard DFT at long range accurately reproduces the experimental band gap and other material properties. We then show that the antiferromagnetic symmetry in the pure α-Fe2O3 crystal is broken by all dopants and that the ligand field theory correctly predicts local magnetic moments on the dopants. We characterize the resulting band gaps for hematite doped by transition metals and the p-block post-transition metals. The specific case of Pd doping is investigated in order to correlate calculated doping energies and optical properties with experimentally observed photocatalytic behavior.
On the accuracy of density functional theory and wave function methods for calculating vertical ionization energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

McKechnie, Scott; Booth, George H.; Cohen, Aron J.

The best practice in computational methods for determining vertical ionization energies (VIEs) is assessed, via reference to experimentally determined VIEs that are corroborated by highly accurate coupled-cluster calculations. These reference values are used to benchmark the performance of density-functional theory (DFT) and wave function methods: Hartree-Fock theory (HF), second-order Møller-Plesset perturbation theory (MP2) and Electron Propagator Theory (EPT). The core test set consists of 147 small molecules. An extended set of six larger molecules, from benzene to hexacene, is also considered to investigate the dependence of the results on molecule size. The closest agreement with experiment is found for ionizationmore » energies obtained from total energy diff calculations. In particular, DFT calculations using exchange-correlation functionals with either a large amount of exact exchange or long-range correction perform best. The results from these functionals are also the least sensitive to an increase in molecule size. In general, ionization energies calculated directly from the orbital energies of the neutral species are less accurate and more sensitive to an increase in molecule size. For the single-calculation approach, the EPT calculations are in closest agreement for both sets of molecules. For the orbital energies from DFT functionals, only those with long-range correction give quantitative agreement with dramatic failing for all other functionals considered. The results offer a practical hierarchy of approximations for the calculation of vertical ionization energies. In addition, the experimental and computational reference values can be used as a standardized set of benchmarks, against which other approximate methods can be compared.« less
Evaluation of modern DFT functionals and G3n-RAD composite methods in the modelization of organic singlet diradicals.

PubMed

López-Carballeira, Diego; Ruipérez, Fernando

2016-04-01

The evaluation of four high-level composite methods based on the modification of Gaussian-3 (G3) theory for radicals and 18 exchange-correlation density functionals, including modern long-range and dispersion-corrected functionals, in the modelization of singlet diradicals has been performed in this work. Structural parameters and properties such as singlet-triplet gaps, electron affinities, ionization potentials, dipole moments, enthalpies of formation, and bond dissociation energies have been calculated in a set of six well-characterized singlet diradicals, and benchmarked against experimental data and wavefunction-based CASSCF/CASPT2 calculations. The complexity of the open-shell singlet ground state is revealed in the difficulties to properly represent the diradical character reported by some DFT functionals, specially those that do not comprise a certain amount of Hartree-Fock exchange in their formulation. We find that STGs, EAs, dipole moments, and thermochemical properties are, in general, satisfactorily calculated, while for IPs larger deviations with respect to the experiments are found in all cases. The best overall performance is accounted for by hybrid functionals, including some of the long-range corrected functionals, but also pure functionals, comprising the kinetic energy density in their formulation, are found to be competent. Composite methods perform satisfactorily, especially G3(MP2)-RAD and G3X(MP2)-RAD, which calculate singlet-triplet gaps and electron affinities more accurately. On the other hand, G3-RAD and G3X-RAD provide better ionization potentials. This study emphasizes that the use of recently developed functionals, within the broken symmetry approximation, is an appropriate tool for the simulation of organic singlet diradicals, with similar accuracy compared to more expensive composite methods. Nevertheless, suitable selection of the methodology is still crucial for the accomplishment of accurate results.
Long-term orbit prediction for China's Tiangong-1 spacecraft based on mean atmosphere model

NASA Astrophysics Data System (ADS)

Tang, Jingshi; Liu, Lin; Miao, Manqian

Tiangong-1 is China's test module for future space station. It has gone through three successful rendezvous and dockings with Shenzhou spacecrafts from 2011 to 2013. For the long-term management and maintenance, the orbit sometimes needs to be predicted for a long period of time. As Tiangong-1 works in a low-Earth orbit with an altitude of about 300-400 km, the error in the a priori atmosphere model contributes significantly to the rapid increase of the predicted orbit error. When the orbit is predicted for 10-20 days, the error in the a priori atmosphere model, if not properly corrected, could induce the semi-major axis error and the overall position error up to a few kilometers and several thousand kilometers respectively. In this work, we use a mean atmosphere model averaged from NRLMSIS00. The a priori reference mean density can be corrected during precise orbit determination (POD). For applications in the long-term orbit prediction, the observations are first accumulated. With sufficiently long period of observations, we are able to obtain a series of the diurnal mean densities. This series bears the recent variation of the atmosphere density and can be analyzed for various periods. After being properly fitted, the mean density can be predicted and then applied in the orbit prediction. We show that the densities predicted with this approach can serve to increase the accuracy of the predicted orbit. In several 20-day prediction tests, most predicted orbits show semi-major axis errors better than 700m and overall position errors better than 600km.
Evaluation of Density Corrections to Methane Fluxes Measured by Open-Path Eddy Covariance over Contrasting Landscapes

NASA Astrophysics Data System (ADS)

Chamberlain, Samuel D.; Verfaillie, Joseph; Eichelmann, Elke; Hemes, Kyle S.; Baldocchi, Dennis D.

2017-11-01

Corrections accounting for air density fluctuations due to heat and water vapour fluxes must be applied to the measurement of eddy-covariance fluxes when using open-path sensors. Experimental tests and ecosystem observations have demonstrated the important role density corrections play in accurately quantifying carbon dioxide (CO2) fluxes, but less attention has been paid to evaluating these corrections for methane (CH4) fluxes. We measured CH4 fluxes with open-path sensors over a suite of sites with contrasting CH4 emissions and energy partitioning, including a pavement airfield, two negligible-flux ecosystems (drained alfalfa and pasture), and two high-flux ecosystems (flooded wetland and rice). We found that density corrections successfully re-zeroed fluxes in negligible-flux sites; however, slight overcorrection was observed above pavement. The primary impact of density corrections varied over negligible- and high-flux ecosystems. For negligible-flux sites, corrections led to greater than 100% adjustment in daily budgets, while these adjustments were only 3-10% in high-flux ecosystems. The primary impact to high-flux ecosystems was a change in flux diel patterns, which may affect the evaluation of relationships between biophysical drivers and fluxes if correction bias exists. Additionally, accounting for density effects to high-frequency CH4 fluctuations led to large differences in observed CH4 flux cospectra above negligible-flux sites, demonstrating that similar adjustments should be made before interpreting CH4 cospectra for comparable ecosystems. These results give us confidence in CH4 fluxes measured by open-path sensors, and demonstrate that density corrections play an important role in adjusting flux budgets and diel patterns across a range of ecosystems.
Membrane adaptive optics

NASA Astrophysics Data System (ADS)

Marker, Dan K.; Wilkes, James M.; Ruggiero, Eric J.; Inman, Daniel J.

2005-08-01

An innovative adaptive optic is discussed that provides a range of capabilities unavailable with either existing, or newly reported, research devices. It is believed that this device will be inexpensive and uncomplicated to construct and operate, with a large correction range that should dramatically relax the static and dynamic structural tolerances of a telescope. As the areal density of a telescope primary is reduced, the optimal optical figure and the structural stiffness are inherently compromised and this phenomenon will require a responsive, range-enhanced wavefront corrector. In addition to correcting for the aberrations in such innovative primary mirrors, sufficient throw remains to provide non-mechanical steering to dramatically improve the Field of regard. Time dependent changes such as thermal disturbances can also be accommodated. The proposed adaptive optic will overcome some of the issues facing conventional deformable mirrors, as well as current and proposed MEMS-based deformable mirrors and liquid crystal based adaptive optics. Such a device is scalable to meter diameter apertures, eliminates high actuation voltages with minimal power consumption, provides long throw optical path correction, provides polychromatic dispersion free operation, dramatically reduces the effects of adjacent actuator influence, and provides a nearly 100% useful aperture. This article will reveal top-level details of the proposed construction and include portions of a static, dynamic, and residual aberration analysis. This device will enable certain designs previously conceived by visionaries in the optical community.
Gauge field entanglement in Kitaev's honeycomb model

NASA Astrophysics Data System (ADS)

Dóra, Balázs; Moessner, Roderich

2018-01-01

A spin fractionalizes into matter and gauge fermions in Kitaev's spin liquid on the honeycomb lattice. This follows from a Jordan-Wigner mapping to fermions, allowing for the construction of a minimal entropy ground-state wave function on the cylinder. We use this to calculate the entanglement entropy by choosing several distinct partitionings. First, by partitioning an infinite cylinder into two, the -ln2 topological entanglement entropy is reconfirmed. Second, the reduced density matrix of the gauge sector on the full cylinder is obtained after tracing out the matter degrees of freedom. This allows for evaluating the gauge entanglement Hamiltonian, which contains infinitely long-range correlations along the symmetry axis of the cylinder. The matter-gauge entanglement entropy is (Ny-1 )ln2 , with Ny the circumference of the cylinder. Third, the rules for calculating the gauge sector entanglement of any partition are determined. Rather small correctly chosen gauge partitions can still account for the topological entanglement entropy in spite of long-range correlations in the gauge entanglement Hamiltonian.
Axial Length Variation Impacts on Superficial Retinal Vessel Density and Foveal Avascular Zone Area Measurements Using Optical Coherence Tomography Angiography.

PubMed

Sampson, Danuta M; Gong, Peijun; An, Di; Menghini, Moreno; Hansen, Alex; Mackey, David A; Sampson, David D; Chen, Fred K

2017-06-01

To evaluate the impact of image magnification correction on superficial retinal vessel density (SRVD) and foveal avascular zone area (FAZA) measurements using optical coherence tomography angiography (OCTA). Participants with healthy retinas were recruited for ocular biometry, refraction, and RTVue XR Avanti OCTA imaging with the 3 × 3-mm protocol. The foveal and parafoveal SRVD and FAZA were quantified with custom software before and after correction for magnification error using the Littman and the modified Bennett formulae. Relative changes between corrected and uncorrected SRVD and FAZA were calculated. Forty subjects were enrolled and the median (range) age of the participants was 30 (18-74) years. The mean (range) spherical equivalent refractive error was -1.65 (-8.00 to +4.88) diopters and mean (range) axial length was 24.42 mm (21.27-28.85). Images from 13 eyes were excluded due to poor image quality leaving 67 for analysis. Relative changes in foveal and parafoveal SRVD and FAZA after correction ranged from -20% to +10%, -3% to +2%, and -20% to +51%, respectively. Image size correction in measurements of foveal SRVD and FAZA was greater than 5% in 51% and 74% of eyes, respectively. In contrast, 100% of eyes had less than 5% correction in measurements of parafoveal SRVD. Ocular biometry should be performed with OCTA to correct image magnification error induced by axial length variation. We advise caution when interpreting interocular and interindividual comparisons of SRVD and FAZA derived from OCTA without image size correction.
General relativistic corrections in density-shear correlations

NASA Astrophysics Data System (ADS)

Ghosh, Basundhara; Durrer, Ruth; Sellentin, Elena

2018-06-01

We investigate the corrections which relativistic light-cone computations induce on the correlation of the tangential shear with galaxy number counts, also known as galaxy-galaxy lensing. The standard-approach to galaxy-galaxy lensing treats the number density of sources in a foreground bin as observable, whereas it is in reality unobservable due to the presence of relativistic corrections. We find that already in the redshift range covered by the DES first year data, these currently neglected relativistic terms lead to a systematic correction of up to 50% in the density-shear correlation function for the highest redshift bins. This correction is dominated by the fact that a redshift bin of number counts does not only lens sources in a background bin, but is itself again lensed by all masses between the observer and the counted source population. Relativistic corrections are currently ignored in the standard galaxy-galaxy analyses, and the additional lensing of a counted source populations is only included in the error budget (via the covariance matrix). At increasingly higher redshifts and larger scales, these relativistic and lensing corrections become however increasingly more important, and we here argue that it is then more efficient, and also cleaner, to account for these corrections in the density-shear correlations.
High-resolution gamma ray attenuation density measurements on mining exploration drill cores, including cut cores

NASA Astrophysics Data System (ADS)

Ross, P.-S.; Bourke, A.

2017-01-01

Physical property measurements are increasingly important in mining exploration. For density determinations on rocks, one method applicable on exploration drill cores relies on gamma ray attenuation. This non-destructive method is ideal because each measurement takes only 10 s, making it suitable for high-resolution logging. However calibration has been problematic. In this paper we present new empirical, site-specific correction equations for whole NQ and BQ cores. The corrections force back the gamma densities to the "true" values established by the immersion method. For the NQ core caliber, the density range extends to high values (massive pyrite, 5 g/cm3) and the correction is thought to be very robust. We also present additional empirical correction factors for cut cores which take into account the missing material. These "cut core correction factors", which are not site-specific, were established by making gamma density measurements on truncated aluminum cylinders of various residual thicknesses. Finally we show two examples of application for the Abitibi Greenstone Belt in Canada. The gamma ray attenuation measurement system is part of a multi-sensor core logger which also determines magnetic susceptibility, geochemistry and mineralogy on rock cores, and performs line-scan imaging.
Kinetic Monte Carlo modeling of the efficiency roll-off in a multilayer white organic light-emitting device

NASA Astrophysics Data System (ADS)

Mesta, M.; van Eersel, H.; Coehoorn, R.; Bobbert, P. A.

2016-03-01

Triplet-triplet annihilation (TTA) and triplet-polaron quenching (TPQ) in organic light-emitting devices (OLEDs) lead to a roll-off of the internal quantum efficiency (IQE) with increasing current density J. We employ a kinetic Monte Carlo modeling study to analyze the measured IQE and color balance as a function of J in a multilayer hybrid white OLED that combines fluorescent blue with phosphorescent green and red emission. We investigate two models for TTA and TPQ involving the phosphorescent green and red emitters: short-range nearest-neighbor quenching and long-range Förster-type quenching. Short-range quenching predicts roll-off to occur at much higher J than measured. Taking long-range quenching with Förster radii for TTA and TPQ equal to twice the Förster radii for exciton transfer leads to a fair description of the measured IQE-J curve, with the major contribution to the roll-off coming from TPQ. The measured decrease of the ratio of phosphorescent to fluorescent component of the emitted light with increasing J is correctly predicted. A proper description of the J-dependence of the ratio of red and green phosphorescent emission needs further model refinements.
Spatial pattern corrections and sample sizes for forest density estimates of historical tree surveys

Treesearch

Brice B. Hanberry; Shawn Fraver; Hong S. He; Jian Yang; Dan C. Dey; Brian J. Palik

2011-01-01

The U.S. General Land Office land surveys document trees present during European settlement. However, use of these surveys for calculating historical forest density and other derived metrics is limited by uncertainty about the performance of plotless density estimators under a range of conditions. Therefore, we tested two plotless density estimators, developed by...
In vivo imaging of the rodent eye with swept source/Fourier domain OCT

PubMed Central

Liu, Jonathan J.; Grulkowski, Ireneusz; Kraus, Martin F.; Potsaid, Benjamin; Lu, Chen D.; Baumann, Bernhard; Duker, Jay S.; Hornegger, Joachim; Fujimoto, James G.

2013-01-01

Swept source/Fourier domain OCT is demonstrated for in vivo imaging of the rodent eye. Using commercial swept laser technology, we developed a prototype OCT imaging system for small animal ocular imaging operating in the 1050 nm wavelength range at an axial scan rate of 100 kHz with ~6 µm axial resolution. The high imaging speed enables volumetric imaging with high axial scan densities, measuring high flow velocities in vessels, and repeated volumetric imaging over time. The 1050 nm wavelength light provides increased penetration into tissue compared to standard commercial OCT systems at 850 nm. The long imaging range enables multiple operating modes for imaging the retina, posterior eye, as well as anterior eye and full eye length. A registration algorithm using orthogonally scanned OCT volumetric data sets which can correct motion on a per A-scan basis is applied to compensate motion and merge motion corrected volumetric data for enhanced OCT image quality. Ultrahigh speed swept source OCT is a promising technique for imaging the rodent eye, proving comprehensive information on the cornea, anterior segment, lens, vitreous, posterior segment, retina and choroid. PMID:23412778
Horizontal Line-of-Sight Turbulence Over Near-Ground Paths and Implications for Adaptive Optics Corrections in Laser Communications.

PubMed

Levine, B M; Martinsen, E A; Wirth, A; Jankevics, A; Toledo-Quinones, M; Landers, F; Bruno, T L

1998-07-20

Atmospheric turbulence over long horizontal paths perturbs phase and can also cause severe intensity scintillation in the pupil of an optical communications receiver, which limits the data rate over which intensity-based modulation schemes can operate. The feasibility of using low-order adaptive optics by applying phase-only corrections over horizontal propagation paths is investigated. A Shack-Hartmann wave-front sensor was built and data were gathered on paths 1 m above ground and between a 1- and 2.5-km range. Both intensity fluctuations and optical path fluctuation statistics were gathered within a single frame, and the wave-front reconstructor was modified to allow for scintillated data. The temporal power spectral density for various Zernike polynomial modes was used to determine the effects of the expected corrections by adaptive optics. The slopes of the inertial subrange of turbulence were found to be less than predicted by Kolmogorov theory with an infinite outer scale, and the distribution of variance explained by increasing order was also found to be different. Statistical analysis of these data in the 1-km range indicates that at communications wavelengths of 1.3 mum, a significant improvement in transmitted beam quality could be expected most of the time, to a performance of 10% Strehl ratio or better.
Benchmark study of ionization potentials and electron affinities of armchair single-walled carbon nanotubes using density functional theory

NASA Astrophysics Data System (ADS)

Zhou, Bin; Hu, Zhubin; Jiang, Yanrong; He, Xiao; Sun, Zhenrong; Sun, Haitao

2018-05-01

The intrinsic parameters of carbon nanotubes (CNTs) such as ionization potential (IP) and electron affinity (EA) are closely related to their unique properties and associated applications. In this work, we demonstrated the success of optimal tuning method based on range-separated (RS) density functionals for both accurate and efficient prediction of vertical IPs and electron affinities (EAs) of a series of armchair single-walled carbon nanotubes C20n H20 (n = 2–6) compared to the high-level IP/EA equation-of-motion coupled-cluster method with single and double substitutions (IP/EA-EOM-CCSD). Notably, the resulting frontier orbital energies (–ε HOMO and –ε LUMO) from the tuning method exhibit an excellent approximation to the corresponding IPs and EAs, that significantly outperform other conventional density functionals. In addition, it is suggested that the RS density functionals that possess both a fixed amount of exact exchange in the short-range and a correct long-range asymptotic behavior are suitable for calculating electronic structures of finite-sized CNTs. Next the performance of density functionals for description of various molecular properties such as chemical potential, hardness and electrophilicity are assessed as a function of tube length. Thanks to the efficiency and accuracy of this tuning method, the related behaviors of much longer armchair single-walled CNTs until C200H20 were studied. Lastly, the present work is proved to provide an efficient theoretical tool for future materials design and reliable characterization of other interesting properties of CNT-based systems.
Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources.

PubMed

Tornero-López, Ana M; Guirado, Damián; Perez-Calatayud, Jose; Ruiz-Arrebola, Samuel; Simancas, Fernando; Gazdic-Santic, Maja; Lallena, Antonio M

2013-12-01

Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction. In this work, the authors examined the behavior of the PTW 34051 SourceCheck ionization chamber when measuring the air kerma strength of (125)I seeds. Four different SourceCheck chambers were analyzed. With each one of them, two series of measurements of the air kerma strength for (125)I selectSeed(TM) brachytherapy sources were performed inside a pressure chamber and varying the pressure in a range from 747 to 1040 hPa (560 to 780 mm Hg). The temperature and relative humidity were kept basically constant. An analogous experiment was performed by taking measurements at different altitudes above sea level. Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization chamber they are undercorrected. At a typical atmospheric situation of 933 hPa (700 mm Hg) and 20 °C, this undercorrection turns out to be 1.5%. Corrected measurements show a residual linear dependence on the density and, as a consequence, an additional density dependent correction must be applied. The slope of this residual linear density dependence is different for each SourceCheck chamber investigated. The results obtained by taking measurements at different altitudes are compatible with those obtained with the pressure chamber. Variations of the altitude and changes in the weather conditions may produce significant density corrections, and that effect should be taken into account. This effect is chamber-dependent, indicating that a specific calibration is necessary for each particular chamber. To our knowledge, this correction has not been considered so far for SourceCheck ionization chambers, but its magnitude cannot be neglected in clinical practice. The atmospheric pressure and temperature at which the chamber was calibrated need to be taken into account, and they should be reported in the calibration certificate. In addition, each institution should analyze the particular response of its SourceCheck ionization chamber and compute the adequate correction factors. In the absence of a suitable pressure chamber, a possibility for this assessment is to take measurements at different altitudes, spanning a wide enough air density range.
Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tornero-López, Ana M.; Guirado, Damián; Ruiz-Arrebola, Samuel

2013-12-15

Purpose: Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction. In this work, the authors examined the behavior of the PTW 34051 SourceCheck ionization chamber when measuring themore » air kerma strength of {sup 125}I seeds.Methods: Four different SourceCheck chambers were analyzed. With each one of them, two series of measurements of the air kerma strength for {sup 125}I selectSeed{sup TM} brachytherapy sources were performed inside a pressure chamber and varying the pressure in a range from 747 to 1040 hPa (560 to 780 mm Hg). The temperature and relative humidity were kept basically constant. An analogous experiment was performed by taking measurements at different altitudes above sea level.Results: Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization chamber they are undercorrected. At a typical atmospheric situation of 933 hPa (700 mm Hg) and 20 °C, this undercorrection turns out to be 1.5%. Corrected measurements show a residual linear dependence on the density and, as a consequence, an additional density dependent correction must be applied. The slope of this residual linear density dependence is different for each SourceCheck chamber investigated. The results obtained by taking measurements at different altitudes are compatible with those obtained with the pressure chamber.Conclusions: Variations of the altitude and changes in the weather conditions may produce significant density corrections, and that effect should be taken into account. This effect is chamber-dependent, indicating that a specific calibration is necessary for each particular chamber. To our knowledge, this correction has not been considered so far for SourceCheck ionization chambers, but its magnitude cannot be neglected in clinical practice. The atmospheric pressure and temperature at which the chamber was calibrated need to be taken into account, and they should be reported in the calibration certificate. In addition, each institution should analyze the particular response of its SourceCheck ionization chamber and compute the adequate correction factors. In the absence of a suitable pressure chamber, a possibility for this assessment is to take measurements at different altitudes, spanning a wide enough air density range.« less
75 FR 1799 - Terminate Long Range Aids to Navigation (Loran-C) Signal

Federal Register 2010, 2011, 2012, 2013, 2014

2010-01-13

... to Navigation (Loran-C) Signal AGENCY: U.S. Coast Guard, DHS. ACTION: Notice; correction. SUMMARY... 998). The document announced termination of the Long Range Aids to Navigation (Loran-C) Signal...

Isostatic and Decompensative Gravity Anomalies of the Arabian Plate and Surrounding Regions: a Key for the Crustal Structure

NASA Astrophysics Data System (ADS)

Kaban, M. K.; El Khrepy, S.; Al-Arifi, N. S.

2016-12-01

The isostatic anomalies are often considered as one of the most useful correction of the gravity field for investigation of the upper crust structure in many practical applications. By applying this correction, a substantial part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomaly, can be removed. With this approach, it is not even necessary to know the deep density structure of the crust and upper mantle in details; it is sufficient to prescribe some type of compensation (regional vs. local) and a compensation depth. However, even when all the parameters are chosen correctly, this reduction of the gravity field does not show the full gravity effect of unknown anomalies in the crust. The last ones should be also compensated to some extent; therefore their impact is substantially reduced by the isostatic compensation. Long ago (Cordell et al., 1991), it was suggested a so-called decompensative correction of the isostatic anomalies, which provides a possibility to separate these effects. However, the decompensative correction is very sensitive to the parameters of the compensation scheme. In the present study we analyse the ways to choose these parameters and extend this approach by assuming a possibility for the regional compensation via elastic deformations of the lithosphere. Based on this technique, we estimate the isostatic and decompensative anomalies for the Arabian plate and surrounding regions. The parameters of the isostatic model are chosen based on previous studies. It was demonstrated that the decompensative correction is very significant at the mid-range wavelengths and may exceed 100 mGal, therefore ignoring this effect would lead to wrong conclusions about the upper crust structure. The total amplitude of the decompensative anomalies reaches ±250 mGal, evidencing for both, large density anomalies of the upper crust (including sediments) and strong isostatic disturbances of the lithosphere. These results improve the knowledge about the crustal structure in the Middle East. Cordell, L., Zorin, Y. A., & Keller, G. R. (1991). The decompensative gravity anomaly and deep structure of the region of the Rio Grande rift. Journal of Geophysical Research: Solid Earth (1978-2012), 96(B4), 6557-6568.
A small-volume PVTX system for broadband spectroscopic calibration of downhole optical sensors

NASA Astrophysics Data System (ADS)

Jones, Christopher Michael; Pelletier, Michael T.; Atkinson, Robert; Shen, Jing; Moore, Jeff; Anders, Jimmy; Perkins, David L.; Myrick, Michael L.

2017-07-01

An instrument is presented that is capable of measuring the optical spectrum (long-wave ultraviolet through short-wave mid-infrared) of fluids under a range of temperature and pressure conditions from ambient pressure up to 138 MPa (20 000 psi) and 422 K (300 °F) using ˜5 ml of fluid. Temperature, pressure, and density are measured in situ in real-time, and composition is varied by adding volatile and nonvolatile components. The stability and accuracy of the conditions are reported for pure ethane, and the effects of temperature and pressure on characteristic regions of the optical spectrum of ethane are illustrated after correction for temperature and pressure effects on the optical cell path length, as well as normalization to the measured density. Molar absorption coefficients and integrated molar absorption coefficients for several vibrational combination bands are presented.
RADIO ASTROMETRY OF THE CLOSE ACTIVE BINARY HR 5110

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbuhl, E.; Mutel, R. L.; Lynch, C.

2015-09-20

The close active binary HR 5110 was observed at six epochs over 26 days using a global very long baseline interferometry array at 15.4 GHz. We used phase referencing to determine the position of the radio centroid at each epoch with an uncertainty significantly smaller than the component separation. After correcting for proper motion and parallax, we find that the centroid locations of all six epochs have barycenter separations consistent with an emission source located on the KIV secondary, and not in an interaction region between the stars or on the F primary. We used a homogeneous power-law gyrosynchrotron emissionmore » model to reproduce the observed flux densities and fractional circular polarization. The resulting ranges of mean magnetic field strength and relativistic electron densities are of the order of 10 G and 10{sup 5} cm{sup −3}, respectively, in the source region.« less
7 CFR 275.3 - Federal monitoring.

Code of Federal Regulations, 2012 CFR

2012-01-01

... necessitate long range analytical and evaluative measures for corrective action development shall be... effective. In addition, FNS will examine the State agency's corrective action monitoring and evaluative...
7 CFR 275.3 - Federal monitoring.

Code of Federal Regulations, 2013 CFR

2013-01-01

... necessitate long range analytical and evaluative measures for corrective action development shall be... effective. In addition, FNS will examine the State agency's corrective action monitoring and evaluative...
7 CFR 275.3 - Federal monitoring.

Code of Federal Regulations, 2010 CFR

2010-01-01

... necessitate long range analytical and evaluative measures for corrective action development shall be... effective. In addition, FNS will examine the State agency's corrective action monitoring and evaluative...
7 CFR 275.3 - Federal monitoring.

Code of Federal Regulations, 2011 CFR

2011-01-01

... necessitate long range analytical and evaluative measures for corrective action development shall be... effective. In addition, FNS will examine the State agency's corrective action monitoring and evaluative...
7 CFR 275.3 - Federal monitoring.

Code of Federal Regulations, 2014 CFR

2014-01-01

... necessitate long range analytical and evaluative measures for corrective action development shall be... effective. In addition, FNS will examine the State agency's corrective action monitoring and evaluative...
Communication: Accurate higher-order van der Waals coefficients between molecules from a model dynamic multipole polarizability

DOE PAGES

Tao, Jianmin; Rappe, Andrew M.

2016-01-20

Due to the absence of the long-range van der Waals (vdW) interaction, conventional density functional theory (DFT) often fails in the description of molecular complexes and solids. In recent years, considerable progress has been made in the development of the vdW correction. However, the vdW correction based on the leading-order coefficient C 6 alone can only achieve limited accuracy, while accurate modeling of higher-order coefficients remains a formidable task, due to the strong non-additivity effect. Here, we apply a model dynamic multipole polarizability within a modified single-frequency approximation to calculate C 8 and C 10 between small molecules. We findmore » that the higher-order vdW coefficients from this model can achieve remarkable accuracy, with mean absolute relative deviations of 5% for C 8 and 7% for C 10. As a result, inclusion of accurate higher-order contributions in the vdW correction will effectively enhance the predictive power of DFT in condensed matter physics and quantum chemistry.« less
Refraction corrections for surveying

NASA Technical Reports Server (NTRS)

Lear, W. M.

1979-01-01

Optical measurements of range and elevation angle are distorted by the earth's atmosphere. High precision refraction correction equations are presented which are ideally suited for surveying because their inputs are optically measured range and optically measured elevation angle. The outputs are true straight line range and true geometric elevation angle. The 'short distances' used in surveying allow the calculations of true range and true elevation angle to be quickly made using a programmable pocket calculator. Topics covered include the spherical form of Snell's Law; ray path equations; and integrating the equations. Short-, medium-, and long-range refraction corrections are presented in tables.
Close-range photogrammetry with video cameras

NASA Technical Reports Server (NTRS)

Burner, A. W.; Snow, W. L.; Goad, W. K.

1985-01-01

Examples of photogrammetric measurements made with video cameras uncorrected for electronic and optical lens distortions are presented. The measurement and correction of electronic distortions of video cameras using both bilinear and polynomial interpolation are discussed. Examples showing the relative stability of electronic distortions over long periods of time are presented. Having corrected for electronic distortion, the data are further corrected for lens distortion using the plumb line method. Examples of close-range photogrammetric data taken with video cameras corrected for both electronic and optical lens distortion are presented.
Close-Range Photogrammetry with Video Cameras

NASA Technical Reports Server (NTRS)

Burner, A. W.; Snow, W. L.; Goad, W. K.

1983-01-01

Examples of photogrammetric measurements made with video cameras uncorrected for electronic and optical lens distortions are presented. The measurement and correction of electronic distortions of video cameras using both bilinear and polynomial interpolation are discussed. Examples showing the relative stability of electronic distortions over long periods of time are presented. Having corrected for electronic distortion, the data are further corrected for lens distortion using the plumb line method. Examples of close-range photogrammetric data taken with video cameras corrected for both electronic and optical lens distortion are presented.
Long-range Coulomb forces and localized bonds.

PubMed

Preiser; Lösel; Brown; Kunz; Skowron

1999-10-01

The ionic model is shown to be applicable to all compounds in which the atoms carry a net charge and their electron density is spherically symmetric regardless of the covalent character of the bonding. By examining the electric field generated by an array of point charges placed at the positions of the ions in over 40 inorganic compounds, we show that the Coulomb field naturally partitions itself into localized regions (bonds) which are characterized by the electric flux that links neighbouring ions of opposite charge. This flux is identified with the bond valence, and Gauss' law with the valence-sum rule, providing a secure theoretical foundation for the bond-valence model. The localization of the Coulomb field provides an unambiguous definition of coordination number and our calculations show that, in addition to the expected primary coordination sphere, there are a number of weak bonds between cations and the anions in the second coordination sphere. Long-range Coulomb interactions are transmitted through the crystal by the application of Gauss' law at each of the intermediate atoms. Bond fluxes have also been calculated for compounds containing ions with non-spherical electron densities (e.g. cations with stereoactive lone electron pairs). In these cases the point-charge model continues to describe the distant field, but multipoles must be added to the point charges to give the correct local field.
Sedimentation dynamics and equilibrium profiles in multicomponent mixtures of colloidal particles.

PubMed

Spruijt, E; Biesheuvel, P M

2014-02-19

In this paper we give a general theoretical framework that describes the sedimentation of multicomponent mixtures of particles with sizes ranging from molecules to macroscopic bodies. Both equilibrium sedimentation profiles and the dynamic process of settling, or its converse, creaming, are modeled. Equilibrium profiles are found to be in perfect agreement with experiments. Our model reconciles two apparently contradicting points of view about buoyancy, thereby resolving a long-lived paradox about the correct choice of the buoyant density. On the one hand, the buoyancy force follows necessarily from the suspension density, as it relates to the hydrostatic pressure gradient. On the other hand, sedimentation profiles of colloidal suspensions can be calculated directly using the fluid density as apparent buoyant density in colloidal systems in sedimentation-diffusion equilibrium (SDE) as a result of balancing gravitational and thermodynamic forces. Surprisingly, this balance also holds in multicomponent mixtures. This analysis resolves the ongoing debate of the correct choice of buoyant density (fluid or suspension): both approaches can be used in their own domain. We present calculations of equilibrium sedimentation profiles and dynamic sedimentation that show the consequences of these insights. In bidisperse mixtures of colloids, particles with a lower mass density than the homogeneous suspension will first cream and then settle, whereas particles with a suspension-matched mass density form transient, bimodal particle distributions during sedimentation, which disappear when equilibrium is reached. In all these cases, the centers of the distributions of the particles with the lowest mass density of the two, regardless of their actual mass, will be located in equilibrium above the so-called isopycnic point, a natural consequence of their hard-sphere interactions. We include these interactions using the Boublik-Mansoori-Carnahan-Starling-Leland (BMCSL) equation of state. Finally, we demonstrate that our model is not limited to hard spheres, by extending it to charged spherical particles, and to dumbbells, trimers and short chains of connected beads.
New type of dummy layout pattern to control ILD etch rate

NASA Astrophysics Data System (ADS)

Pohland, Oliver; Spieker, Julie; Huang, Chih-Ta; Govindaswamy, Srikanth; Balasinski, Artur

2007-12-01

Adding dummy features (waffles) to drawn geometries of the circuit layout is a common practice to improve its manufacturability. As an example, local dummy pattern improves MOSFET line and space CD control by adjusting short range optical proximity and reducing the aggressiveness of its correction features (OPC) to widen the lithography process window. Another application of dummy pattern (waffles) is to globally equalize layout pattern density, to reduce long-range inter-layer dielectric (ILD) thickness variations after the CMP process and improve contact resistance uniformity over the die area. In this work, we discuss a novel type of dummy pattern with a mid-range interaction distance, to control the ILD composition driven by its deposition and etch process. This composition is reflected on sidewall spacers and depends on the topography of the underlying poly pattern. During contact etch, it impacts the etch rate of the ILD. As a result, the deposited W filling the damascene etched self-aligned trench contacts in the ILD may electrically short to the underlying gates in the areas of isolated poly. To mitigate the dependence of the ILD composition on poly pattern distribution, we proposed a special dummy feature generation with the interaction range defined by the ILD deposition and etch process. This helped equalize mid-range poly pattern density without disabling the routing capability with damascene trench contacts in the periphery which would have increased the layout footprint.
B97-3c: A revised low-cost variant of the B97-D density functional method

NASA Astrophysics Data System (ADS)

Brandenburg, Jan Gerit; Bannwarth, Christoph; Hansen, Andreas; Grimme, Stefan

2018-02-01

A revised version of the well-established B97-D density functional approximation with general applicability for chemical properties of large systems is proposed. Like B97-D, it is based on Becke's power-series ansatz from 1997 and is explicitly parametrized by including the standard D3 semi-classical dispersion correction. The orbitals are expanded in a modified valence triple-zeta Gaussian basis set, which is available for all elements up to Rn. Remaining basis set errors are mostly absorbed in the modified B97 parametrization, while an established atom-pairwise short-range potential is applied to correct for the systematically too long bonds of main group elements which are typical for most semi-local density functionals. The new composite scheme (termed B97-3c) completes the hierarchy of "low-cost" electronic structure methods, which are all mainly free of basis set superposition error and account for most interactions in a physically sound and asymptotically correct manner. B97-3c yields excellent molecular and condensed phase geometries, similar to most hybrid functionals evaluated in a larger basis set expansion. Results on the comprehensive GMTKN55 energy database demonstrate its good performance for main group thermochemistry, kinetics, and non-covalent interactions, when compared to functionals of the same class. This also transfers to metal-organic reactions, which is a major area of applicability for semi-local functionals. B97-3c can be routinely applied to hundreds of atoms on a single processor and we suggest it as a robust computational tool, in particular, for more strongly correlated systems where our previously published "3c" schemes might be problematic.
Valence and charge-transfer optical properties for some SinCm (m, n ≤ 12) clusters: Comparing TD-DFT, complete-basis-limit EOMCC, and benchmarks from spectroscopy

NASA Astrophysics Data System (ADS)

Lutz, Jesse J.; Duan, Xiaofeng F.; Ranasinghe, Duminda S.; Jin, Yifan; Margraf, Johannes T.; Perera, Ajith; Burggraf, Larry W.; Bartlett, Rodney J.

2018-05-01

Accurate optical characterization of the closo-Si12C12 molecule is important to guide experimental efforts toward the synthesis of nano-wires, cyclic nano-arrays, and related array structures, which are anticipated to be robust and efficient exciton materials for opto-electronic devices. Working toward calibrated methods for the description of closo-Si12C12 oligomers, various electronic structure approaches are evaluated for their ability to reproduce measured optical transitions of the SiC2, Si2Cn (n = 1-3), and Si3Cn (n = 1, 2) clusters reported earlier by Steglich and Maier [Astrophys. J. 801, 119 (2015)]. Complete-basis-limit equation-of-motion coupled-cluster (EOMCC) results are presented and a comparison is made between perturbative and renormalized non-iterative triples corrections. The effect of adding a renormalized correction for quadruples is also tested. Benchmark test sets derived from both measurement and high-level EOMCC calculations are then used to evaluate the performance of a variety of density functionals within the time-dependent density functional theory (TD-DFT) framework. The best-performing functionals are subsequently applied to predict valence TD-DFT excitation energies for the lowest-energy isomers of SinC and Sin-1C7-n (n = 4-6). TD-DFT approaches are then applied to the SinCn (n = 4-12) clusters and unique spectroscopic signatures of closo-Si12C12 are discussed. Finally, various long-range corrected density functionals, including those from the CAM-QTP family, are applied to a charge-transfer excitation in a cyclic (Si4C4)4 oligomer. Approaches for gauging the extent of charge-transfer character are also tested and EOMCC results are used to benchmark functionals and make recommendations.
Algorithm refinement for stochastic partial differential equations: II. Correlated systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexander, Francis J.; Garcia, Alejandro L.; Tartakovsky, Daniel M.

2005-08-10

We analyze a hybrid particle/continuum algorithm for a hydrodynamic system with long ranged correlations. Specifically, we consider the so-called train model for viscous transport in gases, which is based on a generalization of the random walk process for the diffusion of momentum. This discrete model is coupled with its continuous counterpart, given by a pair of stochastic partial differential equations. At the interface between the particle and continuum computations the coupling is by flux matching, giving exact mass and momentum conservation. This methodology is an extension of our stochastic Algorithm Refinement (AR) hybrid for simple diffusion [F. Alexander, A. Garcia,more » D. Tartakovsky, Algorithm refinement for stochastic partial differential equations: I. Linear diffusion, J. Comput. Phys. 182 (2002) 47-66]. Results from a variety of numerical experiments are presented for steady-state scenarios. In all cases the mean and variance of density and velocity are captured correctly by the stochastic hybrid algorithm. For a non-stochastic version (i.e., using only deterministic continuum fluxes) the long-range correlations of velocity fluctuations are qualitatively preserved but at reduced magnitude.« less
Theory of thermal conductivity in the disordered electron liquid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwiete, G., E-mail: schwiete@uni-mainz.de; Finkel’stein, A. M.

2016-03-15

We study thermal conductivity in the disordered two-dimensional electron liquid in the presence of long-range Coulomb interactions. We describe a microscopic analysis of the problem using the partition function defined on the Keldysh contour as a starting point. We extend the renormalization group (RG) analysis developed for thermal transport in the disordered Fermi liquid and include scattering processes induced by the long-range Coulomb interaction in the sub-temperature energy range. For the thermal conductivity, unlike for the electrical conductivity, these scattering processes yield a logarithmic correction that may compete with the RG corrections. The interest in this correction arises from themore » fact that it violates the Wiedemann–Franz law. We checked that the sub-temperature correction to the thermal conductivity is not modified either by the inclusion of Fermi liquid interaction amplitudes or as a result of the RG flow. We therefore expect that the answer obtained for this correction is final. We use the theory to describe thermal transport on the metallic side of the metal–insulator transition in Si MOSFETs.« less
Conservation laws, vertex corrections, and screening in Raman spectroscopy

NASA Astrophysics Data System (ADS)

Maiti, Saurabh; Chubukov, Andrey V.; Hirschfeld, P. J.

2017-07-01

We present a microscopic theory for the Raman response of a clean multiband superconductor, with emphasis on the effects of vertex corrections and long-range Coulomb interaction. The measured Raman intensity, R (Ω ) , is proportional to the imaginary part of the fully renormalized particle-hole correlator with Raman form factors γ (k ⃗) . In a BCS superconductor, a bare Raman bubble is nonzero for any γ (k ⃗) and diverges at Ω =2 Δmax , where Δmax is the largest gap along the Fermi surface. However, for γ (k ⃗) = constant, the full R (Ω ) is expected to vanish due to particle number conservation. It was sometimes stated that this vanishing is due to the singular screening by long-range Coulomb interaction. In our general approach, we show diagrammatically that this vanishing actually holds due to vertex corrections from the same short-range interaction that gives rise to superconductivity. We further argue that long-range Coulomb interaction does not affect the Raman signal for any γ (k ⃗) . We argue that vertex corrections eliminate the divergence at 2 Δmax . We also argue that vertex corrections give rise to sharp peaks in R (Ω ) at Ω <2 Δmin (the minimum gap along the Fermi surface), when Ω coincides with the frequency of one of the collective modes in a superconductor, e.g., Leggett and Bardasis-Schrieffer modes in the particle-particle channel, and an excitonic mode in the particle-hole channel.

Long range Debye-Hückel correction for computation of grid-based electrostatic forces between biomacromolecules

PubMed Central

2014-01-01

Background Brownian dynamics (BD) simulations can be used to study very large molecular systems, such as models of the intracellular environment, using atomic-detail structures. Such simulations require strategies to contain the computational costs, especially for the computation of interaction forces and energies. A common approach is to compute interaction forces between macromolecules by precomputing their interaction potentials on three-dimensional discretized grids. For long-range interactions, such as electrostatics, grid-based methods are subject to finite size errors. We describe here the implementation of a Debye-Hückel correction to the grid-based electrostatic potential used in the SDA BD simulation software that was applied to simulate solutions of bovine serum albumin and of hen egg white lysozyme. Results We found that the inclusion of the long-range electrostatic correction increased the accuracy of both the protein-protein interaction profiles and the protein diffusion coefficients at low ionic strength. Conclusions An advantage of this method is the low additional computational cost required to treat long-range electrostatic interactions in large biomacromolecular systems. Moreover, the implementation described here for BD simulations of protein solutions can also be applied in implicit solvent molecular dynamics simulations that make use of gridded interaction potentials. PMID:25045516
Spin-orbit coupling and transport in strongly correlated two-dimensional systems

NASA Astrophysics Data System (ADS)

Huang, Jian; Pfeiffer, L. N.; West, K. W.

2017-05-01

Measuring the magnetoresistance (MR) of ultraclean GaAs two-dimensional holes for a large rs range of 20-50, two striking behaviors in relation to the spin-orbit coupling (SOC) emerge in response to strong electron-electron interaction. First, in exact correspondence to the zero-field metal-to-insulator transition (MIT), the sign of the MR switches from being positive in the metallic regime to being negative in the insulating regime when the carrier density crosses the critical density pc of MIT (rs˜39 ). Second, as the SOC-driven correction Δ ρ to the MR decreases with reducing carrier density (or the in-plane wave vector), it exhibits an upturn in the close proximity just above pc where rs is beyond 30, indicating a substantially enhanced SOC effect. This peculiar behavior echoes with a trend of delocalization long suspected for the SOC-interaction interplay. Meanwhile, for p 40 , in contrast to the common belief that a magnet field enhances Wigner crystallization, the negative MR is likely linked to enhanced interaction.
A simple but fully nonlocal correction to the random phase approximation

NASA Astrophysics Data System (ADS)

Ruzsinszky, Adrienn; Perdew, John P.; Csonka, Gábor I.

2011-03-01

The random phase approximation (RPA) stands on the top rung of the ladder of ground-state density functional approximations. The simple or direct RPA has been found to predict accurately many isoelectronic energy differences. A nonempirical local or semilocal correction to this direct RPA leaves isoelectronic energy differences almost unchanged, while improving total energies, ionization energies, etc., but fails to correct the RPA underestimation of molecular atomization energies. Direct RPA and its semilocal correction may miss part of the middle-range multicenter nonlocality of the correlation energy in a molecule. Here we propose a fully nonlocal, hybrid-functional-like addition to the semilocal correction. The added full nonlocality is important in molecules, but not in atoms. Under uniform-density scaling, this fully nonlocal correction scales like the second-order-exchange contribution to the correlation energy, an important part of the correction to direct RPA, and like the semilocal correction itself. For the atomization energies of ten molecules, and with the help of one fit parameter, it performs much better than the elaborate second-order screened exchange correction.
The RPA Atomization Energy Puzzle.

PubMed

Ruzsinszky, Adrienn; Perdew, John P; Csonka, Gábor I

2010-01-12

There is current interest in the random phase approximation (RPA), a "fifth-rung" density functional for the exchange-correlation energy. RPA has full exact exchange and constructs the correlation with the help of the unoccupied Kohn-Sham orbitals. In many cases (uniform electron gas, jellium surface, and free atom), the correction to RPA is a short-ranged effect that is captured by a local spin density approximation (LSDA) or a generalized gradient approximation (GGA). Nonempirical density functionals for the correction to RPA were constructed earlier at the LSDA and GGA levels (RPA+), but they are constructed here at the fully nonlocal level (RPA++), using the van der Waals density functional (vdW-DF) of Langreth, Lundqvist, and collaborators. While they make important and helpful corrections to RPA total and ionization energies of free atoms, they correct the RPA atomization energies of molecules by only about 1 kcal/mol. Thus, it is puzzling that RPA atomization energies are, on average, about 10 kcal/mol lower than those of accurate values from experiment. We find here that a hybrid of 50% Perdew-Burke-Ernzerhof GGA with 50% RPA+ yields atomization energies much more accurate than either one does alone. This suggests a solution to the puzzle: While the proper correction to RPA is short-ranged in some systems, its contribution to the correlation hole can spread out in a molecule with multiple atomic centers, canceling part of the spread of the exact exchange hole (more so than in RPA or RPA+), making the true exchange-correlation hole more localized than in RPA or RPA+. This effect is not captured even by the vdW-DF nonlocality, but it requires the different kind of full nonlocality present in a hybrid functional.
A predictive model for the tokamak density limit

DOE PAGES

Teng, Q.; Brennan, D. P.; Delgado-Aparicio, L.; ...

2016-07-28

We reproduce the Greenwald density limit, in all tokamak experiments by using a phenomenologically correct model with parameters in the range of experiments. A simple model of equilibrium evolution and local power balance inside the island has been implemented to calculate the radiation-driven thermo-resistive tearing mode growth and explain the density limit. Strong destabilization of the tearing mode due to an imbalance of local Ohmic heating and radiative cooling in the island predicts the density limit within a few percent. Furthermore, we found the density limit and it is a local edge limit and weakly dependent on impurity densities. Ourmore » results are robust to a substantial variation in model parameters within the range of experiments.« less
Surface tension and long range corrections of cylindrical interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bourasseau, E.; Malfreyt, P.; Ghoufi, A., E-mail: aziz.ghoufi@univ-rennes1.fr

2015-12-21

The calculation of the surface tension of curved interfaces has been deeply investigated from molecular simulation during this last past decade. Recently, the thermodynamic Test-Area (TA) approach has been extended to the calculation of surface tension of curved interfaces. In the case of the cylindrical vapour-liquid interfaces of water and Lennard-Jones fluids, it was shown that the surface tension was independent of the curvature of the interface. In addition, the surface tension of the cylindrical interface is higher than that of the planar interface. Molecular simulations of cylindrical interfaces have been so far performed (i) by using a shifted potential,more » (ii) by means of large cutoff without periodic boundary conditions, or (iii) by ignoring the long range corrections to the surface tension due to the difficulty to estimate them. Indeed, unlike the planar interfaces there are no available operational expressions to consider the tail corrections to the surface tension of cylindrical interfaces. We propose here to develop the long range corrections of the surface tension for cylindrical interfaces by using the non-exponential TA (TA2) method. We also extend the formulation of the Mecke-Winkelmann corrections initially developed for planar surfaces to cylindrical interfaces. We complete this study by the calculation of the surface tension of cylindrical surfaces of liquid tin and copper using the embedded atom model potentials.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Tokár, K.; Derian, R.; Mitas, L.

Using explicitly correlated fixed-node quantum Monte Carlo and density functional theory (DFT) methods, we study electronic properties, ground-state multiplets, ionization potentials, electron affinities, and low-energy fragmentation channels of charged half-sandwich and multidecker vanadium-benzene systems with up to 3 vanadium atoms, including both anions and cations. It is shown that, particularly in anions, electronic correlations play a crucial role; these effects are not systematically captured with any commonly used DFT functionals such as gradient corrected, hybrids, and range-separated hybrids. On the other hand, tightly bound cations can be described qualitatively by DFT. A comparison of DFT and quantum Monte Carlo providesmore » an in-depth understanding of the electronic structure and properties of these correlated systems. The calculations also serve as a benchmark study of 3d molecular anions that require a balanced many-body description of correlations at both short- and long-range distances.« less
Thrust Measurement of Dielectric Barrier Discharge (DBD) Plasma Actuators

NASA Astrophysics Data System (ADS)

Ashpis, David E.; Laun, Matthew C.

2013-11-01

DBD plasma actuators generate a wall-jet that can be used for active flow control. We used an analytical balance to measure the thrust generated by the actuator, it is a common metric of its performance without external flow. We found that the measured force is afflicted by several problems; it drifts in time, not always repeatable, is unstable, and depends on the manner the voltage is applied. We report results of investigations of these issues. Tests were conducted on an actuator constructed of 1/4 inch thick high-density polyethylene (HDPE) dielectric with 100 mm long offset electrodes, with applied voltages up to 48 kV p-p and frequencies from 32 Hz to 2.5 kHz, and pure Sine and Trapezoidal waveforms. The relative humidity was in the range of 51-55%, corresponding to moisture range of 10,500 to13,000 ppm mass. Force readings were up to 500 mg, (approximately 50 mN/m). We found that the measured force is the net of the positive thrust generated by the wall-jet and an ``anti-thrust'' acting in the opposite direction. We propose a correction procedure that yields the plasma-generated thrust. The correction is based on voltage-dependent anti-thrust measured in the low frequency range of 20-40 Hz. We found that adjacent objects in a test setup affect the measured thrust, and verified it by comparing experiments with and without a metal enclosure, grounded and ungrounded. Uncorrected thrust varied by up to approximately +/-100%, and the corrected thrust variations were up to approximately 30%. Supported by NASA's FAP/Aerospace Sciences Project.
Creating a normative database of age-specific 3D geometrical data, bone density, and bone thickness of the developing skull: a pilot study.

PubMed

Delye, Hans; Clijmans, Tim; Mommaerts, Maurice Yves; Sloten, Jos Vnder; Goffin, Jan

2015-12-01

Finite element models (FEMs) of the head are used to study the biomechanics of traumatic brain injury and depend heavily on the use of accurate material properties and head geometry. Any FEM aimed at investigating traumatic head injury in children should therefore use age-specific dimensions of the head, as well as age-specific material properties of the different tissues. In this study, the authors built a database of age-corrected skull geometry, skull thickness, and bone density of the developing skull to aid in the development of an age-specific FEM of a child's head. Such a database, containing age-corrected normative skull geometry data, can also be used for preoperative surgical planning and postoperative long-term follow-up of craniosynostosis surgery results. Computed tomography data were processed for 187 patients (age range 0-20 years old). A 3D surface model was calculated from segmented skull surfaces. Skull models, reference points, and sutures were processed into a MATLAB-supported database. This process included automatic calculation of 2D measurements as well as 3D measurements: length of the coronal suture, length of the lambdoid suture, and the 3D anterior-posterior length, defined as the sum of the metopic and sagittal suture. Skull thickness and skull bone density calculations were included. Cephalic length, cephalic width, intercoronal distance, lateral orbital distance, intertemporal distance, and 3D measurements were obtained, confirming the well-established general growth pattern of the skull. Skull thickness increases rapidly in the first year of life, slowing down during the second year of life, while skull density increases with a fast but steady pace during the first 3 years of life. Both skull thickness and density continue to increase up to adulthood. This is the first report of normative data on 2D and 3D measurements, skull bone thickness, and skull bone density for children aged 0-20 years. This database can help build an age-specific FEM of a child's head. It can also help to tailor preoperative virtual planning in craniosynostosis surgery toward patient-specific normative target values and to perform objective long-term follow-up in craniosynostosis surgery.
The mechanics of unrest at Long Valley caldera, California. 2. Constraining the nature of the source using geodetic and micro-gravity data

USGS Publications Warehouse

Battaglia, Maurizio; Segall, P.; Roberts, C.

2003-01-01

We model the source of inflation of Long Valley caldera by combining geodetic and micro-gravity data. Uplift from GPS and leveling, two-color EDM measurements, and residual gravity change determinations are used to estimate the intrusion geometry, assuming a vertical prolate ellipsoidal source. The U.S. Geological Survey occupied the Long Valley gravity network six times from 1980 to 1985. We reoccupied this network twice, in the summer of 1998 (33 stations), and the summer of 1999 (37 stations). Before gravity data can be used to estimate the density of the intrusion, they must be corrected for the effect of vertical deformation (the free-air effect) and changes in the water table. We use geostatistical techniques to interpolate uplift and water table changes at the gravity stations. The inflation source (a vertical prolate ellipsoid) is located 5.9 km beneath the resurgent dome with an aspect ratio equal to 0.475, a volume change from 1982 to 1999 of 0.136 km3 and a density of around 1700 kg/m3. A bootstrap method was employed to estimate 95% confidence bounds for the parameters of the inflation model. We obtained a range of 0.105-0.187 km3 for the volume change, and 1180-2330 kg/m3 for the density. Our results do not support hydrothermal fluid intrusion as the primary cause of unrest, and confirm the intrusion of silicic magma beneath Long Valley caldera. Failure to account for the ellipsoidal nature of the source biases the estimated source depth by 2.9 km (a 33% increase), the volume change by 0.019 km3 (a 14% increase) and the density by about 1200 kg/m3 (a 40% increase). ?? 2003 Elsevier B.V. All rights reserved.
How does implant distribution affect 3D correction and bone-screw forces in thoracic adolescent idiopathic scoliosis spinal instrumentation?

PubMed

Le Navéaux, Franck; Larson, A Noelle; Labelle, Hubert; Wang, Xiaoyu; Aubin, Carl-Éric

2016-11-01

Optimal implant densities and configurations for thoracic spine instrumentation to treat adolescent idiopathic scoliosis remain unknown. The objective was to computationally assess the biomechanical effects of implant distribution on 3D curve correction and bone-implant forces. 3D patient-specific biomechanical spine models based on a multibody dynamic approach were created for 9 Lenke 1 patients who underwent posterior instrumentation (main thoracic Cobb: 43°-70°). For each case, a factorial design of experiments was used to generate 128 virtual implant configurations representative of existing implant patterns used in clinical practice. All instances except implant configuration were the same for each surgical scenario simulation. Simulation of the 128 implant configurations scenarios (mean implant density=1.32, range: 0.73-2) revealed differences of 2° to 10° in Cobb angle correction, 2° to 7° in thoracic kyphosis and 2° to 7° in apical vertebral rotation. The use of more implants, at the concave side only, was associated with higher Cobb angle correction (r=-0.41 to -0.90). Increased implant density was associated with higher apical vertebral rotation correction for seven cases (r=-0.20 to -0.48). It was also associated with higher bone-screw forces (r=0.22 to 0.64), with an average difference between the least and most constrained instrumentation constructs of 107N per implant at the end of simulated instrumentation. Low-density constructs, with implants mainly placed on the concave side, resulted in similar simulated curve correction as the higher-density patterns. Increasing the number of implants allows for only limited improvement of 3D correction and overconstrains the instrumentation construct, resulting in increased forces on the implants. Copyright © 2016 Elsevier Ltd. All rights reserved.
Sensing properties of pristine boron nitride nanostructures towards alkaloids: A first principles dispersion corrected study

NASA Astrophysics Data System (ADS)

Roondhe, Basant; Dabhi, Shweta D.; Jha, Prafulla K.

2018-05-01

To understand the underlying physics behind the interaction of biomolecules with the nanomaterials to use them practically as bio-nanomaterials is very crucial. A first principles calculation under the frame work of density functional theory is executed to investigate the electronic structures and binding properties of alkaloids (Caffeine and Nicotine) over single walled boron nitride nanotube (BNNT) and boron nitride nanoribbon (BNNR) to determine their suitability towards filtration or sensing of these molecules. We have also used GGA-PBE scheme with the inclusion of Van der Waals (vdW) interaction based on DFT-D2. Increase in the accuracy by incorporating the dispersion correction in the calculation is observed for the long range Van der Waals interaction. Binding energy range of BNNT and BNNR with both alkaloids have been found to be -0.35 to -0.76 eV and -0.45 to -0.91 eV respectively which together with the binding distance shows physisorption binding of these molecules to the both nanostructures. The transfer of charge between the BN nanostructures and the adsorbed molecule has also been analysed by using Lowdin charge analysis. The sensitivity of both nanostructures BNNT and BNNR towards both alkaloids is observed through electronic structure calculations, density of states and quantum conductance. The binding of both alkaloids with BNNR is stronger. The analysis of the calculated properties suggests absence of covalent interaction between the considered species (BNNT/BNNR) and alkaloids. The study may be useful in designing the boron nitride nanostructure based sensing device for alkaloids.
Normal modes of weak colloidal gels

NASA Astrophysics Data System (ADS)

Varga, Zsigmond; Swan, James W.

2018-01-01

The normal modes and relaxation rates of weak colloidal gels are investigated in calculations using different models of the hydrodynamic interactions between suspended particles. The relaxation spectrum is computed for freely draining, Rotne-Prager-Yamakawa, and accelerated Stokesian dynamics approximations of the hydrodynamic mobility in a normal mode analysis of a harmonic network representing several colloidal gels. We find that the density of states and spatial structure of the normal modes are fundamentally altered by long-ranged hydrodynamic coupling among the particles. Short-ranged coupling due to hydrodynamic lubrication affects only the relaxation rates of short-wavelength modes. Hydrodynamic models accounting for long-ranged coupling exhibit a microscopic relaxation rate for each normal mode, λ that scales as l-2, where l is the spatial correlation length of the normal mode. For the freely draining approximation, which neglects long-ranged coupling, the microscopic relaxation rate scales as l-γ, where γ varies between three and two with increasing particle volume fraction. A simple phenomenological model of the internal elastic response to normal mode fluctuations is developed, which shows that long-ranged hydrodynamic interactions play a central role in the viscoelasticity of the gel network. Dynamic simulations of hard spheres that gel in response to short-ranged depletion attractions are used to test the applicability of the density of states predictions. For particle concentrations up to 30% by volume, the power law decay of the relaxation modulus in simulations accounting for long-ranged hydrodynamic interactions agrees with predictions generated by the density of states of the corresponding harmonic networks as well as experimental measurements. For higher volume fractions, excluded volume interactions dominate the stress response, and the prediction from the harmonic network density of states fails. Analogous to the Zimm model in polymer physics, our results indicate that long-ranged hydrodynamic interactions play a crucial role in determining the microscopic dynamics and macroscopic properties of weak colloidal gels.
Finite-size effects in simulations of electrolyte solutions under periodic boundary conditions

NASA Astrophysics Data System (ADS)

Thompson, Jeffrey; Sanchez, Isaac

The equilibrium properties of charged systems with periodic boundary conditions may exhibit pronounced system-size dependence due to the long range of the Coulomb force. As shown by others, the leading-order finite-size correction to the Coulomb energy of a charged fluid confined to a periodic box of volume V may be derived from sum rules satisfied by the charge-charge correlations in the thermodynamic limit V -> ∞ . In classical systems, the relevant sum rule is the Stillinger-Lovett second-moment (or perfect screening) condition. This constraint implies that for large V, periodicity induces a negative bias of -kB T(2 V) - 1 in the total Coulomb energy density of a homogeneous classical charged fluid of given density and temperature. We present a careful study of the impact of such finite-size effects on the calculation of solute chemical potentials from explicit-solvent molecular simulations of aqueous electrolyte solutions. National Science Foundation Graduate Research Fellowship Program, Grant No. DGE-1610403.
Fermi orbital self-interaction corrected electronic structure of molecules beyond local density approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hahn, T., E-mail: torsten.hahn@physik.tu-freiberg.de; Liebing, S.; Kortus, J.

2015-12-14

The correction of the self-interaction error that is inherent to all standard density functional theory calculations is an object of increasing interest. In this article, we apply the very recently developed Fermi-orbital based approach for the self-interaction correction [M. R. Pederson et al., J. Chem. Phys. 140, 121103 (2014) and M. R. Pederson, J. Chem. Phys. 142, 064112 (2015)] to a set of different molecular systems. Our study covers systems ranging from simple diatomic to large organic molecules. We focus our analysis on the direct estimation of the ionization potential from orbital eigenvalues. Further, we show that the Fermi orbitalmore » positions in structurally similar molecules appear to be transferable.« less
Optical-model potential for electron and positron elastic scattering by atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salvat, Francesc

2003-07-01

An optical-model potential for systematic calculations of elastic scattering of electrons and positrons by atoms and positive ions is proposed. The electrostatic interaction is determined from the Dirac-Hartree-Fock self-consistent atomic electron density. In the case of electron projectiles, the exchange interaction is described by means of the local-approximation of Furness and McCarthy. The correlation-polarization potential is obtained by combining the correlation potential derived from the local density approximation with a long-range polarization interaction, which is represented by means of a Buckingham potential with an empirical energy-dependent cutoff parameter. The absorption potential is obtained from the local-density approximation, using the Born-Ochkurmore » approximation and the Lindhard dielectric function to describe the binary collisions with a free-electron gas. The strength of the absorption potential is adjusted by means of an empirical parameter, which has been determined by fitting available absolute elastic differential cross-section data for noble gases and mercury. The Dirac partial-wave analysis with this optical-model potential provides a realistic description of elastic scattering of electrons and positrons with energies in the range from {approx}100 eV up to {approx}5 keV. At higher energies, correlation-polarization and absorption corrections are small and the usual static-exchange approximation is sufficiently accurate for most practical purposes.« less
Kinetic Monte Carlo modeling of the efficiency roll-off in a multilayer white organic light-emitting device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mesta, M.; Coehoorn, R.; Bobbert, P. A.

2016-03-28

Triplet-triplet annihilation (TTA) and triplet-polaron quenching (TPQ) in organic light-emitting devices (OLEDs) lead to a roll-off of the internal quantum efficiency (IQE) with increasing current density J. We employ a kinetic Monte Carlo modeling study to analyze the measured IQE and color balance as a function of J in a multilayer hybrid white OLED that combines fluorescent blue with phosphorescent green and red emission. We investigate two models for TTA and TPQ involving the phosphorescent green and red emitters: short-range nearest-neighbor quenching and long-range Förster-type quenching. Short-range quenching predicts roll-off to occur at much higher J than measured. Taking long-rangemore » quenching with Förster radii for TTA and TPQ equal to twice the Förster radii for exciton transfer leads to a fair description of the measured IQE-J curve, with the major contribution to the roll-off coming from TPQ. The measured decrease of the ratio of phosphorescent to fluorescent component of the emitted light with increasing J is correctly predicted. A proper description of the J-dependence of the ratio of red and green phosphorescent emission needs further model refinements.« less
A new empirical potential energy function for Ar2

NASA Astrophysics Data System (ADS)

Myatt, Philip T.; Dham, Ashok K.; Chandrasekhar, Pragna; McCourt, Frederick R. W.; Le Roy, Robert J.

2018-06-01

A critical re-analysis of all available spectroscopic and virial coefficient data for Ar2 has been used to determine an improved empirical analytic potential energy function that has been 'tuned' to optimise its agreement with viscosity, diffusion and thermal diffusion data, and whose short-range behaviour is in reasonably good agreement with the most recent ab initio calculations for this system. The recommended Morse/long-range potential function is smooth and differentiable at all distances, and incorporates both the correct theoretically predicted long-range behaviour and the correct limiting short-range functional behaviour. The resulting value of the well depth is ? cm-1 and the associated equilibrium distance is re = 3.766 (±0.002) Å, while the 40Ar s-wave scattering length is -714 Å.
Nonempirical Semilocal Free-Energy Density Functional for Matter under Extreme Conditions.

PubMed

Karasiev, Valentin V; Dufty, James W; Trickey, S B

2018-02-16

Realizing the potential for predictive density functional calculations of matter under extreme conditions depends crucially upon having an exchange-correlation (XC) free-energy functional accurate over a wide range of state conditions. Unlike the ground-state case, no such functional exists. We remedy that with systematic construction of a generalized gradient approximation XC free-energy functional based on rigorous constraints, including the free-energy gradient expansion. The new functional provides the correct temperature dependence in the slowly varying regime and the correct zero-T, high-T, and homogeneous electron gas limits. Its accuracy in the warm dense matter regime is attested by excellent agreement of the calculated deuterium equation of state with reference path integral Monte Carlo results at intermediate and elevated T. Pressure shifts for hot electrons in compressed static fcc Al and for low-density Al demonstrate the combined magnitude of thermal and gradient effects handled well by this functional over a wide T range.
Nonempirical Semilocal Free-Energy Density Functional for Matter under Extreme Conditions

NASA Astrophysics Data System (ADS)

Karasiev, Valentin V.; Dufty, James W.; Trickey, S. B.

2018-02-01

Realizing the potential for predictive density functional calculations of matter under extreme conditions depends crucially upon having an exchange-correlation (X C ) free-energy functional accurate over a wide range of state conditions. Unlike the ground-state case, no such functional exists. We remedy that with systematic construction of a generalized gradient approximation X C free-energy functional based on rigorous constraints, including the free-energy gradient expansion. The new functional provides the correct temperature dependence in the slowly varying regime and the correct zero-T , high-T , and homogeneous electron gas limits. Its accuracy in the warm dense matter regime is attested by excellent agreement of the calculated deuterium equation of state with reference path integral Monte Carlo results at intermediate and elevated T . Pressure shifts for hot electrons in compressed static fcc Al and for low-density Al demonstrate the combined magnitude of thermal and gradient effects handled well by this functional over a wide T range.

Tuning the effective fine structure constant in graphene: opposing effects of dielectric screening on short- and long-range potential scattering.

PubMed

Jang, C; Adam, S; Chen, J-H; Williams, E D; Das Sarma, S; Fuhrer, M S

2008-10-03

We reduce the dimensionless interaction strength alpha in graphene by adding a water overlayer in ultrahigh vacuum, thereby increasing dielectric screening. The mobility limited by long-range impurity scattering is increased over 30%, due to the background dielectric constant enhancement leading to a reduced interaction of electrons with charged impurities. However, the carrier-density-independent conductivity due to short-range impurities is decreased by almost 40%, due to reduced screening of the impurity potential by conduction electrons. The minimum conductivity is nearly unchanged, due to canceling contributions from the electron-hole puddle density and long-range impurity mobility. Experimental data are compared with theoretical predictions with excellent agreement.
Entanglement entropy for the long-range Ising chain in a transverse field.

PubMed

Koffel, Thomas; Lewenstein, M; Tagliacozzo, Luca

2012-12-28

We consider the Ising model in a transverse field with long-range antiferromagnetic interactions that decay as a power law with their distance. We study both the phase diagram and the entanglement properties as a function of the exponent of the interaction. The phase diagram can be used as a guide for future experiments with trapped ions. We find two gapped phases, one dominated by the transverse field, exhibiting quasi-long-range order, and one dominated by the long-range interaction, with long-range Néel ordered ground states. We determine the location of the quantum critical points separating those two phases. We determine their critical exponents and central charges. In the phase with quasi-long-range order the ground states exhibit exotic corrections to the area law for the entanglement entropy coexisting with gapped entanglement spectra.
[Long-term results of posterior chamber phakic intraocular lens implantation for correction of high ametropia].

PubMed

Le Loir, M; Cochener, B

2012-06-01

To assess efficacy, stability and safety of posterior chamber phakic intraocular lens implantation with STAAR Visian ICL for correction of high ametropia, with a mean follow-up of 5 years (3.5-10 years). Ninety eyes of 53 highly ametropic patients (45 myopia, ten hyperopia and 35 with mixed astigmatism) were included in a retrospective single-surgeon study, using primarily the V4 ICL model (87 eyes). We studied pre- and postoperative refractive efficacy, endothelial cell density, crystalline lens opacification and intraocular clearances within the various compartments of the eye. Mean uncorrected visual acuity was 0.77 at the 12th postoperative month; 17 of 90 eyes required adjunctive photoablation for residual astigmatism. Forty-eight percent of eyes gained at least one line of best corrected visual acuity. After implantation, the decrease in endothelial cell density remained stable at 0.69%/year, and 91% of eyes showed no opacification of the crystalline lens. Mean endothelium-ICL and ICL-crystalline lens distances were 2.41 mm and 0.52 mm respectively. Overall patient satisfaction achieved was 96% at 36 months postoperatively. These results demonstrate efficacy, stability and safety of the ICL V4 phakic IOL for the correction of high ametropia. Long-term follow-up did not show a significant increase in cataract formation in implanted eyes. Copyright © 2012. Published by Elsevier Masson SAS.
A method to estimate the neutral atmospheric density near the ionospheric main peak of Mars

NASA Astrophysics Data System (ADS)

Zou, Hong; Ye, Yu Guang; Wang, Jin Song; Nielsen, Erling; Cui, Jun; Wang, Xiao Dong

2016-04-01

A method to estimate the neutral atmospheric density near the ionospheric main peak of Mars is introduced in this study. The neutral densities at 130 km can be derived from the ionospheric and atmospheric measurements of the Radio Science experiment on board Mars Global Surveyor (MGS). The derived neutral densities cover a large longitude range in northern high latitudes from summer to late autumn during 3 Martian years, which fills the gap of the previous observations for the upper atmosphere of Mars. The simulations of the Laboratoire de Météorologie Dynamique Mars global circulation model can be corrected with a simple linear equation to fit the neutral densities derived from the first MGS/RS (Radio Science) data sets (EDS1). The corrected simulations with the same correction parameters as for EDS1 match the derived neutral densities from two other MGS/RS data sets (EDS2 and EDS3) very well. The derived neutral density from EDS3 shows a dust storm effect, which is in accord with the Mars Express (MEX) Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars measurement. The neutral density derived from the MGS/RS measurements can be used to validate the Martian atmospheric models. The method presented in this study can be applied to other radio occultation measurements, such as the result of the Radio Science experiment on board MEX.
Combining Density Functional Theory and Green's Function Theory: Range-Separated, Nonlocal, Dynamic, and Orbital-Dependent Hybrid Functional.

PubMed

Kananenka, Alexei A; Zgid, Dominika

2017-11-14

We present a rigorous framework which combines single-particle Green's function theory with density functional theory based on a separation of electron-electron interactions into short- and long-range components. Short-range contribution to the total energy and exchange-correlation potential is provided by a density functional approximation, while the long-range contribution is calculated using an explicit many-body Green's function method. Such a hybrid results in a nonlocal, dynamic, and orbital-dependent exchange-correlation functional of a single-particle Green's function. In particular, we present a range-separated hybrid functional called srSVWN5-lrGF2 which combines the local-density approximation and the second-order Green's function theory. We illustrate that similarly to density functional approximations, the new functional is weakly basis-set dependent. Furthermore, it offers an improved description of the short-range dynamic correlation. The many-body contribution to the functional mitigates the many-electron self-interaction error present in many density functional approximations and provides a better description of molecular properties. Additionally, we illustrate that the new functional can be used to scale down the self-energy and, therefore, introduce an additional sparsity to the self-energy matrix that in the future can be exploited in calculations for large molecules or periodic systems.
Long range intermolecular interactions between the alkali diatomics Na2, K2, and NaK

NASA Astrophysics Data System (ADS)

Zemke, Warren T.; Byrd, Jason N.; Michels, H. Harvey; Montgomery, John A.; Stwalley, William C.

2010-06-01

Long range interactions between the ground state alkali diatomics Na2-Na2, K2-K2, Na2-K2, and NaK-NaK are examined. Interaction energies are first determined from ab initio calculations at the coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory, including counterpoise corrections. Long range energies calculated from diatomic molecular properties (polarizabilities and dipole and quadrupole moments) are then compared with the ab initio energies. A simple asymptotic model potential ELR=Eelec+Edisp+Eind is shown to accurately represent the intermolecular interactions for these systems at long range.
Long range intermolecular interactions between the alkali diatomics Na(2), K(2), and NaK.

PubMed

Zemke, Warren T; Byrd, Jason N; Michels, H Harvey; Montgomery, John A; Stwalley, William C

2010-06-28

Long range interactions between the ground state alkali diatomics Na(2)-Na(2), K(2)-K(2), Na(2)-K(2), and NaK-NaK are examined. Interaction energies are first determined from ab initio calculations at the coupled-cluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory, including counterpoise corrections. Long range energies calculated from diatomic molecular properties (polarizabilities and dipole and quadrupole moments) are then compared with the ab initio energies. A simple asymptotic model potential E(LR)=E(elec)+E(disp)+E(ind) is shown to accurately represent the intermolecular interactions for these systems at long range.
Excitation energies from range-separated time-dependent density and density matrix functional theory.

PubMed

Pernal, Katarzyna

2012-05-14

Time-dependent density functional theory (TD-DFT) in the adiabatic formulation exhibits known failures when applied to predicting excitation energies. One of them is the lack of the doubly excited configurations. On the other hand, the time-dependent theory based on a one-electron reduced density matrix functional (time-dependent density matrix functional theory, TD-DMFT) has proven accurate in determining single and double excitations of H(2) molecule if the exact functional is employed in the adiabatic approximation. We propose a new approach for computing excited state energies that relies on functionals of electron density and one-electron reduced density matrix, where the latter is applied in the long-range region of electron-electron interactions. A similar approach has been recently successfully employed in predicting ground state potential energy curves of diatomic molecules even in the dissociation limit, where static correlation effects are dominating. In the paper, a time-dependent functional theory based on the range-separation of electronic interaction operator is rigorously formulated. To turn the approach into a practical scheme the adiabatic approximation is proposed for the short- and long-range components of the coupling matrix present in the linear response equations. In the end, the problem of finding excitation energies is turned into an eigenproblem for a symmetric matrix. Assignment of obtained excitations is discussed and it is shown how to identify double excitations from the analysis of approximate transition density matrix elements. The proposed method used with the short-range local density approximation (srLDA) and the long-range Buijse-Baerends density matrix functional (lrBB) is applied to H(2) molecule (at equilibrium geometry and in the dissociation limit) and to Be atom. The method accounts for double excitations in the investigated systems but, unfortunately, the accuracy of some of them is poor. The quality of the other excitations is in general much better than that offered by TD-DFT-LDA or TD-DMFT-BB approximations if the range-separation parameter is properly chosen. The latter remains an open problem.
Density functional theory and chromium: Insights from the dimers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Würdemann, Rolf; Kristoffersen, Henrik H.; Moseler, Michael

2015-03-28

The binding in small Cr clusters is re-investigated, where the correct description of the dimer in three charge states is used as criterion to assign the most suitable density functional theory approximation. The difficulty in chromium arises from the subtle interplay between energy gain from hybridization and energetic cost due to exchange between s and d based molecular orbitals. Variations in published bond lengths and binding energies are shown to arise from insufficient numerical representation of electron density and Kohn-Sham wave-functions. The best functional performance is found for gradient corrected (GGA) functionals and meta-GGAs, where we find severe differences betweenmore » functionals from the same family due to the importance of exchange. Only the “best fit” from Bayesian error estimation is able to predict the correct energetics for all three charge states unambiguously. With this knowledge, we predict small bond-lengths to be exclusively present in Cr{sub 2} and Cr{sub 2}{sup −}. Already for the dimer cation, solely long bond-lengths appear, similar to what is found in the trimer and in chromium bulk.« less
Nonequilibrium forces following quenches in active and thermal matter.

PubMed

Rohwer, Christian M; Solon, Alexandre; Kardar, Mehran; Krüger, Matthias

2018-03-01

Nonequilibrium systems with conserved quantities like density or momentum are known to exhibit long-ranged correlations. This, in turn, leads to long-ranged fluctuation-induced (Casimir) forces, predicted to arise in a variety of nonequilibrium settings. Here, we study such forces, which arise transiently between parallel plates or compact inclusions in a gas of particles, following a change ("quench") in temperature or activity of the medium. Analytical calculations, as well as numerical simulations of passive or active Brownian particles, indicate two distinct forces: (i) The immediate effect of the quench is adsorption or desorption of particles of the medium to the immersed objects, which in turn initiates a front of relaxing (mean) density. This leads to time-dependent density-induced forces. (ii) A long-term effect of the quench is that density fluctuations are modified, manifested as transient (long-ranged) (pair-)correlations that relax diffusively to their (short-ranged) steady-state limit. As a result, transient fluctuation-induced forces emerge. We discuss the properties of fluctuation-induced and density-induced forces as regards universality, relaxation as a function of time, and scaling with distance between objects. Their distinct signatures allow us to distinguish the two types of forces in simulation data. Our simulations also show that a quench of the effective temperature of an active medium gives rise to qualitatively similar effects to a temperature quench in a passive medium. Based on this insight, we propose several scenarios for the experimental observation of the forces described here.
Nonequilibrium forces following quenches in active and thermal matter

NASA Astrophysics Data System (ADS)

Rohwer, Christian M.; Solon, Alexandre; Kardar, Mehran; Krüger, Matthias

2018-03-01

Nonequilibrium systems with conserved quantities like density or momentum are known to exhibit long-ranged correlations. This, in turn, leads to long-ranged fluctuation-induced (Casimir) forces, predicted to arise in a variety of nonequilibrium settings. Here, we study such forces, which arise transiently between parallel plates or compact inclusions in a gas of particles, following a change ("quench") in temperature or activity of the medium. Analytical calculations, as well as numerical simulations of passive or active Brownian particles, indicate two distinct forces: (i) The immediate effect of the quench is adsorption or desorption of particles of the medium to the immersed objects, which in turn initiates a front of relaxing (mean) density. This leads to time-dependent density-induced forces. (ii) A long-term effect of the quench is that density fluctuations are modified, manifested as transient (long-ranged) (pair-)correlations that relax diffusively to their (short-ranged) steady-state limit. As a result, transient fluctuation-induced forces emerge. We discuss the properties of fluctuation-induced and density-induced forces as regards universality, relaxation as a function of time, and scaling with distance between objects. Their distinct signatures allow us to distinguish the two types of forces in simulation data. Our simulations also show that a quench of the effective temperature of an active medium gives rise to qualitatively similar effects to a temperature quench in a passive medium. Based on this insight, we propose several scenarios for the experimental observation of the forces described here.
Theoretical Study of Trimethylacetic Acid Adsorption on CeO 2 (111) Surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Weina; Thevuthasan, S.; Wang, Wenliang

We investigated trimethylacetic acid (TMAA) adsorption on stoichiometric and oxygen-deficient CeO 2(111) surfaces using density functional theory that accounts for the on-site Coulomb interaction via a Hubbard term (DFT+U) and long-range dispersion correction. Both the molecular state and dissociative state (TMAA → TMA– + H +) were identified on stoichiometric and oxygen-deficient CeO 2(111) surfaces. For the stoichiometric surface, two thermodynamically favorable configurations with adsorption energies of the order of -30 kcal/mol are identified; one is a molecule adsorption state, and the other one is a dissociative state. For the oxygen-deficient surface, dissociative states are more favorable than molecular states.more » Moreover, the most favorable configuration is the dissociative adsorption of TMAA with the adsorption energy of the order of -77 kcal/mol. The dissociated TMA moiety takes the position of oxygen vacancy, forming three Ce–O bonds. The signature vibrational frequencies for these thermodynamically stable structures are reported as well as their electronic structures. The effects of long-range dispersion interactions are found to be negligible for geometries but important for adsorption energies.« less
Theoretical Study of Trimethylacetic Acid Adsorption on CeO 2 (111) Surface

DOE PAGES

Wang, Weina; Thevuthasan, S.; Wang, Wenliang; ...

2016-01-11

We investigated trimethylacetic acid (TMAA) adsorption on stoichiometric and oxygen-deficient CeO 2(111) surfaces using density functional theory that accounts for the on-site Coulomb interaction via a Hubbard term (DFT+U) and long-range dispersion correction. Both the molecular state and dissociative state (TMAA → TMA– + H +) were identified on stoichiometric and oxygen-deficient CeO 2(111) surfaces. For the stoichiometric surface, two thermodynamically favorable configurations with adsorption energies of the order of -30 kcal/mol are identified; one is a molecule adsorption state, and the other one is a dissociative state. For the oxygen-deficient surface, dissociative states are more favorable than molecular states.more » Moreover, the most favorable configuration is the dissociative adsorption of TMAA with the adsorption energy of the order of -77 kcal/mol. The dissociated TMA moiety takes the position of oxygen vacancy, forming three Ce–O bonds. The signature vibrational frequencies for these thermodynamically stable structures are reported as well as their electronic structures. The effects of long-range dispersion interactions are found to be negligible for geometries but important for adsorption energies.« less
Correlations and enlarged superconducting phase of t -J⊥ chains of ultracold molecules on optical lattices

NASA Astrophysics Data System (ADS)

Manmana, Salvatore R.; Möller, Marcel; Gezzi, Riccardo; Hazzard, Kaden R. A.

2017-10-01

We compute physical properties across the phase diagram of the t -J⊥ chain with long-range dipolar interactions, which describe ultracold polar molecules on optical lattices. Our results obtained by the density-matrix renormalization group indicate that superconductivity is enhanced when the Ising component Jz of the spin-spin interaction and the charge component V are tuned to zero and even further by the long-range dipolar interactions. At low densities, a substantially larger spin gap is obtained. We provide evidence that long-range interactions lead to algebraically decaying correlation functions despite the presence of a gap. Although this has recently been observed in other long-range interacting spin and fermion models, the correlations in our case have the peculiar property of having a small and continuously varying exponent. We construct simple analytic models and arguments to understand the most salient features.
Optimized equation of the state of the square-well fluid of variable range based on a fourth-order free-energy expansion.

PubMed

Espíndola-Heredia, Rodolfo; del Río, Fernando; Malijevsky, Anatol

2009-01-14

The free energy of square-well (SW) systems of hard-core diameter sigma with ranges 1 < or = lambda < or = 3 is expanded in a perturbation series. This interval covers most ranges of interest, from short-ranged SW fluids (lambda approximately 1.2) used in modeling colloids to long ranges (lambda approximately 3) where the van der Waals classic approximation holds. The first four terms are evaluated by means of extensive Monte Carlo simulations. The calculations are corrected for the thermodynamic limit and care is taken to evaluate and to control the various sources of error. The results for the first two terms in the series confirm well-known independent results but have an increased estimated accuracy and cover a wider set of well ranges. The results for the third- and fourth-order terms are novel. The free-energy expansion for systems with short and intermediate ranges, 1 < or = lambda < or = 2, is seen to have properties similar to those of systems with longer ranges, 2 < or = lambda < or = 3. An equation of state (EOS) is built to represent the free-energy data. The thermodynamics given by this EOS, confronted against independent computer simulations, is shown to predict accurately the internal energy, pressure, specific heat, and chemical potential of the SW fluids considered and for densities 0 < or = rho sigma(3) < or = 0.9 including subcritical temperatures. This fourth-order theory is estimated to be accurate except for a small region at high density, rho sigma(3) approximately 0.9, and low temperature where terms of still higher order might be needed.
Subaru Telescope limits on cosmological variations in the fine-structure constant

NASA Astrophysics Data System (ADS)

Murphy, Michael T.; Cooksey, Kathy L.

2017-11-01

Previous, large samples of quasar absorption spectra have indicated some evidence for relative variations in the fine-structure constant (Δα/α) across the sky. However, they were likely affected by long-range distortions of the wavelength calibration, so it is important to establish a statistical sample of more reliable results from multiple telescopes. Here we triple the sample of Δα/α measurements from the Subaru Telescope which have been `supercalibrated' to correct for long-range distortions. A blinded analysis of the metallic ions in six intervening absorption systems in two Subaru quasar spectra provides no evidence for α variation, with a weighted mean of Δα/α = 3.0 ± 2.8stat ± 2.0sys parts per million (1σ statistical and systematic uncertainties). The main remaining systematic effects are uncertainties in the long-range distortion corrections, absorption profile models, and errors from redispersing multiple quasar exposures on to a common wavelength grid. The results also assume that terrestrial isotopic abundances prevail in the absorbers; assuming only the dominant terrestrial isotope is present significantly lowers Δα/α, though it is still consistent with zero. Given the location of the two quasars on the sky, our results do not support the evidence for spatial α variation, especially when combined with the 21 other recent measurements which were corrected for, or resistant to, long-range distortions. Our spectra and absorption profile fits are publicly available.
Short, intermediate and long range order in amorphous ices

NASA Astrophysics Data System (ADS)

Martelli, Fausto; Torquato, Salvatore; Giovanbattista, Nicolas; Car, Roberto

Water exhibits polyamorphism, i.e., it exists in more than one amorphous state. The most common forms of glassy water are the low-density amorphous (LDA) and the high-density amorphous (HDA) ices. LDA, the most abundant form of ice in the Universe, transforms into HDA upon isothermal compression. We model the transformation of LDA into HDA under isothermal compression with classical molecular dynamics simulations. We analyze the molecular structures with a recently introduced scalar order metric to measure short and intermediate range order. In addition, we rank the structures by their degree of hyperuniformity, i.e.,the extent to which long range density fluctuations are suppressed. F.M. and R.C. acknowledge support from the Department of Energy (DOE) under Grant No. DE-SC0008626.
Vibronic coupling simulations for linear and nonlinear optical processes: Simulation results

NASA Astrophysics Data System (ADS)

Silverstein, Daniel W.; Jensen, Lasse

2012-02-01

A vibronic coupling model based on time-dependent wavepacket approach is applied to simulate linear optical processes, such as one-photon absorbance and resonance Raman scattering, and nonlinear optical processes, such as two-photon absorbance and resonance hyper-Raman scattering, on a series of small molecules. Simulations employing both the long-range corrected approach in density functional theory and coupled cluster are compared and also examined based on available experimental data. Although many of the small molecules are prone to anharmonicity in their potential energy surfaces, the harmonic approach performs adequately. A detailed discussion of the non-Condon effects is illustrated by the molecules presented in this work. Linear and nonlinear Raman scattering simulations allow for the quantification of interference between the Franck-Condon and Herzberg-Teller terms for different molecules.
FPGA implementation of advanced FEC schemes for intelligent aggregation networks

NASA Astrophysics Data System (ADS)

Zou, Ding; Djordjevic, Ivan B.

2016-02-01

In state-of-the-art fiber-optics communication systems the fixed forward error correction (FEC) and constellation size are employed. While it is important to closely approach the Shannon limit by using turbo product codes (TPC) and low-density parity-check (LDPC) codes with soft-decision decoding (SDD) algorithm; rate-adaptive techniques, which enable increased information rates over short links and reliable transmission over long links, are likely to become more important with ever-increasing network traffic demands. In this invited paper, we describe a rate adaptive non-binary LDPC coding technique, and demonstrate its flexibility and good performance exhibiting no error floor at BER down to 10-15 in entire code rate range, by FPGA-based emulation, making it a viable solution in the next-generation high-speed intelligent aggregation networks.
Valence and charge-transfer optical properties for some SinCm (m, n ≤ 12) clusters: Comparing TD-DFT, complete-basis-limit EOMCC, and benchmarks from spectroscopy.

PubMed

Lutz, Jesse J; Duan, Xiaofeng F; Ranasinghe, Duminda S; Jin, Yifan; Margraf, Johannes T; Perera, Ajith; Burggraf, Larry W; Bartlett, Rodney J

2018-05-07

Accurate optical characterization of the closo-Si 12 C 12 molecule is important to guide experimental efforts toward the synthesis of nano-wires, cyclic nano-arrays, and related array structures, which are anticipated to be robust and efficient exciton materials for opto-electronic devices. Working toward calibrated methods for the description of closo-Si 12 C 12 oligomers, various electronic structure approaches are evaluated for their ability to reproduce measured optical transitions of the SiC 2 , Si 2 C n (n = 1-3), and Si 3 C n (n = 1, 2) clusters reported earlier by Steglich and Maier [Astrophys. J. 801, 119 (2015)]. Complete-basis-limit equation-of-motion coupled-cluster (EOMCC) results are presented and a comparison is made between perturbative and renormalized non-iterative triples corrections. The effect of adding a renormalized correction for quadruples is also tested. Benchmark test sets derived from both measurement and high-level EOMCC calculations are then used to evaluate the performance of a variety of density functionals within the time-dependent density functional theory (TD-DFT) framework. The best-performing functionals are subsequently applied to predict valence TD-DFT excitation energies for the lowest-energy isomers of Si n C and Si n-1 C 7-n (n = 4-6). TD-DFT approaches are then applied to the Si n C n (n = 4-12) clusters and unique spectroscopic signatures of closo-Si 12 C 12 are discussed. Finally, various long-range corrected density functionals, including those from the CAM-QTP family, are applied to a charge-transfer excitation in a cyclic (Si 4 C 4 ) 4 oligomer. Approaches for gauging the extent of charge-transfer character are also tested and EOMCC results are used to benchmark functionals and make recommendations.

Phantom studies investigating extravascular density imaging for partial volume correction of 3-D PET /sup 18/FDG studies

NASA Astrophysics Data System (ADS)

Wassenaar, R. W.; Beanlands, R. S. B.; deKemp, R. A.

2004-02-01

Limited scanner resolution and cardiac motion contribute to partial volume (PV) averaging of cardiac PET images. An extravascular (EV) density image, created from the subtraction of a blood pool scan from a transmission image, has been used to correct for PV averaging in H/sub 2//sup 15/O studies using 2-D imaging but not with 3-D imaging of other tracers such as /sup 18/FDG. A cardiac phantom emulating the left ventricle was used to characterize the method for use in 3-D PET studies. Measurement of the average myocardial activity showed PV losses of 32% below the true activity (p<0.001). Initial application of the EV density correction still yielded a myocardial activity 13% below the true value (p<0.001). This failure of the EV density image was due to the 1.66 mm thick plastic barrier separating the myocardial and ventricular chambers within the phantom. Upon removal of this artifact by morphological dilation of the blood pool, the corrected myocardial value was within 2% of the true value (p=ns). Spherical ROIs (diameter of 2 to 10 mm), evenly distributed about the myocardium, were also used to calculate the average activity. The EV density image was able to account for PV averaging throughout the range of diameters to within a 5% accuracy, however, a small bias was seen as the size of the ROIs increased. This indicated a slight mismatch between the emission and transmission image resolutions, a result of the difference in data acquisitions (i.e., span and ring difference) and default smoothing. These results show that the use of EV density image to correct for PV averaging is possible with 3-D PET. A method of correcting barrier effects in phantoms has been presented, as well as a process for evaluating resolution mismatch.
Conditions where random phase approximation becomes exact in the high-density limit

NASA Astrophysics Data System (ADS)

Morawetz, Klaus; Ashokan, Vinod; Bala, Renu; Pathak, Kare Narain

2018-04-01

It is shown that, in d -dimensional systems, the vertex corrections beyond the random phase approximation (RPA) or G W approximation scales with the power d -β -α of the Fermi momentum if the relation between Fermi energy and Fermi momentum is ɛf˜pfβ and the interacting potential possesses a momentum power law of ˜p-α . The condition d -β -α <0 specifies systems where RPA is exact in the high-density limit. The one-dimensional structure factor is found to be the interaction-free one in the high-density limit for contact interaction. A cancellation of RPA and vertex corrections render this result valid up to second order in contact interaction. For finite-range potentials of cylindrical wires a large-scale cancellation appears and is found to be independent of the width parameter of the wire. The proposed high-density expansion agrees with the quantum Monte Carlo simulations.
Hydrodynamic limit of Wigner-Poisson kinetic theory: Revisited

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akbari-Moghanjoughi, M.; International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Ruhr University Bochum, D-44780 Bochum

2015-02-15

In this paper, we revisit the hydrodynamic limit of the Langmuir wave dispersion relation based on the Wigner-Poisson model in connection with that obtained directly from the original Lindhard dielectric function based on the random-phase-approximation. It is observed that the (fourth-order) expansion of the exact Lindhard dielectric constant correctly reduces to the hydrodynamic dispersion relation with an additional term of fourth-order, beside that caused by the quantum diffraction effect. It is also revealed that the generalized Lindhard dielectric theory accounts for the recently discovered Shukla-Eliasson attractive potential (SEAP). However, the expansion of the exact Lindhard static dielectric function leads tomore » a k{sup 4} term of different magnitude than that obtained from the linearized quantum hydrodynamics model. It is shown that a correction factor of 1/9 should be included in the term arising from the quantum Bohm potential of the momentum balance equation in fluid model in order for a correct plasma dielectric response treatment. Finally, it is observed that the long-range oscillatory screening potential (Friedel oscillations) of type cos(2k{sub F}r)/r{sup 3}, which is a consequence of the divergence of the dielectric function at point k = 2k{sub F} in a quantum plasma, arises due to the finiteness of the Fermi-wavenumber and is smeared out in the limit of very high electron number-densities, typical of white dwarfs and neutron stars. In the very low electron number-density regime, typical of semiconductors and metals, where the Friedel oscillation wavelength becomes much larger compared to the interparticle distances, the SEAP appears with a much deeper potential valley. It is remarked that the fourth-order approximate Lindhard dielectric constant approaches that of the linearized quantum hydrodynamic in the limit if very high electron number-density. By evaluation of the imaginary part of the Lindhard dielectric function, it is shown that the Landau-damping region in ω-k plane increases dramatically by increase of the electron number-density.« less
Imputation of Missing Genotypes From Sparse to High Density Using Long-Range Phasing

USDA-ARS?s Scientific Manuscript database

Related individuals in a population share long chromosome segments which trace to a common ancestor. We describe a long-range phasing algorithm that makes use of this property to phase whole chromosomes and simultaneously impute a large number of missing markers. We test our method by imputing marke...
Aberrant patterns of local and long-range functional connectivity densities in schizophrenia

PubMed Central

Tian, Hongjun; Li, Jie; Qu, Hongru; Cheng, Langlang; Zhu, Jingjing; Zhuo, Chuanjun

2017-01-01

Schizophrenia is a disorder of brain dysconnectivity, and both the connection strength and connection number are disrupted in patients with schizophrenia. The functional connectivity density (FCD) can reflect alterations in the connection number. Alterations in the global FCD (gFCD) in schizophrenia were previously demonstrated; however, alterations in two other indices of the pathological characteristics of the brain, local FCD (lFCD) and long-range FCD (lrFCD), have not been revealed. To investigate lFCD and lrFCD alterations in patients with schizophrenia, 95 patients and 93 matched healthy controls were examined using structural and resting-state functional magnetic resonance imaging scanning. lFCD and lrFCD were measured using FCD mapping, and differences were identified using a two-sample t-test in a voxel-wise manner, with age and gender considered to increase variability. Multiple comparisons were performed using a false discovery rate method with a corrected threshold of P<0.05. Our analysis showed that lFCD was primarily decreased in the postcentral gyrus, right calcarine sulcus, and inferior occipital gyrus lobule, but increased in the bilateral subcortical regions. The differences in lFCD were more pronounced and complicated than those in lrFCD. In summary, in contrast with previous studies that focused on the connection strength, our findings, from the perspective of connection number, indicate that schizophrenia is a disorder of brain dysconnectivity, particularly affecting the local functional connectivity network, and support the hypothesis that schizophrenia is associated with a widespread cortical functional connectivity/activity deficit, with hyper- and/or hypo-connectivity/activity coexisting in some cortical or subcortical regions. PMID:28654893
Aberrant patterns of local and long-range functional connectivity densities in schizophrenia.

PubMed

Liu, Chuanxin; Zhang, Wei; Chen, Guangdong; Tian, Hongjun; Li, Jie; Qu, Hongru; Cheng, Langlang; Zhu, Jingjing; Zhuo, Chuanjun

2017-07-18

Schizophrenia is a disorder of brain dysconnectivity, and both the connection strength and connection number are disrupted in patients with schizophrenia. The functional connectivity density (FCD) can reflect alterations in the connection number. Alterations in the global FCD (gFCD) in schizophrenia were previously demonstrated; however, alterations in two other indices of the pathological characteristics of the brain, local FCD (lFCD) and long-range FCD (lrFCD), have not been revealed. To investigate lFCD and lrFCD alterations in patients with schizophrenia, 95 patients and 93 matched healthy controls were examined using structural and resting-state functional magnetic resonance imaging scanning. lFCD and lrFCD were measured using FCD mapping, and differences were identified using a two-sample t-test in a voxel-wise manner, with age and gender considered to increase variability. Multiple comparisons were performed using a false discovery rate method with a corrected threshold of P<0.05. Our analysis showed that lFCD was primarily decreased in the postcentral gyrus, right calcarine sulcus, and inferior occipital gyrus lobule, but increased in the bilateral subcortical regions. The differences in lFCD were more pronounced and complicated than those in lrFCD. In summary, in contrast with previous studies that focused on the connection strength, our findings, from the perspective of connection number, indicate that schizophrenia is a disorder of brain dysconnectivity, particularly affecting the local functional connectivity network, and support the hypothesis that schizophrenia is associated with a widespread cortical functional connectivity/activity deficit, with hyper- and/or hypo-connectivity/activity coexisting in some cortical or subcortical regions.
Correlation Decay in Fermionic Lattice Systems with Power-Law Interactions at Nonzero Temperature

NASA Astrophysics Data System (ADS)

Hernández-Santana, Senaida; Gogolin, Christian; Cirac, J. Ignacio; Acín, Antonio

2017-09-01

We study correlations in fermionic lattice systems with long-range interactions in thermal equilibrium. We prove a bound on the correlation decay between anticommuting operators and generalize a long-range Lieb-Robinson-type bound. Our results show that in these systems of spatial dimension D with, not necessarily translation invariant, two-site interactions decaying algebraically with the distance with an exponent α ≥2 D , correlations between such operators decay at least algebraically to 0 with an exponent arbitrarily close to α at any nonzero temperature. Our bound is asymptotically tight, which we demonstrate by a high temperature expansion and by numerically analyzing density-density correlations in the one-dimensional quadratic (free, exactly solvable) Kitaev chain with long-range pairing.
van der Waals interactions are critical in Car-Parrinello molecular dynamics simulations of porphyrin-fullerene dyads.

PubMed

Karilainen, Topi; Cramariuc, Oana; Kuisma, Mikael; Tappura, Kirsi; Hukka, Terttu I

2015-04-05

The interplay between electrostatic and van der Waals (vdW) interactions in porphyrin-C60 dyads is still under debate despite its importance in influencing the structural characteristics of such complexes considered for various applications in molecular photovoltaics. In this article, we sample the conformational space of a porphyrin-C60 dyad using Car-Parrinello molecular dynamics simulations with and without empirical vdW corrections. Long-range vdW interactions, which are poorly described by the commonly used density functional theory functionals, prove to be essential for a proper dynamics of the dyad moieties. Inclusion of vdW corrections brings porphyrin and C60 close together in an orientation that is in agreement with experimental observations. The structural differences arising from the vdW corrections are shown to be significant for several properties and potentially less important for others. Additionally, our Mulliken population analysis reveals that contrary to the common belief, porphyrin is not the primary electron donating moiety for C60 . In the considered dyad, fullerene's affinity for electrons is primarily satisfied by charge transfer from the amide group of the linker. However, we show that in the absence of another suitable bound donor, C60 can withdraw electrons from porphyrin if it is sufficiently close. © 2015 Wiley Periodicals, Inc.
Increasing Range and Lethality of Extended-Range Munitions (ERMS) using Numerical Weather Prediction (NWP) and the AUV Workbench to Compute a Ballistic Correction (BALCOR)

DTIC Science & Technology

2006-12-01

2 D . APPROACH TAKEN......................................................................................3 E...7 d . FORCEnet.................................................................................8 D . HISTORY OF LONG-RANGE PROJECTILES (LRPS...46 D . NUMERICAL WEATHER MODELING CENTERS...............................47 1. Fleet Numerical Meteorological
Nonempirical Semilocal Free-Energy Density Functional for Matter under Extreme Conditions

DOE PAGES

Karasiev, Valentin V.; Dufty, James W.; Trickey, S. B.

2018-02-14

The potential for density functional calculations to predict the properties of matter under extreme conditions depends crucially upon having a non-empirical approximate free energy functional valid over a wide range of state conditions. Unlike the ground-state case, no such free-energy exchange- correlation (XC) functional exists. We remedy that with systematic construction of a generalized gradient approximation XC free-energy functional based on rigorous constraints, including the free energy gradient expansion. The new functional provides the correct temperature dependence in the slowly varying regime and the correct zero-T, high-T, and homogeneous electron gas limits. Application in Kohn-Sham calculations for hot electrons inmore » a static fcc Aluminum lattice demon- strates the combined magnitude of thermal and gradient effects handled by this functional. Its accuracy in the increasingly important warm dense matter regime is attested by excellent agreement of the calculated deuterium equation of state with reference path integral Monte Carlo results at intermediate and elevated temperatures and by low density Al calculations over a wide T range.« less
Nonempirical Semilocal Free-Energy Density Functional for Matter under Extreme Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karasiev, Valentin V.; Dufty, James W.; Trickey, S. B.

The potential for density functional calculations to predict the properties of matter under extreme conditions depends crucially upon having a non-empirical approximate free energy functional valid over a wide range of state conditions. Unlike the ground-state case, no such free-energy exchange- correlation (XC) functional exists. We remedy that with systematic construction of a generalized gradient approximation XC free-energy functional based on rigorous constraints, including the free energy gradient expansion. The new functional provides the correct temperature dependence in the slowly varying regime and the correct zero-T, high-T, and homogeneous electron gas limits. Application in Kohn-Sham calculations for hot electrons inmore » a static fcc Aluminum lattice demon- strates the combined magnitude of thermal and gradient effects handled by this functional. Its accuracy in the increasingly important warm dense matter regime is attested by excellent agreement of the calculated deuterium equation of state with reference path integral Monte Carlo results at intermediate and elevated temperatures and by low density Al calculations over a wide T range.« less
Vision 20/20: Magnetic resonance imaging-guided attenuation correction in PET/MRI: Challenges, solutions, and opportunities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehranian, Abolfazl; Arabi, Hossein; Zaidi, Habib, E-mail: habib.zaidi@hcuge.ch

Attenuation correction is an essential component of the long chain of data correction techniques required to achieve the full potential of quantitative positron emission tomography (PET) imaging. The development of combined PET/magnetic resonance imaging (MRI) systems mandated the widespread interest in developing novel strategies for deriving accurate attenuation maps with the aim to improve the quantitative accuracy of these emerging hybrid imaging systems. The attenuation map in PET/MRI should ideally be derived from anatomical MR images; however, MRI intensities reflect proton density and relaxation time properties of biological tissues rather than their electron density and photon attenuation properties. Therefore, inmore » contrast to PET/computed tomography, there is a lack of standardized global mapping between the intensities of MRI signal and linear attenuation coefficients at 511 keV. Moreover, in standard MRI sequences, bones and lung tissues do not produce measurable signals owing to their low proton density and short transverse relaxation times. MR images are also inevitably subject to artifacts that degrade their quality, thus compromising their applicability for the task of attenuation correction in PET/MRI. MRI-guided attenuation correction strategies can be classified in three broad categories: (i) segmentation-based approaches, (ii) atlas-registration and machine learning methods, and (iii) emission/transmission-based approaches. This paper summarizes past and current state-of-the-art developments and latest advances in PET/MRI attenuation correction. The advantages and drawbacks of each approach for addressing the challenges of MR-based attenuation correction are comprehensively described. The opportunities brought by both MRI and PET imaging modalities for deriving accurate attenuation maps and improving PET quantification will be elaborated. Future prospects and potential clinical applications of these techniques and their integration in commercial systems will also be discussed.« less
Vision 20/20: Magnetic resonance imaging-guided attenuation correction in PET/MRI: Challenges, solutions, and opportunities.

PubMed

Mehranian, Abolfazl; Arabi, Hossein; Zaidi, Habib

2016-03-01

Attenuation correction is an essential component of the long chain of data correction techniques required to achieve the full potential of quantitative positron emission tomography (PET) imaging. The development of combined PET/magnetic resonance imaging (MRI) systems mandated the widespread interest in developing novel strategies for deriving accurate attenuation maps with the aim to improve the quantitative accuracy of these emerging hybrid imaging systems. The attenuation map in PET/MRI should ideally be derived from anatomical MR images; however, MRI intensities reflect proton density and relaxation time properties of biological tissues rather than their electron density and photon attenuation properties. Therefore, in contrast to PET/computed tomography, there is a lack of standardized global mapping between the intensities of MRI signal and linear attenuation coefficients at 511 keV. Moreover, in standard MRI sequences, bones and lung tissues do not produce measurable signals owing to their low proton density and short transverse relaxation times. MR images are also inevitably subject to artifacts that degrade their quality, thus compromising their applicability for the task of attenuation correction in PET/MRI. MRI-guided attenuation correction strategies can be classified in three broad categories: (i) segmentation-based approaches, (ii) atlas-registration and machine learning methods, and (iii) emission/transmission-based approaches. This paper summarizes past and current state-of-the-art developments and latest advances in PET/MRI attenuation correction. The advantages and drawbacks of each approach for addressing the challenges of MR-based attenuation correction are comprehensively described. The opportunities brought by both MRI and PET imaging modalities for deriving accurate attenuation maps and improving PET quantification will be elaborated. Future prospects and potential clinical applications of these techniques and their integration in commercial systems will also be discussed.
Morphology of central California continental margin, revealed by long-range side-scan sonar (GLORIA)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gardner, J.V.; McCulloch, D.S.; Eittreim, S.L.

1985-02-01

Leg 2 of the 4-leg USGS EEZ-SCAN 84 program used GLORIA long-range side-scan sonar to survey the region from Pt. Conception to just south of Pt. Arena, from the shelf break to the 200-nmi coverage. The overlapping digital sonographs were slant-range and anamorphically corrected, and a photomosaic of the sonographs was constructed at a scale of 1:375,000 (1 in. = 11.1 km). The underlying bed rock appears to be an important control in shaping the morphology of this margin. Several faults have sea-floor expression and lie subparallel to the margin. The density of canyons and gullies on the slope variesmore » from south to north, probably because of variations in the characteristics of the bed rock. The slope west of San Francisco is the most dissected segment of the central California slope. Monterey Fan is covered by large-scale bed forms (5-15 m amplitude and 1.5-2.0 km wavelength) over much of its surface. Monterey channel crosses southwestward across the fan, but abruptly turns south along a 40-km long surface fault that coincides with a well-mapped meander loop. The channel loops to the north then turns southward crossing the entire Monterey Fan, at its distal reaches, changes to a broad, braided pattern. Major slumps on the margin have long (> 30 km) scarps, some have slump folds, and one has a debris-flow deposit that can be acoustically traced for more than 75 km. Seventeen new seamounts were mapped. Taney Seamounts are large, rimmed, calderas with diameters of about 15 km each; these appear to be very large explosive or summit-collapse features.« less
Effect of cutoff radius, long range interaction and temperature controller on thermodynamic properties of fluids: Methanol as an example

NASA Astrophysics Data System (ADS)

Obeidat, Abdalla; Jaradat, Adnan; Hamdan, Bushra; Abu-Ghazleh, Hind

2018-04-01

The best spherical cutoff radius, long range interaction and temperature controller were determined using surface tension, density, and diffusion coefficients of van Leeuwen and Smit methanol. A quite good range of cutoff radii from 0.75 to 1.45 nm has been studied on Coulomb cut-off and particle mesh Ewald (PME) long range interaction to determine the best cutoff radius and best long range interaction as well for four sets of temperature: 200, 230, 270 and 300 K. To determine the best temperature controller, the cutoff radius of 1.25 nm was fixed using PME long range interaction on calculating the above properties at low temperature range: 200-300 K.
Exploring cavity-mediated long-range interactions in a dilute quantum gas

NASA Astrophysics Data System (ADS)

Landig, Renate; Mottl, Rafael; Brennecke, Ferdinand; Baumann, Kristian; Donner, Tobias; Esslinger, Tilman

2013-05-01

We report on the observation of a characteristic change in the excitation spectrum of a Bose-Einstein condensate and increased density fluctuations due to cavity-mediated atom-atom interactions. Increasing the strength of the interaction leads to a softening of an excitation mode at finite momentum, preceding a superfluid to supersolid phase transition. The observed behavior is reminiscent of a roton minimum, as predicted for quantum gases with long-range interactions. We create long-range interactions in the BEC using a non-resonant transverse pump beam which induces virtual photon exchange via the vacuum field of an optical cavity. The mode softening is spectroscopically studied across the phase transition using a variant of Bragg spectroscopy. At the phase transition a diverging density response is observed which is linked to increased density fluctuations. Using the cavity dissipation channel we monitor these fluctuations in real-time and identify the influence of measurement backaction onto the critical behavior of the system.
Effect of fuel density and heating value on ram-jet airplane range

NASA Technical Reports Server (NTRS)

Henneberry, Hugh M

1952-01-01

An analytical investigation of the effects of fuel density and heating value on the cruising range of a ram-jet airplane was made. Results indicate that with present-day knowledge of chemical fuels, neither very high nor very low fuel densities have any advantages for long-range flight. Of the fuels investigated, the borohydrides and metallic boron have the greatest range potential. Aluminum and aluminum hydrocarbon slurries were inferior to pure hydrocarbon fuel and boron-hydrocarbon slurries were superior on a range basis. It was concluded that the practical difficulties associated with the use of liquid hydrogen fuel cannot be justified on a range basis.
Corrigendum to Aerosol impacts on California winter clouds and precipitation during CalWater 2011: local pollution versus long-range transported dust published in Atmos. Chem. Phys., 14, 81–101, 2014

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Jiwen; Leung, Lai-Yung R.; DeMott, Paul J.

2014-05-01

In the paper “Aerosol impacts on California winter clouds and precipitation during CalWater 2011: local pollution versus long-range transported dust” by J. Fan et al., wrong versions of Fig. 8 and Fig. 12 were published. Please find the correct figures below.
The chiral quark condensate and pion decay constant in nuclear matter at next-to-leading order

NASA Astrophysics Data System (ADS)

Lacour, A.; Oller, J. A.; Meißner, U.-G.

2010-12-01

Making use of the recently developed chiral power counting for the physics of nuclear matter (Oller et al 2010 J. Phys. G: Nucl. Part. Phys. 37 015106, Lacour et al Ann. Phys. at press), we evaluate the in-medium chiral quark condensate up to next-to-leading order for both symmetric nuclear matter and neutron matter. Our calculation includes the full in-medium iteration of the leading order local and one-pion exchange nucleon-nucleon interactions. Interestingly, we find a cancellation between the contributions stemming from the quark mass dependence of the nucleon mass appearing in the in-medium nucleon-nucleon interactions. Only the contributions originating from the explicit quark mass dependence of the pion mass survive. This cancellation is the reason of previous observations concerning the dominant role of the long-range pion contributions and the suppression of short-range nucleon-nucleon interactions. We find that the linear density contribution to the in-medium chiral quark condensate is only slightly modified for pure neutron matter by the nucleon-nucleon interactions. For symmetric nuclear matter, the in-medium corrections are larger, although smaller compared to other approaches due to the full iteration of the lowest order nucleon-nucleon tree-level amplitudes. Our calculation satisfies the Hellmann-Feynman theorem to the order worked out. Also we address the problem of calculating the leading in-medium corrections to the pion decay constant. We find that there are no extra in-medium corrections that violate the Gell-Mann-Oakes-Renner relation up to next-to-leading order.
Response theory of the ergodic many-body delocalized phase: Keldysh Finkel'stein sigma models and the 10-fold way

NASA Astrophysics Data System (ADS)

Liao, Yunxiang; Levchenko, Alex; Foster, Matthew S.

2017-11-01

We derive the finite temperature Keldysh response theory for interacting fermions in the presence of quenched short-ranged disorder, as applicable to any of the 10 Altland-Zirnbauer classes in an Anderson delocalized phase with at least a U(1) continuous symmetry. In this formulation of the interacting Finkel'stein nonlinear sigma model, the statistics of one-body wave functions are encoded by the constrained matrix field, while physical correlations follow from the hydrodynamic density or spin response field, which decouples the interactions. Integrating out the matrix field first, we obtain weak (anti) localization and Altshuler-Aronov quantum conductance corrections from the hydrodynamic response function. This procedure automatically incorporates the correct infrared cutoff physics, and in particular gives the Altshuler-Aronov-Khmelnitsky (AAK) equations for dephasing of weak (anti)localization due to electron-electron collisions. We explicate the method by deriving known quantumcorrections in two dimensions for the symplectic metal class AII, as well as the spin-SU(2) invariant superconductor classes C and CI. We show that quantum conductance corrections due to the special modes at zero energy in nonstandard classes are automatically cut off by temperature, as previously expected, while the Wigner-Dyson class Cooperon modes that persist to all energies are cut by dephasing. We also show that for short-ranged interactions, the standard self-consistent solution for the dephasing rate is equivalent to a particular summation of diagrams via the self-consistent Born approximation. This should be compared to the corresponding AAK solution for long-ranged Coulomb interactions, which exploits the Markovian noise correlations induced by thermal fluctuations of the electromagnetic field. We discuss prospects for exploring the many-body localization transition as a dephasing catastrophe in short-range interacting models, as encountered by approaching from the ergodic side.

The long-range shelling of Paris and physical chemistry problems of extremely long-range firing

NASA Astrophysics Data System (ADS)

Stettbacher, A.

1986-04-01

The 128-km long-range artillery shelling of Paris is discussed considering its physical and chemical make-up from the vantage point of the technology in 1919. It compares this shelling with a hypothetical 240-km shelling and concludes that the most important influence on shelling range distance to be air resistance. The amount of air resistance and the resulting velocity deceleration depend on the air's density and the shell's velocity and configuration.
SU-D-206-05: A Critical Look at CBCT-Based Dose Calculation Accuracy as It Is Applied to Adaptive Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bejarano Buele, A; Sperling, N; Parsai, E

2016-06-15

Purpose: Cone-beam CTs (CBCT) obtained from On-Board Imaging Devices (OBI) are increasingly being used for dose calculation purposes in adaptive radiotherapy. Patient and target morphology are monitored and the treatment plan is updated using CBCT. Due to the difference in image acquisition parameters, dose calculated in a CBCT can differ from planned dose. We evaluate the difference between dose calculation in kV CBCT and simulation CT, and the effect of HU-density tables in dose discrepancies Methods: HU values for various materials were obtained using a Catphan 504 phantom for a simulator CT (CTSIM) and two different OBI systems using threemore » imaging protocols: Head, Thorax and Pelvis. HU-density tables were created in the TPS for each OBI image protocol. Treatment plans were made on each Catphan 504 dataset and on the head, thorax and pelvis sections of an anthropomorphic phantom, with and without the respective HU-density table. DVH information was compared among OBI systems and planning CT. Results: Dose calculations carried on the Catphan 504 CBCTs, with and without the respective CT-density table, had a maximum difference of −0.65% from the values on the planning CT. The use of the respective HU-density table decreased the percent differences from planned values by half in most of the protocols. For the anthropomorphic phantom datasets, the use of the correct HU-density table reduced differences by 0.89% on OBI1 and 0.59% on OBI2 for the head, 0.49% on OBI1 for the thorax, and 0.25% on OBI2 for the pelvis. Differences from planned values without HU-density correction ranged from 3.13% (OBI1, thorax) to 0.30% (OBI2, thorax). Conclusion: CT-density tables in the TPS yield acceptable differences when used in partly homogeneous medium. Further corrections are needed when the medium contains pronounced density differences for accurate CBCT calculation. Current difference range (1–3%) can be clinically acceptable.« less
Electron density and gas density measurements in a millimeter-wave discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaub, S. C., E-mail: sschaub@mit.edu; Hummelt, J. S.; Guss, W. C.

2016-08-15

Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 μs long at 110 GHz and 2.2 μs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal tomore » the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.« less
Assessing the density functional theory-based multireference configuration interaction (DFT/MRCI) method for transition metal complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Escudero, Daniel, E-mail: escudero@kofo.mpg.de, E-mail: thiel@kofo.mpg.de; Thiel, Walter, E-mail: escudero@kofo.mpg.de, E-mail: thiel@kofo.mpg.de

2014-05-21

We report an assessment of the performance of density functional theory-based multireference configuration interaction (DFT/MRCI) calculations for a set of 3d- and 4d-transition metal (TM) complexes. The DFT/MRCI results are compared to published reference data from reliable high-level multi-configurational ab initio studies. The assessment covers the relative energies of different ground-state minima of the highly correlated CrF{sub 6} complex, the singlet and triplet electronically excited states of seven typical TM complexes (MnO{sub 4}{sup −}, Cr(CO){sub 6}, [Fe(CN){sub 6}]{sup 4−}, four larger Fe and Ru complexes), and the corresponding electronic spectra (vertical excitation energies and oscillator strengths). It includes comparisons withmore » results from different flavors of time-dependent DFT (TD-DFT) calculations using pure, hybrid, and long-range corrected functionals. The DFT/MRCI method is found to be superior to the tested TD-DFT approaches and is thus recommended for exploring the excited-state properties of TM complexes.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Lessard, Francois; Archambault, Louis; Plamondon, Mathieu

Purpose: Photon dosimetry in the kilovolt (kV) energy range represents a major challenge for diagnostic and interventional radiology and superficial therapy. Plastic scintillation detectors (PSDs) are potentially good candidates for this task. This study proposes a simple way to obtain accurate correction factors to compensate for the response of PSDs to photon energies between 80 and 150 kVp. The performance of PSDs is also investigated to determine their potential usefulness in the diagnostic energy range. Methods: A 1-mm-diameter, 10-mm-long PSD was irradiated by a Therapax SXT 150 unit using five different beam qualities made of tube potentials ranging from 80more » to 150 kVp and filtration thickness ranging from 0.8 to 0.2 mmAl + 1.0 mmCu. The light emitted by the detector was collected using an 8-m-long optical fiber and a polychromatic photodiode, which converted the scintillation photons to an electrical current. The PSD response was compared with the reference free air dose rate measured with a calibrated Farmer NE2571 ionization chamber. PSD measurements were corrected using spectra-weighted corrections, accounting for mass energy-absorption coefficient differences between the sensitive volumes of the ionization chamber and the PSD, as suggested by large cavity theory (LCT). Beam spectra were obtained from x-ray simulation software and validated experimentally using a CdTe spectrometer. Correction factors were also obtained using Monte Carlo (MC) simulations. Percent depth dose (PDD) measurements were compensated for beam hardening using the LCT correction method. These PDD measurements were compared with uncorrected PSD data, PDD measurements obtained using Gafchromic films, Monte Carlo simulations, and previous data. Results: For each beam quality used, the authors observed an increase of the energy response with effective energy when no correction was applied to the PSD response. Using the LCT correction, the PSD response was almost energy independent, with a residual 2.1% coefficient of variation (COV) over the 80-150-kVp energy range. Monte Carlo corrections reduced the COV to 1.4% over this energy range. All PDD measurements were in good agreement with one another except for the uncorrected PSD data, in which an over-response was observed with depth (13% at 10 cm with a 100 kVp beam), showing that beam hardening had a non-negligible effect on the PSD response. A correction based on LCT compensated very well for this effect, reducing the over-response to 3%.Conclusion: In the diagnostic energy range, PSDs show high-energy dependence, which can be corrected using spectra-weighted mass energy-absorption coefficients, showing no considerable sign of quenching between these energies. Correction factors obtained by Monte Carlo simulations confirm that the approximations made by LCT corrections are valid. Thus, PSDs could be useful for real-time dosimetry in radiology applications.« less
Spatially unresolved SED fitting can underestimate galaxy masses: a solution to the missing mass problem

NASA Astrophysics Data System (ADS)

Sorba, Robert; Sawicki, Marcin

2018-05-01

We perform spatially resolved, pixel-by-pixel Spectral Energy Distribution (SED) fitting on galaxies up to z ˜ 2.5 in the Hubble eXtreme Deep Field (XDF). Comparing stellar mass estimates from spatially resolved and spatially unresolved photometry we find that unresolved masses can be systematically underestimated by factors of up to 5. The ratio of the unresolved to resolved mass measurement depends on the galaxy's specific star formation rate (sSFR): at low sSFRs the bias is small, but above sSFR ˜ 10-9.5 yr-1 the discrepancy increases rapidly such that galaxies with sSFRs ˜ 10-8 yr-1 have unresolved mass estimates of only one-half to one-fifth of the resolved value. This result indicates that stellar masses estimated from spatially unresolved data sets need to be systematically corrected, in some cases by large amounts, and we provide an analytic prescription for applying this correction. We show that correcting stellar mass measurements for this bias changes the normalization and slope of the star-forming main sequence and reduces its intrinsic width; most dramatically, correcting for the mass bias increases the stellar mass density of the Universe at high redshift and can resolve the long-standing discrepancy between the directly measured cosmic SFR density at z ≳ 1 and that inferred from stellar mass densities (`the missing mass problem').
DOE Office of Scientific and Technical Information (OSTI.GOV)

Mishra, Tapan; Das, B. P.; Pai, Ramesh V.

We present a scenario where a supersolid is induced in one of the components of a mixture of two species bosonic atoms where there are no long-range interactions. We study a system of normal and hard-core boson mixture with only the former possessing long-range interactions. We consider three cases: the first where the total density is commensurate and the other two where it is incommensurate to the lattice. By suitable choices of the densities of normal and hard-core bosons and the interaction strengths between them, we predict that the charge density wave and the supersolid orders can be induced inmore » the hard-core species as a result of the competing interatomic interactions.« less
Effect of van der Waals interactions on the stability of SiC polytypes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawanishi, Sakiko, E-mail: s-kawa@tagen.tohoku.ac.jp; Mizoguchi, Teruyasu

2016-05-07

Density functional theory calculations with a correction of the long-range dispersion force, namely, the van der Waals (vdW) force, are performed for SiC polytypes. The lattice parameters are in good agreement with those obtained from the experiments. Furthermore, the stability of the polytypes in the experiments, which show 3C-SiC as the most stable, is reproduced by the present calculations. The effects of the vdW force on the electronic structure and the stability of polytypes are discussed. We observe that the vdW interaction is more sensitive to the cubic site than the hexagonal site. Thus, the influence of the vdW forcemore » increases with decreasing the hexagonality of the polytype, which results in the confirmation that the most stable polytype is 3C-SiC.« less
Need for optimal body composition data analysis using air-displacement plethysmography in children and adolescents.

PubMed

Bosy-Westphal, Anja; Danielzik, Sandra; Becker, Christine; Geisler, Corinna; Onur, Simone; Korth, Oliver; Bührens, Frederike; Müller, Manfred J

2005-09-01

Air-displacement plethysmography (ADP) is now widely used for body composition measurement in pediatric populations. However, the manufacturer's software developed for adults leaves a potential bias for application in children and adolescents, and recent publications do not consistently use child-specific corrections. Therefore we analyzed child-specific ADP corrections with respect to quantity and etiology of bias compared with adult formulas. An optimal correction protocol is provided giving step-by-step instructions for calculations. In this study, 258 children and adolescents (143 girls and 115 boys ranging from 5 to 18 y) with a high prevalence of overweight or obesity (28.0% in girls and 22.6% in boys) were examined by ADP applying the manufacturer's software as well as published equations for child-specific corrections for surface area artifact (SAA), thoracic gas volume (TGV), and density of fat-free mass (FFM). Compared with child-specific equations for SAA, TGV, and density of FFM, the mean overestimation of the percentage of fat mass using the manufacturer's software was 10% in children and adolescents. Half of the bias derived from the use of Siri's equation not corrected for age-dependent differences in FFM density. An additional 3 and 2% of bias resulted from the application of adult equations for prediction of SAA and TGV, respectively. Different child-specific equations used to predict TGV did not differ in the percentage of fat mass. We conclude that there is a need for child-specific equations in ADP raw data analysis considering SAA, TGV, and density of FFM.
Extensive TD-DFT Benchmark: Singlet-Excited States of Organic Molecules.

PubMed

Jacquemin, Denis; Wathelet, Valérie; Perpète, Eric A; Adamo, Carlo

2009-09-08

Extensive Time-Dependent Density Functional Theory (TD-DFT) calculations have been carried out in order to obtain a statistically meaningful analysis of the merits of a large number of functionals. To reach this goal, a very extended set of molecules (∼500 compounds, >700 excited states) covering a broad range of (bio)organic molecules and dyes have been investigated. Likewise, 29 functionals including LDA, GGA, meta-GGA, global hybrids, and long-range-corrected hybrids have been considered. Comparisons with both theoretical references and experimental measurements have been carried out. On average, the functionals providing the best match with reference data are, one the one hand, global hybrids containing between 22% and 25% of exact exchange (X3LYP, B98, PBE0, and mPW1PW91) and, on the other hand, a long-range-corrected hybrid with a less-rapidly increasing HF ratio, namely LC-ωPBE(20). Pure functionals tend to be less consistent, whereas functionals incorporating a larger fraction of exact exchange tend to underestimate significantly the transition energies. For most treated cases, the M05 and CAM-B3LYP schemes deliver fairly small deviations but do not outperform standard hybrids such as X3LYP or PBE0, at least within the vertical approximation. With the optimal functionals, one obtains mean absolute deviations smaller than 0.25 eV, though the errors significantly depend on the subset of molecules or states considered. As an illustration, PBE0 and LC-ωPBE(20) provide a mean absolute error of only 0.14 eV for the 228 states related to neutral organic dyes but are completely off target for cyanine-like derivatives. On the basis of comparisons with theoretical estimates, it also turned out that CC2 and TD-DFT errors are of the same order of magnitude, once the above-mentioned hybrids are selected.
Predicting vapor liquid equilibria using density functional theory: A case study of argon

NASA Astrophysics Data System (ADS)

Goel, Himanshu; Ling, Sanliang; Ellis, Breanna Nicole; Taconi, Anna; Slater, Ben; Rai, Neeraj

2018-06-01

Predicting vapor liquid equilibria (VLE) of molecules governed by weak van der Waals (vdW) interactions using the first principles approach is a significant challenge. Due to the poor scaling of the post Hartree-Fock wave function theory with system size/basis functions, the Kohn-Sham density functional theory (DFT) is preferred for systems with a large number of molecules. However, traditional DFT cannot adequately account for medium to long range correlations which are necessary for modeling vdW interactions. Recent developments in DFT such as dispersion corrected models and nonlocal van der Waals functionals have attempted to address this weakness with a varying degree of success. In this work, we predict the VLE of argon and assess the performance of several density functionals and the second order Møller-Plesset perturbation theory (MP2) by determining critical and structural properties via first principles Monte Carlo simulations. PBE-D3, BLYP-D3, and rVV10 functionals were used to compute vapor liquid coexistence curves, while PBE0-D3, M06-2X-D3, and MP2 were used for computing liquid density at a single state point. The performance of the PBE-D3 functional for VLE is superior to other functionals (BLYP-D3 and rVV10). At T = 85 K and P = 1 bar, MP2 performs well for the density and structural features of the first solvation shell in the liquid phase.
Density and temperature characterization of long-scale length, near-critical density controlled plasma produced from ultra-low density plastic foam

PubMed Central

Chen, S. N.; Iwawaki, T.; Morita, K.; Antici, P.; Baton, S. D.; Filippi, F.; Habara, H.; Nakatsutsumi, M.; Nicolaï , P.; Nazarov, W.; Rousseaux, C.; Starodubstev, M.; Tanaka, K. A.; Fuchs, J.

2016-01-01

The ability to produce long-scale length (i.e. millimeter scale-length), homogeneous plasmas is of interest in studying a wide range of fundamental plasma processes. We present here a validated experimental platform to create and diagnose uniform plasmas with a density close or above the critical density. The target consists of a polyimide tube filled with an ultra low-density plastic foam where it was heated by x-rays, produced by a long pulse laser irradiating a copper foil placed at one end of the tube. The density and temperature of the ionized foam was retrieved by using x-ray radiography and proton radiography was used to verify the uniformity of the plasma. Plasma temperatures of 5–10 eV and densities around 1021 cm−3 are measured. This well-characterized platform of uniform density and temperature plasma is of interest for experiments using large-scale laser platforms conducting High Energy Density Physics investigations. PMID:26923471
Keesom coefficients in gases

NASA Astrophysics Data System (ADS)

Magnasco, Valerio; Battezzati, Michele; Rapallo, Arnaldo; Costa, Camilla

2006-09-01

T-dependent long-range Keesom coefficients are evaluated up to the R-10 term for small values of the dimensionless parameter |a|. For large values of |a| corrections must be introduced mostly for the dipole-dipole term, the correct values of C6 being best obtained from a recently derived asymptotic formula. The corresponding attractive energies are the isotropic electrostatic contributions to the interaction energy and are temperature-dependent. Comparison with long-range induction and dispersion energy results for some simple polar axially symmetric molecules in the gas phase shows that at R = 10 a0 and T = 293 K the electrostatic dipole-dipole component is dominant for ∣ a11∣ > 0.5. For centrosymmetric molecules the corresponding electrostatic contribution is usually negligible with respect to dispersion.
Right adolescent idiopathic thoracic curve (Lenke 1 A and B): does cost of instrumentation and implant density improve radiographic and cosmetic parameters?

PubMed

Yang, Scott; Jones-Quaidoo, Sean M; Eager, Matthew; Griffin, Justin W; Reddi, Vasantha; Novicoff, Wendy; Shilt, Jeffrey; Bersusky, Ernesto; Defino, Helton; Ouellet, Jean; Arlet, Vincent

2011-07-01

In adolescent idiopathic scoliosis (AIS) there has been a shift towards increasing the number of implants and pedicle screws, which has not been proven to improve cosmetic correction. To evaluate if increasing cost of instrumentation correlates with cosmetic correction using clinical photographs. 58 Lenke 1A and B cases from a multicenter AIS database with at least 3 months follow-up of clinical photographs were used for analysis. Cosmetic parameters on PA and forward bending photographs included angular measurements of trunk shift, shoulder balance, rib hump, and ratio measurements of waist line asymmetry. Pre-op and follow-up X-rays were measured for coronal and sagittal deformity parameters. Cost density was calculated by dividing the total cost of instrumentation by the number of vertebrae being fused. Linear regression and spearman's correlation were used to correlate cost density to X-ray and photo outcomes. Three independent observers verified radiographic and cosmetic parameters for inter/interobserver variability analysis. Average pre-op Cobb angle and instrumented correction were 54° (SD 12.5) and 59% (SD 25) respectively. The average number of vertebrae fused was 10 (SD 1.9). The total cost of spinal instrumentation ranged from $6,769 to $21,274 (Mean $12,662, SD $3,858). There was a weak positive and statistically significant correlation between Cobb angle correction and cost density (r = 0.33, p = 0.01), and no correlation between Cobb angle correction of the uninstrumented lumbar spine and cost density (r = 0.15, p = 0.26). There was no significant correlation between all sagittal X-ray measurements or any of the photo parameters and cost density. There was good to excellent inter/intraobserver variability of all photographic parameters based on the intraclass correlation coefficient (ICC 0.74-0.98). Our method used to measure cosmesis had good to excellent inter/intraobserver variability, and may be an effective tool to objectively assess cosmesis from photographs. Since increasing cost density only improves mildly the Cobb angle correction of the main thoracic curve and not the correction of the uninstrumented spine or any of the cosmetic parameters, one should consider the cost of increasing implant density in Lenke 1A and B curves. In the area of rationalization of health care expenses, this study demonstrates that increasing the number of implants does not improve any relevant cosmetic or radiographic outcomes.
Method for detecting and correcting for isotope burn-in during long-term neutron dosimetry exposure

DOEpatents

Ruddy, Francis H.

1988-01-01

A method is described for detecting and correcting for isotope burn-in during-long term neutron dosimetry exposure. In one embodiment, duplicate pairs of solid state track recorder fissionable deposits are used, including a first, fissionable deposit of lower mass to quantify the number of fissions occuring during the exposure, and a second deposit of higher mass to quantify the number of atoms of for instance .sup.239 Pu by alpha counting. In a second embodiment, only one solid state track recorder fissionable deposit is used and the resulting higher track densities are counted with a scanning electron microscope. This method is also applicable to other burn-in interferences, e.g., .sup.233 U in .sup.232 Th or .sup.238 Pu in .sup.237 Np.
Improved correlation between CT emphysema quantification and pulmonary function test by density correction of volumetric CT data based on air and aortic density.

PubMed

Kim, Song Soo; Seo, Joon Beom; Kim, Namkug; Chae, Eun Jin; Lee, Young Kyung; Oh, Yeon Mok; Lee, Sang Do

2014-01-01

To determine the improvement of emphysema quantification with density correction and to determine the optimal site to use for air density correction on volumetric computed tomography (CT). Seventy-eight CT scans of COPD patients (GOLD II-IV, smoking history 39.2±25.3 pack-years) were obtained from several single-vendor 16-MDCT scanners. After density measurement of aorta, tracheal- and external air, volumetric CT density correction was conducted (two reference values: air, -1,000 HU/blood, +50 HU). Using in-house software, emphysema index (EI) and mean lung density (MLD) were calculated. Differences in air densities, MLD and EI prior to and after density correction were evaluated (paired t-test). Correlation between those parameters and FEV1 and FEV1/FVC were compared (age- and sex adjusted partial correlation analysis). Measured densities (HU) of tracheal- and external air differed significantly (-990 ± 14, -1016 ± 9, P<0.001). MLD and EI on original CT data, after density correction using tracheal- and external air also differed significantly (MLD: -874.9 ± 27.6 vs. -882.3 ± 24.9 vs. -860.5 ± 26.6; EI: 16.8 ± 13.4 vs. 21.1 ± 14.5 vs. 9.7 ± 10.5, respectively, P<0.001). The correlation coefficients between CT quantification indices and FEV1, and FEV1/FVC increased after density correction. The tracheal air correction showed better results than the external air correction. Density correction of volumetric CT data can improve correlations of emphysema quantification and PFT. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.
Aging and functional brain networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomasi D.; Tomasi, D.; Volkow, N.D.

2011-07-11

Aging is associated with changes in human brain anatomy and function and cognitive decline. Recent studies suggest the aging decline of major functional connectivity hubs in the 'default-mode' network (DMN). Aging effects on other networks, however, are largely unknown. We hypothesized that aging would be associated with a decline of short- and long-range functional connectivity density (FCD) hubs in the DMN. To test this hypothesis, we evaluated resting-state data sets corresponding to 913 healthy subjects from a public magnetic resonance imaging database using functional connectivity density mapping (FCDM), a voxelwise and data-driven approach, together with parallel computing. Aging was associatedmore » with pronounced long-range FCD decreases in DMN and dorsal attention network (DAN) and with increases in somatosensory and subcortical networks. Aging effects in these networks were stronger for long-range than for short-range FCD and were also detected at the level of the main functional hubs. Females had higher short- and long-range FCD in DMN and lower FCD in the somatosensory network than males, but the gender by age interaction effects were not significant for any of the networks or hubs. These findings suggest that long-range connections may be more vulnerable to aging effects than short-range connections and that, in addition to the DMN, the DAN is also sensitive to aging effects, which could underlie the deterioration of attention processes that occurs with aging.« less
Improved Phase Corrections for Transoceanic Tsunami Data in Spatial and Temporal Source Estimation: Application to the 2011 Tohoku Earthquake

NASA Astrophysics Data System (ADS)

Ho, Tung-Cheng; Satake, Kenji; Watada, Shingo

2017-12-01

Systemic travel time delays of up to 15 min relative to the linear long waves for transoceanic tsunamis have been reported. A phase correction method, which converts the linear long waves into dispersive waves, was previously proposed to consider seawater compressibility, the elasticity of the Earth, and gravitational potential change associated with tsunami motion. In the present study, we improved this method by incorporating the effects of ocean density stratification, actual tsunami raypath, and actual bathymetry. The previously considered effects amounted to approximately 74% for correction of the travel time delay, while the ocean density stratification, actual raypath, and actual bathymetry, contributed to approximately 13%, 4%, and 9% on average, respectively. The improved phase correction method accounted for almost all the travel time delay at far-field stations. We performed single and multiple time window inversions for the 2011 Tohoku tsunami using the far-field data (>3 h travel time) to investigate the initial sea surface displacement. The inversion result from only far-field data was similar to but smoother than that from near-field data and all stations, including a large sea surface rise increasing toward the trench followed by a migration northward along the trench. For the forward simulation, our results showed good agreement between the observed and computed waveforms at both near-field and far-field tsunami gauges, as well as with satellite altimeter data. The present study demonstrates that the improved method provides a more accurate estimate for the waveform inversion and forward prediction of far-field data.
On the representation of many-body interactions in water

DOE PAGES

Medders, Gregory R.; Gotz, Andreas W.; Morales, Miguel A.; ...

2015-09-09

Our recent work has shown that the many-body expansion of the interactionenergy can be used to develop analytical representations of global potential energy surfaces (PESs) for water. In this study, the role of short- and long-range interactions at different orders is investigated by analyzing water potentials that treat the leading terms of the many-body expansion through implicit (i.e., TTM3-F and TTM4-F PESs) and explicit (i.e., WHBB and MB-pol PESs) representations. Moreover, it is found that explicit short-range representations of 2-body and 3-body interactions along with a physically correct incorporation of short- and long-range contributions are necessary for an accurate representationmore » of the waterinteractions from the gas to the condensed phase. Likewise, a complete many-body representation of the dipole moment surface is found to be crucial to reproducing the correct intensities of the infrared spectrum of liquid water.« less
Comparison of Quantum Dots-in-a-Double-Well and Quantum Dots-in-a-Well Focal Plane Arrays in the Long-Wave Infrared

DTIC Science & Technology

2011-07-01

taken with the same camera head, operating temperature, range of calibrated blackbody illuminations, and using the same long-wavelength IR ( LWIR ) f/2...measurements shown in this article and are tabulated for comparison purposes only. Images were taken with all four devices using an f/2 LWIR lens (8–12 μm...These were acquired after a nonuniformity correction. A custom image-scaling algorithm was used to avoid the standard nonuniformity corrected scaling

Non-Newtonian gravity or gravity anomalies?

NASA Technical Reports Server (NTRS)

Rubincam, David P.; Chao, B. Fong; Schatten, Kenneth H.; Sager, William W.

1988-01-01

Geophysical measurements of G differ from laboratory values, indicating that gravity may be non-Newtonian. A spherical harmonic formulation is presented for the variation of (Newtonian) gravity inside the Earth. Using the GEM-10B Earth Gravitational Field Model, it is shown that long-wavelength gravity anomalies, if not corrected, may masquerade as non-Newtonian gravity by providing significant influences on experimental observation of delta g/delta r and G. An apparent contradiction in other studies is also resolved: i.e., local densities appear in equations when average densities of layers seem to be called for.
Laterality patterns of brain functional connectivity: gender effects.

PubMed

Tomasi, Dardo; Volkow, Nora D

2012-06-01

Lateralization of brain connectivity may be essential for normal brain function and may be sexually dimorphic. Here, we study the laterality patterns of short-range (implicated in functional specialization) and long-range (implicated in functional integration) connectivity and the gender effects on these laterality patterns. Parallel computing was used to quantify short- and long-range functional connectivity densities in 913 healthy subjects. Short-range connectivity was rightward lateralized and most asymmetrical in areas around the lateral sulcus, whereas long-range connectivity was rightward lateralized in lateral sulcus and leftward lateralizated in inferior prefrontal cortex and angular gyrus. The posterior inferior occipital cortex was leftward lateralized (short- and long-range connectivity). Males had greater rightward lateralization of brain connectivity in superior temporal (short- and long-range), inferior frontal, and inferior occipital cortices (short-range), whereas females had greater leftward lateralization of long-range connectivity in the inferior frontal cortex. The greater lateralization of the male's brain (rightward and predominantly short-range) may underlie their greater vulnerability to disorders with disrupted brain asymmetries (schizophrenia, autism).
Laterality Patterns of Brain Functional Connectivity: Gender Effects

PubMed Central

Tomasi, Dardo; Volkow, Nora D.

2012-01-01

Lateralization of brain connectivity may be essential for normal brain function and may be sexually dimorphic. Here, we study the laterality patterns of short-range (implicated in functional specialization) and long-range (implicated in functional integration) connectivity and the gender effects on these laterality patterns. Parallel computing was used to quantify short- and long-range functional connectivity densities in 913 healthy subjects. Short-range connectivity was rightward lateralized and most asymmetrical in areas around the lateral sulcus, whereas long-range connectivity was rightward lateralized in lateral sulcus and leftward lateralizated in inferior prefrontal cortex and angular gyrus. The posterior inferior occipital cortex was leftward lateralized (short- and long-range connectivity). Males had greater rightward lateralization of brain connectivity in superior temporal (short- and long-range), inferior frontal, and inferior occipital cortices (short-range), whereas females had greater leftward lateralization of long-range connectivity in the inferior frontal cortex. The greater lateralization of the male's brain (rightward and predominantly short-range) may underlie their greater vulnerability to disorders with disrupted brain asymmetries (schizophrenia, autism). PMID:21878483
Solar Radiation Measurements Onboard the Research Aircraft HALO

NASA Astrophysics Data System (ADS)

Lohse, I.; Bohn, B.; Werner, F.; Ehrlich, A.; Wendisch, M.

2014-12-01

Airborne measurements of the separated upward and downward components of solar spectral actinic flux densities for the determination of photolysis frequencies and of upward nadir spectral radiance were performed with the HALO Solar Radiation (HALO-SR) instrument package onboard the High Altitude and Long Range Research Aircraft (HALO). The instrumentation of HALO-SR is characterized and first measurement data from the Next-generation Aircraft Remote-Sensing for Validation Studies (NARVAL) campaigns in 2013 and 2014 are presented. The measured data are analyzed in the context of the retrieved microphysical and optical properties of clouds which were observed underneath the aircraft. Detailed angular sensitivities of the two optical actinic flux receivers were determined in the laboratory. The effects of deviations from the ideal response are investigated using radiative transfer calculations of atmospheric radiance distributions under various atmospheric conditions and different ground albedos. Corresponding correction factors are derived. Example photolysis frequencies are presented, which were sampled in the free troposphere and lower stratosphere over the Atlantic Ocean during the 2013/14 HALO NARVAL campaigns. Dependencies of photolysis frequencies on cloud cover, flight altitude and wavelength range of the photolysis process are investigated. Calculated actinic flux densities in the presence of clouds benefit from the measured spectral radiances. Retrieved cloud optical thicknesses and effective droplet radii are used as model input for the radiative transfer calculations. By comparison with the concurrent measurements of actinic flux densities the retrieval approach is validated. Acknowledgements: Funding by the Deutsche Forschungsgemeinschaft within the priority program HALO (BO 1580/4-1, WE 1900/21-1) is gratefully acknowledged.
Determining Accuracy of Thermal Dissipation Methods-based Sap Flux in Japanese Cedar Trees

NASA Astrophysics Data System (ADS)

Su, Man-Ping; Shinohara, Yoshinori; Laplace, Sophie; Lin, Song-Jin; Kume, Tomonori

2017-04-01

Thermal dissipation method, one kind of sap flux measurement method that can estimate individual tree transpiration, have been widely used because of its low cost and uncomplicated operation. Although thermal dissipation method is widespread, the accuracy of this method is doubted recently because some tree species materials in previous studies were not suitable for its empirical formula from Granier due to difference of wood characteristics. In Taiwan, Cryptomeria japonica (Japanese cedar) is one of the dominant species in mountainous area, quantifying the transpiration of Japanese cedar trees is indispensable to understand water cycling there. However, no one have tested the accuracy of thermal dissipation methods-based sap flux for Japanese cedar trees in Taiwan. Thus, in this study we conducted calibration experiment using twelve Japanese cedar stem segments from six trees to investigate the accuracy of thermal dissipation methods-based sap flux in Japanese cedar trees in Taiwan. By pumping water from segment bottom to top and inserting probes into segments to collect data simultaneously, we compared sap flux densities calculated from real water uptakes (Fd_actual) and empirical formula (Fd_Granier). Exact sapwood area and sapwood depth of each sample were obtained from dying segment with safranin stain solution. Our results showed that Fd_Granier underestimated 39 % of Fd_actual across sap flux densities ranging from 10 to 150 (cm3m-2s-1); while applying sapwood depth corrected formula from Clearwater, Fd_Granier became accurately that only underestimated 0.01 % of Fd_actual. However, when sap flux densities ranging from 10 to 50 (cm3m-2s-1)which is similar with the field data of Japanese cedar trees in a mountainous area of Taiwan, Fd_Granier underestimated 51 % of Fd_actual, and underestimated 26 % with applying Clearwater sapwood depth corrected formula. These results suggested sapwood depth significantly impacted on the accuracy of thermal dissipation method; hence, careful determination of sapwood depth is the key for the accurate transpiration estimates. This study also apply the derived results to long-term field data in the mountainous area in Taiwan.
Nonlocal effects in nonisothermal hydrodynamics from the perspective of beyond-equilibrium thermodynamics.

PubMed

Hütter, Markus; Brader, Joseph M

2009-06-07

We examine the origins of nonlocality in a nonisothermal hydrodynamic formulation of a one-component fluid of particles that exhibit long-range correlations, e.g., due to a spherically symmetric, long-range interaction potential. In order to furnish the continuum modeling with physical understanding of the microscopic interactions and dynamics, we make use of systematic coarse graining from the microscopic to the continuum level. We thus arrive at a thermodynamically admissible and closed set of evolution equations for the densities of momentum, mass, and internal energy. From the consideration of an illustrative special case, the following main conclusions emerge. There are two different source terms in the momentum balance. The first is a body force, which in special circumstances can be related to the functional derivative of a nonlocal Helmholtz free energy density with respect to the mass density. The second source term is proportional to the temperature gradient, multiplied by the nonlocal entropy density. These two source terms combine into a pressure gradient only in the absence of long-range effects. In the irreversible contributions to the time evolution, the nonlocal contributions arise since the self-correlations of the stress tensor and heat flux, respectively, are nonlocal as a result of the microscopic nonlocal correlations. Finally, we point out specific points that warrant further discussions.
Three methods for estimating a range of vehicular interactions

NASA Astrophysics Data System (ADS)

Krbálek, Milan; Apeltauer, Jiří; Apeltauer, Tomáš; Szabová, Zuzana

2018-02-01

We present three different approaches how to estimate the number of preceding cars influencing a decision-making procedure of a given driver moving in saturated traffic flows. The first method is based on correlation analysis, the second one evaluates (quantitatively) deviations from the main assumption in the convolution theorem for probability, and the third one operates with advanced instruments of the theory of counting processes (statistical rigidity). We demonstrate that universally-accepted premise on short-ranged traffic interactions may not be correct. All methods introduced have revealed that minimum number of actively-followed vehicles is two. It supports an actual idea that vehicular interactions are, in fact, middle-ranged. Furthermore, consistency between the estimations used is surprisingly credible. In all cases we have found that the interaction range (the number of actively-followed vehicles) drops with traffic density. Whereas drivers moving in congested regimes with lower density (around 30 vehicles per kilometer) react on four or five neighbors, drivers moving in high-density flows respond to two predecessors only.
Electron correlation and the self-interaction error of density functional theory

NASA Astrophysics Data System (ADS)

Polo, Victor; Kraka, Elfi; Cremer, Dieter

The self-interaction error (SIE) of commonly used DFT functionals has been systematically investigated by comparing the electron density distribution ρ( r ) generated by self-interaction corrected DFT (SIC-DFT) with a series of reference densities obtained by DFT or wavefunction theory (WFT) methods that cover typical electron correlation effects. Although the SIE of GGA functionals is considerably smaller than that of LDA functionals, it has significant consequences for the coverage of electron correlation effects at the DFT level of theory. The exchange SIE mimics long range (non-dynamic) pair correlation effects, and is responsible for the fact that the electron density of DFT exchange-only calculations resembles often that of MP4, MP2 or even CCSD(T) calculations. Changes in the electron density caused by SICDFT exchange are comparable with those that are associated with HF exchange. Correlation functionals contract the density towards the bond and the valence region, thus taking negative charge out of the van der Waals region where these effects are exaggerated by the influence of the SIE of the correlation functional. Hence, SIC-DFT leads in total to a relatively strong redistribution of negative charge from van der Waals, non-bonding, and valence regions of heavy atoms to the bond regions. These changes, although much stronger, resemble those obtained when comparing the densities of hybrid functionals such as B3LYP with the corresponding GGA functional BLYP. Hence, the balanced mixing of local and non-local exchange and correlation effects as it is achieved by hybrid functionals mimics SIC-DFT and can be considered as an economic way to include some SIC into standard DFT. However, the investigation shows also that the SIC-DFT description of molecules is unreliable because the standard functionals used were optimized for DFT including the SIE.
Improved correction for the tissue fraction effect in lung PET/CT imaging

NASA Astrophysics Data System (ADS)

Holman, Beverley F.; Cuplov, Vesna; Millner, Lynn; Hutton, Brian F.; Maher, Toby M.; Groves, Ashley M.; Thielemans, Kris

2015-09-01

Recently, there has been an increased interest in imaging different pulmonary disorders using PET techniques. Previous work has shown, for static PET/CT, that air content in the lung influences reconstructed image values and that it is vital to correct for this ‘tissue fraction effect’ (TFE). In this paper, we extend this work to include the blood component and also investigate the TFE in dynamic imaging. CT imaging and PET kinetic modelling are used to determine fractional air and blood voxel volumes in six patients with idiopathic pulmonary fibrosis. These values are used to illustrate best and worst case scenarios when interpreting images without correcting for the TFE. In addition, the fractional volumes were used to determine correction factors for the SUV and the kinetic parameters. These were then applied to the patient images. The kinetic parameters K1 and Ki along with the static parameter SUV were all found to be affected by the TFE with both air and blood providing a significant contribution to the errors. Without corrections, errors range from 34-80% in the best case and 29-96% in the worst case. In the patient data, without correcting for the TFE, regions of high density (fibrosis) appeared to have a higher uptake than lower density (normal appearing tissue), however this was reversed after air and blood correction. The proposed correction methods are vital for quantitative and relative accuracy. Without these corrections, images may be misinterpreted.
Air density dependence of the soft X-ray PTW 34013 ionization chamber.

PubMed

Torres Del Río, Julia; Forastero, Cristina; Tornero-López, Ana M; López, Jesús J; Guirado, Damián; Perez-Calatayud, José; Lallena, Antonio M

2018-02-01

We studied the dependence on air density of the response of the PTW 34013 ionization chamber, recently upgraded for dosimetry control of low energy X-ray beams. Measurements were performed by changing the pressure conditions inside a pressure chamber. The behavior of the measurements against the air density inside this chamber was analyzed. X-ray beams generated with 50, 70, 100, 150 and 200 kVp and the two electrometer polarities were considered. For all beams studied, measurements corrected with the conventional temperature and pressure factor showed a residual dependence on the air density that was described with a linear function of the air density. For the 50 and 70 kVp beams, corrected measurements remained ∼1% smaller than the value found at standard pressure/temperature conditions, for both electrometer polarities and for the air density range typical in clinical conditions. For air densities smaller than the standard one, measurements found for 100, 150 and 200 kVp beams were below or above the value found at standard pressure and temperature when the negative or positive electrometer polarities were used, respectively. The differences with the measurements at standard conditions were less than 1% for the 100 kVp beam and below 4% for the other two beams. The PTW 34013 ionization chamber showed a dependence on the air density that is not properly described with the usual temperature and pressure correction factor. This residual dependence is negligible for low energy beams, for which this chamber is recommended, but is more substantial for beams with energy above 80 kVp. Copyright © 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
Long Range Debye-Hückel Correction for Computation of Grid-based Electrostatic Forces Between Biomacromolecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mereghetti, Paolo; Martinez, M.; Wade, Rebecca C.

Brownian dynamics (BD) simulations can be used to study very large molecular systems, such as models of the intracellular environment, using atomic-detail structures. Such simulations require strategies to contain the computational costs, especially for the computation of interaction forces and energies. A common approach is to compute interaction forces between macromolecules by precomputing their interaction potentials on three-dimensional discretized grids. For long-range interactions, such as electrostatics, grid-based methods are subject to finite size errors. We describe here the implementation of a Debye-Hückel correction to the grid-based electrostatic potential used in the SDA BD simulation software that was applied to simulatemore » solutions of bovine serum albumin and of hen egg white lysozyme.« less
Long-range synchrony of gamma oscillations and auditory hallucination symptoms in schizophrenia

PubMed Central

Mulert, C.; Kirsch; Pascual-Marqui, Roberto; McCarley, Robert W.; Spencer, Kevin M.

2010-01-01

Phase locking in the gamma-band range has been shown to be diminished in patients with schizophrenia. Moreover, there have been reports of positive correlations between phase locking in the gamma-band range and positive symptoms, especially hallucinations. The aim of the present study was to use a new methodological approach in order to investigate gamma-band phase synchronization between the left and right auditory cortex in patients with schizophrenia and its relationship to auditory hallucinations. Subjects were 18 patients with chronic schizophrenia (SZ) and 16 healthy control (HC) subjects. Auditory hallucination symptom scores were obtained using the Scale for the Assessment of Positive Symptoms. Stimuli were 40-Hz binaural click trains. The generators of the 40 Hz-ASSR were localized using eLORETA and based on the computed intracranial signals lagged interhemispheric phase locking between primary and secondary auditory cortices was analyzed. Current source density of the 40 ASSR response was significantly diminished in SZ in comparison to HC in the right superior and middle temporal gyrus (p<0.05). Interhemispheric phase locking was reduced in SZ in comparison to HC for the primary auditory cortices (p<0.05) but not in the secondary auditory cortices. A significant positive correlation was found between auditory hallucination symptom scores and phase synchronization between the primary auditory cortices (p<0.05, corrected for multiple testing) but not for the secondary auditory cortices. These results suggest that long-range synchrony of gamma oscillations is disturbed in schizophrenia and that this deficit is related to clinical symptoms such as auditory hallucinations. PMID:20713096
Transport coefficients of hard-sphere mixtures. II. Diameter ratio 0. 4 and mass ratio 0. 03 at low density

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erpenbeck, J.J.

1992-02-15

The transport coefficients of shear viscosity, thermal conductivity, thermal diffusion, and mutual diffusion are estimated for a binary, equimolar mixture of hard spheres having a diameter ratio of 0.4 and a mass ratio of 0.03 at volumes of 5{ital V}{sub 0}, 10{ital V}{sub 0}, and 20{ital V}{sub 0} (where {ital V}{sub 0}=1/2 {radical}2 {ital N} {ital tsum}{sub {ital a}} x{sub {ital a}}{sigma}{sub {ital a}}{sup 3}, {ital x}{sub {ital a}} are mole fractions, {sigma}{sub {ital a}} are diameters, and {ital N} is the number of particles) through Monte Carlo, molecular-dynamics calculations using the Green-Kubo formulas. Calculations are reported for as fewmore » as 108 and as many as 4000 particles, but not for each value of the volume. Both finite-system and long-time-tail corrections are applied to obtain estimates of the transport coefficients in the thermodynamic limit; corrections of both types are found to be small. The results are compared with the predictions of the revised Enskog theory and the linear density corrections to that theory are reported. The mean free time is also computed as a function of density and the linear and quadratic corrections to the Boltzmann theory are estimated. The mean free time is also compared with the expression from the Mansoori-Carnahan-Starling-Leland equation of state.« less
Fit Point-Wise AB Initio Calculation Potential Energies to a Multi-Dimension Long-Range Model

NASA Astrophysics Data System (ADS)

Zhai, Yu; Li, Hui; Le Roy, Robert J.

2016-06-01

A potential energy surface (PES) is a fundamental tool and source of understanding for theoretical spectroscopy and for dynamical simulations. Making correct assignments for high-resolution rovibrational spectra of floppy polyatomic and van der Waals molecules often relies heavily on predictions generated from a high quality ab initio potential energy surface. Moreover, having an effective analytic model to represent such surfaces can be as important as the ab initio results themselves. For the one-dimensional potentials of diatomic molecules, the most successful such model to date is arguably the ``Morse/Long-Range'' (MLR) function developed by R. J. Le Roy and coworkers. It is very flexible, is everywhere differentiable to all orders. It incorporates correct predicted long-range behaviour, extrapolates sensibly at both large and small distances, and two of its defining parameters are always the physically meaningful well depth {D}_e and equilibrium distance r_e. Extensions of this model, called the Multi-Dimension Morse/Long-Range (MD-MLR) function, linear molecule-linear molecule systems and atom-non-linear molecule system. have been applied successfully to atom-plus-linear molecule, linear molecule-linear molecule and atom-non-linear molecule systems. However, there are several technical challenges faced in modelling the interactions of general molecule-molecule systems, such as the absence of radial minima for some relative alignments, difficulties in fitting short-range potential energies, and challenges in determining relative-orientation dependent long-range coefficients. This talk will illustrate some of these challenges and describe our ongoing work in addressing them. Mol. Phys. 105, 663 (2007); J. Chem. Phys. 131, 204309 (2009); Mol. Phys. 109, 435 (2011). Phys. Chem. Chem. Phys. 10, 4128 (2008); J. Chem. Phys. 130, 144305 (2009) J. Chem. Phys. 132, 214309 (2010) J. Chem. Phys. 140, 214309 (2010)
Intramolecular Charge Transfer States in the Condensed Phase

NASA Astrophysics Data System (ADS)

Williams, C. F.; Herbert, J. M.

2009-06-01

Time-Dependent Density Functional Theory (TDDFT) with long range corrected functionals can give accurate results for the energies of electronically excited states involving Intramolecular Charge Transfer (ICT) in large molecules. If this is combined with a Molecular Mechanics (MM) representation of the surrounding solvent this technique can be used to interpret the results of condensed phase UV-Vis Spectroscopy. Often the MM region is represented by a set of point charges, however this means that the solvent cannot repolarize to adapt to the new charge distribution as a result of ICT and so the excitation energies to ICT states are overestimated. To solve this problem an algorithm that interfaces TDDFT with the polarizable force-field AMOEBA is presented; the effect of solvation on charge transfer in species such as 4,4'dimethylaminobenzonitrile (DMABN) is discussed. M.A. Rohrdanz, K.M. Martins, and J.M. Herbert, J. Chem. Phys. 130 034107 (2008).
Dark matter with pseudoscalar-mediated interactions explains the DAMA signal and the galactic center excess.

PubMed

Arina, Chiara; Del Nobile, Eugenio; Panci, Paolo

2015-01-09

We study a Dirac dark matter particle interacting with ordinary matter via the exchange of a light pseudoscalar, and analyze its impact on both direct and indirect detection experiments. We show that this candidate can accommodate the long-standing DAMA modulated signal and yet be compatible with all exclusion limits at 99(S)% C.L. This result holds for natural choices of the pseudoscalar-quark couplings (e.g., flavor universal), which give rise to a significant enhancement of the dark matter-proton coupling with respect to the coupling to neutrons. We also find that this candidate can accommodate the observed 1-3 GeV gamma-ray excess at the Galactic center and at the same time have the correct relic density today. The model could be tested with measurements of rare meson decays, flavor changing processes, and searches for axionlike particles with mass in the MeV range.
Heavy right-handed neutrino dark matter and PeV neutrinos at IceCube

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dev, P.S. Bhupal; Kazanas, D.; Mohapatra, R.N.

2016-08-17

We discuss a simple non-supersymmetric model based on the electroweak gauge group SU(2){sub L}×SU(2){sup ′}×U(1){sub B−L} where the lightest of the right-handed neutrinos, which are part of the leptonic doublet of SU(2){sup ′}, play the role of a long-lived unstable dark matter with mass in the multi-PeV range. We use a resonant s-channel annihilation to obtain the correct thermal relic density and relax the unitarity bound on dark matter mass. In this model, there exists a 3-body dark matter decay mode producing tau leptons and neutrinos, which could be the source for the PeV cascade events observed in the IceCubemore » experiment. The model can be tested with more precise flavor information of the highest-energy neutrino events in future data.« less
Heavy Right-Handed Neutrino Dark Matter and PeV Neutrinos at IceCube

NASA Technical Reports Server (NTRS)

Bhupal Dev, P. S.; Kazanas, D.; Mohapatra, R. N.; Teplitz, V. L.; Zhang, Yongchao

2016-01-01

We discuss a simple non-supersymmetric model based on the electroweak gauge group SU(2) (sub L) times SU(2) prime times U(1) (Sub B-L) where the lightest of the right-handed neutrinos, which are part of the leptonic doublet of SU(2) prime, play the role of a long-lived unstable dark matter with mass in the multi-Peta-electronvolt range. We use a resonant s-channel annihilation to obtain the correct thermal relic density and relax the unitarity bound on dark matter mass. In this model, there exists a 3-body dark matter decay mode producing tau leptons and neutrinos, which could be the source for the Peta-electronvolt cascade events observed in the IceCube experiment. The model can be tested with more precise flavor information of the highest-energy neutrino events in future data.
High-harmonic generation in amorphous solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

You, Yong Sing; Yin, Yanchun; Wu, Yi

High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging. Here we report the observation of high-harmonic generation from amorphous fused silica. We also decouple the role of long-range periodicity by comparingmore » harmonics generated from fused silica and crystalline quartz, which contain the same atomic constituents but differ in long-range periodicity. These results advance current understanding of the strong-field processes leading to high-harmonic generation in solids with implications for the development of robust and compact extreme ultraviolet light sources.« less
High-harmonic generation in amorphous solids

DOE PAGES

You, Yong Sing; Yin, Yanchun; Wu, Yi; ...

2017-09-28

High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging. Here we report the observation of high-harmonic generation from amorphous fused silica. We also decouple the role of long-range periodicity by comparingmore » harmonics generated from fused silica and crystalline quartz, which contain the same atomic constituents but differ in long-range periodicity. These results advance current understanding of the strong-field processes leading to high-harmonic generation in solids with implications for the development of robust and compact extreme ultraviolet light sources.« less

76 FR 66321 - Long Range Transportation Plan for Fish and Wildlife Service Lands in Hawai`i, Idaho, Northern...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-26

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Importance of the Decompensative Correction of the Gravity Field for Study of the Upper Crust: Application to the Arabian Plate and Surroundings

NASA Astrophysics Data System (ADS)

Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

2017-01-01

The isostatic correction represents one of the most useful "geological" reduction methods of the gravity field. With this correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. However, even this reduction does not show the full gravity effect of unknown anomalies in the upper crust since their impact is substantially reduced by the isostatic compensation. We analyze a so-called decompensative correction of the isostatic anomalies, which provides a possibility to separate these effects. It was demonstrated that this correction is very significant at the mid-range wavelengths and may exceed 100 m/s2 (mGal), therefore ignoring this effect would lead to wrong conclusions about the upper crust structure. At the same time, the decompensative correction is very sensitive to the compensation depth and effective elastic thickness of the lithosphere. Therefore, these parameters should be properly determined based on other studies. Based on this technique, we estimate the decompensative correction for the Arabian plate and surrounding regions. The amplitude of the decompensative anomalies reaches ±250 m/s2 10-5 (mGal), evidencing for both, large density anomalies of the upper crust (including sediments) and strong isostatic disturbances of the lithosphere. These results improve the knowledge about the crustal structure in the Middle East.
Monitoring long-range electron transfer pathways in proteins by stimulated attosecond broadband X-ray Raman spectroscopy

DOE PAGES

Zhang, Yu; Biggs, Jason D.; Govind, Niranjan; ...

2014-10-09

In this study, long-range electron transfer (ET) plays a key role in many biological energy conversion and synthesis processes. We show that nonlinear spectroscopy with attosecond X-ray pulses provides a real time movie of the evolving oxidation states and electron densities around atoms, and can probe these processes with high spatial and temporal resolution. This is demonstrated in a simulation study of the stimulated X-ray Raman (SXRS) signals in Re-modified azurin, which had long served as a benchmark for long-range ET in proteins. Nonlinear SXRS signals are sensitive to the local electronic structure and should offer a novel window formore » long-range ET.« less
Non-empirical exchange-correlation parameterizations based on exact conditions from correlated orbital theory.

PubMed

Haiduke, Roberto Luiz A; Bartlett, Rodney J

2018-05-14

Some of the exact conditions provided by the correlated orbital theory are employed to propose new non-empirical parameterizations for exchange-correlation functionals from Density Functional Theory (DFT). This reparameterization process is based on range-separated functionals with 100% exact exchange for long-range interelectronic interactions. The functionals developed here, CAM-QTP-02 and LC-QTP, show mitigated self-interaction error, correctly predict vertical ionization potentials as the negative of eigenvalues for occupied orbitals, and provide nice excitation energies, even for challenging charge-transfer excited states. Moreover, some improvements are observed for reaction barrier heights with respect to the other functionals belonging to the quantum theory project (QTP) family. Finally, the most important achievement of these new functionals is an excellent description of vertical electron affinities (EAs) of atoms and molecules as the negative of appropriate virtual orbital eigenvalues. In this case, the mean absolute deviations for EAs in molecules are smaller than 0.10 eV, showing that physical interpretation can indeed be ascribed to some unoccupied orbitals from DFT.
Non-empirical exchange-correlation parameterizations based on exact conditions from correlated orbital theory

NASA Astrophysics Data System (ADS)

Haiduke, Roberto Luiz A.; Bartlett, Rodney J.

2018-05-01

Some of the exact conditions provided by the correlated orbital theory are employed to propose new non-empirical parameterizations for exchange-correlation functionals from Density Functional Theory (DFT). This reparameterization process is based on range-separated functionals with 100% exact exchange for long-range interelectronic interactions. The functionals developed here, CAM-QTP-02 and LC-QTP, show mitigated self-interaction error, correctly predict vertical ionization potentials as the negative of eigenvalues for occupied orbitals, and provide nice excitation energies, even for challenging charge-transfer excited states. Moreover, some improvements are observed for reaction barrier heights with respect to the other functionals belonging to the quantum theory project (QTP) family. Finally, the most important achievement of these new functionals is an excellent description of vertical electron affinities (EAs) of atoms and molecules as the negative of appropriate virtual orbital eigenvalues. In this case, the mean absolute deviations for EAs in molecules are smaller than 0.10 eV, showing that physical interpretation can indeed be ascribed to some unoccupied orbitals from DFT.
A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries

PubMed Central

Dong, S.; Wang, X.

2016-01-01

Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries. PMID:27163909
Determination of 210Pb concentration in NORM waste - An application of the transmission method for self-attenuation corrections for gamma-ray spectrometry

NASA Astrophysics Data System (ADS)

Bonczyk, Michal

2018-07-01

This article deals with the problem of the self-attenuation of low-energy gamma-rays from the isotope of lead 210Pb (46.5 keV) in industrial waste. The 167 samples of industrial waste, belonging to nine categories, were tested by means of gamma spectrometry in order to determine 210Pb activity concentration. The experimental method for self-attenuation corrections for gamma rays emitted by lead isotope was applied. Mass attenuation coefficients were determined for energy of 46.5 keV. Correction factors were calculated based on mass attenuation coefficients, sample density and thickness. A mathematical formula for correction calculation was evaluated. The 210Pb activity concentration obtained varied in the range from several Bq·kg-1 up to 19,810 Bq kg-1. The mass attenuation coefficients varied across the range of 0.19-4.42 cm2·g-1. However, the variation of mass attenuation coefficient within some categories of waste was relatively small. The calculated corrections for self-attenuation were 0.98 - 6.97. The high value of correction factors must not be neglect in radiation risk assessment.
Including screening in van der Waals corrected density functional theory calculations: the case of atoms and small molecules physisorbed on graphene.

PubMed

Silvestrelli, Pier Luigi; Ambrosetti, Alberto

2014-03-28

The Density Functional Theory (DFT)/van der Waals-Quantum Harmonic Oscillator-Wannier function (vdW-QHO-WF) method, recently developed to include the vdW interactions in approximated DFT by combining the quantum harmonic oscillator model with the maximally localized Wannier function technique, is applied to the cases of atoms and small molecules (X=Ar, CO, H2, H2O) weakly interacting with benzene and with the ideal planar graphene surface. Comparison is also presented with the results obtained by other DFT vdW-corrected schemes, including PBE+D, vdW-DF, vdW-DF2, rVV10, and by the simpler Local Density Approximation (LDA) and semilocal generalized gradient approximation approaches. While for the X-benzene systems all the considered vdW-corrected schemes perform reasonably well, it turns out that an accurate description of the X-graphene interaction requires a proper treatment of many-body contributions and of short-range screening effects, as demonstrated by adopting an improved version of the DFT/vdW-QHO-WF method. We also comment on the widespread attitude of relying on LDA to get a rough description of weakly interacting systems.
Laser-driven shock compression of gold foam in the terapascal pressure range

NASA Astrophysics Data System (ADS)

Liu, Wei; Duan, Xiaoxi; Jiang, Shaoen; Wang, Zhebin; Sun, Liang; Liu, Hao; Yang, Weiming; Zhang, Huan; Ye, Qing; Wang, Peng; Li, Yulong; Yi, Lin; Dong, Suo

2018-06-01

Shock compression experiments are carried out on gold foam with an initial density of 3.2 g/cm3 through indirectly laser-driven shock waves at the SG-III prototype laser facility. The impedance-matching technique is applied to determine the equation-of-state (EOS) data of the shocked gold foam. A passive shock breakout diagnostic system is employed to obtain the shock velocities in both the standard material and gold foam. The gold foams are compressed to a maximum density of 20 g/cm3 under a shock pressure of about 2 TPa. The effects of the unsteadiness of shock waves on the EOS measurement are quantitatively analyzed and corrected. The correction of unsteady waves, as well as the good planarity of the shock waves and the low preheating of the gold foam, contributes high-confidence EOS data for the gold foam. The corrected experimental data are compared with the Hugoniot states from the SESAME library. The comparison suggests that the database is suitable for describing the states of gold foam with an initial density of 3.2 g/cm3 under a pressure of about 2 TPa.
Long-ranged Fermi-Pasta-Ulam systems in thermal contact: Crossover from q-statistics to Boltzmann-Gibbs statistics

NASA Astrophysics Data System (ADS)

Bagchi, Debarshee; Tsallis, Constantino

2017-04-01

The relaxation to equilibrium of two long-range-interacting Fermi-Pasta-Ulam-like models (β type) in thermal contact is numerically studied. These systems, with different sizes and energy densities, are coupled to each other by a few thermal contacts which are short-range harmonic springs. By using the kinetic definition of temperature, we compute the time evolution of temperature and energy density of the two systems. Eventually, for some time t >teq, the temperature and energy density of the coupled system equilibrate to values consistent with standard Boltzmann-Gibbs thermostatistics. The equilibration time teq depends on the system size N as teq ∼Nγ where γ ≃ 1.8. We compute the velocity distribution P (v) of the oscillators of the two systems during the relaxation process. We find that P (v) is non-Gaussian and is remarkably close to a q-Gaussian distribution for all times before thermal equilibrium is reached. During the relaxation process we observe q > 1 while close to t =teq the value of q converges to unity and P (v) approaches a Gaussian. Thus the relaxation phenomenon in long-ranged systems connected by a thermal contact can be generically described as a crossover from q-statistics to Boltzmann-Gibbs statistics.
Size-dependent error of the density functional theory ionization potential in vacuum and solution

DOE PAGES

Sosa Vazquez, Xochitl A.; Isborn, Christine M.

2015-12-22

Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potentialmore » for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. As a result, in vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.« less
Size-dependent error of the density functional theory ionization potential in vacuum and solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sosa Vazquez, Xochitl A.; Isborn, Christine M., E-mail: cisborn@ucmerced.edu

2015-12-28

Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potentialmore » for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. In vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.« less
Exploring the limit of accuracy for density functionals based on the generalized gradient approximation: Local, global hybrid, and range-separated hybrid functionals with and without dispersion corrections

DOE PAGES

Mardirossian, Narbe; Head-Gordon, Martin

2014-03-25

The limit of accuracy for semi-empirical generalized gradient approximation (GGA) density functionals is explored in this paper by parameterizing a variety of local, global hybrid, and range-separated hybrid functionals. The training methodology employed differs from conventional approaches in 2 main ways: (1) Instead of uniformly truncating the exchange, same-spin correlation, and opposite-spin correlation functional inhomogeneity correction factors, all possible fits up to fourth order are considered, and (2) Instead of selecting the optimal functionals based solely on their training set performance, the fits are validated on an independent test set and ranked based on their overall performance on the trainingmore » and test sets. The 3 different methods of accounting for exchange are trained both with and without dispersion corrections (DFT-D2 and VV10), resulting in a total of 491 508 candidate functionals. For each of the 9 functional classes considered, the results illustrate the trade-off between improved training set performance and diminished transferability. Since all 491 508 functionals are uniformly trained and tested, this methodology allows the relative strengths of each type of functional to be consistently compared and contrasted. Finally, the range-separated hybrid GGA functional paired with the VV10 nonlocal correlation functional emerges as the most accurate form for the present training and test sets, which span thermochemical energy differences, reaction barriers, and intermolecular interactions involving lighter main group elements.« less
Electron Density Calibration for Radiotherapy Treatment Planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrera-Martinez, F.; Rodriguez-Villafuerte, M.; Martinez-Davalos, A.

2006-09-08

Computed tomography (CT) images are used as basic input data for most modern radiosurgery treatment planning systems (TPS). CT data not only provide anatomic information to delineate target volumes, but also allow the introduction of corrections for tissue inhomogeneities into dose calculations during the treatment planning procedure. These corrections involve the determination of a relationship between tissue electron density ({rho}e) and their corresponding Hounsfield Units (HU). In this work, an elemental analysis of different commercial tissue equivalent materials using Scanning Electron Microscopy was carried out to characterize their chemical composition. The tissue equivalent materials were chosen to ensure a largemore » range of {rho}e to be included in the CT scanner calibration. A phantom was designed and constructed with these materials to simulate the size of a human head.« less
Numerically Exact Long Time Magnetization Dynamics Near the Nonequilibrium Kondo Regime

NASA Astrophysics Data System (ADS)

Cohen, Guy; Gull, Emanuel; Reichman, David; Millis, Andrew; Rabani, Eran

2013-03-01

The dynamical and steady-state spin response of the nonequilibrium Anderson impurity model to magnetic fields, bias voltages, and temperature is investigated by a numerically exact method which allows access to unprecedentedly long times. The method is based on using real, continuous time bold Monte Carlo techniques--quantum Monte Carlo sampling of diagrammatic corrections to a partial re-summation--in order to compute the kernel of a memory function, which is then used to determine the reduced density matrix. The method owes its effectiveness to the fact that the memory kernel is dominated by relatively short-time properties even when the system's dynamics are long-ranged. We make predictions regarding the non-monotonic temperature dependence of the system at high bias voltage and the oscillatory quench dynamics at high magnetic fields. We also discuss extensions of the method to the computation of transport properties and correlation functions, and its suitability as an impurity solver free from the need for analytical continuation in the context of dynamical mean field theory. This work is supported by the US Department of Energy under grant DE-SC0006613, by NSF-DMR-1006282 and by the US-Israel Binational Science Foundation. GC is grateful to the Yad Hanadiv-Rothschild Foundation for the award of a Rothschild Fellowship.
Phase diagram of the quantum Ising model with long-range interactions on an infinite-cylinder triangular lattice

NASA Astrophysics Data System (ADS)

Saadatmand, S. N.; Bartlett, S. D.; McCulloch, I. P.

2018-04-01

Obtaining quantitative ground-state behavior for geometrically-frustrated quantum magnets with long-range interactions is challenging for numerical methods. Here, we demonstrate that the ground states of these systems on two-dimensional lattices can be efficiently obtained using state-of-the-art translation-invariant variants of matrix product states and density-matrix renormalization-group algorithms. We use these methods to calculate the fully-quantitative ground-state phase diagram of the long-range interacting triangular Ising model with a transverse field on six-leg infinite-length cylinders and scrutinize the properties of the detected phases. We compare these results with those of the corresponding nearest neighbor model. Our results suggest that, for such long-range Hamiltonians, the long-range quantum fluctuations always lead to long-range correlations, where correlators exhibit power-law decays instead of the conventional exponential drops observed for short-range correlated gapped phases. Our results are relevant for comparisons with recent ion-trap quantum simulator experiments that demonstrate highly-controllable long-range spin couplings for several hundred ions.
40 CFR 1065.690 - Buoyancy correction for PM sample media.

Code of Federal Regulations, 2010 CFR

2010-07-01

... Buoyancy correction for PM sample media. (a) General. Correct PM sample media for their buoyancy in air if you weigh them on a balance. The buoyancy correction depends on the sample media density, the density of air, and the density of the calibration weight used to calibrate the balance. The buoyancy...
Incoherent vs. coherent behavior in the normal state of copper oxide superconductors

NASA Technical Reports Server (NTRS)

Tesanovic, Zlatko

1991-01-01

The self-consistent quantum fluctuations around the mean-field Hartree-Fock state of the Hubbard model provide a very good description of the ground state and low temperature properties of a 2-D itinerant antiferromagnet. Very good agreement with numerical calculations and experimental data is obtained by including the one- and two-loop spin wave corrections to various physical quantities. In particular, the destruction of the long-range order above the Neel temperature can be understood as a spontaneous generation of a length-scale epsilon(T), which should be identified as the spin correlation length. For finite doping, the question of the Hartree-Fock starting point becomes a more complex one since an extra hole tends to self-trap in antiferromagnetic background. Such quantum defects in an underlying antiferromagnetic state can be spin-bags or vortex-like structures and tend to suppress the long-range order. If motion of the holes occurs on a time-scale shorter than the one associated with the motion of these quantum defects of a spin background, one obtains several important empirical features of the normal state of CuO superconductors like linear T-dependence of resistivity, the cusp in the tunneling density of states, etc. As opposed to a familiar Fermi-liquid behavior, the phenomenology of the above system is dominated by a large incoherent piece of a single hole propagator, resulting in many unusual normal state properties.
DFTBaby: A software package for non-adiabatic molecular dynamics simulations based on long-range corrected tight-binding TD-DFT(B)

NASA Astrophysics Data System (ADS)

Humeniuk, Alexander; Mitrić, Roland

2017-12-01

A software package, called DFTBaby, is published, which provides the electronic structure needed for running non-adiabatic molecular dynamics simulations at the level of tight-binding DFT. A long-range correction is incorporated to avoid spurious charge transfer states. Excited state energies, their analytic gradients and scalar non-adiabatic couplings are computed using tight-binding TD-DFT. These quantities are fed into a molecular dynamics code, which integrates Newton's equations of motion for the nuclei together with the electronic Schrödinger equation. Non-adiabatic effects are included by surface hopping. As an example, the program is applied to the optimization of excited states and non-adiabatic dynamics of polyfluorene. The python and Fortran source code is available at http://www.dftbaby.chemie.uni-wuerzburg.de.
Peelle's pertinent puzzle using the Monte Carlo technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawano, Toshihiko; Talou, Patrick; Burr, Thomas

2009-01-01

We try to understand the long-standing problem of the Peelle's Pertinent Puzzle (PPP) using the Monte Carlo technique. We allow the probability density functions to be any kind of form to assume the impact of distribution, and obtain the least-squares solution directly from numerical simulations. We found that the standard least squares method gives the correct answer if a weighting function is properly provided. Results from numerical simulations show that the correct answer of PPP is 1.1 {+-} 0.25 if the common error is multiplicative. The thought-provoking answer of 0.88 is also correct, if the common error is additive, andmore » if the error is proportional to the measured values. The least squares method correctly gives us the most probable case, where the additive component has a negative value. Finally, the standard method fails for PPP due to a distorted (non Gaussian) joint distribution.« less

Subsurface Density Structure of Taurus Littrow Valley Using Apollo 17 Gravity Data

NASA Astrophysics Data System (ADS)

Urbancic, N.; Ghent, R. R.; Johnson, C.; Stanley, S.; Hatch, D.; Carroll, K. A.; Williamson, M. C.; Garry, W. B.; Talwani, M.

2016-12-01

The Traverse Gravimeter Experiment (TGE) from the Apollo 17 mission was the first and only successful gravity survey on the surface of the Moon, revealing the local gravity field at Taurus Littrow Valley (TLV). Satellite surveys are resolution-limited due to their altitudes, making the TGE dataset a novel tool to probe the near-surface, fine-scale (<1 km) subsurface density structure of the Moon. TLV is hypothesized to be a basalt-filled graben oriented radial to Serenitatis basin. Talwani et al. [Apollo 17 Preliminary Science Report, 13 (1973)] used 2D correction and modelling techniques to derive a 1 km thickness for the subsurface basalt, assuming a rectangular geometry and densities derived from Apollo samples. We used modern 3D correction and modelling techniques and recent high-resolution Lunar Reconnaisance Orbiter topographic and image datasets to reinvestigate the subsurface structure of TLV, assuming a trapezoidal geometry for the valley. Updated topographic maps led to significant improvements in the accuracy of free-air, Bouguer and terrain corrections applied to the data. To determine the underlying geometry for TLV, we tested a range of possible thicknesses (T), dips (θ) and positions for the graben fill. We found that the thickness and position used by Talwani et al. represent the best fit to the data, but with walls that dip 30°. From sensitivity analyses we quantified the effect that different noise levels have on determining the correct model parameters. We found that less than 4 mgal noise in the gravity measurements is required to determine the valley position to within 1 km. At the noise level from the TGE data of ˜3.1 mgal, for an input model with θ=90° and a T=1 km, there will be a range in model dips and thicknesses, with θ=45-90° and T=0.9-1.1 km. Even for noise levels of 1 mgal, the range in parameters is θ=72-90° and T=0.95-1.05 km. These noise constraints are crucial for informing the design of future lunar gravimetry experiments.
Prediction of protein long-range contacts using an ensemble of genetic algorithm classifiers with sequence profile centers.

PubMed

Chen, Peng; Li, Jinyan

2010-05-17

Prediction of long-range inter-residue contacts is an important topic in bioinformatics research. It is helpful for determining protein structures, understanding protein foldings, and therefore advancing the annotation of protein functions. In this paper, we propose a novel ensemble of genetic algorithm classifiers (GaCs) to address the long-range contact prediction problem. Our method is based on the key idea called sequence profile centers (SPCs). Each SPC is the average sequence profiles of residue pairs belonging to the same contact class or non-contact class. GaCs train on multiple but different pairs of long-range contact data (positive data) and long-range non-contact data (negative data). The negative data sets, having roughly the same sizes as the positive ones, are constructed by random sampling over the original imbalanced negative data. As a result, about 21.5% long-range contacts are correctly predicted. We also found that the ensemble of GaCs indeed makes an accuracy improvement by around 5.6% over the single GaC. Classifiers with the use of sequence profile centers may advance the long-range contact prediction. In line with this approach, key structural features in proteins would be determined with high efficiency and accuracy.
Momentum-space cluster dual-fermion method

NASA Astrophysics Data System (ADS)

Iskakov, Sergei; Terletska, Hanna; Gull, Emanuel

2018-03-01

Recent years have seen the development of two types of nonlocal extensions to the single-site dynamical mean field theory. On one hand, cluster approximations, such as the dynamical cluster approximation, recover short-range momentum-dependent correlations nonperturbatively. On the other hand, diagrammatic extensions, such as the dual-fermion theory, recover long-ranged corrections perturbatively. The correct treatment of both strong short-ranged and weak long-ranged correlations within the same framework is therefore expected to lead to a quick convergence of results, and offers the potential of obtaining smooth self-energies in nonperturbative regimes of phase space. In this paper, we present an exact cluster dual-fermion method based on an expansion around the dynamical cluster approximation. Unlike previous formulations, our method does not employ a coarse-graining approximation to the interaction, which we show to be the leading source of error at high temperature, and converges to the exact result independently of the size of the underlying cluster. We illustrate the power of the method with results for the second-order cluster dual-fermion approximation to the single-particle self-energies and double occupancies.
Consistent structures and interactions by density functional theory with small atomic orbital basis sets.

PubMed

Grimme, Stefan; Brandenburg, Jan Gerit; Bannwarth, Christoph; Hansen, Andreas

2015-08-07

A density functional theory (DFT) based composite electronic structure approach is proposed to efficiently compute structures and interaction energies in large chemical systems. It is based on the well-known and numerically robust Perdew-Burke-Ernzerhoff (PBE) generalized-gradient-approximation in a modified global hybrid functional with a relatively large amount of non-local Fock-exchange. The orbitals are expanded in Ahlrichs-type valence-double zeta atomic orbital (AO) Gaussian basis sets, which are available for many elements. In order to correct for the basis set superposition error (BSSE) and to account for the important long-range London dispersion effects, our well-established atom-pairwise potentials are used. In the design of the new method, particular attention has been paid to an accurate description of structural parameters in various covalent and non-covalent bonding situations as well as in periodic systems. Together with the recently proposed three-fold corrected (3c) Hartree-Fock method, the new composite scheme (termed PBEh-3c) represents the next member in a hierarchy of "low-cost" electronic structure approaches. They are mainly free of BSSE and account for most interactions in a physically sound and asymptotically correct manner. PBEh-3c yields good results for thermochemical properties in the huge GMTKN30 energy database. Furthermore, the method shows excellent performance for non-covalent interaction energies in small and large complexes. For evaluating its performance on equilibrium structures, a new compilation of standard test sets is suggested. These consist of small (light) molecules, partially flexible, medium-sized organic molecules, molecules comprising heavy main group elements, larger systems with long bonds, 3d-transition metal systems, non-covalently bound complexes (S22 and S66×8 sets), and peptide conformations. For these sets, overall deviations from accurate reference data are smaller than for various other tested DFT methods and reach that of triple-zeta AO basis set second-order perturbation theory (MP2/TZ) level at a tiny fraction of computational effort. Periodic calculations conducted for molecular crystals to test structures (including cell volumes) and sublimation enthalpies indicate very good accuracy competitive to computationally more involved plane-wave based calculations. PBEh-3c can be applied routinely to several hundreds of atoms on a single processor and it is suggested as a robust "high-speed" computational tool in theoretical chemistry and physics.
Real-time observation of fluctuations in a driven-dissipative quantum many-body system undergoing a phase transition

NASA Astrophysics Data System (ADS)

Donner, Tobias

2015-03-01

A Bose-Einstein condensate whose motional degrees of freedom are coupled to a high-finesse optical cavity via a transverse pump beam constitutes a dissipative quantum many-body system with long range interactions. These interactions can induce a structural phase transition from a flat to a density-modulated state. The transverse pump field simultaneously represents a probe of the atomic density via cavity- enhanced Bragg scattering. By spectrally analyzing the light field leaking out of the cavity, we measure non-destructively the dynamic structure factor of the fluctuating atomic density while the system undergoes the phase transition. An observed asymmetry in the dynamic structure factor is attributed to the coupling to dissipative baths. Critical exponents for both sides of the phase transition can be extracted from the data. We further discuss our progress in adding strong short-range interactions to this system, in order to explore Bose-Hubbard physics with cavity-mediated long-range interactions and self-organization in lower dimensions.
Conductance of a quantum wire at low electron density

NASA Astrophysics Data System (ADS)

Matveev, Konstantin

2006-03-01

We study the transport of electrons through a long quantum wire connecting two bulk leads. As the electron density in the wire is lowered, the Coulomb interactions lead to short-range crystalline ordering of electrons. In this Wigner crystal state the spins of electrons form an antiferromagnetic Heisenberg spin chain with exponentially small exchange coupling J. Inhomogeneity of the electron density due to the coupling of the wire to the leads results in violation of spin-charge separation in the device. As a result the spins affect the conductance of the wire. At zero temperature the low-energy spin excitations propagate freely through the wire, and its conductance remains 2e^2/h. At finite temperature some of the spin excitations are reflected by the wire and contribute to its resistance. Since the energy of the elementary excitations in the spin chain (spinons) cannot exceed πJ/2, the conductance of the wire acquires an exponentially small negative correction δG - (-πJ/2T) at low temperatures T J. At higher temperatures, T J, most of the spin excitations in the leads are reflected by the wire, and the conductance levels off at a new universal value e^2/h. This result is consistent with experimental observations of a mini-plateau of conductance at e^2/h in quantum wires in the absence of magnetic field.
Drift-corrected Odin-OSIRIS ozone product: algorithm and updated stratospheric ozone trends

NASA Astrophysics Data System (ADS)

Bourassa, Adam E.; Roth, Chris Z.; Zawada, Daniel J.; Rieger, Landon A.; McLinden, Chris A.; Degenstein, Douglas A.

2018-01-01

A small long-term drift in the Optical Spectrograph and Infrared Imager System (OSIRIS) stratospheric ozone product, manifested mostly since 2012, is quantified and attributed to a changing bias in the limb pointing knowledge of the instrument. A correction to this pointing drift using a predictable shape in the measured limb radiance profile is implemented and applied within the OSIRIS retrieval algorithm. This new data product, version 5.10, displays substantially better both long- and short-term agreement with Microwave Limb Sounder (MLS) ozone throughout the stratosphere due to the pointing correction. Previously reported stratospheric ozone trends over the time period 1984-2013, which were derived by merging the altitude-number density ozone profile measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) II satellite instrument (1984-2005) and from OSIRIS (2002-2013), are recalculated using the new OSIRIS version 5.10 product and extended to 2017. These results still show statistically significant positive trends throughout the upper stratosphere since 1997, but at weaker levels that are more closely in line with estimates from other data records.
Processing techniques for digital sonar images from GLORIA.

USGS Publications Warehouse

Chavez, P.S.

1986-01-01

Image processing techniques have been developed to handle data from one of the newest members of the remote sensing family of digital imaging systems. This paper discusses software to process data collected by the GLORIA (Geological Long Range Inclined Asdic) sonar imaging system, designed and built by the Institute of Oceanographic Sciences (IOS) in England, to correct for both geometric and radiometric distortions that exist in the original 'raw' data. Preprocessing algorithms that are GLORIA-specific include corrections for slant-range geometry, water column offset, aspect ratio distortion, changes in the ship's velocity, speckle noise, and shading problems caused by the power drop-off which occurs as a function of range.-from Author
The effect of metal density in thoracic adolescent idiopathic scoliosis.

PubMed

Rushton, Paul R P; Elmalky, Mahmoud; Tikoo, Agnivesh; Basu, Saumyajit; Cole, Ashley A; Grevitt, Michael P

2016-10-01

Determine impact of metal density on curve correction and costs in thoracic adolescent idiopathic scoliosis (AIS). Ascertain if increased metal density is required for larger or stiffer curves. Multicentre retrospective case series of patients with Lenke 1-2 AIS treated with single-stage posterior only surgery using a standardized surgical technique; constructs using >80 % screws with variable metal density. All cases had >2-year follow up. Outcomes measures included coronal and sagittal radiographic outcomes, metal density (number of instrumented pedicles vs total available), fusion length and cost. 106 cases included 94 female. 78 Lenke 1. Mean age 14 years (9-26). Mean main thoracic (MT) Cobb angle 63° corrected to 22° (66 %). No significant correlations were present between metal density and: (a) coronal curve correction rates of the MT (r = 0.13, p = 0.19); (b) lumbar curve frontal correction (r = -0.15, p = 0.12); (c) correction index in MT curve (r = -0.10, p = 0.32); and (d) correction index in lumbar curve (r = 0.11, p = 0.28). Metal density was not correlated with change in thoracic kyphosis (r = 0.22, p = 0.04) or lumbosacral lordosis (r = 0.27, p = 0.01). Longer fusions were associated with greater loss of thoracic kyphosis (r = -0.31, p = 0.003). Groups differing by preoperative curve size and stiffness had comparable corrections with similar metal density. The pedicle screw cost represented 21-29 % of overall cost of inpatient treatment depending on metal density. Metal density affects cost but not the coronal and sagittal correction of thoracic AIS. Neither larger nor stiffer curves necessitate high metal density.
Importance of the correlation contribution for local hybrid functionals: range separation and self-interaction corrections.

PubMed

Arbuznikov, Alexei V; Kaupp, Martin

2012-01-07

Local hybrid functionals with their position-dependent exact-exchange admixture are a conceptually simple and promising extension of the concept of a hybrid functional. Local hybrids based on a simple mixing of the local spin density approximation (LSDA) with exact exchange have been shown to be successful for thermochemistry, reaction barriers, and a range of other properties. So far, the combination of this generation of local hybrids with an LSDA correlation functional has been found to give the most favorable results for atomization energies, for a range of local mixing functions (LMFs) governing the exact-exchange admixture. Here, we show that the choice of correlation functional to be used with local hybrid exchange crucially influences the parameterization also of the exchange part as well as the overall performance. A novel ansatz for the correlation part of local hybrids is suggested based on (i) range-separation of LSDA correlation into short-range (SR) and long-range (LR) parts, and (ii) partial or full elimination of the one-electron self-correlation from the SR part. It is shown that such modified correlation functionals allow overall larger exact exchange admixture in thermochemically competitive local hybrids than before. This results in improvements for reaction barriers and for other properties crucially influenced by self-interaction errors, as demonstrated by a number of examples. Based on the range-separation approach, a fresh view on the breakdown of the correlation energy into dynamical and non-dynamical parts is suggested.
Impact of a primordial magnetic field on cosmic microwave background B modes with weak lensing

NASA Astrophysics Data System (ADS)

Yamazaki, Dai G.

2018-05-01

We discuss the manner in which the primordial magnetic field (PMF) suppresses the cosmic microwave background (CMB) B mode due to the weak-lensing (WL) effect. The WL effect depends on the lensing potential (LP) caused by matter perturbations, the distribution of which at cosmological scales is given by the matter power spectrum (MPS). Therefore, the WL effect on the CMB B mode is affected by the MPS. Considering the effect of the ensemble average energy density of the PMF, which we call "the background PMF," on the MPS, the amplitude of MPS is suppressed in the wave number range of k >0.01 h Mpc-1 . The MPS affects the LP and the WL effect in the CMB B mode; however, the PMF can damp this effect. Previous studies of the CMB B mode with the PMF have only considered the vector and tensor modes. These modes boost the CMB B mode in the multipole range of ℓ>1000 , whereas the background PMF damps the CMB B mode owing to the WL effect in the entire multipole range. The matter density in the Universe controls the WL effect. Therefore, when we constrain the PMF and the matter density parameters from cosmological observational data sets, including the CMB B mode, we expect degeneracy between these parameters. The CMB B mode also provides important information on the background gravitational waves, inflation theory, matter density fluctuations, and the structure formations at the cosmological scale through the cosmological parameter search. If we study these topics and correctly constrain the cosmological parameters from cosmological observations, including the CMB B mode, we need to correctly consider the background PMF.
Quantification of seasonal biomass effects on cosmic-ray soil water content determination

NASA Astrophysics Data System (ADS)

Baatz, R.; Bogena, H. R.; Hendricks Franssen, H.; Huisman, J. A.; Qu, W.; Montzka, C.; Korres, W.; Vereecken, H.

2013-12-01

The novel cosmic-ray soil moisture probes (CRPs) measure neutron flux density close to the earth surface. High energy cosmic-rays penetrate the Earth's atmosphere from the cosmos and become moderated by terrestrial nuclei. Hydrogen is the most effective neutron moderator out of all chemical elements. Therefore, neutron flux density measured with a CRP at the earth surface correlates inversely with the hydrogen content in the CRP's footprint. A major contributor to the amount of hydrogen in the sensor's footprint is soil water content. The ability to measure changes in soil water content within the CRP footprint at a larger-than-point scale (~30 ha) and at high temporal resolution (hourly) make these sensors an appealing measurement instrument for hydrologic modeling purposes. Recent developments focus on the identification and quantification of major uncertainties inherent in CRP soil moisture measurements. In this study, a cosmic-ray soil moisture network for the Rur catchment in Western Germany is presented. It is proposed to correct the measured neutron flux density for above ground biomass yielding vegetation corrected soil water content from cosmic-ray measurements. The correction for above ground water equivalents aims to remove biases in soil water content measurements on sites with high seasonal vegetation dynamics such as agricultural fields. Above ground biomass is estimated as function of indices like NDVI and NDWI using regression equations. The regression equations were obtained with help of literature information, ground-based control measurements, a crop growth model and globally available data from the Moderate Resolution Imaging Spectrometer (MODIS). The results show that above ground biomass could be well estimated during the first half of the year. Seasonal changes in vegetation water content yielded biases in soil water content of ~0.05 cm3/cm3 that could be corrected for with the vegetation correction. The vegetation correction has particularly high potential when applied at long term cosmic-ray monitoring sites and the cosmic-ray rover.
Use of diphosphonates to correct disorders in calcium metabolism and mineral composition of bone tissue with 60-day hypokinesia in rats

NASA Technical Reports Server (NTRS)

Morukov, B. V.; Zaychik, V. YE.; Ivanov, V. M.; Orlov, O. I.

1988-01-01

Compounds of the diphosphonate group suppress bone resorption and bone tissue metabolism, from which it was assumed that they can be used for the prevention of osteoporosis and disorders of calcium homeostasis in humans during space flight. Two compounds of this group were used for preventive purposes in 60 day hypokinesia in rats. The results showed that diphosphonates have a marked effect on calcium metabolism and the condition of the bone tissues under conditions of long term hypokinesia: they reduce the content of ionized calcium in blood, delay the loss of calcium and phosphorus by the bone tissue, and to a considerable degree prevent reduction of bone density. This confirms the possibility of using compounds of this group for correcting and preventing changes of bone tissue and mineral metabolism during long term hypokinesia.
Treatment of low bone density in young people with cystic fibrosis: a multicentre, prospective, open-label observational study of calcium and calcifediol followed by a randomised placebo-controlled trial of alendronate.

PubMed

Bianchi, Maria Luisa; Colombo, Carla; Assael, Baroukh M; Dubini, Antonella; Lombardo, Mariangela; Quattrucci, Serena; Bella, Sergio; Collura, Mirella; Messore, Barbara; Raia, Valeria; Poli, Furio; Bini, Rita; Albanese, Carlina V; De Rose, Virginia; Costantini, Diana; Romano, Giovanna; Pustorino, Elena; Magazzù, Giuseppe; Bertasi, Serenella; Lucidi, Vincenzina; Traverso, Gabriella; Coruzzo, Anna; Grzejdziak, Amelia D

2013-07-01

Long-term complications of cystic fibrosis include osteoporosis and fragility fractures, but few data are available about effective treatment strategies, especially in young patients. We investigated treatment of low bone mineral density in children, adolescents, and young adults with cystic fibrosis. We did a multicentre trial in two phases. We enrolled patients aged 5-30 years with cystic fibrosis and low bone mineral density, from ten cystic fibrosis regional centres in Italy. The first phase was an open-label, 12-month observational study of the effect of adequate calcium intake plus calcifediol. The second phase was a 12-month, double-blind, randomised, placebo-controlled, parallel group study of the efficacy and safety of oral alendronate in patients whose bone mineral apparent density had not increased by 5% or more by the end of the observational phase. Patients were randomly assigned to either alendronate or placebo. Both patients and investigators were masked to treatment assignment. We used dual x-ray absorptiometry at baseline and every 6 months thereafter, corrected for body size, to assess lumbar spine bone mineral apparent density. We assessed bone turnover markers and other laboratory parameters every 3-6 months. The primary endpoint was mean increase of lumbar spine bone mineral apparent density, assessed in the intention-to-treat population. This study is registered with ClinicalTrials.gov, number NCT01812551. We screened 540 patients and enrolled 171 (mean age 13·8 years, SD 5·9, range 5-30). In the observational phase, treatment with calcium and calcifediol increased bone mineral apparent density by 5% or more in 43 patients (25%). 128 patients entered the randomised phase. Bone mineral apparent density increased by 16·3% in the alendronate group (n=65) versus 3·1% in the placebo group (n=63; p=0·0010). 19 of 57 young people (33·3%) receiving alendronate attained a normal-for-age bone mineral apparent density Z score. In the observational phase, five patients had moderate episodes of hypercalciuria, which resolved after short interruption of calcifediol treatment. During the randomised phase, one patient taking alendronate had mild fever versus none in the placebo group; treatment groups did not differ significantly for other adverse events. Correct calcium intake plus calcifediol can improve bone mineral density in some young patients with cystic fibrosis. In those who do not respond to calcium and calcifediol alone, alendronate can safely and effectively increase bone mineral density. Telethon Foundation (Italy). Copyright © 2013 Elsevier Ltd. All rights reserved.
Broadband EIT borehole measurements with high phase accuracy using numerical corrections of electromagnetic coupling effects

NASA Astrophysics Data System (ADS)

Zhao, Y.; Zimmermann, E.; Huisman, J. A.; Treichel, A.; Wolters, B.; van Waasen, S.; Kemna, A.

2013-08-01

Electrical impedance tomography (EIT) is gaining importance in the field of geophysics and there is increasing interest for accurate borehole EIT measurements in a broad frequency range (mHz to kHz) in order to study subsurface properties. To characterize weakly polarizable soils and sediments with EIT, high phase accuracy is required. Typically, long electrode cables are used for borehole measurements. However, this may lead to undesired electromagnetic coupling effects associated with the inductive coupling between the double wire pairs for current injection and potential measurement and the capacitive coupling between the electrically conductive shield of the cable and the electrically conductive environment surrounding the electrode cables. Depending on the electrical properties of the subsurface and the measured transfer impedances, both coupling effects can cause large phase errors that have typically limited the frequency bandwidth of field EIT measurements to the mHz to Hz range. The aim of this paper is to develop numerical corrections for these phase errors. To this end, the inductive coupling effect was modeled using electronic circuit models, and the capacitive coupling effect was modeled by integrating discrete capacitances in the electrical forward model describing the EIT measurement process. The correction methods were successfully verified with measurements under controlled conditions in a water-filled rain barrel, where a high phase accuracy of 0.8 mrad in the frequency range up to 10 kHz was achieved. The corrections were also applied to field EIT measurements made using a 25 m long EIT borehole chain with eight electrodes and an electrode separation of 1 m. The results of a 1D inversion of these measurements showed that the correction methods increased the measurement accuracy considerably. It was concluded that the proposed correction methods enlarge the bandwidth of the field EIT measurement system, and that accurate EIT measurements can now be made in the mHz to kHz frequency range. This increased accuracy in the kHz range will allow a more accurate field characterization of the complex electrical conductivity of soils and sediments, which may lead to the improved estimation of saturated hydraulic conductivity from electrical properties. Although the correction methods have been developed for a custom-made EIT system, they also have potential to improve the phase accuracy of EIT measurements made with commercial systems relying on multicore cables.
RCS measurements, transformations, and comparisons under cylindrical and plane wave illumination

NASA Astrophysics Data System (ADS)

Vokura, V. J.; Balanis, Constantine A.; Birtcher, Craig R.

1994-03-01

Monostatic RCS measurements of a long bar (at X-band) and of a scale model aircraft (at C-band) were performed under the quasi-plane wave illumination produced by a dual parabolic-cylinder CATR. At Arizona State University's ElectroMagnetic Anechoic Chamber (EMAC) facility, these measurements were repeated under the cylindrical wave illumination produced by a March Microwave Single-Plane Collimating Range (SPCR). The SPRC measurements were corrected using corrected using the 'reference target method.' The corrected SPCR measurements are in good agreement with the CATR measurements.
Curvature and frontier orbital energies in density functional theory

NASA Astrophysics Data System (ADS)

Kronik, Leeor; Stein, Tamar; Autschbach, Jochen; Govind, Niranjan; Baer, Roi

2013-03-01

Perdew et al. [Phys. Rev. Lett 49, 1691 (1982)] discovered and proved two different properties of exact Kohn-Sham density functional theory (DFT): (i) The exact total energy versus particle number is a series of linear segments between integer electron points; (ii) Across an integer number of electrons, the exchange-correlation potential may ``jump'' by a constant, known as the derivative discontinuity (DD). Here, we show analytically that in both the original and the generalized Kohn-Sham formulation of DFT, the two are in fact two sides of the same coin. Absence of a derivative discontinuity necessitates deviation from piecewise linearity, and the latter can be used to correct for the former, thereby restoring the physical meaning of the orbital energies. Using selected small molecules, we show that this results in a simple correction scheme for any underlying functional, including semi-local and hybrid functionals as well as Hartree-Fock theory, suggesting a practical correction for the infamous gap problem of DFT. Moreover, we show that optimally-tuned range-separated hybrid functionals can inherently minimize both DD and curvature, thus requiring no correction, and show that this can be used as a sound theoretical basis for novel tuning strategies.
Precursor of superfluidity in a strongly interacting Fermi gas with negative effective range

NASA Astrophysics Data System (ADS)

Tajima, Hiroyuki

2018-04-01

We investigate theoretically the effects of pairing fluctuations in an ultracold Fermi gas near a Feshbach resonance with a negative effective range. By employing a many-body T -matrix theory with a coupled fermion-boson model, we show that the single-particle density of states exhibits the so-called pseudogap phenomenon, which is a precursor of superfluidity induced by strong pairing fluctuations. We clarify the region where strong pairing fluctuations play a crucial role in single-particle properties, from the broad-resonance region to the narrow-resonance limit at the divergent two-body scattering length. We also extrapolate the effects of pairing fluctuations to the positive-effective-range region from our results near the narrow Feshbach resonance. Results shown in this paper are relevant to the connection between ultracold Fermi gases and low-density neutron matter from the viewpoint of finite-effective-range corrections.
Strain effects and intermixing at the Si surface: Importance of long-range elastic corrections in first-principles calculations

DOE PAGES

Béland, Laurent Karim; Machado-Charry, Eduardo; Pochet, Pascal; ...

2014-10-06

Here we investigate Ge mixing at the Si(001) surface and characterize the 2 N Si(001) reconstruction by means of hybrid quantum and molecular mechanics calculations (QM/MM). Avoiding fake elastic dampening, this scheme allows to correctly take into account long range deformation induced by reconstructed and defective surfaces. We focus in particular on the dimer vacancy line (DVL) and its interaction with Ge adatoms. We first show that calculated formation energies for these defects are highly dependent on the choice of chemical potential and that the latter must be chosen carefully. Characterizing the effect of the DVL on the deformation field,more » we also find that the DVL favors Ge segregation in the fourth layer close to the DVL. Using the activation-relaxation technique (ART nouveau) and QM/MM, we show that a complex diffusion path permits the substitution of the Ge atom in the fourth layer, with barriers compatible with mixing observed at intermediate temperature. We also show that the use of QM/MM results in much more signi cant corrections at the saddle points (up to 0.5 eV) that at minima, demonstrating its importance for describing kinetics correctly.« less
Error estimates for (semi-)empirical dispersion terms and large biomacromolecules.

PubMed

Korth, Martin

2013-10-14

The first-principles modeling of biomaterials has made tremendous advances over the last few years with the ongoing growth of computing power and impressive developments in the application of density functional theory (DFT) codes to large systems. One important step forward was the development of dispersion corrections for DFT methods, which account for the otherwise neglected dispersive van der Waals (vdW) interactions. Approaches at different levels of theory exist, with the most often used (semi-)empirical ones based on pair-wise interatomic C6R(-6) terms. Similar terms are now also used in connection with semiempirical QM (SQM) methods and density functional tight binding methods (SCC-DFTB). Their basic structure equals the attractive term in Lennard-Jones potentials, common to most force field approaches, but they usually use some type of cutoff function to make the mixing of the (long-range) dispersion term with the already existing (short-range) dispersion and exchange-repulsion effects from the electronic structure theory methods possible. All these dispersion approximations were found to perform accurately for smaller systems, but error estimates for larger systems are very rare and completely missing for really large biomolecules. We derive such estimates for the dispersion terms of DFT, SQM and MM methods using error statistics for smaller systems and dispersion contribution estimates for the PDBbind database of protein-ligand interactions. We find that dispersion terms will usually not be a limiting factor for reaching chemical accuracy, though some force fields and large ligand sizes are problematic.

Toward chemical accuracy in the description of ion-water interactions through many-body representations. Alkali-water dimer potential energy surfaces

NASA Astrophysics Data System (ADS)

Riera, Marc; Mardirossian, Narbe; Bajaj, Pushp; Götz, Andreas W.; Paesani, Francesco

2017-10-01

This study presents the extension of the MB-nrg (Many-Body energy) theoretical/computational framework of transferable potential energy functions (PEFs) for molecular simulations of alkali metal ion-water systems. The MB-nrg PEFs are built upon the many-body expansion of the total energy and include the explicit treatment of one-body, two-body, and three-body interactions, with all higher-order contributions described by classical induction. This study focuses on the MB-nrg two-body terms describing the full-dimensional potential energy surfaces of the M+(H2O) dimers, where M+ = Li+, Na+, K+, Rb+, and Cs+. The MB-nrg PEFs are derived entirely from "first principles" calculations carried out at the explicitly correlated coupled-cluster level including single, double, and perturbative triple excitations [CCSD(T)-F12b] for Li+ and Na+ and at the CCSD(T) level for K+, Rb+, and Cs+. The accuracy of the MB-nrg PEFs is systematically assessed through an extensive analysis of interaction energies, structures, and harmonic frequencies for all five M+(H2O) dimers. In all cases, the MB-nrg PEFs are shown to be superior to both polarizable force fields and ab initio models based on density functional theory. As previously demonstrated for halide-water dimers, the MB-nrg PEFs achieve higher accuracy by correctly describing short-range quantum-mechanical effects associated with electron density overlap as well as long-range electrostatic many-body interactions.
SU-E-T-608: Perturbation Corrections for Alanine Dosimeters in Different Phantom Materials in High-Energy Photon Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voigts-Rhetz, P von; Czarnecki, D; Anton, M

Purpose: Alanine dosimeters are often used for in-vivo dosimetry purposes in radiation therapy. In a Monte Carlo study the influence of 20 different surrounding/phantom materials for alanine dosimeters was investigated. The investigations were performed in high-energy photon beams, covering the whole range from {sup 60}Co up to 25 MV-X. The aim of the study is the introduction of a perturbation correction k{sub env} for alanine dosimeters accounting for the environmental material. Methods: The influence of different surrounding materials on the response of alanine dosimeters was investigated with Monte Carlo simulations using the EGSnrc code. The photon source was adapted withmore » BEAMnrc to a {sup 60}Co unit and an Elekta (E{sub nom}=6, 10, 25 MV-X) linear accelerator. Different tissue-equivalent materials ranging from cortical bone to lung were investigated. In addition to available phantom materials, some material compositions were taken and scaled to different electron densities. The depth of the alanine detectors within the different phantom materials corresponds to 5 cm depth in water, i.e. the depth is scaled according to the electron density (n{sub e}/n{sub e,w}) of the corresponding phantom material. The dose was scored within the detector volume once for an alanine/paraffin mixture and once for a liquid water voxel. The relative response, the ratio of the absorbed dose to alanine to the absorbed dose to water, was calculated and compared to the corresponding ratio under reference conditions. Results: For each beam quality the relative response r and the correction factor for the environment kenv was calculated. k{sub env}=0.9991+0.0049 *((n{sub e}/n{sub e,w})−0.7659){sup 3} Conclusion: A perturbation correction factor k{sub env} accounting for the phantom environment has been introduced. The response of the alanine dosimeter can be considered independent of the surrounding material for relative electron densities (n{sub e}/n{sub e,w}) between 1 and 1.4. For denser materials such as bone or much less dense surroundings such as lung, a small correction would be appropriate.« less
Short-Time Glassy Dynamics in Viscous Protein Solutions with Competing Interactions

DOE PAGES

Godfrin, P. Douglas; Hudson, Steven; Hong, Kunlun; ...

2015-11-24

Although there have been numerous investigations of the glass transition for colloidal dispersions with only a short-ranged attraction, less is understood for systems interacting with a long-ranged repulsion in addition to this attraction, which is ubiquitous in aqueous protein solutions at low ionic strength. Highly puri ed concentrated lysozyme solutions are used as a model system and investigated over a large range of protein concentrations at very low ionic strength. Newtonian liquid behavior is observed at all concentrations, even up to 480 mg/mL, where the zero shear viscosity increases by more than three orders of magnitude with increasing concentration. Remarkably,more » despite this macroscopic liquid-like behavior, the measurements of the dynamics in the short-time limit shows features typical of glassy colloidal systems. Investigation of the inter-protein structure indicates that the reduced short-time mobility of the protein is caused by localized regions of high density within a heterogeneous density distribution. This structural heterogeneity occurs on intermediate range length scale, driven by the competing potential features, and is distinct from commonly studied colloidal gel systems in which a heterogeneous density distribution tends to extend to the whole system. The presence of long-ranged repulsion also allows for more mobility over large length and long time scales resulting in the macroscopic relaxation of the structure. The experimental results provide evidence for the need to explicitly include intermediate range order in theories for the macroscopic properties of protein solutions interacting via competing potential features.« less
Modelling Sensory Limitation: The Role of Tree Selection, Memory and Information Transfer in Bats’ Roost Searching Strategies

PubMed Central

Ruczyński, Ireneusz; Bartoń, Kamil A.

2012-01-01

Sensory limitation plays an important role in the evolution of animal behaviour. Animals have to find objects of interest (e.g. food, shelters, predators). When sensory abilities are strongly limited, animals adjust their behaviour to maximize chances for success. Bats are nocturnal, live in complex environments, are capable of flight and must confront numerous perceptual challenges (e.g. limited sensory range, interfering clutter echoes). This makes them an excellent model for studying the role of compensating behaviours to decrease costs of finding resources. Cavity roosting bats are especially interesting because the availability of tree cavities is often limited, and their quality is vital for bats during the breeding season. From a bat’s sensory point of view, cavities are difficult to detect and finding them requires time and energy. However, tree cavities are also long lasting, allowing information transfer among conspecifics. Here, we use a simple simulation model to explore the benefits of tree selection, memory and eavesdropping (compensation behaviours) to searches for tree cavities by bats with short and long perception range. Our model suggests that memory and correct discrimination of tree suitability are the basic strategies decreasing the cost of roost finding, whereas perceptual range plays a minor role in this process. Additionally, eavesdropping constitutes a buffer that reduces the costs of finding new resources (such as roosts), especially when they occur in low density. We conclude that natural selection may promote different strategies of roost finding in relation to habitat conditions and cognitive skills of animals. PMID:23028666
Experimental testing of four correction algorithms for the forward scattering spectrometer probe

NASA Technical Reports Server (NTRS)

Hovenac, Edward A.; Oldenburg, John R.; Lock, James A.

1992-01-01

Three number density correction algorithms and one size distribution correction algorithm for the Forward Scattering Spectrometer Probe (FSSP) were compared with data taken by the Phase Doppler Particle Analyzer (PDPA) and an optical number density measuring instrument (NDMI). Of the three number density correction algorithms, the one that compared best to the PDPA and NDMI data was the algorithm developed by Baumgardner, Strapp, and Dye (1985). The algorithm that corrects sizing errors in the FSSP that was developed by Lock and Hovenac (1989) was shown to be within 25 percent of the Phase Doppler measurements at number densities as high as 3000/cc.
A DNA-based molecular motor that can navigate a network of tracks

NASA Astrophysics Data System (ADS)

Wickham, Shelley F. J.; Bath, Jonathan; Katsuda, Yousuke; Endo, Masayuki; Hidaka, Kumi; Sugiyama, Hiroshi; Turberfield, Andrew J.

2012-03-01

Synthetic molecular motors can be fuelled by the hydrolysis or hybridization of DNA. Such motors can move autonomously and programmably, and long-range transport has been observed on linear tracks. It has also been shown that DNA systems can compute. Here, we report a synthetic DNA-based system that integrates long-range transport and information processing. We show that the path of a motor through a network of tracks containing four possible routes can be programmed using instructions that are added externally or carried by the motor itself. When external control is used we find that 87% of the motors follow the correct path, and when internal control is used 71% of the motors follow the correct path. Programmable motion will allow the development of computing networks, molecular systems that can sort and process cargoes according to instructions that they carry, and assembly lines that can be reconfigured dynamically in response to changing demands.
Formation of the –N(NO)N(NO)– polymer at high pressure and stabilization at ambient conditions

PubMed Central

Xiao, Hai; An, Qi; Goddard, William A.; Liu, Wei-Guang; Zybin, Sergey V.

2013-01-01

A number of exotic structures have been formed through high-pressure chemistry, but applications have been hindered by difficulties in recovering the high-pressure phase to ambient conditions (i.e., one atmosphere and 300 K). Here we use dispersion-corrected density functional theory [PBE-ulg (Perdew-Burke-Ernzerhof flavor of DFT with the universal low gradient correction for long range London dispersion)] to predict that above 60 gigapascal (GPa) the most stable form of N2O (the laughing gas in its molecular form) is a one-dimensional polymer with an all-nitrogen backbone analogous to cis-polyacetylene in which alternate N are bonded (ionic covalent) to O. The analogous trans-polymer is only 0.03∼0.10 eV/molecular unit less stable. Upon relaxation to ambient conditions, both polymers relax below 14 GPa to the same stable nonplanar trans-polymer. The predicted phonon spectrum and dissociation kinetics validates the stability of this trans-poly-NNO at ambient conditions, which has potential applications as a type of conducting nonlinear optical polymer with all-nitrogen chains and as a high-energy oxidizer for rocket propulsion. This work illustrates in silico materials discovery particularly in the realm of extreme conditions (very high pressure or temperature). PMID:23503849
Observation of Neutral Sodium Above Mercury During the Transit of November 8, 2006

NASA Technical Reports Server (NTRS)

Potter, A. E.; Killen, R. M.; Reardon, Kevin P.; Bida, T. A.

2013-01-01

We mapped the absorption of sunlight by sodium vapor in the exosphere of Mercury during the transit of Mercury on November 8, 2006, using the IBIS Interferometric BIdimensional Spectrometer at the Dunn Solar Telescope operated by the National Solar Observatory at Sunspot, New Mexico. The measurements were reduced to line-of-sight equivalent widths for absorption at the sodium D2 line around the shadow of Mercury. The sodium absorption fell off exponentially with altitude up to about 600 km. However there were regions around north and south polar-regions where relatively uniform sodium absorptions extended above 1000 km. We corrected the 0-600 km altitude profiles for seeing blur using the measured point spread function. Analysis of the corrected altitude distributions yielded surface densities, zenith column densities, temperatures and scale heights for sodium all around the planet. Sodium absorption on the dawn side equatorial terminator was less than on the dusk side, different from previous observations of the relative absorption levels. We also determined Earthward velocities for sodium atoms, and line widths for the absorptions. Earthward velocities resulting from radiation pressure on sodium averaged 0.8 km/s, smaller than a prediction of 1.5 km/s. Most line widths were in the range of 20 mA after correction for instrumental broadening, corresponding to temperatures in the range of 1000 K.
Author Correction: Low frequency transcranial electrical stimulation does not entrain sleep rhythms measured by human intracranial recordings.

PubMed

Lafon, Belen; Henin, Simon; Huang, Yu; Friedman, Daniel; Melloni, Lucia; Thesen, Thomas; Doyle, Werner; Buzsáki, György; Devinsky, Orrin; Parra, Lucas C; Liu, Anli

2018-02-28

It has come to our attention that we did not specify whether the stimulation magnitudes we report in this Article are peak amplitudes or peak-to-peak. All references to intensity given in mA in the manuscript refer to peak-to-peak amplitudes, except in Fig. 2, where the model is calibrated to 1 mA peak amplitude, as stated. In the original version of the paper we incorrectly calibrated the computational models to 1 mA peak-to-peak, rather than 1 mA peak amplitude. This means that we divided by a value twice as large as we should have. The correct estimated fields are therefore twice as large as shown in the original Fig. 2 and Supplementary Figure 11. The corrected figures are now properly calibrated to 1 mA peak amplitude. Furthermore, the sentence in the first paragraph of the Results section 'Intensity ranged from 0.5 to 2.5 mA (current density 0.125-0.625 mA mA/cm 2 ), which is stronger than in previous reports', should have read 'Intensity ranged from 0.5 to 2.5 mA peak to peak (peak current density 0.0625-0.3125 mA/cm 2 ), which is stronger than in previous reports.' These errors do not affect any of the Article's conclusions.
A computerized Langmuir probe system

NASA Astrophysics Data System (ADS)

Pilling, L. S.; Bydder, E. L.; Carnegie, D. A.

2003-07-01

For low pressure plasmas it is important to record entire single or double Langmuir probe characteristics accurately. For plasmas with a depleted high energy tail, the accuracy of the recorded ion current plays a critical role in determining the electron temperature. Even for high density Maxwellian distributions, it is necessary to accurately model the ion current to obtain the correct electron density. Since the electron and ion current saturation values are, at best, orders of magnitude apart, a single current sensing resistor cannot provide the required resolution to accurately record these values. We present an automated, personal computer based data acquisition system for the determination of fundamental plasma properties in low pressure plasmas. The system is designed for single and double Langmuir probes, whose characteristics can be recorded over a bias voltage range of ±70 V with 12 bit resolution. The current flowing through the probes can be recorded within the range of 5 nA-100 mA. The use of a transimpedance amplifier for current sensing eliminates the requirement for traditional current sensing resistors and hence the need to correct the raw data. The large current recording range is realized through the use of a real time gain switching system in the negative feedback loop of the transimpedance amplifier.
Ab Initio Calculated Results Require New Formulations for Properties in the Limit of Zero Density: The Viscosity of Methane (CH4)

NASA Astrophysics Data System (ADS)

Laesecke, Arno; Muzny, Chris D.

2017-12-01

A wide-ranging formulation for the viscosity of methane in the limit of zero density is presented. Using ab initio calculated data of Hellmann et al. (J Chem Phys 129, 064302, 2008) from 80 K to 1500 K, the functional form was developed by guided symbolic regression with the constraints of correct extrapolation to T → 0 and in the high-temperature limit. The formulation was adjusted to the recalibrated experimental data of May et al. (Int J Thermophys 28, 1085-1110, 2007) so that these are represented within their estimated expanded uncertainty of 0.053 % (k = 2) in their temperature range from 210.756 K to 391.551 K. Based on comparisons with original data and recalibrated viscosity ratio measurements, the expanded uncertainty of the new correlation is estimated outside this temperature range to be 0.2 % to 700 K, 0.5 % to 1100 K, 1 % to 1500 K, and physically correct at higher temperatures. At temperatures below 210 K, the new correlation agrees with recalibrated experimental data within 0.3 % down to 150 K. Hellmann et al. estimated the expanded uncertainty of their calculated data at 1 % to 80 K. The new formulation extrapolates without a singularity to T→ 0.
Transition from disordered to long-range ordered nanoparticles on Al2O3/Ni3Al(111)

NASA Astrophysics Data System (ADS)

Alyabyeva, N.; Ouvrard, A.; Zakaria, A.-M.; Charra, F.; Bourguignon, B.

2018-06-01

Application of preparation recipes of the literature failed to produce an ordered array of NPs on our particular Ni3Al sample. This has motivated a systematic survey of Pd NP nucleation as a function of experimental parameters. We have shown that the increase of oxidation temperature during the preparation of Al2O3 ultra-thin film on Ni3Al(111) leads to a transition from disordered to long-range ordered Pd nanoparticle (NP) nucleation. Alumina films were prepared at different temperatures ranging from 990 to 1140 K. Crystallinity, electronic structure of the alumina film and Pd nucleation and growth have been investigated using Low Energy Electron Diffraction and Scanning Tunnelling Microscopy. NP density and long-range order nucleation along the so-called "dot structure" of 4.2 nm periodicity, strongly increase for temperatures higher than a threshold value of 1070 ± 20 K. This transition relies on the alumina film improvement and suggests that the modulation of Pd adsorption energy at nucleation centres which is necessary to nucleate NPs at ordered sites, requires higher preparation temperature. Long-range ordered NPs with a high density were obtained 140 K above reported recipes in the literature. This optimized temperature has been tested on a fresh sample (issued from the same supplier) for which just a few cleanings were enough to obtain long-range ordered NPs. Presumably the variability of the optimal oxidation temperature for our samples with respect to the literature is related to fluctuations of the stoichiometry from sample to sample.
On the Measurement of Elemental Abundance Ratios in Inner Galaxy H II Regions

NASA Technical Reports Server (NTRS)

Simpson, Janet P.; Rubin, Robert H.; Colgan, Sean W. J.; Erickson, Edwin F.; Haas, Michael R.

2004-01-01

Although abundance gradients in the Milky Way Galaxy certainly exist, details remain uncertain, particularly in the inner Galaxy, where stars and H II regions in the Galactic plane are obscured optically. In this paper we revisit two previously studied, inner Galaxy H II regions: G333.6-0.2 and W43. We observed three new positions in G333.6-0.2 with the Kuiper Airborne Observatory and reobserved the central position with the Infrared Space Observatory's Long Wavelength Spectrometer in far-infrared lines of S++, N++, N+, and O++. We also added the N+ lines at 122 and 205 microns to the suite of lines measured in W43 by Simpson et al.. The measured electron densities range from approx. 40 to over 4000 per cu cm in a single HII region, indicating that abundance analyses must consider density variations, since the critical densities of the observed lines range from 40 to 9000 per cu cm. We propose a method to handle density variations and make new estimates of the S/H and N/H abundance ratios. We find that our sulfur abundance estimates for G333.6-0.2 and W43 agree with the S/H abundance ratios expected for the gradient previously reported by Simpson et al., with the S/H values revised to be smaller owing to changes in collisional excitation cross sections. The estimated N/H, S/H, and N/S ratios are the most reliable because of their small corrections for unseen ionization states (< or approx. 10%). The estimated N/S ratios for the two sources are smaller than what would be calculated from the N/H and S/H ratios in our previous paper. If all low excitation H II regions had similar changes to their N/S ratios as a result of adding measurements of N+ to previous measurements of N++, there would be no or only a very small gradient in N/S. This is interesting because nitrogen is considered to be a secondary element and sulfur is a primary element in galactic chemical evolution calculations. We compute models of the two H II regions to estimate corrections for the other unseen ionization states. We find, with large uncertainties, that oxygen does not, have a high abundance, with the result that the N/O ratio is as high (approx. 0.35) as previously reported. The reasons for the uncertainty in the ionization corrections for oxygen are both the non-uniqueness of the H II region models and the sensitivity of these models to different input atomic data and stellar atmosphere models. We discuss these predictions and conclude that only a few of the latest models adequately reproduce H II region observations, including the well-known, relatively-large observed Ne++/O++ ratios in low- and moderate-excitation H II regions.
The Schwarzschild effect of the dosimetry film Kodak EDR 2.

PubMed

Djouguela, A; Kollhoff, R; Rubach, A; Harder, D; Poppe, B

2005-11-07

The magnitude of the Schwarzschild effect or failure of the reciprocity law has been experimentally investigated for the dosimetry film EDR 2 from Kodak. When the dose rate applied to achieve a given dose was reduced by a factor of 12, the net optical density was reduced by up to 5%. The clinical importance of this effect is negligible as long as the films are calibrated at a value of the dose rate approximately representative of the dose rates occurring in the target volume, but in target regions of strongly reduced dose rate the Schwarzschild effect should be allowed for by a correction of the net optical density.
Self-assembled pit arrays as templates for the integration of Au nanocrystals in oxide surfaces.

PubMed

Konstantinović, Z; Sandiumenge, F; Santiso, J; Balcells, Ll; Martínez, B

2013-02-07

We report on the fabrication of long-range ordered arrays of Au nanocrystals (sub-50 nm range) on top of manganite (La(2/3)Sr(1/3)MnO(3)) thin films achieving area densities around 2 × 10(10) gold nanocrystals per cm(2), well above the densities achievable by using conventional nanofabrication techniques. The gold-manganite interface exhibits excellent conduction properties. Long-range order is achieved by a guided self-assembling process of Au nanocrystals on self-organized pit-arrays acting as a template for the nucleation of gold nanocrystals. Self-organization of pits on the manganite film surface promoted by the underlying stepped SrTiO(3) substrate is achieved by a fine tuning of the growth kinetic pathway, taking advantage of the unusual misfit strain relaxation behaviour of manganite films.
The performance and relationship among range-separated schemes for density functional theory

NASA Astrophysics Data System (ADS)

Nguyen, Kiet A.; Day, Paul N.; Pachter, Ruth

2011-08-01

The performance and relationship among different range-separated (RS) hybrid functional schemes are examined using the Coulomb-attenuating method (CAM) with different values for the fractions of exact Hartree-Fock (HF) exchange (α), long-range HF (β), and a range-separation parameter (μ), where the cases of α + β = 1 and α + β = 0 were designated as CA and CA0, respectively. Attenuated PBE exchange-correlation functionals with α = 0.20 and μ = 0.20 (CA-PBE) and α = 0.25 and μ = 0.11 (CA0-PBE) are closely related to the LRC-ωPBEh and HSE functionals, respectively. Time-dependent density functional theory calculations were carried out for a number of classes of molecules with varying degrees of charge-transfer (CT) character to provide an assessment of the accuracy of excitation energies from the CA functionals and a number of other functionals with different exchange hole models. Functionals that provided reasonable estimates for local and short-range CT transitions were found to give large errors for long-range CT excitations. In contrast, functionals that afforded accurate long-range CT excitation energies significantly overestimated energies for short-range CT and local transitions. The effects of exchange hole models and parameters developed for RS functionals for CT excitations were analyzed in detail. The comparative analysis across compound classes provides a useful benchmark for CT excitations.
Numerical investigation of finite-volume effects for the HVP

NASA Astrophysics Data System (ADS)

Boyle, Peter; Gülpers, Vera; Harrison, James; Jüttner, Andreas; Portelli, Antonin; Sachrajda, Christopher

2018-03-01

It is important to correct for finite-volume (FV) effects in the presence of QED, since these effects are typically large due to the long range of the electromagnetic interaction. We recently made the first lattice calculation of electromagnetic corrections to the hadronic vacuum polarisation (HVP). For the HVP, an analytical derivation of FV corrections involves a two-loop calculation which has not yet been carried out. We instead calculate the universal FV corrections numerically, using lattice scalar QED as an effective theory. We show that this method gives agreement with known analytical results for scalar mass FV effects, before applying it to calculate FV corrections for the HVP. This method for numerical calculation of FV effects is also widely applicable to quantities beyond the HVP.
The nature of three-body interactions in DFT: Exchange and polarization effects

NASA Astrophysics Data System (ADS)

Hapka, Michał; Rajchel, Łukasz; Modrzejewski, Marcin; Schäffer, Rainer; Chałasiński, Grzegorz; Szcześniak, Małgorzata M.

2017-08-01

We propose a physically motivated decomposition of density functional theory (DFT) 3-body nonadditive interaction energies into the exchange and density-deformation (polarization) components. The exchange component represents the effect of the Pauli exclusion in the wave function of the trimer and is found to be challenging for density functional approximations (DFAs). The remaining density-deformation nonadditivity is less dependent upon the DFAs. Numerical demonstration is carried out for rare gas atom trimers, Ar2-HX (X = F, Cl) complexes, and small hydrogen-bonded and van der Waals molecular systems. None of the tested semilocal, hybrid, and range-separated DFAs properly accounts for the nonadditive exchange in dispersion-bonded trimers. By contrast, for hydrogen-bonded systems, range-separated DFAs achieve a qualitative agreement to within 20% of the reference exchange energy. A reliable performance for all systems is obtained only when the monomers interact through the Hartree-Fock potential in the dispersion-free Pauli blockade scheme. Additionally, we identify the nonadditive second-order exchange-dispersion energy as an important but overlooked contribution in force-field-like dispersion corrections. Our results suggest that range-separated functionals do not include this component, although semilocal and global hybrid DFAs appear to imitate it in the short range.
Absolute distance measurement with correction of air refractive index by using two-color dispersive interferometry.

PubMed

Wu, Hanzhong; Zhang, Fumin; Liu, Tingyang; Li, Jianshuang; Qu, Xinghua

2016-10-17

Two-color interferometry is powerful for the correction of the air refractive index especially in the turbulent air over long distance, since the empirical equations could introduce considerable measurement uncertainty if the environmental parameters cannot be measured with sufficient precision. In this paper, we demonstrate a method for absolute distance measurement with high-accuracy correction of air refractive index using two-color dispersive interferometry. The distances corresponding to the two wavelengths can be measured via the spectrograms captured by a CCD camera pair in real time. In the long-term experiment of the correction of air refractive index, the experimental results show a standard deviation of 3.3 × 10^-8 for 12-h continuous measurement without the precise knowledge of the environmental conditions, while the variation of the air refractive index is about 2 × 10^-6. In the case of absolute distance measurement, the comparison with the fringe counting interferometer shows an agreement within 2.5 μm in 12 m range.
Long term measurement of lake evaporation using a pontoon mounted Eddy Covariance system

NASA Astrophysics Data System (ADS)

McGowan, H. A.; McGloin, R.; McJannet, D.; Burn, S.

2011-12-01

Accurate quantification of evaporation from water storages is essential for design of water management and allocation policy that aims to balance demands for water without compromising the sustainability of future water resources, particularly during periods of prolonged and severe drought. Precise measurement of evaporation from lakes and dams however, presents significant research challenges. These include design and installation of measurement platforms that can withstand a range of wind and wave conditions; accurate determination of the evaporation measurement footprint and the influence of changing water levels. In this paper we present results from a two year long deployment of a pontoon mounted Eddy Covariance (EC) system on a 17.2ha irrigation reservoir in southeast Queensland, Australia. The EC unit included a CSAT-3 sonic anemometer (Campbell Scientific, Utah, United States) and a Li-Cor CS7500 open-path H2O/CO2 infrared gas analyzer (LiCor, Nebraska, United States) at a height of 2.2m, a net radiometer (CNR1, Kipp & Zonen, Netherlands) at a height of 1.2m and a humidity and temperature probe (HMP45C,Vaisala, Finland) at 2.3m. The EC unit was controlled by a Campbell Scientific CR3000 data logger with flux measurements made at 10 Hz and block averaged values logged every 15 minutes. Power to the EC system was from mounted solar panels that charged deep cycle lead-acid batteries while communication was via a cellphone data link. The pontoon was fitted with a weighted central beam and gimbal ring system that allowed self-levelling of the instrumentation and minimized dynamic influences on measurements (McGowan et al 2010; Wiebe et al 2011). EC measurements were corrected for tilt errors using the double rotation method for coordinate rotation described by Wilczak et al. (2001). High and low frequency attenuation of the measured co-spectrum was corrected using Massman's (2000) method for estimating frequency response corrections, while measurements were corrected for density fluctuations using the method of Webb-Pearman-Leuning (Webb et al. 1980). The evaporation measurement footprint over the reservoir was determined using the SCADIS one and a half order turbulence closure footprint model (Sogachev and Lloyd, 2004). Comparison of EC measured evaporation rates show excellent agreement with independent measurement of evaporation by scintillometer under a wide range of conditions (McJannet et al 2011). They confirm that pontoon mounted EC systems offer a robust, highly portable and reliable cost effective approach for accurate quantification of evaporation from reservoirs.

Exchange and correlation effects on plasmon dispersions and Coulomb drag in low-density electron bilayers

NASA Astrophysics Data System (ADS)

Badalyan, S. M.; Kim, C. S.; Vignale, G.; Senatore, G.

2007-03-01

We investigate the effect of exchange and correlation (XC) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a different approach, which employs dynamic XC kernels in the calculation of the bilayer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. The spectrum of bilayer plasmons and the drag resistivity are calculated in a broad range of temperatures taking into account both intra- and interlayer correlation effects. We observe that both plasmon modes are strongly affected by XC corrections. After the inclusion of the complex dynamic XC kernels, a decrease of the electron density induces shifts of the plasmon branches in opposite directions. This is in stark contrast with the tendency observed within random phase approximation that both optical and acoustical plasmons move away from the boundary of the particle-hole continuum with a decrease in the electron density. We find that the introduction of XC corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the random phase approximation is found to disappear when the XC corrections are included. Our numerical results at low temperatures are in good agreement with the results of recent experiments by Kellogg [Solid State Commun. 123, 515 (2002)].
Electron and Positron Stopping Powers of Materials

National Institute of Standards and Technology Data Gateway

SRD 7 NIST Electron and Positron Stopping Powers of Materials (PC database for purchase) The EPSTAR database provides rapid calculations of stopping powers (collisional, radiative, and total), CSDA ranges, radiation yields and density effect corrections for incident electrons or positrons with kinetic energies from 1 keV to 10 GeV, and for any chemically defined target material.
A wide range real-time synchronous demodulation system for the dispersion interferometer on HL-2M

NASA Astrophysics Data System (ADS)

Wu, Tongyu; Zhang, Wei; Yin, Zejie

2017-09-01

A real-time synchronous demodulation system has been developed for the dispersion interferometer on a HL-2M tokamak. The system is based on the phase extraction method which uses a ratio of modulation amplitudes. A high-performance field programmable gate array with pipeline process capabilities is used to realize the real time synchronous demodulation algorithm. A fringe jump correction algorithm is applied to follow the fast density changes of the plasma. By using the Peripheral Component Interconnect Express protocol, the electronics can perform real-time density feedback with a temporal resolution of 100 ns. Some experimental results presented show that the electronics can obtain a wide measurement range of 2.28 × 1022 m-2 with high precision.
Excitation energies from Görling-Levy perturbation theory along the range-separated adiabatic connection

NASA Astrophysics Data System (ADS)

Rebolini, Elisa; Teale, Andrew M.; Helgaker, Trygve; Savin, Andreas; Toulouse, Julien

2018-06-01

A Görling-Levy (GL)-based perturbation theory along the range-separated adiabatic connection is assessed for the calculation of electronic excitation energies. In comparison with the Rayleigh-Schrödinger (RS)-based perturbation theory this GL-based perturbation theory keeps the ground-state density constant at each order and thus gives the correct ionisation energy at each order. Excitation energies up to first order in the perturbation have been calculated numerically for the helium and beryllium atoms and the hydrogen molecule without introducing any density-functional approximations. In comparison with the RS-based perturbation theory, the present GL-based perturbation theory gives much more accurate excitation energies for Rydberg states but similar excitation energies for valence states.
Political Mechanisms for Long-Range Survival and Development

NASA Astrophysics Data System (ADS)

Marshall, W.

As the first species aware of extinction and capable of proactively ensuring our long-term survival and development, it is striking that we do not do so with the rigor, formality, and foresight it requires. Only from a reactive posture have we responded to the challenges of global warfare, human rights, environmental concerns, and sustainable development. Despite our awareness of the possibility for extinction and apocalyptic set-backs to our evolution, and despite the existence of long-range studies-which must still be dramatically increased-proactive global policy implementation regarding our long-term survival and development is arguably non-existent. This lack of long-term policy making can be attributed in part to the lack of formal political mechanisms to facilitate longer-range policy making that extends 30 years or more into the future. Political mechanisms for infusing long-range thinking, research, and strategic planning into the policy-making process can help correct this shortcoming and provide the motivation needed to adequately address long-term challenges with the political rigor required to effectively establish and implement long-term policies. There are some efforts that attempt to address longer-range issues, but those efforts often do not connect to the political process, do not extend 30 or more years into the future, are not well-funded, and are not sufficiently systemic. Political mechanisms for long-range survival and prosperity could correct these inadequacies by raising awareness, providing funding, and most importantly, leveraging political rigor to establish and enforce long-range strategic planning and policies. The feasibility of such mechanisms should first be rigorously studied and assessed in a feasibility study, which could then inform implementation. This paper will present the case for such a study and suggest some possible political mechanisms that should be investigated further in the proposed study. This work is being further developed at the Space Generation Summit (SGS), an event at World Space Congress (WSC) which shall unite international students and young professionals to develop a youth vision and strategy for the peaceful uses of space. SGS, endorsed by the United Nations, will take place from October 11-13th, during which the 200 delegates will discuss ongoing youth space activities, particularly those stemming from the UNISPACE-III/SGF and taken forward by the Space Generation Advisory Council. Delegates will address a variety of topics with the goal of devising new recommendations according to the theme, 'Accelerating Our Pace in Space'. The material presented here and in other technical sessions throughout WSC includes the findings of these discussions. Links: http://www.unsgac.org/sgs
Density functional theory study of the conformational space of an infinitely long polypeptide chain

NASA Astrophysics Data System (ADS)

Ireta, Joel; Scheffler, Matthias

2009-08-01

The backbone conformational space of infinitely long polyalanine is investigated with density-functional theory and mapping the potential energy surface in terms of (L, θ) cylindrical coordinates. A comparison of the obtained (L, θ) Ramachandran-like plot with results from an extended set of protein structures shows excellent conformity, with the exception of the polyproline II region. It is demonstrated the usefulness of infinitely long polypeptide models for investigating the influence of hydrogen bonding and its cooperative effect on the backbone conformations. The results imply that hydrogen bonding together with long-range electrostatics is the main actuator for most of the structures assumed by protein residues.
Dust-Corrected Star Formation Rates in Galaxies with Outer Rings

NASA Astrophysics Data System (ADS)

Kostiuk, I.; Silchenko, O.

2018-03-01

The star formation rates SFR, as well as the SFR surface densities ΣSFR and absolute stellar magnitudes MAB, are determined and corrected for interinsic dust absorption for 34 disk galaxies of early morphological types with an outer ring structure and ultraviolet emission from the ring. These characteristic are determined for the outer ring structures and for the galaxies as a whole. Data from the space telescopes GALEX (in the NUV and FUV ultraviolet ranges) and WISE (in the W4 22 μm infrared band) are used. The average relative deviation in the corrected SFR and ΣSFR derived from the NUV and FUV bands is only 19.0%, so their averaged values are used for statistical consideration. The relations between the dust-corrected SFR characteristics, UV colours, the galaxy morphological type, absolute magnitude are illustrated.
Study on the physical and non-physical drag coefficients for spherical satellites

NASA Astrophysics Data System (ADS)

Man, Haijun; Li, Huijun; Tang, Geshi

In this study, the physical and non-physical drag coefficients (C_D) for spherical satellites in ANDERR are retrieved from the number density of atomic oxygen and the orbit decay data, respectively. We concern on what changes should be taken to the retrieved physical C_D and non-physical C_D as the accuracy of the atmospheric density model is improved. Firstly, Lomb-Scargle periodograms to these C_D series as well as the environmental parameters indicate that: (1) there are obvious 5-, 7-, and 9-day periodic variations in the daily Ap indices and the solar wind speed at 1 AU as well as the model density, which has been reported as a result from the interaction between the corotating solar wind and the magnetosphere; (2) The same short periods also exist in the retrieved C_D except for the significance level for each C_D series; (3) the physical and non-physical C_D have behaved almost homogeneously with model densities along the satellite trajectory. Secondly, corrections to each type of C_D are defined as the differences between the values derived from the density model of NRLMSISE-00 and that of JB2008. It has shown that: (1) the bigger the density corrections are, the bigger the corrections to C_D of both types have. In addition, corrections to the physical C_D distribute within an extension of 0.05, which is about an order lower than the extension that the non-physical C_D distribute (0.5). (2) Corrections to the non-physical C_D behaved reciprocally to the density corrections, while a similar relationship is also existing between corrections to the physical C_D and that of the model density. (3) As the orbital altitude are lower than 200 km, corrections to the C_D and the model density are both decreased asymptotically to zero. Results in this study highlight that the physical C_D for spherical satellites should play an important role in technique renovations for accurate density corrections with the orbital decay data or in searching for a way to decouple the product of density and C_D wrapped in the orbital decay data.
Double counting in the density functional plus dynamical mean-field theory of transition metal oxides

NASA Astrophysics Data System (ADS)

Dang, Hung

2015-03-01

Recently, the combination of density functional theory (DFT) and dynamical mean-field theory (DMFT) has become a widely-used beyond-mean-field approach for strongly correlated materials. However, not only is the correlation treated in DMFT but also in DFT to some extent, a problem arises as the correlation is counted twice in the DFT+DMFT framework. The correction for this problem is still not well-understood. To gain more understanding of this ``double counting'' problem, I provide a detailed study of the metal-insulator transition in transition metal oxides in the subspace of oxygen p and transition metal correlated d orbitals using DFT+DMFT. I will show that the fully charge self-consistent DFT+DMFT calculations with the standard ``fully-localized limit'' (FLL) double counting correction fail to predict correctly materials such as LaTiO3, LaVO3, YTiO3 and SrMnO3 as insulators. Investigations in a wide range of the p- d splitting, the d occupancy, the lattice structure and the double counting correction itself will be presented to understand the reason behind this failure. I will also show that if the double counting correction is chosen to reproduce the p- d splitting consistent with experimental data, the DFT+DMFT approach can still give reasonable results in comparison with experiments.
Quantum measurement-induced antiferromagnetic order and density modulations in ultracold Fermi gases in optical lattices

NASA Astrophysics Data System (ADS)

Mazzucchi, Gabriel; Caballero-Benitez, Santiago F.; Mekhov, Igor B.

2016-08-01

Ultracold atomic systems offer a unique tool for understanding behavior of matter in the quantum degenerate regime, promising studies of a vast range of phenomena covering many disciplines from condensed matter to quantum information and particle physics. Coupling these systems to quantized light fields opens further possibilities of observing delicate effects typical of quantum optics in the context of strongly correlated systems. Measurement backaction is one of the most funda- mental manifestations of quantum mechanics and it is at the core of many famous quantum optics experiments. Here we show that quantum backaction of weak measurement can be used for tailoring long-range correlations of ultracold fermions, realizing quantum states with spatial modulations of the density and magnetization, thus overcoming usual requirement for a strong interatomic interactions. We propose detection schemes for implementing antiferromagnetic states and density waves. We demonstrate that such long-range correlations cannot be realized with local addressing, and they are a consequence of the competition between global but spatially structured backaction of weak quantum measurement and unitary dynamics of fermions.
Exploration of the Factors That Support Learning: Web-Based Activity and Testing Systems in Community College Algebra [Conference Long Paper

ERIC Educational Resources Information Center

Hauk, Shandy; Matlen, Bryan J.

2017-01-01

This is an extended conference proceedings report [Long Paper] based on a shorter contributed report at the same conference. A variety of computerized learning platforms exist. In mathematics, most include sets of problems to complete. Feedback to users ranges from a single word like "Correct!" to offers of hints and partially- to…
Decadal timescale variability of the Enceladus plumes inferred from Cassini images

NASA Astrophysics Data System (ADS)

Ingersoll, Andrew P.; Ewald, Shawn P.

2017-01-01

The brightness of the Enceladus plumes varies with position in the satellite's eccentric orbit, with altitude above the surface, and with time from one year to the next. Hedman et al. (2013, hereinafter H13) were the first to report these variations. They used data from Cassini's Visible and Infrared Mapping Spectrometer (VIMS). Here we present brightness observations from Cassini's Imaging Science Subsystem (ISS), which has 40 times higher spatial resolution than VIMS. Our unit of measure is slab density, the total mass of particles in a horizontal slab per unit thickness of the slab. Using slab density is one approach to correcting for the variation of brightness with wavelength and scattering angle. Approaches differ mainly by a multiplicative scaling factor that depends on particle density, which is uncertain. All approaches lead to the same qualitative conclusions and agree with the conclusions from VIMS. We summarize our conclusions as follows: At all altitudes between 50 and 200 km, the corrected brightness is 4-5 times greater when Enceladus is farther from Saturn (near apocenter) than when it is closer (near pericenter). A secondary maximum occurs after pericenter and before apocenter. Corrected brightness vs. altitude is best described as a power law whose negative exponent is greatest in magnitude at apocenter, indicating a slower launch speed for the particles at apocenter than at other points in the orbit. Corrected brightness decreased by roughly a factor of two during much of the period 2005-2015. The last is our principal result, and we offer three hypotheses to explain it. One is a long-period tide-the decreasing phase of an 11-year cycle in orbital eccentricity; another is buildup of ice at the throats of the vents; and the third is seasonal change-the end of summer at the south pole.
Determination of PM mass emissions from an aircraft turbine engine using particle effective density

NASA Astrophysics Data System (ADS)

Durdina, L.; Brem, B. T.; Abegglen, M.; Lobo, P.; Rindlisbacher, T.; Thomson, K. A.; Smallwood, G. J.; Hagen, D. E.; Sierau, B.; Wang, J.

2014-12-01

Inventories of particulate matter (PM) emissions from civil aviation and air quality models need to be validated using up-to-date measurement data corrected for sampling artifacts. We compared the measured black carbon (BC) mass and the total PM mass determined from particle size distributions (PSD) and effective density for a commercial turbofan engine CFM56-7B26/3. The effective density was then used to calculate the PM mass losses in the sampling system. The effective density was determined using a differential mobility analyzer and a centrifugal particle mass analyzer, and increased from engine idle to take-off by up to 60%. The determined mass-mobility exponents ranged from 2.37 to 2.64. The mean effective density determined by weighting the effective density distributions by PM volume was within 10% of the unit density (1000 kg/m3) that is widely assumed in aircraft PM studies. We found ratios close to unity between the PM mass determined by the integrated PSD method and the real-time BC mass measurements. The integrated PSD method achieved higher precision at ultra-low PM concentrations at which current mass instruments reach their detection limit. The line loss model predicted ∼60% PM mass loss at engine idle, decreasing to ∼27% at high thrust. Replacing the effective density distributions with unit density lead to comparable estimates that were within 20% and 5% at engine idle and high thrust, respectively. These results could be used for the development of a robust method for sampling loss correction of the future PM emissions database from commercial aircraft engines.
High density, optically corrected, micro-channel cooled, v-groove monolithic laser diode array

DOEpatents

Freitas, Barry L.

1998-01-01

An optically corrected, micro-channel cooled, high density laser diode array achieves stacking pitches to 33 bars/cm by mounting laser diodes into V-shaped grooves. This design will deliver>4kW/cm2 of directional pulsed laser power. This optically corrected, micro-channel cooled, high density laser is usable in all solid state laser systems which require efficient, directional, narrow bandwidth, high optical power density pump sources.
Binary phase lock loops for simplified OMEGA receivers

NASA Technical Reports Server (NTRS)

Burhans, R. W.

1974-01-01

A sampled binary phase lock loop is proposed for periodically correcting OMEGA receiver internal clocks. The circuit is particularly simple to implement and provides a means of generating long range 3.4 KHz difference frequency lanes from simultaneous pair measurements.
Single and double multiphoton ionization of Li and Be atoms by strong laser fields

NASA Astrophysics Data System (ADS)

Telnov, Dmitry; Heslar, John; Chu, Shih-I.

2011-05-01

The time-dependent density functional theory with self-interaction correction and proper asymptotic long-range potential is extended for nonperturbative treatment of multiphoton single and double ionization of Li and Be atoms by strong 800 nm laser fields. We make use of the time-dependent Krieger-Li-Iafrate (TDKLI) exchange-correlation potential with the integer discontinuity which improves the description of the double ionization process. However, we have found that the discontinuity of the TDKLI potential is not sufficient to reproduce the characteristic feature of double ionization. This may happen because the discontinuity of the TDKLI potential is related to the spin particle numbers only and not to the total particle number. Introducing a discontinuity with respect to the total particle number to the exchange-correlation potential, we were able to obtain the knee structure in the intensity dependence of the double ionization probability of Be. This work was partially supported by DOE and NSF and by NSC-Taiwan.
Electronic structure and optical spectra of semiconducting carbon nanotubes functionalized by diazonium salts

NASA Astrophysics Data System (ADS)

Ramirez, Jessica; Mayo, Michael L.; Kilina, Svetlana; Tretiak, Sergei

2013-02-01

We report density functional (DFT) calculations on finite-length semiconducting carbon nanotubes covalently and non-covalently functionalized by aryl diazonium moieties and their chlorinated derivatives. For these systems, we investigate (i) an accuracy of different functionals and basis sets, (ii) a solvent effect, and (iii) the impact of the chemical functionalization on optical properties of nanotubes. In contrast to B3LYP, only long-range-corrected functionals, such as CAM-B3LYP and wB97XD, properly describe the ground and excited state properties of physisorbed molecules. We found that physisorbed cation insignificantly perturbs the optical spectra of nanotubes. In contrast, covalently bound complexes demonstrate strong redshifts and brightening of the lowest exciton that is optically dark in pristine nanotubes. However, the energy and oscillator strength of the lowest state are dictated by the position of the molecule on the nanotube. Thus, if controllable and selective chemical functionalization is realized, the PL of nanotubes could be improved.
Long-range fluctuations and multifractality in connectivity density time series of a wind speed monitoring network

NASA Astrophysics Data System (ADS)

Laib, Mohamed; Telesca, Luciano; Kanevski, Mikhail

2018-03-01

This paper studies the daily connectivity time series of a wind speed-monitoring network using multifractal detrended fluctuation analysis. It investigates the long-range fluctuation and multifractality in the residuals of the connectivity time series. Our findings reveal that the daily connectivity of the correlation-based network is persistent for any correlation threshold. Further, the multifractality degree is higher for larger absolute values of the correlation threshold.
Estimation of the parameters of disturbances on long-range radio-communication paths

NASA Astrophysics Data System (ADS)

Gerasimov, Iu. S.; Gordeev, V. A.; Kristal, V. S.

1982-09-01

Radio propagation on long-range paths is disturbed by such phenomena as ionospheric density fluctuations, meteor trails, and the Faraday effect. In the present paper, the determination of the characteristics of such disturbances on the basis of received-signal parameters is considered as an inverse and ill-posed problem. A method for investigating the indeterminacy which arises in such determinations is proposed, and a quantitative analysis of this indeterminacy is made.
Earth GRAM-99 and Trace Constituents

NASA Technical Reports Server (NTRS)

Justus, C. G.; Duvall, Aleta; Keller, Vernon W.

2004-01-01

Global Reference Atmospheric Model (GRAM-99) is an engineering-level model of Earth's atmosphere. It provides both mean values and perturbations for density, temperature, pressure, and winds, as well as monthly- and geographically-varying trace constituent concentrations. From 0-27 km, GRAM thermodynamics and winds are based on National Oceanic and Atmospheric Administration Global Upper Air Climatic Atlas (GUACA) climatology. Above 120 km, GRAM is based on the NASA Marshall Engineering Thermosphere (MET) model. In the intervening altitude region, GRAM is based on Middle Atmosphere Program (MAP) climatology that also forms the basis of the 1986 COSPAR International Reference Atmosphere (CIRA). Atmospheric composition is represented in GRAM by concentrations of both major and minor species. Above 120 km, MET provides concentration values for N2, O2, Ar, O, He, and H. Below 120 km, species represented also include H2O, O3, N2O, CO, CH4, and CO2. At COSPAR 2002 a comparison was made between GRAM constituents below 120 km and those provided by Naval Research Laboratory (NRL) climatology. No current need to update GRAM constituent climatology in that height range was identified. This report examines GRAM (MET) constituents between 100 and 1000 km altitudes. Discrepancies are noted between GRAM (MET) constituent number densities and mass density or molecular weight. Near 110 km altitude, there is up to about 25% discrepancy between MET number density and mass density (with mass density being valid and number densities requiring adjustment). Near 700 km altitude there is also up to about 25% discrepancy between MET number density and mean molecular weight (with molecular weight requiring adjustment). In neither case are MET mass density estimates invalidated. These discrepancies have been traced to MET subroutines SLV (which affects 90-170 km height range) and SLVH (which affects helium above 440 km altitude). With these discrepancies corrected, results are presented to illustrate GRAM (MET) constituent mole fractions in terms of height-latitude cross sections from 100 to 1000 km altitude, and latitude-longitude 'maps' at 450 km (approximate height of International Space Station). Plans are discussed for an update of MET (and GRAM) to correct these constituent inconsistencies and to incorporate several new thermospheric model features.

Challenging the cosmological constant

NASA Astrophysics Data System (ADS)

Kaloper, Nemanja

2007-09-01

We outline a dynamical dark energy scenario whose signatures may be simultaneously tested by astronomical observations and laboratory experiments. The dark energy is a field with slightly sub-gravitational couplings to matter, a logarithmic self-interaction potential with a scale tuned to ˜10 eV, as is usual in quintessence models, and an effective mass m influenced by the environmental energy density. Its forces may be suppressed just below the current bounds by the chameleon-like mimicry, whereby only outer layers of mass distributions, of thickness 1/m, give off appreciable long range forces. After inflation and reheating, the field is relativistic, and attains a Planckian expectation value before Hubble friction freezes it. This can make gravity in space slightly stronger than on Earth. During the matter era, interactions with nonrelativistic matter dig a minimum close to the Planck scale. However, due to its sub-gravitational matter couplings the field will linger away from this minimum until the matter energy density dips below ˜10 eV. Then it starts to roll to the minimum, driving a period of cosmic acceleration. Among the signatures of this scenario may be dark energy equation of state w≠-1, stronger gravity in dilute mediums, that may influence BBN and appear as an excess of dark matter, and sub-millimeter corrections to Newton's law, close to the present laboratory limits.
40 CFR 1065.690 - Buoyancy correction for PM sample media.

Code of Federal Regulations, 2014 CFR

2014-07-01

... media. 1065.690 Section 1065.690 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... Buoyancy correction for PM sample media. (a) General. Correct PM sample media for their buoyancy in air if you weigh them on a balance. The buoyancy correction depends on the sample media density, the density...
40 CFR 1065.690 - Buoyancy correction for PM sample media.

Code of Federal Regulations, 2011 CFR

2011-07-01

... media. 1065.690 Section 1065.690 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... Buoyancy correction for PM sample media. (a) General. Correct PM sample media for their buoyancy in air if you weigh them on a balance. The buoyancy correction depends on the sample media density, the density...
40 CFR 1065.690 - Buoyancy correction for PM sample media.

Code of Federal Regulations, 2012 CFR

2012-07-01

... media. 1065.690 Section 1065.690 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... Buoyancy correction for PM sample media. (a) General. Correct PM sample media for their buoyancy in air if you weigh them on a balance. The buoyancy correction depends on the sample media density, the density...
40 CFR 1065.690 - Buoyancy correction for PM sample media.

Code of Federal Regulations, 2013 CFR

2013-07-01

... media. 1065.690 Section 1065.690 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... Buoyancy correction for PM sample media. (a) General. Correct PM sample media for their buoyancy in air if you weigh them on a balance. The buoyancy correction depends on the sample media density, the density...
High-precision Ru isotopic measurements by multi-collector ICP-MS.

PubMed

Becker, Harry; Dalpe, Claude; Walker, Richard J

2002-06-01

Ruthenium isotopic data for a pure Aldrich ruthenium nitrate solution obtained using a Nu Plasma multi collector inductively coupled plasma-mass spectrometer (MC-ICP-MS) shows excellent agreement (better than 1 epsilon unit = 1 part in 10(4)) with data obtained by other techniques for the mass range between 96 and 101 amu. External precisions are at the 0.5-1.7 epsilon level (2sigma). Higher sensitivity for MC ICP-MS compared to negative thermal ionization mass spectrometry (N-TIMS) is offset by the uncertainties introduced by relatively large mass discrimination and instabilities in the plasma source-ion extraction region that affect the long-term reproducibility. Large mass bias correction in ICP mass spectrometry demands particular attention to be paid to the choice of normalizing isotopes. Because of its position in the mass spectrum and the large mass bias correction, obtaining precise and accurate abundance data for 104Ru by MC-ICP-MS remains difficult. Internal and external mass bias correction schemes in this mass range may show similar shortcomings if the isotope of interest does not lie within the mass range covered by the masses used for normalization. Analyses of meteorite samples show that if isobaric interferences from Mo are sufficiently large (Ru/Mo < 10(4)), uncertainties on the Mo interference correction propagate through the mass bias correction and yield inaccurate results for Ru isotopic compositions. Second-order linear corrections may be used to correct for these inaccuracies, but such results are generally less precise than N-TIMS data.
High density, optically corrected, micro-channel cooled, v-groove monolithic laser diode array

DOEpatents

Freitas, B.L.

1998-10-27

An optically corrected, micro-channel cooled, high density laser diode array achieves stacking pitches to 33 bars/cm by mounting laser diodes into V-shaped grooves. This design will deliver > 4kW/cm{sup 2} of directional pulsed laser power. This optically corrected, micro-channel cooled, high density laser is usable in all solid state laser systems which require efficient, directional, narrow bandwidth, high optical power density pump sources. 13 figs.
Composition of the Earth's inner core from high-pressure sound velocity measurements in Fe-Ni-Si alloys

NASA Astrophysics Data System (ADS)

Antonangeli, Daniele; Siebert, Julien; Badro, James; Farber, Daniel L.; Fiquet, Guillaume; Morard, Guillaume; Ryerson, Frederick J.

2010-06-01

We performed room-temperature sound velocity and density measurements on a polycrystalline alloy, Fe0.89Ni0.04Si0.07, in the hexagonal close-packed (hcp) phase up to 108 GPa. Over the investigated pressure range the aggregate compressional sound velocity is ∼ 9% higher than in pure iron at the same density. The measured aggregate compressional (VP) and shear (VS) sound velocities, extrapolated to core densities and corrected for anharmonic temperature effects, are compared with seismic profiles. Our results provide constraints on the silicon abundance in the core, suggesting a model that simultaneously matches the primary seismic observables, density, P-wave and S-wave velocities, for an inner core containing 4 to 5 wt.% of Ni and 1 to 2 wt.% of Si.
Source-Free Exchange-Correlation Magnetic Fields in Density Functional Theory.

PubMed

Sharma, S; Gross, E K U; Sanna, A; Dewhurst, J K

2018-03-13

Spin-dependent exchange-correlation energy functionals in use today depend on the charge density and the magnetization density: E xc [ρ, m]. However, it is also correct to define the functional in terms of the curl of m for physical external fields: E xc [ρ,∇ × m]. The exchange-correlation magnetic field, B xc , then becomes source-free. We study this variation of the theory by uniquely removing the source term from local and generalized gradient approximations to the functional. By doing so, the total Kohn-Sham moments are improved for a wide range of materials for both functionals. Significantly, the moments for the pnictides are now in good agreement with experiment. This source-free method is simple to implement in all existing density functional theory codes.
Wave-function-based approach to quasiparticle bands: Insight into the electronic structure of c-ZnS

NASA Astrophysics Data System (ADS)

Stoyanova, A.; Hozoi, L.; Fulde, P.; Stoll, H.

2011-05-01

Ab initio wave-function-based methods are employed for the study of quasiparticle energy bands of zinc-blende ZnS, with focus on the Zn 3d “semicore” states. The relative energies of these states with respect to the top of the S 3p valence bands appear to be poorly described as compared to experimental values not only within the local density approximation (LDA), but also when many-body corrections within the GW approximation are applied to the LDA or LDA + U mean-field solutions [T. Miyake, P. Zhang, M. L. Cohen, and S. G. Louie, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.245213 74, 245213 (2006)]. In the present study, we show that for the accurate description of the Zn 3d states a correlation treatment based on wave-function methods is needed. Our study rests on a local Hamiltonian approach which rigorously describes the short-range polarization and charge redistribution effects around an extra hole or electron placed into the valence respective conduction bands of semiconductors and insulators. The method also facilitates the computation of electron correlation effects beyond relaxation and polarization. The electron correlation treatment is performed on finite clusters cut off the infinite system. The formalism makes use of localized Wannier functions and embedding potentials derived explicitly from prior periodic Hartree-Fock calculations. The on-site and nearest-neighbor charge relaxation lead to corrections of several eV to the Hartree-Fock band energies and gap. Corrections due to long-range polarization are of the order of 1.0 eV. The dispersion of the Hartree-Fock bands is only slightly affected by electron correlations. We find the Zn 3d “semicore” states to lie ~9.0 eV below the top of the S 3p valence bands, in very good agreement with values from valence-band x-ray photoemission.
Dynamic density functional theory with hydrodynamic interactions: theoretical development and application in the study of phase separation in gas-liquid systems.

PubMed

Kikkinides, E S; Monson, P A

2015-03-07

Building on recent developments in dynamic density functional theory, we have developed a version of the theory that includes hydrodynamic interactions. This is achieved by combining the continuity and momentum equations eliminating velocity fields, so the resulting model equation contains only terms related to the fluid density and its time and spatial derivatives. The new model satisfies simultaneously continuity and momentum equations under the assumptions of constant dynamic or kinematic viscosity and small velocities and/or density gradients. We present applications of the theory to spinodal decomposition of subcritical temperatures for one-dimensional and three-dimensional density perturbations for both a van der Waals fluid and for a lattice gas model in mean field theory. In the latter case, the theory provides a hydrodynamic extension to the recently studied dynamic mean field theory. We find that the theory correctly describes the transition from diffusive phase separation at short times to hydrodynamic behaviour at long times.
Dynamic density functional theory with hydrodynamic interactions: Theoretical development and application in the study of phase separation in gas-liquid systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kikkinides, E. S.; Monson, P. A.

Building on recent developments in dynamic density functional theory, we have developed a version of the theory that includes hydrodynamic interactions. This is achieved by combining the continuity and momentum equations eliminating velocity fields, so the resulting model equation contains only terms related to the fluid density and its time and spatial derivatives. The new model satisfies simultaneously continuity and momentum equations under the assumptions of constant dynamic or kinematic viscosity and small velocities and/or density gradients. We present applications of the theory to spinodal decomposition of subcritical temperatures for one-dimensional and three-dimensional density perturbations for both a van dermore » Waals fluid and for a lattice gas model in mean field theory. In the latter case, the theory provides a hydrodynamic extension to the recently studied dynamic mean field theory. We find that the theory correctly describes the transition from diffusive phase separation at short times to hydrodynamic behaviour at long times.« less
Theory of advection-driven long range biotic transport

USDA-ARS?s Scientific Manuscript database

We propose a simple mechanistic model to examine the effects of advective flow on the spread of fungal diseases spread by wind-blown spores. The model is defined by a set of two coupled non-linear partial differential equations for spore densities. One equation describes the long-distance advectiv...
Imputation of missing genotypes from sparse to high density using long-range phasing

USDA-ARS?s Scientific Manuscript database

Related individuals share potentially long chromosome segments that trace to a common ancestor. A phasing algorithm (ChromoPhase) that utilizes this characteristic of finite populations was developed to phase large sections of a chromosome. In addition to phasing, ChromoPhase imputes missing genotyp...
Estimation of boiling points using density functional theory with polarized continuum model solvent corrections.

PubMed

Chan, Poh Yin; Tong, Chi Ming; Durrant, Marcus C

2011-09-01

An empirical method for estimation of the boiling points of organic molecules based on density functional theory (DFT) calculations with polarized continuum model (PCM) solvent corrections has been developed. The boiling points are calculated as the sum of three contributions. The first term is calculated directly from the structural formula of the molecule, and is related to its effective surface area. The second is a measure of the electronic interactions between molecules, based on the DFT-PCM solvation energy, and the third is employed only for planar aromatic molecules. The method is applicable to a very diverse range of organic molecules, with normal boiling points in the range of -50 to 500 °C, and includes ten different elements (C, H, Br, Cl, F, N, O, P, S and Si). Plots of observed versus calculated boiling points gave R²=0.980 for a training set of 317 molecules, and R²=0.979 for a test set of 74 molecules. The role of intramolecular hydrogen bonding in lowering the boiling points of certain molecules is quantitatively discussed. Crown Copyright © 2011. Published by Elsevier Inc. All rights reserved.
Accurate genomic predictions for BCWD resistance in rainbow trout are achieved using low-density SNP panels: Evidence that long-range LD is a major contributing factor.

PubMed

Vallejo, Roger L; Silva, Rafael M O; Evenhuis, Jason P; Gao, Guangtu; Liu, Sixin; Parsons, James E; Martin, Kyle E; Wiens, Gregory D; Lourenco, Daniela A L; Leeds, Timothy D; Palti, Yniv

2018-06-05

Previously accurate genomic predictions for Bacterial cold water disease (BCWD) resistance in rainbow trout were obtained using a medium-density single nucleotide polymorphism (SNP) array. Here, the impact of lower-density SNP panels on the accuracy of genomic predictions was investigated in a commercial rainbow trout breeding population. Using progeny performance data, the accuracy of genomic breeding values (GEBV) using 35K, 10K, 3K, 1K, 500, 300 and 200 SNP panels as well as a panel with 70 quantitative trait loci (QTL)-flanking SNP was compared. The GEBVs were estimated using the Bayesian method BayesB, single-step GBLUP (ssGBLUP) and weighted ssGBLUP (wssGBLUP). The accuracy of GEBVs remained high despite the sharp reductions in SNP density, and even with 500 SNP accuracy was higher than the pedigree-based prediction (0.50-0.56 versus 0.36). Furthermore, the prediction accuracy with the 70 QTL-flanking SNP (0.65-0.72) was similar to the panel with 35K SNP (0.65-0.71). Genomewide linkage disequilibrium (LD) analysis revealed strong LD (r 2 ≥ 0.25) spanning on average over 1 Mb across the rainbow trout genome. This long-range LD likely contributed to the accurate genomic predictions with the low-density SNP panels. Population structure analysis supported the hypothesis that long-range LD in this population may be caused by admixture. Results suggest that lower-cost, low-density SNP panels can be used for implementing genomic selection for BCWD resistance in rainbow trout breeding programs. © 2018 The Authors. This article is a U.S. Government work and is in the public domain in the USA. Journal of Animal Breeding and Genetics published by Blackwell Verlag GmbH.
Isostatic gravity map of the Nevada Test Site and vicinity, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ponce, D.A.; Harris, R.N.; Oliver, H.W.

1988-12-31

The isostatic gravity map of the Nevada Test Site (NTS) and vicinity is based on about 16,000 gravity stations. Principal facts of the gravity data were listed by Harris and others (1989) and their report included descriptions of base stations, high-precision and absolute gravity stations, and data accuracy. Observed gravity values were referenced to the International Gravity Standardization Net 1971 gravity datum described by Morelli (1974) and reduced using the Geodetic Reference System 1967 formula for the normal gravity on the ellipsoid (International Union of Geodesy and Geophysics, 1971). Free-air, Bouguer, curvature, and terrain corrections for a standard reduction densitymore » of 2.67 g/cm{sup 3} were made to compute complete Bouguer anomalies. Terrain corrections were made to a radial distance of 166.7 km from each station using a digital elevation model and a computer procedure by Plouff (1977) and, in general, include manually estimated inner-zone terrain corrections. Finally, isostatic corrections were made using a procedure by Simpson and others (1983) based on an Airy-Heiskanen model with local compensation (Heiskanen and Moritz, 1967) with an upper-crustal density of 2.67 g/cm{sup 3}, a crustal thickness of 25 km, and a density contrast between the lower-crust and upper-mantle of 0.4 g/cm{sup 3}. Isostatic corrections help remove the effects of long-wavelength anomalies related to topography and their compensating masses and, thus, enhance short- to moderate-wavelength anomalies caused by near surface geologic features. 6 refs.« less
Dislocation density evolution of AA 7020-T6 investigated by in-situ synchrotron diffraction under tensile load

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Z.Y., E-mail: zhengye.zhong@hzg.de; Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, D-21502 Geesthacht; Brokmeier, H.-G.

2015-10-15

The dislocation density evolution along the loading axis of a textured AA 7020-T6 aluminum alloy during uniaxial tension was investigated by in-situ synchrotron diffraction. The highly parallel synchrotron beam at the High Energy Materials Science beamline P07 in PETRA III, DESY, offers excellent conditions to separate different influences for line broadening from which micro-strains are obtained using the modified Williamson–Hall method which is also for defect density investigations. During tensile loading the dislocation density evolution was documented from the as-received material (initial micro-strain state) to the relaxation of the strains during elastic deformation. After yield, the increasing rate of dislocationmore » density growth was relatively fast till half-way between yield and UTS. After that, the rate started to decrease and the dislocation density fluctuated as the elongation increased due to the generation and annihilation of dislocations. When dislocation generation is dominant, the correlation between the flow stress and dislocation density satisfies the Taylor equation. Besides, a method to correct the thickness effect on peak broadening is developed in the present study. - Highlights: • In-situ synchrotron diffraction was applied to characterize peak broadening. • Dislocation evolution along the loading axis during uniaxial tension was investigated. • A method to correct the sample thickness effect on peak broadening was developed. • Dislocation density and flow stress satisfy the Taylor equation at a certain range. • The texture before load and after sample fracture was analyzed.« less
Anatomically correct visualization of the human upper airway using a high-speed long range optical coherence tomography system with an integrated positioning sensor

NASA Astrophysics Data System (ADS)

Jing, Joseph C.; Chou, Lidek; Su, Erica; Wong, Brian J. F.; Chen, Zhongping

2016-12-01

The upper airway is a complex tissue structure that is prone to collapse. Current methods for studying airway obstruction are inadequate in safety, cost, or availability, such as CT or MRI, or only provide localized qualitative information such as flexible endoscopy. Long range optical coherence tomography (OCT) has been used to visualize the human airway in vivo, however the limited imaging range has prevented full delineation of the various shapes and sizes of the lumen. We present a new long range OCT system that integrates high speed imaging with a real-time position tracker to allow for the acquisition of an accurate 3D anatomical structure in vivo. The new system can achieve an imaging range of 30 mm at a frame rate of 200 Hz. The system is capable of generating a rapid and complete visualization and quantification of the airway, which can then be used in computational simulations to determine obstruction sites.
Orbital measurements of the Earth's radiation budget during the first decade of the space program

NASA Technical Reports Server (NTRS)

Bandeen, W. R.

1982-01-01

The instrumentation and data analysis methods applied to data from the Explorer 7, TIROS 2, 3, 4, and 7, and Nimbus 2 and 3 experimental satellites are summarized. Problems encountered in analyzing these data included: determining the value of the solar constant, inaccuracies introduced by degradation of the sensors in orbit, the need to infer the total reflected and emitted radiation from filtered measurements, the development of corrections for anisotropy in order to determine the outgoing flux densities at the moment of measurement, and the development of corrections to account for diurnal variability. The corrections for long- and shortwave anisotropy and historical determinations of the solar constant and albedo are treated in detail. These early measurements indicated that the planetary albedo was lower, the emitted radiation higher, and the equator-to-pole gradient of net radiation greater than previously supposed.

Dark energy homogeneity in general relativity: Are we applying it correctly?

NASA Astrophysics Data System (ADS)

Duniya, Didam G. A.

2016-04-01

Thus far, there does not appear to be an agreed (or adequate) definition of homogeneous dark energy (DE). This paper seeks to define a valid, adequate homogeneity condition for DE. Firstly, it is shown that as long as w_x ≠ -1, DE must have perturbations. It is then argued, independent of w_x, that a correct definition of homogeneous DE is one whose density perturbation vanishes in comoving gauge: and hence, in the DE rest frame. Using phenomenological DE, the consequence of this approach is then investigated in the observed galaxy power spectrum—with the power spectrum being normalized on small scales, at the present epoch z=0. It is found that for high magnification bias, relativistic corrections in the galaxy power spectrum are able to distinguish the concordance model from both a homogeneous DE and a clustering DE—on super-horizon scales.
Interaction between colloidal particles on an oil-water interface in dilute and dense phases.

PubMed

Parolini, Lucia; Law, Adam D; Maestro, Armando; Buzza, D Martin A; Cicuta, Pietro

2015-05-20

The interaction between micron-sized charged colloidal particles at polar/non-polar liquid interfaces remains surprisingly poorly understood for a relatively simple physical chemistry system. By measuring the pair correlation function g(r) for different densities of polystyrene particles at the decane-water interface, and using a powerful predictor-corrector inversion scheme, effective pair-interaction potentials can be obtained up to fairly high densities, and these reproduce the experimental g(r) in forward simulations, so are self consistent. While at low densities these potentials agree with published dipole-dipole repulsion, measured by various methods, an apparent density dependence and long range attraction are obtained when the density is higher. This condition is thus explored in an alternative fashion, measuring the local mobility of colloids when confined by their neighbors. This method of extracting interaction potentials gives results that are consistent with dipolar repulsion throughout the concentration range, with the same magnitude as in the dilute limit. We are unable to rule out the density dependence based on the experimental accuracy of our data, but we show that incomplete equilibration of the experimental system, which would be possible despite long waiting times due to the very strong repulsions, is a possible cause of artefacts in the inverted potentials. We conclude that to within the precision of these measurements, the dilute pair potential remains valid at high density in this system.
The design and assembly of aluminum mirrors of a three-mirror-anastigmat telescope

NASA Astrophysics Data System (ADS)

Chang, Shenq-Tsong; Lin, Yu-Chuan; Wu, Kun-Huan; Lien, Chun-Chieh; Huang, Ting-Ming; Tsay, Ho-Lin; Chan, Chia-Yen

2017-09-01

Better ground sampling distance (GSD) has been a trend for earth observation satellites. A long-focal-length telescope is required accordingly in systematic point of view. On the other hand, there is size constraint for such long-focal-length telescope especially in space projects. Three-mirror-anastigmat (TMA) was proven to have excellent features of correcting aberrations, wide spectral range and shorter physical requirement [1-3].
Differential Solutions Using Long-Range Dual-Frequency GPS Correction Data

DTIC Science & Technology

2002-09-01

coordinates the network of CORS sites to provide range measurement data to users in the United States. The data is available, via the Internet , to...of 3-dimensional positioning activities throughout the United States (NGS, 2002). CORS data is posted daily on the Internet from which the user may...KING AZ Scottsdale COSA 1998/258 -------- 5 sec H CofS AZ Tolleson
American Indian influence on fire regimes in Calfornia's coastal ranges

USGS Publications Warehouse

Keeley, Jon E.

2004-01-01

Understanding the historical pattern of human impacts on landscapes is critical to correctly interpreting the ecological basis for vegetation distribution. In some parts of the world, such as the Mediterranean Basin, a long and intensive utilization of resources has greatly altered the distribution of forests and woodlands. Was vegetation distribution in the coastal ranges of California similarly influenced by humans before Euro-American colonization?
Effect of higher implant density on curve correction in dystrophic thoracic scoliosis secondary to neurofibromatosis Type 1.

PubMed

Li, Yang; Yuan, Xinxin; Sha, Shifu; Liu, Zhen; Zhu, Weiguo; Qiu, Yong; Wang, Bin; Yu, Yang; Zhu, Zezhang

2017-10-01

OBJECTIVE The aim of this study was to investigate how implant density affects radiographic results and clinical outcomes in patients with dystrophic scoliosis secondary to neurofibromatosis Type 1 (NF1). METHODS A total of 41 patients with dystrophic scoliosis secondary to NF1 who underwent 1-stage posterior correction between June 2011 and December 2013 were included. General information about patients was recorded, as were preoperative and postoperative scores from Scoliosis Research Society (SRS)-22 questionnaires. Pearson correlation analysis was used to analyze the associations among implant density, coronal Cobb angle correction rate and correction loss at last follow-up, change of sagittal curve, and apical vertebral translation. Patients were then divided into 2 groups: those with low-density and those with high-density implants. Independent-sample t-tests were used to compare demographic data, radiographic findings, and clinical outcomes before surgery and at last follow-up between the groups. RESULTS Significant correlations were found between the implant density and the coronal correction rate of the main curve (r = 0.505, p < 0.01) and the coronal correction loss at final follow-up (r = -0.379, p = 0.015). There was no significant correlation between implant density and change of sagittal profile (p = 0.662) or apical vertebral translation (p = 0.062). The SRS-22 scores improved in the appearance, activity, and mental health domains within both groups, but there was no difference between the groups in any of the SRS-22 domains at final follow-up (p > 0.05 for all). CONCLUSIONS Although no significant differences between the high- and low-density groups were found in any of the SRS-22 domains at final follow-up, higher implant density was correlated with superior coronal correction and less postoperative correction loss in patients with dystrophic NF1-associated scoliosis.
Dark matter, long-range forces, and large-scale structure

NASA Technical Reports Server (NTRS)

Gradwohl, Ben-Ami; Frieman, Joshua A.

1992-01-01

If the dark matter in galaxies and clusters is nonbaryonic, it can interact with additional long-range fields that are invisible to experimental tests of the equivalence principle. We discuss the astrophysical and cosmological implications of a long-range force coupled only to the dark matter and find rather tight constraints on its strength. If the force is repulsive (attractive), the masses of galaxy groups and clusters (and the mean density of the universe inferred from them) have been systematically underestimated (overestimated). We explore the consequent effects on the two-point correlation function, large-scale velocity flows, and microwave background anisotropies, for models with initial scale-invariant adiabatic perturbations and cold dark matter.
Hidden asymmetry and long range rapidity correlations

NASA Astrophysics Data System (ADS)

Bialas, A.; Bzdak, A.; Zalewski, K.

2012-04-01

Interpretation of long-range rapidity correlations in terms of the fluctuating rapidity density distribution of the system created in high-energy collisions is proposed. When applied to recent data of the STAR Collaboration, it shows a substantial asymmetric component in the shape of this system in central Au-Au collisions, implying that boost invariance is violated on the event-by-event basis even at central rapidity. This effect may seriously influence the hydrodynamic expansion of the system.
A high-rate long-life Li4Ti5O12/Li[Ni0.45Co0.1Mn1.45]O4 lithium-ion battery.

PubMed

Jung, Hun-Gi; Jang, Min Woo; Hassoun, Jusef; Sun, Yang-Kook; Scrosati, Bruno

2011-11-01

Lithium batteries are receiving considerable attention as storage devices in the renewable energy and sustainable road transport fields. However, low-cost, long-life lithium batteries with higher energy densities are required to facilitate practical application. Here we report a lithium-ion battery that can be cycled at rates as high as 10 C has a life exceeding 500 cycles and an operating temperature range extending from -20 to 55 °C. The estimated energy density is 260 W h kg(-1), which is considerably higher than densities delivered by the presently available Li-ion batteries.
Role of exact exchange in thermally-assisted-occupation density functional theory: A proposal of new hybrid schemes.

PubMed

Chai, Jeng-Da

2017-01-28

We propose hybrid schemes incorporating exact exchange into thermally assisted-occupation-density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] for an improved description of nonlocal exchange effects. With a few simple modifications, global and range-separated hybrid functionals in Kohn-Sham density functional theory (KS-DFT) can be combined seamlessly with TAO-DFT. In comparison with global hybrid functionals in KS-DFT, the resulting global hybrid functionals in TAO-DFT yield promising performance for systems with strong static correlation effects (e.g., the dissociation of H 2 and N 2 , twisted ethylene, and electronic properties of linear acenes), while maintaining similar performance for systems without strong static correlation effects. Besides, a reasonably accurate description of noncovalent interactions can be efficiently achieved through the inclusion of dispersion corrections in hybrid TAO-DFT. Relative to semilocal density functionals in TAO-DFT, global hybrid functionals in TAO-DFT are generally superior in performance for a wide range of applications, such as thermochemistry, kinetics, reaction energies, and optimized geometries.
Restoring The Azimuthal Symmetry Of Charged Particle Lateral Density In The Range Of KASCADE-Grande

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sima, O.; Rebel, H.; Apel, W. D.

2010-11-24

KASCADE-Grande, an extension of the former KASCADE experiment, is a multi-component Extensive Air Shower (EAS) experiment located in Karlsruhe Institute of Technology (Campus North), Germany. An important observable for analyzing the EAS is the lateral density of charged particles in the intrinsic shower plane. This observable is deduced from the basic information provided by the Grande scintillators - the energy deposit - first in the observation plane, by using a Lateral Energy Correction Function (LECF), then in the intrinsic shower plane, by applying an adequate mapping procedure. In both steps azimuthal.
Restoring The Azimuthal Symmetry Of Charged Particle Lateral Density In The Range Of KASCADE-Grande

NASA Astrophysics Data System (ADS)

Sima, O.; Rebel, H.; Apel, W. D.; Arteaga, J. C.; Bekk, K.; Bertaina, M.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Buchholz, P.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Engler, J.; Finger, M.; Fuhrmann, D.; Ghia, P. L.; Gils, H. J.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Klages, H. O.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Mayer, H. J.; Melissas, M.; Milke, J.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Oehlschläger, J.; Ostapchenko, S.; Over, S.; Palmieri, N.; Petcu, M.; Pierog, T.; Roth, M.; Schieler, H.; Schröder, F. G.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.

2010-11-01

KASCADE-Grande, an extension of the former KASCADE experiment, is a multi-component Extensive Air Shower (EAS) experiment located in Karlsruhe Institute of Technology (Campus North), Germany. An important observable for analyzing the EAS is the lateral density of charged particles in the intrinsic shower plane. This observable is deduced from the basic information provided by the Grande scintillators-the energy deposit-first in the observation plane, by using a Lateral Energy Correction Function (LECF), then in the intrinsic shower plane, by applying an adequate mapping procedure. In both steps azimuthal.
Abnormal functional connectivity density in children with anisometropic amblyopia at resting-state.

PubMed

Wang, Tianyue; Li, Qian; Guo, Mingxia; Peng, Yanmin; Li, Qingji; Qin, Wen; Yu, Chunshui

2014-05-14

Amblyopia is a developmental disorder resulting from anomalous binocular visual input in early life. Task-based neuroimaging studies have widely investigated cortical functional impairments in amblyopia, but changes in spontaneous neuronal functional activities in amblyopia remain largely unknown. In the present study, functional connectivity density (FCD) mapping, an ultrafast data-driven method based on fMRI, was applied for the first time to investigate changes in cortical functional connectivities in amblyopia during the resting-state. We quantified and compared both short- and long-range FCD in both the brains of children with anisometropic amblyopia (AAC) and normal sighted children (NSC). In contrast to the NSC, the AAC showed significantly decreased short-range FCD in the inferior temporal/fusiform gyri, parieto-occipital and rostrolateral prefrontal cortices, as well as decreased long-range FCD in the premotor cortex, dorsal inferior parietal lobule, frontal-insular and dorsal prefrontal cortices. Furthermore, most regions with reduced long-range FCD in the AAC showed decreased functional connectivity with occipital and posterior parietal cortices in the AAC. The results suggest that chronically poor visual input in amblyopia not only impairs the brain's short-range functional connections in visual pathways and in the frontal cortex, which is important for cognitive control, but also affects long-range functional connections among the visual areas, posterior parietal and frontal cortices that subserve visuomotor and visual-guided actions, visuospatial attention modulation and the integration of salient information. This study provides evidence for abnormal spontaneous brain activities in amblyopia. Copyright © 2014 Elsevier B.V. All rights reserved.
Long-range epidemic spreading in a random environment.

PubMed

Juhász, Róbert; Kovács, István A; Iglói, Ferenc

2015-03-01

Modeling long-range epidemic spreading in a random environment, we consider a quenched, disordered, d-dimensional contact process with infection rates decaying with distance as 1/rd+σ. We study the dynamical behavior of the model at and below the epidemic threshold by a variant of the strong-disorder renormalization-group method and by Monte Carlo simulations in one and two spatial dimensions. Starting from a single infected site, the average survival probability is found to decay as P(t)∼t-d/z up to multiplicative logarithmic corrections. Below the epidemic threshold, a Griffiths phase emerges, where the dynamical exponent z varies continuously with the control parameter and tends to zc=d+σ as the threshold is approached. At the threshold, the spatial extension of the infected cluster (in surviving trials) is found to grow as R(t)∼t1/zc with a multiplicative logarithmic correction and the average number of infected sites in surviving trials is found to increase as Ns(t)∼(lnt)χ with χ=2 in one dimension.
The hairpin resonator: A plasma density measuring technique revisited

NASA Astrophysics Data System (ADS)

Piejak, R. B.; Godyak, V. A.; Garner, R.; Alexandrovich, B. M.; Sternberg, N.

2004-04-01

A microwave resonator probe is a resonant structure from which the relative permittivity of the surrounding medium can be determined. Two types of microwave resonator probes (referred to here as hairpin probes) have been designed and built to determine the electron density in a low-pressure gas discharge. One type, a transmission probe, is a functional equivalent of the original microwave resonator probe introduced by R. L. Stenzel [Rev. Sci. Instrum. 47, 603 (1976)], modified to increase coupling to the hairpin structure and to minimize plasma perturbation. The second type, a reflection probe, differs from the transmission probe in that it requires only one coaxial feeder cable. A sheath correction, based on the fluid equations for collisionless ions in a cylindrical electron-free sheath, is presented here to account for the sheath that naturally forms about the hairpin structure immersed in plasma. The sheath correction extends the range of electron density that can be accurately measured with a particular wire separation of the hairpin structure. Experimental measurements using the hairpin probe appear to be highly reproducible. Comparisons with Langmuir probes show that the Langmuir probe determines an electron density that is 20-30% lower than the hairpin. Further comparisons, with both an interferometer and a Langmuir probe, show hairpin measurements to be in good agreement with the interferometer while Langmuir probe measurements again result in a lower electron density.
Long-range Prethermal Time Crystals

NASA Astrophysics Data System (ADS)

Machado, Francisco; Meyer, Gregory D.; Else, Dominic; Olund, Christopher; Nayak, Chetan; Yao, Norman Y.

2017-04-01

Driven quantum systems have recently enabled the realization of a discrete time crystal - an intrinsically out-of-equilibrium phase of matter. One strategy to prevent the drive-induced, runaway heating of the time crystal is the presence of strong disorder leading to many-body localization (MBL). A more elegant, disorder-less approach is simply to work in the prethermal regime where time crystalline order can persist to exponentially long times. One key difference between prethermal and MBL time crystals is that the former is prohibited from existing in one dimensional systems with short-range interactions. In this work, we demonstrate that long-range interactions can stabilize a one dimensional prethermal time crystal. By numerically studying the pre-thermal regime, we find evidence for a phase transition out of the time crystal as a function of increasing energy density. Finally, generalizations of previous analytical bounds for the heating time-scale of driven quantum systems to long-range interactions will also be discussed.
Modeling of long-range memory processes with inverse cubic distributions by the nonlinear stochastic differential equations

NASA Astrophysics Data System (ADS)

Kaulakys, B.; Alaburda, M.; Ruseckas, J.

2016-05-01

A well-known fact in the financial markets is the so-called ‘inverse cubic law’ of the cumulative distributions of the long-range memory fluctuations of market indicators such as a number of events of trades, trading volume and the logarithmic price change. We propose the nonlinear stochastic differential equation (SDE) giving both the power-law behavior of the power spectral density and the long-range dependent inverse cubic law of the cumulative distribution. This is achieved using the suggestion that when the market evolves from calm to violent behavior there is a decrease of the delay time of multiplicative feedback of the system in comparison to the driving noise correlation time. This results in a transition from the Itô to the Stratonovich sense of the SDE and yields a long-range memory process.
Density functional theory studies on the structures and electronic communication of meso-ferrocenylporphyrins: long range orbital coupling via porphyrin core.

PubMed

Zhang, Lijuan; Qi, Dongdong; Zhang, Yuexing; Bian, Yongzhong; Jiang, Jianzhuang

2011-02-01

The molecular and electronic structures together with the electronic absorption spectra of a series of metal free meso-ferrocenylporphyrins, namely 5-ferrocenylporphyrin (1), 5,10-diferrocenylporphyrin (2), 5,15-diferrocenylporphyrin (3), 5,10,15-triferrocenylporphyrin (4), and 5,10,15,20-tetraferrocenylporphyrin (5) have been studied with the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. For the purpose of comparative studies, metal free porphyrin without any ferrocenyl group (0) and isolated ferrocene (6) were also calculated. The effects of the number and position of meso-attached ferrocenyl substituents on their molecular and electronic structures, atomic charges, molecular orbitals, and electronic absorption spectra of 1-5 were systematically investigated. The orbital coupling is investigated in detail, explaining well the long range coupling of ferrocenyl substituents connected via porphyrin core and the systematic change in the electronic absorption spectra of porphyrin compounds. Copyright © 2010 Elsevier Inc. All rights reserved.
Evaluation of Technologies to Complement/Replace Mass Spectrometers in the Tritium Facilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tovo, L. L.; Lascola, R. J.; Spencer, W. A.

2005-08-30

The primary goal of this work is to determine the suitability of the Infraran sensor for use in the Palladium Membrane Reactor. This application presents a challenge for the sensor, since the process temperature exceeds its designed operating range. We have demonstrated that large baseline offsets, comparable to the sensor response to the analyte, are obtained if cool air is blown across the sensor. We have also shown that there is a strong environmental component to the noise. However, the current arrangement does not utilize a reference detector. The strong correlation between the CO and H{sub 2}O sensor responses tomore » environmental changes indicate that a reference detector can greatly reduce the environmental sensitivity. In fact, incorporation of a reference detector is essential for the sensor to work in this application. We have also shown that the two sensor responses are adequately independent. Still, there are several small corrections which must to be made to the sensor response to accommodate chemical and physical effects. Interactions between the two analytes will alter the relationship between number density and pressure. Temperature and pressure broadening will alter the relationship between absorbance and number density. The individual effects are small--on the order of a few percent or less--but cumulatively significant. Still, corrections may be made if temperature and total pressure are independently measured and incorporated into a post-analysis routine. Such corrections are easily programmed and automated and do not represent a significant burden for installation. The measurements and simulations described above indicate that with appropriate corrections, the Infraran sensor can approach the 1-1.5% measurement accuracy required for effective PMR process control. It is also worth noting that the Infraran may be suitable for other gas sensing applications, especially those that do not need to be made in a high-temperature environment. Any gas with an infrared absorption (methane, ammonia, etc.) may be detected so long as an appropriate bandpass filter can be manufactured. Note that homonuclear diatomic molecules (hydrogen and its isotopes, nitrogen, oxygen) do not have infrared absorptions. We have shown that the sensor response may be adequately predicted using commercially available software. Measurement of trace concentrations is limited by the broad spectral bandpass, since the total signal includes non-absorbed frequencies. However, cells with longer pathlengths can be designed to address this problem.« less
Chromatic aberrations correction for imaging spectrometer based on acousto-optic tunable filter with two transducers.

PubMed

Zhao, Huijie; Wang, Ziye; Jia, Guorui; Zhang, Ying; Xu, Zefu

2017-10-02

The acousto-optic tunable filter (AOTF) with wide wavelength range and high spectral resolution has long crystal and two transducers. A longer crystal length leads to a bigger chromatic focal shift and the double-transducer arrangement induces angular mutation in diffracted beam, which increase difficulty in longitudinal and lateral chromatic aberration correction respectively. In this study, the two chromatic aberrations are analyzed quantitatively based on an AOTF optical model and a novel catadioptric dual-path configuration is proposed to correct both the chromatic aberrations. The test results exhibit effectiveness of the optical configuration for this type of AOTF-based imaging spectrometer.

Advances in the characterization of InAs/GaSb superlattice infrared photodetectors

NASA Astrophysics Data System (ADS)

Wörl, A.; Daumer, V.; Hugger, T.; Kohn, N.; Luppold, W.; Müller, R.; Niemasz, J.; Rehm, R.; Rutz, F.; Schmidt, J.; Schmitz, J.; Stadelmann, T.; Wauro, M.

2016-10-01

This paper reports on advances in the electro-optical characterization of InAs/GaSb short-period superlattice infrared photodetectors with cut-off wavelengths in the mid-wavelength and long-wavelength infrared ranges. To facilitate in-line monitoring of the electro-optical device performance at different processing stages we have integrated a semi-automated cryogenic wafer prober in our process line. The prober is configured for measuring current-voltage characteristics of individual photodiodes at 77 K. We employ it to compile a spatial map of the dark current density of a superlattice sample with a cut-off wavelength around 5 μm patterned into a regular array of 1760 quadratic mesa diodes with a pitch of 370 μm and side lengths varying from 60 to 350 μm. The different perimeter-to-area ratios make it possible to separate bulk current from sidewall current contributions. We find a sidewall contribution to the dark current of 1.2×10-11 A/cm and a corrected bulk dark current density of 1.1×10-7 A/cm2, both at 200 mV reverse bias voltage. An automated data analysis framework can extract bulk and sidewall current contributions for various subsets of the test device grid. With a suitable periodic arrangement of test diode sizes, the spatial distribution of the individual contributions can thus be investigated. We found a relatively homogeneous distribution of both bulk dark current density and sidewall current contribution across the sample. With the help of an improved capacitance-voltage measurement setup developed to complement this technique a residual carrier concentration of 1.3×1015 cm-3 is obtained. The work is motivated by research into high performance superlattice array sensors with demanding processing requirements. A novel long-wavelength infrared imager based on a heterojunction concept is presented as an example for this work. It achieves a noise equivalent temperature difference below 30 mK for realistic operating conditions.
Long-term follow-up of echolalia and question answering.

PubMed

Foxx, R M; Faw, G D

1990-01-01

A long-term follow-up of echolalia and correct question answering was conducted for 6 subjects from three previously published studies. The follow-up periods ranged from 26 to 57 months. In a training site follow-up, subjects were exposed to baseline/posttraining conditions in which the original trainer and/or a novel person(s) presented trained and untrained questions. Four subjects displayed echolalia below baseline levels, and another did so in some assessments. Overall, echolalia was lower than in baseline in 80.6% of the follow-ups. Five subjects displayed correct responding above baseline levels. No clear differences were noted in correct responding or echolalia between the trainer and novel-person presentations or between trained and untrained questions. In a follow-up in a natural environment conducted by a novel person, lower than baseline levels of echolalia were displayed by 3 subjects; 2 subjects displayed lower than baseline levels in some assessments. Two subjects consistently displayed correct responding above baseline, and 3 did so occasionally. Issues related to the study of maintenance are discussed.
Long-term follow-up of echolalia and question answering.

PubMed Central

Foxx, R M; Faw, G D

1990-01-01

A long-term follow-up of echolalia and correct question answering was conducted for 6 subjects from three previously published studies. The follow-up periods ranged from 26 to 57 months. In a training site follow-up, subjects were exposed to baseline/posttraining conditions in which the original trainer and/or a novel person(s) presented trained and untrained questions. Four subjects displayed echolalia below baseline levels, and another did so in some assessments. Overall, echolalia was lower than in baseline in 80.6% of the follow-ups. Five subjects displayed correct responding above baseline levels. No clear differences were noted in correct responding or echolalia between the trainer and novel-person presentations or between trained and untrained questions. In a follow-up in a natural environment conducted by a novel person, lower than baseline levels of echolalia were displayed by 3 subjects; 2 subjects displayed lower than baseline levels in some assessments. Two subjects consistently displayed correct responding above baseline, and 3 did so occasionally. Issues related to the study of maintenance are discussed. PMID:2249974
Performance characterization of Lithium-ion cells possessing carbon-carbon composite-based anodes capable of operating over a wide temperature range

NASA Technical Reports Server (NTRS)

Smart, M. C.; Hossain, S.; Ratnakumar, B. V.; Loutfy, R.; Whitcanack, L. D.; Chin, K. B.; Davies, E. D.; Surampudi, S.; Narayanan, S. R.

2004-01-01

NASA has interest in secondary energy storage batteries that display high specific energy, high energy density, long life characteristics, and perform well over a wide range of temperatures, in order to enable a number of future applications.
The SDSS-IV MaNGA Sample: Design, Optimization, and Usage Considerations

NASA Astrophysics Data System (ADS)

Wake, David A.; Bundy, Kevin; Diamond-Stanic, Aleksandar M.; Yan, Renbin; Blanton, Michael R.; Bershady, Matthew A.; Sánchez-Gallego, José R.; Drory, Niv; Jones, Amy; Kauffmann, Guinevere; Law, David R.; Li, Cheng; MacDonald, Nicholas; Masters, Karen; Thomas, Daniel; Tinker, Jeremy; Weijmans, Anne-Marie; Brownstein, Joel R.

2017-09-01

We describe the sample design for the SDSS-IV MaNGA survey and present the final properties of the main samples along with important considerations for using these samples for science. Our target selection criteria were developed while simultaneously optimizing the size distribution of the MaNGA integral field units (IFUs), the IFU allocation strategy, and the target density to produce a survey defined in terms of maximizing signal-to-noise ratio, spatial resolution, and sample size. Our selection strategy makes use of redshift limits that only depend on I-band absolute magnitude (M I ), or, for a small subset of our sample, M I and color (NUV - I). Such a strategy ensures that all galaxies span the same range in angular size irrespective of luminosity and are therefore covered evenly by the adopted range of IFU sizes. We define three samples: the Primary and Secondary samples are selected to have a flat number density with respect to M I and are targeted to have spectroscopic coverage to 1.5 and 2.5 effective radii (R e ), respectively. The Color-Enhanced supplement increases the number of galaxies in the low-density regions of color-magnitude space by extending the redshift limits of the Primary sample in the appropriate color bins. The samples cover the stellar mass range 5× {10}8≤slant {M}* ≤slant 3× {10}11 {M}⊙ {h}-2 and are sampled at median physical resolutions of 1.37 and 2.5 kpc for the Primary and Secondary samples, respectively. We provide weights that will statistically correct for our luminosity and color-dependent selection function and IFU allocation strategy, thus correcting the observed sample to a volume-limited sample.
Effect of correlations on the polarizability of the one component plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carini, P.R.

Correlational effects on the dynamical polarizability ..cap alpha..(k,..omega..) of the one component plasma (OCP) are investigated in both the weak (..gamma.. < 1) and strong (..gamma.. < 1) coupling regions (..gamma.. is the plasma parameter, ..gamma.. = k/sup 3//4..pi..n where k/sup -1/ is the Debye length and n is the number density. In the weak coupling region a numerical solution is presented over a wide range of frequencies of the complete first order (in ..gamma..) correction to the dynamical polarizability which fully accounts for dynamical screening effects and is exact in the long wavelength and weak coupling limits (k ..-->..more » 0, ..gamma.. ..-->.. 0). This complete result is compared with a similar numerical solution for the dynamical polarizability obtained from the Golden-Kalman (GK) dynamical theory for strongly coupled plasmas. Contrary to previous results reported in the literature it was found that both theories predict the change in the dispersion of the long wavelength plasmons due to finite ..gamma.. effects to be that the slope of the plasmon dispersion curve decreases from its Bohm-Gross value as the plasma parameter increases from 0. In the strong coupling region two hydrodynamical model solutions of the GK dynamical theory for the polarizability are presented.« less
Microscopic Approach to the Nonlinear Elasticity of Compressed Emulsions

NASA Astrophysics Data System (ADS)

Jorjadze, Ivane; Pontani, Lea-Laetitia; Brujic, Jasna

2013-01-01

Using confocal microscopy, we measure the packing geometry and interdroplet forces as a function of the osmotic pressure in a 3D emulsion system. We assume a harmonic interaction potential over a wide range of volume fractions and attribute the observed nonlinear elastic response of the pressure with density to the first corrections to the scaling laws of the microstructure away from the critical point. The bulk modulus depends on the excess contacts created under compression, which leads to the correction exponent α=1.5. Microscopically, the nonlinearities manifest themselves as a narrowing of the distribution of the pressure per particle as a function of the global pressure.
On-top density functionals for the short-range dynamic correlation between electrons of opposite and parallel spin

NASA Astrophysics Data System (ADS)

Hollett, Joshua W.; Pegoretti, Nicholas

2018-04-01

Separate, one-parameter, on-top density functionals are derived for the short-range dynamic correlation between opposite and parallel-spin electrons, in which the electron-electron cusp is represented by an exponential function. The combination of both functionals is referred to as the Opposite-spin exponential-cusp and Fermi-hole correction (OF) functional. The two parameters of the OF functional are set by fitting the ionization energies and electron affinities, of the atoms He to Ar, predicted by ROHF in combination with the OF functional to the experimental values. For ionization energies, the overall performance of ROHF-OF is better than completely renormalized coupled-cluster [CR-CC(2,3)] and better than, or as good as, conventional density functional methods. For electron affinities, the overall performance of ROHF-OF is less impressive. However, for both ionization energies and electron affinities of third row atoms, the mean absolute error of ROHF-OF is only 3 kJ mol-1.
Orientational order as the origin of the long-range hydrophobic effect.

PubMed

Banerjee, Saikat; Singh, Rakesh S; Bagchi, Biman

2015-04-07

The long range attractive force between two hydrophobic surfaces immersed in water is observed to decrease exponentially with their separation-this distance-dependence of effective force is known as the hydrophobic force law (HFL). We explore the microscopic origin of HFL by studying distance-dependent attraction between two parallel rods immersed in 2D Mercedes Benz model of water. This model is found to exhibit a well-defined HFL. Although the phenomenon is conventionally explained by density-dependent theories, we identify orientation, rather than density, as the relevant order parameter. The range of density variation is noticeably shorter than that of orientational heterogeneity. The latter is comparable to the observed distances of hydrophobic force. At large separation, attraction between the rods arises primarily from a destructive interference among the inwardly propagating oppositely oriented heterogeneity generated in water by the two rods. As the rods are brought closer, the interference increases leading to a decrease in heterogeneity and concomitant decrease in free energy of the system, giving rise to the effective attraction. We notice formation of hexagonal ice-like structures at the onset of attractive region which suggests that metastable free energy minimum may play a role in the origin of HFL.
Orientational order as the origin of the long-range hydrophobic effect

NASA Astrophysics Data System (ADS)

Banerjee, Saikat; Singh, Rakesh S.; Bagchi, Biman

2015-04-01

The long range attractive force between two hydrophobic surfaces immersed in water is observed to decrease exponentially with their separation—this distance-dependence of effective force is known as the hydrophobic force law (HFL). We explore the microscopic origin of HFL by studying distance-dependent attraction between two parallel rods immersed in 2D Mercedes Benz model of water. This model is found to exhibit a well-defined HFL. Although the phenomenon is conventionally explained by density-dependent theories, we identify orientation, rather than density, as the relevant order parameter. The range of density variation is noticeably shorter than that of orientational heterogeneity. The latter is comparable to the observed distances of hydrophobic force. At large separation, attraction between the rods arises primarily from a destructive interference among the inwardly propagating oppositely oriented heterogeneity generated in water by the two rods. As the rods are brought closer, the interference increases leading to a decrease in heterogeneity and concomitant decrease in free energy of the system, giving rise to the effective attraction. We notice formation of hexagonal ice-like structures at the onset of attractive region which suggests that metastable free energy minimum may play a role in the origin of HFL.
Dipole polarizability, sum rules, mean excitation energies, and long-range dispersion coefficients for buckminsterfullerene C 60

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Thakkar, Ajit J.

2011-11-01

Experimental photoabsorption cross-sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and the high-energy behavior of the dipole-oscillator-strength density are used to construct dipole oscillator strength distributions for buckminsterfullerene (C60). The distributions are used to predict dipole sum rules Sk, mean excitation energies Ik, the frequency dependent polarizability, and C6 coefficients for the long-range dipole-dipole interactions of C60 with a variety of atoms and molecules.
Dual origin of pairing in nuclei

NASA Astrophysics Data System (ADS)

Idini, A.; Potel, G.; Barranco, F.; Vigezzi, E.; Broglia, R. A.

2016-11-01

The pairing correlations of the nucleus 120Sn are calculated by solving the Nambu-Gor'kov equations, including medium polarization effects resulting from the interweaving of quasiparticles, spin and density vibrations, taking into account, within the framework of nuclear field theory (NFT), processes leading to self-energy and vertex corrections and to the induced pairing interaction. From these results one can not only demonstrate the inevitability of the dual origin of pairing in nuclei, but also extract information which can be used at profit to quantitatively disentangle the contributions to the pairing gap Δ arising from the bare and from the induced pairing interaction. The first is the strong 1 S 0 short-range NN potential resulting from meson exchange between nucleons moving in time reversal states within an energy range of hundreds of MeV from the Fermi energy. The second results from the exchange of vibrational modes between nucleons moving within few MeV from the Fermi energy. Short- ( v p bare) and long-range ( v p ind) pairing interactions contribute essentially equally to nuclear Cooper pair stability. That is to the breaking of gauge invariance in open-shell superfluid nuclei and thus to the order parameter, namely to the ground state expectation value of the pair creation operator. In other words, to the emergent property of generalized rigidity in gauge space, and associated rotational bands and Cooper pair tunneling between members of these bands.
Impact of NO2 horizontal heterogeneity on tropospheric NO2 vertical columns retrieved from satellite, multi-axis differential optical absorption spectroscopy, and in situ measurements

NASA Astrophysics Data System (ADS)

Mendolia, D.; D'Souza, R. J. C.; Evans, G. J.; Brook, J.

2013-01-01

Tropospheric NO2 vertical column densities were retrieved for the first time in Toronto, Canada using three methods of differing spatial scales. Remotely-sensed NO2 vertical column densities, retrieved from multi-axis differential optical absorption spectroscopy and satellite remote sensing, were evaluated by comparison with in situ vertical column densities derived using a pair of chemiluminescence monitors situated 0.01 and 0.5 km above ground level. The chemiluminescence measurements were corrected for the influence of NOz, which reduced the NO2 concentrations at 0.01 and 0.5 km by 8 ± 1% and 12 ± 1%, respectively. The average absolute decrease in the chemiluminescence NO2 measurement as a result of this correction was less than 1 ppb. Good correlation was observed between the remotely sensed and in situ NO2 vertical column densities (Pearson R ranging from 0.68 to 0.79), but the in situ vertical column densities were 27% to 55% greater than the remotely-sensed columns. These results indicate that NO2 horizontal heterogeneity strongly impacted the magnitude of the remotely-sensed columns. The in situ columns reflected an urban environment with major traffic sources, while the remotely-sensed NO2 vertical column densities were representative of the region, which included spatial heterogeneity introduced by residential neighbourhoods and Lake Ontario. Despite the difference in absolute values, the reasonable correlation between the vertical column densities determined by three distinct methods increased confidence in the validity of the values provided by each of the methods.
Developing population models with data from marked individuals

USGS Publications Warehouse

Hae Yeong Ryu,; Kevin T. Shoemaker,; Eva Kneip,; Anna Pidgeon,; Patricia Heglund,; Brooke Bateman,; Thogmartin, Wayne E.; Reşit Akçakaya,

2016-01-01

Population viability analysis (PVA) is a powerful tool for biodiversity assessments, but its use has been limited because of the requirements for fully specified population models such as demographic structure, density-dependence, environmental stochasticity, and specification of uncertainties. Developing a fully specified population model from commonly available data sources – notably, mark–recapture studies – remains complicated due to lack of practical methods for estimating fecundity, true survival (as opposed to apparent survival), natural temporal variability in both survival and fecundity, density-dependence in the demographic parameters, and uncertainty in model parameters. We present a general method that estimates all the key parameters required to specify a stochastic, matrix-based population model, constructed using a long-term mark–recapture dataset. Unlike standard mark–recapture analyses, our approach provides estimates of true survival rates and fecundities, their respective natural temporal variabilities, and density-dependence functions, making it possible to construct a population model for long-term projection of population dynamics. Furthermore, our method includes a formal quantification of parameter uncertainty for global (multivariate) sensitivity analysis. We apply this approach to 9 bird species and demonstrate the feasibility of using data from the Monitoring Avian Productivity and Survivorship (MAPS) program. Bias-correction factors for raw estimates of survival and fecundity derived from mark–recapture data (apparent survival and juvenile:adult ratio, respectively) were non-negligible, and corrected parameters were generally more biologically reasonable than their uncorrected counterparts. Our method allows the development of fully specified stochastic population models using a single, widely available data source, substantially reducing the barriers that have until now limited the widespread application of PVA. This method is expected to greatly enhance our understanding of the processes underlying population dynamics and our ability to analyze viability and project trends for species of conservation concern.
Hyperuniformity, quasi-long-range correlations, and void-space constraints in maximally random jammed particle packings. I. Polydisperse spheres.

PubMed

Zachary, Chase E; Jiao, Yang; Torquato, Salvatore

2011-05-01

Hyperuniform many-particle distributions possess a local number variance that grows more slowly than the volume of an observation window, implying that the local density is effectively homogeneous beyond a few characteristic length scales. Previous work on maximally random strictly jammed sphere packings in three dimensions has shown that these systems are hyperuniform and possess unusual quasi-long-range pair correlations decaying as r(-4), resulting in anomalous logarithmic growth in the number variance. However, recent work on maximally random jammed sphere packings with a size distribution has suggested that such quasi-long-range correlations and hyperuniformity are not universal among jammed hard-particle systems. In this paper, we show that such systems are indeed hyperuniform with signature quasi-long-range correlations by characterizing the more general local-volume-fraction fluctuations. We argue that the regularity of the void space induced by the constraints of saturation and strict jamming overcomes the local inhomogeneity of the disk centers to induce hyperuniformity in the medium with a linear small-wave-number nonanalytic behavior in the spectral density, resulting in quasi-long-range spatial correlations scaling with r(-(d+1)) in d Euclidean space dimensions. A numerical and analytical analysis of the pore-size distribution for a binary maximally random jammed system in addition to a local characterization of the n-particle loops governing the void space surrounding the inclusions is presented in support of our argument. This paper is the first part of a series of two papers considering the relationships among hyperuniformity, jamming, and regularity of the void space in hard-particle packings.
Plasma electron analysis: Voyager plasma science experiment

NASA Technical Reports Server (NTRS)

Sittler, E. C., Jr.

1983-01-01

The Plasma Science Experiment (PLS) on the Voyager spacecraft provide data on the plasma ions and electrons in the interplanetary medium and the magnetospheres of the giant planets Jupiter and Saturn. A description of the analysis used to obtain electron parameters (density, temperature, etc.) from the plasma science experiment PLS electron measurements which cover the energy range from 10 eV to 5950 eV is presented. The electron sensor (D cup) and its transmission characteristics are described. A derivation of the fundamental analytical expression of the reduced distribution function F(e) is given. The electron distribution function F(e), used in the moment integrations, can be derived from F(e). Positive ions produce a correction current (ion feedthrough) to the measured electron current, which can be important to the measurements of the suprathermal electron component. In the case of Saturn, this correction current, which can either add to or subtract from the measured electron current, is less than 20% of the measured signal at all times. Comments about the corrections introduced by spacecraft charging to the Saturn encounter data, which can be important in regions of high density and shadow when the spacecraft can become negatively charged are introduced.
Charge density on thin straight wire, revisited

NASA Astrophysics Data System (ADS)

Jackson, J. D.

2000-09-01

The question of the equilibrium linear charge density on a charged straight conducting "wire" of finite length as its cross-sectional dimension becomes vanishingly small relative to the length is revisited in our didactic presentation. We first consider the wire as the limit of a prolate spheroidal conductor with semi-minor axis a and semi-major axis c when a/c<<1. We then treat an azimuthally symmetric straight conductor of length 2c and variable radius r(z) whose scale is defined by a parameter a. A procedure is developed to find the linear charge density λ(z) as an expansion in powers of 1/Λ, where Λ≡ln(4c2/a2), beginning with a uniform line charge density λ0. We show, for this rather general wire, that in the limit Λ>>1 the linear charge density becomes essentially uniform, but that the tiny nonuniformity (of order 1/Λ) is sufficient to produce a tangential electric field (of order Λ0) that cancels the zeroth-order field that naively seems to belie equilibrium. We specialize to a right circular cylinder and obtain the linear charge density explicitly, correct to order 1/Λ2 inclusive, and also the capacitance of a long isolated charged cylinder, a result anticipated in the published literature 37 years ago. The results for the cylinder are compared with published numerical computations. The second-order correction to the charge density is calculated numerically for a sampling of other shapes to show that the details of the distribution for finite 1/Λ vary with the shape, even though density becomes constant in the limit Λ→∞. We give a second method of finding the charge distribution on the cylinder, one that approximates the charge density by a finite polynomial in z2 and requires the solution of a coupled set of linear algebraic equations. Perhaps the most striking general observation is that the approach to uniformity as a/c→0 is extremely slow.
The density-salinity relation of standard seawater

NASA Astrophysics Data System (ADS)

Schmidt, Hannes; Seitz, Steffen; Hassel, Egon; Wolf, Henning

2018-01-01

The determination of salinity by means of electrical conductivity relies on stable salt proportions in the North Atlantic Ocean, because standard seawater, which is required for salinometer calibration, is produced from water of the North Atlantic. To verify the long-term stability of the standard seawater composition, it was proposed to perform measurements of the standard seawater density. Since the density is sensitive to all salt components, a density measurement can detect any change in the composition. A conversion of the density values to salinity can be performed by means of a density-salinity relation. To use such a relation with a target uncertainty in salinity comparable to that in salinity obtained from conductivity measurements, a density measurement with an uncertainty of 2 g m-3 is mandatory. We present a new density-salinity relation based on such accurate density measurements. The substitution measurement method used is described and density corrections for uniform isotopic and chemical compositions are reported. The comparison of densities calculated using the new relation with those calculated using the present reference equations of state TEOS-10 suggests that the density accuracy of TEOS-10 (as well as that of EOS-80) has been overestimated, as the accuracy of some of its underlying density measurements had been overestimated. The new density-salinity relation may be used to verify the stable composition of standard seawater by means of routine density measurements.
Dependence of Excited State Potential Energy Surfaces on the Spatial Overlap of the Kohn-Sham Orbitals and the Amount of Nonlocal Hartree-Fock Exchange in Time-Dependent Density Functional Theory.

PubMed

Plötner, Jürgen; Tozer, David J; Dreuw, Andreas

2010-08-10

Time-dependent density functional theory (TDDFT) with standard GGA or hybrid exchange-correlation functionals is not capable of describing the potential energy surface of the S1 state of Pigment Yellow 101 correctly; an additional local minimum is observed at a twisted geometry with substantial charge transfer (CT) character. To investigate the influence of nonlocal exact orbital (Hartree-Fock) exchange on the shape of the potential energy surface of the S1 state in detail, it has been computed along the twisting coordinate employing the standard BP86, B3LYP, and BHLYP xc-functionals as well as the long-range separated (LRS) exchange-correlation (xc)-functionals LC-BOP, ωB97X, ωPBE, and CAM-B3LYP and compared to RI-CC2 benchmark results. Additionally, a recently suggested Λ-parameter has been employed that measures the amount of CT in an excited state by calculating the spatial overlap of the occupied and virtual molecular orbitals involved in the transition. Here, the error in the calculated S1 potential energy curves at BP86, B3LYP, and BHLYP can be clearly related to the Λ-parameter, i.e., to the extent of charge transfer. Additionally, it is demonstrated that the CT problem is largely alleviated when the BHLYP xc-functional is employed, although it still exhibits a weak tendency to underestimate the energy of CT states. The situation improves drastically when LRS-functionals are employed within TDDFT excited state calculations. All tested LRS-functionals give qualitatively the correct potential energy curves of the energetically lowest excited states of P. Y. 101 along the twisting coordinate. While LC-BOP and ωB97X overcorrect the CT problem and now tend to give too large excitation energies compared to other non-CT states, ωPBE and CAM-B3LYP are in excellent agreement with the RI-CC2 results, with respect to both the correct shape of the potential energy curve as well as the absolute values of the calculated excitation energies.
Complex angular and torsional deformities (distal femoral malunions). Preoperative planning using stereolithography and surgical correction with locking plate fixation in four dogs.

PubMed

DeTora, Michael D; Boudrieau, Randy J

2016-09-20

To describe the surgical technique of complex distal femoral deformity correction with the aid of stereolithography apparatus (SLA) biomodels, stabilized with locking plate fixation. Full-size replica epoxy bone biomodels of the affected femurs (4 dogs/ 5 limbs) were used as templates for surgical planning. A rehearsal procedure was performed on the biomodels aided by a guide wire technique and stabilized with locking plate fixation. Surgery performed in all dogs was guided by the rehearsal procedure. All pre-contoured implants were subsequently used in the definitive surgical procedure with minimal modification. All dogs had markedly improved, with near normal functional outcomes; all but one had a mild persistent lameness at the final in-hospital follow-up examination (mean: 54.4 weeks; range: 24-113 weeks after surgery). All femurs healed without complications (mean: 34 weeks, median: 12 weeks; range: 8-12 weeks for closing osteotomies, and 26-113 weeks for opening wedge osteotomies). Long-term follow-up examination (mean: 28.6 months; range: 5-42 months) revealed all but one owner to be highly satisfied with the outcome. Complications were observed in two dogs: prolonged tibiotarsal joint decreased flexion that resolved with physical therapy. In one of these dogs, iatrogenic transection of the long digital extensor tendon was repaired, and the other had a peroneal nerve neurapraxia. Stereolithography apparatus biomodels and rehearsal surgery simplified the definitive surgical corrections of complex femoral malunions and resulted in good functional outcomes.

Application of a renormalization-group treatment to the statistical associating fluid theory for potentials of variable range (SAFT-VR).

PubMed

Forte, Esther; Llovell, Felix; Vega, Lourdes F; Trusler, J P Martin; Galindo, Amparo

2011-04-21

An accurate prediction of phase behavior at conditions far and close to criticality cannot be accomplished by mean-field based theories that do not incorporate long-range density fluctuations. A treatment based on renormalization-group (RG) theory as developed by White and co-workers has proven to be very successful in improving the predictions of the critical region with different equations of state. The basis of the method is an iterative procedure to account for contributions to the free energy of density fluctuations of increasing wavelengths. The RG method has been combined with a number of versions of the statistical associating fluid theory (SAFT), by implementing White's earliest ideas with the improvements of Prausnitz and co-workers. Typically, this treatment involves two adjustable parameters: a cutoff wavelength L for density fluctuations and an average gradient of the wavelet function Φ. In this work, the SAFT-VR (variable range) equation of state is extended with a similar crossover treatment which, however, follows closely the most recent improvements introduced by White. The interpretation of White's latter developments allows us to establish a straightforward method which enables Φ to be evaluated; only the cutoff wavelength L then needs to be adjusted. The approach used here begins with an initial free energy incorporating only contributions from short-wavelength fluctuations, which are treated locally. The contribution from long-wavelength fluctuations is incorporated through an iterative procedure based on attractive interactions which incorporate the structure of the fluid following the ideas of perturbation theories and using a mapping that allows integration of the radial distribution function. Good agreement close and far from the critical region is obtained using a unique fitted parameter L that can be easily related to the range of the potential. In this way the thermodynamic properties of a square-well (SW) fluid are given by the same number of independent intermolecular model parameters as in the classical equation. Far from the critical region the approach provides the correct limiting behavior reducing to the classical equation (SAFT-VR). In the critical region the β critical exponent is calculated and is found to take values close to the universal value. In SAFT-VR the free energy of an associating chain fluid is obtained following the thermodynamic perturbation theory of Wertheim from the knowledge of the free energy and radial distribution function of a reference monomer fluid. By determining L for SW fluids of varying well width a unique equation of state is obtained for chain and associating systems without further adjustment of critical parameters. We use computer simulation data of the phase behavior of chain and associating SW fluids to test the accuracy of the new equation.
One-dimensional continuum electronic structure with the density-matrix renormalization group and its implications for density-functional theory.

PubMed

Stoudenmire, E M; Wagner, Lucas O; White, Steven R; Burke, Kieron

2012-08-03

We extend the density matrix renormalization group to compute exact ground states of continuum many-electron systems in one dimension with long-range interactions. We find the exact ground state of a chain of 100 strongly correlated artificial hydrogen atoms. The method can be used to simulate 1D cold atom systems and to study density-functional theory in an exact setting. To illustrate, we find an interacting, extended system which is an insulator but whose Kohn-Sham system is metallic.
A classical density-functional theory for describing water interfaces.

PubMed

Hughes, Jessica; Krebs, Eric J; Roundy, David

2013-01-14

We develop a classical density functional for water which combines the White Bear fundamental-measure theory (FMT) functional for the hard sphere fluid with attractive interactions based on the statistical associating fluid theory variable range (SAFT-VR). This functional reproduces the properties of water at both long and short length scales over a wide range of temperatures and is computationally efficient, comparable to the cost of FMT itself. We demonstrate our functional by applying it to systems composed of two hard rods, four hard rods arranged in a square, and hard spheres in water.
Does a Single Eigenstate Encode the Full Hamiltonian?

NASA Astrophysics Data System (ADS)

Garrison, James R.; Grover, Tarun

2018-04-01

The eigenstate thermalization hypothesis (ETH) posits that the reduced density matrix for a subsystem corresponding to an excited eigenstate is "thermal." Here we expound on this hypothesis by asking: For which class of operators, local or nonlocal, is ETH satisfied? We show that this question is directly related to a seemingly unrelated question: Is the Hamiltonian of a system encoded within a single eigenstate? We formulate a strong form of ETH where, in the thermodynamic limit, the reduced density matrix of a subsystem corresponding to a pure, finite energy density eigenstate asymptotically becomes equal to the thermal reduced density matrix, as long as the subsystem size is much less than the total system size, irrespective of how large the subsystem is compared to any intrinsic length scale of the system. This allows one to access the properties of the underlying Hamiltonian at arbitrary energy densities (or temperatures) using just a single eigenstate. We provide support for our conjecture by performing an exact diagonalization study of a nonintegrable 1D quantum lattice model with only energy conservation. In addition, we examine the case in which the subsystem size is a finite fraction of the total system size, and we find that, even in this case, many operators continue to match their canonical expectation values, at least approximately. In particular, the von Neumann entanglement entropy equals the thermal entropy as long as the subsystem is less than half the total system. Our results are consistent with the possibility that a single eigenstate correctly predicts the expectation values of all operators with support on less than half the total system, as long as one uses a microcanonical ensemble with vanishing energy width for comparison. We also study, both analytically and numerically, a particle-number conserving model at infinite temperature that substantiates our conjectures.
Total carbon and nitrogen in mineral soil after 26 years of prescribed fire: Long Valley and Fort Valley Experimental Forests

Treesearch

Daniel G. Neary; Sally M. Haase; Steven T. Overby

2008-01-01

Prescribed fire was introduced to high density ponderosa pine stands at Fort Valley and Long Valley Experimental Forests in 1976. This paper reports on mineral soil total carbon (C) and nitrogen (N) at Long Valley. Total soil C and N levels were highly variable and exhibited an increasing, but inconsistent, concentration trend related to burn interval. Total N ranged...
Demonstration of electronic design automation flow for massively parallel e-beam lithography

NASA Astrophysics Data System (ADS)

Brandt, Pieter; Belledent, Jérôme; Tranquillin, Céline; Figueiro, Thiago; Meunier, Stéfanie; Bayle, Sébastien; Fay, Aurélien; Milléquant, Matthieu; Icard, Beatrice; Wieland, Marco

2014-07-01

For proximity effect correction in 5 keV e-beam lithography, three elementary building blocks exist: dose modulation, geometry (size) modulation, and background dose addition. Combinations of these three methods are quantitatively compared in terms of throughput impact and process window (PW). In addition, overexposure in combination with negative bias results in PW enhancement at the cost of throughput. In proximity effect correction by over exposure (PEC-OE), the entire layout is set to fixed dose and geometry sizes are adjusted. In PEC-dose to size (DTS) both dose and geometry sizes are locally optimized. In PEC-background (BG), a background is added to correct the long-range part of the point spread function. In single e-beam tools (Gaussian or Shaped-beam), throughput heavily depends on the number of shots. In raster scan tools such as MAPPER Lithography's FLX 1200 (MATRIX platform) this is not the case and instead of pattern density, the maximum local dose on the wafer is limiting throughput. The smallest considered half-pitch is 28 nm, which may be considered the 14-nm node for Metal-1 and the 10-nm node for the Via-1 layer, achieved in a single exposure with e-beam lithography. For typical 28-nm-hp Metal-1 layouts, it was shown that dose latitudes (size of process window) of around 10% are realizable with available PEC methods. For 28-nm-hp Via-1 layouts this is even higher at 14% and up. When the layouts do not reach the highest densities (up to 10∶1 in this study), PEC-BG and PEC-OE provide the capability to trade throughput for dose latitude. At the highest densities, PEC-DTS is required for proximity correction, as this method adjusts both geometry edges and doses and will reduce the dose at the densest areas. For 28-nm-hp lines critical dimension (CD), hole&dot (CD) and line ends (edge placement error), the data path errors are typically 0.9, 1.0 and 0.7 nm (3σ) and below, respectively. There is not a clear data path performance difference between the investigated PEC methods. After the simulations, the methods were successfully validated in exposures on a MAPPER pre-alpha tool. A 28-nm half pitch Metal-1 and Via-1 layouts show good performance in resist that coincide with the simulation result. Exposures of soft-edge stitched layouts show that beam-to-beam position errors up to ±7 nm specified for FLX 1200 show no noticeable impact on CD. The research leading to these results has been performed in the frame of the industrial collaborative consortium IMAGINE.
Thioarsenides: A case for long-range Lewis acid-base-directed van der Waals interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibbs, Gerald V.; Wallace, Adam F.; Downs, R. T.

2011-04-01

Electron density distributions, bond paths, Laplacian and local energy density properties have been calculated for a number of As4Sn (n = 3,4,5) thioarsenide molecular crystals. On the basis of the distributions, the intramolecular As-S and As-As interactions classify as shared bonded interactions and the intermolecular As-S, As-As and S-S interactions classify as closed-shell van der Waals bonded interactions. The bulk of the intermolecular As-S bond paths link regions of locally concentrated electron density (Lewis base regions) with aligned regions of locally depleted electron density (Lewis acid regions) on adjacent molecules. The paths are comparable with intermolecular paths reported for severalmore » other molecular crystals that link aligned Lewis base and acid regions in a key-lock fashion, interactions that classified as long range Lewis acid-base directed van der Waals interactions. As the bulk of the intermolecular As-S bond paths (~70%) link Lewis acid-base regions on adjacent molecules, it appears that molecules adopt an arrangement that maximizes the number of As-S Lewis acid-base intermolecular bonded interactions. The maximization of the number of Lewis acid-base interactions appears to be connected with the close-packed array adopted by molecules: distorted cubic close-packed arrays are adopted for alacránite, pararealgar, uzonite, realgar and β-AsS and the distorted hexagonal close-packed arrays adopted by α- and β-dimorphite. A growth mechanism is proposed for thioarsenide molecular crystals from aqueous species that maximizes the number of long range Lewis acid-base vdW As-S bonded interactions with the resulting directed bond paths structuralizing the molecules as a molecular crystal.« less
High-resolution 14C dating of a 25,000-year lake-sediment record from equatorial East Africa

NASA Astrophysics Data System (ADS)

Blaauw, Maarten; van Geel, Bas; Kristen, Iris; Plessen, Birgit; Lyaruu, Anna; Engstrom, Daniel R.; van der Plicht, Johannes; Verschuren, Dirk

2011-10-01

We dated a continuous, ˜22-m long sediment sequence from Lake Challa (Mt. Kilimanjaro area, Kenya/Tanzania) to produce a solid chronological framework for multi-proxy reconstructions of climate and environmental change in equatorial East Africa over the past 25,000 years. The age model is based on a total of 168 AMS 14C dates on bulk-organic matter, combined with a 210Pb chronology for recent sediments and corrected for a variable old-carbon age offset. This offset was estimated by i) pairing bulk-organic 14C dates with either 210Pb-derived time markers or 14C dates on grass charcoal, and ii) wiggle-matching high-density series of bulk-organic 14C dates. Variation in the old-carbon age offset through time is relatively modest, ranging from ˜450 yr during glacial and late glacial time to ˜200 yr during the early and mid-Holocene, and increasing again to ˜250 yr today. The screened and corrected 14C dates were calibrated sequentially, statistically constrained by their stratigraphical order. As a result their constrained calendar-age distributions are much narrower, and the calibrated dates more precise, than if each 14C date had been calibrated on its own. The smooth-spline age-depth model has 95% age uncertainty ranges of ˜50-230 yr during the Holocene and ˜250-550 yr in the glacial section of the record. The δ 13C values of paired bulk-organic and grass-charcoal samples, and additional 14C dating on selected turbidite horizons, indicates that the old-carbon age offset in Lake Challa is caused by a variable contribution of old terrestrial organic matter eroded from soils, and controlled mainly by changes in vegetation cover within the crater basin.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, J; Zhang, W; Lu, J

Purpose: To investigate the accuracy and feasibility of dose calculations using kilovoltage cone beam computed tomography in cervical cancer radiotherapy using a correction algorithm. Methods: The Hounsfield units (HU) and electron density (HU-density) curve was obtained for both planning CT (pCT) and kilovoltage cone beam CT (CBCT) using a CIRS-062 calibration phantom. The pCT and kV-CBCT images have different HU values, and if the HU-density curve of CBCT was directly used to calculate dose in CBCT images may have a deviation on dose distribution. It is necessary to normalize the different HU values between pCT and CBCT. A HU correctionmore » algorithm was used for CBCT images (cCBCT). Fifteen intensity-modulated radiation therapy (IMRT) plans of cervical cancer were chosen, and the plans were transferred to the pCT and cCBCT data sets without any changes for dose calculations. Phantom and patient studies were carried out. The dose differences and dose distributions were compared between cCBCT plan and pCT plan. Results: The HU number of CBCT was measured by several times, and the maximum change was less than 2%. To compare with pCT, the CBCT and cCBCT has a discrepancy, the dose differences in CBCT and cCBCT images were 2.48%±0.65% (range: 1.3%∼3.8%) and 0.48%±0.21% (range: 0.1%∼0.82%) for phantom study, respectively. For dose calculation in patient images, the dose differences were 2.25%±0.43% (range: 1.4%∼3.4%) and 0.63%±0.35% (range: 0.13%∼0.97%), respectively. And for the dose distributions, the passing rate of cCBCT was higher than the CBCTs. Conclusion: The CBCT image for dose calculation is feasible in cervical cancer radiotherapy, and the correction algorithm offers acceptable accuracy. It will become a useful tool for adaptive radiation therapy.« less
Measurement of electron density using reactance cutoff probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

You, K. H.; Seo, B. H.; Kim, J. H.

2016-05-15

This paper proposes a new measurement method of electron density using the reactance spectrum of the plasma in the cutoff probe system instead of the transmission spectrum. The highly accurate reactance spectrum of the plasma-cutoff probe system, as expected from previous circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], was measured using the full two-port error correction and automatic port extension methods of the network analyzer. The electron density can be obtained from the analysis of the measured reactance spectrum, based on circuit modeling. According to the circuit simulation results, the reactance cutoff probe can measure themore » electron density more precisely than the previous cutoff probe at low densities or at higher pressure. The obtained results for the electron density are presented and discussed for a wide range of experimental conditions, and this method is compared with previous methods (a cutoff probe using the transmission spectrum and a single Langmuir probe).« less
Simulation study on characteristics of long-range interaction in randomly asymmetric exclusion process

NASA Astrophysics Data System (ADS)

Zhao, Shi-Bo; Liu, Ming-Zhe; Yang, Lan-Ying

2015-04-01

In this paper we investigate the dynamics of an asymmetric exclusion process on a one-dimensional lattice with long-range hopping and random update via Monte Carlo simulations theoretically. Particles in the model will firstly try to hop over successive unoccupied sites with a probability q, which is different from previous exclusion process models. The probability q may represent the random access of particles. Numerical simulations for stationary particle currents, density profiles, and phase diagrams are obtained. There are three possible stationary phases: the low density (LD) phase, high density (HD) phase, and maximal current (MC) in the system, respectively. Interestingly, bulk density in the LD phase tends to zero, while the MC phase is governed by α, β, and q. The HD phase is nearly the same as the normal TASEP, determined by exit rate β. Theoretical analysis is in good agreement with simulation results. The proposed model may provide a better understanding of random interaction dynamics in complex systems. Project supported by the National Natural Science Foundation of China (Grant Nos. 41274109 and 11104022), the Fund for Sichuan Youth Science and Technology Innovation Research Team (Grant No. 2011JTD0013), and the Creative Team Program of Chengdu University of Technology.
Macroscopically constrained Wang-Landau method for systems with multiple order parameters and its application to drawing complex phase diagrams

NASA Astrophysics Data System (ADS)

Chan, C. H.; Brown, G.; Rikvold, P. A.

2017-05-01

A generalized approach to Wang-Landau simulations, macroscopically constrained Wang-Landau, is proposed to simulate the density of states of a system with multiple macroscopic order parameters. The method breaks a multidimensional random-walk process in phase space into many separate, one-dimensional random-walk processes in well-defined subspaces. Each of these random walks is constrained to a different set of values of the macroscopic order parameters. When the multivariable density of states is obtained for one set of values of fieldlike model parameters, the density of states for any other values of these parameters can be obtained by a simple transformation of the total system energy. All thermodynamic quantities of the system can then be rapidly calculated at any point in the phase diagram. We demonstrate how to use the multivariable density of states to draw the phase diagram, as well as order-parameter probability distributions at specific phase points, for a model spin-crossover material: an antiferromagnetic Ising model with ferromagnetic long-range interactions. The fieldlike parameters in this model are an effective magnetic field and the strength of the long-range interaction.
Lightning propagation and flash density in squall lines as determined with radar

NASA Technical Reports Server (NTRS)

Mazur, V.; Rust, W. D.

1983-01-01

Lightning echo rise times and range-time variations due to discharge propagation are determined using S and L band radars, and the evolution of precipitation reflectivity and the associated lightning activity in squall lines is investigated using VHF and L band radars. The rise time of radar echoes can be explained by ionized channel propagation through the radar beams. Speeds of at least 250,000 m/s are found from measurements of the radial velocity of streamer propagation along the antenna beam. The range-time variations in lightning echoes indicate that either new ionization occurs as streamers develop into different parts of the cloud, channel delay occurs during which adequate ionization exists for radar detection, or continuing current occurs. Determinations of the lightning flash density for a squall line in the U.S. show that the maximum lightning density tends to be near the leading edge of the precipitation cores in developing cells. Long discharges are produced as a cell in the squall line develops and the total lightning density increases, although short discharges predominate. As the cell dissipates, short flashes diminish or cease and the long flashes dominate the lightning activity.
Robust Wave-front Correction in a Small Scale Adaptive Optics System Using a Membrane Deformable Mirror

NASA Astrophysics Data System (ADS)

Choi, Y.; Park, S.; Baik, S.; Jung, J.; Lee, S.; Yoo, J.

A small scale laboratory adaptive optics system using a Shack-Hartmann wave-front sensor (WFS) and a membrane deformable mirror (DM) has been built for robust image acquisition. In this study, an adaptive limited control technique is adopted to maintain the long-term correction stability of an adaptive optics system. To prevent the waste of dynamic correction range for correcting small residual wave-front distortions which are inefficient to correct, the built system tries to limit wave-front correction when a similar small difference wave-front pattern is repeatedly generated. Also, the effect of mechanical distortion in an adaptive optics system is studied and a pre-recognition method for the distortion is devised to prevent low-performance system operation. A confirmation process for a balanced work assignment among deformable mirror (DM) actuators is adopted for the pre-recognition. The corrected experimental results obtained by using a built small scale adaptive optics system are described in this paper.
Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory.

PubMed

Sissay, Adonay; Abanador, Paul; Mauger, François; Gaarde, Mette; Schafer, Kenneth J; Lopata, Kenneth

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.
Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sissay, Adonay; Abanador, Paul; Mauger, François

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagatingmore » the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.« less
On the simple random-walk models of ion-channel gate dynamics reflecting long-term memory.

PubMed

Wawrzkiewicz, Agata; Pawelek, Krzysztof; Borys, Przemyslaw; Dworakowska, Beata; Grzywna, Zbigniew J

2012-06-01

Several approaches to ion-channel gating modelling have been proposed. Although many models describe the dwell-time distributions correctly, they are incapable of predicting and explaining the long-term correlations between the lengths of adjacent openings and closings of a channel. In this paper we propose two simple random-walk models of the gating dynamics of voltage and Ca(2+)-activated potassium channels which qualitatively reproduce the dwell-time distributions, and describe the experimentally observed long-term memory quite well. Biological interpretation of both models is presented. In particular, the origin of the correlations is associated with fluctuations of channel mass density. The long-term memory effect, as measured by Hurst R/S analysis of experimental single-channel patch-clamp recordings, is close to the behaviour predicted by our models. The flexibility of the models enables their use as templates for other types of ion channel.
Performance of an Optimally Tuned Range-Separated Hybrid Functional for 0-0 Electronic Excitation Energies.

PubMed

Jacquemin, Denis; Moore, Barry; Planchat, Aurélien; Adamo, Carlo; Autschbach, Jochen

2014-04-08

Using a set of 40 conjugated molecules, we assess the performance of an "optimally tuned" range-separated hybrid functional in reproducing the experimental 0-0 energies. The selected protocol accounts for the impact of solvation using a corrected linear-response continuum approach and vibrational corrections through calculations of the zero-point energies of both ground and excited-states and provides basis set converged data thanks to the systematic use of diffuse-containing atomic basis sets at all computational steps. It turns out that an optimally tuned long-range corrected hybrid form of the Perdew-Burke-Ernzerhof functional, LC-PBE*, delivers both the smallest mean absolute error (0.20 eV) and standard deviation (0.15 eV) of all tested approaches, while the obtained correlation (0.93) is large but remains slightly smaller than its M06-2X counterpart (0.95). In addition, the efficiency of two other recently developed exchange-correlation functionals, namely SOGGA11-X and ωB97X-D, has been determined in order to allow more complete comparisons with previously published data.
Characterizing pixel and point patterns with a hyperuniformity disorder length

NASA Astrophysics Data System (ADS)

Chieco, A. T.; Dreyfus, R.; Durian, D. J.

2017-09-01

We introduce the concept of a "hyperuniformity disorder length" h that controls the variance of volume fraction fluctuations for randomly placed windows of fixed size. In particular, fluctuations are determined by the average number of particles within a distance h from the boundary of the window. We first compute special expectations and bounds in d dimensions, and then illustrate the range of behavior of h versus window size L by analyzing several different types of simulated two-dimensional pixel patterns—where particle positions are stored as a binary digital image in which pixels have value zero if empty and one if they contain a particle. The first are random binomial patterns, where pixels are randomly flipped from zero to one with probability equal to area fraction. These have long-ranged density fluctuations, and simulations confirm the exact result h =L /2 . Next we consider vacancy patterns, where a fraction f of particles on a lattice are randomly removed. These also display long-range density fluctuations, but with h =(L /2 )(f /d ) for small f , and h =L /2 for f →1 . And finally, for a hyperuniform system with no long-range density fluctuations, we consider "Einstein patterns," where each particle is independently displaced from a lattice site by a Gaussian-distributed amount. For these, at large L ,h approaches a constant equal to about half the root-mean-square displacement in each dimension. Then we turn to gray-scale pixel patterns that represent simulated arrangements of polydisperse particles, where the volume of a particle is encoded in the value of its central pixel. And we discuss the continuum limit of point patterns, where pixel size vanishes. In general, we thus propose to quantify particle configurations not just by the scaling of the density fluctuation spectrum but rather by the real-space spectrum of h (L ) versus L . We call this approach "hyperuniformity disorder length spectroscopy".
Characterizing pixel and point patterns with a hyperuniformity disorder length.

PubMed

Chieco, A T; Dreyfus, R; Durian, D J

2017-09-01

We introduce the concept of a "hyperuniformity disorder length" h that controls the variance of volume fraction fluctuations for randomly placed windows of fixed size. In particular, fluctuations are determined by the average number of particles within a distance h from the boundary of the window. We first compute special expectations and bounds in d dimensions, and then illustrate the range of behavior of h versus window size L by analyzing several different types of simulated two-dimensional pixel patterns-where particle positions are stored as a binary digital image in which pixels have value zero if empty and one if they contain a particle. The first are random binomial patterns, where pixels are randomly flipped from zero to one with probability equal to area fraction. These have long-ranged density fluctuations, and simulations confirm the exact result h=L/2. Next we consider vacancy patterns, where a fraction f of particles on a lattice are randomly removed. These also display long-range density fluctuations, but with h=(L/2)(f/d) for small f, and h=L/2 for f→1. And finally, for a hyperuniform system with no long-range density fluctuations, we consider "Einstein patterns," where each particle is independently displaced from a lattice site by a Gaussian-distributed amount. For these, at large L,h approaches a constant equal to about half the root-mean-square displacement in each dimension. Then we turn to gray-scale pixel patterns that represent simulated arrangements of polydisperse particles, where the volume of a particle is encoded in the value of its central pixel. And we discuss the continuum limit of point patterns, where pixel size vanishes. In general, we thus propose to quantify particle configurations not just by the scaling of the density fluctuation spectrum but rather by the real-space spectrum of h(L) versus L. We call this approach "hyperuniformity disorder length spectroscopy".

Nonlocal and Nonadiabatic Effects in the Charge-Density Response of Solids: A Time-Dependent Density-Functional Approach

NASA Astrophysics Data System (ADS)

Panholzer, Martin; Gatti, Matteo; Reining, Lucia

2018-04-01

The charge-density response of extended materials is usually dominated by the collective oscillation of electrons, the plasmons. Beyond this feature, however, intriguing many-body effects are observed. They cannot be described by one of the most widely used approaches for the calculation of dielectric functions, which is time-dependent density functional theory (TDDFT) in the adiabatic local density approximation (ALDA). Here, we propose an approximation to the TDDFT exchange-correlation kernel which is nonadiabatic and nonlocal. It is extracted from correlated calculations in the homogeneous electron gas, where we have tabulated it for a wide range of wave vectors and frequencies. A simple mean density approximation allows one to use it in inhomogeneous materials where the density varies on a scale of 1.6 rs or faster. This kernel contains effects that are completely absent in the ALDA; in particular, it correctly describes the double plasmon in the dynamic structure factor of sodium, and it shows the characteristic low-energy peak that appears in systems with low electronic density. It also leads to an overall quantitative improvement of spectra.
Nonlocal and Nonadiabatic Effects in the Charge-Density Response of Solids: A Time-Dependent Density-Functional Approach.

PubMed

Panholzer, Martin; Gatti, Matteo; Reining, Lucia

2018-04-20

The charge-density response of extended materials is usually dominated by the collective oscillation of electrons, the plasmons. Beyond this feature, however, intriguing many-body effects are observed. They cannot be described by one of the most widely used approaches for the calculation of dielectric functions, which is time-dependent density functional theory (TDDFT) in the adiabatic local density approximation (ALDA). Here, we propose an approximation to the TDDFT exchange-correlation kernel which is nonadiabatic and nonlocal. It is extracted from correlated calculations in the homogeneous electron gas, where we have tabulated it for a wide range of wave vectors and frequencies. A simple mean density approximation allows one to use it in inhomogeneous materials where the density varies on a scale of 1.6 r_{s} or faster. This kernel contains effects that are completely absent in the ALDA; in particular, it correctly describes the double plasmon in the dynamic structure factor of sodium, and it shows the characteristic low-energy peak that appears in systems with low electronic density. It also leads to an overall quantitative improvement of spectra.
Effect of the lithospheric thermal state on the Moho interface: A case study in South America

NASA Astrophysics Data System (ADS)

Bagherbandi, Mohammad; Bai, Yongliang; Sjöberg, Lars E.; Tenzer, Robert; Abrehdary, Majid; Miranda, Silvia; Alcacer Sanchez, Juan M.

2017-07-01

Gravimetric methods applied for Moho recovery in areas with sparse and irregular distribution of seismic data often assume only a constant crustal density. Results of latest studies, however, indicate that corrections for crustal density heterogeneities could improve the gravimetric result, especially in regions with a complex geologic/tectonic structure. Moreover, the isostatic mass balance reflects also the density structure within the lithosphere. The gravimetric methods should therefore incorporate an additional correction for the lithospheric mantle as well as deeper mantle density heterogeneities. Following this principle, we solve the Vening Meinesz-Moritz (VMM) inverse problem of isostasy constrained by seismic data to determine the Moho depth of the South American tectonic plate including surrounding oceans, while taking into consideration the crustal and mantle density heterogeneities. Our numerical result confirms that contribution of sediments significantly modifies the estimation of the Moho geometry especially along the continental margins with large sediment deposits. To account for the mantle density heterogeneities we develop and apply a method in order to correct the Moho geometry for the contribution of the lithospheric thermal state (i.e., the lithospheric thermal-pressure correction). In addition, the misfit between the isostatic and seismic Moho models, attributed mainly to deep mantle density heterogeneities and other geophysical phenomena, is corrected for by applying the non-isostatic correction. The results reveal that the application of the lithospheric thermal-pressure correction improves the RMS fit of the VMM gravimetric Moho solution to the CRUST1.0 (improves ∼ 1.9 km) and GEMMA (∼1.1 km) models and the point-wise seismic data (∼0.7 km) in South America.
Bipolar and Monopolar Lithium-Ion Battery Technology at Yardney

NASA Technical Reports Server (NTRS)

Russell, P.; Flynn, J.; Reddy, T.

1996-01-01

Lithium-ion battery systems offer several advantages: intrinsically safe; long cycle life; environmentally friendly; high energy density; wide operating temperature range; good discharge rate capability; low self-discharge; and no memory effect.
Damage Detection for Historical Architectures Based on Tls Intensity Data

NASA Astrophysics Data System (ADS)

Li, Q.; Cheng, X.

2018-04-01

TLS (Terrestrial Laser Scanner) has long been preferred in the cultural heritage field for 3D documentation of historical sites thanks to its ability to acquire the geometric information without any physical contact. Besides the geometric information, most TLS systems also record the intensity information, which is considered as an important measurement of the spectral property of the scanned surface. Recent studies have shown the potential of using intensity for damage detection. However, the original intensity is affected by scanning geometry such as range and incidence angle and other factors, thus making the results less accurate. Therefore, in this paper, we present a method to detect certain damage areas using the corrected intensity data. Firstly, two data-driven models have been developed to correct the range and incidence angle effect. Then the corrected intensity is used to generate 2D intensity images for classification. After the damage areas being detected, they are re-projected to the 3D point cloud for better visual representation and further investigation. The experiment results indicate the feasibility and validity of the corrected intensity for damage detection.
Burst and inter-burst duration statistics as empirical test of long-range memory in the financial markets

NASA Astrophysics Data System (ADS)

Gontis, V.; Kononovicius, A.

2017-10-01

We address the problem of long-range memory in the financial markets. There are two conceptually different ways to reproduce power-law decay of auto-correlation function: using fractional Brownian motion as well as non-linear stochastic differential equations. In this contribution we address this problem by analyzing empirical return and trading activity time series from the Forex. From the empirical time series we obtain probability density functions of burst and inter-burst duration. Our analysis reveals that the power-law exponents of the obtained probability density functions are close to 3 / 2, which is a characteristic feature of the one-dimensional stochastic processes. This is in a good agreement with earlier proposed model of absolute return based on the non-linear stochastic differential equations derived from the agent-based herding model.
Electrical conductivity of the Earth's mantle after one year of SWARM magnetic field measurements

NASA Astrophysics Data System (ADS)

Civet, François; Thebault, Erwan; Verhoeven, Olivier; Langlais, Benoit; Saturnino, Diana

2015-04-01

We present a global EM induction study using L1b Swarm satellite magnetic field measurements data down to a depth of 2000 km. Starting from raw measurements, we first derive a model for the main magnetic field, correct the data for a lithospheric field model, and further select the data to reduce the contributions of the ionospheric field. These computations allowed us to keep a full control on the data processes. We correct residual field from outliers and estimate the spherical harmonic coefficients of the transient field for periods between 2 and 256 days. We used full latitude range and all local times to keep a maximum amount of data. We perform a Bayesian inversion and construct a Markov chain during which model parameters are randomly updated at each iteration. We first consider regular layers of equal thickness and extra layers are added where conductivity contrast between successive layers exceed a threshold value. The mean and maximum likelihood of the electrical conductivity profile is then estimated from the probability density function. The obtained profile particularly shows a conductivity jump in the 600-700 km depth range, consistent with the olivine phase transition at 660 km depth. Our study is the first one to show such a conductivity increase in this depth range without any a priori informations on the internal strucutres. Assuming a pyrolitic mantle composition, this profile is interpreted in terms of temperature variations in the depth range where the probability density function is the narrowest. We finally obtained a temperature gradient in the lower mantle close to adiabatic.
The liquid-vapor equilibria of TIP4P/2005 and BLYPSP-4F water models determined through direct simulations of the liquid-vapor interface.

PubMed

Hu, Hongyi; Wang, Feng

2015-06-07

In this paper, the surface tension and critical properties for the TIP4P/2005 and BLYPSP-4F models are reported. A clear dependence of surface tension on the van der Waals cutoff radius (rvdw) is shown when van der Waals interactions are modeled with a simple cutoff scheme. A linear extrapolation formula is proposed that can be used to determine the infinite rvdw surface tension through a few simulations with finite rvdw. A procedure for determining liquid and vapor densities is proposed that does not require fitting to a profile function. Although the critical temperature of water is also found to depend on the choice of rvdw, the dependence is weaker. We argue that a rvdw of 1.75 nm is a good compromise for water simulations when long-range van der Waals correction is not applied. Since the majority of computational programs do not support rigorous treatment of long-range dispersion, the establishment of a minimal acceptable rvdw is important for the simulation of a variety of inhomogeneous systems, such as water bubbles, and water in confined environments. The BLYPSP-4F model predicts room temperature surface tension marginally better than TIP4P/2005 but overestimates the critical temperature. This is expected since only liquid configurations were fit during the development of the BLYPSP-4F potential. The potential is expected to underestimate the stability of vapor and thus overestimate the region of stability for the liquid.
Dynamic Simulation of Random Packing of Polydispersive Fine Particles

NASA Astrophysics Data System (ADS)

Ferraz, Carlos Handrey Araujo; Marques, Samuel Apolinário

2018-02-01

In this paper, we perform molecular dynamic (MD) simulations to study the two-dimensional packing process of both monosized and random size particles with radii ranging from 1.0 to 7.0 μm. The initial positions as well as the radii of five thousand fine particles were defined inside a rectangular box by using a random number generator. Both the translational and rotational movements of each particle were considered in the simulations. In order to deal with interacting fine particles, we take into account both the contact forces and the long-range dispersive forces. We account for normal and static/sliding tangential friction forces between particles and between particle and wall by means of a linear model approach, while the long-range dispersive forces are computed by using a Lennard-Jones-like potential. The packing processes were studied assuming different long-range interaction strengths. We carry out statistical calculations of the different quantities studied such as packing density, mean coordination number, kinetic energy, and radial distribution function as the system evolves over time. We find that the long-range dispersive forces can strongly influence the packing process dynamics as they might form large particle clusters, depending on the intensity of the long-range interaction strength.
[Endothelial keratoplasty: Descemet stripping (DSEK) using TAN EndoGlide™ device: case series].

PubMed

Pazos, Henrique Santiago Baltar; Pazos, Paula Fernanda Morais Ramalho Baltar; Nogueira Filho, Pedro Antônio; Grisolia, Ana Beatriz Diniz; Silva, André Berger Emiliano; Gomes, José Álvaro Pereira

2011-01-01

To report the results of Descemet stripping endothelial keratoplasty (DSEK) using the TAN EndoGlideTM device to facilitate the insertion of the endothelial membrane. Prospective clinical study that included nine patients presenting corneal edema secondary to endothelial dysfunction. Best corrected visual acuity, refraction, central corneal thickness, endothelial cell density and complications were analyzed after a six-month follow-up. There was a significant improvement in the corneal edema and visual acuity in 7 patients (77.78%). The best corrected visual acuity ranged between 20/40 and 20/200. The average density of endothelial cells in six months varied between 1,305 cells/mm² and 2,346 cells/mm² with an average loss of 33.14% cells. Detachment of part of the graft was observed in one eye (11.11%) and primary failure of the endothelial transplantation occurred in 2 eyes (22.22%). The device TAN EndoGlideTM facilitates the introduction of the graft in Descemet stripping endothelial keratoplasty.
Energy density in the Maxwell-Chern-Simons theory

NASA Astrophysics Data System (ADS)

Wesolowski, Denne; Hosotani, Yutaka; Chakravarty, Sumantra

1994-12-01

A two-dimensional nonrelativistic fermion system coupled to both electromagnetic gauge fields and Chern-Simons gauge fields is analyzed. Polarization tensors relevant in the quantum Hall effect and anyon superconductivity are obtained as simple closed integrals and are evaluated numerically for all momenta and frequencies. The correction to the energy density is evaluated in the random phase approximation (RPA) by summing an infinite series of ring diagrams. It is found that the correction has significant dependence on the particle number density. In the context of anyon superconductivity, the energy density relative to the mean field value is minimized at a hole concentration per lattice plaquette (0.05-0.06)(pca/ħ)2 where pc and a are the momentum cutoff and lattice constant, respectively. At the minimum the correction is about -5% to -25%, depending on the ratio 2mwc/p2c where wc is the frequency cutoff. In the Jain-Fradkin-Lopez picture of the fractional quantum Hall effect the RPA correction to the energy density is very large. It diverges logarithmically as the cutoff is removed, implying that corrections beyond RPA become important at large momentum and frequency.
The effect of retained intramedullary nails on tibial bone mineral density.

PubMed

Allen, J C; Lindsey, R W; Hipp, J A; Gugala, Z; Rianon, N; LeBlanc, A

2008-07-01

Intramedullary nailing has become a standard treatment for adult tibial shaft fractures. Retained intramedullary nails have been associated with stress shielding, although their long-term effect on decreasing tibial bone mineral density is currently unclear. The purpose of this study was to determine if retained tibial intramedullary nails decrease tibial mineral density in patients with successfully treated fractures. Patients treated with statically locked intramedullary nails for isolated, unilateral tibia shaft fractures were studied. Inclusion required that fracture had healed radiographically and that the patient returned to the pre-injury activity level. Data on patient demographic, fracture type, surgical technique, implant, and post-operative functional status were tabulated. Dual energy X-ray absorptiometry was used to measure bone mineral density in selected regions of the affected tibia and the contralateral intact tibia. Image reconstruction software was employed to ensure symmetry of the studied regions. Twenty patients (mean age 43; range 22-77 years) were studied at a mean of 29 months (range 5-60 months) following intramedullary nailing. There was statistically significant reduction of mean bone mineral density in tibiae with retained intramedullary nails (1.02 g/cm(2) versus 1.06 g/cm(2); P=0.04). A significantly greater decrease in bone mineral density was detected in the reamed versus non-reamed tibiae (-7% versus +6%, respectively; P<0.05). The present study demonstrates a small, but statistically significant overall bone mineral density decrease in healed tibiae with retained nails. Intramedullary reaming appears to be a factor potentiating the reduction of tibia bone mineral density in long-term nail retention.
On the normalization of the minimum free energy of RNAs by sequence length.

PubMed

Trotta, Edoardo

2014-01-01

The minimum free energy (MFE) of ribonucleic acids (RNAs) increases at an apparent linear rate with sequence length. Simple indices, obtained by dividing the MFE by the number of nucleotides, have been used for a direct comparison of the folding stability of RNAs of various sizes. Although this normalization procedure has been used in several studies, the relationship between normalized MFE and length has not yet been investigated in detail. Here, we demonstrate that the variation of MFE with sequence length is not linear and is significantly biased by the mathematical formula used for the normalization procedure. For this reason, the normalized MFEs strongly decrease as hyperbolic functions of length and produce unreliable results when applied for the comparison of sequences with different sizes. We also propose a simple modification of the normalization formula that corrects the bias enabling the use of the normalized MFE for RNAs longer than 40 nt. Using the new corrected normalized index, we analyzed the folding free energies of different human RNA families showing that most of them present an average MFE density more negative than expected for a typical genomic sequence. Furthermore, we found that a well-defined and restricted range of MFE density characterizes each RNA family, suggesting the use of our corrected normalized index to improve RNA prediction algorithms. Finally, in coding and functional human RNAs the MFE density appears scarcely correlated with sequence length, consistent with a negligible role of thermodynamic stability demands in determining RNA size.
On the Normalization of the Minimum Free Energy of RNAs by Sequence Length

PubMed Central

Trotta, Edoardo

2014-01-01

The minimum free energy (MFE) of ribonucleic acids (RNAs) increases at an apparent linear rate with sequence length. Simple indices, obtained by dividing the MFE by the number of nucleotides, have been used for a direct comparison of the folding stability of RNAs of various sizes. Although this normalization procedure has been used in several studies, the relationship between normalized MFE and length has not yet been investigated in detail. Here, we demonstrate that the variation of MFE with sequence length is not linear and is significantly biased by the mathematical formula used for the normalization procedure. For this reason, the normalized MFEs strongly decrease as hyperbolic functions of length and produce unreliable results when applied for the comparison of sequences with different sizes. We also propose a simple modification of the normalization formula that corrects the bias enabling the use of the normalized MFE for RNAs longer than 40 nt. Using the new corrected normalized index, we analyzed the folding free energies of different human RNA families showing that most of them present an average MFE density more negative than expected for a typical genomic sequence. Furthermore, we found that a well-defined and restricted range of MFE density characterizes each RNA family, suggesting the use of our corrected normalized index to improve RNA prediction algorithms. Finally, in coding and functional human RNAs the MFE density appears scarcely correlated with sequence length, consistent with a negligible role of thermodynamic stability demands in determining RNA size. PMID:25405875
Heavy and Light Quarks with Lattice Chiral Fermions

NASA Astrophysics Data System (ADS)

Liu, K. F.; Dong, S. J.

The feasibility of using lattice chiral fermions which are free of O(a) errors for both the heavy and light quarks is examined. The fact that the effective quark propagators in these fermions have the same form as that in the continuum with the quark mass being only an additive parameter to a chirally symmetric anti-Hermitian Dirac operator is highlighted. This implies that there is no distinction between the heavy and light quarks and no mass dependent tuning of the action or operators as long as the discretization error O(m2a2) is negligible. Using the overlap fermion, we find that the O(m2a2) (and O(ma2)) errors in the dispersion relations of the pseudoscalar and vector mesons and the renormalization of the axial-vector current and scalar density are small. This suggests that the applicable range of ma may be extended to ~0.56 with only 5% error, which is a factor of ~2.4 larger than the corresponding range of the improved Wilson action. We show that the generalized Gell-Mann-Oakes-Renner relation with unequal masses can be utilized to determine the finite ma corrections in the renormalization of the matrix elements for the heavy-light decay constants and semileptonic decay constants of the B/D meson.
Development of Coarse Grained Models for Long Chain Alkanes

NASA Astrophysics Data System (ADS)

Gyawali, Gaurav; Sternfield, Samuel; Hwang, In Chul; Rick, Steven; Kumar, Revati; Rick Group Team; Kumar Group Team

Modeling aggregation in aqueous solution is a challenge for molecular simulations as it involves long time scales, a range of length scales, and the correct balance of hydrophobic and hydrophilic interactions. We have developed a coarse-grained model fast enough for the rapid testing of molecular structures for their aggregation properties. This model, using the Stillinger-Weber potential, achieves efficiency through a reduction in the number of interaction sites and the use of short-ranged interactions. The model can be two to three orders of magnitude more efficient than conventional all atom simulations, yet through a careful parameterization process and the use of many-body interactions can be remarkably accurate. We have developed models for long chain alkanes in water that reproduce the thermodynamics and structure of water-alkane and liquid alkane systems.
Locality of correlation in density functional theory.

PubMed

Burke, Kieron; Cancio, Antonio; Gould, Tim; Pittalis, Stefano

2016-08-07

The Hohenberg-Kohn density functional was long ago shown to reduce to the Thomas-Fermi (TF) approximation in the non-relativistic semiclassical (or large-Z) limit for all matter, i.e., the kinetic energy becomes local. Exchange also becomes local in this limit. Numerical data on the correlation energy of atoms support the conjecture that this is also true for correlation, but much less relevant to atoms. We illustrate how expansions around a large particle number are equivalent to local density approximations and their strong relevance to density functional approximations. Analyzing highly accurate atomic correlation energies, we show that EC → -AC ZlnZ + BCZ as Z → ∞, where Z is the atomic number, AC is known, and we estimate BC to be about 37 mhartree. The local density approximation yields AC exactly, but a very incorrect value for BC, showing that the local approximation is less relevant for the correlation alone. This limit is a benchmark for the non-empirical construction of density functional approximations. We conjecture that, beyond atoms, the leading correction to the local density approximation in the large-Z limit generally takes this form, but with BC a functional of the TF density for the system. The implications for the construction of approximate density functionals are discussed.
Metastability and avalanche dynamics in strongly correlated gases with long-range interactions

NASA Astrophysics Data System (ADS)

Hruby, Lorenz; Dogra, Nishant; Landini, Manuele; Donner, Tobias; Esslinger, Tilman

2018-03-01

We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity. The scattering comes with an atomic density modulation, which is measured by the photon flux leaking from the cavity. We initialize the system in a Mott-insulating state and then rapidly increase the global coupling strength. We observe that the system falls into either of two distinct final states. One is characterized by a low photon flux, signaling a Mott insulator, and the other is characterized by a high photon flux, which we associate with a density wave. Ramping the global coupling slowly, we observe a hysteresis loop between the two states—a further signature of metastability. A comparison with a theoretical model confirms that the metastability originates in the competition between short- and global-range interactions. From the increasing photon flux monitored during the switching process, we find that several thousand atoms tunnel to a neighboring site on the timescale of the single-particle dynamics. We argue that a density modulation, initially forming in the compressible surface of the trapped gas, triggers an avalanche tunneling process in the Mott-insulating region.
Electronic and Spectral Properties of RRhSn (R = Gd, Tb) Intermetallic Compounds

NASA Astrophysics Data System (ADS)

Knyazev, Yu. V.; Lukoyanov, A. V.; Kuz'min, Yu. I.; Gupta, S.; Suresh, K. G.

2018-02-01

The investigations of electronic structure and optical properties of GdRhSn and TbRhSn were carried out. The calculations of band spectrum, taking into account the spin polarization, were performed in a local electron density approximation with a correction for strong correlation effects in 4f shell of rare earth metal (LSDA + U method). The optical studies were done by ellipsometry in a wide range of wavelengths, and the set of spectral and electronic characteristics was determined. It was shown that optical absorption in a region of interband transitions has a satisfactory explanation within a scope of calculations of density of electronic states carried out.
Understanding the atmospheric measurement and behavior of perfluorooctanoic acid.

PubMed

Webster, Eva M; Ellis, David A

2012-09-01

The recently reported quantification of the atmospheric sampling artifact for perfluorooctanoic acid (PFOA) was applied to existing gas and particle concentration measurements. Specifically, gas phase concentrations were increased by a factor of 3.5 and particle-bound concentrations by a factor of 0.1. The correlation constants in two particle-gas partition coefficient (K(QA)) estimation equations were determined for multiple studies with and without correcting for the sampling artifact. Correction for the sampling artifact gave correlation constants with improved agreement to those reported for other neutral organic contaminants, thus supporting the application of the suggested correction factors for perfluorinated carboxylic acids. Applying the corrected correlation constant to a recent multimedia modeling study improved model agreement with corrected, reported, atmospheric concentrations. This work confirms that there is sufficient partitioning to the gas phase to support the long-range atmospheric transport of PFOA. Copyright © 2012 SETAC.

Training apartment upkeep skills to rehabilitation clients: a comparison of task analytic strategies.

PubMed Central

Williams, G E; Cuvo, A J

1986-01-01

The research was designed to validate procedures to teach apartment upkeep skills to severely handicapped clients with various categorical disabilities. Methodological features of this research included performance comparisons between general and specific task analyses, effect of an impasse correction baseline procedure, social validation of training goals, natural environment assessments and contingencies, as well as long-term follow-up. Subjects were taught to perform upkeep responses on their air conditioner-heating unit, electric range, refrigerator, and electrical appliances within the context of a multiple-probe across subjects experimental design. The results showed acquisition, long-term maintenance, and generalization of the upkeep skills to a nontraining apartment. General task analyses were recommended for assessment and specific task analyses for training. The impasse correction procedure generally did not produce acquisition. PMID:3710947
Continuous light absorption photometer for long-term studies

NASA Astrophysics Data System (ADS)

Ogren, John A.; Wendell, Jim; Andrews, Elisabeth; Sheridan, Patrick J.

2017-12-01

A new photometer is described for continuous determination of the aerosol light absorption coefficient, optimized for long-term studies of the climate-forcing properties of aerosols. Measurements of the light attenuation coefficient are made at blue, green, and red wavelengths, with a detection limit of 0.02 Mm-1 and a precision of 4 % for hourly averages. The uncertainty of the light absorption coefficient is primarily determined by the uncertainty of the correction scheme commonly used to convert the measured light attenuation to light absorption coefficient and ranges from about 20 % at sites with high loadings of strongly absorbing aerosols up to 100 % or more at sites with low loadings of weakly absorbing aerosols. Much lower uncertainties (ca. 40 %) for the latter case can be achieved with an advanced correction scheme.
On corrected formula for irradiated graphene quantum conductivity

NASA Astrophysics Data System (ADS)

Firsova, N. E.

2017-09-01

Graphene membrane irradiated by weak activating periodic electric field in terahertz range is considered. The corrected formula for the graphene quantum conductivity is found. The obtained formula gives complex conjugate results when radiation polarization direction is clockwise or it is opposite clockwise. The found formula allows us to see that the graphene membrane is an oscillating contour. Its eigen frequency coincides with a singularity point of the conductivity and depends on the electrons concentration. So the graphene membrane could be used as an antenna or a transistor and its eigen frequency could be tuned by doping in a large terahertz-infrared frequency range. The obtained formula allows us also to calculate the graphene membrane quantum inductivity and capacitance. The found dependence on electrons concentration is consistent with experiments. The method of the proof is based on study of the time-dependent density matrix. The exact solution of von Neumann equation for density matrix is found for our case in linear approximation on the external field. On this basis the induced current is studied and then the formula for quantum conductivity as a function of external field frequency and temperature is obtained. The method of the proof suggested in this paper could be used to study other problems. The found formula for quantum conductivity can be used to correct the SPPs Dispersion Relation and for the description of radiation process. It would be useful to take the obtained results into account when constructing devices containing graphene membrane nanoantenna. Such project could make it possible to create wireless communications among nanosystems. This would be promising research area of energy harvesting applications.
Ship Effect Neutron Measurements And Impacts On Low-Background Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aguayo Navarrete, Estanislao; Kouzes, Richard T.; Siciliano, Edward R.

2013-10-01

The primary particles entering the upper atmosphere as cosmic rays create showers in the atmosphere that include a broad spectrum of secondary neutrons, muons and protons. These cosmic-ray secondaries interact with materials at the surface of the Earth, yielding prompt backgrounds in radiation detection systems, as well as inducing long-lived activities through spallation events, dominated by the higher-energy neutron secondaries. For historical reasons, the multiple neutrons produced in spallation cascade events are referred to as “ship effect” neutrons. Quantifying the background from cosmic ray induced activities is important to low-background experiments, such as neutrino-less double beta decay. Since direct measurementsmore » of the effects of shielding on the cosmic-ray neutron spectrum are not available, Monte Carlo modeling is used to compute such effects. However, there are large uncertainties (orders of magnitude) in the possible cross-section libraries and the cosmic-ray neutron spectrum for the energy range needed in such calculations. The measurements reported here were initiated to validate results from Monte Carlo models through experimental measurements in order to provide some confidence in the model results. The results indicate that the models provide the correct trends of neutron production with increasing density, but there is substantial disagreement between the model and experimental results for the lower-density materials of Al, Fe and Cu.« less
Total carbon and nitrogen in mineral soil after 26 years of prescribed fire: Long Valley and Fort Valley Experimental Forests (P-53)

Treesearch

Daniel G. Neary; Sally M. Haase; Steven T. Overby

2008-01-01

Prescribed fire was introduced to high density ponderosa pine stands at Fort Valley and Long Valley Experimental Forests in 1976. This paper reports on mineral soil total carbon (C) and nitrogen (N) at Long Valley. Total soil C and N levels were highly variable and exhibited an increasing, but inconsistent, concentration trend related to burn interval. Total N ranged...
DOE Office of Scientific and Technical Information (OSTI.GOV)

Dósa, M.; Erdős, G., E-mail: dosa.melinda@wigner.mta.hu

Open magnetic flux in the heliosphere is determined from the radial component of the magnetic field vector measured onboard interplanetary space probes. Previous Ulysses research has shown remarkable independence of the flux density from heliographic latitude, explained by super-radial expansion of plasma. Here we are investigating whether any longitudinal variation exists in the 50 year long OMNI magnetic data set. The heliographic longitude of origin of the plasma package was determined by applying a correction according to the solar wind travel time. Significant recurrent enhancements of the magnetic flux density were observed throughout solar cycle 23, lasting for several years.more » Similar, long-lasting recurring features were observed in the solar wind velocity, temperature and the deviation angle of the solar wind velocity vector from the radial direction. Each of the recurrent features has a recurrence period slightly differing from the Carrington rotation rate, although they show a common trend in time. Examining the coronal temperature data of ACE leads to the possible explanation that these long-term structures are caused by slow–fast solar wind interaction regions. A comparison with MESSENGER data measured at 0.5 au shows that these longitudinal magnetic modulations do not exist closer to the Sun, but are the result of propagation.« less
Phase separation and long-wavelength charge instabilities in spin-orbit coupled systems

NASA Astrophysics Data System (ADS)

Seibold, G.; Bucheli, D.; Caprara, S.; Grilli, M.

2015-01-01

We investigate a two-dimensional electron model with Rashba spin-orbit interaction where the coupling constant g=g(n) depends on the electronic density. It is shown that this dependence may drive the system unstable towards a long-wavelength charge density wave (CDW) where the associated second-order instability occurs in close vicinity to global phase separation. For very low electron densities the CDW instability is nesting-induced and the modulation follows the Fermi momentum kF. At higher density the instability criterion becomes independent of kF and the system may become unstable in a broad momentum range. Finally, upon filling the upper spin-orbit split band, finite momentum instabilities disappear in favor of phase separation alone. We discuss our results with regard to the inhomogeneous phases observed at the LaAlO3/SrTiO3 or LaTiO3/SrTiO3 interfaces.
Non-pairwise additivity of the leading-order dispersion energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hollett, Joshua W., E-mail: j.hollett@uwinnipeg.ca

2015-02-28

The leading-order (i.e., dipole-dipole) dispersion energy is calculated for one-dimensional (1D) and two-dimensional (2D) infinite lattices, and an infinite 1D array of infinitely long lines, of doubly occupied locally harmonic wells. The dispersion energy is decomposed into pairwise and non-pairwise additive components. By varying the force constant and separation of the wells, the non-pairwise additive contribution to the dispersion energy is shown to depend on the overlap of density between neighboring wells. As well separation is increased, the non-pairwise additivity of the dispersion energy decays. The different rates of decay for 1D and 2D lattices of wells is explained inmore » terms of a Jacobian effect that influences the number of nearest neighbors. For an array of infinitely long lines of wells spaced 5 bohrs apart, and an inter-well spacing of 3 bohrs within a line, the non-pairwise additive component of the leading-order dispersion energy is −0.11 kJ mol{sup −1} well{sup −1}, which is 7% of the total. The polarizability of the wells and the density overlap between them are small in comparison to that of the atomic densities that arise from the molecular density partitioning used in post-density-functional theory (DFT) damped dispersion corrections, or DFT-D methods. Therefore, the nonadditivity of the leading-order dispersion observed here is a conservative estimate of that in molecular clusters.« less
An accurate analytic description of neutrino oscillations in matter

NASA Astrophysics Data System (ADS)

Akhmedov, E. Kh.; Niro, Viviana

2008-12-01

A simple closed-form analytic expression for the probability of two-flavour neutrino oscillations in a matter with an arbitrary density profile is derived. Our formula is based on a perturbative expansion and allows an easy calculation of higher order corrections. The expansion parameter is small when the density changes relatively slowly along the neutrino path and/or neutrino energy is not very close to the Mikheyev-Smirnov-Wolfenstein (MSW) resonance energy. Our approximation is not equivalent to the adiabatic approximation and actually goes beyond it. We demonstrate the validity of our results using a few model density profiles, including the PREM density profile of the Earth. It is shown that by combining the results obtained from the expansions valid below and above the MSW resonance one can obtain a very good description of neutrino oscillations in matter in the entire energy range, including the resonance region.
Variational Problems with Long-Range Interaction

NASA Astrophysics Data System (ADS)

Soave, Nicola; Tavares, Hugo; Terracini, Susanna; Zilio, Alessandro

2018-06-01

We consider a class of variational problems for densities that repel each other at a distance. Typical examples are given by the Dirichlet functional and the Rayleigh functional D(u) = \\sum_{i=1}^k \\int_{Ω} |\
CRUST 5.1: A global crustal model at 5° x 5°

USGS Publications Warehouse

Mooney, Walter D.; Laske, Gabi; Masters, T. Guy

1998-01-01

We present a new global model for the Earth's crust based on seismic refraction data published in the period 1948–1995 and a detailed compilation of ice and sediment thickness. An extensive compilation of seismic refraction measurements has been used to determine the crustal structure on continents and their margins. Oceanic crust is modeled with both a standard model for normal oceanic crust, and variants for nonstandard regions, such as oceanic plateaus. Our model (CRUST 5.1) consists of 2592 5° × 5° tiles in which the crust and uppermost mantle are described by eight layers: (1) ice, (2) water, (3) soft sediments, (4) hard sediments, (5) crystalline upper, (6) middle, (7) lower crust, and (8) uppermost mantle. Topography and bathymetry are adopted from a standard database (ETOPO-5). Compressional wave velocity in each layer is based on field measurements, and shear wave velocity and density are estimated using recently published empirical Vp- Vs and Vp-density relationships. The crustal model differs from previous models in that (1) the thickness and seismic/density structure of sedimentary basins is accounted for more completely, (2) the velocity structure of unmeasured regions is estimated using statistical averages that are based on a significantly larger database of crustal structure, (3) the compressional wave, shear wave, and density structure have been explicitly specified using newly available constraints from field and laboratory studies. Thus this global crustal model is based on substantially more data than previous models and differs from them in many important respects. A new map of the thickness of the Earth's crust is presented, and we illustrate the application of this model by using it to provide the crustal correction for surface wave phase velocity maps. Love waves at 40 s are dominantly sensitive to crustal structure, and there is a very close correspondence between observed phase velocities at this period and those predicted by CRUST 5.1. We find that the application of crustal corrections to long-period (167 s) Rayleigh waves significantly increases the variance in the phase velocity maps and strengthens the upper mantle velocity anomalies beneath stable continental regions. A simple calculation of crustal isostacy indicates significant lateral variations in upper mantle density. The model CRUST 5.1 provides a complete description of the physical properties of the Earth's crust at a scale of 5° × 5° and can be used for a wide range of seismological and nonseismological problems.
Thermal effects in supernova matter

NASA Astrophysics Data System (ADS)

Constantinou, Constantinos

A crucial ingredient in simulations of core collapse supernova (SN) explosions is the equation of state (EOS) of nucleonic matter for densities extending from 10-7 fm-3 to 1 ffm-3, temperatures up to 50 MeV, and proton-to-baryon fraction in the range 0 to 1/2. SN explosions release 99% of the progenitor star's gravitational potential energy in the form of neutrinos and, additionally, they are responsible for populating the universe with elements heavier than 56Fe. Therefore, the importance of understanding this phenomenon cannot be overstated as it could shed light onto the underlying nuclear and neutrino physics. A realistic EOS of SN matter must incorporate the nucleon-nucleon interaction in a many-body environment. We treat this problem with a non-relativistic potential model as well as relativistic mean-field theoretical one. In the former approach, we employ the Skyrme-like Hamiltonian density constructed by Akmal, Pandharipande, and Ravenhall which takes into account the long scattering lengths of nucleons that determine the low density characteristics. In the latter, we use a Walecka-like Lagrangian density supplemented by non-linear interactions involving scalar, vector, and isovector meson exchanges, calibrated so that known properties of nuclear matter are reproduced. We focus on the bulk homogeneous phase and calculate its thermodynamic properties as functions of baryon density, temperature, and proton-to-baryon ratio. The exact numerical results are then compared to those in the degenerate and non-degenerate limits for which analytical formulae have been derived. We find that the two models bahave similarly for densities up to nuclear saturation but exhibit differences at higher densities most notably in the isospin susceptibilities, the chemical potentials, and the pressure. The importance of the correct momentum dependence in the single particle potential that fits optical potentials of nucleon-nucleus scattering was highlighted in the context of intermediate energy heavy-ion collisions. To explore the effect momentum-dependent interactions have on the thermal properties of dense matter we study a schematic model constructed by Welke et al. in which the appropriate momentum dependence that fits optical potential data is built through finite-range exchange forces of the Yukawa type. We look into the finite-temperature properties of this model in the context of infinite, isospin-symmetric nucleonic matter. The exact numerical results are compared to analytical ones in the quantum regime where we rely on Landau's Fermi-Liquid Theory, and in the classical regime where the state variables are obtained through a steepest descent calculation. Detailed comparisons with similarly calibrated Skyrme models are also performed. We find that the high-density behavior of the thermal pressure is once again a differentiating feature. We attribute this to the temperature dependence of the energy spectrum of the finite-range and the meson-exchange models which leads to a higher specific heat and thus a lower pressure.
Fat fraction bias correction using T1 estimates and flip angle mapping.

PubMed

Yang, Issac Y; Cui, Yifan; Wiens, Curtis N; Wade, Trevor P; Friesen-Waldner, Lanette J; McKenzie, Charles A

2014-01-01

To develop a new method of reducing T1 bias in proton density fat fraction (PDFF) measured with iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). PDFF maps reconstructed from high flip angle IDEAL measurements were simulated and acquired from phantoms and volunteer L4 vertebrae. T1 bias was corrected using a priori T1 values for water and fat, both with and without flip angle correction. Signal-to-noise ratio (SNR) maps were used to measure precision of the reconstructed PDFF maps. PDFF measurements acquired using small flip angles were then compared to both sets of corrected large flip angle measurements for accuracy and precision. Simulations show similar results in PDFF error between small flip angle measurements and corrected large flip angle measurements as long as T1 estimates were within one standard deviation from the true value. Compared to low flip angle measurements, phantom and in vivo measurements demonstrate better precision and accuracy in PDFF measurements if images were acquired at a high flip angle, with T1 bias corrected using T1 estimates and flip angle mapping. T1 bias correction of large flip angle acquisitions using estimated T1 values with flip angle mapping yields fat fraction measurements of similar accuracy and superior precision compared to low flip angle acquisitions. Copyright © 2013 Wiley Periodicals, Inc.
Charge ordering in ionic fluids mediate repulsive surface interactions

NASA Astrophysics Data System (ADS)

Dasbiswas, Kinjal; Ludwig, Nicholas B.; Zhang, Hao; Talapin, Dmitri; Vaikuntanathan, Suri

Recent experiments on ionic fluids, such as surface force measurements in organic ionic liquids and the observation of colloidal stability in inorganic molten salts, suggest the presence of long-ranged repulsive forces. These cannot be explained within the classical Debye-Hückel theory for dilute electrolytes. We argue that such repulsive interactions can arise from long-range (several nm) charge density oscillations induced by a surface that preferentially binds one of the ionic species in an ionic fluid. We present a continuum theory that accounts for such charge layering based on a frustrated Ising model that incorporates both long-range Coulombic and short-range steric interactions. The mean-field analytic treatment qualitatively matches results from molecular simulations. A careful analysis of the ionic correlation functions arising from such charge ordering may also explain the long electrostatic screening lengths observed in various ionic fluids and their non-monotonic dependence on the electrolyte concentration. We acknowledge the University of Chicago for support.
Dark matter and the equivalence principle

NASA Technical Reports Server (NTRS)

Frieman, Joshua A.; Gradwohl, Ben-Ami

1991-01-01

If the dark matter in galaxies and clusters is nonbaryonic, it can interact with additional long-range fields that are invisible to experimental tests of the equivalence principle. The astrophysical and cosmological implications of a long-range force coupled only to the dark matter are discussed and rather tight constraints on its strength are found. If the force is repulsive (attractive), the masses of galaxy groups and clusters (and the mean density of the universe inferred from them) have been systematically underestimated (overestimated). Such an interaction also has unusual implications for the growth of large-scale structure.
Fine Structure of a Laser-Plasma Filament in Air

NASA Astrophysics Data System (ADS)

Eisenmann, Shmuel; Pukhov, Anatoly; Zigler, Arie

2007-04-01

The ability to select and stabilize a single filament during propagation of an ultrashort high-intensity laser pulse in air makes it possible to examine the longitudinal structure of the plasma channel left in its wake. We present detailed measurements of plasma density variations along laser propagation. Over the length of the filament, electron density variations of 3 orders of magnitude are measured. They display evidence of a meter-long postionization range, along which a self-guided structure is observed coupled with a low plasma density, corresponding to ˜3 orders of magnitude decrease from the peak density level.
Principal facts for gravity stations in the Elko, Steptoe Valley, Coyote Spring Valley, and Sheep Range areas, eastern and southern Nevada

USGS Publications Warehouse

Berger, D.L.; Schaefer, D.H.; Frick, E.A.

1990-01-01

Principal facts for 537 gravity stations in the carbonate-rock province of eastern and southern Nevada are tabulated and presented. The gravity data were collected in support of groundwater studies in several valleys. The study areas include the Elko area, northern Steptoe Valley, Coyote Spring Valley, and the western Sheep Range area. The data for each site include values for latitude, longitude, altitude, observed gravity, free- air anomaly, terrain correction, and Bouguer anomaly (calculated at a bedrock density of 2.67 g/cu cm. (USGS)
Patterns of conifer tree regeneration following an autumn wildfire event in the western Oregon Cascade Range, USA.

Treesearch

Andrew J. Larson; Jerry F. Franklin

2005-01-01

We investigated the effect of fire severity and environmental conditions on conifer tree regeneration 11 years after an autumn wildfire in the western Oregon Cascade Range. Conifer tree seedlings, including those of Pseudotsuga menziesii, established promptly and at high densities following fire, in contrast to long establishment periods documented...
Critical role for hierarchical geospatial analyses in the design of fluvial research, assessment, and management

EPA Science Inventory

River science and management can be conducted at a range of spatiotemporal scales from reach to basin levels as long as the project goals and questions are matched correctly with the study design’s spatiotemporal scales and dependent variables. These project goals should also inc...
Range-Separated Brueckner Coupled Cluster Doubles Theory

NASA Astrophysics Data System (ADS)

Shepherd, James J.; Henderson, Thomas M.; Scuseria, Gustavo E.

2014-04-01

We introduce a range-separation approximation to coupled cluster doubles (CCD) theory that successfully overcomes limitations of regular CCD when applied to the uniform electron gas. We combine the short-range ladder channel with the long-range ring channel in the presence of a Bruckner renormalized one-body interaction and obtain ground-state energies with an accuracy of 0.001 a.u./electron across a wide range of density regimes. Our scheme is particularly useful in the low-density and strongly correlated regimes, where regular CCD has serious drawbacks. Moreover, we cure the infamous overcorrelation of approaches based on ring diagrams (i.e., the particle-hole random phase approximation). Our energies are further shown to have appropriate basis set and thermodynamic limit convergence, and overall this scheme promises energetic properties for realistic periodic and extended systems which existing methods do not possess.

Real-Time Quantum Dynamics of Long-Range Electronic Excitation Transfer in Plasmonic Nanoantennas.

PubMed

Ilawe, Niranjan V; Oviedo, M Belén; Wong, Bryan M

2017-08-08

Using large-scale, real-time, quantum dynamics calculations, we present a detailed analysis of electronic excitation transfer (EET) mechanisms in a multiparticle plasmonic nanoantenna system. Specifically, we utilize real-time, time-dependent, density functional tight binding (RT-TDDFTB) to provide a quantum-mechanical description (at an electronic/atomistic level of detail) for characterizing and analyzing these systems, without recourse to classical approximations. We also demonstrate highly long-range electronic couplings in these complex systems and find that the range of these couplings is more than twice the conventional cutoff limit considered by Förster resonance energy transfer (FRET)-based approaches. Furthermore, we attribute these unusually long-ranged electronic couplings to the coherent oscillations of conduction electrons in plasmonic nanoparticles. This long-range nature of plasmonic interactions has important ramifications for EET; in particular, we show that the commonly used "nearest-neighbor" FRET model is inadequate for accurately characterizing EET even in simple plasmonic antenna systems. These findings provide a real-time, quantum-mechanical perspective for understanding EET mechanisms and provide guidance in enhancing plasmonic properties in artificial light-harvesting systems.
Estimating vegetative biomass from LANDSAT-1 imagery for range management

NASA Technical Reports Server (NTRS)

Seevers, P. M.; Drew, J. V.; Carlson, M. P.

1975-01-01

Evaluation of LANDSAT-1, band 5 data for use in estimation of vegetative biomass for range management decisions was carried out for five selected range sites in the Sandhills region of Nebraska. Analysis of sets of optical density-vegetative biomass data indicated that comparisons of biomass estimation could be made within one frame but not between frames without correction factors. There was high correlation among sites within sets of radiance value-vegetative biomass data and also between sets, indicating comparisons of biomass could be made within and between frames. Landsat-1 data are shown to be a viable alternative to currently used methods of determining vegetative biomass production and stocking rate recommendations for Sandhills rangeland.
Probing the role of long-range interactions in the dynamics of a long-range Kitaev chain

NASA Astrophysics Data System (ADS)

Dutta, Anirban; Dutta, Amit

2017-09-01

We study the role of long-range interactions (more precisely, the long-range superconducting gap term) on the nonequilibrium dynamics considering a long-range p -wave superconducting chain in which the superconducting term decays with distance between two sites in a power-law fashion characterized by an exponent α . We show that the Kibble-Zurek scaling exponent, dictating the power-law decay of the defect density in the final state reached following a slow (in comparison to the time scale associated with the minimum gap in the spectrum of the Hamiltonian) quenching of the chemical potential μ across a quantum critical point, depends nontrivially on the exponent α as long as α <2 ; on the other hand, for α >2 , we find that the exponent saturates to the corresponding well-known value of 1 /2 expected for the short-range model. Furthermore, studying the dynamical quantum phase transitions manifested in the nonanalyticities in the rate function of the return possibility I (t ) in subsequent temporal evolution following a sudden change in μ , we show the existence of a new region; in this region, we find three instants of cusp singularities in I (t ) associated with a single sector of Fisher zeros. Notably, the width of this region shrinks as α increases and vanishes in the limit α →2 , indicating that this special region is an artifact of the long-range nature of the Hamiltonian.
Geometric Corrections for Topographic Distortion from Side Scan Sonar Data Obtained by ANKOU System

NASA Astrophysics Data System (ADS)

Yamamoto, Fujio; Kato, Yukihiro; Ogasawara, Shohei

The ANKOU is a newly developed, full ocean depth, long-range vector side scan sonar system. The system provides real time vector side scan sonar data to produce backscattering images and bathymetric maps for seafloor swaths up to 10 km on either side of ship's centerline. Complete geometric corrections are made using towfish attitude and cross-track distortions known as foreshortening and layover caused by violation of the flat bottom assumption. Foreshortening and layover refers to pixels which have been placed at an incorrect cross-track distance. Our correction of this topographic distortion is accomplished by interpolating a bathymetric profile and ANKOU phase data. We applied these processing techniques to ANKOU backscattering data obtained from off Boso Peninsula, and confirmed their efficiency and utility for making geometric corrections of side scan sonar data.
Study of Saturn Electrostatic Discharges in a Wide Range of Timec SCALES

NASA Astrophysics Data System (ADS)

Mylostna, K.; Zakharenko, V.; Konovalenko, A.; Kolyadin, V.; Zarka, P.; Griemeier, J.-M.; Litvinenko, G.; Sidorchuk, M.; Rucker, H.; Fischer, G.; Cecconi, B.; Coffre, A.; Denis, L.; Nikolaenko, V.; Shevchenko, V.

Saturn Electrostatic discharges (SED) are sporadic broadband impulsive radio bursts associated with lightning in Saturnian atmosphere. After 25 years of space investigations in 2006 the first successful observations of SED on the UTR-2 radio telescope were carried out [1]. Since 2007 a long-term program of ED search and study in the Solar system has started. As a part of this program the unique observations with high time resolution were taken in 2010. New possibilities of UTR-2 radio telescope allowed to provide a long-period observations and study with high temporal resolution. This article presents the results of SED study in a wide range of time scales: from seconds to microseconds. For the first time there were obtained a low frequency spectrum of SED. We calculated flux densities of individual bursts at the maximum achievable time resolution. Flux densities of most intensive bursts reach 4200 Jy.
Density of the continental roots: Compositional and thermal contributions

USGS Publications Warehouse

Kaban, M.K.; Schwintzer, P.; Artemieva, I.M.; Mooney, W.D.

2003-01-01

The origin and evolution of cratonic roots has been debated for many years. Precambrian cratons are underlain by cold lithospheric roots that are chemically depleted. Thermal and petrologic data indicate that Archean roots are colder and more chemically depleted than Proterozoic roots. This observation has led to the hypothesis that the degree of depletion in a lithospheric root depends mostly on its age. Here we test this hypothesis using gravity, thermal, petrologic, and seismic data to quantify differences in the density of cratonic roots globally. In the first step in our analysis we use a global crustal model to remove the crustal contribution to the observed gravity. The result is the mantle gravity anomaly field, which varies over cratonic areas from -100 to +100 mGal. Positive mantle gravity anomalies are observed for cratons in the northern hemisphere: the Baltic shield, East European Platform, and the Siberian Platform. Negative anomalies are observed over cratons in the southern hemisphere: Western Australia, South America, the Indian shield, and Southern Africa. This indicates that there are significant differences in the density of cratonic roots, even for those of similar age. Root density depends on temperature and chemical depletion. In order to separate these effects we apply a lithospheric temperature correction using thermal estimates from a combination of geothermal modeling and global seismic tomography models. Gravity anomalies induced by temperature variations in the uppermost mantle range from -200 to +300 mGal, with the strongest negative anomalies associated with mid-ocean ridges and the strongest positive anomalies associated with cratons. After correcting for thermal effects, we obtain a map of density variations due to lithospheric compositional variations. These maps indicate that the average density decrease due to the chemical depletion within cratonic roots varies from 1.1% to 1.5%, assuming the chemical boundary layer has the same thickness as the thermal boundary layer. The maximal values of the density drop are in the range 1.7-2.5%, and correspond to the Archean portion of each craton. Temperatures within cratonic roots vary strongly, and our analysis indicates that density variations in the roots due to temperature are larger than the variations due to chemical differences. ?? 2003 Elsevier Science B.V. All rights reserved.
Magma intrusion beneath long valley caldera confirmed by temporal changes in gravity

PubMed

Battaglia; Roberts; Segall

1999-09-24

Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as -107 +/- 6 microgals (1 microgal = 10(-8) meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 +/- 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 x 10(3) to 4.1 x 10(3) kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.
Magma intrusion beneath Long Valley caldera confirmed by temporal changes in gravity

USGS Publications Warehouse

Battaglia, Maurizio; Roberts, C.; Segall, P.

1999-01-01

Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as -107 ?? 6 microgals (1 microgal = 10-8 meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 ?? 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 x 103 to 4.1 x 103 kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.
Mask patterning process using the negative tone chemically amplified resist TOK OEBR-CAN024

NASA Astrophysics Data System (ADS)

Irmscher, Mathias; Beyer, Dirk; Butschke, Joerg; Hudek, Peter; Koepernik, Corinna; Plumhoff, Jason; Rausa, Emmanuel; Sato, Mitsuru; Voehringer, Peter

2004-08-01

Optimized process parameters using the TOK OEBR-CAN024 resist for high chrome load patterning have been determined. A tight linearity tolerance for opaque and clear features, independent on the local pattern density, was the goal of our process integration work. For this purpose we evaluated a new correction method taking into account electron scattering and process influences. The method is based on matching of measured pattern geometry by iterative back-simulation using multiple Gauss and/or exponential functions. The obtained control function acts as input for the proximity correction software PROXECCO. Approaches with different pattern oversize and two Cr thicknesses were accomplished and the results have been reported. Isolated opaque and clear lines could be realized in a very tight linearity range. The increasing line width of small dense lines, induced by the etching process, could be corrected only partially.
Preliminary Analysis of the Performance of the Landsat 8/OLI Land Surface Reflectance Product

NASA Technical Reports Server (NTRS)

Vermote, Eric; Justice, Chris; Claverie, Martin; Franch, Belen

2016-01-01

The surface reflectance, i.e., satellite derived top of atmosphere (TOA) reflectance corrected for the temporally, spatially and spectrally varying scattering and absorbing effects of atmospheric gases and aerosols, is needed to monitor the land surface reliably. For this reason, the surface reflectance, and not TOA reflectance, is used to generate the greater majority of global land products, for example, from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) sensors. Even if atmospheric effects are minimized by sensor design, atmospheric effects are still challenging to correct. In particular, the strong impact of aerosols in the visible and near infrared spectral range can be difficult to correct, because they can be highly discrete in space and time (e.g., smoke plumes) and because of the complex scattering and absorbing properties of aerosols that vary spectrally and with aerosol size, shape, chemistry and density.
BLACK HOLE MASS AND EDDINGTON RATIO DISTRIBUTION FUNCTIONS OF X-RAY-SELECTED BROAD-LINE AGNs AT z {approx} 1.4 IN THE SUBARU XMM-NEWTON DEEP FIELD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nobuta, K.; Akiyama, M.; Ueda, Y.

2012-12-20

In order to investigate the growth of supermassive black holes (SMBHs), we construct the black hole mass function (BHMF) and Eddington ratio distribution function (ERDF) of X-ray-selected broad-line active galactic nuclei (AGNs) at z {approx} 1.4 in the Subaru XMM-Newton Deep Survey (SXDS) field. A significant part of the accretion growth of SMBHs is thought to take place in this redshift range. Black hole masses of X-ray-selected broad-line AGNs are estimated using the width of the broad Mg II line and 3000 A monochromatic luminosity. We supplement the Mg II FWHM values with the H{alpha} FWHM obtained from our NIRmore » spectroscopic survey. Using the black hole masses of broad-line AGNs at redshifts between 1.18 and 1.68, the binned broad-line AGN BHMFs and ERDFs are calculated using the V{sub max} method. To properly account for selection effects that impact the binned estimates, we derive the corrected broad-line AGN BHMFs and ERDFs by applying the maximum likelihood method, assuming that the ERDF is constant regardless of the black hole mass. We do not correct for the non-negligible uncertainties in virial BH mass estimates. If we compare the corrected broad-line AGN BHMF with that in the local universe, then the corrected BHMF at z = 1.4 has a higher number density above 10{sup 8} M{sub Sun} but a lower number density below that mass range. The evolution may be indicative of a downsizing trend of accretion activity among the SMBH population. The evolution of broad-line AGN ERDFs from z = 1.4 to 0 indicates that the fraction of broad-line AGNs with accretion rates close to the Eddington limit is higher at higher redshifts.« less
An angle-supported foldable phakic intraocular lens for correction of myopia: A five-year follow-up.

PubMed

Alió, J L; Plaza-Puche, A B; Cavas, F; Yébana Rubio, P; Sala, E

2017-01-01

To evaluate the efficacy and safety of an angle-supported foldable phakic intraocular lens (pIOL) for the correction of moderate to high myopia after 5 years follow-up. Prospective and retrospective, observational, longitudinal, non-randomised consecutive series of cases conducted on a total of 100 eyes of 67 patients with moderate to high myopia implanted with an Acrysof Cachet pIOL (Alcon Laboratories Inc.) with the aim of minimising the refractive error. The ages ranged between 18 to 60years. Uncorrected distance visual acuity (UDVA), manifest refraction, corrected distance visual acuity (CDVA), endothelial cells density, pIOL position, intraocular pressure, and complications were recorded preoperatively and during the 5 year follow-up. Five years after implantation, the mean manifest spherical equivalent refraction reduced significantly from -11.62±3.35 dioptres (D) to -0.33±0.85D. UDVA was 20/20 or better in 5 of 25 cases (20%), and 20/40 or better in 22 cases (88%). CDVA was 20/20 or better in 17 cases (68%), and 20/32 or better in 23 cases (92%) of eyes. The residual refractive error was within ±0.50D of emmetropia in 12 cases (48%), and within ±1.00D in 19 cases (76%). Mean endothelial cell loss at 5 years was 11.8% central, and 13.7% peripheral. Mean endothelium-pIOL distance was 2.11±0.18mm, and mean pIOL-crystalline distance was 0.88±0.20mm. This angle supported pIOL provided a favourable refractive correction and predictability, as well as acceptable safety in patients with moderate to high myopia. Although endothelial cell density decreased over 5years, the results are within the range reported in previous studies with other pIOLs. Copyright © 2016 Sociedad Española de Oftalmología. Publicado por Elsevier España, S.L.U. All rights reserved.
Calibration of the Oscillating Screen Viscometer

NASA Technical Reports Server (NTRS)

Berg, Robert F.; Moldover, Michael R.

1993-01-01

We have devised a calibration procedure for the oscillating screen viscometer which can provide the accuracy needed for the flight measurement of viscosity near the liquid-vapor critical point of xenon. The procedure, which makes use of the viscometer's wide bandwidth and hydrodynamic similarity, allows the viscometer to be self-calibrating. To demonstrate the validity of this procedure we measured the oscillator's transfer function under a wide variety of conditions. We obtained data using CO2 at temperatures spanning a temperature range of 35 K and densities varying by a factor of 165, thereby encountering viscosity variations as great as 50%. In contrast the flight experiment will be performed over a temperature range of 29 K and at only a single density, and the viscosity is expected to change by less than 40%. The measurements show that, after excluding data above 10 Hz (where frequency-dependent corrections are poorly modeled) and making a plausible adjustment to the viscosity value used at high density, the viscometer's behavior is fully consistent with the use of hydrodynamic similarity for calibration. Achieving this agreement required understanding a 1% anelastic effect present in the oscillator's torsion fiber.
Appropriate description of intermolecular interactions in the methane hydrates: an assessment of DFT methods.

PubMed

Liu, Yuan; Zhao, Jijun; Li, Fengyu; Chen, Zhongfang

2013-01-15

Accurate description of hydrogen-bonding energies between water molecules and van der Waals interactions between guest molecules and host water cages is crucial for study of methane hydrates (MHs). Using high-level ab initio MP2 and CCSD(T) results as the reference, we carefully assessed the performance of a variety of exchange-correlation functionals and various basis sets in describing the noncovalent interactions in MH. The functionals under investigation include the conventional GGA, meta-GGA, and hybrid functionals (PBE, PW91, TPSS, TPSSh, B3LYP, and X3LYP), long-range corrected functionals (ωB97X, ωB97, LC-ωPBE, CAM-B3LYP, and LC-TPSS), the newly developed Minnesota class functionals (M06-L, M06-HF, M06, and M06-2X), and the dispersion-corrected density functional theory (DFT) (DFT-D) methods (B97-D, ωB97X-D, PBE-TS, PBE-Grimme, and PW91-OBS). We found that the conventional functionals are not suitable for MH, notably, the widely used B3LYP functional even predicts repulsive interaction between CH(4) and (H(2)O)(6) cluster. M06-2X is the best among the M06-Class functionals. The ωB97X-D outperforms the other DFT-D methods and is recommended for accurate first-principles calculations of MH. B97-D is also acceptable as a compromise of computational cost and precision. Considering both accuracy and efficiency, B97-D, ωB97X-D, and M06-2X functional with 6-311++G(2d,2p) basis set without basis set superposition error (BSSE) correction are recommended. Though a fairly large basis set (e.g., aug-cc-pVTZ) and BSSE correction are necessary for a reliable MP2 calculation, DFT methods are less sensitive to the basis set and BSSE correction if the basis set is sufficient (e.g., 6-311++G(2d,2p)). These assessments provide useful guidance for choosing appropriate methodology of first-principles simulation of MH and related systems. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.
Endocrine and cardiometabolic cord blood characteristics of offspring born to mothers with and without polycystic ovary syndrome.

PubMed

Daan, Nadine M P; Koster, Maria P H; Steegers-Theunissen, Regine P; Eijkemans, Marinus J C; Fauser, B C J M

2017-01-01

To compare the endocrine and cardiometabolic cord blood characteristics of offspring of mothers with polycystic ovary syndrome (PCOS) with those of healthy controls. Cross-sectional case control study. University medical centers. Offspring from mothers with PCOS (n = 61) and healthy controls (n = 82). Cord blood withdrawal from neonates. Cord blood estradiol, androstenedione, dehydroepiandrosterone sulfate (DHEAS), testosterone, sex hormone-binding globulin, free androgen index (FAI), insulin, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, c-reactive protein, adiponectin, and leptin. Androstenedione and leptin concentrations were increased in the offspring of women with PCOS compared with the controls: androstenedione median 2.9 (interquartile range [IQR] 2.3-3.9) nmol/L vs. 2.2 [IQR 1.6-2.7] nmol/L; and leptin median 13.6 [IQR 8.3-22.9] μg/L vs. 9.8 [IQR 6.0-16.5] μg/L. After adjusting for maternal and pregnancy-related confounders (such as maternal age, gestational age, birth weight), androstenedione appeared associated with PCOS in both male (relative change 1.36 [1.04; 1.78]) and female offspring (relative change 1.40 [1.08; 1.82]). Similarly, in male offspring the leptin concentrations appeared associated with PCOS after correction for confounders (relative change 1.55 [1.12; 2.14]). After correction for multiple testing, these associations attenuated. Observed results suggest that androstenedione concentrations are increased in the cord blood of male and female offspring of women with PCOS, although this requires confirmation. This finding would support the hypothesis that a maternal hyperandrogenic environment during pregnancy in women with PCOS may predispose their offspring to fetal hyperandrogenism. The potential associations between fetal hyperandrogenism and long-term health effects remain to be elucidated. NCT00821379. Copyright © 2016 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.
On trends in historical marine wind data

NASA Technical Reports Server (NTRS)

Cardone, Vincent J.; Greenwood, Juliet G.; Cane, Mark A.

1990-01-01

Long-period variations which include a trend toward strengthening winds over the last three decades have on the one hand been suggested to be real climatic changes, and on the other artifacts of the evolution of measuring techniques. An examination is presently conducted of individual ship reports from three regions with high data densities, in order to resolve this dispute. Even with corrections for instrumental effects, the pre-1950 winds appear weaker than post-1950 winds; the most probable explanation is the absence of universal sea state and Beaufort force standards prior to 1946.
Convergence of Defect-Correction and Multigrid Iterations for Inviscid Flows

NASA Technical Reports Server (NTRS)

Diskin, Boris; Thomas, James L.

2011-01-01

Convergence of multigrid and defect-correction iterations is comprehensively studied within different incompressible and compressible inviscid regimes on high-density grids. Good smoothing properties of the defect-correction relaxation have been shown using both a modified Fourier analysis and a more general idealized-coarse-grid analysis. Single-grid defect correction alone has some slowly converging iterations on grids of medium density. The convergence is especially slow for near-sonic flows and for very low compressible Mach numbers. Additionally, the fast asymptotic convergence seen on medium density grids deteriorates on high-density grids. Certain downstream-boundary modes are very slowly damped on high-density grids. Multigrid scheme accelerates convergence of the slow defect-correction iterations to the extent determined by the coarse-grid correction. The two-level asymptotic convergence rates are stable and significantly below one in most of the regions but slow convergence is noted for near-sonic and very low-Mach compressible flows. Multigrid solver has been applied to the NACA 0012 airfoil and to different flow regimes, such as near-tangency and stagnation. Certain convergence difficulties have been encountered within stagnation regions. Nonetheless, for the airfoil flow, with a sharp trailing-edge, residuals were fast converging for a subcritical flow on a sequence of grids. For supercritical flow, residuals converged slower on some intermediate grids than on the finest grid or the two coarsest grids.
[Picture naming and memory in children: phonological and semantic effects].

PubMed

Scheuer, Claudia Ines; Stivanin, Luciene; Mangilli, Laura Davidson

2004-01-01

[corrected] The relation between picture naming and the short and long term memories. to verify the ability of picture naming based on phonological and semantic queues, relating it to memory. 80 pictures selected from a set of 400 (Cycowicz et al., 1997) were presented to 80 children with ages ranging from 3 to 6 years. Responses were classified in semantic and phonologic errors and number of correct answers. The effect of the articulatory complexity was significant and the effect of the semantic complexity was not significant. Naming is the result of memory activation which is organized in categories, physical properties and function; phonologic effects do interfere in the activity of naming, whereas the semantic effects reflect that the long term memory is organized in categories which are dependant of the context and of the development.
Thermodynamically constrained correction to ab initio equations of state

DOE Office of Scientific and Technical Information (OSTI.GOV)

French, Martin; Mattsson, Thomas R.

2014-07-07

We show how equations of state generated by density functional theory methods can be augmented to match experimental data without distorting the correct behavior in the high- and low-density limits. The technique is thermodynamically consistent and relies on knowledge of the density and bulk modulus at a reference state and an estimation of the critical density of the liquid phase. We apply the method to four materials representing different classes of solids: carbon, molybdenum, lithium, and lithium fluoride. It is demonstrated that the corrected equations of state for both the liquid and solid phases show a significantly reduced dependence ofmore » the exchange-correlation functional used.« less
An integrate-and-fire model to generate spike trains with long-range dependence.

PubMed

Richard, Alexandre; Orio, Patricio; Tanré, Etienne

2018-06-01

Long-range dependence (LRD) has been observed in a variety of phenomena in nature, and for several years also in the spiking activity of neurons. Often, this is interpreted as originating from a non-Markovian system. Here we show that a purely Markovian integrate-and-fire (IF) model, with a noisy slow adaptation term, can generate interspike intervals (ISIs) that appear as having LRD. However a proper analysis shows that this is not the case asymptotically. For comparison, we also consider a new model of individual IF neuron with fractional (non-Markovian) noise. The correlations of its spike trains are studied and proven to have LRD, unlike classical IF models. On the other hand, to correctly measure long-range dependence, it is usually necessary to know if the data are stationary. Thus, a methodology to evaluate stationarity of the ISIs is presented and applied to the various IF models. We explain that Markovian IF models may seem to have LRD because of non-stationarities.

Dual origin of pairing in nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Idini, A.; Potel, G.; Barranco, F.

The pairing correlations of the nucleus {sup 120}Sn are calculated by solving the Nambu–Gor’kov equations, including medium polarization effects resulting from the interweaving of quasiparticles, spin and density vibrations, taking into account, within the framework of nuclear field theory (NFT), processes leading to self-energy and vertex corrections and to the induced pairing interaction. From these results one can not only demonstrate the inevitability of the dual origin of pairing in nuclei, but also extract information which can be used at profit to quantitatively disentangle the contributions to the pairing gap Δ arising from the bare and from the induced pairingmore » interaction. The first is the strong {sup 1}S{sub 0} short-range NN potential resulting from meson exchange between nucleons moving in time reversal states within an energy range of hundreds of MeV from the Fermi energy. The second results from the exchange of vibrational modes between nucleons moving within few MeV from the Fermi energy. Short- (v{sub p}{sup bare}) and long-range (v{sub p}{sup ind}) pairing interactions contribute essentially equally to nuclear Cooper pair stability. That is to the breaking of gauge invariance in open-shell superfluid nuclei and thus to the order parameter, namely to the ground state expectation value of the pair creation operator. In other words, to the emergent property of generalized rigidity in gauge space, and associated rotational bands and Cooper pair tunneling between members of these bands.« less
Geometric model from microscopic theory for nuclear absorption

NASA Technical Reports Server (NTRS)

John, Sarah; Townsend, Lawrence W.; Wilson, John W.; Tripathi, Ram K.

1993-01-01

A parameter-free geometric model for nuclear absorption is derived herein from microscopic theory. The expression for the absorption cross section in the eikonal approximation, taken in integral form, is separated into a geometric contribution that is described by an energy-dependent effective radius and two surface terms that cancel in an asymptotic series expansion. For collisions of light nuclei, an expression for the effective radius is derived from harmonic oscillator nuclear density functions. A direct extension to heavy nuclei with Woods-Saxon densities is made by identifying the equivalent half-density radius for the harmonic oscillator functions. Coulomb corrections are incorporated, and a simplified geometric form of the Bradt-Peters type is obtained. Results spanning the energy range from 1 MeV/nucleon to 1 GeV/nucleon are presented. Good agreement with experimental results is obtained.
Geometric model for nuclear absorption from microscopic theory

NASA Technical Reports Server (NTRS)

John, S.; Townsend, L. W.; Wilson, J. W.; Tripathi, R. K.

1993-01-01

A parameter-free geometric model for nuclear absorption is derived from microscopic theory. The expression for the absorption cross section in the eikonal approximation taken in integral form is separated into a geometric contribution, described by an energy-dependent effective radius, and two surface terms which are shown to cancel in an asymptotic series expansion. For collisions of light nuclei, an expression for the effective radius is derived using harmonic-oscillator nuclear density functions. A direct extension to heavy nuclei with Woods-Saxon densities is made by identifying the equivalent half density radius for the harmonic-oscillator functions. Coulomb corrections are incorporated and a simplified geometric form of the Bradt-Peters type obtained. Results spanning the energy range of 1 MeV/nucleon to 1 GeV/nucleon are presented. Good agreement with experimental results are obtained.
Adjustment of spatio-temporal precipitation patterns in a high Alpine environment

NASA Astrophysics Data System (ADS)

Herrnegger, Mathew; Senoner, Tobias; Nachtnebel, Hans-Peter

2018-01-01

This contribution presents a method for correcting the spatial and temporal distribution of precipitation fields in a mountainous environment. The approach is applied within a flood forecasting model in the Upper Enns catchment in the Central Austrian Alps. Precipitation exhibits a large spatio-temporal variability in Alpine areas. Additionally the density of the monitoring network is low and measurements are subjected to major errors. This can lead to significant deficits in water balance estimation and stream flow simulations, e.g. for flood forecasting models. Therefore precipitation correction factors are frequently applied. For the presented study a multiplicative, stepwise linear correction model is implemented in the rainfall-runoff model COSERO to adjust the precipitation pattern as a function of elevation. To account for the local meteorological conditions, the correction model is derived for two elevation zones: (1) Valley floors to 2000 m a.s.l. and (2) above 2000 m a.s.l. to mountain peaks. Measurement errors also depend on the precipitation type, with higher magnitudes in winter months during snow fall. Therefore, additionally, separate correction factors for winter and summer months are estimated. Significant improvements in the runoff simulations could be achieved, not only in the long-term water balance simulation and the overall model performance, but also in the simulation of flood peaks.
Combined natural gamma ray spectral/litho-density measurements applied to complex lithologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quirein, J.A.; Gardner, J.S.; Watson, J.T.

1982-09-01

Well log data has long been used to provide lithological descriptions of complex formations. Historically, most of the approaches used have been restrictive because they assumed fixed, known, and distinct lithologies for specified zones. The approach described in this paper attempts to alleviate this restriction by estimating the ''probability of a model'' for the models suggested as most likely by the reservoir geology. Lithological variables are simultaneously estimated from response equations for each model and combined in accordance with the probability of each respective model. The initial application of this approach has been the estimation of calcite, quartz, and dolomitemore » in the presence of clays, feldspars, anhydrite, or salt. Estimations were made by using natural gamma ray spectra, photoelectric effect, bulk density, and neutron porosity information. For each model, response equations and parameter selections are obtained from the thorium vs potassium crossplot and the apparent matrix density vs apparent volumetric photoelectric cross section crossplot. The thorium and potassium response equations are used to estimate the volumes of clay and feldspar. The apparent matrix density and volumetric cross section response equations can then be corrected for the presence of clay and feldspar. A test ensures that the clay correction lies within the limits for the assumed lithology model. Results are presented for varying lithologies. For one test well, 6,000 feet were processed in a single pass, without zoning and without adjusting more than one parameter pick. The program recognized sand, limestone, dolomite, clay, feldspar, anhydrite, and salt without analyst intervention.« less
Size effects under homogeneous deformation of single crystals: A discrete dislocation analysis

NASA Astrophysics Data System (ADS)

Guruprasad, P. J.; Benzerga, A. A.

Mechanism-based discrete dislocation plasticity is used to investigate the effect of size on micron scale crystal plasticity under conditions of macroscopically homogeneous deformation. Long-range interactions among dislocations are naturally incorporated through elasticity. Constitutive rules are used which account for key short-range dislocation interactions. These include junction formation and dynamic source and obstacle creation. Two-dimensional calculations are carried out which can handle high dislocation densities and large strains up to 0.1. The focus is laid on the effect of dimensional constraints on plastic flow and hardening processes. Specimen dimensions ranging from hundreds of nanometers to tens of microns are considered. Our findings show a strong size-dependence of flow strength and work-hardening rate at the micron scale. Taylor-like hardening is shown to be insufficient as a rationale for the flow stress scaling with specimen dimensions. The predicted size effect is associated with the emergence, at sufficient resolution, of a signed dislocation density. Heuristic correlations between macroscopic flow stress and macroscopic measures of dislocation density are sought. Most accurate among those is a correlation based on two state variables: the total dislocation density and an effective, scale-dependent measure of signed density.
Breast density quantification using magnetic resonance imaging (MRI) with bias field correction: A postmortem study

PubMed Central

Ding, Huanjun; Johnson, Travis; Lin, Muqing; Le, Huy Q.; Ducote, Justin L.; Su, Min-Ying; Molloi, Sabee

2013-01-01

Purpose: Quantification of breast density based on three-dimensional breast MRI may provide useful information for the early detection of breast cancer. However, the field inhomogeneity can severely challenge the computerized image segmentation process. In this work, the effect of the bias field in breast density quantification has been investigated with a postmortem study. Methods: T1-weighted images of 20 pairs of postmortem breasts were acquired on a 1.5 T breast MRI scanner. Two computer-assisted algorithms were used to quantify the volumetric breast density. First, standard fuzzy c-means (FCM) clustering was used on raw images with the bias field present. Then, the coherent local intensity clustering (CLIC) method estimated and corrected the bias field during the iterative tissue segmentation process. Finally, FCM clustering was performed on the bias-field-corrected images produced by CLIC method. The left–right correlation for breasts in the same pair was studied for both segmentation algorithms to evaluate the precision of the tissue classification. Finally, the breast densities measured with the three methods were compared to the gold standard tissue compositions obtained from chemical analysis. The linear correlation coefficient, Pearson's r, was used to evaluate the two image segmentation algorithms and the effect of bias field. Results: The CLIC method successfully corrected the intensity inhomogeneity induced by the bias field. In left–right comparisons, the CLIC method significantly improved the slope and the correlation coefficient of the linear fitting for the glandular volume estimation. The left–right breast density correlation was also increased from 0.93 to 0.98. When compared with the percent fibroglandular volume (%FGV) from chemical analysis, results after bias field correction from both the CLIC the FCM algorithms showed improved linear correlation. As a result, the Pearson's r increased from 0.86 to 0.92 with the bias field correction. Conclusions: The investigated CLIC method significantly increased the precision and accuracy of breast density quantification using breast MRI images by effectively correcting the bias field. It is expected that a fully automated computerized algorithm for breast density quantification may have great potential in clinical MRI applications. PMID:24320536
Breast density quantification using magnetic resonance imaging (MRI) with bias field correction: a postmortem study.

PubMed

Ding, Huanjun; Johnson, Travis; Lin, Muqing; Le, Huy Q; Ducote, Justin L; Su, Min-Ying; Molloi, Sabee

2013-12-01

Quantification of breast density based on three-dimensional breast MRI may provide useful information for the early detection of breast cancer. However, the field inhomogeneity can severely challenge the computerized image segmentation process. In this work, the effect of the bias field in breast density quantification has been investigated with a postmortem study. T1-weighted images of 20 pairs of postmortem breasts were acquired on a 1.5 T breast MRI scanner. Two computer-assisted algorithms were used to quantify the volumetric breast density. First, standard fuzzy c-means (FCM) clustering was used on raw images with the bias field present. Then, the coherent local intensity clustering (CLIC) method estimated and corrected the bias field during the iterative tissue segmentation process. Finally, FCM clustering was performed on the bias-field-corrected images produced by CLIC method. The left-right correlation for breasts in the same pair was studied for both segmentation algorithms to evaluate the precision of the tissue classification. Finally, the breast densities measured with the three methods were compared to the gold standard tissue compositions obtained from chemical analysis. The linear correlation coefficient, Pearson's r, was used to evaluate the two image segmentation algorithms and the effect of bias field. The CLIC method successfully corrected the intensity inhomogeneity induced by the bias field. In left-right comparisons, the CLIC method significantly improved the slope and the correlation coefficient of the linear fitting for the glandular volume estimation. The left-right breast density correlation was also increased from 0.93 to 0.98. When compared with the percent fibroglandular volume (%FGV) from chemical analysis, results after bias field correction from both the CLIC the FCM algorithms showed improved linear correlation. As a result, the Pearson's r increased from 0.86 to 0.92 with the bias field correction. The investigated CLIC method significantly increased the precision and accuracy of breast density quantification using breast MRI images by effectively correcting the bias field. It is expected that a fully automated computerized algorithm for breast density quantification may have great potential in clinical MRI applications.
Inter-annual and seasonal trends in cetacean distribution, density and abundance off southern California

NASA Astrophysics Data System (ADS)

Campbell, Gregory S.; Thomas, Len; Whitaker, Katherine; Douglas, Annie B.; Calambokidis, John; Hildebrand, John A.

2015-02-01

Trends in cetacean density and distribution off southern California were assessed through visual line-transect surveys during thirty-seven California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises from July 2004-November 2013. From sightings of the six most commonly encountered cetacean species, seasonal, annual and overall density estimates were calculated. Blue whales (Balaenoptera musculus), fin whales (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) were the most frequently sighted baleen whales with overall densities of 0.91/1000 km2 (CV=0.27), 2.73/1000 km2 (CV=0.19), and 1.17/1000 km2 (CV=0.21) respectively. Species specific density estimates, stratified by cruise, were analyzed using a generalized additive model to estimate long-term trends and correct for seasonal imbalances. Variances were estimated using a non-parametric bootstrap with one day of effort as the sampling unit. Blue whales were primarily observed during summer and fall while fin and humpback whales were observed year-round with peaks in density during summer and spring respectively. Short-beaked common dolphins (Delphinus delphis), Pacific white-sided dolphins (Lagenorhynchus obliquidens) and Dall's porpoise (Phocoenoidesdalli) were the most frequently encountered small cetaceans with overall densities of 705.83/1000 km2 (CV=0.22), 51.98/1000 km2 (CV=0.27), and 21.37/1000 km2 (CV=0.19) respectively. Seasonally, short-beaked common dolphins were most abundant in winter whereas Pacific white-sided dolphins and Dall's porpoise were most abundant during spring. There were no significant long-term changes in blue whale, fin whale, humpback whale, short-beaked common dolphin or Dall's porpoise densities while Pacific white-sided dolphins exhibited a significant decrease in density across the ten-year study. The results from this study were fundamentally consistent with earlier studies, but provide greater temporal and seasonal resolution.
Relativistic density functional theory with picture-change corrected electron density based on infinite-order Douglas-Kroll-Hess method

NASA Astrophysics Data System (ADS)

Oyama, Takuro; Ikabata, Yasuhiro; Seino, Junji; Nakai, Hiromi

2017-07-01

This Letter proposes a density functional treatment based on the two-component relativistic scheme at the infinite-order Douglas-Kroll-Hess (IODKH) level. The exchange-correlation energy and potential are calculated using the electron density based on the picture-change corrected density operator transformed by the IODKH method. Numerical assessments indicated that the picture-change uncorrected density functional terms generate significant errors, on the order of hartree for heavy atoms. The present scheme was found to reproduce the energetics in the four-component treatment with high accuracy.
Two-dimensional melting of colloids with long-range attractive interactions.

PubMed

Du, Di; Doxastakis, Manolis; Hilou, Elaa; Biswal, Sibani Lisa

2017-02-22

The solid-liquid melting transition in a two-dimensional (2-D) attractive colloidal system is visualized using superparamagnetic colloids that interact through a long-range isotropic attractive interaction potential, which is induced using a high-frequency rotating magnetic field. Various experiments, supported by Monte Carlo simulations, are carried out over a range of interaction potentials and densities to determine structure factors, Lindermann parameters, and translational and orientational order parameters. The system shows a first-order solid-liquid melting transition. Simulations and experiments suggest that dislocations and disclinations simultaneously unbind during melting. This is in direct contrast with reports of 2-D melting of paramagnetic particles that interact with a repulsive interaction potential.
PtSi gimbal-based FLIR for airborne applications

NASA Astrophysics Data System (ADS)

Wallace, Joseph; Ornstein, Itzhak; Nezri, M.; Fryd, Y.; Bloomberg, Steve; Beem, S.; Bibi, B.; Hem, S.; Perna, Steve N.; Tower, John R.; Lang, Frank B.; Villani, Thomas S.; McCarthy, D. R.; Stabile, Paul J.

1997-08-01

A new gimbal-based, FLIR camera for several types of airborne platforms has been developed. The FLIR is based on a PtSi on silicon technology: developed for high volume and minimum cost. The gimbal scans an area of 360 degrees in azimuth and an elevation range of plus 15 degrees to minus 105 degrees. It is stabilized to 25 (mu) Rad-rms. A combination of uniformity correction, defect substitution, and compact optics results in a long range, low cost FLIR for all low-speed airborne platforms.
Analyses for Multistatic Geometric Image Correction.

DTIC Science & Technology

1980-02-01

target points are represented by somewhat different clusters of numbers (representing amplitude of response). This is simply the result of the coarse...0-15,y l. Figure 18. R Versus 40 (Sheet I of 2) 47 TRANSMITTER RECEIVER DIRECTION DIRECTION AT LONG RANGE)1. 109 107 0.9 0.8 GMXS 2 0 MAXɚ 0.7 0.6
Focus on Form and Corrective Feedback Research at the University of Victoria, Canada

ERIC Educational Resources Information Center

Chen, Sibo; Nassaji, Hossein

2018-01-01

The Department of Linguistics at University of Victoria (UVic) in Canada has a long-standing tradition of empirical approaches to the study of theoretical and applied linguistics. As part of the Faculty of Humanities, the department caters to students with a wide range of backgrounds and interests, and provides crucial language teaching support in…
Basic research for the geodynamics program

NASA Technical Reports Server (NTRS)

Mueller, I. I.

1982-01-01

Work performed and data obtained in geodynamic research is reported. The purpose was to obtain utilization of: (1) laser and very long baseline interferometry (VLBI); (2) range difference observation in geodynamics; (3) development of models for ice sheet and crustal deformations. The effects of adopting new precession, nutation and equinox corrections on the terrestrial reference frame are investigated.
A long-term evaluation of biopsy darts and DNA to estimate cougar density

USGS Publications Warehouse

Beausoleil, Richard A.; Clark, Joseph D.; Maletzke, Benjamin T.

2016-01-01

Accurately estimating cougar (Puma concolor) density is usually based on long-term research consisting of intensive capture and Global Positioning System collaring efforts and may cost hundreds of thousands of dollars annually. Because wildlife agency budgets rarely accommodate this approach, most infer cougar density from published literature, rely on short-term studies, or use hunter harvest data as a surrogate in their jurisdictions; all of which may limit accuracy and increase risk of management actions. In an effort to develop a more cost-effective long-term strategy, we evaluated a research approach using citizen scientists with trained hounds to tree cougars and collect tissue samples with biopsy darts. We then used the DNA to individually identify cougars and employed spatially explicit capture–recapture models to estimate cougar densities. Overall, 240 tissue samples were collected in northeastern Washington, USA, producing 166 genotypes (including recaptures and excluding dependent kittens) of 133 different cougars (8-25/yr) from 2003 to 2011. Mark–recapture analyses revealed a mean density of 2.2 cougars/100 km2 (95% CI=1.1-4.3) and stable to decreasing population trends (β=-0.048, 95% CI=-0.106–0.011) over the 9 years of study, with an average annual harvest rate of 14% (range=7-21%). The average annual cost per year for field sampling and genotyping was US$11,265 ($422.24/sample or $610.73/successfully genotyped sample). Our results demonstrated that long-term biopsy sampling using citizen scientists can increase capture success and provide reliable cougar-density information at a reasonable cost.
Body density and diving gas volume of the northern bottlenose whale (Hyperoodon ampullatus).

PubMed

Miller, Patrick; Narazaki, Tomoko; Isojunno, Saana; Aoki, Kagari; Smout, Sophie; Sato, Katsufumi

2016-08-15

Diving lung volume and tissue density, reflecting lipid store volume, are important physiological parameters that have only been estimated for a few breath-hold diving species. We fitted 12 northern bottlenose whales with data loggers that recorded depth, 3-axis acceleration and speed either with a fly-wheel or from change of depth corrected by pitch angle. We fitted measured values of the change in speed during 5 s descent and ascent glides to a hydrodynamic model of drag and buoyancy forces using a Bayesian estimation framework. The resulting estimate of diving gas volume was 27.4±4.2 (95% credible interval, CI) ml kg(-1), closely matching the measured lung capacity of the species. Dive-by-dive variation in gas volume did not correlate with dive depth or duration. Estimated body densities of individuals ranged from 1028.4 to 1033.9 kg m(-3) at the sea surface, indicating overall negative tissue buoyancy of this species in seawater. Body density estimates were highly precise with ±95% CI ranging from 0.1 to 0.4 kg m(-3), which would equate to a precision of <0.5% of lipid content based upon extrapolation from the elephant seal. Six whales tagged near Jan Mayen (Norway, 71°N) had lower body density and were closer to neutral buoyancy than six whales tagged in the Gully (Nova Scotia, Canada, 44°N), a difference that was consistent with the amount of gliding observed during ascent versus descent phases in these animals. Implementation of this approach using longer-duration tags could be used to track longitudinal changes in body density and lipid store body condition of free-ranging cetaceans. © 2016. Published by The Company of Biologists Ltd.
Body density and diving gas volume of the northern bottlenose whale (Hyperoodon ampullatus)

PubMed Central

Miller, Patrick; Narazaki, Tomoko; Isojunno, Saana; Aoki, Kagari; Smout, Sophie; Sato, Katsufumi

2016-01-01

ABSTRACT Diving lung volume and tissue density, reflecting lipid store volume, are important physiological parameters that have only been estimated for a few breath-hold diving species. We fitted 12 northern bottlenose whales with data loggers that recorded depth, 3-axis acceleration and speed either with a fly-wheel or from change of depth corrected by pitch angle. We fitted measured values of the change in speed during 5 s descent and ascent glides to a hydrodynamic model of drag and buoyancy forces using a Bayesian estimation framework. The resulting estimate of diving gas volume was 27.4±4.2 (95% credible interval, CI) ml kg−1, closely matching the measured lung capacity of the species. Dive-by-dive variation in gas volume did not correlate with dive depth or duration. Estimated body densities of individuals ranged from 1028.4 to 1033.9 kg m−3 at the sea surface, indicating overall negative tissue buoyancy of this species in seawater. Body density estimates were highly precise with ±95% CI ranging from 0.1 to 0.4 kg m−3, which would equate to a precision of <0.5% of lipid content based upon extrapolation from the elephant seal. Six whales tagged near Jan Mayen (Norway, 71°N) had lower body density and were closer to neutral buoyancy than six whales tagged in the Gully (Nova Scotia, Canada, 44°N), a difference that was consistent with the amount of gliding observed during ascent versus descent phases in these animals. Implementation of this approach using longer-duration tags could be used to track longitudinal changes in body density and lipid store body condition of free-ranging cetaceans. PMID:27296044
Locality of correlation in density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burke, Kieron; Cancio, Antonio; Gould, Tim

The Hohenberg-Kohn density functional was long ago shown to reduce to the Thomas-Fermi (TF) approximation in the non-relativistic semiclassical (or large-Z) limit for all matter, i.e., the kinetic energy becomes local. Exchange also becomes local in this limit. Numerical data on the correlation energy of atoms support the conjecture that this is also true for correlation, but much less relevant to atoms. We illustrate how expansions around a large particle number are equivalent to local density approximations and their strong relevance to density functional approximations. Analyzing highly accurate atomic correlation energies, we show that E{sub C} → −A{sub C} ZlnZ +more » B{sub C}Z as Z → ∞, where Z is the atomic number, A{sub C} is known, and we estimate B{sub C} to be about 37 mhartree. The local density approximation yields A{sub C} exactly, but a very incorrect value for B{sub C}, showing that the local approximation is less relevant for the correlation alone. This limit is a benchmark for the non-empirical construction of density functional approximations. We conjecture that, beyond atoms, the leading correction to the local density approximation in the large-Z limit generally takes this form, but with B{sub C} a functional of the TF density for the system. The implications for the construction of approximate density functionals are discussed.« less
Density-dependent microbial turnover improves soil carbon model predictions of long-term litter manipulations

NASA Astrophysics Data System (ADS)

Georgiou, Katerina; Abramoff, Rose; Harte, John; Riley, William; Torn, Margaret

2017-04-01

Climatic, atmospheric, and land-use changes all have the potential to alter soil microbial activity via abiotic effects on soil or mediated by changes in plant inputs. Recently, many promising microbial models of soil organic carbon (SOC) decomposition have been proposed to advance understanding and prediction of climate and carbon (C) feedbacks. Most of these models, however, exhibit unrealistic oscillatory behavior and SOC insensitivity to long-term changes in C inputs. Here we diagnose the sources of instability in four models that span the range of complexity of these recent microbial models, by sequentially adding complexity to a simple model to include microbial physiology, a mineral sorption isotherm, and enzyme dynamics. We propose a formulation that introduces density-dependence of microbial turnover, which acts to limit population sizes and reduce oscillations. We compare these models to results from 24 long-term C-input field manipulations, including the Detritus Input and Removal Treatment (DIRT) experiments, to show that there are clear metrics that can be used to distinguish and validate the inherent dynamics of each model structure. We find that widely used first-order models and microbial models without density-dependence cannot readily capture the range of long-term responses observed across the DIRT experiments as a direct consequence of their model structures. The proposed formulation improves predictions of long-term C-input changes, and implies greater SOC storage associated with CO2-fertilization-driven increases in C inputs over the coming century compared to common microbial models. Finally, we discuss our findings in the context of improving microbial model behavior for inclusion in Earth System Models.

Primary Energy Reconstruction from the Charged Particle Densities Recorded with the KASCADE-Grande Detector at 500 m Distance from Shower Core

NASA Astrophysics Data System (ADS)

Toma, G.; Apel, W. D.; Arteaga, J. C.; Bekk, K.; Bertaina, M.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Buchholz, P.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Engler, J.; Finger, M.; Fuhrmann, D.; Ghia, P. L.; Gils, H. J.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Klages, H. O.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Mayer, H. J.; Melissas, M.; Milke, J.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Oehlschläger, J.; Ostapchenko, S.; Over, S.; Palmieri, N.; Petcu, M.; Pierog, T.; Rebel, H.; Roth, M.; Schieler, H.; Schröder, F.; Sima, O.; Trinchero, G. C.; Ulrich, H.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.

2010-11-01

Previous EAS investigations have shown that for a fixed primary energy the charged particle density becomes independent of the primary mass at certain (fixed) distances from the shower core. This feature can be used as an estimator for the primary energy. We present results on the reconstruction of the primary energy spectrum of cosmic rays from the experimentally recorded S(500) observable (the density of charged particles at 500 m distance to the shower core) using the KASCADE-Grande detector array. The KASCADE-Grande experiment is hosted by the Karlsruhe Institute for Technology-Campus North, Karlsruhe, Germany, and operated by an international collaboration. The constant intensity cut (CIC) method is applied to evaluate the attenuation of the S(500) observable with the zenith angle and is corrected for. A calibration of S(500) values with the primary energy has been worked out by simulations and was applied to the data to obtain the primary energy spectrum (in the energy range log10[E0/GeV]∈[7.5,9]). The systematic uncertainties induced by different sources are considered. In addition, a correction based on a response matrix is applied to account for the effects of shower-to-shower fluctuations on the spectral index of the reconstructed energy spectrum.
The computer simulation of automobile use patterns for defining battery requirements for electric cars

NASA Technical Reports Server (NTRS)

Schwartz, H.-J.

1976-01-01

The modeling process of a complex system, based on the calculation and optimization of the system parameters, is complicated in that some parameters can be expressed only as probability distributions. In the present paper, a Monte Carlo technique was used to determine the daily range requirements of an electric road vehicle in the United States from probability distributions of trip lengths, frequencies, and average annual mileage data. The analysis shows that a daily range of 82 miles meets to 95% of the car-owner requirements at all times with the exception of long vacation trips. Further, it is shown that the requirement of a daily range of 82 miles can be met by a (intermediate-level) battery technology characterized by an energy density of 30 to 50 Watt-hours per pound. Candidate batteries in this class are nickel-zinc, nickel-iron, and iron-air. These results imply that long-term research goals for battery systems should be focused on lower cost and longer service life, rather than on higher energy densities
GRB070125: The First Long-Duration Gamma-Ray Burst in a Halo Environment

NASA Technical Reports Server (NTRS)

Bradley, Cenko S.; Fox, Derek B.; Penprase, Brian E.; Kulkarni, Shri R.; Price, Paul A.; Berger, Edo; Kulkarni, Shri R.; Harrison, Fiona A.; Gal-Yam, Avishay; Ofek, Eran O.;

2007-01-01

We present the discovery and high signal-to-noise spectroscopic observations of the optical afterglow of the long-duration gamma-ray burst GRB070125. Unlike all previously observed long-duration afterglows in the redshift range 0.5 < z < 2.0, we find no strong (rest-frame equivalent width W > 1.0 A) absorption features in the wavelength range 4000 - 10000 A. The sole significant feature is a weak doublet we identify as Mg 11 2796 (W = 0.18 +/- 0.02 A), 2803 (W = 0.08 +0I.-01 ) at z = 1.5477 +/- 0.0001. The low observed Mg II and inferred H I column densities are typically observed in galactic halos, far away from the bulk of massive star formation. Deep ground-based imaging reveals no host directly underneath the afterglow to a limit of R > 25.4 mag. Either of the two nearest blue galaxies could host GRB070125; the large offset (d >= 27 kpc) would naturally explain the low column density. To remain consistent with the large local (i.e. parsec scale) circum-burst density inferred from broadband afterglow observations, we speculate GRB070125 may have occurred far away from the disk of its host in a compact star-forming cluster. Such distant stellar clusters, typically formed by dynamical galaxy interactions, have been observed in the nearby universe, and should be more prevalent at z>l where galaxy mergers occur more frequently.

The self-absorption correction factors for 210Pb concentration in mining waste and influence on environmental radiation risk assessment.

PubMed

Bonczyk, Michal; Michalik, Boguslaw; Chmielewska, Izabela

2017-03-01

The radioactive lead isotope 210 Pb occurs in waste originating from metal smelting and refining industry, gas and oil extraction and sometimes from underground coal mines, which are deposited in natural environment very often. Radiation risk assessment requires accurate knowledge about the concentration of 210 Pb in such materials. Laboratory measurements seem to be the only reliable method applicable in environmental 210 Pb monitoring. One of the methods is gamma-ray spectrometry, which is a very fast and cost-effective method to determine 210 Pb concentration. On the other hand, the self-attenuation of gamma ray from 210 Pb (46.5 keV) in a sample is significant as it does not depend only on sample density but also on sample chemical composition (sample matrix). This phenomenon is responsible for the under-estimation of the 210 Pb activity concentration level often when gamma spectrometry is applied with no regard to relevant corrections. Finally, the corresponding radiation risk can be also improperly evaluated. Sixty samples of coal mining solid tailings (sediments created from underground mining water) were analysed. Slightly modified and adapted to the existing laboratory condition, a transmission method has been applied for the accurate measurement of 210 Pb concentration . The observed concentrations of 210 Pb range between 42.2 ÷ 11,700 Bq·kg -1 of dry mass. Experimentally obtained correction factors related to a sample density and elemental composition range between 1.11 and 6.97. Neglecting this factor can cause a significant error or underestimations in radiological risk assessment. The obtained results have been used for environmental radiation risk assessment performed by use of the ERICA tool assuming exposure conditions typical for the final destination of such kind of waste.
ωB97X-V: A 10-parameter, range-separated hybrid, generalized gradient approximation density functional with nonlocal correlation, designed by a survival-of-the-fittest strategy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mardirossian, Narbe; Head-Gordon, Martin

2013-12-18

A 10-parameter, range-separated hybrid (RSH), generalized gradient approximation (GGA) density functional with nonlocal correlation (VV10) is presented in this paper. Instead of truncating the B97-type power series inhomogeneity correction factors (ICF) for the exchange, same-spin correlation, and opposite-spin correlation functionals uniformly, all 16 383 combinations of the linear parameters up to fourth order (m = 4) are considered. These functionals are individually fit to a training set and the resulting parameters are validated on a primary test set in order to identify the 3 optimal ICF expansions. Through this procedure, it is discovered that the functional that performs best onmore » the training and primary test sets has 7 linear parameters, with 3 additional nonlinear parameters from range-separation and nonlocal correlation. The resulting density functional, ωB97X-V, is further assessed on a secondary test set, the parallel-displaced coronene dimer, as well as several geometry datasets. Finally and furthermore, the basis set dependence and integration grid sensitivity of ωB97X-V are analyzed and documented in order to facilitate the use of the functional.« less
Reducing Variability in Orthogonal Reformatted Image Quality Associated With Axial Long-z-Axis CT Angiography.

PubMed

Stein, Erica B; Liu, Peter S; Kazerooni, Ella A; Barber, Karen; Davenport, Matthew S

2016-12-01

The objective of our study was to reduce variation in image quality of orthogonal reformatted images generated from long-z-axis CT angiography (CTA) studies of the upper and lower extremities. Upper and lower extremity CTA studies were targeted at a single health care system. A correctly performed CTA examination was defined as one that met the following three criteria: Sagittal and coronal reformats were obtained, a high-resolution matrix greater than 512 × 512 was used, and reformatted images were available in a distance-measurable format. Baseline data were collected from February 1, 2014, through September 30, 2014. Corrective actions were implemented during three consecutive plan-do-check-act (PDCA) cycles from October 1, 2014, through July 31, 2015, that addressed human, technical, and systematic variations. A 3-month maintenance period followed in which no intervention was performed. Longitudinal data were analyzed monthly using a statistical process control chart (p-chart). The total number of long-z-axis extremity CTA studies analyzed was as follows: 351 CTA studies were analyzed at baseline, 94 at the first PDCA cycle, 92 at the second PDCA cycle, 114 at the third PDCA cycle, and 138 during the maintenance period. The monthly rate of correctly performed studies ranged from 7% to 51% (mean, 38% ± 13% [SD]) during the baseline period, 32-59% (mean, 46% ± 14%) during the first PDCA cycle, 40-81% (mean, 61% ± 21%) during the second PDCA cycle, and 80-82% (mean, 81% ± 0.9%) during the third PDCA cycle. The monthly rate improved to 90-91% (mean, 91% ± 0.5%) during the maintenance period. The upper and lower control limits of the p-chart were upshifted after the second and third PDCA cycles. Correcting systematic and technical variations led to the greatest improvements in reformat accuracy. Obtaining consistently and correctly reformatted images from long-z-axis CTA studies is achievable using iterative PDCA cycles.
Gravitational Lagrangians, Mach's Principle, and the Equivalence Principle in an Expanding Universe

NASA Astrophysics Data System (ADS)

Essén, Hanno

2014-08-01

Gravitational Lagrangians as derived by Fock for the Einstein-Infeld-Hoffmann approach, and by Kennedy assuming only a fourth rank tensor interaction, contain long range interactions. Here we investigate how these affect the local dynamics when integrated over an expanding universe out to the Hubble radius. Taking the cosmic expansion velocity into account in a heuristic manner it is found that these long range interactions imply Mach's principle, provided the universe has the critical density, and that mass is renormalized. Suitable higher order additions to the Lagrangians make the formalism consistent with the equivalence principle.
Long range ordered alloys modified by group IV-B metals

DOEpatents

Liu, Chain T.; Inouye, Henry; Schaffhauser, Anthony C.

1983-01-01

Ductile long range ordered alloys having high critical ordering temperatures exist in the (V,M)(Fe,Ni,Co).sub.3 system having the composition comprising by weight 20.6%-22.6% V, 14-50% Fe, 0-64% Co, and 0-40% Ni, and 0.4-1.4% M, where M is a metal selected from the group consisting of Ti, Zr, Hf, and their mixtures. These modified alloys have an electron density no greater than 8.00 and exhibit marked increases at elevated temperature in ductility and other mechanical properties over previously known ordered alloys.
Proton clouds to measure long-range contacts between nonexchangeable side chain protons in solid-state NMR.

PubMed

Sinnige, Tessa; Daniëls, Mark; Baldus, Marc; Weingarth, Markus

2014-03-26

We show that selective labeling of proteins with protonated amino acids embedded in a perdeuterated matrix, dubbed 'proton clouds', provides general access to long-range contacts between nonexchangeable side chain protons in proton-detected solid-state NMR, which is important to study protein tertiary structure. Proton-cloud labeling significantly improves spectral resolution by simultaneously reducing proton line width and spectral crowding despite a high local proton density in clouds. The approach is amenable to almost all canonical amino acids. Our method is demonstrated on ubiquitin and the β-barrel membrane protein BamA.
Population of 224 realistic human subject-based computational breast phantoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erickson, David W.; Wells, Jered R., E-mail: jered.wells@duke.edu; Sturgeon, Gregory M.

Purpose: To create a database of highly realistic and anatomically variable 3D virtual breast phantoms based on dedicated breast computed tomography (bCT) data. Methods: A tissue classification and segmentation algorithm was used to create realistic and detailed 3D computational breast phantoms based on 230 + dedicated bCT datasets from normal human subjects. The breast volume was identified using a coarse three-class fuzzy C-means segmentation algorithm which accounted for and removed motion blur at the breast periphery. Noise in the bCT data was reduced through application of a postreconstruction 3D bilateral filter. A 3D adipose nonuniformity (bias field) correction was thenmore » applied followed by glandular segmentation using a 3D bias-corrected fuzzy C-means algorithm. Multiple tissue classes were defined including skin, adipose, and several fractional glandular densities. Following segmentation, a skin mask was produced which preserved the interdigitated skin, adipose, and glandular boundaries of the skin interior. Finally, surface modeling was used to produce digital phantoms with methods complementary to the XCAT suite of digital human phantoms. Results: After rejecting some datasets due to artifacts, 224 virtual breast phantoms were created which emulate the complex breast parenchyma of actual human subjects. The volume breast density (with skin) ranged from 5.5% to 66.3% with a mean value of 25.3% ± 13.2%. Breast volumes ranged from 25.0 to 2099.6 ml with a mean value of 716.3 ± 386.5 ml. Three breast phantoms were selected for imaging with digital compression (using finite element modeling) and simple ray-tracing, and the results show promise in their potential to produce realistic simulated mammograms. Conclusions: This work provides a new population of 224 breast phantoms based on in vivo bCT data for imaging research. Compared to previous studies based on only a few prototype cases, this dataset provides a rich source of new cases spanning a wide range of breast types, volumes, densities, and parenchymal patterns.« less
Population of 224 realistic human subject-based computational breast phantoms

PubMed Central

Erickson, David W.; Wells, Jered R.; Sturgeon, Gregory M.; Dobbins, James T.; Segars, W. Paul; Lo, Joseph Y.

2016-01-01

Purpose: To create a database of highly realistic and anatomically variable 3D virtual breast phantoms based on dedicated breast computed tomography (bCT) data. Methods: A tissue classification and segmentation algorithm was used to create realistic and detailed 3D computational breast phantoms based on 230 + dedicated bCT datasets from normal human subjects. The breast volume was identified using a coarse three-class fuzzy C-means segmentation algorithm which accounted for and removed motion blur at the breast periphery. Noise in the bCT data was reduced through application of a postreconstruction 3D bilateral filter. A 3D adipose nonuniformity (bias field) correction was then applied followed by glandular segmentation using a 3D bias-corrected fuzzy C-means algorithm. Multiple tissue classes were defined including skin, adipose, and several fractional glandular densities. Following segmentation, a skin mask was produced which preserved the interdigitated skin, adipose, and glandular boundaries of the skin interior. Finally, surface modeling was used to produce digital phantoms with methods complementary to the XCAT suite of digital human phantoms. Results: After rejecting some datasets due to artifacts, 224 virtual breast phantoms were created which emulate the complex breast parenchyma of actual human subjects. The volume breast density (with skin) ranged from 5.5% to 66.3% with a mean value of 25.3% ± 13.2%. Breast volumes ranged from 25.0 to 2099.6 ml with a mean value of 716.3 ± 386.5 ml. Three breast phantoms were selected for imaging with digital compression (using finite element modeling) and simple ray-tracing, and the results show promise in their potential to produce realistic simulated mammograms. Conclusions: This work provides a new population of 224 breast phantoms based on in vivo bCT data for imaging research. Compared to previous studies based on only a few prototype cases, this dataset provides a rich source of new cases spanning a wide range of breast types, volumes, densities, and parenchymal patterns. PMID:26745896
Diffuse Optical Light in Galaxy Clusters. II. Correlations with Cluster Properties

NASA Astrophysics Data System (ADS)

Krick, J. E.; Bernstein, R. A.

2007-08-01

We have measured the flux, profile, color, and substructure in the diffuse intracluster light (ICL) in a sample of 10 galaxy clusters with a range of mass, morphology, redshift, and density. Deep, wide-field observations for this project were made in two bands at the 1 m Swope and 2.5 m du Pont telescopes at Las Campanas Observatory. Careful attention in reduction and analysis was paid to the illumination correction, background subtraction, point-spread function determination, and galaxy subtraction. ICL flux is detected in both bands in all 10 clusters ranging from 7.6×1010 to 7.0×1011 h-170 Lsolar in r and 1.4×1010 to 1.2×1011 h-170 Lsolar in the B band. These fluxes account for 6%-22% of the total cluster light within one-quarter of the virial radius in r and 4%-21% in the B band. Average ICL B-r colors range from 1.5 to 2.8 mag when k- and evolution corrected to the present epoch. In several clusters we also detect ICL in group environments near the cluster center and up to 1 h-170 Mpc distant from the cluster center. Our sample, having been selected from the Abell sample, is incomplete in that it does not include high-redshift clusters with low density, low flux, or low mass, and it does not include low-redshift clusters with high flux, high mass, or high density. This bias makes it difficult to interpret correlations between ICL flux and cluster properties. Despite this selection bias, we do find that the presence of a cD galaxy corresponds to both centrally concentrated galaxy profiles and centrally concentrated ICL profiles. This is consistent with ICL either forming from galaxy interactions at the center or forming at earlier times in groups and later combining in the center.
The uniform electron gas at warm dense matter conditions

NASA Astrophysics Data System (ADS)

Dornheim, Tobias; Groth, Simon; Bonitz, Michael

2018-05-01

Motivated by the current high interest in the field of warm dense matter research, in this article we review the uniform electron gas (UEG) at finite temperature and over a broad density range relevant for warm dense matter applications. We provide an exhaustive overview of different simulation techniques, focusing on recent developments in the dielectric formalism (linear response theory) and quantum Monte Carlo (QMC) methods. Our primary focus is on two novel QMC methods that have recently allowed us to achieve breakthroughs in the thermodynamics of the warm dense electron gas: Permutation blocking path integral MC (PB-PIMC) and configuration path integral MC (CPIMC). In fact, a combination of PB-PIMC and CPIMC has allowed for a highly accurate description of the warm dense UEG over a broad density-temperature range. We are able to effectively avoid the notorious fermion sign problem, without invoking uncontrolled approximations such as the fixed node approximation. Furthermore, a new finite-size correction scheme is presented that makes it possible to treat the UEG in the thermodynamic limit without loss of accuracy. In addition, we in detail discuss the construction of a parametrization of the exchange-correlation free energy, on the basis of these data - the central thermodynamic quantity that provides a complete description of the UEG and is of crucial importance as input for the simulation of real warm dense matter applications, e.g., via thermal density functional theory. A second major aspect of this review is the use of our ab initio simulation results to test previous theories, including restricted PIMC, finite-temperature Green functions, the classical mapping by Perrot and Dharma-wardana, and various dielectric methods such as the random phase approximation, or the Singwi-Tosi-Land-Sjölander (both in the static and quantum versions), Vashishta-Singwi and the recent Tanaka scheme for the local field correction. Thus, for the first time, thorough benchmarks of the accuracy of important approximation schemes regarding various quantities such as different energies, in particular the exchange-correlation free energy, and the static structure factor, are possible. In the final part of this paper, we outline a way how to rigorously extend our QMC studies to the inhomogeneous electron gas. We present first ab initio data for the static density response and for the static local field correction.
The effect of basis set and exchange-correlation functional on time-dependent density functional theory calculations within the Tamm-Dancoff approximation of the x-ray emission spectroscopy of transition metal complexes.

PubMed

Roper, Ian P E; Besley, Nicholas A

2016-03-21

The simulation of X-ray emission spectra of transition metal complexes with time-dependent density functional theory (TDDFT) is investigated. X-ray emission spectra can be computed within TDDFT in conjunction with the Tamm-Dancoff approximation by using a reference determinant with a vacancy in the relevant core orbital, and these calculations can be performed using the frozen orbital approximation or with the relaxation of the orbitals of the intermediate core-ionised state included. Both standard exchange-correlation functionals and functionals specifically designed for X-ray emission spectroscopy are studied, and it is shown that the computed spectral band profiles are sensitive to the exchange-correlation functional used. The computed intensities of the spectral bands can be rationalised by considering the metal p orbital character of the valence molecular orbitals. To compute X-ray emission spectra with the correct energy scale allowing a direct comparison with experiment requires the relaxation of the core-ionised state to be included and the use of specifically designed functionals with increased amounts of Hartree-Fock exchange in conjunction with high quality basis sets. A range-corrected functional with increased Hartree-Fock exchange in the short range provides transition energies close to experiment and spectral band profiles that have a similar accuracy to those from standard functionals.
Coulomb disorder in three-dimensional Dirac materials

NASA Astrophysics Data System (ADS)

Skinner, Brian

2015-03-01

In three-dimensional materials with a Dirac spectrum, weak short-ranged disorder is essentially irrelevant near the Dirac point. This is manifestly not the case for Coulomb disorder, where the long-ranged nature of the potential produced by charged impurities implies large fluctuations of the disorder potential even when impurities are sparse, and these fluctuations are screened by the formation of electron/hole puddles. Here I outline a theory of such nonlinear screening of Coulomb disorder in three-dimensional Dirac systems, and present results for the typical magnitude of the disorder potential, the corresponding density of states, and the size and density of electron/hole puddles. The resulting conductivity is also discussed.
Thermospheric density and satellite drag modeling

NASA Astrophysics Data System (ADS)

Mehta, Piyush Mukesh

The United States depends heavily on its space infrastructure for a vast number of commercial and military applications. Space Situational Awareness (SSA) and Threat Assessment require maintaining accurate knowledge of the orbits of resident space objects (RSOs) and the associated uncertainties. Atmospheric drag is the largest source of uncertainty for low-perigee RSOs. The uncertainty stems from inaccurate modeling of neutral atmospheric mass density and inaccurate modeling of the interaction between the atmosphere and the RSO. In order to reduce the uncertainty in drag modeling, both atmospheric density and drag coefficient (CD) models need to be improved. Early atmospheric density models were developed from orbital drag data or observations of a few early compact satellites. To simplify calculations, densities derived from orbit data used a fixed CD value of 2.2 measured in a laboratory using clean surfaces. Measurements from pressure gauges obtained in the early 1990s have confirmed the adsorption of atomic oxygen on satellite surfaces. The varying levels of adsorbed oxygen along with the constantly changing atmospheric conditions cause large variations in CD with altitude and along the orbit of the satellite. Therefore, the use of a fixed CD in early development has resulted in large biases in atmospheric density models. A technique for generating corrections to empirical density models using precision orbit ephemerides (POE) as measurements in an optimal orbit determination process was recently developed. The process generates simultaneous corrections to the atmospheric density and ballistic coefficient (BC) by modeling the corrections as statistical exponentially decaying Gauss-Markov processes. The technique has been successfully implemented in generating density corrections using the CHAMP and GRACE satellites. This work examines the effectiveness, specifically the transfer of density models errors into BC estimates, of the technique using the CHAMP and GRACE satellites. Moving toward accurate atmospheric models and absolute densities requires physics based models for CD. Closed-form solutions of CD have been developed and exist for a handful of simple geometries (flat plate, sphere, and cylinder). However, for complex geometries, the Direct Simulation Monte Carlo (DSMC) method is an important tool for developing CD models. DSMC is computationally intensive and real-time simulations for CD are not feasible. Therefore, parameterized models for CD are required. Modeling CD for an RSO requires knowledge of the gas-surface interaction (GSI) that defines the manner in which the atmospheric particles exchange momentum and energy with the surface. The momentum and energy exchange is further influenced by likely adsorption of atomic oxygen that may partially or completely cover the surface. An important parameter that characterizes the GSI is the energy accommodation coefficient, α. An innovative and state-of-the-art technique of developing parameterized drag coefficient models is presented and validated using the GRACE satellite. The effect of gas-surface interactions on physical drag coefficients is examined. An attempt to reveal the nature of gas-surface interactions at altitudes above 500 km is made using the STELLA satellite. A model that can accurately estimate CD has the potential to: (i) reduce the sources of uncertainty in the drag model, (ii) improve density estimates by resolving time-varying biases and moving toward absolute densities, and (iii) increase data sources for density estimation by allowing for the use of a wide range of RSOs as information sources. Results from this work have the potential to significantly improve the accuracy of conjunction analysis and SSA.
Flow and diffusion in channel-guided cell migration.

PubMed

Marel, Anna-Kristina; Zorn, Matthias; Klingner, Christoph; Wedlich-Söldner, Roland; Frey, Erwin; Rädler, Joachim O

2014-09-02

Collective migration of mechanically coupled cell layers is a notable feature of wound healing, embryonic development, and cancer progression. In confluent epithelial sheets, the dynamics have been found to be highly heterogeneous, exhibiting spontaneous formation of swirls, long-range correlations, and glass-like dynamic arrest as a function of cell density. In contrast, the flow-like properties of one-sided cell-sheet expansion in confining geometries are not well understood. Here, we studied the short- and long-term flow of Madin-Darby canine kidney (MDCK) cells as they moved through microchannels. Using single-cell tracking and particle image velocimetry (PIV), we found that a defined averaged stationary cell current emerged that exhibited a velocity gradient in the direction of migration and a plug-flow-like profile across the advancing sheet. The observed flow velocity can be decomposed into a constant term of directed cell migration and a diffusion-like contribution that increases with density gradient. The diffusive component is consistent with the cell-density profile and front propagation speed predicted by the Fisher-Kolmogorov equation. To connect diffusion-mediated transport to underlying cellular motility, we studied single-cell trajectories and occurrence of vorticity. We discovered that the directed large-scale cell flow altered fluctuations in cellular motion at short length scales: vorticity maps showed a reduced frequency of swirl formation in channel flow compared with resting sheets of equal cell density. Furthermore, under flow, single-cell trajectories showed persistent long-range, random-walk behavior superimposed on drift, whereas cells in resting tissue did not show significant displacements with respect to neighboring cells. Our work thus suggests that active cell migration manifests itself in an underlying, spatially uniform drift as well as in randomized bursts of short-range correlated motion that lead to a diffusion-mediated transport. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Bury, Charles S.; Carmichael, Ian; Garman, Elspeth F.

During macromolecular X-ray crystallography experiments, protein crystals held at 100 K have been widely reported to exhibit reproducible bond scission events at doses on the order of several MGy. With the objective to mitigate the impact of radiation damage events on valid structure determination, it is essential to correctly understand the radiation chemistry mechanisms at play. OH-cleavage from tyrosine residues is regularly cited as amongst the most available damage pathways in protein crystals at 100 K, despite a lack of widespread reports of this phenomenon in protein crystal radiation damage studies. Furthermore, no clear mechanism for phenolic C—O bond cleavagemore » in tyrosine has been reported, with the tyrosyl radical known to be relatively robust and long-lived in both aqueous solutions and the solid state. Here, the initial findings of Tyr –OH group damage in a myrosinase protein crystal have been reviewed. Consistent with that study, at increasing doses, clear electron density loss was detectable local to Tyr –OH groups. A systematic investigation performed on a range of protein crystal damage series deposited in the Protein Data Bank has established that Tyr –OH electron density loss is not generally a dominant damage pathway in protein crystals at 100 K. Full Tyr aromatic ring displacement is here proposed to account for instances of observable Tyr –OH electron density loss, with the original myrosinase data shown to be consistent with such a damage model. Also presented are systematic analysis of the effects of other environmental factors, including solvent accessibility and proximity to disulfide bonds or hydrogen bond interactions. Residues in known active sites showed enhanced sensitivity to radiation-induced disordering, as has previously been reported.« less
OH cleavage from tyrosine: debunking a myth

DOE PAGES

Bury, Charles S.; Carmichael, Ian; Garman, Elspeth F.

2017-01-01

During macromolecular X-ray crystallography experiments, protein crystals held at 100 K have been widely reported to exhibit reproducible bond scission events at doses on the order of several MGy. With the objective to mitigate the impact of radiation damage events on valid structure determination, it is essential to correctly understand the radiation chemistry mechanisms at play. OH-cleavage from tyrosine residues is regularly cited as amongst the most available damage pathways in protein crystals at 100 K, despite a lack of widespread reports of this phenomenon in protein crystal radiation damage studies. Furthermore, no clear mechanism for phenolic C—O bond cleavagemore » in tyrosine has been reported, with the tyrosyl radical known to be relatively robust and long-lived in both aqueous solutions and the solid state. Here, the initial findings of Tyr –OH group damage in a myrosinase protein crystal have been reviewed. Consistent with that study, at increasing doses, clear electron density loss was detectable local to Tyr –OH groups. A systematic investigation performed on a range of protein crystal damage series deposited in the Protein Data Bank has established that Tyr –OH electron density loss is not generally a dominant damage pathway in protein crystals at 100 K. Full Tyr aromatic ring displacement is here proposed to account for instances of observable Tyr –OH electron density loss, with the original myrosinase data shown to be consistent with such a damage model. Also presented are systematic analysis of the effects of other environmental factors, including solvent accessibility and proximity to disulfide bonds or hydrogen bond interactions. Residues in known active sites showed enhanced sensitivity to radiation-induced disordering, as has previously been reported.« less
Long-Term Follow-Up of Primary Medical Versus Surgical Treatment of Prolactinomas in Men: Effects on Hyperprolactinemia, Hypogonadism, and Bone Health.

PubMed

Andereggen, Lukas; Frey, Janine; Andres, Robert H; El-Koussy, Marwan; Beck, Jürgen; Seiler, Rolf W; Christ, Emanuel

2017-01-01

In men with prolactinomas, impaired bone density is the principle consequence of hyperprolactinemia-induced hypogonadism. Although dopamine agonists (DAs) are the first-line approach in prolactinomas, surgery can be considered in selected cases. In this study, we aimed to investigate the long-term control of hyperprolactinemia, hypogonadism, and bone health comparing primary medical and surgical therapy in men who had not had prior DA treatment. This is a retrospective case-note study of 44 consecutive men with prolactinomas and no prior DAs managed in a single tertiary referral center. Clinical, biochemical, and radiologic response to the first-line approach were analyzed in the 2 cohorts. Mean age at diagnosis was 47 years (range, 22-78 years). The prevalence of hypogonadism was 86%, and 27% of patients had pathologic bone density at baseline. The primary therapeutic strategy was surgery for 34% and DAs for 66% of patients. Median long-term follow-up was 63 months (range, 17-238 months). Long-term control of hyperprolactinemia required DAs in 53% of patients with primary surgical therapy, versus 90% of patients with primary medical therapy (P = 0.02). Hypogonadism was controlled in 73% of patients. The prevalence of patients with pathologic bone density was 37% at last follow-up, with no differences between the 2 therapeutic cohorts (P = 0.48). Despite control of hyperprolactinemia and hypogonadism in most patients independent of the primary treatment modality, the prevalence of impaired bone health status remains high, and osteodensitometry should be recommended. Copyright © 2016 Elsevier Inc. All rights reserved.

Effects of 8-Year Treatment of Long-Acting Testosterone Undecanoate on Metabolic Parameters, Urinary Symptoms, Bone Mineral Density, and Sexual Function in Men With Late-Onset Hypogonadism.

PubMed

Permpongkosol, Sompol; Khupulsup, Kalayanee; Leelaphiwat, Supatra; Pavavattananusorn, Sarawan; Thongpradit, Supranee; Petchthong, Thanom

2016-08-01

The long-term effects of long-acting testosterone undecanoate (TU) and androgen receptor CAG repeat lengths in Thai men with late-onset hypogonadism (LOH) have not been reported. To analyze the 8-year follow-up effects of intramuscular TU therapy on metabolic parameters, urinary symptoms, bone mineral density, and sexual function and investigate CAG repeat lengths in men with LOH. We reviewed the medical records of 428 men with LOH who had been treated with TU and 5 patients were diagnosed with prostate cancer during TU therapy. There were 120 patients (mean age = 65.6 ± 8.9 years) who had 5 to 8 years of continuous TU supplementation and sufficiently completed records for analysis. Genomic DNA was extracted from peripheral blood and the CAG repeat region was amplified by polymerase chain reaction. Fragment analysis, sequencing, electropherography, and chromatography were performed. The main outcome measure was dynamic parameter changes during testosterone supplementation. TU did not improve all obesity parameters. A statistically significant decrease was found in waist circumference, percentage of body fat, glycated hemoglobin, cholesterol, low-density lipoprotein, and International Prostate Symptom Score (P < .05). TU did not produce differences in body mass index, high-density lipoprotein, triglyceride, or the Aging Male Symptoms score from baseline. However, a statistically significant increase was found in the level of testosterone, prostate-specific antigen, hematocrit, International Index of Erectile Function score, and vertebral and femoral bone mineral density (P < .05). No major adverse cardiovascular events or prostate cancer occurred during this study. The CAG repeat length was 14 to 28 and the median CAG length was 22. There was no association between CAG repeat length and any of the anthropometric measurements. Long-term TU treatment in men with LOH for up to 8 years appears to be safe, tolerable, and effective in correcting obesity parameters. Copyright © 2016 International Society for Sexual Medicine. Published by Elsevier Inc. All rights reserved.
Finite Element Analysis of High Heat Load Deformation and Mechanical Bending Correction of a Beamline Mirror for the APS Upgrade

NASA Astrophysics Data System (ADS)

Goldring, Nicholas

The impending Advanced Photon Source Upgrade (APS-U) will introduce a hard x-ray source that is set to surpass the current APS in brightness and coherence by two to three orders of magnitude. To achieve this, the storage ring light source will be equipped with a multi-bend achromat (MBA) lattice. In order to fully exploit and preserve the integrity of new beams actualized by upgraded storage ring components, improved beamline optics must also be introduced. The design process of new optics for the APS-U and other fourth generation synchrotrons involves the challenge of accommodating unprecedented heat loads. This dissertation presents an ex-situ analysis of heat load deformation and the subsequent mechanical bending correction of a 400 mm long, grazing-incidence, H2O side-cooled, reflecting mirror subjected to x-ray beams produced by the APS-U undulator source. Bending correction is measured as the smallest rms slope error, sigmarms, that can be resolved over a given length of the heat deformed geometry due to mechanical bending. Values of sigmarms in the <0.1 microrad regime represent a given mirror length over which incident x-ray beams from modern sources can be reflected without significant loss of quality. This study assumes a perfectly flat mirror surface and does not account for finish errors or other contributions to sigmarms beyond the scope of thermal deformation and elastic bending. The methodology of this research includes finite element analysis (FEA) employed conjointly with an analytical solution for mechanical bending deflection by means of an end couple. Additionally, the study will focus on two beam power density profiles predicted by the APS-U which were created using the software SRCalc. The profiles account for a 6 GeV electron beam with second moment widths of 0.058 and 0.011 mm in the x- and y- directions respectively; the electron beam is passed through a 4.8 m long, 28 mm period APS-U undulator which produces the x-ray beam incident at a 3 mrad grazing angle on the flat mirror surface for both cases. The first power density profile is the most extreme case created by the undulator at it's closest gap with a critical energy of 3 keV (k y=2.459); the second profile is generated for the case in which the undulator is tuned to emit at 8 keV (ky=1.026). The 3 keV case is of particular interest as it represents one of the most intense peak heat loads predicted to be incident on first optics at the APS-U. The FEA results revealed that the deflection due to the 3 keV heat load yields a 10.9 microrad rms slope error over the full mirror length. The projected correction via the elastic bending of the substrate yields a 0.10 microrad sigma rms within the center longitudinal 300 mm. The FEA also predicts that the 8 keV heat load deflection can be corrected to a sigma rms of 0.11 microrad within the center 300 mm from 1.50 microrad over the entire length. Attempts to optimize the end couple to correct over the entire 400 mm mirror length were unable to resolve the heat load deflection rms slope error to within a <0.1 microrad value for either case. However, if a larger corrected surface is required, a longer mirror can be implemented so as to absorb the heat load of a larger beam than necessary which can then be cut by an aperture to the desired size and energy range.
Experimental study on thermal characteristics of positive leader discharges using Mach-Zehnder interferometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, X., E-mail: zhouxuan12@mails.thu.edu.cn; Zeng, R.; Zhuang, C.

2015-06-15

Leader discharge is one of the main phases in long air gap breakdown, which is characterized by high temperature and high conductivity. It is of great importance to determine thermal characteristics of leader discharges. In this paper, a long-optical-path Mach-Zehnder interferometer was set up to measure the thermal parameters (thermal diameter, gas density, and gas temperature) of positive leader discharges in atmospheric air. IEC standard positive switching impulse voltages were applied to a near-one-meter point-plane air gap. Filamentary channels with high gas temperature and low density corresponding to leader discharges were observed as significant distortions in the interference fringe images.more » Typical diameters of the entire heated channel range from 1.5 mm to 3.5 mm with an average expansion velocity of 6.7 m/s. In contrast, typical diameters of the intensely heated region with a sharp gas density reduction range from 0.4 mm to 1.1 mm, about one third of the entire heated channel. The radial distribution of the gas density is calculated from the fringe displacements by performing an Abel inverse transform. The typical calculated gas density reduction in the center of a propagating leader channel is 80% to 90%, corresponding to a gas temperature of 1500 K to 3000 K based on the ideal gas law. Leaders tend to terminate if the central temperature is below 1500 K.« less
Density Can Be Misleading for Low-Density Species: Benefits of Passive Acoustic Monitoring

PubMed Central

Rogers, Tracey L.; Ciaglia, Michaela B.; Klinck, Holger; Southwell, Colin

2013-01-01

Climate-induced changes may be more substantial within the marine environment, where following ecological change is logistically difficult, and typically expensive. As marine animals tend to produce stereotyped, long-range signals, they are ideal for repeatable surveying. In this study we illustrate the potential for calling rates to be used as a tool for determining habitat quality by using an Antarctic pack-ice seal, the leopard seal, as a model.With an understanding of the vocal behavior of a species, their seasonal and diurnal patterns, sex and age-related differences, an underwater passive-acoustic survey conducted alongside a visual survey in an arc of 4,225 km across the Davis Sea, Eastern Antarctica, showed that while acoustic and visual surveys identified similar regions as having high densities, the acoustic surveys surprisingly identified the opposite regions as being ‘critical’ habitats. Density surveys of species that cannot be differentiated into population classes may be misleading because overall density can be a negative indicator of habitat quality.Under special circumstances acoustics can offer enormous advantage over traditional techniques and open up monitoring to regions that are remote, difficult and expensive to work within, no longer restricting long-term community assessment to resource-wealthy communities. As climatic change affects a broad range of organisms across geographic boundaries we propose that capitalizing on the significant advances in passive acoustic technology, alongside physical acoustics and population modeling, can help in addressing ecological questions more broadly. PMID:23326339
Adiabatic corrections to density functional theory energies and wave functions.

PubMed

Mohallem, José R; Coura, Thiago de O; Diniz, Leonardo G; de Castro, Gustavo; Assafrão, Denise; Heine, Thomas

2008-09-25

The adiabatic finite-nuclear-mass-correction (FNMC) to the electronic energies and wave functions of atoms and molecules is formulated for density-functional theory and implemented in the deMon code. The approach is tested for a series of local and gradient corrected density functionals, using MP2 results and diagonal-Born-Oppenheimer corrections from the literature for comparison. In the evaluation of absolute energy corrections of nonorganic molecules the LDA PZ81 functional works surprisingly better than the others. For organic molecules the GGA BLYP functional has the best performance. FNMC with GGA functionals, mainly BLYP, show a good performance in the evaluation of relative corrections, except for nonorganic molecules containing H atoms. The PW86 functional stands out with the best evaluation of the barrier of linearity of H2O and the isotopic dipole moment of HDO. In general, DFT functionals display an accuracy superior than the common belief and because the corrections are based on a change of the electronic kinetic energy they are here ranked in a new appropriate way. The approach is applied to obtain the adiabatic correction for full atomization of alcanes C(n)H(2n+2), n = 4-10. The barrier of 1 mHartree is approached for adiabatic corrections, justifying its insertion into DFT.
Correction of localized shape errors on optical surfaces by altering the localized density of surface or near-surface layers

DOEpatents

Taylor, John S.; Folta, James A.; Montcalm, Claude

2005-01-18

Figure errors are corrected on optical or other precision surfaces by changing the local density of material in a zone at or near the surface. Optical surface height is correlated with the localized density of the material within the same region. A change in the height of the optical surface can then be caused by a change in the localized density of the material at or near the surface.
Correlation approach to identify coding regions in DNA sequences

NASA Technical Reports Server (NTRS)

Ossadnik, S. M.; Buldyrev, S. V.; Goldberger, A. L.; Havlin, S.; Mantegna, R. N.; Peng, C. K.; Simons, M.; Stanley, H. E.

1994-01-01

Recently, it was observed that noncoding regions of DNA sequences possess long-range power-law correlations, whereas coding regions typically display only short-range correlations. We develop an algorithm based on this finding that enables investigators to perform a statistical analysis on long DNA sequences to locate possible coding regions. The algorithm is particularly successful in predicting the location of lengthy coding regions. For example, for the complete genome of yeast chromosome III (315,344 nucleotides), at least 82% of the predictions correspond to putative coding regions; the algorithm correctly identified all coding regions larger than 3000 nucleotides, 92% of coding regions between 2000 and 3000 nucleotides long, and 79% of coding regions between 1000 and 2000 nucleotides. The predictive ability of this new algorithm supports the claim that there is a fundamental difference in the correlation property between coding and noncoding sequences. This algorithm, which is not species-dependent, can be implemented with other techniques for rapidly and accurately locating relatively long coding regions in genomic sequences.
Reconstructing shifts in vital rates driven by long-term environmental change: a new demographic method based on readily available data.

PubMed

González, Edgar J; Martorell, Carlos

2013-07-01

Frequently, vital rates are driven by directional, long-term environmental changes. Many of these are of great importance, such as land degradation, climate change, and succession. Traditional demographic methods assume a constant or stationary environment, and thus are inappropriate to analyze populations subject to these changes. They also require repeat surveys of the individuals as change unfolds. Methods for reconstructing such lengthy processes are needed. We present a model that, based on a time series of population size structures and densities, reconstructs the impact of directional environmental changes on vital rates. The model uses integral projection models and maximum likelihood to identify the rates that best reconstructs the time series. The procedure was validated with artificial and real data. The former involved simulated species with widely different demographic behaviors. The latter used a chronosequence of populations of an endangered cactus subject to increasing anthropogenic disturbance. In our simulations, the vital rates and their change were always reconstructed accurately. Nevertheless, the model frequently produced alternative results. The use of coarse knowledge of the species' biology (whether vital rates increase or decrease with size or their plausible values) allowed the correct rates to be identified with a 90% success rate. With real data, the model correctly reconstructed the effects of disturbance on vital rates. These effects were previously known from two populations for which demographic data were available. Our procedure seems robust, as the data violated several of the model's assumptions. Thus, time series of size structures and densities contain the necessary information to reconstruct changing vital rates. However, additional biological knowledge may be required to provide reliable results. Because time series of size structures and densities are available for many species or can be rapidly generated, our model can contribute to understand populations that face highly pressing environmental problems.
Reconstructing shifts in vital rates driven by long-term environmental change: a new demographic method based on readily available data

PubMed Central

González, Edgar J; Martorell, Carlos

2013-01-01

Frequently, vital rates are driven by directional, long-term environmental changes. Many of these are of great importance, such as land degradation, climate change, and succession. Traditional demographic methods assume a constant or stationary environment, and thus are inappropriate to analyze populations subject to these changes. They also require repeat surveys of the individuals as change unfolds. Methods for reconstructing such lengthy processes are needed. We present a model that, based on a time series of population size structures and densities, reconstructs the impact of directional environmental changes on vital rates. The model uses integral projection models and maximum likelihood to identify the rates that best reconstructs the time series. The procedure was validated with artificial and real data. The former involved simulated species with widely different demographic behaviors. The latter used a chronosequence of populations of an endangered cactus subject to increasing anthropogenic disturbance. In our simulations, the vital rates and their change were always reconstructed accurately. Nevertheless, the model frequently produced alternative results. The use of coarse knowledge of the species' biology (whether vital rates increase or decrease with size or their plausible values) allowed the correct rates to be identified with a 90% success rate. With real data, the model correctly reconstructed the effects of disturbance on vital rates. These effects were previously known from two populations for which demographic data were available. Our procedure seems robust, as the data violated several of the model's assumptions. Thus, time series of size structures and densities contain the necessary information to reconstruct changing vital rates. However, additional biological knowledge may be required to provide reliable results. Because time series of size structures and densities are available for many species or can be rapidly generated, our model can contribute to understand populations that face highly pressing environmental problems. PMID:23919169
Study of ELM Density Turbulence using the Upgraded Phase Contrast Imaging on DIII-D

NASA Astrophysics Data System (ADS)

Rost, J. C.; Davis, E. M.; Marinoni, A.; Porkolab, M.; Burrell, K. H.

2016-10-01

Recent studies of the turbulent density fluctuations accompanying ELMs in mixed ELM-type discharges have exploited the expanded wavenumber range of the upgraded Phase Contrast Imaging (PCI) diagnostic. The PCI data demonstrate the difference between the fluctuations generated by Type I ELMs, which are broadband in frequency and wavelength, and those generated by Type III ELMs, which are similar in amplitude but restricted to long wavelengths, suggesting that turbulence may play a significant role in Type I ELM transport. The high frequency response of PCI makes it ideal for studying the ELM-associated density fluctuations, which are observed at frequencies up to several MHz, evolve on time scales of 10s of μs, and persist after the magnetic component of the ELM has decayed away. The upgraded PCI, with independent systems for long and short wavelength detection (k < 5 cm-1 and 1 < k < 30 cm-1 respectively), demonstrated coverage of the full wavenumber range of interest. Work supported in part by the US Department of Energy under DE-FG02-94ER54235, DE-FC02-04ER54698, and DE-FC02-99ER54512.
LWIR pupil imaging and longer-term calibration stability

NASA Astrophysics Data System (ADS)

LeVan, Paul D.; Sakoglu, Ünal

2016-09-01

A previous paper described LWIR pupil imaging, and an improved understanding of the behavior of this type of sensor for which the high-sensitivity focal plane array (FPA) operated at higher flux levels includes a reversal in signal integration polarity. We have since considered a candidate methodology for efficient, long-term calibration stability that exploits the following two properties of pupil imaging: (1) a fixed pupil position on the FPA, and (2) signal levels from the scene imposed on significant but fixed LWIR background levels. These two properties serve to keep each pixel operating over a limited dynamic range that corresponds to its location in the pupil and to the signal levels generated at this location by the lower and upper calibration flux levels. Exploiting this property for which each pixel of the Pupil Imager operates over its limited dynamic range, the signal polarity reversal between low and high flux pixels, which occurs for a circular region of pixels near the upper edges of the pupil illumination profile, can be rectified to unipolar integration with a two-level non-uniformity correction (NUC). Images corrected real-time with standard non-uniformity correction (NUC) techniques, are still subject to longer-term drifts in pixel offsets between recalibrations. Long-term calibration stability might then be achieved using either a scene-based non-uniformity correction approach, or with periodic repointing for off-source background estimation and subtraction. Either approach requires dithering of the field of view, by sub-pixel amounts for the first method, or by large off-source motions outside the 0.38 milliradian FOV for the latter method. We report on the results of investigations along both these lines.
A Community-Based IoT Personalized Wireless Healthcare Solution Trial.

PubMed

Catherwood, Philip A; Steele, David; Little, Mike; Mccomb, Stephen; Mclaughlin, James

2018-01-01

This paper presents an advanced Internet of Things point-of-care bio-fluid analyzer; a LoRa/Bluetooth-enabled electronic reader for biomedical strip-based diagnostics system for personalized monitoring. We undertake test simulations (technology trial without patient subjects) to demonstrate potential of long-range analysis, using a disposable test 'key' and companion Android app to form a diagnostic platform suitable for remote point-of-care screening for urinary tract infection (UTI). The 868 MHz LoRaWAN-enabled personalized monitor demonstrated sound potential with UTI test results being correctly diagnosed and transmitted to a remote secure cloud server in every case. Tests ranged over distances of 1.1-6.0 Km with radio path losses from 119-141 dB. All tests conducted were correctly and robustly received at the base station and relayed to the secure server for inspection. The UTI test strips were visually inspected for correct diagnosis based on color change and verified as 100% accurate. Results from testing across a number of regions indicate that such an Internet of Things medical solution is a robust and simple way to deliver next generation community-based smart diagnostics and disease management to best benefit patients and clinical staff alike. This significant step can be applied to any type of home or region, particularly those lacking suitable mobile signals, broadband connections, or even landlines. It brings subscription-free long-range bio-telemetry to healthcare providers and offers savings on regular clinician home visits or frequent clinic visits by the chronically ill. This paper highlights practical hurdles in establishing an Internet of Medical Things network, assisting informed deployment of similar future systems.
A Community-Based IoT Personalized Wireless Healthcare Solution Trial

PubMed Central

Steele, David; Little, Mike; Mccomb, Stephen; Mclaughlin, James

2018-01-01

This paper presents an advanced Internet of Things point-of-care bio-fluid analyzer; a LoRa/Bluetooth-enabled electronic reader for biomedical strip-based diagnostics system for personalized monitoring. We undertake test simulations (technology trial without patient subjects) to demonstrate potential of long-range analysis, using a disposable test ‘key’ and companion Android app to form a diagnostic platform suitable for remote point-of-care screening for urinary tract infection (UTI). The 868 MHz LoRaWAN-enabled personalized monitor demonstrated sound potential with UTI test results being correctly diagnosed and transmitted to a remote secure cloud server in every case. Tests ranged over distances of 1.1–6.0 Km with radio path losses from 119–141 dB. All tests conducted were correctly and robustly received at the base station and relayed to the secure server for inspection. The UTI test strips were visually inspected for correct diagnosis based on color change and verified as 100% accurate. Results from testing across a number of regions indicate that such an Internet of Things medical solution is a robust and simple way to deliver next generation community-based smart diagnostics and disease management to best benefit patients and clinical staff alike. This significant step can be applied to any type of home or region, particularly those lacking suitable mobile signals, broadband connections, or even landlines. It brings subscription-free long-range bio-telemetry to healthcare providers and offers savings on regular clinician home visits or frequent clinic visits by the chronically ill. This paper highlights practical hurdles in establishing an Internet of Medical Things network, assisting informed deployment of similar future systems. PMID:29888145
Modelling relativistic effects in momentum-resolved electron energy loss spectroscopy of graphene

NASA Astrophysics Data System (ADS)

Lyon, K.; Mowbray, D. J.; Miskovic, Z. L.

2018-02-01

We present an analytical model for the electron energy loss through a two-dimensional (2D) layer of graphene, fully taking into account relativistic effects. Using two different models for graphene's 2D conductivity, one a two-fluid hydrodynamic model with an added correction to account for the inter-band electron transitions near the Dirac point in undoped graphene, the other derived from ab initio plane-wave time-dependent density functional theory in the frequency domain (PW-TDDFT-ω) calculations applied on a graphene superlattice, we derive various different expressions for the probability density of energy and momentum transfer from the incident electron to graphene. To further compare with electron energy loss spectroscopy (EELS) experiments that use setups like scanning Transmission Electron Microscopy, we integrated our energy loss functions over a range of wavenumbers, and compared how the choice of range directly affects the shape, position, and relative heights of graphene's π → π* and σ → σ* transition peaks. Comparisons were made with experimental EELS data under different model inputs, revealing again the strong effect that the choice of wavenumber range has on the energy loss.
Temperatures and Altitudes of Jupiter's Ultraviolet Aurora Inferred from GHRS Observations with the Hubble Space Telescope

NASA Astrophysics Data System (ADS)

Kim, Y. H.; Fox, J. L.; Caldwell, John J.

1997-07-01

We observed the jovian UV auroral regions with the Goddard high resolution spectrograph (GHRS) on board the Hubble Space Telescope (HST) on Apr. 29, May 2, and June 10, 1995. Observations of target areas were made in pairs in the two wavelength ranges 1257-1293 Å and 1587-1621 Å. Spectra in the long wavelength range are dominated by emissions of the H2Lyman band system and show well separated rotational features, which we have used to determine the temperatures of the auroral emission regions. Spectra in the short wavelength range are mostly due to emission in the H2Lyman and Werner band systems, but their intensities are reduced by hydrocarbon absorption. The brightest spectral pair was observed toward an area with longitude 155° and jovicentric latitude 58° when the central meridian longitudes (CMLs) were 191° and 203°. This area was found to be bright in our previous HST observations in 1993 and in HST faint object camera images. Assuming that electron impact excitation is the major source of the jovian aurora, we estimate total emission rates in the Lyman band system of about 270 and 46 kR for the long and short wavelength spectra of the pair, respectively. The attenuation of emission rate in the short wavelength spectrum implies a methane column density of about 3 × 1016cm-2, and a temperature of about 450 K is inferred from the long wavelength spectrum of the brightest pair. For all six pairs of observed spectra, we estimate methane column densities in the range (1-7) × 1016cm-2, which, when compared to a standard mid-latitude model, corresponds to a pressure range from a few μbar to a few tens of μbar. The temperatures derived are in the range 400-850 K with a possible tendency toward lower temperatures for higher methane column densities. This tendency and the uncertainty in the temperatures derived may indicate that the temperatures increases rapidly with altitude around the methane homopause in the auroral regions.
Uncertainty analysis of gas flow measurements using clearance-sealed piston provers in the range from 0.0012 g min-1 to 60 g min-1

NASA Astrophysics Data System (ADS)

Bobovnik, G.; Kutin, J.; Bajsić, I.

2016-08-01

This paper deals with an uncertainty analysis of gas flow measurements using a compact, high-speed, clearance-sealed realization of a piston prover. A detailed methodology for the uncertainty analysis, covering the components due to the gas density, dimensional and time measurements, the leakage flow, the density correction factor and the repeatability, is presented. The paper also deals with the selection of the isothermal and adiabatic measurement models, the treatment of the leakage flow and discusses the need for averaging multiple consecutive readings of the piston prover. The analysis is prepared for the flow range (50 000:1) covered by the three interchangeable flow cells. The results show that using the adiabatic measurement model and averaging the multiple readings, the estimated expanded measurement uncertainty of the gas mass flow rate is less than 0.15% in the flow range above 0.012 g min-1, whereas it increases for lower mass flow rates due to the leakage flow related effects. At the upper end of the measuring range, using the adiabatic instead of the isothermal measurement model, as well as averaging multiple readings, proves important.
On the simulation and mitigation of anisoplanatic optical turbulence for long range imaging

NASA Astrophysics Data System (ADS)

Hardie, Russell C.; LeMaster, Daniel A.

2017-05-01

We describe a numerical wave propagation method for simulating long range imaging of an extended scene under anisoplanatic conditions. Our approach computes an array of point spread functions (PSFs) for a 2D grid on the object plane. The PSFs are then used in a spatially varying weighted sum operation, with an ideal image, to produce a simulated image with realistic optical turbulence degradation. To validate the simulation we compare simulated outputs with the theoretical anisoplanatic tilt correlation and differential tilt variance. This is in addition to comparing the long- and short-exposure PSFs, and isoplanatic angle. Our validation analysis shows an excellent match between the simulation statistics and the theoretical predictions. The simulation tool is also used here to quantitatively evaluate a recently proposed block- matching and Wiener filtering (BMWF) method for turbulence mitigation. In this method block-matching registration algorithm is used to provide geometric correction for each of the individual input frames. The registered frames are then averaged and processed with a Wiener filter for restoration. A novel aspect of the proposed BMWF method is that the PSF model used for restoration takes into account the level of geometric correction achieved during image registration. This way, the Wiener filter is able fully exploit the reduced blurring achieved by registration. The BMWF method is relatively simple computationally, and yet, has excellent performance in comparison to state-of-the-art benchmark methods.
[Radiometers performance attenuation and data correction in long-term observation of total radiation and photosynthetically active radiation in typical forest ecosystems in China].

PubMed

Zhu, Zhi-Lin; Sun, Xiao-Min; Yu, Gui-Rui; Wen, Xue-Fa; Zhang, Yi-Ping; Han, Shi-Jie; Yan, Jun-Hua; Wang, Hui-Min

2011-11-01

Based on the total radiation and photosynthetically active radiation (PAR) observations with net radiometer (CNR1) and quantum sensor (Li-190SB) in 4 ChinaFLUX forest sites (Changbaishan, Qianyanzhou, Dinghushan, and Xishuangbanna) in 2003-2008, this paper analyzed the uncertainties and the radiometers performance changes in long-term and continuous field observation. The results showed that the 98% accuracy of the total radiation measured with CNR1 (Q(cNR1)) could satisfy the technical criterion for the sites except Xishuangbanna where the Q(CNR1) was averagely about 7% lower than Q(CM11), the radiation measured with high accuracy pyranometer CM11. For most sites, though the temperature had definite effects on the performance of CNR1, the effects were still within the allowable range of the accuracy of the instrument. Besides temperature, the seasonal fog often occurred in tropical rain forests in Xishuangbanna also had effects on the performance of CNR1. Based on the long-term variations of PAR, especially its ratio to total radiation in the 4 sites, it was found that quantum sensor (Li-190SB) had obvious performance attenuation, with the mean annual attenuation rate being about 4%. To correct the observation error caused by Li-190SB, an attempt was made to give a post-correction of the PAR observations, which could basically eliminate the quantum sensor's performance attenuation due to long-term field measurement.
Fourier-space combination of Planck and Herschel images

NASA Astrophysics Data System (ADS)

Abreu-Vicente, J.; Stutz, A.; Henning, Th.; Keto, E.; Ballesteros-Paredes, J.; Robitaille, T.

2017-08-01

Context. Herschel has revolutionized our ability to measure column densities (NH) and temperatures (T) of molecular clouds thanks to its far infrared multiwavelength coverage. However, the lack of a well defined background intensity level in the Herschel data limits the accuracy of the NH and T maps. Aims: We aim to provide a method that corrects the missing Herschel background intensity levels using the Planck model for foreground Galactic thermal dust emission. For the Herschel/PACS data, both the constant-offset as well as the spatial dependence of the missing background must be addressed. For the Herschel/SPIRE data, the constant-offset correction has already been applied to the archival data so we are primarily concerned with the spatial dependence, which is most important at 250 μm. Methods: We present a Fourier method that combines the publicly available Planck model on large angular scales with the Herschel images on smaller angular scales. Results: We have applied our method to two regions spanning a range of Galactic environments: Perseus and the Galactic plane region around l = 11deg (HiGal-11). We post-processed the combined dust continuum emission images to generate column density and temperature maps. We compared these to previously adopted constant-offset corrections. We find significant differences (≳20%) over significant ( 15%) areas of the maps, at low column densities (NH ≲ 1022 cm-2) and relatively high temperatures (T ≳ 20 K). We have also applied our method to synthetic observations of a simulated molecular cloud to validate our method. Conclusions: Our method successfully corrects the Herschel images, including both the constant-offset intensity level and the scale-dependent background variations measured by Planck. Our method improves the previous constant-offset corrections, which did not account for variations in the background emission levels. The image FITS files used in this paper are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/604/A65
Protein-ligand interaction energies with dispersion corrected density functional theory and high-level wave function based methods.

PubMed

Antony, Jens; Grimme, Stefan; Liakos, Dimitrios G; Neese, Frank

2011-10-20

With dispersion-corrected density functional theory (DFT-D3) intermolecular interaction energies for a diverse set of noncovalently bound protein-ligand complexes from the Protein Data Bank are calculated. The focus is on major contacts occurring between the drug molecule and the binding site. Generalized gradient approximation (GGA), meta-GGA, and hybrid functionals are used. DFT-D3 interaction energies are benchmarked against the best available wave function based results that are provided by the estimated complete basis set (CBS) limit of the local pair natural orbital coupled-electron pair approximation (LPNO-CEPA/1) and compared to MP2 and semiempirical data. The size of the complexes and their interaction energies (ΔE(PL)) varies between 50 and 300 atoms and from -1 to -65 kcal/mol, respectively. Basis set effects are considered by applying extended sets of triple- to quadruple-ζ quality. Computed total ΔE(PL) values show a good correlation with the dispersion contribution despite the fact that the protein-ligand complexes contain many hydrogen bonds. It is concluded that an adequate, for example, asymptotically correct, treatment of dispersion interactions is necessary for the realistic modeling of protein-ligand binding. Inclusion of the dispersion correction drastically reduces the dependence of the computed interaction energies on the density functional compared to uncorrected DFT results. DFT-D3 methods provide results that are consistent with LPNO-CEPA/1 and MP2, the differences of about 1-2 kcal/mol on average (<5% of ΔE(PL)) being on the order of their accuracy, while dispersion-corrected semiempirical AM1 and PM3 approaches show a deviating behavior. The DFT-D3 results are found to depend insignificantly on the choice of the short-range damping model. We propose to use DFT-D3 as an essential ingredient in a QM/MM approach for advanced virtual screening approaches of protein-ligand interactions to be combined with similarly "first-principle" accounts for the estimation of solvation and entropic effects.

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