Elaboration of the alpha-model derived from the BCS theory of superconductivity
Johnston, David C.
2013-10-14
The single-band α-model of superconductivity (Padamsee et al 1973 J. Low Temp. Phys. 12 387) is a popular model that was adapted from the single-band Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity mainly to allow fits to electronic heat capacity versus temperature T data that deviate from the BCS prediction. The model assumes that the normalized superconducting order parameter Δ(T)/Δ(0) and therefore the normalized London penetration depth λL(T)/λL(0) are the same as in BCS theory, calculated using the BCS value αBCS ≈ 1.764 of α ≡ Δ(0)/kBTc, where kB is The single-band α-model of superconductivity (Padamsee et al 1973 J. Low Temp. Phys. 12 387) is a popular model that was adapted from the single-band Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity mainly to allow fits to electronic heat capacity versus temperature T data that deviate from the BCS prediction. The model assumes that the normalized superconducting order parameter Δ(T)/Δ(0) and therefore the normalized London penetration depth λL(T)/λL(0) are the same as in BCS theory, calculated using the BCS value αBCS ≈ 1.764 of α ≡ Δ(0)/kBTc, where kB is Boltzmann's constant and Tc is the superconducting transition temperature. On the other hand, to calculate the electronic free energy, entropy, heat capacity and thermodynamic critical field versus T, the α-model takes α to be an adjustable parameter. Here we write the BCS equations and limiting behaviors for the superconducting state thermodynamic properties explicitly in terms of α, as needed for calculations within the α-model, and present plots of the results versus T and α that are compared with the respective BCS predictions. Mechanisms such as gap anisotropy and strong coupling that can cause deviations of the thermodynamics from the BCS predictions, especially the heat capacity jump at Tc, are considered. Extensions of the α-model that have appeared in the literature, such as the two-band model
Confirmation of BCS Theory and Its Impact on Applications Past and Future
NASA Astrophysics Data System (ADS)
Beasley, Malcolm
2011-03-01
The experimental confirmation of BCS theory established it as the correct microscopic theory of superconductivity. It also led to applications of superconductivity distinct from those based on the Josephson effect and the magnetic properties of superconductors. The most prominent of these are SIS mixers for astronomy and high-Q filters for the cellular phone industry. In this talk we trace these historical developments and consider where today's more novel (beyond simple BCS) superconductors might be useful looking forward.
A modified physiological BCS for prediction of intestinal absorption in drug discovery.
Zaki, Noha M; Artursson, Per; Bergström, Christel A S
2010-10-01
In this study, the influence of physiologically relevant media on the compound position in a biopharmaceutical classification system (BCS) which resembled the intestinal absorption was investigated. Both solubility and permeability limited compounds (n = 22) were included to analyze the importance of each of these on the final absorption. Solubility was determined in three different dissolution media, phosphate buffer pH 6.5 (PhB 6.5), fasted state simulated intestinal fluid (FaSSIF), and fed state simulated intestinal fluid (FeSSIF) at 37 °C, and permeability values were determined using the 2/4/A1 cell line. The solubility data and membrane permeability values were used for sorting the compounds into a BCS modified to reflect the fasted and fed state. Three of the seven compounds sorted as BCS II in PhB 6.5 (high permeability, low solubility) changed their position to BCS I when dissolved in FaSSIF and/or FeSSIF (high permeability, high solubility). These were low dosed (20 mg or less) lipophilic molecules displaying solvation limited solubility. In contrast, compounds having solid-state limited solubility had a minor increase in solubility when dissolved in FaSSIF and/or FeSSIF. Although further studies are needed to enable general cutoff values, our study indicates that low dosed BCS Class II compounds which have solubility normally restricted by poor solvation may behave as BCS Class I compounds in vivo. The large series of compounds investigated herein reveals the importance of investigating solubility and dissolution under physiologically relevant conditions in all stages of the drug discovery process to push suitable compounds forward, to select proper formulations, and to reduce the risk of food effects. PMID:20734997
BCS (Bardeen-Cooper-Schrieffer) primer: A guide to computational methods in superconductivity theory
NASA Astrophysics Data System (ADS)
Sahu, Devaraj; Langner, Andreas; George, Thomas F.
1989-12-01
Because of the recent revival of interest in superconductivity, we have felt that a pedagogical, yet concise review of the fundamental ideas of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity is timely. We discuss the basic ideas of the BCS theory and list the formulae for the thermodynamic quantities of this theory in the usual real-time representation. We also represent these formulae in the alternate imaginary-time representation, which makes hands-on numerical evaluation of the thermodynamic quantities of interest readily accessible. Finally, we point out the limitations of the BCS theory and describe some of its proposed extensions for describing the behavior of some of the new, unconventional superconductors.
NASA Astrophysics Data System (ADS)
Degroote, Matthias; Henderson, Thomas M.; Zhao, Jinmo; Dukelsky, Jorge; Scuseria, Gustavo E.
2016-03-01
We present a similarity transformation theory based on a polynomial form of a particle-hole pair excitation operator. In the weakly correlated limit, this polynomial becomes an exponential, leading to coupled cluster doubles. In the opposite strongly correlated limit, the polynomial becomes an extended Bessel expansion and yields the projected BCS wave function. In between, we interpolate using a single parameter. The effective Hamiltonian is non-Hermitian and this polynomial similarity transformation theory follows the philosophy of traditional coupled cluster, left projecting the transformed Hamiltonian onto subspaces of the Hilbert space in which the wave function variance is forced to be zero. Similarly, the interpolation parameter is obtained through minimizing the next residual in the projective hierarchy. We rationalize and demonstrate how and why coupled cluster doubles is ill suited to the strongly correlated limit, whereas the Bessel expansion remains well behaved. The model provides accurate wave functions with energy errors that in its best variant are smaller than 1% across all interaction strengths. The numerical cost is polynomial in system size and the theory can be straightforwardly applied to any realistic Hamiltonian.
Modified Fermi sphere, pairing gap, and critical temperature for the BCS-BEC crossover
Floerchinger, S.; Wetterich, C.; Scherer, M. M.
2010-06-15
We investigate the phase diagram of two-component fermions in the BCS-BEC (Bose-Einstein condensate) crossover. Using functional renormalization-group equations we calculate the effect of quantum fluctuations on the fermionic self-energy parametrized by a wave-function renormalization, an effective Fermi radius, and the gap. This allows us to follow the modifications of the Fermi surface and the dispersion relation for fermionic excitations throughout the whole crossover region. We also determine the critical temperature of the second-order phase transition to superfluidity. Our results are in agreement with BCS theory including Gorkov's correction for a small negative scattering length a and with an interacting Bose gas for a small positive a. At the unitarity point the result for the gap at zero temperature agrees well with quantum Monte Carlo simulations, while the critical temperature differs.
Two-color spectroscopy of fermions in mean-field BCS-BEC crossover theory
Kostrun, Marijan; Cote, Robin
2006-04-15
We calculate two-photon Raman spectra for fermionic atoms with interactions described by a single-mode mean-field BCS-BEC crossover theory. We compare calculated spectra of interacting and noninteracting systems and find that interactions lead to the appearance of correlated atomic pair signal due to Cooper pairs; splitting of peaks in the spectroscopic signal due to the gap in fermionic dispersion; and attenuation of signal due to the partial conversion of fermions into the corresponding single-mode dimer. By exploring the behavior of these effects, one can obtain quantitative estimates of the BCS parameters from the spectra.
Dynamical description of the fission process using the TD-BCS theory
Scamps, Guillaume; Simenel, Cédric; Lacroix, Denis
2015-10-15
The description of fission remains a challenge for nuclear microscopic theories. The time-dependent Hartree-Fock approach with BCS pairing is applied to study the last stage of the fission process. A good agreement is found for the one-body observables: the total kinetic energy and the average mass asymmetry. The non-physical dependence of two-body observables with the initial shape is discussed.
BCS theory has to be overhauled: Reassurance from numerical survival rate
NASA Astrophysics Data System (ADS)
Zheng, X. H.; Walmsley, D. G.
2016-07-01
The BCS theory has conceptual and numerical difficulties. We have previously overhauled it with a new scheme of phonon-mediated electron pairing that can be expressed analytically in terms of an empirical pairing survival rate factor, S(q) = 0 or 1/2, depending on phonon momentum, q. Now we evaluate S(q) numerically entirely from experimental data on normal state electrical resistivity and on superconducting tunnelling conductance. The empirical and numerical S(q) are reassuringly close in aluminium and lead and particularly so in two other cases, niobium and tantalum.
Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover
Huang Kun; Yu Zengqiang; Yin Lan
2009-05-15
The Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover is derived by the path-integral method. In addition to the standard Ginzburg-Landau equation, a second equation describing the total atom density is obtained. These two coupled equations are necessary to describe both homogeneous and inhomogeneous systems. The Ginzburg-Landau theory is valid near the transition temperature T{sub c} on both sides of the crossover. In the weakly interacting BEC region, it is also accurate at zero temperature where the Ginzburg-Landau equation can be mapped onto the Gross-Pitaevskii (GP) equation. The applicability of GP equation at finite temperature is discussed. On the BEC side, the fluctuation of the order parameter is studied and the renormalization to the molecule coupling constant is obtained.
Self consistent theories of superfluid density and collective modes in BCS-BEC
NASA Astrophysics Data System (ADS)
Boyack, Rufus; Anderson, Brandon; Wu, Chien-Te; Levin, Kathryn
Establishing fully self consistent and sum rule compatible response functions in strongly correlated Fermi superfluids has been a historically challenging subject. In this talk, we present recent progress pertaining to response functions in many-body Fermi systems. We note that even in strict BCS theory, the textbook derivation of density and current response functions in the gradient expansion breaks certain conservation laws such as the compressibility sum rule. To include additional contributions that preserve all expected conservation laws, we show how to exploit Ward identities within two different t-matrix schemes. In this way we address the density-density response (including collective modes) and the superfluid density. Finally, we characterize approximations made in the literature where some consistency requirements have been dropped.
Giant Anharmonicity and Theory of Surprising BCS Superconductivity in MgB2 at 40 K
NASA Astrophysics Data System (ADS)
Yildirim, Taner
2002-03-01
The recent surprise discovery of superconductivity in MgB2 at 40 K has stimulated a great deal of research on this intercalated grahite-like system. Sparked by this discovery, we set out to unlock the structural secrets and, in particular, to reveal the origin of the high Tc in MgB_2; an electron-phonon or other exotic mechanism? To answer this fundamental question, we calculated T_c, its pressure dependence for uni- and biaxial compressions, and the isotope effect from the electronic band structure and lattice dynamics of MgB2 using density functional theory[1-2]. The calculated phonon density of states (DOS) are in excellent agreement with the inelastic neutron scattering measurements. We find that the in-plane boron phonons near the zone-center are very anharmonic and strongly coupled to the planar B sigma bands near the Fermi level. The boron mass and pressure dependence of this mode is found to be the key to quantitatively explaining the observed high T_c, the total isotope effect, and the pressure dependence of T_c. We propose that a stringent test on the hole and phonon based theories of the superconductivity in MgB2 would be a measurement of the biaxial ab-compression dependence of T_c. In collobration with Oguz Gulseren, NIST and UPENN [1] T. Yildirim et. al., Phys. Rev. Lett. 87, 037001 (2001). [2] For details, see http://www.ncnr.nist.gov/staff/taner/mgb2
NASA Astrophysics Data System (ADS)
Anghel, Dragoş-Victor; Nemnes, George Alexandru
2016-09-01
The effective energy of a superconductor Eeff(T) at temperature T is defined as the difference between the total energy at temperature T and the total energy at 0 K. We call the energy of the condensate, Ec, the difference between Eeff and the sum of the quasiparticle energies Eqp. Ec, Eqp, as well as the BCS quasiparticle energy ɛ are positive and depend on the gap energy Δ, which, in turn, depends on the populations of the quasiparticle states (equivalently, they depend on T). So, from the energetic point of view, the superconductor is a Fermi liquid of interacting quasiparticles. We show that the choice of quasiparticles is not unique, but there is an infinite range of possibilities. Some of these possibilities have been explored in the context of the fractional exclusion statistics (FES), which is a general method of describing interacting particle systems as ideal gases. We apply FES here and transform the Fermi liquid of BCS excitations into an ideal gas by redefining the quasiparticle energies. The new FES quasiparticles exhibit the same energy gap as the BCS quasiparticles, but a different DOS, which is finite at any quasiparticle energy. We also discuss the effect of the remnant electron-electron interaction (electron-electron interaction beyond the BCS pairing model) and show that this can stabilize the BCS condensate, increasing the critical temperature.
Chi, Liandi; Wu, Delin; Li, Zhuo; Zhang, Minmin; Liu, Hongchun; Wang, Caifen; Gui, Shuangying; Geng, Meiyu; Li, Haiyan; Zhang, Jiwen
2016-01-01
In answering to the challenge of enzymatic unstability of Biopharmaceutics Classification System (BCS) class II drugs, an effective remote loading strategy was developed to successfully incorporate the drug-cyclodextrin (CD) complex into niosomes to modify the release and stability of a drug candidate, pseudolaric acid B (PAB). Judged by binding constants, and combined solubilization effects of pH and CD complexation on PAB at different pH, the complex internalization driven by a transmembrane pH gradient (from 2.0 to 7.4) and the dynamic shifting of PAB-CD complexation equilibrium at this gradient were introduced. The transfer of PAB-CD complex into the internal aqueous phase of niosomes at 60 °C was primarily verified by synchrotron radiation Fourier transform infrared spectroscopy. The remote loading samples behaved as retarded release at pH 5.8, 6.8, and 7.4, for which the stability of PAB in rat plasma was significantly enhanced (about 8.1-fold), in comparison with niosomes prepared by the passive and lipid bilayer loading of PAB. The drug-carrier interaction based release modeling was further fitted, and the convection rate constant (ks) and free energy difference between free and bound states (ΔG) indicated the strongest PAB-carrier interactions in remote loading niosomes. The remote loading strategy also reduced the CD-cholesterol interaction and provided better physical stability of the system. In conclusion, the remote loading of drug-CD complex into niosomes provides advantages to modify the release and enhance the stability of unstable BCS class II drug. PMID:26569615
NASA Astrophysics Data System (ADS)
Hanai, Ryo; Ohashi, Yoji
2014-03-01
We investigate a two-component Fermi gas with mass imbalance (m↑ ≠m↓ , where mσ is an atomic mass in the σ-component) in the BCS-BEC crossover region. Including pairing fluctuations within a self-consistent T-matrix theory, we examine how the superfluid instability is affected by the presence of mass imbalance. We determine the superfluid region in the phase diagram of a Fermi gas in terms of the temperature, the strength of a pairing interaction, and the ratio of mass imbalance. The superfluid phase transition is shown to always occur even when m↑ ≠m↓ .[2] This behavior of Tc is quite different from the previous result in an extended T-matrix theory,[3] where Tc vanishes at a certain value of m↑ /m↓ > 0 in the BCS regime. Since Fermi condensates with mass imbalance have been discussed in various systems, such as a cold Fermi gas, an exciton(polariton) condensate, as well as color superconductivity, our results would be useful for further understandings of these novel Fermi superfluids. R.H. was supported by Graduate School Doctoral Student Aid Program, Keio University.
Modified Actions for Gravity: Theory and Phenomenology
NASA Astrophysics Data System (ADS)
Sotiriou, Thomas P.
2007-10-01
This thesis is devoted to the study of gravitational theories which can be seen as modifications or generalisations of General Relativity. The motivation for considering such theories, stemming from Cosmology, High Energy Physics and Astrophysics is thoroughly discussed (cosmological problems, dark energy and dark matter problems, the lack of success so far in obtaining a successful formulation for Quantum Gravity). The basic principles which a gravitational theory should follow, and their geometrical interpretation, are analysed in a broad perspective which highlights the basic assumptions of General Relativity and suggests possible modifications which might be made. A number of such possible modifications are presented, focusing on certain specific classes of theories: scalar-tensor theories, metric f(R) theories, Palatini f(R) theories, metric-affine f(R) theories and Gauss--Bonnet theories. The characteristics of these theories are fully explored and attention is payed to issues of dynamical equivalence between them. Also, cosmological phenomenology within the realm of each of the theories is discussed and it is shown that they can potentially address the well-known cosmological problems. A number of viability criteria are presented: cosmological observations, Solar System tests, stability criteria, existence of exact solutions for common vacuum or matter configurations etc. Finally, future perspectives in the field of modified gravity are discussed and the possibility for going beyond a trial-and-error approach to modified gravity is explored.
Modified Sigmund sputtering theory: isotopic puzzle
NASA Astrophysics Data System (ADS)
Zhang, Z. L.; Zhang, L.
2005-05-01
The theory of anisotropic sputtering proposed by Zhang [Z.L. Zhang, Phys. Rev. B 71 026101 (2005).] and [Z.L. Zhang and L. Zhang, Radiat. Eff. Defects Solids 159(5) 301 (2004).] has been generalized to sputtering of isotopic mixtures. The present theory (modified Sigmund theory) has been shown to fit numerous simulations and experimental measurements, including energy and angular distribution of sputtered atoms. In particular, the theory has successfully solved the isotope puzzle of sputtering induced by low energy and heavy ion bombardment.
Thermodynamic properties of modified gravity theories
NASA Astrophysics Data System (ADS)
Bamba, Kazuharu
2016-06-01
We review thermodynamic properties of modified gravity theories, such as F(R) gravity and f(T) gravity, where R is the scalar curvature and T is the torsion scalar in teleparallelism. In particular, we explore the equivalence between the equations of motion for modified gravity theories and the Clausius relation in thermodynamics. In addition, thermodynamics of the cosmological apparent horizon is investigated in f(T) gravity. We show both equilibrium and nonequilibrium descriptions of thermodynamics. It is demonstrated that the second law of thermodynamics in the universe can be met, when the temperature of the outside of the apparent horizon is equivalent to that of the inside of it.
Modified Iterative Extended Hueckel. 1: Theory
NASA Technical Reports Server (NTRS)
Aronowitz, S.
1980-01-01
Iterative Extended Huekel is modified by inclusion of explicit effective internuclear and electronic interactions. The one electron energies are shown to obey a variational principle because of the form of the effective electronic interactions. The modifications permit mimicking of aspects of valence bond theory with the additional feature that the energies associated with valence bond type structures are explicitly calculated. In turn, a hybrid molecular, orbital valence, bond scheme is introduced which incorporates variant total molecular electronic density distributions similar to the way that Iterative Extended Hueckel incorporates atoms.
Modified Interior Distance Functions (Theory and Methods)
NASA Technical Reports Server (NTRS)
Polyak, Roman A.
1995-01-01
In this paper we introduced and developed the theory of Modified Interior Distance Functions (MIDF's). The MIDF is a Classical Lagrangian (CL) for a constrained optimization problem which is equivalent to the initial one and can be obtained from the latter by monotone transformation both the objective function and constraints. In contrast to the Interior Distance Functions (IDF's), which played a fundamental role in Interior Point Methods (IPM's), the MIDF's are defined on an extended feasible set and along with center, have two extra tools, which control the computational process: the barrier parameter and the vector of Lagrange multipliers. The extra tools allow to attach to the MEDF's very important properties of Augmented Lagrangeans. One can consider the MIDFs as Interior Augmented Lagrangeans. It makes MIDF's similar in spirit to Modified Barrier Functions (MBF's), although there is a fundamental difference between them both in theory and methods. Based on MIDF's theory, Modified Center Methods (MCM's) have been developed and analyzed. The MCM's find an unconstrained minimizer in primal space and update the Lagrange multipliers, while both the center and the barrier parameter can be fixed or updated at each step. The MCM's convergence was investigated, and their rate of convergence was estimated. The extension of the feasible set and the special role of the Lagrange multipliers allow to develop MCM's, which produce, in case of nondegenerate constrained optimization, a primal and dual sequences that converge to the primal-dual solutions with linear rate, even when both the center and the barrier parameter are fixed. Moreover, every Lagrange multipliers update shrinks the distance to the primal dual solution by a factor 0 less than gamma less than 1 which can be made as small as one wants by choosing a fixed interior point as a 'center' and a fixed but large enough barrier parameter. The numericai realization of MCM leads to the Newton MCM (NMCM). The
Modified large number theory with constant G
Recami, E.
1983-03-01
The inspiring ''numerology'' uncovered by Dirac, Eddington, Weyl, et al. can be explained and derived when it is slightly modified so to connect the ''gravitational world'' (cosmos) with the ''strong world'' (hadron), rather than with the electromagnetic one. The aim of this note is to show the following. In the present approach to the ''Large Number Theory,'' cosmos and hadrons are considered to be (finite) similar systems, so that the ratio R-bar/r-bar of the cosmos typical length R-bar to the hadron typical length r-bar is constant in time (for instance, if both cosmos and hadrons undergo an expansion/contraction cycle: according to the ''cyclical big-bang'' hypothesis: then R-bar and r-bar can be chosen to be the maximum radii, or the average radii). As a consequence, then gravitational constant G results to be independent of time. The present note is based on work done in collaboration with P.Caldirola, G. D. Maccarrone, and M. Pavsic.
Equilibrium thermodynamics in modified gravitational theories
NASA Astrophysics Data System (ADS)
Bamba, Kazuharu; Geng, Chao-Qiang; Tsujikawa, Shinji
2010-04-01
We show that it is possible to obtain a picture of equilibrium thermodynamics on the apparent horizon in the expanding cosmological background for a wide class of modified gravity theories with the Lagrangian density f(R,ϕ,X), where R is the Ricci scalar and X is the kinetic energy of a scalar field ϕ. This comes from a suitable definition of an energy-momentum tensor of the “dark” component that respects to a local energy conservation in the Jordan frame. In this framework the horizon entropy S corresponding to equilibrium thermodynamics is equal to a quarter of the horizon area A in units of gravitational constant G, as in Einstein gravity. For a flat cosmological background with a decreasing Hubble parameter, S globally increases with time, as it happens for viable f(R) inflation and dark energy models. We also show that the equilibrium description in terms of the horizon entropy S is convenient because it takes into account the contribution of both the horizon entropy S' in non-equilibrium thermodynamics and an entropy production term.
Commonality between BCS and TCS.
Shah, Vinod P; Rădulescu, Flavian Ştefan; Miron, Dalia Simona; Yacobi, Avraham
2016-07-25
Both biopharmaceutics classification system (BCS) and topical drug classification system (TCS) are based on sound scientific principles with the aim of providing biowaiver and reducing regulatory burden without lowering the quality requirements and standards of approval for the drug products. BCS is based on the solubility and permeability properties of the active pharmaceutical ingredient (API, or drug substance) whereas the TCS is based on the qualitative and quantitative composition of the dosage form and the in vitro release rate of the active ingredient as key decision tools. Both BCS and TCS take drug release and dissolution as their guiding principle for providing biowaiver, increasing the availability and affordability of safe and effective medicines to the consumers and at the same time maintaining the drug product quality. PMID:27208656
NASA Astrophysics Data System (ADS)
Parish, Meera M.
2015-09-01
This chapter presents the crossover from the Bardeen-Cooper-Schrieffer (BCS) state of weakly correlated pairs of fermions to the Bose-Einstein condensation (BEC) of diatomic molecules in the atomic Fermi gas. Our aim is to provide a pedagogical review of the BCS-BEC crossover, with an emphasis on the basic concepts, particularly those that are not generally known or are difficult to find in the literature. We shall not attempt to give an exhaustive survey of current research in the limited space here; where possible, we will direct the reader to more extensive reviews.
Lee-Yang cluster expansion approach to the BCS-BEC crossover: BCS and BEC limits
NASA Astrophysics Data System (ADS)
Sakumichi, Naoyuki; Nishida, Yusuke; Ueda, Masahito
2014-03-01
It is shown that a cluster expansion technique, which is usually applied in the high-temperature regime to calcutate virial coefficients, can be applied to evaluate the superfluid transition temperature of the Bardeen-Cooper-Schrieffer (BCS)-Bose-Einstein condensation (BEC) crossover à la Lee and Yang. The transition temperature is identified with the emergence of the singularity in the sum of a certain infinite series of cluster functions. In the weak-coupling limit, we reproduce the Thouless criterion and the number equation of Nozières and Schmitt-Rink, and hence the transition temperature of the BCS theory. In the strong-coupling limit, we reproduce the transition temperature of BEC of noninteracting tightly bound dimers.
Modified contour-improved perturbation theory
Cvetic, Gorazd; Loewe, Marcelo; Martinez, Cristian; Valenzuela, Cristian
2010-11-01
The semihadronic tau decay width allows a clean extraction of the strong coupling constant at low energies. We present a modification of the standard ''contour-improved'' method based on a derivative expansion of the Adler function. The new approach has some advantages compared to contour-improved perturbation theory. The renormalization scale dependence is weaker by more than a factor of 2 and the last term of the expansion is reduced by about 10%, while the renormalization scheme dependence remains approximately equal. The extracted QCD coupling at the tau mass scale is by 2% lower than the contour-improved value. We find {alpha}{sub s}(M{sub Z}{sup 2})=0.1211{+-}0.0010.
Density perturbations in general modified gravitational theories
De Felice, Antonio; Tsujikawa, Shinji; Mukohyama, Shinji
2010-07-15
We derive the equations of linear cosmological perturbations for the general Lagrangian density f(R,{phi},X)/2+L{sub c}, where R is a Ricci scalar, {phi} is a scalar field, and X=-{partial_derivative}{sup {mu}{phi}{partial_derivative}}{sub {mu}{phi}/}2 is a field kinetic energy. We take into account a nonlinear self-interaction term L{sub c}={xi}({phi}) {open_square}{phi}({partial_derivative}{sup {mu}{phi}{partial_derivative}}{sub {mu}{phi}}) recently studied in the context of ''Galileon'' cosmology, which keeps the field equations at second order. Taking into account a scalar-field mass explicitly, the equations of matter density perturbations and gravitational potentials are obtained under a quasistatic approximation on subhorizon scales. We also derive conditions for the avoidance of ghosts and Laplacian instabilities associated with propagation speeds. Our analysis includes most of modified gravity models of dark energy proposed in literature; and thus it is convenient to test the viability of such models from both theoretical and observational points of view.
Strong coupling BCS superconductivity and holography
NASA Astrophysics Data System (ADS)
Kalyana Rama, S.; Sarkar, Swarnendu; Sathiapalan, B.; Sircar, Nilanjan
2011-11-01
We attempt to give a holographic description of the microscopic theory of a BCS superconductor. Exploiting the analogy with chiral symmetry breaking in QCD we use the Sakai-Sugimoto model of two D8 branes in a D4 brane background with finite baryon number. In this case there is a new tachyonic instability which is plausibly the bulk analog of the Cooper pairing instability. We analyze the Yang-Mills approximation to the non-Abelian Dirac-Born-Infeld action. We give some exact solutions of the non-linear Yang-Mills equations in flat space and also give a stability analysis, showing that the instability disappears in the presence of an electric field. The holographic picture also suggests a dependence of T on the number density which is different from the usual (weak coupling) BCS. The flat space solutions are then generalized to curved space numerically and also, in an approximate way, analytically. This configuration should then correspond to the ground state of the boundary superconducting (superfluid) ground state. We also give some preliminary results on Green functions computations in the Sakai-Sugimoto model without any chemical potential.
Constraining modified gravitational theories by weak lensing with Euclid
Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco; Melchiorri, Alessandro; Pagano, Luca; Scaramella, Roberto
2011-01-15
Future proposed satellite missions such as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak-lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios such as those predicted by scalar-tensor and f(R) theories. We find that Euclid will improve constraints expected from the Planck satellite on these modified theories of gravity by 2 orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modifications to gravity.
Flow equations for the BCS-BEC crossover
Diehl, S.; Gies, H.; Pawlowski, J. M.; Wetterich, C.
2007-08-15
The functional renormalization group is used for the BCS-BEC crossover in gases of ultracold fermionic atoms. In a simple truncation, we see how universality and an effective theory with composite bosonic diatom states emerge. We obtain a unified picture of the whole phase diagram. The flow reflects different effective physics at different scales. In the BEC limit as well as near the critical temperature, it describes an interacting bosonic theory.
Microscopic and macroscopic behaviors of Palatini modified gravity theories
Li Baojiu; Mota, David F.; Shaw, Douglas J.
2008-09-15
We show that, within modified gravity, the nonlinear nature of the field equations implies that the usual naieve averaging procedure (replacing the microscopic energy-momentum by its cosmological average) is invalid. We discuss then how the averaging should be performed correctly and show that, as a consequence, at the classical level the physical masses and geodesics of particles, cosmology, and astrophysics in Palatini modified gravity theories are all indistinguishable from the results of general relativity plus a cosmological constant. Palatini gravity is, however, a different theory from general relativity and predicts different internal structures of particles from the latter. On the other hand, and in contrast to classical particles, the electromagnetic field permeates in the space, and hence a different averaging procedure should be applied here. We show that, in general, Palatini gravity theories would then affect the propagation of photons, thus changing the behavior of a Universe dominated by radiation. Finally, Palatini theories also predict alterations to particle physics laws. For example, they can lead to sensitive corrections to the hydrogen energy levels, the measurements of which could be used to place very strong constraints on the properties of viable Palatini gravity theories.
Fast route to nonlinear clustering statistics in modified gravity theories
NASA Astrophysics Data System (ADS)
Winther, Hans A.; Ferreira, Pedro G.
2015-06-01
We propose a simple and computationally fast method for performing N -body simulations for a large class of modified gravity theories with a screening mechanism such as chameleons, symmetrons, and Galileons. By combining the linear Klein-Gordon equation with a screening factor, calculated from analytical solutions of spherical symmetric configurations, we obtain a modified field equation of which the solution is exact in the linear regime while at the same time taking screening into account on nonlinear scales. The resulting modified field equation remains linear and can be solved just as quickly as the Poisson equation without any of the convergence problems that can arise when solving the full equation. We test our method with N -body simulations and find that it compares remarkably well with full simulations well into the nonlinear regime.
Lunar System Constraints on the Modified Theories of Gravity
NASA Astrophysics Data System (ADS)
Exirifard, Qasem
2013-07-01
The Modified Newtonian Dynamics (MOND) paradigm to the missing mass problem requires introducing a functional that is to be identified through observations and experiments. We consider the aquadratic Lagrangian theory as a realization of the MOND. We show that the accurate value of the Earth GM measured by the lunar laser ranging measurements and that by various artificial Earth satellites, including the accurate tracking of the LAGEOS satellites, constrain this functional such that some of the chosen/proposed functional are refuted.
Structure of the number-projected BCS wave function
NASA Astrophysics Data System (ADS)
Dukelsky, J.; Pittel, S.; Esebbag, C.
2016-03-01
We study the structure of the number-projected BCS (PBCS) wave function in the particle-hole basis, displaying its similarities with coupled clusters theory (CCT). The analysis of PBCS together with several modifications suggested by the CCT wave function is carried out for the exactly solvable Richardson model involving a pure pairing Hamiltonian acting in a space of equally spaced, doubly degenerate levels. We point out the limitations of PBCS to describe the nonsuperconducting regime and suggest possible avenues for improvement.
Classifying linearly shielded modified gravity models in effective field theory.
Lombriser, Lucas; Taylor, Andy
2015-01-23
We study the model space generated by the time-dependent operator coefficients in the effective field theory of the cosmological background evolution and perturbations of modified gravity and dark energy models. We identify three classes of modified gravity models that reduce to Newtonian gravity on the small scales of linear theory. These general classes contain enough freedom to simultaneously admit a matching of the concordance model background expansion history. In particular, there exists a large model space that mimics the concordance model on all linear quasistatic subhorizon scales as well as in the background evolution. Such models also exist when restricting the theory space to operators introduced in Horndeski scalar-tensor gravity. We emphasize that whereas the partially shielded scenarios might be of interest to study in connection with tensions between large and small scale data, with conventional cosmological probes, the ability to distinguish the fully shielded scenarios from the concordance model on near-horizon scales will remain limited by cosmic variance. Novel tests of the large-scale structure remedying this deficiency and accounting for the full covariant nature of the alternative gravitational theories, however, might yield further insights on gravity in this regime. PMID:25658988
Wormhole geometries in f(R) modified theories of gravity
Lobo, Francisco S. N.; Oliveira, Miguel A.
2009-11-15
In this work, we construct traversable wormhole geometries in the context of f(R) modified theories of gravity. We impose that the matter threading the wormhole satisfies the energy conditions, so that it is the effective stress-energy tensor containing higher order curvature derivatives that is responsible for the null energy condition violation. Thus, the higher order curvature terms, interpreted as a gravitational fluid, sustain these nonstandard wormhole geometries, fundamentally different from their counterparts in general relativity. In particular, by considering specific shape functions and several equations of state, exact solutions for f(R) are found.
Applying modified Ginzburg-Landau theory to nuclei
NASA Astrophysics Data System (ADS)
Mohammadi, P.; Dehghani, V.; Mehmandoost-Khajeh-Dad, A. A.
2014-11-01
The Ginzburg-Landau theory of phase transitions is modified and used to investigate the heat capacity, energy, entropy, and order parameter of the paired phases of 208Pb,88Sr,48Ca, and 20Ne. We use the Fermi gas model to calculate the thermodynamic properties of the normal phase of the nucleons. Our results show that the total heat capacities of the studied nuclei have an S -shape behavior, which is in accordance with the semi-empirical data, and the order parameter does not approach zero at a specific critical temperature.
Relativistic gravitation theory for the modified Newtonian dynamics paradigm
Bekenstein, Jacob D.
2004-10-15
The modified Newtonian dynamics (MOND) paradigm of Milgrom can boast of a number of successful predictions regarding galactic dynamics; these are made without the assumption that dark matter plays a significant role. MOND requires gravitation to depart from Newtonian theory in the extragalactic regime where dynamical accelerations are small. So far relativistic gravitation theories proposed to underpin MOND have either clashed with the post-Newtonian tests of general relativity, or failed to provide significant gravitational lensing, or violated hallowed principles by exhibiting superluminal scalar waves or an a priori vector field. We develop a relativistic MOND inspired theory which resolves these problems. In it gravitation is mediated by metric, a scalar, and a 4-vector field, all three dynamical. For a simple choice of its free function, the theory has a Newtonian limit for nonrelativistic dynamics with significant acceleration, but a MOND limit when accelerations are small. We calculate the {beta} and {gamma} parameterized post-Newtonian coefficients showing them to agree with solar system measurements. The gravitational light deflection by nonrelativistic systems is governed by the same potential responsible for dynamics of particles. To the extent that MOND successfully describes dynamics of a system, the new theory's predictions for lensing by that system's visible matter will agree as well with observations as general relativity's predictions made with a dynamically successful dark halo model. Cosmological models based on the theory are quite similar to those based on general relativity; they predict slow evolution of the scalar field. For a range of initial conditions, this last result makes it easy to rule out superluminal propagation of metric, scalar, and vector waves.
Dark energy or modified gravity? An effective field theory approach
Bloomfield, Jolyon; Flanagan, Éanna É.; Park, Minjoon; Watson, Scott E-mail: eef3@cornell.edu E-mail: gswatson@syr.edu
2013-08-01
We take an Effective Field Theory (EFT) approach to unifying existing proposals for the origin of cosmic acceleration and its connection to cosmological observations. Building on earlier work where EFT methods were used with observations to constrain the background evolution, we extend this program to the level of the EFT of the cosmological perturbations — following the example from the EFT of Inflation. Within this framework, we construct the general theory around an assumed background which will typically be chosen to mimic ΛCDM, and identify the parameters of interest for constraining dark energy and modified gravity models with observations. We discuss the similarities to the EFT of Inflation, but we also identify a number of subtleties including the relationship between the scalar perturbations and the Goldstone boson of the spontaneously broken time translations. We present formulae that relate the parameters of the fundamental Lagrangian to the speed of sound, anisotropic shear stress, effective Newtonian constant, and Caldwell's varpi parameter, emphasizing the connection to observations. It is anticipated that this framework will be of use in constraining individual models, as well as for placing model-independent constraints on dark energy and modified gravity model building.
3D weak lensing: Modified theories of gravity
NASA Astrophysics Data System (ADS)
Pratten, Geraint; Munshi, Dipak; Valageas, Patrick; Brax, Philippe
2016-05-01
Weak lensing (WL) promises to be a particularly sensitive probe of both the growth of large-scale structure as well as the fundamental relation between matter density perturbations and metric perturbations, thus providing a powerful tool with which we may constrain modified theories of gravity (MG) on cosmological scales. Future deep, wide-field WL surveys will provide an unprecedented opportunity to constrain deviations from General Relativity. Employing a 3D analysis based on the spherical Fourier-Bessel expansion, we investigate the extent to which MG theories will be constrained by a typical 3D WL survey configuration including noise from the intrinsic ellipticity distribution σɛ of source galaxies. Here, we focus on two classes of screened theories of gravity: (i) f (R ) chameleon models and (ii) environmentally dependent dilaton models. We use one-loop perturbation theory combined with halo models in order to accurately model the evolution of the matter power spectrum with redshift in these theories. Using a χ2 analysis, we show that for an all-sky spectroscopic survey, the parameter fR0 can be constrained in the range fR0<5 ×10-6(9 ×10-6) for n =1 (2 ) with a 3 σ confidence level. This can be achieved by using relatively low-order angular harmonics ℓ<100 . Higher-order harmonics ℓ>100 could provide tighter constraints but are subject to nonlinear effects, such as baryonic feedback, that must be accounted for. We also employ a Principal Component Analysis in order to study the parameter degeneracies in the MG parameters. The confusion from intrinsic ellipticity correlation and modification of the matter power spectrum at a small scale due to feedback mechanisms is briefly discussed.
The 'X model': a modified version of the competition theory.
Scott, O C; Révész, L; Edgren, M
1993-10-01
In 1985, Edgren et al. proposed a modified version of the competition theory to explain the interaction of sensitizers and protectors with target molecules damaged by radiation, which was designated the 'X' model. This model incorporates concepts which have been considered previously, namely that a type of radiation damage exists which cannot be chemically repaired, and that cells may contain a naturally occurring sensitizer. The model leads to testable predictions, such as, e.g. the crossing of 'K curves' when the level of protection is varied. It can only be applied to the immediate effects of radiation, i.e. before enzymatic reactions play a part. The present paper is a summary of work carried out since 1985 to test the predictions of the 'X' model and an exposition of the related algebra. PMID:7901298
Kerr-Newman solution in modified teleparallel theory of gravity
NASA Astrophysics Data System (ADS)
Nashed, Gamal G. L.
2015-11-01
A nondiagonal tetrad field having six unknown functions plus an angle Φ, which is a function of the radial coordinate r, azimuthal angle θ and the polar angle ϕ, is applied to the charged field equations of modified teleparallel theory of gravity. A special nonvacuum solution is derived with three constants of integration. The tetrad field of this solution is axially symmetric and its scalar torsion is constant. The associated metric of the derived solution gives Kerr-Newman spacetime. We have shown that the derived solution can be described by a local Lorentz transformations plus a diagonal tetrad field that is the square root of the Kerr-Newman metric. We show that any solution of general relativity (GR) can be a solution in f(T) under certain conditions.
Gravitational Microlensing in Modified Gravity Theories - Inverse-Square Theorem
NASA Astrophysics Data System (ADS)
Asada, H.
2011-02-01
Microlensing studies are usually based on the lens equation that is valid only to the first order in the gravitational constant G and lens mass M. We consider corrections to the conventional lens equation in terms of differentiable functions, so that they can express not only the second-order effects of GM in general relativity but also modified gravity theories. As a generalization of Ebina et al. (Prog. Theor. Phys. 104 (2000), 1317), we show that, provided that the spacetime is static, spherically symmetric and asymptotically flat, the total amplification by microlensing remains unchanged at the linear order of the correction to the deflection angle, if and only if the correction takes a particular form as the inverse square of the impact parameter, whereas the magnification factor for each image is corrected. It is concluded that the light curve shape by microlensing is inevitably changed and will thus allow us to probe modified gravity, unless a modificati on to the deflection angle takes the particular form. No systematic deviation in microlensing observations has been reported. For instance, therefore, the Yukawa-type correction is constrained as the characteristic length > 10^{14} m.
Comparison of different pairing fluctuation approaches to BCS-BEC crossover
Levin, Kathryn Chen Qijin Chien, C.-C. He Yan
2010-02-15
The subject of BCS-Bose-Einstein condensation (BEC) crossover is particularly exciting because of its realization in ultracold atomic Fermi gases and its possible relevance to high temperature superconductors. In this paper we review the body of theoretical work on this subject, which represents a natural extension of the seminal papers by Leggett and by Nozieres and Schmitt-Rink (NSR). The former addressed only the ground state, now known as the 'BCS-Leggett' wave-function, and the key contributions of the latter pertain to calculations of the superfluid transition temperature T{sub c}. These two papers have given rise to two main and, importantly, distinct, theoretical schools in the BCS-BEC crossover literature. The first of these extends the BCS-Leggett ground state to finite temperature and the second extends the NSR scheme away from T{sub c} both in the superfluid and normal phases. It is now rather widely accepted that these extensions of NSR produce a different ground state than that first introduced by Leggett. This observation provides a central motivation for the present paper which seeks to clarify the distinctions in the two approaches. Our analysis shows how the NSR-based approach views the bosonic contributions more completely but treats the fermions as 'quasi-free'. By contrast, the BCS-Leggett based approach treats the fermionic contributions more completely but treats the bosons as 'quasi-free'. In a related fashion, the NSR-based schemes approach the crossover between BCS and BEC by starting from the BEC limit and the BCS-Leggett based scheme approaches this crossover by starting from the BCS limit. Ultimately, one would like to combine these two schemes. There are, however, many difficult problems to surmount in any attempt to bridge the gap in the two theory classes. In this paper we review the strengths and weaknesses of both approaches. The flexibility of the BCS-Leggett based approach and its ease of handling make it widely used in T=0
Perturbations of single-field inflation in modified gravity theory
NASA Astrophysics Data System (ADS)
Qiu, Taotao; Xia, Jun-Qing
2015-05-01
In this paper, we study the case of single field inflation within the framework of modified gravity theory where the gravity part has an arbitrary form f (R). Via a conformal transformation, this case can be transformed into its Einstein frame where it looks like a two-field inflation model. However, due to the existence of the isocurvature modes in such a multi-degree-of-freedom (m.d.o.f.) system, the (curvature) perturbations are not equivalent in two frames, so despite of its convenience, it is illegal to treat the perturbations in its Einstein frame as the "real" ones as we always do for pure f (R) theory or single field with nonminimal coupling. Here by pulling the results of curvature perturbations back into its original Jordan frame, we show explicitly the power spectrum and spectral index of the perturbations in the Jordan frame, as well as how it differs from the Einstein frame. We also fit our results with the newest Planck data. Since there is large parameter space in these models, we show that it is easy to fit the data very well.
Galaxy clustering in 3D and modified gravity theories
NASA Astrophysics Data System (ADS)
Munshi, D.; Pratten, G.; Valageas, P.; Coles, P.; Brax, P.
2016-02-01
We study Modified Gravity (MG) theories by modelling the redshifted matter power spectrum in a spherical Fourier-Bessel basis. We use a fully non-linear description of the real-space matter power spectrum and include the lowest order redshift-space correction (Kaiser effect), taking into account some additional non-linear contributions. Ignoring relativistic corrections, which are not expected to play an important role for a shallow survey, we analyse two different MG scenarios, namely the generalized Dilaton scalar-tensor theories and the f (R) models in the large curvature regime. We compute the 3D power spectrum C^s_{ℓ}(k_1,k_2) for various such MG theories with and without redshift-space distortions, assuming precise knowledge of background cosmological parameters. Using an all-sky spectroscopic survey with Gaussian selection function \\varphi (r)∝ exp (-{r^2/r^2_0}), r_0=150h^{-1} Mpc, and number density of galaxies bar{N} =10^{-4}Mpc^{-3}, we use a χ2 analysis, and find that the lower order (ℓ ≤ 25) multipoles of C^s_ℓ (k,k^' }) (with radial modes restricted to k < 0.2 h Mpc-1) can constraint the parameter f_{R_0} at a level of 2 × 10-5(3 × 10-5) with 3σ confidence for n = 1(2). Combining constraints from higher ℓ > 25 modes can further reduce the error bars and thus in principle make cosmological gravity constraints competitive with Solar system tests. However this will require an accurate modelling of non-linear redshift-space distortions. Using a tomographic β(a)-m(a) parametrization we also derive constraints on specific parameters describing the Dilaton models of MG.
Popov approximation for composite bosons in the BCS-BEC crossover
Pieri, P.; Strinati, G.C.
2005-03-01
Theoretical treatments of the BCS-BEC crossover need to provide as accurate as possible descriptions of the two regimes where the diluteness condition applies, either in terms of the constituent fermions (BCS limit) or of the composite bosons which form as bound-fermion pairs (BEC limit). This has to occur via a single fermionic theory that bridges across these two limiting representations. In this paper, we set up successive improvements of the fermionic theory, that result into composite bosons described at the level of either the Bogoliubov or the Popov approximations for pointlike bosons. This work bears on the recent experimental advances on the BCS-BEC crossover with trapped Fermi atoms, which show the need for accurate theoretical descriptions of the BEC side of the crossover.
Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases
NASA Astrophysics Data System (ADS)
He, Lianyi; Lü, Haifeng; Cao, Gaoqing; Hu, Hui; Liu, Xia-Ji
2015-08-01
We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the two-dimensional mean-field theory indicates that the quantum fluctuations are much more pronounced than those in three dimensions. In this work, we show that the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of two-dimensional Bose gases and determine the ratio of the composite boson scattering length aB to the fermion scattering length a2 D. We find aB≃0.56 a2 D , in good agreement with the exact four-body calculation. We compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.
A modified large number theory with constant G
NASA Astrophysics Data System (ADS)
Recami, Erasmo
1983-03-01
The inspiring “numerology” uncovered by Dirac, Eddington, Weyl, et al. can be explained and derived when it is slightly modified so to connect the “gravitational world” (cosmos) with the “strong world” (hadron), rather than with the electromagnetic one. The aim of this note is to show the following. In the present approach to the “Large Number Theory,” cosmos and hadrons are considered to be (finite) similar systems, so that the ratio{{bar R} / {{bar R} {bar r}} of the cosmos typical lengthbar R to the hadron typical lengthbar r is constant in time (for instance, if both cosmos and hadrons undergo an expansion/contraction cycle—according to the “cyclical bigbang” hypothesis—thenbar R andbar r can be chosen to be the maximum radii, or the average radii). As a consequence, then gravitational constant G results to be independent of time. The present note is based on work done in collaboration with P. Caldirola, G. D. Maccarrone, and M. Pavšič.
A modified Lorentz theory as a test theory of special relativity
NASA Technical Reports Server (NTRS)
Chang, T.; Torr, D. G.; Gagnon, D. R.
1988-01-01
Attention has been given recently to a modified Lorentz theory (MLT) that is based on the generalized Galilean transformation. Some explicit formulas within the framework of MLT, dealing with the one-way velocity of light, slow-clock transport, and the Doppler effect are derived. A number of typical experiments are analyzed on this basis. Results indicate that the empirical equivalence between MLT and special relativity is still maintained to second order terms. The results of previous works that predict that the MLT might be distinguished from special relativity at the third order by Doppler centrifuge tests capable of a fractional frequency detection threshold of 10 to the -15th are confirmed.
Resonant electronic Raman scattering: A BCS-like system
NASA Astrophysics Data System (ADS)
Rodrigues, Leonarde N.; Arantes, A.; Schüller, C.; Bell, M. J. V.; Anjos, V.
2016-05-01
In this paper we investigate the resonant intersubband Raman scattering of two-dimensional electron systems in GaAs-AlGaAs single quantum wells. Self-consistent calculations of the polarized and depolarized Raman cross sections show that the appearance of excitations at the unrenormalized single-particle energy are related to three factors: the extreme resonance regime, the existence of degeneracy in intersubband excitations of the electron gas, and, finally, degeneracy in the interactions between pairs of excitations. It is demonstrated that the physics that governs the problem is similar to the one that gives rise to the formation of the superconducting state in the BCS theory of normal metals. Comparison between experiment and theory shows an excellent agreement.
Evolution from BCS to BEC Superfluidity in Dilute Fermi Gases
NASA Astrophysics Data System (ADS)
de Melo, Carlos A. R. Sa
2006-03-01
I will review briefly some old results [1,2] of the evolution from BCS to BEC superfluidity in dilute Fermi gases, including critical temperature, order parameter amplitude, chemical potential and time dependent Ginzburg-Landau theory for the s-wave channel in three dimensions. Following this discussion, I will present new results for the BCS to BEC evolution of Fermi gases in the p-wave channel [3]. I will make comparisons between s-wave and p-wave superfluidity and point out the main differences between the two cases. Lastly, I will discuss supefluidity of s-wave and p-wave Fermi gases in a restricted two-dimensional geometry (one dimensional optical lattice), where a Berezinkii-Kosterlitz-Thouless-type transition is proposed as the system evolves from the weak to the strong attraction limit. In this case, I will show that spontaneous vortex-antivortex pairs form and that they can condense into a vortex-antivortex lattice at lower temperatures [4]. [1] C. A. R. Sa de Melo, M. Randeria, and J. R. Engelbrecht, PRL 71, 3202 (1993). [2] J. R. Engelbrecht, M. Randeria, and C. A. R. Sa de Melo, PRB 55, 15153 (1997). [3] M. Iskin, and C. A. R. Sa de Melo, cond-mat/0510300 (2005). [4] S. S. Botelho, and C. A. R. Sa de Melo, cond-mat/0509387 (2005).
Creation of wormholes by quantum tunnelling in modified gravity theories
NASA Astrophysics Data System (ADS)
Battarra, Lorenzo; Lavrelashvili, George; Lehners, Jean-Luc
2014-12-01
We study the process of quantum tunnelling in scalar-tensor theories in which the scalar field is nonminimally coupled to gravity. In these theories gravitational instantons can deviate substantially from sphericity and can in fact develop a neck—a feature prohibited in theories with minimal coupling. Such instantons with necks lead to the materialization of bubble geometries containing a wormhole region. We clarify the relationship of neck geometries to violations of the null energy condition, and also derive a bound on the size of the neck relative to that of the instanton.
Theory of nanoscale friction on chemically modified graphene
NASA Astrophysics Data System (ADS)
Ko, Jae-Hyeon; Kim, Yong-Hyun
2013-03-01
Recently, it is known from FFM experiments that friction force on graphene is significantly increased by chemical modification such as hydrogenation, oxidization, and fluorination, whereas adhesion properties are altered marginally. A novel nanotribological theory on two-dimensional materials is proposed on the basis of experimental results and first-principles density-functional theory (DFT) calculations. The proposed theory indicates that the total lateral stiffness that is the proportional constant of friction force is mostly associated with the out-of-plane bending stiffness of two-dimensional materials. This contrasts to the case of three-dimensional materials, in which the shear strength of materials determines nanoscale friction. We will discuss details of DFT calculations and how to generalize the current theory to three dimensional materials.
Effective field theory from modified gravity with massive modes
NASA Astrophysics Data System (ADS)
Capozziello, Salvatore; de Laurentis, Mariafelicia; Paolella, Mariacristina; Ricciardi, Giulia
2015-10-01
Massive gravitational modes in effective field theories can be recovered by extending General Relativity and taking into account generic functions of the curvature invariants, not necessarily linear in the Ricci scalar R. In particular, adopting the minimal extension of f(R) gravity, an effective field theory with massive modes is straightforwardly recovered. This approach allows to evade shortcomings like ghosts and discontinuities if a suitable choice of expansion parameters is performed.
Stability of spherically symmetric solutions in modified theories of gravity
Seifert, Michael D.
2007-09-15
In recent years, a number of alternative theories of gravity have been proposed as possible resolutions of certain cosmological problems or as toy models for possible but heretofore unobserved effects. However, the implications of such theories for the stability of structures such as stars have not been fully investigated. We use our 'generalized variational principle', described in a previous work [M. D. Seifert and R. M. Wald, Phys. Rev. D 75, 084029 (2007)], to analyze the stability of static spherically symmetric solutions to spherically symmetric perturbations in three such alternative theories: Carroll et al.'s f(R) gravity, Jacobson and Mattingly's 'Einstein-aether theory', and Bekenstein's TeVeS theory. We find that in the presence of matter, f(R) gravity is highly unstable; that the stability conditions for spherically symmetric curved vacuum Einstein-aether backgrounds are the same as those for linearized stability about flat spacetime, with one exceptional case; and that the 'kinetic terms' of vacuum TeVeS theory are indefinite in a curved background, leading to an instability.
A Possible Path from BCS through HTS to VHTS
NASA Astrophysics Data System (ADS)
Chu, C. W.
2010-03-01
Three years after celebrating the 50th anniversary of the BCS theory and the 20th anniversary of the discovery of high temperature superconductivity (HTS), it appears to be most fitting for us to contemplate the possibility of very high temperature superconductivity (VHTS). VHTS, preferably at room temperature, if achieved, could change the world both scientifically and technologically. Unfortunately, it has long been considered by some to belong to the domain of science fiction and to occur only ``at an astronomical distance and under an astronomical pressure.'' With the advent of liquid nitrogen superconductivity in 1987, the outlook has become much brighter. Currently, there appears to be no reason, either theoretical or experimental, why VHTS would be impossible, in spite of the 2006 prediction of the death of HTS by 2010-2015 through the so-called scientometric analysis of the publication record of the previous 20 years. The recent discovery of the new class of Fe-pnictide HTSs fuels more cautious optimism. Since its inception, BCS theory has provided the basic framework for the occurrence and understanding of superconductivity, but it has failed to show where and how to find superconductivity at a higher temperature. This may be attributed to the small energy scale of superconductivity in comparison with those of other excitations in the solids. After examining existing data, we believe that a holistic multidisciplinary enlightened empirical approach appears to be the most effective way to discover novel superconductors with higher transition temperatures. In this talk, I shall present several possible approaches toward VHTS that we are currently pursuing, after briefly summarizing what has happened in the long search for HTS and VHTS.
Multicomponent solution in a modified theory of gravity in the early universe
Mohseni Sadjadi, H.
2008-05-15
We study the modified theory of gravity in the Friedmann-Robertson-Walker universe composed of several perfect fluids. We consider the power law inflation and determine the equation of state parameters in terms of the parameters of modified gravity's Lagrangian in the early universe. We also briefly discuss the gravitational baryogenesis in this model.
A modified Lax-Phillips scattering theory for quantum mechanics
NASA Astrophysics Data System (ADS)
Strauss, Y.
2015-07-01
The Lax-Phillips scattering theory is an appealing abstract framework for the analysis of scattering resonances. Quantum mechanical adaptations of the theory have been proposed. However, since these quantum adaptations essentially retain the original structure of the theory, assuming the existence of incoming and outgoing subspaces for the evolution and requiring the spectrum of the generator of evolution to be unbounded from below, their range of applications is rather limited. In this paper, it is shown that if we replace the assumption regarding the existence of incoming and outgoing subspaces by the assumption of the existence of Lyapunov operators for the quantum evolution (the existence of which has been proved for certain classes of quantum mechanical scattering problems), then it is possible to construct a structure analogous to the Lax-Phillips structure for scattering problems for which the spectrum of the generator of evolution is bounded from below.
A modified Lax-Phillips scattering theory for quantum mechanics
Strauss, Y.
2015-07-15
The Lax-Phillips scattering theory is an appealing abstract framework for the analysis of scattering resonances. Quantum mechanical adaptations of the theory have been proposed. However, since these quantum adaptations essentially retain the original structure of the theory, assuming the existence of incoming and outgoing subspaces for the evolution and requiring the spectrum of the generator of evolution to be unbounded from below, their range of applications is rather limited. In this paper, it is shown that if we replace the assumption regarding the existence of incoming and outgoing subspaces by the assumption of the existence of Lyapunov operators for the quantum evolution (the existence of which has been proved for certain classes of quantum mechanical scattering problems), then it is possible to construct a structure analogous to the Lax-Phillips structure for scattering problems for which the spectrum of the generator of evolution is bounded from below.
Lee, Myung W.
2008-01-01
Elastic velocities of water-saturated sandstones depend primarily on porosity, effective pressure, and the degree of consolidation. If the dry-frame moduli are known, from either measurements or theoretical calculations, the effect of pore water on velocities can be modeled using the Gassmann theory. Kuster and Toksoz developed a theory based on wave-scattering theory for a variety of inclusion shapes, which provides a means for calculating dry- or wet-frame moduli. In the Kuster-Toksoz theory, elastic wave velocities through different sediments can be predicted by using different aspect ratios of the sediment's pore space. Elastic velocities increase as the pore aspect ratio increases (larger pore aspect ratio describes a more spherical pore). On the basis of the velocity ratio, which is assumed to be a function of (1-0)n, and the Biot-Gassmann theory, Lee developed a semi-empirical equation for predicting elastic velocities, which is referred to as the modified Biot-Gassmann theory of Lee. In this formulation, the exponent n, which depends on the effective pressure and the degree of consolidation, controls elastic velocities; as n increases, elastic velocities decrease. Computationally, the role of exponent n in the modified Biot-Gassmann theory by Lee is similar to the role of pore aspect ratios in the Kuster-Toksoz theory. For consolidated sediments, either theory predicts accurate velocities. However, for unconsolidated sediments, the modified Biot-Gassmann theory by Lee performs better than the Kuster-Toksoz theory, particularly in predicting S-wave velocities.
Research on a Modified Framework of Implicit Personality Theories
ERIC Educational Resources Information Center
Ziegler, Albert; Stoeger, Heidrun
2010-01-01
There is ample evidence that labeled gifted students exhibit maladaptive behavior patterns. According to Carol Dweck those students who subscribe to a fixed view of their abilities are particularly at risk. In this contribution we extended Dweck's framework and distinguished two aspects of the implicit theory of one's own abilities. We…
Making School Reform Work: A "Mineralogical" Theory of School Modifiability. Fastback 467.
ERIC Educational Resources Information Center
Sternberg, Robert J.
This booklet proposes a different approach to understanding schools, school change, and why attempts at change run into so many difficulties. The text is divided into six parts. It examines issues in school reform and restructuring and offers what is called a Mineralogical Theory of school modifiability. This theory posits that there are eight…
Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases
He, Lianyi; Lu, Haifeng; Cao, Gaoqing; Hu, Hui; Liu, Xia -Ji
2015-08-14
We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the two-dimensional mean-field theory indicates that the quantum fluctuations are much more pronounced than those in three dimensions. In this work, we show thatmore » the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of two-dimensional Bose gases and determine the ratio of the composite boson scattering length aB to the fermion scattering length a2D. We find aB ≃ 0.56a2D, in good agreement with the exact four-body calculation. As a result, we compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.« less
Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi gases
He, Lianyi; Lu, Haifeng; Cao, Gaoqing; Hu, Hui; Liu, Xia -Ji
2015-08-14
We present a theoretical study of the ground state of the BCS-BEC crossover in dilute two-dimensional Fermi gases. While the mean-field theory provides a simple and analytical equation of state, the pressure is equal to that of a noninteracting Fermi gas in the entire BCS-BEC crossover, which is not consistent with the features of a weakly interacting Bose condensate in the BEC limit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of the two-dimensional mean-field theory indicates that the quantum fluctuations are much more pronounced than those in three dimensions. In this work, we show that the inclusion of the Gaussian quantum fluctuations naturally recovers the above features in both the BEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on the boson chemical potential is recovered by the quantum fluctuations. Near the quantum phase transition from the vacuum to the BEC phase, we compare our equation of state with the known grand canonical equation of state of two-dimensional Bose gases and determine the ratio of the composite boson scattering length a_{B} to the fermion scattering length a_{2D}. We find a_{B} ≃ 0.56a_{2D}, in good agreement with the exact four-body calculation. As a result, we compare our equation of state in the BCS-BEC crossover with recent results from the quantum Monte Carlo simulations and the experimental measurements and find good agreements.
Microscopic Theory of Modified Spontaneous Emission in a Dielectric
NASA Astrophysics Data System (ADS)
Berman, P. R.; Milonni, P. W.
2004-02-01
The modification of the radiative decay rate of a source atom embedded in a uniform, isotropic dielectric is calculated to first order in the density of the dielectric atoms using a microscopic approach. In contrast to the recent results of Crenshaw and Bowden [
Halo velocity profiles in screened modified gravity theories
NASA Astrophysics Data System (ADS)
Gronke, M.; Llinares, C.; Mota, D. F.; Winther, H. A.
2015-05-01
Screened modified gravity predicts potentially large signatures in the peculiar velocity field that makes it an interesting probe to test gravity on cosmological scales. We investigate the signatures induced by the Symmetron and a Chameleon f(R) model in the peculiar velocity field using N-body simulations. By studying fifth force and halo velocity profiles, we identify three general categories of effects found in screened modified gravity models: a fully screened regime where we recover Λ cold dark matter to high precision, an unscreened regime where the fifth force is in full operation, and, a partially screened regime where screening occurs in the inner part of a halo, but the fifth force is active at larger radii. These three regimes can be pointed out very clearly by analysing the deviation in the maximum cluster velocity. Observationally, the partially screened regime is of particular interest since an uniform increase of the gravitational force - as present in the unscreened regime - is degenerate with the (dynamical) halo mass estimate, and, thus, hard to detect.
Theory of room temperature ferromagnetism in Cr modified DNA nanowire
NASA Astrophysics Data System (ADS)
Paruğ Duru, Izzet; Değer, Caner; Eldem, Vahap; Kalayci, Taner; Aktaş, Şahin
2016-04-01
We investigated the magnetic properties of Cr3+ (J < 0) ion-modified DNA (M-DNA) nanowire (1000 base) at room temperature under a uniform magnetic field (˜100 Oe) for different doping concentrations. A Monte Carlo simulation method-based Metropolis algorithm is used to figure out the thermodynamic quantities of nanowire formed by Cr M-DNA followed by analysing the dependency of the ferromagnetic behaviour of the M-DNA to dopant concentration. It is understood that ion density/base and ion density/helical of Cr3+ ions can be a tuning parameter, herewith the dopant ratio has an actual importance on the magnetic characterization of M-DNA nanowire (3%-20%). We propose the source of magnetism as an exchange interaction between Cr and DNA helical atoms indicated in the Heisenberg Hamiltonian.
NASA Astrophysics Data System (ADS)
Anderson, Brandon M.; Boyack, Rufus; Wu, Chien-Te; Levin, K.
2016-05-01
In this Rapid Communication we derive the full gauge-invariant electromagnetic response beyond the BCS level using the fermionic superfluid path integral. In the process we identify and redress a failure to satisfy the compressibility sum rule; this shortcoming is associated with the conventional path-integral formulation of BCS-level electrodynamics. The approach in this paper builds on an alternative saddle point scheme. At the mean field level, this leads to the well known gauge-invariant electrodynamics of BCS theory and to the satisfaction of the compressibility sum rule. Moreover, this scheme can be readily extended to address arbitrary higher order fluctuation theories (for example, at the Gaussian level.) At any level this approach will lead to a gauge invariant and compressibility sum rule consistent treatment of electrodynamics and thermodynamics.
Competition between BCS-pairing and “moth-eaten effect” in BEC-BCS crossover
NASA Astrophysics Data System (ADS)
Zhu, Guojun; Combescot, Monique
2012-01-01
We study the change in condensation energy from a single pair of fermionic atoms to a large number of pairs interacting via the reduced BCS potential. We find that the energy-saving due to correlations decreases when the pair number increases because the number of empty states available for pairing gets smaller ("moth-eaten effect"). However, this decrease dominates the 3D kinetic energy increase of the same amount of noninteracting atoms only when the pair number is a sizable fraction of the number of states available for pairing. As a result, in BEC-BCS crossover of 3D systems, the condensation energy per pair first increases and then decreases with pair number while in 2D, it always is controlled by the "moth-eaten effect" and thus simply decreases.
Modified gravity theories: Alternatives to the missing mass and missing energy problems
NASA Astrophysics Data System (ADS)
Soussa, Marc Edward
Modified theories of gravity are examined and shown to be alternative possibilities to the standard paradigms of dark matter and dark energy in explaining the currently observed cosmological phenomenology. Special consideration is given to the relativistic extension of Modified Newtonian Dynamics (MOND) in supplanting the need for dark matter. A specific modification of the Einstein-Hilbert action (whereby an inverse power of the Ricci scalar is added) is shown to serve as an alternative to dark energy.
NASA Astrophysics Data System (ADS)
Zhao, Hongsheng; Li, Baojiu; Bienaymé, Olivier
2010-11-01
We derive a simple analytical expression for the two-body force in a subclass of modified Newtonian dynamics (MOND) theories and make testable predictions in the modification to the two-body orbital period, shape, precession rate, escape speed, etc. We demonstrate the applications of the modified Kepler’s law in the timing of satellite orbits around the Milky Way, and checking the feasibility of MOND in the orbit of the large Magellanic cloud, the M31 galaxy, and the merging bullet clusters. MOND appears to be consistent with satellite orbits although with a tight margin. Our results on two-bodies are also generalized to restricted three-body, many-body problems, rings, and shells.
Modified Coulomb-Dipole Theory for 2e Photoionization
NASA Technical Reports Server (NTRS)
2004-01-01
In the light of recent experiment on 2e photoionization of Li near threshold, we have considered a modification of the Coulomb-dipole theory, retaining the basic assumption that the threshold is dominated by asymmetric events in phase space [implies r(sub 1), k(sub 1)) greater than or equal to 2(r(sub 2), k(sub )]. In this region [in a collinear model, 2/r(sub 12) approached + 2/(r(sub 1)+r(sub 2)] the interaction reduces to V(rIsub 1) is greater than or equal to 2r(sub 2) is identically equal to [(-Z/r(sub 2)-(A-1)/r(sub 1)] + [(-2r(sub 2)/r(sub 1 exp 2)] is identically equal to V(sub c)+[V(sub d)]. For two electron emission Z = 2, thus both electrons see a Coulomb potential (V(sub c)) asymptotically, albeit each seeing a different charge. The residual potential (V(sub d)) is dipole in character. Writing the total psi = psi (sub c) + psi(sub d) = delta psi, and noting that. (T+V(sub c)-E)psy(sub c) = 0 and (T+V(sub c))psi(sub d) = 0 can be solved exactly, we find, substituting psi into the complete Schrod. Eq., that delta psi = -(H-E)(exp -1)(V(sub d) psi(sub 0)+V(sub c psi (sub 1). Using the fact that the absolute value of V(sub c) is much more than the absolute value of V(sub d) in almost all of configuration space, we can replace H by H(sub 0) in 9H-E)(exp -1) to obtain an improved approximation psi (improved) = psi(sub c) + psi(sub d) -(H(sub 0)-E)(exp -1) (V(sub c) psi (sub 0) + V(sub c) psi(sub 1). Here's the Green's function (H(sub 0)-E)(exp -1), can be exhibited explicitly, but the last term in psi (improved) is small, compared to the first two terms. Inserting them into the transition matrix element, which one handles in the usual way, we obtain in the limit E approaches 0, the threshold law: Q(E) alpha E + M(E)E(exp 5/4) + higher order (Eq. 1a). The modulation function, M(E), is a well-defined (but very non-trivial integral, but it is expected to be well approximated by a sinusoidal function containing a dipole phase term (M(E) = c sin[alpha log (E
A New First-Principles Calculation of Field-Dependent RF Surface Impedance of BCS Superconductor
Xiao, Binping; Reece, Charles E.
2014-02-01
There is a need to understand the intrinsic limit of radiofrequency (RF) surface impedance that determines the performance of superconducting RF cavities in particle accelerators. Here we present a field-dependent derivation of Mattis-Bardeen theory of the RF surface impedance of BCS superconductors based on the shifted density of states resulting from coherently moving Cooper pairs. Our theoretical prediction of the effective BCS RF surface resistance (Rs) of niobium as a function of peak surface magnetic field amplitude agrees well with recently reported record low loss resonant cavity measurements from JLab and FNAL with carefully, yet differently, prepared niobium material. The surprising reduction in resistance with increasing field is explained to be an intrinsic effect.
Exploring the Role of Diagnosis in the Modified Labeling Theory of Mental Illness
ERIC Educational Resources Information Center
Kroska, Amy; Harkness, Sarah K.
2008-01-01
According to the modified labeling theory of mental illness, when an individual is diagnosed with a mental illness, cultural ideas associated with the mentally ill become personally relevant and foster negative self-feelings. We explore the way that psychiatric diagnosis shapes this process. Specifically, we examine if and how psychiatric…
Hu, Lan; Grim, Christopher J; Franco, Augusto A; Jarvis, Karen G; Sathyamoorthy, Vengopal; Kothary, Mahendra H; McCardell, Barbara A; Tall, Ben D
2015-12-01
Cronobacter species are emerging food-borne pathogens that cause severe sepsis, meningitis, and necrotizing entercolitis in neonates and infants. Bacterial pathogens such as Escherichia coli and Salmonella species produce extracellular cellulose which has been shown to be involved in rugosity, biofilm formation, and host colonization. In this study the distribution and prevalence of cellulose synthase operon genes (bcsABZC) were determined by polymerase chain reaction (PCR) analysis in 231 Cronobacter strains isolated from clinical, food, environmental, and unknown sources. Furthermore, bcsA and bcsB isogenic mutants were constructed in Cronobacter sakazakii BAA894 to determine their roles. In calcofluor binding assays bcsA and bcsB mutants did not produce cellulose, and their colonial morphotypes were different to that of the parent strain. Biofilm formation and bacterial cell-cell aggregation were significantly reduced in bcsA and bcsB mutants compared to the parental strain. bcsA or bcsAB PCR-negative strains of C. sakazakii did not bind calcofluor, and produced less biofilm and cell-cell aggregation compared to strains possessing bcsAB genes. These data indicated that Cronobacter bcsABZC were present in all clinical isolates and most of food and environmental isolates. bcsA and bcsB genes of Cronobacter were necessary to produce cellulose, and were involved in biofilm formation and cell-cell aggregation. PMID:26338122
Non-BCS thermodynamic properties of H2 S superconductor
NASA Astrophysics Data System (ADS)
Durajski, Artur P.; Szcze&şacute; niak, Radosław; Li, Yinwei
2015-08-01
The present paper determines the thermodynamic properties of the superconducting state in the H2S compound. The values of the pressure from 130 GPa to 180 GPa were taken into consideration. The calculations were performed in the framework of the Eliashberg formalism. In the first step, the experimental course of the dependence of the critical temperature on the pressure was reproduced: TC ∈ < 31, 88 > K, whereas the Coulomb pseudopotential equal to 0.15 was adopted. Next, the following quantities were calculated: the order parameter at the temperature of zero Kelvin (Δ (0)), the specific heat jump at the critical temperature (ΔC (TC) ≡CS (TC) -CN (TC)), and the thermodynamic critical field (HC (0)). It was found that the values of the dimensionless ratios: RΔ ≡ 2 Δ (0) /kBTC , RC ≡ ΔC(TC) /CN (TC) , and RH ≡TCCN (TC) / HC2(0) deviate from the predictions of the BCS theory: RΔ ∈ < 3.64, 4.16 > , RC ∈ < 1.59, 2.24 > , and RH ∈ < 0.144, 0.163 > . Generalizing the results on the whole family of the HnS -type compounds, it was shown that the maximum value of the critical temperature can be equal to ˜290 K, while RΔ,RC and RH adopt the following values: 6.53, 3.99, and 0.093, respectively.
Detecting the BCS pairing amplitude via a sudden lattice ramp in a honeycomb lattice
NASA Astrophysics Data System (ADS)
Tiesinga, Eite; Nuske, Marlon; Mathey, Ludwig
2016-05-01
We determine the exact time evolution of an initial Bardeen-Cooper-Schrieffer (BCS) state of ultra-cold atoms in a hexagonal optical lattice. The dynamical evolution is triggered by ramping the lattice potential up, such that the interaction strength Uf is much larger than the hopping amplitude Jf. The quench initiates collective oscillations with frequency | Uf | /(2 π) in the momentum occupation numbers and imprints an oscillating phase with the same frequency on the order parameter Δ. The latter is not reproduced by treating the time evolution in mean-field theory. The momentum density-density or noise correlation functions oscillate at frequency | Uf | /(2 π) as well as its second harmonic. For a very deep lattice, with negligible tunneling energy, the oscillations of momentum occupation numbers are undamped. Non-zero tunneling after the quench leads to dephasing of the different momentum modes and a subsequent damping of the oscillations. This occurs even for a finite-temperature initial BCS state, but not for a non-interacting Fermi gas. We therefore propose to use this dephasing to detect a BCS state. Finally, we predict that the noise correlation functions in a honeycomb lattice will develop strong anti-correlations near the Dirac point. We acknowledge funding from the National Science Foundation.
Lensing-induced morphology changes in CMB temperature maps in modified gravity theories
NASA Astrophysics Data System (ADS)
Munshi, D.; Hu, B.; Matsubara, T.; Coles, P.; Heavens, A.
2016-04-01
Lensing of the Cosmic Microwave Background (CMB) changes the morphology of pattern of temperature fluctuations, so topological descriptors such as Minkowski Functionals can probe the gravity model responsible for the lensing. We show how the recently introduced two-to-two and three-to-one kurt-spectra (and their associated correlation functions), which depend on the power spectrum of the lensing potential, can be used to probe modified gravity theories such as f(R) theories of gravity and quintessence models. We also investigate models based on effective field theory, which include the constant-Ω model, and low-energy Hořava theories. Estimates of the cumulative signal-to-noise for detection of lensing-induced morphology changes, reaches Script O(103) for the future planned CMB polarization mission COrE+. Assuming foreground removal is possible to lmax=3000, we show that many modified gravity theories can be rejected with a high level of significance, making this technique comparable in power to galaxy weak lensing or redshift surveys. These topological estimators are also useful in distinguishing lensing from other scattering secondaries at the level of the four-point function or trispectrum. Examples include the kinetic Sunyaev-Zel'dovich (kSZ) effect which shares, with lensing, a lack of spectral distortion. We also discuss the complication of foreground contamination from unsubtracted point sources.
Yalçın, Uğur; Sarnık, Mücahit
2013-01-01
The uniform diffracted fields are calculated on PEC cylindrical reflector by Modified Theory of Physical Optics (MTPO). It is aimed to convert the noncontinuous solution to a continuous solution by finding a uniform equation which does not contain any expression converging to 0 in the denominator part. Three axioms of MTPO theory are used to construct the integral equations for the perfectly electrically conducting surface application. The "edge-point" technique is used to find the diffracted field, and uniform solution is to be found via "detour parameter(s)." Finally, the obtained results are to be compared with the nonuniform ones, numerically. PMID:23766679
Axisymmetric Distributions of Thick Circular Plate in a Modified Couple Stress Theory
NASA Astrophysics Data System (ADS)
Kumar, Rajneesh; Marin, Marin; Abbas, Ibrahim A.
2015-07-01
In this paper, the two-dimensional axisymmetric distributions of thick circular plate in modified couple stress theory with heat and mass diffusive sources is investigated. The problem is considered in the context of the theories of thermodiffusion elastic solid with one and two relaxation time developed by Sherief et al. [Int. J. Eng. Sci. 42, 591 (2004)] and Kumar and Kansal [Int. J. Solid Struct. 45, 5890 (2008)] by using Laplace and Hankel transforms technique. The displacements, stress components, temperature change and chemical potential are obtained in transformed domain. Particular cases of interest are also deduced.
Constraining Modified Theories of Gravity with Gravitational-Wave Stochastic Backgrounds.
Maselli, Andrea; Marassi, Stefania; Ferrari, Valeria; Kokkotas, Kostas; Schneider, Raffaella
2016-08-26
The direct discovery of gravitational waves has finally opened a new observational window on our Universe, suggesting that the population of coalescing binary black holes is larger than previously expected. These sources produce an unresolved background of gravitational waves, potentially observable by ground-based interferometers. In this Letter we investigate how modified theories of gravity, modeled using the parametrized post-Einsteinian formalism, affect the expected signal, and analyze the detectability of the resulting stochastic background by current and future ground-based interferometers. We find the constraints that Advanced LIGO would be able to set on modified theories, showing that they may significantly improve the current bounds obtained from astrophysical observations of binary pulsars. PMID:27610838
Awuah, Joel B; Dzade, Nelson Y; Tia, Richard; Adei, Evans; Kwakye-Awuah, Bright; Richard A Catlow, C; de Leeuw, Nora H
2016-04-20
We present density functional theory calculations of the adsorption of arsenic acid (AsO(OH)3) and arsenous acid (As(OH)3) on the Al(iii)-modified natural zeolite clinoptilolite under anhydrous and hydrated conditions. From our calculated adsorption energies, we show that adsorption of both arsenic species is favorable (associative and exothermic) under anhydrous conditions. When the zeolite is hydrated, adsorption is less favourable, with the water molecules causing dissociation of the arsenic complexes, although exothermic adsorption is still observed for some sites. The strength of interaction of the arsenic complexes is shown to depend sensitively on the Si/Al ratio in the Al(iii)-modified clinoptilolite, which decreases as the Si/Al ratio increases. The calculated large adsorption energies indicate the potential of Al(iii)-modified clinoptilolite for arsenic immobilization. PMID:27052997
BCS to Bose crossover: Broken-symmetry state
Engelbrecht, J.R. |; Randeria, M. |; Sa de Melo, C.A.
1997-06-01
A functional integral formulation, used previously to calculate T{sub c} and describe normal state properties of the BCS-Bose crossover, is extended to T{lt}T{sub c}. The saddle point approximation is shown to be qualitatively correct for T{lt}T{sub c} for {ital all} couplings, in contrast to the situation above T{sub c}. Several features of the crossover are described. The difference between the T=0 {open_quotes}pair size{close_quotes} and the (prefactor of the T dependent) Ginzburg-Landau coherence length is pointed out: the two quantities are the same only in the BCS limit. The evolution of the collective modes from the BCS to the Bose regime is discussed together with the mixing of the amplitude and phase in the absence of a particle-hole symmetry. {copyright} {ital 1997} {ital The American Physical Society}
Chern-Simons modified gravity as a torsion theory and its interaction with fermions
Alexander, Stephon; Yunes, Nicolas
2008-06-15
We study the tetrad formulation of Chern-Simons (CS) modified gravity, which adds a Pontryagin term to the Einstein-Hilbert action with a spacetime-dependent coupling field. We first verify that CS modified gravity leads to a theory with torsion, where this tensor is given by an antisymmetric product of the Riemann tensor and derivatives of the CS coupling. We then calculate the torsion in the far field of a weakly gravitating source within the parameterized post-Newtonian formalism, and specialize the result to Earth. We find that CS torsion vanishes only if the coupling vanishes, thus generically leading to a modification of gyroscopic precession, irrespective of the coupling choice. Perhaps most interestingly, we couple fermions to CS modified gravity via the standard Dirac action and find that these further correct the torsion tensor. Such a correction leads to two new results: (i) a generic enhancement of CS modified gravity by the Dirac equation and axial fermion currents; (ii) a new two-fermion interaction, mediated by an axial current and the CS correction. We conclude with a discussion of the consequences of these results in particle detectors and realistic astrophysical systems.
Smoking guns of a bounce in modified theories of gravity through the spectrum of gravitational waves
NASA Astrophysics Data System (ADS)
Bouhmadi-López, Mariam; Morais, João; Henriques, Alfredo B.
2013-05-01
We present an inflationary model preceded by a bounce in a metric theory à la f(R), where R is the scalar curvature of the space-time. The model is asymptotically de Sitter such that the gravitational action tends asymptotically to an Einstein-Hilbert action with an effective cosmological constant; therefore, modified gravity affects only the early stages of the Universe. We then analyze the spectrum of the gravitational waves through the method of the Bogoliubov coefficients by two means: taking into account the gravitational perturbations due to the modified gravitational action in the f(R) setup and simply considering those perturbations inherent to the standard Einstein-Hilbert action. We show that there are distinctive (oscillatory) signals on the spectrum for very low frequencies; i.e., corresponding to modes that are currently entering the horizon.
Applicability of the Newman-Janis algorithm to black hole solutions of modified gravity theories
NASA Astrophysics Data System (ADS)
Hansen, Devin; Yunes, Nicolás
2013-11-01
The Newman-Janis algorithm has been widely used to construct rotating black hole solutions from nonrotating counterparts. While this algorithm was developed within general relativity (GR), it has more recently been applied to nonrotating solutions in modified gravity theories. We find that the application of the Newman-Janis algorithm to an arbitrary non-GR spherically symmetric solution introduces pathologies in the resulting axially symmetric metric. This then establishes that, in general, the Newman-Janis algorithm should not be used to construct rotating black hole solutions outside of General Relativity.
Modified Theories of Gravity with Nonminimal Coupling and the Faint Young Sun Paradox
NASA Astrophysics Data System (ADS)
Iorio, Lorenzo
2016-01-01
A certain general class of modified gravitational theories with nonminimal coupling predicts a "pressure"-type, non-geodesic acceleration for a non-rotating, massive test particle. The resulting orbital perturbations for a two-body system consist of secular rates of change of all the standard orbital elements. The resulting variation of the mutual distance yields a physical mechanism which has the potential capability to explain, in principle, the Faint Young Sun Paradox in terms of a recession of the Earth from the Sun during the Archean.
NASA Astrophysics Data System (ADS)
Sourki, R.; Hoseini, S. A. H.
2016-04-01
This paper investigates the analysis for free transverse vibration of a cracked microbeam based on the modified couple stress theory within the framework of Euler-Bernoulli beam theory. The governing equation and the related boundary conditions are derived by using Hamilton's principle. The cracked beam is modeled by dividing the beam into two segments connected by a rotational spring located at the cracked section. This model invokes the consideration of the additional strain energy caused by the crack and promotes a discontinuity in the bending slope. In this investigation, the influence of diverse crack position, crack severity, material length scale parameter as well as various Poisson's ratio on natural frequencies is studied. A comparison with the previously published studies is made, in which a good agreement is observed. The results illustrate that the aforementioned parameters are playing a significant role on the dynamic behavior of the microbeam.
One-body potential theory of molecules and solids modified semiempirically for electron correlation
NASA Astrophysics Data System (ADS)
March, N. H.
2010-10-01
The study of Cordero, March and Alonso (CMA) for four spherical atoms, Be, Ne, Mg and Ar, semiempirically fine-tunes the Hartree-Fock (HF) ground-state electron density by inserting the experimentally determined ionization potentials. The present Letter, first of all, relates this approach to the very recent work of Bartlett ‘towards an exact correlated orbital theory for electrons’. Both methods relax the requirement of standard DFT that a one-body potential shall generate the exact ground-state density, though both work with high quality approximations. Unlike DFT, the CMA theory uses a modified HF non-local potential. It is finally stressed that this potential generates also an idempotent Dirac density matrix. The CMA approach is thereby demonstrated to relate, albeit approximately, to the DFT exchange-correlation potential.
The black hole merger event GW150914 within a modified theory of General Relativity
NASA Astrophysics Data System (ADS)
Hess, P. O.
2016-08-01
In February 2016 the first observation of gravitational waves were reported. The source of this event, denoted as GW150914, was identified as the merger of two black holes with a about 30 solar masses each, at a distance of approximately 400Mpc. These data where deduced using the Theory of General Relativity. Since 2009 a modified theory was proposed which adds near massive objects phenomenologically the contribution of a dark energy, whose origin are vacuum fluctuations. The dark energy accumulates toward smaller distances, reducing effectively the gravitational constant. In this contribution we show that as a consequence the deduces chirping mass and the luminosity distance are larger. This result suggests that the black hole merger corresponds to two massive black holes near the center of primordial galaxies at large luminosity distance, i.e. large redshifts.
Criterion for DNA melting in the mean-field modified self-consistent phonon theory
NASA Astrophysics Data System (ADS)
Feng, Y.; Prohofsky, E. W.
1991-04-01
We have examined the validity of the first-order-perturbation method in calculating eigenfunctions and the criterion for helix melting of mean-field polymers in the modified self-consistent phonon approach (MSPA) theory. It is found that the instability in the self-consistent solution is due to the breakdown of the first-order perturbation. The instability as a criterion for helix melting is therefore techniquely inappropriate. However, the breakdown of the perturbation is due to facts that are directly related to the onset of softening. Previously predicted melting temperatures for various sequence DNA polymers may still represent good estimates to the actual melting temperatures. An alternative criterion is required to define the melting temperature of the polymer DNA double helix in the MSPA theory.
Disorder effects in the evolution from BCS to BEC superfluidity
NASA Astrophysics Data System (ADS)
Han, Li; de Melo, Carlos A. R. Sa
2009-03-01
We discuss the effects of disorder on the critical temperature of superfluids during the evolution from BCS to BEC. For s-wave superfluids we find that the critical temperature is weakly affected by disorder in the BCS regime as described in Anderson’s theorem, even less affected by disorder at zero chemical potential (near unitarity), but strongly affected by disorder in the BEC regime, where Anderson's theorem does not apply. This suggests that the superfluid is more robust to the effects of disorder at the interaction parameter where the chemical potential vanishes (close to unitarity). We construct a three dimensional phase diagram of critical temperature, disorder and interaction parameter [1], and show that there are regions of localized superfluidity, as well as insulating regions due to Anderson localization of fermions (BCS regime) and molecular bosons (BEC regime). The phase diagram for higher angular momentum (e.g. p-wave and d-wave) is also analyzed, where the effects of disorder are much more dramatic in the BCS regime in comparison to the s-wave case because pair breaking is strong, while the disorder effects in BEC regime are similar to what occurs in the s-wave case. [1] Li Han, C. A. R. Sa de Melo, arXiv:0812.xxxx
NASA Astrophysics Data System (ADS)
Links, Jon; Moghaddam, Amir; Zhang, Yao-Zhong
2013-08-01
We demonstrate the occurrence of free quasi-particle excitations obeying generalized exclusion statistics in a BCS model with asymmetric pair scattering. The results are derived from an exact solution of the Hamiltonian, which was obtained via the algebraic Bethe ansatz utilizing the representation theory of an underlying Yangian algebra. The free quasi-particle excitations are associated with highest weight states of the Yangian algebra, corresponding to a class of analytic solutions of the Bethe ansatz equations.
Quantum quench phase diagrams of an s -wave BCS-BEC condensate
NASA Astrophysics Data System (ADS)
Yuzbashyan, E. A.; Dzero, M.; Gurarie, V.; Foster, M. S.
2015-03-01
We study the dynamic response of an s -wave BCS-BEC (atomic-molecular) condensate to detuning quenches within the two-channel model beyond the weak-coupling BCS limit. At long times after the quench, the condensate ends up in one of three main asymptotic states (nonequilibrium phases), which are qualitatively similar to those in other fermionic condensates defined by a global complex order parameter. In phase I the amplitude of the order parameter vanishes as a power law, in phase II it goes to a nonzero constant, and in phase III it oscillates persistently. We construct exact quench phase diagrams that predict the asymptotic state (including the many-body wave function) depending on the initial and final detunings and on the Feshbach resonance width. Outside of the weak-coupling regime, both the mechanism and the time dependence of the relaxation of the amplitude of the order parameter in phases I and II are modified. Also, quenches from arbitrarily weak initial to sufficiently strong final coupling do not produce persistent oscillations in contrast to the behavior in the BCS regime. The most remarkable feature of coherent condensate dynamics in various fermion superfluids is an effective reduction in the number of dynamic degrees of freedom as the evolution time goes to infinity. As a result, the long-time dynamics can be fully described in terms of just a few new collective dynamical variables governed by the same Hamiltonian only with "renormalized" parameters. Combining this feature with the integrability of the underlying (e.g., the two-channel) model, we develop and consistently present a general method that explicitly obtains the exact asymptotic state of the system.
New two-sided bound on the isotropic Lorentz-violating parameter of modified Maxwell theory
Klinkhamer, F. R.; Schreck, M.
2008-10-15
There is a unique Lorentz-violating modification of the Maxwell theory of photons, which maintains gauge invariance, CPT, and renormalizability. Restricting the modified-Maxwell theory to the isotropic sector and adding a standard spin-(1/2) Dirac particle p{sup {+-}} with minimal coupling to the nonstandard photon {gamma}-tilde, the resulting modified-quantum-electrodynamics model involves a single dimensionless 'deformation parameter', {kappa}-tilde{sub tr}. The exact tree-level decay rates for two processes have been calculated: vacuum Cherenkov radiation p{sup {+-}}{yields}p{sup {+-}}{gamma}-tilde for the case of positive {kappa}-tilde{sub tr} and photon decay {gamma}-tilde{yields}p{sup +}p{sup -} for the case of negative {kappa}-tilde{sub tr}. From the inferred absence of these decays for a particular high-quality ultrahigh-energy-cosmic-ray event detected at the Pierre Auger Observatory and a well-established excess of TeV gamma-ray events observed by the High Energy Stereoscopic System telescopes, a two-sided bound on {kappa}-tilde{sub tr} is obtained, which improves by 8 orders of magnitude upon the best direct laboratory bound. The implications of this result are briefly discussed.
BCS condensate as a special case of the Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Batle, J.; Casas, M.; Fortes, M.; Solís, M. A.; de Llano, M.; Salazar, A.; Valladares, A. A.; Rojo, O.
2001-03-01
Rather general separable interfermionic interactions with sufficient attraction to bind fermions into (bosonic) Cooper pairs (CPs) give [1], in 2D or 3D, a center-of-mass-momentum(CMM)-dependent CP binding energy that is quadratic for any coupling strictly only in the limit of zero Fermi energy, i.e., when the Fermi sea disappears and one is in vacuum. Otherwise, this "dispersion relation" is linear to good approximation---and perfectly so in weak to moderate coupling. Moreover, the CPs break up beyond a certain CMM which vanishes in the zero coupling limit. As a result, the condensate of BCS theory (which generally neglects nonzero CMM CPs) appears to be a special case of the Bose-Einstein condensate of a boson-fermion binary mixture. Chemical and thermal equilibrium in the mixture gives rise [2] to a boson number which is strongly coupling- and temperature-dependent, and generally leads to transition temperatures substantially greater than those predicted by BCS theory. [1] S.K. Adhikari et al., Physica C (in press) and Phys. Rev. B 62 (2000) 8671; M. Casas et al., Physica C 295 (1998) 93; M. Casas et al., Phys. Letters A 245 (1998) 55. [2] M. Casas et al., http://xxx.lanl.gov/abs/cond-mat/0003499.
Probability of primordial black hole pair creation in a modified gravitational theory
Paul, B. C.; Paul, Dilip
2006-10-15
We compute the probability for quantum creation of an inflationary universe with and without a pair of black holes in a modified gravity. The action of the modified theory of gravity contains {alpha}R{sup 2} and {delta}R{sup -1} terms in addition to a cosmological constant ({lambda}) in the Einstein-Hilbert action. The probabilities for the creation of universe with a pair of black holes have been evaluated considering two different kinds of spatial sections, one which accommodates a pair of black holes and the other without black hole. We adopt a technique prescribed by Bousso and Hawking to calculate the above creation probability in a semiclassical approximation using the Hartle-Hawking boundary condition. We note a class of new and physically interesting instanton solutions characterized by the parameters in the action. These instantons may play an important role in the creation of the early universe. We also note that the probability of creation of a universe with a pair of black holes is strongly suppressed with a positive cosmological constant when {delta}=(4{lambda}{sup 2}/3) for {alpha}>0 but it is more probable for {alpha}<-(1/6{lambda}). In the modified gravity considered here instanton solutions are permitted even without a cosmological constant when one begins with a negative {delta}.
BCS-BEC crossover physics in FeSe bulk superconductor
NASA Astrophysics Data System (ADS)
Shibauchi, Takasada
The physics of the crossover between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein-condensate (BEC) limits gives a unified framework of quantum bound (superfluid) states of interacting fermions. This crossover has been studied in the ultracold atomic systems, but is extremely difficult to be realized for electrons in solids. Through the superfluid response, transport, thermoelectric response, and quantum oscillations, we demonstrate that the Fermi energy of the bulk superconductor FeSe is extremely small, with the ratio of the gap to Fermi energy is of the order of unity, which qualifies FeSe to be deep inside the BCS-BEC crossover regime. Thus FeSe appears to be a key material to solve the longstanding issue in the crossover physics; the presence of preformed Cooper pairs giving rise to a pseudogap above the superconducting transition temperature Tc. We report experimental signatures of preformed Cooper pairing well above Tc = 8 . 5 K in clean single crystals of FeSe. Our torque magnetometry reveals distinct diamagnetic signal below T* ~ 20 K indicating that the superconducting fluctuations above the transition temperature are strongly enhanced from the standard Gaussian theory. The transport and thermoelectric coefficients also exhibit distinct anomalies at ~T* , signaling a possible pseudogap formation. The multiband nature with the electron-hole compensation in FeSe may highlight a fundamentally new aspect of the BCS-BEC crossover physics In collaboration with S. Kasahara, T. Yamashita, Y. Matsuda (Kyoto), Y. Mizukami (Tokyo), T. Wolf, F. Hardy, C. Meingast, H. v. Löhneysen (KIT), M. D. Watson, A. I. Coldea (Oxford), T. Terashima (NIMS), W. Knafo (Toulouse), T. Hanaguri (Riken).
Modified Gauss-Bonnet gravity with the Lagrange multiplier constraint as mimetic theory
NASA Astrophysics Data System (ADS)
Astashenok, Artyom V.; Odintsov, Sergei D.; Oikonomou, V. K.
2015-09-01
In this paper we propose and extensively study mimetic f({G}) modified gravity models, with various scenarios of cosmological evolution, with or without extra matter fluids. The easiest formulation is based on the use of the Lagrange multiplier constraint. In certain versions of this theory, it is possible to realize accelerated expansion of the Universe or even unified evolution, which includes inflation with dark energy, and at the same time in the same theoretical framework, dark matter is described by the theory. This is achieved by the re-parametrization of the metric tensor, which introduces a new degree of freedom in the cosmological equations and leads to the appearance of the mimetic ‘dark matter’ component. In the context of the mimetic f({G}) theory, we also provide some quite general reconstruction schemes, which enable us to find which f({G}) gravity generates a specific cosmological evolution. In addition, we also provide the general reconstruction technique for the Lagrange multiplier f({G}) gravity. All our results are accompanied by illustrative examples, with special emphasis on bouncing cosmologies.
Prediction of positive food effect: Bioavailability enhancement of BCS class II drugs.
Raman, Siddarth; Polli, James E
2016-06-15
High-throughput screening methods have increased the number of poorly water-soluble, highly permeable drug candidates. Many of these candidates have increased bioavailability when administered with food (i.e., exhibit a positive food effect). Food is known to impact drug bioavailability through a variety of mechanisms, including drug solubilization and prolonged gastric residence time. In vitro dissolution media that aim to mimic in vivo gastrointestinal (GI) conditions have been developed to lessen the need for fed human bioequivalence studies. The objective of this work was to develop an in vitro lipolysis model to predict positive food effect of three BCS Class II drugs (i.e., danazol, amiodarone and ivermectin) in previously developed lipolysis media. This in vitro lipolysis model was comparatively benchmarked against FeSSIF and FaSSIF media that were modified for an in vitro lipolysis approach, as FeSSIF and FaSSIF are widely used in in vitro dissolution studies. The in vitro lipolysis model accurately predicted the in vivo positive food effect for three model BCS class II drugs. The in vitro lipolysis model has potential use as a screening test of drug candidates in early development to assess positive food effect. PMID:27067239
Chen, Qijin
2016-01-01
BCS-Bose-Einstein condensation (BEC) crossover is effected by increasing pairing strength between fermions from weak to strong in the particle-particle channel, and has attracted a lot of attention since the experimental realization of quantum degenerate atomic Fermi gases. Here we study the effect of the (often dropped) particle-hole channel on the zero T gap Δ(0), superfluid transition temperature Tc, the pseudogap at Tc, and the mean-field ratio 2Δ(0)/, from BCS through BEC regimes, using a pairing fluctuation theory which includes self-consistently the contributions of finite-momentum pairs and features a pseudogap in single particle excitation spectrum. Summing over the infinite particle-hole ladder diagrams, we find a complex dynamical structure for the particle-hole susceptibility χph, and conclude that neglecting the self-energy feedback causes a serious over-estimate of χph. While our result in the BCS limit agrees with Gor'kov et al., the particle-hole channel effect becomes more complex and pronounced in the crossover regime, where χph is reduced by both a smaller Fermi surface and a big (pseudo)gap. Deep in the BEC regime, the particle-hole channel contributions drop to zero. We predict a density dependence of the magnetic field at the Feshbach resonance, which can be used to quantify χph and test different theories. PMID:27183875
Heinen, C; Reuss, S; Saaler-Reinhardt, S; Langguth, P
2013-09-01
The objective of this study was to investigate the potential of λ-carrageenan to work as an absorption modifying excipient in combination with formulations of BCS class 3 substances. Trospium chloride was used as a model BCS class 3 substance. Polyelectrolyte complexes of trospium and λ-carrageenan were produced by layer-by-layer complexation. A λ-carrageenan-containing formulation was administered either in capsules size 9 to rats by gavage or directly into ligated intestinal loops of rats. Exceptionally strong variations were observed in the plasma concentrations of the rats that received λ-carrageenan compared to the control group, but enhanced plasma concentrations were observed only in some of the rats. In vitro permeability studies were performed across Caco2-monolayers and across excised segments of rat jejunum in a modified Ussing chamber to learn more about the mechanism of absorption enhancement. The complex did not show any effect in Caco2-cells, but led to a major enhancement of permeability across excised segments in modified Ussing chambers. Carrageenan did not lead to alterations of tight junctions. The bioavailability enhancing effect thus was most likely due to an interaction of the polyelectrolyte-drug complex with the mucus, which provided an intimate contact between the drug and the absorbing surface. A similar effect was also achievable with other types of carrageenan and was also transferable to other compounds. In conclusion, λ-carrageenan-drug complexes show interesting excipient-drug-epithelium interactions - however, for full utilization of the permeation enhancing potential, an intimate and reproducible contact between absorbing epithelia and the complex is needed. PMID:23958316
Pairing in bulk nuclear matter beyond BCS
Ding, D.; Dickhoff, W. H.; Dussan, H.; Witte, S. J.; Rios, A.; Polls, A.
2014-10-15
The influence of short-range correlations on the spectral distribution of neutrons is incorporated in the solution of the gap equation for the {sup 3}P{sub 2}−{sup 3}F{sub 2} coupled channel in pure neutron matter. This effect is studied for different realistic interactions including one based on chiral perturbation theory. The gap in this channel vanishes at all relevant densities due to the treatment of these correlations. We also consider the effect of long-range correlations by including polarization terms in addition to the bare interaction which allow the neutrons to exchange density and spin fluctuations governed by the strength of Landau parameters allowed to have reasonable values consistent with the available literature. Preliminary results indicate that reasonable values of these parameters do not generate a gap in the {sup 3}P{sub 2}−{sup 3}F{sub 2} coupled channel either for all three realistic interactions although the pairing interaction becomes slightly more attractive.
Bernoulli Euler beam model based on a modified couple stress theory
NASA Astrophysics Data System (ADS)
Park, S. K.; Gao, X.-L.
2006-11-01
A new model for the bending of a Bernoulli-Euler beam is developed using a modified couple stress theory. A variational formulation based on the principle of minimum total potential energy is employed. The new model contains an internal material length scale parameter and can capture the size effect, unlike the classical Bernoulli-Euler beam model. The former reduces to the latter in the absence of the material length scale parameter. As a direct application of the new model, a cantilever beam problem is solved. It is found that the bending rigidity of the cantilever beam predicted by the newly developed model is larger than that predicted by the classical beam model. The difference between the deflections predicted by the two models is very significant when the beam thickness is small, but is diminishing with the increase of the beam thickness. A comparison shows that the predicted size effect agrees fairly well with that observed experimentally.
Andersson, M P
2016-07-28
We have performed density functional theory calculations using our modified DFT-D2 dispersion correction for metals to investigate adsorption of a range of molecules on Pt(111). The agreement between our calculations and experimental adsorption energies ranging from 0 to 3 eV was excellent with a mean absolute deviation of 0.19 eV and a maximum deviation of 0.37 eV. Our results show that the DFT-D2 semiempirical dispersion correction can provide accurate results also for describing adsorption on metals, provided that relevant physical properties of the system are taken into account, such as shorter ranged dispersion because of screening by the conducting electrons and a lower polarizability of the core electrons in metals compared to isolated atoms. PMID:27357643
Covariant anomaly and Hawking radiation from the modified black hole in the rainbow gravity theory
NASA Astrophysics Data System (ADS)
Peng, Jun-Jin; Wu, Shuang-Qing
2008-12-01
Recently, Banerjee and Kulkarni (R. Banerjee, S. Kulkarni, arXiv: 0707. 2449 [hep-th]) suggested that it is conceptually clean and economical to use only the covariant anomaly to derive Hawking radiation from a black hole. Based upon this simplified formalism, we apply the covariant anomaly cancellation method to investigate Hawking radiation from a modified Schwarzschild black hole in the theory of rainbow gravity. Hawking temperature of the gravity’s rainbow black hole is derived from the energy-momentum flux by requiring it to cancel the covariant gravitational anomaly at the horizon. We stress that this temperature is exactly the same as that calculated by the method of cancelling the consistent anomaly.
Binary Mixture of Perfect Fluid and Dark Energy in Modified Theory of Gravity
NASA Astrophysics Data System (ADS)
Shaikh, A. Y.
2016-07-01
A self consistent system of Plane Symmetric gravitational field and a binary mixture of perfect fluid and dark energy in a modified theory of gravity are considered. The gravitational field plays crucial role in the formation of soliton-like solutions, i.e., solutions with limited total energy, spin, and charge. The perfect fluid is taken to be the one obeying the usual equation of state, i.e., p = γρ with γ∈ [0, 1] whereas, the dark energy is considered to be either the quintessence like equation of state or Chaplygin gas. The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied.
Description of C isotopes within RMF+BCS approach
NASA Astrophysics Data System (ADS)
Saxena, G.; Singh, D.; Kaushik, M.
2013-06-01
In the present investigations we have employed relativistic mean-field plus BCS (RMF + BCS) approach to carry out a systematic study for the ground state properties of even-even C Isotopes. One of the prime reason of this study has been to look into the role of low lying states in neutron rich reason near neutron drip line. It is found that irrespective of whether any resonant state exists or not, the occupancy of weakly bound neutron single particle states having low orbital angular momentum, (l = 0 or 1), with a well spread wave function due to the absence or very small strength of centrifugal barrier, helps to cause the occurrence of nuclei with widely extended neutron density. Such nuclei are found to have characteristically very small two-neutron separation energy and large neutron rms radius akin to that observed in weakly bound systems.
Isospin Dependent Pairing Interactions and BCS-BEC crossover
Sagawa, H.; Margueron, J.; Hagino, K.
2008-11-11
We propose new types of density dependent contact pairing interaction which reproduce the pairing gaps in symmetric and neutron matters obtained by a microscopic treatment based on the realistic nucleon-nucleon interaction. The BCS-BEC crossover of neutrons pairs in symmetric and asymmetric nuclear matters is studied by using these contact interactions. It is shown that the bare and screened pairing interactions lead to different features of the BCS-BEC crossover in symmetric nuclear matter. We perform Hartree-Fock-Bogoliubov (HFB) calculations for semi-magic Calcium, Nickel, Tin and Lead isotopes and N = 20, 28, 50 and 82 isotones using these density-dependent pairing interactions. Our calculations well account for the experimental data for the neutron number dependence of binding energy, two neutrons separation energy, and odd-even mass staggering of these isotopes. Especially the interaction IS+IV Bare without the medium polarization effect gives satisfactory results for all the isotopes.
Continuum discretised BCS approach for weakly bound nuclei
NASA Astrophysics Data System (ADS)
Lay, J. A.; Alonso, C. E.; Fortunato, L.; Vitturi, A.
2016-08-01
The Bardeen–Cooper–Schrieffer (BCS) formalism is extended by including the single-particle continuum in order to analyse the evolution of pairing in an isotopic chain from stability up to the drip-line. We propose a continuum discretised generalised BCS based on single-particle pseudostates (PS). These PS are generated from the diagonalisation of the single-particle Hamiltonian within a transformed harmonic oscillator basis. The consistency of the results versus the size of the basis is studied. The method is applied to neutron rich oxygen and carbon isotopes and compared with similar previous works and available experimental data. We make use of the flexibility of the proposed model in order to study the evolution of the occupation of the low-energy continuum when the system becomes weakly bound. We find an increasing influence of the non-resonant continuum as long as the Fermi level approaches the neutron separation threshold.
Particle-hole fluctuations in BCS-BEC crossover
Floerchinger, S.; Scherer, M.; Wetterich, C.; Diehl, S.
2008-11-01
The effect of particle-hole fluctuations for the BCS-BEC crossover is investigated by use of functional renormalization. We compute the Gorkov effect and the critical temperature for the whole range in the scattering length a. On the BCS side for small negative a we recover the Gorkov approximation, while on the BEC side of small positive a the particle-hole fluctuations play no important role, and we find a system of interacting bosons. In the unitarity limit of infinite scattering length our quantitative estimate yields T{sub c}/T{sub F}=0.264. We also investigate the crossover from broad to narrow Feshbach resonances - for the latter we obtain T{sub c}/T{sub F}=0.204 for a{sup -1}=0. A key ingredient for our treatment is the computation of the momentum dependent four-fermion vertex and its bosonization in terms of an effective bound-state exchange.
Description of C isotopes within RMF+BCS approach
Saxena, G.; Singh, D.; Kaushik, M.
2013-06-03
In the present investigations we have employed relativistic mean-field plus BCS (RMF + BCS) approach to carry out a systematic study for the ground state properties of even-even C Isotopes. One of the prime reason of this study has been to look into the role of low lying states in neutron rich reason near neutron drip line. It is found that irrespective of whether any resonant state exists or not, the occupancy of weakly bound neutron single particle states having low orbital angular momentum, (l = 0 or 1), with a well spread wave function due to the absence or very small strength of centrifugal barrier, helps to cause the occurrence of nuclei with widely extended neutron density. Such nuclei are found to have characteristically very small two-neutron separation energy and large neutron rms radius akin to that observed in weakly bound systems.
Park, Bong-Won; Lee, Kun Chang
2011-01-01
The aims of this article are (1) to propose a modified theory of consumption values (MTCV) for investigation of online gamer perceptions of the value of purchasable game items and (2) to apply the developed MTCV to multiple game genres and player age groups. To address these aims, 327 valid questionnaires were obtained and analyzed. The original theory of consumption values (TCV) was modified to apply to the specific characteristics of online games. The original TCV specifies five types of consumption values: functional value, social value, emotional value, conditional value, and epistemic value. After revising the TCV to apply to the examination of online games, we proposed that the MTCV be composed of character competency value, enjoyment value, visual authority value, and monetary value. The validity of the MTCV was proven by statistically analyzing the responses provided by the 327 valid questionnaires. To examine the second aim, experiments were conducted to examine the MTCV in three online game genres-massive multiplayer online role-playing games, first-person shooters games, and casual games. The second aim was also studied via questionnaires that examined the ages of online gamers. It was determined that massive multiplayer online role-playing games players regard visual authority value and monetary value as more important than do casual gamers. It was also determined that younger gamers tend to be more interested in visual authority, whereas older gamers tend to be more interested in character competency. This research provides a foundation for future studies to extend the MTCV to consider other user factors, such as cultural effects. PMID:21288134
Modeling gravity-driven fingering in rough-walled fractures using modified percolation theory
Glass, R.J.
1992-12-31
Pore scale invasion percolation theory is modified for imbibition of.wetting fluids into fractures. The effects of gravity, local aperture field geometry, and local in-plane air/water interfacial curvatureare included in the calculation of aperture filling potential which controls wetted structure growth within the fracture. The inclusion of gravity yields fingers oriented in the direction of the gravitational gradient. These fingers widen and tend to meander and branch more as the gravitational gradient decreases. In-plane interfacial curvature also greatly affects the wetted structure in both horizontal and nonhorizontal fractures causing the formation of macroscopic wetting fronts. The modified percolation model is used to simulate imbibition into an analogue rough-walled fracture where both fingering and horizontal imbibition experiments were previously conducted. Comparison of numerical and experimental results showed reasonably good agreement. This process oriented physical and numerical modeling is-a necessary step toward including gravity-driven fingering in models of flow and transport through unsaturated, fractured rock.
Density functional theory calculations of phenol-modified monolayer silicon nanosheets
NASA Astrophysics Data System (ADS)
Spencer, Michelle J. S.; Morishita, Tetsuya; Bassett, Michael R.
2013-12-01
Silicon nanosheets are one of most exciting recent discoveries, being a two-dimensional form of silicon that is only nanometers thick, with large lateral dimensions. A single atomic layer silicon nanosheet is known as silicene and can be grown with different surface terminations. It has been shown previously that organo-modified silicene can be synthesised with phenyl groups covalently bonded to both sides of the nanosheet, with hydrogen atoms terminating the undercoordinated silicon atoms. In this work, we use density functional theory calculations and ab initio molecular dynamics simulations to determine the effect of hydroxyl (OH) group substitutions on the phenyl-modified silicene. Different positions of the OH groups on the phenyl rings were modelled including ortho-, meta- and para- substituted positions. We found that the meta-substituted position was favoured, followed by the para- then ortho- substituted positions. Our ab initio MD simulations showed that the phenol groups will freely rotate on the nanosheet, aligning so as to form hydrogen bonds between adjacent phenol groups. The unique properties of this material could be useful for future electronic device applications.
BCS instability and finite temperature corrections to tachyon mass in intersecting D1-branes
NASA Astrophysics Data System (ADS)
Chowdhury, Sudipto Paul; Sarkar, Swarnendu; Sathiapalan, B.
2014-09-01
A holographic description of BCS superconductivity is given in [1]. This model was constructed by insertion of a pair of D8-branes on a D4-background. The spectrum of intersecting D8-branes has tachyonic modes indicating an instability which is identified with the BCS instability in superconductors. Our aim is to study the stability of the intersecting branes under finite temperature effects. Many of the technical aspects of this problem are captured by a simpler problem of two intersecting D1-branes on flat background. In the simplified set-up we compute the one-loop finite temperature corrections to the tree-level tachyon mass-squared-squared using the frame-work of SU(2) Yang-Mills theory in (1 + 1)-dimensions. We show that the one-loop two-point functions are ultraviolet finite due to cancellation of ultraviolet divergence between the amplitudes containing bosons and fermions in the loop. The amplitudes are found to be infrared divergent due to the presence of massless fields in the loops. We compute the finite temperature mass-squared correction to all the massless fields and use these temperature dependent masses-squared to compute the tachyonic mass-squared correction. We show numerically the existence of a transition temperature at which the effective mass-squared of the tree-level tachyons becomes zero, thereby stabilizing the brane configuration.
Superfluidity and BCS-BEC crossover of ultracold atomic Fermi gases in mixed dimensions
NASA Astrophysics Data System (ADS)
Zhang, Leifeng; Chen, Qijin
Atomic Fermi gases have been under active investigation in the past decade. Here we study the superfluid and pairing phenomena of a two-component ultracold atomic Fermi gas in the presence of mixed dimensionality, in which one component is confined on a 1D optical lattice whereas the other is free in the 3D continuum. We assume a short-range pairing interaction and determine the superfluid transition temperature Tc and the phase diagram for the entire BCS-BEC crossover, using a pairing fluctuation theory which includes self-consistently the contributions of finite momentum pairs. We find that, as the lattice depth increases and the lattice spacing decreases, the behavior of Tc becomes very similar to that of a population imbalance Fermi gas in a simple 3D continuum. There is no superfluidity even at T = 0 below certain threshold of pairing strength in the BCS regime. Nonmonotonic Tc behavior and intermediate temperature superfluidity emerge, and for deep enough lattice, the Tc curve will split into two parts. Implications for experiment will be discussed. References: 1. Q.J. Chen, Ioan Kosztin, B. Janko, and K. Levin, Phys. Rev. B 59, 7083 (1999). 2. Chih-Chun Chien, Qijin Chen, Yan He, and K. Levin, Phys. Rev. Lett. 97, 090402(2006). Work supported by NSF of China and the National Basic Research Program of China.
Concavity of the collective excitation branch of a Fermi gas in the BEC-BCS crossover
NASA Astrophysics Data System (ADS)
Kurkjian, H.; Castin, Y.; Sinatra, A.
2016-01-01
We study the concavity of the dispersion relation q ↦ωq of the bosonic excitations of a three-dimensional spin-1/2 unpolarized Fermi gas in the random-phase approximation. In the limit of small wave numbers q , we obtain analytically the spectrum up to order 5 in q . In the neighborhood of q =0 , a change in concavity between the convex Bose-Einstein condensation limit and the concave BCS limit takes place at Δ /μ ≃0.869 (1 /kFa ≃-0.144 ), where a is the scattering length between opposite spin fermions, kF is the Fermi wave number and Δ the gap according to BCS theory, and μ is the chemical potential. At that point the branch is concave due to a negative fifth-order term. Our results are supplemented by a numerical study that shows the border between the zone of the (q ,Δ ) plane where q ↦ωq is concave and the zone where it is convex.
Winskel, Heather; Perea, Manuel; Peart, Emma
2014-07-01
In the current study, we tested the generality of the modified receptive field (MRF) theory (Tydgat & Grainger, 2009) with English native speakers (Experiment 1) and Thai native speakers (Experiment 2). Thai has a distinctive alphabetic orthography with visually complex letters (ฝ ฟ or ผ พ) and nonlinear characteristics and lacks interword spaces. We used a two-alternative forced choice (2AFC) procedure to measure identification accuracy for all positions in a string of five characters, which consisted of Roman script letters, Thai letters, or symbols. For the English speakers, we found a similar pattern of results as in previous studies (i.e., a dissociation between letters and symbols). In contrast, for the Thai participants, we found that the pattern for Thai letters, Roman letters and symbols displayed a remarkably similar linear trend. Thus, while we observed qualified support for the MRF theory, in that we found an advantage for initial position, this effect also applied to symbols (i.e., our data revealed a language-specific effect). We propose that this pattern for letters and symbols in Thai has developed as a specialized adaptive mechanism for reading in this visually complex and crowded nonlinear script without interword spaces. PMID:24818534
Unified cosmic history in modified gravity: From F(R) theory to Lorentz non-invariant models
NASA Astrophysics Data System (ADS)
Nojiri, Shin'Ichi; Odintsov, Sergei D.
2011-08-01
The classical generalization of general relativity is considered as the gravitational alternative for a unified description of the early-time inflation with late-time cosmic acceleration. The structure and cosmological properties of a number of modified theories, including traditional F(R) and Hořava-Lifshitz F(R) gravity, scalar-tensor theory, string-inspired and Gauss-Bonnet theory, non-local gravity, non-minimally coupled models, and power-counting renormalizable covariant gravity are discussed. Different representations of and relations between such theories are investigated. It is shown that some versions of the above theories may be consistent with local tests and may provide a qualitatively reasonable unified description of inflation with the dark energy epoch. The cosmological reconstruction of different modified gravities is provided in great detail. It is demonstrated that eventually any given universe evolution may be reconstructed for the theories under consideration, and the explicit reconstruction is applied to an accelerating spatially flat Friedmann-Robertson-Walker (FRW) universe. Special attention is paid to Lagrange multiplier constrained and conventional F(R) gravities, for latter F(R) theory, the effective ΛCDM era and phantom divide crossing acceleration are obtained. The occurrences of the Big Rip and other finite-time future singularities in modified gravity are reviewed along with their solutions via the addition of higher-derivative gravitational invariants.
NASA Astrophysics Data System (ADS)
Kiani, M.; Alavianmehr, M. M.; Otoofat, M.; Mohsenipour, A. A.; Ghatee, A.
2015-11-01
In this work, we identify a simple method for predicting transport properties of fluids over wide ranges of temperatures and pressure. In this respect, the capability of several equations of state (EOS) and second virial coefficient correlations to predict transport properties of fluids including carbon dioxide, methane and argon using modified Enskog theory (MET) is investigated. The transport properties in question are viscosity and thermal conductivity. The results indicate that the SRK EOS employed in the modified Enskog theory outperforms other equations of state. The average absolute deviation was found to be 12.2 and 18.5% for, respectively, the calculated thermal conductivity and viscosity using the MET.
NASA Astrophysics Data System (ADS)
Bussmann-Holder, Annette; Köhler, Jürgen; Whangbo, M.-H.; Bianconi, Antonio; Simon, Arndt
2016-05-01
The recent report of superconductivity under high pressure at the record transition temperature of Tc =203 K in pressurized H2S has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms cannot account for the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope coefficient. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active.
Estimation of thermodynamic properties of Cu-La binary alloy with modified Miedema's theory
NASA Astrophysics Data System (ADS)
Li, Hai-hong; Zhang, Shi-hong; Chen, Yan; Cheng, Ming; Song, Hong-wu; Liu, Jin-song
2016-01-01
According to modified Miedema's theory, mixing enthalpies (Δ H), excess entropies ( S E), excess Gibbs free energy ( G E), and component activities ( a) of Cu-La binary alloy were estimated using the basic thermodynamic principles and some simple physical parameters of Cu and La, such as electronegativity, atomic volume and electron density. Based on the Cu-La binary alloy phase diagram, the Gibbs free energy of the phase precipitation reactions of Cu6La and Cu5La was deduced. The results showed that the values of Δ H, S E, and G E of Cu-La binary alloy were all negative. Compared to the ideal solution, the activities of the components presented a large negative deviation from Raoult's law, which indicated that there was a strong interaction between Cu and La. The calculated data are well consistent with the experimental data. The Gibbs free energies of the phase precipitation reactions of Cu6La are lower than those for Cu5La, which means that Cu6La is thermodynamically more stable than Cu5La. Furthermore, the experimental results show that rareearth rich Cu6La phase particles in copper matrix are formed after La microalloying.
NASA Astrophysics Data System (ADS)
Bel, Julien; Brax, Philippe; Marinoni, Christian; Valageas, Patrick
2015-05-01
The clustering ratio η , a large-scale structure observable originally designed to constrain the shape of the power spectrum of matter density fluctuations, is shown to provide a sensitive probe of the nature of gravity in the cosmological regime. We apply this analysis to F (R ) theories of gravity using the luminous red galaxy sample extracted from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 and 10 catalogs. We find that general relativity (GR), complemented with a Friedmann-Robertson-Walker (FRW) cosmological model with parameters fixed by the Planck satellite, describes extremely well the clustering of galaxies up to z ˜0.6 . On large cosmic scales, the absolute amplitude of deviations from GR, |fR 0|, is constrained to be smaller than 4.6 ×1 0-5 at the 95% confidence level. This bound makes cosmological probes of gravity almost competitive with the sensitivity of Solar System tests, although still one 1 order of magnitude less effective than astrophysical tests. We also extrapolate our results to future large surveys like Euclid and show that the astrophysical bound will certainly remain out of reach for such a class of modified-gravity models that only differ from Λ CDM at low redshifts.
Sound modes at the BCS-BEC crossover
Heiselberg, H.
2006-01-15
First and second sound speeds are calculated for a uniform superfluid gas of Fermi atoms as a function of temperature, density, and interaction strength. The second sound speed is of particular interest as it is a clear signal of a superfluid component and it determines the critical temperature. The sound modes and their dependence on density, scattering length, and temperature are calculated in the BCS, molecular Bose-Einstein condensate (BEC), and unitarity limits and a smooth crossover is extrapolated. It is found that first and second sounds undergo avoided crossing on the BEC side due to mixing. Consequently, they are detectable at crossover both as density and thermal waves in traps.
Cosmological BCS mechanism and the big bang singularity
Alexander, Stephon; Biswas, Tirthabir
2009-07-15
We provide a novel mechanism that resolves the big bang singularity present in Friedman-Lemaitre-Robertson-Walker space-times without the need for ghost fields. Building on the fact that a four-fermion interaction arises in general relativity when fermions are covariantly coupled, we show that at early times the decrease in scale factor enhances the correlation between pairs of fermions. This enhancement leads to a BCS-like condensation of the fermions and opens a gap dynamically driving the Hubble parameter H to zero and results in a nonsingular bounce, at least in some special cases.
Lee, Haw-Long; Chang, Win-Jin
2016-01-01
The modified couple stress theory is adopted to study the sensitivity of a rectangular atomic force microscope (AFM) cantilever immersed in acetone, water, carbon tetrachloride (CCl4), and 1-butanol. The theory contains a material length scale parameter and considers the size effect in the analysis. However, this parameter is difficult to obtain via experimental measurements. In this study, a conjugate gradient method for the parameter estimation of the frequency equation is presented. The optimal method provides a quantitative approach for estimating the material length scale parameter based on the modified couple stress theory. The results show that the material length scale parameter of the AFM cantilever immersed in acetone, CCl4, water, and 1-butanol is 0, 25, 116.3, and 471 nm, respectively. In addition, the vibration sensitivities of the AFM cantilever immersed in these liquids are investigated. The results are useful for the design of AFM cantilevers immersed in liquids. PMID:26402914
Particle-hole duality, integrability, and Russian doll BCS model
NASA Astrophysics Data System (ADS)
Bork, L. V.; Pogosov, W. V.
2015-08-01
We address a generalized Richardson model (Russian doll BCS model), which is characterized by the breaking of time-reversal symmetry. This model is known to be exactly solvable and integrable. We point out that the Russian doll BCS model, on the level of Hamiltonian, is also particle-hole symmetric. This implies that the same state can be expressed both in the particle and hole representations with two different sets of Bethe roots. We then derive exact relations between Bethe roots in the two representations, which can hardly be obtained staying on the level of Bethe equations. In a quasi-classical limit, similar identities for usual Richardson model, known from literature, are recovered from our results. We also show that these relations for Richardson roots take a remarkably simple form at half-filling and for a symmetric with respect to the middle of the interaction band distribution of one-body energy levels, since, in this special case, the rapidities in the particle and hole representations up to the translation satisfy the same system of equations.
Vector-tensor nature of Bekenstein's relativistic theory of modified gravity
Zlosnik, T. G.; Ferreira, P. G.; Starkman, Glenn D.
2006-08-15
Bekenstein's theory of relativistic gravity is conventionally written as a bimetric theory. The two metrics are related by a disformal transformation defined by a dynamical vector field and a scalar field. In this paper we show that the theory can be rewritten as vector-tensor theory akin to Einstein-Aether theories with noncanonical kinetic terms. We discuss some of the implications of this equivalence.
Glass, Joseph E.; Mowbray, Orion P.; Link, Bruce G.; Kristjansson, Sean D.; Bucholz, Kathleen K.
2014-01-01
Background We sought to apply modified labeling theory in a cross-sectional study of alcohol use disorder (AUD) to investigate the mechanisms through which perceived alcohol stigma (PAS) may lead to the persistence of AUD and risk of psychiatric disorder. Methods We conducted structural equation modeling (SEM) including moderated mediation analyses of two waves (W1 and W2) of data from the National Epidemiologic Survey on Alcohol and Related Conditions. We analyzed validated measures of PAS, perceived social support, social network involvement, and psychiatric disorders among (n = 3608) adults with two or more DSM-5 AUD symptoms in the first two of the three years between the W1 and W2 survey. Cross-sectional analyses were conducted owing to the assessment of PAS only at W2. Results Per mediation analyses, lower levels of perceived social support explained the association of PAS with past-year AUD and past-year internalizing psychiatric disorder at W2. The size of the mediated relationship was significantly larger for those classified as labeled (i.e., alcoholic) per their prior alcohol treatment or perceived need (n = 938) as compared to unlabeled (n = 2634), confirming a hypothesis of moderated mediation. Unexpectedly, mediation was also present for unlabeled individuals. Conclusions Lower levels of social support may be an important intermediate outcome of alcohol stigma. Longitudinal data are needed to establish the temporal precedence of PAS and its hypothesized intermediate and distal outcomes. Research is needed to evaluate direct measures of labeling that could replace proxy measures (e.g., prior treatment status) commonly employed in studies of the stigma of psychiatric disorders. PMID:24071569
A Preliminary ZEUS Lightning Location Error Analysis Using a Modified Retrieval Theory
NASA Technical Reports Server (NTRS)
Elander, Valjean; Koshak, William; Phanord, Dieudonne
2004-01-01
The ZEUS long-range VLF arrival time difference lightning detection network now covers both Europe and Africa, and there are plans for further expansion into the western hemisphere. In order to fully optimize and assess ZEUS lightning location retrieval errors and to determine the best placement of future receivers expected to be added to the network, a software package is being developed jointly between the NASA Marshall Space Flight Center (MSFC) and the University of Nevada Las Vegas (UNLV). The software package, called the ZEUS Error Analysis for Lightning (ZEAL), will be used to obtain global scale lightning location retrieval error maps using both a Monte Carlo approach and chi-squared curvature matrix theory. At the core of ZEAL will be an implementation of an Iterative Oblate (IO) lightning location retrieval method recently developed at MSFC. The IO method will be appropriately modified to account for variable wave propagation speed, and the new retrieval results will be compared with the current ZEUS retrieval algorithm to assess potential improvements. In this preliminary ZEAL work effort, we defined 5000 source locations evenly distributed across the Earth. We then used the existing (as well as potential future ZEUS sites) to simulate arrival time data between source and ZEUS site. A total of 100 sources were considered at each of the 5000 locations, and timing errors were selected from a normal distribution having a mean of 0 seconds and a standard deviation of 20 microseconds. This simulated "noisy" dataset was analyzed using the IO algorithm to estimate source locations. The exact locations were compared with the retrieved locations, and the results are summarized via several color-coded "error maps."
NASA Astrophysics Data System (ADS)
Akbarzadeh Khorshidi, Majid; Shariati, Mahmoud
2016-04-01
This paper presents a new investigation for propagation of stress wave in a nanobeam based on modified couple stress theory. Using Euler-Bernoulli beam theory, Timoshenko beam theory, and Reddy beam theory, the effect of shear deformation is investigated. This nonclassical model contains a material length scale parameter to capture the size effect and the Poisson effect is incorporated in the current model. Governing equations of motion are obtained by Hamilton's principle and solved explicitly. This solution leads to obtain two phase velocities for shear deformable beams in different directions. Effects of shear deformation, material length scale parameter, and Poisson's ratio on the behavior of these phase velocities are investigated and discussed. The results also show a dual behavior for phase velocities against Poisson's ratio.
More is Different:. 50 Years of Nuclear BCS
NASA Astrophysics Data System (ADS)
Broglia, R. A.
2013-01-01
At the basis of BCS theory, and associated symmetry breaking phenomena in gauge space, one finds Cooper pair binding. A major question in the nuclear case concerning this issue, regards the relative role played by the bare nucleon-nucleon force and by the interaction induced by the exchange of vibrations between members of Cooper pairs. The exotic nucleus 113Li8 in which two neutrons forming an extended halo, bind weakly to the 9Li core, provides an excellent testing ground to try to shed light on this issue. Theory finds that, in this case, the exchange of collective vibrations associated with the core and with the halo fields, provides an important fraction of the glue binding the pair. Inverse kinematics and active detector based experiments, combined with a quantitative description (based on absolute differential cross sections) of single Cooper pair tunneling, the specific probe of pairing in nuclei, which forces the virtual phonon into a real final state, have tested these predictions with positive results. The extension of structure and reaction studies to open shell (superfluid) nuclei (Sn-isotopes), displaying a strong alignment of quasispin in gauge space, and associated domain wall, as testified by pairing rotational bands excited in terms of single Cooper pair tunneling, provides an overall description of the data within experimental errors. This is also true in connection with pairing vibrations as observed in closed shell nuclei. Many of the concepts which are at the basis of the development associated with a quantitative treatment of the variety of phenomena associated with the spontaneous breaking of gauge symmetry in nuclei have been instrumental in connection with novel studies of soft matter, namely of protein evolution and protein folding. Although the route to these subjects and associated development does not necessarily imply the nuclear physics connection, such a connection has proven qualitatively and quantitatively inspiring. In particular
BCS coupling in a 1D Luttinger liquid
NASA Astrophysics Data System (ADS)
Eneias, R.; Ferraz, A.
2015-12-01
In this work we investigate the effect produced by the BCS coupling in spinless fermions in one spatial dimension. Using bosonization techniques our initial model is rewritten in terms of a sine-Gordon field and a free massless scalar field. As a result the Cooper pair in our scenario is made up of soliton and antisoliton particles. We calculate the single particle Green’s function, the pair correlation function and the optical conductivity associated with the physical fermions and we show how they differ from their conventional quasiparticle analogues. Finally, we compare our results with related experimental findings for high temperature superconductors and we display how they fit qualitatively well the related observed effects produced by the anti-nodal quasiparticles in those materials.
BCS Superconductivity of Dirac Electrons in Graphene Layers
NASA Astrophysics Data System (ADS)
Kopnin, N. B.; Sonin, E. B.
2008-06-01
Possible superconductivity of electrons with the Dirac spectrum is analyzed using the BCS model. We calculate the critical temperature, the superconducting energy gap, and the supercurrent as functions of the doping level and of the pairing interaction strength. Zero doping is characterized by the existence of a quantum critical point such that the critical temperature vanishes below some finite value of the interaction strength. However, the critical temperature remains finite for any nonzero electron or hole doping level when the Fermi energy is shifted away from the Dirac point. As distinct from usual superconductors, the supercurrent density is not proportional to the number of electrons but is strongly decreased due to the presence of the Dirac point.
BCS Superconductivity of Dirac electrons in graphene layers.
Kopnin, N B; Sonin, E B
2008-06-20
Possible superconductivity of electrons with the Dirac spectrum is analyzed using the BCS model. We calculate the critical temperature, the superconducting energy gap, and the supercurrent as functions of the doping level and of the pairing interaction strength. Zero doping is characterized by the existence of a quantum critical point such that the critical temperature vanishes below some finite value of the interaction strength. However, the critical temperature remains finite for any nonzero electron or hole doping level when the Fermi energy is shifted away from the Dirac point. As distinct from usual superconductors, the supercurrent density is not proportional to the number of electrons but is strongly decreased due to the presence of the Dirac point. PMID:18643614
NASA Astrophysics Data System (ADS)
El Araby, Omar; Baeriswyl, Dionys
2014-04-01
The exact ground state of the reduced BCS Hamiltonian is investigated numerically for large system sizes and compared with the BCS ansatz. A "canonical" order parameter is found to be equal to the largest eigenvalue of Yang's reduced density matrix in the thermodynamic limit. Moreover, the limiting values of the exact analysis agree with those obtained for the BCS ground state. Exact results for the ground-state energy, level occupations, and a pseudospin-pseudospin correlation function are also found to converge to the BCS values already for relatively small system sizes. However, discrepancies persist for a pair-pair correlation function, for interlevel correlations of occupancies and for the fidelity susceptibility, even for large system sizes where these quantities have visibly converged to well-defined limits. Our results indicate that there exist nonperturbative corrections to the BCS predictions in the thermodynamic limit.
BCS Biowaivers: Similarities and Differences Among EMA, FDA, and WHO Requirements.
Davit, Barbara M; Kanfer, Isadore; Tsang, Yu Chung; Cardot, Jean-Michel
2016-05-01
The Biopharmaceutics Classification System (BCS), based on aqueous solubility and intestinal permeability, has enjoyed wide use since 1995 as a mechanism for waiving in vivo bioavailability and bioequivalence studies. In 2000, the US-FDA was the first regulatory agency to publish guidance for industry describing how to meet criteria for requesting a waiver of in vivo bioavailability and bioequivalence studies for highly soluble, highly permeable (BCS Class I) drugs. Subsequently, the World Health Organization (WHO) and European Medicines Agency (EMA) published guidelines recommending how to obtain BCS biowaivers for BCS Class III drugs (high solubility, low permeability), in addition to Class I drugs. In 2015, the US-FDA became better harmonized with the EMA and WHO following publication of two guidances for industry outlining criteria for obtaining BCS biowaivers for both Class I and Class III drugs. A detailed review and comparison of the BCS Class I and Class III criteria currently recommended by the US-FDA, EMA, and WHO revealed good convergence of the three agencies with respect to BCS biowaiver criteria. The comparison also suggested that, by applying the most conservative of the three jurisdictional approaches, it should be possible for a sponsor to design the same set of BCS biowaiver studies in preparing a submission for worldwide filing to satisfy US, European, and emerging market regulators. It is hoped that the availability of BCS Class I and Class III biowaivers in multiple jurisdictions will encourage more sponsors to request waivers of in vivo bioavailability/bioequivalence testing using the BCS approach. PMID:26943914
NASA Astrophysics Data System (ADS)
Poletto Rodrigues, Bruno; Deubener, Joachim; Wondraczek, Lothar
2016-05-01
Introducing an interaction parameter γ, we implement modifier interaction and the mixed-alkali effect into bond constraint theory, and apply this extension for simplistic property prediction on ternary phosphate glasses. The severity of the mixed alkali effect results from the interplay of two simultaneous contributions: Bond constraints on the modifier species soften or stiffen with decreasing or increasing γ, respectively. When the modifier size is not too dissimilar the decrease in γ reflects that the alkali ions can easily migrate between different sites, forcing the network to continuously re-accommodate for any subsequent distortions. With increasing size difference, migration becomes increasingly difficult without considerable network deformation. This holds even for smaller ions, where the sluggish dynamics of the larger constituent result in blocking of the fast ion movement, leading to the subsequent increase in γ. Beyond a certain size difference in the modifier pair, a value of γ exceeding unity may indicate the presence of steric hindrance due to the large surrounding modifiers impeding the phosphate network to re-accommodate deformation.
Modified Brans-Dicke theory with space-time anisotropic parameters
Moon, Taeyoon; Oh, Phillial E-mail: ploh@skku.edu
2014-03-01
We consider the ADM formalism of the Brans-Dicke theory and propose a space-time anisotropic extension of the theory by introducing five free parameters. We find that the resulting theory reveals many interesting aspects which are not present in the original BD theory. We first discuss the ghost instability and strong coupling problems which are present in the gravity theory without the full diffeomorphism symmetry and show that they can be avoided in a region of the parameter space. We also perform the post-Newtonian approximation and show that the constraint of the Brans-Dicke parameter ω{sub BD} being large to be consistent with the solar system observations could be evaded in the extended theory. We also discuss that accelerating Universe can be achieved without the need of the potential for the Brans-Dicke scalar.
A Modified Hansen's Theory as Applied to the Motion of Artificial Satellites
NASA Technical Reports Server (NTRS)
Musen, Peter
1960-01-01
This report presents a theory of oblateness perturbations of the orbits of artificial satellites based on Hansen's theory, with modification for adaptation to fast machine computation. The theory permits the easy inclusion of any gravitational terms and is suitable for the deduction of geo-physical and geodetic data from orbit observations on artificial satellites. The computations can be carried out to any desired order compatible with the accuracy of the geodetic parameters.
NASA Astrophysics Data System (ADS)
Dong, Hang; Zhang, Wenyuan; Zhou, Li; Ma, Yongli
2015-11-01
We investigate the transition and damping of low-energy collective modes in a trapped unitary Fermi gas by solving the Boltzmann-Vlasov kinetic equation in a scaled form, which is combined with both the T-matrix fluctuation theory in normal phase and the mean-field theory in order phase. In order to connect the microscopic and kinetic descriptions of many-body Feshbach scattering, we adopt a phenomenological two-fluid physical approach, and derive the coupling constants in the order phase. By solving the Boltzmann-Vlasov steady-state equation in a variational form, we calculate two viscous relaxation rates with the collision probabilities of fermion’s scattering including fermions in the normal fluid and fermion pairs in the superfluid. Additionally, by considering the pairing and depairing of fermions, we get results of the frequency and damping of collective modes versus temperature and s-wave scattering length. Our theoretical results are in a remarkable agreement with the experimental data, particularly for the sharp transition between collisionless and hydrodynamic behaviour and strong damping between BCS and unitary limits near the phase transition. The sharp transition originates from the maximum of viscous relaxation rate caused by fermion-fermion pair collision at the phase transition point when the fermion depair, while the strong damping due to the fast varying of the frequency of collective modes from BCS limit to unitary limit.
Dong, Hang; Zhang, Wenyuan; Zhou, Li; Ma, Yongli
2015-01-01
We investigate the transition and damping of low-energy collective modes in a trapped unitary Fermi gas by solving the Boltzmann-Vlasov kinetic equation in a scaled form, which is combined with both the T-matrix fluctuation theory in normal phase and the mean-field theory in order phase. In order to connect the microscopic and kinetic descriptions of many-body Feshbach scattering, we adopt a phenomenological two-fluid physical approach, and derive the coupling constants in the order phase. By solving the Boltzmann-Vlasov steady-state equation in a variational form, we calculate two viscous relaxation rates with the collision probabilities of fermion’s scattering including fermions in the normal fluid and fermion pairs in the superfluid. Additionally, by considering the pairing and depairing of fermions, we get results of the frequency and damping of collective modes versus temperature and s-wave scattering length. Our theoretical results are in a remarkable agreement with the experimental data, particularly for the sharp transition between collisionless and hydrodynamic behaviour and strong damping between BCS and unitary limits near the phase transition. The sharp transition originates from the maximum of viscous relaxation rate caused by fermion-fermion pair collision at the phase transition point when the fermion depair, while the strong damping due to the fast varying of the frequency of collective modes from BCS limit to unitary limit. PMID:26522094
Dong, Hang; Zhang, Wenyuan; Zhou, Li; Ma, Yongli
2015-01-01
We investigate the transition and damping of low-energy collective modes in a trapped unitary Fermi gas by solving the Boltzmann-Vlasov kinetic equation in a scaled form, which is combined with both the T-matrix fluctuation theory in normal phase and the mean-field theory in order phase. In order to connect the microscopic and kinetic descriptions of many-body Feshbach scattering, we adopt a phenomenological two-fluid physical approach, and derive the coupling constants in the order phase. By solving the Boltzmann-Vlasov steady-state equation in a variational form, we calculate two viscous relaxation rates with the collision probabilities of fermion's scattering including fermions in the normal fluid and fermion pairs in the superfluid. Additionally, by considering the pairing and depairing of fermions, we get results of the frequency and damping of collective modes versus temperature and s-wave scattering length. Our theoretical results are in a remarkable agreement with the experimental data, particularly for the sharp transition between collisionless and hydrodynamic behaviour and strong damping between BCS and unitary limits near the phase transition. The sharp transition originates from the maximum of viscous relaxation rate caused by fermion-fermion pair collision at the phase transition point when the fermion depair, while the strong damping due to the fast varying of the frequency of collective modes from BCS limit to unitary limit. PMID:26522094
Dickman, D; Prieto, P
1987-10-01
A case is presented that shows the usefulness of integrating systems theory and attachment theory in the formulation and treatment of a clinical problem. The 5 year old son of East Indian immigrants presented with persistent psychogenic vomiting associated with pathological family attachments. It was evident that the precarious family equilibrium was stabilized by the child's psychogenic vomiting. The therapeutic team suggested to the family that their problems might be more satisfactorily resolved if the mother and child maintained their link by two-way radio. Three weeks later the vomiting had ceased, the child no longer felt that he needed the radio and both parents had established new patterns of relating to their child, whose attendance and peer socialization at school showed marked improvement. To some extent the rapid resolution of the problems was facilitated by the cultural strengths of the family. PMID:3676993
ERIC Educational Resources Information Center
Meng, Chan Ling; Othman, Jamilah; D'Silva, Jeffrey Lawrence; Omar, Zoharah
2014-01-01
This conceptual paper studies the application of the Theory of Planned Behavior (TBP) in academic dishonesty with the mediating variable of ethical ideologies. The study reviews literature on the Theory of Planned Behavior and past studies pertaining to academic dishonesty. The paper analyses the relationship of the variables of TPB on academic…
ERIC Educational Resources Information Center
Zeedick, Danielle Marie
2010-01-01
During the past several decades, the field of instructional design theory has experienced changes in what is mostly applied to traditional, on-ground education. While instructional design theory has been (and still is being) discussed, constructed, and deconstructed, there has been no agreement among prominent instructional design theory…
Abbasi, Mohammad; Afkhami, Seyed E
2014-12-01
The resonant frequency and sensitivity of an atomic force microscope (AFM) with an assembled cantilever probe (ACP) is analyzed utilizing strain gradient theory, and then the governing equation and boundary conditions are derived by a combination of the basic equations of strain gradient theory and Hamilton's principle. The resonant frequency and sensitivity of the proposed AFM microcantilever are then obtained numerically. The proposed ACP includes a horizontal cantilever, two vertical extensions, and two tips located at the free ends of the extensions that form a caliper. As one of the extensions is located between the clamped and free ends of the AFM microcantilever, the cantilever is modeled as two beams. The results of the current model are compared with those evaluated by both modified couple stress and classical beam theories. The difference in results evaluated by the strain gradient theory and those predicted by the couple stress and classical beam theories is significant, especially when the microcantilever thickness is approximately the same as the material length-scale parameters. The results also indicate that at the low values of contact stiffness, scanning in the higher cantilever modes decrease the accuracy of the proposed AFM ACP. PMID:25205330
Misra, Shikha; Mishra, S. K.; Sodha, M. S.
2013-01-15
The authors have modified Chow's theory of secondary electron emission (SEE) to take account of the fact that the path length of a primary electron in a spherical particle varies between zero to the diameter or x{sub m} the penetration depth depending on the distance of the path from the centre of the particle. Further by including this modified expression for SEE efficiency, the charging kinetics of spherical grains in a Maxwellian plasma has been developed; it is based on charge balance over dust particles and number balance of electrons and ionic species. It is seen that this effect is more pronounced for smaller particles and higher plasma temperatures. Desirable experimental work has also been discussed.
Applying Rasch Model and Generalizability Theory to Study Modified-Angoff Cut Scores
ERIC Educational Resources Information Center
Arce, Alvaro J.; Wang, Ze
2012-01-01
The traditional approach to scale modified-Angoff cut scores transfers the raw cuts to an existing raw-to-scale score conversion table. Under the traditional approach, cut scores and conversion table raw scores are not only seen as interchangeable but also as originating from a common scaling process. In this article, we propose an alternative…
Examination of the Korean Modified Checklist of Autism in Toddlers: Item Response Theory
ERIC Educational Resources Information Center
Seung, HyeKyeung; Ji, Juye; Kim, Soo-Jin; Sung, Inkyung; Youn, Young-Ah; Hong, Gyunghun; Lee, Hyeonjin; Lee, Young Hwan; Lee, Hyunsuk; Youm, Hyun Kyung
2015-01-01
The study examined the clinical utility and psychometric properties of the Korean Modified Checklist of Autism in Toddlers (K-M-CHAT)-2. A sample of 2300 parents of 16- to 36-month-old children was recruited across South Korea. A phone interview was utilized to follow up with participants who initially screened positive for autism spectrum…
Rastgoo, Abbas; Ahmadian, Mohammad Taghi
2013-01-01
Summary The paper presents the effects of fluid flow on the static and dynamic properties of carbon nanotubes that convey a viscous fluid. The mathematical model is based on the modified couple stress theory. The effects of various fluid parameters and boundary conditions on the pull-in voltages are investigated in detail. The applicability of the proposed system as nanovalves or nanosensors in nanoscale fluidic systems is elaborated. The results confirm that the nanoscale system studied in this paper can be properly applied for these purposes. PMID:24367746
NASA Astrophysics Data System (ADS)
Celi, Alessio; Grass, Tobias; Ferris, Andrew J.; Padhi, Bikash; Raventós, David; Simonet, Juliette; Sengstock, Klaus; Lewenstein, Maciej
2016-08-01
Ultracold bosons in a triangular lattice are a promising candidate for observing quantum spin liquid behavior. Here we investigate, for such system, the role of a harmonic trap giving rise to an inhomogeneous density. We construct a modified spin-wave theory for arbitrary filling and predict the breakdown of order for certain values of the lattice anisotropy. These regimes, identified with the spin liquid phases, are found to be quite robust upon changes in the filling factor. This result is backed by an exact diagonalization study on a small lattice.
NASA Astrophysics Data System (ADS)
Valkenburg, Wessel; Hu, Bin
2015-09-01
We present a description for setting initial particle displacements and field values for simulations of arbitrary metric theories of gravity, for perfect and imperfect fluids with arbitrary characteristics. We extend the Zel'dovich Approximation to nontrivial theories of gravity, and show how scale dependence implies curved particle paths, even in the entirely linear regime of perturbations. For a viable choice of Effective Field Theory of Modified Gravity, initial conditions set at high redshifts are affected at the level of up to 5% at Mpc scales, which exemplifies the importance of going beyond Λ-Cold Dark Matter initial conditions for modifications of gravity outside of the quasi-static approximation. In addition, we show initial conditions for a simulation where a scalar modification of gravity is modelled in a Lagrangian particle-like description. Our description paves the way for simulations and mock galaxy catalogs under theories of gravity beyond the standard model, crucial for progress towards precision tests of gravity and cosmology.
Fujioka, Yoshitsugu; Kadono, Keitaro; Fujie, Yasuko; Metsugi, Yukiko; Ogawara, Ken-ichi; Higaki, Kazutaka; Kimura, Toshikiro
2007-06-01
The in-vivo absorbability of drugs categorized into the biopharmaceutics classification system (BCS) class II is very difficult to be predicted because of the large variability in the absorption and/or dissolution kinetics and the lack of an adequate in-vitro system for evaluating the dissolution behavior. We tried to predict the in-vivo absorption kinetics of griseofulvin, categorized into BCS class II, orally administrated as powders into rats, based on Gastrointestinal-Transit-Absorption model (GITA model), consisting of the absorption, dissolution and GI-transit processes. Using the dissolution rate constants (k(dis)) of griseofulvin obtained with JP 1st solution, JP 2nd solution, FaSSIF, FeSSIF and modified SIBLM as a medium, simulation lines were not able to describe the observed mean plasma profile at all. On the other hand, a calculated line provided by employing k(dis) obtained with MREVID 2 (medium reflecting in-vivo dissolution 2), a new medium, was in better agreement with the observed mean plasma profile than existing media, indicating that the utilization of adequate k(dis) value made it possible to predict the in-vivo absorption kinetics of drugs classified into BCS class II based on GITA model and that MREVID 2 could be a useful medium for describing the in-vivo dissolution kinetics. PMID:17442444
Schomber, P.R.
1995-03-01
An ion optics system utilizing a wein filter velocity selector has been modeled and characterized for use as an ion source for an instrument to measure high resolution angular distributions of sputtered neutral atoms. Laser induced fluorescence detection techniques are used to measure ground state and first excited state sputtering angular distributions on a polycrystalline zirconium foil using argon and nitrogen sputter gases. The incident ion beam impact angle has been varied from 15 deg to 75 deg as measured from surface normal and the wein filter velocity selector has been used to select N2+ and N+ ion beams from the nitrogen ion beam. The experimental data gathered are compared to Roosandaal Sanders analytical sputtering theory along with data on xenon and neon. Roosandaal Sanders theory reproduces the near surface normal sputtering behavior but rapidly breaks down as the incident ion beam impact angle moves toward the surface. Modifications to the Roosandaal Sanders equation to introduce adjustable fitting parameters and non-linear least squares fitting of the experimental data to these parameters has been accomplished. The results are discussed relating the fitting parameters to physical constants based in Roosandaal Sanders Theory. Discrepancies in the theory are addressed with extensive discussion on ion surface interaction.
ERIC Educational Resources Information Center
Croff, Julie M.; Clapp, John D.
2015-01-01
Screening, Brief Intervention, and Referral to Treatment (SBIRT) is a model program in the medical context, but it may be missing a large portion of the population with low access to healthcare services. Young adults have the lowest rates of insurance, low healthcare service utilization, and high rates of substance use. Theory driven Screening and…
A PARAMETRIC STUDY OF BCS RF SURFACE IMPEDANCE WITH MAGNETIC FIELD USING THE XIAO CODE
Reece, Charles E.; Xiao, Binping
2013-09-01
A recent new analysis of field-dependent BCS rf surface impedance based on moving Cooper pairs has been presented.[1] Using this analysis coded in Mathematica TM, survey calculations have been completed which examine the sensitivities of this surface impedance to variation of the BCS material parameters and temperature. The results present a refined description of the "best theoretical" performance available to potential applications with corresponding materials.
NASA Technical Reports Server (NTRS)
Yamauchi, G.; Johnson, W.
1984-01-01
A computationally efficient body analysis designed to couple with a comprehensive helicopter analysis is developed in order to calculate the body-induced aerodynamic effects on rotor performance and loads. A modified slender body theory is used as the body model. With the objective of demonstrating the accuracy, efficiency, and application of the method, the analysis at this stage is restricted to axisymmetric bodies at zero angle of attack. By comparing with results from an exact analysis for simple body shapes, it is found that the modified slender body theory provides an accurate potential flow solution for moderately thick bodies, with only a 10%-20% increase in computational effort over that of an isolated rotor analysis. The computational ease of this method provides a means for routine assessment of body-induced effects on a rotor. Results are given for several configurations that typify those being used in the Ames 40- by 80-Foot Wind Tunnel and in the rotor-body aerodynamic interference tests being conducted at Ames. A rotor-hybrid airship configuration is also analyzed.
Deuteron formation in expanding nuclear matter from a strong coupling BCS approach
Baldo, M.; Lombardo, U.; Schuck, P.
1995-08-01
The process of deuteron formation in intermediate heavy ion reactions is approached within the strong coupling BCS theory assuming that the final stage of the reaction can be described as an adiabatic expansion of a piece of nuclear matter. Since the gap equation in the {sup 3}{ital S}{sub 1}-{sup 3}{ital D}{sub 1} channel goes over into the deuteron Schroedinger equation in the low density limit, a smooth transition from the superfluid Cooper pair phase to a Bose deuteron gas is found. For a fixed entropy ranging from 0.5 to 2 units per particle the deuteron fraction, the chemical potential and temperature are reported as a function of density. For densities down to {rho}=0.1 fm{sup {minus}3} and lower, the deuteron-to-nucleon ratio rapidly increases from a density threshold strongly depending on the entropy. Decreasing further the density this ratio tends logarithmically to one. The possible relevance of these results for heavy ion collisions and the shortcomings of the present approach are briefly discussed.
Spin noise and magnetic screening of impurities in a BCS superconductor
NASA Astrophysics Data System (ADS)
Le Dall, Matthias; da Silva, Luis G. G. V. Dias; de Sousa, Rogério
The coupling of a localized impurity to a BCS superconductor (SC) leads to the formation of impurity Cooper-pairs via the proximity effect, generating two bound states within the SC energy gap, the so-called Yu-Rusinov-Shiba (YSR) states. They are similar to the Andreev Bound States that originate from Andreev reflection, e.g. when the impurity is hosted in a Josephson junction, and are known to produce sharp sub-gap resonances in charge noise [de Sousa et al., PRB 2009], providing a natural explanation for the observation of microresonators in superconducting devices [Simmonds et al., PRL 2004]. Here we present a theory for the spin noise generated by magnetic impurities in a SC, and discuss the impact of the Shiba states on models of flux noise in superconducting qubits. We use a combination of analytical methods and the numerical renormalization group technique to calculate the spin noise of an Anderson impurity in a SC, unveiling the competition between the proximity effect and Kondo correlations. Both mechanisms produce magnetic screening and a corresponding reduction in spin noise, giving rise to new insights on the kinds of impurities that are responsible for the observed 1 /fα flux noise in superconducting circuits. This research is supported by NSERC CRD/478366-2015.
Inhomogeneous BCS-BEC crossover for trapped cold atoms in optical lattices
NASA Astrophysics Data System (ADS)
Amaricci, A.; Privitera, A.; Capone, M.
2014-05-01
The BCS-BEC (Bose-Einstein condensation) crossover in a lattice is a powerful paradigm that describes how a superconductor deviates from the Bardeen-Cooper-Schrieffer physics as the attractive interaction increases. Optical lattices loaded with binary mixtures of cold atoms allow one to access this phenomenon experimentally in a clean and controlled way. We show that, however, the possibility to study this phenomenon in actual cold-atoms experiments is limited by the effect of the trapping potential. Real-space dynamical mean-field theory calculations show indeed that interactions and the confining potential conspire to pack the fermions in the center of the trap, which approaches a band insulator when the attraction becomes sizeable. Interestingly, the energy gap is spatially more homogeneous than the superfluid condensate order parameter. We show how this physics reflects in several observables, and we propose an alternative strategy to disentangle the effect of the harmonic potential and measure the intrinsic properties resulting from the interaction strength.
Solution of the Skyrme HF + BCS equation on a 3D mesh
NASA Astrophysics Data System (ADS)
Bonche, P.; Flocard, H.; Heenen, P. H.
2005-09-01
Over the years, the ev8 code has been a very useful tool for the study of nuclear mean-field theory. Its main characteristic is that it solves the Hartree-Fock plus BCS equations for Skyrme type functionals via a discretization of the individual wave-functions on a three-dimensional Cartesian mesh. This allows maximal flexibility in the determination of the nuclear shape by the variational process. For instance, the same mesh can be used to describe the oblate deformed, spherical, prolate deformed, superdeformed and fission configurations of a given nucleus. The quadrupole constraining operator yielding the deformation energy curve covering all these configurations is included in ev8. This version of the code is restricted to even-even nuclei. Program summaryTitle of program:ev8 Catalogue identifier:ADWA Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWA Licensing provisions: none Computers on which the program has been tested: HP-RX4640, Compaq-Digital Alpha GS140, has run on several other platforms Computer for which the program is designed and others on which is has been tested:Unix, Linux Operating systems or monitors under which the program has been tested:FORTRAN-90 Programming language used:depends on problem; example given requires 60 MB Memory required to execute with typical data:yes No. of lines in distributed program, including test data, etc.:11 524 No. of bytes in distributed program, including test data, etc.:89 949 Distribution format:tar.gzip file Nature of the physical problem:By means of the Hartree-Fock plus BCS method using Skyrme type functionals, ev8 allows a study of the evolution of the binding energy of even-even nuclei for various shapes determined by the most general quadrupole constraint. Solution method:The program expands the single-particle wave-functions on a 3D Cartesian mesh. The nonlinear mean-field equations are solved by the
Critical Current, Vortices and Fermionic Bound States in the BEC to BCS Crossover
NASA Astrophysics Data System (ADS)
Sensarma, Rajdeep; Randeria, Mohit; Lun Ho, Tin
2006-03-01
We have analyzed a single vortex at T=0 in a 3D superfluid atomic Fermi gas across a Feshbach resonance[1] using a fully self-consistent Bogoliubov-deGennes approach. From the current flow around a vortex we conclude that unitarity (as= ∞) is the most robust superfluid state in the entire BCS-BEC crossover, with the highest critical velocity vc of about 0.1vF. On either side of unitarity, vc decreases. It is determined by pair breaking on the BCS side and by collective excitations in the BEC regime. In the BCS limit, the order parameter near the vortex core shows a variation on both the scale of kF-1 and of the coherence length ξ, while away from the BCS limit only a variation on the scale of ξ is seen. The density in the core rises quadratically with radial distance and is progressively depleted as one moves from BCS to BEC. The number of fermionic bound states in the core decreases as we move from the BCS to BEC regime. Remarkably, a bound state branch persists even on the BEC side reflecting the composite nature of bosonic molecules.[1] R. Sensarma, M. Randeria and T.L. Ho, cond-mat/0510761
Fernandez-Vizarra, Erika; Bugiani, Marianna; Goffrini, Paola; Carrara, Franco; Farina, Laura; Procopio, Elena; Donati, Alice; Uziel, Graziella; Ferrero, Iliana; Zeviani, Massimo
2007-05-15
We investigated two unrelated children with an isolated defect of mitochondrial complex III activity. The clinical picture was characterized by a progressive encephalopathy featuring early-onset developmental delay, spasticity, seizures, lactic acidosis, brain atrophy and MRI signal changes in the basal ganglia. Both children were compound heterozygotes for novel mutations in the human bc1 synthesis like (BCS1L) gene, which encodes an AAA mitochondrial protein putatively involved in both iron homeostasis and complex III assembly. The pathogenic role of the mutations was confirmed by complementation assays, using a DeltaBcs1 strain of Saccharomyces cerevisiae. By investigating complex III assembly and the structural features of the BCS1L gene product in skeletal muscle, cultured fibroblasts and lymphoblastoid cell lines from our patients, we have demonstrated, for the first time in a mammalian system, that a major function of BCS1L is to promote the maturation of complex III and, more specifically, the incorporation of the Rieske iron-sulfur protein into the nascent complex. Defective BCS1L leads to the formation of a catalytically inactive, structurally unstable complex III. We have also shown that BCS1L is contained within a high-molecular-weight supramolecular complex which is clearly distinct from complex III intermediates. PMID:17403714
Zur, Moran; Hanson, Allison S; Dahan, Arik
2014-09-30
While the solubility parameter is fairly straightforward when assigning BCS classification, the intestinal permeability (Peff) is more complex than generally recognized. In this paper we emphasize this complexity through the analysis of codeine, a commonly used antitussive/analgesic drug. Codeine was previously classified as a low-permeability compound, based on its lower LogP compared to metoprolol, a marker for the low-high permeability class boundary. In contrast, high fraction of dose absorbed (Fabs) was reported for codeine, which challenges the generally recognized Peff-Fabs correlation. The purpose of this study was to clarify this ambiguity through elucidation of codeine's BCS solubility/permeability class membership. Codeine's BCS solubility class was determined, and its intestinal permeability throughout the small intestine was investigated, both in vitro and in vivo in rats. Codeine was found to be unequivocally a high-solubility compound. All in vitro studies indicated that codeine's permeability is higher than metoprolol's. In vivo studies in rats showed similar permeability for both drugs throughout the entire small-intestine. In conclusion, codeine was found to be a BCS Class I compound. No Peff-Fabs discrepancy is involved in its absorption; rather, it reflects the risk of assigning BCS classification based on merely limited physicochemical characteristics. A thorough investigation using multiple experimental methods is prudent before assigning a BCS classification, to avoid misjudgment in various settings, e.g., drug discovery, formulation design, drug development and regulation. PMID:24262076
Theory of the modified two-stream instability in a magnetoplasmadynamic thruster
Hastings, D.E.; Niewood, E. )
1991-04-01
It is shown that for plasma parameters characteristic of those found in magnetoplasmadynamic (MPD) thrusters the modified two-stream instability may exist in the plasma. The critical parameter for triggering this instability is the ratio of the crossfield current to the ion saturation current. Once triggered, this instability greatly increases the plasma resistivity to the flow of the current and heats both ions and electrons. The anomalous momentum-exchange frequency and heating rates are calculated for characteristic MPD thruster parameters. 17 refs.
Long-range density-matrix-functional theory: Application to a modified homogeneous electron gas
Pernal, Katarzyna
2010-05-15
We propose a method that employs functionals of the one-electron reduced density matrix (density matrix) to capture long-range effects of electron correlation. The complementary short-range regime is treated with density functionals. In an effort to find approximations for the long-range density-matrix functional, a modified power functional is applied to the homogeneous electron gas with Coulomb interactions replaced by their corresponding long-range counterparts. For the power {beta}=1/2 and the range-separation parameter {omega}=1/r{sub s}, the functional reproduces the correlation and the kinetic correlation energies with a remarkable accuracy for intermediate and large values of r{sub s}. Analysis of the Euler equation corresponding to this functional reveals correct r{sub s} expansion of the correlation energy in the limit of large r{sub s}. The first expansion coefficient is in very good agreement with that obtained from the modified Wigner-Seitz model.
Lee, M.W.
2002-01-01
The classical Biot-Gassmann theory (BGT) generally overestimates shear-wave velocities of water-saturated sediments. To overcome this problem, a new theory is developed based on BGT and on the velocity ratio as a function of G(1 - ??)n, where ?? is porosity and n and G are constants. Based on laboratory data measured at ultrasonic frequencies, parameters for the new formulation are derived. This new theory is extended to include the effect of differential pressure and consolidation on the velocity ratio by making n a function of differential pressure and the rate of porosity reduction with respect to differential pressure. A scale G is introduced to compensate for discrepancies between measured and predicted velocities, mainly caused by the presence of clay in the matrix. As differential pressure increases and the rate of porosity reduction with respect to differential pressure decreases, the exponent n decreases and elastic velocities increase. Because velocity dispersion is not considered, this new formula is optimum for analyzing velocities measured at ultrasonic frequencies or for sediments having low dispersion characteristics such as clean sandstone with high permeability and lack of grain-scale local flow. The new formula is applied to predict velocities from porosity or from porosity and P-wave velocity and is in good agreement with laboratory and well log data. ?? 2004 Kluwer Academic Publishers. Printed in the Netherlands.
NASA Technical Reports Server (NTRS)
Horai, K.-I.
1981-01-01
A theory of the measurement of the thermal diffusivity of a sample by the modified Angstrom method is developed for the case in which radiative heat loss from the end surface of the sample is not negligible, and applied to measurements performed on lunar samples. Formulas allowing sample thermal diffusivity to be determined from the amplitude decay and phase lag of a temperature wave traveling through the sample are derived for a flat disk sample for which only heat loss from the end surface is important, and a sample of finite diameter and length for which heat loss through the end and side surfaces must be considered. It is noted that in the case of a flat disk, measurements at a single angular frequency of the temperature wave are sufficient, while the sample of finite diameter and length requires measurements at two discrete angular frequencies. Comparison of the values of the thermal diffusivities of two lunar samples of dimensions approximately 1 x 1 x 2 cm derived by the present methods and by the Angstrom theory for a finite bar reveals them to differ by not more than 5%, and indicates that more refined data are required as the measurement theory becomes more complicated.
A Modified Theory of Gravity with Torsion and Its Applications to Cosmology and Particle Physics
NASA Astrophysics Data System (ADS)
Fabbri, Luca; Vignolo, Stefano
2012-10-01
In this paper we consider the most general least-order derivative theory of gravity in which not only curvature but also torsion is explicitly present in the Lagrangian, and where all independent fields have their own coupling constant: we will apply this theory to the case of ELKO fields, which is the acronym of the German Eigenspinoren des LadungsKonjugationsOperators designating eigenspinors of the charge conjugation operator, and thus they are a Majorana-like special type of spinors; and to the Dirac fields, the most general type of spinors. We shall see that because torsion has a coupling constant that is still undetermined, the ELKO and Dirac field equations are endowed with self-interactions whose coupling constant is undetermined: we discuss different applications according to the value of the coupling constants and the different properties that consequently follow. We highlight that in this approach, the ELKO and Dirac field's self-interactions depend on the coupling constant as a parameter that may even make these non-linearities manifest at subatomic scales.
Benchmark of a modified iterated perturbation theory approach on the fcc lattice at strong coupling
NASA Astrophysics Data System (ADS)
Arsenault, Louis-François; Sémon, Patrick; Tremblay, A.-M. S.
2012-08-01
The dynamical mean-field theory approach to the Hubbard model requires a method to solve the problem of a quantum impurity in a bath of noninteracting electrons. Iterated perturbation theory (IPT) has proven its effectiveness as a solver in many cases of interest. Based on general principles and on comparisons with an essentially exact continuous-time quantum Monte Carlo (CTQMC) solver, here we show that the standard implementation of IPT fails away from half-filling when the interaction strength is much larger than the bandwidth. We propose a slight modification to the IPT algorithm that replaces one of the equations by the requirement that double occupancy calculated with IPT gives the correct value. We call this method IPT-D. We recover the Fermi liquid ground state away from half-filling. The Fermi liquid parameters, density of states, chemical potential, energy, and specific heat on the fcc lattice are calculated with both IPT-D and CTQMC as benchmark examples. We also calculated the resistivity and the optical conductivity within IPT-D. Particle-hole asymmetry persists even at coupling twice the bandwidth. A generalization to the multiorbital case is suggested. Several algorithms that speed up the calculations are described in appendixes.
Demján, Tamás; Vörös, Márton; Palummo, Maurizia; Gali, Adam
2014-08-14
Diamondoids are small diamond nanoparticles (NPs) that are built up from diamond cages. Unlike usual semiconductor NPs, their atomic structure is exactly known, thus they are ideal test-beds for benchmarking quantum chemical calculations. Their usage in spintronics and bioimaging applications requires a detailed knowledge of their electronic structure and optical properties. In this paper, we apply density functional theory (DFT) based methods to understand the electronic and optical properties of a few selected pure and modified diamondoids for which accurate experimental data exist. In particular, we use many-body perturbation theory methods, in the G0W0 and G0W0+BSE approximations, and time-dependent DFT in the adiabatic local density approximation. We find large quasiparticle gap corrections that can exceed thrice the DFT gap. The electron-hole binding energy can be as large as 4 eV but it is considerably smaller than the GW corrections and thus G0W0+BSE optical gaps are about 50% larger than the Kohn-Sham (KS) DFT gaps. We find significant differences between KS time-dependent DFT and GW+BSE optical spectra on the selected diamondoids. The calculated G0W0 quasiparticle levels agree well with the corresponding experimental vertical ionization energies. We show that nuclei dynamics in the ionization process can be significant and its contribution may reach about 0.5 eV in the adiabatic ionization energies. PMID:25134572
Apo- and Cellopentaose-bound Structures of the Bacterial Cellulose Synthase Subunit BcsZ
Mazur, Olga; Zimmer, Jochen
2012-10-25
Cellulose, a very abundant extracellular polysaccharide, is synthesized in a finely tuned process that involves the activity of glycosyl-transferases and hydrolases. The cellulose microfibril consists of bundles of linear {beta}-1,4-glucan chains that are synthesized inside the cell; however, the mechanism by which these polymers traverse the cell membrane is currently unknown. In Gram-negative bacteria, the cellulose synthase complex forms a trans-envelope complex consisting of at least four subunits. Although three of these subunits account for the synthesis and translocation of the polysaccharide, the fourth subunit, BcsZ, is a periplasmic protein with endo-{beta}-1,4-glucanase activity. BcsZ belongs to family eight of glycosyl-hydrolases, and its activity is required for optimal synthesis and membrane translocation of cellulose. In this study we report two crystal structures of BcsZ from Escherichia coli. One structure shows the wild-type enzyme in its apo form, and the second structure is for a catalytically inactive mutant of BcsZ in complex with the substrate cellopentaose. The structures demonstrate that BcsZ adopts an ({alpha}/{alpha}){sub 6}-barrel fold and that it binds four glucan moieties of cellopentaose via highly conserved residues exclusively on the nonreducing side of its catalytic center. Thus, the BcsZ-cellopentaose structure most likely represents a posthydrolysis state in which the newly formed nonreducing end has already left the substrate binding pocket while the enzyme remains attached to the truncated polysaccharide chain. We further show that BcsZ efficiently degrades {beta}-1,4-glucans in in vitro cellulase assays with carboxymethyl-cellulose as substrate.
Weak coupling BCS-like superconductivity in the pnictide oxide Ba1-xNaxTi2Sb2O
NASA Astrophysics Data System (ADS)
Lorenz, B.; Gooch, M.; Doan, P.; Tang, Z.; Guloy, A. M.; Chu, C. W.
2014-03-01
We report the results of low-temperature heat capacity measurements of the pnictide oxide superconductor BaTi2Sb2O and the optimally Na-doped compound Na0.15Ba0.85Ti2Sb2O. Temperature- and field-dependent heat capacity data are well described by a single-gap BCS theory. The estimated values for the normal-state Sommerfeld constant, the heat capacity jump at Tc, and the electron-phonon coupling constant are in favor of a conventional weak coupling superconductivity, possibly mediated by electron-phonon interaction. The results are discussed with regard to and compared with recent first-principles calculations. Supported by the DOE, the AFOSR, the T.L.L. Temple Foundation, the J.J. and R. Moores Endowment, and the State of Texas through TCSUH.
NASA Astrophysics Data System (ADS)
Vyasanakere, Jayanth P.; Shenoy, Vijay B.
2013-03-01
A non-Abelian gauge field that induces a spin-orbit coupling on the motion of fermions engenders a BCS-BEC crossover even for weakly attracting fermions. The transition temperature at large spin-orbit coupling is known to be determined by the mass of the emergent boson - the rashbon. We obtain the transition temperature of the system as a function of the spin-orbit coupling by constructing and studying a Gaussian fluctuation (Nozieres-Schmitt-Rink) theory. These results will help guide the upcoming experiments on spin-orbit coupled fermions. In addition, this work suggests a route to enhance the transition temperature of a weakly attracting fermionic system by tuning the spin-orbit coupling. Work supported by CSIR, DST, DAE India
NASA Astrophysics Data System (ADS)
Wu, Shuang-Qing
2009-08-01
The aim of this paper is to investigate the separability of a spin-1/2 spinor field in a five-dimensional rotating, charged black hole constructed by Cvetič and Youm in string theory, in the case when three U(1) charges are set equal. This black hole solution represents a natural generalization of the famous four-dimensional Kerr-Newman solution to five dimensions with the inclusion of a Chern-Simons term to the Maxwell equation. It is shown that the usual Dirac equation cannot be separated by variables in this general spacetime with two independent angular momenta. However if one supplements an additional counterterm into the usual Dirac operator, then the modified Dirac equation for the spin-1/2 spinor particles is separable in this rotating, charged Einstein-Maxwell-Chern-Simons black hole background geometry. A first-order symmetry operator that commutes with the modified Dirac operator has exactly the same form as that previously found in the uncharged Myers-Perry black hole case. It is expressed in terms of a rank-three totally antisymmetric tensor and its covariant derivative. This tensor obeys a generalized Killing-Yano equation and its square is a second-order symmetric Stäckel-Killing tensor admitted by the five-dimensional rotating, charged black hole spacetime.
Wu Shuangqing
2009-08-15
The aim of this paper is to investigate the separability of a spin-1/2 spinor field in a five-dimensional rotating, charged black hole constructed by Cvetic and Youm in string theory, in the case when three U(1) charges are set equal. This black hole solution represents a natural generalization of the famous four-dimensional Kerr-Newman solution to five dimensions with the inclusion of a Chern-Simons term to the Maxwell equation. It is shown that the usual Dirac equation cannot be separated by variables in this general spacetime with two independent angular momenta. However if one supplements an additional counterterm into the usual Dirac operator, then the modified Dirac equation for the spin-1/2 spinor particles is separable in this rotating, charged Einstein-Maxwell-Chern-Simons black hole background geometry. A first-order symmetry operator that commutes with the modified Dirac operator has exactly the same form as that previously found in the uncharged Myers-Perry black hole case. It is expressed in terms of a rank-three totally antisymmetric tensor and its covariant derivative. This tensor obeys a generalized Killing-Yano equation and its square is a second-order symmetric Staeckel-Killing tensor admitted by the five-dimensional rotating, charged black hole spacetime.
O'Callaghan, Clare; Hiscock, Richard
2007-01-01
Following an investigation into oncologic patients' experiences of the helpfulness of music therapy (O'Callaghan & McDermott, 2004), it was considered that examining relationships between specific patient characteristics and their responses could yield further interesting understandings. "Interpretative subgroup analysis" is introduced, which adapts principles of subgroup analysis in quantitative research to textual data analysis. Anonymous written responses from 128 oncologic patients were analyzed to compare responses from (a) those that had one music therapy session with those who had more than one session, (b) males and females, and (c) middle and older aged respondents. The number of music therapy sessions had scant effect on reported music therapy experiences, and males were much more likely to return questionnaires but much less likely to participate. Unlike some females, males always described positive affective responses when experiencing both sad and positive memories. Variations in the middle and older aged subgroups were evident in type of affective response, and emphases in descriptions of memories and music therapy's effect. Implications of these findings for music therapy practice are considered. Interpretive subgroup analysis is recommended for extending understanding of subjective within group experiences in music therapy research incorporating a grounded theory approach and large enough samples. PMID:17645388
An Ontological Model of Behaviour Theory to Generate Personalized Action Plans to Modify Behaviours.
Baig, Wasif; Abidi, Samina; Abidi, Syed Sibte Raza
2016-01-01
Behavior change approaches aim to assist patients in achieving self-efficacy in managing their condition. Social cognitive theory (SCT) stipulates self-efficacy as a central element to behavior change and provides constructs to achieve self-efficacy guided by person-specific action plans. In our work, to administer behaviour change in patient with chronic conditions, our approach entails the computerization of SCT-based self-efficacy constructs in order to generate personalized action plans that are suitable to an individual's current care scenario. We have taken a knowledge management approach, whereby we have computerized the SCT-based self-efficacy constructs in terms of a high-level SCT knowledge model that can be operationalized to generate personalized behaviour change action plans. We have collected and computerized behavior change content targeting healthy living and physical activity. Semantic web technologies have been used to develop the SCT knowledge model, represented in terms of an ontology and SWRL rules. The ontological SCT model can inferred to generate personalized self-management action plans for a given patient profile. We present formative evaluation of the clinical correctness and relevance of the generated personalized action plans for a range of test patient profiles. PMID:27577412
Moment of inertia of neutron star crust in alternative and modified theories of gravity
NASA Astrophysics Data System (ADS)
Staykov, Kalin V.; Ekşi, K. Yavuz; Yazadjiev, Stoytcho S.; Türkoǧlu, M. Metehan; Arapoǧlu, A. Savaş
2016-07-01
The glitch activity of young pulsars arises from the exchange of angular momentum between the crust and the interior of the star. Recently, it was inferred that the moment of inertia of the crust of a neutron star is not sufficient to explain the observed glitches. Such estimates are presumed in Einstein's general relativity in describing the hydrostatic equilibrium of neutron stars. The crust of the neutron star has a spacetime curvature of 14 orders of magnitude larger than that probed in solar system tests. This makes gravity the weakest constrained physics input in the crust-related processes. We calculate the ratio of the crustal to the total moment of inertia of neutron stars in the scalar-tensor theory of gravity and the nonperturbative f (R )=R +a R2 gravity. We find for the former that the crust-to-core ratio of the moment of inertia does not change significantly from what is inferred in general relativity. For the latter, we find that the ratio increases significantly from what is inferred in general relativity in the case of high mass objects. Our results suggest that the glitch activity of pulsars may be used to probe gravity models, although the gravity models explored in this work are not appropriate candidates.
Nobrega, F G; Nobrega, M P; Tzagoloff, A
1992-01-01
Respiratory deficient pet mutants of Saccharomyces cerevisiae assigned to complementation group G2 define a new gene, named BCS1, whose product is shown to be necessary for the expression of functional ubiquinol-cytochrome c reductase (bc1) complex. Immunological assays indicate a gross reduction in the Rieske iron-sulfur subunit in bcs1 mutants, while other subunits of the ubiquinol-cytochrome c reductase complex are present at concentrations comparable to the wild type. Transformation of bcs1 mutants with the iron-sulfur protein gene on a multicopy plasmid led to elevated mitochondrial concentrations of Rieske protein, but did not correct the enzymatic defect, indicating that BCS1 is involved either in forming the active site iron-sulfur cluster or providing a chaperone-like function in assembling the Rieske protein with the other subunits of the complex. Both postulated functions are consistent with the localization of BCS1 in mitochondria. To facilitate further studies on this novel protein, BCS1 was cloned by transformation of a bcs1 mutant and its structure determined. The primary structure of the encoded BCS1 protein bears similarity to a group of proteins that have been implicated in intracellular protein sorting, membrane fusion and regulation of transcription. The region of BCS1 homologous to this diverse group of proteins is approximately 200 amino acids long and includes several signature sequences commonly found in ATPases and nucleotide binding proteins. Images PMID:1327750
Demján, Tamás; Vörös, Márton; Palummo, Maurizia; Gali, Adam
2014-08-14
Diamondoids are small diamond nanoparticles (NPs) that are built up from diamond cages. Unlike usual semiconductor NPs, their atomic structure is exactly known, thus they are ideal test-beds for benchmarking quantum chemical calculations. Their usage in spintronics and bioimaging applications requires a detailed knowledge of their electronic structure and optical properties. In this paper, we apply density functional theory (DFT) based methods to understand the electronic and optical properties of a few selected pure and modified diamondoids for which accurate experimental data exist. In particular, we use many-body perturbation theory methods, in the G{sub 0}W{sub 0} and G{sub 0}W{sub 0}+BSE approximations, and time-dependent DFT in the adiabatic local density approximation. We find large quasiparticle gap corrections that can exceed thrice the DFT gap. The electron-hole binding energy can be as large as 4 eV but it is considerably smaller than the GW corrections and thus G{sub 0}W{sub 0}+BSE optical gaps are about 50% larger than the Kohn-Sham (KS) DFT gaps. We find significant differences between KS time-dependent DFT and GW+BSE optical spectra on the selected diamondoids. The calculated G{sub 0}W{sub 0} quasiparticle levels agree well with the corresponding experimental vertical ionization energies. We show that nuclei dynamics in the ionization process can be significant and its contribution may reach about 0.5 eV in the adiabatic ionization energies.
NASA Astrophysics Data System (ADS)
Ramírez, Carlos; Sánchez, Vicenta; Wang, Chumin
2015-11-01
In this paper, we find analytically the first order solutions of the Bardeen, Cooper and Schrieffer (BCS) Hamiltonian with degenerated single-electron energy levels. The results are compared to the Richardson exact solutions calculated numerically, showing good agreement in the weak interaction limit. Using this first-order solution, we further calculate the number of pairs at the ground state as a function of temperature. In particular, the Bose-Einstein condensation (BEC) temperature is found when the population of ground-state pairs starts growing. This study provides a BEC analysis of the superconductivity for weak coupling regime, which traditionally belongs to the BCS side of the BCS-BEC crossover picture.
Yasuhara, Tomohisa; Sone, Tomomichi; Kohno, Takeyuki; Ogita, Kiyokazu
2015-01-01
A revised core curriculum model for pharmaceutical education, developed on the basis of the principles of outcome-based education, will be introduced in 2015. Inevitably, appropriate assessments of students' academic achievements will be required. Although evaluations of the cognitive domain can be carried out by paper tests, evaluation methods for the attitude domain and problem-solving abilities need to be established. From the viewpoint of quality assurance for graduates, pharmaceutical education reforms have become vital to evaluation as well as learning strategies. To evaluate student academic achievements on problem-solving abilities, authentic assessment is required. Authentic assessment is the evaluation that mimics the context tried in work and life. Specifically, direct evaluation of performances, demonstration or the learners' own work with integrated variety knowledge and skills, is required. To clarify the process of graduate research, we obtained qualitative data through focus group interviews with six teachers and analyzed the data using the modified grounded theory approach. Based on the results, we clarify the performance students should show in graduate research and create a rubric for evaluation of performance in graduate research. PMID:25743905
NASA Astrophysics Data System (ADS)
Ghadiri, Majid; Shafiei, Navvab
2016-04-01
In this study, thermal vibration of rotary functionally graded Timoshenko microbeam has been analyzed based on modified couple stress theory considering temperature change in four types of temperature distribution on thermal environment. Material properties of FG microbeam are supposed to be temperature dependent and vary continuously along the thickness according to the power-law form. The axial forces are also included in the model as the thermal and true spatial variation due to the rotation. Governing equations and boundary conditions have been derived by employing Hamiltonian's principle. The differential quadrature method is employed to solve the governing equations for cantilever and propped cantilever boundary conditions. Validations are done by comparing available literatures and obtained results which indicate accuracy of applied method. Results represent effects of temperature changes, different boundary conditions, nondimensional angular velocity, length scale parameter, different boundary conditions, FG index and beam thickness on fundamental, second and third nondimensional frequencies. Results determine critical values of temperature changes and other essential parameters which can be applicable to design micromachines like micromotor and microturbine.
Chang, I-Chiu; Hsu, Hui-Mei
2012-01-01
Barriers to report incident events using an online information system (IS) may be different from those of a paper-based reporting system. The nationwide online Patient-Safety Reporting System (PSRS) contains a value judgment behind use of the system, similar to the Value of Perceived Consequence (VPC), which is seldom discussed in ISs applications of other disciplines. This study developed a more adequate research framework by integrating the VPC construct into the well-known Unified Theory of Acceptance and Use of Technology (UTAUT) model as a theoretical base to explore the predictors of medical staff's intention to use online PSRS. The results showed that management support was an important factor to influence medical staff's intention of using PSRS. The effects of factors such as performance expectancy, perceived positive, and perceived negative consequence on medical staff's intention of using PSRS were moderated by gender, age, experience, and occupation. The results proved that the modified UTAUT model is significant and useful in predicting medical staff's intention of using the nationwide online PSRS. PMID:22150638
2012-01-01
Background Patients making important medical decisions need to evaluate complex information in the light of their own beliefs, attitudes and priorities. The process can be considered in terms of the theory of planned behaviour. Decision support technologies aim at helping patients making informed treatment choices. Instruments assessing informed choices need to include risk knowledge, attitude (towards therapy) and actual uptake. However, mechanisms by which decision support achieves its goals are poorly understood. Our aim was therefore to develop and validate an instrument modeling the process of multiple sclerosis (MS) patients’ decision making about whether to undergo disease modifying (immuno-)therapies (DMT). Methods We constructed a 30-item patient administered questionnaire to access the elaboration of decisions about DMT in MS according to the theory of planned behaviour. MS-patients’ belief composites regarding immunotherapy were classified according to the domains “attitude”, “subjective social norm” and “control beliefs” and within each domain to either “expectations” or “values” yielding 6 sub-domains. A randomized controlled trial (n = 192) evaluating an evidence based educational intervention tested the instrument’s predictive power regarding intention to use immunotherapy and its sensitivity to the intervention. Results The psychometric properties of the questionnaire were satisfactory (mean item difficulty 62, mean SD 0.9, range 0–3). Responses explain up to 68% of the variability in the intention to use DMT was explained by up to 68% in the total sample. Four weeks after an educational intervention, predictive power was higher in the intervention (IG) compared to the control group (CG) (intention estimate: CG 56% / IG 69%, p = .179; three domains CG 56% / IG 74%, p = .047; six sub-domains CG 64% / IG 78%, p = .073). The IG held more critical beliefs towards immunotherapy (p = .002) and were less
A new approach on JPSS VIIRS BCS and SVS PRT calibration
NASA Astrophysics Data System (ADS)
Wang, Tung R.; Marschke, Steve; Borroto, Michael; Jones, Christopher M.; Chovit, Christopher
2015-05-01
A set of calibrated platinum resistance thermometers (PRT's) was used to monitor the temperature of a Blackbody Calibration Source (BCS) and Space View Source (SVS). BCS is Ground Support Equipment (GSE) used to validate the emissive band calibration of Visible Infrared Imaging Radiometer Suite (VIIRS) of the Joint Polar Satellite System (JPSS). Another GSE, the SVS was used as an optical simulator to provide zero radiance sources for all VIIRS bands. The required PRT temperature 1 uncertainty is less than 0.030K. A process was developed to calibrate the PRTs in its thermal block by selecting a single thermal bath fluid that is compatible with spaceflight, is easy to clean and supported the entire temperature range. The process involves thermal cycling the PRTs that are installed in an aluminum housing using RTV566A prior to calibration. The PRTs were calibrated thermal cycled again and then calibrated once more to verify repeatability. Once completed these PRTs were installed on both the BCS and SVS. The PRT calibration uncertainty was estimated and deemed sufficient to support the effective temperature requirements for the operating temperature range of the BCS and SVS.
BCS-BEC crossover and phase structure of relativistic systems: A variational approach
Chatterjee, Bhaswar; Mishra, Hiranmaya; Mishra, Amruta
2009-01-01
We investigate here the BCS-BEC crossover in relativistic systems using a variational construct for the ground state and the minimization of the thermodynamic potential. This is first studied in a four-fermion point interaction model and with a BCS type ansatz for the ground state with fermion pairs. It is shown that the antiparticle degrees of freedom play an important role in the BCS-BEC crossover physics, even when the ratio of Fermi momentum to the mass of the fermion is small. We also consider the phase structure for the case of fermion pairing with imbalanced populations. Within the ansatz, thermodynamically stable gapless modes for both fermions and antifermions are seen for strong coupling in the Bose-Einstein condensation (BEC) regime. We further investigate the effect of fluctuations of the condensate field by treating it as a dynamical field and generalize the BCS ansatz to include quanta of the condensate field also in a boson-fermion model with quartic self-interaction of the condensate field. It is seen that the critical temperature decreases with inclusion of fluctuations.
ERIC Educational Resources Information Center
Dik, Bryan J.; Eldridge, Brandy M.; Steger, Michael F.; Duffy, Ryan D.
2012-01-01
Research on work as a calling is limited by measurement concerns. In response, the authors introduce the multidimensional Calling and Vocation Questionnaire (CVQ) and the Brief Calling scale (BCS), instruments assessing presence of, and search for, a calling. Study 1 describes CVQ development using exploratory and confirmatory factor analysis…
NQRS Data for C24H20BCs (Subst. No. 1575)
NASA Astrophysics Data System (ADS)
Chihara, H.; Nakamura, N.
This document is part of Subvolume B 'Substances Containing C10H16 … Zn' of Volume 48 'Nuclear Quadrupole Resonance Spectroscopy Data' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains an extract of Section '3.2 Data tables' of the Chapter '3 Nuclear quadrupole resonance data' providing the NQRS data for C24H20BCs (Subst. No. 1575)
Mitochondrial protein import: recognition of internal import signals of BCS1 by the TOM complex.
Stan, Tincuta; Brix, Jan; Schneider-Mergener, Jens; Pfanner, Nikolaus; Neupert, Walter; Rapaport, Doron
2003-04-01
BCS1, a component of the inner membrane of mitochondria, belongs to the group of proteins with internal, noncleavable import signals. Import and intramitochondrial sorting of BCS1 are encoded in the N-terminal 126 amino acid residues. Three sequence elements were identified in this region, namely, the transmembrane domain (amino acid residues 51 to 68), a presequence type helix (residues 69 to 83), and an import auxiliary region (residues 84 to 126). The transmembrane domain is not required for stable binding to the TOM complex. The Tom receptors (Tom70, Tom22 and Tom20), as determined by peptide scan analysis, interact with the presequence-like helix, yet the highest binding was to the third sequence element. We propose that the initial recognition of BCS1 precursor at the surface of the organelle mainly depends on the auxiliary region and does not require the transmembrane domain. This essential region represents a novel type of signal with targeting and sorting functions. It is recognized by all three known mitochondrial import receptors, demonstrating their capacity to decode various targeting signals. We suggest that the BCS1 precursor crosses the TOM complex as a loop structure and that once the precursor emerges from the TOM complex, all three structural elements are essential for the intramitochondrial sorting to the inner membrane. PMID:12640110
NASA Astrophysics Data System (ADS)
Cid, Antonella; Leon, Genly; Leyva, Yoelsy
2016-02-01
scale factor. Apart from some fine-tuned examples such as the linear, and quadratic potential U(Φ) in the Jordan frame, it is true that ``intermediate accelerated'' solutions are generic late-time attractors in a modified Jordan-Brans-Dicke theory.
2015-01-01
The biopharmaceutics classification system (BCS) and biopharmaceutics drug distribution classification system (BDDCS) are complementary classification systems that can improve, simplify, and accelerate drug discovery, development, and regulatory processes. Drug permeability has been widely accepted as a screening tool for determining intestinal absorption via the BCS during the drug development and regulatory approval processes. Currently, predicting clinically significant drug interactions during drug development is a known challenge for industry and regulatory agencies. The BDDCS, a modification of BCS that utilizes drug metabolism instead of intestinal permeability, predicts drug disposition and potential drug–drug interactions in the intestine, the liver, and most recently the brain. Although correlations between BCS and BDDCS have been observed with drug permeability rates, discrepancies have been noted in drug classifications between the two systems utilizing different permeability models, which are accepted as surrogate models for demonstrating human intestinal permeability by the FDA. Here, we recommend the most applicable permeability models for improving the prediction of BCS and BDDCS classifications. We demonstrate that the passive transcellular permeability rate, characterized by means of permeability models that are deficient in transporter expression and paracellular junctions (e.g., PAMPA and Caco-2), will most accurately predict BDDCS metabolism. These systems will inaccurately predict BCS classifications for drugs that particularly are substrates of highly expressed intestinal transporters. Moreover, in this latter case, a system more representative of complete human intestinal permeability is needed to accurately predict BCS absorption. PMID:24628254
Higgs amplitude mode in the BCS superconductors Nb1-xTi(x)N induced by terahertz pulse excitation.
Matsunaga, Ryusuke; Hamada, Yuki I; Makise, Kazumasa; Uzawa, Yoshinori; Terai, Hirotaka; Wang, Zhen; Shimano, Ryo
2013-08-01
Ultrafast responses of BCS superconductor Nb(1-x)Ti(x)N films in a nonadiabatic excitation regime were investigated by using terahertz (THz) pump-THz probe spectroscopy. After an instantaneous excitation with the monocycle THz pump pulse, a transient oscillation emerges in the electromagnetic response in the BCS gap energy region. The oscillation frequency coincides with the asymptotic value of the BCS gap energy, indicating the appearance of the theoretically anticipated collective amplitude mode of the order parameter, namely the Higgs amplitude mode. Our result opens a new pathway to the ultrafast manipulation of the superconducting order parameter by optical means. PMID:23952432
Crossover between BCS and performed-Boson theories with increasing interactions
Randeria, M.
1993-08-01
The author reviews recent work on Fermi systems with attractive interactions of arbitrary strength. First, he describes the results of a functional integral formulation to study the crossover from cooperative Cooper pairing to independent bound state formation and condensation. The inadequacy of a saddle point approximation with increasing coupling is pointed out, and the importance of temporal (quantum) fluctuations for normal state properties at intermediate and strong coupling is emphasized. Next, results from a quantum Monte Carlo simulation of the 2D attractive Hubbard model are described. The intermediate coupling normal state is found to deviate markedly from a canonical Fermi liquid: {open_quotes}spin-gap{close_quotes} behavior, with 1/T{sub 1}T {approximately} {chi}(T), is found in a degenerate Fermi system.
NASA Technical Reports Server (NTRS)
Singh, J. J.; Smith, A. S.; Chan, L. Y.; Yue, G. K.
1982-01-01
Thomson's ion nucleation theory was modified to include the effects of curvature dependence of the microscopic surface tension of field dependent, nonlinear, dielectric properties of the liquid; and of sulfuric acid hydrate formation in binary mixtures of water and sulfuric acid vapors. The modified theory leads to a broadening of the ion cluster spectrum, and shifts it towards larger numbers of H2O and H2SO4 molecules. Whether there is more shifting towards larger numbers of H2O or H2SO4 molecules depends on the relative humidity and relative acidity of the mixture. Usually, a broadening of the spectrum is accompanied by a lowering of the mean cluster intensity. For fixed values of relative humidity and relative acidity, a similar broadening pattern is observed when the temperature is lowered. These features of the modified theory illustrate that a trace of sulfuric acid can facilitate the formation of ultrafine, stable, prenucleation ion clusters as well as the growth of the prenucleation ion clusters towards the critical saddle point conditions, even with low values of relative humidity and relative acidity.
NASA Astrophysics Data System (ADS)
Shreeman, Paul K.
The statistical dynamical diffraction theory, which has been initially developed by late Kato remained in obscurity for many years due to intense and difficult mathematical treatment that proved to be quite challenging to implement and apply. With assistance of many authors in past (including Bushuev, Pavlov, Pungeov, and among the others), it became possible to implement this unique x-ray diffraction theory that combines the kinematical (ideally imperfect) and dynamical (the characteristically perfect diffraction) into a single system of equations controlled by two factors determined by long range order and correlation function within the structure. The first stage is completed by the publication (Shreeman and Matyi, J. Appl. Cryst., 43, 550 (2010)) demonstrating the functionality of this theory with new modifications hence called modified statistical dynamical diffraction theory (mSDDT). The foundation of the theory is also incorporated into this dissertation, and the next stage of testing the model against several ion-implanted SiGe materials has been published: (Shreeman and Matyi, physica status solidi (a)208(11), 2533-2538, 2011). The dissertation with all the previous results summarized, dives into comprehensive analysis of HRXRD analyses complete with several different types of reflections (symmetrical, asymmetrical and skewed geometry). The dynamical results (with almost no defects) are compared with well-known commercial software. The defective materials, to which commercially available modeling software falls short, is then characterized and discussed in depth. The results will exemplify the power of the novel approach in the modified statistical dynamical diffraction theory: Ability to detect and measure defective structures qualitatively and quantitatively. The analysis will be compared alongside with TEM data analysis for verification and confirmation. The application of this theory will accelerate the ability to quickly characterize the relaxed
BEC-BCS crossover in a cold and magnetized two color NJL model
NASA Astrophysics Data System (ADS)
Duarte, Dyana C.; Allen, P. G.; Farias, R. L. S.; Manso, Pedro H. A.; Ramos, Rudnei O.; Scoccola, N. N.
2016-01-01
The BEC-BCS crossover for a Nambu-Jona-Lasinio (NJL) model with diquark interactions is studied in the presence of an external magnetic field. Particular attention is paid to different regularization schemes used in the literature. A thorough comparison of results is performed for the case of a cold and magnetized two-color NJL model. According to our results, the critical chemical potential for the BEC transition exhibits a clear inverse magnetic catalysis effect for magnetic fields in the range 1 ≲e B /mπ2≲20 . As for the BEC-BCS crossover, the corresponding critical chemical potential is very weakly sensitive to magnetic fields up to e B ˜9 mπ2, showing a much smaller inverse magnetic catalysis as compared to the BEC transition, and displays a strong magnetic catalysis from this point on.
Interaction and Disorder Effects across BCS-BEC Crossover in Two-Dimensional Fermi Gases
NASA Astrophysics Data System (ADS)
Tanatar, B.; Khan, A.
2015-03-01
We investigate the effect of static impurities in two-dimensional ultracold atomic Fermi gases. We incorporate disorder from impurities through fluctuations and study its effects on the BCS-BEC crossover. We analyze the effect of quenched disorder for various physical quantities such as chemical potential, pairing gap, density of states, spectral function, and ground-state energy. We extend our study further towards the experimentally viable quantities such as condensate fraction, sound velocity and Landau critical velocity. The results are presented as a function of binding energy and scattering length. We observe negligible effect of disorder in 2D for BCS Cooper pairs and considerable amount of depletion in the BEC regime but intriguingly the results also reveal that disorder effect is masked at the crossover region.
Motion of a Solitonic Vortex in the BEC-BCS Crossover
NASA Astrophysics Data System (ADS)
Ku, Mark J. H.; Ji, Wenjie; Mukherjee, Biswaroop; Guardado-Sanchez, Elmer; Cheuk, Lawrence W.; Yefsah, Tarik; Zwierlein, Martin W.
2014-08-01
We observe a long-lived solitary wave in a superfluid Fermi gas of Li6 atoms after phase imprinting. Tomographic imaging reveals the excitation to be a solitonic vortex, oriented transverse to the long axis of the cigar-shaped atom cloud. The precessional motion of the vortex is directly observed, and its period is measured as a function of the chemical potential in the BEC-BCS crossover. The long period and the correspondingly large ratio of the inertial to the bare mass of the vortex are in good agreement with estimates based on superfluid hydrodynamics that we derive here using the known equation of state in the BEC-BCS crossover.
Dynamic structure factor of a Fermi superfluid in the BEC-BCS crossover
NASA Astrophysics Data System (ADS)
Ghosh, Tarun Kanti
2007-09-01
We consider cigar-shaped Fermi superfluid in the Bose-Einstein condensation (BEC)-BCS crossover. Using the polytropic form of equation of state, we derive low energy multibranch bosonic excitations and the corresponding density fluctuations in three different regimes along the crossover, namely weak-coupling BCS, unitarity, and molecular BEC regimes. Bragg spectroscopy can be used to probe the multibranch nature of the low-energy bosonic excitations by measuring the dynamic structure factor. Therefore we calculate the dynamic structure factor in those three different regimes. In Bragg spectroscopy, an actual observable is momentum imparted to the superfluid due to the Bragg potential. We also present results of the momentum imparted to the superfluid due to the Bragg pulses.
Relativistic BEC-BCS Crossover in a magnetized Nambu-Jona-Lasinio Model
NASA Astrophysics Data System (ADS)
Duarte, Dyana C.; Farias, R. L. S.; Manso, Pedro H. A.; Ramos, Rudnei O.
2016-04-01
The BEC-BCS crossover in the NJL model is studied in the presence of an external magnetic field. Particular attention is given to two different regularization schemes used in the literature and we show how they compare to each other. The comparison is made for the case of a cold and magnetized two color NJL model. We also make a brief discussion about the Nc = 3 case without magnetic fields, as an extension of this work in the future.
BCS-BEC crossover induced by a synthetic non-Abelian gauge field
Vyasanakere, Jayantha P.; Shenoy, Vijay B.; Zhang Shizhong
2011-07-01
We investigate the ground state of interacting spin-(1/2) fermions in three dimensions at a finite density ({rho}{approx}k{sub F}{sup 3}) in the presence of a uniform non-Abelian gauge field. The gauge-field configuration (GFC) described by a vector {lambda}{identical_to}({lambda}{sub x},{lambda}{sub y},{lambda}{sub z}), whose magnitude {lambda} determines the gauge coupling strength, generates a generalized Rashba spin-orbit interaction. For a weak attractive interaction in the singlet channel described by a small negative scattering length (k{sub F}|a{sub s}| < or approx. 1), the ground state in the absence of the gauge field ({lambda}=0) is a BCS (Bardeen-Cooper-Schrieffer) superfluid with large overlapping pairs. With increasing gauge-coupling strength, a non-Abelian gauge field engenders a crossover of this BCS ground state to a BEC (Bose-Einstein condensate) of bosons even with a weak attractive interaction that fails to produce a two-body bound state in free vacuum ({lambda}=0). For large gauge couplings ({lambda}/k{sub F}>>1), the BEC attained is a condensate of bosons whose properties are solely determined by the Rashba gauge field (and not by the scattering length so long as it is nonzero)--we call these bosons ''rashbons.'' In the absence of interactions (a{sub s}=0{sup -}), the shape of the Fermi surface of the system undergoes a topological transition at a critical gauge coupling {lambda}{sub T}. For high-symmetry GFCs we show that the crossover from the BCS superfluid to the rashbon BEC occurs in the regime of {lambda} near {lambda}{sub T}. In the context of cold atomic systems, these results make an interesting suggestion of obtaining BCS-BEC crossover through a route other than tuning the interaction between the fermions.
BCS-BEC crossover induced by a synthetic non-Abelian gauge field
NASA Astrophysics Data System (ADS)
Vyasanakere, Jayantha P.; Zhang, Shizhong; Shenoy, Vijay B.
2011-07-01
We investigate the ground state of interacting spin-(1)/(2) fermions in three dimensions at a finite density (ρ˜kF3) in the presence of a uniform non-Abelian gauge field. The gauge-field configuration (GFC) described by a vector λ≡(λx,λy,λz), whose magnitude λ determines the gauge coupling strength, generates a generalized Rashba spin-orbit interaction. For a weak attractive interaction in the singlet channel described by a small negative scattering length (kF|as|≲1), the ground state in the absence of the gauge field (λ=0) is a BCS (Bardeen-Cooper-Schrieffer) superfluid with large overlapping pairs. With increasing gauge-coupling strength, a non-Abelian gauge field engenders a crossover of this BCS ground state to a BEC (Bose-Einstein condensate) of bosons even with a weak attractive interaction that fails to produce a two-body bound state in free vacuum (λ=0). For large gauge couplings (λ/kF≫1), the BEC attained is a condensate of bosons whose properties are solely determined by the Rashba gauge field (and not by the scattering length so long as it is nonzero)—we call these bosons “rashbons.” In the absence of interactions (as=0-), the shape of the Fermi surface of the system undergoes a topological transition at a critical gauge coupling λT. For high-symmetry GFCs we show that the crossover from the BCS superfluid to the rashbon BEC occurs in the regime of λ near λT. In the context of cold atomic systems, these results make an interesting suggestion of obtaining BCS-BEC crossover through a route other than tuning the interaction between the fermions.
Atypical BCS-BEC crossover induced by quantum-size effects
NASA Astrophysics Data System (ADS)
Shanenko, A. A.; Croitoru, M. D.; Vagov, A. V.; Axt, V. M.; Perali, A.; Peeters, F. M.
2012-09-01
Quantum-size oscillations of the basic physical characteristics of a confined fermionic condensate are a well-known phenomenon. Its conventional understanding is based on the single-particle physics, whereby the oscillations follow variations in the single-particle density of states driven by the size quantization. Here we present a study of a cigar-shaped ultracold superfluid Fermi gas, which demonstrates an important many-body aspect of the quantum-size coherent effects, overlooked previously. The many-body physics is revealed here in the atypical crossover from the Bardeen-Cooper-Schrieffer (BCS) superfluid to the Bose-Einstein condensate (BEC) induced by the size quantization of the particle motion. The single-particle energy spectrum for the transverse dimensions is tightly bound, whereas for the longitudinal direction it resembles a quasi-free dispersion. This results in the formation of a series of single-particle subbands (shells) so that the aggregate fermionic condensate becomes a coherent mixture of subband condensates. Each time when the lower edge of a subband crosses the chemical potential, the BCS-BEC crossover is approached in this subband, and the aggregate condensate contains both BCS and BEC-like components.
Spin-polarized neutron matter: Critical unpairing and BCS-BEC precursor
NASA Astrophysics Data System (ADS)
Stein, Martin; Sedrakian, Armen; Huang, Xu-Guang; Clark, John W.
2016-01-01
We obtain the critical magnetic field required for complete destruction of S -wave pairing in neutron matter, thereby setting limits on the pairing and superfluidity of neutrons in the crust and outer core of magnetars. We find that for fields B ≥1017 G the neutron fluid is nonsuperfluid—if weaker spin 1 superfluidity does not intervene—a result with profound consequences for the thermal, rotational, and oscillatory behavior of magnetars. Because the dineutron is not bound in vacuum, cold dilute neutron matter cannot exhibit a proper BCS-BEC crossover. Nevertheless, owing to the strongly resonant behavior of the n n interaction at low densities, neutron matter shows a precursor of the BEC state, as manifested in Cooper-pair correlation lengths being comparable to the interparticle distance. We make a systematic quantitative study of this type of BCS-BEC crossover in the presence of neutron fluid spin polarization induced by an ultrastrong magnetic field. We evaluate the Cooper-pair wave function, quasiparticle occupation numbers, and quasiparticle spectra for densities and temperatures spanning the BCS-BEC crossover region. The phase diagram of spin-polarized neutron matter is constructed and explored at different polarizations.
BCS, Nambu-Jona-Lasinio, and Han-Nambu: A sketch of Nambu's works in 1960-1965
NASA Astrophysics Data System (ADS)
Fujikawa, Kazuo
2016-06-01
The years 1960-1965 were a remarkable period for Yoichiro Nambu. Starting with a reformulation of BCS theory with emphasis on gauge invariance, he recognized the realization of spontaneous chiral symmetry breaking in particle physics as evidenced by the Goldberger-Treiman relation. A concrete model of Nambu and Jona-Lasinio illustrated the essence of the Nambu-Goldstone theorem and the idea of soft pions. After the proposal of the quark model by Gell-Mann, he together with Han constructed an alternative model of integrally charged quarks with possible non-Abelian gluons. All these remarkable works were performed during the years 1960-1965. Here I briefly review those works following the original papers of Nambu chronologically, together with a brief introduction to a formulation of Noether's theorem and the Ward-Takahashi identities using path integrals. This article is mostly based on a lecture given at the Nambu Memorial Symposium held at Osaka City University in September 2015, where Nambu started his professional career.
Carloni, Sante; Chaichian, Masud; Tureanu, Anca; Nojiri, Shin'ichi; Odintsov, Sergei D.; Oksanen, Markku
2010-09-15
We propose the most general modified first-order Horava-Lifshitz gravity, whose action does not contain time derivatives higher than the second order. The Hamiltonian structure of this theory is studied in all the details in the case of the spatially-flat Friedmann-Robertson-Walker (FRW) space-time, demonstrating many of the features of the general theory. It is shown that, with some plausible assumptions, including the projectability of the lapse function, this model is consistent. As a large class of such theories, the modified Horava-Lifshitz F(R) gravity is introduced. The study of its ultraviolet properties shows that its z=3 version seems to be renormalizable in the same way as the original Horava-Lifshitz proposal. The Hamiltonian analysis of the modified Horava-Lifshitz F(R) gravity shows that it is in general a consistent theory. The F(R) gravity action is also studied in the fixed-gauge form, where the appearance of a scalar field is particularly illustrative. Then the spatially-flat FRW cosmology for this F(R) gravity is investigated. It is shown that a special choice of parameters for this theory leads to the same equations of motion as in the case of traditional F(R) gravity. Nevertheless, the cosmological structure of the modified Horava-Lifshitz F(R) gravity turns out to be much richer than for its traditional counterpart. The emergence of multiple de Sitter solutions indicates the possibility of unification of early-time inflation with late-time acceleration within the same model. Power-law F(R) theories are also investigated in detail. It is analytically shown that they have a quite rich cosmological structure: early-/late-time cosmic acceleration of quintessence, as well as of phantom types. Also it is demonstrated that all the four known types of finite-time future singularities may occur in the power-law Horava-Lifshitz F(R) gravity. Finally, a covariant proposal for (renormalizable) F(R) gravity within the Horava-Lifshitz spirit is presented.
NASA Astrophysics Data System (ADS)
Hanai, R.; Littlewood, P. B.; Ohashi, Y.
2016-05-01
We theoretically investigate a Bose-condensed exciton gas out of equilibrium. Within the framework of the combined BCS-Leggett strong-coupling theory with the non-equilibrium Keldysh formalism, we show how the Bose-Einstein condensation (BEC) of excitons is suppressed to eventually disappear, when the system is in the non-equilibrium steady state. The supply of electrons and holes from the bath is shown to induce quasi-particle excitations, leading to the partial occupation of the upper branch of Bogoliubov single-particle excitation spectrum. We also discuss how this quasi-particle induction is related to the suppression of exciton BEC, as well as the stability of the steady state.
Spectrum and Dynamics of the BCS-BEC Crossover from a Few-Body Perspective
Stecher, Javier von; Greene, Chris H.
2007-08-31
The spectrum of two spin-up and two spin-down fermions in a trap is calculated using a correlated Gaussian basis throughout the range of the BCS-BEC crossover. These accurate calculations provide a few-body solution to the crossover problem. This solution is used to study the time evolution of the system as the scattering length is changed, mimicking experiments with Fermi gases near Fano-Feshbach resonances. The structure of avoiding crossings in the spectrum allow us to understand the dynamics of the system as a sequence of Landau-Zener transitions. Finally, we propose a ramping scheme to study atom-molecule coherence.
Josephson effect in fermionic superfluids across the BEC-BCS crossover
NASA Astrophysics Data System (ADS)
Valtolina, Giacomo; Burchianti, Alessia; Amico, Andrea; Neri, Elettra; Xhani, Klejdja; Seman, Jorge Amin; Trombettoni, Andrea; Smerzi, Augusto; Zaccanti, Matteo; Inguscio, Massimo; Roati, Giacomo
2015-12-01
The Josephson effect is a macroscopic quantum phenomenon that reveals the broken symmetry associated with any superfluid state. Here we report on the observation of the Josephson effect between two fermionic superfluids coupled through a thin tunneling barrier. We show that the relative population and phase are canonically conjugate dynamical variables throughout the crossover from the molecular Bose-Einstein condensate (BEC) to the Bardeen-Cooper-Schrieffer (BCS) superfluid regime. For larger initial excitations from equilibrium, the dynamics of the superfluids become dissipative, which we ascribe to the propagation of vortices through the superfluid bulk. Our results highlight the robust nature of resonant superfluids.
Importance of the single-particle continuum in BCS pairing with a pseudostate basis
NASA Astrophysics Data System (ADS)
Lay, J. A.; Alonso, C. E.; Fortunato, L.; Vitturi, A.
2016-05-01
In a recent work [arXiv:1510.03185] the use of the Transformed Harmonic Oscillator (THO) basis for the discretization of the singleparticle continuum into a Generalized Bardeen-Cooper-Schrieffer (BCS) formalism was proposed for the description of weakly bound nuclei. We make use of the flexibility of this formalism to study the evolution of the pairing when the nucleus becomes more and more weakly bound. Specifically we focus on the evolution of the occupation of the different partial waves in 22O when the Fermi level approaches zero.
Josephson effect in fermionic superfluids across the BEC-BCS crossover.
Valtolina, Giacomo; Burchianti, Alessia; Amico, Andrea; Neri, Elettra; Xhani, Klejdja; Seman, Jorge Amin; Trombettoni, Andrea; Smerzi, Augusto; Zaccanti, Matteo; Inguscio, Massimo; Roati, Giacomo
2015-12-18
The Josephson effect is a macroscopic quantum phenomenon that reveals the broken symmetry associated with any superfluid state. Here we report on the observation of the Josephson effect between two fermionic superfluids coupled through a thin tunneling barrier. We show that the relative population and phase are canonically conjugate dynamical variables throughout the crossover from the molecular Bose-Einstein condensate (BEC) to the Bardeen-Cooper-Schrieffer (BCS) superfluid regime. For larger initial excitations from equilibrium, the dynamics of the superfluids become dissipative, which we ascribe to the propagation of vortices through the superfluid bulk. Our results highlight the robust nature of resonant superfluids. PMID:26680193
Exact Solution for a Trapped Fermi Gas with Population Imbalance and BCS Pairing
Ying Zujian; Cuoco, Mario; Noce, Canio; Zhou Huanqiang
2008-04-11
The problem of a two-component Fermi gas in a harmonic trap, with an imbalanced population and a pairing interaction of zero total momentum, is mapped onto the exactly solvable reduced BCS model. For a one-dimensional trap, the complete ground state diagram is determined with various topological features in ground state energy spectra. In addition to the conventional two-shell density profile of a paired core and polarized outer wings, a three-shell structure as well as a double-peak superfluid distribution are unveiled.
BCS-BEC crossover in two dimensions: A quantum Monte Carlo study
Bertaina, G.
2012-09-26
We investigate the crossover from Bardeen-Cooper-Schrieffer (BCS) superfluidity to Bose-Einstein condensation (BEC) in a two-dimensional Fermi gas at T= 0 using the fixed-node diffusion Monte Carlo method. We calculate the equation of state and the gap parameter as a function of the interaction strength, observing large deviations compared to mean-field predictions. In the BEC regime our results show the important role of dimer-dimer and atom-dimer interaction effects that are completely neglected in the mean-field picture. We also consider the highly polarized gas and the competition between a polaronic and a molecular picture.
Choi, C.H.; Chung, D.S.; Seib, P.A.
1995-02-01
Yeast fermentation was performed on grain and bakery byproducts with and without adding the same volume of brewers` condensed solubles (BCS). Starch material in the grain and bakery byproducts effectively was converted to fermentable sugars with conversion ratios of 93-97% by successive treatments of samples with bacterial {alpha}-amylase and fungal glucoamylase. The yeast fermentation of these enzyme-digested byproducts alone showed that ethanol concentrations of 16.4-42.7 mL/100 g dry solid in the broth were achieved with fermentation efficiencies of 87-96%. Addition of BCS to the grain byproducts increased ethanol concentration by 10-86% by increasing the potential glucose content of the broth. The rates of fermentation measured by CO{sub 2} gas production demonstrated that BCS addition to bakery byproducts reduced the fermentation time from 62-72 h to 34-35 h. In bakery byproducts that were low in amino nitrogen, exhaustion of nitrogenous compounds in substrates was found to be a limiting factor for yeast growth. Because BCS is a rich source of nitrogen, adding BCS to these substrates markedly increased the fermentation rate. 15 refs., 4 figs., 3 tabs.
NASA Astrophysics Data System (ADS)
Odintsov, S. D.; Oikonomou, V. K.; Saridakis, Emmanuel N.
2015-12-01
We investigate the realization of two bouncing paradigms, namely of the superbounce and the loop quantum cosmological ekpyrosis, in the framework of various modified gravities. In particular, we focus on the F(R) , F(G) and F(T) gravities, and we reconstruct their specific subclasses which lead to such universe evolutions. These subclasses constitute from power laws, polynomials, or hypergeometric ansatzes, which can be approximated by power laws. The qualitative similarity of the different effective gravities which realize the above two bouncing cosmologies, indicates that a universality might be lying behind the bounce. Finally, performing a linear perturbation analysis, we show that the obtained solutions are conditionally or fully stable.
Novoderezhkin, Vladimir I; Doust, Alexander B; Curutchet, Carles; Scholes, Gregory D; van Grondelle, Rienk
2010-07-21
We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex. PMID:20643051
Exome sequencing reveals novel BCS1L mutations in siblings with hearing loss and hypotrichosis.
Zhang, Jie; Duo, Lina; Lin, Zhimiao; Wang, Huijun; Yin, Jinghua; Cao, Xu; Zhao, Jiahui; Dai, Lanlan; Liu, Xuanzhu; Zhang, Jianguo; Yang, Yong; Tang, Zhanli
2015-07-15
As a powerful tool to identify the molecular pathogenesis of Mendelian disorders, exome sequencing was used to identify the genetic basis of two siblings with hearing loss and hypotrichosis and clarify the diagnosis. No pathogenic mutations in GJB2, GJB3 and GJB6 genes were found in the siblings. By analysis of exome of the proband, we identified a novel missense (p.R306C) mutation and a nonsense (p.R186*) mutation in the BCS1L gene. Mutations were confirmed by Sanger sequencing. The siblings were compound heterozygotes, and the inheritance mode of autosomal recessive was postulated. BCS1L is the causative gene of Björnstad syndrome, which is characterized by sensorineural hearing loss and pili torti. The longitudinal gutters along the hair shaft were found by scanning electron microscopy in our patient. Therefore the diagnosis of Björnstad syndrome was eventually made for the patients. Our study extends the phenotypic spectrum of Björnstad syndrome and highlights the clinical applicability of exome sequencing as a diagnostic tool for atypical Mendelian disorders. PMID:25895478
Propagation of sound and supersonic bright solitons in superfluid Fermi gases in BCS-BEC crossover
NASA Astrophysics Data System (ADS)
Wen, Wen; Shen, Shun-Qing; Huang, Guoxiang
2010-01-01
We investigate the linear and nonlinear sound propagations in a cigar-shaped superfluid Fermi gas with a large particle number. We first solve analytically the eigenvalue problem of linear collective excitations and provide explicit expressions of all eigenvalues and eigenfunctions, which are valid for all superfluid regimes in the Bardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover. The linear sound speed obtained agrees well with that of a recent experimental measurement. We then consider a weak nonlinear excitation and show that the time evolution of the excitation obeys a Korteweg de Vries equation. Different from the result obtained in quasi-one-dimensional case studied previously, where subsonic dark solitons are obtained via the balance between quantum pressure and nonlinear effect, we demonstrate that bright solitons with supersonic propagating velocity can be generated in the present three-dimensional system through the balance between a waveguidelike dispersion and the interparticle interaction. The supersonic bright solitons obtained display different physical properties in different superfluid regimes and hence can be used to characterize superfluid features of the BCS-BEC crossover.
The bioelectronic connectional system (BCS): a therapeutic target for non ionizing radiation.
Bistolfi, F
1990-01-01
Among cells and extracellular matrix have been demonstrated reciprocal interactions of oriented morphogenesis. As collagen fibers of the matrix, keratin filaments of desmosomes and the cytoskeleton elements are all piezoelectric substances, with particular biophysical characters, it is possible that these three classes of biostructures are the morphological expressions of a large and unitary cooperative system for coherent communication among cells, by means of piezoelectric interactions and photon/phonon transduction of electromagnetic signals, both endogenous and exogenous. The Author has proposed in 1989 to classify this morphofunctional complex as a bioelectronic connectional system (BCS), in which connective tissue is largely included, but the functions of which go well beyond its classical mechanical ones. The hypothesis is consistent both with the model of Welch and Berry (protonic energy continuum) and with the concept of bioplasma (Inyushin, Sedlak et al.). Physiology and pathology of BCS could also work as a starting point for experimental research aiming at inducing order in biostructures by means of non ionizing radiation. PMID:2263396
A real space auxiliary field approach to the BCS-BEC crossover
NASA Astrophysics Data System (ADS)
Tarat, Sabyasachi; Majumdar, Pinaki
2015-03-01
The BCS to BEC crossover in attractive Fermi systems is a prototype of weak to strong coupling evolution in many body physics. While extensive numerical results are available, and several approximate methods have been developed, most of these schemes are unsuccessful in the presence of spatial inhomogeneity. Such situations call for a real space approach that can handle large spatial scales and retain the crucial thermal fluctuations. With this in mind we present comprehensive results of a real space auxiliary field approach to the BCS to BEC crossover in the attractive Hubbard model in two dimensions. The scheme reproduces the Hartree-Fock-Bogoliubov ground state, and leads to a T c scale that agrees with quantum Monte Carlo estimates to within a few percent. We provide results on the T c , amplitude and phase fluctuations, density of states, and the momentum resolved spectral function, over the entire interaction and temperature window. We suggest how the method generalises successfully to the presence of disorder, trapping, and population imbalance.
Proposed experimental test of the theory of hole superconductivity
NASA Astrophysics Data System (ADS)
Hirsch, J. E.
2016-06-01
The theory of hole superconductivity predicts that in the reversible transition between normal and superconducting phases in the presence of a magnetic field there is charge flow in direction perpendicular to the normal-superconductor phase boundary. In contrast, the conventional BCS-London theory of superconductivity predicts no such charge flow. Here we discuss an experiment to test these predictions.
NASA Astrophysics Data System (ADS)
Chubaryan, Edvard; Avagyan, Roland; Harutunyan, Gohar; Kotanjyan, Anna
2016-07-01
Early and late stages of the cosmological expansion are considered on the base of the modified Jordan-Brans-Dicke (JBD) theory, under the assumption φ(y)=αH ^{n} (H is the Hubble constant, n is a parameter equal to four in the inflationary stage and one or two at late stages of the Universe evolution). At late stages, dynamical pattern is obtained with uniformly accelerated expansion for different values of σ (σ is the coupling constant between the gravitational and scalar fields). It is remarkable that for the limiting allowed value of α=9/(2σ) and for large σ, this variant of the theory is equivalent to the de Sitter model in the framework of the Einstein theory in the presence of a scalar field φ(y)=αH ^{2}. Therefore, the quasi exponential growth of the scale factor in the limiting case becomes purely exponential. Note that in the previously considered models the behavior of α was a power law. We also consider the inflationary regime with φ(y)=αH ^{4}. It is shown that in this case a model with slow rolling can be constructed.
NASA Astrophysics Data System (ADS)
Arsenault, Louis-François; Sémon, Patrick; Shastry, B. Sriram; Tremblay, A.-M. S.
2012-02-01
The Dynamical Mean-Field theory(DMFT) approach to the Hubbard model requires a method to solve the problem of a quantum impurity in a bath of non-interacting electrons. Iterated Perturbation Theory(IPT)[1] has proven its effectiveness as a solver in many cases of interest. Based on general principles and on comparisons with an essentially exact Continuous-Time Quantum Monte Carlo (CTQMC)[2], here we show that the standard implementation of IPT fails when the interaction is much larger than the bandwidth. We propose a slight modification to the IPT algorithm by requiring that double occupancy calculated with IPT gives the correct value. We call this method IPT-D. We show how this approximate impurity solver compares with respect to CTQMC. We consider a face centered cubic lattice(FCC) in 3d for different physical properties. We also use IPT-D to study the thermopower using two recently proposed approximations[3]S^* and SKelvin that do not require analytical continuation and show how thermopower is essentially the entropy per particle in the incoherent regime but not in the coherent one.[1]H.Kajueter et al. Phys. Rev. Lett. 77, 131(1996)[2]P. Werner, et al. Phys. Rev. Lett. 97, 076405(2006)[3]B.S. Sriram Shastry Rep. Prog. Phys. 72 016501(2009)
NASA Astrophysics Data System (ADS)
Roy Choudhury, Kaushik; Hughes, S.
2015-08-01
We present a general theory for calculating the spontaneous emission (SE) rate and the photoluminescence intensity of a quantum dot (QD) exciton coupled to an arbitrary structured photonic reservoir and a bath of acoustic phonons. We describe a polaron master equation (ME) approach which includes phonon interaction nonperturbatively and assume a weak coupling with the photon reservoir which is valid in the Purcell coupling regime. As examples of structured photonic reservoirs, we choose the cases of a Lorentzian cavity and a slow-light coupled-cavity waveguide. In analogy with a simple atom, the SE rate of a QD is expected to be proportional to the local density of photon states (LDOS) of the structured reservoir at the resonant frequency of a QD exciton. However, using a polaron ME theory, we show how the phonon-dressed SE rate of a QD is determined by a broad bandwidth of the photonic LDOS, in violation of the well known Fermi's golden rule. This broadband frequency dependence results in rich spontaneous emission enhancement and suppression, manifesting in significant changes in the Purcell factor and photoluminescence intensity as a function of frequency.
ERIC Educational Resources Information Center
Caro, Cary A.
2014-01-01
The Bowl Championship Series served as a collection of bowl games that were designed to crown the national champion in Division One football. The BCS created two classifications of institutions in Division football, those that were granted automatic access (AQ) to the post-season games, and those that were not (non-AQ). The BCS also generated…
Scattering length of composite bosons in the three-dimensional BCS-BEC crossover
NASA Astrophysics Data System (ADS)
Salasnich, L.; Bighin, G.
2015-03-01
We study the zero-temperature grand potential of a three-dimensional superfluid made of ultracold fermionic alkali-metal atoms in the BCS-BEC crossover. In particular, we analyze the zero-point energy of both fermionic single-particle excitations and bosonic collective excitations. The bosonic elementary excitations, which are crucial to obtain a reliable equation of state in the Bose-Einstein condensate regime, are obtained with a low-momentum expansion up to the forth order of the quadratic (Gaussian) action of the fluctuating pairing field. By performing a cutoff regularization and renormalization of Gaussian fluctuations, we find that the scattering length aB of composite bosons, bound states of fermionic pairs, is given by aB=(2 /3 ) aF , where aF is the scattering length of fermions.
Hung, N. Quang; Dang, N. Dinh
2010-05-15
We propose a description of pairing properties in finite systems within the canonical and microcanonical ensembles. The approach is derived by solving the BCS and self-consistent quasiparticle random-phase approximation with the Lipkin-Nogami particle-number projection at zero temperature. The obtained eigenvalues are embedded into the canonical and microcanonical ensembles. The results obtained are found in quite good agreement with the exact solutions of the doubly-folded equidistant multilevel pairing model as well as the experimental data for {sup 56}Fe nucleus. The merit of the present approach resides in its simplicity and its application to a wider range of particle number, where the exact solution is impracticable.
History of Soil Survey and Evolution of the Brazilian Soil Classification System - SiBCS
NASA Astrophysics Data System (ADS)
Cunha dos Anjos, Lúcia Helena; Csekö Nolasco de Carvalho, Claudia; Homem Antunes, Mauro Antonio; Muggler, Cristine Carole
2014-05-01
national soil classification was presented by Marcelo Camargo (Embrapa Soils) and Jacob Bennema (FAO adviser). When Soil Taxonomy was first published in 1975, a field workshop was held in Brazil, and the system was not accepted by the country scientists; one main reason was the usage of climate as a main attribute for suborders. In 1978, the first national soil field correlation meeting was held with the goal of developing the national system, giving origin to the Brazilian Soil Classification System (SiBCS). In 1980, a working group was created by Embrapa Soils and other institutes resulting in four approximations of the system. In 1999, the first edition of the SiBCS was released, followed by a second edition in 2006 and the third in 2013. The SiBCS is a hierarchic system, based on morphogenetic soil attributes, with six categorical levels: order, suborder, great group, subgroup, family, and series. It has 13 soil orders, and it is structured as a key down to subgroup level. Many soil attributes are based on concepts adopted by the Soil Taxonomy (United States) and by the World Reference Base for Soil Resources (WRB - FAO). The development of the SiBCS is supervised by a national executive committee, and information is available at http://www.cnps.embrapa.br/sibcs (in Portuguese).
Nucleation of spontaneous vortices in trapped Fermi gases undergoing a BCS-BEC crossover.
Glatz, A.; Roberts, H.; Aranson, I. S.; Levin, K.
2011-01-01
We study the spontaneous formation of vortices during the superfluid condensation in a trapped fermionic gas subjected to a rapid thermal quench via evaporative cooling. Our work is based on the numerical solution of the time-dependent crossover Ginzburg-Landau equation coupled to the heat diffusion equation. We quantify the evolution of condensate density and vortex length as a function of a crossover phase parameter from BCS to BEC. The more interesting phenomena occur somewhat nearer to the BEC regime and should be experimentally observable; during the propagation of the cold front, the increase in condensate density leads to the formation of supercurrents toward the center of the condensate as well as possible condensate volume oscillations.
BCS-BEC crossover in atomic Fermi gases with a narrow resonance
Jensen, L. M.; Nilsen, H. M.; Watanabe, Gentaro
2006-10-15
We determine the effects on the BCS-BEC crossover of the energy dependence of the effective two-body interaction, which at low energies is determined by the effective range. To describe interactions with an effective range of either sign, we consider a single-channel model with a two-body interaction having an attractive square well and a repulsive square barrier. We investigate the two-body scattering properties of the model, and then solve the Eagles-Leggett equations for the zero temperature crossover, determining the momentum dependent gap and the chemical potential self-consistently. From this we investigate the dependence of the crossover on the effective range of the interaction.
BCS-BEC Crossover on the Two-Dimensional Honeycomb Lattice
Zhao Erhai; Paramekanti, Arun
2006-12-08
The attractive Hubbard model on the honeycomb lattice exhibits, at half filling, a quantum critical point between a semimetal with massless Dirac fermions and an s-wave superconductor (SC). We study the BCS-BEC crossover in this model away from half filling at zero temperature and show that the appropriately defined crossover line (in the interaction-density plane) passes through the quantum critical point at half filling. For a range of densities around half filling, the 'underlying Fermi surface' of the SC, defined as the momentum space locus of minimum energy quasiparticle excitations, encloses an area which changes nonmonotonically with interaction. We also study fluctuations in the SC and the semimetal, and show the emergence of an undamped Leggett mode deep in the SC. Finally, we consider possible implications for ultracold atoms in optical lattices and the high temperature SCs.
Two-band superfluidity from the BCS to the BEC limit
Iskin, M.; Sa de Melo, C. A. R.
2006-10-01
We analyze the evolution of two-band superfluidity from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein condensation (BEC) limit. When the interband interaction is tuned from negative to positive values, a quantum phase transition occurs from a 0-phase to a {pi}-phase state, depending on the relative phase of the two order parameters. Furthermore, population imbalances between the two bands can be created by tuning the intraband or interband interactions. We also find two undamped low-energy collective excitations corresponding to in-phase and out-of-phase modes. Lastly, we derive the coupled Ginzburg-Landau equations, and show that they reduce to coupled Gross-Pitaevskii equations for two types of bosons in the BEC limit.
BCS to BEC evolution for mixtures of fermions with unequal masses
NASA Astrophysics Data System (ADS)
de Melo, Carlos A. R. Sa
2009-03-01
I discuss the zero and finite temperature phase diagrams of a mixture of fermions with unequal masses with and without population imbalance, which may correspond for example to mixtures of ^6Li and ^40K, ^6Li and ^87Sr, or ^40K and ^87Sr in the context of ultracold atoms. At zero temperature and when excess fermions are present, at least three phases may occur as the interaction parameter is changed from the BCS to the BEC regime. These phases correspond to normal, phase separation, or superfluid with coexistence between paired and excess fermions. The zero temperature phase diagram of population imbalance versus interaction parameter presents a remarkable asymmetry between the cases involving excess lighter or heavier fermions [1, 2], in sharp contrast with the symmetric phase diagram corresponding to the case of equal masses. At finite temperatures, the phase separation region of the phase diagram competes with superfluid regions possessing gapless elementary excitations [3] for certain ranges of the interaction parameter depending on the mass ratio. Furthermore, a phase transition may take place between two superfluid phases which are topologically distinct. The precise location of such transition is sensitive to the mass ratio between the two species of fermions. Signatures of this possible topological transition are present in the momentum distribution or structure factor, which may be measured experimentally in time-of-flight or through Bragg scattering, respectively. Lastly, throughout the evolution from BCS to BEC, I discuss the critical current and sound velocity for unequal mass systems as a function of interaction parameter and mass ratio. These quantities may also be measured via the same techniques already used in mixtures of fermions with equal masses. [1] M. Iskin, and C. A. R. Sa de Melo, Phys. Rev. Lett. 97, 100404 (2006). [2] M. Iskin and C. A. R. Sa de Melo, Phys. Rev. A 76, 013601 (2007). [3] Li Han, and C. A. R. Sa de Melo, arXiv:0812.xxxx
Kellar, Joshua A.; Lin, Jui-Ching; Kim, Jun-Hyun; Yoder, Nathan L.; Bevan, Kirk H.; Stokes, Grace Y.; Geiger, Franz M.; Nguyen, SonBinh T.; Bedzyk, Michael J.; Hersam, Mark C.
2009-03-24
Highly conjugated molecules bound to silicon are promising candidates for organosilicon electronic devices and sensors. In this study, 1-bromo-4-ethynylbenzene was synthesized and reacted with a hydrogen-passivated Si(111) surface via ultraviolet irradiation. Through an array of characterization and modeling tools, the binding configuration and morphology of the reacted molecule were thoroughly analyzed. Atomic force microscopy confirmed an atomically flat surface morphology following reaction, while X-ray photoelectron spectroscopy verified reaction to the surface via the terminal alkyne moiety. In addition, synchrotron X-ray characterization, including X-ray reflectivity, X-ray fluorescence, and X-ray standing wave measurements, enabled sub-angstrom determination of the position of the bromine atom with respect to the silicon lattice. This structural characterization was quantitatively compared with density functional theory (DFT) calculations, thus enabling the {pi}-conjugation of the terminal carbon atoms to be deduced. The X-ray and DFT results were additionally corroborated with the vibrational spectrum of the organic adlayer, which was measured with sum frequency generation. Overall, these results illustrate that the terminal carbon atoms in 1-bromo-4-ethynylbenzene adlayers on Si(111) retain {pi}-conjugation, thus revealing alkyne molecules as promising candidates for organosilicon electronics and sensing.
BcsTx3 is a founder of a novel sea anemone toxin family of potassium channel blocker.
Orts, Diego J B; Moran, Yehu; Cologna, Camila T; Peigneur, Steve; Madio, Bruno; Praher, Daniela; Quinton, Loic; De Pauw, Edwin; Bicudo, José E P W; Tytgat, Jan; de Freitas, José C
2013-10-01
Sea anemone venoms have become a rich source of peptide toxins which are invaluable tools for studying the structure and functions of ion channels. In this work, BcsTx3, a toxin found in the venom of a Bunodosoma caissarum (population captured at the Saint Peter and Saint Paul Archipelago, Brazil) was purified and biochemically and pharmacologically characterized. The pharmacological effects were studied on 12 different subtypes of voltage-gated potassium channels (K(V)1.1-K(V)1.6; K(V)2.1; K(V)3.1; K(V)4.2; K(V)4.3; hERG and Shaker IR) and three cloned voltage-gated sodium channel isoforms (Na(V)1.2, Na(V)1.4 and BgNa(V)1.1) expressed in Xenopus laevis oocytes. BcsTx3 shows a high affinity for Drosophila Shaker IR channels over rKv1.2, hKv1.3 and rKv1.6, and is not active on NaV channels. Biochemical characterization reveals that BcsTx3 is a 50 amino acid peptide crosslinked by four disulfide bridges, and sequence comparison allowed BcsTx3 to be classified as a novel type of sea anemone toxin acting on K(V) channels. Moreover, putative toxins homologous to BcsTx3 from two additional actiniarian species suggest an ancient origin of this newly discovered toxin family. PMID:23895459
Lyubimova, Olga; Stoyanov, Stanislav R; Gusarov, Sergey; Kovalenko, Andriy
2015-06-30
The X-ray crystal structure-based models of Iα cellulose nanocrystals (CNC), both pristine and containing surface sulfate groups with negative charge 0-0.34 e/nm(2) produced by sulfuric acid hydrolysis of softwood pulp, feature a highly polarized "crystal-like" charge distribution. We perform sampling using molecular dynamics (MD) of the structural relaxation of neutral pristine and negatively charged sulfated CNC of various lengths in explicit water solvent and then employ the statistical mechanical 3D-RISM-KH molecular theory of solvation to evaluate the solvation structure and thermodynamics of the relaxed CNC in ambient aqueous NaCl solution at a concentration of 0.0-0.25 mol/kg. The MD sampling induces a right-hand twist in CNC and rearranges its initially ordered structure with a macrodipole of high-density charges at the opposite faces into small local spots of alternating charge at each face. This surface charge rearrangement observed for both neutral and charged CNC significantly affects the distribution of ions around CNC in aqueous electrolyte solution. The solvation free energy (SFE) of charged sulfated CNC has a minimum at a particular electrolyte concentration depending on the surface charge density, whereas the SFE of neutral CNC increases linearly with NaCl concentration. The SFE contribution from Na(+) counterions exhibits behavior similar to the NaCl concentration dependence of the whole SFE. An analysis of the 3D maps of Na(+) density distributions shows that these model CNC particles exhibit the behavior of charged nanocolloids in aqueous electrolyte solution: an increase in electrolyte concentration shrinks the electric interfacial layer and weakens the effective repulsion between charged CNC particles. The 3D-RISM-KH method readily treats solvent and electrolyte of a given nature and concentration to predict effective interactions between CNC particles in electrolyte solution. We provide CNC structural models and a modeling procedure for
Research in the theory of condensed matter and elementary particles. (Progress report)
Not Available
1985-01-01
The proposed research is concerned with problems occupying the common ground between quantum field theory and statistical mechanics. The topics under investigation include: superconformal field theory in two dimensions, its relationship to two dimensional critical phenomena and its applications in string theory; the covariant formulation of the superstring theory; formation of large-scale structures and spatial chaos in dynamical systems; fermion-boson mass relations in BCS type theories; and properties of quantum field theories defined over galois fields. 37 refs.
NASA Astrophysics Data System (ADS)
Jung, Timothy Paul
Commercial supersonic travel has strong business potential; however, in order for the Federal Aviation Administration to lift its ban on supersonic flight overland, designers must reduce aircraft sonic boom strength to an acceptable level. An efficient methodology and associated tools for designing aircraft for minimized sonic booms are presented. The computer-based preliminary design tool, RapidF, based on modified linear theory, enables quick assessment of an aircraft's sonic boom with run times less than 30 seconds on a desktop computer. A unique feature of RapidF is that it tracks where on the aircraft each segment of the of the sonic boom came from, enabling precise modifications, speeding the design process. Sonic booms from RapidF are compared to flight test data, showing that it is capability of predicting a sonic boom duration, overpressure, and interior shock locations. After the preliminary design is complete, scaled flight tests should be conducted to validate the low boom design. When conducting such tests, it is insufficient to just scale the length; thus, equations to scale the weight and propagation distance are derived. Using RapidF, a conceptual supersonic business jet design is presented that uses F-function lobe balancing to create a frozen sonic boom using lifting surfaces. The leading shock is reduced from 1.4 to 0.83 psf, and the trailing shock from 1.2 to 0.87 psf, 41% and 28% reductions respectfully. By changing the incidence angle of the surfaces, different sonic boom shapes can be created, and allowing the lobes to be re-balanced for new flight conditions. Computational fluid dynamics is conducted to validate the sonic boom predictions. Off-design analysis is presented that varies weight, altitude, Mach number, and propagation angle, demonstrating that lobe-balance is robust. Finally, the Perceived Level of Loudness metric is analyzed, resulting in a modified design that incorporates other boom minimization techniques to further reduce
NASA Astrophysics Data System (ADS)
Gazit, Snir; Randeria, Mohit; Vishwanath, Ashvin
In two space dimensions, the Z2 lattice gauge theory is known to undergo a zero temperature confinement to de-confinment quantum phase transition . In this work, we study how this transition is modified in the presence of lattice fermions which are minimally coupled to the Z2 gauge field. This may be viewed as an extreme version of the BEC-BCS transition where fermions are confined in the strong coupling phase. We investigate both a square lattice model with a large fermi surface and Dirac fermions realized on a π flux and honeycomb lattices. The models are found to be free of the numerical sign problem for all fermion density. In addition, we introduce a numerical method to stochastically incorporate the Gauss law constraint in a quantum Monte Carlo (QMC) simulation. The phase diagram as a function of the model parameters, chemical potential and temperature is determined by means of a large scale determinant QMC.
Zur, Moran; Gasparini, Marisa; Wolk, Omri; Amidon, Gordon L; Dahan, Arik
2014-05-01
Although recognized as overly conservative, metoprolol is currently the common low/high BCS permeability class boundary reference compound, while labetalol was suggested as a potential alternative. The purpose of this study was to identify the various characteristics that the optimal marker should exhibit, and to investigate the suitability of labetalol as the permeability class reference drug. Labetalol's BCS solubility class was determined, and its physicochemical properties and intestinal permeability were thoroughly investigated, both in vitro and in vivo in rats, considering the complexity of the whole of the small intestine. Labetalol was found to be unequivocally a high-solubility compound. In the pH range throughout the small intestine (6.5-7.5), labetalol exhibited pH-dependent permeability, with higher permeability at higher pH values. While in vitro octanol-buffer partitioning (Log D) values of labetalol were significantly higher than those of metoprolol, the opposite was evident in the in vitro PAMPA permeability assay. The results of the in vivo perfusion studies in rats lay between the two contradictory in vitro studies; metoprolol was shown to have moderately higher rat intestinal permeability than labetalol. Theoretical distribution of the ionic species of the drugs was in corroboration with the experimental in vitro and the in vivo data. We propose three characteristics that the optimal permeability class reference drug should exhibit: (1) fraction dose absorbed in the range of 90%; (2) the optimal marker drug should be absorbed largely via passive transcellular permeability, with no/negligible carrier-mediated active intestinal transport (influx or efflux); and (3) the optimal marker drug should preferably be nonionizable. The data presented in this paper demonstrate that neither metoprolol nor labetalol can be regarded as optimal low/high-permeability class boundary standard. While metoprolol is too conservative due to its complete absorption
NASA Astrophysics Data System (ADS)
Sumi, Tomonari; Maruyama, Yutaka; Mitsutake, Ayori; Koga, Kenichiro
2016-06-01
In the conventional classical density functional theory (DFT) for simple fluids, an ideal gas is usually chosen as the reference system because there is a one-to-one correspondence between the external field and the density distribution function, and the exact intrinsic free-energy functional is available for the ideal gas. In this case, the second-order density functional Taylor series expansion of the excess intrinsic free-energy functional provides the hypernetted-chain (HNC) approximation. Recently, it has been shown that the HNC approximation significantly overestimates the solvation free energy (SFE) for an infinitely dilute Lennard-Jones (LJ) solution, especially when the solute particles are several times larger than the solvent particles [T. Miyata and J. Thapa, Chem. Phys. Lett. 604, 122 (2014)]. In the present study, we propose a reference-modified density functional theory as a systematic approach to improve the SFE functional as well as the pair distribution functions. The second-order density functional Taylor series expansion for the excess part of the intrinsic free-energy functional in which a hard-sphere fluid is introduced as the reference system instead of an ideal gas is applied to the LJ pure and infinitely dilute solution systems and is proved to remarkably improve the drawbacks of the HNC approximation. Furthermore, the third-order density functional expansion approximation in which a factorization approximation is applied to the triplet direct correlation function is examined for the LJ systems. We also show that the third-order contribution can yield further refinements for both the pair distribution function and the excess chemical potential for the pure LJ liquids.
Heinen, Christian A; Reuss, Stefan; Amidon, Gordon L; Langguth, Peter
2013-11-01
In the current study the involvement of ion pair formation between bile salts and trospium chloride (TC), a positively charged Biopharmaceutical Classification System (BCS) class III substance, showing a decrease in bioavailability upon coadministration with food (negative food effect) was investigated. Isothermal titration calorimetry provided evidence of a reaction between TC and bile acids. An effect of ion pair formation on the apparent partition coefficient (APC) was examined using (3)H-trospium. The addition of bovine bile and bile extract porcine led to a significant increase of the APC. In vitro permeability studies of trospium were performed across Caco-2-monolayers and excised segments of rat jejunum in a modified Ussing chamber. The addition of bile acids led to an increase of trospium permeation across Caco-2-monolayers and rat excised segments by approximately a factor of 1.5. The addition of glycochenodeoxycholate (GCDC) was less effective than taurodeoxycholate (TDOC). In the presence of an olive oil emulsion, a complete extinction of the permeation increasing effects of bile salts was observed. Thus, although there are more bile acids in the intestine in the fed state compared to the fasted state, these are not able to form ion pairs with trospium in fed state, because they are involved in the emulsification of dietary fats. In conclusion, the formation of ion pairs between trospium and bile acids can partially explain its negative food effect. Our results are presumably transferable to other organic cations showing a negative food effect. PMID:23750707
Daveson, Barbara; O'Callaghan, Clare
2011-01-01
Many references to time or temporality are located within music therapy literature, however little research has been completed regarding this phenomenon. Findings from a modified grounded theory study about clients' experiences and descriptions of time within the context of music therapy are presented here. The study was informed by the constructivist-interpretive paradigm and a grounded-descriptive statement finding resulted. A 2-staged research methodology was used, comprising a deductive-inductive content analysis of information from the public domain, followed by data-mining of information from a minimum of 160 clients and analysis of data from at least 43 of these 160 clients. Information regarding memory experiences, the duration of music therapy effects, recall and retrieval, and experiences of time are identified. Implications for practice are emphasized, in particular the following is stressed (a) the importance of time orientation and temporal connectedness in relation to identity development, (b) temporal strategies within music experience to assist integration, recall, and retrieval of information, and (c) the importance of and the elements involved in time modification. New explanations for music therapy phenomena are shared, and areas for research highlighted. Benefits of using time dynamically to aid therapeutic process are proposed, and it is concluded that temporal experience within the context of music therapy is important in relation to both practice and research. PMID:21866712
BCS superconductivity near the band edge: Exact results for one and several bands
NASA Astrophysics Data System (ADS)
Valentinis, D.; van der Marel, D.; Berthod, C.
2016-07-01
We revisit the problem of a BCS superconductor in the regime where the Fermi energy is smaller than the Debye energy. This regime is relevant for low-density superconductors such as SrTiO3 that are not in the BEC limit, as well as in the problem of "shape resonances" associated with the confinement of a three-dimensional superconductor. While the problem is not new, exact results were lacking in the low-density limit. In two dimensions, we find that the initial rise of the pairing temperature Tc at low density n is nonanalytic and faster than any power of n . In three dimensions, we also find that Tc is nonanalytic, but starts with zero slope at weak coupling and infinite slope at strong coupling. Self-consistent treatment of the chemical potential and energy dependence of the density of states are crucial ingredients to obtain these results. We also present exact results for multiband systems and confirm our analytical expressions by numerical simulations.
Jannin, Vincent; Chevrier, Stéphanie; Michenaud, Matthieu; Dumont, Camille; Belotti, Silvia; Chavant, Yann; Demarne, Frédéric
2015-11-10
Lipid-based formulations can be effective drug delivery systems for poorly water-soluble chemical entities, provided they are designed with careful selection of the excipients, based on their role in the delivery system and in relation to drug properties. The primary factor leading to increased bioavailability is the administration of the drug in a pre-dissolved state thereby avoiding the dissolution limiting step. All model drugs tested (piroxicam, curcumin and nifedipine) belong to the same chemical space--small BCS class II molecules with logP ranging from 2 to 3. These drugs, exhibiting low to medium logP, are not soluble in lipophilic lipid-based excipients (e.g., vegetable oils). Water-soluble and water-dispersible surfactants are able to dissolve the target dose of each drug in the dosage form and efficiently keep it in solution during dispersion. In vitro digestion testing was necessary to discriminate formulations and enable selection of the most robust one. For each molecule, the system with the best performance during dispersion/digestion tests did not comprise the surfactant which delivered the highest solvent capacity for the drug. This study demonstrates the potential of surfactant-based formulations - i.e., Type IV systems from the lipid formulation classification system - for this type of hydrophobic drug. PMID:26364710