Science.gov

Sample records for field-induced continuum lowering

  1. Continuum lowering - A new perspective

    NASA Astrophysics Data System (ADS)

    Crowley, B. J. B.

    2014-12-01

    What is meant by continuum lowering and ionization potential depression (IPD) in a Coulomb system depends very much upon precisely what question is being asked. It is shown that equilibrium (equation of state) phenomena and non-equilibrium dynamical processes like photoionization are characterized by different values of the IPD. In the former, the ionization potential of an atom embedded in matter is the difference in the free energy of the many-body system between states of thermodynamic equilibrium differing by the ionization state of just one atom. Typically, this energy is less than that required to ionize the same atom in vacuo. Probably, the best known example of this is the IPD given by Stewart and Pyatt (SP). However, it is a common misconception that this formula should apply directly to the energy of a photon causing photoionization, since this is a local adiabatic process that occurs in the absence of a response from the surrounding plasma. To achieve the prescribed final equilibrium state, in general, additional energy, in the form of heat and work, is transferred between the atom and its surroundings. This additional relaxation energy is sufficient to explain the discrepancy between recent spectroscopic measurements of IPD in dense plasmas and the predictions of the SP formula. This paper provides a detailed account of an analytical approach, based on SP, to calculating thermodynamic and spectroscopic (adiabatic) IPDs in multicomponent Coulomb systems of arbitrary coupling strength with Te ≠ Ti. The ramifications for equilibrium Coulomb systems are examined in order to elucidate the roles of the various forms of the IPD and any possible connection with the plasma microfield. The formulation embodies an analytical equation of state (EoS) that is thermodynamically self-consistent, provided that the bound and free electrons are dynamically separable, meaning that the system is not undergoing pressure ionization. Apart from this restriction, the model is

  2. Direct extraction of intense-field-induced polarization in the continuum on the attosecond time scale from transient absorption

    NASA Astrophysics Data System (ADS)

    Li, X.; Haxton, D. J.; Gaarde, M. B.; Schafer, K. J.; McCurdy, C. W.

    2016-02-01

    A procedure is suggested for using transient absorption spectroscopy above the ionization threshold to measure the polarization of the continuum induced by an intense optical pulse. In this way transient absorption measurement can be used to probe subfemtosecond intense field dynamics in atoms and molecules. The method is based on an approximation to the dependence of these spectra on time delay between an attosecond XUV probe pulse and an intense pump pulse that is tested over a wide range of intensities and time delays by all-electrons-active calculations using the multiconfiguration time-dependent Hartree-Fock method in the case of neon.

  3. Proposal for direct measurement of intense-field induced polarization in the continuum on the attosecond time scale using transient absorption

    NASA Astrophysics Data System (ADS)

    McCurdy, C. William; Haxton, Daniel; Li, Xuan

    2015-05-01

    A procedure is proposed for using transient absorption spectroscopy above the ionization threshold to measure the polarization of the continuum induced by an intense optical pulse. In this way transient absorption measurement can be used to probe sub-femtosecond intense field dynamics in atoms and molecules and extract the high frequency polarization that plays a central role in high harmonic generation. The method is based on a robust approximation to the dependence of these spectra on time-delay between an attosecond XUV probe pulse and an intense pump pulse that is verified over a wide range of intensities and time delays by all-electrons-active calculations using the Multiconfiguration Time-Dependent Hartree Fock method. To demonstrate the extraction of the field-induced polarization, we study the transient absorption spectrum of atomic Neon. Work at LBNL supported by USDOE, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, and work at UC Davis supported by USDOE grant No. DESC0007182.

  4. Measurements of continuum lowering in solid-density plasmas created from elements and compounds

    NASA Astrophysics Data System (ADS)

    Ciricosta, O.; Vinko, S. M.; Barbrel, B.; Rackstraw, D. S.; Preston, T. R.; Burian, T.; Chalupský, J.; Cho, B. I.; Chung, H.-K.; Dakovski, G. L.; Engelhorn, K.; Hájková, V.; Heimann, P.; Holmes, M.; Juha, L.; Krzywinski, J.; Lee, R. W.; Toleikis, S.; Turner, J. J.; Zastrau, U.; Wark, J. S.

    2016-05-01

    The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations.

  5. Measurements of continuum lowering in solid-density plasmas created from elements and compounds.

    PubMed

    Ciricosta, O; Vinko, S M; Barbrel, B; Rackstraw, D S; Preston, T R; Burian, T; Chalupský, J; Cho, B I; Chung, H-K; Dakovski, G L; Engelhorn, K; Hájková, V; Heimann, P; Holmes, M; Juha, L; Krzywinski, J; Lee, R W; Toleikis, S; Turner, J J; Zastrau, U; Wark, J S

    2016-01-01

    The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations. PMID:27210741

  6. Measurements of continuum lowering in solid-density plasmas created from elements and compounds

    PubMed Central

    Ciricosta, O.; Vinko, S. M.; Barbrel, B.; Rackstraw, D. S.; Preston, T. R.; Burian, T.; Chalupský, J.; Cho, B. I.; Chung, H. -K.; Dakovski, G. L.; Engelhorn, K.; Hájková, V.; Heimann, P.; Holmes, M.; Juha, L.; Krzywinski, J.; Lee, R. W.; Toleikis, S.; Turner, J. J.; Zastrau, U.; Wark, J. S.

    2016-01-01

    The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations. PMID:27210741

  7. Measurements of continuum lowering in solid-density plasmas created from elements and compounds

    DOE PAGESBeta

    Ciricosta, O.; Vinko, S. M.; Barbrel, B.; Rackstraw, D. S.; Preston, T. R.; Burian, T.; Chalupský, J.; Cho, B. I.; Chung, H. -K.; Dakovski, G. L.; et al

    2016-05-23

    The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. In this study, we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffectedmore » by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. Lastly, the results have implications for the standard approaches to the equation of state calculations.« less

  8. Experimental Measurements and Density Functional Theory Calculations of Continuum Lowering in Strongly Coupled Plasmas

    NASA Astrophysics Data System (ADS)

    Vinko, Sam

    2014-10-01

    An accurate description of the ionization potential depression (IPD) of ions in plasmas due to their interaction with the environment is a fundamental problem in plasma physics, playing a key role in determining the ionization balance, charge state distribution, opacity and plasma equation of state. Here I present the first experimental investigation of the IPD as a function of ionic charge state in a range of dense Mg, Al and Si plasmas, using the Linac Coherent Light Source X-ray free-electron laser. The measurements show significantly larger IPDs than are predicted by the most commonly used models, such as that of Stewart-Pyatt, or the ion-sphere model of Zimmerman-More. Instead, plasma simulations using finite-temperature density functional theory with excited-state projector augmented-wave potentials show excellent agreement with the experimental results and explain the stronger-than-expected continuum lowering through the electronic structure of the valence states in these strong-coupling conditions, which retain much of their atomic characteristics close to the ion core regions. These results have a profound impact on the understanding and modelling of plasmas over a wide range of warm- and hot-dense matter conditions.

  9. Ionization channel of continuum lowering in plasmas: effects of plasma screening, electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Kryukov, N.; Oks, E.

    2013-12-01

    Calculations of continuum lowering (CL) in plasmas evolved from ion sphere models to dicentre models of the plasma state. One of such theories—a percolation theory—calculated CL defined as an absolute value of energy at which an electron becomes bound to a macroscopic portion of plasma ions (a quasi-ionization). Previously one of us derived analytically the value of CL in the ionization channel which was disregarded in the percolation theory. In the present paper we study how the value of CL in the ionization channel is affected by plasma screening, electric and magnetic fields. We show that the screening and the magnetic field decrease the value of CL, inhibiting the ionization, while the electric field increases the value of CL, promoting the ionization. These results should be important for inertial fusion, x-ray lasers, powerful Z-pinches, astrophysics and other applications of high-density plasmas. We also show that the screening stabilizes the nuclear motion of the corresponding Rydberg quasimolecules in some cases and destabilizes it in other cases.

  10. Doing Away with Occupation Probability: A New Way to Model Continuum Lowering at White Dwarf Photosphere Conditions

    NASA Astrophysics Data System (ADS)

    Gomez, Thomas A.; Winget, Donald E.; Montgomery, Michael H.; Kilcrease, Dave; Nagayama, Taisuke

    2016-01-01

    White dwarfs are interesting for a number of applications including studying equations of state, stellar pulsations, and determining the age of the universe.These interesting applications require accurate determination of surface conditions: temperatures and surface gravity (or mass).The most common technique to estimate the temperature and gravity is to find the model spectrun that best fits the observed spectra of a star (known as the spectroscopic method); however, this model rests on our ability to accurately model the hydrogen spectrum at high densities.There are currently disagreements between the spectroscopic method and other techniques to determine mass.We seek to resolve this issue by exploring the continuum lowering (or disappearance of states) of the hydrogen atom.The current formalism, called "occupation probability," defines some criteria for the isolated atom's bound state to be ionized, then extrapolates the continuous spectrum to the same energy threshold.The two are then combined to create the final cross-section.I introduce a new way of calculating the atomic spectrum by doing some averaging of the plasma interaction potential energy (previously used in the physics community) and directly integrating the Schrodinger equation.This technique is a major improvement over the Taylor expansion used to describe the ion-emitter interaction and removes the need of the occupation probability and treats continuum states and discrete states on the same footing in the spectrum calculation.The resulting energy spectrum is in fact many discrete states that when averaged over the electric field distribution in the plasma appears to be a continuum.In the low density limit, the two methods are in agreement, but show some differences at high densities (above 10$^{17} e/cc$) including line shifts near the ``continuum'' edge.

  11. The evolution of organic matter along the lower Amazon River continuum - Óbidos to the ocean

    NASA Astrophysics Data System (ADS)

    Ward, N. D.; Keil, R. G.; Medeiros, P. M.; Brito, D.; Cunha, A.; Sawakuchi, H. O.; Moura, J. S.; Yager, P. L.; Krusche, A. V.; Richey, J. E.

    2013-12-01

    The influence of the Amazon River on global hydrologic and biogeochemical cycling is well recognized. The Amazon River provides roughly 16% of the global freshwater supply to the ocean and is a significant source of CO2 to the atmosphere, outgassing 0.5 Pg C y-1 to the atmosphere--a flux roughly equivalent to the amount of carbon 'sequestered' by the Amazon rainforest (Field et al, 1998; Richey et al., 2002; Malhi et al., 2008). However, much of our understanding of the flux of matter from the Amazon River into the Atlantic Ocean (and atmosphere) is limited to measurements made at and upstream of Óbidos, 900 km upstream from the actual river mouth. Further, there are few to no observations documenting the transformation of organic matter in a parcel of water as it travels downstream of Óbidos into the ocean. Here we explore the hydrological and biogeochemical evolution of the lower Amazon River continuum, from Óbidos to the Atlantic Ocean. A suite of dissolved and particulate organic matter (OM) parameters were measured during a series of five river expeditions with stations at Óbidos, the Tapajós tributary, the mouth of the Lago Grande de Curuai floodplain lake, both the north and south channels of the Amazon River mouth near Macapá, and the confluence of the Amazon and Tocantins Rivers near Belém. In addition to bulk carbon isotopic signatures, a suite of biomarkers including dissolved and particulate lignin-derived phenols were measured to trace the sources and degradation history of terrestrial vascular plant derived OM throughout the continuum. Dissolved and particulate lignin phenol concentrations both correlated positively with river discharge in the Amazon River mainstem, with variable export patterns from the tributaries and floodplains. As organic matter travels along the continuum it is degraded by microbial composition, fuelling gross respiration and CO2 outgassing. The flux of organic carbon to the ocean is chemically recalcitrant as a result of

  12. Flood management along the Lower Mississippi and Rhine Rivers (The Netherlands) and the continuum of geomorphic adjustment

    NASA Astrophysics Data System (ADS)

    Hudson, Paul F.; Middelkoop, Hans; Stouthamer, Esther

    2008-10-01

    the 1928 Mississippi River & Tributaries Act have rapidly infilled, with 67% of the lake area converted to wetlands. In comparison, older oxbow lakes located outside of the embanked floodplain have undergone much lower amounts of infilling, averaging 37% of oxbow lake area converted to wetlands. The floodplain geomorphology is further modified by numerous large floodplain borrow pits and the selective removal of fine-grained deposits, primarily created for dike (levee) construction and maintenance. The Dutch Rhine has been managed for flooding for over eight centuries and exhibits specific types of humanized embanked floodplain geomorphology that require a greater period of adjustment. Dike breaches create ponds (wielen) and sandy splay-like deposits, which represent distinctive anthro-geomorphic environments along the margins of embanked floodplains. Channel stabilization by groynes and dikes has resulted in the formation of new floodplains along Rhine distributaries. The trapping of flood sediments within the embanked floodplain has resulted in aggradation that has reduced the inundation capacity of the embanked floodplain. This geomorphic alteration reduced the effectiveness of the existing flood management infrastructure and has stimulated a change towards a new flood management approach designed to "work with the river". The major conclusions are placed within a conceptual model, and illustrate that; 1. in many instances specific flood management options were constrained by the type of floodplain deposit; 2. geomorphic adjustment to flood management occurs along a time-space continuum; 3. flood management initiates positive feedbacks with unintended geomorphic consequences that require further management options to minimize flood risk.

  13. Magnetic field induced dynamical chaos

    SciTech Connect

    Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra

    2013-12-15

    In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x–y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

  14. Static-field-induced states

    NASA Astrophysics Data System (ADS)

    Gets, Artem V.; Tolstikhin, Oleg I.

    2013-01-01

    Considering an electron interacting with an atomic or molecular potential and an external static electric field, one usually focuses on narrow resonances at negative energies originating from the bound states in the absence of the field; we call them tunneling states (TSs). Meanwhile, there also exist relatively broad resonances at positive energies having no counterparts in the absence of the field; we call them static-field-induced states (SFISs). In this paper, the recently developed weak-field asymptotic theory of TSs [O. I. Tolstikhin , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.053423 84, 053423 (2011)] is extended to SFISs. An asymptotic quantization condition defining the energies of SFISs in an arbitrary potential in the three-dimensional case is derived. The parabolic scattering amplitudes appearing in this quantization condition are defined. The theory is illustrated by calculations for the zero-range and Coulomb potentials. The SFISs in these potentials are found and their energies are shown to be in good agreement with the asymptotic results over a wide interval of the values of the field.

  15. Field induced gap infrared detector

    NASA Technical Reports Server (NTRS)

    Elliott, C. Thomas (Inventor)

    1990-01-01

    A tunable infrared detector which employs a vanishing band gap semimetal material provided with an induced band gap by a magnetic field to allow intrinsic semiconductor type infrared detection capabilities is disclosed. The semimetal material may thus operate as a semiconductor type detector with a wavelength sensitivity corresponding to the induced band gap in a preferred embodiment of a diode structure. Preferred semimetal materials include Hg(1-x)Cd(x)Te, x is less than 0.15, HgCdSe, BiSb, alpha-Sn, HgMgTe, HgMnTe, HgZnTe, HgMnSe, HgMgSe, and HgZnSe. The magnetic field induces a band gap in the semimetal material proportional to the strength of the magnetic field allowing tunable detection cutoff wavelengths. For an applied magnetic field from 5 to 10 tesla, the wavelength detection cutoff will be in the range of 20 to 50 micrometers for Hg(1-x)Cd(x)Te alloys with x about 0.15. A similar approach may also be employed to generate infrared energy in a desired band gap and then operating the structure in a light emitting diode or semiconductor laser type of configuration.

  16. Continuum Nanofluidics.

    PubMed

    Hansen, Jesper S; Dyre, Jeppe C; Daivis, Peter; Todd, Billy D; Bruus, Henrik

    2015-12-15

    This paper introduces the fundamental continuum theory governing momentum transport in isotropic nanofluidic systems. The theory is an extension of the classical Navier-Stokes equation, and includes coupling between translational and rotational degrees of freedom as well as nonlocal response functions that incorporate spatial correlations. The continuum theory is compared with molecular dynamics simulation data for both relaxation processes and fluid flows, showing excellent agreement on the nanometer length scale. We also present practical tools to estimate when the extended theory should be used. It is shown that in the wall-fluid region the fluid molecules align with the wall, and in this region the isotropic model may fail and a full anisotropic description is necessary. PMID:26457405

  17. Field-induced confined states in graphene

    SciTech Connect

    Moriyama, Satoshi; Morita, Yoshifumi; Watanabe, Eiichiro; Tsuya, Daiju

    2014-02-03

    We report an approach to confine the carriers in single-layer graphene, which leads to quantum devices with field-induced quantum confinement. We demonstrated that the Coulomb-blockade effect evolves under a uniform magnetic field perpendicular to the graphene device. Our experimental results show that field-induced quantum dots are realized in graphene, and a quantum confinement-deconfinement transition is switched by the magnetic field.

  18. Electric field-induced softening of alkali silicate glasses

    SciTech Connect

    McLaren, C.; Heffner, W.; Jain, H.; Tessarollo, R.; Raj, R.

    2015-11-02

    Motivated by the advantages of two-electrode flash sintering over normal sintering, we have investigated the effect of an external electric field on the viscosity of glass. The results show remarkable electric field-induced softening (EFIS), as application of DC field significantly lowers the softening temperature of glass. To establish the origin of EFIS, the effect is compared for single vs. mixed-alkali silicate glasses with fixed mole percentage of the alkali ions such that the mobility of alkali ions is greatly reduced while the basic network structure does not change much. The sodium silicate and lithium-sodium mixed alkali silicate glasses were tested mechanically in situ under compression in external electric field ranging from 0 to 250 V/cm in specially designed equipment. A comparison of data for different compositions indicates a complex mechanical response, which is observed as field-induced viscous flow due to a combination of Joule heating, electrolysis and dielectric breakdown.

  19. Electric field-induced softening of alkali silicate glasses

    NASA Astrophysics Data System (ADS)

    McLaren, C.; Heffner, W.; Tessarollo, R.; Raj, R.; Jain, H.

    2015-11-01

    Motivated by the advantages of two-electrode flash sintering over normal sintering, we have investigated the effect of an external electric field on the viscosity of glass. The results show remarkable electric field-induced softening (EFIS), as application of DC field significantly lowers the softening temperature of glass. To establish the origin of EFIS, the effect is compared for single vs. mixed-alkali silicate glasses with fixed mole percentage of the alkali ions such that the mobility of alkali ions is greatly reduced while the basic network structure does not change much. The sodium silicate and lithium-sodium mixed alkali silicate glasses were tested mechanically in situ under compression in external electric field ranging from 0 to 250 V/cm in specially designed equipment. A comparison of data for different compositions indicates a complex mechanical response, which is observed as field-induced viscous flow due to a combination of Joule heating, electrolysis and dielectric breakdown.

  20. Effects of hole doping by neutron irradiation of magnetic field induced electronic phase transitions in graphite

    SciTech Connect

    Singleton, John; Yaguchi, Hiroshi

    2008-01-01

    We have investigated effects of hole doping by fast-neutron irradiation on the magnetic-field induced phase transitions in graphite using specimens irradiated with fast neutrons. Resistance measurements have been done in magnetic fields of up to above 50 T and at temperatures down to about 1.5 K. The neutron irradiation creates lattice defects acting as acceptors, affecting the imbalance of the electron and hole densities and the Fermi level. We have found that the reentrant field from the field induced state back to the normal state shifts towards a lower field with hole doping, suggestive of the participation of electron subbands in the magnetic-field induced state.

  1. Kilometric Continuum Radiation

    NASA Technical Reports Server (NTRS)

    Green, James L.; Boardsen, Scott

    2006-01-01

    Kilometric continuum (KC) is the high frequency component (approximately 100 kHz to approximately 800 kHz) of nonthermal continuum (NTC). Unlike the lower frequency portion of NTC (approximately 5 kHz to approximately 100 kHz) whose source is around the dawn sector, the source of KC occurs at all magnetic local times. The latitudinal beaming of KC as observed by GEOTAIL is, for most events, restricted to plus or minus 15 degrees magnetic latitude. KC has been observed during periods of both low and strong geomagnetic activity, with no significant correlation of wave intensity with K(sub p), index. However statistically the maximum observed frequency of KC emission tends to increase with K(sub p) index, the effect is more pronounced around solar maximum, but is also detected near solar minimum. There is strong evidence that the source region of KC is from the equatorial plasmapause during periods when a portion of the plasmapause moves significantly inwards from its nominal position. Case studies have shown that KC emissions are nearly always associated with plasmaspheric notches, shoulders, and tails. There is a recent focus on trying to understand the banded frequency structure of this emission and its relationship to plasmaspheric density ducts and irregularities in the source region.

  2. Electric field induced spin-polarized current

    DOEpatents

    Murakami, Shuichi; Nagaosa, Naoto; Zhang, Shoucheng

    2006-05-02

    A device and a method for generating an electric-field-induced spin current are disclosed. A highly spin-polarized electric current is generated using a semiconductor structure and an applied electric field across the semiconductor structure. The semiconductor structure can be a hole-doped semiconductor having finite or zero bandgap or an undoped semiconductor of zero bandgap. In one embodiment, a device for injecting spin-polarized current into a current output terminal includes a semiconductor structure including first and second electrodes, along a first axis, receiving an applied electric field and a third electrode, along a direction perpendicular to the first axis, providing the spin-polarized current. The semiconductor structure includes a semiconductor material whose spin orbit coupling energy is greater than room temperature (300 Kelvin) times the Boltzmann constant. In one embodiment, the semiconductor structure is a hole-doped semiconductor structure, such as a p-type GaAs semiconductor layer.

  3. The Suicide Prevention Continuum

    PubMed Central

    Caldwell, Dawn

    2010-01-01

    The suicide prevention continuum illustrates a practical approach to the complex issue of suicide prevention. The continuum evolved from discussions with two Aboriginal communities in Atlantic Canada about suicide and the different types of interventions available. The continuum offers a framework and reference tool to differentiate between the different stages of suicide risk. It illustrates where the Aboriginal Community Youth Resilience Network (ACYRN) fits into suicide prevention and how it contributes to prevention knowledge, capacity building, and policy development. PMID:20835376

  4. Surface modifications by field induced diffusion.

    PubMed

    Olsen, Martin; Hummelgård, Magnus; Olin, Håkan

    2012-01-01

    By applying a voltage pulse to a scanning tunneling microscope tip the surface under the tip will be modified. We have in this paper taken a closer look at the model of electric field induced surface diffusion of adatoms including the van der Waals force as a contribution in formations of a mound on a surface. The dipole moment of an adatom is the sum of the surface induced dipole moment (which is constant) and the dipole moment due to electric field polarisation which depends on the strength and polarity of the electric field. The electric field is analytically modelled by a point charge over an infinite conducting flat surface. From this we calculate the force that cause adatoms to migrate. The calculated force is small for voltage used, typical 1 pN, but due to thermal vibration adatoms are hopping on the surface and even a small net force can be significant in the drift of adatoms. In this way we obtain a novel formula for a polarity dependent threshold voltage for mound formation on the surface for positive tip. Knowing the voltage of the pulse we then can calculate the radius of the formed mound. A threshold electric field for mound formation of about 2 V/nm is calculated. In addition, we found that van der Waals force is of importance for shorter distances and its contribution to the radial force on the adatoms has to be considered for distances smaller than 1.5 nm for commonly used voltages. PMID:22253894

  5. Field-induced superdiffusion and dynamical heterogeneity.

    PubMed

    Gradenigo, Giacomo; Bertin, Eric; Biroli, Giulio

    2016-06-01

    By analyzing two kinetically constrained models of supercooled liquids we show that the anomalous transport of a driven tracer observed in supercooled liquids is another facet of the phenomenon of dynamical heterogeneity. We focus on the Fredrickson-Andersen and the Bertin-Bouchaud-Lequeux models. By numerical simulations and analytical arguments we demonstrate that the violation of the Stokes-Einstein relation and the field-induced superdiffusion observed during a long preasymptotic regime have the same physical origin: while a fraction of probes do not move, others jump repeatedly because they are close to local mobile regions. The anomalous fluctuations observed out of equilibrium in the presence of a pulling force ε,σ_{x}^{2}(t)=〈x_{ε}^{2}(t)〉-〈x_{ε}(t)〉^{2}∼t^{3/2}, which are accompanied by the asymptotic decay α_{ε}(t)∼t^{-1/2} of the non-Gaussian parameter from nontrivial values to zero, are due to the splitting of the probes population in the two (mobile and immobile) groups and to dynamical correlations, a mechanism expected to happen generically in supercooled liquids. PMID:27415189

  6. Surface Modifications by Field Induced Diffusion

    PubMed Central

    Olsen, Martin; Hummelgård, Magnus; Olin, Håkan

    2012-01-01

    By applying a voltage pulse to a scanning tunneling microscope tip the surface under the tip will be modified. We have in this paper taken a closer look at the model of electric field induced surface diffusion of adatoms including the van der Waals force as a contribution in formations of a mound on a surface. The dipole moment of an adatom is the sum of the surface induced dipole moment (which is constant) and the dipole moment due to electric field polarisation which depends on the strength and polarity of the electric field. The electric field is analytically modelled by a point charge over an infinite conducting flat surface. From this we calculate the force that cause adatoms to migrate. The calculated force is small for voltage used, typical 1 pN, but due to thermal vibration adatoms are hopping on the surface and even a small net force can be significant in the drift of adatoms. In this way we obtain a novel formula for a polarity dependent threshold voltage for mound formation on the surface for positive tip. Knowing the voltage of the pulse we then can calculate the radius of the formed mound. A threshold electric field for mound formation of about 2 V/nm is calculated. In addition, we found that van der Waals force is of importance for shorter distances and its contribution to the radial force on the adatoms has to be considered for distances smaller than 1.5 nm for commonly used voltages. PMID:22253894

  7. "Caught in the Continuum"

    ERIC Educational Resources Information Center

    Nisbet, Jan

    2004-01-01

    This article presents a critical review of Steve Taylor's Caught in the Continuum. Steve Taylor describes the flawed thinking associated with the "least restrictive environment" (LRE) principle and the related continuum model of human services that linked severity of disability with segregation, and required improvements in skills as a…

  8. Continuum radiation at Uranus

    SciTech Connect

    Kurth, W.S.; Gurnett, D.A. ); Desch, M.D. )

    1990-02-01

    Uranus has proven to be a radio source of remarkable complexity with as many as six distinctly different types of emission. One Uranian radio emission which has thus far escaped attention is an analog of continuum radiation at Earth, Jupiter, and Saturn. The emission is found to be propagating in the ordinary mode in the range of one to a few kHz on the inbound leg of the Voyager 2 encounter, shortly after the magnetopause crossing. The continuum radiation spectrum at Uranus also includes bands with frequencies as high as 12 kHz or greater on both the inbound and outbound legs. The Uranian continuum radiation is notably weak, making it more like that detected at Saturn than the extremely intense Jovian continuum radiation. The Uranian emission shows some evidence for narrow-band components lying in the same frequency regime as the continuum, completing the analogy with the other planets, which also show narrow-band components superimposed on the continuum spectrum. The authors argue that the low intensity of the Uranian continuum is most likely related to the lack of a density cavity within the Uranian magnetosphere that is deep relative to the solar wind plasma density.

  9. Kernel Continuum Regression.

    PubMed

    Lee, Myung Hee; Liu, Yufeng

    2013-12-01

    The continuum regression technique provides an appealing regression framework connecting ordinary least squares, partial least squares and principal component regression in one family. It offers some insight on the underlying regression model for a given application. Moreover, it helps to provide deep understanding of various regression techniques. Despite the useful framework, however, the current development on continuum regression is only for linear regression. In many applications, nonlinear regression is necessary. The extension of continuum regression from linear models to nonlinear models using kernel learning is considered. The proposed kernel continuum regression technique is quite general and can handle very flexible regression model estimation. An efficient algorithm is developed for fast implementation. Numerical examples have demonstrated the usefulness of the proposed technique. PMID:24058224

  10. The Aquatic Systems Continuum

    NASA Astrophysics Data System (ADS)

    Winter, T. C.

    2004-12-01

    The Aquatic Systems Continuum is a proposed framework for interrelating the physical, chemical, and biological characteristics of aquatic ecosystems. The continuum can be represented by a three-dimensional matrix that relates aquatic ecosystems to their position within hydrologic flow paths (x-axis, a spatial dimension) and their response to climate variability (y-axis). The z-axis describes the structure of biological communities as they relate to the hydrological conditions defined by the x and y axes. The concept is an extension of the Wetland Continuum that was derived from field studies of a prairie pothole wetland complex in North Dakota. At that site, the hydrologic continuum in space is defined by ground-water flow systems. The wetlands are surface-water expressions of larger ground-water watersheds, in which wetlands serve recharge, flow-through, and discharge functions with respect to ground water. The water balance of the wetlands is dominated by precipitation and evaporation. However, the interaction of the wetlands with ground water, although a small part of their water budget, provides the primary control on delivery of major solutes to and from the wetlands. Having monitored these wetlands for more than 25 years, during which time the site had a complete range of climate conditions from drought to deluge, the response of the aquatic communities to a wide variety of climate conditions has been well documented. The Aquatic Systems Continuum extends the model provided by the Wetland Continuum to include rivers and their interaction with ground water. As a result, both ground water and surface water are used to describe terrestrial water flows for all types of aquatic ecosystems. By using the Aquatic Systems Continuum to describe the hydrologic flow paths in all types of terrain, including exchange with atmospheric water, it is possible to design studies, monitoring programs, and management plans for nearly any type of aquatic ecosystem.

  11. Field-induced dynamical properties of the XXZ model on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Maksimov, Pavel; Chernyshev, Alexander

    We present a comprehensive 1 / S study of the field-induced dynamical properties of the nearest-neighbor XXZ antiferromagnet on a honeycomb lattice using the formalism of the nonlinear spin-wave theory developed for this model. External magnetic field controls spin frustration in the system and induces non-collinearity of the spin structure, which is essential for the two-magnon decay processes. Our results include an intriguing field-evolution of the regions of the Brillouin zone where decays of spin excitations are prominent, a thorough analysis of the singularities in the magnon spectra due to coupling to the two-magnon continuum, the asymptotic behavior of the decay rates near high-symmetry points, and inelastic neutron-scattering spin-spin structure factor obtained in the leading 1 / S order. Supported by DOE.

  12. Electric-Field Induced Activation of Dark Excitonic States in Carbon Nanotubes.

    PubMed

    Uda, T; Yoshida, M; Ishii, A; Kato, Y K

    2016-04-13

    Electrical activation of optical transitions to parity-forbidden dark excitonic states in individual carbon nanotubes is reported. We examine electric-field effects on various excitonic states by simultaneously measuring photocurrent and photoluminescence. As the applied field increases, we observe an emergence of new absorption peaks in the excitation spectra. From the diameter dependence of the energy separation between the new peaks and the ground state of E11 excitons, we attribute the peaks to the dark excited states which became optically active due to the applied field. Field-induced exciton dissociation can explain the photocurrent threshold field, and the edge of the E11 continuum states has been identified by extrapolating to zero threshold. PMID:26999284

  13. Examining the Psychosis Continuum

    PubMed Central

    DeRosse, Pamela; Karlsgodt, Katherine H.

    2015-01-01

    The notion that psychosis may exist on a continuum with normal experience has been proposed in multiple forms throughout the history of psychiatry. However, in recent years there has been an exponential increase in efforts aimed at elucidating what has been termed the ‘psychosis continuum’. The present review seeks to summarize some of the more basic characteristics of this continuum and to present some of the recent findings that provide support for its validity. While there is still considerable work to be done, the emerging data holds considerable promise for advancing our understanding of both risk and resilience to psychiatric disorders characterized by psychosis. PMID:26052479

  14. The Continuum of Listening

    ERIC Educational Resources Information Center

    Rud, A. G.; Garrison, Jim

    2007-01-01

    The distinction between "apophatic" and "cataphatic" listening is defined and analyzed. "Apophatic" listening is more or less devoid of cognitivist claims, whereas "cataphatic" listening involves cognition and questioning. Many of the papers in this volume are discussed along the continuum determined by these two types of listening.…

  15. Teacher Education: A Continuum.

    ERIC Educational Resources Information Center

    Momentum, 1990

    1990-01-01

    This document is a theme issue of the journal "Momentum", devoted to the topic "Teacher Education: A Continuum." It contains 15 articles in the central section and 7 articles in a special section subtitled "The Multicultural Challenge." The following articles on the central theme are presented: (1) "Closing the Gap" concerns fusing the college and…

  16. The Creativity Continuum

    ERIC Educational Resources Information Center

    Walling, Donovan R.

    2009-01-01

    Children are innately creative, and the youngest often are the most original because they have yet to be influenced by the creativity of others. One way to think of creative expression is as a continuum. At one end is originality, or the creation of something wholly new, "original." At the other end is replication, or the re-creation of something…

  17. Extragalactic continuum sources.

    NASA Astrophysics Data System (ADS)

    Valtaoja, E.

    1989-09-01

    As with most other high-frequency radio telescopes, continuum work occupies only a small fraction - currently about 5% - of SEST's total time. The importance of these observations in increasing our understanding of quasars and other extragalactic sources is, however, large.

  18. Electric-field Induced Microdynamics of Charged Rods

    NASA Astrophysics Data System (ADS)

    Kang, Kyongok

    2014-12-01

    Electric-field induced phase/state transitions are observed in AC electric fields with small amplitudes and low frequencies in suspensions of charged fibrous viruses (fd), which are model systems for highly charged rod-like colloids. Texture- and particle-dynamics in these field-induced states, and on crossing transition lines, are explored by image time-correlation and dynamic light scattering, respectively. At relatively low frequencies, starting from a system within the isotropic-nematic coexistence region, a transition from a nematic to a chiral nematic is observed, as well as a dynamical state where nematic domains melt and reform. These transitions are preliminary due to field-induced dissociation/association of condensed ions. At higher frequencies a uniform state is formed that is stabilized by hydrodynamic interactions through field-induced electro-osmotic flow where the rods align along the field direction. There is a point in the field-amplitude versus frequency plane where various transition lines meet. This point can be identified as a “non-equilibrium critical point”, in the sense that a length scale and a time scale diverge on approach of that point. The microscopic dynamics exhibits discontinuities on crossing transition lines that were identified independently by means of image and signal correlation spectroscopy.

  19. A study of discrete and continuum joint modeling techniques

    SciTech Connect

    Jung, J.; Brown, S.R.

    1992-05-01

    This paper presents the results of a numerical and experimental study in which finite element and discrete element techniques were used to analyze a layered polycarbonate plate model subjected to uniaxial compression. Also, the two analysis techniques were used to compute the response of an eight meter diameter drift in jointed-rock. The drift was subjected to in-situ and far-field induced thermal stresses. The finite element analyses used a continuum rock model to represent the jointed-rock. A comparison of the analyses showed that the finite element continuum joint model consistently predicted less joint slippage than did the discrete element analyses, although far-field displacements compared well.

  20. The Response Continuum

    SciTech Connect

    Caltagirone, Sergio; Frincke, Deborah A.

    2005-06-17

    Active response is a sequence of actions per- formed speci¯cally to mitigate a detected threat. Response decisions always follow detection: a decision to take `no ac- tion' remains a response decision. However, active response is a complex subject that has received insu±cient formal attention. To facilitate discussion, this paper provides a framework that proposes a common de¯nition, describes the role of response and the major issues surrounding response choices, and ¯nally, provides a model for the process of re- sponse. This provides a common starting point for discus- sion of the full response continuum as an integral part of contemporary computer security.

  1. Field-induced dynamical properties of the XXZ model on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Maksimov, P. A.; Chernyshev, A. L.

    2016-01-01

    We present a comprehensive 1 /S study of the field-induced dynamical properties of the nearest-neighbor XXZ antiferromagnet on a honeycomb lattice using the formalism of nonlinear spin-wave theory developed for this model. The external magnetic field controls spin frustration in the system and induces noncollinearity of the spin structure, which is essential for the two-magnon decay processes. Our results include an intriguing field-evolution of the regions of the Brillouin zone wherein decays of spin excitations are prominent, a detailed classification of the decay channels involving magnons from both excitation branches, and a thorough analysis of the singularities in the magnon spectra due to coupling to the two-magnon continuum, all of which are illustrated for several field and anisotropy values. We highlight a number of features related to either the non-Bravais nature of the lattice or the existence of the Dirac-like points in the spectrum. In addition, the asymptotic behavior of the decay rates near high-symmetry points is analyzed in detail. The inelastic neutron-scattering spin-spin structure factor is obtained in the leading 1 /S order and is shown to exhibit qualitatively distinct fingerprints of the decay-induced magnon dynamics such as quasiparticle peaks broadened by decays and strong spectral weight redistribution.

  2. Deuterium NMR investigations of field-induced director alignment in nematic liquid crystals.

    PubMed

    Sugimura, Akihiko; Luckhurst, Geoffrey R

    2016-05-01

    There have been many investigations of the alignment of nematic liquid crystals by either a magnetic and/or an electric field. The basic features of the important hydrodynamic processes for low molar mass nematics have been characterized for the systems in their equilibrium and non-equilibrium states. These have been created using electric and magnetic fields to align the director and deuterium nuclear magnetic resonance ((2)H NMR) spectroscopy has been used to explore this alignment. Theoretical models based on continuum theory have been developed to complement the experiments and found to describe successfully the static and the dynamic phenomena observed. Such macroscopic behaviour has been investigated with (2)H NMR spectroscopy, in which an electric field in addition to the magnetic field of the spectrometer is used to rotate the director and produce a non-equilibrium state. This powerful technique has proved to be especially valuable for the investigation of nematic liquid crystals. Since the quadrupolar splitting for deuterons observed in the liquid crystal phase is determined by the angle between the director and the magnetic field, time-resolved and time-averaged (2)H NMR spectroscopies can be employed to investigate the dynamic director alignment process in a thin nematic film following the application or removal of an electric field. In this article, we describe some seminal studies to illustrate the field-induced static and dynamic director alignment for low molar mass nematics. PMID:27247284

  3. Magnetic field induced differential neutron phase contrast imaging

    SciTech Connect

    Strobl, M.; Treimer, W.; Walter, P.; Keil, S.; Manke, I.

    2007-12-17

    Besides the attenuation of a neutron beam penetrating an object, induced phase changes have been utilized to provide contrast in neutron and x-ray imaging. In analogy to differential phase contrast imaging of bulk samples, the refraction of neutrons by magnetic fields yields image contrast. Here, it will be reported how double crystal setups can provide quantitative tomographic images of magnetic fields. The use of magnetic air prisms adequate to split the neutron spin states enables a distinction of field induced phase shifts and these introduced by interaction with matter.

  4. Field induced spin chirality and chirality switching in magnetic multilayers

    NASA Astrophysics Data System (ADS)

    Tartakovskaya, Elena V.

    2015-05-01

    The physical origin of the field-induced spin chirality experimentally observed in rare earth multilayers is determined. It is shown that the effect is possible due to the interplay between solid-state exchange interactions (the Ruderman-Kittel-Kasuya-Yosida and the Dsyaloshinsky-Moriya interactions), the external magnetic field and a special confinement of magnetic constituents. The presented model describes a certain temperature dependence of the chirality factor in agreement with experimental data and opens a new way to design nanostructured objects with predicted handedness.

  5. Relativistic Continuum Shell Model

    NASA Astrophysics Data System (ADS)

    Grineviciute, Janina; Halderson, Dean

    2011-04-01

    The R-matrix formalism of Lane and Thomas has been extended to the relativistic case so that the many-coupled channels problem may be solved for systems in which binary breakup channels satisfy a relative Dirac equation. The formalism was previously applied to the relativistic impulse approximation RIA and now we applied it to Quantum Hadrodynamics QHD in the continuum Tamm-Dancoff approximation TDA with the classical meson fields replaced by one-meson exchange potentials. None of the published QHD parameters provide a decent fit to the 15 N + p elastic cross section. The deficiency is also evident in inability of the QHD parameters with the one meson exchange potentials to reproduce the QHD single particle energies. Results with alternate parameters sets are presented. A. M. Lane and R. G. Thomas, R-Matrix Theory of Nuclear Reactions, Reviews of Modern Physics, 30 (1958) 257

  6. Signatures of field-induced intramolecular quantum interference in high-order harmonic generation by laser-irradiated homonuclear diatomics

    NASA Astrophysics Data System (ADS)

    Usachenko, Vladimir; Kim, Vyacheslav; Pyak, Pavel

    2015-05-01

    We report about the results of our theoretical study of the strong-field phenomenon of high-order harmonic generation (HHG) in homonuclear diatomics H2+ andH2 irradiated by a high-intensity laser field of mid-infrared wavelengths corresponding to intermediate values of the so-called Keldysh parameter (γ <= 1). The problem is addressed within the length-gauge (LG) formulation of strong-field approximation (SFA) additionally exploiting the density-functional-theory (DFT) method for numerical composition of initial (laser-free) molecular state using the routines of GAUSSIAN-03 code. The results of our present LG-VGA calculation well reproduce a pronounced interference-related minimum arising in high-frequency region of respective molecular HHG spectra and suggesting clear signatures of the field-induced intramolecular interference corresponding to photoelectron emission to intermediate continuum states from different atomic centers.

  7. Magnetic-field-induced liquid metal droplet manipulation

    NASA Astrophysics Data System (ADS)

    Kim, Daeyoung; Lee, Jeong-Bong

    2015-01-01

    We report magnetic-field-induced liquid metal droplet on-demand manipulation by coating a liquid metal with ferromagnetic materials. The gallium-based liquid metal alloy has a challenging drawback that it is instantly oxidized in ambient air, resulting in surface wetting on most surfaces. When the oxidized surface of the droplet is coated with ferromagnetic materials, it is non-wettable and can be controlled by applying an external magnetic field. We coated the surface of a liquid metal droplet with either an electroplated CoNiMnP layer or an iron (Fe) particle by simply rolling the liquid metal droplet on an Fe particle bed. For a paper towel, the minimum required magnetic flux density to initiate movement of the ~8 μL Fe-particle-coated liquid metal droplet was 50 gauss. Magnetic-field-induced liquid metal droplet manipulation was investigated under both horizontal and vertical magnetic fields. Compared to the CoNiMnP-electroplated liquid metal droplet, the Fe-particle-coated droplet could be well controlled because Fe particles were uniformly coated on the surface of the droplet. With a maximum applied magnetic flux density of ~1,600 gauss, the CoNiMnP layer on the liquid metal broke down, resulting in fragmentation of three smaller droplets, and the Fe particle was detached from the liquid metal surface and was re-coated after the magnetic field had been removed.

  8. Calibration of Electric Field Induced Energy Level Shifts in Argon

    NASA Astrophysics Data System (ADS)

    Hebner, Greg

    1999-10-01

    Argon is a commonly used gas in a number of discharges. As such it is an ideal candidate for spectroscopic based electric field measurements within the sheath and bulk discharge regions. Recently, measurements demonstrated the use of the Stark induced shifts of high lying energy levels in Argon to make spatially and temporally resolved electric field measurements [1]. However, that method relied on the cross calibration of known and calculable shifts in helium discharges to calibrate, in-situ, the energy level shifts in Argon. This poster shows the use of an atomic beam system to calibrate the electric field induced shift of high lying energy levels directly. In addition, data on very high lying argon levels, up to the 20 F manifold, were obtained. Comparison of our electric field induced energy level shift calibration curves with previous work will be shown. The possibility of using this system to calibrate energy level shifts in other gases of technological interest to the microelectronics and lighting industry will be discussed. [1]. J. B. Kim, K. Kawamura, Y. W. Choi, M. D. Bowden, K. Muraoka and V. Helbig, IEEE Transactions on Plasma Science, 26(5), 1556 (1998). This work was performed at Sandia National Laboratories and supported by the United States Department of Energy (DE-AC04-94AL85000).

  9. The Paranoid-Depressive Continuum

    ERIC Educational Resources Information Center

    Johnson, Betty J.

    1977-01-01

    Few investigators have attempted to lay a conceptual base for comparative studies of paranoia and depression within a single general framework. The paranoid-depressive continuum is an attempt to develop such a framework. (Author)

  10. The Intraprofessional Continuum and Cleft.

    PubMed

    Jensen, Clyde B

    2016-08-01

    The continuum cleft is a costly and precarious gap that divides professions on the health professions' continuum. It is an interprofessional phenomenon that is encouraged because health care professions protect their members in professional silos and isolate competing professions in professional cysts. This article uses case studies of the allopathic, osteopathic, naturopathic, and chiropractic professions to contemplate the existence, consequences, and possible mitigation of intraprofessional silos, cysts, and clefts. PMID:27574493

  11. Magnetic-Field Induced Diffraction Patterns from Ferrofluids

    NASA Astrophysics Data System (ADS)

    Rablau, Corneliu; Vaishnava, Prem; Lawes, Gavin; Naik, Ratna

    2011-04-01

    Ferrofluids are stable colloidal suspensions of superparamagnetic nanoparticles in a carrier liquid. We report studies of magneto-optic properties of two ferrofluid systems consisting of tetramethyl-ammonium-hydroxide (TMAH)-coated and of dextran-coated Fe3O4 nanoparticles of nominal sizes of 6 nm and 12 nm respectively suspended in water. Both samples showed superparamagnetic behavior. The static and time-dependent DC-magnetic-field-induced light scattering patterns produced by two orthogonal He-Ne laser beams passing through the ferrofluid samples revealed significant different optical signatures for the two surfactants. Notably, in contrast to the linear diffraction pattern produced by TMAH-coated nanoparticles, a circular diffraction pattern is reported -- for the first time -- in the dextran-coated ferrofluid.

  12. Field-Induced Negative Differential Spin Lifetime in Silicon

    NASA Astrophysics Data System (ADS)

    Li, Jing; Qing, Lan; Dery, Hanan; Appelbaum, Ian

    2012-04-01

    We show that the electric-field-induced thermal asymmetry between the electron and lattice systems in pure silicon substantially impacts the identity of the dominant spin relaxation mechanism. Comparison of empirical results from long-distance spin transport devices with detailed Monte Carlo simulations confirms a strong spin depolarization beyond what is expected from the standard Elliott-Yafet theory even at low temperatures. The enhanced spin-flip mechanism is attributed to phonon emission processes during which electrons are scattered between conduction band valleys that reside on different crystal axes. This leads to anomalous behavior, where (beyond a critical field) reduction of the transit time between spin-injector and spin-detector is accompanied by a counterintuitive reduction in spin polarization and an apparent negative spin lifetime.

  13. Electric field induced second harmonic generation with and without fringes

    NASA Astrophysics Data System (ADS)

    Meshulam, G.; Berkovic, G.; Kotler, Z.; Sa'ar, A.

    2000-09-01

    Electric field induced second harmonic generation (EFISH) is a well-known technique to measure the first hyperpolarizability (β) of organic molecules in solution. The characteristic experimental output is observation of oscillatory fringes of second harmonic radiation as the solution path length is changed and evaluation of β from the fringe amplitude. We present two different cases where even in the absence of these characteristic fringes β may still be evaluated: first, when using absorbing materials, and second, when using broadband laser sources. The ability to determine β by EFISH under these conditions greatly enhances the ability of this technique to measure β values over a wide range of laser frequencies. Measurements of the same molecule's β values at different frequencies are reported, verifying the two-level model for the dispersion of β.

  14. Direct observations of field-induced assemblies in magnetite ferrofluids

    PubMed Central

    Mousavi, N. S. Susan

    2015-01-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05–0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity. PMID:25829566

  15. Direct observations of field-induced assemblies in magnetite ferrofluids

    NASA Astrophysics Data System (ADS)

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  16. Direct observations of field-induced assemblies in magnetite ferrofluids

    SciTech Connect

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-14

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05–0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  17. Field-induced periodic distortions in a nematic liquid crystal: deuterium NMR study and theoretical analysis.

    PubMed

    Sugimura, A; Zakharov, A V

    2011-08-01

    The peculiarities in the dynamic of the director reorientation in a liquid crystal (LC) film under the influence of the electric E field directed at an angle α to the magnetic B field have been investigated both experimentally and theoretically. Time-resolved deuterium NMR spectroscopy is employed to investigate the field-induced director dynamics. Analysis of the experimental results, based on the predictions of hydrodynamic theory including both the director motion and fluid flow, provides an evidence for the appearance of the spatially periodic patterns in 4-n-pentyl-4'-cyanobiphenyl LC film, at the angles α>60∘, in response to the suddenly applied E. These periodic distortions produce a lower effective rotational viscosity. This gives a faster response of the director rotation than for a uniform mode, as observed in our NMR experiment. PMID:21929001

  18. Thermodynamically consistent continuum dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Hochrainer, Thomas

    2016-03-01

    Dislocation based modeling of plasticity is one of the central challenges at the crossover of materials science and continuum mechanics. Developing a continuum theory of dislocations requires the solution of two long standing problems: (i) to represent dislocation kinematics in terms of a reasonable number of variables and (ii) to derive averaged descriptions of the dislocation dynamics (i.e. material laws) in terms of these variables. The kinematic problem (i) was recently solved through the introduction of continuum dislocation dynamics (CDD), which provides kinematically consistent evolution equations of dislocation alignment tensors, presuming a given average dislocation velocity (Hochrainer, T., 2015, Multipole expansion of continuum dislocations dynamics in terms of alignment tensors. Philos. Mag. 95 (12), 1321-1367). In the current paper we demonstrate how a free energy formulation may be used to solve the dynamic closure problem (ii) in CDD. We do so exemplarily for the lowest order CDD variant for curved dislocations in a single slip situation. In this case, a thermodynamically consistent average dislocation velocity is found to comprise five mesoscopic shear stress contributions. For a postulated free energy expression we identify among these stress contributions a back-stress term and a line-tension term, both of which have already been postulated for CDD. A new stress contribution occurs which is missing in earlier CDD models including the statistical continuum theory of straight parallel edge dislocations (Groma, I., Csikor, F.F., Zaiser, M., 2003. Spatial correlations and higher-order gradient terms in a continuum description of dislocation dynamics. Acta Mater. 51, 1271-1281). Furthermore, two entirely new stress contributions arise from the curvature of dislocations.

  19. Magnetic field induced motion behavior of gas bubbles in liquid

    PubMed Central

    Wang, Keliang; Pei, Pucheng; Pei, Yu; Ma, Ze; Xu, Huachi; Chen, Dongfang

    2016-01-01

    The oxygen evolution reaction generally exists in electrochemical reactions. It is a ubiquitous problem about how to control the motion of oxygen bubbles released by the reaction. Here we show that oxygen bubbles during oxygen evolution reaction exhibit a variety of movement patterns in the magnetic field, including directional migration and rotational motion of oxygen bubbles when the magnet in parallel with the electrode, and exclusion movement of oxygen bubbles when the magnet perpendicular to the electrode. The results demonstrate that the direction of oxygen bubbles movement is dependent upon the magnet pole near the electrode, and the kinetics of oxygen bubbles is mainly proportional to intensity of the electromagnetic field. The magnetic-field induced rotational motion of oxygen bubbles in a square electrolyzer can increase liquid hydrodynamics, thus solve the problems of oxygen bubbles coalescence, and uneven distribution of electrolyte composition and temperature. These types of oxygen bubbles movement will not only improve energy saving and metal deposition for energy storage and metal refinery, but also propel object motion in application to medical and martial fields. PMID:26867515

  20. Field-induced negative differential spin lifetime in silicon

    NASA Astrophysics Data System (ADS)

    Li, Jing; Qing, Lan; Dery, Hanan; Appelbaum, Ian

    2012-02-01

    Using experimental measurements of spin transport in undoped silicon, we show that the electric field-induced thermal asymmetry between the electron and lattice systems substantially impacts the identity of the dominant spin relaxation mechanism. In contrast to the Elliott-Yafet theory where intraband phonon absorption leads to spin relaxation, here we induce phonon emission during which electrons are scattered between conduction band valleys that reside on different crystal axes. This leads to anomalous behavior, where reduction of the transit time between spin-injector and spin-detector with larger electric field is accompanied by a counterintuitive reduction in spin polarization and an apparent negative spin lifetime.[4pt] Work at UMD is supported by the Office of Naval Research and the National Science Foundation. We acknowledge the support of the Center for Nanophysics and Advanced Materials and Maryland NanoCenter and its FabLab. Work at UR is supported by AFOSR and NSF (No. FA9550-09-1-0493 and No. DMR 1124601).

  1. Impurities in magnetic-field-induced Luttinger liquid

    NASA Astrophysics Data System (ADS)

    Tsai, Shan-Wen; Maslov, Dmitrii L.; Glazman, Leonid I.

    2001-03-01

    It has been shown recently(C. Biagini, D. L. Maslov, M. Yu. Reizer and L. I. Glazman, `` Magnetic-field-induced Luttinger liquid''), cond-mat/0006407. that a strong magnetic field applied to a bulk metal may induce a Luttinger liquid phase. This is a consequence of the reduced effective dimensionality of charge carriers from 3D to 1D, an effect which is most pronounced in the ultra-quantum limit, when only the lowest Landau level remains populated. We study the effect of impurities in this system. For the case of a point impurity, the calculation of the scattering cross section at a single impurity can be mapped exactly to a 1D problem of tunneling conductance through a barrier for interacting electrons, solved by Yue et al.(D. Yue, L. I. Glazman and K. A. Matveev, Phys. Rev. B 49) (1994) 1966.. Using this mapping, we find that the longitudinal (ɛ=+1) and transverse (ɛ=-1) Drude conductivities exhibit the scaling laws σ_ɛ∝ T^ɛα, where α=2e^2|lnκl_B|/π v_F, and vF and κ are the B-dependent Fermi velocity and screening wavevector, respectively; lB is the magnetic length. The physical reason for such a behavior of the conductivity is the almost 1D form of the Friedel oscillation around a single point impurity in the strong magnetic field.

  2. Deconstructing field-induced ketene isomerization through Lagrangian descriptors.

    PubMed

    Craven, Galen T; Hernandez, Rigoberto

    2016-02-01

    The time-dependent geometrical separatrices governing state transitions in field-induced ketene isomerization are constructed using the method of Lagrangian descriptors. We obtain the stable and unstable manifolds of time-varying transition states as dynamic phase space objects governing configurational changes when the ketene molecule is subjected to an oscillating electric field. The dynamics of the isomerization reaction are modeled through classical trajectory studies on the Gezelter-Miller potential energy surface and an approximate dipole moment model which is coupled to a time-dependent electric field. We obtain a representation of the reaction geometry, over varying field strengths and oscillation frequencies, by partitioning an initial phase space into basins labeled according to which product state is reached at a given time. The borders between these basins are in agreement with those obtained using Lagrangian descriptors, even in regimes exhibiting chaotic dynamics. Major outcomes of this work are: validation and extension of a transition state theory framework built from Lagrangian descriptors, elaboration of the applicability for this theory to periodically- and aperiodically-driven molecular systems, and prediction of regimes in which isomerization of ketene and its derivatives may be controlled using an external field. PMID:26778728

  3. Magnetic field induced motion behavior of gas bubbles in liquid.

    PubMed

    Wang, Keliang; Pei, Pucheng; Pei, Yu; Ma, Ze; Xu, Huachi; Chen, Dongfang

    2016-01-01

    The oxygen evolution reaction generally exists in electrochemical reactions. It is a ubiquitous problem about how to control the motion of oxygen bubbles released by the reaction. Here we show that oxygen bubbles during oxygen evolution reaction exhibit a variety of movement patterns in the magnetic field, including directional migration and rotational motion of oxygen bubbles when the magnet in parallel with the electrode, and exclusion movement of oxygen bubbles when the magnet perpendicular to the electrode. The results demonstrate that the direction of oxygen bubbles movement is dependent upon the magnet pole near the electrode, and the kinetics of oxygen bubbles is mainly proportional to intensity of the electromagnetic field. The magnetic-field induced rotational motion of oxygen bubbles in a square electrolyzer can increase liquid hydrodynamics, thus solve the problems of oxygen bubbles coalescence, and uneven distribution of electrolyte composition and temperature. These types of oxygen bubbles movement will not only improve energy saving and metal deposition for energy storage and metal refinery, but also propel object motion in application to medical and martial fields. PMID:26867515

  4. Time-resolved electric-field-induced second harmonic

    NASA Astrophysics Data System (ADS)

    Meshulam, Guilia; Berkovic, Garry; Kotler, Zvi

    2001-12-01

    One limitation of using electric field induced second harmonic (EFISH) to determine the molecular first hyperpolarizability (beta) of nonlinear optical molecules lies in the fact that part of the second harmonic signal comes from the second hyperpolarizability (gamma) produced by mixing two optical fields with the DC field. In analyzing EFISH results, the second hyperpolarizability contribution of the studied molecules is generally neglected. We present a modified time resolved EFISH technique that allows us, in a single experiment, to determine separately the beta and the gamma contributions. We study para-nitro aniline dissolved in Glycerol, a highly viscous solvent, and apply the DC field via a high voltage pulse with a fast rise time of approximately 40 nsec. As a result, the orientation of the molecules under the applied electric field is slow relative to the build-up of the field, enabling us to directly measure only the DC induced second harmonic (gamma contribution), at the beginning of the HV pulse. The pure beta contribution is determined from the difference between this signal and the conventional EFISH signal at the plateau of the HV pulse. Our result confirm that the gamma contribution is indeed less than 10% of the total.

  5. Possible Electric-Field-Induced Superconducting States in Doped Silicene

    PubMed Central

    Zhang, Li-Da; Yang, Fan; Yao, Yugui

    2015-01-01

    Silicene has been synthesized recently, with experimental evidence showing possible superconductivity in the doped case. The noncoplanar low-buckled structure of this material inspires us to study the pairing symmetry of the doped system under a perpendicular external electric field. Our study reveals that the electric field induces an interesting quantum phase transition from the singlet chiral d + id′-wave superconducting phase to the triplet f-wave one. The emergence of the f-wave pairing results from the sublattice-symmetry-breaking caused by the electric field and the ferromagnetic-like intra-sublattice spin correlations at low dopings. Due to the enhanced density of states, the superconducting critical temperature of the system is enhanced by the electric field remarkably. Furthermore, we design a particular dc SQUID experiment to detect the quantum phase transition predicted here. Our results, if confirmed, will inject a new vitality to the familiar Si-based industry through adopting doped silicene as a tunable platform to study different types of exotic unconventional superconductivities. PMID:25644143

  6. Kinetics of Field-Induced Surface Patterns on PMMA.

    PubMed

    Peng, Jyun-Siang; Yang, Fuqian; Chiang, Donyau; Lee, Sanboh

    2016-05-10

    A simple model was developed to analyze the growth of a liquid pillar under the action of an electric field between two parallel electrodes. A quadratic relationship between time and the diameter of the pillar was obtained. The diameter of the pillar increases with time. Large electric field assists the growth of the liquid pillar, while a liquid with a large viscosity hinders the growth of the liquid pillar. The field-induced formation and growth of PMMA pillars on PMMA films were observed using the configuration of a parallel capacitor. Pillars of larger sizes and smaller densities were formed on thicker PMMA films than on thinner PMMA films. The root-mean-square ( https://en.wikipedia.org/wiki/Root_mean_square ) diameter of the pillars increases with the increase of the annealing time and annealing temperature. The growth behavior of the pillars can be described by an Arrhenius relation with an activation energy of 24.4 kJ/mol, suggesting that the growth of the pillars is controlled by a thermal activation process. PMID:27094160

  7. Magnetic field induced motion behavior of gas bubbles in liquid

    NASA Astrophysics Data System (ADS)

    Wang, Keliang; Pei, Pucheng; Pei, Yu; Ma, Ze; Xu, Huachi; Chen, Dongfang

    2016-02-01

    The oxygen evolution reaction generally exists in electrochemical reactions. It is a ubiquitous problem about how to control the motion of oxygen bubbles released by the reaction. Here we show that oxygen bubbles during oxygen evolution reaction exhibit a variety of movement patterns in the magnetic field, including directional migration and rotational motion of oxygen bubbles when the magnet in parallel with the electrode, and exclusion movement of oxygen bubbles when the magnet perpendicular to the electrode. The results demonstrate that the direction of oxygen bubbles movement is dependent upon the magnet pole near the electrode, and the kinetics of oxygen bubbles is mainly proportional to intensity of the electromagnetic field. The magnetic-field induced rotational motion of oxygen bubbles in a square electrolyzer can increase liquid hydrodynamics, thus solve the problems of oxygen bubbles coalescence, and uneven distribution of electrolyte composition and temperature. These types of oxygen bubbles movement will not only improve energy saving and metal deposition for energy storage and metal refinery, but also propel object motion in application to medical and martial fields.

  8. Field-Induced Magnetic Phenomena in Molecule-Based Magnets

    NASA Astrophysics Data System (ADS)

    Kmety, Carmen R.

    2001-03-01

    Understanding the relationship between the crystal structure and magnetic ordering is crucial for the design of three-dimensional molecule-based magnets with high ordering temperatures. In this talk, we introduce a novel series of molecule-based magnets consisting of transition metal ions (Mn, Fe, Co, Ni or Cu) coordinated with the organic ligand dicyanamide [N(CN)_2]^-.(J.L. Manson et al. al.), Chem. Mater. 10, 2552 (1998); S.R. Batten et al. al., Chem. Commun. (Cambridge) 1998, 439; M. Kurmoo et al. al., New J. Chem. 22, 1515 (1998). The crystal structures for all compounds are isomorphous in the paramagnetic regime as well as in the ordered state. However, the compounds with transition metal ions having six or less electrons in the 3d orbitals order as canted antiferromagnets (AFM) while the ones with seven or more electrons order as ferromagnets (FM). The spin orientation is nearly in perpendicular directions for the AFM versus FM systems.(C.R. Kmety et al. al.), Phys. Rev. B 60, 60 (1999).^,(C.R. Kmety et al. al.), Phys. Rev. B 62, 5576 (2000). An external magnetic field induces a spin rotation transition in the Mn compound and an energy-level crossing for the Fe compound.(C.R. Kmety and A.J. Epstein, National High Magnetic Field Laboratory 2000 Annual Research Review.) The possible origins of the variability of the magnetic structure for the first row transition metal ions compounds will be discussed.

  9. Submillimeter Continuum Observations of Comets

    NASA Technical Reports Server (NTRS)

    Jewitt, David

    1998-01-01

    The aim of this proposal was to study the submillimeter continuum emission from comets. The study was based mainly on the exploitation of the world's leading submillimeter telescope, the JCMT (James Clerk Maxwell Telescope) on Mauna Kea. Submillimeter wavelengths provide a unique view of cometary physics for one main reason. The cometary size distribution is such that the scattering cross-section is dominated by small dust grains, while the mass is dominated by the largest particles. Submillimeter continuum radiation samples cometary particles much larger than those sampled by more common observations at shorter (optical and infrared) wavelengths and therefore provides a nearly direct measure of the cometary dust mass.

  10. Lagrangian continuum dynamics in ALEGRA.

    SciTech Connect

    Wong, Michael K. W.; Love, Edward

    2007-12-01

    Alegra is an ALE (Arbitrary Lagrangian-Eulerian) multi-material finite element code that emphasizes large deformations and strong shock physics. The Lagrangian continuum dynamics package in Alegra uses a Galerkin finite element spatial discretization and an explicit central-difference stepping method in time. The goal of this report is to describe in detail the characteristics of this algorithm, including the conservation and stability properties. The details provided should help both researchers and analysts understand the underlying theory and numerical implementation of the Alegra continuum hydrodynamics algorithm.

  11. Calorimetric Study of Magnetic Field-Induced Phase Transitions in - Fulvalenium) -

    NASA Astrophysics Data System (ADS)

    Fortune, Nathanael Alexander

    The particular class of organic conductors known as the Bechgaard salts exhibit a variety of highly anisotropic magnetic, thermal, and electrical phenomena. At low temperatures (below 10 kelvin), the application of a strong magnetic field establishes an effectively lower-dimensional anisotropic Fermi surface, as manifested in a variety of quasi one dimensional and quasi two dimensional thermodynamic and transport properties. Most dramatically, an increasing magnetic field--after suppression of superconductivity, induces a second order phase transition from a metallic to a spin density wave semimetal, followed by a series of first order phase transitions between density wave semimetallic states. This thesis concerns the thermodynamic nature of the low temperature magnetic field induced phase transitions in the Bechgaard charge-transfer salt (TMTSF)2-Cl(O)4. Presented here are the first measurements of the specific heat in magnetic fields up to 30 tesla, as well as the design and construction of a small sample calorimeter capable of operating at dilution refrigerator temperatures in the challenging environment of the high field resistive Bitter magnets. From transport measurements, the existence of a magnetic field induced reentrance into the metallic state has previously been inferred. In this thesis, the unambiguous bulk thermodynamic character of the reentrance is calorimetrically demonstrated. The behavior of the electronic specific heat at the reentrant transition is shown to be consistent with magnetic field enhanced localization. Additionally, quantum oscillations in the high field semimetallic state and the presence of additional structure above the reentrant field are observed. Although these oscillations have also been observed in magnetoresistance and magnetization, the magnitude of the oscillations in the specific heat calls into question all known models for the physical origin of these oscillations.

  12. PAD in women: the ischemic continuum.

    PubMed

    Pollak, Amy West

    2015-06-01

    Lower extremity peripheral arterial disease (PAD) is part of the ischemic continuum of atherosclerotic vascular disease and is associated with an increased risk of myocardial infarction, stroke, and cardiovascular death. Compared to men, women with PAD are more likely to have asymptomatic disease or atypical symptoms. PAD in women is associated with decreased exercise capacity, reduced quality of life, increased risk of depression, as well as a greater risk of acute cardiovascular events and cardiovascular mortality than male counterparts. Ensuring an appropriate diagnosis of women with PAD offers an opportunity to begin risk factor modification therapy, improve walking capacity and make a timely referral for revascularization if needed. It is critical to highlight the sex-based disparities in lower extremity PAD so that we may work to improve outcomes for women with PAD. PMID:25939674

  13. A Math Continuum, Part D.

    ERIC Educational Resources Information Center

    Zander, Del; And Others

    Evaluation sheets and developmental checklists, prepared by three special education departments, are provided to facilitate continuous measurement of student progress in elementary school mathematics. One hundred forty-three objectives are given, and each is followed by a continuum-oriented set of worksheet-type pages on mathematics skills. The…

  14. Population transfer through the continuum

    SciTech Connect

    Nakajima, T.; Elk, M.; Zhang, J.; Lambropoulos, P. Foundation of Research and Technology Hellas, Institute of Electronic Structure and Laser and Department of Physics, University of Crete, P.O. Box 1527, Heraklion 711 10, Crete Department of Physics, University of Southern California, Los Angeles, California 90089-0484 )

    1994-08-01

    We show that complete population transfer is not in general possible through continuum intermediate states. We present a formal theoretical argument and supporting numerical results. In addition, the behavior of the system is compared with the well-known [Lambda] system.

  15. Parameter identification in continuum models

    NASA Technical Reports Server (NTRS)

    Banks, H. T.; Crowley, J. M.

    1983-01-01

    Approximation techniques for use in numerical schemes for estimating spatially varying coefficients in continuum models such as those for Euler-Bernoulli beams are discussed. The techniques are based on quintic spline state approximations and cubic spline parameter approximations. Both theoretical and numerical results are presented.

  16. Learner Continuums and Speech Communities.

    ERIC Educational Resources Information Center

    Amastae, Jon

    1981-01-01

    A method for analyzing acquisition-like patterns in the English consonants used by Spanish-English bilinguals is presented which allows a distinction to be made between individual and group phenomena. An analysis of a bilingual community in southern Texas shows that there is a continuum of use of the standard English consonants not occurring in…

  17. High magnetic field induced changes of gene expression in arabidopsis

    PubMed Central

    Paul, Anna-Lisa; Ferl, Robert J; Meisel, Mark W

    2006-01-01

    Background High magnetic fields are becoming increasingly prevalent components of non-invasive, biomedical imaging tools (such as MRI), thus, an understanding of the molecular impacts associated with these field strengths in biological systems is of central importance. The biological impact of magnetic field strengths up to 30 Tesla were investigated in this study through the use of transgenic Arabidopsis plants engineered with a stress response gene consisting of the alcohol dehydrogenase (Adh) gene promoter driving the β-glucuronidase (GUS) gene reporter. Methods Magnetic field induced Adh/GUS activity was evaluated with histochemical staining to assess tissue specific expression and distribution, and with quantitative, spectrofluometric assays to measure degree of activation. The evaluation of global changes in the Arabidopsis genome in response to exposure to high magnetic fields was facilitated with Affymetrix Gene Chip microarrays. Quantitative analyses of gene expression were performed with quantitative real-time polymerase-chain-reaction (qRT-PCR). Results Field strengths in excess of about 15 Tesla induce expression of the Adh/GUS transgene in the roots and leaves. From the microarray analyses that surveyed 8000 genes, 114 genes were differentially expressed to a degree greater than 2.5 fold over the control. These results were quantitatively corroborated by qRT-PCR examination of 4 of the 114 genes. Conclusion The data suggest that magnetic fields in excess of 15 Tesla have far-reaching effect on the genome. The wide-spread induction of stress-related genes and transcription factors, and a depression of genes associated with cell wall metabolism, are prominent examples. The roles of magnetic field orientation of macromolecules and magnetophoretic effects are discussed as possible factors that contribute to the mounting of this response. PMID:17187667

  18. Continuum descriptions of cytoskeletal dynamics

    PubMed Central

    2013-01-01

    This tutorial presents an introduction into continuum descriptions of cytoskeletal dynamics. In contrast to discrete models in which each molecule keeps its identity, such descriptions are given in terms of averaged quantities per unit volume like the number density of a certain molecule. Starting with a discrete description for the assembly dynamics of cytoskeletal filaments, we derive the continuity equation, which serves as the basis of many continuum theories. We illustrate the use of this approach with an investigation of spontaneous cytoskeletal polymerization waves. Such waves have by now been observed in various cell types and might help to orchestrate cytoskeletal dynamics during cell spreading and locomotion. Our analysis shows how processes at the scale of single molecules, namely, the nucleation of new filaments and filament treadmilling, can lead to the spontaneous appearance of coherent traveling waves on scales spanning many filament lengths. For readers less familiar with calculus, we include an informal introduction to the Taylor expansion. PMID:24565412

  19. Differential Complexes in Continuum Mechanics

    NASA Astrophysics Data System (ADS)

    Angoshtari, Arzhang; Yavari, Arash

    2015-04-01

    We study some differential complexes in continuum mechanics that involve both symmetric and non-symmetric second-order tensors. In particular, we show that the tensorial analogue of the standard grad-curl-div complex can simultaneously describe the kinematics and the kinetics of motion of a continuum. The relation between this complex and the de Rham complex allows one to readily derive the necessary and sufficient conditions for the compatibility of displacement gradient and the existence of stress functions on non-contractible bodies.We also derive the local compatibility equations in terms of the Green deformation tensor for motions of 2D and 3D bodies, and shells in curved ambient spaces with constant curvatures.

  20. Continuum representations of cellular solids

    SciTech Connect

    Neilsen, M.K.

    1993-09-01

    Cellular materials consist of interconnected struts or plates which form cells. The struts or plates are constructed from a variety of metals, polymers, ceramics and wood products. Cellular materials are often used in impact limiters for shipping containers to protect the contents from accidental impact events. These materials exhibit a variety of complex behavior when subjected to crushing loads. This research focuses on the development of continuum representations of cellular solids that can be used in the finite element analysis of shipping container accidents. A significant portion of this work is the development of a new methodology to relate localized deformations to appropriate constitutive descriptions. This methodology provides the insight needed to select constitutive descriptions for cellular solids that capture the localized deformations that are observed experimentally. Constitutive relations are developed for two different cellular materials, aluminum honeycomb and polyurethane foam. These constitutive relations are based on plasticity and continuum damage theories. Plasticity is used to describe the permanent deformation exhibited by both aluminum honeycomb and polyurethane foam. Continuum damage is needed to capture the change in elastic parameters due to cracking of the polyurethane cell wall materials. The new constitutive description of polyurethane foam is implemented in both static and dynamic finite element codes, and analytical and numerical predictions are compared with available experimental data.

  1. Continuum radiation in planetary magnetospheres

    NASA Technical Reports Server (NTRS)

    Kurth, W. S.

    1991-01-01

    With the completion of the Voyager tour of the outer planets, radio and plasma wave instruments have executed the first survey of the wave spectra of Earth, Jupiter, Saturn, Uranus, and Neptune. One of the most notable conclusions of this survey is that there is a great deal of qualitative similarity in both the plasma wave and radio wave spectra from one magnetosphere to the next. In particular, in spite of detailed differences, most of the radio emissions at each of the planets have been tentatively classified into two primary categories. First, the most intense emissions are generally associated with the cyclotron maser instability. Second, a class of weaker emissions can be found at each of the magnetospheres which appears to be the result of conversion from intense electrostatic emissions at the upper hybrid resonance frequency into (primarily) ordinary mode radio emission. It is this second category, often referred to as nonthermal continuum radiation, which we will discuss in this review. We review the characteristics of the continuum spectrum at each of the planets, discuss the source region and direct observations of the generation of the emissions where available, and briefly describe the theories for the generation of the emissions. Over the past few years evidence has increased that the linear mode conversion of electrostatic waves into the ordinary mode can account for at least some of the continuum radiation observed. There is no definitive evidence which precludes the possibility that a nonlinear mechanism may also be important.

  2. 77 FR 45367 - Continuum of Care Homeless Assistance Grant Application; Continuum of Care Application

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-31

    ... URBAN DEVELOPMENT Continuum of Care Homeless Assistance Grant Application; Continuum of Care Application... subject proposal. Pre-established communities, called Continuums of Care (CoC), will complete the Exhibit 1 of the Continuum of Care Homeless Assistance application which collects data about the...

  3. The impact of a Continuum of Care Resident Pharmacist on heart failure readmissions and discharge instructions at a community hospital

    PubMed Central

    Backes, Andrea C

    2015-01-01

    Purpose: To examine the impact of a Continuum of Care Resident Pharmacist on (1) heart failure 30-day hospital readmissions and (2) compliance with Joint Commission Heart Failure core measure 1 at a community hospital. Methods: The Continuum of Care Network led by a Continuum of Care Resident Pharmacist was established in August 2011. The Continuum of Care Resident Pharmacist followed Continuum of Care Network patients and retrospectively collected data from August 2011 to December 2012. Thirty-day readmission rates for Continuum of Care Network heart failure patients versus non-Continuum of Care Network heart failure patients were compared and analyzed. Joint Commission Heart Failure core measure 1 compliance rates were retrospectively collected from January 2011 and compared to data after establishment of the Continuum of Care Network. Results: In all, 162 Continuum of Care Network patients and 470 non-Continuum of Care Network patients were discharged with a diagnosis of heart failure from August 2011 to December 2012. Continuum of Care Network heart failure patients had a lower 30-day all-cause readmission rate compared to non-Continuum of Care Network heart failure patients (12% versus 24%, respectively; p = 0.005). In addition, Heart Failure core measure 1 compliance rates improved from the 80th percentile to the 90th percentile after implementation of the Continuum of Care Network (p = 0.004). The top three interventions performed by the Continuum of Care Resident Pharmacist were discharge counseling (74.1%), providing a MedActionPlan™ (68.5%), and resolving medication reconciliation discrepancies (64.8%). Conclusion: The study findings suggest that a Continuum of Care Resident Pharmacist contributed to lowered heart failure readmission rates and improved Heart Failure core measure 1 compliance rates. Future randomized, controlled trials are needed to confirm these findings. PMID:26770775

  4. Continuum Theory of Retroviral Capsids

    NASA Astrophysics Data System (ADS)

    Nguyen, T. T.; Bruinsma, R. F.; Gelbart, W. M.

    2006-02-01

    We present a self-assembly phase diagram for the shape of retroviral capsids, based on continuum elasticity theory. The spontaneous curvature of the capsid proteins drives a weakly first-order transition from spherical to spherocylindrical shapes. The conical capsid shape which characterizes the HIV-1 retrovirus is never stable under unconstrained energy minimization. Only under conditions of fixed volume and/or fixed spanning length can the conical shape be a minimum energy structure. Our results indicate that, unlike the capsids of small viruses, retrovirus capsids are not uniquely determined by the molecular structure of the constituent proteins but depend in an essential way on physical constraints present during assembly.

  5. Magnetic field induced minigap in double quantum wells

    SciTech Connect

    Simmons, J.A.; Lyo, S.K.; Klem, J.F.; Harff, N.E. |

    1994-07-01

    We report discovery of a partial energy gap, or minigap, in strongly coupled double quantum wells (QWs), due to an anticrossing of the two QW dispersion curves. The anticrossing and minigap are induced by an in-plane magnetic field B{sub {parallel}}, and give rise to large distortions in the Fermi surface and density of states, including a Van Hove singularity. Sweeping B{sub {parallel}} moves the minigap through the Fermi level, with the upper and lower gap edges producing a sharp maximum and minimum in the low-temperature in-plane conductance, in agreement with theoretical calculations. The gap energy may be directly determined from the data.

  6. Buckling of graded coatings: A continuum model

    NASA Astrophysics Data System (ADS)

    Chiu, Tz-Cheng

    2000-12-01

    Requirements for the protection of hot section components in many high temperature applications such as earth-to-orbit winged planes and advanced turbine systems have led to the application of thermal barrier coatings (TBCs) that utilize ceramic coatings on metal substrates. An alternative concept to homogeneous ceramic coatings is the functionally graded materials (FGM) in which the composition of the coating is intentionally graded to improve the bonding strength and to reduce the magnitude of the residual and thermal stresses. A widely observed failure mode in such layered systems is known to be interface cracking that leads to spallation fracture. In most cases, the final stage of the failure process for a thin coating appears to be due to buckling instability under thermally or mechanically induced compressive stress. The objective of this study is to develop a solution to the buckling instability problem by using continuum elasticity rather than a structural mechanics approach. The emphasis in the solution will be on the investigation of the effect of material inhomogeneity in graded coatings on the instability load, the postbuckling behavior, and fracture mechanics parameters such as the stress intensity factors and strain energy release rate. In this analysis, a nonlinear continuum theory is employed to examine the interface crack problem. The analytical solution of the instability problem permits the study of the effect of material inhomogeneity upon the inception of buckling and establishes benchmark results for the numerical solutions of related problems. To study the postbuckling behavior and to calculate the stress intensity factors and strain energy release rate a geometrically nonlinear finite element procedure with enriched crack-tip element is developed. Both plane strain and axisymmetric interface crack problems in TBCs with either homogeneous or graded coating are then considered by using the finite element procedure. It is assumed that the

  7. Rosuvastatin along the cardiovascular continuum: from JUPITER to AURORA.

    PubMed

    Barrios, Vivencio; Escobar, Carlos

    2009-11-01

    Dyslipidemia is one of the major causes of atherosclerosis, although in the last few years an increase in cholesterol control rates has been reported. However, results from the European Action on Secondary and Primary Prevention by Intervention to Reduce Events (EUROASPIRE) surveys indicate that approximately 50% of the patients with ischemic heart disease still do not attain LDL-cholesterol goals despite the use of lipid-lowering therapy (including statins). Rosuvastatin is a new and potent statin that produces greater reductions of LDL-cholesterol when compared with other agents in this class. Furthermore, rosuvastatin provides additional benefits in the lipid profile such as increased HDL-cholesterol, and decreased triglycerides, total cholesterol, apolipoprotein B and apolipoprotein B:A-1 ratio. Cardiovascular disease is a continuum: from risk factors to subclinical organ damage and finally to overt clinical cardiovascular disease. Several trials have investigated the effects of rosuvastatin along this cardiovascular continuum. The results provided by the GALAXY program emphasize the importance of the early treatment with rosuvastatin in the cardiovascular continuum to achieve the greatest benefit. In this paper, the efficacy and safety of rosuvastatin along the cardiovascular continuum is reviewed. PMID:19900015

  8. Conductivity of continuum percolating systems

    NASA Astrophysics Data System (ADS)

    Stenull, Olaf; Janssen, Hans-Karl

    2001-11-01

    We study the conductivity of a class of disordered continuum systems represented by the Swiss-cheese model, where the conducting medium is the space between randomly placed spherical holes, near the percolation threshold. This model can be mapped onto a bond percolation model where the conductance σ of randomly occupied bonds is drawn from a probability distribution of the form σ-a. Employing the methods of renormalized field theory we show to arbitrary order in ɛ expansion that the critical conductivity exponent of the Swiss-cheese model is given by tSC(a)=(d-2)ν+max[φ,(1-a)-1], where d is the spatial dimension and ν and φ denote the critical exponents for the percolation correlation length and resistance, respectively. Our result confirms a conjecture that is based on the ``nodes, links, and blobs'' picture of percolation clusters.

  9. Micropolar continuum in spatial description

    NASA Astrophysics Data System (ADS)

    Ivanova, Elena A.; Vilchevskaya, Elena N.

    2016-06-01

    Within the spatial description, it is customary to refer thermodynamic state quantities to an elementary volume fixed in space containing an ensemble of particles. During its evolution, the elementary volume is occupied by different particles, each having its own mass, tensor of inertia, angular and linear velocities. The aim of the present paper is to answer the question of how to determine the inertial and kinematic characteristics of the elementary volume. In order to model structural transformations due to the consolidation or defragmentation of particles or anisotropic changes, one should consider the fact that the tensor of inertia of the elementary volume may change. This means that an additional constitutive equation must be formulated. The paper suggests kinetic equations for the tensor of inertia of the elementary volume. It also discusses the specificity of the inelastic polar continuum description within the framework of the spatial description.

  10. Continuum Fitting HST QSO Spectra

    NASA Technical Reports Server (NTRS)

    Tytler, David; Oliversen, Ronald J. (Technical Monitor)

    2002-01-01

    The Principal Component Analysis (PCA) method which we are using to fit and describe QSO spectra relies upon the fact that QSO continuum are generally very smooth and simple except for emission and absorption lines. To see this we need high signal-to-noise (S/N) spectra of QSOs at low redshift which have relatively few absorption lines in the Lyman-a forest. We need a large number of such spectra to use as the basis set for the PCA analysis which will find the set of principal component spectra which describe the QSO family as a whole. We have found that too few HST spectra have the required S/N and hence we need to supplement them with ground based spectra of QSOs at higher redshift. We have many such spectra and we have been working to make them suitable for this analysis. We have concentrated on this topic since 12/15/01.

  11. Field-Induced Rheology in Uniaxial and Biaxial Fields

    SciTech Connect

    MARTIN, JAMES E.

    1999-10-22

    Steady and oscillatory shear 3-D simulations of electro- and magnetorheology in uniaxial and biaxial fields are presented, and compared to the predictions of the chain model. These large scale simulations are three dimensional, and include the effect of Brownian motion. In the absence of thermal fluctuations, the expected shear thinning viscosity is observed in steady shear, and a striped phase is seen to rapidly form in a uniaxial field, with a shear slip zone in each sheet. However, as the influence of Brownian motion increases, the fluid stress decreases, especially at lower Mason numbers, and the striped phase eventually disappears, even when the fluid stress is still high. In a biaxial field, an opposite trend is seen, where Brownian motion decreases the stress most significantly at higher Mason numbers. to account for the uniaxial steady shear data they propose a microscopic chain model of the role played by thermal fluctuations on the rheology of ER and MR fluids that delineates the regimes where an applied field can impact the fluid viscosity, and gives an analytical prediction for the thermal effect. In oscillatory shear, a striped phase again appears in uniaxial field, at strain amplitudes greater than {approx} 0.15, and the presence of a shear slip zone creates strong stress nonlinearities at low strain amplitudes. In a biaxial field, a shear slip zone is not created, and so the stress nonlinearities develop only at expected strain amplitudes. The nonlinear dynamics of these systems is shown to be in good agreement with the Kinetic Chain Model.

  12. Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals.

    PubMed

    Śliwa, I; Jeżewski, W; Kuczyński, W

    2016-01-01

    Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples. PMID:26871130

  13. Electric-field-induced interfacial instabilities of a soft elastic membrane confined between viscous layers

    NASA Astrophysics Data System (ADS)

    Dey, Mohar; Bandyopadhyay, Dipankar; Sharma, Ashutosh; Qian, Shizhi; Joo, Sang Woo

    2012-10-01

    We explore the electric-field-induced interfacial instabilities of a trilayer composed of a thin elastic film confined between two viscous layers. A linear stability analysis (LSA) is performed to uncover the growth rate and length scale of the different unstable modes. Application of a normal external electric field on such a configuration can deform the two coupled elastic-viscous interfaces either by an in-phase bending or an antiphase squeezing mode. The bending mode has a long-wave nature, and is present even at a vanishingly small destabilizing field. In contrast, the squeezing mode has finite wave-number characteristics and originates only beyond a threshold strength of the electric field. This is in contrast to the instabilities of the viscous films with multiple interfaces where both modes are found to possess long-wave characteristics. The elastic film is unstable by bending mode when the stabilizing forces due to the in-plane curvature and the elastic stiffness are strong and the destabilizing electric field is relatively weak. In comparison, as the electric field increases, a subdominant squeezing mode can also appear beyond a threshold destabilizing field. A dominant squeezing mode is observed when the destabilizing field is significantly strong and the elastic films are relatively softer with lower elastic modulus. In the absence of liquid layers, a free elastic film is also found to be unstable by long-wave bending and finite wave-number squeezing modes. The LSA asymptotically recovers the results obtained by the previous formulations where the membrane bending elasticity is approximately incorporated as a correction term in the normal stress boundary condition. Interestingly, the presence of a very weak stabilizing influence due to a smaller interfacial tension at the elastic-viscous interfaces opens up the possibility of fabricating submicron patterns exploiting the instabilities of a trilayer.

  14. Effective long-range interlayer interactions and electric-field-induced subphases in ferrielectric liquid crystals

    NASA Astrophysics Data System (ADS)

    Chandani, A. D. L.; Fukuda, Atsuo; Vij, Jagdish K.; Takanishi, Yoichi; Iida, Atsuo

    2016-04-01

    Microbeam resonant x-ray scattering experiments recently revealed the sequential emergence of electric-field-induced subphases (stable states) with exceptionally large unit cells consisting of 12 and 15 smectic layers. We explain the emergence of the field-induced subphases by the quasimolecular model based on the Emelyanenko-Osipov long-range interlayer interactions (LRILIs) together with our primitive way of understanding the frustration in clinicity using the qE number defined as qE=|[R ] -[L ] | /([R ] +[L ] ) ; here [R ] and [L ] refer to the numbers of smectic layers with directors tilted to the right and to the left, respectively, in the unit cell of a field-induced subphase. We show that the model actually stabilizes the field-induced subphases with characteristic composite unit cells consisting of several blocks, each of which is originally a ferrielectric three-layer unit cell stabilized by the LRILIs, but some of which would be modified to become ferroelectric by an applied electric field. In a similar line of thought, we also try to understand the puzzling electric-field-induced birefringence data in terms of the LRILIs.

  15. A continuum model for interconnected lattice trusses

    NASA Technical Reports Server (NTRS)

    Balakrishnan, A. V.

    1992-01-01

    A continuum model for interconnected lattice trusses based on the 1D Timoshenko beam approximation is developed using the NASA-LRC Phase Zero Evolutionary Model. The continuum model dynamics is presented in the canonical wave-equation form in a Hilbert space.

  16. Turbulent fluid motion 3: Basic continuum equations

    NASA Technical Reports Server (NTRS)

    Deissler, Robert G.

    1991-01-01

    A derivation of the continuum equations used for the analysis of turbulence is given. These equations include the continuity equation, the Navier-Stokes equations, and the heat transfer or energy equation. An experimental justification for using a continuum approach for the study of turbulence is given.

  17. Electron-ion continuum-continuum mixing in dissociative recombination

    NASA Technical Reports Server (NTRS)

    Guberman, Steven L.

    1993-01-01

    In recent calculations on the dissociative recombination (DR) of the v=1 vibrational level of the ground state of N2(+), N2(+)(v=1) + e(-) yields N + N, we have observed an important continuun-continuum mixing process involving the open channels on both sides of N2(+)(v=1) + e(-) yields N2(+)(v=0) + e(-). In vibrational relaxation by electron impact (immediately above) the magnitude of the cross section depends upon the strength of the interaction between these continua. In DR of the v=1 ion level, these continua can also interact in the entrance channel, and the mixing can have a profound effect upon the DR cross section from v=1, as we illustrate in this paper. In our theoretical calculations of N2(+) DR using multichannel quantum defect theory (MQDT), the reactants and products in the two above equations are described simultaneously. This allows us to calculate vibrational relaxation and excitation cross sections as well as DR cross sections. In order to understand the mixing described above, we first present a brief review of the prior results for DR of the v=0 level of N2(+).

  18. Field-induced activation of metal oxide semiconductor for low temperature flexible transparent electronic device applications

    NASA Astrophysics Data System (ADS)

    Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony; Haglund, Amada; Ward, Thomas Zac; Mandrus, David; Rack, Philip

    Amorphous metal-oxide semiconductors have been extensively studied as an active channel material in thin film transistors due to their high carrier mobility, and excellent large-area uniformity. Here, we report the athermal activation of amorphous indium gallium zinc oxide semiconductor channels by an electric field-induced oxygen migration via gating through an ionic liquid. Using field-induced activation, a transparent flexible thin film transistor is demonstrated on a polyamide substrate with transistor characteristics having a current ON-OFF ratio exceeding 108, and saturation field effect mobility of 8.32 cm2/(V.s) without a post-deposition thermal treatment. This study demonstrates the potential of field-induced activation as an athermal alternative to traditional post-deposition thermal annealing for metal oxide electronic devices suitable for transparent and flexible polymer substrates. Materials Science and Technology Division, ORBL, Oak Ridge, TN 37831, USA.

  19. Ultrasonic propagation: a technique to reveal field induced structures in magnetic nanofluids.

    PubMed

    Parekh, Kinnari; Patel, Jaykumar; Upadhyay, R V

    2015-07-01

    The paper reports the study of magnetic field induced structures in magnetic nanofluid investigated through ultrasonic wave propagation. Modified Tarapov's theory is used to study variation in velocity anisotropy with magnetic field. The types of field induced structures depend upon the chemical structure of the carrier in which magnetic nanoparticles are dispersed. Our study indicates formation of fractals and chain respectively, in transformer oil and kerosene based fluid. This difference is explained on the basis of particle-particle interaction and particle-medium interaction. PMID:25791205

  20. MIRO Continuum Calibration for Asteroid Mode

    NASA Technical Reports Server (NTRS)

    Lee, Seungwon

    2011-01-01

    MIRO (Microwave Instrument for the Rosetta Orbiter) is a lightweight, uncooled, dual-frequency heterodyne radiometer. The MIRO encountered asteroid Steins in 2008, and during the flyby, MIRO used the Asteroid Mode to measure the emission spectrum of Steins. The Asteroid Mode is one of the seven modes of the MIRO operation, and is designed to increase the length of time that a spectral line is in the MIRO pass-band during a flyby of an object. This software is used to calibrate the continuum measurement of Steins emission power during the asteroid flyby. The MIRO raw measurement data need to be calibrated in order to obtain physically meaningful data. This software calibrates the MIRO raw measurements in digital units to the brightness temperature in Kelvin. The software uses two calibration sequences that are included in the Asteroid Mode. One sequence is at the beginning of the mode, and the other at the end. The first six frames contain the measurement of a cold calibration target, while the last six frames measure a warm calibration target. The targets have known temperatures and are used to provide reference power and gain, which can be used to convert MIRO measurements into brightness temperature. The software was developed to calibrate MIRO continuum measurements from Asteroid Mode. The software determines the relationship between the raw digital unit measured by MIRO and the equivalent brightness temperature by analyzing data from calibration frames. The found relationship is applied to non-calibration frames, which are the measurements of an object of interest such as asteroids and other planetary objects that MIRO encounters during its operation. This software characterizes the gain fluctuations statistically and determines which method to estimate gain between calibration frames. For example, if the fluctuation is lower than a statistically significant level, the averaging method is used to estimate the gain between the calibration frames. If the

  1. Continuum methods in lattice perturbation theory

    SciTech Connect

    Becher, Thomas G

    2002-11-15

    We show how methods of continuum perturbation theory can be used to simplify perturbative lattice calculations. We use the technique of asymptotic expansions to expand lattice loop integrals around the continuum limit. After the expansion, all nontrivial dependence on momenta and masses is encoded in continuum loop integrals and the only genuine lattice integrals left are tadpole integrals. Using integration-by-parts relations all of these can be expressed in terms of a small number of master integrals. Four master integrals are needed for bosonic one loop integrals, sixteen in QCD with Wilson or staggered fermions.

  2. Electro-optic contribution to field-induced Raman scattering in alkali halides

    SciTech Connect

    Subbaswamy, K.R.; Mahan, G.D.

    1985-10-15

    The electro-optic contribution to the field-induced first-order Raman scattering cross section in alkali halide crystals is calculated using measured values for hyperpolarizabilities. The electro-optic contribution is much larger than the previously reported atomic displacement contribution. The results cast some doubt on the accuracy of the reported hyperpolarizability values.

  3. Commitment to Quality throughout the Continuum.

    ERIC Educational Resources Information Center

    Gillet, Pamela

    1995-01-01

    This editorial by the president of the Council for Exceptional Children indicates the organization's support of a continuum of special education placements for students with special needs and calls for improving transition of students from one placement to another. (JDD)

  4. Periodic amplitude variations in Jovian continuum radiation

    NASA Astrophysics Data System (ADS)

    Kurth, W. S.; Gurnett, D. A.; Scarf, F. L.

    1986-12-01

    An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both 5 and 10 horus. Contrary to a plausible initial idea, the continuum amplitudes are not organized by the position of the observer relative to the dense plasma sheet. Instead, there seem to be perferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clocklike modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude solar wind alignment to the amplitude of the continuum radiation implies that the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.

  5. Application of continuum- and hybrid models in karst spring catchments

    NASA Astrophysics Data System (ADS)

    Rehrl, Christoph; Birk, Steffen

    2010-05-01

    further implies that inferences of aquifer properties from spring hydrographs are potentially impaired by ignoring turbulent flow effects. Thus, the adequate representation of turbulent flow in karst models might deserve equal or even more attention than the general pros and cons of continuum and hybrid models discussed in the literature. Moreover this study focuses on the applicability of the single-continuum approach (CFP mode 2) regarding the typical discharge dynamics of spring catchments. The continuum model is currently tested using the well investigated Gallusquelle catchment (Schwäbische Alb, Germany). The Gallusquelle hydrograph show significant variations in the spring discharge while the hydraulic head within the catchment changes only moderately. This strong variability within the hydrograph was already modelled using a double-continuum model but poses a serious challenge when using the lower-parameterised single-continuum approach.

  6. Continuum absorption in the vicinity of the toroidicity-induced Alfvén gap

    NASA Astrophysics Data System (ADS)

    Li, Meng; Breizman, Boris; Zheng, Linjin

    2015-11-01

    This work examines the resonant dissipative response of the Alfvén continuum to an oscillating driving current when the driving frequency is slightly outside the edges of the toroidicity-induced spectral gap. The problem is motivated by the need to the describe the continuum absorption in the frequency chirping events for energetic-particle-driven modes. A key element of this problem is the negative interference of the two closely spaced continuum crossing points. We explain why the continuum absorption can have very different features. This difference is closely related to the Toroidicity-induced Alfvén Eigenmode(TAE) theory that the eigenmode frequency can be arbitrarily close to the upper edge of the gap, whereas the lower edge of the gap is always a finite distance away from the closest eigenmode. This work was supported by the U.S. Department of Energy Contracts DE-FG02-04ER-54742.

  7. Geometric continuum regularization of quantum field theory

    SciTech Connect

    Halpern, M.B. . Dept. of Physics)

    1989-11-08

    An overview of the continuum regularization program is given. The program is traced from its roots in stochastic quantization, with emphasis on the examples of regularized gauge theory, the regularized general nonlinear sigma model and regularized quantum gravity. In its coordinate-invariant form, the regularization is seen as entirely geometric: only the supermetric on field deformations is regularized, and the prescription provides universal nonperturbative invariant continuum regularization across all quantum field theory. 54 refs.

  8. Noise scaling in continuum percolating films

    NASA Astrophysics Data System (ADS)

    Garfunkel, G. A.; Weissman, M. B.

    1985-07-01

    Measurements of the scaling of 1/f noise magnitude versus resistance were made in metal films as the metal was removed by sandblasting. This procedure gives an approximate experimental realization of a Swiss-cheese continuum-percolation model, for which theory indicates some scaling properties very different from lattice percolation. The ratio of the resistance and noise exponents was in strong disagreement with lattice-percolation predictions and agreed approximately with simple continuum predictions.

  9. Polarizable Atomic Multipole Solutes in a Poisson-Boltzmann Continuum

    PubMed Central

    Schnieders, Michael J.; Baker, Nathan A.; Ren, Pengyu; Ponder, Jay W.

    2008-01-01

    Modeling the change in the electrostatics of organic molecules upon moving from vacuum into solvent, due to polarization, has long been an interesting problem. In vacuum, experimental values for the dipole moments and polarizabilities of small, rigid molecules are known to high accuracy; however, it has generally been difficult to determine these quantities for a polar molecule in water. A theoretical approach introduced by Onsager used vacuum properties of small molecules, including polarizability, dipole moment and size, to predict experimentally known permittivities of neat liquids via the Poisson equation. Since this important advance in understanding the condensed phase, a large number of computational methods have been developed to study solutes embedded in a continuum via numerical solutions to the Poisson-Boltzmann equation (PBE). Only recently have the classical force fields used for studying biomolecules begun to include explicit polarization in their functional forms. Here we describe the theory underlying a newly developed Polarizable Multipole Poisson-Boltzmann (PMPB) continuum electrostatics model, which builds on the Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field. As an application of the PMPB methodology, results are presented for several small folded proteins studied by molecular dynamics in explicit water as well as embedded in the PMPB continuum. The dipole moment of each protein increased on average by a factor of 1.27 in explicit water and 1.26 in continuum solvent. The essentially identical electrostatic response in both models suggests that PMPB electrostatics offers an efficient alternative to sampling explicit solvent molecules for a variety of interesting applications, including binding energies, conformational analysis, and pKa prediction. Introduction of 150 mM salt lowered the electrostatic solvation energy between 2–13 kcal/mole, depending on the formal charge of the protein, but had only a

  10. 34 CFR 300.115 - Continuum of alternative placements.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 34 Education 2 2012-07-01 2012-07-01 false Continuum of alternative placements. 300.115 Section... Continuum of alternative placements. (a) Each public agency must ensure that a continuum of alternative... services. (b) The continuum required in paragraph (a) of this section must— (1) Include the...

  11. Influence of thermal agitation on the electric field induced precessional magnetization reversal with perpendicular easy axis

    SciTech Connect

    Cheng, Hongguang Deng, Ning

    2013-12-15

    We investigated the influence of thermal agitation on the electric field induced precessional magnetization switching probability with perpendicular easy axis by solving the Fokker-Planck equation numerically with finite difference method. The calculated results show that the thermal agitation during the reversal process crucially influences the switching probability. The switching probability can be achieved is only determined by the thermal stability factor Δ of the free layer, it is independent on the device dimension, which is important for the high density device application. Ultra-low error rate down to the order of 10{sup −9} can be achieved for the device of thermal stability factor Δ of 40. Low damping factor α material should be used for the free layer for high reliability device applications. These results exhibit potential of electric field induced precessional magnetization switching with perpendicular easy axis for ultra-low power, high speed and high density magnetic random access memory (MRAM) applications.

  12. Fields induced by three-dimensional dislocation loops in anisotropic magneto-electro-elastic bimaterials

    NASA Astrophysics Data System (ADS)

    Han, Xueli; Pan, Ernie; Sangghaleh, Ali

    2013-08-01

    The coupled elastic, electric and magnetic fields produced by an arbitrarily shaped three-dimensional dislocation loop in general anisotropic magneto-electro-elastic (MEE) bimaterials are derived. First, we develop line-integral expressions for the fields induced by a general dislocation loop. Then, we obtain analytical solutions for the fields, including the extended Peach-Koehler force, due to some useful dislocation segments such as straight line and elliptic arc. The present solutions contain the piezoelectric, piezomagnetic and purely elastic solutions as special cases. As numerical examples, the fields induced by a square and an elliptic dislocation loop in MEE bimaterials are studied. Our numerical results show the coupling effects among different fields, along with various interesting features associated with the dislocation and interface.

  13. In situ imaging of field-induced hexagonal columns in magnetite ferrofluids.

    PubMed

    Klokkenburg, Mark; Erné, Ben H; Meeldijk, Johannes D; Wiedenmann, Albrecht; Petukhov, Andrei V; Dullens, Roel P A; Philipse, Albert P

    2006-11-01

    Field-induced structures in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment are analyzed on a single-particle level by in situ cryogenic transmission electron microscopy (2D). The field-induced columnar phase locally exhibits hexagonal symmetry and confirms the structures observed in simulations for ferromagnetic dipolar fluids in 2D. The columns are distorted by lens-shaped voids, due to the weak interchain attraction relative to field-directed dipole-dipole attraction. Both dipolar coupling and the dipole concentration determine the dimensions and the spatial arrangement of the columns. Their regular spacing manifests long-range end-pole repulsions that eventually dominate the fluctuation-induced attractions between dipole chains that initiate the columnar transition. PMID:17155554

  14. Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching

    NASA Astrophysics Data System (ADS)

    Nan, Tianxiang; Emori, Satoru; Peng, Bin; Wang, Xinjun; Hu, Zhongqiang; Xie, Li; Gao, Yuan; Lin, Hwaider; Jiao, Jie; Luo, Haosu; Budil, David; Jones, John G.; Howe, Brandon M.; Brown, Gail J.; Liu, Ming; Sun, Nian

    2016-01-01

    Electric-field modulation of magnetism in strain-mediated multiferroic heterostructures is considered a promising scheme for enabling memory and magnetic microwave devices with ultralow power consumption. However, it is not well understood how electric-field-induced strain influences magnetic relaxation, an important physical process for device applications. Here, we investigate resonant magnetization dynamics in ferromagnet/ferroelectric multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct strain states provided by electric-field-induced ferroelectric phase transition. The strain not only modifies magnetic anisotropy but also magnetic relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic Gilbert damping by electric field, which is attributed to strain-induced tuning of spin-orbit coupling. By contrast, a small but measurable change in extrinsic linewidth broadening is attributed to inhomogeneous ferroelastic domain switching during the phase transition of the PMN-PT substrate.

  15. Electric field induced by collective vortex creep in superconductors with fractal clusters of normal phase

    NASA Astrophysics Data System (ADS)

    Kuzmin, Yu. I.; Pleshakov, I. V.

    2016-02-01

    The influence of the collective creep of magnetic flux on the electric field induced in a superconducting composite with fractal cluster structure is considered. Current-voltage ( I- V) characteristics of these superconductors are determined with allowance for the influence of the fractal dimensionality of boundaries of the normal phase clusters and the height of pinning barriers on the nonlinearity of I- V characteristics at small transport currents. A relationship is established between the collective pinning and vortex glass state that is formed in superconductors with a fractal cluster structure. It is shown that the intensity of an electric field induced in the case of collective creep is smaller than that for Anderson-Kim creep.

  16. Direct measurements of the magnetic field induced by optically polarized sup 3 He atoms

    SciTech Connect

    Gudoshnikov, S.A.; Snigirev, O.V. ); Kozlov, A.N.; Maslennikov, Y.V.; Serebrjakov, A.Y. )

    1991-03-01

    This paper reports on an alternative magnetic field induced by the standard cell of the optically pumped {sup 3}He magnetometer directly measured by the SQUID-based second-order gradiometer with signal-to-noise ratio higher than 6. The magnitude of the measured field equal to 5 {times} 10{sup {minus}13} T at the 5-cm distance from the cell axis and transverse relaxation time T{sub 2} equal to 7 minutes have been found.

  17. A luminescent heptanuclear DyIr6 complex showing field-induced slow magnetization relaxation.

    PubMed

    Zeng, Dai; Ren, Min; Bao, Song-Song; Li, Li; Zheng, Li-Min

    2014-08-01

    The first example of iridium/lanthanide phosphonates, i.e. [DyIr6(ppy)12(bpp)2(bppH)4](CF3SO3)·8H2O (1) (ppy(-) = 2-phenylpyridine, bpp(2-) = 2-pyridylphosphonate) is reported. It shows dual functions with the photoluminescence and field-induced slow magnetization relaxation originating from the Ir and Dy moieties, respectively. PMID:24942060

  18. Electron correlations in semiconductors: Bulk cohesive properties and magnetic-field-induced Wigner crystal at heterojunctions

    SciTech Connect

    Louie, S.G.; Zhu, X.

    1992-08-01

    A correlated wavefunction variational quantum Monte Carlo approach to the studies of electron exchange and correlation effects in semiconductors is presented. Applications discussed include the cohesive and structural properties of bulk semiconductors, and the magnetic-field-induced Wigner electron crystal in two dimensions. Landau level mixing is shown to be important in determining the transition between the quantum Hall liquid and the Wigner crystal states in the regime of relevant experimental parameters.

  19. Microstructural and continuum evolution modeling of sintering.

    SciTech Connect

    Braginsky, Michael V.; Olevsky, Eugene A.; Johnson, D. Lynn; Tikare, Veena; Garino, Terry J.; Arguello, Jose Guadalupe, Jr.

    2003-12-01

    deformation during. The continuum portion is based on a finite element formulation that allows 3D components to be modeled using SNL's nonlinear large-deformation finite element code, JAS3D. This tool provides a capability to model sintering of complex three-dimensional components. The model was verified by comparing to simulations results published in the literature. The model was validated using experimental results from various laboratory experiments performed by Garino. In addition, the mesoscale simulations were used to study anisotropic shrinkage in aligned, elongated powder compacts. Anisotropic shrinkage occurred in all compacts with aligned, elongated particles. However, the direction of higher shrinkage was in some cases along the direction of elongation and in other cases in the perpendicular direction depending on the details of the powder compact. In compacts of simple-packed, mono-sized, elongated particles, shrinkage was higher in the direction of elongation. In compacts of close-packed, mono-sized, elongated particles and of elongated particles with a size and shape distribution, the shrinkage was lower in the direction of elongation. We also explored the concept of a sintering stress tensor rather than the traditional sintering stress scalar concept for the case of anisotropic shrinkage. A thermodynamic treatment of this is presented. A method to calculate the sintering stress tensor is also presented. A user-friendly code that can simulate microstructural evolution during sintering in 2D and in 3D was developed. This code can run on most UNIX platforms and has a motif-based GUI. The microstructural evolution is shown as the code is running and many of the microstructural features, such as grain size, pore size, the average grain boundary length (in 2D) and area (in 3D), etc. are measured and recorded as a function of time. The overall density as the function of time is also recorded.

  20. A Radio Continuum Study of Dwarf Galaxies: 6 cm imaging of LITTLE THINGS

    NASA Astrophysics Data System (ADS)

    Kitchener, Ben; Brinks, Elias; Heesen, Volker; Hunter, Deidre Ann; Zhang, Hongxin; Rau, Urvashi; Rupen, Michael P.; Little Things Collaboration

    2015-01-01

    To bypass uncertainties introduced by extinction caused by dust at optical wavelengths, we examine to what extent the radio continuum can probe star formation (SF) in dwarf galaxies. We provide VLA 6-cm C-array (4 to 8 GHz) radio continuum images with integrated flux densities for 40 dwarf galaxies taken from LITTLE THINGS. We find 27 harbor significant emission coincident with SF tracers; 17 are new detections. We infer the average thermal fraction to be 39 +- 25%. The LITTLE THINGS galaxies follow the Condon radio continuum - star formation rate (SFR) relation down to an SFR of 0.1 Msol/yr. At lower rates they follow a power-law characterized by a slope of 1.2 +- 0.1 with a scatter of 0.2 dex . We interpret this as an underproduction of the non-thermal radio continuum component. When considering the non-thermal radio continuum to star formation rate slope on its own, we find the slope to be 1.2. The magnetic field strength we find is typically 9.4 +- 3.8 muG in and around star forming regions which is similar to that in spiral galaxies. In a few dwarfs, the magnetic field strength can reach as high as 30 muG in localized 100 pc star forming regions. The underproduction of non-thermal radio continuum is likely due to the escape of Cosmic Ray electrons from the galaxy. The LITTLE THINGS galaxies are consistent with the radio continuum - far infrared luminosity relation. We observe a power-law slope of 1.06 +- 0.08 with a scatter of 0.24 dex which suggests that the 'conspiracy' of the radio continuum - far infrared relation continues to hold even for dwarf galaxies.

  1. Continuum Absorption Coefficient of Atoms and Ions

    NASA Technical Reports Server (NTRS)

    Armaly, B. F.

    1979-01-01

    The rate of heat transfer to the heat shield of a Jupiter probe has been estimated to be one order of magnitude higher than any previously experienced in an outer space exploration program. More than one-third of this heat load is due to an emission of continuum radiation from atoms and ions. The existing computer code for calculating the continuum contribution to the total load utilizes a modified version of Biberman's approximate method. The continuum radiation absorption cross sections of a C - H - O - N ablation system were examined in detail. The present computer code was evaluated and updated by being compared with available exact and approximate calculations and correlations of experimental data. A detailed calculation procedure, which can be applied to other atomic species, is presented. The approximate correlations can be made to agree with the available exact and experimental data.

  2. Defining and testing a granular continuum element

    SciTech Connect

    Rycroft, Chris H.; Kamrin, Ken; Bazant, Martin Z.

    2007-12-03

    Continuum mechanics relies on the fundamental notion of amesoscopic volume "element" in which properties averaged over discreteparticles obey deterministic relationships. Recent work on granularmaterials suggests a continuum law may be inapplicable, revealinginhomogeneities at the particle level, such as force chains and slow cagebreaking. Here, we analyze large-scale Discrete-Element Method (DEM)simulations of different granular flows and show that a "granularelement" can indeed be defined at the scale of dynamical correlations,roughly three to five particle diameters. Its rheology is rather subtle,combining liquid-like dependence on deformation rate and solid-likedependence on strain. Our results confirm some aspects of classicalplasticity theory (e.g., coaxiality of stress and deformation rate),while contradicting others (i.e., incipient yield), and can guide thedevelopment of more realistic continuum models.

  3. Continuum damping of ideal toroidal Alfven eigenmodes

    SciTech Connect

    Zhang, X.D.; Zhang, Y.Z.; Mahajan, S.M.

    1993-08-01

    A perturbation theory based on the two dimensional (2D) ballooning transform is systematically developed for ideal toroidal Alfven eigenmodes (TAEs). A formula, similar to the Fermi golden rule for decaying systems in quantum mechanics, is derived for the continuum damping rate of the TAE; the decay (damping) rate is expressed explicitly in terms of the coupling of the TAE to the continuum spectrum. Numerical results are compared with previous calculations. It is found that in some narrow intervals of the parameter m{cflx {epsilon}} the damping rate varies very rapidly. These regions correspond precisely to the root missing intervals of the numerical solution by Rosenbluth et al.

  4. Stratospheric infrared continuum absorptions observed by the ATMOS instrument

    NASA Technical Reports Server (NTRS)

    Rinsland, C. P.; Zander, R.; Namkung, J. S.; Farmer, C. B.; Norton, R. H.

    1989-01-01

    A quantitative analysis of infrared continuum absorption features observed in ATMOS/Spacelab 3 (1985) spectra of the lower stratosphere is reported. Continuous absorption produced primarily by the collision-induced fundamental vibration-rotation band of O2 and to a lesser extent by the superposition of H2O far line wings has been observed in the 1400 to 1800/cm interval below tangent heights of about 25 km. Continuum optical depths measured in microwindows nearly free of atmospheric line absorption are 0.78 + or - 0.06 times those calculated with the O2 absorption coefficients of Timofeyev and Tonkov (1978). Transmittance measurements in microwindows between 2395 and 2535/cm have been used to study continuous absorption from the collision induced fundamental vibration-rotation band of N2 and the far wings of strong CO2 lines. The measured transmittances have been analyzed to derive best fit absorption coefficients for the N2 pressure-induced band at lower stratospheric temperatures (about 210 K).

  5. Understanding the Continuum Spectra of Short Soft Gamma Repeater Bursts

    NASA Technical Reports Server (NTRS)

    Gogus, Ersin; Woods, Peter M.; Kouveliotou, Chryssa; Finger, Mark H.; Lenter, Geoffrey; Patel, Sandeep K.; Swank, Jean

    2006-01-01

    The spectra of short soft gamma repeater (SGR) bursts at photon energies above -15 keV are often well described by an optically thin thermal bremsstrahlung model (i.e., F(E) - E^-1 * exp(-E/kT) ) with kT=20-40 keV. However, the spectral shape burst continuum at lower photon energies (down to -2 keV) is not well established. It is important to better understand the SGR burst spectral properties at lower energies since inadequate description of the burst spectral continuum could lead to incorrect conclusions, such as existence of spectral lines. Here, we present detailed spectral investigations (in 2-200 keV) of 163 bursts from SGR 1806-20, all detected with Rossi X-ray Timing Explorer during the 2004 active episode that included the giant flare on 27 December 2004. We find that the great majority of burst spectra are well represented by the combination of a blackbody plus a OTTB models.

  6. Continuum absorption in the vicinity of the toroidicity-induced Alfvén gap

    SciTech Connect

    Li, M.; Breizman, B. N.; Zheng, L. J.; Chen, Eugene Y.

    2015-12-04

    Excitation of Alfvén modes is commonly viewed as a concern for energetic particle confinement in burning plasmas. The 3.5 MeValpha particles produced by fusion may be affected as well as other fast ions in both present and future devices. Continuum damping of such modes is one of the key factors that determine their excitation thresholds and saturation levels. This work examines the resonant dissipative response of the Alfvén continuum to an oscillating driving current when the driving frequency is slightly outside the edges of the toroidicity-induced spectral gap. The problem is largely motivated by the need to describe the continuum absorption in the frequency sweeping events. Akey element of this problem is the negative interference of the two closely spaced continuum crossing points.Weexplain why the lower and upper edges of the gap can have very different continuum absorption features. Lastly, the difference is associated with an eigenmode whose frequency can be arbitrarily close to the upper edge of the gap whereas the lower edge of the gap is always a finite distance away from the closest eigenmode.

  7. Continuum absorption in the vicinity of the toroidicity-induced Alfvén gap

    NASA Astrophysics Data System (ADS)

    Li, M.; Breizman, B. N.; Zheng, L. J.; Chen, Eugene Y.

    2015-12-01

    Excitation of Alfvén modes is commonly viewed as a concern for energetic particle confinement in burning plasmas. The 3.5 MeV alpha particles produced by fusion may be affected as well as other fast ions in both present and future devices. Continuum damping of such modes is one of the key factors that determine their excitation thresholds and saturation levels. This work examines the resonant dissipative response of the Alfvén continuum to an oscillating driving current when the driving frequency is slightly outside the edges of the toroidicity-induced spectral gap. The problem is largely motivated by the need to describe the continuum absorption in the frequency sweeping events. A key element of this problem is the negative interference of the two closely spaced continuum crossing points. We explain why the lower and upper edges of the gap can have very different continuum absorption features. The difference is associated with an eigenmode whose frequency can be arbitrarily close to the upper edge of the gap whereas the lower edge of the gap is always a finite distance away from the closest eigenmode.

  8. Parental Involvement to Parental Engagement: A Continuum

    ERIC Educational Resources Information Center

    Goodall, Janet; Montgomery, Caroline

    2014-01-01

    Based on the literature of the field, this article traces a continuum between parental involvement with schools, and parental engagement with children's learning. The article seeks to shed light on an area of confusion; previous research has shown that different stakeholder groups understand "parental engagement" in different ways.…

  9. Continuum treatment of electronic polarization effect.

    PubMed

    Tan, Yu-Hong; Luo, Ray

    2007-03-01

    A continuum treatment of electronic polarization has been explored for in molecular mechanics simulations in implicit solvents. The dielectric constant for molecule interior is the only parameter in the continuum polarizable model. A value of 4 is found to yield optimal agreement with high-level ab initio quantum mechanical calculations for the tested molecular systems. Interestingly, its performance is not sensitive to the definition of molecular volume, in which the continuum electronic polarization is defined. In this model, quantum mechanical electrostatic field in different dielectric environments from vacuum, low-dielectric organic solvent, and water can be used simultaneously in atomic charge fitting to achieve consistent treatment of electrostatic interactions. The tests show that a single set of atomic charges can be used consistently in different dielectric environments and different molecular conformations, and the atomic charges transfer well from training monomers to tested dimers. The preliminary study gives us the hope of developing a continuum polarizable force field for more consistent simulations of proteins and nucleic acids in implicit solvents. PMID:17362100

  10. Continuum treatment of electronic polarization effect

    NASA Astrophysics Data System (ADS)

    Tan, Yu-Hong; Luo, Ray

    2007-03-01

    A continuum treatment of electronic polarization has been explored for in molecular mechanics simulations in implicit solvents. The dielectric constant for molecule interior is the only parameter in the continuum polarizable model. A value of 4 is found to yield optimal agreement with high-level ab initio quantum mechanical calculations for the tested molecular systems. Interestingly, its performance is not sensitive to the definition of molecular volume, in which the continuum electronic polarization is defined. In this model, quantum mechanical electrostatic field in different dielectric environments from vacuum, low-dielectric organic solvent, and water can be used simultaneously in atomic charge fitting to achieve consistent treatment of electrostatic interactions. The tests show that a single set of atomic charges can be used consistently in different dielectric environments and different molecular conformations, and the atomic charges transfer well from training monomers to tested dimers. The preliminary study gives us the hope of developing a continuum polarizable force field for more consistent simulations of proteins and nucleic acids in implicit solvents.

  11. A Multiscale Morphing Continuum Description for Turbulence

    NASA Astrophysics Data System (ADS)

    Chen, James; Wonnell, Louis

    2015-11-01

    Turbulence is a flow physics phenomena invlolving multiple length scales. The popular Navier- Stokes equations only possess one length/time scale. Therefore, extremely fine mesh is needed for DNS attempting to resolve the small scale motion, which comes with a burden of excessive computational cost. For practical application with complex geometries, the research society rely on RANS and LES, which requre turbulence model or subgrid scale (SGS) model for closure problems. Different models not only lead to different results but usually are invalidated on solid physical grounds, such as objectivity and entropy principle.The Morphing Continuum Theory (MCT) is a high-order continuum theory formulated under the framework of thermalmechanics for physics phenomena involving microstructure. In this study, a theoretical perspective for the multiscale nature of the Morphing Continuum Theory is connected with the multiscale nature of turbulence physics. The kinematics, balance laws, constitutive equations and a Morphing Continuum description of turbulence are introduced. The equations were numerically implemented for a zero pressure gradient flat plate. The simulations are compate with the laminar, transitional and turbulence cases.

  12. Modal kinematics for multisection continuum arms.

    PubMed

    Godage, Isuru S; Medrano-Cerda, Gustavo A; Branson, David T; Guglielmino, Emanuele; Caldwell, Darwin G

    2015-06-01

    This paper presents a novel spatial kinematic model for multisection continuum arms based on mode shape functions (MSF). Modal methods have been used in many disciplines from finite element methods to structural analysis to approximate complex and nonlinear parametric variations with simple mathematical functions. Given certain constraints and required accuracy, this helps to simplify complex phenomena with numerically efficient implementations leading to fast computations. A successful application of the modal approximation techniques to develop a new modal kinematic model for general variable length multisection continuum arms is discussed. The proposed method solves the limitations associated with previous models and introduces a new approach for readily deriving exact, singularity-free and unique MSF's that simplifies the approach and avoids mode switching. The model is able to simulate spatial bending as well as straight arm motions (i.e., pure elongation/contraction), and introduces inverse position and orientation kinematics for multisection continuum arms. A kinematic decoupling feature, splitting position and orientation inverse kinematics is introduced. This type of decoupling has not been presented for these types of robotic arms before. The model also carefully accounts for physical constraints in the joint space to provide enhanced insight into practical mechanics and impose actuator mechanical limitations onto the kinematics thus generating fully realizable results. The proposed method is easily applicable to a broad spectrum of continuum arm designs. PMID:25969947

  13. An oculomotor continuum from exploration to fixation

    PubMed Central

    Otero-Millan, Jorge; Macknik, Stephen L.; Langston, Rachel E.; Martinez-Conde, Susana

    2013-01-01

    During visual exploration, saccadic eye movements scan the scene for objects of interest. During attempted fixation, the eyes are relatively still but often produce microsaccades. Saccadic rates during exploration are higher than those of microsaccades during fixation, reinforcing the classic view that exploration and fixation are two distinct oculomotor behaviors. An alternative model is that fixation and exploration are not dichotomous, but are instead two extremes of a functional continuum. Here, we measured the eye movements of human observers as they either fixed their gaze on a small spot or scanned natural scenes of varying sizes. As scene size diminished, so did saccade rates, until they were continuous with microsaccadic rates during fixation. Other saccadic properties varied as function of image size as well, forming a continuum with microsaccadic parameters during fixation. This saccadic continuum extended to nonrestrictive, ecological viewing conditions that allowed all types of saccades and fixation positions. Eye movement simulations moreover showed that a single model of oculomotor behavior can explain the saccadic continuum from exploration to fixation, for images of all sizes. These findings challenge the view that exploration and fixation are dichotomous, suggesting instead that visual fixation is functionally equivalent to visual exploration on a spatially focused scale. PMID:23533278

  14. Clinical Integration Managing across the care continuum.

    PubMed

    Karash, Julius A; Larson, Laurie

    2016-06-01

    In the changing world of health care, the traditional boundaries are vanishing and hospitals and others must integrate care within their own organizations, as well as externally, across the care continuum. Here are three approaches to accomplishing just that. PMID:27468454

  15. Some Continuum Aspects of Data Assimilation

    NASA Technical Reports Server (NTRS)

    Cohn, Stephen E.; Menard, Richard

    1999-01-01

    A long-sought goal in data assimilation is to build more fully the time dimension into the data assimilation process. Truly four-dimensional data assimilation requires evolving second-moment information, namely the estimation error covariance, along with the state estimate itself. The continuum evolution equations for the estimation error covariance constitute a system of partial differential equations in six space dimensions, forced by a model error covariance and by the observations themselves. The high dimensionality of this system poses a difficult computational problem. Numerous methods have been proposed for approximate, discrete solution of this system of equations. Four-dimensional variational schemes solve these equations indirectly, while schemes based on Kalman filtering solve the equations more directly, usually on a small subspace of the full six-dimensional space. In both cases, most proposed solution methods are not derived from the continuum covariance evolution equations themselves. Instead, most methods simply inherit the discretization used for evolving the state estimate, either in the form of a discrete tangent linear model or, in the case of ensemble schemes, in the form of a fully nonlinear discrete model. In this lecture we show that solutions of the continuum covariance evolution equations possess simple properties that are not readily satisfied upon discretization of the equations. we give numerical examples illustrating that "inherited" discretizations sometimes fail to produce meaningfully accurate solutions. Finally, we suggest alternative discretization methods that may yield more faithful approximate solutions of the continuum problem.

  16. Structured photoionization continuum of superheated cesium vapor

    NASA Astrophysics Data System (ADS)

    Pichler, G.; Makdisi, Y.; Kokaj, J.; Thomas, N.; Mathew, J.

    2015-08-01

    We studied the absorption spectrum of dense cesium vapor in an all-sapphire cell with a special emphasis on the highly structured photoionization continuum. This continuum appears to be composed of atomic and molecular contributions which can be separated by means of additional superheating of the cesium vapor in the sapphire cell. This was possible due to the small amount of cesium filling which completely evaporated at a temperature of around 450 °C. This enabled the overheating of cesium dimers which greatly reduced its concentration at a temperature of 900 °C, leaving almost pure atomic Cs vapor. The analysis of the thermal destruction indicated that the highly structured molecular component of the photoionization continuum can be entirely attributed to cesium dimers. We discuss the possible origin of the structured photoionization continuum as stemming from the absorption process from the ground state of the Cs2 molecule to the doubly excited Cs2** molecule located above Cs2+ molecular ionization limit. The corresponding potential curves are subjected to mutual interactions and autoionization.

  17. Structured photoionization continuum of cesium vapor

    NASA Astrophysics Data System (ADS)

    Pichler, Goran; Makdisi, Yacoub; Kokaj, Jahja; Thomas, Nicky; Mathew, Joseph; AMIP Team

    2015-05-01

    We studied absorption spectrum of dense cesium vapor in an all-sapphire cell with a special emphasis on the highly structured photoionization continuum. This continuum appears to be composed of atomic and molecular contributions which can be separated by means of additional superheating of the sapphire cell. This was possible due to the small amount of cesium filling which completely evaporated at temperature of about 450 °C. This enabled the overheating of cesium dimers which almost disappeared at a temperature of 900 °C leaving pure atomic Cs vapor. The analysis of the thermal destruction indicated that the highly structured molecular component of the photoionization continuum can be entirely attributed to cesium dimers. We discuss the possible origin of the structured photoionization continuum as stemming from the absorption process from the ground Cs2 molecule to the doubly excited Cs2** molecule located above the molecular ionization limit Cs2+.The corresponding potential curves are subjected to a mutual interactions and autoionization.

  18. Aims, Modes, and the Continuum of Discourse.

    ERIC Educational Resources Information Center

    Beale, Walter H.

    A framework for the study of discourse, based on the analysis of three superordinate features of discourse (asymmetry, hierarchy, and continuum), is proposed in this paper. The paper begins by noting the confusion in terminology that exists in the world of composition pedagogy and theory; pointing to the need for a framework for testing,…

  19. 3D holography: from discretum to continuum

    NASA Astrophysics Data System (ADS)

    Bonzom, Valentin; Dittrich, Bianca

    2016-03-01

    We study the one-loop partition function of 3D gravity without cosmological constant on the solid torus with arbitrary metric fluctuations on the boundary. To this end we employ the discrete approach of (quantum) Regge calculus. In contrast with similar calculations performed directly in the continuum, we work with a boundary at finite distance from the torus axis. We show that after taking the continuum limit on the boundary — but still keeping finite distance from the torus axis — the one-loop correction is the same as the one recently found in the continuum in Barnich et al. for an asymptotically flat boundary. The discrete approach taken here allows to identify the boundary degrees of freedom which are responsible for the non-trivial structure of the one-loop correction. We therefore calculate also the Hamilton-Jacobi function to quadratic order in the boundary fluctuations both in the discrete set-up and directly in the continuum theory. We identify a dual boundary field theory with a Liouville type coupling to the boundary metric. The discrete set-up allows again to identify the dual field with degrees of freedom associated to radial bulk edges attached to the boundary. Integrating out this dual field reproduces the (boundary diffeomorphism invariant part of the) quadratic order of the Hamilton-Jacobi functional. The considerations here show that bulk boundary dualities might also emerge at finite boundaries and moreover that discrete approaches are helpful in identifying such dualities.

  20. Continuum modeling of large lattice structures: Status and projections

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Mikulas, Martin M., Jr.

    1988-01-01

    The status and some recent developments of continuum modeling for large repetitive lattice structures are summarized. Discussion focuses on a number of aspects including definition of an effective substitute continuum; characterization of the continuum model; and the different approaches for generating the properties of the continuum, namely, the constitutive matrix, the matrix of mass densities, and the matrix of thermal coefficients. Also, a simple approach is presented for generating the continuum properties. The approach can be used to generate analytic and/or numerical values of the continuum properties.

  1. Magnetic field induced suppression of the forward bias current in Bi2Se3/Si Schottky barrier diodes

    NASA Astrophysics Data System (ADS)

    Jin, Haoming; Hebard, Arthur

    Schottky diodes formed by van der Waals bonding between freshly cleaved flakes of the topological insulator Bi2Se3 and doped silicon substrates show electrical characteristics in good agreement with thermionic emission theory. The motivation is to use magnetic fields to modulate the conductance of the topologically protected conducting surface state. This surface state in close proximity to the semiconductor surface may play an important role in determining the nature of the Schottky barrier. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics were obtained for temperatures in the range 50-300 K and magnetic fields, both perpendicular and parallel to the interface, as high as 7 T. The I-V curve shows more than 6 decades linearity on semi-logarithmic plots, allowing extraction of parameters such as ideality (η), zero-voltage Schottky barrier height (SBH), and series resistance (Rs). In forward bias we observe a field-induced decrease in current which becomes increasingly more pronounced at higher voltages and lower temperature, and is found to be correlated with changes in Rs rather than other barrier parameters. A comparison of changes in Rs in both field direction will be made with magnetoresistance in Bi2Se3 transport measurement. The work is supported by NSF through DMR 1305783.

  2. Block versus continuum deformation in the Western United States

    USGS Publications Warehouse

    King, G.; Oppenheimer, D.; Amelung, F.

    1994-01-01

    The relative role of block versus continuum deformation of continental lithosphere is a current subject of debate. Continuous deformation is suggested by distributed seismicity at continental plate margins and by cumulative seismic moment sums which yield slip estimates that are less than estimates from plate motion studies. In contrast, block models are favored by geologic studies of displacement in places like Asia. A problem in this debate is a lack of data from which unequivocal conclusions may be reached. In this paper we apply the techniques of study used in regions such as the Alpine-Himalayan belt to an area with a wealth of instrumental data-the Western United States. By comparing plate rates to seismic moment release rates and assuming a typical seismogenic layer thickness of 15 km it appears that since 1850 about 60% of the Pacific-North America motion across the plate boundary in California and Nevada has occurred seismically and 40% aseismically. The San Francisco Bay area shows similar partitioning between seismic and aseismic deformation, and it can be shown that within the seismogenic depth range aseismic deformation is concentrated near the surface and at depth. In some cases this deformation can be located on creeping surface faults, but elsewhere it is spread over a several kilometer wide zone adjacent to the fault. These superficial creeping deformation zones may be responsible for the palaeomagnetic rotations that have been ascribed elsewhere to the surface expression of continuum deformation in the lithosphere. Our results support the dominant role of non-continuum deformation processes with the implication that deformation localization by strain softening must occur in the lower crust and probably the upper mantle. Our conclusions apply only to the regions where the data are good, and even within the Western United States (i.e., the Basin and Range) deformation styles remain poorly resolved. Nonetheless, we maintain that block motion is the

  3. Field-Induced Lifshitz Transition without Metamagnetism in CeIrIn5

    NASA Astrophysics Data System (ADS)

    Aoki, D.; Seyfarth, G.; Pourret, A.; Gourgout, A.; McCollam, A.; Bruin, J. A. N.; Krupko, Y.; Sheikin, I.

    2016-01-01

    We report high magnetic field measurements of magnetic torque, thermoelectric power, magnetization, and the de Haas-van Alphen effect in CeIrIn5 across 28 T, where a metamagnetic transition was suggested in previous studies. The thermoelectric power displays two maxima at 28 and 32 T. Above 28 T, a new, low de Haas-van Alphen frequency with a strongly enhanced effective mass emerges, while the highest frequency observed at low field disappears entirely. This suggests a field-induced Lifshitz transition. However, longitudinal magnetization does not show any anomaly up to 33 T, thus ruling out a metamagnetic transition at 28 T.

  4. Rectifying the Optical-Field-Induced Current in Dielectrics: Petahertz Diode

    NASA Astrophysics Data System (ADS)

    Lee, J. D.; Yun, Won Seok; Park, Noejung

    2016-02-01

    Investigating a theoretical model of the optical-field-induced current in dielectrics driven by strong few-cycle laser pulses, we propose an asymmetric conducting of the current by forming a heterojunction made of two distinct dielectrics with a low hole mass (mh*≪me*) and low electron mass (me*≪mh* ), respectively. This proposition introduces the novel concept of a petahertz (1015 Hz ) diode to rectify the current in the petahertz domain, which should be a key ingredient for the electric signal manipulation of future light-wave electronics. Further, we suggest the candidate dielectrics for the heterojunction.

  5. Electric field induced localization phenomena in a ladder network with superlattice configuration: Effect of backbone environment

    NASA Astrophysics Data System (ADS)

    Dutta, Paramita; Maiti, Santanu K.; Karmakar, S. N.

    2014-09-01

    Electric field induced localization properties of a tight-binding ladder network in presence of backbone sites are investigated. Based on Green's function formalism we numerically calculate two-terminal transport together with density of states for different arrangements of atomic sites in the ladder and its backbone. Our results lead to a possibility of getting multiple mobility edges which essentially plays a switching action between a completely opaque to fully or partly conducting region upon the variation of system Fermi energy, and thus, support in fabricating mesoscopic or DNA-based switching devices.

  6. Dipolar field-induced spin-wave waveguides for spin-torque magnonics

    NASA Astrophysics Data System (ADS)

    Demidov, V. E.; Urazhdin, S.; Zholud, A.; Sadovnikov, A. V.; Demokritov, S. O.

    2015-01-01

    We use high-resolution imaging to study the propagation of spin waves in magnonic waveguides created by the dipolar magnetic fields of microscopic patterns. We show that the characteristics of spin-wave modes in such waveguides depend strongly on their geometry. In particular, by tuning the geometrical parameters, field-induced confinement for both the edge and the center waveguide modes can be achieved, enabling control over the spin-wave transmission characteristics. The studied waveguiding structures are particularly promising for the implementation of magnonic devices utilizing spin-torque phenomena.

  7. A field induced guide-antiguide modulator of GaAs-AlGaAs

    NASA Technical Reports Server (NTRS)

    Huang, T. C.; Chung, Y.; Young, D. B.; Dagli, N.; Coldren, L. A.

    1991-01-01

    A guide-antiguide modulator of GaAs-AlGaAs using the electric-field-induced waveguide concept was demonstrated. The device was formed with a central waveguide electrode sandwiched between two antiguide electrodes on the surface of a p-i-n multiple quantum well (MQW). Switching between lateral guiding and antiguiding was accomplished by reverse biasing either the central electrode or the adjacent electrodes to increase the index beneath these respective regions. The on-off ratio was measured to be 20:1 with a propagation loss of the on-state of about 5 dB/mm.

  8. Magnetic-Field-Induced Rotation of Polarized Light Emission from Monolayer WS2

    NASA Astrophysics Data System (ADS)

    Schmidt, Robert; Arora, Ashish; Plechinger, Gerd; Nagler, Philipp; Granados del Águila, Andrés; Ballottin, Mariana V.; Christianen, Peter C. M.; Michaelis de Vasconcellos, Steffen; Schüller, Christian; Korn, Tobias; Bratschitsch, Rudolf

    2016-08-01

    We control the linear polarization of emission from the coherently emitting K+ and K- valleys (valley coherence) in monolayer WS2 with an out-of-plane magnetic field of up to 25 T. The magnetic-field-induced valley Zeeman splitting causes a rotation of the emission polarization with respect to the excitation by up to 35° and reduces the polarization degree by up to 16%. We explain both of these phenomena with a model based on two noninteracting coherent two-level systems. We deduce that the coherent light emission from the valleys decays with a time constant of τc=260 fs .

  9. Magnetic-field-induced microwave losses in epitaxial Bi-Sr-Ca-Cu-O films

    SciTech Connect

    Silva, E.; Giura, M.; Marcon, R.; Fastampa, R. ); Balestrino, G.; Marinelli, M.; Milani, E. )

    1992-06-01

    Magnetic-field-induced microwave losses in epitaxial {ital c}-axis-oriented Bi-Sr-Ca-Cu-O films have been observed. At low magnetic field, the behavior of the absorption is qualitatively analogous to that already observed in granular samples. The dominant part is attributed to the dephasing of a network of Josephson junctions. A structural analysis shows evidence of such a network. The dependence of the absorption on the angle between the magnetic field and the {ital a}-{ital b} plane is consistent with this model.

  10. Homochiral mononuclear Dy-Schiff base complexes showing field-induced double magnetic relaxation processes.

    PubMed

    Ren, Min; Xu, Zhong-Li; Wang, Ting-Ting; Bao, Song-Song; Zheng, Ze-Hua; Zhang, Zai-Chao; Zheng, Li-Min

    2016-01-14

    A pair of enantiopure mononuclear dysprosium/salen-type complexes (Et3NH)[Dy((R,R)/(S,S)-3-NO2salcy)2] (/), where 3-NO2salcyH2 represents N,N'-(1,2-cyclohexanediylethylene)bis(3-nitrosalicylideneiminato), are reported. The enantiomer contains two crystallographically independent dysprosium(iii) ions, each chelated by two enantiopure 3-NO2salcy(2-) ligands forming a [DyN4O4] core. Detailed magnetic studies on compound reveal a field-induced dual magnetic relaxation behavior, originating from single ion anisotropy and intermolecular interactions, respectively. PMID:26621766

  11. Dipolar field-induced spin-wave waveguides for spin-torque magnonics

    SciTech Connect

    Demidov, V. E.; Urazhdin, S.; Zholud, A.; Sadovnikov, A. V.; Demokritov, S. O.

    2015-01-12

    We use high-resolution imaging to study the propagation of spin waves in magnonic waveguides created by the dipolar magnetic fields of microscopic patterns. We show that the characteristics of spin-wave modes in such waveguides depend strongly on their geometry. In particular, by tuning the geometrical parameters, field-induced confinement for both the edge and the center waveguide modes can be achieved, enabling control over the spin-wave transmission characteristics. The studied waveguiding structures are particularly promising for the implementation of magnonic devices utilizing spin-torque phenomena.

  12. Analysis and design of nonlocal spin devices with electric-field-induced spin-transport acceleration

    SciTech Connect

    Takamura, Yota; Akushichi, Taiju; Shuto, Yusuke; Sugahara, Satoshi

    2015-05-07

    We apply electric-field-induced acceleration for spin transport to a four-terminal nonlocal device and theoretically analyze its Hanle-effect signals. The effect of the ferromagnetic contact widths of the spin injector and detector on the signals is carefully discussed. Although Hanle-effect signals are randomized owing to the effect of the contact widths, this can be excluded by selecting an appropriate electric field for acceleration of spin transport. Spin lifetime can be correctly extracted by nonlocal devices with electric-field acceleration even using the spin injector and detector with finite contact widths.

  13. Field-induced macroscopic barrier model for persistent photoconductivity in nanocrystalline oxide thin-film transistors

    NASA Astrophysics Data System (ADS)

    Choi, Hyun-Sik; Jeon, Sanghun

    2014-03-01

    Persistent photoconductivity (PPC) in nanocrystalline InZnO thin-film transistors (TFTs) was studied using carrier fluctuation measurements and transient analysis. Low-frequency noise measurements and decay kinetics indicate that the band bending by the external field together with the ionized oxygen vacancy (Vo++) generated during the light exposure is the main cause of the PPC phenomenon. Based on these observations, a field-induced macroscopic barrier model is proposed as the origin of PPC for InZnO TFTs. In particular, this model explains that the carrier separation between e and Vo++ is induced by the external field applied to the three electrodes inside the transistor.

  14. Field induced polarization and magnetization behaviour of Gd-doped lead magnesium niobate ceramics

    NASA Astrophysics Data System (ADS)

    Pandey, Adityanarayan; Gupta, Surya Mohan; Nigam, Arun Kumar

    2016-05-01

    Both superparaelectric and superparamagnetic behaviour has been observed in rare earth magnetic ion Gd3+ doped Lead Magnesium Niobate (Gd-PMN). Field induced polarization and magnetization studies reveal hystresis loss free P-E and M-H loop at 300K and 5K, respectively. Temperature dependence of inverse susceptibility plot shows deviation at a temperature "td" when fitted with the Curie-Weiss law. This deviation has been attributed to transition from paramagnetic to superparamagnetic behaviour as reported in amorphous Pd-Ni-Fe-P alloys.

  15. Observations of continuum depression in warm dense matter with x-ray Thomson scattering.

    PubMed

    Fletcher, L B; Kritcher, A L; Pak, A; Ma, T; Döppner, T; Fortmann, C; Divol, L; Jones, O S; Landen, O L; Scott, H A; Vorberger, J; Chapman, D A; Gericke, D O; Mattern, B A; Seidler, G T; Gregori, G; Falcone, R W; Glenzer, S H

    2014-04-11

    Detailed measurements of the electron densities, temperatures, and ionization states of compressed CH shells approaching pressures of 50 Mbar are achieved with spectrally resolved x-ray scattering. Laser-produced 9 keV x-rays probe the plasma during the transient state of three-shock coalescence. High signal-to-noise x-ray scattering spectra show direct evidence of continuum depression in highly degenerate warm dense matter states with electron densities ne>1024  cm-3. The measured densities and temperatures agree well with radiation-hydrodynamic modeling when accounting for continuum lowering in calculations that employ detailed configuration accounting. PMID:24765979

  16. Continuum emission in the 1980 July 1 solar flare

    NASA Technical Reports Server (NTRS)

    Zirin, H.; Neidig, D. F.

    1981-01-01

    Comparison of continuum measurements of the July 1, 1980 flare at Big Bear Solar Observatory and Sacramento Peak Observatory show strong blue emission kernels with the ratio of Balmer continuum (Bac):3862 A continuum:continuum above 4275 A to be about 10:5:1. The blue continuum at 3862 A is too strong to be explained by unresolved lines. The Bac intensity was 2.5 times the photosphere and the strongest 3826 A continuum was 2 times the photosphere. The brightest continuum kernel occurred late in the flare, after the hard X-ray peak and related in time to an isolated peak in the 2.2 MeV line, suggesting that that continuum was excited by protons above 20 MeV.

  17. Emission Lines and the High Energy Continuum

    NASA Technical Reports Server (NTRS)

    Green, Paul

    1998-01-01

    Quasars show many striking relationships between line and continuum radiation whose origins remain a mystery. FeII, [OIII], Hbeta, and HeII emission line properties correlate with high energy continuum properties such as the relative strength of X-ray emission, and X-ray continuum slope. At the same time, the shape of the high energy continuum may vary with luminosity. An important tool for studying global properties of Quasi Stellar Objects (QSOs) is the co-addition of data for samples of QSOS. We use this to show that X-ray bright (XB) QSOs show stronger emission lines in general, but particularly from the narrow line region. The difference in the [OIII]/Hbeta ratio is particularly striking, and even more so when blended FeII emission is properly subtracted. Weaker narrow forbidden lines ([OII] and NeV) are enhanced by factors of 2 to 3 in both UV and optical XB composite spectra. The physical origin of these diverse and interrelated correlations has yet to be determined. Unfortunately, many physically informative trends intrinsic to QSOs may be masked by dispersion in the data due to either low signal-to-noise or variability. An important tool for studying global properties of QSOs is the co-addition of data for samples of QSOS. We use this to show that X-ray bright (XB) QSOs show stronger emission lines in general, but particularly from the narrow line region. The difference in the [OIII]/Hbeta ratio is particularly striking, and even more so when blended Fell emission is properly subtracted. Weaker narrow forbidden lines ([OII] and NeV) are enhanced by factors of 2 to 3 in both UV and optical XB composite spectra. We describe a large-scale effort now underway to probe these effects in large samples, using both data and analysis as homogeneous as possible. Using an HST FOS Atlas of QSO spectra, with primary comparison to ROSAT PSPC spectral constraints, we will model the Big Blue Bump, its relationship to luminosity and QSO type, and we will analyze and

  18. Continuum Damping of Free-boundary TAE with AEGIS

    NASA Astrophysics Data System (ADS)

    Chen, Eugene; Berk, Herb; Breizman, Boris; Zheng, Linjin

    2010-11-01

    An extension has been added to the ideal MHD code AEGIS (Adaptive EiGenfunction Independent Solutions) to estimate continuum damping of an Alfvenic mode. In our scheme we analyze the determinant arising from attempting to match solutions at the surface of the plasma vacuum interface. A zero of the determinant corresponds to an eigenvalue of the system. When continuum damping exists in a stable system, the eigenmode cannot be calculated by an integration along the real axis (in principle integration in deformed regions of the complex plane is required). The approach we take here is to scan the value of the determinant as a function of complex frequency where the imaginary part of the frequency is positive. The analytic continuation of the determinant gives an estimate of the root in the lower half plane, from which the damping rate is extracted. A complicating factor in our procedure is that the positions of a pole and zero of a determinant is frequently comparable to the damping rate. Hence, the search procedure must account for both the zero and pole structure of the determinant. It is interesting to note that the root of the pole corresponds to the eigenvalue of the problem where an ideal conducting wall is placed on the plasma vacuum interface. We are attempting to apply our new subroutine to realistic equilibria, such as C-Mod.

  19. Capillary effects in drainage in heterogeneous porous media: Continuum modeling, experiments and pore network simulations

    SciTech Connect

    Xu, Baomin; Yortsos, Y.C.

    1993-04-01

    We investigate effects of capillary heterogeneity induced by variations in permeability in the direction of displacement in heterogeneous porous media under drainage conditions. The investigation is three-pronged and uses macroscopic simulation, based on the standard continuum equations, experiments with the use of an acoustic technique and pore network numerical models. It is found that heterogeneity affects significantly the saturation profiles, the effect being stronger at lower rates. A good agreement is found between the continuum model predictions and the experimental results based on which it can be concluded that capillary heterogeneity effects in the direction of displacement act much like a body force (e.g. gravity). A qualitative agreement is also found between the continuum approach and the pore network numerical models, which is expected to improve when finite size effects in the pore network simulations diminish. The results are interpreted with the use of invasion percolation concepts.

  20. Variability of Lyman-alpha and the ultraviolet continuum of 3C 446

    NASA Technical Reports Server (NTRS)

    Bregman, J. N.; Glassgold, A. E.; Huggins, P. J.; Kinney, A. L.

    1986-01-01

    IUE observations have been conducted over the 1230-3175 A range for the violently variable quasar 3C 446, beginning in June 1980, at intervals of 1.2, 2.2, 0.5, and 0.4 yr. Strong absorption of the continuum was found below 1830 A, probably corresponding to a Lyman edge at z of 1.00 + or - 0.01. The absence of Mg II 2798 A absorption implies that the column density is in the lower end of the range, unless the gas is metal-poor. The Lyman-alpha emission line was detected in five spectra; relative to the number of ionizing protons, the line strengths are the same as in normal quasars, and line equivalent widths are small due to the continuum's rise redward of 912 A, which is much steeper than in normal quasars. The Lyman-alpha line and the nearby continuum vary so as to maintain constant equivalent width.

  1. Spectral and polarization structure of field-induced photonic bands in cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Palto, S. P.; Barnik, M. I.; Geivandov, A. R.; Kasyanova, I. V.; Palto, V. S.

    2015-09-01

    Transmission of planar layers of cholesteric liquid crystals is studied in pulsed electric fields perpendicular to the helix axis at normal incidence of both linearly polarized and unpolarized light. Spectral and light polarization properties of the primary photonic band and the field-induced bands up to fourth order of Bragg selective reflection are studied in detail. In our experiments we have achieved an electric field strength several times higher than the theoretical values corresponding to the critical field of full helix unwinding. However, the experiments show that despite the high strength of the electric field applied the helix does not unwind, but strongly deforms, keeping its initial spatial period. Strong helix deformation results in distinct spectral band splitting, as well as very high field-induced selective reflectance that can be applied in lasers and other optoelectronic devices. Peculiarities of inducing and splitting the bands are discussed in terms of the scattering coefficient approach. All observed effects are confirmed by numerical simulations. The simulations also show that liquid crystal surface anchoring is not the factor that prevents the helix unwinding. Thus, the currently acknowledged concept of continuous helix unwinding in the electric field should be reconsidered.

  2. Spontaneous and field-induced magnetic transitions in YBaCo2O5.5

    SciTech Connect

    Bobrovskii, Vladimir; Kazantsev, Vadim; Mirmelstein, Aleksey; Mushnikov, Nikolai; Proskurnina, Natalia; Voronin, Vladimir; Pomjakushina, Ekaterina; Conder, Kazimierz; Podlesnyak, Andrey A

    2009-01-01

    A detailed study of magnetic properties of cobaltite YBaCo{sub 2}O{sub 5.5} has been performed in high (up to 35 T) magnetic fields and under hydrostatic pressure up to 0.8 GPa. The temperatures of paramagnet-ferromagnet (PM-FM) and ferromagnet-antiferromagnet (FM-AF) phase transitions and their pressure derivatives have been determined. It has been revealed that in the compound with yttrium, in contrast to those with magnetic rare earth atoms, the AF-FM field-induced magnetic phase transition is accompanied by a considerable field hysteresis below 240 K, and the magnetic field of 35 T is not sufficient to complete this transition at low temperatures. The hysteresis value depends on the magnetic field sweep rate, which considered as an evidence of magnetic viscosity that is especially strong in the region of coexistence of the FM and AF phases. High values of susceptibility for the field-induced FM phase show that Co spin state in these compounds changes in strong magnetic field.

  3. Probing of field-induced structures and their dynamics in ferrofluids using oscillatory rheology.

    PubMed

    Felicia, Leona J; Philip, John

    2014-10-21

    We probe field-induced structures and their dynamics in ferrofluids using oscillatory rheology. The magnetic field dependence of the relaxation time and crossover modulus showed two distinct regions, indicating the different microstructures in those regions. The observed relaxation at various magnetic field strengths indicates that side chains are attached to the pinned single-sphere-width chains between the rheometer plates. Our results suggest that the ferrofluid under a magnetic field exhibits a soft solidlike behavior whose relaxation is governed by the imposed strain rate and the magnetic field. Using the scaling factors obtained from the frequency and modulus at the crossover point in the oscillatory rheological measurements, the constant strain-rate frequency sweep data is superimposed onto a single master curve. The frequency scaling factor increases with the strain rate as a power law with an exponent close to unity, whereas the amplitude scaling factor is almost strain-rate-independent at high magnetic field strengths. These findings are useful for a better understanding of field-induced ordering of nanoparticles in fluids and their optimization for practical applications. PMID:25268053

  4. Fabrication of Crystals and Devices for Studies of Field Induced Superconductivity

    NASA Astrophysics Data System (ADS)

    Kloc, Christian

    2002-03-01

    It was demonstrated that injection of electrons or holes into materials using field effect transistor can transform the surface layer into a metal or at low enough temperatures even into a superconductor. Which substances could exhibit electric field induced superconductivity is currently not well know. Superconductivity has been successfully induced in single crystals of arenes, (pentacene Tc = 2 K, tetracene Tc = 2.7K, anthracene Tc = 4 K) oligophenylenevinylenes (trimer Tc =4.2K , tetramer Tc=2.9 K and pentamer, Tc= 2 K) sexithiophene, polymer thin film (regioregular polythiophene, Tc = 2.35 K) and single crystals of pure and intercalated fullerenes (hole and electron doped C60 Tc = 52 and 11K, C70, Tc = 7K and substituted C60, Tc = up to 117 K). Additional, Schon et al. have reported the observation of field induced superconductivity in copper oxide compounds. Despite of relative simple device structures, they consist of semiconducting single crystals or well oriented thin films, metal source and drain electrodes, an aluminum oxide dielectric layer and a conducting gate electrode, the fabrication is onerous and the significance of particular technological steps to functionality of a whole device is not well explored. In this presentation I would like to discuss these technological procedures leading to superconducting devices and further developments in search for high temperature superconducting organics.

  5. Spin-dependent masses and field-induced quantum critical points

    NASA Astrophysics Data System (ADS)

    McCollam, A.; Daou, R.; Julian, S. R.; Bergemann, C.; Flouquet, J.; Aoki, D.

    2005-04-01

    We discuss spin-dependent mass enhancements associated with field-induced quantum critical points in heavy-fermion systems. We have recently observed this phenomenon on a branch of the Fermi surface of CeRu2Si2 above its metamagnetic transition, complementing earlier work. In CeCoIn5, at high fields above a field-induced quantum critical point, we see a strong spin-dependence of the effective mass on the thermodynamically dominant sheets of the Fermi surface. These observations reinforce the suggestion that ‘missing mass’ in some cerium-based heavy-fermion systems will be found on heavy spin-polarised branches of the Fermi surface. In all cases where this phenomenon is observed the linear coefficient of specific heat is field dependent; however, CeCoIn5 seems to be the first such heavy-fermion system in which the f-electrons are definitely contributing to the Fermi volume, which puts it beyond the existing theory intended for metamagnetic systems.

  6. Field-induced phase transitions in an antiferroelectric liquid crystal using the pyroelectric effect

    PubMed

    Shtykov; Vij; Lewis; Hird; Goodby

    2000-08-01

    The antiferroelectric liquid crystal (AFLC) under investigation possesses different helical polar phases. Measurements of pyroelectric response of these phases as a function of temperature and bias field have elucidated the ability of this method for investigating the nature of antiferroelectric phases and phase transitions under the bias field. The pyroelectric signal as a function of the bias field at fixed temperatures and as a function of temperature for fixed bias fields was measured for different phases of the investigated AFLC material. A theoretical model describing the pyroelectric response in different phases of AFLC is given, and the experimental results are interpreted. The threshold fields for field induced phase transitions are determined. The type of field induced phase transition from the AF phase in particular is found to be dependent on the temperature within its range. The properties of an unusual ferrielectric phase existing between ferrielectric chiral smectic-C (SmC*) and antiferroelectric AF phases are studied in a great detail. The results confirm that this phase is one of the incommensurate phases, predicted by the axial next-nearest neighbor Ising model and Landau model for this temperature region. PMID:11088695

  7. Decomposition of field-induced transmembrane potential responses of single cardiac cells.

    PubMed

    Sharma, Vinod; Lu, Steven N; Tung, Leslie

    2002-09-01

    In this study, we used a multi-site optical mapping system to record field-induced responses of single cells isolated from guinea pig hearts. The cells were stained with voltage sensitive dye di-8-ANEPPS and stimulated with two uniform field (S1-S2) pulses along their longitudinal axes. The first pulse (S1 = 5 ms, <10 V/cm) was applied during rest and elicited an action potential. The second pulse (S2 = 10 ms, 4-50 V/cm) was applied 15 ms after the break of the S1 pulse (during the action potential plateau). The transmembrane potential responses, Vm(F)s, were optically recorded from up to 12 sites along the cell length using a fiber optic based optical mapping system at a resolution of 17 or 25 microm. The field-induced Vm(F)s had a complex spatio-temporal pattern. We show that these responses can be decomposed into simpler components. The first component, termed the differential-mode component (Vmd(F)), is like the response of a passive cell. The second component, termed the common-mode component (Vmc(F)), is identical all along the cell and adds a constant offset to the differential mode response of various sites along the cell length, to produce the total Vm(F) responses of the cell. PMID:12214875

  8. Magnetic-field-induced orientational order in the isotropic phase of hard colloidal platelets

    SciTech Connect

    Beek, D. van der; Petukhov, A.V.; Vroege, G.J.; Lekkerkerker, H.N.W.; Davidson, P.; Ferre, J.; Jamet, J.P.; Wensink, H.H.; Bras, W.

    2006-04-15

    The magnetic-field-induced orientational order in the isotropic phase of colloidal gibbsite [Al(OH){sub 3}] platelets is studied by means of optical birefringence and small-angle x-ray scattering (SAXS) techniques. The suspensions display field-induced ordering at moderate field strengths (a few Tesla), which increases with increasing particle concentration. The gibbsite particles align their normals perpendicular to the magnetic field and hence possess a negative anisotropy of their diamagnetic susceptibility {delta}{chi}. The results can be described following a simple, Onsager-like approach. A simplified model is derived that allows one to obtain the orientational distribution function directly from the scattering data. However, it leads to an underestimate of the diamagnetic susceptibility anisotropy {delta}{chi}. This accounts for the difference between the {delta}{chi} values provided by the two experimental techniques (SAXS and magneto-optics). The order of magnitude {delta}{chi}{approx}10{sup -22} J/T{sup 2} lies in between that of goethite suspensions and that of suspensions of organic particles.

  9. SYSTEMATIC CONTINUUM ERRORS IN THE Ly{alpha} FOREST AND THE MEASURED TEMPERATURE-DENSITY RELATION

    SciTech Connect

    Lee, Khee-Gan

    2012-07-10

    Continuum fitting uncertainties are a major source of error in estimates of the temperature-density relation (usually parameterized as a power-law, T {proportional_to} {Delta}{sup {gamma}-1}) of the intergalactic medium through the flux probability distribution function (PDF) of the Ly{alpha} forest. Using a simple order-of-magnitude calculation, we show that few percent-level systematic errors in the placement of the quasar continuum due to, e.g., a uniform low-absorption Gunn-Peterson component could lead to errors in {gamma} of the order of unity. This is quantified further using a simple semi-analytic model of the Ly{alpha} forest flux PDF. We find that under(over)estimates in the continuum level can lead to a lower (higher) measured value of {gamma}. By fitting models to mock data realizations generated with current observational errors, we find that continuum errors can cause a systematic bias in the estimated temperature-density relation of ({delta}({gamma})) Almost-Equal-To -0.1, while the error is increased to {sigma}{sub {gamma}} Almost-Equal-To 0.2 compared to {sigma}{sub {gamma}} Almost-Equal-To 0.1 in the absence of continuum errors.

  10. Optimizing commensality of radio continuum and spectral line observations in the era of the SKA

    NASA Astrophysics Data System (ADS)

    Maddox, Natasha; Jarvis, M. J.; Oosterloo, T. A.

    2016-08-01

    The substantial decrease in star formation density from z=1 to the present day is curious given the relatively constant neutral gas density over the same epoch. Future radio astronomy facilities, including the SKA and pathfinder telescopes, will provide pioneering measures of both the gas content of galaxies and star formation activity over cosmological timescales. Here we investigate the commensalities between neutral atomic gas (HI) and radio continuum observations, as well as the complementarity of the data products. We start with the proposed HI and continuum surveys to be undertaken with the SKA precursor telescope MeerKAT, and building on this, explore optimal combinations of survey area coverage and depth of proposed HI and continuum surveys to be undertaken with the SKA1-MID instrument. Intelligent adjustment of these observational parameters results in a tiered strategy that minimises observation time while maximising the value of the dataset, both for HI and continuum science goals. We also find great complementarity between the HI and continuum datasets, with the spectral line HI data providing redshift measurements for gas-rich, star-forming galaxies with stellar masses Mstellar~10^9 Msun to z~0.3, a factor of three lower in stellar mass than would be feasible to reach with large optical spectroscopic campaigns.

  11. FAR-ULTRAVIOLET CONTINUUM EMISSION: APPLYING THIS DIAGNOSTIC TO THE CHROMOSPHERES OF SOLAR-MASS STARS

    SciTech Connect

    Linsky, Jeffrey L.; Bushinsky, Rachel; Ayres, Tom; France, Kevin; Fontenla, Juan

    2012-01-20

    The far-ultraviolet (FUV) continuum flux is recognized as a very sensitive diagnostic of the temperature structure of the Sun's lower chromosphere. Until now analysis of the available stellar FUV data has shown that solar-type stars must also have chromospheres, but quantitative analyses of stellar FUV continua require far higher quality spectra and comparison with new non-LTE chromosphere models. We present accurate far-ultraviolet (FUV, 1150-1500 A) continuum flux measurements for solar-mass stars, made feasible by the high throughput and very low detector background of the Cosmic Origins Spectrograph on the Hubbble Space Telescope. We show that the continuum flux can be measured above the detector background even for the faintest star in our sample. We find a clear trend of increasing continuum brightness temperature at all FUV wavelengths with decreasing rotational period, which provides an important measure of magnetic heating rates in stellar chromospheres. Comparison with semiempirical solar flux models shows that the most rapidly rotating solar-mass stars have FUV continuum brightness temperatures similar to the brightest faculae seen on the Sun. The thermal structure of the brightest solar faculae therefore provides a first-order estimate of the thermal structure and heating rate for the most rapidly rotating solar-mass stars in our sample.

  12. Optimizing commensality of radio continuum and spectral line observations in the era of the SKA

    NASA Astrophysics Data System (ADS)

    Maddox, Natasha; Jarvis, M. J.; Oosterloo, T. A.

    2016-08-01

    The substantial decrease in star formation density from z = 1 to the present day is curious given the relatively constant neutral gas density over the same epoch. Future radio astronomy facilities, including the Square Kilometre Array (SKA) and pathfinder telescopes, will provide pioneering measures of both the gas content of galaxies and star formation activity over cosmological time-scales. Here we investigate the commensalities between neutral atomic gas (H I) and radio continuum observations, as well as the complementarity of the data products. We start with the proposed H I and continuum surveys to be undertaken with the SKA precursor telescope MeerKAT, and building on this, explore optimal combinations of survey area coverage and depth of proposed H I and continuum surveys to be undertaken with the SKA1-MID instrument. Intelligent adjustment of these observational parameters results in a tiered strategy that minimizes observation time while maximizing the value of the data set, both for H I and continuum science goals. We also find great complementarity between the H I and continuum data sets, with the spectral line H I data providing redshift measurements for gas-rich, star-forming galaxies with stellar masses M* ˜ 109 M⊙ to z ˜ 0.3, a factor of 3 lower in stellar mass than would be feasible to reach with large optical spectroscopic campaigns.

  13. Mesoscopic and continuum modelling of angiogenesis.

    PubMed

    Spill, F; Guerrero, P; Alarcon, T; Maini, P K; Byrne, H M

    2015-02-01

    Angiogenesis is the formation of new blood vessels from pre-existing ones in response to chemical signals secreted by, for example, a wound or a tumour. In this paper, we propose a mesoscopic lattice-based model of angiogenesis, in which processes that include proliferation and cell movement are considered as stochastic events. By studying the dependence of the model on the lattice spacing and the number of cells involved, we are able to derive the deterministic continuum limit of our equations and compare it to similar existing models of angiogenesis. We further identify conditions under which the use of continuum models is justified, and others for which stochastic or discrete effects dominate. We also compare different stochastic models for the movement of endothelial tip cells which have the same macroscopic, deterministic behaviour, but lead to markedly different behaviour in terms of production of new vessel cells. PMID:24615007

  14. Models of Uranium continuum radio emission

    NASA Technical Reports Server (NTRS)

    Romig, Joseph H.; Evans, David R.; Sawyer, Constance B.; Schweitzer, Andrea E.; Warwick, James W.

    1987-01-01

    Uranium continuum radio emission detected by the Voyager 2 Planetary Radio Astronomy experiment during the January 1986 encounter is considered. The continuum emissions comprised four components (equatorial emissions, anomaly emissions, strong nightside emissions, and weak nightside emissions) associated with different sources. The equatorial emissions appeared most prominently during the days before closest approach and extended from 40 kHz or below to about 120 kHz. The anomaly emissions were seen about 12 hours before closest approach and extended to about 250 kHz. The agreement found between Miranda's phase and strong radio emission at 20.4 kHz, just after closest approach, suggests intense dynamic activity on the Miranda L shell.

  15. A continuum model of transcriptional bursting

    PubMed Central

    Corrigan, Adam M; Tunnacliffe, Edward; Cannon, Danielle; Chubb, Jonathan R

    2016-01-01

    Transcription occurs in stochastic bursts. Early models based upon RNA hybridisation studies suggest bursting dynamics arise from alternating inactive and permissive states. Here we investigate bursting mechanism in live cells by quantitative imaging of actin gene transcription, combined with molecular genetics, stochastic simulation and probabilistic modelling. In contrast to early models, our data indicate a continuum of transcriptional states, with a slowly fluctuating initiation rate converting the gene between different levels of activity, interspersed with extended periods of inactivity. We place an upper limit of 40 s on the lifetime of fluctuations in elongation rate, with initiation rate variations persisting an order of magnitude longer. TATA mutations reduce the accessibility of high activity states, leaving the lifetime of on- and off-states unchanged. A continuum or spectrum of gene states potentially enables a wide dynamic range for cell responses to stimuli. DOI: http://dx.doi.org/10.7554/eLife.13051.001 PMID:26896676

  16. Continuum of Collaboration: Little Steps for Little Feet

    ERIC Educational Resources Information Center

    Powell, Gwynn M.

    2013-01-01

    This mini-article outlines a continuum of collaboration for faculty within a department of the same discipline. The goal of illustrating this continuum is showcase different stages of collaboration so that faculty members can assess where they are as a collective and consider steps to collaborate more. The separate points along a continuum of…

  17. Spatiotemporal dynamics of continuum neural fields

    NASA Astrophysics Data System (ADS)

    Bressloff, Paul C.

    2012-01-01

    We survey recent analytical approaches to studying the spatiotemporal dynamics of continuum neural fields. Neural fields model the large-scale dynamics of spatially structured biological neural networks in terms of nonlinear integrodifferential equations whose associated integral kernels represent the spatial distribution of neuronal synaptic connections. They provide an important example of spatially extended excitable systems with nonlocal interactions and exhibit a wide range of spatially coherent dynamics including traveling waves oscillations and Turing-like patterns.

  18. Improvements in continuum modeling for biomolecular systems

    NASA Astrophysics Data System (ADS)

    Yu, Qiao; Ben-Zhuo, Lu

    2016-01-01

    Modeling of biomolecular systems plays an essential role in understanding biological processes, such as ionic flow across channels, protein modification or interaction, and cell signaling. The continuum model described by the Poisson- Boltzmann (PB)/Poisson-Nernst-Planck (PNP) equations has made great contributions towards simulation of these processes. However, the model has shortcomings in its commonly used form and cannot capture (or cannot accurately capture) some important physical properties of the biological systems. Considerable efforts have been made to improve the continuum model to account for discrete particle interactions and to make progress in numerical methods to provide accurate and efficient simulations. This review will summarize recent main improvements in continuum modeling for biomolecular systems, with focus on the size-modified models, the coupling of the classical density functional theory and the PNP equations, the coupling of polar and nonpolar interactions, and numerical progress. Project supported by the National Natural Science Foundation of China (Grant No. 91230106) and the Chinese Academy of Sciences Program for Cross & Cooperative Team of the Science & Technology Innovation.

  19. A Continuum Theory of Thermal Transpiration

    NASA Astrophysics Data System (ADS)

    Bielenberg, James; Brenner, Howard

    2003-11-01

    A rational, continuum mechanical description is given for the pressure drop that develops in a closed capillary tube subject to an imposed temperature gradient. This phenomenon, termed thermal transpiration, has been experimentally demonstrated in systems at vanishing Knudsen numbers, yet no purely continuum mechanical description has, until now, been given. Previous hybrid solutions (dating back to Maxwell in 1879) have utilized the classical, incompressible flow equations along with molecularly derived slip boundary conditions. This solution approach will be briefly discussed and shown to be dynamically consistent yet energetically flawed. Subsequently, we will apply a novel reformulation of continuum-mechanics and -thermodynamics, which clearly distinguishes between the Lagrangian (tracer) and the barycentric velocities, to generate a solution for the thermal pressure drop developed in a closed system. Explicitly, the phenomena at hand will be shown to be entirely analogous to Poiseuille flow in tube, albeit with the tacit recognition that the ``flow'' we are speaking of is defined in a dynamic sense rather than in the more traditional, kinematic mass-flux based sense. This solution will be show to be free of ad hoc parameters, consistent with experimental results, and in accordance with classical macroscopic thermodynamics. Beyond its purely scientific importance, this phenomenon may find applications in the emerging area of micro-fluidic pumping.

  20. Bipotential continuum models for granular mechanics

    NASA Astrophysics Data System (ADS)

    Goddard, Joe

    2014-03-01

    Most currently popular continuum models for granular media are special cases of a generalized Maxwell fluid model, which describes the evolution of stress and internal variables such as granular particle fraction and fabric,in terms of imposed strain rate. It is shown how such models can be obtained from two scalar potentials, a standard elastic free energy and a ``dissipation potential'' given rigorously by the mathematical theory of Edelen. This allows for a relatively easy derivation of properly invariant continuum models for granular media and fluid-particle suspensions within a thermodynamically consistent framework. The resulting continuum models encompass all the prominent regimes of granular flow, ranging from the quasi-static to rapidly sheared, and are readily extended to include higher-gradient or Cosserat effects. Models involving stress diffusion, such as that proposed recently by Kamrin and Koval (PRL 108 178301), provide an alternative approach that is mentioned in passing. This paper provides a brief overview of a forthcoming review articles by the speaker (The Princeton Companion to Applied Mathematics, and Appl. Mech. Rev.,in the press, 2013).

  1. The emission line - continuum connection in galaxies

    NASA Astrophysics Data System (ADS)

    Sodre, Laerte; Albernaz-Sirico, Ana Carolina

    2015-08-01

    Star-forming galaxies with a blue continuum tend to present prominent emission lines, whereas in red galaxies emission lines are associated mostly to nuclear activity or to certain stellar populations, like post-AGB stars. In this work we have used tools of machine learning to investigate how theemission line equivalent widths of galaxies are related to their optical continuum. From the analysis of a sample of high S/N spectra of SDSS/DR9 we show that indeed it is possible to estimate with good accuracy the equivalent width of the most intense emission lines from galaxy continuum information only for star-forming galaxies and AGNs (LINERS and Seyfer 2 emitters) by using simple relationships (linear and/or polynomial models) between the EWs and the relative flux at certain wavelengths. An important motivation for this work is to produce realistic spectra to test the data reduction pipelines of the new generation of galaxy surveys, like J-PAS and PFS/SuMIRe.

  2. Lattice Boltzmann algorithm for continuum multicomponent flow.

    PubMed

    Halliday, I; Hollis, A P; Care, C M

    2007-08-01

    We present a multicomponent lattice Boltzmann simulation for continuum fluid mechanics, paying particular attention to the component segregation part of the underlying algorithm. In the principal result of this paper, the dynamics of a component index, or phase field, is obtained for a segregation method after U. D'Ortona [Phys. Rev. E 51, 3718 (1995)], due to Latva-Kokko and Rothman [Phys. Rev. E 71 056702 (2005)]. The said dynamics accord with a simulation designed to address multicomponent flow in the continuum approximation and underwrite improved simulation performance in two main ways: (i) by reducing the interfacial microcurrent activity considerably and (ii) by facilitating simulational access to regimes of flow with a low capillary number and drop Reynolds number [I. Halliday, R. Law, C. M. Care, and A. Hollis, Phys. Rev. E 73, 056708 (2006)]. The component segregation method studied, used in conjunction with Lishchuk's method [S. V. Lishchuk, C. M. Care, and I. Halliday, Phys. Rev. E 67, 036701 (2003)], produces an interface, which is distributed in terms of its component index; however, the hydrodynamic boundary conditions which emerge are shown to support the notion of a sharp, unstructured, continuum interface. PMID:17930175

  3. Polymer Fluid Dynamics: Continuum and Molecular Approaches.

    PubMed

    Bird, R B; Giacomin, A J

    2016-06-01

    To solve problems in polymer fluid dynamics, one needs the equations of continuity, motion, and energy. The last two equations contain the stress tensor and the heat-flux vector for the material. There are two ways to formulate the stress tensor: (a) One can write a continuum expression for the stress tensor in terms of kinematic tensors, or (b) one can select a molecular model that represents the polymer molecule and then develop an expression for the stress tensor from kinetic theory. The advantage of the kinetic theory approach is that one gets information about the relation between the molecular structure of the polymers and the rheological properties. We restrict the discussion primarily to the simplest stress tensor expressions or constitutive equations containing from two to four adjustable parameters, although we do indicate how these formulations may be extended to give more complicated expressions. We also explore how these simplest expressions are recovered as special cases of a more general framework, the Oldroyd 8-constant model. Studying the simplest models allows us to discover which types of empiricisms or molecular models seem to be worth investigating further. We also explore equivalences between continuum and molecular approaches. We restrict the discussion to several types of simple flows, such as shearing flows and extensional flows, which are of greatest importance in industrial operations. Furthermore, if these simple flows cannot be well described by continuum or molecular models, then it is not necessary to lavish time and energy to apply them to more complex flow problems. PMID:27276553

  4. Electronic continuum model for molecular dynamics simulations.

    PubMed

    Leontyev, I V; Stuchebrukhov, A A

    2009-02-28

    A simple model for accounting for electronic polarization in molecular dynamics (MD) simulations is discussed. In this model, called molecular dynamics electronic continuum (MDEC), the electronic polarization is treated explicitly in terms of the electronic continuum (EC) approximation, while the nuclear dynamics is described with a fixed-charge force field. In such a force-field all atomic charges are scaled to reflect the screening effect by the electronic continuum. The MDEC model is rather similar but not equivalent to the standard nonpolarizable force-fields; the differences are discussed. Of our particular interest is the calculation of the electrostatic part of solvation energy using standard nonpolarizable MD simulations. In a low-dielectric environment, such as protein, the standard MD approach produces qualitatively wrong results. The difficulty is in mistreatment of the electronic polarizability. We show how the results can be much improved using the MDEC approach. We also show how the dielectric constant of the medium obtained in a MD simulation with nonpolarizable force-field is related to the static (total) dielectric constant, which includes both the nuclear and electronic relaxation effects. Using the MDEC model, we discuss recent calculations of dielectric constants of alcohols and alkanes, and show that the MDEC results are comparable with those obtained with the polarizable Drude oscillator model. The applicability of the method to calculations of dielectric properties of proteins is discussed. PMID:19256627

  5. Field-Induced Crystalline-to-Amorphous Phase Transformation on the Si Nano-Apex and the Achieving of Highly Reliable Si Nano-Cathodes

    PubMed Central

    Huang, Yifeng; Deng, Zexiang; Wang, Weiliang; Liang, Chaolun; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

    2015-01-01

    Nano-scale vacuum channel transistors possess merits of higher cutoff frequency and greater gain power as compared with the conventional solid-state transistors. The improvement in cathode reliability is one of the major challenges to obtain high performance vacuum channel transistors. We report the experimental findings and the physical insight into the field induced crystalline-to-amorphous phase transformation on the surface of the Si nano-cathode. The crystalline Si tip apex deformed to amorphous structure at a low macroscopic field (0.6~1.65 V/nm) with an ultra-low emission current (1~10 pA). First-principle calculation suggests that the strong electrostatic force exerting on the electrons in the surface lattices would take the account for the field-induced atomic migration that result in an amorphization. The arsenic-dopant in the Si surface lattice would increase the inner stress as well as the electron density, leading to a lower amorphization field. Highly reliable Si nano-cathodes were obtained by employing diamond like carbon coating to enhance the electron emission and thus decrease the surface charge accumulation. The findings are crucial for developing highly reliable Si-based nano-scale vacuum channel transistors and have the significance for future Si nano-electronic devices with narrow separation. PMID:25994377

  6. Field-Induced Crystalline-to-Amorphous Phase Transformation on the Si Nano-Apex and the Achieving of Highly Reliable Si Nano-Cathodes.

    PubMed

    Huang, Yifeng; Deng, Zexiang; Wang, Weiliang; Liang, Chaolun; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

    2015-01-01

    Nano-scale vacuum channel transistors possess merits of higher cutoff frequency and greater gain power as compared with the conventional solid-state transistors. The improvement in cathode reliability is one of the major challenges to obtain high performance vacuum channel transistors. We report the experimental findings and the physical insight into the field induced crystalline-to-amorphous phase transformation on the surface of the Si nano-cathode. The crystalline Si tip apex deformed to amorphous structure at a low macroscopic field (0.6~1.65 V/nm) with an ultra-low emission current (1~10 pA). First-principle calculation suggests that the strong electrostatic force exerting on the electrons in the surface lattices would take the account for the field-induced atomic migration that result in an amorphization. The arsenic-dopant in the Si surface lattice would increase the inner stress as well as the electron density, leading to a lower amorphization field. Highly reliable Si nano-cathodes were obtained by employing diamond like carbon coating to enhance the electron emission and thus decrease the surface charge accumulation. The findings are crucial for developing highly reliable Si-based nano-scale vacuum channel transistors and have the significance for future Si nano-electronic devices with narrow separation. PMID:25994377

  7. Field-Induced Crystalline-to-Amorphous Phase Transformation on the Si Nano-Apex and the Achieving of Highly Reliable Si Nano-Cathodes

    NASA Astrophysics Data System (ADS)

    Huang, Yifeng; Deng, Zexiang; Wang, Weiliang; Liang, Chaolun; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

    2015-05-01

    Nano-scale vacuum channel transistors possess merits of higher cutoff frequency and greater gain power as compared with the conventional solid-state transistors. The improvement in cathode reliability is one of the major challenges to obtain high performance vacuum channel transistors. We report the experimental findings and the physical insight into the field induced crystalline-to-amorphous phase transformation on the surface of the Si nano-cathode. The crystalline Si tip apex deformed to amorphous structure at a low macroscopic field (0.6~1.65 V/nm) with an ultra-low emission current (1~10 pA). First-principle calculation suggests that the strong electrostatic force exerting on the electrons in the surface lattices would take the account for the field-induced atomic migration that result in an amorphization. The arsenic-dopant in the Si surface lattice would increase the inner stress as well as the electron density, leading to a lower amorphization field. Highly reliable Si nano-cathodes were obtained by employing diamond like carbon coating to enhance the electron emission and thus decrease the surface charge accumulation. The findings are crucial for developing highly reliable Si-based nano-scale vacuum channel transistors and have the significance for future Si nano-electronic devices with narrow separation.

  8. T-wave sources, slopes, rough bottoms and continuum

    NASA Astrophysics Data System (ADS)

    Odom, Robert I.; Soukup, Darin J.

    2002-05-01

    Bathymetry plays a strong role in the excitation of T-waves by breaking strict mode orthogonality and permitting energy from higher order modes to couple to the lower order modes comprising the T-phase. Observationally (Dziak, 2001) earthquakes with a strong strike-slip component are more efficient at generating T-waves than normal fault mechanisms with the same moment magnitude. It is shown that fault type and orientation correlates strongly with T-wave excitation efficiency. For shallow sources, the discrete modes contribute to the majority of the seismic source field, which is then scattered into the acoustic modes by irregular bathymetry. However, the deeper the earthquake source, the more important the continuum component of the spectrum becomes for the excitation. Deterministic bathymetry and random roughness enter the modal scattering theory as separate terms, and allow the relative contributions from the slope conversion mechanism and bottom roughness to be directly compared. [Work supported by the National Ocean Partnership Program.

  9. QCD thermodynamics with continuum extrapolated Wilson fermions. II.

    NASA Astrophysics Data System (ADS)

    Borsanyi, Szabolcs; Hoelbling, Christian; Toth, Balint C.; Durr, Stephan; Krieg, Stefan; Szabo, Kalman K.; Fodor, Zoltan; Katz, Sandor D.; Nogradi, Daniel; Trombitas, Norbert

    2015-07-01

    We continue our investigation of 2 +1 flavor QCD thermodynamics using dynamical Wilson fermions in the fixed scale approach. Two additional pion masses, approximately 440 MeV and 285 MeV, are added to our previous work at 545 MeV. The simulations were performed at 3 or 4 lattice spacings at each pion mass. The renormalized chiral condensate, strange quark number susceptibility and Polyakov loop is obtained as a function of the temperature and we observe a decrease in the light chiral pseudocritical temperature as the pion mass is lowered while the pseudocritical temperature associated with the strange quark number susceptibility or the Polyakov loop is only mildly sensitive to the pion mass. These findings are in agreement with previous continuum results obtained in the staggered formulation.

  10. A robust, coupled approach for atomistic-continuum simulation.

    SciTech Connect

    Aubry, Sylvie; Webb, Edmund Blackburn, III; Wagner, Gregory John; Klein, Patrick A.; Jones, Reese E.; Zimmerman, Jonathan A.; Bammann, Douglas J.; Hoyt, Jeffrey John; Kimmer, Christopher J.

    2004-09-01

    This report is a collection of documents written by the group members of the Engineering Sciences Research Foundation (ESRF), Laboratory Directed Research and Development (LDRD) project titled 'A Robust, Coupled Approach to Atomistic-Continuum Simulation'. Presented in this document is the development of a formulation for performing quasistatic, coupled, atomistic-continuum simulation that includes cross terms in the equilibrium equations that arise due to kinematic coupling and corrections used for the calculation of system potential energy to account for continuum elements that overlap regions containing atomic bonds, evaluations of thermo-mechanical continuum quantities calculated within atomistic simulations including measures of stress, temperature and heat flux, calculation used to determine the appropriate spatial and time averaging necessary to enable these atomistically-defined expressions to have the same physical meaning as their continuum counterparts, and a formulation to quantify a continuum 'temperature field', the first step towards constructing a coupled atomistic-continuum approach capable of finite temperature and dynamic analyses.

  11. X-ray microtomography of field-induced macro-structures in a ferrofluid.

    SciTech Connect

    Lee, W.; X-Ray Science Division

    2010-09-01

    X-ray microtomography is used to visualize, in-situ, the three-dimensional nature of the magnetic field induced macro-structures (>1 ?m) inside a bulk (not, vert, similar1 mm diameter) magnetite-particle-mineral oil ferrofluid sample. Columnar structures of not, vert, similar10 ?m diameter were seen under a 0.35 kG applied magnetic field, while labyrinth type structures not, vert, similar4 ?m in width were seen at 0.55 kG. The structures have height/width aspect ratios >100. The results show that the magnetite volume fraction is not constant within the structures and on average is considerably less than a random sphere packing model.

  12. Magnetic-field-induced rotation of light with orbital angular momentum

    SciTech Connect

    Shi, Shuai; Ding, Dong-Sheng Zhou, Zhi-Yuan; Li, Yan; Zhang, Wei; Shi, Bao-Sen

    2015-06-29

    Light carrying orbital angular momentum (OAM) has attractive applications in the fields of precise optical measurements and high capacity optical communications. We study the rotation of a light beam propagating in warm {sup 87}Rb atomic vapor using a method based on magnetic-field-induced circular birefringence. The dependence of the rotation angle on the magnetic field makes it appropriate for weak magnetic field measurements. We quote a detailed theoretical description that agrees well with the experimental observations. The experiment shown here provides a method to measure the magnetic field intensity precisely and expands the application of OAM-carrying light. This technique has advantage in measurement of magnetic field weaker than 0.5 G, and the precision we achieved is 0.8 mG.

  13. Effect of dimerization on the field-induced birefringence in ferrofluids.

    PubMed

    Szczytko, Jacek; Vaupotič, Nataša; Osipov, Mihail A; Madrak, Karolina; Górecka, Ewa

    2013-06-01

    The magnetic-field-induced birefringence in a ferrofluid composed of spherical cobalt nanoparticles has been studied both experimentally and theoretically. The considerable induced birefringence determined experimentally has been attributed to the formation of chains of nanoparticles. The birefringence has been measured as a function of the external magnetic field and the volume fraction (f) of nanoparticles. It is quadratic in f as opposed to the Faraday effect, which is linear in f. Experimental results agree well with the theoretical model based on a simple density functional approach. For dilute solutions the experimental results can be explained by assuming that only dimers of nanoparticles are formed while the concentration of longer chains is negligible. PMID:23848690

  14. Electric field-induced reversible trapping of microtubules along metallic glass microwire electrodes

    NASA Astrophysics Data System (ADS)

    Kim, Kyongwan; Sikora, Aurélien; Nakayama, Koji S.; Umetsu, Mitsuo; Hwang, Wonmuk; Teizer, Winfried

    2015-04-01

    Microtubules are among bio-polymers providing vital functions in dynamic cellular processes. Artificial organization of these bio-polymers is a requirement for transferring their native functions into device applications. Using electrophoresis, we achieve an accumulation of microtubules along a metallic glass (Pd42.5Cu30Ni7.5P20) microwire in solution. According to an estimate based on migration velocities of microtubules approaching the wire, the electrophoretic mobility of microtubules is around 10-12 m2/Vs. This value is four orders of magnitude smaller than the typical mobility reported previously. Fluorescence microscopy at the individual-microtubule level shows microtubules aligning along the wire axis during the electric field-induced migration. Casein-treated electrodes are effective to reversibly release trapped microtubules upon removal of the external field. An additional result is the condensation of secondary filamentous structures from oriented microtubules.

  15. Field-Induced Lifshitz Transition without Metamagnetism in CeIrIn(5).

    PubMed

    Aoki, D; Seyfarth, G; Pourret, A; Gourgout, A; McCollam, A; Bruin, J A N; Krupko, Y; Sheikin, I

    2016-01-22

    We report high magnetic field measurements of magnetic torque, thermoelectric power, magnetization, and the de Haas-van Alphen effect in CeIrIn_{5} across 28 T, where a metamagnetic transition was suggested in previous studies. The thermoelectric power displays two maxima at 28 and 32 T. Above 28 T, a new, low de Haas-van Alphen frequency with a strongly enhanced effective mass emerges, while the highest frequency observed at low field disappears entirely. This suggests a field-induced Lifshitz transition. However, longitudinal magnetization does not show any anomaly up to 33 T, thus ruling out a metamagnetic transition at 28 T. PMID:26849611

  16. Field-induced exciton condensation in LaCoO3

    NASA Astrophysics Data System (ADS)

    Sotnikov, A.; Kuneš, J.

    2016-07-01

    Motivated by recent observation of magnetic field induced transition in LaCoO3 we study the effect of external field in systems close to instabilities towards spin-state ordering and exciton condensation. We show that, while in both cases the transition can be induced by an external field, temperature dependencies of the critical field have opposite slopes. Based on this result we argue that the experimental observations select the exciton condensation scenario. We show that such condensation is possible due to high mobility of the intermediate spin excitations. The estimated width of the corresponding dispersion is large enough to overrule the order of atomic multiplets and to make the intermediate spin excitation propagating with a specific wave vector the lowest excitation of the system.

  17. Magnetic-field-induced diameter-selective synthesis of single-walled carbon nanotubes.

    PubMed

    Su, Yanjie; Zhang, Yaozhong; Wei, Hao; Zhang, Liling; Zhao, Jiang; Yang, Zhi; Zhang, Yafei

    2012-03-01

    We report a facile and scalable approach to synthesize single-walled carbon nanotubes (SWNTs) with selected diameter distribution by applying a magnetic field perpendicular to the electric field in the arc plasma region. It is found that this magnetic field-induced diameter-selectivity strategy enables the control of the SWNTs with different diameter distributions in different regions, and the diameter-selective efficiency could be enhanced by modifying the direction of magnetic field. Our results indicate that the motions of the catalysts with different particle sizes, positive carbon ions and electrons are significantly influenced by the magnetic field and electromagnetic force, resulting in the different nucleation and growth processes of SWNTs due to the collective interactions between the magnetic field and arc plasma. This approach would enable a viable route towards the synthesis of SWNTs with desired diameter through the tuning of arc parameters in the arc discharge process. PMID:22301844

  18. Picosecond Electric-Field-Induced Threshold Switching in Phase-Change Materials.

    PubMed

    Zalden, Peter; Shu, Michael J; Chen, Frank; Wu, Xiaoxi; Zhu, Yi; Wen, Haidan; Johnston, Scott; Shen, Zhi-Xun; Landreman, Patrick; Brongersma, Mark; Fong, Scott W; Wong, H-S Philip; Sher, Meng-Ju; Jost, Peter; Kaes, Matthias; Salinga, Martin; von Hoegen, Alexander; Wuttig, Matthias; Lindenberg, Aaron M

    2016-08-01

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag_{4}In_{3}Sb_{67}Te_{26}. Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales-faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch. PMID:27541475

  19. Picosecond Electric-Field-Induced Threshold Switching in Phase-Change Materials

    NASA Astrophysics Data System (ADS)

    Zalden, Peter; Shu, Michael J.; Chen, Frank; Wu, Xiaoxi; Zhu, Yi; Wen, Haidan; Johnston, Scott; Shen, Zhi-Xun; Landreman, Patrick; Brongersma, Mark; Fong, Scott W.; Wong, H.-S. Philip; Sher, Meng-Ju; Jost, Peter; Kaes, Matthias; Salinga, Martin; von Hoegen, Alexander; Wuttig, Matthias; Lindenberg, Aaron M.

    2016-08-01

    Many chalcogenide glasses undergo a breakdown in electronic resistance above a critical field strength. Known as threshold switching, this mechanism enables field-induced crystallization in emerging phase-change memory. Purely electronic as well as crystal nucleation assisted models have been employed to explain the electronic breakdown. Here, picosecond electric pulses are used to excite amorphous Ag4In3Sb67Te26 . Field-dependent reversible changes in conductivity and pulse-driven crystallization are observed. The present results show that threshold switching can take place within the electric pulse on subpicosecond time scales—faster than crystals can nucleate. This supports purely electronic models of threshold switching and reveals potential applications as an ultrafast electronic switch.

  20. Magnetic-Field-Induced Insulator-Conductor Transition in SU(2) Quenched Lattice Gauge Theory

    SciTech Connect

    Buividovich, P.V.; Kharzeev, D.; Chernodub, M.N., Kalaydzhyan, T., Luschevskaya, E.V., and M.I. Polikarpov

    2010-09-24

    We study the correlator of two vector currents in quenched SU(2) lattice gauge theory with a chirally invariant lattice Dirac operator with a constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of a magnetic field, while for other components the correlation length slightly decreases. We apply the maximal entropy method to extract the corresponding spectral function. In the limit of zero frequency this spectral function yields the electric conductivity of quenched theory. We find that in the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field.

  1. Raman thermometry: Effective temperature of the nonuniform temperature field induced by a Gaussian laser

    SciTech Connect

    Očenášek, Jan Voldřich, Josef

    2015-12-21

    Raman spectroscopy is a widely applied analytical technique with numerous applications that is based on inelastic scattering of monochromatic light, which is typically provided by a laser. Irradiation of a sample by a laser beam is always accompanied by an increase in the sample temperature, which may be unwanted or may be beneficial for studying temperature-related effects and determining thermal parameters. This work reports analyses of the temperature field induced by a Gaussian laser to calculate the Raman scattered intensity related to each temperature value of the nonuniform field present on the sample. The effective temperature of the probed field, calculated as an average weighted by the laser intensity, is demonstrated to be about 70% of the maximum temperature irrespective of the absorption coefficient or the laser focus. Finally, using crystalline silicon as a model material, it is shown that this effective value closely approximates the temperature value identified from the thermally related peak shift.

  2. Field-induced exciton condensation in LaCoO3.

    PubMed

    Sotnikov, A; Kuneš, J

    2016-01-01

    Motivated by recent observation of magnetic field induced transition in LaCoO3 we study the effect of external field in systems close to instabilities towards spin-state ordering and exciton condensation. We show that, while in both cases the transition can be induced by an external field, temperature dependencies of the critical field have opposite slopes. Based on this result we argue that the experimental observations select the exciton condensation scenario. We show that such condensation is possible due to high mobility of the intermediate spin excitations. The estimated width of the corresponding dispersion is large enough to overrule the order of atomic multiplets and to make the intermediate spin excitation propagating with a specific wave vector the lowest excitation of the system. PMID:27461512

  3. Field-induced magnetostructural transition in Gd5ge4 studied by pulsed magnetic fields

    SciTech Connect

    Ouyang, Z.W.; Nojiri, H.; Yoshii, S.; Rao, G.H.; Wang, Y.C.; Pecharsky, V.K.; Gschneidner Jr., K.A.

    2008-05-22

    The field-induced magnetostructural transformation in Gd{sub 5}Ge{sub 4} was examined by magnetization measurements in pulsed magnetic fields. The low-temperature irreversibility of the transition can be destroyed by the magnetocaloric effect, and depending on the heat exchange between the sample and its surroundings, the irreversibility (or kinetic arrest) can also be retained. Measurements by using various magnetic-field sweep rates were conducted to examine the dynamic response of the system in the transition region. The critical fields for the magnetostructural transition below 20 K are field sweep rate dependent--the larger the field sweep rate, the higher the critical field. However, this rate dependence is readily suppressed with increasing temperature.

  4. Field-induced growth of self-annealing suspended colloidal monolayers

    NASA Astrophysics Data System (ADS)

    Han, Ming; Luijten, Erik; Luijten Research Group Team

    2015-03-01

    Due to their reduced dimensionality, flexible sheet-like materials have numerous applications, e.g. offering the potential to serve as functional coatings or as a system for encapsulation, akin to biologic membranes. Here we report the ability to generate large ordered, flexible, and suspended monolayers via field-induced self-assembly. We employ anisotropic polarizable colloidal particles and stimulate their reversible aggregation by applying a static external electric field. Through molecular dynamics simulations with a self-consistent calculation of the induced dipole moments, we demonstrate that such particles form monolayers capable of eliminating defects and dislocations, and even self-healing. Potential applications, such as tube formation, are also discussed.

  5. Electric-Field-Induced Dissociation of Heavy Rydberg Ion-Pair States

    SciTech Connect

    Reinhold, Carlos O; Yoshida, S.; Dunning, F. B.

    2011-01-01

    A classical trajectory Monte Carlo approach is used to simulate the dissociation of H+..F and K+..Cl heavy Rydberg ion pairs induced by a ramped electric-field, a technique used experimentally to detect and probe ion-pair states. The simulations include the effects of the strong short-range repulsive interaction associated with ion-pair scattering and provide results in good agreement with experimental data for Stark wavepackets probed by a ramped field, demonstrating that many of the characteristics of field-induced dissociation can be well described using a purely classical model. The data also show that states with a given value of principal quantum number (i.e., binding energy) can dissociate over a broad range of applied fields, the exact field being governed by the initial orbital angular momentum and orientation of the state.

  6. Field-induced exciton condensation in LaCoO3

    PubMed Central

    Sotnikov, A.; Kuneš, J.

    2016-01-01

    Motivated by recent observation of magnetic field induced transition in LaCoO3 we study the effect of external field in systems close to instabilities towards spin-state ordering and exciton condensation. We show that, while in both cases the transition can be induced by an external field, temperature dependencies of the critical field have opposite slopes. Based on this result we argue that the experimental observations select the exciton condensation scenario. We show that such condensation is possible due to high mobility of the intermediate spin excitations. The estimated width of the corresponding dispersion is large enough to overrule the order of atomic multiplets and to make the intermediate spin excitation propagating with a specific wave vector the lowest excitation of the system. PMID:27461512

  7. Hysteretic DC electrowetting by field-induced nano-structurations on polystyrene films.

    PubMed

    Sawane, Yogesh B; Datar, Suwarna; Ogale, Satishchandra B; Banpurkar, Arun G

    2015-04-01

    Electrowetting (EW) offers executive wetting control of conductive liquids on several polymer surfaces. We report a peculiar electrowetting response for aqueous drops on a polystyrene (PS) dielectric surface in the presence of silicone oil. After the first direct current (DC) voltage cycle, the droplet failed to regain Young's angle, yielding contact angle hysteresis, which is close to a value found in ambient air. We conjecture that the hysteretic EW response appears from in situ surface modification using electric field induced water-ion contact with PS surface inducing nano-structuration by electro-hydrodynamic (EHD) instability. Atomic force microscopy confirms the formation of nano-structuration on the electrowetted surface. The effects of molecular weight, applied electric field, water conductivity and pH on nano-structuration are studied. Finally, the EW based nano-structuration on PS surface is used for the enhanced loading of aqueous dyes on hydrophobic surfaces. PMID:25690856

  8. Giant electric-field-induced strain in lead-free piezoelectric materials.

    PubMed

    Chen, Lan; Yang, Yurong; Meng, X K

    2016-01-01

    First-principles calculations are performed to investigate the structures, electrical, and magnetic properties of compressive BiFeO3 films under electric-field and pressure perpendicular to the films. A reversible electric-field-induced strain up 10% is achieved in the compressive BiFeO3 films. The giant strain originates from rhombohedral-tetragonal (R-T) phase transition under electric-filed, and is recoverable from tetragonal-rhombohedral (T-R) phase transition by compressive stress. Additionally, the weak ferromagnetism in BiFeO3 films is largely changed in R-T phase transition under electric-filed and T-R phase transition under pressure - reminiscent of magnetoelectric effect and magnetoelastic effect. These results suggest exciting device opportunities arising from the giant filed-induced strain, large magnetoelectric effect and magnetoelastic effect. PMID:27139526

  9. Dispersion of Electric-Field-Induced Faraday Effect in Magnetoelectric Cr2O3

    NASA Astrophysics Data System (ADS)

    Wang, Junlei; Binek, Christian

    2016-03-01

    The frequency dependence of the electric-field-induced magneto-optical Faraday effect is investigated in the magnetoelectric antiferromagnet chromia. Two electrically induced Faraday signals superimpose in proportion to the linear magnetoelectric susceptibility α and the antiferromagnetic order parameter η . The relative strength of these contributions is determined by the frequency of the probing light and can be tuned between extreme characteristics following the temperature dependence of α or η . The frequency dependence is analyzed in terms of electric dipole transitions of perturbed Cr3 + crystal-field states. The results allow us to measure voltage-controlled selection, isothermal switching, and temperature dependence of η in a tabletop setup. The voltage-specific Faraday rotation is independent of the sample thickness, making the method scalable and versatile down to the limit of dielectric breakdown.

  10. Giant Magnetic Field-induced Phase Transitions in Dimeric Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Salili, Seyyed Muhammad; Salamonczyk, Miroslaw; Tamba, Maria-Gabriela; Sprunt, Samuel; Mehl, Georg; Jakli, Antal; Gleeson, James; Kent Group Collaboration; Hull Group Collaboration

    Liquid crystals are responsive to external fields such as electric, magnetic fields. The first experimental observation of dependence of isotropic to nematic phase transition on the applied magnetic field was done using a strong magnetic field on bent-core nematogens and the phase transition temperature exhibited an upshift of 0.7 C at B =30 T. We report on measurements of giant magnetic field-induced isotropic-nematic transition of chainsticks (nunchuks) type dimeric liquid crystals. Upon using the B =25 T split-helix resistive solenoid magnet at NHMFL, we have observed up to 18 C upshift of the isotropic to nematic phase transition temperature at B =22T. We discuss the results within the context of differential thermodynamic potential and the two basic mean-field theories. To our knowledge, this is the first observation of such huge shifts in the phase transitions of thermotropic liquid ctystals

  11. Giant electric-field-induced strain in lead-free piezoelectric materials

    NASA Astrophysics Data System (ADS)

    Chen, Lan; Yang, Yurong; Meng, X. K.

    2016-05-01

    First-principles calculations are performed to investigate the structures, electrical, and magnetic properties of compressive BiFeO3 films under electric-field and pressure perpendicular to the films. A reversible electric-field-induced strain up 10% is achieved in the compressive BiFeO3 films. The giant strain originates from rhombohedral-tetragonal (R-T) phase transition under electric-filed, and is recoverable from tetragonal-rhombohedral (T-R) phase transition by compressive stress. Additionally, the weak ferromagnetism in BiFeO3 films is largely changed in R-T phase transition under electric-filed and T-R phase transition under pressure – reminiscent of magnetoelectric effect and magnetoelastic effect. These results suggest exciting device opportunities arising from the giant filed-induced strain, large magnetoelectric effect and magnetoelastic effect.

  12. Giant electric-field-induced strain in lead-free piezoelectric materials

    PubMed Central

    Chen, Lan; Yang, Yurong; Meng, X. K.

    2016-01-01

    First-principles calculations are performed to investigate the structures, electrical, and magnetic properties of compressive BiFeO3 films under electric-field and pressure perpendicular to the films. A reversible electric-field-induced strain up 10% is achieved in the compressive BiFeO3 films. The giant strain originates from rhombohedral-tetragonal (R-T) phase transition under electric-filed, and is recoverable from tetragonal-rhombohedral (T-R) phase transition by compressive stress. Additionally, the weak ferromagnetism in BiFeO3 films is largely changed in R-T phase transition under electric-filed and T-R phase transition under pressure – reminiscent of magnetoelectric effect and magnetoelastic effect. These results suggest exciting device opportunities arising from the giant filed-induced strain, large magnetoelectric effect and magnetoelastic effect. PMID:27139526

  13. Magnetic-Field-Induced Rotation of Polarized Light Emission from Monolayer WS_{2}.

    PubMed

    Schmidt, Robert; Arora, Ashish; Plechinger, Gerd; Nagler, Philipp; Granados Del Águila, Andrés; Ballottin, Mariana V; Christianen, Peter C M; Michaelis de Vasconcellos, Steffen; Schüller, Christian; Korn, Tobias; Bratschitsch, Rudolf

    2016-08-12

    We control the linear polarization of emission from the coherently emitting K^{+} and K^{-} valleys (valley coherence) in monolayer WS_{2} with an out-of-plane magnetic field of up to 25 T. The magnetic-field-induced valley Zeeman splitting causes a rotation of the emission polarization with respect to the excitation by up to 35° and reduces the polarization degree by up to 16%. We explain both of these phenomena with a model based on two noninteracting coherent two-level systems. We deduce that the coherent light emission from the valleys decays with a time constant of τ_{c}=260  fs. PMID:27563997

  14. Magnetic-field-induced ferroelectric polarization reversal in magnetoelectric composites revealed by piezoresponse force microscopy

    NASA Astrophysics Data System (ADS)

    Miao, Hongchen; Zhou, Xilong; Dong, Shuxiang; Luo, Haosu; Li, Faxin

    2014-07-01

    Controlling electric polarization (or magnetization) in multiferroic materials with external magnetic fields (or electric fields) is very important for fundamental physics and spintronic devices. Although there has been some progress on magnetic-field-induced polarization reversal in single-phase multiferroics, such behavior has so far never been realized in composites. Here we show that it is possible to reverse ferroelectric polarization using magnetic fields in a bilayer Terfenol-D/PMN-33%PT composite. We realized this by ferroelectric domain imaging using piezoresponse force microscopy (PFM) under applied magnetic field loading. The internal electric field caused by the magnetoelectric (ME) effect in the PMN-PT crystal is considered as the driving force for the 180° polarization switching, and its existence is verified by switching spectroscopy PFM testing under a series of external magnetic fields. A quantitative method is further suggested to estimate the local ME coefficient based on the switching spectroscopy PFM testing results.

  15. Magnetic-field-induced ferroelectric polarization reversal in magnetoelectric composites revealed by piezoresponse force microscopy.

    PubMed

    Miao, Hongchen; Zhou, Xilong; Dong, Shuxiang; Luo, Haosu; Li, Faxin

    2014-08-01

    Controlling electric polarization (or magnetization) in multiferroic materials with external magnetic fields (or electric fields) is very important for fundamental physics and spintronic devices. Although there has been some progress on magnetic-field-induced polarization reversal in single-phase multiferroics, such behavior has so far never been realized in composites. Here we show that it is possible to reverse ferroelectric polarization using magnetic fields in a bilayer Terfenol-D/PMN-33%PT composite. We realized this by ferroelectric domain imaging using piezoresponse force microscopy (PFM) under applied magnetic field loading. The internal electric field caused by the magnetoelectric (ME) effect in the PMN-PT crystal is considered as the driving force for the 180° polarization switching, and its existence is verified by switching spectroscopy PFM testing under a series of external magnetic fields. A quantitative method is further suggested to estimate the local ME coefficient based on the switching spectroscopy PFM testing results. PMID:24953042

  16. Electric field-induced magnetic switching in Mn:ZnO film

    SciTech Connect

    Ren, S. X.; Sun, G. W.; Zhao, J.; Dong, J. Y.; Zhao, X.; Chen, W.; Wei, Y.; Ma, Z. C.

    2014-06-09

    A large magnetic modulation, accompanied by stable bipolar resistive switching (RS) behavior, was observed in a Mn:ZnO film by applying a reversible electric field. A significant enhancement of the ferromagnetism of the film, to about five times larger than that in the initial (as-grown) state (IS), was obtained by switching the film into the low resistance state. X-ray photoelectron spectroscopy demonstrated the existence of abundant oxygen vacancies in the IS of the film. We suggest that this electric field-induced magnetic switching effect originates with the migration and redistribution of oxygen vacancies during RS. Our work indicates that electric switching is an effective and simple method to increase the ferromagnetism of diluted magnetic oxide films. This provides a promising direction for research in spintronic devices.

  17. Dynamics of magnetic particles near a surface: model and experiments on field-induced disaggregation.

    PubMed

    van Reenen, A; Gao, Y; de Jong, A M; Hulsen, M A; den Toonder, J M J; Prins, M W J

    2014-04-01

    Magnetic particles are widely used in biological research and bioanalytical applications. As the corresponding tools are progressively being miniaturized and integrated, the understanding of particle dynamics and the control of particles down to the level of single particles become important. Here, we describe a numerical model to simulate the dynamic behavior of ensembles of magnetic particles, taking account of magnetic interparticle interactions, interactions with the liquid medium and solid surfaces, as well as thermal diffusive motion of the particles. The model is verified using experimental data of magnetic field-induced disaggregation of magnetic particle clusters near a physical surface, wherein the magnetic field properties, particle size, cluster size, and cluster geometry were varied. Furthermore, the model clarifies how the cluster configuration, cluster alignment, magnitude of the field gradient, and the field repetition rate play a role in the particle disaggregation process. The simulation model will be very useful for further in silico studies on magnetic particle dynamics in biotechnological tools. PMID:24827250

  18. Theory of magnetic-field-induced polarization flop in spin-spiral multiferroics

    NASA Astrophysics Data System (ADS)

    Mochizuki, Masahito

    2015-12-01

    The magnetic-field-induced 90∘ flop of ferroelectric polarization P in a spin-spiral multiferroic material TbMnO3 is theoretically studied based on a microscopic spin model. I find that the direction of the P flop or the choice of +Pa or -Pa after the flop is governed by magnetic torques produced by the applied magnetic field H acting on the Mn spins and thus is selected in a deterministic way, in contradistinction to the naively anticipated probabilistic flop. This mechanism resolves a puzzle of the previously reported memory effect in the P direction depending on the history of the magnetic-field sweep, and enables controlled switching of multiferroic domains by externally applied magnetic fields. My Monte-Carlo analysis also uncovers that the magnetic structure in the P ∥a phase under H ∥b is not a previously anticipated simple a b -plane spin cycloid but a conical spin structure.

  19. Continuum absorption in the vicinity of the toroidicity-induced Alfvén gap

    DOE PAGESBeta

    Li, M.; Breizman, B. N.; Zheng, L. J.; Chen, Eugene Y.

    2015-12-04

    Excitation of Alfvén modes is commonly viewed as a concern for energetic particle confinement in burning plasmas. The 3.5 MeValpha particles produced by fusion may be affected as well as other fast ions in both present and future devices. Continuum damping of such modes is one of the key factors that determine their excitation thresholds and saturation levels. This work examines the resonant dissipative response of the Alfvén continuum to an oscillating driving current when the driving frequency is slightly outside the edges of the toroidicity-induced spectral gap. The problem is largely motivated by the need to describe the continuummore » absorption in the frequency sweeping events. Akey element of this problem is the negative interference of the two closely spaced continuum crossing points.Weexplain why the lower and upper edges of the gap can have very different continuum absorption features. Lastly, the difference is associated with an eigenmode whose frequency can be arbitrarily close to the upper edge of the gap whereas the lower edge of the gap is always a finite distance away from the closest eigenmode.« less

  20. Interpreting angina: symptoms along a gender continuum

    PubMed Central

    Crea-Arsenio, Mary; Shannon, Harry S; Velianou, James L; Giacomini, Mita

    2016-01-01

    Background ‘Typical’ angina is often used to describe symptoms common among men, while ‘atypical’ angina is used to describe symptoms common among women, despite a higher prevalence of angina among women. This discrepancy is a source of controversy in cardiac care among women. Objectives To redefine angina by (1) qualitatively comparing angina symptoms and experiences in women and men and (2) to propose a more meaningful construct of angina that integrates a more gender-centred approach. Methods Patients were recruited between July and December 2010 from a tertiary cardiac care centre and interviewed immediately prior to their first angiogram. Symptoms were explored through in-depth semi-structured interviews, transcribed verbatim and analysed concurrently using a modified grounded theory approach. Angiographically significant disease was assessed at ≥70% stenosis of a major epicardial vessel. Results Among 31 total patients, 13 men and 14 women had angiograpically significant CAD. Patients describe angina symptoms according to 6 symptomatic subthemes that array along a ‘gender continuum’. Gender-specific symptoms are anchored at each end of the continuum. At the centre of the continuum, are a remarkably large number of symptoms commonly expressed by both men and women. Conclusions The ‘gender continuum’ offers new insights into angina experiences of angiography candidates. Notably, there is more overlap of shared experiences between men and women than conventionally thought. The gender continuum can help researchers and clinicians contextualise patient symptom reports, avoiding the conventional ‘typical’ versus ‘atypical’ distinction that can misrepresent gendered angina experiences. PMID:27158523

  1. The role of Rydberg and continuum levels in computing high harmonic generation spectra of the hydrogen atom using time-dependent configuration interaction

    SciTech Connect

    Luppi, Eleonora; Head-Gordon, Martin

    2013-10-28

    We study the role of Rydberg bound-states and continuum levels in the field-induced electronic dynamics associated with the High-Harmonic Generation (HHG) spectroscopy of the hydrogen atom. Time-dependent configuration-interaction (TD-CI) is used with very large atomic orbital (AO) expansions (up to L= 4 with sextuple augmentation and off-center functions) to describe the bound Rydberg levels, and some continuum levels. To address the lack of ionization losses in TD-CI with finite AO basis sets, we employed a heuristic lifetime for energy levels above the ionization potential. The heuristic lifetime model is compared against the conventional atomic orbital treatment (infinite lifetimes), and a third approximation which is TD-CI using only the bound levels (continuum lifetimes go to zero). The results suggest that spectra calculated using conventional TD-CI do not converge with increasing AO basis set size, while the zero lifetime and heuristic lifetime models converge to qualitatively similar spectra, with implications for how best to apply bound state electronic structure methods to simulate HHG. The origin of HHG spectral features including the cutoff and extent of interference between peaks is uncovered by separating field-induced coupling between different types of levels (ground state, bound Rydberg levels, and continuum) in the simulated electronic dynamics. Thus the origin of deviations between the predictions of the semi-classical three step model and the full simulation can be associated with particular physical contributions, which helps to explain both the successes and the limitations of the three step model.

  2. The Luminosity Dependence of Quasar UV Continuum Slope: Dust Extinction Scenario

    NASA Astrophysics Data System (ADS)

    Xie, Xiaoyi; Shao, Zhengyi; Shen, Shiyin; Liu, Hui; Li, Linlin

    2016-06-01

    We investigate the UV continuum slope α of a large quasar sample from SDSS DR7. By using specific continuum windows, we build two samples at lower (0.71\\lt z\\lt 1.19) and higher (1.90\\lt z\\lt 3.15) redshifts, which correspond to the continuum slopes at longer (near-UV) and shorter (far-UV) rest wavelength ranges, respectively. Overall, the average continuum slopes are ‑0.36 and ‑0.51 for {α }{{NUV}} and {α }{{FUV}} with similar dispersions {σ }α ∼ 0.5. For both samples, we confirm the luminosity dependence of the continuum slope, i.e., fainter quasars have redder spectra. We further find that both {α }{{NUV}} and {α }{{FUV}} have a common upper limit (∼ 1/3), which is almost independent of the quasar luminosity {L}{{bol}}. This finding implies that the intrinsic quasar continuum (or the bluest quasar), at any luminosity, obeys the standard thin-disk model. We propose that the other quasars with redder α are caused by the reddening from the dust locally. With this assumption, we employ the dust extinction scenario to model the observed {L}{{bol}}{--}α relation. We find that a typical value of E(B-V)∼ 0.1{--}0.3 {mag} (depending on the types of extinction curve) of the quasar local dust is enough to explain the discrepancy of α between the observation (∼ -0.5) and the standard accretion disk model prediction (∼ 1/3).

  3. Continuum regularization of gauge theory with fermions

    SciTech Connect

    Chan, H.S.

    1987-03-01

    The continuum regularization program is discussed in the case of d-dimensional gauge theory coupled to fermions in an arbitrary representation. Two physically equivalent formulations are given. First, a Grassmann formulation is presented, which is based on the two-noise Langevin equations of Sakita, Ishikawa and Alfaro and Gavela. Second, a non-Grassmann formulation is obtained by regularized integration of the matter fields within the regularized Grassmann system. Explicit perturbation expansions are studied in both formulations, and considerable simplification is found in the integrated non-Grassmann formalism.

  4. Continuum description of avalanches in granular media.

    SciTech Connect

    Aranson, I. S.; Tsimring, L. S.

    2000-12-05

    A continuum theory of partially fluidized granular flows is proposed. The theory is based on a combination of the mass and momentum conservation equations with the order parameter equation which describes the transition between flowing and static components of the granular system. We apply this model to the dynamics of avalanches in chutes. The theory provides a quantitative description of recent observations of granular flows on rough inclined planes (Daerr and Douady 1999): layer bistability, and the transition from triangular avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating uphill for larger angles.

  5. Dust continuum spectra from model HII regions

    NASA Technical Reports Server (NTRS)

    Aannestad, P. A.; Emery, R. J.

    1989-01-01

    The infrared spectrum emitted by nebular dust, heated by the ionizing stars in H II blisters and spherical H II regions, is calculated for various model parameters. Absorption of the non-ionizing radiation in a neutral layer is included. Heating by the Lyman alpha photon field is taken into account. The dust is composed of silicate and graphite grains, and evaporation of the grains in the inner region is considered. The models are presented with a view to interpretation of infrared observations of dusty H II regions and can be applied directly to the infrared astronomy satellite survey data. The continuum emission is compared with calculated fine structure line emission.

  6. Continuum modeling of clustering of myxobacteria

    PubMed Central

    Harvey, Cameron W.; Alber, Mark; Tsimring, Lev S.; Aranson, Igor S.

    2013-01-01

    In this paper we develop a continuum theory of clustering in ensembles of self-propelled inelastically colliding rods with applications to collective dynamics of common gliding bacteria Myxococcus Xanthus. A multiphase hydrodynamic model that couples densities of oriented and isotropic phases is described. This model is used for the analysis of an instability that leads to spontaneous formation of directionally moving dense clusters within initially dilute isotropic “gas” of myxobacteria. Numerical simulations of this model confirm the existence of stationary dense moving clusters and also elucidate the properties of their collisions. The results are shown to be in a qualitative agreement with experiments. PMID:23712128

  7. Radiation from charges in the continuum limit

    SciTech Connect

    Ianconescu, Reuven

    2013-06-15

    It is known that an accelerating charge radiates according to Larmor formula. On the other hand, any DC current following a curvilinear path, consists of accelerating charges, but in such case the radiated power is 0. The scope of this paper is to analyze and quantify how a system of charges goes from a radiating state to a non radiating state when the charges distribution goes to the continuum limit. Understanding this is important from the theoretical point of view and the results of this work are applicable to particle accelerator, cyclotron and other high energy devices.

  8. Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum

    NASA Astrophysics Data System (ADS)

    Aurière, M.; López Ariste, A.; Mathias, P.; Lèbre, A.; Josselin, E.; Montargès, M.; Petit, P.; Chiavassa, A.; Paletou, F.; Fabas, N.; Konstantinova-Antova, R.; Donati, J.-F.; Grunhut, J. H.; Wade, G. A.; Herpin, F.; Kervella, P.; Perrin, G.; Tessore, B.

    2016-06-01

    Context. Betelgeuse is an M supergiant that harbors spots and giant granules at its surface and presents linear polarization of its continuum. Aims: We have previously discovered linear polarization signatures associated with individual lines in the spectra of cool and evolved stars. Here, we investigate whether a similar linearly polarized spectrum exists for Betelgeuse. Methods: We used the spectropolarimeter Narval, combining multiple polarimetric sequences to obtain high signal-to-noise ratio spectra of individual lines, as well as the least-squares deconvolution (LSD) approach, to investigate the presence of an averaged linearly polarized profile for the photospheric lines. Results: We have discovered the existence of a linearly polarized spectrum for Betelgeuse, detecting a rather strong signal (at a few times 10-4 of the continuum intensity level), both in individual lines and in the LSD profiles. Studying its properties and the signal observed for the resonant Na i D lines, we conclude that we are mainly observing depolarization of the continuum by the absorption lines. The linear polarization of the Betelgeuse continuum is due to the anisotropy of the radiation field induced by brightness spots at the surface and Rayleigh scattering in the atmosphere. We have developed a geometrical model to interpret the observed polarization, from which we infer the presence of two brightness spots and their positions on the surface of Betelgeuse. We show that applying the model to each velocity bin along the Stokes Q and U profiles allows the derivation of a map of the bright spots. We use the Narval linear polarization observations of Betelgeuse obtained over a period of 1.4 yr to study the evolution of the spots and of the atmosphere. Conclusions: Our study of the linearly polarized spectrum of Betelgeuse provides a novel method for studying the evolution of brightness spots at its surface and complements quasi-simultaneous observations obtained with PIONIER at the

  9. Mid-IR super-continuum generation

    NASA Astrophysics Data System (ADS)

    Islam, Mohammed N.; Xia, Chenan; Freeman, Mike J.; Mauricio, Jeremiah; Zakel, Andy; Ke, Kevin; Xu, Zhao; Terry, Fred L., Jr.

    2009-02-01

    A Mid-InfraRed FIber Laser (MIRFIL) has been developed that generates super-continuum covering the spectral range from 0.8 to 4.5 microns with a time-averaged power as high as 10.5W. The MIRFIL is an all-fiber integrated laser with no moving parts and no mode-locked lasers that uses commercial off-the-shelf parts and leverages the mature telecom/fiber optics platform. The MIRFIL power can be easily scaled by changing the repetition rate and modifying the erbium-doped fiber amplifier. Some of the applications using the super-continuum laser will be described in defense, homeland security and healthcare. For example, the MIRFIL is being applied to a catheter-based medical diagnostic system to detect vulnerable plaque, which is responsible for most heart attacks resulting from hardening-of-the-arteries or atherosclerosis. More generally, the MIRFIL can be a platform for selective ablation of lipids without damaging normal protein or smooth muscle tissue.

  10. The Urban Watershed Continuum: Biogeochemistry of Carbon

    NASA Astrophysics Data System (ADS)

    Kaushal, S.; Belt, K.; Smith, C.; Newcomb, K.; Newcomer, T. A.; Smith, R.; Duan, S.; Findlay, S.; Groffman, P. M.; Mayer, P. M.

    2012-12-01

    Urban ecosystems are constantly evolving, and they are expected to change in both space and time. We explore the relationship between infrastructure and ecosystem function relevant to the inorganic and organic carbon cycle along urban watersheds across spatial and temporal dimensions. We provide examples from watersheds of the Baltimore Ecosystem Study Long-Term Ecological (LTER) and Washington D.C. Urban Long-Term Research Area (ULTRA EX) sites with varying land use and contrasting sanitary sewer systems. At a stream and river network scale, there are distinct longitudinal patterns in dissolved inorganic carbon, dissolved organic carbon, and particulate carbon concentrations from suburban headwaters to progressively urbanized receiving waters. There are also distinct changes in stable isotopic signatures of organic carbon and inorganic carbon suggesting shifts in carbon sources and processing throughout urban stream and river networks. Longitudinal patterns appear to be related to in-stream transformations, as suggested by high frequency sensor measurements, mass balances, and diurnal sampling. We suggest that stream and river networks act as "transformers" of watershed nitrogen and phosphorus pollution to increasingly generate carbon throughout the urban watershed continuum via biological processes. Additionally, sources and quality of carbon may vary with watershed inputs from suburban headwaters to progressively urbanized downstream reaches. The role of the urban watershed continuum as a "transporter" and "transformer" of organic matter has important implications for anticipating changes in the forms and reactivity of carbon delivered to receiving waters and coastal zones.

  11. Continuum robot arms inspired by cephalopods

    NASA Astrophysics Data System (ADS)

    Walker, Ian D.; Dawson, Darren M.; Flash, Tamar; Grasso, Frank W.; Hanlon, Roger T.; Hochner, Binyamin; Kier, William M.; Pagano, Christopher C.; Rahn, Christopher D.; Zhang, Qiming M.

    2005-05-01

    In this paper, we describe our recent results in the development of a new class of soft, continuous backbone ("continuum") robot manipulators. Our work is strongly motivated by the dexterous appendages found in cephalopods, particularly the arms and suckers of octopus, and the arms and tentacles of squid. Our ongoing investigation of these animals reveals interesting and unexpected functional aspects of their structure and behavior. The arrangement and dynamic operation of muscles and connective tissue observed in the arms of a variety of octopus species motivate the underlying design approach for our soft manipulators. These artificial manipulators feature biomimetic actuators, including artificial muscles based on both electro-active polymers (EAP) and pneumatic (McKibben) muscles. They feature a "clean" continuous backbone design, redundant degrees of freedom, and exhibit significant compliance that provides novel operational capacities during environmental interaction and object manipulation. The unusual compliance and redundant degrees of freedom provide strong potential for application to delicate tasks in cluttered and/or unstructured environments. Our aim is to endow these compliant robotic mechanisms with the diverse and dexterous grasping behavior observed in octopuses. To this end, we are conducting fundamental research into the manipulation tactics, sensory biology, and neural control of octopuses. This work in turn leads to novel approaches to motion planning and operator interfaces for the robots. The paper describes the above efforts, along with the results of our development of a series of continuum tentacle-like robots, demonstrating the unique abilities of biologically-inspired design.

  12. Polarized Continuum Radiation from Stellar Atmospheres

    NASA Astrophysics Data System (ADS)

    Harrington, J. Patrick

    2015-10-01

    Continuum scattering by free electrons can be significant in early type stars, while in late type stars Rayleigh scattering by hydrogen atoms or molecules may be important. Computer programs used to construct models of stellar atmospheres generally treat the scattering of the continuum radiation as isotropic and unpolarized, but this scattering has a dipole angular dependence and will produce polarization. We review an accurate method for evaluating the polarization and limb darkening of the radiation from model stellar atmospheres. We use this method to obtain results for: (i) Late type stars, based on the MARCS code models (Gustafsson et al. 2008), and (ii) Early type stars, based on the NLTE code TLUSTY (Lanz and Hubeny 2003). These results are tabulated at http://www.astro.umd.edu/~jph/Stellar_Polarization.html. While the net polarization vanishes for an unresolved spherical star, this symmetry is broken by rapid rotation or by the masking of part of the star by a binary companion or during the transit of an exoplanet. We give some numerical results for these last cases.

  13. Accurate Molecular Polarizabilities Based on Continuum Electrostatics

    PubMed Central

    Truchon, Jean-François; Nicholls, Anthony; Iftimie, Radu I.; Roux, Benoît; Bayly, Christopher I.

    2013-01-01

    A novel approach for representing the intramolecular polarizability as a continuum dielectric is introduced to account for molecular electronic polarization. It is shown, using a finite-difference solution to the Poisson equation, that the Electronic Polarization from Internal Continuum (EPIC) model yields accurate gas-phase molecular polarizability tensors for a test set of 98 challenging molecules composed of heteroaromatics, alkanes and diatomics. The electronic polarization originates from a high intramolecular dielectric that produces polarizabilities consistent with B3LYP/aug-cc-pVTZ and experimental values when surrounded by vacuum dielectric. In contrast to other approaches to model electronic polarization, this simple model avoids the polarizability catastrophe and accurately calculates molecular anisotropy with the use of very few fitted parameters and without resorting to auxiliary sites or anisotropic atomic centers. On average, the unsigned error in the average polarizability and anisotropy compared to B3LYP are 2% and 5%, respectively. The correlation between the polarizability components from B3LYP and this approach lead to a R2 of 0.990 and a slope of 0.999. Even the F2 anisotropy, shown to be a difficult case for existing polarizability models, can be reproduced within 2% error. In addition to providing new parameters for a rapid method directly applicable to the calculation of polarizabilities, this work extends the widely used Poisson equation to areas where accurate molecular polarizabilities matter. PMID:23646034

  14. Atomistic to continuum modeling of solidification microstructures

    SciTech Connect

    Karma, Alain; Tourret, Damien

    2015-09-26

    We summarize recent advances in modeling of solidification microstructures using computational methods that bridge atomistic to continuum scales. We first discuss progress in atomistic modeling of equilibrium and non-equilibrium solid–liquid interface properties influencing microstructure formation, as well as interface coalescence phenomena influencing the late stages of solidification. The latter is relevant in the context of hot tearing reviewed in the article by M. Rappaz in this issue. We then discuss progress to model microstructures on a continuum scale using phase-field methods. We focus on selected examples in which modeling of 3D cellular and dendritic microstructures has been directly linked to experimental observations. Finally, we discuss a recently introduced coarse-grained dendritic needle network approach to simulate the formation of well-developed dendritic microstructures. The approach reliably bridges the well-separated scales traditionally simulated by phase-field and grain structure models, hence opening new avenues for quantitative modeling of complex intra- and inter-grain dynamical interactions on a grain scale.

  15. Atomistic to continuum modeling of solidification microstructures

    DOE PAGESBeta

    Karma, Alain; Tourret, Damien

    2015-09-26

    We summarize recent advances in modeling of solidification microstructures using computational methods that bridge atomistic to continuum scales. We first discuss progress in atomistic modeling of equilibrium and non-equilibrium solid–liquid interface properties influencing microstructure formation, as well as interface coalescence phenomena influencing the late stages of solidification. The latter is relevant in the context of hot tearing reviewed in the article by M. Rappaz in this issue. We then discuss progress to model microstructures on a continuum scale using phase-field methods. We focus on selected examples in which modeling of 3D cellular and dendritic microstructures has been directly linked tomore » experimental observations. Finally, we discuss a recently introduced coarse-grained dendritic needle network approach to simulate the formation of well-developed dendritic microstructures. The approach reliably bridges the well-separated scales traditionally simulated by phase-field and grain structure models, hence opening new avenues for quantitative modeling of complex intra- and inter-grain dynamical interactions on a grain scale.« less

  16. Three-dimensional electric field visualization utilizing electric-field-induced second-harmonic generation in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Chen, I.-Hsiu; Chu, Shi-Wei; Bresson, Francois; Tien, Ming-Chun; Shi, Jin-Wei; Sun, Chi-Kuang

    2003-08-01

    An electric-field-induced second-harmonic-generation signal in a nematic liquid crystal is used to map the electric field in an integrated-circuit-like sample. Since the electric-field-induced second-harmonic-generation signal intensity exhibits a strong dependence on the polarization of the incident laser beam, both the amplitude and the orientation of the electric field vectors can be measured. Combined with scanning second-harmonic-generation microscopy, three-dimensional electric field distribution can be easily visualized with high spatial resolution of the order of 1 μm.

  17. Inhomogeneous ordered states and translational nature of the gauge group in the landau continuum theory: I. General analysis

    SciTech Connect

    Braginsky, A. Ya.

    2007-07-15

    A phenomenological continuum theory of phase transitions to a global inhomogeneous state of a crystal must take into account the compensating fields that represent the fields of stresses caused by dislocations appearing at the boundaries between local homogeneous regions. These compensating fields, which are introduced in order to satisfy the condition of invariance of the Landau potential with respect to the operation of translation, enter into the theory via extended derivatives of the local order parameters with respect to macroscopic coordinates of the local homogeneous regions in the crystal. Because of this extension of derivatives, the theory of phase transitions to an inhomogeneous state must include the theory of elasticity, in which a potential of the stress field induced by the phase transition is proportional to the compensating field magnitude. The Kroener equation, which describes the state of dislocations induced by spatially inhomogeneous ordering, appears in this theory as a result of minimization of the Landau potential with respect to the compensating fields.

  18. Non-coherent continuum scattering as a line polarization mechanism

    SciTech Connect

    Del Pino Alemán, T.; Manso Sainz, R.; Trujillo Bueno, J. E-mail: rsainz@iac.es

    2014-03-20

    Line scattering polarization can be strongly affected by Rayleigh scattering at neutral hydrogen and Thomson scattering at free electrons. Often a depolarization of the continuum results, but the Doppler redistribution produced by the continuum scatterers, which are light (hence, fast), induces more complex interactions between the polarization in spectral lines and in the continuum. Here we formulate and solve the radiative transfer problem of scattering line polarization with non-coherent continuum scattering consistently. The problem is formulated within the spherical tensor representation of atomic and light polarization. The numerical method of solution is a generalization of the Accelerated Lambda Iteration that is applied to both the atomic system and the radiation field. We show that the redistribution of the spectral line radiation due to the non-coherence of the continuum scattering may modify the shape of the emergent fractional linear polarization patterns significantly, even yielding polarization signals above the continuum level in intrinsically unpolarizable lines.

  19. Continuum capture in the three-body problem

    SciTech Connect

    Sellin, I A

    1980-01-01

    The three-body problem, especially the problem of electron capture to the continuum in heavy particle collisions is reviewed. Major topics covered include: second born-induced asymmetry in electron capture to the continuum; historical context, links to other tests of atomic scattering theory; experiments characterizing the velocity distribution of ECC electrons; other atomic physics tests of high velocity Born expansions; atom capture; capture by positrons; and pion capture to the continuum. (GHT)

  20. Radio continuum and far-infrared emission of spiral galaxies: Implications of correlations

    NASA Technical Reports Server (NTRS)

    Rengarajan, T. N.; Iyengar, K. V. K.

    1990-01-01

    Researchers present a study extending the correlation seen between radio continuum and far-infrared emissions from spiral galaxies to a lower frequency of 408 MHz and also as a function of radio spectral index. The tight correlation seen between the two luminosities is then used to constrain several parameters governing the emissions such as the changes in star formation rate and mass function, frequency of supernovae that are parents of the interstellar electrons and factors governing synchrotron radio emission.

  1. Continuum Fatigue Damage Modeling for Use in Life Extending Control

    NASA Technical Reports Server (NTRS)

    Lorenzo, Carl F.

    1994-01-01

    This paper develops a simplified continuum (continuous wrp to time, stress, etc.) fatigue damage model for use in Life Extending Controls (LEC) studies. The work is based on zero mean stress local strain cyclic damage modeling. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modeling. Stress based continuum models are derived. Extension to plastic strain-strain rate models are also presented. Application of these models to LEC applications is considered. Progress toward a nonzero mean stress based continuum model is presented. Also, new nonlinear explicit equation forms in terms of stress amplitude are also derived for this case.

  2. High Magnetic Field-Induced Birefringence in Lyotropic Chromonic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Ostapenko, T.; Nastishin, Yu.; Gleeson, J. T.; Sprunt, S. N.; Lavrentovich, O. D.; Collings, P. J.

    2009-03-01

    We studied the effect of magnetic-field induced birefringence of a 14% solution of disodium cromoglycate (DSCG) in water at temperatures above the nematic-isotropic coexistence region. According to Landau-deGennes mean field theory, we expect to find a linear relationship between the inverse of the induced birefringence, δn, and the quantity (T-T*), where T* is the stability limit of the isotropic phase. Using the 31 T resistive magnet at the National High Magnetic Field Laboratory, we observed that, as we increase the temperature above the coexistence region, we deviate from this linear dependence. Our data shows that δn goes to zero, whereas Landau-deGennes predicts that δn should decrease asymptotically. This may be due to the lack of isodesmic aggregate formation at a finite temperature above the coexistence region.Supported by NSF (DMR-0710544 and DMR-0606160). Work performed at NHMFL, supported by NSF cooperative agreements DMR-0084173, the State of Florida and the DOE.

  3. Revival of oscillation from mean-field-induced death: Theory and experiment.

    PubMed

    Ghosh, Debarati; Banerjee, Tanmoy; Kurths, Jürgen

    2015-11-01

    The revival of oscillation and maintaining rhythmicity in a network of coupled oscillators offer an open challenge to researchers as the cessation of oscillation often leads to a fatal system degradation and an irrecoverable malfunctioning in many physical, biological, and physiological systems. Recently a general technique of restoration of rhythmicity in diffusively coupled networks of nonlinear oscillators has been proposed in Zou et al. [Nat. Commun. 6, 7709 (2015)], where it is shown that a proper feedback parameter that controls the rate of diffusion can effectively revive oscillation from an oscillation suppressed state. In this paper we show that the mean-field diffusive coupling, which can suppress oscillation even in a network of identical oscillators, can be modified in order to revoke the cessation of oscillation induced by it. Using a rigorous bifurcation analysis we show that, unlike other diffusive coupling schemes, here one has two control parameters, namely the density of the mean-field and the feedback parameter that can be controlled to revive oscillation from a death state. We demonstrate that an appropriate choice of density of the mean field is capable of inducing rhythmicity even in the presence of complete diffusion, which is a unique feature of this mean-field coupling that is not available in other coupling schemes. Finally, we report the experimental observation of revival of oscillation from the mean-field-induced oscillation suppression state that supports our theoretical results. PMID:26651763

  4. Giant low field magnetocaloric effect and field-induced metamagnetic transition in TmZn

    NASA Astrophysics Data System (ADS)

    Li, Lingwei; Yuan, Ye; Zhang, Yikun; Namiki, Takahiro; Nishimura, Katsuhiko; Pöttgen, Rainer; Zhou, Shengqiang

    2015-09-01

    The magnetic properties and the magnetocaloric effect (MCE) in TmZn have been studied by magnetization and heat capacity measurements. The TmZn compound exhibits a ferromagnetic state below a Curie temperature of TC = 8.4 K and processes a field-induced metamagnetic phase transition around and above TC. A giant reversible MCE was observed in TmZn. For a field change of 0-5 T, the maximum values of magnetic entropy change (-ΔSMmax) and adiabatic temperature change (ΔTadmax) are 26.9 J/kg K and 8.6 K, the corresponding values of relative cooling power and refrigerant capacity are 269 and 214 J/kg, respectively. Particularly, the values of -ΔSMmax reach 11.8 and 19.6 J/kg K for a low field change of 0-1 and 0-2 T, respectively. The present results indicate that TmZn could be a promising candidate for low temperature and low field magnetic refrigeration.

  5. Electric-field-induced Spontaneous Magnetization and Phase Transitions in Zigzag Boron Nitride Nanotubes

    PubMed Central

    Bai, Lang; Gu, Gangxu; Xiang, Gang; Zhang, Xi

    2015-01-01

    We demonstrate an alternative scheme for realizing spin polarizations in semiconductor nanostructures by an all-electric way. The electronic and magnetic properties of the model system, zigzag pristine boron nitride nanotubes (BNNTs), are investigated under a transverse electric field (E) through spin-polarized density functional theory calculations. As E increases, the band gap of BNNTs is reduced due to charge redistribution induced by the asymmetry of electrostatic potential energy, and BNNTs experience rich phase transitions, such as semiconductor-metal transition and nonmagnetic (NM) metal-ferromagnetic (FM) metal transitions. Electric-field-induced magnetization occurs when a sufficiently high density of states at the Fermi level in the vicinity of metal-insulator transition is reached due to the redistribution of electronic bands and charge transferring across the BNNTs. Further analysis show that the spontaneous magnetization is derived from the localized nature of the 2p states of B and N, and the ferromagnetic coupling is stabilized by Zener’s double-exchange mechanism. Our results may provide a viable way to realize spintronic devices for applications. PMID:26206393

  6. Surface mapping of field-induced piezoelectric strain at elevated temperature employing full-field interferometry.

    PubMed

    Stevenson, Tim; Quast, Tatjana; Bartl, Guido; Schmitz-Kempen, Thorsten; Weaver, Paul M

    2015-01-01

    Piezoelectric actuators and sensors are widely used for flow control valves, including diesel injectors, ultrasound generation, optical positioning, printing, pumps, and locks. Degradation and failure of material and electrical properties at high temperature typically limits these applications to operating temperatures below 200°C, based on the ubiquitous Pb(Zr,Ti)O3 ceramic. There are, however, many applications in sectors such as automotive, aerospace, energy and process control, and oil and gas, where the ability to operate at higher temperatures would open up new markets for piezoelectric actuation. Presented here is a review of recent progress and initial results toward a European effort to develop measurement techniques to characterize high-temperature materials. Full-field, multi-wavelength absolute length interferometry has, for the first time, been used to map the electric-field-induced piezoelectric strain across the surface of a PZT ceramic. The recorded variation as a function of temperature has been evaluated against a newly developed commercial single-beam system. Conventional interferometry allows measurement of the converse piezoelectric effect with high precision and resolution, but is often limited to a single point, average measurement and to limited sample environments because of optical aberrations in varying atmospheres. Here, the full-field technique allows the entire surface to be analyzed for strain and, in a bespoke sample chamber, for elevated temperatures. PMID:25585393

  7. Electric field induced Lyman-α emission of a hydrogen beam for electric field measurements

    SciTech Connect

    Chérigier-Kovacic, L. Doveil, F.; Ström, P.; Lejeune, A.

    2015-06-15

    Electric field induced Lyman-α emission is a new way of measuring weak electric fields in vacuum and in a plasma. It is based on the emission of Lyman-α radiation (121.6 nm) by a low-energy metastable H atom beam due to Stark-quenching of the 2s level induced by the field. In this paper, we describe the technique in detail. Test measurements have been performed in vacuum between two plates polarized at a controlled voltage. The intensity of emitted radiation, proportional to the square of the field modulus, has been recorded by a lock-in technique, which gives an excellent signal to noise ratio. These measurements provide an in situ calibration that can be used to obtain the absolute value of the electric field. A diagnostic of this type can help to address a long standing challenge in plasma physics, namely, the problem of measuring electric fields without disturbing the equilibrium of the system that is being studied.

  8. Background-free electric field-induced second harmonic generation with interdigitated combs of electrodes.

    PubMed

    Jašinskas, Vidmantas; Gedvilas, Mindaugas; Račiukaitis, Gediminas; Gulbinas, Vidmantas

    2016-06-15

    The electric field-induced second harmonic (EFISH) generation is a powerful tool for the investigation of optical nonlinearities, material polarization, internal electric fields, and other properties of photonic materials and devices. A conventional generation of the second harmonics (SH) in materials with the disturbed centrosymmetry causes a field-independent background to EFISH and limits its applications. Here we suggest and analyze the application of the interdigitated combs of electrodes for EFISH generation in thin films. Interdigitated electrodes form an optical transmission amplitude diffraction grating. Phase matching of the EFISH radiation creates unusual diffraction fringes with the zero intensity along the zeroth order direction and with the diffraction angles different from diffraction angles of incident fundamental laser radiation and its second harmonics. It enables a simple geometrical separation of the EFISH signal from a conventional SH background, simplifies the sample preparation, and provides additional experimental possibilities. We demonstrate applicability of the suggested technique for characterization of submicrometer thickness organic films of transparent and resonantly interacting polymers and of their mixtures. PMID:27304282

  9. Three-dimensionality of field-induced magnetism in a high-temperature superconductor.

    PubMed

    Lake, B; Lefmann, K; Christensen, N B; Aeppli, G; McMorrow, D F; Ronnow, H M; Vorderwisch, P; Smeibidl, P; Mangkorntong, N; Sasagawa, T; Nohara, M; Takagi, H

    2005-09-01

    Many physical properties of high-temperature superconductors are two-dimensional phenomena derived from their square-planar CuO2 building blocks. This is especially true of the magnetism from the copper ions. As mobile charge carriers enter the CuO2 layers, the antiferromagnetism of the parent insulators, where each copper spin is antiparallel to its nearest neighbours, evolves into a fluctuating state where the spins show tendencies towards magnetic order of a longer periodicity. For certain charge-carrier densities, quantum fluctuations are sufficiently suppressed to yield static long-period order, and external magnetic fields also induce such order. Here we show that, in contrast to the chemically controlled order in superconducting samples, the field-induced order in these same samples is actually three-dimensional, implying significant magnetic linkage between the CuO2 planes. The results are important because they show that there are three-dimensional magnetic couplings that survive into the superconducting state, and coexist with the crucial inter-layer couplings responsible for three-dimensional superconductivity. Both types of coupling will straighten the vortex lines, implying that we have finally established a direct link between technical superconductivity, which requires zero electrical resistance in an applied magnetic field and depends on vortex dynamics, and the underlying antiferromagnetism of the cuprates. PMID:16100515

  10. Probing of field-induced structures and tunable rheological properties of surfactant capped magnetically polarizable nanofluids.

    PubMed

    Felicia, Leona J; Philip, John

    2013-01-01

    Oil-based nanofluid containing surfactant-capped magnetite nanoparticles are synthesized by a simple coprecipitation approach, and their magnetorheological properties are studied for different magnetic field strengths and volume fractions. We observe a distinct "plateau-like region" in the shear thinning viscosity curve, under an external magnetic field, possibly due to a peculiar alignment of the chains with respect to the field direction where the structure is stable against fragmentation. The observed plateau regime is reminiscent to that of kinetically arrested gel networks. Interestingly, such a plateau regime has been observed only above certain critical magnetic field when the dipolar interaction strength is much greater than the thermal energy where the aggregation becomes a nonequilibrium transport-limited process. The good collapse of specific viscosity data against Mason number for different magnetic field strengths onto a single curve suggests the dominance of hydrodynamic and magnetic forces on thermal force above a certain magnetic field strength. The observed increase in both static and dynamic yield stresses under the magnetic field confirms the formation of columnar structures that hinder the flow behavior. The hysteresis observed in the magnetic sweep experiments shows the inability of the chains to relax within the measurement time. The dynamic measurements confirm that the field-induced structures impart elastic behavior to the dispersion, which is found to increase with magnetic field and saturates at higher field strengths. PMID:23210900