scholarly journals Pinching a glass reveals key properties of its soft spots

2020 ◽  
Vol 117 (10) ◽  
pp. 5228-5234 ◽  
Author(s):  
Corrado Rainone ◽  
Eran Bouchbinder ◽  
Edan Lerner
Keyword(s):  
Density Of States ◽  
Effective Temperature ◽  
Nonequilibrium Thermodynamic ◽  
Characteristic Size ◽  
Length Scale ◽  
Low Frequencies ◽  
Glass Physics ◽  
Physical Information ◽  
Key Questions

It is now well established that glasses feature quasilocalized nonphononic excitations—coined “soft spots”—, which follow a universal ω4 density of states in the limit of low frequencies ω. All glass-specific properties, such as the dependence on the preparation protocol or composition, are encapsulated in the nonuniversal prefactor of the universal ω4 law. The prefactor, however, is a composite quantity that incorporates information both about the number of quasilocalized nonphononic excitations and their characteristic stiffness, in an apparently inseparable manner. We show that by pinching a glass—i.e., by probing its response to force dipoles—one can disentangle and independently extract these two fundamental pieces of physical information. This analysis reveals that the number of quasilocalized nonphononic excitations follows a Boltzmann-like law in terms of the parent temperature from which the glass is quenched. The latter, sometimes termed the fictive (or effective) temperature, plays important roles in nonequilibrium thermodynamic approaches to the relaxation, flow, and deformation of glasses. The analysis also shows that the characteristic stiffness of quasilocalized nonphononic excitations can be related to their characteristic size, a long sought-for length scale. These results show that important physical information, which is relevant for various key questions in glass physics, can be obtained through pinching a glass.

scholarly journals Model Atmospheres for X-ray Bursting Neutron Stars

1987 ◽  
Vol 125 ◽  
pp. 251-251
Author(s):  
Richard A. London ◽  
Ronald E. Taam ◽  
W. Michael Howard
Keyword(s):  
Neutron Stars ◽  
Electron Scattering ◽  
Effective Temperature ◽  
Radiation Spectrum ◽  
Temperature Structure ◽  
Atmospheric Models ◽  
Low Frequencies ◽  
X Ray ◽  
Initial Rise ◽  
Improper Use

Self consistent neutron star atmospheric models have been constructed which include the effects of Comptonization, free-free and bound-free absorption. It has been demonstrated that for parameters relevant to x-ray bursting neutron stars the atmosphere does not radiate like a blackbody during any phase of an x-ray burst. In particular, during the initial rise and final decline of the burst the temperature structure of the atmosphere is affected by backwarming associated with the high opacity due to free-free processes at low frequencies to an extent that the radiation spectrum is shifted to higher energies than a blackbody of the same effective temperature. On the other hand, near the peak of the burst, the opacity is more gray-like as the electron scattering opacity dominates; however, in this case thermalizaton of the radiation field occurs at such large optical depths (τ ∼ 5) that the spectral temperature is higher than the effective temperature. This result is found despite the importance of Comptonization in the thermalization process. Thus, the super Eddington fluxes implied by the spectral data alone are misleading and result from the improper use of the spectral temperature for the effective temperature. For neutron stars characterized by a soft equation of state and radiating near the Eddington effective temperature, fluxes obtained in this way could be overestimated by a factor of about 5.

A Boundary Layer Transition Model

1996 ◽  
Author(s):  
Mark W. Johnson ◽  
Ali H. Ercan
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Test Cases ◽  
Length Scale ◽  
Transition Model ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Turbulent Length Scale

A new boundary layer transition model is presented which relates the velocity fluctuations near the wall to the formation of turbulent spots. A relationship for the near wall velocity frequency spectra is also established, which indicates an increasing bias towards low frequencies as the skin friction coefficient for the boundary layer decreases. This result suggests that the dependence of transition on the turbulent length scale is greatest at low freestream turbulence levels. This transition model is incorporated in a conventional boundary layer integral technique and is used to predict eight of the ERCOFTAC test cases. Three of these test cases are for nominally zero pressure gradient and the remaining five are for a pressure distribution typical of an aft loaded turbine blade. The model is demonstrated to predict the development of the boundary layer through transition reasonably accurately for all the test cases. The sensitivity of start of transition to the turbulent length scale at low freestream turbulence levels is also demonstrated.

Effective temperature for hopping transport in a Gaussian density of states

2008 ◽  
Vol 77 (19) ◽  
Author(s):  
F. Jansson ◽  
S. D. Baranovskii ◽  
F. Gebhard ◽  
R. Österbacka
Keyword(s):  
Density Of States ◽  
Effective Temperature ◽  
Hopping Transport ◽  
Gaussian Density

Photoconductivity and Density of States in “Microstructural” Amorphous Silicon

1997 ◽  
Vol 467 ◽  
Author(s):  
B. G. Budaguan ◽  
A. A. Aivazov ◽  
A. G. Radosel'sky ◽  
A. A. Popov
Keyword(s):  
Atomic Force Microscopy ◽  
Comparative Analysis ◽  
Density Of States ◽  
Characteristic Size ◽  
High Deposition Rate ◽  
Measured Temperature ◽  
Force Microscopy ◽  
Atomic Force ◽  
Analysis Of Results ◽  
Recombination Kinetics

ABSTRACTIt has been reported in previous works that using of RF 55 kHz PECVD method allows to deposit microstructural inhomogeneous a-Si:H films at high deposition rate (10–20Å/c) and with high photoconductivity The structural analysis with using of IR spectroscopy and atomic force microscopy (AFM) performed in this work have shown that these films possess a relatively regular microstructure consisting of “grains” with characteristic size of∼300–500Å. The regular microstructure of investigated films differs them from inhomogeneous a-Si:H with deteriorate electronic properties. At the same time the diffraction analysis didn't reveal the presence of microcrystals. Therefore, we denoted our films as “microstructural” a-Si:H films In this work we performed the modeling of the photoconductivity of “microstructural” a-Si:H films to analyze the density-of-states (DOS) responsible for recombination kinetics For this purpose different approaches to photoconductivity modeling have been used to simulate the experimentally measured temperature dependence of photoconductivity The comparative analysis of results of these simulations and ESR measurements have shown that recombination in high photoconductive ‘microstructural’ films is controlled by deep neutral states

MAXIMUM DYNAMICAL DISORDER IN AMORPHOUS GaAs

1994 ◽  
Vol 08 (03) ◽  
pp. 169-172 ◽  
Author(s):  
M.A. GRADO CAFFARO ◽  
M. GRADO CAFFARO
Keyword(s):  
Optical Absorption ◽  
Absorption Coefficient ◽  
Density Of States ◽  
Far Infrared ◽  
Conduction Band Edge ◽  
Infrared Range ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Low Frequencies ◽  
Dynamical Disorder

Maximum dynamical disorder in amorphous gallium arsenide is investigated in a special way. In particular, this maximum disorder refers to distance and it is investigated in the context of optical absorption at very low frequencies in the far-infrared range when the photon energy is larger than 2Ec, Ec being the energy at the conduction band edge. Absorption coefficient is calculated and compared with experimental work. Phonon density of states is also evaluated.

scholarly journals Effect of Grain Boundaries on the Vibrational Properties of Phononic Crystals

MRS Advances ◽  
2017 ◽  
Vol 2 (28) ◽  
pp. 1463-1468
Author(s):  
Ralf Meyer
Keyword(s):  
Grain Boundaries ◽  
Density Of States ◽  
Low Frequency ◽  
Phononic Crystals ◽  
Model Systems ◽  
Vibrational Properties ◽  
Low Frequencies ◽  
Peak Structure ◽  
Uniform Manner ◽  
Dynamics Simulations

ABSTRACTThe influence of grain boundaries on the vibrational properties of nanoscale phononic crystals is studied with the help of molecular dynamics simulations. The low-frequency vibrational density of states of phononic crystals made from single crystal and polycrystalline silicon are derived from the simulations. The results show that the presence of grain boundaries leads to an increase of the density of states and a change of its peak structure at low frequencies. Calculations of the band structure of the model systems along one direction reveal that the grain boundaries affect the bands differently and in a non-uniform manner.

The Effect of Mean Loading on the Fluctuating Loads Induced on Aerofoils by a Turbulent Stream

1980 ◽  
Vol 31 (1) ◽  
pp. 56-69 ◽  
Author(s):  
P.J. Mckeough ◽  
J.M.R. Graham
Keyword(s):  
Wind Tunnel ◽  
Isotropic Turbulence ◽  
Three Dimensional ◽  
Length Scale ◽  
Grid Turbulence ◽  
Angle Of Incidence ◽  
Mean Flow ◽  
Low Frequencies ◽  
The Mean ◽  
Naca 0015

SummaryThis paper analyses the unsteady lift produced on a thin aerofoil by an arbitrary three-dimensional gust. In particular, it evaluates the effects of α, the angle of incidence of the aerofoil to the mean stream. A thin aerofoil theory which includes the effects of distortion of the turbulence by the mean flow field of the aerofoil is applied to the case of an aerofoil in isotropic turbulence. Some computed results are compared with measurements made on a NACA 0015 aerofoil in grid turbulence in a wind tunnel. It is shown that for isotropic turbulence the effect of mean incidence on the lift spectrum is of order α2, and is significant at low frequencies for the length scale ratios tested.

scholarly journals Бозонный пик в аморфном графене в рамках модели устойчивых случайных матриц

2020 ◽  
Vol 62 (11) ◽  
pp. 1907
Author(s):  
И.O. Райков ◽  
Д.А. Конюх ◽  
A.Н. Ипатов ◽  
Д.А. Паршин
Keyword(s):  
Density Of States ◽  
Boson Peak ◽  
Force Constants ◽  
Optical Phonons ◽  
Low Frequencies ◽  
Van Hove Singularities ◽  
Amorphous Graphene ◽  
Sufficient Strength

We study the role of disorder in the force constants distribution on the acoustical and optical phonons in amorphous graphene. It is shown that for a sufficient strength of disorder the boson peak appears in the density of states. With increasing strength of disorder, the peak moves to low frequencies together with Yung modulus. For sufficiently small disorder we have the Van-Hove singularities in the vibration density of states. With increasing disorder, these singularities transform together to one boson peak. The first disappears optical phonons then the acoustical one. The same investigation was done for flexural modes. We show that these modes disappear in disorder in already weak perturbations and transforms to phonons.

The quantum theory of one-electron states at surfaces and interfaces

1971 ◽  
Vol 324 (1558) ◽  
pp. 257-273 ◽  
Keyword(s):  
Quantum Theory ◽  
Density Of States ◽  
Surface States ◽  
Green Functions ◽  
Matrix Elements ◽  
Electron States ◽  
Surfaces And Interfaces ◽  
The Matrix ◽  
Physical Information ◽  
Secular Determinant

The matching of the wavefunction at an arbitrary surface is formulated in terms of Green functions. If G 1 and G 2 are the resolvents for media 1 and 2, respectively, and G s is the re­solvent for a system consisting of 1 and 2 in contact through an interface (not necessarily abrupt), then G s is fully obtained in terms of G 1 and G 2 . By taking suitable matrix elements one obtains: (i) a secular determinant for the matching eigenvalues (surface states); (ii) a for­mula for the wavefunction everywhere, and (iii) a formula for the density of states. The case of a film is studied in the same way. The formalism is illustrated with a few examples. This paper deals with the physical information contained in the matrix elements of G s between points which are either on the surface or else on the same side, but the method yields also the matrix elements across the surface, which are important for the theory of dielectric responses in a system with an interface.

Biomimetic materials: An introduction

1992 ◽  
Vol 50 (2) ◽  
pp. 1020-1021 ◽  
Author(s):  
M. Sarikaya ◽  
J. T. Staley ◽  
I. A. Aksay
Keyword(s):  
Self Assembly ◽  
Structural Control ◽  
Hierarchical Structures ◽  
Ceramic Composites ◽  
Advanced Materials ◽  
Length Scale ◽  
Spider Webs ◽  
Biomimetic Materials ◽  
Synthetic Materials ◽  
All Ceramic

Biomimetics is an area of research in which the analysis of structures and functions of natural materials provide a source of inspiration for design and processing concepts for novel synthetic materials. Through biomimetics, it may be possible to establish structural control on a continuous length scale, resulting in superior structures able to withstand the requirements placed upon advanced materials. It is well recognized that biological systems efficiently produce complex and hierarchical structures on the molecular, micrometer, and macro scales with unique properties, and with greater structural control than is possible with synthetic materials. The dynamism of these systems allows the collection and transport of constituents; the nucleation, configuration, and growth of new structures by self-assembly; and the repair and replacement of old and damaged components. These materials include all-organic components such as spider webs and insect cuticles (Fig. 1); inorganic-organic composites, such as seashells (Fig. 2) and bones; all-ceramic composites, such as sea urchin teeth, spines, and other skeletal units (Fig. 3); and inorganic ultrafine magnetic and semiconducting particles produced by bacteria and algae, respectively (Fig. 4).

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