22 research outputs found
Interaction of quasilocal harmonic modes and boson peak in glasses
The direct proportionality relation between the boson peak maximum in
glasses, , and the Ioffe-Regel crossover frequency for phonons,
, is established. For several investigated materials . At the frequency the mean free path of the
phonons becomes equal to their wavelength because of strong resonant
scattering on quasilocal harmonic oscillators. Above this frequency phonons
cease to exist. We prove that the established correlation between
and holds in the general case and is a direct consequence of
bilinear coupling of quasilocal oscillators with the strain field.Comment: RevTex, 4 pages, 1 figur
Recommended from our members
Theory of femtosecond photon echo decay in semiconductors
The authors investigate a mechanism responsible for the observed very short times of the photon echo decay (of the order of a few femtoseconds) in semiconductors. It is associated with the loss of phase memory as a result of interaction of the mixed state (associated with interband transitions) with an unscreened random Coulomb potential of the photocarriers or with a random static potential of the impurities. Qualitative physical consideration enabling one to visualize the process of echo decay are presented. They have introduced a new time characteristic of a system of interacting electrons. This is the time of phase breaking, {tau}{sub {var_phi}} which they calculate within the eikonal approximation using a diagrammatic technique. It is shown that {tau}{sub {var_phi}} is typically much shorter than both the period of plasma oscillations and the time of electron-electron collisions. The screening of Coulomb potential cannot build up during this time. {tau}{sub {var_phi}} is proportional to n{sup {minus}1/d} (where n is the carrier concentration, d the dimensionality of a system) which is consistent with the experimental results
Fluctuation of the Correlation Dimension and the Inverse Participation Number at the Anderson Transition
The distribution of the correlation dimension in a power law band random
matrix model having critical, i.e. multifractal, eigenstates is numerically
investigated. It is shown that their probability distribution function has a
fixed point as the system size is varied exactly at a value obtained from the
scaling properties of the typical value of the inverse participation number.
Therefore the state-to-state fluctuation of the correlation dimension is
tightly linked to the scaling properties of the joint probability distribution
of the eigenstates.Comment: 4 pages, 5 figure
ПОЛУЧЕНИЕ БЕСКЛЕТОЧНОГО МАТРИКСА ХРЯЩА ТРАХЕИ ДЛЯ ТКАНЕИНЖЕНЕРНЫХ КОНСТРУКЦИЙ
Background: Tissue-engineered trachea transplantation remains the last chance for a variety of patients suffering from severe cicatricial tracheal stenosis. Despite the series of carried studies, the final solution hasn’t been found. Creating a functionally complete hyaline cartilage graft in vitro still presents a fundamental problem, and a number of researchers consider it as the key to a successful tracheal tissue-engineering.Aims: The study aimed to investigate the capability of detergent complex and DNAse I for human tracheal cartilage decellularization in short-time exposition for acellular scaffold obtaining.Materials and methods: Isolated from cadaveric trachea human native cartilage was used for decellularization by ensimatic-detergent complex including Triton X-100, DMSO, and DNAse I. The scaffold was characterised by histological examinations, analysis of the residual DNA content, and cell metabolic activity colorimetric test with culture in the scaffold fragments.Results: The obtained scaffolds presented highly porous structure mostly composed of collagen and glycosaminoglycans with an insignificant residual DNA level, absence of citotoxicity, and capability for cell proliferative activity stimulation.Conclusions: Thus, the study provides a new short-time technology for hyaline cartilage decellularization in order to achieve acellular scaffolds in step with the tissue engineering requirements.Обоснование. Трансплантация тканеинженерной трахеи остается единственной надеждой для множества пациентов, страдающих тяжелыми рубцовыми стенотическими поражениями трахеи. Несмотря на существенное число выполненных исследований, окончательного решения проблемы пока не найдено. Вопрос о возможности создания функционально полноценной гиалиновой хрящевой ткани в трансплантате in vitro остается открытым, и ряд исследователей видят в нем ключ к успешному решению современных задач тканевой инженерии трахеи.Цель исследования ― оценить способность комбинации детергентов и ДНКазы I к децеллюляризации хрящевой ткани трахеи человека при кратковременном воздействии для получения бесклеточного матрикса-носителя.Методы. В исследовании использовался нативный хрящ человека, выделяемый из трахеи трупного донора и децеллюляризируемый комплексом детергентов и энзимов, включающих Тритон X-100, DMSO и ДНКазу I. Свойства получаемого матрикса-носителя оценивались в ходе гистологических исследований, анализа содержания остаточной ДНК в препарате и колориметрического теста метаболической активности клеток при культивировании на фрагментах носителя.Результаты. Полученные матриксы-носители обладали пористой структурой, преимущественно представленной коллагеном и гликозаминогликанами, демонстрировали низкий уровень остаточной ДНК, лишены цитотоксичности и способны стимулировать пролиферативную клеточную активность.Заключение. Результаты данного исследования позволили предложить новый метод непродолжительной децеллюляризации гиалиновой хрящевой ткани с получением клеточных носителей, отвечающих основным требованиям тканевой инженерии
Critical statistics in a power-law random banded matrix ensemble
We investigate the statistical properties of the eigenvalues and eigenvectors
in a random matrix ensemble with . It is known that
this model shows a localization-delocalization transition (LDT) as a function
of the parameter . The model is critical at and the eigenstates
are multifractals. Based on numerical simulations we demonstrate that the
spectral statistics at criticality differs from semi-Poisson statistics which
is expected to be a general feature of systems exhibiting a LDT or `weak
chaos'.Comment: 4 pages in PS including 5 figure
Dimensionality dependence of the wave function statistics at the Anderson transition
The statistics of critical wave functions at the Anderson transition in three
and four dimensions are studied numerically. The distribution of the inverse
participation ratios (IPR) is shown to acquire a scale-invariant form in
the limit of large system size. Multifractality spectra governing the scaling
of the ensemble-averaged IPRs are determined. Conjectures concerning the IPR
statistics and the multifractality at the Anderson transition in a high spatial
dimensionality are formulated.Comment: 4 pages, 4 figure
Effect of Nuclear Quadrupole Interaction on the Relaxation in Amorphous Solids
Recently it has been experimentally demonstrated that certain glasses display
an unexpected magnetic field dependence of the dielectric constant. In
particular, the echo technique experiments have shown that the echo amplitude
depends on the magnetic field. The analysis of these experiments results in the
conclusion that the effect seems to be related to the nuclear degrees of
freedom of tunneling systems. The interactions of a nuclear quadrupole
electrical moment with the crystal field and of a nuclear magnetic moment with
magnetic field transform the two-level tunneling systems inherent in amorphous
dielectrics into many-level tunneling systems. The fact that these features
show up at temperatures , where the properties of amorphous materials
are governed by the long-range interaction between tunneling systems,
suggests that this interaction is responsible for the magnetic field dependent
relaxation. We have developed a theory of many-body relaxation in an ensemble
of interacting many-level tunneling systems and show that the relaxation rate
is controlled by the magnetic field. The results obtained correlate with the
available experimental data. Our approach strongly supports the idea that the
nuclear quadrupole interaction is just the key for understanding the unusual
behavior of glasses in a magnetic field.Comment: 18 pages, 9 figure
Anomalously localized states and multifractal correlations of critical wavefunctions in two-dimensional electron systems with spin-orbital interactions
Anomalously localized states (ALS) at the critical point of the Anderson
transition are studied for the SU(2) model belonging to the two-dimensional
symplectic class. Giving a quantitative definition of ALS to clarify
statistical properties of them, the system-size dependence of a probability to
find ALS at criticality is presented. It is found that the probability
increases with the system size and ALS exist with a finite probability even in
an infinite critical system, though the typical critical states are kept to be
multifractal. This fact implies that ALS should be eliminated from an ensemble
of critical states when studying critical properties from distributions of
critical quantities. As a demonstration of the effect of ALS to critical
properties, we show that the distribution function of the correlation dimension
of critical wavefunctions becomes a delta function in the thermodynamic limit
only if ALS are eliminated.Comment: 7 pages, 6 figure
Multifractality of Hamiltonians with power-law transfer terms
Finite-size effects in the generalized fractal dimensions are
investigated numerically. We concentrate on a one-dimensional disordered model
with long-range random hopping amplitudes in both the strong- and the
weak-coupling regime. At the macroscopic limit, a linear dependence of on
is found in both regimes for values of q \alt 4g^{-1}, where is the
coupling constant of the model.Comment: RevTex4, 5 two-column pages, 5 .eps figures, to be published in Phys.
Rev.
Frequency behavior of Raman coupling coefficient in glasses
Low-frequency Raman coupling coefficient of 11 different glasses is
evaluated. It is found that the coupling coefficient demonstrates a universal
linear frequency behavior near the boson peak maximum and a superlinear
behavior at very low frequencies. The last observation suggests vanishing of
the coupling coefficient when frequency tends to zero. The results are
discussed in terms of the vibration wavefunction that combines features of
localized and extended modes.Comment: 8 pages, 9 figure