The Origin of the Boson Peak and the Thermal Conductivity Plateau in Low Temperature Glasses

We argue that the intrinsic glassy degrees of freedom in amorphous solids giving rise to the thermal conductivity plateau and the ``boson peak'' in the heat capacity at moderately low temperatures are directly connected to those motions giving rise to the two-level like excitations seen at still lower temperatures. These degrees of freedom can be thought of as strongly anharmonic transitions between the local minima of the glassy energy landscape that are accompanied by ripplon-like domain wall motions of the glassy mosaic structure predicted to occur at $T_g$ by the random first order transition theory. The energy spectrum of the vibrations of the mosaic depends on the glass transition temperature, the Debye frequency and the molecular length scale. The resulting spectrum reproduces the experimental low temperature Boson peak. The ``non-universality'' of the thermal conductivity plateau depends on $k_B T_g/\hbar \omega_D$ and arises from calculable interactions with the phonons.Comment: 4 pages, submitted to PR

Stress distribution and the fragility of supercooled melts

We formulate a minimal ansatz for local stress distribution in a solid that includes the possibility of strongly anharmonic short-length motions. We discover a broken-symmetry metastable phase that exhibits an aperiodic, frozen-in stress distribution. This aperiodic metastable phase is characterized by many distinct, nearly degenerate configurations. The activated transitions between the configurations are mapped onto the dynamics of a long range classical Heisenberg model with 6-component spins and anisotropic couplings. We argue the metastable phase corresponds to a deeply supercooled non-polymeric, non-metallic liquid, and further establish an order parameter for the glass-to-crystal transition. The spin model itself exhibits a continuous range of behaviors between two limits corresponding to frozen-in shear and uniform compression/dilation respectively. The two regimes are separated by a continuous transition controlled by the anisotropy in the spin-spin interaction, which is directly related to the Poisson ratio $\sigma$ of the material. The latter ratio and the ultra-violet cutoff of the theory determine the liquid configurational entropy. Our results suggest that liquid's fragility depends on the Poisson ratio in a non-monotonic way. The present ansatz provides a microscopic framework for computing the configurational entropy and relaxational spectrum of specific substances.Comment: 11 pages, 5 figures, Final version published in J Phys Chem

Universality in Glassy Low-Temperature Physics

We propose a microscopic translationally invariant glass model which exhibits two level tunneling systems with a broad range of asymmetries and barrier heights in its glassy phase. Their distribution is qualitatively different from what is commonly assumed in phenomenological models, in that symmetric tunneling systems are systematically suppressed. Still, the model exhibits the usual glassy low-temperature anomalies. Universality is due to the collective origin of the glassy potential energy landscape. We obtain a simple explanation also for the mysterious {\em quantitative} universality expressed in the unusually narrow universal glassy range of values for the internal friction plateau.Comment: 4 pages, 5 figures, uses RevTeX

What are the interactions in quantum glasses?

The form of the low-temperature interactions between defects in neutral glasses is reconsidered. We analyse the case where the defects can be modelled either as simple 2-level tunneling systems, or tunneling rotational impurities. The coupling to strain fields is determined up to 2nd order in the displacement field. It is shown that the linear coupling generates not only the usual $1/r^3$ Ising-like interaction between the rotational tunneling defect modes, which cause them to freeze around a temperature $T_G$, but also a random field term. At lower temperatures the inversion symmetric tunneling modes are still active - however the coupling of these to the frozen rotational modes, now via the 2nd-order coupling to phonons, generates another random field term acting on the inversion symmetric modes (as well as shorter-range $1/r^5$ interactions between them). Detailed expressions for all these couplings are given.Comment: 12 pages, 2 figures. Minor modifications, published versio

Лазерные фазовые дальномеры: пути повышения точности

   Scientific and technological progress in the field of geodetic and industrial measurements in terms of the use of laser rangefinders operating in ranges up to 5000 meters has led to a reduction in the error of such measuring instruments over the past ten years by two or more times. Such rapid development of high-precision rangefinder technologies has led to a significant revision of the requirements for their metrological support, as well as to the need to develop a new generation of length standards, the stock of metrological accuracy of which would provide an assessment of the metrological characteristics of all types of existing and promising length measuring instruments with a laser rangefinder. To solve this problem, the Institute’s staff conducted research within the framework of a number of thematic research and development works in terms of developing the appearance of a new generation of length standards operating in the range up to 5000 meters in an open atmosphere. Within the framework of this article, one of the developed models of a high-precision complex of measuring instruments for length and coordinate increments is considered, which is a serial high-precision laser phase light meter, modified by the institute’s staff in terms of the system for receiving and processing measuring signals. At the same time, in order to increase the accuracy of length measurements using the developed range finder layout, it is proposed to investigate ways to reduce the errors of the model components of the boundaries of its error. To ensure the smallest error in determining the hardware correction of the rangefinder layout, it is proposed to use funds from the state primary special standard of the unit of length. As promising ways to reduce the error in determining the phase difference of signals, it is proposed to use digital recording and signal processing devices that implement a method for calculating the phase difference of signals by mathematically processing the recorded data using a specially developed computational algorithm based on Fourier analysis. For the most accurate determination of the values of the pulse repetition frequency of signals and the values of the speed of light on the measured track, it is proposed to improve the means of determining these indicators. The use of the proposed methods to improve the accuracy of measuring the length of laser phase rangefinders allows you to provide the necessary margin of metrological accuracy.   Научно-технический прогресс в сфере геодезических и промышленных измерений в части использования лазерных дальномеров, работающих в диапазонах до 5 000 метров, привел к уменьшению погрешности выше перечисленных средств измерений за последние десять лет в два и более раза. Следствием такого стремительного развития технологий высокоточной дальнометрии стал значительный пересмотр требований по их метрологическому обеспечению, а также необходимость разработки нового поколения эталонов длины, запас метрологической точности которых обеспечивал бы оценку метрологических характеристик всех типов существующих и перспективных средств измерений длины, имеющих в своем составе лазерный светодальномер. Для решения этой задачи авторами в рамках ряда тематических научно-исследовательских опытно-конструкторских работ проводились исследования с целью разработки нового поколения эталонов длины, работающих в диапазоне до 5 000 метров, в условиях открытой атмосферы. В данной статье рассмотрен один из разработанных макетов высокоточного комплекса средств измерений длины и приращений координат. Макет представляет собой высокоточный лазерный фазовый дальномер с доработанной системой приема и обработки измерительных сигналов. С помощью данного макета дальномера предлагается исследовать пути уменьшения составляющих его погрешности с целью повышения точности измерений длины. Для обеспечения наименьшей погрешности определения аппаратурной поправки макета дальномера могут служить средства из состава Государственного первичного специального эталона единицы длины. В качестве перспективных путей уменьшения погрешности определения разности фаз сигналов представляется возможным использовать устройства цифровой регистрации и обработки сигналов, в которых реализован метод расчета разности фаз сигналов путем математической обработки зарегистрированных данных с помощью специально разработанного вычислительного алгоритма на основе Фурье-анализа. Наиболее точное определение значений частоты следования импульсных сигналов и значений скорости света на измеряемой трассе может быть получено благодаря использованию высокоточных средств определения данных показателей. Реализация предложенных авторами методов повышения точности измерений длины лазерных фазовых дальномеров позволяет обеспечивать необходимый запас метрологической точности

The Ultimate Fate of Supercooled Liquids

In recent years it has become widely accepted that a dynamical length scale {\xi}_{\alpha} plays an important role in supercooled liquids near the glass transition. We examine the implications of the interplay between the growing {\xi}_{\alpha} and the size of the crystal nucleus, {\xi}_M, which shrinks on cooling. We argue that at low temperatures where {\xi}_{\alpha} > {\xi}_M a new crystallization mechanism emerges enabling rapid development of a large scale web of sparsely connected crystallinity. Though we predict this web percolates the system at too low a temperature to be easily seen in the laboratory, there are noticeable residual effects near the glass transition that can account for several previously observed unexplained phenomena of deeply supercooled liquids including Fischer clusters, and anomalous crystal growth near T_g

Механизмы приобретенной резистентности к анти-EGFR-препаратам при немелкоклеточном раке легкого, не связанной с мутацией Т790М, и их значение в клинической практике

The prospects of treatment strategies for patients with non-small cell lung cancer (NSCLC) featuring the acquired resistance to tyrosine kinase inhibitors, not associated with the Т790М mutation, are quite vast from a scientific point of view, but in routine clinical practice they are not yet available in full. Understanding the mechanisms of acquired resistance to tyrosine kinase inhibitors is important for clinicians from the perspective of the possibility of forming more effective options for the second and subsequent treatment of NSCLC. The most studied and frequent mechanism causing the formation of the acquired resistance is the appearance of the Т790М mutation in 20 exons of the EGFR gene. This article describes the current understanding of the mechanisms of acquired resistance to tyrosine kinase inhibitors not associated with the mutation of T790M, the evolution of views concerning the treatment of NSCLC, progressing in the course of the treatment by this group of drugs. Taking into account the diversity of unresolved issues and directions of further scientific research, we should not forget about the available research results and the ability to use the described options in routine clinical practice in a proper way.Перспективы лечебных стратегий пациентов с немелкоклеточным раком легкого (НМРЛ) и наличием приобретенной резистентности к ингибиторам тирозинкиназы, не связанной с мутацией Т790М, с научных позиций достаточно широки, но в рутинной клинической практике в полном объеме пока недоступны. Понимание механизмов приобретенной резистентности к ингибиторам тирозинкиназы важно для клиницистов с позиции возможностей формирования более эффективных опций 2-й и последующих линий терапии НМРЛ. Наиболее изученным и частым механизмом, обусловливающим формирование приобретенной резистентности, является возникновение мутации Т790М в экзоне 20 гена EGFR. В данной статье представлены современные представления о механизмах приобретенной резистентности к ингибиторам тирозинкиназы, не связанной с мутацией Т790М, кратко изложена эволюция взглядов на лечение НМРЛ, прогрессирующего на фоне применения препаратов этой группы. Принимая во внимание многогранность нерешенных вопросов и направлений дальнейших научных поисков, нельзя забывать об имеющихся результатах исследований и умении грамотного использования описанных опций в рутинной клинической практике

Analysis of Protein Markers in Plasma of Patients with Drug Dependence Syndrome: Observational Clinical Study

Background. In drug addiction treatment, the diagnostic process is based on the chemical toxicological determination of the intoxication substrate or its metabolite. Laboratory monitoring and prediction issues that could form the basis of secondary prevention remain unresolved. Specific nervous tissue proteins are considered to be the most promising laboratory markers of drug pathology.Objective — to determine some potential biomarkers of protein-chemical nature in the plasma of patients with drug dependence syndrome.Methods. The study was conducted according to the design of an observational clinical trial at the Narcological Dispensary of Krasnodar Krai in the period from 07.2021 to 07.2022. The main group (group 2) included 31 patients diagnosed with substance dependence syndrome. The control group (group 1, n = 15) consisted of healthy subjects submitted to occupational medical examinations. During the detoxification-stabilization therapy and rehabilitation, 5 proteins were determined in the plasma: brainand glial-derived neurotrophic factors, neuron-specific enolase, alpha-synuclein and calcium-binding protein S100B. Statistical analysis of the data involved the Mann-Whitney test for comparing the values of the control and experimental groups and the Wilcoxon test for comparing the values of one group obtained at different stages of observation. The calculations were carried out using StatPlus version 7 (AnalystSoft Inc., USA).Results. A total of 31 patients were included in the main group, 18 of them were followed up with a diagnosis of opioid dependence syndrome (n = 11) or psychostimulant dependence syndrome (n = 7). Patients dropped out of the study due to their refusal to participate in the study or undergo rehabilitation, or due to relapse of the disease. When admitted to the hospital, patients indicated a 45% decrease in brain-derived neurotrophic factor in the plasma ( p < 0.001), and a 3.9-fold decrease after rehabilitation course ( p < 0.001). Glial-derived neurotrophic factor in the plasma exceeded the controls 1.9 times ( p < 0.001) upon admission to hospital, but rapidly returned to normal values thereafter. Level of neuron-specific enolase in the plasma was also poor, 36% lower than the controls ( p <0.001), but approached the control values by the end of rehabilitation.Conclusion. The study obtained data indicating the changes in neurotrophic factors in the blood plasma of patients with opioid or psychostimulant dependence. The rehabilitation period was marked by a relatively rapid improving level of neurotrophins; however, brain-derived neurotrophic factor remained reduced despite the successful treatment, which may indicate the irreversible changes

Detection of hidden structures for arbitrary scales in complex physical systems

Recent decades have experienced the discovery of numerous complex materials. At the root of the complexity underlying many of these materials lies a large number of contending atomic- and largerscale configurations. In order to obtain a more detailed understanding of such systems, we need tools that enable the detection of pertinent structures on all spatial and temporal scales. Towards this end, we suggest a new method that applies to both static and dynamic systems which invokes ideas from network analysis and information theory. Our approach efficiently identifies basic unit cells, topological defects, and candidate natural structures. The method is particularly useful where a clear definition of order is lacking, and the identified features may constitute a natural point of departure for further analysis

The Shapes of Cooperatively Rearranging Regions in Glass Forming Liquids

The shapes of cooperatively rearranging regions in glassy liquids change from being compact at low temperatures to fractal or ``stringy'' as the dynamical crossover temperature from activated to collisional transport is approached from below. We present a quantitative microscopic treatment of this change of morphology within the framework of the random first order transition theory of glasses. We predict a correlation of the ratio of the dynamical crossover temperature to the laboratory glass transition temperature, and the heat capacity discontinuity at the glass transition, Delta C_p. The predicted correlation agrees with experimental results for the 21 materials compiled by Novikov and Sokolov.Comment: 9 pages, 6 figure