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

Aging, jamming, and the limits of stability of amorphous solids

Apart from not having crystallized, supercooled liquids can be considered as being properly equilibrated and thus can be described by a few thermodynamic control variables. In contrast, glasses and other amorphous solids can be arbitrarily far away from equilibrium and require a description of the history of the conditions under which they formed. In this paper we describe how the locality of interactions intrinsic to finite-dimensional systems affects the stability of amorphous solids far off equilibrium. Our analysis encompasses both structural glasses formed by cooling and colloidal assemblies formed by compression. A diagram outlining regions of marginal stability can be adduced which bears some resemblance to the quasi-equilibrium replica meanfield theory phase diagram of hard sphere glasses in high dimensions but is distinct from that construct in that the diagram describes not true phase transitions but kinetic transitions that depend on the preparation protocol. The diagram exhibits two distinct sectors. One sector corresponds to amorphous states with relatively open structures, the other to high density, more closely-packed ones. The former transform rapidly owing to there being motions with no free energy barriers; these motions are string-like locally. In the dense region, amorphous systems age via compact activated reconfigurations. The two regimes correspond, in equilibrium, to the collisional or uniform liquid and the so called landscape regime, respectively. These are separated by a spinodal line of dynamical crossovers. Owing to the rigidity of the surrounding matrix in the landscape, high-density part of the diagram, a sufficiently rapid pressure quench adds compressive energy which also leads to an instability toward string-like motions with near vanishing barriers. (SEE REST OF ABSTRACT IN THE ARTICLE.)Comment: submitted to J Phys Chem

Comparison and Uncertainty Quantification of Two-Fluid Models forBubbly Flows with NEPTUNE_CFD and STAR-CCM+

International audienceThe nuclear industry is interested in better understanding the behavior of turbulent boiling flowsand in using modern computational tools for the design and analysis of advanced fuels and reactorsand for simulation and study of mitigation strategies in accident scenarios. Such interests serve asdrivers for the advancement of the 3-dimensional multiphase Computational Fluid Dynamicsapproach. A pair of parallel efforts have been underway in Europe and in the United States, theNEPTUNE and CASL programs respectively, that aim at delivering advanced simulation tools thatwill enable improved safety and economy of operations of the reactor fleet. Results from acollaboration between these two efforts, aimed at advancing the understanding of multiphaseclosures for pressurized water reactor (PWR) application, are presented. Particular attention is paidto the assessment and analysis of the different physical models implemented in NEPTUNE_CFDand STAR-CCM+ codes used in the NEPTUNE and the CASL programs respectively, forapplication to turbulent two-phase bubbly flows. The experiments conducted by Liu and Bankoff(Liu, 1989; Liu and Bankoff 1993a and b) are selected for benchmarking, and predictions from thetwo codes are presented for a broad range of flow conditions and with void fractions varyingbetween 0 and 50percent. Comparison of the CFD simulations and experimental measurements revealsthat a similar level of accuracy is achieved in the two codes. The differences in both sets of closuremodels are analyzed, and their capability to capture the main features of the flow over a wide rangeof experimental conditions are discussed. This analysis paves the way for future improvements ofexisting two-fluid models. The benchmarks are further leveraged for a systematic study of thepropagation of model uncertainties. This provides insights into mechanisms that lead to complexinteractions between individual closures (of the different phenomena) in the multiphase CFDapproach. As such, it is seen that the multi-CFD-code approach and the principled uncertaintyquantification approach are both of great value in assessing the limitations and the level of maturityof multiphase hydrodynamic closures

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

Electronic structure and the glass transition in pnictide and chalcogenide semiconductor alloys. Part I: The formation of the ppσpp\sigma-network

Semiconductor glasses exhibit many unique optical and electronic anomalies. We have put forth a semi-phenomenological scenario (J. Chem. Phys. 132, 044508 (2010)) in which several of these anomalies arise from deep midgap electronic states residing on high-strain regions intrinsic to the activated transport above the glass transition. Here we demonstrate at the molecular level how this scenario is realized in an important class of semiconductor glasses, namely chalcogen and pnictogen containing alloys. Both the glass itself and the intrinsic electronic midgap states emerge as a result of the formation of a network composed of $\sigma$-bonded atomic $p$-orbitals that are only weakly hybridized. Despite a large number of weak bonds, these $pp\sigma$-networks are stable with respect to competing types of bonding, while exhibiting a high degree of structural degeneracy. The stability is rationalized with the help of a hereby proposed structural model, by which $pp\sigma$-networks are symmetry-broken and distorted versions of a high symmetry structure. The latter structure exhibits exact octahedral coordination and is fully covalently-bonded. The present approach provides a microscopic route to a fully consistent description of the electronic and structural excitations in vitreous semiconductors.Comment: 22 pages, 17 figures, revised version, final version to appear in J. Chem. Phy

Influence of Different Catalysts and Solvents on the General Base Catalytical Esterification of Polyoxyethylene Sorbitan Trioleate with Maleic Anhydride and Styrene-Co-Maleic Anhydride

The general base catalitycal esterification of Polyoxyethylene sorbitane Trioleate with maleic anhydride (Ma) and styrene-co-maleic anhydride (Sma) using pyridine as catalyst is described. We investigated the effect of different factors on the yield of reaction product. The analysis of the effect of different factors on the process of catalytical esterification showed that the catalysts and solvents can be arranged by their activity in the following order: sulfuric acid > toluene sulfonic acid > triethylamine > pyridine > without a catalyst and dimethylsulfoxide (DMSO) > O-xylene > dimethylformamide (DMF), respectively. It should be noted that pyridine to its activity is not significantly inferior to the traditional catalysts and with DMSO using the yield of product is increasing. It is concluded that the reaction proceeds by 2nd order. It was found that decreasing the temperature of reaction to a lower temperature, where there is an intensive incubation period, leads to decreasing of yield of polyesters. The rate constant and activation energy were calculated. It was found that the process occurred on 98% at 130 °С and 80 minutes for PoesTo/Ma and on 88% at 150 °С and 40 minutes for PoesTo/Sma. For preparation of reaction product to analysis new methods were developed. It was shown, that on 1H and 13C spectra an overlap of the individual peaks or their close concentration in one area is observed, which makes it not possible to complete the analysis of the spectra. 1H and 13C spectra give a preliminary idea of the structure of the reaction products. It is concluded that 2-D NMR measurements more useful for further confirming of structure of PoesTo/Ma and PoesTo/Sma. HLB shown that we obtained two different surfactants where by catalytical esterification the hydrophilic part of Tween in PoesTo/Ma and the lipophilic part in PoesTo/Sma was increased

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

Oxidative stress markers in patients suffering from opioid and psychostimulant dependence syndrome

Background. The available data from clinical studies suggest the essential role of free radical processes in the pathogenesis of drug dependence syndrome. At the same time, there is a limited understanding of using markers of oxidative stress in laboratory monitoring and prediction of drug pathology.Objective. To characterize changes in promising indicators of oxidative stress in patients with psychostimulant and opioid dependence syndrome.Material and Methods. The total study population was divided into three groups of men aged 23–35: healthy controls (n = 20), patients with the opioid (n = 20) and psychostimulant (n = 20) dependence syndrome. Patients were analyzed for the oxidative stress markers while being in therapy for addiction syndrome aimed at treating mental disorders and detoxification.Results. The study of antioxidant activity and blood plasma thiol groups did not reveal any significant differences between patients suffering from opioid and psychostimulant addiction. The values of the parameters mentioned above were maintained by 20–30% lower than the control indices throughout the entire study. The nature of changes in erythrocyte suspension parameters was not so unambiguous. Thus, patients with opioid dependence syndrome were characterized by a 91% increase in thiobarbituric acid (TBA)-reactive materials in the setting of a slightly altered state of the glutathione system parameters. Psychostimulant dependent patients revealed relatively low level of the products of biomolecule oxidative modifications in the erythrocytes that is 52% higher compared to the control values. It decreased during the therapy, but glutathione concentration reduction by 33% and an imbalance of glutathione metabolism were determined.Conclusion. The course of the opioid dependence syndrome is characterized by a pronounced intensification of free radical processes while the common trait for psychostimulant abusers is significant changes in the antioxidant defense system. Therefore, in the first case, it is most justified to conduct a laboratory assessment of indicators of oxidative damage, and in the second one, it is also advisable to determine the markers of the state of individual links of the antioxidant system

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

Changes in indicators of the prooxidant-antioxidant system in patients with drug addiction during the rehabilitation

Background: Despite the positive dynamics in this scientific area, the prevalence of drug pathology in Russia and other countries of the world remains unfavorable. Determination of laboratory markers of pathobiochemical processes which are characteristic to the patients with substance use disorder is promising from the standpoint of monitoring the course of the disease and evaluating the effectiveness of therapy.Objective: To determine the characteristic changes in oxidative homeostasis of patients with addiction to psychostimulants and opioids at the rehabilitation and anti‑relapse stage.Material and methods: The study was performed with the participation of 20 relatively healthy male volunteers and 18 male patients with addiction to opioids or psychostimulants who then became participants of the rehabilitation and anti‑relapse course of treatment. Changes in oxidative stress markers during rehabilitation and anti‑relapse treatment were studied.Results: In comparison to the control values at the initial stage of the study, patients of the main group demonstrated decreased values of the iron‑reducing ability of blood plasma – by 25%, as well as those of the sorption radical ability of blood plasma – by 30%; the content of thiol groups of blood plasma proteins decreased by 24% while the concentration of glutathione in erythrocyte suspension lowered by 26%. The level of TBA‑reactive products in erythrocyte suspension corresponded to the control level. The performed rehabilitation manipulations contributed to the partial normalization of oxidative homeostasis, which was confirmed by a statistically significant increase in the ability of radical sorption of blood plasma by 20% and the concentration of reduced glutathione in erythrocyte suspension by 28% in comparison to the initial values of the corresponding parameters in patients of the 2nd group. The TBA‑reactive products remained within the control values.Conclusion: The studied markers are suitable for monitoring the state of oxidative homeostasis in patients with opioid or psychostimulant addiction, the imbalance of which at the end of the rehabilitation and anti‑relapse stage also indicates the prospects for strengthening the antioxidant component as part of drug or nutritional correction