Thermal boundary resistance at Si/Ge interfaces determined by approach-to-equilibrium molecular dynamics simulations

The thermal boundary resistance of Si/Ge interfaces as been determined using approach-to-equilibrium molecular dynamics simulations. Assuming a reciprocal linear dependence of the thermal boundary resistance, a length-independent bulk thermal boundary resistance could be extracted from the calculation resulting in a value of 3.76x10$^{-9}$ m$^2$ K/W for a sharp Si/Ge interface and thermal transport from Si to Ge. Introducing an interface with finite thickness of 0.5 nm consisting of a SiGe alloy, the bulk thermal resistance slightly decreases compared to the sharp Si/Ge interface. Further growth of the boundary leads to an increase in the bulk thermal boundary resistance. When the heat flow is inverted (Ge to Si), the thermal boundary resistance is found to be higher. From the differences in the thermal boundary resistance for different heat flow direction, the rectification factor of the Si/Ge has been determined and is found to significantly decrease when the sharp interface is moderated by introduction of a SiGe alloy in the boundary layer.Comment: 7 pages, 6 figure

Antarctic Glacial and Subglacial Topography

1. The data is collected and generalized according to 48,000km of surface traverses in Antarctica during the last 15 years. An evaluation is made of reliability of material and methods of study of the ice cover thickness, evaluation of precision of levelling methods and prospects of aeromagnetic, radar and electrical methods for the study of the ice cover thickness of Antarctica. Methods are suggested which allow to make indirect evaluation of the relief of the subglacial bed of Antarctica according to the relief and inclination of the sufrace, crevassing of the ice cover and geological structures. 2. By application of the material on subglacial bed relief YU.N. AVSYUK, L.I. IVASHUTINA, A.P. KAPITZA and O.G. SOROKHTIN compiled the map of subglacial bed relief of Antarctica. The horizontal contours are drawn every 500m. In the process of Antarctic researches new large forms of sub-ice relief were revealed : Gamburtsev Mts., Vernadsky Mts., Golitsin Mts., Shchukin Mts., Schmidt Plateau, East Plateau, West Plateau. In the process of generalization of materials large faults were found in Antarctica : the Trans-Antarctic trough. 3. The map of the thickness of ice cover in Antarctica has been made by the method of graphical subtraction by using the map of subglacial relief of Antarctica and the map of ice cover surface. The amount of ice in Antarctica was estimated according to that map, which makes 24 million km^3 of ice. 4. On the basis of the analysis of the map of ice cover surface a map has been compiled of the lines of ice flow, and the main ice divides and centers of ice diffluence in Antarctica were determined. 5. Geophysical data testify that the earth\u27s crust in Antarctica is in the state of isostatic equilibrium, while at the same time separate forms of the relief have deviations of mean values of the free air anomaly, which allow to propose a hypothesis about the general reduction of the ice cover of Antarctica in the Holocene. The general retreat of glaciers does not contradict the separate data about shortperiod (within tens or hundreds of years) advances of ice cover edge. 7. The analysis of data about the subglacial relief of Antarctica has been used in calculation of the uprising values of the earth\u27s crust after deglaciation, and a map is compiled predicting contours of the continent in the Post-Glacial Period with compensational uprising. 8. Major trends are suggested of the study of subglacial bed of Antarctica and of the ice cover relief for the solution of the most important glaciological and geomorphological problems of Antarctica

Solitary waves on falling liquid films in the inertia-dominated regime

We offer new insights and results on the hydrodynamics of solitary waves on inertia-dominated falling liquid films using a combination of experimental measurements, direct numerical simulations (DNS) and low-dimensional (LD) modelling. The DNS are shown to be in very good agreement with experimental measurements in terms of the main wave characteristics and velocity profiles over the entire range of investigated Reynolds numbers. And, surprisingly, the LD model is found to predict accurately the film height even for inertia-dominated films with high Reynolds numbers. Based on a detailed analysis of the flow field within the liquid film, the hydrodynamic mechanism responsible for a constant, or even reducing, maximum film height when the Reynolds number increases above a critical value is identified, and reasons why no flow reversal is observed underneath the wave trough above a critical Reynolds number are proposed. The saturation of the maximum film height is shown to be linked to a reduced effective inertia acting on the solitary waves as a result of flow recirculation in the main wave hump and in the moving frame of reference. Nevertheless, the velocity profile at the crest of the solitary waves remains parabolic and self-similar even after the onset of flow recirculation. The upper limit of the Reynolds number with respect to flow reversal is primarily the result of steeper solitary waves at high Reynolds numbers, which leads to larger streamwise pressure gradients that counter flow reversal. Our results should be of interest in the optimisation of the heat and mass transport characteristics of falling liquid films and can also serve as a benchmark for future model development

On the theory of superfluidity

We investigate the properties of dispersion spectra of one-dimensional periodic Bose systems with repulsive interparticle interactions. These systems with sufficient large interactions can support metastable supercurrent states, which correspond to the local minima of the dispersion spectra at non-zero momenta. The existence of local minima in the spectra and the energy barriers, which separate the minima, can be explained in terms of Bose exchange symmetry. We extend our study to the case of higher dimensional Bose systems. We suggest that superfluidity could be understood as a Bose exchange effect.Comment: simplified version; added references; 6 pages, 6 figure

Denaturalized nature - strategies of representation in selected works of Penelope Siopis and William Kentridge.

A Dissertation submitted to the Faculty of Arts, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Arts in Fine Arts.American critic Hal Foster argues that conceptions of 'the natural' are not universal, they are historically and discursively produced, There is no unmediated presence of 'the natural' in painting. He proposes 'denaturalization' as a form of critical postmodemist aesthetic which questions universalist tendencies in contemporary cultural production" This research examines selected theories and visual. representations of 'the natural' in order to explore different ways in which Foster's notion of denaturalization may be productive in assessing the complexity of critical visual art practice in South Africa. My approach to the topic is largely fragmentary in order to reflect on and engage with the diverse terms of 'the natural' as manifest in visual art practice. To this end I discuss selected works of contemporary South African artists William Kentridge and Penelope'Siopis, While Foster's notion of denaturalization is productive in trying to engage with"critical issues' of art practice it is difficulr, if not impossible to determine if cenaln works conform with either his notion of a postmodernism of resistance or postmodernism of reaction. I will also explore the notion of denaturalization with reference to my practical work.Andrew Chakane 201

Possible field-tuned SIT in high-Tc superconductors: implications for pairing at high magnetic fields

The behavior of some high temperature superconductors (HTSC) such as $\rm La_{2-x}Sr_{x}CuO_{4}$ and $\rm Bi_{2}Sr_{2-x}La_xCuO_{6+\delta}$, at very high magnetic field, is similar to that of thin films of amorphous InOx near the magnetic field-tuned superconductor-insulator transition. Analyzing the InOx data at high fields in terms of persisting local pairing amplitude, we argue by analogy that local pairing amplitude also persists well into the dissipative state of the HTSCs, the regime commonly denoted as the "normal state" in very high magnetic field experiments.Comment: Revised figures and reference

BLOXY: Providing Transparent and Generic BFT-Based Ordering Services for Blockchains

With the wide-spread use of blockchain technology, Byzantine fault-tolerant (BFT) protocols are explored as a means to achieve consensus on which transactions should be processed next. BFT protocols are not a one-size-fits-all solution: they should be chosen according to the blockchain's use case, which can range from supply chain management to decentralised storage, requiring specialisation e.g. regarding throughput, latency, or level of decentralisation. Previously, consensus protocols were usually hardcoded into the blockchain infrastructure and could not be exchanged, therefore inhibiting flexible use of an otherwise generic blockchain infrastructure. Hyperledger Fabric claims to provide modular consensus and support for crash-fault and Byzantine fault tolerant protocols. However, integrating a BFT protocol has shown that Fabric's architecture is currently not well-suited for this fault model as it requires substantial changes and thereby breaks Fabric's modularity. This also has to be repeated for each integrated BFT protocol. In this paper, we present Bloxy, a blockchain-aware trusted proxy running on the replica that encapsulates all BFT client functionality. Bloxy enables transparent access to generic BFT frameworks and preserves Fabric's modularity even for the Byzantine fault model. It runs inside a trusted execution environment based on Intel's Software Guard Extensions. Bloxy offers blockchain-specific communication mechanisms as well as short-term block storage to handle crashes or disconnects to ensure that all nodes receive block updates. We implemented two Bloxy-based ordering services based on PBFT and the hybrid BFT protocol Hybster. Our evaluation shows that our approach increases throughput by up to 71% compared to directly integrated BFT protocols

Towards Low-Latency Byzantine Agreement Protocols Using RDMA

Byzantine fault tolerance (BFT) protocols can mitigate attacks and errors and are increasingly investigated as consensus protocols in blockchains. However, they are traditionally considered costly in terms of message complexity and latency due to the required multiple rounds of message exchanges. With the availability of Remote Direct Memory Access (RDMA) in data centers, message exchange latency can be reduced compared to TCP, as RDMA enables kernel bypassing and thereby avoids intermediate data copying. Retaining the performance benefits for RDMA during its integration, however, is non-trivial and error-prone. While the use of RDMA has previously been explored for key/value stores, databases and distributed file systems, agreement protocols especially for BFT have so far been neglected. We investigate the usage of RDMA in the Reptor BFT protocol for low-latency agreement and show first steps towards an RDMA-enabled consensus protocol. For this, we present RUBIN, a framework offering similar functionality to the Java NIO selector, which can handle multiple network connections efficiently with a single thread and is employed in several BFT protocol implementations such as BFT-SMART and UpRight

Erosion waves: transverse instabilities and fingering

Two laboratory scale experiments of dry and under-water avalanches of non-cohesive granular materials are investigated. We trigger solitary waves and study the conditions under which the front is transversally stable. We show the existence of a linear instability followed by a coarsening dynamics and finally the onset of a fingering pattern. Due to the different operating conditions, both experiments strongly differ by the spatial and time scales involved. Nevertheless, the quantitative agreement between the stability diagram, the wavelengths selected and the avalanche morphology reveals a common scenario for an erosion/deposition process.Comment: 4 pages, 6 figures, submitted to PR