Performance Evaluation of Range Queries in Key Value Stores

Recently there has been a considerable increase in the number of different Key-Value stores, for supporting data storage and applications on the cloud environment. While all these solutions try to offer highly available and scalable services on the cloud, they are significantly different with each other in terms of the architecture and types of the applications, they try to support. Considering three widely-used such systems: Cassandra, HBase and Voldemort; in this paper we compare them in terms of their support for different types of query workloads. We are mainly focused on the range queries. Unlike HBase and Cassandra that have built-in support for range queries, Voldemort does not support this type of queries via its available API. For this matter, practical techniques are presented on top of Voldemort to support range queries. Our performance evaluation is based on mixed query workloads, in the sense that they contain a combination of short and long range queries, beside other types of typical queries on key-value stores such as lookup and update. We show that there are trade-offs in the performance of the selected system and scheme, and the types of the query workloads that can be processed efficiently.     

Low Temperature Hall Effect Investigation of Conducting Polymer-Carbon Nanotubes Composite Network

Polypyrrole (PPy) and polypyrrole-carboxylic functionalized multi wall carbon nanotube composites (PPy/f-MWCNT) were synthesized by in situ chemical oxidative polymerization of pyrrole on the carbon nanotubes (CNTs). The structure of the resulting complex nanotubes was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The effects of f-MWCNT concentration on the electrical properties of the resulting composites were studied at temperatures between 100 K and 300 K. The Hall mobility and Hall coefficient of PPy and PPy/f-MWCNT composite samples with different concentrations of f-MWCNT were measured using the van der Pauw technique. The mobility decreased slightly with increasing temperature, while the conductivity was dominated by the gradually increasing carrier density.     

Kinetic study of H-terminated silicon nanowires oxidation in very first stages

Oxidation of silicon nanowires (Si NWs) is an undesirable phenomenon that has a detrimental effect on their electronic properties. To prevent oxidation of Si NWs, a deeper understanding of the oxidation reaction kinetics is necessary. In the current work, we study the oxidation kinetics of hydrogen-terminated Si NWs (H-Si NWs) as the starting surfaces for molecular functionalization of Si surfaces. H-Si NWs of 85-nm average diameter were annealed at various temperatures from 50°C to 400°C, in short-time spans ranging from 5 to 60 min. At high temperatures (T ≥ 200°C), oxidation was found to be dominated by the oxide growth site formation (made up of silicon suboxides) and subsequent silicon oxide self-limitation. Si-Si backbond oxidation and Si-H surface bond propagation dominated the process at lower temperatures (T < 200°C).     

Scattering from loaded grooves

Electromagnetic scattering from a two-dimensional groove recessed in an arbitrarily thick conducting screen is studied. The groove may be empty or loaded with a lossy material which may or may not completely fill the cavity. For the partially loaded groove, the filling material is assumed electrically dense so that the standard impedance boundary condition is applicable at the top surface of the material. Employing a full-wave analysis, integral equations are derived for the tangential components of the electric field over the aperture. It is shown that the equations are identical for both partially loaded and completely loaded (or empty) cases provided that the aperture admittance of the groove is treated as the equivalent admittance of the internal medium looking into the aperture, thus simplifying the integral equations. When the groove is completely filled by a dense material, the formulation reduces to that corresponding to a direct application of the impedance boundary condition over the aperture.     

Room‐Temperature Partial Conversion of α‐FAPbI3 Perovskite Phase via PbI2 Solvation Enables High‐Performance Solar Cells

The two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI₃ hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI₃, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI₃, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI₂ into the α‐FAPbI₃ perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI₂ precursor from its different states are compared. α‐FAPbI₃ forms spontaneously and efficiently at room temperature from P₂ (ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI₂) to 17.23(±0.28)% (from solvated PbI₂) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA⁺ cation without the need for Cs⁺ or mixed halide formulation.     

Robust and efficient memory management in Apache AsterixDB

Traditional relational database systems handle data by dividing their memory into sections such as a buffer cache and working memory, assigning a memory budget to each section to efficiently manage a limited amount of overall memory. They also assign memory budgets to memory-intensive operators such as sorts and joins and control the allocation of memory to these operators; each memory-intensive operator attempts to maximize its memory usage to reduce disk I/O cost. Implementing such memory-intensive operators requires a careful design and application of appropriate algorithms that properly utilize memory. Today's Big Data management systems need the ability to handle large amounts of data similarly, as it is unrealistic to assume that truly big data will fit into memory. In this article, we share our memory management experiences in Apache AsterixDB, an open-source Big Data management software platform that scales out horizontally on shared-nothing commodity computing clusters. We describe the implementation of AsterixDB's memory-intensive operators and their designs related to memory management. We also discuss memory management at the global (cluster) level. We conducted an experimental study using several synthetic and real datasets to explore the impact of this work. We believe that future Big Data management system builders can benefit from these experiences.     

A review on the role of materials science in solar cells

The demand for energy of modern society is constantly increasing. The desire for environmental-friendly alternative energy resources with the least dependency on fossil fuels is growing. Solar energy is an important technology for many reasons and is worthy of urgent attention. Indeed, it has experienced rapid growth over the last few years. It is expected to become truly main stream when the breakeven of high performance is achieved and its cost becomes comparable with other energy sources. Various approaches have been proposed to enhance the efficiency of solar cells. This paper reviews some current initiatives and critical issues on the efficiency improvement of solar cells from the material sciences and chemistry perspectives.     

Plasmonic Nickel Nanoantennas

The fundamental optical properties of pure nickel nanostructures are studied by far‐field extinction spectroscopy and optical near‐field microscopy, providing direct experimental evidence of the existence of particle plasmon resonances predicted by theory. Experimental and calculated near‐field maps allow for unambiguous identification of dipolar plasmon modes. By comparing calculated near‐field and far‐field spectra, dramatic shifts are found between the near‐field and far‐field plasmon resonances, which are much stronger than in gold nanoantennas. Based on a simple damped harmonic oscillator model to describe plasmonic resonances, it is possible to explain these shifts as due to plasmon damping.     

Isolation enhancement between tightly spaced compact unidirectional patch‐antennas on multilayer EBG surfaces

In this article, ultracompact unidirectional patch antennas are used in different two‐antenna systems for biomedical applications at 5.2 GHz. Multilayer mushroom type electromagnetic bandgap (EBG) structures are designed as slow‐wave medium to reduce the size of the individual patch antennas to 0.1λ₀ by 0.18λ₀. Various techniques are investigated herein to improve antenna isolation for an enhanced Multiple‐Input Multiple‐Output (MIMO) performance. First, the coupling between 0.3λ₀‐spaced antennas is verified to occur dominantly through radiation and near‐field coupling between the patches rather than through substrate‐bound modes. Second, various configurations are proposed to suppress antenna coupling. These approaches include reorientation of the antennas and employment of parasitic radiators between the patches. A novel design is presented in which a unidirectional parasitic slot radiator on an EBG reflector is inserted between the antennas to decouple them. Measurement results confirm efficacy of these approaches in mitigating antenna coupling by more than 11 dB in the operating bandwidth of the antennas. The compact patch antennas maintain efficiency values of higher than 70%. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:30–38, 2015.     

Influence of yarn texture on the mechanical properties of textile composite castings

In this research, mechanical properties of textile composite castings used for immobilizing a damaged limb have been studied. For this purpose, a fabric composite was made using a new knitted fabric and textured yarn for the first time. This composite possesses suitable mechanical properties. Mechanical and physical properties such as tensile, bending, and thickness of materials were studied. Results indicate that the use of textured yarns instead of flat yarns increases the amount of resin retainment in fabrics. Furthermore, it decreases tensile modulus and bending modulus of fabrics. Properties of the castings produced were compared with a valid commercial casting. Sample with textured warp and weft, with linear density of 1,500 den of weft, had the best physical and mechanical properties among produced samples. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers