Particle Accretion Mechanism Underlies Biological Crystal Growth from an Amorphous Precursor Phase

Many biogenic minerals are composed of aggregated particles at the nanoscale. These minerals usually form through the transformation of amorphous precursors into single crystals inside a privileged space controlled by the organism. Here, in vitro experiments aimed at understanding the factors responsible for producing such single crystals with aggregated particle texture are presented. Crystallization is achieved by a two‐step reaction in which amorphous calcium carbonate (ACC) is first precipitated and then transformed into calcite in small volumes of water and in the presence of additives. The additives used are gel‐forming molecules, phosphate ions, and the organic extract from sea urchin embryonic spicules ‐ all are present in various biogenic crystals that grow via the transformation of ACC. Remarkably, this procedure yields faceted single‐crystals of calcite that maintain the nanoparticle texture. The crystals grow predominantly by the accretion of ACC nanoparticles, which subsequently crystallize. Gels and phosphate ions stabilize ACC via a different mechanism than sea urchin spicule macromolecules. It is concluded that the unique nanoparticle texture of biogenic minerals results from formation pathways that may differ from one another, but given the appropriate precursor and micro‐environment, share a common particle accretion mechanism.     

Minmax scheduling problems with a common due-window

This paper focuses on a minmax due-window assignment problem. The goal is to schedule the jobs and the due-window such that the highest cost among all jobs is minimized. The objective function contains four cost components: for earliness, tardiness, due-window starting time and due-window size. We present a polynomial time solution for the case of a single machine and for a two-machine flow-shop. The cases of parallel identical machines and uniform machines are NP-hard, and simple heuristics and lower bounds are introduced and tested numerically.     

Active and passive pressures with seismically induced changes in the direction of surface-friction forces

Conditions favorable to the development, and characteristic features of the accounting of the “reverse” direction of surface-friction forces at the contact between a retaining wall and soil medium with determination of the latter's lateral pressure are indicated. Basic computational relationships are presented for steep and inclined walls, and also the results of the mathematical modeling of the “structure/soil-medium” system with variation of the latter's computational parameters are presented. A general computational algorithm, which takes into account any direction of contact-friction forces, and a program that runs the algorithm on a computer, as well as tables of the range of combinations of initial parameters, including parameters that account for seismic effects, are developed. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 14–18, May–June, 1996.     

Public owners' satisfaction with consultancy practices in Saudi Arabia

Between 1970 and 1985 the public expenditure on three development plans in Saudi Arabia amounted to 1940 billion Saudi Riyals. This paper addresses the professional relationship between the public owners and the local architectural and engineering practices which has been measured in the form of overall satisfaction under a five-point scale ranging from excellent to poor, a second aspect identified satisfaction related to the design service and finally, a measure of satisfaction was gained from owners' response to their professional relationship with the practices.     

Autothermal reforming of methane over Ni/γ-Al2O3 catalysts: the enhancement effect of small quantities of noble metals

The effect of introducing small amounts of Pt, Pd and Ir (<0.3% by weight) into Ni/γAl₂O₃ catalysts (15% Ni w/w) for the autothermal reforming of methane (ATR) was investigated. While the unpromoted catalyst took the partial oxidation of methane to equilibrium, the promoted ones increased the methane conversion in ATR. No electronic modifications of nickel sites were observed with the addition of noble metals, but they did cause an increase in metal surface area. The effect of noble metals on this reaction, under these conditions, was assigned to this expansion of the metal surface.     

The Dead Sea: A scheme for a solar lake

A theoretical scheme for modifying a salt basin into a solar lake is examined with respect to the Dead Sea. The mixing is reduced by a net of floating wind breaks. The discharge from the salt evaporation ponds of the Dead Sea chemical plants is used as a fource for ascending dense water at a rate of 0.7 m yr⁻¹. This keeps the halocline against the residual mixing. In order to maximize the efficiency of the deep water formation in the salt evaporation ponds and to minimize the requirements of the wind breaks, the surface salinity of the solar lake is calculated to be 15 per cent, where the deep water will be kept at its present salinity, i.e. 26 per cent.The rate in which mixing converts kinetic to potential energy over the Dead Sea is estimated to be 2 × 10⁻⁴ W m⁻². For the operation of the solar lake the wind breaks are required to reduce it by one order. For a temperature of 80°C the optimum depth of the halocline is 1.3–1.5 m and the theoretical recovery rate of energy is estimated to be 50–70 W of heat and 9–12 W m⁻² for a Carnot engine, depending on the extinction coefficient.     

Chemical synthesis and expression of the HIV-1 Rev protein

The HIV-1 Rev protein is responsible for shuttling partially spliced and unspliced viral mRNA out of the nucleus. This is a crucial step in the HIV-1 lifecycle, thus making Rev an attractive target for the design of anti-HIV drugs. Despite its importance, there is a lack of structural, biophysical, and quantitative information about Rev. This is mainly because of its tendency to undergo self-assembly and aggregation; this makes it very difficult to express and handle. To address this knowledge gap, we have developed two new highly efficient and reproducible methods to prepare Rev in large quantities for biochemical and structural studies: 1) Chemical synthesis by using native chemical ligation coupled with desulfurization. Notably, we have optimized our synthesis to allow for a one-pot approach for the ligation and desulfurization steps; this reduced the number of purification steps and enabled the obtaining of desired protein in excellent yield. Several challenges emerged during the design of this Rev synthesis, such as racemization, reduced solubility, formylation during thioester synthesis, and the necessity for using orthogonal protection during desulfurization; solutions to these problems were found. 2) A new method for expression and purification by using a vector that contained an HLT tag, followed by purification with a Ni column, a cation exchange column, and gel filtration. Both methods yielded highly pure and folded Rev. The CD spectra of the synthetic and recombinant Rev proteins were identical, and consistent with a predominantly helical structure. These advances should facilitate future studies that aim at a better understanding of the structure and function of the protein.     

RF数模转换器促进通信信号的直接合成

本文讨论RF数模转换器对于通信系统的实际应用,例如有线通信、无线通信基础设施基站、无线回程及其他此类系统;另外回顾了推动RF DAC技术发展的重要规范,以及一些用于实施此类系统的常见无线电架构;解释了与RF DAC设计相关的挑战,并讨论了一些权衡取舍和可能的解决方案;评论了封装设计考虑和印刷电路板设计;介绍了适合电缆前端发射器的RF DAC的测量结果。RFDAC的特性和性能适合为针对多载波、多频段、多标准无线电发射器的软件定义无线电系统提供解决方案。     

A marine unicellular alga in diets of pregnant and lactating rats as a source of ω3 fatty acids for the developing brain of their progeny

The period of brain development in rats occurs during the late pregnancy and early lactation periods. During that time a large quantity of omega-3 (ω3) long-chain polyunsaturated fatty acids, mostly decosahexaenoic acid, is deposited in the brain lipids of the developing and growing pup. A dietary source of ω3 fatty acid should be provided during this period to the dams' diet to assure sufficient of ω3 fatty acids to the developing progeny. Although a wide variety of lipids from plants and marine animals was examined in this respect, we provide herein for the first time, experimental data that indicate that the marine unicellular alga Nannochloropsis can be efficiently used as a dietary source of the ω3 fatty acid eicosapentaenoic acid for pregnant and lactating dams. Furthermore, the dietary ω3 lipids of the alga are efficiently transferred to the developing foetus and pups to support the requirements for normal brain development.     

First attempts at prediction of DNA strand-break yields using nanodosimetric data

We present the first results of our attempts to correlate yields of ionisation clusters in a gas model of DNA and corresponding double-strand break (DSB) yields in irradiated plasmids, using a simple statistical model of DNA lesion formation. Based on the same statistical model, we also provide a comparison of simulated nanodosimetric data for electrons and published DSB yields obtained with the PARTRAC code.