Computer simulation of stone frame sawing process using diamond blades

Based on the results of scratching tests with single point tools and single segments in a previous study, the contact area between stone and blade, the number of effective cutting edges and the cutting forces per diamond grit, per segment and blade in the frame sawing process are simulated by computer. The number of diamond grits per unit area, the distribution of diamond grits per segment and the effective depth of cut of diamond grits are calculated by a new method. The Monte Carlo method is applied to generate the position of diamond grits randomly. The results show that in cutting stroke, only half of the diamond grits on the segment surface cut stone with the depth of cut increasing and a limited moving distance. The interactions of the grooves created by different segments remove the stone and generate the saw kerf. The simulation results of cutting forces are consistent in tendency with the data tested in a frame sawing machine. Cutting feed and the cutting performance of the segments are the major factors which determine the cutting forces and segment wear. The optimized constant contact area between blade and stone depends on the segment spaces, the segment number and the segment size, the ratio of the length of block and the effective cutting length of blade etc.     

High resolution gas volume change sensor

Changes of gas quantity in a system can be measured either by measuring pressure changes or by measuring volume changes. As sensitive pressure sensors are readily available, pressure change is the commonly used technique. In many physiologic systems, however, buildup of pressure influences the gas exchange mechanisms, thus changing the gas quantity change rate. If one wants to study the gas flow in or out of a biological gas pocket, measurements need to be done at constant pressure. In this article we present a highly sensitive sensor for quantitative measurements of gas volume change at constant pressure. The sensor is based on optical detection of the movement of a droplet of fluid enclosed in a capillary. The device is easy to use and delivers gas volume data at a rate of more than 15 measurements/s and a resolution better than 0.06 microl. At the onset of a gas quantity change the sensor shows a small pressure artifact of less than 15 Pa, and at constant change rates the pressure artifact is smaller than 10 Pa or 0.01% of ambient pressure.     

A new method for the fast determination of the data retention lifetime of UV EPROM’s

The newly developped method involves a controlled partial erasure of a charged ultraviolet erasable programmable read only memory device followed by a period of high temperature storage. The model is based on two assumptions: the amount of charge stored at the floating gate of a programmed cell is assumed to be equal throughout a component and the trip the minimum level of charge stored at the floating gate of a programmed cell, has a Gaussian distribution throughout a component. The experimental data are well described by the model. After implementation of the experimental results in the model we extrapolate the data retention lifetimes of the UVEPROM’S under operational conditions. Our measurements show that most of the tested UVEPROM devices (64 ko to 256 ko) have a similar operational lifetime, only the charge leakage activation energy differs (0.35 to 0.9 eV) depending on the type of component. In conclusion this method and model are suitable for a fast determination of UVEPROM’S data retention lifetimes under operational conditions.     

The dufour gland and the secretion placed on eggs of two species of social wasps,Liostenogaster flavolineata andParischnogaster jacobsoni (vespidae: Stenogastrinae)

The secretion placed on eggs and fed to larvae and the ant guard placed on the nest stalk ofParischnogaster jacobsoni contain the same hydrocarbons and in approximately the same proportions as is found in the Dufour gland. The secretion on eggs is a mixture of the contents of the Dufour gland and nectar. The emulsifying agent is a palmitic acid salt. Similarly, inLiostenogaster flavolineata, the egg secretion is an emulsion of nectar and Dufour gland secretion, which contains alkoxyethanol emulsifiers, found in nature for the first time.     

Electrodeposition of BiVO4 with needle-like flower architecture for high performance photoelectrochemical splitting of water

Photoelectrochemical (PEC) water splitting is a green and sustainable approach capable of driving mass hydrogen production in the future. To realize this vision, development of a well-performing photoelectrode is highly demanded. In this comprehensive study, electrodeposition technique was applied for fabricating BiVO₄ films by regulating the deposition time from 1 min until 9 min. Interestingly, the morphology, crystallinity, chemical structure, and optical properties of BiVO₄ films depend strongly on the deposition time. It is found that BiVO₄ layer deposited for 7 min with a cross-section thickness of around 321.1–326.5 nm showed the optimum performance, whereby the photocurrent reached up to ~0.32 mA/cm^?2 at 1.23 V vs. RHE. The deposited BiVO₄ represents tiny and long petals, similar to “needle” nanostructures, which is embedded closely into compact agglomerates. Such morphology enables the BiVO₄ films to perform efficiently as photoanode in PEC cells. Besides, high crystallinity is detected from the sharp peaks of XRD and Raman analysis, as well as good light absorption capability that are the main contributors to the enhancement of PEC performance. In addition to the facile fabrication offered by electrodeposition method, the non-toxic attributes and the impressive PEC performance of the optimum BiVO₄ layer could serve as an interesting option for other applications such as gas sensors, solar cells, degradation of pollutants and photocatalytic water splitting.     

Structures of Alcohol Dehydrogenases from Ralstonia and Sphingobium spp. Reveal the Molecular Basis for Their Recognition of ‘Bulky–Bulky’ Ketones

Alcohol dehydrogenases (ADHs) are applied in industrial synthetic chemistry for the production of optically active secondary alcohols. However, the substrate spectrum of many ADHs is narrow, and few, for example, are suitable for the reduction of prochiral ketones in which the carbonyl group is bounded by two bulky and/or hydrophobic groups; so-called ‘bulky–bulky’ ketones. Recently two ADHs, RasADH from Ralstonia sp. DSM 6428, and SyADH from Sphingobium yanoikuyae DSM 6900, have been described, which are distinguished by their ability to accept bulky–bulky ketones as substrates. In order to examine the molecular basis of the recognition of these substrates the structures of the native and NADPH complex of RasADH, and the NADPH complex of SyADH have been determined and refined to resolutions of 1.5, 2.9 and 2.5 Å, respectively. The structures reveal hydrophobic active site tunnels near the surface of the enzymes that are well-suited to the recognition of large hydrophobic substrates, as determined by modelling of the bulky–bulky substrate n-pentyl phenyl ketone. The structures also reveal the bases for NADPH specificity and (S)-stereoselectivity in each of the biocatalysts for n-pentyl phenyl ketone and related substrates.