First-principles approach to the calculation of electronic spectra in clusters

We discuss a method for first-principles calculations of photoemission spectra in small clusters, going well beyond a standard density functional theory-local density approximation (DFT-LDA) approach. Starting with a DFT-LDA calculation, we evaluate self-energy contributions to the quasiparticle energies of an electron or hole in the GW scheme, where the self-energy Σ = GW is constructed from the one-particle Green's function G and the RPA screened Coulomb interaction W. The contributions of structural relaxation are taken into account. We show the importance of these effects at the example of the photoemission spectrum of SiH₄. We also briefly discuss results for longer hydrogenated silicon chains, and address the problem of optical absorption.     

The effect of nitrogen and sulphur compounds on extreme pressure lubrication

This paper reports the synthesis of hydroxyheptadecyl-substituted-1,3,4-thiadiazoles and mercapto-1,2,4-triazoles and the evaluation of extreme pressure activity of their admixtures (0.5% and 1% w/ v) with a paraffinic oil in a four-ball test. Alloy steel bearing balls of 12.7 mm diameter were used as test specimens. All the additives exhibited good activity in reducing wear and increasing the values of mean Hertz load (MHL) and flash temperature parameter (FTP) as compared to the base fluid. The presence of p-methoxy- and p-chloro- groups in the thiadiazole and mercapto triazole rings has been found to enhance the activity of these additives. Scanning Auger Electron Spectroscopy surface studies were conducted to analyse the additive-metal interaction.     

Effect of pH and ionic strength on phospholipid nanomechanics and on deposition process onto hydrophilic surfaces measured by AFM

The effect of ion-binding on a zwitterionic phospholipid such as 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) has been studied by measuring the zeta potential value of the unilamellar liposomes present in solution while varying the pH and the ionic strength in independent experiments. We have experimentally confirmed that DMPC binds cations, resulting in an increase of the zeta potential value. The liposome surface charge has been proved to have a strong effect on the supported bilayer formation on hydrophilic, negatively charged surfaces such as mica and silicon oxide as atomic force microscopy images reveal. Furthermore, thanks to force spectroscopy measurements we have proved that ion-binding also affects the nanomechanical response of the system, since it increases the force that has to be exerted on the membrane in order to puncture it. Last but not least, the nanomechanics of the bilayer does not depend on the substrate, thus implying that membrane properties are not influenced by the supporting material.     

Comparison between polyaniline‐phosphate and polypyrrole‐phosphate composite coatings for mild steel corrosion protection

Polyaniline, polypyrrole and their composites have been deposited on mild steel electrode from aqueous oxalic acid solution by using cyclic voltammetry (CV) technique. The resulting coatings were characterized by scanning electron microscopy and EDX analysis. The protective performance against corrosion of these coatings is evaluated by using electrochemical impedance spectroscopy (EIS) technique in corrosive solution (3.5% NaCl). Impedance data indicates a noticeable enhancement of protection against corrosion processes. Also, comparison of polyaniline‐phosphate and polypyrrole‐phosphate coatings indicates better corrosion protection with polyaniline‐phosphate coatings.     

Study of the behavior of an organic coating applied on the storage reservoirs of oil in a medium of 3% NaCl solution and in marine environment

The paints are used extensively in various fields, especially for the protection of the oil installations such as the storage reservoirs of crude oil. Reducing possession cost and applying the new hygiene and security standards imply the necessity to deepen the knowledge of the physico‐chemical processes of ageing coatings in the first stage and their impact on the corrosion of the substrate. The tests have been carried out on a primer, and on painted steel plates completely immersed in a 3% NaCl solution. The survey of the water absorption and the kinetics deterioration of the paints have been achieved especially by means of electrochemical impedance spectroscopy under the test of salt spray. The barrier weakness of the primer paint, due to the existence of two capacitive loops observed on the Nyquist's diagrams has been put in evidence. While the study of the resistance of the complete system by the test accelerated in the salt spray shows that the system of painting presents a good resistance up to 196 hours, which is equivalent to 8 years of exposure.     

Determination of metals in wine with atomic spectroscopy (flame-AAS, GF-AAS and ICP-AES); a review

Metals in wine occur at the mg l 1 level or less and, though not directly related to the taste of the final product, their content should be determined because excess is undesirable, and in some cases prohibited, due to potential toxicity. Lead content in wine, for example, is restricted in several states by legislation to guarantee consumer health protection. Of several methods for metal determination, techniques of atomic spectroscopy are the most sensitive and rapid. Most of the elements present in wine can be determined with these techniques, at concentrations ranging from the mg l -1 to the μg l -1 level. Here, inductively coupled plasma-atomic emission spectrometry (ICP-AES), flame atomic absorption spectrometry (flame-AAS) and graphite furnace-atomic absorption spectrometry (GF-AAS) are compared for their characteristics as employed in metal determination in wine.     

MOS结构深能级瞬态谱的测试与分析

叙述了一种采用MOS结构研究半导体深能级陷阱的深能级瞬态谱(DLTS)测试与分析方法。该方法简便易行,适用范围广。通过对n-Al_(0.2)Ga_(0.8)As中深能级的研究表明,MOS结构和p~+-n结构的DLTS结果相同。     

A fast detector for single-shot positron annihilation lifetime spectroscopy

When an intense sub-nanosecond positron pulse impinges upon a target, a pulse of γ-rays is created which can yield information concerning electron–positron pairs just prior to annihilation. Many conventional γ-ray detectors are unable to exploit the timing information contained within such pulses, and we describe here the development of a fast detector that is able to do so. Using a single-crystal PbF₂ Cherenkov radiator coupled to a fast photomultiplier tube (PMT), we have produced a detector with a time response of 4 ns (primarily determined by the PMT response), as well as a low-efficiency detector with a sub-nanosecond response. Since 511 keV photons produce very little Cherenkov light, the problem of photomultiplier saturation is mitigated and this detector is therefore well suited to single-shot positron annihilation lifetime spectroscopy (SSPALS) measurements.