Thermodynamic anomaly of the free damped quantum particle: the bath perspective

By varying the orientation of the applied magnetic field with respect to the normal of a two-dimensional electron gas, the chemical potential and the specific heat reveal persistent spin splitting in all field ranges. The corresponding shape of the thermodynamic quantities distinguishes whether the Rashba spin-orbit interaction (RSOI), the Zeeman term or both dominate the splitting. The interplay of the tilting of the magnetic field and RSOI resulted to an amplified splitting even in weak fields. The effects of changing the RSOI strength and the Landau level broadening are also investigated.     

2000 Vol.11 No.8 P.Preparation of AChE Inhibitors From Jujubogenin

A dammarane derivative dihydrojujubogenin-2-en-1-one, which possesses a skeleton and pharmacophore partially similar to those of Territrem B, a potent AChE inhibitor, was synthesized via three different paths. The anti-AChE activity of this compound and related analogue was measured.     

High impact shock testing of fiber-optic components

MIL-S-901 High Impact Shock tests were performed on commercial-grade and ruggedized fiber-optic connectors, splices, and switches. Both single-mode and multimode connectors and splices were tested. Only multimode switches were tested. Transient losses of varying magnitudes and durations were observed. Most components suffered no permanent degradation.     

A beamline for time resolved photoelectron microscopy on magnetic materials at the Swiss light source

We describe the “Surface/Interface: Microscopy” beamline currently under construction at the Paul Scherrer Institut. This beamline will use a photoemission electron microscope to study the electronic and magnetic structure of materials. Its photon energy range will be 94–2000 eV.

To allow time resolved measurements with millisecond resolution we use a new scheme allowing to switch the photon helicity optically without perturbing the electron orbit. Two identical elliptical insertion devices are placed behind each other in the same straight section. They can produce light with opposing helicities. These two sources are separated horizontally by introducing a small static parallel offset in the electron orbit. Switching between the two rays of opposite helicities is done mechanically at the horizontal focus behind the monochromator. The two sources are brought to overlap on the sample by slightly defocussing the refocussing mirror.

A commercial microscope (Δx20 nm resolution) is adapted to the synchrotron by various upgrades. These include a software combining microscope and beamline control, a computer controlled mechanical alignment system, a separate sample preparation chamber, and sample cooling using liquid nitrogen. The beamline will be available for user operation in 2002.     

湖北十堰绿松石中杂质矿物自然硒的谱学研究

近期在湖北绿松石市场上出现一种带有肉眼可见的灰黑色异形杂质的绿松石,于此种绿松石的研究甚少。故选取来自湖北省十堰的一块该种绿松石原石,蓝色绿松石基底上布满形态各异、大小不一的灰黑色杂质,放大观察可见灰黑色杂质矿物呈金属光泽。对灰黑色杂质采用激光剥蚀电感耦合等离子体质谱仪进行原位微区微量元素测试、背散射电子图像物相观察、主量化学成分测试采用能谱仪进行半定量测试和电子探针定量测试以及显微激光拉曼光谱仪测试。灰黑色杂质矿物的LA-ICP-MS测试激光剥蚀束斑直径及深度的影响,测试结果表现为灰黑色杂质矿物和少量绿松石的混合物的化学成分含量,灰黑色杂质矿物处Se含量为95 927～221 394 μg·g-1明显高于蓝色基底绿松石中Se的含量（146～212 μg·g-1）,灰黑色杂质处的测试结果中CuO含量为7.47%～9.28%、Al₂O₃含量为28.1%～35.7%,P₂O₅含量为30.1%～37.8%为少量绿松石混杂产生;背散射电子图像表明杂质矿物结晶颗粒细小,细小的杂质矿物与绿松石混杂在一起,他形的杂质矿物为多个晶体集合在一起形成的集合体,能谱测试结果表明杂质矿物主要含有Al,P,Fe,Cu和Se,电子探针主量化学成分定量测试结果表明杂质矿物主要含有Se,含量为79.34%～87.97%,此外,由于杂质矿物结晶颗粒细小,杂质矿物集合体中可见杂质矿物与绿松石混杂,因此化学成分定量测试结果中还呈现有绿松石中的Al,P,Fe,Cu和Al含量约为0.93%～4.13%,Cu含量约为1.30%～2.04%,P含量约为0.66%～2.40%,Fe含量约为0.31%;杂质矿物的显微激光拉曼光谱峰为位于144和235 cm-1处的尖锐拉曼谱峰,结合化学成分谱学测试结果可鉴别该杂质矿物主要为自然硒。硒矿物是绿松石中新发现的杂质矿物,绿松石中杂质矿物自然硒的发现可以为珠宝从业者鉴别绿松石提供有效的鉴定依据。     

噻吩基和呋喃基四硫富瓦烯的合成及电化学性质

提供了一种合成噻吩基和呋喃基四硫富有瓦烯（ＴＴＦ）的方法，并用其合成了３种未见文献报道的噻吩基ＴＴＦ（Ⅶａ，Ⅷｂ，Ⅶｃ）和２种呋喃基ＴＴＦ（Ⅶｄ１，Ⅶｄ２）研究这些化合物的循环伏安行为及有关电化学性质，制得了一种Ⅶｂ与ＴＣＮＱ反应生成的电荷转移络合物，讨论了噻吩基ＴＴＦ和呋喃基ＴＴＦ在产物构型和电化学性质方面的差别。     

Quantitative studies on the peroxidation of human low-density lipoprotein initiated by superoxide and by charged and neutral alkylperoxyl radicals.

Rates of peroxidation of human LDL and rates of consumption of the LDL's alpha-tocopherol (TocH) have been measured at 37 degrees C. Peroxidation was initiated by radicals generated in the aerated aqueous phase at known rates by thermal decomposition of appropriate precursors: superoxide (O2(*-)/HOO(*)) from a hyponitrite and alkylperoxyls (ROO(*), two positively charged, one negatively charged and one neutral) from azo compounds. The efficiencies of escape from the solvent cage of the geminate pair of neutral carbon-centered radicals was found to be 0.1, but it was 0.5 for the three charged radicals, a result attributed to radical/radical Coulombic repulsion within the cage. All four alkylperoxyls initiated and terminated tocopherol-mediated peroxidation (TMP) with about equal efficiency and essentially all of these radicals that were generated were consumed in these two reactions. TMP is a radical chain process, and when initiated by the alkylperoxyls, the rate of LDL peroxidation was faster in the early stages while TocH was present than later, after all of this "antioxidant" had been consumed. In contrast, only about 3-4% of the generated superoxide radicals reacted in any measurable fashion with TocH-containing LDL at pH's from 7.6 to 6.5 and peroxidation was much slower than with a similar rate of generation of alkylperoxyls. After all the TocH had been consumed, LDL peroxidation was negligible at pH 7.6 and 7.4, but at pH 6.8 and 6.5, the peroxidation rates showed a large increase over the rates while the TocH had been present. That is, endogenous TocH behaves as an antioxidant in LDL subjected to attack by the physiologically relevant superoxide radical, whereas TocH behaves as a prooxidant in LDL subjected to attack by the probably far less physiologically important alkylperoxyls. Rates of LDL peroxidation initiated by superoxide increased as the pH was decreased, and the results are consistent with the initiation of peroxidation of fresh LDL occurring via H-atom abstraction from TocH by HOO(*) to form the Toc(*) radical and termination by reaction of O2(*-) with Toc(*), a process that occurs partly by addition leading to TocH consumption and partly by electron plus proton transfer leading to the regeneration of TocH.     

Kinetic solvent effects on proton and hydrogen atom transfers from phenols. Similarities and differences

Bimolecular rate constants for proton transfer from six phenols to the anthracene radical anion have been determined in up to eight solvents using electrochemical techniques. Effects of hydrogen bonding on measured rate constants were explored over as wide a range of phenolic hydrogen-bond donor (HBD) and solvent hydrogen-bond acceptor (HBA) activities as practical. The phenols' values ranged from 0.261 (2-MeO-phenol) to 0.728 (3,5-Cl(2)-phenol), and the solvents' values from 0.44 (MeCN) to 1.00 (HMPA), where and are Abraham's parameters describing relative HBD and HBA activities (J. Chem. Soc., Perkin Trans. 2 1989, 699; 1990, 521). Rate constants for H-atom transfer (HAT) in HBA solvents, k(S), are extremely well correlated via log k(S) = log k(0) - 8.3 , where k(0) is the rate constant in a non-HBA solvent (Snelgrove et al. J. Am. Chem. Soc. 2001, 123, 469). The same equation describes the general features of proton transfers (k(S) decreases as increases, slopes of plots of log k(S) against increase as increases). However, in some solvents, k(S) values deviate systematically from the least-squares log k(S) versus correlation line (e.g., in THF and MeCN, k(S) is always smaller and larger, respectively, than "expected"). These deviations are attributed to variations in the solvents' anion solvating abilities (THF and MeCN are poor and good anion solvators, respectively). Values of log k(S) for proton transfer, but not for HAT, give better correlations with Taft et al.'s (J. Org. Chem. 1983, 48, 2877) beta scale of solvent HBA activities than with . The beta scale, therefore, does not solely reflect solvents' HBA activities but also contains contributions from anion solvation.     

Abnormal solvent effects on hydrogen atom abstractions. 1. The reactions of phenols with 2,2-diphenyl-1-picrylhydrazyl (dpph*) in alcohols

Rate constants, k(ArOH/dpph*)(S), for hydrogen atom abstraction from 13 hindered and nonhindered phenols by the diphenylpicrylhydrazyl radical, dpph*, have been determined in n-heptane and a number of alcoholic and nonalcoholic, hydrogen-bond accepting solvents. Abnormally enhanced k(ArOH/dpph*)(S) values of have been observed in alcohols. It is proposed that this is due to partial ionization of the phenols and a very fast electron transfer from phenoxide anion to dpph*. The popular assessment of the antioxidant activities of phenols with dpph* in alcohol solvents will generally lead to an overestimation of their activities.