M?ssbauer study of dissimilatory reduction of iron contained in glauconite by alkaliphilic bacteria

⁵⁷Fe M?ssbauer investigations of glauconite and new solid phases formed during the process of the bacterial growth in alkaline environment were carried out at room temperature, 78 K and 4.8 K. The magnetically ordered phase formed during bioleaching of glauconite by G. ferrihydriticus in pure culture or in combination with Cl. alkalicellulosi represented as a mixture of off-stoichiometric magnetite and maghemite. In case of combined binary bacterium culture growth the relative content of magnetically ordered phase was more than for the G. ferrihydriticus growth.     

Mössbauer spectroscopy in studying magnetite formed by iron- and sulfate-reducing bacteria

The kinetics of iron mineral formation by thermophilic dissimilatory iron reducing bacteria using Fe(III) amorphous hydroxide and acetate CH₃COO^? as an electron acceptor and donor, respectively, was investigated by Mössbauer spectroscopy. The effects of various physical and chemical conditions and the presence of an inert organic substance on the formation of biogenic minerals were considered. The production of magnetite due to microbial sulfate reduction by hyperthermophilic dissimilatory sulfate-reducing microorganisms was investigated by Mössbauer spectroscopy methods.     

Iron minerals formed by dissimilatory iron-and sulfur reducing bacteria studied by Mössbauer spectrometry

Zero-field and in-field Mössbauer investigations and electron paramagnetic resonance (EPR) measurements to follow the kinetics of the iron mineral formation by thermophilic dissimilatory anaerobic Fe(III)-reducing bacteria (strain Z-0001) and anaerobic alkaliphilic bacteria (strain Z-0531) were carried out.     

硫酸盐还原菌分泌胞外多聚物吸附Cu2+的特性

为探讨硫酸盐还原菌胞外多聚物(EPS)吸附Cu2+的特性,采用热力学平衡实验研究了EPS对Cu2+的吸附行为,并通过红外光谱(FTIR)和带能谱仪的扫描电镜(SEM-EDS)分析EPS吸附Cu2+前后官能团以及元素组成的变化来研究EPS吸附Cu2+的机理.结果表明,硫酸盐还原菌EPS对Cu2+的吸附平衡能较好地用Fre...     

Protective performances of two anti-graffiti treatments towards sulfite and sulfate formation in SO2 polluted model environment

Specific strategies for protection are being developed to counter both the staining and corrosive effects of polluted air in cities, as well as to allow for efficient removal of unwanted graffiti paintings. These protection strategies employ molecules with tailored functionalities, e.g. being hydrophobic, while maintaining porosity for molecular water vapour permeation.The present study employs SO₂ and water to probe the behaviors of two anti-graffiti treatments, a water-base fluoroalkylsiloxane (“Protectosil Antigraffiti” marketed by Degussa) and an organically modified silicate (Ormosil) synthesized from a polymer chain (polydimethyl siloxane, PDMS) and two network forming alkoxides (Zr propoxide and methyl triethoxy silane, MTES) dissolved in n-propanol, on five building materials, comprising limestone, aged lime mortar, hydrated cement mortar, granite, and brick material.The materials were exposed to a synthetic atmosphere for 20 h in a climate chamber, 0.78 ± 0.03 ppm of SO₂ and 95% RH. Diffuse reflectance Fourier transform infrared (DR-FTIR) spectra were registered before and after exposure in the climate chamber in the cases of both treated and untreated samples. DR-FTIR, scanning electron microscope (SEM) images and energy dispersive X-ray (EDX) analyses, suggest the anti-graffiti Ormosil to suppress formation of calcium sulfite hemihydrate (the primary initial product of the reaction of calcium compounds with SO₂ and water) on carbonate materials (limestone and lime mortar).In case of the granite, brick and cement mortar, Ormosil has a negligible influence on the SO₂ capture. While no sulfite formation was detected by DR-FTIR, gypsum is inferred to form due to metal oxides and minority compounds catalysed oxidation of sulfite to sulfate. In case of brick, this understanding finds support from SEM images as well as EDX. A priori presence of gypsum in hydrated cement mortars prevents positive identification by SEM. However, support for sulfur accumulation in hydrated cement mortar is provided by means of EDX.In case of a second anti-graffiti considered, Protectosil, no influence of the anti-graffiti treatment on the SO₂ uptake of any of the building materials was observed.     

Electrocatalytic determination of sulfite using a modified carbon nanotubes paste electrode: application for determination of sulfite in real samples

This paper introduces a carbon paste electrode modified with ferrocene and carbon nanotubes as a voltammetric sensor for determination of sulfite at pH 7.0. The results showed that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurred at a potential about 280?mV less positive than the unmodified carbon paste electrode. Kinetic parameters such as electron transfer coefficient (??) and heterogeneous rate constant (k) for sulfite were also determined using electrochemical approaches. Under the optimized conditions, the electrocatalytic oxidation peak current of sulfite showed two linear dynamic ranges with a detection limit of 0.1???M for sulfite. The proposed method was examined as a selective, simple, and precise method for voltammetric determination of sulfite in some real samples such as weak liquor from wood and paper industry, boiler water, river water, industrial water, and tap water.     

Characterization of cross-polarization modulation on a two channel WDM system

This article contributes experimental corroboration of cross-polarization modulation (XPolM). A continuous wave probe signal is remotely controlled by a modulated pump signal. Experimental results show that the state of polarization (SOP) evolution of the probe signal resembles that of the pump signal to a confined region on the Poincaré sphere. Further a bit pattern is transmitted on the probe signal by making use of cross-phase modulation induced nonlinear polarization rotation of the probe signal. The article also gives evidence to the detrimental effect cross phase modulation may have on polarization mode dispersion compensators. The results show that the degree of polarization degradation of a probe signal in a two model wavelength division multiplexing system deteriorates with an increase in the power ratio between the pump and probe signal.     

两种宽谱带蓝光发射材料的制备、表征及光学特性

合成了两种以钙为中心金属离子的有机电致发光材料2-(2-羟基苯基)苯并噻唑钙Ca(BTZ)₂和2-(2-羟基苯基苯并噻唑)-(1,10-邻菲罗啉)合钙Ca(BTZ)₂phen。通过红外光谱、紫外-可见光吸收光谱、循环伏安曲线、原子力显微镜以及光致发光光谱表征了材料的结构、光学带隙、能带结构、成膜性以及光学性能。实验结果表明,在DMSO溶液中,Ca(BTZ)₂的紫外吸收峰主要为290,330,422nm;Ca(BTZ)₂phen的紫外吸收峰主要为292,330,428nm。Ca(BTZ)₂的荧光发射峰为458nm和500nm,色坐标为x=0.2176,y=0.3223;Ca(BTZ)₂phen的荧光发射峰主要为465nm和514nm,色坐标为x=0.2418,y=0.3817。利用真空热蒸镀法可以得到均匀致密的Ca(BTZ)₂phen的薄膜,其粗糙度为1.56。Ca(BTZ)₂薄膜也有望通过旋涂制备。实验发现Ca(BTZ)₂与Ca(BTZ)₂phen的荧光光谱几乎覆盖整个可见光区域,为宽谱带发光材料,有望设计成合理的器件结构实现白光发射。     

Characterization of two electrode systems for corona-charging of non-woven filter media

The aim of this paper is to provide a better understanding of the corona-charging process of non-woven electret filters for automotive and medical applications. The experiments were performed on polypropylene samples: 500-μm-thick non-woven fabrics (fiber diameter: 24 μm), laid on a grounded plate electrode and subjected to positive or negative corona generated either by a dual wire–cylinder electrode or by a triode-type electrode set. The paper reports the results of current–voltage characteristics measurements, as well as the repartition of the current density at the surface of the grounded electrode.     

Characterization of two coupled radial line transformers in dual-diode millimeter wave oscillators

Two mutually coupled radial line transformers mounted in a common rectangular waveguide of dual—diode millimeter wave oscillator are characterized by a hybrid technique based on Galerkin's method combined with collocation technique. The external circuit impedances looking outside from each of two active devices are calculated. A large number of numerical results of the external circuit impedances as a function of the structural parameters have been obtained. Some original conclusions have been made, which are helpful to the design and the adjustment of the dual—diode oscillators.     

The reversibility of dissimilatory sulphate reduction and the cell-internal multi-step reduction of sulphite to sulphide: insights from the oxygen isotope composition of sulphate

Dissimilatory sulphate reduction (DSR) leads to an overprint of the oxygen isotope composition of sulphate by the oxygen isotope composition of water. This overprint is assumed to occur via cell-internally formed sulphuroxy intermediates in the sulphate reduction pathway. Unlike sulphate, the sulphuroxy intermediates can readily exchange oxygen isotopes with water. Subsequent to the oxygen isotope exchange, these intermediates, e.g. sulphite, are re-oxidised by reversible enzymatic reactions to sulphate, thereby incorporating the oxygen used for the re-oxidation of the sulphur intermediates. Consequently, the rate and expression of DSR-mediated oxygen isotope exchange between sulphate and water depend not only on the oxygen isotope exchange between sulphuroxy intermediates and water, but also on cell-internal forward and backward reactions. The latter are the very same processes that control the extent of sulphur isotope fractionation expressed by DSR. Recently, the measurement of multiple sulphur isotope fractionation has successfully been applied to obtain information on the reversibility of individual enzymatically catalysed steps in DSR. Similarly, the oxygen isotope signature of sulphate has the potential to reveal complementary information on the reversibility of DSR. The aim of this work is to assess this potential. We derived a mathematical model that links sulphur and oxygen isotope effects by DSR, assuming that oxygen isotope effects observed in the oxygen isotopic composition of ambient sulphate are controlled by the oxygen isotope exchange between sulphite and water and the successive cell-internal oxidation of sulphite back to sulphate. Our model predicts rapid DSR-mediated oxygen isotope exchange for cases where the sulphur isotope fractionation is large and slow exchange for cases where the sulphur isotope fractionation is small. Our model also demonstrates that different DSR-mediated oxygen isotope equilibrium values are observed, depending on the importance of oxygen isotope exchange between sulphite and water relative to the re-oxidation of sulphite. Comparison of model results to experimental data further leads to the conclusion that sulphur isotope fractionation in the reduction of sulphite to sulphide is not a single-step process.     

Scattering from two non-overlapping centers

The scattering of a particle by two non-overlapping fixed centers is studied in the limit where the individual scattering take place in one partial wave only. The resulting scattering amplidtude and its generalized phaseshifts are obtained in closed analytical form. Numerical calculations are presented in the case of d-waves.     

Social behavior of bacteria: from physics to complex organization

I describe how bacteria develop complex colonial patterns by utilizing intricate communication capabilities, such as quorum sensing, chemotactic signaling and exchange of genetic information (plasmids) Bacteria do not store genetically all the information required for generating the patterns for all possible environments. Instead, additional information is cooperatively generated as required for the colonial organization to proceed. Each bacterium is, by itself, a biotic autonomous system with its own internal cellular informatics capabilities (storage, processing and assessments of information). These afford the cell certain plasticity to select its response to biochemical messages it receives, including self-alteration and broadcasting messages to initiate alterations in other bacteria. Hence, new features can collectively emerge during self-organization from the intra-cellular level to the whole colony. Collectively bacteria store information, perform decision make decisions (e.g. to sporulate) and even learn from past experience (e.g. exposure to antibiotics)-features we begin to associate with bacterial social behavior and even rudimentary intelligence. I also take Schrdinger’s’ “feeding on negative entropy” criteria further and propose that, in addition organisms have to extract latent information embedded in the environment. By latent information we refer to the non-arbitrary spatio-temporal patterns of regularities and variations that characterize the environmental dynamics. In other words, bacteria must be able to sense the environment and perform internal information processing for thriving on latent information embedded in the complexity of their environment. I then propose that by acting together, bacteria can perform this most elementary cognitive function more efficiently as can be illustrated by their cooperative behavior.     

Characterization of a soil ilmenite developed from basalt

A natural ilmenite was extracted from the silt fraction of a soil developed from basalt of Minas Gerais State, Brazil. The sample was characterized by chemical analysis, X-ray diffraction, magnetic measurements and Mössbauer spectroscopy. The Mössbauer spectrum at 293 K shows two doublets: a major subspectrum of Fe²⁺ (relative area 74%) and a minor one of Fe³⁺ (26%). An incipient magnetic structure appears at 85 K, with a broadline sextet. These results may be explained by supposing that the separate is a solid solutionxFeTiO₃ · (1–x)Fe₂O₃, withx=0.85, which is magnetically ordered at low temperature. The lattice parameters for this hexagonal structure area=0.5082±0.0001 nm andc=1.398±0.001 nm.On leave of absence from the Departamento de Química, Universidade Federal de ViÇosa, 36570 000 ViÇosa (MG), Brazil.     

旋转致密双星的引力波特征

研究了轨道和旋转效果到2.5阶后牛顿旋转致密双星拉格朗日动力学与引力波的关系, 分析了有序和混沌轨道的引力波特征.发现当加速度不考虑辐射项时, 有序双星系统辐射的引力波具有周期或拟周期的特征, 而混沌双星系统辐射的引力波却具有明显的混沌特征.当加速度含有辐射项贡献时, 双星必会出现并合现象.此时, 原保守有序双星系统需较长时间才能完成并合过程, 引力波形在双星并合前仍保留拟周期的基本特点;然而, 原保守混沌双星系统仅在较短时间内就会并合, 但因并合时间太短, 无法获取足够的动力学信息导致引力波形的特征不易分辨.     

Characterization of cylindrical particles from their acoustic emission

A method for determining the size and size distribution of cylindrical particles is described It is based on the fact that rigid particles, when they impinge on each other, emit acoustic waves whose frequencies are related to the particle size and the size distribution. The emitted frequencies are related to the ratio of the diameter to the squared length of the particles.     

Characterization of luminescent chromophore obtained from silica spheres

Blue light emitting chromophores have been separated from silica spheres by soaking them into acetone for 120 days. The luminescent chromophores were not obtained from other solvents, including ether, methanol, ethanol, 2-propanol, chloroform and tetrahydrofuran. According to the Fourier transform infrared spectrum, the luminescent material is composed of C–OH, –CH₂, –CH₃, C=O, and Si–O–Si. UV–visible absorption peak of the chromophore is at 5.17 eV (240 nm). Field emission scanning electron microscope images show small cracks on the surface of aged spheres. The luminescence peak was at 2.81 eV (441 nm) for excitation energy between 3.88 and 3.35 eV and slightly shifted toward lower energy for excitation energy lower than 3.35 eV. The deconvoluted luminescent spectrum shows two emission bands at 3.08 and 2.74 eV, which are well-matched the oxygen deficient center model. Compared to the absorption peak (5.17 eV) and the emission peak (2.81 eV), large Stokes shift (2.36 eV) is observed.     

Characterization of third-harmonic generation from femtosecond laser-excited silicon

Third-harmonic generation (THG) from silicon crystals excited by femtosecond pulses has been studied. THG as a function of probe pulse delay from linear and circularly polarized probe pulses was examined. Both polarizations exhibit a fast, 300 fs drop in THG when the Si is pumped by pulses with fluence above the melting threshold. This drop for both polarizations indicates that electronic effects dominate THG in laser-melted Si since structural effects should principally influence THG from linearly polarized probes, suggesting that care needs to be exercised in interpreting THG signal as an ultrafast probe of crystalline structure in semiconductors.