Surface passivation of crystalline silicon by Cat-CVD amorphous and nanocrystalline thin silicon films

In this work, we study the electronic surface passivation of crystalline silicon with intrinsic thin silicon films deposited by Catalytic CVD. The contactless method used to determine the effective surface recombination velocity was the quasi-steady-state photoconductance technique. Hydrogenated amorphous and nanocrystalline silicon films were evaluated as passivating layers on n- and p-type float zone silicon wafers. The best results were obtained with amorphous silicon films, which allowed effective surface recombination velocities as low as 60 and 130 cm s⁻¹ on p- and n-type silicon, respectively. To our knowledge, these are the best results ever reported with intrinsic amorphous silicon films deposited by Catalytic CVD. The passivating properties of nanocrystalline silicon films strongly depended on the deposition conditions, especially on the filament temperature. Samples grown at lower filament temperatures (1600 °C) allowed effective surface recombination velocities of 450 and 600 cm s⁻¹ on n- and p-type silicon.     

Assembly of purified GDP-tubulin into microtubules induced by taxol and taxotere: reversibility, ligand stoichiometry, and competition

Purified tubulin fully liganded to GDP at the exchangeable nucleotide binding site has been prepared by a new direct nucleotide exchange procedure. This normally inactive GDP-tubulin is driven to assemble into microtubules by the binding of the antitumor drug taxol or its more soluble side-chain analogue Taxotere in Mg(2+)-containing buffer, and it disassembles by cooling the solution. Therefore this ligand-induced equilibrium microtubule assembly system dispenses with the requirement of a gamma-phosphate-metal cation ligand bound at the nucleotide site for tubulin to be active. GDP-tubulin can also form characteristic pseudo-ordered aggregates of double rings. These aggregates dissociate upon warming or by addition of GTP. Back-substitution of the nucleotide gamma-phosphate permits glycerol-induced assembly without taxol and reduces the critical protein concentration required for drug-induced microtubule assembly by a factor of 2.6 +/- 0.1. The ligand-induced assembly is maximal at taxol or Taxotere concentrations equimolar with tubulin, and both drugs bind to assembled tubulin with a stoichiometry of 0.99 +/- 0.04 ligand per alpha beta dimer. Taxotere apparently competes with taxol for the same binding site, with 1.9 +/- 0.1 times larger effective affinity. Similarly, the Taxotere-induced assembly of GDP-tubulin or GTP-tubulin proceeds with a critical protein concentration 2.1 +/- 0.1 times smaller than with taxol.     

Role of the colchicine ring A and its methoxy groups in the binding to tubulin and microtubule inhibition

The roles of the methoxy substituents on ring A of two ring colchicine (COL) analogues were probed by the synthesis of a number of drugs and the examination of their effect on binding to tubulin, inhibition of microtubule assembly, and induction of GTPase activity. Selective elimination of ring A methoxy groups at positions 2, 3, and 4 weakened all three processes. The effects on binding and inhibition were independent of the nature of ring C (or C'). Specifically, excision of the 2- or 3-methoxy groups weakened binding by ca. 0.4 kcal mol-1, while that of the 4-methoxy group of ring A was weakened by 1.36 +/- 0.15 kcal mol-1. The effect on the inhibition of microtubule assembly, expressed as the equilibrium constant for the binding of the tubulin-drug complex to the end of a microtubule, was more complex and strongly dependent on the nature of ring C (or C'). This was attributed to the abilities of various groups on ring C' to overcome the wobbling in the tubulin-drug complex introduced by the weakening of the anchoring provided by ring A. It is concluded that ring A of COL is not germane to the mechanism of the inhibition of tubulin self-assembly. It serves only as a complex-stabilizing anchor. The control of this process resides in the interactions that key oxygen atoms of ring C of COL or C' of structural analogues establish with the protein. It is proposed that the 4-methoxy group of ring A serves as a key attachment point for immobilization of the drugs on the protein.     

Development of a liquid chromatography-electrospray-tandem mass spectrometry method for the quantitative determination of benzoxazinone derivatives in plants

A new method for the quantification of benzoxazinone derivatives in extracts of wheat foliage and root samples using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS-MS) is described. Using this method, the characterization, separation, and quantitative detection of a mixture of six naturally occurring 1,4-benzoxazin-3(4H)-one derivatives, including the hydroxamic acids (DIMBOA, DIBOA), lactams (HBOA, and HMBOA), benzoxazilinones (BOA, MBOA), and two synthetic methoxylated variations of DIBOA and HBOA, was achieved. The application of a novel, highly modified reversed-phase LC column, the dodecyl (C12) TMS end-capped Synergi MAX-RP, enhanced the on-line chromatographic separation through improvements to component resolution, analyte stability and peak shape and also to the column lifetime. The complete ESI-MS-MS precursor-product ion fragmentation pathways for the benzoxazinone derivatives are described for the first time and used to deduce a generic fragmentation pattern for the compound class. Characteristic transitions for the benzoxazinones were thus used in the developed analytical method enabling reliable quantification with simultaneous screening for other potentially present derivatives, while eliminating interferences from other coeluting contaminants from the complex plant extract matrix. Quantitative analysis was done in the multiple reaction monitoring mode, using two specific combinations of a precursor-product ion transitions for each compound. The ESI-MS-MS detection method offered improvements to the sensitivity and selectivity, as compared with previously applied LC methods, with detection limits down to 0.002-0.023 ng/microL. The developed method was demonstrated by analyzing foliages and roots of six different wheat cultivars using pressurized liquid extraction-solid-phase extraction cleanup-LC-ESI-MS-MS. The analytes were detected in the range of 0.7-207 microg/g of dry weight.     

Effect of starvation on organ blood flow in the senescent rat

Since the first true hernioplasty performed by Edoardo Bassini more than 100 years ago (1884) all surgical reconstruction techniques have shared a common defect i.e. tension on suture line. This is the first etiologic factor of recurrent hernia. On the contrary by the use of modern prosthetic materials (mesh and plug) it is now possible to marriage all hernia repairs without distorting normal body anatomy and avoid undesirable tensions. The technique proposed is simple, efficient, characterized by a rapid performing procedure, giving way to an excellent clinical outcome: postoperative pain relief permitting the patient to resume in a short time his normal physical activities. In this paper the authors present their experience in wall defects reconstruction by means of outpatient surgery and in general anesthesia in the period spanning from 1994 to 1996. Five different types of hernia mesh in hernioplasty procedures were evaluated and used.     

Neonatal infection by Streptococcus agalactiae. Multicenter study in the area of Barcelona, Spain

BACKGROUND: Streptococcus agalactiae or streptococcus group B (SGB) is the main etiologic agent of early neonatal sepsis. A multicenter study was performed with the aim of determining the incidence and characteristics of this disease in our medium and contribute the design of an adequate prevention protocol. METHODS: Ten hospitals and two primary health care centers were implicated in the study; 103 microbiology confirmed episodes of SGB neonatal sepsis (blood and/or LCR positive) were reported from 1994 to 1996. RESULTS: The incidence of early SGB neonatal sepsis was 1.48/1,000 live births with a mortality of 8.7%. The cultures, for detecting the state of the SGB carrier were performed in only 26 (25%) of the patients. At least one of the factors described for risk of perinatal SGB infection was observed in 46% of the mothers, with the most frequent being prolonged amniorrhea (26%), intrapartum fever (17%), and early delivery (14%). At the time of delivery only 10.7% of the mothers received endovenous antibiotherapy. CONCLUSIONS: From these results the following recommendations have been made: a) detection of SGB carriers by the systematic practice of blood cultures in the last weeks of gestation and b) the administration of intrapartum antibiotic prophylaxis in both early births (< 37 weeks) and in all the SGB carriers should be undertaken. With these measures we aim to decrease the neonatal infections by streptococcus group B.     

动感和光创造的空间

本文是保罗·安德鲁对自己建筑创作思想发展的回顾与总结、建筑师对个性化和风格问题毫不关心,他所追求的是作品内在的连贯性,明晰性及其与外界的关系．他关注空间本身,关注自然光在空间中的演出,关注溶解在光线中的结构形式。他坚信通过与诗、文学、绘画和科学的交流能使建筑更丰富。只有当建筑以谦逊的姿态出现时,它才能获得艺术带来的意外的天赐之福,充满活力,充满无法预知的期待。     

Structure,Synthesis, and Applications of TiO2 Nanobelts

TiO₂ semiconductor nanobelts have unique structural and functional properties, which lead to great potential in many fields, including photovoltaics, photocatalysis, energy storage, gas sensors, biosensors, and even biomaterials. A review of synthetic methods, properties, surface modification, and applications of TiO₂ nanobelts is presented here. The structural features and basic properties of TiO₂ nanobelts are systematically discussed, with the many applications of TiO₂ nanobelts in the fields of photocatalysis, solar cells, gas sensors, biosensors, and lithium‐ion batteries then introduced. Research efforts that aim to overcome the intrinsic drawbacks of TiO₂ nanobelts are also highlighted. These efforts are focused on the rational design and modification of TiO₂ nanobelts by doping with heteroatoms and/or forming surface heterostructures, to improve their desirable properties. Subsequently, the various types of surface heterostructures obtained by coupling TiO₂ nanobelts with metal and metal oxide nanoparticles, chalcogenides, and conducting polymers are described. Further, the charge separation and electron transfer at the interfaces of these heterostructures are also discussed. These properties are related to improved sensitivity and selectivity for specific gases and biomolecules, as well as enhanced UV and visible light photocatalytic properties. The progress in developments of near‐infrared‐active photocatalysts based on TiO₂ nanobelts is also highlighted. Finally, an outline of important directions of future research into the synthesis, modification, and applications of this unique material is given.     

Accurate analytical expressions for stripping voltammetry in the Henry adsorption limit

A strategy is developed to derive accurate analytical expressions for low-coverage cathodic stripping voltammetry. The procedure relies on the observation that diffusion affects the location of simulated voltammetric waves but not their shape, provided that physisorption of the analyte is negligible. As a proof of the generality of the proposed approach and having in mind the stripping of thiols, analytical solutions are derived for the cathodic stripping of monomers, dimers, and a mixture of monomers and dimers, whose reliability is proved by their comparison with numerically simulated voltammograms. Application to the deposition and reductive desorption of mercaptoacetic acid at a mercury electrode demonstrates that these approximate solutions can be used to get insights into the interfacial organization of incipient films. For this particular system, a transition from monomeric to dimeric behavior is identified upon increasing the thiol surface concentration. Further generalization of the proposed methodology is achieved by deriving an approximate analytical solution for thin-layer anodic stripping voltammetry, which is satisfactorily compared to the existing summation series solution.     

Curcumin associated magnetite nanoparticles inhibit in vitro melanoma cell growth

Curcumin is a natural product possessing therapeutic properties but the low water solubility of this compound limits its use. We have successfully incorporated curcumin into a bilayer of dodecanoic acid attached to magnetite nanoparticles in an effort to maximize solubility and delivery efficiency. Curcumin/magnetite nanoparticles were characterized using diffused reflectance infra-red fourier transform spectroscopy (DRIFTS) and X-ray powder diffraction (XRD). Moreover curcumin associated magnetite nanoparticles inhibited in vitro melanoma cell growth. An inhibitory concentration (IC50) of 66.0 +/- 3.0 microM (48 +/- 2.2 microg-iron/mL) was observed for the curcumin/magnetite nanoparticles. Fluorescent microscopy revealed that curcumin associated magnetite nanoparticles were internalized by the melanoma cells and remained in the cytoplasm. The curcumin/magnetic nanoparticles synthesized in this study possess magnetic and water solubility properties making this a novel curcumin formulation with therapeutic potential.