Thermal conductivity imaging at micrometre-scale resolution for combinatorial studies of materials

Combinatorial methods offer an efficient approach for the development of new materials. Methods for generating combinatorial samples of materials, and methods for characterizing local composition and structure by electron microprobe analysis and electron-backscatter diffraction are relatively well developed. But a key component for combinatorial studies of materials is high-spatial-resolution measurements of the property of interest, for example, the magnetic, optical, electrical, mechanical or thermal properties of each phase, composition or processing condition. Advances in the experimental methods used for mapping these properties will have a significant impact on materials science and engineering. Here we show how time-domain thermoreflectance can be used to image the thermal conductivity of the cross-section of a Nb-Ti-Cr-Si diffusion multiple, and thereby demonstrate rapid and quantitative measurements of thermal transport properties for combinatorial studies of materials. The lateral spatial resolution of the technique is 3.4 microm, and the time required to measure a 100 x 100 pixel image is approximately 1 h. The thermal conductivity of TiCr(2) decreases by a factor of two in crossing from the near-stoichiometric side of the phase to the Ti-rich side; and the conductivity of (Ti,Nb)(3)Si shows a strong dependence on crystalline orientation.     

Characterization of the binding site for inhibitors of the HPV11 E1-E2 protein interaction on the E2 transactivation domain by photoaffinity labeling and mass spectrometry

An indandione-containing class of inhibitors abrogates DNA replication of human papillomavirus (HPV) types 6 and 11 by binding reversibly to the transactivation domain (TAD) of the viral E2 protein and inhibiting its interaction with the viral E1 helicase. To locate the binding site of this class of protein-protein interaction inhibitors, a benzophenone derivative was used to generate an irreversibly labeled E2-TAD polypeptide. The single site of covalent modification of the E2-TAD was identified by proteolytic digestions using trypsin, LysC, and V8 proteases and characterization of the resulting peptides by LC-MS procedures. Through this methodology, the benzophenone attachment point was located at the terminal methyl of residue Met101. Evidence further pinpointed the site of photoaffinity attachment to the terminal carbon atom, which is significant in providing a definitive example of the ability to locate photoinduced cross-linking to a polypeptide with atomic resolution using solely mass spectrometric detection. The location of the inhibitor binding site vis-à-vis the Glu39 and Glu100 residues sensitive to mutation for HPV 11 E2-TAD is discussed in relation to the crystal structure of the E2-TAD from the related HPV type 16.     

Infrared-visible sum frequency generation investigation of Cu corrosion inhibition with benzotriazole

Infrared-visible sum frequency generation spectroscopy is used to investigate the corrosion inhibitor benzotriazole (BTAH) adsorbed on Cu(100) and Cu(111) in acidic solution. Potential-dependent in situ spectra indicate that the adsorbed molecule is the benzotriazole anion (BTA-) at all potentials investigated. The Cu(100) surface is shown to form an ordered adlayer at all potentials probed, while the Cu(111) face is shown to be disordered at negative potentials, but to order with applied positive potential. The ordered adlayer is shown to consist of the BTA- in two configurations, one coordinated to the surface and Cu+ ions in solution and the other coordinated only to the surface. The BTA- coordinated to Cu+ is shown to be more stable with respect to Cl- addition than BTA- coordinated to only the surface. This study demonstrates the viability of using sum frequency generation to study corrosion inhibition in situ.     

Antimicrobial-resistant Salmonella serovars isolated from imported foods

A total of 187 Salmonella isolates representing 82 serotypes recovered from 4072 imported foods in the year 2000 by the U.S. Food and Drug Administration field laboratories were tested for their susceptibility to 17 antimicrobials of human and veterinary importance. Fifteen (8%) isolates were resistant to at least one antimicrobial, and five (2.7%) were resistant to three or more antimicrobials. Most of the isolates (n=9) exhibited resistance to tetracycline. Four isolates from catfish or tilapia from Taiwan or Thailand also demonstrated resistance to nalidixic acid. These nalidixic acid-resistant Salmonella isolates possessed a point mutation at the Ser83 or Asp87 position in DNA gryase, resulting in amino acid substitutions to phenylalanine, tyrosine, or asparagine. One Salmonella Derby isolated from frozen anchovies imported from Cambodia was resistant to six antimicrobials including ampicillin, amoxicillin/clavulanic acid, chloramphenicol, sulfamethoxazole, tetracycline, and trimethoprim/sulfamethoxazole. Of seven isolates displaying resistance to sulfonamides, only one S. Derby and one Salmonella Agona contained class 1 integrons that were further shown to possess the aadA and pse-1 genes conferring resistance to streptomycin and ampicillin, respectively. This study indicates that antimicrobial-resistant Salmonella are present in imported foods, primarily of seafood origin, and stresses the need for continued surveillance of foodborne zoonotic bacterial pathogens from imported foods entering the United States.     

Reproducibility in fabrication and analytical performance of polyaniline-coated nanoelectrospray emitters

Nanoelectrospray ionization mass spectrometry is an ideal technique for analysis of biomolecules when sample quantities are limited. With the use of this technique, 1-2 microL of sample can be electrosprayed for long time periods (hours) because of the low flow rate (nanoliters per minute) attainable. However, the long-term durability of such emitters has been an impediment to the routine use of nanoelectrospray. The development of longer-lasting nanoelectrospray emitters has often resulted in increasingly complex and tedious fabrication processes. Furthermore, an easily produced, reproducible, and durable nanoelectrospray emitter is the ultimately desired goal. Here, the reproducibility of the inner diameters and geometry for nanoelectrospray emitter glass substrates is assessed using scanning electron microscopy (SEM). The results indicate that provided that glass pulling parameters remain constant, reproducible inner diameters can be produced from glass capillary tubing within the same batch; however, there are interbatch differences. In addition, SEM revealed reproducible taper geometry could also be obtained. Borosilicate and fused-silica nanoelectrospray emitters produced by these protocols were then coated with polyaniline, and their analytical figures of merit were determined using a triple quadrupole mass analyzer. Over a 1-h run, polyaniline-coated emitters showed fairly stable signal with coefficients of variation ranging from 8.92 to 27.6%. Single-scan detection limits below 1 amol were achieved for polyaniline-coated fused-silica emitters for flow rates averaging <10 nL/min. Linear mass spectrometric response with solution concentration was observed for the polyaniline-coated emitters over the range 10 nM-10 microM, with coefficients of variation ranging from 1.44 to 7.26%. This indicates that when nanelectrospray emitter inner diameters are made reproducibly, it is possible to achieve linear quantitative response for nanoelectrospray.     

Scanning electrochemical microscopy of membrane transport in the reverse imaging mode

Scanning electrochemical microscopy (SECM), operated in reverse imaging mode (RIM), has been used to visualize the steady-state transport of molecules entering into porous membranes. RIM imaging is advantageous for investigating transport across biological membranes in situations where the SECM tip can access only the exterior membrane surface. Examples of RIM images of a synthetic membrane (mica with pores filled with the ion-selective polymer Nafion) and a biological membrane (hairless mouse skin) recorded during diffusive and iontophoretic transport, are reported. RIM imaging during diffusive transport allows visualization of the depletion of solute molecules in the solution adjacent to the pore openings. However, an accumulation of solute molecules above the pore opening is observed during iontophoresis, which is a consequence of the separation of the solute from the solvent (i.e., ultrafiltration). The separation results from differences in the rates of molecule transfer across the pore/solution interface when electroosmotic flow is operative. The results suggest that RIM imaging may be useful for measuring the kinetics of interfacial molecule transfer at biological membranes.     

Use of a 13C tracer to quantify the plasma appearance of a physiological dose of lutein in humans

Increased intake of lutein from vegetables promotes increased density of the macular pigment and therefore may protect against age-related macular degeneration. Our objective was to use a ¹³C tracer and high-precision gas chromatography-combustion interfaced-isotope ratio mass spectrometry (GC-C-IRMS) to investigate metabolism of a lutein dose equivalent to that absorbed from vegetables. Biosynthetic per-labeled (>99% ¹³C) lutein was purified from a commercially available extract of algal biomass. Subjects (n=4) ingested 3 mg of [¹³C]lutein with a standardized low-carotenoid breakfast. Blood samples were collected at baseline and then hourly for 12 h; additional blood samples were drawn at 16, 24, 48, 72, 96, 192, 360, and 528 h. To produce perhydro-β-carotene suitable for analysis by GC-C-IRMS, the plasma lutein fraction was hydrogenated on palladium-on-carbon catalyst with acid-catalyzed hydrogenolysis. The stable carbon isotope (¹³C/¹²C) ratio measured by GC-C-IRMS was used to calculate the plasma concentration of [¹³C]lutein. There was a rapid increase in [¹³C]lutein in plasma until peak enrichment at 16 h followed by a decline to the next measurement at 24 h. At 528 h, small changes in ¹³C enrichment from baseline could still be measured in plasma lutein. High-precision GC-C-IRMS enables complete definition of the appearance and disappearance of [¹³C]lutein in plasma after ingestion of a dose similar to that absorbed from foods.     

英国西伦敦奥迪中心

<正>项目背景2002年1月英国奥迪公司委托威尔金森·艾尔建筑事务所设计西伦敦奥迪中心大楼。该设计团队多年一直受雇于奥迪公司,设计了英国范围内各地区的新一代奥迪总部。此次的设计任务是为奥迪公司设计出一个能够在通往伦敦中心的主干道上加强公司形象的大楼。     

计算机病毒解析

计算机病毒可造成很大危害——破坏你的文件,甚至使系统瘫痪。本文将介绍它是如何进行传播的。