Grain boundary effect on electron-beam-induced current in La3Ga5.5Ta0.5O14 crystal

La₃Ga_5.5Ta_0.5O₁₄ crystal recently attracted more attention due to its superior electromechanical properties and high Q × f product. We report that the first electron-beam-induced current experiment on La₃Ga_5.5Ta_0.5O₁₄ single crystal. This method is employed to study the effect of the crystal's grain boundary on the incident electron beam. The experimental results clearly show that when the electron beam scans over the grain boundary of the crystal, a fraction of the carriers recombine at the grain boundary and is unavailable for the current generation. This recombination rate will be enhanced when the electron beam was close to the boundary and cause a dip in the collected current. Although the crystal is an insulator, this effect still can be observed if the coating metal is proper to be chosen. It is also pointed out that the different diffusion lengths of the crystal might be due to the tilted grain boundary.     

Circumpolar study of perfluoroalkyl contaminants in polar bears (Ursus maritimus)

Perfluoroalkyl substances were determined in liver tissues and blood of polar bears (Ursus maritimus) from five locations in the North American Arctic and two locations in the European Arctic. Concentrations of perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate, heptadecafluorooctane sulfonamide, and perfluoroalkyl carboxylates with C(8)-C(15) perfluorinated carbon chains were determined using liquid chromatography tandem mass spectrometry. PFOS concentrations were significantly correlated with age at four of seven sampling locations, while gender was not correlated to concentration for any compound measured. Populations in South Hudson Bay (2000-2730 ng/g wet wt), East Greenland (911-2140 ng/g wet wt), and Svalbard (756-1290 ng/g wet wt) had significantly (P < 0.05) higher PFOS concentrations than western populations such as the Chukchi Sea (435-729 ng/g wet wt). Concentrations of perfluorocarboxylic acids (PFCAs) with adjacent chain lengths (i.e., C9:C10 and C10:C11) were significantly correlated (P < 0.05), suggesting PFCAs have a common source within a location, but there were differences in proportions of PFCAs between eastern and western location sources. Concentrations of PFOS in liver tissue at five locations were correlated with concentrations of four polychlorinated biphenyl congeners (180, 153, 138, and 99) in adipose tissue of bears in the same populations, suggesting similar transport pathways and source regions of PFOS or precursors.     

Temporal trends of perfluoroalkyl contaminants in polar bears (Ursus maritimus) from two locations in the North American Arctic, 1972-2002

Perfluoroalkyl substances are globally distributed anthropogenic contaminants. Their production and use have increased dramatically from the early 1980s. While many recent publications have reported concentrations of perfluorooctane sulfonate (PFOS) and other perfluoroalkyl acids (PFAs) in biotic and abiotic samples, only limited work has addressed temporal trends. In this study we analyzed archived polar bear(Ursus maritimus) livertissue samples from two geographic locations in the North American Arctic, collected from 1972 to 2002. The eastern group, taken from the vicinity of northern Baffin Island, Canada, comprised 31 samples, and the western group, from the vicinity of Barrow, Alaska, comprised 27 samples. Samples were analyzed for perfluorocarboxylic acids (PFCAs) from carbon chain length C8 to C15, perfluorohexane sulfonate, PFOS, the neutral precursor perfluorooctane sulfonamide (PFOSA), as well as 8:2 and 10:2 fluorotelomer acids and their alpha,beta unsaturated acid counterparts. Concentrations of PFOS and PFCAs with carbon chain lengths from C9 to C11 showed an exponential increase between 1972 and 2002 at both locations. Doubling times ranged from 3.6 +/- 0.9 years for perfluorononanoic acid in the eastern group to 13.1 +/- 4.0 years for PFOS in the western group. PFOSA showed decreasing concentrations over time at both locations, while the remaining PFAs showed no significant trends or were not detected in any sample. The doubling time for PFOS was similar to the doubling time of production of perfluoroctylsulfonyl-fluoride-based products during the 1990s.     

Favorable effects of weak acids on negative-ion electrospray ionization mass spectrometry

Despite widespread use in pharmacokinetic, drug metabolism, and pesticide residue studies, little is known about the factors governing response during reversed-phase liquid chromatography coupled with negative-ion electrospray ionization (ESI(-)) mass spectrometry. We examined the effects of various mobile-phase modifiers on the ESI(-) response of four selective androgen receptor modulators using a postcolumn infusion system. Acetic, propionic, and butyric acid improved the ESI(-) responses of analytes to varying extents at low concentrations. Formic acid suppressed ionization, as did neutral salts (ammonium formate, ammonium acetate) and bases (ammonium hydroxide, triethylamine) under most conditions. Two modifiers (2,2,2-trifluoroethanol, formaldehyde) that produce anions with high gas-phase proton affinity increased ESI(-) responses. However, the concentrations of these modifiers required to enhance ESI(-) response were higher than that of acidic modifiers, which is a phenomenon likely related to their low pK(a) values. 2,2,2-Trifluoroethanol increased response of more hydrophobic compounds but decreased response of a more hydrophilic compound. Formaldehyde improved response of all the compounds, especially the hydrophilic compound with lower surface activity. In summary, these results suggest that an ideal ESI(-) modifier should provide cations that can be easily electrochemically reduced and produce anions with small molecular volume and high gas-phase proton affinity.     

Continuous monitoring of a restriction enzyme digest of DNA on a microchip with automated capillary sample introduction

Continuous analysis of a DNA restriction enzyme digest on a microfabricated device is demonstrated with minimal intervention and enhanced time resolution. A 62-base-pair fragment of dsDNA containing a KpnI site was used to demonstrate this process. A capillary was used to transfer sample from a single reaction mix to a microfabricated chip with parallel separation lanes. The 6-carboxyfluorescein-labeled DNA fragments were detected with a CCD camera as they separated in the lanes, which were filled with linear polyacrylamide. The products of the restriction enzyme digest were monitored for up to 60 min at an average sampling rate of 1 injection/46 s, with consecutive injections as short as 1 injection/14 s. The digest was injected directly into the chip, eliminating the need for any sample-handling steps after addition of the enzyme to the reaction mix. The effects of temperature and restriction enzyme concentration were briefly examined, as well. This work shows the potential of this method to provide valuable information about the process of restriction enzyme cleavage.     

Suomi NPP/VIIRS: improving drought watch,crop loss prediction,and food security

Since 1990, the role of satellite observations for climate and land services increased considerably, especially with the introduction in 2011 of the new generation of NOAA operational satellites, called Suomi NPOSS Polar-Orbiting Partnership (S-NPP). S-NPP will continue as the Joint Polar Satellite System (JPSS) for the next two decades. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the S-NPP spacecraft is accommodating the best technical and scientific features of its predecessors and has several new important features. S-NPP and JPSS, in addition to data collection, will address the impacts of climate and weather on industries, water, energy, population health, and other resources and activities. This article discusses how these operational satellites improve early drought detection, monitoring its features (intensity, duration, area, etc.) and prediction of agricultural losses; how fast the Earth’s natural resources deteriorate; and whether the current warm climate intensifies droughts and increases its area and duration. These climate services have already become available to the global community (http://www.star.nesdis.noaa.gov/smcd/emb/vci/VH/index.php). The S-NPP/VIIRS data permits its users to enhance long-term environmental data records, thereby improving the ability to estimate global warming, land-cover changes, and better monitoring of environmental resources.     

Nitrosamine carcinogens also swim in chlorinated pools

Highly carcinogenic N-nitrosodialkylamine (nitrosamine) disinfection byproducts were quantified in chlorinated swimming pools, hot tubs, and aquaria. N-Nitrosodimethylamine, the most abundant nitrosamine detected, was measured in swimming pools and hot tubs at levels up to 500-fold greater than the drinking water concentration of 0.7 ng/L associated with a one in one million lifetime cancer risk. Temperature, enclosure, amine and nitrite precursor loading, and the use of disinfection schemes with reduced chlorine doses contributed to statistically significant variability in its occurrence. N-Nitrosodibutylamine and N-nitrosopiperidine were also detected but together represented <5% of the total analyte distribution. The presence of N-nitrodimethylamine at levels comparable to N-nitrosodimethylamine points to a competition between the nitration and nitrosation of amines in chlorinated recreational waters. Since nitrosamines can cause bladder cancer, the significance of our measurements needs clarification with respect to recent epidemiological results that are suggestive of a link between swimming in chlorinated pools and bladder cancer.     

Alcohol Consumption Moderates the Link Between Cannabis Use and Cannabis Dependence in an Internet Survey.

The link between cannabis use and cannabis dependence remains poorly understood. Some people use cannabis regularly without signs of dependence; others show dependence despite using less. This study examined alcohol consumption as a moderator of this association. A sample of 476 people (primarily Caucasian men) who used cannabis at least once per week reported their alcohol consumption, cannabis use, and cannabis dependence symptoms in an Internet survey. Regressions revealed significant interactions between measures of cannabis use and alcohol consumption when predicting cannabis dependence. Cannabis use covaried with cannabis dependence, particularly in people who consumed alcohol frequently or in large amounts per week. Despite limitations, these data suggest that alcohol may decrease the safety of cannabis consumption. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

浅析移动多媒体的货币化进程

过去的一年，流行的视频网站、兴趣社区（Communities of interest）、社交网络的普及和个性化需求出现成倍增长。虽然以分钟计算，多媒体服务和使用率均创下历史新高，但服务提供商和内容提供者仍然在根据消费者和企业的需求，不断调整着他们的收益和推出新服务模式。