覆盖三个十倍频程的锁定同步正弦波发生器

测试、校准、普通系统操作等模拟应用经常需要具有准确的振幅和频率、THDf总谐波失真）很低的正弦波形。一些应用要求此类波形发生器能用外部时序信号使其输出准确同步。简单的正弦波发生器能提供多个性能级别，但保持低THD和恒定振幅是个问题，特别是如果输出和同步信号必须在扩展的频率范围内保持锁定的话。     

W-Hotel简约主义引发的感官神话

现代建筑派大师之一的密斯·凡德罗有句名言:"Less is more","少即是多"衍生出的简约主义,倡导"简约而不简单"的生活哲学.它是被建筑师、画家、音乐家、作家不停探索的美学定义,一种文化倾向,一种时尚潮流.     

Android第二季度帮助智能手机厂商取得成功

据iSuppli公司,在第二季度10大智能手机厂商中,增长最快的厂商大多采用了Android操作系统,这表明谷歌的Android系统势头增强. Droid手机专业厂商HTC,第二季度智能手机出货量比第一季度大增63.1%,增长率居业内之首.     

The impact of orthokeratology lens wear on binocular vision and accommodation: A short-term prospective study

Purpose

To investigate the effects of short-term orthokeratology (OK) on accommodation and binocular visual function in young adults.

TESPI: Thermal Electric Solar Panel Integration

A photovoltaic panel with a heat extraction system is studied. The solution we suggest consists in superimposing a water layer on the PV panel: the water layer absorbs the infrared radiation leaving the visible part almost unaffected. This allows a good PV efficiency and heat production. This particular setup is called Thermal Electric Solar Panel Integration (TESPI) and it is discussed in detail both for the electric and the thermal part. The engineering problems are briefly analyzed and results of an experimental campaign are given. A definition of the global thermal-electric efficiency is given.     

Energy efficiency and renewable energy under extreme conditions: Case studies from Antarctica

This article showcases a range of small and large scale energy efficiency and renewable energy deployments at Antarctic research stations and field camps. Due to the cold and harsh environment, significant amounts of fuel are needed to support humans working and living in Antarctica. The purchase, transportation and storage of large amounts of fossil fuel entail significant economic costs and environmental risks and have motivated developments in energy efficiency and renewable energy deployment. Over the past three decades, improved building design, behavioral change, cogeneration, solar collectors, solar panels and wind turbines have been found to be effective in Antarctica, demonstrating that harsh environmental conditions and technological barriers do not have to limit the deployment of energy efficiency and renewable energy. The ambition to run entire stations or field camps on 100% renewable energy is increasingly common and feasible. While the power requirements of Antarctic research stations are small compared to urban installations on other continents, these case studies clearly demonstrate that if energy efficiency and renewable energy can be deployed widely on the coldest, darkest and most remote continent of the world, their deployment should be more widespread and encouraged on other continents.     

Reactive and stimuli-responsive maleic anhydride containing macromers – multi-functional cross-linkers and building blocks for hydrogel fabrication

Macromers with functional groups that allow for chemical derivatization, polymerization reactions or impart specific physico-chemical properties are functional building blocks for polymeric systems used in different biomedical applications. With this motivation, a series of oligomeric macromers was synthesized by free radical polymerization of maleic anhydride (MA) with N-isopropylacrylamide (NiPAAm) and pentaerythritol diacrylate monostearate (PEDAS). This chemical design provides anhydride groups for effective reactivity of the macromers with amines and other nucleophiles, copolymerized NiPAAm for temperature responsiveness and lipophilic stearate domains for increased hydrogel stability. Macromers were synthesized with different MA co-monomer feeds and oligomeric molecules (Mn below 5000 Da) were obtained with MA contents between 7% and 27% as determined by titration. The fraction of chemically intact anhydrides was calculated to range from 75% to 80%. The ability of the macromers to cross-link di- or oligovalent amines as a function of MA content was investigated rheologically. It was also demonstrated that monovalent amines, e.g. aminofluorescein, could be grafted to the macromer chain utilizing only a fraction of the anhydride functionalities. The derivatized macromers could still participate in cross-linking reactions due to the remaining anhydrides. Temperature sensitivity was shown for aqueous solutions of macromers with fully dissociated anhydride groups. The solutions were additionally responsive to changes in calcium ion concentration and pH. Extracts from macromer cross-linked polyether hydrogels showed no toxicity on L929 fibroblasts.The macromers have perspective as biocompatible cross-linkers for hydrogel fabrication from various biomacromolecules with the opportunity to decorate the gels with monoamine molecules that alter the biological or physico-chemical properties.     

Bacteria Loads from Point and Nonpoint Sources in an Urban Watershed

A pathogen impaired watershed in Houston, Tex., was studied to assess the spatial and temporal nature of point and nonpoint bacterial load contributions. End-of-pipe sampling at wastewater treatment plant effluent and storm sewers discharging under dry weather conditions was undertaken. Relatively low concentrations of E. coli were found in wastewater treatment effluent, with a geometric mean of 5 MPN/dL, while dry weather storm sewer discharges exhibited a geometric mean concentration of 212 MPN/dL. Loads from both point and nonpoint sources of E. coli were calculated and compared to in-stream bacteria loads. Nonpoint loads were estimated using an event mean concentration approach on an annual basis. Nonpoint source (NPS) loads were the primary source of bacteria loading to the bayou. Wastewater treatment plant and dry weather storm sewer loads, however, dominated in dry weather conditions. While NPS loads remained relatively constant from headwaters to the mouth of the bayou, point source loads exhibited greater spatial variability depending on the distribution of the discharging pipes. The study points to the need for spatial and temporal considerations in managing bacterial pollution in streams.     

Structures of Mn clusters

The geometries of several Mn clusters in the size range Mn₁₃-Mn{on23} are studied via the generalized gradient approximation to density functional theory. For the 13-and 19-atom clusters, the icosahedral structures are found to be most stable, while for the 15-atom cluster, the bcc structure is more favoured. The clusters show ferrimagnetic spin configurations.     

Variables influencing judgments of correlational relations.

Investigated the effects of 3 variables on 72 undergraduates' ability to assess correlational relations. These variables were (a) the form in which the stimulus information was presented (i.e., in continuous or binary form), (b) the actual magnitude of the correlation presented in the stimulus information, and (c) the Ss' expectancy concerning the relation in question. Ss judged the correlation between pairs of variables on the basis of serially presented items describing instances of their co-occurrence. Both direct estimates of correlation and phi coefficients derived from frequency estimates were used as measures of perceived covariation. Results indicate that Ss' estimates of correlation were significantly influenced by all 3 factors. Ss' judgments were sensitive to the difference between high and low correlations in the stimulus information, but they reflected this difference to a greater extent when the information was presented in binary, rather than continuous, form. Also, Ss made higher estimates of correlation when they expected the variables to be correlated than when they did not expect them to be correlated. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)