Photoluminescence of hydrophilic silicon nanocrystals in aqueous solutions

Stable aqueous solutions of undecylenic-acid-grafted silicon nanocrystals (Si-nc) were prepared. The time evolution of the photoluminescence properties of these hydrophilic silicon nanocrystals has been followed on different timescales (hours and days). On a short timescale (hours), Si-nc tend to agglomerate while the PL lineshape and intensity are stable. Agglomeration can be reduced by using suitable surfactants. On a long timescale (days), oxidation of Si-nc occurs even in the presence of surfactants. These two observations render Si-nc very useful as a labeling agent for biosensing.     

杰昆·索罗拉火车站,巴伦西亚,西班牙

何谓永恒城市与火车之间的爱恨情仇/关系源远流长,有过激情四溢的乐章,也有过痛苦折磨的片断,有过甜蜜美好的瞬间,也有公诸于众的背叛。而今,两者之间的关系历经变化,今非昔比。然而在巴伦西亚的杰昆·索罗拉火车站,城市与火车之间的激情烈焰仍在燃烧。新车站在允许高速火车进行停靠的同时,完成了将铁轨迁入地下的工程:     

广告,从中国文化中脱颖而出

广告是源于生活,又从生活中升华的艺术.中国广告的奇花异葩也只有在中国肥沃的历史文化土壤中才能茁壮成长.在这则美的空调的广告中,聪明又简单的创意,直接而真实的视觉演绎以及亲切又幽默的概念传达,让你看后回味无穷.     

Impact modification of polypropylene

This paper compares the modification mechanism provided by ethylene‐octene (EO) copolymer to that of ethylene‐propylene‐diene terpolymer (EPDM) rubber. Within the limits of this study, the highest impact strength was achieved at 30–40% rubber content, regardless of the rubber type. An increase in rubber melt viscosity resulted in overall greater impact strength. At the optimum concentration, the high‐viscosity (MFI = 1 to 5) EO rubber provided modification mainly via a crazing mechanism, while the EPDM rubber functioned by energy dissipation through the three‐dimensional network structure formed with the polypropylene matrix. This paper also discusses the effects of the processing conditions on the physical properties of PP/EPR copolymer. An increase in processing temperature and screw speed resulted in a reduced number of discrete rubber particles and nearly no or very slight increase in impact strength, but a very significant reduction in tensile strength and tensile modulus.     

Polymere und Copolymere mit reaktionsfähigen Gruppen. Copolymerisation von Glycidyl-β-methylitaconat und Styrol

In part I of this series the results of sedimentation velocity experiments with the polyelectrolyte Polyvinylpyrrolidone-Blancophor are described. The combination of the Svedberg formula and an equation of Tiselius describing the charge- and salt-effects gives the possibility to describe the change of the frictional coefficient as a function of charge and screening quantitatively. The resulting frictional coefficients resp. the dimensions of the coil of this polyelectrolyte change in a wide range with the charge density and the counterion concentration.     

Comparison of QUV accelerated weathering to outdoor exposure for PVC compounds

Weathering characteristics of the PVC compounds used for exterior applications, such as house siding, window and door frames, must be determined in order to predict their performance in actual use. In this study color weatherability of various PVC compounds, determined in the QUV accelerated weatherometer, was compared to the outdoor exposure in Arizona, Ohio, and Florida. The effect of the compound base formulation and color on correlation of the QUV to the outdoor weathering has been also analyzed.     

Predicting heat buildup due to the sun's energy

PVC building products such as siding, windows, and roofings are exposed to the sun. Absorption of the sun's energy leads to a temperature rise, which may cause dimensional control problems, such as expansion and, in severe cases, distortion of the PVC products. The amount of heat buildup in the product depends on the color and/or pigment system of the PVC compound. Generally, the darker the color, the more the sun's energy is absorbed and the higher the temperature heat buildup. Because of the growing demand for darker colors of PVC building products, a test for measuring temperature rise to predict performance of the product in actual use is needed. A laboratory test method for predicting maximum heat buildup due to the sun is described in this paper. The effects of the sample thickness and gloss, carbon black and titanium dioxide levels, and the distance of an infrared heat source from the sample on the heat buildup are also presented in the paper.     

Weakly useful sequences

An infinite binary sequence x is defined to be

(i) strongly useful if there is a computable time bound within which every decidable sequence is Turing reducible to x; and

(ii) weakly useful if there is a computable time bound within which all the sequences in a non-measure 0 subset of the set of decidable sequences are Turing reducible to x.

Juedes, Lathrop, and Lutz [Theorectical Computer Science 132 (1994) 37] proved that every weakly useful sequence is strongly deep in the sense of Bennett [The Universal Turing Machine: A Half-Century Survey, 1988, 227] and asked whether there are sequences that are weakly useful but not strongly useful. The present paper answers this question affirmatively. The proof is a direct construction that combines the martingale diagonalization technique of Lutz [SIAM Journal on Computing 24 (1995) 1170] with a new technique, namely, the construction of a sequence that is “computably deep” with respect to an arbitrary, given uniform reducibility. The abundance of such computably deep sequences is also proven and used to show that every weakly useful sequence is computably deep with respect to every uniform reducibility.

Poly (vinyl chloride) processing morphology

This paper describes how morphology of PVC changes in the Brabender mixing head. At the range of temperatures used for PVC processing, the Brabender torque-time curve shows minimum torque and maximum torque. The minimum torque is associated with a breakdown of 150 μm PVC grains and 10 μm agglomerates resulting in the release of the 1μm primary particles. The torque increases from minimal interaction between primary particles to the point where primary particles agglomerate at maximum torque so that fibriles can be formed when PVC samples are swollen in acetone and sheard. Further heating reduces the viscosity resulting in lower torque even though residual primary particles still exist with much particle to particle interaction. Primary particle structure disappears at about 215° C with complete melting.     

Caffeine (1, 3, 7-trimethylxanthine) in Foods: A Comprehensive Review on Consumption,Functionality, Safety,and Regulatory Matters

ABSTRACT: Caffeine ranks as one of the top most commonly consumed dietary ingredients throughout the world. It is naturally found in coffee beans, cacao beans, kola nuts, guarana berries, and tea leaves including yerba mate. The total daily intake, as well as the major source of caffeine varies globally; however, coffee and tea are the 2 most prominent sources. Soft drinks are also a common source of caffeine as well as energy drinks, a category of functional beverages. Moderate caffeine consumption is considered safe and its use as a food ingredient has been approved, within certain limits, by numerous regulatory agencies around the world. Performance benefits attributed to caffeine include physical endurance, reduction of fatigue, and enhancing mental alertness and concentration. Caffeine has also been recently linked to weight loss and consequent reduction of the overall risks for developing the metabolic syndrome. However, the caloric contribution of caffeine-sweetened beverages needs to be considered in the overall energy balance. Despite all these benefits the potential negative effects of excessive caffeine intake should also be considered, particularly in children and pregnant women.