Two Methods for Retrieving UV Index for All Cloud Conditions from Sky Imager Products or Total SW Radiation Measurements

Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern‐hemisphere mid‐latitude site where a 10‐years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short‐time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%).     

Oligonucleotide hybridization observed by surface plasmon optical techniques

Surface plasmon spectroscopy and microscopy are employed to study the hybridization reaction of an oligonucleotide ten-mer from solution to its complement immobilized to a solid support. It is shown that a dilute target monolayer is necessary to allow for an effective dimerization process. Parallel multi-site detection of the DNA binding is demonstrated to be possible with surface plasmon microscopy without the need for any extra labeling of the reaction partners. The simultaneous quantitative evaluation of the degree of dimerization to many different target areas, each as small as a few μm² and each functionalized by different oligonucleotide sequences, can be accomplished by two-dimensional image analysis and should be relevant for DNA sequencing protocols.     

UV radiation: balancing risks and benefits

We use action spectra published by the International Commission on Illumination to examine diurnal, seasonal and latitudinal variations in erythemally weighted (sunburning) UV-a health risk, and vitamin D-weighted UV-a health benefit. Vitamin D-weighted UV is more strongly dependent on ozone and solar zenith angle. Consequently, its diurnal, seasonal and geographic variability is more pronounced than for erythemally weighted UV. We then investigate relationships between the two quantities. An algorithm is developed and used to relate vitamin D production to the widely used UV index, to help the public to optimize their exposure to UV radiation. In the summer at noon, there should at mid-latitudes be sufficient UV to photosynthesize optimal vitamin D in approximately 1 min for full body exposure, whereas skin damage occurs after approximately 15 min. Further, while it should be possible to photosynthesize vitamin D in the winter at mid-latitudes, the amount of skin that must be exposed is larger than from the hands and face alone. This raises the question of whether the action spectrum for vitamin D production is correct, since studies have reported that production of vitamin D is not possible in the winter at mid-latitudes.     

The influence of nanoparticle fillers on the morphology of a spin-cast thin film polymer blend

Polymer/nanoparticle composite films are receiving growing attention thanks to their potential for application in ultra-thin electronic and optical devices. Polymer blend demixing has been shown to be a suitable technique for the structuring of polymer thin films and the patterning of nanoparticles (NP) within them. In this work we show that the morphology of thin polymer films made by spin-casting a polymer blend solution containing NP fillers on a surface depends strongly on the concentration of NP fillers. More specifically, polystyrene/polymethylmethacrylate (PS/PMMA) films formed from a toluene solution, and which demix following a nucleation and growth mechanism, were studied. It was found that both the height and the surface density of PMMA domains increased as the concentration of CoPt:Cu NPs in the film was increased. We find that similar effects are induced in a NP-free PS/PMMA demixed film upon increasing the molecular weight of the PS molecules. This suggests that under certain conditions the NPs and the polymer molecules in the blend do not behave as separate species but form aggregates.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

Existence and Uniqueness of Fixed Points for Markov Operators and Markov Processes

This paper concerns a Markov operator T on a space L₁, and aMarkov process P which defines a Markov operator on a spaceM of finite signed measures. For T, the paper presents necessaryand sufficient conditions for:

a the existence of invariant probabilitydensities (IPDs)

b the existence of strictly positive IPDs,and

c the existence and uniqueness of IPDs.

Similar resultson invariant probability measures for P are presented. The basicapproach is to pose a fixed-point problem as the problem ofsolving a certain linear equation in a suitable Banach space,and then obtain necessary and sufficient conditions for thisequation to have a solution. 1991 Mathematics Subject Classification:60J05, 47B65, 47N30.     

库仑加线性位基态解析解

应用新发展的单一轨迹积分方法求解库仑加线性位的基态量子波函数,得到基态能量和波函数的一般解析表达式,并讨论了解的收敛性.应用此方法讨论了重夸克偶素系统.