Solar pumped laser

A solar pumped laser is described in which the lasant is a gas that will photodissociate and lase when subjected to sunrays. Sunrays are collected and directed onto the gas lasant to cause it to lase. Applications to laser propulsion and laser power transmission are discussed

Chaotic hysteresis in an adiabatically oscillating double well

We consider the motion of a damped particle in a potential oscillating slowly between a simple and a double well. The system displays hysteresis effects which can be of periodic or chaotic type. We explain this behaviour by computing an analytic expression of a Poincar'e map.Comment: 4 pages RevTeX, 3 PS figs, uses psfig.sty. Submitted to Phys. Rev. Letters. PS file also available at http://dpwww.epfl.ch/instituts/ipt/berglund.htm

Разработка способов, алгоритмов и программ обнаружения и исправления пакетных или независимых ошибок при передаче данных по каналам связи

Настоящая научно-квалификационная работа посвящена разработке способов, алгоритмов и программ обнаружения и исправления ошибок при передаче данных по каналам связи для обеспечения целостности и надёжности передаваемых команд и данных между устройствами вычислительно техники, а также при считывании данных из запоминающих устройств.The present scientific and qualification work is devoted to the development of methods, algorithms and programs for detecting and correcting errors in the transmission of data over communication channels to ensure the integrity and reliability of the transmitted commands and data between computing devices, as well as when reading data from memory devices

Ten‐Year Secular Trends in Youth Violence: Results From the Philadelphia Youth Risk Behavior Survey 2003‐2013

BACKGROUNDYouth violence reduction is a public health priority, yet few studies have examined secular trends in violence among urban youth, who may be particularly vulnerable to numerous forms of violence. This study examines 10‐year secular trends in the prevalence of violence‐related behaviors among Philadelphia high school students.METHODSRepeated cross‐sectional data were analyzed from 5 waves of the Philadelphia Youth Risk Behavior Survey (YRBS) from 2003 to 2013. Sex‐specific multivariate regression models were used to examine secular trends in multiple types of violence, accounting for age, race/ethnicity, and sampling strategy.RESULTSIn 2013, the most prevalent violent behavior was physical fighting among boys (38.4%) and girls (32.7%). Among girls, the prevalence of sexual assault and suicide attempts declined between 2003 and 2013 (β = −0.13, p = .04 and β = −0.14, p = .007, respectively). Among boys, significant declines in carrying a weapon (β = −0.31, p < .001), carrying a gun (β = −0.16, p = .01), and physical fighting (β = −0.35, p = .001) were observed.CONCLUSIONSWhereas the prevalence of some forms of violence stabilized or declined among Philadelphia youth during 2003‐2013 time span, involvement in violence‐related behaviors remains common among this population. Continued surveillance and evidence‐based violence reduction strategies are needed to address violence among urban youth.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136403/1/josh12491_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136403/2/josh12491.pd

Ab initio simulations of liquid systems: Concentration dependence of the electric conductivity of NaSn alloys

Liquid NaSn alloys in five different compositions (20, 40, 50, 57 and 80% sodium) are studied using density functional calculations combined with molecular dynamics(Car-Parrinello method). The frequency-dependent electric conductivities for the systems are calculated by means of the Kubo-Greenwood formula. The extrapolated DC conductivities are in good agreement with the experimental data and reproduce the strong variation with the concentration. The maximum of conductivity is obtained, in agreement with experiment, near the equimolar composition. The strong variation of conductivity, ranging from almost semiconducting up to metallic behaviour, can be understood by an analysis of the densities-of-states.Comment: LaTex 6 pages and 2 figures, to appear in J.Phys. Cond. Ma

Ab initio simulations of liquid NaSn alloys: Zintl anions and network formation

Using the Car-Parrinello technique, ab initio molecular dynamics simulations are performed for liquid NaSn alloys in five different compositions (20, 40, 50, 57 and 80 % sodium). The obtained structure factors agree well with the data from neutron scattering experiments. The measured prepeak in the structure factor is reproduced qualitatively for most compositions. The calculated and measured positions of all peaks show the same trend as function of the composition.\\ The dynamic simulations also yield information about the formation and stability of Sn$_4$ clusters (Zintl anions) in the liquid. In our simulations of compositions with 50 and 57 % sodium we observe the formation of networks of tin atoms. Thus, isolated tin clusters are not stable in such liquids. For the composition with 20 % tin only isolated atoms or dimers of tin appear, ``octet compounds'' of one Sn atom surrounded by 4 Na atoms are not observed.Comment: 12 pages, Latex, 3 Figures on reques