The longitudinal thickness of air-shower fronts

Linsely (1983) has proposed a technique for the detection and analysis of air showers at large distances from the shower axis based on a measurement of the shower front thickness and the assumption that this thickness is closely related to the core distance. Some of the problems involved with realizing such a technique were investigated, and some related observations are reported. The practical problems of how consistent the measurements of the shower front would be, how one would use the measurement, and how the rate of triggered events would depend on the minimum pulse width required are studied

Finding the Exact Maximum Impedance Resonant Frequency of a Practical Parallel Resonant Circuit without Calculus

A practical parallel resonant circuit has a resistor in series with an inductor, and that combination is in parallel with a capacitor. For such a circuit, it is well known that there are two possible definitions for the resonant frequency: (i) the resonant frequency , p f which is the frequency at which the phase of the total impedance is zero, and (ii) the resonant frequency m f , which is the frequency that achieves maximum magnitude of the total impedance. To find the latter traditionally requires calculus. However, in this paper, the authors show how m f can be found exactly without using calculus. By modifying a formula that is given as an approximation to m f in a popular technology textbook, an improvement in the accuracy of the approximation was achieved. Furthermore, a novel expression for the exact maximum impedance, as a function of Q = L /C / R.was derived. This has been approximated by previous authors as 2 RQ forQ ³ 10. However, in this report, the authors show that this approximation has a percentage error less than _2% forQ ³ 5, and less than −10% forQ ³ 2.Furthermore, it can be shown that the maximum impedance is also accurately approximated by ( ) 2 2 R Q 1+Q , which has an excellent percentage error performance, even forQ = 1, with a percentage error of only −4% for this value, and less than −0.6% forQ ³ 1.5. Finally, the authors used PSpice simulations to verify their results

Entropy concepts and DNA investigations

Topological and metric entropies of the DNA sequences from different organisms were calculated. Obtained results were compared each other and with ones of corresponding artificial sequences. For all envisaged DNA sequences there is a maximum of heterogeneity. It falls in the block length interval [5,7]. Maximum distinction between natural and artificial sequences is shifted on 1-3 position from the maximum of heterogeneity to the right as for metric as for topological entropy. This point on the specificity of real DNA sequences in the interval.Comment: 10 pages 7 figures submitted to PL

Quark structure of hadrons and high energy collisions

There exists a large field for phenomenological models in which the knowledge of the structure of hadrons in terms of QCD constituents obtained from deep inelastic scatterings is related to their behaviour in soft processes. One of the simplest and oldest models is the additive quark model, with the rules of quark statistics following from it. Originally, the relations of quark combinatorics for hadron yields were based on the qualitative description of a multiparticle production process as a process of the production of non-correlated quarks and antiquarks followed by their subsequent fusion into hadrons [20],[21]. As a large amount of new precision measurements appear, and, on the other hand, our understanding of QCD becomes deeper, a new level of understanding of quark-gluon physics in the region of soft interactions forces us to review the relations of quark combinatorics. To do so, an especially good possibility is provided by the experimental data for hadronic Z^0 decays which allow us to check the relations of quark combinatorics for a new type of processes: quark jets in the decays Z^0 -> q\bar{q} -> hadrons [32].Comment: 55 pages, 23 figure

Variety and Volatility in Financial Markets

We study the price dynamics of stocks traded in a financial market by considering the statistical properties both of a single time series and of an ensemble of stocks traded simultaneously. We use the $n$ stocks traded in the New York Stock Exchange to form a statistical ensemble of daily stock returns. For each trading day of our database, we study the ensemble return distribution. We find that a typical ensemble return distribution exists in most of the trading days with the exception of crash and rally days and of the days subsequent to these extreme events. We analyze each ensemble return distribution by extracting its first two central moments. We observe that these moments are fluctuating in time and are stochastic processes themselves. We characterize the statistical properties of ensemble return distribution central moments by investigating their probability density functions and temporal correlation properties. In general, time-averaged and portfolio-averaged price returns have different statistical properties. We infer from these differences information about the relative strength of correlation between stocks and between different trading days. Lastly, we compare our empirical results with those predicted by the single-index model and we conclude that this simple model is unable to explain the statistical properties of the second moment of the ensemble return distribution.Comment: 10 pages, 11 figure

Portfolio Optimization and the Random Magnet Problem

Diversification of an investment into independently fluctuating assets reduces its risk. In reality, movement of assets are are mutually correlated and therefore knowledge of cross--correlations among asset price movements are of great importance. Our results support the possibility that the problem of finding an investment in stocks which exposes invested funds to a minimum level of risk is analogous to the problem of finding the magnetization of a random magnet. The interactions for this ``random magnet problem'' are given by the cross-correlation matrix {\bf \sf C} of stock returns. We find that random matrix theory allows us to make an estimate for {\bf \sf C} which outperforms the standard estimate in terms of constructing an investment which carries a minimum level of risk.Comment: 12 pages, 4 figures, revte

The specialty choices of graduates from Brighton and Sussex Medical School: a longitudinal cohort study

BACKGROUND Since 2007 junior doctors in the UK have had to make major career decisions at a point when previously many had not yet chosen a specialty. This study examined when doctors in this new system make specialty choices, which factors influence choices, and whether doctors who choose a specialty they were interested in at medical school are more confident in their choice than those doctors whose interests change post-graduation. METHODS Two cohorts of students in their penultimate year at one medical school (n = 227/239) were asked which specialty interested them as a career. Two years later, 210/227 were sent a questionnaire measuring actual specialty chosen, confidence, influence of perceptions of the specialty and experiences on choice, satisfaction with medicine, personality, self-efficacy, and demographics. Medical school and post-graduation choices in the same category were deemed 'stable'. Predictors of stability, and of not having chosen a specialty, were calculated using bootstrapped logistic regression. Differences between specialties on questionnaire factors were analysed. RESULTS 50% responded (n = 105/277; 44% of the 239 Year 4 students). 65% specialty choices were 'stable'. Factors univariately associated with stability were specialty chosen, having enjoyed the specialty at medical school or since starting work, having first considered the specialty earlier. A regression found doctors who chose psychiatry were more likely to have changed choice than those who chose general practice. Confidence in the choice was not associated with stability. Those who chose general practice valued lifestyle factors. A psychiatry choice was associated with needing a job and using one's intellect to help others. The decision to choose surgical training tended to be made early. Not having applied for specialty training was associated with being lower on agreeableness and conscientiousness. CONCLUSION Medical school experiences are important in specialty choice but experiences post-graduation remain significant, particularly in some specialties (psychiatry in our sample). Career guidance is important at medical school and should be continued post-graduation, with senior clinicians supported in advising juniors. Careers advice in the first year post-graduation may be particularly important, especially for specialties which have difficulty recruiting or are poorly represented at medical school