Level Crossing Analysis of the Stock Markets

We investigate the average frequency of positive slope $\nu_{\alpha}^{+}$, crossing for the returns of market prices. The method is based on stochastic processes which no scaling feature is explicitly required. Using this method we define new quantity to quantify stage of development and activity of stocks exchange. We compare the Tehran and western stock markets and show that some stocks such as Tehran (TEPIX) and New Zealand (NZX) stocks exchange are emerge, and also TEPIX is a non-active market and financially motivated to absorb capital.Comment: 6 pages and 4 figure

Light scattering from an amplifying medium bounded by a randomly rough surface: A numerical study

We study by numerical simulations the scattering of $s$-polarized light from a rough dielectric film deposited on the planar surface of a semi-infinite perfect conductor. The dielectric film is allowed to be either active or passive, situations that we model by assigning negative and positive values, respectively, to the imaginary part $\epsilon_2$ of the dielectric constant of the film. We study the reflectance ${\cal R}$ and the total scattered energy ${\cal U}$ for the system as functions of both $\epsilon_2$ and the angle of incidence of the light. Furthermore, the positions and widths of the enhanced backscattering and satellite peaks are discussed. It is found that these peaks become narrower and higher when the amplification of the system is increased, and that their widths scale linearly with $\epsilon_2$. The positions of the backscattering peaks are found to be independent of $\epsilon_2$, while we find a weak dependence on this quantity in the positions of the satellite peaks.Comment: Revtex, 9 pages, 9 figure

JUMPING STRATEGIES IN A VOLLEYBALL AND A BALLET SPECIFIC JUMP

INTRODUCTION The performance of a maximal vertical jump fram a static preparatory position (SQJ) or starting with a counter movement (CMJ) implies transformation of rotation about the hip, knee and ankle joints to a maximal translatory movement. Different strategies have been proposed for this transformation. Previously both sequential and simullaneous strategies have been proposed as optimal for maximal vertical jumping (1 & 2). The purpose of this study was to analyze ]umping strategies in a sport and dance specific maximal vertical jump. The hypothesis was that the technical demands of the Jumps would preset the strategy. Six male subjects participated in the study three professional ballet dancers and three elite volleyball players. In the ballet specific jump (BSJ) the legs were outward rotated, one foot was placed in front of and close to the other foot and the upper body kept upright. Three elite volleyball players performed the jump used for the smash (VSJ) including a three step preliminary run up and a farcefull arm swing. Afterwards all six subjects performed SQJ and CMJ. The ]umps were recorded on high speed film (500Hz) combined with registrations trom an AMTI force platform and EMG recordings from the major lower extremity muscles Net joint moments and joint work ware calculated by inverse dynamics. The strategy of the jumps was determined on the basis of angular kinematics and the pattern of nel joint moments of the two dominant joints RESULTS For BSJ the jumping height (h) was 0.22O.28m.The war!< contribution from the knee and ankle joint were 50-70% and 47-63% of the total work respectively while the work at the hip joint showed a negative contribution of 13-17% caused by a net hip flexor moment. Because of the specific ballet position the hip extension took place in the frontal plane and mgluteus maximus could not contribute to the extension. The concentric activity in mrectus femoris could partly explain the hip flexor moment. The knee and ankle joint initiated the extension phase simultaneously and the net joint moments peaked also simultaneously Therefore, the strategy could be defined as simultaneous. For VSJ h was 0.310.45m. The work contribution fram the knee and hip joints were 22-60% and 35-62% of the total work respectively. The hip joint began the extension phase before the body center of mass had reached its lowest position (sn The knee extension began 40-100ms after s.j. The peaks of the net joint moments of the hip and knee showed a similar pattern. Accordingly, the strategy could be defined as sequentiaL The sequential joint extension could partly be explained by the forcefull armswing pressing down and giving negative momentum in the downward phase and by this delaying the knee extension. In SQJ and CMJ h was 0.22-0.36m and 0.33-0AOm. The work contribution from the knee was 64.5%(SE 5.9) and 76.0% (SE 9.2) and from the hip 18.8% (SE 5.8) and 133% (SE 8.7). One ballet dancer and one volleyball player performed SQJ and CMJ with a simultaneous strategy while the otller four subjects used a sequential strategy. CONCLUSION In a maximal vertical jump fram ballet and from volleyball the technical demands preset the jumping strategy. When the subjects were asked to perform SQJ and CMJ the choice of strategy seemed individual and not connected to the training background. REFERENCES (1) Hudson, J.L. (1986). Med Sci. Sports Exerc, 18,242-251 (2) Babbert, M.F. & van lngen Schenau, G.J. (1986). J Biomechanics, 21, 249•26

Median Statistics, H_0, and the Accelerating Universe

(Abridged) We develop median statistics that provide powerful alternatives to chi-squared likelihood methods and require fewer assumptions about the data. Applying median statistics to Huchra's compilation of nearly all estimates of the Hubble constant, we find a median value H_0=67 km/s/Mpc. Median statistics assume only that the measurements are independent and free of systematic errors. This estimate is arguably the best summary of current knowledge because it uses all available data and, unlike other estimates, makes no assumption about the distribution of measurement errors. The 95% range of purely statistical errors is +/- 2 km/s/Mpc. The statistical precision of this result leads us to analyze the range of possible systematic errors in the median, which we estimate to be roughly +/- 5 km/s/Mpc (95% limits), dominating over the statistical errors. A Bayesian median statistics treatment of high-redshift Type Ia supernovae (SNe Ia) apparent magnitude versus redshift data from Riess et al. yields a posterior probability that the cosmological constant Lambda > 0 of 70 or 89%, depending on the prior information used. The posterior probability of an open universe is about 47%. Analysis of the Perlmutter et al. high-redshift SNe Ia data show the best-fit flat-Lambda model favored over the best-fit Lambda = 0 open model by odds of 366:1; corresponding Riess et al. odds are 3:1 (assuming prior odds of 1:1).Median statistics analyses of the SNe Ia data do not rule out a time-variable Lambda model, and may even favor it over a time-independent Lambda and a Lambda = 0 open model.Comment: Significant revisions include discussion of systematic errors in the median of H_0. Accepted for publication in The Astrophysical Journal, v548, February 20, 2001 issue. 47 pages incl. figures and table