Electrical and radiation characteristics of semilarge photoconductive terahertz emitters

We present experimental characterization of semilarge photoconductive emitters, including their electrical/photoconductive parameters and terahertz spectra. A range of emitters were studied and fabricated on both LT-GaAs and SI-GaAs, having a variety of electrode geometries. The spatial cone of terahertz radiation was defined. The dependencies of the photocurrent and the terahertz power on the bias voltage and the laser power were determined. A Fourier-transform interferometer is used to determine the terahertz spectra and to clarify the effects of the substrate and electrode geometry

Scaling property and peculiar velocity of global monopoles

We investigate the scaling property of global monopoles in the expanding universe. By directly solving the equations of motion for scalar fields, we follow the time development of the number density of global monopoles in the radiation dominated (RD) universe and the matter dominated (MD) universe. It is confirmed that the global monopole network relaxes into the scaling regime and the number per hubble volume is a constant irrespective of the cosmic time. The number density $n(t)$ of global monopoles is given by $n(t) \simeq (0.43\pm0.07) / t^{3}$ during the RD era and $n(t) \simeq (0.25\pm0.05) / t^{3}$ during the MD era. We also examine the peculiar velocity $v$ of global monopoles. For this purpose, we establish a method to measure the peculiar velocity by use of only the local quantities of the scalar fields. It is found that $v \sim (1.0 \pm 0.3)$ during the RD era and $v \sim (0.8 \pm 0.3)$ during the MD era. By use of it, a more accurate analytic estimate for the number density of global monopoles is obtained.Comment: 17 pages, 8 figures, to appear in Phys. Rev.

Two types of S phase precipitates in Al-Cu-Mg alloys

Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) have been used to study S phase precipitation in an Al-4.2Cu-1.5Mg-0.6Mn-0.5Si (AA2024) and an Al-4.2Cu-1.5Mg-0.6Mn-0.08Si (AA2324) (wt-%) alloy. In DSC experiments on as solution treated samples two distinct exothermic peaks are observed in the range 250 to 350°C, whereas only one peak is observed in solution treated and subsequently stretched or cold worked samples. Samples heated to 270°C and 400°C at a rate of 10°C/min in the DSC have been studied by TEM. The selected area diffraction patterns show that S phase precipitates with the classic orientation relationship form during the lower temperature peak, and for the solution treated samples, the higher temperature peak is caused by the formation of a second type of S phase precipitates which have an orientation relationship that is rotated by ~4 degrees to the classic one. The effects of Si and cold work on the formation of second type of S precipitates have been discussed

On homogeneous statistical distributions exoplanets for their dynamic parameters

Correct distributions of extrasolar systems for their orbital parameters (semi-major axes, period, eccentricity) and physical characteristics (mass, spectral type of parent star) are received. Orbital resonances in extrasolar systems are considered. It is shown, that the account of more thin effects, including with use of wavelet methods, in obviously incorrectly reduced distributions it is not justified, to what the homogeneous statistical distributions for dynamic parameters of exoplanets, received in the present work, testify.Comment: 9 pages, 15 figures; International Conference "100 years since Tunguska phenomenon: Past, present and future", (June 26-28, 2008. Russia, Moscow), Lomonosov readings 2009 (Moscow State University

The effects of man-marking on work intensity in small-sided soccer games

The aim of this study was to examine the effect of manipulating defensive rules: with and without man-marking (MM and NMM) on exercise intensity in 3 vs. 3 small-sided games (SSGs). Twelve adolescent soccer players (age: 16.2 ± 0.7 years; body mass: 55.7 ± 6.4 kg; body height: 1.70 ± 0.07 m) participated in this repeated measures study. Each participant performed in four different SSGs formats: 3 vs. 3 MM with and without goals and 3 vs. 3 NMM with and without goals. Each SSG lasted 3 x 4 minutes interspersed with 4 minutes passive recovery. The percentage heart rate reserve (%HRreserve) was recorded continuously during SSG and session-rating of perceived exertion (session-RPE) after the SSG. MANOVA showed that defensive rule had significant effects on intensity (F = 5.37, p < 0.01). Specifically, MM during SSG induced significantly higher %HRreserve compared to NMM (Goal: 80.5 vs. 75.7%; No goal: 80.5 vs. 76.1%; p < 0.05, effect size = 0.91-1.06), irrespective of the presence or absence of goals. However, only MM with the presence of goals induced significant higher session-RPE compared to NMM (7.1 vs. 6.0; p < 0.05, effect size = 1.36), whereas no difference in session-RPE was observed between MM and NMM (7.4 vs. 6.9; p > 0.05, effect size = 0.63) when no goals were used. Higher intra-class reliability and lower coefficient of variation values were also reported in MM as compared to NMM. This study in youth soccer players shows there is ~4.5% increase in heart rate response by using the man-marking in 3 vs. 3 SSG thus the intensity of SSG can be significantly increased when using man-marking tactics

Spatial period-multiplying instabilities of hexagonal Faraday waves

A recent Faraday wave experiment with two-frequency forcing reports two types of `superlattice' patterns that display periodic spatial structures having two separate scales. These patterns both arise as secondary states once the primary hexagonal pattern becomes unstable. In one of these patterns (so-called `superlattice-II') the original hexagonal symmetry is broken in a subharmonic instability to form a striped pattern with a spatial scale increased by a factor of 2sqrt{3} from the original scale of the hexagons. In contrast, the time-averaged pattern is periodic on a hexagonal lattice with an intermediate spatial scale (sqrt{3} larger than the original scale) and apparently has 60 degree rotation symmetry. We present a symmetry-based approach to the analysis of this bifurcation. Taking as our starting point only the observed instantaneous symmetry of the superlattice-II pattern presented in and the subharmonic nature of the secondary instability, we show (a) that the superlattice-II pattern can bifurcate stably from standing hexagons; (b) that the pattern has a spatio-temporal symmetry not reported in [1]; and (c) that this spatio-temporal symmetry accounts for the intermediate spatial scale and hexagonal periodicity of the time-averaged pattern, but not for the apparent 60 degree rotation symmetry. The approach is based on general techniques that are readily applied to other secondary instabilities of symmetric patterns, and does not rely on the primary pattern having small amplitude

Photoelectron diffraction: from phenomenological demonstration to practical tool

The potential of photoelectron diffraction—exploiting the coherent interference of directly-emitted and elastically scattered components of the photoelectron wavefield emitted from a core level of a surface atom to obtain structural information—was first appreciated in the 1970s. The first demonstrations of the effect were published towards the end of that decade, but the method has now entered the mainstream armoury of surface structure determination. This short review has two objectives: First, to outline the way that the idea emerged and the way this evolved in my own collaboration with Neville Smith and his colleagues at Bell Labs in the early years: Second, to provide some insight into the current state-of-the art in application of (scanned-energy mode) photoelectron diffraction to address two key issue in quantitative surface structure determination, namely, complexity and precision. In this regard a particularly powerful aspect of photoelectron diffraction is its elemental and chemical-state specificity

Evaluation of sweetpotato (Ipomoea batatas (L.) Lam.) germplasm from north-eastern Uganda through a Farmer Participatory Approach

Ugandan farmers grow many landrace sweetpotato varieties, but some of these are relatively low yielding and susceptible to pests. The objective of the present research was to involve farmers in a large-scale assessment of Ugandan farmers’ varieties to rapidly identify those with superior yield performance, pest resistance and consumer acceptance. One hundred sixty distinct farmers’ varieties collected from Lira, Soroti, Katakwi, Kumi and Pallisa Districts of North-eastern Uganda were evaluated in on-station trials. Trials were conducted at two sites (Serere Agricultural and Animal Research Institute and Arapai Agricultural College) in Soroti District in the second rainy season of 1999. Twenty-five farmers from surrounding areas participated in trial harvest at each site. At harvest, fresh storage root yield, foliage yield, and dry matter content were determined by researchers. Farmers observed a number of characteristics and rated each entry with respect to the following variables: general impression, dry matter content, pests, and defects. A strong positive correlation was observed between farmers’ general impression and yield and harvest index in the trials. Farmers selected 10 superior varieties from each trial for further multi-environment, on-station and on-farm trials. Coincidentally, nine of the selected varieties were common to both sites