The GEO 600 laser system

Interferometric gravitational wave detectors require high optical power, single frequency lasers with very good beam quality and high amplitude and frequency stability as well as high long-term reliability as input light source. For GEO 600 a laser system with these properties is realized by a stable planar, longitudinally pumped 12 W Nd:YAG rod laser which is injection-locked to a monolithic 800 mW Nd:YAG non-planar ring oscillator. Frequency control signals from the mode cleaners are fed to the actuators of the non-planar ring oscillator which determines the frequency stability of the system. The system power stabilization acts on the slave laser pump diodes which have the largest influence on the output power. In order to gain more output power, a combined Nd:YAGNd:YVO4 system is scaled to more than 22 W

Error Estimates on Parton Density Distributions

Error estimates on parton density distributions are presently based on the traditional method of least squares minimisation and linear error propagation in global QCD fits. We review the underlying assumptions and the various mathematical representations of the method and address some technical issues encountered in such a global analysis. Parton distribution sets which contain error information are described.Comment: Latex, 12 pages, 5 figures. Needs iopart.cls and iopart12.clo. Presented at New Trends in HERA Physics 2001, Ringberg Castle, Tegernsee, Germany, June 17-22, 200

Strong Effects of Network Architecture in the Entrainment of Coupled Oscillator Systems

Entrainment of randomly coupled oscillator networks by periodic external forcing applied to a subset of elements is numerically and analytically investigated. For a large class of interaction functions, we find that the entrainment window with a tongue shape becomes exponentially narrow for networks with higher hierarchical organization. However, the entrainment is significantly facilitated if the networks are directionally biased, i.e., closer to the feedforward networks. Furthermore, we show that the networks with high entrainment ability can be constructed by evolutionary optimization processes. The neural network structure of the master clock of the circadian rhythm in mammals is discussed from the viewpoint of our results.Comment: 15 pages, 11 figures, RevTe

Pair distribution function in a two-dimensional electron gas

We calculate the pair distribution function, $g(r)$, in a two-dimensional electron gas and derive a simple analytical expression for its value at the origin as a function of $r_s$. Our approach is based on solving the Schr\"{o}dinger equation for the two-electron wave function in an appropriate effective potential, leading to results that are in good agreement with Quantum Monte Carlo data and with the most recent numerical calculations of $g(0)$. [C. Bulutay and B. Tanatar, Phys. Rev. B {\bf 65}, 195116 (2002)] We also show that the spin-up spin-down correlation function at the origin, $g_{\uparrow \downarrow}(0)$, is mainly independent of the degree of spin polarization of the electronic system.Comment: 5 figures, pair distribution dependence with distance is calculate

Superconducting Volume Fraction in Overdoped Regime of La_2-x_Sr_x_CuO_4_: Implication for Phase Separation from Magnetic-Susceptibility Measurement

We have grown a single crystal of La_2-x_Sr_x_CuO_4_ in which the Sr concentration, x, continuously changes from 0.24 to 0.29 in the overdoped regime and obtained many pieces of single crystals with different x values by slicing the single crystal. From detailed measurements of the magnetic susceptibility, chi, of each piece, it has been found that the absolute value of chi at the measured lowest temperature 2 K, |chi_2K_|, on field cooling rapidly decreases with increasing x as well as the superconducting (SC) transition temperature. As the value of |chi_2K_| is regarded as corresponding to the SC volume fraction in a sample, it has been concluded that a phase separation into SC and normal-state regions occurs in a sample of La_2-x_Sr_x_CuO_4_ in the overdoped regime.Comment: 4 pages, 3 figures, ver. 2 has been accepted in J. Phys. Soc. Jp

Bounds on the cosmogenic neutrino flux

Under the assumption that some part of the observed highest energy cosmic rays consists of protons originating from cosmological distances, we derive bounds on the associated flux of neutrinos generated by inelastic processes with the cosmic microwave background photons. We exploit two methods. First, a power-like injection spectrum is assumed. Then, a model-independent technique, based on the inversion of the observed proton flux, is presented. The inferred lower bound is quite robust. As expected, the upper bound depends on the unknown composition of the highest energy cosmic rays. Our results represent benchmarks for all ultrahigh energy neutrino telescopes.Comment: 12 pages, 6 figure

Efeito da adubação nitrogenada e altura de corte sobre o capim tanzânia

The aim of this work was the evaluation of production and quality of  Panicum maximum  Jacq. cv. Tanzania as a function of height of cut and nitrogen feeding. The experiment was installed in vase inside greenhouse, in Presidente Prudente-SP, during the period of april to october 2007. The design was random blocks with ten treatments arranged in a factorial scheme of five nitrogen doses (0, 20, 40, 80 e 160 kg ha-1) and two cutting height (20 e 40 cm). The nitrogen was applied per crop cycle. The first was made at 45 days after emergence when they were harvested for leveling, and the other two applications were made shortly after the first and second cut, with the interval between cycles of 35 days, used urea. With the cutting height of Panicum maximum at 20 cm soil were the highest yields of dry matter in the three cycles of crops. The highest dry matter yield cut at 20 cm were obtained with intermediate doses of N, different from plants cut to 40 cm, where the maximum yields of dry matter were achieved at the highest N rate applied in all cutting cycles. The largest of Panicum maximum  tillering and higher responses to nitrogen fertilization on the production of tillers occurred in the first cycle, regardless of cutting height. The crude protein content was influenced by nitrogen levels in the first cycle and the cutting height to 20 cm, reaching a maximum level of crude protein (12.5%) with application of 80 kg ha-1 N.O trabalho objetivou avaliar produção e qualidade do capim Tanzânia em razão da altura de corte e adubação nitrogenada. O experimento foi conduzido em vasos, em casa de vegetação, no município de Presidente Prudente-SP, durante os meses de abril a outubro de 2007. O delineamento experimental foi em blocos ao acaso, em esquema fatorial 5x2, sendo cinco doses de nitrogênio (0, 20, 40, 80 e 160 kg ha-1) e duas alturas de cortes (20 e 40 cm). O nitrogênio foi aplicado por ciclo de cultivo, ou seja, aos 45 dias após a emergência quando foi realizado o corte de nivelamento, e as outras duas aplicações foram realizadas logo após o primeiro e segundo corte, com intervalo entre ciclos de 35 dias, sendo utilizado uréia. Com a altura de corte a 20 cm do solo ocorreram as maiores produções de matéria seca nos três ciclos de cultivos. As maiores produções de matéria seca de Panicum maximum cortadas a 20 cm foram obtidas com doses  intermediárias de N, diferente das plantas cortadas a 40 cm, em que as produções máximas de matéria seca foram alcançadas com a maior dose de N aplicada, em todos os ciclos de corte. O maior perfilhamento de Panicum maximum e as maiores respostas à adubação nitrogenada quanto à produção de perfilhos ocorreram no primeiro ciclo de cultivo, independente da altura de corte. O teor de proteína bruta foi influenciado pelas doses de nitrogênio no primeiro ciclo e na altura de corte a 20 cm, alcançando teor máximo de proteína bruta (12,5%) com a aplicação de 80 kg ha-1 de N