Discretized Energy Minimization in a Wave Guuide with point Sources

An anti-noise problem on a finite time interval is solved by minimization of a quadratic functional on the Hilbert space of square integrable controls. To this end, the one-dimensional wave equation with point sources and pointwise reflecting boundary conditions is decomposed into a system for the two propagating components of waves. Wellposedness of this system is proved for a class of data that includes piecewise linear initial conditions and piecewise constant forcing functions. It is shown that for such data the optimal piecewise constant control is the solution of a sparse linear system. Methods for its computational treatment are presented as well as examples of their applicability. The convergence of discrete approximations to the general optimization problem is demonstrated by finite element methods.     

Self‐phase‐locked degenerate femtosecond optical parametric oscillator based on BiB3O6

A self‐phase‐locked degenerate femtosecond optical parametric oscillator (OPO) based on the birefringent nonlinear material, bismuth triborate, BiB₃O₆, synchronously‐pumped by a Kerr‐lens‐mode‐locked Ti:sapphire laser at 800 nm is described. By exploiting versatile phase‐matching properties of BiB₃O₆, including large spectral and angular acceptance for parametric generation and low group velocity dispersion in the optical xz plane, stable self‐phase‐locked degenerate OPO operation centered at 1600 nm is demonstrated using collinear type I (e → oo) interaction in a 1.5‐mm crystal at room temperature. The degenerate OPO output spectrum extends over 46 nm (∼5.4 THz) with 190 fs pulse duration for input pump pulses of 155 fs with a bandwidth of 7 nm. Phase coherence between the pump and degenerate output is verified using f‐2f interferometry, and discrete frequency beats caused by different carrier‐envelope‐offset frequencies are measured using radio frequency measurements. Photo shows a 1.5‐mm BiB₃O₆ crystal used as a nonlinear gain medium in a degenerate self‐phase‐locked femtosecond OPO operating at room temperature. The green beam is the result of non‐phase‐matched sum‐frequency mixing between the pump light and the sub‐harmonic OPO field at degeneracy.     

Laser Stark Spectroscopy and Isotopic Separation

A potentially useful scheme for photoselective isotope enrichment is presented. The selective laser excitation step is accomplished by utilizing the Stark effect to shift molecular transitions into resonance with laser frequencies. The method is demonstrated for isotope separation of ¹³C, ¹⁵N and ²H. Laser Stark spectroscopy can sensitively detect as few as 10⁹ molecules in the optical path, thus the isotopic separation can be achieved from industrial sample mixtures containing natural abundances. A comparison of the isotopic enrichment efficiency using the present method of “exact” resonance and the previously used method of “near” resonance excitation is also given.     

An angular resolved pulsed UV LED photoelectron source for KATRIN

The KArlsruher TRItium Neutrino experiment KATRIN aims to determine the mass of the electron antineutrino with a sensitivity of 0.2 eV/c² on m(ν_e) at 90% confidence level by measuring the kinematics of the tritium beta decay with a spectrometer of MAC-E filter-type. To investigate the properties of the spectrometer, electron sources with special properties are needed. A pulsed UV LED photoelectron source with angular selectivity has been developed for this purpose. The principle has been successfully tested during measurements at the spectrometer of the Mainz neutrino mass experiment.     

New analytical and CWENO numerical solutions for axisymmetric horizontal flows with heat sources

Some new nonlinear analytical solutions are found for axisymmetric horizontal flows dominated by strong heat sources. These flows are common in multiscale atmospheric and oceanic flows such as hurricane embryos and ocean gyres. The analytical solutions are illustrated with several examples. The proposed exact solutions provide analytical support for previous numerical observations and can be also used as benchmark problems for validating numerical models. A central weighted essentially non-oscillatory (CWENO) reconstruction is also employed for numerical simulation of the corresponding integro-differential equations. Due to the use of the same polynomial reconstruction for all derivatives and integral terms, the balance between those terms is well preserved, and the method can precisely reproduce the exact solutions, which are hard to capture by traditional upwind schemes. The developed analytical solutions were employed to evaluate the performance of the numerical method, which showed an excellent performance of the numerical model in terms of numerical diffusion and oscillation.     

Gamma-ray astronomy by the air shower technique: Performance and perspectives

Summary The techniques for γ-ray astronomy at energies ≥10 TeV using air shower detectors are discussed. The results, based on a number of large arrays, are negative, with no point sources being identified. While the contributions to γ-ray astronomy so far have been only upper limits, these arrays in the future will make significant progress in the understanding of cosmic rays in the energy range 10¹³ eV to 10¹⁶ eV. Also, contributions to solar physics are being made by observations of shape and time dependence of the shadow of the Sun as observed in cosmic rays. For the advancement of γ-ray astronomy a greater sensitivity is required in the energy region of 10 TeV. A number of promising techniques to accomplish a greater sensitivity are discussed. They include the enlargement of the Tibet array at 4300 meters altitude, the array of open photomultipliers at La Palma (AIROBICC), which views the shower by the Cherenkov photons produced in the atmosphere, and the instrumentation of a pond at Los Alamos with photomultipliers (Milagro). Invited talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

成批排队在自相似流量中的应用

本针对当前的网络流量特征引入了成批排队的自相似流量模型M^X/D/1，得到了系统大小分布，等待时间分布及容量受限时的阻塞概率等，并结合实际网络流量的跟踪测试数据，进行了实验研究。     

Source Characteristics and Contaminant Plume Evolution

This study investigated how features of mass distribution within a source area control the pattern of contaminant plume evolution. A series of numerical trials was conducted which simulated contaminant migration in a three-dimensional saturated porous media with multiple source patches representing zones of contamination. Results showed that the extent of mixing near the source was greatly affected by both advection and dispersive mixing processes. The factors affecting the concentration distribution in the dissolved plume were size and distribution of source patches, dispersivity values, and the ratio of total patch area to the source area. The influence of dispersive mixing increased as the size of source patches decreased. However, dispersion was less important when patches were clustered or the ratio of total patch area to the source area increased. The variations in concentration values near the source, which were caused by differences in sizes and distribution of patches, diminished as the contaminant traveled further from the source. This result implies that detailed information on source characteristics generally would not be required beyond a certain travel distance. The exception in this regard is the ratio of total patch area to the source area, i.e., a zero-difference point. However, the location of this zero-difference point cannot be predicted easily because the location was affected by several source characteristics.     

Absolute continuity of information channels

Let [X, v, Y] be an abstract information channel with the input X = (X, ) and the output Y = (Y, ) which are measurable spaces, and denote by L(Y) = L(Y, ) the Banach space of all bounded signed measures with finite total variation as norm. The channel distribution ν(·,·) is considered as a function defined on (X, ) and valued in L(Y). It will be proved that, if the measurable space (Y, ) is countably generated, then the is a strongly measurable function from X into L(Y) if and only if there exists a probability measure μ on (Y, ) which dominates every measure ν(x, ·) (x X). Furthermore, under this condition, the Radon-Nikodym derivative ν(x, dy)/μ(dy) is jointly measurable with respect to the product measure space (X, , m) (Y, , μ) where m is any but fixed probability measure of (X, ). As an application, it will be shown that the channel given as above is uniformly approximated by channels of Hibert-Schmidt type.     

How Robust are the EGRET AGN gamma-ray identifications?

Summary Several AGNs have been proposed as identifications of gamma-ray sources discovered by CGRO. Using the NED database, we show that these AGNs are not the only extragalactic objects within the error boxes of the sources. Therefore, an in-depth study is needed on a case-by-case basis to access the most probable counterparts of the gamma-ray sources. A comparison with the COS-B database is also presented. 28Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.