Man's flight in space

Apollo project - progress and national benefit

[NASA's Manned Flight Programs- Gemini and Apollo] News Release

Manned space flight research projects - Gemini and Apoll

Extinction for two parabolic stochastic PDE's on the lattice

It is well known that, starting with finite mass, the super-Brownian motion dies out in finite time. The goal of this article is to show that with some additional work, one can prove finite time die-out for two types of systems of stochastic differential equations on the lattice Z^d. Our first system involves the heat equation on the lattice Z^d, with a nonlinear noise term u(t,x)^gamma dB_x(t), with 1/2 <= gamma < 1. The B_x are independent Brownian motions. When gamma = 1/2, the measure which puts mass u(t,x) at x is a super-random walk and it is well-known that the process becomes extinct in finite time a.s. Finite-time extinction is known to be a.s. false if gamma = 1. For 1/2 < gamma < 1, we show finite-time die-out by breaking up the solution into pieces, and showing that each piece dies in finite time. Our second example involves the mutually catalytic branching system of stochastic differential equations on Z^d, which was first studied by Dawson and Perkins. Roughly speaking, this process consists of 2 superprocesses with the continuous time simple random walk as the underlying spatial motion. Furthermore, each process stimulates branching and dying in the other process. By using a somewhat different argument, we show that, depending on the initial conditions, finite time extinction of one type may occur with probability 0, or with probability arbitrarily close to 1

The Helios mechanical despin drive assembly for the high-gain antenna reflector

Helios is the German-American solar probe which comes within 0.31 Astronomical Units of the sun. A special thermal design and a dry lubrication system have resulted in successful operation up to now, with Helios having finished its first orbit around the sun

A lattice test of strong coupling behaviour in QCD at finite temperature

We propose a set of lattice measurements which could test whether the deconfined, quark-gluon plasma, phase of QCD shows strong coupling aspects at temperatures a few times the critical temperature for deconfinement, in the region where the conformal anomaly becomes unimportant. The measurements refer to twist-two operators which are not protected by symmetries and which in a strong-coupling scenario would develop large, negative, anomalous dimensions, resulting in a strong suppression of the respective lattice expectation values in the continuum limit. Special emphasis is put on the respective operator with lowest spin (the spin-2 operator orthogonal to the energy-momentum tensor within the renormalization flow) and on the case of quenched QCD, where this operator is known for arbitrary values of the coupling: this is the quark energy-momentum tensor. The proposed lattice measurements could also test whether the plasma constituents are pointlike (as expected at weak coupling), or not.Comment: 16 page

Light-like mesons and deep inelastic scattering in finite-temperature AdS/CFT with flavor

We use the holographic dual of a finite-temperature, strongly-coupled, gauge theory with a small number of flavors of massive fundamental quarks to study meson excitations and deep inelastic scattering (DIS) in the low-temperature phase, where the mesons are stable. We show that a high-energy flavor current with nearly light-like kinematics disappears into the plasma by resonantly producing mesons in highly excited states. This mechanism generates the same DIS structure functions as in the high temperature phase, where mesons are unstable and the current disappears through medium-induced parton branching. To establish this picture, we derive analytic results for the meson spectrum, which are exact in the case of light-like mesons and which corroborate and complete previous, mostly numerical, studies in the literature. We find that the meson levels are very finely spaced near the light-cone, so that the current can always decay, without a fine-tuning of its kinematics.Comment: 43 pages, 6 figure

CCD-photometry of comets at large heliocentric distances

CCD imaging and time series photometry are used to determine the state of activity, nuclear properties and eventually the rotational motion of cometary nuclei. Cometary activity at large heliocentric distances and mantle evolution are not yet fully understood. Results of observations carried out at the 2.1 telescope on Kitt Peak April 10-12 and May 15-16, 1991 are discussed. Color values and color-color diagrams are presented for several comets and asteroids. Estimations of nuclear radii and shapes are given