Gaseous Electronics

Contains research objectives and reports on one research project.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E

Achromatic Emission Velocity Measurements in Luminous Flows

A new velocity measurement instrument for luminous flows was developed by Science Research Laboratory for NASA. The SIEVE (Segmented Image Emission VElocimeter) instrument uses broadband light emitted by the flow for the velocity measurement. This differs from other velocimetry techniques in that it does not depend on laser illumination and/or light scattering from particles in the flow. The SIEVE is a passive, non-intrusive diagnostic. By moving and adjusting the imaging optics, the SIEVE can provide three-dimensional mapping of a flow field and determine turbulence scale size. A SIEVE instrument was demonstrated on an illuminated rotating disk to evaluate instrument response and noise and on an oxy-acetylene torch to measure flame velocities. The luminous flow in rocket combustors and plumes is an ideal subject for the SIEVE velocity measurement technique

Gaseous Electronics

Contains reports on two research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E

Multi-user interference mitigation under limited feedback requirements for WCDMA systems with base station cooperation

One of the techniques that has been recently identified for dealing with multi-user interference (MUI) in future communications systems is base station (BS) cooperation or joint processing. However, perfect MUI cancellation with this technique demands severe synchronization requirements, perfect and global channel state information (CSI), and an increased backhaul and signaling overhead. In this paper, we consider a more realistic layout with the aim of mitigating the MUI, where only local CSI is available at the BSs. Due to synchronization inaccuracies and errors in the channel estimation, the system becomes partially asynchronous. In the downlink of wideband code division multiple access based systems, this asynchronism stands for the loss of the orthogonality of the spreading codes allocated to users and thus, for an increase in the MUI level of the system. In this contribution, we propose a framework for mitigating the MUI which builds in three main steps: definition of a cooperation area based on the channel characteristics, statistical modeling of the average MUI power experienced by each user and a specific spreading code allocation scheme for users served with joint processing. This code allocation assigns spreading codes to users in such a way that minimum average cross-correlation between active users can be achieved. Interestingly, these steps can be performed with a limited amount of extra feedback from the user's side

ENERGY ABSORPTION AND VIBRATIONAL HEATING IN MOLECULES FOLLOWING INTENSE LASER EXCITATION

$^{1}$ C. R. Jones and H. P. Broida, J. Chem. Phys. 60, 4369 (1974). This work was supported, in part, by the Air Force Office of Scientific Research and the National Science Foundation.Author Institution: Massachusetts Institute of Technology; Los Alamos Scientific Laboratory, Univeresity of California; Los Alamos Scientific Laboratory, Columbia UniversityResonant absorption of energy from an intense laser pulse and its distribution in high vibrational states of the absorbing molecules have been studied in the regime where V-V collisions populate high-lying vibrationa1 states. The model assumes that the pulse duration $T_{p} \gg T_{vv}, T_{vt} \gg T_{p}$, and that the pulse equalized $n_{0}$ and $n_{1}, n_{v}$, being the population of $|v{>}$. The number of absorbed quanta/mol. is then calculated to be $(1 - n_{1})^{2}$, with $1/n^{2}_{1} + 4(1n \ 2n_{1}) = 4 + T_{p}/T_{vv}$. To test the theory, the absorption of a 0.1J 2-4 $\mu$sec P(32) $CO_{2}$ laser pulse by the $\nu 3(v =0 \rightarrow 1)$ fundamental of $CH_{3}F$ is being studied. The observed absorption of 2-3 quanta/mol. implies $T_{vv} \sim 1 \ \mu$sec-Torr, Evidence that all energy goes into vibrations has been obtained by measuring the vibrational temperature $(T_{v})$ using a new laser-induced fluorescence technique. Measurements show $T_{v} \simeq 2000^\circ K$, in good agreement with model