ABTRACTS 2000

To meet the requirements for stimulated rotational Raman scattering experiments, we constructed a high power, narrow bandwidth, passively Q-switched,

Nd:YAG laser.In order to obtain relatively high power and stable output, we increased the mode volume in a short cavity by introducing an intra-cavity telescope to

expand the beam through the gain medium.We used an intra-cavity etalon and relied on gain competition to achieve near single longitudinal mode operation.This

technique produced interesting laser output.In the non Q-switched cavity, we observed relaxation oscillations.After adding the Q-switch, we were able to produce

either multiple pulses or a single pulse per flash of the flashlamps.By directing the laser beam through two amplifiers, we acquired Q-switched output at 300

mJ/pulse with FWHM of 60 ns.

Differential scanning calorimetry was used to study the interdiffusion between copper and tin.The samples studied were trilayers comprised of two layers of copper

with one tin layer in between.Soldering flux was applied to the surfaces of the metals and then the layers were pressed together without codeformation.The samples

were hermetically sealed in an Al pan in an Ar atmosphere ata pressure under 10 Pa.A differential scanning calorimeter (Perkin-Elmer DSC-2 interfaced to a computer) heated the samples at a constant rate up to various temperatures between 500K and 610K.Data taken from the DSC was analyzed to determine the

temperature dependent reaction constant of the growing intermetallic.Several samples were quenched to room temperature at varying points throughout the run. Each of these specimens was placed in epoxy and polished.The cross section of each trilayer was examined by optical microscopy and SEM (scanning electron microscopy) in order to define each stage of the reaction.As suspected from previous studies, Cu6Sn5 grew initially, followed by Cu3Sn.Rates of reaction for

Cu6Sn5 were quantified in the preliminary stages of the reaction, where no Cu3Sn was observed to be growing.These reaction rates are compared to those

previously obtained for longer times and larger length scales.

The Drift Chambers of the Phenix Detector of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) are being constructed at

Stony Brook. The Drift Chamber uses 6400 wires to observe particles emitted from gold-gold nuclear collisions in the Phenix detector. To read and record the

signals received from these wires, each Drift Chamber is equipped with 160 ASD8-TMC circuit boards.Each board receives information from 40 wires. The

boards are built with six ASD8 chips (8 channel PreAmplifier, Shaper, and Discriminator chips) and ten TMC chips (Time Memory Cell chips). When an ASD8

chip receives a signal from a wire, it determines whether the signal is an actual signal or background noise.If it is found to be a real signal, the ASD8 chip sends a

logic pulse to the TMC chip. The TMC chip receives these pulses and records the time at which they are received. The information gathered from these chips is

then used to determine the paths of the particles emitted after the collisions. A procedure and testing protocol was established to determine the operational capability

of each of the circuit boards.

A single stage Hebbian neural network was created for use in perceptive experiments involving artificial intelligence.The network was designed to

actively assign weights to neurons depending on the sensory input. This gives a powerful way of dividing the perception space into manageable

sections.A multi-tiered approach was then used to further divide the perception space.This allowed coarse or fine information to be passed to

the rest of the artificial intelligence depending on relative importance.

We studied tracking and software development, with an emphasis on the search for better ways to find low momentum particles in detector event reconstruction.

We were interested in particle-antiparticle mixing in the neutral D-meson system. This particular decay has importance for matter-antimatter interactions, yet

study of it has been consistently hindered by poor event reconstruction. We wrote a software package called BinGo. BinGo is a portable, object-oriented set of pattern recognition tools written in C++ which uses a managing class called Scungili to organize the work of a variety of LayerSet objects that perform general track finding. We coded a first LayerSet class called DCTrack, which consists of a dictionary based algorithm designed for extremely fast track finding. The program divides the area of the detector into bins and then compares the hits found in an actual event against simulated detector data. We also developed a mechanism for different DCTrackLayerSet objects to communicate over the course of an event. Each LayerSet object can access a list of the hits used in tracks found by previousDCTrackLayerSets and then use this list to more efficiently filter out detector noise. We finally wrote a second LayerSet class force particle tracks into a spiral. The CurlerLayerSet keys in on the characteristic pattern of successive hits in a single layer of the detectorleft by these particles and reports these hits as a track. It also estimates the transverse momentum and original angular trajectory of the track as a function of the location of the turnover hits.

Five classical, or suspected classical Cepheids and two suspected beta Cepheids were observed utilizing the V, R and I filters of the Wellesley College 24’’

telescope between June and September 1999.My purpose was to determine the period of these variable stars, listed as unknown in the IBVS / GCVS catalog, and

further, to investigate the type of variability exhibited.During the process of calibrating and photometering these images in IRAF I discovered a CCD readout

problem and wrote programs to correct and salvage these images.Of the objects observed periods were determined for two.V1820 Cygni exhibits a light curve that

may disqualify it from the beta Cepheid category.Suspected delta Cepheid V651 Herculis proved to be an eclipsing binary system.