Addition of hydroperoxy-alkyl radicals to molecular oxygen leads to chain branching in autoignition and engine knock, and in low temperature oxidation of paraffins. Rate constants and product channels for reaction of hydroperoxy-propyl radicals with O{sub 2} are estimated using thermodynamic properties, bimolecular quantum Kassel analysis and transition state theory. Thermochemistry of relevant molecules and radicals is estimated using group additivity and bond dissociation groups for radicals. Results show that rates of the hydroperoxy-propyl radical addition to O{sub 2} are near their high pressure limits at {ge} 1 atm. Main products at 1--15 atm are stabilization, reverse reaction to hydroperoxy-propyl + O{sub 2} and alkyl carbonyl + OH. Reactions of the stabilized adducts, dissociation rates and product channels are estimated using unimolecular quantum Kassel analysis, because stabilization is the most important hydroperoxy-propyl radical + O{sub 2} product channel. Below 700 K, the stabilized peroxy adducts react primarily to hydroperoxy-carbonyl + OH, products which lead to chain branching. Above 700K, the stabilized peroxy adducts react primarily to hydroperoxy-propyl radical + O{sub 2}, initial reactants, which inhibits the overall oxidation. This switchover in channels correlates well observed negative temperature coefficient behavior for propane oxidation. Rate expressions for reaction of each of the three …

We discuss preliminary results of a search for top quarks using their decays in two di-lepton, with the D0 detector at Fermilab. The present analysis has been optimized to search for a top with mass near 100{sub c{sup 2}}/{sup GeV}, consistent with published limits. In the event sample corresponding to an integrated luminosity of 15pb{sup {minus}1} we observe two events passing all selection cuts. The number of events observed is consistent with the expected number of background events. Consequently, we do not claim the observation of a top decay in the present event sample. We note however, that the kinematic properties of one of the events appear to be far removed from known backgrounds. We discuss the event and show results of the mass likelihood analysis when applied to this event.

A chemical kinetic model has been developed which describes pyrolysis, ignition and oxidation of many small hydrocarbon fuels over a wide range of experimental conditions. Fuels include carbon monoxide and hydrogen, methane and other alkane species up to n-butane, ethylene, propene, acetylene, and oxygenated species such as methanol, acetaldehyde and ethanol. Formation of some larger intermediate and product species including benzene, butadiene, large olefins, and cyclopentadiene has been treated in a semi-empirical manner. The reaction mechanism has been tested for conditions that do not involve transport and diffusional processes, including plug flow and stirred reactors, batch reactors and shock tubes. The present kinetic model and its validation differ from previous reaction mechanisms in two ways. First, in addition to conventional combustion data, experiments more commonly associated with chemical engineering problems such as oxidative coupling, oxidative pyrolysis and steam cracking are used to test the reaction mechanism, making it even more general than previous models. In addition, H atom abstraction and some other reaction rates, even for the smaller C{sub 2}, C{sub 3} and C{sub 4} species, are treated using approximations that facilitate future extensions to larger fuels in a convenient manner. Construction of the reaction mechanism and comparisons with experimental …

We simulated the flow field and flame propagation near top dead center in a generic large-bore internal combustion engine using the COYOTE computer program, which is based on the full Navier-Stokes equations for a fluid mixture. The combustion chamber is a right circular cylinder, and the main charge is uniformly premixed. The calculations are axisymmetric. The results illustrate the differences in flow patterns, flame propagation, and thermal NO production between ignition with a spark plug and with a small prechamber. In the spark-ignited case, the flame propagates away from the spark plug approximately as a segment of a spherical surface, just as expected. With the prechamber, a high speed jet of hot combustion products shoots into the main chamber, quickly producing a large flame sheet that spreads along the piston face. The prechamber run consumes all of the fuel in half the time required by the spark-ignited case. The two cases produce comparable amounts of thermal NO at the end of fuel combustion.

We present results from searches for top quark production in p{bar p} collisions at the Tevatron collider based on an integrated luminosity of 7.5 pb{sup {minus}1} obtained during the 1992--1993 ran. The present results are confined to decay modes where both the top and anti-top quarks in the event decay semi-leptonically to the ee and e{mu} channels. A lower limit of 103 (99) GeV/c{sup 2} is obtained at 95% confidence level for the top quark mass from the absence of events consistent with standard model top quark decays with background subtraction (no background subtraction). We do however observe one event in the e{mu} channel which cannot be explained by the known backgrounds. While we make no claim that this event is due to top quark decay, it is not inconsistent with a top quark mass in the range 130--170 GeV/c{sup 2}

We present results from searches for top quark production in p[bar p] collisions at the Tevatron collider based on an integrated luminosity of 7.5 pb[sup [minus]1] obtained during the 1992--1993 ran. The present results are confined to decay modes where both the top and anti-top quarks in the event decay semi-leptonically to the ee and e[mu] channels. A lower limit of 103 (99) GeV/c[sup 2] is obtained at 95% confidence level for the top quark mass from the absence of events consistent with standard model top quark decays with background subtraction (no background subtraction). We do however observe one event in the e[mu] channel which cannot be explained by the known backgrounds. While we make no claim that this event is due to top quark decay, it is not inconsistent with a top quark mass in the range 130--170 GeV/c[sup 2]

The Atomic Vapor Laser Isotope Separation (AVLIS) program has been using laser absorption spectroscopy to monitor vapor densities for over 15 years. Laser absorption spectroscopy has proven itself to be an accurate and reliable method to monitor both density and composition. During this time the diagnostic has moved from a research tool toward a robust component of a process control system. The hardware used for this diagnostic is discussed elsewhere at this symposium. This paper describes how the laser absorption spectroscopy diagnostic is used as a component of a process control system as well as supplying detailed measurements on vapor densities, composition, flow velocity, internal and kinetic temperatures, and constituent distributions. Examples will be drawn from the uranium AVLIS program. In addition potential applications such as composition control in the production of metal matrix composites or aircraft alloys will be discussed.

Effects of variations in natural gas composition on autoignition of natural gas under direct-injection (DI) diesel engine conditions were studied experimentally in a constant-volume combustion vessel and computationally using a chemical kinetic model. Four fuel blends were investigated: pure methane, a capacity weighted mean natural gas, a high ethane content natural gas, and a natural gas with added propane typical of peak shaving conditions. Experimentally measured ignition delays were longest for pure methane and became progressively shorter as ethane and propane concentrations increased. At conditions characteristic of a DI compression ignition natural gas engine at Top Dead Center (CR=23:1, p = 6.8 MPa, T = 1150K), measured ignition delays for the four fuels varied from 1.8 ms for the peak shaving and high ethane gases to 2.7 ms for pure methane. Numerically predicted variations in ignition delay as a function of natural gas composition agreed with these measurements.

This paper presents an analysis of the mean time between failures (MTBF) and availability history of the Varian VGT8140, 400 Watt, 140 GHz Gyrotron that was operated on the Microwave Tokamak Experiment (MTX) at the Lawrence Livermore National Laboratory (LLNL).

The requirements and design of a laser system to generate a sodium- layer beacon is presented. Early results of photometry and wavefront sensing are given.

The authors have implemented a particle-in-cell method on a 32 transputer computing network. The tests have shown that the performance of this system reaches 1/8 of the equivalent one for the code optimized for a CRAY Y-MP/2E. The system performance analysis shows that this network remains cost-effective until expanded approximately up to 100 transputers. This transputer equipment has provided an efficient computational tool for investigating a novel physical phenomenon -- a collisionless mechanism for separation of different elements in colliding plasma beams.

Three methods for simplifying FAST Diagrams are described which can encourage its use in construction-type value studies and bridge the gap between Information and Creativity. ``Project-FAST,`` ``Dormant- FAST`` and ``Quick-FAST`` are explained by examples which illustrate how the problem-solving capabilities of Function Analysis can be derived even from shorthand versions of FAST.

We have developed a fast, sensitive neutron detector for recording the fusion reaction-rate history of inertial-confinement fusion (ICF) experiments. The detector is based on the fast rise-time of a commercial plastic scintillator (BC-422) and has a response < 25-ps FWHM. A thin piece of scintillator material acts as a neutron-to- light converter. A zoom lens images light from the scintillator surface to a high-speed (15 ps) optical streak camera for recording. The zoom lens allows the scintillator to be positioned between 1 and 50 cm from a target. The camera simulaneously records an optical fiducial pulse which allows the camera time base to be calibrated relative to the incident laser power. Bursts of x rays formed by focusing 20-ps, 2.5-TW laser pulses onto gold disk targets demonstrate the detector resolution to be < 25 ps. We have recorded burn histories for deuterium/tritium-filled targets producing as few as 3 {times} 10{sup 7} neutrons.

The task of routing a 2-relation on an n-processor completely connected optical communication parallel computer (OCPC) is considered. A lower bound is presented that applies to any randomized distributed algorithm for this task: specifically, it is shown that the expected number of steps required to route a 2-relation is {Omega}({radical} log log n) in the worst case. For comparison, the best upper bound known is O(log log n).

The National Storage Laboratory (NSL) at the National Energy Research Supercomputer Center (NERSC) is a prototype facility which is developing data storage and retrieval techniques using hardware that includes a hierarchy of storage devices. The ultimate goal is to store terabytes of data and achieve rapid retrieval times compatible with the type of media where the data is stored. Files stored in the NSL are accessed directly using the Network File System (NFS); in the future, the Andrew File System (AFS) is expected to be used. System level control of files is available using the File Transfer Protocol (FTP) or a set of program-callable routines. We have experimented with storing and retrieving data from fusion experiments at LLNL and at General Atomics in San Diego, California, using computers running UNIX and VMS operating systems. We discuss some issues associated with accessing files whose names are known, but which are not immediately available, the time required for retrieval, and other pertinent parameters.