Using Collider Event Topology in the Search for the Six-Jet Decay of Top Quark-Antiquark Pairs

We investigate the use of the event topology as a tool in the search for the six-jet decay of top-pair production in proton-antiproton collisions at 1.8 TeV. Modified Fox-Wolfram "shape" variables, H_i, are employed to help distinguish the top-pair signal from the ordinary QCD multi-jet background. The H's can be constructed directly from the calorimeter cells or from jets. Events are required to lie in a region of H-space defined by L_i < H_i < R_i for i=1,...,,6, where the left, L_i, and right, R_i, cuts are determined by a genetic algorithm (GA) procedure to maximize the signal over the square root of the background. We are able to reduce the background over the signal to less than a factor of 100 using purely topological methods without using jet multiplicity cuts and without the aid of b-quark tagging.Comment: LaTeX, 19 pages, 13 figure

Production of large transverse momentum dileptons and photons in pppp, dAdA and AAAA collisions by photoproduction processes

The production of large $P_{T}$ dileptons and photons originating from photoproduction processes in $pp$, $dA$ and $AA$ collisions is calculated. We find that the contribution of dileptons and photons produced by photoproduction processes is not prominent at RHIC energies. However, the numerical results indicate that the modification of photoproduction processes becomes evident in the large $P_{T}$ region for $pp$, $dA$ and $AA$ collisions at LHC energies.Comment: 10 figure

Real photons produced from photoproduction in pppp collisions

We calculate the production of real photons originating from the photoproduction in relativistic $pp$ collisions. The Weizs$\ddot{\mathrm{a}}$cker-Williams approximation in the photoproduction is considered. Numerical results agree with the experimental data from Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC). We find that the modification of the photoproduction is more prominent in large transverse momentum region.Comment: 2 figure

Observations of spatial and velocity structure in the Orion Molecular Cloud

Observations are reported of H2 IR emission in the S(1) v=1-0 line at 2.121 microns in the Orion Molecular Cloud, OMC1, using the GriF instrument on the Canada-France-Hawaii Telescope. GriF is a combination of adaptive optics and Fabry-Perot interferometry, yielding a spatial resolution of 0.15" to 0.18" and a velocity discrimination as high as 1 km/s. Thanks to the high spatial and velocity resolution of the GriF data, 193 bright H2 emission regions can be identified in OMC1. The general characteristics of these features are described in terms of radial velocities, brightness and spatial displacement of maxima of velocity and brightness, the latter to yield the orientation of flows in the plane of the sky. Strong spatial correlation between velocity and bright H2 emission is found and serves to identify many features as shocks. Important results are: (i) velocities of the excited gas illustrate the presence of a zone to the south of BN-IRc2 and Peak 1, and the west of Peak 2, where there is a powerful blue-shifted outflow with an average velocity of -18 km/s. This is shown to be the NIR counterpart of an outflow identified in the radio from source I, a very young O-star. (ii) There is a band of weak velocity features (<5 km/s) in Peak 1 which may share a common origin through an explosive event, in the BN-IRc2 region, with the fast-moving fingers (or bullets) to the NW of OMC1. (iii) A proportion of the flows are likely to represent sites of low mass star formation and several regions show multiple outflows, probably indicative of multiple star formation within OMC1. The high spatial and velocity resolution of the GriF data show these and other features in more detail than has previously been possible.Comment: 27 pages, 19 figures, submitted to A&A Version 2: Several additions, including a section on protostellar candidates in OMC1, have been made based on the referee's suggestions v3: corrected typograph

Fouling mechanisms in constant flux crossflow ultrafiltration

Four fouling models due to Hermia (complete pore blocking, intermediate pore blocking, cake filtration and standard pore blocking), have long been used to describe membrane filtration and fouling in constant transmembrane pressure (ΔP) operation of membranes. A few studies apply these models to constant flux dead-end filtration systems. However, these models have not been reported for constant flux crossflow filtration, despite the frequent use of this mode of membrane operation in practical applications. We report derivation of these models for constant flux crossflow filtration. Of the four models, complete pore blocking and standard pore blocking were deemed inapplicable due to contradicting assumptions and relevance, respectively. Constant flux crossflow fouling experiments of dilute latex bead suspensions and soybean oil emulsions were conducted on commercial poly (ether sulfone) flat sheet ultrafiltration membranes to explore the models’ abilities to describe such data. A model combining intermediate pore blocking and cake filtration appeared to give the best agreement with the experimental data. Below the threshold flux, both the intermediate pore blocking model and the combined model fit the data well. As permeate flux approached and passed the threshold flux, the combined model was required for accurate fits. Based on this observation, a physical interpretation of the threshold flux is proposed: the threshold flux is the flux below which cake buildup is negligible and above which cake filtration becomes the dominant fouling mechanism

A Toy Model of Flying Snake's Glide

We have developed a toy model of flying snake's glide [J.J. Socha, Nature vol. 418 (2002) 603.] by modifying a model for a falling paper. We have found that asymmetric oscillation is a key about why snake can glide. Further investigation for snake's glide will provide us details about how it can glide without a wing.Comment: 6 pages, to be submitted to J. Phys. Soc. Jpn. Revised Version submitted to the abov

Persistent junk solutions in time-domain modeling of extreme mass ratio binaries

In the context of metric perturbation theory for non-spinning black holes, extreme mass ratio binary (EMRB) systems are described by distributionally forced master wave equations. Numerical solution of a master wave equation as an initial boundary value problem requires initial data. However, because the correct initial data for generic-orbit systems is unknown, specification of trivial initial data is a common choice, despite being inconsistent and resulting in a solution which is initially discontinuous in time. As is well known, this choice leads to a "burst" of junk radiation which eventually propagates off the computational domain. We observe another unintended consequence of trivial initial data: development of a persistent spurious solution, here referred to as the Jost junk solution, which contaminates the physical solution for long times. This work studies the influence of both types of junk on metric perturbations, waveforms, and self-force measurements, and it demonstrates that smooth modified source terms mollify the Jost solution and reduce junk radiation. Our concluding section discusses the applicability of these observations to other numerical schemes and techniques used to solve distributionally forced master wave equations.Comment: Uses revtex4, 16 pages, 9 figures, 3 tables. Document reformatted and modified based on referee's report. Commentary added which addresses the possible presence of persistent junk solutions in other approaches for solving master wave equation

Local dependence of ion temperature gradient on magnetic configuration, rotational shear and turbulent heat flux in MAST

Experimental data from the Mega Amp Spherical Tokamak (MAST) is used to show that the inverse gradient scale length of the ion temperature R/LTi (normalized to the major radius R) has its strongest local correlation with the rotational shear and the pitch angle of the magnetic field (or, equivalently, an inverse correlation with q/{\epsilon}, the safety factor/the inverse aspect ratio). Furthermore, R/LTi is found to be inversely correlated with the gyro-Bohm-normalized local turbulent heat flux estimated from the density fluctuation level measured using a 2D Beam Emission Spectroscopy (BES) diagnostic. These results can be explained in terms of the conjecture that the turbulent system adjusts to keep R/LTi close to a certain critical value (marginal for the excitation of turbulence) determined by local equilibrium parameters (although not necessarily by linear stability).Comment: 6 pages, 3 figures, submitted to PR