Time Evolution of Jets and Perturbative Color Neutralization

In-medium production of leading hadrons in hard reactions, carrying the main fraction of the jet momentum, involves two stages: (i) the parton originated from the hard process propagates through the medium radiating gluons due to the initial hard collision, as well as to multiple interactions in the medium; (ii) perturbative color neutralization, e.g. picking up an anti-colored parton produced perturbatively, followed by evolution and attenuation of the (pre)hadron in the medium. The color neutralization (or production) length for leading hadrons is controlled by coherence, energy conservation and Sudakov suppression. The pT-broadening is a sensitive and model independent probe for the production length. The color neutralization time is expected to shrink with rising hard scale. In particular, we found a very fast energy dissipation by a highly virtual parton: half of the jet energy is radiated during the first Fermi. Energy conservation makes the production of leading hadrons at longer times difficult.Comment: Based on talk given by B.K. at the Fifth International Conference on Perspectives in Hadronic Physics, Trieste, May 200

Microgravity Particle Dynamics

This research seeks to identify the experiment design parameters for future flight experiments to better resolve the effects of thermal and velocity gradients on gas-solid flows. By exploiting the reduced body forces and minimized thermal convection current of reduced gravity experiments, features of gas-solid flow normally masked by gravitationally induced effects can be studied using flow regimes unattainable under unigravity. This paper assesses the physical scales of velocity, length, time, thermal gradient magnitude, and velocity gradient magnitude likely to be involved in laminar gas-solid multiphase flight experiments for 1-100 micro-m particles

Particle experiments in thermal and velocity gradients

The physical scales of velocity, length, time, thermal gradient magnitude likely to be involved in gas-solid multiphase flight experiments are assessed for 1-100 micron particles

Frequency-selective near-field enhancement of radiative heat transfer via photonic-crystal slabs: a general computational approach for arbitrary geometries and materials

We demonstrate the possibility of achieving enhanced frequency-selective near-field radiative heat transfer between patterned (photonic crystal) slabs at designable frequencies and separations, exploiting a general numerical approach for computing heat transfer in arbitrary geometries and materials based on the finite-difference time-domain method. Our simulations reveal a tradeoff between selectivity and near-field enhancement as the slab--slab separation decreases, with the patterned heat transfer eventually reducing to the unpatterned result multiplied by a fill factor (described by a standard proximity approximation). We also find that heat transfer can be further enhanced at selective frequencies when the slabs are brought into a glide-symmetric configuration, a consequence of the degeneracies associated with the non-symmorphic symmetry group

Predictors of excellent early outcome after total hip arthroplasty

<p>Abstract</p> <p>Background</p> <p>Not all patients gain the same degree of improvement from total hip replacement and the reasons for this are not clear. Many investigators have assessed predictors of general outcome after hip surgery. This study is unique in its quest for the predictors of the best possible early outcome.</p> <p>Methods</p> <p>We prospectively collected data on 1318 total hip replacements. Prior to surgery patient characteristics, demographics and co-morbidities were documented. Hip function and general health was assessed using the Harris Hip score (HHS) and the Short-Form 36 respectively. The HHS was repeated at three years. We took a maximal HHS of 100 to represent an excellent outcome (102 patients). Multiple logistic regression analysis was used to identify independent predictors of excellent outcome.</p> <p>Results</p> <p>The two strongest predictive factors in achieving an excellent result were young age and a high pre-operative HHS (p = 0.001).</p> <p>Conclusions</p> <p>It was the young and those less disabled from their arthritis that excelled at three years. When making a decision about the timing of hip arthroplasty surgery it is important to take into account the age and pre-operative function of the patient. Whether these patients continue to excel however will be the basis of future research.</p

Higgs Hadroproduction at Large Feynman x

We propose a novel mechanism for the production of the Higgs boson in inclusive hadronic collisions, which utilizes the presence of heavy quarks in the proton wave function. In these inclusive reactions the Higgs boson acquires the momenta of both the heavy quark and antiquark and thus carries 80% or more of the projectile's momentum. We predict that the cross section ${d \sigma/d x_F}(p \bar p \to H X)$ for the inclusive production of the Standard Model Higgs coming from intrinsic bottom Fock states is of order 150 fb at LHC energies, peaking in the region of $x_F \sim 0.9$. Our estimates indicate that the corresponding cross section coming from gluon-gluon fusion at $x_F = 0.9$ is relatively negligible and therefore the peak from intrinsic bottom should be clearly visible for experiments with forward detection capabilities. The predicted cross section for the production of the Standard Model Higgs coming from intrinsic heavy quark Fock states in the proton is sufficiently large that detection at the Tevatron and the LHC may be possible.Comment: 23 pages, 5 figure

Breakdown of QCD factorization at large Feynman x

Recent measurements by the BRAHMS collaboration of high-pT hadron production at forward rapidities at RHIC found the relative production rate(d-Au)/(p-p) to be suppressed, rather than enhanced. Examining other known reactions (forward production of light hadrons, the Drell-Yan process, heavy flavor production, etc.), one notes that all of these display a similar property, namely, their cross sections in nuclei are suppressed at large xF. Since this is the region where x2 is minimal, it is tempting to interpret this as a manifestation of coherence, or of a color glass condensate, whereas it is actually a simple consequence of energy conservation and takes place even at low energies. We demonstrate that in all these reactions there is a common suppression mechanism that can be viewed, alternatively, as a consequence of a reduced survival probability for large rapidity gap processes in nuclei, Sudakov suppression, an enhanced resolution of higher Fock states by nuclei, or an effective energy loss that rises linearly with energy. Our calculations agree with data.Comment: 12 pages Latex, 8 figures (only technical corrections in the replacement

Exceptional del Pezzo hypersurfaces

We compute global log canonical thresholds of a large class of quasismooth well-formed del Pezzo weighted hypersurfaces in $\mathbb{P}(a_{1},a_{2},a_{3},a_{4})$. As a corollary we obtain the existence of orbifold K\"ahler--Einstein metrics on many of them, and classify exceptional and weakly exceptional quasismooth well-formed del Pezzo weighted hypersurfaces in $\mathbb{P}(a_{1},a_{2},a_{3},a_{4})$.Comment: 149 pages, one reference adde