Signatures of four-particle correlations associated with exciton-carrier interactions in coherent spectroscopy on bulk GaAs

Transient four-wave mixing studies of bulk GaAs under conditions of broad bandwidth excitation of primarily interband transitions have enabled four-particle correlations tied to degenerate (exciton-exciton) and nondegenerate (exciton-carrier) interactions to be studied. Real two-dimensional Fourier-transform spectroscopy (2DFTS) spectra reveal a complex response at the heavy-hole exciton emission energy that varies with the absorption energy, ranging from dispersive on the diagonal, through absorptive for low-energy interband transitions to dispersive with the opposite sign for interband transitions high above band gap. Simulations using a multilevel model augmented by many-body effects provide excellent agreement with the 2DFTS experiments and indicate that excitation-induced dephasing (EID) and excitation-induced shift (EIS) affect degenerate and nondegenerate interactions equivalently, with stronger exciton-carrier coupling relative to exciton-exciton coupling by approximately an order of magnitude. These simulations also indicate that EID effects are three times stronger than EIS in contributing to the coherent response of the semiconductor

Living Up to Expectations: Computing Expert Responses

In cooperative man-machine interaction, it is necessary but not sufficient for a system to respond truthfully and informatively to a user\u27s question. In particular, if the system has reason to believe that its planned response might mislead the user, then it must block that conclusion by modifying its response. This paper focuses on identifying and avoiding potentially misleading responses by acknowledging types of \u27informing behavior\u27 usually expected of an expert. We attempt to give a formal account of several types of assertions that should be included in response to questions concerning the achievement of some goal (in addition to the simple answer), lest the questioner otherwise be misled

The Modified Weighted Slab Technique: Models and Results

In an attempt to understand the source and propagation of galactic cosmic rays we have employed the Modified Weighted Slab technique along with recent values of the relevant cross sections to compute primary to secondary ratios including B/C and Sub-Fe/Fe for different galactic propagation models. The models that we have considered are the disk-halo diffusion model, the dynamical halo wind model, the turbulent diffusion model and a model with minimal reacceleration. The modified weighted slab technique will be briefly discussed and a more detailed description of the models will be given. We will also discuss the impact that the various models have on the problem of anisotropy at high energy and discuss what properties of a particular model bear on this issue.Comment: LaTeX - AASTEX format, Submitted to ApJ, 8 figures, 20 page

Space, Time and Color in Hadron Production Via e+e- -> Z0 and e+e- -> W+W-

The time-evolution of jets in hadronic e+e- events at LEP is investigated in both position- and momentum-space, with emphasis on effects due to color flow and particle correlations. We address dynamical aspects of the four simultanously-evolving, cross-talking parton cascades that appear in the reaction e+e- -> gamma/Z0 -> W+W- -> q1 q~2 q3 q~4, and compare with the familiar two-parton cascades in e+e- -> Z0 -> q1 q~2. We use a QCD statistical transport approach, in which the multiparticle final state is treated as an evolving mixture of partons and hadrons, whose proportions are controlled by their local space-time geography via standard perturbative QCD parton shower evolution and a phenomenological model for non-perturbative parton-cluster formation followed by cluster decays into hadrons. Our numerical simulations exhibit a characteristic `inside-outside' evolution simultanously in position and momentum space. We compare three different model treatments of color flow, and find large effects due to cluster formation by the combination of partons from different W parents. In particular, we find in our preferred model a shift of several hundred MeV in the apparent mass of the W, which is considerably larger than in previous model calculations. This suggests that the determination of the W mass at LEP2 may turn out to be a sensitive probe of spatial correlations and hadronization dynamics.Comment: 52 pages, latex, 18 figures as uu-encoded postscript fil

Polynomials, Riemann surfaces, and reconstructing missing-energy events

We consider the problem of reconstructing energies, momenta, and masses in collider events with missing energy, along with the complications introduced by combinatorial ambiguities and measurement errors. Typically, one reconstructs more than one value and we show how the wrong values may be correlated with the right ones. The problem has a natural formulation in terms of the theory of Riemann surfaces. We discuss examples including top quark decays in the Standard Model (relevant for top quark mass measurements and tests of spin correlation), cascade decays in models of new physics containing dark matter candidates, decays of third-generation leptoquarks in composite models of electroweak symmetry breaking, and Higgs boson decay into two tau leptons.Comment: 28 pages, 6 figures; version accepted for publication, with discussion of Higgs to tau tau deca

The Origin of Galactic Cosmic Rays

Motivated by recent measurements of the major components of the cosmic radiation around 10 TeV/nucleon and above, we discuss the phenomenology of a model in which there are two distinct kinds of cosmic ray accelerators in the galaxy. Comparison of the spectra of hydrogen and helium up to 100 TeV per nucleon suggests that these two elements do not have the same spectrum of magnetic rigidity over this entire region and that these two dominant elements therefore receive contributions from different sources.Comment: To be published in Physical Review D, 13 pages, with 3 figures, uuencode

Vegetative Buffer and Fly Ash Pad Surface Material System Application for Reducing Runoff, Sediment and Nutrient Losses from Livestock Manure Windrow Composting Facilities

Applying livestock manures to agricultural cropland continues to contribute significant levels of sediment and nutrient pollutants to streams and other water bodies. Vegetative buffers have been extensively demonstrated to reduce surface runoff flow, sediment, and nutrient losses. The coal-fired combustion by-product fly ash also has been shown to exhibit significant water-absorption and phosphorus-sorbing properties. This study investigated a vegetative buffer and fly ash pad surface material system for reducing runoff flow and water quality effects from a livestock manure windrow composting facility. Surface runoff, runoff percent of rainfall, total solids, nitrate-nitrogen, ortho-phosphorus, and total phosphorus were researched during 2002-2004 at a central Iowa dairy cow manure windrow composting research facility. Three compost windrow: vegetative buffer area ratios comprised the surface runoff treatments that included 1:1, 1:0.5, and 1:0 (no buffer control) area ratios, respectively. The 1:1 and 1:0.5 area ratios represented a 6.0 m-wide x 23 m-long fly ash composting pad area compared to vegetative buffer areas of equal and one-half size, respectively, with three replications of each treatment for a total of nine runoff plots in a randomized complete block design. Results from this study showed significantly high levels of runoff flow, sediment, and nutrients from the 1:0 control plots compared to the 1:1 and 1:0.5 vegetative buffer plots. The 1:1 and 1:0.5 vegetative buffer treatments were not significantly different and average runoff loss reductions from the 1:1 and 1:0.5 vegetative buffer plots were 98% and 93%, respectively, when compared to the 1:0 control plots. These findings underscore the efficacy of vegetative buffers in reducing surface runoff flow, sediment, and nutrient losses from a livestock manure windrow composting operation. Mass balance analysis results also indicated 41% and 26% of ortho-phosphorus were lost from the compost windrows during the 2004 early season and late season composting periods, respectively. However, only 0.1% and 0.4% of ortho-phosphorus were lost to runoff from the 1:0 control plots during the respective 2004 early season and late season composting periods. These results indicate the significantly lower ortho-phosphorus losses in runoff are attributed to the inherent chemical and physical phosphorus-sorption characteristics of the fly ash composting pad surface material. This vegetative buffer and fly ash pad surface material system application can significantly reduce surface runoff flow, sediment, and nutrient losses from a livestock manure windrow composting facility

Printing in a Pandemic: 3D printing solutions for healthcare during COVID-19. A Protocol for a PRISMA systematic review

Introduction: The COVID-19 pandemic had an unprecedented global socioeconomic impact. Responses to pandemics include strategies to accumulate vast stockpiles of vital medical equipment. In such times of desperation, 3D-printing could be a life-saving alternative. / Methods: We undertook a PRISMA systematic review of 3D printing solutions in response to COVID-19 utilising the PICO methodology. The objectives were to identify the uses of 3D printing during the COVID-19 pandemic, determine the extent of preclinical testing, comparison to commercial alternatives, presence of regulatory approvals and replicability regarding the description of the printing parameters and the availability of the print file. / Results: Literature searches of MEDLINE (OVID interface)/ PubMed identified 601 studies. Of these, 10 studies fulfilled the inclusion and exclusion criteria. Reported uses of 3D printing included personal protective equipment (PPE), nasopharyngeal swabs and adjunctive anaesthetic equipment. Few studies undertook formal safety and efficacy testing before clinical use with only one study comparing to the commercial equivalent. Six articles made their model print files available for wider use. / Conclusion: We describe a protocol for a systematic review of 3D-printed healthcare solutions in response to COVID-19. This remains a viable method of producing vital healthcare equipment when supply chains are exhausted. We hope that this will serve as a summary of innovative 3D-printed solutions during the peak of the pandemic and also highlight concerns and omissions regarding safety and efficacy testing that should be addressed urgently in preparation for a subsequent resurgences and future pandemics