Formation of plasma around a small meteoroid: 1. Kinetic theory

This article is a companion to Dimant and Oppenheim [2017] https://doi.org/10.1002/2017JA023963.This paper calculates the spatial distribution of the plasma responsible for radar head echoes by applying the kinetic theory developed in the companion paper. This results in a set of analytic expressions for the plasma density as a function of distance from the meteoroid. It shows that at distances less than a collisional mean free path from the meteoroid surface, the plasma density drops in proportion to 1/R where R is the distance from the meteoroid center; and, at distances much longer than the mean‐free‐path behind the meteoroid, the density diminishes at a rate proportional to 1/R2. The results of this paper should be used for modeling and analysis of radar head echoes.This work was supported by NSF grant AGS-1244842. (AGS-1244842 - NSF

Encounter complexes and dimensionality reduction in protein-protein association

An outstanding challenge has been to understand the mechanism whereby proteins associate. We report here the results of exhaustively sampling the conformational space in protein–protein association using a physics-based energy function. The agreement between experimental intermolecular paramagnetic relaxation enhancement (PRE) data and the PRE profiles calculated from the docked structures shows that the method captures both specific and non-specific encounter complexes. To explore the energy landscape in the vicinity of the native structure, the nonlinear manifold describing the relative orientation of two solid bodies is projected onto a Euclidean space in which the shape of low energy regions is studied by principal component analysis. Results show that the energy surface is canyon-like, with a smooth funnel within a two dimensional subspace capturing over 75% of the total motion. Thus, proteins tend to associate along preferred pathways, similar to sliding of a protein along DNA in the process of protein-DNA recognition

Critical research and advanced technology (CRT) support project

A critical technology base for utility and industrial gas turbines by planning the use of coal-derived fuels was studied. Development tasks were included in the following areas: (1) Combustion - investigate the combustion of coal-derived fuels and methods to minimize the conversion of fuel-bound nitrogen to NOx; (2) materials - understand and minimize hot corrosion; (3) system studies - integrate and focus the technological efforts. A literature survey of coal-derived fuels was completed and a NOx emissions model was developed. Flametube tests of a two-stage (rich-lean) combustor defined optimum equivalence ratios for minimizing NOx emissions. Sector combustor tests demonstrated variable air control to optimize equivalence ratios over a wide load range and steam cooling of the primary zone liner. The catalytic combustion of coal-derived fuels was demonstrated. The combustion of coal-derived gases is very promising. A hot-corrosion life prediction model was formulated and verified with laboratory testing of doped fuels. Fuel additives to control sulfur corrosion were studied. The intermittent application of barium proved effective. Advanced thermal barrier coatings were developed and tested. Coating failure modes were identified and new material formulations and fabrication parameters were specified. System studies in support of the thermal barrier coating development were accomplished

Scalar resonances in a unitary π−π\pi-\pi SS-wave model for D+→π+π−π+D^+ \to \pi^+ \pi^- \pi^+

We propose a model for $D^+ \to \pi^+ \pi^- \pi^+$ decays following experimental results which indicate that the two-pion interaction in the $S$-wave is dominated by the scalar resonances $f_0(600)/\sigma$ and $f_0(980)$. The weak decay amplitude for $D^+\to R \pi^+$, where $R$ is a resonance that subsequently decays into $\pi^+\pi^-$, is constructed in a factorization approach. In the $S$-wave, we implement the strong decay $R\to \pi^-\pi^+$ by means of a scalar form factor. This provides a unitary description of the pion-pion interaction in the entire kinematically allowed mass range $m_{\pi\pi}^2$ from threshold to about 3 GeV$^2$. In order to reproduce the experimental Dalitz plot for \Dppp, we include contributions beyond the $S$-wave. For the $P$-wave, dominated by the $\rho(770)^0$, we use a Breit-Wigner description. Higher waves are accounted for by using the usual isobar prescription for the $f_2(1270)$ and $\rho(1450)^0$. The major achievement is a good reproduction of the experimental $m_{\pi\pi}^2$ distribution, and of the partial as well as the total \Dppp branching ratios. Our values are generally smaller than the experimental ones. We discuss this shortcoming and, as a byproduct, we predict a value for the poorly known $D\to \sigma$ transition form factor at $q^2=m_\pi^2$.Comment: 23 pages, 2 figures. Two new equations. The value for the strength of the contribution of the scalar form factor now agrees with other results in the literature. Main results unchanged. Version to appear in Phys. Rev.

An inquiry-based learning approach to teaching information retrieval

The study of information retrieval (IR) has increased in interest and importance with the explosive growth of online information in recent years. Learning about IR within formal courses of study enables users of search engines to use them more knowledgeably and effectively, while providing the starting point for the explorations of new researchers into novel search technologies. Although IR can be taught in a traditional manner of formal classroom instruction with students being led through the details of the subject and expected to reproduce this in assessment, the nature of IR as a topic makes it an ideal subject for inquiry-based learning approaches to teaching. In an inquiry-based learning approach students are introduced to the principles of a subject and then encouraged to develop their understanding by solving structured or open problems. Working through solutions in subsequent class discussions enables students to appreciate the availability of alternative solutions as proposed by their classmates. Following this approach students not only learn the details of IR techniques, but significantly, naturally learn to apply them in solution of problems. In doing this they not only gain an appreciation of alternative solutions to a problem, but also how to assess their relative strengths and weaknesses. Developing confidence and skills in problem solving enables student assessment to be structured around solution of problems. Thus students can be assessed on the basis of their understanding and ability to apply techniques, rather simply their skill at reciting facts. This has the additional benefit of encouraging general problem solving skills which can be of benefit in other subjects. This approach to teaching IR was successfully implemented in an undergraduate module where students were assessed in a written examination exploring their knowledge and understanding of the principles of IR and their ability to apply them to solving problems, and a written assignment based on developing an individual research proposal

Analysis of the Neurogenesis: Prepattern gene network сontrolling the first stage in Drosophila melanogaster bristle pattern development

The external insect chitinous skeleton is unable to respond to stimuli; the external signals are received by specialized receptors. Drosophila perceives the tactile stimuli by its external sensory organs, the microchaetes and macrochaetes residing on the head and back (notum). The microchaetes (hairs) are numerous and arranged in perfect rows along the body. The macrochaetes (bristles) are rather few and are strictly positioned on the head and notum, being referred to as bristle pattern. Bristles act as mechanoreceptors, providing balance for flying drosophila. The proper bristle pattern of an adult fly develops through several stages. Its basic stage is formation of prepattern for the future bristles, represented by proneural clusters. The proneural clusters separate from the ectodermal cells in imaginal discs in the third instar larvae and early prepupae. They are induced by prepattern factors, identified with the transcription factors driving expression of their target genes in certain disc regions. Reconstruction of the gene network controlling prepattern development and its analysis are for the first time described as well as the principles underlying arrangement and function of this network. The hierarchical structure of the network, its key components, and regulatory circuits are identified. The network comprises 80 entities interconnected via 109 regulatory interactions. The key objects of the network, displaying the greatest connectivity with its other components, are the ASC proneural proteins encoded by the achaete and scute genes, and the proteins Decapentaplegic (Dpp) and Wingless (Wg). The structure of the network is hierarchical and has at least three control levels. The network acts as a gene ensemble owing to coordinated functioning of the regulatory circuits controlling activities of the corresponding genes both within and between the levels. The resulting effect of the network operation consists in activation of the AS-C, proneural genes, the expression of which distinguishes the cells of proneural cluster from the surrounding ectodermal cells

The bristle pattern development in Drosophila melanogaster: the prepattern and achaete-scute genes

The external drosophila mechanoreceptors, residing on the head and body of imago, are represented by bristles of different sizes (macrochaetes and microchaetes). Macrochaetes are arranged in the species-specifc bristle pattern, where each of them is strictly positioned. The bristle pattern is formed starting from its prototype (prepattern) in the imaginal disc. The position specifcity of future mechanoreceptors is determined by local expression of two proneural genes, achaete (ac) and scute (sc) belonging to the AS-C complex, in response to the action of certain factors, referred to as prepattern factors, nonuniformly distributed in the ectoderm of imaginal discs. The topography of their total distribution defnes the bristle prepattern. Thus, the full-fledged adult bristle pattern is the result of interaction of two systems – the prepattern and the system responding to prepattern, i. e., the achaete and scute genes. A considerable volume of miscellaneous experimental data related to various aspects in development of the bristle pattern has been so far accumulated; however, any formalized and detailed representation of the molecular genetic interaction of the prepattern factors with both each other and the achaete-scute genes is yet absent. This review systematizes the available data on the regular patterns of this interaction and shows that local expression of these genes is determined by hierarchical two-level control system comprising both direct and indirect regulators of their activities. A generalized scheme of the system containing the functional interactions of its components is proposed. The structural organization and principles of operation of the hierarchical molecular genetic system enabling the local expression of ASC genes and the resulting formation of ordered bristle pattern are described

One loop calculation in lattice QCD with domain-wall quarks

One loop corrections to the domain-wall quark propagator are calculated in massless QCD. It is shown that no additative counter term to the current quark mass is generated in this theory, and the wave function renormalization factor of the massless quark is explicitly evaluated. We also show that an analysis with a simple mean-field approximation can explain properties of the massless quark in numerical simulations of QCD with domain-wall quarks.Comment: 24 pages, REVTeX, with 3 epsf figure

Vector like gauge theories with almost massless fermions on the lattice

A truncation of the overlap (domain wall fermions) is studied and a criterion for reliability of the approximation is obtained by comparison to the exact overlap formula describing massless quarks. We also present a truncated version of regularized, pure gauge, supersymmetric models. The mechanism for generating almost masslessness is shown to be a generalized see-saw which can also be viewed as a version of Froggatt-Nielsen's method for obtaining natural large mass hierarchies. Viewed in this way the mechanism preserving the mass hierarchy naturally avoids preserving even approximately axial U(1). The new insights into the source of the mass hierarchy suggest ways to increase the efficiency of numerical simulations of QCD employing the truncated overlap.Comment: 35 pages, TeX, 4 figures using eps

Combinations of idelalisib with rituximab and/or bendamustine in patients with recurrent indolent non-Hodgkin lymphoma

Key Points Combining phosphatidylinositol-3-kinase δ inhibition with rituximab, bendamustine, or both is feasible and active in relapsed iNHL. The safety of novel combinations should be proven in phase 3 trials before adoption in clinical practice.</jats:p