9,133 research outputs found
Gluon polarization in the proton
We combine heavy-quark renormalization group arguments with our understanding
of the nucleon's wavefunction to deduce a bound on the gluon polarization Delta
g in the proton. The bound is consistent with the values extracted from spin
experiments at COMPASS and RHIC.Comment: 4 page
Transverse Momentum in Semi-Inclusive Polarized Deep Inelastic Scattering and the Spin-Flavor Structure of the Proton
The non-valence spin-flavor structure of the nucleon extracted from
semi-inclusive measurements of polarized deep inelastic scattering depends
strongly on the transverse momentum of the detected hadrons which are used to
determine the individual polarized sea distributions. This physics may explain
the recent HERMES observation of a positively polarized strange sea through
semi-inclusive scattering, in contrast to the negative strange sea polarization
deduced from inclusive polarized deep inelastic scattering.Comment: 4 pages, revtex style, 2 figure
Roles and regulation of membrane-associated serine proteases
Pericellular proteolytic activity affects many aspects of cellular behaviour, via mechanisms involving processing of the extracellular matrix, growth factors and receptors. The serine proteases have exquisitely sensitive regulatory mechanisms in this setting, involving both receptor-bound and transmembrane proteases. Receptor-bound proteases are exemplified by the uPA (urokinase plasminogen activator)/uPAR (uPAR receptor) plasminogen activation system. The mechanisms initiating the activity of this proteolytic system on the cell surface, a critical regulatory point, are poorly understood. We have found that the expression of the TTSP (type II transmembrane serine protease) matriptase is highly regulated in leucocytes, and correlates with the presence of active uPA on their surface. Using siRNA (small interfering RNA), we have demonstrated that matriptase specifically activates uPAR-associated pro-uPA. The uPA/uPAR system has been implicated in the activation of the plasminogen-related growth factor HGF (hepatocyte growth factor). However, we find no evidence for this, but instead that HGF can be activated by both matriptase and the related TTSP hepsin in purified systems. Hepsin is of particular interest, as the proteolytic cleavage sequence of HGF is an ‘ideal substrate’ for hepsin and membrane-associated hepsin activates HGF with high efficiency. Both of these TTSPs can be activated autocatalytically at the cell surface, an unusual mechanism among the serine proteases. Therefore these TTSPs have the capacity to be true upstream initiators of proteolytic activity with subsequent downstream effects on cell behaviour
Dynamical Instabilities and Deterministic Chaos in Ballistic Electron Motion in Semiconductor Superlattices
We consider the motion of ballistic electrons within a superlattice miniband
under the influence of an alternating electric field. We show that the
interaction of electrons with the self-consistent electromagnetic field
generated by the electron current may lead to the transition from regular to
chaotic dynamics. We estimate the conditions for the experimental observation
of this deterministic chaos and discuss the similarities of the superlattice
system with the other condensed matter and quantum optical systems.Comment: 6 pages, RevTEX; 4 fig
The Spin Structure of the Nucleon
This article reviews our present understanding of QCD spin physics: the
proton spin puzzle and new developments aimed at understanding the transverse
structure of the nucleon. We discuss present experimental investigations of the
nucleon's internal spin structure, the theoretical interpretation of the
different measurements and the open questions and challenges for future
investigation.Comment: Review, 43 pages, 23 figures, to appear in Reviews of Modern Physic
Initiation Writes
Diversity in the academy means more than simply having people of color present on faculty; it may mean that institutions will begin to see some variation in the meaning of scholarship
Registration and course selection processes of entering freshmen and the effects on academic success and retention at a midsize public university
This mixed-methods study concentrated on students who participated in a 2-day freshman orientation program and registered for courses at a midsize metropolitan 4-year public university located in the southeastern United States. This study examined three cohorts of entering freshmen as they progressed through the course-registration process of freshman orientation and then one full academic year. There was also consideration of the institutional departments involved in the process and their perceptions of the experience. The quantitative portion of this mixed-methods study was based on Bean and Metzner’s (1985) longitudinal tracking system for nontraditional student attrition. Two frameworks were used for the qualitative portion of the study. The first was constructivist grounded theory due to its research of a university process, and how this process may impact various independent departments in the institution. The second portion of the qualitative review was narrative inquiry; the lived experience of the researcher with respect to the preregistration process provided a program evaluation of the process itself. The first research question addressed the combination of student characteristics that best predicted first-year student academic success. Across all academic success markers, female students were more likely to be successful than male students. The second research question asked what combination of the six academic outcome variables best predicted first-year student retention at the University of Tennessee at Chattanooga (UTC). The variables with the most significant impacts were UTC grade point average (GPA), semester earned credits, attempted overall credits, and the completion of preregistration. The third research question considered if the method of first-time course registration was significant in student retention. It was determined that the preregistration process had a positive impact. Finally, the fourth research question was a consideration of the perceived impact of the Academic Interest Questionnaire (AIQ) on administrative processes. Through narrative inquiry, the AIQ was found to have improved over time, and the majority of academic departments have become vested in the process. The narrative findings were supported by interview responses
A Game of Attribute Decomposition for Software Architecture Design
Attribute-driven software architecture design aims to provide decision
support by taking into account the quality attributes of softwares. A central
question in this process is: What architecture design best fulfills the
desirable software requirements? To answer this question, a system designer
needs to make tradeoffs among several potentially conflicting quality
attributes. Such decisions are normally ad-hoc and rely heavily on experiences.
We propose a mathematical approach to tackle this problem. Game theory
naturally provides the basic language: Players represent requirements, and
strategies involve setting up coalitions among the players. In this way we
propose a novel model, called decomposition game, for attribute-driven design.
We present its solution concept based on the notion of cohesion and
expansion-freedom and prove that a solution always exists. We then investigate
the computational complexity of obtaining a solution. The game model and the
algorithms may serve as a general framework for providing useful guidance for
software architecture design. We present our results through running examples
and a case study on a real-life software project.Comment: 23 pages, 5 figures, a shorter version to appear at 12th
International Colloquium on Theoretical Aspects of Computing (ICTAC 2015
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