135,008 research outputs found
Helper T cells for cytotoxic T lymphocytes need not be I region restricted.
We investigated the antigenic requirements for restimulation of H-2- restricted cytolytic T lymphocytes (CTL) in vitro to determine whether H-2 I region-restricted helper T cells are required in these responses. In one set of experiments, we studied the in vitro response of (responder x nonresponder)F(1) female T cells to the male antigen H-Y. We chose to examine this response because it has been suggested that the defect in nonresponder strains is a failure of helper T cells to recognize H-Y in association with nonresponder I region determinants. However, we find that nonresponder male stimulator cells are as effective as F(1) male stimulator cells at inducing H-Y-specific CTL responses. This finding calls into question reports that secondary CTL responses to H-Y are dependent upon the activation of H-Y- specific helper T cells restricted to responder type I region determinants. In a second set of experiments, we examined the requirements for restimulation of H-2-restricted T cells specific for minor-histocompatibility antigens from long-term mixed lymphocyte cultures. These cultures were established by repeatedly restimulating cultures of specific T cells with H- 2-matched stimulator cells expressing foreign minor histocompatibility antigens. We found that H-2D-restricted T ceils, including CTL, could be restimulated with cells that were matched with the responding cells at only the D region genes. This response did not appear to result from positive allogeneic effects or from antigen processing and representation by responder type APC that might contaminate the cultures. Thus, we find no evidence for a requirement for I region-restricted helper T cells in these CTL responses. However, helper T cells are required because we find that CTL lines derived by limit-dilution cloning from these long-term MLC are absolutely dependent upon exogenous helper factors for growth. The most simple interpretation of these results is that the helper cells are restricted to H-2 antigens other than I region antigens or to antigens that code outside of the H-2 complex. Finally, we show that factor-dependent CTL lines must recognize their specific antigen to proliferate, even in the presence of exogenous factors. The requirement of activated CTL for antigen to proliferate provides an explanation for how specific CTL can be selectively enriched in MLC by specific antigen stimulation. Furthermore, it is at variance with reports that memory CTL or activated CTL require only interleukin 2 for restimulation
Positive selection of V beta 8+ CD4-8- thymocytes by class I molecules expressed by hematopoietic cells.
A small subset of T cells of mature phenotype express the alpha/beta T cell receptor, but not CD4 and CD8 coreceptors (alpha/beta double-negative [DN] cells). The repertoire of V beta usage of alpha/beta DN cells is strongly biased towards V beta 8 expression, suggesting that the formation of the population is subject to selection. We now report that deficiency of class I expression leads to a strongly depressed frequency of V beta 8+ DN cells, but has little effect on V beta 8- DN cells. Studies of hematopoietic chimeras between class I+ and class I- mice demonstrated that expression of class I molecules by hematopoietic cells is necessary and sufficient for selection of most V beta 8 DN cells. The lack of a role for class I expression by thymic epithelial cells suggests that the mechanism of selection of these cells by class I differs significantly from the mechanism of selection of conventional T cells. Models to explain the selection of these cells as well as their possible function in vivo are discussed
Class I dependence of the development of CD4+ CD8- NK1.1+ thymocytes.
A small subset of functionally active CD4+ CD8- thymocytes express the NK1.1 marker, as do most CD4-CD8- NK1.1+ thymocytes. Previous studies have failed to implicate a role for major histocompatibility complex (MHC) or related molecules in the selection of the CD4+ CD8- NK1.1+ subset. We report here that the development of most of these cells is sharply reduced in class I-deficient mice, but not in class II-deficient mice. Hence, some CD4+ T cells are class I dependent and not class II dependent. Unlike conventional T cells, however, the development of NK1.1+ thymocytes in both the CD4+ CD8- and CD4- CD8- subsets is dependent on class I MHC expression by hematopoietic cells and not thymic epithelial cells. We propose that these populations are selected by nonpolymorphic class Ib or CD1 molecules
Light-emitting current of electrically driven single-photon sources
The time-dependent tunnelling current arising from the electron-hole
recombination of exciton state is theoretically studied using the
nonequilibrium Green's function technique and the Anderson model with two
energy levels. The charge conservation and gauge invariance are satisfied in
the tunnelling current. Apart from the classical capacitive charging and
discharging behavior, interesting oscillations superimpose on the tunnelling
current for the applied rectangular pulse voltage.Comment: 14 pages, 5 figure
A competitive environment for exploratory query expansion
Most information workers query digital libraries many times a day. Yet people have little opportunity to hone their skills in a controlled environment, or compare their performance with others in an objective way. Conversely, although search engine logs record how users evolve queries, they lack crucial information about the user's intent. This paper describes an environment for exploratory query expansion that pits users against each other and lets them compete, and practice, in their own time and on their own workstation. The system captures query evolution behavior on predetermined information-seeking tasks. It is publicly available, and the code is open source so that others can set up their own competitive environments
Extracting corpus specific knowledge bases from Wikipedia
Thesauri are useful knowledge structures for assisting information retrieval. Yet their production is labor-intensive, and few domains have comprehensive thesauri that cover domain-specific concepts and contemporary usage. One approach, which has been attempted without much success for decades, is to seek statistical natural language processing algorithms that work on free text. Instead, we propose to replace costly professional indexers with thousands of dedicated amateur volunteers--namely, those that are producing Wikipedia. This vast, open encyclopedia represents a rich tapestry of topics and semantics and a huge investment of human effort and judgment. We show how this can be directly exploited to provide WikiSauri: manually-defined yet inexpensive thesaurus structures that are specifically tailored to expose the topics, terminology and semantics of individual document collections. We also offer concrete evidence of the effectiveness of WikiSauri for assisting information retrieval
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The Volcker Rule: A Legal Analysis
This report provides an introduction to the Volcker Rule, which is the regulatory regime imposed upon banking institutions and their affiliates under Section 619 of the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010 (P.L. 111-203). The Volker Rule is designed to prohibit âbanking entitiesâ from engaging in all forms of âproprietary tradingâ (i.e., making investments for their own âtrading accountsâ)âactivities that former Federal Reserve Chairman Paul A. Volcker often condemned as contrary to conventional banking practices and a potential risk to financial stability. The statutory language provides only general outlines of prohibited activities and exceptions. Through it, however, Congress has empowered five federal financial regulators with authority to conduct coordinated rulemakings to fill in the details and complete the difficult task of crafting regulations to identify prohibited activities, while continuing to permit activities considered essential to the safety and soundness of banking institutions or to the maintenance of strong capital markets. In December 2014, more than two years after enactment of the law, coordinated implementing regulations were issued by the Office of the Comptroller of the Currency (OCC), the Federal Deposit Insurance Corporation (FDIC), the Board of Governors of the Federal Reserve System (FRB), the Securities and Exchange Commission (SEC), and the Commodity Futures Trading Commission (CFTC).
The Rule is premised on a two-pronged central core restricting activities by âbanking entitiesââa term that includes all FDIC-insured bank and thrift institutions; all bank, thrift, or financial holding companies; all foreign banking operations with certain types of presence in the United States; and all affiliates and subsidiaries of any of these entities. Specifically, the Rule broadly prohibits banking entities from engaging in âproprietary tradingâ and from making investments in or having relationships with hedge and similar âcovered fundsâ that are exempt from registering with the CFTC as commodity pool operators or with the SEC under the Investment Advisors Act. The Rule couples its broad prohibitions with numerous exclusions and by designating myriad activities as permissible so long as various terms and conditions are met, unless they otherwise would involve or result in a material conflict of interest; a material exposure to high-risk assets or high-risk trading strategies; pose a threat to the safety and soundness of the banking entity; or pose a threat to the financial stability of the United States.
The exceptions to the ban on proprietary trading include underwriting by securities underwriters; market-making âdesigned not to exceed the reasonably expected near term demands of clientsâ; trading in government securities; fiduciary activities; insurance company portfolio investments; and risk-mitigating hedging activities. The ban on investing in and owning âcovered fundsâ exempts certain types of funds, under specified conditions, and permits de minimis investment in any such fund up to 3% of the outstanding ownership interests of the fund with an aggregate cap on the total ownership interest in âcovered fundsâ of 3% of the banking entityâs core capital.
To prevent evasion, the Rule has extensive requirements mandating comprehensive compliance programs that include ongoing management involvement, precise metrics measuring risk assessment, verification and documentation of any activities conducted under one of the Ruleâs exceptions or exclusions, and recurring reports and assessments. Full compliance is required by July 21, 2015, subject to the possibility that further extensions may be provided by the regulators. In the case of investments involving âilliquid fundsâ subject to contractual provisions seriously impacting their marketability or sale, full divestiture might not be required until July 21, 2022
Selfdual spaces with complex structures, Einstein-Weyl geometry and geodesics
We study the Jones and Tod correspondence between selfdual conformal
4-manifolds with a conformal vector field and abelian monopoles on
Einstein-Weyl 3-manifolds, and prove that invariant complex structures
correspond to shear-free geodesic congruences. Such congruences exist in
abundance and so provide a tool for constructing interesting selfdual
geometries with symmetry, unifying the theories of scalar-flat Kahler metrics
and hypercomplex structures with symmetry. We also show that in the presence of
such a congruence, the Einstein-Weyl equation is equivalent to a pair of
coupled monopole equations, and we solve these equations in a special case. The
new Einstein-Weyl spaces, which we call Einstein-Weyl ``with a geodesic
symmetry'', give rise to hypercomplex structures with two commuting
triholomorphic vector fields.Comment: 30 pages, 7 figures, to appear in Ann. Inst. Fourier. 50 (2000
Extending Greenstone for Institutional Repositories
We examine the problem of designing a generalized system for building institutional repositories. Widely used schemes such as DSpace are tailored to a particular set of requirements: fixed metadata set; standard view when searching and browsing; pre-determined sequence for depositing items; built-in workflow for vetting new items. In contrast, Fedora builds in flexibility: institutional repositories are just one possible instantiationâhowever generality incurs a high overhead and uptake has been sluggish. This paper shows how existing components of the Greenstone software can be repurposed to provide a generalized institutional repository that falls between these extremes
The Effects of Characteristics of the Board of Commissioners and Audit Committee on the Level of Risk Disclosure in Financial Sector Service Companies in the Banking Sector Listed on the Indonesia Stock Exchange in the Period 2015-2017
The aim of this study is to examine the effects of the board of commissioners and audit committee characteristics such as the proportion of independent commissioners, the board of commissioner size, frequency of board meetings, audit committee size, the proportion of independent audit committee and frequency of audit committee meetings on the level of risk disclosures. The results show that the frequency of board meetings, the proportion of independent audit committee and frequency of audit committee meetings significantly affect the level of risk disclosures, while the proportion of independent commissioners, the board of commissioner size, and audit committee size do not significantly affect the level of risk disclosures. The results show that the proportion of independent commissioners, the board of commissioner size, frequency of board meetings, audit committee size, the proportion of independent audit committee and frequency of audit committee meetings simultaneously have significant effects on the level of risk disclosures. The results of the study provide investors the information regarding the risk that companies could have, and they are also useful as a basis for making decision
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