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

Scholars Forum: A New Model For Scholarly Communication

Scholarly journals have flourished for over 300 years because they successfully address a broad range of authors' needs: to communicate findings to colleagues, to establish precedence of their work, to gain validation through peer review, to establish their reputation, to know the final version of their work is secure, and to know their work will be accessible by future scholars. Eventually, the development of comprehensive paper and then electronic indexes allowed past work to be readily identified and cited. Just as postal service made it possible to share scholarly work regularly and among a broad readership, the Internet now provides a distribution channel with the power to reduce publication time and to expand traditional print formats by supporting multi-media options and threaded discourse. Despite widespread acceptance of the web by the academic and research community, the incorporation of advanced network technology into a new paradigm for scholarly communication by the publishers of print journals has not materialized. Nor have journal publishers used the lower cost of distribution on the web to make online versions of journals available at lower prices than print versions. It is becoming increasingly clear to the scholarly community that we must envision and develop for ourselves a new, affordable model for disseminating and preserving results, that synthesizes digital technology and the ongoing needs of scholars. In March 1997, with support from the Engineering Information Foundation, Caltech sponsored a Conference on Scholarly Communication to open a dialogue around key issues and to consider the feasibility of alternative undertakings. A general consensus emerged recognizing that the certification of scholarly articles through peer review could be "decoupled" from the rest of the publishing process, and that the peer review process is already supported by the universities whose faculty serve as editors, members of editorial boards, and referees. In the meantime, pressure to enact regressive copyright legislation has added another important element. The ease with which electronic files may be copied and forwarded has encouraged publishers and other owners of copyrighted material to seek means for denying access to anything they own in digital form to all but active subscribers or licensees. Furthermore, should publishers retain the only version of a publication in a digital form, there is a significant risk that this material may eventually be lost through culling little-used or unprofitable back-files, through not investing in conversion expense as technology evolves, through changes in ownership, or through catastrophic physical events. Such a scenario presents an intolerable threat to the future of scholarship

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

High-Resolution Simulations of Cosmic Microwave Background non-Gaussian Maps in Spherical Coordinates

We describe a new numerical algorithm to obtain high-resolution simulated maps of the Cosmic Microwave Background (CMB), for a broad class of non-Gaussian models. The kind of non-Gaussianity we account for is based on the simple idea that the primordial gravitational potential is obtained by a non-linear but local mapping from an underlying Gaussian random field, as resulting from a variety of inflationary models. Our technique, which is based on a direct realization of the potential in spherical coordinates and fully accounts for the radiation transfer function, allows to simulate non-Gaussian CMB maps down to the Planck resolution ($\ell_{\rm max} \sim 3,000$), with reasonable memory storage and computational time.Comment: 9 pages, 5 figures. Submitted to ApJ. A version with higher quality figures is available at http://www.pd.infn.it/~liguori/content.htm

Comparison of Magnetic Anomalies of Lithospheric Origin Measured by Satellite and Airborne Magnetometers over Western Canada

Crustal magnetic anomaly data from the OGO 2, 4 and 6 (Pogo) satellites are compared with upward-continued aeromagnetic data between 50 deg -85 deg N latitude and 220 deg - 260 deg E longitude. Agreement is good both in anomaly location and in amplitude, giving confidence that it is possible to proceed with the derivation and interpretation of satellite anomaly maps in all parts of the globe. The data contain a magnetic high over the Alpha ridge suggesting continental composition and a magnetic low over the southern Canada basin and northern Canadian Arctic islands (Sverdrup basin). The low in the Sverdrup basin corresponds to a region of high heat flow, suggesting a shallow Curie isotherm. A ridge of high field, with two distinct peaks in amplitude, is found over the northern portion of the platform deposits and a relative high is located in the central portion of the Churchill province. No features are present to indicate a magnetic boundary between Slave and Bear provinces, but a trend change is evident between Slave and Churchill provinces. South of 60 deg latitude a broad magnetic low is located over very thick (40-50 km) crust, interpreted to be a region of low magnetization

ITERA: IDL Tool for Emission-line Ratio Analysis

We present a new software tool to enable astronomers to easily compare observations of emission line ratios with those determined by photoionization and shock models, ITERA, the IDL Tool for Emission-line Ratio Analysis. This tool can plot ratios of emission lines predicted by models and allows for comparison of observed line ratios against grids of these models selected from model libraries associated with the tool. We provide details of the libraries of standard photoionization and shock models available with ITERA, and, in addition, present three example emission line ratio diagrams covering a range of wavelengths to demonstrate the capabilities of ITERA. ITERA, and associated libraries, is available from \url{http://www.brentgroves.net/itera.html}Comment: Accepted for New Astronomy, 3 figures. ITERA tool available to download from http://www.brentgroves.net/itera.htm

Nonlinear Evolution of the Genus Statistics with Zel'dovich Approximation

Evolution of genus density is calculated from Gaussian initial conditions using Zel'dovich approximation. A new approach is introduced which formulates the desired quantity in a rotationally invariant manner. It is shown that normalized genus density does not depend on the initial spectral shape but is a function of the fluctuation amplitude only.Comment: 21 pages, 6 Postscript figures, LaTe

Lagrangian bias in the local bias model

It is often assumed that the halo-patch fluctuation field can be written as a Taylor series in the initial Lagrangian dark matter density fluctuation field. We show that if this Lagrangian bias is local, and the initial conditions are Gaussian, then the two-point cross-correlation between halos and mass should be linearly proportional to the mass-mass auto-correlation function. This statement is exact and valid on all scales; there are no higher order contributions, e.g., from terms proportional to products or convolutions of two-point functions, which one might have thought would appear upon truncating the Taylor series of the halo bias function. In addition, the auto-correlation function of locally biased tracers can be written as a Taylor series in the auto-correlation function of the mass; there are no terms involving, e.g., derivatives or convolutions. Moreover, although the leading order coefficient, the linear bias factor of the auto-correlation function is just the square of that for the cross-correlation, it is the same as that obtained from expanding the mean number of halos as a function of the local density only in the large-scale limit. In principle, these relations allow simple tests of whether or not halo bias is indeed local in Lagrangian space. We discuss why things are more complicated in practice. We also discuss our results in light of recent work on the renormalizability of halo bias, demonstrating that it is better to renormalize than not. We use the Lognormal model to illustrate many of our findings.Comment: 14 pages, published on JCA