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Search Results: 1 - 10 of 155687 matches for " F. X. Hartmann "
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Constraints from $^{26}$Al Measurements on the Galaxy's Recent Global Star Formation Rate and Core Collapse Supernovae Rate
F. X. Timmes,R. Diehl,D. H. Hartmann
Physics , 1997, DOI: 10.1086/303913
Abstract: Gamma-rays from the decay of $^{26}$Al offer a stringent constraint on the Galaxy's global star formation rate over the past million years, supplementing other methods for quantifying the recent Galactic star formation rate, such as equivalent widths of H$\alpha$ emission. Advantages and disadvantages of using $^{26}$Al gamma-ray measurements as a tracer of the massive star formation rate are analyzed. Estimates of the Galactic $^{26}$Al mass derived from COMPTEL measurements are coupled with a simple, analytical model of the $^{26}$Al injection rate from massive stars and restrict the Galaxy's recent star formation rate to \hbox{5 $\pm$ 4 M\sun yr$^{-1}$}. In addition, we show that the derived $^{26}$Al mass implies a present day \hbox{Type II + Ib} supernovae rate of 3.4 $\pm$ 2.8 per century, which seems consistent with other independent estimates of the Galactic core collapse supernova rate. If some independent measure of the massive star initial mass function or star formation rate or \hbox{Type II + Ib} supernovae rate were to become available (perhaps through estimates of the Galactic $^{60}$Fe mass), then a convenient way to restrain, or possibly determine, the other parameters is presented.
A Novel Method for Real-Time, Continuous, Fluorescence-Based Analysis of Anti-DNA Abzyme Activity in Systemic Lupus
Michelle F. Cavallo,Anna M. Kats,Ran Chen,James X. Hartmann
Autoimmune Diseases , 2012, DOI: 10.1155/2012/814048
A Novel Method for Real-Time, Continuous, Fluorescence-Based Analysis of Anti-DNA Abzyme Activity in Systemic Lupus
Michelle F. Cavallo,Anna M. Kats,Ran Chen,James X. Hartmann,Mirjana Pavlovic
Autoimmune Diseases , 2012, DOI: 10.1155/2012/814048
Abstract: Systemic Lupus Erythematosus (SLE) is an autoimmune disease characterized by the production of antibodies against a variety of self-antigens including nucleic acids. These antibodies are cytotoxic, catalytic (hydrolyzing DNA, RNA, and protein), and nephritogenic. Current methods for investigating catalytic activities of natural abzymes produced by individuals suffering from autoimmunity are mostly discontinuous and often employ hazardous reagents. Here we demonstrate the utility of dual-labeled, fluorogenic DNA hydrolysis probes in highly specific, sensitive, continuous, fluorescence-based measurement of DNA hydrolytic activity of anti-ssDNA abzymes purified from the serum of patients suffering from SLE. An assay for the presence and levels of antibodies exhibiting hydrolytic activity could facilitate disease diagnosis, prediction of flares, monitoring of disease state, and response to therapy. The assay may allow indirect identification of additional targets of anti-DNA antibodies and the discovery of molecules that inhibit their activity. Combined, these approaches may provide new insights into molecular mechanisms of lupus pathogenesis. 1. Introduction Systemic Lupus Erythematosus (SLE) is a chronic, multifactorial, antigen-driven, systemic, autoimmune disease which often presents a broad spectrum of clinical entities. SLE is characterized by the production of an array of inflammation-inducing autoantibodies of IgG and IgM isotypes directed against nuclear antigens, including single-stranded (ss) and double-stranded (ds) DNA. High titers of both antibody classes are involved in disease development and associated with flare [1–4]. Titer of either species allows for differentiation between lupus patients and healthy donors and for monitoring patients in flare and with inactive disease [5–9]. Accordingly, anti-DNA antibody levels in patient sera are used to monitor disease activity and progression [10–12]. However, according to Shoenfeld et al. (1988), although titers vary significantly, anti-DNA antibodies are always detectable in the sera of all healthy mammals [13]. Additionally, methods for quantifying antibody titer can produce greatly varying results from the same serum sample [5] and simply measuring the titer of anti-DNA antibodies does not provide detailed information about antibody functionality or potential pathogenicity. Assaying for antibody hydrolytic activity, in addition to monitoring titer, may allow physicians to better predict changes in disease cycle as well as researchers to illuminate potential roles for abzymes in perpetuation of
The Production of Ti44 and Co60 in Supernova
F. X. Timmes,S. E. Woosley,D. H. Hartmann,R. D. Hoffman
Physics , 1995, DOI: 10.1086/177323
Abstract: The production of the radioactive isotopes $^{44}$Ti and $^{60}$Co in all types of supernovae is examined and compared to observational constraints including Galactic $\gamma$--ray surveys, measurements of the diffuse 511 keV radiation, $\gamma$--ray observations of Cas A, the late time light curve of SN 1987A, and isotopic anomalies found in silicon carbide grains in meteorites. The (revised) line flux from $^{44}$Ti decay in the Cas A supernova remnant reported by COMPTEL on the Compton Gamma-Ray Observatory is near the upper bound expected from our models. The necessary concurrent ejection of $^{56}$Ni would also imply that Cas A was a brighter supernova than previously thought unless extinction in the intervening matter was very large. Thus, if confirmed, the reported amount of $^{44}$Ti in Cas A provides very interesting constraints on both the supernova environment and its mechanism. The abundances of $^{44}$Ti and $^{60}$Co ejected by Type II supernovae are such that gamma-radiation from $^{44}$Ti decay SN 1987A could be detected by a future generation of gamma-ray telescopes and that the decay of $^{60}$Co might provide an interesting contribution to the late time light curve of SN 1987A and other Type II supernovae. To produce the solar $^{44}$Ca abundance and satisfy all the observational constraints, nature may prefer at least the occasional explosion of sub-Chandrasekhar mass white dwarfs as Type Ia supernovae. Depending on the escape fraction of positrons due to $^{56}$Co made in all kinds of Type Ia supernovae, a significant fraction of the steady state diffuse 511 keV emission may arise from the annihilation of positrons produced during the decay of $^{44}$Ti to $^{44}$Ca. The Ca and Ti isotopic anomalies in pre-solar grains confirm the production of $^{44}$Ti in supernovae and that
26Al and 60Fe From Supernova Explosions
F. X. Timmes,S. E. Woosley,D. H. Hartmann,R. D. Hoffman,T. A. Weaver,F. Matteucci
Physics , 1995, DOI: 10.1086/176046
Abstract: Using recently calculated yields for Type II supernovae, along with models for chemical evolution and the distribution of mass in the interstellar medium, the current abundances and spatial distributions of two key gamma-ray radioactivities, $^{26}$Al and $^{60}$Fe, are determined. The estimated steady state production rates are 2.0 $\pm$ 1.0 M\sun \ Myr$^{-1}$ for $^{26}$Al and 0.75 $\pm$ 0.4 M\sun \ Myr$^{-1}$ for $^{60}$Fe. This corresponds to 2.2 $\pm$ 1.1 M\sun \ of $^{26}$Al and 1.7 $\pm$ 0.9 M\sun \ of $^{60}$Fe in the present interstellar medium. Sources of uncertainty are discussed, one of the more important being the current rate of core collapse supernovae in the Galaxy. Our simple model gives three per century, but reasonable changes in the star formation rate could easily accommodate a core collapse rate one-half as large, and thus one-half the yields. When these stellar and chemical evolution results are mapped into a three dimensional model of the Galaxy, the calculated 1809 keV gamma-ray flux map is consistent with the {\it Compton Gamma Ray Observatory} observations of a steep decline in the flux outside a longitude of $\pm$ 50$^\circ$ from the Galactic center, and the slight flux enhancements observed in the vicinity of spiral arms. Other potential stellar sources of $^{26}$Al and $^{60}$Fe are mentioned, especially the possibility of $^{60}$Fe synthesis in Type Ia supernovae. Predictions for the $^{60}$Fe mass distribution, total mass, and flux map are given.
Large scale Gd-beta-diketonate based organic liquid scintillator production for antineutrino detection
C. Aberle,C. Buck,B. Gramlich,F. X. Hartmann,M. Lindner,S. Sch?nert,U. Schwan,S. Wagner,H. Watanabe
Physics , 2011, DOI: 10.1088/1748-0221/7/06/P06008
Abstract: Over the course of several decades, organic liquid scintillators have formed the basis for successful neutrino detectors. Gadolinium-loaded liquid scintillators provide efficient background suppression for electron antineutrino detection at nuclear reactor plants. In the Double Chooz reactor antineutrino experiment, a newly developed beta-diketonate gadolinium-loaded scintillator is utilized for the first time. Its large scale production and characterization are described. A new, light yield matched metal-free companion scintillator is presented. Both organic liquids comprise the target and "Gamma Catcher" of the Double Chooz detectors.
Interpolation in the Nevanlinna class and harmonic majorants
A. Hartmann,X. Massaneda,A. Nicolau,P. Thomas
Mathematics , 2003,
Abstract: We consider a free interpolation problem in Nevanlinna and Smirnov classes and find a characterization of the corresponding interpolating sequences in terms of the existence of harmonic majorants of certain functions. We also consider the related problem of characterizing positive functions in the disc having a harmonic majorant. An answer is given in terms of a dual relation which involves positive measures in the disc with bounded Poisson balayage. We deduce necessary and sufficient geometric conditions, both expressed in terms of certain maximal functions.
Elimination of the Landau Ghost from Chiral Solitons
J. Hartmann,F. Beck,W. Bentz
Physics , 1994, DOI: 10.1103/PhysRevC.50.3088
Abstract: We show a practical way based on the K\"{a}ll\'{e}n-Lehmann representation for the two-point functions to eliminate the instability of the vacuum against formation of small sized meson configurations in the chiral $\sigma$ model.
N* Masses from QCD Sum Rules
X. Liu,F. X. Lee
Physics , 2001,
Abstract: We report N* masses in the spin-1/2 and spin-3/2 sectors using the method of QCD Sum Rules. They are based on three independent sets derived from generalized interpolating fields. The predictive ability of each sum rule is examined by a Monte-Carlo based analysis procedure in which all three phenomenological parameters (mass, coupling, threshold) are extracted simultaneously. A parity projection technique is also studied.
Monster in the Dark: The Ultraluminous GRB 080607 and its Dusty Environment
Daniel A. Perley,A. N. Morgan,A. Updike,F. Yuan,C. W. Akerlof,A. A. Miller,J. S. Bloom,S. B. Cenko,W. Li,A. V. Filippenko,J. X. Prochaska,D. A. Kann,N. R. Butler,P. Christian,D. H. Hartmann,P. Milne,E. S. Rykoff,W. Rujopakarn,J. C. Wheeler,G. G. Williams
Physics , 2010, DOI: 10.1088/0004-6256/141/2/36
Abstract: We present early-time optical through infrared photometry of the bright gamma-ray burst GRB 080607, starting only 6 s following the initial trigger in the rest frame. Complemented by our previously published spectroscopy, this high-quality photometric dataset allows us to solve for the extinction properties of the redshift 3.036 sightline, giving perhaps the most detailed information on the ultraviolet continuum absorption properties of any sightline outside our Local Group to date. The extinction properties are not adequately modeled by any ordinary extinction template (including the average Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud curves), partially because the 2175-Angstrom feature (while present) is weaker by about a factor of two than when seen under similar circumstances locally. However, the spectral energy distribution is exquisitely fitted by the more general Fitzpatrick & Massa (1990) parameterization of Local-Group extinction, putting it in the same family as some peculiar Milky Way extinction curves. After correcting for this (considerable, A_V = 3.3 +/- 0.4 mag) extinction, GRB 080607 is revealed to have been among the most optically luminous events ever observed, comparable to the naked-eye burst GRB 080319B. Its early peak time (t_rest < 6 s) indicates a high initial Lorentz factor (Gamma > 600), while the extreme luminosity may be explained in part by a large circumburst density. Only because of its early high luminosity could the afterglow of GRB 080607 be studied in such detail in spite of the large attenuation and great distance, making this burst an excellent prototype for the understanding of other highly obscured extragalactic objects, and of the class of "dark" GRBs in particular.
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