6,901 research outputs found
Systematics of Heavy Quark Production at HERA
We discuss heavy quark and quarkonium production in various kinematic regions
at the HERA ep collider. In contrast to fixed target experiments, collider
kinematics allows the possibility of detailed measurements of particle
production in the proton fragmentation region. One thus can study parton
correlations in the proton Fock states materialized by the virtual photon
probe. We discuss various configurations of inelastic electron-proton
scattering, including peripheral, diffractive, and deep inelastic processes. In
particular, we show that intrinsic heavy quark Fock states can be identified by
the observation of quarkonium production at large and a low mean
transverse momentum which is insensitive to the virtuality of the photon.Comment: 17 pages, postscript. To obtain a copy of this paper send e-mail to
[email protected]
Phylogeny, ultrastructure, histopathology and prevalence of Myxobolus oliveirai sp. nov., a parasite of Brycon hilarii (Characidae) in the Pantanal wetland, Brazil
This paper presents the morphological, histological and ultrastructural characteristics of Myxobolus oliveirai sp. nov., a parasite of the gill filaments in Brycon hilarii from the Brazilian Pantanal. Out of 216 B. hilariispecimens examined (126 wild and 90 cultivated), 38.1% of wild specimens (n = 48) were infected. The parasites form elongated plasmodia primarily in the tip of gill filaments, reaching about 3 mm in length. A thorough comparison with all the Myxobolus species described from South American hosts, as well as nearly all the Myxobolus species described so far is provided. Partial sequencing of the 18S rDNA gene revealed a total of 1,527 bp. The Myxobolus species parasite of B. hilarii did not match any of the Myxozoa available in GenBank. In the phylogenetic analysis, M. oliveirai sp. nov. composed a monophyletic group with eight other species: five species of Myxobolus parasites of mugilid fishes, two parasites of pangasiid and one of centrarchid. Infection prevalence values of the parasite revealed no significant differences between wet and dry seasons or between males and females. The importance of the infection to the farming of the host species is emphasized.FAPESPCEPTA - ICMBioCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES
Phylogeny, ultrastructure, histopathology and prevalence of Myxobolus oliveirai sp. nov., a parasite of Brycon hilarii (Characidae) in the Pantanal wetland, Brazil
This paper presents the morphological, histological and ultrastructural characteristics of Myxobolus oliveirai sp. nov., a parasite of the gill filaments in Brycon hilarii from the Brazilian Pantanal. Out of 216 B. hilariispecimens examined (126 wild and 90 cultivated), 38.1% of wild specimens (n = 48) were infected. The parasites form elongated plasmodia primarily in the tip of gill filaments, reaching about 3 mm in length. A thorough comparison with all the Myxobolus species described from South American hosts, as well as nearly all the Myxobolus species described so far is provided. Partial sequencing of the 18S rDNA gene revealed a total of 1,527 bp. The Myxobolus species parasite of B. hilarii did not match any of the Myxozoa available in GenBank. In the phylogenetic analysis, M. oliveirai sp. nov. composed a monophyletic group with eight other species: five species of Myxobolus parasites of mugilid fishes, two parasites of pangasiid and one of centrarchid. Infection prevalence values of the parasite revealed no significant differences between wet and dry seasons or between males and females. The importance of the infection to the farming of the host species is emphasized1056762769sem informaçã
Color-Octet Fraction in J/Psi Production and Absorption
The cross section between a pair and a nucleon is small and
sensitive to the separation if the pair is in a color-singlet
state, but very large and insensitive to the separation if it is in a
color-octet state. We use this property in an absorption model involving both
color components to deduce the color structure of pairs produced in
reactions. Our analysis shows that the NA3, NA38 and E772
data are not inconsistent with the theoretical picture that color-octet and
color-singlet precursors are produced in roughly equal proportions if the
produced color-singlet precursors are pointlike and transparent. However, if
the color-singlet precursors are not transparent but have a cross section of a
few mb, these data do show a definite preference for a larger fraction of
color-singlet precursors. In either case, the color-octet fraction increases
with , approaching unity as becomes large.Comment: 9 pages, updated to include new result
A novel method to identify Post-Aire stages of medullary thymic epithelial cell differentiation
Leukocyte and lymphoid organ ontogeny
Autoimmune regulator+ (Aire) medullary thymic epithelial cells (mTECs) play a critical role in tolerance induction. Several studies demonstrated that Aire+mTECs differentiate further into Post-Aire cells. Yet, the identification of terminal stages of mTEC maturation depends on unique fate-mapping mouse models. Herein, we resolve this limitation by segmenting the mTEChi(MHCIIhiCD80hi) compartment into mTECA/hi (CD24−Sca1−), mTECB/hi (CD24+Sca1−), and mTECC/hi (CD24+Sca1+). While mTECA/hi included mostly Aire-expressing cells, mTECB/hi contained Aire+ and Aire− cells and mTECC/hi were mainly composed of cells lacking Aire. The differential expression pattern of Aire led us to investigate the precursor-product relationship between these subsets. Strikingly, transcriptomic analysis of mTECA/hi, mTECB/hi, and mTECC/hi sequentially mirrored the specific genetic program of Early-, Late- and Post-Aire mTECs. Corroborating their Post-Aire nature, mTECC/hi downregulated the expression of tissue-restricted antigens, acquired traits of differentiated keratinocytes, and were absent in Aire-deficient mice. Collectively, our findings reveal a new and simple blueprint to survey late stages of mTEC differentiation
On the Delta V_HB_bump parameter in Globular Clusters
We present new empirical estimates of the Delta V_HB_bump parameter for 15
Galactic globular clusters (GGCs) using accurate and homogeneous ground-based
optical data. Together with similar evaluations available in the literature, we
ended up with a sample of 62 GGCs covering a very broad range in metal content
(-2.16<=[M/H]<=-0.58 dex). Adopting the homogeneous metallicity scale provided
either by Kraft & Ivans (2004) or by Carretta et al. (2009), we found that the
observed Delta V_HB_bump parameters are larger than predicted. In the
metal-poor regime ([M/H]<=-1.7, -1.6 dex) 40% of GCs show discrepancies of
2sigma (~0.40 mag) or more. Evolutionary models that account either for alpha-
and CNO-enhancement or for helium enhancement do not alleviate the discrepancy
between theory and observations. The outcome is the same if we use the new
Solar heavy-element mixture. The comparison between alpha- and CNO-enhanced
evolutionary models and observations in the Carretta et al. metallicity scale
also indicates that observed Delta V_HB_bump parameters, in the metal-rich
regime ([M/H]=>0), might be systematically smaller than predicted
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