Field Dependent Specific-Heat of Rare Earth Manganites

The low temperature specific heat C(H) of several rare-earth manganites (La_(0.7)Sr_(0.3)MnO_(3), Nd_(0.5)Sr_(0.5)MnO_(3), Pr_(0.5)Sr_(0.5)MnO_(3), La_(0.67)Ca_(0.33)MnO$_(3), La_(0.5)Ca_(0.5)MnO_(3), La_(0.45)Ca_(0.55)MnO_(3) and La_(0.33)Ca_(0.67)MnO_(3)) was measured as a function of magnetic field. We observed behaviour consistent with thermodynamic expectations, i.e., C(H) decreases with field for ferromagnetic metallic compounds by an amount which is in quantitative agreement with spin wave theory. We also find that C(H) increases with field in most compounds with a charge-ordered antiferromagnetic ground state. In compounds which show evidence of a coexistence of ferromagnetic metallic and antiferromagnetic charge-ordered states, C(H) displays some unusual non-equilibrium effects presumably associated with the phase-separation of the two states. We also observe a large anomalous low temperature specific heat at the doping induced metal-insulator transition (at x = 0.50) in La_(1-x)Ca_(x)MnO_(3).Comment: 13 pages, LATEX, 7 PDF figure

Isospin splitting in heavy baryons and mesons

A recent general analysis of light-baryon isospin splittings is updated and extended to charmed baryons. The measured $\Sigma_c$ and $\Xi_c$ splittings stand out as being difficult to understand in terms of two-body forces alone. We also discuss heavy-light mesons; though the framework here is necessarily less general, we nevertheless obtain some predictions that are not strongly model-dependent.Comment: 12 pages REVTEX 3, plus 4 uuencoded ps figures, CMU-HEP93-

Work function changes in the double layered manganite La1.2Sr1.8Mn2O7

We have investigated the behaviour of the work function of La1.2Sr1.8Mn2O7 as a function of temperature by means of photoemission. We found a decrease of 55 +/- 10 meV in going from 60 K to just above the Curie temperature (125 K) of the sample. Above T_C the work function appears to be roughly constant. Our results are exactly opposite to the work function changes calculated from the double-exchange model by Furukawa, but are consistent with other measurements. The disagreement with double-exchange can be explained using a general thermodynamic relation valid for second order transitions and including the extra processes involved in the manganites besides double-exchange interaction.Comment: 6 pages, 4 figures included in tex

Parity violating target asymmetry in electron - proton scattering

We analyze the parity-violating (PV) components of the analyzing power in elastic electron-proton scattering and discuss their sensitivity to the strange quark contributions to the proton weak form factors. We point out that the component of the analyzing power along the momentum transfer is independent of the electric weak form factor and thus compares favorably with the PV beam asymmetry for a determination of the strangeness magnetic moment. We also show that the transverse component could be used for constraining the strangeness radius. Finally, we argue that a measurement of both components could give experimental information on the strangeness axial charge.Comment: 24 pages, Latex, 5 eps figures, submitted to Phys.Rev.

Hsp70 in mitochondrial biogenesis

The family of hsp70 (70 kilodalton heat shock protein) molecular chaperones plays an essential and diverse role in cellular physiology, Hsp70 proteins appear to elicit their effects by interacting with polypeptides that present domains which exhibit non-native conformations at distinct stages during their life in the cell. In this paper we review work pertaining to the functions of hsp70 proteins in chaperoning mitochondrial protein biogenesis. Hsp70 proteins function in protein synthesis, protein translocation across mitochondrial membranes, protein folding and finally the delivery of misfolded proteins to proteolytic enzymes in the mitochondrial matrix

Meson Cloud of the Nucleon in Polarized Semi-Inclusive Deep-Inelastic Scattering

We investigate the possibility of identifying an explicit pionic component of the nucleon through measurements of polarized $\Delta^{++}$ baryon fragments produced in deep-inelastic leptoproduction off polarized protons, which may help to identify the physical mechanism responsible for the breaking of the Gottfried sum rule. The pion-exchange model predicts highly correlated polarizations of the $\Delta^{++}$ and target proton, in marked contrast with the competing diquark fragmentation process. Measurement of asymmetries in polarized $\Lambda$ production may also reveal the presence of a kaon cloud in the nucleon.Comment: 23 pages REVTeX, 7 uuencoded figures, accepted for publication in Zeit. Phys.

The Tug1 locus is essential for male fertility

Background: Several long noncoding RNAs (lncRNAs) have been shown to function as central components of molecular machines that play fundamental roles in biology. While the number of annotated lncRNAs in mammalian genomes has greatly expanded, their functions remain largely uncharacterized. This is compounded by the fact that identifying lncRNA loci that have robust and reproducible phenotypes when mutated has been a challenge. Results: We previously generated a cohort of 20 lncRNA loci knockout mice. Here, we extend our initial study and provide a more detailed analysis of the highly conserved lncRNA locus, Taurine Upregulated Gene 1 (Tug1). We report that Tug1 knockout male mice are sterile with complete penetrance due to a low sperm count and abnormal sperm morphology. Having identified a lncRNA loci with a robust phenotype, we wanted to determine which, if any, potential elements contained in the Tug1 genomic region (DNA, RNA, protein, or the act of transcription) have activity. Using engineered mouse models and cell-based assays, we provide evidence that the Tug1 locus harbors three distinct regulatory activities - two noncoding and one coding: (i) a cis DNA repressor that regulates many neighboring genes, (ii) a lncRNA that can regulate genes by a trans-based function, and finally (iii) Tug1 encodes an evolutionary conserved peptide that when overexpressed impacts mitochondrial membrane potential. Conclusions: Our results reveal an essential role for the Tug1 locus in male fertility and uncover three distinct regulatory activities in the Tug1 locus, thus highlighting the complexity present at lncRNA loci

The Physics of Cluster Mergers

Clusters of galaxies generally form by the gravitational merger of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. Some of the basic physical properties of mergers will be discussed, with an emphasis on simple analytic arguments rather than numerical simulations. Semi-analytic estimates of merger rates are reviewed, and a simple treatment of the kinematics of binary mergers is given. Mergers drive shocks into the intracluster medium, and these shocks heat the gas and should also accelerate nonthermal relativistic particles. X-ray observations of shocks can be used to determine the geometry and kinematics of the merger. Many clusters contain cooling flow cores; the hydrodynamical interactions of these cores with the hotter, less dense gas during mergers are discussed. As a result of particle acceleration in shocks, clusters of galaxies should contain very large populations of relativistic electrons and ions. Electrons with Lorentz factors gamma~300 (energies E = gamma m_e c^2 ~ 150 MeV) are expected to be particularly common. Observations and models for the radio, extreme ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles accelerated in these mergers are described.Comment: 38 pages with 9 embedded Postscript figures. To appear in Merging Processes in Clusters of Galaxies, edited by L. Feretti, I. M. Gioia, and G. Giovannini (Dordrecht: Kluwer), in press (2001

Liouville theorems for harmonic maps

We prove several Liouville theorems for harmonic maps between certain classes of Riemannian manifolds. In particular, the results can be applied to harmonic maps from the Euclidean space ( R m , g 0 ) to a large class of Riemannian manifolds. Our assumptions on the harmonic maps concern the asymptotic behavior of the maps at ∞.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46575/1/222_2005_Article_BF02100594.pd