108 research outputs found
Self-Renormalization of the Classical Quasilocal Energy
Pointlike objects cause many of the divergences that afflict physical
theories. For instance, the gravitational binding energy of a point particle in
Newtonian mechanics is infinite. In general relativity, the analog of a point
particle is a black hole and the notion of binding energy must be replaced by
quasilocal energy. The quasilocal energy (QLE) derived by York, and elaborated
by Brown and York, is finite outside the horizon but it was not considered how
to evaluate it inside the horizon. We present a prescription for finding the
QLE inside a horizon, and show that it is finite at the singularity for a
variety of types of black hole. The energy is typically concentrated just
inside the horizon, not at the central singularity.Comment: 7 pages, 4 figure
Brown-York Energy and Radial Geodesics
We compare the Brown-York (BY) and the standard Misner-Sharp (MS) quasilocal
energies for round spheres in spherically symmetric space-times from the point
of view of radial geodesics. In particular, we show that the relation between
the BY and MS energies is precisely analogous to that between the
(relativistic) energy E of a geodesic and the effective (Newtonian) energy
E_{eff} appearing in the geodesic equation, thus shedding some light on the
relation between the two. Moreover, for Schwarzschild-like metrics we establish
a general relationship between the BY energy and the geodesic effective
potential which explains and generalises the recently observed connection
between negative BY energy and the repulsive behaviour of geodesics in the
Reissner-Nordstrom metric. We also comment on the extension of this connection
between geodesics and the quasilocal BY energy to regions inside a horizon.Comment: v3: 7 pages, shortened and revised version to appear in CQ
Bunching instability of rotating relativistic electron layers and coherent synchrotron radiation
We study the stability of a collisionless, relativistic, finite-strength,
cylindrical layer of charged particles in free space by solving the linearized
Vlasov-Maxwell equations and compute the power of the emitted electromagnetic
waves. The layer is rotating in an external magnetic field parallel to the
layer. This system is of interest to understanding the high brightness
temperature of pulsars which cannot be explained by an incoherent radiation
mechanism. Coherent synchrotron radiation has also been observed recently in
bunch compressors used in particle accelerators. We consider equilibrium layers
with a `thermal' energy spread and therefore a non-zero radial thickness. The
particles interact with their retarded electromagnetic self-fields. The effect
of the betatron oscillations is retained. A short azimuthal wavelength
instability is found which causes a modulation of the charge and current
densities. The growth rate is found to be an increasing function of the
azimuthal wavenumber, a decreasing function of the Lorentz factor, and
proportional to the square root of the total number of electrons. We argue that
the growth of the unstable perturbation saturates when the trapping frequency
of electrons in the wave becomes comparable to the growth rate. Owing to this
saturation we can predict the radiation spectrum for a given set of parameters.
Our predicted brightness temperatures are proportional to the square of the
number of particles and scale by the inverse five-third power of the azimuthal
wavenumber which is in rough accord with the observed spectra of radio pulsars.Comment: 15 pages, 9 figures, LaTeX; presented at the April Meeting in Denver,
Colorado 2004; numerous typos corrected, one approximation removed, one new
proof added, accepted for publication in Phys. Rev.
A Novel Mouse Synaptonemal Complex Protein Is Essential for Loading of Central Element Proteins, Recombination, and Fertility
The synaptonemal complex (SC) is a proteinaceous, meiosis-specific structure that is highly conserved in evolution. During meiosis, the SC mediates synapsis of homologous chromosomes. It is essential for proper recombination and segregation of homologous chromosomes, and therefore for genome haploidization. Mutations in human SC genes can cause infertility. In order to gain a better understanding of the process of SC assembly in a model system that would be relevant for humans, we are investigating meiosis in mice. Here, we report on a newly identified component of the murine SC, which we named SYCE3. SYCE3 is strongly conserved among mammals and localizes to the central element (CE) of the SC. By generating a Syce3 knockout mouse, we found that SYCE3 is required for fertility in both sexes. Loss of SYCE3 blocks synapsis initiation and results in meiotic arrest. In the absence of SYCE3, initiation of meiotic recombination appears to be normal, but its progression is severely impaired resulting in complete absence of MLH1 foci, which are presumed markers of crossovers in wild-type meiocytes. In the process of SC assembly, SYCE3 is required downstream of transverse filament protein SYCP1, but upstream of the other previously described CE–specific proteins. We conclude that SYCE3 enables chromosome loading of the other CE–specific proteins, which in turn would promote synapsis between homologous chromosomes
corona Is Required for Higher-Order Assembly of Transverse Filaments into Full-Length Synaptonemal Complex in Drosophila Oocytes
The synaptonemal complex (SC) is an intricate structure that forms between homologous chromosomes early during the meiotic prophase, where it mediates homolog pairing interactions and promotes the formation of genetic exchanges. In Drosophila melanogaster, C(3)G protein forms the transverse filaments (TFs) of the SC. The N termini of C(3)G homodimers localize to the Central Element (CE) of the SC, while the C-termini of C(3)G connect the TFs to the chromosomes via associations with the axial elements/lateral elements (AEs/LEs) of the SC. Here, we show that the Drosophila protein Corona (CONA) co-localizes with C(3)G in a mutually dependent fashion and is required for the polymerization of C(3)G into mature thread-like structures, in the context both of paired homologous chromosomes and of C(3)G polycomplexes that lack AEs/LEs. Although AEs assemble in cona oocytes, they exhibit defects that are characteristic of c(3)G mutant oocytes, including failure of AE alignment and synapsis. These results demonstrate that CONA, which does not contain a coiled coil domain, is required for the stable ‘zippering’ of TFs to form the central region of the Drosophila SC. We speculate that CONA's role in SC formation may be similar to that of the mammalian CE proteins SYCE2 and TEX12. However, the observation that AE alignment and pairing occurs in Tex12 and Syce2 mutant meiocytes but not in cona oocytes suggests that the SC plays a more critical role in the stable association of homologs in Drosophila than it does in mammalian cells
SYNOPSIS OF THE GENUS PISEINOTECUS WITH DESCRIPTION OF PISEINOTECUS-EVELINAE SPEC-NOV
Volume: 23Start Page: 21End Page: 2
Die embryonale Erythropoiese der Charadriiformes
Volume: 70Start Page: 677End Page: 68
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