2,122 research outputs found
Equation of state of cosmic strings with fermionic current-carriers
The relevant characteristic features, including energy per unit length and
tension, of a cosmic string carrying massless fermionic currents in the
framework of the Witten model in the neutral limit are derived through
quantization of the spinor fields along the string. The construction of a Fock
space is performed by means of a separation between longitudinal modes and the
so-called transverse zero energy solutions of the Dirac equation in the vortex.
As a result, quantization leads to a set of naturally defined state parameters
which are the number densities of particles and anti-particles trapped in the
cosmic string. It is seen that the usual one-parameter formalism for describing
the macroscopic dynamics of current-carrying vortices is not sufficient in the
case of fermionic carriers.Comment: 30 pages, 15 figures, uses ReVTeX, equation of state corrected,
comments and references added. Accepted for publication in Phys. Rev.
LEP1 vs. Future Colliders: Effective Operators And Extended Gauge Group
In an effective Lagrangian approach to physics beyond the Standard Model, it
has been argued that imposing invariance severely restricts
the discovery potential of future colliders. We exhibit a possible way out in
an extended gauge group context.Comment: 14 pages , CERN-TH.6573/92 ULB.TH.04/92 (phyzzx, 3 eps-figs incl.
On the gravitational, dilatonic and axionic radiative damping of cosmic strings
We study the radiation reaction on cosmic strings due to the emission of
dilatonic, gravitational and axionic waves. After verifying the (on average)
conservative nature of the time-symmetric self-interactions, we concentrate on
the finite radiation damping force associated with the half-retarded minus
half-advanced ``reactive'' fields. We revisit a recent proposal of using a
``local back reaction approximation'' for the reactive fields. Using
dimensional continuation as convenient technical tool, we find, contrary to
previous claims, that this proposal leads to antidamping in the case of the
axionic field, and to zero (integrated) damping in the case of the
gravitational field. One gets normal positive damping only in the case of the
dilatonic field. We propose to use a suitably modified version of the local
dilatonic radiation reaction as a substitute for the exact (non-local)
gravitational radiation reaction. The incorporation of such a local
approximation to gravitational radiation reaction should allow one to complete,
in a computationally non-intensive way, string network simulations and to give
better estimates of the amount and spectrum of gravitational radiation emitted
by a cosmologically evolving network of massive strings.Comment: 48 pages, RevTex, epsfig, 1 figure; clarification of the domain of
validity of the perturbative derivation of the string equations of motion,
and of their renormalizabilit
Separability of Rotational Effects on a Gravitational Lens
We derive the deflection angle up to due to a Kerr gravitational
lens with mass and specific angular momentum . It is known that at the
linear order in and the Kerr lens is observationally equivalent to the
Schwarzschild one because of the invariance under the global translation of the
center of the lens mass. We show, however, nonlinear couplings break the
degeneracy so that the rotational effect becomes in principle separable for
multiple images of a single source. Furthermore, it is distinguishable also for
each image of an extended source and/or a point source in orbital motion. In
practice, the correction at becomes for the
supermassive black hole in our galactic center. Hence, these nonlinear
gravitational lensing effects are too small to detect by near-future
observations.Comment: 12 pages (RevTeX); accepted for publication in Phys. Rev.
Inhibition of NF-κB-mediated signaling by the cyclin-dependent kinase inhibitor CR8 overcomes pro-survival stimuli to induce apoptosis in chronic lymphocytic leukemia cells
Purpose: Chronic lymphocytic leukemia (CLL) is currently incurable with standard chemotherapeutic agents, highlighting the need for novel therapies. Overcoming proliferative and cytoprotective signals generated within the microenvironment of lymphoid organs is essential for limiting CLL progression and ultimately developing a cure.
Experimental Design: We assessed the potency of cyclin-dependent kinase (CDK) inhibitor CR8, a roscovitine analog, to induce apoptosis in primary CLL from distinct prognostic subsets using flow cytometry–based assays. CLL cells were cultured in in vitro prosurvival and proproliferative conditions to mimic microenvironmental signals in the lymphoid organs, to elucidate the mechanism of action of CR8 in quiescent and proliferating CLL cells using flow cytometry, Western blotting, and quantitative real-time PCR.
Results: CR8 was 100-fold more potent at inducing apoptosis in primary CLL cells than roscovitine, both in isolated culture and stromal-coculture conditions. Importantly, CR8 induced apoptosis in CD40-ligated CLL cells and preferentially targeted actively proliferating cells within these cultures. CR8 treatment induced downregulation of the antiapoptotic proteins Mcl-1 and XIAP, through inhibition of RNA polymerase II, and inhibition of NF-κB signaling at the transcriptional level and through inhibition of the inhibitor of IκB kinase (IKK) complex, resulting in stabilization of IκBα expression.
Conclusions: CR8 is a potent CDK inhibitor that subverts pivotal prosurvival and proproliferative signals present in the tumor microenvironment of CLL patient lymphoid organs. Our data support the clinical development of selective CDK inhibitors as novel therapies for CLL
The Wahlquist-Newman solution
Based on a geometrical property which holds both for the Kerr metric and for
the Wahlquist metric we argue that the Kerr metric is a vacuum subcase of the
Wahlquist perfect-fluid solution. The Kerr-Newman metric is a physically
preferred charged generalization of the Kerr metric. We discuss which geometric
property makes this metric so special and claim that a charged generalization
of the Wahlquist metric satisfying a similar property should exist. This is the
Wahlquist-Newman metric, which we present explicitly in this paper. This family
of metrics has eight essential parameters and contains the Kerr-Newman-de
Sitter and the Wahlquist metrics, as well as the whole Pleba\'nski limit of the
rotating C-metric, as particular cases. We describe the basic geometric
properties of the Wahlquist-Newman metric, including the electromagnetic field
and its sources, the static limit of the family and the extension of the
spacetime across the horizon.Comment: LaTeX, 18 pages, no figures. Accepted for publication in Phys. Rev.
Hall effect in the marginal Fermi liquid regime of high-Tc superconductors
The detailed derivation of a theory for transport in quasi-two-dimensional
metals, with small-angle elastic scattering and angle-independent inelastic
scattering is presented. The transport equation is solved for a model Fermi
surface representing a typical cuprate superconductor. Using the small-angle
elastic and the inelastic scattering rates deduced from angle-resolved
photoemission experiments, good quantitative agreement with the observed
anomalous temperature dependence of the Hall angle in optimally doped cuprates
is obtained, while the resistivity remains linear in temperature. The theory is
also extended to the frequency-dependent complex Hall angle
Opportunities for feeding forages to pigs in Uganda
Pigs can play an important role in risk diversification and livelihood security of many smallholder
and poor households in Uganda. Women and youth/children provide most of the pigproduction
labour, especially for forage collection, feeding and watering; and they are responsible
for about 90% of pigs produced in Uganda. In the smallholder production systems practised
both in rural and peri-urban areas, a variety of forage species are traditionally used for pig feeding,
the majority of them being gathered for several hours every day. Overall, there is an overreliance
on feeding crop residues, ‘weeds’ and forages both through collection and scavenging/
tethering, usually not meeting the nutritional requirements of pigs, which results in slow
growth rates. Data on feeding pigs in Uganda were collected during focus group discussions
and key informant interviews in three districts, Masaka, Mukono and Kamuli, during the years
2013–2014.
In Uganda, there has been generally limited research on pigs and pig systems, while forage
research has traditionally focused on feeding ruminants. A comprehensive literature review on
feeding forages to pigs in the tropics revealed that it is mainly animal nutritionists who concern
themselves with nutritional effects of forages on the animals and their suitability as pig feeds;
aspects of integrating cultivated forages into crop-livestock production systems, labour requirements,
gender issues, and economic returns are essentially not considered. Despite the widely
recognised constraint of insufficient animal feeds, especially during dry seasons, adoption of
cultivated forages in the tropics has been generally slow, and hindering factors have not been
fully understood. Some cultivated forages show nutritional attributes suitable for pigs, technically
making them an option to supplement pigs with farm-grown forages instead of purchased
concentrates. A paradox of feeding forages to pigs in Uganda has been identified, though, that
suggests a decreasing use potential of forages along a gradient from extensive (mostly rural)
to intensive (more urban) smallholder systems, whereas CIAT’s Tropical Forages Program presumes
an increasing forage adoption potential along a gradient from subsistence- to marketoriented
smallholder systems. Investigating this paradox carefully may help better understand
reasons and conditions of smallholders under which cultivated forages may be adopted or not
Structure of the ovaries of the Nimba otter shrew, Micropotamogale lamottei, and the Madagascar hedgehog tenrec, Echinops telfairi
The otter shrews are members of the subfamily Potamogalinae within the family Tenrecidae. No description of the ovaries of any member of this subfamily has been published previously. The lesser hedgehog tenrec, Echinops telfairi, is a member of the subfamily Tenrecinae of the same family and, although its ovaries have not been described, other members of this subfamily have been shown to have ovaries with non-antral follicles. Examination of these two species illustrated that non-antral follicles were characteristic of the ovaries of both species, as was clefting and lobulation of the ovaries. Juvenile otter shrews range from those with only small follicles in the cortex to those with 300- to 400-mu m follicles similar to those seen in non-pregnant and pregnant adults. As in other species, most of the growth of the oocyte occurred when follicles had one to two layers of granulosa cells. When larger follicles became atretic in the Nimba otter shrew, hypertrophy of the theca interna produced nodules of glandular interstitial tissue. In the tenrec, the hypertrophying theca interna cells in most large follicles appeared to undergo degeneration. Both species had some follicular fluid in the intercellular spaces between the more peripheral granulosa cells. It is suggested that this fluid could aid in separation of the cumulus from the remaining granulosa at ovulation. The protruding follicles in lobules and absence of a tunica albuginea might also facilitate ovulation of non-antral follicles. Ovaries with a thin-absent tunica albuginea and follicles with small-absent antra are widespread within both the Eulipotyphla and in the Afrosoricida, suggesting that such features may represent a primitive condition in ovarian development. Lobulated and deeply crypted ovaries are found in both groups but are not as common in the Eulipotyphla making inclusion of this feature as primitive more speculative. Copyright (C) 2005 S. Karger AG, Basel
Mass, Angular Momentum and Thermodynamics in Four-Dimensional Kerr-AdS Black Holes
In this paper, the connection between the Lorentz-covariant counterterms that
regularize the four-dimensional AdS gravity action and topological invariants
is explored. It is shown that demanding the spacetime to have a negative
constant curvature in the asymptotic region permits the explicit construction
of such series of boundary terms. The orthonormal frame is adapted to
appropriately describe the boundary geometry and, as a result, the boundary
term can be expressed as a functional of the boundary metric, extrinsic
curvature and intrinsic curvature. This choice also allows to write down the
background-independent Noether charges associated to asymptotic symmetries in
standard tensorial formalism. The absence of the Gibbons-Hawking term is a
consequence of an action principle based on a boundary condition different than
Dirichlet on the metric. This argument makes plausible the idea of regarding
this approach as an alternative regularization scheme for AdS gravity in all
even dimensions, different than the standard counterterms prescription. As an
illustration of the finiteness of the charges and the Euclidean action in this
framework, the conserved quantities and black hole entropy for four-dimensional
Kerr-AdS are computed.Comment: 15 pages,no figures,few references added,JHEP forma
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