485 research outputs found
Motion of charged particles around a rotating black hole in a magnetic field
We study the effects of an external magnetic field, which is assumed to be
uniform at infinity, on the marginally stable circular motion of charged
particles in the equatorial plane of a rotating black hole. We show that the
magnetic field has its greatest effect in enlarging the region of stability
towards the event horizon of the black hole. Using the Hamilton-Jacobi
formalism we obtain the basic equations governing the marginal stability of the
circular orbits and their associated energies and angular momenta. As
instructive examples, we review the case of the marginal stability of the
circular orbits in the Kerr metric, as well as around a Schwarzschild black
hole in a magnetic field. For large enough values of the magnetic field around
a maximally rotating black hole we find the limiting analytical solutions to
the equations governing the radii of marginal stability. We also show that the
presence of a strong magnetic field provides the possibility of relativistic
motions in both direct and retrograde innermost stable circular orbits around a
Kerr black hole.Comment: 25 pages, 2 figure
Holographic mesons in various dimensions
We calculate the spectrum of fluctuations of a probe Dk-brane in the
background of N Dp-branes, for k=p,p+2,p+4 and p< 5. The result corresponds to
the mesonic spectrum of a (p+1)-dimensional super-Yang-Mills (SYM) theory
coupled to `dynamical quarks', i.e., fields in the fundamental representation
-- the latter are confined to a defect for k=p and p+2. We find a universal
behaviour where the spectrum is discrete and the mesons are deeply bound. The
mass gap and spectrum are set by the scale M ~ m_q/g_{eff}(m_q), where m_q is
the mass of the fundamental fields and g_{eff}(m_q) is the effective coupling
evaluated at the quark mass, i.e. g_{eff}^2(m_q)=g_{ym}^2 N m_q^{p-3}. We
consider the evolution of the meson spectra into the far infrared of
three-dimensional SYM, where the gravity dual lifts to M-theory. We also argue
that the mass scale appearing in the meson spectra is dictated by holography.Comment: 44 pages, 2 figures; v2: typos corrected, references adde
Comparison of Jet Quenching Formalisms for a Quark-Gluon Plasma "Brick"
We review the currently available formalisms for radiative energy loss of a
high-momentum parton in a dense strongly interacting medium. The underlying
theoretical framework of the four commonly used formalisms is discussed and the
differences and commonalities between the formalisms are highlighted. A
quantitative comparison of the single gluon emission spectra as well as the
energy loss distributions is given for a model system consisting of a uniform
medium with a fixed length of L=2 fm and L=5 fm (the `Brick'). Sizable
quantitative differences are found. The largest differences can be attributed
to specific approximations that are made in the calculation of the radiation
spectrum.Comment: 30 pages, 24 figures update version2: added curves with large x to
Figure 14, Higher Twist curves to Figs 19, 20, plus some changes in the text
(introduction/summary, discussion of Fig 14 and HT section
Carboplatin (CBDCA), iproplatin (CHIP), and high dose cisplatin in hypertonic saline evaluated for tubular nephrotoxicity
We compared the acute tubular nephrotoxicity of three platinum compounds in children and adults with solid tumors by monitoring the urinary excretion of alanine aminopeptidase, N -acetyl-β-D-glucosaminidase, and total protein. Cisplatin (100 mg/m 2 ) was administered with mannitol, or at a twofold larger total dosage (50 mg/m 2 per day for 4 days) in a 3% saline infusion. Carboplatin (300 mg/m 2 ) was administered in combination with 5-fluorouracil, and iproplatin was administered in dosages ranging from 216 to 388 mg/m 2 . Enzymuria and proteinuria induced by cisplatin at a total dosage of 200 mg/m 2 on a divided schedule did not significantly differ from that observed for the single 100 mg/m 2 dose. Enzymuria and proteinuria induced by carboplatin and iproplatin were significantly less than that for cisplatin; however, one patient developed chronic tubular damage after three courses of carboplatin, and the acute tubular toxicity of iproplatin in one of 15 patients was exceptional. Our findings support the value of administering cisplatin in hypertonic saline on a divided schedule as a strategy to reduce acute tubular damage. Although carboplatin and iproplatin are less nephrotoxic than cisplatin, occasionally patients experience subclinical acute or chronic tubular damage that may lead to overt nephrotoxicity with continued therapy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46915/1/280_2004_Article_BF00296257.pd
NMR and NQR Fluctuation Effects in Layered Superconductors
We study the effect of thermal fluctuations of the s-wave order parameter of
a quasi two dimensional superconductor on the nuclear spin relaxation rate near
the transition temperature Tc. We consider both the effects of the amplitude
fluctuations and the Berezinskii-Kosterlitz-Thouless (BKT) phase fluctuations
in weakly coupled layered superconductors. In the treatment of the amplitude
fluctuations we employ the Gaussian approximation and evaluate the longitudinal
relaxation rate 1/T1 for a clean s-wave superconductor, with and without pair
breaking effects, using the static pair fluctuation propagator D. The increase
in 1/T1 due to pair breaking in D is overcompensated by the decrease arising
from the single particle Green's functions. The result is a strong effect on
1/T1 for even a small amount of pair breaking. The phase fluctuations are
described in terms of dynamical BKT excitations in the form of pancake
vortex-antivortex (VA) pairs. We calculate the effect of the magnetic field
fluctuations caused by the translational motion of VA excitations on 1/T1 and
on the transverse relaxation rate 1/T2 on both sides of the BKT transitation
temperature T(BKT)<Tc. The results for the NQR relaxation rates depend strongly
on the diffusion constant that governs the motion of free and bound vortices as
well as the annihilation of VA pairs. We discuss the relaxation rates for real
multilayer systems where the diffusion constant can be small and thus increase
the lifetime of a VA pair, leading to an enhancement of the rates. We also
discuss in some detail the experimental feasibility of observing the effects of
amplitude fluctuations in layered s-wave superconductors such as the
dichalcogenides and the effects of phase fluctuations in s- or d-wave
superconductors such as the layered cuprates.Comment: 38 pages, 12 figure
Pitfalls of Professionalism? Military Academies and Coup Risk
Military academies tend to be strongly linked to the professionalization of the armed forces. This explains why many countries in the world have created such institutions. The following article studies a potential negative externality stemming from military schools: increased coup risk. We argue that military academies may create, inculcate, and strengthen cohesive views that could conflict with incumbent policies, and that these schools establish networks among military officers that may facilitate coordination necessary for plotting a putsch. We also contend and empirically demonstrate that these negative side effects of military academies are in particular pronounced in nondemocracies, that is, military academies have diverse effects across regime types. This work has significant implications for our understanding civil–military relations. Furthermore, we contribute to the literature on military education and professionalization, as we suggest that military academies are important vehicles through which coups can emerge predominantly in authoritarian states
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