854 research outputs found
Approach to the extremal limit of the Schwarzschild-de Sitter black hole
The quasinormal-mode spectrum of the Schwarzschild-de Sitter black hole is
studied in the limit of near-equal black-hole and cosmological radii. It is
found that the mode_frequencies_ agree with the P"oschl-Teller approximation to
one more order than previously realized, even though the effective_potential_
does not. Whether the spectrum approaches the limiting one uniformly in the
mode index is seen to depend on the chosen units (to the order investigated). A
perturbation framework is set up, in which these issues can be studied to
higher order in future.Comment: REVTeX4, 4pp., no figures. N.B. "Alec" is my first, and "Maassen van
den Brink" my family name. v2: added numerical verificatio
Prediction of thyroid C-cell carcinogenicity after chronic administration of GLP1-R agonists in rodents Toxicology and Applied Pharmacology
Increased incidence of C-cell carcinogenicity has been observed for glucagon-like-protein-1 receptor (GLP-1r)
agonists in rodents. It is suggested that the duration of exposure is an indicator of carcinogenic potential in rodents
of the different products on the market. Furthermore, the role of GLP-1-related mechanisms in the induction
of C-cell carcinogenicity has gained increased attention by regulatory agencies. This study proposes an
integrative pharmacokinetic/pharmacodynamic (PKPD) framework to identify explanatory factors and characterize
differences in carcinogenic potential of the GLP-1r agonist products. PK models for four products
(exenatide QW (once weekly), exenatide BID (twice daily), liraglutide and lixisenatide) were developed using
nonlinear mixed effects modelling. Predicted exposure was subsequently linked to GLP-1r stimulation using in
vitro GLP-1r potency data. A logistic regression model was then applied to exenatide QW and liraglutide data
to assess the relationship between GLP-1r stimulation and thyroid C-cell hyperplasia incidence as pre-neoplastic
predictor of a carcinogenic response. The model showed a significant association between predicted GLP-1r stimulation
and C-cell hyperplasia after 2 years of treatment. The predictive performance of the model was evaluated
using lixisenatide, for which hyperplasia data were accurately described during the validation step. The use of a
model-based approach provided insight into the relationship between C-cell hyperplasia and GLP-1r stimulation
for all four products, which is not possible with traditional data analysis methods. It can be concluded that both
pharmacokinetics (exposure) and pharmacodynamics (potency for GLP-1r) factors determine C-cell hyperplasia
incidence in rodents. Our work highlights the pharmacological basis for GLP-1r agonist-induced C-cell carcinogenicity.
The concept is promising for application to other drug classes
Single Hole Green's Functions in Insulating Copper Oxides at Nonzero Temperature
We consider the single hole dynamics in a modified model at finite
temperature. The modified model includes a next nearest () and next-next
nearest () hopping. The model has been considered before in the zero
temperature limit to explain angle resolved photo-emission measurements. We
extend this consideration to the case of finite temperature where long-range
anti-ferromagnetic order is destroyed, using the self-consistent Born
approximation. The Dyson equation which relates the single hole Green's
functions for a fixed pseudo-spin and for fixed spin is derived. The Green's
function with fixed pseudo-spin is infrared stable but the Green's function
with fixed spin is close to an infrared divergency. We demonstrate how to
renormalize this Green's function in order to assure numerical convergence. At
non-zero temperature the quasi-particle peaks are found to shift down in energy
and to be broadened.Comment: 7 pages, RevTex, 5 Postscript figure
Conductive Cooling of SDD and SSD Front-End Chips for ALICE
We present analysis, technology developments and test results of the heat drain system of the SDD and SSD front-end electronics for the ALICE Inner Tracker System (ITS). Application of super thermoconductive carbon fibre thin plates provides a practical solution for the development of miniature motherboards for the FEE chips situated inside the sensitive ITS volume. Unidirectional carbon fibre motherboards of 160 -300 micron thickness ensure the mounting of the FEE chips and an efficient heat sink to the cooling arteries. Thermal conductivity up to 1.3 times better than copper is achieved while preserving a negligible multiple scattering contribution by the material (less than 0.15 percent of X/Xo)
Optical conductivity in the normal state fullerene superconductors
We calculate the optical conductivity, , in the normal state
fullerene superconductors by self-consistently including the impurity
scatterings, the electron-phonon and electron-electron Coulomb interactions.
The finite bandwidth of the fullerenes is explicitely considered, and the
vertex corection is included Nambu in calculating the renormalized
Green's function. is obtained by calculating the
current-current correlation function with the renormalized Green's function in
the Matsubara frequency and then performing analytic continuation to the real
frequency at finite temperature. The Drude weight in is
strongly suppressed due to the interactions and transfered to the mid-infrared
region around and above 0.06 eV which is somewhat less pronounced and much
broader compared with the expermental observation by DeGiorgi .Comment: 6 pages, 4 figures. To be published in Physical Review B, July 1
Frenkel and charge transfer excitons in C60
We have studied the low energy electronic excitations of C60 using momentum
dependent electron energy-loss spectroscopy in transmission. The momentum
dependent intensity of the gap excitation allows the first direct experimental
determination of the energy of the 1Hg excitation and thus also of the total
width of the multiplet resulting from the gap transition. In addition, we could
elucidate the nature of the following excitations - as either Frenkel or charge
transfer excitons.Comment: RevTEX, 3 Figures, to appear in Phys. Rev.
Effect of magnetic frustration on single-hole spectral function in the t-t'-t''-J model
We examine the effect of the magnetic frustration J' on the single-hole
spectral function in the t-t'-t''-J model. At zero temperature, the exact
diagonalization (ED) and the self-consistent Born approximation (SCBA) methods
are used. We find that the frustration suppresses the quasiparticle (QP) weight
at small momentum k, whereas the QP peak at k=(pi/2,pi/2) remains sharp. We
also show the temperature dependence of the single-hole spectral function by
using the ED method. It is found that the lineshapes at (pi/2,0) and
(pi/2,pi/2) show different temperature dependence. These findings are
consistent with the angle-resolved photoemission data on Sr2CuO2Cl2, and
indicate the importance of the magnetic frustration on the electronic states of
the insulating cuprates.Comment: 5 pages, 3 EPS figures, REVTeX, To be published in Phys. Rev. B, Vol.
59, Num. 3 (15 Jan. 1999
Numerical analysis of quasinormal modes in nearly extremal Schwarzschild-de Sitter spacetimes
We calculate high-order quasinormal modes with large imaginary frequencies
for electromagnetic and gravitational perturbations in nearly extremal
Schwarzschild-de Sitter spacetimes. Our results show that for low-order
quasinormal modes, the analytical approximation formula in the extremal limit
derived by Cardoso and Lemos is a quite good approximation for the quasinormal
frequencies as long as the model parameter is small enough, where
and are the black hole horizon radius and the surface gravity,
respectively. For high-order quasinormal modes, to which corresponds
quasinormal frequencies with large imaginary parts, on the other hand, this
formula becomes inaccurate even for small values of . We also find
that the real parts of the quasinormal frequencies have oscillating behaviors
in the limit of highly damped modes, which are similar to those observed in the
case of a Reissner-Nordstr{\" o}m black hole. The amplitude of oscillating
as a function of approaches a non-zero
constant value for gravitational perturbations and zero for electromagnetic
perturbations in the limit of highly damped modes, where denotes the
quasinormal frequency. This means that for gravitational perturbations, the
real part of quasinormal modes of the nearly extremal Schwarzschild-de Sitter
spacetime appears not to approach any constant value in the limit of highly
damped modes. On the other hand, for electromagnetic perturbations, the real
part of frequency seems to go to zero in the limit.Comment: 9 pages, 7 figures, to appear in Physical Review
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