1,887 research outputs found
Anderson transition in the three dimensional symplectic universality class
We study the Anderson transition in the SU(2) model and the Ando model. We
report a new precise estimate of the critical exponent for the symplectic
universality class of the Anderson transition. We also report numerical
estimation of the function.Comment: 4 pages, 5 figure
Critical Behavior of the Conductivity of Si:P at the Metal-Insulator Transition under Uniaxial Stress
We report new measurements of the electrical conductivity sigma of the
canonical three-dimensional metal-insulator system Si:P under uniaxial stress
S. The zero-temperature extrapolation of sigma(S,T -> 0) ~\S - S_c\^mu shows an
unprecidentedly sharp onset of finite conductivity at S_c with an exponent mu =
1. The value of mu differs significantly from that of earlier stress-tuning
results. Our data show dynamical sigma(S,T) scaling on both metallic and
insulating sides, viz. sigma(S,T) = sigma_c(T) F(\S - S_cT^y) where sigma_c(T)
is the conductivity at the critical stress S_c. We find y = 1/znu = 0.34 where
nu is the correlation-length exponent and z the dynamic critical exponent.Comment: 5 pages, 4 figure
Revisiting the Theory of Finite Size Scaling in Disordered Systems: \nu Can Be Less Than 2/d
For phase transitions in disordered systems, an exact theorem provides a
bound on the finite size correlation length exponent: \nu_{FS}<= 2/d. It is
believed that the true critical exponent \nu of a disorder induced phase
transition satisfies the same bound. We argue that in disordered systems the
standard averaging introduces a noise, and a corresponding new diverging length
scale, characterized by \nu_{FS}=2/d. This length scale, however, is
independent of the system's own correlation length \xi. Therefore \nu can be
less than 2/d. We illustrate these ideas on two exact examples, with \nu < 2/d.
We propose a new method of disorder averaging, which achieves a remarkable
noise reduction, and thus is able to capture the true exponents.Comment: 4 pages, Latex, one figure in .eps forma
Evaluation of Novel Imidazotetrazine Analogues Designed to Overcome Temozolomide Resistance and Glioblastoma Regrowth
The cellular responses to two new temozolomide (TMZ) analogues, DP68 and DP86, acting against glioblastoma multi- forme (GBM) cell lines and primary culture models are reported. Dose–response analysis of cultured GBM cells revealed that DP68 is more potent than DP86 and TMZ and that DP68 was effective even in cell lines resistant to TMZ. On the basis of a serial neurosphere assay, DP68 inhibits repop- ulation of these cultures at low concentrations. The efficacy of these compounds was independent of MGMT and MMR func- tions. DP68-induced interstrand DNA cross-links were dem- onstrated with H2O2-treated cells. Furthermore, DP68 induced a distinct cell–cycle arrest with accumulation of cells in S phase that is not observed for TMZ. Consistent with this biologic response, DP68 induces a strong DNA damage response, including phosphorylation of ATM, Chk1 and Chk2 kinases, KAP1, and histone variant H2AX. Suppression of FANCD2 expression or ATR expression/kinase activity enhanced anti- glioblastoma effects of DP68. Initial pharmacokinetic analysis revealed rapid elimination of these drugs from serum. Collec- tively, these data demonstrate that DP68 is a novel and potent antiglioblastoma compound that circumvents TMZ resistance, likely as a result of its independence from MGMT and mismatch repair and its capacity to cross-link strands of DN
Does a magnetic field modify the critical behaviour at the metal-insulator transition in 3-dimensional disordered systems?
The critical behaviour of 3-dimensional disordered systems with magnetic
field is investigated by analyzing the spectral fluctuations of the energy
spectrum. We show that in the thermodynamic limit we have two different
regimes, one for the metallic side and one for the insulating side with
different level statistics. The third statistics which occurs only exactly at
the critical point is {\it independent} of the magnetic field. The critical
behaviour which is determined by the symmetry of the system {\it at} the
critical point should therefore be independent of the magnetic field.Comment: 10 pages, Revtex, 4 PostScript figures in uuencoded compressed tar
file are appende
Scaling of the Conductivity with Temperature and Uniaxial Stress in Si:B at the Metal-Insulator Transition
Using uniaxial stress to tune Si:B through the metal-insulator transition we
find the conductivity at low temperatures shows an excellent fit to scaling
with temperature and stress on both sides of the transition. The scaling
functions yield the conductivity in the metallic and insulating phases, and
allow a reliable determination of the temperature dependence in the critical
regions on both sides of the transition
Conductivity of Metallic Si:B near the Metal-Insulator Transition: Comparison between Unstressed and Uniaxially Stressed Samples
The low-temperature dc conductivities of barely metallic samples of p-type
Si:B are compared for a series of samples with different dopant concentrations,
n, in the absence of stress (cubic symmetry), and for a single sample driven
from the metallic into the insulating phase by uniaxial compression, S. For all
values of temperature and stress, the conductivity of the stressed sample
collapses onto a single universal scaling curve. The scaling fit indicates that
the conductivity of si:B is proportional to the square-root of T in the
critical range. Our data yield a critical conductivity exponent of 1.6,
considerably larger than the value reported in earlier experiments where the
transition was crossed by varying the dopant concentration. The larger exponent
is based on data in a narrow range of stress near the critical value within
which scaling holds. We show explicitly that the temperature dependences of the
conductivity of stressed and unstressed Si:B are different, suggesting that a
direct comparison of the critical behavior and critical exponents for stress-
tuned and concentration-tuned transitions may not be warranted
Absence of non-linear Meissner effect in YBa2Cu3O6.95
We present measurements the field and temperature dependence of the
penetration depth (lambda) in high purity, untwinned single crystals of
YBa2Cu3O6.95 in all three crystallographic directions. The temperature
dependence of lambda is linear down to low temperatures, showing that our
crystals are extremely clean. Both the magnitude and temperature dependence of
the field dependent correction to lambda however, are considerably different
from that predicted from the theory of the non-linear Meissner effect for a
d-wave superconductor (Yip-Sauls theory). Our results suggest that the
Yip-Sauls effect is either absent or is unobservably small in the Meissner
state of YBa2Cu3O6.95.Comment: 4 pages, 4 figures (Latex file + Postscipt figures
Image of the Energy Gap Anisotropy in the Vibrational Spectum of a High Temperature Superconductor
We present a new method of determining the anisotropy of the gap function in
layered high-Tc superconductors. Careful inelastic neutron scattering
measurements at low temperature of the phonon dispersion curves in the (100)
direction in La_(1.85)Sr_(.15)CuO_4 would determine whether the gap is
predominately s-wave or d-wave. We also propose an experiment to determine the
gap at each point on a quasi-two-dimensional Fermi surface.Comment: 12 pages + 2 figures (included
Retargeted adenoviruses for radiation-guided gene delivery
The combination of radiation with radiosensitizing gene delivery or oncolytic viruses promises to provide an advantage that could improve the therapeutic results for glioblastoma. X-rays can induce significant molecular changes in cancer cells. We isolated the GIRLRG peptide that binds to radiation-inducible 78 kDa glucose-regulated protein (GRP78), which is overexpressed on the plasma membranes of irradiated cancer cells and tumor-associated microvascular endothelial cells. The goal of our study was to improve tumor-specific adenovirus-mediated gene delivery by selectively targeting the adenovirus binding to this radiation-inducible protein. We employed an adenoviral fiber replacement approach to conduct a study of the targeting utility of GRP78-binding peptide. We have developed fiber-modified adenoviruses encoding the GRP78-binding peptide inserted into the fiber-fibritin. We have evaluated the reporter gene expression of fiber-modified adenoviruses in vitro using a panel of glioma cells and a human D54MG tumor xenograft model. The obtained results demonstrated that employment of the GRP78-binding peptide resulted in increased gene expression in irradiated tumors following infection with fiber-modified adenoviruses, compared with untreated tumor cells. These studies demonstrate the feasibility of adenoviral retargeting using the GRP78-binding peptide that selectively recognizes tumor cells responding to radiation treatment
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