361 research outputs found
Quasi-bound states of Schrodinger and Dirac electrons in magnetic quantum dot
The properties of a two-dimensional electron are investigated in the presence
of a circular step magnetic field profile. Both electrons with parabolic
dispersion as well as Dirac electrons with linear dispersion are studied. We
found that in such a magnetic quantum dot no electrons can be confined.
Nevertheless close to the Landau levels quasi-bound states can exist with a
rather long life time.Comment: 9 pages, 10 figure
Co-crystalization and in vitro biological characterization of 5-Aryl-4-(5-substituted-2-4-dihydroxyphenyl)-1,2,3-thiadiazole Hsp90 inhibitors
A potential therapeutic strategy for targeting cancer that has gained much interest is the inhibition of the ATP binding and ATPase activity of the molecular chaperone Hsp90. We have determined the structure of the human Hsp90α N-terminal domain in complex with a series of 5-aryl-4-(5-substituted-2-4-dihydroxyphenyl)-1,2,3-thiadiazoles. The structures provide the molecular details for the activity of these inhibitors. One of these inhibitors, ICPD 34, causes a structural change that affects a mobile loop, which adopts a conformation similar to that seen in complexes with ADP, rather than the conformation generally seen with the pyrazole/isoxazole-resorcinol class of inhibitors. Competitive binding to the Hsp90 N-terminal domain was observed in a biochemical assay, and these compounds showed antiproliferative activity and induced apoptosis in the HCT116 human colon cancer cell line. These inhibitors also caused induction of the heat shock response with the upregulation of Hsp72 and Hsp27 protein expression and the depletion of Hsp90 clients, CRAF, ERBB2 and CDK4, thus confirming that antiproliferative activity was through the inhibition of Hsp90. The presence of increased levels of the cleavage product of PARP indicated apoptosis in response to Hsp90 inhibitors. This work provides a framework for the further optimization of thiadiazole inhibitors of Hsp90. Importantly, we demonstrate that the thiadiazole inhibitors display a more limited core set of interactions relative to the clinical trial candidate NVP-AUY922, and consequently may be less susceptible to resistance derived through mutations in Hsp9
Currents in a many-particle parabolic quantum dot under a strong magnetic field
Currents in a few-electron parabolic quantum dot placed into a perpendicular
magnetic field are considered. We show that traditional ways of investigating
the Wigner crystallization by studying the charge density correlation function
can be supplemented by the examination of the density-current correlator.
However, care must be exercised when constructing the correct projection of the
multi-dimensional wave function space. The interplay between the magnetic field
and Euler-liquid-like behavior of the electron liquid gives rise to persistent
and local currents in quantum dots. We demonstrate these phenomena by collating
a quasi-classical theory valid in high magnetic fields and an exact numerical
solution of the many-body problem.Comment: Uses RevTeX4, figures included in the tex
Quantum states in a magnetic anti-dot
We study a new system in which electrons in two dimensions are confined by a
non homogeneous magnetic field. The system consists of a heterostructure with
on top of it a superconducting disk. We show that in this system electrons can
be confined into a dot region. This magnetic anti-dot has the interesting
property that the filling of the dot is a discrete function of the magnetic
field. The circulating electron current inside and outside the anti-dot can be
in opposite direction for certain bound states. And those states exhibit a
diamagnetic to paramagnetic transition with increasing magnetic field. The
absorption spectrum consists of many peaks, some of which violate Kohn's
theorem, and which is due to the coupling of the center of mass motion with the
other degrees of freedom.Comment: 6 pages, 12 ps figure
Resistance effects due to magnetic guiding orbits
The Hall and magnetoresistance of a two dimensional electron gas subjected to
a magnetic field barrier parallel to the current direction is studied as
function of the applied perpendicular magnetic field. The recent experimental
results of Nogaret {\em et al.} [Phys. Rev. Lett. {\bf 84}, 2231 (2000)] for
the magneto- and Hall resistance are explained using a semi-classical theory
based on the Landauer-B\"{u}ttiker formula. The observed positive
magnetoresistance peak is explained as due to a competition between a decrease
of the number of conducting channels as a result of the growing magnetic field,
from the fringe field of the ferromagnetic stripe as it becomes magnetized, and
the disappearance of snake orbits and the subsequent appearance of cycloidlike
orbits.Comment: 7 pages, 7 figure
Magnetic edge states of impenetrable stripe
The electron motion in a strong perpendicular magnetic field close to the
impenetrable stripe is considered by making use of the singular integral
equation technique. The energy spectrum is calculated and compared with the
energy spectrum of the round antidot.Comment: REVTeX4 format, 9 pages with 9 figures (*.eps
The two electron artificial molecule
Exact results for the classical and quantum system of two vertically coupled
two-dimensional single electron quantum dots are obtained as a function of the
interatomic distance (d) and with perpendicular magnetic field. The classical
system exhibits a second order structural transition as a function of d which
is smeared out and shifted to lower d values in the quantum case. The
spin-singlet - spin-triplet oscillations are shifted to larger magnetic fields
with increasing d and are quenched for a sufficiently large interatomic
distance.Comment: 4 pages, 4 ps figure
Two ground-state modifications of quantum-dot beryllium
Exact electronic properties of a system of four Coulomb-interacting
two-dimensional electrons in a parabolic confinement are reported. We show that
degenerate ground states of this system are characterized by qualitatively
different internal electron-electron correlations, and that the formation of
Wigner molecule in the strong-interaction regime is going on in essentially
different ways in these ground states.Comment: 5 pages, incl 5 Figures and 2 Table
Dephasing time of disordered two-dimensional electron gas in modulated magnetic fields
The dephasing time of disordered two-dimensional electron gas in a modulated
magnetic field is studied. It is shown that in the weak inhomogeneity limit,
the dephasing rate is proportional to the field amplitude, while in strong
inhomogeneity limit the dependence is quadratic. It is demonstrated that the
origin of the dependence of dephasing time on field amplitude lies in the
nature of corresponding single-particle motion. A semiclassical Monte Carlo
algorithm is developed to study the dephasing time, which is of qualitative
nature but efficient in uncovering the dependence of dephasing time on field
amplitude for arbitrarily complicated magnetic-field modulation. Computer
simulations support analytical results. The crossover from linear to quadratic
dependence is then generalized to the situation with magnetic field modulated
periodically in one direction with zero mean, and it is argued that this
crossover can be expected for a large class of modulated magnetic fields.Comment: 8 pages, 2 figure
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