5,861 research outputs found
The maximum density droplet to lower density droplet transition in quantum dots
We show that, Landau level mixing in two-dimensional quantum dot wave
functions can be taken into account very effectively by multiplying the exact
lowest Landau level wave functions by a Jastrow factor which is optimized by
variance minimization. The comparison between exact diagonalization and fixed
phase diffusion Monte Carlo results suggests that the phase of the many-body
wave functions are not affected much by Landau level mixing. We apply these
wave functions to study the transition from the maximum density droplet state
(incipient integer quantum Hall state with angular momentum L=N(N-1)/2) to
lower density droplet states (L>N(N-1)/2).Comment: 8 pages, 5 figures, accepted for publication in Phys. Rev.
Classical and quantum scattering by a Coulomb potential
For relativistic energies the small angle classical cross section for
scattering on a Coulomb potential agrees with the first Born approximation for
quantum cross section for scalar particle only in the leading term. The
disagreement in other terms can be avoided if the sum of all corrections to the
first Born approximation for large enough Coulomb charge contain the classical
terms which are independent of that charge. A small part of the difference in
classical and quantum cross sections may be attributed to the fact that the
relativistic quantum particle can rush through the field without interaction.
We expect that smaller impact parameters and spin facilitate this affect.Comment: 5pages, no figure
Expression of a human cartilage procollagen gene (COL2A1) in mouse 3T3 cells.
Expression in a recombinant system has been difficult to obtain for any of the major fibrillar collagens that require processing by eight or more post-translational enzymes. Here, two DNA constructs were designed so that the promoter region of the gene for the pro-alpha 1(I) chain of human type I procollagen drove expression of the human type II procollagen gene in mouse NIH 3T3 cells, a culture line that normally synthesizes type I procollagen but not any cartilage-specific protein such as type II procollagen. Both constructs were expressed as both mRNA and protein. In clones expressing the construct at high levels, the steady-state levels of mRNA and the production of type II procollagen were comparable to the mRNA levels and production of type I procollagen from the endogenous mouse genes. Comparison of clones containing the two constructs demonstrated that sequences extending 80 base pairs beyond the major polyadenylation signal of the gene are not in themselves sufficient for correct termination and 3\u27 processing of RNA transcripts. The results strongly suggest that specific sequences present in a downstream 3.5-kilobase SphI/SphI fragment determine the termination of the transcription. Of special importance is that the system will make it possible to examine the consequences of mutations in the human type II procollagen gene on the processing of RNA transcripts and on the functional properties of the protein simply by using the genomic DNA from leukocytes or other non-cartilaginous sources
Different mechanics of snap-trapping in the two closely related carnivorous plants Dionaea muscipula and Aldrovanda vesiculosa
The carnivorous aquatic Waterwheel Plant (Aldrovanda vesiculosa L.) and the
closely related terrestrial Venus Flytrap (Dionaea muscipula SOL. EX J. ELLIS)
both feature elaborate snap-traps, which shut after reception of an external
mechanical stimulus by prey animals. Traditionally, Aldrovanda is considered as
a miniature, aquatic Dionaea, an assumption which was already established by
Charles Darwin. However, videos of snapping traps from both species suggest
completely different closure mechanisms. Indeed, the well-described snapping
mechanism in Dionaea comprises abrupt curvature inversion of the two trap
lobes, while the closing movement in Aldrovanda involves deformation of the
trap midrib but not of the lobes, which do not change curvature. In this paper,
we present the first detailed mechanical models for these plants, which are
based on the theory of thin solid membranes and explain this difference by
showing that the fast snapping of Aldrovanda is due to kinematic amplification
of the bending deformation of the midrib, while that of Dionaea unambiguously
relies on the buckling instability that affects the two lobes.Comment: accepted in Physical Review
Random Topologies and the emergence of cooperation: the role of short-cuts
We study in detail the role of short-cuts in promoting the emergence of
cooperation in a network of agents playing the Prisoner's Dilemma Game (PDG).
We introduce a model whose topology interpolates between the one-dimensional
euclidean lattice (a ring) and the complete graph by changing the value of one
parameter (the probability p to add a link between two nodes not already
connected in the euclidean configuration). We show that there is a region of
values of p in which cooperation is largely enhanced, whilst for smaller values
of p only a few cooperators are present in the final state, and for p
\rightarrow 1- cooperation is totally suppressed. We present analytical
arguments that provide a very plausible interpretation of the simulation
results, thus unveiling the mechanism by which short-cuts contribute to promote
(or suppress) cooperation
Exchange effects on electron scattering through a quantum dot embedded in a two-dimensional semiconductor structure
We have developed a theoretical method to study scattering processes of an
incident electron through an N-electron quantum dot (QD) embedded in a
two-dimensional (2D) semiconductor. The generalized Lippmann-Schwinger
equations including the electron-electron exchange interaction in this system
are solved for the continuum electron by using the method of continued
fractions (MCF) combined with 2D partial-wave expansion technique. The method
is applied to a one-electron QD case. Cross-sections are obtained for both the
singlet and triplet couplings between the incident electron and the QD electron
during the scattering. The total elastic cross-sections as well as the
spin-flip scattering cross-sections resulting from the exchange potential are
presented. Furthermore, inelastic scattering processes are also studied using a
multichannel formalism of the MCF.Comment: 11 pages, 4 figure
Stanniocalcin-1 Regulates Extracellular ATP-Induced Calcium Waves in Human Epithelial Cancer Cells by Stimulating ATP Release from Bystander Cells
Background: The epithelial cell response to stress involves the transmission of signals between contiguous cells that can be visualized as a calcium wave. In some cell types, this wave is dependent on the release of extracellular trinucleotides from injured cells. In particular, extracellular ATP has been reported to be critical for the epithelial cell response to stress and has recently been shown to be upregulated in tumors in vivo. Methodology/Principal Findings: Here, we identify stanniocalcin-1 (STC1), a secreted pleiotrophic protein, as a critical mediator of calcium wave propagation in monolayers of pulmonary (A549) and prostate (PC3) epithelial cells. Addition of STC1 enhanced and blocking STC1 decreased the distance traveled by an extracellular ATP-dependent calcium wave. The same effects were observed when calcium was stimulated by the addition of exogenous ATP. We uncover a positive feedback loop in which STC1 promotes the release of ATP from cells in vitro and in vivo. Conclusions/Significance: The results indicated that STC1 plays an important role in the early response to mechanical injury by epithelial cells by modulating signaling of extracellular ATP. This is the first report to describe STC1 as a modulator o
Exact solution of the Zeeman effect in single-electron systems
Contrary to popular belief, the Zeeman effect can be treated exactly in
single-electron systems, for arbitrary magnetic field strengths, as long as the
term quadratic in the magnetic field can be ignored. These formulas were
actually derived already around 1927 by Darwin, using the classical picture of
angular momentum, and presented in their proper quantum-mechanical form in 1933
by Bethe, although without any proof. The expressions have since been more or
less lost from the literature; instead, the conventional treatment nowadays is
to present only the approximations for weak and strong fields, respectively.
However, in fusion research and other plasma physics applications, the magnetic
fields applied to control the shape and position of the plasma span the entire
region from weak to strong fields, and there is a need for a unified treatment.
In this paper we present the detailed quantum-mechanical derivation of the
exact eigenenergies and eigenstates of hydrogen-like atoms and ions in a static
magnetic field. Notably, these formulas are not much more complicated than the
better-known approximations. Moreover, the derivation allows the value of the
electron spin gyromagnetic ratio to be different from 2. For
completeness, we then review the details of dipole transitions between two
hydrogenic levels, and calculate the corresponding Zeeman spectrum. The various
approximations made in the derivation are also discussed in details.Comment: 18 pages, 4 figures. Submitted to Physica Script
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