5,563 research outputs found
THE TIGHT-BINDING APPROACH TO THE DIELECTRIC RESPONSE IN THE MULTIBAND SYSTEMS
Starting from the random phase approximation for the weakly coupled multiband
tightly-bounded electron systems, we calculate the dielectric matrix in terms
of intraband and interband transitions. The advantages of this representation
with respect to the usual plane-wave decomposition are pointed out. The
analysis becomes particularly transparent in the long wavelength limit, after
performing the multipole expansion of bare Coulomb matrix elements. For
illustration, the collective modes and the macroscopic dielectric function for
a general cubic lattice are derived. It is shown that the dielectric
instability in conducting narrow band systems proceeds by a common softening of
one transverse and one longitudinal mode. Furthermore, the self-polarization
corrections which appear in the macroscopic dielectric function for finite band
systems, are identified as a combined effect of intra-atomic exchange
interactions between electrons sitting in different orbitals and a finite
inter-atomic tunneling.Comment: 20 pages, LaTeX, no figure
Distinct magnetotransport and orbital fingerprints of chiral bobbers
While chiral magnetic skyrmions have been attracting significant attention in
the past years, recently, a new type of a chiral particle emerging in thin
films a chiral bobber has been theoretically predicted and
experimentally observed. Here, based on theoretical arguments, we provide a
clear pathway to utilizing chiral bobbers for the purposes of future
spintronics by uncovering that these novel chiral states possess inherent
transport fingerprints that allow for their unambiguous electrical detection in
systems comprising several types of chiral states. We reveal that unique
transport and orbital characteristics of bobbers root in the non-trivial
magnetization distribution in the vicinity of the Bloch points, and demonstrate
that tuning the details of the Bloch point topology can be used to drastically
alter the emergent response properties of chiral bobbers to external fields,
which bears great potential for engineering chiral dynamics and cognitive
computing.Comment: Supplementary available upon reques
Finding the optimum activation energy in DNA breathing dynamics: A Simulated Annealing approach
We demonstrate how the stochastic global optimization scheme of Simulated
Annealing can be used to evaluate optimum parameters in the problem of DNA
breathing dynamics. The breathing dynamics is followed in accordance with the
stochastic Gillespie scheme with the denaturation zones in double stranded DNA
studied as a single molecule time series. Simulated Annealing is used to find
the optimum value of the activation energy for which the equilibrium bubble
size distribution matches with a given value. It is demonstrated that the
method overcomes even large noise in the input surrogate data.Comment: 9 pages, 4 figures, iop article package include
Phase Rotation, Cooling And Acceleration Of Muon Beams: A Comparison Of Different Approaches
Experimental and theoretical activities are underway at CERN with the aim of
examining the feasibility of a very-high-flux neutrino source. In the present
scheme, a high-power proton beam (some 4 MW) bombards a target where pions are
produced. The pions are collected and decay to muons under controlled optical
condition. The muons are cooled and accelerated to a final energy of 50 GeV
before being injected into a decay ring where they decay under well-defined
conditions of energy and emittance.
We present the most challenging parts of the whole scenario, the muon
capture, the ionisation-cooling and the first stage of the muon acceleration.
Different schemes, their performance and the technical challenges are compared.Comment: LINAC 2000 CONFERENCE, paper ID No. THC1
Monitoring induced gene expression of single cells in a multilayer microchip
We present a microfluidic system that facilitates long-term measurements of single cell response to external stimuli. The difficulty of addressing cells individually was overcome by using a two-layer microfluidic device. The top layer is designed for trapping and culturing of cells while the bottom layer is employed for supplying chemical compounds that can be transported towards the cells in defined concentrations and temporal sequences. A porous polyester membrane that supports transport and diffusion of compounds from below separates the microchannels of both layers. The performance and potential of the device are demonstrated using human embryonic kidney cells (HEK293) transfected with an inducible gene expression system. Expression of a fluorescent protein (ZsGreen1-DR) is observed while varying the concentration and exposure time of the inducer tetracycline. The study reveals the heterogeneous response of the cells as well as average responses of tens of cells that are analyzed in parallel. The microfluidic platform enables systematic studies under defined conditions and is a valuable tool for general single cell studies to obtain insights into mechanisms and kinetics that are not accessible by conventional macroscopic methods. Figure A two-layer microfluidic device is presented that facilitates measurements of single cell response to external stimul
Modified critical correlations close to modulated and rough surfaces
Correlation functions are sensitive to the presence of a boundary. Surface
modulations give rise to modified near surface correlations, which can be
measured by scattering probes. To determine these correlations, we develop a
perturbative calculation in deformations in height from a flat surface. The
results, combined with a renormalization group around four dimensions, are also
used to predict critical behavior near a self-affinely rough surface. We find
that a large enough roughness exponent can modify surface critical behavior.Comment: 4 pages, 1 figure. Revised version as published in Phys. Rev. Lett.
86, 4596 (2001
Struktur von Proton-Proton-Streuereignissen bei hoher Schwerpunktsenergie mit identifiziertem Teilchen grossen Transversalimpulses
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