21,400 research outputs found
Separation of long DNA chains using non-uniform electric field: a numerical study
We study migration of DNA molecules through a microchannel with a series of
electric traps controlled by an ac electric field. We describe the motion of
DNA based on Brownian dynamics simulations of a beads-spring chain. Our
simulation demonstrates that the chain captured by an electrode escapes from
the binding electric field due to thermal fluctuation. We find that the
mobility of chain would depend on the chain length; the mobility sharply
increases when the length of a chain exceeds a critical value, which is
strongly affected by the amplitude of the applied ac field. Thus we can adjust
the length regime, in which this microchannel well separates DNA molecules,
without changing the structure of the channel. We also present a theoretical
insight into the relation between the critical chain length and the field
amplitude.Comment: 12 pages, 9 figure
Screened hybrid functional applied to 3d^0-->3d^8 transition-metal perovskites LaMO3 (M=Sc-Cu): influence of the exchange mixing parameter on the structural, electronic and magnetic properties
We assess the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened
hybrid density functional scheme applied to the perovskite family LaMO3
(M=Sc-Cu) and discuss the role of the mixing parameter alpha (which determines
the fraction of exact Hartree-Fock exchange included in the density functional
theory (DFT) exchange-correlation functional) on the structural, electronic,
and magnetic properties. The physical complexity of this class of compounds,
manifested by the largely varying electronic characters
(band/Mott-Hubbard/charge-transfer insulators and metals), magnetic orderings,
structural distortions (cooperative Jahn-Teller like instabilities), as well as
by the strong competition between localization/delocalization effects
associated with the gradual filling of the t_2g and e_g orbitals, symbolize a
critical and challenging case for theory. Our results indicates that HSE is
able to provide a consistent picture of the complex physical scenario
encountered across the LaMO3 series and significantly improve the standard DFT
description. The only exceptions are the correlated paramagnetic metals LaNiO3
and LaCuO3, which are found to be treated better within DFT. By fitting the
ground state properties with respect to alpha we have constructed a set of
'optimum' values of alpha from LaScO3 to LaCuO3: it is found that the 'optimum'
mixing parameter decreases with increasing filling of the d manifold (LaScO3:
0.25; LaTiO3 & LaVO3: 0.10-0.15; LaCrO3, LaMnO3, and LaFeO3: 0.15; LaCoO3:
0.05; LaNiO3 & LaCuO3: 0). This trend can be nicely correlated with the
modulation of the screening and dielectric properties across the LaMO3 series,
thus providing a physical justification to the empirical fitting procedure.Comment: 32 pages, 29 figure
Black hole formation in bidimensional dilaton gravity coupled to scalar matter systems
This work deals with the formation of black hole in bidimensional dilaton
gravity coupled to scalar matter fields. We investigate two scalar matter
systems, one described by a sixth power potential and the other defined with
two scalar fields containing up to the fourth power in the fields. The
topological solutions that appear in these cases allow the formation of black
holes in the corresponding dilaton gravity models.Comment: Latex, 9 pages. Published in Mod. Phys. Lett. A14 (1999) 268
Localization of the relative phase via measurements
When two independently-prepared Bose-Einstein condensates are released from
their corresponding traps, the absorbtion image of the overlapping clouds
presents an interference pattern. Here we analyze a model introduced by
Javanainen and Yoo (J. Javanainen and S. M. Yoo, Phys. Rev. Lett. 76, 161
(1996)), who considered two atomic condensates described by plane waves
propagating in opposite directions. We present an analytical argument for the
measurement-induced breaking of the relative phase symmetry in this system,
demonstrating how the phase gets localized after a large enough number of
detection events.Comment: 8 pages, 1 figur
Approaching the adiabatic timescale with machine-learning
The control and manipulation of quantum systems without excitation is
challenging, due to the complexities in fully modeling such systems accurately
and the difficulties in controlling these inherently fragile systems
experimentally. For example, while protocols to decompress Bose-Einstein
condensates (BEC) faster than the adiabatic timescale (without excitation or
loss) have been well developed theoretically, experimental implementations of
these protocols have yet to reach speeds faster than the adiabatic timescale.
In this work, we experimentally demonstrate an alternative approach based on a
machine learning algorithm which makes progress towards this goal. The
algorithm is given control of the coupled decompression and transport of a
metastable helium condensate, with its performance determined after each
experimental iteration by measuring the excitations of the resultant BEC. After
each iteration the algorithm adjusts its internal model of the system to create
an improved control output for the next iteration. Given sufficient control
over the decompression, the algorithm converges to a novel solution that sets
the current speed record in relation to the adiabatic timescale, beating out
other experimental realizations based on theoretical approaches. This method
presents a feasible approach for implementing fast state preparations or
transformations in other quantum systems, without requiring a solution to a
theoretical model of the system. Implications for fundamental physics and
cooling are discussed.Comment: 7 pages main text, 2 pages supporting informatio
Multipole analysis of spin observables in vector meson photoproduction
A multipole analysis of vector meson photoproduction is formulated as a
generalization of the pseudoscalar meson case. Expansion of spin observables in
the multipole basis and behavior of these observables near threshold and
resonances are examined.Comment: 15 pages, latex, 2 figure
Charged particle display
An optical shutter based on charged particles is presented. The output light
intensity of the proposed device has an intrinsic dependence on the
interparticle spacing between charged particles, which can be controlled by
varying voltages applied to the control electrodes. The interparticle spacing
between charged particles can be varied continuously and this opens up the
possibility of particle based displays with continuous grayscale.Comment: typographic errors corrected in Eqs (37) and (39); published in
Journal of Applied Physics; doi:10.1063/1.317648
Towards T1-limited magnetic resonance imaging using Rabi beats
Two proof-of-principle experiments towards T1-limited magnetic resonance
imaging with NV centers in diamond are demonstrated. First, a large number of
Rabi oscillations is measured and it is demonstrated that the hyperfine
interaction due to the NV's 14N can be extracted from the beating oscillations.
Second, the Rabi beats under V-type microwave excitation of the three hyperfine
manifolds is studied experimentally and described theoretically.Comment: 6 pages, 8 figure
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