14,682 research outputs found
Periodically driven stochastic un- and refolding transitions of biopolymers
Mechanical single molecule experiments probe the energy profile of
biomolecules. We show that in the case of a profile with two minima (like
folded/unfolded) periodic driving leads to a stochastic resonance-like
phenomenon. We demonstrate that the analysis of such data can be used to
extract four basic parameters of such a transition and discuss the statistical
requirements of the data acquisition. As advantages of the proposed scheme, a
polymeric linker is explicitly included and thermal fluctuations within each
well need not to be resolved.Comment: 7 pages, 5 figures, submitted to EP
CLIC Drive Beam and LHC Based Fel-Nucleus Collider
The feasibility of a CLIC-LHC based FEL-nucleus collider is investigated. It
is shown that the proposed scheme satisfies all requirements of an ideal photon
source for the Nuclear Resonance Fluorescence method. The physics potential of
the proposed collider is illustrated for a beam of Pb nuclei.Comment: Presented at PAC05, 16-20 May 2005, Knoxville, TN, US
Solitonic-exchange mechanism of surface~diffusion
We study surface diffusion in the framework of a generalized
Frenkel-Kontorova model with a nonconvex transverse degree of freedom. The
model describes a lattice of atoms with a given concentration interacting by
Morse-type forces, the lattice being subjected to a two-dimensional substrate
potential which is periodic in one direction and nonconvex (Morse) in the
transverse direction. The results are used to describe the complicated
exchange-mediated diffusion mechanism recently observed in MD simulations [J.E.
Black and Zeng-Ju Tian, Phys. Rev. Lett. {\bf 71}, 2445-2448(1993)].Comment: 22 Revtex pages, 9 figures to appear in Phys. Rev.
Dynamical phase diagram of the dc-driven underdamped Frenkel-Kontorova chain
Multistep dynamical phase transition from the locked to the running state of
atoms in response to a dc external force is studied by MD simulations of the
generalized Frenkel-Kontorova model in the underdamped limit. We show that the
hierarchy of transition recently reported [Braun et al, Phys. Rev. Lett. 78,
1295 (1997)] strongly depends on the value of the friction constant. A simple
phenomenological explanation for the friction dependence of the various
critical forces separating intermediate regimes is given.Comment: 12 Revtex Pages, 4 EPS figure
Dynamics of Vortex Shells in Mesoscopic Superconducting Corbino Disks
In mesoscopic superconducting disks vortices form shell structures as
recently observed in Nb disks. We study the dynamics of such vortices, driven
by an external current I_0, in a Corbino setup. At very low I_0, the system
exhibits rigid body rotation while at some critical current I_c,i vortex shells
rotate separately with angular velocities omega_i. This critical current I_c,i
has a remarkable non-monotonous dependence on the applied magnetic field which
is due to a dynamically-induced structural transition with a rearrangement of
vortices over the shells similar to the Coster-Kronig transition in hollow
atoms. Thermally-activated externally-driven flux motion in a disk with pinning
centers explains experimentally observed omega_i as a function of I_0 and T and
the dynamically-induced melting transition.Comment: 5 pages, 5 figure
Arthropod diversity and pest dynamics in various production input levels and cropping system strategies
Non-Peer ReviewedEconomic viability and soil degradation are major issues facing farmers in the grassland ecozone of the Northern Great Plains. Crop diversification, reduced fallow and reduced inputs are being promoted in an effort to address these issues. A systems approach is applied as the experimental framework with which to monitor and assess alternate input and cropping strategies. The design, data collection and evaluation are based on the collaborative efforts of crop, pest, economic and soil scientists. This paper highlights the role of arthropods (insects, spiders, mites) in the assessment of farming systems. Arthropods are the most diverse group of organisms in most ecosystems. Many species, including beneficial and pest species, are well-suited to characterizing the ecosystems that they inhabit. Ecosystem-based, arthropod baselines are viewed by the authors as an integral component in evaluating farming systems
Perturbative QCD Correction to the Light-Cone Sum Rule for the and Couplings
The and couplings have previously been derived from a QCD
light-cone sum rule in leading order. Here, we describe the calculation of the
correction to the twist 2 term of this sum rule. The result is
used for a first next-to-leading order analysis. We obtain and , where the error indicates the remaining
theoretical uncertainty.Comment: 11 pages, 1 figure, Latex, epsfi
Ultrafast spin polarization control of Dirac fermions in topological insulators
Three-dimensional topological insulators (TIs) are characterized by
spin-polarized Dirac-cone surface states that are protected from backscattering
by time-reversal symmetry. Control of the spin polarization of topological
surface states (TSSs) using femtosecond light pulses opens novel perspectives
for the generation and manipulation of dissipationless surface spin currents on
ultrafast timescales. Using time-, spin-, and angle-resolved spectroscopy, we
directly monitor for the first time the ultrafast response of the spin
polarization of photoexcited TSSs to circularly-polarized femtosecond pulses of
infrared light. We achieve all-optical switching of the transient out-of-plane
spin polarization, which relaxes in about 1.2 ps. Our observations establish
the feasibility of ultrafast optical control of spin-polarized Dirac fermions
in TIs and pave the way for novel optospintronic applications at ultimate
speeds.Comment: 9 pages, 4 figure
Discovery of Radio/X-ray/Optical Resolved Supernova Remnants in the Center of the Andromeda Galaxy
We have detected a spatially resolved supernova remnant (SNR) in the center
of the Andromeda Galaxy, in radio, X-ray, and optical wavelengths. These
observations provide the highest spatial resolution imaging of a
radio/X-ray/optical SNR in that galaxy to date. The multi-wavelength
morphology, radio spectral index, X-ray colors, and narrow-band optical imaging
are consistent with a shell-type SNR. A second SNR is also seen resolved in
both radio and X-ray. By comparing the morphological sturcture of the SNRs in
different wavelengths and with that in our own Galaxy, we can study the shock
morphologies of SNRs in the Andromeda Galaxy. The proximity of the SNRs to the
core suggests high interstellar medium density in the vicinity of the SNRs in
the center of the Andromeda Galaxy.Comment: 5 pages, 3 figures, accepted for publication in ApJ
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