6,612 research outputs found
Now the wars are over: The past, present and future of Scottish battlefields
Battlefield archaeology has provided a new way of appreciating historic battlefields. This paper provides a summary of the long history of warfare and conflict in Scotland which has given rise to a large number of battlefield sites. Recent moves to highlight the archaeological importance of these sites, in the form
of Historic Scotland’s Battlefields Inventory are discussed, along with some of the problems associated with the preservation and management of these important
cultural sites
Stochastic unraveling of Redfield master equations and its application to electron transfer problems
A method for stochastic unraveling of general time-local quantum master
equations (QMEs) is proposed. The present kind of jump algorithm allows a
numerically efficient treatment of QMEs which are not in Lindblad form, i.e.
are not positive semidefinite by definition. The unraveling can be achieved by
allowing for trajectories with negative weights. Such a property is necessary,
e.g. to unravel the Redfield QME and to treat various related problems with
high numerical efficiency. The method is successfully tested on the damped
harmonic oscillator and on electron transfer models including one and two
reaction coordinates. The obtained results are compared to those from a direct
propagation of the reduced density matrix (RDM) as well as from the standard
quantum jump method. Comparison of the numerical efficiency is performed
considering both the population dynamics and the RDM in the Wigner phase space
representation.Comment: accepted in J. Chem. Phys.; 26 pages, 6 figures; the order of
authors' names on the title page correcte
End states, ladder compounds, and domain wall fermions
A magnetic field applied to a cross linked ladder compound can generate
isolated electronic states bound to the ends of the chain. After exploring the
interference phenomena responsible, I discuss a connection to the domain wall
approach to chiral fermions in lattice gauge theory. The robust nature of the
states under small variations of the bond strengths is tied to chiral symmetry
and the multiplicative renormalization of fermion masses.Comment: 10 pages, 4 figures; final version for Phys. Rev. Let
Dynamics of quantum dissipation systems interacting with Fermion and Boson grand canonical bath ensembles: Hierarchical equations of motion approach
A hierarchical equations of motion formalism for a quantum dissipation system
in a grand canonical bath ensemble surrounding is constructed, on the basis of
the calculus-on-path-integral algorithm, together with the parametrization of
arbitrary non-Markovin bath that satisfies fluctuation-dissipation theorem. The
influence functionals for both the Fermion or Boson bath interaction are found
to be of the same path-integral expression as the canonical bath, assuming they
all satisfy the Gaussian statistics. However, the equation of motion formalism
are different, due to the fluctuation-dissipation theories that are distinct
and used explicitly. The implications of the present work to quantum transport
through molecular wires and electron transfer in complex molecular systems are
discussed.Comment: 12page
New Finite Element Models and Seismic Analyses of the Telescopes at WM Keck Observatory
On 15 October 2006 a large earthquake damaged both telescopes at Keck observatory resulting in weeks of observing downtime. A significant portion of the downtime was attributed to recovery efforts repairing damage to telescope bearing journals, radial pad support structures and encoder subsystems. Inadequate damping and strength in the seismic restraint design and the lack of break-away features on the azimuth radial pads are key design deficiencies. In May, 2011 a feasibility study was conducted to review several options to enhance the protection of the telescopes with the goal to minimize the time to bring the telescopes back into operation after a large seismic event. At that time it was determined that new finite element models of the telescope structures were required to better understand the telescope responses to design earthquakes required by local governing building codes and the USGS seismic data collected at the site on 15 October 2006. These models were verified by comparing the calculated natural frequencies from the models to the measured frequencies obtained from the servo identification study and comparing the time history responses of the telescopes to the October 2006 seismic data to the actual observed damages. The results of two finite element methods, response spectrum analysis and time history analysis, used to determine seismic demand forces and seismic response of each telescope to the design earthquakes were compared. These models can be used to evaluate alternate seismic restraint design options for both Keck telescopes
Self-organization of actin filament orientation in the dendritic-nucleation/array-treadmilling model
Author Posting. © The Author(s), 2006. This is the author's version of the work. It is posted here by permission of National Academy of Sciences of the USA for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 104 (2007): 7086-7091, doi:10.1073/pnas.0701943104.The dendritic-nucleation/array-treadmilling model provides a conceptual framework for
the generation of the actin network driving motile cells. We have incorporated it into a 2-D,
stochastic computer model to study lamellipodia via the self-organization of filament
orientation patterns. Essential dendritic-nucleation sub-models were incorporated,
including discretized actin monomer diffusion, Monte-Carlo filament kinetics, and flexible
filament and plasma membrane mechanics. Model parameters were estimated from the
literature and simulation, providing values for the extent of the leading edge
branching/capping-protective zone (5.4 nm) and the auto-catalytic branch rate (0.43 /s).
For a given set of parameters the system evolved to a steady state filament count and
velocity, at which total branching and capping rates were equal only for specific
orientations; net capping eliminated others. The standard parameter set evoked a sharp
preference for the ±35 deg. filaments seen in lamellipodial electron micrographs, requiring
~ 12 generations of successive branching to adapt to a 15 deg. change in protrusion
direction. This pattern was robust with respect to membrane surface and bending energies
and to actin concentrations, but required protection from capping at the leading edge and
branching angles greater than 60 deg. A +70/0/-70 deg. pattern was formed with flexible
filaments ~ 100 nm or longer and with velocities less than ~ 20% of free polymerization
rates
Quantum resource estimates for computing elliptic curve discrete logarithms
We give precise quantum resource estimates for Shor's algorithm to compute
discrete logarithms on elliptic curves over prime fields. The estimates are
derived from a simulation of a Toffoli gate network for controlled elliptic
curve point addition, implemented within the framework of the quantum computing
software tool suite LIQ. We determine circuit implementations for
reversible modular arithmetic, including modular addition, multiplication and
inversion, as well as reversible elliptic curve point addition. We conclude
that elliptic curve discrete logarithms on an elliptic curve defined over an
-bit prime field can be computed on a quantum computer with at most qubits using a quantum circuit of at most Toffoli gates. We are able to classically simulate the
Toffoli networks corresponding to the controlled elliptic curve point addition
as the core piece of Shor's algorithm for the NIST standard curves P-192,
P-224, P-256, P-384 and P-521. Our approach allows gate-level comparisons to
recent resource estimates for Shor's factoring algorithm. The results also
support estimates given earlier by Proos and Zalka and indicate that, for
current parameters at comparable classical security levels, the number of
qubits required to tackle elliptic curves is less than for attacking RSA,
suggesting that indeed ECC is an easier target than RSA.Comment: 24 pages, 2 tables, 11 figures. v2: typos fixed and reference added.
ASIACRYPT 201
Energy spectrum, density of states and optical transitions in strongly biased narrow-gap quantum wells
We study theoretically the effect of an electric field on the electron states
and far-infrared optical properties in narrow-gap lead salt quantum wells. The
electron states are described by a two-band Hamiltonian. An application of a
strong electric field across the well allows the control of the energy gap
between the two-dimensional (2D) states in a wide range. A sufficiently strong
electric field transforms the narrow-gap quantum well to a nearly gapless 2D
system, whose electron energy spectrum is described by linear dispersion
relations \epsilon_{\sigma} (k) ~\pm (k-k_{\sigma}), where k_{\sigma} are the
field-dependent 2D momenta corresponding to the minimum energy gaps for the
states with spin numbers \sigma. Due to the field-induced shift of the 2D
subband extrema away from k=0 the density of states has inverse-square-root
divergencies at the edges. This property may result in a considerable increase
of the magnitude of the optical absorption and in the efficiency of the
electrooptical effect.Comment: Text 18 pages in Latex/Revtex format, 7 Postscript figure
Immunogenicity of DTaP-IPV-Hib and MenC vaccines in the UK when administered with a 13-valent pneumococcal conjugate vaccine
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