547 research outputs found
Full capacitance matrix of coupled quantum dot arrays: static and dynamical effects
We numerically calculated the full capacitance matrices for both
one-dimensional (1D) and two-dimensional (2D) quantum-dot arrays. We found it
is necessary to use the full capacitance matrix in modeling coupled quantum dot
arrays due to weaker screening in these systems in comparison with arrays of
normal metal tunnel junctions. The static soliton potential distributions in
both 1D and 2D arrays are well approximated by the unscreened (1/r) coulomb
potential, instead of the exponential fall-off expected from the often used
nearest neighbor approximation. The Coulomb potential approximation also
provides a simple expression for the full inverse capacitance matrix of uniform
quantum dot arrays. In terms of dynamics, we compare the current-voltage (I-V)
characteristics of voltage biased 1D arrays using either the full capacitance
matrix or its nearest neighbor approximation. The I-V curves show clear
differences and the differences become more pronounced when larger arrays are
considered.Comment: 8 pages preprint format, 3 PostScript figure
Thermal fluctuation field for current-induced domain wall motion
Current-induced domain wall motion in magnetic nanowires is affected by
thermal fluctuation. In order to account for this effect, the
Landau-Lifshitz-Gilbert equation includes a thermal fluctuation field and
literature often utilizes the fluctuation-dissipation theorem to characterize
statistical properties of the thermal fluctuation field. However, the theorem
is not applicable to the system under finite current since it is not in
equilibrium. To examine the effect of finite current on the thermal
fluctuation, we adopt the influence functional formalism developed by Feynman
and Vernon, which is known to be a useful tool to analyze effects of
dissipation and thermal fluctuation. For this purpose, we construct a quantum
mechanical effective Hamiltonian describing current-induced domain wall motion
by generalizing the Caldeira-Leggett description of quantum dissipation. We
find that even for the current-induced domain wall motion, the statistical
properties of the thermal noise is still described by the
fluctuation-dissipation theorem if the current density is sufficiently lower
than the intrinsic critical current density and thus the domain wall tilting
angle is sufficiently lower than pi/4. The relation between our result and a
recent result, which also addresses the thermal fluctuation, is discussed. We
also find interesting physical meanings of the Gilbert damping alpha and the
nonadiabaticy parameter beta; while alpha characterizes the coupling strength
between the magnetization dynamics (the domain wall motion in this paper) and
the thermal reservoir (or environment), beta characterizes the coupling
strength between the spin current and the thermal reservoir.Comment: 16 page, no figur
Studi Performa Migrasi Ipv4 ke Ipv6 pada Metode Dual Stack
Dengan ketersedian (space) dari pengalamatan IPv4 yang telah sedikit, itu telah menjadi alasan utama bagi penyedia layanan, Perusahaan, pengembang aplikasi, dan pemerintah untuk memulai beralih dengan IPv6. Sebuah migrasi dari IPv4 ke IPv6 sulit dicapai. Karena beberapa mekanisme yang diperlukan untuk menjamin kelancaran, komunikasi dan peralihan secara utuh ke IPv6. Tidak hanya transisi, integrasi IPv6 juga diperlukan ke dalam jaringan yang ada. Solusi (mekanisme) dapat dibagi menjadi tiga kategori: dual stack, tunneling dan translation. Dalam proyek ini mekanisme tr ansisi Dual-Stack diimplementasikan di GNS3 (Graphical Network Simulator), menggunakan CISCO router. Jaringan ini dilihat dengan bantuan Wireshark (Packet analyzer). kedua topologi dibandingkan, Dual-Stack dan Tunneling, yang dapat diamati dengan menangkap paket pada interface router
Interplay between plastic deformations and optical properties of metal surfaces : a multiscale study
The force method to calculate stress intensity factors for arbitrary meshes
The force method is a simple and accurate technique to obtain the stress intensity
factors (SIF) for both modes I, II and also mixed I+II modes of fracture. The method uses the summation of internal nodal forces in the vicinity of the crack tip to compute SIFs. Recently, de Morais1 showed that the force method is able to yield accurate SIF values from FE models constructed with regular meshes of linear elements. In this paper, the force method is applied
successfully to general finite element meshes, in such a way that it can be used on crack propagation algorithms with arbitrary crack paths
Effect of spin diffusion on current generated by spin motive force
Spin motive force is a spin-dependent force on conduction electrons induced
by magnetization dynamics. In order to examine its effects on magnetization
dynamics, it is indispensable to take into account spin accumulation, spin
diffusion, and spin-flip scattering since the spin motive force is in general
nonuniform. We examine the effects of all these on the way the spin motive
force generates the charge and spin currents in conventional situations, where
the conduction electron spin relaxation dynamics is much faster than the
magnetization dynamics. When the spin-dependent electric field is spatially
localized, which is common in experimental situations, we find that the
conservative part of the spin motive force is unable to generate the charge
current due to the cancelation effect by the diffusion current. We also find
that the spin current is a nonlocal function of the spin motive force and can
be effectively expressed in terms of nonlocal Gilbert damping tensor. It turns
out that any spin independent potential such as Coulomb potential does not
affect our principal results. At the last part of this paper, we apply our
theory to current-induced domain wall motion.Comment: 14 pages, 2 figures, some of important errors were corrected but we
recommend to see PRB paper if one can acces
Optical Conductivity in Mott-Hubbard Systems
We study the transfer of spectral weight in the optical spectra of a strongly
correlated electron system as a function of temperature and interaction
strength. Within a dynamical mean field theory of the Hubbard model that
becomes exact in the limit of large lattice coordination, we predict an
anomalous enhancement of spectral weight as a function of temperature in the
correlated metallic state and report on experimental measurements which agree
with this prediction in . We argue that the optical conductivity
anomalies in the metal are connected to the proximity to a crossover region in
the phase diagram of the model.Comment: 12 pages and 4 figures, to appear in Phys. Rev. Lett., v 75, p 105
(1995
An unexpected Ireland–Claisen rearrangement cascade during the synthesis of the tricyclic core of Curcusone C: Mechanistic elucidation by trial-and-error and automatic artificial force-induced reaction (AFIR) computations
In the course of a total synthesis effort directed toward the natural product curcusone C, the Stoltz group discovered an unexpected thermal rearrangement of a divinylcyclopropane to the product of a formal Cope/1,3-sigmatropic shift sequence. Since the involvement of a thermally forbidden 1,3-shift seemed unlikely, theoretical studies involving two approaches, the “trial-and-error” testing of various conceivable mechanisms (Houk group) and an “automatic” approach using the Maeda–Morokuma AFIR method (Morokuma group) were applied to explore the mechanism. Eventually, both approaches converged on a cascade mechanism shown to have some partial literature precedent: Cope rearrangement/1,5-sigmatropic silyl shift/Claisen rearrangement/retro-Claisen rearrangement/1,5-sigmatropic silyl shift, comprising a quintet of five sequential thermally allowed pericyclic rearrangements
Increased accuracy of starch granule type quantification using mixture distributions
Background: The proportion of granule types in wheat starch is an important characteristic that can affect its functionality. It is widely accepted that granule types are either large, disc-shaped A-type granules or small, spherical B-type granules. Additionally, there are some reports of the tiny C-type granules. The differences between these granule types are due to its carbohydrate composition and crystallinity which is highly, but not perfectly, correlated with the granule size. A majority of the studies that have considered granule types analyse them based on a size threshold rather than chemical composition. This is understandable due to the expense of separating starch into different types. While the use of a size threshold to classify granule type is a low-cost measure, this results in misclassification. We present an alternative, statistical method to quantify the proportion of granule types by a fit of the mixture distribution, along with an R package, a web based app and a video tutorial for how to use the web app to enable its straightforward application. Results: Our results show that the reliability of the gen otypic effects increase approximately 60% using the proportions of the A-type and B-type granule estimated by the mixture distribution over the standard size-threshold measure. Although there was a marginal drop in reliability for C-type granules. The latter is likely due to the low observed genetic variance for C-type granules. Conclusions: The determination of the proportion of granule types from size-distribution is better achieved by using the mixing probabilities from the fit of the mixture distribution rather than using a size-threshold
Resonant-Cavity-Induced Phase Locking and Voltage Steps in a Josephson Array
We describe a simple dynamical model for an underdamped Josephson junction
array coupled to a resonant cavity. From numerical solutions of the model in
one dimension, we find that (i) current-voltage characteristics of the array
have self-induced resonant steps (SIRS), (ii) at fixed disorder and coupling
strength, the array locks into a coherent, periodic state above a critical
number of active Josephson junctions, and (iii) when active junctions are
synchronized on an SIRS, the energy emitted into the resonant cavity is
quadratic with . All three features are in agreement with a recent
experiment [Barbara {\it et al}, Phys. Rev. Lett. {\bf 82}, 1963 (1999)]}.Comment: 4 pages, 3 eps figures included. Submitted to PRB Rapid Com
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