128,787 research outputs found
Optical transitions and nature of Stokes shift in spherical CdS quantum dots
We study the structure of the energy spectra along with the character of the
states participating in optical transitions in colloidal CdS quantum dots (QDs)
using the {\sl ab initio} accuracy charge patching method combined with the
%pseudopotential based folded spectrum calculations of electronic structure of
thousand-atom nanostructures. In particular, attention is paid to the nature of
the large resonant Stokes shift observed in CdS quantum dots. We find that the
top of the valence band state is bright, in contrast with the results of
numerous {\bf kp} calculations, and determine the limits of
applicability of the {\bf kp} approach. The calculated electron-hole
exchange splitting suggests the spin-forbidden valence state may explain the
nature of the ``dark exciton'' in CdS quantum dots.Comment: 5 pages, 4 figure
Efficient Active Learning for Image Classification and Segmentation using a Sample Selection and Conditional Generative Adversarial Network
Training robust deep learning (DL) systems for medical image classification
or segmentation is challenging due to limited images covering different disease
types and severity. We propose an active learning (AL) framework to select most
informative samples and add to the training data. We use conditional generative
adversarial networks (cGANs) to generate realistic chest xray images with
different disease characteristics by conditioning its generation on a real
image sample. Informative samples to add to the training set are identified
using a Bayesian neural network. Experiments show our proposed AL framework is
able to achieve state of the art performance by using about 35% of the full
dataset, thus saving significant time and effort over conventional methods
Knowledge based cloud FE simulation of sheet metal forming processes
The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the efficiency and lowering the development time of such processes, whilst reducing costs involved in trial-and-error prototyping. Recent focus on the substitution of steel components with aluminum alloy alternatives in the automotive and aerospace sectors has increased the need to simulate the forming behavior of such alloys for ever more complex component geometries. However these alloys, and in particular their high strength variants, exhibit limited formability at room temperature, and high temperature manufacturing technologies have been developed to form them. Consequently, advanced constitutive models are required to reflect the associated temperature and strain rate effects. Simulating such behavior is computationally very expensive using conventional FE simulation techniques. This paper presents a novel Knowledge Based Cloud FE (KBC-FE) simulation technique that combines advanced material and friction models with conventional FE simulations in an efficient manner thus enhancing the capability of commercial simulation software packages. The application of these methods is demonstrated through two example case studies, namely: the prediction of a material's forming limit under hot stamping conditions, and the tool life prediction under multi-cycle loading conditions
Models for the magnetic ac susceptibility of granular superferromagnetic CoFe/AlO
The magnetization and magnetic ac susceptibility, ,
of superferromagnetic systems are studied by numerical simulations. The
Cole-Cole plot, vs. , is used as a tool for classifying
magnetic systems by their dynamical behavior. The simulations of the
magnetization hysteresis and the ac susceptibility are performed with two
approaches for a driven domain wall in random media. The studies are motivated
by recent experimental results on the interacting nanoparticle system
CoFe/AlO showing superferromagnetic behavior. Its
Cole-Cole plot indicates domain wall motion dynamics similarly to a disordered
ferromagnet, including pinning and sliding motion. With our models we can
successfully reproduce the features found in the experimental Cole-Cole plots.Comment: 8 pages, 6 figure
Cooling of Nanomechanical Resonator Based on Periodical Coupling to Cooper Pair Box
We propose and study an active cooling mechanism for the nanomechanical
resonator (NAMR) based on periodical coupling to a Cooper pair box (CPB), which
is implemented by a designed series of magnetic flux pluses threading through
the CPB. When the initial phonon number of the NAMR is not too large, this
cooling protocol is efficient in decreasing the phonon number by two to three
orders of magnitude. Our proposal is theoretically universal in cooling various
boson systems of single mode. It can be specifically generalized to prepare the
nonclassical state of the NAMR.Comment: 5pages,3figure
The Fourth Element: Characteristics, Modelling, and Electromagnetic Theory of the Memristor
In 2008, researchers at HP Labs published a paper in {\it Nature} reporting
the realisation of a new basic circuit element that completes the missing link
between charge and flux-linkage, which was postulated by Leon Chua in 1971. The
HP memristor is based on a nanometer scale TiO thin-film, containing a
doped region and an undoped region. Further to proposed applications of
memristors in artificial biological systems and nonvolatile RAM (NVRAM), they
also enable reconfigurable nanoelectronics. Moreover, memristors provide new
paradigms in application specific integrated circuits (ASICs) and field
programmable gate arrays (FPGAs). A significant reduction in area with an
unprecedented memory capacity and device density are the potential advantages
of memristors for Integrated Circuits (ICs). This work reviews the memristor
and provides mathematical and SPICE models for memristors. Insight into the
memristor device is given via recalling the quasi-static expansion of Maxwell's
equations. We also review Chua's arguments based on electromagnetic theory.Comment: 28 pages, 14 figures, Accepted as a regular paper - the Proceedings
of Royal Society
On Solving a Generalized Chinese Remainder Theorem in the Presence of Remainder Errors
In estimating frequencies given that the signal waveforms are undersampled
multiple times, Xia et. al. proposed to use a generalized version of Chinese
remainder Theorem (CRT), where the moduli are which are
not necessarily pairwise coprime. If the errors of the corrupted remainders are
within \tau=\sds \max_{1\le i\le k} \min_{\stackrel{1\le j\le k}{j\neq i}}
\frac{\gcd(M_i,M_j)}4, their schemes can be used to construct an approximation
of the solution to the generalized CRT with an error smaller than .
Accurately finding the quotients is a critical ingredient in their approach. In
this paper, we shall start with a faithful historical account of the
generalized CRT. We then present two treatments of the problem of solving
generalized CRT with erroneous remainders. The first treatment follows the
route of Wang and Xia to find the quotients, but with a simplified process. The
second treatment considers a simplified model of generalized CRT and takes a
different approach by working on the corrupted remainders directly. This
approach also reveals some useful information about the remainders by
inspecting extreme values of the erroneous remainders modulo . Both of
our treatments produce efficient algorithms with essentially optimal
performance. Finally, this paper constructs a counterexample to prove the
sharpness of the error bound
IDENTIFYING FREQUENT SEAFOOD PURCHASERS IN THE NORTHEASTERN U.S.
Factors affecting the frequency of purchase of fish and other seafood for at-home and restaurant consumption by Northeastern consumers were investigated. Cluster analysis identified six groups of consumers with similar perceptions of the attributes of fish. Demographic and cluster membership variables were employed in logistic regressions to identify the characteristics of frequent at-home use and restaurant purchasers. At-home purchase was more likely to be frequent among respondents with white collar occupations, older ages, urban/suburban and New England residence, recreational fishing participation, and membership in one of five attitudinal clusters. Restaurant purchase was more likely to be frequent among whites and among those with higher incomes, white collar occupations, recreational fishing involvement and among members of two clusters with favorable attitudes toward fish; it was less likely to be frequent in households with children age 10 and under present.Consumer/Household Economics,
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