86,583 research outputs found
A breakdown voltage model for implanted resurf p-LDMOS device on n+ buried layer
This paper presents an analytical expression of the breakdown voltage of a high voltage implanted RESURF p-LDMOS device which uses the n+ buried layer as an effective device substrate. In this model, the doping profile of the buried layer is considered and discussed. The implant dose for the drift region to implement the RESURF principle is also described by this model. Results calculated from this model are verified by experimental values
Triplet-Tuning: A Novel Family of Non-Empirical Exchange-Correlation Functionals
In the framework of DFT, the lowest triplet excited state, T, can be
evaluated using multiple formulations, the most straightforward of which are
UDFT and TDDFT. Assuming the exact XC functional is applied, UDFT and TDDFT
provide identical energies for T (), which is also a constraint
that we require our XC functionals to obey. However, this condition is not
satisfied by most of the popular XC functionals, leading to inaccurate
predictions of low-lying, spectroscopically and photochemically important
excited states, such as T and S. Inspired by the optimal tuning
strategy for frontier orbital energies [Stein, Kronik, and Baer, {\it J. Am.
Chem. Soc.} {\bf 2009}, 131, 2818], we proposed a novel and non-empirical
prescription of constructing an XC functional in which the agreement between
UDFT and TDDFT in is strictly enforced. Referred to as "triplet
tuning", our procedure allows us to formulate the XC functional on a
case-by-case basis using the molecular structure as the exclusive input,
without fitting to any experimental data. The first triplet tuned XC
functional, TT-PBEh, is formulated as a long-range-corrected hybrid of
PBE and HF functionals [Rohrdanz, Martins, and Herbert, {\it J. Chem. Phys.}
{\bf 2009}, 130, 054112] and tested on four sets of large organic molecules.
Compared to existing functionals, TT-PBEh manages to provide more
accurate predictions for key spectroscopic and photochemical observables,
including but not limited to , , , and
, as it adjusts the effective electron-hole interactions to arrive at the
correct excitation energies. This promising triplet tuning scheme can be
applied to a broad range of systems that were notorious in DFT for being
extremely challenging
A case study of speculative financial bubbles in the South African stock market 2003-2006
We tested 45 indices and common stocks traded in the South African stock
market for the possible existence of a bubble over the period from Jan. 2003 to
May 2006. A bubble is defined by a faster-than-exponential acceleration with
significant log-periodic oscillations. The faster-than-exponential acceleration
characteristics are tested with several different metrics, including
nonlinearity on the logarithm of the price and power law fits. The log-periodic
properties are investigated in detail using the first-order log-periodic
power-law (LPPL) formula, the parametric detrending method, the
-analysis, and the second-order Weierstrass-type model, resulting in a
consistent and robust estimation of the fundamental angular log-frequency
, in reasonable agreement with previous estimations on many
other bubbles in developed and developing markets. Sensitivity tests of the
estimated critical times and of the angular log-frequency are performed by
varying the first date and the last date of the stock price time series. These
tests show that the estimated parameters are robust. With the insight of 6
additional month of data since the analysis was performed, we observe that many
of the stocks on the South Africa market experienced an abrupt drop mid-June
2006, which is compatible with the predicted for several of the stocks,
but not all. This suggests that the mini-crash that occurred around mid-June of
2006 was only a partial correction, which has resumed into a renewed bubbly
acceleration bound to end some times in 2007, similarly to what happened on the
S&P500 US market from Oct. 1997 to Aug. 1998.Comment: 20 Latex pages including 10 figures + an appendix (1 table, 10
figures
Durability and service life of concrete repairs in the presence of cracks
Engineered Cementitious Composite (ECC) has been proposed to be one of the most promising repair materials due to its unique high ductility and tight crack width control. In concrete repairs, the shrinkage of repair materials is restrained by concrete substrate, and the repair material therefore often cracks. When ECC is used as repair material, the crack width is much smaller compared to normal concrete. The tight crack width of ECC retards the penetration of water and harmful substances and thus enhances the durability of concrete repairs. This paper is aimed to explore the chloride penetration in cracked ECC repairs and to assess the service life of the repair systems. Rapid chloride migration tests was conducted to investigate the chloride penetration profile. Based on the experimental results, the service life of repair systems was evaluated
On mesh refinement and accuracy of numerical solutions
This paper investigates mesh refinement and its relation with the accuracy of the boundary element method (BEM) and the finite element method (FEM). TO this end an isotropic homogeneous spherical volume conductor, for which the analytical solution is available, wag used. The numerical results obtained with the BEM and FEM were compared with the results of the andytical solution. The results show that the accuracy of the numerical solutions is improved by enriching a mesh only if the enriched mesh not only incorporates a greater number of nodes but also follows more closely the actual geometry of the volume conductor involved
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Towards Prediction of Non-Radiative Decay Pathways in Organic Compounds I: The Case of Naphthalene Quantum Yields
Many emerging technologies depend on human’s ability to control and manipulate the excited-state properties of molecular systems. These technologies include fluorescent labeling in biomedical imaging, light harvesting in photovoltaics, and electroluminescence in light-emitting devices. All of these systems suffer from non-radiative loss pathways that dissipate electronic energy as heat, which causes the overall system efficiency to be directly linked to quantum yield (Φ) of the molecular excited state. Unfortunately, Φ is very difficult to predict from first principles because the description of a slow non-radiative decay mechanism requires an accurate description of long-timescale excited-state quantum dynamics. In the present study, we introduce an efficient semiempirical method of calculating the fluorescence quantum yield (Φfl) for molecular chromophores, which, based on machine learning, converts simple electronic energies computed using time-dependent density functional theory (TDDFT) into an estimate of Φfl. As with all machine learning strategies, the algorithm needs to be trained on fluorescent dyes for which Φfl’s are known, so as to provide a black-box method which can later predict Φfl’s for chemically similar chromophores that have not been studied experimentally. As a first illustration of how our proposed algorithm can be trained, we examine a family of 25 naphthalene derivatives. The simplest application of the energy gap law is found to be inadequate to explain the rates of internal conversion (IC) or intersystem crossing (ISC) – the electronic properties of at least one higher-lying electronic state (Sn or Tn) or one far-from-equilibrium geometry are typically needed to obtain accurate results. Indeed, the key descriptors turn out to be the transition state between the Franck–Condon minimum a distorted local minimum near an S0/S1 conical intersection (which governs IC) and the magnitude of the spin–orbit coupling (which governs ISC). The resulting Φfl’s are predicted with reasonable accuracy (±22%), making our approach a promising ingredient for high-throughput screening and rational design of the molecular excited states with desired Φ’s. We thus conclude that our model, while semi-empirical in nature, does in fact extract sound physical insight into the challenge of describing non-radiative relaxations
Tactical fixed job scheduling with spread-time constraints
We address the tactical fixed job scheduling problem with spread-time constraints.
In such a problem, there are a fixed number of classes of machines and a fixed number of groups of jobs. Jobs of the same group can only be processed by machines of a given set of classes. All jobs have their fixed
start and end times. Each machine is associated with a cost according to its machine class. Machines have spread-time constraints, with which each machine
is only available for L consecutive time units from the start time of the earliest job assigned to it. The objective is to minimize the total cost of the machines used to process all the jobs. For this strongly NP-hard problem, we develop a branch-and-price algorithm, which solves instances with up to 300 jobs, as compared with CPLEX, which cannot solve instances of 100 jobs.
We further investigate the influence of machine flexibility by computational experiments. Our results show that limited machine flexibility is sufficient in most situations
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