1,240 research outputs found
Atomistic pseudopotential calculations of the optical properties of InAs/InP self-assembled quantum dots
We present a comprehensive study of the optical properties of InAs/InP
self-assembled quantum dots (QDs) using an empirical pseudopotential method and
configuration interaction treatment of the many-particle effects. The results
are compared to those of InAs/GaAs QDs. The main results are: (i) The alignment
of emission lines of neutral exciton, charged exciton and biexciton in InAs/InP
QDs is quite different from that in InAs/GaAs QDs. (ii) The hidden correlation
in InAs/InP QDs is 0.7 - 0.9 meV, smaller than that in InAs/GaAs QDs. (iii) The
radiative lifetimes of neutral exciton, charged exciton and biexciton in
InAs/InP QDs are about twice longer than those in InAs/GaAs QDs. (v) The phase
diagrams of few electrons and holes in InAs/InP QDs differ greatly from those
in InAs/GaAs QDs. The filling orders of electrons and holes are shown to obey
the Hund's rule and Aufbau principle, and therefore the photoluminescence
spectra of highly charged excitons are very different from those of InAs/GaAs
QDs.Comment: 10 pages, 11 figure
Accelerated Inexact Composite Gradient Methods for Nonconvex Spectral Optimization Problems
This paper presents two inexact composite gradient methods, one inner
accelerated and another doubly accelerated, for solving a class of nonconvex
spectral composite optimization problems. More specifically, the objective
function for these problems is of the form where and
are differentiable nonconvex matrix functions with Lipschitz continuous
gradients, is a proper closed convex matrix function, and both and
can be expressed as functions that operate on the singular values of their
inputs. The methods essentially use an accelerated composite gradient method to
solve a sequence of proximal subproblems involving the linear approximation of
and the singular value functions underlying and . Unlike other
composite gradient-based methods, the proposed methods take advantage of both
the composite and spectral structure underlying the objective function in order
to efficiently generate their solutions. Numerical experiments are presented to
demonstrate the practicality of these methods on a set of real-world and
randomly generated spectral optimization problems
Acting out our dam future: science-based role-play simulations as mechanisms for learning and natural resource planning
Science often does not make its way into decisions, leading to a problematic gap between scientific and societal progress. To tackle this issue, our research tests a novel science-based negotiation simulation that integrates a role-play simulation (RPS) with a system dynamics model (SDM). In RPSs, stakeholders engage in a mock decision-making process (reflecting real-life institutional arrangements and scientific knowledge) for a set period. System dynamics models (SDMs) are visual tools used to simulate the interactions and feedback within a complex system. We test the integration of the two approaches with stakeholders in New England via a series of two consecutive workshops across two states. The workshops engage stakeholders from diverse groups to foster dialogue, learning, and creativity. Participants discuss a hypothetical (yet realistic) decision scenario to consider scientific information and explore dam management options that meet one another\u27s interests. In the first workshop, participants contributed to the design of the fictionalized dam decision scenario and the SDM. In the second workshop, participants assumed another representative\u27s role and discussed dam management options for the fictionalized scenario. This presentation will briefly report on the practical design of this science-based role-play, and particularly emphasize preliminary results of workshop outcomes, which were evaluated using debriefing sessions, surveys, concept mapping exercises, and interviews. Results will determine the extent to which this new knowledge production process leads to learning, use of science, and more collaborative decision-making about dams in New England and beyond
A Double Jaw Hand Designed for Multi-object Assembly
This paper presents a double jaw hand for industrial assembly. The hand
comprises two orthogonal parallel grippers with different mechanisms. The inner
gripper is made of a crank-slider mechanism which is compact and able to firmly
hold objects like shafts. The outer gripper is made of a parallelogram that has
large stroke to hold big objects like pulleys. The two grippers are connected
by a prismatic joint along the hand's approaching vector. The hand is able to
hold two objects and perform in-hand manipulation like pull-in (insertion) and
push-out (ejection). This paper presents the detailed design and implementation
of the hand, and demonstrates the advantages by performing experiments on two
sets of peg-in-multi-hole assembly tasks as parts of the World Robot Challenge
(WRC) 2018 using a bimanual robot
The Long-term Radiative Evolution of Anomalous X-ray Pulsar 1E 2259+586 after its 2002 Outburst
We present an analysis of five X-ray Multi-Mirror Mission (XMM) observations
of the anomalous X-ray pulsar (AXP) 1E 2259+586 taken in 2004 and 2005 during
its relaxation following its 2002 outburst. We compare these data with those of
five previous XMM observations taken in 2002 and 2003, and find the observed
flux decay is well described by a power-law of index -0.69+/-0.03. As of
mid-2005, the source may still have been brighter than preoutburst, and was
certainly hotter. We find a strong correlation between hardness and flux, as
seen in other AXP outbursts. We discuss the implications of these results for
the magnetar model.Comment: 23 Pages, 4 figures, 3 tables, published on Ap
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