902 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
Laboratory photo-chemistry of covalently bonded fluorene clusters: observation of an interesting PAH bowl-forming mechanism
The fullerene C, one of the largest molecules identified in the
interstellar medium (ISM), has been proposed to form top-down through the
photo-chemical processing of large (more than 60 C-atoms) polycyclic aromatic
hydrocarbon (PAH) molecules. In this article, we focus on the opposite process,
investigating the possibility that fullerenes form from small PAHs, in which
bowl-forming plays a central role. We combine laboratory experiments and
quantum chemical calculations to study the formation of larger PAHs from
charged fluorene clusters. The experiments show that with visible laser
irradiation, the fluorene dimer cation -
[CHCH] - and the fluorene trimer cation -
[CHCHCH] - undergo
photo-dehydrogenation and photo-isomerization resulting in bowl structured
aromatic cluster-ions, CH and CH,
respectively. To study the details of this chemical process, we employ quantum
chemistry that allows us to determine the structures of the newly formed
cluster-ions, to calculate the hydrogen loss dissociation energies, and to
derive the underlying reaction pathways. These results demonstrate that smaller
PAH clusters (with less than 60 C-atoms) can convert to larger bowled
geometries that might act as building blocks for fullerenes, as the
bowl-forming mechanism greatly facilitates the conversion from dehydrogenated
PAHs to cages. Moreover, the bowl-forming induces a permanent dipole moment
that - in principle - allows to search for such species using radio astronomy.Comment: 8 pages, 7 figures, accepte
Ethical and professional issues: Reflections on course evolution, innovation and student engagement.
At INSPIRE 2013 we outlined our efforts to develop a core first year undergraduate course entitled ‘Computing Technology in Society’. A primary course objective is to demonstrate the potential impact that ever more complex, interconnected digital systems may have on the both the individual and on society in general. This provides the backdrop against which we endeavour to foster an ethos in which students are encouraged to establish a personal ethical position in relation to the application and deployment of digital systems. Here we reflect on further progress in developing this course with particular reference to ongoing curriculum development, student evaluation and, most crucially, student engagement. Additionally, we outline developments relating to our integration of technologies into the educational experience. We draw on our experience with the CTIS course to consider broader ramifications of technology infusion, particularly in relation to increased VLE integration and the streaming/recording of lectures.n/
Iteration-complexity of a proximal augmented Lagrangian method for solving nonconvex composite optimization problems with nonlinear convex constraints
This paper proposes and analyzes a proximal augmented Lagrangian (NL-IAPIAL)
method for solving smooth nonconvex composite optimization problems with
nonlinear -convex constraints, i.e., the constraints are convex with
respect to the order given by a closed convex cone . Each NL-IAPIAL
iteration consists of inexactly solving a proximal augmented Lagrangian
subproblem by an accelerated composite gradient (ACG) method followed by a
Lagrange multiplier update. Under some mild assumptions, it is shown that
NL-IAPIAL generates an approximate stationary solution of the constrained
problem in inner iterations, where
is a given tolerance. Numerical experiments are also given to illustrate the
computational efficiency of the proposed method
A Long Cytoplasmic Loop Governs the Sensitivity of the Anti-viral Host Protein SERINC5 to HIV-1 Nef
We recently identified the multipass transmembrane protein SERINC5 as an antiviral protein that can potently inhibit HIV-1 infectivity and is counteracted by HIV-1 Nef. We now report that the anti-HIV-1 activity, but not the sensitivity to Nef, is conserved among vertebrate SERINC5 proteins. However, a Nef-resistant SERINC5 became Nef sensitive when its intracellular loop 4 (ICL4) was replaced by that of Nef-sensitive human SERINC5. Conversely, human SERINC5 became resistant to Nef when its ICL4 was replaced by that of a Nef-resistant SERINC5. In general, ICL4 regions from SERINCs that exhibited resistance to a given Nef conferred resistance to the same Nef when transferred to a sensitive SERINC, and vice versa. Our results establish that human SERINC5 can be modified to restrict HIV-1 infectivity even in the presence of Nef
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