2,042 research outputs found
Realisations of Symmetry
We perform a systematic investigation of free-scalar realisations of the
Za\-mo\-lod\-chi\-kov algebra in which the operator product of two
spin-three generators contains a non-zero operator of spin four which has
vanishing norm. This generalises earlier work where such an operator was
required to be absent. By allowing this spin-four null operator we obtain
several realisations of the algebra both in terms of two scalars as well
as in terms of an arbitrary number of free scalars. Our analysis is
complete for the case of two-scalar realisations.Comment: 14 pages, LATEX, UG-6/9
Daris, a low-frequency distributed aperture array for radio astronomy in space
DARIS (Distributed Aperture Array for Radio Astronomy in Space) is a radio astronomy space mission concept aimed at observing the low-frequency radio sky in the range 1-10 MHz. Because of the Earth's ionospheric disturbances and opaqueness, this frequency range can only be observed from space. The astronomical science cases include sensitive extragalactic surveys, radio transients such as Jupiter-like burst and Crab-like pulses, and coronal mass ejection tracking. The focus of the DARIS concept study is on feasibility aspects of a distributed aperture synthesis array in space, consisting of small satellite nodes and a mother-ship. The study selected suitable science cases, antenna concepts, communications, signal processing, orbital design, and mission analysis. With current-day technologies a satellite cluster can be built consisting of at least eight satellite nodes and a mother-ship, which could be launched with a Soyuz rocket from Kourou. Such a satellite cluster would open up the last unexplored frequency range for astronomy
Cofactor regeneration by a soluble pyridine nucleotide transhydrogenase for biological production of hydromorphone
We have applied the soluble pyridine nucleotide transhydrogenase of Pseudomonas fluorescens to a cell-free system for the regeneration of the nicotinamide cofactors NAD and NADP in the biological production of the important semisynthetic opiate drug hydromorphone. The original recombinant whole-cell system suffered from cofactor depletion resulting from the action of an NADP(+)-dependent morphine dehydrogenase and an NADH-dependent morphinone reductase. By applying a soluble pyridine nucleotide transhydrogenase, which can transfer reducing equivalents between NAD and NADP, we demonstrate with a cell-free system that efficient cofactor cycling in the presence of catalytic amounts of cofactors occurs, resulting in high yields of hydromorphone. The ratio of morphine dehydrogenase, morphinone reductase, and soluble pyridine nucleotide transhydrogenase is critical for diminishing the production of the unwanted by-product dihydromorphine and for optimum hydromorphone yields. Application of the soluble pyridine nucleotide transhydrogenase to the whole-cell system resulted in an improved biocatalyst with an extended lifetime. These results demonstrate the usefulness of the soluble pyridine nucleotide transhydrogenase and its wider application as a tool in metabolic engineering and biocatalysis
Mapping dynamic social networks in real life using participants' own smartphones
AbstractInterpersonal relationships are vital for our daily functioning and wellbeing. Social networks may form the primary means by which environmental influences determine individual traits. Several studies have shown the influence of social networks on decision-making, behaviors and wellbeing. Smartphones have great potential for measuring social networks in a real world setting. Here we tested the feasibility of using people's own smartphones as a data collection platform for face-to-face interactions. We developed an application for iOS and Android to collect Bluetooth data and acquired one week of data from 14 participants in our organization. The Bluetooth scanning statistics were used to quantify the time-resolved connection strength between participants and define the weights of a dynamic social network. We used network metrics to quantify changes in network topology over time and non-negative matrix factorization to identify cliques or subgroups that reoccurred during the week. The scanning rate varied considerably between smartphones running Android and iOS and egocentric networks metrics were correlated with the scanning rate. The time courses of two identified subgroups matched with two meetings that took place that week. These findings demonstrate the feasibility of using participants' own smartphones to map social network, whilst identifying current limitations of using generic smartphones. The bias introduced by variations in scanning rate and missing data is an important limitation that needs to be addressed in future studies
The generation of hierarchic structures via robust 3D topology optimisation
Commonly used building structures often show a hierarchic layout of structural elements. It can be questioned whether such a layout originates from practical considerations, e.g. related to its construction, or that it is (relatively) optimal from a structural point of view. This paper investigates this question by using topology optimisation in an attempt to generate hierarchical structures. As an arbitrarily standard design case, the principle of a traditional timber floor that spans in one direction is used. The optimisation problem is first solved using classical sensitivity and density filtering. This leads indeed to solutions with a hierarchic layout, but they are practically unusable as the floor boarding is absent. A Heaviside projection is therefore considered next, but this does not solve the problem. Finally, a robust approach is followed, and this does result in a design similar to floor boarding supported by timber joists. The robust approach is then followed to study a floor with an opening, two floors that span in two directions, and an eight-level concrete building. It can be concluded that a hierarchic layout of structural elements likely originates from being optimal from a structural point of view. Also clear is that this conclusion cannot be obtained by means of standard topology optimisation based on sensitivity or density filtering (as often found in commercial finite element codes); robust 3D optimisation is required to obtain a usable, constructible (or in the future: 3D printable) structural design, with a crisp black-and-white density distribution
Bag-in-the-lens intraocular lens in paediatric cataract surgery: intraoperative and postoperative outcomes
Purpose: To report intra- and postoperative surgical outcome using the bag-in-the-lens (BIL) technique in paediatric cataract surgery.
Methods: In a retrospective case series, we studied the outcomes of children aged <12 years operated for cataract with the bag-in-the-lens intraocular lens (IOL), with a minimum of 6 months of follow-up.
Results: Since 2013, 50 eyes in 30 patients <12 years (20 bilateral and 10 unilateral) have been operated at our department with the BIL technique, with a median follow-up time of 33.5 months (range 6â77). Median age at surgery was 49.5 months (4â139). In one case, the IOL luxated through the capsulorhexes to the vitreous, but could be secured and repositioned as planned without further difficulties. Anterior vitrectomy was necessary in one case due to prolapse of vitreous to the anterior chamber during surgery. No other intraoperative complications occurred. Visual axis opacification (VAO) developed in four eyes (8%). So far, only one of these has needed a reoperation with clearing of the secondary cataract. A complete absence of VAO was thus seen throughout the study period in 92%. In two eyes, postoperative iris capture occurred. In both cases, surgical repositioning of the iris was needed. No eyes developed secondary glaucoma during the study period.
Conclusion: The BIL technique seems to be a safe surgical procedure in paediatric cataract, with significantly less complications and need for additional surgery compared with the conventional lens-in-the-bag technique.publishedVersio
Generalized Conformal Quantum Mechanics of D0-brane
We study the generalized conformal quantum mechanics of the probe D0-brane in
the near horizon background of the bound state of source D0-branes. We
elaborate on the relationship of such model to the M theory in the light cone
frame.Comment: 14 pages, RevTeX, revised version with added references to appear in
Phys. Rev.
N=8 matter coupled AdS_3 supergravities
Following the recent construction of maximal (N=16) gauged supergravity in
three dimensions, we derive gauged D=3, N=8 supergravities in three dimensions
as deformations of the corresponding ungauged theories with scalar manifolds
SO(8,n)/(SO(8)x SO(n)). As a special case, we recover the N=(4,4) theories with
local SO(4) = SO(3)_L x SO(3)_R, which reproduce the symmetries and massless
spectrum of D=6, N=(2,0) supergravity compactified on AdS_3 x S^3.Comment: 11 pages, LaTeX2
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