12,154 research outputs found
‘I create therefore I virtually exist’: digital content creation, virtual consumption, and motivation in Second Life
User-generated content (UGC) has been receiving increasing attention given its spread throughout digital media platforms and applications. Previous research focusing on Web 2.0 based platforms highlighted linkages with personal characteristics, user attitudes, and social as well as individual motivators. Interestingly, UGC has not been addressed on other platforms such as 3D virtual worlds, and the purpose of the current study is to fill this gap in the literature. More specifically, we explore virtual content creation within the particular 3D virtual world of Second Life, via comparing key demographic, usage and motivational attributes of creator versus non-creator residents. Results revealed differential patterns as a function of age, gender and usage. Digital content creators were also more likely to purchase goods reflecting stability, expand greater financial resources on the Second Life Marketplace, and while acknowledging greater difficulty in ease of use, reported higher esteem and self-actualization. Implications for scholars and practitioners are discussed.info:eu-repo/semantics/publishedVersio
Bronchus Cardiacus Accessorius Dexter
The diagnosis of bronchus cardiacus accessorius dexter (BCAD) has occurred in 25 cases
during the bronchoscopic investigations of 30,000 adult patients of the authors. In most of the
cases, this bronchial anomaly has been revealed as an accessory phenomenon, nevertheless, in
one of the patients, it was the source of a considerable hemorrhage. In another case reported
here in detail, it occurred together with multiple developmental anomalies, such as
tracheobronchomegaly, mitral valve prolapse, pectus excavatum, hypoplasy of sinus frontalis
on the right side, inguinal hernia on the left side and hyperlipidemia type IV. Family
analysis did not confirm the presence of any chromosomal disorders or accumulation of
similar developmental anomalies. The forms and frequency of associations of the anomalies
are surveyed on the basis of literary data. The recognition of BCAD is of diagnostic
importance, since it may explain the persistence of some bronchopulmonary symptoms;
furthermore, the exploration of the associated abnormal vascular branches may be very useful
in case of an eventual thoracic surgical intervention
Extreme Supernova Models for the Superluminous Transient ASASSN-15lh
The recent discovery of the unprecedentedly superluminous transient
ASASSN-15lh (or SN 2015L) with its UV-bright secondary peak challenges all the
power-input models that have been proposed for superluminous supernovae. Here
we examine some of the few viable interpretations of ASASSN-15lh in the context
of a stellar explosion, involving combinations of one or more power inputs. We
model the lightcurve of ASASSN-15lh with a hybrid model that includes
contributions from magnetar spin-down energy and hydrogen-poor circumstellar
interaction. We also investigate models of pure circumstellar interaction with
a massive hydrogen-deficient shell and discuss the lack of interaction features
in the observed spectra. We find that, as a supernova ASASSN-15lh can be best
modeled by the energetic core-collapse of a ~40 Msun star interacting with a
hydrogen-poor shell of ~20 Msun. The circumstellar shell and progenitor mass
are consistent with a rapidly rotating pulsational pair-instability supernova
progenitor as required for strong interaction following the final supernova
explosion. Additional energy injection by a magnetar with initial period of 1-2
ms and magnetic field of 0.1-1 x 10^14 G may supply the excess luminosity
required to overcome the deficit in single-component models, but this requires
more fine-tuning and extreme parameters for the magnetar, as well as the
assumption of efficient conversion of magnetar energy into radiation. We thus
favor a single-input model where the reverse shock formed in a strong SN
ejecta-CSM interaction following a very powerful core-collapse SN explosion can
supply the luminosity needed to reproduce the late-time UV-bright plateau.Comment: 8 pages, 3 figure
Nonlinear screening in two-dimensional electron gases
We have performed self-consistent calculations of the nonlinear screening of
a point charge Z in a two-dimensional electron gas using a density functional
theory method. We find that the screened potential for a Z=1 charge supports a
bound state even in the high density limit where one might expect perturbation
theory to apply. To explain this behaviour, we prove a theorem to show that the
results of linear response theory are in fact correct even though bound states
exist.Comment: 4 pages, 4 figure
Guided Microwave Detection of Corrosion Product in Insulated Pipelines
Corrosion under insulation (CUI) is a common cause of pipeline failure in the oil and gas industry. Its detection with conventional inspection techniques is challenging due to the presence of the insulation layer and a protective metallic cladding that prevent direct access to the pipe surface. Guided microwave testing has been proposed as a cost-effective approach to screen an extended length of a pipeline for the presence of water, which is a necessary precursor for CUI. The pipe and metallic cladding naturally form a large coaxial transmission line in which the insulation acts as a dielectric and supports the propagation of microwave signals. The inspection is performed by launching the signal from an array of antennas permanently installed at one location along the pipeline. Wet insulation is then detected according to the radar principle since water results in the partial reflection of the incident microwave owing to the permittivity contrast between dry and wet insulation. This paper reviews the underpinning principles of longrange guided microwave testing and presents a new study aimed at enhancing the selectivity of the technique by detecting corrosion product inside the insulation which is more reliable indicator of CUI progression
Finite-level systems, Hermitian operators, isometries, and a novel parameterization of Stiefel and Grassmann manifolds
In this paper we obtain a description of the Hermitian operators acting on
the Hilbert space \C^n, description which gives a complete solution to the
over parameterization problem. More precisely we provide an explicit
parameterization of arbitrary -dimensional operators, operators that may be
considered either as Hamiltonians, or density matrices for finite-level quantum
systems. It is shown that the spectral multiplicities are encoded in a flag
unitary matrix obtained as an ordered product of special unitary matrices, each
one generated by a complex -dimensional unit vector, . As a
byproduct, an alternative and simple parameterization of Stiefel and Grassmann
manifolds is obtained.Comment: 21 page
Parametrization of semi-dynamical quantum reflection algebra
We construct sets of structure matrices for the semi-dynamical reflection
algebra, solving the Yang-Baxter type consistency equations extended by the
action of an automorphism of the auxiliary space. These solutions are
parametrized by dynamical conjugation matrices, Drinfel'd twist representations
and quantum non-dynamical -matrices. They yield factorized forms for the
monodromy matrices.Comment: LaTeX, 24 pages. Misprints corrected, comments added in Conclusion on
construction of Hamiltonian
Design study of an integrated aerobraking orbital transfer vehicle
An aerobraking orbital transfer vehicle (AOTV) concept, which has an aerobrake structure that is integrated with the propulsion stage, is discussed. The concept vehicle is to be assembled in space and is space-based. The advantages of aeroassist over an all propulsive vehicle are discussed and it is shown that the vehicle considered is very competitive with inflatable and deployable concepts from mass and performance aspects. The aerobrake geometry is an ellipsoidally blunted, raked-off, elliptical wide-angle cone with a toroidal skirt. Propellant tanks, engines, and subsystems are integrated into a closed, isogrid aerobrake structure which provides rigidity. The vehicle has two side-firing, gimbaled RL-10 type engines and carries 38,000 kg of useable propellant. The trajectory during aerobraking is determined from an adaptive guidance logic, and the heating is determined from engineering correlations as well as 3-D Navier-Stokes solutions. The AOTV is capable of placing 13,500 kg payload into geosynchronous Earth orbit (GEO) or carrying a LEO-GEO-LEO round-trip payload of 7100 kg. A two-stage version considered for lunar missions results in a lunar surface delivery capability of 18,000 kg or a round-trip capability of 6800 kg with 3860 kg delivery-only capability
Guided Wave Tomography of Pipe Bends
Detection and monitoring of corrosion and erosion damage in pipe bends are open challenges due to the curvature of the elbow, the complex morphology of these defects, and their unpredictable location. Combining model based inversion with guided ultrasonic waves propagating along the elbow and inside its walls, offers the possibility of mapping wall-thickness losses over the entire bend and from a few permanently installed transducers under the realm of guided wave tomography (GWT). This paper provides the first experimental demonstration of GWT of pipe bends based on a novel curved ray tomography algorithm and an optimal transducer configuration consisting of two ring arrays mounted at the ends of the elbow and a line of transducers fixed to the elbow extrados. Using realistic, localized corrosion defects it is shown that detection of both the presence and progression of damage can be achieved with 100% sensitivity regardless of damage position around the bend. Importantly, this is possible for defects as shallow as 0.50% of wall thickness (WT) and for maximum depth increments of just 0.25% of WT. However, due to the highly irregular profile of corrosion defects, GWT generally underestimates maximum depth relative to the values obtained from 3-D laser scans of the same defects, leading in many cases to errors between 4 and 8% of WT
Some remarks on quasi-Hermitian operators
A quasi-Hermitian operator is an operator that is similar to its adjoint in
some sense, via a metric operator, i.e., a strictly positive self-adjoint
operator. Whereas those metric operators are in general assumed to be bounded,
we analyze the structure generated by unbounded metric operators in a Hilbert
space. Following our previous work, we introduce several generalizations of the
notion of similarity between operators. Then we explore systematically the
various types of quasi-Hermitian operators, bounded or not. Finally we discuss
their application in the so-called pseudo-Hermitian quantum mechanics.Comment: 18page
- …