69 research outputs found
Entrepreneurial attributes for success in the small hotel sector: a fuzzy-set QCA approach
By examining small hotels in Spain, this research contributes to understanding
how human capital, social capital, and contingency factors interact to build a success
model based on high hotel occupancy rates, profit, and profit per employee. Human capital
theory, social capital theory, and multilevel theory provide the theoretical basis for this
research. The study used fuzzy-set qualitative comparative analysis applied to a sample of
51 small Spanish hotels. The results reveal the existence of different configurations that
lead to the desired performance outcomes. Each configuration combines two or three
causal conditions. The results also reflect the difficulties that small hotels may face in
reconciling different performance objectives. This paper thus provides solutions for
managers, who must make strategic decisions based on existing conditions both inside and
outside their organisations. The findings discussed herein can thus help small hotels better
define their performance objectives by considering their individual characteristics. The
findings can also help new small hotel entrepreneurs better understand the conditions
required for success in this highly competitive market.info:eu-repo/semantics/publishedVersio
Cosmic Microwave Background anisotropies from second order gravitational perturbations
This paper presents a complete analysis of the effects of second order
gravitational perturbations on Cosmic Microwave Background anisotropies, taking
explicitly into account scalar, vector and tensor modes. We also consider the
second order perturbations of the metric itself obtaining them, for a universe
dominated by a collision-less fluid, in the Poisson gauge, by transforming the
known results in the synchronous gauge. We discuss the resulting second order
anisotropies in the Poisson gauge, and analyse the possible relevance of the
different terms. We expect that, in the simplest scenarios for structure
formation, the main effect comes from the gravitational lensing by scalar
perturbations, that is known to give a few percent contribution to the
anisotropies at small angular scales.Comment: 15 pages, revtex, no figures. Version to be published in Phys. Rev.
On the dynamic adaptation of language models based on dialogue information
We present an approach to adapt dynamically the language models (LMs) used by a speech recognizer that is part of a spoken dialogue system. We have developed a grammar generation strategy that automatically adapts the LMs using the semantic information that the user provides (represented as dialogue concepts), together with the information regarding the intentions of the speaker (inferred by the dialogue manager, and represented as dialogue goals). We carry out the adaptation as a linear interpolation between a background LM, and one or more of the LMs associated to the dialogue elements (concepts or goals) addressed by the user. The interpolation weights between those models are automatically estimated on each dialogue turn, using measures such as the posterior probabilities of concepts and goals, estimated as part of the inference procedure to determine the actions to be carried out. We propose two approaches to handle the LMs related to concepts and goals. Whereas in the first one we estimate a LM for each one of them, in the second one we apply several clustering strategies to group together those elements that share some common properties, and estimate a LM for each cluster. Our evaluation shows how the system can estimate a dynamic model adapted to each dialogue turn, which helps to improve the performance of the speech recognition (up to a 14.82% of relative improvement), which leads to an improvement in both the language understanding and the dialogue management tasks
Giant Superfluorescent Bursts from a Semiconductor Magnetoplasma
Currently, considerable resurgent interest exists in the concept of
superradiance (SR), i.e., accelerated relaxation of excited dipoles due to
cooperative spontaneous emission, first proposed by Dicke in 1954. Recent
authors have discussed SR in diverse contexts, including cavity quantum
electrodynamics, quantum phase transitions, and plasmonics. At the heart of
these various experiments lies the coherent coupling of constituent particles
to each other via their radiation field that cooperatively governs the dynamics
of the whole system. In the most exciting form of SR, called superfluorescence
(SF), macroscopic coherence spontaneously builds up out of an initially
incoherent ensemble of excited dipoles and then decays abruptly. Here, we
demonstrate the emergence of this photon-mediated, cooperative, many-body state
in a very unlikely system: an ultradense electron-hole plasma in a
semiconductor. We observe intense, delayed pulses, or bursts, of coherent
radiation from highly photo-excited semiconductor quantum wells with a
concomitant sudden decrease in population from total inversion to zero. Unlike
previously reported SF in atomic and molecular systems that occur on nanosecond
time scales, these intense SF bursts have picosecond pulse-widths and are
delayed in time by tens of picoseconds with respect to the excitation pulse.
They appear only at sufficiently high excitation powers and magnetic fields and
sufficiently low temperatures - where various interactions causing decoherence
are suppressed. We present theoretical simulations based on the relaxation and
recombination dynamics of ultrahigh-density electron-hole pairs in a quantizing
magnetic field, which successfully capture the salient features of the
experimental observations.Comment: 21 pages, 4 figure
Flux pinning by regular arrays of ferromagnetic dots
The pinning of flux lines by two different types of regular arrays of
submicron magnetic dots is studied in superconducting Pb films; rectangular Co
dots with in-plane magnetization are used as pinning centers to investigate the
influence of the magnetic stray field of the dots on the pinning phenomena,
whereas multilayered Co/Pt dots with out-of-plane magnetization are used to
study the magnetic interaction between the flux lines and the magnetic moment
of the dots. For both types of pinning arrays, matching anomalies are observed
in the magnetization curves versus perpendicular applied field at integer and
rational multiples of the first matching field, which correspond to stable flux
configurations in the artificially created pinning potential. By varying the
magnetic domain structure of the Co dots with in-plane magnetization, a clear
influence of the stray field of the dots on the pinning efficiency is found.
For the Co/Pt dots with out-of-plane magnetization, a pronounced field
asymmetry is observed in the magnetization curves when the dots are magnetized
in a perpendicular field prior to the measurement. This asymmetry can be
attributed to the interaction of the out-of-plane magnetic moment of the Co/Pt
dots with the local field of the flux lines and indicates that flux pinning is
stronger when the magnetic moment of the dot and the field of the flux line
have the same polarity.Comment: 7 pages including figures; submitted for publication in Physica C
(Proceedings ESF-Vortex Conference, 18-24 Sept. 1999, Crete, Greece
Predicting non-invasive ventilation failure in children from the SpO₂/FiO₂ (SF) ratio
PURPOSE:
Our objective was to assess whether SpO₂/FiO₂ (SF) ratio could be a useful NIV outcome predictor in children with acute respiratory failure (ARF) and tried to develop a predictive model of NIV failure.
METHODS:
Prospective, observational, multicenter study. Episodes of ARF-fulfilling inclusion criteria from 15 January 2010 to 14 January 2011 were treated with NIV according to a pre-established protocol. Clinical variables were collected at baseline and at 1, 2, 6, 12 and 24 h. Failure criterion was the need for endotracheal intubation. Failures were considered as "early" if occurring ≤6 h after NIV initiation, "intermediate" if occurring between 6 and 24 h, and "late" if occurring after 24 h. Variables with a p < 0.1 in univariate analysis corrected by age were included in multivariate analysis. Models were calculated based on multivariate analysis.
RESULTS:
During the study period, 390 episodes were included. NIV success rate was 81.3 %. Among ARF causes, failure occurred most frequently in ARDS episodes. The failure predictive model for the whole sample included SF ratio at 1 h, age and PRISM III-24 (area under the curve AUC of 0.755). For early NIV failures, SF ratio at 1 h was the only variable within model (AUC 0.748). The analysis of intermediate NIV failures identified 3 variables independently linked to NIV outcome: PRISM III-24, RR decrease at 6 h, and SF ratio at 6 h (AUC 0.895). No model was identified for late NIV failure.
CONCLUSIONS:
SF ratio is a reliable predictor of early NIV failure in children
On the sensitivity of the HAWC observatory to gamma-ray bursts
We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very
high-energy gamma-ray observatory currently under construction in Mexico at an
altitude of 4100 m. It will observe atmospheric air showers via the water
Cherenkov method. HAWC will consist of 300 large water tanks instrumented with
4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main
DAQ system reads out coincident signals in the tanks and reconstructs the
direction and energy of individual atmospheric showers. The scaler DAQ counts
the hits in each photomultiplier tube (PMT) in the detector and searches for a
statistical excess over the noise of all PMTs. We show that HAWC has a
realistic opportunity to observe the high-energy power law components of GRBs
that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The
two DAQ systems have an energy threshold that is low enough to observe events
similar to GRB 090510 and GRB 090902b with the characteristics observed by
Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs
which in turn could help to understanding about e-pair attenuation in GRB jets,
extragalactic background light absorption, as well as establishing the highest
energy to which GRBs accelerate particles
Mycobacterial dihydrofolate reductase inhibitors identified using chemogenomic methods and in vitro validation.
The lack of success in target-based screening approaches to the discovery of antibacterial agents has led to reemergence of phenotypic screening as a successful approach of identifying bioactive, antibacterial compounds. A challenge though with this route is then to identify the molecular target(s) and mechanism of action of the hits. This target identification, or deorphanization step, is often essential in further optimization and validation studies. Direct experimental identification of the molecular target of a screening hit is often complex, precisely because the properties and specificity of the hit are not yet optimized against that target, and so many false positives are often obtained. An alternative is to use computational, predictive, approaches to hypothesize a mechanism of action, which can then be validated in a more directed and efficient manner. Specifically here we present experimental validation of an in silico prediction from a large-scale screen performed against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis. The two potent anti-tubercular compounds studied in this case, belonging to the tetrahydro-1,3,5-triazin-2-amine (THT) family, were predicted and confirmed to be an inhibitor of dihydrofolate reductase (DHFR), a known essential Mtb gene, and already clinically validated as a drug target. Given the large number of similar screening data sets shared amongst the community, this in vitro validation of these target predictions gives weight to computational approaches to establish the mechanism of action (MoA) of novel screening hit
Local Luminous Infrared Galaxies: Spatially resolved mid-infrared observations with Spitzer/IRS
Luminous Infrared (IR) Galaxies (LIRGs) are an important cosmological class
of galaxies as they are the main contributors to the co-moving star formation
rate density of the universe at z=1. In this paper we present a GTO Spitzer IRS
program aimed to obtain spectral mapping of a sample of 14 local (d<76Mpc)
LIRGs. The data cubes map, at least, the central 20arcsec x 20arcsec to
30arcsec x 30arcsec regions of the galaxies, and use all four IRS modules
covering the full 5-38micron spectral range. The final goal of this project is
to characterize fully the mid-IR properties of local LIRGs as a first step to
understanding their more distant counterparts. In this paper we present the
first results of this GTO program. The IRS spectral mapping data allow us to
build spectral maps of the bright mid-IR emission lines (e.g., [NeII], [NeIII],
[SIII], H_2), continuum, the 6.2 and 11.3micron PAH features, and the 9.7micron
silicate feature, as well as to extract 1D spectra for regions of interest in
each galaxy. The IRS data are used to obtain spatially resolved measurements of
the extinction using the 9.7micron silicate feature, and to trace star forming
regions using the neon lines and the PAH features. We also investigate a number
of AGN indicators, including the presence of high excitation emission lines and
a strong dust continuum emission at around 6micron. We finally use the
integrated Spitzer/IRS spectra as templates of local LIRGs. We discuss several
possible uses for these templates, including the calibration of the star
formation rate of IR-bright galaxies at high redshift. We also predict the
intensities of the brightest mid-IR emission lines for LIRGs as a function of
redshift, and compare them with the expected sensitivities of future space IR
missions.Comment: Accepted for publication in Advances in Space Researc
Erratum to ‘QTPIE: Charge transfer with polarization current equalization. A fluctuating charge model with correct asymptotics’ [Chem. Phys. Lett. 438 (2007) 315]
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