3,957 research outputs found
Quantum Modelling of Electro-Optic Modulators
Many components that are employed in quantum information and communication
systems are well known photonic devices encountered in standard optical fiber
communication systems, such as optical beamsplitters, waveguide couplers and
junctions, electro-optic modulators and optical fiber links. The use of these
photonic devices is becoming increasingly important especially in the context
of their possible integration either in a specifically designed system or in an
already deployed end-to-end fiber link. Whereas the behavior of these devices
is well known under the classical regime, in some cases their operation under
quantum conditions is less well understood. This paper reviews the salient
features of the quantum scattering theory describing both the operation of the
electro-optic phase and amplitude modulators in discrete and continuous-mode
formalisms. This subject is timely and of importance in light of the increasing
utilization of these devices in a variety of systems, including quantum key
distribution and single-photon wavepacket measurement and conformation. In
addition, the paper includes a tutorial development of the use of these models
in selected but yet important applications, such as single and multi-tone
modulation of photons, two-photon interference with phase-modulated light or
the description of amplitude modulation as a quantum operation.Comment: 29 pages, 10 figures, Laser and Photonics Reviews (in press
Artificial Contraception is Associated With Increased Numbers of Induced Abortions
Since the sexual revolution, it has been a widely accepted fact that contraceptives have been a necessity for our society. They seem to be the best way to prevent unwanted pregnancies that would otherwise result from sexual unions between two people unprepared for the commitment of raising any or additional children. It almost goes without saying that the more effective and available contraceptives become, the less likely women who wish to avoid pregnancy will become pregnant and the fewer induced abortions they will seek. In reality, the information available concerning abortions and the women who obtain them points to a different conclusion. The more effective and available contraceptives become in a society, the more widespread the practice of induced abortions becomes. On the other hand, natural family planning has been associated with fewer induced abortions when an unplanned pregnancy results. This paper will present a sample of the information available, attempt to draw conclusions, and discuss the possible reasons that contraceptives are unavoidably linked to increasing numbers of induced abortions and that, conversely, natural family planning is associated with very few or no induced abortions. </jats:p
Novel metaheuristic for parameter estimation in nonlinear dynamic biological systems
BACKGROUND: We consider the problem of parameter estimation (model calibration) in nonlinear dynamic models of biological systems. Due to the frequent ill-conditioning and multi-modality of many of these problems, traditional local methods usually fail (unless initialized with very good guesses of the parameter vector). In order to surmount these difficulties, global optimization (GO) methods have been suggested as robust alternatives. Currently, deterministic GO methods can not solve problems of realistic size within this class in reasonable computation times. In contrast, certain types of stochastic GO methods have shown promising results, although the computational cost remains large. Rodriguez-Fernandez and coworkers have presented hybrid stochastic-deterministic GO methods which could reduce computation time by one order of magnitude while guaranteeing robustness. Our goal here was to further reduce the computational effort without loosing robustness. RESULTS: We have developed a new procedure based on the scatter search methodology for nonlinear optimization of dynamic models of arbitrary (or even unknown) structure (i.e. black-box models). In this contribution, we describe and apply this novel metaheuristic, inspired by recent developments in the field of operations research, to a set of complex identification problems and we make a critical comparison with respect to the previous (above mentioned) successful methods. CONCLUSION: Robust and efficient methods for parameter estimation are of key importance in systems biology and related areas. The new metaheuristic presented in this paper aims to ensure the proper solution of these problems by adopting a global optimization approach, while keeping the computational effort under reasonable values. This new metaheuristic was applied to a set of three challenging parameter estimation problems of nonlinear dynamic biological systems, outperforming very significantly all the methods previously used for these benchmark problems
Open Strings in IIB Orientifold Reductions
We consider type IIB compactifications on a general 4D group manifold with
different types of possible spacetime filling O-planes and the corresponding
D-branes parallel to them. Once fluxes allowed by the associated orientifold
projection are included, a 6D gauged supergravity is
obtained. In this paper we show how the consistent coupling to dynamical open
strings living on the spacetime filling D-branes may be captured by the
inclusion of extra vector multiplets and extra embedding tensor deformations on
the gauged supergravity side. As a result, the quadratic constraints on the
embedding tensor consistently reproduce the source corrected 10D Bianchi
identities. Furthermore, the field strength modifications induced by the open
string sector could potentially be understood as U-dual versions of the
Green-Schwarz terms. Finally, the entire scalar potential of the theory exactly
matches the one obtained from reduction of the bulk action plus the source
contributions.Comment: 45 pages, 1 figur
Cecal Ligation and Puncture-Induced Sepsis Promotes Brown Adipose Tissue Inflammation Without Any Impact on Expression of Thermogenic-Related Genes
Background and Aims: The negative effects of chronic low-level inflammation on adipose tissue physiology have been extensively demonstrated, whereas the effects of acute inflammation are less studied. Here, we aimed to investigate the effects of sepsis-induced acute inflammation on gene expression markers of brown and white adipose tissue functionality. Methods: Brown adipose tissue (BAT) and perirenal white adipose tissue (prWAT) gene expression markers were analyzed in cecal ligation and puncture (CLP)-induced sepsis mice model. Results: CLP-induced sepsis attenuated expression of adipogenesis-related genes, in parallel to increased Tnf, Il6, and Ltf gene expression in prWAT. In contrast, CLP-induced sepsis resulted in increased expression of pro-inflammatory genes (Il6, Ltf, and Lbp) in BAT, without affecting expression of genes encoding for thermogenic activity. Conclusion: Sepsis promotes both prWAT and BAT inflammation, associated with reduced adipogenesis-related gene expression in prWAT, without significant effects on BAT thermogenic genes
Applying Model-Driven Paradigm for the Improvement of Web Requirement Validation
This paper proposes an approach for Web requirements validation by applying
the model-driven paradigm in classical requirements validation techniques. In particular,
we present how the Navigational Development Techniques (NDT) approach exploits the
model-driven paradigm to improve its requirements validation task by exploring tool cases
that systematize or even automate the application of requirements validation techniques.
Our solution is validated by applying it in a real industrial environment. The results and
the learned lessons are presented accordingly
Influencia de las condiciones ambientales en la germinación y supervivencia inicial del pino silvestre en el Valle del Lozoya(Madrid)
El objetivo de este estudio fue evaluar los factores micrometeorológicos que afectan a la regeneración del pino resinero en la Tierra de Pinares Segoviana. Se registró durante un perÃodo vegetativo completo la temperatura del suelo y la temperatura de la capa de aire más próximo al suelo. La temperatura del suelo alcanzó máximos de 56 ºC desde el mes de julio a septiembre, en perÃodos de más de 4 horas seguidas durante 2-5 dÃas consecutivos y la temperatura del aire más próximo al suelo, donde viven las plántulas recién nacidas, alcanzó valores de hasta 56 ºC desde junio a septiembre, durante perÃodos de más de 4,5 horas en periodos de 7 dÃas consecutivos. En las plántulas objeto de estudio se identificaron heridas en el cuello de la raÃz lo que indica que las altas temperaturas producen cambios fisiológicos y morfológicos en las plántulas comprometiendo su supervivencia y la de la regeneración de estos montes. El análisis estadÃstico mostró que los puntos de muestreo seleccionados no presentaron grandes diferencias respecto a las variables microclimáticas consideradas
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