Computational alternatives to obtain time optimal jet engine control

Two computational methods to determine an open loop time optimal control sequence for a simple single spool turbojet engine are described by a set of nonlinear differential equations. Both methods are modifications of widely accepted algorithms which can solve fixed time unconstrained optimal control problems with a free right end. Constrained problems to be considered have fixed right ends and free time. Dynamic programming is defined on a standard problem and it yields a successive approximation solution to the time optimal problem of interest. A feedback control law is obtained and it is then used to determine the corresponding open loop control sequence. The Fletcher-Reeves conjugate gradient method has been selected for adaptation to solve a nonlinear optimal control problem with state variable and control constraints

Strengthening measurements from the edges: application-level packet loss rate estimation

Network users know much less than ISPs, Internet exchanges and content providers about what happens inside the network. Consequently users cannot either easily detect network neutrality violations or readily exercise their market power by knowledgeably switching ISPs. This paper contributes to the ongoing efforts to empower users by proposing two models to estimate -- via application-level measurements -- a key network indicator, i.e., the packet loss rate (PLR) experienced by FTP-like TCP downloads. Controlled, testbed, and large-scale experiments show that the Inverse Mathis model is simpler and more consistent across the whole PLR range, but less accurate than the more advanced Likely Rexmit model for landline connections and moderate PL

Instabilities and sensitivities in a flow over a rotationally flexible cylinder with a rigid splitter plate

This paper investigates the origin of flow-induced instabilities and their sensitivities in a flow over a rotationally flexible circular cylinder with a rigid splitter plate. A linear stability and sensitivity problem is formulated in the Eulerian frame by considering the geometric nonlinearity arising from the rotational motion of the cylinder which is not present in the stationary or purely translating stability methodology. This nonlinearity needs careful and consistent treatment in the linearised problem particularly when considering the Eulerian frame or reference adopted in this study and not so widely considered. Two types of instabilities arising from the fluid-structure interaction are found. The first type of the instabilities is the stationary symmetry-breaking mode, which was well reported in previous studies. This instability exhibits a strong correlation with the length of the recirculation zone. A detailed analysis of the instability mode and its sensitivity reveals the importance of the flow near the tip region of the plate for the generation and control of this instability mode. The second type is an oscillatory torsional flapping mode, which has not been well reported. This instability typically emerges when the length of the splitter plate is sufficiently long. Unlike the symmetry breaking mode, it is not so closely correlated with the length of the recirculation zone. The sensitivity analysis however also reveals the crucial role played by the flow near the tip region in this instability. Finally, it is found that many physical features of this instability are reminiscent of those of the flapping (or flutter instability) observed in a flow over a flexible plate or a flag, suggesting that these instabilities share the same physical origin

Survival probabilities of loggerhead sea turtles (<i>Caretta caretta</i>) estimated from capture-mark-recapture data in the Mediterranean Sea

Las probabilidades de supervivencia de la tortuga boba (Caretta caretta) se han estimado por primera vez en el Mediterráneo analizando datos de 3254 marcajes y 134 recapturas en esta región. La mayoría de las tortugas eran juveniles encontrados en el mar. Las recapturas fueron reavistamientos de individuos vivos y recuperaciones de individuos muertos. Los datos se analizaron mediante el modelo de Baker, versión modificada del de Cormack-Jolly-Seber que puede combinar recaptura, reavistamientos de individuos vivos e individuos recuperados muertos. Se obtuvo una probabilidad de supervivencia anual de 0.73 (IC 95% = 0.67-0.78; n=3254), y debe considerarse como una estima conservativa debido a una desconocida, aunque no insignificante, tasa de perdida de marcados. Este estudio ofrece una estima preliminar de las probabilidades de supervivencia de los estadios de desarrollo "en el mar" para la población mediterránea amenazada de tortuga boba marina, y proporciona las primeras observaciones sobre la magnitud de la sospechada mortalidad inducida por el hombre en la región. El modelo, utilizado aquí por primera vez en tortugas marinas podría ser utilizado para obtener estimas de supervivencia a partir de otros datos con pocas o sin recapturas reales, pero con otros tipos de datos de recaptura frecuentemente producidos por programas de marcado de estos animales de amplia distribución

Scattering of Giant Holes

We study scalar excitations of high spin operators in N=4 super Yang-Mills theory, which are dual to solitons propagating on a long folded string in AdS_3 x S^1. In the spin chain description of the gauge theory, these are associated to holes in the magnon distribution in the sl(2,R) sector. We compute the all-loop hole S-matrix from the asymptotic Bethe ansatz, and expand in leading orders at weak and strong coupling. The worldsheet S-matrix of solitonic excitations on the GKP string is calculated using semiclassical quantization. We find an exact agreement between the gauge theory and string theory results.Comment: 13 pages. v2: minor corrections, references adde

Screening for hazardous alcohol use and dependence in psychiatric in-patients using the AUDIT questionnaire

The Alcohol Use Disorders Identification Test (AUDIT) has been used to screen for hazardous and harmful alcohol consumption among general hospital populations but not in psychiatric patients. Using the AUDIT, we assessed alcohol use in patients with four major types of psychiatric disorder, namely mood, adjustment, anxiety and psychotic disorders. Nine hundred and ninety consecutive admissions to the psychiatric units of two hospitals during a 12-month period underwent assessment. In each diagnostic group a high proportion of patients was alcohol-dependent. Among those with mood disorders 25.4% of men were alcohol-dependent, compared with 16.3% of women, while 34.5% of men with anxiety disorder were alcohol-dependent compared with 25.0% of women. Both gender differences were statistically significant. The differences were even greater for adjustment disorder (44.4% vs. 14.5%) and psychosis (29.2% and 4.2%, respectively). More men than women with anxiety disorder were classified as hazardous (24.1% vs. 11.7%) or harmful drinkers (13.8% vs. 3.3%), but for the other diagnostic groupings the percentages in these drinking categories were more nearly similar. Thus, there is a high rate of excessive alcohol consumption in people with psychiatric disorders, especially males. Such individuals may be particularly vulnerable to complications of alcohol misuse such as suicide and exacerbation of their disorder. The potential for decreased severity of psychiatric symptoms and a reduction in the number of hospital admissions following cessation or reduction in alcohol consumption is considerable. The AUDIT is a simple screening device for investigating alcohol use and dependence, and offers a means of initiating intervention in this population

Noise Measurement of Interacting Ferromagnetic Particles with High Resolution Hall Microprobes

We present our first experimental determination of the magnetic noise of a superspinglass made of < 1 pico-liter frozen ferrofluid. The measurements were performed with a local magnetic field sensor based on Hall microprobes operated with the spinning current technique. The results obtained, though preliminary, qualitatively agree with the theoretical predictions of Fluctuation-Dissipation theorem (FDT) violation [1].Comment: 4pages, 2 figure

Simulation of tillage systems impact on soil biophysical properties using the SALUS model

A sustainable land management has been defined as the management system that allows for production, while minimizing risk, maintaining quality of soil and water. Tillage systems can significantly decrease soil carbon storage and influence the soil environment of a crop. Crop growth models can be useful tools in evaluating the impact of different tillage systems on soil biophysical properties and on the growth and final yield of the crops. The objectives of this paper were i) to illustrate the SALUS model and its tillage component; ii) to evaluate the effects of different tillage systems on water infiltration and time to ponding, iii) to simulate the effect of tillage systems on some soil biophysical properties. The SALUS (System Approach to Land Use Sustainability) model is designed to simulate continuous crop, soil, water and nutrient conditions under different tillage and crop residues management strategies for multiple years. Predictions of changes in surface residue, bulk density, runoff, drainage and evaporation were consistent with expected behaviours of these parameters as described in the literature. The experiment to estimate the time to ponding curve under different tillage system confirmed the theory and showed the beneficial effects of the residue on soil surface with respect to water infiltration. It also showed that the no-tillage system is a more appropriate system to adopt in areas characterized by high intensity rainfal