2,270 research outputs found
The Use of Seemingly Unrelated Regression (SUR) to Predict the Carcass Composition of Lambs
The aim of this study was to develop and evaluate models for predicting the carcass composition of lambs. Forty male lambs of two different breeds were included in our analysis. The lambs were slaughtered and their hot carcass weight was obtained. After cooling for 24 hours, the subcutaneous fat thickness was measured between the 12th and 13th rib and the total breast bone tissue thickness was taken in the middle of the second sternebrae. The left side of all carcasses was dissected into five components and the proportions of lean meat, subcutaneous fat, intermuscular fat, kidney and knob channel fat, and bone plus remainder were otained. Our models for carcass composition were fitted using the SUR estimator which is novel in this area. The results were compared to OLS estimates and evaluated by several statistical measures. As the models are intended to predict carcass composition, we particularly focussed on the PRESS statistic, because it assesses the precision of the model in predicting carcass composition. Our results showed that the SUR estimator performed better in predicting LMP and IFP than the OLS estimator. Although objective carcass classification systems could be improved by using the SUR estimator, it has never been used before for predicting carcass composition.Carcass, Quality, Ordinary least squares, Seemingly unrelated regression
A worldwide model for boundaries of urban settlements
The shape of urban settlements plays a fundamental role in their sustainable
planning. Properly defining the boundaries of cities is challenging and remains
an open problem in the Science of Cities. Here, we propose a worldwide model to
define urban settlements beyond their administrative boundaries through a
bottom-up approach that takes into account geographical biases intrinsically
associated with most societies around the world, and reflected in their
different regional growing dynamics. The generality of the model allows to
study the scaling laws of cities at all geographical levels: countries,
continents, and the entire world. Our definition of cities is robust and holds
to one of the most famous results in Social Sciences: Zipf's law. According to
our results, the largest cities in the world are not in line with what was
recently reported by the United Nations. For example, we find that the largest
city in the world is an agglomeration of several small settlements close to
each other, connecting three large settlements: Alexandria, Cairo, and Luxor.
Our definition of cities opens the doors to the study of the economy of cities
in a systematic way independently of arbitrary definitions that employ
administrative boundaries
Recomendações e protocolos de actuação terapêutica: relevância para a qualidade da prescrição
A prescrição de um ou mais agentes farmacológicos
constitui a forma de terminar a maior parte das
consultas médicas. O modo como os medicamentos
são utilizados tem consequências óbvias para a
saúde dos indivíduos e das populações e para a utilização
eficiente dos recursos de saúde disponíveis.
Este assunto interessa aos decisores políticos, aos
profissionais de saúde, aos doentes e ao público
em geral
Inference for Ecological Dynamical Systems: A Case Study of Two Endemic Diseases
A Bayesian Markov chain Monte Carlo method is used to infer parameters for an open stochastic epidemiological model: the Markovian susceptible-infected-recovered (SIR) model, which is suitable for modeling and simulating recurrent epidemics. This allows exploring two major problems of inference appearing in many mechanistic population models. First, trajectories of these processes are often only partly observed. For example, during an epidemic the transmission process is only partly observable: one cannot record infection times. Therefore, one only records cases (infections) as the observations. As a result some means of imputing or reconstructing individuals in the susceptible cases class must be accomplished. Second, the official reporting of observations (cases in epidemiology) is typically done not as they are actually recorded but at some temporal interval over which they have been aggregated. To address these issues, this paper investigates the following problems. Parameter inference for a perfectly sampled open Markovian SIR is first considered. Next inference for an imperfectly observed sample path of the system is studied. Although this second problem has been solved for the case of closed epidemics, it has proven quite difficult for the case of open recurrent epidemics. Lastly, application of the statistical theory is made to measles and pertussis epidemic time series data from 60 UK cities
Pulse phase and precession phase resolved spectroscopy of Her X-1: studying a representative Main-On with RXTE
We performed a detailed pulse phase resolved spectroscopy of the accreting
binary X-ray pulsar Her X-1 in the energy range 3.5-75 keV and have established
pulse phase profiles for all spectral parameters. For the centroid of the
cyclotron line, the photon index and the flux of the 6.4 keV iron line, we have
studied the variation as a function of 35 d phase. We analyzed RXTE
observations of the Main-On of November 2002. Four different time intervals of
about 1 d duration were selected to provide a good coverage of a complete
Main-On. The intervals are centered at 35 d phase 0.03, 0.10, 0.15, and 0.20,
respectively. All spectral parameters show a strong modulation with pulse
phase. While the centroid energy of the cyclotron line follows roughly the
shape of the pulse profile, both the photon index and the iron line intensity
exhibit distinct minima around the peak of the X-ray pulse. With respect to
variations of the observed profiles with 35 d phase, we find that there is a
clear evolution of the shape of the pulse profiles (flux versus pulse phase), a
moderate increase of the maximum cyclotron line energy (found around pulse
phase 0.7), but no significant evolution of the shape of the pulse phase
profiles of the cyclotron line energy, the spectral power law index or the iron
line intensity. The variation of spectral parameters as a function of the pulse
phase provides important information about the system: 1. the disappearance of
the Fe line flux near the highest continuum flux may be an indication of a
hollow cone geometry of the accretion structure; ii. the apparent
non-dependence of the cyclotron line energy profiles on 35 d phase provides a
new possibility to test the model of free precession of the neutron star,
proposed to be responsible for the systematic variations in the pulse profiles.Comment: 10 pages, 11 figures, Accepted by A&A on the 22/12/201
Enhanced propagation of motile bacteria on surfaces due to forward scattering
How motile bacteria move near a surface is a problem of fundamental
biophysical interest and is key to the emergence of several phenomena of
biological, ecological and medical relevance, including biofilm formation.
Solid boundaries can strongly influence a cell's propulsion mechanism, thus
leading many flagellated bacteria to describe long circular trajectories stably
entrapped by the surface. Experimental studies on near-surface bacterial
motility have, however, neglected the fact that real environments have typical
microstructures varying on the scale of the cells' motion. Here, we show that
micro-obstacles influence the propagation of peritrichously flagellated
bacteria on a flat surface in a non-monotonic way. Instead of hindering it, an
optimal, relatively low obstacle density can significantly enhance cells'
propagation on surfaces due to individual forward-scattering events. This
finding provides insight on the emerging dynamics of chiral active matter in
complex environments and inspires possible routes to control microbial ecology
in natural habitats
Creating safety nets through semi-parametric index-based insurance: A simulation for Northern Ghana
In West Africa, farm income is highly exposed to risks from crop failure in the drier, inland areas, and from fluctuations in (world market) prices in the wetter coastal areas. As individuals and even extended families are poorly equipped to deal with these, provision of social safety nets is required Our paper reviews the situation in Ghana and the way in which the new financial instrument of index-based insurance might contribute to better it, focusing on the estimation of a crop indemnification scheme for farmers in Northern Ghana. It recalls that in a poor rural area like Northern Ghana, provision of social safety almost coincides with food security management, and must, therefore, distinguish three basic subtasks: distributing income entitlements (possibly indemnification payments from insurance) to the poor, ensuring collection of taxes (possibly insurance premiums) to fund the arrangement, and assuring delivery of staple goods, such as food to the all households, including the poor. We point out that crop insurance, in any form can at best entitle the poor, and with adequate premiums, become adequately funded, albeit that current experience suggests that farmers tend to be reluctant and to find it difficult to fulfill their obligations. Our main remark is, however, that unless the actual availability of goods is assured, the indemnification from crop insurance will under droughts only cause prices to rise and channel away scarce food from the uninsured to the insured. In short, in poor areas such as Northern Ghana co-ordinated food security management is key, particularly under severe droughts, with crop insurance possibly playing a role in the spheres of entitlement and taxation. Turning to the modalities of crop insurance, we mention the advantages of the index-based approach, which as compared to the individualized contracts of commercial insurance greatly reduces transaction costs by basing the indemnification payments on objectively and easily measurable variables, such as rainfall data collected at weather stations, and world prices of main export goods. Our contribution is an improvement of the indemnification schedules. Rather than specifying a synthetic schedule or estimating is as a parametric form, we estimate it as an optimal indemnification that minimizes farmers' risk of having their income drop below the poverty line, while restricting the indemnification to be an unknown function of index variables on weather and prices. We adapt kernel learning technique to conduct this estimation, so as to ensure that the schedule is self-financing, up to a subsidy. Our application is for Northern Ghana where poverty is highest and farming conditions are most risky. We test the scheme's performance as a social safety net in terms of its capacity to reduce basis risk and alleviate poverty. Although our schedule definitely outperforms the parametric forms, basis risk and associated poverty remain considerable.Risk and Uncertainty,
Liquidity spillover effects of equity offerings over dual-class shares
We study the spillover effect from equity offerings over dual-class shares. Whereas, evidence has been found that a seasoned equity offering improves stock liquidity, the effect over the liquidity of different type shares of the same firm has not been explored. We use equity offerings of five Latin American countries: Brazil, Chile, Colombia, Mexico and Peru, during 1995 to 2012, because dual-class shares are widely used in the regions. In spite of the expected information asymmetry reduction, using panel data models we found a stock liquidity reduction of dual-class shares upon the offering; consistent with trading migration effects, according with the theory of inventory costs
Server selection on the internet using passive probing
This paper describes a server selection mechanism for connection oriented services based on passive probing. The criterion of selection is the quality of service expected from each server, expressed as a function of availability and response time. Measures from previous connections to servers made by local clients are used to continuously update a QoS database which the prediction algorithm uses to compute the response time expected in subsequent connections. The forecasting approach is mainly based on prior measurements of TCP connection establishment time. The maximum segment size in a connection is also considered. The proposed metric is compared with other ones normally used to measure network proximity. Results show that the proposed server selection mechanism achieves a reduction of response time of over 50 percent compared with a random selection mechanism
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