Mode stability in delta Scuti stars: linear analysis versus observations in open clusters

A comparison between linear stability analysis and observations of pulsation modes in five delta Scuti stars, belonging to the same cluster, is presented. The study is based on the work by Michel et al. (1999), in which such a comparison was performed for a representative set of model solutions obtained independently for each individual star considered. In this paper we revisit the work by Michel et al. (1999) following, however, a new approach which consists in the search for a single, complete, and coherent solution for all the selected stars, in order to constrain and test the assumed physics describing these objects. To do so, refined descriptions for the effects of rotation on the determination of the global stellar parameters and on the adiabatic oscillation frequency computations are used. In addition, a crude attempt is made to study the role of rotation on the prediction of mode instabilities.The present results are found to be comparable with those reported by Michel et al. (1999). Within the temperature range log T_eff = 3.87-3.88 agreement between observations and model computations of unstable modes is restricted to values for the mixing-length parameter alpha_nl less or equal to 1.50. This indicates that for these stars a smaller value for alpha_nl is required than suggested from a calibrated solar model. We stress the point that the linear stability analysis used in this work still assumes stellar models without rotation and that further developments are required for a proper description of the interaction between rotation and pulsation dynamics.Comment: 8 pages, 4 figures, 3 tables. (MNRAS, in press

Theoretical analysis of REM-based handover algorithm for heterogeneous networks

© 2013 IEEE. Handover has been a widely studied topic since the beginning of the mobile communications era, but with the advent of another generation, it is worth seeing it with fresh eyes. Data traffic is expected to keep growing as new use cases will coexist under the same umbrella, e.g., vehicle-to-vehicle or massive-machine-type communications. Heterogeneous networks will give way to multi-tiered networks, and mobility management will become challenging once again. Under the current approach, based uniquely on measurements, the number of handovers will soar, so will the signaling. We propose a handover algorithm that employs multidimensional radio-cognitive databases, namely radio environment maps, to predict the best network connection according to the user's trajectory. Radio environment maps have been extensively used in spectrum-sharing scenarios, and recently, some advances in other areas have been supported by them, such as coverage deployment or interference management. We also present a geometric model that translates the 3GPP specifications into geometry and introduce a new framework that can give useful insights into our proposed technique's performance. We validate our framework through Monte Carlo simulations, and the results show that a drastic reduction of at least 10% in the ping-pong handovers can be achieved, thus reducing the signaling needed

A Modeling Study of the Spring 2011 Extreme US Weather Activity

The spring of 2011 was characterized by record-breaking tornadic activity with substantial loss of life and destruction of property. While a waning La Nina and other atmospheric teleconnections have been implicated in the development of these extreme weather events, a quantitative assessment of their causes is still lacking. This study uses high resolution (1/4 lat/lon) GEOS-5 AGCM experiments to quantify the role of SSTs and soil moisture in the development of the extreme weather activity with a focus on April - the month of peak tornadic activity. The simulations, consisting of 22-member ensembles of three-month long simulations (initialized March 1st) reproduce the main features of the observed large-scale changes including the below-normal temperature and above-normal precipitation in the Central US, and the hot and dry conditions to the south. Various sensitivity experiments are conducted to separate the roles of the SST, soil moisture and the initial atmospheric conditions in the development and predictability of the atmospheric conditions (wind shear, moisture, etc.) favoring the severe weather activity and flooding

Strategy for the inversion of Hinode spectropolarimetric measurements in the quiet Sun

In this paper we propose an inversion strategy for the analysis of spectropolarimetric measurements taken by {\em Hinode} in the quiet Sun. The spectropolarimeter of the Solar Optical Telescope aboard {\em Hinode} records the Stokes spectra of the \ion{Fe}{i} line pair at 630.2 nm with unprecendented angular resolution, high spectral resolution, and high sensitivity. We discuss the need to consider a {\em local} stray-light contamination to account for the effects of telescope diffraction. The strategy is applied to observations of a wide quiet Sun area at disk center. Using these data we examine the influence of noise and initial guess models in the inversion results. Our analysis yields the distributions of magnetic field strengths and stray-light factors. They show that quiet Sun internetwork regions consist mainly of hG fields with stray-light contaminations of about 0.8.Comment: To appear in Publications of the Astronomical Society of Japan, 8 pages, 10 figure

Radiative Impacts of Cloud Heterogeneity and Overlap in an Atmospheric General Circulation Model

The radiative impacts of introducing horizontal heterogeneity of layer cloud condensate, and vertical overlap of condensate and cloud fraction are examined with the aid of a new radiation package operating in the GEOS-5 Atmospheric General Circulation Model. The impacts are examined in terms of diagnostic top-of-the-atmosphere shortwave (SW) and longwave (LW) cloud radiative effect (CRE) calculations for a range of assumptions and parameter specifications about the overlap. The investigation is conducted for two distinct cloud schemes, the one that comes with the standard GEOS-5 distribution, and another which has been recently used experimentally for its enhanced GEOS-5 distribution, and another which has been recently used experimentally for its enhanced cloud microphysical capabilities; both are coupled to a cloud generator allowing arbitrary cloud overlap specification. We find that cloud overlap radiative impacts are significantly stronger for the operational cloud scheme for which a change of cloud fraction overlap from maximum-random to generalized results to global changes of SW and LW CRE of approximately 4 Watts per square meter, and zonal changes of up to approximately 10 Watts per square meter. This is because of fewer occurrences compared to the other scheme of large layer cloud fractions and of multi-layer situations with large numbers of atmospheric being simultaneously cloudy, conditions that make overlap details more important. The impact on CRE of the details of condensate distribution overlap is much weaker. Once generalized overlap is adopted, both cloud schemes are only modestly sensitive to the exact values of the overlap parameters. We also find that if one of the CRE components is overestimated and the other underestimated, both cannot be driven towards observed values by adjustments to cloud condensate heterogeneity and overlap alone

Энергетическое влияние степени гидратации этанола и коэффициента избыточного воздуха (α) на использование смесей этанол-бензина в двигателях с искровым зажиганием

The objective of this study was to evaluate energetically the effect of hydration degree and mixture type (rich mixture α = 0,85 and lean mixture α = 0,15) on the use of ethanol and gasoline mixtures in spark ignition engines. The experiments were carried out in the Propulsion Laboratory of the Faculty of Engineering Sciences of Agrarian University of Havana (AUH). The JACTO model engine used has an effective power of 1,2 kW, speed 580 rpm, combustion chamber volume 34 cm3. Before combustion, the degree of ethanol hydration was determined (80 %; 85 %; 90 %; 95 %). Taking into account the influence of the percentage of purity of ethanol and air excess coefficient (α), when using combustible mixtures, analyses were carried out on the following parameters: air-fuel ratio (ra/f) and fuel-air ratio (rf/a); internal energy of combustion products (Uz); the number of moles of raw materials in the mixture for gasoline engines (M1) and the number of moles of products during combustion (M2). Based on the experimental work performed and the energy analysis of the combustion process, it was shown that the mixture of gasoline E-10-EH-80 % received more air and fuel than ratio necessary to achieve combustion, reaching 11,781 kg (air)/kg (fuel) for α = 0,85 and 15,309 kg (air)/kg (fuel) for α = 1,15. This is due to the fact that this is a mixture with increased moisture, because it contains more oxygen atoms, which impoverishes the mixture, and guarantees the best quality in the combustion process. But rich mixtures (α = 0,85) were the most energy efficient, which is associated with an increase in the octane number, that is, the antiknock ability of the fuel mixture used, which improves the quality of combustion, although it reduces the energy output during an explosion (detonation).Цель этого исследования – энергетически оценить влияние степени гидратации и типа смеси (богатой смеси α = 0,85 и бедной смеси α = 0,15) на использование смесей этанола и бензина в двигателях с искровым зажиганием. Эксперименты проводились в Лаборатории двигателей Факультета технических наук Гаванского аграрного университета (УНАХ). Используемый двигатель модели JACTO имеет эффективную мощность 1,2 кВт. Частота вращения – 580 об./мин, объём камеры сгорания – 34 см3. Перед сжиганием определяли степень гидратации этанола (80 %; 85 %; 90 %; 95 %). С учётом влияния процента чистоты этанола и коэффициента избыточного воздуха (α) при использовании горючих смесей были проведены анализы следующих параметров: соотношение воздух-топливо (св/т) и соотношение топливо-воздух (ст/в); внутренняя энергия продуктов сгорания (Uz); количество молей исходных веществ в смеси для бензиновых двигателей (M1) и количество молей продуктов при сгорании (M2).На основе выполненных экспериментальных работ и энергетического анализа процесса сгорания показано, что в смеси бензина E‑10-EH‑80 % содержалось большее соотношение воздуха и топлива, чем необходимо для достижения сгорания. Это соотношение достигает 11,781 кг (воздуха)/кг (топлива) для α = 0,85 и 15,309 кг (воздуха)/кг (топлива) для α = 1,15. Это связано с тем, что компоненты с повышенным содержанием влаги обедняют смесь и гарантируют лучшее сгорание. При этом богатые смеси (α = 0,85) оказались наиболее энергоэффективны по причине увеличения октанового числа и соответственно улучшения антидетонационных способностей используемой топливной смеси. Однако, с другой стороны, возможно снижение энергетической эффективности при появлении детонационных процессов

The effect of temperature and enzyme concentration in the transesterification process of synthetic microalgae oil

Throughout the world, the fossil fuel has supplied around the 80% of the energetic requirements, in Colombia alone 95.1% of energetic demand is made by the transportation sector solely, supplied by oil, kerosene, gasoline and diesel, this sector has an extremely small participation with biofuel of 3%, which is represented only by biodiesel. Microalgae had been proposed as biofactories with a remarkable third generation biofuels production. The culture of the microorganism comprehends interesting characteristics as countless environments where its natural growth could be replicated in fresh, salty and even sewage waters, with a higher growth rate and a higher oil production. The implementation of enzymes in the transesterification process have generated a good curiosity in the field, due to its mild reactions conditions, lesser energetic requirements, a high standard in the selection of the enzymes with the objective of avoiding the formation of soaps, creating in this way cleaner products and sub-products, in which the separation of the phases biodiesel/glycerol, give the possibility to recuperate the bio catalyzer and high output of reactions. However, the high volume of medium required to obtain lipids is one of the major drawbacks to test the viability of these enzymes. The present study aims to design an enzymatic transesterification process for the production of biodiesel form synthetic Chlorella oil. The synthetic oil was designed according to the lipid profile of C 16:0, C16:1, C18:0, C18:1, C18:2 and C18:3 from Chlorella spp CHL2 cultured on Bold Basal media under limited concentrations of NaNO3. The enzymatic transesterification efficiency was evaluated by the implementation of a 22 experimental factorial design (temperature and lipase concentration) under a 3: 1 molar ratio of alcohol:oil and a fixed reaction time of 6 hours. The obtained results show that, in order to obtain superior yields of biodiesel (>91%) the transesterification process must be carried out under temperature conditions close to 38°C and lipase concentrations of 5%

Performance of McRAS-AC in the GEOS-5 AGCM: aerosol-cloud-microphysics, precipitation, cloud radiative effects, and circulation

A revised version of the Microphysics of clouds with Relaxed Arakawa-Schubert and Aerosol-Cloud interaction scheme (McRAS-AC) including, among others, a new ice nucleation parameterization, is implemented in the GEOS-5 AGCM. Various fields from a 10-yr-long integration of the AGCM with McRAS-AC are compared with their counterparts from an integration of the baseline GEOS-5 AGCM, as well as satellite observations. Generally McRAS-AC simulations have smaller biases in cloud fields and cloud radiative effects over most of the regions of the Earth than the baseline GEOS-5 AGCM. Two systematic biases are identified in the McRAS-AC runs: one is underestimation of cloud particle numbers around 40° S–60° S, and one is overestimate of cloud water path during the Northern Hemisphere summer over the Gulf Stream and North Pacific. Sensitivity tests show that these biases potentially originate from biases in the aerosol input. The first bias is largely eliminated in a test run using 50% smaller radius of sea-salt aerosol particles, while the second bias is substantially reduced when interactive aerosol chemistry is turned on. The main weakness of McRAS-AC is the dearth of low-level marine stratus clouds, a probable outcome of lack of explicit dry-convection in the cloud scheme. Nevertheless, McRAS-AC largely simulates realistic clouds and their optical properties that can be improved further with better aerosol input. An assessment using the COSP simulator in a 1-yr integration provides additional perspectives for understanding cloud optical property differences between the baseline and McRAS-AC simulations and biases against satellite data. Overall, McRAS-AC physically couples aerosols, the microphysics and macrophysics of clouds, and their radiative effects and thereby has better potential to be a valuable tool for climate modeling research

Beating patterns of filaments in viscoelastic fluids

Many swimming microorganisms, such as bacteria and sperm, use flexible flagella to move through viscoelastic media in their natural environments. In this paper we address the effects a viscoelastic fluid has on the motion and beating patterns of elastic filaments. We treat both a passive filament which is actuated at one end, and an active filament with bending forces arising from internal motors distributed along its length. We describe how viscoelasticity modifies the hydrodynamic forces exerted on the filaments, and how these modified forces affect the beating patterns. We show how high viscosity of purely viscous or viscoelastic solutions can lead to the experimentally observed beating patterns of sperm flagella, in which motion is concentrated at the distal end of the flagella

Cosmological Inhomogeneities with Bose-Einstein Condensate Dark Matter

We consider the growth of cosmological perturbations to the energy density of dark matter during matter domination when dark matter is a scalar field that has undergone Bose-Einstein condensation. We study these inhomogeneities within the framework of both Newtonian gravity, where the calculation and results are more transparent, and General Relativity. The direction we take is to derive analytical expressions, which can be obtained in the small pressure limit. Throughout we compare our results to those of the standard cosmology, where dark matter is assumed pressureless, using our analytical expressions to showcase precise differences. We find, compared to the standard cosmology, that Bose-Einstein condensate dark matter leads to a scale factor, gravitational potential and density contrast that increase at faster rates.Comment: 17 pages, 2 figures; typos corrected, references adde