The High Energy Emission of the Crab Nebula from 20 keV to 6 MeV with INTEGRAL

The SPI spectrometer aboard the INTEGRAL mission observes regularly the Crab Nebula since 2003. We report on observations distributed over 5.5 years and investigate the variability of the intensity and spectral shape of this remarkable source in the hard X-rays domain up to a few MeV. While single power law models give a good description in the X-ray domain (mean photon index ~ 2.05) and MeV domain (photon index ~ 2.23), crucial information are contained in the evolution of the slope with energy between these two values. This study has been carried out trough individual observations and long duration (~ 400 ks) averaged spectra. The stability of the emission is remarkable and excludes a single power law model. The slopes measured below and above 100 keV agree perfectly with the last values reported in the X-ray and MeV regions respectively, but without indication of a localized break point. This suggests a gradual softening in the emission around 100 keV and thus a continuous evolution rather than an actual change in the mechanism parameters. In the MeV region, no significant deviation from the proposed power law model is visible up to 5-6 MeV. Finally, we take advantage of the spectroscopic capability of the instrument to seek for previously reported spectral features in the covered energy range with negative results for any significant cyclotron or annihilation emission on 400 ks timescales. Beyond the scientific results, the performance and reliability of the SPI instrument is explicitly demonstrated, with some details about the most appropriate analysis method.Comment: accepted for publication in ApJ; 4 figures, 2 table

An experimental investigation of the aerodynamics and cooling of a horizontally-opposed air-cooled aircraft engine installation

A flight-test based research program was performed to investigate the aerodynamics and cooling of a horizontally-opposed engine installation. Specific areas investigated were the internal aerodynamics and cooling mechanics of the installation, inlet aerodynamics, and exit aerodynamics. The applicable theory and current state of the art are discussed for each area. Flight-test and ground-test techniques for the development of the cooling installation and the solution of cooling problems are presented. The results show that much of the internal aerodynamics and cooling technology developed for radial engines are applicable to horizontally opposed engines. Correlation is established between engine manufacturer's cooling design data and flight measurements of the particular installation. Also, a flight-test method for the development of cooling requirements in terms of easily measurable parameters is presented. The impact of inlet and exit design on cooling and cooling drag is shown to be of major significance

A NLO analysis on fragility of dihadron tomography in high energy AAAA collisions

The dihadron spectra in high energy $AA$ collisions are studied within the NLO pQCD parton model with jet quenching taken into account. The high $p_T$ dihadron spectra are found to be contributed not only by jet pairs close and tangential to the surface of the dense matter but also by punching-through jets survived at the center while the single hadron high $p_T$ spectra are only dominated by surface emission. Consequently, the suppression factor of such high-$p_T$ hadron pairs is found to be more sensitive to the initial gluon density than the single hadron suppression factor.Comment: 4 pages, 4 figures, proceedings for the 19th international Conference on ultra-relativistic nucleus-nucleus collisions (QM2006), Shanghai, China, November 14-20, 200

Assessment of semicircular canal function. Part 1 - Measurements of subjective effects produced by triangular waveforms of angular velocity

Nystagmus and sensation of rotation from semicircular canal stimulation by triangular waveforms of angular velocit

Role of coronal mass ejections in the heliospheric Hale cycle

[1] The 11-year solar cycle variation in the heliospheric magnetic field strength can be explained by the temporary buildup of closed flux released by coronal mass ejections (CMEs). If this explanation is correct, and the total open magnetic flux is conserved, then the interplanetary-CME closed flux must eventually open via reconnection with open flux close to the Sun. In this case each CME will move the reconnected open flux by at least the CME footpoint separation distance. Since the polarity of CME footpoints tends to follow a pattern similar to the Hale cycle of sunspot polarity, repeated CME eruption and subsequent reconnection will naturally result in latitudinal transport of open solar flux. We demonstrate how this process can reverse the coronal and heliospheric fields, and we calculate that the amount of flux involved is sufficient to accomplish the reversal within the 11 years of the solar cycle

Lateral Variation in Crustal Structure of the Northern Tibetan Plateau Inferred from Teleseismic Receiver Functions

We investigate lateral variations in crustal structure across the northern boundary of the Tibetan Plateau using the receiver functions at three broadband stations deployed during the 1991-1992 Tibet PASSCAL experiment. The first 5 sec of the receiver functions vary systematically with backazimuth: the radial receiver functions are symmetric across the N-S axis while the tangential receiver functions are antisymmetric across this axis. This symmetry can be modeled by E-W striking dipping interfaces in the upper-middle crust. The strike direction is consistent with the E-W trend of surface geology. Modeling a P-to-S converted phase in the receiver functions at each station suggests that there is a mid-crustal low-velocity layer with its upper boundary dipping 20° to 30° to the south. In addition, a shallow northward-dipping interface is responsible for the “double-peaked” direct P arrivals in the radial receiver functions and large tangential motions at one of the stations. The low-velocity layer, together with other geological and seismological observations, suggests that there is a hot, possibly partial melt zone in the middle crust of northern Tibet. Alternately, dipping velocity interfaces might be associated with some buried thrust faults in the upper crust that accommodated crust shortening during the plateau formation

Determinants of propensity of tertiary agricultural students in Ghana to enter agribusiness as a self-employment venture

The study aimed to identify factors that affect the decision of tertiary agricultural students in Ghana to enter agribusiness as a self-employment venture after graduation. The results showed that tertiary agricultural students in Ghana were predominantly males with little or no farming background. They had a rather moderate propensity to enter self-employed agribusiness. The propensity was based on the perception that agribusiness was beneficial, sustainable, and had a bright future. A significant and positive relationship was found between the propensity to enter self-employed agribusiness and availability of inputs, training received by students and supportive policies. However, a significant and negative relationship was found between students' propensity to enter self-employed agribusiness and the desire for other competing enterprises as well as risks and constraints in agribusiness. The most important determinants of the decision of tertiary level agricultural students to enter into agribusiness were found to be attraction to other businesses such as NGOs, non-agricultural manufacturing industries and banks; training received; perceived constraints; and needs for self- employment in agribusiness. The results indicate that the propensity of agricultural graduates to enter self-employed agribusiness may be increased by (1) making agribusiness attractive by increasing its competitiveness with respect to other enterprises, ( 2) modifying the curricula to make agricultural training at the tertiary level more practical, (3) making it easier to acquire production inputs for agribusiness, and (4) improving the policy environment with supportive policies to minimize risk and constraints in agribusiness.. La recherche était entreprise pour identifier les facteurs qui influencent la decision d'étudiants agricoles du niveau supérieur au Ghana de s'établir dans les agro-industries comme une entreprise de travailleur indépendant après l'obtention du diplôme. Les résultats montraient que les étudiants agricoles de l'enseignement supérieur au Ghana étaient principalement mâles avec peu ou sans expérience d'agriculture. Ils avaient plutôt une propension modérée de s'établir dans l'agro-industrie de travailleur indépendant. Cette propension est fondée sur l'idée que l'agro-industrie est bénéfique, durable et avait un avenir brillant. Un rapport considérable et positif était découvert entre la propension de s'établir dans l'agro-industrie de travailleur indépendant et la disponibilité d'intrants, la formation reçue par les étudiants et les politiques d'appui. Un rapport considérable et négatif était toutefois découvert entre la propension d'étudiants de s'établir dans les agro-industries indépendantes et le désir pour d'autres entreprises en concurrence ainsi que les risques et les contraintes d'agro-industries. Les déterminants les plus importants de la decision d'étudiants agricoles du niveau supérieur de s'établir dans les agro-industries étaient découverts d'être l'attrait aux autres entreprises telles que les ONGs, les industries manufacturières non-agricoles et les banques; la formation reçue; les contraintes remarquées; et les besoins requis pour l'indépendant en agro-industrie. Les résultats indiquent que la propension de licenciés agricoles de s'établir dans l'agro-industrie comme travailleurs indépendants pourrait être augmenté par (1) la transformation d'agro-industrie en la rendant attirante par l'augmentation de sa compétitivité relativement aux autres entreprises, (2) la modification du programme scolaire pour rendre la formation agricole au niveau supérieur plus pratique, (3) la facilitation de l'acquisition de resources de production pour l'agro-industrie, et (4) l'amélioration de l'environnement politique avec les politiques d'appui pour réduire au minimum le risque et les contraintes d'agro-industrie. Ghana Journal of Agricultural Science Vol. 39 (1) 2006: pp. 41-5

Uncertainties in determining parton distributions at large x

We critically examine uncertainties in parton distribution functions (PDFs) at large x arising from nuclear effects in deuterium F2 structure function data. Within a global PDF analysis, we assess the impact on the PDFs from uncertainties in the deuteron wave function at short distances and nucleon off-shell effects, the use of relativistic kinematics, as well as the use of less a restrictive parametrization of the d/u ratio. We find that in particular the d-quark and gluon PDFs vary significantly with the choice of nuclear model. We highlight the impact of these uncertainties on the determination of the neutron structure function, and on W boson production and parton luminosity at the Tevatron and the LHC. Finally, we discuss prospects for new measurements sensitive to the d-quark and gluon distributions but insensitive to nuclear corrections.Comment: 37 pages, 13 figures. Final published versio