Rho-rho production in two-photon collisions

The measurement of exclusive ρρ production in two-photon interactions at LEP, γγ ∗ → ρρ, was studied at two-photon center-of-mass energies of 1.1 GeV ≤ Wγγ ≤ 3 GeV and photon virtualities of Q 2 < 0.02 GeV2 and 0.2 ≤ Q 2 ≤ 30 GeV2 . These data allow on the one hand a comparison to QCD and the generalised vector dominance model (GVDM). On the other hand, the large kinematical range permits to check models with exotic mesons

Von der Evaluation von Lernsoftware zur Gestaltung von Unterricht

In der Forschung zur Wirkung der neuen Medien kann oft beobachtet werden, dass mediale und (unterrichts-)methodische Einflüsse nicht auseinander gehalten werden. Daher wurde bislang wenig systematisch untersucht, unter welchen instruktionalen Bedingungen der Einsatz einer bestimmten Software überhaupt effektiv Lernen unterstützt. Wir schlagen eine Evaluationsmethode vor, die vom Konstrukt der Lernumgebung ausgeht und plädieren dafür, Software unter der möglichst umfassenden Kontrolle der Parameter der jeweiligen Lernumgebung zu evaluieren. Auf diese Weise können Erkenntnisse darüber gewonnen werden, unter welchen Bedingungen das Potenzial einer bestimmten Software zur Geltung kommt und wie Software didaktisch begründet im Unterricht eingesetzt werden sollte

Experience of shocks, household wealth and expectation formation: Evidence from smallholder farmers in Kenya

When faced with uncertain events, decision‐makers form expectations about the events’ likelihood of occurrence. However, the drivers and moderators of such expectations are still poorly understood, especially for farm decision‐makers in developing countries whose incomes are very risky by nature. This article analyses the dynamic shock expectation formation process of farmers in Kenya with regard to a range of shock events using a unique panel dataset. The results suggest that farmers are more likely to update their expectation regarding a specific adverse shock when they have recently been affected by that shock or by more shocks in general. In case of price shocks, farmers are also more likely to update expectations when a larger proportion of fellow village members was affected. However, household wealth moderates the relationship between shock expectation and experience, such that wealthier households are less likely to update their expectations following a shock. A better understanding of the drivers of expectation formation can help in the design of better risk management instruments that increase farmers’ resilience.Peer Reviewe

Quel est l'impact de l'indice de masse corporelle pré-gestationnel insuffisant et d'une prise de poids gestationnelle inférieure à la norme, notamment chez les femmes souffrant d'anorexie, sur le poids de naissance de l'enfant et la prématurité: travail de Bachelor

Introduction : Des préoccupations autours de poids sont présentes lors de grossesse chez beaucoup de femmes, notamment chez celle qui souffrent de troubles alimentaires. L’obésité et la prise de poids gestationnelle excessive sont aujourd’hui des problèmes de santé dont les conséquences sont bien connues tandis que les effets des phénomènes inverses restent ambigus. Objectif : le but de cette revue de littérature était de mettre en évidence les effets du souspoids pré-gestationel et de la faible prise de poids gestationnelle [PDPG], notamment chez des femmes souffrant d’anorexie, sur la prématurité et le poids de naissance de l’enfant. Méthode : Une revue systématique de la littérature scientifique a été élaborée à partir de huit études sélectionnées, en fonction de critères précis, dans les bases de données de la littérature scientifique actuelle (CINHAL, Cochrane Database of Systematic Reviews, MEDLINE, MIDIRS). Résultats : Selon une étude, un indice de masse corporelle [IMC] pré-gestationnel inférieur à la norme induirait une augmentation significative du risque d’accoucher prématurément comparé à un IMC normal. Selon les études retenues qui traitaient de ce sujet, l’anorexie n’avait pas d’impact sur la prématurité et n’augmenterait pas les risques d’avoir un nourrisson petit pour l’âge gestationnel [SGA]. Trois études relevaient une augmentation du risque d’avoir un SGA chez les femmes en sous-poids, comparées aux femmes de poids normal. Une des études démontrait qu’une PDPG insuffisante provoquait une augmentation du risque d’avoir un SGA, comparée à une PDPG adéquate. Deux des études démontraient qu’une PDPG insuffisante aggravait le taux de SGA chez les femmes en sous-poids. En effet, le sous-poids et la faible PDPG diminueraient le poids de naissance de l’enfant. Conclusion : Le résultat principal qui ressort de cette revue de littérature est qu’un IMC prégestationnel inférieur à la norme et une PDPG inférieure aux recommandations, influent, de façons indépendantes ou couplées, sur le poids de naissance du nouveau-né. Ainsi les femmes souffrant de sous-poids et les femmes ayant eu une faible PDPG, ont un taux plus élevé de SGA et d’enfant ayant un petit poids de naissance, comparées aux femmes de poids normal et ayant une PDPG dans les normes. Une attention toute particulière doit donc être mise en place quant au suivi des femmes en sous-poids et des femmes ayant une PDPG inférieure aux recommandations de l’IOM (2009), afin de mieux prendre en soins le nouveau-né et la femme

Probing the Canis Major stellar over-density as due to the Galactic warp

Proper-motion, star counts and photometric catalog simulations are used to explain the detected stellar over-density in the region of Canis Major (CMa), claimed to be the core of a disrupted dwarf galaxy (Martin et al. 2004, Bellazzini et al. 2003), as due to the Galactic warp and flare in the external disk. We compare the kinematics of CMa M-giant selected sample with surrounding Galactic disk stars in the UCAC2 catalog and find no peculiar proper motion signature: CMa stars mimic thick disk kinematics. Moreover, when taking into account the Galactic warp and flare of the disk, 2MASS star count profiles reproduce the CMa stellar over-density. This star count analysis is confirmed by direct comparison with synthetic color-magnitude diagrams simulated with the Besancon models (Robin et al. 2003) that include the warp and flare of the disk. The presented evidence casts doubt on the identification of the CMa over-density as the core of a disrupted Milky Way satellite. This however does not make clear the origin of over-densities responsible for the ring structure in the anticenter direction of the Galactic halo (Newberg et al. 2002; Yanny et al. 2003; Zaggia et al. 2004, in preparation).Comment: Accepted for publication in A&A Letters, 4 page

DC Electric Fields, Associated Plasma Drifts, and Irregularities Observed on the C/NOFS Satellite

Results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. Compared to data obtained during more active solar conditions, the ambient DC electric fields and their associated E x B drifts are variable and somewhat weak, typically < 1 mV/m. Although average drift directions show similarities to those previously reported, eastward/outward during day and westward/downward at night, this pattern varies significantly with longitude and is not always present. Daytime vertical drifts near the magnetic equator are largest after sunrise, with smaller average velocities after noon. Little or no pre-reversal enhancement in the vertical drift near sunset is observed, attributable to the solar minimum conditions creating a much reduced neutral dynamo at the satellite altitude. The nighttime ionosphere is characterized by larger amplitude, structured electric fields, even where the plasma density appears nearly quiescent. Data from successive orbits reveal that the vertical drifts and plasma density are both clearly organized with longitude. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. The VEFI data represents a new set of measurements that are germane to numerous fundamental aspects of the electrodynamics and irregularities inherent to the Earth s low latitude ionosphere

Deprojection of light distributions of nearby systems: perspective effect and non-uniqueness

Deriving the 3-dimensional volume density distribution from a 2-dimensional light distribution of a system yields generally non-unique results. The case for nearby dust-free systems is studied, taking into account the extra constraints from the perspective effect. It is shown analytically that a new form of non-uniqueness exists. We can design a Phantom Spheroid (PS) for a nearby system which preserves the intrinsic mirror symmetry and projected surface brightness of the system while changing the shape and the major-axis orientation of the system. A family of analytical models are given as functions of the distance ($D_0$) to the object and the amount ($\gamma$) of the superimposed PS density. The PS density, different from the well-known konuses of extragalactic systems, makes the luminosity of the system vary slightly with the distance $D_0$. The physical ranges for $\gamma$ and the major axis angles are constrained analytically by requiring a positive volume density everywhere. These models suggest that observations other than surface brightness maps are required to lift the degeneracy in the tilt angles and axis ratio of the central bar of the Milky Way.Comment: 21 single-spaced pages including 12 figures. Submitted to MNRA

DC and Structured Electric Fields Observed on the C/NOFS Satellite and Their Association with Longitude, Plasma Density, and Solar Activity

Observations of DC electric fields and associated E x B plasma drifts gathered by the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite are presented. We show statistical averages of the vector fields and resulting E x B plasma flows for the first three years of operations as a function of season, longitude, local time, and Fl 0.7 conditions. Magnetic field data from the VEFI science magnetometer are used to compute the plasma flows. Although typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night, the data from DC electric field detector often reveal variations from this pattern that depend on longitude, solar activity, and plasma density. Clear "wave-4" tidal effects in both electric field components have been detected and will be presented. Zonal plasma drifts show a marked variation with solar activity and may be used as a proxy for neutral winds at night. Evidence for pre-reversal enhancements in the meridional drifts that depend on solar activity is present for some longitudes, and are corroborated by clear evidence in the plasma density data that the spacecraft journeyed below the F-peak during evenings when the rise in the ionosphere is most pronounced. In addition to DC electric fields, the data reveal considerable electric field structures at large scales (approx 100's of km) that are usually confined to the nightside. Although such electric field structures are typically associated with plasma density depletions and structures, what is surprising is the number of cases in which large amplitude, structured DC electric fields are observed without a significant plasma density counterpart structure, including their appearance at times when the ambient plasma density appears relatively quiescent. We investigate the mapping of structured electric fields along magnetic field lines from distant locations and consider tropospheric thunderstorm sources to explain some of the observations. The dependence of the structuring on season and solar activity will be reported and discussed

DC Electric Fields and Associated Plasma Drifts Observed with the C/NOFS Satellite

Initial DC electric field observations and associated plasma drifts are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite. We present statistical averages of the vector fields for the first year of operations that include both the zonal and radial components of the resulting E x B plasma flows at low latitudes. Magnetic field data from the VEFI science magnetometer are used to compute the plasma flows. The DC electric field detector reveals zonal and radial electric fields that undergo strong diurnal variations, typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night. There is considerable variation in the large scale DC electric field data, in both the daytime and nighttime cases, with enhanced structures typically observed at night. In general, the measured zonal DC electric field amplitudes include excursions that extend within the 0.4 - 2 m V/m range, corresponding to E x B drifts of the order of 30-150 m/s. The average vertical or radial electric fields may exceed the zonal fields in amplitude by a factor of 1.5 to 2. Although the data compare well, in a general sense, with previous satellite observations and statistical patterns of vertical ion drifts, the E x B drifts we report from C/NOFS rarely show a pronounced pre-reversal enhancement after sunset. We attribute this to a combination of extreme solar minimum conditions and the fact that the C/NOFS orbit of 401 by 867 km carries the probes essentially above the lower altitude regions where the wind-driven dynamo might be expected to create enhanced upwards drifts in the early evening. Evidence for wavenumber 4 tidal effects and other longitudinal signatures have been detected and will be presented. We also discuss off-equatorial electric fields and their relation to the ambient plasma density