Cross-section measurements in the NOMAD experiment

The NOMAD experiment collected valuable neutrino data samples, matching both the large statistics of massive calorimeters and the reconstruction quality of bubble chambers. This paper describes the recent measurements of neutrino cross-sections on carbon target. The approach followed for cross-section modeling is also explained.Comment: Proceedings of the NuInt05 conference, Okayama September 200

Anti-Lambda polarization in high energy pp collisions with polarized beam

We study the polarization of the anti-Lambda particle in polarized high energy pp collisions at large transverse momenta. The anti-Lambda polarization is found to be sensitive to the polarization of the anti-strange sea of the nucleon. We make predictions using different parameterizations of the polarized quark distribution functions. The results show that the measurement of longitudinal anti-Lambda polarization can distinguish different parameterizations, and that similar measurements in the transversely polarized case can give some insights into the transversity distribution of the anti-strange sea of nucleon.Comment: 11 pages, 4 figure

Supernovae and the Nature of the Dark Energy

The use of Type Ia supernovae as calibrated standard candles is one of the most powerful tools to study the expansion history of the universe and thereby its energy components. While the analysis of some ~50 supernovae at redshifts around z~0.5 have provided strong evidence for an energy component with negative pressure, ``dark energy'', more data is needed to enable an accurate estimate of the amount and nature of this energy. This might be accomplished by a dedicated space telescope, the SuperNova / Acceleration Probe (2000; SNAP), which aims at collecting a large number of supernovae with z<2. In this paper we assess the ability of the SNAP mission to determine various properties of the ``dark energy.'' To exemplify, we expect SNAP, if operated for three years to study Type Ia supernovae, to be able to determine the parameters in a linear equation of state w(z)=w0 + w1 z to within a statistical uncertainty of +-0.04 for w0 and +0.15,-0.17 for w1 assuming that the universe is known to be flat and an independent high precision (sigma_{Omega_m}=0.015) measurement of the mass density Omega_m, is used to constrain the fit. An additional improvement can be obtained if a large number of low-z, as well as high-z, supernovae are included in the sample.Comment: 13 pages, submitted to A&

Hédi Bouraoui. Les Jumelles de l’oncle Sam.

Une étude statistique des données météorologiques de Trappes conduit à un modèle de prévision de l'irradiation solaire globale de ce site au pas de temps de l'heure et montre la stabilité du modèle au cours de l'année. On étudie ensuite l'évolution de cette irradiation conditionnellement à celle de la nébulosité mesurée toutes les trois heures. On aboutit ainsi à une simulation simple de l'irradiation à partir d'une pré-simulation des nébulosités par un modèle semi-markovien

Comments on scalar-tensor representation of nonlocally corrected gravity

The scalar-tensor representation of nonlocally corrected gravity is considered. Some special solutions of the vacuum background equations were obtained that indicate to the nonequivalence of the initial theory and its scalar-tensor representation.Comment: 6 pages, refs adde

Propellant Variety and Affordability: A Strength of Pulsed Cathodic Arc Propulsion Systems

Most spacecraft propulsion systems require specific propellants with stringent quallity requirements. Examples include high purity xenon, krypton or argon used by many Hall and ion thrusters, where propellant contamination can corrode parts of the thruster, in particular the neutraliser cathode, leading to thruster failure[1]. The same is true in most chemical thrusters, which often require not only high propellant purity, but filtration to prevent particulate intrusion [2]. Propellant purity requirements lead to availability restrictions, which impacts propellant pricing. The standard defining RP-1, the refined kerosene derivative utilised in many launch vehicles, stipulates such stringent composition requirements that only petroleum sourced from a few wells is considered economic to refine into RP-1 due to the scale of the market and quality required [3, 4]. Similarly, the purity restrictions on aerospace grade noble gasses limits their production to only a few atmosphere separation units worldwide, which has led to supply shocks due to the Russo-Ukrainian War. These shocks have abated somewhat in the last few months, but the scarcity of these feedstocks makes them vulnerable to similar disruptions in future. Recent reductions in launch cost has seen the cost of Xe propellant become a more important factor in mission cost analysis than was previously the case. The aggregate costs of propellant for a small satellite constellation has, recently, become a larger fraction of total mission costs, and thus has driven innovation in gas-fed electric propulsion systems[5, 6]. Alternative propulsion technologies can utilise fundamentally different propellants to the noble gasses and reactive chemicals of traditional propulsion systems. One such example of this are Pulsed Cathodic Arc Thrusters (PCAT). This technology requires solid conductive propellants, which naturally suggests most metals and their alloys for consideration, as well as materials such as graphitic carbon [7]. Some of the better performing metals in PCAT are used industrially for producing various useful alloys, as well as being used as sputtering targets and source cathodes in related plasma deposition sources [8]. Additionally, common aerospace alloys can be used as propellant, enabling a use-case for on-orbit recycling to mitigate the growing orbital debris population [9]. In this work we describe the operating principles of this technology before describing work done to fly operational systems. Current projects to further develop the technology in collaboration with partners are also discussed

Using Space Domain Awareness Tools and Electric Propulsion to Evade Space Debris

As more spacecraft use electric propulsion for altitude change, constellation management, and end-of-life disposal, attention is being given to other use-cases such as debris avoidance. While the growing population of all-electric GEO satellites and all-electric LEO megaconstellation satellites have demonstrated successful collision avoidance to date, they either operate in orbits with a smaller debris population (e.g., the GEO satellites) or have power budgets scaled to support high communications throughput which can be applied to propulsion systems as needed[1]. There has been doubt expressed that small spacecraft of more limited power supplies can host electric propulsion systems with sufficient thrust to enable the rapid orbit changes required for debris avoidance in LEO. In this work we use data from public sources on orbit conjunctions and conservative assumptions of propulsion system capability to illustrate the ability of properly scaled propulsion systems to evade debris objects on short notice

Photometry of supernovae in an image series : methods and application to the Supernova Legacy Survey (SNLS)

We present a technique to measure lightcurves of time-variable point sources on a spatially structured background from imaging data. The technique was developed to measure light curves of SNLS supernovae in order to infer their distances. This photometry technique performs simultaneous PSF photometry at the same sky position on an image series. We describe two implementations of the method: one that resamples images before measuring fluxes, and one which does not. In both instances, we sketch the key algorithms involved and present the validation using semi-artificial sources introduced in real images in order to assess the accuracy of the supernova flux measurements relative to that of surrounding stars. We describe the methods required to anchor these PSF fluxes to calibrated aperture catalogs, in order to derive SN magnitudes. We find a marginally significant bias of 2 mmag of the after-resampling method, and no bias at the mmag accuracy for the non-resampling method. Given surrounding star magnitudes, we determine the systematic uncertainty of SN magnitudes to be less than 1.5 mmag, which represents about one third of the current photometric calibration uncertainty affecting SN measurements. The SN photometry delivers several by-products: bright star PSF flux mea- surements which have a repeatability of about 0.6%, as for aperture measurements; we measure relative astrometric positions with a noise floor of 2.4 mas for a single-image bright star measurement; we show that in all bands of the MegaCam instrument, stars exhibit a profile linearly broadening with flux by about 0.5% over the whole brightness range.Comment: Accepted for publication in A&A. 20 page

An Efficient Approach to Obtaining Large Numbers of Distant Supernova Host Galaxy Redshifts

We use the wide-field capabilities of the 2dF fibre positioner and the AAOmega spectrograph on the Anglo-Australian Telescope (AAT) to obtain redshifts of galaxies that hosted supernovae during the first three years of the Supernova Legacy Survey (SNLS). With exposure times ranging from 10 to 60 ksec per galaxy, we were able to obtain redshifts for 400 host galaxies in two SNLS fields, thereby substantially increasing the total number of SNLS supernovae with host galaxy redshifts. The median redshift of the galaxies in our sample that hosted photometrically classified Type Ia supernovae (SNe Ia) is 0.77, which is 25% higher than the median redshift of spectroscopically confirmed SNe Ia in the three-year sample of the SNLS. Our results demonstrate that one can use wide-field fibre-fed multi-object spectrographs on 4m telescopes to efficiently obtain redshifts for large numbers of supernova host galaxies over the large areas of sky that will be covered by future high-redshift supernova surveys, such as the Dark Energy Survey.Comment: 22 pages, 4 figures, accepted for publication in PAS