A new mutation in the pufL gene responsible for the terbutryn resistance phenotype in Rubrivivax gelatinosus

AbstractRubrivivax gelatinosus is a facultative phototrophic non-sulfur bacterium belonging to the β subclass of the purple bacteria. A terbutryn-resistant mutant of R. gelatinosus has been isolated and characterized. Increased resistance levels to terbutryn (300-fold), atrazine (6-fold) and o-phenanthroline (3-fold) were observed for the mutant compared with wild type. Sequence analysis of the mutant revealed a new mutation in the pufL gene coding for the L subunit of the reaction centre (RC) at codon 192 leading to an amino-acid substitution from Gly in the wild type to Asp in the mutant. This substitution is located in the D helix of the L subunit, suggesting an interaction between terbutryn and this part of the polypeptide in the RC of R. gelatinosus. This is the first report of a mutation leading to herbicide resistance and affecting the D helix in purple bacteria. Furthermore R. gelatinosus wild type is highly sensitive to o-phenanthroline compared with other purple bacteria (Rhodobacter capsulatus and Rhodobacter sphaeroides). Sequence comparison of the L subunit from six purple bacteria in which o-phenanthroline sensitivity was measured suggests that SerL226 might be responsible for this phenotype

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

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

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

PHotometry Assisted Spectral Extraction (PHASE) and identification of SNLS supernovae

Aim: We present new extraction and identification techniques for supernova (SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration. Method: The new spectral extraction method takes full advantage of photometric information from the Canada-France-Hawai telescope (CFHT) discovery and reference images by tracing the exact position of the supernova and the host signals on the spectrogram. When present, the host spatial profile is measured on deep multi-band reference images and is used to model the host contribution to the full (supernova + host) signal. The supernova is modelled as a Gaussian function of width equal to the seeing. A chi-square minimisation provides the flux of each component in each pixel of the 2D spectrogram. For a host-supernova separation greater than <~ 1 pixel, the two components are recovered separately and we do not use a spectral template in contrast to more standard analyses. This new procedure permits a clean extraction of the supernova separately from the host in about 70% of the 3rd year ESO/VLT spectra of the SNLS. A new supernova identification method is also proposed. It uses the SALT2 spectrophotometric template to combine the photometric and spectral data. A galaxy template is allowed for spectra for which a separate extraction of the supernova and the host was not possible. Result: These new techniques have been tested against more standard extraction and identification procedures. They permit a secure type and redshift determination in about 80% of cases. The present paper illustrates their performances on a few sample spectra.Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&

The DICE calibration project: design, characterization, and first results

We describe the design, operation, and first results of a photometric calibration project, called DICE (Direct Illumination Calibration Experiment), aiming at achieving precise instrumental calibration of optical telescopes. The heart of DICE is an illumination device composed of 24 narrow-spectrum, high-intensity, light-emitting diodes (LED) chosen to cover the ultraviolet-to-near-infrared spectral range. It implements a point-like source placed at a finite distance from the telescope entrance pupil, yielding a flat field illumination that covers the entire field of view of the imager. The purpose of this system is to perform a lightweight routine monitoring of the imager passbands with a precision better than 5 per-mil on the relative passband normalisations and about 3{\AA} on the filter cutoff positions. The light source is calibrated on a spectrophotometric bench. As our fundamental metrology standard, we use a photodiode calibrated at NIST. The radiant intensity of each beam is mapped, and spectra are measured for each LED. All measurements are conducted at temperatures ranging from 0{\deg}C to 25{\deg}C in order to study the temperature dependence of the system. The photometric and spectroscopic measurements are combined into a model that predicts the spectral intensity of the source as a function of temperature. We find that the calibration beams are stable at the $10^{-4}$ level -- after taking the slight temperature dependence of the LED emission properties into account. We show that the spectral intensity of the source can be characterised with a precision of 3{\AA} in wavelength. In flux, we reach an accuracy of about 0.2-0.5% depending on how we understand the off-diagonal terms of the error budget affecting the calibration of the NIST photodiode. With a routine 60-mn calibration program, the apparatus is able to constrain the passbands at the targeted precision levels.Comment: 25 pages, 27 figures, accepted for publication in A&

Can hyperbolic phase of Brans-Dicke field account for Dark Matter?

We show that the introduction of a hyperbolic phase for Brans-Dicke (BD) field results in a flat vacuum cosmological solution of Hubble parameter H and fractional rate of change of BD scalar field, F which asymptotically approach constant values. At late stages, hyperbolic phase of BD field behaves like dark matter

Asymmetric Gravitational Lenses in TeVeS and Application to the Bullet Cluster

Aims: We explore the lensing properties of asymmetric matter density distributions in Bekenstein's Tensor-Vector-Scalar theory (TeVeS). Methods: Using an iterative Fourier-based solver for the resulting non-linear scalar field equation, we numerically calculate the total gravitational potential and derive the corresponding TeVeS lensing maps. Results: Considering variations on rather small scales, we show that the lensing properties significantly depend on the lens's extent along the line of sight. Furthermore, all simulated TeVeS convergence maps strongly track the dominant baryonic components, non-linear effects, being capable of counteracting this trend, turn out to be very small. Setting up a toy model for the cluster merger 1E0657-558, we infer that TeVeS cannot explain observations without assuming an additional dark mass component in both cluster centers, which is in accordance with previous work.Comment: LaTex, 14 pages, 10 figures, references added, 2 figures removed, minor text changes to fit accepted version (A&A

Verification of Exhaust Quasineutrality in a Pulsed Cathodic Arc Thruster Testbed

Electric propulsion systems have become more common on-orbit in recent years due to their many benefits[1]. Most flight-rated systems generate thrust by producing an ion beam directed away from the spacecraft, which must then be neutralised to ensure proper spacecraft operation [2]. Despite decades of flight heritage, neutraliser lifetime is one of the more common life-limiting factors for Hall and ion thrusters [2, 3]. Systems currently under development that generate neutral plasma jets do not require a neutraliser, removing failure modes and reducing system complexity [4]. Neumann Space has developed to flight-readiness a pulsed cathodic arc thruster, which does not require a neutraliser. Here we present work done using the inner surface of a steel vacuum chamber as a Faraday cup to capture the exhaust of a pulsed cathodic arc thruster testbed, instrumented to measure charge flow and verify exhaust neutrality