Damped Lyman Alpha Systems at z<1.65: The Expanded SDSS HST Sample

We present results of our HST Cycle 11 Survey for low-redshift (z<1.65) DLAs in the UV spectra of quasars selected from the SDSS Early Data Release. These quasars have strong intervening MgII-FeII systems which are known signatures of high column density neutral gas. In total, UV observations of Ly-alpha absorption in 197 MgII systems with z<1.65 and rest equivalent width (REW) W2796 \ge 0.3A have now been obtained. The main results are: (1) 36(+/- 6)% of systems with W2796 \ge 0.5 A and FeII W2600 \ge 0.5 A are DLAs. This increases to 42(+/- 7)% for systems with W2796/W2600 0.1 A. (2) The mean N(HI) of MgII systems with 0.3 A \le W2796 < 0.6 A is a factor of ~36 lower than that of systems with W2796 \ge 0.6 A. (3) The DLA incidence per unit redshift is consistent with no evolution for z <~ 2 (Omega_L=0.7, Omega_M = 0.3), but exhibits significant evolution for z >~ 2. (4) Omega_{DLA} is constant for 0.5<z<5.0 to within the uncertainties. This is larger than Omega_{gas}(z=0) by a factor of ~2. (5) The slope of the N(HI) distribution does not change significantly with redshift. However, the low redshift distribution is marginally flatter due to the higher fraction of high N(HI) systems in our sample. (6) Finally, using the precision of MgII survey statistics, we find that there may be evidence of a decreasing Omega_{DLA} from z=0.5 to z=0. We reiterate the conclusion of Hopkins, Rao, & Turnshek that very high columns of neutral gas might be missed by DLA surveys because of their very small cross sections, and therefore, that Omega_{DLA} might not include the bulk of the neutral gas mass in the Universe. (Abridged)Comment: Accepted for publication in ApJ. 22 pages, 22 figure

Differentiated, promoter-specific response of [4Fe-4S] NsrR DNA-binding to reaction with nitric oxide

NsrR is an iron-sulfur cluster protein that regulates the nitric oxide (NO) stress response of many bacteria. NsrR from Streptomyces coelicolor regulates its own expression and that of only two other genes, hmpA1 and hmpA2, which encode HmpA enzymes predicted to detoxify NO. NsrR binds promoter DNA with high affinity only when coordinating a [4Fe-4S] cluster. Here we show that reaction of [4Fe-4S] NsrR with NO affects DNA-binding differently depending on the gene promoter. Binding to the hmpA2 promoter was abolished at ~2 NO per cluster, while for the hmpA1 and nsrR promoters, ~4 and ~8 NO molecules, respectively, were required to abolish DNA binding. Spectroscopic and kinetic studies of the NO reaction revealed a rapid, multi-phase, non-concerted process involving up to 8 – 10 NO molecules per cluster, leading to the formation of several iron-nitrosyl species. A distinct intermediate was observed at ~2 NO per cluster, along with two further intermediates at ~4 and ~6 NO. The NsrR nitrosylation reaction was not significantly affected by DNA-binding. These results show that NsrR regulates different promoters in response to different concentrations of NO. Spectroscopic evidence indicates that this is achieved by different NO-FeS complexes

NP-hardness of decoding quantum error-correction codes

Though the theory of quantum error correction is intimately related to the classical coding theory, in particular, one can construct quantum error correction codes (QECCs) from classical codes with the dual containing property, this does not necessarily imply that the computational complexity of decoding QECCs is the same as their classical counterparts. Instead, decoding QECCs can be very much different from decoding classical codes due to the degeneracy property. Intuitively, one expect degeneracy would simplify the decoding since two different errors might not and need not be distinguished in order to correct them. However, we show that general quantum decoding problem is NP-hard regardless of the quantum codes being degenerate or non-degenerate. This finding implies that no considerably fast decoding algorithm exists for the general quantum decoding problems, and suggests the existence of a quantum cryptosystem based on the hardness of decoding QECCs.Comment: 5 pages, no figure. Final version for publicatio

Impact of the MSBR concept technology on long-lived radio-toxicity and proliferation resistance

The MSBR (Molten Salt Breeder Reactor) was an industrial project designed at the beginning of the seventies at Oak Ridge National Laboratory and based on Thorium. Just before, the MSRE worked very well during four years with molten fuel. The MSBR system, where a maximum breeding was wanted, included a graphite moderated core with the circulation of a 71.7%LiF-16%BeF2-12%ThF4-0.3%UF4 salt and a pyro-chemical reprocessing unit. To obtain a maximum breeding ratio, Protactinium was extracted and stored allowing decay out of the neutron flux. This required the entire salt volume to be reprocessed in ten days, the gaseous fission products and Minor Actinides being extracted continuously by helium bubbling and pyro-chemical methods. The doubling time was evaluated to around 25 years. The project has since been re-evaluated especially within the frame of the EURATOM concerted Action MOST. To have an acceptable global reactivity feedback coefficient, studies have shown various possibilities based on core geometry, neutron moderation ratio and salt composition. When requiring only a breeding ratio of one, it is possible to avoid continuous reprocessing and to strongly simplify it. These various options will be discussed. The detailed inventory will be given showing clearly the interest of the Thorium Molten Salt Reactor where the production of Americium and Curium is a factor of one hundred lower that for the U-Pu RNR. The amount of Uranium 232 which is always produced in the Thorium cycle will be calculated as well as its decay rate since its decay chain eventually results in a 2.6 MeV γ –ray which may be used to detect and hence control the U233 fuel movements. As the U233 has to be produced in other reactors (PWR, RNR or other MSR), special cares have to be taken and will be discussed

Barkhausen Noise Analysis by Surrounding Coil

The Barkhausen effect (or Barkhausen noise)[1], discovered in 1919, was initially identified as the revealing of irreversible and discontinuous changes of magnetisation induced by an external magnetic field[2]. The interest of Barkhausen noise as a non destructive testing technique of magnetic materials is due to the interaction between the magnetic microstructure (magnetic domains, Bloch wall motion dynamic), microstructural state and stress state of the material [3,4,5,6]

Tackling coolant freezing in generation-IV molten salt reactors

In this study we describe an experimental system designed to simulate the conditions of transient freezing which can occur in abnormal behaviour of molten salt reactors (MSRs). Freezing of coolant is indeed one of the main technical challenges preventing the deployment of MSR. First a novel experimental technique is presented by which it is possible to accurately track the growth of the solidified layer of fluid near a cold surface in an internal flow of liquid. This scenario simulates the possible solidification of a molten salt coolant over a cold wall inside the piping system of the MSR. Specifically, we conducted measurements using water as a simulant for the molten salt, and liquid nitrogen to achieve high heat removal rate at the wall. Particle image velocimetry and planar induced fluorescence were used as diagnostic techniques to track the growth of the solid layer. In addition this study describes a thermo-hydraulic model which has been used to characterise transient freezing in internal flow and compares the said model with the experiments. The numerical simulations were shown to be able to capture qualitatively and quantitatively all the essential processes involved in internal flow transient freezing. Accurate numerical predictive tools such the one presented in this work are essential in simulating the behaviour of MSR under accident conditions

Calibration and monitoring of the GENEPI neutron source for the MUSE IV experiment

Rapport intern

Effects of Dust on Gravitational Lensing by Spiral Galaxies

Gravitational lensing of an optical QSO by a spiral galaxy is often counteracted by dust obscuration, since the line-of-sight to the QSO passes close to the center of the galactic disk. The dust in the lens is likely to be correlated with neutral hydrogen, which in turn should leave a Lyman-alpha absorption signature on the QSO spectrum. We use the estimated dust-to-gas ratio of the Milky-Way galaxy as a mean and allow a spread in its values to calculate the effects of dust on lensing by low redshift spiral galaxies. Using a no-evolution model for spirals at z<1 we find (in Lambda=0 cosmologies) that the magnification bias due to lensing is stronger than dust obscuration for QSO samples with a magnitude limit B<16. The density parameter of neutral hydrogen, Omega_HI, is overestimated in such samples and is underestimated for fainter QSOs.Comment: 18 pages, 4 figures, ApJ, in pres