On Bounded Weight Codes

The maximum size of a binary code is studied as a function of its length N, minimum distance D, and minimum codeword weight W. This function B(N,D,W) is first characterized in terms of its exponential growth rate in the limit as N tends to infinity for fixed d=D/N and w=W/N. The exponential growth rate of B(N,D,W) is shown to be equal to the exponential growth rate of A(N,D) for w <= 1/2, and equal to the exponential growth rate of A(N,D,W) for 1/2< w <= 1. Second, analytic and numerical upper bounds on B(N,D,W) are derived using the semidefinite programming (SDP) method. These bounds yield a non-asymptotic improvement of the second Johnson bound and are tight for certain values of the parameters

Comparative limnology of high-elevation lakes and reservoirs and their downstream effects

Reservoirs are abundant worldwide, and have profound effects on downstream flow, water chemistry, and downstream biotic communities. However, studies focused on reservoir effects rarely contrast them with lakes, which provide a comparison of natural climatic conditions without the influence of reservoir management. I compared five high-elevation lakes and five reservoirs in the Sierra Nevada, over three years which encompassed a wide range of snowpacks and flow regimes. I sampled lake, reservoir, and outlet stream water chemistry year-round across the three years to quantify seasonal effects of reservoir management. In addition to outlet water chemistry, I collected benthic macroinvertebrates from lake and reservoir outlets during the ice-free season in conjunction with discharge to determine the effects of reservoir management on downstream invertebrate communities. In 2017, I measured aquatic carbon dioxide and diffusive flux from lakes and reservoirs, beginning under ice and until the end of the ice free season, to determine potential sources of high-elevation aquatic CO2 supersaturation and characterize ice-free season CO2 temporal dynamics. Lake and reservoir nutrient concentrations did not differ in any season or year across the study period. Linear mixed models developed surface and bottom water nutrient concentrations showed that the primary controls were related to basin characteristics and snowpack, but reservoir management in the form of seasonal drawdown was a significant predictor of surface nitrate and both hypolimnetic ammonium and SRP, and indicated that reservoir water deep-release export diminished hypolimnetic nutrient accumulation. Reservoir mean annual discharge was elevated relative to lakes, which in summer and fall of 2016 and 2017 caused significantly higher export of nutrients from reservoirs. However, elevated ammonium export did not cause divergence of lake and reservoir invertebrate assemblages in those seasons, nor did they differ in any season. Other flow metrics, such as peak annual flow and the recession period, were similar between lake and reservoir outlets across years despite reservoir management. Instead, non-metric multidimensional scaling showed that invertebrate communities were related to elevated flow, but not related to low flow metrics such as baseflow and minimum flows, which were greater below reservoirs. Reservoir management altered flow regimes and nutrient flux, but interannual climactic variability was more important for determining invertebrate community structure. Carbon dioxide was supersaturated in lake and reservoir surface waters for most of the ice-free season of 2017 despite low rates of ecosystem metabolism. Diffusive flux highest for the first 40 days after ice-off, and did not differ significantly between lakes and reservoirs, but was low relative to other water bodies. Linear mixed modeling indicated that the summer CO2 concentrations were primarily related to the duration of ice cover, allowing CO2 to accumulate under ice, which indicates that annual snowpack is a major determinant of summer CO2 evasion

Propagation and organization in lattice random media

We show that a signal can propagate in a particular direction through a model random medium regardless of the precise state of the medium. As a prototype, we consider a point particle moving on a one-dimensional lattice whose sites are occupied by scatterers with the following properties: (i) the state of each site is defined by its spin (up or down); (ii) the particle arriving at a site is scattered forward (backward) if the spin is up (down); (iii) the state of the site is modified by the passage of the particle, i.e. the spin of the site where a scattering has taken place, flips ($\uparrow \Leftrightarrow \downarrow$). We consider one dimensional and triangular lattices, for which we give a microscopic description of the dynamics, prove the propagation of a particle through the scatterers, and compute analytically its statistical properties. In particular we prove that, in one dimension, the average propagation velocity is $= 1/(3-2q)$, with $q$ the probability that a site has a spin $\uparrow$, and, in the triangular lattice, the average propagation velocity is independent of the scatterers distribution: $= 1/8$. In both cases, the origin of the propagation is a blocking mechanism, restricting the motion of the particle in the direction opposite to the ultimate propagation direction, and there is a specific re-organization of the spins after the passage of the particle. A detailed mathematical analysis of this phenomenon is, to the best of our knowledge, presented here for the first time.Comment: 30 pages, 15 separate figures (in PostScript); submitted to J. Stat. Phy

The Photooxidation of Hexabromorhenate(IV) in Ethyl Bromide

Irradiation at 254 or 313 nm of solutions of (Bu4N)2[ReBr6] in ethyl bromide exposed to air causes complete conversion of the hexabromorhenate(IV) to perrhenate ion. The rate of the reaction is linearly dependent on the incident light intensity and on a combination of the fraction of light absorbed by the rhenium complex and the fraction absorbed by the ethyl bromide. The experimental results are consistent with a mechanism in which the peroxy radical CH3CH(Br)OO, produced in both the solvent-initiated and metal-initiated pathways, oxidizes [ReBr6]2− by electron transfer

Traitement de données bioinformatiques massives (Big Data)

The volumes of bioinformatics data available on the Web are constantly increasing.Access and joint exploitation of these highly distributed data (i.e, available in distributed Webdata sources) and highly heterogeneous (in text or tabulated les including images, in dierentformats, described with dierent levels of detail and dierent levels of quality ...) is essential forthe biological knowledge to progress. The purpose of this short report is to present in a simpleway the problems of the joint use of bioinformatics data.Les volumes des donnees bioinformatiques disponibles sur le Web sont en constanteaugmentation. L'acces et l'exploitation conjointe de ces donnees tres reparties (i.e., disponiblesdans des sources de donnees distribuees sur le Web) et fortement heterogenes (sous forme textuelleou sous forme de chiers tabules, incluant ou non des images, decrites avec dierents niveaux dedetails et de qualite. . . ), est essentielle pour que les connaissances en biologie puissent progresser.L'objectif de ce rapport est de presenter de facon simple les problemes poses par l'utilisationconjointe des donnees bioinformatiques

Galaxy Formation In The Reionization Epoch As Hinted By Wide Field Camera 3 Observations Of The Hubble Ultra Deep Field

We present a large sample of candidate galaxies at z~7--10, selected in the HUDF using the new observations made by the HST/WFC3. Our sample is composed of 20 z-dropouts, 15 Y-dropouts, and 20 J-dropouts. The surface densities of the z-dropouts are close to what predicted by earlier studies, however, those of the Y- and J-dropouts are quite unexpected. While no Y- or J-dropouts have been found at AB < 28.0 mag, their surface densities seem to increase sharply at fainter levels. While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed, the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z~7 to 10. Motivated by such steep increases, we tentatively propose a set of Schechter function parameters to describe the LFs at z~8 and 10. As compared to their counterpart at z~7, here L* decreases by ~ 6.5x and Phi* increases by 17--90x. Although such parameters are not yet demanded by the existing observations, they are allowed and seem to agree with the data better than other alternatives. If these LFs are still valid beyond our current detection limit, this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z~10, which, while seemingly exotic, would naturally fit in the picture of the cosmic hydrogen reionization. These early galaxies could easily account for the ionizing photon budget required by the reionization, and they would imply that the global star formation rate density might start from a very high value at z~10, rapidly reach the minimum at z~7, and start to rise again towards z~6. In this scenario, the majority of the stellar mass that the universe assembled through the reionization epoch seems still undetected by current observations at z~6. [Abridged]Comment: accepted for publication in Research in Astronomy and Astrophysic

The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey

We discuss the very red objects found in the first field of the Caltech Faint Galaxy Redshift Survey, for which the observations and analysis are now complete. In this field, which is 15 arcmin$^2$ and at J005325+1234 there are 195 objects with $K_s < 20$ mag, of which 84% have redshifts. The sample includes 24 spectroscopically confirmed Galactic stars, 136 galaxies, three AGNs, and 32 objects without redshifts. About 10% of the sample has $(R-K) \ge 5$ mag. Four of these objects have redshifts, with $0.78 \le z \le 1.23$. Three of these are based on absorption features in the mid-UV, while the lowest redshift object shows the standard features near 4000\AA. Many of the objects still without redshifts have been observed spectroscopically, and no emission lines were seen in their spectra. We believe they are galaxies with $z \sim 1 - 1.5$ that are red due to their age and stellar content and not to some large amount of internal reddening from dust. Among the many other results from this survey of interest here is a determination of the median extinction in the mid-UV for objects with strong emission line spectra at $z \sim 1 - 1.3$. The result is extinction by a factor of $\sim$2 at 2400\AA.Comment: 6 pages, Latex, with 2 figures. To be published in the proceedings of the conference "Infrared Surveys: A Prelude to SIRTF