Build, Resist, Be Resilient, and Rebuild: Advising as a Womxn of Color

Racial battle fatigue, cultural taxation, and the challenge of practicing self-care in the midst of tumultuous racial campus climate are all powerful forces that affect how Advisors of Color show up in their relationships with college students. Through scholarly personal narrative, the author conceptualizes the role of building, resistance, resilience, and rebuilding through their journey as a Womxn of Color advising student groups at a predominantly white institution

Experimental evidence for fast cluster formation of chain oxygen vacancies in YBa2Cu3O7-d being at the origin of the fishtail anomaly

We report on three different and complementary measurements, namely magnetisation measurements, positron annihilation spectroscopy and NMR measurements, which give evidence that the formation of oxygen vacancy clusters is on the origin of the fishtail anomaly in YBa2Cu3O7-d. While in the case of YBa2Cu3O7.0 the anomaly is intrinsically absent, it can be suppressed in the optimally doped state where vacancies are present. We therefore conclude that the single vacancies or point defects can not be responsible for this anomaly but that clusters of oxygen vacancies are on its origin.Comment: 10 pages, 4 figures, submitted to PR

Observation of out-of-phase bilayer plasmons in YBa_2Cu_3O_7-delta

The temperature dependence of the c-axis optical conductivity \sigma(\omega) of optimally and overdoped YBa_2Cu_3O_x (x=6.93 and 7) is reported in the far- (FIR) and mid-infrared (MIR) range. Below T_c we observe a transfer of spectral weight from the FIR not only to the condensate at \omega = 0, but also to a new peak in the MIR. This peak is naturally explained as a transverse out-of-phase bilayer plasmon by a model for \sigma(\omega) which takes the layered crystal structure into account. With decreasing doping the plasmon shifts to lower frequencies and can be identified with the surprising and so far not understood FIR feature reported in underdoped bilayer cuprates.Comment: 7 pages, 3 eps figures, Revtex, epsfi

An exact plane-stress solution for a class of problems in orthotropic elasticity

An exact solution for the stress field within a rectangular slab of orthotropic material is found using a two dimensional Fourier series formulation. The material is required to be in plane stress, with general stress boundary conditions, and the principle axes of the material must be parallel to the sides of the rectangle. Two load cases similar to those encountered in materials testing are investigated using the solution. The solution method has potential uses in stress analysis of composite structures

Star-forming Galaxies in the 'Redshift Desert'

We describe results of optical and near-IR observations of a large spectroscopic sample of star-forming galaxies photometrically-selected to lie in the redshift range 1.4 < z < 2.5, often called the ``redshift desert'' because of historical difficulty in obtaining spectroscopic redshifts in this range. We show that the former ``redshift desert'' is now very much open to observation.Comment: 10 pages, 6 figures, to appear in the Proceedings of the ESO/USM/MPE Workshop on "Multiwavelength Mapping of Galaxy Formation and Evolution", eds. R. Bender and A. Renzin

Identification de composés génotoxiques dans les eaux de boisson

Depuis la mise en évidence de trihalométhanes dans les eaux potables en 1974, de multiples travaux ont démontré la présence de nombreux composés génotoxiques dans l'eau de boisson. L'eau potable obtenue à partir d'eau de surface subit un traitement incluant généralement une étape de chloration. Il est aujourd'hui largement admis que l'activité génotoxique des eaux de boisson provient principalement de la chloration des substances humiques, composés organiques naturels contenus dans l'eau brute et issus de la dégradation des déchets animaux et végétaux. Les très faibles concentrations en composés génotoxiques dans les eaux potables nécessitent la concentration des échantillons, procédé qui risque toutefois de modifier la génotoxicité. Plusieurs tests mettant en oeuvre des cellules procaryotes ou eucaryotes, des plantes ou des mammifères, ont permis de mettre en évidence les effets génotoxiques dans des eaux potables chlorées. L'identification des composés génotoxiques est réalisée au moyen des données de la spectrométrie de masse et de la spectroscopie UV ou RMN (proton ou carbone). Ces agents sont généralement non volatils, acides et polaires. Bien que certains composés inorganiques interviennent parfois, la majeure partie de la génotoxicité est attribuée aux agents organohalogénés (bromés ou/et chlorés), les principaux étant les trihalométhanes, acides acétiques, acétonitriles, cétones, et hydroxyfuranones. La fixation de normes contribue à limiter l'exposition des populations aux agents potentiellement dangereux. La qualité des eaux de boisson peut être accrue en utilisant une eau brute moins chargée en matière organique, et en améliorant le traitement chimique tout en veillant à conserver la qualité microbiologique de l'eau produite.In 1974, two independent studies - one in the Netherlands and the other in the United States - demonstrated the occurrence of trihalomethanes in drinking water. Following studies showed that these chemicals were common contaminants of drinking water and that chloroform, i.e. one of these trihalomethanes, was carcinogenic in rodents. Further investigations demonstrated that extracts of chlorinated drinking water induced significant mutagenicity in the Ames/Salmonella assay. In the present paper we will fist discuss the methods used to detect the genotoxic activity of drinking water and, then, the methods developed to identify the compounds responsible for this activity. After this, we will present the main genotoxic chemicals identified in drinking water, before finally considering several propositions to limit the exposure of populations to these genotoxic compounds.Drinking water is usually produced through a multistage process which includes one or several chlorination steps. It is now widely accepted that the genotoxic activity of drinking water mainly originates from the reaction of chlorine with humic substances present in raw water. Humic substances are natural organic matters (resulting from the degradation of plants and animal tissues) of very complex structure with most chemical functions arranged in aromatic rings or aliphatic chains. The identification of a genotoxic activity in drinking water usually requires concentration of the water samples. Even though such a process implies a probable qualitative/quantitative alteration of the constituents of water samples, the extremely low amounts of genotoxic compounds in drinking water require concentration steps. Among the many genotoxicity tests carried out, the Ames test (which detects reverse mutations in bacteria Salmonella typhimurium) is the assay which was the most frequently used in the field of drinking water mutagenicity. Other tests were performed on eucaryotic cells. Assays detecting micronuclei or chromosomal aberrations in plants, or mutations in mold, yeast, or maize enabled the detection of genotoxic effects of drinking water extracts. Tests on mammal cells also showed that drinking water extracts induced point mutations, sister chromatid exchanges, chromosomal aberrations and micronuclei. In vivo tests on aquatic organims such as newt or mussels demonstrated the micronuclei inducing effect of unconcentrated drinking water samples.Regarding the identification of the compounds responsible for the genotoxicity, it is obviously not possible to identify all of the thousands of chemicals that may be involved. But such a process is important in order to evaluate the specific genotoxicity and the risk associated with (at least) the main chemicals occurring in drinking water. The identification process usually follows three steps: 1. concentration of the sample can be performed using reverse osmosis, freeze drying, liquid-liquid extraction, and/or adsorption on non ionic resin followed by extraction with organic solvent; 2. the purification step uses one or a combination of chromatographic techniques (TLC, packed column liquid chromatography, HPLC or GC); 3. structural identification of the chemical is performed using data from mass spectrometry, and proton and carbon NMR, or UV spectroscopy. The analysis of the genotoxic compounds of drinking water showed that they are rather non-volatile, quite acid and not stable at high pH, rather polar, and with a mean molecular weigh around 200.Turning now to the identity of these compounds, it is considered that the genotoxicity of drinking water is mainly due to organohalogenated chemicals. Some inorganic chemicals (this class of chemicals is usually not recovered in drinking water extracts) which induce genotoxic or carcinogenic effects must, however, be recalled. Arsenic, nitrates, bromates and radon are natural or human-activity-related drinking water contaminants which are responsible for cancers in rodents or in humans. Among the many genotoxic or carcinogenic organohalogenated compounds identified in drinking water, the most abundant chemicals are chlorinated and/or brominated trihalomethanes. Other important groups of compounds are chlorinated and/or brominated derivatives of acetic acids, acetonitriles, ketones, phenolic compounds. The chlorinated hydroxyfuranones, although present at concentrations lower than 0.1 µg/l in drinking water, can be responsible for more than half of the Ames mutagenicity. MX, the most potent of these chlorohydroxyfuranones, has been submitted to intensive toxicological studies worldwide and was very recently identified as a potent carcinogen in rats.Now that the presence of genotoxic compounds in drinking waters is a well documented and accepted fact, the perspectives lies in the better identification of the impact of these drinking water contaminants. The development of more sensitive tests such as the Comet assay (detection of DNA strand breaks) or the 32P postlabelling assay (detection of DNA adducts) should be pursued. Moreover, the interaction between genotoxic compounds and DNA must be investigated more thoroughly, including the identification of adduct structures. More globally, it is of interest to better assess the impact of these agents on public health and on the occurrence of specific human cancers. At present, even though a few individual water contaminants are classified as human probable carcinogens, the chlorinated drinking water (in itself) is not considered as carcinogenic to humans. Exposure to these potentially harmful agents can be limited with 1. improving drinking water quality - i.e. decreasing the formation of genotoxins - by using raw water containing lower amounts of organic matter; and 2. modifying the water chemical treatment by using lower amounts of chlorine and/or combining chlorine with other disinfectants. The public health can also be protected by the setting of guidelines for drinking water: each compound identified as dangerous would be given a concentration threshold which should never be exceeded. The Environmental Protection Agency in the U.S.A. and the World Health Organisation are authorities setting such guidelines. Finally, we believe it is important to limit the concentration of genotoxic compounds in drinking water as much as possible, and one way to do so is to use chlorine in smaller amounts and in a more efficient way. But it is of paramount importance to keep in mind that the disinfection process (in which chlorine still plays a major role) and the providing of a microbiologically safe drinking water should never be jeopardized