The Asymmetric Rotor. IX. The Heavy Water Bands at 2787 cm^–1 and 5373 cm^–1

The combination band (110) of the two stretching fundamentals of D2O is reported and analyzed to yield nu0=5373.2 cm^–1 and the excited state moments of inertia 1.910, 3.931, and 5.929×10^–40 g cm^2. The same method of analysis applied to the unsymmetrical fundamental band (100) envelope gives nu0=2787.5 cm^–1 and the excited state moments 1.881, 3.876, and 5.843×10^–40 g cm^2

The infra-red spectrum of hydrogen peroxide

The absorption spectrum of hydrogen peroxide vapor was examined under low dispersion in the range 2–15µ. Four bands were observed at 3590, 2630, 1255, and 877 cm^–1. The spectrum of the liquid also was measured between 2 and 21µ; it showed five bands at about 3400, 2780, 1350, 880, and 550 cm^–1. The last one, which seems very diffuse, is presumably the torsional oscillation of the OH groups; as such it corresponds to a potential energy barrier of the order of 4 kcal./mole. New assignments are proposed in agreement with the model of Penney and Sutherland. Under high dispersion the second harmonic O--H frequency was found to consist of two identical hybrid bands at 7036.6 and 7041.8 cm^–1, of which the rotational constant for the ground state is in perfect agreement with that already found for the third harmonic band. The explanation given previously for the doublet character of the vibrational levels of hydrogen peroxide is further substantiated by the present results. From both vibrational and rotational data the O--H distance in hydrogen peroxide appears to be slightly greater than that in water

Toxicité de l'ion fluorure envers les organismes d'eau douce et effets de la dureté - revue et nouvelle analyse de données existantes

Les plus importantes sources anthropiques de fluorures dans les systèmes d'eau douce comprennent les eaux usées municipales, les industries productrices de fertilisants et les alumineries. Plusieurs études montrent que la toxicité des fluorures est réduite lorsque le test toxicologique est réalisé en eau dure plutôt qu'en eau douce. Trois mécanismes peuvent être invoqués pour expliquer une telle tendance : (I) influence des ions de dureté (Ca2+ ; Mg2+) sur les organismes tests (soit au niveau de la barrière biologique séparant l'organisme de son milieu, soit au niveau de leur métabolisme interne); (II) complexation entre le fluorure et les ions de dureté dans le milieu d'exposition, menant à une réduction de la concentration en fluorure libre (F-); (III) précipitation de fluorite (CaF2) dans les milieux d'exposition, menant à une réduction de la concentration effective en fluorures. Pour identifier le ou les mécanisme(s) responsables de l'effet protecteur de la dureté, nous avons réalisé une revue de la littérature existante sur les poissons, les invertébrés et les insectes aquatiques d'eau douce. Parmi ces études, les plus complètes ont été sélectionnées et la spéciation des fluorures modélisée pour chaque cas. Les modélisations réalisées indiquent que la spéciation physique du fluorure (distinction entre les espèces dissoutes et particulaires) a beaucoup plus d'importance que sa spéciation chimique en solution dans les systèmes étudiés.Important anthropogenic sources of fluoride to the aquatic environment include municipal waste waters and effluents from fertilizer producing plants and aluminum refineries. Many studies have demonstrated that fluoride toxicity to aquatic organisms is reduced when the toxicological test is performed in hard water rather than soft water. In principle at least three mechanisms could explain this trend: (I) a direct beneficial influence of the hardness cations (Ca2+ ; Mg2+) on the test organism (either externally, at an epithelial membrane, or internally); (II) complexation between fluoride and the hardness cations, leading to a reduction in free the fluoride concentration (F-) in the exposure media; (III) fluorite precipitation (CaF2) in the exposure media, leading to a reduction in the effective fluoride concentration. The present literature review was designed to identify which of these mechanisms might be responsible for the apparent protective effect of hardness on fluoride toxicity.An inventory of the existing literature on the toxicity of fluoride to freshwater fish, invertebrates and aquatic insects was prepared. The most complete studies were selected and the chemical data needed to model cation and anion speciation in the exposure media were extracted from the papers. Speciation at equilibrium was then modelled using as input data the total concentrations of the key constituents (calcium, magnesium, fluoride and chloride), together with the temperature and the pH.The initial speciation calculations revealed a particularity of the chemical systems studied: frequently precipitation of fluorite (CaF2) was predicted by the speciation model (MINEQL+), but the article from which the data had been extracted did not mention the appearance of a precipitate. Fluorite solubility, at a pH of 7 and at an ionic strength of 2.7 mM, is approximately 17 mg CaF2 /L (0.22 mM). When high fluoride concentrations are used in hard water, both fluoride and calcium concentrations are predicted to decrease markedly as a result of fluorite precipitation. This analysis of the published results thus suggests that the reported lower toxicity of fluoride in hard waters is likely due to the chemical precipitation of CaF2 and MgF2, resulting in a decrease in the effective fluoride concentration to which the test organisms are exposed. In other words, changes in the physical speciation of fluoride (i.e., its distribution among dissolved and particulate species) are much more important than changes in its chemical speciation in solution.Given the low solubility of fluoride in hard waters, it would seem difficult if not impossible to carry out fluoride toxicity tests in hard water. However, in a few fluoride toxicity studies the researchers checked for precipitation by monitoring fluoride and calcium concentrations throughout the toxicity test. In some of these cases, even though speciation calculations predicted fluorite formation at the exposure concentrations used, the authors did not detect any precipitation; these systems were thus apparently in a metastable, over-saturated state, where the kinetics of precipitation were slow relative to the duration of the toxicity test. The chemical equilibrium software was used to simulate fluoride speciation in these systems, by allowing the over-saturated solid phases to remain in solution. In particular, we looked for evidence that under such circumstances the hardness cations exerted a beneficial effect. However, no clear picture emerged from this second analysis: two of the studies designed particularly to test the effect of calcium on fluoride toxicity showed a protective effect, whereas one study indicated the opposite effect, i.e. an increase in fluoride toxicity as the calcium concentration was raised. All fish studies for which calcium concentrations were available (N=20 studies; 58 toxicity tests) were pooled and tested for a possible calcium effect on fluoride toxicity. No relationship was observed between fluoride ion toxicity (LC50, expressed as calculated free [F-]) and calculated dissolved calcium concentrations for these pooled data (Fig. 2). Fluorite solubility was the most important factor influencing the data point distribution in the relationship. The same exercise was performed for all the invertebrate studies (N=11 studies; 22 toxicity tests) but again no relationship was found (Fig. 3).Several factors other than hardness affect fluoride toxicity to aquatic organisms. Fluoride toxicity to fish increased with exposure duration up to 200 h, where it reached a threshold LC50 level around 100 mg/L (5.3 mM) expressed as free fluoride (Fig. 4). Fish life stage (Fig. 5), the temperature of the exposure media (Fig. 6) and the chloride concentration also affected fluoride toxicity in fish. For invertebrates, fluoride toxicity increased with exposure duration but to a lesser extent than for fish.In summary, water hardness clearly reduces fluoride toxicity to aquatic organisms by limiting the equilibrium solubility of the fluoride ion. However, in those cases where the precipitation of CaF2 (s) and MgF2 (s) is slow, and where the hardness cations and fluoride co-exist in the dissolved state in the exposure medium, the experimental evidence for a protective effect of hardness on fluoride toxicity is equivocal. To answer the question, new experiments should be performed under conditions that take into account the behaviour of calcium and fluoride in the natural environment. Metastable environments where fluoride concentrations exceed the solubility limit imposed by CaF2 or MgF2 could be reproduced in laboratory toxicity tests by using continuous flow systems. For tests below the solubility limit, toxicity tests with varying levels of Ca or Mg could be designed to stay within the solubility range of CaF2 or MgF2. In both cases, dissolved calcium, magnesium and fluoride concentrations should be monitored throughout the toxicity tests

The Infra-Red Bands of Hydrogen Peroxide at lambda9720 and the Structure and Torsional Oscillation of Hydrogen Peroxide

A high dispersion study of the OH bands of hydrogen peroxide in the photographic infra-red is described. The rotational structure of the two hybrid bands at 10,283.68 cm^—1 and 10,291.08 cm^—1 is analyzed. The small moment of inertia of hydrogen peroxide is found to be 2.786 × 10^—40 g cm^2 while the harmonic mean of the two larger moments of inertia is found to be approximately 33.9 × 10^—40 g cm^2. The planar cis-configuration is ruled out spectroscopically and it is concluded that hydrogen peroxide exists in a non-planar form. It is tentatively decided that the vibrational levels of hydrogen peroxide are doubled and that the double minimum potential associated with the internal rotation of the OH groups has a high and a low barrie

The Carbon Content of Intergalactic Gas at z=4.25 and its Evolution Toward z=2.4

This paper presents ionization-corrected measurements of the carbon abundance in intergalactic gas at 4.0 < z < 4.5, using spectra of three bright quasars obtained with the MIKE spectrograph on Magellan. By measuring the CIV strength in a sample of 131 discrete HI-selected quasar absorbers with \rho/\bar{\rho}>1.6, we derive a median carbon abundance of [C/H]=-3.55, with lognormal scatter of approximately ~0.8 dex. This median value is a factor of two to three lower than similar measurements made at z~2.4 using CIV and OVI. The strength of evolution is modestly dependent on the choice of UV background spectrum used to make ionization corrections, although our detection of an abundance evolution is generally robust with respect to this model uncertainty. We present a framework for analyzing the effects of spatial fluctuations in the UV ionizing background at frequencies relevant for CIV production. We also explore the effects of reduced flux between 3-4 Rydbergs (as from HeII Lyman series absorption) on our abundance estimates. At HeII line absorption levels similar to published estimates the effects are very small, although a larger optical depth could reduce the strength of the abundance evolution. Our results imply that ~50% of the heavy elements seen in the IGM at z~2.4 were deposited in the 1.3 Gyr between z~4.3 and z~2.4. The total implied mass flux of carbon into the Lyman alpha forest would constitute ~30% of the IMF-weighted carbon yield from known star forming populations over this period.Comment: Accepted for publication in the Astrophysical Journal. 23 pages, 24 figures, 2 table

Ejector applications in refrigeration and heating: An overview of modelling, operation and recent developments

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kühn – Berlin: Universitätsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]The utilization of ejectors in heat pump systems as compression components, alone or in combination with other equipment, have gained renewed interest as a thermally driven solution for low temperature heat recovery and upgrading and more efficient energy use. This paper summarizes the main findings and trends, in the area of heat driven ejector based machines using low boiling point working fluids. An overall view of such systems is provided by presenting the ejector principles of physics and the latest developments on ejector design, operation and modeling approaches. Aspects related to the analysis of the complex interacting phenomena taking place in these systems for high performance are highlighted. Conventional and improved ejector heat pump cycles of interest employing ejectors alone or boosted combinations are presented and discussed, and their potential applications are indicated. Finally, sample theoretical and experimental results obtained at CanmetENERGY on ejector operation and design are reported

Measuring the Sources of the Intergalactic Ionizing Flux

We use a wide-field (0.9 square degree) X-ray sample with optical and GALEX ultraviolet observations to measure the contribution of Active Galactic Nuclei (AGNs) to the ionizing flux as a function of redshift. Our analysis shows that the AGN contribution to the metagalactic ionizing background peaks around z=2. The measured values of the ionizing background from the AGNs are lower than previous estimates and confirm that ionization from AGNs is insufficient to maintain the observed ionization of the intergalactic medium (IGM) at z>3. We show that only sources with broad lines in their optical spectra have detectable ionizing flux and that the ionizing flux seen in an AGN is not correlated with its X-ray color. We also use the GALEX observations of the GOODS-N region to place a 2-sigma upper limit of 0.008 on the average ionization fraction fnu(700 A)/fnu(1500 A) for 626 UV selected galaxies in the redshift range z=0.9-1.4. We then use this limit to estimate an upper bound to the galaxy contribution in the redshift range z=0-5. If the z~1.15 ionization fraction is appropriate for higher redshift galaxies, then contributions from the galaxy population are also too low to account for the IGM ionization at the highest redshifts (z>4).Comment: 15 pages, Accepted by The Astrophysical Journa

The origin of ultra diffuse galaxies: stellar feedback and quenching

We test if the cosmological zoom-in simulations of isolated galaxies from the FIRE project reproduce the properties of ultra diffuse galaxies. We show that stellar feedback-generated outflows that dynamically heat galactic stars, together with a passively aging stellar population after imposed quenching (from e.g. infall into a galaxy cluster), naturally reproduce the observed population of red UDGs, without the need for high spin halos or dynamical influence from their host cluster. We reproduce the range of surface brightness, radius and absolute magnitude of the observed z=0 red UDGs by quenching simulated galaxies at a range of different times. They represent a mostly uniform population of dark matter-dominated galaxies with M_star ~1e8 Msun, low metallicity and a broad range of ages. The most massive simulated UDGs require earliest quenching and are therefore the oldest. Our simulations provide a good match to the central enclosed masses and the velocity dispersions of the observed UDGs (20-50 km/s). The enclosed masses of the simulated UDGs remain largely fixed across a broad range of quenching times because the central regions of their dark matter halos complete their growth early. A typical UDG forms in a dwarf halo mass range of Mh~4e10-1e11 Msun. The most massive red UDG in our sample requires quenching at z~3 when its halo reached Mh ~ 1e11 Msun. If it, instead, continues growing in the field, by z=0 its halo mass reaches > 5e11 Msun, comparable to the halo of an L* galaxy. If our simulated dwarfs are not quenched, they evolve into bluer low-surface brightness galaxies with mass-to-light ratios similar to observed field dwarfs. While our simulation sample covers a limited range of formation histories and halo masses, we predict that UDG is a common, and perhaps even dominant, galaxy type around Ms~1e8 Msun, both in the field and in clusters.Comment: 20 pages, 13 figures; match the MNRAS accepted versio

A Vacuum Spectrograph for the Infra-Red

A description is given of a 1-meter focus vacuum grating spectrometer for the infra-red which is distinguished by its versatility and compactness of design. The vacuum container is tubular in form and all optical parts are mounted on a carriage which is readily retractable from the case for adjustment. A novel feature is the use of a sine screw drive which gives a linear wave-length scale. A representative spectrum tracing is given