86 research outputs found
Superconducting BSCCO Ceramics as Additive to the Zinc Electrode Mass in the Rechargeable Nickel-Zinc Batteries
The electronic conductivity of the main component of the zinc electrode in the rechargeable zinc-nickel battery – ZnO, is rather poor and this is the main reason for the electrochemical heterogeneity of the anode mass and the loss of active surface area during charge/discharge cycling with a corresponding negative effect on the electrode characteristics In the present work, the possibility of application of superconductive cuprate Bi-Pb-Sr-Ca-Cu-O (BSCCO) ceramic as a multifunctional conductive additive to the zinc electrode mass is studied. Powder samples of the BSCCO ceramic Bi1,7Pb0,3Sr2Ca2Cu3Ox are produced by two-stage solid-state synthesis and they are physicochemically characterized. The XRD patterns and SEM observation reveal a well crystallized single phase of superconducting 2212 BSCCO system with average crystallite size 5-10 µm. The chemical stability of BSCCO ceramics in highly alkaline medium of the Ni-Zn battery is confirmed by structural and morphological analysis (XRD, SEM and EDX) of the samples before and after prolong exposure (96 h) to 7M KOH. The electrochemical tests are carried out by a specially designed prismatic alkaline Ni-Zn battery cell with conventional sintered type nickel electrodes and pasted zinc electrode with active electrode mass based on ZnO (88 wt.%) and addition of BSCCO powder or acetylene black as conductive additives. The study show that the zinc electrode with BSCCO superconducting ceramic additive exhibits very good cycleability, remarkable capacity stability and much higher discharge capacity at prolong charge/discharge cycling in comparison to the zinc electrode with the “classic” carbon conductive additive. It is suggested that the addition of BSCCO ceramics improves not only conductivity of the electrode mass and reduces the gas evolution but also stabilizes porosity structure. The results obtained prove the possibility of application of superconducting BSCCO ceramics as a multifunctional additive to the active mass of the zinc electrodes for alkaline battery systems
On the Influence of Uncertainties in Chemical Reaction Rates on Results of the Astrochemical Modelling
With the chemical reaction rate database UMIST95 (Millar et al. 1997) we
analyze how uncertainties in rate constants of gas-phase chemical reactions
influence the modelling of molecular abundances in the interstellar medium.
Random variations are introduced into the rate constants to estimate the
scatter in theoretical abundances. Calculations are performed for dark and
translucent molecular clouds where gas phase chemistry is adequate. Similar
approach was used by Pineau des Forets & Roueff (2000) for the study of
chemical bistability. All the species are divided into 6 sensitivity groups
according to the value of the scatter in their model abundances computed with
varied rate constants. It is shown that the distribution of species within
these groups depends on the number of atoms in a molecule and on the adopted
physical conditions. The simple method is suggested which allows to single out
reactions that are most important for the evolution of a given species.Comment: 4 pages. To appear in the proceedings of the 4th Cologne-Bonn Zermatt
Symposiu
Isotopic abundances of carbon and nitrogen in Jupiter-family and Oort Cloud comets
The 12C14N/12C15N and 12C14N/13C14N isotopic ratios are determined for the
first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically
peculiar Oort Cloud comet C/1999 S4 (LINEAR). By comparing these measurements
to previous ones derived for six other Oort Cloud comets (including one of
Halley-type), we find that both the carbon and nitrogen isotopic ratios are
constant within the uncertainties. The mean values are 12C/13C ~ 90 and 14N/15N
\~ 145 for the eight comets. These results strengthen the view that CN radicals
originate from refractory organics formed in the protosolar molecular cloud and
subsequently incorporated in comets.Comment: Accepted for publication in A&A letter
A divergent heritage for complex organics in Isheyevo lithic clasts
Primitive meteorites are samples of asteroidal bodies that contain a high proportion of chemically complex organic matter (COM) including prebiotic molecules such as amino acids, which are thought to have been delivered to Earth via impacts during the early history of the Solar System. Thus, understanding the origin of COM, including their formation pathway(s) and environment(s), is critical to elucidate the origin of life on Earth as well as assessing the potential habitability of exoplanetary systems. The Isheyevo CH/CBb carbonaceous chondrite contains chondritic lithic clasts with variable enrichments in 15N believed to be of outer Solar System origin. Using transmission electron microscopy (TEM-EELS) and in situ isotope analyses (SIMS and NanoSIMS), we report on the structure of the organic matter as well as the bulk H and N isotope composition of Isheyevo lithic clasts. These data are complemented by electron microprobe analyses of the clast mineral chemistry and bulk Mg and Cr isotopes obtained by inductively coupled plasma and thermal ionization mass spectrometry, respectively (MC-ICPMS and TIMS). Weakly hydrated (A) clasts largely consist of Mg-rich anhydrous silicates with local hydrated veins composed of phyllosilicates, magnetite and globular and diffuse organic matter. Extensively hydrated clasts (H) are thoroughly hydrated and contain Fe-sulfides, sometimes clustered with organic matter, as well as magnetite and carbonates embedded in a phyllosilicate matrix. The A-clasts are characterized by a more 15N-rich bulk nitrogen isotope composition (δ15N = 200–650‰) relative to H-clasts (δ15N = 50–180‰) and contain extremely 15N-rich domains with δ15N 15N-rich domains show that the lithic clast diffuse organic matter is typically more 15N-rich than globular organic matter. The correlated δ15N values and C/N ratios of nanoglobules require the existence of multiple organic components, in agreement with the H isotope data. The combined H and N isotope data suggest that the organic precursors of the lithic clasts are defined by an extremely 15N-poor (similar to solar) and D-rich component for H-clasts, and a moderately 15N-rich and D-rich component for A-clasts. In contrast, the composition of the putative fluids is inferred to include D-poor but moderately to extremely 15N-rich H- and N-bearing components. The variable 15N enrichments in H- and A-clasts are associated with structural differences in the N bonding environments of their diffuse organic matter, which are dominated by amine groups in H-clasts and nitrile functional groups in A-clasts. We suggest that the isotopically divergent organic precursors in Isheyevo clasts may be similar to organic moieties in carbonaceous chondrites (CI, CM, CR) and thermally recalcitrant organic compounds in ordinary chondrites, respectively. The altering fluids, which are inferred to cause the 15N enrichments observed in the clasts, may be the result of accretion of variable abundances of NH3 and HCN ices. Finally, using bulk Mg and Cr isotope composition of clasts, we speculate on the accretion regions of the various primitive chondrites and components and the origin of the Solar System’s N and H isotope variability
A low fraction of nitrogen in molecular form in a dark cloud
Nitrogen is the fifth most abundant element in the Universe. In the interstellar medium, it has been thought to be mostly molecular (N-2)(1). However, N-2 has no observable rotational or vibrational transitions, so its abundance in the interstellar medium remains poorly known. In comets, the N-2 abundance is very low(2,3), while the elemental nitrogen abundance is deficient with respect to the solar value. Moreover, large nitrogen isotopic anomalies are observed in meteorites and interstellar dust particles(4). Here we report the N2H+ (and by inference the N-2) abundance inside a cold dark molecular cloud. We find that only a small fraction of nitrogen in the gas phase is molecular, with most of it being atomic. Because the compositions of comets probably reflect those of dark clouds(5), this result explains the low N-2 abundance in comets. We argue that the elemental nitrogen abundance deficiency in comets can be understood if the atomic oxygen abundance is lower than predicted by present chemical models. Furthermore, the lack of molecular nitrogen in molecular clouds explains the nitrogen anomalies in meteorites and interstellar dust particles, as nitrogen fractionation is enhanced if gaseous nitrogen is atomic(6).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62670/1/nature04919.pd
Characterization and Control of the Microbial Community Affiliated with Copper or Aluminum Heat Exchangers of HVAC Systems
Microbial growth in heating ventilation and air-conditioning (HVAC) systems with the subsequent contamination of indoor air is of increasing concern. Microbes and the subsequent biofilms grow easily within heat exchangers. A comparative study where heat exchangers fabricated from antimicrobial copper were evaluated for their ability to limit microbial growth was conducted using a full-scale HVAC system under conditions of normal flow rates using single-pass outside air. Resident bacterial and fungal populations were quantitatively assessed by removing triplicate sets of coupons from each exchanger commencing the fourth week after their installation for the next 30 weeks. The intrinsic biofilm associated with each coupon was extracted and characterized using selective and differential media. The predominant organisms isolated from aluminum exchangers were species of Methylobacterium of which at least three colony morphologies and 11 distinct PFGE patterns we found; of the few bacteria isolated from the copper exchangers, the majority were species of Bacillus. The concentrations and type of bacteria recovered from the control, aluminum, exchangers were found to be dependent on the type of plating media used and were 11,411–47,257 CFU cm−2 per coupon surface. The concentration of fungi was found to average 378 CFU cm−2. Significantly lower concentrations of bacteria, 3 CFU cm−2, and fungi, 1 CFU cm−2, were recovered from copper exchangers regardless of the plating media used. Commonly used aluminum heat exchangers developed stable, mixed, bacterial/fungal biofilms in excess of 47,000 organisms per cm2 within 4 weeks of operation, whereas the antimicrobial properties of metallic copper were able to limit the microbial load affiliated with the copper heat exchangers to levels 99.97 % lower during the same time period
The CH2CN- molecule: Carrier of the lambda8037 diffuse interstellar band?
The hypothesis that the cyanomethyl anion CH2CN- is responsible for the
relatively narrow diffuse interstellar band (DIB) at 8037.8 +- 0.15 Angstroms
is examined with reference to new observational data. The 0_0^0 absorption band
arising from the ^1B_1 - X ^1A' transition from the electronic ground state to
the first dipole-bound state of the anion is calculated for a rotational
temperature of 2.7 K using literature spectroscopic parameters and results in a
rotational contour with a peak wavelength of 8037.78 Angstroms. By comparison
with diffuse band and atomic line absorption spectra of eight heavily-reddened
Galactic sightlines, CH2CN- is found to be a plausible carrier of the
lambda8037 diffuse interstellar band provided the rotational contour is
Doppler-broadened with a b parameter between 16 and 33 km/s that depends on the
specific sightline. Convolution of the calculated CH2CN- transitions with the
optical depth profile of interstellar Ti II results in a good match with the
profile of the narrow lambda8037 DIB observed towards HD 183143, HD 168112 and
Cyg OB2 8a. The rotational level populations may be influenced by nuclear spin
statistics, resulting in the appearance of additional transitions from K_a = 1
of ortho CH2CN- near 8025 and 8050 Angstroms that are not seen in currently
available interstellar spectra. For CH2CN- to be the carrier of the lambda8037
diffuse interstellar band, either a) there must be mechanisms that convert
CH2CN- from the ortho to the para form, or b) the chemistry that forms CH2CN-
must result in a population of K_a'' levels approaching a Boltzmann
distribution near 3 K
Carbon budget and carbon chemistry in Photon Dominated Regions
We present a study of small carbon chains and rings in Photon Dominated
Regions (PDRs) performed at millimetre wavelengths. Our sample consists of the
Horsehead nebula (B33), the rho,Oph L1688 cloud interface, and the
cometary-shaped cloud IC63. Using the IRAM 30-m telescope, the SEST and the
Effelsberg 100-m teles cope at Effelsberg., we mapped the emission of \cch,
c-C3H2 and C4H, and searched for heavy hydrocarbons such as c-C3H, l-C3H,
l-C3H2, l-C4H2 and C6H. The large scale maps show that small hydrocarbons are
present until the edge of all PDRs, which is surprising as they are expected to
be easily destroyed by UV radiation. Their spatial distribution reasonably
agrees with the aromatic emission mapped in mid-IR wavelength bands. Their
abundances relative to H2 are relatively high and comparable to the ones
derived in dark clouds such as L134N or TMC-1, known as efficient carbon
factories. In particular, we report the first detection of C6H in a PDR. We
have run steady-state PDR models using several gas-phase chemical networks
(UMIST95 and the New Standard Model) and conclude that both networks fail in
reproducing the high abundances of some of these hydrocarbons by an order of
magnitude. The high abundance of hydrocarbons in the PDR may suggest that the
photo-erosion of UV-irradiated large carbonaceous compounds could efficiently
feed the ISM with small carbon clusters or molecules. This new production
mechanism of carbon chains and rings could overcome their destruction by the UV
radiation field. Dedicated theoretical and laboratory measurements are required
in order to understand and implement these additional chemical routes.Comment: 18 pages, 12 figure
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