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21.
A thermosonimetric study has shown that the Phase II/III polymorphic transition of hexachloroethane emits acoustic signals. This solid-solid phase transition is known to occur by a nucleation-growth process during which a nucleus of the new phase, once formed, grows at the expense of the mother phase to form a complete crystal without fracture. Acoustic emissions from a conditioned multi-crystal sample have been used to study the transition. Acoustic activity correlated well with dilatometric measurements. Frequency analysis on waveforms of many hundreds of individual acoustic emissions revealed marked differences between individual signals. Principal-components analysis on 24 signal features revealed a single dispersed cluster with a highly non-uniform distribution of signals. These experiments provided highly reproducible average power spectra. Time-resolved acoustic power spectra were also generated. These additional types of information cannot be obtained by other techniques. 相似文献
22.
Kariuki NN Luo J Maye MM Hassan SA Menard T Naslund HR Lin Y Wang C Engelhard MH Zhong CJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):11240-11246
This paper reports findings of an investigation of the synthesis of monolayer-capped binary gold-silver (AuAg) bimetallic nanoparticles that is aimed at understanding the control factors governing the formation of the bimetallic compositions. The synthesis of alkanethiolate-capped AuAg nanoparticles was carried out using two related synthetic protocols using aqueous sodium borohydride as a reducing agent. One involves a two-phase reduction of AuCl(4)(-), which is dissolved in organic solution, and Ag(+), which is dissolved in aqueous solution. The other protocol involves a two-phase reduction of AuCl(4)(-) and AgBr(2)(-), both of which are dissolved in the same organic solution. AuAg nanoparticles of 2-3 nm core sizes with different compositions in the range of 0-100% Au have been synthesized. The two synthetic routes were compared in terms of bimetallic composition and size properties. Our new findings have allowed us to establish the correlation between synthetic feeding of metals and metal compositions in the bimetallic nanoparticles, which have important implications to the exploration of gold-based bimetallic nanoparticles for constructing sensing and catalytic nanomaterials. 相似文献
23.
A sensitive spectrophotometric method has been developed for the determination of ziram in water, vegetables and grains. The method is based on the dissociation of dithiocarbamate complex of zinc with thiocyanate and rhodamine 6G at pH 4 to form a pink coloured complex that is stabilized by gelatin. The method is simple and Beer's law is obeyed over the concentration range of 0.05-1 ppm of ziram. The method is free from interference of similar dithiocarbamate fungicides containing Mn(2+) and Fe(3+) ions. 相似文献
24.
Mathew D. Penrose 《Journal of statistical physics》1994,77(1-2):3-15
LetG
R
be the graph obtained by joining all sites ofZ
d which are separated by a distance of at mostR. Let (G
R
) denote the connective constant for counting the self-avoiding walks in this graph. Let (G
R
) denote the coprresponding constant for counting the trees embedded inG
R
. Then asR, (G
R
) is asymptotic to the coordination numberk
R ofG
R
, while (G
R
) is asymptotic toek
R. However, ifd is 1 or 2, then (G
R
)-k
R
diverges to –.Dedicated to Oliver Penrose on this occasion of his 65th birthday. 相似文献
25.
26.
Lazarus EA Navratil GA Greenfield CM Strait EJ Austin ME Burrell KH Casper TA Baker DR DeBoo JC Doyle EJ Durst R Ferron JR Forest CB Gohil P Groebner RJ Heidbrink WW Hong R Houlberg WA Howald AW Hsieh C Hyatt AW Jackson GL Kim J Lao LL Lasnier CJ Leonard AW Lohr J La Haye RJ Maingi R Miller RL Murakami M Osborne TH Perkins LJ Petty CC Rettig CL Rhodes TL Rice BW Sabbagh SA Schissel DP Scoville JT Snider RT Staebler GM Stallard BW Stambaugh RD St John HE Stockdale RE Taylor PL Thomas DM 《Physical review letters》1996,77(13):2714-2717
27.
Summary Microgram amounts of metal ions have been separated using stannic antimonate paper. Most of the separations can be accomplished within 15 minutes.
Zusammenfassung Unter Verwendung von Zinn(IV)antimonat-Papier lassen sich Mikromengen zahlreicher Metallionen trennen. Die meisten Trennungen lassen sich innerhalb 15 min durchführen.相似文献
28.
29.
Seasonal fluctuation of DNA photodamage in marine plankton assemblages at Palmer Station, Antarctica
Meador J Jeffrey WH Kase JP Pakulski JD Chiarello S Mitchell DL 《Photochemistry and photobiology》2002,75(3):266-271
Ultraviolet radiation-induced DNA damage frequencies were measured in DNA dosimeters and natural plankton communities during the austral spring at Palmer Station, Antarctica, during the 1999-2000 field season. We found that the fluence of solar ultraviolet-B radiation (UV-B) at the earth's surface correlated with stratospheric ozone concentrations, with significant ozone depletion observed because of "ozone hole" conditions. To verify the interdependence of ozone depletion and DNA damage in natural microbial communities, seawater was collected daily or weekly from Arthur Harbor at Palmer Station, Antarctica, throughout "ozone season," exposed to ambient sunlight between 0600 and 1800 h and fractionated using membrane filtration to separate phytoplankton and bacterioplankton populations. DNA from these fractions was isolated and DNA damage measured using radioimmunoassay. Under low-ozone conditions cyclobutane dimer concentrations in bacterioplankton and phytoplankton communities were maximal. DNA damage measured in dosimeters correlated closely with ozone concentrations and UV-B fluence. Our studies offer further support to the theory that stratospheric deozonation is detrimental to marine planktonic organisms in the Southern Ocean. 相似文献
30.
The determination of Al2O3, in bulk coal samples to an accuracy of about 0.2% Al2O3 has been achieved by means of a thermal-neutron activation technique based on the reaction 27Al(n,γ)28Al. In the analysed samples, which had widely different compositions, the Al2O3 concentrations ranged from 1 to 11% and the ash contents from 7 to 40%. Al2O3 concentrations measured by x-ray fluorescence showed a linear relationship with both the 1.78-MeV γ-ray count following the decay of 28Al and the thermal-neutron count near the samples during irradiation. The linear relationship, which was obtained by regression analysis of the experimental data, determined the Al2O3concentrations with a standard deviation of 0.24% Al2O3. The particle sizes in the samples ranged from —0.5 to —40 mm, the moisture contents ranged from 1 to 6%, and the sample weights ranged from 8 to 11 kg. However, inclusion of these parameters in the regression analysis did not significantly improve the results for Al2O3. 相似文献