4,288 research outputs found
Homogeneous nucleation in spatially inhomogeneous systems
Homogeneous nucleation of a vapor in the presence of the loss of clusters by diffusion and
thermophoretic drift is investigated. Analytical results are obtained for the cluster size
distribution and the rate of nucleation by solving the modified kinetic equation for nucleation.
The implications of cluster loss by diffusion and phoretic drift on the onset of the homogeneous
nucleation of silicon vapor in the horizontal epitaxial chemical vapor deposition reactor is
discussed. The range of conditions under which the loss of subcritical clusters by diffusion and
drift becomes important for the interpretation of diffusion cloud chamber experimental data of
the onset conditions of the homogeneous nucleation of vapors is also delineated
Binary nucleation in acidâwater systems. I. Methanesulfonic acidâwater
Experimental measurements of binary nucleation between methanesulfonic acid and water vapor were carried out for relative acidities (Ra), 0.05<Ra<0.65, and relative humidities (Rh), 0.06<Rh<0.65, using a continuous flow mixing-type device. The number concentration of particles leaving the nucleation and growth tube was measured as a function of the initial relative humidity and the relative acidity in the temperature range from 20 to 30 °C. Particle size distributions were also measured and found to vary with the amount of water and acid present. The system was simulated to predict the total number of particles and the total mass of acid in the aerosol phase using a simple integral model and classical binary nucleation theory allowing for the formation of acidâwater hydrates in the gas phase. At low particle concentrations, condensation rates did not significantly change the saturation levels and the nucleation rates were estimated from the total number concentration data as functions of Ra, Rh, and temperature. The values of experimental and theoretical nucleation rates differed significantly, with Jexpt/Jtheor changing as a function of temperature from 10^â8 to 10^â4 as temperature varied from 20 to 30 °C. This work represents the first systematic experimental study of the temperature dependence of binary nucleation
Binary nucleation in acidâwater systems. II. Sulfuric acidâwater and a comparison with methanesulfonic acidâwater
This work presents a systematic investigation of binary nucleation rates for sulfuric acid and water and the effect of temperature on these rates at isothermal, subsaturated conditions. The results from nucleation rate measurements for the sulfuric acid (H2SO4)âwater system are discussed and compared to those previously presented for methanesulfonic acid (MSA)âwater [B. E. Wyslouzil, J. H. Seinfeld, R. C. Flagan, and K. Okuyama, J. Chem. Phys. (submitted)]. Experiments were conducted at relative humidities (Rh) ranging from 0.006<Rh<0.65, relative acidities (Ra) in the range of 0.04<Ra<0.46, and at three temperatures, T=20, 25, and 30 °C, in the continuous flow mixing-type apparatus described in Paper I. Particles were formed by binary nucleation and grew by condensation as the mixed stream flowed through an isothermal glass tube. Number concentrations observed at the exit of the nucleation and growth tube as a function of Rh and Ra are extremely sensitive to the binary nucleation rate, and from these data the nucleation rate was estimated as a function of saturation level and temperature. Particle size distributions were also measured using a specially constructed differential mobility analyzer. As anticipated, the H2SO4 particles formed by nucleation and growth are much smaller than those formed in the MSAâwater experiments, but particle size distribution measurements confirm that most of the particles formed are being observed. The ratio of experimental to theoretical nucleation rates, Jexpt/Jtheor, was found to be a strong function of the predicted number of acid molecules in the critical nucleus for both the H2SO4âwater and MSAâwater systems
Complete mitochondrial DNA sequence of the parasitic honey bee mite Varroa destructor (Mesostigmata : Varroidae)
Varroa destructor is a parasite mite of the eastern honey bee Apis cerana, which is native to Asia. The European honey bee Apis mellifera was imported to Asia from Europe and the USA for apiculture in the 19th century. In a short period of time, V. destructor parasitized the artificially introduced honey bees. Varroa destructor was estimated to have spread around the world with A. mellifera when it was exported from Asia to locations worldwide about 50âyears ago. The mitochondrial DNA of the parasitic honey bee mite V. destructor was analyzed using next-generation sequencing. The complete mitochondrial genome of V. destructor was identified as a 16,476-bp circular molecule containing 13 protein-coding genes (PCGs), 22 tRNA genes, two rRNA genes, and one AT-rich control region. The heavy strand was predicted to have nine PCGs and 13 tRNA genes, whereas the light strand was predicted to contain four PCGs, nine tRNA genes, and two rRNA genes. All PCGs began with ATA as the start codon, except COIII and CytB, which had ATG as the start codon. Stop codons were of two types: TAA for eight genes and TAG for five genes. Molecular phylogenetic analysis revealed that V. destructor from Japan was genetically distant from that of France. A high base substitution rate of 2.82% was also confirmed between the complete mitochondrial DNA sequences of V. destructor from Japan and the USA, suggesting that one Varroa mite strain found in the USA is not from Japan
Enhanced quasiparticle heat conduction of the multigap superconductor Lu2Fe3Si5
The thermal transport measurements have been made on the Fe-based
superconductor Lu2Fe3Si5 (Tc ~ 6 K) down to a very low temperature Tc/120. The
field and temperature dependences of the thermal conductivity confirm the
multigap superconductivity with fully opened gaps on the whole Fermi surfaces.
In comparison to MgB2 as a typical example of the multigap superconductor in a
p-electron system, Lu2Fe3Si5 reveals a remarkably enhanced quasiparticle heat
conduction in the mixed state. The results can be interpreted as a consequence
of the electronic correlations derived from Fe 3d-electrons.Comment: 5 pages, 4 figure
Electrons doped in cubic perovskite SrMnO3: isotropic metal versus chainlike ordering of Jahn-Teller polarons
Single crystals of electron-doped SrMnO3 with a cubic perovskite structure
have been systematically investigated as the most canonical
(orbital-degenerate) double-exchange system, whose ground states have been
still theoretically controversial. With only 1-2% electron doping by Ce
substitution for Sr, a G-type antiferromagnetic metal with a tiny spin canting
in a cubic lattice shows up as the ground state, where the Jahn-Teller polarons
with heavy mass are likely to form. Further electron doping above 4%, however,
replaces this isotropic metal with an insulator with tetragonal lattice
distortion, accompanied by a quasi-one-dimensional 3z^2-r^2 orbital ordering
with the C-type antiferromagnetism. The self-organization of such dilute
polarons may reflect the critical role of the cooperative Jahn-Teller effect
that is most effective in the originally cubic system.Comment: 5 pages, 4 figure
Complete mitochondrial DNA sequence of the small hive beetle Aethina tumida (Insecta: Coleoptera) from Hawaii
We analyzed the complete mitochondrial genome of the small hive beetle Aethina tumida, a major honeybee pest that was accidentally transported to the Hawaii Islands, USA. The mitochondrial genome of A. tumida was identified as a 15,198âbp circular molecule containing 13 protein-coding genes, 22 tRNA genes, and two rRNA genes, along with one Aâ+âT-rich control region. The average AT content was found to be 76.2%. The heavy strand was predicted to have nine protein-coding and 14 tRNA genes; while the light strand was predicted to contain four protein-coding, eight tRNA, and two rRNA genes. Among the 13 PCGs, the initiation codon ATT was found in five, ATA in three, ATG in four, and TTG in one gene. Six PCGs used TAA as the stop codon, whereas three PCGs used TAG as the stop codon. Incomplete stop codon TA (COIII, ND5, and ND4) and T (COII) were identified. We found that the genetic distance between A. tumida from Hawaii and the beetlesâ natural home South Africa, was small, indicating that the Hawaii population may have originated for the South Africa region
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