916 research outputs found
Semidirect product gauge group and quantization of hypercharge
In the Standard Model the hypercharges of quarks and leptons are not
determined by the gauge group alone. We show that, if we choose the semidirect product group
as its gauge group,
the hyperchages are settled to be . In
addition, the conditions for gauge-anomaly cancellation give strong
constraints. As a result, the ratios of the hypercharges are uniquely
determined and the gravitational anomaly is automatically canceled. The
standard charge assignment to quarks and leptons can be properly reproduced.
For exotic matter fields their hypercharges are also discussed.Comment: 17 pages, 2 tables; LaTeX; typos corrected, references added or
replaced, argument in Secs. 2 and 3 revised, results unchanged; to be
published in Phys. Rew.
Effects of mechanical rotation on spin currents
We study the Pauli--Schr\"odinger equation in a uniformly rotating frame of
reference to describe a coupling of spins and mechanical rotations. The
explicit form of the spin-orbit interaction (SOI) with the inertial effects due
to the mechanical rotation is presented. We derive equations of motion for a
wavepacket of electrons in two-dimensional planes subject to the SOI. The
solution is a superposition of two cyclotron motions with different frequencies
and a circular spin current is created by the mechanical rotation.Comment: 4 pages, 2 figure
Photometric Observations of Star Formation Activity in Early Type Spirals
We observationally study the current star formation activities of early type
spiral galaxies. We construct a complete sample of 15 early type spirals having
far-infrared (FIR) to optical B band luminosity ratios, L(FIR)/L(B), larger
than the average of the type, and make their CCD imaging of the R and H-alpha
bands. The equivalent widths of H-alpha emission increase with increasing
L(FIR)/L(B), indicating that L(FIR)/L(B) can be an indicator of star formation
for such early type spirals with star formation activities higher than the
average. For all of the observed early type spirals, the extended HII regions
exist at the central regions with some asymmetric features. H-alpha emission is
more concentrated to the galactic center than the R band light, and the degree
of the concentration increases with the star formation activity. We also
analyze the relation between the star formation activities and the existence of
companion galaxies in the sample galaxies and other bright early type spirals.
No correlation is found and this suggests that the interaction is not
responsible for all of the star formation activities of early type spirals.Comment: LaTex, 23 pages (2 tables included), plus 9 Postscript figures & 1
table. To be published in AJ (November issue
Can we grow certified eucalypt plantations in subtropical Australia? An insect pest management perspective
In the past few years several Australia forestry companies have set in place procedures for certification in sustainable forest management (Forest Stewardship Council and Australian Forestry Standard). Eucalypt plantation forestry in sub-tropical New South Wales and Queensland is substantially different from that in temperate southern Australia, with currently the majority of plantations grown for long-rotation sawlogs, and a range of tree species different from that planted for pulp in southern Australia. Also, the major insect pests in this region are multivoltine and active for much of the year, due to the warmer climate and the short milder winters, compared to shorter periods of activity of larvae of any one species of mostly univoltine insects in temperate Australia. Insect pest management strategies currently used in Australia include tree improvement, improved site-species matching, and chemical control, mostly using an integrated pest management approach. Monitoring is essential for correct timing of insecticide application but, due to limited resources, forestry companies in Australia struggle to monitor effectively for multiple insect pests over extended periods of insect activity. Because of the relative immaturity of the plantation industry in subtropical Australia, and the sensitivity over the use of chemical insecticides by Government forestry organisations (the major growers), little research has been conducted on establishing integrated pest management strategies. In contrast, such strategies, including regular monitoring and chemical control, have been developed in temperate Australia. There are regional issues for cost-effective management of insect pests in relation to certification, including targeted use of slow-release systemic insecticides and future development of insect-active pheromones, kairomones, and synomones. There are many areas that require further research before forest companies in subtropical Australia will be able to sustain forest certification over the long term
Linkage disequilibrium of evolutionarily conserved regions in the human genome
BACKGROUND: The strong linkage disequilibrium (LD) recently found in genic or exonic regions of the human genome demonstrated that LD can be increased by evolutionary mechanisms that select for functionally important loci. This suggests that LD might be stronger in regions conserved among species than in non-conserved regions, since regions exposed to natural selection tend to be conserved. To assess this hypothesis, we used genome-wide polymorphism data from the HapMap project and investigated LD within DNA sequences conserved between the human and mouse genomes. RESULTS: Unexpectedly, we observed that LD was significantly weaker in conserved regions than in non-conserved regions. To investigate why, we examined sequence features that may distort the relationship between LD and conserved regions. We found that interspersed repeats, and not other sequence features, were associated with the weak LD tendency in conserved regions. To appropriately understand the relationship between LD and conserved regions, we removed the effect of repetitive elements and found that the high degree of sequence conservation was strongly associated with strong LD in coding regions but not with that in non-coding regions. CONCLUSION: Our work demonstrates that the degree of sequence conservation does not simply increase LD as predicted by the hypothesis. Rather, it implies that purifying selection changes the polymorphic patterns of coding sequences but has little influence on the patterns of functional units such as regulatory elements present in non-coding regions, since the former are generally restricted by the constraint of maintaining a functional protein product across multiple exons while the latter may exist more as individually isolated units
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