10,668 research outputs found
On -quasinormal subgroups of finite groups
Let be a finite group and some
partition of the set of all primes , that is, , where and for all . We say that is -primary
if is a -group for some . A subgroup of is said to
be: -subnormal in if there is a subgroup chain such that either
or is -primary for all ,
modular in if the following conditions hold: (i) for all such that , and (ii) for
all such that . In this paper, a subgroup of
is called -quasinormal in if is modular and
-subnormal in . We study -quasinormal subgroups of . In
particular, we prove that if a subgroup of is -quasinormal in
, then for every chief factor of between and the
semidirect product is -primary.Comment: 9 page
First Principles Study of Work Functions of Double Wall Carbon Nanotubes
Using first-principles density functional calculations, we investigated work
functions (WFs) of thin double-walled nanotubes (DWNTs) with outer tube
diameters ranging from 1nm to 1.5nm. The results indicate that work function
change within this diameter range can be up to 0.5 eV, even for DWNTs with same
outer diameter. This is in contrast with single-walled nanotubes (SWNTs) which
show negligible WF change for diameters larger than 1nm. We explain the WF
change and related charge redistribution in DWNTs using charge equilibration
model (CEM). The predicted work function variation of DWNTs indicates a
potential difficulty in their nanoelectronic device applications.Comment: 11 pages, 3 figures, to appear as rapid communication on Physical
Review
TimeTrader: Exploiting Latency Tail to Save Datacenter Energy for On-line Data-Intensive Applications
Datacenters running on-line, data-intensive applications (OLDIs) consume
significant amounts of energy. However, reducing their energy is challenging
due to their tight response time requirements. A key aspect of OLDIs is that
each user query goes to all or many of the nodes in the cluster, so that the
overall time budget is dictated by the tail of the replies' latency
distribution; replies see latency variations both in the network and compute.
Previous work proposes to achieve load-proportional energy by slowing down the
computation at lower datacenter loads based directly on response times (i.e.,
at lower loads, the proposal exploits the average slack in the time budget
provisioned for the peak load). In contrast, we propose TimeTrader to reduce
energy by exploiting the latency slack in the sub- critical replies which
arrive before the deadline (e.g., 80% of replies are 3-4x faster than the
tail). This slack is present at all loads and subsumes the previous work's
load-related slack. While the previous work shifts the leaves' response time
distribution to consume the slack at lower loads, TimeTrader reshapes the
distribution at all loads by slowing down individual sub-critical nodes without
increasing missed deadlines. TimeTrader exploits slack in both the network and
compute budgets. Further, TimeTrader leverages Earliest Deadline First
scheduling to largely decouple critical requests from the queuing delays of
sub- critical requests which can then be slowed down without hurting critical
requests. A combination of real-system measurements and at-scale simulations
shows that without adding to missed deadlines, TimeTrader saves 15-19% and
41-49% energy at 90% and 30% loading, respectively, in a datacenter with 512
nodes, whereas previous work saves 0% and 31-37%.Comment: 13 page
Distinguishing technicolor models via tt-bar productions at polarized photon colliders
We study top quark pair productions at a polarized photon collider from an
e(+)e(-) linear collider (LC) in various improved technicolor model, namely,
the one-family walking technicolor model, the top-color-assisted technicolor
model, and the top-color-assisted multiscale technicolor model. Recent
constraint on the top-pion mass from the precision data of R(b) is considered.
It is shown that, considering only the statistical errors, a polarized photon
collider from a 500 GeV LC with an integrated luminosity of 500 inverse fb is
sufficient for distinguishing the three improved technicolor models
experimentally.Comment: 7 pages, 6 figures, to appear in Physical Review
Quality Assurance Testing for Screening Defective Aluminum Die-cast Rotors of Squirrel Cage Induction Machines
Off-line Flux Injection Test Probe for Screening Defective Rotors in Squirrel Cage Induction Machines
Research on the drag reduction performance induced by the counterflowing jet for waverider with variable blunt radii
Waverider will endure the huge aero-heating in the hypersonic flow, thus, it need be blunt for the leading edge. However, the aerodynamic performance will decrease for the blunt waverider because of the drag hoik. How to improve the aerodynamic performance and reduce the drag and aero-heating is very important. The variable blunt radii method will improve the aerodynamic performance, however, the huge aero-heating and bow shock wave at the head is still serious. In the current study, opposing jet is used in the waverider with variable blunt radii to improve its performance. The three-dimensional coupled implicit Reynolds-averaged Navier-Stokes(RANS) equation and the two equation SST k–ω turbulence model have been utilized to obtain the flow field properties. The numerical method has been validated against the available experimental data in the open literature. The obtained results show that the L/D will drop 7–8% when R changes from 2 to 8. The lift coefficient will increase, and the drag coefficient almost keeps the same when the variable blunt radii method is adopted, and the L/D will increase. The variable blunt radii method is very useful to improve the whole characteristics of blunt waverider and the L/D can improve 3%. The combination of the variable blunt radii method and opposing jet is a novel way to improve the whole performance of blunt waverider, and L/D can improve 4–5%. The aperture as a novel way of opposing jet is suitable for blunt waverider and also useful to improve the aerodynamic and aerothermodynamic characteristics of waverider in the hypersonic flow. There is the optimal P0in/P0 that can make the detached shock wave reattach the lower surface again so that the blunt waverider can get the better aerodynamic performance
-vacuum and inflationary bispectrum
In this paper, we discuss the non-Guassianity originated from the
-vacuum on the CMB anisotropy. For -vacuum, there exist
correlation between points in the acausal two patches of de Sitter spactime.
Such kind of correlation can lead to large local form non-Guassianity in
-vacuum. For the single field slow-roll inflationary scenario, the
spacetime is in a quasi-de Sitter phase during the inflation. We will show that
the -vacuum in this case will lead to non-Gaussianity with
distinguished feature, of a large local form and a very different shape.Comment: 39 pages, 8 figures, references added, minor changes, accepted by
Phys.Rev.
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