221 research outputs found
On The Unsteady Aerodynamics Of Road Vehicles In The Dynamic Motions
Unsteady aerodynamics of road vehicles in dy-namic pitching motion were investigated by numerical analysis. Dynamic coupling simulation of flow and vehicle motion was realized based on a large eddy simulation (LES) technique with moving boundary methods. Fully unstructured finite volume code previously developed was implemented for the road vehicle aerodynamics. Arbitrary Lagrangean-Eulerian (ALE) method was employed to handle vehicleâs ro-tating motion, particularly the dynamic pitching. This vehicle motion type is chosen because of the unsteady aerodynamics are expected to be crucial in regards to the comfort of passenger. By using the numerical simulation, a method to estimate the vehicleâs aerodynamic damping was proposed
T-odd Correlations in the Decay of Scalar Fermions
We define a CP sensitive asymmetry in the sfermion decays \ti f \to f
\ti\chi^0_j \ell \bar \ell, f \ti\chi^0_j q \bar q, based on triple product
correlations between the momenta of the outgoing fermions. We study this
asymmetry in the MSSM with complex parameters. We show that the asymmetry is
sensitive to the phases of the parameters and . The leading
contribution stems from the decay chain \ti f\to f \ti\chi^0_j\to f
\ti\chi^0_1 Z\to f \ti\chi^0_1 \ell \bar \ell (f \ti\chi^0_1 q \bar q), for
which we obtain analytic formulae for the amplitude squared. The asymmetry can
go up to 3% for \ti f\to f \ti\chi^0_1 \ell \bar \ell, and up to 20% for \ti
f\to f \ti\chi^0_1 q \bar q. We also estimate the rates necessary to measure
the asymmetry.Comment: 18 pages, 5 figures, 2 tables; comments and references added; two
tables added; version to appear in Eur. Phys.
First-Principles Study on Structural Properties of GeO and SiO under Compression and Expansion Pressure
The detailed analysis of the structural variations of three GeO and
SiO polymorphs (-quartz, -cristobalite, and rutile) under
compression and expansion pressure is reported. First-principles total-energy
calculations reveal that the rutile structure is the most stable phase among
the phases of GeO, while SiO preferentially forms quartz. GeO
tetrahedras of quartz and cristobalite GeO phases at the equilibrium volume
are more significantly distorted than those of SiO. Moreover, in the case
of quartz GeO and cristobalite GeO, all O-Ge-O bond angles vary when
the volume of the GeO bulk changes from the equilibrium point, which causes
further deformation of tetrahedra. In contrast, the tilt angle formed by
Si-O-Si in SiO markedly changes. This flexibility of the O-Ge-O bonds
reduces the stress at the Ge/GeO interface due to the lattice-constant
mismatch and results in the low defective interface observed in the experiments
[Matsubara \textit{et al.}: Appl. Phys. Lett. \textbf{93} (2008) 032104; Hosoi
\textit{et al.}: Appl. Phys. Lett. \textbf{94} (2009) 202112].Comment: 15 pages, 5 figures and 2 table
Gamma-ray and radio tests of the e+e- excess from DM annihilations
PAMELA and ATIC recently reported an excess in e+e- cosmic rays. We show that
if it is due to Dark Matter annihilations, the associated gamma-ray flux and
the synchrotron emission produced by e+e- in the galactic magnetic field
violate HESS and radio observations of the galactic center and HESS
observations of dwarf Spheroidals, unless the DM density profile is
significantly less steep than the benchmark NFW and Einasto profiles.Comment: 16 pages, 4 figures; v2: normalizations fixed in Table 2 and typos
corrected (no changes in the analysis nor the results), some references and
comments added; v3: minor additions, matches published versio
Prospects for the direct detection of neutralino dark matter in orbifold scenarios
We analyse the phenomenology of orbifold scenarios from the heterotic
superstring, and the resulting theoretical predictions for the direct detection
of neutralino dark matter. In particular, we study the parameter space of these
constructions, computing the low-energy spectrum and taking into account the
most recent experimental and astrophysical constraints, as well as imposing the
absence of dangerous charge and colour breaking minima. In the remaining
allowed regions the spin-independent part of the neutralino-proton cross
section is calculated and compared with the sensitivity of dark matter
detectors. In addition to the usual non universalities of the soft terms in
orbifold scenarios due to the modular weight dependence, we also consider
D-term contributions to scalar masses. These are generated by the presence of
an anomalous U(1), providing more flexibility in the resulting soft terms, and
are crucial in order to avoid charge and colour breaking minima. Thanks to the
D-term contribution, large neutralino detection cross sections can be found,
within the reach of projected dark matter detectors.Comment: 51 pages, 25 figure
Closed String Field Theory with Dynamical D-brane
We consider a closed string field theory with an arbitrary matter current as
a source of the closed string field. We find that the source must satisfy a
constraint equation as a consequence of the BRST invariance of the theory. We
see that it corresponds to the covariant conservation law for the matter
current, and the equation of motion together with this constraint equation
determines the classical behavior of both the closed string field and the
matter. We then consider the boundary state (D-brane) as an example of a
source. We see that the ordinary boundary state cannot be a source of the
closed string field when the string coupling g turns on. By perturbative
expansion, we derive a recursion relation which represents the bulk
backreaction and the D-brane recoil. We also make a comment on the rolling
tachyon boundary state.Comment: 30 pages, LaTeX2e, no figures. Typos are correcte
SU(4) Instantons on Calabi-Yau Threefolds with Z_2 x Z_2 Fundamental Group
Structure group SU(4) gauge vacua of both weakly and strongly coupled
heterotic superstring theory compactified on torus-fibered Calabi-Yau
threefolds Z with Z_2 x Z_2 fundamental group are presented. This is
accomplished by constructing invariant, stable, holomorphic rank four vector
bundles on the simply connected cover of Z. Such bundles can descend either to
Hermite-Yang-Mills instantons on Z or to twisted gauge fields satisfying the
Hermite-Yang-Mills equation corrected by a non-trivial flat B-field. It is
shown that large families of such instantons satisfy the constraints imposed by
particle physics phenomenology. The discrete parameter spaces of those families
are presented, as well as a lower bound on the dimension of the continuous
moduli of any such vacuum. In conjunction with Z_2 x Z_2 Wilson lines, these
SU(4) gauge vacua can lead to standard-like models at low energy with an
additional U(1)_{B-L} symmetry. This U(1)_{B-L} symmetry is very helpful in
naturally suppressing nucleon decay.Comment: 68 pages, no figure
Evaluation of persistent-mode operation in a superconducting MgB2 coil in solid nitrogen
We report the fabrication of a magnesium diboride (MgB2) coil and evaluate its persistent-mode operation in a system cooled by a cryocooler with solid nitrogen (SN2) as a cooling medium. The main purpose of SN2 was to increase enthalpy of the cold mass. For this work, an in situ processed carbon-doped MgB2 wire was used. The coil was wound on a stainless steel former in a single layer (22 turns), with an inner diameter of 109 mm and height of 20 mm without any insulation. The two ends of the coil were then joined to make a persistent-current switch to obtain the persistent-current mode. After a heat treatment, the whole coil was installed in the SN2 chamber. During operation, the resultant total circuit resistance was estimated to be \u3c7.4x10â14 Ω at 19.5 K±1.5 K, which meets the technical requirement for magnetic resonance imaging application
Present and Future CP Measurements
We review theoretical and experimental results on CP violation summarizing
the discussions in the working group on CP violation at the UK phenomenology
workshop 2000 in Durham.Comment: 104 pages, Latex, to appear in Journal of Physics
Inflation in Realistic D-Brane Models
We find successful models of D-brane/anti-brane inflation within a string
context. We work within the GKP-KKLT class of type IIB string vacua for which
many moduli are stabilized through fluxes, as recently modified to include
`realistic' orbifold sectors containing standard-model type particles. We allow
all moduli to roll when searching for inflationary solutions and find that
inflation is not generic inasmuch as special choices must be made for the
parameters describing the vacuum. But given these choices inflation can occur
for a reasonably wide range of initial conditions for the brane and antibrane.
We find that D-terms associated with the orbifold blowing-up modes play an
important role in the inflationary dynamics. Since the models contain a
standard-model-like sector after inflation, they open up the possibility of
addressing reheating issues. We calculate predictions for the CMB temperature
fluctuations and find that these can be consistent with observations, but are
generically not deep within the scale-invariant regime and so can allow
appreciable values for as well as predicting a potentially
observable gravity-wave signal. It is also possible to generate some admixture
of isocurvature fluctuations.Comment: 39 pages, 21 figures; added references; identified parameters
combining successful inflation with strong warping, as needed for consistency
of the approximation
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