497 research outputs found
Switched reluctance motor design for electric vehicles based on harmonics and back EMF analysis
Permanent magnet synchronous motors are widely accepted in automotive applications. The high torque density, high rotational speed with maximum efficiency in electric vehicle applications is technically challenging for motor design. However, these machines are expensive and difficult to work at high-temperature harsh environment due to permanent magnets demagnetisation features. Alternatively, switched reluctance motors can provide similar output characteristics and a wider speed. Thus these are considered to be more fault tolerant and more reliable. This study proposes a 20 kW, three-phase switched reluctance motor and analyse its overall performance and harmonic contents. The study is conducted by optimising the slot filling factor, excitation voltage and switching sequence of an asymmetrical half bridge converter. A finite element model is used to predict the core and copper losses and other influencing parameters. Simulation results are presented and analysed the effectiveness of the proposed switched reluctance motor (SRM)
Erratum to: Localization of Fatty Acyl and Double Bond Positions in Phosphatidylcholines Using a Dual Stage CID Fragmentation Coupled with Ion Mobility Mass Spectrometry.
A high content molecular fragmentation for the analysis of phosphatidylcholines (PC) was achieved utilizing a two-stage [trap (first generation fragmentation) and transfer (second generation fragmentation)] collision-induced dissociation (CID) in combination with travelling-wave ion mobility spectrometry (TWIMS). The novel aspects of this work reside in the fact that a TWIMS arrangement was used to obtain a high level structural information including location of fatty acyl substituents and double bonds for PCs in plasma, and the presence of alkali metal adduct ions such as [M + Li](+) was not required to obtain double bond positions. Elemental compositions for fragment ions were confirmed by accurate mass measurements. A very specific first generation fragment ion m/z 577 (M-phosphoryl choline) from the PC [16:0/18:1 (9Z)] was produced, which by further CID generated acylium ions containing either the fatty acyl 16:0 (C(15)H(31)CO(+), m/z 239) or 18:1 (9Z) (C(17)H(33)CO(+), m/z 265) substituent. Subsequent water loss from these acylium ions was key in producing hydrocarbon fragment ions mainly from the α-proximal position of the carbonyl group such as the hydrocarbon ion m/z 67 (+H(2)C-HC = CH-CH = CH(2)). Formation of these ions was of important significance for determining double bonds in the fatty acyl chains. In addition to this, and with the aid of (13)C labeled lyso-phosphatidylcholine (LPC) 18:1 (9Z) in the ω-position (methyl) TAP fragmentation produced the ion at m/z 57. And was proven to be derived from the α-proximal (carboxylate) or distant ω-position (methyl) in the LPC. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s13361-011-0172-2) contains supplementary material, which is available to authorized users
Pion Freeze-Out Time in Pb+Pb Collisions at 158 A GeV/c Studied via pi-/pi+ and K-/K+ Ratios
The effect of the final state Coulomb interaction on particles produced in
Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment
through the study of the pi-/pi+ and K-/K+ ratios measured as a function of
transverse mass. While the ratio for kaons shows no significant transverse mass
dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with
an enhancement that increases with centrality. A silicon pad detector located
near the target is used to estimate the contribution of hyperon decays to the
pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in
which the Coulomb interaction has been incorporated allows to place constraints
on the time of the pion freeze-out.Comment: 9 pages, 12 figure
Central Pb+Pb Collisions at 158 A GeV/c Studied by Pion-Pion Interferometry
Two-particle correlations have been measured for identified negative pions
from central 158 AGeV Pb+Pb collisions and fitted radii of about 7 fm in all
dimensions have been obtained. A multi-dimensional study of the radii as a
function of kT is presented, including a full correction for the resolution
effects of the apparatus. The cross term Rout-long of the standard fit in the
Longitudinally CoMoving System (LCMS) and the vl parameter of the generalised
Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a
boost invariant expansion. The shapes of the correlation functions in Qinv and
Qspace have been analyzed in detail. They are not Gaussian but better
represented by exponentials. As a consequence, fitting Gaussians to these
correlation functions may produce different radii depending on the acceptance
of the experimental setup used for the measurement.Comment: 13 pages including 10 figure
Search for Disoriented Chiral Condensates in 158 AGeV Pb+Pb Collisions
The restoration of chiral symmetry and its subsequent breaking through a
phase transition has been predicted to create regions of Disoriented Chiral
Condensates (DCC). This phenomenon has been predicted to cause anomalous
fluctuations in the relative production of charged and neutral pions in
high-energy hadronic and nuclear collisions. The WA98 experiment has been used
to measure charged and photon multiplicities in the central region of 158 AGeV
Pb+Pb collisions at the CERN SPS. In a sample of 212646 events, no clear DCC
signal can be distinguished. Using a simple DCC model, we have set a 90% C.L.
upper limit on the maximum DCC production allowed by the data.Comment: 20 Pages, LaTeX, uses elsart.cls, 8 eps figures included, submitted
to Physics Letters
Single Spin Asymmetry in Polarized Proton-Proton Elastic Scattering at GeV
We report a high precision measurement of the transverse single spin
asymmetry at the center of mass energy GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The was measured
in the four-momentum transfer squared range \GeVcSq, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
and its -dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this , we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure
Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at GeV
We present first measurements of the evolution of the differential transverse
momentum correlation function, {\it C}, with collision centrality in Au+Au
interactions at GeV. {\it C} exhibits a strong dependence
on collision centrality that is qualitatively similar to that of number
correlations previously reported. We use the observed longitudinal broadening
of the near-side peak of {\it C} with increasing centrality to estimate the
ratio of the shear viscosity to entropy density, , of the matter formed
in central Au+Au interactions. We obtain an upper limit estimate of
that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
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