617 research outputs found
Numerical Study for a Marine Current Turbine Blade Performance under Varying Angle of Attack
Energy generation from marine currents is a promising technology for sustainable development. The success of using marine current turbines to tap the ocean hydrodynamic energy depends on predicting the hydrodynamic characteristics and performance of such turbines. This paper presents an analysis of the two-dimensional flow using commercial CFD software over a marine current turbine blade. The 2D flow is simulated for HF-SX NACA foil modified from S1210 NACA foil at various angles of attack with Reynolds number of 19×104, which represents the marine current flow. The hydrofoil is designed with considerations for lift and drag coefficients. The flow is simulated by solving the steady-state Navier-Stokes equations coupled with the k-ω shear stress transport (SST) turbulence model. The aim of this work is to study the effect of the angle of attack on the lift and drag coefficients. The computational domain is composed of non-homogenous structured meshing, with sufficient refinement of the domain near the foil blade in order to capture the boundary layer effects. Hence, all calculations are done at constant flow velocity while varying the angle attack for every model tested. The results have shown that the drag and lift coefficient, Cd and Cl coefficient increases with increasing the value of the angle of attack, ratio Cl/Cd curve related on performance at the peak 7o angle of attack
Magnetic monopoles from gauge theory phase transitions
Thermal fluctuations of the gauge field lead to monopole formation at the
grand unified phase transition in the early Universe, even if the transition is
merely a smooth crossover. The dependence of the produced monopole density on
various parameters is qualitatively different from theories with global
symmetries, and the monopoles have a positive correlation at short distances.
The number density of monopoles may be suppressed if the grand unified symmetry
is only restored for a short time by, for instance, nonthermal symmetry
restoration after preheating.Comment: 5 pages, updated to match the version published in PRD
(http://link.aps.org/abstract/PRD/v68/e021301) on 11 July 200
The risk of cardiac failure following metal-on-metal hip arthroplasty
Aims
The aim of this study was to determine whether patients with metal-on-metal (MoM)
arthroplasties of the hip have an increased risk of cardiac failure compared with those with
alternative types of arthroplasties (non-MoM).
Patients and Methods
A linkage study between the National Joint Registry, Hospital Episodes Statistics and records
of the Office for National Statistics on deaths was undertaken. Patients who underwent
elective total hip arthroplasty between January 2003 and December 2014 with no past history
of cardiac failure were included and stratified as having either a MoM (n = 53 529) or a nonMoM
(n = 482 247) arthroplasty. The primary outcome measure was the time to an
admission to hospital for cardiac failure or death. Analysis was carried out using data from
all patients and from those matched by propensity score.
Results
The risk of cardiac failure was lower in the MoM cohort compared with the non-MoM cohort
(adjusted hazard ratio (aHR) 0.901; 95% confidence interval (CI) 0.853 to 0.953). The risk of
cardiac failure was similar following matching (aHR 0.909; 95% CI 0.838 to 0.987) and the
findings were consistent in subgroup analysis.
Conclusion
The risk of cardiac failure following total hip arthroplasty was not increased in those in
whom MoM implants were used, compared with those in whom other types of prostheses
were used, in the first seven years after surgery.
Cite this article: Bone Joint J 2018;100-B:20–
The effects of cold working on sensitization and intergranular corrosion behavior of AISI 304 stainless steel
The effects of prior cold rolling of up to an 80 pct reduction in thickness on the sensitization-desensitization behavior of Type AISI 304 stainless steel and its susceptibility to intergranular corrosion have been studied by electrochemical potentiokinetic reactivation (EPR) and Strauss-test methods. The results indicate that the prior deformation accelerated the sensitization as compared to the undeformed stainless steel. The deformed Type 304 stainless steel experienced desensitization at higher temperatures and times, and it was found to be enhanced by increased cold deformation. This could be attributed to the increased long-range chromium diffusion, possibly brought on by increasing pipe diffusion and vacancies. The role of the deformation-induced martensite (DIM) and texture, introduced by uniaxial cold rolling, on the sensitization-desensitization kinetics has also been discussed. This study could not reveal any systematic relationship between texture and the degree of sensitization (DOS) obtained. The effect of DIM on DOS seems to be pronounced at 500 °C when the steel retained significant amounts of DIM; however, the retained DIM is insignificant at higher sensitization times and temperatures
Lifetime Differences, direct CP Violation and Partial Widths in D0 Meson Decays to K+K- and pi+pi-
We describe several measurements using the decays D0->K+K- and pi+pi-. We
find the ratio of partial widths, Gamma(D0->K+K-)/Gamma(D0->pi+pi-), to be
2.96+/-0.16+/-0.15, where the first error is statistical and the second is
systematic. We observe no evidence for direct CP violation, obtaining A_CP(KK)
= (0.0+/-2.2+/-0.8)% and A_CP(pipi = (1.9+/-3.2+/-0.8)%. In the limit of no CP
violation we measure the mixing parameter y_CP = -0.012+/-0.025+/-0.014 by
measuring the lifetime difference between D0->K+ K- or pi+pi- and the CP
neutral state, D0->K-pi+. We see no evidence for mixing.Comment: 14 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, submitted to PRD, Rapid Communicatio
Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance
We have made a first measurement of the lepton momentum spectrum in a sample
of events enriched in neutral B's through a partial reconstruction of B0 -->
D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the
Upsilon(4S) resonance by the CLEO II detector, is compared directly to the
inclusive lepton spectrum from all Upsilon(4S) events in the same data set.
These two spectra are consistent with having the same shape above 1.5 GeV/c.
From the two spectra and two other CLEO measurements, we obtain the B0 and B+
semileptonic branching fractions, b0 and b+, their ratio, and the production
ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950
(+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57
+- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes,
tau+/tau0.Comment: 14 page, postscript file also available at
http://w4.lns.cornell.edu/public/CLN
Measurement of the Mass Splittings between the States
We present new measurements of photon energies and branching fractions for
the radiative transitions: Upsilon(2S)->gamma+chi_b(J=0,1,2). The masses of the
chi_b states are determined from the measured radiative photon energies. The
ratio of mass splittings between the chi_b substates,
r==(M[J=2]-M[J=1])/(M[J=1]-M[J=0]) with M the chi_b mass, provides information
on the nature of the bbbar confining potential. We find
r(1P)=0.54+/-0.02+/-0.02. This value is in conflict with the previous world
average, but more consistent with the theoretical expectation that r(1P)<r(2P);
i.e., that this mass splittings ratio is smaller for the chi_b(1P) triplet than
for the chi_b(2P) triplet.Comment: 11 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Radiative Decay Modes of the Meson
Using data recorded by the CLEO-II detector at CESR we have searched for four
radiative decay modes of the meson: ,
, , and . We
obtain 90% CL upper limits on the branching ratios of these modes of , , and
respectively.Comment: 15 page postscript file, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
- …