1,347 research outputs found
Vibration Environment and the Rockets
AbstractRockets are subjected to vibrations in various operational phases. Source of vibration may be due to air turbulence, propeller noise, engine noise, stage separation, pyro ignition, release mechanism etc. Some of the sections of rocket houses electronic equipments for data acquisition, navigation purposes etc. Any Structure possessing mass and elasticity vibrate under external disturbances. Electronic equipment can be subjected to many different forms of vibration over a wide range of frequencies and acceleration levels. Vibration is usually considered to be an detrimental condition and can produce many different types of failures in electronic equipment. It is always an endeavour to alleviate or minimize the vibration amplitudes. Wide variety of structures and their components are susceptible to vibration as they are subjected to time dependent forces. If the vibration amplitude of structure escalates to the upper levels, the failure of structures takes place. Vibration suppression has greater significance for aero-space structures, which houses sophisticated electronic equipments, as the high vibration amplitudes hinder the performance of such equipments. In this study it is demonstrated that Tuned Mass Dampers (TMDs) placed with individual modal tuning shows satisfactory performance for the structure subjected to wide band harmonic excitation, transient or random excitations
On the fourth-order accurate compact ADI scheme for solving the unsteady Nonlinear Coupled Burgers' Equations
The two-dimensional unsteady coupled Burgers' equations with moderate to
severe gradients, are solved numerically using higher-order accurate finite
difference schemes; namely the fourth-order accurate compact ADI scheme, and
the fourth-order accurate Du Fort Frankel scheme. The question of numerical
stability and convergence are presented. Comparisons are made between the
present schemes in terms of accuracy and computational efficiency for solving
problems with severe internal and boundary gradients. The present study shows
that the fourth-order compact ADI scheme is stable and efficient
A study on the impact of CYP2C19 genotype and platelet reactivity assay on patients undergoing PCI
AbstractBackgroundA thorough understanding of the patient's genotype and their functional response to a medication is necessary for improving event free survival. Several outcome studies support this view particularly if the patient is to be started on clopidogrel due to the prevalence of clopidogrel resistance. Such guided therapy has reduced the incidence of Major Adverse Cardiac Events (MACE) after stent implantation.MethodsBetween August 2013 and August 2014, 200 patients with coronary artery disease undergoing percutaneous coronary intervention (PCI) were prescribed any one of the anti-platelet medications such as clopidogrel, prasugrel or ticagrelor and offered testing to detect CYP2C19 gene mutations along with a platelet reactivity assay (PRA). Intended outcome was modification of anti-platelet therapy defined as either dose escalation of clopidogrel or replacement of clopidogrel with prasugrel or ticagrelor for the patients in clopidogrel arm, and replacement of ticagrelor or prasugrel with clopidogrel if those patients were non-carrier of mutant genes and also if they demonstrated bleeding tendencies in the ticagrelor and prasugrel arms.ConclusionClopidogrel resistance was observed to be 16.5% in our study population. PRA was useful in monitoring the efficacy of thienopyridines. By having this test, one can be safely maintained on clopidogrel in non-carriers, or with increased dose of clopidogrel in intermediate metabolizers or with newer drugs such as ticagrelor or prasugrel in poor metabolizers. Patients on ticagrelor and prasugrel identified as non-carriers of gene mutations for clopidogrel metabolism could be offered clopidogrel resulting in economic benefits to the patients. Patients at high risk of bleeding were also identified by the PRA
Nonperturbative aspects of the quark-photon vertex
The electromagnetic interaction with quarks is investigated through a
relativistic, electromagnetic gauge-invariant treatment. Gluon dressing of the
quark-photon vertex and the quark self-energy functions is described by the
inhomogeneous Bethe-Salpeter equation in the ladder approximation and the
Schwinger-Dyson equation in the rainbow approximation respectively. Results for
the calculation of the quark-photon vertex are presented in both the time-like
and space-like regions of photon momentum squared, however emphasis is placed
on the space-like region relevant to electron scattering. The treatment
presented here simultaneously addresses the role of dynamically generated
vector bound states and the approach to asymptotic behavior. The
resulting description is therefore applicable over the entire range of momentum
transfers available in electron scattering experiments. Input parameters are
limited to the model gluon two-point function, which is chosen to reflect
confinement and asymptotic freedom, and are largely constrained by the obtained
bound-state spectrum.Comment: 8 figures available on request by email, 25 pages, Revtex,
DOE/ER/40561-131-INT94-00-5
Exploiting the short wavelength gain of silica-based thulium-doped fiber amplifiers
Short wavelength operation (1650-1800 nm) of silica-based thulium-doped fiber amplifiers (TDFAs) is investigated. We report the first demonstration of in-band diode-pumped silica-based TDFAs working in the 1700-1800 nm waveband. Up to 29 dB of small-signal gain is achieved in this spectral region, with an operation wavelength accessible by diode pumping as short as 1710 nm. Further gain extension toward shorter wavelengths is realized in a fiber laser pumped configuration. A silica-based TDFA working in the 1650-1700 nm range with up to 29 dB small-signal gain and noise figure as low as 6.5 dB is presented
Exact Gravitational Shockwaves and Planckian Scattering on Branes
We obtain a solution describing a gravitational shockwave propagating along a
Randall-Sundrum brane. The interest of such a solution is twofold: on the one
hand, it is the first exact solution for a localized source on a
Randall-Sundrum three-brane. On the other hand, one can use it to study forward
scattering at Planckian energies, including the effects of the continuum of
Kaluza-Klein modes. We map out the different regimes for the scattering
obtained by varying the center-of-mass energy and the impact parameter. We also
discuss exact shockwaves in ADD scenarios with compact extra dimensions.Comment: 19 pages, 3 figures. v2: references added, minor improvements and
small errors correcte
Charge symmetry breaking via rho-omega mixing from model quark-gluon dynamics
The quark-loop contribution to the mixing self-energy
function is calculated using a phenomenologically successful QCD-based model
field theory in which the and mesons are composite
bound states. In this calculation the dressed quark propagator, obtained from a
model Dyson-Schwinger equation, is confining. In contrast to previous studies,
the meson- vertex functions are characterised by a strength and range
determined by the dynamics of the model; and the calculated off-mass-shell
behaviour of the mixing amplitude includes the contribution from the calculated
diagonal meson self-energies. The mixing amplitude is shown to be very
sensitive to the small isovector component of dynamical chiral symmetry
breaking. The spacelike quark-loop mixing-amplitude generates an insignificant
charge symmetry breaking nuclear force.Comment: 11 Pages, 3 figures uuencoded and appended to this file, REVTEX 3.0.
ANL-PHY-7718-TH-94, KSUCNR-004-94. [!! PostScript file format corrected.
Retrieve by anonymous ftp from theory.phy.anl.gov (130.202.20.190), directory
pub: mget wpfig*.ps Three files.
Calculating the jet-quenching parameter in STU background
In this paper we use the AdS/CFT correspondence to compute the jet-quenching
parameter in a N=2 thermal plasma. We consider the general three-charge black
hole and discuss some special cases. We add a constant electric field to the
background and find the effect of the electric field on the jet-quenching
parameter. Also we include higher derivative terms and obtain the first-order
correction for the jet-quenching parameter.Comment: 17 pages, 3 figures, revised versio
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