924 research outputs found
Improved turbine disk design to increase reliability of aircraft jet engines
An analytical study was conducted on a bore entry cooled turbine disk for the first stage of the JT8D-17 high pressure turbine which had the potential to improve disk life over existing design. The disk analysis included the consideration of transient and steady state temperature, blade loading, creep, low cycle fatigue, fracture mechanics and manufacturing flaws. The improvement in life of the bore entry cooled turbine disk was determined by comparing it with the existing disk made of both conventional and advanced (Astroloy) disk materials. The improvement in crack initiation life of the Astroloy bore entry cooled disk is 87% and 67% over the existing disk made of Waspaloy and Astroloy, respectively. Improvement in crack propagation life is 124% over the Waspaloy and 465% over the Astroloy disks. The available kinetic energies of disk fragments calculated for the three disks indicate a lower fragment energy level for the bore entry cooled turbine disk
Nonlinear Realization and Weyl Scale Invariant p=2 Brane
The action of Weyl scale invariant p=2 brane which breaks the target super
Weyl scale symmetry in the N=1, D=4 superspace down to the lower dimensional
Weyl symmetry W(1,2) is derived by the approach of nonlinear realization. The
dual form action for the Weyl scale invariant supersymmetric D2 brane is also
constructed. The interactions of localized matter fields on the brane with the
Nambu-Goldstone fields associated with the breaking of the symmetries in the
superspace and one spatial translation directions are obtained through the
Cartan one-forms of the Coset structures. The covariant derivatives for the
localized matter fields are also obtained by introducing Weyl gauge field as
the compensating field corresponding to the local scale transformation on the
brane world volume.Comment: 20 page
Fluctuating initial conditions in heavy-ion collisions from the Glauber approach
In the framework of the Glauber approach we analyze the shape parameters of
the early-formed system and their event-by-event fluctuations. We test a
variety of models: the conventional wounded nucleon model, a model admixing
binary collisions to the wounded nucleons, a model with hot spots, as well as
the hot-spot model where the deposition of energy occurs with a superimposed
probability distribution. We look in detail at the so-called participant
multipole moments, obtained by an averaging procedure where in each event the
system is translated to its center of mass and aligned with the major principal
axis of the ellipse of inertia. Quantitative comparisons indicate substantial
relative effects for eccentricity in variants of Glauber models. On the other
hand, the dependence of the scaled standard deviation of the participant
eccentricity on the chosen model is weak. For all models the values range from
about 0.5 for the central collisions to about 0.3-0.4 for peripheral
collisions, both for the gold-gold and copper-copper collisions. They are
dominated by statistics and change only by 10-15% from model to model. We
provide an approximate analytic expansion for the multipole moments and their
fluctuations given in terms of the fixed-axes moments. For central collisions
and in the absence of correlations it gives the simple formula for the scaled
standard deviation of the participant eccentricity: sqrt(4/pi-1). Similarly, we
obtain expansions for the radial profiles of the multipole distributions. We
investigate the relevance of the shape-fluctuation effects for jet quenching
and find them important only for very central events. Finally, we argue how
smooth hydro leads to the known result v_4 ~ v_2^2, and further to the
prediction Delta v_4/v_4 = 2 Delta v_2/v_2.Comment: 20 pages, 15 figures, additions include comparison to the CGC result
Superposition models and the multiplicity fluctuations in heavy ion collisions
A class of simple superposition models based on the Glauber picture of
multiple collisions is compared with the data on the centrality dependence of
the multiplicity distributions in a central rapidity bin. We show how the
results depend on the specific assumptions concerning the distributions in the
number of participants and their relations to the distributions of the number
of produced hadrons in various phase space bins. None of the versions of the
model describes satisfactorily the centrality dependence of the scaled
dispersion.Comment: 9 pages, 5 figures, a misprint in formula corrected, accepted for
publication in EPJ
Ultra-relativistic nuclear collisions: event shape engineering
The evolution of the system created in a high energy nuclear collision is
very sensitive to the fluctuations in the initial geometry of the system. In
this letter we show how one can utilize these large fluctuations to select
events corresponding to a specific initial shape. Such an "event shape
engineering" opens many new possibilities in quantitative test of the theory of
high energy nuclear collisions and understanding the properties of high density
hot QCD matter.Comment: 6 pages, 5 figure
Exploring a potential Achilles heel of Mycobacterium tuberculosis: defining the ClpC1 interactome
[no abstract available
Hotter, Denser, Faster, Smaller...and Nearly-Perfect: What's the matter at RHIC?
The experimental and theoretical status of the ``near perfect fluid'' at RHIC
is discussed. While the hydrodynamic paradigm for understanding collisions at
RHIC is well-established, there remain many important open questions to address
in order to understand its relevance and scope. It is also a crucial issue to
understand how the early equilibration is achieved, requiring insight into the
active degrees of freedom at early times.Comment: 10 Pages, 13 Figures, submitted to the proceedings of the Second
Meeting of the APS Topical Group on Hadronic Physics, Nashville, TN, October
22-24, 200
Trace initial interaction from final state observable in relativistic heavy ion collisions
In order to trace the initial interaction in ultra-relativistic heavy ion
collision in all azimuthal directions, two azimuthal multiplicity-correlation
patterns -- neighboring and fixed-to-arbitrary angular-bin correlation patterns
-- are suggested. From the simulation of Au + Au collisions at 200 GeV by using
the Monte Carlo models RQMD with hadron re-scattering and AMPT with and without
string melting, we observe that the correlation patterns change gradually from
out-of-plane preferential one to in-plane preferential one when the centrality
of collision shifts from central to peripheral, meanwhile the anisotropic
collective flow v_2 keeps positive in all cases. This regularity is found to be
model and collision energy independent. The physics behind the two opposite
trends of correlation patterns, in particular, the presence of out-of-plane
correlation patterns at RHIC energy, are discussed.Comment: 5pages, 4figure
Comparing the energy spectra of ultra-high energy cosmic rays measured with EAS arrays
The energy spectra of ultra-high energy cosmic rays (CRs) measured with giant
extensive air shower (EAS) arrays exhibit discrepancies between the flux
intensities and/or estimated CR energies exceeding experimental errors. The
well-known intensity correction factor due to the dispersion of the measured
quantity in the presence of a rapidly falling energy spectrum is insufficient
to explain the divergence. Another source of systematic energy determination
error is proposed concerning the charged particle density measured with the
surface arrays, which arises due to simplifications (namely, the superposition
approximation) in nucleus-nucleus interaction description applied to the shower
modeling. Making use of the essential correction factors results in congruous
CR energy spectra within experimental errors. Residual differences in the
energy scales of giant arrays can be attributed to the actual overall accuracy
of the EAS detection technique used. CR acceleration and propagation model
simulations using the dip and ankle scenarios of the transition from galactic
to extragalactic CR components are in agreement with the combined energy
spectrum observed with EAS arrays.Comment: Accepted for publication in Ap
Experimental study of local strong parity violation in relativistic nuclear collisions
Parity-odd domains, corresponding to non-trivial topological solutions of the
QCD vacuum, might be created in relativistic heavy ions collisions. These
domains are predicted to lead to charge separation along the system orbital
momentum of the system created in non-central collisions. Three-particle mixed
harmonics azimuthal correlator is a \P even observable but directly sensitive
to the charge separation effect. Using this observable to analyze Au+Au and
Cu+Cu collisions at and 62 GeV, STAR detects a signal
consistent with several of the theoretical expectations. Possible contributions
from effects not related to parity violation are studied with existing event
generators, which fail to describe the data. Future directions in studying the
effect are discussed.Comment: Proceedings, plenary invited talk at Quark Matter 2009 Conference,
Knoxville, Tennessee. One reference added. Final versio
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