1,124 research outputs found
Matching of the Heavy-Light Currents with NRQCD Heavy and Improved Naive Light Quarks
One-loop matching of heavy-light currents is carried out for a highly
improved lattice action, including the effects of mixings with dimension 4
O(1/M) and O(a) operators. We use the NRQCD action for heavy quarks, the Asqtad
improved naive action for light quarks, and the Symanzik improved glue action.
These results are being used in recent heavy meson decay constant and
semileptonic form factor calculations on the MILC dynamical configurations.Comment: 3 pages, 3 figures. Talk presented at Lattice2004(heavy
B Leptonic Decays and B- bar B Mixing with 2+1 Flavors of Dynamical Quarks
Calculations of B leptonic decays and B- bar B mixing using NRQCD heavy and
Asqtad light valence quarks on the MILC dynamical configurations are described.
Smearing has been implemented to substantially reduce the statistical errors of
the matrix elements needed for the determination of f_B. The four-fermion
matrix elements needed for the determination of f_{B_s}^2B_{B_s} have been
calculated and a preliminary result is given.Comment: 3 pages, 3 figures, talk given at Lattice2004(heavy), Batavia,
Illinois, 21-26 Jun 200
Clinical implications of the anisotropic analytical algorithm for IMRT treatment planning and verification
PURPOSE:
To determine the implications of the use of the Anisotropic Analytical Algorithm(AAA) for the production and dosimetric verification of IMRT plans for treatments of the
prostate, parotid, nasopharynx and lung.
METHODS:
72 IMRT treatment plans produced using the Pencil Beam Convolution (PBC)algorithm were recalculated using the AAA and the dose distributions compared. 24 of the
plans were delivered to inhomogeneous phantoms and verification measurements made using a pinpoint ionisation chamber. The agreement between the AAA and measurement
was determined.
RESULTS:
Small differences were seen in the prostate plans, with the AAA predicting slightly lower minimum PTV doses. In the parotid plans, there were small increases in the lens and
contralateral parotid doses while the nasopharyngeal plans revealed a reduction in the volume of the PTV covered by the 95% isodose (the V95%) when the AAA was used. Large
changes were seen in the lung plans, the AAA predicting reductions in the minimum PTV dose and large reductions in the V95%. The AAA also predicted small increases in the mean
dose to the normal lung and the V20. In the verification measurements, all AAA calculations were within 3% or 3.5mm distance to agreement of the measured doses.
Conclusions: The AAA should be used in preference to the PBC algorithm for treatments involving low density tissue but this may necessitate re-evaluation of plan acceptability
criteria. Improvements to the Multi-Resolution Dose Calculation algorithm used in the inverse planning are required to reduce the convergence error in the presence of lung tissue. There was excellent agreement between the AAA and verification measurements for all sites
Stress Analysis and Testing at the Marshall Space Flight Center to Study Cause and Corrective Action of Space Shuttle External Tank Stringer Failures
After the launch scrub of Space Shuttle mission STS-133 on November 5, 2010, large cracks were discovered in two of the External Tank intertank stringers. The NASA Marshall Space Flight Center, as managing center for the External Tank Project, coordinated the ensuing failure investigation and repair activities with several organizations, including the manufacturer, Lockheed Martin. To support the investigation, the Marshall Space Flight Center formed an ad-hoc stress analysis team to complement the efforts of Lockheed Martin. The team undertook six major efforts to analyze or test the structural behavior of the stringers. Extensive finite element modeling was performed to characterize the local stresses in the stringers near the region of failure. Data from a full-scale tanking test and from several subcomponent static load tests were used to confirm the analytical conclusions. The analysis and test activities of the team are summarized. The root cause of the stringer failures and the flight readiness rationale for the repairs that were implemented are discussed
form factors from lattice QCD with static b quarks
We present a lattice QCD calculation of form factors for the decay , which is a promising channel for determining the CKM
matrix element at the Large Hadron Collider. In this initial study
we work in the limit of static b quarks, where the number of independent form
factors reduces to two. We use dynamical domain-wall fermions for the light
quarks, and perform the calculation at two different lattice spacings and at
multiple values of the light-quark masses in a single large volume. Using our
form factor results, we calculate the
differential decay rate in the range , and
obtain the integral . Combined with future experimental data,
this will give a novel determination of with about 15\% theoretical
uncertainty. The uncertainty is dominated by the use of the static
approximation for the b quark, and can be reduced further by performing the
lattice calculation with a more sophisticated heavy-quark action.Comment: 14 pages, 5 figure
A 3 gigabit/second bit interleaving time division multiplexer and a time division demultiplexer for high speed computing and communications systems
Releasable locking mechanisms
In the aerospace field spacecraft components are held together by separation systems until a specific time when they must be separated or deployed. Customarily a threaded joining bolt engages one of the components to be joined, and a threaded nut is placed on that bolt against the other component so they can be drawn together by a releasable locking assembly. The releasable locking assembly herein includes a plunger having one end coupled to one end of a plunger bolt. The other end is flanged to abut and compress a coil spring when the plunger is advanced toward the interface plane between the two components. When the plunger is so advanced toward the interface plane, the end of the plunger bolt can be connected to the joining bolt. Thus during retraction the joining bolt is drawn to one side of the interface plane by the force of the expanding spring
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