48,659 research outputs found
High Speed Balancing Applied to the T700 Engine
The work performed under Contracts NAS3-23929 and NAS3-24633 is presented. MTI evaluated the feasibility of high-speed balancing for both the T700 power turbine rotor and the compressor rotor. Modifications were designed for the existing Corpus Christi Army Depot (CCAD) T53/T55 high-speed balancing system for balancing T700 power turbine rotors. Tests conducted under these contracts included a high-speed balancing evaluation for T700 power turbines in the Army/NASA drivetrain facility at MTI. The high-speed balancing tests demonstrated the reduction of vibration amplitudes at operating speed for both low-speed balanced and non-low-speed balanced T700 power turbines. In addition, vibration data from acceptance tests of T53, T55, and T700 engines were analyzed and a vibration diagnostic procedure developed
A reciprocal theorem for a mixture theory
A dynamic reciprocal theorem for a linearized theory of interacting media is developed. The constituents of the mixture are a linear elastic solid and a linearly viscous fluid. In addition to Steel's field equations, boundary conditions and inequalities on the material constants that have been shown by Atkin, Chadwick and Steel to be sufficient to guarantee uniqueness of solution to initial-boundary value problems are used. The elements of the theory are given and two different boundary value problems are considered. The reciprocal theorem is derived with the aid of the Laplace transform and the divergence theorem and this section is concluded with a discussion of the special cases which arise when one of the constituents of the mixture is absent
Object-oriented construction of a multigrid electronic-structure code with Fortran 90
We describe the object-oriented implementation of a higher-order
finite-difference density-functional code in Fortran 90. Object-oriented models
of grid and related objects are constructed and employed for the implementation
of an efficient one-way multigrid method we have recently proposed for the
density-functional electronic-structure calculations. Detailed analysis of
performance and strategy of the one-way multigrid scheme will be presented.Comment: 24 pages, 6 figures, to appear in Comput. Phys. Com
Accurate ab initio anharmonic force field and heat of formation for silane, SiH_4
From large basis set coupled cluster calculations and a minor empirical
adjustment, an anharmonic force field for silane has been derived that is
consistently of spectroscopic quality ( on vibrational
fundamentals) for all isotopomers of silane studied. Inner-shell polarization
functions have an appreciable effect on computed properties and even on
anharmonic corrections. From large basis set coupled cluster calculations and
extrapolations to the infinite-basis set limit, we obtain TAE_0=303.80 \pm 0.18
kcal/mol, which includes an anharmonic zero-point energy (19.59 kcal/mol),
inner-shell correlation (-0.36 kcal/mol), scalar relativistic corrections
(-0.70 kcal/mol), and atomic spin-orbit corrections (-0.43 kcal/mol). In
combination with the recently revised \HVSI{0}, we obtain , in between the two established
experimental values.Comment: Mol. Phys., in pres
Disorder Enhanced Spin Polarization in Diluted Magnetic Semiconductors
We present a theoretical study of diluted magnetic semiconductors that
includes spin-orbit coupling within a realistic host band structure and treats
explicitly the effects of disorder due to randomly substituted Mn ions. While
spin-orbit coupling reduces the spin polarization by mixing different spin
states in the valence bands, we find that disorder from Mn ions enhances the
spin polarization due to formation of ferromagnetic impurity clusters and
impurity bound states. The disorder leads to large effects on the hole carriers
which form impurity bands as well as hybridizing with the valence band. For Mn
doping 0.01 < x < 0.04, the system is metallic with a large effective mass and
low mobility
Stem cell mechanobiology
Stem cells are undifferentiated cells that are capable of proliferation, self-maintenance and differentiation towards specific cell phenotypes. These processes are controlled by a variety of cues including physicochemical factors associated with the specific mechanical environment in which the cells reside. The control of stem cell biology through mechanical factors remains poorly understood and is the focus of the developing field of mechanobiology. This review provides an insight into the current knowledge of the role of mechanical forces in the induction of differentiation of stem cells. While the details associated with individual studies are complex and typically associated with the stem cell type studied and model system adopted, certain key themes emerge. First, the differentiation process affects the mechanical properties of the cells and of specific subcellular components. Secondly, that stem cells are able to detect and respond to alterations in the stiffness of their surrounding microenvironment via induction of lineage-specific differentiation. Finally, the application of external mechanical forces to stem cells, transduced through a variety of mechanisms, can initiate and drive differentiation processes. The coalescence of these three key concepts permit the introduction of a new theory for the maintenance of stem cells and alternatively their differentiation via the concept of a stem cell 'mechano-niche', defined as a specific combination of cell mechanical properties, extracellular matrix stiffness and external mechanical cues conducive to the maintenance of the stem cell population.<br/
W4 theory for computational thermochemistry: in pursuit of confident sub-kJ/mol predictions
In an attempt to improve on our earlier W3 theory [J. Chem. Phys. {\bf 120},
4129 (2004)] we consider such refinements as more accurate estimates for the
contribution of connected quadruple excitations (), inclusion of
connected quintuple excitations (), diagonal Born-Oppenheimer
corrections (DBOC), and improved basis set extrapolation procedures. Revised
experimental data for validation purposes were obtained from the latest version
of the ATcT (Active Thermochemical Tables) Thermochemical Network. We found
that the CCSDTQCCSDT(Q) difference converges quite rapidly with the basis
set, and that the formula
1.10[CCSDT(Q)/cc-pVTZ+CCSDTQ/cc-pVDZCCSDT(Q)/cc-pVDZ] offers a very reliable
as well as fairly cost-effective estimate of the basis set limit
contribution. The largest contribution found in the present work is
on the order of 0.5 kcal/mol (for ozone). DBOC corrections are significant at
the 0.1 kcal/mol level in hydride systems. . Based on the accumulated
experience, a new computational thermochemistry protocol for first-and
second-row main-group systems, to be known as W4 theory, is proposed. Our W4
atomization energies for a number of key species are in excellent agreement
(better than 0.1 kcal/mol on average, 95% confidence intervals narrower than 1
kJ/mol) with the latest experimental data obtained from Active Thermochemical
Tables. A simple {\em a priori} estimate for the importance of post-CCSD(T)
correlation contributions (and hence a pessimistic estimate for the error in a
W2-type calculation) is proposed.Comment: J. Chem. Phys., in press; electronic supporting information available
at http://theochem.weizmann.ac.il/web/papers/w4.htm
Cloning and characterisation of multiple ferritin isoforms in the Atlantic salmon (Salmo salar)
Peer reviewedPublisher PD
A weighted cellular matrix-tree theorem, with applications to complete colorful and cubical complexes
We present a version of the weighted cellular matrix-tree theorem that is
suitable for calculating explicit generating functions for spanning trees of
highly structured families of simplicial and cell complexes. We apply the
result to give weighted generalizations of the tree enumeration formulas of
Adin for complete colorful complexes, and of Duval, Klivans and Martin for
skeleta of hypercubes. We investigate the latter further via a logarithmic
generating function for weighted tree enumeration, and derive another
tree-counting formula using the unsigned Euler characteristics of skeleta of a
hypercube and the Crapo -invariant of uniform matroids.Comment: 22 pages, 2 figures. Sections 6 and 7 of previous version simplified
and condensed. Final version to appear in J. Combin. Theory Ser.
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