42,507 research outputs found
Fuel transfer system permits rapid coupling
Docking and fuel transfer system provides an efficient method for transferring fuel from a tanker to another vehicle. With this system, no triggering operation is required prior to docking, the support system can be rigidized by simply locking the rams of shock absorbers, and no separate fuel line coupling action is required
New correction procedures for the fast field program which extend its range
A fast field program (FFP) algorithm was developed based on the method of Lee et al., for the prediction of sound pressure level from low frequency, high intensity sources. In order to permit accurate predictions at distances greater than 2 km, new correction procedures have had to be included in the algorithm. Certain functions, whose Hankel transforms can be determined analytically, are subtracted from the depth dependent Green's function. The distance response is then obtained as the sum of these transforms and the Fast Fourier Transformation (FFT) of the residual k dependent function. One procedure, which permits the elimination of most complex exponentials, has allowed significant changes in the structure of the FFP algorithm, which has resulted in a substantial reduction in computation time
Chiral Green's Functions in Superconformal Field Theory
By solving the Ward identities in a superconformal field theory we find the
unique three-point Green's functions composed of chiral superfields for N =
1,2,3,4 supersymmetry. We show that the N=1 four-point function with R-charge
equal to one is uniquely determined by the Ward identities up to the
specification of four constants. We discuss why chiral Green's functions above
three-points, with total R-charge greater than N, are not uniquely determined.Comment: 32 pages, no figures, LaTeX2e forma
Asynchronous Variational Integrators
We describe a new class of asynchronous variational integrators (AVI) for nonlinear
elastodynamics. The AVIs are distinguished by the following attributes: (i)
The algorithms permit the selection of independent time steps in each element, and
the local time steps need not bear an integral relation to each other; (ii) the algorithms
derive from a spacetime form of a discrete version of Hamiltonâs variational
principle. As a consequence of this variational structure, the algorithms conserve
local momenta and a local discrete multisymplectic structure exactly.
To guide the development of the discretizations, a spacetime multisymplectic
formulation of elastodynamics is presented. The variational principle used incorporates
both configuration and spacetime reference variations. This allows a unified
treatment of all the conservation properties of the system.A discrete version of reference
configuration is also considered, providing a natural definition of a discrete
energy. The possibilities for discrete energy conservation are evaluated.
Numerical tests reveal that, even when local energy balance is not enforced
exactly, the global and local energy behavior of the AVIs is quite remarkable, a
property which can probably be traced to the symplectic nature of the algorith
The thickness of the shower disc as observed in showers produced by primaries above 10 (19)eV
The thickness of the shower disk has been measured in showers initiated by primaries of energy to 10 the 19th power eV using the large area water Cerenkov detectors of the Haverah Park array. Results are presented which (1) provide supporting evidence for the accuracy of analysis procedures in giant showers, (2) offer an evaluation of the mini-array technique for the detection of giant showers and (3) extend earlier work on developmental fluctuations above 10 to the 19th power eV
Generalised Space-time and Gauge Transformations
We consider the generalised space-time introduced by the author in 2003 in
the context of the non-linear realisation of the semi-direct product of E11 and
its first fundamental representation. For all the fields we propose gauge
transformations which are compatible with the underlying E11 structure. A
crucial role is played by the generalised vielbein that the generalised
space-time possess. We work out the explicit form of the gauge transformations,
at low levels, in four, five and eleven dimensions.Comment: 33 page
Heterobimetallic Complexes of Rhenium and Zinc: Potential Catalysts for Homogeneous Syngas Conversion
6-(Diphenylphosphino)-2,2âČ-bipyridine (PNN) coordinates to rhenium carbonyls in both Îș^1(P) and Îș^2(N,N) modes; in the former, the free bpy moiety readily binds to zinc alkyls and halides. [Re(Îș^1(P)-PNN)(CO)_5][OTf] reacts with dialkylzinc reagents to form [Re(Îș^1(P)-PNN·ZnR)(CO)_4(ÎŒ_(2-)C(O)R)][OTf] (R = Me, Et, Bn), in which an alkyl group has been transferred to a carbonyl carbon and the resulting monoalkyl Zn is bound both to the bpy nitrogens and the acyl oxygen. ZnCl_2 binds readily to the bpy group in Re(Îș^1(P)-PNN)(CO)_4Me, and the resulting adduct undergoes facile migratory insertion, assisted by the Lewis acidic pendent Zn, to yield Re(Îș^1(P)-PNN·ZnCl)(ÎŒ_(2-)Cl)(CO)_3(ÎŒ_(2-)C(O)Me), in which one of the chlorides occupies the sixth coordination site on Re. Migratory insertion is inhibited by THF or other ethers that can coordinate to ZnCl_2. Migratory insertion is also observed for Re(Îș1(P)-PNN)(CO)_4(CH_2Ph) but not for Re(Îș^1(P)-PNN)(CO)_4(CH_2OCH_3); coordination of the methoxy oxygen to Zn appears to block its ability to coordinate to the carbonyl oxygen and facilitate migratory insertion. Intramolecular Lewis acid promoted hydride transfer from [(dmpe)_2PtH][PF_6] to a carbonyl in [Re(Îș^1(P)-PNN)(CO)_5][OTf] results in formation of a Reâformyl species; additional hydride transfer leads to a novel ReâZn-bonded product along with some formal dehyde
E11 and Spheric Vacuum Solutions of Eleven- and Ten dimensional Supergravity Theories
In view of the newly conjectured Kac-Moody symmetries of supergravity
theories placed in eleven and ten dimensions, the relation between these
symmetry groups and possible compactifications are examined. In particular, we
identify the relevant group cosets that parametrise the vacuum solutions of AdS
x S type.Comment: discussion improve
The size of the nucleosome
The structural origin of the size of the 11 nm nucleosomal disc is addressed.
On the nanometer length-scale the organization of DNA as chromatin in the
chromosomes involves a coiling of DNA around the histone core of the
nucleosome. We suggest that the size of the nucleosome core particle is
dictated by the fulfillment of two criteria: One is optimizing the volume
fraction of the DNA double helix; this requirement for close-packing has its
root in optimizing atomic and molecular interactions. The other criterion being
that of having a zero strain-twist coupling; being a zero-twist structure is a
necessity when allowing for transient tensile stresses during the
reorganization of DNA, e.g., during the reposition, or sliding, of a nucleosome
along the DNA double helix. The mathematical model we apply is based on a
tubular description of double helices assuming hard walls. When the base-pairs
of the linker-DNA is included the estimate of the size of an ideal nucleosome
is in close agreement with the experimental numbers. Interestingly, the size of
the nucleosome is shown to be a consequence of intrinsic properties of the DNA
double helix.Comment: 11 pages, 5 figures; v2: minor modification
Generalised geometry, eleven dimensions and E11
We construct the non-linear realisation of E11 and its first fundamental
representation in eleven dimensions at low levels. The fields depend on the
usual coordinates of space-time as well as two form and five form coordinates.
We derive the terms in the dynamics that contain the three form and six form
fields and show that when we restricted their field dependence to be only on
the usual space-time we recover the correct self-duality relation. Should this
result generalise to the gravity fields then the non-linear realisation is an
extension of the maximal supergravity theory, as previously conjectured. We
also comment on the connections between the different approaches to generalised
geometry.Comment: 17 pages, Trivial typos corrected in version one and a substantial
note added which gives the equation of motion relating the gravity field to
its dua
- âŠ