29,550 research outputs found
Perspectives on Pfaffians of Heterotic World-sheet Instantons
To fix the bundle moduli of a heterotic compactification one has to
understand the Pfaffian one-loop prefactor of the classical instanton
contribution. For compactifications on elliptically fibered Calabi-Yau spaces X
this can be made explicit for spectral bundles and world-sheet instantons
supported on rational base curves b: one can express the Pfaffian in a closed
algebraic form as a polynomial, or it may be understood as a theta-function
expression. We elucidate the connection between these two points of view via
the respective perception of the relevant spectral curve, related to its
extrinsic geometry in the ambient space (the elliptic surface in X over b) or
to its intrinsic geometry as abstract Riemann surface. We identify, within a
conceptual description, general vanishing loci of the Pfaffian, and derive
bounds on the vanishing order, relevant to solutions of W=dW=0.Comment: 40 pages; minor changes, discussion section 1.1 adde
An Improved Procedure for Laboratory Rearing of the Corn Earworm, \u3ci\u3eHeliothis Zea\u3c/i\u3e (Lepidoptera: Noctuidae)
An improved method for the laboratory rearing of the corn earworm. Heliothis zea, described. The rearing medium is a modification of the commonly used wheat germ An oviposition chamber, a feeder for adults, and a simple and inexpensive contrnlled humidity chamber are described
A study to determine the flight characteristics and handling qualitites of variable geometry spacecraft. Volume 3: Low L/D concept with fold-down wings
A study was conducted to determine the flight characteristics and wing deployment transients for a variable geometry spacecraft concept having a hypersonic lift-to-drag ratio near 1.0, and employing fold-down wings. Unpowered flight conditions were considered throughout the study. The body of the spacecraft uses a trapezoidal cross section. The variable geometry wings, stowed in the sides of the vehicle, are deployed at transonic speeds
Acoustic tests of a 15.2 centimeter-diameter potential flow convergent nozzle
An experimental investigation of the jet noise radiated to the far field from a 15.2-cm-diam potential flow convergent nozzle has been conducted. Tests were made with unheated airflow over a range of subsonic nozzle exhaust velocities from 62 to 310m/sec. Mean and turbulent velocity measurements in the flow field of the nozzle exhaust indicated no apparent flow anomalies. Acoustic measurements yielded data uncontaminated by internal and/or background noise to velocities as low as 152m/sec. Finally, no significantly different acoustic characteristics between the potential flow nozzle and simple convergent nozzles were found
Role of geometrical symmetry in thermally activated processes in clusters of interacting dipolar moments
Thermally activated magnetization decay is studied in ensembles of clusters
of interacting dipolar moments by applying the master-equation formalism, as a
model of thermal relaxation in systems of interacting single-domain
ferromagnetic particles. Solving the associated master-equation reveals a
breakdown of the energy barrier picture depending on the geometrical symmetry
of structures. Deviations are most pronounced for reduced symmetry and result
in a strong interaction dependence of relaxation rates on the memory of system
initialization. A simple two-state system description of an ensemble of
clusters is developed which accounts for the observed anomalies. These results
follow from a semi-analytical treatment, and are fully supported by kinetic
Monte-Carlo simulations.Comment: 9 pages, 6 figure
Flame zone of a composite propellant expanded by a laser source
Technique scales flame structure linearly with gas kinetic mean free path, which increases two to three orders of magnitude as pressure decreases like amount. Kinetic and transport time scales expand in proportion so that regression rates for laser-induced flames are two to three orders of magnitude slower
de Finetti reductions for correlations
When analysing quantum information processing protocols one has to deal with
large entangled systems, each consisting of many subsystems. To make this
analysis feasible, it is often necessary to identify some additional structure.
de Finetti theorems provide such a structure for the case where certain
symmetries hold. More precisely, they relate states that are invariant under
permutations of subsystems to states in which the subsystems are independent of
each other. This relation plays an important role in various areas, e.g., in
quantum cryptography or state tomography, where permutation invariant systems
are ubiquitous. The known de Finetti theorems usually refer to the internal
quantum state of a system and depend on its dimension. Here we prove a
different de Finetti theorem where systems are modelled in terms of their
statistics under measurements. This is necessary for a large class of
applications widely considered today, such as device independent protocols,
where the underlying systems and the dimensions are unknown and the entire
analysis is based on the observed correlations.Comment: 5+13 pages; second version closer to the published one; new titl
Extended Hodge Theory for Fibred Cusp Manifolds
For a particular class of pseudo manifolds, we show that the intersection
cohomology groups for any perversity may be naturally represented by extended
weighted harmonic forms for a complete metric on the regular stratum with
respect to some weight determined by the perversity. Extended weighted
harmonic forms are harmonic forms that are almost in the given weighted
space for the metric in question, but not quite. This result is akin to the
representation of absolute and relative cohomology groups for a manifold with
boundary by extended harmonic forms on the associated manifold with cylindrical
ends. As in that setting, in the unweighted case, the boundary values of
the extended harmonic forms define a Lagrangian splitting of the boundary space
in the long exact sequence relating upper and lower middle perversity
intersection cohomology groups.Comment: 26 page
Combinatorial Games with a Pass: A dynamical systems approach
By treating combinatorial games as dynamical systems, we are able to address
a longstanding open question in combinatorial game theory, namely, how the
introduction of a "pass" move into a game affects its behavior. We consider two
well known combinatorial games, 3-pile Nim and 3-row Chomp. In the case of Nim,
we observe that the introduction of the pass dramatically alters the game's
underlying structure, rendering it considerably more complex, while for Chomp,
the pass move is found to have relatively minimal impact. We show how these
results can be understood by recasting these games as dynamical systems
describable by dynamical recursion relations. From these recursion relations we
are able to identify underlying structural connections between these "games
with passes" and a recently introduced class of "generic (perturbed) games."
This connection, together with a (non-rigorous) numerical stability analysis,
allows one to understand and predict the effect of a pass on a game.Comment: 39 pages, 13 figures, published versio
Composite solid propellant flame microstructure determination Annual report, 23 Jun. 1967 - 22 Jun. 1968
Composite solid propellant flame microstructure determination
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