12,590 research outputs found
(M-theory-)Killing spinors on symmetric spaces
We show how the theory of invariant principal bundle connections for
reductive homogeneous spaces can be applied to determine the holonomy of
generalised Killing spinor covariant derivatives of the form in a purely algebraic and algorithmic way, where is a left-invariant homomorphism. Specialising this
to the case of symmetric M-theory backgrounds (i.e. with a
symmetric space and an invariant closed 4-form), we derive several criteria
for such a background to preserve some supersymmetry and consequently find all
supersymmetric symmetric M-theory backgrounds.Comment: Updated abstract for clarity. Added missing geometries to section 6.
Main result stand
Studies of ''soft tooling'' for a semi- toroidal test tank Final report
Unfeasibility of soft tooling for semi-toroidal test tan
Attosecond electron pulses for 4D diffraction and microscopy
In this contribution, we consider the advancement of ultrafast electron diffraction and microscopy to cover the attosecond time domain. The concept is centered on the compression of femtosecond electron packets to trains of 15-attosecond pulses by the use of the ponderomotive force in synthesized gratings of optical fields. Such attosecond electron pulses are significantly shorter than those achievable with extreme UV light sources near 25 nm ({approx}50 eV) and have the potential for applications in the visualization of ultrafast electron dynamics, especially of atomic structures, clusters of atoms, and some materials
Deflation at Turnaround for Oscillatory Cosmology
It is suggested that dark energy in a brane world can help reconcile an
infinitely cyclic cosmology with the second law of thermodynamics. A cyclic
cosmology is described, in which dark energy with constant equation of state
leads to a turnaround at finite future time, when entropy is decreased by a
huge factor equal to the inverse of its enhancement during the initial
inflation. Thermodynamic consistency of cyclicity requires the arrow of time to
reverse during contraction. Entropy reduction in the contracting phase is
infinitesimally smaller than entropy increase during expansion.Comment: 11 pages late
Looking for Intermediate-Mass Black Holes
A discussion of the entropy of the universe leads to the suggestion of very
many intermediate-mass black holes between thirty and three hundred thousand
solar masses in the halo. It is consistent with observations on wide binaries
as well as microlensing and considerations of disk stability that such IMBHs
constitute all cold dark matterComment: 4pp latex. Plenary talk at BSM-LHC conference, Northeastern
University, June 200
Entropy of Contracting Universe in Cyclic Cosmology
Following up a recent proposal \cite{BF} for a cyclic model based on phantom
dark energy, we examine the content of the contracting universe (cu) and its
entropy . We find that beyond dark energy the universe contains on
average zero or at most a single photon which if present immediately after
turnaround has infinitesimally energy which subsequently blue shifts to produce
pairs. These statements are independent of the equation of state
of dark energy provided . Thus and
if observations confirm the entropy problem is solved. We discuss
the absence of a theoretical lower bound on , then
describe an anthropic fine tuning argument that renders unlikely extremely
small . The present bound already implies a time
until turnaround of Gy.Comment: 5 pages late
CHARTS FOR EQUILIBRIUM FLOW PROPERTIES OF AIR IN HYPERVELOCITY NOZZLES
Charts for equilibrium flow properties of air in hypervelocity nozzle
Changes in the Balance Sheet of the U.S. Manufacturing Sector, 1926-1977
This is a report on the results of a research project, sponsored by the NBER's Program on Financial Markets and Monetary Economics, which involves the collection and organization of income account and balance sheet data, at the firm level, for the years 1926-77. The primary data source for the study is Moody's Industrial Manual. Working at the firm level, it is possible to obtain accurate information on the market values of traded securities.This paper presents and discusses some of the aggregate characteristics of the dataset and also reports the results of estimating a simple portfolio model which attempts to explain changes in firm balance sheet flows for the periods 1927-35 and 1965-77.The data collected for the study, as well as software necessary to manage them efficiently, are available from the authors. An NBER Technical Paper will shortly be available to describe the dataset and software in detail.
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