1,210 research outputs found
Computer program compatible with a laser nephelometer
The laser nephelometer data system was updated to provide magnetic tape recording of data, and real time or near real time processing of data to provide particle size distribution and liquid water content. Digital circuits were provided to interface the laser nephelometer to a Data General Nova 1200 minicomputer. Communications are via a teletypewriter. A dual Linc Magnetic Tape System is used for program storage and data recording. Operational programs utilize the Data General Real-Time Operating System (RTOS) and the ERT AIRMAP Real-Time Operating System (ARTS). The programs provide for acquiring data from the laser nephelometer, acquiring data from auxiliary sources, keeping time, performing real time calculations, recording data and communicating with the teletypewriter
Penrose Limits and RG Flows
The Penrose-Gueven limit simplifies a given supergravity solution into a
pp-wave background. Aiming at clarifying its relation to renormalization group
flow we study the Penrose-Guven limit of supergravity backgrounds that are dual
to non-conformal gauge theories. The resulting backgrounds fall in a class
simple enough that the quantum particle is exactly solvable. We propose a map
between the effective time-dependent quantum mechanical problem and the RG flow
in the gauge theory. As a testing ground we consider explicitly two Penrose
limits of the infrared fixed point of the Pilch-Warner solution. We analyze the
corresponding gauge theory picture and write down the operators which are the
duals of the low lying string states. We also address RG flows of a different
nature by considering the Penrose-Gueven limit of a stack of N D_p branes. We
note that in the far IR (for p<3)the limit generically has negative
mass-squared. This phenomenon signals, in the world sheet picture, the
necessity to transform to another description. In this regard, we consider
explicitly the cases of M2 from D2 and F1 from D1 .Comment: 35 pp, 6 figure
Penrose limits, supergravity and brane dynamics
We investigate the Penrose limits of classical string and M-theory
backgrounds. We prove that the number of (super)symmetries of a supergravity
background never decreases in the limit. We classify all the possible Penrose
limits of AdS x S spacetimes and of supergravity brane solutions. We also
present the Penrose limits of various other solutions: intersecting branes,
supersymmetric black holes and strings in diverse dimensions, and cosmological
models. We explore the Penrose limit of an isometrically embedded spacetime and
find a generalisation to spaces with more than one time. Finally, we show that
the Penrose limit is a large tension limit for all branes including those with
fields of Born--Infeld type.Comment: 67 page
Exploring Differences in Business Undergraduate Perceptions by Preferred Classroom Delivery Mode
The purpose of this study was to compare business undergraduate online/hybrid course perceptions across three different preferred classroom environment delivery modes: online, hybrid or face-to-face (F2F). Four different perceptions were measured: perceived favorability of online/hybrid courses (PFoOc); intent to recommend online/hybrid courses; perceived learning; and timely graduation. Undergraduates who were taking at least one online or hybrid class voluntarily completed an online survey. In the fall 2015 a complete-data sample n of 264 respondents was obtained and in the spring 2016 the complete-data sample n was 272. Consistent results across both samples were found for three of four outcomes. Undergraduates who preferred either online or hybrid classroom delivery had significantly higher PFoOC and intent to recommend online/hybrid courses than students preferring F2F. There were no differences in perceived timely graduation across the three classroom delivery mode groups, and inconsistent results were found for perceived learning. The fall sample showed no differences on perceived learning but for the spring sample, undergraduates preferring either an online or hybrid delivery mode perceived higher learning than F2F preferred-mode students. A new, short four-item measure of PFoOC was found to reliable. As universities increase their online and hybrid course offerings keeping course integrity or equivalence between F2F and online/hybrid course sections will be important. Ways to increase the PFoOC for undergraduates who prefer F2F are suggested. Increased PFoOC should lead to higher intent to recommend online/hybrid courses
Homogeneity and plane-wave limits
We explore the plane-wave limit of homogeneous spacetimes. For plane-wave
limits along homogeneous geodesics the limit is known to be homogeneous and we
exhibit the limiting metric in terms of Lie algebraic data. This simplifies
many calculations and we illustrate this with several examples. We also
investigate the behaviour of (reductive) homogeneous structures under the
plane-wave limit.Comment: In memory of Stanley Hobert, 33 pages. Minor corrections and some
simplification of Section 4.3.
Parallelisable Heterotic Backgrounds
We classify the simply-connected supersymmetric parallelisable backgrounds of
heterotic supergravity. They are all given by parallelised Lie groups admitting
a bi-invariant lorentzian metric. We find examples preserving 4, 8, 10, 12, 14
and 16 of the 16 supersymmetries.Comment: 17 pages, AMSLaTe
Dirac-Hestenes spinor fields in Riemann-Cartan spacetime
In this paper we study Dirac-Hestenes spinor fields (DHSF) on a
four-dimensional Riemann-Cartan spacetime (RCST). We prove that these fields
must be defined as certain equivalence classes of even sections of the Clifford
bundle (over the RCST), thereby being certain particular sections of a new
bundle named Spin-Clifford bundle (SCB). The conditions for the existence of
the SCB are studied and are shown to be equivalent to the famous Geroch's
theorem concerning to the existence of spinor structures in a Lorentzian
spacetime. We introduce also the covariant and algebraic Dirac spinor fields
and compare these with DHSF, showing that all the three kinds of spinor fields
contain the same mathematical and physical information. We clarify also the
notion of (Crumeyrolle's) amorphous spinors (Dirac-K\"ahler spinor fields are
of this type), showing that they cannot be used to describe fermionic fields.
We develop a rigorous theory for the covariant derivatives of Clifford fields
(sections of the Clifford bundle (CB)) and of Dirac-Hestenes spinor fields. We
show how to generalize the original Dirac-Hestenes equation in Minkowski
spacetime for the case of a RCST. Our results are obtained from a variational
principle formulated through the multiform derivative approach to Lagrangian
field theory in the Clifford bundle.Comment: 45 pages, special macros kapproc.sty and makro822.te
Power-law singularities in string theory and M-theory
We extend the definition of the Szekeres-Iyer power-law singularities to
supergravity, string and M-theory backgrounds, and find that are characterized
by Kasner type exponents. The near singularity geometries of brane and some
intersecting brane backgrounds are investigated and the exponents are computed.
The Penrose limits of some of these power-law singularities have profiles
for . We find the range of the
exponents for which and the frequency squares are bounded by 1/4. We
propose some qualitative tests for deciding whether a null or timelike
spacetime singularity can be resolved within string theory and M-theory based
on the near singularity geometry and its Penrose limits.Comment: 32 page
New Penrose Limits and AdS/CFT
We find a new Penrose limit of AdS_5 x S^5 giving the maximally
supersymmetric pp-wave background with two explicit space-like isometries. This
is an important missing piece in studying the AdS/CFT correspondence in certain
subsectors. In particular whereas the Penrose limit giving one space-like
isometry is useful for the SU(2) sector of N=4 SYM, this new Penrose limit is
instead useful for studying the SU(2|3) and SU(1,2|3) sectors. In addition to
the new Penrose limit of AdS_5 x S^5 we also find a new Penrose limit of AdS_4
x CP^3.Comment: 30 page
Generalized BF Theory in Superspace as Underlying Theory of 11D Supergravity
We construct a generalized BF theory in superspace that can embed
eleven-dimensional supergravity theory. Our topological BF theory can
accommodate all the necessary Bianchi identities for teleparallel superspace
supergravity in eleven-dimensions, as the simplest but nontrivial solutions to
superfield equations for our superspace action. This indicates that our theory
may have solutions other than eleven-dimensional supergravity, accommodating
generalized theories of eleven-dimensional supergravity. Therefore our
topological theory can be a good candidate for the low energy limit of
M-theory, as an underlying fundamental theory providing a `missing link'
between eleven-dimensional supergravity and M-theory.Comment: 16 pages, latex, two new paragraphs in section 4 and in Concluding
Remarks with two new reference
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