457 research outputs found
Biophysical, morphological, canopy optical property, and productivity data from the Superior National Forest
Described here are the results of a NASA field experiment conducted in the Superior National Forest near Ely, Minnesota, during the summers of 1983 and 1984. The purpose of the experiment was to examine the use of remote sensing to provide measurements of biophysical parameters in the boreal forests. Leaf area index, biomass, net primary productivity, canopy coverage, overstory and understory species composition data are reported for about 60 sites, representing a range of stand density and age for aspen and spruce. Leaf, needle, and bark high-resolution spectral reflectance and transmittance data are reported for the major boreal forest species. Canopy bidirectional reflectance measurements are provided from a helicopter-mounted Barnes Multiband Modular Radiometer (MMR) and the Thematic Mapper Simulator (TMS) on the NASA C-130 aircraft
On the worldsheet theories of strings dual to free large N gauge theories
We analyze in detail some properties of the worldsheet of the closed string
theories suggested by Gopakumar to be dual to free large N SU(N) gauge theories
(with adjoint matter fields). We use Gopakumar's prescription to translate the
computation of space-time correlation functions to worldsheet correlation
functions for several classes of Feynman diagrams, by explicit computations of
Strebel differentials. We compute the worldsheet operator product expansion in
several cases and find that it is consistent with general worldsheet conformal
field theory expectations. A peculiar property of the construction is that in
several cases the resulting worldsheet correlation functions are non-vanishing
only on a sub-space of the moduli space (say, for specific relations between
vertex positions). Another strange property we find is that for a conformally
invariant space-time theory, the mapping to the worldsheet does not preserve
the special conformal symmetries, so that the full conformal group is not
realized as a global symmetry on the worldsheet (even though it is, by
construction, a symmetry of all integrated correlation functions).Comment: 60 pages, 17 figures, latex. v2: Added references and a minor
correctio
From Matrices to Strings and Back
We discuss an explicit construction of a string dual for the Gaussian matrix
model. Starting from the matrix model and employing Strebel differential
techniques we deduce hints about the structure of the dual string. Next,
following these hints a worldheet theory is constructed. The correlators in
this string theory are assumed to localize on a finite set of points in the
moduli space of Riemann surfaces. To each such point one associates a Feynman
diagram contributing to the correlator in the dual matrix model, and thus
recasts the worldsheet expression as a sum over Feynman diagrams.Comment: 27 pages, 3 figure
Pair Interaction Potentials of Colloids by Extrapolation of Confocal Microscopy Measurements of Collective Structure
A method for measuring the pair interaction potential between colloidal
particles by extrapolation measurement of collective structure to infinite
dilution is presented and explored using simulation and experiment. The method
is particularly well suited to systems in which the colloid is fluorescent and
refractive index matched with the solvent. The method involves characterizing
the potential of mean force between colloidal particles in suspension by
measurement of the radial distribution function using 3D direct visualization.
The potentials of mean force are extrapolated to infinite dilution to yield an
estimate of the pair interaction potential, . We use Monte Carlo (MC)
simulation to test and establish our methodology as well as to explore the
effects of polydispersity on the accuracy. We use poly-12-hydroxystearic
acid-stabilized poly(methyl methacrylate) (PHSA-PMMA) particles dispersed in
the solvent dioctyl phthalate (DOP) to test the method and assess its accuracy
for three different repulsive systems for which the range has been manipulated
by addition of electrolyte.Comment: 35 pages, 14 figure
Triangulated Surfaces in Twistor Space: A Kinematical Set up for Open/Closed String Duality
We exploit the properties of the three-dimensional hyperbolic space to
discuss a simplicial setting for open/closed string duality based on (random)
Regge triangulations decorated with null twistorial fields. We explicitly show
that the twistorial N-points function, describing Dirichlet correlations over
the moduli space of open N-bordered genus g surfaces, is naturally mapped into
the Witten-Kontsevich intersection theory over the moduli space of N-pointed
closed Riemann surfaces of the same genus. We also discuss various aspects of
the geometrical setting which connects this model to PSL(2,C) Chern-Simons
theory.Comment: 35 pages, references added, slightly revised introductio
A paradigm of open/closed duality: Liouville D-branes and the Kontsevich model
We argue that topological matrix models (matrix models of the Kontsevich
type) are examples of exact open/closed duality. The duality works at finite N
and for generic `t Hooft couplings. We consider in detail the paradigm of the
Kontsevich model for two-dimensional topological gravity. We demonstrate that
the Kontsevich model arises by topological localization of cubic open string
field theory on N stable branes. Our analysis is based on standard worldsheet
methods in the context of non-critical bosonic string theory. The stable branes
have Neumann (FZZT) boundary conditions in the Liouville direction. Several
generalizations are possible.Comment: v2: References added; a new section with generalization to non-zero
bulk cosmological constant; expanded discussion on topological localization;
added some comment
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HRM practices used to promote pro-environmental behavior: a UK survey
To date, the extent to which UK organizations use human resource management (HRM) practices to promote pro-environmental behavior through workplace HRM policies and initiatives is under-researched within the literature. Therefore, this paper presents results of a survey investigating current HRM practices used to promote pro-environmental behavior in a sample of 214 UK organizations representing different sizes and industry sectors. Overall, findings indicated that HRM practices are not used to a great extent to encourage employees to become more pro-environmental. The most prevalent practices used within organizations incorporated elements of management involvement supporting the idea that managers are the gatekeepers to environmental performance. Although organizations indicated that some HRM practices were more effective than others at encouraging pro-environmental behavior in their staff, only a very small percentage of organizations actually conducted any form of evaluation; organizations consequently lack clear evidence as to whether their HRM practices actually result in employee behavior change. Practical implications and future research directions are discussed
A long-lasting measles epidemic in Maroua, Cameroon 2008-2009: mass vaccination as response to the epidemic.
A measles outbreak occurred in Maroua, Cameroon, from January 2008 to April 2009. In accordance with recent World Health Organization guidelines, an outbreak-response immunization (ORI) was conducted in January 2009. The aim of this study was to investigate the causes of the epidemic in order to guide vaccination strategies
A Bright, Slow Cryogenic Molecular Beam Source for Free Radicals
We demonstrate and characterize a cryogenic buffer gas-cooled molecular beam
source capable of producing bright beams of free radicals and refractory
species. Details of the beam properties (brightness, forward velocity
distribution, transverse velocity spread, rotational and vibrational
temperatures) are measured under varying conditions for the molecular species
SrF. Under typical conditions we produce a beam of brightness 1.2 x 10^11
molecules/sr/pulse in the rovibrational ground state, with 140 m/s forward
velocity and a rotational temperature of approximately 1 K. This source
compares favorably to other methods for producing beams of free radicals and
refractory species for many types of experiments. We provide details of
construction that may be helpful for others attempting to use this method.Comment: 15 pages, 14 figure
Mappings of least Dirichlet energy and their Hopf differentials
The paper is concerned with mappings between planar domains having least
Dirichlet energy. The existence and uniqueness (up to a conformal change of
variables in the domain) of the energy-minimal mappings is established within
the class of strong limits of homeomorphisms in the
Sobolev space , a result of considerable interest in the
mathematical models of Nonlinear Elasticity. The inner variation leads to the
Hopf differential and its trajectories.
For a pair of doubly connected domains, in which has finite conformal
modulus, we establish the following principle:
A mapping is energy-minimal if and only if
its Hopf-differential is analytic in and real along the boundary of .
In general, the energy-minimal mappings may not be injective, in which case
one observes the occurrence of cracks in . Nevertheless, cracks are
triggered only by the points in the boundary of where fails to be
convex. The general law of formation of cracks reads as follows:
Cracks propagate along vertical trajectories of the Hopf differential from
the boundary of toward the interior of where they eventually terminate
before making a crosscut.Comment: 51 pages, 4 figure
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