4,566 research outputs found
Higher-Dimensional Algebra VII: Groupoidification
Groupoidification is a form of categorification in which vector spaces are
replaced by groupoids, and linear operators are replaced by spans of groupoids.
We introduce this idea with a detailed exposition of "degroupoidification": a
systematic process that turns groupoids and spans into vector spaces and linear
operators. Then we present three applications of groupoidification. The first
is to Feynman diagrams. The Hilbert space for the quantum harmonic oscillator
arises naturally from degroupoidifying the groupoid of finite sets and
bijections. This allows for a purely combinatorial interpretation of creation
and annihilation operators, their commutation relations, field operators, their
normal-ordered powers, and finally Feynman diagrams. The second application is
to Hecke algebras. We explain how to groupoidify the Hecke algebra associated
to a Dynkin diagram whenever the deformation parameter q is a prime power. We
illustrate this with the simplest nontrivial example, coming from the A2 Dynkin
diagram. In this example we show that the solution of the Yang-Baxter equation
built into the A2 Hecke algebra arises naturally from the axioms of projective
geometry applied to the projective plane over the finite field with q elements.
The third application is to Hall algebras. We explain how the standard
construction of the Hall algebra from the category of representations of a
simply-laced quiver can be seen as an example of degroupoidification. This in
turn provides a new way to categorify - or more precisely, groupoidify - the
positive part of the quantum group associated to the quiver.Comment: 67 pages, 14 eps figures; uses undertilde.sty. This is an expanded
version of arXiv:0812.486
Automated CNC Micromachining for Integrated THz Waveguide Circuits
Computer Numerically Controlled (CNC) machining
of splitblock waveguide circuits has become the primary method
of constructing terahertz waveguide circuits. The majority of
these circuits have been made on traditional CNC machining
centers or on custom-made laboratory machining systems. At
both the University of Arizona and Arizona State University, we
have developed techniques for machining splitblock waveguide
circuits using purpose-built ultra high precision CNC
machining centers designed for micromachining. These systems
combine the automation of a traditional CNC machining center,
including a high capacity toolchanger, workpiece and tool
metrology systems and a large work volume, with the precision
of custom laboratory systems. The systems at UofA and ASU
are built by Kern Micro and deliver typical measured
dimensional accuracies of 2-3 microns. Waveguide surface
finish has been measured with a Veeco white light
interferometric microscope to be Ra~75 nm. Tools of sizes
between 25 microns and 10mm are available, with toolchanger
capacities of 24-32 tools
Smallholder Participation in Agricultural Value Chains: Comparative Evidence from Three Continents
Supermarkets, specialized wholesalers, and processors and agro-exportersâ agricultural value chains have begun to transform the marketing channels into which smallholder farmers sell produce in low-income economies. We develop a conceptual framework through which to study contracting between smallholders and a commodity-processing firm. We then conduct an empirical meta-analysis of agricultural value chains in five countries across three continents (Ghana, India, Madagascar, Mozambique, and Nicaragua). We document patterns of participation, the welfare gains associated with participation, reasons for non-participation, the significant extent of contract non-compliance, and the considerable dynamism of these value chains, as farmers and firms enter and exit frequently.
Millimeter and Submillimeter Survey of the R Corona Australis Region
Using a combination of data from the Antarctic Submillimeter Telescope and
Remote Observatory (AST/RO), the Arizona Radio Observatory Kitt Peak 12m
telescope and the Arizona Radio Observatory 10m Heinrich Hertz Telescope, we
have studied the most active part of the R CrA molecular cloud in multiple
transitions of Carbon Monoxide, HCO and 870\micron continuum emission.
Since R CrA is nearby (130 pc), we are able to obtain physical spatial
resolution as high as 0.01pc over an area of 0.16 pc, with velocity
resolution finer than 1 km/s. Mass estimates of the protostar driving the
mm-wave emission derived from HCO, dust continuum emission and kinematic
techniques point to a young, deeply embedded protostar of 0.5-0.75
M, with a gaseous envelope of similar mass. A molecular outflow is
driven by this source that also contains at least 0.8 M of molecular
gas with 0.5 L of mechanical luminosity. HCO lines show the
kinematic signature of infall motions as well as bulk rotation. The source is
most likely a Class 0 protostellar object not yet visible at near-IR
wavelengths. With the combination of spatial and spectral resolution in our
data set, we are able to disentangle the effects of infall, rotation and
outflow towards this young object.Comment: 29 pages, 9 figures. Accepted for publication in the Astrophysical
Journa
Warm-Dense Molecular Gas in the ISM of Starbursts, LIRGs and ULIRGs
The role of star formation in luminous and ultraluminous infrared galaxies is
a hotly debated issue: while it is clear that starbursts play a large role in
powering the IR luminosity in these galaxies, the relative importance of
possible enshrouded AGNs is unknown. It is therefore important to better
understand the role of star forming gas in contributing to the infrared
luminosity in IR-bright galaxies. The J=3 level of 12CO lies 33K above ground
and has a critical density of ~1.5 X 10^4 cm^-3. The 12CO(J=3-2) line serves as
an effective tracer for warm-dense molecular gas heated by active star
formation. Here we report on 12CO (J=3-2) observations of 17 starburst spirals,
LIRGs and ULIRGs which we obtained with the Heinrich Hertz Submillimeter
Telescope on Mt. Graham, Arizona.
Our main results are the following: 1. We find a nearly linear relation
between the infrared luminosity and warm-dense molecular gas such that the
infrared luminosity increases as the warm-dense molecular gas to the power
0.92; We interpret this to be roughly consistent with the recent results of Gao
& Solomon (2004a,b). 2. We find L_IR/M_H2 ratios ranging from ~10 to ~128
L_sun/M_sun using a standard CO-H2 conversion factor of 3 X 10^20 cm^-2 (K km
s^-1)^-1. If this conversion factor is ~an order of magnitude less, as
suggested in a recent statistical survey (Yao et al. 2003), then 2-3 of our
objects may have significant contributions to the L_IR by dust-enshrouded AGNs.Comment: 15 Pages, 2 figures, Accepted for Publication in Ap
The Chimpanzee Model of Viral Hepatitis: Advances in Understanding the Immune Response and Treatment of Viral Hepatitis
Chimpanzees (Pan troglodytes) have contributed to diverse fields of biomedical research due to their close genetic relationship to humans and in many instances due to the lack of any other animal model. This review focuses on the contributions of the chimpanzee model to research on hepatitis viruses where chimpanzees represented the only animal model (hepatitis B and C) or the most appropriate animal model (hepatitis A). Research with chimpanzees led to the development of vaccines for HAV and HBV that are used worldwide to protect hundreds of millions from these diseases and, where fully implemented, have provided immunity for entire generations. More recently, chimpanzee research was instrumental in the development of curative therapies for hepatitis C virus infections. Over a span of 40 years, this research would identify the causative agent of NonA,NonB hepatitis, validate the molecular tools for drug discovery, and provide safety and efficacy data on the therapies that now provide a rapid and complete cure of HCV chronic infections. Several cocktails of antivirals are FDA approved that eliminate the virus following 12 weeks of once-per-day oral therapy. This represents the first cure of a chronic viral disease and, once broadly implemented, will dramatically reduce the occurrence of cirrhosis and liver cancer. The recent contributions of chimpanzees to our current understanding of T cell immunity for HCV, development of novel therapeutics for HBV, and the biology of HAV are reviewed. Finally, a perspective is provided on the events leading to the cessation of the use of chimpanzees in research and the future of the chimpanzees previously used to bring about these amazing breakthroughs in human healthcare
Smallholder Participation in Agricultural Value Chains: Comparative Evidence from Three Continents
Supermarkets, specialized wholesalers, and processors and agro-exportersâ agricultural value chains have begun to transform the marketing channels into which smallholder farmers sell produce in low-income economies. We develop a conceptual framework through which to study contracting between smallholders and a commodity-processing firm. We then conduct an empirical meta-analysis of agricultural value chains in five countries across three continents (Ghana, India, Madagascar, Mozambique, and Nicaragua). We document patterns of participation, the welfare gains associated with participation, reasons for non-participation, the significant extent of contract non-compliance, and the considerable dynamism of these value chains, as farmers and firms enter and exit frequently.Agricultural Value Chains, Contract Farming, Africa, Asia, Latin America
Star Formation in the Northern Cloud Complex of NGC 2264
We have made continuum and spectral line observations of several outflow
sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope
(HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics
and outflow energetics of the young stellar systems observed and assesses the
impact star formation is having on the surrounding cloud environment. Our data
set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows
associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS
25 and 27, respectively, in the northern cloud complex. Complementary 870
micron continuum maps were made with the HHT 19 channel bolometer array. Our
results indicate that there is a weak (approximately less than 0.5%) coupling
between outflow kinetic energy and turbulent energy of the cloud. An analysis
of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining
their dynamical integrity except where outflowing material directly interacts
with the core, such as along the outflow axes.Comment: 28 pages including 6 figures, to be published in ApJ 01 July 2006,
v645, 1 issu
Plans for a 10-m Submillimeter-wave Telescope at the South Pole
A 10 meter diameter submillimeter-wave telescope has been proposed for the
NSF Amundsen-Scott South Pole Station. Current evidence indicates that the
South Pole is the best submillimeter-wave telescope site among all existing or
proposed ground-based observatories. Proposed scientific programs place
stringent requirements on the optical quality of the telescope design. In
particular, reduction of the thermal background and offsets requires an
off-axis, unblocked aperture, and the large field of view needed for survey
observations requires shaped optics. This mix of design elements is well-suited
for large scale (square degree) mapping of line and continuum radiation from
submillimeter-wave sources at moderate spatial resolutions (4 to 60 arcsecond
beam size) and high sensitivity (milliJansky flux density levels). the
telescope will make arcminute angular scale, high frequency Cosmic Microwave
Background measurements from the best possible ground-based site, using an
aperture which is larger than is currently possible on orbital or airborne
platforms. Effective use of this telescope will require development of large
(1000 element) arrays of submillimeter detectors which are background-limited
when illuminated by antenna temperatures near 50 K.Comment: 12 pages, 3 figure
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