2,206 research outputs found
The Merits of Separating Global Warming from Extension Education Sustainability Programs
Using the rhetoric of global warming to support the adoption of sustainable practices beneficial to society limits their adoption. Climate data are about to fall outside the models used to settle the global warming issue. Atmospheric carbon dioxide continues to increase, while temperature, since 1998, has decreased. The science is becoming unsettling. Is it time for Extension educators to reevaluate sustainability programming and de-emphasize climate and concentrate instead on the many other beneficial aspects of moving toward a more sustainable future at all levels of Extension programming—agriculture, natural resources, the environment, health, nutrition, and housing
Teaching Hardware Design of Fixed-Point Digital Signal Processing Systems
Signal processing theory and practice are enabling and driving forces behind multimedia devices, communications systems, and even such diverse fields as automotive and medical systems. Over 90 % of the signal processing systems on the market used fixed-point arithmetic because of the cost, power, and area savings that fixed-point systems provide. However, most colleges and universities do not teach or teach only a very little fixed-point signal processing. This issue is being addressed slowly around the country but now a new challenge or opportunity presents itself. As reconfigurable logic technology matures, field-programmable gate arrays (FPGAs) are increasingly used for signal processing systems. They have the advantage of tremendous throughput, great flexibility, and system integration. The challenge is that signal processing in FPGAs is a much less constrained problem than signal processing in special purpose microprocessors. The opportunity arises in that it is now possible to explore more options and, more especially, to take a more systems-level approach to signal processing systems. In short, designing a signal processing system using FPGAs provides opportunities to look at many system design issues and trade-offs in a classroom setting. We have developed a course to teach signal processing in FPGAs at Georgia Institute of Technology and in this paper we consider the challenges and methods of teaching fixedpoint system design in this course. We discuss the topics chosen and how they differ from traditional microprocessor-based courses. We also discuss how systems engineering concepts are woven into the course.
Increasing planet-stirring efficiency of debris disks by "projectile stirring" and "resonant stirring"
Extrasolar debris disks are detected by observing dust, which is thought to
be released during planetesimal collisions. This implies that planetesimals are
dynamically excited ("stirred"), such that collisions are sufficiently common
and violent. The most frequently considered stirring mechanisms are
self-stirring by disk self-gravity, and planet-stirring via secular
interactions. However, these models face problems when considering disk mass,
self-gravity, and planet eccentricity, leading to the possibility that other,
unexplored mechanisms instead stir debris. We hypothesize that planet-stirring
could be more efficient than the traditional secular model implies, due to two
additional mechanisms. First, a planet at the inner edge of a debris disk can
scatter massive bodies onto eccentric, disk-crossing orbits, which then excite
debris ("projectile stirring"). Second, a planet can stir debris over a wide
region via broad mean-motion resonances, both at and between nominal resonance
locations ("resonant stirring"). Both mechanisms can be effective even for
low-eccentricity planets, unlike secular-planet-stirring. We run N-body
simulations across a broad parameter space, to determine the viability of these
new stirring mechanisms. We quantify stirring levels using a bespoke program
for assessing Rebound debris simulations, which we make publicly available. We
find that even low-mass projectiles can stir disks, and verify this with a
simple analytic criterion. We also show that resonant stirring is effective for
planets above ~0.5 MJup. By proving that these mechanisms can increase
planet-stirring efficiency, we demonstrate that planets could still be stirring
debris disks even in cases where conventional (secular) planet-stirring is
insufficient.Comment: 21 pages, 16 figures, accepted for publication in MNRA
Theory of Spike Spiral Waves in a Reaction-Diffusion System
We discovered a new type of spiral wave solutions in reaction-diffusion
systems --- spike spiral wave, which significantly differs from spiral waves
observed in FitzHugh-Nagumo-type models. We present an asymptotic theory of
these waves in Gray-Scott model. We derive the kinematic relations describing
the shape of this spiral and find the dependence of its main parameters on the
control parameters. The theory does not rely on the specific features of
Gray-Scott model and thus is expected to be applicable to a broad range of
reaction-diffusion systems.Comment: 4 pages (REVTeX), 2 figures (postscript), submitted to Phys. Rev.
Let
Discovery of a Galaxy Cluster via Weak Lensing
We report the discovery of a cluster of galaxies via its weak gravitational
lensing effect on background galaxies, the first spectroscopically confirmed
cluster to be discovered through its gravitational effects rather than by its
electromagnetic radiation. This fundamentally different selection mechanism
promises to yield mass-selected, rather than baryon or photon-selected, samples
of these important cosmological probes. We have confirmed this cluster with
spectroscopic redshifts of fifteen members at z=0.276, with a velocity
dispersion of 615 km/s. We use the tangential shear as a function of source
photometric redshift to estimate the lens redshift independently and find z_l =
0.30 +- 0.08. The good agreement with the spectroscopy indicates that the
redshift evolution of the mass function may be measurable from the imaging data
alone in shear-selected surveys.Comment: revised version with minor changes, to appear in ApJ
Two-sided estimates of minimum-error distinguishability of mixed quantum states via generalized Holevo-Curlander bounds
We prove a concise factor-of-2 estimate for the failure rate of optimally
distinguishing an arbitrary ensemble of mixed quantum states, generalizing work
of Holevo [Theor. Probab. Appl. 23, 411 (1978)] and Curlander [Ph.D. Thesis,
MIT, 1979]. A modification to the minimal principle of Cocha and Poor
[Proceedings of the 6th International Conference on Quantum Communication,
Measurement, and Computing (Rinton, Princeton, NJ, 2003)] is used to derive a
suboptimal measurement which has an error rate within a factor of 2 of the
optimal by construction. This measurement is quadratically weighted and has
appeared as the first iterate of a sequence of measurements proposed by Jezek
et al. [Phys. Rev. A 65, 060301 (2002)]. Unlike the so-called pretty good
measurement, it coincides with Holevo's asymptotically optimal measurement in
the case of nonequiprobable pure states. A quadratically weighted version of
the measurement bound by Barnum and Knill [J. Math. Phys. 43, 2097 (2002)] is
proven. Bounds on the distinguishability of syndromes in the sense of
Schumacher and Westmoreland [Phys. Rev. A 56, 131 (1997)] appear as a
corollary. An appendix relates our bounds to the trace-Jensen inequality.Comment: It was not realized at the time of publication that the lower bound
of Theorem 10 has a simple generalization using matrix monotonicity (See [J.
Math. Phys. 50, 062102]). Furthermore, this generalization is a trivial
variation of a previously-obtained bound of Ogawa and Nagaoka [IEEE Trans.
Inf. Theory 45, 2486-2489 (1999)], which had been overlooked by the autho
Probing the Relation Between X-ray-Derived and Weak-Lensing-Derived Masses for Shear-Selected Galaxy Clusters: I. A781
We compare X-ray and weak-lensing masses for four galaxy clusters that
comprise the top-ranked shear-selected cluster system in the Deep Lens Survey.
The weak-lensing observations of this system, which is associated with A781,
are from the Kitt Peak Mayall 4-m telescope, and the X-ray observations are
from both Chandra and XMM-Newton. For a faithful comparison of masses, we adopt
the same matter density profile for each method, which we choose to be an NFW
profile. Since neither the X-ray nor weak-lensing data are deep enough to well
constrain both the NFW scale radius and central density, we estimate the scale
radius using a fitting function for the concentration derived from cosmological
hydrodynamic simulations and an X-ray estimate of the mass assuming
isothermality. We keep this scale radius in common for both X-ray and
weak-lensing profiles, and fit for the central density, which scales linearly
with mass. We find that for three of these clusters, there is agreement between
X-ray and weak-lensing NFW central densities, and thus masses. For the other
cluster, the X-ray central density is higher than that from weak-lensing by 2
sigma. X-ray images suggest that this cluster may be undergoing a merger with a
smaller cluster. This work serves as an additional step towards understanding
the possible biases in X-ray and weak-lensing cluster mass estimation methods.
Such understanding is vital to efforts to constrain cosmology using X-ray or
weak-lensing cluster surveys to trace the growth of structure over cosmic time.Comment: 14 pages, 7 figures, matches version in Ap
Application performance of elements in a floating–gate FPAA
Field–programmable analog arrays (FPAAs) provide a method for rapidly prototyping analog systems. Currently available commercial and academic FPAAs are typically based on operational amplifiers (or other similar analog primitives) with only a few computational elements per chip. While their specific architectures vary, their small sizes and often restrictive interconnect designs leave current FPAAs limited in functionality, flexibility, and usefulness. In this paper, we explore the use of floating–gate devices as the core programmable element in a signal processing FPAA. A generic FPAA architecture is presented that offers increased functionality and flexibility in realizing analog systems. In addition, the computational analog elements are shown to be widely and accurately programmable while remaining small in area. 1. LOW–POWER SIGNAL PROCESSING The future of FPAAs lie in their ability to speed the implementatio
Boolean network model predicts cell cycle sequence of fission yeast
A Boolean network model of the cell-cycle regulatory network of fission yeast
(Schizosaccharomyces Pombe) is constructed solely on the basis of the known
biochemical interaction topology. Simulating the model in the computer,
faithfully reproduces the known sequence of regulatory activity patterns along
the cell cycle of the living cell. Contrary to existing differential equation
models, no parameters enter the model except the structure of the regulatory
circuitry. The dynamical properties of the model indicate that the biological
dynamical sequence is robustly implemented in the regulatory network, with the
biological stationary state G1 corresponding to the dominant attractor in state
space, and with the biological regulatory sequence being a strongly attractive
trajectory. Comparing the fission yeast cell-cycle model to a similar model of
the corresponding network in S. cerevisiae, a remarkable difference in
circuitry, as well as dynamics is observed. While the latter operates in a
strongly damped mode, driven by external excitation, the S. pombe network
represents an auto-excited system with external damping.Comment: 10 pages, 3 figure
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