6,532 research outputs found
Estimates of Stellar Weak Interaction Rates for Nuclei in the Mass Range A=65-80
We estimate lepton capture and emission rates, as well as neutrino energy
loss rates, for nuclei in the mass range A=65-80. These rates are calculated on
a temperature/density grid appropriate for a wide range of astrophysical
applications including simulations of late time stellar evolution and x-ray
bursts. The basic inputs in our single particle and empirically inspired model
are i) experimentally measured level and weak decay information, ii) estimates
of matrix elements for allowed experimentally-unmeasured transitions based on
the systematics of experimentally observed allowed transitions, and iii)
estimates of the centroids of the GT resonances motivated by shell model
calculations in the fp shell as well as by (n,p) and (p,n) experiments.
Transitions involving Fermi resonances (isobaric analog states) are also
included and dominate the rates for many interesting proton rich nuclei for
which an experimentally-determined ground state lifetime is unavailable. To
compare our results with more detailed shell model based calculations we also
calculate weak rates for nuclei in the mass range A=60-65 for which Langanke
and Martinez-Pinedo have provided rates. The typical deviation in the electron
capture and B- decay rates for these ~30 nuclei is less than a factor of two or
three for a wide range of temperature and density appropriate for pre-supernova
stellar evolution. We also discuss some subtleties associated with the
partition functions used in calculations of stellar weak rates and show that
the proper treatment of the partition functions is essential for estimating
high temperature beta decay rates. Partition functions based on un-converged
Lanczos calculations can result in estimates of high temperature beta decay
rates that are systematically low.Comment: Tables of rates for nuclei in the mass range A=66-110 are available
from J. Prue
Interactive Correspondence Analysis in a Dynamic Object-Oriented Environment
A highly interactive, user-friendly object-oriented software package written in LispStat is introduced that performs simple and multiple correspondence analysis, and profile analysis. These three techniques are integrated into a single environment driven by a user-friendly graphical interface that takes advantage of Lisp-Stat's advanced graphical capabilities. Techniques that assess the stability of the solution are also introduced. Some of the features of the package include colored graphics, incremental graph zooming capabilities, manual point separation to determine identities of overlapping points, and stability and fit measures. The features of the package are used to show some interesting trends in a large educational dataset.
Pesticide Use and IPM Adoption: Does IPM Reduce Pesticide Use in the United States?
In 2001, the United States General Accounting Office issued a report entitled âManagement Improvements Needed to Further Promote Integrated Pest Management.â This report documents that overall agricultural pesticide usage increased from 1992 to 2000 while the use of the most toxic levels of pesticides have decreased. The USDA suggests that these changes in pesticide use could have been caused by integrated pest management (IPM) adoption. However, the GAO maintains that there is not enough evidence to support this claim. This paper contributes to this debate by estimating the relationship between pesticide use and IPM practices adopted for number of commodities across the nation from 1996 to 2005. The paper exploits an aggregated data set that combines surveys from different crops and different years, but it also examines specific surveys conducted on cotton and corn crops to better control for other factors that could affect pesticide use. The paper applies multiple definitions of IPM and uses different spatial variables to control for environmental effects that affect pesticide use. Although some specific strategies such as GM adoption decreased the amount of active ingredients sprayed on cotton and corn, the results suggest that on average the adoption of IPM strategies lead to slightly increased pesticide spending and pounds of active ingredient sprayed per acre. This result is confirmed in both the analysis on the aggregated data as well as the analysis of the cotton and corn data. The results also suggest that fixed environmental factors explain a significant amount of chemical spending and pesticide use in the United States. The significance of these factors demonstrates the importance of research and programs that aid farmers in making intelligent pesticide use decisions at the local level.Pesticide Use, Integrated Pest Management, Corn Production, Cotton Production, Agricultural and Food Policy, Environmental Economics and Policy,
Harnessing resilience: biased voltage overscaling for probabilistic signal processing
A central component of modern computing is the idea that computation requires
determinism. Contrary to this belief, the primary contribution of this work shows that
useful computation can be accomplished in an error-prone fashion. Focusing on low-power
computing and the increasing push toward energy conservation, the work seeks to sacrifice
accuracy in exchange for energy savings.
Probabilistic computing forms the basis for this error-prone computation by diverging from the requirement of determinism and allowing for randomness within computing.
Implemented as probabilistic CMOS (PCMOS), the approach realizes enormous energy sav-
ings in applications that require probability at an algorithmic level. Extending probabilistic
computing to applications that are inherently deterministic, the biased voltage overscaling
(BIVOS) technique presented here constrains the randomness introduced through PCMOS.
Doing so, BIVOS is able to limit the magnitude of any resulting deviations and realizes
energy savings with minimal impact to application quality.
Implemented for a ripple-carry adder, array multiplier, and finite-impulse-response (FIR)
filter; a BIVOS solution substantially reduces energy consumption and does so with im-
proved error rates compared to an energy equivalent reduced-precision solution. When
applied to H.264 video decoding, a BIVOS solution is able to achieve a 33.9% reduction in
energy consumption while maintaining a peak-signal-to-noise ratio of 35.0dB (compared to
14.3dB for a comparable reduced-precision solution).
While the work presented here focuses on a specific technology, the technique realized
through BIVOS has far broader implications. It is the departure from the conventional
mindset that useful computation requires determinism that represents the primary innovation of this work. With applicability to emerging and yet to be discovered technologies,
BIVOS has the potential to contribute to computing in a variety of fashions.PhDCommittee Chair: Anderson, David; Committee Member: Conte, Thomas; Committee Member: Ferri, Bonnie; Committee Member: Hasler, Paul; Committee Member: Mooney, Vincen
Sensor Management for Tracking in Sensor Networks
We study the problem of tracking an object moving through a network of
wireless sensors. In order to conserve energy, the sensors may be put into a
sleep mode with a timer that determines their sleep duration. It is assumed
that an asleep sensor cannot be communicated with or woken up, and hence the
sleep duration needs to be determined at the time the sensor goes to sleep
based on all the information available to the sensor. Having sleeping sensors
in the network could result in degraded tracking performance, therefore, there
is a tradeoff between energy usage and tracking performance. We design sleeping
policies that attempt to optimize this tradeoff and characterize their
performance. As an extension to our previous work in this area [1], we consider
generalized models for object movement, object sensing, and tracking cost. For
discrete state spaces and continuous Gaussian observations, we derive a lower
bound on the optimal energy-tracking tradeoff. It is shown that in the low
tracking error regime, the generated policies approach the derived lower bound
Sensor Scheduling for Energy-Efficient Target Tracking in Sensor Networks
In this paper we study the problem of tracking an object moving randomly
through a network of wireless sensors. Our objective is to devise strategies
for scheduling the sensors to optimize the tradeoff between tracking
performance and energy consumption. We cast the scheduling problem as a
Partially Observable Markov Decision Process (POMDP), where the control actions
correspond to the set of sensors to activate at each time step. Using a
bottom-up approach, we consider different sensing, motion and cost models with
increasing levels of difficulty. At the first level, the sensing regions of the
different sensors do not overlap and the target is only observed within the
sensing range of an active sensor. Then, we consider sensors with overlapping
sensing range such that the tracking error, and hence the actions of the
different sensors, are tightly coupled. Finally, we consider scenarios wherein
the target locations and sensors' observations assume values on continuous
spaces. Exact solutions are generally intractable even for the simplest models
due to the dimensionality of the information and action spaces. Hence, we
devise approximate solution techniques, and in some cases derive lower bounds
on the optimal tradeoff curves. The generated scheduling policies, albeit
suboptimal, often provide close-to-optimal energy-tracking tradeoffs
Competing Narratives: Choosing the Tiger in Ang Lee's Life of Pi
Life of Piâs global resonance, international production team, and cos- mopolitan director are mainstream Hollywoodâs answer to the de- mands of a âworld cinemaâ marketplace. Having grossed over 482 million coming from theaters outside North America, Life of Pi earned more in mainland China than the United States and was Hollywoodâs highest earning release in India for 2012. Ignoring these notable facts, reviewers often focus upon the filmâs spiritual themes and impressive visual effects, but Leeâs interpretation clearly resonates in the global political climate. Though his films speak to an international audience, for whom does Ang Lee speak? Scholars such as Rey Chow, Emilie Yeh, Darrell Da- vis, Shu-mei Shih, and Gina Marchetti examine Leeâs work through a transnational lens, though much of this work remains framed within a regional discourse. By reviewing this scholarship, this paper dis- cusses the critical connections between these interpretations and my own reading of Life of Pi as a cosmopolitan allegory of migration and survival.published_or_final_versio
Light Element Synthesis in High Entropy Relativistic Flows Associated with Gamma Ray Bursts
We calculate and discuss the light element freeze-out nucleosynthesis in high
entropy winds and fireballs for broad ranges of entropy-per-baryon, dynamic
timescales characterizing relativistic expansion, and neutron-to-proton ratios.
With conditions characteristic of Gamma Ray Bursts (GRBs) we find that
deuterium production can be prodigious, with final abundance values 2H/H
approximately 2%, depending on the fireball isospin, late time dynamics, and
the effects of neutron decoupling- induced high energy non-thermal nuclear
reactions. This implies that there potentially could be detectable local
enhancements in the deuterium abundance associated with GRB events.Comment: 14 pages 3 figure
- âŠ