17,002 research outputs found
A Migration Study of \u3ci\u3eStelidota Geminata\u3c/i\u3e (Coleoptera: Nitidulidae)
The strawberry sap beetle, Stelidota geminata (Say), is a major pest of strawberries in the northeastern United States. Further knowledge of the migratory habits of this insect pest can enhance the effectiveness of pest management strategies. This nitidulid was shown to migrate from its overwintering sites to one of its primary reproductive sites, strawberry fields, in late May. The beetle population peaked in the third week in July, 1993 in the strawberry field and then gradually declined. In 1994, the peak, as well as the total population, was much greater than in 1993. Furthermore, S. geminata was concentrated in the transition areas surrounding the strawberry fields prior to the ripening of the fruit
GRB Energetics and the GRB Hubble Diagram: Promises and Limitations
We present a complete sample of 29 GRBs for which it has been possible to
determine temporal breaks (or limits) from their afterglow light curves. We
interpret these breaks within the framework of the uniform conical jet model,
incorporating realistic estimates of the ambient density and propagating error
estimates on the measured quantities. In agreement with our previous analysis
of a smaller sample, the derived jet opening angles of those 16 bursts with
redshifts result in a narrow clustering of geometrically-corrected gamma-ray
energies about E_gamma = 1.33e51 erg; the burst-to-burst variance about this
value is a factor of 2.2. Despite this rather small scatter, we demonstrate in
a series of GRB Hubble diagrams, that the current sample cannot place
meaningful constraints upon the fundamental parameters of the Universe. Indeed
for GRBs to ever be useful in cosmographic measurements we argue the necessity
of two directions. First, GRB Hubble diagrams should be based upon fundamental
physical quantities such as energy, rather than empirically-derived and
physically ill-understood distance indicators. Second, a more homogeneous set
should be constructed by culling sub-classes from the larger sample. These
sub-classes, though now first recognizable by deviant energies, ultimately must
be identifiable by properties other than those directly related to energy. We
identify a new sub-class of GRBs (``f-GRBs'') which appear both underluminous
by factors of at least 10 and exhibit a rapid fading at early times. About
10-20% of observed long-duration bursts appear to be f-GRBs.Comment: Accepted to the Astrophysical Journal (20 May 2003). 19 pages, 3
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The impact of competition on management quality: evidence from public hospitals
We analyse the causal impact of competition on managerial quality and hospital performance. To address the endogeneity of market structure we analyse the English public hospital sector where entry and exit are controlled by the central government. Because closing hospitals in areas where the governing party is expecting a tight election race (“marginals”) is rare due to the fear of electoral defeat, we can use political marginality as an instrumental variable for the number of hospitals in a geographical area. We find that higher competition results in higher management quality, measured using a new survey tool, and improved hospital performance. Adding a rival hospital increases management quality by 0.4 standard deviations and increases survival rates from emergency heart attacks by 9.7%. We confirm the robustness of our IV strategy to “hidden policies” that could be used in marginal districts to improve hospital management and to changes in capacity that may follow from hospital closure
The Extremal Function for the Complex Ball for Generalized Notions of Degree and Multivariate Polynomial Approximation
We discuss the Siciak-Zaharjuta extremal function of pluripotential theory
for the unit ball in C^d for spaces of polynomials with the notion of degree
determined by a convex body P. We then use it to analyze the approximation
properties of such polynomial spaces, and how these may differ depending on the
function f to be approximated
The Radio Afterglow From GRB 980519: A Test of the Jet and Circumstellar Models
We present multi-frequency radio observations from the afterglow of GRB
980519 beginning 7.2 hours after the gamma-ray burst and ending 63 days later.
The fast decline in the optical and X-ray light curves for this burst has been
interpreted either as afterglow emission originating from a collimated outflow
-- a jet -- or the result of a blast wave propagating into a medium whose
density is shaped by the wind of an evolved massive star. These two models
predict divergent behavior for the radio afterglow, and therefore, radio
observations are capable, in principle, of discriminating between the two. We
show that a wind model describes the subsequent evolution of the radio
afterglow rather well. However, we see strong modulation of the light curve,
which we interpret as diffractive scintillation. These variations prevent us
from decisively rejecting the jet model.Comment: ApJ, submitte
The Discovery and Broad-band Follow-up of the Transient Afterglow of GRB 980703
We report on the discovery of the radio, infrared and optical transient
coincident with an X-ray transient proposed to be the afterglow of GRB 980703.
At later times when the transient has faded below detection, we see an
underlying galaxy with R=22.6; this galaxy is the brightest host galaxy (by
nearly 2 magnitudes) of any cosmological GRB thus far. In keeping with an
established trend, the GRB is not significantly offset from the host galaxy.
Interpreting the multi-wavelength data in the framework of the popular fireball
model requires that the synchrotron cooling break was between the optical and
X-ray bands on July 8.5 UT and that the intrinsic extinction of the transient
is Av=0.9. This is somewhat higher than the extinction for the galaxy as a
whole, as estimated from spectroscopy.Comment: 5 pages, 3 figures, and 2 tables. Submitted to the Astrophysical
Journal Letters on 27 August 199
Preserving Context Privacy in Distributed Hash Table Wireless Sensor Networks.
Wireless Sensor Networks (WSN) are often deployed in hostile or difficult scenarios, such as military battlefields and disaster recovery, where it is crucial for the network to be highly fault tolerant, scalable and decentralized. For this reason, peer-to-peer primitives such as Distributed Hash Table (DHT), which can greatly enhance the scalability and resilience of a network, are increasingly being introduced in the design of WSN's. Securing the communication within the WSN is also imperative in hostile settings. In particular, context information, such as the network topology and the location and identity of base stations (which collect data gathered by the sensors and are a central point of failure) can be protected using traffic encryption and anonymous routing. In this paper, we propose a protocol achieving a modified version of onion routing over wireless sensor networks based on the DHT paradigm. The protocol prevents adversaries from learning the network topology using traffic analysis, and therefore preserves the context privacy of the network. Furthermore, the proposed scheme is designed to minimize the computational burden and power usage of the nodes, through a novel partitioning scheme and route selection algorithm
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