623 research outputs found
Brushtail possum (Trichosurus vulpecula) social interactions and their implications for bovine tuberculosis epidemiology
The brushtail possum is the main reservoir of bovine tuberculosis in New Zealand. Disease prevalence is generally higher in males than in females. This has conventionally been assumed due to greater infection rates of males, but recent work has raised the hypothesis that it may instead be driven by survival differences. With bovine tuberculosis transmission among possums most likely occurring between individuals in close proximity, here we analyse social networks built on data from wild possums collared with contact loggers inhabiting a native New Zealand forest, to investigate whether there is mechanistic support for higher male infection rates. Our results revealed that adult female possums were generally just as connected with adult male possums as other adult males are, with male-female connection patterns not being significantly different. This result suggest that the new 'survivorship' hypothesis for the sex bias is more likely than the conventional 'infection rate' hypothesis. © 2018 Copyright 2018 by Koninklijke Brill NV, Leiden, The Netherlands
(47171) 1999 TC36, A Transneptunian Triple
We present new analysis of HST images of (47171) 1999 TC36 that confirm it as
a triple system. Fits to the point-spread function consistently show that the
apparent primary is itself composed of two similar-sized components. The two
central components, A1 and A2, can be consistently identified in each of nine
epochs spread over seven years of time. In each instance the component
separation, ranging from 0.023+/-0.002 to 0.031+/-0.003 arcsec, is roughly one
half of the Hubble Space Telescope's diffraction limit at 606 nm. The orbit of
the central pair has a semi-major axis of a~867 km with a period of P~1.9 days.
These orbital parameters yield a system mass that is consistent with Msys =
12.75+/-0.06 10^18 kg derived from the orbit of the more distant secondary,
component B. The diameters of the three components are dA1= 286(+45,-38) km,
dA2= 265(+41,-35 km and dB= 139(+22,-18) km. The relative sizes of these
components are more similar than in any other known multiple in the solar
system. Taken together, the diameters and system mass yield a bulk density of
p=542(+317,-211) kg m^-3. HST Photometry shows that component B is variable
with an amplitude of >=0.17+/-0.05 magnitudes. Components A1 and A2 do not show
variability larger than 0.08+/-0.03 magnitudes approximately consistent with
the orientation of the mutual orbit plane and tidally-distorted equilibrium
shapes. The system has high specific angular momentum of J/J'=0.93, comparable
to most of the known Transneptunian binaries.Comment: 16 pages, 8 figures, 6 tables. Accepted to Icaru
Experimental demonstration of intermodal dispersion in a two-core optical fiber
The recent prediction that intermodal dispersion can play a significant role in pulse evolution in a two-core optical fiber was confirmed experimentally. A picosecond pulse at 1.548µm launched into one core of a meters-long two-core fiber was found to come out of either core of the fiber as two temporally separate pulses. By measuring the time delay between these two pulses, the intermodal dispersion in the fiber was estimated to be 1.13ps/m, in good agreement with theory
Optical Bumps in Cosmological GRBs as Supernovae
From both photometric and broadband spectral monitoring of gamma-ray burst
(GRB) lightcurve ``bumps,'' particularly in GRB 011121, a strong case grew for
a supernova (SN) origin. The GRB-SN connection was finally solidified beyond a
reasonable doubt with the discovery that the bump in GRB 030329 was
spectroscopically similar to a bright Type Ic SN. In light of this result, I
redress the previous SN bump claims and conclude that 1) the distribution of
GRB-SN bump peak magnitudes is consistent with the local Type Ibc SNe peak
distribution and suggest that 2) the late-time bumps in all long-duration GRBs
are likely supernovae.Comment: 5 pages, 2 figures. To be published in Proc. IAU Colloquium #192
``Supernovae (10 years of SN1993J),'' held 22-26 April 2003, Valencia, Spain.
Editors: J.M. Marcaide and K.W. Weiler. Uses svmult.cl
Local field factors in a polarized two-dimensional electron gas
We derive approximate expressions for the static local field factors of a
spin polarized two-dimensional electron gas which smoothly interpolate between
their small- and large-wavevector asymptotic limits. For the unpolarized
electron gas, the proposed analytical expressions reproduce recent diffusion
Monte Carlo data. We find that the degree of spin polarization produces
important modifications to the local factors of the minority spins, while the
local field functions of the majority spins are less affected.Comment: 8 pages, 10 figure
Prevention of tracheal cartilage injury with modified Griggs technique during percutaneous tracheostomy - Randomized controlled cadaver study
Introduction: Tracheal stenosis is the most common severe late complication of percutaneous tracheostomy causing significant decrease in quality of life. Applying modified Griggs technique reduced the number of late tracheal stenoses observed in our clinical study. The aim of this study was to investigate the mechanism of this relationship. Materials and methods: Forty-six cadavers were randomized into two groups according to the mode of intervention during 2006-2008. Traditional versus modified Griggs technique was applied in the two groups consequently. Wider incision, surgical preparation, and bidirectional forceps dilation of tracheal wall were applied in modified technique. Injured cartilages were inspected by sight and touch consequently. Age, gender, level of intervention, and number of injured tracheal cartilages were registered. Results: Significantly less frequent tracheal cartilage injury was observed after modified (9%) than original (91%) Griggs technique (p<0.001). A moderate association between cartilage injury and increasing age was observed, whereas the level of intervention (p=0.445) and to gender (p=0.35) was not related to injury. Risk of cartilage injury decreased significantly (OR: 0.0264, 95%, CI: 0.005-0.153) with modified Griggs technique as determined in adjusted logistic regression model. Discussion: Modified Griggs technique decreased the risk of tracheal cartilage injury significantly in our cadaver study. This observation may explain the decreased number of late tracheal stenosis after application of the modified Griggs method. © 2012 Akadémiai Kiadó, Budapes
The Correlated Colors of Transneptunian Binaries
We report resolved photometry of the primary and secondary components of 23
transneptunian binaries obtained with the Hubble Space Telescope. V-I colors of
the components range from 0.7 to 1.5 with a median uncertainty of 0.06
magnitudes. The colors of the primaries and secondaries are correlated with a
Spearman rank correlation probability of 99.99991%, 5 sigma for a normal
distribution. Fits to the primary vs. secondary colors are identical to within
measurement uncertainties. The color range of binaries as a group is
indistinguishable from that of the larger population of apparently single
transneptunian objects. Whatever mechanism produced the colors of apparently
single TNOs acted equally on binary systems. The most likely explanation is
that the colors of transneptunian objects and binaries alike are primordial and
indicative of their origin in a locally homogeneous, globally heterogeneous
protoplanetary disk.Comment: 28 pages, 4 figure, 4 tables. accepted to Icaru
Correlation energy of a two-dimensional electron gas from static and dynamic exchange-correlation kernels
We calculate the correlation energy of a two-dimensional homogeneous electron
gas using several available approximations for the exchange-correlation kernel
entering the linear dielectric response of the system.
As in the previous work of Lein {\it et al.} [Phys. Rev. B {\bf 67}, 13431
(2000)] on the three-dimensional electron gas, we give attention to the
relative roles of the wave number and frequency dependence of the kernel and
analyze the correlation energy in terms of contributions from the plane. We find that consistency of the kernel with the electron-pair
distribution function is important and in this case the nonlocality of the
kernel in time is of minor importance, as far as the correlation energy is
concerned. We also show that, and explain why, the popular Adiabatic Local
Density Approximation performs much better in the two-dimensional case than in
the three-dimensional one.Comment: 9 Pages, 4 Figure
An Evaluation of Ballute Entry Systems for Lunar Return Missions
AIAA Atmospheric Flight Mechanics Conference
August 2006, Keystone, CO.This study investigates the advantages and feasibility of using ballutes for Earth entry at
lunar return velocities. Using analysis methods suitable for conceptual design and assuming
a CEV type entry vehicle, multiple entry strategies were investigated. Entries that jettison
the ballute after achieving low Earth orbit conditions were shown to reduce heating rates to
within reusable thermal protection system limits. Deceleration was mitigated to
approximately four g's when a moderate amount of lift was applied subsequent to ballute
jettison. Primary ballute size drivers are the thermal limitations and areal densities of the
ballute material. Performance requirements for both of those metrics were generated over a
range of total ballute system masses. Lastly, preliminary investigation of a lower mass cargo
variant of the CEV allowed for additional reduction of ballute system mass. However,
ballute system mass as a percentage of the total entry mass was shown to be relatively
independent of the entry mass
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