1,161 research outputs found
Forest fragmentation and the distribution, abundance and conservation of the Tana river red colobus ( Procolobus rufomitratus)
Evidence suggests that habitat heterogeneity, disturbance, disease, predation and food resources influence primate population abundance. However, few studies have focused on what habitat factors determine the probability that a primate species will occur in a habitat fragment. We analysed forest habitat and colobus population attributes to determine factors that influenced occurrence and abundance of the critically endangered Tana River red colobus. The probability of colobus inhabiting forests was positively related to the relative amount of habitat edge and canopy tree species composition. Most of the variance in the density of colobus monkeys was explained by basal area of food trees (per ha), basal area per food tree, density of food trees, and basal area per tree for all trees. We conclude that effective conservation of primates in fragmented habitats may require strategies that consider factors that influence both the occurrence of a species and its relative abundance
Optical and Infrared Analysis of Type II SN 2006BC
We present nebular phase optical imaging and spectroscopy and near/mid-IR
imaging of the Type II SN 2006bc. Observations reveal the central wavelength of
the symmetric H line profile to be red-shifted with respect to the host
galaxy H emission by day 325. Such an phenomenon has been argued to
result from an asymmetric explosion in the iron-peak elements resulting in a
larger mass of Ni and higher excitation of hydrogen on the far side of
the SN explosion. We also observe a gradual blue-shifting of this H
peak which is indicative of dust formation in the ejecta. Although showing a
normal peak brightness, V -17.2, for a core-collapse SN, 2006bc fades by
6 mag during the first 400 days suggesting either a relatively low
Ni yield, an increase in extinction due to new dust, or both. A short
duration flattening of the light curve is observed from day 416 to day 541
suggesting an optical light echo. Based on the narrow time window of this echo,
we discuss implications on the location and geometry of the reflecting ISM.
With our radiative transfer models, we find an upper limit of 2 x 10
M of dust around SN 2006bc. In the event that all of this dust were
formed during the SN explosion, this quantity of dust is still several orders
of magnitude lower than that needed to explain the large quantities of dust
observed in the early universe.Comment: 6 pages, 10 figures, accepted for publication in Ap
The Rise Times of High and Low Redshift Type Ia Supernovae are Consistent
We present a self-consistent comparison of the rise times for low- and
high-redshift Type Ia supernovae. Following previous studies, the early light
curve is modeled using a t-squared law, which is then mated with a modified
Leibundgut template light curve. The best-fit t-squared law is determined for
ensemble samples of low- and high-redshift supernovae by fitting simultaneously
for all light curve parameters for all supernovae in each sample. Our method
fully accounts for the non-negligible covariance amongst the light curve
fitting parameters, which previous analyses have neglected. Contrary to Riess
et al. (1999), we find fair to good agreement between the rise times of the
low- and high-redshift Type Ia supernovae. The uncertainty in the rise time of
the high-redshift Type Ia supernovae is presently quite large (roughly +/- 1.2
days statistical), making any search for evidence of evolution based on a
comparison of rise times premature. Furthermore, systematic effects on rise
time determinations from the high-redshift observations, due to the form of the
late-time light curve and the manner in which the light curves of these
supernovae were sampled, can bias the high-redshift rise time determinations by
up to +3.6/-1.9 days under extreme situations. The peak brightnesses - used for
cosmology - do not suffer any significant bias, nor any significant increase in
uncertainty.Comment: 18 pages, 4 figures, Accepted for publication in the Astronomical
Journal. Also available at http://www.lbl.gov/~nugent/papers.html Typos were
corrected and a few sentences were added for improved clarit
Annual Variation in Habitat Use by White-footed Mice, Peromyscus leucopus: The Effects of Forest Patch Size, Edge and Surrounding Vegetation Type
White-footed Mice (Peromyscus leucopus) were trapped for two years in the exterior matrix, edge, and interior forest habitat sections of six forests patches in a fragmented agricultural landscape. We used data on the capture locations of P. leucopus individuals from the two years, which differed in rainfall (i.e., summer of 2000 with 50% more rain than summer of 1999), to assess how patch size, edge habitat, and surrounding habitat type influence habitat use and movements in populations of this forest habitat generalist. We found that the proportion of individuals subsequently captured in the forest edge from the exterior was 16 times greater in the wet year than in the dry year and approximately twice as many P. leucopus were not subsequently recaptured from the exterior matrix in the dry year compared to the wet year. For each year, captures between habitats did not differ in relation to patch size, edge forest habitat, or exterior matrix type. These results illustrate the generalist habitat preferences of P. leucopus, but emphasize annual variation in their behavior and distribution
Short term fat feeding rapidly increases plasma insulin but does not result in dyslipidaemia
Although the association between obesity and hypertension is well known, the underlying mechanism remains elusive. Previously, we have shown that 3 week fat feeding in rabbits produces greater visceral adiposity, hypertension, tachycardia and elevated renal sympathetic nerve activity compared to rabbits on a normal diet. Because hyperinsulinaemia, hyperleptinemia and dyslipidaemia are independent cardiovascular risk factors associated with hypertension we compared plasma insulin, leptin and lipid profiles in male New Zealand White rabbits fed a normal fat diet (NFD 4.3% fat, n = 11) or high fat diet (HFD 13.4% fat, n = 13) at days 1, 2, 3 and weeks 1, 2, 3 of the diet. Plasma concentrations of diacylglyceride (DG), triacylglyceride (TG), ceramide and cholesteryl esters (CE) were obtained after analysis by liquid chromatography mass spectrometry. Plasma insulin and glucose increased within the first 3 days of the diet in HFD rabbits (P <0.05) and remained elevated at week 1 (P <0.05). Blood pressure and heart rate followed a similar pattern. By contrast, in both groups, plasma leptin levels remained unchanged during the first few days (P >0.05), increasing by week 3 in fat fed animals alone (P <0.05). Concentrations of total DG, TG, CE and Ceramide at week 3 did not differ between groups (P >0.05). Our data show plasma insulin increases rapidly following consumption of a HFD and suggests that it may play a role in the rapid rise of blood pressure. Dyslipidaemia does not appear to contribute to the hypertension in this animal model
The absolute infrared magnitudes of type Ia supernovae
The absolute luminosities and homogeneity of early-time infrared (IR) light
curves of type Ia supernovae are examined. Eight supernovae are considered.
These are selected to have accurately known epochs of maximum blue light as
well as having reliable distance estimates and/or good light curve coverage.
Two approaches to extinction correction are considered. Owing to the low
extinction in the IR, the differences in the corrections via the two methods
are small. Absolute magnitude light curves in the J, H and K-bands are derived.
Six of the events, including five established ``Branch-normal'' supernovae show
similar coeval magnitudes. Two of these, SNe 1989B and 1998bu, were observed
near maximum infrared light. This occurs about 5 days {\it before} maximum blue
light. Absolute peak magnitudes of about -19.0, -18.7 and -18.8 in J, H & K
respectively were obtained. The two spectroscopically peculiar supernovae in
the sample, SNe 1986G and 1991T, also show atypical IR behaviour. The light
curves of the six similar supernovae can be represented fairly consistently
with a single light curve in each of the three bands. In all three IR bands the
dispersion in absolute magnitude is about 0.15 mag, and this can be accounted
for within the uncertainties of the individual light curves. No significant
variation of absolute IR magnitude with B-band light curve decline rate, Delta
m_{15}(B), is seen over the range 0.87<Delta m_{15}(B)<1.31. However, the data
are insufficient to allow us to decide whether or not the decline rate relation
is weaker in the IR than in the optical region. IR light curves of type Ia
supernovae should eventually provide cosmological distance estimates which are
of equal or even superior quality to those obtained in optical studies.Comment: 19 pages, 9 figures, MNRAS in press (includes Referee's changes
What lies beneath? The role of informal and hidden networks in the management of crises
Crisis management research traditionally focuses on the role of formal communication networks in the escalation and management of organisational crises. Here, we consider instead informal and unobservable networks. The paper explores how hidden informal exchanges can impact upon organisational decision-making and performance, particularly around inter-agency working, as knowledge distributed across organisations and shared between organisations is often shared through informal means and not captured effectively through the formal decision-making processes. Early warnings and weak signals about potential risks and crises are therefore often missed. We consider the implications of these dynamics in terms of crisis avoidance and crisis management
SN 2002cv: A Heavily Obscured Type Ia Supernova
We present VRIJHK photometry, and optical and near-infrared spectroscopy, of
the heavily extinguished Type Ia supernova (SN) 2002cv, located in NGC 3190,
which is also the parent galaxy of the Type Ia SN 2002bo. SN 2002cv, not
visible in the blue, has a total visual extinction of 8.74 +- 0.21 mag. In
spite of this we were able to obtain the light curves between -10 and +207 days
from the maximum in the I band, and also to follow the spectral evolution,
deriving its key parameters. We found the peak I-band brightness to be Imax =
16.57 +- 0.10 mag, the maximum absolute I magnitude to be MmaxI = -18.79 +-
0.20, and the parameter dm15(B) specifying the width of the B-band light curve
to be 1.46 +- 0.17 mag. The latter was derived using the relations between this
parameter and dm40(I) and the time interval dtmax(I) between the two maxima in
the I-band light curve. As has been found for previously observed, highly
extinguished SNe Ia, a small value of 1.59 +- 0.07 was obtained here for the
ratio Rv of the total-to-selective extinction ratio for SN 2002cv, which
implies a small mean size for the grains along the line of sight toward us.
Since it was found for SN 2002bo a canonical value of 3.1, here we present a
clear evidence of different dust properties inside NGC 3190.Comment: 18 pages, 18 figures. Accepted for publication in MNRAS. Added
co-author
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