1,981 research outputs found
Spruce Budworm Weight and Fecundity: Means, Frequency Distributions, and Correlations for Two Populations (Lepidoptera: Tortricidae)
Pupal weights and fecundities of spruce budworm from Minnesota had different means, coefficients of variation, and frequency distributions than spruce budworm from New Hampshire. The two variables were correlated in one of the populations but not the other
Reproductive Compatibility Within and Among Spruce Budworm (Lepidoptera: Tortricidae) Populations
Spruce bud worm moths collected as larvae from two species of host trees in four populations were mated in single pairs in two years. In 1980 but not 1981, more of the intra-population matings than the inter-population matings were fertile. Host tree origin was not a significant factor in the level of sterility
Searching for Millisecond Pulsars: Surveys, Techniques and Prospects
Searches for millisecond pulsars (which we here loosely define as those with
periods 20 ms) in the Galactic field have undergone a renaissance in the
past five years. New or recently refurbished radio telescopes utilizing cooled
receivers and state-of-the art digital data acquisition systems are carrying
out surveys of the entire sky at a variety of radio frequencies. Targeted
searches for millisecond pulsars in point sources identified by the {\it Fermi}
Gamma-ray Space Telescope have proved phenomenally successful, with over 50
discoveries in the past five years. The current sample of millisecond pulsars
now numbers almost 200 and, for the first time in 25 years, now outnumbers
their counterparts in Galactic globular clusters. While many of these searches
are motivated to find pulsars which form part of pulsar timing arrays, a wide
variety of interesting systems are now being found. Following a brief overview
of the millisecond pulsar phenomenon, we describe these searches and present
some of the highlights of the new discoveries in the past decade. We conclude
with predictions and prospects for ongoing and future surveys.Comment: 16 pages, 3 figures, accepted for publication in Classical and
Quantum gravit
Gravitational wave background from rotating neutron stars
The background of gravitational waves produced by the ensemble of rotating
neutron stars (which includes pulsars, magnetars and gravitars) is
investigated. A formula for \Omega(f) (commonly used to quantify the
background) is derived, properly taking into account the time evolution of the
systems since their formation until the present day. Moreover, the formula
allows one to distinguish the different parts of the background: the
unresolvable (which forms a stochastic background) and the resolvable. Several
estimations of the background are obtained, for different assumptions on the
parameters that characterize neutron stars and their population. In particular,
different initial spin period distributions lead to very different results. For
one of the models, with slow initial spins, the detection of the background can
be rejected. However, other models do predict the detection of the background
by the future ground-based gravitational wave detector ET. A robust upper limit
for the background of rotating neutron stars is obtained; it does not exceed
the detection threshold of two cross-correlated Advanced LIGO interferometers.
If gravitars exist and constitute more than a few percent of the neutron star
population, then they produce an unresolvable background that could be detected
by ET. Under the most reasonable assumptions on the parameters characterizing a
neutron star, the background is too faint. Previous papers have suggested
neutron star models in which large magnetic fields (like the ones that
characterize magnetars) induce big deformations in the star, which produce a
stronger emission of gravitational radiation. Considering the most optimistic
(in terms of the detection of gravitational waves) of these models, an upper
limit for the background produced by magnetars is obtained; it could be
detected by ET, but not by BBO or DECIGO.Comment: 25 pages, 15 figure
A Search for Sub-millisecond Pulsations in Unidentified FIRST and NVSS Radio Sources
We have searched 92 unidentified sources from the FIRST and NVSS 1400 MHz
radio survey catalogs for radio pulsations at 610 MHz. The selected radio
sources are bright, have no identification with extragalactic objects, are
point-like and are more than 5% linearly polarized. Our search was sensitive to
sub-millisecond pulsations from pulsars with dispersion measures (DMs) less
than 500 pc cm-3 in the absence of scattering. We have detected no pulsations
from these sources and consider possible effects which might prevent detection.
We conclude that as a population, these sources are unlikely to be pulsars.Comment: 8 pages, including 2 tables and 1 figure. Accepted for publication in
A
On the detectability of extragalactic fast radio transients
Recent discoveries of highly dispersed millisecond radio bursts by Thornton
et al. in a survey with the Parkes radio telescope at 1.4 GHz point towards an
emerging population of sources at cosmological distances whose origin is
currently unclear. Here we demonstrate that the scattering effects at lower
radio frequencies are less than previously thought, and that the bursts could
be detectable at redshifts out to about in surveys below 1 GHz. Using a
source model in which the bursts are standard candles with bolometric
luminosities ergs/s uniformly distributed per unit
comoving volume, we derive an expression for the observed peak flux density as
a function of redshift and use this, together with the rate estimates found by
Thornton et al. to find an empirical relationship between event rate and
redshift probed by a given survey. The non-detection of any such events in
Arecibo 1.4 GHz survey data by Deneva et al., and the Allen Telescope Array
survey by Simeon et al. is consistent with our model. Ongoing surveys in the
1--2 GHz band should result in further discoveries. At lower frequencies,
assuming a typical radio spectral index , the predicted peak flux
densities are 10s of Jy. As a result, surveys of such a population with current
facilities would not necessarily be sensitivity limited and could be carried
out with small arrays to maximize the sky coverage. We predict that sources may
already be present in 350-MHz surveys with the Green Bank Telescope. Surveys at
150 MHz with 30 deg fields of view could detect one source per hour above
30 Jy.Comment: 5 pages, 2 figures, Accepted for publication in MNRAS on 2013 July
25. Received 2013 July 24; in original form 2013 May 3
The technology & practices of the New South Wales fishing industry 1850-1930
This study is intended to explore these two significant forces at play/ as mirrored in the technology used in the New South Wales fishing industry from 1850 to 1930. A significant feature of the development of Australian fishing technology has been the adaptation of foreign technology to the local conditions. This process has been continual and can still be seen in the present expansion into the 200 mile zone with the adoption of the large purse seiners in the tuna fishery.
Thus this thesis is concerned with the manner in which Australian fishermen converted essentially British and North American fishing techniques and technology to meet the particular environmental, marketing and economic conditions of New South Wales. It would appear that fishermen came to Australia with a preconceived technology and were then presented with the problem of adapting this foreign technology to the peculiar environmental and social conditions of New South Wales. The end result proved such a highly successful adaptation that it has remained in use to the present day
Beyond walking and cycling: scoping small-wheel modes
Active travel beyond walking and cycling – by small-wheel modes such as inline skating, skateboarding and push scooting, among others – needs more understanding in terms of the design, maintenance and management issues it may present in the future. These modes – especially their use for travel rather than leisure pursuits – are rarely quantified outside of accident statistics and the focus of qualitative study in the governance of public space conflict or the sociology of childhood activities. This paper reports on a scoping study exploring the potential for small-wheel modes among other means of ‘human locomotion’. The study first recruited local transport officers and people using these modes, as well as academic experts. The study found that there are differences between the views of planning officers and users of these modes that need to be investigated further to arrive at solid conclusions and advice for the design, maintenance and management issues needed both now and in a future that allows more variety and choice in human locomotion for active travel. The use of user-generated digital data for data capture, analysis and mapping was also explored
Observations of 20 millisecond pulsars in 47 Tucanae at 20 cm
We have used a new observing system on the Parkes radio telescope to carry
out a series of pulsar observations of the globular cluster 47 Tucanae at 20-cm
wavelength. We detected all 11 previously known pulsars, and have discovered
nine others, all of which are millisecond pulsars in binary systems. We have
searched the data for relatively short orbital period systems, and found one
pulsar with an orbital period of 96 min, the shortest of any known radio
pulsar.
The increased rate of detections with the new system resulted in improved
estimates of the flux density of the previously known pulsars, determination of
the orbital parameters of one of them, and a coherent timing solution for
another one. Five of the pulsars now known in 47 Tucanae have orbital periods
of a few hours and implied companion masses of only ~ 0.03 Msun. Two of these
are eclipsed at some orbital phases, while three are seen at all phases at 20
cm but not always at lower frequencies. Four and possibly six of the other
binary systems have longer orbital periods and companion masses ~ 0.2 Msun,
with at least two of them having relatively large orbital eccentricities. All
20 pulsars have rotation periods in the range 2-8 ms.Comment: 15 pages, 6 embedded EPS figures, to be published in The
Astrophysical Journa
Propagation of gravitational waves in multimetric gravity
We discuss the propagation of gravitational waves in a recently discussed
class of theories containing N >= 2 metric tensors and a corresponding number
of standard model copies. Using the formalism of gauge-invariant linear
perturbation theory we show that all gravitational waves propagate at the speed
of light. We then employ the Newman-Penrose formalism to show that two to six
polarizations of gravitational waves may exist, depending on the parameters
entering the equations of motion. This corresponds to E(2) representations N_2,
N_3, III_5 and II_6. We finally apply our general discussion to a recently
presented concrete multimetric gravity model and show that it is of class N_2,
i.e., it allows only two tensor polarizations, as it is the case for general
relativity. Our results provide the theoretical background for tests of
multimetric gravity theories using the upcoming gravitational wave experiments.Comment: 21 pages, no figures, journal versio
- …