12,392 research outputs found
Geodetic Precession in PSR B1913+16
We review the observational evidence for geodetic precession in PSR B1913+16
and present the latest observations and results from modelling the system
geometry and beam.Comment: 4 pages,to appear in "Radio Pulsars" (ASP Conf. Ser.), eds. M.
Bailes, D. Nice, & S. Thorset
Jamming under tension in polymer crazes
Molecular dynamics simulations are used to study a unique expanded jammed
state. Tension transforms many glassy polymers from a dense glass to a network
of fibrils and voids called a craze. Entanglements between polymers and
interchain friction jam the system after a fixed increase in volume. As in
dense jammed systems, the distribution of forces is exponential, but they are
tensile rather than compressive. The broad distribution of forces has important
implications for fibril breakdown and the ultimate strength of crazes.Comment: 4 pages, 4 figure
Perturbations with angular momentum of Robinson-Trautman spacetimes
We study the possible asymptotically flat perturbations of Robinson-Trautman
spacetimes. We differentiate between algebraically special perturbations and
general perturbations. The equations that determine physically realistic
spacetimes with angular momentum are presented.Comment: 23 pages, no figure
Temporal Leakage and Its Effects on Resolution in Deconvolution of Ultrasonic Signals
A common problem in ultrasonic nondestructive evaluation is the limitation imposed by the oscillatory nature of the ultrasonic pulse. Echoes from closely spaced reflectors often overlap and interfere, obscuring the true nature of the defect or layered system. Many deconvolution methods have been developed to remove the oscillatory response of the transducer from the received ultrasonic echo thereby improving the temporal resolution. While these methods have worked well on simulated signals, the results on real data have generally been much poorer [1-7]. Ultrasonic pulse shape variations, nonlinear effects or the breakdown of other model assumptions all contribute to this lower performance on real signals. An additional problem which has undergone little investigation is temporal leakage; it is very common and produces inaccuracy in the position and amplitude of deconvolved features. An understanding of its nature may help to improve resolution when deconvolving real signal
Temperature rather than photoperiod controls growth cessation and dormancy in Sorbus species
Environmental regulation of growth and dormancy of four Sorbus genotypes was studied in controlled environments. Emphasis was placed on assessment of the presence and nature of the deficient photoperiodic dormancy regulation system that has previously been reported for some woody Rosaceae species. Two genotypes of Sorbus aucuparia L. maintained indeterminate growth for 8 weeks and 9 weeks at temperatures of 15 °C and 21 °C in both 20 h and 10 h photoperiods, while at 9 °C, in the same photoperiodic conditions, they immediately ceased growing. At the higher temperatures, initiation of new leaves (nodes) was unaffected by photoperiod, while internode elongation was significantly enhanced by long days (LD). However, even after prolonged exposure to 9 °C, most plants resumed growth when moved to high temperature and LD, indicating a shallow state of dormancy. Seedlings of Sorbus intermedia (J. F. Ehrh.) Pers. and micro-propagated plantlets of S. commixta Hedl. ‘Dodong’ were also unaffected by photoperiod during primary growth, but failed to elongate and gradually became dormant regardless of temperature and day-length conditions. However, after chilling and breaking of dormancy, the plants elongated vigorously but changed to a determinate mode of growth. Furthermore, a temperature of 9 °C was found to be fully effective for breaking dormancy in S. intermedia plants. It is concluded that deficient photoperiodic dormancy control seems widespread in the Rosaceae and that, in such plants, both dormancy induction and release is brought about by low temperature. The potential impacts of climate change on such trees are discussed
Analyzing First-Person Stories Based on Socializing, Eating and Sedentary Patterns
First-person stories can be analyzed by means of egocentric pictures acquired
throughout the whole active day with wearable cameras. This manuscript presents
an egocentric dataset with more than 45,000 pictures from four people in
different environments such as working or studying. All the images were
manually labeled to identify three patterns of interest regarding people's
lifestyle: socializing, eating and sedentary. Additionally, two different
approaches are proposed to classify egocentric images into one of the 12 target
categories defined to characterize these three patterns. The approaches are
based on machine learning and deep learning techniques, including traditional
classifiers and state-of-art convolutional neural networks. The experimental
results obtained when applying these methods to the egocentric dataset
demonstrated their adequacy for the problem at hand.Comment: Accepted at First International Workshop on Social Signal Processing
and Beyond, 19th International Conference on Image Analysis and Processing
(ICIAP), September 201
Antimicrobial Efficacy of the Silver Wound Dressing Biatain Ag in a Disc Carrier Test Simulating Wound Secretion
Aim: The efficacy of antimicrobial compounds included in wound dressings has been determined using the quantitative suspension test according to EN 13727 before. However, as suspension tests are not an accurate reflection of the conditions under which wound antiseptics are used, it was investigated if a disc carrier test would yield results simulating practical conditions on wound surfaces. A silver-leaching foam wound dressing was used for evaluation of the disc carrier test method. Method: The disc carriers consisted of circular stainless-steel discs measuring 2 cm in diameter and 1.5 mm in thickness, complying with the requirements of EN 10088-2. Carriers were contaminated with Staphylococcus aureus, methicillin-resistant S. aureus or Pseudomonas aeruginosa, respectively, together with an artificial wound secretion and left to dry at room temperature for 30 min. The wound dressings being tested were placed on the discs for the length of the exposure time, and after neutralization by thioglycolate in phosphate-buffered saline the number of surviving test organisms was then counted. The logarithmic reduction factor was calculated from the difference between the initial inoculum and the number of recovered test organisms. Results: The disc carrier test allowed determination of an antimicrobial efficacy in a realistic setting. It also imposed more stringent requirements on efficacy over time than the quantitative suspension test. The silver foam wound dressing showed a time-dependent antimicrobial efficacy. After 24-hour application time, the reduction factors against S. aureus, P. aeruginosa and the methicillin-resistant S. aureus were 1.9 ± 0.15, 2.1 ± 0.14 and 3.1 ± 0.18, respectively. Conclusion: The disc carrier test was a useful method for testing the antimicrobial efficacy of a foam silver dressing. The antimicrobial dressing exhibited an antimicrobial effect after 3 h and achieved a reduction >2 log against the tested bacterial strains in the presence of a simulated wound secretion after 24 h
Observations of pulsars at 9 millimetres
The behaviour of the pulsar spectrum at high radio frequencies can provide
decisive information about the nature of the radio emission mechanism. We
report recent observations of a selected sample of pulsars at lambda=9mm (32
GHz) with the 100-m Effelsberg radio telescope.Three pulsars, PSR B0144+59, PSR
B0823+26, and PSR B2022+50, were detected for the first time at this frequency.
We confirm the earlier flux density measurements for a sample of six pulsars,
and we are able to place upper flux density limits for another 12 pulsars. We
find that all pulsar spectra have a simple form that can be described using
only three parameters, one of which is the lifetime of short nano-pulses in the
emission region.The study of the transition region from coherent to incoherent
emission needs further and more sensitive observations at even higher radio
frequencies.Comment: to appear in A&A (in press), 7 pages, 3 figure
Anomalous scattering of highly dispersed pulsars
We report multifrequency measurements of scatter broadening times for nine
highly dispersed pulsars over a wide frequency range (0.6 -- 4.9 GHz). We find
the scatter broadening times to be larger than expected and to scale with
frequency with an average power-law index of , i.e. significantly
less than that expected from standard theories. Such possible discrepancies
have been predicted very recently by Cordes & Lazio.Comment: 7 pages, 4 figures, accepted for publication in ApJ Letter
Toward An Empirical Theory of Pulsar Emission. VII. On the Spectral Behavior of Conal Beam Radii and Emission Heights
In this paper we return to the old problem of conal component-pair widths and
profile dimensions. Observationally, we consider a set of 10 pulsars with
prominent conal component pairs, for which well measured profiles exist over
the largest frequency range now possible. Apart from some tendency to narrow at
high frequency, the conal components exhibit almost constant widths. We use all
three profile measures, the component separation as well as the outside
half-power and 10% widths, to determine conal beam radii, which are the focus
of our subsequent analysis. These radii at different frequencies are well
fitted by a relationship introduced by Thorsett (1991), but the resulting
parameters are highly correlated. Three different types of behavior are found:
one group of stars exhibits a continuous variation of beam radius which can be
extrapolated down to the stellar surface along the ``last open field lines''; a
second group exhibits beam radii which asymptotically approach a minimum high
frequency value that is 3--5 times larger; and a third set shows almost no
spectral change in beam radius at all. The first two behaviors are associated
with outer-cone component pairs; whereas the constant separation appears to
reflect inner-cone emission.Comment: 21 pages, 11 figures, accepted for publication in Astrophysical
Journal, uses aaste
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