1,463 research outputs found
Breeding structure of Drosophila buzzatii in relation to competition in prickly pears (Opuntia ficus-indica)
Breeding structure of Drosophila buzzatii in relation to competition in prickly pears (Opuntia ficus-indica)
International audienc
Application of Artificial Neural Networks to Identify Equilibration in Computer Simulations
Determining which microstates generated by a thermodynamic simulation are representative of the ensemble for which sampling is desired is a ubiquitous, underspecified problem. Artificial neural networks are one type of machine learning algorithm that can provide a reproducible way to apply pattern recognition heuristics to underspecified problems. Here we use the open-source TensorFlow machine learning library and apply it to the problem of identifying which hypothetical observation sequences from a computer simulation are equilibrated and which are not. We generate training populations and test populations of observation sequences with embedded linear and exponential correlations. We train a two-neuron artificial network to distinguish the correlated and uncorrelated sequences. We find that this simple network is good enough for \u3e 98% accuracy in identifying exponentially-decaying energy trajectories from molecular simulations
Asteroseismological Observations of the Central Star of the Planetary Nebula NGC 1501
We report on a global CCD time-series photometric campaign to decode the
pulsations of the nucleus of the planetary nebula NGC1501. The star is hot and
hydrogen-deficient, similar to the pre-white-dwarf PG 1159 stars. NGC1501 shows
pulsational brightness variations of a few percent with periods ranging from 19
to 87 minutes. The variations are very complex, suggesting a pulsation spectrum
that requires a long unbroken time series to resolve. Our CCD photometry of the
star covers a two-week period in 1991 November, and used a global network of
observatories. We obtained nearly continuous coverage over an interval of one
week in the middle of the run. We have identified 10 pulsation periods, ranging
from 5235 s down to 1154 s. We find strong evidence that the modes are indeed
nonradial g-modes. The ratios of the frequencies of the largest-amplitude modes
agree with those expected for modes that are trapped by a density discontinuity
in the outer layers. We offer a model for the pulsation spectrum that includes
a common period spacing of 22.3 s and a rotation period of 1.17 days; the
period spacing allows us to assign a seismological mass of 0.55+/-0.03 Msun.Comment: 12 pages, AASTEX, 7 tables, 6 EPS figures, to appear in AJ, 12/96
Corrected version repairs table formatting and adds missing Table
Recommended from our members
The impact of component performance on the overall cycle performance of small-scale low temperature organic Rankine cycles
Low temperature organic Rankine cycles offer a promising technology for the generation of power from low temperature heat sources. Small-scale systems (~10kW) are of significant interest, however there is a current lack of commercially viable expanders. For a potential expander to be economically viable for small-scale applications it is reasonable to assume that the same expander must have the ability to be implemented within a number of different ORC applications. It is therefore important to design and optimise the cycle considering the component performance, most notably the expander, both at different thermodynamic conditions, and using alternative organic fluids. This paper demonstrates a novel modelling methodology that combines a previously generated turbine performance map with cycle analysis to establish at what heat source conditions optimal system performance can be achieved using an existing turbine design. The results obtained show that the same turbine can be effectively utilised within a number of different ORC applications by changing the working fluid. By selecting suitable working fluids, this turbine can be used to convert pressurised hot water at temperatures between 360K and 400K, and mass flow rates between 0.45kg/s and 2.7kg/s, into useful power with outputs between 1.5kW and 27kW. This is a significant result since it allows the same turbine to be implemented into a variety of applications, improving the economy of scale. This work has also confirmed the suitability of the candidate turbine for a range of low temperature ORC applications
Null Geodesics in Five Dimensional Manifolds
We analyze a class of 5D non-compact warped-product spaces characterized by
metrics that depend on the extra coordinate via a conformal factor. Our model
is closely related to the so-called canonical coordinate gauge of Mashhoon et
al. We confirm that if the 5D manifold in our model is Ricci-flat, then there
is an induced cosmological constant in the 4D sub-manifold. We derive the
general form of the 5D Killing vectors and relate them to the 4D Killing
vectors of the embedded spacetime. We then study the 5D null geodesic paths and
show that the 4D part of the motion can be timelike -- that is, massless
particles in 5D can be massive in 4D. We find that if the null trajectories are
affinely parameterized in 5D, then the particle is subject to an anomalous
acceleration or fifth force. However, this force may be removed by
reparameterization, which brings the correct definition of the proper time into
question. Physical properties of the geodesics -- such as rest mass variations
induced by a variable cosmological ``constant'', constants of the motion and 5D
time-dilation effects -- are discussed and are shown to be open to experimental
or observational investigation.Comment: 19 pages, REVTeX, in press in Gen. Rel. Gra
Increasing Short-Stay Unplanned Hospital Admissions among Children in England; Time Trends Analysis '97-'06
BACKGROUND: Timely care by general practitioners in the community keeps children out of hospital and provides better continuity of care. Yet in the UK, access to primary care has diminished since 2004 when changes in general practitioners' contracts enabled them to 'opt out' of providing out-of-hours care and since then unplanned pediatric hospital admission rates have escalated, particularly through emergency departments. We hypothesised that any increase in isolated short stay admissions for childhood illness might reflect failure to manage these cases in the community over a 10 year period spanning these changes.
METHODS AND FINDINGS: We conducted a population based time trends study of major causes of hospital admission in children 2 days. By 2006, 67.3% of all unplanned admissions were isolated short stays <2 days. The increases in admission rates were greater for common non-infectious than infectious causes of admissions.
CONCLUSIONS: Short stay unplanned hospital admission rates in young children in England have increased substantially in recent years and are not accounted for by reductions in length of in-hospital stay. The majority are isolated short stay admissions for minor illness episodes that could be better managed by primary care in the community and may be evidence of a failure of primary care services
Fulminant hepatic failure in murine hepatitis virus strain 3 infection: tissue-specific expression of a novel fgl2 prothrombinase.
Gravitational Microlensing Evidence for a Planet Orbiting a Binary Star System
The study of extra-solar planetary systems has emerged as a new discipline of
observational astronomy in the past few years with the discovery of a number of
extra-solar planets. The properties of most of these extra-solar planets were
not anticipated by theoretical work on the formation of planetary systems. Here
we report observations and light curve modeling of gravitational microlensing
event MACHO-97-BLG-41, which indicates that the lens system consists of a
planet orbiting a binary star system. According to this model, the mass ratio
of the binary star system is 3.8:1 and the stars are most likely to be a late K
dwarf and an M dwarf with a separation of about 1.8 AU. A planet of about 3
Jupiter masses orbits this system at a distance of about 7 AU. If our
interpretation of this light curve is correct, it represents the first
discovery of a planet orbiting a binary star system and the first detection of
a Jovian planet via the gravitational microlensing technique. It suggests that
giant planets may be common in short period binary star systems.Comment: 11 pages, with 1 color and 2 b/w Figures included (published version
Whole Earth Telescope observations of the hot helium atmosphere pulsating white dwarf EC 20058-5234
We present the analysis of a total of 177h of high-quality optical
time-series photometry of the helium atmosphere pulsating white dwarf (DBV) EC
20058-5234. The bulk of the observations (135h) were obtained during a WET
campaign (XCOV15) in July 1997 that featured coordinated observing from 4
southern observatory sites over an 8-day period. The remaining data (42h) were
obtained in June 2004 at Mt John Observatory in NZ over a one-week observing
period. This work significantly extends the discovery observations of this
low-amplitude (few percent) pulsator by increasing the number of detected
frequencies from 8 to 18, and employs a simulation procedure to confirm the
reality of these frequencies to a high level of significance (1 in 1000). The
nature of the observed pulsation spectrum precludes identification of unique
pulsation mode properties using any clearly discernable trends. However, we
have used a global modelling procedure employing genetic algorithm techniques
to identify the n, l values of 8 pulsation modes, and thereby obtain
asteroseismic measurements of several model parameters, including the stellar
mass (0.55 M_sun) and T_eff (~28200 K). These values are consistent with those
derived from published spectral fitting: T_eff ~ 28400 K and log g ~ 7.86. We
also present persuasive evidence from apparent rotational mode splitting for
two of the modes that indicates this compact object is a relatively rapid
rotator with a period of 2h. In direct analogy with the corresponding
properties of the hydrogen (DAV) atmosphere pulsators, the stable low-amplitude
pulsation behaviour of EC 20058 is entirely consistent with its inferred
effective temperature, which indicates it is close to the blue edge of the DBV
instability strip. (abridged)Comment: 19 pages, 8 figures, 5 tables, MNRAS accepte
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