Plant canopy shape and the influences on UV exposures to the canopy

The solar spectra at selected sites over hemispherical, conical and pinnacle plant canopy models has been evaluated with a dosimetric technique. The irradiance at the sites varies by up to a factor of 0.31 compared to the irradiance on a horizontal plane. The biologically effective (UVBE) exposures evaluated with the dosimetric technique at sites over the plant canopy are up to 19% of that on a horizontal plane. Compared to a spectroradiometer, the technique provides a more practicable method of measuring the UVBE exposures at multiple sites over a plant canopy. Usage of a dosimeter at one site to provide the exposures at that site for different sun angles introduces an error of more than 50%. Knowledge of the spectra allowed the UV and UVBE exposures to be calculated at each site along with the exposures to the entire canopies. These were dependent on the sun angle and the canopy shape. For plant damage, the UVBE was a maximum of about 1.4 mJ cm-2/min. Compared to the hemispherical canopy, the UVBE exposure for generalised plant damage was 45% less for the pinnacle canopy and 23% less for the conical canopy. The canopy exposures could not be determined from measurements of the ambient exposure

A Black Hole of > 6 Solar Masses in the X-ray Nova XTE J1118+480

Observations of the quiescent X-ray nova XTE J1118+480 with the new 6.5-m MMT have revealed that the velocity amplitude of the dwarf secondary is 698 +/- 14 km/s and the orbital period of the system is 0.17013 +/- 0.00010 d. The implied value of the mass function, f(M) = 6.00 +/- 0.36 solar masses, provides a hard lower limit on the mass of the compact primary that greatly exceeds the maximum allowed mass of a neutron star. Thus we conclude that the compact primary is a black hole. Among the eleven dynamically established black-hole X-ray novae, the large mass function of XTE J1118+480 is rivaled only by that of V404 Cyg. We estimate that the secondary supplies 34% +/- 8% of the total light at 5900A and that its spectral type is in the range K5V to M1V. A double-humped I-band light curve is probably due to ellipsoidal modulation, although this interpretation is not entirely secure because of an unusual 12-minute offset between the spectroscopic and photometric ephemerides. Assuming that the light curve is ellipsoidal, we present a provisional analysis which indicates that the inclination of the system is high and the mass of the black hole is correspondingly modest. The broad Balmer emission lines (FWHM = 2300-2900 km/s) also suggest a high inclination. For the range of spectral types given above, we estimate a distance of 1.8 +/- 0.6 kpc.Comment: 4 pages, 2 figures, to appear in ApJ Letters; Minor changes to Fig 1

Developing a Model to Simulate the Effect of Hypothermia on Cerebral Blood Flow and Metabolism

Hypoxic ischemic encephalopathy (HIE) is a significant cause of death and neurological disability in newborns. Therapeutic hypothermia at 33.5 °C is one of the most common treatments in HIE and generally improves outcome; however 45-55% of injuries still result in death or severe neurodevelopmental disability. We have developed a systems biology model of cerebral oxygen transport and metabolism to model the impact of hypothermia on the piglet brain (the neonatal preclinical animal model) tissue physiology. This computational model is an extension of the BrainSignals model of the adult brain. The model predicts that during hypothermia there is a 5.1% decrease in cerebral metabolism, 1.1% decrease in blood flow and 2.3% increase in cerebral tissue oxygenation saturation. The model can be used to simulate effects of hypothermia on the brain and to help interpret bedside recordings

Response of VIRGO detectors to pre-big-bang gravitons

The sensitivity achievable by a pair of VIRGO detectors to stochastic and isotropic gravitational wave backgrounds produced in pre-big-bang models is discussed in view of the development of a second VIRGO interferometer. We describe a semi-analytical technique allowing to compute the signal-to-noise ratio for (monotonic or non-monotonic) logarithmic energy spectra of relic gravitons of arbitrary slope. We apply our results to the case of two correlated and coaligned VIRGO detectors and we compute their achievable sensitivities. We perform our calculations both for the usual case of minimal string cosmological scenario and in the case of a non-minimal scenario where a long dilaton dominated phase is present prior to the onset of the ordinary radiation dominated phase. In this framework, we investigate possible improvements of the achievable sensitivities by selective reduction of the thermal contributions (pendulum and pendulum's internal modes) to the noise power spectra of the detectors. Since a reduction of the shot noise does not increase significantly the expected sensitivity of a VIRGO pair (in spite of the relative spatial location of the two detectors) our findings support the experimental efforts directed towards a substantial reduction of thermal noise.Comment: 23 pages in Latex styl

Gravitational wave bursts from cusps and kinks on cosmic strings

The strong beams of high-frequency gravitational waves (GW) emitted by cusps and kinks of cosmic strings are studied in detail. As a consequence of these beams, the stochastic ensemble of GW's generated by a cosmological network of oscillating loops is strongly non Gaussian, and includes occasional sharp bursts that stand above the ``confusion'' GW noise made of many smaller overlapping bursts. Even if only 10% of all string loops have cusps these bursts might be detectable by the planned GW detectors LIGO/VIRGO and LISA for string tensions as small as $G \mu \sim 10^{-13}$. In the implausible case where the average cusp number per loop oscillation is extremely small, the smaller bursts emitted by the ubiquitous kinks will be detectable by LISA for string tensions as small as $G \mu \sim 10^{-12}$. We show that the strongly non Gaussian nature of the stochastic GW's generated by strings modifies the usual derivation of constraints on $G \mu$ from pulsar timing experiments. In particular the usually considered ``rms GW background'' is, when G \mu \gaq 10^{-7}, an overestimate of the more relevant confusion GW noise because it includes rare, intense bursts. The consideration of the confusion GW noise suggests that a Grand Unified Theory (GUT) value $G \mu \sim 10^{-6}$ is compatible with existing pulsar data, and that a modest improvement in pulsar timing accuracy could detect the confusion noise coming from a network of cuspy string loops down to $G \mu \sim 10^{-11}$. The GW bursts discussed here might be accompanied by Gamma Ray Bursts.Comment: 24 pages, 3 figures, Revtex, submitted to Phys. Rev.

Phenomenology of a realistic accelerating universe using only Planck-scale physics

Modern data is showing increasing evidence that the Universe is accelerating. So far, all attempts to account for the acceleration have required some fundamental dimensionless quantities to be extremely small. We show how a class of scalar field models (which may emerge naturally from superstring theory) can account for acceleration which starts in the present epoch with all the potential parameters O(1) in Planck units.Comment: 4 pages including 4 figures. Final version accepted for publication in PRL with expanded discussion of the relationship to other quintessence research. No changes to our own wor

Vacuum defects without a vacuum

Topological defects can arise in symmetry breaking models where the scalar field potential $V(\phi)$ has no minima and is a monotonically decreasing function of $|\phi|$. The properties of such vacuumless defects are quite different from those of the ``usual'' strings and monopoles. In some models such defects can serve as seeds for structure formation, or produce an appreciable density of mini-black holes.Comment: 11 pages, REVTeX, 1 Postscript figure. Minor changes. Final version, to appear in Phys. Rev.

An HST/WFPC Survey of Bright Young Clusters in M31. II. Photometry of Less Luminous Clusters in the Fields

We report on the properties of 89 low mass star clusters located in the vicinity of luminous young clusters (blue globulars) in the disk of M31. 82 of the clusters are newly detected. We have determined their integrated magnitudes and colors, based on a series of Hubble Space Telescope Wide Field/Planetary Camera 2 exposures in blue and red (HST filters F450W and F814W). The integrated apparent magnitudes range from F450W = 17.5 to 22.5, and the colors indicate a wide range of ages. Stellar color-magnitude diagrams for all clusters were obtained and those with bright enough stars were fit to theoretical isochrones to provide age estimates. The ages range from 12 Myr to >500 Myr. Reddenings, which average E(F450 - F814) = 0.59 with a dispersion of 0.21 magnitudes, were derived from the main sequence fitting for those clusters. Comparison of these ages and integrated colors with single population theoretical models with solar abundances suggests a color offset of 0.085 magnitudes at the ages tested. Estimated ages for the remaining clusters are based on their measured colors. The age-frequency diagram shows a steep decline of number with age, with a large decrease in number per age interval between the youngest and the oldest clusters detected.Comment: 20 pages, 9 figure

Review of Methods of Power-Spectrum Analysis as Applied to Super-Kamiokande Solar Neutrino Data

To help understand why different published analyses of the Super-Kamiokande solar neutrino data arrive at different conclusions, we have applied six different methods to a standardized problem. The key difference between the various methods rests in the amount of information that each processes. A Lomb-Scargle analysis that uses the mid times of the time bins and ignores experimental error estimates uses the least information. A likelihood analysis that uses the start times, end times, and mean live times, and takes account of the experimental error estimates, makes the greatest use of the available information. We carry out power-spectrum analyses of the Super-Kamiokande 5-day solar neutrino data, using each method in turn, for a standard search band (0 to 50 yr-1). For each method, we also carry out a fixed number (10,000) of Monte-Carlo simulations for the purpose of estimating the significance of the leading peak in each power spectrum. We find that, with one exception, the results of these calculations are compatible with those of previously published analyses. (We are unable to replicate Koshio's recent results.) We find that the significance of the peaks at 9.43 yr-1 and at 43.72 yr-1 increases progressively as one incorporates more information into the analysis procedure.Comment: 21 pages, 25 figure

Evaluating the quality of evidence from a network meta-analysis

Systematic reviews that collate data about the relative effects of multiple interventions via network meta-analysis are highly informative for decision-making purposes. A network meta-analysis provides two types of findings for a specific outcome: the relative treatment effect for all pairwise comparisons, and a ranking of the treatments. It is important to consider the confidence with which these two types of results can enable clinicians, policy makers and patients to make informed decisions. We propose an approach to determining confidence in the output of a network meta-analysis. Our proposed approach is based on methodology developed by the Grading of Recommendations Assessment, Development and Evaluation (GRADE) Working Group for pairwise meta-analyses. The suggested framework for evaluating a network meta-analysis acknowledges (i) the key role of indirect comparisons (ii) the contributions of each piece of direct evidence to the network meta-analysis estimates of effect size; (iii) the importance of the transitivity assumption to the validity of network meta-analysis; and (iv) the possibility of disagreement between direct evidence and indirect evidence. We apply our proposed strategy to a systematic review comparing topical antibiotics without steroids for chronically discharging ears with underlying eardrum perforations. The proposed framework can be used to determine confidence in the results from a network meta-analysis. Judgements about evidence from a network meta-analysis can be different from those made about evidence from pairwise meta-analyses. © 2014 Salanti et al