The Effects of Cyclone Hudah on the Forest of Masoala Peninsula, Madagascar

Cyclones regularly impact the east coast of Madagascar but almost nothing is known about their effects on Malagasy ecosystems. On 2 April 2000 the powerful winds of Cyclone Hudah struck the humid forests in the northern part of Masoala Peninsula. An analysis of satellite images revealed that 3 % of the forest here was severely damaged or 22 % when just the forest of the northeast was considered. In 2001 the vegetation in this area was studied using fifteen 0.1 ha plots located in differently impacted sites. The cyclone had caused tree death (up to 53 % of the trunks within a plot); a reduction in trunk basal area (to 64 %); uprooting (to 46 %); snapping of trunks (to 51 %); reduction of crown volume (to mean of 83 %); an increase in herbs, liana and woody pioneer species and decrease in saplings of primary forest species; an increase in vegetation in the “shrub” layer and decrease in vegetation in the “canopy” layer. Among a sample of 340 trees killed by the cyclone, 39 % were uprooted, 37 % snapped, and 24 % were still standing. Mortality was relatively low for trees with either small or large trunk diameter compared to trees with intermediate size. In 2003 the plots were re - examined. Six had been impacted by human activities (fire or timber exploitation). A comparison between the vegetation in 2001 and 2003 in 6 plots that had been moderately or seriously impacted by Cyclone Hudah but not impacted by human activity revealed a further decrease in trunk density, an increase in the frequency of herbs and woody pioneers, a decrease in the frequency of liana and saplings of primary forest trees in the “shrub layer”, and an increase of vegetation in the “shrub layer” but decrease of vegetation in the “canopy layer”. The lack of recovery of this vegetation towards its pre - cyclone state may be explained by the impact of Cyclone Ihary, in 2002. Recovery may yet occur provided the vegetation is not impacted by human activities, particularly burning, that can derail this process. It is recommended that following cyclones conservation managers prioritize fire control

Day - time feeding ecology of Eulemur cinereiceps in the Agnalazaha Forest, Mahabo - Mananivo, Madagascar

The Agnalazaha Forest, a degraded fragment of littoral forest in southeast Madagascar, contains a small population of the endangered Eulemur cinereiceps To better conserve this species its feeding ecology was described by habituating two groups and recording their activities, the food types and species exploited, and the location of food trees by focal animal sampling. The lemurs’ environment was also described by measuring forest structure, and monitoring climate and phenology. In total, the groups were observed for 498 hours over 11 months. Monthly time spent feeding averaged 9.6 % of total observation time. The species was highly frugivorous (93 % of total time spent feeding). 55 different plant species were exploited for food. Time spent feeding and diet were not simply related to rainfall and temperature nor to food type availability. The two groups’ home ranges were 54.9 ha and 58.4 ha and showed a 40 % overlap. The overlap occurred in the swamp forest, which is rich in food plants. To improve the conservation of E. cinereiceps at the Agnalazaha Forest, it is recommended that: The swamp forest be included within the zone of strict conservation; important lemur food plants used for restoration; and alternative sources of timber and fuel wood provided for the local population, thereby allowing greater forest regeneration

The effect of poloidal velocity shear on the local development of current-driven instabilities

We perform a local (short-wavelength) linear stability analysis of an axisymmetric column of magnetized plasma with a nearly toroidal magnetic field and a smooth poloidal velocity shear by perturbing the equations of relativistic magnetohydrodynamics. We identify two types of unstable modes, which we call 'exponential' and 'overstable', respectively. The exponential modes are present in the static equilibria and their growth rates decrease with increasing velocity shear. The overstable modes are driven by the effects of velocity shear and dominate the exponential modes for sufficiently high shear values. We argue that these local instabilities can provide an important energy dissipation mechanism in astrophysical relativistic jets. Strong co-moving velocity shear arises naturally in the magnetic acceleration mechanism, therefore it may play a crucial role in converting Poynting-flux-dominated jets into matter-dominated jets, regulating the global acceleration and collimation processes, and producing the observed emission of blazars and gamma-ray bursts.Comment: 8 pages, 5 figures, submitted to MNRA

New insights into the evolution of the FR I radio galaxy 3C 270 (NGC 4261) from VLA and GMRT radio observations

We present Giant Metrewave Radio Telescope (GMRT) 240 MHz observations of the nearby luminous FR I radio source 3C 270, in the group-central elliptical NGC 4261. Combining these data with reprocessed Very Large Array (VLA) 1.55 and 4.8 GHz observations, we produce spectral index maps that reveal a constant spectral index along the jets and a gradual steepening from the ends of the jets through the lobes towards the nucleus. A Jaffe & Perola (JP) model fitted to the integrated spectrum of the source gives an asymptotic low-frequency index of $\alpha_{inj}=0.53_{-0.02}^{+0.01}$, while JP models fitted to the observed spectral index trend along the lobes allow us to estimate radiative ages of $\sim29$ Myr and $\sim37$ Myr for the west and east lobes respectively. Our age estimates are a factor of two lower than the 75-Myr upper limit derived from X-ray data (O'Sullivan et al. 2011). We find unlikely the scenario of an early supersonic phase in which the lobe expanded into the ISM at approximately Mach 6 (3500 km s$^{-1}$), and suggest that either the source underwent multiple AGN outbursts with possible large changes in jet power, or possibly that the source age that we find is due to a backflow that transports young electrons from the jet tips through the lobes toward the nucleus relatively quickly. We calculate that in the lobes the energy ratio of non-radiating to radiating particles is $\sim4-24$ indicating significant gas entrainment. If the lobes are in pressure balance with their surroundings, the total energy required to heat the entrained material is $10^{58}$ erg, $\sim$40% of the total enthalpy of the lobes.Comment: 14 pages, 11 figures, 8 tables. Accepted for publication by MNRAS. Revised throughout in response to referee's comment

A Merger Scenario for the Dynamics of Abell 665

We present new redshift measurements for 55 galaxies in the vicinity of the rich galaxy cluster Abell 665. When combined with results from the literature, we have good velocity measurements for a sample of 77 confirmed cluster members from which we derive the cluster's redshift z=0.1829 +/- 0.0005 and line-of-sight velocity dispersion of 1390 +/- 120 km/s. Our analysis of the kinematical and spatial data for the subset of galaxies located within the central 750 kpc reveals only subtle evidence for substructure and non-Gaussianity in the velocity distribution. We find that the brightest cluster member is not moving significantly relative to the other galaxies near the center of the cluster. On the other hand, our deep ROSAT high resolution image of A665 shows strong evidence for isophotal twisting and centroid variation, thereby confirming previous suggestions of significant substructure in the hot X-ray--emitting intracluster gas. In light of this evident substructure, we have compared the optical velocity data with N-body simulations of head-on cluster mergers. We find that a merger of two similar mass subclusters (mass ratios of 1:1 or 1:2) seen close to the time of core-crossing produces velocity distributions that are consistent with that observed.Comment: 30 pages and 7 figures. Accepted by the Astrophysical Journal Full resoultion figures 1 and 3 available in postscript at http://www.physics.rutgers.edu/~percy/A665paper.htm

Approche expérimentale de l’utilisation de glyphosate dans le contrôle de Melaleuca quinquenervia (Myrtaceae), une espèce envahissante dans la réserve communautaire de la forêt d’Analalava-Foulpointe (Madagascar)

Le Niaouli Melaleuca quinquenervia est une des espèces envahissantes les plus agressives à Madagascar et elle gagne de plus en plus de terrain en colonisant des milieux marécageux autour de la Nouvelle Aire Protégée de la forêt d’Analalava Foulpointe. L’inquiétude sur son envahissement augmente, et même si l’éradication paraît d’ores et déjà impossible, il convient de trouver dès maintenant une solution efficace pour contrôler son expansion jusqu’à l’aire protégée. Seul le contrôle chimique peut être envisagé pour cette espèce qui fait preuve d’une grande résilience face à la coupe et au feu. Cette étude vise à identifier le meilleur protocole d’utilisation de glyphosate dans le contrôle de l’invasion de M. quinquenervia dans la forêt d’Analalava Foulpointe. Cinq solutions de glyphosate de concentrations différentes, S1 (0 g /l), S2 (90 g/l), S3 (180 g/l), S4 (270g/l) et S5 (360g/l) ont été testées sur 200 individus, soit 40 individus pour chaque solution. Les solutions de glyphosate sur la surface coupée du tronc d’un individu ont été appliquées soit au pinceau, soit au pulvérisateur. Des suivis ont été faits pendant quatre mois, observant l’état des individus traités et l’impact du traitement sur les plantes ligneuses environnantes. La plupart des individus traités sont morts, présentant plus de 85% de taux de mortalité. Certaines plantes non ciblées ont été touchées (19 % des individus recensés), quel que soit la concentration en ingrédient actif de glyphosate et l’équipement utilisés. De cette expérience, le meilleur protocole d’utilisation de glyphosate est la concentration de 90 g/l de l’ingrédient actif appliquée sur la surface coupée d’un tronc traité en utilisant un pinceau.Melaleuca quinquenervia, one of the most aggressive invasive species in Madagascar, gains more and more ground and colonizes wetland environments around the New Protected Area of the Analalava forest in Foulpointe. Concerns over its invasion increase and even if eradication seems already impossible, we must now find an effective solution to control its expansion towards the protected area. Only chemical control may be considered for this species, given its resilience to cutting and fire. This study aims at identifying the best protocol for the use of glyphosate in controlling the invasion of M. quinquenervia in the Analalava forest in Foulpointe. Five solutions of different concentrations of glyphosate, S1 (0 g/l), S2 (90 g/l), S3 (180 g/l), S4 (270 g/l), and S5 (360 g/l) were tested on 200 individuals, or 40 individuals for each solution. Glyphosate solutions were applied on the cut surface of the trunk of an individual using either a brush or a sprayer. The controls were done for four months by observing the status on treated individuals and the impacts of the treatment on non - target plants. Most individuals treated are dead, showing an 85 % rate mortality. Some non - target plants were affected (19 % of the surveyed ones), regardless of the concentration of active ingredient glyphosate and of the equipment used. From these experiments, the best protocol for the glyphosate use is a concentration of 90 g/l of the active ingredient applied to the cut surface of the trunk treaty using a brush

The Dynamical State fo the Starless Dense Core FeSt 1-457: A Pulsating Globule?

High resolution molecular line observations of CS, HCO+, C18O and N2H+ were obtained toward the starless globule FeSt 1-457 in order to investigate its kinematics and chemistry. The HCO+ and CS spectra show clear self-reversed and asymmetric profiles across the face of the globule. The sense of the observed asymmetry is indicative of the global presence of expansion motions in the outer layers of the globule. These motions appear to be subsonic and significantly below the escape velocity of the globule. Comparison of our observations with near-infrared extinction data indicate that the globule is gravitationally bound. Taken together these considerations lead us to suggest that the observed expansion has its origin in an oscillatory motion of the outer layers of the globule which itself is likely in a quasi-stable state near hydrostatic equilibrium. Analysis of the observed linewidths of CO and N2H+ confirm that thermal pressure is the dominant component of the cloud's internal support. A simple calculation suggests that the dominant mode of pulsation would be an l = 2 mode with a period of 0.3 Myr. Deformation of the globule due to the large amplitude l = 2 oscillation may be responsible for the double-peaked structure of the core detected in high resolution extinction maps. Detailed comparison of the molecular-line observations and extinction data provides evidence for significant depletion of C18O and perhaps HCO+ while N2H+ may be undepleted to a cloud depth of about 40 magnitudes of visual extinction.Comment: to appear in ApJ vol 665 20 August 2007

Hydrodynamical simulations of the Sunyaev--Zel'dovich effect

We use a hydrodynamical N-body code to generate simulated maps, of size one square degree, of the thermal SZ effect. We study three different cosmologies; the currently-favoured low-density model with a cosmological constant, a critical-density model and a low-density open model. We stack simulation boxes corresponding to different redshifts in order to include contributions to the Compton y-parameter out to the highest necessary redshifts. Our main results are: 1. The mean y-distortion is around $4 \times 10^{-6}$ for low-density cosmologies, and $1 \times 10^{-6}$ for critical density. These are below current limits, but not by a wide margin in the former case. 2. In low-density cosmologies, the mean y-distortion comes from a broad range of redshifts, the bulk coming from $z < 2$ and a tail out to $z \sim 5$. For critical-density models, most of the contribution comes from $z < 1$. 3. The number of SZ sources above a given $y$ depends strongly on instrument resolution. For a one arcminute beam, there is around 0.1 sources per square degree with $y > 10^{-5}$ in a critical-density Universe, and around 8 such sources per square degree in low-density models. Low-density models with and without a cosmological constant give very similar results. 4. We estimate that the {\sc Planck} satellite will be able to see of order 25000 SZ sources if the Universe has a low density, or around 10000 if it has critical density.Comment: 9 pages LaTeX file with eleven figures (including four in colour) incorporated (uses mn.sty and epsf). Further colour images and animations at http://star-www.cpes.susx.ac.uk/~andrewl/sz/sz.html Updated to match published versio

Quasar Proper Motions and Low-Frequency Gravitational Waves

We report observational upper limits on the mass-energy of the cosmological gravitational-wave background, from limits on proper motions of quasars. Gravitational waves with periods longer than the time span of observations produce a simple pattern of apparent proper motions over the sky, composed primarily of second-order transverse vector spherical harmonics. A fit of such harmonics to measured motions yields a 95%-confidence limit on the mass-energy of gravitational waves with frequencies <2e-9 Hz, of <0.11/h*h times the closure density of the universe.Comment: 15 pages, 1 figure. Also available at http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/index.htm

The Brightest Cluster Galaxy in Abell 85: The Largest Core Known so far

We have found that the brightest cluster galaxy (BCG) in Abell~85, Holm 15A, displays the largest core so far known. Its cusp radius, $r_{\gamma} = 4.57 \pm 0.06$ kpc ($4.26^{\prime\prime}\pm 0.06^{\prime\prime}$), is more than 18 times larger than the mean for BCGs, and $\geq1$ kpc larger than A2261-BCG, hitherto the largest-cored BCG (Postman, Lauer, Donahue, et al. 2012) Holm 15A hosts the luminous amorphous radio source 0039-095B and has the optical signature of a LINER. Scaling laws indicate that this core could host a supermassive black hole (SMBH) of mass $M_{\bullet}\thicksim (10^{9}-10^{11})\,M_{\odot}$. We suggest that cores this large represent a relatively short phase in the evolution of BCGs, whereas the masses of their associated SBMH might be set by initial conditions.Comment: 14 pages, 3 figure, 2 tables, accepted for publication in ApJ Letters on October 6th, 2014, replacement of previous manuscript submitted on May 30th, 2014 to astro-p