What Does It Cost to Harvest Grass Silage?

Many farmers thinking about putting up grass silage are wondering, How much will it cost? Let\u27s see what it does cost so you can do a better job of weighing the advantages against the costs of ensiling part of a crop

Quantifying the challenges of detecting unseen planetary companions with transit timing variations

Both ground and space-based transit observatories are poised to significantly increase the number of known transiting planets and the number of precisely measured transit times. The variation in a planet's transit times may be used to infer the presence of additional planets. Deducing the masses and orbital parameters of such planets from transit time variations (TTVs) alone is a rich and increasingly relevant dynamical problem. In this work, we evaluate the extent of the degeneracies in this process, systematically explore the dependence of TTV signals on several parameters and provide phase space plots that could aid observers in planning future observations. Our explorations are focused on a likely-to-be prevalent situation: a known transiting short-period Neptune or Jupiter-sized planet and a suspected external low-mass perturber on a nearly-coplanar orbit. Through approximately 10^7 N-body simulations, we demonstrate how TTV signal amplitudes may vary by orders of magnitude due to slight variations in any one orbital parameter (0.001 AU in semimajor axis, 0.005 in eccentricity, or a few degrees in orbital angles), and quantify the number of consecutive transit observations necessary in order to obtain a reasonable opportunity to characterize the unseen planet (approximately greater or equal to 50 observations). Planets in or near period commensurabilities of the form p:q, where p < 21 and q < 4, produce distinct TTV signatures, regardless of whether the planets are actually locked in a mean motion resonance. We distinguish these systems from the secular systems in our explorations. Additionally, we find that computing the autocorrelation function of a TTV signal can provide a useful diagnostic for identifying possible orbits for additional planets and suggest that this method could aid integration of TTV signals in future studies of particular exosystems.Comment: 53 pages total, including 18 figures, 1 table, and 1 appendix. Accepted for publication in ApJ. Better resolution plots will appear in online journa

Density and population estimation of the Bornean elephant (elephas maximus borneensis) in Sabah

Problem statement: In Asia, four elephant subspecies have been identified, Elephas maximus maximus from Sri Lanka, Elephas maximus summatranus from Sumatra, Elephas maximus borneensis (based on recent DNA analysis) from Borneo and Elephas maximus indicus, from mainland Asia. The Bornean elephant has a limited distribution and is found only in the northeastern part of the island, (Malaysian Sabah and Indonesian Kalimantan). Previous estimations for the population in Sabah have ranged between 500-2000 elephants. These estimations have been carried out through a non-systematic approach, either via interview or from direct sightings or extrapolating population count data from limited sites. In order to prepare the conservation plan for this species in Sabah, there is a need to establish reliable information on their density and population size. The main objective of this study was to determine the elephant density and population size in five main elephant managed ranges in Sabah. Approach: In this study, relative distribution and spatial density of the Bornean elephant was developed and established, using a systematic line transect survey and a long term monitoring of dung decay rates. We conducted the elephant population census in Sabah between July 2007 and December 2008. Using a line-transect dung-count methodology, we surveyed 216 line transects; with a total distance of 186.12 km, in five main elephant managed ranges. Namely (i) Tabin Wildlife Reserve, (ii) Lower Kinabatangan, (iii) Central Forest, (iv) North Kinabatangan and (v) Ulu Kalumpang. Results: We presented the elephant density estimate using long term monitoring of dung decay rates. In each range, the elephant’s density varied depending on the size of the suitable habitat. The size of the suitable habitat was derived from WWF’s study report (WWF-Malaysia, 2008). Densities were analyzed following line-transect analysis guidelines and were computed using the software Distance v6.0. Conclusion: Our survey indicated that approximately 2,040 (95% CI: 1,184-3,652) elephants remain in the five main ranges in Sabah, with the largest population being in the unprotected central forests. Elephant density was highest in ranges where habitat has been removed and elephants are concentrated in remaining forest areas. These results provide new baseline data for the elephant population in Sabah

Selenomethionine and methyl selenocysteine: multiple-dose pharmacokinetics in selenium-replete men

According to the Nutritional Prevention of Cancer (NPC) trial, a selenized yeast supplement containing selenium, 200 mcg/day, decreased the incidence of total cancer, cancers of the prostate, colon and lung, and cancer mortality. The active agent in the selenized yeast supplement was assumed to be selenomethionine (SEMET), although the supplement had not been well speciated. The SELECT study, largely motivated by the NPC trial, enrolling nearly 40 times as many subjects, showed unequivocally that selenium 200 mcg/day, with selenium in the form of SEMET, does not protect selenium-replete men against prostate or other major cancer. The agent tested by SELECT, pure SEMET, could have been different from the selenized yeast tested in NPC. One of the selenium forms suspected of having chemopreventive effects, and which may have been present in the NPC agent, is methyl selenocysteine (MSC). This study, with 29 selenium-replete patients enrolled in a randomized, double-blind trial, compared the multiple-dose toxicity, pharmacokinetics and pharmacodynamics of MSC and SEMET. Patients were on trial for 84 days. No toxicity was observed. Although SEMET supplementation increased blood selenium concentration more than MSC did, neither form had a more than minimal impact on the two major selenoproteins: selenoprotein P(SEPP1) and glutathione peroxidase(GPX)

The Physical Parameters of the Micro-quasar S26 in the Sculptor Group Galaxy NGC 7793

NGC 7793 - S26 is an extended source (350 pc $\times$ 185 pc) previously studied in the radio, optical and x-ray domains. It has been identified as a micro-quasar which has inflated a super bubble. We used Integral Field Spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to analyse spectra between 3600--7000 \AA. This allowed us to derive fluxes and line ratios for selected nebular lines. Applying radiative shock model diagnostics, we estimate shock velocities, densities, radiative ages and pressures across the object. We show that S26 is just entering its radiative phase, and that the northern and western regions are dominated by partially-radiative shocks due to a lower density ISM in these directions. We determine a velocity of expansion along the jet of 330 km s$^{-1}$, and a velocity of expansion of the bubble in the minor axis direction of 132 km s$^{-1}$. We determine the age of the structure to be $4.1\times10^5$ yr, and the jet energy flux to be $(4-10)\times10^{40}$ erg s$^{-1}$ The jet appears to be collimated within $\sim0.25$ deg, and to undergo very little precession. If the relativistic $\beta \sim 1/3$, then some 4 M$_{\odot}$ of relativistic matter has already been processed through the jet. We conclude that the central object in S26 is probably a Black Hole with a mass typical of the ultra-luminous X-ray source population which is currently consuming a fairly massive companion through Roche Lobe accretion.Comment: Accepted for publication in MNRAS; 12 pages, 7 figures and 3 table

The shallow shelf approximation as a "sliding law" in a thermomechanically coupled ice sheet model

The shallow shelf approximation is a better ``sliding law'' for ice sheet modeling than those sliding laws in which basal velocity is a function of driving stress. The shallow shelf approximation as formulated by \emph{Schoof} [2006a] is well-suited to this use. Our new thermomechanically coupled sliding scheme is based on a plasticity assumption about the strength of the saturated till underlying the ice sheet in which the till yield stress is given by a Mohr-Coulomb formula using a modeled pore water pressure. Using this scheme, our prognostic whole ice sheet model has convincing ice streams. Driving stress is balanced in part by membrane stresses, the model is computable at high spatial resolution in parallel, it is stable with respect to parameter changes, and it produces surface velocities seen in actual ice streams.Comment: 12 pages of text; 4 tables; 27 figures; submitted to JGR Earth Surfac

On the formation of hot Neptunes and super-Earths

The discovery of short-period Neptune-mass objects, now including the remarkable system HD69830 (Lovis et al. 2006) with three Neptune analogues, raises difficult questions about current formation models which may require a global treatment of the protoplanetary disc. Several formation scenarios have been proposed, where most combine the canonical oligarchic picture of core accretion with type I migration (e.g. Terquem & Papaloizou 2007) and planetary atmosphere physics (e.g. Alibert et al. 2006). To date, published studies have considered only a small number of progenitors at late times. This leaves unaddressed important questions about the global viability of the models. We seek to determine whether the most natural model -- namely, taking the canonical oligarchic picture of core accretion and introducing type I migration -- can succeed in forming objects of 10 Earth masses and more in the innermost parts of the disc. This problem is investigated using both traditional semianalytic methods for modelling oligarchic growth as well as a new parallel multi-zone N-body code designed specifically for treating planetary formation problems with large dynamic range (McNeil & Nelson 2009). We find that it is extremely difficult for oligarchic tidal migration models to reproduce the observed distribution. Even under many variations of the typical parameters, we form no objects of mass greater than 8 Earth masses. By comparison, it is relatively straightforward to form icy super-Earths. We conclude that either the initial conditions of the protoplanetary discs in short-period Neptune systems were substantially different from the standard disc models we used, or there is important physics yet to be understood.Comment: 19 pages, 18 figures. Final version accepted to MNRAS 30 September 200