World status of wild Rangifer tarandus populations

We recognized 184 herds of wild Rangifer tarandus, 102 in North America, 55 in Europe, 24 in Asia and 3 on South Georgia. Seventy-five percent of the world population of 3.3 to 3.9 million animals occurred in nine herds. All seven herds larger than 120 000 animals were censused by some means of aerial photography and all were increasing. Herds between 20 000 and 120 000 were most often censused using aerial strip transect methods, while total counts were usually employed to census smaller herds. The most pronounced changes in Rangifer herd status between 1979 and 1985 occurred in North America where population "estimates for five herds increased by a total of about one million animals. Part of this increase is attributable to a change from visual to photographic surveys. Eighty-three percent of North American, 88% of European, and 68% of Asian herds were stable or increasing

Ice and mineral licks used by caribou in winter

In winter, barren-ground caribou obtain minerals from ice and soil licks. Between December and April we have seen caribou cratering on the surface of frozen lakes and licking the ice. Ice samples from eight licks on four lakes contained concentrations of calcium, magnesium, sodium, potassium, phosphorus, chloride and sulphate many times higher than in the surrounding unlicked ice or than would be expected in lake water. Soil licks being used in March and June had high concentrations of calcium, magnesium, sodium phosphorus and potassium. In winter caribou may be seeking supplements of all of the major mineral elements (calcium, magnesium, sodium and potassium) at ice and soil licks because lichens, their staple winter diet, are low in minerals and may also reduce the absorption of some minerals

Space tug propulsion system failure mode, effects and criticality analysis

For purposes of the study, the propulsion system was considered as consisting of the following: (1) main engine system, (2) auxiliary propulsion system, (3) pneumatic system, (4) hydrogen feed, fill, drain and vent system, (5) oxygen feed, fill, drain and vent system, and (6) helium reentry purge system. Each component was critically examined to identify possible failure modes and the subsequent effect on mission success. Each space tug mission consists of three phases: launch to separation from shuttle, separation to redocking, and redocking to landing. The analysis considered the results of failure of a component during each phase of the mission. After the failure modes of each component were tabulated, those components whose failure would result in possible or certain loss of mission or inability to return the Tug to ground were identified as critical components and a criticality number determined for each. The criticality number of a component denotes the number of mission failures in one million missions due to the loss of that component. A total of 68 components were identified as critical with criticality numbers ranging from 1 to 2990

The relationship between food intake and predation risk in migratory caribou and implications to caribou and wolf population dynamics

We examined the hypothesis that spring migration in barren-ground caribou (Rangifer tarandus) enhances access to high quality food, reduces predation risks or both. We related our findings to the hypothesis that one of the consequences of migration is that prey populations cannot be regulated by predation because predators are unable to respond numerically to changes in abundance of migratory prey. In the Northwest Territories, migration to calving grounds by pregnant cows reduced the risk of predation on neonates. Wolf (Canis lupus) densities on calving grounds averaged only 22% of winter range densities because most wolves denned near tree line. The quality and quantity of food that was available to cows that migrated to calving grounds was lower than for bulls and other caribou that lagged far behind the pregnant cows during spring migration. Fecal nitrogen levels were higher in bulls than in cows in late May and early June but there were no differences in mid or late June. Areas occupied by bulls in late May had a greater biomass of live sedges than on the calving ground in early June. It appears that although food in July is abundant and nutritious, insect harassment prevents efficient feeding. Body fat reserves in both sexes declined to almost zero by mid-July, the lowest level of the year. Insect numbers declined in August and body fat levels increased to the highest level of the year by early September. Because the timing of caribou's return to the hunting ranges of tree line denning wolves was related to caribou density, our data were inconsistent with the suggested consequence of migration. Tree line denning by wolves and density-dependent changes in caribou migration suggests a mechanism for population regulation in caribou and wolves. We suggest that the process is as follows; when caribou numbers increase, some density-dependent factor causes range expansion in August (e.g., competition for food) causing caribou to return earlier to the hunting ranges of tree line denning wolves, more denning wolves have access to caribou, wolf pup survival increases and wolf numbers increase. The effect on caribou population growth will depend on the timing and magnitude of the wolf numerical response

Finding the Center of Mass of a Soft Spring

This article shows how to use calculus to find the center of mass position of a soft cylindrical helical spring that is suspended vertically. The spring is non-uniformly stretched by the action of gravity. A general expression for the vertical position of the center of mass is obtained.Comment: LaTeX, 7 pages, 2 figures. Minor changes to agree with published versio

New Langevin and Gradient Thermostats for Rigid Body Dynamics

We introduce two new thermostats, one of Langevin type and one of gradient (Brownian) type, for rigid body dynamics. We formulate rotation using the quaternion representation of angular coordinates; both thermostats preserve the unit length of quaternions. The Langevin thermostat also ensures that the conjugate angular momenta stay within the tangent space of the quaternion coordinates, as required by the Hamiltonian dynamics of rigid bodies. We have constructed three geometric numerical integrators for the Langevin thermostat and one for the gradient thermostat. The numerical integrators reflect key properties of the thermostats themselves. Namely, they all preserve the unit length of quaternions, automatically, without the need of a projection onto the unit sphere. The Langevin integrators also ensure that the angular momenta remain within the tangent space of the quaternion coordinates. The Langevin integrators are quasi-symplectic and of weak order two. The numerical method for the gradient thermostat is of weak order one. Its construction exploits ideas of Lie-group type integrators for differential equations on manifolds. We numerically compare the discretization errors of the Langevin integrators, as well as the efficiency of the gradient integrator compared to the Langevin ones when used in the simulation of rigid TIP4P water model with smoothly truncated electrostatic interactions. We observe that the gradient integrator is computationally less efficient than the Langevin integrators. We also compare the relative accuracy of the Langevin integrators in evaluating various static quantities and give recommendations as to the choice of an appropriate integrator.Comment: 16 pages, 4 figure

Duct Excision is Still Necessary to Rule out Breast Cancer in Patients Presenting with Spontaneous Bloodstained Nipple Discharge

Introduction. Spontaneous nipple discharge is the third most common reason for presentation to a symptomatic breast clinic. Benign and malignant causes of spontaneous nipple discharge continue to be difficult to distinguish. We analyse our experience of duct excisions for spontaneous nipple discharge to try to identify features that raise suspicion of breast cancer and to identify features indicative of benign disease that would be suitable for nonoperative management. Methods. Details of one hundred and ninety-four patients who underwent duct excision for spontaneous nipple discharge between 1995 and 2005 were analysed. Results. Malignant disease was identified in 11 (5.7%) patients, 4 invasive and 7 insitu, which was 10.2% of those presenting with bloodstained discharge. All patients with malignant disease had bloodstained discharge. Discharge due to malignant disease was more likely to be bloodstained than that due to benign causes (Fisher's exact test, 2-tailed P value = 0.00134). Conclusion. Our findings do not support a policy of conservative management of spontaneous bloodstained nipple discharge. Cases of demonstrable spontaneous bloodstained nipple discharge should undergo duct excision to prevent malignant lesions being missed

A self-consistent, multivariate method for the determination of gas-phase rate coefficients, applied to reactions of atmospheric VOCs and the hydroxyl radical

Gas-phase rate coefficients are fundamental to understanding atmospheric chemistry, yet experimental data are not available for the oxidation reactions of many of the thousands of volatile organic compounds (VOCs) observed in the troposphere. Here, a new experimental method is reported for the simultaneous study of reactions between multiple different VOCs and OH, the most important daytime atmospheric radical oxidant. This technique is based upon established relative rate concepts but has the advantage of a much higher throughput of target VOCs. By evaluating multiple VOCs in each experiment, and through measurement of the depletion in each VOC after reaction with OH, the OH + VOC reaction rate coefficients can be derived. Results from experiments conducted under controlled laboratory conditions were in good agreement with the available literature for the reaction of 19 VOCs, prepared in synthetic gas mixtures, with OH. This approach was used to determine a rate coefficient for the reaction of OH with 2,3-dimethylpent-1-ene for the first time; k =  5.7 (±0.3)  ×  10⁻¹¹ cm³ molecule⁻¹ s⁻¹. In addition, a further seven VOCs had only two, or fewer, individual OH rate coefficient measurements available in the literature. The results from this work were in good agreement with those measurements. A similar dataset, at an elevated temperature of 323 (±10) K, was used to determine new OH rate coefficients for 12 aromatic, 5 alkane, 5 alkene and 3 monoterpene VOC + OH reactions. In OH relative reactivity experiments that used ambient air at the University of York, a large number of different VOCs were observed, of which 23 were positively identified. Due to difficulties with detection limits and fully resolving peaks, only 19 OH rate coefficients were derived from these ambient air samples, including 10 reactions for which data were previously unavailable at the elevated reaction temperature of T =  323 (±10) K

Direct measurements of OH and other product yields from the HO2 + CH3C(O)O2 reaction

The reaction CH3C(O)O2 + HO2 → CH3C(O)OOH+O2 (Reaction R5a), CH3C(O)OH+O3 (Reaction R5b), CH3+CO2+OH+O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293±2)K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a) = 0.37±0.10, α(R5b) =0.12±0.04 and α(R5c) =0.51±0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5) =(2.4±0.4)×10-11 cm3 molecule-1 s-1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5% in OH concentrations in tropical rainforest areas and increases of up to 10% at altitudes of 6-8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx