2,087 research outputs found
The ACD Model: Predictability of the Time Between Concecutive Trades
Forecasting ability of several parameterizations of ACD models are compared to benchmark linear autoregressions for inter-trade durations. The estimation of parametric ACD models requires both the choice of a conditional density for durations and the specification of a functional form for the conditional mean duration. Our results provide guidance for choosing among different parameterizations and for developing better forecasting models to predict one-step-ahead, multi-step-ahead, and the whole density of time durations. For evaluating density forecasts, we propose a new constructive test, which is based on the series of probability integral transforms. The choice of the conditional distribution for inter-trade durations does not seem to affect the out-of sample performances of the ACD at short, as well as longer, horizons. Yet, this choice becomes critical when forecasting the density.
The Analysis of Emission Lines; A Meeting in Honour of the 70th Birthdays of D. E. Osterbrock and M. J. Seaton
A review of the field of astronomical spectroscopy with emphasis on emission lines in astrophysical plasmas is presented. A brief history of UV spectroscopy instruments is given, following by a discussion and tabulation of major atlases of UV emission-line objects to date (mid-1994). A discussion of the major diagnostic UV emission lines in the approx. 912-3200 A spectral region that are useful for determining electron densities, temperatures, abundances, and extinction in low- to moderate density plasmas is given, with examples of applications to selected objects. The review concludes by presenting some recent results from HST, HUT, and IUE on UV emission-line spectroscopy of nebulae and active galaxies
Feeling the pressure: Differences in blood pressure among working undergraduate students
Studies have shown that being employed while pursuing post-secondary education may lead to higher levels of perceived stress and unhealthy behaviours. The current study involved a hierarchical regression model to analyze both perceived stress and blood pressure (BP) as a function of the number of hours worked per week (HW). Seventy-four undergraduate students from the from the University of Windsor completed measures of perceived stress, coping, physical activity, and daily hassles, and had their BP recorded after ten minutes of rest. There was a correlation between HW and systolic BP (r = .23, p = .04). Problem-focused coping was negatively associated with levels of perceived stress (r = -.23, p \u3c .05), whereas emotion-focused coping was positively associated (r = -.57, p \u3c .001). Energy drink users had higher HW than non-users (t = 2.14, p \u3c .05). There was no change in BP from before and after questionnaire administration
Spitzer observations of extragalactic H II regions - III. NGC 6822 and the hot star, H II region connection
Using the short-high module of the Infrared Spectrograph on the Spitzer Space
Telescope, we have measured the [S IV] 10.51, [Ne II] 12.81, [Ne III] 15.56,
and [S III] 18.71-micron emission lines in nine H II regions in the dwarf
irregular galaxy NGC 6822. These lines arise from the dominant ionization
states of the elements neon (Ne, Ne) and sulphur (S,
S), thereby allowing an analysis of the neon to sulphur abundance ratio
as well as the ionic abundance ratios Ne/Ne and S/S.
By extending our studies of H II regions in M83 and M33 to the lower
metallicity NGC 6822, we increase the reliability of the estimated Ne/S ratio.
We find that the Ne/S ratio appears to be fairly universal, with not much
variation about the ratio found for NGC 6822: the median (average) Ne/S ratio
equals 11.6 (12.20.8). This value is in contrast to Asplund et al.'s
currently best estimated value for the Sun: Ne/S = 6.5. In addition, we
continue to test the predicted ionizing spectral energy distributions (SEDs)
from various stellar atmosphere models by comparing model nebulae computed with
these SEDs as inputs to our observational data, changing just the stellar
atmosphere model abundances. Here we employ a new grid of SEDs computed with
different metallicities: Solar, 0.4 Solar, and 0.1 Solar. As expected, these
changes to the SED show similar trends to those seen upon changing just the
nebular gas metallicities in our plasma simulations: lower metallicity results
in higher ionization. This trend agrees with the observations.Comment: 22 pages, 13 figures. To be published in MNRAS. reference added and
typos fixed. arXiv admin note: text overlap with arXiv:0804.0828, which is
paper II by Rubin et al. (2008
Pouvons-nous rĂ©duire la dose dâazote aprĂšs un retour de prairie?
Affiche prĂ©sentĂ©e dans le cadre du Colloque de l'ARC, «Des racines et des ailes pour la recherche collĂ©giale», dans le cadre du 85e CongrĂšs de lâAcfas, UniversitĂ© McGill, MontrĂ©al, les 8 et 9 mai 2017.Au QuĂ©bec, les Ă©missions de gaz Ă effet de serre (GES) dâorigine agricole reprĂ©sentent prĂšs de 8 % des Ă©missions totales. Environ 40 % des Ă©missions agricoles dĂ©coule de lâusage des engrais minĂ©raux et des engrais de ferme. Tout apport excĂ©dentaire dâengrais azotĂ© dans les cultures se traduit par des Ă©missions supplĂ©mentaires dâoxyde nitreux (N2O), un puissant gaz Ă effet de serre qui contribue aux Ă©missions de GES. Plusieurs Ă©tudes ont dĂ©montrĂ© que la culture de maĂŻs nâavait pas besoin dâapports importants dâazote en postlevĂ©e, aprĂšs des retours de prairie. En collaboration avec des producteurs agricoles, 16 sites dâessais de fertilisation azotĂ©e ont Ă©tĂ© implantĂ©s sur des retours de prairie ayant reçu des engrais de ferme. Les traitements consistaient Ă apporter 4 doses dâazote minĂ©ral (0, 40, 80 et 120 kg N/ha). La teneur en nitrates du sol ainsi que les rendements Ă la rĂ©colte ont Ă©tĂ© Ă©valuĂ©s. La teneur en nitrates a confirmĂ© lâeffet significatif de la prairie et des engrais de ferme sur la teneur en azote disponible pour le maĂŻs. Lâapport dâazote minĂ©ral nâa pas eu dâeffet significatif sur les rendements en azote, Ă lâexception dâun site. Le maĂŻs cultivĂ© sur un retour de prairie ne nĂ©cessite pas un ajout dâengrais minĂ©ral. Ăliminer lâapport dâazote rĂ©duit tant les Ă©missions de GES que les dĂ©penses en engrais pour les producteurs
Totally Destructive Many-Particle Interference
In a general, multi-mode scattering setup, we show how the permutation
symmetry of a many-particle input state determines those scattering unitaries
which exhibit strictly suppressed many-particle transition events. We formulate
purely algebraic suppression laws that identify these events and show that the
many-particle interference at their origin is robust under weak disorder and
imperfect indistinguishability of the interfering particles. Finally, we
demonstrate that all suppression laws so far described in the literature are
embedded in the general framework that we here introduce.Comment: 6 pages, 2 figure
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