5,722 research outputs found
Enhancement of perfluorooctanoate and perfluorooctanesulfonate activity at acoustic cavitation bubble interfaces
Acoustic cavitation driven by ultrasonic irradiation decomposes and mineralizes the recalcitrant perfluorinated surfactants perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Pyrolytic cleavage of the ionic headgroup is the rate-determining step. In this study, we examine the sonochemical adsorption of PFOX, where X = S for PFOS and A for PFOA, by determining kinetic order and absolute rates over an initial PFOX concentration range of 20 nM to 200 ÎŒM. Sonochemical PFOX kinetics transition from pseudo-first-order at low initial concentrations, [PFOX]_i 40 ÎŒM, as the bubble interface sites are saturated. At PFOX concentrations below 100 ÎŒM, concentration-dependent rates were modeled with LangmuirâHinshelwood (LH) kinetics. Empirically determined rate maximums, V_(Max)^(âPFOA) = 2230 ± 560 nM min^â1 and V_(Max)^(âPFOS) = 230 ± 60 nM min^â1, were used in the LH model, and sonochemical surface activities were estimated to be K_(Sono)^(PFOS) = 120000 M^â1 and K_(Sono)^(PFOA) = 28500 M^â1, 60 and 80 times greater than equilibrium surface activities, K_(Eq)^(PFOS) and K_(Eq)^(PFOA). These results suggest enhanced sonochemical degradation rates for PFOX when the bubble interface is undersaturated. The present results are compared to previously reported sonochemical kinetics of nonvolatile surfactants
LOGISTIC REGRESSION ANALYSIS TO DETERMINE FACTORS CONTRIBUTING TO SUMMER FEEDLOT DEATHS
Summer heat has already been identified as a major factor for cattle deaths in the feedlot. This study attempts to assess what other factors contribute to and/or influence cattle deaths. Identifying multiple factors that contribute to summer feedlot deaths could aid feedlot managers in implementation of mitigation strategies and minimize the loss of nearly finished cattle. Daily pen, cattle, and nutritional characteristics were recorded and included in this generalized linear mixed model analysis. Cattle data were obtained from cattle pens at a single location from July 1, 2010 to July 31, 2010. Hourly weather data were acquired from this feed yard while solar radiation was received from a neighboring town. Rather than using multiple weather variables, a single comprehensive climate index that summarizes several weather variables is used to capture the apparent feel of the weather. After reviewing the data, a statistical model is developed and odds ratios are computed for statistical inference. According to these odds ratios, cattle fed on severe west slopes had significantly higher odds of death than other types of slopes. Analysis of feed intake indicates pens consuming 16 pounds of feed per head or less during July 16 â 18 have higher odds of death than other consumption levels
Quantitative Determination of the Complex Polarizability of Individual Nanoparticles by Scanning Cavity Microscopy
COMPARING FUNCTIONAL DATA ANALYSIS AND HYSTERESIS LOOPS WHEN TESTING TREATMENTS FOR REDUCING HEAT STRESS IN DAIRY COWS
Various techniques are commonly used to reduce heat stress, including sprayers and misters, shading, and changes in feed. Oftentimes studies are performed where researchers do not control the times when animals use shading or other means available to reduce heat stress, making it hard to test differences between treatments. Two methods are used on data from a study where Holstein cows were given free access to weight activated âcow showers.â Functional data analysis can be used to model body temperature as a function of time and environmental variables such as the Heat Load Index. Differences between treatment groups can be tested using a Functional Bayesian MCMC model. Alternatively hysteresis loops, such as the ellipse, formed by a plot of air temperature or the Heat Load Index against body temperature over the course of a day can be estimated and their parameters used to test differences between cows with access to showers and cows without. Results from an R package hysteresis, which can estimate these loops and their parameters are illustrated. Functional data analysis allows for looser assumptions regarding the body temperature curve and the ability to look for differences between groups at specific time points, while hysteresis loops give the ability to look at heat stress over the course of a day holistically in terms of parameters such as amplitude, lag, internal heat load and central values
COMPARISON OF SAS PROC NLIN AND NLMIXED FOR PARAMETER ESTIMATION IN PET MODEL
Cattle body temperatures were measured under semi-controlled hot cyclic chamber temperatures. The four-parameter nonlinear PET model, is used to estimate body temperature in cattle challenged by heat stress. For each steer, the parameters can be estimated by the Nlin procedure and the sensitivity of each animal can be studied. It is also desirable to generalize the results by using the Nlmixed procedure to combine both the fixed and random effects. When comparing the results from the two procedures, we found heterogeneity among animals and/or days caused convergence problems for proc Nlmixed. Simulation studies were used to study how deviations from homogeneity effected the accuracy of parameter estimates, coverage of confidence intervals, and measures of nonlinear behavior when using the PET model to describe the dynamics of heat stress in cattle
Connectivity and tree structure in finite graphs
Considering systems of separations in a graph that separate every pair of a
given set of vertex sets that are themselves not separated by these
separations, we determine conditions under which such a separation system
contains a nested subsystem that still separates those sets and is invariant
under the automorphisms of the graph.
As an application, we show that the -blocks -- the maximal vertex sets
that cannot be separated by at most vertices -- of a graph live in
distinct parts of a suitable tree-decomposition of of adhesion at most ,
whose decomposition tree is invariant under the automorphisms of . This
extends recent work of Dunwoody and Kr\"on and, like theirs, generalizes a
similar theorem of Tutte for .
Under mild additional assumptions, which are necessary, our decompositions
can be combined into one overall tree-decomposition that distinguishes, for all
simultaneously, all the -blocks of a finite graph.Comment: 31 page
The Dipole Anisotropy of the 2mass Redshift Survey
We estimate the flux weighted acceleration on the Local Group (LG) from the
near-infrared Two Micron All Sky Redshift Survey (2MRS). The near-infrared flux
weighted dipoles are very robust because they closely approximate a mass
weighted dipole, bypassing the effects of redshift distortions and require no
preferred reference frame. We use this method with the redshift information to
determine the change in dipole with distance. The LG dipole seemingly converges
by 60 Mpc/h. Assuming convergence, the comparison of the 2MRS flux dipole and
the CMB dipole provides a value for the combination of the mass density and
luminosity bias parameters Omega_m^0.6/b_L= 0.40+/-0.09.Comment: 4 pages, 2 figures, Contribution to Rencontres de Moriond: Contents
and Structures of the Universe, March 18-25, 2006, La Thuil
NATO and CSDP: party and public positioning in Germany and France
This is the final version. Available on open access from the NATO Defense College via the link in this recordVolkswagen Foundatio
Generalized Interpolation Material Point Approach to High Melting Explosive with Cavities Under Shock
Criterion for contacting is critically important for the Generalized
Interpolation Material Point(GIMP) method. We present an improved criterion by
adding a switching function. With the method dynamical response of high melting
explosive(HMX) with cavities under shock is investigated. The physical model
used in the present work is an elastic-to-plastic and thermal-dynamical model
with Mie-Gr\"uneissen equation of state. We mainly concern the influence of
various parameters, including the impacting velocity , cavity size , etc,
to the dynamical and thermodynamical behaviors of the material. For the
colliding of two bodies with a cavity in each, a secondary impacting is
observed. Correspondingly, the separation distance of the two bodies has a
maximum value in between the initial and second impacts. When the
initial impacting velocity is not large enough, the cavity collapses in a
nearly symmetric fashion, the maximum separation distance increases
with . When the initial shock wave is strong enough to collapse the cavity
asymmetrically along the shock direction, the variation of with
does not show monotonic behavior. Our numerical results show clear indication
that the existence of cavities in explosive helps the creation of ``hot
spots''.Comment: Figs.2,4,7,11 in JPG format; Accepted for publication in J. Phys. D:
Applied Physic
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