207 research outputs found
Dynamic modeling of three-phase upflow fixed-bed reactor including pore diffusion
The dynamics of a three-phase upflow fixed-bed reactor are investigated using a non-isothermal heterogeneous model including gas–liquid and liquid–solid mass transfer and diffusion/reaction phenomena inside the catalyst. The partial differential and algebraic equations involving three integration variables (time and two space coordinates) are solved via discretization of the spatial coordinates coupled with the Gear method. For a multistep hydrogenation on a shell catalyst, the model exhibits significant effects of the external and above all internal resistance to hydrogen transfer but also non-trivial internal hydrocarbons concentration profiles. A simplified model is compared with the extended one and with experimental data in transient regime. In the investigated conditions—hydrocarbons in large excess—the diffusion of hydrocarbons appears to be actually not limiting, so that the simplest model predicts accurately the transient reactor behavior
Contributions of upper gut hormones and motility to the energy intake-suppressant effects of intraduodenal nutrients in healthy, lean men - a pooled-data analysis
Accepted: 8 August 2016We have previously identified pyloric pressures and plasma cholecystokinin (CCK) concentrations as independent determinants of energy intake following administration of intraduodenal lipid and intravenous CCK. We evaluated in healthy men whether these parameters also determine energy intake in response to intraduodenal protein, and whether, across the nutrients, any predominant gastrointestinal (GI) factors exist, or many factors make small contributions. Data from nine published studies, in which antropyloroduodenal pressures, GI hormones, and GI /appetite perceptions were measured during intraduodenal lipid or protein infusions, were pooled. In all studies energy intake was quantified immediately after the infusions. Specific variables for inclusion in a mixed-effects multivariable model for determination of independent predictors of energy intake were chosen following assessment for collinearity, and within-subject correlations between energy intake and these variables were determined using bivariate analyses adjusted for repeated measures. In models based on all studies, or lipid studies, there were significant effects for amplitude of antral pressure waves, premeal glucagon-like peptide-1 (GLP-1) and time-to-peak GLP-1 concentrations, GLP-1 AUC and bloating scores (P < 0.05), and trends for basal pyloric pressure (BPP), amplitude of duodenal pressure waves, peak CCK concentrations, and hunger and nausea scores (0.05 < P ≤ 0.094), to be independent determinants of subsequent energy intake. In the model including the protein studies, only BPP was identified as an independent determinant of energy intake (P < 0.05). No single parameter was identified across all models, and effects of the variables identified were relatively small. Taken together, while GI mechanisms contribute to the regulation of acute energy intake by lipid and protein, their contribution to the latter is much less. Moreover, the effects are likely to reflect small, cumulative contributions from a range of interrelated factors.Gudrun Schober, Kylie Lange, Robert E. Steinert, Amy T. Hutchison, Natalie D. Luscombe-Marsh, Maria F. Landrock, Michael Horowitz, Radhika V. Seimon and Christine Feinle-Bisse
Self-help interventions for anxiety disorders: An overview.
Anxiety disorders are highly prevalent and are associated with a marked impairment in quality of life and a huge economic cost to society. Unfortunately, a considerable number of people who struggle with anxiety do not seek or receive adequate treatment. Self-help interventions have been proposed to constitute a relatively cheap, effective, efficient, and low-threshold intervention for anxiety disorders. This paper offers a critical discussion of their advantages and disadvantages and the evidence for their effectiveness. We conclude that guided self-help can play a major role in mental health care for patients with anxiety disorders. However, several research questions need to be answered before broad-scale dissemination is possible. The Internet will continue to play a prominent role in the further development of this field of research and clinical practice
How Does CMB + BBN Constrain New Physics?
Recent cosmic microwave background (CMB) results from BOOMERANG, MAXIMA, and
DASI provide cosmological constraints on new physics that can be competitive
with those derived from Big Bang Nucleosynthesis (BBN). In particular, both CMB
and BBN can be used to place limits on models involving neutrino degeneracy and
additional relativistic degrees of freedom. However, for the case of the CMB,
these constraints are, in general, sensitive to the assumed priors. We examine
the CMB and BBN constraints on such models and study the sensitivity of ``new
physics" to the assumed priors. If we add a constraint on the age of the
universe (t_0 \ga 11 Gyr), then for models with a cosmological constant, the
range of baryon densities and neutrino degeneracy parameters allowed by the CMB
and BBN is fairly robust: , \deln \la 6, \xi_e \la
0.3. In the absence of new physics, models without a cosmological constant are
only marginally compatible with recent CMB observations (excluded at the 93%
confidence level).Comment: 6 pages, 5 figures; version to appear in Phys. Rev.
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV
We report the STAR measurement of Phi meson production in Au+Au and p+p
collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi
spectra and yields are obtained at mid-rapidity for five centrality bins in
Au+Au collisions and for non-singly-diffractive p+p collisions. It is found
that the Phi transverse momentum distributions from Au+Au collisions are better
fitted with a single-exponential while the p+p spectrum is better described by
a double-exponential distribution. The measured nuclear modification factors
indicate that Phi production in central Au+Au collisions is suppressed relative
to peripheral collisions when scaled by the number of binary collisions. The
systematics of versus centrality and the constant Phi/K- ratio versus beam
species, centrality, and collision energy rule out kaon coalescence as the
dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let
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