31,849 research outputs found
Optimization of cholesterol removal, growth and fermentation patterns of Lactobacillus acidophilus ATCC 4962 in the presence of mannitol, fructo-oligosaccharide and inulin: a response surface methodology approach
Aims: To optimize cholesterol removal by Lactobacillus acidophilus ATCC 4962 in the presence of prebiotics, and study the growth and fermentation patterns of the prebiotics. Methods and Results: Lactobacillus acidophilus ATCC 4962 was screened in the presence of six prebiotics, namely sorbitol, mannitol, maltodextrin, hi-amylose maize, fructo-oligosaccharide (FOS) and inulin in order to determine the best combination for highest level of cholesterol removal. The first-order model showed that the combination of inoculum size, mannitol, FOS and inulin was best for removal of cholesterol. The second-order polynomial regression model estimated the optimum condition of the factors for cholesterol removal by L. acidophilus ATCC 4962 to be 2.64% w/v inoculum size, 4.13% w/v mannitol, 3.29% w/v FOS and 5.81% w/v inulin. Analyses of growth, mean doubling time and short-chain fatty acid (SCFA) production using quadratic models indicated that cholesterol removal and the production of SCFA were growth associated. Conclusions: Optimum cholesterol removal was obtained from the fermentation of L. acidophilus ATCC 4962 in the presence of mannitol, FOS and inulin. Cholesterol removal and the production of SCFA appeared to be growth associated and highly influenced by the prebiotics. Significance and Impact of the Study: Response surface methodology proved reliable in developing the model, optimizing factors and analysing interaction effects. The results provide better understanding on the interactions between probiotic and prebiotics for the removal of cholesterol
Boundary layer analysis of the Navier-Stokes equations with Generalized Navier boundary conditions
We study the weak boundary layer phenomenon of the Navier-Stokes equations in
a 3D bounded domain with viscosity, , under generalized Navier
friction boundary conditions, in which we allow the friction coefficient to be
a (1, 1) tensor on the boundary. When the tensor is a multiple of the identity
we obtain Navier boundary conditions, and when the tensor is the shape operator
we obtain conditions in which the vorticity vanishes on the boundary. By
constructing an explicit corrector, we prove the convergence of the
Navier-Stokes solutions to the Euler solution as the viscosity vanishes. We do
this both in the natural energy norm with a rate of order as
well as uniformly in time and space with a rate of order near the boundary and in the interior,
where decrease to 0 as the regularity of the initial velocity
increases. This work simplifies an earlier work of Iftimie and Sueur, as we use
a simple and explicit corrector (which is more easily implemented in numerical
applications). It also improves a result of Masmoudi and Rousset, who obtain
convergence uniformly in time and space via a method that does not yield a
convergence rate.Comment: Additional references and several typos fixe
Effect of type of load on stress analysis of thin-walled ducts
The standard procedure for qualifying the design of duct (pipe) systems in the Space Shuttle Main Engine (SSME) has been fairly well defined. However, since pipe elbows are quite common and important in the SSME duct systems, a clear understanding of the detailed stress profile of the components is necessary for accurate structural and life assessments. This study was initiated to predict the stress profile at/near the tangent point along the cross section of the duct under various types of loads. Also, this study was further extended to understand the stiffening effect on stresses due to pressure at the tangent point. The intention of this study was to identify the importance of selecting proper locations for mounting strain gauges and to utilize the obtained results to anchor dynamic models for accurate structural and life assessments of the SSME ducts under a dynamic environment. The finite element method was utilized in this study
Association of PET-measured myocardial flow reserve with echocardiography-estimated pulmonary artery systolic pressure in patients with hypertrophic cardiomyopathy
BackgroundPulmonary hypertension (PH) is a known complication of HCM and is a strong predictor of mortality. We aim to investigate the relationship between microvascular dysfunction measured by quantitative PET and PH in HCM patients.MethodsEighty-nine symptomatic HCM patients were included in the study. Each patient underwent two 20-min 13N-NH3 dynamic PET scans for rest and stress conditions, respectively. A 2-tissue irreversible compartmental model was used to fit the segments time activity curves for estimating segmental and global myocardial blood flow (MBF) and myocardial flow reserve (MFR). Echocardiographic derived PASP was utilized to estimate PH.ResultsPatients were categorized into two groups across PASP: PH (PASP > 36 mmHg) and no-PH (PASP ≤ 36 mmHg). patients with PH had larger left atrium, ratio of higher inflow early diastole (E) and atrial contraction (A) waves, E/A, and ratio of inflow and peak early diastolic waves, E/e', significantly reduced global stress MBF (1.85 ± 0.52 vs. 2.13 ± 0.56 ml/min/g; p = 0.024) and MFR (2.21 ± 0.57 vs. 2.62 ± 0.75; p = 0.005), while the MBFs at rest between the two groups were similar. There were significant negative correlations between global stress MBF/MFR and PASP (stress MBF: r = -0.23, p = 0.03; MFR: r = -0.32, p = 0.002); for regional MBF and MFR measurements, the highest linear correlation coefficients were observed in the septal wall (stress MBF: r = -0.27, p = 0.01; MFR: r = -0.31, p = 0.003). Global MFR was identified to be independent predictor for PH in multivariate regression analysis.ConclusionEchocardiography-derived PASP is negatively correlated with global MFR measured by 13N-NH3 dynamic PET. Global MFR is suggested to be an index of PH in HCM patients.</div
The Solar pp and hep Processes in Effective Field Theory
The strategy of modern effective field theory is exploited to pin down
accurately the flux factors for the and processes in the Sun.
The technique used is to combine the high accuracy established in few-nucleon
systems of the "standard nuclear physics approach" (SNPA) and the systematic
power counting of chiral perturbation theory (ChPT) into a consistent effective
field theory framework. Using highly accurate wave functions obtained in the
SNPA and working to \nlo3 in the chiral counting for the current, we make
totally parameter-free and error-controlled predictions for the and
processes in the Sun.Comment: 5 pages, aipproc macros are included. Talk given at International
Nuclear Physics Conference 2001, Berkeley, California, July 30 - August 3,
200
Orthogonal vertical velocity dispersion distributions produced by bars
In barred galaxies, the contours of stellar velocity dispersions ()
are generally expected to be oval and aligned with the orientation of bars.
However, many double-barred (S2B) galaxies exhibit distinct peaks on
the minor axis of inner bars, which we termed "-humps," while two local
minima are present close to the ends of inner bars, i.e.,
"-hollows." Analysis of numerical simulations shows that
-humps or hollows should play an important role in generating the
observed -humps+hollows in low-inclination galaxies. In order to
systematically investigate the properties of in barred galaxies, we
apply the vertical Jeans equation to a group of well-designed three-dimensional
bar+disk(+bulge) models. A vertically thin bar can lower along the
bar and enhance it perpendicular to the bar, thus generating
-humps+hollows. Such a result suggests that -humps+hollows
can be generated by the purely dynamical response of stars in the presence of
a, sufficiently massive, vertically thin bar, even without an outer bar. Using
self-consistent -body simulations, we verify the existence of vertically
thin bars in the nuclear-barred and S2B models which generate prominent
-humps+hollows. Thus the ubiquitous presence of -humps+hollows
in S2Bs implies that inner bars are vertically thin. The addition of a bulge
makes the -humps more ambiguous and thus tends to somewhat hide the
-humps+hollows. We show that may be used as a kinematic
diagnostic of stellar components that have different thickness, providing a
direct perspective on the morphology and thickness of nearly face-on bars and
bulges with integral field unit spectroscopy.Comment: 14 pages, 16 figures. Accepted for publication in Ap
Ab Initio Theory of Gate Induced Gaps in Graphene Bilayers
We study the gate voltage induced gap that occurs in graphene bilayers using
\textit{ab initio} density functional theory. Our calculations confirm the
qualitative picture suggested by phenomenological tight-binding and continuum
models. We discuss enhanced screening of the external interlayer potential at
small gate voltages, which is more pronounced in the \textit{ab initio}
calculations, and quantify the role of crystalline inhomogeneity using a
tight-binding model self-consistent Hartree calculation.Comment: 7 pages, 7 figures; the effect of r3 coupling included; typo
correcte
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