Detection and location of a partial blockage in a pipeline using damping of fluid transients

The effects of a partial blockage on pipeline transients are investigated analytically. A partial blockage is simulated using an orifice equation, and the influence of the blockage on the unsteady pipe flow is considered in the governing equations using a Dirac delta function. A simplified, linear dimensionless governing equation has been derived, and an analytical solution expressed in terms of a Fourier series has been developed under nonvarying boundary conditions. The linear analysis indicates that pipe friction and a partial blockage both introduce damping on fluid transients. The friction damping and blockage damping are exponential for each of the individual harmonic components. For each individual harmonic component, the blockage-induced damping depends on the blockage magnitude and position and is also independent of measurement location and the transient event. A new blockage detection method using the blockage-induced transient damping is developed based on the analytical solution. The magnitude of the blockage-induced damping rate indicates the size of the blockage, and the ratios of different damping rates can be used to locate the blockage. The proposed blockage detection method has been successfully used in detecting, locating, and quantifying a pipe blockage based on laboratory experiments. [Abstract from author

Carotid Intima-Media Thickness Progression in HIV-Infected Adults Occurs Preferentially at the Carotid Bifurcation and Is Predicted by Inflammation.

BackgroundShear stress gradients and inflammation have been causally associated with atherosclerosis development in carotid bifurcation regions. The mechanism underlying higher levels of carotid intima-media thickness observed among HIV-infected individuals remains unknown.Methods and resultsWe measured carotid intima-media thickness progression and development of plaque in the common carotid, bifurcation region, and internal carotid artery in 300 HIV-infected persons and 47 controls. The median duration of follow-up was 2.4 years. When all segments were included, the rate of intima-media thickness progression was greater in HIV-infected subjects compared with controls after adjustment for traditional risk factors (0.055 vs. 0.024 mm/year, P=0.016). Rate of progression was also greater in the bifurcation region (0.067 vs. 0.025 mm/year, P=0.042) whereas differences were smaller in the common and internal regions. HIV-infected individuals had a greater incidence of plaque compared with controls in the internal (23% vs. 6.4%, P=0.0037) and bifurcation regions (34% vs. 17%, P=0.014). Among HIV-infected individuals, the rate of progression in the bifurcation region was more rapid compared with the common carotid, internal, or mean intima-media thickness; in contrast, progression rates among controls were similar at all sites. Baseline hsCRP was elevated in HIV-infected persons and was a predictor of progression in the bifurcation region.ConclusionsAtherosclerosis progresses preferentially in the carotid bifurcation region in HIV-infected individuals. hsCRP, a marker of inflammation, is elevated in HIV and is associated with progression in the bifurcation region. These data are consistent with a model in which the interplay between hemodynamic shear stresses and HIV-associated inflammation contribute to accelerated atherosclerosis. (J Am Heart Assoc. 2012;1:jah3-e000422 doi: 10.1161/JAHA.111.000422.)Clinical trial registrationURL: http://clinicaltrials.gov. Unique identifier: NCT01519141

Low-Froude-number stable flows past mountains

A new approximate analysis is presented for stably stratified flows at low Froude number F past mountains of heightH. In the “top” layer where the streamlines pass above the surface of themountain, there is a perturbation flow. This approximately matches the lower flow in the “middle” ‘horizontal’ layer [M] in which the streamlines pass round the mountain in nearly horizontal planes, as in Drazin’s (DRAZIN P. G., On the steady flow of a fluid of variable density past an obstacle, Tellus, 13 (1961) 239-251) model. The pressure associated with the diverging streamlines on the lee side of the summit layer flow drives the separated flow in the horizontal layer (which is not included in Drazin’s model). This explains the vortical wake flow in experiments and in the “inviscid” computations of Smolarkiewicz and Rotunno (SMOLARKIEWICZ P. K. and ROTUNNO R., Low Froude number flow past three-dimensional obstacles. Part I: Baroclinically generated lee vortices, J. Atmos. Sci., 46 (1989) 1154-1164). A method for estimating the height HT FH of the cut-off mountain is derived, as a function of upstream shear, mountain shape and other parameters. Recent laboratory experiments have confirmed how the curvature of the oncoming shear flow profile

Thermal conductivity of lightly Sr- and Zn-doped La2_2CuO4_4 single crystals

Both ab-plane and c-axis thermal conductivities ($\kappa_{ab}$ and $\kappa_c$) of lightly doped La$_{2-x}$Sr$_x$CuO$_4$ and La$_2$Cu$_{1-y}$Zn$_y$O$_4$ single crystals ($x$ or $y$ = 0 -- 0.04) are measured from 2 to 300 K. It is found that the low-temperature phonon peak (at 20 -- 25 K) is significantly suppressed upon Sr or Zn doping even at very low doping, though its precise doping dependences show interesting differences between the Sr and Zn dopants, or between the $ab$ plane and the c axis. Most notably, the phonon peak in $\kappa_c$ decreases much more quickly with Sr doping than with Zn doping, while the phonon-peak suppression in $\kappa_{ab}$ shows an opposite trend. It is discussed that the scattering of phonons by stripes is playing an important role in the damping of the phonon heat transport in lightly doped LSCO, in which static spin stripes has been observed by neutron scattering. We also show $\kappa_{ab}$ and $\kappa_c$ data of La$_{1.28}$Nd$_{0.6}$Sr$_{0.12}$CuO$_4$ and La$_{1.68}$Eu$_{0.2}$Sr$_{0.12}$CuO$_4$ single crystals to compare with the data of the lightly doped crystals for the discussion of the role of stripes. At high temperature, the magnon peak (i.e., the peak caused by the spin heat transport near the N\'{e}el temperature) in $\kappa_{ab}(T)$ is found to be rather robust against Zn doping, while it completely disappears with only 1% of Sr doping.Comment: 7 pages, 4 figures, accepted for publication in Phys. Rev.

Sodium atoms and clusters on graphite: a density functional study

Sodium atoms and clusters (N<5) on graphite (0001) are studied using density functional theory, pseudopotentials and periodic boundary conditions. A single Na atom is observed to bind at a hollow site 2.45 A above the surface with an adsorption energy of 0.51 eV. The small diffusion barrier of 0.06 eV indicates a flat potential energy surface. Increased Na coverage results in a weak adsorbate-substrate interaction, which is evident in the larger separation from the surface in the cases of Na_3, Na_4, Na_5, and the (2x2) Na overlayer. The binding is weak for Na_2, which has a full valence electron shell. The presence of substrate modifies the structures of Na_3, Na_4, and Na_5 significantly, and both Na_4 and Na_5 are distorted from planarity. The calculated formation energies suggest that clustering of atoms is energetically favorable, and that the open shell clusters (e.g. Na_3 and Na_5) can be more abundant on graphite than in the gas phase. Analysis of the lateral charge density distributions of Na and Na_3 shows a charge transfer of about 0.5 electrons in both cases.Comment: 20 pages, 6 figure

Stochastic stability versus localization in chaotic dynamical systems

We prove stochastic stability of chaotic maps for a general class of Markov random perturbations (including singular ones) satisfying some kind of mixing conditions. One of the consequences of this statement is the proof of Ulam's conjecture about the approximation of the dynamics of a chaotic system by a finite state Markov chain. Conditions under which the localization phenomenon (i.e. stabilization of singular invariant measures) takes place are also considered. Our main tools are the so called bounded variation approach combined with the ergodic theorem of Ionescu-Tulcea and Marinescu, and a random walk argument that we apply to prove the absence of ``traps'' under the action of random perturbations.Comment: 27 pages, LaTe

Increasing peptide identifications and decreasing search times for ETD spectra by pre-processing and calculation of parent precursor charge

<p>Abstract</p> <p>Background</p> <p>Electron Transfer Dissociation [ETD] can dissociate multiply charged precursor polypeptides, providing extensive peptide backbone cleavage. ETD spectra contain charge reduced precursor peaks, usually of high intensity, and whose pattern is dependent on its parent precursor charge. These charge reduced precursor peaks and associated neutral loss peaks should be removed before these spectra are searched for peptide identifications. ETD spectra can also contain ion-types other than c and z<b>˙</b>. Modifying search strategies to accommodate these ion-types may aid in increased peptide identifications. Additionally, if the precursor mass is measured using a lower resolution instrument such as a linear ion trap, the charge of the precursor is often not known, reducing sensitivity and increasing search times. We implemented algorithms to remove these precursor peaks, accommodate new ion-types in noise filtering routine in OMSSA and to estimate any unknown precursor charge, using Linear Discriminant Analysis [LDA].</p> <p>Results</p> <p>Spectral pre-processing to remove precursor peaks and their associated neutral losses prior to protein sequence library searches resulted in a 9.8% increase in peptide identifications at a 1% False Discovery Rate [FDR] compared to previous OMSSA filter. Modifications to the OMSSA noise filter to accommodate various ion-types resulted in a further 4.2% increase in peptide identifications at 1% FDR. Moreover, ETD spectra when searched with charge states obtained from the precursor charge determination algorithm is shown to be up to 3.5 times faster than the general range search method, with a minor 3.8% increase in sensitivity.</p> <p>Conclusion</p> <p>Overall, there is an 18.8% increase in peptide identifications at 1% FDR by incorporating the new precursor filter, noise filter and by using the charge determination algorithm, when compared to previous versions of OMSSA.</p