136 research outputs found
Viscosity effects on sand flow regimes and transport velocity in horizontal pipelines
Solids transport in multiphase systems is one of the issues under the umbrella of ‘‘flow assurance.’ But unlike issues such as waxes and hydrates, solids transport has received relatively little interest to date. The overall aim of this research was to investigate the fluid viscosity effects on sand particle transport characteristics in pipelines. Investigations were conducted using a 3-inch test facility for oil and a 4- inch flow loop for water and CMC experiments. Three oil viscosities were used including 105 cP, 200 cP and 340 cP. The sand used had a density of 2650 kg/m3 and a median diameter of 0.2 mm. The sand loadings were 50 lb/1000 bbl and 200lb/1000bbl. Based on the King et al (2000) sand minimum transport condition definition, the sand transport velocity for water, CMC solutions and oil (105 cP, 200 cP and 340 cP) were determined by visual observation and camera. The observed sand/oil flow regimes were compared. For oil/sand tests, it was observed that the dominant regime when approaching the critical sand transport velocity was the sliding sand bed, sand dunes were notably absent. However, for water and 7 cP CMC solution, sand dunes and sliding sand bed regimes were observed when approaching the sand transport velocity. For 20cP CMC solution, it was observed that the sand particles in the region between the main dunes were very active compared to those within the dunes
Extraction of from the Decay
We develop the perturbative QCD formalism including Sudakov effects for
semi-leptonic meson decays. We evaluate the differential decay rate of
, and find that the perturbative calculation is reliable for
the energy fraction of the pion above 0.3. Combining predictions from the soft
pion theorems, we extract the value of the matrix element which is
roughly .Comment: 10 pages, CCUTH-94-05, IP-ASTP-13-9
Semi-universal portfolios with transaction costs
Ministry of Education, Singapore under its Academic Research Funding Tier
Chiral Lagrangians for Radiative Decays of Heavy Hadrons
The radiative decays of heavy mesons and heavy baryons are studied in a
formalism which incorporates both the heavy quark symmetry and the chiral
symmetry. The chiral Lagrangians for the electromagnetic interactions of heavy
hadrons consist of two pieces: one from gauging electromagnetically the
strong-interaction chiral Lagrangian, and the other from the anomalous magnetic
moment interactions of the heavy baryons and mesons. Due to the heavy quark
spin symmetry, the latter contains only one independent coupling constant in
the meson sector and two in the baryon sector. These coupling constants only
depend on the light quarks and can be calculated in the nonrelativistic quark
model. However, the charm quark is not heavy enough and the contribution from
its magnetic moment must be included. Applications to the radiative decays
and are given. Together with our previous results
on the strong decay rates of and , predictions are obtained for the total widths and
branching ratios of and . The decays and are discussed to illustrate the important roles played by both the heavy
quark symmetry and the chiral symmetry.Comment: 30 pages (one figure, available on request), CLNS 92/1158 and
IP-ASTP-13-9
Effective Lagrangian Approach to Weak Radiative Decays of Heavy Hadrons
Motivated by the observation of the decay by
CLEO, we have systematically analyzed the two-body weak radiative decays of
bottom and charmed hadrons. There exist two types of weak radiative decays: One
proceeds through the short-distance transition and the other
occurs through -exchange accompanied by a photon emission. Effective
Lagrangians are derived for the -exchange bremsstrahlung processes at the
quark level and then applied to various weak electromagnetic decays of heavy
hadrons. Predictions for the branching ratios of and
\Xi_b^0\to\xip_c^0\gamma are given. In particular, we found . Order of magnitude
estimates for the weak radiative decays of charmed hadrons: and
are also presented. Within this approach, the decay asymmetry for antitriplet
to antitriplet heavy baryon weak radiative transitions is uniquely predicted by
heavy quark symmetry. The electromagnetic penguin contribution to
is estimated by two different methods and its
branching ratio is found to be of order . We conclude that
weak radiative decays of bottom hadrons are dominated by the short-distance
mechanism.Comment: 28 pages + 3 figures (not included), CLNS 94/1278, IP-ASTP-04-94.
[Main changes in this revised version: (i) Sect 2 and subsection 4.1 are
revised, (ii) A MIT bag method for calculating the decay rate of is presented, (iii) All predictions are updated using the
newly available 1994 Particle Data Group, and (iv) Appendix and subsections
3.3 and 4.4 are deleted.
Corrections to Chiral Dynamics of Heavy Hadrons: (I) 1/M Correction
In earlier publications we have analyzed the strong and radiative decays of
heavy hadrons in a formalism which incorporates both heavy-quark and chiral
symmetries. In particular, we have derived a heavy-hadron chiral Lagrangian
whose coupling constants are related by the heavy-quark flavor-spin symmetry
arising from the QCD Lagrangian with infinitely massive quarks. In this paper,
we re-examine the structure of the above chiral Lagrangian by including the
effects of corrections in the heavy quark effective theory. The
relations among the coupling constants, originally derived in the heavy-quark
limit, are modified by heavy quark symmetry breaking interactions in QCD. Some
of the implications are discussed.Comment: PHYZZX, 45 pages, 1 figure (not included), CLNS 93/1192,
IP-ASTP-02-93, ITP-SB-93-0
Identification of the tyrosine phosphatase PTP-MEG2 as an antagonist of hepatic insulin signaling
SummaryInsulin resistance is a primary defect in type 2 diabetes characterized by impaired peripheral glucose uptake and insufficient suppression of hepatic glucose output. Insulin signaling inhibits liver glucose production by inducing nuclear exclusion of the gluconeogenic transcription factor FOXO1 in an Akt-dependent manner. Through the concomitant application of genome-scale functional screening and quantitative image analysis, we have identified PTP-MEG2 as a modulator of insulin-dependent FOXO1 subcellular localization. Ectopic expression of PTP-MEG2 in cells inhibited insulin-induced phosphorylation of the insulin receptor, while RNAi-mediated reduction of PTP-MEG2 transcript levels enhanced insulin action. Additionally, adenoviral-mediated depletion of PTP-MEG2 in livers of diabetic (db/db) mice resulted in insulin sensitization and normalization of hyperglycemia. These data implicate PTP-MEG2 as a mediator of blood glucose homeostasis through antagonism of insulin signaling, and suggest that modulation of PTP-MEG2 activity may be an effective strategy in the treatment of type 2 diabetes
Perturbative QCD Analysis of Meson Decays
Resummation of large QCD radiative corrections, including leading and
next-to-leading logarithms, in pion electromagnetic form factor is reviewed.
Similar formalism is applied to exclusive processes involving heavy mesons, and
leads to Sudakov suppression for the semi-leptonic decay . It is
found that, with the inclusion of Sudakov effects, perturbative QCD analysis of
this decay is possible for the energy fraction of the pion above 0.3. By
combining predictions from the soft pion theorems, we estimate that the upper
limit of the KM matrix element is roughly 0.003.Comment: 26 pages in latex, figures are available for reques
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