1,578 research outputs found
Wall effects on pressure fluctuations in turbulent channel flow
The purpose of the present paper is to study the influence of wall-echo on
pressure fluctuations , and on statistical correlations containing ,
{\em viz} redistribution , pressure diffusion , and
velocity/pressure-gradient . We extend the usual analysis of
turbulent correlations containing pressure fluctuations in wall-bounded
\tsc{dns} computations [Kim J.: {\em J. Fluid Mech.} {\bf 205} (1989)
421--451], separating not only into rapid and slow
parts [Chou P.Y.: {\em Quart. Appl. Math.} {\bf 3} (1945)
38--54], but further into volume ( and
) and surface (wall-echo;
and ) terms. An algorithm, based on a Green's function
approach, is developed to compute the above splittings for various correlations
containing pressure fluctuations (redistribution, pressure diffusion,
velocity/pressure-gradient), in fully developed turbulent plane channel flow.
This exact analysis confirms previous results based on a method-of-images
approximation [Manceau R., Wang M., Laurence D.: {\em J. Fluid Mech.} {\bf 438}
(2001) 307--338] showing that, at the wall, and
are usually of the same sign and approximately equal. The above
results are then used to study the contribution of each mechanism on the
pressure correlations in low Reynolds-number plane channel flow, and to discuss
standard second-moment-closure modelling practices
Logarithmic Moduli Spaces for Surfaces of Class VII
In this paper we describe logarithmic moduli spaces of pairs (S,D) consisting
of minimal surfaces S of class VII with positive second Betti number b_2
together with reduced divisors D of b_2 rational curves. The special case of
Enoki surfaces has already been considered by Dloussky and Kohler. We use
normal forms for the action of the fundamental group of the complement of D and
for the associated holomorphic contraction germ from (C^2,0) to (C^2,0).Comment: Minor correction of the dimension of the moduli spac
Organic molecules in the protoplanetary disk of DG Tau revealed by ALMA
Planets form in protoplanetary disks and inherit their chemical compositions.
It is thus crucial to map the distribution and investigate the formation of
simple organics, such as formaldehyde and methanol, in protoplanetary disks. We
analyze ALMA observations of the nearby disk-jet system around the T Tauri star
DG Tau in the o-HCO and CHOH E,
A transitions at an unprecedented resolution of ,
i.e., au at a distance of 121 pc. The HCO emission originates from
a rotating ring extending from au with a peak at au, i.e., at
the edge of the 1.3mm dust continuum. CHOH emission is not detected down to
an r.m.s. of 3 mJy/beam in the 0.162 km/s channel. Assuming an ortho-to-para
ratio of 1.8-2.8 the ring- and disk-height-averaged HCO column density is
cm, while that of CHOH is
cm. In the inner au no o-HCO emission
is detected with an upper limit on its beam-averaged column density of
cm. The HCO ring in the disk of DG Tau is
located beyond the CO iceline (R au). This suggests that the
HCO abundance is enhanced in the outer disk due to formation on grain
surfaces by the hydrogenation of CO ice. The emission peak at the edge of the
mm dust continuum may be due to enhanced desorption of HCO in the gas phase
caused by increased UV penetration and/or temperature inversion. The
CHOH/HCO abundance ratio is , in agreement with disk chemistry
models. The inner edge of the HCO ring coincides with the radius where the
polarization of the dust continuum changes orientation, hinting at a tight link
between the HCO chemistry and the dust properties in the outer disk and at
the possible presence of substructures in the dust distribution.Comment: 8 pages, 6 figures, accepted for publication on A&A Letter
Role of Quantum Confinement in Luminescence Efficiency of Group IV Nanostructures
Experimental results obtained previously for the photoluminescence efficiency
(PL) of Ge quantum dots (QDs) are theoretically studied. A
- plot of PL versus QD diameter () resulted in an
identical slope for each Ge QD sample only when . We
identified that above 6.2 nm: due to a changing
effective mass (EM), while below 4.6 nm: due to
electron/ hole confinement. We propose that as the QD size is initially
reduced, the EM is reduced, which increases the Bohr radius and interface
scattering until eventually pure quantum confinement effects dominate at small
Experimental study of Taylor's hypothesis in a turbulent soap film
An experimental study of Taylor's hypothesis in a quasi-two-dimensional
turbulent soap film is presented. A two probe laser Doppler velocimeter enables
a non-intrusive simultaneous measurement of the velocity at spatially separated
points. The breakdown of Taylor's hypothesis is quantified using the cross
correlation between two points displaced in both space and time; correlation is
better than 90% for scales less than the integral scale. A quantitative study
of the decorrelation beyond the integral scale is presented, including an
analysis of the failure of Taylor's hypothesis using techniques from
predictability studies of turbulent flows. Our results are compared with
similar studies of 3D turbulence.Comment: 27 pages, + 19 figure
BCKDH: the missing link in apicomplexan mitochondrial metabolism is required for full virulence of Toxoplasma gondii and Plasmodium berghei
While the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii are thought to primarily depend on glycolysis for ATP synthesis, recent studies have shown that they can fully catabolize glucose in a canonical TCA cycle. However, these parasites lack a mitochondrial isoform of pyruvate dehydrogenase and the identity of the enzyme that catalyses the conversion of pyruvate to acetyl-CoA remains enigmatic. Here we demonstrate that the mitochondrial branched chain ketoacid dehydrogenase (BCKDH) complex is the missing link, functionally replacing mitochondrial PDH in both T. gondii and P. berghei. Deletion of the E1a subunit of T. gondii and P. berghei BCKDH significantly impacted on intracellular growth and virulence of both parasites. Interestingly, disruption of the P. berghei E1a restricted parasite development to reticulocytes only and completely prevented maturation of oocysts during mosquito transmission. Overall this study highlights the importance of the molecular adaptation of BCKDH in this important class of pathogens
A birational mapping with a strange attractor: Post critical set and covariant curves
We consider some two-dimensional birational transformations. One of them is a
birational deformation of the H\'enon map. For some of these birational
mappings, the post critical set (i.e. the iterates of the critical set) is
infinite and we show that this gives straightforwardly the algebraic covariant
curves of the transformation when they exist. These covariant curves are used
to build the preserved meromorphic two-form. One may have also an infinite post
critical set yielding a covariant curve which is not algebraic (transcendent).
For two of the birational mappings considered, the post critical set is not
infinite and we claim that there is no algebraic covariant curve and no
preserved meromorphic two-form. For these two mappings with non infinite post
critical sets, attracting sets occur and we show that they pass the usual tests
(Lyapunov exponents and the fractal dimension) for being strange attractors.
The strange attractor of one of these two mappings is unbounded.Comment: 26 pages, 11 figure
Impact of nonconvergence and various approximations of the partition function on the molecular column densities in the interstellar medium
We emphasize that the completeness of the partition function, that is, the use of a converged partition function at the typical temperature
range of the survey, is very important to decrease the uncertainty on this quantity and thus to derive reliable interstellar molecular
densities. In that context, we show how the use of different approximations for the rovibrational partition function together with
some interpolation and/or extrapolation procedures may affect the estimate of the interstellar molecular column density. For that
purpose, we apply the partition function calculations to astronomical observations performed with the IRAM-30m telescope towards
the NGC 7538–IRS1 source of two N-bearing molecules: isocyanic acid (HNCO, a quasilinear molecule) and methyl cyanide (CH3CN,
a symmetric top molecule). The case of methyl formate (HCOOCH3), which is an asymmetric top O-bearing molecule containing
an internal rotor is also discussed. Our analysis shows that the use of different partition function approximations leads to relative
differences in the resulting column densities in the range 9–43%. Thus, we expect this work to be relevant for surveys of sources with
temperatures higher than 300K and to observations in the infrared.This work is partly supported by CMST COST Action
CM1401 Our Astro-Chemical History and CMST COST Action CM1405
MOLIM. The work of C.F. is supported by the French National Research
Agency in the framework of the Investissements d’Avenir program (ANR-15-
IDEX-02), through the funding of the “Origin of Life” project of the Université
Grenoble-Alpes. C.C. and C.F. acknowledge funding from the European
Research Council (ERC) under the European Union’s Horizon 2020 research
and innovation programme, for the Project “The Dawn of Organic Chemistry”
(DOC), grant agreement No 741002. I.K. would like to thank the French
programme of Chimie Interstellaire PCMI. C.F. and D.F. acknowledge support
from the Italian Ministry of Education, Universities and Research, project
SIR (RBSI14ZRHR). E.A.B. acknowledges support from NSF (AST-1514670)
and NASA (NNX16AB48G). M.C. acknowledges the financial support from
FIS2014-53448-C2-2-P (MINECO, Spain), from the Centro de Estudios Avanzados
de Física, Matemáticas y Computación (CEAFMC) of the University of
Huelva and from the Consejería de Conocimiento, Investigación y Universidad,
Junta de Andalucía and European Regional Development Fund (ERDF), ref.
SOMM17/6105/UGR
Congenital pulmonary adenomatoid malformation: Indication and management of fetal shunting in our center
Objective: Congenital pulmonary adenomatoid malformations (CPAM) are increasingly diagnosed in recent years thanks to the expert hands and the technology of ultrasonography used in antenatal diagnosis. The purpose was to examine a series of cases referred to our fetalmaternal tertiary center for lung disease and to present the natural course, treatment and outcome of antenatally diagnosed cystic lung disease. Material and Methods: We proposed a retrospective study (October 2003 to September 2016) in a single center. Prenatal and postnatal data of fetus, with suspected CPAM, where analyzed. Results: We studied 34 cases. One child was excluded post-natally because at birth diagnosis of esophageal duplication was made. Mean gestational age at the diagnosis was 22 weeks (range 21 to 28). Thoracoamniotic shunting was performed in 9 cases. In 8 cases, it was an intra-cystic drain and in 1 case, a pleuroamniotic drain. Mean gestational age for drainage was 25 weeks (range 22 to 28). Mean gestational age at delivery was 38 weeks. All patients underwent postnatal radiological assessment. Anatomical surgical resection was performed in all cases: immediately at birth in 7 symptomatic cases, in the first year of life for 1 case that became symptomatic and 1 patient died immediately at birth due to severe respiratory distress. Conclusion: Antenatally diagnosed CPAM have an excellent prognosis. We propose invasive prenatal thoracoamniotic shunting in rare cases with unequivocal fetal compromise (i.e., polydramnios and hydrops)
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