108 research outputs found

    Spectral link and macroscopic non-universality in turbulent plane Couette flow

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    In fully developed turbulent plane Couette flow the classical experimental data of frictional factor f versus Reynolds number Re display well-known disparities which have long remained unexplained. These disparities are accompanied by previously unnoticed disparities in the wakes, and only in the wakes, of the attendant mean-velocity profiles (MVPs). To help explain these experimental data, we apply the model of the \u27spectral link\u27 for MVPs to turbulent plane Couette flows. The model links the dissipative range, the inertial range, and the energetic range of the standard phenomenological model of the spectrum of turbulent kinetic energy to, respectively, the buffer layer, the log layer, and the wake of the MVPs. By assessing the empirical data using the spectral model, we argue for the existence, in plane Couette flow, of multiple states of turbulence which differ from one another only at the largest lengthscales in the flow, corresponding to the energetic range, where the spectrum is subject to finite-domain effects. Thus, the multiplicity of turbulent states is entirely consistent with small-scale universality, and the experimental data on plane Couette flow pose no challenge to the phenomenological theory of turbulence. Our findings might apply more broadly to a general class of flows engendered by moving boundaries

    Spectral theory of turbulent flows

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    In this doctoral thesis we formulate a spectral theory of the mean-velocity profiles (MVPs) of wall-bounded turbulent flows and use the spectral theory along with dimensional analysis and similarity methods to shed some new theoretical light on several outstanding problems in the interpretation of the extensive empirical data available on such flows. The spectral theory applies to turbulent flows of both constant-density and stratified fluids, and is predicated on the derivation, which we accomplish via a control-volume analysis, of a “spectral link” between the MVPs and the eddy velocity distribution (or, alternatively, the spectrum of turbulent kinetic energy) of the phenomenological theory of turbulence. This spectral link is bijective in that it relates each successive layer of a MVP to, and only to, the corresponding range of the eddy velocity distribution (the buffer layer to the dissipative range, the log layer to the inertial range, and the wake to the energetic range), with the implication that it is possible to infer the internal structure of a turbulent state, as one would by parsing through the successive ranges of the eddy velocity distribution, by parsing instead through the successive layers of the attendant MVP. We use the spectral theory to argue that a number of well-known, and as yet unresolved, disparities in the classical experimental data on friction factor in turbulent plane Couette flows stem from the existence of multiple states of turbulence that differ only at the largest length scales in the flow, corresponding to the energetic range, and are therefore consistent with small-scale universality. We also apply the spectral theory to thermally-stratified plane Couette flows of a type relevant to the atmosphere and conclude that the spectral link remains bijective in the presence of thermal stratification, but the layers of the MVPs are altered by buoyancy. For the intermediate region, which is the only to have been previously theoretically studied, the spectral theory makes predictions in accord with the classical scaling of the Monin-Obukhov similarity theory (MOST); for the other regions (that which is near the wall and that which is far from the wall and extends beyond the intermediate region), the predictions of the spectral theory are in accord with a new set of scaling laws, which we are able to derive on the basis of dimensional analysis and similarity assumptions. We hope that our findings will foster the formulation of better spectral models which might help opening up new prospects of gaining further theoretical insight into turbulence, “the most important unsolved problem of classical physics”.Okinawa Institute of Science and Technology Graduate Universit

    The radio properties of the OH megamaser galaxy IRAS 02524+2046

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    We present results from VLBI observations of continuum and OH line emission in IRAS 02524+2046 and also arcsecond-scale radio properties of this galaxy using VLA archive data. We found that there is no significant detection of radio continuum emission from VLBI observations. The arcsecond-scale radio images of this source show no clear extended emission, the total radio flux density at L and C band are around 2.9 mJy and 1.0 mJy respectively, which indicate a steep radio spectral index between the two band. Steep spectral index, low brightness temperature and high qq-ratio (the FIR to the radio flux density), which are three critical indicators in classification of radio activity in the nuclei of galaxies, are all consistent with the classification of this source as a starburst galaxy from its optical spectrum. The high-resolution line profile show that both of \textbf{the 1665 and 1667 MHz OH maser} line have been detected which show three and two clear components respectively. The channel maps show that the maser emission are distributed in a region \sim 210 pc ×\times 90 pc, the detected maser components at different region show similar double spectral feature, which might be an evidence that this galaxy is at a stage of major merger as seen from the optical morphology.Comment: 13pages,9 figures, accepted by A&

    Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

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    Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0-6.1 and 0.6-1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface. (C) 2014 American Vacuum Societyclos

    A novel function of the mitochondrial transcription factor Mtf1 in fission yeast; Mtf1 regulates the nuclear transcription of srk1

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    In eukaryotic cells, Mtf1 and its homologues function as mitochondrial transcription factors for the mitochondrial RNA polymerase in the mitochondrion. Here we show that in fission yeast Mtf1 exerts a non-mitochondrial function as a nuclear factor that regulates transcription of srk1, which is a kinase involved in the stress response and cell cycle progression. We first found Mtf1 expression in the nucleus. A ChIP-chip approach identified srk1 as a putative Mtf1 target gene. Over expression of Mtf1 induced transcription of the srk1 gene and Mtf1 deletion led to a reduction in transcription of the srk1 gene in vivo. Mtf1 overexpression causes cell elongation in a srk1 dependent manner. Mtf1 overexpression can cause cytoplasmic accumulation of Cdc25. We also provide biochemical evidence that Mtf1 binds to the upstream sequence of srk1. This is the first evidence that a mitochondrial transcription factor Mtf1 can regulate a nuclear gene. Mtf1 may also have a role in cell cycle progression

    Identification and characterization of the mitochondrial RNA polymerase and transcription factor in the fission yeast Schizosaccharomyces pombe

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    We have characterized the mitochondrial transcription factor (Mtf1) and RNA polymerase (Rpo41) of Schizosaccharomyces pombe. Deletion mutants show Mtf1 or Rpo41 to be essential for cell growth, cell morphology and mitochondrial membrane potential. Overexpression of Mtf1 and Rpo41 can induce mitochondrial transcription. Mtf1 and Rpo41 can bind and transcribe mitochondrial promoters in vitro and the initiating nucleotides were the same in vivo and in vitro. Mtf1 is required for efficient transcription. We discuss the functional differences between Mtf1 and Rpo41 of S. pombe with Saccharomyces cerevisiae and higher organisms. In contrast to S. cerevisiae, the established model for mitochondrial transcription, S. pombe, a petite-negative yeast, resembles higher organisms that cannot tolerate the loss of mitochondrial function. The S. pombe and human mitochondrial genomes are similar in size and much smaller than that of S. cerevisiae. This is an important first step in the development of S. pombe as an alternative and complementary model system for molecular genetic and biochemical studies of mitochondrial transcription and mitochondrial–nuclear interactions. This is the first systematic study of the cellular function and biochemistry of Rpo41 and Mtf1 in S. pombe

    Abnormalities of White Matter Microstructure in Unmedicated Obsessive-Compulsive Disorder and Changes after Medication

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    BACKGROUND: Abnormalities of myelin integrity have been reported in obsessive-compulsive disorder (OCD) using multi-parameter maps of diffusion tensor imaging (DTI). However, it was still unknown to what degree these abnormalities might be affected by pharmacological treatment. OBJECTIVE: To investigate whether the abnormalities of white matter microstructure including myelin integrity exist in OCD and whether they are affected by medication. METHODOLOGY AND PRINCIPAL FINDINGS: Parameter maps of DTI, including fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD), were acquired from 27 unmedicated OCD patients (including 13 drug-naïve individuals) and 23 healthy controls. Voxel-based analysis was then performed to detect regions with significant group difference. We compared the DTI-derived parameters of 15 patients before and after 12-week Selective Serotonin Reuptake Inhibitor (SSRI) therapies. Significant differences of DTI-derived parameters were observed between OCD and healthy groups in multiple structures, mainly within the fronto-striato-thalamo-cortical loop. An increased RD in combination with no change in AD among OCD patients was found in the left medial superior frontal gyrus, temporo-parietal lobe, occipital lobe, striatum, insula and right midbrain. There was no statistical difference in DTI-derived parameters between drug-naive and previously medicated OCD patients. After being medicated, OCD patients showed a reduction in RD of the left striatum and right midbrain, and in MD of the right midbrain. CONCLUSION: Our preliminary findings suggest that abnormalities of white matter microstructure, particularly in terms of myelin integrity, are primarily located within the fronto-striato-thalamo-cortical circuit of individuals with OCD. Some abnormalities may be partly reversed by SSRI treatment
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