TY - JOUR
AB - Generally, the motion of fluids is smooth and laminar at low speeds but becomes highly disordered and turbulent as the velocity increases. The transition from laminar to turbulent flow can involve a sequence of instabilities in which the system realizes progressively more complicated states, or it can occur suddenly. Once the transition has taken place, it is generally assumed that, under steady conditions, the turbulent state will persist indefinitely. The flow of a fluid down a straight pipe provides a ubiquitous example of a shear flow undergoing a sudden transition from laminar to turbulent motion. Extensive calculations and experimental studies have shown that, at relatively low flow rates, turbulence in pipes is transient, and is characterized by an exponential distribution of lifetimes. They also suggest that for Reynolds numbers exceeding a critical value the lifetime diverges (that is, becomes infinitely large), marking a change from transient to persistent turbulence. Here we present experimental data and numerical calculations covering more than two decades of lifetimes, showing that the lifetime does not in fact diverge but rather increases exponentially with the Reynolds number. This implies that turbulence in pipes is only a transient event (contrary to the commonly accepted view), and that the turbulent and laminar states remain dynamically connected, suggesting avenues for turbulence control.
AU - Björn Hof
AU - Westerweel, Jerry
AU - Schneider, Tobias M
AU - Eckhardt, Bruno
ID - 2791
IS - 7107
JF - Nature
TI - Finite lifetime of turbulence in shear flows
VL - 443
ER -
TY - JOUR
AB - Transition to turbulence in pipe flow has posed a riddle in fluid dynamics since the pioneering experiments of Reynolds[1]. Although the laminar flow is linearly stable for all flow rates, practical pipe flows become turbulent at large enough flow speeds. Turbulence arises suddenly and fully without distinct steps and without a clear critical point. The complexity of this problem has puzzled mathematicians, physicists and engineers for more than a century and no satisfactory explanation of this problem has been given. In a very recent theoretical approach it has been suggested that unstable solutions of the Navier Stokes equations may hold the key to understanding this problem. In numerical studies such unstable states have been identified as exact solutions for the idealized case of a pipe with periodic boundary conditions[2, 3]. These solutions have the form of waves extending through the entire pipe and travelling in the streamwise direction at a phase speed close to the bulk velocity of the fluid. With the aid of a recently developed high-speed stereoscopic Particle Image Velocimetry (PIV) system, we were able to observe transients of such unstable solutions in turbulent pipe flow[4].
AU - Björn Hof
AU - van Doorne, Casimir W
AU - Westerweel, Jerry
AU - Nieuwstadt, Frans T
ID - 2792
JF - Fluid Mechanics and its Applications
TI - Observation of nonlinear travelling waves in turbulent pipe flow
VL - 78
ER -
TY - JOUR
AB - IL-10 is a potent anti-inflammatory and immunomodulatory cytokine, exerting major effects in the degree and quality of the immune response. Using a newly generated IL-10 reporter mouse model, which easily allows the study of IL-10 expression from each allele in a single cell, we report here for the first time that IL-10 is predominantly monoallelic expressed in CD4+ T cells. Furthermore, we have compelling evidence that this expression pattern is not due to parental imprinting, allelic exclusion, or strong allelic bias. Instead, our results support a stochastic regulation mechanism, in which the probability to initiate allelic transcription depends on the strength of TCR signaling and subsequent capacity to overcome restrictions imposed by chromatin hypoacetylation. In vivo Ag-experienced T cells show a higher basal probability to transcribe IL-10 when compared with naive cells, yet still show mostly monoallelic IL-10 expression. Finally, statistical analysis on allelic expression data shows transcriptional independence between both alleles. We conclude that CD4+ T cells have a low probability for IL-10 allelic activation resulting in a predominantly monoallelic expression pattern, and that IL-10 expression appears to be stochastically regulated by controlling the frequency of expressing cells, rather than absolute protein levels per cell.
AU - Calado, Dinis P
AU - Tiago Paixao
AU - Holmberg, Dan
AU - Haury, Matthias
ID - 2894
IS - 8
JF - Journal of Immunology
TI - Stochastic Monoallelic Expression of IL 10 in T Cells
VL - 177
ER -
TY - CHAP
AB - Most binocular stereo algorithms assume that all scene elements are visible from both cameras. Scene elements that are visible from only one camera, known as occlusions, pose an important challenge for stereo. Occlusions are important for segmentation, because they appear near discontinuities. However, stereo algorithms tend to ignore occlusions because of their difficulty. One reason is that occlusions require the input images to be treated symmetrically, which complicates the problem formulation. Worse, certain depth maps imply physically impossible scene configurations, and must be excluded from the output. In this chapter we approach the problem of binocular stereo with occlusions from an energy minimization viewpoint. We begin by reviewing traditional stereo methods that do not handle occlusions. If occlusions are ignored, it is easy to formulate the stereo problem as a pixel labeling problem, which leads to an energy function that is common in early vision. This kind of energy function can he minimized using graph cuts, which is a combinatorial optimization technique that has proven to be very effective for low-level vision problems. Motivated by this, we have designed two graph cut stereo algorithms that are designed to handle occlusions. These algorithms produce promising experimental results on real data with ground truth.
AU - Vladimir Kolmogorov
AU - Zabih, Ramin
ID - 2921
T2 - Handbook of Mathematical Models in Computer Vision
TI - Graph cut algorithms for binocular stereo with occlusions
ER -
TY - JOUR
AB - We demonstrate for different protein samples that three-dimensional HNCO and HNCA correlation spectra may be recorded in a few minutes acquisition time using the band-selective excitation short-transient sequences presented here. This opens new perspectives for the NMR structural investigation of unstable protein samples and real-time site-resolved studies of protein kinetics.
AU - Schanda, Paul
AU - Van Melckebeke, Hélène
AU - Brutscher, Bernhard
ID - 8488
IS - 28
JF - Journal of the American Chemical Society
KW - Colloid and Surface Chemistry
KW - Biochemistry
KW - General Chemistry
KW - Catalysis
SN - 0002-7863
TI - Speeding up three-dimensional protein NMR experiments to a few minutes
VL - 128
ER -
TY - JOUR
AB - Structure elucidation of proteins by either NMR or X‐ray crystallography often requires the screening of a large number of samples for promising protein constructs and optimum solution conditions. For large‐scale screening of protein samples in solution, robust methods are needed that allow a rapid assessment of the folding of a polypeptide under diverse sample conditions. Here we present HET‐SOFAST NMR, a highly sensitive new method for semi‐quantitative characterization of the structural compactness and heterogeneity of polypeptide chains in solution. On the basis of one‐dimensional 1H HET‐SOFAST NMR data, obtained on well‐folded, molten globular, partially‐ and completely unfolded proteins, we define empirical thresholds that can be used as quantitative benchmarks for protein compactness. For 15N‐enriched protein samples, two‐dimensional 1H‐15N HET‐SOFAST correlation spectra provide site‐specific information about the structural heterogeneity along the polypeptide chain.
AU - Schanda, Paul
AU - Forge, Vincent
AU - Brutscher, Bernhard
ID - 8489
IS - S1
JF - Magnetic Resonance in Chemistry
SN - 0749-1581
TI - HET-SOFAST NMR for fast detection of structural compactness and heterogeneity along polypeptide chains
VL - 44
ER -
TY - JOUR
AB - We demonstrate the feasibility of recording 1H–15N correlation spectra of proteins in only one second of acquisition time. The experiment combines recently proposed SOFAST-HMQC with Hadamard-type 15N frequency encoding. This allows site-resolved real-time NMR studies of kinetic processes in proteins with an increased time resolution. The sensitivity of the experiment is sufficient to be applicable to a wide range of molecular systems available at millimolar concentration on a high magnetic field spectrometer.
AU - Schanda, Paul
AU - Brutscher, Bernhard
ID - 8490
IS - 2
JF - Journal of Magnetic Resonance
KW - Nuclear and High Energy Physics
KW - Biophysics
KW - Biochemistry
KW - Condensed Matter Physics
SN - 1090-7807
TI - Hadamard frequency-encoded SOFAST-HMQC for ultrafast two-dimensional protein NMR
VL - 178
ER -
TY - JOUR
AU - Kaloshin, Vadim
AU - Saprykina, Maria
ID - 8513
IS - 2
JF - Discrete & Continuous Dynamical Systems - A
SN - 1553-5231
TI - Generic 3-dimensional volume-preserving diffeomorphisms with superexponential growth of number of periodic orbits
VL - 15
ER -
TY - JOUR
AB - We study the extent to which the Hausdorff dimension of a compact subset of an infinite-dimensional Banach space is affected by a typical mapping into a finite-dimensional space. It is possible that the dimension drops under all such mappings, but the amount by which it typically drops is controlled by the ‘thickness exponent’ of the set, which was defined by Hunt and Kaloshin (Nonlinearity12 (1999), 1263–1275). More precisely, let $X$ be a compact subset of a Banach space $B$ with thickness exponent $\tau$ and Hausdorff dimension $d$. Let $M$ be any subspace of the (locally) Lipschitz functions from $B$ to $\mathbb{R}^{m}$ that contains the space of bounded linear functions. We prove that for almost every (in the sense of prevalence) function $f \in M$, the Hausdorff dimension of $f(X)$ is at least $\min\{ m, d / (1 + \tau) \}$. We also prove an analogous result for a certain part of the dimension spectra of Borel probability measures supported on $X$. The factor $1 / (1 + \tau)$ can be improved to $1 / (1 + \tau / 2)$ if $B$ is a Hilbert space. Since dimension cannot increase under a (locally) Lipschitz function, these theorems become dimension preservation results when $\tau = 0$. We conjecture that many of the attractors associated with the evolution equations of mathematical physics have thickness exponent zero. We also discuss the sharpness of our results in the case $\tau > 0$.
AU - OTT, WILLIAM
AU - HUNT, BRIAN
AU - Kaloshin, Vadim
ID - 8514
IS - 3
JF - Ergodic Theory and Dynamical Systems
SN - 0143-3857
TI - The effect of projections on fractal sets and measures in Banach spaces
VL - 26
ER -
TY - CONF
AB - We consider the evolution of a set carried by a space periodic incompressible stochastic flow in a Euclidean space. We
report on three main results obtained in [8, 9, 10] concerning long time behaviour for a typical realization of the stochastic flow. First, at time t most of the particles are at a distance of order √t away from the origin. Moreover, we prove a Central Limit Theorem for the evolution of a measure carried by the flow, which holds for almost every realization of the flow. Second, we show the existence of a zero measure full Hausdorff dimension set of points, which
escape to infinity at a linear rate. Third, in the 2-dimensional case, we study the set of points visited by the original set by time t. Such a set, when scaled down by the factor of t, has a limiting non random shape.
AU - Kaloshin, Vadim
AU - DOLGOPYAT, D.
AU - KORALOV, L.
ID - 8515
SN - 9789812562012
T2 - XIVth International Congress on Mathematical Physics
TI - Long time behaviour of periodic stochastic flows
ER -