Toward a structural understanding of turbulent drag reduction: nonlinear coherent states in viscoelastic shear flows

Nontrivial steady flows have recently been found that capture the main structures of the turbulent buffer layer. We study the effects of polymer addition on these "exact coherent states" (ECS) in plane Couette flow. Despite the simplicity of the ECS flows, these effects closely mirror those observed experimentally: Structures shift to larger length scales, wall-normal fluctuations are suppressed while streamwise ones are enhanced, and drag is reduced. The mechanism underlying these effects is elucidated. These results suggest that the ECS are closely related to buffer layer turbulence.     

Development of non-lethal sampling of carbon and nitrogen stable isotope ratios in salmonids: effects of lipid and inorganic components of fins

The preferred tissue for analyses of fish stable isotope ratios for most researchers is muscle, the sampling of which typically requires the specimen to be sacrificed. The use of non-destructive methods in fish isotopic research has been increasing recently, but as yet is not a standard procedure. Previous studies have reported varying levels of success regarding the utility of non-lethally obtained stable isotope materials, e.g. fins, but none have accounted for the potential compounding effects of inorganic components of fin rays or lipids. Comparisons of carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of muscle with adipose and caudal fin of two salmonids, Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.), revealed that caudal fin can be used as a non-destructive surrogate for muscle in stable isotope analysis, but that adipose fin, where available, is a better proxy. The use of a published model to inexpensively counteract the confounding effect of lipids, which are depleted in ¹³C, greatly improved the relationship between fish muscle and fins. However, efforts to account for the inorganic components of fin rays were counterproductive and required twice the biomass of fins clipped from each fish. As this experiment was conducted on wild fish, controlled laboratory studies are required to confirm these field observations.     

A determination of the Cabibbo-Kobayashi-Maskawa parameter |V us| using KL decays

We present a determination of the Cabibbo-Kobayashi-Maskawa parameter |V(us)| based on new measurements of the six largest K(L) branching fractions and semileptonic form factors by the KTeV (E832) experiment at Fermilab. We find |V(us)|=0.2252+/-0.0008(KTeV)+/-0.0021(ext), where the errors are from KTeV measurements and from external sources. We also use the measured branching fractions to determine the CP violation parameter |eta(+-)|=(2.228+/-0.005(KTeV)+/-0.009(ext))x10(-3).     

MuSR study of weakly magnetic Y(Co1−x Al x )2

All previous experiments have suggested that Y(Co_1−x Al _x )₂ is a weak itinerant ferromagnet for 0.12<x<0.20. The muon transverse damping rate (λ) increases rapidly near the Curie point forx≥0.155 and for one sample withx=0.145. The value of λ increases with decreasing temperature for other samples withx<0.155 but shows no feature at the Curie point.     

The number of k‐SAT functions

We study the number SAT(k; n) of Boolean functions of n variables that can be expressed by a k‐SAT formula. Equivalently, we study the number of subsets of the n‐cube 2ⁿ that can be represented as the union of (n ? k)‐subcubes. In The number of 2‐SAT functions (Isr J Math, 133 (2003), 45–60) the authors and Imre Leader studied SAT(k; n) for k ≤ n/2, with emphasis on the case k = 2. Here, we prove bounds on SAT(k; n) for k ≥ n/2; we see a variety of different types of behavior. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 22: 227–247, 2003     

Constructing effective actions for N = 1 supersymmetry theories: Symmetry principles and ward identities

The implications of the anomalous superconformal Ward identities for the construction of effective actions describing the low-energy dynamics of supersymmetry theories are investigated. The results apply to any N = 1 supersymmetry theory with an anomaly structure,

$\text{D}{}^{\mathrm{<mtext>\alpha </mtext><mtext>?</mtext>}}\text{V}{}_{\mathrm{<mtext>\alpha </mtext><mtext>\alpha </mtext><mtext>?</mtext>}}\text{+2D}{}_{\mathrm{\alpha }}\text{S=0}$

, where $\text{V}{}_{\mathrm{<mtext>\alpha </mtext><mtext>\alpha </mtext><mtext>?</mtext>}}$ is the supercurrent and the chiral superfield S represents the anomaly.     

Graphs whose every transitive orientation contains almost every relation

Given a graphG onn vertices and a total ordering ≺ ofV(G), the transitive orientation ofG associated with ≺, denotedP(G; ≺), is the partial order onV(G) defined by settingx<y inP(G; ≺) if there is a pathx=x ₁ x ₂…x _r=y inG such thatx ₁ ≺x _j for 1≦i<j≦r. We investigate graphsG such that every transitive orientation ofG contains ₂ ⁿ −o(n ²) relations. We prove that almost everyG _n,p satisfies this requirement if , but almost noG _n,p satisfies the condition if (pn log log logn)/(logn log logn) is bounded. We also show that every graphG withn vertices and at mostcn logn edges has some transitive orientation with fewer than ₂ ⁿ −δ(c)n ² relations. Partially supported by MCS Grant 8104854.     

Functional MRI of working memory and selective attention in vibrotactile frequency discrimination

Background  

Focal lesions of the frontal, parietal and temporal lobe may interfere with tactile working memory and attention. To characterise the neural correlates of intact vibrotactile working memory and attention, functional MRI was conducted in 12 healthy young adults. Participants performed a forced-choice vibrotactile frequency discrimination task, comparing a cue stimulus of fixed frequency to their right thumb with a probe stimulus of identical or higher frequency. To investigate working memory, the time interval between the 2 stimuli was pseudo-randomized (either 2 or 8 s). To investigate selective attention, a distractor stimulus was occasionally presented contralaterally, simultaneous to the probe.