Undulatory swimming in fluids with polymer networks

The motility behavior of the nematode Caenorhabditis elegans in polymeric solutions of varying concentrations is systematically investigated in experiments using tracking and velocimetry methods. As the polymer concentration is increased, the solution undergoes a transition from the semi-dilute to the concentrated regime, where these rod-like polymers entangle, align, and form networks. Remarkably, we find an enhancement in the nematode's swimming speed of approximately 65% in concentrated solutions compared to semi-dilute solutions. Using velocimetry methods, we show that the undulatory swimming motion of the nematode induces an anisotropic mechanical response in the fluid. This anisotropy, which arises from the fluid micro-structure, is responsible for the observed increase in swimming speed.Comment: Published 1 November 2013 in Europhysics Letter

Universal Heat Conduction in YBa_2Cu_3O_6.9

The thermal conductivity of YBa_2Cu_3O_6.9 was measured at low temperatures in untwinned single crystals with concentrations of Zn impurities from 0 to 3% of Cu. A linear term kappa_0/T = 0.19 mW/K^2.cm is clearly resolved as T -> 0, and found to be virtually independent of Zn concentration. The existence of this residual normal fluid strongly validates the basic theory of transport in unconventional superconductors. Moreover, the observed universal behavior is in quantitative agreement with calculations for a gap function of d-wave symmetry.Comment: Latex file, 4 pages, 3 EPS figures, to appear in Physical Review Letter

Symmetries of differential-difference dynamical systems in a two-dimensional lattice

Classification of differential-difference equation of the form $\ddot{u}_{nm}=F_{nm}\big(t, \{u_{pq}\}|_{(p,q)\in \Gamma}\big)$ are considered according to their Lie point symmetry groups. The set $\Gamma$ represents the point $(n,m)$ and its six nearest neighbors in a two-dimensional triangular lattice. It is shown that the symmetry group can be at most 12-dimensional for abelian symmetry algebras and 13-dimensional for nonsolvable symmetry algebras.Comment: 24 pages, 1 figur

Angular position of nodes in the superconducting gap of YBCO

The thermal conductivity of a YBCO single crystal has been studied as a function of the relative orientation of the crystal axes and a magnetic field rotating in the Cu-O planes. Measurements were carried out at several temperatures below T_c and at a fixed field of 30 kOe. A four-fold symmetry characteristic of a superconducting gap with nodes at odd multiples of 45 degrees in k-space was resolved. Experiments were performed to exclude a possible macroscopic origin for such a four-fold symmetry such as sample shape or anisotropic pinning. Our results impose an upper limit of 10% on the weight of the s-wave component of the essentially d-wave superconducting order parameter of YBCO.Comment: 10 pages, 4 figure

Combining and optimizing NIRS and EEG to study interictal epileptic discharges

We describe our ongoing application of NIRS-EEG to the study of inter-ictal discharges in adult epilepsy. We discuss optimizing NIRS-EEG data acquisition and analysis and we present preliminary NIRS-EEG results for an epileptic patient. © 2012 OSA

Relating spatial perspective taking to the perception of other's affordances: providing a foundation for predicting the future behavior of others

Understanding what another agent can see relates functionally to the understanding of what they can do. We propose that spatial perspective taking and perceiving other's affordances, while two separate spatial processes, together share the common social function of predicting the behavior of others. Perceiving the action capabilities of others allows for a common understanding of how agents may act together. The ability to take another's perspective focuses an understanding of action goals so that more precise understanding of intentions may result. This review presents an analysis of these complementary abilities, both in terms of the frames of reference and the proposed sensorimotor mechanisms involved. Together, we argue for the importance of reconsidering the role of basic spatial processes to explain more complex behaviors

Incremental and Predictive Validity of the Antisocial Process Screening Device in a Community Sample of Male and Female Ethnic Minority and Caucasian Youth

The Antisocial Process Screening Device (APSD) is a well-supported tool for assessing psychopathic features in youth. However, most research with the APSD has been derived from clinical and forensic samples comprised mainly of male Caucasian and African American adolescents. In this prospective study, the incremental and predictive validity of the self-report APSD for violent and non-violent offending was examined in an ethnically diverse community sample of male and female youth (N = 335) aged 12 to 14. High-school students from a moderate sized city in Western Canada completed the self-report APSD and then completed the Self-Report of Offending 6 months later. Receiver Operating Characteristics analysis indicated that APSD total and subscale scores were predictive of violent and non-violent offending at 6-month follow-up with moderate to large effect sizes. In addition, total scores on the APSD added incremental predictive utility above and beyond traditional criminogenic predictors of youth offending (i.e., prior offending, delinquent peer affiliation, poor school achievement, substance use, low parental monitoring). Although sex differences emerged in the predictive utility of the Impulsivity subscale of the APSD vis-à-vis violent offending, sex did not moderate the relationship between APSD total, Narcissism, or Callous/Unemotional scores and offending. In addition, the predictive utility of the APSD did not vary as a function of the youth’s ethnic background. These findings suggest that: (1) the self-report APSD may have utility for risk or threat assessment with normative school populations, (2) APSD findings from higher risk samples generalize to a lower risk sample of high-school youth, and (3) predictive utility of APSD total scores do not differ across male and female Caucasian and ethnic minority youth. &nbsp

Soil weathering rates in 21 catchments of the Canadian Shield

Soil mineral weathering represents an essential source of nutrient base cation (Ca, Mg and K) for forest growth in addition to provide a buffering power against precipitation acidity for soils and surface waters. Weathering rates of base cations were obtained for 21 catchments located within the temperate and the boreal forest of the Canadian Shield with the geochemical model PROFILE. Weathering rates ranged from 0.58 to 4.46 kmol<sub>c</sub> ha<sup>−1</sup> yr<sup>−1</sup> and their spatial variation within the studied area was mostly in agreement with spatial variations in soil mineralogy. Weathering rates of Ca and Mg were significantly correlated (<i>r</i> = 0.80 and 0.64) with their respective lake concentrations. Weathering rates of K and Na did not correlate with lake concentrations of K and Na. The modeled weathering rates for each catchment were also compared with estimations of net catchment exportations. The result show that modeled weathering rates of Ca were not significantly different than the net catchment exportations while modeled weathering rates of Mg were higher by 51%. Larger differences were observed for K and Na weathering rates that were significantly different than net catchment exportations being 6.9 and 2.2 times higher than net exportations, respectively. The results for K were expected given its high reactivity with biotic compartments and suggest that most of the K produced by weathering reactions was retained within soil catchments and/or above ground biomass. This explanation does not apply to Na, however, which is a conservative element in forest ecosystems because of the insignificant needs of Na for soil microorganisms and above ground vegetations. It raises concern about the liability of the PROFILE model to provide reliable values of Na weathering rates. Overall, we concluded that the PROFILE model is powerful enough to reproduce spatial geographical gradients in weathering rates for relatively large areas as well as adequately predict absolute weathering rates values for the sum of base cations, Ca and Mg