Computation of turbulent boundary layers on curved surfaces, 1 June 1975 - 31 January 1976

An accurate method was developed for predicting effects of streamline curvature and coordinate system rotation on turbulent boundary layers. A new two-equation model of turbulence was developed which serves as the basis of the study. In developing the new model, physical reasoning is combined with singular perturbation methods to develop a rational, physically-based set of equations which are, on the one hand, as accurate as mixing-length theory for equilibrium boundary layers and, on the other hand, suitable for computing effects of curvature and rotation. The equations are solved numerically for several boundary layer flows over plane and curved surfaces. For incompressible boundary layers, results of the computations are generally within 10% of corresponding experimental data. Somewhat larger discrepancies are noted for compressible applications

Evaporation of a Kerr black hole by emission of scalar and higher spin particles

We study the evolution of an evaporating rotating black hole, described by the Kerr metric, which is emitting either solely massless scalar particles or a mixture of massless scalar and nonzero spin particles. Allowing the hole to radiate scalar particles increases the mass loss rate and decreases the angular momentum loss rate relative to a black hole which is radiating nonzero spin particles. The presence of scalar radiation can cause the evaporating hole to asymptotically approach a state which is described by a nonzero value of $a_* \equiv a / M$. This is contrary to the conventional view of black hole evaporation, wherein all black holes spin down more rapidly than they lose mass. A hole emitting solely scalar radiation will approach a final asymptotic state described by $a_* \simeq 0.555$. A black hole that is emitting scalar particles and a canonical set of nonzero spin particles (3 species of neutrinos, a single photon species, and a single graviton species) will asymptotically approach a nonzero value of $a_*$ only if there are at least 32 massless scalar fields. We also calculate the lifetime of a primordial black hole that formed with a value of the rotation parameter $a_{*}$, the minimum initial mass of a primordial black hole that is seen today with a rotation parameter $a_{*}$, and the entropy of a black hole that is emitting scalar or higher spin particles.Comment: 22 pages, 13 figures, RevTeX format; added clearer descriptions for variables, added journal referenc

Surface effects on nanowire transport: numerical investigation using the Boltzmann equation

A direct numerical solution of the steady-state Boltzmann equation in a cylindrical geometry is reported. Finite-size effects are investigated in large semiconducting nanowires using the relaxation-time approximation. A nanowire is modelled as a combination of an interior with local transport parameters identical to those in the bulk, and a finite surface region across whose width the carrier density decays radially to zero. The roughness of the surface is incorporated by using lower relaxation-times there than in the interior. An argument supported by our numerical results challenges a commonly used zero-width parametrization of the surface layer. In the non-degenerate limit, appropriate for moderately doped semiconductors, a finite surface width model does produce a positive longitudinal magneto-conductance, in agreement with existing theory. However, the effect is seen to be quite small (a few per cent) for realistic values of the wire parameters even at the highest practical magnetic fields. Physical insights emerging from the results are discussed.Comment: 15 pages, 7 figure

Contributions of organic and inorganic matter to sediment volume and accretion in tidal wetlands at steady state

A mixing model derived from first principles describes the bulk density ( BD) of intertidal wetland sediments as a function of loss on ignition (LOI). The model assumes that the bulk volume of sediment equates to the sum of self-packing volumes of organic and mineral components or BD = 1 / [LOI/k(1) + (1-LOI) / k(2)], where k(1) and k(2) are the self-packing densities of the pure organic and inorganic components, respectively. The model explained 78 % of the variability in total BD when fitted to 5075 measurements drawn from 33 wetlands distributed around the conterminous United States. The values of k(1) and k(2) were estimated to be 0.085 + / - 0.0007 g cm(-3) and 1.99 + / - 0.028 g cm(-3), respectively. Based on the fitted organic density (k(1)) and constrained by primary production, the model suggests that the maximum steady state accretion arising from the sequestration of refractory organic matter is \u3c = 0.3 cm yr (-1). Thus, tidal peatlands are unlikely to indefinitely survive a higher rate of sea-level rise in the absence of a significant source of mineral sediment. Application of k(2) to a mineral sediment load typical of East and eastern Gulf Coast estuaries gives a vertical accretion rate from inorganic sediment of 0.2 cm yr(-1). Total steady state accretion is the sum of the parts and therefore should not be greater than 0.5 cm yr(-1) under the assumptions of the model. Accretion rates could deviate from this value depending on variation in plant productivity, root: shoot ratio, suspended sediment concentration, sediment-capture efficiency, and episodic events

Galaxy Interactions in Compact Groups II: abundance and kinematic anomalies in HCG 91c

Galaxies in Hickson Compact Group 91 (HCG 91) were observed with the WiFeS integral field spectrograph as part of our ongoing campaign targeting the ionized gas physics and kinematics inside star forming members of compact groups. Here, we report the discovery of HII regions with abundance and kinematic offsets in the otherwise unremarkable star forming spiral HCG 91c. The optical emission line analysis of this galaxy reveals that at least three HII regions harbor an oxygen abundance ~0.15 dex lower than expected from their immediate surroundings and from the abundance gradient present in the inner regions of HCG 91c. The same star forming regions are also associated with a small kinematic offset in the form of a lag of 5-10 km/s with respect to the local circular rotation of the gas. HI observations of HCG 91 from the Very Large Array and broadband optical images from Pan-STARRS suggest that HCG 91c is caught early in its interaction with the other members of HCG 91. We discuss different scenarios to explain the origin of the peculiar star forming regions detected with WiFeS, and show that evidence point towards infalling and collapsing extra-planar gas clouds at the disk-halo interface, possibly as a consequence of long-range gravitational perturbations of HCG 91c from the other group members. As such, HCG 91c provides evidence that some of the perturbations possibly associated with the early phase of galaxy evolution in compact groups impact the star forming disk locally, and on sub-kpc scales.Comment: 25 pages, 21 figures, MNRAS accepted. Until publication of the article, the interactive component of Figure 4 is available at this URL: http://www.mso.anu.edu.au/~fvogt/website/misc.htm

A Comparison of Maternal versus Paternal Nonverbal Behavior During Child Pain

Parental behavior plays a significant role in children's pain response. Prior research has found generally no differences between mothers’ and fathers’ verbal behavior during child pain. This study compared mothers’ and fathers’ nonverbal behavior during child pain. Nonverbal behavior of mothers (n= 39) and fathers (n= 39) of 39 children (20 boys) aged 8 to 12 years who participated in the cold pressor task (counterbalanced once with each parent) was coded. A range of nonverbal behaviors were coded, including distraction, physical proximity, physical comfort/reassurance, procedure-related attending behavior, and fidgeting. The most common behaviors parents engaged in were fidgeting, procedure-related attending behaviors, and physical proximity. Results indicated that the types of nonverbal behavior parents engage in did not differ between mothers and fathers. However, children of mothers who engaged in more physical comfort/reassurance reported higher levels of pain intensity, and children of mothers who engaged in more procedure-related attending behaviors had lower pain tolerance. Further, both mothers and fathers who engaged in higher levels of verbal nonattending behaviors also engaged in lower levels of nonverbal procedure-related attending behaviors. These findings further support the importance of considering the influence of mothers and fathers in children's pain, and provide novel insights into the role of nonverbal behavior

Children\u27s memory for painful procedures: the relationship of pain intensity, anxiety, and adult behaviors to subsequent recall.

OBJECTIVE: To examine whether children\u27s experience of pain intensity and anxiety, and adult behaviors during venepuncture, were related to children\u27s memories of the procedure. METHODS: Participants were 48 children (24 males, 24 females) between the ages of 5 and 10 years who underwent venepuncture. The venepunctures were videotaped and adult behaviors were coded. Children self-reported their pain intensity and anxiety immediately and 2 weeks following venepuncture and answered contextual questions at follow-up. RESULTS: Children who initially reported higher levels of pain tended to over-estimate their anxiety at follow-up, whereas children who reported lower levels of pain accurately- or under-estimated their anxiety. Staff coping-promoting behaviors predicted the accuracy of children\u27s contextual memories. Staff and parent behaviors did not predict children\u27s recalled pain intensity and anxiety. CONCLUSIONS: Results indicate that children\u27s direct experience of pain intensity and staff behaviors during venepuncture are related to their memories. These data highlight the importance of effective pain management during medical procedures