Invasive thistles reduce the productivity of pastures and rangelands because their structural defenses make them unpalatable to grazing livestock. However, plants potentially alter their growth patterns, including their allocation of resources to defense, in response to the presence of competing vegetation. Understanding the effects of competition on the structural defense of problematic pasture weeds can inform management plans that reduce the economic harm caused by these pests. We grew musk thistle (Carduus nutans L., also commonly called nodding thistle) in a fully crossed factorial field experiment in a single abandoned pasture in 2017 with two experimental factors: the level of thistle infestation (1 thistle or 5, resulting in densities of 4 or 20 plants m−2) and the presence or absence of grazing (simulated by weekly trimming of competing vegetation). We assessed the effects of treatments on defense by counting prickles >3-mm long on leaves. Our analysis included leaf age and leaf size as covariates. Competition reduced the number of prickles present on leaves. Regression analysis showed that an increase from, for example, 50 g to 200 g of competing vegetation within 50 by 50 cm study plots reduced the expected average number of prickles on intermediate-aged leaves with average length 25.5 cm by 76.9 prickles per leaf, or 41%. This pattern was similar for leaves of all ages, although the oldest leaves generally had fewer prickles than younger leaves. We did not observe differences in defense structures between plants neighbored by conspecifics and those neighbored by other competitors. Carduus nutans has been previously managed using high densities of grazers, and this practice may be more likely to damage less-defended individuals such as those we observed in our treatments with competition. This finding suggests that maintaining competition in pastures may increase C. nutans vulnerability to grazing.

We report the structure and synthesis approach for obtaining a ceramic nanocomposite pellet comprising ∼50 nm-sized TaC nanoparticles. A mixture of Ta metal powder and the carbon precursor 1,2,4,5-tetraphenylethynyl benzene, pelletized by vacuum pressing at 131 MPa, on further thermal treatment with Ar at 1400 °C yields such a ceramic composite. On air oxidation, the TaC nanoparticles are converted to Ta2O5 nanoparticles at 760 °C. Hardness measurements revealed that the composite exhibited a global hardness in the range of 1.23–1.57 GPa. However, nanoindentation studies showed that, locally, hardness of the TaC nanoparticles (∼15 GPa) approached that of the densified TaC ceramic. Superconducting studies of the pellet consistently exhibited two transitions with T c values of 10 K and 8.5 K, respectively, that corresponded to bulk TaC and to a component of unknown origin. The results discuss the morphological and constitutional characterizations of the TaC nanoparticle-containing composite.

Background: The influence of psychotherapy on neurocognition in post-traumatic stress disorder (PTSD) has not been examined methodically. This is despite evidence that pre-treatment learning and memory has been associated with treatment success and that executive function theories emphasize weak executive functions (especially inhibition/switching) are associated with PTSD. Objectives: To determine (1) if higher pre-treatment learning/memory, inhibition/switching, or both predict treatment success; and (2) if treatment success is associated with specific improvement in inhibition/switching and not learning/memory or working memory, another aspect of executive function. Methods: Pre-treatment neurocognition and neurocognitive changes (inhibition/switching, learning/memory, working memory) were examined in female veterans with PTSD. They were evaluated before and after 16-weeks of group psychotherapy for PTSD that included three counterbalanced modules (cognitive restructuring therapy, exposure therapy, skills training) with fidelity checks for therapist adherence. Results: Only pre-treatment learning/memory predicted better treatment outcome. Treatment success was associated with improvement in inhibition/switching only, even after controlling for mild traumatic brain injury, and changes in depressive symptoms, working memory, and learning/memory. Conclusions: Our finding that learning/memory predicted treatment success is consistent with previous studies. We extended these studies by showing that the effect was restricted to learning/memory, which is contrary to the executive function theory of PTSD. In contrast, the fact that only inhibition/switching significantly improved with better treatment success is consistent with its potential importance in maintaining PTSD symptoms. Future research should determine whether inhibition/switching abilities are a risk for development and maintenance of PTSD or whether such abilities have a broader reciprocal relationship with PTSD symptom change. (JINS, 2016, 22, 643–651)

A stationary phase method is developed for the asymptotic evaluation, as R → ∞, of oscillatory sums of the form

It is extended to multidimensional sums. Numerical comparisons demonstrate the accuracy of the asymptotic approximations. The results are applied to the practical estimation of the number of lattice points in large domains in ℝ2.

The embryonic heart and vascular bed interact dynamically to support rapid growth of the embryo during cardiovascular development. Pressure-volume relations define ventricular function during alterations in loading conditions. We analyzed these relationships in the embryonic heart in order to define ventricular function and the response of the ventricle and vascular bed to acute changes in preload. We simultaneously measured ventricular pressure and recorded 60 video images per second in n≥6 stage 16, 18 and 21 white Leghorn chick embryos at baseline and during the infusion of 1–2 microliters of physiologic buffer into the venous sinus (sinus venosus). Ventricular tetany was then induced with the topical application of 2 Molar sodium chloride. Video fields were traced for ventricular pressure and epicardial cross-sectional area. Cross-sectional area was converted to volume assuming ellipsoid geometry, and cavity volume was calculated as total volume minus wall volume derived from the tetanized heart. We defined end-diastole at the onset of ventricular contraction and end-systole at maximum pressure/volume ratio. Stroke volume increased linearly with end-diastolic volume. End-diastolic pressure-volume relations were positive and linear, and end-systolic pressure-volume relations were curvilinear downward. Arterial elastance decreased with growth of the embryo and with volume infusion. Pressure-volume loop area, an index of consumption of energy, doubled between the embryonic stages. Thus, embryonic ventricular pressure-volume relations define diastolic and systolic function at rest and in response to altered preload.

Two impinging two-dimensional incompressible inviscid fluid jets of known widths and velocities produce two outgoing jets. The speeds of the outgoing jets are readily determined from the Bernoulli equation. Their two widths and two directions (four quantities) are related by conservation of mass and conservation of two components of momentum (three relations). Because these three conservation relations do not suffice to determine the four unknowns, Milne-Thomson (1968) states on p. 302 that ‘a unique solution is, in general, not possible’. He incorrectly attributes this indeterminateness to disregard of ‘the initial conditions from which this steady motion is supposed to arise’.

Asymptotic methods are used to determine the dispersion equation for disturbances of rotating parallel flows in shallow water. From this equation the unstable modes and their growth rates are determined. The solution involves seven asymptotic expansions which are matched together. The results supplement and extend those which have been obtained previously using numerical methods by Griffiths, Killworth & Stern (1982) and by Hayashi & Young (1987).

The stability or instability of various linear shear flows in shallow water is considered. The linearized equations for waves on the surface of each flow are solved exactly in terms of known special functions. For unbounded shear flows, the exact reflection and transmission coefficients R and T for waves incident on the flow, are found. They are shown to satisfy the relation |R|2= 1+ |T|2, which proves that over reflection occurs at all wavenumbers. For flow bounded by a rigid wall, R is found. The poles of R yield the eigenvalue equation from which the unstable mides can be found. For flow in a channel, with two rigid walls, the eigenvalue equation for the modes is obtained. The results are compared with previous numerical results.

Two-dimensional free surface flows without waves, produced by a submerged sink in a reservoir, are computed numerically for various configurations. For a sink above the horizontal bottom of a layer of fluid, there are solutions for all values of the Froude number F greater than some particular value. However, when the fluid is sufficiently deep, there is an additional solution for one special value of F < 1. The results for a sink at the vertex of a sloping bottom, treated by Craya and by Hocking, and for a sink in fluid of infinite depth, treated by Tuck & Vanden-Broeck, are confirmed and extended. In particular it is shown that as the bottom tends to the horizontal, the solution for a sink at the vertex of a sloping bottom approaches a solution for a horizontal bottom with F = 1. However solutions are found for all values of the Froude number F [ges ] 1 for a sink on a horizontal bottom.

The steady motion of a flat surfboard propelled by a solitary wave is considered. The shape of the free surface and the flow of the fluid are determined numerically by series truncation for flows without spray or splash. These flows all bifurcate from the uniform horizontal flow at the critical value of the Froude number. Various limiting cases of these special flows are described analytically. Flows past submerged hydrofoils are discussed also.

The flow of a liquid with a free surface over a weir in a channel is calculated numerically for thin weirs in channels of various depths, and for broad-crested weirs in channels of infinite depth. The results show that the upstream velocity, as well as the entire flow, are determined by the height of the free surface far upstream and by the geometry of the weir and channel, in agreement with observation. The discharge coefficient is computed for a thin weir, and a formula for it is given that applies when the height of the weir is large compared to the height of the upstream free surface above the top of the weir. The coefficients in this formula are close to those found empirically.

Coupled nonlinear equations are derived for the amplitudes of two small-amplitude resonantly interacting gravity waves in water of non-uniform depth. Such resonance is possible only for wavelengths long compared to the depth. It is shown that the same equations are obtained from the exact Euler equations, from the nonlinear shallow water theory, and from the Boussinesq equations.

The deformation of an axisymmetric bubble or drop in a uniform flow of constant velocity U is computed numerically. The flow is assumed to be inviscid and incompressible. The problem is formulated as a nonlinear integrodifferential system of equations for the bubble surface and for the potential function on the surface. These equations are discretized and the resulting algebraic system is solved by Newton's method. For U = 0 the bubble is a sphere. The results show that as U increases the bubble becomes oblate, spreading out in the direction normal to the flow and contracting in the direction of the flow. Then the poles get pushed in and ultimately they touch each other. The results also show that there is a maximum value of the Weber number above which there is no steady axially symmetric bubble. This value is somewhat smaller than the approximate value obtained by Moore (1965) but close to that found by El Sawi (1974). We also compute the added mass, the drag on the bubble, and its terminal velocity in a gravitational field, for large Reynolds numbers.

The effective viscosity of a suspension is defined to be the four-tensor that relates the average deviatoric stress to the average rate of strain. We determine the effective viscosity of an array of spheres centred on the points of a periodic lattice in an incompressible Newtonian fluid. The formulation involves the traction exerted on a single sphere by the fluid, and an integral equation for this traction is derived. For lattices with cubic symmetry the effective viscosity tensor involves just two parameters. They are computed numerically for simple, body-centred and face-centred cubic lattices of spheres with solute concentrations up to 90% of the close-packing concentration. Asymptotic results for high concentrations are obtained for arbitrary lattice geometries, and found to be in good agreement with the numerical results for cubic lattices. The low-concentration asymptotic expansions of Zuzovsky also agree well with the numerical results.

Steady two-dimensional jets of inviscid incompressible fluid, rising and falling under gravity, are calculated numkrically. The shape of each jet depends upon a single parameter, the Froude number $\lambda = q_{r\m c}(Qg)^{-\frac{1}{3}}$, which ranges from zero to infinity. Here qc is the velocity at the crest of the jet, i.e. the highest point of the upper surface, Q is the flux in the jet. and g is the acceleration of gravity. For λ = ∞ the jet is slender and parabolic. It becomes thicker as λ decreases, and reaches a limiting form at λ = 0. Then there is a stagnation point at the crest, where the surface makes a 120° angle with itself. This angle is predicted by the same argument Stokes used in his study of water waves.

The problem is formulated as an integro-differential equation for the two free surfaces of the jet, This equation is dlscretized to yield a set of nonlinear equations, which are solved numerically by Newton's method. In addition, asymptotic results for large λ are obtained analytically. Graphs of the results are presented.