Aerodynamic characteristics of a hypersonic parachute

Newtonian theory, both in the form of the Modified-Newtonian and the Newton- Busemann pressure laws, is used to find the shape, cloth area and drag of the axisymmetric canopy of a hypersonic parachute, whose only load-carrying fibres are longitudinal ones. As an example, an estimate is made of the size of canopy needed to give a drag of 20,000 lb. in flight at a Mach number of 10 at 100,000 feet altitude

Small and medium agility dogs alter their kinematics when the distance between hurdles differs

There is currently a lack of research examining the health and welfare implications for competitive agility dogs. The aim of this study was to examine if jump kinematics and apparent joint angles in medium (351 mm - 430 mm to the withers) and small (< 350 mm to the withers) agility dogs altered when distances between consecutive upright hurdles differ. Dogs ran a course of nine hurdles; three set at 3.6 m apart; three at 4 m apart and three at 5 m apart. Both medium (P=0.044) and small (P=0.006) dogs landed closer to the hurdle when consecutive hurdles were set at 3.6 m apart, with small dogs jumping slower at this distance (P=0.006). Results indicate that jump kinematics, but not apparent joint angles, alter when the spacing between hurdles differs. These findings may have implications for the health and welfare of agility dogs and should be used to inform future changes to rules and regulations

Slender shapes offering minimum drag in free-molecular flow

Analytical expressions are obtained for the optimum shapes which minimise the drag of a slender axisymmetric body in free-molecular flow, provided the drag expression is simplified using the slenderness assumption. The problem is formulated as one of Mayer type in the calculus of variations and solved by using the Buler-Lagrange equations together with the transversality condition. The shapes derived are optimum subject to constraints on thickness, length, wetted area and volume. In the particular cases solved any two of these four quantities are fixed while the remaining two are free. The expression for the shape of the body when thickness is free is obtained in closed form

Variational analysis of self-focusing of intense ultrashort pulses in gases

By using perturbation theory we derive an expression for the electrical field of a Gaussian laser pulse propagating in a gas medium. This expression is used as a trial solution in a variational method to get quasianalytical solutions for the width, intensity and self-focusing distance of ultrashort pulse. The approximation gives an improved agreement with results of numerical simulations for a broad range of values of the input power of the pulse than previous analytical results available in the literature.Comment: 19 pages, 8 figure

Two-peaked and flat-top perfect bright solitons in epsilon-near-zero nonlinear metamaterials: novel Kerr self-trapping mechanisms

We analytically investigate transverse magnetic (TM) spatial bright solitons, as exact solutions of Maxwell's equations, propagating through nonlinear metamaterials whose linear dielectric permittivity is very close to zero and whose effective nonlinear Kerr parameters can be tailored to achieve values not available in standard materials. Exploiting the fact that, in the considered medium, linear and nonlinear polarization can be comparable at feasible and realistic optical intensities, we identify two novel self-trapping mechanisms able to support two-peaked and flat-top solitons, respectively. Specifically, these two novel mechanisms are based on the occurrence of critical points at which the effective nonlinear permittivity vanishes, the two mechanisms differing in the way the compensation between linear and nonlinear polarization is achieved through the non-standard values of the nonlinear parameters.Comment: 7 pages, 4 figure

Metrics that matter for assessing the ocean biological carbon pump

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Buesseler, K. O., Boyd, P. W., Black, E. E., & Siegel, D. A. Metrics that matter for assessing the ocean biological carbon pump. Proceedings of the National Academy of Sciences of the United States of America, (2020): 201918114, doi: 10.1073/pnas.1918114117.The biological carbon pump (BCP) comprises wide-ranging processes that set carbon supply, consumption, and storage in the oceans’ interior. It is becoming increasingly evident that small changes in the efficiency of the BCP can significantly alter ocean carbon sequestration and, thus, atmospheric CO2 and climate, as well as the functioning of midwater ecosystems. Earth system models, including those used by the United Nation’s Intergovernmental Panel on Climate Change, most often assess POC (particulate organic carbon) flux into the ocean interior at a fixed reference depth. The extrapolation of these fluxes to other depths, which defines the BCP efficiencies, is often executed using an idealized and empirically based flux-vs.-depth relationship, often referred to as the “Martin curve.” We use a new compilation of POC fluxes in the upper ocean to reveal very different patterns in BCP efficiencies depending upon whether the fluxes are assessed at a fixed reference depth or relative to the depth of the sunlit euphotic zone (Ez). We find that the fixed-depth approach underestimates BCP efficiencies when the Ez is shallow, and vice versa. This adjustment alters regional assessments of BCP efficiencies as well as global carbon budgets and the interpretation of prior BCP studies. With several international studies recently underway to study the ocean BCP, there are new and unique opportunities to improve our understanding of the mechanistic controls on BCP efficiencies. However, we will only be able to compare results between studies if we use a common set of Ez-based metrics.We thank the many scientists whose ideas and contributions over the years are the foundation of this paper. This includes A. Martin, who led the organization of the BIARRITZ group (now JETZON) workshop in July 2019, discussions at which helped to motivate this article. We thank D. Karl for pointing us in the right direction for this paper format at PNAS and two thoughtful reviewers who through their comments helped to improve this manuscript. Support for writing this piece is acknowledged from several sources, including the Woods Hole Oceanographic Institution’s Ocean Twilight Zone project (K.O.B.); NASA as part of the EXport Processes in the global Ocean from RemoTe Sensing (EXPORTS) program (K.O.B. and D.A.S.). E.E.B. was supported by a postdoctoral fellowship through the Ocean Frontier Institute at Dalhousie University. P.W.B. was supported by the Australian Research Council through a Laureate (FL160100131)

The Action of Certain Organic Silver Compounds on the Potato Root Eelworm, Heterodera schachtii, Schmidt, With Notes on the Biology of the Parasite, and Additional Papers

Abstract Not Provided

Model-Independent Semileptonic Form Factors Using Dispersion Relations

We present a method for parametrizing heavy meson semileptonic form factors using dispersion relations, and from it produce a two-parameter description of the B -> B elastic form factor. We use heavy quark symmetry to relate this function to B -> D* l nu form factors, and extract |V_cb|=0.0355^{+0.0029}_{-0.0025} from experimental data with a least squares fit. Our method eliminates model-dependent uncertainties inherent in choosing a parametrization for the extrapolation of the differential decay rate to threshold.Comment: uses lanlmac(harvmac) and epsf, 12 pages, 1 eps figure included (Talk by BG at the 6-th International Symposium on Heavy Flavour Physics, Pisa, Italy, 6--10 June, 1995

QCD Thermodynamics with Improved Actions

The thermodynamics of the SU(3) gauge theory has been analyzed with tree level and tadpole improved Symanzik actions. A comparison with the continuum extrapolated results for the standard Wilson action shows that improved actions lead to a drastic reduction of finite cut-off effects already on lattices with temporal extent $N_\tau=4$. Results for the pressure, the critical temperature, surface tension and latent heat are presented. First results for the thermodynamics of four-flavour QCD with an improved staggered action are also presented. They indicate similarly large improvement factors for bulk thermodynamics.Comment: Talk presented at LATTICE96(finite temperature) 4 pages, LaTeX2e file, 6 eps-file