Large Bi-2212 single crystal growth by the floating-zone technique

Effects of the growth velocity on the crystal growth behavior of Bi_2Sr_2Ca_1Cu_2O_x (Bi-2212) have been studied by floating zone technique. The results show that a necessary condition for obtaining large single crystals along the c-axis is that the solid-liquid interface of a growing rod maintains a stable planar growth front. The planar liquid-solid growth interface tends to break down into a cellular interface, while the growth velocity is higher than 0.25 mm/h. Single crystals of up to 50x7.2x7 mm3 along the a-, b- and caxes have been cut in a 7.2 mm diameter rod with optimum growth conditions. Tconset is 91 K measured by magnetic properties measurement system (MPMS) for as-grown crystals. Optical polarization microscope and neutron diffraction show that the quality of the single crystals is good.Comment: 5 pages, 4 figure

Radion Stabilization in Compact Hyperbolic Extra Dimensions

We consider radion stabilization in hyperbolic brane-world scenarios. We demonstrate that in the context of Einstein gravity, matter fields which stabilize the extra dimensions must violate the null energy condition. This result is shown to hold even allowing for FRW-like expansion on the brane. In particular, we explicitly demonstrate how one putative source of stabilizing matter fails to work, and how others violate the above condition. We speculate on a number of ways in which we may bypass this result, including the effect of Casimir energy in these spaces. A brief discussion of supersymmetry in these backgrounds is also given.Comment: 16 pages, 1 figur

Particle size segregation and diffusion in saturated granular flows: Implications for grain sorting in debris flows

Sorting of rocks, boulders, and silt/sand-sized particles according to their size is a characteristic feature of debris flow deposits and is an active process during flow which significantly affects the mobility. The degree at which size sorting occurs in debris flows depends on the relative magnitudes of granular processes such as particle size segregation and diffusion. Since debris flows are fluid-saturated phenomena, accurate modelling of size sorting requires the understanding of the influence of fluids on these processes, which have not been systematically studied. Here, we present simulation results and the associated empirical expressions for particle size segregation and diffusion which take into account fluid effects due to buoyant and drag forces. These expressions are developed through scaling analysis of data obtained from coupled granular-fluid simulations of saturated bi-disperse mixtures under simple shear. We further show that using these scaling relationships, an existing segregation-diffusion continuum equation can be extended to model particle sorting in debris flows with various types of fluids

Helicopter handling qualities: a study in pilot control compensation

The research reported in this paper is aimed at the development of a metric to quantify and predict the extent of pilot control compensation required to fly a wide range of mission task elements. To do this, the utility of a range of time- and frequency-domain measures to examine pilot control activity whilst flying hover/low-speed and forward flight tasks are explored. The tasks were performed by two test pilots using both the National Research Council (Canada)’s Bell 412 Advanced Systems Research Aircraft and the University of Liverpool’s HELIFLIGHT-R simulator. Handling qualities ratings were awarded for each of the tasks and compared with a newly developed weighted adaptive control compensation metric based on discrete pilot inputs, showing good correlation. Moreover, in combination with a time-varying frequency-domain exposure, the proposed metric is shown to be useful for understanding the relationship between the pilot’s subjective assessment, measured control activity and task performance. By collating the results from the subjective and objective metrics for a range of different mission task elements, compensation boundaries are proposed to predict and verify the subjective assessments from the Cooper-Harper Handling Qualities Rating scale.Engineering and Physical Sciences Research Council (EP/P031277/1 and EP/P030009/1

Analysis of particle production in ultra-relativistic heavy ion collisions within a two-source statistical model

The experimental data on hadron yields and ratios in central lead-lead and gold-gold collisions at 158 AGeV/$c$ (SPS) and $\sqrt{s} = 130$ AGeV (RHIC), respectively, are analysed within a two-source statistical model of an ideal hadron gas. A comparison with the standard thermal model is given. The two sources, which can reach the chemical and thermal equilibrium separately and may have different temperatures, particle and strangeness densities, and other thermodynamic characteristics, represent the expanding system of colliding heavy ions, where the hot central fireball is embedded in a larger but cooler fireball. The volume of the central source increases with rising bombarding energy. Results of the two-source model fit to RHIC experimental data at midrapidity coincide with the results of the one-source thermal model fit, indicating the formation of an extended fireball, which is three times larger than the corresponding core at SPS.Comment: 6 pages, REVTEX

Violation of energy-per-hadron scaling in a resonance matter

Yields of hadrons, their average masses and energies per hadron at the stage of chemical freeze-out in (ultra)relativistic heavy-ion collisions are analyzed within the statistical model. The violation of the scaling / = 1 GeV observed in Au+Au collisions at $\sqrt{s}$ = 130 AGeV is linked to the formation of resonance-rich matter with a considerable fraction of baryons and antibaryons. The rise of the energy-per-hadron ratio in baryon-dominated matter is discussed. A violation of the scaling condition is predicted for a very central zone of heavy-ion collisions at energies around 40 AGeV.Comment: 5 pages incl. 3 figures and 2 tables, to be published in Phys. Rev.

Impact dynamics of debris flow against slit dam: Experimental and numerical investigation

Debris flows are gravity-driven phenomena common in mountainous regions that are hazardous to downstream facilities. To mitigate the impacts of these disastrous processes, structural countermeasures such as slit dams are constructed in gullies and along mountain slopes. Existing studies on the impact dynamics of debris flows against slit dams typically focus only on the flow characteristics but fail to take the geometry of the structure into account. Here we develop an analytical model, derived from the momentum approach, that allows for the estimation of the runup height and impact load of debris flows on slit dams. The model is validated against discrete element simulations and small-scale flume experiments. It is found that the runup height is controlled by both the Froude number and slit size. The proposed analytical model can predict the runup height well within a certain range of Froude numbers. Results from experiments further reveal that the fontal dynamic pressure is sensitive to the flow properties whereas the peak dynamic pressure is strongly affected by the slit size

Case Studies to Illustrate the Rotorcraft Certification by Simulation Process; CS27/29 Dynamic Stability Requirements

This paper is one of a set presented at the 49th European Rotorcraft Forum displaying results from the EU Clean Sky 2 project, Rotorcraft Certification by Simulation (RoCS). The process developed by the RoCS team provides guidance on the requirements for the use of simulation in certification and features four case studies that illustrate aspects of the process applied using flight simulation models and flight test data provided by Leonardo Helicopters. This paper presents the case study on Dynamic Stability, for the relevant certification paragraphs in the EASA Certification Specifications CS-27 and CS-29. The Dynamic Stability paragraphs from the Specifications are described and results from simulation model fidelity assessment, and updating compared with test data, are presented for a reference flight condition. The credibility of extrapolations of the flight simulation model results to conditions at higher altitude, different airspeeds and vertical rates of climb are then discussed. Preliminary results from piloted simulation trials, with a new flight test manoeuvre, are included to illustrate flight simulator fidelity assessment methods and to explore the veracity of the stability margins set by the Certification Specifications

Rotorcraft Flight Simulation to support Aircraft Certification: A Review of the State of the Art with an Eye to Future Applications

This paper presents the approach for Rotorcraft Certification by Simulation proposed within the RoCS project. In particular, the aspects of model validation and credibility assessment through the usage of uncertainty quantification techniques are reviewed, and some lesson learned are presented. It is shown that the increase of effort required to thoroughly evaluate the capability of the simulation model is often counterbalanced by the advantages of the insight that can be obtained and possibly exploited also for design purposes. It is shown that the numerical approaches, and in some cases even the tools required to perform the necessary uncertainty analyses are publicly available and can be directly employed. This paper is one of a set presented at the 49th European Rotorcraft Forum discussing results from the EU Clean Sky 2 project, Rotorcraft Certification by Simulation (RoCS)

Tensor Correlations Measured in 3He(e,e'pp)n

We have measured the 3He(e,e'pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum, $p_{tot}$. For pair relative momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low $p_{tot}$ and rises to approximately 0.5 at large $p_{tot}$. This shows the dominance of tensor over central correlations at this relative momentum.Comment: 4 pages, 4 figures, submitted to PR