12,672 research outputs found
Interim user's manual for boundary layer integral matrix procedure, version J
A computer program for analyzing two dimensional and axisymmetric nozzle performance with a variety of wall boundary conditions is described. The program has been developed for application to rocket nozzle problems. Several aids to usage of the program and two auxiliary subroutines are provided. Some features of the output are described and three sample cases are included
Boundary layer integral matrix procedure code modifications and verifications
A summary of modifications to Aerotherm's Boundary Layer Integral Matrix Procedure (BLIMP) code is presented. These modifications represent a preliminary effort to make BLIMP compatible with other JANNAF codes and to adjust the code for specific application to rocket nozzle flows. Results of the initial verification of the code for prediction of rocket nozzle type flows are discussed. For those cases in which measured free stream flow conditions were used as input to the code, the boundary layer predictions and measurements are in excellent agreement. In two cases, with free stream flow conditions calculated by another JANNAF code (TDK) for use as input to BLIMP, the predictions and the data were in fair agreement for one case and in poor agreement for the other case. The poor agreement is believed to result from failure of the turbulent model in BLIMP to account for laminarization of a turbulent flow. Recommendations for further code modifications and improvements are also presented
The structure of trailing vortices generated by model rotor blades
Hot-wire anemometry to analyze the structure and geometry of rotary wing trailing vortices is studied. Tests cover a range of aspect ratios and blade twist. For all configurations, measured vortex strength correlates well with maximum blade-bound circulation. Measurements of wake geometry are in agreement with classical data for high-aspect ratios. The detailed vortex structure is similar to that found for fixed wings and consists of four well defined regions--a viscous core, a turbulent mixing region, a merging region, and an inviscid outer region. A single set of empirical formulas for the entire set of test data is described
Resonance modes in a 1D medium with two purely resistive boundaries: calculation methods, orthogonality and completeness
Studying the problem of wave propagation in media with resistive boundaries
can be made by searching for "resonance modes" or free oscillations regimes. In
the present article, a simple case is investigated, which allows one to
enlighten the respective interest of different, classical methods, some of them
being rather delicate. This case is the 1D propagation in a homogeneous medium
having two purely resistive terminations, the calculation of the Green function
being done without any approximation using three methods. The first one is the
straightforward use of the closed-form solution in the frequency domain and the
residue calculus. Then the method of separation of variables (space and time)
leads to a solution depending on the initial conditions. The question of the
orthogonality and completeness of the complex-valued resonance modes is
investigated, leading to the expression of a particular scalar product. The
last method is the expansion in biorthogonal modes in the frequency domain, the
modes having eigenfrequencies depending on the frequency. Results of the three
methods generalize or/and correct some results already existing in the
literature, and exhibit the particular difficulty of the treatment of the
constant mode
Collisionless Magnetic Reconnection via Alfven Eigenmodes
We propose an analytic approach to the problem of collisionless magnetic
reconnection formulated as a process of Alfven eigenmodes' generation and
dissipation. Alfven eigenmodes are confined by the current sheet in the same
way that quantum mechanical waves are confined by the tanh^2 potential. The
dynamical time scale of reconnection is the system scale divided by the
eigenvalue propagation velocity of the n=1 mode. The prediction of the n=1 mode
shows good agreement with the in situ measurement of the
reconnection-associated Hall fields
An interacting quark-diquark model of baryons
A simple quark-diquark model of baryons with direct and exchange interactions
is constructed. Spectrum and form factors are calculated and compared with
experimental data. Advantages and disadvantages of the model are discussed.Comment: 13 pages, 3 eps-figures, accepted by Phys.Rev. C Rapid Communication
Collaboration in museums and health research
This study reflects on the range of collaborations in two distinct but thematically linked UCL research projects which consider the role of culture in health promotion: Museums on Prescription (2014–2017), in partnership with Canterbury Christ Church University, explores the value of heritage encounters in social prescribing for lonely older adults at risk of social isolation; and Not So Grim Up North (2016–2018), in conjunction with Whitworth Art Gallery, University of Manchester and Tyne & Wear Archives & Museums, investigates the health and wellbeing impacts of museum activities for stroke survivors; older adults with dementia; and mental health and addiction recovery service-users. Both projects employ a mixed-methods approach using quantitative and qualitative data. The research projects have been developed and delivered through collaborations between interdisciplinary university researchers, museum practitioners, health and social care professionals and end-users. Collaboration has taken different forms including co-developing evaluation methods, co-disseminating outputs, and through advisory boards. This study reflects on the opportunities and challenges of collaboration, noting the language and practice dissonance across different fields and the importance of finding common ground. It also highlights the considerable amount of time that is required to build genuine collaborative relationships, which is not often acknowledged in research outputs
Casimir Force at a Knife's Edge
The Casimir force has been computed exactly for only a few simple geometries,
such as infinite plates, cylinders, and spheres. We show that a parabolic
cylinder, for which analytic solutions to the Helmholtz equation are available,
is another case where such a calculation is possible. We compute the
interaction energy of a parabolic cylinder and an infinite plate (both perfect
mirrors), as a function of their separation and inclination, and ,
and the cylinder's parabolic radius . As , the proximity force
approximation becomes exact. The opposite limit of corresponds to a
semi-infinite plate, where the effects of edge and inclination can be probed.Comment: 5 pages, 3 figures, uses RevTeX; v2: expanded conclusions; v3: fixed
missing factor in Eq. (3) and incorrect diagram label (no changes to
results); v4: fix similar factor in Eq. (16) (again no changes to results
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