7,869 research outputs found
Reliability analysis of structural ceramic components using a three-parameter Weibull distribution
Described here are nonlinear regression estimators for the three-Weibull distribution. Issues relating to the bias and invariance associated with these estimators are examined numerically using Monte Carlo simulation methods. The estimators were used to extract parameters from sintered silicon nitride failure data. A reliability analysis was performed on a turbopump blade utilizing the three-parameter Weibull distribution and the estimates from the sintered silicon nitride data
Analysis of whisker-toughened ceramic components: A design engineer's viewpoint
The use of ceramics components in gas turbines, cutting tools, and heat exchangers has been limited by the relatively low flaw tolerance of monolithic ceramics. The development of whisker toughened ceramic composites offers the potential for considerable improvement in fracture toughness as well as strength. However, the variability of strength is still too high for the application of deterministic design approaches. Several phenomenological reliability theories proposed for this material system are reviewed and the development is reported of a public domain computer algorithm. This algorithm, when coupled with a general purpose finite element program, predicts the fast fracture reliability of a structural component under multiaxial loading conditions
Alcohol and healthy ageing: a challenge for alcohol policy
Objectives:
This paper presents findings of a qualitative study of older people's use of alcohol during retirement and identifies ways that an improved understanding of older people's drinking can inform policy approaches to alcohol and active and healthy ageing.
Study design:
Qualitative semi-structured interviews conducted with a self-selecting sample of retired people.
Methods:
Participants were recruited from three geographical locations in the West of Scotland. A quota sampling design was used to ensure a broad spread of participants in terms of socio-economic position, age and gender. In total 40 participants were interviewed and the data analysed thematically using Braun and Clarke's (2006) approach.
Results:
Amongst those who used alcohol, it was most often framed in terms of pleasure, relaxation, socialising and as a way to mark the passage of time. Alcohol was often associated with social occasions and interactions both in private and in public spaces. There were also many examples of the use of imposed routines to limit alcohol use and of a decreasing volume of alcohol being consumed as participants aged. This suggests that older people are often active in constructing what they regard as ‘healthier’ routines around alcohol use. However, processes and circumstances associated with ageing can lead to risk of social isolation and/or increased alcohol consumption. Such processes include retirement from paid work and other ‘biographical disruptions’ such as caring for a partner, bereavement and/or loss of social networks.
Conclusions:
These findings highlight processes that can result in changes in drinking habits and routines. Whilst these processes can be associated with a reduction or cessation of alcohol use as people age, they can also be associated with increased risk of harmful alcohol consumption. Fractured or disrupted routines, particularly those associated with bereavement or the burden of caring responsibilities, through increasing the risk of loneliness and isolation, can construct increased risk of harmful alcohol consumption. These findings reframe the pathway of risk between ageing and alcohol-related harm by highlighting the vulnerability to harmful drinking practices brought by fracture or sudden change of routine. The findings point to a role for public health in supporting the reconstruction of routines that provide structure and meaning and can be used to actively manage the benefits and harms associated with drinking
Particle acceleration efficiencies in astrophysical shear flows
The acceleration of energetic particles in astrophysical shear flows is
analyzed. We show that in the presence of a non-relativistic gradual velocity
shear, power law particle momentum distributions
may be generated, assuming a momentum-dependent scattering time , with . We consider possible acceleration sites in
astrophysical jets and study the conditions for efficient acceleration. It is
shown, for example, that in the presence of a gradual shear flow and a
gyro-dependent particle mean free path, synchrotron radiation losses no longer
stop the acceleration once it has started to work efficiently. This suggests
that shear acceleration may naturally account for a second, non-thermal
population of energetic particles in addition to a shock-accelerated one. The
possible relevance of shear acceleration is briefly discussed with reference to
the relativistic jet in the quasar 3C 273.Comment: 6 pages, 2 figures; typos corrected wrt to published version, Proc.
of the "International Symposium on High Energy Gamma-Ray Astronomy"
Heidelberg (2004), eds. F.A. Aharonian, H.J. Voelk and D. Horns (AIP, NY
Dynamic RKKY interaction between magnetic moments in graphene nanoribbons
Graphene has been identified as a promising material with numerous
applications, particularly in spintronics. In this paper we investigate the
peculiar features of spin excitations of magnetic units deposited on graphene
nanoribbons and how they can couple through a dynamical interaction mediated by
spin currents. We examine in detail the spin lifetimes and identify a pattern
caused by vanishing density of states sites in pristine ribbons with armchair
borders. Impurities located on these sites become practically invisible to the
interaction, but can be made accessible by a gate voltage or doping. We also
demonstrate that the coupling between impurities can be turned on or off using
this characteristic, which may be used to control the transfer of information
in transistor-like devices.Comment: 10 pages, 10 figure
Noninteractive Macroscopic Reliability Model for Ceramic Matrix Composites With Orthotropic Material Symmetry
A macroscopic noninteractive reliability model for ceramic matrix composites is presented. The model is multiaxial and applicable to composites that can be characterized as orthotropic. Tensorial invariant theory is used to create an integrity basis with invariants that correspond to physical mechanisms related to fracture. This integrity basis is then used to construct a failure funciton per unit volume (or area) of material. It is assumed that the overall strength of the composite is governed by weakest link theory. This leads to a Weibull type model similar in nature to the principle of independent action (PIA) model for isotropic monolithic ceramics. An experimental program to obtain model parameters is briefly discussed. In addition, qualitative features of the model are illustrated by presenting reliability surfaces for various model parameters
Early out-of-equilibrium beam-plasma evolution
We solve analytically the out-of-equilibrium initial stage that follows the
injection of a radially finite electron beam into a plasma at rest and test it
against particle-in-cell simulations. For initial large beam edge gradients and
not too large beam radius, compared to the electron skin depth, the electron
beam is shown to evolve into a ring structure. For low enough transverse
temperatures, the filamentation instability eventually proceeds and saturates
when transverse isotropy is reached. The analysis accounts for the variety of
very recent experimental beam transverse observations.Comment: to appear in Phys. Rev. Letter
Reliability Analysis of Structural Ceramic Components Using a Three-parameter Weibull Distribution
This paper describes nonlinear regression estimators for the three-parameter Weibull distribution. Issues relating to the bias and invariance associated with these estimators are examined numerically using Monte Carlo simulation methods. The estimators were used to extract parameters from sintered silicon nitride failure data. A reliability analysis was performed on a turbopump blade utilizing the three-parameter Weibull distribution and the estimates from the sintered silicon nitride data
An Integro-Differential Equation of the Fractional Form: Cauchy Problem and Solution
Producción CientíficaWe solve the Cauchy problem defined by the fractional partial differential
equation [∂tt − κD]u = 0, with D the pseudo-differential Riesz operator of first
order, and certain initial conditions. The
solution of the Cauchy problem resulting from the substitution of the Gaussian pulse
u(x, 0) by the Dirac delta distribution ϕ(x) = μδ(x) is obtained as corollary.MINECO grant MTM2014-57129-C2-1-P
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