52,517 research outputs found
An approach to market analysis for lighter than air transportation of freight
An approach is presented to marketing analysis for lighter than air vehicles in a commercial freight market. After a discussion of key characteristics of supply and demand factors, a three-phase approach to marketing analysis is described. The existing transportation systems are quantitatively defined and possible roles for lighter than air vehicles within this framework are postulated. The marketing analysis views the situation from the perspective of both the shipper and the carrier. A demand for freight service is assumed and the resulting supply characteristics are determined. Then, these supply characteristics are used to establish the demand for competing modes. The process is then iterated to arrive at the market solution
Effects of the roller feed ratio on wrinkling failure in conventional spinning of a cylindrical cup
In this study, wrinkling failure in conventional spinning of a cylindrical cup has been investigated by using both finite element (FE) analysis and experimental methods. FE simulation models of a spinning experiment have been developed using the explicit finite element solution method provided by the software Abaqus. The severity of wrinkles is quantified by calculating the standard deviation of the radial coordinates of element nodes on the edge of the workpiece obtained from the FE models. The results show that the severity of wrinkles tends to increase when increasing the roller feed ratio. A forming limit study for wrinkling has been carried out and shows that there is a feed ratio limit beyond which the wrinkling failure will take place. Provided that the feed ratio is kept below this limit, the wrinkling failure can be prevented. It is believed that high compressive tangential stresses in the local forming zone are the causes of the wrinkling failure. Furthermore, the computational performance of the solid and shell elements in simulating the spinning process are examined and the tool forces obtained from wrinkling and wrinkle-free models are compared. Finally, the effects of the feed ratio on variations of the wall thickness of the spun cylindrical cup are investigated. </jats:p
Self-consistent simulations of a von K\'arm\'an type dynamo in a spherical domain with metallic walls
We have performed numerical simulations of boundary-driven dynamos using a
three-dimensional non-linear magnetohydrodynamical model in a spherical shell
geometry. A conducting fluid of magnetic Prandtl number Pm=0.01 is driven into
motion by the counter-rotation of the two hemispheric walls. The resulting flow
is of von K\'arm\'an type, consisting of a layer of zonal velocity close to the
outer wall and a secondary meridional circulation. Above a certain forcing
threshold, the mean flow is unstable to non-axisymmetric motions within an
equatorial belt. For fixed forcing above this threshold, we have studied the
dynamo properties of this flow. The presence of a conducting outer wall is
essential to the existence of a dynamo at these parameters. We have therefore
studied the effect of changing the material parameters of the wall (magnetic
permeability, electrical conductivity, and thickness) on the dynamo. In common
with previous studies, we find that dynamos are obtained only when either the
conductivity or the permeability is sufficiently large. However, we find that
the effect of these two parameters on the dynamo process are different and can
even compete to the detriment of the dynamo. Our self-consistent approach allow
us to analyze in detail the dynamo feedback loop. The dynamos we obtain are
typically dominated by an axisymmetric toroidal magnetic field and an axial
dipole component. We show that the ability of the outer shear layer to produce
a strong toroidal field depends critically on the presence of a conducting
outer wall, which shields the fluid from the vacuum outside. The generation of
the axisymmetric poloidal field, on the other hand, occurs in the equatorial
belt and does not depend on the wall properties.Comment: accepted for publication in Physical Review
Inviscid helical magnetorotational instability in cylindrical Taylor-Couette flow
This paper presents the analysis of axisymmetric helical magnetorotational
instability (HMRI) in the inviscid limit, which is relevant for astrophysical
conditions. The inductionless approximation defined by zero magnetic Prandtl
number is adopted to distinguish the HMRI from the standard MRI in the
cylindrical Taylor-Couette flow subject to a helical magnetic field. Using a
Chebyshev collocation method convective and absolute instability thresholds are
computed in terms of the Elsasser number for a fixed ratio of inner and outer
radii \lambda=2 and various ratios of rotation rates and helicities of the
magnetic field. It is found that the extension of self-sustained HMRI modes
beyond the Rayleigh limit does not reach the astrophysically relevant Keplerian
rotation profile not only in the narrow- but also in the finite-gap
approximation. The Keppler limit can be attained only by the convective HMRI
mode provided that the boundaries are perfectly conducting. However, this mode
requires not only a permanent external excitation to be observable but also has
a long axial wave length, which is not compatible with limited thickness of
astrophysical accretion disks.Comment: 12 pages, 9 figures, published version with a few typos correcte
The effect of chemotherapeutic agents on telomere length maintenance in breast cancer cell lines
Copyright @ 2014 the authors. This article is made available through the Brunel Open Access Publishing Fund. It is distributed under the terms of the
Creative Commons Attribution Noncommercial License which permits
any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and the source are credited.Mammalian telomeric DNA consists of tandem repeats of the sequence TTAGGG associated with a specialized set of proteins, known collectively as Shelterin. These telosomal proteins protect the ends of chromosomes against end-to-end fusion and degradation. Short telomeres in breast cancer cells confer telomere dysfunction and this can be related to Shelterin proteins and their level of expression in breast cancer cell lines. This study investigates whether expression of Shelterin and Shelterin-associated proteins are altered, and influence the protection and maintenance of telomeres, in breast cancer cells. 5-aza-2'-deoxycytidine (5-aza-CdR) and trichostatin A (TSA) were used in an attempt to reactivate the expression of silenced genes. Our studies have shown that Shelterin and Shelterin-associated genes were down-regulated in breast cancer cell lines; this may be due to epigenetic modification of DNA as the promoter region of POT1 was found to be partially methylated. Shelterin genes expression was up-regulated upon treatment of 21NT breast cancer cells with 5-aza-CdR and TSA. The telomere length of treated 21NT cells was measured by q-PCR showed an increase in telomere length at different time points. Our studies have shown that down-regulation of Shelterin genes is partially due to methylation in some epithelial breast cancer cell lines. Removal of epigenetic silencing results in up-regulation of Shelterin and Shelterin-associated genes which can then lead to telomere length elongation and stability
Three-dimensionality in quasi-two dimensional flows: recirculations and barrel effects
A scenario is put forward for the appearance of three-dimensionality both in
quasi-2D rotating flows and quasi-2D magnetohydrodynamic (MHD) flows. We show
that 3D recirculating flows and currents originate in wall boundary layers and
that, unlike in ordinary hydrodynamic flows, they cannot be ignited by
confinement alone. They also induce a second form of three-dimensionality with
quadratic variations of velocities and current across the channel. This
scenario explains both the common tendency of these flows to two-dimensionality
and the mechanisms of the recirculations through a single formal analogy
covering a wide class of flow including rotating and MHD flows. These
trans-disciplinary effects are thus active in atmospheres, oceans or the
cooling blankets of nuclear fusion reactors.Comment: 6 pages, 1 Figur
Weakly nonlinear stability analysis of MHD channel flow using an efficient numerical approach
We analyze weakly nonlinear stability of a flow of viscous conducting liquid
driven by pressure gradient in the channel between two parallel walls subject
to a transverse magnetic field. Using a non-standard numerical approach, we
compute the linear growth rate correction and the first Landau coefficient,
which in a sufficiently strong magnetic field vary with the Hartmann number as
and
. These
coefficients describe a subcritical transverse velocity perturbation with the
equilibrium amplitude
which exists at Reynolds numbers below the linear stability threshold
We find that the flow
remains subcritically unstable regardless of the magnetic field strength. Our
method for computing Landau coefficients differs from the standard one by the
application of the solvability condition to the discretized rather than
continuous problem. This allows us to bypass both the solution of the adjoint
problem and the subsequent evaluation of the integrals defining the inner
products, which results in a significant simplification of the method.Comment: 16 pages, 10 figures, revised version (to appear in Phys Fluids
Mentoring to reduce antisocial behaviour in childhood
The effects of social interventions need to be examined in real life situations as well as studie
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