12,627 research outputs found
Influence of a magnetic fluxon on the vacuum energy of quantum fields confined by a bag
We study the simultaneous influence of boundary conditions and external
fields on quantum fluctuations by considering vacuum zero-point energies for
quantum fields in the presence of a magnetic fluxon confined by a bag, circular
and spherical for bosons and circular for fermions. The Casimir effect is
calculated in a generalized cut-off regularization after applying zeta-function
techniques to eigenmode sums and using recent techniques about Bessel zeta
functions at negative arguments
Complete zeta-function approach to the electromagnetic Casimir effect for spheres and circles
A technique for evaluating the electromagnetic Casimir energy in situations
involving spherical or circular boundaries is presented. Zeta function
regularization is unambiguously used from the start and the properties of
Bessel and related zeta functions are central. Nontrivial results concerning
these functions are given. While part of their application agrees with previous
knowledge, new results like the zeta-regularized electromagnetic Casimir energy
for a circular wire are included.Comment: accepted in Ann. Phy
Spin-torque generation by dc or ac voltages in magnetic layered structures
A general expression of the current induced spin torque in a magnetic layered
structure in the presence of external dc or ac voltages is derived in the
framework of the scattering matrix approach. A detailed analysis is performed
for a magnetic-nonmagnetic-magnetic trilayer connected to external leads in the
presence of dc voltage bias in the ballistic regime. Alternatively, the
possibility of producing spin torque by means of the adiabatic ac modulation of
external gate voltages (quantum pumping) is proposed and discussed
Entrepreneurship, innovation and the triple helix model: evidence from Oxfordshire and Cambridgeshire
This paper focuses on how regions become entrepreneurial and the extent to which the actors in the triple helix model are dominant at particular stages in development. It uses the case studies of Oxfordshire and Cambridgeshire in the UK to explore this theme. Both can now be described as ‘regional triple helix spaces’ (Etzkowitz 2008), and form two points of the Golden Triangle of Oxford, Cambridge and London universities. As entrepreneurial regions, however, they differ in a number of respects. This is not surprising given their differing geo-historical contexts. However, by comparing the two similar counties but which have their own distinctive features we are able to explore different dynamics which lead to the inception, implementation, consolidation and renewal (Etzkowitz and Klofsten 2005) of regions characterised by very high levels of technology-based entrepreneurship
Energy Shaping Control of an Inverted Flexible Pendulum Fixed to a Cart
Control of compliant mechanical systems is increasingly being researched for
several applications including flexible link robots and ultra-precision
positioning systems. The control problem in these systems is challenging,
especially with gravity coupling and large deformations, because of inherent
underactuation and the combination of lumped and distributed parameters of a
nonlinear system. In this paper we consider an ultra-flexible inverted pendulum
on a cart and propose a new nonlinear energy shaping controller to keep the
pendulum at the upward position with the cart stopped at a desired location.
The design is based on a model, obtained via the constrained Lagrange
formulation, which previously has been validated experimentally. The controller
design consists of a partial feedback linearization step followed by a standard
PID controller acting on two passive outputs. Boundedness of all signals and
(local) asymptotic stability of the desired equilibrium is theoretically
established. Simulations and experimental evidence assess the performance of
the proposed controller.Comment: 11 pages, 7 figures, extended version of the NOLCOS 2016 pape
A cryptic promoter in potato virus X vector interrupted plasmid construction
BACKGROUND: Potato virus X has been developed into an expression vector for plants. It is widely used to express foreign genes. In molecular manipulation, the foreign genes need to be sub-cloned into the vector. The constructed plasmid needs to be amplified. Usually, during amplification stage, the foreign genes are not expressed. However, if the foreign gene is expressed, the construction work could be interrupted. Two different viral genes were sub-cloned into the vector, but only one foreign gene was successfully sub-cloned. The other foreign gene, canine parvovirus type 2 (CPV-2) VP1 could not be sub-cloned into the vector and amplified without mutation (frame shift mutation). RESULTS: A cryptic promoter in the PVX vector was discovered with RT-PCR. The promoter activity was studied with Northern blots and Real-time RT-PCR. CONCLUSION: It is important to recognize the homologous promoter sequences in the vector when a virus is developed as an expression vector. During the plasmid amplification stage, an unexpected expression of the CPV-2 VP1 gene (not in the target plants, but in E. coli) can interrupt the downstream work
Neural networks in geophysical applications
Neural networks are increasingly popular in geophysics.
Because they are universal approximators, these
tools can approximate any continuous function with an
arbitrary precision. Hence, they may yield important
contributions to finding solutions to a variety of geophysical applications.
However, knowledge of many methods and techniques
recently developed to increase the performance
and to facilitate the use of neural networks does not seem
to be widespread in the geophysical community. Therefore,
the power of these tools has not yet been explored to
their full extent. In this paper, techniques are described
for faster training, better overall performance, i.e., generalization,and the automatic estimation of network size
and architecture
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