51,825 research outputs found
A survey on cyber security for smart grid communications
A smart grid is a new form of electricity network with high fidelity power-flow control, self-healing, and energy reliability and energy security using digital communications and control technology. To upgrade an existing power grid into a smart grid, it requires significant dependence on intelligent and secure communication infrastructures. It requires security frameworks for distributed communications, pervasive computing and sensing technologies in smart grid. However, as many of the communication technologies currently recommended to use by a smart grid is vulnerable in cyber security, it could lead to unreliable system operations, causing unnecessary expenditure, even consequential disaster to both utilities and consumers. In this paper, we summarize the cyber security requirements and the possible vulnerabilities in smart grid communications and survey the current solutions on cyber security for smart grid communications. © 2012 IEEE
Tribo-corrosion properties of cobalt-based medical implant alloys in simulated biological environments
Tribological problems and corrosion degradation have been recognized as essential risks for total joint replacements, especially for all-metal arthroplasty. Few studies have focused on the interactions between tribology and corrosion (tribocorrosion) for implant materials. This paper addresses the importance of understanding tribocorrosion and the evaluation of such materials in simulated biological environments. Due to the complex effect of proteins on tribocorrosion, which has been demonstrated in previous studies, this study focuses towards understanding the effects of amino acids as aspects of material degradation. Dulbecco’s Modified Eagle’s Medium (DMEM) is a cell culture solution. It contains comparable amount and types of amino acids to normal synovial fluid in human joints. 0.36% NaCl solution was employed to isolate the biological species. Three materials were tested; High carbon (HC) CoCrMo (contains 0.19% carbon), low carbon (LC) CoCrMo (widely used materials for total joint replacement) and stainless steel UNS S31603 (316L). Integrated electrochemical tests supported by measurement of friction and near surface chemical analysis were carried out to enable their tribocorrosion behaviour to be fully characterized. As a general conclusion, amino acids were found to react with materials under tribological contacts and form complex organometallic/oxides which lubricate the metallic sample surface. Tribocorrosion plays a very important role in material degradation in the studied environments. HC CoCrMo shows superior wear, corrosion and tribocorrosion resistance – the material characteristics and their effect on the different tribocorrosion processes are discussed
Mathematical modelling and experimental validation of electrostatic sensors for rotational speed measurement
Recent research has demonstrated that electrostatic sensors can be applied to the measurement of rotational speed with excellent repeatability and accuracy under a range of conditions. However, the sensing mechanism and fundamental characteristics of the electrostatic sensors are still largely unknown and hence the design of the sensors is not optimised for rotational speed measurement. This paper presents the mathematical modelling of strip electrostatic sensors for rotational speed measurement and associated experimental studies for the validation of the modelling results. In the modelling, an ideal point charge on the surface of the rotating object is regarded as an impulse input to the sensing system. The fundamental characteristics of the sensor, including spatial sensitivity, spatial filtering length and signal bandwidth, are quantified from the developed model. The effects of the geometric dimensions of the electrode, the distance between the electrode and the rotor surface and the rotational speed being measured on the performance of the sensor are analyzed. A close agreement between the modelling results and experimental measurements has been observed under a range of conditions. Optimal design of the electrostatic sensor for a given rotor size is suggested and discussed in accordance with the modelling and experimental results
Decay Widths of X(1835) as Nucleon-Antinucleon Bound State
Partial decay widths of various decay channels of the X(1835) are evaluated
in the 3P0 quark model, assuming that the X(1835) is a nucleon-antinucleon
bound state. It is found that the decays to rho+rho, omega+omega and
pion+a0(1450) dominate over other channels, and that the product branching
fractions of J/psi to pion+pion+eta and J/psi to pion+pion+eta' are in the same
order. We suggest that the X(1835) may be searched in the pion+a0(1450)
channel.Comment: Changed X(1850) to X(1835) in Abstrac
Combined large-N_c and heavy-quark operator analysis for the chiral Lagrangian with charmed baryons
The chiral Lagrangian with charmed baryons of spin and
is analyzed. We consider all counter terms that are relevant at
next-to-next-to-next-to-leading order (NLO) in a chiral extrapolation of
the charmed baryon masses. At NLO we find 16 low-energy parameters. There
are 3 mass parameters for the anti-triplet and the two sextet baryons, 6
parameters describing the meson-baryon vertices and 7 symmetry breaking
parameters. The heavy-quark spin symmetry predicts four sum rules for the
meson-baryon vertices and degenerate masses for the two baryon sextet fields.
Here a large- operator analysis at NLO suggests the relevance of one
further spin-symmetry breaking parameter. Going from NLO to NLO adds 17
chiral symmetry breaking parameters and 24 symmetry preserving parameters. For
the leading symmetry conserving two-body counter terms involving two baryon
fields and two Goldstone boson fields we find 36 terms. While the heavy-quark
spin symmetry leads to sum rules, an expansion in at
next-to-leading order (NLO) generates parameter relations. A
combined expansion leaves 3 unknown parameters only. For the symmetry breaking
counter terms we find 17 terms, for which there are sum rules from the
heavy-quark spin symmetry and sum rules from a expansion at
NLO.Comment: 34 pages - one table - corrections applie
Dynamics of small trapped one-dimensional Fermi gas under oscillating magnetic fields
Deterministic preparation of an ultracold harmonically trapped
one-dimensional Fermi gas consisting of a few fermions has been realized by the
Heidelberg group. Using Floquet formalism, we study the time dynamics of two-
and three-fermion systems in a harmonic trap under an oscillating magnetic
field. The oscillating magnetic field produces a time-dependent interaction
strength through a Feshbach resonance. We explore the dependence of these
dynamics on the frequency of the oscillating magnetic field for
non-interacting, weakly interacting, and strongly interacting systems. We
identify the regimes where the system can be described by an effective
two-state model and an effective three-state model. We find an unbounded
coupling to all excited states at the infinitely strong interaction limit and
several simple relations that characterize the dynamics. Based on our findings,
we propose a technique for driving transition from the ground state to the
excited states using an oscillating magnetic field.Comment: 11 pages, 7 figure
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