14,992 research outputs found
A Generalized Construction of OFDM M-QAM Sequences With Low Peak-to-Average Power Ratio
A construction of -QAM sequences is given and an upper bound of the
peak-to-mean envelope power ratio (PMEPR) is determined. Some former works can
be viewed as special cases of this construction.Comment: published by Advances in Mathematics of Communication
Design, development and testing of miniature instruments for flexible endoscopy
This thesis describes the design and development of single-stitch and chain-stitch endoscopic sewing machines for flexible endoscopy as well as devices and methods for tying knots and cutting thread at flexible endoscopy. The work also includes a comparative study of clipping methods for endoscopic haemostasis and a feasibility study of a wireless endoscope that might allow images to be transmitted from sites in the gastrointestinal tract without wires, cables or fibre optic bundles. The development and testing of simple prototypes of such an endoscope are reported. Chapter 1 reviews the surgical instruments and methods used for tissue approximation in general surgery, laparoscopic surgery and flexible endoscopic surgery. The design of existing, conventional sewing machines and the ways in which they form stitches are also considered. In Chapter 2, a comparative study of clipping methods for endoscopic haemostasis is reported. In Chapter 3, the design and development of new single-stitch endoscopic sewing machines are described, together with data on the clinical use of one of these machines. In Chapter 4, studies of ways of improving endoscopic vision during endoscopic sewing and the effects of needle size and the size and shape of the suction cavity are reported. In Chapter 5, the design and development of novel chain-stitch endoscopic sewing machines are reported. These make use of two new catch mechanisms. In Chapter 6, knot tying at flexible endoscopy is considered, and a number of new devices and methods are described and clinical results reported. In Chapter 7, cutting thread at flexible endoscopy is described. Several new endoscopic thread cutting devices and methods together with results are presented. In Chapter 8, a feasibility study of wireless endoscopy is reported. The study includes tests of the concept of wireless endoscopes made using prototypes constructed from miniature CCD cameras and microwave transmitters. Finally, some concluding remarks relating to the work described in this thesis are given
Statistics of Chaotic Resonances in an Optical Microcavity
Distributions of eigenmodes are widely concerned in both bounded and open
systems. In the realm of chaos, counting resonances can characterize the
underlying dynamics (regular vs. chaotic), and is often instrumental to
identify classical-to-quantum correspondence. Here, we study, both
theoretically and experimentally, the statistics of chaotic resonances in an
optical microcavity with a mixed phase space of both regular and chaotic
dynamics. Information on the number of chaotic modes is extracted by counting
regular modes, which couple to the former via dynamical tunneling. The
experimental data are in agreement with a known semiclassical prediction for
the dependence of the number of chaotic resonances on the number of open
channels, while they deviate significantly from a purely
random-matrix-theory-based treatment, in general. We ascribe this result to the
ballistic decay of the rays, which occurs within Ehrenfest time, and
importantly, within the timescale of transient chaos. The present approach may
provide a general tool for the statistical analysis of chaotic resonances in
open systems.Comment: 5 pages, 5 figures, and a supplemental informatio
Fourth generation Majorana neutrino, dark matter and Higgs physics
We consider extensions of the standard model with fourth generation fermions
(SM4) in which extra symmetries are introduced such that the transitions
between the fourth generation fermions and the ones in the first three
generations are forbidden. In these models, the stringent lower bounds on the
masses of fourth generation quarks from direct searches are relaxed, and the
lightest fourth neutrino is allowed to be stable and light enough to trigger
the Higgs boson invisible decay. In addition, the fourth Majorana neutrino can
be a subdominant but highly detectable dark matter component. We perform a
global analysis of the current LHC data on the Higgs production and decay in
this type of SM4. The results show that the mass of the lightest fourth
Majorana neutrino is confined in the range GeV. Within the allowed
parameter space, the predicted effective cross-section for spin-independent
DM-nucleus scattering is , which is close to the current Xenon100 upper limit and is
within the reach of the Xenon1T experiment in the near future. The predicted
spin-dependent cross sections can also reach .Comment: arXiv admin note: substantial text overlap with arXiv:1110.293
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