636 research outputs found
Vector quantization of images using visual masking functions
Journal ArticleABSTRACT This paper presents an image compression technique that incorporates visual masking functions in vector quantizer systems. Visual masking functions provide a description of the maximum amount of noise that can be present in an image, while remaining undetected when the image is viewed by an observer. The basic idea employed in this work is that of a spatially varying distortion measure which is defined to be zero where the error involved is below a threshold level defined by the visual masking function. A gradient based algorithm is used to generate the vector quantizer codebooks. Experimental results involving subband vector quantization and a perceptual masking function recently proposed by Safranek and Johnston are presented in this paper
Non-contact rack and pinion powered by the lateral Casimir force
The lateral Casimir force is employed to propose a design for a potentially
wear-proof rack and pinion with no contact, which can be miniaturized to
nano-scale. The robustness of the design is studied by exploring the relation
between the pinion velocity and the rack velocity in the different domains of
the parameter space. The effects of friction and added external load are also
examined. It is shown that the device can hold up extremely high velocities,
unlike what the general perception of the Casimir force as a weak interaction
might suggest.Comment: 4 pages, submitted for publication on 17 Jan 0
Labor Laws and Innovation
Stringent labor laws can provide firms a commitment device to not punish short-run failures and thereby spur their employees to pursue value-enhancing innovative activities. Using patents and citations as proxies for innovation, we identify this effect by exploiting the time-series variation generated by staggered country-level changes in dismissal laws. We find that within a country, innovation and economic growth are fostered by stringent laws governing dismissal of employees, especially in the more innovation-intensive sectors. Firm-level tests within the United States that exploit a discontinuity generated by the passage of the federal Worker Adjustment and Retraining Notification Act confirm the cross-country evidence.
Analysis of the compatibility of dental implant systems in fibula free flap reconstruction
As a result of major ablative surgery, head and neck oncology patients can be left with significant defects in the orofacial region. The resultant defect raises the need for advanced reconstruction techniques. The reconstruction in this region is aimed at restoring function and facial contour. The use of vascularised free flaps has revolutionised the reconstruction in the head and neck. Advances in reconstruction techniques have resulted in continuous improvement of oral rehabilitation. For example, endosteal implants are being used to restore the masticatory function by the way of prosthetic replacement of the dentition. Implant rehabilitation usually leads to improved facial appearance, function, restoration of speech and mastication. Suitable dental implant placement’s site requires satisfactory width, height and quality of bone. Reconstruction of hard tissue defects therefore will need to be tailored to meet the needs for implant placement. The aim of this feasibility study was to assess the compatibility of five standard commercially available dental implant systems (Biomet 3i, Nobel Biocare, Astra tech, Straumann and Ankylos) for placement into vascularised fibula graft during the reconstruction of oromandibular region. Radiographs (2D) of the lower extremities from 142 patients in the archives of the Department of Radiology in University College London Hospitals (UCLH) were analysed in this study. These radiographs were from 61 females and 81 males. Additionally, 60 unsexed dry fibular bones, 30 right sided, acquired from the collection of the Department of Anatomy, University College London (UCL) were also measured to account for the 3D factor. In the right fibula (dry bone), 90% of the samples measured had a width of 13.1 mm. While in the left fibula (dry bone), 90% of the samples measured had a width of 13.3 mm. Fibulas measured on radiographs had a width of 14.3 mm in 90% of the samples. The length ranges of the dental implants used in this study were: 7-13 mm (Biomet 3i), 10-13 mm (Nobel biocare), 8-13 mm (Astra Tech), 8-12 mm (Straumann ) and 8-11 mm (Ankylos). This study reached a conclusion that the width of fibula is sufficient for placement of most frequently used dental implants for oral rehabilitation after mandibular reconstructive procedures
On relaxations of the max -cut problem formulations
A tight continuous relaxation is a crucial factor in solving mixed integer
formulations of many NP-hard combinatorial optimization problems. The
(weighted) max -cut problem is a fundamental combinatorial optimization
problem with multiple notorious mixed integer optimization formulations. In
this paper, we explore four existing mixed integer optimization formulations of
the max -cut problem. Specifically, we show that the continuous relaxation
of a binary quadratic optimization formulation of the problem is: (i) stronger
than the continuous relaxation of two mixed integer linear optimization
formulations and (ii) at least as strong as the continuous relaxation of a
mixed integer semidefinite optimization formulation. We also conduct a set of
experiments on multiple sets of instances of the max -cut problem using
state-of-the-art solvers that empirically confirm the theoretical results in
item (i). Furthermore, these numerical results illustrate the advances in the
efficiency of global non-convex quadratic optimization solvers and more general
mixed integer nonlinear optimization solvers. As a result, these solvers
provide a promising option to solve combinatorial optimization problems. Our
codes and data are available on GitHub
Plastic flow of persistent currents in two dimensional strongly interacting systems
The local persistent current in two dimensional strongly interacting systems
is investigated. As the interaction strength is enhanced the current in the
sample undergoes a transition from diffusive to ordered flow. The strong
interacting flow has the characteristics of a plastic flow through dislocations
in the pinned charge density wave which develops in the system at low
densities.Comment: 12 pages, 4 figures, accepted for publication in Phys. Rev. B (RC
Dynamic response of isolated Aharonov-Bohm rings coupled to an electromagnetic resonator
We have measured the flux dependence of both real and imaginary conductance
of isolated mesoscopic rings at 310 MHz. The rings are coupled to
a highly sensitive electromagnetic superconducting micro-resonator and lead to
a perturbation of the resonance frequency and quality factor. This experiment
provides a new tool for the investigation of the conductance of mesoscopic
systems without any connection to invasive probes. It can be compared with
recent theoretical predictions emphasizing the differences between isolated and
connected geometries and the relation between ac conductance and persistent
currents. We observe periodic oscillations on both components of the
magnetoconductance. The oscillations of the imaginary conductance whose sign
corresponds to diamagnetism in zero field, are 3 times larger than the Drude
conductance . The real part of the periodic magnetoconductance is of the
order of and is apparently negative in low field. It is thus notably
different from the weak localisation oscillations observed in connected rings,
which are much smaller and opposite in sign.Comment: 4 pages, revtex, epsf, 4 Postscript file
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