16,137 research outputs found
Shape Calculus for Shape Energies in Image Processing
Many image processing problems are naturally expressed as energy minimization
or shape optimization problems, in which the free variable is a shape, such as
a curve in 2d or a surface in 3d. Examples are image segmentation, multiview
stereo reconstruction, geometric interpolation from data point clouds. To
obtain the solution of such a problem, one usually resorts to an iterative
approach, a gradient descent algorithm, which updates a candidate shape
gradually deforming it into the optimal shape. Computing the gradient descent
updates requires the knowledge of the first variation of the shape energy, or
rather the first shape derivative. In addition to the first shape derivative,
one can also utilize the second shape derivative and develop a Newton-type
method with faster convergence. Unfortunately, the knowledge of shape
derivatives for shape energies in image processing is patchy. The second shape
derivatives are known for only two of the energies in the image processing
literature and many results for the first shape derivative are limiting, in the
sense that they are either for curves on planes, or developed for a specific
representation of the shape or for a very specific functional form in the shape
energy. In this work, these limitations are overcome and the first and second
shape derivatives are computed for large classes of shape energies that are
representative of the energies found in image processing. Many of the formulas
we obtain are new and some generalize previous existing results. These results
are valid for general surfaces in any number of dimensions. This work is
intended to serve as a cookbook for researchers who deal with shape energies
for various applications in image processing and need to develop algorithms to
compute the shapes minimizing these energies
Isophote curves on timelike surfaces in Minkowski 3-space
Isophote comprises a locus of the surface points whose normal vectors make a
constant angle with a fixed vector. In this paper, isophote curves are studied
on timelike surfaces in Minkowski 3-space E31. The axises of spacelike and
timelike isophote curves are found via their Darboux frames. Subsequently, the
relationship between isophotes and slant helices is shown on timelike surfaces.Comment: 11 pages. arXiv admin note: text overlap with arXiv:1203.438
An Evaluation of Faculty use of the Digital Library at Ankara University, Turkey
New consortial buying models have dramatically increased the availability of online resources, particularly journal articles, in the universities and technical institutes of developing countries. The degree of acceptance and pattern of use of such materials is of great interest to library collection development. Ankara University surveyed faculty members regarding their awareness and use of these electronic materials
A tunable X-band SiGe HBT single stage cascode LNA
This paper presents an X-band silicon-germanium (SiGe) single stage cascode tunable low-noise amplifier (LNA) for active phased array transmit/receive modules. LNA is implemented by using IHP SiGe heterojunction bipolar transistors (HBTs) 0.25-μm SGB25V technology. Cadence is used in collaboration with ADS during schematic and layout design and the results depict that designed LNA dissipates 15.36 mW from an 2.4 V DC power supply and the maximum gain around 18 dB in X-band while not exceeding the 2.4 dB noise figure (NF). Reverse gain of the LNA is very low (<-40 dB). Input terminal is matched so that S11 is below -10 dB in X-band
Do the effects of vitamin d supplementation on muscle strength differ according to age?
Introduction: Vitamin D plays an important role in musculoskeletal health and its use improves muscle strength. However, the effect of vitamin D use on muscle strength in women of different ages is yet to be investigated. Therefore, in this study, we aimed to evaluate the effect of vitamin D use on muscle strength in women of different age groups and determine the differences of muscle strength gain between age groups. Materials and Method: Sixty-three women with calcidiol levels<30 ng/mL were randomly assigned and stratified by their age group as follows: Group I (aged 40–49 years), Group II (aged 50–59 years) and Group III (aged 60–69 years). Calcidiol levels, body mass index, fat free mass, percent fat, grip strength, arm curl, chair stand and isokinetic concentric flexor and extensor peak torque and power at 60°•s−1 and 180°•s−1 were assessed at baseline and six months after oral cholecalciferol supplementation. Results: Vitamin D supplementation caused significant improvement in body mass index, arm curl, grip strength and knee flexor and extensor peak torque and power at 60°•s−1 and 180°•s−1 in all groups (p<0.05). Knee flexor power at 60°•s−1 and extensor power at 180°•s−1 were significantly higher in group I than in group III (p<0.025). Conclusion: Muscle strength in response to vitamin D supplementation increased in all age groups, and isokinetic muscle power was the highest in the youngest age group studied. © 2018, Geriatrics Society. All rights reserved
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