7,747 research outputs found
Coherent optical implementations of the fast Fourier transform and their comparison to the optical implementation of the quantum Fourier transform
Optical structures to implement the discrete Fourier transform (DFT) and fast Fourier transform (FFT) algorithms for discretely sampled data sets are considered. In particular, the decomposition of the FFT algorithm into the basic Butterfly operations is described, as this allows the algorithm to be fully implemented by the successive coherent addition and subtraction of two wavefronts (the subtraction being performed after one has been appropriately phase shifted), so facilitating a simple and robust hardware implementation based on waveguided hybrid devices as employed in coherent optical detection modules. Further, a comparison is made to the optical structures proposed for the optical implementation of the quantum Fourier transform and they are shown to be very similar
Comparison of spatial domain optimal trade-off maximum average correlation height (OT-MACH) filter with scale invariant feature transform (SIFT) using images with poor contrast and large illumination gradient
A spatial domain optimal trade-off Maximum Average Correlation Height (OT-MACH) filter has been previously developed and shown to have advantages over frequency domain implementations in that it can be made locally adaptive to spatial variations in the input image background clutter and normalised for local intensity changes. In this paper we compare the performance of the spatial domain (SPOT-MACH) filter to the widely applied data driven technique known as the Scale Invariant Feature Transform (SIFT). The SPOT-MACH filter is shown to provide more robust recognition performance than the SIFT technique for demanding images such as scenes in which there are large illumination gradients. The SIFT method depends on reliable local edge-based feature detection over large regions of the image plane which is compromised in some of the demanding images we examined for this work. The disadvantage of the SPOTMACH filter is its numerically intensive nature since it is template based and is implemented in the spatial domain. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
SDO/HMI survey of emerging active regions for helioseismology
Observations from the Solar Dynamics Observatory (SDO) have the potential for
allowing the helioseismic study of the formation of hundreds of active regions,
which would enable us to perform statistical analyses. Our goal is to collate a
uniform data set of emerging active regions observed by the SDO/HMI instrument
suitable for helioseismic analysis up to seven days before emergence. We
restricted the sample to active regions that were visible in the continuum and
emerged into quiet Sun largely avoiding pre-existing magnetic regions. As a
reference data set we paired a control region (CR), with the same latitude and
distance from central meridian, with each emerging active region (EAR). We call
this data set, which is currently comprised of 105 emerging active regions
observed between May 2010 and November 2012, the SDO Helioseismic Emerging
Active Region (SDO/HEAR) survey. To demonstrate the utility of a data set of a
large number of emerging active regions, we measure the relative east-west
velocity of the leading and trailing polarities from the line-of-sight
magnetogram maps during the first day after emergence. The latitudinally
averaged line-of-sight magnetic field of all the EARs shows that, on average,
the leading (trailing) polarity moves in a prograde (retrograde) direction with
a speed of 121 +/- 22 m/s (-70 +/- 13 m/s) relative to the Carrington rotation
rate in the first day. However, relative to the differential rotation of the
surface plasma, the east-west velocity is symmetric, with a mean of 95 +/- 13
m/s. The SDO/HEAR data set will not only be useful for helioseismic studies,
but will also be useful to study other features such as the surface magnetic
field evolution of a large sample of EARs.Comment: Accepted by Astronomy and Astrophysics, 11 figures, one longtable;
update corrects units in Figure
The size of Selmer groups for the congruent number problem, II
The oldest problem in the theory of elliptic curves is to determine which positive integers D can be the common difference of a three term arithmetic progres-sion of squares of rational numbers. Such integers D are known as congruent numbers. Equivalently one may ask which elliptic curve
Precise measurements of UV atomic lines: Hyperfine structure and isotope shifts in the 398.8 nm line of Yb
We demonstrate a technique for frequency measurements of UV transitions with
sub-MHz precision. The frequency is measured using a ring-cavity resonator
whose length is calibrated against a reference laser locked to the line
of Rb. We have used this to measure the 398.8 nm line of atomic Yb. We report isotope shifts of all the
seven stable isotopes, including the rarest isotope Yb. We have been
able to resolve the overlapping Yb() and Yb
transitions for the first time. We also obtain high-precision measurements of
excited-state hyperfine structure in the odd isotopes, Yb and
Yb. The measurements resolve several discrepancies among earlier
measurements.Comment: 7 pages, 6 figure
Liquid filled canyons on Titan
In May 2013 the Cassini RADAR altimeter observed channels in Vid Flumina, a drainage network
connected to Titan’s second largest hydrocarbon sea, Ligeia Mare. Analysis of these altimeter echoes shows
that the channels are located in deep (up to ~570 m), steep-sided, canyons and have strong specular surface
reflections that indicate they are currently liquid filled. Elevations of the liquid in these channels are at the
same level as Ligeia Mare to within a vertical precision of about 0.7 m, consistent with the interpretation of
drowned river valleys. Specular reflections are also observed in lower order tributaries elevated above the
level of Ligeia Mare, consistent with drainage feeding into the main channel system
Effect of fatigue loading on structure and functional behaviour of fascicles from energy-storing tendons
Tendons can broadly be categorized according to their function: those that act purely to position the limb and those that have an additional function as energy stores. Energy-storing tendons undergo many cycles of large deformations during locomotion, and so must be able to extend and recoil efficiently, rapidly and repeatedly. Our previous work has shown rotation in response to applied strain in fascicles from energy-storing tendons, indicating the presence of helical substructures which may provide greater elasticity and recovery. In the current study, we assessed how preconditioning and fatigue loading affect the ability of fascicles from the energy-storing equine superficial digital flexor tendon to extend and recoil. We hypothesized that preconditioned samples would exhibit changes in microstructural strain response, but would retain their ability to recover. We further hypothesized that fatigue loading would result in sample damage, causing further alterations in extension mechanisms and a significant reduction in sample recovery. The results broadly support these hypotheses: preconditioned samples showed some alterations in microstructural strain response, but were able to recover following the removal of load. However, fatigue loaded samples showed visual evidence of damage and exhibited further alterations in extension mechanisms, characterized by decreased rotation in response to applied strain. This was accompanied by increased hysteresis and decreased recovery. These results suggest that fatigue loading results in a compromised helix substructure, reducing the ability of energy-storing tendons to recoil. A decreased ability to recoil may lead to an impaired response to further loading, potentially increasing the likelihood of injury
Thoughts about talk in romantic relationships: Similarity makes for attraction (and happiness, too)
Abstract OnlyThis current study assessed whether heterosexual dating partners are similar in their values about communication and how well such similarities predict partners’ attraction to one another and satisfaction with their relationship. Participants were 135 couples who described themselves as “seriously involved”; and had been dating for an average of 15 months. They completed a version of Burleson and Samter's (1990) Communication Functions Questionnaire, which assesses the value placed on several distinct communication skills and activities, and multiple measures of interpersonal attraction and relationship satisfaction. Correlational analyses indicated that partners’ evaluations of communication skills and activities were not significantly related. However, degree of similarity in couples’ communication values was moderately related to the assessments of attraction and satisfaction, demonstrating that partners with similar communication values were more attracted to one another and more satisfied with their relationship. In particular, similarities in the value placed on affectively oriented forms of communication such as ego support, comforting, and conflict management were significantly associated with indices of partner attraction and relationship satisfaction. Subsidiary analyses indicated that the similarities in couples’ communication values were not due to convergence (the tendency to become more similar over time). The results are discussed in terms of how cognitive similarities, especially those directly implicated in the conduct of a relationship, may contribute to the health and well being of that relationship
Birth, death and diffusion of interacting particles
Individual-based models of chemical or biological dynamics usually consider
individual entities diffusing in space and performing a birth-death type
dynamics. In this work we study the properties of a model in this class where
the birth dynamics is mediated by the local, within a given distance, density
of particles. Groups of individuals are formed in the system and in this paper
we concentrate on the study of the properties of these clusters (lifetime,
size, and collective diffusion). In particular, in the limit of the interaction
distance approaching the system size, a unique cluster appears which helps to
understand and characterize the clustering dynamics of the model.Comment: 15 pages, 6 figures, Iop style. To appear in Journal of Physics A:
Condensed matte
Acupuncture for chronic neck pain: a pilot for a randomised controlled trial
Background: Acupuncture is increasingly being used for many conditions including chronic neck pain. However the evidence remains inconclusive, indicating the need for further well-designed research. The aim of this study was to conduct a pilot randomised controlled parallel arm trial, to establish key features required for the design and implementation of a large-scale trial on acupuncture for chronic neck pain. Methods: Patients whose GPs had diagnosed neck pain were recruited from one general practice, and randomised to receive usual GP care only, or acupuncture ( up to 10 treatments over 3 months) as an adjunctive treatment to usual GP care. The primary outcome measure was the Northwick Park Neck Pain Questionnaire (NPQ) at 3 months. The primary analysis was to determine the sample size for the full scale study. Results: Of the 227 patients with neck pain identified from the GP database, 28 (12.3%) consenting patients were eligible to participate in the pilot and 24 (10.5%) were recruited to the trial. Ten patients were randomised to acupuncture, receiving an average of eight treatments from one of four acupuncturists, and 14 were randomised to usual GP care alone. The sample size for the full scale trial was calculated from a clinically meaningful difference of 5% on the NPQ and, from this pilot, an adjusted standard deviation of 15.3%. Assuming 90% power at the 5% significance level, a sample size of 229 would be required in each arm in a large-scale trial when allowing for a loss to follow-up rate of 14%. In order to achieve this sample, one would need to identify patients from databases of GP practices with a total population of 230,000 patients, or approximately 15 GP practices roughly equal in size to the one involved in this study (i.e. 15,694 patients). Conclusion: This pilot study has allowed a number of recommendations to be made to facilitate the design of a large-scale trial, which in turn will help to clarify the existing evidence base on acupuncture for neck pain
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