3,652 research outputs found
Symmetry sensitivities of Derivative-of-Gaussian filters
We consider the measurement of image structure using linear filters, in particular derivative-of-Gaussian (DtG) filters, which are an important model of V1 simple cells and widely used in computer vision, and whether such measurements can determine local image symmetry. We show that even a single linear filter can be sensitive to a symmetry, in the sense that specific responses of the filter can rule it out. We state and prove a necessary and sufficient, readily computable, criterion for filter symmetry-sensitivity. We use it to show that the six filters in a second order DtG family have patterns of joint sensitivity which are distinct for 12 different classes of symmetry. This rich symmetry-sensitivity adds to the properties that make DtG filters well-suited for probing local image structure, and provides a set of landmark responses suitable to be the foundation of a nonarbitrary system of feature categories
Electron spin resonance of nitrogen-vacancy centers in optically trapped nanodiamonds
Using an optical tweezers apparatus, we demonstrate three-dimensional control
of nanodiamonds in solution with simultaneous readout of ground-state
electron-spin resonance (ESR) transitions in an ensemble of diamond
nitrogen-vacancy (NV) color centers. Despite the motion and random orientation
of NV centers suspended in the optical trap, we observe distinct peaks in the
measured ESR spectra qualitatively similar to the same measurement in bulk.
Accounting for the random dynamics, we model the ESR spectra observed in an
externally applied magnetic field to enable d.c. magnetometry in solution. We
estimate the d.c. magnetic field sensitivity based on variations in ESR line
shapes to be ~50 microTesla/Hz^1/2. This technique may provide a pathway for
spin-based magnetic, electric, and thermal sensing in fluidic environments and
biophysical systems inaccessible to existing scanning probe techniques.Comment: 29 pages, 13 figures for manuscript and supporting informatio
Divergence Model for Measurement of Goos-Hanchen Shift
In this effort a new measurement technique for the lateral Goos-Hanchen shift is developed, analyzed, and demonstrated. The new technique uses classical image formation methods fused with modern detection and analysis methods to achieve higher levels of sensitivity than obtained with prior practice. Central to the effort is a new mathematical model of the dispersion seen at a step shadow when the Goos-Hanchen effect occurs near critical angle for total internal reflection. Image processing techniques are applied to measure the intensity distribution transfer function of a new divergence model of the Goos-Hanchen phenomena providing verification of the model. This effort includes mathematical modeling techniques, analytical derivations of governing equations, numerical verification of models and sensitivities, optical design of apparatus, image processin
Model-independent test of gravity with a network of ground-based gravitational-wave detectors
The observation of gravitational waves with a global network of
interferometric detectors such as advanced LIGO, advanced Virgo, and KAGRA will
make it possible to probe into the nature of space-time structure. Besides
Einstein's general theory of relativity, there are several theories of
gravitation that passed experimental tests so far. The gravitational-wave
observation provides a new experimental test of alternative theories of gravity
because a gravitational wave may have at most six independent modes of
polarization, of which properties and number of modes are dependent on theories
of gravity. This paper proposes a method to reconstruct the independent modes
of polarization in time-series data of an advanced detector network. Since the
method does not rely on any specific model, it gives model-independent test of
alternative theories of gravity
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