2,249 research outputs found
Relevance thresholds in system evaluations
We introduce and explore the concept of an individual's relevance threshold as a way of reconciling differences in outcomes between batch and user experiments
Single atom edge-like states via quantum interference
We demonstrate how quantum interference may lead to the appearance of robust
edge-like states of a single ultracold atom in a two-dimensional optical
ribbon. We show that these states can be engineered either within the manifold
of local ground states of the sites forming the ribbon, or of states carrying
one unit of angular momentum. In the former case, we show that the
implementation of edge-like states can be extended to other geometries, such as
tilted square lattices. In the latter case, we suggest to use the winding
number associated to the angular momentum as a synthetic dimension.Comment: 5 pages, 5 figure
Wave-vector and polarization dependence of conical refraction
We experimentally address the wave-vector and polarization dependence of the
internal conical refraction phenomenon by demonstrating that an input light
beam of elliptical transverse profile refracts into two beams after passing
along one of the optic axes of a biaxial crystal, i.e. it exhibits double
refraction instead of refracting conically. Such double refraction is
investigated by the independent rotation of a linear polarizer and a
cylindrical lens. Expressions to describe the position and the intensity
pattern of the refracted beams are presented and applied to predict the
intensity pattern for an axicon beam propagating along the optic axis of a
biaxial crystal
User performance versus precision measures for simple search tasks
Several recent studies have demonstrated that the type of improvements in information retrieval system effectiveness reported in forums such as SIGIR and TREC do not translate into a benefit for users. Two of the studies used an instance recall task, and a third used a question answering task, so perhaps it is unsurprising that the precision based measures of IR system effectiveness on one-shot query evaluation do not correlate with user performance on these tasks. In this study, we evaluate two different information retrieval tasks on TREC Web-track data: a precision-based user task, measured by the length of time that users need to find a single document that is relevant to a TREC topic; and, a simple recall-based task, represented by the total number of relevant documents that users can identify within five minutes. Users employ search engines with controlled mean average precision (MAP) of between 55% and 95%. Our results show that there is no significant relationship between system effectiveness measured by MAP and the precision-based task. A significant, but weak relationship is present for the precision at one document returned metric. A weak relationship is present between MAP and the simple recall-based task
Trapping of Bose-Einstein condensates in a three-dimensional dark focus generated by conical refraction
We present a novel type of three-dimensional dark focus optical trapping
potential for ultra-cold atoms and Bose-Einstein condensates. This 'optical
bottle' is created with blue-detuned laser light exploiting the phenomenon of
conical refraction occurring in biaxial crystals. We present experiments on
confining a Rb87 Bose-Einstein condensate in this potential and derive the
trapping frequencies and potential barriers under the harmonic approximation
and the conical refraction theory
Polarization tailored novel vector beams based on conical refraction
Coherent vector beams with involved states of polarization (SOP) are
widespread in the literature, having applications in laser processing,
super-resolution imaging and particle trapping. We report novel vector beams
obtained by transforming a Gaussian beam passing through a biaxial crystal, by
means of the conical refraction phenomenon. We analyze both experimentally and
theoretically the SOP of the different vector beams generated and demonstrate
that the SOP of the input beam can be used to control both the shape and the
SOP of the transformed beam. We also identify polarization singularities of
such beams for the first time and demonstrate their control by the SOP of an
input beam
Optical vault: reconfigurable bottle beam by conically refracted light
We employ conical refraction of light in a biaxial crystal to create an
optical bottle for trapping and manipulation of particles. We show that by just
varying the polarization of the input light the bottle can be opened and closed
at will. We experimentally demonstrate stable photophoretic trapping and
controllable loading and unloading of light absorbing particles in the trap.Comment: 4 pages, 5 figure
Retesting visual fields: Utilizing prior information to decrease test-retest variability in glaucoma
PURPOSE. To determine whether sensitivity estimates from an individual's previous visual field tests can be incorporated into perimetric procedures to improve accuracy and reduce test-retest variability at subsequent visits. METHODS. Computer simulation was used to determine the error, distribution of errors and presentation count for a series of perimetric algorithms. Baseline procedures were Full Threshold and Zippy Estimation by Sequential Testing (ZEST). Retest strategies were (1) allowing ZEST to continue from the previous test without reinitializing the probability density function [pdf], (2) running ZEST with a Gaussian pdf centered about the previous result; (3) retest minimizing uncertainty (REMU), a new procedure combining suprathreshold and ZEST procedures incorporating prior test information. Empiric visual field data of 265 control and 163 patients with glaucoma were input into the simulation. Four error conditions were modeled: patients who make no errors, 15% false-positive (FP) with 3% false-negative (FN) errors, 15% FN with 3% FP errors, and 20% FP with 20% FN errors. RESULTS. If sensitivity was stable from test to retest, an the retest algorithms were faster than the baseline algorithms by, on average, one presentation per location and are significantly more accurate (P < 0.05). When visual fields changed from test to retest, REMU was faster and more accurate than the other retest approaches and the baseline procedures. Relative to the baseline procedures, REMU showed decreased test-retest variability in impaired regions of Visual field. CONCLUSIONS. The obvious approaches to retest, such as continuing the previous procedure or seeding with previous values, have limitations when sensitivity changes between tests. REMU, however, significantly improves both accuracy and precision of testing and displays minimal bias, even when fields change and patients make errors
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