Centroid Measurement Research Articles

THE SLOAN DIGITAL SKY SURVEY REVERBERATION MAPPING PROJECT: BIASES IN z > 1.46 REDSHIFTS DUE TO QUASAR DIVERSITY

ABSTRACT We use the coadded spectra of 32 epochs of Sloan Digital Sky Survey (SDSS) Reverberation Mapping Project observations of 482 quasars with z > 1.46 to highlight systematic biases in the SDSS- and Baryon Oscillation Spectroscopic Survey (BOSS)-pipeline redshifts due to the natural diversity of quasar properties. We investigate the characteristics of this bias by comparing the BOSS-pipeline redshifts to an estimate from the centroid of He ii λ1640. He ii has a low equivalent width but is often well-defined in high-S/N spectra, does not suffer from self-absorption, and has a narrow component which, when present (the case for about half of our sources), produces a redshift estimate that, on average, is consistent with that determined from [O ii] to within the He ii and [O ii] centroid measurement uncertainties. The large redshift differences of ∼1000 km s−1, on average, between the BOSS-pipeline and He ii-centroid redshifts, suggest there are significant biases in a portion of BOSS quasar redshift measurements. Adopting the He ii-based redshifts shows that C iv does not exhibit a ubiquitous blueshift for all quasars, given the precision probed by our measurements. Instead, we find a distribution of C iv-centroid blueshifts across our sample, with a dynamic range that (i) is wider than that previously reported for this line, and (ii) spans C iv centroids from those consistent with the systemic redshift to those with significant blueshifts of thousands of kilometers per second. These results have significant implications for measurement and use of high-redshift quasar properties and redshifts, and studies based thereon.

DISTANCE, AN IMPORTANT VARIABLE IN NURSING HOME SELECTION FOR PRIMARY CONTACT IN KENTUCKY MARKET

ABSTRACT This research study was conducted to determine how distance varies by primary contact of a nursing home resident, when determining the selection of a nursing home for the resident that receives care in the state of Kentucky. The distance measurement will be based on the distance of the primary contact to the nursing home (using centroid measurement with zip code data). Nursing home markets have been defined primary through geo-political boundaries; however, this study will utilize a process of using distance that was first used by North and Bowblis (2011). This study reviewed 4,370 admissions from 27 nursing homes in the state of Kentucky. The data was processed through a quantitative ANOVA test to compare the nursing home market through resident specific zip codes and primary contacts of the weak and strong market. This analysis will provide additional insight for researchers, scholar practitioners, and nursing home administrators in identifying specific target markets of prospective nursing home residents in the state of Kentucky. Keywords Nursing home resident, primary contact, zip code distance, Means, Nursing home market, Quantitative, Data Analysis.

A Global-Shutter Centroiding Measurement CMOS Image Sensor With Star Region SNR Improvement for Star Trackers

A star tracker is a critical sensor for determining and controlling the attitude of a satellite. It utilizes a complementary metal–oxide–semiconductor (CMOS)-active pixel sensor to map the star field onto the focal plane. Starlight is measured and star centroids are calculated to estimate attitude knowledge. In this paper, we present a CMOS image sensor for star centroid measurement in star trackers. To improve sensitivity to low-level starlight, the capacitive transimpedance amplifier pixel is used as the detector. To improve centroiding accuracy, the proposed sensor architecture allows star pixels, pixels that are above a star threshold, to cluster together. The mean value of all the pixels in this cluster is calculated. The star signals are then amplified in relation to this mean value. This increases the signal-to-noise ratio in star regions in line with their starlight intensity. An adaptive region-of-interest readout architecture is also proposed, which reports only star regions instead of the entire frame. The proof-of-concept chip, containing a $128 \times 128$ pixel array, was fabricated using AMS 0.35- $\mu \text{m}$ CMOS Opto process. Each pixel has a size of $31.2 \times 31.2~\mu \text{m}^{2}$ . The measurement results show that centroiding accuracy increases with higher centroiding gain. Within a limited exposure time, the relative centroiding accuracy can surpass that of a commercial image sensor by more than 1%.

Use of Doppler Parameters for Ship Velocity Computation in SAR Images

This paper deals with the exploitation of Doppler centroid measurements for ship velocity estimation from focused single-look complex synthetic aperture radar (SAR) images. An algorithm is presented, which can be used as a discrimination tool to reduce the false alarm rate of standard adaptive threshold detectors and to complement the ship detection task with velocity estimation. The outputs are the indication of the presence of a moving target and the estimate of its slant range velocity. After a review of its theoretical background, algorithm features and performance are verified by application to TerraSAR-X data. The proposed method performs robust Doppler spectrum derivation for candidate ship targets and background pixels. The presented results show that the estimated radial velocity is in very good agreement (5% root-mean-square deviation) with that resulting from the azimuth offset method. Rejection of bright sea features and azimuth ambiguities is also demonstrated, taking advantage of the performed velocity analysis.

Ultrasound and acoustic analysis of sibilant fricatives in preadolescents and adults.

This study describes the production of sibilant fricatives /s/ and /∫/, comparing Scottish English speaking preadolescent children with adults. The materials were the sequences /əCa/ and /əCi/ produced by 15 adults and 15 children aged between 10 and 12 years old. Quantitative analyses were carried out on both spectral information and on ultrasound imaging data on tongue shape, taken from nine successive time points during the fricative. The two groups of speakers were very similar to each other in the articulatory and acoustic characteristics distinguishing the two fricatives. Age-related differences in the fricative centroid measure occurred at consonant-vowel boundaries, with lower values in the preadolescents. Within-speaker variability was mostly similar across age groups, with the exception of the fricative centroid for /∫/, which was significantly more variable in preadolescents than in adults. Throughout the consonant duration, both groups consistently differentiated between the two consonants in both the fricative centroid and in one measure of tongue shape.

Hybrid Approach for Single Text Document Summarization Using Statistical and Sentiment Features

Summarization is a way to represent same information in concise way with equal sense. This can be categorized in two type Abstractive and Extractive type. Our work is focused around Extractive summarization. A generic approach to extractive summarization is to consider sentence as an entity, score each sentence based on some indicative features to ascertain the quality of sentence for inclusion in summary. Sort the sentences on the score and consider top n sentences for summarization. Mostly statistical features have been used for scoring the sentences. A hybrid model for a single text document summarization is being proposed. This hybrid model is an extraction based approach, which is combination of Statistical and semantic technique. The hybrid model depends on the linear combination of statistical measures: sentence position, TF-IDF, Aggregate similarity, centroid, and semantic measure. The idea to include sentiment analysis for salient sentence extraction is derived from the concept that emotion plays an important role in communication to effectively convey any message hence, it can play a vital role in text document summarization. For comparison, five system summaries have been generated: Proposed Work, MEAD system, Microsoft system, OPINOSIS system, and Human generated summary, and evaluation is done using ROUGE score.

Technical requirements and uncertainty of far field laser spot centroid measurement using array detection method

Array detection method is widely used for measuring the far field laser centroids. The influence of array detector's aperture and dynamic range on the far field laser power was analyzed on the basis of the measurement method and measurement process for the laser spot centroid. The effect of array detector's spatial resolution and spatial duty ratio on the far field laser spot centroid was simulated, and the results were verified by performing experiments, enabling the determination of the technology requirements for the array detector. The expression for the laser spot centroid uncertainty was deduced on the basis of the uncertainty theory and laser spot centroid expression, and the sources of uncertainty were analyzed. The results will be of great importance for measuring the far field laser spot centroids and designing array detectors.

Kalman Filtering–Based Probabilistic Nowcasting of Object-Oriented Tracked Convective Storms

AbstractThe weather radar–based object-oriented convective storm tracking is a standard approach for analyzing and nowcasting convective storms. However, the majority of current storm-tracking algorithms provide nowcasts only in a deterministic fashion with limited ability to estimate the related uncertainties.This paper proposes a method for probabilistic nowcasting of convective storms that addresses the issue of uncertainty of nowcasts. The approach first utilizes a two-dimensional radar-based storm identification and tracking algorithm in conjunction with the Kalman filtering of noisy measurements of storm centroid with the continuous white noise acceleration model. The resulting smoothed estimates of storm centroid and velocity components and their error covariance values are then applied to nowcast the probability of storm occurrence.To verify the approach, 20–60-min nowcasts were computed every 5 min using composite weather radar data in Finland including approximately 22 000 tracked storms. The verification shows that the algorithm is applicable in both deterministic and probabilistic manner. Moreover, the forecast probabilities are consistent with observed frequencies of the storms, especially with 20- and 30-min nowcasts. The accuracy of the probabilistic nowcasts was evaluated through the Brier skill score with respect to the deterministic nowcasts and nowcasts based on observation persistence and sample climatology. The results show that the proposed nowcasting method has an improved accuracy over all of the reference forecast types.

A High Dynamic Range CMOS Image Sensor With Dual-Exposure Charge Subtraction Scheme

In this paper, we present a CMOS image sensor for star centroid measurement for the application of star trackers. We propose a new capacitive transimpedance amplifier pixel architecture with in-pixel charge subtraction scheme. The pixel is able to achieve high signal-to-noise ratio for dim stars and, at the same time, to avoid saturation for bright stars. A prototype sensor was fabricated using Global Foundry 65-nm mixed-signal CMOS process. Experimental results show that the sensor can achieve 3.8 V/lux·s and 12 dB extension of dynamic range. For the saturated star in conventional method, the centroiding accuracy is improved by over 0.1 pixels after performing charge subtraction.

Optical Navigation Using Planet’s Centroid and Apparent Diameter in Image

Recent interest in sending humans to the moon, Mars, or other destinations beyond low Earth orbit has created an increased need for autonomous spacecraft navigation. Because traditional navigation approaches rely on ground-based tracking, new onboard techniques are necessary for the crew to safely return to Earth in the event of a communication systems failure. This paper investigates how images of a planet or moon may be used to perform autonomous navigation through the centroid and apparent diameter measurement type. If a planet is modeled as a triaxial ellipsoid, then it will project to an ellipse in an image. A new approach, which allows estimation of the spacecraft position relative to the observed planet using the full set of parameters describing an ellipse that is fit to points along the planet’s lit horizon, is presented. The performances of a number of different ellipse-fitting algorithms are also evaluated. Finally, the covariance of the solution is derived, and simulation results are presented.

Correcting the beam centroid motion in an induction accelerator and reducing the beam breakup instability

Axial beam centroid and beam breakup (BBU) measurements were conducted on an 80 ns FWHM, intense relativistic electron bunch with an injected energy of 3.8 MV and current of 2.9 kA. The intense relativistic electron bunch is accelerated and transported through a nested solenoid and ferrite induction core lattice consisting of 64 elements, exiting the accelerator with a nominal energy of 19.8 MeV. The principal objective of these experiments is to quantify the coupling of the beam centroid motion to the BBU instability and validate the theory of this coupling for the first time. Time resolved centroid measurements indicate a reduction in the BBU amplitude, $⟨\ensuremath{\xi}⟩$, of 19% and a reduction in the BBU growth rate ($\mathrm{\ensuremath{\Gamma}}$) of 4% by reducing beam centroid misalignments $\ensuremath{\sim}50%$ throughout the accelerator. An investigation into the contribution of the misaligned elements is made. An alignment algorithm is presented in addition to a qualitative comparison of experimental and calculated results which include axial beam centroid oscillations, BBU amplitude, and growth with different dipole steering.

Micrometer accuracy method for small-scale laser focal spot centroid measurement

Abstract The measurement of the centroid of small-scale laser focal spot is one of the most promising technologies for small-scale laser focal spot precise positioning. A method of two-dimensional scanning with CCD has been conducted to precisely measure the centroid of the small-scale laser focal spot (diameter in microns) by obtaining the change curve for gray value. The theoretical analysis is consistent with the experimental results.

Research on Flexible Centroid Measurement Method for Segments of Large-Thrust Carrier Rocket

A new flexible centroid measurement method is provided in order to meet actual demands for centroid measurement of large-thrust carrier rocket segments. The method has the benefit of utilizing a laser tracker to accurately measure positions of support points of a weighing sensor and geometrical parameters associated with an attitude status of each segment to be measured, thereby solving the problem of a traditional three-point method that measuring accuracy in centroid measurement depends on both mechanical equipment machining accuracy and positioning accuracy. The analysis result shows that the method provided herein has an engineering application value and can realize measurement to high accuracy, automation and universality for large-thrust carrier rocket segments.

Scalable spatial superresolution using entangled photons.

N00N states-maximally path-entangled states of N photons-exhibit spatial interference patterns sharper than any classical interference pattern. This is known as superresolution. However, even given perfectly efficient number-resolving detectors, the detection efficiency of all previous measurements of such interference would decrease exponentially with the number of photons in the N00N state, often leading to the conclusion that N00N states are unsuitable for spatial measurements. A technique known as the "optical centroid measurement" has been proposed to solve this and has been experimentally verified for photon pairs; here we present the first extension beyond two photons, measuring the superresolution fringes of two-, three-, and four-photon N00N states. Moreover, we compare the N00N-state interference to the corresponding classical superresolution interference. Although both provide the same increase in spatial frequency, the visibility of the classical fringes decreases exponentially with the number of detected photons. Our work represents an essential step forward for quantum-enhanced measurements, overcoming what was believed to be a fundamental challenge to quantum metrology.

Increasing the intensity of an induction accelerator and reduction of the beam breakup instability

A 7 cm cathode has been deployed for use on a 3.8 MV, 80 ns (FWHM) Blumlein, to increase the extracted electron current from the nominal 1.7 to 2.9 kA. The intense relativistic electron bunch is accelerated and transported through a nested solenoid and ferrite induction core lattice consisting of 64 elements, exiting the accelerator with a nominal energy of 19.8 MeV. The principal objective of these experiments is to quantify the space-charge limitations on the beam quality, its coupling with the beam breakup (BBU) instability, and provide an independent validation of the BBU theory in a higher current regime, $\mathrm{I}>2\text{ }\mathrm{kA}$. Time resolved centroid measurements indicate a reduction in BBU $>10\ifmmode\times\else\texttimes\fi{}$ with simply a 50% increase in the average B-field used to transport the beam through the accelerator. A qualitative comparison of experimental and calculated results are presented, which include time resolved current density distributions, radial BBU amplitude relative to the calculated beam envelope, and frequency analyzed BBU amplitude with different accelerator lattice tunes.

An adaptive threshold method for improving astrometry of space debris CCD images

Optical survey is a main technique for observing space debris, and precisely measuring the positions of space debris is of great importance. Due to several factors, e.g. the angle object normal to the observer, the shape as well as the attitude of the object, the variations of observed characteristics for low earth orbital space debris are distinct. When we look at optical CCD images of observed objects, the size and brightness are varying, hence it’s difficult to decide the threshold during centroid measurement and precise astrometry. Traditionally the threshold is given empirically and constantly in data reduction, and obviously it’s not suitable for data reduction of space debris. Here we offer a solution to provide the threshold. Our method assumes that the PSF (point spread function) is Gaussian and estimates the signal flux by a directly two-dimensional Gaussian fit, then a cubic spline interpolation is performed to divide each initial pixel into several sub-pixels, at last the threshold is determined by the estimation of signal flux and the sub-pixels above threshold are separated to estimate the centroid. A trail observation of the fast spinning satellite Ajisai is made and the CCD frames are obtained to test our algorithm. The calibration precision of various threshold is obtained through the comparison between the observed equatorial position and the reference one, the latter are obtained from the precise ephemeris of the satellite. The results indicate that our method reduces the total errors of measurements, it works effectively in improving the centering precision of space debris images.

Localization Algorithm based on Improved Weighted Centroid in Wireless Sensor Networks

Location technology is becoming more and more important in wireless sensor networks. The weighted centroid localization offers a fast and simple algorithm for the location equipment in wireless sensor networks. The algorithm derives from the centroid measurement and calculation device of the adjacent anchor in the average coordinate. After the analysis of the radio propagation loss model, the most appropriate log-distance distribution model is selected to simulate the signal propagation. Based on the centroid algorithm and the weighted centroid algorithm, this paper proposes an ellipse centroid localization algorithm. This algorithm makes use of ellipse’s characteristic to estimate the unknown node’s coordinate. The main idea of ellipse centroid localization algorithm is the precision control factor that can control the algorithm’s location precision. In ellipse centroid localization algorithm, node is extended as anchor in order to strengthen anchor density’s dynamic characteristic. The simulation result shows the ellipse centroid localization algorithm is more effective than the centroid algorithm and the weighted centroid precision algorithm

Numerical simulations of optical centroid measurements with nonclassical fields

Optical imaging methods are typically restricted to a resolution of order of the probing light wavelength $\lambda_p$ by the Rayleigh diffraction limit. This limit can be circumvented by making use of multiphoton detection of correlated $N$-photon states, having an effective wavelength $\lambda_p/N$. But the required $N$-photon detection usually renders these schemes impractical. To overcome this limitation, recently, so-called optical centroid measurements (OCM) have been proposed which replace the multi-photon detectors by an array of single-photon detectors. Complementary to the existing approximate analytical results, we explore the approach using numerical experiments by sampling and analyzing detection events from the initial state wave function. This allows us to quantitatively study the approach also beyond the constraints set by the approximate analytical treatment, to compare different detection strategies, and to analyze other classes of input states.

Cluster Detection Analysis Using Fuzzy RelationalDatabase

In order to handle imprecise and ambiguous information, the application of fuzzy set theory for the design of database, information storage and retrieval systems has been gaining popularity recently. This paper gives emphasis on the basic characteristics of fuzzy relational databases, their properties, along with the data clustering in database systems. Indian premier league dataset has been considered for the detection of clusters. Several clustering parameters like centroid, radius and Manhattan distance measure have been applied. The definition of clusters as well as the membership function has been implemented using PL/SQL. The results obtained from Indian premier league batting statistics dataset detect two clusters, namely Cluster 1 and Cluster 2. Finally, this article proposed a fuzzy database organization and clustering of records which provides efficient and accurate fuzzy retrieval.

How does noise affect amplitude and latency measurement of event‐related potentials (ERPs)? A methodological critique and simulation study

There is considerable variability in the quantification of event-related potential (ERP) amplitudes and latencies. We examined susceptibility of ERP quantification measures to incremental increases in background noise through published ERP data and simulations. Measures included mean amplitude, adaptive mean, peak amplitude, peak latency, and centroid latency. Results indicated mean amplitude was the most robust against increases in background noise. The adaptive mean measure was more biased, but represented an efficient estimator of the true ERP signal particularly for individual-subject latency variability. Strong evidence is provided against using peak amplitude. For latency measures, the peak latency measure was less biased and less efficient than the centroid latency measurement. Results emphasize the prudence in reporting the number of trials retained for averaging as well as noise estimates for groups and conditions when comparing ERPs.