Accuracy Better (accuracy + better)

Distribution by Scientific Domains

Selected Abstracts

Optical and infrared photometry of new very low-mass stars and brown dwarfs in the , Orionis cluster

V. J. S. Bjar
Abstract We present an RI photometric survey covering an area of 430 arcmin2 around the multiple star , Orionis. The observations were conducted with the 0.8 m IAC-80 Telescope at the Teide Observatory. The survey limiting R and I magnitudes are 22.5 and 21, and completeness magnitudes 21 and 20, respectively. We have selected 53 candidates from the I vs. R,I colour-magnitude diagram (I = 14,20) that follow the previously known photometric sequence of the cluster. Adopting an age of 2,4 Myr for the cluster, we find that these objects span a mass range from 0.35 M, to 0.015 M,. We have performed J -band photometry of 52 candidates and Ks photometry for 12 of them, with the result that 50 follow the expected infrared sequence for the cluster, thus confirming with great confidence that the majority of the candidates are bona fide members. JHKs photometry from the Two Micron All Sky Survey (2MASS) is available for 50 of the candidates and are in good agreement with our data. Out of 48 candidates, which have photometric accuracies better than 0.1 mag in all bands, only three appear to show near-infrared excesses. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

An algebraic algorithm for generation of three-dimensional grain maps based on diffraction with a wide beam of hard X-rays

T. Markussen
A reconstruction method is presented for generation of three-dimensional maps of the grain boundaries within powders or polycrystals. The grains are assumed to have a mosaic spread below 1. They are mapped by diffraction with a wide beam of hard X-rays, using a setup similar to that of parallel-beam absorption contrast tomography. First the diffraction spots are sorted with respect to grain of origin. Next, for each grain the reconstruction is performed by an algebraic algorithm known as three-dimensional ART. From simulations it is found that reconstructions with a spatial accuracy better than the pixel size of the detector can be obtained from as few as five diffraction spots. The results are superior to three-dimensional reconstructions based on the same data using a variant of the filtered back-projection algorithm. In comparison with layer-by-layer type reconstructions based on the two-dimensional ART algorithm, as introduced by Poulsen & Fu [J. Appl. Cryst. (2003), 36, 1062,1068], the quality of the maps is found to be similar, provided that five to ten spots are available for analysis, while data acquisition with the three-dimensional method is much faster. The three-dimensional ART methodology is validated on experimental data. With state-of-the-art detectors, the spatial accuracy is estimated to be 5,m. [source]

Invasive breast cancers detected by screening mammography: A detailed comparison of computer-aided detection-assisted single reading and double reading

JN Cawson
Summary To compare double reading plus arbitration for discordance, (currently best practice, (BP)) with computer-aided-detection (CAD)-assisted single reading (CAD-R) for detection of invasive cancers detected within BreastScreen Australia. Secondarily, to examine characteristics of cancers detected/rejected using each method. Mammograms of 157 randomly selected double-read invasive cancers were mixed 1:9 with normal cancers (total 1569), all detected in a BreastScreen service. Cancers were detected by two readers or one reader (C2 and C1 cancers, ratio 70:30%) in the program. The 1569 film-screen mammograms were read by two radiologists (reader A (RA) and reader B(RB)), with findings recorded before and after CAD. Discordant findings with BP were resolved by arbitration. We compared CAD-assisted reading (CAD-RA, CAD-RB) with BP, and CAD and arbitration contribution to findings. We correlated cancer size, sensitivity and mammographic density with detection methods. BP sensitivity 90.4% compared with CAD-RA sensitivity 86.6% (P = 0.12) and CAD-RB 94.3% (P = 0.14). CAD-RB specificity was less than BP (P = 0.01). CAD sensitivity was 93%, but readers rejected most positive CAD prompts. After CAD, reader's sensitivity increased 1.9% and specificity dropped 0.2% and 0.8%. Arbitration decreased specificity 4.7%. Receiving operator curves analysis demonstrated BP accuracy better than CAD-RA, borderline significance (P = 0.07), but not CAD-RB. Secondarily, cancer size was similar for BP and CAD-R. Cancers recalled after arbitration (P = 0.01) and CAD-R (P = 0.10) were smaller. No difference in cancer size or sensitivity between reading methods was found with increasing breast density. CAD-R and BP sensitivity and cancer detection size were not significantly different. CAD-R specificity was significantly lower for one reader. [source]

Leaf green-up in a semi-arid African savanna -separating tree and grass responses to environmental cues

S. Archibald
Abstract Question: Can satellite time series be used to identify tree and grass green-up dates in a semi-arid savanna system, and are there predictable environmental cues for green-up for each life form? Location: Acacia nigrescens /Combretum apiculatum savanna, Kruger National Park, South Africa (25 S, 31 E). Methods: Remotely-sensed data from the MODIS sensor were used to provide a five year record of greenness (NDVI) between 2000 and 2005. The seasonal and inter-annual patterns of leaf display of trees and grasses were described, using additional ecological information to separate the greening signal of each life form from the satellite time series. Linking this data to daily meteorological and soil moisture data allowed the cues responsible for leaf flush in trees and grasses to be identified and a predictive model of savanna leaf-out was developed. This was tested on a 22-year NDVI dataset from the Advanced Very High Resolution Radiometer. A day length cue for tree green-up predicted 86% of the green-ups with an accuracy better than one month. A soil moisture and day length cue for grass green-up predicted 73% of the green-ups with an accuracy better than a month, and 82% within 45 days. This accuracy could be improved if the temporal resolution of the satellite data was shortened from the current two weeks. Conclusions: The data show that at a landscape scale savanna trees have a less variable phenological cycle (within and between years) than grasses. Realistic biophysical models of savanna systems need to take this into account. Using climatic data to predict these dynamics is a feasible approach. [source]

Inkjet Printing of Polymer Micro-Arrays and Libraries: Instrumentation, Requirements, and Perspectives

Berend-Jan de Gans
Abstract This article reviews commercially available instrumentation for inkjet printing of polymer micro-arrays for combinatorial materials research, and requirements thereof. These include a print head positioning accuracy better than 10 ,m and a minimum drop volume of 100 pL. Commercially available instruments that fulfill these requirements can be divided into two categories, depending on whether they receive ink from a reservoir (dispense mode) or through fluid aspiration (pipette mode). Instruments belonging to the first category are restricted to the preparation of polymer blend micro-arrays. These consist of a few substances mixed in various ratios. The other instruments can be used for the preparation of both micro-arrays of large numbers of different pure polymer compounds and polymer blend micro-arrays. Moreover, ways to mix compounds are discussed. [source]

Three-dimensional refractive index reconstruction with quantitative phase tomography

N.M. Dragomir
Abstract Optical tomography based on quantitative phase microscopy is used to determine nondestructively and with high spatial resolution the three-dimensional (3D) refractive index distributions within optical fiber devices. After obtaining a series of phase images of the fiber as it is rotated around its longitudinal axis at regularly-spaced angular positions, filtered backprojection is used to reconstruct a 3D map of the refractive index. The 3D refractive index distribution of the join region between two fusion spliced optical fibers is reconstructed with accuracy better than 10,3. Microsc. Res. Tech., 2008. 2007 Wiley-Liss, Inc. [source]

Secondary ion formation of low molecular weight organic dyes in time-of-flight static secondary ion mass spectrometry

Jens Lenaerts
Time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) was used to characterize thin layers of oxy- and thiocarbocyanine dyes on Ag and Si. Apart from adduct ions a variety of structural fragment ions were detected for which a fragmentation pattern is proposed. Peak assignments were confirmed by comparing spectra of dyes with very similar structures. All secondary ions were assigned with a mass accuracy better than 50,ppm. The intensity of molecular ions as well as fragment ions has been studied as a function of the type of organic dye, the substrate, the layer thickness and the type of primary ion. A large yield difference of two orders of magnitude was observed between the precursor ions of cationic carbocyanine dyes and the protonated molecules of the anionic dyes. Fragment ions, on the other hand, yielded similar intensities for both types of dye. As the dye layers deposited on an Ag substrate yielded higher secondary ion intensities than those deposited on a Si substrate, the Ag metal clearly acts as a promoting agent for secondary ion formation. The effect was more pronounced for precursor signals than for fragment ions. The promoting effect decreased as the deposited layer thickness of the organic dye layer was increased. Copyright 2003 John Wiley & Sons, Ltd. [source]