3,358 research outputs found
Voice Compression and Communications: Principles and Applications for Fixes and Wireless Channels
No full textUp-to-date, expert coverage of topics in wireless voice communications Voice communication is the most important facet of mobile radio service. Even when the predicted surge of wireless data and Internet services becomes a reality, voice will remain the most natural means of human communication. Voice Compression and Communications details issues in wireless voice communications and treats compression, channel coding, and wireless transmission as a joint subject. Part I covers background material, whereas Part II provides detailed information on both proprietary and standardized analysis-by-synthesis codecs, including the speech codecs of virtually all existing wireline-based and wireless systems. Parts III and IV discuss mainly research-based wideband, audio, as well as very low-rate schemes likely to find their way into future standards. Voice Compression and Communications describes fundamental concepts in a non-mathematical way early in the book for those with only a background knowledge of signal processing and communications. More advanced readers will find detailed discussions of theoretical principles, future concepts, and solutions to various specific wireless voice communications problems
1973-10-25 Morehead State Concert and Lecture Series J.P. Donleavy
No full textRenowned author J.P. Donleavy speaks on the plight of an author and the methods to write, recorded on October 25, 1973
Entrainment and detrainment rates from the piv measurements at the top of laboratory analogs of stratocumulus and cumulus clouds
No full textWe analyze mixing at the top of laboratory analogs of convective clouds: stratocumulus and cumulus to investigate entrainment of environmental air into the cloud. We retrieve two components of air velocity using Particle Image Velocimetry technique. Suitable image processing allows to determine cloud–clear air interface. Using velocity differences between cloudy and clear sides of the interface we calculate entrainment / detrainment rates
Vortex Dynamics in The Transitional and Turbulent Wake of 6:1 Prolate Spheroid at 45-deg incidence angle
No full textThe incompressible flow past a 6:1 prolate spheroid with an inclination angle of 45o at Re = 3,000 has been studied by means of direct numerical simulations (DNS). The Reynolds number is based on the inflow velocity and minor-axis length. The preliminary results presented here are focused mainly on vortex dynamics and vortical structures in the wake. The wake behind this configuration starts almost symmetric but is soon strongly deflected and bent as it evolves to the intermediate wake. A pair of unequal-strength vortices dominates the intermediate wake, of which one exhibits the shape of a long vortex tube while the other rapidly breaks down into turbulent-like vortical structures
Ocular aberrations measured by the fourier-based waveScan and zernike-based LADARwave hartmann-shack aberrometers
No full textPURPOSE: To evaluate agreements in lower and higher order aberration measurements by two Hartmann-Shack wavefront-sensing devices. METHODS: Using the VISX WaveScan and Alcon LADARWave aberrometers, ocular aberrations at a fixed optical zone of 6 mm were measured on 36 eyes of 18 patients. A tunable light intensity source was used to control pupil size, which was checked using infrared pupillometry. Repeatability of measurements was evaluated using the intra-class correlation coefficient with 3 consecutive measurements on each aberrometer. RESULTS: Mean absolute defocus for WaveScan and LADARWave was 2.82±2.69 and 2.93±3.24 rootmean-square (RMS) μm, whereas astigmatism was 0.81±0.49 and 0.87±0.57 μm, respectively. Pearson correlation coefficients between the two aberrometers were 0.908 and 0.870 for defocus and astigmatism, respectively, whereas higher order aberration correlation was less tight (Pearson correlation coefficient=0.596 for coma, 0.746 for trefoil, 0.836 for spherical aberration, 0.637 for secondary astigmatism, and 0.963 for quadrafoil [P.001 for all]). The LADARWave had a tendency to display more spherical aberration than the WaveScan, especially at high aberration values, with mean absolute difference in measurement of 0.12±0.08 μm, and only 44percent of eyes having less than ±0.10 RMS pm of difference. The mean total higher order aberration absolute difference was 0.14±0.14 μm, with only 50percent of eyes within ±0.1 RMS of agreement. Vector analysis revealed appreciable discrepancies in third- and fourth-order directional Zernike components, while showing similar values for fifth-order components. Intra-class correlation coefficient values for both aberrometers over different aberration orders showed excellent repeatability. CONCLUSIONS: The WaveScan and LADARWave share similar lower order aberration measurements, but display significantly different higher order aberration values.ATCHISON DA, 1995, VISION RES, V35, P313, DOI 10.1016-0042-6989(94)00139-D; Awwad ST, 2006, J CATARACT REFR SURG, V32, P203, DOI 10.1016-j.jcrs.2005.08.058; Chalita MR, 2003, J REFRACT SURG, V19, pS682; Dai GM, 2006, OPT LETT, V31, P501, DOI 10.1364-OL.31.000501; de Castro LEF, 2007, ACTA OPHTHALMOL SCAN, V85, P106, DOI 10.1111-j.1600-0420.2006.00757.x; FLEISS JL, 1973, EDUC PSYCHOL MEAS, V33, P613, DOI 10.1177-001316447303300309; Holladay JT, 2002, J REFRACT SURG, V18, P683; HOWLAND HC, 1977, J OPT SOC AM, V67, P1508, DOI 10.1364-JOSA.67.001508; Kaemmerer M, 2000, J REFRACT SURG, V16, pS584; Klyce SD, 2004, J REFRACT SURG, V20, pS537; Liang CL, 2005, J CATARACT REFR SURG, V31, P2153, DOI 10.1016-j.jcrs.2005.04.040; LIANG JZ, 1994, J OPT SOC AM A, V11, P1949, DOI 10.1364-JOSAA.11.001949; BLAND JM, 1986, LANCET, V1, P307; Molebny VV, 2000, J REFRACT SURG, V16, pS572; Mrochen M, 2000, J REFRACT SURG, V16, pS570; Mrochen M, 2000, J REFRACT SURG, V16, P116; Reinstein Dan Z, 2004, Ophthalmol Clin North Am, V17, P191, DOI 10.1016-j.ohc.2004.03.005; Solomon Kerry D, 2004, Ophthalmol Clin North Am, V17, P119, DOI 10.1016-j.ohc.2004.02.003; Thibos LN, 2000, J REFRACT SURG, V16, pS56335
Experimental characterisation of large scale structures in a high Reynolds number turbulent boundary layer
No full textA very large field of view (4δ x 1δ) with a good spatial resolution owing to the use of four 2k x 2k pixel cameras was conducted in a flat plate boundary layer at two Reynolds numbers (Reθ ≈7,500 and 20,000). Comparing the flow statistics with previously obtained hot-wire data under similar flow conditions show good agreement. The goal of this experiment is to detect and characterise the large scale motions which develop in the log region of a high Reynolds number turbulent boundary layer
Letter from J.P. Bradley to Mr. [William] S. Martin The Dominguez Estate Company, June 28, 1940
No full textRegarding attached payment by Mr. K.L. Schaap settling his account
Optical fibre sensors, past, present and future - a personal view
No full textThe field of optical fibre sensors has been an attractive area of research, ever since the mid 1980s, at a time when optical fibre communications technology had already started to find commercial success. The area was of great academic interest because of the wide variety of direct and indirect interactions with these new optical waveguides, both physical and chemical, which were seen to be possible. Much of the early research, mostly by academics who had previously worked in fibre communications, was highly speculative, and initially found very little commercial application. Even then, however, many confidently believed it to have great future potential. The difficulty at that time was that most existing electrical sensors were relatively cheap, and of course this technology was far more mature, whereas the fibre sensor area lacked many of the simple building blocks necessary for simple, reliable and cost-effective production. Many of the early sensors therefore, quite naturally struggled to find a competitive position. Since then, the many years of research has resulted in an increasing variety of available low-cost optical fibre components becoming available and the research on the sensor technology has lead to many truly useful sensors for what are still niche areas, but ones having real commercial potential. As a result, prospects for wider application are becoming better each year. The paper will start in a tutorial manner, by discussing and classifying the types of optical fibre sensors, discuss the care that has to be taken in their design, and will include a few case studies of some of the very early sensors. It will then go on to describe where several types of sensors have found successful application in the last decade. Finally, the author will discuss the areas where he believes they are likely to find increasing commercial success in future. Please note that the paper will present a personal view of the area, by a research scientist/engineer who has worked in the optical fibre sensors field since 1986, initially as an industrial researcher and later returning as an academic, and who is now active as a freelance consultant in the area
Author response
No full textMost motile bacteria sense and respond to their environment through a transmembrane chemoreceptor array whose structure and function have been well-studied, but many species also contain an additional cluster of chemoreceptors in their cytoplasm. Although the cytoplasmic cluster is essential for normal chemotaxis in some organisms, its structure and function remain unknown. Here we use electron cryotomography to image the cytoplasmic chemoreceptor
cluster in Rhodobacter sphaeroides and Vibrio cholerae. We show that just like transmembrane arrays, cytoplasmic clusters contain trimers-of-receptor-dimers organized in 12-nm hexagonal arrays. In contrast to transmembrane arrays, however, cytoplasmic clusters comprise two CheA/
CheW baseplates sandwiching two opposed receptor arrays. We further show that cytoplasmic fragments of normally transmembrane E. coli chemoreceptors form similar sandwiched structures in the presence of molecular crowding agents. Together these results suggest that the 12-nm
hexagonal architecture is fundamentally important and that sandwiching and crowding can replace the stabilizing effect of the membrane
The accuracy of the double-K adjustment for third-generation intraocular lens calculation formulas in previous keratorefractive surgery eyes
No full textPurpose: To evaluate the effect of the double-K (DK) modification on third-generation formulas. Methods: Thirty-eight previously myopic and 24 previously hyperopic eyes that underwent phacoemulsification with intraocular lens (IOL) insertion after Laser in situ keratomileusis (LASIK) were evaluated. Pre-LASIK refraction and keratometry, post-LASIK topography, axial length (AL), IOL type and power, and 1-month postphacoemulsification refraction were recorded spherical equivalent after phacoemulsification (SEpostphaco). Measured corneal power was adjusted using published and validated methods for postmyopic and posthyperopic LASIK. For each eye, and using SEpostphaco, different DK-IOL formulas were used to calculate the corresponding IOL power, the outcome measure, which was compared with the implanted IOL. Results: DK-Holladay 1 yielded the highest Pearson correlation coefficient (PCC), 0.955 for myopes and 0.943 for high myopes (AL26 mm). Mean error (ME) and mean absolute error (MAE) for myopes for DK Sanders-Retzlaff-Kraff theoretical formula [DK-SRK-T] were 0.44±0.84 D and 0.75±0.61 D for DK-SRK-T compared with-0.04±0.67 D and 0.52±0.40 D for DK-Holladay 1 (P0.001 and P=0.016, respectively), and 0.03±0.88 and 0.64±0.58 for DK-Hoffer Q. For high myopes, ME and MAE were 0.75±0.81 D and 0.84±0.69 D for DK-SRK-T, and-0.05±0.74 D (P0.0001) and 0.57±0.45 D (P=0.019) for DK-Holladay 1. About 29percent of DK-SRK-T eyes with large AL had MAE1.5 D, compared with 0percent for DK-Holladay 1 and 14percent for DK-Hoffer-Q. Eyes with previous hyperopic LASIK faired similarly for all formulas, with similar PCCs, and only 8percent in each category with MAE1.5 D. Conclusions: DK-SRK-T overestimates IOL power in eyes with large AL, especially with concomitant steep pre-lasik keratometry. Among third-generation formulas, DK-Holladay 1 seems more accurate to use in postmyopic LASIK eyes. © 2013 Contact Lens Association of Ophthalmologists.Aramberri J, 2003, J CATARACT REFR SURG, V29, P2063, DOI 10.1016-S0886-3350(03)00232-3; Awwad ST, 2009, OPHTHALMOLOGY, V116, P393, DOI 10.1016-j.ophtha.2008.09.045; Awwad ST, 2008, J CATARACT REFR SURG, V34, P1070, DOI 10.1016-j.jcrs.2008.03.020; Awwad ST, 2007, J CATARACT REFR SURG, V33, P1045, DOI 10.1016-j.jcrs.2007.03.018; Borasio E, 2006, J CATARACT REFR SURG, V32, P2004, DOI 10.1016-j.jcrs.2006.08.037; Feiz V, 2001, CORNEA, V20, P792, DOI 10.1097-00003226-200111000-00003; HAIGIS W, 1993, J CATARACT REFR SURG, V19, P442; HOFFER KJ, 1993, J CATARACT REFR SURG, V19, P700; Hoffer KJ, 2002, ARCH OPHTHALMOL-CHIC, V120, P500; Hoffer KJ, 2000, J CATARACT REFR SURG, V26, P1233, DOI 10.1016-S0886-3350(00)00376-X; HOLLADAY JT, 1988, J CATARACT REFR SURG, V14, P17; Ianchulev T, 2005, J CATARACT REFR SURG, V31, P1530, DOI 10.1016-j.jcrs.2005.01.035; Kalski RS, 1997, J REFRACT SURG, V13, P362; Langenbucher Achim, 2004, Curr Opin Ophthalmol, V15, P1, DOI 10.1097-00055735-200402000-00002; Livingston EH, 2004, J SURG RES, V119, P117, DOI 10.1016-j.jss.2004.02.008; Mackool RJ, 2006, J CATARACT REFR SURG, V32, P435, DOI 10.1016-j.jcrs.2005.11.045; Masket S, 2006, J CATARACT REFR SURG, V32, P430, DOI 10.1016-j.jcrs.2005.12.106; Narvaez J, 2006, J CATARACT REFR SURG, V32, P2050, DOI 10.1016-j.jcrs.2006.09.009; Odenthal MTP, 2003, ARCH OPHTHALMOL-CHIC, V121, P1071, DOI 10.1001-archopht.121.7.1071; Randleman JB, 2002, CORNEA, V21, P751, DOI 10.1097-00003226-200211000-00003; RETZLAFF JA, 1990, J CATARACT REFR SURG, V16, P333; Rosa N, 2002, J REFRACT SURG, V18, P720; Rosa N, 2005, J CATARACT REFR SURG, V31, P254, DOI 10.1016-j.jcrs.2004.12.014; SANDERS DR, 1990, J CATARACT REFR SURG, V16, P341; Seitz B, 2000, Curr Opin Ophthalmol, V11, P35, DOI 10.1097-00055735-200002000-00006; Seitz B, 2000, J REFRACT SURG, V16, P349; Seitz B, 1999, OPHTHALMOLOGY, V106, P693, DOI 10.1016-S0161-6420(99)90153-7; Siganos DS, 1996, J REFRACT SURG, V12, pS278; Tsang CSL, 2003, J CATARACT REFR SURG, V29, P1358, DOI 10.1016-S0886-3350(02)01976-4; Wang L, 2002, J CATARACT REFR SURG, V28, P954, DOI 10.1016-S0886-3350(02)01318-4; Wang L, 2004, OPHTHALMOLOGY, V111, P1825, DOI 10.1016-j.ophtha.2004.04.0220
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