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Leads

Distribution by Scientific Domains

Medical Sciences	28%
Life Sciences	17%
Chemistry	17%
Polymers and Materials Science	7%
Business, Economics, Finance and Accounting	6%
Humanities and Social Sciences	5%
Physics and Astronomy	4%
Engineering	4%
Earth and Environmental Science	3%
5 Other Domains	9%

Kinds of Leads

right precordial lead

ventricular pacing lead

water lead

white lead

Terms modified by Leads

lead electrocardiogram

lead zirconate titanate

Selected Abstracts

The LEAD Portal: a TeraGrid gateway and application service architecture

CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 6 2007
Marcus Christie
Abstract The Linked Environments for Atmospheric Discovery (LEAD) Portal is a science application portal designed to enable effective use of Grid resources in exploring mesoscale meteorological phenomena. The aim of the LEAD Portal is to provide a more productive interface for doing experimental work by the meteorological research community, as well as bringing weather research to a wider class of users, meaning pre-college students in grades 6,12 and undergraduate college students. In this paper, we give an overview of the LEAD project and the role that LEAD portal is playing in reaching its goals. We then describe the various technologies we are using to bring powerful and complex scientific tools to educational and research users. These technologies,a fine-grained capability based authorization framework, an application service factory toolkit, and a Web services-based workflow execution engine and supporting tools,enable our team to deploy these once inaccessible, stovepipe scientific codes onto a Grid where they can be collectively utilized. Copyright © 2006 John Wiley & Sons, Ltd. [source]

NEW APPROACHES ON THE ARCHAIC TRADE IN THE NORTH-EASTERN IBERIAN PENINSULA: EXPLOITATION AND CIRCULATION OF LEAD AND SILVER

OXFORD JOURNAL OF ARCHAEOLOGY, Issue 2 2010
NÚRIA RAFEL
Summary A wide-ranging study based on compositional and isotopic analyses of minerals and manufactured objects from the north-eastern Iberian Peninsula and their respective archaeological and cultural contexts demonstrates significant lead mineral exploitation in the El Priorat area (Tarragona province) linked to Phoenician trade (seventh,sixth centuries BC). This exploitation continued, despite losing intensity, until the Romanization of the territory. Our project also aims to determine the nature and origin of the lead and silver supply in the northern Iberian territory surrounding the Phocaean enclave of Emporion, especially with regard to the demands of the colonial mint. The behaviour pattern of the circulation of lead, silver and copper in Catalonia in the period studied indicates a plurality of contemporary supply sources, although, at least from the fifth century BC onward, minerals and metals from the south-eastern Iberian Peninsula take on considerable importance. [source]

MINERALOGY OF MEDIEVAL SLAGS FROM LEAD AND SILVER SMELTING (BOHUTÍN, P,ÍBRAM DISTRICT, CZECH REPUBLIC): TOWARDS ESTIMATION OF HISTORICAL SMELTING CONDITIONS*

ARCHAEOMETRY, Issue 6 2009
V. ETTLER
Slags from the Pb/Ag medieval (14th century) smelting plant located at Bohutín, P,íbram district, Czech Republic, were studied from the mineralogical and geochemical points of view. Two types of slags were distinguished: (i) quenched slags formed mainly by Pb-rich glass and unmelted residual grains of SiO2 and feldspars, and (ii) crystallized slags mainly composed of Fe-rich olivine (fayalite) and glass. The mean log viscosity value of the slags calculated for 1200°C was 2.119 Pa s. The morphology of olivine crystals was used to estimate the cooling rates of the melt, for some slags indicating rates > 1450°C/h. The projection of the bulk composition of slags onto the SiO2,PbO,FeO ternary system was used for rough temperature estimates of slag formation, lying probably between 800 and 1200°C. [source]

Evaluation of simple non-invasive techniques for assessment of lower extremity arterial disease

CLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 3 2005
David Sahli
Summary Objective:, To evaluate the reproducibility and precision of three, simple, non-invasive methods to measure blood pressure (BP) in the lower extremities by comparing reproducibility and sensitivity in finding abnormally low BP between ankle blood pressure (ABP) and toe blood pressure (TBP), by studying the concordance between TBP in toe 1 and 2 and evaluating the pole-pox method in patients with diabetes and lower extremity arterial disease (LEAD). Subjects and methods:, The BP was measured twice, 1 week apart, in arms and legs in 13 controls and 12 patients with diabetes. ABP was assessed by using a Doppler pen for pulse registration. TBP was obtained by using a small cuff and a pulse oximetry sensor at toe 1 and 2. In eleven patients with diabetes and previously known LEAD ABP was obtained through the pole-pox method. Results:, No significant difference in reproducibility between absolute BPs and indices (coefficients of variation <9%) was found. A non-significant improvement with 4,8% in the sensitivity in detecting LEAD was seen when BP indices were used instead of absolute BP. A significant correlation in the variation over time for systemic and TBP (r = 0·34, P = 0·015) and a strong correlation was found between TBP measured at toe 1 and 2, respectively (r = 0·99, P<0·001) was found. TBP measured with pole-pox method were significantly correlated with measurements made by the ordinary cuff technique (r = 0·75, P<0·001). Conclusions:, The use of TBP and ABP indices instead of absolute BP does not improve the reproducibility but may improve the sensitivity with respect to detection of LEAD, especially in patients with diabetes. The pole-pox method may be used as an alternative screening method in patients with diabetes and LEAD. [source]

Examining career success of minority and women emergency medical technicians (EMTs): A LEADS project

HUMAN RESOURCE DEVELOPMENT QUARTERLY, Issue 4 2008
Darlene F. Russ-Eft
Emergency medical technicians (EMTs) are a critical segment in prehospital medical care. This study examined EMT-paramedic career success focused on minorities and women, as part of the Longitudinal Emergency Medical Technician Attributes and Demographics Study (LEADS). The LEADS data come from a representative sampling of EMTs throughout the United States. Analyses examined factors related to objective and subjective career success and did so with samples from 2000 and 2004. Regression results showed that education, experience, and hours worked predicted objective career success. In contrast, satisfaction with others and with supervisor predicted subjective career success. Minority status was not related to either objective or subjective career success, while gender appeared to have a negative influence on objective career success but was unrelated to subjective career success. Implications for HRD practitioners and researchers are discussed. [source]

A USB kit for digital I/O applications in a digital electronics lab designed by using PIC16C765 microcontroller

COMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 2 2009
Ali Buldu
Abstract In this article, a USB Kit is designed by using Microchip's PIC16C765 microcontroller that has a low-speed USB serial interface engine. It is used to communicate with and/or through USB port for digital I/O applications in a Digital Electronics Lab. In this education kit, two groups of keys (switches) and a group of LED are used to realize the experiments about logic gate applications included in Electronics and Computer Education Department's curriculum of Marmara University and also included in other faculties' curriculums related to the engineering science all around the world. In designed board, one of the key groups is 8-bit software-controlled by using simulator interface and the other is 8-bit user-controlled by using real switches existing on the board. © 2008 Wiley Periodicals, Inc. Comput Appl Eng Educ 17: 131,138, 2009; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae20172 [source]

Improvement of Postfractional Laser Erythema with Light-Emitting Diode Photomodulation

DERMATOLOGIC SURGERY, Issue 5 2009
TINA S. ALSTER MD
BACKGROUND The most common side effects of fractional laser skin treatment are erythema and edema. Low-level light therapy and light-emitting diode (LED) devices have been used to stimulate fibroblast activity and hasten wound healing. OBJECTIVE To determine whether LED treatment immediately after fractional laser skin resurfacing affects the severity and duration of postoperative eythema. MATERIALS AND METHODS Twenty patients received treatment with a 590-nm wavelength LED array to randomly selected facial halves immediately after undergoing full-face fractional laser skin resurfacing with a 1,550-nm erbium-doped fiber laser. Differences in erythema between LED-treated and untreated facial halves were recorded at 24, 48, and 96 hours post-treatment. RESULTS The LED-treated facial halves were less erythematous in all 20 patients 24 hours postoperatively. The six patients who received the highest mean energy densities during fractional laser treatment continued to exhibit decreased erythema in the LED-treated areas at 48 hours. At 96 hours post-treatment, no discernible differences between facial halves were observed in any patient. CONCLUSIONS Photomodulation with a 590-nm-wavelength LED array can decrease the intensity and duration of postfractional laser treatment erythema. [source]

Lux vs. wavelength in light treatment of Seasonal Affective Disorder

ACTA PSYCHIATRICA SCANDINAVICA, Issue 3 2009
J. L. Anderson
Objective:, Published dosing guidelines for treatment of Seasonal Affective Disorder (SAD) refer to photopic lux, which is not appropriate for short-wavelength light. Short wavelengths are most potent for many non-visual responses to light. If SAD therapy were similarly mediated, standards utilizing lux risk overestimating necessary dose. We investigated antidepressant responses to light using two light-emitting diode (LED) sources, each emitting substantial short-wavelength light, but <2500 lux. Method:, A randomized, double-blind trial investigated 3-week 45 min/day out-patient treatment with blue-appearing (goLITE®) or blue-enriched white-appearing light in 18 moderately-depressed adults (12F, 49.1 ± 9.5 years). Equivalent numbers of photons within the short-wavelength range were emitted, but the white source emitted twice as many photons overall and seven-fold more lux. Results:, Depression ratings (SIGH-ADS; http://www.cet.org) decrease averaged 82% (SD = 17%) from baseline (P < 0.0001) in both white- and blue-light groups. Both sources were well tolerated. Conclusion:, Short-wavelength LED light sources may be effective in SAD treatment at fewer lux than traditional fluorescent sources. [source]

Development of 230,270 nm AlGaN-based deep-UV LEDs

ELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 3 2010
Hideki Hirayama
Abstract We demonstrated AlGaN multi-quantum well (MQW) deep-ultraviolet (UV) light-emitting diodes (LEDs) with wavelengths in the range of 227.5 to 273 nm fabricated on high-quality AlN buffers on sapphire substrates grown by metal-organic chemical vapor deposition (MOCVD). We realized crack-free, thick AlN buffers on sapphire with a low threading dislocation density (TDD) and an atomically flat surface by using the ammonia (NH3) pulse-flow multilayer (ML) growth technique. We obtained single-peaked operation of an AlGaN-MQW LED with a wavelength of 227.5 nm, which is the shortest wavelength of AlGaN-based LED on sapphire. The maximum output power and the external quantum efficiency (EQE) of the 261- and 227.5-nm LEDs were 1.65 mW and 0.23% in room-temperature (RT) continuous-wave (CW) operation, and 0.15 mW and 0.2% in RT pulsed operation, respectively. © 2010 Wiley Periodicals, Inc. Electron Comm Jpn, 93(3): 24,33, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10197 [source]

Separation of Nile Blue-labelled fatty acids by CE with absorbance detection using a red light-emitting diode

ELECTROPHORESIS, Issue 8 2007
Michael C. Breadmore Dr.
Abstract The separation of fatty acids derivatised with Nile Blue (NB) by CE with detection using a red light-emitting diode (LED) was examined. NB was selected as the derivatisation agent due to its high molar absorption coefficient of 76,000,M,1cm,1 at 633,nm, making it well suited for sensitive absorbance detection using a red 635,nm LED. NB-labelled fatty acids were separated by both MEKC using SDS micelles, i -PrOH and n -BuOH and by NACE in a number of solvents including MeOH, EtOH and ACN. The sensitivity of NACE was superior to MEKC, with detection limits of 5×10,7,7×10,7,M obtained for each acid, approximately 20 times lower than the MEKC method. The NACE detection limits are approximately 100 times lower than previous reports on the separation of fatty acids by CE using indirect absorbance detection, ten times lower than using indirect fluorescence detection and are inferior only to those obtained using precapillary derivatisation and direct fluorescence detection. The efficiency of the NACE method was also superior to MEKC and allowed the separation of unsaturated fatty acids to be examined, although it was not possible to baseline-resolve linoleic (C18:2) and linolenic (C18:3) acids in a reasonable time. The method was used to analyse the fatty acid profile of two edible oils, namely sunflower and sesame oils, after alkali hydrolysis, where it was possible to identify both the saturated and unsaturated fatty acids in each sample. [source]

Light-emitting diode-induced fluorescence detection of native proteins in capillary electrophoresis

ELECTROPHORESIS, Issue 21 2005
Chanan Sluszny
Abstract A continuous-wave 280 nm light-emitting diode (LED) was used as the excitation source for native fluorescence detection of proteins in CE. The operating current and temperature of the LED were optimized in order to achieve high luminescence power. It was found that a forward current of 30,mA and a temperature of approximately 5°C gave the best S/N. By using a set of two ball lenses to focus light from the LED, we achieved a spot of approximately 200,,m with a power of 0.1,0.2,mW on the detection window. Fluorescence was collected with a ball lens at 90° angle through a bandpass filter onto a photomultiplier tube. In CZE an LOD of 20,nM for conalbumin was reached. In capillary gel electrophoresis all eight proteins from a commercial standard kit were detected with high S/N. For a 10,,g/mL total protein mixture, S/N was better than 3 for all proteins in solution. Further improvement in LOD should be possible on utilization of an LED with higher luminescence power. [source]

Determination of the bacterial pathogen Edwardsiella tarda in fish species by capillary electrophoresis with blue light-emitting diode-induced fluorescence

ELECTROPHORESIS, Issue 18-19 2004
Lijun Yu
Abstract High-performance capillary electrophoresis (HPCE) has been applied to the identification, separation, and quantitation of intact bacteria. We demonstrate that a pathogen (Edwardsiella tarda) which causes systemic infection in commercially important fish species can be rapidly identified and determined (<10 min) after direct injection into fish fluid by CE blue light-emitting diode (LED)-induced fluorescence. SYTO 13 (488 nm/509 nm), a cell-permeable green nucleic acid stain, was used to stain the cells. Remarkably high efficiency (>1 200,000 theoretical plates/m) was achieved with this rapid and efficient CE method. It was found that proper sample vortexing (90 s) would be beneficial to disperse aggregated cells and facilitate the focusing of intact cells during electrophoresis. Ionization of the surface constituents of Edwardsiella tarda cells provided efficient surface charges for the intact cells to be separated from the EOF and damaged or lysed cells when the separation was performed in running buffer (3.94 mM Tris, 0.56 mM borate, 0.013 mM EDTA) at pH 10.5. The limit of detection (LOD) and recovery were found to be 4.2×104 cells/mL and 70.0%, respectively. This proposed CE method could become an effective tool for diagnosis and tracking of certain diseases caused by bacteria in fish species as well as in human beings. [source]

Violet light emitting diode-induced fluorescence detection combined with on-line sample concentration techniques for use in capillary electrophoresis

ELECTROPHORESIS, Issue 17 2003
Chih-Hsin Tsai
Abstract The first application of a violet light-emitting diode (LED) for fluorescence detection in capillary electrophoresis (CE) is described. The utility of violet LED (peak emission wavelength at 410 nm, , 2 mW) for fluorescence detection is demonstrated by examining reserpine and dopamine-labeled NDA (naphthalene-2,3-dicarboxaldehyde), respectively. The detection limit for reserpine was determined to be 2.5×10,6 M by normal micellar electrokinetic capillary chromatography (MEKC) and this was improved to 2.0×10,9 M and 2.0×10,10 M when sweeping-MEKC and cation-selective exhaustive injection (CSEI)-sweep-MEKC techniques were applied, respectively. In addition, the detection limit of NDA-labeled dopamine was determined to be 6.3×10,6 M by means of normal MEKC and this was improved to 3.0×10,8 M when the sweeping-MEKC mode was applied. [source]

Functional neuroanatomy of the human near/far response to blur cues: eye-lens accommodation/vergence to point targets varying in depth

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2004
Hans O. Richter
Abstract The purpose of this study was to identify the networks involved in the regulation of visual accommodation/vergence by contrasting the cortical functions subservient to eye-lens accommodation with those evoked by foveal fixation. Neural activity was assessed in normal volunteers by changes in rCBF measured with PET. Thirteen right-handed subjects participated in three monocular tasks: (i) resting with eyes closed; (ii) sustained foveal fixation upon a LED at 1.2 m (0.83 D); and (iii) accommodating alternately on a near (24 cm, 4.16 D) vs. a far (3.0 m, 0.33 D) LED alternately illuminated in sequential 2 s epochs. The contrast between the conditions of near/far accommodation and of constant foveal fixation revealed activation in cerebellar hemispheres and vermis; middle and inferior temporal cortex (BA 20, 21, 37); striate cortex and associative visual areas (BA 17/18). Comparison of the condition of constant fixation with the condition of resting with closed eyes indicated activation of cerebellar hemispheres and vermis; visual cortices (BA 17/18); a right hemisphere dominant network encompassing prefrontal (BA 6, 9, 47), superior parietal (BA 7), and superior temporal (BA 40) cortices; and bilateral thalamus. The contrast between the conditions of near/far accommodation with closed-eye rest reflected an incremental summation of the activations found in the previous comparisons (i.e. activations associated with constant fixation). Neural circuits activated selectively during the near/far response to blur cues over those during constant visual fixation, occupy posterior structures that include occipital visual regions, cerebellar hemispheres and vermis, and temporal cortex. [source]

Influence of light energy and power density on the microhardness of two nanohybrid composites

EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2008
Kerstin Gritsch
The purpose of this study was to investigate the role of light parameters on nanohybrid composite curing. Two nanohybrid resins were cured by two light-emitting diode (LED) devices and by one quartz-tungsten-halogen (QTH) device using different combinations of energy density and power density (8 J cm,2 and 400 mW cm,2; 8 J cm,2 and 1,000 mW cm,2; 16 J cm,2 and 400 mW cm,2; and 16 J cm,2,1,000 mW cm,2). The effects of these combinations on polymerization were assessed by measuring the Vickers microhardness. Data differed for the two composites and varied according to the light parameters and the nature of the curing device. For both resins, an energy density of 16 J cm,2 yielded the best microhardness values at both the top and the bottom of the sample, independently of the power density. When using a lower energy density of 8 J cm,2, a modulated power density was required to achieve proper curing at the bottom of the sample: 8 J cm,2 and 400 mW cm,2 induced greater values at the bottom surface. At an energy density of 16 J cm,2, the power density was not relevant (no significant differences were found between 400 and 1,000 mW cm,2), except when the emission spectra of the light-curing units (LCUs) did not match exactly with the absorption spectra of the photoinitators included in the resins (greatest values with 16 J cm,2 and1,000 mW cm,2). These results suggest that above a certain energy density threshold, the power density may not significantly influence the polymerization kinetics. [source]

Effect of irradiation type (LED or QTH) on photo-activated composite shrinkage strain kinetics, temperature rise, and hardness

EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 6 2002
Norbert Hofmann
This study compares commercially available light-emitting diode (LED) lights with a quartz tungsten halogen (QTH) unit for photo-activating resin-based composites (RBC). Shrinkage strain kinetics and temperature within the RBC were measured simultaneously using the ,deflecting disc technique' and a thermocouple. Surface hardness (Knoop) at the bottom of 1.5-mm thick RBC specimens was measured 24 h after irradiation to indicate degree of cure. Irradiation was performed for 40 s using either the continuous or the ramp-curing mode of a QTH and a LED light (800 mW cm,2 and 320 mW cm,2, respectively) or the continuous mode of a lower intensity LED light (160,mW cm,2). For Herculite XRV and Filtek Z250 (both containing only camphoroquinone as a photo-initiator) the QTH and the stronger LED light produced similar hardness, while in the case of Definite (containing an additional photo-activator absorbing at lower wavelength) lower hardness was observed after LED irradiation. The temperature rise during polymerization and heating from radiation were lower with LED compared to QTH curing. The fastest increase of polymerization contraction was observed after QTH continuous irradiation, followed by the stronger and the weaker LED light in the continuous mode. Ramp curing decreased contraction speed even more. Shrinkage strain after 60 min was greater following QTH irradiation compared with both LED units (Herculite, Definite) or with the weaker LED light (Z250). [source]

Enhancement of Light Extraction Through the Wave-Guiding Effect of ZnO Sub-microrods in InGaN Blue Light-Emitting Diodes

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010
Ki Seok Kim
Abstract The improvement of the light extraction efficiency (LEE) of a conventional InGaN blue light-emitting diode (LED) by the incorporation of one-dimensional ZnO sub-microrods is reported. The LEE is improved by 31% through the wave-guiding effect of ZnO sub-microrods compared to LEDs without the sub-microrods. Different types of ZnO microrods/sub-microrods are produced using a simple non-catalytic wet chemical growth method at a low temperature (90,°C) on an indium-tin-oxide (ITO) top contact layer with no seed layer. The crystal morphologies of needle-like or flat-top hexagonal structures, and the ZnO microrods/sub-microrod density and size are easily modified by controlling the pH value and growth time. The wave-guiding phenomenon within the ZnO rods is observed using confocal scanning electroluminescence microscopy and micro-electroluminescence spectra. [source]

Plasmonic Enhancement or Energy Transfer?

ADVANCED FUNCTIONAL MATERIALS, Issue 13 2009
Its Potential for Light-Emitting Devices, Lanthanide-Doped Silicate Glasses, On the Luminescence of Gold-, Silver-
Abstract With the technique of synchrotron X-ray activation, molecule-like, non-plasmonic gold and silver particles in soda-lime silicate glasses can be generated. The luminescence energy transfer between these species and lanthanide(III) ions is studied. As a result, a significant lanthanide luminescence enhancement by a factor of up to 250 under non-resonant UV excitation is observed. The absence of a distinct gold and silver plasmon resonance absorption, respectively, the missing nanoparticle signals in previous SAXS and TEM experiments, the unaltered luminescence lifetime of the lanthanide ions compared to the non-enhanced case, and an excitation maximum at 300,350,nm (equivalent to the absorption range of small noble metal particles) indicate unambiguously that the observed enhancement is due to a classical energy transfer between small noble metal particles and lanthanide ions, and not to a plasmonic field enhancement effect. It is proposed that very small, molecule-like noble metal particles (such as dimers, trimers, and tetramers) first absorb the excitation light, undergo a singlet-triplet intersystem crossing, and finally transfer the energy to an excited multiplet state of adjacent lanthanide(III) ions. X-ray lithographic microstructuring and excitation with a commercial UV LED show the potential of the activated glass samples as bright light-emitting devices with tunable emission colors. [source]

Analysis of Improved Efficiency of InGaN Light-Emitting Diode With Bottom Photonic Crystal Fabricated by Anodized Aluminum Oxidxe

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Sang-Wan Ryu
Abstract The improved performance of a bottom photonic crystal (PC) light-emitting diode (LED) is analyzed based on internal quantum efficiency (,int) and light-extraction efficiency (,ex). The bottom PC is fabricated by anodized aluminum oxide nanopatterns and InGaN quantum wells (QWs) are grown over it. Transmission electron microscopy images reveal that threading dislocations are blocked at the nanometer-sized air holes, resulting in improved optical emission efficiency of the QWs. From temperature-dependent photoluminescence measurements, the enhancement of ,int is estimated to be 12%. Moreover, the enhancement of ,ex is simulated to be 7% by the finite-difference time-domain method. The fabricated bottom PC LED shows a 23% higher optical power than a reference, which is close to the summation of enhancements in ,int and ,ex. Therefore, the bottom PC improves LED performance through higher optical quality of QWs as well as increased light extraction. [source]

Increased Color-Conversion Efficiency in Hybrid Light-Emitting Diodes utilizing Non-Radiative Energy Transfer

ADVANCED MATERIALS, Issue 5 2010
Soontorn Chanyawadee
An efficient hybrid color-conversion light-emitting device consisting of colloidal nanocrystal quantum dots (NQDs) and a surface-patterned GaN-based LED is demonstrated (see figure). Excitation in a surface-patterned LED is efficiently transferred to NQD emitters via non-radiative energy transfer. A twofold enhancement of the NQD emission is achieved. [source]

Recent Progress in GaN-Based Light-Emitting Diodes

ADVANCED MATERIALS, Issue 45 2009
Haiqiang Jia
Abstract In the last few years the GaN-based white light-emitting diode (LED) has been remarkable as a commercially available solid-state light source. To increase the luminescence power, we studied GaN LED epitaxial materials. First, a special maskless V-grooved c -plane sapphire was fabricated, a GaN lateral epitaxial overgrowth method on this substrate was developed, and consequently GaN films are obtained with low dislocation densities and an increased light-emitting efficiency (because of the enhanced reflection from the V-grooved plane). Furthermore, anomalous tunneling-assisted carrier transfer in an asymmetrically coupled InGaN/GaN quantum well structure was studied. A new quantum well structure using this effect is designed to enhance the luminescent efficiency of the LED to ,72%. Finally, a single-chip phosphor-free white LED is fabricated, a stable white light is emitted for currents from 20 to 60,mA, which makes the LED chip suitable for lighting applications. [source]

A White LED Driver Using a Buck,Boost Converter

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 5 2010
Kei Eguchi Member
Abstract For mobile backlighting applications, a white LED (WLED) driver using a buck,boost converter is proposed in this letter. Unlike conventional converters using boost converters, 2×/1.5× charge pumps, and so on, the proposed converter offers the negative stepped-down voltage to drive the LED's cathode only when the input voltage is insufficient to drive a 1× transfer mode. Furthermore, unlike the LED backlight using charge pumps, the proposed converter can adjust the output voltage by controlling the duty factor of the clock pulse. Thus, the proposed converter can realize high power efficiency. The validity of the proposed converter is confirmed by simulations and experiments. © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film

ADVANCED MATERIALS, Issue 27 2009
Xiao-Mei Zhang
Bright n-ZnO nanowire/p-GaN film hybrid heterojunction light-emitting-diode (LED) devices are fabricated by directly growing n-type ZnO-nanowire arrays on p-GaN wafers. UV,blue electroluminescence emission was observed from the heterojunction diodes, and the heterojunction LED device exhibited a high sensitivity in responding to UV irradiation. [source]

Transillumination by light-emitting diode facilitates peripheral venous cannulations in infants and small children

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 8 2010
K. HOSOKAWA
Background: Transillumination facilitates the visualization of peripheral veins in infants and children. The clinical usefulness of light-emitting diode (LED)-powered devices has not been thoroughly studied. Methods: We randomly assigned 136 infants and children weighing <15 kg, undergoing general anesthesia, to red LED-powered transillumination (TM group, n=67) vs. the usual method (UM group, n=69) of peripheral venous cannulations. Venous puncture was performed following anesthesia induction with sevoflurane and nitrous oxide. The primary and secondary study endpoints were the rate of successful cannulations at initial attempt, and the duration of insertion attempts, respectively. Results: The median score of the estimated cannulation difficulty before attempted puncture was similar in both groups. The success rates at first attempt were 75% and 61% (NS) and mean±SD times to successful venous access were 47±34 and 68±66 s (NS) in the TM and UM groups, respectively. The cannulation procedures were completed significantly earlier in the TM group than in the UM group (hazard ratio, 1.59; 95% confidence interval, 1.03,2.47; P=0.03). In the subgroup of infants and children <2 years old, venous cannulation was successful at first attempt in 73% and 49% in the TM group (n=44) and in the UM group (n=47), respectively (P=0.03). Conclusions: LED-powered transillumination devices facilitated peripheral venous cannulations in small infants and children. [source]

Electrothermal model of optocoupler for SPICE

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 4 2009
Krzysztof Górecki
Abstract In the paper a new electrothermal model of the optocoupler for SPICE is proposed. The model is based on electrical models of the LED and the bipolar phototransistor with their parameters dependent on temperature, their thermal models including both the self-heating phenomenon and the mutual thermal interactions between the LED and the phototransistor, and the dependences describing electrical power dissipated in these components. The final form of the electrothermal model of the optocoupler elaborated by the authors, dedicated to the d.c. and a.c. computations, was implemented in SPICE. The usefulness of the new model was experimentally verified for the optocoupler 4N25. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Fluorescence spectra of Pr3+ ions in phosphate materials calculated by the DVME method

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2009
Y. Kowada
Abstract Recently, fluorescence spectra of rare-earth ions in oxide materials are very attractive for the applications of the optical amplification in optical fiber communications, white LED, etc. However, it has been difficult to calculate the fluorescence spectra of rare-earth ions by the first principle method. In this study, we used the relativistic discrete-variational multielectron (DVME) method, which is a configuration-interaction (CI) calculation program using the molecular orbitals obtained by the relativistic DV-X, method. We applied this method for the calculation of the fluorescence spectrum of the Pr3+ ions in phosphate materials. The transition probability of the fluorescence was calculated in the same manner of the absorption. The obtained theoretical fluorescence spectrum was in good agreement with the experimental one, though the intensity of each peak was deeply dependent on the configuration of the surrounding structural units. The results suggested that the DVME method was useful for the calculation of not only absorption but also fluorescence spectra of rare-earth ions in oxide materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

The use of light-emitting diode therapy in the treatment of photoaged skin

JOURNAL OF COSMETIC DERMATOLOGY, Issue 3 2007
FACCS, FRACGP, Fabien Baez MBBS, MAACS, MCPSA
Summary Background, Light-emitting diode (LED) therapy is an increasingly popular methodology for the treatment of sun damage. Combination use of light wavelengths reported to stimulate collagen synthesis and accelerate fibroblast,myofibroblast transformation may display a composite rejuvenative effect. Objective, To clinically assess reduction in sun damage signs following a 5-week course of LED therapy and to assess subject's perception of the treatment. Methods, Thirteen subjects with wrinkles or fine lines in the periorbital and nasolabial region and those presenting Glogau scale photodamage grade II,III received nine 20-min duration light treatments using the OmniluxÔ LED system. The treatments combined wavelengths of 633 and 830 nm at fluences of 126 and 66 J/cm2, respectively. Sun-damage reduction was assessed at 6, 9, and 12 weeks by clinical photography and patient satisfaction scores. Results, The majority of subjects displayed "moderate" (50%) or "slight" (25%) response to treatment at investigator assessment. Treatment of the periorbital region was reported more effective than the nasolabial region. At 12-week follow-up, 91% of subjects reported improved skin tone, and 82% reported enhanced smoothness of skin in the treatment area. Conclusion, Good response to LED therapy has been shown in this modest sample. Larger trials are needed to assess optimum frequency of light treatments and overall treatment time. [source]

Accuracy of LED and Halogen Radiometers Using Different Light Sources

JOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2006
Howard W. Roberts dmd
ABSTRACT Purpose:, To determine the accuracy of commercially available, handheld light-emitting diode (LED) and halogen-based radiometers using LED and quartz-tungsten-halogen (QTH) curing lights with light guides of various diameters. Methods:, The irradiance of an LED curing light (L.E.Demetron 1, SDS/Kerr, Orange, CA, USA) and a QTH curing light (Optilux 501, SDS/Kerr) were measured using multiple units of an LED (Demetron L.E.D. Radiometer, SDS/Kerr) and a halogen radiometer (Demetron 100, SDS/Kerr) and compared with each other and to a laboratory-grade power meter (control). Measurements were made using five light guides with distal light guide diameters of 4, 7, 8, 10, and 12.5 mm. For each light guide, five readings were made with each of three radiometers of each radiometer type. Data were analyzed with two-way analysis of variance/Tukey; ,=0.05. Results:, In general, both handheld radiometer types exhibited significantly different irradiance readings compared with the control meter. Additionally, readings between radiometer types were found to differ slightly, but were correlated. In general, the LED radiometer provided slightly lower irradiance readings than the halogen radiometer, irrespective of light source. With both types of handheld radiometers, the use of the larger-diameter light guides tended to overestimate the irradiance values as seen in the control, while smaller-diameter light guides tended to underestimate. CLINICAL SIGNIFICANCE The evaluated LED or halogen handheld radiometers may be used interchangeably to determine the irradiance of both LED and QTH visible-light-curing units. Measured differences between the two radiometer types were small and probably not clinically significant. However, the diameter of light guides may affect the accuracy of the radiometers, with larger-diameter light guides overestimating and smaller-diameter guides underestimating the irradiance value measured by the control instrument. [source]

QUARTZ-TUNGSTEN-HALOGEN AND LIGHT-EMITTING DIODE CURING LIGHTS

JOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 3 2006
Kraig S. Vandewalle DDS
Curing lights are an integral part of the daily practice of restorative dentistry. Quartz-tungsten-halogen (QTH), plasma-arc (PAC), argon laser, and light-emitting diode (LED) curing lights are currently commercially available. The QTH curing light has a long, established history as a workhorse for composite resin polymerization in dental practices and remains the most common type of light in use today. Its relatively broad emission spectrum allows the QTH curing light to predictably initiate polymerization of all known photo-activated resin-based dental materials. However, the principal output from these lamps is infrared energy, with the generation of high heat. Filters are used to reduce the emitted heat energy and provide further restriction of visible light to correlate better with the narrower absorbance spectrum of photo-initiators. The relatively inefficient emission typically requires corded handpieces with noisy fans. PAC lights generate a high voltage pulse that creates hot plasma between two electrodes in a xenon-filled bulb. The irradiance of PAC lights is much higher than the typical QTH curing light, but PAC lights are more expensive and generate very high heat with an inefficient emission spectrum similar to that of QTH bulbs. Light emitted from an argon laser is very different from that emitted from the halogen or PAC lights. The photons produced are coherent and do not diverge; therefore, lasers concentrate more photons of specific frequency into a tiny area. With very little infrared output, unwanted heat is minimized. However, argon lasers are very expensive and inefficient due to a small curing tip. LED curing lights have been introduced to the market with the promise of more efficient polymerization, consistent output over time without degradation, and less heat emission in a quiet, compact, portable device. This review evaluates some of the published research on LED and QTH curing lights. [source]

Detection of Pretreated Fingerprint Fluorescence Using an LED-based Excitation System

JOURNAL OF FORENSIC SCIENCES, Issue 4 2008
Masahisa Takatsu Ph.D.
Abstract:, Optimization of a light emitting diode (LED)-based excitation system for the detection of pretreated fingerprint fluorescence is described. Fluorescent ridges can usually be excited by irradiation with forensic light sources such as xenon arc lamps or quartz-halogen lamps with high-power output and suitable filters. However, they are too expensive for many crime laboratories in smaller organizations. We concentrated on LEDs which have advantages over conventional light sources in that they are simpler and of lower cost, but the power output and quality of each individual LED unit is not sufficient for the detection of weak fluorescent ridges. To resolve this subject, blue and green LED arrays composed of ninety LED units were adopted and suitable low pass filters for them were designed. An experimental system, consisting of blue and green LED arrays with the suitable low pass filters for illumination, high pass filters for viewing, a digital camera and a computer, was tested. The fluorescent images of cyanoacrylate ester fumed/rhodamine 6G stained fingerprint on white polyethylene sheet and weak fluorescent ridges of ninhydrin/indium chloride treated fingerprint on white paper were successfully detected and photographed. It was shown that the improvement of LED beam in intensity and quality can compensate the disadvantages, resulting in well-contrasted images. [source]