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The increasing resistance of methicillin‐resistant Staphylococcusaureus to antibiotics is a major challenge faced by mankind in thehistory of medical science and according to United Nations, 700‐000 patients worldwide die every year from an infection with multidrug‐resistant organisms (MROs). Aluminum gallium nitride‐based 228 nm Far‐ultraviolet‐C (Far‐UVC) lightsources can be safely used as a germicidal application in both manned as wellas in unmanned environments against these MROs. Previously, the 228 nm Far‐UVC light‐emitting diode (LED) with emission power of 1 mW was reported by ourgroup, however, the value of external quantum efficiency (EQE) was not reportedusing conventional thick Ni (20 nm)/Au (100 nm) p‐electrode. Herein, animproved Far‐UVC LED on c‐Sapphire is attempted using a special technique in SR4000 type of metal‐organic chemical vapor deposition reactor to control the Al composition in n‐AlGaN buffer and across the 2 inch‐wafer. As a result, the light emission power of 1.8 mW and EQE of 0.32% in 228 nm Far‐UVC LED aresuccessfully achieved using very thin p‐electrode (Ni/Au). However, arelatively high junction temperature of ≈100°C around thejunction of Far‐UVC LED is observed. Finally, some simple heat‐sink modules forheat dissipation of Far‐UVC LED panel with light power of 30 mW are implemented. [ABSTRACT FROM AUTHOR]

ABSTRACT Santiago de Chile is one of the most polluted South American cities, concentrating its pollution episodes during winter. Daily [PM.sub.2.5] (particulate matter [PM] ≤ 2.5 µm in aerodynamic diameter) [...]

A junction termination extension avalanche photodiode (APD) is evaluated for x-ray detection. Findings reveal that the structure posses the potential to make very low-noise detectors with high reliability after optimization of the implanted charge.

ABSTRACT Santiago, Chile, is one of the most polluted cities in South America. As a response, over the past 15 yr, numerous pollution reduction programs have been implemented by the [...]

ABSTRACT Daily particle samples were collected in Santiago, Chile, at four urban locations from January 1, 1989, through December 31, 2001. Both fine PM with [d.sub.a] ********** INTRODUCTION Santiago, Chile, [...]

ABSTRACT The optical absorption coefficient, particulate matter with an aerodynamic diameter The data also show an increase in P[M.sub.2.5] and EC concentration during winter and an increase in the ratio [...]

The authors have evaluated the performance of an avalanche photodiodes (APD)/Lutetium oxyorthosilicate (LSO) module for use in positron emission tomography systems. They have used a recently developed APD detector in combination with a 3 x 3 x 30 [mm.sup.3] LSO scintillator to measure the depth of interaction of 511 keV photons from a [sup.22]Na source. The detectors were built using standard planar technology for silicon devices. Photodiodes with 3 mm diameter active area have been produced by deep boron diffusion, followed by shallow boron and phosphor diffusion. Because the structure has not been optimized yet, the authors only obtained a gain of 6 at 1300 V. A simple noise analysis of the detector characteristics indicate that they are still capable of measuring 511 keV photons with sufficient energy resolution for depth of interaction position measurement from a long LSO scintillator, in spite of the low gain, the authors have obtained an energy resolution of 25% full-width at half-maximum (FWHM) with a single APD and the 3 x 3 x 30 [mm.sup.3] scintillator, better resolution (23%)is obtained when the scintillator is coupled to two APDs and the spectrum is obtained from the sum of the detectors. DOI resolution varies with the position of interaction being 5.3 and 8.6 mm FWHM at 2 and 28 mm from the APD, respectively. Index Terms--Avalanche photodiode, depth of interaction, LSO scintillator, PET module.

The gain and noise characteristics of avalanche photodiode (APD) arrays of the bevel-edge type were calculated. Results showed that the noise of the APD array is dominated by the interpixel resistance at low voltages. In calculating the frequency response of the APD arrays and comparing it with PIN diodes, it is shown that APD's have better performance than at high frequencies.

We have designed and built a compact, low-cost automated system to measure the optical absorption coefficient of air. Because most of the light absorption is due to black carbon, this method is a direct measure of the amount of black carbon in the atmosphere. The equipment was used to measure absorption over a period of one year in a central area of Santiago. Our results show a strong correlation with the daily traffic pattern. The highest value of the absorption coefficient during most of the year occurs during the morning rush hour (0700-0800), and the lowest value either early in the morning (0300-0500) or in the afternoon (1400-1700). The absorption coefficient also shows a strong dependence with the season of the year, with values 10-20 times higher in winter than in summer. The data show that, during most of the year, the amount of black carbon present in the atmosphere is due to traffic. At night, during winter, the high concentration of black carbon is due to the temperature inversion effect. [C] 2000 Optical Society of America OCIS codes: 010.1120, 010.1320, 010.1100.

A deep-diffused large-area avalanche photodiode (APD) without bevel or grooves has been designed and built for use in low-light-level applications. The design does not incorporate a bevel edge or grooves to avoid early breakdown at the surface. The APD has been built using standard planar technology for silicon devices. Photodiodes with 2- and 3-mm diameter active area have been produced by deep boron diffusion, followed by shallow boron and phosphor diffusion. Gain up to six is obtained at 1300 V before surface breakdown. The dark current is dependent on external voltage and is only 50-100 nA below breakdown. The energy resolution from a [sup.57]Co X-ray source (6.4 keV) was measured to be 1.47 keV, which corresponds to 174 rms electron noise. The energy resolution of a [sup.137]Cs source with an APD coupled to a 3 x 3 x 3 [mm.sup.3] CsI(TI) scintillator was 14.5%. We have also performed simulations of the gain and breakdown voltage that correlate well with the results. Index Terms--Avalanche photodiode, gain, photodetector.

The optical absorption coefficient, particulate matter with an aerodynamic diameter <2.5 µm, and elemental carbon (EC) have been measured simultaneously during winter and spring of 2000 in the western part of Santiago, Chile (Pudahuel district). The optical measurements were carried out with a low-cost instrument recently developed at the University of Santiago. From the data, a site-specific mass absorption coefficient of 4.45 ± 0.01 m²/g has been found for EC. In addition, a mass absorption coefficient of 1.02 ± 0.03 m²/g has been obtained for PM2.5. These coefficients can be used during the colder months (May--August) to obtain EC concentration or PM2.5 from a measurement of the light absorption coefficient (σa). The high correlation that has been found between these variables indicates that σa is a good indicator of the degree of contamination of urbanized areas. The data also show an increase in PM2.5 and EC concentration during winter and an increase in the ratio of EC to PM2.5. When the EC/PM2.5 ratio is calculated during rush hour (7:00 a.m.--11:00 a.m.) and during part of the night (9:00 p.m.--2:00 a.m.), it is found that the increase is caused by higher concentration levels of EC at night. These results suggest that the rise in the EC concentration is caused by emissions from heating and air mass transport of pollution from other parts of the city, while traffic contribution remains approximately constant. [ABSTRACT FROM AUTHOR]

Daily particle samples were collected in Santiago, Chile,at four urban locations from January 1, 1989, through December 31, 2001. Both fine PM with da <2.5 µm (PM2.5) and coarse PM with 2.5 < da <10 µm (PM2.5-10) were collected using dichotomous samplers. The inhalable particle fraction, PM10, was determined as the sum of fine and coarse concentrations .Wind speed, temperature and relative humidity (RH) were also measured continuously. Average concentrations of PM2.5 for the 1989-2001 period ranged from 38.5 µg/m3 to 53 µg/m3. For PM2.5-10 levels ranged from 35.8-48.2 µg/m3 and for PM10 results were 74.4-101.2 µg/m3 across the four sites. Both annual and daily PM2.5 and PM10 concentration levels exceeded the U.S. National Ambient Air Quality Standards and the European Union concentration limits. Mean PM2.5 levels during the cold season (April through September) were more than twice as high as those observed in the warm season (October through March); whereas coarse particle levels were similar in both seasons. PM concentration trends were investigated using regression models, controlling for site, weekday, month, wind speed, temperature, and RH. Results showed that PM2.5 concentrations decreased substantially, 52% over the 12-year period (1989 - 2000), whereas PM2.5-10 concentrations increased by ∼50% in the first 5 years and then decreased by a similar percentage over the following 7 years. These decreases were evident even after controlling for significant climatic effects. These results suggest that the pollution reduction programs developed and implemented by the Comisión Nacional del Medio Ambiente (CONAMA) have been effective in reducing particle levels in the Santiago Metropolitan region. However, particle levels... [ABSTRACT FROM AUTHOR]