An instrument has been designed and constructed for the simultaneous determination of nitrogen dioxide (NO2) and peroxyacetyl nitrate (PAN) in atmospheric samples. The instrument’s design is based on separation by fast gas chromatography (GC) with a 30 ft capillary column (DB-1) followed by detection by luminol chemiluminescence. The chemiluminescent reaction between NO2 or PAN and luminol takes place at the gas–liquid interface on the surface of a solid support. The chemiluminescent emission at 425 nm is detected with a photon counting module. The instrument is controlled by a 1.8 GHz Notebook computer with a WINDOWS 2000 operating system and a custom software application programmed in LABVIEW. Detection limits are in the low parts per trillion (ppt) with a time resolution of 30 s to 1 min. The instrument was operated during the Mexico City Metropolitan Area/Mexico City Megacity 2003 collaborative air quality study. Results for NO2 from this fast GC method were compared with results from a co-located differential optical absorption spectrometer (DOAS) and a tunable diode laser absorption spectromenter (TDLAS). The results support the application of the new luminol-based instrument for atmospheric measurements.
In recent years, the feature size of silicon devices has decreased at a steady rate. Each step in feature size has required a reduction in operating voltage. As today's system designers seek to maximize performance, they use a wide variety of integrated circuits. The result is a system that requires many different supply voltages for various devices in the system. It is not unusual for a system today to require seven or eight different voltages and systems with twelve or more voltages are not uncommon.To meet this challenge, the traditional distributed power architecture has been extended to create the Intermediate Bus Architecture. This paper explores the Intermediate Bus Architecture and highlights areas of special concern to system and power system developers. I. THE PROBLEMComputing and communications equipment in the 1980s typically used +5 V as the system voltage for logic. Fans and disk drives were typically operated from either +12 V or +24 V. Small amounts of -12 V and -5 V may have been used for some communications circuits. These system voltages remained the same until the late 1980s when integrated circuit (IC) makers introduced +3.3 V devices. Towards the end of the 1990s the size of IC features devices started declining rapidly from 350-500 microns to the 65-100 micron devices available today [1]. In that time the typical IC operating voltages have decreased from +3.3 V to +1.0-1.2 V. In the next five years IC feature size is predicted to shrink to as little as 25 microns and operating voltages to +0.7-0.9 V [2]. Table I shows typical voltages used in computing, networking and communications equipment today. TABLE I. TYPICAL SYSTEM VOLTAGES Voltage Typical Load(s) +12 Fans, Disk Drives, Communications +5 Logic, Standby Power +3.3 Logic, Standby Power +2.5 Logic, Memory +1.8 Logic +1.5 Logic +1.25 Memory Termination +1.2 Logic +0.7 -1.7 High Performance MicroprocessorsThis rapid change in semiconductor technology has created a challenge for the system designer. To get the best performance or the best cost to performance ratio, system designers end up with a wide range of power supply voltages in their systems. Power supplies voltages required in a typical high performance server product are shown in Table II. TABLE II. TYPICAL POWER SUPPLY OUTPUTS REQUIRED IN A HIGH PERFORMANCE SERVER Power Supply Output Used For +12 V Disk Drives, Magnetic And Optical +8-12 V, Variable Fans +5 V Legacy logic +3.3 V Logic +3.3 V Standby Always On Bias Power +2.5 V Logic, Memory +1.8 V Logic +1.5 V Logic +1.25 V Memory Termination +1.2 V Logic +1.2-1.7 V, Variable Processor #1 Power +1.2-1.7 V, Variable Processor #2 Power -12 V CommunicationsThis typical system has thirteen different outputs required of the power system. Most of the low voltages supplying logic have narrow regulation bands that will require sensing and controlling the voltage right at the point of use. Also, several of the outputs have special requirements such as:• An output power than can be varied under system control to vary the fan voltage and s...
When awake goats were subjected to isobaric gas switching from saturation (17 hours) on 4.7 atmospheres of nitrogen (0.3 atmosphere of oxygen) to 4.7 atmospheres of helium (0.3 atmosphere of oxygen), bubbles detected by 5-megahertz Doppler ultrasound in the posterior vena cava 20 to 60 minutes after the switch continued for 4 hours. Similar experiments carried out at 6.7 atmospheres of inert gas and 0.3 atmosphere of oxygen produced more bubbles for as long as 12 hours after the gas switch. This is believed to be the first objective demonstration of the phenomenon of deep isobaric supersaturation under transient operational diving conditions at relatively shallow diving depths. Detection of bubbles by Doppler ultrasound confirms the potential importance of the phenomenon to shallow saturation diving and holds promise for better quantitification of its effects as well as those of its counterpart, isobaric undersaturation, which can confer a decompression advantage.
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