Aerosol and Precipitation Chemistry at a Remote Himalayan Site in Nepal

As a part of a year long aerosol measurement program in the Nepal Himalayas, a series of 12 h samples of aerosol and event-based samples of precipitation were collected in postmonsoon, 1996; premonsoon, 1997; and monsoon, 1997. Results show that diurnal variations in the regional valley wind system are responsible for variations in the major ion (Na + , NH 4 + , K + , Mg 2+ , Ca 2+ , Cl - , NO 3 - , and SO 4 -2 ) concentrations in the aerosol. On time scales greater than a day, changes in atmospheric circulation and associated changes in the precipitation regime have an important effect on aerosol ion concentrations. Periods of high major ion concentration in the aerosol generally coincide with similar periods in precipitation chemistry, although a linear relationship between concentrations in these 2 media is not robust due to limited data. High scavenging ratio values are found for all species except SO 4 2- . Nitrate, Cl - , and NH 4 + are enriched in the precipitation compared to the aerosol, implying the presence of gaseous acidic species (HNO 3 and HCl) and gaseous NH 3 in the air. Ammonium was also enriched with respect to SO 4 2- in aerosol during a dry episode in the monsoon season. This may represent relatively local sources of NH 3 (from neighboring villages) and was not scavenged due to the lack of precipitation. Empirical orthogonal function (EOF) analysis clearly shows the presence of 2 dominant pollutant transport mechanisms for the premonsoon and monsoon seasons (i.e., valley wind system and monsoon circulation). Although physically different, these 2 transport mechanisms follow similar transport pathways and transport aerosol into the Himalayas from similar source regions. Further, EOF analysis suggests a southerly maritime signal in the aerosol during monsoon and a more distant westerly maritime signal during premonsoon. Our results support the potential for using glaciochemical records from the Himalayas to investigate variations in the strength of past monsoon circulation and westerly disturbances.     

Multiphase mass transport in mini/micro-channels microreactor

This paper describes a computational study of two-phase gas/liquid flow in mini/micro-scale reaction channels at low Reynolds numbers. The direct fluorination of toluene is used as a sample process. We consider two different configurations, a falling film and membrane microreactor. The detailed mathematical model of the processes in these configurations is based on mass and momentum conservation equations, which are solved numerically using the finite element method.

Gas-phase mass transport in both reactor configurations is analysed by means of the mathematical model. For fully developed gas flow a correlation for the gas-phase mass transport is developed in terms of the Sherwood and the relative Reynolds number. It is shown that the flow pattern in this regime and entrance effects strongly influence mass transport from the bulk flow to the reaction plane. The velocity profile for the falling film reactor yields higher Sherwood numbers compared to the membrane reactor. The latter has the advantage over the falling film reactor that the gas and liquid phases are decoupled and operating conditions and channel design can be freely chosen.     

Process-Structure-Reflectance Correlations for TiB2 Films Prepared by Chemical Vapor Deposition

The process-structure-reflectance interrelationships for TiB₂ films prepared by CVD were determined using statistically designed experiments. A hot wall CVD reactor employing graphite substrates and the TiCl₄+ BCl₃+ H₂ reagent system were used at pressures of 2.7 and 6.7 kPa. Single-phase polycrystalline TiB₂ films were obtained. An increasing percentage of the grains were oriented with their (001) planes parallel to the substrate as the deposition temperature was increased and as the BCl₃:TiCl₄ ratio decreased. Grain size increased from ∼0.5 to 3 µm as the deposition temperature was increased from 900° to 1100°C and as the coating rate was decreased from 0.6 to 0.1 µm/min. Fine-grained, smooth, highly reflective films were obtained at low deposition temperatures and high BCl₃:TiCl₄ ratios.     

元代丽水保定窑青瓷化学组成的研究

应用质子激发Ｘ荧光分析技术测定了元明时期丽水保定窑青瓷胎和釉的化学组成,对保定窑青瓷胎和釉的主量化学组分和痕量化学组分的均匀性进行了分析。应用模式识别方法,将保定窑青瓷与历代青瓷的化学组成进行比较。     

Evaluation of stainless steel cathodes and a bicarbonate buffer for hydrogen production in microbial electrolysis cells using a new method for measuring gas production

Microbial electrolysis cells (MECs) are often examined for hydrogen production using non-sustainable phosphate buffered solutions (PBS), although carbonate buffers have been shown to work in other bioelectrochemical systems with a platinum (Pt) catalyst. Stainless steel (SS) has been shown to be an effective catalyst for hydrogen evolution in MECs, but it has not been tested with carbonate buffers. We evaluated the combined using of SS cathodes and a bicarbonate buffer (BBS) at the applied voltages of 0.5, 0.7 and 0.9 V using a new inexpensive method for measuring gas production called the gas bag method (GBM). This method achieved an average error of only 5.0% based on adding known volumes of gas to the bag. Using the GBM, hydrogen production with SS and a BBS was 26.6 ± 1.8 mL which compared well to 26.4 ± 2.8 mL using Pt and BBS, and 26.8 ± 2.5 mL with a Pt cathode and PBS. Electrical energy efficiency was highest with a SS cathode and BBS at 159 ± 17%, compared to 126 ± 14% for the Pt cathode and BBS, and 134 ± 17% for a Pt cathode and PBS. The main disadvantage of the SS was a lower gas production rate of 1.1 ± 0.3 m³ H₂-m⁻³ d⁻¹ with BBS and 1.2 ± 0.3 m³ H₂-m⁻³ d⁻¹ with PBS, compared to 1.7 ± 0.4 m³ H₂-m⁻³ d⁻¹ with Pt and PBS. These results show that the GBM is an effective new method for measuring gas production of anaerobic gas production processes, and that SS and bicarbonate buffers can be used to effectively produce hydrogen in MECs.     

Potential GPRS 900/180-MHz and WCDMA 1900-MHz interference to medical devices

This study compared the potential for interference to medical devices from radio frequency (RF) fields radiated by GSM 900/1800-MHz, general packet radio service (GPRS) 900/1800-MHz, and wideband code division multiple access (WCDMA) 1900-MHz handsets. The study used a balanced half-wave dipole antenna, which was energized with a signal at the standard power level for each technology, and then brought towards the medical device while noting the distance at which interference became apparent. Additional testing was performed with signals that comply with the requirements of the international immunity standard to RF fields, IEC 61000-4-3. The testing provides a sense of the overall interference impact that GPRS and WCDMA (frequency division duplex) may have, relative to current mobile technologies, and to the internationally recognized standard for radiated RF immunity. Ten medical devices were tested: two pulse oximeters, a blood pressure monitor, a patient monitor, a humidifier, three models of cardiac defibrillator, and two models of infusion pump. Our conclusion from this and a related study on consumer devices is that WCDMA handsets are unlikely to be a significant interference threat to medical electronics at typical separation distances.     

Applications of one-cycle control to improve the interconnection of a solid oxide fuel cell and electric power system with a dynamic load

Adding distributed generation (DG) is a desirable strategy for providing highly efficient and environmentally benign services for electric power, heating, and cooling. The interface between a solid oxide fuel cell (SOFC), typical loads, and the electrical grid is simulated in Matlab/Simulink and analyzed to assess the interactions between DG and the electrical grid. A commercial building load profile is measured during both steady-state and transient conditions. The load data are combined with the following models that are designed to account for physical features: a One-Cycle Control grid-connected inverter, a One-Cycle Control active power filter, an SOFC, and capacitor storage. High penetration of DG without any power filter increases the percentage of undesirable harmonics provided by the grid, but combined use of an inverter and active power filter allows the DG system interconnection to improve the grid tie-line flow by lowering total harmonic distortion and increasing the power factor to unity.     

Efficiency trends in electric machines and drives

Almost all electricity in the UK is generated by rotating electrical generators, and approximately half of it is used to drive electrical motors. This means that efficiency improvements to electrical machines can have a very large impact on energy consumption. The key challenges to increased efficiency in systems driven by electrical machines lie in three areas: to extend the application of variable-speed electric drives into new areas through reduction of power electronic and control costs; to integrate the drive and the driven load to maximise system efficiency; and to increase the efficiency of the electrical drive itself. In the short to medium term, efficiency gains within electrical machines will result from the development of new materials and construction techniques. Approximately a quarter of new electrical machines are driven by variable-speed drives. These are a less mature product than electrical machines and should see larger efficiency gains over the next 50 years. Advances will occur, with new types of power electronic devices that reduce switching and conduction loss. With variable-speed drives, there is complete freedom to vary the speed of the driven load. Replacing fixed-speed machines with variable-speed drives for a high proportion of industrial loads could mean a 15–30% energy saving. This could save the UK 15 billion kWh of electricity per year which, when combined with motor and drive efficiency gains, would amount to a total annual saving of 24 billion kWh.     

The Human Centrifuge

Life on Earth has developed at unit gravity, 9.81 m/s², which was a major factor especially when vertebrates emerged from water onto land in the late Devonian, some 375 million years ago. But how would nature have evolved on a larger planet? We are able to address this question simply in experiments using centrifuges. Based on these studies we have gained valuable insights in the physiological process in plants and animals. They adapt to a new steady state suitable for the high-g environments applied. Information on mammalian adaptations to hyper-g is interesting or may be even vital for human space exploration programs. It has been shown in long duration animal hypergravity studies, ranging from snails, rats to primates, that various structures like muscles, bones, neuro-vestibular, or the cardio-vascular system are affected. However, humans have never been exposed to a hyper-g environment for long durations. Centrifuge studies involving humans are mostly in the order of hours. The current work on human centrifuges are all focused on short arm systems to apply short periods of artificial gravity in support of long duration space missions in ISS or to Mars. In this paper we will address the possible usefulness of a large human centrifuge on Earth. In such a centrifuge a group of humans can be exposed to hypergravity for, in principle, an unlimited period of time like living on a larger planet. The input from a survey under scientists working in the field of gravitational physiology, but also other disciplines, will be discussed.     

A repair-replace strategy based on usage rate for items sold with a two-dimensional warranty

When a repairable item fails under warranty, the manufacturer has the option of either repairing the failed item or replacing it with a new one. In this paper, a repair-replace strategy is discussed for the manufacturer of a product sold with a two-dimensional warranty. The strategy is based on a specified region of the warranty defined in terms of age and usage with the first failure in the region rectified by replacement and all other failures being minimally repaired. An accelerated failure time (AFT) model is used to allow for the effect of usage rate on item degradation.