Shortcut model for predicting refrigeration cycle performance

Compression refrigeration systems are very widely used to provide cooling to sub-ambient processes. The power demand of the cycle depends strongly on the temperature at which cooling is required, the temperature at which the refrigerant is condensed, as well as the type of refrigerant being used. At lower temperatures (typically lower than -40 °C), complex refrigeration schemes, such as cascaded refrigeration cycles, may be needed, increasing the complexity of the models used to predict the power requirements for a given cooling demand. This work proposes a simple model for predicting the power consumption of such complex cycles, based on regression of more rigorous process simulation models. A simple linear refrigeration model which relates the actual power demand of a refrigeration cycle to the ideal performance (i.e. the Carnot cycle) is developed. The model predicts the power demand prior to design of the refrigeration scheme given the condensing and evaporation temperatures of the refrigerant. The model predictions are shown to be in good agreement with those of more accurate simulation models. Case studies demonstrate the validity of the refrigeration model. The predicted power demand is shown to be within 10 % of that of Branan (2005). The simplicity of the model enables its use for optimizing the design conditions of a complex refrigeration cycle and/or the associated processing conditions

Design of Novel Algorithm and Architecture for Gaussian Based Color Image Enhancement System for Real Time Applications

This paper presents the development of a new algorithm for Gaussian based color image enhancement system. The algorithm has been designed into architecture suitable for FPGA/ASIC implementation. The color image enhancement is achieved by first convolving an original image with a Gaussian kernel since Gaussian distribution is a point spread function which smoothen the image. Further, logarithm-domain processing and gain/offset corrections are employed in order to enhance and translate pixels into the display range of 0 to 255. The proposed algorithm not only provides better dynamic range compression and color rendition effect but also achieves color constancy in an image. The design exploits high degrees of pipelining and parallel processing to achieve real time performance. The design has been realized by RTL compliant Verilog coding and fits into a single FPGA with a gate count utilization of 321,804. The proposed method is implemented using Xilinx Virtex-II Pro XC2VP40-7FF1148 FPGA device and is capable of processing high resolution color motion pictures of sizes of up to 1600x1200 pixels at the real time video rate of 116 frames per second. This shows that the proposed design would work for not only still images but also for high resolution video sequences.Comment: 15 pages, 15 figure

Multiple organ failure - death of consumer protection?

The enormously profitable complementary medicines, dietary supplements and traditional medicines markets are largely unregulated internationally and South Africa. Attempts to ensure that consumers are not exposed to harmful or ineffective products have met with varying success around the world

Investigation of chlorine radical chemistry in the Eyjafjallajkull volcanic plume using observed depletions in non-methane hydrocarbons

As part of the effort to understand volcanic plume composition and chemistry during the eruption of the Icelandic volcano Eyjafjallajkull, the CARIBIC atmospheric observatory was deployed for three special science flights aboard a Lufthansa passenger aircraft. Measurements made during these flights included the collection of whole air samples, which were analyzed for non-methane hydrocarbons (NMHCs). Hydrocarbon concentrations in plume samples were found to be reduced to levels below background, with relative depletions characteristic of reaction with chlorine radicals (Cl). Recent observations of halogen oxides in volcanic plumes provide evidence for halogen radical chemistry, but quantitative data for free halogen radical concentrations in volcanic plumes were absent. Here we present the first observation-based calculations of Cl radical concentrations in volcanic plumes, estimated from observed NMHC depletions. Inferred Cl concentrations were between 1.3 × 10 and 6.6 × 10 Cl cm. The relationship between NMHC variability and local lifetimes was used to investigate the ratio between OH and Cl within the plume, with [OH]/[Cl] estimated to be ∼37. Copyright 2011 by the American Geophysical Union

Culture and the remembering of trauma

This research investigated the influence of culture and posttraumatic stress disorder (PTSD) on global autobiographical remembering (Study 1a) and on the phenomenological properties (Study 1b) and memory-content variables (Study 1c) of trauma-specific autobiographical remembering. Australian, British, and Iranian trauma survivors with and without PTSD completed the Autobiographical Memory Test, Self-Defining Memory Task, and Autobiographical Memory Questionnaire and provided trauma- and negative-memory narratives. We found that there were pan-cultural deficits and distortions in the global autobiographical remembering of participants with PTSD (Study 1a). In addition, the presence of PTSD moderated the usual effect of culture on the phenomenological properties of the trauma memory (Study 1b). Finally, participants with PTSD, regardless of cultural background, had significantly fewer expressions of autonomy and self-determination in their autobiographical remembering than did those without PTSD (Study 1c). The findings suggest that pan-culturally, individuals with PTSD have similar disruptions and distortions in their autobiographical remembering

Gyroscopic motion of superfluid trapped atomic condensates

The gyroscopic motion of a trapped Bose gas containing a vortex is studied. We model the system as a classical top, as a superposition of coherent hydrodynamic states, by solution of the Bogoliubov equations, and by integration of the time-dependent Gross-Pitaevskii equation. The frequency spectrum of Bogoliubov excitations, including quantum frequency shifts, is calculated and the quantal precession frequency is found to be consistent with experimental results, though a small discrepancy exists. The superfluid precession is found to be well described by the classical and hydrodynamic models. However the frequency shifts and helical oscillations associated with vortex bending and twisting require a quantal treatment. In gyroscopic precession, the vortex excitation modes $m=\pm 1$ are the dominant features giving a vortex kink or bend, while the $m=+2$ is found to be the dominant Kelvin wave associated with vortex twisting.Comment: 18 pages, 7 figures, 1 tabl

Comparison of aromatic hydrocarbon measurements made by PTR-MS, DOAS and GC-FID during the MCMA 2003 Field Experiment

A comparison of aromatic hydrocarbon measurements is reported for the CENICA supersite in the district of Iztapalapa during the Mexico City Metropolitan Area field experiment in April 2003 (MCMA 2003). Data from three different measurement methods were compared: a Proton Transfer Reaction Mass Spectrometer (PTR-MS), long path measurements using a UV Differential Optical Absorption Spectrometer (DOAS), and Gas Chromatography-Flame Ionization analysis (GC-FID) of canister samples. The principle focus was on the comparison between PTR-MS and DOAS data. Lab tests established that the PTR-MS and DOAS calibrations were consistent for a suite of aromatic compounds including benzene, toluene, p-xylene, ethylbenzene, 1,2,4-trimethylbenzene, phenol and styrene. The point sampling measurements by the PTR-MS and GC-FID showed good correlations (r=0.6), and were in reasonable agreement for toluene, C2-alkylbenzenes and C3-alkylbenzenes. The PTR-MS benzene data were consistently high, indicating interference from ethylbenzene fragmentation for the 145 Td drift field intensity used in the experiment. Correlations between the open-path data measured at 16-m height over a 860-m path length (retroreflector in 430 m distance), and the point measurements collected at 37-m sampling height were best for benzene (r=0.61), and reasonably good for toluene, C2-alkylbenzenes, naphthalene, styrene, cresols and phenol (r>0.5). There was good agreement between DOAS and PTR-MS measurements of benzene after correction for the PTR-MS ethylbenzene interference. Mixing ratios measured by DOAS were on average a factor of 1.7 times greater than the PTR-MS data for toluene, C2-alkylbenzenes, naphthalene and styrene. The level of agreement for the toluene data displayed a modest dependence on wind direction, establishing that spatial gradients – horizontal, vertical, or both – in toluene mixing ratios were significant, and up to a factor of 2 despite the fact that all measurements were conducted above roof level. Our analysis highlights a potential problem in defining a VOC sampling strategy that is meaningful for the comparison with photochemical transport models: meaningful measurements require a spatial fetch that is comparable to the grid cell size of models, which is typically a few 10 km2. Long-path DOAS measurements inherently average over a larger spatial scale than point measurements. The spatial representativeness can be further increased if observations are conducted outside the surface roughness sublayer, which might require measurements at altitudes as high as 10 s of metres above roof level.Alexander von Humboldt-Stiftung (Feodor Lynen fellowship)Henry & Camille Dreyfus Foundation (Postdoctral Fellowship in Environmental Chemistry

Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 & 2003 field campaigns

A wide array of volatile organic compound (VOC) measurements was conducted in the Valley of Mexico during the MCMA-2002 and 2003 field campaigns. Study sites included locations in the urban core, in a heavily industrial area and at boundary sites in rural landscapes. In addition, a novel mobile-laboratory-based conditional sampling method was used to collect samples dominated by fresh on-road vehicle exhaust to identify those VOCs whose ambient concentrations were primarily due to vehicle emissions. Four distinct analytical techniques were used: whole air canister samples with Gas Chromatography/Flame Ionization Detection (GC-FID), on-line chemical ionization using a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous real-time detection of olefins using a Fast Olefin Sensor (FOS), and long path measurements using UV Differential Optical Absorption Spectrometers (DOAS). The simultaneous use of these techniques provided a wide range of individual VOC measurements with different spatial and temporal scales. The VOC data were analyzed to understand concentration and spatial distributions, diurnal patterns, origin and reactivity in the atmosphere of Mexico City. The VOC burden (in ppbC) was dominated by alkanes (60%), followed by aromatics (15%) and olefins (5%). The remaining 20% was a mix of alkynes, halogenated hydrocarbons, oxygenated species (esters, ethers, etc.) and other unidentified VOCs. However, in terms of ozone production, olefins were the most relevant hydrocarbons. Elevated levels of toxic hydrocarbons, such as 1,3-butadiene, benzene, toluene and xylenes, were also observed. Results from these various analytical techniques showed that vehicle exhaust is the main source of VOCs in Mexico City and that diurnal patterns depend on vehicular traffic in addition to meteorological processes. Finally, examination of the VOC data in terms of lumped modeling VOC classes and its comparison to the VOC lumped emissions reported in other photochemical air quality modeling studies suggests that some alkanes are underestimated in the emissions inventory, while some olefins and aromatics are overestimated