Analysis of exergetic performance for a solar air heater with metal foam fins

In this experimental study, an exergetic analysis is presented for solar air heaters (SAHs) that have absorber plates equipped with different fin arrangements. The following two types of fins were used: solid fins (conventional) and metal foam fins. Longitudinal, staggered, and corrugated fin arrangements in SAHs were investigated under the weather conditions experienced in Baghdad, Iraq in February to April 2018. The exergy efficiency and exergy loss of the SAHs were evaluated for five air mass flow rates ranging from 0.011 to 0.059 kg/s. Based on the exergy analysis, SAHs with metal foam fins are more efficient than those with solid fins. In addition, corrugated metal foam fins introduce more turbulent flow than the other fin configurations. It was found that the exergy loss and the exergy efficiency were directly proportional to the values of solar irradiance and air mass flow rates. At solar noon, the maximum values for exergy change were 127 and 89 W/m² for air mass flow rates of 0.011 and 0.059 kg/s, respectively.     

The Thermal-Stability of Oligomers in Alpha-Pinene Secondary Organic Aerosol

Recent studies characterizing laboratory generated secondary organic aerosol (SOA) have shown that 50% or more of the particle mass is made up of oligomeric species, which based on molecular weight and structure should be nonvolatile. On the other hand, about 75% the particle mass is lost when SOA is passed through a denuder heated to 100°C, suggesting that it is semi-volatile. To study the reason for this discrepancy, the chemical effects of a thermal denuder (TD) on oligomers in laboratory SOA formed by ozonolysis of α-pinene were examined with high-resolution molecular mass spectrometry. Both monomers and oligomers in the particle phase were lost to the gas phase upon heating to 100°C. Additionally, when the species released to the gas phase during heating were allowed to readsorb onto the remaining particle mass, almost all of the readsorbed material was monomeric. Both of these observations suggest that oligomers decompose when heated in a TD. Chemical analysis of the remaining particle mass after passing through the TD showed formation of many new compounds that corresponded to oligomer decomposition products. While similar experiments should be performed with other aerosol types, these results suggest that care must be taken when attempting to use a TD at an elevated temperature to infer the volatility of SOA at ambient temperature.

Copyright 2012 American Association for Aerosol Research     

Stratification and mixing in large floodplain lakes along the lower Amazon River

Large, shallow lakes are common in the extensive floodplains throughout the tropics. To determine controls on their mixing dynamics, we instrumented 5 stations in two shallow, connected tropical lakes on the lower Amazon floodplain with meteorological and temperature sensors. A tight relation between changes in thermal structure and L_MO/h (the ratio of the Monin-Obukhov length scale to the depth of the actively mixing layer) indicates the sensitivity of thermal structure to wind speed relative to heating and cooling. Four regimes led to variations in mixing: (i) high solar radiation with light winds in the mid-morning to early afternoon resulted in shallow stratification, 0?<?L_MO/h?<?1; (ii) afternoons with higher winds caused the diurnal thermocline to downwell and heat to mix to deeper layers, L_MO/h?>?1; (iii) by late afternoon, buoyancy flux became negative and L_MO/h?<??1 and with u_1W and w₁ both >0.06?m?s^?1, mixing from wind and cooling co-occurred; and (iv) convection dominated mixing on nights with light winds, ?1?<?L_MO/h?<?0. Pattern (ii) occurred mid-day if winds were higher. When winds were intermittent and regime (i) predominated mid-day, changes in heat content were primarily determined by one dimensional processes of heating and cooling. When easterly winds were sustained and regime (ii) occurred mid-day, heat was transported west in the day, and colder water upwelled to the west or was advected to the west and north at night. Subtle differences in wind speed determined the extent to which advection moderated the thermal structure.     

Song of the burbot: Under-ice acoustic signaling by a freshwater gadoid fish

Burbot (Lota lota) are northern freshwater gadoid fish that spawn under ice-cover, making their reproductive behavior largely unknown to science. Some members of the cod family vocalize as part of their mating system. These calls are produced by rapidly contracting drumming muscles on their swim bladders. Burbot also possess drumming muscles, like their marine counterparts, which may enable them to vocalize. To assess the potential for burbot to make calls, pre-spawning adult burbot were collected and placed in a large under-ice enclosure in Great Slave Lake, Northwest Territories, Canada, along with a recorder that monitored low frequency sound over their spawning period. The recorded acoustic data revealed that burbot called coincident with the onset of their spawning period and that the call signatures were stereotypical of swim bladder generated vocalizations made by other gadoid fishes. Burbot showed a wide repertoire of calls, from slow knocks to fast buzzing, similar to the closely related haddock (Melanogrammus aeglefinus). Although never-before documented, calling by fish under ice-cover is likely an important part of the mating system of under-ice spawning gadoids because light limitation would reduce the usefulness of visual cues. These under-ice communications may be affected by anthropogenic noise from increasing resource development in northern regions.     

Spontaneously reactive plasma polymer micropatterns

A combination of spontaneous reactive chemical domains bounded by non-fouling zones provides a means to covalently immobilize biomolecules in structured, spatially defined arrays. These arrays have application in a wide range of biotechnologies including tissue engineering, proteomics, and diagnostics. In this paper, we describe the fabrication of multi-chemistry micropatterns from plasma polymers. X-ray photoelectron spectroscopy (XPS), together with Time-of-Flight Static Secondary Ion Mass Spectrometry (ToF-SSIMS) and confocal imaging has been utilized to confirm the reactivity and integrity of micropatterns fabricated from amine-reactive maleic anhydride (ppMA) on non-fouling tetraglyme (ppTg). The covalent immobilization of antibodies via the formation of amide linkages with the anhydride groups occurs only in the ppMA domains, while antibody activity is confirmed via their ability to attract specific fluorescent antigens. These micropatterns therefore provide a convenient and effective platform for covalently immobilizing biomolecules in spatially defined areas without the need for multiple step wet chemical immobilization strategies.     

Stress-related growth, positive reframing, and emotional processing in the prediction of post-trauma functioning among veterans in mental health treatment.

The role of stress related growth (SRG) in posttrauma functioning is currently uncertain and may be obscured by the overlap between SRG and key coping strategies. Utilizing a veteran sample in mental health treatment, the current study examined whether SRG accounts for unique variance in the severity of posttraumatic stress disorder (PTSD), depression, and Disorders of Extreme Stress Not Otherwise Specified (DESNOS) beyond the effects of two general coping strategies, emotional processing and positive reframing. Curvilinear relationships were evident between SRG and outcome measures, such that individuals with moderate SRG reported the greatest distress, and individuals with the lowest and highest SRG scores reported lower distress. In regression analyses, SRG accounted for significant variance in lower PTSD, depression, and DESNOS while accounting for demographics, trauma type, emotional processing, and positive reframing. The results suggest that SRG captures variance in posttrauma functioning that may be distinct from general emotional processing and positive reframing coping and provides further evidence for a curvilinear relationship between SRG and measures of psychological distress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning iterative dispatching rules for job shop scheduling with genetic programming

This study proposes a new type of dispatching rule for job shop scheduling problems. The novelty of these dispatching rules is that they can iteratively improve the schedules by utilising the information from completed schedules. While the quality of the schedule can be improved, the proposed iterative dispatching rules (IDRs) still maintain the easiness of implementation and low computational effort of the traditional dispatching rules. This feature makes them more attractive for large-scale manufacturing systems. A genetic programming (GP) method is developed in this paper to evolve IDRs for job shop scheduling problems. The results show that the proposed GP method is significantly better than the simple GP method for evolving composite dispatching rules. The evolved IDRs also show their superiority to the benchmark dispatching rules when tested on different problem instances with makespan and total weighted tardiness as the objectives. Different aspects of IDRs are also investigated and the insights from these analyses are used to enhance the performance of IDRs.     

A new aperture coupled microstrip slot antenna

A new aperture coupled design is proposed for microstrip slot antennas to improve their radiation performance. The proposed design is based on a new aperture coupling technique in which the slot is fed by a microstrip line and coupled to several parasitic patch radiators etched on the opposite side from the slot. In contrast to the combination of a slot and a microstrip patch in conventional aperture coupled microstrip antennas, the patches here are employed to reduce the radiation into the half-space that they occupy and increase the radiation in the other half-space. Therefore, the slot antenna can produce radiation patterns with a high front-back ratio. The above objective is achieved by optimizing standing wave distributions of the aperture electric field in the slot through the adjustment of the position of the patches along the axis of the slot. In this paper, design considerations are given, and the results are validated by numerical simulations and experimental measurements.     

Using system dynamics to evaluate control strategies for mosquito-borne diseases spread by human travel

The aim of this paper is to evaluate the effectiveness of control strategies for diseases transmitted by the Aedes albopictus mosquito (the “Asian tiger”) and spread by human travel. This mosquito, which has become established in southern Europe in recent years, is a vector for many diseases. For example, an outbreak of chikungunya, hitherto regarded as a tropical disease, occurred in Italy in 2007. The initial case was a person who had acquired the disease overseas. Mosquito-borne infections can only be spread over large distances by human travel, as the flight range of mosquitos is very limited. A system dynamics model has been developed which describes the mosquito life-cycle, the natural history of mosquito-borne disease in humans and mosquitos, and human behaviour including travel. Potential disease control strategies include chemical treatments to destroy either larvae or adult mosquitos, campaigns to influence human behaviour, or quarantine of infectious people. In this paper, which is based on the Italian chikungunya outbreak, this model is used to study and compare the effect of different control strategies, where the various actions are combined in different ways and implemented for different time periods.