METHODS: Combustion pollutant concentrations were measured during the scripted operation of natural gas cooking burners in nine homes. In addition to a base condition of closed windows, no forced air unit (FAU) use, and no mechanical exhaust, additional experiments were conducted while operating an FAU and/or vented range hood. Test homes included a 26m 2 tworoom apartment, a 134m 2 first floor flat, and seven detached homes of 117-226m 2 . There were four single-story, four two-story and one 1.5 story homes. Cooktop use entailed boiling and simmering activities, using water as a heat sink. Oven and broiler use also were simulated. Timeresolved concentrations of carbon dioxide (CO2), nitric oxide (NO), nitrogen oxides (NOX), nitrogen dioxide (NO2), particles with diameters of 6 nm or larger (PN), carbon monoxide (CO), and fine particulate matter (PM2.5) were measured in the kitchen (K) and bedroom area (BR) of each home. CO2, NO, NO2, and PN data from sequential experiments were analyzed to quantify the contribution of burner use to the highest 1h and 4h time-integrated concentrations in each room.RESULTS: Four of the nine homes had kitchen 1h NO2 exceed the national ambient air quality standard (100 ppb). Two other homes had 1h NO2 exceed 50 ppb in the kitchen, and three had 1h NO2 above 50 ppb in the bedroom, suggesting substantial exposures to anyone at home when burners are used for a single substantial event. In all homes, the highest 1h kitchen PN exceeded 2 x10 5 cm -3 -h, and the highest 4h PN exceeded 3 x10 5 cm -3 -hr in all homes. The lowest 1h kitchen/bedroom ratios were 1.3-2.1 for NO in the apartment and two open floor plan homes. The largest K/BR ratios of 1h NO2 were in a two-story 1990s home retrofitted for deep energy savings: ratios in this home were 3.3 to 6.6. Kitchen 1h ratios of NO, NO2 and PN to CO2 were used to calculate fuel normalized emission factors (ng J -1 ). Range hood use substantially reduced cooking burner pollutant concentrations both in the kitchen and bedroom of several homes. A hood with large capture volume and a measured flow of 108 L/s reduced concentrations 80-95%.IMPLICATIONS: These measurements demonstrate that operation of natural gas cooking burners without venting can cause short-term kitchen concentrations of NO2 to exceed the US outdoor health standard, and can elevate concentrations of NO, NO2, and ultrafine particles throughout the home. Results are generally consistent with a recent simulation study that estimated widespread 1h NO2 exposures exceeding 100 ppb in homes that use gas burners without venting. While operating a venting range hood can greatly reduce pollutant levels from burner use (and presumably from cooking as well), performance varies widely across hoods. Increased awareness of the need to ventilate when cooking would substantially reduce in-home exposure to NO2 and ultrafine particles in California homes. Helping consumers select effective hoods, for example by publishing capture efficiency performance ratings, also would help reduce ex...
A genomic collection of haploid Saccharomyces cerevisiae deletion strains provides a unique resource for systematic analysis of gene interactions. Double-mutant haploid strains can be constructed by the synthetic genetic array (SGA) method, wherein a query mutation is introduced by mating to mutant arrays, selection of diploid double mutants, induction of meiosis, and selection of recombinant haploid doublemutant progeny. The mechanism of haploid selection is mating-type-regulated auxotrophy (MRA), by which prototrophy is restricted to a particular haploid genotype generated only as a result of meiosis. MRA escape leads to false-negative genetic interaction results because postmeiotic haploids that are supposed to be under negative selection instead proliferate and mate, forming diploids that are heterozygous at interacting loci, masking phenotypes that would be observed in a pure haploid double-mutant culture. This work identified factors that reduce MRA escape, including insertion of terminator and repressor sequences upstream of the MRA cassette, deletion of silent mating-type loci, and utilization of a-type instead of a-type MRA. Modifications engineered to reduce haploid MRA escape reduced false negative results in SGA-type analysis, resulting in .95% sensitivity for detecting gene-gene interactions.
We evaluate an ambient, bidirectional thermal network, which uses a single circuit for both district heating and cooling. When in net more cooling is needed than heating, the system circulates from a central plant in one direction. When more heating is needed, the system circulates in the opposite direction. A large benefit of this design is that buildings can recover waste heat from each other directly.We analyze the thermodynamic performance of the bidirectional system. Because the bidirectional system represents the state-of-the-art in design for district systems, its peak energy efficiency represents an upper bound on the thermal performance of any district heating and cooling system. However, because any network has mechanical and thermal distribution losses, we develop a diversity criterion to understand when the bidirectional system may be a more energy-efficient alternative to modern individualbuilding systems. We show that a simple model of a low-density, high-distribution loss network is more efficient than aggregated individual buildings if there is at least 1 unit of cooling energy per 5.7 units of simultaneous heating energy (or vice versa). We apply this criterion to reference building profiles in three cities to look for promising clusters.
In an effort to make higher efficiency power systems, several joint fuel cell / combustion-based cycles have been proposed and modeled. Mitsubishi Heavy Industries has recently built such a system with a solid-oxide fuel cell gas turbine plant, and is now working on a variant that includes a bottoming steam cycle. They report their double and triple cycles have LHV efficiencies greater than 52% and 70%, respectively. In order to provide insight into the thermodynamics behind such efficiencies, this study attempts to reverse engineer the Mitsubishi Heavy Industries system from publicly available data. The information learned provides the starting point for a computer model of the triple cycle. An exergy analysis is used to compare the triple cycle to its constituent sub-cycles, in particular the natural gas combined cycle. This analysis provides insights into the benefits of integrating the fuel cell and gas turbine architectures in a manner that improves the overall system performance to previously unseen efficiencies.
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