Quantifying fine particle emission events from time‐resolved measurements: Method description and application to 18 California low‐income apartments

PM_2.5 exposure is associated with significant health risk. Exposures in homes derive from both outdoor and indoor sources, with emissions occurring primarily in discrete events. Data on emission event magnitudes and schedules are needed to support simulation‐based studies of exposures and mitigations. This study applied an identification and characterization algorithm to quantify time‐resolved PM_2.5 emission events from data collected during 224 days of monitoring in 18 California apartments with low‐income residents. We identified and characterized 836 distinct events with median and mean values of 12 and 30 mg emitted mass, 16 and 23 minutes emission duration, 37 and 103 mg/h emission rates, and pseudo‐first–order decay rates of 1.3 and 2.0/h. Mean event‐averaged concentrations calculated using the determined event characteristics agreed to within 6% of measured values for 14 of the apartments. There were variations in event schedules and emitted mass across homes, with few events overnight and most emissions occurring during late afternoons and evenings. Event characteristics were similar during weekdays and weekends. Emitted mass was positively correlated with number of residents (Spearman coefficient, ρ=.10), bedrooms (ρ=.08), house volume (ρ=.29), and indoor‐outdoor CO₂ difference (ρ=.27). The event schedules can be used in probabilistic modeling of PM_2.5 in low‐income apartments.     

Indoor air quality in California homes with code-required mechanical ventilation

Data were collected in 70 detached houses built in 2011-2017 in compliance with the mechanical ventilation requirements of California's building energy efficiency standards. Each home was monitored for a 1-week period with windows closed and the central mechanical ventilation system operating. Pollutant measurements included time-resolved fine particulate matter (PM_2.5) indoors and outdoors and formaldehyde and carbon dioxide (CO₂) indoors. Time-integrated measurements were made for formaldehyde, NO₂, and nitrogen oxides (NO_X) indoors and outdoors. Operation of the cooktop, range hood, and other exhaust fans was continuously recorded during the monitoring period. Onetime diagnostic measurements included mechanical airflows and envelope and duct system air leakage. All homes met or were very close to meeting the ventilation requirements. On average, the dwelling unit ventilation fan moved 50% more airflow than the minimum requirement. Pollutant concentrations were similar to or lower than those reported in a 2006-2007 study of California new homes built in 2002-2005. Mean and median indoor concentrations were lower by 44% and 38% for formaldehyde and 44% and 54% for PM_2.5. Ventilation fans were operating in only 26% of homes when first visited, and the control switches in many homes did not have informative labels as required by building standards.     

Improvement of mechanical properties of polylactide by equal channel multiple angular extrusion

The combination of high strength and toughness is always the goal of high-performance polymer materials for industrial use. This study addresses the potentialities of a solid state equal-channel multiple-angular extrusion (ECMAE) in production of polylactide (PLA) with simultaneous improvement in toughness, strength, and thermal stability. Chain extender Joncryl was used to form PLA with different chain length and morphology (linear or branched PLA). It is demonstrated that simple shear deformation implemented in ECMAE results in formation of an orientation order, an increase in the degree of crystallinity, and the creation of α crystals with an increased degree of perfection. The value of the effects achieved depends on the type of PLA morphology. The best result is observed in the case of linear PLA. ECMAE-modified linear PLA possess the better combination of strength, modulus, and ductility than the branched one. Compared with neat linear PLA, ECMAE-modified linear PLA shows 12%, 26%, 217%, and 40% increase in tensile strength, Young's modulus, strain at break and impact strength, respectively. Additionally, the storage modulus shows an improved thermal stability of ECMAE-modified PLA.     

Response of consumer and research grade indoor air quality monitors to residential sources of fine particles

The ability to inexpensively monitor PM_2.5 to identify sources and enable controls would advance residential indoor air quality (IAQ) management. Consumer IAQ monitors incorporating low‐cost optical particle sensors and connections with smart home platforms could provide this service if they reliably detect PM_2.5 in homes. In this study, particles from typical residential sources were generated in a 120 m³ laboratory and time‐concentration profiles were measured with 7 consumer monitors (2‐3 units each), 2 research monitors (Thermo pDR‐1500, MetOne BT‐645), a Grimm Mini Wide‐Range Aerosol Spectrometer (GRM), and a Tapered Element Oscillating Microbalance with Filter Dynamic Measurement System (FDMS), a Federal Equivalent Method for PM_2.5. Sources included recreational combustion (candles, cigarettes, incense), cooking activities, an unfiltered ultrasonic humidifier, and dust. FDMS measurements, filter samples, and known densities were used to adjust the GRM to obtain time‐resolved mass concentrations. Data from the research monitors and 4 of the consumer monitors—AirBeam, AirVisual, Foobot, Purple Air—were time correlated and within a factor of 2 of the estimated mass concentrations for most sources. All 7 of the consumer and both research monitors substantially under‐reported or missed events for which the emitted mass was comprised of particles smaller than 0.3 μm diameter.     

Wear behavior of Pb–Mo–S solid lubricating coatings

Amorphous Pb–Mo–S coatings 200 to 510 nm thick were deposited by dual ion-beam deposition (IBD) onto steel and Si substrates. Coating wear studies were performed using ball-on-flat reciprocating sliding with steel ball counterfaces in dry air. Tests were run between 1 and 100,000 sliding cycles, and wear depths measured by interference microscopy. Morphology and chemistry of the as-deposited coatings and worn surfaces were investigated with optical microscopy, micro-Raman spectroscopy and cross-section high resolution transmission electron microscopy (HRTEM). Pb–Mo–S coatings were found to be quite wear resistant; no more than 25% of the coating thickness was removed by 10,000 sliding cycles. Two wear mechanisms were identified. At the nanometer scale, wear proceeded in a two-part process: transformation of the coating surface to MoS₂, then layer-by-layer removal of MoS₂. At the micrometer scale, wear occurred by plowing. The long endurance of Pb–Mo–S coatings was attributed to slow wear of the coatings, with lubricant redistribution processes playing a minor role.     

Interleaved converters operation based on CMC

A new family of low-ripple DC-to-DC switching converters based on a parallel connection of N-identical boost converters with current-mode control (CMC) is presented. The CMC strategy ensures that all the converters operate at the same duty cycle, sharing an equal amount of input current and forcing the output voltage to be an integer multiple (N) of the input voltage. As a result, the total input current and output voltage ripples are extremely low. The generation of control signals from inductor currents feedback without using external triangular or sawtooth signals is another characteristic of the new converter family     

Sintered metallic foams for biodegradable bone replacement materials

The iron open cell foams were synthesized by the replication method based on powder metallurgical technologies as biodegradable bone replacement material. Open cell metal foams provide extraordinary combinations of the properties. Samples containing carbon nanotubes (CNTs) and Mg were produced with the aim to affect degradation rate and enhance the biocompatibility. The microstructure, corrosion behaviour and in vitro biocompatibilities were investigated by scanning electron microscopy, immersion tests in Hank’s solution during the time of 8 weeks, cytotoxicity and haemolysis tests. The addition of CNTs and Mg induced the higher surface inhomogeneity and roughness, which was more pronounced for Fe–Mg sample. The homogenous degradation on the whole surface was registered for bare iron sample, while progressive local corrosion sites were found on the surface of samples with CNTs and Mg. Highest corrosion rate was determined for Fe–Mg sample which came to be disintegrated after 3 weeks of immersion. The slowest degradation rate was detected for Fe–CNTs sample. The fast dieback of fibroblast cells was registered under static conditions in monolayer cell culture. However, all the experimental samples were found to be highly haemocompatible. Additionally, the haemolysis percentage value of about 2 % determined for Fe–Mg sample proved its good performance for blood vessel related cellular application.     

微量Ag对形变Cu-Fe原位复合材料组织和性能的影响

采用熔铸-中间热处理-形变工艺制备了Cu-14Fe及Cu-14Fe-0.06Ag原位复合材料,利用光学显微镜、扫描电镜、数字微欧计及液晶电子拉力试验机研究了微量Ag对Cu-14Fe合金微观组织、力学性能及导电性能的影响。结果表明,微量Ag的加入使Cu-14Fe合金枝晶组织更发达且枝晶臂直径更小,相同形变量下形成的纤维更加细小均匀,材料的强度显著提高,电导率也有所上升,伸长率略有提高,冷加工性能明显改善。     

Antimicrobial Resistance: Challenges and Perspectives

In 2006, the Institute of Food Technologists (IFT) published an Expert Report entitled “Antimicrobial Resistance: Implications for the Food System” (IFT 2006). That report summarized current scientific knowledge pertaining to the public‐health impact of antimicrobial use in the food system and the development and control of antimicrobial resistance. Since that time, intense interest in this topic has continued within the regulatory and scientific communities as well as the general public. This IFT Scientific Status Summary serves to update that 2006 IFT Expert Report by briefly reviewing new scientific evidence relevant to the goals of the initial report and providing a number of key observations and conclusions.     

Smells Like Home: Chemically Mediated Co-Habitation of Two Termite Species in a Single Nest

Termite nests often are referred to as the most elaborate constructions of animals. However, some termite species do not build a nest at all and instead found colonies inside the nests of other termites. Since these so-called inquilines do not need to be in direct contact with the host population, the two colonies usually live in separate parts of the nest. Adaptations of both the inquiline and its host are likely to occur to maintain the spatial exclusion and reduce the costs of potential conflicts. Among them, mutual avoidance, based on chemical cues, is expected. We investigated chemical aspects of cohabitation between Constrictotermes cavifrons (Nasutitermitinae) and its obligatory inquiline Inquilinitermes inquilinus (Termitinae). Inquiline soldiers produce in their frontal glands a blend of wax esters, consisting of the C₁₂ alcohols (3Z)-dodec enol, (3Z,6Z)-dodecadienol, and dodecanol, esterified with different fatty acids. The C₁₂ alcohols appear to be cleaved gradually from the wax esters, and they occur in the frontal gland, in soldier headspace, and in the walls of the inquiline part of the nest. Electrophysiological experiments revealed that (3Z)-dodecenol and (3Z,6Z)-dodecadienol are perceived by workers of both species. Bioassays indicated that inquiline soldier heads, as well as the two synthetic compounds, are attractive to conspecific workers and elicit an arresting behavior, while host soldiers and workers avoid these chemicals at biologically relevant amounts. These observations support the hypothesis that chemically mediated spatial separation of the host and the inquiline is an element of a conflict-avoidance strategy in these species.