A person’s ability to discriminate fine differences in tone frequency is vital for everyday hearing such as listening to speech and music. This ability can be improved through training (i.e., tone frequency learning). Depending on stimulus configurations and training procedures, tone frequency learning can either transfer to new frequencies, which would suggest learning of a general task structure, or show significant frequency specificity, which would suggest either changes in neural representations of trained frequencies, or reweighting of frequency-specific neural responses. Here we tested the hypothesis that frequency specificity in tone frequency learning can be abolished with a double-training procedure. Specifically, participants practiced tone frequency discrimination at 1 or 6 kHz, presumably encoded by different temporal or place coding mechanisms, respectively. The stimuli were brief tone pips known to produce significant specificity. Tone frequency learning was indeed initially highly frequency specific (Experiment 1). However, with additional exposure to the other untrained frequency via an irrelevant temporal interval discrimination task, or even background play during a visual task, learning transferred completely (1-to-6 kHz or 6-to-1 kHz) (Experiments 2-4). These results support general task structure learning, or concept learning in our term, in tone frequency learning despite initial frequency specificity. They also suggest strategies to design efficient auditory training in practical settings.
To get a comprehensive source apportionment of the non-refractory submicron aerosol (NR-PM,), a merged dataset of the organic fragments and the inorganic species, measured by an aerosol chemical speciation monitor (ACSM) during winter 2014 in Shijiazhuang, was used as input for positive matrix factorization (PMF) analysis using the multilinear engine (ME-2) algorithm. Four primary factors were resolved by constraining the profiles of the previously separated organic factors, while three unconstrained secondary factors were resolved. Secondary factors (sum of organic and inorganic components) accounted for over half of NR-PM, during normal days (NDs, 58% or 105.7 mu g m(-3)) and Chinese New Year (CNY, 79% or 72.6 mu g m(-3)). Among the organic components of the total secondary aerosol, 38-48% (8.0-14.4 mu g m(-3)) of the oxygenated organic aerosol (OOA) was attributed to the nitrate-rich OOA (i.e., OOA-NO3) factor, indicating that a part of the OOA was freshly formed and/or had similar volatility as nitrate. In comparison, a portion of 25-26% (5.5-7.7 mu g m(-3)) of the OOA was attributed to the regionally transported sulfate-rich OOA (i.e., OOA-SO4) while 26-37% (7.3-7.4 mu g m(-3)) of the OOA to aged primary aerosol. The positive relationship between OOA-SO4 and aerosol liquid water content (ALWC) in the same air mass suggested an aqueous-phase reaction pathway, which produced nearly half as much OOA as sulfate (12.0-17.0 mu g m(-3)), while photochemical reactions could produce similar amounts of OOA as nitrate (8.6-15.4 mu g m(-3)), as indicated by the positive relationship between OOA-NO3 and O-x (O-3 + NO2). During CNY, the NR-PM, concentrations (91.9 mu g m(-3)) were reduced by similar to 50% when compared to the nonholiday periods (182.7 mu g m(-3)). This reduction was primarily due to the reduced anthropogenic activities, resulting in a 65-89% reduction in the primary emissions from traffic, cooking, biomass burning, and coal combustion, as well as a 1-44% reduction in secondary factors. The results in our study have significant implications for controlling primary emissions, while joint measures over a regional scale are needed to reduce the secondary aerosols in Shijiazhuang.
Per- and polyfluoroalkyl substances (PFAS) have emerged as a major concern in aquatic systems worldwide due to their widespread applications and health concerns. Perfluorooctanoic acid (PFOA) is one of the most-detected PFAS. Yet, a cost-effective technology has been lacking for the degradation of PFAS due to their resistance to conventional treatment processes. To address this challenge, we prepared a novel adsorptive photocatalyst, referred to Fe/TNTs@AC, based on low-cost commercial activated carbon (AC) and TiO2. The composite material exhibited synergistic adsorption and photocatalytic activity and enabled a novel “concentrate-&-destroy” strategy for rapid and complete degradation of PFOA in water. Fe/TNTs@AC was able to adsorb PFOA within a few minutes, thereby effectively concentrating the target contaminant on the photoactive sites. Subsequently, Fe/TNTs@AC was able to degrade >90% of PFOA that was preconcentrated on the solid in 4 h under UV irradiation (254 nm, 21 mW cm‒2), of which 62% was completely mineralized to F−. The efficient photodegradation also regenerated Fe/TNTs@AC, eliminating the need for expensive chemical regenerants, and after six cycles of adsorption/photodegradation, the material showed no significant drop in adsorption capacity or photocatalytic activity. Simulations based on the density functional theory (DFT) revealed that Fe/TNTs@AC adsorbs PFOA in the side-on parallel mode, facilitating the subsequent photocatalytic degradation of PFOA. According to the DFT analysis, scavenger tests, and analysis of degradation intermediates, PFOA decomposition is initiated by direct hole oxidation, which activates the molecule and leads to a series of decarboxylation, C–F bond cleavage, and chain shortening reactions. The innovative “concentrate-&-destroy” strategy may significantly advance conventional adsorption or photochemical treatment of PFAS-contaminated water and holds the potential to degrade PFOA, and potentially other PFAS, more cost-effectively.
Although there are many studies of particulate matter (PM) pollution in Beijing, the sources and processes of secondary PM species during haze periods remain unclear. Limited studies have investigated the PM formation in highly polluted environments under low- and high-relative-humidity (RH) conditions. Herein, we present a systematic comparison of species in submicron particles (PM1) in wintertime Beijing (29 December 2014 to 28 February 2015) for clean periods and pollution periods under low- and high-RH conditions. PM1 species were measured with an aerosol chemical species monitor (ACSM) and an Aethalometer. Sources and processes for organic aerosol (OA) were resolved by positive matrix factorization (PMF) with a multilinear engine 2 (ME-2). The comparisons for clean, low-RH pollution and high-RH pollution periods are made from three different aspects, namely (a) mass concentration, (b) mass fraction and (c) growth rate in diurnal profiles. OA is the dominant component of PM1, with an average mass concentration of 56.7 mu g m(-3) (46 %) during high-RH pollution and 67.7 mu g m(-3) (54 %) during low-RH pollution periods. Sulfate had higher concentration and mass fraction during high-RH pollution periods, while nitrate had higher concentration and mass fraction during low-RH pollution periods. The diurnal variations of nitrate and oxygenated organic aerosol (OOA) showed a daytime increase in their concentrations during all three types of periods. Nitrate had similar growth rates during low-RH (0.40 mu g m(-3) h(-1)) and high-RH (0.55 mu g m(-3) h(-1)) pollution periods. OOA had a higher growth rate during low- RH pollution periods (1.0 mu g m(-3) h(-1)) than during high-RH pollution periods (0.40 mu g m(-3) h(-1)). In contrast, sulfate had a decreasing trend during low-RH pollution periods, while it increased significantly with a growth rate of 0.81 mu g m(-3) h(-1) during high-RH pollution periods. These distinctions in mass concentrations, mass fractions and daytime growth rates may be explained by the difference in the formation processes affected by meteorological conditions. In particular, photochemical oxidation and aqueous-phase processes may both produce sulfate and nitrate. The relative importance of the two pathways, however, differs under different meteorological conditions. Additional OOA formation under high-RH (> 70 %) conditions suggests aqueous-related formation pathways. This study provides a general picture of the haze formation in Beijing under different meteorological conditions.
Abstract Special surface plays a crucial role in nature as well as in industry. Here, the surface morphology evolution of ZnO during wet etching is studied by in situ liquid cell transmission electron microscopy and ex situ wet chemical etching. Many hillocks are observed on the (0001¯) O-terminated surface of ZnO nano/micro belts during in situ etching. Nanoparticles on the apex of the hillocks are observed to be essential for the formation of the hillocks, providing direct experimental evidence of the micromasking mechanism. The surfaces of the hillocks are identified to be 011¯3¯ crystal facets, which is different from the known fact that 011¯1¯ crystal facets appear on the (0001¯) O-terminated surface of ZnO after wet chemical etching. O2 plasma treatment is found to be the key factor for the appearance of 011¯3¯ instead of 011¯1¯ crystal facets after etching for both ZnO nano/micro belts and bulk materials. The synergistic effect of acidic etching and O-rich surface caused by O2 plasma treatment is proposed to be the cause of the appearance of 011¯3¯ crystal facets. This method can be extended to control the surface morphology of other materials during wet chemical etching.
The COP9 signalosome (CSN) is a conserved protein complex, typically composed of eight subunits (designated as CSN1 to CSN8) in higher eukaryotes such as plants and animals, but of fewer subunits in some lower eukaryotes such as yeasts. The CSN complex is originally identified in plants from a genetic screen for mutants that mimic light‐induced photomorphogenic development when grown in the dark. The CSN complex regulates the activity of cullin‐RING ligase (CRL) families of E3 ubiquitin ligase complexes, and play critical roles in regulating gene expression, cell proliferation, and cell cycle. This review aims to summarize the discovery, composition, structure, and function of CSN in the regulation of plant development in response to external (light and temperature) and internal cues (phytohormones).