221 research outputs found
Active thermal metasurfaces for remote heating/cooling by mimicking negative thermal conductivity
Remote temperature control can be obtained by a long-focus thermal lens that
can focus heat fluxes into a spot far away from the back surface of the lens
and create a virtual thermal source/sink in the background material, around
which the temperature field distribution can be remotely controlled by changing
the parameters of the thermal lens. However, due to the lack of negative
thermal conductivity, the existing thermal lenses have extremely short focal
lengths and cannot be used to remotely control the temperature field around the
virtual thermal source/sink. In this study, we theoretically propose a general
approach to equivalently realize negative thermal conductivity by elaborately
distributed active thermal metasurface (ATMS), then use the proposed ATMS to
implement a novel thermal lens with long focal length designed by
transformation thermodynamics, and experimentally verify the performance of the
designed long-focus thermal lens with measured focal length f=19.8mm for remote
heating/cooling. The proposed method expands the scope of the thermal
conductivity and open up new ways to realize unprecedented thermal effects with
effective negative thermal conductivity, such as "thermal surface plasmon
polaritons", thermal superlens, thermal tunneling effect, and thermal invisible
gateway
Analysis of Spatial-Temporal Variation of Agricultural Drought and Its Response to ENSO over the Past 30 Years in the Huang-Huai-Hai Region, China
This study constructed a time series of the seasonal Temperature Vegetation Dryness Index (TVDI) based on a remotely sensed dataset from the National Oceanic and Atmospheric Administration/Advanced Very High Resolution Radiometer (NOAA/AVHRR) and Earth Observing System/Moderate Resolution Imaging Spectroradiometer (EOS/MODIS). We examined the spatiotemporal variation in drought in the Huang-Huai-Hai region of China during the period from 1981 to 2011. Combined with the El Niño and southern oscillation (ENSO) indicator (i.e., the Sea Surface Temperature Anomaly, SSTA of the El Niño 3.4 area), the spatial and temporal relationship of agricultural drought in this region and ENSO was analyzed. The results showed that drought demonstrated a significant downward trend (95% confidence level) which covered 38.01 ~ 55.13% of the farmland in this region. In addition, the largest area of drought reducing appeared in winter. The significant decreasing tendency of agricultural drought started from the late 20th and early 21st centuries, whose variation cycles were mainly between 2.5 to 5 a (year). TVDI series were closely correlated to the ENSO index sequences at the 2.5 to 7 a cycle, and there was a delay from 0.16 to 1.40 a between them. However, the correlation between TVDI and ENSO index series was less. These findings show that there is a relationship between the spatiotemporal changes of agricultural drought in the Huang-Huai-Hai region of China and ENSO events over the recent 30 years
The symbiotic bacteria Alcaligenes faecalis of the entomopathogenic nematodes Oscheius spp. exhibit potential biocontrol of plant- and entomopathogenic fungi
Soil-dwelling entomopathogenic nematodes (EPNs) kill arthropod hosts by injecting their symbiotic bacteria into the host hemolymph and feed on the bacteria and the tissue of the dying host for several generations cycles until the arthropod cadaver is completely depleted. The EPN-bacteria-arthropod cadaver complex represents a rich energy source for the surrounding opportunistic soil fungal biota and other competitors. We hypothesized that EPNs need to protect their food source until depletion and that the EPN symbiotic bacteria produce volatile and non-volatile exudations that deter different soil fungal groups in the soil. We isolated the symbiotic bacteria species (Alcaligenes faecalis) from the EPN Oscheius spp. and ran infectivity bioassays against entomopathogenic fungi (EPF) as well as against plant pathogenic fungi (PPF). We found that both volatile and non-volatile symbiotic bacterial exudations had negative effects on both EPF and PPF. Such deterrent function on functionally different fungal strains suggests a common mode of action of A.faecalis bacterial exudates, which has the potential to influence the structure of soil microbial communities, and could be integrated into pest management programs for increasing crop protection against fungal pathogens
The Zn(II)2Cys6-Type Transcription Factor ADA-6 Regulates Conidiation, Sexual Development, and Oxidative Stress Response in Neurospora crassa
Conidiation and sexual development are critical for reproduction, dispersal and better-adapted survival in many filamentous fungi. The Neurospora crassa gene ada-6 encodes a Zn(II)2Cys6-type transcription factor, whose deletion resulted in reduced conidial production and female sterility. In this study, we confirmed the positive contribution of ada-6 to conidiation and sexual development by detailed phenotypic characterization of its deletion mutant and the complemented mutant. To understand the regulatory mechanisms of ADA-6 in conidiation and sexual development, transcriptomic profiles generated by RNA-seq from the Δada-6 mutant and wild type during conidiation and sexual development were compared. During conidial development, differential expressed genes (DEGs) between the Δada-6 mutant and wild type are mainly involved in oxidation-reduction process and single-organism metabolic process. Several conidiation related genes are positively regulated by ADA-6, including genes that positively regulate conidiation (fluffy and acon-3), and genes preferentially expressed during conidial development (eas, con-6, con-8, con-10, con-13, pcp-1, and NCU9357), as the expression of these genes were lower in the Δada-6 mutant compared to wild type during conidial development. Phenotypic observation of deletion mutants for other genes with unknown function down-regulated by ada-6 deletion revealed that deletion mutants for four genes (NCU00929, NCU05260, NCU00116, and NCU04813) produced less conidia than wild type. Deletion of ada-6 resulted in female sterility, which might be due to that ADA-6 affects oxidation-reduction process and transmembrane transport process, and positively regulates the transcription of pre-2, poi-2, and NCU05832, three key genes participating in sexual development. In both conidiation and the sexual development process, ADA-6 regulates the transcription of cat-3 and other genes participating in reactive oxygen species production according to RNA-seq data, indicating a role of ADA-6 in oxidative stress response. This was further confirmed by the results that deletion of ada-6 led to hypersensitivity to oxidants H2O2 and menadione. Together, these results proved that ADA-6, as a global regulator, plays a crucial role in conidiation, sexual development, and oxidative stress response of N. crassa
Heating of multi‐species upflowing ion beams observed by Cluster on March 28, 2001
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149495/1/epp320083.pd
Salt Freeze-Thaw Damage Characteristics of Concrete based on Computed Tomography
Freeze–thaw damage and salt erosion are important factors that influence the durability of concrete. In this study, degradation laws of concrete in salt freeze–thaw environment were discussed from the microscopic perspective based on the 3D reconstruction of computed tomography images. A damage model based on concrete aggregate volume and porosity was constructed. Furthermore, the main causes of concrete degradation in the salt freeze–thaw environment were analyzed. Results reveal that, with the increase in salt freeze–thaw cycles, the damage of concrete intensifies gradually, and the uniaxial compressive strength declines steadily. Concrete damages have two causes, namely, changes in concrete porosity and variations in concrete aggregate volume. Damages caused by aggregate volume changes are divided into frost heaving and peeling. In accordance with the constructed damage model, the porosity of concrete materials changes slightly, whereas concrete aggregate volume varies significantly. Aggregate volume changes are the main causes of intensified concrete damages and decreased compressive strength. Research conclusions provide theoretical references to disclosing microscopic damage mechanism of concrete in the salt freeze–thaw environment
Mastering Complex Control in MOBA Games with Deep Reinforcement Learning
We study the reinforcement learning problem of complex action control in the
Multi-player Online Battle Arena (MOBA) 1v1 games. This problem involves far
more complicated state and action spaces than those of traditional 1v1 games,
such as Go and Atari series, which makes it very difficult to search any
policies with human-level performance. In this paper, we present a deep
reinforcement learning framework to tackle this problem from the perspectives
of both system and algorithm. Our system is of low coupling and high
scalability, which enables efficient explorations at large scale. Our algorithm
includes several novel strategies, including control dependency decoupling,
action mask, target attention, and dual-clip PPO, with which our proposed
actor-critic network can be effectively trained in our system. Tested on the
MOBA game Honor of Kings, our AI agent, called Tencent Solo, can defeat top
professional human players in full 1v1 games.Comment: AAAI 202
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