127 research outputs found
Study of the Breathing Effect of Reciprocating Compressor Under Duty Cycle Regulation (DCR) Capacity Control by Simulation and Experiment
Duty Cycle Regulation is a new method for capacity control of reciprocating compressor. Like other suction-valve-unloaded methods, the DCR method would inevitably cause the Breathing Effect. In this article, the internal flow and heat transfer in the compressor under DCR control are analyzed using CFD simulation. The geometrical model of the breathing effect has already been worked out. The numerical analysis and experimental research have been fulfilled. The flow conditions of the breathing effect during the DCR process, the temperature field in suction chamber and cylinder after some breathing effect cycles, and the capacity regulation results using DCR method are obtained. FLUENT is used to compute temperature variation after some periods of regulation. It is found that after 20 periods of regulation the suction temperature is about 32K higher than the one in normal process of compressor. Through the numerical analysis and experiment, it could be concluded that the temperature rise resulted from the breathing effect affects the suction and discharge temperature, capacity and energy consumption. Based on the results of this work, the performance of reciprocating compressor could be improved by eliminating the influence of breathing effect
Stable and highly sensitive gas sensors based on semiconducting oxide nanobelts
©2002 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: : http://link.aip.org/link/?APPLAB/81/1869/1DOI:10.1063/1.1504867Gas sensors have been fabricated using the single-crystalline SnO₂ nanobelts. Electrical
characterization showed that the contacts were ohmic and the nanobelts were sensitive to
environmental polluting species like CO and NO₂ , as well as to ethanol for breath analyzers and
food control applications. The sensor response, defined as the relative variation in conductance due
to the introduction of the gas, is 4160% for 250 ppm of ethanol and 21550% for 0.5 ppm NO₂ at
400 °C. The results demonstrate the potential of fabricating nanosized sensors using the integrity of
a single nanobelt with a sensitivity at the level of a few ppb
UperFormer: A Multi-scale Transformer-based Decoder for Semantic Segmentation
While a large number of recent works on semantic segmentation focus on
designing and incorporating a transformer-based encoder, much less attention
and vigor have been devoted to transformer-based decoders. For such a task
whose hallmark quest is pixel-accurate prediction, we argue that the decoder
stage is just as crucial as that of the encoder in achieving superior
segmentation performance, by disentangling and refining the high-level cues and
working out object boundaries with pixel-level precision. In this paper, we
propose a novel transformer-based decoder called UperFormer, which is
plug-and-play for hierarchical encoders and attains high quality segmentation
results regardless of encoder architecture. UperFormer is equipped with
carefully designed multi-head skip attention units and novel upsampling
operations. Multi-head skip attention is able to fuse multi-scale features from
backbones with those in decoders. The upsampling operation, which incorporates
feature from encoder, can be more friendly for object localization. It brings a
0.4% to 3.2% increase compared with traditional upsampling methods. By
combining UperFormer with Swin Transformer (Swin-T), a fully transformer-based
symmetric network is formed for semantic segmentation tasks. Extensive
experiments show that our proposed approach is highly effective and
computationally efficient. On Cityscapes dataset, we achieve state-of-the-art
performance. On the more challenging ADE20K dataset, our best model yields a
single-scale mIoU of 50.18, and a multi-scale mIoU of 51.8, which is on-par
with the current state-of-art model, while we drastically cut the number of
FLOPs by 53.5%. Our source code and models are publicly available at:
https://github.com/shiwt03/UperForme
High-density vertically aligned multiwalled carbon nanotubes with tubular structures
Ammonia (NH3) gas was thought to be essential for the growth of vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) and led to the formation of bamboo-like structures. Here, we show that VA-MWCNTs with ideal tubular structures can be grown on substrates by various mixed gases with or without NH3 gas. The growth of these VA-MWCNTs is guided by a growth model that combined the dissociative adsorption of acetylene molecules (C2H2) and the successive vapor-liquid-solid growth mechanism. Results indicate that the key factor for growing these VA-MWCNTs is a balance between the decomposition rate of the C2H2 molecules on the iron catalyst and the subsequent diffusion and segregation rates of carbon
Structural control of vertically aligned multiwalled carbon nanotubes by radio-frequency plasmas
Plasma-enhanced chemical vapor deposition is the only technique for growing individual vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) at desired locations. Inferior graphitic order has been a long-standing issue that has prevented realistic applications of these VA-MWCNTs. Previously, these VA-MWCNTs were grown by a one-plasma approach. Here, we demonstrate the capability of controlling graphitic order and diameters of VA-MWCNTs by decoupling the functions of the conventional single plasma into a dual-plasma configuration. Our results indicate that the ionic flux and kinetic energy of the growth species are important for improving graphitic order of VA-MWCMTs
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Phosphor-converted white light-emitting diodes for indoor illumination need to be warm-white (i.e., correlated color temperature \u3c4000 \u3eK) with good color rendition (i.e., color rendering index \u3e80). However, no single-phosphor, single-emitting-center-converted white light-emitting diodes can simultaneously satisfy the color temperature and rendition requirements due to the lack of sufficient red spectral component in the phosphors’ emission spectrum. Here, we report a new yellow Ba0.93Eu0.07Al2O4phosphor that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component. Warm-white emissions with correlated color temperature 80 were readily achieved when combining the Ba0.93Eu0.07Al2O4 phosphor with a blue light-emitting diode (440–470 nm). This study demonstrates that warm-white light-emitting diodes with high color rendition (i.e., color rendering index \u3e80) can be achieved based on single-phosphor, single-emitting-center conversion
Tracking the Evolution of HIV/AIDS in China from 1989–2009 to Inform Future Prevention and Control Efforts
BACKGROUND: To determine policy implications, this analysis tracks the evolution of HIV/AIDS infection across China to understand current trends and potential risk factors. METHODS AND PRINCIPAL FINDINGS: A retrospective study with spatial analytical model and multilevel spatial models was conducted among 326,157 HIV/AIDS cases reported from 1989-2009. The results indicate that the distribution of HIV/AIDS was clustered at the county level with different directional distributions across China from 2003 to 2009. Compared to 2003, by 2009 there was a 122% increase in HIV cases among rural residents, 294% increase among urban residents, 211% increase among migrants, and 237% increase among permanent residents. The overall proportion of HIV by different routes of transmission showed dramatic changes with a 504% increase in sexual transmission of HIV, 90% decrease in blood/plasma transmission, and 35% decrease in injecting drug user transmission. Sexual transmission was the major transmission route among women (44%) and the elderly (59% in men, 44% in women) as well as among permanent (36%) and urban residents (33%). Among those <65 years old, women increased more than men, but among those ≥ 65 years, men increased more than women. Migrants contributed to the variance of HIV infection between counties but not within counties. The length of highway and urbanization combined with illiteracy were risk factors for HIV/AIDS. CONCLUSIONS/SIGNIFICANCE: Rates of HIV/AIDS among permanent urban residents, particularly women and elderly men, have increased significantly in recent years. To prevent HIV from spreading further among the general population, additional attention should be paid to these populations as well as to migrants
Fabrication of CuO nanoparticle interlinked microsphere cages by solution method
Here we report a very simple method to convert conventional CuO powders to nanoparticle interlinked microsphere cages by solution method. CuO is dissolved into aqueous ammonia, and the solution is diluted by alcohol and dip coating onto a glass substrate. Drying at 80 °C, the nanostructures with bunchy nanoparticles of Cu(OH)2can be formed. After the substrate immerges into the solution and we vaporize the solution, hollow microspheres can be formed onto the substrate. There are three phases in the as-prepared samples, monoclinic tenorite CuO, orthorhombic Cu(OH)2, and monoclinic carbonatodiamminecopper(II) (Cu(NH3)2CO3). After annealing at 150 °C, the products convert to CuO completely. At annealing temperature above 350 °C, the hollow microspheres became nanoparticle interlinked cages
The Effects of Hydrogen Peroxide on the Circadian Rhythms of Microcystis aeruginosa
Background: The cyanobacterium Microcystis aeruginosa is one of the principal bloom-forming cyanobacteria present in a wide range of freshwater ecosystems. M. aeruginosa produces cyanotoxins, which can harm human and animal health. Many metabolic pathways in M. aeruginosa, including photosynthesis and microcystin synthesis, are controlled by its circadian rhythms. However, whether xenobiotics affect the cyanobacterial circadian system and change its growth, physiology and biochemistry is unknown. We used real-time PCR to study the effect of hydrogen peroxide (H2O2) on the expression of clock genes and some circadian genes in M. aeruginosa during the light/dark (LD) cycle. Results: The results revealed that H 2O 2 changes the expression patterns of clock genes (kaiA, kaiB, kaiC and sasA) and significantly decreases the transcript levels of kaiB, kaiC and sasA. H2O2 treatment also decreased the transcription of circadian genes, such as photosynthesis-related genes (psaB, psbD1 and rbcL) and microcystin-related genes (mcyA, mcyD and mcyH), and changed their circadian expression patterns. Moreover, the physiological functions of M. aeruginosa, including its growth and microcystin synthesis, were greatly influenced by H 2O 2 treatment during LD. These results indicate that changes in the cyanobacterial circadian system can affect its physiological and metabolic pathways. Conclusion: Our findings show that a xenobiotic can change the circadian expression patterns of its clock genes t
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