184 research outputs found
Performance evaluation of the GCR block ACK mechanism in IEEE 802.11aa networks
With the growing demand for multimedia services, video streams have become major traffic sources
in the Internet. However, it is challenging to transmit multimedia streams over IEEE 802.11 Wireless
Local Area Networks (WLANs) with high performance and reliability. As a solution to improve
system efficiency, a new standard, 802.11aa, is introduced to provide much more reliable
and robust transfer of video stream by introducing several new service features. In this thesis,
we analyze the performance of the Groupcast with Retries (GCR) Block ACK scheme as one of
the most important features in this standard based on Markov chain models. The properties of
groupcast service and block acknowledgement will be merged together in our model. Besides, we
take into account the memory feature of the wireless channel and extend it into multi-receivers
in accordance with the standard. In particular, the proposed model is built on fixed block size,
a type of communication technique in which the block size is kept as fixed during transmission.
Furthermore, the lost position of a packet in the block is taken into consideration for in-depth
analysis.
Numerical results show that under the groupcast with constant retry limit and fixed block size
transmission mechanism, the network throughput will be reduced with the growing number of
receiving terminals. Compared with the throughput result for the variable block size mechanism
obtained from our previous study, we found that with the increasing number of stations, the
performance of the fixed block size mechanism is much more stable with respect to the number
of stations and channel memory property. However, the variable block size transmission scheme
exhibits much better throughput performance when the number of stations is small
The Environmental Plasticity of Diverse Body Color Caused by Extremely Long Photoperiods and High Temperature in Saccharosydne procerus (Homoptera: Delphacidae)
Melanization reflects not only body color variation but also environmental plasticity. It is a strategy that helps insects adapt to environmental change. Different color morphs may have distinct life history traits, e.g., development time, growth rate, and body weight. The green slender planthopper Saccharosydne procerus (Matsumura) is the main pest of water bamboo (Zizania latifolia). This insect has two color morphs. The present study explored the influence of photoperiod and its interaction with temperature in nymph stage on adult melanism. Additionally, the longevity, fecundity, mating rate, and hatching rate of S. procerus were examined to determine whether the fitness of the insect was influenced by melanism under different temperature and photoperiod. The results showed that a greater number of melanic morphs occurred if the photoperiod was extremely long. A two-factor ANOVA showed that temperature and photoperiod both have a significant influence on melanism. The percentages of variation explained by these factors were 45.53% and 48.71%, respectively. Moreover, melanic morphs had greater advantages than non-melanic morphs under an environmental regime of high temperatures and a long photoperiod, whereas non-melanic morphs were better adapted to cold temperatures and a short photoperiod. These results cannot be explained by the thermal melanism hypothesis. Thus, it may be unavailable to seek to explain melanism in terms of only one hypothesis
mcLARO: Multi-Contrast Learned Acquisition and Reconstruction Optimization for simultaneous quantitative multi-parametric mapping
Purpose: To develop a method for rapid sub-millimeter T1, T2, T2* and QSM
mapping in a single scan using multi-contrast Learned Acquisition and
Reconstruction Optimization (mcLARO).
Methods: A pulse sequence was developed by interleaving inversion recovery
and T2 magnetization preparations and single-echo and multi-echo gradient echo
acquisitions, which sensitized k-space data to T1, T2, T2* and magnetic
susceptibility. The proposed mcLARO used a deep learning framework to optimize
both the multi-contrast k-space under-sampling pattern and the image
reconstruction based on image feature fusion. The proposed mcLARO method with
R=8 under-sampling was validated in a retrospective ablation study using fully
sampled data as reference and evaluated in a prospective study using separately
acquired conventionally sampled quantitative maps as reference standard.
Results: The retrospective ablation study showed improved image sharpness of
mcLARO compared to the baseline network without multi-contrast sampling pattern
optimization or image feature fusion, and negligible bias and narrow 95% limits
of agreement on regional T1, T2, T2* and QSM values were obtained by the
under-sampled reconstructions compared to the fully sampled reconstruction. The
prospective study showed small or negligible bias and narrow 95% limits of
agreement on regional T1, T2, T2* and QSM values by mcLARO (5:39 mins) compared
to reference scans (40:03 mins in total).
Conclusion: mcLARO enabled fast sub-millimeter T1, T2, T2* and QSM mapping in
a single scan
Global Alignment of Carbon Nanotubes via High Precision Microfluidic Dead-End Filtration
Single wall carbon nanotubes (SWCNTs) dispersed by negatively charged sodium deoxycholate (DOC) or positively charged cetrimonium bromide (CTAB) are shown to assemble into aligned films (3.8 cm2) on polycarbonate membranes by slow flow dead-end filtration. Global alignment (S2D max â 0.85) is obtained on both pristine polyvinylpyrrolidone (PVP) coated membranes and those with an intentional 150â600 nm groove pattern from hot embossing. In all cases, a custom microfluidic setup capable of precise control and measurement of the volume rate, transmembrane pressure, and the filtration resistance is used to follow SWCNT film formation. Conditions associated with the formation of SWCNT crystallites or their global alignment are identified and these are discussed in terms of membrane fouling and the interaction potential between the surface of the membrane and nanotubes. SWCNT alignment is characterized by cross-polarized microscopy, atomic force microscopy, scanning electron microscopy (SEM), and Raman spectroscopy
Density effects on nanoparticle transport in the hyporheic zone
A carbon solution composed of nanoparticles was used in experiments designed to explore nanoparticle transport characteristics within the hyporheic zone of a riverbed. Experiments and numerical simulations demonstrated that nanoparticle transport in the hyporheic zone is affected by hydraulic head gradients due to river flow-bedform interactions as well as density gradients associated with the nano-carbon solution. Differences with similar flow/transport situations were examined, and it was found that particulate-enhanced density can change hyporheic transport appreciably. In addition to density, particle settling enhances downward movement of the nano-carbon plume in the riverbed. While nanoparticle transport in the upper hyporheic zone is largely controlled by advection due to flow driven by head gradients at the bed surface, density gradients and particle settling influence the transport process significantly in the lower hyporheic zone. During the transport process, nanoparticles become deposited due to attachment to sand particles and filtration by small pores in the bed. Compared with transport where density variations are minimal, the particulate-induced density gradient induces downward transport of nanoparticles and entrained liquids, leading to deposition/accumulation at the base of the bed
Characterization of a Novel, Cold-Adapted, and Thermostable Laccase-Like Enzyme With High Tolerance for Organic Solvents and Salt and Potent Dye Decolorization Ability, Derived From a Marine Metagenomic Library
Synthetic dyes are widely used in many industries, but they cause serious environmental problems due to their carcinogenic and mutagenic properties. In contrast to traditional physical and chemical treatments, biodegradation is generally considered an environmental-friendly, efficient, and inexpensive way to eliminate dye contaminants. Here, a novel laccase-like enzyme Lac1326 was cloned from a marine metagenomic library. It showed a maximum activity at 60°C, and it retained more than 40% of its maximal activity at 10°C and more than 50% at 20â70°C. Interestingly, the laccase behaved stably below 50°C, even in commonly used water-miscible organic solvents. The enzyme decolorized all tested dyes with high decolorization efficiency. This thermostable enzyme with high decolorization activity and excellent tolerance of organic solvents and salt has remarkable potential for bioremediation of dye wastewater. It is thus proposed as an industrial enzyme
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