32 research outputs found
An enhanced pulse position modulation (PPM) in ultra-wideband (UWB) systems
Simplicity, transmission rate, and bit error rate (BER) performance are three major concerns for ultra-wideband (UWB) systems. The main advantage of existing pulse-position modulation (PPM) schemes is simplicity, but their BER performance is poorer than that of an on-off-keying (OOK) modulation scheme, and their transmission rate is lower than that of an OOK scheme. In this research project, I will explore a novel PPM scheme, which can maintain the simplicity of the PPM schemes as well as achieve a BER performance and a transmission rate similar to the OOK scheme. During the research, I will thoroughly investigate the relationship between pulse position allocation and the BER performance and the transmission rate of UWB systems through computer simulations and theoretical analysis, and develop a whole set of design rules for the novel PPM scheme
Oriented Graphene Nanoribbons Embedded in Hexagonal Boron Nitride Trenches
Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the
potential to be used in high-performance graphene-based semiconductor
electronics. However, controlled growth of GNRs on dielectric substrates
remains a challenge. Here, we report the successful growth of GNRs directly on
hexagonal boron nitride substrates with smooth edges and controllable widths
using chemical vapour deposition. The approach is based on a type of template
growth that allows for the in-plane epitaxy of mono-layered GNRs in
nano-trenches on hexagonal boron nitride with edges following a zigzag
direction. The embedded GNR channels show excellent electronic properties, even
at room temperature. Such in-plane hetero-integration of GNRs, which is
compatible with integrated circuit processing, creates a gapped channel with a
width of a few benzene rings, enabling the development of digital integrated
circuitry based on GNRs.Comment: 32 pages, 4 figures, Supplementary informatio
Direct observation of layer-stacking and oriented wrinkles in multilayer hexagonal boron nitride
Hexagonal boron nitride (h-BN) has long been recognized as an ideal substrate
for electronic devices due to its dangling-bond-free surface, insulating nature
and thermal/chemical stability. Therefore, to analyse the lattice structure and
orientation of h-BN crystals becomes important. Here, the stacking order and
wrinkles of h-BN are investigated by transmission electron microscopy (TEM). It
is experimentally confirmed that the layers in the h-BN flakes are arranged in
the AA' stacking. The wrinkles in a form of threefold network throughout the
h-BN crystal are oriented along the armchair direction, and their formation
mechanism was further explored by molecular dynamics simulations. Our findings
provide a deep insight about the microstructure of h-BN and shed light on the
structural design/electronic modulations of two-dimensional crystals.Comment: 7 pages, 5 figure
To Set Up a Logistic Regression Prediction Model for Hepatotoxicity of Chinese Herbal Medicines Based on Traditional Chinese Medicine Theory
Aims. To establish a logistic regression (LR) prediction model for hepatotoxicity of Chinese herbal medicines (HMs) based on traditional Chinese medicine (TCM) theory and to provide a statistical basis for predicting hepatotoxicity of HMs. Methods. The correlations of hepatotoxic and nonhepatotoxic Chinese HMs with four properties, five flavors, and channel tropism were analyzed with chi-square test for two-way unordered categorical data. LR prediction model was established and the accuracy of the prediction by this model was evaluated. Results. The hepatotoxic and nonhepatotoxic Chinese HMs were related with four properties (p<0.05), and the coefficient was 0.178 (p<0.05); also they were related with five flavors (p<0.05), and the coefficient was 0.145 (p<0.05); they were not related with channel tropism (p>0.05). There were totally 12 variables from four properties and five flavors for the LR. Four variables, warm and neutral of the four properties and pungent and salty of five flavors, were selected to establish the LR prediction model, with the cutoff value being 0.204. Conclusions. Warm and neutral of the four properties and pungent and salty of five flavors were the variables to affect the hepatotoxicity. Based on such results, the established LR prediction model had some predictive power for hepatotoxicity of Chinese HMs
Minimizing the programming power of phase change memory by using graphene nanoribbon edge-contact
Nonvolatile phase change random access memory (PCRAM) is regarded as one of
promising candidates for emerging mass storage in the era of Big Data. However,
relatively high programming energy hurdles the further reduction of power
consumption in PCRAM. Utilizing narrow edge-contact of graphene can effectively
reduce the active volume of phase change material in each cell, and therefore
realize low-power operation. Here, we demonstrate that a write energy can be
reduced to about ~53.7 fJ in a cell with ~3 nm-wide graphene nanoribbon (GNR)
as edge-contact, whose cross-sectional area is only ~1 nm2. It is found that
the cycle endurance exhibits an obvious dependence on the bias polarity in the
cell with structure asymmetry. If a positive bias was applied to graphene
electrode, the endurance can be extended at least one order longer than the
case with reversal of polarity. The work represents a great technological
advance for the low power PCRAM and could benefit for in-memory computing in
future.Comment: 14 pages, 4 figure
Isolating hydrogen in hexagonal boron nitride bubbles by a plasma treatment
Atomically thin hexagonal boron nitride (h-BN) is often regarded as an
elastic film that is impermeable to gases. The high stabilities in thermal and
chemical properties allow h-BN to serve as a gas barrier under extreme
conditions.In this work, we demonstrate the isolation of hydrogen in bubbles of
h-BN via plasma treatment.Detailed characterizations reveal that the substrates
do not show chemical change after treatment. The bubbles are found to withstand
thermal treatment in air,even at 800 degree celsius. Scanning transmission
electron microscopy investigation shows that the h-BN multilayer has a unique
aligned porous stacking nature, which is essential for the character of being
transparent to atomic hydrogen but impermeable to hydrogen molecules. We
successfully demonstrated the extraction of hydrogen gases from gaseous
compounds or mixtures containing hydrogen element. The successful production of
hydrogen bubbles on h-BN flakes has potential for further application in
nano/micro-electromechanical systems and hydrogen storage.Comment: 55 pages, 33figure
Linkage between tree species richness and soil microbial diversity improves phosphorus bioavailability
Increased availability of soil phosphorus (P) has recently been recognised as an underlying driving factor for the positive relationship between plant diversity and ecosystem function. The effects of plant diversity on the bioavailable forms of P involved in biologically mediated rhizospheric processes and how the link between plant and soil microbial diversity facilitates soil P bioavailability, however, remain poorly understood. - This study quantified four forms of bioavailable P (CaCl2-P, citric-P, enzyme-P and HCl-P) in mature subtropical forests using a novel biologically based approach, which emulates how rhizospheric processes influence the release and supply of available P. Soil microbial diversity was measured by Illumina high-throughput sequencing. - Our results suggest that tree species richness significantly affects soil microbial diversity (p < 0.05), increases litter decomposition, fine-root biomass and length and soil organic carbon and thus increases the four forms of bioavailable P. A structural equation model that links plants, soil microbes and P forms indicated that soil bacterial and fungal diversity play dominant roles in mediating the effects of tree species richness on soil P bioavailability. - An increase in the biodiversity of plants, soil bacteria and fungi could maintain soil P bioavailability and alleviate soil P limitations. Our results imply that biodiversity strengthens plant and soil feedback and increases P recycling