Showing papers by "Harbin Institute of Technology published in 2012"

Recent advances in micro-/nano-structured hollow spheres for energy applications: From simple to complex systems

Abstract: Hollow micro-/nano-structured materials are now playing an important role in cutting edge innovations for energy conversion and storage technologies such as solar cells, fuel cells, lithium ion batteries and super capacitors. These materials show great promise in addressing growing environmental concerns for cleaner power sources at a time of increasing global demand for energy. In this perspective, we show that complex multi-shelled micro-/nano-materials show significant material advantages in many applications over conventional simple hollow structures. We also summarize the vast array of synthetic strategies used to create multi-shelled hollow structures, and discuss the possible application of these novel materials for power generation and storage. Finally, the emergent challenges and future developments of multi-shelled hollow structures are further discussed.

Stability and Stabilization of Switched Linear Systems With Mode-Dependent Average Dwell Time

Abstract: In this paper, the stability and stabilization problems for a class of switched linear systems with mode-dependent average dwell time (MDADT) are investigated in both continuous-time and discrete-time contexts. The proposed switching law is more applicable in practice than the average dwell time (ADT) switching in which each mode in the underlying system has its own ADT. The stability criteria for switched systems with MDADT in nonlinear setting are firstly derived, by which the conditions for stability and stabilization for linear systems are also presented. A numerical example is given to show the validity and potential of the developed techniques.

Photoredox functionalization of C–H bonds adjacent to a nitrogen atom

Abstract: The functionalization of C–H bonds and the visible light photoredox catalysis represent two prominent challenges in organic chemistry. In this regard, the combination of visible-light catalysis and C–H bond functionalization adjacent to a tertiary amine has been successfully developed in the past three years. In this tutorial review, we aim to give a brief overview of this issue and state the main results obtained in the reactions.

Synthesis of Few-Layer GaSe Nanosheets for High Performance Photodetectors

Abstract: Two-dimensional (2D)semiconductornanomaterials holdgreatpromisesforfutureelectronics and optics. In this paper, a 2D nanosheets of ultrathin GaSe has been prepared by using mechanical cleavage and solvent exfoliation method. Single- and few-layer GaSe nanosheets areexfoliatedonanSiO2/SisubstrateandcharacterizedbyatomicforcemicroscopyandRaman spectroscopy. Ultrathin GaSe-based photodetector shows a fast response of 0.02 s, high responsivityof2.8AW � 1 andhighexternalquantumefficiencyof1367%at254nm,indicating that the two-dimensional nanostructure of GaSe is a new promising material for high performance photodetectors.

(α-NaYbF4:Tm3+)/CaF2 Core/Shell Nanoparticles with Efficient Near-Infrared to Near-Infrared Upconversion for High-Contrast Deep Tissue Bioimaging

Abstract: We describe the development of novel and biocompatible core/shell (α-NaYbF(4):Tm(3+))/CaF(2) nanoparticles that exhibit highly efficient NIR(in)-NIR(out) upconversion (UC) for high contrast and deep bioimaging. When excited at ~980 nm, these nanoparticles emit photoluminescence (PL) peaked at ~800 nm. The quantum yield of this UC PL under low power density excitation (~0.3 W/cm(2)) is 0.6 ± 0.1%. This high UC PL efficiency is realized by suppressing surface quenching effects via heteroepitaxial growth of a biocompatible CaF(2) shell, which results in a 35-fold increase in the intensity of UC PL from the core. Small-animal whole-body UC PL imaging with exceptional contrast (signal-to-background ratio of 310) is shown using BALB/c mice intravenously injected with aqueously dispersed nanoparticles (700 pmol/kg). High-contrast UC PL imaging of deep tissues is also demonstrated, using a nanoparticle-loaded synthetic fibrous mesh wrapped around rat femoral bone and a cuvette with nanoparticle aqueous dispersion covered with a 3.2 cm thick animal tissue (pork).

Synergistic effects from graphene and carbon nanotubes enable flexible and robust electrodes for high-performance supercapacitors.

Abstract: Flexible and lightweight energy storage systems have received tremendous interest recently due to their potential applications in wearable electronics, roll-up displays, and other devices. To manufacture such systems, flexible electrodes with desired mechanical and electrochemical properties are critical. Herein we present a novel method to fabricate conductive, highly flexible, and robust film supercapacitor electrodes based on graphene/MnO2/CNTs nanocomposites. The synergistic effects from graphene, CNTs, and MnO2 deliver outstanding mechanical properties (tensile strength of 48 MPa) and superior electrochemical activity that were not achieved by any of these components alone. These flexible electrodes allow highly active material loading (71 wt % MnO2), areal density (8.80 mg/cm2), and high specific capacitance (372 F/g) with excellent rate capability for supercapacitors without the need of current collectors and binders. The film can also be wound around 0.5 mm diameter rods for fabricating full cells...

Bisphenol S in Urine from the United States and Seven Asian Countries: Occurrence and Human Exposures

Abstract: As concern regarding the toxic effects of bisphenol A (BPA) grows, BPA in many consumer products is gradually being replaced with compounds such as bisphenol S (BPS). Nevertheless, data on the occurrence of BPS in human specimens are limited. In this study, 315 urine samples, collected from the general populations in the United States, China, India, Japan, Korea, Kuwait, Malaysia, and Vietnam, were analyzed for the presence of total BPS (free plus conjugated) concentrations by high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). BPS was detected in 81% of the urine samples analyzed at concentrations ranging from below the limit of quantitation (LOQ; 0.02 ng/mL) to 21 ng/mL (geometric mean: 0.168 ng/mL). The urinary BPS concentration varied among countries, and the highest geometric mean concentration [1.18 ng/mLor 0.933 μg/g creatinine (Cre)] of BPS was found in urine samples from Japan, followed by the United States (0.299 ng/mL, 0.304 μg/g Cre), China (0.226 ng/mL, 0.223 μg/g Cr...

Reliable Fuzzy Control for Active Suspension Systems With Actuator Delay and Fault

Abstract: This paper is focused on reliable fuzzy H∞ controller design for active suspension systems with actuator delay and fault. The Takagi-Sugeno (T-S) fuzzy model approach is adapted in this study with the consideration of the sprung and the unsprung mass variation, the actuator delay and fault, and other suspension performances. By the utilization of the parallel-distributed compensation scheme, a reliable fuzzy H∞ performance analysis criterion is derived for the proposed T-S fuzzy model. Then, a reliable fuzzy H∞ controller is designed such that the resulting T-S fuzzy system is reliable in the sense that it is asymptotically stable and has the prescribed H∞ performance under given constraints. The existence condition of the reliable fuzzy H∞ controller is obtained in terms of linear matrix inequalities (LMIs) Finally, a quarter- vehicle suspension model is used to demonstrate the effectiveness and potential of the proposed design techniques.

Critical factors on manufacturing processes of natural fibre composites

Abstract: Elevated environmental awareness of the general public in reducing carbon footprints and the use nonnaturally decomposed solid wastes has resulted in an increasing use of natural materials, biodegradable and recyclable polymers and their composites for a wide range of engineering applications. The properties of natural fibre reinforced polymer composites are generally governed by the pre-treated process of fibre and the manufacturing process of the composites. These properties can be tailored for various types of applications by properly selecting suitable fibres, matrices, additives and production methods. Besides, due to the complexity of fibre structures, different mechanical performances of the composites are obtained even with the use of the same fibre types with different matrices. Some critical issues like poor wettability, poor bonding and degradation at the fibre/matrix interface (a hydrophilic and hydrophobic effect) and damage of the fibre during the manufacturing process are the main causes of the reduction of the composites’ strength. In this paper, different manufacturing processes and their suitability for natural fibre composites, based on the materials, mechanical and thermal properties of the fibres and matrices are discussed in detail.

Occurrence of eight bisphenol analogues in indoor dust from the United States and several Asian countries: implications for human exposure.

Abstract: Bisphenol A has been reported to be a ubiquitous contaminant in indoor dust, and human exposure to this compound is well documented. Information on the occurrence of and human exposure to other bisphenol analogues is limited. In this study, eight bisphenol analogues, namely 2,2-bis(4-hydroxyphenyl)propane (BPA), 4,4′-(hexafluoroisopropylidene)diphenol (BPAF), 4,4′-(1-phenylethylidene)bisphenol (BPAP), 2,2-bis(4-hydroxyphenyl)butane (BPB), 4,4′-dihydroxydiphenylmethane (BPF), 4,4′-(1,4-phenylenediisopropylidene)bisphenol (BPP), 4,4′- sulfonyldiphenol (BPS), and 4,4′-cyclohexylidenebisphenol (BPZ), were determined in indoor dust samples (n = 156) collected from the United States (U.S.), China, Japan, and Korea. Samples were extracted by solid–liquid extraction, purified by automated solid phase extraction methods, and determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The total concentrations of bisphenols (∑BPs; sum of eight bisphenols) in dust were in the range of 0.026–111 μg/g (geo...

A Novel Approach to Filter Design for T–S Fuzzy Discrete-Time Systems With Time-Varying Delay

Abstract: In this paper, the problem of l2- l∞ filtering for a class of discrete-time Takagi-Sugeno (T-S) fuzzy time-varying delay systems is studied. Our attention is focused on the design of full- and reduced-order filters that guarantee the filtering error system to be asymptotically stable with a prescribed H∞ performance. Sufficient conditions for the obtained filtering error system are proposed by applying an input-output approach and a two-term approximation method, which is employed to approximate the time-varying delay. The corresponding full- and reduced-order filter design is cast into a convex optimization problem, which can be efficiently solved by standard numerical algorithms. Finally, simulation examples are provided to illustrate the effectiveness of the proposed approaches.

Neighborhood Component Feature Selection for High-Dimensional Data

Abstract: Feature selection is of considerable importance in data mining and machine learning, especially for high dimensional data. In this paper, we propose a novel nearest neighbor-based feature weighting algorithm, which learns a feature weighting vector by maximizing the expected leave-one-out classification accuracy with a regularization term. The algorithm makes no parametric assumptions about the distribution of the data and scales naturally to multiclass problems. Experiments conducted on artificial and real data sets demonstrate that the proposed algorithm is largely insensitive to the increase in the number of irrelevant features and performs better than the state-of-the-art methods in most cases.

Core/Shell NaGdF4:Nd3+/NaGdF4 Nanocrystals with Efficient Near-Infrared to Near-Infrared Downconversion Photoluminescence for Bioimaging Applications

Abstract: We have synthesized core/shell NaGdF4:Nd3+/NaGdF4 nanocrystals with an average size of 15 nm and exceptionally high photoluminescence (PL) quantum yield. When excited at 740 nm, the nanocrystals manifest spectrally distinguished, near-infrared to near-infrared (NIR-to-NIR) downconversion PL peaked at ∼900, ∼1050, and ∼1300 nm. The absolute quantum yield of NIR-to-NIR PL reached 40% for core–shell nanoparticles dispersed in hexane. Time-resolved PL measurements revealed that this high quantum yield was achieved through suppression of nonradiative recombination originating from surface states and cross relaxations between dopants. NaGdF4:Nd3+/NaGdF4 nanocrystals, synthesized in organic media, were further converted to be water-dispersible by eliminating the capping ligand of oleic acid. NIR-to-NIR PL bioimaging was demonstrated both in vitro and in vivo through visualization of the NIR-to-NIR PL at ∼900 nm under incoherent lamp light excitation. The fact that both excitation and the PL of these nanocrystals...

Adaptive Sliding Mode Fault Tolerant Attitude Tracking Control for Flexible Spacecraft Under Actuator Saturation

Abstract: A novel fault tolerant attitude tracking control scheme is developed for flexible spacecraft with partial loss of actuator effectiveness fault. Neural networks are first introduced to account for system uncertainties, and an adaptive sliding mode controller is derived by using on-line updating law to estimate the bound of actuator fault such that any information of the fault is not required. To further address actuator saturation problem, a modified fault tolerant control law is then presented to ensure that the resulting control signal will never incur saturation. It is shown that the roll, pitch and yaw angle trajectories can globally asymptotically track the desired attitude in the face of faulty actuator, system uncertainties, external disturbances and even actuator saturation. A simulation example of a flexible spacecraft is given to illustrate the effectiveness of the proposed controller.

Robust Sliding Mode Control for Discrete Stochastic Systems With Mixed Time Delays, Randomly Occurring Uncertainties, and Randomly Occurring Nonlinearities

Abstract: This paper investigates the robust sliding mode control (SMC) problem for a class of uncertain nonlinear stochastic systems with mixed time delays. Both the sectorlike nonlinearities and the norm-bounded uncertainties enter into the system in random ways, and such randomly occurring uncertainties and randomly occurring nonlinearities obey certain mutually uncorrelated Bernoulli distributed white noise sequences. The mixed time delays consist of both the discrete and the distributed delays. The time-varying delays are allowed in state. By employing the idea of delay fractioning and constructing a new Lyapunov-Krasovskii functional, sufficient conditions are established to ensure the stability of the system dynamics in the specified sliding surface by solving a certain semidefinite programming problem. A full-state feedback SMC law is designed to guarantee the reaching condition. A simulation example is given to demonstrate the effectiveness of the proposed SMC scheme.

Indirect evaporative cooling : Past, present and future potentials

Abstract: This paper reported a review based study into the Indirect Evaporative Cooling (IEC) technology, which was undertaken from a variety of aspects including background, history, current status, concept, standardisation, system configuration, operational mode, research and industrialisation, market prospect and barriers, as well as the future focuses on RD good distribution of the water stream across the wet surface of the exchanger plate (tube) and adequate (matching up the evaporation) control of the water flow rate are critical to achieving the expected system performance. It was noticed that the IEC devices were always in combined operation with other cooling measures and the commonly available IEC related operational modes are (1) IEC/DEC system; (2) IEC/DEC/mechanical vapour compression system; (3) IEC/desiccant system; (4) IEC/chilled water system; and (5) IEC/heat pipe system. The future potential operational modes may also cover the IEC-inclusive fan coil units, air handle units, cooling towers, solar driven desiccant cycle, and Rankine cycle based power generation system etc. Future works on the IEC technology may focus on (1) heat exchanger structure and material; (2) water flowing, distribution and treatment; (3) incorporation of the IEC components into conventional air conditioning products to enable combined operation between the IEC and other cooling devices; (4) economic, environment and social impacts; (5) standardisation and legislation; (6) public awareness and other dissemination measures; and (7) manufacturing and commercialisation. All above addressed efforts may help increase the market ratio of the IEC to around 20% in the next 20 years, which will lead to significant saving of fossil fuel consumption and cut of carbon emission related to buildings.

A high thermoelectric figure of merit ZT > 1 in Ba heavily doped BiCuSeO oxyselenides

Abstract: A high ZT value of ∼1.1 at 923 K in the BiCuSeO system is achieved via heavily doping with Ba and refining grain sizes (200–400 nm), which is higher than any thermoelectric oxide. Excellent thermal and chemical stabilities up to 923 K and high thermoelectric performance confirm that the BiCuSeO system is promising for thermoelectric power generation applications.

Efficient Subgraph Matching on Billion Node Graphs

Abstract: The ability to handle large scale graph data is crucial to an increasing number of applications. Much work has been dedicated to supporting basic graph operations such as subgraph matching, reachability, regular expression matching, etc. In many cases, graph indices are employed to speed up query processing. Typically, most indices require either super-linear indexing time or super-linear indexing space. Unfortunately, for very large graphs, super-linear approaches are almost always infeasible. In this paper, we study the problem of subgraph matching on billion-node graphs. We present a novel algorithm that supports efficient subgraph matching for graphs deployed on a distributed memory store. Instead of relying on super-linear indices, we use efficient graph exploration and massive parallel computing for query processing. Our experimental results demonstrate the feasibility of performing subgraph matching on web-scale graph data.