探析工程机械设备的“三分用,七分养”

随着工程建设项目的不断增加,机械化施工越来越普及,如何提高机械设备的工作效率、降低使用成本、延长使用寿命、确保安全施工,是所有工程机械用户所关心的共性问题。笔者从事工程机械专业技术教学、培训二十多年,根据自己的经验,对柴油机、变矩器和变速器、液压系统、制动系统、电器设备和轮胎的维护保养要点进行了简要的分析说明。帮助用户走出工程机械维护保养工作中的误区,解决用户所面临的实际问题。

Chemical constituents of marine medicinal mangrove plant Sonneratia caseolaris

Twenty-four compounds including eight steroids （1-8）, nine triterpenoids （9-16, 24）, three flavonoids （20-22）, and four benzenecarboxylic derivatives （17-19, 23） were isolated and identified from stems and twigs of medicinal mangrove plant Sonneratia caseolaris. The structures of the isolated compounds were determined by extensive analysis of their spectroscopic data. Among these rnetabolites, compounds 1, 4-20 and 22-24 were isolated and identified for the first time from S. caseolaris. In the in vitro cytotoxic assay against SMMC-7721 human hepatoma cells, compound 21 （3＇,4＇,5,7-tetrahydroxyflavone） exhibited significant activity with IC50 2.8 μg/mL, while oleanolic acid （14）, 3,3＇-di-O-methyl ether ellagic acid （18）, and 3,3＇,4-O-tri-O-methyl ether ellagic acid （19） showed weak activity. None of these compounds displayed significant antibacterial activites.

Evapotranspiration Estimation Based on MODIS Products and Surface Energy Balance Algorithms for Land(SEBAL) Model in Sanjiang Plain,Northeast China

In this study,the Surface Energy Balance Algorithms for Land(SEBAL) model and Moderate Resolution Imaging Spectroradiometer(MODIS) products from Terra satellite were combined with meteorological data to estimate evapotranspiration(ET) over the Sanjiang Plain,Northeast China.Land cover/land use was classified by using a recursive partitioning and regression tree with MODIS Normalized Difference Vegetation Index(NDVI) time series data,which were reconstructed based on the Savitzky-Golay filtering approach.The MODIS product Quality Assessment Science Data Sets(QA-SDS) was analyzed and all scenes with valid data covering more than 75% of the Sanjiang Plain were selected for the SEBAL modeling.This provided 12 overpasses during 184-day growing season from May 1st to October 31st,2006.Daily ET estimated by the SEBAL model was misestimaed at the range of-11.29% to 27.57% compared with that measured by Eddy Covariance system(10.52% on average).The validation results show that seasonal ET from the SEBAL model is comparable to that from ground observation within 8.86% of deviation.Our results reveal that the time series daily ET of different land cover/use increases from vegetation on-going until June or July and then decreases as vegetation senesced.Seasonal ET is lower in dry farmland(average(Ave):491 mm) and paddy field(Ave:522 mm) and increases in wetlands to more than 586 mm.As expected,higher seasonal ET values are observed for the Xingkai Lake in the southeastern part of the Sanjiang Plain(Ave:823 mm),broadleaf forest(Ave:666 mm) and mixed wood(Ave:622 mm) in the southern/western Sanjiang Plain.The ET estimation with SEBAL using MODIS products can provide decision support for operational water management issues.

A new variable step-size LMS method and its application in DOA estimation of OFDMA signals

To meet the requirements of quick positioning of mobile terminals from base stations(BSs)or third-party devices,as well as to improve the convergence speed and reduce the steady state maladjustment of the least mean square(LMS)method,a new logarithmic-sigmoid variable step-size LMS(LG-SVSLMS)was proposed and applied to estimate the direction of arrival(DOA)of orthogonal frequency division multiple access(OFDMA)signals.Based on the proposed LG-SVSLMS,a non-blind DOA estimation system for OFDMA signals was constructed.The proposed LG-SVSLMS adopts a new multi-parameter step-size update function which combines the sigmoid function and the logarithmic function.It controls the adjustment magnitude of step-size during the initial and steady state phases of the LMS method to achieve both a high convergence speed and low steady state maladjustment.Finally,simulation was conducted to verify the performance of the LG-SVSLMS.The simulation results show that the non-blind DOA estimation system based on the LG-SVSLMS can accurately estimate the DOA of the target signal in the scenario where interference signals from multi-source and multi-path fading signals arrive at the third-party devices asynchronously with the target signal,and the estimation deviation is within±3°.The non-blind DOA estimation for OFDMA signals with the proposed LG-SVSLMS is of great significance for the instant positioning technology of mobile terminals based on the adaptive antenna array.

Quantum Information Splitting of an Arbitrary Three-Qubit State by Using Cluster States and Bell States

A new application of cluster states is investigated for quantum information splitting （QIS） of an arbitrary three-qubit state. In our scheme, a four-qubit cluster state and a Bell state are shared by a sender （Alice）, a controller （Charlie）, and a receiver （Bob）. Both the sender and controller only need to perform Bell-state measurements （BSMs）, the receiver can reconstruct the arbitrary three-qubit state by performing some appropriately unitary transformations on his qubits after he knows the measured results of both the sender and the controller. This QIS scheme is deterministic.

A Ternary Ruthenium（II） 2,2′ ：6′,2″-Terpyridine Complex Having Intramolecular Tr-Tr Stacking Interaction with Ancillary Benzyl Groups of the Mixed Ligand

A new ruthenium（II） complex with two different types oftridentate ligands was synthesized, 2,2′：6′,2″-terpyridine （tpy） and 2,6-Bis（（N-benzyl）aminomethyl）pyridine （bbap）： [Ru（tpy）（bbap）]2＋ （1）. This compound was designed to form intramolecular π-π stacking interaction between tpy and substituted benzyl groups of bbap. The single-crystal X-ray diffraction analysis revealed that 1 crystallized with orthorhombic space group Aea2 and the ruthenium center has a distorted octahedral coordination geometry with fully chelated tpy and bbap ligands. Simultaneously, in the crystal structure of 1, the central part of ligating tpy was stacked and sandwiched with a pair of capped benzyl substituent groups of bbap, the nearest atomic distance being N...C = 3.28 A.

Interactions Among Peakons, Dromions, and Compactons for a （2＋1）-Dimensional Soliton System

Starting from the known variable separation excitations of a(2 + 1)-dimensional generalized Ablowitz-Kaup-Newell-Segur system,rich coherent structures can be derived.The interactions among different types of solitary waves like peakons,dromions,and compactons are investigated and some novel features or interesting behaviors are revealed.The results show that the interactions for peakon-dromion,compacton-dromion,and peakon-compacton may be completely nonelastic or completely elastic.

Three Dimension Finite Element Analysis of the Influence Factors of Stress Responses in the Roadbed and Ground under a Moving Load

Focusing on the vibration of the roadbed and ground induced by high-speed train load, a three dimensional finite element model which includes the roadbed and horizontal layered site is established to study how the site conditions, the load moving speed and the depth of the soil element influence the soil element stress response. Based on a track-subsoil analytical model in which the rail is simulated as an Euler-Bernoulli beam resting on Winkler foundation in the vertical plane, the reaction force between the sleeper and roadbed excited by a single axle is presented, and then that is exerted on relevant elements to simulate the moving load. The dynamic response in the roadbed and subsoil excited by a single axle moving load is computed based on the parallel computing platform of the ABAQUS finite element software, and the stress time-history, stress path and curves of the principal stress axes rotation of the soil element under the track are presented. The results show that： the soil element stress path is an apple-shaped curve in the horizontal shear stress τd versus the stress difference （σsh - σch ）/2 coordinate system; the principal stress axes rotate 180° for the soil element under the load moving line during the load running, and the stress state changes from the pure shear to triaxial shear and then back to the pure shear again. The element dynamic stress increases as the moving load speed increases, which increases sharply when the load speed approaches the Rayleigh wave velocity of soil layer; the site conditions and the soil element depth affect the soil element stress path significantly.

Photolysis of benzophenone with two-step two-laser excitation

The first laser excites a molecule to a lower triplet state and another sequential laser excites it resonantly to higher triplet states or makes it ionization. This two-step two-laser method provides a novel way to study the electron transfer or charge transfer of excited molecules. The higher excited benzophenone and its radical cation can be observed under the time-resolved absorption method when it was excited to lower triplet state by one laser and another one exciting it to higher triplet states resonantly. The higher excited benzophenone molecules undergoing inter-molecular hydrogen abstraction with iso-propylalcohol molecules are faster than the lower ones.

Three dimensional carbon substrate materials for electrolysis of water

Water splitting is an important approach for energy conversion to obtain hydrogen and oxygen. Apart from solar water splitting, electrochemical method plays a key role in the booming field, and it is urgent to develop novel and efficient catalysts to accelerate water splitting reaction. Recently, newly emerging self-supported materials, especially three dimensional（3D） carbon substrate electrochemical catalysts, have attracted great attention benefiting from their fantastic catalytic performances, such as large surface area,enhanced conductivity, tunable porosity, and so on. This review summarizes the outstanding materials used for hydrogen evolution reaction and oxygen evolution reaction. And catalysts that acted as both anode and cathode in two-electrode systems for overall water splitting are introduced systematically. The opportunities and challenges of 3D carbon substrate materials for electrochemical water splitting are proposed.

Photophysical and photochemical processes of riboflavin (vitamin B_2) by means of the transient absorption spectra in aqueous solution

Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of riboflavin (RF, vitamin B2) were studied in detail in aqueous solution. The excited triplet state of riboflavin (3RF*) was produced with 337 nm laser, while under 248 nm irradiation, both3RF* and hydrated electron (eaq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity of3RF* including energy transfer, electron transfer and hydrogen abstraction. The RF·+ was generated by oxidation of SO4 ·-radical with the aim of confirming the results of photolysis.

Biophysical studies of the interaction between a triazole derivative and bovine serum albumin by multi-spectroscopic and molecular modeling methods

The interaction between 3-thiol-4-(2,4-dichlorobenzylideneamino)-5-methyl-4H-1,2,4-triazole (CBTZ) and bovine serum albumin (BSA) under physiological conditions was investigated by fluorescence,UV-vis absorption and circular dichroism (CD) spectroscopy as well as molecular modeling methods. The result of fluorescence experiment indicates the static quenching as a result of the formation of the CBTZ-BSA complex. The binding constants (Ka) at different temperatures were calculated according to the modified Stern-Volmer equation. The enthalpy change (-H) and entropy change (-S) were determined based on the van′t Hoff equation. Both negative-H and-S indicated that van der Waals and hydrogen-bonding forces were the dominant intermolecular forces to stabilize the CBTZ-BSA complex. Site marker competitive replacement experiments demonstrated that binding of CBTZ to BSA primarily took place in sub-domain IIA (Sudlow's site I). The binding distance (r = 7.2 nm) between CBTZ and the tryptophan residue of BSA was estimated according to the theory of fluorescence resonance energy transfer (FRET). The conformational studies by circular dichroism (CD) and three-dimensional fluorescence spectroscopy showed that the presence of CBTZ induced minor changes of the secondary structure of BSA. Molecular modeling study further confirmed the binding mode obtained experimentally.

Excitation Spectrum and Momentum Distribution of Bose-Hubbard Model with On-site Two-and Three-Body Interaction

An effective action for Bose-Hubbard model with two-and three-body on-site interaction in a square optical lattice is derived in the frame of a strong-coupling approach developed by Sengupta and Dupuis.From this effective action,superfluid-Mott insulator(MI) phase transition,excitation spectrum and momentum distribution for two phases are calculated by taking into account Gaussian fluctuation about the saddle-point approximation.In addition the effects of three-body interaction are also discussed.

Understanding the interactions between tris(pentafluoroethyl)-trifluorophosphate-based ionic liquid and small molecules from molecular dynamics simulation

Tris(pentafluoroethyl)trifluorophosphate ([FEP])-based ionic liquids have been widely applied in many fields. For better understanding the properties of [FEP]-based ionic liquids, the interactions between 1-hexyl-3-methylimidazolium ([hmim])[FEP] and small molecules were investigated by molecular dynamics simulations in this work. The small molecules are water, methanol and dimethyl ether. The united-atom (UA) force fields were proposed for methanol and dimethyl ether based on AMBER force field. The densities, enthalpies of vaporization, excess molar properties, and diffusion coefficients of the mixtures were calculated, as well as the microscopic structures characterized by radial distribution functions. Both of the results of the excess energies and microscopic properties show that the strongest interaction is between [hmim][FEP] and dimethyl ether, whereas the interaction between [hmim][FEP] and water is the weakest. Moreover, [hmim][FEP] is more hydrophobic than [hmim] hexafluorophosphate ([PF6]), and the three solutes are mainly distributed around [FEP] anion.

Dendrimer/inorganic nanomaterial composites: Tailoring preparation,properties,functions,and applications of inorganic nanomaterials with dendritic architectures

Inorganic nanomaterials have a variety of fascinating properties and a wide range of promising applications.However,they often suffer from instability and poor processibility.To solve it,dendrimers,a special family of macromolecules having a unique three-dimensional architecture,provide one of the excellent solutions.In addition,the site-selective functionalization of the specific elements in the dendritic structure endows the nanohybrid system new functions and applications.Inspired by such ideas,a variety of dendrimer/inorganic nanomaterial composites have been designed and exploited.This review article selects a number of representative examples,and illustrates their preparation,characterization,properties,and applications.The influence and the unique features that originate from the introduced dendritic structures are particularly discussed.

Spatial expansion and potential of construction land use in the Yangtze River Delta

Based on remote sensing data of the Yangtze River Delta(YRD) in the years of 1991, 2001 and 2008, the paper built an index system of land use potential restraint factors in YRD, according to geological condition, terrain condition, water area, natural reserve area and basic farmland, and evaluated construction land potential based on the platform of GIS spatial analysis model. The results showed that:(1) the construction land increased rapidly since 1991 and reached 24,951.21 km2 in 2008, or 21.27% of the total area. Among all the cities in the YRD, Shanghai took the greatest percentage, followed by Jiangsu and Zhejiang. Spatially, areas where government departments are located became the growth center of construction land. Prefecture-level cities were the fastest growth region and the changing trend showed circle layered characteristics and significant increase with Shanghai and Suzhou as the core.(2) The higher the quality of construction land potentials(CLP), the smaller the number of CLP units. High sensitive area accounted for the largest percentage(40.14%) among all types of constraint regions and this was followed by medium sensitive region(31.53%) of the whole region.(3) The comprehensive CLP in the YRD was 24,989.65 km2, or 21.76% of the total YRD. The land use potential showed spatial distribution imbalance. CLP of Zhejiang was obviously larger than that of Jiangsu. CLP was insufficient in regional central city. Moreover, CLP in the YRD formed a circle layered spatial pattern that increasingly expanded centered in prefecture-level cities. Low potential area expanded from north to south. High potential area was mainly located in south YRD. Areas with zero potential in the YRD formed a northwest-southeast "Y-shaped" spatial pattern in north Hangzhou Bay.(4) CLP per capita in YRD was 0.045 ha/person and also unevenly distributed. Some 25.57% of the study units at county level nearly had no construction land and 8.24% of the units had CLP per capita below the national average level. CLP per capita in less than 25% of the county-level units was larger than the YRD average level, which were mainly located in Zhejiang. Therefore, research on the construction potential area in YRD was favorable for analysis of the development status and potential space of this region under the background of rapid urbanization and industrialization.

Application of probability distribution in order to fit the diameter and natural and man-made height of oak species in two stands in Hyrcanian forests

In order to study the fitting of some characteristics like low diameter at breast height （DBH）, the height and height to the beginning of crown of the Oak species in two man-made and natural forests of this species in north of Guilan＇s forests, Tooshi and Radarposhte forests were selected. A 100% inventory was done on a one-hectare sample plot in Tooshi man-made forests and on a two-hectare sample plot in Radarposhte natural forests. The results from this study showed that, in order to fit the diameter and the height of the Oak trees in man-made stands, Johnson＇s SB and normal statistical distributions have more capabilities and the three-parameter gamma and the three- parameter Weibull distributions are appropriate for diameters and heights of the natural Oak trees in Radarposhte forest, respectively.