力、物体的平衡专题复习

一、考向导析 本章内容在整个物理知识体系中属于基础知识,解决问题的方法更是广泛应用于力、热、电等内容中,同时本章又是进入高三复习的第一章,所以夯实基础,把握重点是本章的学习目标.

A Hypothesis Regarding the Origin of Additional Surface Acidity in Solid Complexes with Same Metal Cations

Based on the criteria for additional surface acidity generation in composite oxides and composite fluorides proposed by Tanabe and Kemnitz et al.A hypothesis for the origin of additional surface acidity in solid composites with the same metal cations is proposed.The surface acidsites of We analyze three types of solid composite systems,that is,CrF_(3)/Cr_(2)O_(3),MgF_(2)/MgO,and ZnF_(2)/ZnO,is systematically analyzed,which agrees with experimental results.Accordingly,the origin of additional surface acidity in these solid composites is reasonably explained,and the types of acidic sites are also predicted.

Gibberellin homeostasis and plant height control by EUI and a role for gibberellin in root gravity responses in rice

The rice Eui （ELONGATED UPPERMOST INTERNODE） gene encodes a cytochrome P450 monooxygenase that deactivates bioactive gibberellins （GAs）. In this study, we investigated controlled expression of the Eui gene and its role in plant development. We found that Eui was differentially induced by exogenous GAs and that the Eui promoter had the highest activity in the vascular bundles. The eui mutant was defective in starch granule development in root caps and Eui overexpression enhanced starch granule generation and gravity responses, revealing a role for GA in root starch granule development and gravity responses. Experiments using embryoless half-seeds revealed that RAmylA and GAmyb were highly upregulated in eui aleurone ceils in the absence of exogenous GA. In addition, the GA biosynthesis genes GA3oxl and GA20ox2 were downregulated and GA2oxl was upregulated in eui seedlings. These results indicate that EUI is involved in GA homeostasis, not only in the internodes at the heading stage, but also in the seedling stage, roots and seeds. Disturbing GA homeostasis affected the expression of the GA signaling genes GID1 （GIBBERELLIN INSENSITIVE DWARF 1）, GID2 and SLR1. Transgenic RNA interference of the Eui gene effectively increased plant height and improved heading performance. By contrast, the ectopic expression of Eui under the promoters of the rice GA biosynthesis genes GA3ox2 and GA2Oox2 significantly reduced plant height. These results demonstrate that a slight increase in Eui expression could dramatically change rice morphology, indicating the practical application of the Eui gene in rice molecular breeding for a high yield potential.

Mass Loss from Glaciers in the Chinese Altai Mountains between 1959 and 2008 Revealed Based on Historical Maps, SRTM, and ASTER Images

Mass loss of glaciers in the Chinese Altai was detected using geodetic methods based on topographical maps(1959), the Shuttle Radar Topography Mission(SRTM) Digital Elevation Model(DEM)(2000), and the Advanced Space-borne Thermal Emission and Reflection Radiometer(ASTER) stereo images(2008). The results indicate that a continued and accelerating shrinkage has occurred in the Chinese Altai Mountains during the last 50 years, with mass deficits of 0.43 ± 0.02 and0.54 ± 0.13 m a-1 water equivalent(w.e.) during the periods 1959-1999 and 1999-2008, respectively.Overall, the Chinese Altai Mountains have lost 7.06 ±0.44 km3 in ice volume(equivalent to-0.43 ± 0.03 m a-1 w.e.) from 1959-2008. The spatial heterogeneity in mass loss was potentially affected by comprehensive changes in temperature and precipitation, and had a substantial correlation withglacier size and topographic settings. Comparison shows that in the Chinese Altai Mountains glaciers have experienced a more rapid mass loss than those in the Tianshan and northwestern Tibetan Plateau(TP), and the mass balance of glaciers was slightly less negative relative to those in the Russian Altai, Himalaya, and southern TP.

Nutritive Equilibrium in Rice Plant Populations for High Yield

The effects of nitrogen, phosphorus and potassium application level, seed rate and transplanting density on the growth and development of rice plants were studied to find out nutrient status in high-yielding rice plants and to increase grain yield by adequate fertilization. There was an equilibrium relationship among nutrient elements for high-yielding rice plant populations. The equilibrium index of nutrient amount, content and distribution in high-yielding rice plants should be generally greater than-2 but less than 2. The optimum nutritive proportion of nitrogen: phosphorus: potassium assimilated by the plants was about 10: 2: 9 at the ripening stage. But the content and the proportion varied with the growth stages. Therefore, the nutrient in rice plant populations should be in a dynamic equilibrium, so as to achieve high yield.

Influence of Pore Size,Salinity and Gas Composition upon the Hydrate Formation Conditions

An experimental device was set up to study the hydrate formation conditions.Effects of pore size,salinity,and gas composition on the formation and dissociation of hydrates were investigated.The result indicates that the induction time for the formation of hydrates in porous media is shorter than that in pure water.The decrease in pore size,by decreasing the size of glass beads,increases the equilibrium pressure when the salinity and temperature are kept constant.In addition,higher salinity causes higher equilibrium pressure when the pore size and temperature are kept constant.It is found that the effects of pore size and salinity on the hydrate equilibrium are quite different.At lower methane concentration,the hydrate equilibrium is achieved at lower pressure and higher temperature.

Application of Equilibrium Partitioning Approach to the Derivation of Sediment Quality Guidelines for Metals in Dianchi Lake

For the past 20 years, numerous studies have been carried out on the application of equilibrium partitioning approach （EqPA） for the derivation of sediment quality guidelines （SQGs）. However, for metals, few Equilibrium-partitioning- based numerical SQGs have been developed or are currently available because of the confounding factors mediating the bioavailability of metals. A study was conducted at Dianchi Lake, which is a heavily eutrophicated lake on the Yunnan- Guizhou Plateau, China with the focus on the measurement of partitioning coefficient （Kp） and SQGs derivation and normalization to acid volatile sulfide （AVS）, fine material, and organic carbon. Using new normalization methods, SQGs were formulated for seven metals including copper, zinc, lead, cadmium, chromium, mercury, and arsenic in Dianchi Lake. In Dianchi Lake sediments, the fine material contributed 25.4%-36.0% to the SQG values, with the largest contribution to the SQG value of mercury; AVS contributed 2.9%-75.0% to the SQG values, with the largest contribution to the SQG value of cadmium. This indicated that the fine material and the AVS were the most important controlling factors to the bioavailability of mercury and caximium, respectively. The contribution of total organic carbon （TOC） to the SQG values of copper and leaxi was 3.8% and 7.1%, respectively, indicating that at relatively lower concentrations, the contribution of TOC was not significant. In addition to normalization methods, appropriate procedures for the application of EqPA including sample collection, storage, and analysis are also essential to improve the reliability of SQGs. The normalized Dianchi Lake SQGs were higher than most of the empirically based SQGs developed in North America, but lower than Hong Kong interim SQGs except for cadmium and arsenic. The differences could be attributed to the approaches used for derivation of SQGs and the water quality criteria adopted and the differences in the physical and chemical characteristics of the sediments.

Electromotive Force for Solid Oxide Fuel Cells Using Biomass Produced Gas as Fuel

The electromotive force （e.m.f.） of solid oxide fuel cells using biomass produced gas （BPG） as the fuels is calculated at 700-1,200 K using an in-house computer program, based on thermodynamic equilibrium analysis. Tour program also predicts the concentration of oxygen in the fuel chamber as well as the concentration of equilibrium species such as H2, CO, CO2 and CH4. Compared with using hydrogen as a fuel, the e.m.f. for cells using BPG as the fuels is relative low and strongly influenced by carbon deposition. To remove carbon deposition, the optimum amount of H2O to add is determined at various operating temperatures. Further the e.m.f, for cells based on yttria stabilized zirconia and doped ceria as electrolytes are compared. The study reveals that when using BPG as fuel, the depression of e.m.f, for a SOFC using doped ceria as electrolyte is relatively small when compared with that using Yttria stabilized zirconia.

Hepatic expression and cellular distribution of the glucose transporter family

Glucose and other carbohydrates are transported into cells using members of a family of integral membrane glucose transporter (GLUT) molecules. To date 14 members of this family, also called the solute carrier 2A proteins have been identified which are divided on the basis of transport characteristics and sequence similarities into several families (Classes 1 to 3). The expression of these different receptor subtypes varies between different species, tissues and cellular subtypes and each has differential sensitivities to stimuli such as insulin. The liver is a contributor to metabolic carbohydrate homeostasis and is a major site for synthesis, storage and redistribution of carbohydrates. Situations in which the balance of glucose homeostasis is upset such as diabetes or the metabolic syndrome can lead metabolic disturbances that drive chronic organ damage and failure, confirming the importance of understanding the molecular regulation of hepatic glucose homeostasis. There is a considerable literature describing the expression and function of receptors that regulate glucose uptake and release by hepatocytes, the most import cells in glucose regulation and glycogen storage. However there is less appreciation of the roles of GLUTs expressed by non parenchymal cell types within the liver, all of which require carbohydrate to function. A better understanding of the detailed cellular distribution of GLUTs in human liver tissue may shed light on mechanisms underlying disease pathogenesis. This review summarises the available literature on hepatocellular expression of GLUTs in health and disease and highlights areas where further investigation is required.

Vapor-Liquid Equilibrium of Copolymer＋ Solvent Systems： Experimental Data and Thermodynamic Modeling with New UNIFAC Groups

Vapor-liquid equilibrium （VLE） data for copolymer solutions are necessary for several chemical processes. However, VLE data for copolymer solutions in the published report are rare. In this study, experimental VLE data for binary systems copolymer＋solvent were obtained using a gravimetric-sorption apparatus. The studied systems were hexane＋poly （21% acrylonitrile-co-butadiene）, hexane＋poly （33% acrylonitrile-co-butadiene）, hexane＋poly （51% acrylonitrile-co-butadiene）, hexane＋poly （23% styrene-co-butadiene）, hexane＋poly （45% styrene-co-butadiene）, and benzene＋poly （44% styrene-co-methyl methacrylate） in the range 50-70℃. The experimental data were correlated with the UNIFAC and Elbro-FV group contribution models for the activity coefficient. Two sets of functional groups had been used to represent the monomers in copolymers： literature groups and new proposed groups. The mean deviations between experimental and calculated mass fractions about 2.4% with Elbro- FV and 13.3% with Zhong were observed when the groups proposed in this study were used, and of 3.5% for E1- bro-FV and 13.2% for Zhong, when literature grouns were used.

Prediction of Phase Behavior for Styrene/CO2/Polystyrene Mixtures

A lattice fluid model, Sanchez-Lacombe equation, is used to predict the phase behavior for a styrene/CO2/polystyrene ternary sys-tem. The binary parameters involved in the equation were optimized using experimental data. Phase diagrams and the distribution coefficients of styrene between polymer phase and fluid phase are obtained over a wide range of pressure, temperature and composition. The analysis of ter-nary phase diagrams indicates that this system at relatively high pressure or low temperature may display two-phase equilibrium, and at low pressures or high temperatures three-phase equilibrium may appear. The distribution coefficients of styrene between the fluid phase and the polymer phase increase asymptotically to unity when the concentration of styrene increases. The results provide thermodynamic knowledge for further exploitation of supercritical carbon dioxide assisted devolatilization and impregnation.

Computation of three-finger equilibrium and force-closure grasps

We proved a new necessary and sufficient condition for 2D three finger equilibrium grasps and implemented an geometrical algorithm for computing force closure grasps of arbitrary 2D objects in this article. The algorithm is quite simple and only needs some algebraic calculations. Finally, we implemented the algorithm and confirmed its usefulness by an example.

Impact of Solid / Vapour Equilibria on Conditions of Crystallization of Pharmaceutical Compounds

The influence of solvent (in its gaseous state) on the stability of crystallized organic compounds was investigated. Through two examples of studies on the solid/vapour equilibria made in our lab, several behaviors were highlighted: (i) a new hydrated phase (thermodynamically stable) of an active pharmaceutical ingredient (API) was detected after the recrystallization starting from a deliquescent state, (ii) a spontaneous resolution of a hydrated racemic compound towards an anhydrous conglomerate can occur during the desolvation under the precise conditions of temperature and humidity. This study illustrates that knowledge about solid/vapour equilibrium is a crucial step during the complete characterization of solid organic compounds.

Experimental and simulation study of nylon 6 solid–liquid extraction process

The solid–liquid extraction process of nylon 6 to eliminate small molecules, i.e., caprolactam(CL), cyclic dimers(CD) and cyclic trimers(CT), is investigated in detail by both batch extraction experiments and numerical simulations. In the batch extraction experiments, due to the small molecules attaching to the polymeric surface, the basic physical mechanism shifts from surface diffusion to internal diffusion as the extraction proceeded. The experimental data are well reproduced by a diffusion model consisting of two distinct steps, characterized as surface diffusion and internal diffusion. Furthermore, based on the established mass transfer mechanism and diffusion model of the two distinct steps, the equilibrium constants and internal diffusion coefficients of CL, CD and CT are acquired. An industrial countercurrent extraction tower is further simulated. It is found that the extraction efficiency of CL can be significantly improved by increasing the temperature at the bottom portion of the tower. The elimination of CD, which can be greatly promoted by a high-concentration CL-water solution, is controlled by mass transfer resistance, whereas the removal of CL is mainly affected by the equilibrium.

Two New Solutions of Non-constant-α Force-Free Magnetic Field

Two new solutions for non-constant-α force-free magnetic field are found analytically. Implications of the results to astrophysical solar plasmas as well tokamak plasmas are discussed.

Optimal scenario balance of reduction in costs and greenhouse gas emissions for municipal solid waste management

To reduce carbon intensity, an improved management method balancing the reduction in costs and greenhouse gas(GHG)emissions is required for Tianjin's waste management system. Firstly, six objective functions, namely, cost minimization, GHG minimization, eco-efficiency minimization, cost maximization, GHG maximization and eco-efficiency maximization, are built and subjected to the same constraints with each objective function corresponding to one scenario. Secondly, GHG emissions and costs are derived from the waste flow of each scenario. Thirdly, the range of GHG emissions and costs of other potential scenarios are obtained and plotted through adjusting waste flow with infinitely possible step sizes according to the correlation among the above six scenarios. And the optimal scenario is determined based on this range. The results suggest the following conclusions. 1) The scenarios located on the border between scenario cost minimization and GHG minimization create an optimum curve, and scenario GHG minimization has the smallest eco-efficiency on the curve; 2) Simple pursuit of eco-efficiency minimization using fractional programming may be unreasonable; 3) Balancing GHG emissions from incineration and landfills benefits Tianjin's waste management system as it reduces GHG emissions and costs.

Modeling multiple chemical equilibrium for reactive extraction of naproxen enantiomers with HP-β-CD as hydrophilic selector

Reactive extraction is an emerging technology for large-scale continuous resolution of drug enantiomers. The enantioselective extraction of R,S-naproxen by hydrophilic HP-β-CD in 1,2-dichloroethane was studied at 5℃. The experimental data were described by a reactive extraction model with a homogeneous aqueous phase reaction of R,S-naproxen with HP-β-CD which couples a complete description of chemical equilibria in aqueous phase with the overall phase equilibria of the system. Important parameters of this model were determined experimentally. The physical distribution coefficients for molecular and ionic NAP were 0.041 and 1.730, respectively. Here we show that the efficiency of extraction depends strongly on two process variables including pH and HP-β-CD concentration. The model predictions are compared graphically with the results of pre- vious experiments and there is a good agreement between each other. By the use of modeling and experiment, an optimized extraction condition with pH of 2.5 and HP-β-CD concentration of 0.1 mol/L was obtained with high enantioselectivity （a） of 1.59 and performance factor （pf） of 0,049. The model gives a good means of predicting enantiomers partitioning over a range of experimental conditions.

Impaired function of the suprachiasmatic nucleus rescues the loss of body temperature homeostasis caused by time-restricted feeding

The suprachiasmatic nucleus(SCN)is the master circadian pacemaker that drives body temperature rhythm.Time-restricted feeding(TRF)has potential as a preventative or therapeutic approach against many diseases.The potential side effects of TRF remain unknown.Here we show that daily 4-h TRF treatment in mice can severely impair body temperature homeostasis and can result in lethality.Nearly half of the mice died at 21℃,and all mice died at 18℃during 4-h TRF.This effect was modulated by the circadian clock and was associated with severe hypothermia due to loss of body temperature homeostasis.Remarkably,disrupting the circadian clock by SCN lesions or constant light rescued lethality during TRF.Analysis of circadian gene expression in the dorsomedial hypothalamus(DMH)demonstrated that TRF reprograms rhythmic transcriptome in DMH and suppresses expression of genes,such as Ccr5 and Calcrl,which are involved in thermoregulation.Together,our results demonstrated a potent effect of TRF on body temperature homeostasis and the role of SCN function in this process.Our results further suggested that circadian arrhythmicity can have potential beneficial effects under certain stress conditions.

Liquid-liquid interfacial tension of equilibrated mixtures of ionic liquids and hydrocarbons

Ionic liquids are possible alternative solvents for the separation of aromatic and aliphatic hydrocarbons by liquid-liquid extrac- tion. Interfacial tension is an important property to consider in the design of liquid-liquid extraction processes. In this work, the liquid-liquid interfacial tension and the mutual solubility at 25 ℃ have been measured for a series of biphasic, equilibrated mixtures of an ionic liquid and a hydrocarbon. In particular, the ionic liquids 1-alkyl-3-methylimidazolium bis（trifluorome- thanesulfonyl）imide （with the alkyl substituent being ethyl, hexyl or decyl）, 1-ethyl-3-methylimidazolium ethylsulfate, and 1-ethyl-3-methylimidazolium methanesulfonate have been selected, as well as the hydrocarbons benzene, hexane, ethylben- zene, and octane. The selected sets of ionic liquids and hydrocarbons allow the analysis of the influence of a series of effects on the interfacial tension. For example, the interfacial tension decreases with an increase in the length of the alkyl substituent chain of the cation or with an increase of the degree of charge delocalisation in the anion of the ionic liquid. Also, the interfa- cial tension with the aromatic hydrocarbons is markedly lower than that with the aliphatic hydrocarbons. A smaller effect is caused by variation of the size of the hydrocarbon. Some of the observed trends can be explained from the mutual solubility of the hydrocarbon and the ionic liquid.