Glass Transition Temperatures Studied by MD Simulation of Some Alkali Metasilicates

Abstract

Molecular dynamics simulation of some alkali metasilicates (M₂SiO₃, M = Li, Na, K) was performed to compare glass transition temperatures, T_g , defined in various ways. The potential parameters derived from ab initio MO calculations were used and found to reproduce the inflection of V-T relation on cooling the system. The T_g defined by the inflection point corresponds well to that defined by geometrical changes of coordination polyhedra found in previous work. The self-diffusion coefficients of the alkali ions in higher temperature regions were shown to be related to the amount of free volume in these systems.     

Intermolecular Interaction of Fluoro Propanes

Abstract

Intermolecular interaction is investigated for an isomeric pair of fluoro propane, CH₃CF₂CF₃ (HFC–245cb, CB) and CH₂FCF₂CHF₂ (HFC–245ca, CA). CB has a larger dipole moment than CA. This may suggest that CB has a larger intermolecular attractive interaction than CA; the reverse is, however, found from the experimental data: normal boiling point, critical temperature, and heat of vaporization. Systematic ab initio calculations have been done for both CB dimer and CA dimer, and confirmed that the former has a smaller attractive interaction than the latter.

On the basis of these calculations, analytic functions have been constructed as the pair potential models for the two isomers. Each of these models has 11 Lennard-Jones and Coulomb interaction sites in the molecule. The present models can explain why CB dimer has a smaller attractive interaction than CA dimer, and they will easily be extended to a series of fluoro propanes, and make it possible to perform the systematic molecular simulation studies.     

A Model of the Photosynthesizing Leaf

A model is proposed for the relationship between net photosynthetic rate (N) and light Intensity at a given concentration of CO₂ in the air ([CO₂]_a). The model provides a prediction of the sum of the diffusion resistances (Σr), the capacity (K) of the leaf to fix CO₂, the concentration of CO₂ at the point of photosynthesis ([CO₂]_g), and the respiration rate (R). The model fits the available data well and provides a frame work by which future research may be guided. The calculated values of [CO₂]_g decreased from [CO₂]_g at the compensation point to a nearly constant value at high tight intensities. [CO₂]_g high light infensitit-s range from 32 to 144 μ/l (volume) depending on the species. When these values of [CO₂]_g, are used in the diffusion equation, the resulting levels of the mesophyll resistance (r_m) are lower than those calculated by using the assumptions that [CO₂]_g equals zero. The plants which had (he higher photosynthetic rates at a given light intensity and [CO₂]_a had grealer values of [CO₂]_g than those with lower photo-synthetic rates. The calculated rates of respiration of wheat leaves were twice as high as those measured in the dark. This suggests that the light respiration rate may be twice as great as the dark respiration rate at the same temperature. The calculated values of K demonstrate variability within and between species. The maximum N was independent of K. A relationship between K and the maximum quantum efficiency, at constant levels of [CO₂]_g, was demonstrated in several species. The Σr was inversely related to the maximum rate of photosynthesis for the species investigated. The values of r_m calculated for cotton were inversely related to [CO₂]_a suggesting that the transfer of [CO₂] in the cell may involve a concentration dependent chemical reaction in addition to or rather than a physical diffusion process.     

Responses to temperature,heavy metal and sediment stress by the giant clam Tridacna squamosa

Increasing seawater temperature, heavy metal concentration and sediment load, all represent environmental stress factors found in the Gulf of Thailand. In the present study we investigate and compare the physiological responses of exposure to increased water temperature (+ 3°C) and copper (50 μg Cu/l) by the giant clam Tridacna squamosa, and the behavioural response to sedimentation.

Both temperature and copper caused significant decrease in P_g: R ratios, although by different physiological responses. In clams exposed to copper, the decrease in P_g: R is caused by reduced photosynthesis, whereas the clams exposed to increased temperature maintained a high photosynthetic rate, but significantly increased their respiration.

Clams responded to additional sediment with increased activity. This augmented activity was further increased for clams previously stressed by copper.     

Crystal structure and magnetic behavior of a copper(II)-(pyrazine 2,3-dicarboxylate) coordination polymer: 3D architecture stabilized by H-bonding

Reaction of Cu(ClO₄)₂ · 6H₂O and pyrazine 2,3-dicarboxylate (pzdc) in aqueous ammonia medium results [Cu(pyrazine 2,3-dicarboxylate)(H₂O)₂] · H₂O (1). The X-ray single crystal structure reveals that the compound is a 1D polymeric sinusoidal infinite chain which through intra- and inter-molecular hydrogen bonding interactions, involving lattice and coordinated water molecules with dicarboxylate oxygens and pyrazine nitrogens, gives rise to a 3D architecture. The variable temperature magnetic measurements show weak antiferromagnetic interactions between the Cu(II) centers. The best fit parameters through the typical equation for a uniform copper (II) chain are: J=−0.25 cm⁻¹, g=2.17, R=1.3×10−6. The EPR spectrum does not alter with temperature (from r.t. to 4 K). The spectra are typical for square-pyramidal geometry of copper(II) ions, g_∥=2.24 and g_⊥=2.10 (average g=2.15, in good agreement to the value obtained by susceptibility fit).     

On the Uniqueness of the Reverse Monte Carlo Simulation for Molecular Liquids

Abstract

A careful analysis of the three dimensional structures of liquid Chlorine produced by the Reverse Monte Carlo (RMC) and Molecular Dynamics (MD) techniques is presented. The analysis allows us to measure the degree of uniqueness between the potential and the atom-atom distribution functions, g _aa(r), in the case of pairwise potentials formed by isotropic and anisotropic site-site interactions. The g _aa(r) obtained from MD simulations are used as ‘experimental’ input data in the RMC procedure and the constraint of rigid molecules is imposed. The particle configurations produced by RMC are then studied by using a recently proposed general method for analysing the local order in liquids. The same analysis applied to the particle configurations produced by the conventional MD simulation yields a set of partial distribution functions which relates the main features of the g _aa(r) to microscopic pair geometries. The comparison between the partial centre-centre g _cc(r) shows that the three dimensional structures, produced by MD and RMC simulations, agree very well when only isotropic site-site interactions act. In this case RMC produces the same radial distribution function g(r, ω₁, ω₂) as that obtained from the original MD configurations; it is therefore a valid tool for deriving a complete information on the physical properties of a fluid. For anisotropic site-site interactions the partial g _cc(r) of MD and RMC differ significantly and show that the three dimensional structures, produced by MD and RMC simulations, differ too. The discrepancies are particularly evident for the T shaped configurations and affect the values of the potential energy. Therefore, even if the potential is purely pairwise additive, the use of the atomic radial distribution function as input data and the imposition of atomic constraints which model the molecules as hard dumbbells are not sufficient to bring the RMC procedure towards the ‘true’ microscopic structure of the liquid; the presence of non central forces between sites disrupts the bijective correspondence between the potential and the g _aa(r).     

Leaf temperature effects on gas exchange in Quercus ilex L. growing under field conditions

ABSTRACT

Gas exchange temperature dependence in Quercus ilex shrubs growing in the Mediterranean maquis was analysed. The gas exchange trend was monitored during the year: photosynthetic activity (A _net) reached the highest average rates in early spring and autumn (12.5 µmol m^-2s^-1 was the absolute maximum A _net measured) and the lowest rates were monitored in the middle of June. There was a good correlation (r = 0.72) between A _net and g _s (A _net = 4.1246 ln g _s + 4316; P < 0.01), indicating that stomatal control of CO₂ diffusion plays an important role in controlling photosynthetic activity. Leaf temperature allowing the highest photosynthetic and stomatal conductance rates of Quercus ilex were in the range 17.5 – 29°C. A _net and g_s dropped below half its maximum value when leaf temperatures were below 11.5°C and above 35.7°C. Transpiration rates (E) were strongly related to leaf temperature; E increased as leaf temperature increased and the highest E rates were monitored in June, despite a 46% decrease in g _s. Leaf water loss from transpiration, during the drought period, could result in leaf water stress which would exacerbate heat effects on photosynthesis. During summer, the increase in leaf temperatures decreased g _s which in turn decreased A _net. Consequently, stomatal control in Quercus ilex may be considered as an adaptive strategy during drought.     

MD Simulations of Liquids with Td,Oh Molecular Symmetry

Abstract

A new method is proposed for the calculation of intermolecular interactions in Molecular Dynamics simulations of liquids with T_d, O_h molecular symmetry. The new algorithm is based on the separation of the pair potential into a short-range and a long-range contribution described by a site-site and a spherical centre-centre potential model respectively using an additional cutoff distance. Test calculations for the Lennard-Jones fluids CCl₄ and SF₆ show significant savings in CPU time. We compare thermodynamic properties, pair correlation functions and a few dynamic autocorrelation functions obtained with the novel strategy with results of the commonly used algorithm for systems containing 864 molecules. Since no significant differences appear the new algorithm may be suggested as a useful contribution to the area of Molecular Dynamics simulation of liquids with these rather high molecular symmetries.     

Austausch zweier ungleichaltriger Bruten des Trauerschn?ppers(Muscicapa h. hypoleuca Pallas)

Summary Five eight day old nestlings of the Pied Flycatcher(Muscicapa h. hypoleuca) were exchanged for six sixteen day old nestlings. a) The parent birds, at least the female, getting the young ones, seemed to underestimate the food requirements of the brood, their feeding frequency remaining below the value known to be normal at this age. The parents receiving the changlings nearly ready to fly, over-adjusted their feedingrate, especially the female bringing much more food than the male, wo already cared for two flown young. b) One pair fed nestlings for only 8 days, the other pair for at least 22 days. Comparison with other passerine species reveals, that in certain cases reduction of the feeding time in the nest to nearly zero has been brought about experimentally, but that the possible upper limit of this interval has not been carefully examined in either species.

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Herrn Dozent Dr.v. Haartman danke ich herzlich für die kritische Durchsicht des Manuskriptes und für Verbesserungsvorschläge.     

Low‐Temperature Reduction Strategy Synthesized Si/Ti3C2 MXene Composite Anodes for High‐Performance Li‐Ion Batteries

Silicon is attracting enormous attention due to its theoretical capacity of 4200 mAh g^?1 as an anode for Li‐ion batteries (LIBs). It is of fundamental importance and challenge to develop low‐temperature reaction route to controllably synthesize Si/Ti₃C₂ MXene LIBs anodes. Herein, a novel and efficient strategy integrating in situ orthosilicate hydrolysis and a low‐temperature reduction process to synthesize Si/Ti₃C₂ MXene composites is reported. The hydrolysis of tetraethyl orthosilicate leads to homogenous nucleation and growth of SiO₂ nanoparticles on the surface of Ti₃C₂ MXene. Subsequently, SiO₂ nanoparticles are reduced to Si via a low‐temperature (200 °C) reduction route. Importantly, Ti₃C₂ MXene not only provides fast transfer channels for Li⁺ and electrons, but also relieves volume expansion of Si during cycling. Moreover, the characteristics of excellent pseudocapacitive performance and high conductivity of Ti₃C₂ MXene can synergistically contribute to the enhancement of energy storage performance. As expected, Ti₃C₂/Si anode exhibits an outstanding specific capacity of 1849 mAh g^?1 at 100 mA g^?1, even retaining 956 mAh g^?1 at 1 A g^?1. The low‐temperature synthetic route to Si/Ti₃C₂ MXene electrodes and involved battery‐capacitive dual‐model energy storage mechanism has potential in the design of novel high‐performance electrodes for energy storage devices.     

Theoretical Investigation of the Molecular Structure of the πκ DNA Base Pair

Abstract

The structure of the nonclassical πκ base pair (7–methyl-oxoformycin … 2,4-diaminopyrimidine) was studied at the ab initio Hartree-Fock (HF) and MP2 levels using the 6–31G* and 6–31G** basis sets. The πκ base pair is bound by three parallel hydrogen bonds with the donor-acceptor-donor recognition pattern. Recently, these bases were proposed as an extension of the genetic alphabet from four to six letters (Piccirilli et al. Nature 343, 33(1990)). By the HF/6- 31G* method with full geometry optimization we calculated the 12 degree propeller twist for the minimum energy structure of this complex. The linearity of hydrogen bonds is preserved in the twisted structure by virtue of the pyramidal arrangement of the κ-base amino groups. The rings of both the π and κ molecules remain nearly planar. This nonplanar structure of the πκ base pair is only 0.1 kcal/mol more stable than the planar (Cs) conformation. The HF/6- 31G* level gas-phase interaction energy of πκ (—13.5 kcal/mol) calculated by us turned out to be nearly the same as the interaction energy obtained previously for the adenine-thymine base pair (—13.4 kcal/mol) at the same computational level. The inclusion of p-polarization functions on hydrogens, electron correlation effects (MP2/6–31G** level), and the correction for the basis set superposition error (BSSE) increase this energy to -14.0 kcal/mol.     

Response of dark respiration to temperature in Eriophorum vaginatum from a 30-year-old transplant experiment in Alaska

Background: In the Arctic region, temperature increases are expected to be greater under anticipated climate change than the global average. Understanding how dark respiration (R_d) of common Arctic plant species acclimates to changes in the environment is therefore important for predicting changes to the Arctic carbon balance.

Aims: The aim of this study is to investigate the influence of genotype and growing environment on R_d, the temperature response (Q₁₀) of R_d, and foliar N (N_leaf) of the Arctic sedge Eriophorum vaginatum.

Methods: We measured R_d, and determined its Q₁₀ and N_leaf of E. vaginatum populations that were reciprocally transplanted 30 years previously along a latitudinal transect of 370 km in northern Alaska.

Results: R_d and Q₁₀ did not differ among populations (ecotypes) of E. vaginatum, but the local environment had a significant effect on both variables. R_d as well as N_leaf was higher in northern, colder sites, while Q₁₀ was lower there.

Conclusions: R_d in the different populations of E. vaginatum is a very plastic trait and controlled by growing environment, as is N_leaf. The lower Q₁₀ values in the northern sites were most likely a consequence of substrate inhibition of R_d at higher temperatures.     

Effects of high-temperature stress on various biomembranes of leaf cells in situ and in vitro

The sensitivity of photosynthetic and respiratory functions to supraoptimal temperature stress was compared after heating of leaves, protoplasts and membrane systems of spinach (Spinacia oleracea L. cv. Monatol) and lettuce (Valerianella locusta [L.] Betcke) in situ and in vitro.

After heating of whole leaves or protoplasts, endogenous respiration was not or only slightly affected at temperatures which caused a marked decrease of photosynthesis. This was manifested when mitochondria and thylakoids were isolated from heat-treated leaves. In the presence of exogenous substrates, mitochondrial electron transport and phosphorylation were even somewhat stimulated compared to the controls.

Inactivation of net CO₂ uptake of whole leaves following heat stress and of the photochemical activities of chloroplast membranes isolated from heat-treated leaves of the same origin occurred nearly simultaneously. In protoplasts, photosynthesis was inactivated at temperatures far below those which caused drastic changes in the integrity of the tonoplast and the plasmalemma. This indicates that damage occurring within the chloroplasts rather than alterations in the compartmentation of the cell is responsible for the high sensitivity of photosynthesis to supraoptimal temperature stress.

Mitochondria and thykaloids isolated from the same preparation of intact leaves under comparable conditions and subjected to heat treatment in vitro, however, were inactivated nearly in the same temperature range. Thus, mitochondria are much more stable within their cytoplasmic environment.

     

Molecular Mechanics Studies of Dinucleoside Methylphosphonates: Influence of Methylphosphonate and its Chirality on the Phosphodiester Conformation

Abstract

Molecular mechanics studies are performed on single stranded as well as base paired forms of dinucleoside methylphosphonates comprising different base sequences for both the Sand R-isomers of methylphosphonate (MP). S-MP produces noticeable distortions in the geometry, locally at the phosphate center, and this enables the stereochemical feasibility of compact g^? g^? phosphodiester. Besides, it tends to perturb the conformations around the P- 03′ and glycosyl bonds, causing minor variations in stacking interactions. In single stranded dinucleosides, the gain in adjacent base stacking interaction energies seems to be sufficient to overcome the barrier to P-03′ bond rotation arising due to S-MP…sugar interaction, and this results in transition to a compact phosphodiester (B_I-type) from an initial extended phosphodiester (B_II-type) conformation. Such a thing seems rather difficult in base pair constrained duplexes. Dinucleosides with R-MP behave analogous to normal phosphate duplexes as the methyl group is away from the sugar. It is found that dinucleoside methylphosphonates are energetically less favoured than the corresponding dinucleoside phosphates mainly due to the depletion of contributions from electrostatic attractive interactions involving the base and sugar with the methylphosphonate consequent to the nonionic nature of the latter. Neither S-MP nor R-MP seem to significantly alter the stereochemistry of duplex structure.     

Impact of high-pressure processing on diffusion in polyethylene based on molecular dynamics simulation

Abstract

The impact of high-pressure processing (HPP) on dissusion of antioxidant butylated hydroxytoluene (BHT) in polyethylene (PE) was discussed via the molecular dynamics method. Furthermore, the glass transition temperatures (T_g), the accessible free volumes of PE and the diffusion coefficients of BHT in PE at different HPP treatments were calculated, and the diffusion trajectories of the BHT molecules in PE were also presented. Finally, the diffusion mechanism of BHT in PE under HPP was analyzed based on the aforementioned simulation results. The results show that the T_g of PE increases under high pressure while the fractional free volume (FFV) reduces, and the diffusion coefficient decreases with the pressure on the rise. The diffusion trajectories of BHT in PE under HPP indicate that the BHT molecules are trapped and slowly wriggle in a narrow path among PE molecular chains due to the extreme high pressure. However, the high temperature has an opposite effect on the diffusion behavior of BHT in PE compared with high pressure. As the temperature rises, the FFV of PE and the diffusion coefficient of BHT in PE are elevated. This study is helpful to the research of high-pressure food safety and packaging migration.     

A Versatile Polymer Support Useful for Large-Scale Synthesis of DNA for Biomedical Applications

Abstract

A suitably derivatized MercKogel^R 1 as an efficient solid support for the large-scale synthesis of DNA for biomedical applications, is described. Partial hydrolysis of these polyvinylacetate resins with 0.5 M NaOH solution¹ at room temperature for 30–80 min. yielded carriers 1 that could be loaded with 120, 150, 258, and 368 μmoles of nucleosides g^?1.

     

The Nature of Conformational Correlations in α- and β-Anomers of Nucleic Acid Components in Aqueous Solution by Nuclear Magnetic Resonance

Abstract

The solution distribution of combinations of the sugar ring puckering domains, C2′endo(S), C3′endo(N), and C4′-C5′ rotamers, +sc(g⁺), ap(t), -sc(g^?), in α and β-anomers in ribo- and deoxyribo- pyrimidine nucleic acid components can be determined from vicinal coupling constants (M. Remin, J. Biomol. Str. Dyn. 2, 211 (1984). A general correlation pattern with a conformational constant λ, reflecting an intrinsic physical property of the sugar - side chain ensemble, is developed and expressed in terms of four principles:

I) The +sc rotamer contributes to the C3′endo population to a higher extent (1 - Y_t) than to C2′endo,(l-Y_t-Y_g-/X_s).

II) The ap rotamer contributes to both C2′endo and C3′endo populations to the same extent (Y_t).

III) The—sc rotamer contributes only to the C2′endo population, (Y_g-/X_s).

IV) The molar fractions X_s, Y_t and Y_g- of conformations C2′endo, ap and—sc, respectively, are strongly correlated, λ = (Y_g-/X_s)/Y_t ≈ 0.5, and therefore Y_t is a basic variable parameter which determines all others in the correlation pattern.

In α-anomers, regardless of the type and conformation of the sugar ring and base, the molar fraction Y_t = 0.37 ± 0.02. This finding means that different α-anomers show one correlation pattern free of the influence of the base. In β-anomers, structure and conformation of the base are important factors which modulate (through Y_t) the correlation pattern, conserving its fundamental features. Y_t is considerably increased by a syn-oriented pyrimidine base, but decreases when the base is anti. The transition from anti to syn orientation of the base is followed by destabilization of (C2′endo, +sc) in favor of (C3′endo, ap). The principles of conformational correlations rationalize a variety of correlations observed in the past.     

Mapping the Binding Site of Aflatoxin B1 in DNA: Molecular Modeling of the Binding Sites for the N(7)-Guanine Adduct of Aflatoxin B1 in Different DNA Sequences

Abstract

Aflatoxin B, (AFB₁), a potent mutagen and carcinogen, forms an adduct exclusively at the N(7) position of guanine, but the structure of this adduct in double stranded DNA is not known. Molecular modeling (using the program, PSFRODO) in conjunction with molecular mechanical calculation (using the program, AMBER) are used to assess the binding modes available to this AFB₁ adduct TVvo modes appear reasonable; in one the AFB₁ moiety is intercalated between the base pair containing the adducted guanine and the adjacent base pair on the 5₁-side in reference to the adducted guanine, while in the second it is bound externally in the major groove of DNA Rotational flexibilty appears feasible in the latter providing four, potential binding sites. Molecular modeling reveals that the binding sites around the reactive guanine in different sequences are not uniformly compatible for interaction with AFB₁. As the sequence is changed, one particular external binding site would be expected to give a pattern of reactivities that is reasonably consistent with the observed sequence specificity of binding that AFB₁ shows in its reaction with DNA (Benasutti, M., Ejadi, S., Whitlow, M. D. and Loechler, E. L. (1988) Biochemistry 27, 472–481). The AFB₁ moiety is face-stacked in the major groove with its long axis approximately perpendicular to the helix axis. Favorable interactions are formed between exocyclic amino groups that project into the major groove on cytosines and adenines surrounding the reactive guanine, and oxygens in AFB₁; unfavorable interactions involve van der Waals contacts between the methyl group on thymine and the AFB₁ moiety. “Some of the sequence specificity of binding data can be rationalized more readily if it is assumed that 5′-GG-3′ sequences adopt an A-DNA structure.” Based upon molecular modeling/potential energy minimization calculation, it is difficult to predict how reactivity would change in different DNA sequences in the case of the intercalative binding mode; however, several arguments suggest that intercalation might not be favored. From these considerations a model of the structure for the transition state in reaction of AFB, with DNA is proposed involving one particular external binding site.     

Preparation and characterization of amino and carboxyl functionalized core-shell Fe3O4/SiO2 for L-asparaginase immobilization: A comparison study

Abstract

Magnetic nanoparticles are well known as facile and effective support for enzyme immobilization since they have a high surface area, large surface-to-volume ratio, easy separation, a fast and high enzyme loading. This study aims to provide insights on whether acidic or basic modified particles are more effective for L-asparaginase (ASNase) immobilization. Therefore, amino (Fe₃O₄/SiO₂/NH₂) and carboxyl-functionalized (Fe₃O₄/SiO₂/COOH) particles were prepared. The functional groups, crystalline structure, magnetic properties, morphology, chemical composition and thermal behaviour of the prepared modified nanoparticles were examined via Fourier-transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), vibrating-sample magnetometer (VSM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX). Under the optimum conditions, the immobilized enzymes were more stable within a certain range of temperatures and pH values in comparison to free enzyme. On the other hand, the immobilized enzymes showed greater stability after incubation for 3?h at 50?°C. The free enzyme maintained only 30% of its initial activity for 4?weeks at 4?°C, while Fe₃O₄/SiO₂/NH₂/ASNase and Fe₃O₄/SiO₂/COOH/ASNase retained more than 78.9% and 56.5% of initial activities under the same conditions, respectively. Moreover, Fe₃O₄/SiO₂/NH₂/ASNase (77.2%) and Fe₃O₄/SiO₂/COOH/ASNase (57.4%) displayed excellent operational stability after 17 repeated cycles. These findings suggested that the Fe₃O₄/SiO₂/NH₂ and Fe₃O₄/SiO₂/COOH may be utilized as efficient and sustainable supports to developed immobilized ASNase in several biotechnological applications.     

桂花树冠层气孔导度模型的优化及其参数分析

冠层气孔导度(g_c)是许多陆面过程模型中的重要参数,提高对冠层气孔导度的模拟精度非常重要。以环境因子阶乘的Jarvis形式的模型是气孔导度模型中的典型代表,但研究中不同的环境因子有不同的响应方程和参数。研究认为不同的响应方程有不同的模拟效果,并通过比较各环境因子的不同响应方程组合的模型的模拟效果来确定最优的g_c模型。以桂花树为例,测定了树干液流、茎水势和微气象环境,用Penman-Monteith(PM)方程反推计算冠层气孔导度并检验不同方程组合的16种模型。模型的参数用DiffeRential Evolution Adaptive Metropolis(DREAM)模型优化。结果表明这种方法能够有效地找到各环境因子最优的响应方程,从而最优化g_c模型。优化的g_c模型很好地模拟了桂花树冠层气孔导度的变化,尤其是对干旱的响应,模拟值与PM计算值的相关系数和均方根误差分别为0.803和0.000623 m/s。同时也证明了模型中温度函数f(T)1的现象并非个例,由于温度(T)和水汽压亏缺(D)常是高度相关的,建议在以后的g_c模型研究中应把T和D看成一个影响因子,但f(T)1的这种现象是否具有全球性还有待进一步研究证实。