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DNA and its conformational transition can be used to design nanometer-scale structures, nano-tweezers and nanomechanical devices. Experiments and molecular simulations have been used to study the concentration effect on the A-DNA→B-DNA conformational transition, but a systematical investigation on counterion effect on the dynamics of this transition has not been reported up to now. In present work, restrained and unrestrained molecular dynamics (MD) simulations have been performed to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA transitions in aqueous solutions with different alkali metal counterions. The DNA duplex d(CGCGAATTCGCG)2, coion Cl− and counterions Li+, Na+, K+, Rb+ and Cs+ as well as water molecule were considered using the PARM99 force field in the AMBER8 package. It was found that B-form DNA is more stable than A-form DNA in aqueous electrolyte solutions with different alkali metal counterions. Increasing KCl concentration in solution hinders the A-DNA→B-DNA transition and the transition times for different alkali metal counterions conform to neither the simple sequence related to naked ion size nor to hydrated diameter, but an apparently abnormal sequence of K+ < Rb+ < Cs+ < Na+ < Li+. This abnormal sequence can be well understood in terms of an electrostatic model based on the effective cation diameters and the modified mean-spherical approximation (MMSA). The present results provide valuable information for the design of DNA-based nanomaterials and nanodevices.

Personalization information retrieval is very useful in information retrieval system, the user profile can be used to represent the favorites or interests of user. Many methods to personalization have been studied in extending query with user profile. A proposed navel method which use the context of long-term user profile with multiple domain to extend query model under the unigram language model framework, uses the new query model to retrieve and get more interesting results for users. Combined with psudo relevance feedback model, the proposed method get better performance. Experimental results show that the proposed method in this paper is effective.

Personalization information retrieval is very useful in information retrieval system, the user profile can be used to represent the favorites or interests of user. This paper introduces how to automatically learn user interests, build user profiles and re-rank search results.A topic directory method is proposed to calculate the semantic similarity, which takes multi-inheritance into consideration, and then optimize the computing process based on the tree structure of inheritance relationship. Experiments are conducted to compare our method with the popular directory based search methods (e.g., Google Directory Search). Experimental results show that the proposed method in this paper can effectively capture personalization and improve the accuracy of personalized search over existing approaches.

Unrestrained molecular dynamics (MD) simulations have been carried out to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA conformational transitions in aqueous RbCl solutions. The PARM99 force field in the AMBER8 package was used to investigate the effect of RbCl concentration on the dynamics of the A→B conformational transition in the DNA duplex d(CGCGAATTCGCG)2. Canonical A- and B-form DNA were assumed for the initial conformation and the final conformation had a length per complete turn that matched the canonical B-DNA. The DNA structure was monitored for 3.0 ns and the distances between the C5′ atoms were obtained from the simulations. It was found that all of the double stranded DNA strands of A-DNA converged to the structure of B-form DNA within 1.0 ns during the unrestrained MD simulations. In addition, increasing the RbCl concentration in aqueous solution hindered the A→B conformational transition and the transition in aqueous RbCl solution was faster than that in aqueous NaCl solution for the same electrolyte strength. The effects of the types and concentrations of counterions on the dynamics of the A→B conformational transition can be understood in terms of the variation in water activity and the number of accumulated counterions in the major grooves of A-DNA. The rubidium ion distributions around both fixed A-DNA and B-DNA were obtained using the restrained MD simulations to help explain the effect of RbCl concentration on the dynamics of the A→B conformational transition.

Adsorption of carbon monoxide on different Ag + -exchange sites of Ag–ZSM-5 zeolite has been investigated using density functional theory. The coordination and local geometry of the Ag + ion in Ag–ZSM-5 as well as adsorption structures and energies of CO adsorbed on these sites are explored extensively. The structure of Ag + -exchange sites, location of the Al atom on the T site, and number of the Al atoms contained in the sites are considered in the theoretical calculations. The calculated results show that the Ag O coordination number of two is strongly preferred before and after CO adsorption. The Ag O bond lengths are in a broad range of 2.2–2.9 A, and the Ag C bond lengths for CO adsorbed on Ag–ZSM-5 zeolite are calculated to be 2.0–2.2 A. Both Ag O and Ag C bond lengths for CO–Ag–ZSM-5 complex are longer than those for CO–Cu–ZSM-5 complex. The calculated adsorption energy of CO adsorbed on the I2 sites is between 28.5 and 29.6 kcal/mol, and that on the Z5, Z6, M5 and M6 sites containing one Al atom on the T position is between 11.3 and 18.9 kcal/mol whereas the calculated adsorption energy of CO adsorbed on the M7 site containing one Al atom is 19.9 kcal/mol. The introduction of the two Al atoms to the Ag + -exchange site results in a reduction of CO adsorption energy. In general, the adsorption energy of CO on Ag–ZSM-5 is lower than that on Cu–ZSM-5. The predicted coordination of the Ag + ion, bond lengths of Ag O and Ag C as well as adsorption energy are in accord with available experimental results.

A Web information retrieval algorithm based on Web page segment is designed, the key idea of which is to segment each Web page into different topic areas or segments according to its HTML tags and contents since Web pages are semi-structure. First, the algorithm builds a HTML tag tree, and then it combines nodes in the tree under the rule of content similarity and visual similarity. During the process of retrieval and ranking, the algorithm makes full use of the segmentation information to sequence the relevant pages. The experimental results show that this method is able to improve the precision in search significantly and it is also a good reference for the design of the future search engines.

The effects of solid-fluid interactions on the vapor-liquid phase diagram, coexistence density, relative volatility and vaporization enthalpy have been investigated for confined binary systems of CO2-CH4, CO2-N2 and CH4-N2. The Gibbs ensemble Monte Carlo (GEMC) simulation results indicate that the confinement and the solid-fluid interaction have significant influences on the vapor-liquid equilibrium properties. The confinement and the strength of the solid-fluid interaction make the p-x i phase diagram move to higher pressure regions. They also make the two-phase region become narrower for each binary mixture. The strength of the solid-fluid interactions can cause increases in the coexistence liquid and vapor densities, and cause the decrease of the relative volatility and the vaporization enthalpy for the systems studied. As the pore width is decreased, the two-phase region of the binary mixture becomes narrower.

Based on the thermodynamic perturbation theory for polymer, a new equation is proposed by incorporating a wide range of molecular flexibility and perturbative interactions to describe the isotropic...

Two nonlinear optical crystals, BaVO(IO3)5 and BaTaO(IO3)5, are designed by substituting Nb with V and Ta, respectively, in BaNbO(IO3)5, which is itself a recently synthesized infrared nonlinear optical (NLO) material. The designs of BaVO(IO3)5 and BaTaO(IO3)5 from BaNbO(IO3)5 are based on the following motivation: BaVO(IO3)5 should have a larger second-harmonic generation (SHG) coefficient than BaNbO(IO3)5, as V will result in a stronger second-order Jahn-Teller effect than Nb due to its smaller ion radius, at the same time, BaTaO(IO3)5 should have a larger laser-damage threshold, due to the fact that Ta has a smaller electronegativity leading to a greater band-gap. Established on reliable first-principle calculations, it is demonstrated that BaVO(IO3)5 has a much larger SHG coefficient than BaNbO(IO3)5 (23.42 &times, 10&minus, 9 vs. 18.66 &times, 9 esu), and BaTaO(IO3)5 has a significantly greater band-gap than BaNbO(IO3)5 (4.20 vs. 3.55 eV). Meanwhile, the absorption spectra and birefringences of both BaVO(IO3)5 and BaTaO(IO3)5 are acceptable for practice, suggesting that these two crystals can both be expected to be excellent infrared NLO materials.

In this work, we relate the self-diffusion coefficient to the residual entropy of the system according to the free volume theory and scaling principle. The viscosity equation for a freely jointed Lennard-Jones chain fluid is then obtained from the expression of self-diffusion coefficient by applying the Stokes–Einstein equation. The real polyatomic compounds are modeled as chains of tangent Lennard-Jones segments. The segment size and energy parameter as well as chain length (expressed by the number of segments) are obtained from the experimental viscosity data. The proposed viscosity equation reproduces the experimental viscosity data with an average absolute deviation of 5.12% for 18 polyatomic compounds (1600 data points) over wide ranges of temperature and pressure. For engineering applications, the generalized model parameters for normal alkanes with the number of carbon atoms n > 3 are proposed. The segment energy parameter is suggested to be evaluated from the critical temperature, and the segment size parameter and chain length are correlated with the number of carbon atoms in an alkane molecule.

The Gibbs ensemble Monte Carlo simulation is used to investigate the vapor–liquid phase behavior of a binary Lennard–Jones mixture confined in a slit-like pore at reduced temperature T* = 1.0. Our simulation program is tested by comparing the simulated phase diagram with the previous simulation results from various methods. Then phase diagrams of a binary asymmetric Lennard–Jones mixture confined in the slit-like pores are investigated by varying the pore width and fluid–pore wall interaction. The asymmetric system studied exhibits azeotropic behavior. The pore walls are symmetric but selective to the two components. The simulated results indicate that both the pore width and interactions between fluid and the pore wall have significant influence on the vapor–liquid phase diagram for the binary Lennard–Jones mixture. When the interaction energy parameter between component 1 and the pore wall is fixed, the azeotropic point is shifted from the bulk azeotropic composition to component 2-rich side of the phase diagram as the interaction strength between component 2 and the pore wall is increased. In the meantime, both the azeotropic pressure and the relative volatility increase significantly. As the pore becomes narrower, it is found that the azeotropic pressure increases significantly while the azeotropic composition remains almost unchanged. The phase selectivity decreases as the pore becomes narrower in the whole range of composition. All the simulated results suggest that the azeotropic point of a binary mixture can be shifted or even be removed by the confinement and the relative volatility for vapor–liquid equilibria can be changed greatly by changing the pore width or fluid–pore wall interactions.

Structural and kinetic properties of vitamin E in biomembranes provide the key to understanding the biological functions of this lipophilic vitamin. We report a series of molecular dynamics simulations of two alpha-tocopherol/phosphatidylcholine systems and two alpha-tocopherol/phosphatidylethanolamine systems in water at 280, 310, and 350 K. The preferential position, hydrogen bonding, orientation, and dynamic properties of the alpha-tocopherol molecule in the bilayers have been examined. In all the four systems simulated, the vitamin remains in one leaflet of lipid bilayer at 280 and 310 K but flips over from one side to the other at 350 K within 200 ns of the simulation. The hydroxyl oxygen in the headgroup of alpha-tocopherol preferred a location between the third and the fifth carbon atom in the sn-2 acyl chains of the lipids. Hydrogen bonding analysis shows that the hydrogen bonds are mainly with the oxygens of the fatty acid esters rather than with the phosphate oxygens of the lipid molecule, and those with the amino groups are trivial in the case of phosphatidylethanolamines, at all three temperatures. The hydrogen bonds with phosphatidylethanolamines are more stable than those with phosphatidylcholines at low temperatures. The orientation of alpha-tocopherol in the bilayers is relatively flexible: the chromanol ring takes various tilt angles with respect to the bilayer normal, and the isoprenyl chain is mobile and able to adopt many different conformers. Calculation of lateral diffusion coefficients of alpha-tocopherol and phospholipid molecules shows that alpha-tocopherol has a comparable diffusion rate with phospholipid molecules at the gel phase but diffuses more rapidly than lipid molecules at the liquid-crystal phase.

The structural properties of fully hydrated distearoylphosphatidylcholine (DSPC) and distearoylphosphatidylethanolamine (DSPE) bilayers near the main phase transition were investigated using molecular dynamics simulations on the basis of a united-atom model. Although largely similar in their molecular structures, the two lipids were found with different molecular packing modes at temperatures below the phase transition. For DSPC, three packing modes, namely, cross-tilt, partially interdigitated, and "mixed" gel phases, were observed, while, for DSPE, the lipid tails were almost perpendicular to the lipid surface. Above the main transition temperature, both lipid bilayers transformed into a disordered liquid-crystal phase with marked greater area per lipid and gauche % of the acyl chains and smaller bilayer thickness and order parameter, in comparison with the gel phase. The transformation process of liquid-crystal to gel phase was proved to experience the nucleation and growth stages in a hexagonal manner. The electron density profiles of some major components of both lipid bilayers at various temperatures have been calculated, and the results reveal that both lipid bilayers have less interdigitation around the main transition temperature.

Mutual diffusion coefficients of concentrated 1:1 electrolyte solutions are investigated using a modified mean spherical approximation (MSA), in which the effective cationic diameter is a function of total ionic strength. We apply this improved MSA to calculate the equilibrium pair correlation function, and the Smoluchowski equation is used for the dynamics. We compare the calculated mutual diffusion coefficients of 18 uni-valence electrolyte solutions for molar concentrations up to 4.0 mol/L known experimental data. Good agreement between theoretical results and the experimental mutual diffusion coefficients are found for all the cases studied.

The ion density profiles and mean electrostatic potentials around DNA from the Monte Carlo simulations are compared with the predictions of the Poisson–Boltzmann equation and the density functional theory. The DNA molecules are modeled as a charged cylinder while the ions are represented as charged hard spheres with different diameter. In the density functional theory, the Helmholtz free energy functional due to hard-sphere repulsion and electrostatic interaction are obtained from the modified fundamental measure theory and a quadratic functional Taylor expansion, respectively. The results show that due to the inclusion of the ion–ion correlation, the density functional theory is more accurate than the Poisson–Boltzmann equation. The density functional theory gives accurate ion structures and mean electrostatic potentials near the surface of DNA. When the established density functional theory is combined with the cell model, the osmotic coefficients of aqueous DNA–electrolyte solutions can be predicted. The results show that the DFT-cell model captures the essential features of the experimental osmotic coefficient, but fails to give a quantitative description. Possible reasons for this discrepancy are discussed.

Activity coefficients at infinite dilution are reported for ten solutes (heptane, octane, nonane, decane, benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene) in sulfolane at temperatures T = (333.15 to 373.15) K. These data were measured with the help of gas−liquid chromatography (GC) in which sulfolane was used as the stationary phase. The results show good agreement with the activity coefficients at infinite dilution obtained from various methods in the literature. The temperature dependence of the activity coefficients found in the GC experiments could be confirmed using the excess enthalpy data. The present data can be used to determine and compare the selective effect caused by the addition of sulfolane to a given binary mixture in the separation processes such as extractive distillation and solvent extraction. The calculated selectivity suggests that both sulfolane and ionic liquid [HMIM+][BF4-] can act as a good solvent in separating aromatic and aliphatic compounds.

To investigate globular protein-protein and protein-salt interactions in electrolyte solutions, a potential of mean force including hard-core repulsion, van der Waals attraction and electric double layer repulsion is proposed in this work. Both van der Waals attraction and double-layer repulsion are represented using hard spheres with two-Yukawa tails. The explicit analytical solution of osmotic pressure is derived from the first-order mean spherical approximation. From the comparison between the calculated and experimental values of osmotic pressures for aqueous bovine serum albumin (BSA), lysozyme, alpha-chymotrypsin, and immuno-gamma-globulins (IgG) solutions, we found that the proposed model is adequate for the description of the interactions between proteins at low ionic strength and small self-association of protein molecules. At high ionic strength, the charge inversions of protein molecules should be taken into account.

The space-charge (SC) model and the Teorell–Meyer–Sievers (TMS) model are widely employed to calculate the membrane potential of charged porous membranes in 1-1 electrolyte solutions, but few works with the other kinds of electrolyte solutions have been reported. In this article, membrane potentials for 1-1, 1-2, 2-1 and 2-2 electrolyte solutions have been calculated numerically based on the two models using parameters of concentration, pore radius and surface charge density. The results suggest that equivalent electrolyte concentration is more suitable to characterize the membrane potential in different kinds of electrolyte solutions than electrolyte concentration. Membrane potential approaches to the Nernst potential in the low concentration region, which indicates membrane potential in monovalent cation electrolyte solution is twice as large as that in divalent cation electrolyte solution. In the high concentration region, membrane potential is close to the diffusion potential, which implies membrane potential would be reversed if the diffusion coefficient ratio of coion and counterion is larger than 1.0. While in the intermediate concentration region, membrane potential as a function of electrolyte concentration is almost linear. In the comparison of the SC and TMS models, theoretical predictions by the two models for 1-2, 2-1 and 2-2 electrolyte solutions appear to be similar to those for 1-1 electrolyte solutions reported earlier by Westermann-Clark and Christoforou [3]. The two models coincide with each other when the radius, rp, is less than 5.0 nm and the dimensionless charge density in the pore wall, q0 is less than 1.0. Otherwise, the TMS model would overestimate the membrane potential. Furthermore, the membrane potential shows dependence on the ratio of the volume charge density to equivalent electrolyte concentration, ξf, q0 and rp by the SC model, but only varies with ξf irrespective of q0 and rp by the TMS model. These findings have a significant influence on the establishment of an appropriate theory to evaluate membrane potentials in different electrolyte solutions.

A density functional theory is proposed to investigate the effects of polymer monomer-monomer and monomer-wall attractions on the density profile, chain configuration, and equilibrium capillary phase transition of a freely jointed multi-Yukawa fluid confined in a slitlike pore. The excess Helmholtz energy functional is constructed by using the modified fundamental measure theory, Wertheim's first-order thermodynamic perturbation theory, and Rosenfeld's perturbative method, in which the bulk radial distribution function and direct correlation function of hard-core multi-Yukawa monomers are obtained from the first-order mean spherical approximation. Comparisons of density profiles and bond orientation correlation functions of inhomogeneous chain fluids predicted from the present theory with the simulation data show that the present theory is very accurate, superior to the previous theory. The present theory predicts that the polymer monomer-monomer attraction lowers the strength of oscillations for density profiles and bond orientation correlation functions and makes the excess adsorption more negative. It is interesting to find that the equilibrium capillary phase transition of the polymeric fluid in the hard slitlike pore occurs at a higher chemical potential than in bulk condition, but as the attraction of the pore wall is increased sufficiently, the chemical potential for equilibrium capillary phase transition becomes lower than that for bulk vapor-liquid equilibrium.

The equilibrium selective adsorption and fluxes of oxygen/nitrogen binary gas mixtures through carbon membranes are investigated at 303 K, respectively, using a grand canonical Monte Carlo simulation and a dual control volume grand canonical molecular dynamics method. The carbon membrane pores are modeled as slit-like pores with a two-dimensional structure where carbon atoms are placed according to the structure of graphite layers. The effect of the membrane thickness, bulk pressure, and pore width on the equilibrium selective adsorption and dynamic separation factor is discussed. Meanwhile a new iteration approach to calculate the flux and dynamic separation factor of binary gas mixtures through membranes is proposed, by which we can simulate the permeation and fluxes of gases through the membranes in the presence of pressure gradient and consider the effect of pressure and composition of low-pressure side in the meantime. The simulated results show that bulk pressure and membrane thickness have no effect on the equilibrium selectivity, but they have a great effect on the fluxes and dynamic separation factors of gases. The pore width impacts the equilibrium selectivity and dynamic separation factors strongly, especially when the pore width is very small. Molecular sieving dominates the separation of oxygen/nitrogen in non-equilibrium simulations. But due to the comparable molecular size of oxygen and nitrogen, we have to modify the carbon membranes in order to improve dynamic separation of atmosphere.

Because of the increasing interest in studying the phenomenon exhibited by charge-stabilized colloidal suspensions in confining geometry, we present a density functional theory (DFT) for a hard-core multi-Yukawa fluid. The excess Helmholtz free-energy functional is constructed by using the modified fundamental measure theory and Rosenfeld's perturbative method, in which the bulk direct correlation function is obtained from the first-order mean spherical approximation. To validate the established theory, grand canonical ensemble Monte Carlo (GCMC) simulations are carried out to determine the density profiles and surface excesses of multi-Yukawa fluid in a slitlike pore. Comparisons of the theoretical results with the GCMC data suggest that the present DFT gives very accurate density profiles and surface excesses of multi-Yukawa fluid in the slitlike pore as well as the radial distribution functions of the bulk fluid. Both the DFT and the GCMC simulations predict the depletion of the multi-Yukawa fluid near a nonattractive wall, while the mean-field theory fails to describe this depletion in some cases. Because the simple form of the direct correlation function is used, the present DFT is computationally as efficient as the mean-field theory, but reproduces the simulation data much better than the mean-field theory.

Monte Carlo simulations have been carried out to investigate supercritical ethanol using the OPLS–UA [W.L. Jorgensen, Optimized intermolecular potential functions for liquid alcohols, J. Phys. Chem. 90 (1986) 1276–1284] and TraPPE–UA [B. Chen, J.J. Potoff, J.I. Siepmann, Monte Carlo calculations for alcohols and their mixtures with alkanes. Transferable potentials for phase equilibria. Part 5: united-atom description of primary, secondary, and tertiary alcohols, J. Phys. Chem. B 105 (2001) 3093–3104] force fields. Two potentials were compared and TraPPE potential performed better in reproducing densities as a function of pressure, so, it was selected in further structural analysis. The pair distribution functions were obtained and their pressure and temperature dependence were analyzed. In addition, a serial two dimensional distribution functions were plotted to depict the detailed structure of liquid and supercritical ethanol. Based on a widely used geometric criterion, hydrogen bonding statistical results showed that the hydrogen bonds become weaker but still exist under supercritical condition, which are in good agreement with recent experimental measurements. The hydrogen bonds of water, methanol and ethanol were compared and ethanol has nearly the same behavior as methanol under supercritical conditions.

A density functional theory is applied to calculating the local density profiles of colloids confined in a slit-like pore as well as the radial distribution functions of bulk colloids. The interaction between the colloidal particles is described using a hard-core Yukawa model. The excess Helmholtz energy functional is a combination of the modified fundamental measure theory of Yu and Wu (2002) for the hard-core contribution and a corrected mean-field theory for the attractive contribution. Comparison with the results from the Monte Carlo simulations shows that the corrected theory improves the density profiles of colloids in the vicinity of contact over the original mean-field theory. Both the present corrected theory and simulations suggest that there are depletion and desorption for the colloid with strong attraction between particles at low temperature.

The structural properties and transport properties of electrolyte solutions are investigated by smart Brownian dynamics simulation based on the primitive model. To test the simulation program, the radial distribution functions of ions g +- (r) and g ++ (r) for KCl solution are calculated and compared with the results of previous simulations. And then, the effects of ions diameter and concentration on the structural properties and transport properties of electrolyte solution at 298 K are extensively simulated. The results indicate that both the radial distribution function and the self-diffusion coefficient are more sensitive to the ion size than salt concentration. As the radius ratio of cation to anion increases, self-diffusion coefficients of both cation and anion become larger.

A density-functional theory is proposed to describe the density profiles of small ions around an isolated colloidal particle in the framework of the restricted primitive model where the small ions have uniform size and the solvent is represented by a dielectric continuum. The excess Helmholtz energy functional is derived from a modified fundamental measure theory for the hard-sphere repulsion and a quadratic functional Taylor expansion for the electrostatic interactions. The theoretical predictions are in good agreement with the results from Monte Carlo simulations and from previous investigations using integral-equation theory for the ionic density profiles and the zeta potentials of spherical particles at a variety of solution conditions. Like the integral-equation approaches, the density-functional theory is able to capture the oscillatory density profiles of small ions and the charge inversion (overcharging) phenomena for particles with elevated charge density. In particular, our density-functional theory predicts the formation of a second counterion layer near the surface of highly charged spherical particle. Conversely, the nonlinear Poisson-Boltzmann theory and its variations are unable to represent the oscillatory behavior of small ion distributions and charge inversion. Finally, our density-functional theory predicts charge inversion even in a 1:1 electrolyte solution as long as the salt concentration is sufficiently high.

In this work, we report an investigation by means of density functional theory (DFT) of the adsorption of hydrogen and the separation of hydrogen–carbon monoxide mixture in an isolated single-walled carbon nanotube. The theory is based on a perturbative construction of free energy functional for inhomogeneous pure fluid and binary fluid mixture. The reformulated Rosenfeld's fundamental-measure theory using the excess Helmholtz energy density from the Boublik–Mansoori–Carnahan–Starling–Leland equation of state proposed by Yu and Wu (J. Chem. Phys. 117 (2002) 10156) is applied to represent the pure and binary hard-sphere repulsive interaction, and Weeks–Chandler–Andersen perturbation theory is used to build the attractive contribution. The density profiles in three sizes of tubes at 300 K and reduced bulk density from 0.2 to 0.7 for pure hydrogen and hydrogen–carbon monoxide mixture are obtained. The theoretical calculations are in good agreement with the simulation results in this work and other data available in literature. The adsorption of hydrogen and the selectivity of hydrogen–carbon monoxide mixture are predicted from DFT and the adsorption characteristics of the isolated cylindrical wall is discussed.

Canonical-ensemble Monte Carlo simulation and an improved fundamental-measure theory are applied to calculating the structures and chemical potentials of neutral and associating spherical particles confined in rectangular or corrugated microchannels. It is found that the confinement significantly affects the distributions of neutral spheres in the microchannels, especially at high densities or near the confining surfaces. However, for associating particles, the combined effects of packing and association lead to virtually uniform density distributions. The density profiles calculated from the density functional theory agree well with simulation results for neutral hard spheres in both rectangular and corrugated microchannels except when the average packing density inside the channel is near the freezing point.

In substitution of path integral isomorphism of the quantum particle, an effective polymer ring model is proposed in the density functional calculation for hydrogen adsorption in single-walled carbon nanotubes. The excess intrinsic Helmholtz energy for quantum particles includes contributions from hard-sphere repulsion, interatomic bonding and soft attraction. The first two contributions are considered through the method developed by Yu and Wu [J. Chem. Phys. 117, 2368 (2002)], and the last contribution is obtained from mean field approximation using Weeks–Chandler–Anderson potential. The theoretical predictions are in good agreement with Monte Carlo simulation data for the density distributions of the hydrogen molecule inside the tube. In addition, the proposed model is applied to the calculation of the adsorption isotherms of hydrogen at 100 and 150 K. The present model is simpler than the current existing theories for quantum fluids.