Free Energy

With the publication of Wilfred Bion’s text 'Learning from Experience', psychoanalysis was afforded a new schema for understanding the processes and implications involved in an infant’s contact with their caregivers. As a result, our conception of some of the most fundamental phenomena of psychic life was significantly enriched. By proposing his theory of alpha-functioning, Bion mapped out how meaningful connections to the internal and external worlds become established in the mind. In contrast, and through working clinically with psychotic patients, Bion revealed how these ties can catastrophically come undone. It is with these ideas, as well as their links to a corresponding set of neuroscientific constructs relating to the Markov blanket and principally developed by Karl Friston, that this paper is concerned. Through an investigation of the psychic functioning originally dubbed ‘dream-work-alpha’, the paper’s first section focuses on how Bion conceived of the creation of a ‘contact-barrier’ that allows for the differentiation of consciousness from an unconscious mind. Casting the ramifications of this organisation in sharp relief, the psychotic disorganisation of the contact-barrier is then explored. The discussion subsequently broadens to incorporate contemporary theories from free energy neuroscience that bear significant and illuminating relations to the psychoanalytic ideas espoused by Bion over half a century ago. Finally, through posing a series of three questions with accompanying discussions, a superimposition of these theoretical schemas is attempted. These suggestions directly address 1. whether there is an intimate connection between the interoceptive contact-barrier and the exteroceptive Markov blanket, 2. whether a disobjectalising of the contact-barrier may be reflected as a tear in the functional fabric of the Markov blanket, and 3. what the clinical implications are of working at the level of the projected surface. Ultimately, the aim of the paper is to expose relevant points of contact within and between the varying conceptual frameworks; frameworks that ultimately derive from disciplines that are both concerned with examining the underlying mechanisms of the mind-brain.

Salicylate synthase from Mycobacterium tuberculosis, MbtI, initiates the biosynthesis of siderophores by converting chorismate to salicylate. Nevertheless, three more distinct activities for wild-type MbtI have been detected in vitro: isochorismate synthase, isochorismate pyruvate lyase, and chorismate mutase. In this work, hybrid Quantum Mechanics/Molecular Mechanics methods have been used to get the first simulation of the chorismate mutase activity of MbtI.

The two opponents, toxin (CcdB, LetB or LetD, protein G, LynB) and antidote (CcdA, LetA, protein H, LynA), in the plasmid addiction system ccd of the F plasmid were studied by different biophysical methods. The thermodynamic stability was measured at different temperatures combining denaturant and thermally induced unfolding. It was found that both proteins denature in a two-state equilibrium (native dimer versus unfolded monomer) and that CcdA has a signi®cantly lower thermodynamic stability. Using a numerical model, which was developed earlier by us, and on the basis of the determined thermodynamic parameters the concentration dependence of the denaturation transition temperature was obtained for both proteins. This concentration dependence may be of physiological signi®cance, as the concentration of both ccd addiction proteins cannot exceed a certain limit because their expression is controlled by autoregulation. The in¯uence of DNA on the thermal stability of the two proteins was probed. It was found that cognate DNA increases the melting temperature of CcdA. In the presence of non-speci®c DNA the thermal stability was not changed. The melting temperature of CcdB was not in¯uenced by the applied double-stranded oligonucleotides, neither cognate nor unspeci®c.

We consider the theoretical setting of a superfluid like 3He in a rotating container, which is set between the two layers of a type-II superconductor. We describe the superfluid vortices as a 2-dimensional Ising-like model on a triangular lattice in presence of local magnetic fields. The interaction term of the superfluid vortices with the Abrikosov vortices of the superconductor appears then as a symmetry breaking term in the free energy. Such a term gives a higher probability of quantum tunnelling across the potential barrier for bubbles nucleation, thus favouring quantum cavitation.

The behavior of binary mixtures of carbon dioxide+alkanol (1-butanol, 2-butanol, 1-pentanol, or 2-pentanol) at high pressures was modeled using the Stryjek-Vera version of the Peng-Robinson equation of state. Two mixing rules were compared for this purpose: the classical one-fluid van der Waals and the Wong-Sandler mixing rules. In the case of the latter mixing rule, the NRTL model for the excess Gibbs free energy was used. We observed that both mixing rules can reproduce the qualitative aspects of the critical diagrams of these binary mixtures. A comparison of the results shows that there is no clear superiority of one mixing rule over the other in terms of the ability to predict the critical behavior of these mixtures.

Mode of interactions of three flavonoids [morin (M), quercetin (Q), and rutin (R)] with chicken blood ds.DNA (ck.DNA) has been investigated spectrophotometrically at different temperatures including body temperature (310 K) and at two physiological pH values, i.e. 7.4 (human blood pH) and 4.7 (stomach pH). The binding constants, K f , evaluated using Benesi-Hildebrand equation showed that the flavonoids bind effectively through intercalation at both pH values and body temperature. Quercetin, somehow, showed greater binding capabilities with DNA. The free energies of flavonoid-DNA complexes indicated the spontaneity of their binding. The order of binding constants of three flavonoids at both pH values were found to be K f(Q) > K f(R) > K f(M) and at 310 K.

Pure diblock copolymer melts exhibit a narrow range of conditions at which bicontinuous and cocontinuous phases are stable; such conditions and the morphology of such phases can be tuned by the use of additives. In this work, we have studied a bidisperse system of diblock copolymers using theory and simulation. In particular, we elucidated how a short, lamellar-forming diblock copolymer modifies the phase behavior of a longer, cylinder-forming diblock copolymer. In a narrow range of intermediate compositions, self-consistent field theory predicts the formation of a gyroid phase although particle-based simulations show that three phases compete: the gyroid phase, a disordered cocontinuous phase, and the cylinder phase, all having free energies within error bars of each other. Former experimental studies of a similar system have yielded an unidentified, partially irregular bicontinuous phase, and our simulations suggest that at such conditions the formation of a partially transformed network phase is indeed plausible. Close examination of the spatial distribution of chains reveals that packing frustration (manifested by chain stretching and low density spots) occurs in the majority-block domains of the three competing phases simulated. In all cases, a double interface around the minority-block domains is also detected with the outer one formed by the short chains, and the inner one formed by the longer chains.

It is shown experimentally that the desorption of sodium decyl sulphate from the liquid/air interface is purely diffusion controlled, while the desorption of higher surface active surfactants such as the non-ionic surfactants Triton X-100 and tridecyl dimethyl phosphine oxide obeys a mixed mechanism. The desorption kinetics of β-lactoglobulin (BLG) and β-casein is, however, determined by a barrier mechanism. From the analysis of the BLG and β-casein desorption kinetics at different temperatures the activation energy of desorption is calculated. The values obtained are rather close to the free energy of adsorption. The theoretical model of desorption kinetics predicts that these two energetic parameters are similar if the adsorption activation energy is low. This explains why substances with a higher adsorption activity have a lower desorption rate. Adsorption kinetics studies for β-casein with and without forced convection show the same equilibrium surface tension values. This leads to the conclusion that the protein adsorption at liquid interfaces is thermodynamically reversible, although the slow desorption kinetics would allow to assume it to be an irreversible process.

The phase diagram of water as obtained from computer simulations is presented for the first time for two of the most popular models of water, TIP4P and SPC=E. This Letter shows that the prediction of the phase diagram is an extremely stringent test for any water potential function, and that it may be useful in developing improved potentials. The TIP4P model provides a qualitatively correct description of the phase diagram, unlike the SPC=E model which fails in this purpose. New behavior not yet observed experimentally is predicted by the simulations: the existence of metastable reentrant behavior in the melting curves of the low density ices (I; III; V) such that it could be possible to transform them into amorphous phases by adequate changes in pressure.

First-principles phase equilibria calculations often overestimate an order-disorder transition temperature due to the neglect of local lattice distortion effects originated from the mixture of elements of different atomic sizes. The lattice vibration effects introduced through the Debye-Grü neisen theory within the quasi-harmonic approximation has proven to be quite effective in circumventing the inconveniences. With the preferential enhancement of the stability of a disordered phase by introducing the lattice vibration effects, the transition temperature was reduced considerably. In order to gain further insight into the lattice vibration effects, a systematic investigation of the vibrational free energy of the Debye-Grü neisen theory is attempted on the two-dimensional square lattice which constitutes a prototype study prior to the firstprinciples calculations on realistic alloy systems. A particular focus of the present study is placed on the effects of Debye temperatures of constituent phases on the transition temperature. It is shown that lattice softening by lattice vibration stabilizes the disordered phase by reducing the energy expended to accommodate atoms of different sizes, which is manifested by the reduction of the curvature of the atomic potentials. It is, however, predicted that an opposite case can also take place. When the Debye temperature of an ordered phase is lower than that of the pure metals, the ordered phase is more stabilized and the inclusion of the lattice vibration effects in the free energy raises the resultant transition temperature.

Cell attachment and spreading to titanium-based alloy surfaces is a major parameter in implant technology. In this paper, substratum surface hydrophobicity, surface free energy, interfacial free energy and surface roughness were investigated to ascertain which of these parameters is predominant in human fibroblast spreading. Two methods for contact angle measurement were compared: the sessile drop method and the captive bubble two-probe method. The relationship between surface roughness and the sessile drop contact angles of various engineered titanium surfaces such as commercial pure titanium (cp-Ti), titanium -aluminium -vanadium alloy (Ti -6Al -4V), and titaniumnickel (NiTi), was shown. Surface free energy (SFE) calculations were performed from contact angles obtained on smooth samples based on the same alloys in order to eliminate the roughness effect. SFE of the surfaces have been calculated using the Owens -Wendt (OW) and Van Oss (VO) approaches with the sessile drop method. The OW calculations are used to obtain the dispersive (c d ) and polar (c p ) component of SFE, and the VO approach allows to reach the apolar (c LW ) and the polar acid -base component (c ab ) of the surface. From captive bubble contact angle experiments (air or octane bubble under water), the interfacial free energy of the different surfaces in water was obtained. A relationship between cell spreading and the polar component of SFE was found. Interfacial free energy values were low for all the investigated surfaces indicating good biocompatibility for such alloys. D

The aggregation and interface behavior of alkyltrimethylammonium bromides (C n H 2n؉1 (CH 3 ) 3 N ؉ Br ؊ : C n TMA with n ‫؍‬ 14, 16, 18) have been investigated in concentrated orthophosphoric acid by means of surface tension measurements. Adsorption of these cationic surfactants at the interface between air and aqueous H 3 PO 4 solutions has been determined at 298 K using the Wilehlmy plate method. Measurements in the most concentrated H 3 PO 4 -H 2 O mixture (95% by weight of acid or 17.5 mol/L) were done at the n-decane/H 3 PO 4 interface using the ring method to avoid any contamination with atmospheric moisture. The critical micelle concentration (CMC), the maximum surface concentration, and surface pressure of C 16 TMA in water-H 3 PO 4 mixtures and of the homologous series of surfactants, C n TMA, in 95%-H 3 PO 4 , were determined at 323 K. Benzene has been used as a test solute for solubilization measurements in 95%-H 3 PO 4 containing C 16 TMA micelles. From this experimental work, it can be concluded that micelles are forming even in the most concentrated solutions in acid and that the CMC displays a large depression between 4 and 10 mol/L of H 3 PO 4 . The maximum surface concentration increases by steps in the lowest (0 to 1 mol/L) and highest range of concentration (8 to 10 mol/L) in acid. The Klevens equation relating the CMC in relation to the chain length of the surfactants holds in 95%-H 3 PO 4 . Values obtained for the parameters of the Klevens equation and for the free energy of micellization in 95%-H 3 PO 4 have been compared to other strongly acidic media like concentrated sulfuric or methanesulfonic acids.

The bagasse fly ash, an industrial solid waste of sugar industry, was used for the removal of cadmium and nickel from wastewater. As much as 90% removal of cadmium and nickel is possible in about 60 and 80 min, respectively, under the batch test conditions. Effect of various operating ...

A Mg/Fe hydrotalcite-like-compound (HTlc) was prepared and its affinity toward the removal of SeO 2− 3 from an aqueous medium was studied as a function of pH, time, temperature, particle dose, and SeO 2− 3 concentration. The fraction of SeO 2− 3 removal increases with decrease in both pH and temperature. The adsorption data are fitted to the Langmuir adsorption isotherm in the temperature range 303-333 K, and the thermodynamic parameters viz. standard Gibbs' free energy change (G •), enthalpy change (H •), and entropy change (S •) are calculated. The negative value of H • indicates that the adsorption process is exothermic. The apparent equilibrium constants (K a) are also calculated and found to decrease with increase in temperature.

The influence of the concentration of the purine (PU) and adenine (AD) on the corrosion of copper in 0.5 M Na 2 SO 4 solutions (pH 6.8) was studied. The investigations involved electrochemical polarization methods as well as electrochemical quartz crystal microbalance (EQCM) techniques. The inhibition efficiency increases with an increase in the concentration of PU and AD. Adherent layers of inhibitors were postulated to account for the protective effect. The adsorptions of inhibitors were found to occur on the surface of copper according to the Langmuir isotherm. The values of standard free energies of adsorption suggest the chemical adsorption of PU and AD on the copper surface.

The inhibitor effect of tryptamine on the corrosion of mild steel in 0.5 M hydrochloric acid at 30°C was investigated using linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increases with an increase in concentration of tryptamine. At 500 ppm tryptamine the inhibition efficiency calculated by these techniques is around 97%. Cathodic and anodic polarization curves of mild steel in the presence of different concentrations of tryptamine at 30°C reveal that it is a mixed type inhibitor. Tryptamine follows Langmuir adsorption with adsorption free energy of À35.07 kJ mol À1 .

RNA folding is a kinetic process governed by the competition of a large number of structures stabilized by the transient formation of base pairs that may induce complex folding pathways and the formation of misfolded structures. Despite of its importance in modern biophysics, the current understanding of RNA folding kinetics is limited by the complex interplay between the weak base-pair interactions that stabilize the native structure and the disordering effect of thermal forces. The possibility of mechanically pulling individual molecules offers a new perspective to understand the folding of nucleic acids. Here we investigate the folding and misfolding mechanism in RNA secondary structures pulled by mechanical forces. We introduce a model based on the identification of the minimal set of structures that reproduce the patterns of force-extension curves obtained in single molecule experiments. The model requires only two fitting parameters: the attempt frequency at the level of individual base pairs and a parameter associated to a free energy correction that accounts for the configurational entropy of an exponentially large number of neglected secondary structures. We apply the model to interpret results recently obtained in pulling experiments in the three-helix junction S15 RNA molecule (RNAS15). We show that RNAS15 undergoes force-induced misfolding where force favors the formation of a stable non-native hairpin. The model reproduces the pattern of unfolding and refolding force-extension curves, the distribution of breakage forces and the misfolding probability obtained in the experiments.

The unfolding of a protein by the application of an external force pulling two atoms of the protein can be detected by atomic force and optical tweezers technologies as have been broadly demonstrated in the past decade. Variation of the applied force results in a modulation of the free-energy barrier to unfolding and thus, the rate of the process, which is often assumed to have single exponential kinetics. It has been recently shown that it is experimentally feasible, through the use of force clamps, to estimate the distribution of unfolding times for a population of proteins initially in the native state. In this Letter we show how the analysis of such distributions under a range of forces can provide unique information about the underlying free-energy surface such as the height of the free-energy barrier, the preexponential factor and the force dependence of the unfolding kinetics without resorting to ad hoc kinetic models.

The purpose of this study was to describe the problem-solving behaviors of experts and novices engaged in solving seven chemical equilibrium problems. Thirteen novices (five highschool students, five undergraduate majors, and three nonmajors) and ten experts (six doctoral students and four faculty members) were videotaped as they individually solved standard chemical equilibrium problems. The nature of the problems was such that they required more than mere recall or algorithmic learning and yet simple enough to provide the novices a reasonable chance of solving them. Extensive analysis of the think-aloud protocols produced 27 behavioral tendencies that can be used to describe and differentiate between successful and unsuccessful problem solvers. Successful solvers' perceptions of the problem were characterized by careful analysis and reasoning of the task, use of related principles and concepts to justify their answers, frequent checks of the consistency of answers and reasons, and better quality of procedural and strategic knowledge. Unsuccessful subjects had many knowledge gaps and misconceptions about the nature of chemical equilibrium. Even faculty experts were sometimes unable to correctly apply common chemical principles during the problem-solving process. Important theoretical concepts such as molar enthalpy, heat of reaction, free energy of formation, and free energy of reaction were rarely used by novices in explaining problems.

The study of the thermodynamical stability of Fe 80 Ni 20 nanoparticles in the framework of embedded-atom method and moleculardynamics simulations shows evidence of large surface contributions to the free energy for particles with diameters up to 15 nm or more. The change of the free energy compared to its bulk value leads to a reduction of the martensitic equilibrium temperature, M 0 , and can suppress martensitic transformations in small particles. In addition the formation of martensite can be suppressed due to the lack of pre-existing nucleation sites necessary to overcome the energy barrier along the transformation path from austenite to martensite.

Complex equilibria and phase transformations involving diffusion can now be calculated quickly and efficiently. Detailed examples are given for cases which involve varying degrees of non-equilibrium and therefore time-dependence. Despite very good agreement between such calculations and experimental results, many potential end-users are still not convinced that such techniques could be usefully applied to their own specific problems. Friendly graphic interface versions of calculating software are now generally available, so the authors conclude that the most likely source of the reluctance to use such tools lies in the formulation of relevant questions and the interpretation of the results. Although the potential impact of such tools was foreseen many years ago [M. Hillert, Calculation of phase equilibria, in: Conference on Phase Transformations, 1968], few changes in the relevant teaching curricula have taken into account the availability and power of such techniques. This paper has therefore been designed not only as a collection of interesting problems, but also highlights the critical steps needed to achieve a solution. Each example includes a presentation of the "real" problem, any simplifications that are needed for its solution, the adopted thermodynamic formulation, and a critical evaluation of the results. The availability of such examples should facilitate changes in subject matter that will both make it easier for the next generation of students to use these tools, and at the same time reduce the time and effort currently needed to solve such problems by less efficient methods. The first set of detailed examples includes the deoxidation of steel by aluminum; heat balance calculations associated with ladle additions to steel; the determination of conditions that avoid undesirable inclusions; the role of methane in sintering atmospheres; interface control during the physical vapour deposition of cemented carbide; oxidation of γ-TiAl materials; and simulation of the thermolysis of metallorganic precursors for Si-C-N ceramics and interface reaction of yttrium silicates with SiC-coated C/C-SiC composites for heat shield applications. A second set of examples, more dependent on competitive nucleation and growth, includes segregation and carburization in multicomponent steels and features a series of sophisticated simulatons using DICTRA software. Interfacial and strain energies become increasingly important in defining phase nucleation and morphology in such problems, but relatively little information is available compared to free energy and diffusion databases. The final section therefore demonstrates how computational thermodynamics, semi-empirical atomistic approaches and first-principles calculations are being used to aid filling this gap in our knowledge.

In this paper we describe an approach for teaching the relation between chemical equilibrium and free energy that is, according to our experience, very efficient and enlightening. This approach has a strong visual appeal and can be used at different levels, from simple presentation of the results as graphs of free energy versus reaction mixture composition, up to full derivation of formulas to find the equations of the curves.

Coriander leaves are widely used in cooking throughout the world. Thermal degradation kinetics of chlorophyll a, b, and total chlorophyll in coriander leaf puree was investigated at varying levels of pH (4.5-8.5) and processing temperature (80-145°C). Coriander puree at pH 4.5 was processed at 80°to 100°C, whereas that at pH 5.5 to 8.5 was processed at 105°to 145°C. Chlorophyll degradation followed first-order reaction kinetics. Good agreement was found between estimated and experimental chlorophyll retention in all cases (R 2 >0.80). Activation energies ranged from 6.57 to 96.00 kJ/mol. Reaction rate and activation energy data indicated that chlorophylls were more stable at alkaline pH. Transition state theory was applied to estimate the enthalpy, entropy, and Gibbs free energy of activation. Enthalpy of activation (ΔH # ) ranged from 3.46 to 91.99 kJ/mol, whereas entropy of activation (ΔS # ) ranged from −0.265 to −0.047 kJ/(mol K). The overall free energy change was 107.55 kJ/mol. Results indicated that, the compensation effect did not exist for chlorophyll degradation in coriander puree during thermal processing.

The present paper is aimed to investigate and develop cheap adsorption methods for colour removal from wastewater using waste material de-oiled mustard as adsorbent. De-oiled mustard, a biosorbent, was successfully utilized for removing a water-soluble xanthene dye, Erythrosine from wastewater. Kinetic studies of adsorption of Erythrosine at de-oiled mustard were carried out at 30 • C, using aqueous solutions with 5 × 10 −5 M concentration of Erythrosine. The adsorption process followed a pseudo-first order model. The equilibrium process can be well described by both Freundlich and Langmuir models, at 30, 40 and 50 • C. Free energy of adsorption (G •), enthalpy (H •), and entropy (S •) changes were calculated to predict the nature of adsorption. The estimated values for G • were −12.81 × 10 3 and −12.57 × 10 3 over activated carbon and activated de-oiled mustard at 203 K (30 • C), indicate toward a spontaneous process. The positive value for H • indicates that the adsorption of Erythrosine dye to de-oiled mustard is an endothermic process.

The critical micelle concentration (cmc) of TX-100 in formamide (FA) was determined from surface tension measurements as functions of temperature and NaCl concentration. At 25°C, cmc was also determined by the fluorescence method. For the sake of comparison, micellization parameters of TX-100 were also determined in water. cmc, aggregation number, and standard free energy of micellization in FA are about 400 times higher, 10 times lower, and 2 times higher than in water, respectively. On increasing the temperature, cmc in FA shows a slight increase, whereas in water it decreases. The logarithm of relative cmc decreases linearly with added NaCl concentration in both FA and water, and the rate of this decrease is surprisingly equal in the two solvents. Micellization of TX-100 is exothermic in FA, but endothermic in water. The cloud point (CP) of TX-100 was determined in FA + water medium and that in pure FA was estimated to be $233°C when [TX-100] = 0.15 mol kg À1 . Surface excess values of TX-100 were calculated from Gibbs and Langmuir adsorption isotherms. Values of standard free energy of adsorption calculated from the Rosen-Aronson equation and from the Langmuir adsorption isotherm are comparable. The ratio of the surface tension of the solvent to that at the cmc has been demonstrated as a novel scale for measuring solvophobicity.

The interaction between the zwitterionic buffers (3-[N-bis(2-hydroxyethyl)amino]-2-hydroxy propane sulfonic acid, N-(2-actamido)-2aminoethane sulfonic acid, and 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxy propane sulfonic acid) with some divalent transition metal ions (Cu II , Ni II , Co II , Zn II , and Mn II ) were studied at different temperatures (298.15 to 328.15) K at ionic strength I = 0.1 mol AE dm À3 NaNO 3 and in the presence of 10%, 30%, and 50% (w/w) dioxene by using potentiometry. The thermodynamic stability constants were calculated as well as the free energy change for the 1:1 binary complexation. The protonation constants of the zwitterionic buffers were also determined potentiometrically under the above conditions.

The adsorption of lead onto date palm fibers (palm fibers) and leaf base of palm (petiole) has been examined in aqueous solution by considering the influence of various parameters such as contact time, solution pH, adsorbent dosage, particle sizes, ionic strength, and temperature. The adsorption of Pb(II) increased with an increase of contact time. The optimal range of pH for Pb(II) adsorption is 3.0–4.5. The linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both models fitted well. The monolayer adsorption capacity of Pb(II) on palm fibers and petiole was found as 18.622 and 20.040 mg/g, respectively, at pH 4.5 and 25°C. Dubinin-Radushkevich (D-R) isotherm model was also applied to equilibrium data. The mean free energy of adsorption (2.397 and 4.082 kJ/mol) onto palm fibers and petiole, respectively, may be carried out via physisorption mechanism. Pseudo-first-order rate equation and pseudo-second-order rate equation were applied to study the adsorption kinetics. In comparison to first-order kinetic model, pseudo-second-order model described well the adsorption kinetics of Pb(II) onto palm fibers and petiole from aqueous solution. From the results of the thermodynamic analysis, Gibbs free energy ΔG, enthalpy change ΔH, and entropy ΔS were determined. The positive value of ΔH suggests that interaction of Pb(II) adsorbed by palm fibers is endothermic. In contrast, the negative value of ΔH indicates that interaction of Pb(II) ions by petiole is exothermic. The negative value of ΔG indicates that the adsorption of Pb(II) ions on both palm fibers and petiole is a spontaneous process.

Gas-phase enthalpies of formation, acidities, and strain energies of the [m, n]polyprismanes (m ‡ 2; n 5 3-8; m 3 n £ 16): a CBS-Q//B3, G4MP2, and G4 theoretical study Abstract Gas-phase standard state (298.15 K, 1 atm) enthalpies of formation (D f H (g) o ) and enthalpies (D acid H (g) o ) and free energies (D acid G (g) o ) of acid dissociation were calculated for the [m, n]polyprismanes (m C 2; n = 3-8; m 9 n B 16) using the composite method CBS-Q//B3, G4MP2, and G4 levels of theory. Excellent agreement was obtained between the theoretical estimates and experimental values for [2, 4]polyprismane (cubane), the only member with reliable experimental data. Gas-phase acidities of the [2, 3], , and [2, 5]polyprismanes correlate well with percent s-character of the C-H bonds as determined by nuclear magnetic resonance spectroscopy. Based on this correlation, and calculations on the [2, n] (n = 3-8) series, no substantial change in the gas-phase acidity or C-H bond s-character is expected with increasing [2,n] polyprismane ring size at n = 6-8. Where three or more stacked [m, n]polyprismane rings are present (m [ 2), geometry optimizations for the deprotonated anions converged on cage-opened non-prismatic geometries, suggesting these compounds may be structurally unstable to gas-phase deprotonation/protonation cycles and potentially preventing reliable experimental measurement or calculation of their acidities. Total strain energies (E str ) increase with larger [m, n]polyprismane size, and strain energies per one C-C bond (E str CC ) increase with increasing stack height within a given ring size series. Within a given stack height, E str CC reaches a minimum with a ring size of five, increasing with either decreasing or increasing ring size away from this minima. E str and E str CC do not correlate with gas-phase acidity, likely because the deprotonated anionic [2, n]polyprismane geometry retains approximately equal strain as the undissociated species despite substantial geometry changes due to carbon acid dissociation.

The miscibility of the dicyanate of bisphenol A, with three dicyanate monomers, with aryl/alkylene ether backbones is studied at different compositions of a binary blend. Solubility parameters are calculated for dicyanate monomers and selected oligmers using the methods of Small and Fedors to predict compatibility. The results are evaluated in terms of the accuracy of the model in reproducing observed data. Gibbs free energy of mixing (∆G mix) values for selected blends are calculated using the BLENDS module of Cerius 2. Empirical data (HPLC and MS) are used to inform the construction of selected models to represent different stages of polymer conversion. DMTA analysis is performed to examine the thermo-mechanical properties of the resulting blends and compared with the simulated blend data.

The phase diagram of water as obtained from computer simulations is presented for the first time for two of the most popular models of water, TIP4P and SPC=E. This Letter shows that the prediction of the phase diagram is an extremely stringent test for any water potential function, and that it may be useful in developing improved potentials. The TIP4P model provides a qualitatively correct description of the phase diagram, unlike the SPC=E model which fails in this purpose. New behavior not yet observed experimentally is predicted by the simulations: the existence of metastable reentrant behavior in the melting curves of the low density ices (I; III; V) such that it could be possible to transform them into amorphous phases by adequate changes in pressure.

The mechanism of the hydrogen evolution and reduction reactions on a nickel electrode has been examined several times, mainly because of the potential application of this material in water electrolysers and fuel cells. This work presents the results of electrochemical studies of hydrogen evolution and reduction on nickel plate in 30 wt% KOH at different temperatures ranging from 28 to 77-C. Kinetic parameters were obtained by steady state polarization experiments, compleme@d by cyclic voltammetry. Nickel showed an improved performance with increaGng temperature. It has been observed that a temperature increase from 28 to 77'C results iq an almost equal Tafel slope of 80 mV dcc-*. This bchaviour could be the impact of such factors as variation of the adsorbed hydrogen coverage with potential or the entropic contribution to the free energy of activation. However, some controversy still remains. Current density values increase with increasing temperature. A current-time dependence curve shows that the current density is constant up to 200 s, then it decreases with time. However, after loo0 s, current density is again constant and remains so up to 3000s. The apparent energy of activation AH was calculated from the Arrhenius plot.

A comparative study of 5-amino-1,2,4-triazole (5-ATA), 5-amino-3-mercapto-1,2,4-triazole (5-AMT), 5-amino-3-methylthio-1,2,4-triazole (5-AMeTT) and 1-amino-3-methylthio-1,2,4-triazole (1-AMeTT) as inhibitors for mild steel corrosion in 0.1 M HCl solution at 20 • C was carried out. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of these inhibitors under the influence of various experimental conditions. Measurements of open circuit potential (OCP) as a function of time till reaching the steady-state potentials (E st ) were also established. The studies have shown that 5-AMT was the most efficient inhibitor reaching values of inhibition efficiency (IE%) up to 96% at a concentration of 10 −3 M. Polarization curves showed that the four studied compounds act as mixed inhibitors. The potential of zero charge (PZC) of mild steel was determined in 0.1 M HCl in the absence and presence of the studied inhibitors. The effect of chemical structure of the four tested inhibitors was discussed. Results obtained from OCP versus time, polarization and impedance measurements are in good agreement.

The biosorption of Acid Red 337 and Acid Blue 324 from aqueous solution on Enteromorpha prolifera was investigated in a batch system. Optimum initial pH and temperature values for AB 324 and AR 337 dyes were found as 3.0 and 2.0, 25 and 30 • C, respectively and the optimum dye uptake amounts per unit mass were obtained at 0.5 g/l biosorbent concentration for both dyes. The Langmuir, Freundlich and Redlich-Peterson adsorption models were applied to experimental equilibrium data and the isotherm constants were calculated using Polymath 4.1 software. The monolayer covarage capacities of E. prolifera for AB 324 and AR 337 were obtained as 160.6 and 210.9 mg/g, respectively. It was observed that the biosorption data fitted well to Redlich-Peterson model than the other models. The external diffusion and intraparticle diffusion models were also applied to biosorption data of AR 337 and AB 324 and it was found that both the surface adsorption as well as intraparticle diffusion contribute to the actual adsorption process. The constants obtained from the pseudo-second order kinetic model at different temperatures were evaluated and the activation energies for the biosorption of AB 324 and AR 337 were found to be −31.5 and −19.87 kJ/mol, respectively. Thermodynamic parameters such as enthalpy, entropy and Gibb's free energy changes were also calculated and it was concluded that the biosorption of these acidic dyes on E. prolifera was exothermic in nature.

We demonstrate that interferometric lithography provides a fast, simple approach to the production of patterns in self-assembled monolayers (SAMs) with high resolution over square centimeter areas. As a proof of principle, two-beam interference patterns, formed using light from a frequency-doubled argon ion laser (244 nm), were used to pattern methyl-terminated SAMs on gold, facilitating the introduction of hydroxyl-terminated adsorbates and yielding patterns of surface free energy with a pitch of ca. 200 nm. The photopatterning of SAMs on Pd has been demonstrated for the first time, with interferometric exposure yielding patterns of surface free energy with similar features sizes to those obtained on gold. Gold nanostructures were formed by exposing SAMs to UV interference patterns and then immersing the samples in an ethanolic solution of mercaptoethylamine, which etched the metal substrate in exposed areas while unoxidized thiols acted as a resist and protected the metal from dissolution. Macroscopically extended gold nanowires were fabricated using single exposures and arrays of 66 nm gold dots at 180 nm centers were formed using orthogonal exposures in a fast, simple process. Exposure of oligo(ethylene glycol)-terminated SAMs to UV light caused photodegradation of the protein-resistant tail groups in a substrate-independent process. In contrast to many protein patterning methods, which utilize multiple steps to control surface binding, this single step process introduced aldehyde functional groups to the SAM surface at exposures as low as 0.3 J cm -2 , significantly less than the exposure required for oxidation of the thiol headgroup. Although interferometric methods rely upon a continuous gradient of exposure, it was possible to fabricate well-defined protein nanostructures by the introduction of aldheyde groups and removal of protein resistance in nanoscopic regions. Macroscopically extended, nanostructured assemblies of streptavidin were formed. Retention of functionality in the patterned materials was demonstrated by binding of biotinylated proteins.

The discovery that the protease from the human immunodeficiency virus Department of Biology and the Biocalorimetry Center (HIV) belongs to the aspartic protease family has generated renewed interest in this class of proteins. In this paper, the interactions of endothiapepsin, an The Johns Hopkins University aspartic proteinase from the fungus Endothia parasitica, with the inhibitor 3400 N. Charles Street/144 Mudd Hall, Baltimore, MD pepstatin A have been studied by high-sensitivity calorimetric techniques.

This study investigates the crystallization kinetics of palm stearin (PS), a palm oil fraction, in blends with sesame seed oil. The results indicate that the crystallization behavior of PS in sesame oil is mainly associated with the crystallization of tripalmitin. Therefore, crystallization of blends of 26, 42, 60, and 80% (wt/vol) PS in sesame oil was described by equations developed for simpler systems (e.g., Fisher and Turnbull equation). The isothermal crystallization, melting profile, and fitting of the kinetics of nucleation to the Fisher and Turnbull equation showed that the 26, 42, and 60% PS/sesame oil blends crystallized mainly in the β1′ polymorph state. In contrast, the 80% blend crystallized in two different polymorph states (i.e., β1′ at T⪯307.6 K and β1 at T≽308.2 K). The data indicated that, in spite of the higher concentration of PS in the 80% PS/sesame oil system, crystallization in the β1 state required more free energy for nucleation (δG c ) than β1′ crystallization in the 26, 42, and 60% PS/sesame oil. At the low cooling rate used (1 K/min) it was observed that, for a particular PS blend, the higher the effective supercooling the higher the viscosity of the oil phase and the smaller the induction time of crystallization (Ti). Additionally, the β1′ crystals from PS, developed at the highest effective supercooling investigated, were smaller than the β1 crystals obtained at lower effective supercooling.

Pure Y2O3 and Y2O3-ZrO2 solid solutions have been prepared by melt atomization and by pyrolysis of nitrate solutions. Extended solubility is readily achieved in both techniques for the entire composition range investigated: melts with 0.30% ZrO2 and precursors with 0.50% ZrO2. However, solidification of under cooled droplets yields almost exclusively single phase powders with the structure of cubic yttria (D5(sub 3)). In contrast, the pyrolysis route leads to a sequence of metastable microstructures beginning with a nanocrystalline disordered fluorite-based (C1) solid solution. Further heating leads to the evolution of much larger (micron size) flake crystals with a (001) texture, concurrent with partial ordering of the oxygen ions to the sites occupied in the D5(sub 3) addition.

We present a maximum likelihood argument for the Bennett acceptance ratio method, and derive a simple formula for the variance of free energy estimates generated using this method. This derivation of the acceptance ratio method, using a form of logistic regression, a common statistical technique, allows us to shed additional light on the underlying physical and statistical properties of the method. For example, we demonstrate that the acceptance ratio method yields the lowest variance for any estimator of the free energy which is unbiased in the limit of large numbers of measurements.

In the majority of citrus juices, bitterness is mainly ascribed to the presence of limonoids (triterpenes) and flavanone glycosides (flavonoids), namely limonin and naringin. In this study, the selective removal of limonin and naringin from citrus juice by batch adsorption to different materials was investigated. Since the removal of reducing sugars, pigments and vitamin C may also occur, the eventual adsorption of these compounds was also investigated. The following adsorbents were tested: activated diatomaceous earths, granulated activated carbon and synthetic neutral resins (Amberlite XAD-4, XAD-7 and XAD-16). Both Freundlich and Langmuir isotherm models showed a good fit to the adsorption of limonin to the resins used. Concerning naringin adsorption, a good fit of these models was only observed when the XAD-7 resin was used. Sigmoidal profiles were obtained for the adsorption of limonin to granular activated carbon. Unfavourable isotherms were also observed for limonin and naringin adsorption to activated earths. These isotherm adsorption profiles can be explained by a multilayer adsorption phenomenon. The highest adsorption efficiency for the bitter compounds was observed when synthetic neutral resin, Amberlite XAD-7 was used. The separation factor limonin/naringin varied from 16 (with earths) to 57 (with XAD-7 resin). The adsorption of sugars and pigments to the resins was low. No adsorption of vitamin C was detected for any of the adsorbents tested. The estimated affinity and separation factors show that the neutral resins tested are adequate for the selective removal of limonin from orange juices. The estimated values of free energy of adsorption, lower than-13.3 kJ mol-1 K-1 , indicate that a physiosorption process occurred.

A simulation based comparative study of the polarization hysteresis of the ferroelectric capacitor using various ferroelectric models is presented. A 2-dimensional finite element device-level model was implemented using SILVACO's ATLAS device simulator to generate the polarization hysteresis characteristics for Au/Poly(vinylidene fluoride-trifluoroethylene)/Au metal-insulator-metal (MIM) device. Landau free energy expression for electric field in terms of polarization is also implemented in the MATLAB to produce the polarization hysteresis curve of polycrystalline ferroelectrics. The main drawback of these models was their inability to predict polarization saturation at the same electric field limits for which the experimental device was saturating. A new model for ferroelectric hysteresis based on curve fitting algorithm is derived that forces the polarization to be saturated at desired electric field. The MATLAB simulation of this model and the experimental hysteresis is compared which shows an excellent level of agreement.

We simulate the phase segregation of a deeply quenched binary mixture with an initial concentration gradient. Our theoretical model follows the standard model H, where convection and di!usion are coupled via a body force, expressing the tendency of the demixing system to minimize its free energy. This driving force induces a material #ux much larger than that due to pure molecular di!usion, as in a typical case the Peclet number , expressing here the ratio of thermal to viscous forces, is of the order of 10.