667 research outputs found
Cavity-ligand binding in a simple two-dimensional water model
By means of Monte Carlo computer simulations in the isothermal-isobaric
ensemble, we investigated the interaction of a hydrophobic ligand with the
hydrophobic surfaces of various curvatures (planar, convex and concave). A
simple two-dimensional model of water, hydrophobic ligand and surface was used.
Hydration/dehidration phenomena concerning water molecules confined close to
the molecular surface were investigated. A notable dewetting of the hydrophobic
surfaces was observed together with the reorientation of the water molecules
close to the surface. The hydrogen bonding network was formed to accommodate
cavities next to the surfaces as well as beyond the first hydration shell. The
effects were most strongly pronounced in the case of concave surfaces having
large curvature. This simplified model can be further used to evaluate the
thermodynamic fingerprint of the docking of hydrophobic ligands.Comment: 6 pages, 5 figure
Primitive model electrolytes. A comparison of the HNC approximation for the activity coefficient with Monte Carlo data
Accuracy of the mean activity coefficient expression
(Hansen-Vieillefosse-Belloni equation), valid within the hypernetted chain
(HNC) approximation, was tested in a wide concentration range against new Monte
Carlo (MC) data for +1:-1 and +2:-2 primitive model electrolytes. The
expression has an advantage that the excess chemical potential can be obtained
directly, without invoking the time consuming Gibbs-Duhem calculation. We found
the HNC results for the mean activity coefficient to be in good agreement with
the machine calculations performed for the same model. In addition, the
thermodynamic consistency of the HNC approximation was tested. The mean
activity coefficients, calculated via the Gibbs-Duhem equation, seem to follow
the MC data slightly better than the Hansen-Vieillefosse-Belloni expression.
For completeness of the calculation, the HNC excess internal energies and
osmotic coefficients are also presented. These results are compared with the
calculations based on other theories commonly used to describe electrolyte
solutions, such as the mean spherical approximation, Pitzer's extension of the
Debye-H\"uckel theory, and the Debye-H\"uckel limiting law.Comment: 15 pages, 6 figure
Apple superficial scald preventi1on by vapour treatments
Superficial scald is a postharvest physiological disorder of apples characterized by browning of apple skin during prolonged storage. It has been hypothesized that conjugated triene hydroperoxides (CTH) attack cell membranes causing membrane perturbation and the manifestation of the disorder. The purpose of this study was to compare the common synthetic antioxidant diphenylamine (DPA) treatment with postharvest vapour treatments for superficial scald prevention. Apples cv. ‚Granny Smith™ were treated with ethanol, methanol and »apple aroma« vapours. The influence of these treatments on scald susceptibility and sensorial quality of apples was examined. The ethanol treatments were effective in superficial scald prevention but they caused a high incidence of internal browning after two months of storage. The 10 day treatments at 20 °C developed very pronounced internal browning after storage. The aroma treatment was the least effective in apple scald prevention but no internal disorders appeared after storage. Apples treated with methanol at 20 °C retain a great deal of their initial green colour. Vapour treatments demonstrated to be potential methods for scald prevention. Additional research is needed to minimise the internal disorders of treated fruit
Modelling the ion-exchange equilibrium in nanoporous materials
Distribution of a two component electrolyte mixture between the model
adsorbent and a bulk aqueous electrolyte solution was studied using the replica
Ornstein-Zernike theory and the grand canonical Monte Carlo method. The
electrolyte components were modelled to mimic the HCl/NaCl and HCl/CaCl_2
mixtures, respectively. The matrix, invaded by the primitive model electrolyte
mixture, was formed from monovalent negatively charged spherical obstacles. The
solution was treated as a continuous dielectric with the properties of pure
water. Comparison of the pair distribution functions (obtained by the two
methods) between the various ionic species indicated a good agreement between
the replica Ornstein-Zernike results and machine calculations. Among
thermodynamic properties, the mean activity coefficient of the invaded
electrolyte components was calculated. Simple model for the ion-exchange resin
was proposed. The selectivity calculations yielded qualitative agreement with
the following experimental observations: (i) selectivity increases with the
increasing capacity of the adsorbent (matrix concentration), (ii) the adsorbent
is more selective for the ion having higher charge density if its fraction in
mixture is smaller.Comment: 12 pages, 9 figure
Total phenol content and antioxidant activity of water solutions of plant extracts
Water solutions of extracts were investigated for total phenol content, flavonoid content and antioxidant activity. Susceptibility to degradation of water solutions of plant extracts, under light and in the dark, during storage at room temperature was investigated in order to determine their stability prior to their application for fortification of food products. Large dispersion of total phenol (TP) content in the investigated model solutions of selected extracts (olive leaves, green tea, red grape, red wine, pine bark PE 5:1, pine bark PE 95 %, resveratrol), ranging from 11.10 mg GAE/100 mL to 92.19 mg GAE/100 mL was observed. Consequently, large dispersion of total flavonoids (TF) content (8.89 mg to 61.75 mg CTE/100 mL) was also observed. Since phenols have been mostly responsible for antioxidant activity of extracts, in most cases, antioxidant activity followed the TP content. That was proven by estimation of correlation coefficient between the total phenol content and antioxidant activity. Correlation coefficients between investigated parameters ranged from 0.5749 to 0.9604. During storage of 5 weeks at room temperature loss of phenols and flavonoids occurred. Antioxidant activity decreased with the decrease of TP and TF content. Degradations of phenols and flavonoids were more pronounced in samples stored at light
A New Method for the Determination of Water Content in Extra Dry Gases
The water content in extra dry gases can be determined by
the condensation of water vapor on the cooled walls of the container.
After separation, vapor pressure is measured at room temperature
by the Pirani vacuummeter. In favorable conditions water
content as low as 1 μg per liter of gas at NTP can be detected
Governance of interdependent ecosystem services and common-pool resources
Environmental governance is recognized as a key issue in many natural and social sciences. It is highly relevant for ecosystem services and common-pool resources as well. Both fields overlap yet have typically been studied separately. Therefore, this study aimed a) to examine the emerging body of literature that incorporates concepts from both fields of research and considers governance challenges, and b) to identify policy tools and recommendations presented for addressing those challenges. The analysis of thirty-nine selected peer-review papers revealed the multiplicity of interacting governance challenges with three major categories: environmental, socioeconomic, and problems of governance itself. Governance is impeded by institutional mismatches, exclusion of local actors, corruption, and perverse policies. The proposed policy recommendations most often suggest changes in institutional arrangements and increasing scientific understanding. Meeting human needs, and increasing social equity and justice were recognized broadly as integral for improving governance, yet correlations among governance problems and solutions appear elusive. These findings extend theoretical reasoning, while carrying practical implications for policy, governance and environmental stewardship. The analysis implies that policies to improve human conditions will be key for improved environmental governance, but more research is needed to learn which types of policy recommendations prove successful given diverse local contexts
Application of Replica Ornstein-Zernike equations in studies of the adsorption of electrolyte mixtures in disordered matrices of charged particles
The Replica Ornstein-Zernike (ROZ) equations were used to study the adsorption of ions from electrolyte mixtures.
The adsorbent was represented as a quenched primitive model +1:-1 size symmetric electrolyte, while
the mobile particles were ions differing in charge and/or size. The ROZ equations in hypernetted-chain (HNC)
approximation were tested against new Monte Carlo results in the grand canonical ensemble; good agreement
between the two methods was obtained. The ROZ/HNC theory was then used to study the exclusion
coefficients as a function of size and/or charge asymmetry of the annealed ions.Реплiчне рiвняння Орнштейна-Цернiке (РОЦ) застосоване для вивчення адсорбцiї iонiв iз сумiшей
електролiтiв. Адсорбент розглядається у виглядi замороженої примiтивної +1:-1 моделi розмiрно
симетричного електролiту, тодi як рухомi частинки – це iони, що вiдрiзняються зарядом та/або роз-
мiрами. Данi, що отриманi з рiвняння РОЦ у гiперланцюжковому наближеннi (ГЛН), порiвняно з но-
вими результатами Монте-Карло моделювання у великому канонiчному ансамблi i виявлено хороше
узгодження мiж обома методами. Теорiю РОЦ/ГЛН далi було використано для вивчення коефiцiєнтiв
виключення, в залежностi вiд параметрiв розмiрної та/або зарядової асиметрiй нерухомих iонiв
Disclosing physician ratings: performance effects and the difficulty of altering rating consensus
I examine effects of a health care system's policy to publicly disclose patient ratings of its physicians. I find evidence that this policy leads to performance improvement by the disclosed, subjective ratings and also by undisclosed, objective measures of quality. These effects are consistent with multitasking theory, in that physicians respond to the disclosure by providing more of a shared input—time with patients—that benefits performance by ratings and underlying quality. I also find, as predicted by information cascade theory, that the ratings become jammed to some degree near initially disclosed values. Specifically, raters observe the pattern of initial ratings and follow suit by providing similar ratings. Finally, I find evidence that physicians anticipate rating jamming and so concentrate their effort on earlier performance in order to set a pattern of high ratings that later ratings follow. These results demonstrate that the disclosure of subjective ratings can benefit performance broadly but can also shift effort toward earlier performance
Influence of solvent granularity on the effective interaction between charged colloidal suspensions
We study the effect of solvent granularity on the effective force between two
charged colloidal particles by computer simulations of the primitive model of
strongly asymmetric electrolytes with an explicitly added hard sphere solvent.
Apart from molecular oscillating forces for nearly touching colloids which
arise from solvent and counterion layering, the counterions are attracted
towards the colloidal surfaces by solvent depletion providing a simple
statistical description of hydration. This, in turn, has an important influence
on the effective forces for larger distances which are considerably reduced as
compared to the prediction based on the primitive model. When these forces are
repulsive, the long-distance behaviour can be described by an effective Yukawa
pair potential with a solvent-renormalized charge. As a function of colloidal
volume fraction and added salt concentration, this solvent-renormalized charge
behaves qualitatively similar to that obtained via the Poisson-Boltzmann cell
model but there are quantitative differences. For divalent counterions and
nano-sized colloids, on the other hand, the hydration may lead to overscreened
colloids with mutual attraction while the primitive model yields repulsive
forces. All these new effects can be accounted for through a solvent-averaged
primitive model (SPM) which is obtained from the full model by integrating out
the solvent degrees of freedom. The SPM was used to access larger colloidal
particles without simulating the solvent explicitly.Comment: 14 pages, 16 craphic
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