Decoherence via the dynamical casimir effect

We derive a master equation for a mirror interacting with the vacuum field via radiation pressure. The dynamical Casimir effect leads to decoherence of a superposition state in a time scale that depends on the degree of "macroscopicity" of the state components, and which may be much shorter than the relaxation time scale. Coherent states are selected by the interaction as pointer states.     

Bimodal pore size distributions for carbons: experimental results and computational studies

It is well known that the bimodal shape of the pore size distribution (PSD) curves is typical for various carbonaceous materials (of different origin and/or treated thermally or chemically). A systematic investigation of this effect has been discussed using the Nguyen and Do method with proposed recently the ASA algorithm. A series of numerically generated adsorption isotherms (N(2), T=77 K) and experimental data were analyzed. We investigated various possible situations related to the shape of the PSD curves, i.e., the intensity of the both peaks, their mutual location and the vanishing of one of them. Moreover, the problem in the similarity of the local adsorption isotherms from the range of pore widths corresponding to the gap between peaks is discussed. The analysis of obtained results (as well as published by others) shows that the bimodal shape of the pore size distributions is a characteristic feature for many adsorbents possessing even a small amount of micropores. It is shown that this feature results from the similarity of the local adsorption isotherm in the range of the pore widths for which the gap between peaks (related to the primary and secondary micropore filling mechanism) exists.     

The Finite Pore Volume GAB Adsorption Isotherm Model as a Simple Tool to Estimate a Diameter of Cylindrical Nanopores

The finite pore volume Guggenheim–Anderson–de Boer (fpv-GAB) adsorption isotherm model has been considered as a simple tool which not only enables us to analyze the shape of isotherms theoretically, but also provides information about pore diameter. The proposed methodology is based on the geometrical considerations and the division of the adsorption space into two parts: the monolayer and the multilayer space. The ratio of the volumes of these two spaces is unambiguously related to the pore diameter. This ratio can be simply determined from the N₂ adsorption isotherm by its fitting with the use of fpv-GAB model. The volume ratio is equal to the ratio of the adsorption capacities in the monolayer and the multilayer—two of the best-fit parameters. The suggested approach has been verified using a series of isotherms simulated inside ideal carbon nanotubes. The adsorption data for some real adsorbents has also been used during tests. The studies performed have proven that diameters estimated with the use of the proposed method are comparable with the geometrical sizes or diameters published by others and based on the application of more sophisticated methods. For pores wider than 3 nm, the relative error does not exceed a few percent. The approach based on the fpv-GAB model reflects well the differences in pore sizes for the series of materials. Therefore, it can be treated as a convenient tool to compare various samples.     

Enhanced adsorption of paracetamol on closed carbon nanotubes by formation of nanoaggregates: carbon nanotubes as potential materials in hot-melt drug deposition-experiment and simulation

We present the new results of systematic studies of paracetamol adsorption on closed, commercially available, unmodified carbon nanotubes. The results of thermal analysis, static adsorption measurements and the comparison with phenol adsorption data lead to suggestion that the formation of paracetamol nanoaggregates in the interstitial spaces between nanotubes occurs. This effect is also confirmed by the results of (performed in two ways) independent dynamic measurements and by molecular dynamics simulation technique. Next, we show that the behavior of adsorbed paracetamol during heating leads to the creation of a new drug delivery system. The properties of this system depend on the type of applied nanotubes and the parameters of the process called hot-melt drug deposition. Thus, we conclude that confined nanoaggregate formation, as well as hot-melt deposition should be promising effects in the preparation of highly effective, new drug delivery systems.     

Carbon nanotubes as potential material for drug delivery—experiment and simulation

We discuss the factors influencing the properties of new drug delivery system, composed of carbon nanotubes and analgesic antipyretic drug—paracetamol. Basing on experimental data it is shown, that by a simple manipulation with the heating time at the stage of system preparation, one can easily change the rate of the drug delivery. Moreover, this rate can be changed in a very wide range. Finally, using Molecular Dynamics simulation we also discuss the orientation and properties of drug molecules at different stages of the hot melt deposition process.     

Equilibrium clusters in concentrated lysozyme protein solutions

We have studied the structure of salt-free lysozyme at 293 K and pH 7.8 using molecular simulations and experimental SAXS effective potentials between proteins at three volume fractions, ?=0.012, 0.033, and 0.12. We found that the structure of lysozyme near physiological conditions strongly depends on the volume fraction of proteins. The studied lysozyme solutions are dominated by monomers only for ?≤0.012; for the strong dilution 70% of proteins are in a form of monomers. For ?=0.033 only 20% of proteins do not belong to a cluster. The clusters are mainly elongated. For ?=0.12 almost no individual particles exits, and branched, irregular clusters of large extent appear. Our simulation study provides new insight into the formation of equilibrium clusters in charged protein solutions near physiological conditions.     

The primary photophysics of the Avena sativa phototropin 1 LOV2 domain observed with time-resolved emission spectroscopy

The phototropins are blue-light receptors that base their light-dependent action on the reversible formation of a covalent bond between a flavin mononucleotide (FMN) cofactor and a conserved cysteine in light, oxygen or voltage (LOV) domains. The primary reactions of the Avena sativa phototropin 1 LOV2 domain were investigated by means of time-resolved and low-temperature fluorescence spectroscopy. Synchroscan streak camera experiments revealed a fluorescence lifetime of 2.2 ns in LOV2. A weak long-lived component with emission intensity from 600 to 650 nm was assigned to phosphorescence from the reactive FMN triplet state. This observation allowed determination of the LOV2 triplet state energy level at physiological temperature at 16600 cm(-1). FMN dissolved in aqueous solution showed pH-dependent fluorescence lifetimes of 2.7 ns at pH 2 and 3.9-4.1 ns at pH 3-8. Here, too, a weak phosphorescence band was observed. The fluorescence quantum yield of LOV2 increased from 0.13 to 0.41 upon cooling the sample from 293 to 77 K. A pronounced phosphorescence emission around 600 nm was observed in the LOV2 domain between 77 and 120 K in the steady-state emission.     

MRI measurement of blood-brain barrier permeability following spontaneous reperfusion in the starch microsphere model of ischemia

Quantification of the acute increases in blood-brain barrier (BBB) permeability that occur subsequent to experimental ischemic injury has been limited to single time-point, invasive methodologies. Although permeability can be qualitatively assessed to visualise regional changes during sequential studies on the same animal using contrast-enhanced magnetic resonance imaging (MRI), quantitative information on the magnitude of change is required to compare barrier function during sequential studies on the same animal or between different animals. Recently, improvements in MRI tracer kinetic models and in MR hardware design mean that an estimate of permeability in vivo can now be obtained with acceptable accuracy and precision. We report here the use of such methods to study acute changes following spontaneous reperfusion in an animal model of ischemia. We have obtained estimates of BBB permeability following spontaneous reperfusion, subsequent to forebrain ischemia by unilateral carotid injection of starch microspheres in the rat. T2*-weighted and diffusion-trace imaging were used to monitor the initial reduction in CBF and the time-course of ischemia, respectively. Following reperfusion, an intraveneous bolus of dimeglumine gadopentetate (Gd-DTPA) and horseradish peroxidase (HRP) was given during a continuous acquisition of T1 maps with a 48 s temporal resolution. Permeability maps were constructed using a 4-compartment model; K(trans), the permeability-surface area product of the capillary walls was estimated to be 9.2 +/- 0.6 x 10(-4) min(-1) in the cortex. Visualisation of the regional extent of HRP extravasation on histological sections following termination of the experiment demonstrated very little correspondence to the region of Gd-DTPA leakage. Quantitative MRI assessment of BBB permeability following ischemia-reperfusion is consistent with published values obtained by invasive methods. Differences between Gd-DTPA-enhancement and HRP may reflect differences in the molecular size of the tracers.     

Porosity of closed carbon nanotubes compressed using hydraulic pressure

Experimental data of nitrogen adsorption (T = 77.3 K) from gaseous phase measured on commercial closed carbon nanotubes are presented. Additionally, we show the results of N₂ adsorption on compressed (using hydraulic press) CNTs. In order to explain the experimental observations the results of GCMC simulations of N₂ adsorption on isolated or bundled multi-walled closed nanotubes (four models of bundles) are discussed. We show that the changes of the experimental adsorption isotherms are related to the compression of the investigated adsorbents. They are qualitatively similar to the theoretical observations. Taking into account all results it is concluded that in the “architecture” of nanotubes very important role has been played by isolated nanotubes.     

Adsorption potential distributions for carbons having defined pore structure—GCMC simulations of the effect of heterogeneity

Adsorption Potential Distribution (APD) is one of the most important and widely propagated by Jaroniec and co-workers method since it is modeless. Using the GCMC simulation of Ar adsorption in pores with well defined geometry (slit-like, cylindrical, hexagonal and quadratic) we study the effect of heterogeneity on the APDs. The heterogeneity is introduced by controlled removal of carbon atoms from the first internal layer of an adsorbent. Since defects are introduced for pores having different initial geometries it is possible to study the systematic changes in the APD curves. Electronic Supplementary Material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.