How to compare diffusion processes assessed by single-particle tracking and pulsed field gradient nuclear magnetic resonance

Heterogeneous diffusion processes occur in many different fields such as transport in living cells or diffusion in porous media. A characterization of the transport parameters of such processes can be achieved by ensemble-based methods, such as pulsed field gradient nuclear magnetic resonance (PFG NMR), or by trajectory-based methods obtained from single-particle tracking (SPT) experiments. In this paper, we study the general relationship between both methods and its application to heterogeneous systems. We derive analytical expressions for the distribution of diffusivities from SPT and further relate it to NMR spin-echo diffusion attenuation functions. To exemplify the applicability of this approach, we employ a well-established two-region exchange model, which has widely been used in the context of PFG NMR studies of multiphase systems subjected to interphase molecular exchange processes. This type of systems, which can also describe a layered liquid with layer-dependent self-diffusion coefficients, has also recently gained attention in SPT experiments. We reformulate the results of the two-region exchange model in terms of SPT-observables and compare its predictions to that obtained using the exact transformation which we derived.Comment: v2: 14 pages, 6 figures, several enhancements, added references; v1: 7 pages, 3 figure

Entropy-driven enhanced self-diffusion in confined reentrant supernematics

We present a molecular dynamics study of reentrant nematic phases using the Gay-Berne-Kihara model of a liquid crystal in nanoconfinement. At densities above those characteristic of smectic A phases, reentrant nematic phases form that are characterized by a large value of the nematic order parameter $S\simeq1$. Along the nematic director these "supernematic" phases exhibit a remarkably high self-diffusivity which exceeds that for ordinary, lower-density nematic phases by an order of magnitude. Enhancement of self-diffusivity is attributed to a decrease of rotational configurational entropy in confinement. Recent developments in the pulsed field gradient NMR technique are shown to provide favorable conditions for an experimental confirmation of our simulations.Comment: 10 pages, 5 figure

Freezing and melting transitions of liquids in mesopores with ink-bottle geometry

Freezing and melting behavior of nitrobenzene in mesoporous silicon with different pore size and with different porous structure have been studied using H-1 NMR cryoporometry. With the bulk phase surrounding the porous monoliths, in materials with uniform channel-like pores distinct pore-size-dependent freezing and melting transitions have been measured. These data were further used for the analysis of the fluid behavior in samples with modulated porous structure, namely linear pores with alternating cross-section. We have, in particular, considered two materials consisting of channel sections, which were separated by almost identical channel `necks' but notably differed in the respective channel diameters. In the smaller channel segments, the observed shift in the freezing temperature provides direct evidence of the relevance of a pore-blocking mechanism, i.e. of the retardation in the propagation of a solid front by the channel necks. In the channel segments with larger diameter, on the other hand, freezing is found to be initiated by homogeneous nucleation.DF

Statistical Analysis of Consequences Caused by the Collisions of Soaring Drops of Organic Coal-Water Fuel

The paper examines the processes of collision of the soaring organic coal - water fuel (OCWF) drops in the specialized combustion chamber in case of direct injection of suspension with the subsequent crushing, decay and coagulation. High speed video registration is used. The fuel composition is prepared with the use of a coal conversion waste (filter-cake "G"), turbine oil waste, water and a plasticizer. The statistical analysis of consequences of impingement of OCWF drops at their movement in an oxidizer flotation (temperature is about 800-840 K) with their following deformation is carried out. The conditions when the processes of coagulation, disintegration or crushing of drops are dominated are established

Ignition of the Soaring Droplet Sets of Waste-Derived Coal-Water Slurry With Petrochemicals

We have analyzed the ignition of droplet sets of waste-derived coal-water slurry with petrochemicals for the case of their soaring inside special combustion chamber. The fuel composition consists of filter cake of bituminous coal type G, waste turbine oil, water and plasticizer. Features of the ignition process were emphasized for groups of three soaring droplets in comparison with single droplet ignition. The ignition delay times were registered for particles that were deformed or segregated due to the interaction of initial fuel droplets with walls of the combustion chamber

The role of string-like, supramolecular assemblies in reentrant supernematic liquid crystals

Using a combination of isothermal-isobaric Monte Carlo and microcanonical molecular dynamics we investigate the relation between structure and self-diffusion in various phases of a model liquid crystal using the Gay-Berne-Kihara potential. These molecules are confined to a mesoscopic slit-pore with atomically smooth substrate surfaces. As reported recently [see M. G. Mazza {\em et al.}, Phys. Rev. Lett. {\bf 105}, 227802 (2010)], a reentrant nematic (RN) phase may form at sufficiently high pressures/densities. This phase is characterized by a high degree of nematic order and a substantially enhanced self-diffusivity in the direction of the director $\hat{\bm{n}}$ which exceeds that of the lower-density nematic and an intermittent smectic A phase by about an order of magnitude. Here we demonstrate that the unique transport behavior in the RN phase may be linked to a confinement-induced packing effect which causes the formation of supramolecular, string-like conformations. The strings consist of several individual molecules that are capable of travelling in the direction of $\hat{\bm{n}}$ as individual "trains" consisting of chains of molecular "cars". Individual trains run in parallel and may pass each other at sufficiently high pressures.Comment: 24 page

Spectral variations of AeBe Herbig stars in the Mon R1 association

We present the change in the Halpha emission-line profile of the spectra of some AeBe Herbig stars. In the spectrum of VY Mon, Halpha may have one of three profile types: P Cyg, P Cyg III or single line in accordance with the brightness variations of the star. HD259431 now shows a double Halpha profile with the red component stronger than the blue component, while in the earlier observations the blue peak was higher than the red peak. Finally, the last Halpha profile of LkHalpha215 is very similar to that obtained by Finkenzeller et al.Comment: 4pages, 3figure

New Approach to Study the Ignition Processes of Organic Coal-Water Fuels in an Oxidizer Flow

To converge the conditions of organic water-coal fuel composition combustion in the typical power equipment we developed a new approach and installed an experimental setup, eliminating the traditional fixing the fuel droplets on the thermocouples or rods. Specialized cone-shaped chamber was used to implement the process of lingering of organic water-coal fuel droplets. Necessary and sufficient conditions for the lingering of organic water-coal fuel droplets were established. We determined the parameters of the system (droplet size of 0.4-0.6 mm, temperatures 823-903 K and the velocity of the oxidizer flow 1.5-6 m/s) at which the droplets were consistently ignited in the process of lingering. Minimum temperatures and ignition delay times of organic water-coal fuel droplets based on brown coal, used motor, turbine, transformer oils, kerosene, gasoline and water were defined

A Massive Jet Ejection Event from the Microquasar SS 433 Accompanying Rapid X-Ray Variability

Microquasars occasionally exhibit massive jet ejections which are distinct from the continuous or quasi-continuous weak jet ejections. Because those massive jet ejections are rare and short events, they have hardly been observed in X-ray so far. In this paper, the first X-ray observation of a massive jet ejection from the microquasar SS 433 with the Rossi X-ray Timing Explorer (RXTE) is reported. SS 433 undergoing a massive ejection event shows a variety of new phenomena including a QPO-like feature near 0.1 Hz, rapid time variability, and shot-like activities. The shot-like activity may be caused by the formation of a small plasma bullet. A massive jet may be consist of thousands of those plasma bullets ejected from the binary system. The size, mass, internal energy, and kinetic energy of the bullets and the massive jet are estimated.Comment: 21 pages including 5 figures, submitted to Ap