Bela Farago - Academia.edu (original) (raw)
Papers by Bela Farago
Adsorption, 2005
Diffusion of linear alkanes in 5A zeolite crystals has been studied by several different experime... more Diffusion of linear alkanes in 5A zeolite crystals has been studied by several different experimental techniques. In the range C3–C8 the diffusivity decreases regularly with carbon number (with a corresponding increase in activation energy) and there is good agreement between ZLC values and the data provided by the “microscopic” techniques (PFG NMR and Quasi-Elastic Neutron Scattering). At higher carbon numbers
Physica B: Condensed Matter, 1999
A new ultra-high-resolution neutron spin-echo spectrometer at the ILL, Grenoble, extends the time... more A new ultra-high-resolution neutron spin-echo spectrometer at the ILL, Grenoble, extends the time range for measurements of the intermediate scattering function S(q,t) far beyond what has previously been possible. This new dynamic range approaching the microsecond opens up the possibility for exploring dynamic phenomena which have been previously unobservable. The various design ideas for the three operational modes (standard, neutron
EPJ direct, 2002
The poor knowledge of the spin-dependent neutron scattering length of 3 He has until now handicap... more The poor knowledge of the spin-dependent neutron scattering length of 3 He has until now handicapped nuclear four body theory and the interpretation of excitations in the quantum liquid. We have measured, for the first time directly, the real part of the bound incoherent neutron scattering length, b i of 3 He. A neutron spin echo spectrometer was used to detect pseudomagnetic precession of polarised neutrons passing through polarised 3 He gas. Any absolute calibrations of sample and beam parameters were avoided using simple transmission measurements with nonpolarised neutrons. The only a priory information required was the spin-dependent neutron absorption cross section of 3 He. The result is b i = −2.365(20) fm, which reduces the prior uncertainty by a factor 30. The corresponding new value of the bound incoherent scattering cross section is σi = 1.532(12) barn. Including the known value of the coherent neutron scattering length, we obtain new values for the real parts of the free triplet and singlet neutron scattering lengths, a − = 7.370(58) fm and a + = 3.278(53) fm.
AIP Conference Proceedings, 1999
The single-chain and collective motions of polymer chains in melts are directly observable by neu... more The single-chain and collective motions of polymer chains in melts are directly observable by neutron spin-echo spectroscopy (NSE). This method has both the necessary spatial resolution (10Å 500Å) as well as the adapted time domain from fractions of a ns to several 100ns. ...
Journal de Physique, 1988
2014 On présente la première étude par diffusion quasi élastique des neutrons ultrafroids de la d... more 2014 On présente la première étude par diffusion quasi élastique des neutrons ultrafroids de la dynamique des bicouches lipidiques. La variation en température du transfert d'énergie des lipides aux neutrons diffusés en fonction de la température, ainsi que la comparaison avec les résultats obtenus par échos de spins de neutrons montrent que ce transfert est déterminé par la diffusion latérale des molécules lipidiques dans la gamme des microsecondes couverte par l'expérience. Pour les bicouches de dipalmitoyl-phosphatidyl-choline à 45° on obtient un coefficient de diffusion de 2, 6 10-7cm2/s, un peu plus grand que les valeurs obtenues par photoblanchiment. Cette méthode de diffusion des neutrons ultrafroids est complémentaire de la technique de photoblanchiment, car elle mesure la diffusion latérale des lipides sur des distances de l'ordre de 20 Å, alors que cette dernière mesure les mouvements latéraux sur 10 03BCm.
MRS Proceedings, 2003
ABSTRACTThe phase separation behaviour and the dynamics of concentration fluctuations of binary l... more ABSTRACTThe phase separation behaviour and the dynamics of concentration fluctuations of binary liquid mixtures are strongly influenced by confinement effects. We have investigated this confinement effect for the binary system isobutyric acid iBA + D2O imbibed into a mesoporous silica glass (CPG-10). The dynamics of the mixture are studied in the one-phase region as well as in the phase-separated state by means of neutron spin echo spectroscopy (NSE). Moreover, the averaged structures of the liquid are explored by means of small angle neutron scattering (SANS) leading to a length scale 4 < ξ < 9 nm for the fluctuations. The associated effective diffusion coefficient Deff as obtained for NSE is found to decrease with temperature ny nearly one order of magnitude in the temperature range from 75°C to 25°C.
Physica B: Condensed Matter, 2007
In this paper I will try to present some recent results on less usual subjects, which I believe a... more In this paper I will try to present some recent results on less usual subjects, which I believe are forward pointing to fields which might develop faster as new sources/instruments become available. The first deals with an assembly of spherical microemulsions which under certain conditions self-organize themselves into a cubic phase. Applying contrast variation and covering the large dynamical range
Progress in Colloid & Polymer Science
Oil-in-water microemulsions of nonionic surfactants of type C"E, with various hydrocarbons have b... more Oil-in-water microemulsions of nonionic surfactants of type C"E, with various hydrocarbons have been characterized by means of small-angle-neutron-scattering
The density correlation function F(q,t) of the two similar substituted aromatic liquids, Toluene ... more The density correlation function F(q,t) of the two similar substituted aromatic liquids, Toluene and m-Toluidine, is studied by coherent neutron spin-echo and time-of-flight scattering for wave vectors q around the maximum q_max of the total static structure factor S_m(q) in the supercooled i.e. high density state far away from the normal fluid state. The wave-vector dependence of the mean structural
Physica B: Condensed Matter, 2004
We report a neutron spin echo (NSE) and dynamic light scattering (DLS) study of droplet dynamics ... more We report a neutron spin echo (NSE) and dynamic light scattering (DLS) study of droplet dynamics in a microemulsion at high droplet packing fraction (Φdroplet∼62%). NSE measurements in range qr⪢1 allow to investigate the short-range Brownian motion of droplets trapped within the cages formed by their nearest neighbors. For a particular scattering contrast, NSE also reveals, for q values around
Physica B: Condensed Matter, 2007
We have investigated flux lines in low-and high-T c superconductors using unpolarized and polariz... more We have investigated flux lines in low-and high-T c superconductors using unpolarized and polarized neutron techniques. In high-T c materials, we observe transitions from triangular to square flux line lattices (FLLs) which probably represent the effects of d-wave pairing. In ...
University-The occurrence of an arrest transition in concentrated colloid suspensions and its dep... more University-The occurrence of an arrest transition in concentrated colloid suspensions and its dependence on the interaction potential is a hot topic in soft matter. Such arrest transitions can also occur in concentrated protein solutions, as they exist e.g. in biological cells or are increasingly used in pharmaceutical formulations. Here we demonstrate the applicability of concepts from colloid science to understand the dynamics of concentrated protein solutions. In this presentation we report a combination of 3D light scattering, small-angle X-ray scattering and neutron spin echo measurements to study the structural properties as well as the collective and self diffusion of proteins in highly concentrated solutions on the relevant length and time scales. We demonstrate that various arrest scenarios indeed exist for different globular proteins. The proteins chosen are different bovine lens crystallins. We report examples of hard and attractive glass transitions and arrested spinodal decomposition directly linked to the effective pair potentials determined in static scattering experiments for the different proteins. We discuss these different arrest scenarios in view of possible applications of dense protein solutions as well as in view of their possible relevance for living systems.
Journal de Physique II, 1997
Physical Review Letters, 1987
We have employed neutron spin-echo techniques to study the dynamics of the shape fluctuation of m... more We have employed neutron spin-echo techniques to study the dynamics of the shape fluctuation of microemulsion droplets. It is found that the scattering spectrum of a droplet system with a labeled layer of surfactants exhibits a sharp peak in the relaxation frequency spectrum. We have determined that the fluctuations are driven mainly by the bending modes on the surface, and the height of the peak allows us to measure the surface elastic bending coe%cient directly.
Physical Review E, 1999
conclude that the procedure followed by us for analyzing data of glass-forming polymers, which is... more conclude that the procedure followed by us for analyzing data of glass-forming polymers, which is based on a Williams-like ansatz, is not suited for the merging region of the ␣ and  dielectric processes. They claim that a simple addition ansatz is the correct procedure. In this Reply, by considering new dielectric data of six different polymers, we show that our procedure seems to be certainly suitable for describing the merging region without any ad hoc assumption. Moreover, we also show that an unbiased application of the addition ansatz in fact gives support to the procedure followed by us. ͓S1063-651X͑99͒03007-X͔
Review of Scientific Instruments, 2009
This paper describes the design and experimental tests of a novel neutron spin analyzer optimized... more This paper describes the design and experimental tests of a novel neutron spin analyzer optimized for wide angle spin echo spectrometers. The new design is based on nonremanent magnetic supermirrors, which are magnetized by vertical magnetic fields created by NdFeB high field permanent magnets. The solution presented here gives stable performance at moderate costs in contrast to designs invoking remanent supermirrors. In the experimental part of this paper we demonstrate that the new design performs well in terms of polarization, transmission, and that high quality neutron spin echo spectra can be measured.
Physical Review Letters, 2009
Physical Review Letters, 2003
Dynamics of dense microemulsion droplets forming ordered cellular phases as temperature increases... more Dynamics of dense microemulsion droplets forming ordered cellular phases as temperature increases are investigated by neutron spin echo spectroscopy (NSE). The shape fluctuations of droplets are shown using a specific contrast. Their relaxation time f is obtained by analysis of the NSE curves, which also reveals the short-range Brownian motion (diffusion constant D 0) of the ''caged'' droplets. The thermal dependence of D 0 and f supports the notion of entropically driven interdroplet steric repulsion stabilizing the cellular phases.
![Research paper thumbnail of Dynamic Properties of Semidilute Solutions at the Theta Point [Phys. Rev. Lett. 77, 3673 (1996)]](https://attachments.academia-assets.com/114533295/thumbnails/1.jpg)
](Physical Review Letters, 1997
Equation (2) should read as follows: S͑q, t͒ exp͓2͑t͞t c ͒ b ͔; b 2͞3 for qL. 1 .
Adsorption, 2005
Diffusion of linear alkanes in 5A zeolite crystals has been studied by several different experime... more Diffusion of linear alkanes in 5A zeolite crystals has been studied by several different experimental techniques. In the range C3–C8 the diffusivity decreases regularly with carbon number (with a corresponding increase in activation energy) and there is good agreement between ZLC values and the data provided by the “microscopic” techniques (PFG NMR and Quasi-Elastic Neutron Scattering). At higher carbon numbers
Physica B: Condensed Matter, 1999
A new ultra-high-resolution neutron spin-echo spectrometer at the ILL, Grenoble, extends the time... more A new ultra-high-resolution neutron spin-echo spectrometer at the ILL, Grenoble, extends the time range for measurements of the intermediate scattering function S(q,t) far beyond what has previously been possible. This new dynamic range approaching the microsecond opens up the possibility for exploring dynamic phenomena which have been previously unobservable. The various design ideas for the three operational modes (standard, neutron
EPJ direct, 2002
The poor knowledge of the spin-dependent neutron scattering length of 3 He has until now handicap... more The poor knowledge of the spin-dependent neutron scattering length of 3 He has until now handicapped nuclear four body theory and the interpretation of excitations in the quantum liquid. We have measured, for the first time directly, the real part of the bound incoherent neutron scattering length, b i of 3 He. A neutron spin echo spectrometer was used to detect pseudomagnetic precession of polarised neutrons passing through polarised 3 He gas. Any absolute calibrations of sample and beam parameters were avoided using simple transmission measurements with nonpolarised neutrons. The only a priory information required was the spin-dependent neutron absorption cross section of 3 He. The result is b i = −2.365(20) fm, which reduces the prior uncertainty by a factor 30. The corresponding new value of the bound incoherent scattering cross section is σi = 1.532(12) barn. Including the known value of the coherent neutron scattering length, we obtain new values for the real parts of the free triplet and singlet neutron scattering lengths, a − = 7.370(58) fm and a + = 3.278(53) fm.
AIP Conference Proceedings, 1999
The single-chain and collective motions of polymer chains in melts are directly observable by neu... more The single-chain and collective motions of polymer chains in melts are directly observable by neutron spin-echo spectroscopy (NSE). This method has both the necessary spatial resolution (10Å 500Å) as well as the adapted time domain from fractions of a ns to several 100ns. ...
Journal de Physique, 1988
2014 On présente la première étude par diffusion quasi élastique des neutrons ultrafroids de la d... more 2014 On présente la première étude par diffusion quasi élastique des neutrons ultrafroids de la dynamique des bicouches lipidiques. La variation en température du transfert d'énergie des lipides aux neutrons diffusés en fonction de la température, ainsi que la comparaison avec les résultats obtenus par échos de spins de neutrons montrent que ce transfert est déterminé par la diffusion latérale des molécules lipidiques dans la gamme des microsecondes couverte par l'expérience. Pour les bicouches de dipalmitoyl-phosphatidyl-choline à 45° on obtient un coefficient de diffusion de 2, 6 10-7cm2/s, un peu plus grand que les valeurs obtenues par photoblanchiment. Cette méthode de diffusion des neutrons ultrafroids est complémentaire de la technique de photoblanchiment, car elle mesure la diffusion latérale des lipides sur des distances de l'ordre de 20 Å, alors que cette dernière mesure les mouvements latéraux sur 10 03BCm.
MRS Proceedings, 2003
ABSTRACTThe phase separation behaviour and the dynamics of concentration fluctuations of binary l... more ABSTRACTThe phase separation behaviour and the dynamics of concentration fluctuations of binary liquid mixtures are strongly influenced by confinement effects. We have investigated this confinement effect for the binary system isobutyric acid iBA + D2O imbibed into a mesoporous silica glass (CPG-10). The dynamics of the mixture are studied in the one-phase region as well as in the phase-separated state by means of neutron spin echo spectroscopy (NSE). Moreover, the averaged structures of the liquid are explored by means of small angle neutron scattering (SANS) leading to a length scale 4 < ξ < 9 nm for the fluctuations. The associated effective diffusion coefficient Deff as obtained for NSE is found to decrease with temperature ny nearly one order of magnitude in the temperature range from 75°C to 25°C.
Physica B: Condensed Matter, 2007
In this paper I will try to present some recent results on less usual subjects, which I believe a... more In this paper I will try to present some recent results on less usual subjects, which I believe are forward pointing to fields which might develop faster as new sources/instruments become available. The first deals with an assembly of spherical microemulsions which under certain conditions self-organize themselves into a cubic phase. Applying contrast variation and covering the large dynamical range
Progress in Colloid & Polymer Science
Oil-in-water microemulsions of nonionic surfactants of type C"E, with various hydrocarbons have b... more Oil-in-water microemulsions of nonionic surfactants of type C"E, with various hydrocarbons have been characterized by means of small-angle-neutron-scattering
The density correlation function F(q,t) of the two similar substituted aromatic liquids, Toluene ... more The density correlation function F(q,t) of the two similar substituted aromatic liquids, Toluene and m-Toluidine, is studied by coherent neutron spin-echo and time-of-flight scattering for wave vectors q around the maximum q_max of the total static structure factor S_m(q) in the supercooled i.e. high density state far away from the normal fluid state. The wave-vector dependence of the mean structural
Physica B: Condensed Matter, 2004
We report a neutron spin echo (NSE) and dynamic light scattering (DLS) study of droplet dynamics ... more We report a neutron spin echo (NSE) and dynamic light scattering (DLS) study of droplet dynamics in a microemulsion at high droplet packing fraction (Φdroplet∼62%). NSE measurements in range qr⪢1 allow to investigate the short-range Brownian motion of droplets trapped within the cages formed by their nearest neighbors. For a particular scattering contrast, NSE also reveals, for q values around
Physica B: Condensed Matter, 2007
We have investigated flux lines in low-and high-T c superconductors using unpolarized and polariz... more We have investigated flux lines in low-and high-T c superconductors using unpolarized and polarized neutron techniques. In high-T c materials, we observe transitions from triangular to square flux line lattices (FLLs) which probably represent the effects of d-wave pairing. In ...
University-The occurrence of an arrest transition in concentrated colloid suspensions and its dep... more University-The occurrence of an arrest transition in concentrated colloid suspensions and its dependence on the interaction potential is a hot topic in soft matter. Such arrest transitions can also occur in concentrated protein solutions, as they exist e.g. in biological cells or are increasingly used in pharmaceutical formulations. Here we demonstrate the applicability of concepts from colloid science to understand the dynamics of concentrated protein solutions. In this presentation we report a combination of 3D light scattering, small-angle X-ray scattering and neutron spin echo measurements to study the structural properties as well as the collective and self diffusion of proteins in highly concentrated solutions on the relevant length and time scales. We demonstrate that various arrest scenarios indeed exist for different globular proteins. The proteins chosen are different bovine lens crystallins. We report examples of hard and attractive glass transitions and arrested spinodal decomposition directly linked to the effective pair potentials determined in static scattering experiments for the different proteins. We discuss these different arrest scenarios in view of possible applications of dense protein solutions as well as in view of their possible relevance for living systems.
Journal de Physique II, 1997
Physical Review Letters, 1987
We have employed neutron spin-echo techniques to study the dynamics of the shape fluctuation of m... more We have employed neutron spin-echo techniques to study the dynamics of the shape fluctuation of microemulsion droplets. It is found that the scattering spectrum of a droplet system with a labeled layer of surfactants exhibits a sharp peak in the relaxation frequency spectrum. We have determined that the fluctuations are driven mainly by the bending modes on the surface, and the height of the peak allows us to measure the surface elastic bending coe%cient directly.
Physical Review E, 1999
conclude that the procedure followed by us for analyzing data of glass-forming polymers, which is... more conclude that the procedure followed by us for analyzing data of glass-forming polymers, which is based on a Williams-like ansatz, is not suited for the merging region of the ␣ and  dielectric processes. They claim that a simple addition ansatz is the correct procedure. In this Reply, by considering new dielectric data of six different polymers, we show that our procedure seems to be certainly suitable for describing the merging region without any ad hoc assumption. Moreover, we also show that an unbiased application of the addition ansatz in fact gives support to the procedure followed by us. ͓S1063-651X͑99͒03007-X͔
Review of Scientific Instruments, 2009
This paper describes the design and experimental tests of a novel neutron spin analyzer optimized... more This paper describes the design and experimental tests of a novel neutron spin analyzer optimized for wide angle spin echo spectrometers. The new design is based on nonremanent magnetic supermirrors, which are magnetized by vertical magnetic fields created by NdFeB high field permanent magnets. The solution presented here gives stable performance at moderate costs in contrast to designs invoking remanent supermirrors. In the experimental part of this paper we demonstrate that the new design performs well in terms of polarization, transmission, and that high quality neutron spin echo spectra can be measured.
Physical Review Letters, 2009
Physical Review Letters, 2003
Dynamics of dense microemulsion droplets forming ordered cellular phases as temperature increases... more Dynamics of dense microemulsion droplets forming ordered cellular phases as temperature increases are investigated by neutron spin echo spectroscopy (NSE). The shape fluctuations of droplets are shown using a specific contrast. Their relaxation time f is obtained by analysis of the NSE curves, which also reveals the short-range Brownian motion (diffusion constant D 0) of the ''caged'' droplets. The thermal dependence of D 0 and f supports the notion of entropically driven interdroplet steric repulsion stabilizing the cellular phases.
Physical Review Letters, 1997
Equation (2) should read as follows: S͑q, t͒ exp͓2͑t͞t c ͒ b ͔; b 2͞3 for qL. 1 .