Alexander Kolesnikov - Profile on Academia.edu (original) (raw)

Papers by Alexander Kolesnikov

Journal of Molecular Structure, 2002

The method of measuring proton momentum distributions by neutron Compton scattering (NCS) is desc... more The method of measuring proton momentum distributions by neutron Compton scattering (NCS) is described. Results on a hydrogen bonded potassium dihydrogen phosphate (KDP) single crystal are presented. For the first time NCS measurements are used to reconstruct the proton momentum, wavefunction and Born-Oppenheimer potential. The results provide clear evidence that the ferroelectric transition in KDP is mediated by a quantum tunnelling transition in the hydrogen bonds of the structure. There is a narrowing of the proton momentum distribution as the temperature is raised through the transition, which is consistent with quantum tunnelling between two sites above, but not below, the transition. The separation of the potential wells, derived from the data, is consistent with diffraction data and the calculated transition frequencies are consistent with infrared data.

Physical review letters, Jan 3, 2018

The duality between the localized and itinerant nature of magnetism in 5f-electron systems has be... more The duality between the localized and itinerant nature of magnetism in 5f-electron systems has been a long-standing puzzle. Here, we report inelastic neutron scattering measurements, which reveal both local and itinerant aspects of magnetism in a single-crystalline system of UPt_{2}Si_{2}. In the antiferromagnetic state, we observe a broad continuum of diffuse magnetic scattering with a resonancelike gap of ≈7 meV and the surprising absence of coherent spin waves, suggestive of itinerant magnetism. While the gap closes above the Néel temperature, strong dynamic spin correlations persist to a high temperature. Nevertheless, the size and temperature dependence of the total magnetic spectral weight can be well described by a local moment with J=4. Furthermore, polarized neutron measurements reveal that the magnetic fluctuations are mostly transverse, with little or none of the longitudinal component expected for itinerant moments. These results suggest that a dual description of local...

Biophysical Journal, 2014

Dynamic crossover phenomenon in confined supercooled water and its relation to the existence of a liquid-liquid critical point in water

AIP Conference Proceedings, 2008

ABSTRACT We have observed a Fragile‐to‐Strong Dynamic Crossover (FSC) phenomenon of the α‐relaxat... more ABSTRACT We have observed a Fragile‐to‐Strong Dynamic Crossover (FSC) phenomenon of the α‐relaxation time and self‐diffusion constant in confined supercooled water. The α‐relaxation time is measured by Quasielastic Neutron Scattering (QENS) experiments and the self‐diffusion constant by Nuclear Magnetic Resonance (NMR) experiments. Water is confined in 1‐d geometry in cylindrical pores of nanoscale silica materials, MCM‐41‐S and in Double‐Wall Carbon Nanotubes (DWNT). The crossover phenomenon can also be observed from appearance of a Boson peak in Incoherent Inelastic Neutron Scattering experiments. We observe a pronounced violation of the Stokes‐Einstein Relation at and below the crossover temperature at ambient pressure. Upon applying pressure to the confined water, the crossover temperature is shown to track closely the Widom line emanating from the existence of a liquid‐liquid critical point in an unattainable deeply supercooled state of bulk water. Relation of the dynamic crossover phenomenon to the existence of a density minimum in supercooled confined water is discussed. Finally, we discuss a role of the FSC of the hydration water in a biopolymer that controls the biofunctionality of the biopolymer.

Extraction of metals from natural waters: A neutron characterization of the nanostructured manganese-oxide-based adsorbents

Physica B: Condensed Matter, 2006

ABSTRACT A methodology has been developed for extraction of metals, i.e., lithium, gold and inorg... more ABSTRACT A methodology has been developed for extraction of metals, i.e., lithium, gold and inorganic arsenic, from natural waters using nanostructured manganese-oxide-based adsorbents. The methods are extremely efficient, highly selective, recyclable, and environmentally benign. A key process to functionalize the Li-, Au- and As-adsorption relies on the protonation of nanoparticles of Mn-spinel, Mn2O3- and Bi-doped Mn2O3 adsorbents, respectively, so that proper exchange or redox reactions with the targeted metal ions or complexes become possible in spite of the very dilute contents in aqueous solutions. We have applied small-to-wide angle neutron diffraction and inelastic scattering to determine the fractal-like morphology of the nanocomposites, the mixed crystal phases therein and the atomic dynamics. In the case of the pure and hydrogenated Mn-spinel, the neutron data were compared with first-principles calculations of the phonon density of states and the local vibrations modes of adsorbed hydrogen atoms.

The Journal of Chemical Physics, 2008

The vibrational density of states of amorphous beryllium hydride ͑a-BeH 2 ͒ and lithium beryllium... more The vibrational density of states of amorphous beryllium hydride ͑a-BeH 2 ͒ and lithium beryllium hydrides have been studied using inelastic neutron scattering, infrared, and Raman spectroscopies. The positions of the symmetrical ͑120-180 meV͒ and antisymmetrical ͑200-260 meV͒ Be-H stretching modes and those of the H-Be-H bending mode ͑50-120 meV͒ have been determined and the results discussed and compared with recent theoretical calculations. With the addition of lithium to the beryllium hydride network, the vibrational bands are shifted to lower energies, indicating a less rigid network.

The Journal of Physical Chemistry A, 2007

due to only translational modes, is larger than that for anatase water at all temperatures, while... more due to only translational modes, is larger than that for anatase water at all temperatures, while the contributions from the librational modes are smaller. A gradual increase of the librational contribution to C p for anatase water (larger than for ice-Ih) with temperature results in total C p being larger for anatase water than for ice-Ih above ~180 K. .

Journal of Alloys and Compounds, 2007

Single-walled carbon nanotubes (SWNT) were loaded with 5.2 wt% hydrogen at a hydrogen pressure of... more Single-walled carbon nanotubes (SWNT) were loaded with 5.2 wt% hydrogen at a hydrogen pressure of 3 GPa and T = 620 K, quenched to 80 K and studied at ambient pressure and 15 K by inelastic neutron scattering (INS) in the range of energy transfers 3-400 meV. An analysis of the measured INS spectra showed that the quenched SWNT & H sample contained hydrogen in two different forms, as H atoms covalently bound to the carbon atoms (∼4.7 wt%) and as H 2 molecules (∼0.5 wt%) exhibiting nearly free rotational behavior. Annealing the sample in vacuum at 332 K removed about 65% of the H 2 molecules and annealing at 623 K removed all of them. This demonstrates that H 2 molecules were kept in this sample more tightly than in earlier studied SWNT & H samples that were hydrogenated at lower pressures and temperatures and lost all molecular hydrogen on heating in vacuum to room temperature.

The Journal of …, 2006

The visual cycle is a chain of biochemical reactions that regenerate visual pigment following exp... more The visual cycle is a chain of biochemical reactions that regenerate visual pigment following exposure to light. Initial steps, the liberation of all-trans retinal and its reduction to all-trans retinol by retinol dehydrogenase (RDH), take place in photoreceptors. We performed comparative microspectrophotometric and microfl uorometric mea- surements on a variety of rod and cone photoreceptors isolated from salamander retinae to

Glass Ceramics for High Resolution Imaging

Glass-ceramic materials are being developed for use in digital mammography systems. The materials... more Glass-ceramic materials are being developed for use in digital mammography systems. The materials are transparent x-ray storage phosphors, which are potentially less expensive than competing materials with superior performance. The materials do not suffer from loss of resolution and increased noise due to light scattering from grain boundaries, as do the currently available polycrystalline materials. The glass ceramics are based

Nanomaterials

Inelastic Neutron Scattering (INS) spectroscopy has provided a unique insight into the magnetodym... more Inelastic Neutron Scattering (INS) spectroscopy has provided a unique insight into the magnetodymanics of nanoscale copper (II) oxide (CuO). We present evidence for the propagation of magnons in the directions of the ordering vectors of both the commensurate and helically modulated incommensurate antiferromagnetic phases of CuO. The temperature dependency of the magnon spin-wave intensity (in the accessible energy-range of the experiment) conforms to the Bose population of states at low temperatures (T ≤ 100 K), as expected for bosons, then intensity significantly increases, with maximum at about 225 K (close to TN), and decreases at higher temperatures. The obtained results can be related to gradual softening of the dispersion curves of magnon spin-waves and decreasing the spin gap with temperature approaching TN on heating, and slow dissipation of the short-range dynamic spin correlations at higher temperatures. However, the intensity of the magnon signal was found to be particle ...

Phonon spectra of ordered PdCuH and PdAgH prepared under a high hydrogen pressure

Physica B: Condensed Matter

ABSTRACT

Applied Physics Letters, Mar 2, 2009

Extracting dispersive magnetic excitations from inelastic neutron scattering data usually require... more Extracting dispersive magnetic excitations from inelastic neutron scattering data usually requires large single crystals. We present a simple yet powerful method for extracting such information from polycrystalline or powder data for one-dimensional systems. We demonstrate the effectiveness of this data treatment by extracting dispersion curves from powder inelastic neutron scattering data on the one-dimensional spin-half systems: CuGeO 3 and Rb 2 Cu 2 Mo 3 O 12. For many such materials, it is not possible to grow sufficiently large crystals and this method offers a quick and efficient way to study their magnetic excitations.

An Inelastic Neutron Scattering Study of Confined Surface Water on Rutile Nanoparticles

J Phys Chem a, 2009

The vibrational density of states (VDOS) for water confined on the surface of rutile-TiO(2) nanop... more The vibrational density of states (VDOS) for water confined on the surface of rutile-TiO(2) nanoparticles has been extracted from low temperature inelastic neutron scattering spectra. Two rutile-TiO(2) nanoparticle samples that differ in their respective levels of hydration, namely TiO(2) x 0.37 H(2)O (1) and TiO(2) x 0.22 H(2)O (2) have been studied. The temperature dependency of the heat capacities for the two samples has been quantified from the VDOS. The results from this study are compared with previously reported data for water confined on anatase-TiO(2) nanoparticles.

Energetics of carbon nanotubes: insights from calorimetry and neutron scattering

New quantum state of protons and electrons in nano-confined water

ABSTRACT Neutron Compton Scattering provides a means of directly and accurately measuring the mom... more ABSTRACT Neutron Compton Scattering provides a means of directly and accurately measuring the momentum distribution of protons in water, which is determined primarily by the protons ground state wavefunction. We find that in water confined on scales of ˜20å, this wave function responds to the details of the confinement, corresponds to a strongly anharmonic local potential, shows evidence in some cases of coherent delocalization in double wells, and involves differences in zero point kinetic energy of the protons from that of bulk water at room temperature of -40 to +120 meV. This behavior is a generic feature of nanoscale confinement, and in particular, this state should be that which is present in water confined in biological cells. It is exhibited here in 16 å inner diameter carbon nanotubes, two different hydrated proton exchange membranes (PEMs), Nafion 1120 and Dow 858, and has been seen earlier in xerogel and 14 å diameter carbon nanotubes. The existence of this state is confirmed by xray Compton scattering measurements of the electron momentum distribution.

Investigation of phonon-like excitation in hydrated protein powders by neutron scattering

Fast proton hopping detection in ice I{sub h} by quasi-elastic neutron scattering

Physical Review Letters, 2016

Using neutron scattering and ab initio simulations, we document the discovery of a new "quantum t... more Using neutron scattering and ab initio simulations, we document the discovery of a new "quantum tunneling state" of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. In addition, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.