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Software development for data reduction and analysis at large research facilities is increasingly professionalized, and internationally coordinated. To foster software quality and sustainability, and to facilitate collaboration, representatives from software groups of European neutron and muon facilities have agreed on a set of guidelines for development practices, infrastructure, and functional and non-functional product properties. These guidelines have been derived from actual practices in software projects from the EU funded consortium ‘Science and Innovation with Neutrons in Europe in 2020’ (SINE2020), and have been enriched through extensive literature review. Besides guiding the work of the professional software engineers in our computing groups, we hope to influence scientists who are willing to contribute their own data treatment software to our community. Moreover, this work may also provide inspiration to scientific software development beyond the neutron and muon field.

To describe multiple Bragg reflection from a thick, ideally imperfect crystal, the transport equations are reformulated in three-dimensional phase space and solved by spectral collocation in the depth coordinate. Example solutions illustrate the orientational spread of multiply reflected rays and the distortion of rocking curves, especially for finite detectors., The generalized Darwin–Hamilton equations [Wuttke (2014 ▸). Acta Cryst. A70, 429–440] describe multiple Bragg reflection from a thick, ideally imperfect crystal. These equations are simplified by making full use of energy conservation, and it is demonstrated that the conventional two-ray Darwin–Hamilton equations are obtained as a first-order approximation. Then an efficient numeric solution method is presented, based on a transfer matrix for discretized directional distribution functions and on spectral collocation in the depth coordinate. Example solutions illustrate the orientational spread of multiply reflected rays and the distortion of rocking curves, especially if the detector only covers a finite solid angle.

BornAgain is a free and open-source multi-platform software framework for simulating and fitting X-ray and neutron reflectometry, off-specular scattering, and grazing-incidence small-angle scattering (GISAS). This paper concentrates on GISAS., BornAgain is a free and open-source multi-platform software framework for simulating and fitting X-ray and neutron reflectometry, off-specular scattering, and grazing-incidence small-angle scattering (GISAS). This paper concentrates on GISAS. Support for reflectometry and off-specular scattering has been added more recently, is still under intense development and will be described in a later publication. BornAgain supports neutron polarization and magnetic scattering. Users can define sample and instrument models through Python scripting. A large subset of the functionality is also available through a graphical user interface. This paper describes the software in terms of the realized non-functional and functional requirements. The web site https://www.bornagainproject.org/ provides further documentation.

Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Apparent singularities, all removable, are discussed in detail. Cancellation near the singularities causes a loss of precision that can be avoided by using series expansions. An important application domain is small‐angle scattering by nanocrystals., Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Series expansions are used to ensure numeric precision close to apparent singularities. image

β-casein undergoes a reversible endothermic self-association, forming protein micelles of limited size. In its functional state, a single β-casein monomer is unfolded, which creates a high structural flexibility, supposed to play a major role in preventing the precipitation of calcium phosphate particles. We characterize the structural flexibility in terms of nano-second molecular motions, depending on the temperature by quasi-elastic neutron scattering. Our major questions are: Does the self- association reduce the chain flexibility? How does the dynamic spectrum of disordered caseins differ from a compactly globular protein? How does the dynamic spectrum of β-casein in solution differ from that of a protein in hydrated powder states? We report on two relaxation processes on a nano-second and a sub-nano-second time scale for β-casein in solution. Both processes are analyzed by Brownian Oscillator model, by which the spring constant can be defined in the isotropic parabolic potential. The slower process, which is analyzed by neutron spin echo, seems a characteristic feature of the unfolded structure. It requires bulk solvent and is not seen in hydrated protein powders. The faster process, which is analyzed by neutron backscattering, has a smaller amplitude and requires hydration water, which is also observed with folded proteins in the hydrated state. The self-association had no significant influence on internal relaxation, and thus a β-casein protein monomer flexibility is preserved in the micelle. We derive spring constants of the faster and slower motions of β-caseins in solution, and compared them with those of some proteins in various states; folded or hydrated powder.

The crystal structures of (2,4,6-CH3PyH)3Sb2Cl9 (TMPCA) and (2,4,6-CH3PyH)3Bi2Cl9 (TMPCB) (Py – pyridine) have been determined at 100 K by the single crystal X-ray diffraction method. TMPCA and TMPCB crystallize in the monoclinic C2/c and triclinic P1 polar space group, respectively. In both cases the asymmetric part is comprised of three nonequivalent 2,4,6-trimethylpyridinium cations and a discrete M2Cl93− anion. The Bi2Cl93− moiety forms a face-sharing bi-octahedron, whereas in a case of Sb2Cl93− we deal with two pyramids connected by a corner. The inelastic neutron scattering spectra (INS) were recorded for TMPCA at low temperatures (4–50 K). Two peaks on each side of the central elastic line have been observed at ca. 4.8 and 2.9 μeV, the high energy peak exhibits an excitation energy value equal to ca. 6 meV. For TMPCA and TMPCB the 1H NMR spin–lattice relaxation times, T1, have been measured in the temperature region 15–410 K. The flattening of the T1 (spin–lattice) vs. reciprocal temperature, 1/T, dependence between 30 K and 15 K indicates the incoherent tunneling effect of the methyl group being treated as the quantum rotor. The conclusions drawn from the 1H NMR results as regards to the tunneling of the CH3 groups in the pyridinium cations are consistent with the tunneling peaks observed in the INS spectra.

Performing quasielastic neutron scattering measurements and analyzing both elastic and quasielasic contributions, we study protein and water dynamics of hydrated elastin. At low temperatures, hydration-independent methyl group rotation dominates the findings. It is characterized by a Gaussian distribution of activation energies centered at about Em = 0.17 eV. At ∼195 K, coupled protein–water motion sets in. The hydration water shows diffusive motion, which is described by a Gaussian distribution of activation energies with Em = 0.57 eV. This Arrhenius behavior of water diffusion is consistent with previous results for water reorientation, but at variance with a fragile-to-strong crossover at ∼225 K. The hydration-related elastin backbone motion is localized and can be attributed to the cage rattling motion. We speculate that its onset at ∼195 K is related to a secondary glass transition, which occurs when a β relaxation of the protein has a correlation time of τβ ∼ 100 s. Moreover, we show that its temperature-dependent amplitude has a crossover at the regular glass transition Tg = 320 K of hydrated elastin, where the α relaxation of the protein obeys τα ∼ 100 s. By contrast, we do not observe a protein dynamical transition when water dynamics enters the experimental time window at ∼240 K.

In the 7th Environment Action Programme, the European Commission targets two essential goals in the handling of substances and materials known by the buzzwords “non-toxic environment” and “circular economy”. There are numerous interfaces in product, waste and chemicals legislation in these two areas. This leads to conflicting objectives, e.g. with regard to the classification of waste in analogy to chemicals as well as at the border between waste and secondary raw materials that are further processed into products. We investigate how these conflicting objectives can be mitigated or resolved. In our view, it is necessary to provide operators in the waste management sector with considerably more information on the composition of used products than before; this should include not only hazardous substances but also materials that interfere with the recycling process as well as recyclable or valuable materials. Waste management legislation largely follows risk considerations—a 1:1 transfer of hazard classifications of chemicals and products to waste management would be counterproductive to achieving the Commission’s objectives. In the case of contaminated secondary raw materials, their input into products can be justified in specific cases. However, this requires a risk assessment that includes in particular physicochemical factors, patterns of utilisation and controlled collection routes. Internationally recognised lists of secondary materials are an important condition for determining end-of-waste status and thus for increasing material recycling. A common guiding principle for chemicals policy and waste management is urgently needed.

We have investigated the ferromagnetic phase transition of elemental Co by high-resolution neutron backscattering spectroscopy. We monitored the splitting of the nuclear levels by the hyperfine field at the Co nucleus. The energy of this hyperfine splitting is identified as the order parameter of the ferromagnetic phase transition. By measuring the temperature dependence of the energy we determined the critical exponent [Formula: see text] and the ferromagnetic Curie temperature of [Formula: see text] K. The present result of the critical exponent agrees better with the predicted value (0.367) of the three-dimensional Heisenberg model than that determined previously by nuclear magnetic resonance.

The authors of this contribution comment on the ‘tricky relationships’ of chemicals, waste and product legislation. Considering the interfaces and intersections of these frameworks they formulate eminent policy recommendations aimed to ensure that ‘Circular Economies’ are capable of avoiding the ‘recycling’ of problematic chemical substances present in (waste) raw materials.

A description is presented of the NeXus data format for X-ray and neutron scattering and muon spectroscopy., NeXus is an effort by an international group of scientists to define a common data exchange and archival format for neutron, X-ray and muon experiments. NeXus is built on top of the scientific data format HDF5 and adds domain-specific rules for organizing data within HDF5 files, in addition to a dictionary of well defined domain-specific field names. The NeXus data format has two purposes. First, it defines a format that can serve as a container for all relevant data associated with a beamline. This is a very important use case. Second, it defines standards in the form of application definitions for the exchange of data between applications. NeXus provides structures for raw experimental data as well as for processed data.

In a series of papers, Frauenfelder et al. (1⇓–3) propose a radical reinterpretation of incoherent neutron scattering by complex systems, specifically by protein hydration water, drawing into doubt the “currently accepted model, used for > 50 y” (3). Under this model they subsume not only assumptions about the scattering target (sample) but also the theory that connects sample and scattering signal. Effectively, they attack the insight (4) that the dynamic structure factor S ( q , ω ) (which they incorrectly call “the scattering intensity”) abstracts from scattering kinematics and depends only on nuclear position operators acting on the sample. They claim that the established theory … [↵][1]1Email: j.wuttke{at}fz-juelich.de. [1]: #xref-corresp-1-1

An inconsistent approximation in Wuttke [Acta Cryst. (2014), A70, 429–440] is corrected. Section 3.5 on the polar angle random walk is withdrawn.

High-resolution neutron instrumentation has a long tradition in Garching: The backscattering and the resonance spin-echo method were developed here. While the old FRM reactor allowed little more than a demonstration of principle, the FRM II, in operation since 2005, has become a leading location for »real« instruments, especially in view of its excellent cold-neutron source. In this article, we will present four high-resolution spectrometers: TOFTOF (time of flight), SPHERES (backscattering), J-NSE (spin echo) and RESEDA (resonance spin-echo). They are all located in the first neutron guide hall of FRM II using an end position of a cold neutron guide [1]. TOFTOF and RESEDA are built and operated by Technische Universitat Munchen (TUM, for user access see http://http://user.frm2.tum.de), SPHERES and J-NSE by the Julich Centre for Neutron Science (JCNS, http://www.jcns.info).

We have investigated the hyperfine interaction in Co 2 SiO 4 by inelastic neutron scattering with a high resolution back-scattering neutron spectrometer. The energy spectrum measured from a Co 2 SiO 4 powder sample revealed inelastic peaks at E = 1.387 ± 0.006 μ eV at T =3.5 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and finally merge with the elastic peak at the electronic magnetic ordering temperature T N ≈ 50 K . The inelastic peaks have been interpreted to be due to the transition between hyperfine-split nuclear level of the 59 Co isotopes with spin I = 7 2 . The temperature dependence of the energy of the inelastic peak in Co 2 SiO 4 showed that this energy can be considered to be the order parameter of the antiferromagnetic phase transition. The determined hyperfine splitting in Co 2 SiO 4 deviates from the linear relationship between the ordered electronic magnetic moment and the hyperfine splitting in Co, Co–P amorphous alloys and CoO presumably due to the presence of unquenched orbital moment. These results are very similar to those of CoF 2 recently reported by Chatterji and Schneider [7].

Protein dynamics manifested through structural flexibility play a central role in the function of biological molecules. Here we explore the substrate-mediated change in protein flexibility of an antibiotic target enzyme, Clostridium botulinum dihydrodipicolinate synthase. We demonstrate that the substrate, pyruvate, stabilizes the more active dimer-of-dimers or tetrameric form. Surprisingly, there is little difference between the crystal structures of apo and substrate-bound enzyme, suggesting protein dynamics may be important. Neutron and small-angle X-ray scattering experiments were used to probe substrate-induced dynamics on the sub-second timescale, but no significant changes were observed. We therefore developed a simple technique, coined protein dynamics-mass spectrometry (ProD-MS), which enables measurement of time-dependent alkylation of cysteine residues. ProD-MS together with X-ray crystallography and analytical ultracentrifugation analyses indicates that pyruvate locks the conformation of the dimer that promotes docking to the more active tetrameric form, offering insight into ligand-mediated stabilization of multimeric enzymes.

Incoherent neutron scattering by water confined in carbon nanohorns was measured with the backscattering spectrometer SPHERES and analyzed in exemplary breadth and depth. Quasielastic spectra admit δ-plus-Kohlrausch fits over a wide q and T range. From the q and T dependence of fitted amplitudes and relaxation times, however, it becomes clear that the fits do not represent a uniform physical process, but that there is a crossover from localized motion at low T to diffusive α relaxation at high T. The crossover temperature of about 210 to 230 K increases with decreasing wave number, which is incompatible with a thermodynamic strong-fragile transition. Extrapolated diffusion coefficients D(T) indicate that water motion is at room temperature about 2.5 times slower than in the bulk; in the supercooled state this factor becomes smaller. At even higher temperatures, where the α spectrum is essentially flat, a few percentages of the total scattering go into a Lorentzian with a width of about 1.6μeV, probably due to functional groups on the surface of the nanohorns.

We have measured the dynamics of water confined in a porous magnesium carbonate material, Upsalite®, using the high-resolution neutron backscattering spectrometer SPHERES. We found quasielastic scattering that does not flatten out up to 360 K, which means that the dynamics of water are much slower than in other matrix materials. Specifically, a single Lorentzian line could be fitted to the quasielastic part of the acquired spectra between 220 and 360 K. This, accompanied by an elastic line from dynamically frozen water present at all experimental temperatures, even above the melting point, signaled a significant amount of bound or slow water.

Hydration water is the natural matrix of biological macromolecules and is essential for their activity in cells. The coupling between water and protein dynamics has been intensively studied, yet it remains controversial. Here we combine protein perdeuteration, neutron scattering and molecular dynamics simulations to explore the nature of hydration water motions at temperatures between 200 and 300 K, across the so-called protein dynamical transition, in the intrinsically disordered human protein tau and the globular maltose binding protein. Quasi-elastic broadening is fitted with a model of translating, rotating and immobile water molecules. In both experiment and simulation, the translational component markedly increases at the protein dynamical transition (around 240 K), regardless of whether the protein is intrinsically disordered or folded. Thus, we generalize the notion that the translational diffusion of water molecules on a protein surface promotes the large-amplitude motions of proteins that are required for their biological activity., Hydration water plasticizes protein structures and is essential for their biological functions, such as enzymatic catalysis. Here, the authors use neutron scattering and molecular dynamics simulations to study hydration water at the dynamical transition of folded and disordered proteins.

We have studied the microscopic dynamics of the bulk glass forming alloy Zr46.8Ti8.2Cu7.5Ni10Be27.5 with quasi-elastic neutron scattering. In contrast to simple metals the equilibrium liquid has a two-step structural relaxation as do other liquids in their supercooled state. The fast β-relaxation is in quantitative agreement with the scaling function of mode-coupling theory, with a crossover temperature, Tc, some 50% greater than the caloric glass transition temperature. The longer time α-relaxation reveals a failure of the Stokes–Einstein relation.

We want to review the applications of high-frequency-flippers in neutron spin echo and related fields: Two separated flippers of this type can replace a homogenous static magnetic field in a spin-echo spectrometer. We describe the spin-echo instruments at Saclay and Berlin relying on such flippers and present some measurements. By tilting these coils with respect to the beam axis, one can determine line widths of phonons with unprecedented precision. First experiments are shown. With two flippers driven at different frequencies one can realise an instrument (“MIEZE”), where the intensity at the detector is modulated with a frequency up to several MHz. Its use for high-resolution quasielastic scattering from protonated samples is demonstrated. The high-frequency signal may be used for “neutron computer holography” – we discuss a possible realisation.

Liquid ${\mathrm{Zr}}_{46.8}{\mathrm{Ti}}_{8.2}{\mathrm{Cu}}_{7.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{27.5}$ has been studied by quasielastic neutron scattering. The microscopic dynamics of this bulk glass forming alloy deviates qualitatively from simple metallic liquids; it shows two-step structural relaxation like other liquids in their supercooled state. Unexpectedly for a nonfragile system, fast $\ensuremath{\beta}$ relaxation is in full accord with the mode-coupling theory of the liquid to glass transition. The long-time $\ensuremath{\alpha}$ relaxation suggests failure of the Stokes-Einstein relation.

We present a first scattering experiment with MIEZE, a new high-resolution neutron spectrometer, located in the guide hall of the Laboratoire Leon Brillouin. As a variant of neutron spin-echo it measures the intermediate scattering function. In opposition to spinecho it is able to measure spin-incoherent scattering without attenuation of the signal. This was demonstrated on the first sample, viscous glycerol at two different temperatures.

Symmetric Bragg-case reflections from a thick, ideally imperfect, crystal slab are studied mostly by analytical means. The scattering transfer function of a thin mosaic layer is derived and brought into a form that allows for analytical approximations or easy quadrature. The Darwin–Hamilton equations are generalized, lifting the restriction of wavevectors to a two-dimensional scattering plane. A multireflection expansion shows that wavevector diffusion can be studied independently of the real-space coordinate. Combining analytical arguments and Monte Carlo simulations, multiple Bragg reflections are found to result in a minor correction of the reflected intensity, a moderate broadening of the reflected azimuth angle distribution, a considerable modification of the polar angle distribution, and a noticeable shift and distortion of rocking curves.

Motion of 57Fe can be observed on a scale of nsec to μsec through nuclear resonant forward scattering of synchrotron radiation. Additional information is obtained by measuring simultaneously incoherent nuclear resonant scattering at nonzero angles. In a glass, one measures the Lamb-Mosbauer factor; in the viscous phase, structural relaxation is observed directly. We apply the method to ferrocene / dibutylphthalate between 140 and 205 K. The mean relaxation times do not follow the observed temperature dependence of other, macroscopic relaxation measurements. We attribute this to a strong wavenumber dependence of the relaxation time. The prospects of nuclear resonant scattering for studying the dynamics of viscous liquids are discussed.

The resolution of neutron backscattering spectrometers deteriorates at small scattering angles where analyzers deviate from exact backscattering. By reducing the azimuth angle range of the analyzers, the resolution can be improved with little loss of peak intensity. Measurements at the spectrometer SPHERES are in excellent agreement with simulations, which proves the dominance of geometric effects.

We present the neutron resonance spinecho-spectrometer (NRSE) that was recently installed at the LLB-Saclay. Brief quantum mechanical descriptions of the spectrometer principle and of the main components, the RF-flippers, are given. We also discuss the technological details of these flippers. The spinecho-curves clearly demonstrate the good performance of the instrument. A first quasielastic neutron scattering measurement on the structural relaxations of the glass former deuterated glycerol shows the high flexibility and reliability of the new spectrometer, but also indicates the need to increase the primary intensity, planned in near future.

The recent discovery of bulk metallic glasses opened the possibility to study their metastable melt far above the glass transition temperature. Alloying 57Fe to the glass ZrTiCuNiBe we succeeded in performing Mossbauer absorption experiments up to 70 K above Tg. While quasi-elastic broadening from structural relaxation was not detected, the Lamb-Mossbauer factor shows an anomalous decrease. From previous neutron spectroscopy, we exclude phonon anharmonicity as a cause. The missing elastic intensity can therefore be ascribed to a fast relaxation process. This is a first indication that the glass transition scenario predicted by mode coupling theory and observed in a number of different systems also applies to metallic alloys.

Incoherent neutron-backscattering and field gradient NMR are combined to measure the self-correlation function of protons in glycerol. Extensive simulations reveal and delimit systematic effects of multiple scattering. At microscopic wave numbers, tagged-particle motion couples strongly to structural relaxation. Between 1 and 0.1 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$ a crossover to diffusional motion is observed: quasielastic stretching diminishes and the wave-number dependence of the mean relaxation time approaches ${\mathit{q}}^{\mathrm{\ensuremath{-}}2}$. \textcopyright{} 1996 The American Physical Society.

Quasielastic neutron scattering measures ia a very direct way the decay of density correlations in the time range psec … nsec and on length scales of the order of angstroms. It seems therefore ideally suited to directly observe the critical dynamics predicted by the mode coupling theory of the glass transition. We review results obtained in a small number of model fluids.

We have measured coherent neutron scattering from deuterated orthoterphenyl on a spin echo and a backscattering spectrometer. In agreement with mode coupling theory, pair correlations decay in two steps and follow the same scaling laws as those found previously for self-correlations. The temperature evolution of the intermediate plateau is compatible with the previously established ${\mathit{T}}_{\mathit{c}}$=290 K. The spatial resolution has not been sufficient to fully resolve oscillations of parameters as functions of Q, which are predicted by mode coupling theory. Within this limitation, we find that the double peak structure of S(Q) is not expressed in the nonergodicity parameter ${\mathit{f}}_{\mathit{Q}}^{\mathit{c}}$ and that the de Gennes narrowing is missing.

Polarization fluctuations are measured in a 2/spl times/90 km optical fiber encapsulated in the lightning protection cable of a high-voltage transmission line. Results are correlated to the wind speed and to the current in the high-voltage line.

The observation of biological activity in solvent-free protein–polymer surfactant hybrids challenges the view of aqueous and nonaqueous solvents being unique promoters of protein dynamics linked to function. Here, we combine elastic incoherent neutron scattering and specific deuterium labeling to separately study protein and polymer motions in solvent-free hybrids. Myoglobin motions within the hybrid are found to closely resemble those of a hydrated protein, and motions of the polymer surfactant coating are similar to those of the hydration water, leading to the conclusion that the polymer surfactant coating plasticizes protein structures in a way similar to hydration water.

SPHERES (SPectrometer with High Energy RESolution) is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Juelich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 micro-eV, a dynamic range of +-31 micro-eV, and a signal-to-noise ratio of up to 1750:1., Comment: 12 pages, 7 figures, 2 tables. Supplemental material consists of 3 pages, 2 figures, 2 tables

The volume of e-waste being generated is growing rapidly, due to the wide use of this equipment, both in developed countries and in developing countries. Significant amounts of used electrical and electronic goods are exported from Europe to developing countries. Condition and quality of the exported used electronics, however, suggest that a significant proportion of the exported equipment can be expected to be non- or not completely functioning.

Hydration water is vital for various macromolecular biological activities, such as specific ligand recognition, enzyme activity, response to receptor binding, and energy transduction. Without hydration water, proteins would not fold correctly and would lack the conformational flexibility that animates their three-dimensional structures. Motions in globular, soluble proteins are thought to be governed to a certain extent by hydration-water dynamics, yet it is not known whether this relationship holds true for other protein classes in general and whether, in turn, the structural nature of a protein also influences water motions. Here, we provide insight into the coupling between hydration-water dynamics and atomic motions in intrinsically disordered proteins (IDP), a largely unexplored class of proteins that, in contrast to folded proteins, lack a well-defined three-dimensional structure. We investigated the human IDP tau, which is involved in the pathogenic processes accompanying Alzheimer disease. Combining neutron scattering and protein perdeuteration, we found similar atomic mean-square displacements over a large temperature range for the tau protein and its hydration water, indicating intimate coupling between them. This is in contrast to the behavior of folded proteins of similar molecular weight, such as the globular, soluble maltose-binding protein and the membrane protein bacteriorhodopsin, which display moderate to weak coupling, respectively. The extracted mean square displacements also reveal a greater motional flexibility of IDP compared with globular, folded proteins and more restricted water motions on the IDP surface. The results provide evidence that protein and hydration-water motions mutually affect and shape each other, and that there is a gradient of coupling across different protein classes that may play a functional role in macromolecular activity in a cellular context.

In a recent contribution to this journal, Magazù, Migliardo, and Benedetto suggest to determine relaxation times from inflection points in the elastic neutron scattering intensity as function of (1) resolution time or (2) temperature. Method (1) can be generalized into a scaling law. Method (2) is only approximately valid; its application to protein data does not back a wavenumber-independent dynamic transition.

The transition metal-based oxide YBaCo${}_{3}$FeO${}_{7}$ is structurally related to the mineral Swedenborgite SbNaBe${}_{4}$O${}_{7}$, a polar noncentrosymmetric crystal system. The magnetic Co${}_{3}$Fe sublattice consists of a tetrahedral network containing kagome-like layers with trigonal interlayer sites. This geometry causes frustration effects for magnetic ordering, which were investigated by magnetization measurements, M\"ossbauer spectroscopy, polarized neutron diffraction, and neutron spectroscopy. Magnetization measurement and neutron diffraction do not show long range ordering even at low temperature (1 K), although a strong antiferromagnetic coupling (\ensuremath{\sim}2000 K) is deduced from the magnetic susceptibility. Below 590 K we observe two features, a spontaneous weak anisotropic magnetization hysteresis along the polar crystallographic axis and a hyperfine field on the Fe kagome sites, whereas the Fe spins on the interlayer sites remain idle. Below \ensuremath{\sim}50 K the onset of a hyperfine field shows the development of moments static on the M\"ossbauer time scale also for the Fe interlayer sites. Simultaneously, an increase of spin correlations is found by polarized neutron diffraction. The relaxation part of the dynamic response has been further investigated by high-resolution neutron spectroscopy, which reveals that the spin correlations start to freeze below \ensuremath{\sim}50 K. Monte Carlo simulations show that the neutron scattering results at lower temperatures are compatible with a recent proposal that the particular geometric frustration in the Swedenborgite structure promotes quasi--one-dimensional partial order.

The crystal and molecular structures of 4,4(')- and 6,6(')-dimethyl-2,2(')-bipyridyl complexes with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) have been determined and compared with those of the complex with the 5,5(')-derivative, which is known to possess interesting antiferroelectric properties. In the crystalline state, all three compounds form hydrogen bonded chains with N(+)-H···O(-) and O-H···N bridges on both sides of the bipyridyl constituent. The comparison of three derivatives indicates that the N(+)-H···O(-) hydrogen bonds are shortest for the 5,5(')-dimethyl complex. The 4,4(')- and 6,6(')-derivatives do not show any ferroelectric feature. The 6,6(')-one is, however, characterized by a continuous phase transition, revealed in the differential scanning calorimetry, dilatometric, and dielectric characteristics. The tunneling splitting measured by neutron backscattering in the energy range ±30 μeV for the neat dimethyl bipyridyls and their complexes with CLA indicates that the different splittings are primarily due to the crystal packing effect and that charge transfer between interacting compounds plays only a minor role.

Innermolecular motion in Na3AlH6 gives rise to a Lorentzian spectrum with a wavenumber-independent width of about 1 micro-eV at 180 deg C, which is probably due to rotation of AlH6 tetrahedra. There is no such quasielastic line in NaAlH4 or NaH. Based on this finding, time-resolved measurements on the neutron backscattering spectrometer SPHERES were used to monitor the decomposition kinetics of sodium alanate, NaAlH4 to Na3AlH6 to NaH. Both reaction steps were found to be accelerated by autocatalysis, most likely at the surfaces of Na3AlH6 and NaH crystallites., Comment: J. Phys. Condensed Matter (in press)

Mode coupling theory (MCT) of the glass transition predicts the existence of a dynamic anomaly of supercooled liquids at a characteristic temperature T c well above the caloric glass transition temperature T g . A series of neutron scattering and NMR experiments on van der Waals liquids - a typical example of which is orthoterphenyl (OTP) - have been performed to test three predictions and to point out signatures of the glass transition. This contribution is meant to review our results in a concise manner: there is strong evidence for a T c according to MCT from Debye-Waller factors, from line shape studies of the dynamic structure factor and from a comparison of self-diffusion and viscosity. NMR relaxation below T c shows that there is at least one secondary process which so far is not accounted for by MCT and that the supercooled liquid becomes truely nonergodic closely above T g on a time scale of a few seconds.

We present an extended set of incoherent neutron scattering measurements on the van der Waals liquido-terphenyl, obtained by time-of-flight and backscattering spectroscopy. In the supercooled liquid regime, data from three instruments are combined and analysed in terms of the selfcorrelationS(Q, t). In the time range 1...100 ps, the crossover from α-to β-relaxation is well described by the masterfunction of mode coupling theory, and fitted parameters are consistent with the previously established critical temperatureT c [Z. Phys. B83, 175 (1991)]. In the glassy regime, vibrations are harmonic and can be described by a density of states. Deviations at lowQ are quantitatively explained by a multiple scattering simulation. Throughout the article, experimental difficulties are discussed in some detail.

Thin layers of water on biomolecular and other nanostructured surfaces can be supercooled to temperatures not accessible with bulk water. Chen et al. [Proc. Natl. Acad. Sci. U.S.A. 103, 9012 (2006)]10.1073/pnas.0602474103 suggested that anomalies near 220 K observed by quasielastic neutron scattering can be explained by a hidden critical point of bulk water. Based on more sensitive measurements of water on perdeuterated phycocyanin, using the new neutron backscattering spectrometer SPHERES, and an improved data analysis, we present results that show no sign of such a fragile-to-strong transition. The inflection of the elastic intensity at 220 K has a dynamic origin that is compatible with a calorimetric glass transition at 170 K. The temperature dependence of the relaxation times is highly sensitive to data evaluation; it can be brought into perfect agreement with the results of other techniques, without any anomaly.

The crystal structure of 2:1 picric acid (PAH) with tetramethylpyrazine (TMP) was determined by using X-ray diffraction studies. Two equivalent N+-H center dot center dot center dot O- hydrogen bonds are formed with the length of 2.601 angstrom (calculated 2.640 angstrom). In the IR spectra very broad doublet at ca. 2000 and 2400 cm(-1) is observed, which can be interpreted as due to symmetric and asymmetric N+-H vibrations. In neutron backscattering two tunnel splittings are observed, in agreement with the symmetry of 2:1 assemblies. At 4 K the tunnel peaks are located at 3.17 and 4.24 mu eV. (C) 2010 Elsevier B.V. All rights reserved.