The cold neutron imaging and diffraction instrument IMAT at the second target station of the pulsed neutron source ISIS is currently being commissioned and prepared for user operation. IMAT will enable white-beam neutron radiography and tomography. One of the benefits of operating on a pulsed source is to determine the neutron energy via a time of flight measurement, thus enabling energy-selective and energy-dispersive neutron imaging, for maximizing image contrasts between given materials and for mapping structure and microstructure properties. We survey the hardware and software components for data collection and image analysis on IMAT, and provide a step-by-step procedure for operating the instrument for energy-dispersive imaging using a two-phase metal test object as an example.

Electrospray emission is interpreted in terms of dielectrophoretic forces. A new model.

Characterization of pigments in archaeological finds requires an experimental approach able to avoid the destruction or perturbation of the artwork. Surface Enhanced Raman Spectroscopy technique may provide useful information in terms of chemical composition by using very small sample quantities and without samples manipulation. In this paper some pigments and an archeological find, discovered in Messina, have been analyzed with new SERS substrates prepared with Pulsed Laser Deposition (PLD) technique with two different instrumentations. In both cases we quenched the fluorescence phenomena and enhanced Raman peaks.

This work presents the first neutron characterization of artefacts from the grave-goods of Kha and Merit, a unique cultural treasure of mankind and preserved at the Museo Egizio in Turin. This magnificent collection, discovered in the early years of the last century, includes an impressive amount of artefacts such as coffins, textiles, metallic and ceramic pottery, and alabaster containers. The present study investigates two sealed potteries, using enhanced Neutron Tomography, Radiography, and Prompt Gamma Activation Analysis techniques. The neutron probe provides access to the morphological reconstructions of the inner parts of the vases and to map, with unprecedented details, the elemental composition of the surfaces and bulk areas of the potteries. The present work extends the knowledge to hitherto unknown contents of the sealed vases unlocking their secrets.

A new neutron imaging and diffraction facility, called IMAT, is currently being commissioned at the ISIS pulsed neutron spallation source. IMAT will take advantage of neutron time-of-flight measurement techniques for flexible neutron energy selection and effective energy discrimination. The instrument will be completed and commissioned within the next few months, after neutrons have been recently delivered to the sample area. From 2016 IMAT will enable white-beam neutron radiography and tomography as well as energy-dependent neutron imaging. The facility will offer a spatial resolution down to 50 microns for a field of view of up to 400 cm(2). IMAT will be operated as a user facility for material science applications and will be open for developments of time-of-flight imaging methods.

A cold neutron imaging and diffraction instrument, IMAT, is currently being constructed at the ISIS second target station. IMAT will capitalize on time-of-flight transmission and diffraction techniques available at a pulsed neutron source. Analytical techniques will include neutron radiography, neutron tomography, energy-selective neutron imaging, and spatially resolved diffraction scans for residual strain and texture determination. Commissioning of the instrument will start in 2015, with timeresolving imaging detectors and two diffraction detector prototype modules. IMAT will be operated as a user facility for material science applications and will be open for developments of time-of-flight imaging methods.

Recently, the observation of an anomalously large electrorheological effect in the dispersion of nanosized particles of titania in octanoid acid has been reported. Such an enhanced effect was not observed in the similar dispersion of micrometric particles or in more conventional suspensions of silica in silicon oil. It was suggested that this effect could be promoted by the formation of a thin layer of solvent molecules on the surface of the titania particles. We propose the measurement of electrically induced optical birefringence as a suitable independent method for testing this working hypothesis. In this paper, we report the results from the investigations of the dilute dispersions of 32 nm TiO2 particles in two insulating fluids: silicone oil and octanoic acid. A comparison of the experimental birefringence data with the theoretical predictions suggests that TiO2 nanoparticles behave like permanent electric dipoles, although induced dipoles are expected in the case of the titania material. The source of such behaviour has been individuated at the particle/solvent interface and the different possibilities of the permanent dipole origin are discussed. The lower value of the dipole moment observed in octanoic acid dispersion is explained in terms of a specific particle/solvent interaction leading to the formation of a solvent coating around the particle. The results highlight that electro-optical properties are related to electrorheological performance and that both methods can be considered as supportive for testing electrically driven phenomena in complex fluids.

Electrospray ionization (ESI) is a widely adopted soft ionization method for mass spectroscopy (MS). In spite of the undeniable success of the technique, its mechanisms are difficult to be analytically modelled because the process is characterized by non-equilibrium conditions. The common belief is that the formation of gas-phase ions takes place at the apex of the Taylor cone via electrophoretic charging. The charge balance implies that a conversion of electrons to ions should occur at the metal-liquid interface of the injector needle. We have detected that the above description is based on unproved assumptions which are not consistent with the correct evaluation of the problem. The comparison between experiments performed under the usual geometry and observations obtained under symmetric field configurations suggests that the emitted droplets cannot be significantly charged or, at least, that any possible ionization mechanism is so poorly efficient to ensure that columbic forces cannot play a major role in jet formation, even in cases where the liquid consists of a solution of ionic species. Further work is required to clearly understand how ionization occurs in ESI-MS. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

The return of supercooled water to a stable equilibrium condition is an irreversible process which, in large enough samples, takes place adiabatically. We investigated this phenomenon in water by fast imaging techniques. As water freezes, large energy and density fluctuations promote the spatial coexistence of solid and liquid phases at different temperatures. Upon synchronously monitoring the time evolution of the local temperature, we observed a sharp dynamic transition between a fast and a slow decay regime at about 266.6 K. We construe the observed phenomenon in terms of the temperature dependence of heat transfers from solid and liquid volumes already at their bulk coexistence temperature towards adjacent still supercooled liquid regions. These findings can be justified by observing that convective motions induced by thermal gradients in a supercooled liquid near coexistence are rapidly suppressed as the nucleated solid fraction overcomes, at low enough temperatures, a characteristic percolation threshold.

This work highlights the peculiar electrorheological (ER) effect shown by suspensions of TiO2 nanoparticles (~ 5 nm) in octanoic acid. Such suspensions show a marked increase in viscosity already at very low applied fields (~ 400 V/mm). This has been attributed to the octanoic acid chemical nature and in particular to its fluidity and its capability to establish interactions with the TiO2 nanoparticle surface. The study was performed as a function of nanoparticle volume fraction (?) in the range 3-10% and surprisingly no scaling with ? of the ER performance was observed. The low cost of materials involved, the simplicity of fluid preparation, and the ER response already at unusually low electric fields constitute important factors which deserve to be tailored for large scale and mass application.

In this paper, we present the autofocusing system of the imaging instrument to be used on IMAT, a new neutron-imaging facility under construction at the ISIS (UK) target station 2. We have compared 16 different autofocus algorithms to select the one with the best performance. The algorithms have been evaluated by using both a qualitative analysis and a quantitative one. An overall score has been computed and the "contrast based" algorithm has been selected for the autofocusing system. The adopted setup together with the described autofocusing system makes the camera a userfriendly imaging device allowing the optimization of beam time use.

The influence of interactions between particle surface and host fluids in electrorheological suspensions is explored. It is observed that dispersions of nanosized particles of titania in octanoid acid exhibit an anomalously large electrorheologic effect when compared with a similar dispersion of micrometric particles or with a more conventional colloidal suspension of silica in silicone oil. The effect is interpreted as originated by the formation of a thin layer of octanoid acid molecules with the surface of the titania solid particle. The experimental data are fitted with the outcomes of a modified version of conductive models existing in the literature. It is suggested that anomalous large electrorheological effect is mainly originated by the increasing of the effective radius of the nanometric particles, which results in an increasing of the effective volume fraction of the dispersed phase. It is also shown that the deformation of the soft shell around the solid particles, induced by Coulombic force, plays a not negligible role. Some hints for tailoring electrorheologic fluids suitable for different applications are proposed.

We performed a Brillouin scattering experiment on deeply supercooled water and compared the results with similar literature data obtained both at the same and at higher values of the exchanged wave vector. The whole set of available experimental data can be well reproduced with the use of the generalized hydrodynamic model where all the involved thermodynamic parameters are fixed to their literature values. On the contrary, the model based on the memory function approach generates the wrong estimates for measurables when the same values of the thermodynamic parameters are used. This result confirms our recent criticisms against the utilization of models originating from linear response theory [Phys. Rev. E 84, 051202 (2011)]. The inconsistency between models explains apparent discrepancies between the different conclusions on water acoustic behavior which may be found in the literature. We demonstrate that the observed behavior can be explained by assuming only a single relaxation process that is typical of any viscoelastic system. With all thermodynamics quantities fixed, the hydrodynamic description needs only two parameters to model the experimental data, namely, the relaxation time and the high-frequency limit of the sound velocity. The whole body of the experimental data can be well reproduced when the relaxation time behaves in an Arrhenian manner and the difference between the relaxed and not relaxed sound velocities is a constant. The high-frequency sound velocity is never higher than 2200 m/s. We conclude that, at least from experiments performed within the hydrodynamic regime, there is no indication for a fast sound close to the hypersonic velocity observed in ice.

The irreversible return of a supercooled liquid to stable thermodynamic equilibrium often begins as a fast process which adiabatically drives the system to solid-liquid coexistence. Only at a later stage will solidification proceed with the expected exchange of thermal energy with the external bath. In this paper we discuss some aspects of the adiabatic freezing of metastable water at constant pressure. In particular, we investigated the thermal behavior of the isobaric gap between the molar volume of supercooled water and that of the warmer ice-water mixture which eventually forms at equilibrium. The available experimental data at ambient pressure, extrapolated into the metastable region within the scheme provided by the reference IAPWS-95 formulation, show that water ordinarily expands upon (partially) freezing under isenthalpic conditions. However, the same scheme also suggests that, for increasing undercoolings, the volume gap is gradually reduced and eventually vanishes at a temperature close to the currently estimated homogeneous ice nucleation temperature. This behavior is contrasted with that of substances which do not display a volumetric anomaly. The effect of increasing pressures on the alleged volume crossover from an expanded to a contracted ice-water mixture is also discussed.

This work focuses on the dynamic phenomena emerging in self-assembled transient intermolecular networks formed when two different surfactants are mixed. In particular, the relaxation processes in liquid mixtures composed by bis(2-ethylhexyl)amine (BEEA) and octanoic acid (OA) in the whole composition range has been investigated by dielectric spectroscopy and Brillouin spectroscopy. A thorough analysis of all the experimental data consistently suggests that, mainly driven by acid-base interactions arising when the two surfactants are mixed, supra-molecular aggregates formation causes the slowing down of molecular dynamics. This, in turn, reflects to longer-range relaxations. These changes have been found to be composition-dependent, involving strong departures of the mixture physico-chemical properties from an ideal behaviour, and reflecting the structural and dynamical features of local structures. In particular, the peculiar dynamic processes occurring in these local inter-molecular structures, have been found to be the factors responsible for the observed and quite surprising increase of direct-current conductivity which occurs when two different (and pretty non-conductive) surfactants are mixed. The discovery can be used not only to design novel materials for application purposes but also to shed more light on the basic principles regulating charge migration in structured liquid systems

In spite of decades of efforts, the puzzle of understanding the anomalies of liquid water remains unsolved. Several plausible theoretical scenarios have been proposed, but distinguishing among them requires accessing temperatures below the homogeneous nucleation temperature Th, which for bulk water is an experimentally impossible task. A widely adopted way for bypassing such a difficulty consists in studying the behavior of samples confined in nanopores, supercooled aqueous salt solutions, or in investigating samples transiently heated or cooled. In this paper, we compare the results obtained from Raman experiments on supercooled bulk water and supercooled LiCl aqueous solutions. The obtained results indicate that while at relatively high temperatures water in ionic solution can appear indistinguishable from bulk water, large differences are detected after further cooling. The comparison with very recent experimental data on water confined in nanopores suggests generalizing our result for every kind of confinement. Even if an experiment carried out under space-time constraints can produce results that match those from bulk water (in the temperature range where bulk water data are available), we cannot assume that the matching will persist at lower temperatures. This implies that the interpretation of many literature experimental results should be reconsidered. A coherent picture of existing experimental data can be obtained accepting the idea that amorphous water is not a metastable state and that homogeneous nucleation temperature represents a metastability limit.

We present a single pixel prototype of a pixelated Bragg edge detector for neutron transmission measurements. The optical signal coming from a scintillator is collected by an optical fiber and is detected by an avalanche photodiode. A fast, Field Programmable Gate Array based, readout allows to obtain transmission spectra within reasonable acquisition times. The performances of the instrument have been tested by measuring the transmission spectra of iron powder samples with two different scintillators. The instrument accuracy in detecting the Bragg edges positions is comparable with the state of the art for similar devices.

Some Brillouin scattering experiments on aqueous solution of Polyethylene glycol and Polyethylene glycol dimethyl ether are presented. In all the systems non-Debye relaxation processes have been detected, occurring on the picosecond time scale. The average values of the relaxation time distributions fail to follow simple Arrhenius behaviours. The temperature evolution of the relaxation time is adequately fitted after the adoption of a phenomenological Vogel-Fulcher-Tamman model. In spite of the different temperature and concentration dependences observed for each system, a unique scaling behaviour has been evidenced, at relatively low water contents, when the real and imaginary parts of the loss modulus are plotted as a function of a reduced reverse temperature, T0/T, being T0 the values of the arrest temperature as obtained by the Vogel- Fulcher-Tamman fits. The observation of a unique scaling law, for aqueous solutions of polymers characterized by the same average molecular weight but with different end groups, suggests for the establishment of similar hydrogen bonded local structures where water plays a main role, acting as a stabilizer bridging neighbouring polymer chains. The possible physical meanings of the phenomenological fitting parameters are discussed in the framework of recent approaches and the results are compared with literature reports on similar systems.