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We report on Differential Evolution for Analytic Continuation (DEAC): a parameter-free evolutionary algorithm to generate the dynamic structure factor from imaginary time correlation functions. Our approach to this long-standing problem in quantum many-body physics achieves enhanced spectral fidelity while using fewer compute (CPU) hours. The need for fine-tuning of algorithmic control parameters is eliminated by embedding them within the genome to be optimized for this evolutionary computation based algorithm. Benchmarks are presented for models where the dynamic structure factor is known exactly, and experimentally relevant results are included for quantum Monte Carlo simulations of bulk $^4$He below the superfluid transition temperature., Comment: 10 pages, 6 figures. For associated data and code repository see: https://github.com/DelMaestroGroup/papers-code-DEAC

We report high-resolution neutron Compton scattering measurements of liquid $^4$He under saturated vapor pressure. There is excellent agreement between the observed scattering and ab initio predictions of its lineshape. Quantum Monte Carlo calculations predict that the Bose condensate fraction is zero in the normal fluid, builds up rapidly just below the superfluid transition temperature, and reaches a value of approximately $7.5\%$ below 1 K. We also used model fit functions to obtain from the scattering data empirical estimates for the average atomic kinetic energy and Bose condensate fraction. These quantities are also in excellent agreement with ab initio calculations. The convergence between the scattering data and Quantum Monte Carlo calculations is strong evidence for a Bose broken symmetry in superfluid $^4$He.

We investigate the behavior of the collective excitations of adsorbed $^4$He in an ordered hexagonal mesopore, examining the crossover from a thin film to a confined fluid. Here we present the inelastic scattering results as a function of filling at constant temperature. We find a monotonic transition of the maxon excitation as a function of filling. This has been interpreted as corresponding to an increasing density of the adsorbed helium, which approaches the bulk value as filling increases. The roton minimum exhibits a more complicated behavior that does not monotonically approach bulk values as filling increases. The full pore scattering resembles the bulk liquid accompanied by a layer mode. The maxon and roton scattering, taken together, at intermediate fillings does not correspond to a single bulk liquid dispersion at negative, low, or high pressure., Comment: 9 pages, 10 figures

Solid molecular oxygen presents an interesting example of a low-temperature crystal which exists within several different magnetic phases. When solid solutions of argon and oxygen are formed with molar concentrations of oxygen between 60 and 80 %, a new structural and magnetic phase, known as the $$\delta $$ -phase, appears at low temperatures. In order to investigate the nature of the $$\delta $$ -phase, we carried out SQUID magnetometry measurements solid argon-oxygen solutions made up of 74 % oxygen and 26 % argon. In particular, we performed measurements of the magnetic susceptibility of the solid solutions over complete temperature cycles and isothermally as a function of time. Taken together, the experimental data demonstrate that that the $$\delta $$ -phase is not an equilibrium thermodynamic state of the solid solutions, but is instead only a metastable state.

The effects of confinement, disorder, and reduced dimensionality upon quantum fluids have been studied by the adsorption of liquid helium in porous media. The effects of extreme, nanoscale confinement upon its microscopic excitations are not presently understood. Several previous experiments have suggested that at sufficiently low temperature, the roton mean free path is set by the restricted geometry. Here we show that the lifetime of the roton excitation is unaffected when superfluid helium is confined within cylindrical pores only a few nanometers in diameter. The temperature dependence of its lifetime are found to be identical to the bulk fluid, implying that the lifetime is not set by the scale of the confinement. Our results demonstrate that the rotons in the pore center propagate without being modified by the confining media, unlike the collective excitations of classical fluids.

We have constructed a neutron imaging station at the Low Energy Neutron Source (LENS), located within the Center for the Exploration of Energy and Matter at Indiana University. In contrast to many existing neutron imaging stations, we utilize a broad range of neutron energies, extending into the fast neutron regime, to take advantage of the higher fluxes and larger penetrating power of these high-energy neutrons. The imaging station consists of a collimator to define the beam, a rotating sample stage, and a cooled charge-coupled device camera (Alta U6) using a scintillator. A LiF + ZnS screen is used to produce scintillation light. Typical image collection times are a few seconds for a aperture to sample distance ratio of 100, yielding a spatial resolution of 0.2 × 0.2 mm 2 . Examples of the scanned and calculated image are presented.

The Low Energy Neutron Source at Indiana University began construction in the fall of 2003, and the facility has now been producing cold neutrons for approximately 8 years. LENS now has three instruments in operation on its cold target station as well as a facility for investigating neutron radiation effects on a second target station. Instrumentation development continues to represent a significant fraction of the activity at LENS, with the current activities focused primarily on neutron spin manipulation and moderator development. Research into the effects of confinement on simple and complex fluids has dominated our materials investigations. In this paper, we summarize recent activities in these areas using each of the instruments and provide an update on our operational experience over the last few years.

We have developed a circuit to demonstrate the phase relationships between resistive and reactive elements in series RLC circuits. We utilize a differential amplifier to allow the phases of the three elements and the current to be simultaneously displayed on an inexpensive four channel oscilloscope. We have included a novel circuit that provides a visual indication of the magnitude and direction of the voltage or current using LEDs. This allows the phase relationships to be demonstrated directly using the very intuitive measurement of the brightness of a light.

The coat protein of positive-stranded RNA viruses often contains a positively-charged tail that extends toward the center of the capsid and interacts with the viral genome. Electrostatic interaction between the tail and the RNA has been postulated as a major force in virus assembly and stabilization. The goal of this work is to examine the correlation between electrostatic interaction and the amount of RNA packaged in the tripartite Brome Mosaic Virus (BMV). Nanoindentation experiment using atomic force microscopy showed that the stiffness of BMV virions with different RNAs varied by a ten-fold higher range than would be predicted by electrostatics. BMV mutants with decreased positive charges encapsidated lower amounts of RNA while mutants with increased positive charges packaged additional RNAs up to ~900 nucleotides. However, the extra RNAs included truncated BMV RNAs, an additional copy of RNA4, potential cellular RNAs, or a combination of the three, indicating that change in the charge of the capsid could result in several different outcomes in RNA encapsidation. In addition, mutant with specific arginines changed to lysines in the capsid also exhibited defects in the specific encapsidation of one or more of the four BMV positive-strand RNAs. The experimental results indicate that electrostatics is a major component in RNA encapsidation, but was unable to account for all of the observed effects on RNA encapsidation. Thermodynamic modeling incorporating the electrostatics was able to predict the approximate length of the RNA to be encapsidated for the majority of mutant virions, but not for a mutant with extreme clustered positive charges. Cryo-electron microscopy of virions that encapsidated an additional copy of RNA4 revealed that, despite the increase in RNA encapsidated, the capsid structure was minimally changed. These results experimentally demonstrated the impact of electrostatics and additional restraints in the encapsidation of BMV RNAs, which could be applicable to other viruses.

The Indiana University Low Energy Neutron Source (LENS) production target was recently upgraded to handle the high power 13 MeV proton pulsed beam. The target, a 2 inch diameter beryllium disk, is 1.2 millimeters thick allowing the 13 MeV protons to pass completely through the target and stop in the cooling water eliminating the buildup of protons inside the beryllium. This change along with upgrading the cooling water system has produced the most reliable target to date for LENS operations. Details about the failure modes will be presented.

We have used small angle X-ray scattering (SAXS) to quantitatively characterize the morphology of vertically aligned (VA) multiwall carbon nanotube (MWCNT) arrays. We examined the extent of alignment of MWCNTs in terms of order parameter by analyzing SAXS intensity as a function of azimuthal angle. The SAXS measurements at different heights of CNT arrays from the substrate reveal two distinct morphologies and increasing alignment. We are able to quantitatively characterize a real variation in CNT diameters of the VA-MWCNTs through model fitting of the SAXS spectra. It found that the average CNT diameter increases with increasing distance from the substrate.

The nano size zinc oxide (ZnO) was successfully synthesized at low temperature solution method. The structural characterization, size and distribution of synthesized ZnO particles were performed using X-ray diffraction (XRD) and neutron scattering technique. The hybrid polymer-metal oxide bulk heterojunction solar cell has been fabricated by blending of ZnO and regioregular poly(3-hexylthiophene) (P3HT) through solution process and flow coating on the flexible substrate. The decrease in the photoluminescence (PL) emission intensity more than 79% for ZnO:P3HT composites film indicates high charge generation efficiency. The cell shows the V oc and I sc of 0.33 V and 6.5 mA/cm 2 , respectively. The performance and stability of cell were investigated using UV illumination of white light.

The construction of new neutron facilities in Europe, Japan and the United States signals the need for many kinds of neutron detectors. In order to address a portion of this need, we are developing low-cost, reliable, medium-resolution (1–2.5 cm), single-wire-per-tube neutron gaseous detectors for moderate counting rates of about 10 6 counts/m 2 /s that are capable of being used in a vacuum environment. The detectors are fabricated with square tubes in order to avoid the efficiency problems of round tubes. Components used on the interior of the detector are chosen to have low outgassing rates. The detectors are baked while attached to a vacuum pumping station in order to assure a long lifetime without changing the gas.

The low-energy neutron source (LENS) is currently under construction at the Indiana University Cyclotron Facility. LENS is a long-pulse neutron source utilizing low-energy (p,xn) reactions on a beryllium target to produce neutrons. There are several unique features of the LENS facility. The low proton beam energy of 13 MeV results in a low heat load on the moderator system, enabling the operation of the moderator at temperatures lower than 10 K. The low beam energies also result in relatively low activation of the materials surrounding the target and moderator, thus enabling rapid prototyping and turnaround times for a moderator studies program.

We present quasi-elastic neutron scattering measurements of the diffusion of H 2 adsorbed in porous MCM-48, a silica glass, with an ordered pore network. Quasi-elastic scattering of hydrogen adsorbed within the pore network was used to monitor the liquid–solid transitions of the absorbed fluid. Unlike other porous media of similar pore size, where supercooling of the liquid–solid transition by 3–4 K was observed, no suppression of the transition was observed for MCM-48. Furthermore, no hysteresis between freezing and melting is observed, as in other porous media. The diffusion constant for the confined liquid has been extracted from the measurements, and the hydrogen adsorbed in the MCM-48 has a slightly higher diffusion constant than bulk liquid H 2 .

A partnership between Penn State University and a suburban high school allowed high school students to complete a calculus-based high school physics II course in mechanics and electricity/magnetism. This course was not an AP course or a traditional high school second-level course but was modeled on the dynamic physics course at Penn State. This article describes the strategies and technology tools used, data on student outcomes and achievement, and the development and implementation of the course.

The properties of molecular hydrogen adsorbed in Britesorb were studied through inelastic neutron scattering. We have measured both the rotational energy levels and the momentum distribution at bilayer and nearly full pore fillings. Splitting of the J=1 rotational energy levels is observed for molecular hydrogen adsorbed on the surface, while the rotational properties of the hydrogen adsorbed after monolayer completion is consistent with behavior in the bulk. Additionally, the measurement of the momentum distribution showed that the mean kinetic energy of the molecules in the bilayer is 88 K±7 K. The kinetic energy measured in the nearly full pore was 81 K±6 K, which is consistent with a simple model in which the behavior of the monolayer is dominated by the interaction with the surface of the pore wall but H2 adsorbed after monolayer completion is bulk like.

A detailed study has been performed to investigate the effect of frame overlap in a cold neutron chopper spectrometer. The basic spectrometer is defined by two high-speed choppers, one near the moderator to shape the pulse from the moderator, and one near the sample to define energy resolution. Using ray-tracing timing diagrams, we have observed that there are regions along the guide where the trajectories of neutrons with different velocities converge temporally at characteristic points along the spectrometer. At these points of convergence, a frame overlap chopper would be totally ineffective, allowing neutrons of all velocities to pass through. Conversely, at points where trajectories of different velocity neutrons are divergent, a frame overlap chopper is most effective. An analytical model to describe this behaviour has been developed, and leads us to the counterintuitive conclusion that the optimum position for a frame overlap chopper is as close to the initial chopper as possible. We further demonstrate that detailed Monte Carlo simulations produce results which are consistent with this model.

High-resolution quasi-elastic neutron scattering measurements have been performed on molecular hydrogen in zeolite 13X. Previous NMR measurements suggested that the freezing temperature is suppressed from 14 K down to 8 K. In contrast, previous intermediate resolution quasi-elastic neutron scattering studies suggested freezing occurred between 25 and 35 K. Unfortunately, the limited instrumental resolution available in the previous quasi-elastic neutron scattering study was not sufficient to show this point definitively. We report new quasi-elastic neutron scattering measurements with very high resolution that show no evidence of mobile hydrogen below 25 K, which is well above the bulk liquid-solid transition temperature for hydrogen. A quasi-elastic component appears between 25 and 30 K indicating the presence of mobile H2. However, the width and momentum dependence of the quasi-elastic scattering are much different than would be expected for the diffusive motion of liquid hydrogen in this temperature range. Instead, we find that a slow diffusive component representing jumps between well-defined sites appears first at low temperatures. As the temperature is raised, a faster liquid like diffusive component appears.

New measurements of the roton excitations in superfluid 4He have been made using the IRIS spectrometer (energy resolution ∼20 μeV at the roton energy) at the ISIS spallation neutron source. The roton energy was determined over a temperature range of 0.56 to 1.61 K. High resolution (energy resolution

We report high-resolution neutron inelastic-scattering measurements of the roton energy and linewidth of superfluid {sup 4}He confined in 95{percent} porosity aerogel glass for temperatures 0.08{lt}T{lt}1.2 K. The confined roton line shape can be described well by a damped harmonic oscillator (DHO) function, as in the bulk. The energy of the confined roton is essentially temperature independent over this temperature range. The roton linewidth does not exhibit a finite width of greater than 0.1 {mu}eV at low temperature. This result is in contrast to previous measurements carried out at lower resolution. {copyright} {ital 1999} {ital The American Physical Society}

The diffusion of molecular hydrogen adsorbed in zeolite 13X at high coverage`s has been studied by quasi-elastic neutron scattering for temperatures ranging from 0 to 60 K. No diffusive motion was observed, within instrumental resolution, at temperatures below 20 K, well above the bulk melting point of H{sub 2}, in contrast to recent NMR studies. The diffusive motion of the adsorbed H{sub 2} could be described by a liquid like jump diffusion model above 35 K. The diffusion coefficient demonstrates an Arrhenius behavior: D = D{sub 0} exp(E/kT), with D{sub 0} = 1.2 {times} 10{sup {minus}8} m{sup 2}/s and an activation energy of E = 62 K. The inelastic scattering spectrum has also been studied. The scattering consisted of several peaks superimposed on a broad background extending from 1 meV to above 100 meV and is consistent with rotational transitions for a hindered rotor in a strong orientational potential with a broad distribution of barrier heights.

Neutron diffraction studies of the static structure factor S(Q) of water confined in the pore space of cement samples have been carried out for temperatures from 170 to 293 K. At high temperatures, when the water in the pores is liquid, a fraction of the water molecules are strongly bound to specific adsorption sites on the crystalline components of the cement. On cooling, the water in the pore space solidifies at 245 K into a cubic structure different from that of bulk water at similar temperatures.

We report the results of x-ray diffraction studies of Ar and Kr confined in Vycor glass. The freezing and melting temperatures of both Ar and Kr were suppressed well below their bulk freezing points. On solidification, both samples crystallized in a disordered hexagonal close packed structure similar to that observed in molecular dynamics simulations of confined solids. A new solid-solid phase transition is observed at a reduced temperature of ${T/T}_{f}\ensuremath{\approx}0.5$ when confined to Vycor. Below this temperature the disordered hexagonal closed packed structure coexists with the fcc structure.

The orientational properties of n-H2confined in Vycor have been studied via inelastic neutron spectroscopy. We observe two distinct rotational transitions which we ascribe to H2in the center of the pore and H2strongly bound to the surface. The molecules on the surface can be modeled as rotationally hindered rotors, and a distribution of orientational potentials is extracted.

Inelastic neutron scattering has been used to probe the collective excitations of superfluid helium confined to silica aerogel. Confinement in porous aerogel results in a crossover behavior in the temperature dependence of the roton where the energy is relatively temperature independent below 1.9 K and strongly temperature dependent above 1.9 K. As in the bulk liquid, the relationship between the microscopic excitation spectrum and the macroscopic thermodynamics of the confined system are found to be in good agreement.

We present high-precision measurements of the dynamics of single atoms in superfluid ${}^{4}\mathrm{He}$ at $T=1.6 \mathrm{K}$ and saturated vapor pressure. The measurements were taken on the MARI instrument at the ISIS neutron-scattering facility, Rutherford-Appleton Laboratory. From the measurements we obtain a condensate fraction ${n}_{0}=6.0\ifmmode\pm\else\textpm\fi{}2.0%$ at $T=1.6 \mathrm{K}$. The final-state effects (FSE's) in the atomic response are also determined from the data in the form of a final-state broadening function, $R(Q,y)$. We find that this FS function is the same in the superfluid at $T=1.6 \mathrm{K}$ as that determined previously in normal ${}^{4}\mathrm{He}$ at $T=2.3 \mathrm{K}$. If we reanalyze the data assuming that the superfluid has no condensate, i.e., ${n}_{0}=0$, then the data requires that the normal $n(\mathbf{k})$ change dramatically between $T=2.3 \mathrm{K}$ and $T=1.6 \mathrm{K}$. Since such a change in $n(\mathbf{k})$ is physically unexpected, given that $\mathrm{kT}$ is much less than the zero-point energy, the data requires that a new contribution, such as a condensate, enter $n(\mathbf{k})$ in the superfluid.

Inelastic neutron scattering measurements of the roton in superfluid helium confined in two different porosity aerogels are presented. The temperature dependence of the roton energy exhibits an anomalous crossover behavior at T c = 1.9 K. Below T c the roton energy is found to be weakly temperature dependent while above T c it is very strongly temperature dependent. The roton lifetime for the confined liquid also display a weak crossover behavior. A simple qualitative model for this behavior in terms of a confined length scale is discussed.

The structure of solid confined in porous Vycor glass has been studied as a function of temperature via x-ray diffraction. The confined solid has the same structure as the bulk solid but with a slightly larger lattice constant of 5.644 A at 150 K compared to the bulk lattice constant of 5.624 A at the same temperature. Broad diffraction peaks are observed indicating that the solid phase of the in the pores forms in small crystallites approximately 160 A in diameter. This is comparable to the pore dimensions in the Vycor indicating that solidification occurs separately in each of the pores. A large temperature-independent static disorder, analogous to the Debye - Waller factor, was observed in the form of strong damping of the Bragg peaks with increasing Q.

Two different microscopic phases have been observed via inelastic neutron scattering for superfluid helium confined within highly monodisperse, smooth, and unidimensional silica pores. When the helium forms a thin film on the pore walls, it supports a dramatically modified phonon-roton spectrum as well as a 2D surface roton. The energies of these modified phonon-roton modes are consistent with predictions for a dilute, low-density film, while the energy of the 2D surface roton corresponds to that of a dense film. The relatively smooth and weak surface potential of the substrate permits the formation of a film with large dilute regions and only small compressed regions. When the pores are saturated with liquid, the modified phonon-roton spectrum disappears, and bulk-like modes coexist with the 2D surface roton. Presumably, bulk-like liquid occupies the core volume of the pores and high density liquid layers are present at the liquid-solid interface. These findings clearly connect the nature of the excitations to the local density of the liquid.

We have carried out magnetic neutron diffraction studies of a single crystal of neodymium at high pressure, using clamp cells on the diffractometer D10 at the Institut Laue-Langevin, Grenoble. The magnetic ordering was investigated at pressures up to 14 kbar in the temperature range 1.4-25 K. A number of quite different magnetic phases were observed, including the coexistence of ferromagnetic and antiferromagnetic ordering of moments on the inequivalent crystallographic sites. The structures formed and the population of the different symmetrically equivalent domains appear to be affected by complex interactions between the cubic-site ferromagnetism, the antiferromagnetic hexagonal-site ordering and a uniaxial component of stress.

The elastic, quasi-elastic, and deep inelastic scattering of para-hydrogen in porous vycor glass have been measured in both the solid and liquid phase. At temperatures above 12 K, the H2 in the pores can be described as a bulk-like liquid with a single tightly bound layer at the pore surface. At temperatures below 8 K, the hydrogen in the pores is solidified into a crystalline structure different from that of the bulk. No indication of migration of the hydrogen out of the pores as recently proposed to explain torsional oscillator measurements, is observed. The momentum distribution of the hydrogen in the pores at both low and high temperatures is Gaussian and shows no indication of a Base condensate peak.

Neutron diffraction studies of normal deuterium in porous vycor glass have been carried out at temperatures in the range 4 to 20 K as a function of pore filling. For pore fillings, f, above f = 0.6 we find that the D2 in the pores forms a crystalline solid with a large amorphous component. The appearance of the crystalline phase is characterized by supercooling and hysteresis of the liquid-solid transition in agreement with previous thermodynamic studies. The crystalline phase has a structure which is different from the bulk and exhibits a large correlation length. Pore fillings below f = 0.6 show no sign of crystalline ordering, although enhanced short range ordering is observed.

Deep inelastic neutron scattering measurements on liquid4He have been carried out for temperatures from 0.35 K to 4.2 K and densities from 0.125 to 0.200g/cm3 at a momentum transfer of 23 A−1. These measurements are at large enough momentum transfer that deviations from the Impulse Approximation are accurately described by current theories and information on the single particle momentum distribution may be extracted from the measured scattering. The scattering exhibits non-Gausian behavior in both the normal liquid and superfluid phases. A distinct change in the scattering, marked by a reduction in the width and increased deviations from the classical Gaussian shape, occurs at the suerfluid transition. We present a comparison of our experimental results with recent calculations at a variety of temperatures and densities and show that theory and experiment are in excellent agreement. We also present model scattering functions, obtained by correcting for instrumental resolution and final state effects, that represent the scattering in the IA limit. Finally, we present values for the average kinetic energy and the Bose condensate fraction over a broad range densities and temperatures.

We present high-resolution neutron Compton scattering measurements of liquid $^3$He below its renormalized Fermi temperature. Theoretical predictions are in excellent agreement with the experimental data when instrumental resolution and final state effects are accounted for. Our results resolve the long-standing inconsistency between theoretical and experimental estimates of the average atomic kinetic energy., Comment: 5 pages, 4 figures

Measurement of the specific heat and small angle neutron scattering studies for nCB liquid crystals confined to the 0.05 μm diameter pores of Millipore filters, a fibrous porous substrate, reveal that in spite of the interconnection and restrictive size, smectic layers are formed. The existence of this long range smectic order that increases with decreasing temperature is in contrast to findings in other porous geometries where a smectic phase is either absent or greatly suppressed by the confinement. For 9CB, we also study the possible effects of confinement on the critical behavior at the second order smectic-A to nematic phase transition.

The thermodynamic and structural properties of octylcyanobiphenyl (8CB) confined to the highly restrictive and randomly interconnected pores of Vycor glass were studied via AC calorimetry, DSC, and small angle neutron scattering. The weakly first order nematic to isotropic phase transition is absent and replaced by a continuous evolution of local orientational ordering with decreasing temperature. The results are consistent with predictions from a model that treats the host media as a collection of noninteracting pore segments. The continuous smectic-A to nematic phase transition is also absent with no evidence of any smectic ordering. In addition, crystallization is replaced by a glass-like melting transition with indications of another melting transition at much lower temperatures.

Using high-precision neutron-scattering data, we show that the momentum distribution, n(k), in normal He differs significantly from the classical, Maxwell-Boltzmann distribution while n(k) in liquid neon is Maxwellian. Final-state contributions to the scattering function are also determined from the data. In helium these are most conveniently represented as a final-state broadening function and in neon as additive corrections to the impulse approximation. Neutron-scattering experiments at high momentum transfer Q, measure single-particle properties and especially atomic momentum distributions n (k), in condensed matter. ' The n (k} is obtained directly if the observed dynamic structure factor, S(Q, co), is well approximated by the impulse approximation (IA). In the IA, the atom struck by the neutron is assumed to recoil freely without interacting with its neighbors. However, in practice, the recoil is not free and the final-state (FS) interactions greatly complicate the interpretation of experimental data. In the past, information on n (k) could only be obtained using theoretical input to account for FS effects or by treating them as additive corrections. In this paper we demonstrate, for two contrasting liquids, He and Ne, that both n (k) and the FS effects can be simultaneously extracted. This is possible only by considering the Q dependence of high-quality scattering data over a broad range of momentum transfers. Rather than attempting to reach the highest possible momentum transfer, A'Q, we emphasize precision at intermediate Q ( ~30 A ') where FS effects are not small and can be identified in the data. The analysis method consists of expanding the intermediate scattering function, S(g, t), the Fourier transform of S (Q, co), in powers of the time t, and treating the expansion parameters (cumulants) as free parameters to be determined by a fit to the experimental data. The parameters associated with n (k) and FS effects can be separated through the measured Q dependence of the parameters in this expansion. Liquid He and Ne represent contrasting systems which illustrate the method. We now sketch the expansion method (laid out in detail by Cxlyde ), present the data, display n (k), atomic kinetic energy Ek, and the final-state effects. It is convenient to work with the longitudinal momen

We report small-angle neutron scattering studies of liquid helium mixtures confined in Mobil Crystalline Material-41 (MCM-41), a porous silica glass with narrow cylindrical nanopores (d=3.4 nm). MCM-41 is an ideal model adsorbent for fundamental studies of gas sorption in porous media because its monodisperse pores are arranged in a 2D triangular lattice. The small-angle scattering consists of a series of diffraction peaks whose intensities are determined by how the imbibed liquid fills the pores. Pure (4)He adsorbed in the pores show classic, layer-by-layer film growth as a function of pore filling, leaving the long range symmetry of the system intact. In contrast, the adsorption of (3)He-(4)He mixtures produces a structure incommensurate with the pore lattice. Neither capillary condensation nor preferential adsorption of one helium isotope to the pore walls can provide the symmetry-breaking mechanism. The scattering is consistent with the formation of randomly distributed liquid-liquid microdomains ∼2.3 nm in size, providing evidence that confinement in a nanometer scale capillary can drive local phase separation in quantum liquid mixtures.

We have measured the structure of D[sub 2] adsorbed in zeolite 13[ital X] at temperatures in the range 5.5 to 80 K at a variety of fillings. We find that the D[sub 2] molecules adsorb into well-defined adsorbtion sites in the zeolite structure. Two distinct adsorbtion sites, with binding energies on the order of 40 and 80 K, have been identified. No evidence for bulklike liquid or solid behavior of the D[sub 2] adsorbed in the pores has been observed. Once the adsorbtion sites are saturated D[sub 2] is no longer adsorbed into the pores and forms a bulk phase on the surface of the zeolite.

Deep inelastic neutron scattering measurements have been carried out to measure the kinetic energy and condensate fraction in liquid $^{3}\mathrm{\ensuremath{-}}^{4}$He mixtures. Samples with $^{3}\mathrm{He}$ concentration on the order of 10% were studied at 1.4 K and 2.3--2.5 K. The condensate fraction was found to be 0.18\ifmmode\pm\else\textpm\fi{}0.03, much larger than theoretical predictions. The measured kinetic energies of the $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ in the mixture remain the same as their values in the pure phase, in disagreement with current theoretical predictions.

The design and performance of the new cold neutron chopper spectrometer (CNCS) at the Spallation Neutron Source in Oak Ridge are described. CNCS is a direct-geometry inelastic time-of-flight spectrometer, designed essentially to cover the same energy and momentum transfer ranges as IN5 at ILL, LET at ISIS, DCS at NIST, TOFTOF at FRM-II, AMATERAS at J-PARC, PHAROS at LANSCE, and NEAT at HZB, at similar energy resolution. Measured values of key figures such as neutron flux at sample position and energy resolution are compared between measurements and ray tracing Monte Carlo simulations, and good agreement (better than 20% of absolute numbers) has been achieved. The instrument performs very well in the cold and thermal neutron energy ranges, and promises to become a workhorse for the neutron scattering community for quasielastic and inelastic scattering experiments.

Deep Inelastic Neutron Scattering measurements of water confined in mesoporous silica have been carried out. The experiment has been performed at room temperature on dry and on hydrated samples in order to investigate the interaction between the protons and the silanol groups of the confining surface. With this aim we could control the hydration of the pores in such a way as to adsorb 3.0 water molecules per nm2, corresponding to a 1 to 1 ratio with the silanol groups of the surface. DINS measurements directly measure the mean kinetic energy and the momentum distribution of the protons. A detailed analysis of the hydrated sample has been performed in order to separate the contributions of the protons in the system, allowing us to determine the arrangement of water molecules on the silanol groups. We find that the hydrogen bond of the water proton with the oxygen of the silanol group is much stronger than the hydrogen bonds of bulk water. © the Owner Societies. 2011.

The properties of the superfluid phase of liquid have fascinated physicists since they were first observed (1). The most spectacular manifestation of the superfluid phase, which exists in the liquid below 2.17 K at saturated vapor pressure, is its ability to transfer heat without a thermal gradient and to flow without viscosity. Superfluidity, like its cousin superconductivity, is a macroscopic manifestation of the microscopic quantum effects governing the behavior of atoms. In both these phenomena the microscopic explanation for these macroscopic effects is the phenomena of Bose condensation.

We present a new method for extracting the condensate fraction from deep inelastic neutron scattering studies of superfluid helium. This method employs a model for the momentum distribution that incorporates the known limiting behavior from many-body theories and takes into account final-state effects present in deep inelastic neutron scattering measurements. We apply this procedure to deep inelastic neutron scattering measurements of helium over a wide range of temperatures and densities in the superfluid, normal liquid, and solid phases.