26 research outputs found
High Frequency dynamics in metallic glasses
Using Inelastic X-ray Scattering we studied the collective dynamics of the
glassy alloy NiZr in the first pseudo Brillouin zone, an
energy-momentum region still unexplored in metallic glasses. We determine key
properties such as the momentum transfer dependence of the sound velocity and
of the acoustic damping, discussing the results in the general context of
recently proposed pictures for acoustic dynamics in glasses. Specifically, we
demonstrate the existence in this strong glass of well defined (in the Ioffe
Regel sense) acoustic-like excitations well above the Boson Peak energy.Comment: 4 pages, 4 .eps figures, accepted in Phys. Rev. Let
Collective excitations in liquid D2 confined within the mesoscopic pores of a MCM-41 molecular sieve
We present a comparative study of the excitations in bulk and liquid D2
confined within the pores of MCM-41. The material (Mobile Crystalline
Material-41) is a silicate obtained by means of a template that yields a
partially crystalline structure composed by arrays of nonintersecting hexagonal
channels of controlled width having walls made of amorphous SiO2. Its porosity
was characterized by means of adsorption isotherms and found to be composed by
a regular array of pores having a narrow distribution of sizes with a most
probable value of 2.45 nm. The assessment of the precise location of the sample
within the pores is carried out by means of pressure isotherms. The study was
conducted at two pressures which correspond to pore fillings above the
capillary condensation regime. Within the range of wave vectors where
collective excitations can be followed up (0.3<Q<3.0 −1), we found
confinement brings forward a large shortening of the excitation lifetimes that
shifts the characteristic frequencies to higher energies. In addition, the
coherent quasielastic scattering shows signatures of reduced diffusivity.Comment: 6 page
Suppression of Superfluidity of He in a Nanoporous Glass by Preplating a Kr Layer
Helium in nanoporous media has attracted much interest as a model Bose system
with disorder and confinement. Here we have examined how a change in porous
structure by preplating a monolayer of krypton affects the superfluid
properties of He adsorbed or confined in a nanoporous Gelsil glass, which
has a three-dimensional interconnected network of nanopores of 5.8 nm in
diameter. Isotherms of adsorption and desorption of nitrogen show that
monolayer preplating of Kr decreases the effective pore diameter to 4.7 nm and
broadens the pore size distribution by about eight times from the sharp
distribution of the bare Gelsil sample. The superfluid properties were studied
by a torsional oscillator for adsorbed film states and pressurized liquid
states, both before and after the monolayer Kr preplating. In the film states,
both the superfluid transition temperature and the superfluid
density decrease about 10 percent by Kr preplating. The suppression of film
superfluidity is attributed to the quantum localization of He atoms by the
randomness in the substrate potential, which is caused by the
preplating--induced broadening of the pore size distribution. In the
pressurized liquid states, the superfluid density is found
to increase by 10 percent by Kr preplating, whereas is
decreased by 2 percent at all pressures. The unexpected enhancement of
might indicate the existence of an unknown disorder effect
for confined He.Comment: 27 pages, 8 figures, submitted to J. Phys. Soc. Jp
Internet of Things for Water Sustainability
The water is a finite resource. The issue of sustainable withdrawal of freshwater is a vital concern being faced by the community. There is a strong connection between the energy, food, and water which is referred to as water-food-energy nexus. The agriculture industry and municipalities are struggling to meet the demand of water supply. This situation is particularly exacerbated in the developing countries. The projected increase in world population requires more fresh water resources. New technologies are being developed to reduce water usage in the field of agriculture (e.g., sensor guided autonomous irrigation management systems). Agricultural water withdrawal is also impacting ground and surface water resources. Although the importance of reduction in water usage cannot be overemphasized, major efforts for sustainable water are directed towards the novel technology development for cleaning and recycling. Moreover, currently, energy technologies require abundant water for energy production. Therefore, energy sustainability is inextricably linked to water sustainability. The water sustainability IoT has a strong potential to solve many challenges in water-food-energy nexus. In this chapter, the architecture of IoT for water sustainability is presented. An in-depth coverage of sensing and communication technologies and water systems is also provided
Quantum effects in the single particle kinetic energy of high density fluid <sup>4</sup>He
Deep inelastic neutron-scattering measurements have been performed in dense fluid 4He along three isochores at number densities 33, 38, and 45 nm-3 and temperatures ranging from 4.35 to 56 K. Data have been analyzed in the plane-wave impulse-approximation framework to obtain the root-mean-square values of the single-particle momentum along a given direction px. The density and temperature behavior of the derived mean kinetic energies is discussed in comparison with a simple harmonic model for the fluid and with quantum simulations performed using a path-integral Monte Carlo code. The comparison with the harmonic models sheds light on the density dependence of the zero-point kinetic energy of the particles and points out the inadequacy of a single-frequency Einstein-oscillator model in describing its temperature dependence. The quantum simulation results are in substantial agreement with the experimental data although systematic deviations are found as the density is increased