Transitions among crystal, glass, and liquid in a binary mixture with changing particle size ratio and temperature

Using molecular dynamics simulation we examine changeovers among crystal, glass, and liquid at high density in a two dimensional binary mixture. We change the ratio between the diameters of the two components and the temperature. The transitions from crystal to glass or liquid occur with proliferation of defects. We visualize the defects in terms of a disorder variable "D_j(t)" representing a deviation from the hexagonal order for particle j. The defect structures are heterogeneous and are particularly extended in polycrystal states. They look similar at the crystal-glass crossover and at the melting. Taking the average of "D_j(t)" over the particles, we define a disorder parameter "D(t)", which conveniently measures the degree of overall disorder. Its relaxation after quenching becomes slow at low temperature in the presence of size dispersity. Its steady state average is small in crystal and large in glass and liquid.Comment: 7 pages, 10 figure

Polarizability of interacting atoms: Relation to collision-induced light scattering and dielectric models

The polarizability tensor of a pair of interacting He atoms has been calculated as a function of internuclear separation r using the fully self-consistent Hartree-Fock theory. It was found that the trace of the polarizability tensor, α(r), to which the second dielectric virial coefficient Bε is directly proportional, decreases with decreasing r, giving a theoretical value of Bε=-0.093 a.u. at room temperature, compared with the experimental result Bε=-0.06±0.04 a.u., measured by Orcutt and Cole [J. Chem. Phys. 46, 697 (1967)]. This is the first calculation that predicts the correct sign of Bε. We conclude that for He the effects of overlap are of opposite sign from and of sufficient magnitude to overcome the contributions of the van der Waals interaction to α(r). Furthermore, the anisotropy of the pair polarizability β(r) can be represented by a simple form: β(r)=6α2r-3-λ e-r/r0, where r0=0.74 a.u., and the collision-induced light-scattering spectrum predicted by this form has an essentially exponential line shape. These results are in qualitative agreement with recent work on collision-induced light-scattering spectra from rare gases

Evaluating a palliative care education programme for domiciliary care workers

Background: Many domiciliary care workers have reported low confidence and isolation when delivering end of life care in patients’ homes. Project Extension for Community Healthcare Outcomes (ECHO) is an initiative that has demonstrated success in increasing confidence and knowledge of end of life care in UK nursing home and community hospice workers, but it has not been evaluated with domiciliary care workers. Aim: To test the acceptability of Project ECHO to domiciliary care workers as a means of increasing their knowledge of, and confidence in, delivering palliative care, and its effectiveness in reducing their isolation by developing a community of practice. Method: A service evaluation, involving one domiciliary care agency delivering care in the community, was conducted from May 2018 to April 2019. The participants were 25 home care workers who were employed by the agency. Participants were invited to attend an event at which gaps in their knowledge were identified, and a curriculum of learning on the Project ECHO programme was developed. The learning involved 12 educational sessions over 12 months, with each session teaching a different component of palliative care. Questionnaires were completed by the participants before and after the educational sessions to assess their effect. In addition, a focus group was conducted with four of the participants. Results: Comparison of the questionnaires completed before and after participating in the education sessions revealed an increase in self-reported knowledge across all 12 topics of the curriculum and an increase in confidence in seven of the 12 topics. However, attendance across the 12 sessions was variable, with no more than nine being attended by any one participant. Conclusion: Palliative care education for domiciliary care staff using ECHO methodology was well received, relevant and accessible, and may have the potential to improve self-assessed knowledge and confidence. However, finding an ideal time for as many staff to attend as possible may be challenging

Ferrofluids as thermal ratchets

Colloidal suspensions of ferromagnetic nano-particles, so-called ferrofluids, are shown to be suitable systems to demonstrate and investigate thermal ratchet behavior: By rectifying thermal fluctuations, angular momentum is transferred to a resting ferrofluid from an oscillating magnetic field without net rotating component. Via viscous coupling the noise driven rotation of the microscopic ferromagnetic grains is transmitted to the carrier liquid to yield a macroscopic torque. For a simple setup we analyze the rotation of the ferrofluid theoretically and show that the results are compatible with the outcome of a simple demonstration experiment.Comment: 4 pages, 3 figures, corrected version, improved figures, to be published in Phys. Rev. Let

Enumerating Finitary Processes

We show how to efficiently enumerate a class of finite-memory stochastic processes using the causal representation of -machines. We characterize -machines in the language of automata theory and adapt a recent algorithm for generating accessible deterministic finite automata, pruning this over-large class down to that of -machines. As an application, we exactly enumerate topological -machines up to eight states and six-letter alphabets

Dispersity-Driven Melting Transition in Two Dimensional Solids

We perform extensive simulations of $10^4$ Lennard-Jones particles to study the effect of particle size dispersity on the thermodynamic stability of two-dimensional solids. We find a novel phase diagram in the dispersity-density parameter space. We observe that for large values of the density there is a threshold value of the size dispersity above which the solid melts to a liquid along a line of first order phase transitions. For smaller values of density, our results are consistent with the presence of an intermediate hexatic phase. Further, these findings support the possibility of a multicritical point in the dispersity-density parameter space.Comment: In revtex format, 4 pages, 6 postscript figures. Submitted to PR

Comment on "Magnetoviscosity and relaxation in ferrofluids"

It is shown and discussed how the conventional system of hydrodynamic equations for ferrofluids was derived. The set consists of the equation of fluid motion, the Maxwell equations, and the magnetization equation. The latter was recently revised by Felderhof [Phys. Rev. E, v.62, p.3848 (2000)]. His phenomenological magnetization equation looks rather like corresponding Shliomis' equation, but leads to wrong consequences for the dependence of ferrofluid viscosity and magnetization relaxation time on magnetic field.Comment: 6 pages, 1 figure, Submitted to Phys. Rev.

RARS2 mutations in a sibship with infantile spasms

Pontocerebellar hypoplasia is a group of heterogeneous neurodevelopmental disorders characterized by reduced volume of the brainstem and cerebellum. We report two male siblings who presented with early infantile clonic seizures, and then developed infantile spasms associated with prominent isolated cerebellar hypoplasia/atrophy on magnetic resonance imaging (MRI). Using whole exome sequencing techniques, both were found to be compound heterozygotes for one previously reported and one novel mutation in the gene encoding mitochondrial arginyl-tRNA synthetase 2 (RARS2). Mutations in this gene have been classically described in pontocerebellar hypoplasia type six (PCH6), a phenotype characterized by early (often intractable) seizures, profound developmental delay, and progressive pontocerebellar atrophy. The electroclinical spectrum of PCH6 is broad and includes a number of seizure types: myoclonic, generalized tonic-clonic, and focal clonic seizures. Our report expands the characterization of the PCH6 disease spectrum and presents infantile spasms as an associated electroclinical phenotype