Relation between the High Density Phase and the Very-High Density Phase of Amorphous Solid Water

It has been suggested that high-density amorphous (HDA) ice is a structurally arrested form of high-density liquid (HDL) water, while low-density amorphous (LDA) ice is a structurally arrested form of low-density liquid (LDL) water. Recent experiments and simulations have been interpreted to support the possibility of a second "distinct" high-density structural state, named very high-density amorphous (VHDA) ice, questioning the LDL-HDL hypothesis. We test this interpretation using extensive computer simulations, and find that VHDA is a more stable form of HDA and that in fact VHDA should be considered as the amorphous ice of the quenched HDL.Comment: 5 pages, 4 fig

Optimal trap shape for a Bose gas with attractive interactions

Dilute Bose gas with attractive interactions is considered at zero temperature, when practically all atoms are in Bose-Einstein condensate. The problem is addressed aiming at answering the question: What is the optimal trap shape allowing for the condensation of the maximal number of atoms with negative scattering lengths? Simple and accurate analytical formulas are derived allowing for an easy analysis of the optimal trap shapes. These analytical formulas are the main result of the paper.Comment: Latex file, 21 page

Spectroscopy on two coupled flux qubits

We have performed spectroscopy measurements on two coupled flux qubits. The qubits are coupled inductively, which results in a $\sigma_1^z\sigma_2^z$ interaction. By applying microwave radiation, we observe resonances due to transitions from the ground state to the first two excited states. From the position of these resonances as a function of the magnetic field applied we observe the coupling of the qubits. The coupling strength agrees well with calculations of the mutual inductance

Condensation of Ideal Bose Gas Confined in a Box Within a Canonical Ensemble

We set up recursion relations for the partition function and the ground-state occupancy for a fixed number of non-interacting bosons confined in a square box potential and determine the temperature dependence of the specific heat and the particle number in the ground state. A proper semiclassical treatment is set up which yields the correct small-T-behavior in contrast to an earlier theory in Feynman's textbook on Statistical Mechanics, in which the special role of the ground state was ignored. The results are compared with an exact quantum mechanical treatment. Furthermore, we derive the finite-size effect of the system.Comment: 18 pages, 8 figure

Covariant description of kinetic freeze out through a finite time-like layer

The Freeze Out (FO) problem is addressed for a covariant FO probability and a finite FO layer with a time-like normal vector continuing the line of studies introduced in Ref. [1]. The resulting post FO momentum distribution functions are presented and discussed. We show that in general the post FO distributions are non-thermal and asymmetric distributions even for time-like FO situations.Comment: 10 pages, 12 figures, major rewrite with changed content, corrected typos and new references adde

Two-dimensional percolation at the free water surface and its relation with the surface tension anomaly of water

The percolation temperature of the lateral hydrogen bonding network of the molecules at the free water surface is determined by means of molecular dynamics computer simulation and identification of the truly interfacial molecules analysis for six different water models, including three, four, and five site ones. The results reveal that the lateral percolation temperature coincides with the point where the temperature derivative of the surface tension has a minimum. Hence, the anomalous temperature dependence of the water surface tension is explained by this percolation transition. It is also found that the hydrogen bonding structure of the water surface is largely model-independent at the percolation threshold; the molecules have, on average, 1.90 +/- 0.07 hydrogen bonded surface neighbors. The distribution of the molecules according to the number of their hydrogen bonded neighbors at the percolation threshold also agrees very well for all the water models considered. Hydrogen bonding at the water surface can be well described in terms of the random bond percolation model, namely, by the assumptions that (i) every surface water molecule can form up to 3 hydrogen bonds with its lateral neighbors and (ii) the formation of these hydrogen bonds occurs independently from each other. (C) 2014 AIP Publishing LLC

In beweging! Over de ontwikkeling van de identiteit van een kennisorganisatie in een veranderende context

On the move! About organizational identity formation in a changing context How does the identity of an organization develop in a permanently changing environment on which it depends and with which it is intertwined through networks? This question forms the subject of a case study performed by the Netherlands Institute for Sport and Physical Activity (NISB). Tackling problems and attaining goals requires the exchange and combination of goods, services and expertise. To achieve that, organizations work together in networks. Social problems, however, tend to be complex because they involve different parties with different backgrounds and different interests. Moreover, constant changes in the environment constantly require a response from organizations to safeguard their position. Confronted with changes, organizations are faced with dilemmas. These dilemmas reveal value contrasts that organizations have to deal with and that lead them to constantly reconsider their identity. Dilemmas and decision-making have been selected as the starting point for data collection in the study, the results of which show that, in order to preserve its mission, the NISB is constantly adapting its identity to suit the environment. In other words, a robust working method and a stable mission constantly create a new interactive identity. In beweging! Over de ontwikkeling en handhaving van de identiteit van een kennisorganisatie in een veranderende context Hoe ontwikkelt de identiteit van een organisatie zich in een permanent veranderende omgeving waarmee zij via netwerken verweven is en waarvan zij afhankelijk is? Deze vraag is onderwerp van een casestudy, uitgevoerd bij het Nederlands Instituut voor Sport en Bewegen (NISB). Bij de aanpak van problemen en het realiseren van doelstellingen is uitwisseling en bundeling van goederen, diensten en expertise noodzakelijk. Daartoe werken organisaties samen in netwerken. Maatschappelijke problemen zijn dikwijls complex omdat verschillende partijen vanuit uiteenlopende achtergronden en belangen betrokken zijn. Daar komt bij dat voortdurende veranderingen in de omgeving steeds vragen om een reactie van organisaties, dit met het oog op het behoud van haar positie. In de confrontatie met veranderingen stuiten organisaties op dilemma’s. Deze dilemma’s maken waardetegenstellingen zichtbaar, waar organisaties niet omheen kunnen en die vervolgens leiden tot een vrijwel permanente heroverweging van de identiteit van de organisatie. Dilemma’s en besluitvorming zijn gekozen als aangrijpingspunt voor de dataverzameling in het onderzoek. De resultaten laten zien hoe NISB, met behoud van haar missie, voortdurend haar identiteit aanpast aan haar omgeving. Met andere woorden, er is steeds sprake van interactieve identiteitsvorming die mogelijk gemaakt wordt door een robuuste werkwijze en een stabiele missi

Density anomaly in a competing interactions lattice gas model

We study a very simple model of a short-range attraction and an outer shell repulsion as a test system for demixing phase transition and density anomaly. The phase-diagram is obtained by applying mean field analysis and Monte Carlo simulations to a two dimensional lattice gas with nearest-neighbors attraction and next-nearest-neighbors repulsion (the outer shell). Two liquid phases and density anomaly are found. The coexistence line between these two liquid phases meets a critical line between the fluid and the low density liquid at a tricritical point. The line of maximum density emerges in the vicinity of the tricritical point, close to the demixing transition

Spin superfluidity and spin-orbit gauge symmetry fixing

The Hamiltonian describing 2D electron gas, in a spin-orbit active medium, can be cast into a consistent non-Abelian gauge field theory leading to a proper definition of the spin current. The generally advocated gauge symmetric version of the theory results in current densities that are gauge covariant, a fact that poses severe concerns on their physical nature. We show that in fact the problem demands gauge fixing, leaving no room to ambiguity in the definition of physical spin currents. Gauge fixing also allows for polarized edge excitations not present in the gauge symmetric case. The scenario here is analogous to that of superconductivity gauge theory. We develop a variational formulation that accounts for the constraints between U(1) physical fields and SU(2) gauge fields and show that gauge fixing renders a physical matter and radiation currents and derive the particular consequences for the Rashba SO interaction.Comment: to appear in EP