Monte Carlo Simulation of Ising Models with Dipole Interaction

Recently, a new memory effect was found in the metamagnetic domain structure of the diluted Ising antiferromagnet $Fe_x Mg_{1-x} Cl_2$ by domain imaging with Faraday contrast. Essential for this effect is the dipole interaction. We simulate the low temperature behavior of diluted Ising-antiferromagnets by a Monte Carlo simulation considering long range interaction. The metamagnetic domain structure occurring due to the dipole interaction is investigated by graphical representation. In the model considered the antiferromagnetic state is stable for an external magnetic field smaller than a lower boundary $B_{c1}$ while for fields larger than an upper boundary $B_{c2}$ the system is in the saturated paramagnetic phase, where the spins are ferromagnetically polarized. For magnetic fields in between these two boundaries a mixed phase occurs consisting of ferromagnetic domains in an antiferromagnetic background. The position of these ferromagnetic domains is stored in the system: after a cycle in which the field is first removed and afterwards applied again the domains reappear at their original positions. The reason for this effect can be found in the frozen antiferromagnetic domain state which occurs after removing the field.Comment: Latex, 10 pages; 3 postsript-figures, compressed tar-file, uuencoded, report 10109

Surgery during holiday periods and prognosis in oesophageal cancer: a population-based nationwide Swedish cohort study

OBJECTIVE: Previous studies indicate an increased short-term and long-term mortality from major cancer surgery performed towards the end of the working week or during the weekend. We hypothesised that the prognosis after major cancer surgery is also negatively influenced by surgery conducted during holiday periods. SETTING: Population-based nationwide Swedish cohort study. PARTICIPANTS: Patients undergoing oesophagectomy for oesophageal cancer between 1987 and 2010. Among 1820 included patients, 206 (11.3%) and 373 (20.5%) patients were operated on during narrow and wide holiday periods, respectively. INTERVENTIONS: Narrow (7 weeks) and wide (14 weeks) Swedish holiday periods. PRIMARY AND SECONDARY OUTCOME MEASURES: 90-day all-cause, 5-year all-cause and 5-year disease-specific mortality. RESULTS: Narrow holiday period did not increase all-cause 90-day (HR=0.84, 95% CI 0.53 to 1.33), all-cause 5-year (HR=1.01, 95% CI 0.85 to 1.21) or disease-specific 5-year mortality (HR=1.04, 95% CI 0.87 to 1.26). Similarly, wide holiday period did not increase the risk of 90-day (HR=0.79, 95% CI 0.55 to 1.13), all-cause 5-year (HR=0.96, 95% CI 0.84 to 1.1) or disease-specific 5-year mortality (HR=1.03, 95% CI 0.89 to 1.19). CONCLUSIONS: No measurable effects of holiday periods on short-term or longer term mortality following surgery for oesophageal cancer were observed in this population-based study, indicating that an adequate surgical experience was maintained during holiday periods

Achieving a healthy indoor environment by using an emissions barrier to stop the spread of chemicals from a building into the indoor air

An emissions barrier was used in a premises due to complaints about the indoor air quality (IAQ) as a result of emissions from the building in question. The emissions comprised chlorophenols/chloroanisoles and polycyclic aromatic hydrocarbons (PAH) from treated wood and volatile organic compounds (VOCs), mainly 2-ethylhexanol, from polyvinyl chloride (PVC) flooring and the glue used to paste the flooring onto a concrete slab. Attaching the barrier at the surfaces from where the emissions were spread (floor, walls, ceilings) resulted in a fresh and odour-free indoor air. We conclude that using an emissions barrier in buildings made unhealthy by moisture is an efficient way of restoring pleasant and healthy indoor air

Higher order finite difference schemes for the magnetic induction equations

We describe high order accurate and stable finite difference schemes for the initial-boundary value problem associated with the magnetic induction equations. These equations model the evolution of a magnetic field due to a given velocity field. The finite difference schemes are based on Summation by Parts (SBP) operators for spatial derivatives and a Simultaneous Approximation Term (SAT) technique for imposing boundary conditions. We present various numerical experiments that demonstrate both the stability as well as high order of accuracy of the schemes.Comment: 20 page

Mechanics from Calorimetry: Probing the Elasticity of Responsive Hydrogels

Temperature-sensitive hydrogels based on polymers such as poly(N-isopropylacrylamide) (PNIPAM) undergo a volume phase transition in response to changes in temperature. During this transition, distinct changes in both thermal and mechanical properties are observed. Here, we illustrate and exploit the inherent thermodynamic link between thermal and mechanical properties by showing that the compressive elastic modulus of PNIPAM hydrogels can be probed using differential scanning calorimetry. We validate our approach by using conventional osmotic compression tests. Our method could be particularly valuable for determining the mechanical response of thermosensitive submicron-sized and/or oddly shaped particles, to which standard methods are not readily applicable

Supernovae data and perturbative deviation from homogeneity

We show that a spherically symmetric perturbation of a dust dominated $\Omega=1$ FRW universe in the Newtonian gauge can lead to an apparent acceleration of standard candles and provide a fit to the magnitude-redshift relation inferred from the supernovae data, while the perturbation in the gravitational potential remains small at all scales. We also demonstrate that the supernovae data does not necessarily imply the presence of some additional non-perturbative contribution by showing that any Lemaitre-Tolman-Bondi model fitting the supernovae data (with appropriate initial conditions) will be equivalent to a perturbed FRW spacetime along the past light cone.Comment: 8 pages, 3 figures; v2: 1 figure added, references added/updated, minor modifications and clarifications, matches published versio