Superfluidity versus localization in bulk 4He at zero temperature

We present a zero-temperature quantum Monte Carlo calculation of liquid $^4$He immersed in an array of confining potentials. These external potentials are centered in the lattice sites of a fcc solid geometry and, by modifying their well depth and range, the system evolves from a liquid phase towards a progressively localized system which mimics a solid phase. The superfluid density decreases with increasing order, reaching a value $\rho_{\rm s}/\rho = 0.079(16)$ when the Lindemann's ratio of the model equals the experimental value for solid $^4$He.Comment: 5 pages,5 figure

Mechanism for nonequilibrium symmetry breaking and pattern formation in magnetic films

Magnetic thin films exhibit a strong variation in properties depending on their degree of disorder. Recent coherent x-ray speckle experiments on magnetic films have measured the loss of correlation between configurations at opposite fields and at the same field, upon repeated field cycling. We perform finite temperature numerical simulations on these systems that provide a comprehensive explanation for the experimental results. The simulations demonstrate, in accordance with experiments, that the memory of configurations increases with film disorder. We find that non-trivial microscopic differences exist between the zero field spin configuration obtained by starting from a large positive field and the zero field configuration starting at a large negative field. This seemingly paradoxical beahvior is due to the nature of the vector spin dynamics and is also seen in the experiments. For low disorder, there is an instability which causes the spontaneous growth of line-like domains at a critical field, also in accord with experiments. It is this unstable growth, which is highly sensitive to thermal noise, that is responsible for the small correlation between patterns under repeated cycling. The domain patterns, hysteresis loops, and memory properties of our simulated systems match remarkably well with the real experimental systems.Comment: 12 pages, 10 figures Added comparison of results with cond-mat/0412461 and some more discussio

Crystal structure of aluminium cyclononaphosphate, Al3P9O27

Al3O27P9, trigonal, P3̄c1 (No. 165), a = 10.935(2) Å, c = 9.191(2) Å, V = 951.8 Å3, Z = 8, Rgt(F) = 0.037, wRref(F2) = 0.094, T = 293 K

Magnetic Properties of a Two-Dimensional Mixed-Spin System

Using a Langmuir-Blodgett (LB) synthesis method, novel two-dimensional (2D) mixed-spin magnetic systems, in which each magnetic layer is both structurally and magnetically isolated, have been generated. Specifically, a 2D Fe-Ni cyanide-bridged network with a face-centered square grid structure has been magnetically and structurally characterized. The results indicate the presence of ferromagnetic exchange interactions between the Fe$^{3+}$ ($S=1/2$) and Ni$^{2+}$ (S=1) centers.Comment: 2 pages, 3 figs., submitted 23rd International Conference on Low Temperature Physics (LT-23), Aug. 200

Why the \u3ci\u3eGrey\u27s Anatomy\u3c/i\u3e Myth Clouds the Real Value of Emergency Care

Advanced radiology tests such as CT scans, MRIs and ultrasounds have dramatically changed how patients are diagnosed and treated. Just a decade ago, patients were still being subjected to exploratory surgery, in which a surgeon cuts open the abdomen to look for problems; today, CT scans allow doctors to make diagnoses without a scalpel

Post-HMO Health Care: Are ACOs the Answer?

Remember the 1990s retrospective lists always include Nirvana, Monica Lewinsky and Wayne\u27s World, but leave out another major product that defined American life in the \u2790s: the health maintenance organization, or HMO — that nefarious health-insurance plan that seemed expressly designed to prevent you from seeing the doctor of your choice or receiving the treatments recommended by doctors, all under the guise of lowering costs and improving medical care. Of course HMOs are still around, but they are no longer central to the national discussion on health care. Why? For the most part, HMOs have eased limits on patient choice and treatments

Why Doctors Order Too Many Tests (It\u27s Not Just to Avoid Lawsuits)

Advanced radiology tests such as CT scans, MRIs and ultrasounds have dramatically changed how patients are diagnosed and treated. Just a decade ago, patients were still being subjected to exploratory surgery, in which a surgeon cuts open the abdomen to look for problems; today, CT scans allow doctors to make diagnoses without a scalpel

McDonald\u27s Medicine: Are We Too Impatient to Wait for Care?

The prospect of waiting for health care is not only distasteful to Americans, it\u27s downright threatening: indeed, the specter of Canadian-style waiting lists for certain tests and procedures evoked enough American-style fear that it became a key Republican talking point to challenge the concept of government-subsidized health care