Power loss and electromagnetic energy density in a dispersive metamaterial medium

The power loss and electromagnetic energy density of a metamaterial consisting of arrays of wires and split-ring resonators (SRRs) are investigated. We show that a field energy density formula can be derived consistently from both the electrodynamic (ED) approach and the equivalent circuit (EC) approach. The derivations are based on the knowledge of the dynamical equations of the electric and magnetic dipoles in the medium and the correct form of the power loss. We discuss the role of power loss in determining the form of energy density and explain why the power loss should be identified first in the ED derivation. When the power loss is negligible and the field is harmonic, our energy density formula reduces to the result of Landau's classical formula. For the general case with finite power loss, our investigation resolves the apparent contradiction between the previous results derived by the EC and ED approaches.Comment: 10 pages, 1 figure, Submitted to Phys. Rev.

Unusual Glass-Forming Ability of Bulk Amorphous Alloys Based on Ordinary Metal Copper

We report the unusual glass-forming ability (GFA) of a family of Cu-based alloys, Cu46Zr47–xAl7Yx (0<x<=10, in at. %), and investigate the origin of this unique property. By an injection mold casting method, these alloys can be readily solidified into amorphous structures with the smallest dimension ranging from 4 mm up to 1 cm without detectable crystallinity. Such superior GFA is found primarily due to the alloying effect of Y, which lowers the alloy liquidus temperature and brings the composition closer to a quaternary eutectic. Other beneficial factors including appropriate atomic-size mismatch and large negative heat of mixing among constituent elements are also discussed

Comparison of robust tests for genetic association using case-control studies

In genetic studies of complex diseases, the underlying mode of inheritance is often not known. Thus, the most powerful test or other optimal procedure for one model, e.g. recessive, may be quite inefficient if another model, e.g. dominant, describes the inheritance process. Rather than choose among the procedures that are optimal for a particular model, it is preferable to see a method that has high efficiency across a family of scientifically realistic models. Statisticians well recognize that this situation is analogous to the selection of an estimator of location when the form of the underlying distribution is not known. We review how the concepts and techniques in the efficiency robustness literature that are used to obtain efficiency robust estimators and rank tests can be adapted for the analysis of genetic data. In particular, several statistics have been used to test for a genetic association between a disease and a candidate allele or marker allele from data collected in case-control studies. Each of them is optimal for a specific inheritance model and we describe and compare several robust methods. The most suitable robust test depends somewhat on the range of plausible genetic models. When little is known about the inheritance process, the maximum of the optimal statistics for the extreme models and an intermediate one is usually the preferred choice. Sometimes one can eliminate a mode of inheritance, e.g. from prior studies of family pedigrees one may know whether the disease skips generations or not. If it does, the disease is much more likely to follow a recessive model than a dominant one. In that case, a simpler linear combination of the optimal tests for the extreme models can be a robust choice.Comment: Published at http://dx.doi.org/10.1214/074921706000000491 in the IMS Lecture Notes--Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

Minimum Energy Path to Membrane Pore Formation and Rupture

We combine dynamic self-consistent field theory with the string method to calculate the minimum energy path to membrane pore formation and rupture. In the regime where nucleation can occur on experimentally relevant time scales, the structure of the critical nucleus is between a solvophilic stalk and a locally thinned membrane. Classical nucleation theory fails to capture these molecular details and significantly overestimates the free energy barrier. Our results suggest that thermally nucleated rupture may be an important factor for the low rupture strains observed in lipid membranes

Formation and properties of new Ni-based amorphous alloys with critical casting thickness up to 5 mm

New Ni-based bulk metallic glasses were synthesized in NixCua−xTiyZrb−yAl10 (a~b~45 at.%) system, based on a ternary alloy, Ni45Ti20Zr35. The additions of Al and Cu greatly increase the glass-forming ability (GFA). The best GFA is located around Ni40Cu5Ti16.5Zr28.5Al10, from which fully amorphous samples of up to 5 mm thickness were successfully fabricated by an injection mold casting method. These alloys exhibit high glass-transition temperatures Tg ~ 760 to 780 K, and relatively wide undercooled-liquid regions ΔT (defined by the difference between Tg and the first crystallization temperature Tx1 upon heating) ~ 40–50 K. Mechanical tests on these alloys show quite high Vicker's Hardness ~ 780 to 862 kg/mm^2, Young's modulus ~ 111 to 134 GPa, shear modulus ~ 40 to 50 GPa and high fracture strength ~ 2.3 to 2.4 GPa. The effect of small Si-addition and a discrepancy between GFA and ΔT are also reported. The exceptional GFA and the all-metallic compositions give these new alloys excellent promise for both scientific and engineering applications

A Kinetic Model for the Enzymatic Action of Cellulase

We develop a mechanochemical model for the dynamics of cellulase, a two-domain enzyme connected by a peptide linker, as it extracts and hydrolyzes a cellulose polymer from a crystalline substrate. We consider two random walkers, representing the catalytic domain (CD) and the carbohydrate binding module (CBM), whose rates for stepping are biased by the coupling through the linker and the energy required to lift the cellulose polymer from the crystalline surface. Our results show that the linker length and stiffness play a critical role in the cooperative action of the CD and CBM domains and that, for a given linker length, the steady-state hydrolysis shows a maximum at some intermediate linker stiffness. The maximum hydrolysis rate corresponds to a transition of the linker from a compressed to an extended conformation, where the system exhibits maximum fluctuation, as measured by the variance of the separation distance between the two domains and the dispersion around the mean hydrolysis speed. In the range of experimentally known values of the parameters of our model, improving the intrinsic hydrolytic activity of the CD leads to a proportional increase in the overall hydrolysis rate