Condensed Matter Theory

Abstract:

We study the classical Heisenberg model for spins on a pyrochlore lattice interacting via long range dipole-dipole forces and nearest neighbor exchange. Antiferromagnetic exchange alone is known not to induce ordering in this system. We analyze low temperature order resulting from the combined interactions, both by using a mean-field approach and by examining the energy cost of fluctuations about an ordered state. We discuss behavior as a function of the ratio of the dipolar and exchange interaction strengths and find two types of ordered phase. We relate our results to the recent experimental work and reproduce and extend the theoretical calculations on the pyrochlore compound, Gd$_2$Ti$_2$O$_7$, by Raju \textit{et al.}, Phys. Rev. B {\bf 59}, 14489 (1999).

Abstract:

Lattice Boltzmann simulations are used to study the phase ordering of a system quenched into a lamellar phase. Hydrodynamic modes are found to be essential for the fluid to avoid frozen metastable configurations and reach the equilibrium state. We also show that a shear imposed on an equilibrium array of droplets can induce a micellar-lamellar transition. ©Société Itoliana di Fisica.

Abstract:

Objective

The purpose of this study was to compare the accuracy and reproducibility of different methods for calculating breast volume when using measurements made on mammograms.

Materials and methods

The volumes of 32 breasts were determined by pathologic evaluation of mastectomy specimens. Two radiologists independently measured breast height and width on the preoperative craniocaudal mammograms and measured height, width, and width at half-height on mediolateral oblique mammograms. Compression thicknesses used on the craniocaudal and mediolateral oblique projections were recorded. Volume was then calculated using six different formulas. The accuracy of each method was determined and compared using bivariate and univariate linear regression analyses. Interobserver variability in measurement was also assessed.

Results

The most accurate method for calculating breast volume was the one that assumed a half-elliptic cylinder shape for the compressed breast in the craniocaudal projection. Measurements made on the craniocaudal view were more reproducible than those made on the mediolateral oblique view.

Conclusion

Breast volume can be accurately and reproducibly determined on mammograms by making two measurements on the craniocaudal view and knowing the compression thickness. This information may be useful to plastic surgeons, investigators who study parenchymal patterns, and physicians who examine cancer patients being considered for breast conservation surgery.