Magnetic properties of the two-dimensional Heisenberg model on a triangular lattice

The spin Green's function of the antiferromagnetic Heisenberg model on a triangular lattice is calculated using Mori's projection operator technique. At T=0 the spin excitation spectrum is shown to have gaps at the wave vectors of the classical Neel ordering. This points to the absence of the antiferromagnetic long-range order in the ground state. The calculated spin correlation on the neighboring sites of the same sublattice is in good agreement with the value derived from exact diagonalization. The temperature dependencies of the spin correlations and the gaps are calculated.Comment: 5 pages, 3 figure

A Microeconomic Study of Commercial Real Estate Brokerage Firms

While residential brokerage has been widely studied, the operating characteristics on income property brokerage firms have received little attention in the literature. In this paper, we analyze results from a survey of income property brokers to measure profitability scale effects, and expenditures at the firm level. We find that while scale economies exist for expenses, net income per producer falls as firms grow; the optimally sized firm is comparatively small. Although inconsistencies with results from recent residential brokerage studies may relate to the survey period, they may also support a view that residential and income brokerage firms are structurally different.

On the tear resistance of skin.

Tear resistance is of vital importance in the various functions of skin, especially protection from predatorial attack. Here, we mechanistically quantify the extreme tear resistance of skin and identify the underlying structural features, which lead to its sophisticated failure mechanisms. We explain why it is virtually impossible to propagate a tear in rabbit skin, chosen as a model material for the dermis of vertebrates. We express the deformation in terms of four mechanisms of collagen fibril activity in skin under tensile loading that virtually eliminate the possibility of tearing in pre-notched samples: fibril straightening, fibril reorientation towards the tensile direction, elastic stretching and interfibrillar sliding, all of which contribute to the redistribution of the stresses at the notch tip

Women with a Reduced Ovarian Complement May Have an Increased Risk for a Child with Down Syndrome

Advanced maternal age is the only well-established risk factor for trisomy 21 Down syndrome (DS), but the basis of the maternal-age effect is not known. In a population-based, case-control study of DS, women who reported surgical removal of all or part of an ovary or congenital absence of one ovary were significantly more likely to have delivered a child with DS than were women who did not report a reduced ovarian complement (odds ratio 9.61; 95% confidence interval 1.18–446.3). Because others have observed that women who have had an ovary removed exhibit elevated levels of FSH and similar hallmarks of advanced maternal age, our finding suggests that the physiological status of the ovary is key to the maternal-age effect. In addition, it suggests that women with a reduced ovarian complement should be offered prenatal diagnosis

High pressure evolution of Fe2_{2}O3_{3} electronic structure revealed by X-ray absorption

We report the first high pressure measurement of the Fe K-edge in hematite (Fe$_2$O$_3$) by X-ray absorption spectroscopy in partial fluorescence yield geometry. The pressure-induced evolution of the electronic structure as Fe$_2$O$_3$ transforms from a high-spin insulator to a low-spin metal is reflected in the x-ray absorption pre-edge. The crystal field splitting energy was found to increase monotonically with pressure up to 48 GPa, above which a series of phase transitions occur. Atomic multiplet, cluster diagonalization, and density-functional calculations were performed to simulate the pre-edge absorption spectra, showing good qualitative agreement with the measurements. The mechanism for the pressure-induced phase transitions of Fe$_2$O$_3$ is discussed and it is shown that ligand hybridization significantly reduces the critical high-spin/low-spin pressure.Comment: 5 pages, 4 figures and 1 tabl

Hydrology and Glaciers in the Upper Indus Basin

Examines the state of the science associated with the snow and ice hydrology in the Upper Indus Basin (IUB), reviewing the literature and data available on the present and projected role of glaciers, snow fields, and stream flow. Considerable speculation but little analysis exists concerning the importance of glaciers in the volume and timing of flow in the Indus River and its tributaries, as well as on the potential impact of climate change on these rivers. A simple model estimates that glacier runoff contributes approximately 18 percent of the total flow, making melt water from the winter snowpack the most probable source for a majority of the remaining 82 percent, and leaving future runoff regimes to be determined primarily by changes in winter precipitation and summer temperatures. To improve the hydrologic predictability of the UIB requires major investment in snow and ice hydrology monitoring stations, further scientific research, and forecasting