Time dependent mean field theory of the superfluid-insulator phase transition

We develop a time-dependent mean field approach, within the time-dependent variational principle, to describe the Superfluid-Insulator quantum phase transition. We construct the zero temperature phase diagram both of the Bose-Hubbard model (BHM), and of a spin-S Heisenberg model (SHM) with the XXZ anisotropy. The phase diagram of the BHM indicates a phase transition from a Mott insulator to a compressibile superfluid phase, and shows the expected lobe-like structure. The SHM phase diagram displays a quantum phase transition between a paramagnetic and a canted phases showing as well a lobe-like structure. We show how the BHM and Quantum Phase model (QPM) can be rigorously derived from the SHM. Based on such results, the phase boundaries of the SHM are mapped to the BHM ones, while the phase diagram of the QPM is related to that of the SHM. The QPM's phase diagram obtained through the application of our approach to the SHM, describes the known onset of the macroscopic phase coherence from the Coulomb blockade regime for increasing Josephson coupling constant. The BHM and the QPM phase diagrams are in good agreement with Quantum Monte Carlo results, and with the third order strong coupling perturbative expansion.Comment: 15 pages, 8 figures. To be published in Phys. Rev.

Vascular Remodeling in Health and Disease

The term vascular remodeling is commonly used to define the structural changes in blood vessel geometry that occur in response to long-term physiologic alterations in blood flow or in response to vessel wall injury brought about by trauma or underlying cardiovascular diseases.1, 2, 3, 4 The process of remodeling, which begins as an adaptive response to long-term hemodynamic alterations such as elevated shear stress or increased intravascular pressure, may eventually become maladaptive, leading to impaired vascular function. The vascular endothelium, owing to its location lining the lumen of blood vessels, plays a pivotal role in regulation of all aspects of vascular function and homeostasis.5 Thus, not surprisingly, endothelial dysfunction has been recognized as the harbinger of all major cardiovascular diseases such as hypertension, atherosclerosis, and diabetes.6, 7, 8 The endothelium elaborates a variety of substances that influence vascular tone and protect the vessel wall against inflammatory cell adhesion, thrombus formation, and vascular cell proliferation.8, 9, 10 Among the primary biologic mediators emanating from the endothelium is nitric oxide (NO) and the arachidonic acid metabolite prostacyclin [prostaglandin I2 (PGI2)], which exert powerful vasodilatory, antiadhesive, and antiproliferative effects in the vessel wall

The Pricing of the Emergent Leasehold (Possessory) Estates of Ghana

The paper develops hedonic analyses of the pricing of leasehold versus freehold estates in Ghana. The motivation of the paper is the passage of Act 267(5) in 1992 that effectively abolished outright sale of stool lands in Ghana. Stool lands are lands controlled by tribal "chiefs." Act 267(5) prohibits the sale of freehold estates for stool lands. There are two important findings in this study. The first is that freeholds tend to attract premium prices relative to leaseholds. This supports the bundle-of-rights argument. The second is that the effect of the 1992 Act is indeed capitalized into land prices because of the relative increase in the supply of leaseholds vis-à-vis freeholds. Specifically, the price of freeholds increased relative to the price of leaseholds after the constitutional event. The study also finds that transactions involving stools and individuals, usually perceived to be associated with litigation risk (or title insecurity) relative to government lands, are sold at a discount. Transactions noted to have a history of litigation are also associated with price discounts. The estimated coefficients on all the variables representing services to the site like water, electricity and access roads are significantly positive, indicating a high demand for such essential services. Copyright 2004 by the American Real Estate and Urban Economics Association