Modeling Magnetic Anisotropy of Single Chain Magnets in ∣d/J∣≥1|d/J| \geq 1 Regime

Single molecule magnets (SMMs) with single-ion anisotropies $\mathbf d$, comparable to exchange interactions J, between spins have recently been synthesized. In this paper, we provide theoretical insights into the magnetism of such systems. We study spin chains with site spins, s=1, 3/2 and 2 and on-site anisotropy $\mathbf d$ comparable to the exchange constants between the spins. We find that large $\mathbf d$ leads to crossing of the states with different $M_S$ values in the same spin manifold of the $\mathbf d = 0$ limit. For very large $\mathbf d$'s we also find that the $M_S$ states of the higher energy spin states descend below the $M_S$ states of the ground state spin manifold. Total spin in this limit is no longer conserved and describing the molecular anisotropy by the constants $D_M$ and $E_M$ is not possible. However, the total spin of the low-lying large $M_S$ states is very nearly an integer and using this spin value it is possible to construct an effective spin Hamiltonian and compute the molecular magnetic anisotropy constants $D_M$ and $E_M$. We report effect of finite sizes, rotations of site anisotropies and chain dimerization on the effective anisotropy of the spin chains

Modeling Molecular Magnets with Large Exchange and On-Site Anisotropies

Spins in molecular magnets can experience both anisotropic exchange interactions and on-site magnetic anisotropy. In this paper we study the effect of exchange anisotropy on the molecular magnetic anisotropy both with and without on-site anisotropy. When both the anisotropies are small, we find that the axial anisotropy parameter $D_M$ in the effective spin Hamiltonian is the sum of the individual contributions due to exchange and on-site anisotropies. We find that even for axial anisotropy of about $15\%$, the low energy spectrum does not correspond to a single parent spin manifold but has intruders states arising from other parent spin. In this case, the low energy spectrum can not be described by an effective Hamiltonian spanning the parent spin space. We study the magnetic susceptibility, specific heat as a function of temperature and magnetization as a function of applied field to characterize the system in this limit. We find that there is synergy between the two anisotropies, particularly for large systems with higher site spins.Comment: 30 pages, 11 figures and 3 tables. Supporting information included after the main articl

Study of heat sources and sinks and generation of available potential energy in the Indian region during the southwest monsoon season

The total vertical velocity and the heating field were evaluated for a portion of the Indian region for a typical monsoon day in July 1966 using a two-level geostrophic model. The generation of zonal and eddy available potential energy was computed with these values of heating and cooling. Both forms of available potential energy seem to be generated by diabatic processes. The generation of eddy available potential energy may be due to the released latent heat of condensation

Papillary thyroid cancer: sporadic or inherited?

Background: Papillary thyroid cancer (PTC) is one of the most common thyroid malignancies, with an increase in incidence rates over the past few decades. Although the exact cause of thyroid cancer in most patients is still unclear, the possibility of genetic predisposition to PTC cannot be overlooked. Here, we report a case study of PTC, in which the family was extensively affected, with each family member diagnosed with either benign or malignant thyroid neoplasms, or functional thyroid disorder.Method: A 57-year-old white female with a past medical history of hypothyroidism, and a significant family history of multiple thyroid cancers, was found to have new onset thyroid nodules during a routine screening ultrasound. Fine needle aspiration revealed suspicious papillary carcinoma (follicular variant). The patient underwent total thyroidectomy.Results: The histology report revealed total colloid nodules in the right lobe with focal calcification, lymphocytic thyroiditis, and two foci of papillary microcarcinoma. The patient subsequently underwent radioactive iodine ablation therapy, along with pilocarpine and thyrogen injection.Conclusion: This case study illustrates the need for awareness of the possibility of genetic predisposition to, as well female preponderance of, familial PTC.Keywords: papillary thyroid cancer, familial, sporadic, genetic associatio

REE geochemistry of ore zones in the Archean auriferous schist belts of the eastern Dharwar Craton, south India

The eastern Dharwar Craton of southern India includes at least three ~2700Ma supracrustal belts (schist belts) which have mesothermal, quartz-carbonate vein gold mineralization emplaced within the sheared metabasalts. In the Hutti and the Kolar schist belts, the host rocks are amphibolites and the ore veins have been flanked by only a thin zone of biotitic alteration; in the Ramagiri belt, however, the host rocks to the veins have been affected by more extensive but lower temperature alteration by fluids. The rare earth element (REE) geochemistry of the host metabasalts, alteration zones, ore veins and the bulk sulfides separated from the ore veins and the alteration zones suggest that • the REE chemistry of the immediate host rocks has been modified by fluids which added LREE, • the REE abundance of the ore veins vary with the amount of host rock fragments included in the veins, • the sulfides formed during mineralization have significant REE concentration with patterns nearly identical to the ore veins and alteration zones and • therefore the ore fluids involved in gold mineralization here could be LREE enriched. Because alteration and mineralization involved addition of REE, more LREE compared to HREE, the fluids could be of higher temperature origin. The initial Nd isotope ratios in the host rocks ("Nd calculated at 2700 Ma) showed a large variation (+8 to -4) and a deep crustal source for the fluid REE seems likely. A crustal source for Pb and Os in the ore samples of Kolar belt has previously been suggested (Krogstadet al 1995; Walkeret al 1989). Such a source for ore fluids is consistent with a late Archean (2500Ma) accretionary origin for the terrains of the eastern Dharwar Craton

An efficient optimum interpolation scheme for objective analysis over Indian region

In the optimum interpolation scheme, the weights for the observations are computed by solving a set of linear equations for every grid point. As the number of observations increases particularly over data-rich regions, the matrix dimension increases and the computer time required to solve these equations to determine weights increases considerably. In order to reduce the computer time for computing the weights, Tanguay and Robert suggested schemes in which the gaussian function representing the autocorrelation function has been approximated by a second-order and also by a fourth-order Taylor series expansion. This resulted in the solution of matrices of order 4 or 9 respectively to obtain weighting functions irrespective of the number of observations used in the analysis. In the present study, the analyses of mean sea level pressure and geopotential height at 700 mbar level have been carried out for five days using the above two schemes and the regular OI scheme. The analyses are found to be similar in all the three cases suggesting that a lot of computer time could be saved without sacrificing the analysis accuracy by using the modified scheme in which the second-order approximation is utilized