Protein crystallization in vivo

Protein crystallization in vivo provides some fascinating examples of biological self-assembly. Here, we provide a selective survey to show the diversity of functions for which protein crystals are used, and the physical properties of the crystals thatare exploited. Where known, we emphasize how the nature of the protein-protein interactions leads to control of the crystallization behaviour.Comment: 17 pages, 1 figur

Solicited and Unsolicited Credit Ratings: A Global Perspective

We conducted a global study of the long-term issuer ratings of nonfinancial firms from Standard and Poor's Ratings Services (S&P) for the period 1998–2003. Specifically, we focused on the solicited versus unsolicited ratings and sample-selection bias in the analysis. Unlike the literature, we adopted an improved method using Wooldridge’s instrumental-variable approach to mitigate the concern of specification errors in Heckman’s model. We found that the probability of seeking a long-term issuer rating is positively related to the size and profitability of the firm, and negatively related to the growth opportunities and debt levels of the firm. The credit rating is positively related to the sovereign rating, size, and profitability of the issuer, and negatively related to the debt ratio of the issuer. Consistent with the literature, we found sample-selection bias in credit ratings. Our findings suggest that the firms with solicited ratings seem to be more profitable, more liquid, and have lower leverage than the issuers with unsolicited ratings. After controlling for sample-selection bias and some key financial ratios, we found that unsolicited firms, on average, seem to have lower long-term issuer ratings.corporate long-term issuer ratings; solicited and unsolicited

Least-Squares Approximation by Elements from Matrix Orbits Achieved by Gradient Flows on Compact Lie Groups

Let $S(A)$ denote the orbit of a complex or real matrix $A$ under a certain equivalence relation such as unitary similarity, unitary equivalence, unitary congruences etc. Efficient gradient-flow algorithms are constructed to determine the best approximation of a given matrix $A_0$ by the sum of matrices in $S(A_1), ..., S(A_N)$ in the sense of finding the Euclidean least-squares distance $$\min \{\|X_1+ ... + X_N - A_0\|: X_j \in S(A_j), j = 1, >..., N\}.$$ Connections of the results to different pure and applied areas are discussed

Bulk and wetting phenomena in a colloidal mixture of hard spheres and platelets

Density functional theory is used to study binary colloidal fluids consisting of hard spheres and thin platelets in their bulk and near a planar hard wall. This system exhibits liquid-liquid coexistence of a phase that is rich in spheres (poor in platelets) and a phase that is poor in spheres (rich in platelets). For the mixture near a planar hard wall, we find that the phase rich in spheres wets the wall completely upon approaching the liquid demixing binodal from the sphere-poor phase, provided the concentration of the platelets is smaller than a threshold value which marks a first-order wetting transition at coexistence. No layering transitions are found in contrast to recent studies on binary mixtures of spheres and non-adsorbing polymers or thin hard rods.Comment: 6 pages, 4 figure