4,807 research outputs found
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
Polydispersity Effects in Colloid-Polymer Mixtures
We study phase separation and transient gelation in a mixture consisting of
polydisperse colloids and non-adsorbing polymers, where the ratio of the
average size of the polymer to that of the colloid is approximately 0.063.
Unlike what has been reported previously for mixtures with somewhat lower
colloid polydispersity, the addition of polymers does not expand the
fluid-solid coexistence region. Instead, we find a region of fluid-solid
coexistence which has an approximately constant width but an unexpected
re-entrant shape. We detect the presence of a metastable gas-liquid binodal,
which gives rise to two-stepped crystallization kinetics that can be
rationalized as the effect of fractionation. Finally, we find that the
separation into multiple coexisting solid phases at high colloid volume
fractions predicted by equilibrium statistical mechanics is kinetically
suppressed before the system reaches dynamical arrest.Comment: 11 pages, 5 figure
Cyclin F Is Degraded during G2-M by Mechanisms Fundamentally Different from Other Cyclins
Cyclin F, a cyclin that can form SCF complexes and bind to cyclin B, oscillates in the cell cycle with a pattern similar to cyclin A and cyclin B. Ectopic expression of cyclin F arrests the cell cycle in G2/M. How the level of cyclin F is regulated during the cell cycle is completely obscure. Here we show that, similar to cyclin A, cyclin F is degraded when the spindle assembly checkpoint is activated and accumulates when the DNA damage checkpoint is activated. Cyclin F is a very unstable protein throughout much of the cell cycle. Unlike other cyclins, degradation of cyclin F is independent of ubiquitination and proteasome-mediated pathways. Interestingly, proteolysis of cyclin F is likely to involve metalloproteases. Rapid destruction of cyclin F does not require the N-terminal F-box motif but requires the COOH-terminal PEST sequences. The PEST region alone is sufficient to interfere with the degradation of cyclin F and confer instability when fused to cyclin A. These data show that although cyclin F is degraded at similar time as the mitotic cyclins, the underlying mechanisms are entirely distinct
Diffusive Evolution of Stable and Metastable Phases II: Theory of Non-Equilibrium Behaviour in Colloid-Polymer Mixtures
By analytically solving some simple models of phase-ordering kinetics, we
suggest a mechanism for the onset of non-equilibrium behaviour in
colloid-polymer mixtures. These mixtures can function as models of atomic
systems; their physics therefore impinges on many areas of thermodynamics and
phase-ordering. An exact solution is found for the motion of a single, planar
interface separating a growing phase of uniform high density from a
supersaturated low density phase, whose diffusive depletion drives the
interfacial motion. In addition, an approximate solution is found for the
one-dimensional evolution of two interfaces, separated by a slab of a
metastable phase at intermediate density. The theory predicts a critical
supersaturation of the low-density phase, above which the two interfaces become
unbound and the metastable phase grows ad infinitum. The growth of the stable
phase is suppressed in this regime.Comment: 27 pages, Latex, eps
Scaling of dynamics with the range of interaction in short-range attractive colloids
We numerically study the dependence of the dynamics on the range of
interaction for the short-range square well potential. We find that,
for small , dynamics scale exactly in the same way as thermodynamics,
both for Newtonian and Brownian microscopic dynamics. For interaction ranges
from a few percent down to the Baxter limit, the relative location of the
attractive glass line and the liquid-gas line does not depend on . This
proves that in this class of potentials, disordered arrested states (gels) can
be generated only as a result of a kinetically arrested phase separation.Comment: 4 pages, 4 figure
Double solid twistor spaces: the case of arbitrary signature
In a recent paper (math.DG/0701278) we constructed a series of new Moishezon
twistor spaces which is a kind of variant of the famous LeBrun twistor spaces.
In this paper we explicitly give projective models of another series of
Moishezon twistor spaces on nCP^2 for arbitrary n>2, which can be regarded as a
generalization of the twistor spaces of a 'double solid type' on 3CP^2 studied
by Kreussler, Kurke, Poon and the author. Similarly to the twistor spaces of
'double solid type' on 3CP^2, projective models of present twistor spaces have
a natural structure of double covering of a CP^2-bundle over CP^1. We
explicitly give a defining polynomial of the branch divisor of the double
covering whose restriction to fibers are degree four. If n>3 these are new
twistor spaces, to the best of the author's knowledge. We also compute the
dimension of the moduli space of these twistor spaces. Differently from
math.DG/0701278, the present investigation is based on analysis of
pluri-(half-)anticanonical systems of the twistor spaces.Comment: 30 pages, 3 figures; v2: title changed (the original title was
"Explicit construction of new Moishezon twistor spaces, II".
Relation Between First Arrival Time and Permeability in Self-Affine Fractures with Areas in Contact
We demonstrate that the first arrival time in dispersive processes in
self-affine fractures are governed by the same length scale characterizing the
fractures as that which controls their permeability. In one-dimensional channel
flow this length scale is the aperture of the bottle neck, i.e., the region
having the smallest aperture. In two dimensions, the concept of a bottle neck
is generalized to that of a minimal path normal to the flow. The length scale
is then the average aperture along this path. There is a linear relationship
between the first arrival time and this length scale, even when there is strong
overlap between the fracture surfaces creating areas with zero permeability. We
express the first arrival time directly in terms of the permeability.Comment: EPL (2012)
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