Credit Ratings as Coordination Mechanisms

In this paper, we provide a novel rationale for credit ratings. The rationale that we propose is that credit ratings can serve as a coordinating mechanism in situations where multiple equilibria can obtain. We show that credit ratings provide a "focal point" for firms and their investors. We explore the vital, but previously overlooked implicit contractual relationship between a credit rating agency and a firm. Credit ratings can help fix the desired equilibrium and as such play an economically meaningful role. Our model provides several empirical predictions and insights regarding the expected price impact of ratings changes, the discreteness in funding cost changes, and the effect of the focus of organizations on the efficacy of credit ratings.http://deepblue.lib.umich.edu/bitstream/2027.42/39841/3/wp457.pd

Infinitesimal local operations and differential conditions for entanglement monotones

Much of the theory of entanglement concerns the transformations that are possible to a state under local operations with classical communication (LOCC); however, this set of operations is complicated and difficult to describe mathematically. An idea which has proven very useful is that of the {\it entanglement monotone}: a function of the state which is invariant under local unitary transformations and always decreases (or increases) on average after any local operation. In this paper we look on LOCC as the set of operations generated by {\it infinitesimal local operations}, operations which can be performed locally and which leave the state little changed. We show that a necessary and sufficient condition for a function of the state to be an entanglement monotone under local operations that do not involve information loss is that the function be a monotone under infinitesimal local operations. We then derive necessary and sufficient differential conditions for a function of the state to be an entanglement monotone. We first derive two conditions for local operations without information loss, and then show that they can be extended to more general operations by adding the requirement of {\it convexity}. We then demonstrate that a number of known entanglement monotones satisfy these differential criteria. Finally, as an application, we use the differential conditions to construct a new polynomial entanglement monotone for three-qubit pure states. It is our hope that this approach will avoid some of the difficulties in the theory of multipartite and mixed-state entanglement.Comment: 21 pages, RevTeX format, no figures, three minor corrections, including a factor of two in the differential conditions, the tracelessness of the matrix in the convexity condition, and the proof that the local purity is a monotone under local measurements. The conclusions of the paper are unaffecte

Credit Ratings as Coordination Mechanisms

In this paper, we provide a novel rationale for credit ratings. The rationale that we propose is that credit ratings can serve as a coordinating mechanism in situations where multiple equilibria can obtain. We show that credit ratings provide a "focal point" for firms and their investors. We explore the vital, but previously overlooked implicit contractual relationship between a credit rating agency and a firm. Credit ratings can help fix the desired equilibrium and as such play an economically meaningful role. Our model provides several empirical predictions and insights regarding the expected price impact of ratings changes, the discreteness in funding cost changes, and the effect of the focus of organizations on the efficacy of credit ratings.coordination, credit ratings, multiple equilibria

Projection neurons in lamina III of the rat spinal cord are selectively innervated by local dynorphin-containing excitatory neurons

Large projection neurons in lamina III of the rat spinal cord that express the neurokinin 1 receptor are densely innervated by peptidergic primary afferent nociceptors and more sparsely by low-threshold myelinated afferents. However, we know little about their input from other glutamatergic neurons. Here we show that these cells receive numerous contacts from nonprimary boutons that express the vesicular glutamate transporter 2 (VGLUT2), and form asymmetrical synapses on their dendrites and cell bodies. These synapses are significantly smaller than those formed by peptidergic afferents, but provide a substantial proportion of the glutamatergic synapses that the cells receive (over a third of those in laminae I–II and half of those in deeper laminae). Surprisingly, although the dynorphin precursor preprodynorphin (PPD) was only present in 4–7% of VGLUT2 boutons in laminae I–IV, it was found in 58% of the VGLUT2 boutons that contacted these cells. This indicates a highly selective targeting of the lamina III projection cells by glutamatergic neurons that express PPD, and these are likely to correspond to local neurons (interneurons and possibly projection cells). Since many PPD-expressing dorsal horn neurons respond to noxious stimulation, this suggests that the lamina III projection cells receive powerful monosynaptic and polysynaptic nociceptive input. Excitatory interneurons in the dorsal horn have been shown to possess IA currents, which limit their excitability and can underlie a form of activity-dependent intrinsic plasticity. It is therefore likely that polysynaptic inputs to the lamina III projection neurons are recruited during the development of chronic pain states

Hearing in the Juvenile Green Sea Turtle (Chelonia mydas): A Comparison of Underwater and Aerial Hearing Using Auditory Evoked Potentials

Sea turtles spend much of their life in aquatic environments, but critical portions of their life cycle, such as nesting and hatching, occur in terrestrial environments, suggesting that it may be important for them to detect sounds in both air and water. In this study we compared underwater and aerial hearing sensitivities in five juvenile green sea turtles (Chelonia mydas) by measuring auditory evoked potential responses to tone pip stimuli. Green sea turtles detected acoustic stimuli in both media, responding to underwater stimuli between 50 and 1600 Hz and aerial stimuli between 50 and 800 Hz, with maximum sensitivity between 200 and 400 Hz underwater and 300 and 400 Hz in air. When underwater and aerial hearing sensitivities were compared in terms of pressure, green sea turtle aerial sound pressure thresholds were lower than underwater thresholds, however they detected a wider range of frequencies underwater. When thresholds were compared in terms of sound intensity, green sea turtle sound intensity level thresholds were 2–39 dB lower underwater particularly at frequencies below 400 Hz. Acoustic stimuli may provide important environmental cues for sea turtles. Further research is needed to determine how sea turtles behaviorally and physiologically respond to sounds in their environment

The Ionization State of Sodium in Galactic Winds

Roughly 80% of Ultraluminous Infrared Galaxies (ULIRGs) show blue shifted absorption in the resonance lines of neutral sodium, indicating that cool winds are common in such objects, as shown by Rupke et al and by Martin. The neutral sodium (NaI) columns indicated by these absorption lines are ~ 10^{13}-3x10^{14}/cm^2, while the bolometric luminosity varies by a factor of only four. We show that the gas in ULIRG outflows is likely to be in photoionization equilibrium. The very small ULIRG sample of Goldader et al. demonstrates that the ratio of ultraviolet flux to far infrared flux varies by a factor $\sim100$ from object to object. While the Goldader sample does not overlap with those of Rupke et al. and Martin, we show that such a large variation in ultraviolet flux will produce a similar variation in the column of neutral sodium for a fixed mass flux and density. However, if the cold gas is in pressure equilibrium with a hot outflow with a mass loss rate similar to the star formation rate, the range of ionization state is significantly smaller. Measurements of the UV flux for objects in the Martin and Rupke et al. catalogs will definitively determine if photoionization effects are responsible for the wide variation seen in the sodium columns. If they are, a determination of the gas density and mass loss rate in the cool winds will follow, with attendant improvements in our understanding of wind driving mechanisms and of the effects of galaxies on their surroundings.Comment: 14 pages, 5 figures, submitted to Ap

Two-dimensional, Time-dependent, Multi-group, Multi-angle Radiation Hydrodynamics Test Simulation in the Core-Collapse Supernova Context

We have developed a time-dependent, multi-energy-group, and multi-angle (S$_n$) Boltzmann transport scheme for radiation hydrodynamics simulations, in one and two spatial dimensions. The implicit transport is coupled to both 1D (spherically-symmetric) and 2D (axially-symmetric) versions of the explicit Newtonian hydrodynamics code VULCAN. The 2D variant, VULCAN/2D, can be operated in general structured or unstructured grids and though the code can address many problems in astrophysics it was constructed specifically to study the core-collapse supernova problem. Furthermore, VULCAN/2D can simulate the radiation/hydrodynamic evolution of differentially rotating bodies. We summarize the equations solved and methods incorporated into the algorithm and present results of a time-dependent 2D test calculation. A more complete description of the algorithm is postponed to another paper. We highlight a 2D test run that follows for 22 milliseconds the immediate post-bounce evolution of a collapsed core. We present the relationship between the anisotropies of the overturning matter field and the distribution of the corresponding flux vectors, as a function of energy group. This is the first 2D multi-group, multi-angle, time-dependent radiation/hydro calculation ever performed in core collapse studies. Though the transport module of the code is not gray and does not use flux limiters (however, there is a flux-limited variant of VULCAN/2D), it still does not include energy redistribution and most velocity-dependent terms.Comment: 19 pages, plus 13 figures in JPEG format. Submitted to the Astrophysical Journa

The quantum to classical transition for random walks

We look at two possible routes to classical behavior for the discrete quantum random walk on the line: decoherence in the quantum ``coin'' which drives the walk, or the use of higher-dimensional coins to dilute the effects of interference. We use the position variance as an indicator of classical behavior, and find analytical expressions for this in the long-time limit; we see that the multicoin walk retains the ``quantum'' quadratic growth of the variance except in the limit of a new coin for every step, while the walk with decoherence exhibits ``classical'' linear growth of the variance even for weak decoherence.Comment: 4 pages RevTeX 4.0 + 2 figures (encapsulated Postscript). Trimmed for length. Minor corrections + one new referenc