Folding Kinetics of Protein Like Heteropolymers

Using a simple three-dimensional lattice copolymer model and Monte Carlo dynamics, we study the collapse and folding of protein-like heteropolymers. The polymers are 27 monomers long and consist of two monomer types. Although these chains are too long for exhaustive enumeration of all conformations, it is possible to enumerate all the maximally compact conformations, which are 3x3x3 cubes. This allows us to select sequences that have a unique global minimum. We then explore the kinetics of collapse and folding and examine what features determine the various rates. The folding time has a plateau over a broad range of temperatures and diverges at both high and low temperatures. The folding time depends on sequence and is related to the amount of energetic frustration in the native state. The collapse times of the chains are sequence independent and are a few orders of magnitude faster than the folding times, indicating a two-phase folding process. Below a certain temperature the chains exhibit glass-like behavior, characterized by a slowing down of time scales and loss of self-averaging behavior. We explicitly define the glass transition temperature (Tg), and by comparing it to the folding temperature (Tf), we find two classes of sequences: good folders with Tf > Tg and non-folders with Tf < Tg.Comment: 23 pages (plus 10 figures included in a seperate file) LaTeX, no local report nu

A New Method to Calibrate the Magnitudes of Type Ia Supernovae at Maximum Light

We present a new empirical method for fitting multicolor light curves of Type Ia supernovae. Our method combines elements from two widely used techniques in the literature: the delta_m15 template fitting method and the Multicolor Light-Curve Shape method. An advantage of our technique is the ease of adding new colors, templates, or parameters to the fitting procedure. We use a large sample of published light curves to calibrate the relations between the absolute magnitudes at maximum and delta_m15 in BVRI filters. We find that individual subsamples from a given survey or publication have significantly tighter relationships between light curve shape and luminosity than the relationship derived from the sum of all the samples, pointing to uncorrected systematic errors in the photometry, mainly in BV filters. Using our method, we calculate luminosity distances and host galaxy reddening to 89 SNe in the Hubble flow and construct a low-z Hubble diagram. The dispersion of the SNe in the Hubble diagram is 0.20 mag, or an error of ~9% in distance to a single SN. Our technique produces similar or smaller dispersion in the low-z Hubble diagram than other techniques in the literature.Comment: 43 pages, 16 figures, 6 tables, accepted by ApJ. For additional material go to http://www.astronomy.ohio-state.edu/~prieto/paper_dm15/dm15.htm

Bank Failure: Evidence from the Colombia Financial Crisis

This paper identifies the main bank specific determinants of bank failure during the financial crisis in Colombia using duration analysis. Using partial likelihood estimation, it shows that the process of failure of financial institutions during that period can be explained by differences in financial health and prudence across institutions. The capitalization ratio is the most significant indicator explaining bank failure. Increases in this ratio lead to a reduction in the hazard rate of failure at any given moment in time. Of special relevance, this ratio exhibits a non-linear component. Our results thus provide empirical support for existing regulatory practice. Other important variables explaining bank failure dynamics are bank's size and profitability.

Survival of Medicare Patients After Enrollment in Hospice Programs

Background: Each year more than 220,000 Medicare beneficiaries receive care from hospice programs designed to enhance the quality of the end of life. Enrollment requires certification by a physician that the patient has a life expectancy of less than six months. We examined how long before death patients enrolled in hospice programs. Methods: Using 1990 Medicare claims data, we analyzed the characteristics and survival of 6451 hospice patients followed for a minimum of 27 months with respect to mortality. Results: The patients' mean age was 76.4 years; 92.4 percent were white. Half the patients were women, and 80.2 percent had cancer of some type. The most common diagnoses were lung cancer (21.4 percent), colorectal cancer (10.5 percent), and prostate cancer (7.4 percent). The median survival after enrollment was only 36 days, and 15.6 percent of the patients died within 7 days. At the other extreme, 14.9 percent of the patients lived longer than six months. Survival varied substantially according to diagnosis, even after adjustment for age and coexisting conditions. The unadjusted survival after enrollment was shortest for those with renal failure, those with leukemia or lymphoma, and those with liver or biliary cancer; it was longest for those with chronic lung disease, those with dementia, and those with breast cancer. Patients at for-profit, larger, outpatient, or newer hospices lived longer after enrollment than those in other types of hospice programs. Conclusions: Most patients who enter hospice care do so late in the course of their terminal illnesses. The timing of enrollment in hospice programs varies substantially with the characteristics of the patients and the hospices.Sociolog

Rotational properties of the Haumea family members and candidates: Short-term variability

Haumea is one of the most interesting and intriguing transneptunian objects (TNOs). It is a large, bright, fast rotator, and its spectrum indicates nearly pure water ice on the surface. It has at least two satellites and a dynamically related family of more than ten TNOs with very similar proper orbital parameters and similar surface properties. The Haumean family is the only one currently known in the transneptunian belt. Various models have been proposed but the formation of the family remains poorly understood. In this work, we have investigated the rotational properties of the family members and unconfirmed family candidates with short-term variability studies, and report the most complete review to date. We present results based on five years of observations and report the short-term variability of five family members, and seven candidates. The mean rotational periods, from Maxwellian fits to the frequency distributions, are 6.27+/-1.19 h for the confirmed family members, 6.44+/-1.16 h for the candidates, and 7.65+/-0.54 h for other TNOs (without relation to the family). According to our study, there is a suggestion that Haumea family members rotate faster than other TNOs, however, the sample of family member is still too limited for a secure conclusion. We also highlight the fast rotation of 2002 GH32. This object has a 0.36+/-0.02 mag amplitude lightcurve and a rotational period of about 3.98 h. Assuming 2002 GH32 is a triaxial object in hydrostatic equilibrium, we derive a lower limit to the density of 2.56 g cm^-3. This density is similar to Haumea's and much more dense than other small TNO densities.Comment: Accepted for publication, A

Small is Different Size, Political Representation and Governance

In the theoretical literature on government design, few variables have received more attention than the size of the polity. Since Plato’s famous prediction that the optimal size of a political unit should be 5040 free citizens, the list of thinkers concerned about state size would include Aristotle, Montesquieu, Rousseau, and many of the founding fathers, among many others. One of the fathers of modern political science, Robert Dahl, devoted great attention to what he called the “elemental question of what is appropriate unit for a democratic political system … Among the vast number of theoretically possible ways of dividing up the inhabitants of this globe into more or less separate political systems, … are there any principles that instruct us as to how one ought to bound some particular collection of people, in order that they may rule themselves?” (Dahl 1967: 953). Economists have not neglected these issues, as they conform the core of the fiscal federalism literature (Oates 1972). A more recent literature, pioneered by Alesina and Spolaore’s work (1997, 2003), provides an elegant formal theoretical framework incorporating both political and economic elements in order to highlight the fundamental trade-off that the choice of the size of the policy inevitably faces: Large polities find it easier to provide more public goods, but confront the costly political problem of greater heterogeneity of preferences among the population