An Empirical Biomarker-based Calculator for Autosomal Recessive Polycystic Kidney Disease - The Nieto-Narayan Formula

Autosomal polycystic kidney disease (ARPKD) is associated with progressive enlargement of the kidneys fuelled by the formation and expansion of fluid-filled cysts. The disease is congenital and children that do not succumb to it during the neonatal period will, by age 10 years, more often than not, require nephrectomy+renal replacement therapy for management of both pain and renal insufficiency. Since increasing cystic index (CI; percent of kidney occupied by cysts) drives both renal expansion and organ dysfunction, management of these patients, including decisions such as elective nephrectomy and prioritization on the transplant waitlist, could clearly benefit from serial determination of CI. So also, clinical trials in ARPKD evaluating the efficacy of novel drug candidates could benefit from serial determination of CI. Although ultrasound is currently the imaging modality of choice for diagnosis of ARPKD, its utilization for assessing disease progression is highly limited. Magnetic resonance imaging or computed tomography, although more reliable for determination of CI, are expensive, time-consuming and somewhat impractical in the pediatric population. Using a well-established mammalian model of ARPKD, we undertook a big data-like analysis of minimally- or non-invasive serum and urine biomarkers of renal injury/dysfunction to derive a family of equations for estimating CI. We then applied a signal averaging protocol to distill these equations to a single empirical formula for calculation of CI. Such a formula will eventually find use in identifying and monitoring patients at high risk for progressing to end-stage renal disease and aid in the conduct of clinical trials.Comment: 3 tables and 8 figure

Conformal Field Theory as Microscopic Dynamics of Incompressible Euler and Navier-Stokes Equations

We consider the hydrodynamics of relativistic conformal field theories at finite temperature. We show that the limit of slow motions of the ideal hydrodynamics leads to the non-relativistic incompressible Euler equation. For viscous hydrodynamics we show that the limit of slow motions leads to the non-relativistic incompressible Navier-Stokes equation. We explain the physical reasons for the reduction and discuss the implications. We propose that conformal field theories provide a fundamental microscopic viewpoint of the equations and the dynamics governed by them.Comment: 4 page

The role of securitization in mortgage renegotiation

We study the effects of securitization on renegotiation of distressed residential mortgages over the current financial crisis. Unlike prior studies, we employ unique data that directly observe lender renegotiation actions and cover more than 60% of the U.S. mortgage market. Exploiting within-servicer variation in these data, we find that bank-held loans are 26% to 36% more likely to be renegotiated than comparable securitized mortgages (4.2 to 5.7% in absolute terms). Also, modifications of bank-held loans are more efficient: conditional on a modification, bank-held loans have lower post-modification default rates by 9% (3.5% in absolute terms). Our findings support the view that frictions introduced by securitization create a significant challenge to effective renegotiation of residential loans.Mortgage loans ; Asset-backed financing ; Securities ; Mortgages

Do financial counseling mandates improve mortgage choice and performance? Evidence from a legislative experiment

We explore the effects of mandatory third-party review of mortgage contracts on the terms, availability, and performance of mortgage credit. Our study is based on a legislative experiment in which the State of Illinois required “high-risk” mortgage applicants acquiring or refinancing properties in 10 specific zip codes to submit loan offers from state-licensed lenders to review by HUD-certified financial counselors. We document that the legislation led to declines in both the supply of and demand for credit in the treated areas. Controlling for the salient characteristics of the remaining borrowers and lenders, we find that the ex post default rates among counseled low-FICO-score borrowers were about 4.5 percentage points lower than those among similar borrowers in the control group. We attribute this result to actions of lenders responding to the presence of external review and, to a lesser extent, to counseled borrowers renegotiating their loan terms. We also find that the legislation pushed some borrowers to choose less risky loan products in order to avoid counseling.Financial literacy ; Mortgage loans ; Households - Finance

Market-based loss mitigation practices for troubled mortgages following the financial crisis

The meltdown in residential real-estate prices that commenced in 2006 resulted in unprecedented mortgage delinquency rates. Until mid-2009, lenders and servicers pursued their own individual loss mitigation practices without being significantly influenced by government intervention. Using a unique dataset that precisely identifies loss mitigation actions, we study these methods—liquidation, repayment plans, loan modification, and refinancing—and analyze their effectiveness. We show that the majority of delinquent mortgages do not enter any loss mitigation program or become a part of foreclosure proceedings within 6 months of becoming distressed. We also find that it takes longer to complete foreclosures over time, potentially due to congestion. We further document large heterogeneity in practices across servicers, which is not accounted for by differences in borrower population. ; Consistent with the idea that securitization induces agency conflicts, we confirm that the likelihood of modification of securitized loans is up to 70% lower relative to portfolio loans. Finally, we find evidence that affordability (as opposed to strategic default due to negative equity) is the prime reason for redefault following modifications. While modification terms are more favorable for weaker borrowers, greater reductions in mortgage payments and/or interest rates are associated with lower redefault rates. Our regression estimates suggest that a 1 percentage point decline in mortgage interest rate is associated with a nearly 4 percentage point decline in default probability. This finding is consistent with the Home Affordable Modification Program (HAMP) focus on improving mortgage affordability.Asset-backed financing ; Financial crises ; Securities ; Mortgages

Observational learning computations in neurons of the human anterior cingulate cortex

When learning from direct experience, neurons in the primate brain have been shown to encode a teaching signal used by algorithms in artificial intelligence: the reward prediction error (PE)—the difference between how rewarding an event is, and how rewarding it was expected to be. However, in humans and other species learning often takes place by observing other individuals. Here, we show that, when humans observe other players in a card game, neurons in their rostral anterior cingulate cortex (rACC) encode both the expected value of an observed choice, and the PE after the outcome was revealed. Notably, during the same task neurons recorded in the amygdala (AMY) and the rostromedial prefrontal cortex (rmPFC) do not exhibit this type of encoding. Our results suggest that humans learn by observing others, at least in part through the encoding of observational PEs in single neurons in the rACC

The bound on viscosity and the generalized second law of thermodynamics

We describe a new paradox for ideal fluids. It arises in the accretion of an \textit{ideal} fluid onto a black hole, where, under suitable boundary conditions, the flow can violate the generalized second law of thermodynamics. The paradox indicates that there is in fact a lower bound to the correlation length of any \textit{real} fluid, the value of which is determined by the thermodynamic properties of that fluid. We observe that the universal bound on entropy, itself suggested by the generalized second law, puts a lower bound on the correlation length of any fluid in terms of its specific entropy. With the help of a new, efficient estimate for the viscosity of liquids, we argue that this also means that viscosity is bounded from below in a way reminiscent of the conjectured Kovtun-Son-Starinets lower bound on the ratio of viscosity to entropy density. We conclude that much light may be shed on the Kovtun-Son-Starinets bound by suitable arguments based on the generalized second law.Comment: 11 pages, 1 figure, published versio

Evolution of collision numbers for a chaotic gas dynamics

We put forward a conjecture of recurrence for a gas of hard spheres that collide elastically in a finite volume. The dynamics consists of a sequence of instantaneous binary collisions. We study how the numbers of collisions of different pairs of particles grow as functions of time. We observe that these numbers can be represented as a time-integral of a function on the phase space. Assuming the results of the ergodic theory apply, we describe the evolution of the numbers by an effective Langevin dynamics. We use the facts that hold for these dynamics with probability one, in order to establish properties of a single trajectory of the system. We find that for any triplet of particles there will be an infinite sequence of moments of time, when the numbers of collisions of all three different pairs of the triplet will be equal. Moreover, any value of difference of collision numbers of pairs in the triplet will repeat indefinitely. On the other hand, for larger number of pairs there is but a finite number of repetitions. Thus the ergodic theory produces a limitation on the dynamics.Comment: 4 pages, published versio