A Bayesian approach to bandwidth selection for multivariate kernel regression with an application to state-price density estimation.

Multivariate kernel regression is an important tool for investigating the relationship between a response and a set of explanatory variables. It is generally accepted that the performance of a kernel regression estimator largely depends on the choice of bandwidth rather than the kernel function. This nonparametric technique has been employed in a number of empirical studies including the state-price density estimation pioneered by Aït-Sahalia and Lo (1998). However, the widespread usefulness of multivariate kernel regression has been limited by the difficulty in computing a data-driven bandwidth. In this paper, we present a Bayesian approach to bandwidth selection for multivariate kernel regression. A Markov chain Monte Carlo algorithm is presented to sample the bandwidth vector and other parameters in a multivariate kernel regression model. A Monte Carlo study shows that the proposed bandwidth selector is more accurate than the rule-of-thumb bandwidth selector known as the normal reference rule according to Scott (1992) and Bowman and Azzalini (1997). The proposed bandwidth selection algorithm is applied to a multivariate kernel regression model that is often used to estimate the state-price density of Arrow-Debreu securities. When applying the proposed method to the S&P 500 index options and the DAX index options, we find that for short-maturity options, the proposed Bayesian bandwidth selector produces an obviously different state-price density from the one produced by using a subjective bandwidth selector discussed in Aït-Sahalia and Lo (1998).Black-Scholes formula, Likelihood, Markov chain Monte Carlo, Posterior density.

Fluid oscillations in a laboratory geyser with a bubble trap

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Rudolph, M. L., Sohn, R. A., & Lev, E.. Fluid oscillations in a laboratory geyser with a bubble trap. Journal of Volcanology and Geothermal Research, 368, (2018):100-110. doi:10.1016/j.jvolgeores.2018.11.003.Geysers are rare geologic features that episodically erupt water and steam. While it is understood that the eruptions are triggered by the conversion of thermal to kinetic energy during decompression of hot uids, geysers commonly exhibit a range of dynamic behaviors in-between and during eruptions that have yet to be adequately explained. In-situ measurements of temperature and pressure as well as remote geophysical techniques have revealed oscillatory behavior across a range of timescales, ranging from eruption cycles to impulsive bubble collapse events. Many geysers, including Old faithful in Yellowstone National Park, USA, are believed to have o set subsurface reservoirs (referred to as a `bubble trap') that can trap and accumulate noncondensable gas or steam entering the system. The impact of a bubble trap on the dynamic behaviors of the system, however, has not been fully established. We constructed a laboratory bubble trap and performed a series of experiments to study how uids oscillate back and forth between the eruption conduit and laterally-offseet reservoir in-between eruptions. We present a new theoretical model based on Hamiltonian mechanics that successfully predicts the oscillation frequencies observed in our experiments based on the conduit system geometry, the amount of gas that has accumulated in the bubble trap, and the amount of liquid water in the system. We demonstrate that when scaled to Old Faithful Geyser, this mechanism is capable of producing oscillations at the observed frequencies.The authors thank Paul Fucile and Glenn Macdonald for engineering support in designing and constructing the laboratory analog geyser rig. Funding for the laboratory geyser was provided by the US National Science Foundation grant EAR-1516361. EL was funded through a RISE award from Columbia University.2019-11-1

Comment on "Plasma ionization by annularly bounded helicon waves" [Phys . Plasmas 13, 063501 (2006)]

The neoclassical calculation of the helicon wave theory contains a fundamental flaw. Use is made of a proportional relationship between the magnetic field and its curl to derive the Helmholtz equation describing helicon wave propagation; however, by the fundamental theorem of Stokes, the curl of the magnetic field must be perpendicular to that portion of the field contributing to the local curl. Reexamination of the equations of motion indicates that only electromagnetic waves propagate through a stationary region of constant pressure in a fully ionized, neutral medium.Comment: 7 pages, 1 figure, to be published in Phys. Plasmas, http://link.aip.org/link/?PHPAEN/16/054701/

Fibronectin and Cyclic Strain Improve Cardiac Progenitor Cell Regenerative Potential In Vitro.

Cardiac progenitor cells (CPCs) have rapidly advanced to clinical trials, yet little is known regarding their interaction with the microenvironment. Signaling cues present in the microenvironment change with development and disease. This work aims to assess the influence of two distinct signaling moieties on CPCs: cyclic biaxial strain and extracellular matrix. We evaluate four endpoints for improving CPC therapy: paracrine signaling, proliferation, connexin43 expression, and alignment. Vascular endothelial growth factor A (about 900 pg/mL) was secreted by CPCs cultured on fibronectin and collagen I. The application of mechanical strain increased vascular endothelial growth factor A secretion 2-4-fold for CPCs cultured on poly-L-lysine, laminin, or a naturally derived cardiac extracellular matrix. CPC proliferation was at least 25% higher on fibronectin than that on other matrices, especially for lower strain magnitudes. At 5% strain, connexin43 expression was highest on fibronectin. With increasing strain magnitude, connexin43 expression decreased by as much as 60% in CPCs cultured on collagen I and a naturally derived cardiac extracellular matrix. Cyclic mechanical strain induced the strongest CPC alignment when cultured on fibronectin or collagen I. This study demonstrates that culturing CPCs on fibronectin with 5% strain magnitude is optimal for their vascular endothelial growth factor A secretion, proliferation, connexin43 expression, and alignment

Reliability of histopathologic diagnosis of fibrotic interstitial lung disease: an international collaborative standardization project

Malaltia pulmonar intersticial; Fibrosi pulmonar; Pneumònia intersticial habitualEnfermedad pulmonar intersticial; Fibrosis pulmonar; Neumonía intersticial habitualInterstitial lung disease; Pulmonary fibrosis; Usual interstitial pneumoniaBackground Current interstitial lung disease (ILD) diagnostic guidelines assess criteria across clinical, radiologic and pathologic domains. Significant interobserver variation in histopathologic evaluation has previously been shown but the specific source of these discrepancies is poorly documented. We sought to document specific areas of difficulty and develop improved criteria that would reduce overall interobserver variation. Methods Using an internet-based approach, we reviewed selected images of specific diagnostic features of ILD histopathology and whole slide images of fibrotic ILD. After an initial round of review, we confirmed the presence of interobserver variation among our group. We then developed refined criteria and reviewed a second set of cases. Results The initial round reproduced the existing literature on interobserver variation in diagnosis of ILD. Cases which were pre-selected as inconsistent with usual interstitial pneumonia/idiopathic pulmonary fibrosis (UIP/IPF) were confirmed as such by multi-observer review. Cases which were thought to be in the spectrum of chronic fibrotic ILD for which UIP/IPF were in the differential showed marked variation in nearly all aspects of ILD evaluation including extent of inflammation and extent and pattern of fibrosis. A proposed set of more explicit criteria had only modest effects on this outcome. While we were only modestly successful in reducing interobserver variation, we did identify specific reasons that current histopathologic criteria of fibrotic ILD are not well defined in practice. Conclusions Any additional classification scheme must address interobserver variation in histopathologic diagnosis of fibrotic ILD order to remain clinically relevant. Improvements to tissue-based diagnostics may require substantial resources such as larger datasets or novel technologies to improve reproducibility. Benchmarks should be established for expected outcomes among clinically defined subgroups as a quality metric.This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors

Interview with Lawrence Weigel, Kilian Leiker, Lark Lowell Gunther, Ida L. Steward, and Wesson G. Shelly

Interviews with Lawrence Weigel, Kilian Leiker, Lark Lowell Gunther, Ida L. Steward, and Wesson G. Shelly. This recording is unavailable.https://scholars.fhsu.edu/sackett/1099/thumbnail.jp