163 research outputs found
Kernel Choice Matters for Boundary Inference using Local Polynomial Density: With Application to Manipulation Testing
Local polynomial density (LPD) estimation has become an essential tool for
boundary inference, including manipulation tests for regression discontinuity.
It is common sense that kernel choice is not critical for LPD estimation, in
analogy to standard kernel smoothing estimation. This paper, however, points
out that kernel choice has a severe impact on the performance of LPD, based on
both asymptotic and non-asymptotic theoretical investigations. In particular,
we show that the estimation accuracy can be extremely poor with commonly used
kernels with compact support, such as the triangular and uniform kernels.
Importantly, this negative result implies that the LPD-based manipulation test
loses its power if a compactly supported kernel is used. As a simple but
powerful solution to this problem, we propose using a specific kernel function
with unbounded support. We illustrate the empirical relevance of our results
with numerous empirical applications and simulations, which show large
improvements
Higher-Order Asymptotic Properties of Kernel Density Estimator with Global Plug-In and Its Accompanying Pilot Bandwidth
This study investigates the effect of bandwidth selection via a plug-in
method on the asymptotic structure of the nonparametric kernel density
estimator. We generalise the result of Hall and Kang (2001) and find that the
plug-in method has no effect on the asymptotic structure of the estimator up to
the order of for a bandwidth
and any kernel order when the kernel order for pilot estimation is
high enough. We also provide the valid Edgeworth expansion up to the order of
and find that, as long as the is high enough
, the plug-in method has an effect from on the term whose convergence rate is
. In other words, we
derive the exact achievable convergence rate of the deviation between the
distribution functions of the estimator with a deterministic bandwidth and with
the plug-in bandwidth. In addition, we weaken the conditions on kernel order
for pilot estimation by considering the effect of pilot bandwidth
associated with the plug-in bandwidth. We also show that the bandwidth
selection via the global plug-in method possibly has an effect on the
asymptotic structure even up to the order of .
Finally, Monte Carlo experiments are conducted to see whether our approximation
improves previous results
Doubly Robust Uniform Confidence Bands for Group-Time Conditional Average Treatment Effects in Difference-in-Differences
We consider a panel data analysis to examine the heterogeneity in treatment
effects with respect to a pre-treatment covariate of interest in the staggered
difference-in-differences setting of Callaway and Sant'Anna (2021). Under
standard identification conditions, a doubly robust estimand conditional on the
covariate identifies the group-time conditional average treatment effect given
the covariate. Focusing on the case of a continuous covariate, we propose a
three-step estimation procedure based on nonparametric local polynomial
regressions and parametric estimation methods. Using uniformly valid
distributional approximation results for empirical processes and multiplier
bootstrapping, we develop doubly robust inference methods to construct uniform
confidence bands for the group-time conditional average treatment effect
function. The accompanying R package didhetero allows for easy implementation
of the proposed methods.Comment: R package: https://tkhdyanagi.github.io/didhetero
Phosphorylation-induced conformation of beta(2)-adrenoceptor related to arrestin recruitment revealed by NMR
The C-terminal region of G-protein-coupled receptors (GPCRs), stimulated by agonist binding, is phosphorylated by GPCR kinases, and the phosphorylated GPCRs bind to arrestin, leading to the cellular responses. To understand the mechanism underlying the formation of the phosphorylated GPCR-arrestin complex, we performed NMR analyses of the phosphorylated beta(2)-adrenoceptor (beta(2)AR) and the phosphorylated beta(2)AR-beta-arrestin 1 complex, in the lipid bilayers of nanodisc. Here we show that the phosphorylated C-terminal region adheres to either the intracellular side of the transmembrane region or lipids, and that the phosphorylation of the C-terminal region allosterically alters the conformation around M215(5.54) and M279(6.41), located on transemembrane helices 5 and 6, respectively. In addition, we found that the conformation induced by the phosphorylation is similar to that corresponding to the beta-arrestin-bound state. The phosphorylation-induced structures revealed in this study propose a conserved structural motif of GPCRs that enables beta-arrestin to recognize dozens of GPCRs.Peer reviewe
Expression of nampt in hippocampal and cortical excitatory neurons is critical for cognitive function
Nicotinamide adenine dinucleotide (NAD(+)) is an enzyme cofactor or cosubstrate in many essential biological pathways. To date, the primary source of neuronal NAD(+) has been unclear. NAD(+) can be synthesized from several different precursors, among which nicotinamide is the substrate predominantly used in mammals. The rate-limiting step in the NAD(+) biosynthetic pathway from nicotinamide is performed by nicotinamide phosphoribosyltransferase (Nampt). Here, we tested the hypothesis that neurons use intracellular Nampt-mediated NAD(+) biosynthesis by generating and evaluating mice lacking Nampt in forebrain excitatory neurons (CaMKIIαNampt(−/−) mice). CaMKIIαNampt(−/−) mice showed hippocampal and cortical atrophy, astrogliosis, microgliosis, and abnormal CA1 dendritic morphology by 2–3 months of age. Importantly, these histological changes occurred with altered intrahippocampal connectivity and abnormal behavior; including hyperactivity, some defects in motor skills, memory impairment, and reduced anxiety, but in the absence of impaired sensory processes or long-term potentiation of the Schaffer collateral pathway. These results clearly demonstrate that forebrain excitatory neurons mainly use intracellular Nampt-mediated NAD(+) biosynthesis to mediate their survival and function. Studying this particular NAD(+) biosynthetic pathway in these neurons provides critical insight into their vulnerability to pathophysiological stimuli and the development of therapeutic and preventive interventions for their preservation
Mossbauer studies on FeSe and FeTe
We carried out 57Fe Mossbauer measurements for FeSe and Fe1.08Te to
investigate the magnetic properties. There was no sign of magnetic ordering
above 4.2 K for superconducting FeSe. The magnetic sextet corresponding to
antiferromagnetic ordering of Fe in low-spin state was observed for
non-superconducting Fe1.08Te.Comment: 5 pages, 2 figures, proceedings of M2S conferenc
HIGH-DOSE-RATE AFTERLOADING INTRACAVITARY IRRADIATION AND EXPANDABLE METALLIC BILIARY ENDOPROSTHESIS FOR MALIGNANT BILIARY OBSTRUCTION
A double lumen catheter was developed as an applicator for the remote afterloading system (RALS) of ⁶⁰Co for the intracavitary irradiation of an obstructed common bile duct due to gallbladder cancer in 1 case and by cholangiocarcinoma in 7 cases. This was followed by the biliary endoprosthesis with expandable metallic stents to maintain patency. The mean survival period after treatment was not long (14 weeks). However, removal of the external drainage tube was possible in 7 of the 8 cases, and none of the 8 cases showed dislodgement or deformity of the stent, or obstruction of the bile duct in the stent-inserted area. This combination effectively provided palliation, and has considerable potential for malignant biliary obstruction
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