Bootstrap-Based Inference for Cube Root Asymptotics

This paper proposes a valid bootstrap-based distributional approximation for M-estimators exhibiting a Chernoff (1964)-type limiting distribution. For estimators of this kind, the standard nonparametric bootstrap is inconsistent. The method proposed herein is based on the nonparametric bootstrap, but restores consistency by altering the shape of the criterion function defining the estimator whose distribution we seek to approximate. This modification leads to a generic and easy-to-implement resampling method for inference that is conceptually distinct from other available distributional approximations. We illustrate the applicability of our results with four examples in econometrics and machine learning

Inference in Linear Regression Models with Many Covariates and Heteroskedasticity

The linear regression model is widely used in empirical work in Economics, Statistics, and many other disciplines. Researchers often include many covariates in their linear model specification in an attempt to control for confounders. We give inference methods that allow for many covariates and heteroskedasticity. Our results are obtained using high-dimensional approximations, where the number of included covariates are allowed to grow as fast as the sample size. We find that all of the usual versions of Eicker-White heteroskedasticity consistent standard error estimators for linear models are inconsistent under this asymptotics. We then propose a new heteroskedasticity consistent standard error formula that is fully automatic and robust to both (conditional)\ heteroskedasticity of unknown form and the inclusion of possibly many covariates. We apply our findings to three settings: parametric linear models with many covariates, linear panel models with many fixed effects, and semiparametric semi-linear models with many technical regressors. Simulation evidence consistent with our theoretical results is also provided. The proposed methods are also illustrated with an empirical application

Project-X and its connection to neutrino physics

Project X is a new high intensity proton source that is being planned at Fermilab to usher in a new era of high intensity physics. The high intensity frontier can provide a wealth of new measurements--the most voracious consumer of protons is the long baseline neutrino program, but with the proton source upgrades being planned there are even more protons available than current neutrino targets can withstand. Those protons can provide a rich program on their own of muon physics and neutrino scattering physics that is complimentary to the long baseline program. In this article we discuss the physics motivation for Project X that comes from these short baseline experiments, and also the status of the design of this new source and what it will take to move forward on that design

O VI Emission Imaging of a Galaxy with the Hubble Space Telescope: a Warm Gas Halo Surrounding the Intense Starburst SDSS J115630.63+500822.1

We report results from a new HST study of the OVI 1032,1038\AA\ doublet in emission around intensely star-forming galaxies. The programme aims to characterize the energy balance in starburst galaxies and gas cooling in the difficult-to-map coronal temperature regime of 2-5 x $10^5$K. We present the first resolved image of gas emission in the OVI line. Our target, SDSS J1156+5008, is very compact in the continuum but displays OVI emission to radii of 23 kpc. The surface brightness profile is well fit by an exponential with a scale of 7.5kpc. This is ten times the size of the photoionized gas, and we estimate that 1/6 the total OVI luminosity comes from resonantly scattered continuum radiation. Spectroscopy - which closely resembles a stacked sample of archival spectra - confirms the OVI emission, and determines the column density and outflow velocity from blueshifted absorption. The combination of measurements enables several new calculations with few assumptions. The OVI regions fill only ~$10^{-3}$ of the volume. By comparing the cooling time with the cloud sound-crossing time, the cooling distance with the size, and the pressure in the OVI and nebular gas, we conclude that the OVI-bearing gas cannot have been lifted to the scale height at this temperature, and must be cooling in situ through this coronal temperature regime. The coronal phase contains ~1% of the ionized mass, and its kinetic energy is currently ~1% of the budget set by supernova feedback. However a much larger amount of the gas must have cooled through this phase during the star formation episode. The outflow exceeds the escape velocity and the gas may become unbound, but it will recombine before it escapes and become visible to Lyman (and OI) spectroscopy. The mapping of this gas represents a crucial step in further constraining galaxy formation scenarios and guiding the development of future satellites.Comment: Accepted by the Astrophysical Journal. 25 pages, 11 figures. Section 7 presents calculated properties of warm halo gas. Version 2 fixes PDF compatibility issue for some PDF viewer

A New Optimised Quadrupole Pick-up Design Using Magnetic Coupling

The idea of quadrupole pick-ups, sensitive to beam size, dates back several decades. Such pick-ups measure the quantity $\sigma^2_x-\sigma^2_y$, where $\sigma_x$ and $\sigma_y$ are the horizontal and vertical r.m.s. beam sizes. Thus, a quadrupole pick-up is a candidate for non-invasive study of processes such as coherent beam width oscillations due to injection mismatch. Up to now, quadrupole pick-ups have been produced essentially by enhancing the electronics of normal position pick-ups to produce the so-called quadrupole signal, with little or no effort being put into the design of the pick-up itself. In developing a quadrupole pick-up for the CERN PS, however, it has been found necessary to optimise the pick-up design. The result is a somewhat unconventional pick-up, where magnetic coupling is employed to suppress the otherwise very strong, and undesired, common mode-signal. In this paper, the basic design idea and the final optimised design are presented, together with simulations, test bench measurements and real beam data

Conceptual mechanization studies for a horizon definition spacecraft structures and thermal subsystem

Conceptual mechanization for horizon definition spacecraft structures and thermal subsystem - spin-stabilized, hexagonal cylinder for launch of two-stage Improved Delta /DSV-3N