Using LISA-like Gravitational Wave Detectors to Search for Primordial Black Holes

Primordial black hole (PBH), which can be naturally produced in the early universe, remains a promising dark matter candidate . It can merge with a supermassive black hole (SMBH) in the center of a galaxy and generate gravitational wave (GW) signals in the favored frequency region of LISA-like experiments. In this work, we initiate the study on the event rate calculation for such extreme mass ratio inspirals (EMRI). Including the sensitivities of various proposed GW detectors, we find that such experiments offer a novel and outstanding tool to test the scenario where PBH constitutes (fraction of) dark matter. The PBH energy density fraction of DM ($f_\text{PBH}$) could potentially be explored as small as $10^{-3} \sim 10^{-4}$. Further, LISA has the capability to search for PBH mass upto $10^{-2} \sim 10^{-1} M_\odot$. Other proposed GW experiments can probe lower PBH mass regime.Comment: 8 pages, 2 figure

Instability of standing waves of the Schrödinger equation with inhomogeneous nonlinearity

This paper is concerned with the inhomogeneous nonlinear Shrödinger equation (INLS-equation)iu_t + Δu + V(Єx)│u│^pu = 0, x Є R^N. In the critical and supercritical cases p ≥ 4/N, with N ≥ 2, it is shown here that standing-wave solutions of (INLS-equation) on H^1(R^N) perturbation are nonlinearly unstable or unstable by blow-up under certain conditions on the potential term V with a small Є > 0

Formation and Characterization of Columnar Porous SiC Fabricated by Photo-electrochemical Etching

The major part of this work concentrates on the details of the physical aspects of the columnar pore formation in the Si-face (0001), the C-face (000-1), and the a-face (11-20) of n-type 4H and 6H SiC samples using photoelectrochemical etching. The electrochemical etching of p-type 4H and 6H crystals is also illustrated. In Si-face n-type 4H and 6H SiC, the columnar pores are about one ¦Ìm in diameter. The formed porous layer is of high porosity and thus fragile. The formation of a hybrid partial columnar porous structure to improve the mechanical strength is discussed in detail. Nano-columnar pores are successfully fabricated in C-face n-type 4H and 6H SiC. The self-organized columnar pores have diameters of about 20 nm. The interpore spacing from center to center is between 40-60 nm depending on the etching conditions. The porous layer can be as thick as 200 ¦Ìm. The porosity of the porous structure is about 0.1. Systematic studies on the experimental control parameters, such as voltage, reaction temperature, surface roughness, HF concentration, and doping concentration, have been performed and are explained in detail. The formation mechanisms are discussed extensively based on crystallographic aspects, diffusion limited aggregation, impedance spectroscopy, voltammetry, equivalent circuits, and semiconductor/electrolyte interface (similar to a Schottky semiconductor/metal interface) electrochemistry. The 20 nm diameter nano-columnar pore formation has also been observed on the a-face n-type 6H SiC. The experimental observations are recorded and the voltage effects on the formed porous structure are discussed. In the electrochemical etching of p-type 4H and 6H SiC, the electrochemical polishing, porosity dependence on the current density, porosity variation during the etching and doping effects on the porous formation are discussed. The five appendices contain information about: (1) my publication list, (2) technical notes about the fabrication of porous SiC, (3) technical notes about the fabrication of porous Al2O3, (4) operation procedures and technical notes about the mechanical polishing of SiC, and (5) operation procedures and technical notes about the Varian 936-60 Leak Detector and the E-beam Evaporator in our laboratory

Safety Ramifications of A Change in Pedestrian Crosswalk Law: A Case Study of Oregon, USA

Pedestrians are some of the most vulnerable road users as they are not protected by safety devices, and must also share the road with vehicles traveling at dangerous speeds, particularly during road crossings. In 2011, the state of Oregon changed their traffic laws to be more accommodating to pedestrians by giving right of way to pedestrians using a crosswalk, regardless if whether the crosswalk is marked or unmarked. This paper estimates a panel logit model to evaluate the efficacy of the law in preventing pedestrian fatalities. Pedestrian fatalities are shown to decrease over time, with smaller likelihood of a fatality outcome in the years following the change in pedestrian crossing laws. To the authors’ knowledge, it is the first time panel logit models have been used in evaluating pedestrian safety. Results indicate that panel logit models are an alternative to using Box-Tiao intervention models to analyze the long term effects of policy changes, as they allow for the consideration of crash exposure factors as well as temporal effects