arXiv subjects

Andrew He

Publications and source records attributed to Andrew He.

4 recordsLinked to original sources

arXiv2024

Endoscopic Fourier-transform infrared spectroscopy through a fiber microprobe

Fourier-transform infrared spectroscopy (FTIR) is a powerful analytical method for not only the chemical identification of solid, liquid, and gas species, but also the quantification of their concentration. However, the chemical quantification capability of FTIR is significantly hindered when the analyte is surrounded by a strong IR absorbing medium, such as liquid solutions. To overcome this limit, here we develop an IR fiber microprobe that can be inserted into liquid medium, and obtain full FTIR spectra at points of interest. To benchmark this endoscopic FTIR method, we insert the microprobe into bulk water covering a ZnSe substrate and measure the IR transmittance of water as a function of the probe-substrate distance. The obtained vibrational modes, overall transmittance vs z profiles, quantitative absorption coefficients, and micro z-section IR transmittance spectra are all consistent with the standard IR absorption properties of water. The results pave the way for endoscopic chemical profiling inside bulk liquid solutions, promising for applications in many biological, chemical, and electrochemical systems.

physics.ins-det↗

arXiv2023

DeepMartNet -- A Martingale Based Deep Neural Network Learning Method for Dirichlet BVPs and Eigenvalue Problems of Elliptic PDEs in R^d

In this paper, we propose DeepMartNet - a Martingale based deep neural network learning method for solving Dirichlet boundary value problems (BVPs) and eigenvalue problems for elliptic partial differential equations (PDEs) in high dimensions or domains with complex geometries. The method is based on Varadhan's Martingale problem formulation for the BVPs/eigenvalue problems where a loss function enforcing the Martingale property for the PDE solution is used for an efficient optimization by sampling the stochastic processes associated with corresponding elliptic operators. High dimensional numerical results for BVPs of the linear and nonlinear Poisson-Boltzmann equation and eigenvalue problems of the Laplace equation and a Fokker-Planck equation demonstrate the capability of the proposed DeepMartNet learning method in solving high dimensional PDE problems.

math.NA↗

arXiv2014

An Elementary Proof of the Cayley Formula Using Random Maps

Cayley's formula states that the number of labelled trees on $n$ vertices is $n^{n-2}$, and many of the current proofs involve complex structures or rigorous computation. We present a bijective proof of the formula by providing an elementary calculation of the probability that a cycle occurs in a random map from an $n$-element set to an $n+1$-element set.

math.CO↗

arXiv2013

A Simple Proof of the Cayley Formula using Random Graphs

We present a nice result on the probability of a cycle occurring in a randomly generated graph. We then provide some extensions and applications, including the proof of the famous Cayley formula, which states that the number of labeled trees on $n$ vertices is $n^{n-2}.$

math.CO↗