A ground state potential energy surface for H2 using Monte Carlo methods

Using variational Monte Carlo and a simple explicitly correlated wave function we have computed the Born-Oppenheimer energy of the H2 ground state (X 1Sigmag+) at 24 internuclear distances. We have also calculated the diagonal correction to the Born-Oppenheimer approximation and the lowest-order relativistic corrections at each distance using variational Monte Carlo techniques. The nonadiabatic values are evaluated from numerical derivatives of the wave function with respect to the nuclear coordinates. With this potential energy surface we have computed several of the lowest vibrational-rotational energies for this system. Our results are in good agreement with the best values found in the literature.     

Relativistic calculations using Monte Carlo methods: one-electron systems

Variance minimization and Monte Carlo integration are used to evaluate the four-component Dirac equation for a number of one-electron atomic and diatomic systems. This combination produces accurate energies, is relatively simple to implement, and exhibits few of the problems associated with traditional techniques.     

Experimental comparisons of statistical uncertainties in analysis of nuclear spectra with the Cambio software application

Cambio is a software application well-suited for analysis of high-resolution nuclear spectral data in which the critical information resides in well-masked peaks or in which the data are sparse and good statistics cannot be obtained. The statistical uncertainty in the results is reported in terms of standard deviations. In the practical use of any analysis application, it is important to have a good understanding of the accuracy of the reported statistical uncertainties in the results. The authors report the results of an experiment that provides a quantitative measure of the accuracy of the reported uncertainties in analyses using Cambio. Ten calibration sources ranging in activity from 25 to 450 kBq were placed 20.5 m from a bare, 100 % relative-efficient high-purity germanium detector. Peaks in these sources occur from 20 to 2,800 keV. Data were accumulated for 128 h to create a parent spectrum from which 1024 8-hour statistically-equivalent daughter spectra were created by random sampling of the parent spectrum data. The parent spectrum was analyzed by fitting parameters which included an underlying continuum, a background of natural peaks adjusted by detector efficiency and material attenuation, and a foreground of the ten sources adjusted by detector efficiency only. Each of the daughter spectra were then analyzed starting with the parameters of the fit to the parent spectrum and then minimizing Chi-square with respect to changes in these parameters. The standard deviations of the estimated activities of the sources from all 1024 spectra were then calculated and compared to the reported statistical uncertainty in the activities and peak areas of the sources.     

Decay rates of select magnetic quadrupole transitions in helium

Using a set of explicitly correlated trial wavefunctions that describe the three lowest singlet and triplet states of the helium atom with symmetry S, P, and D, we calculate the decay rates for all possible magnetic quadrupole (M2) transitions: m³P₂→n¹S₀, m¹P₁→n³S₁, m³D₃→n¹P₁, and m¹D₂→n³P₂. Our values are in excellent agreement with the best results in the literature. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Analysis of nuclear spectra with non-linear techniques and its implementation in the Cambio software application

Popular nuclear spectral analysis applications typically use either the results of a peak search or of the best match of a set of linear templates as the basis for their conclusions. These well‐proven methods work well in controlled environments. However, they often fail in cases where the critical information resides in well-masked peaks, where the data is sparse and good statistics cannot be obtained, and where little is known about the detector that was used. These conditions are common in emergency analysis situations, but are also common in radio‐assay situations where background radiation is high and time is limited. To address these limitations, non‐linear fitting techniques have been introduced into an application called “Cambio” suitable for public use. With this approach, free parameters are varied in iterative steps to converge to values that minimize differences between the actual data and the approximating functions that correspond to the values of the parameters. For each trial nuclide, a single parameter is varied that often has a strongly non‐linear dependence on other, simultaneously varied parameters for energy calibration, attenuation by intervening matter, detector resolution, and peak-shape deviations. A brief overview of this technique and its implementation is presented, together with an example of its performance and differences from more common methods of nuclear spectral analysis.     

Noise Characterization for Laser Interferometer Gravitational Wave Detectors

This work incorporates a review of the status, in Australia, of data analysis for gravitational wave detection using laser interferometers, within an overview of the present state of such research in the world generally. In this context, data analysis refers not so much to signal simulation as to what might be called the thorough process of noise characterization and the subsequent, quality-controlled signal extraction. To the extent that problems identified here arise for all currently planned instruments, there is necessarily a global component to the discussion presented. In Australia, there are unique circumstances, associated with attempting to carry out work in gravitational wave detection, which demand also a local aspect to the ensuing discussion.     

Interferometric ultrafast SOA-based optical switches: From devices to applications

All-optical switches are fundamental building blocks for future, high-speed optical networks that utilize optical time division multiplexing (OTDM) techniques to achieve single channel data rates exceeding 100 Gb/s. Interferometric optical switches using semiconductor optical amplifier (SOA) non-linearities perform efficient optical switching with < 500 fJ of control energy and are approaching optical sampling bandwidths of nearly 1 THz. In this paper, we review work underway at Princeton University to characterize and demonstrate these optical switches as processing elements in practical networks and systems. Three interferometric optical switch geometries are presented and characterized. We discuss limitations on the minimum temporal width of the switching window and prospects for integrating the devices. Using these optical switches as demultiplexers, we demonstrate two 100-Gb/s testbeds for photonic packet switching. In addition to the optical networking applications, we have explored simultaneous wavelength conversion and pulse width management. We have also designed high bandwidth sampling systems using SOA-based optical switches as analog optical sampling gates capable of analyzing optical waveforms with bandwidths exceeding 100 GHz. We believe these devices represent a versatile approach to all-optical processing as a variety of applications can be performed without significantly changing the device architecture.     

Oscillator strengths of helium computed using Monte Carlo methods

We have optimized trial wave functions for the three lowest states of the helium atom with symmetry 1S, 1P, 1D, 3S, 3P, and 3D using variational Monte Carlo methods. With these wave functions we then computed dipole oscillator strengths for the 1S-1P, 1P-1D, 3S-3P, and 3P-3D transitions using the length, velocity, and acceleration forms. Our values are in good agreement with the best results found in the literature.