William B. Dress

Angle-resolved polarization-dependent photoemission spectra of benzenethiol adsorbed on Cu(110)

Abstract Angle-resolved photoelectron spectra of benzenethiol chemisorbed on the Cu(110) face have been obtained with p - and s -polarized HeI (21.2 eV) radiation at room temperature. Comparison with the gas-phase spectrum and molecular-orbital correlation diagrams indicates that the benzenethiol bonds to the copper by way of the sulfur, rather than phenyl ring π-orbitals, and that the adsorption is dissociative, yielding a phenyl sulfide (mercaptide) surface species. An analysis of the polarization/angular dependence of the band intensities and comparison to symmetry-allowed transitions confirms that the molecule has the plane of the phenyl ring perpendicular to the surface. The assumed C 2v symmetry together with packing considerations further allows the orientation of the molecule and nature of the bonding to be suggested.

A photospectrometer realized in a standard integrated circuit process

A photospectrometer has been realized in a standard integrated circuit (IC) process. Only the masks, materials, and fabrication steps inherent to this IC process were used (i.e., no post processing to add mechanical or optical devices for filtering). The spectrometer was composed of a set of 18 photodetectors with independent spectral responses. The responses of these devices were weighted and summed to form outputs proportional to the input optical power in discrete wavelength bands in the region from ∼400 to ∼1100 nm . With the solution space restricted to a 60 nm band, this instrument could resolve Gaussian input spectra (σ=5 nm ) with a peak-to-peak spacing of less than 15 nm. This device could easily be integrated with additional analog, digital, or wireless circuits to realize a true laboratory instrument on-a-chip.

Description of a polarized source of He i radiation for surface studies

A polarized radiation source has been designed and built for use in angular-resolved photoelectron spectroscopy on surfaces of single crystals under ultrahigh vacuum. The light from a discharge in helium is polarized by a triple reflection from a series of gold mirrors, producing a plane-polarized beam of He i radiation (21.22 eV) with a polarization of 80%. The plane of polarization can be rotated through more than 180 degrees without breaking vacuum. Details of the construction of the lamps are given, together with how it is integrated into the overall operation of the electron spectrometer. As an illustration of the lamps potential, data are shown on the photoemission studies of the (110) and (111) faces of copper as a function of both the orientation angle of the crystal and the polarization vector. A brief discussion of the future development and possible uses of the lamp is included.

Wavelet-based acoustic recognition of aircraft

We describe a wavelet-based technique for identifying aircraft from acoustic emissions during takeoff and landing. Tests show that the sensor can be a single, inexpensive hearing-aid microphone placed close to the ground. The paper describes data collection, analysis by various techniques, methods of event classification, and extraction of certain physical parameters from wavelet subspace projections. The primary goal of this paper is to show that wavelet analysis can be used as a divide-and- conquer first step in signal processing, providing simplification and noise filtering. The idea is to project the original signal onto the orthogonal wavelet subspaces, both details and approximations. Subsequent analysis, such as system identification, nonlinear systems analysis, and feature extraction, is then carried out on the various signal subspaces.

Automated alignment system for aspheric mirrors

This paper describes measurement algorithms and control procedures that can be effectively applied to the automation of an alignment procedure for paraboloidal optical mirrors. Interferometric alignment of an off-axis paraboloidal optical mirror can be a tedious and labor- intensive process. We review a previous solution to the alignment problem that employs a corner-cube retroreflector and present a method of automating this process using an imaging interferometer coupled to a processing system that controls a set of actuators. The relevant image-processing algorithms are described, and the actuator-control system is discussed. Methods of extending this solution to the automatic alignment of other aspheric optics are explored.

Enclosed space detection system (ESDS)

The Enclosed Space Detection System is a device to detect the presence of persons hiding in the enclosed spaces of a vehicle. The system operates by detecting the presence of the human ballistocardiogram.

A hardware implementation of multiresolution filtering for broadband instrumentation

The authors have constructed a wavelet processing board that implements a 14-level wavelet transform. The board uses a high-speed analog-to-digital (A/D) converter, a hardware queue, and five fixed-point digital signal processing (DSP) chips in a parallel pipeline architecture. All five processors are independently programmable. The board is designed as a general purpose engine for instrumentation applications requiring near real-time wavelet processing or multiscale filtering. The present application is the processing engine of a magnetic field monitor that covers 305 Hz through 5 MHz. The monitor is used for the detection of peak values of magnetic fields in nuclear power plants. This paper describes the design, development, simulation, and testing of the system. Specific issues include the conditioning of real-world signals for wavelet processing, practical trade-offs between queue length and filter length, selection of filter coefficients, simulation of a 14-octave filter bank, and limitations imposed by a fixed-point processor. Test results from the completed wavelet board are included.

A Bayesian approach to extracting meaning from system behavior

The modeling relation and its reformulation to include the semiotic hierarchy is essential for the understanding, control, and successful re-creation of natural systems. This presentation will argue for a careful application of Rosens modeling relationship (1985, 1991) to the problems of intelligence and autonomy in natural and artificial systems. The methods of Bayesian and maximum entropy parameter estimation have been applied to measurements of system observables to directly infer the underlying differential equations generating system behavior. This is computationally efficient, since only location parameters enter into the maximum-entropy calculations; nonlinear parameters are unneeded. Such an approach more directly extracts the semantics inherent in a given system by going to the root of system meaning as expressed by abstract form or shape. Empirical models are embodied by the differential equations underlying, producing, or describing the behavior of a process as measured or tracked by a particular variable set. The a priori models are probability structures that capture syntactical relationships within the formal system that mirrors the natural system under observation. Inductive learning is a prescription for incorporating the current, and possibly changing, empirical model into an iterative syntactical relationship. The probabilistic nature of the model descriptions replaces rigid structures. The structures evolve with both new knowledge and temporal evolution of the system.

Wavelet-based enhancements to nuclear quadrupole resonance explosives detectors

Nuclear Quadrupole Resonance (NQR) is effective for the detecting and identification of certain types of explosives such as RDX, PETN and TNT. In explosive detection, the NQR response of certain 14N nuclei present in the crystalline material is proved. The 14N nuclei possess a nuclear quadrupole moment which in the presence of an electric field gradient produces an energy level splitting which may be excited by radio-frequency magnetic fields. Pulsing on the sample with a radio signal of the appropriate frequency produces a transient NQR response which may then be detected. Since the resonant frequency is dependent upon both the quadrupole moment of the 14N nucleus and the nature of the local electric field gradients, it is very compound specific. Under DARPA sponsorship, the authors are using multiresolution methods to investigate the enhancement of operation of NQR explosives detectors used for mine detection. For this application, NQR processing time must be reduced to less than one second. False alarm response due to acoustic and piezoelectric ringing must be suppressed. Also, as TNT is the most prevalent explosive found in land mines NWR detection of TNT must be made practical despite unfavorable relaxation times. All three issues require improvement in signal-to-noise ratio, and all would benefit from improved feature extraction. This paper reports some of the insights provided by multiresolution methods that can be used to obtain these improvements. It includes results of multiresolution analysis of experimentally observed NQR signatures for RDX response and various false alarm signatures in the absence of explosive compounds.

Optical interconnect for large-scale systems

This paper presents a switchless, optical interconnect module that serves as a node in a network of identical distribution modules for large-scale systems. Thousands to millions of hosts or endpoints may be interconnected by a network of such modules, avoiding the need for multi-level switches. Several common network topologies are reviewed and their scaling properties assessed. The concept of message-flow routing is discussed in conjunction with the unique properties enabled by the optical distribution module where it is shown how top-down software control (global routing tables, spanning-tree algorithms) may be avoided.