Quantum mechanics: cleaning up metaphysical baggage

The dynamic electronic structure of atoms and molecules can be directly observed by means of the (e, 2e) reaction, which measures the distribution of energies and momenta of two electrons in coincidence after a knockout reaction initiated by an electron beam of known momentum incident on a molecular gas target. The molecular state for each event is identified by the electron separation energy. The recoil momentum for each event is known from the difference of measured initial and final momenta. It has been verified that values of this momentum are equal under suitable conditions to the momentum of the electron in the target immediately before knockout. Thus the spherically-averaged electron momentum distribution for each molecular orbital is measured. This is directly related to molecular orbitals calculated by the methods of quantum chemistry. Properties obtained by this method for different types of molecules are discussed.     

SIR-C data quality and calibration results

The SIR-C/X-SAR imaging radar took its first flight on the Space Shuttle Endeavour in April 1994 and flew for a second time in October 1994. This multifrequency radar has fully polarimetric capability at L- and C-band, and a single polarization at X-band (X-SAR). The Endeavour missions were designated the Space Radar Laboratory-1 (SRL-1) and -2 (SRL-2). Calibration of polarimetric L- and C-band data for all the different modes SIR-C offers is an especially complicated problem. The solution involves extensive analysis of pre-flight test data to come up with a model of the system, analysis of in-flight test data to determine the antenna pattern and gains of the system during operation, and analysis of data from over fourteen calibration sites distributed around the SIR-C/X-SAR orbit track. The SRL missions were the first time a multifrequency polarimetric imaging radar employing a phased array antenna has been flown in space. Calibration of SIR-C data products involved some unique technical problems given the complexity of the radar system. In this paper, the approach adopted for calibration of SIR-C data is described and the calibration performance of the data products is presented     

Modifications to the Water Vapor Continuum in the Microwave Suggested by Ground-Based 150-GHz Observations

Ground-based observations from two different radiometers are used to evaluate commonly used microwave/millimeter-wave propagation models at 150 GHz. This frequency has strong sensitivity to changes in precipitable water vapor (PWV) and cloud liquid water. The observations were collected near Hesselbach, Germany, as part of the Atmospheric Radiation Measurement program's support of the General Observing Period and the Convective and Orographic Precipitation Study. The observations from the two radiometers agree well with each other, with a slope of 0.993 and a mean bias of 0.12 K. The observations demonstrate that the relative sensitivity of the different absorption models to PWV in clear-sky conditions at 150 GHz is significant and that four models differ significantly from the observed brightness temperature. These models were modified to get agreement with the 150-GHz observations, where the PWV ranged from 0.35 to 2.88 cm. The models were modified by adjusting the strength of the foreign- and self-broadened water vapor continuum coefficients, where the magnitude was model dependent. In all cases, the adjustment to the two components of the water vapor continuum was in opposite directions (i.e., increasing the contribution from the foreign-broadened component while decreasing contribution from the self-broadened component or vice versa). While the original models had significant disagreements relative to each other, the resulting modified models show much better agreement relative to each other throughout the microwave spectrum. The modified models were evaluated using independent observations at 31.4 GHz.     

A method for the manual extraction of business rules from legacy source code

One of the main barriers to the successful migration of legacy systems is lack of information about the system to be migrated.With the complexity of modern information systems, it is rarely the case that an organisation has a complete end-to-endunderstanding of its systems, business processes and information. This is particularly true of the business rules enforced by suchsystems, which are often poorly documented (if at all) and incompletely understood by those who own, use and maintain suchsystems. These business rules must be migrated, along with the other system functionality, but this is difficult when they areburied deep within the source code of the system. In this paper, we propose a method for the discovery of business rules throughinspection of the source code of legacy systems. We also describe the results of a comprehensive evaluation exercise undertakenwithin BT, in which the method was applied to a legacy system about to undergo migration. The results of this study indicatedconsiderable success for the method in extracting valid business rules, but also highlighted some weaknesses. Most significantly,the cost of applying the method is a factor of the size and complexity of the system being analysed, and not of the number ofbusiness rules elicited. In order to address this, we propose a cut-down version of the method that can be used to produce a quickestimate of the likely yield of business rules from a program. Together, these two forms of the method aid personnel engaged insystem migration projects in making maximum use of the scarce resources are available for business rule discovery.     

Direct digital synthesizer with ROM-Less architecture at 13-GHz clock frequency in InP DHBT technology

A direct digital synthesizer (DDS) implemented in InP double heterojunction bipolar transistor (DHBT) technology is reported. The DDS has a ROM-less architecture and instead uses digital logic for phase conversion. The DDS operates up to a 13 GHz clock rate and is capable of synthesizing output frequencies up to 6.5 GHz. Measured spurious free dynamic range (SFDR)ranged from 34 dBc at low frequency control words (FCWs) to 26.67 dBc at high FCWs. The test circuit is implemented with 1646 transistors and consumes 5.42W of power     

A reexamination of forward masking in the auditory nerve

Forward masking, as measured behaviorally, is defined as an increase in a signal's detection threshold resulting from a preceding masker. Previously, forward masking in the auditory nerve has been measured as a reduction in the neural response to a signal when preceded by a masker. However, detection threshold depends on both the magnitude of the response to the signal and the variance of the response. Thus changes in detectability cannot be inferred from response reduction alone. Relkin and Pelli (1987) have described a two-interval forced-choice procedure that may be used to measure the threshold for the detection of a probe signal in recordings of spike counts in single auditory neurons. These methods have been used to study the forward masking of characteristic frequency probe tones by characteristic frequency maskers as masker intensity was varied. Although the masker does reduce the detectability of the probe tone, it was found that the threshold shifts are much less than those observed behaviorally, particularly for intense maskers. In part, the small threshold shifts can be attributed to the reduction in response variance following the masker, which is the result of the adaptation of spontaneous activity. These results imply that behavioral forward masking must result from suboptimal processing of spike counts from auditory neurons at a location central to the auditory nerve.     

High-Brightness Wavelength Beam Combined Semiconductor Laser Diode Arrays

We report the wavelength beam combining of an array of high-power high-brightness 970-nm slab-coupled optical waveguide lasers. A 50-W peak power under quasi-continuous-wave (CW) operation was measured in an output beam with a beam quality of M_x,y ²=1.2, and 30 W under CW operation was measured with a beam quality of M_x,y ²=2     

Design of an ultra fast pipelined wavelength scheduler for optical burst switching

Optical Burst Switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over DWDM links without encountering O/E/O conversion. In OBS, before the transmission of a data burst, a burst header is transmitted through an electronic control path, setting up and tearing down optical paths on-the-fly. Data bursts can remain in the optical domain and pass through the OBS network transparently. Unfortunately, system performance will be greatly degraded, if burst scheduling requests cannot be processed in time. This article quantitatively studied the negative impact of control path overloading on the performance of OBS networks. Results have shown that control path overloading greatly affects the performance of the OBS routers, especially for systems with large WDM channel counts. In order to remove this performance bottleneck, we have designed and implemented an ultra fast pipelined burst scheduler that is able to process a burst request every two clock cycles, regardless of the number of WDM channels per link. The design has been implemented in Verilog HDL and synthesized to FPGAs. Circuit level simulation results confirm the correctness of the design. The circuit has achieved 100 MHz in Altera Cyclone II devices, allowing the scheduler to process a burst request every 20 ns. To the authors’ best knowledge, this is the fastest implementation of burst scheduling algorithms.     

4-bit adder-accumulator at 41-GHz clock frequency in InP DHBT technology

A 41-GHz 4-b adder-accumulator test circuit implemented in InP double heterojunction bipolar transistor (DHBT) technology using 624 transistors is reported. High clock rates are obtained by combining the logic functions into pipelined latches. The adder-accumulator contains a single-level parallel-gated carry circuit that is used as a step toward reduced power consumption. The carry circuit has a maximum clock frequency of 55 GHz. The accumulator architecture employs modular, pipelined 2-b adders and is cascadable to 2 N-bits. The test circuit includes a 4-b digital to analog converter (DAC) that facilitates demonstration of high-speed operation.