QUANTIFICATION OF BITUMEN PARTICLES IN AEROSOL AND SOIL SAMPLES USING HP-GPC

A method for identifying and quantifying bitumen particles, generated from the wear of roadway asphalts, in aerosol and soil samples has been developed. Bitumen is found to be the only contributor to airborne particles containing organic molecules with molecular weights larger than 2000 g pr. mol. These are separated and identified using High Performance Gel Permeation Chromatography (HP-GPC) with fluorescence detection. As an additional detection method Infra Red spectrometry (IR) is employed for selected samples, The methods have been used on aerosol, soil and other samples.     

Measurement uncertainties arising from unpowered shipment of dcvoltage references

We have measured the hysteresis in output voltage arising from loss of power for three Fluke 732B dc voltage references. Continuously powering the internal temperature-controlled oven provides the best accuracy with such Zener-diode-based dc voltage references. Batteries are used to provide power continuity when shipping between laboratories. We have shown that for these particular instruments, an apparent hysteresis induced by humidity is likely to dominate any hysteresis arising from loss of battery power when transit between laboratories takes three days or more. Our conclusion is that as much, if not more, care needs to be taken when dealing with humidity than with loss of battery power when shipping between laboratories. When the highest accuracy of dc voltage comparison is required, it becomes necessary to apply voltage corrections using the measured values of humidity coefficients and the relative humidity occurring during transit     

Low threshold current densities for II-VI lasers

II-VI-semiconductor-based, green-light-emitting laser diodes with significantly improved characteristics are reported. Threshold current densities of 42 A/cm² are obtained. Novel contacts also lead to a 25% reduction in the threshold voltage and to an increased device lifetime by a factor of 24 as compared to previous results     

Successfully detecting and correcting false friends using channel profiles

The detection and correction of false friends—also called real-word errors—is a notoriously difficult problem. On realistic data, the break-even point for automatic correction so far could not be reached: the number of additional infelicitous corrections outnumbered the useful corrections. We present a new approach where we first compute a profile of the error channel for the given text. During the correction process, the profile (1) helps to restrict attention to a small set of “suspicious” lexical tokens of the input text where it is “plausible” to assume that the token represents a false friend. In this way, recognition of false friends is improved. Furthermore, the profile (2) helps to isolate the “most promising” correction suggestion for “suspicious” tokens. Using a conventional word trigram statistics for disambiguation we obtain a correction method that can be successfully applied to unrestricted text. In experiments for OCR documents, we show significant accuracy gains by fully automatic correction of false friends.     

REST2: High-performance solar radiation model for cloudless-sky irradiance, illuminance, and photosynthetically active radiation – Validation with a benchmark dataset

REST2, a high-performance model to predict cloudless-sky broadband irradiance, illuminance and photosynthetically active radiation (PAR) from atmospheric data, is presented. Its derivation uses the same two-band scheme as in the previous CPCR2 model, but with numerous improvements. Great attention is devoted to precisely account for the effect of aerosols, in particular.Detailed research-class measurements from Billings, OK are used to assess the performance of the model for the prediction of direct, diffuse and global broadband irradiance. These measurements were made in May 2003 during a sophisticated radiative closure experiment, which involved the best radiometric instrumentation currently available and many ancillary instruments. As a whole, these exceptional measurements constitute the only known modern benchmark dataset made specifically to test the intrinsic performance of radiation models. Using this dataset as reference, it is shown that REST2 performs better than CPCR2 for irradiance, illuminance or PAR predictions. The availability of the turbidity data required by REST2 or other similar models is also discussed, as well as the effect that turbidity has on each component of broadband irradiance, PAR irradiance and illuminance, and on the diffuse/global PAR ratio.