Measurements of chemical warfare agent degradation products using an electrophoresis microchip with contactless conductivity detector

This paper reports on a microfluidic device for the screening of organophosphonate nerve agent degradation products. The miniaturized system relies on an efficient chip-based separation of alkyl methylphosphonic acids (breakdown products of Sarin, Soman, and VX nerve agents) followed by their sensitive contactless conductivity detection. Experimental parameters relevant to the separation and detection processes have been optimized to yield high sensitivity (with 48-86 microg L(-1) detection limits), fast response (50 s for a three alkyl methylphosphonic acid mixture), high precision (RSD = 3.8-5.0%), and good linearity (over the 0.3-100 mg L(-1) range). Applicability to natural (river) water samples is demonstrated. The new microsystem offers promise for monitoring degradation products of chemical warfare agents, with advantages of speed/warning, efficiency, portability, sample size, and cost compared to conventional ion chromatography or capillary electrophoresis systems.     

4-Nitro-7-piperazino-2,1,3-benzoxadiazole as a reagent for monitoring of airborne isocyanates by liquid chromatography

4-Nitro-7-piperazino-2,1,3-benzoxadiazole (NBDPZ) is presented as a new reagent for the determination of mono- and diisocyanates in air samples. NBDPZ readily reacts with the airborne analytes, thus yielding the corresponding urea derivatives, which are subsequently separated by means of reversed-phase liquid chromatography. On a phenyl-modified stationary phase, excellent baseline separation for numerous mono- and diisocyanate derivatives is obtained. Both diode array and fluorescence detection are performed with limits of detection of 11-35 and 5-9 nmol/L for the individual derivatives, respectively. In contrast to established derivatizing agents for the analysis of isocyanates, NBDPZ provides for increased selectivity due to the favorable detection wavelengths in the visible range (UV/visible, absorption maximums approximately 480 nm; fluorescence, excitation maximums approximately 470 nm, emission maximums approximately 535 nm). In addition, the high molar absorptivities of the reagent and the derivatives provide excellent sensitivity that is superior to most literature-known methods. Finally, air sampling methods comprising both the use of impingers and test tubes are developed and successfully applied to the determination of isocyanates in gaseous samples. Excellent recovery reaching values of >90% is observed for each of the two techniques investigated.     

Holographically recorded photopolymer diffractive optical element for holographic and electronic speckle-pattern interferometry

A diffractive optical element is described that can be used to implement a very simple self-aligning electronic speckle-pattern interferometer and holographic interferometer that requires only a laser source and a camera in the optical setup.     

Retrieval of the ultraviolet aerosol optical depth during a spring campaign in the Bavarian Alps

A measurement campaign was organized in March 1999 in the Bavarian Alps as part of the European project, Characteristics of the UV Radiation Field in the Alps (CUVRA), to analyze the effect of altitude, aerosols, and snow cover on ground-level UV spectral irradiance. We present the results of simultaneous measurements of aerosol optical depth (AOD) made at various sites on two cloudless days in March 1999. The two days exhibited different aerosol conditions. Results derived from spectral measurements of UV irradiance are compared with data from filter radiometer measurements made at discrete wavelengths extending from the UV to the near IR. The different methods generated values for the AOD that were in good agreement. This result confirms that one can use either method to retrieve the AOD with an uncertainty of approximately 0.03-0.05. On 18 March, high turbidity was observed at low altitude (400-nm AOD approximately 0.5 at 700 m above sea level), and the AOD decreased regularly with altitude; on 24 March, the turbidity was much less (0.11 at 700 m above sea level). On both days very low AODs (0.05-0.09) were measured at 3000 m above sea level. The spectral dependence of the AOD is often parameterized by the angstrom relationship; the alpha parameter is generally difficult or impossible to retrieve from spectral measurements because of the relatively narrow wavelength range (320-400 nm), and only one of the spectro-radiometers used during the campaign permits this retrieval. In most cases, during this field campaign, alpha was found by filter sunphotometers to be 1.1-1.5.     

Autocompensating interferometer for measuring the changes in refractive index of supercooled water as a function of temperature at 632.8 nm

An interferometric arrangement that automatically compensates for thermal expansion was used to examine the changes in the refractive index of liquid water at 632.8 nm as a function of temperature from 10 to -15 degrees C. By combining the results of this research with existing data, we calculated the absolute refractive index in the supercooled region with an accuracy ranging from 3 x 10(-6) to 1 x 10(-6). A direct observation of the refractive-index maximum of water is reported for the first time to our knowledge and found to occur between 0 and 0.1 degrees C.     

On functionally graded balls and cones

The heat equation, for both steady and unsteady situations, is considered when the material parameters are spherically symmetric functions of position. Explicit separated solutions are derived when the material parameters are exponential functions; the radial part of these solutions is given in terms of confluent hypergeometric functions or Whittaker functions. In the steady case, explicit solutions are found when the conductivity k(r)= exp(–r ^q), where and q are parameters with q>0. The behaviour near the tip of a spherically-graded cone is also investigated.     

Pathomechanisms of work-related musculoskeletal disorders: conceptual issues

Work-related musculoskeletal disorders (WRMSDs) by definition are a subset of musculoskeletal disorders (MSDs) that arise out of occupational exposures. While traditional exposure assessment techniques have proved to be successful in identifying ergonomic exposures that are epidemiologically linked to these disorders, some are troubled by the lack of one-to-one correspondence between specific occupational exposure profiles and specific MSDs. In the absence of more sophisticated hypotheses that might explain the occurrence of WRMSDs in a variety of exposure patterns, the aetiologic relationships may (again) be called into question. Another unanswered question is whether specific types of WRMSDs have qualitatively different exposure-response relationships. A clearer understanding of the underlying pathomechanisms associated with specific WRMSDs could help future researchers better determine how and when various occupational exposure profiles become pathogenic. Such knowledge could also be used to design exposure assessment tools to capture exposure information more relevant to the risk of WRMSDs. The main goals of this paper are to summarize several recently described pathomechanisms, most of which have been discussed primarily in clinical and experimental literature that might not be widely read by occupational health scientists. Suggestions are made as to how future research could evaluate whether these phenomena are relevant to the effects of physical exposures and the underlying disease processes of common WRMSDs.     

Effects of display design on performance in a simulated ship navigation environment

Although automation is playing an increasing role on the ship's bridge, empirical research on the effectiveness of alternative bridge designs is limited. In this paper, we describe an experimental study of the benefits of integrated information display, using a computerized simulation of a highly automated ship's bridge. The study compared three types of interface design, which presented radar and electronic chart information to the operator in different ways: (a) integrated display, (b) functionally-separate display, and (c) spatially-separate display. Effects were examined in relation to time on watch and scenario complexity. Following extensive training on the task, 39 participants were tested over a 4-h experimental session, during which they encountered a sequence of collision scenarios of varying complexity. Using a dual-task methodology, a range of measures of primary and secondary task performance were taken, together with assessment of information sampling behaviour and subjective operator state (workload, fatigue, anxiety and situation awareness). The results indicated slight navigational advantages of the integrated display over the two alternative display types, although it also incurred higher levels of operator cost, particularly fatigue. There were no marked effects of time on watch, but more complex scenarios were associated with impaired performance, increased workload and reduced situation awareness. Overall, the findings have suggested some benefits of integrating primary information sources in a ship's bridge environment. The study further confirms the value of experimental simulations as tools for investigating design issues for ship's bridge automation.     

Activity-dependent development of axonal and dendritic delays, or, why synaptic transmission should be unreliable

Systematic temporal relations between single neuronal activities or population activities are ubiquitous in the brain. No experimental evidence, however, exists for a direct modification of neuronal delays during Hebbian-type stimulation protocols. We show that in fact an explicit delay adaptation is not needed if one assumes that the synaptic strengths are modified according to the recently observed temporally asymmetric learning rule with the downregulating branch dominating the upregulating branch. During development, slow, unbiased fluctuations in the transmission time, together with temporally correlated network activity, may control neural growth and implicitly induce drifts in the axonal delays and dendritic latencies. These delays and latencies become optimally tuned in the sense that the synaptic response tends to peak in the soma of the postsynaptic cell if this is most likely to fire. The nature of the selection process requires unreliable synapses in order to give successful synapses an evolutionary advantage over the others. The width of the learning function also determines the preferred dendritic delay and the preferred width of the postsynaptic response. Hence, it may implicitly determine whether a synaptic connection provides a precisely timed or a broadly tuned "contextual" signal.     

United States copyright law and digital sampling: Adding color to a grey area

This study evaluates the current application of United States copyright law in music sampling cases and used the Danger Mouse's Grey Album as a case in point. The following research questions structured the investigation: Are the current applications of United States copyright law appropriate for digital sampling in an international intellectual property environment? Is the practice of digital sampling stealing or recycling? How might the American legislature change copyright law to more clearly guide musical artists on the use of digital sampling? The research includes a review of sampling and its history, international and American copyright history, and the applicable elements of the Copyright Act of 1976, as well as interviews with legal professionals and musicians. The research suggests that the Copyright Act of 1976 is not adequate to address the technology and practices of digital sampling musicians, and that Congress needs to act precisely to amend the law and meet international legal standards.