Noncontact measurement of electrostatic fields: verification of modeled potentials within ion mobility spectrometer drift tube designs

The heart of an ion mobility spectrometer is the drift region where ion separation occurs. While the electrostatic potentials within a drift tube design can be modeled, no method for independently validating the electrostatic field has previously been reported. Two basic drift tube designs were modeled using SIMION 7.0 to reveal the expected electrostatic fields: (1) A traditional alternating set of electrodes and insulators and (2) a truly linear drift tube. One version of the alternating electrode/insulator drift tube and two versions of linear drift tubes were then fabricated. The stacked alternating electrodes/insulators were connected through a resistor network to generate the electrostatic gradient in the drift tube. The two linear drift tube designs consisted of two types of resistive drift tubes with one tube consisting of a resistive coating within an insulating tube and the other tube composed of resistive ferrites. The electrostatic fields within each type of drift tube were then evaluated by a noncontact method using a Kelvin-Zisman type electrostatic voltmeter and probe (results for alternative measurement methods provided in supplementary material). The experimental results were then compared with the electrostatic fields predicted by SIMION. Both the modeling and experimental measurements reveal that the electrostatic fields within a stacked ion mobility spectrometer drift tube are only pseudo-linear, while the electrostatic fields within a resistive drift tube approach perfect linearity.     

Coagulation dynamics of fractal flocs induced by enmeshment and electrostatic patch mechanisms

The size and structure of flocs during floc formation were monitored for various coagulation mechanisms. Two distinctive mechanisms, namely, enmeshment and electrostatic patch, govern the dynamics of kaolin particles coagulation by polyaluminum chloride (PACl). They were investigated by small angle static light scattering (SASLS) and solid-state ²⁷Al NMR. In addition, a novel wet SEM (WSEM) was used in-situ to image the morphology of the aggregate in aqueous solution. Synthetic suspended particles were coagulated by two PACl products, a commercial product (PACl) and one laboratory product (PACl-E). The PACl-E contained more than 60% Al₁₃ while the PACl contained only 7% Al₁₃, with large percentage of colloidal Al. For coagulation by PACl at neutral pH and high dosage where the strong repulsion between particles occurs, the enmeshment ruled by reaction-limited aggregation (RLA) results in larger sweep flocs as well as higher fractal dimensional structure. For coagulation by PACl-E at alkaline pH and low dosage, the flocs were coagulated predominately by electrostatic patch with Al₁₃ aggregates. At such condition, it is likely that diffusion-limited aggregation (DLA) predominately rule PACl-E coagulation. The fractal dimension (D_s) values of PACl and PACl-E flocs formed at enmeshment and electrostatic patch increased with dosage, respectively. When breakage of flocs occurs, the breakage rate of PACl-E flocs is slower than that of sweep flocs. By WSEM imaging, the adsorption of spherical Al precipitates onto the particles was observed to form sweep flocs with a rough and ragged contour, while the PACl-E flocs were formed with a smooth and glossy structure.     

Internal dose assessments: uncertainty studies and update of ideas guidelines and databases within CONRAD project

The work of Task Group 5.1 (uncertainty studies and revision of IDEAS guidelines) and Task Group 5.5 (update of IDEAS databases) of the CONRAD project is described. Scattering factor (SF) values (i.e. measurement uncertainties) have been calculated for different radionuclides and types of monitoring data using real data contained in the IDEAS Internal Contamination Database. Based upon this work and other published values, default SF values are suggested. Uncertainty studies have been carried out using both a Bayesian approach as well as a frequentist (classical) approach. The IDEAS guidelines have been revised in areas relating to the evaluation of an effective AMAD, guidance is given on evaluating wound cases with the NCRP wound model and suggestions made on the number and type of measurements required for dose assessment.     

Subsecond detection of physiological adenosine concentrations using fast-scan cyclic voltammetry

Adenosine modulates blood flow and neurotransmission and may be protective during pathological conditions such as ischemia and stroke. A real-time sensor of adenosine concentrations is needed to understand its physiological actions and the extent of receptor activation. Microelectrodes are advantageous for in vivo measurements because they are small and can make fast measurements. The goal of this study was to characterize detection of physiological adenosine concentration changes at carbon-fiber microelectrodes with subsecond temporal resolution. The oxidation potential of adenosine is +1.3 V, so fast-scan cyclic voltammetry (FSCV) was performed with an applied potential from -0.4 to 1.5 V and back at 400 V/s every 100 ms. Two oxidation peaks were detected for adenosine with T-650 carbon fibers. The second oxidation peak at 1.0 V occurs after the initial oxidation at 1.5 V and is due to a sequential oxidation step. Adsorption was maximized to obtain detection limits of 15 nM, lower than basal adenosine concentrations in the brain. The electrode was insensitive to the metabolite inosine and seven times more sensitive to adenosine than ATP. The enzymatic degradation of adenosine was monitored with FSCV. This microelectrode sensor will be valuable for biological monitoring of adenosine.     

Packaging postponement: a global packaging strategy

Postponement applications have been growing in recent years as international firms increasingly develop global products that are customized for local markets. The purpose of this article is to provide an understanding of the logistical principles of postponement and speculation. It explores the factors that favour packaging postponement: (a) modular products that can be customized for local markets; (b) products that gain volume, weight or value from packing; (c) unpredictable demand; (d) a large number of market‐based variations for a single formulation; and (e) situations where economies of scale in packaging and logistics can be optimized. Examples are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

Students’ perceptions of teaching technologies, application of technologies, and academic performance

This study examined business students’ perceptions of four objectives (i.e., Enjoyment, Learning, Motivation, and Career Application) across five teaching technologies (i.e., Projector, PowerPoint, Video, the Internet, and Lecture), business professors’ effective application of technologies, and students’ academic performance. We collected data from 215 students at a regional state university in the USA. We developed Students’ Perceptions of Technology Scale, SPOTS, specifically for the present study, used the most rigorous criteria, and investigated reliability, convergent and discriminant validity, exploratory and confirmatory factor analysis, and measurement invariance of this scale. Mean scores revealed that Video conveyed the highest amount of Enjoyment. PowerPoint provided the highest amount of Learning and Motivation. The Internet provided the highest Career Application for future jobs. Younger students preferred Video, whereas older students favored Lecture. Regression results showed that the use of Video for Learning, Projector and Lecture for Enjoyment, PowerPoint for career and Motivation, and the Internet for Learning contributed to professors’ teaching effectiveness. Students’ high ratings for professors’ effective use of the Lecture method and low expectation for the use of a Projector predicted their self-reported GPA (academic performance). Professors may use a different mix of technologies in the classroom and use them creatively in order to promote the most Learning for students and satisfy students’ Learning needs and objectives.     

Sub-Critical Crack Growth Behavior of a Low-Temperature Co-Fired Ceramic

The strength of sintered low-temperature co-fired ceramic (LTCC) disks was measured under dry (<2% relative humidity [RH]) and wet (98% RH) conditions, using ring-on-ring, biaxial-flexure testing in the stressing rate range of 0.002–2 MPa/s. The empirical sub-critical crack growth parameters, n and A , were calculated. The values of the parameters in the wet environment were higher than in the dry environment. It is argued that the high RH n value is more representative of material behavior. Results of fractographic examination are reported and expected lifetime and safe design stresses for LTCC are calculated.     

Detection of low-abundance protein phosphorylation by selective (18)o labeling and mass spectrometry

Reversible phosphorylation regulates the majority of intracellular networking and pathways. The study of this widely explored post-translational modification is usually challenged by low stoichiometric levels of modification. Many approaches have been developed to overcome this problem and to achieve rigorous characterization of protein phosphorylation. We describe a method for enhanced detection of low-abundance protein phosphorylation that uses selective introduction of (18)O label into phosphorylation sites with H(2)(18)O and mass spectrometric detection. The method was applied to introduce (18)O label into bacterially expressed Aurora A kinase phosphorylation sites and resulted in the representation of phosphorylated peptides as doublets or triplets according to the number of phosphate groups. A total of 28 phosphopeptides were observed by this method.