Packed extraction columns: A review of correlations for maximum throughput

A considerable amount of experimental data on maximum flow rates of countercurrently flowing liquid phases in packed columns has been published and a number of correlations for flooding velocities have been proposed. In the present paper various correlations are tested, using the same set of experimental results selected according to plausible criteria. The results of the test are presented in a consistent manner. Reasons why the result arrived at in this review differ from the recommendation given in Reference 10 are discussed.     

Osmotic pressure of very dilute liquid mixtures of3He in4He

The osmotic pressure of very dilute liquid mixtures of³He in⁴He has been measured for the concentration range 0.08–0.6 mole%³He, and the temperature range 20–400 mK. The results are used to check the validity of different proposals for the³He–³He effective interaction.Work supported in part by the Gerald I. Swope Fund and the Batsheva de Rothschild Foundation.     

Zur Frage der Entstehung von Nitrosaminen bei der Reaktion von Monosacchariden mit Aminos?uren (Maillard-Reaktion)

Zusammeufassung Zur Überprüfung des Auftretens von Nitrosaminen [2] im Rahmen der Maillard-Reaktion wurden die flüchtigen Produkte verschiedener Glucose-Aminosäure-Modell-gemische durch Kombination von Gaschromatographie and Massenspektrometrie, Polarographie und Dünnschicht-Chromatographie untersucht. Das Auftreten von Nitrosaminen kann durch die Ergebnisse eindeutig ausgeschlossen werden.

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The problem of formation of nitrosamines by reacting monosaccharides with aminoacids (maillard-reaction)

Summary For proving the formation of nitrosamines applying maillardconditions [2] we tested the volatile reaction products of various glucose-aminoacid mixtures by coupling gas chromatography and mass spectrometry, polarography and thin-layer chromatography. The appearence of nitrosamines could undoubtedly be excluded according to the results.

     

Temperature gradients in the channels of a single‐screw extruder

We used a temperature‐sensitive fluorescent dye, perylene, to monitor the true resin temperature during extrusion of polycarbonate. The measurement involved doping polycarbonate with perylene and detecting fluorescence with an optical sensor that accesses a standard instrumentation port on a barrel of a single‐screw extruder. The sensor's confocal optics design permits fluorescence intensity measurements as a function of position. Using a previously established calibration function, temperature and temperature gradients were obtained from the measured fluorescence. Because the origin of the measurement is the fluorescent dye molecule that is soluble in the resin, this method allows temperature measurement of the polymer without interference from the surrounding metal parts. With the sensor looking over the screw, temperature profiles from the barrel wall to the core of the screw were obtained as a function of screw speed, screw design and resin melt flow rate. Polym. Eng. Sci. 44:2148–2157, 2004. © 2004 Society of Plastics Engineers.

1 This paper is a contribution from the National Institute of Standards and Technology, and, thus, is not subject to copyright in the United States.

     

Solid fuel combustion experiments in microgravity using a continuous fuel dispenser and related numerical simulations

The conventional way of determining the flammability characteristics of a material involves a number of tedious single-sample tests to distinguish flammable from non-flammable conditions. A novel test device and fuel configuration has been developed that permits multiple successive tests for indefinite lengths of thin solid materials. In this device, a spreading flame can be established and held at a fixed location in front of optimized diagnostics while continuous variations of test parameters are made. This device is especially well-suited to conducting experiments in space (e.g. aboard the International Space Station) where the limited resources of stowage, volume, and crew time pose major constraints. A prototype version of this device was tested successfully in both a normal gravity laboratory and during low-gravity aircraft trials. As part of this ongoing study of material flammability behavior, a numerical model of concurrent-flow flame spread is used to simulate the flame. Two and three-dimensional steady-state forms of the compressible Navier-Stokes equations with chemical reactions and gas and solid radiation are solved. The model is used to assist in the design of the test apparatus and to interpret the results of microgravity experiments. This paper describes details of the fuel testing device and planned experiment diagnostics. A special fuel, developed to optimize use of the special testing device, is described. Some results of the numerical flame spread model are presented to explain the three-dimensional nature of flames spreading in concurrent flow and to show how the model is used as an experiment design tool.     

Computer-assisted assessment of depression and function in older primary care patients

We wanted to test the psychometric reliability and validity of self-reported information on psychological and functional status gathered by computer in a sample of primary care outpatients. Persons aged 65 years and older visiting a primary care medical practice in Baltimore (n=240) were approached. Complete baseline data were obtained for 54 patients and 34 patients completed 1-week retest follow-up. Standard instruments were administered by computer and also given as paper and pencil tests. Test-retest reliability estimates were calculated and comparisons across mode of administration were made. Separately, an interviewer administered a questionnaire to gauge patient attitudes and feelings after using the computer. Most participants (72%) reported no previous computer use. Nevertheless, inter-method reliability of the GDS15 at baseline (0.719, n=47), intra-method reliability of the computer in time (0.797, n=31), inter-method reliability of the CESDR20 at baseline (0.740, n=53), and the correlation between the CESDR20 computer version at baseline and follow-up (0.849, n=34) were all excellent. The inter-method reliability of the CESDR20 at follow-up (0.615, n=37) was lower but still acceptable. Although 28% were anxious prior to using the computer testing system, that percent decreased to 19% while using the system. The efficiency and reliability in comparison to the paper instruments were good or better. Even though most participants had not ever used a computer prior to participating in the study, they had generally favorable attitudes toward the use of computers, and also reported having favorable experience with the computer testing system.     

Integrating Guidance into Relational Reinforcement Learning

Reinforcement learning, and Q-learning in particular, encounter two major problems when dealing with large state spaces. First, learning the Q-function in tabular form may be infeasible because of the excessive amount of memory needed to store the table, and because the Q-function only converges after each state has been visited multiple times. Second, rewards in the state space may be so sparse that with random exploration they will only be discovered extremely slowly. The first problem is often solved by learning a generalization of the encountered examples (e.g., using a neural net or decision tree). Relational reinforcement learning (RRL) is such an approach; it makes Q-learning feasible in structural domains by incorporating a relational learner into Q-learning. The problem of sparse rewards has not been addressed for RRL. This paper presents a solution based on the use of reasonable policies to provide guidance. Different types of policies and different strategies to supply guidance through these policies are discussed and evaluated experimentally in several relational domains to show the merits of the approach.     

Structural relationships between measures based on heart beat intervals: potential for improved risk assessment

Decreased left ventricular ejection fraction is the most commonly used risk factor for identification of patients at high-risk for lethal ventricular arrhythmic events. Twenty-four-hour electrocardiographic (ECG) approaches to risk stratification include: counts of ventricular premature contractions (VPCs), measures of heart rate variability (HRV), and heart rate turbulence (HRT) which has two components, turbulence onset and turbulence slope (TS). Refinement of these ECG risk stratifiers could enhance their clinical utility. We explored the structural relationships between heart rate (HR) and HRV and HRT measures. Our goal was to separate out the component of these measures due to the underlying average heart rate (HR), thus potentially reducing the variability of the measures and increasing their power to stratify risk. We proposed re-scaling tachograms of heart-beat intervals so that the re-scaled tachogram has a HR of 75 (or equivalently an average interval of 800 ms) and calculating HRV and HRT from the rescaled time series. We also explored the relationship between the number of VPCs and HRT. We showed that TS is structurally related to the number of VPCs (and hence to the length of the ECG recording). We proposed an adjusted TS that is independent of the number of VPCs. We also addressed the ability of shorter ECG recording to estimate HRV and HRT measures. We evaluated standard and rescaled HRV and HRT measures using qualifying ambulatory ECG recordings from 744 patients in the Cardiac Arrhythmia Suppression Trial. We found that measures based on the rescaled tachogram had reduced variance (20% to 40%). Correlations between measures were also substantially reduced. We also found substantial circadian effects on some, but not all HRV indices, not explained by the circadian pattern in HR and possibly pointing to additional measures for risk prediction. In conclusion, we found that adjusting for HR and the number of VPCs in heart-beat related ambulatory ECG measures has the potential to significantly improve the power of these measures to risk stratify cardiac patients.     

Kinematisch bedingte Auswanderungserscheinungen bei periodisch schwingenden Waagen

Zusammenfassung W?gungen auf Hebelwaagen sind statische Messungen. Der Schwerkraft der zu w?genden Masse wird von der Waage eine konstante Me?kraft entgegengesetzt. Da sich jedoch innerhalb des selbstanzeigenden Bereichs die Me?kraft unter ?nderung des Ausschlags der Hebelkette selbst?ndig einstellt, bilden Waagen schwingungsf?hige Systeme, und zwar im allgemeinen nichtlineare Schwinger mit entsprechenden Eigenschaften. Unter diesen nimmt das Auswandern der Anzeige eine besondere Stellung ein, weil sich dabei die Mittellage der Schwingung gegenüber der statischen Gleichgewichtslage verschiebt. Diese Verschiebung kann von einem W?ger oder einem Me?wertgeber grunds?tzlich nicht erkannt werden und geht voll als Fehler in die W?gung ein.