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.

     

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.     

Compact spot-size converters with fiber-matched antiresonant reflecting optical waveguides

We propose a concept for InGaAsP-InP 1.55-microm lasers integrated with spot-size converters based on modal interference between the modes of the structure formed by an active waveguide and an underlying fiber-matched antiresonant reflecting optical waveguide. Simulation results show that the spot-size converters exhibit low transformation loss, and narrowed far-field emission patterns (10 degrees x 20 degrees) and reduce the coupling loss to standard single-mode fibers from 8 to 2.6 dB over lengths approximately 200 microm shorter than the adiabatic concept. A tolerant design to fabrication variations is also proposed, which could be realized by standard processing techniques.     

The Hydrogeochemistry of Arsenic in the Clara Mine,Germany

Abstract.   The oxidative dissolution of primary arsenic-bearing sulfide minerals in barite-fluorite veins is a potential source of arsenic in the Clara Mine. Geological structures, especially the mineral veins, provide potential pathways for the water. The highest arsenic concentrations are found in ground water within the eastern part of the mine. Arsenic and major ions are positively correlated and provide evidence that arsenic is likely derived locally from the water-vein/water-rock interaction. Geochemical modeling with PHREEQC shows all the arsenate mineral phases to be significantly undersaturated, although secondary arsenate minerals are common in the oxidized part of the deposit. The mine waters plot near the boundary of Fe(OH)₃ and Fe²⁺ in the pH-Eh diagram for the As-Fe-S-H₂O-system. Arsenic occurs as the 5-valent species and . Statistical analysis illustrates a strong association between As, Fe, pH, and HCO₃. Oxidation of the primary As-bearing minerals, such as pyrite and arsenopyrite, and the subsequent behavior of the oxyanion, arsenate, generally controls the distribution and speciation of arsenic. The low concentrations of dissolved As is due to co-precipitation and adsorption of arsenate by Fe, Al, and Mn (oxy)hydroxides.     

Coded excitation with spectrum inversion (CEXSI) for ultrasound array imaging

In this paper, a scheme called coded excitation with spectrum inversion (CEXSI) is presented. An established optimal binary code whose spectrum has no s and possesses the least variation is encoded as a burst for transmission. Using this optimal code, the decoding filter can be derived directly from its inverse spectrum. Various transmission techniques can be used to improve energy coupling within the system pass-band. We demonstrate its potential to achieve excellent decoding with very low (<80 dB) side-lobes. For a 2.6 /spl mu/s code, an array element with a center frequency of 10 MHz and fractional bandwidth of 38%, range side-lobes of about 40 dB have been achieved experimentally with little compromise in range resolution. The signal-to-noise ratio (SNR) improvement also has been characterized at about 14 dB. Along with simulations and experimental data, we present a formulation of the scheme, according to which CEXSI can be extended to improve SNR in sparse array imaging in general.     

Synthesis of Si3N4 using sepiolite and various sources of carbon

Sepiolite of Turkish origin was used as Si precursor in the syntheses of silicon nitride (Si₃N₄) powders by carbothermal reduction-nitridation (CRN) by mixing with several reducing agents i.e. charcoal, carbon black and petroleum coke as discrete particles and acrylonitrile as an intercalation medium. Purified sepiolite samples with a pre-determined C/SiO₂ ratio of 4 yielded Si₃N₄ powders after firing at temperatures 1300–1475°C under continuous nitrogen flow. The various sepiolite-reducing agent combinations were evaluated. The / ratio and secondary phase content of the powders after CRN were found to depend on temperature, time, heating rate and on the physicochemical properties of the precursor used such as, surface area and mixing of the reactants.