Melting model for modular self wiping co-rotating twin screw extruders

A model for the melting process in a self wiping co-rotating twin screw extruder is described. Self-wiping co-rotating twin screw extruders are modular and starve fed. This leads to melting mechanisms that are different from single screw extruders. The melting process in the modular screw configurations generally occurs in specialized sections such as kneading disk blocks. The model, based on our previous experimental observations, considers the formation of two stratified layers of melt in contact with the hot barrel and solid pellets in contact with the relatively colder screw. In the kneading disk blocks, a part of the solid bed is blocked because of the relative stagger between successive disks. The model predicts both the location of melting and melting lengths in a screw configuration. Calculations for individual screw elements and kneading disc elements are presented first. Melting in a modular configuration of these elements is then considered. The effect of operating variables such as mass flow rate and screw speed on melting is then studied. The model is put in a dimensionless form and the effect of various dimensionless groups is discussed. We make a comparison to the experiment and agreement is good.     

Comparison of iterative decoder performance with union bounds for short frame turbo codes

We consider short frame turbo codes, suitable for delay-sensitive services such as conversational speech, or for encoding single ATM cells. We compare the uniform interleaver bound of Benedetto and Montorsi, and a union bound obtained by estimating the weight distribution due to the actual pseudo-random interleaver, with the simulated BER using an iterative decoder. We show that the uniform interleaver bound is significantly pessimistic at high SNR, where the random interleaver union bound is quite close. However, at lower SNR the ber exceeds the union bound, showing that it does not achieve ml decoding. We also consider half rate turbo codes formed by puncturing various proportions of the data and parity sequences, and adapt the uniform interleaver bounds for these codes. We show that while the union bounds predict better performance for data-punctured codes, in practice they perform better only at high snr and for limited proportions of data puncturing.     

Stigmatized sources and persuasion: Prejudice as a determinant of argument scrutiny.

Two experiments examined the viability of several explanations for why majority group individuals process persuasive messages from stigmatized sources more than those from nonstigmatized sources. in each study. majority group participants who either were high or low in prejudice or were high or low in ambivalence toward a stigmatized source's group were exposed to a persuasive communication attributed to a stigmatized (Black, Experiment 1; homosexual, Experiment 2) or nonstigmatized (White, Experiment 1; heterosexual, Experiment 2) source. In both studies, source stigmatization increased message scrutiny only among those who were low in prejudice toward the stigmatized group. This finding is most consistent with the view that people scrutinize messages from stigmatized sources in order to guard against possibly unfair reactions by themselves or others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Azoospermia due to aperistalsis of the vas deferens: successful treatment with pseudoephedrine

Three patients presenting with infertility were found to have low volume azoospermia. All 3 were taking sympatholytic medications; 2 were taking antipsychotics and 1 was taking an alpha-blocker. Low volume azoospermia may result from the use of sympatholytic medications, which cause aperistalsis of the adrenergically innervated vas deferens and seminal vesicles. Two patients had normal spermatogenesis on biopsy and were unobstructed on vasography. In 1 patient, biopsy and vasography were avoided. Pseudoephedrine, a sympathomimetic agent, was given to all 3 patients, resulting in marked improvement in semen analysis parameters. A trial of pseudoephedrine can obviate the need for biopsy and vasography in such patients.     

Residual stresses in marine coatings under simulated service conditions

Studies have been made of the effect of cyclic temperature changes and wet/dry cycling on the residual stresses in marine coatings applied to steel substrates. A thermoplastic and a thermoset have been use as single coatings and as bi-layers consisting of the thermoset applied on top of the thermoplastic. Cyclic changes associated with differential thermal expansion/contraction between substrate and coating and with water absorption or desorption were observed, and it was found in addition that progressive changes in residual stress were sometimes superimposed on the cyclic changes. The effect was larger with the thermoplastic coating than with the thermoset. The stresses developed in the bi-layers were generally smaller than those in single layer coatings and were generally less sensitive to the cyclic changes in conditions. The effects were partly controlled by the thicknesses of the two layers in the bi-layer coatings. Stresses as high as 6 MPa were measured during the course of this work, a significant fraction of the failure strength of the coatings.     

ELIMIMATION OF RANDOM DEFACTS IN AEROSPACE MATERIALS

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Nanocomposite Materials Formed by Ion Implantation

Ion implantation has become a versatile and powerful technique for synthesizing nanometer‐scale clusters and crystals embedded in the near‐surface region of a variety of hosts in order to create nanocomposite materials with often unique optical, magnetic, and other properties. Here we review some of the principal features of this nanophase materials synthesis technique as well as the materials properties that are exhibited by nanocomposites created by using ion beams. Outstanding difficulties and future research directions are also discussed.     

Autonomous mobile robot global self-localization using Kohonen and region-feature neural networks

This article presents and compares two neural network-based approaches to global self-localization (GSL) for autonomous mobile robots using: (1) a Kohonen neural network, and (2) a region-feature neural network (RFNN). Both approaches categorize discrete regions of space (topographical nodes) in a manner similar to optical character recognition (OCR). That is, the mapped sonar data assumes the form of a character unique to that region. Hence, it is believed that an autonomous vehicle can determine which room it is in from sensory data gathered from exploration. With a robust exploration routine, the GSL solution can be time-, translation-, and rotation-invariant. The GSL solution can also become independent of the mobile robot used to collect the sensor data. This suggests that a single robot can transfer its knowledge of various learned regions to other mobile robots. The classification rate of both approaches are comparable and, thus, worthy of presentation. The observed pros and cons of both approaches are also discussed. © 1997 John Wiley & Sons, Inc.     

Photodegradation of polypropylene containing a nucleating agent

The effect of including 0.5 wt % talc on the photodegradation behavior of polypropylene (PP) was investigated in injection-molded samples exposed to ultraviolet radiation (UV) in the laboratory for periods of up to 24 weeks. The structure of the talc-nucleated samples was characterized by X-ray diffraction and light microscopy and compared with that of nonnucleated PP, and the information was used to explain the differences in their photodegradation behavior. Measurements of the extent of chemical degradation were made by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), and they showed that there is no significant effect of a nucleating agent on the kinetics of photooxidation. PP bars containing a nucleating agent showed a larger reduction in mechanical properties with UV exposure and a partial recovery in properties after prolonged exposure was observed with both types of samples. An increase in crystallinity during UV exposure (chemicrystallization) was detected by X-ray diffraction and differential scanning calorimetry (DSC) and the dependence with exposure time was similar in nucleated and nonnucleated samples. DSC was also used to determine the melting behavior and transition temperatures of the specimens during exposure and after recrystallization from the melt. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2505–2517, 1997     

Exploiting Airline Reservation Technologies to Improve Navy Training Management

The Navy trains hundreds of thousands of students every year. For Navy training, yield management means offering the right school seats to the right customers (e.g. active duty, reservists, foreign nationals) at the right time to maximize fleet readiness. The yield management methods will permit the Navy to make the best use of its limited training resources. This paper discusses the yield management technologies that will be tightly integrated into the Navy's new on-line training seat reservation system.