Single stage, low noise advanced technology fan. Volume 3: Acoustic design

The acoustic design for a half-scale fan vehicle, which would have application on an advanced transport aircraft, is described. The single stage advanced technology fan was designed to a pressure ratio of 1.8 at a tip speed of 503 m/sec (1,650 ft/sec). The two basic approaches taken in the acoustic design were: (1) minimization of noise at the source, and (2) suppression of the generated noise in the inlet and bypass exhaust duct. Suppression of the generated noise is accomplished in the inlet through use of the hybrid concept (wall acoustic treatment plus airflow acceleration suppression) and in the exhaust duct with extensive acoustic treatment including a splitter. The goal of the design was attainment of twenty effective perceived noise decibels (20 EPNdB) below current Federal Air Regulation noise standards for a full-scale fan at the takeoff, cutback, and approach conditions. Predicted unsuppressed and suppressed fore and aft maximum perceived noise levels indicate that the cutback condition is the most critical with respect to the goal, which is probably unattainable for that condition. This is also true for aft radiated noise in the approach condition

The Discourse of Voicemail

This paper attempts to determine to what degree voicemail messages can be considered a discourse genre – that is, to what degree and in what ways they appear to be uniform across speakers. Thirty-seven voice messages were recorded from the cellular phones of three University of Michigan students. The messages were analyzed in terms of their overall structure, the discursive functions that were executed therein, and the specific words, phrases and prosodic strategies that were used to execute certain functions. The messages were found to have highly uniform openings and closings, and the message bodies were found to reduce to a small set of discursive functions. In addition, certain words, phrases and devices appeared frequently and in predictable locations within the messages. It is concluded that voicemail message-leaving is a highly structured act governed by conventions that arise both from face-to-face conversation and from the specific constraints of the medium

Do multiple conditions elicit the visual redundant signals effect in simple response times?

The redundant signals effect, or redundancy gain, is an increase in human processing efficiency when target redundancy is introduced into a display. An advantage for two visual signals over one has been found in a wide variety of speeded response time tasks, but does not always occur and may be weakened by some task parameters. These disparate results suggest that visual redundancy gain is not a unitary effect, but is instead based on different underlying mechanisms in different tasks. The current study synthesizes previous theories applied to redundancy gain into the three-conditions hypothesis, which states that visual redundancy gain depends on the presence of at least one of three factors: visual identicalness between multiple targets, familiarity with multiple similar targets, or prepotentiation for multiple different targets. In a series of four simple response time experiments, participants responded to single targets presented to one side of the visual field, or to bilateral targets presented to both sides of the visual field. The first three experiments each explored one condition, the first experiment by comparing identical to non-identical random shapes to examine visual identicalness, the second by comparing familiar to unfamiliar letters to examine familiarity, and the third by comparing previewed with non-previewed random shapes to examine prepotentiation. Finally, the fourth experiment employed letters that varied in familiarity, identicalness, and preview, to examine whether or not the three hypothesized causes have multiplicative effects on redundancy. Results indicated that participants were able to benefit equally from redundancy regardless of identicalness, familiarity, or prepotentiation, but that they did so by ignoring one target in the redundant-target trials. These results suggest that redundancy gain may need to be even further divided into more than three underlying mechanisms, with a serial processing mechanism that can be used for stimuli that are not familiar, prepotentiated, or identical

The promise and perils of molecular combing

Dynamic Molecular Combing (DMC) is a method of making visible single molecules of DNA. The method stretches the molecules, attaching them to a glass coverslip; labels them with an intercalating dye or fluorescent antibodies; and images the molecules with fluorescent microscopy. After combing, fluorescent in situ hybridization (FISH) can be used to inspect regions on the DNA molecule. DMC is especially technically challenging for undergraduate research laboratories. To make the technique accessible to an undergraduate laboratory this project addresses three challenges: pH of buffer solution, NaOH exposure time, and halogenated thymidine exposure time in yeast (Saccharomyces cerevisiae). A serial pH experiment is necessary to determine optimal pH in any given laboratory. The optimal NaOH exposure time is 20 minutes. Despite using flow cytometry to determine the amount of time spent in S phase, the expected correlation between halogenated thymidine exposure and labeled tract length was not found, leaving the third challenge for further optimization

An experimental study of polymer electrolyte fuel cell operation at sub-freezing temperatures

The ability of polymer electrolyte fuel cells (PEFCs) to startup at subfreezing temperatures is governed by whether it is able to overcome the freezing point (0°C) before product ice prevents the electrochemical reactions. In this work, we experimentally investigated the coulombs of charge Qc transferred in PEFCs under subfreezing operation before the output voltage drops to 0.0V. PEFCs with various membranes and catalyst-layer thicknesses, ionomer-carbon ratios, operating current density, and initial hydration of PEFCs were studied, and their influences on cold-start performance and coulombs of charge were experimentally measured. We find that subfreezing temperature, ionomer-catalyst ratio, and catalyst-layer thickness, significantly affect the amount of charge transferred before operational failure, whereas the membrane thickness and initial hydration level have limited effect for the considered cases. © 2013 The Electrochemical Society

Subfreezing operation of polymer electrolyte fuel cells: Ice formation and cell performance loss

In this work, we investigate the cold-start operation of polymer electrolyte fuel cells (PEFCs) through high-resolution neutron radiography, experimental testing, theoretical evaluation, and comparison with model prediction. Ice formation location, voltage evolution, and loss of the electro-catalyst surface area (ECSA) are examined. A dimensionless parameter , characterizing the spatial variation of the reaction rate across the cathode catalyst layer, is discussed at subfreezing temperature using newly determined membrane ionic conductivity. The evaluation identifies the operating range that the reaction rate can be treated uniform across the catalyst layer, in which the model is valid. © 2012 Elsevier Ltd. All rights reserved