Aeroacoutic characteristics of a large, variable-pitch, variable-speed fan system

The acoustic and aerodynamic performance of the new drive fans for the NASA Ames 40- by 80-/80- by 120-foot wind tunnel was investigated. Results show that a fan system with variable-speed and variable-pitch rotor blades allows the operator to control noise and energy consumption, at a given mass flow rate, through the choice of blade speed and pitch. A low speed and high blade pitch will generally create the least noise at the least energy cost. An empirical method is described which predicts the sound power of this fan system reasonably well

Low-speed wind-tunnel tests of a large-scale inflatable structure paraglider

Aerodynamic characteristics of inflatable structure paraglider tested in wind tunne

A facial expression for anxiety.

Anxiety and fear are often confounded in discussions of human emotions. However, studies of rodent defensive reactions under naturalistic conditions suggest anxiety is functionally distinct from fear. Unambiguous threats, such as predators, elicit flight from rodents (if an escape-route is available), whereas ambiguous threats (e.g., the odor of a predator) elicit risk assessment behavior, which is associated with anxiety as it is preferentially modulated by anti-anxiety drugs. However, without human evidence, it would be premature to assume that rodent-based psychological models are valid for humans. We tested the human validity of the risk assessment explanation for anxiety by presenting 8 volunteers with emotive scenarios and asking them to pose facial expressions. Photographs and videos of these expressions were shown to 40 participants who matched them to the scenarios and labeled each expression. Scenarios describing ambiguous threats were preferentially matched to the facial expression posed in response to the same scenario type. This expression consisted of two plausible environmental-scanning behaviors (eye darts and head swivels) and was labeled as anxiety, not fear. The facial expression elicited by unambiguous threat scenarios was labeled as fear. The emotion labels generated were then presented to another 18 participants who matched them back to photographs of the facial expressions. This back-matching of labels to faces also linked anxiety to the environmental-scanning face rather than fear face. Results therefore suggest that anxiety produces a distinct facial expression and that it has adaptive value in situations that are ambiguously threatening, supporting a functional, risk-assessing explanation for human anxiet

An experimental investigation of two large annular diffusers with swirling and distorted inflow

Two annular diffusers downstream of a nacelle-mounted fan were tested for aerodynamic performance, measured in terms of two static pressure recovery parameters (one near the diffuser exit plane and one about three diameters downstream in the settling duct) in the presence of several inflow conditions. The two diffusers each had an inlet diameter of 1.84 m, an area ratio of 2.3, and an equivalent cone angle of 11.5, but were distinguished by centerbodies of different lengths. The dependence of diffuser performance on various combinations of swirling, radially distorted, and/or azimuthally distorted inflow was examined. Swirling flow and distortions in the axial velocity profile in the annulus upstream of the diffuser inlet were caused by the intrinsic flow patterns downstream of a fan in a duct and by artificial intensification of the distortions. Azimuthal distortions or defects were generated by the addition of four artificial devices (screens and fences). Pressure recovery data indicated beneficial effects of both radial distortion (for a limited range of distortion levels) and inflow swirl. Small amounts of azimuthal distortion created by the artificial devices produced only small effects on diffuser performance. A large artificial distortion device was required to produce enough azimuthal flow distortion to significantly degrade the diffuser static pressure recovery

Geometry dependence of the clogging transition in tilted hoppers

We report the effect of system geometry on the clogging of granular material flowing out of flat-bottomed hoppers with variable aperture size D. For such systems, there exists a critical aperture size Dc at which there is a divergence in the time for a flow to clog. To better understand the origins of Dc, we perturb the system by tilting the hopper an angle Q and mapping out a clogging phase diagram as a function of Q and D. The clogging transition demarcates the boundary between the freely-flowing (large D, small Q) and clogging (small D, large Q) regimes. We investigate how the system geometry affects Dc by mapping out this phase diagram for hoppers with either a circular hole or a rectangular narrow slit. Additionally, we vary the grain shape, investigating smooth spheres (glass beads), compact angular grains (beach sand), disk-like grains (lentils), and rod-like grains (rice). We find that the value of Dc grows with increasing Q, diverging at pi-Qr where Qr is the angle of repose. For circular apertures, the shape of the clogging transition is the same for all grain types. However, this is not the case for the narrow slit apertures, where the rate of growth of the critical hole size with tilt angle depends on the material

Conceptualizing accelerated internationalization in the born global firm: A dynamic capabilities perspective

Existing approaches at explaining accelerated internationalization of born global firms are incomplete as they do not capture the learning that is undertaken by these firms and their founders prior to the firm's legal establishment. Building on the extant literature and drawing on the dynamic capabilities view of competitive strategy, this paper presents a conceptual model of born global firm internationalization. We conjecture that a set of dynamic capabilities that are built and nurtured by internationally-oriented entrepreneurial founders enable these firms to develop cutting-edge knowledge intensive products, paving the way for their accelerated market entry. We develop propositions and offer concluding remarks

Characterization of cathepsin B specificity by site-directed mutagenesis. Importance of Glu245 in the S2-P2 specificity for arginine and its role in transition state stabilization.

The pH dependence of cathepsin B-catalyzed hydrolyzes is very complex. At least seven dissociable groups are involved in the binding and hydrolysis of 7-amido-4-methyl coumarin and p-nitroaniline (pNA)-based substrates containing a P1 Arg and either a Phe or Arg at the P2 position. By site-directed mutagenesis we show that a previous suggestion, that Arg202 is one of the groups which influences the pH dependence of cathepsin B-catalyzed hydrolysis of the Z-Arg-Arg-pNA substrate, is not valid. However, it was found that Glu245, which has a pKa of 5.1 in rat cathepsin B, is responsible for the S2-P2 specificity for Arg-containing substrates and controls the pH dependence of their hydrolysis. Furthermore, the data indicate that Glu245, which forms a hydrogen bond with the guanidinium group of the substrate's P2 Arg, contributes about 1.8 kcal/mol to transition state stabilization in the protonated state and about 0.6 kcal/mol in the deprotonated state. Mutation of Glu245 to Gln results in a 16-fold decrease in kcat but does not affect Km. While cathepsin B has a 7-fold preference for Phe over Arg at the P2 position of a substrate, binding of the aromatic side chain does not appear to be influenced by Glu245

Estimating Probability Distributions from Complex Models with Bifurcations: The Case of Ocean Circulation Collapse

Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).Studying the uncertainty in computationally expensive models has required the development of specialized methods, including alternative sampling techniques and response surface approaches. However, existing techniques for response surface development break down when the model being studied exhibits discontinuities or bifurcations. One uncertain variable that exhibits this behavior is the thermohaline circulation (THC) as modeled in three-dimensional general circulation models. This is a critical uncertainty for climate change policy studies. We investigate the development of a response surface for studying uncertainty in THC using the Deterministic Equivalent Modeling Method, a stochastic technique using expansions in orthogonal polynomials. We show that this approach is unable to reasonably approximate the model response. We demonstrate an alternative representation that accurately simulates the model’s response, using a basis function with properties similar to the model’s response over the uncertain parameter space. This indicates useful directions for future methodological improvements.This research was supported in part by the Methods and Models for Integrated Assessments Program of the National Science Foundation, Grant ATM-9909139, by the Office of Science (BER), U.S. Department of Energy, Grant Nos. DE-FG02-02ER63468 and DE-FG02-93ER61677, and by the MIT Joint Program on the Science and Policy of Global Change (JPSPGC)

Relative Roles of Climate Sensitivity and Forcing in Defining the Ocean Circulation Response to Climate Change

Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).The response of the ocean’s meridional overturning circulation (MOC) to increased greenhouse gas forcing is examined using a coupled model of intermediate complexity, including a dynamic 3D ocean subcomponent. Parameters are the increase in CO2 forcing (with stabilization after a specified time interval) and the model’s climate sensitivity. In this model, the cessation of deep sinking in the north “Atlantic” (hereinafter, a “collapse”), as indicated by changes in the MOC, behaves like a simple bifurcation. The final surface air temperature (SAT) change, which is closely predicted by the product of the radiative forcing and the climate sensitivity, determines whether a collapse occurs. The initial transient response in SAT is largely a function of the forcing increase, with higher sensitivity runs exhibiting delayed behavior; accordingly, high CO2-low sensitivity scenarios can be assessed as a recovering or collapsing circulation shortly after stabilization, whereas low CO2-high sensitivity scenarios require several hundred additional years to make such a determination. We also systemically examine how the rate of forcing, for a given CO2 stabilization, affects the ocean response. In contrast with previous studies based on results using simpler ocean models, we find that except for a narrow range of marginally stable to marginally unstable scenarios, the forcing rate has little impact on whether the run collapses or recovers. In this narrow range, however, forcing increases on a time scale of slow ocean advective processes results in weaker declines in overturning strength and can permit a run to recover that would otherwise collapse.This research was supported in part by the Methods and Models for Integrated Assessments Program of the National Science Foundation, Grant ATM-9909139, by the Office of Science (BER), U.S. Department of Energy, Grant No. DE-FG02-93ER61677, and by the MIT Joint Program on the Science and Policy of Global Change (JPSPGC)

Remotely Supported Prehospital Ultrasound : Real-Time Communication Technology for Remote and Rural Communities

Highlands & Islands Enterprise, UK Technology Strategy Board’s Space and Life Sciences Catapult, University of Aberdeen’s dot.rural Digital Economy HubPeer reviewedPublisher PD