Reynolds number limits for jet propulsion: A numerical study of simplified jellyfish

The Scallop Theorem states that reciprocal methods of locomotion, such as jet propulsion or paddling, will not work in Stokes flow (Reynolds number = 0). In nature the effective limit of jet propulsion is still in the range where inertial forces are significant. It appears that almost all animals that use jet propulsion swim at Reynolds numbers (Re) of about 5 or more. Juvenile squid and octopods hatch from the egg already swimming in this inertial regime. The limitations of jet propulsion at intermediate Re is explored here using the immersed boundary method to solve the two-dimensional Navier Stokes equations coupled to the motion of a simplified jellyfish. The contraction and expansion kinematics are prescribed, but the forward and backward swimming motions of the idealized jellyfish are emergent properties determined by the resulting fluid dynamics. Simulations are performed for both an oblate bell shape using a paddling mode of swimming and a prolate bell shape using jet propulsion. Average forward velocities and work put into the system are calculated for Reynolds numbers between 1 and 320. The results show that forward velocities rapidly decay with decreasing Re for all bell shapes when Re < 10. Similarly, the work required to generate the pulsing motion increases significantly for Re < 10. When compared actual organisms, the swimming velocities and vortex separation patterns for the model prolate agree with those observed in Nemopsis bachei. The forward swimming velocities of the model oblate jellyfish after two pulse cycles are comparable to those reported for Aurelia aurita, but discrepancies are observed in the vortex dynamics between when the 2D model oblate jellyfish and the organism

Quantitative Risk-Based Analysis for Military Counterterrorism Systems

The article of record as published may be found at http://dx.doi.org/10.1002/sysThis paper presents a realistic and practical approach to quantitatively assess the risk-reduction capabilities of military counterterrorism systems in terms of damage cost and casualty figures. The comparison of alternatives is thereby based on absolute quantities rather than an aggregated utility or value provided by multicriteria decision analysis methods. The key elements of the approach are (1) the use of decision-attack event trees for modeling and analyzing scenarios, (2) a portfolio model approach for analyzing multiple threats, and (3) the quantitative probabilistic risk assessment matrix for communicating the results. Decision-attack event trees are especially appropriate for modeling and analyzing terrorist attacks where the sequence of events and outcomes are time-sensitive. The actions of the attackers and the defenders are modeled as decisions and the outcomes are modeled as probabilistic events. The quantitative probabilistic risk assessment matrix provides information about the range of the possible outcomes while retaining the simplicity of the classic safety risk assessment matrix based on Mil-Std-882D. It therefore provides a simple and reliable tool for comparing alternatives on the basis of risk including confidence levels rather than single point estimates. This additional valuable information requires minimal additional effort. The proposed approach is illustrated using a simplified but realistic model of a destroyer operating in inland restricted waters. The complex problem of choosing a robust counterterrorism protection system against multiple terrorist threats is analyzed by introducing a surrogate multi-threat portfolio. The associated risk profile provides a practical approach for assessing the robustness of different counterterrorism systems against plausible terrorist threats. The paper documents the analysis for a hypothetical case of three potential threats.This work was performed as part of the Naval Postgraduate School institutionally funded research

A Two-Coordinate Nickel Imido Complex That Effects C−H Amination

An exceptionally low coordinate nickel imido complex, (IPr*)Ni═N(dmp) (2) (dmp = 2,6-dimesitylphenyl), has been prepared by the elimination of N_2 from a bulky aryl azide in its reaction with (IPr*)Ni(η^6-C_7H_8) (1). The solid-state structure of 2 features two-coordinate nickel with a linear C−Ni−N core and a short Ni−N distance, both indicative of multiple-bond character. Computational studies using density functional theory showed a Ni═N bond dominated by Ni(dπ)−N(pπ) interactions, resulting in two nearly degenerate singly occupied molecular orbitals (SOMOs) that are Ni−N π* in character. Reaction of 2 with CO resulted in nitrene-group transfer to form (dmp)NCO and (IPr*)Ni(CO)_3 (3). Net C−H insertion was observed in the reaction of 2 with ethene, forming the vinylamine (dmp)NH(CH═CH_2) (5) via an azanickelacyclobutane intermediate, (IPr*)Ni{N,C:κ^2-N(dmp)CH_2CH_2} (4)

Arctic Centre: Rovaniemi, Finland

The Arctic Centre, developed in response to the City of Rovaniemi\u27s issuance of an ideas competition, is a complex incorporating two facilities: the Arctic Museum and the Lapland Provincial Museum

NDM-509: FULL-SCALE TEST METHODS FOR MULTI-LAYER CLADDING SYSTEMS: WIND TUNNEL VS. MULTI-CHAMBER AIRBOX

Wind loads on multi-layer wall systems are complicated because the loads on each particular layer are poorly understood and difficult to quantify. This is because of pressure equalization, which is the mechanism whereby the pressures on the external building surface are transmitted through the air-permeable outer layer to interior layers. Recent testing at IBHS in a full-scale wind tunnel has shown that the extent of pressure equalization is more limited than is assumed in the test standard, ASTM D3679-13. Multi-chamber pressure testing performed by the authors at the Insurance Research Lab for Better Homes was able to capture these features in these results using more commonly utilized ASTM-style (airbox) testing. The objective of the current study is to examine the effects that the pressure time history inputs have when comparing the full-scale wind tunnel method data with that from the multi-chamber airbox method. This is accomplished by comparing the power spectral densities of the external and cavity pressures, as well as fitting the peak pressure equalization factor data to a Gumbel distribution. From a comparison of the power spectral densities of each airbox vs. the relevant full-scale, wind-tunnel external pressures, it was noted that larger airboxes created a larger source of error of the peak pressures in the system

Marshall University Music Department Presents the Symphonic Band Spring Concert, Gregory A. Richmond, conductor, featuring: Dr. Ben Miller, soloist, Matthew Chaffins, graduate conductor, and the world premiere of, H.M.S. Surprise Suite, by Dr. Stephen Lawson

https://mds.marshall.edu/music_perf/1449/thumbnail.jp

Attending to Eliza: Rapid brain responses reflect competence attribution in virtual social feedback processing

Schindler S, Miller GA, Kißler J. Attending to Eliza: Rapid brain responses reflect competence attribution in virtual social feedback processing. Social Cognitive and Affective Neuroscience. 2019;14(10):1073-1086.In the age of virtual communication, the source of a message is often inferred rather than perceived, raising the question of how sender attributions affect content processing. We investigated this issue in an evaluative feedback scenario. Participants were told that an expert psychotherapist, a layperson or a randomly acting computer was going to give them online positive, neutral or negative personality feedback while high-density EEG was recorded. Sender attribution affected processing rapidly, even though the feedback was on average identical. Event-related potentials revealed a linear increase with attributed expertise beginning 150 ms after disclosure and most pronounced for N1, P2 and early posterior negativity components. P3 and late positive potential amplitudes were increased for both human senders and for emotionally significant (positive or negative) feedback. Strikingly, feedback from a putative expert prompted large P3 responses, even for inherently neutral content. Source analysis localized early enhancements due to attributed sender expertise in frontal and somatosensory regions and later responses in the posterior cingulate and extended visual and parietal areas, supporting involvement of mentalizing, embodied processing and socially motivated attention. These findings reveal how attributed sender expertise rapidly alters feedback processing in virtual interaction and have implications for virtual therapy and online communication.how attributed sender expertise rapidly alters feedback processing in virtual interaction and have implications for virtual therapy and on-line communication.</jats:p

Dietary patterns of school-age children in Scotland : association with socio-economic indicators, physical activity and obesity

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