Social Norms: Do We Love Norms Too Much?

Social norms are often cited as the cause of many social phenomena, especially as an explanation for prosocial family and relationship behaviors. And yet maybe we love the idea of social norms too much, as suggested by our failure to subject them to rigorous test. Compared to the detail in social norms theoretical orientations, there is very little detail in tests of normative theories. To provide guidance to researchers who invoke social norms as explanations, we catalog normative orientations that have been proposed to account for consistent patterns of action. We call on researchers to conduct tests of normative theories and the processes such theories assert

Trajectory Design Leveraging Low-Thrust, Multi-Body Equilibria and Their Manifolds

A key challenge in low-thrust trajectory design is generating preliminary solutions that simultaneously specify the spacecraft position and velocity vectors, as well as the thrust history. To mitigate this difficulty, dynamical structures within a combined low-thrust circular restricted 3-body problem (CR3BP) are investigated as candidate solutions to seed initial low-thrust trajectory designs. The addition of low-thrust to the CR3BP modifies the locations and stability of the equilibria, offering novel geometries for mission applications. Transfers between these novel equilibria are constructed by leveraging the associated stable and unstable manifolds and insights from the low-thrust CR3BP

Dead-time effects on the voltage spectrum of a PWM inverter

An inverter converts a direct-current power supply to an alternating-current power supply. This con- version is achieved by switching the output between the inputs at high frequency. The resulting output voltage may be described by a high-frequency train of variable-width pulses. Pulse widths are slowly modulated so that this output waveform contains a prescribed low-frequency component, which may then be isolated by an appropriate filtering regime. Techniques for determining the full harmonic spec- trum of input and output voltages and currents are well established, at least for an idealised mathematical model of the inverter. However, this model assumes that changes of inverter configuration can be ef- fected instantaneously, which is not quite the case in practice. In fact, a small amount of dead time must be incorporated into switching regimes in order to avoid short circuits of the input. Although dead time is an important feature of real power conversion devices, its effects on output voltage spectra have not previously been fully determined (except by imposing rather restrictive approximations). This situation is remedied in the present paper, in which we present closed-form expressions for the coefficients of the harmonic spectrum, corroborated by simulations

Dust Explosions and Collapsed Ductwork

PresentationOne of the more obvious consequences of a dust deflagration inside process equipment or a structure is the mechanical damage caused by shock (compression) waves. This overpressure damage is revealed through the displacement of equipment, the outward deformation or rupture of enclosures constructed of ductile materials, or the projection of missiles. However, a different type of damage is sometimes observed in the ductwork connecting process equipment. In particular, the ductwork is collapsed as if it were subjected to an external, rather than an internal pressure. The phenomenon that causes this collapse of thin-walled conduit is a gas dynamic process called an expansion wave. When a dust deflagration travels through a conduit, it accelerates and causing a rise in pressure. When the dust deflagration is vented (say through a deflagration vent), the discharge of the high pressure combustion products causes the formation of an expansion wave that travels in the reverse direction from the vent backwards. The expansion wave causes the pressure in the ductwork to fall below atmospheric pressure. The sub-atmospheric pressure, in turn, causes the ductwork to fail by buckling. In this study, we examine the gas dynamics of the expansion wave, demonstrate how to calculate the degree of pressure drop caused by the expansion wave, and illustrate the concept with case studies of dust explosions

Enhancing spatial detection accuracy for syndromic surveillance with street level incidence data

<p>Abstract</p> <p>Background</p> <p>The Department of Defense Military Health System operates a syndromic surveillance system that monitors medical records at more than 450 non-combat Military Treatment Facilities (MTF) worldwide. The Electronic Surveillance System for Early Notification of Community-based Epidemics (ESSENCE) uses both temporal and spatial algorithms to detect disease outbreaks. This study focuses on spatial detection and attempts to improve the effectiveness of the ESSENCE implementation of the spatial scan statistic by increasing the spatial resolution of incidence data from zip codes to street address level.</p> <p>Methods</p> <p>Influenza-Like Illness (ILI) was used as a test syndrome to develop methods to improve the spatial accuracy of detected alerts. Simulated incident clusters of various sizes were superimposed on real ILI incidents from the 2008/2009 influenza season. Clusters were detected using the spatial scan statistic and their displacement from simulated loci was measured. Detected cluster size distributions were also evaluated for compliance with simulated cluster sizes.</p> <p>Results</p> <p>Relative to the ESSENCE zip code based method, clusters detected using street level incidents were displaced on average 65% less for 2 and 5 mile radius clusters and 31% less for 10 mile radius clusters. Detected cluster size distributions for the street address method were quasi normal and sizes tended to slightly exceed simulated radii. ESSENCE methods yielded fragmented distributions and had high rates of zero radius and oversized clusters.</p> <p>Conclusions</p> <p>Spatial detection accuracy improved notably with regard to both location and size when incidents were geocoded to street addresses rather than zip code centroids. Since street address geocoding success rates were only 73.5%, zip codes were still used for more than one quarter of ILI cases. Thus, further advances in spatial detection accuracy are dependant on systematic improvements in the collection of individual address information.</p