Studies on proper simulation during static testing of forward speed effects on fan noise

Significant differences exist in the noise generated by engines in flight and engines operating on the test stand. It was observed that these differences can be reduced by the use of an inflow control structure (ICS) in the static test configuration. The results of the third phase of a three phase program are described. The work performed in the first two phases which dealt with the development of a model for atmospheric turbulence, studies of fan noise generated by rotor turbulence interaction, and the development of an inflow control structure design system are summarized. The final phase of the program covers procedures for performing static testing with an ICS projecting the resulting static test data to actual flight test data. Included is a procedures report which covers the design system and techniques for static testing and projecting the static data to flight

A Barren Landscape?

We consider the generation of a non-perturbative superpotential in F-theory compactifications with flux. We derive a necessary condition for the generation of such a superpotential in F-theory. For models with a single volume modulus, we show that the volume modulus is never stabilized by either abelian instantons or gaugino condensation. We then comment on how our analysis extends to a larger class of compactifications. From our results, it appears that among large volume string compactifications, metastable de Sitter vacua (should any exist) are non-generic.Comment: 14 pages, comments adde

Resolving singular forces in cavity flow: Multiscale modeling from atoms to millimeters

A multiscale approach for fluid flow is developed that retains an atomistic description in key regions. The method is applied to a classic problem where all scales contribute: The force on a moving wall bounding a fluid-filled cavity. Continuum equations predict an infinite force due to stress singularities. Following the stress over more than six decades in length in systems with characteristic scales of millimeters and milliseconds allows us to resolve the singularities and determine the force for the first time. The speedup over pure atomistic calculations is more than fourteen orders of magnitude. We find a universal dependence on the macroscopic Reynolds number, and large atomistic effects that depend on wall velocity and interactions.Comment: 4 pages,3 figure

Contact and Friction of Nano-Asperities: Effects of Adsorbed Monolayers

Molecular dynamics simulations are used to study contact between a rigid, nonadhesive, spherical tip with radius of order 30nm and a flat elastic substrate covered with a fluid monolayer of adsorbed chain molecules. Previous studies of bare surfaces showed that the atomic scale deviations from a sphere that are present on any tip constructed from discrete atoms lead to significant deviations from continuum theory and dramatic variability in friction forces. Introducing an adsorbed monolayer leads to larger deviations from continuum theory, but decreases the variations between tips with different atomic structure. Although the film is fluid, it remains in the contact and behaves qualitatively like a thin elastic coating except for certain tips at high loads. Measures of the contact area based on the moments or outer limits of the pressure distribution and on counting contacting atoms are compared. The number of tip atoms making contact in a time interval grows as a power of the interval when the film is present and logarithmically with the interval for bare surfaces. Friction is measured by displacing the tip at a constant velocity or pulling the tip with a spring. Both static and kinetic friction rise linearly with load at small loads. Transitions in the state of the film lead to nonlinear behavior at large loads. The friction is less clearly correlated with contact area than load.Comment: RevTex4, 17 pages, 13 figure

Unexpected hard-object feeding in Western lowland gorillas

The cranial morphology of the earliest known hominins in the genus Australopithecus remains unclear. The oldest species in this genus (Australopithecus anamensis, specimens of which have been dated to 4.2–3.9 million years ago) is known primarily from jaws and teeth, whereas younger species (dated to 3.5–2.0 million years ago) are typically represented by multiple skulls. Here we describe a nearly complete hominin cranium from Woranso-Mille (Ethiopia) that we date to 3.8 million years ago. We assign this cranium to A. anamensis on the basis of the taxonomically and phylogenetically informative morphology of the canine, maxilla and temporal bone. This specimen thus provides the first glimpse of the entire craniofacial morphology of the earliest known members of the genus Australopithecus. We further demonstrate that A. anamensis and Australopithecus afarensis differ more than previously recognized and that these two species overlapped for at least 100,000 years—contradicting the widely accepted hypothesis of anagenesis

Social influence and moment-to-moment changes in young adults’ mood and psychotic symptoms

Background: • Social situations can have a significant impact on young people’s mood and mental experiences. • More specifically, we want to know how someone’s perceived social influence in social situations relates to their mood and psychotic symptoms. • Past studies have found connections between lower perceived social status (rank, comparison, and related concepts) and psychotic symptoms anxiety, depression, and other mood related psychopathology. • We use experience sampling methods to capture moment-to-moment changes in mood and psychotic symptoms in a variety of social settings

Seasonal controls on nearshore dissolved oxygen variability and hypoxia in a coastal embayment

Declining dissolved oxygen (DO) is emerging as an increasingly important stressor in nearshore ecosystems, and there is a growing need to better understand DO dynamics and hypoxia risk in this highly variable environment. In this study, we collected data from monthly cruises on the inner shelf, continuous nearshore moorings inside and outside a small coastal upwelling embayment (San Luis Obispo Bay in Central California), and weekly phytoplankton measurements inside the bay during the upwelling season. Nearshore DO was generally dominated by low-frequency synoptic variability, with increased DO variance near the surface relative to the bottom and inside the bay compared to outside. Two nearshore hypoxic regimes were identified. In the first regime, which occurred during periods of strong upwelling in the spring across all nearshore sites, the nearshore bottom water temperature-DO (T-DO) relationship was aligned with that found offshore, suggesting hypoxia was driven by the direct advection and cross-shelf exchange of low DO subthermocline waters from the shelf. This period also coincided with minimal water-column stratification, small vertical DO differences, and a diatom-dominated phytoplankton assemblage. In the second regime, which occurred during summer months and was characterized by weaker upwelling, strong stratification, and dinoflagellate-dominated phytoplankton assemblage, the near-bottom T-DO relationship inside the bay deviated significantly from that on the shelf offshore. These hypoxic events inside the bay were likely driven by localized respiration and lack of ventilation of bottom waters due to strong stratification. Collectively, these observations reveal a shift in the strength and magnitude of physical versus biological processes driving nearshore DO dynamics. The high spatiotemporal variability of DO dynamics in upwelling bays means that they are likely to be at the forefront of ecosystem impacts of and adaptions to climate change, and may act as sentinel systems or “canaries on the coast.

Improving Predictions for Helium Emission Lines

We have combined the detailed He I recombination model of Smits with the collisional transitions of Sawey & Berrington in order to produce new accurate helium emissivities that include the effects of collisional excitation from both the 2 (3)S and 2 (1) S levels. We present a grid of emissivities for a range of temperature and densities along with analytical fits and error estimates. Fits accurate to within 1% are given for the emissivities of the brightest lines over a restricted range for estimates of primordial helium abundance. We characterize the analysis uncertainties associated with uncertainties in temperature, density, fitting functions, and input atomic data. We estimate that atomic data uncertainties alone may limit abundance estimates to an accuracy of 1.5%; systematic errors may be greater than this. This analysis uncertainty must be incorporated when attempting to make high accuracy estimates of the helium abundance. For example, in recent determinations of the primordial helium abundance, uncertainties in the input atomic data have been neglected.Comment: ApJ, accepte