Apollo guidance, navigation, and control: Candidate configuration trade study, Stellar-Inertial Measurement System (SIMS) for an Earth Observation Satellite (EOS)

The ten candidate SIMS configurations were reduced to three in preparation for the final trade comparison. The report emphasizes subsystem design trades, star availability studies, data processing (smoothing) methods, and the analytical and simulation studies at subsystem and system levels from which candidate accuracy estimates will be presented

Identifying Roadkill Hotspots Using a Running Average

The identification of roadkill hotspots is necessary prior to the consideration of wildlife road mortality mitigation measures. In a previous study, 178 roadkill specimens were tallied via a driving survey along 21.4 km (13.3 mi) on three connected roadways in Baldwin County, Georgia. Roadkill locations were recorded to the nearest 0.16 km (0.1 mi) using the vehicle odometer. In the current study, location data were used to generate three graphical displays of roadkill distribution: 1) a linear graph of roadkills per 0.16 km (0.1 mi) bin; 2) a linear graph of roadkills per 0.8 km (0.5 mi) bin; and 3) a linear graph with a continuous running average incorporating 0.48 km (0.3 mi). The number and position of the peaks on each graph were compared in relation to roadway features that may influence animal movement and mortality such as vegetative boundaries, stream crossings, hills, and curves. The running average plot provided the best visual illustration of roadkill hotspot locations in relation to roadside features. The running average is a good technique to quickly and accurately identify hotspot locations and could help resource managers plan mitigation strategies to decrease wildlife road mortality

A variable temperature ultrahigh vacuum atomic force microscope

A new atomic force microscope (AFM) that operates in ultrahigh vacuum (UHV) is described. The sample is held fixed with spring clamps while the AMF cantilever and deflection sensor are scanned above it. Thus, the sample is easily coupled to a liquid nitrogen cooled thermal reservoir which allows AFM operation from ≈ 100 K to room temperature. AFM operation above room temperature is also possible. The microscope head is capable of coarse x-y positioning over millimeter distances so that AFM images can be taken virtually anywhere upon a macroscopic sample. The optical beam deflection scheme is used for detection, allowing simultaneous normal and lateral force measurements. The sample can be transferred from the AFM stage to a low energy electron diffraction/Auger electron spectrometer stage for surface analysis. Atomic lattice resolution AFM images taken in UHV are presented at 110, 296, and 430 K

Building Writing Identities: Integrating Explicit Strategies with Authentic Writing Experiences to Engage At-Promise Writers

The message of what constitutes good writing instruction, though promulgated for decades, has not always nor consistently trickled down to P–12 schools, where writing instruction is often focused on preparing students for success on standardized tests and where prescriptive and formulaic approaches to teaching writing are prevalent. Part of the reason for this might be that teachers are not always familiar enough with authentic writing experiences that adequately engage all learners. As scholars in the fields of literacy and special education, respectively, the authors combine their collective expertise to address this concern. They offer skills-based tools and strategies that can be integrated into authentic writing experiences to promote critical thinking and creativity, build students’ writing identities, and help at-promise learners gain and maintain writing momentum. A balanced approach that harmonizes different orientations and paradigms lends credibility to this piece as an example of what educators joining together to form a coalition for student support can look like. This article is positioned to bridge the divide between seemingly dichotomous perspectives. Through the strategies and ideas the authors share, teachers will be better equipped to give at-promise writers reasons to believe in themselves and their writerly capabilities

Atomic scale coexistence of periodic and quasiperiodic order in a 2-fold Al-Ni-Co decagonal quasicrystal surface

Decagonal quasicrystals are made of pairs of atomic planes with pentagonal symmetry periodically stacked along a 10-fold axis. We have investigated the atomic structure of the 2-fold surface of a decagonal Al-Ni-Co quasicrystal using scanning tunneling microscopy. The surface consists of terraces separated by steps of heights 1.9, 4.7, 7.8, and 12.6 Å containing rows of atoms parallel to the 10-fold direction with an internal periodicity of 4 Å. The rows are arranged aperiodically, with separations that follow a Fibonacci sequence and inflation symmetry. The results indicate that the surfaces are preferentially Al-terminated and in general agreement with bulk models

Tribological properties of quasicrystals: Effect of aperiodic versus periodic surface order

We investigated the nanoscale tribological properties of a decagonal quasicrystal using a combination of atomic force microscopy and scanning tunneling microscopy in ultrahigh vacuum. This combination permitted a variety of in situ measurements, including atomic-scale structure, friction and adhesion force, tip-sample current, and topography. We found that thiol-passivated tips can be used for reproducible studies of the tip-quasicrystal contact while nonpassivated probes adhere irreversibly to the clean quasicrystalline surface causing permanent modifications. The most remarkable results were obtained on the twofold surface of the Al-Ni-Co decagonal quasicrystal where atoms are arranged periodically along the tenfold axis and aperiodically in the perpendicular direction. Strong friction anisotropy was observed on this surface, with high friction along the periodic direction and low friction in the aperiodic direction

Elastic and inelastic deformations of ethylene-passivated tenfold decagonal Al-Ni-Co quasicrystal surfaces

The adhesion and friction force properties between a tenfold Al‐Ni‐Co decagonal quasicrystal and a titanium nitride (TiN)-coated tip were investigated using an atomic force microscope in ultrahigh vacuum. To suppress the strong chemical adhesion found in the clean quasicrystal surfaces, the sample was exposed to ethylene that formed a protective passivating layer. We show that the deformation mechanism of the tip-substrate junction changes from elastic to inelastic at a threshold pressure of 3.8 to 4.0 GPa. Images of the indentation marks left above the threshold pressure indicate the absence of new steps, and indicate that surface damage is not accompanied by formation of slippage planes or dislocations, as found in plastically deforming crystalline materials. This is consistent with the lack of translational periodicity of quasicrystals. The work of adhesion in the inelastic regime is five times larger than in the elastic one, plausibly as a result of the displacement of the passivating layer. In the elastic regime, the friction dependence on load is accurately described by the Derjaguin-Müller-Toporov (DMT) model, consistent with the high hardness of both the TiN tip and the quasicrystal sample. Above the threshold pressure, the friction versus load curve deviates from the DMT model, indicating that chemical bond formation and rupture contribute to the energy dissipation