Design and Testing of an Additively Manufactured CubeSat Structural Bus

Recent innovations in additive manufacturing and design capabilities have opened the door for more opportunities to integrate multiple functions into a structural de- sign. Specifically, 3D printing through advanced laser powder bed fusion of metal powder allows for the development and integration of advanced structures that were previously unachievable. The demonstration of these techniques on a small satellite results in a structural bus consisting of various external and internal features, increasing its functionality and capabilities beyond simply providing structural support. 3D printing a multi-functional CubeSat bus with these integrated features such as internal lattices and wiring tabs demonstrates a new way of thinking going forward: modularizing the structural design and incorporating various capabilities that can meet a unique or generic satellite mission. This research addresses the design and testing of an additively manufactured CubeSat structural bus. 3D printing capabilities were harnessed to incorporate lattices into the walls of the structure, increasing its natural frequency and decreasing mass. The 3D printed unloaded CubeSat structure was vibration tested to NASA GEVS qualification levels, and showed no damage and proved survivability under these loading conditions

Development of 2-Dimensional Cloud Rise Model to Analyze Initial Nuclear Cloud Rise

The objective of this research is to create a two-dimensional cloud rise model that could be used instead of the current one-dimensional cloud rise model in the Defense Land Fallout Intepretive Code (DELFIC) option of the Hazard Prediction and Assessment Capability (HPAC). The model includes numerical analysis of partial differential equations involving pressure, potential temperature, horizontal and vertical winds, and specific humidity. The 2-D model developed provides a much more detailed definition of the physical properties within the mushroom cloud than the 1-D DELFIC option. This is particularly useful in fallout studies on particle formation, fractionation, and particle location within the rising/risen cloud. The analysis model created for this study is the result of modifications to a convective cloud simulation. The primary modification to the convective cloud model is the incorporation of initial conditions for a nuclear cloud similar to those used in DELFIC’s initial conditions module. The code is compared to atmospheric test data for verification purposes

Structural Studies in the Mafic and Ultramafic Rocks of the Lewis Hills, Western Newfoundland

Table of contents:CHAPTER I. INTRODUCTIONCHAPTER II. REGIONAL GEOLOGYCHAPTER III. THE LEWIS HILLS COMPARED TO THE NORTHERN AREAS OF THE BAY OF ISLAND COMPLEXCHAPTER IV. PETROGRAPHYCHAPTER V. STRUCTURAL GEOLOGYCHAPTER VI. SUMMARY, CONCLUSIONS, AND SPECULATIONSBIBLIOGRAPHYAPPENDIX I. CONTOURED STEREOGRAPHIC PROJECTIONS OF FOLIATIONS AND LINEATIONS IN THE HINES POND ARE

Temporal and spatial variability in the composition of lavas exposed along the Western Blanco Transform Fault

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 6 (2005): Q11009, doi:10.1029/2005GC001026.The northern scarp of the western Blanco Transform (BT) fault zone provides a "tectonic window" into crust generated at an intermediate-rate spreading center, exposing a ~2000 m vertical section of lavas and dikes. The lava unit was sampled by submersible during the Blancovin dive program in 1995, recovering a total of 61 samples over vertical distances of ~1000 m and a lateral extent of ~13 km. Major elements analyses of 40 whole rock samples exhibit typical tholeiitic fractionation trends of increasing FeO*, Na2O, and TiO2 and decreasing Al2O3 and CaO with decreasing MgO. The lava suite shows a considerable range in extent of crystallization, including primitive samples (Mg# 64) and evolved FeTi basalts (FeO>12%;TiO2>2%). Based on rare earth element and trace element data, all of the lavas are incompatible-element depleted normal mid-ocean ridge basalts (N-MORB;La/SmN<1). The geochemical systematics suggest that the lavas were derived from a slightly heterogeneous mantle source, and crystallization occurred in a magmatic regime of relatively low magma flux and/or high cooling rate, consistent with magmatic processes occurring along the present-day southern Cleft Segment. The BT scarp reveals the oceanic crust in two-dimensional space, allowing us to explore temporal and spatial relationships in the horizontal and vertical directions. As a whole, the data do not appear to form regular spatial trends; rather, primitive lavas tend to cluster shallower and toward the center of the study area, while more evolved lavas are present deeper and toward the west and east. Considered within a model for construction of the upper crust, these findings suggest that the upper lavas along the BT scarp may have been emplaced off-axis, either by extensive off-axis flow or off-axis eruption, while the lower lavas represent axial flows that have subsided with time. A calculation based on an isochron model for construction of the upper crust suggests that the Cleft Segment requires at least ~50 ka to build the lower extrusive section, consistent to first order with independent estimates for the construction of intermediate-spreading rate crust.This work was supported by the US National Science Foundation (OCE 02- 22154 to E.K. and J.K. and OCE 9400623 to M.T.)

Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

The uppermost oceanic crust produced at the superfast spreading (∼142 km Ma −1, full‐spreading rate) southern East Pacific Rise (EPR) during the Gauss Chron is exposed in a tectonic window along the northeastern wall of the Pito Deep Rift. Paleomagnetic analysis of fully oriented dike (62) and gabbro (5) samples from two adjacent study areas yield bootstrapped mean remanence directions of 38.9° ± 8.1°, −16.7° ± 15.6°, n = 23 (Area A) and 30.4° ± 8.0°, −25.1° ± 12.9°, n = 44 (Area B), both are significantly distinct from the Geocentric Axial Dipole expected direction at 23° S. Regional tectonics and outcrop‐scale structural data combined with bootstrapped remanence directions constrain models that involve a sequence of three rotations that result in dikes restored to subvertical orientations related to (1) inward‐tilting of crustal blocks during spreading (Area A = 11°, Area B = 22°), (2) clockwise, vertical‐axis rotation of the Easter Microplate (A = 46°, B = 44°), and (3) block tilting at Pito Deep Rift (A = 21°, B = 10°). These data support a structural model for accretion at the southern EPR in which outcrop‐scale faulting and block rotation accommodates spreading‐related subaxial subsidence that is generally less than that observed in crust generated at a fast spreading rate exposed at Hess Deep Rift. These data also support previous estimates for the clockwise rotation of crust adjacent to the Easter Microplate. Dike sample natural remanent magnetization (NRM) has an arithmetic mean of 5.96 A/m ± 3.76, which suggests that they significantly contribute to observed magnetic anomalies from fast‐ to superfast‐spread crust

Direct evidence from anisotropy of magnetic susceptibility for lateral melt migration at superfast spreading centers

Rare, fault‐bounded escarpments expose natural cross sections of ocean crust in several areas and provide an unparalleled opportunity to study the end products of tectonic and magmatic processes that operated at depth beneath oceanic spreading centers. We mapped the geologic structure of ocean crust produced at the East Pacific Rise (EPR) and now exposed along steep cliffs of the Pito Deep Rift near the northern edge of the Easter microplate. The upper oceanic crust in this area is typified by basaltic lavas underlain by a sheeted dike complex comprising northeast striking, moderately to steeply southeast dipping dikes. Paleomagnetic remanence of oriented blocks of dikes collected with both Alvin and Jason II indicate clockwise rotation of ∼61° related to rotation of the microplate indicating structural coupling between the microplate and crust of the Nazca Plate to the north. The consistent southeast dip of dikes formed as the result of tilting at the EPR shortly after their injection. Anisotropy of magnetic susceptibility of dikes provides well‐defined magmatic flow directions that are dominantly dike‐parallel and shallowly plunging. Corrected to their original EPR orientation, magma flow is interpreted as near‐horizontal and parallel to the ridge axis. These data provide the first direct evidence from sheeted dikes in ocean crust for along‐axis magma transport. These results also suggest that lateral transport in dikes is important even at fast spreading ridges where a laterally continuous subaxial magma chamber is present

Optogenetic Release of ACh Induces Rhythmic Bursts of Perisomatic IPSCs in Hippocampus

Acetylcholine (ACh) influences a vast array of phenomena in cortical systems. It alters many ionic conductances and neuronal firing behavior, often by regulating membrane potential oscillations in populations of cells. Synaptic inhibition has crucial roles in many forms of oscillation, and cholinergic mechanisms regulate both oscillations and synaptic inhibition. In vitro investigations using bath-application of cholinergic receptor agonists, or bulk tissue electrical stimulation to release endogenous ACh, have led to insights into cholinergic function, but questions remain because of the relative lack of selectivity of these forms of stimulation. To investigate the effects of selective release of ACh on interneurons and oscillations, we used an optogenetic approach in which the light-sensitive non-selective cation channel, Channelrhodopsin2 (ChR2), was virally delivered to cholinergic projection neurons in the medial septum/diagonal band of Broca (MS/DBB) of adult mice expressing Cre-recombinase under the control of the choline-acetyltransferase (ChAT) promoter. Acute hippocampal slices obtained from these animals weeks later revealed ChR2 expression in cholinergic axons. Brief trains of blue light pulses delivered to untreated slices initiated bursts of ACh-evoked, inhibitory post-synaptic currents (L-IPSCs) in CA1 pyramidal cells that lasted for 10's of seconds after the light stimulation ceased. L-IPSC occurred more reliably in slices treated with eserine and a very low concentration of 4-AP, which were therefore used in most experiments. The rhythmic, L-IPSCs were driven primarily by muscarinic ACh receptors (mAChRs), and could be suppressed by endocannabinoid release from pyramidal cells. Finally, low-frequency oscillations (LFOs) of local field potentials (LFPs) were significantly cross-correlated with the L-IPSCs, and reversal of the LFPs near s. pyramidale confirmed that the LFPs were driven by perisomatic inhibition. This optogenetic approach may be a useful complementary technique in future investigations of endogenous ACh effects

Indication of Density-Dependent Changes in Growth and Maturity of the Barndoor Skate on Georges Bank

Drastic increases or decreases in biomass often result in density-dependent changes in life history characteristics within a fish population. Acknowledging this phenomenon and in light of the recent biomass increase in Barndoor Skate Dipturus laevis, the current study re-evaluated the growth rate and sexual maturity of 244 specimens collected from 2009-2011within closed areas I and II on Georges Bank, USA. Ages were estimated using vertebral band counts from skate that ranged from 21 to 129cm TL. The von Bertalanffy growth function was applied to pooled age-at-length data. Parameter estimates from the current study of L = 155cm TL and k = 0.10 represent a significant decrease from previously reported parameters of L = 167cm TL and k = 0.14. In addition to changes in growth parameters, age at 50% maturity for both males (based on clasper length, testes mass, and percent mature spermatocytes) and females (based on data from shell gland mass, ovary mass, and follicle diameter) increased by 3years and 4years, respectively. Based on our results and the 10- to 12-year gap in the collection of samples, it is likely that Barndoor Skate within this region have exhibited pliability in life history parameters