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Background Additive manufacturing (AM) is rapidly growing, with new AM methods continually in development. Alloys processed with novel methods require systematic characterization to understand and validate the materials, especially for demanding fields. Objective This study characterized the mechanical properties and failure mechanisms of a Ti-6Al-4V alloy manufactured with bound metal deposition (BMD), a form of metal extrusion (MEX) AM. Methods Specimens made of Ti64 were printed via Desktop Metal’s Studio System 2 through a printing, debinding, and sintering process. The microstructure was analyzed with optical metallography and a newly developed open-source porosity analysis tool. Scanning electron microscopy (SEM), optical microscopy, and compositional analysis of green, brown, and sintered parts were conducted to study the material and its failure modes. Sintered specimens were tensile and hardness tested. Results As-sintered specimens exhibited ductility more than 10 times lower than wrought Ti64, partially due to contamination/impurity that formed brittle α -case titanium. Sources of contamination may have included the sacrificial Al 2 O 3 interlayer, the wax/polymer binder, and/or impurity introduction from the furnace. Fractography imaging found quasi-cleavage fracture initiating at areas of high surface roughness along the ceramic interlayer surface of the parts and transitioning into dimple rupture and intergranular decohesion. Conclusions Elevated contamination levels, high surface roughness, and internal porosity led to low elongation and ultimate strength in the Ti64 BMD alloy. With the processing route presented here, BMD for Ti64 may not be suitable for applications that demand high ductility and strength with minimal impurities, although with process refinement, the method may be promising for certain applications

The Light-only Liquid Xenon experiment (LoLX) employs a small-scale detector equipped with 96 Hamamatsu VUV4 silicon photomultipliers (SiPMs) submerged in 5 kg of liquid xenon (LXe) to perform characterization measurements of light production, transport and detection in xenon. In this work, we perform a novel measurement of the “external cross-talk” (ExCT) of SiPMs, where photons produced in the avalanche escape the device and produce correlated signals on other SiPMs. SiPMs are the photodetector technology of choice for next generation rare-event search experiments; understanding the sources and effects of correlated noise in SiPMs is critical for producing accurate estimates of detector performance and sensitivity projections. We measure the probability to observe ExCT through timing correlation of detected photons in low-light conditions within LoLX. Measurements of SiPM ExCT are detector dependent; thus the ExCT process is simulated and modelled using the Geant4 framework. Utilizing simulations, we determine the average transport and detection efficiency for ExCT photons within LoLX, a necessary input to extract the true ExCT probability and detector independent photon emission intensity. For an applied overvoltage of 4 V and 5 V, we measure a mean number of photons emitted into LXe per avalanche of 0 . 5 - 0.2 + 0.3 and 0 . 6 - 0.2 + 0.3 , respectively. Using an optical model to describe photon transmission through the SiPM surface, this corresponds to an estimated photon yield inside the bulk silicon of 20 - 9 + 11 and 25 - 9 + 12 photons per avalanche. The relative increase in intensity of SiPM ExCT emission between 4 and 5 V is consistent with expectation for the linear increase of gain with respect to overvoltage.

Spectral measurements of ultraviolet-B radiation made at Toronto since 1989 indicate that the intensity of light at wavelengths near 300 nanometers has increased by 35 percent per year in winter and 7 percent per year in summer. The wavelength dependence of these trends indicates that the increase is caused by the downward trend in total ozone that was measured at Toronto during the same period. The trend at wavelengths between 320 and 325 nanometers is essentially zero.

A putative driver of global amphibian decline is the panzootic chytrid fungus Batrachochytrium dendrobatidis (Bd). While Bd has been documented across continental Africa, its distribution in West Africa remains ambiguous. We tested 793 West African amphibians (one caecilian and 61 anuran species) for the presence of Bd. The samples originated from seven West African countries - Bénin, Burkina Faso, Côte d'Ivoire, Ghana, Guinea, Liberia, Sierra Leone - and were collected from a variety of habitats, ranging from lowland rainforests to montane forests, montane grasslands to humid and dry lowland savannahs. The species investigated comprised various life-history strategies, but we focused particularly on aquatic and riparian species. We used diagnostic PCR to screen 656 specimen swabs and histology to analyse 137 specimen toe tips. All samples tested negative for Bd, including a widespread habitat generalist Hoplobatrachus occipitalis which is intensively traded on the West African food market and thus could be a potential dispersal agent for Bd. Continental fine-grained (30 arc seconds) environmental niche models suggest that Bd should have a broad distribution across West Africa that includes most of the regions and habitats that we surveyed. The surprising apparent absence of Bd in West Africa indicates that the Dahomey Gap may have acted as a natural barrier. Herein we highlight the importance of this Bd-free region of the African continent - especially for the long-term conservation of several threatened species depending on fast flowing forest streams (Conraua alleni (\"Vulnerable\") and Petropedetes natator (\"Near Threatened\")) as well as the \"Critically Endangered\" viviparous toad endemic to the montane grasslands of Mount Nimba (Nimbaphrynoides occidentalis).

A new algorithm to retrieve nitrogen dioxide (NO2) column densities using MKIV (\"Mark IV\") Brewer spectrophotometers is described. The method includes several improvements, such as a more recent spectroscopic data set, the reduction of measurement noise, interference by other atmospheric species and instrumental settings, and a better determination of the zenith sky air mass factor. The technique was tested during an ad hoc calibration campaign at the high-altitude site of Izaña (Tenerife, Spain) and the results of the direct sun and zenith sky geometries were compared to those obtained by two reference instruments from the Network for the Detection of Atmospheric Composition Change (NDACC): a Fourier Transform Infrared Radiometer (FTIR) and an advanced visible spectrograph (RASAS-II) based on the differential optical absorption spectrometry (DOAS) technique. To determine the extraterrestrial constant, an easily implementable extension of the standard Langley technique for very clean sites without tropospheric NO2 was developed which takes into account the daytime linear drift of stratospheric nitrogen dioxide due to photochemistry. The measurement uncertainty was thoroughly determined by using a Monte Carlo technique. Poisson noise and wavelength misalignments were found to be the most influential contributors to the overall uncertainty, and possible solutions are proposed for future improvements. The new algorithm is backward-compatible, thus allowing for the reprocessing of historical data sets.

Physiological function in ectotherms is tightly linked to body temperature. As a result, the thermal sensitivity of physiological function may evolve to optimize fitness across different thermal environments. One hypothesis for the evolution of thermal sensitivity, coadaptation, predicts that optimal temperatures for performance should evolve to match the temperatures that an organism experiences in nature. Another hypothesis, countergradient variation, posits that genetic variation can compensate for decreased performance in cool environments, leading to physiological phenotypes that do not track environmental temperatures. On Mo’orea, French Polynesia, thermal ecology and physiology were studied in two morphologically similar skinks that differ in habitat use. Previous studies show thatEmoia impartends to inhabit closed-canopy and interior habitats that are cooler compared to those inhabited byEmoia cyanura, but these differences had not been quantified on Mo’orea. The goal of this study was to determine whether this pattern of habitat partitioning exists on Mo’orea and relates to interspecific differences in thermal physiology and to evaluate whether the evolution of thermal sensitivity supports coadaptation or countergradient variation. I found thatE. imparinhabits closed-canopy habitats with cooler substrates and with higher altitudes compared to habitats ofE. cyanura. Although the two species do not differ significantly in critical thermal minimum,E. imparhas a significantly lower preferred body temperature and critical thermal maximum than doesE. cyanura. Despite a preference for cooler habitats and temperatures,E. imparhas a warmer optimal temperature for sprint speed and sprints faster thanE. cyanuraat all temperatures, which supports the countergradient model of thermal adaptation. These results are robust to three different curve-fitting functions and support the view that generalist/specialist trade-offs do not universally constrain the evolution of performance curves.

During the Arctic polar springtime, dramatic ozone losses occur not only in the stratosphere but also in the underlying troposphere 1 . These tropospheric ozone loss events have been observed over large areas 2 , 3 in the planetary boundary layer (PBL) throughout the Arctic 4 , 5 . They are associated with enhanced concentrations of halogen species 1 , 6 , 7 , 8 , 9 and are probably caused by catalytic reactions involving bromine monoxide (BrO) and perhaps also chlorine monoxide (ClO) 1 , 10 , 11 , 12 . The origin of the BrO, the principle species driving the ozone destruction, is thought to be the autocatalytic release of bromine from sea salt accumulated on the Arctic snow pack 10 , 11 , 13 , followed by photolytic and heterogeneous reactions which produce and recycle the oxide 10 , 11 , 14 , 15 . Satellite observations have shown the horizontal and temporal extent of large BrO enhancements in the Arctic troposphere 16 , 17 , but the vertical distribution of the BrO has remained uncertain. Here we report BrO observations obtained from a high-altitude aircraft that suggest the presence of significant amounts of BrO not only in the PBL but also in the free troposphere above it. We believe that the BrO is transported from the PBL into the free troposphere through convection over large Arctic ice leads (openings in the pack ice). The convective transport also lifts ice crystals and water droplets well above the PBL 18 , 19 , thus providing surfaces for heterogeneous reactions that can recycle BrO from less-reactive forms and thereby maintain its ability to affect the chemistry of the free troposphere.

The Extended-range Atmospheric Emitted Radiance Interferometer (E-AERI) was installed at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut, Canada in October 2008. Spectra from the E-AERI provide information about the radiative balance and budgets of trace gases in the Canadian high Arctic. Measurements are taken every 7 min year-round, including polar night when the solar-viewing spectrometers at PEARL are not operated. This allows E-AERI measurements to fill the gap in the PEARL dataset during the four months of polar night. Measurements were taken year-round in 2008–2009 at the PEARL Ridge Lab, which is 610 m a.s.l. (above sea-level), and from 2011 onwards at the Zero-Altitude PEARL Auxiliary Lab (0PAL), which is at sea level 15 km from the Ridge Lab. Total columns of O3, CO, CH4, and N2O have been retrieved using a modified version of the SFIT2 retrieval algorithm adapted for emission spectra. This provides the first ground-based nighttime measurements of these species at Eureka. Changes in the total columns driven by photochemistry and dynamics are observed. Analyses of E-AERI retrievals indicate accurate spectral fits (root-mean-square residuals consistent with noise) and a 10–15% uncertainty in the total column, depending on the trace gas. O3 comparisons between the E-AERI and a Bruker IFS 125HR Fourier transform infrared (FTIR) spectrometer, three Brewer spectrophotometers, two UV-visible ground-based spectrometers, and a System D'Analyse par Observations Zenithales (SAOZ) at PEARL are made from 2008–2009 and for 2011. 125HR CO, CH4, and N2O columns are also compared with the E-AERI measurements. Mean relative differences between the E-AERI and the other spectrometers are 1–10% (14% is for the un-smoothed profiles), which are less than the E-AERI's total column uncertainties. The E-AERI O3 and CO measurements are well correlated with the other spectrometers (r > 0.92 with the 125HR). The 24 h diurnal cycle and 365-day seasonal cycle of CO are observed and their amplitudes are quantified by the E-AERI (6–12 and 46%, respectively). The seasonal variability of H2O has an impact on the retrievals, leading to larger uncertainties in the summer months. Despite increased water vapour at the lower-altitude site 0PAL, measurements at 0PAL are consistent with measurements at PEARL.

In the fall of 2010, Senator Patrick Leahy introduced a bill that would have overridden a New Deal-era federal statute forbidding retired Justices from serving by designation on the Supreme Court of the United States. The Leahy bill would have authorized the Court to recall willing retired Justices to substitute for recused Justices. This Article uses the Leahy bill as a springboard for considering a number of important constitutional and policy questions, including whether the possibility of 4—4 splits justifies the substitution of a retired Justice for an active one; whether permitting retired Justices to substitute for recused Justices would violate Article III's requirement that there be \"one supreme Court\"; and whether the ethical limitations on extrajudicial activities should be the same for active and retired judges and Justices. In addition to relying on published material, we draw on information gleaned from our interview with retired Justice Stevens, who was the original source of the Leahy proposal.