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Accurate information about the number of cats living outdoors and how they respond to different kinds of management are necessary to quell debates about outdoor cat policy. The DC Cat Count will develop the tools and methodologies needed to realize this possibility and make them available for broader use. This three-year initiative represents a major collaboration between animal welfare organizations and wildlife scientists. Its unique and innovative approach is to use the best scientific methods to quantify all subpopulations of cats in the District of Columbia (outdoor, owned, and shelter cats), concurrently test and optimize simpler methods that can be used to measure cat populations by diverse users at scale, and identify the types of interventions that are likely to accomplish desired outcomes most efficiently. Ultimately, we believe that this approach is more likely to improve outcomes for both cats and wildlife than a continuation of the status quo.

The complete set of intrinsic dimensionless parameters of a packaged and fiber-pigtailed distributed feedback (DFB) semiconductor laser are extracted from the non-linear operational stability boundaries of the optical-injection-locking (OIL) architecture. Specifically, this procedure is done by relating the intrinsic parameters to the injection ratios corresponding to the Hopf bifurcation points at zero detuning, as well as the detuning of the Hopf-Saddle-Node point. The bifurcation points of the injected laser's operational space are found by coupling its output into a high-resolution optical spectrum analyzer. This is enabled by establishing a 30 dB side mode suppression ratio between the central mode and Period 1 oscillations to define the boundaries of Stable Locking. Along with the laser's threshold current and free-running relaxation oscillation frequencies, performing these measurements over a range of pumping values allows for the calculation of the laser's linewidth enhancement factor, irrespective of the device packaging. Utilizing a high pump approximation, the remaining dimensionless parameters are extracted after obtaining the photon lifetime. Using this approach, the operational capabilities of an arbitrarily-packaged laser can be determined, allowing for the analysis of an injected laser's operational space for a variety high-frequency and dynamical applications.

A semi-analytical dimensionless formula is presented for predicting the period-one frequency of an optically-injected laser over a wide range of injection powers and positive detunings. The result shows that for any given injected optical power, there exists an optimal detuning at which the period-one frequency is maximized. The formula is applied to a tabletop optical injection system with a commercially-available quantum-well distributed feedback laser with previously unknown design parameters. By extrapolating the linearity of the period-one frequencies at zero-detuning and weak-injection regimes, the physical control parameters of the laser are approximated to the analytical formula for wide ranges of injection powers and positive detunings. The accuracy of the model is experimentally verified, achieving period-one frequencies as high as 84.7 GHz.

Free-roaming cats are a conservation concern in many areas but identifying their impacts and developing mitigation strategies requires a robust understanding of their distribution and density patterns. Urban and residential areas may be especially relevant in this process because free-roaming cats are abundant in these anthropogenic landscapes. Here, we estimate the occupancy and density of free-roaming cats in Washington D.C. and relate these metrics to known landscape and social factors. We conducted an extended camera trap survey of public and private spaces across D.C., and analyzed data collected from 1,483 camera deployments from 2018-2020. We estimated citywide cat distribution by fitting hierarchical occupancy models and further estimated cat abundance using a novel random thinning spatial capture-recapture model that allows for the use of photos that can and cannot be identified to individual. Within this model, we utilized individual covariates that provided identity exclusions between photos of unidentifiable cats with inconsistent coat patterns, thus increasing the precision of abundance estimates. This combined model also allowed for unbiased estimation of density when animals cannot be identified to individual at the same rate as for free-roaming cats whose identifiability depended on their coat characteristics. Cat occupancy and abundance declined with increasing distance from residential areas, an effect that was more pronounced in wealthier neighborhoods. There was noteworthy absence of cats detected in larger public spaces and forests. Realized densities ranged from 0.02-1.75 cats/ha in sampled areas, resulting in a district-wide estimate of ~ 7,296 free-roaming cats. Ninety percent of cat detections lacked collars and nearly 35% of known individuals were ear-tipped, indicative of district Trap-Neuter-Return (TNR) programs. These results suggest that we mainly sampled and estimated the unowned cat subpopulation, such that indoor/outdoor housecats were not well represented. The precise estimation of cat population densities is difficult due to the varied behavior of subpopulations within free-roaming cat populations (housecats, stray and feral cats), but our methods provide a first step in establishing citywide baselines to inform data-driven management plans for free-roaming cats in urban environments. This article is protected by copyright. All rights reserved.

The implantation and rapid thermal annealing of sulfur (S+) ions has previously been shown to be an effective method in non-epitaxially attaining hole carrier concentrations as high as $1\times {10^{19}} \; \rm cm^{-3}$ in gallium antimonide (GaSb). This technique was used to fabricate a photovoltaic diode by delta-doping the front surface of a p-type GaSb substrate and forming a p++/p junction. The steep potential created using this process is increased by strong Fermi level pinning at the metal/p++ interface, resulting in a camel diode with a barrier height of 0.51 eV. A post-fabrication etch process succeeded in improving the short circuit current density to 41.8 mA/cm $^2$ and the internal quantum efficiency to 90% by enhancing the carrier lifetime away from the front metal contact grid. Likewise, the open circuit voltage improved to 0.21 V, with an intrinsic fill factor above 40%. These results offer the potential of a significantly higher power output than similar non-epitaxial devices made on n-type GaSb substrates.

A tunable photonic oscillator with continuous tuning from 5–200 GHz is modeled and realized using period 1 dynamics in an injection-locking system. The measured frequencies match the values predicted based on the injection ratio, optical detuning, and extracted operating parameters of the free-running diode laser.

This article is protected by copyright. All rights reserved. With the accelerating pace of global change, it is imperative that we obtain rapid inventories of the status and distribution of wildlife for ecological inferences and conservation planning. To address this challenge, we launched the SNAPSHOT USA project, a collaborative survey of terrestrial wildlife populations using camera traps across the United States. For our first annual survey, we compiled data across all 50 states during a 14-week period (17 August - 24 November of 2019). We sampled wildlife at 1509 camera trap sites from 110 camera trap arrays covering 12 different ecoregions across four development zones. This effort resulted in 166,036 unique detections of 83 species of mammals and 17 species of birds. All images were processed through the Smithsonian's eMammal camera trap data repository and included an expert review phase to ensure taxonomic accuracy of data, resulting in each picture being reviewed at least twice. The results represent a timely and standardized camera trap survey of the USA. All of the 2019 survey data are made available herein. We are currently repeating surveys in fall 2020, opening up the opportunity to other institutions and cooperators to expand coverage of all the urban-wild gradients and ecophysiographic regions of the country. Future data will be available as the database is updated at eMammal.si.edu/snapshot-usa, as well as future data paper submissions. These data will be useful for local and macroecological research including the examination of community assembly, effects of environmental and anthropogenic landscape variables, effects of fragmentation and extinction debt dynamics, as well as species-specific population dynamics and conservation action plans. There are no copyright restrictions; please cite this paper when using the data for publication. Publisher PDF

Urbanization is increasing globally, fragmenting habitats and prompting human–wildlife conflict. Urban wildlife research is concurrently expanding, but sampling methods are often biased towards large and intact habitats in public green spaces, neglecting the far more abundant, but degraded, habitats in the urban matrix. Here, we introduce the Five P’s of Urban Ecology—Partnerships, Planning, Placements, Public participation and Processing—as a path to overcoming the logistical barriers often associated with camera-trapping in the urban matrix. Though the Five P’s can be applied to a variety of urban sampling methods, we showcase the camera-trapping efforts of the DC Cat Count project in Washington, DC, as a case study. We compared occupancy models for eight urban mammal species using broad categorizations of land cover and local land use to determine drivers of mammal occurrence within the urban matrix as compared with urban habitat patches. Many native species maintained a strong association with large, semi-natural green spaces, but occupancy was not limited to these locations, and in some cases, the use of private yards and the built environment were not notably different. Furthermore, some species exhibited higher occupancy probabilities in developed areas over green spaces. Though seemingly intuitive, we offer advice on how to greatly reduce habitat-biased sampling methods in urban wildlife research and illustrate the importance of doing so to ensure accurate results that support the formation of effective urban planning and policy.

An optically-injected semiconductor laser is characterized with no prior knowledge of the physical design parameters. Employing the two Hopf bifurcation points at zero-detuning and Hopf-Saddle-Node point, its operating parameters are extracted.

Urban heat islands affect animal behavior broadly, but their effects on food webs are less understood. In November 2018, camera trap serendipity led to the detection of a red-tailed hawk (Buteo jamaicensis) preying upon an eastern worm snake (Carphophis amoenus amoenus) in Washington, D.C. – a previously undescribed trophic interaction. While red-tailed hawk activity is known to peak in cooler months, above-ground snake activity is expected to cease as winter approaches. We hypothesized this previously undescribed interaction was facilitated by the urban heat island effect prolonging the warm season in urban areas. To explore this hypothesis, we paired eastern worm snake observations from the iNaturalist platform with the monthly average temperatures from their nearest weather monitoring stations. Worm snake observations in areas at least 1 °C cooler than the average monthly urban temperature occurred between April and September. In contrast, observations in warmer, more developed areas (i.e. the urban heat island) occurred between March and December. Though other factors may be at play, we propose that relatively warmer winter temperatures found in urban ecosystems will continue to prompt novel trophic interactions as urban landscapes become more prolific.

GaSb cells grown by MBE have high quality material growth, but struggle to overcome high sheet resistance in p-type emitter designs. To overcome this issue, GaSb photovoltaic devices with a p-type emitter were fabricated and coated with a single layer of graphene. Graphene's intrinsic transport properties and low optical transparency make it a suitable candidate for use as a transparent conducting electrode. By adding single layer graphene to the surface of the fabricated GaSb photovoltaics, the series resistance and shunt resistance are improved, with an associated increase in fill factor and efficiency.

Ion implantation has been studied relatively little as a nonepitaxial doping method for GaSb due in part to anomalous swelling that occurs at high doses. Aside from beryllium (Be+), there has been little success in identifying other ions as an implant species to dope a GaSb substrate p-type. In this paper, the role of sulfur (S+) as an implant species is investigated for doping GaSb and compared to Be+. Whereas the Be+ implant yields modest hole concentrations as a result of incomplete dopant activation, the S+ implant at a similar dose level realizes p-type carrier concentrations above 1 × 1019 cm−3 with sheet densities as high as 3.5 times the total implanted dose. X-ray diffraction spectroscopy shows that a postimplant anneal at 600 °C successfully recovers the crystallinity of the material, but atomic force microscopy suggests that surface damage may be the cause of the high carrier concentration from the sulfur implant. Preliminary photovoltaic data are reported for a device that employs the sulfur implant technique into a p-type GaSb substrate.Ion implantation has been studied relatively little as a nonepitaxial doping method for GaSb due in part to anomalous swelling that occurs at high doses. Aside from beryllium (Be+), there has been little success in identifying other ions as an implant species to dope a GaSb substrate p-type. In this paper, the role of sulfur (S+) as an implant species is investigated for doping GaSb and compared to Be+. Whereas the Be+ implant yields modest hole concentrations as a result of incomplete dopant activation, the S+ implant at a similar dose level realizes p-type carrier concentrations above 1 × 1019 cm−3 with sheet densities as high as 3.5 times the total implanted dose. X-ray diffraction spectroscopy shows that a postimplant anneal at 600 °C successfully recovers the crystallinity of the material, but atomic force microscopy suggests that surface damage may be the cause of the high carrier concentration from the sulfur implant. Preliminary photovoltaic data are reported for a device that employs the sulfur i...

An optimization it done on the fill factor of an M BE-grown p-on-n (iaSb photovoltaic by reducing the series resistance brought on by the layout of the front metal electrodes while simultaneously minimizing their coverage area. The optimization indicates a variation in the substrate carrier lifetime.

GaSb thermophotovoltaic (TPV) devices were fabricated using a Molecular Beam Epitaxy (MBE) technique. Different emitter thicknesses (d e ) were studied to maximize the TPV cell’s short circuit current density. In this regard, the fabricated TPV device’s emitter was incrementally wet-etched and characterized to find the optimal thickness value. Simulations were performed using the Crosslight APSYS® platform over the full-spectrum range in order to predict device performance for different designs, while maximizing the photocurrent generation and enhancing the emitter sheet resistance. TPV devices were characterized electrically and optically. These experimental data showed that the etched emitter has minimal impact on the measured short circuit current density (J sc ) while simulated results demonstrated an optimal d e of 200 nm. Keywords: Large-area GaSb Thermophotovoltaic (TPV) Devices, Emitter Thickness, Short Circuit Current Density, Optimization, Carrier Lifetime. 1. INTRODUCTION

GaSb thermophotovoltaic cells fabricated using Molecular Beam Epitaxy (MBE) and ion implantation techniques are studied. Challenges including different defect formation mechanisms using MBE and ion-induced defects using ion implantation were investigated by cross-sectional Transmission Electron Microscopy (XTEM), X-Ray Diffraction spectroscopy (XRD) and Scanning Electron Microscopy (SEM). For MBE grown TPVs, several approaches were used to suppress defects, including substrate preparation and using different MBE reactors. For ion-implanted TPVs, different implant doses and energies were tested to minimize the crystal damage and various Rapid Thermal Anneal (RTA) process recipes were studied to maximize the crystal recovery. Large area TPV cells with 1 × 1 cm dimensions were fabricated using these techniques, then electrically and optically characterized. Ideality factors and dark saturation currents were measured and compared for various TPVs.