Controls on dissolved organic carbon quantity and chemical character in temperate rivers of North America

Understanding the processes controlling the transfer and chemical composition of dissolved organic carbon (DOC) in freshwater systems is crucial to understanding the carbon cycle and the effects of DOC on water quality. Previous studies have identified watershed‐scale controls on bulk DOC flux and concentration among small basins but fewer studies have explored controls among large basins or simultaneously considered the chemical composition of DOC. Because the chemical character of DOC drives riverine biogeochemical processes such as metabolism and photodegradation, accounting for chemical character in watershed‐scale studies will improve the way bulk DOC variability in rivers is interpreted. We analyzed DOC quantity and chemical character near the mouths of 17 large North American rivers, primarily between 2008 and 2010, and identified watershed characteristics that controlled variability. We quantified DOC chemical character using both specific ultraviolet absorbance at 254 nm (SUVA254) and XAD‐resin fractionation. Mean DOC concentration ranged from 2.1 to 47 mg C L−1 and mean SUVA254 ranged from 1.3 to 4.7 L mg C−1 m−1. We found a significant positive correlation between basin wetland cover and both bulk DOC concentration (R2 = 0.78; p \u3c 0.0001) and SUVA254 (R2 = 0.91; p \u3c 0.0001), while other land use characteristics were not correlated. The strong wetland relationship with bulk DOC concentration is similar to that found by others in small headwater catchments. However, two watersheds with extremely long surface water residence times, the Colorado and St. Lawrence, diverged from this wetland relationship. These results suggest that the role of riverine processes in altering the terrestrial DOC signal at the annual scale was minimal except in river systems with long surface water residence times. However, synoptic DOC sampling of both quantity and character throughout river networks will be needed to more rigorously test this finding. The inclusion of DOC chemical character will be vital to achieving a more complete understanding of bulk DOC dynamics in large river systems

Multi-Gain-Stage InGaAs Avalanche Photodiode with Enhanced Gain and Reduced Excess Noise

We report the design, fabrication, and test of an InGaAs avalanche photodiode (APD) for 950-1650 nm wavelength sensing applications. The APD is grown by molecular beam epitaxy on InP substrates from lattice-matched InGaAs and InAlAs alloys. Avalanche multiplication inside the APD occurs in a series of asymmetric gain stages whose layer ordering acts to enhance the rate of electron-initiated impact ionization and to suppress the rate of hole-initiated ionization when operated at low gain. The multiplication stages are cascaded in series, interposed with carrier relaxation layers in which the electric field is low, preventing avalanche feedback between stages. These measures result in much lower excess multiplication noise and stable linear-mode operation at much higher avalanche gain than is characteristic of APDs fabricated from the same semiconductor alloys in bulk. The noise suppression mechanism is analyzed by simulations of impact ionization spatial distribution and gain statistics, and measurements on APDs implementing the design are presented. The devices employing this design are demonstrated to operate at linear-mode gain in excess of 6000 without avalanche breakdown. Excess noise characterized by an effective impact ionization rate ratio below 0.04 were measured at gains over 1000

Bridging the gap: pracademics in foreign policy

In his seminal work Bridging the Gap: Theory and Practice in Foreign Policy, Alexander George (1993) lamented the great divide between academia and the foreign policymaking community, arguing that greater interaction between scholars and policymakers would produce better policy. We share George's belief that scholars and practitioners each have much to offer the other. In fact, a wide spectrum of opportunities exists for scholars in the field of political science to engage in meaningful public service that can enhance every aspect of their careers, as well as contribute to international understanding

Transcranial Direct Current Stimulation: A viable therapeutic option for depression?

Transcranial direct current stimulation (tDCS) is a form of neurostimulation that has recently regained popularity in its experimental use. tDCS utilizes a direct current applied to the scalp via electrodes to induce long-term changes to cortical excitability. A series of recent studies and reviews concluded its efficacy as a potential treatment for major depressive disorder. However, further research is required to establish effective montages and intensities of treatment to promote efficacy while reducing adverse effects. These potential future studies should include wider representative samples with more detailed reporting of adverse effects. Until then, this perspective piece argues that tDCS should continue to be considered as a potential addition to the therapies used to manage depression

Iñupiaq Knowledge of Polar Bears (Ursus maritimus) in the Southern Beaufort Sea, Alaska

Successful wildlife management depends upon coordination and consultation with local communities. However, much of the research used to inform management is often derived solely from data collected directly from wildlife. Indigenous people living in the Arctic have a close connection to their environment, which provides unique opportunities to observe their environment and the ecology of Arctic species. Further, most northern Arctic communities occur within the range of polar bears (nanuq, Ursus maritimus) and have experienced significant climatic changes. Here, we used semi-structured interviews from 2017 to 2019 to document Iñupiaq knowledge of polar bears observed over four decades in four Alaskan communities in the range of the Southern Beaufort Sea polar bear subpopulation: Wainwright, Utqiaġvik, Nuiqsut, and Kaktovik. All but one of 47 participants described directional and notable changes in sea ice, including earlier ice breakup, later ice return, thinner ice, and less multiyear pack ice. These changes corresponded with observations of bears spending more time on land during the late summer and early fall in recent decades—observations consistent with scientific and Indigenous knowledge studies in Alaska, Canada, and Greenland. Participants noted that polar bear and seal body condition and local abundance either varied geographically or exhibited no patterns. However, participants described a recent phenomenon of bears being exhausted and lethargic when arriving on shore in the summer and fall after extensive swims from the pack ice. Further, several participants suggested that maternal denning is occurring more often on land than sea ice. Participants indicated that village and regional governments are increasingly challenged to obtain resources needed to keep their communities safe as polar bears spend more time on land, an issue that is likely to be exacerbated both in this region and elsewhere as sea ice loss continues. La gestion réussie de la faune dépend des efforts de coordination et de consultation avec les collectivités locales. Toutefois, il arrive souvent qu’une grande partie de la recherche utilisée pour éclairer la gestion dérive uniquement des données recueillies directement de la faune. Les peuples autochtones qui vivent dans l’Arctique entretiennent des liens étroits avec leur environnement, ce qui crée des occasions uniques d’observer l’environnement et l’écologie des espèces de l’Arctique. Il y a également lieu de remarquer que la plupart des collectivités du nord de l’Arctique se trouvent dans l’aire de répartition des ours polaires (nanuq, Ursus) et connaissent d’importants changements climatiques. Dans le cadre de cette étude, nous nous sommes appuyés sur des entrevues semi-structurées réalisées entre 2017 et 2019 pour documenter les connaissances des Iñupiaq au sujet des ours polaires découlant d’observations échelonnées sur quatre décennies dans quatre collectivités de l’Alaska situées dans l’aire de répartition de la sous-population d’ours polaires du sud de la mer de Beaufort : Wainwright, Utqiaġvik, Nuiqsut et Kaktovik. Les 47 participants, sauf un, ont décrit des changements directionnels et remarquables en ce qui a trait à la glace de mer, dont des débâcles plus hâtives, le retour plus tardif de la glace, de la glace plus mince et moins de banquises pluriannuelles. Ces changements correspondent aux observations d’ours qui passent plus de temps sur la terre ferme en fin d’été et en début d’automne au cours des dernières décennies. Ces observations coïncident avec les études sur les connaissances scientifiques et autochtones réalisées en Alaska, au Canada et au Groenland. Les participants ont fait remarquer que la condition corporelle des ours polaires et des phoques ainsi que leur abondance à l’échelle locale variaient d’une région à l’autre ou n’affichaient aucune tendance. Cependant, les participants ont décrit un phénomène récent selon lequel les ours sont épuisés et léthargiques lorsqu’ils arrivent sur la rive à l’été et à l’automne, après avoir parcouru de longues distances à la nage depuis les banquises. Aussi, plusieurs participants ont laissé entendre que les aires de mise bas se retrouvent plus souvent sur la terre ferme que sur la glace de mer. Les participants ont indiqué que le gouvernement des villages et les gouvernements régionaux ont de plus en plus de difficulté à obtenir les ressources nécessaires pour assurer la sécurité de leurs collectivités, car les ours polaires passent plus de temps sur la terre ferme, un enjeu qui risque de s’aggraver, tant dans cette région qu’ailleurs, à mesure que la glace de mer continuera de perdre de l’ampleur.

Non-Local Model for the Spatial Distribution of Impact Ionization Events in Avalanche Photodiodes

We report an extension of the analytical dead space multiplication theory that provides the means to theoretically determine the spatial distribution of electron and hole impact-ionization events in an arbitrarily specified heterojunction multiplication region. The model can be used to understand the role of the dead space in regularizing the locations of impact ionization. It can also be utilized to analyze, design, and optimize new generations of ultra-low noise, multistaged gain avalanche photodiodes based upon judiciously energizing and relaxing carriers to enhance electron impact ionization and suppress hole impact ionization

Observations on Shorefast Ice Dynamics in Arctic Alaska and the Responses of the Iñupiat Hunting Community

Although shorefast sea ice forms a platform that facilitates travel, camping, and hunting by Iñupiat subsistence hunters and fishers in the western Arctic, the nearshore sea-ice zone remains an unforgiving and dynamic environment. Traditional hunters constantly hone site-specific experiences and skills with which to optimize the reward-to-risk ratio inherent in operating from this coastal ice. Nearshore ice conditions nevertheless can change suddenly, endangering even the most experienced subsistence hunters. This study examines two (of several) 20th-century events, 40 years apart, in which shorefast ice failed, threatening Iñupiat whale hunters with loss of confidence, livelihood, and life. These events differed in character. In one event, the shorefast ice was "crushed" by moving ice floes. In the other, the shorefast ice broke free of land. Our examination focuses on the relationship of subsistence hunters to the ice, the environmental causes of ice failures, the evolving technology for predicting ice behavior, and the longer-term implications of global change for this system. The complexity of geophysical processes underlying coastal ice behavior makes ice failures unpredictable. Thus, hunters must assume and manage risk. The variable and uncertain environment to which whale hunters are accustomed has produced an inherent flexibility that has helped them adapt to new conditions and will continue to do so in the future.Bien que la banquise côtière constitue une plate-forme qui permet aux Iñupiat de l'Arctique de l'Ouest de se déplacer et de camper lorsqu'ils pratiquent la chasse et la pêche de subsistance, la zone de banquise proche du littoral reste un milieu dynamique qui ne pardonne pas. Les chasseurs traditionnels améliorent constamment les habiletés et l'expérience reliées à des sites particuliers, qui leur permettent d'optimiser le rapport récompense-risque inhérent au fait de travailler depuis la glace côtière. Les conditions de cette dernière peuvent toutefois changer brusquement, mettant en danger même les chasseurs de subsistance les plus chevronnés. Cette étude se penche sur deux (parmi plusieurs) épisodes survenus au XXe siècle, à 40 ans d'écart, durant lesquels la banquise côtière s'est rompue, ébranlant la confiance des baleiniers Iñupiat et menaçant leur moyen de subsistance ainsi que leur vie. Ces événements étaient de nature différente. Dans l'un, la glace côtière avait été «écrasée» par des floes en dérive. Dans l'autre, la banquise côtière s'était détachée de la terre ferme. Notre étude se concentre sur le rapport entre les chasseurs de subsistance et la glace, les causes environnementales de la fragilisation de la glace, la technologie mise au point actuellement qui permettrait de prédire le comportement de la glace, et les implications à long terme du changement climatique pour ce système. La complexité des processus géophysiques sous-jacents au comportement de la banquise côtière fait que les ruptures de la banquise sont imprévisibles. Les chasseurs doivent donc assumer le risque et le gérer. L'environnement variable et incertain auquel sont accoutumés les chasseurs de baleine leur a donné une souplesse inhérente qui les a aidés à s'adapter à de nouvelles conditions et continuera de le faire dans l'avenir

Rapid creation of BAC-based human artificial chromosome vectors by transposition with synthetic alpha-satellite arrays

Efficient construction of BAC-based human artificial chromosomes (HACs) requires optimization of each key functional unit as well as development of techniques for the rapid and reliable manipulation of high-molecular weight BAC vectors. Here, we have created synthetic chromosome 17-derived alpha-satellite arrays, based on the 16-monomer repeat length typical of natural D17Z1 arrays, in which the consensus CENP-B box elements are either completely absent (0/16 monomers) or increased in density (16/16 monomers) compared to D17Z1 alpha-satellite (5/16 monomers). Using these vectors, we show that the presence of CENP-B box elements is a requirement for efficient de novo centromere formation and that increasing the density of CENP-B box elements may enhance the efficiency of de novo centromere formation. Furthermore, we have developed a novel, high-throughput methodology that permits the rapid conversion of any genomic BAC target into a HAC vector by transposon-mediated modification with synthetic alpha-satellite arrays and other key functional units. Taken together, these approaches offer the potential to significantly advance the utility of BAC-based HACs for functional annotation of the genome and for applications in gene transfer

Discrimination of Photon- and Dark-Initiated Signals in Multiple Gain Stage APD Photoreceivers

We demonstrate the ability of linear mode single carrier multiplication (SCM) avalanche photodiode (APD)-based optical receivers to discriminate single-photon-initiated avalanche events from dark-current-initiated events. Because of their random spatial origin in discrete regions of the depletion region, in the SCM APD the dark-generated carriers multiply differently than the photon-generated carriers. This causes different count distributions and necessitates different statistical descriptions of the signal contributions from photon- and dark-originating impulse responses. To include dark carriers in the performance models of the SCM APD, we considered the influence of the spatial origin of the ionization chains on a receiver\u27s noise performance over the times the optical pulse is integrated by the receiver\u27s decision circuits. We compare instantaneous (time-resolved) numeric and pseudo-DC analytical models to measured SCM APD data. It is shown that it is necessary to consider both the distribution of spatial origin and the instantaneous properties of the ionization chains to describe statistically an SCM APD receiver. The ability of SCM APD receivers to discriminate single photon events from single dark events is demonstrated, and the effective gain and excess noise contributions of the light- and dark-initiated avalanche events and their influence on receiver sensitivity and signal-to-noise characteristics are shown

Traditional Knowledge of the Bowhead Whale (Balaena mysticetus) around St. Lawrence Island, Alaska

Despite considerable research on the bowhead whale (Balaena mysticetus) in Alaskan waters, relatively little has been conducted in the northern Bering Sea. To help fill this gap, we documented traditional knowledge of bowhead whales held by Yupik whalers of St. Lawrence Island, Alaska. Results include descriptions of the seasonal movements, distribution, and abundance of bowheads near St. Lawrence Island. The bowhead population appears to be increasing, as is the number of young whales seen. Changing environmental conditions are influencing distribution, leading to a somewhat earlier spring migration and a greater presence of whales near the island in winter. Hunters describe two bowhead migration paths near the island. It is unknown whether these two paths are used by two genetically different groups of whales, or whether the animals are simply responding differently to oceanographic conditions or geography. Our findings are consistent with studies of this bowhead population conducted elsewhere and suggest that additional research is needed to determine possible migratory (or genetic) differences between the two migrations of whales seen at St. Lawrence Island.Bien que de nombreuses recherches aient été effectuées sur la baleine boréale (Balaena mysticetus) dans les eaux alaskiennes, peu de recherches ont été réalisées dans le nord de la mer de Béring. Afin de combler ce vide, nous avons pris note des connaissances traditionnelles des chasseurs de baleines yupik en matière de baleines boréales sur l’île Saint-Laurent, en Alaska. Les données obtenues prennent la forme de la description des mouvements saisonniers, de la répartition et de l’abondance des baleines boréales près de l’île Saint-Laurent. La population de baleines boréales semble augmenter, comme c’est aussi le cas du nombre de jeunes baleines. L’évolution des conditions environnementales a des effets sur la répartition des baleines et engendre une migration un peu plus hâtive au printemps de même qu’une plus grande présence de baleines près de l’île l’hiver. Les chasseurs décrivent deux chemins de migration pour les baleines boréales. Nous ne savons pas si ces deux chemins sont empruntés par deux groupes de baleines différents du point de vue génétique ou si les baleines réagissent simplement différemment aux conditions océanographiques ou géographiques. Nos constatations sont conformes aux études de cette population de baleines boréales réalisées ailleurs et laissent croire que des recherches plus poussées s’avèrent nécessaires pour déterminer les différences migratoires (ou génétiques) entre les deux migrations de baleines en évidence à l’île Saint-Laurent