It has been proposed that entangled two-photon absorption (E2PA) can be observed with up to 1010 lower photon flux than its classical counterpart, therefore enabling ultralow-power two-photon ...fluorescence microscopy. However, there is a significant controversy regarding the magnitude of this quantum enhancement in excitation efficiency. We investigated the fluorescence signals from Rhodamine 6G and LDS798 excited with a CW laser or an entangled photon pair source at ∼1060 nm. We observed a signal that originates from hot-band absorption (HBA), which is one-photon absorption from thermally populated vibrational levels of the ground electronic state. This mechanism, which has not been previously discussed in the context of E2PA, produces a signal with a linear power dependence, as would be expected for E2PA. For the typical conditions under which E2PA measurements are performed, contributions from the HBA process could lead to a several orders of magnitude overestimate of the quantum advantage.
In the Arctic Ocean's southern Beaufort Sea (SB), the length of the sea ice melt season (i.e., period between the onset of sea ice break-up in summer and freeze-up in fall) has increased ...substantially since the late 1990s. Historically, polar bears (Ursus maritimus) of the SB have mostly remained on the sea ice year-round (except for those that came ashore to den), but recent changes in the extent and phenology of sea ice habitat have coincided with evidence that use of terrestrial habitat is increasing. We characterized the spatial behavior of polar bears spending summer and fall on land along Alaska's north coast to better understand the nexus between rapid environmental change and increased use of terrestrial habitat. We found that the percentage of radiocollared adult females from the SB subpopulation coming ashore has tripled over 15 years. Moreover, we detected trends of earlier arrival on shore, increased length of stay, and later departure back to sea ice, all of which were related to declines in the availability of sea ice habitat over the continental shelf and changes to sea ice phenology. Since the late 1990s, the mean duration of the open-water season in the SB increased by 36 days, and the mean length of stay on shore increased by 31 days. While on shore, the distribution of polar bears was influenced by the availability of scavenge subsidies in the form of subsistence-harvested bowhead whale (Balaena mysticetus) remains aggregated at sites along the coast. The declining spatio-temporal availability of sea ice habitat and increased availability of human-provisioned resources are likely to result in increased use of land. Increased residency on land is cause for concern given that, while there, bears may be exposed to a greater array of risk factors including those associated with increased human activities.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
Using the shadow insurance setting, we study the interplay between tax and nontax incentives in income shifting. Shadow insurance involves intercompany transactions designed to help firms ...meet regulatory capital requirements. However, prior to the Tax Cuts and Jobs Act of 2017 (TCJA), foreign-owned life insurance firms could save taxes by using shadow insurance to shift U.S. profits to tax havens. Consistent with expectations, we find that while nontax incentives appear to be the dominant factor behind firms' use of shadow insurance, tax considerations also played a role for certain firms. We also find that shadow insurance is associated with lower liquid asset holdings and increased credit risk. Overall, our results suggest that taxes were an important incentive for foreign-owned life insurance firms to use shadow insurance pre-TCJA. Moreover, in this setting, nontax considerations appeared to have motivated U.S.-owned firms' use of tax havens.
Animal movement is a fundamental ecological process affecting the survival and reproduction of individuals, the structure of populations, and the dynamics of communities. Methods to quantify animal ...movement and spatiotemporal abundances, however, are generally separate and therefore omit linkages between individual‐level and population‐level processes. We describe an integrated spatial capture–recapture (SCR) movement model to jointly estimate (1) the number and distribution of individuals in a defined spatial region and (2) movement of those individuals through time. We applied our model to a study of polar bears (Ursus maritimus) in a 28,125 km2 survey area of the eastern Chukchi Sea, USA in 2015 that incorporated capture–recapture and telemetry data. In simulation studies, the model provided unbiased estimates of movement, abundance, and detection parameters using a bivariate normal random walk and correlated random walk movement process. Our case study provided detailed evidence of directional movement persistence for both male and female bears, where individuals regularly traversed areas larger than the survey area during the 36‐day study period. Scaling from individual‐ to population‐level inferences, we found that densities varied from <0.75 bears/625 km2 grid cell/day in nearshore cells to 1.6–2.5 bears/grid cell/day for cells surrounded by sea ice. Daily abundance estimates ranged from 53 to 69 bears, with no trend across days. The cumulative number of unique bears that used the survey area increased through time due to movements into and out of the area, resulting in an estimated 171 individuals using the survey area during the study (95% credible interval 124–250). Abundance estimates were similar to a previous multiyear integrated population model using capture–recapture and telemetry data (2008–2016; Regehr et al., Scientific Reports 8:16780, 2018). Overall, the SCR–movement model successfully quantified both individual‐ and population‐level space use, including the effects of landscape characteristics on movement, abundance, and detection, while linking the movement and abundance processes to directly estimate density within a prescribed spatial region and temporal period. Integrated SCR–movement models provide a generalizable approach to incorporate greater movement realism into population dynamics and link movement to emergent properties including spatiotemporal densities and abundances.
ABSTRACT
Glacier surface mass balance (SMB) observations for the Andes Cordillera are limited and therefore estimates of the SMB contribution to sea‐level rise are highly uncertain. Here (in Part 3), ...we simulate glacier surface meteorological and hydrological conditions and trends for the Andes Cordillera (1979/80–2013/14; 35 years), covering the tropical latitudes in the north down to the sub‐polar latitudes in the far south, including the Northern Patagonia Icefield (NPI) and Southern Patagonia Icefield (SPI). Surface meteorological conditions and heat‐ and mass‐transfer processes were simulated for all glaciers having an area equal to or greater than 0.5 km2. SnowModel – a fully integrated energy balance, blowing‐snow distribution, multi‐layer snowpack, and runoff routing model – was used to simulate glacier SMBs for the Andes Cordillera. The Randolph Glacier Inventory (RGI; v. 4.0) and NASA Modern‐Era Retrospective Analysis for Research and Applications (MERRA) products, downscaled in SnowModel, allowed us to conduct relatively high‐resolution (1‐km horizontal grid; 3‐h time step) simulations of glacier air temperature, precipitation, sublimation, evaporation, runoff, and SMB. These simulated glacier SMBs were verified against both independent direct observed annual glacier SMB and satellite gravimetry and altimetry derived SMB, indicating a good agreement. For Andes glaciers, the 35‐year mean annual SMB was found to be −1.13 m water equivalent (w.e.), while the cumulative SMB was −39.6 m w.e., which is equal to a cumulative SMB contribution of 3.4 mm sea‐level equivalent (SLE) (∼0.1 mm SLE per year). However, for both NPI and SPI, the mean SMB was positive (where likely calving explains why geodetic estimates are negative). For the Andes Cordillera, the simulated mean glacier‐specific runoff was 41 L s−1 km−2, while for NPI and SPI it was 213 and 198 L s−1 km−2, respectively, indicating available water resources from NPI and SPI.
1. The conservation of many wildlife species requires understanding the demographic effects of climate change, including interactions between climate change and harvest, which can provide cultural, ...nutritional or economic value to humans. 2. We present a demographic model that is based on the polar bear Ursus maritimus life cycle and includes density-dependent relationships linking vital rates to environmental carrying capacity (K). Using this model, we develop a state-dependent management framework to calculate a harvest level that (i) maintains a population above its maximum net productivity level (MNPL; the population size that produces the greatest net increment in abundance) relative to a changing K, and (ii) has a limited negative effect on population persistence. 3. Our density-dependent relationships suggest that MNPL for polar bears occurs at approximately 0-69 (95% CI = 0-63-0-74) of K. Population growth rate at MNPL was approximately 0-82 (95% CI = 0-79-0-84) of the maximum intrinsic growth rate, suggesting relatively strong compensation for human-caused mortality. 4. Our findings indicate that it is possible to minimize the demographic risks of harvest under climate change, including the risk that harvest will accelerate population declines driven by loss of the polar bear's sea-ice habitat. This requires that (i) the harvest rate – which could be 0 in some situations – accounts for a population's intrinsic growth rate, (ii) the harvest rate accounts for the quality of population data (e.g. lower harvest when uncertainty is large), and (iii) the harvest level is obtained by multiplying the harvest rate by an updated estimate of population size. Environmental variability, the sex and age of removed animals and risk tolerance can also affect the harvest rate. 5. Synthesis and applications. We present a coupled modelling and management approach for wildlife that accounts for climate change and can be used to balance trade-offs among multiple conservation goals. In our example application to polar bears experiencing sea-ice loss, the goals are to maintain population viability while providing continued opportunities for subsistence harvest. Our approach may be relevant to other species for which near-term management is focused on human factors that directly influence population dynamics within the broader context of climate-induced habitat degradation.
The fundamental dynamics of ultracold atomtronic devices are reflected in their phonon modes of excitation. We probe such a spectrum by applying a harmonically driven potential barrier to a 23Na ...Bose-Einstein condensate in a ring-shaped trap. This perturbation excites phonon wavepackets. When excited resonantly, these wavepackets display a regular periodic structure. The resonant frequencies depend upon the particular configuration of the barrier, but are commensurate with the orbital frequency of a Bogoliubov sound wave traveling around the ring. Energy transfer to the condensate over many cycles of the periodic wavepacket motion causes enhanced atom loss from the trap at resonant frequencies. Solutions of the time-dependent Gross-Pitaevskii equation exhibit quantitative agreement with the experimental data. We also observe the generation of supersonic shock waves under conditions of strong excitation, and collisions of two shock wavepackets.
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•PCNA increases the fidelity of Dbh polymerase on a deletion-hotspot sequence.•The interaction stimulates incorporation of the correct, but not incorrect, nucleotide.•A minimal duplex ...length of 18 bp is required for PCNA to stimulate polymerase activity.•Structural modeling suggests that PCNA induces a conformational change in Dbh.
Dbh is a Y-family translesion DNA polymerase from Sulfolobus acidocaldarius, an archaeal species that grows in harsh environmental conditions. Biochemically, Dbh displays a distinctive mutational profile, creating single-base deletion mutations at extraordinarily high frequencies (up to 50 %) in specific repeat sequences. In cells, however, Dbh does not appear to contribute significantly to spontaneous frameshifts in these same sequence contexts. This suggests that either the error-prone DNA synthesis activity of Dbh is reduced in vivo and/or Dbh is restricted from replicating these sequences. Here, we test the hypothesis that the propensity for Dbh to make single base deletion mutations is reduced through interaction with the S. acidocaldarius heterotrimeric sliding clamp processivity factor, PCNA-123. We first confirm that Dbh physically interacts with PCNA-123, with the interaction requiring both the PCNA-1 subunit and the C-terminal 10 amino acids of Dbh, which contain a predicted PCNA-interaction peptide (PIP) motif. This interaction stimulates the polymerase activity of Dbh, even on short, linear primer-template DNA, by increasing the rate of nucleotide incorporation. This stimulation requires an intact PCNA-123 heterotrimer and a DNA duplex length of at least 18 basepairs, the minimal length predicted from structural data to bind to both the polymerase and the clamp. Finally, we find that PCNA-123 increases the fidelity of Dbh on a single-base deletion hotspot sequence 3-fold by promoting an increase in the rate of correct, but not incorrect, nucleotide addition and propose that PCNA-123 induces Dbh to adopt a more active conformation that is less prone to creating deletions during DNA synthesis.
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