Strange metal behavior is ubiquitous in correlated materials, ranging from cuprate superconductors to bilayer graphene, and may arise from physics beyond the quantum fluctuations of a Landau order ...parameter. In quantum-critical heavy-fermion antiferromagnets, such physics may be realized as critical Kondo entanglement of spin and charge and probed with optical conductivity. We present terahertz time-domain transmission spectroscopy on molecular beam epitaxy-grown thin films of YbRh
Si
, a model strange-metal compound. We observed frequency over temperature scaling of the optical conductivity as a hallmark of beyond-Landau quantum criticality. Our discovery suggests that critical charge fluctuations play a central role in the strange metal behavior, elucidating one of the long-standing mysteries of correlated quantum matter.
Abstract
Using existing data can be a reliable and cost-effective way to predict species distributions, and particularly useful for recovering or expanding species. We developed a current gray wolf (
...Canis lupus
) distribution model for the western Great Lakes region, USA, and evaluated the spatial transferability of single-state models to the region. This study is the first assessment of transferability in a wide-ranging carnivore, as well as one of few developed for large spatial extents. We collected 3500 wolf locations from winter surveys in Minnesota (2017–2019), Wisconsin (2019–2020), and Michigan (2017–2020). We included 10 variables: proportion of natural cover, pastures, and crops; distance to natural cover, agriculture, developed land, and water; major and minor road density; and snowfall (1-km res.). We created a regional ensemble distribution by weight-averaging eight models based on their performance. We also developed single-state models, and estimated spatial transferability using two approaches: state cross-validation and extrapolation. We assessed performance by quantifying correlations, receiver operating characteristic curves (ROC), sensitivities, and two niche similarity indices. The regional area estimated to be most suitable for wolves during winter (threshold = maximum sensitivity/specificity) was 106,465 km
2
(MN = 48,083 km
2
, WI = 27,757 km
2
, MI = 30,625 km
2
) and correctly predicted 88% of wolf locations analyzed. Increasing natural cover and distance to crops were consistently important for determining regional and single-state wolf distribution. Extrapolation (vs. cross-validation) produced results with the greatest performance metrics, and were most similar to the regional model, yet good internal performance was unrelated to greater extrapolation performance. Factors influencing species distributions are scale-dependent and can vary across areas due to behavioral plasticity. When extending inferences beyond the current occurrence of individuals, assessing variation in ecology such as habitat selection, as well as methodological factors including model performance, will be critical to avoid poor scientific interpretations and develop effective conservation applications. In particular, accurate distribution models for recovering or recovered carnivores can be used to develop plans for habitat management, quantify potential of unoccupied habitat, assess connectivity modeling, and mitigate conflict, facilitating long-term species persistence.
Habitat selection studies facilitate assessing and predicting species distributions and habitat connectivity, but habitat selection can vary temporally and among individuals, which is often ignored. ...We used GPS telemetry data from 96 Gray wolves (Canis lupus) in the western Great Lakes region of the USA to assess differences in habitat selection while wolves exhibited resident (territorial) or non-resident (dispersing or floating) movements and discuss implications for habitat connectivity. We used a step-selection function (SSF) to assess habitat selection by wolves exhibiting resident or non-resident movements, and modeled circuit connectivity throughout the western Great Lakes region. Wolves selected for natural land cover and against areas with high road densities, with no differences in selection among wolves when resident, dispersing, or floating. Similar habitat selection between resident and non-resident wolves may be due to similarity in environmental conditions, when non-resident movements occur largely within established wolf range rather than near the periphery or beyond the species range. Alternatively, non-resident wolves may travel through occupied territories because higher food availability or lower human disturbance outweighs risks posed by conspecifics. Finally, an absence of differences in habitat selection between resident and non-resident wolf movements may be due to other unknown reasons. We recommend considering context-dependency when evaluating differences in movements and habitat use between resident and non-resident individuals. Our results also provide independent validation of a previous species distribution model and connectivity analysis suggesting most potential wolf habitat in the western Great Lakes region is occupied, with limited connectivity to unoccupied habitat.
We report on gallium droplet nucleation on silicon (100) substrates with and without the presence of the native oxide. The gallium deposition is carried out under ultra-high vacuum conditions at ...temperatures between 580 and 630 °C. The total droplet volume, obtained from a fit to the diameter-density relation, is used for sample analysis on clean silicon surfaces. Through a variation of the 2D equivalent Ga thickness, the droplet diameter was found to be between 250-1000 nm. Longer annealing times resulted in a decrease of the total droplet volume. Substrate temperatures of 630 °C and above led to Ga etching into the Si substrates and caused Si precipitation around the droplets. In contrast, we obtained an almost constant diameter distribution around 75 nm over a density range of more than two orders of magnitude in the presence of a native oxide layer. Furthermore, the droplet nucleation was found to correlate with the density of surface features on the 'epi-ready' wafer.
We present the design simulation and characterization of a quantum cascade detector operating at 4.3μm wavelength. Array integration and packaging processes were investigated. The device operates in ...the 4.3μm CO
absorption region and consists of 64 pixels. The detector is designed fully compatible to standard processing and material growth methods for scalability to large pixel counts. The detector design is optimized for a high device resistance at elevated temperatures. A QCD simulation model was enhanced for resistance and responsivity optimization. The substrate illuminated pixels utilize a two dimensional Au diffraction grating to couple the light to the active region. A single pixel responsivity of 16mA/W at room temperature with a specific detectivity D
of 5⋅10
cmHz/W was measured.
A diagonal optically active transition in a quantum cascade detector is introduced as optimization parameter to obtain quality factor matching between a photodetector and a cavity. A more diagonal ...transition yields both higher extraction efficiency and lower noise, while the reduction of the absorption strength is compensated by the resonant cavity. The theoretical limits of such a scheme are obtained, and the impact of losses and cavity processing variations are evaluated. By optimizing the quantum design for a high quality cavity, a specific detectivity of 10(9) Jones can be calculated for λ = 8μm and T = 300K.
The integer quantum Hall effect is a well-studied phenomenon at frequencies below about 100 Hz. The plateaus in high-frequency Hall conductivity were experimentally proven to retain up to 33 GHz, but ...the behavior at higher frequencies has remained largely unexplored. Using continuous-wave terahertz spectroscopy, the complex Hall conductivity of GaAs/AlGaAs heterojunctions was studied in the range of 69–1100 GHz. Above 100 GHz, the quantum plateaus are strongly smeared out and replaced by weak quantum oscillations in the real part of the conductivity. The amplitude of the oscillations decreases with increasing frequency. Near 1 THz, the Hall conductivity does not reveal any features related to the filling of Landau levels. Similar oscillations are observed in the imaginary part as well; this effect has no analogy at zero frequency. This experimental picture is in disagreement with existing theoretical considerations of the high-frequency quantum Hall effect.
•Lethal control did not affect attitudes or inclinations to kill wolves illegally.•Agency trust, risk perception, and empowerment are related to tolerance of wolves.•Focus groups provide more ...comprehensive understanding of complex wildlife issues.
Numerous studies report majorities of survey respondents hold positive attitudes toward wolves. However, a 2001–2009 panel study found declining tolerance of wolves among residents of Wisconsin’s wolf range. Poaching, believed to be increasing, has been an important source of mortality in Wisconsin’s wolf population since the 1980s. We conducted focus groups, with an accompanying anonymous questionnaire survey of participants, among farmers and hunters in Wisconsin’s wolf range to gain a more in-depth understanding of attitudes towards wolves and inclinations to poach wolves. Whereas our study was originally designed to examine the effects of an experimental lethal-control program on inclination to poach, oscillating wolf-management authority shifted our focus from a single intervention to a suite of changes in policy and management. Following federal delisting of the Western Great Lakes wolf population in January 2012, Wisconsin implemented lethal-depredation control and created the state’s first legalized wolf-harvest season in October 2012. We convened focus groups before and after these changes. Pre- and post-survey results showed majorities of respondents held negative attitudes toward wolves with no decrease in inclination to poach, suggesting lethal-control measures, in the short term, may be ineffective for increasing tolerance. Participants expressed favorable attitudes toward lethal-control measures, but believed there were limitations in the implementation of the lethal-control measures. Focus group discussions revealed elements of positivity toward wolves not revealed by questionnaires, as well as several thematic areas, such as fear, empowerment, and trust, that may inform the development of interventions designed to increase tolerance of wolves and other controversial species.
Cougars (Puma concolor) have lost substantial portions of their historical range yet increased sightings suggest potential for re-establishment in some regions; greater understanding of potential ...distribution and connectivity is necessary to make sound management and policy decisions. Specifically, the Great Lakes region of the USA will likely be an important area for cougar range expansion into the Midwest and Eastern USA. We used verified cougar observations to model and predict potential distribution and connectivity in the Great Lakes region. We compiled all confirmed observations of cougars from Michigan, Minnesota, and Wisconsin (2010–2020); which resulted in 180 reports (154 images/videos, 20 signs, 6 mortalities). We developed an ensemble distribution model (1 km res) based on three machine learning methods. We used weighted cost-distances to identify linkages between core areas and circuit theory to model overall connectivity potential. We calculated selection ratios for land covers (30 m res) at fine and coarse scales. The ensemble distribution model had good performance (ROC of 0.94). Suitability was positively associated with increasing vegetation structure, lower distance to natural cover, and mid-high terrain ruggedness. Forest covers were always selected for regardless of scale, and human development was avoided only at the coarser scale. We identified 191 core patches and 362 linkages connecting them; only 50.1% of them were located within legally protected areas. We identified high regional connectivity in a generally west-east direction. Successful conservation of large carnivores like cougars will depend on conserving not only habitat patches and linkages but also efforts to facilitate long-term coexistence.
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