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Observations of Turbulence in Stratified Flow
No full textVarious theoretical properties of the structure function are evaluated. Additional functions are constructed to describe the overall influence of stratification, the anisotropy and intermittency of the turbulence, and the asymmetry of the main drafts.
These functions and the usual spectral decomposition are computed from aircraft-measured turbulence data collected in nocturnal boundary layers and in turbulence over mountainous terrain. Certain features of the turbulence are found to depend more on stability than on the external situation. Three general types of turbulence are found: 1) intermittent turbulence driven by shear-driven overturning; 2) continuous turbulence where strong drafts in the presence of shear are characterized by sharp boundaries or microfronts, particularly on their upstream sides; and 3) weaker continuous turbulence. The costructure fields are generally consistent with vertical gradient transfer. However, the bora turbulence on larger scales is dominated by horizontal motions perpendicular to the mean shea
In situ cosmogenic radiocarbon production and 2-D ice flow line modeling for an Antarctic blue ice area
Get PDFRadiocarbon measurements at ice margin sites and blue ice areas can potentially be used for ice dating, ablation rate estimates and paleoclimatic reconstructions. Part of the measured signal comes from in situ cosmogenic ¹⁴C production in ice, and this component must be well understood before useful information can be extracted from ¹⁴C data. We combine cosmic ray scaling and production estimates with a two-dimensional ice flow line model to study cosmogenic ¹⁴C production at Taylor Glacier, Antarctica. We find (1) that ¹⁴C production through thermal neutron capture by nitrogen in air bubbles is negligible; (2) that including ice flow patterns caused by basal topography can lead to a surface ¹⁴C activity that differs by up to 25% from the activity calculated using an ablation-only approximation, which is used in all prior work; and (3) that at high ablation margin sites, solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10%. As part of this effort we model two-dimensional ice flow along the central flow line of Taylor Glacier. We present two methods for parameterizing vertical strain rates, and assess which method is more reliable for Taylor Glacier. Finally, we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error. The results presented here can inform ongoing and future ¹⁴C and ice flow studies at ice margin sites, including important paleoclimatic applications such as the reconstruction of paleoatmospheric ¹⁴C content of methane
Defining and measuring the mean residence time of lateral surface transient storage zones in small streams
Get PDFSurface transient storage (STS) has functional significance in stream ecosystems because it increases solute interaction with sediments. After volume, mean residence time is the most important metric of STS, but it is unclear how this can be measured accurately or related to other timescales and field-measureable parameters. We studied mean residence time of lateral STS in small streams over Reynolds numbers (Re) 5000–200,000 and STS width to length (W/L) aspect ratios between 0.2–0.75. Lateral STS have flow fields characterized by a shear layer spanning the length of the STS entrance, and one primary gyre and one or more secondary gyre(s) in the STS. The study's purpose was to define, measure, and compare residence timescales: volume to discharge ratio (Langmuir timescale); area under normalized concentration curve; and characteristic time of exponential decay, and to compare these timescales to field measureable parameters. The best estimate of STS mean residence time—primary gyre residence time—was determined to be the first characteristic time of exponential decay. An apparent mean residence time can arise, which is considerably larger than other timescales, if probes are placed within secondary gyre(s). The Langmuir timescale is the minimum mean residence time, and is linearly correlated to channel velocity and STS width. The lateral STS mean residence time can be predicted using a physically based hydromorphic timescale derived by Uijttewaal et al. (2001) with an entrainment coefficient of 0.031 ± 0.009 for the Re and W/L studied
Line Transect Surveys Underdetect Terrestrial Mammals: Implications for the Sustainability of Subsistence Hunting
Get PDFConservation of Neotropical game species must take into account the livelihood and food security needs of local human populations. Hunting management decisions should therefore rely on abundance and distribution data that are as representative as possible of true population sizes and dynamics. We simultaneously applied a commonly used encounter-based method and an infrequently used sign-based method to estimate hunted vertebrate abundance in a 48,000-km² indigenous landscape in southern Guyana. Diurnal direct encounter data collected during three years along 216, four-kilometer -long transects consistently under-detected many diurnal and nocturnal mammal species readily detected through sign. Of 32 species analyzed, 31 were detected by both methods; however, encounters did not detect one and under-detected another 12 of the most heavily hunted species relative to sign, while sign under-detected 12 never or rarely collected species relative to encounters. The six most important game animals in the region, all ungulates, were not encountered at 11–40% of village and control sites or on 29–72% of transects where they were detected by sign. Using the sign methodology, we find that tapirs, one of the terrestrial vertebrates considered most sensitive to overexploitation, are present at many sites where they were never visually detected during distance sampling. We find that this is true for many other species as well. These high rates of under-detection suggest that behavioral changes in hunted populations may affect apparent occurrence and abundance of these populations. Accumulation curves (detection of species on transects) were much steeper for sign for 12 of 16 hunted species than for encounters, but that pattern was reversed for 12 of 16 species unhunted in our area. We conclude that collection of sign data is an efficient and effective method of monitoring hunted vertebrate populations that complements encounter and camera-trapping methods in areas impacted by hunting. Sign surveys may be the most viable method for large-scale, management-oriented studies in remote areas, particularly those focused on community-based wildlife management.Data Availability Statement: Data not provided includes village names, hunters, and hunting details due to ethical human rights concerns linked to indigenous peoples of the area. Agreements with indigenous people limit data to use by our research group. All other relevant data are within the paper and its Supporting Information files
Three-Dimensional Reflectance Traction Microscopy
Get PDFCells in three-dimensional (3D) environments exhibit very different biochemical and biophysical phenotypes compared to the behavior of cells in two-dimensional (2D) environments. As an important biomechanical measurement, 2D traction force microscopy can not be directly extended into 3D cases. In order to quantitatively characterize the contraction field, we have developed 3D reflectance traction microscopy which combines confocal reflection imaging and partial volume correlation postprocessing. We have measured the deformation field of collagen gel under controlled mechanical stress. We have also characterized the deformation field generated by invasive breast cancer cells of different morphologies in 3D collagen matrix. In contrast to employ dispersed tracing particles or fluorescently-tagged matrix proteins, our methods provide a label-free, computationally effective strategy to study the cell mechanics in native 3D extracellular matrix
Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline
Get PDFWe report zero kinetic energy (ZEKE) photoelectron spectroscopy of benzo[h]quinoline (BhQ) via resonantly enhanced multiphoton ionization (REMPI) through the first electronically excited state S₁. From the simulated REMPI spectra with and without Herzberg–Teller coupling, we conclude that vibronic coupling plays a minor but observable role in the electronic excitation to the S₁ state. We further compare the S₁ state of BhQ with the first two electronically excited states of phenanthrene, noticing a similarity of the S₁ state of BhQ with the second electronically excited state S₂ of phenanthrene. In the ZEKE spectra of BhQ, the vibrational frequencies of the cationic state D₀ are consistently higher than those of the intermediate neutral state, indicating enhanced bonding upon ionization. The sparse ZEKE spectra, compared with the spectrum of phenanthrene containing rich vibronic activities, further imply that the nitrogen atom has attenuated the structural change between S₁ and D₀ states. We speculate that the nitrogen atom can withdraw an electron in the S₁ state and donate an electron in the D₀ state, thereby minimizing the structural change during ionization. The origin of the first electronically excited state is determined to be 29 410 ± 5 cm⁻¹, and the adiabatic ionization potential is determined to be 65 064 ± 7 cm⁻¹
Cuesta-MarcosAlfonsoCropSoilScienceUSDABarleyCore.pdf
No full textNew sources of genetic diversity must be incorporated into plant breeding programs if they are to continue increasing grain
yield and quality, and tolerance to abiotic and biotic stresses. Germplasm collections provide a source of genetic and
phenotypic diversity, but characterization of these resources is required to increase their utility for breeding programs. We
used a barley SNP iSelect platform with 7,842 SNPs to genotype 2,417 barley accessions sampled from the USDA National
Small Grains Collection of 33,176 accessions. Most of the accessions in this core collection are categorized as landraces or
cultivars/breeding lines and were obtained from more than 100 countries. Both STRUCTURE and principal component
analysis identified five major subpopulations within the core collection, mainly differentiated by geographical origin and
spike row number (an inflorescence architecture trait). Different patterns of linkage disequilibrium (LD) were found across
the barley genome and many regions of high LD contained traits involved in domestication and breeding selection. The
genotype data were used to define ‘mini-core’ sets of accessions capturing the majority of the allelic diversity present in the
core collection. These ‘mini-core’ sets can be used for evaluating traits that are difficult or expensive to score. Genome-wide
association studies (GWAS) of ‘hull cover’, ‘spike row number’, and ‘heading date’ demonstrate the utility of the core
collection for locating genetic factors determining important phenotypes. The GWAS results were referenced to a new
barley consensus map containing 5,665 SNPs. Our results demonstrate that GWAS and high-density SNP genotyping are
effective tools for plant breeders interested in accessing genetic diversity in large germplasm collections
SchmittnerAndreasCEOASImprovedParameterization_SupplementaryMaterial.zip
No full textTwo modifications to an existing scheme of tidal
mixing are implemented in the coarse resolution ocean component
of a global climate model. First, the vertical distribution
of energy flux out of the barotropic tide is determined
using high resolution bathymetry. This shifts the levels of
mixing higher up in the water column and leads to a stronger
mid-depth meridional overturning circulation in the model.
Second, the local dissipation efficiency for diurnal tides is
assumed to be larger than that for the semi-diurnal tides poleward
of 30°. Both modifications are shown to improve agreement
with observational estimates of diapycnal diffusivities
based on microstructure measurements and circulation indices.
We also assess impacts of different spatial distributions
of the barotropic energy loss. Estimates based on satellite
altimetry lead to larger diffusivities in the deep ocean and
hence a stronger deep overturning circulation in our climate
model that is in better agreement with observation based estimates
compared to those based on a tidal model
MellbyeBrettMolecularCellularBiologyPhysiologicalFrameworkRegulation.pdf
No full textMany bacteria possess cell density-dependent quorum-sensing (QS) systems that often regulate cooperative secretions involved
in host-microbe or microbe-microbe interactions. These secretions, or “public goods,” are frequently coregulated by stress and
starvation responses. Here we provide a physiological rationale for such regulatory complexity in the opportunistic pathogen
Pseudomonas aeruginosa. Using minimal-medium batch and chemostat cultures, we comprehensively characterized specific
growth rate-limiting macronutrients as key triggers for the expression of extracellular enzymes and metabolites directly controlled
by the las and rhl QS systems. Expression was unrelated to cell density, depended on the secreted product’s elemental
composition, and was induced only when the limiting nutrient was not also a building block of the product; rhl-dependent products
showed the strongest response, caused by the largely las-independent induction of the regulator RhlR and its cognate signal.
In agreement with the prominent role of the rhl system, slow growth inverted the las-to-rhl signal ratio, previously considered a
characteristic distinguishing between planktonic and biofilm lifestyles. Our results highlight a supply-driven, metabolically prudent
regulation of public goods that minimizes production costs and thereby helps stabilize cooperative behavior. Such regulation
would be beneficial for QS-dependent public goods that act broadly and nonspecifically, and whose need cannot always be
accurately assessed by the producing cell. Clear differences in the capacities of the las and rhl systems to integrate starvation signals
help explain the existence of multiple QS systems in one cell
ChangChih-Hung(Alex)CBEEHighRateSynthesis(SupportingInformation).pdf
No full textThe reaction conditions for the synthesis of Cu-BTC (BTC = benzene-1,3,5-tricarboxylic acid) were elucidated using a continuous-flow microreactor-assisted solvothermal system to achieve crystal size and phase control. A high-rate synthesis of Cu-BTC metal-organic frameworks with BET surface area of more than 1600 m²/g (Langmuir surface area of more than 2000 m²/g) and with a 97% production yield could be achieved with a total reaction time of 5 minutes