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The efficiency and selectivity of SPECIFIC-CP, a widely used method for selective double cross-polarization in triple-resonance magic angle spinning solid-state NMR, is improved by performing the tangential-shaped (13)C irradiation at an offset frequency that meets the Lee-Goldburg condition (LG-SPECIFIC-CP). This is demonstrated on polycrystalline samples of uniformly (13)C, (15)N labeled N-acetyl-leucine and N-formyl-Met-Leu-Phe-OH (MLF) at 700MHz and 900MHz (1)H resonance frequencies, respectively. For the single (13)Cα of N-acetyl-leucine, relative to conventional broad band cross-polarization, the SPECIFIC-CP signal has 47% of the intensity. Notably, the LG-SPECIFIC-CP signal has 72% of the intensity, essentially the theoretical maximum. There were no other changes in the experimental parameters. The three (13)Cα signals in MLF show some variation in intensities, reflecting the relatively narrow bandwidth of a frequency-offset procedure, and pointing to future developments for this class of experiment.

Sediment suspension and transport driven by waves and currents play a significant role in both the ecological and physical environments of large lakes. Lake Michigan has faced a rapidly increasing water level associated with intensified wind waves in the past decade. To investigate the spatiotemporal characteristics of suspended sediment concentration (SSC) and associated coastal sediment budgets in southern Lake Michigan, a 30‐year (1991–2020) hindcast was performed using a coupled wave‐current‐ sediment model (SWAN‐FVCOM‐CSTMS). We found that in southern Lake Michigan, the basin‐wide mean SSC increased, and the coastal sediment loss accelerated dramatically, corresponding with intensified waves, currents and lake water level rises over the past decade. The basin‐wide mean SSC, coastal sediment loss, wave height, wind speed, current speed, and water level in southern Lake Michigan are highly correlated. Spatially, the results reveal decreases in coastal SSC and sediment loss in the western portion of the southern basin, while the eastern sectors show an increase in both metrics. This reflects a clear shift in the wave climate and hydrodynamic environment. The alterations in long‐term coastal sediment budgets imply that considerable shoreline transformations are being influenced by modifications in the wave climate. Understanding the spatiotemporal characteristics of SSC and coastal sediment budgets is crucial for strategic water resource management and coastal infrastructure planning. [ABSTRACT FROM AUTHOR]

Disturbances act as powerful structuring forces on ecosystems. To ask whether environmental microbial communities have capacity to recover after a large disturbance event, we conducted a whole-ecosystem manipulation, during which we imposed an intense disturbance on freshwater microbial communities by artificially mixing a temperate lake during peak summer thermal stratification. We employed environmental sensors and water chemistry analyses to evaluate the physical and chemical responses of the lake, and bar-coded 16S ribosomal RNA gene pyrosequencing and automated ribosomal intergenic spacer analysis (ARISA) to assess the bacterial community responses. The artificial mixing increased mean lake temperature from 14 to 20 °C for seven weeks after mixing ended, and exposed the microorganisms to very different environmental conditions, including increased hypolimnion oxygen and increased epilimnion carbon dioxide concentrations. Though overall ecosystem conditions remained altered (with hypolimnion temperatures elevated from 6 to 20 °C), bacterial communities returned to their pre-manipulation state as some environmental conditions, such as oxygen concentration, recovered. Recovery to pre-disturbance community composition and diversity was observed within 7 (epilimnion) and 11 (hypolimnion) days after mixing. Our results suggest that some microbial communities have capacity to recover after a major disturbance.

This study presents the meteotsunami behavior in response to different storm types in the coasts of southern Asia-Pacific Ocean from 16 years water level records. Through the size-frequency analysis, the dangerous meteotsunami, wave height exceeding 0.3 m, can occur up to 44 events per year. Notably, during the extreme waves of the 2007 event, wave heights reached approximately 0.9-1.5 m in the Taiwan Strait and the western coastal areas of Taiwan. We have classified storms into six types by radar reflectivity images and satellite-derived precipitation. Findings indicate that predicted wave heights caused by bows and typhoons could reach hazardous magnitude of exceeding 2 m in a 100-yr interval. Spatial and temporal analysis reveals that meteotsunami occurrences are most frequent in the western regions during the winter to early spring months (December to April). Of all meteotsunami occurrences, cluster storms are identified as the most prevalent atmospheric forcing, accounting for 60% of meteostunamis. Typhoons have a 20% association with meteotsunamis along the east coasts of Taiwan during late summer to autumn. On the east coasts, typhoon type-induced events may be attributed to the combination effect of meteotsunamis and infra-gravity waves. Overall, this study provides the first comprehensive examination of meteotsunami-storm characteristics and their associated hazard risks in the coastal areas of the southern Asia-Pacific Ocean. [ABSTRACT FROM AUTHOR]

Lake warming can negatively impact cool-water fishes through both temperature and oxygen stress. We modeled the joint dynamics of water column temperature and oxygen to quantify oxythermal habitat for yellow perch (Percaflavescens) in Fish Lake, Wisconsin, USA. To estimate annual oxythermal stress, we developed a novel metric (cumulative oxythermal stress dosage; COSD) that integrates both stress duration and stress magnitude. We find that COSD better predicts observed perch declines than the published TDO3 metric (temperature at depth where dissolved oxygen is 3 mg x [L.sup.-1]), which was developed for cold-water fish. Simulations show increases in COSD between 1911 and 2014, punctuated by a sharp rise since 1989. Extreme COSD years result from the intersection of high maximum daily dosage and prolonged duration exceeding the tolerance threshold. Temperature perturbation experiments to explore future climate scenarios reveal that COSD would increase greatly if the atmosphere warms by >3[degrees]C. Applying the COSD metric broadly to temperate lakes could help direct management efforts toward the ecosystems most likely to serve as climate refugia for cold- and cool-water fishes in the future. Le rechauffement des lacs peut avoir une incidence negative sur les poissons d'eau temperee par le biais de stress associes tant a la temperature qu'a l'oxygene. Nous avons modelise la dynamique combinee de la temperature et de l'oxygene dans la colonne d'eau pour quantifier l'habitat oxythermique pour la perchaude (Perca flavescens) dans le lac Fish (Wisconsin, Etats-Unis). Afin d'estimer le stress oxythermique annuel, nous avons mis au point une nouvelle mesure (le dosage du stress oxythermique cumulatif, COSD), qui integre la duree et la magnitude du stress. Nous constatons que le COSD predit mieux les baisses observees des perchaudes que la TDO3 (temperature a la profondeur ou la concentration d'oxygene dissous est de 3 mg x [L.sup.-1]), une mesure mise au point pour les poissons d'eau froide. Les simulations montrent des augmentations du COSD de 1911 a 2014 dont une augmentation abrupte depuis 1989. Les annees de valeurs extremes du COSD decoulent de l'intersection de valeurs journalieres maximums elevees et d'une longue duree depassant le seuil de tolerance. Des experiences de perturbation de la temperature visant a explorer des scenarios de climat futur revelent que le COSD augmenterait considerablement pour un rechauffement de l'atmosphere de plus de 3[degrees]C. L'application large du COSD aux lacs temperes pourrait aider a orienter les efforts de gestion vers les ecosystemes les plus susceptibles de servir de refuges climatiques pour les poissons d'eau froide et d'eau temperee. [Traduit par la Redaction], Introduction In lakes, water temperature and dissolved oxygen (DO) substantially affect the survival and growth of fish (Fry 1971; Magnuson et al. 1979; Coutant 1990; Jacobson et al. 2010). Fish [...]

An efficient nonhydrostatic model with the embedded Boussinesq-type like equations at the free surface is presented to simulate surface waves from shallow to deep water. The new free-surface treatment yields an accurate expression of vertical distribution of nonhydrostatic pressure. This approach is free of the irrotational flow assumption. Two locations of reference velocities obtained through interpolations of nonhydrostatic velocities are used to optimize frequency dispersion for a wide range of wave conditions. Accuracy and efficiency of the model is critically tested against analytical solutions and experimental data. Overall, the present nonhydrostatic model using a small number of vertical layers (i.e., 2-4) is capable of resolving dispersive wave motions with various effects. DOI: 10.1061/(ASCE)WW.1943-5460.0000032 CE Database subject headings: Surface waves; Wave dispersion; Boussinesq equations; Currents; Wave velocity; Shallow water; Deep water. Author keywords: Non-hydrostatic; Implicit method; Free-surface waves; dispersion, Boussinesq-type equations; Sheared current, reference velocity.

A nonhydrostatic model with a higher-order top-layer pressure treatment is developed. Accuracy with respect to linear wave dispersion and wave nonlinearity is carefully examined. The model is thereafter applied to simulate nonlinear deep-water wave groups. For slowly modulated wave groups, the model well predicts the characteristics of bichromatic waves better than those obtained by the fourth-order nonlinear Schrodinger equation and the multilayer Boussinesq model. For fast evolution of focusing wave groups, the model accurately captures the limiting extreme wave conditions. Particularly the predicted local wave steepness of a narrow-banded wave group is higher than that of a broad-banded wave group, supporting the importance of spectral bandwidth in determining the limiting wave condition in the previous study. Overall, the agreement between the model's results and experimental data are excellent, demonstrating the capability of the model on resolving wave-wave interactions in the nonlinear deep-water wave groups. DOI: 10.1061/(ASCE)EM.1943-7889.0000078 CE Database subject headings: Hydrostatics; Deep water; Water waves; Wave groups. Author keywords: Nonhydrostatic; Top-layer pressure treatment; Bichromatic waves; Focusing waves; Deep-water wave groups; Nonlinear wave-wave interactions.

The results of laboratory experiments on transient (short lived), extreme (highest nonbreaking) waves on depth-varying currents are reported. A new feedback control wave focusing method on currents was developed to create transient, extreme waves in the presence of desired depth-varying currents at the prescribed position. Both wave profiles and time series of surface displacements were measured to examine the spatial and temporal characteristics of extreme waves. Wavelengths estimated from dispersion relations consistently underestimated those measured directly from the video images of transient extreme waves. This underestimation well correlates with a proposed wavelength asymmetry parameter [xi] (a ratio of the trough length to the crest length), suggesting the rapid change of a transient wave profile during a wave cycle. The effects of the current shear on transient, extreme wave profiles are recognized. The negative shear increased the limiting wave steepness but reduced the vertical asymmetry. The vertical asymmetry could be remarkably augmented by the positive current shear, while the limiting wave steepness was reduced. These results were clearly observed in the spatial wave profiles, but not in the time series of the surface displacement. DOI: 10.1061/(ASCE)0733-9399(2006)132:9(1015) CE Database subject headings: Transient flow; Shear waves; Asymmetry; Currents; Laboratory tests.

A fully nonhydrostatic model is tested by simulating a range of surface-wave motions, including linear dispersive waves, nonlinear Stokes waves, wave propagation over bottom topographies, and wave--current interaction. The model uses an efficient implicit method to solve the unsteady, three-dimensional, Navier-Stokes equations and the fully nonlinear free-surface boundary conditions. A new top-layer pressure treatment is incorporated to fully include the nonhydrostatic pressure effect. The model results are verified against either analytical solutions or experimental data. It is found that the model using a small number of vertical layers is capable of accurately simulating both the free-surface elevation and vertical flow structure. By further examining the model's performance of resolving wave dispersion and nonlinearity, the model's efficiency and accuracy are demonstrated. DOI: 10.1061/(ASCE)0733-9399(2006)132:4(447) CE Database subject headings: Surface waves; Nonlinear response; Wave dispersion; Wave propagation.

Measurement of vertical profiles of the critical shear stress, [[tau].sub.c] and the erosion rate, E, from the same undisturbed sediment core is crucial for modeling the resuspension of fine-grained natural sediments. The automated sediment erosion testing system (ASETS) was developed to determine profiles of [[tau].sub.c] and E with centimeter spatial (vertical) resolution in an undisturbed (Shelby tube) sediment core, whose surface was eroded by steady turbulent flow through a flume. The unique feature of ASETS is that it is a real-time imaging method that accurately determines the position of the core surface during erosion for both calculating the vertical profile of E and controlling a motor-driver system that automatically pushes up the core to maintain its surface flush with the flume bottom. Undisturbed, field cores were tested over a range of flow (average bed shear stress, [[tau].sub.b]) conditions. The amount of eroded sediment from both optical backscattering measurements and the imaging method were in good agreement, which validated ASETS. Measured vertical profiles of [[tau].sub.c] and E were similar to those reported in literature. E correlated well with [([[tau].sub.b] - [[tau].sub.c]).sup.2], which agrees with previous results in literature. CE Database subject headings: Sediment; Erosion; Shear stress; Turbulent flow; Laboratory equipment; Imaging techniques; Digital techniques.