Drowning incidents and conditions due to hidden flash rips in Lake Michigan.

Flash rips are episodic bursts of water jetting offshore, which can lead to drowning incidents by sweeping swimmers offshore without warning, thus posing a hidden and unrecognized danger to beachgoers. This study reveals hazards of flash rips by investigating a series of drowning incidents along coasts of Lake Michigan during a series of storm events on July 18-21, 2019. Occurrences and causes of flash rips were depicted through webcam image observations, storm features of atmospheric disturbances, hydrodynamic circumstances of wind waves and meteorologically induced water level fluctuations, and model-reconstructed nearshore circulations. Results shows that flash rips were generated during or after storms through nearshore processes of storm-induced wind waves and meteorologically induced water level fluctuations. With small wind waves, low water level fluctuations, and a timing delay of rip occurrences relative to the causative convective storms, flash rips pose a hidden hazard to unaware swimmers. Historical observations for incidents in Lake Michigan between 2002 and 2019 further show that dry conditions or fair weathers and a calm water signature at the beach can likely generate unexpected hidden flash rips, resulting in the highest drowning risks. There is an urgent need for communication, education, and prediction/forecast of hidden flash rips to the Laurentian Great Lakes and worldwide coastal communities.

Unexpected rip currents induced by a meteotsunami.

A tragic drowning event occurred along southeastern beaches of Lake Michigan on a sunny and calm July 4, 2003, hours after a fast-moving convective storm had crossed the lake. Data forensics indicates that a moderate-height (~0.3 m) meteotsunami was generated by the fast-moving storm impacting the eastern coast of the lake. Detailed Nearshore Area (DNA) modeling forensics on a high-resolution spatial O(1 m) grid reveals that the meteotsunami wave generated unexpected rip currents, changing the nearshore condition from calm to hazardous in just a few minutes and lasting for several hours after the storm. Cross-comparison of rip current incidents and meteotsunami occurrence databases suggests that meteotsunamis present severe water safety hazards and high risks, more frequently than previously recognized. Overall, meteorological tsunamis are revealed as a new generation mechanism of rip currents, thus posing an unexpected beach hazard that, to date, has been ignored.

Drivers and Management Implications of Long-Term Cisco Oxythermal Habitat Decline in Lake Mendota, WI.

Cisco (Coregonus artedi) are an important indicator species for cold-water lake habitats in the Great Lakes region, and many populations have been extirpated at their southern range limit over the last century. Understanding the roles of climate and water quality in these extirpations should inform protection of cold-water fishes. Using the water temperature at the depth where dissolved oxygen falls to 3 mg L-1 (TDO3) as a metric, we investigated the roles of climate and water quality as drivers of habitat availability for cisco in Lake Mendota, WI, USA from 1976 to 2013. We find that summer (Jun-Aug) air temperatures, spring (Mar-May) phosphorus load, and spring inflow influence summer TDO3. Warm air temperatures lead to the greatest increases in TDO3, whereas reduced phosphorus loads can reduce TDO3, thus alleviating oxythermal stress. Under air temperatures expected under the A1B climate change scenario, a 25% reduction in phosphorus load would stabilize TDO3 at current levels, while a 75% reduction in phosphorus loading would be required to expand oxythermal habitat. Costs of these reductions are estimated to range from US$16.9 million (-25%) to US$155-167 million (-75%) over a 20-year period but may be feasible by expanding upon current watershed phosphorus reduction initiatives if sustained funding were available. Identifying targeted reductions will become increasingly important throughout the region as warmer temperatures and longer stratification reduces cool- and cold-water fish habitat in many Midwestern lakes under the expected future climate.

Water Exclosure Treatment System (WETS): An innovative device for minimizing beach closures.

A Water Exclosure Treatment System (WETS) is developed and installed to minimize the occurrence of beach closures due to algae and Escherchia coli (E. coli) in an inland lake. WETS consists of an "exclosure" sub-system with a five-sided polypropylene, barrier that excludes offshore lake contaminated water from the swimming area. Inside the exclosure, water is pumped to a portable filtration-ultraviolet treatment sub-system with three components. First, heavy debris like aquatic plants are removed through a strainer. Second, fine particles are removed through a sand filter and backwashing is automated through a program logic controller triggered by pressure sensor readings. Third, pathogens, algae, bacteria, and viruses are inactivated through ultraviolet (UV) disinfection. To determine sizing of sand filters and evaluation of efficiency of UV disinfection and aid in the design of the inlet and outlet locations for the pump system, computational fluid dynamics modeling with a Lagrangian particle-tracking method are employed. Flushing time is determined to range from 0.67 to 1.89days. Residence time maps reveal inlet and outlet locations play an important role in depicting the duration of particles within the swimming area. Comprehensive water quality sampling is conducted and analyzed with ANOVA testing reveal that water quality parameters inside the exclosure are significantly different than those outside. There have been no beach closures issued since deployment of WETS. Overall, WETS, an innovative Water Exclosure Treatment System, provides safe, clean water inside the exclosure for minimizing beach closure.

Meteotsunamis in the Laurentian Great Lakes.

The generation mechanism of meteotsunamis, which are meteorologically induced water waves with spatial/temporal characteristics and behavior similar to seismic tsunamis, is poorly understood. We quantify meteotsunamis in terms of seasonality, causes, and occurrence frequency through the analysis of long-term water level records in the Laurentian Great Lakes. The majority of the observed meteotsunamis happen from late-spring to mid-summer and are associated primarily with convective storms. Meteotsunami events of potentially dangerous magnitude (height > 0.3 m) occur an average of 106 times per year throughout the region. These results reveal that meteotsunamis are much more frequent than follow from historic anecdotal reports. Future climate scenarios over the United States show a likely increase in the number of days favorable to severe convective storm formation over the Great Lakes, particularly in the spring season. This would suggest that the convectively associated meteotsunamis in these regions may experience an increase in occurrence frequency or a temporal shift in occurrence to earlier in the warm season. To date, meteotsunamis in the area of the Great Lakes have been an overlooked hazard.

Magic angle Lee-Goldburg frequency offset irradiation improves the efficiency and selectivity of SPECIFIC-CP in triple-resonance MAS solid-state NMR.

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.

Lake microbial communities are resilient after a whole-ecosystem disturbance.

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.

Resistance, resilience and recovery: aquatic bacterial dynamics after water column disturbance.

For lake microbes, water column mixing acts as a disturbance because it homogenizes thermal and chemical gradients known to define the distributions of microbial taxa. Our first objective was to isolate hypothesized drivers of lake bacterial response to water column mixing. To accomplish this, we designed an enclosure experiment with three treatments to independently test key biogeochemical changes induced by mixing: oxygen addition to the hypolimnion, nutrient addition to the epilimnion, and full water column mixing. We used molecular fingerprinting to observe bacterial community dynamics in the treatment and control enclosures, and in ambient lake water. We found that oxygen and nutrient amendments simulated the physical-chemical water column environment following mixing and resulted in similar bacterial communities to the mixing treatment, affirming that these were important drivers of community change. These results demonstrate that specific environmental changes can replicate broad disturbance effects on microbial communities. Our second objective was to characterize bacterial community stability by quantifying community resistance, recovery and resilience to an episodic disturbance. The communities in the nutrient and oxygen amendments changed quickly (had low resistance), but generally matched the control composition by the 10th day after treatment, exhibiting resilience. These results imply that aquatic bacterial assemblages are generally stable in the face of disturbance.

1H-13C separated local field spectroscopy of uniformly 13C labeled peptides and proteins.

By incorporating homonuclear decoupling on both the (1)H and (13)C channels it is feasible to obtain high-resolution two-dimensional separated local field spectra of peptides and proteins that are 100% labeled with (13)C. Dual-PISEMO (Polarization Inversion Spin Exchange Modulated Observation) can be performed as a conventional two-dimensional experiment, or with windowed detection as a one-dimensional experiment that offers flexibility as a building block for shiftless and other multidimensional triple-resonance experiments with the inclusion of (15)N irradiation. The triple-resonance MAGC probe used to perform these experiments at 500 MHz is described.

Probes for high field solid-state NMR of lossy biological samples.

In solid-state NMR hydrated samples of biopolymers are susceptible to radio frequency heating and have a significant impact on probe tuning frequency and performance parameters such as sensitivity. These considerations are increasingly important as magnetic field strengths increase with improved magnet technology. Recent developments in the design, construction, and performance of probes for solid-state NMR experiments on stationary lossy biological samples at high magnetic fields are reviewed.

(1)H-(13)C Hetero-nuclear dipole-dipole couplings of methyl groups in stationary and magic angle spinning solid-state NMR experiments of peptides and proteins.

(13)C NMR of isotopically labeled methyl groups has the potential to combine spectroscopic simplicity with ease of labeling for protein NMR studies. However, in most high resolution separated local field experiments, such as polarization inversion spin exchange at the magic angle (PISEMA), that are used to measure (1)H-(13)C hetero-nuclear dipolar couplings, the four-spin system of the methyl group presents complications. In this study, the properties of the (1)H-(13)C hetero-nuclear dipolar interactions of (13)C-labeled methyl groups are revealed through solid-state NMR experiments on a range of samples, including single crystals, stationary powders, and magic angle spinning of powders, of (13)C(3) labeled alanine alone and incorporated into a protein. The spectral simplifications resulting from proton detected local field (PDLF) experiments are shown to enhance resolution and simplify the interpretation of results on single crystals, magnetically aligned samples, and powders. The complementarity of stationary sample and magic angle spinning (MAS) measurements of dipolar couplings is demonstrated by applying polarization inversion spin exchange at the magic angle and magic angle spinning (PISEMAMAS) to unoriented samples.

Treatment of distal femoral fracture by minimally invasive percutaneous plate osteosynthesis: comparison between the dynamic condylar screw and the less invasive stabilization system.

BACKGROUND: Treatment of distal femoral fractures by percutaneous plating without direct manipulation of the fracture fragments leads to good clinical outcome. Percutaneous plating has traditionally involved using a dynamic condylar screw (DCS) and the less invasive stabilization system (LISS) was reported. The biomechanical study showed that the LISS had the enhanced ability to withstand higher loads. However, there were no clinical comparison study of distal femoral fractures treated with DCS and LISS. The aim of this study was to outline any differences in clinical and radiological results between the DCS and the LISS for treating distal femoral fractures. METHODS: Forty-five supracondylar or intercondylar femoral fractures were treated by minimally invasive percutaneous plating with the DCS or the LISS without bone graft. There were 26 patients with 26 fractures in the DCS group and 19 patients with 19 fractures in the LISS group. The data of the clinical and radiographic outcomes were compared between the two different fixation devices. RESULTS: Complete union was achieved in 41 of the 45 patients (91.1%). The success rate was 96.2% in the DCS group and 94.7% in the LISS group (p = 0.672). The mean fusion time was 19.18 weeks in the DCS group and 19.38 weeks in the LISS group (p = 0.835). The average range of motion of the knee joint was 111.65 degrees in the DCS group and 116.26 degrees in the LISS group (p = 0.334). Early implant failure only occurred in the DCS group (11.5%, p = 0.252, odds ratio = 1.826 [95% CI: 1.387-2.404]). The total complication rate was 15.4% in the DCS group and 15.8% in the LISS group (p = 0.641). The mean loss of coronal fracture fragment angle was -0.77 degrees in the DCS group and -0.19 degrees in the LISS group (p = 0.125). CONCLUSION: Minimally invasive percutaneous plating with the DCS or the LISS provides good outcome with few complications in the treatment of distal femoral fractures. Both systems minimize soft tissue trauma. LISS seems to have lower risk of early implant loosening than the DCS.

A Modified Alderman-Grant Coil makes possible an efficient cross-coil probe for high field solid-state NMR of lossy biological samples.

The design, construction, and performance of a cross-coil double-resonance probe for solid-state NMR experiments on lossy biological samples at high magnetic fields are described. The outer coil is a Modified Alderman-Grant Coil (MAGC) tuned to the (1)H frequency. The inner coil consists of a multi-turn solenoid coil that produces a B(1) field orthogonal to that of the outer coil. This results in a compact nested cross-coil pair with the inner solenoid coil tuned to the low frequency detection channel. This design has several advantages over multiple-tuned solenoid coil probes, since RF heating from the (1)H channel is substantially reduced, it can be tuned for samples with a wide range of dielectric constants, and the simplified circuit design and high inductance inner coil provides excellent sensitivity. The utility of this probe is demonstrated on two electrically lossy samples of membrane proteins in phospholipid bilayers (bicelles) that are particularly difficult for conventional NMR probes. The 72-residue polypeptide embedding the transmembrane helices 3 and 4 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) (residues 194-241) requires a high salt concentration in order to be successfully reconstituted in phospholipid bicelles. A second application is to paramagnetic relaxation enhancement applied to the membrane-bound form of Pf1 coat protein in phospholipid bicelles where the resistance to sample heating enables high duty cycle solid-state NMR experiments to be performed.

A strip-shield improves the efficiency of a solenoid coil in probes for high-field solid-state NMR of lossy biological samples.

A strip-shield inserted between a high inductance double-tuned solenoid coil and the glass tube containing the sample improves the efficiency of probes used for high-field solid-state NMR experiments on lossy aqueous samples of proteins and other biopolymers. A strip-shield is a coil liner consisting of thin copper strips layered on a PTFE (polytetrafluoroethylene) insulator. With lossy samples, the shift in tuning frequency is smaller, the reduction in Q, and RF-induced heating are all significantly reduced when the strip-shield is present. The performance of 800MHz (1)H/(15)N and (1)H/(13)C double-resonance probes is demonstrated on aqueous samples of membrane proteins in phospholipid bilayers.

Shiftless nuclear magnetic resonance spectroscopy.

The acquisition and analysis of high resolution one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectra without chemical shift frequencies are described. Many variations of shiftless NMR spectroscopy are feasible. A two-dimensional experiment that correlates the dipole-dipole and dipole-dipole couplings in the model peptide , (15)N labeled N-acetyl-leucine is demonstrated. In addition to the resolution of resonances from individual sites in a single crystal sample, the bond lengths and angles are characterized by the two-dimensional powder pattern obtained from a polycrystalline sample.

Proton-detected separated local field spectroscopy.

PISEMO, a separated local field experiment that can be performed with either direct (15)N (or (13)C) detection or indirect (1)H detection, is demonstrated on a single crystal of a model peptide. The (1)H signals modulated by (1)H-(15)N heteronuclear dipole-dipole couplings are observed stroboscopically in the windows of the multiple-pulse sequence used to attenuate (1)H-(1)H homonuclear dipole-dipole couplings. (1)H-detection yields spectra with about 2.5 times the signal to noise ratio observed with (15)N-detection under equivalent conditions. Resolution in both the (15)N chemical shift and (1)H-(15)N heteronuclear dipole-dipole coupling dimensions is similar to that observed with PISEMA, however, since only on-resonance pulses are utilized, the bandwidth is better.

An efficient (1)H/(31)P double-resonance solid-state NMR probe that utilizes a scroll coil.

The construction and performance of a scroll coil double-resonance probe for solid-state NMR on stationary samples is described. The advantages of the scroll coil at the high resonance frequencies of (1)H and (31)P include: high efficiency, minimal perturbations of tuning by a wide range of samples, minimal RF sample heating of high dielectric samples of biopolymers in aqueous solution, and excellent RF homogeneity. The incorporation of a cable tie cinch for mechanical stability of the scroll coil is described. Experimental results obtained on a Hunter Killer Peptide 1 (HKP1) interacting with phospholipid bilayers of varying lipid composition demonstrate the capabilities of this probe on lossy aqueous samples.

Three-dimensional structure of the transmembrane domain of Vpu from HIV-1 in aligned phospholipid bicelles.

The three-dimensional backbone structure of the transmembrane domain of Vpu from HIV-1 was determined by solid-state NMR spectroscopy in two magnetically-aligned phospholipid bilayer environments (bicelles) that differed in their hydrophobic thickness. Isotopically labeled samples of Vpu(2-30+), a 36-residue polypeptide containing residues 2-30 from the N-terminus of Vpu, were incorporated into large (q = 3.2 or 3.0) phospholipid bicelles composed of long-chain ether-linked lipids (14-O-PC or 16-O-PC) and short-chain lipids (6-O-PC). The protein-containing bicelles are aligned in the static magnetic field of the NMR spectrometer. Wheel-like patterns of resonances characteristic of tilted transmembrane helices were observed in two-dimensional (1)H/(15)N PISEMA spectra of uniformly (15)N-labeled Vpu(2-30+) obtained on bicelle samples with their bilayer normals aligned perpendicular or parallel to the direction of the magnetic field. The NMR experiments were performed at a (1)H resonance frequency of 900 MHz, and this resulted in improved data compared to lower-resonance frequencies. Analysis of the polarity-index slant-angle wheels and dipolar waves demonstrates the presence of a transmembrane alpha-helix spanning residues 8-25 in both 14-O-PC and 16-O-PC bicelles, which is consistent with results obtained previously in micelles by solution NMR and mechanically aligned lipid bilayers by solid-state NMR. The three-dimensional backbone structures were obtained by structural fitting to the orientation-dependent (15)N chemical shift and (1)H-(15)N dipolar coupling frequencies. Tilt angles of 30 degrees and 21 degrees are observed in 14-O-PC and 16-O-PC bicelles, respectively, which are consistent with the values previously determined for the same polypeptide in mechanically-aligned DMPC and DOPC bilayers. The difference in tilt angle in C14 and C16 bilayer environments is also consistent with previous results indicating that the transmembrane helix of Vpu responds to hydrophobic mismatch by changing its tilt angle. The kink found in the middle of the helix in the longer-chain C18 bilayers aligned on glass plates was not found in either of these shorter-chain (C14 or C16) bilayers.

SPINAL modulated decoupling in high field double- and triple-resonance solid-state NMR experiments on stationary samples.

Continuous wave irradiation has limited bandwidth for heteronuclear 1H decoupling at high fields and for 13C decoupling in 1H/13C/15N triple-resonance experiments. SPINAL-16 modulation is shown to improve the efficiency of 1H and 13C heteronuclear decoupling on single crystals of peptides and on magnetically aligned samples of membrane proteins in bicelles, which is of particular importance because aqueous samples of biomolecules are lossy at high fields, which limits the strengths of the RF fields that can be applied.

Structure of the coat protein in Pf1 bacteriophage determined by solid-state NMR spectroscopy.

The atomic resolution structure of Pf1 coat protein determined by solid-state NMR spectroscopy of magnetically aligned filamentous bacteriophage particles in solution is compared to the structures previously determined by X-ray fiber and neutron diffraction, the structure of its membrane-bound form, and the structure of fd coat protein. These structural comparisons provide insights into several biological properties, differences between class I and class II filamentous bacteriophages, and the assembly process. The six N-terminal amino acid residues adopt an unusual "double hook" conformation on the outside of the bacteriophage particle. The solid-state NMR results indicate that at 30 degrees C, some of the coat protein subunits assume a single, fully structured conformation, and some have a few mobile residues that provide a break between two helical segments, in agreement with structural models from X-ray fiber and neutron diffraction, respectively. The atomic resolution structure determined by solid-state NMR for residues 7-14 and 18-46, which excludes the N-terminal double hook and the break between the helical segments, but encompasses more than 80% of the backbone including the distinct kink at residue 29, agrees with that determined by X-ray fiber diffraction with an RMSD value of 2.0 A. The symmetry and distance constraints determined by X-ray fiber and neutron diffraction enable the construction of an accurate model of the bacteriophage particle from the coordinates of the coat protein monomers.