Extreme Water Velocities: Topographical Amplification of Wave-Induced Flow in the Surf Zone of Rocky Shores

Water velocities as high as 25 m s-1 have been recorded in the surf zone of wave-swept rocky shores-velocities more than twice the phase speed of the breaking waves with which they are associated. How can water travel twice as fast as the waveform that initially induces its velocity? We explore the possibility that the interaction of a wave with the local topography of the shore can greatly amplify the water velocities imposed on intertidal plants and animals. Experiments in a laboratory wave tank show that interactions between bores refracted by a prowlike beach can produce jets in which the velocity is nearly twice the bore\u27s phase speed. This velocity can be further amplified by a factor of 1.3-1.6 if the jet strikes a vertical wall. This type of topographically induced amplification of water velocity could result in substantial spatial variation in wave-induced hydrodynamic forces and might thereby help to explain the patchwork nature of disturbance that is characteristic of intertidal communities

Intravenous tPA therapy does not worsen acute intracerebral hemorrhage in mice

Tissue plasminogen activator (tPA) is the only FDA-approved treatment for reperfusing ischemic strokes. But widespread use of tPA is still limited by fears of inadvertently administering tPA in patients with intracerebral hemorrhage (ICH). Surprisingly, however, the assumption that tPA will worsen ICH has never been biologically tested. Here, we assessed the effects of tPA in two models of ICH. In a mouse model of collagenase-induced ICH, hemorrhage volumes and neurological deficits after 24 hrs were similar in saline controls and tPA-treated mice, whereas heparin-treated mice had 3-fold larger hematomas. In a model of laser-induced vessel rupture, tPA also did not worsen hemorrhage volumes, while heparin did. tPA is known to worsen neurovascular injury by amplifying matrix metalloproteinases during cerebral ischemia. In contrast, tPA did not upregulate matrix metalloproteinases in our mouse ICH models. In summary, our experimental data do not support the assumption that intravenous tPA has a deleterious effect in acute ICH. However, due to potential species differences and the inability of models to fully capture the dynamics of human ICH, caution is warranted when considering the implications of these findings for human therapy

Fermi surface induced lattice distortion in NbTe2_2

The origin of the monoclinic distortion and domain formation in the quasi two-dimensional layer compound NbTe$_2$ is investigated. Angle-resolved photoemission shows that the Fermi surface is pseudogapped over large portions of the Brillouin zone. Ab initio calculation of the electron and phonon bandstructure as well as the static RPA susceptibility lead us to conclude that Fermi surface nesting and electron-phonon coupling play a key role in the lowering of the crystal symmetry and in the formation of the charge density wave phase

Aging and the Environment: A Research Framework

The rapid growth in the number of older Americans has many implications for public health, including the need to better understand the risks posed to older adults by environmental exposures. Biologic capacity declines with normal aging; this may be exacerbated in individuals with pre-existing health conditions. This decline can result in compromised pharmacokinetic and pharmacodynamic responses to environmental exposures encountered in daily activities. In recognition of this issue, the U.S. Environmental Protection Agency (EPA) is developing a research agenda on the environment and older adults. The U.S. EPA proposes to apply an environmental public health paradigm to better understand the relationships between external pollution sources → human exposures → internal dose → early biologic effect → adverse health effects for older adults. The initial challenge will be using information about aging-related changes in exposure, pharmacokinetic, and pharmacodynamic factors to identify susceptible subgroups within the diverse population of older adults. These changes may interact with specific diseases of aging or medications used to treat these conditions. Constructs such as “frailty” may help to capture some of the diversity in the older adult population. Data are needed regarding a) behavior/activity patterns and exposure to the pollutants in the microenvironments of older adults; b) changes in absorption, distribution, metabolism, and excretion with aging; c) alterations in reserve capacity that alter the body’s ability to compensate for the effects of environmental exposures; and d) strategies for effective communication of risk and risk reduction methods to older individuals and communities. This article summarizes the U.S. EPA’s development of a framework to address and prioritize the exposure, health effects, and risk communications concerns for the U.S. EPA’s evolving research program on older adults as a susceptible subpopulation

Spontaneously exsolved free gas during major storms as an ephemeral gas source for pockmark formation

Abrupt fluid emissions from shallow marine sediments pose a threat to seafloor installations like wind farms and offshore cables. Quantifying such fluid emissions and linking pockmarks, the seafloor manifestations of fluid escape, to flow in the sub-seafloor remains notoriously difficult due to an incomplete understanding of the underlying physical processes. Here, using a compositional multi-phase flow model, we test plausible gas sources for pockmarks in the south-eastern North Sea, which recent observations suggest have formed in response to major storms. We find that the mobilization of pre-existing gas pockets is unlikely because free gas, due to its high compressibility, damps the propagation of storm-induced pressure changes deeper into the subsurface. Rather, our results point to spontaneous appearance of a free gas phase via storm-induced gas exsolution from pore fluids. This mechanism is primarily driven by the pressure-sensitivity of gas solubility, and the appearance of free gas is largely confined to sediments in the vicinity of the seafloor. We show that in highly permeable sediments containing gas-rich pore fluids, wave-induced pressure changes result in the appearance of a persistent gas phase. This suggests that seafloor fluid escape structures are not always proxies for overpressured shallow gas and that periodic seafloor pressure changes can induce persistent free gas phase to spontaneously appear. Key Points - Storm-induced pressure changes can lead to spontaneous appearance of free gas phase near the seafloor - This process is driven by pressure-sensitive phase instabilities - This mechanism could help explain elusive gas sources in recently observed pockmarks in the North Se

Calcification-driven CO2emissions exceed blue Carbon sequestration in a carbonate seagrass meadow

Long-term Blue Carbon burial in seagrass meadows is complicated by other carbon and alkalinity exchanges that shape net carbon sequestration. We measured a suite of such processes, including denitrification, sulfur, and inorganic carbon cycling, and assessed their impact on air-water CO2 exchange in a typical seagrass meadow underlain by carbonate sediments. Eddy covariance measurements reveal a consistent source of CO2 to the atmosphere at an average rate of 610 ± 990 μmol m-2 hour-1 during our study and 700 ± 660 μmol m-2 hour-1 (6.1 mol m-2 year-1) over an annual cycle. Net alkalinity consumption by ecosystem calcification explains \u3e95% of the observed CO2 emissions, far exceeding organic carbon burial and anaerobic alkalinity generation. We argue that the net carbon sequestration potential of seagrass meadows may be overestimated if calcification-induced CO2 emissions are not accounted for, especially in regions where calcification rates exceed net primary production and burial