A method for inverting ratio–ratio data to estimate end-member compositions in mixing problems

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 352 (2013): 63–69, doi:10.1016/j.chemgeo.2013.06.002.I discuss the general problem of fitting mixing models to ratio-ratio data, and derive formulae for applying non-linear Maximum Likelihood methods for parameter estimation. To estimate mixing model parameters in the under-determined inversion it is necessary to introduce prior constraints, which I implement by penalizing the likelihood function for variations from a starting model. I illustrate practical aspects of the inverse problem by applying the method to synthetic data for a ternary system of putative mantle reservoirs using Sr, Nd, and Pb isotope ratios. I fit the synthetic data using two different starting models to demonstrate the sensitivity of the gradient method used to solve the non-linear inverse to the starting model and the necessity of inspecting the final model to avoid spurious results. I include Matlab scripts to facilitate starting model selection and to perform binary and ternary ratio-ratio inversions as an Electronic Appendix

Spectral analysis of vertical temperature profile time-series data in Yellowstone Lake sediments

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 57(4), (2021): e2020WR028430, https://doi.org/10.1029/2020WR028430.We use yearlong vertical temperature profile time-series (seven thermistors at evenly spaced depth intervals from 10 to 70 cm) from five sites in and around the Deep Hole thermal area, southeast of Stevenson Island, Yellowstone Lake, to investigate heat and mass fluxes across the lake floor. The records demonstrate that thermal gradients in surficial sediments are modulated by a rich spectrum of bottom water temperature variations generated by hydrodynamic processes, and that sites inside the thermal area also respond to hydrothermal variations. We develop and implement a new method for estimating the sediment effective thermal diffusivity and pore fluid vertical flow rate that exploits the full spectrum of observed temperature variations to generate the parameter estimates, uncertainties, and metrics to assess statistical significance. Sediments at sites outside thermal areas have gradients of ∼7.5°C/m, in situ thermal diffusivities of ∼1.6 × 10−7 m2/s consistent with highly porous (80–90%) siliceous sediments, and experience hypolentic flow in the upper ∼20 cm. Sites inside the Deep Hole thermal area exhibit considerable spatial and temporal variability, with gradients of 1–32°C/m, and higher thermal diffusivities of ∼2–12 × 10−7 m2/s, consistent with hydrothermal alteration of biogenic silica to clays, quartz, and pyrite. Upward pore fluid flow at these sites is observed across multiple depth intervals, with maximum values of ∼3 cm/day. The observed spatial and temporal variability within the thermal area is consistent with upward finger flow combined with short wavelength convection within the porous sediments above a steam reservoir.This research was supported by the National Science Foundation Grants EAR-1516361 to Robert A. Sohn and EAR-1515283 to Robert N. Harris, and by the Independent Research and Development Program at the Woods Hole Oceanographic Institution (Robert A. Sohn). All work in Yellowstone National Park was completed under an authorized Yellowstone research permit (YELL-2018-SCI-7018)

Correlation scales of digital elevation models in developed coastal environments

Accuracy of digital elevation models (DEMs) often depends on how features of different spatial scales are represented. Scale dependence is particularly important in low gradient coastal environments where small vertical errors can affect large areas and where representation of fine scale topographic features can influence how DEMs are used for modeling inundation. It is commonly observed that different types of DEMs represent larger, coarse-scale topographic features similarly but differ in how they represent smaller, finer-scale features. The spatial-scale dependence of DEM accuracy can be quantified in terms of the correlation scale (λC); the spatial wavelength above which models agree with spectral coherency > 0.5 and below which they differ. We compare cross spectral analyses of the GDEM2 and SRTM global DEMs with 14,572 LiDAR-derived elevations along transects in diverse coastal environments of New York City. Both global DEMs have positive bias relative to LiDAR ground elevations, but bias (μ) and uncertainty (σ) of GDEM2 (μ: 8.1 m; σ: 7.6 m) are significantly greater than those of SRTM (μ: 1.9 m; σ: 3.6 m). Cross-spectral coherency between GDEM2 and the LiDAR DEM begins to roll-off at scales of λ < ~ 3 km, while coherency between SRTM and the LiDAR DEM begins to roll-off at scales of λ < ~ 1 km. The correlation scale below which coherency with LiDAR attains a signal to noise ratio of 1 is ~ 1 km for GDEM2 and ~ 0.5 km for SRTM; closely matching the divergence scales where the surface roughness of the land cover exceeds the roughness of the underlying terrain

Sonic boom configuration minimization

The topics covered include the following: the sonic boom 'big picture'; current low boom technology; Mach number impact on gross weight; equal loudness equivalent areas; performance and sizing results; potential configuration modifications; equivalent area matching; and impact of nose bluntness on aerodynamic characteristics

Poroelastic response of mid-ocean ridge hydrothermal systems to ocean tidal loading : implications for shallow permeability structure

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 43 (2016): 1660–1668, doi:10.1002/2015GL066479.We use the time delay between tidal loading and exit-fluid temperature response for hydrothermal vents to model the poroelastic behavior and shallow upflow zone (SUZ) effective permeability structure of three mid-ocean ridge (MOR) sites with different spreading rates. Hydrothermal vents at Lucky Strike field exhibit relatively small phase lags corresponding to high SUZ effective permeabilities of ≥ ~10−10 m2, with variations that we interpret as resulting from differences in the extrusive layer thickness. By contrast, vents at East Pacific Rise site exhibit relatively large phase lags corresponding to low SUZ effective permeabilities of ≤ ~10−13 m2. Vents at Main Endeavour field exhibit both high and low phase lags, suggestive of a transitional behavior. Our results demonstrate that tidal forcing perturbs hydrothermal flow across the global MOR system, even in places where the tidal amplitude is very low, and that the flow response can be used to constrain variations in SUZ permeability structure beneath individual vent fields.This research was funded by Woods Hole Oceanographic Institution (USA). Thibaut Barreyre was supported by WHOI's Deep Ocean Exploration Institute (DOEI) postdoctoral scholarship.2016-08-2

OMP Peptides Activate the DegS Stress-Sensor Protease by a Relief of Inhibition Mechanism

In the E. coli periplasm, C-terminal peptides of misfolded outer-membrane porins (OMPs) bind to the PDZ domains of the trimeric DegS protease, triggering cleavage of a transmembrane regulator and transcriptional activation of stress genes. We show that an active-site DegS mutation partially bypasses the requirement for peptide activation and acts synergistically with mutations that disrupt contacts between the protease and PDZ domains. Biochemical results support an allosteric model, in which these mutations, active-site modification, and peptide/substrate binding act in concert to stabilize proteolytically active DegS. Cocrystal structures of DegS in complex with different OMP peptides reveal activation of the protease domain with varied conformations of the PDZ domain and without specific contacts from the bound OMP peptide. Taken together, these results indicate that the binding of OMP peptides activates proteolysis principally by relieving inhibitory contacts between the PDZ domain and the protease domain of DegS.United States. Dept. of Energy (Office of Basic Energy Sciences, contract DE-AC02-06CH11357))National Institutes of Health (U.S.) (NIH-NCRR award RR-15301)National Institutes of Health (U.S.) (NIH postdoctoral fellowship (F32AI-074245-01A1))National Institutes of Health (U.S.) (NIH grant AI-16892

OMP Peptides Modulate the Activity of DegS Protease by Differential Binding to Active and Inactive Conformations

Upon sensing misfolded outer-membrane porins (OMPs) in the periplasm, the E. coli DegS protease cleaves RseA, a transmembrane regulator, transmitting a signal to activate cytoplasmic gene expression. Misfolding is detected by binding of normally inaccessible OMP sequences to the DegS-PDZ domain, which relieves allosteric inhibition and activates proteolysis. Here we show that DegS stimulation can be regulated by OMP peptide affinity for the active and for the inactive protease conformations, as well as by preferential substrate binding to active DegS. Based on the effects of mutations in the peptide-binding pocket of the PDZ domain and elsewhere, we suggest an allosteric pathway that links peptide binding to DegS activation. These results explain fast responses to envelope stress; demonstrate that the protein-unfolding response, even under catastrophic conditions, can be tailored by the peptide sequences that become accessible to DegS; and suggest strategies for control of related PDZ proteases by allosteric effectors.National Institutes of Health (U.S.) (NIH grant AI-16892)National Institutes of Health (U.S.) (NIH postdoctoral fellowship (AI-074245-01A1)

On the Economic Sources of Stock Market Volatility

We revisit the relation between stock market volatility and macroeconomic activity using a new class of component models that distinguish short run from secular movements. We combine insights from Engle and Rangel (2007) and the recent work on mixed data sampling (MIDAS), as in e.g. Ghysels, Santa-Clara, and Valkanov (2005). The new class of models is called GARCH-MIDAS, since it uses a mean reverting unit daily GARCH process, similar to Engle and Rangel (2007), and a MIDAS polynomial which applies to monthly, quarterly, or bi-annual macroeconomic or financial variables. We study long historical data series of aggregate stock market volatility, starting in the 19th century, as in Schwert (1989). We formulate models with the long term component driven by inflation and industrial production growth that are at par in terms of out-of-sample prediction for horizons of one quarter and out-perform more traditional time series volatility models at longer horizons. Hence, imputing economic fundamentals into volatility models pays off in terms of long horizon forecasting. We also find that at a daily level, inflation and industrial production growth, account for between 10 % and 35 % of one-day ahead volatility prediction. Hence, macroeconomic fundamentals play a significant role even at short horizons. Unfortunately, all the models - purely time series ones as well as those driven by economic variables - feature structural breaks over the entire sample spanning roughly a century and a half of daily data. Consequently, our analysis also focuses on subsamples - pre-WWI, the Great Depression era, and post-WWII (also split to examine the so called Great Moderation). Our main findings remain valid across subsamples

Microearthquake evidence for reaction-driven cracking within the Trans-Atlantic Geotraverse active hydrothermal deposit

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 119 (2014): 822–839, doi:10.1002/2013JB010110.We detected 32,078 very small, local microearthquakes (average ML = −1) during a 9 month deployment of five ocean bottom seismometers on the periphery of the Trans-Atlantic Geotraverse active mound. Seismicity rates were constant without any main shock-aftershock behavior at ~243 events per day at the beginning of the experiment, 128 events per day after an instrument failed, and 97 events per day at the end of the experiment when whale calls increased background noise levels. The microearthquake seismograms are characterized by durations of <1 s and most have single-phase P wave arrivals (i.e., no S arrivals). We accurately located 6207 of the earthquakes, with hypocenters clustered within a narrow depth interval from ~50 to 125 m below seafloor on the south and west flanks of the deposit. We model the microearthquakes as reaction-driven fracturing events caused by anhydrite deposition in the secondary circulation system of the hydrothermal mound and show that under reasonable modeling assumptions an average event represents a volume increase of 31–58 cm3, yielding an annual (seismogenic) anhydrite deposition rate of 27–51 m3.This work was supported in part by the U.S. National Science Foundation, National Science and Engineering Graduate Fellowship, and the Woods Hole Oceanographic Institution Deep Ocean Exploration Institute.2014-09-1

UV Properties of Galactic Globular Clusters with GALEX II. Integrated colors

We present ultraviolet (UV) integrated colors of 44 Galactic globular clusters (GGCs) observed with the Galaxy Evolution Explorer (GALEX) in both FUV and NUV bands. This data-base is the largest homogeneous catalog of UV colors ever published for stellar systems in our Galaxy. The proximity of GGCs makes it possible to resolve many individual stars even with the somewhat low spatial resolution of GALEX. This allows us to determine how the integrated UV colors are driven by hot stellar populations, primarily horizontal branch stars and their progeny. The UV colors are found to be correlated with various parameters commonly used to define the horizontal branch morphology. We also investigate how the UV colors vary with parameters like metallicity, age, helium abundance and concentration. We find for the first time that GCs associated with the Sagittarius dwarf galaxy have (FUV-V) colors systematically redder than GGCs with the same metallicity. Finally, we speculate about the presence of an interesting trend, suggesting that the UV color of GCs may be correlated with the mass of the host galaxy, in the sense that more massive galaxies possess bluer clusters.Comment: Accepted for publication by The Astronomical Journal. 36 pages, 9 figures, 1 tabl