bluuebunny/crossref_metadata_2025 huggingface dataset:
Oscillation of the Ionosphere at Planetary‐Wave Periods
Authors: Forbes J. M. , Maute A. , Zhang X. , Hagan M. E.
Published: August 2018

F‐region ionospheric oscillations at planetary‐wave (PW) periods (2–20 days) are investigated, with primary focus on those oscillations transmitted to the ionosphere by PW modulation of the vertically propagating tidal spectrum. Tidal effects are isolated by specifically designed numerical experiments performed with the National Center for Atmospheric Research thermosphere‐ionosphere‐electrodynamics general circulation model for October 2009, when familiar PW and tides are present in the model. Longitude versus day‐of‐month perturbations in topside F‐region electron density (Ne) of order ±30–50% at PW periods occur as a result of PW‐modulated tides. At a given height, these oscillations are mainly due to vertical oscillations in the F layer of order ±15–40 km. These vertical movements are diagnosed in terms of changes in the F2‐layer peak height, ΔhmF2, which are driven by the vertical projections of E × B drifts and field‐aligned in situ neutral winds. E × B drifts dominate at the magnetic equator, while the two sources play more equal roles between 20° and 40° magnetic latitudes in each hemisphere. The in situ neutral wind effect arises from vertical propagation of PW‐modulated tides, whereas the E × B drifts originate from dynamo‐generated electric fields produced by the E‐region component of the same wind field; the former represents a new coupling mechanism for production of ionospheric oscillations at PW periods. Roughly half the above‐mentioned variability in Ne and hmF2 is associated with zonally symmetric (S0) oscillations, which contribute at about half the level of low‐level magnetic activity during October 2009. The thermosphere‐ionosphere‐electrodynamics general circulation model simulates the S0 oscillations in Ne observed from the CHAMP satellite well during this period and reveals that S0 oscillations in E × B play a significant role in driving S0 oscillations in ΔhmF2, in addition to neutral winds.
Ab Initio Prediction of Potassium Partitioning Into Earth's Core
Authors: Xiong Zhihua , Tsuchiya Taku , Taniuchi Takashi
Published: August 2018

Potassium partitioning between molten silicates and liquid iron alloys is the fundamental process determining its incorporation into the Earth's core. In this study, it is investigated using the method of the ab initio molecular dynamics simulation combined with the thermodynamic integration technique. Results suggest that the potassium incorporation into iron alloys positively depends on temperature, while the effect of pressure is insignificant. Moreover, the existence of oxygen in liquid iron alloys significantly enhances the potassium solubility therein, whereas sulfur and silicon only have negligible effects. Electronic structure analyses reveal that potassium remains alkali‐metallic in liquid iron alloy systems under all conditions in this study, which is distinct from the characteristics reported for solid potassium. Atomic structure analyses indicate that the oxygen coordination number around potassium atom increases with oxygen concentration in liquid iron alloys, supporting the oxygen concentration dependence of the potassium partitioning between molten silicates and liquid iron alloys. Using the obtained partitioning coefficients combined with geochemical property, the maximum potassium concentration in the Earth's core is estimated to be ~30 ppm, which would be unlikely to affect the thermal evolution of the Earth's core significantly.
Sustained Upwelling of Subsurface Iron Supplies Seasonally Persistent Phytoplankton Blooms Around the Southern Kerguelen Plateau, Southern Ocean
Authors: Schallenberg Christina , Bestley Sophie , Klocker Andreas , Trull Thomas W. , Davies Diana M. , Gault‐Ringold Melanie , Eriksen Ruth , Roden Nicholas P. , Sander Sylvia G. , Sumner Michael , Townsend Ashley T. , van der Merwe Pier , Westwood Karen , Wuttig Kathrin , Bowie Andrew
Published: August 2018

Although the supply of iron generally limits phytoplankton productivity in the Southern Ocean, substantial seasonal blooms are observed over and downstream of the Kerguelen plateau in the Indian sector of the Southern Ocean. Surprisingly, of the oceanic blooms, those associated with the deeper southern plateau last much longer (~3 months) than the northern bloom (~1‐month downstream of northern plateau). In this study, iron supply mechanisms around the southern plateau were investigated, obtaining profiles of dissolved iron (<0.2 μm, dFe) to 2,000‐m deep at 25 stations during austral summer 2016. The dFe concentrations in surface waters (≤100‐m depth) ranged from below the detection limit (DL, median of 0.026 nmol/kg) to 0.34 nmol/kg near the Antarctic shelf, with almost half the data points below detection. These low and—with few exceptions—largely spatially invariant concentrations, presumably driven by seasonal drawdown of this essential micronutrient by phytoplankton, could not explain observed patterns in chlorophyll a. In contrast, dFe concentrations (0.05–1.27 nmol/kg) in subsurface waters (100–800 m) showed strong spatial variations that can explain bloom patterns around the southern Kerguelen plateau when considered in the context of frontal locations and associated frontal processes, including upwelling, that may increase the upward supply of dFe in the region. This sustained vertical dFe supply distinguishes the southern blooms from the bloom downstream of the northern Kerguelen plateau and explains their persistence through the season.
Cross‐Polarization GMF for High Wind Speed and Surface Stress Retrieval
Authors: Troitskaya Yu. , Abramov V. , Baidakov G. , Ermakova O. , Zuikova E. , Sergeev D. , Ermoshkin A. , Kazakov V. , Kandaurov A. , Rusakov N. , Poplavsky E. , Vdovin M.
Published: August 2018

This paper describes the construction of geophysical model function (GMF) for wind speed and surface stress retrieval at high winds from cross‐polarized radar backscatter at the water surface. The starting point is the laboratory experiment designed for the study of X‐band backscattering from water surface. In particular, it was shown that cross‐polarized normalized radar cross section (NRCS) keeps sensitivity to wind friction velocity at high winds alternatively to co‐polarized radar return. Basing on the analysis of the Doppler spectra and simultaneous measurements of parameters of surface waves, we suggest a hypothesis that at high winds the cross‐polarized backscattered signal is formed mainly due to scattering from wave breakers. The hypothesis is supported by the experimentally detected proportionality between the power of the scattered signal at cross polarization and the area swept by wave breakers. These results obtained in the laboratory environment are applied for constructing the similar dependencies for field conditions. Using the phenomenological statistical physics approach, a parameterization of active whitecap coverage fraction dependence on wind friction velocity is suggested. With the use of this parameterization, the empirical function expressing the cross‐polarized NRCS by u* is derived. Using the surface drag parameterization applicable at strong winds, this dependence is verified on the base of available data sets containing collocated satellite measurements of cross‐polarized C‐band NRCS and ground measurements of wind speed. GMFs for u* and U10 retrieval are suggested. Analysis shows that taking into account the angular dependence of cross‐polarized radar backscattered power improves the accuracy of wind speed and wind friction velocity retrieval.
Method to Estimate Water Vapor Supersaturation in the Ambient Activation Process Using Aerosol and Droplet Measurement Data
Authors: Shen Chuanyang , Zhao Chunsheng , Ma Nan , Tao Jiangchuan , Zhao Gang , Yu Yingli , Kuang Ye
Published: August 2018

Water vapor supersaturation, as one of the most important environmental parameters during the formation of clouds or fogs, cannot be directly measured, and few studies have been carried out to estimate it in the ambient activation process. In this study, a new method to estimate the water vapor supersaturation based on the inverse application of κ‐Köhler theory is proposed. Aerosol hygroscopic parameter κ, dry particle size distributions, and wet droplet size distributions were employed and a comparison of predicted droplet number concentration with the measurement results was made to obtain the effective supersaturation during the activation process. Using this method, we acquired the supersaturations varying from 0.01% to 0.05% in a fog episode observed in the North China Plain. In this fog episode, both hydrated unactivated droplets and activated droplets play a part in the total detected droplet number concentrations with the unactivated droplets' ratio decreasing with size. The sensitivity study was also made to evaluate the effects of droplet and aerosol hygroscopic measurement errors on the supersaturation ratio estimation. Water vapor supersaturation obtained with this method can be regarded as an effective value and can be further applied to cloud analysis in the future. This method is only based on conventional measurements of aerosol and droplets and does not rely on any other data, which makes it flexible and easy to perform. Calculated supersaturations and critical diameters can also deepen the understanding of ambient activation process and corresponding interactions between aerosol and droplet characteristics.
Regional Similarities and NOx‐Related Increases in Biogenic Secondary Organic Aerosol in Summertime Southeastern United States
Authors: Liu Jun , Russell Lynn M. , Ruggeri Giulia , Takahama Satoshi , Claflin Megan S. , Ziemann Paul J. , Pye Havala O. T. , Murphy Benjamin N. , Xu Lu , Ng Nga L. , McKinney Karena A. , Budisulistiorini Sri Hapsari , Bertram Timothy H. , Nenes Athanasios , Surratt Jason D.
Published: August 2018

During the 2013 Southern Oxidant and Aerosol Study, Fourier transform infrared spectroscopy (FTIR) and aerosol mass spectrometer (AMS) measurements of submicron mass were collected at Look Rock (LRK), Tennessee, and Centreville (CTR), Alabama. Carbon monoxide and submicron sulfate and organic mass concentrations were 15–60% higher at CTR than at LRK, but their time series had moderate correlations (r ~ 0.5). However, NOxhad no correlation (r = 0.08) between the two sites with nighttime‐to‐early‐morning peaks 3–10 times higher at CTR than at LRK. Organic mass (OM) sources identified by FTIR Positive Matrix Factorization (PMF) had three very similar factors at both sites: fossil fuel combustion‐related organic aerosols, mixed organic aerosols, and biogenic organic aerosols (BOA). The BOA spectrum from FTIR is similar (cosine similarity > 0.6) to that of lab‐generated particle mass from the photochemical oxidation of both isoprene and monoterpenes under high NOxconditions from chamber experiments. The BOA mass fraction was highest during the night at CTR but in the afternoon at LRK. AMS PMF resulted in two similar pairs of factors at both sites and a third nighttime NOx‐related factor (33% of OM) at CTR but a daytime nitrate‐related factor (28% of OM) at LRK. NOxwas correlated with BOA and LO‐OOA for NOxconcentrations higher than 1 ppb at both sites, producing 0.5 ± 0.1 μg/m3for CTR‐LO‐OOA and 1.0 ± 0.3 μg/m3for CTR‐BOA additional biogenic OM for each 1 ppb increase of NOx.
Investigating the Potential of Using Satellite‐Based Precipitation Radars as Reference for Evaluating Multisatellite Merged Products
Authors: Khan S. , Maggioni V. , Kirstetter P.‐E.
Published: August 2018

This work investigates the viability of using the Global Precipitation Mission (GPM) Dual‐frequency Precipitation Radar (DPR) as a reference for evaluating multisatellite precipitation products in locations where a ground‐based reference is not available. The Integrated Multi‐Satellite Retrievals for Global Precipitation Measurement (IMERG) version V05 products (early, late, and final) and the microwave‐only (MW) and infrared‐only (IR) components are evaluated against two reference data sets, derived from the Multi‐Radar/Multi‐Sensor System suite of products (MRMS) and the level‐2 DPR (2ADPR). The analysis focuses on a 2‐year period (2014–2015), excluding winters to evaluate liquid‐phase precipitation only. Systematic and random errors are assessed between the satellite‐based products and the MRMS‐based reference. Systematic error for the IMERG early, late, and final products and the MW component are shown to be comparable to those of 2ADPR, while the IR component exhibits a larger bias. Random errors of the IR estimates are found to be 1 order of magnitude larger than the 2ADPR random error. Thus, the hypothesis of using 2ADPR as a benchmark for quantifying uncertainties associated with IMERG holds true for evaluating random errors associated with IR precipitation estimates. Errors in the IR component are then investigated as a function of climatology and seasonality across contiguous United States. The temperate, oceanic, and subtropical climates show the best performance in terms of probability of detection and success ratio, whereas arid‐desert manifests the smallest root‐mean‐square errors. This work suggests that climatic zone‐specific error characterization model is necessary to estimate uncertainties associated with the IMERG products.
Larger Sensitivity of Precipitation Extremes to Aerosol Than Greenhouse Gas Forcing in CMIP5 Models
Authors: Lin Lei , Wang Zhili , Xu Yangyang , Fu Qiang , Dong Wenjie
Published: August 2018

The sensitivity of precipitation extremes (PEs; i.e., the change in PE per degree of change in global mean surface temperature) to aerosol and greenhouse gas (GHG) forcings is examined using the twentieth century historical multimodel ensemble simulations from the Coupled Model Intercomparison Program phase 5 (CMIP5). We find a robustly larger sensitivity of PE to aerosols than GHGs across all available models. The aerosol/GHG‐induced sensitivity ratios for globe‐averaged monthly maximum consecutive 5‐day precipitation (RX5day) and maximum 1‐day precipitation (RX1day) in the multimodel ensemble are 1.6 and 1.4, respectively. Over land, the corresponding ratios for RX5day and RX1day are 2.3 and 1.8, respectively. In particular, the aerosol forcing leads to several times greater sensitivity than GHG forcing in West Africa, eastern China, South and Southeast Asia, northwestern South America, and Eastern Europe. The atmospheric energy balance, dynamical adjustment, and vertical structure of forcing, all contribute to the difference in the PE sensitivity to the two forcings. It is shown that the fast response primarily contributes to the greater‐than‐one aerosol‐to‐GHG ratios of the PE sensitivities, as for the mean precipitation. This is because of a stronger rainfall suppression effect induced by the GHG atmospheric forcing. We also find that the aerosol‐to‐GHG ratios of the PE sensitivities depend on the defined extreme precipitation indices. The aerosol‐to‐GHG sensitivity ratio is larger for more loosely defined PE, and it gradually converges to one for more severely defined PE. Our results further highlight the importance of considering the anthropogenic aerosol reduction in projecting the change in PE.
The Effect of Mars‐Relevant Soil Analogs on the Water Uptake of Magnesium Perchlorate and Implications for the Near‐Surface of Mars
Authors: Primm K. M. , Gough R. V. , Wong J. , Rivera‐Valentin E. G. , Martinez G. M. , Hogancamp J. V. , Archer P. D. , Ming D. W. , Tolbert M. A.
Published: August 2018

The water uptake and release by perchlorate salts have been well studied since the first in situ identification of such salts in the Martian soil by the Phoenix mission in 2008. However, there have been few studies on the effect of the insoluble regolith minerals on the interaction of perchlorate with water vapor. In this work, we investigate the impact of a Mars‐relevant mineral, montmorillonite, and a Mars soil analog, Mojave Mars Simulant (MMS), on the deliquescence (transition from dry crystalline to aqueous via water vapor absorption), ice formation, and efflorescence (transition from aqueous to dry crystalline via loss of water) of pure magnesium perchlorate. We studied mixtures of magnesium perchlorate hexahydrate with either montmorillonite or MMS. Although montmorillonite and MMS are materials that may serve as nuclei for either ice nucleation or salt efflorescence, we find that these soil analogs did not affect the phase transitions of magnesium perchlorate. The salt‐mineral mixture behaved similarly, within estimated uncertainties, to pure magnesium perchlorate in all cases. Experiments were performed in both N2 and CO2 atmospheres, with no detectable difference. We use data from the Mars Science Laboratory Rover Environmental Monitoring Station instrument and the Phoenix Thermal and Electrical Conductivity Probe, as well as modeling of the shallow subsurface, to determine the likelihood of these perchlorate phase transitions occurring at Gale Crater and the northern arctic plains (Vastitas Borealis). We find that aqueous solutions are predicted in the shallow subsurface of the Phoenix landing site, but not predicted at Gale Crater.
Equation of State of SiC at Extreme Conditions: New Insight Into the Interior of Carbon‐Rich Exoplanets
Authors: Miozzi F. , Morard G. , Antonangeli D. , Clark A. N. , Mezouar M. , Dorn C. , Rozel A. , Fiquet G.
Published: August 2018

There is a direct relation between the composition of a host star and that of the planets orbiting around it. As such, the recent discovery of stars with unusual chemical composition, notably enriched in carbon instead of oxygen, supports the existence of exoplanets with a chemistry dominated by carbides instead of oxides. Accordingly, several studies have been recently conducted on the Si–C binary system at high pressure and temperature. Nonetheless, the properties of carbides at the pressure‐temperature conditions of exoplanets interiors are still inadequately constrained, effectively hampering reliable planetary modeling. Here we present an in situ X‐ray diffraction study of the Si–C binary system up to 200 GPa and 3,500 K, significantly enlarging the pressure range explored by previous experimental studies. The large amount of collected data allows us to properly investigate the phase diagram and to refine the Clapeyron slope of the transition line from the zinc blende to the rock salt structure. Furthermore, the pressure‐volume‐temperature equation of state is provided for the high‐pressure phase, characterized by low compressibility and thermal expansion. Our results are used to model idealized C‐rich exoplanets of end‐members composition. In particular, we derived mass‐radius relations and performed numerical simulations defining rheological parameters and initial conditions which lead to onset of convection in such SiC planets. We demonstrate that if restrained to silicate‐rich mantle compositions, the interpretation of mass‐radius relations may underestimate the interior diversity of exoplanets.
Fine Vertical Structures at the Cloud Heights of Venus Revealed by Radio Holographic Analysis of Venus Express and Akatsuki Radio Occultation Data
Authors: Imamura Takeshi , Miyamoto Mayu , Ando Hiroki , Häusler Bernd , Pätzold Martin , Tellmann Silvia , Tsuda Toshitaka , Aoyama Yuichi , Murata Yasuhiro , Takeuchi Hiroshi , Yamazaki Atsushi , Toda Tomoaki , Tomiki Atsushi
Published: August 2018

Radio occultation (RO) is one of the most efficient techniques for studying fine vertical structures in planetary atmospheres. However, the geometrical optics (GO) method, which has been used for the analysis of RO data, suffers blurring by the finite width (Fresnel scale) of the radio ray and cannot decipher multipath propagation, which also prevents retrieval of fine structures. Here we apply Full Spectrum Inversion (FSI), which is one of the radio holographic methods, to RO data taken in Venus Express and Akatsuki missions to retrieve fine structures in Venus' cloud‐level atmosphere. The temperature profiles obtained by FSI achieve vertical resolutions of ~150 m, which is much higher than the typical resolution of 400–700 m in GO, and resolve structures in multipath regions. Thin, near‐neutral layers are found to be ubiquitous at cloud heights; we suggest here that those layers are caused by the mixing associated with the breaking of short‐wavelength gravity waves. The wavenumber spectra of small‐scale structures are consistent with the semiempirical spectrum of saturated gravity waves and show larger amplitudes at higher latitudes. Temperature profiles in the high latitudes frequently show a sharp temperature minimum near the cloud top, below which the vertical temperature gradient is near adiabat, implying that the sharp temperature minimum is created by adiabatic cooling associated with convective plumes that impinge on the overlying stable layer.
Constraints on Lunar Crustal Porosity From the Gravitational Signature of Impact Craters
Authors: Ding Min , Soderblom Jason M. , Bierson Carver J. , Nimmo Francis , Milbury Colleen , Zuber Maria T.
Published: August 2018

Based on Gravity Recovery and Interior Laboratory (GRAIL) observations and the Lunar Orbiter Laser Altimeter (LOLA) crater database, we constrain the spatial variations in the Moon's crustal porosity (ϕc) to a depth of several kilometers using the gravity anomalies of 4,864 midsized craters (those with a diameter of 20–100 km). For each crater, we estimated the local ϕc by quantifying the gravitational effects of impact‐induced porosity change and postimpact breccia infill. The crustal porosity model was uniquely determined assuming a global mean ϕc of 12%, although a trade‐off exists between the porosity of postimpact breccia infill and the (preimpact) crustal porosity that results in zero net porosity change underlying the crater floor. At this crustal porosity the effects of impact bulking and compaction compensate each other to yield zero crater residual Bouguer anomaly (RBA), when the effect of postimpact infill is excluded. For lower crustal porosities, bulking dominates to produce a negative RBA; for higher crustal porosities, compaction dominates to produce a positive RBA. Spatial kriging and statistical tests suggest lower‐than‐average ϕc in the western nearside maria and southern South Pole‐Aitken (SP‐A) basin, in contrast to higher‐than‐average values in the southwestern periphery of the nearside maria. Most of the large impact basins, presumably formed before the majority of the midsized craters we analyzed, show reduced porosities relative to their immediate surroundings.
SH Seismoelectric Response of a Glacier: An Analytic Study
Authors: Monachesi L. B. , Zyserman F. I. , Jouniaux L.
Published: August 2018

In this work we derive the analytic solutions to the system of equations modeling, within the framework of Pride's theory, the seismic‐to‐electromagnetic conversions taking place in a glacial environment. Considering a one‐dimensional approach, we set a pure shear horizontal wave seismic source on top of an elastic medium representing the glacier, which overlies a porous medium fully saturated with water, representing the glacier bed. The obtained solutions allow to separately represent and analyze the induced electromagnetic responses, the so called coseismic waves, for both the electric and magnetic fields along with the signals originated at the glacier bottom, the electric interface response, and magnetic interface response. We also propose approximate solutions, useful to be used in a fast inversion algorithm. We analyze the characteristics of the induced electromagnetic signals and their dependence on the type of glacier bed, considering an unconsolidated one and a consolidated one. The main results of the present paper are manifold, on the one hand, the mentioned analytic solutions, on the other hand, that the electric interface response originated at the glacier bottom is proportional to the electric current density at this depth, and depends on textural and electrical properties of the basement. We also showed that the amplitude of the electric interface response is three orders of magnitude higher than the amplitude of the electric coseismic field. This fact reinforces the idea proposed in our previous works that it would be interesting to test shear horizontal seismoelectrics as a possible geophysical prospecting and monitoring tool.
The Influence of Storms on Sand Wave Evolution: A Nonlinear Idealized Modeling Approach
Authors: Campmans G. H. P. , Roos P. C. , de Vriend H. J. , Hulscher S. J. M. H.
Published: August 2018

We present a new 2DV nonlinear process‐based morphodynamic model to investigate the effects of storms, specifically wind‐driven flow and wind waves, on finite amplitude tidal sand wave evolution. Simulations are performed on periodic domains of two lengths: (i) on a 350‐m domain, comparable to the wavelength of observed sand waves, we study the evolution toward equilibrium shapes, and (ii) on a 4‐km domain, we study the evolution from a randomly perturbed seabed. Our model results demonstrate that both wind‐driven flow and wind waves reduce sand wave height and tend to increase wavelength. Wind‐driven flow breaks the tidal symmetry, resulting in horizontal sand wave asymmetry and migration. Waves alone do not induce migration but can enhance migration induced by, for example, tidal asymmetry and wind‐driven flow. On the 350‐m domain, we further find that migration rates decrease with increasing sand wave height. However, in an irregular sand wave field, large sand waves tend to overtake the smaller ones, suggesting a complicated interaction among neighboring bed forms. The above results concern steady state storm conditions. However, since storms occur on an intermittent basis, we also simulated a synthetic storm climate consisting of alternating short periods of storm conditions and long periods of fair‐weather conditions. Simulations reveal a dynamic equilibrium with sand wave heights significantly below those obtained for tide‐only conditions, also for relatively short storm duration. Our work identifies mechanisms that explain why sand wave heights are generally overpredicted by numerical models that do not include storm processes.
Response of Marine‐Terminating Glaciers to Forcing: Time Scales, Sensitivities, Instabilities, and Stochastic Dynamics
Authors: Robel Alexander A. , Roe Gerard H. , Haseloff Marianne
Published: August 2018

Recent observations indicate that many marine‐terminating glaciers in Greenland and Antarctica are currently retreating and thinning, potentially due to long‐term trends in climate forcing. In this study, we describe a simple two‐stage model that accurately emulates the response to external forcing of marine‐terminating glaciers simulated in a spatially extended model. The simplicity of the model permits derivation of analytical expressions describing the marine‐terminating glacier response to forcing. We find that there are two time scales that characterize the stable glacier response to external forcing, a fast time scale of decades to centuries, and a slow time scale of millennia. These two time scales become unstable at different thresholds of bed slope, indicating that there are distinct slow and fast forms of the marine ice sheet instability. We derive simple expressions for the approximate magnitude and transient evolution of the stable glacier response to external forcing, which depend on the equilibrium glacier state and the strength of nonlinearity in forcing processes. The slow response rate of marine‐terminating glaciers indicates that current changes at some glaciers are set to continue and accelerate in coming centuries in response to past climate forcing and that the current extent of change at these glaciers is likely a small fraction of the future committed change caused by past climate forcing. Finally, we find that changing the amplitude of natural fluctuations in some nonlinear forcing processes, such as ice shelf calving, changes the equilibrium glacier state.
Seasonal Trends in Surface pCO2 and Air‐Sea CO2 Fluxes in Apalachicola Bay, Florida, From VIIRS Ocean Color
Authors: Joshi Ishan D. , Ward Nicholas D. , D'Sa Eurico J. , Osburn Christopher L. , Bianchi Thomas S. , Oviedo‐Vargas Diana
Published: August 2018

Estuaries have been recognized as important sources of carbon dioxide (CO2) to the atmosphere; however, contributions of these systems to regional and global carbon budgets are not well constrained due to limited information on seasonal and spatial variability. In this study, we use satellite remote sensing to obtain seasonal pCO2 distribution and air‐sea CO2 fluxes in Apalachicola Bay, a national estuarine research reserve located in the northern Gulf of Mexico that receives seasonally varying dissolved organic matter‐rich waters from the Apalachicola River. A combination of time series (2005–2016) and seasonal field observations (2015–2016) of pH and biophysical variables were used to develop seasonal pH‐pCO2 relationships for obtaining surface pCO2 estimates and air‐sea CO2 fluxes from Visible and Infrared Imaging Radiometer Suite (VIIRS) ocean color data. Monthly and seasonal maps of pCO2 and air‐sea CO2 fluxes showed a general trend of higher fluxes in winter and summer corresponding to high river flow and warm water temperatures. However, CO2 fixation via photosynthesis and low water temperatures contributed to lower fluxes to the atmosphere in spring and fall, respectively. Throughout the study period, Apalachicola Bay was a net source of CO2 with large seasonal and spatial variability and a mean annual CO2 flux to the atmosphere of 3.4 ± 3.1 mol·m−2·year−1 (9.4 ± 8.5 mmol·m−2·day−1), consistent with fluxes reported for other estuaries. This study demonstrates the critical role that satellite observations can play to improve the estuarine contributions to the global carbon flux estimates.
Disentangling Climate and LAI Effects on Seasonal Variability in Water Use Efficiency Across Terrestrial Ecosystems in China
Authors: Li Yue , Shi Hao , Zhou Lei , Eamus Derek , Huete Alfredo , Li Longhui , Cleverly James , Hu Zhongmin , Harahap Mahrita , Yu Qiang , He Liang , Wang Shaoqiang
Published: August 2018

Water use efficiency (WUE), the ratio of gross primary productivity (GPP) over evapotranspiration (ET), is a critical ecosystem function. However, it is difficult to distinguish the individual effects of climatic variables and leaf area index (LAI) on WUE, mainly due to the high collinearity among these factors. Here we proposed a partial least squares regression‐based sensitivity algorithm to confront the issue, which was first verified at seven ChinaFlux sites and then applied across China. The results showed that across all biomes in China, monthly GPP (0.42–0.65), ET (0.33–0.56), and WUE (0.01–0.31) showed positive sensitivities to air temperature, particularly in croplands in northeast China and forests in southwest China. Radiation exerted stronger effects on ET (0.55–0.78) than GPP (0.19–0.65), resulting in negative responses (−0.44 to 0.04) of WUE to increased radiation among most biomes. Increasing precipitation stimulated both GPP (0.06–0.17) and ET (0.05–0.12) at the biome level, but spatially negative effects of excessive precipitation were also found in some grasslands. Both monthly GPP (−0.01 to 0.29) and ET (0.02–0.12) showed weak or moderate responses to vapor pressure deficit among biomes, resulting in weak response of monthly WUE to vapor pressure deficit (−0.04 to 0.08). LAI showed positive effects on GPP (0.18–0.60), ET (0–0.23), and WUE (0.13–0.42) across biomes, particularly on WUE in grasslands (0.42 ± 0.30). Our results highlighted the importance of LAI in influencing WUE against climatic variables. Furthermore, the sensitivity algorithm can be used to inform the design of manipulative experiments and compare with factorial simulations for discerning effects of various variables on ecosystem functions.
Genomics in neurodevelopmental disorders: an avenue to personalized medicine
Authors: Tărlungeanu Dora C. , Novarino Gaia
Published: August 2018

Despite the remarkable number of scientific breakthroughs of the last 100 years, the treatment of neurodevelopmental disorders (e.g., autism spectrum disorder, intellectual disability) remains a great challenge. Recent advancements in genomics, such as whole-exome or whole-genome sequencing, have enabled scientists to identify numerous mutations underlying neurodevelopmental disorders. Given the few hundred risk genes that have been discovered, the etiological variability and the heterogeneous clinical presentation, the need for genotype—along with phenotype-based diagnosis of individual patients has become a requisite. In this review we look at recent advancements in genomic analysis and their translation into clinical practice.
Whole exome sequencing identifies an AMBN missense mutation causing severe autosomal-dominant amelogenesis imperfecta and dentin disorders
Authors: Lu Ting , Li Meiyi , Xu Xiangmin , Xiong Jun , Huang Cheng , Zhang Xuelian , Hu Aiqin , Peng Ling , Cai Decheng , Zhang Leitao , Wu Buling , Xiong Fu
Published: August 2018

Tooth development is a complex process that involves precise and time-dependent orchestration of multiple genetic, molecular, and cellular interactions. Ameloblastin (AMBN, also named “amelin” or “sheathlin”) is the second most abundant enamel matrix protein known to have a key role in amelogenesis. Amelogenesis imperfecta (AI [MIM: 104500]) refers to a genetically and phenotypically heterogeneous group of conditions characterized by inherited developmental enamel defects. The hereditary dentin disorders comprise a variety of autosomal-dominant genetic symptoms characterized by abnormal dentin structure affecting either the primary or both the primary and secondary teeth. The vital role of Ambn in amelogenesis has been confirmed experimentally using mouse models. Only two cases have been reported of mutations of AMBN associated with non-syndromic human AI. However, no AMBN missense mutations have been reported to be associated with both human AI and dentin disorders. We recruited one kindred with autosomal-dominant amelogenesis imperfecta (ADAI) and dentinogenesis imperfecta/dysplasia characterized by generalized severe enamel and dentin defects. Whole exome sequencing of the proband identified a novel heterozygous C-T point mutation at nucleotide position 1069 of the AMBN gene, causing a Pro to Ser mutation at the conserved amino acid position 357 of the protein. Exfoliated third molar teeth from the affected family members were found to have enamel and dentin of lower mineral density than control teeth, with thinner and easily fractured enamel, short and thick roots, and pulp obliteration. This study demonstrates, for the first time, that an AMBN missense mutation causes non-syndromic human AI and dentin disorders.
Looking at sound: optoacoustics with all-optical ultrasound detection
Authors: Wissmeyer Georg , Pleitez Miguel A. , Rosenthal Amir , Ntziachristos Vasilis
Published: August 2018

Originally developed for diagnostic ultrasound imaging, piezoelectric transducers are the most widespread technology employed in optoacoustic (photoacoustic) signal detection. However, the detection requirements of optoacoustic sensing and imaging differ from those of conventional ultrasonography and lead to specifications not sufficiently addressed by piezoelectric detectors. Consequently, interest has shifted to utilizing entirely optical methods for measuring optoacoustic waves. All-optical sound detectors yield a higher signal-to-noise ratio per unit area than piezoelectric detectors and feature wide detection bandwidths that may be more appropriate for optoacoustic applications, enabling several biomedical or industrial applications. Additionally, optical sensing of sound is less sensitive to electromagnetic noise, making it appropriate for a greater spectrum of environments. In this review, we categorize different methods of optical ultrasound detection and discuss key technology trends geared towards the development of all-optical optoacoustic systems. We also review application areas that are enabled by all-optical sound detectors, including interventional imaging, non-contact measurements, magnetoacoustics, and non-destructive testing.
Digital plasmonic holography
Authors: Nelson Joseph W. , Knefelkamp Greta R. , Brolo Alexandre G. , Lindquist Nathan C.
Published: August 2018

We demonstrate digital plasmonic holography for direct in-plane imaging with propagating surface-plasmon waves. Imaging with surface plasmons suffers from the lack of simple in-plane lenses and mirrors. Lens-less digital holography techniques, however, rely on digitally decoding an interference pattern between a reference wave and an object wave. With far-field diffractive optics, this decoding scheme provides a full recording, i.e., a hologram, of the amplitude and phase of the object wave, giving three-dimensional information from a two-dimensional recording. For plasmonics, only a one-dimensional recording is needed, and both the phase and amplitude of the propagating plasmons can be extracted for high-resolution in-plane imaging. Here, we demonstrate lens-less, point-source digital plasmonic holography using two methods to record the plasmonic holograms: a dual-probe near-field scanning optical microscope and lithographically defined circular fluorescent screens. The point-source geometry gives in-plane magnification, allowing for high-resolution imaging with relatively lower-resolution microscope objectives. These results pave the way for a new form of in-plane plasmonic imaging, gathering the full complex wave, without the need for plasmonic mirrors or lenses.
Climatic modulation of surface acidification rates through summertime wind forcing in the Southern Ocean
Authors: Xue Liang , Cai Wei-Jun , Takahashi Taro , Gao Libao , Wanninkhof Rik , Wei Meng , Li Kuiping , Feng Lin , Yu Weidong
Published: August 2018

While the effects of the Southern Annular Mode (SAM), a dominant climate variability mode in the Southern Ocean, on ocean acidification have been examined using models, no consensus has been reached. Using observational data from south of Tasmania, we show that during a period with positive SAM trends, surface water pH and aragonite saturation state at 60°–55° S (Antarctic Zone) decrease in austral summer at rates faster than those predicted from atmospheric CO2 increase alone, whereas an opposite pattern is observed at 50°–45° S (Subantarctic Zone). Together with other processes, the enhanced acidification at 60°–55° S may be attributed to increased westerly winds that bring in more “acidified” waters from the higher latitudes via enhanced meridional Ekman transport and from the subsurface via increased vertical mixing. Our observations support climatic modulation of ocean acidification superimposed on the effect of increasing atmospheric CO2.
Optical emission near a high-impedance mirror
Authors: Esfandyarpour Majid , Curto Alberto G. , Kik Pieter G. , Engheta Nader , Brongersma Mark L.
Published: August 2018

Solid state light emitters rely on metallic contacts with a high sheet-conductivity for effective charge injection. Unfortunately, such contacts also support surface plasmon polariton and lossy wave excitations that dissipate optical energy into the metal and limit the external quantum efficiency. Here, inspired by the concept of radio-frequency high-impedance surfaces and their use in conformal antennas we illustrate how electrodes can be nanopatterned to simultaneously provide a high DC electrical conductivity and high-impedance at optical frequencies. Such electrodes do not support SPPs across the visible spectrum and greatly suppress dissipative losses while facilitating a desirable Lambertian emission profile. We verify this concept by studying the emission enhancement and photoluminescence lifetime for a dye emitter layer deposited on the electrodes.
Quantum confined peptide assemblies with tunable visible to near-infrared spectral range
Authors: Tao Kai , Fan Zhen , Sun Leming , Makam Pandeeswar , Tian Zhen , Ruegsegger Mark , Shaham-Niv Shira , Hansford Derek , Aizen Ruth , Pan Zui , Galster Scott , Ma Jianjie , Yuan Fan , Si Mingsu , Qu Songnan , Zhang Mingjun , Gazit Ehud , Li Junbai
Published: August 2018

Quantum confined materials have been extensively studied for photoluminescent applications. Due to intrinsic limitations of low biocompatibility and challenging modulation, the utilization of conventional inorganic quantum confined photoluminescent materials in bio-imaging and bio-machine interface faces critical restrictions. Here, we present aromatic cyclo-dipeptides that dimerize into quantum dots, which serve as building blocks to further self-assemble into quantum confined supramolecular structures with diverse morphologies and photoluminescence properties. Especially, the emission can be tuned from the visible region to the near-infrared region (420 nm to 820 nm) by modulating the self-assembly process. Moreover, no obvious cytotoxic effect is observed for these nanostructures, and their utilization for in vivo imaging and as phosphors for light-emitting diodes is demonstrated. The data reveal that the morphologies and optical properties of the aromatic cyclo-dipeptide self-assemblies can be tuned, making them potential candidates for supramolecular quantum confined materials providing biocompatible alternatives for broad biomedical and opto-electric applications.
PARP2 mediates branched poly ADP-ribosylation in response to DNA damage
Authors: Chen Qian , Kassab Muzaffer Ahmad , Dantzer Françoise , Yu Xiaochun
Published: August 2018

Poly(ADP-ribosyl)ation (PARylation) is a posttranslational modification involved in multiple biological processes, including DNA damage repair. This modification is catalyzed by poly(ADP-ribose) polymerase (PARP) family of enzymes. PARylation is composed of both linear and branched polymers of poly(ADP-ribose) (PAR). However, the biochemical mechanism of polymerization and biological functions of branched PAR chains are elusive. Here we show that PARP2 is preferentially activated by PAR and subsequently catalyzes branched PAR chain synthesis. Notably, the direct binding to PAR by the N-terminus of PARP2 promotes the enzymatic activity of PARP2 toward the branched PAR chain synthesis. Moreover, the PBZ domain of APLF recognizes the branched PAR chain and regulates chromatin remodeling to DNA damage response. This unique feature of PAR-dependent PARP2 activation and subsequent PARylation mediates the participation of PARP2 in DNA damage repair. Thus, our results reveal an important molecular mechanism of branched PAR synthesis and a key biological function of branched PARylation.
Author Correction: Interfacial photochemistry at the ocean surface is a global source of organic vapors and aerosols
Authors: Brüggemann Martin , Hayeck Nathalie , George Christian
Published: August 2018

The authors became aware of a mistake in the data displayed in the original version of the paper. Specifically, for the calculation of the total emission estimates (i.e., from an average molecular weight and summed laboratory production values for all VOCs), the authors mistakenly added seasonal estimates to the annual estimates because both values are stored in the same variable of the code. Eventually, this additional sum resulted in a doubling of emission estimates.

As a result of this, the following changes have been made to the originally published version of this Article:

The fifth sentence of the abstract originally read “Our results indicate global emissions of 46.4–184 Tg C yr–1 of organic vapors from the oceans into the marine atmosphere and a potential contribution to organic aerosol mass of more than 60% over the remote ocean.” In the corrected version “46.4–184 Tg C yr–1” is replaced by “23.2–91.9 Tg C yr-1”

The seventh sentence of the second paragraph of the Introduction originally read “We infer global emissions of 65.0–257 Tg yr–1 (46.4–184 Tg C yr–1) of organic vapors from the oceans into the marine atmosphere.” In the corrected version, “65.0–257 Tg yr–1 (46.4–184 Tg C yr–1)” is replaced by “32.5–129 Tg C yr−1 (23.2–91.9 Tg C yr-1)”.

The last sentence of the first paragraph of the Results subheading “Marine isoprene emissions from interfacial photochemistry” originally read “In the same way, we infer total emissions of organic vapors from abiotic interfacial photochemistry in the range of 65.0–257 Tg yr–1 (46.4–184 Tg C yr–1), hence, contributing significantly to marine VOC emissions.” In the corrected version, “65.0–257 Tg yr–1 (46.4–184 Tg C yr–1)” is replaced by “32.5–129 Tg C yr−1 (23.2–91.9 Tg C yr−1)”.

This has been corrected in both the PDF and the HTML versions of the Article. While the new estimates are lower than previously reported this error does not affect the original discussion or conclusions of the Article. The authors apologize for the confusion caused by this mistake.
Visual and modular detection of pathogen nucleic acids with enzyme–DNA molecular complexes
Authors: Ho Nicholas R. Y. , Lim Geok Soon , Sundah Noah R. , Lim Diana , Loh Tze Ping , Shao Huilin
Published: August 2018

Rapid, visual detection of pathogen nucleic acids has broad applications in infection management. Here we present a modular detection platform, termed enzyme-assisted nanocomplexes for visual identification of nucleic acids (enVision). The system consists of an integrated circuit of enzyme–DNA nanostructures, which function as independent recognition and signaling elements, for direct and versatile detection of pathogen nucleic acids from infected cells. The built-in enzymatic cascades produce a rapid color readout for the naked eye; the assay is thus fast (<2 h), sensitive (<10 amol), and readily quantified with smartphones. When implemented on a configurable microfluidic platform, the technology demonstrates superior programmability to perform versatile computations, for detecting diverse pathogen targets and their virus–host genome integration loci. We further design the enVision platform for molecular-typing of infections in patient endocervical samples. The technology not only improves the clinical inter-subtype differentiation, but also expands the intra-subtype coverage to identify previously undetectable infections.
Light-induced mechanical response in crosslinked liquid-crystalline polymers with photoswitchable glass transition temperatures
Authors: Yue Youfeng , Norikane Yasuo , Azumi Reiko , Koyama Emiko
Published: August 2018

Energy conversion of light into mechanical work is of fundamental interest in applications. In particular, diligent molecular design on nanoscale, in order to achieve efficient photomechanical effects on macroscopic scale, has become one of the most interesting study topics. Here, by incorporating a “photomelting” azobenzene monomer crosslinked into liquid crystalline (LC) networks, we generate photoresponsive polymer films that exhibit reversible photoswitchable glass transition temperatures (Tg) at room temperature (~20 °C) and photomechanical actuations under the stimulus of UV/visible light. The trans-to-cis isomerization of azo chromophores results in a change in Tg of the crosslinked LC polymers. The Tg of the polymer network is higher than room temperature in the trans-form and lower than room temperature in the cis-form. We demonstrate the photoswitchable Tg contribute to the photomechanical bending and a new mechanism for photomechanical bending that attributes the process to an inhomogeneous change in Tg of the film is proposed.