The Link Between Climate Warming and Break-Up of Ice Shelves in the Antarctic Peninsula

A review of in situ and remote-sensing data covering the ice shelves of the Antarctic Peninsula provides a series of characteristics closely associated with rapid shelf retreat: deeply embayed ice fronts; calving of myriad small elongate bergs in punctuated events; increasing flow speed; and the presence of melt ponds on the ice-shelf surface in the vicinity of the break-ups. As climate has warmed in the Antarctic Peninsula region, melt-season duration and the extent of ponding have increased. Most break-up events have occurred during longer melt seasons, suggesting that meltwater itself, not just warming, is responsible. Regions that show melting without pond formation are relatively unchanged. Melt ponds thus appear to be a robust harbinger of ice-shelf retreat. We use these observations to guide a model of ice-shelf flow and the effects of meltwater. Crevasses present in a region of surface ponding will likely fill to the brim with water. We hypothesize (building on Weertman (1973), Hughes (1983) and Van der Veen (1998)) that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat. A thermodynamic finite-element model is used to evaluate ice flow and the strain field, and simple extensions of this model are used to investigate crack propagation by meltwater. The model results support the hypothesis

Seismic Performance of Integral Abutment Highway Bridges in Illinois

The seismic behavior of integral abutment bridges (IABs) is of particular interest in southern Illinois, where proximity to the New Madrid Seismic Zone may create significant ground motion accelerations during an earthquake. IABs are common in modern bridge construction due to their lack of expansion joints between the superstructure and abutment, which leads to decreased environmental damage at the abutment seat when compared to stub abutment bridges. However, elimination of expansion joints can also lead to development of complex soil-structure-interaction limit states at the abutment and its foundation when an IAB is subjected to lateral loads. This report examines the seismic behavior of typical IABs in southern Illinois and develops feedback and recommendations for improving IAB seismic designs. This is accomplished through modeling IABs as a whole bridge system, subjecting the models to representative ground motions, monitoring the behavior of key IAB components, using the monitored results to form a comprehensive view of seismic behavior, and employing the developed knowledge to form recommendations for improving IAB seismic performance. IAB models are developed in OpenSees through nonlinear modeling of multiple components, as well as the connections between components, representing typical IAB designs for Illinois, and are then subjected to 1000-year return period hazard ground motions developed specifically for southern Illinois. Incremental dynamic analyses are also performed. IABs of varying superstructure materials, span configurations, bearing layouts, pier heights, and foundation soil conditions are dynamically analyzed using the sets of developed ground motions. Damage to pier columns is especially prominent in IABs with shorter piers and longer abutment-to-abutment spans, while abutment foundation damage in terms of yielding, local buckling, and rupture of the piles frequently occurs in many IAB variants. Recommendations on design modifications to improve the seismic behavior of IABs by limiting the level of damage to these components are also investigated through modifying elastomeric bearing side retainer strength, fixed bearing strength, pier column size, and backfill contributions.IDOT-R27-133Ope

Seismic Performance of Seat-Type Abutment Highway Bridges in Illinois

This study assesses the seismic performance of quasi-isolated highway bridges with seat-type abutments, validates the current IDOT design strategy, and provides recommendations for improving a bridge’s seismic behavior. To encompass common configurations of highway bridges with non-seismically designed bearing components employed as sacrificial connections between superstructures and substructures, a suite of prototype bridges with variations in span arrangement, girder type, skew angle, pier column height, and foundation soil condition were studied. Detailed three-dimensional nonlinear finite-element models were developed for the bridges, incorporating various critical structural components and geotechnical mechanisms. Multi-mode adaptive pushover analyses were conducted to investigate bridge response characteristics in terms of the force distribution among substructures, the sequence of limit state occurrences, the fusing of sacrificial connections, and the vulnerability of critical bridge components. Eigenvalue modal analyses were also performed in the elastic and inelastic deformation states to reveal modal response characteristics of the bridges. The study culminated in an extensive seismic performance assessment of quasi-isolated bridges, for which thousands of nonlinear dynamic time-history analyses were carried out. The bridges were subjected to a suite of site-specific earthquake ground motions, taking into account the site condition and the regional seismicity of Cairo, Illinois. Assessment results validated that the current quasi-isolation bridge design strategy is generally effective, and the majority of the studied prototype bridges are unlikely to fail in global collapse when subjected to horizontal earthquake ground motions with a 1,000-year return period in deep southern Illinois. Although most of the prototype bridges exhibited satisfactory seismic performance, the response of a small number of them demonstrated a risk of bearing unseating and severe pier column damage. With the aim of improving the seismic performance of these bridges, preliminary recommendations for calibrating the current design strategy were proposed, and their efficacy was demonstrated by comparative studies.IDOT-R27-133Ope

Asynchronous behavior of outlet glaciers feeding Godthåbsfjord (Nuup Kangerlua) and the triggering of Narsap Sermia's retreat in SW Greenland

We assess ice loss and velocity changes between 1985 and 2014 of three tidewater and fiveland terminating glaciers in Godthabsfjord (Nuup Kangerlua), Greenland. Glacier thinning accounted for 43.8 +/- 0.2 km(3) of ice loss, equivalent to 0.10 mm eustatic sea-level rise. An additional 3.5 +/- 0.3 km(3) was lost to the calving retreats of Kangiata Nunaata Sermia (KNS) and Narsap Sermia (NS), two tidewater glaciers that exhibited asynchronous behavior over the study period. KNS has retreated 22 km from its Little Ice Age (LIA) maximum (1761 AD), of which 0.8 km since 1985. KNS has stabilized in shallow water, but seasonally advects a 2 km long floating tongue. In contrast, NS began retreating from its LIA moraine in 2004-06 (0.6 km), re-stabilized, then retreated 3.3 km during 2010-14 into an over-deepened basin. Velocities at KNS ranged 5-6 km a(-1), while at NS they increased from 1.5 to 5.5 km a(-1) between 2004 and 2014. We present comprehensive analyses of glacier thinning, runoff, surface mass balance, ocean conditions, submarine melting, bed topography, ice melange and conclude that the 2010-14 NS retreat was triggered by a combination of factors but primarily by an increase in submarine melting.We thank W. Dryer and D. Podrasky for assistance with fieldwork and L. Kenefic for assisting with digitizing glacier front positions. CH2 M HILL Polar Services and Air Greenland provided logistics support. The SPOT-5 images used for the 2008 DEM were provided by the SPIRIT program (Centre National d'Etudes Spatiales, France). The DigitalGlobe Worldview images used for the 2014 DEM were obtained from P. Morin. Terminus positions were derived from Landsat images courtesy of the U.S. Geological Survey. Funding was provided by the US National Science Foundation (NSF) Office of Polar Programs (OPP) grants NSF PLR-0909552 and NSF PLR-0909333. Cassotto is supported by NASA under the Earth and Space Science Fellowship Program (Grant NNX14AL29H). K. K. Kjeldsen acknowledges support from the Danish Council Research for Independent Research (grant no. DFF-409000151). K. Kjaer is thanked for his support during the earlier phases of this study. On-ice weather stations are operated by GEUS (Denmark) within the Programme for Monitoring of the Greenland Ice Sheet (PROMICE). J. Mortensen acknowledges support from IIKNN (Greenland), DEFROST project of the Nordic Centre of Excellence program "Interaction between Climate Change and the Cryosphere" and the Greenland Ecosystem Monitoring Programme (www. g-e-m. dk).S. Rysgaard was funded by the Canada Excellence Research Chair Programme. Additional funding was provided by the Geophysical Institute, University of Alaska Fairbanks, and Greenland Climate Research Centre. Scientific editor H. Fricker and reviewers H. Jiskoot and G. Cogley provided very constructive feedback that helped improve the paper.Peer ReviewedRitrýnt tímari

Modification of ground motions for use in Central North America: Southern Illinois surface ground motions for structural analysis

The lack of ground motion time history records with a 1000-year return period hazard for Central North America (CNA) often requires earthquake engineering researchers in the area to develop ground motions of their own. This report briefly describes a procedure for developing 1000-year return period ground motion time history records, and this procedure was applied for 10 sites in southern Illinois. Accompanying this report are 20 individual ground motion time history records developed at each of the 10 sites (for a total of 200 ground motions). These ground motions may be useful for various purposes including in dynamic structural analyses of bridges and other structures in southern Illinois (and potentially other CNA regions). The accompanying ground motions are developed following the detailed procedure presented in Kozak et al. [2017]. See "Has Parts" for persistent link to ground motion data files.Ope

Fabrication and Characterization of Electrospun Semiconductor Nanoparticle—Polyelectrolyte Ultra-Fine Fiber Composites for Sensing Applications

Fluorescent composite fibrous assembles of nanoparticle-polyelectrolyte fibers are useful multifunctional materials, utilized in filtration, sensing and tissue engineering applications, with the added benefits of improved mechanical, electrical or structural characteristics over the individual components. Composite fibrous mats were prepared by electrospinning aqueous solutions of 6 wt% poly(acrylic acid) (PAA) loaded with 0.15 and 0.20% v/v, carboxyl functionalized CdSe/ZnS nanoparticles (SNPs). The resulting fluorescent composite fibrous mats exhibits recoverable quenching when exposed to high humidity. The sensor response is sensitive to water concentration and is attributed to the change in the local charges around the SNPs due to deprotonation of the carboxylic acids on the SNPs and the surrounding polymer matrix

Conformational Plasticity of proNGF

Nerve Growth Factor is an essential protein that supports neuronal survival during development and influences neuronal function throughout adulthood, both in the central and peripheral nervous system. The unprocessed precursor of NGF, proNGF, seems to be endowed with biological functions distinct from those of the mature protein, such as chaperone-like activities and apoptotic and/or neurotrophic properties. We have previously suggested, based on Small Angle X-ray Scattering data, that recombinant murine proNGF has features typical of an intrinsically unfolded protein. Using complementary biophysical techniques, we show here new evidence that clarifies and widens this hypothesis through a detailed comparison of the structural properties of NGF and proNGF. Our data provide direct information about the dynamic properties of the pro-peptide and indicate that proNGF assumes in solution a compact globular conformation. The N-terminal pro-peptide extension influences the chemical environment of the mature protein and protects the protein from proteolytic digestion. Accordingly, we observe that unfolding of proNGF involves a two-steps mechanism. The distinct structural properties of proNGF as compared to NGF agree with and rationalise a different functional role of the precursor

ALMA Observations of the DART Impact: Characterizing the Ejecta at Sub-Millimeter Wavelengths

We report observations of the Didymos-Dimorphos binary asteroid system using the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Compact Array (ACA) in support of the Double Asteroid Redirection Test (DART) mission. Our observations on UT 2022 September 15 provided a pre-impact baseline and the first measure of Didymos-Dimorphos' spectral emissivity at $\lambda=0.87$ mm, which was consistent with the handful of siliceous and carbonaceous asteroids measured at millimeter wavelengths. Our post-impact observations were conducted using four consecutive executions each of ALMA and the ACA spanning from T$+$3.52 to T$+$8.60 hours post-impact, sampling thermal emission from the asteroids and the impact ejecta. We scaled our pre-impact baseline measurement and subtracted it from the post-impact observations to isolate the flux density of mm-sized grains in the ejecta. Ejecta dust masses were calculated for a range of materials that may be representative of Dimorphos' S-type asteroid material. The average ejecta mass over our observations is consistent with 1.3--6.4$\times10^7$ kg, with the lower and higher values calculated for amorphous silicates and for crystalline silicates, respectively. Owing to the likely crystalline nature of S-type asteroid material, the higher value is favored. These ejecta masses represent 0.3--1.5\% of Dimorphos' total mass and are in agreement with lower limits on the ejecta mass based on measurements at optical wavelengths. Our results provide the most sensitive measure of mm-sized material in the ejecta and demonstrate the power of ALMA for providing supporting observations to spaceflight missions