The Impact of Basal Roughness on Inland Thwaites Glacier Sliding

Swath radar technology enables three-dimensional mapping of modern glacier beds over large areas at resolutions that are higher than those typically used in ice-flow models. These data may enable new understanding of processes at the ice-bed interface. Here, we use two densely surveyed swath-mapped topographies (<50 m² resolution) of Thwaites Glacier to investigate the sensitivity of inferred basal friction proxies to bed roughness magnitude and orientation. Our work suggests that along-flow roughness influences inferred friction more than transverse-flow roughness, which agrees with analytic form-drag sliding theory. Using our model results, we calculate the slip length (the ratio of internal shear to basal slip). We find excellent agreement between the numerically derived slip lengths and slip lengths predicted by analytic form-drag sliding theory, which suggests that unresolved short wavelength bed roughness may control sliding in the Thwaites interior.

A-09 Challenges in Measuring Repetitive Head Impacts, Cognition, and Eye Movements in High School Football Players

Purpose: Assess the feasibility of measuring Repetitive Head Impacts (RHI), cognition, and eye movements across a single season of high school football. Methods: Twelve players were provided an instrumented mouthguard (3200 Hz; Prevent Biometrics, Edina, MA) to evaluate RHI. Mouthguard use was assessed by total impacts and number of games/practices. Seven players also agreed to complete cognitive (ImPACT) and custom eye-tracking (500 Hz; EyeLink II) assessments pre-, mid-, and post-season. Multiple repeated measure ANOVA’s were completed using standard composite scores for ImPACT and oculomotor metrics. Results: Fifty percent of players ever used their mouthguard, and substantial variability in total impacts (M = 86.5, SD = 98.0, Range = 7–277) and number of games/practices (M = 9.8, SD = 7.6, Range = 2–23) were observed among players who did use their mouthguard. Specific completion rates for the 3 cognitive and 3 eye-tracking assessments were 71% each, and 57% of players completed all 6 scheduled assessments. Repeated measures ANOVA indicated Visual Motor Speed (VMS) improved between assessments (p = 0.015). Post hoc analysis showed both VMS and Verbal Memory increased from pre- to mid-season (−5.30(95%CI, −10.47 to −0.12), p = 0.046), (−0.20(95%CI, −13.00 to −1.41), p = 0.024). Conclusions: Variability in mouthguard use and missing assessment rates represent practical challenges in prospectively measuring RHI and utilizing multiple longitudinal assessment methods in high school football players. Although ImPACT results should be interpreted cautiously, future research should consider the potential role of practice effects and/or intentionally poor pre-season effort to explain the increase in performance during the season. A larger sample size will increase the possibility of measuring the effect of RHI on assessment outcomes.

Understanding of Contemporary Regional Sea-Level Change and the Implications for the Future

Global sea level provides an important indicator of the state of the warming climate, but changes in regional sea level are most relevant for coastal communities around the world. With improvements to the sea-level observing system, the knowledge of regional sea-level change has advanced dramatically in recent years. Satellite measurements coupled with in situ observations have allowed for comprehensive study and improved understanding of the diverse set of drivers that lead to variations in sea level in space and time. Despite the advances, gaps in the understanding of contemporary sea-level change remain and inhibit the ability to predict how the relevant processes may lead to future change. These gaps arise in part due to the complexity of the linkages between the drivers of sea-level change. Here we review the individual processes which lead to sea-level change and then describe how they combine and vary regionally. The intent of the paper is to provide an overview of the current state of understanding of the processes that cause regional sea-level change and to identify and discuss limitations and uncertainty in our understanding of these processes. Areas where the lack of understanding or gaps in knowledge inhibit the ability to provide the needed information for comprehensive planning efforts are of particular focus. Finally, a goal of this paper is to highlight the role of the expanded sea-level observation network-particularly as related to satellite observations-in the improved scientific understanding of the contributors to regional sea-level change.

An Intensive Observation of Calving at Helheim Glacier, East Greenland

Calving of glacial ice into the ocean from the Greenland Ice Sheet is an important component of global sea level rise. The calving process itself is relatively poorly observed, understood, and modeled; as such, it represents a bottleneck in improving future global sea level estimates in climate models. We organized a pilot project to observe the calving process at Helheim Glacier in East Greenland in an effort to better understand it. During an intensive one-week survey, we deployed a suite of instrumentation including a terrestrial radar interferometer, GPS receivers, seismometers, tsunameters, and an automated weather station. This effort captured a calving process and measured various glaciological, oceanographic, and atmospheric parameters before, during, and after the event. One outcome of our observations is evidence that the calving process actually consists of a number of discrete events, spread out over time, in this instance over at least two days. This time span has implications for models of the process. Realistic projections of future global sea level will depend on accurate parametrization of calving, which will require more sustained observations.

Human adenovirus-vectored foot-and-mouth disease vaccines: establishment of a vaccine product profile through in vitro testing

Next generation, foot-and-mouth disease (FMD) molecular vaccines based on replication deficient human adenovirus serotype 5 viral vectored delivery of FMD capsid genes (AdFMD) are being developed by the United States Dept. of Homeland Security and industry partners. The strategic goal of this program is to develop AdFMD licensed vaccines for the USA National Veterinary Stockpile for use, if needed, as emergency response tools during an FMD outbreak. This vaccine platform provides a unique opportunity to develop a set of in vitro analytical parameters to generate an AdFMD vaccine product profile to replace the current lot release test for traditional, inactivated FMD vaccines that requires FMDV challenge in livestock. The possibility of an indirect FMD vaccine potency test based on a serological alternative was initially investigated for a lead vaccine candidate, Adt.A24. Results show that serum virus neutralization (SVN) based serology testing for Adt.A24 vaccine lot release is not feasible, at least not in the context of vaccine potency assessment at one week post-vaccination. Thus, an in vitro infectious titer assay (tissue culture infectious dose 50, TCID50) which measures FMD infectious (protein expression) titer was established. Pre-validation results show acceptable assay variability and linearity and these data support further studies to validate the TCID50 assay as a potential potency release test. In addition, a quantitative physiochemical assay (HPLC) and three immunochemical assays (Fluorescent Focus-Forming Unit (FFU); tissue culture expression dose 50 (TCED50); Western blot) were developed for potential use as in vitro assays to monitor AdFMD vaccine lot-to-lot consistency and other potential applications. These results demonstrate the feasibility of using a traditional modified-live vaccine virus infectivity assay in combination with a set of physiochemical and immunochemical tests to build a vaccine product profile that will ensure the each AdFMD vaccine lot released is similar to a reference vaccine of proven clinical safety and efficacy.

Thematic Roles Assigned along the Garden Path Linger

In the literature dealing with the reanalysis of garden path sentences such as While the man hunted the deer ran into the woods, it is generally assumed either that people completely repair their initial incorrect syntactic representations to yield a final interpretation whose syntactic structure is fully consistent with the input string or that the parse fails. In a series of five experiments, we explored the possibility that partial reanalyses take place. Specifically, we examined the conditions under which part of the initial incorrect analysis persists at the same time that part of the correct final analysis is constructed. In Experiments 1a and 1b, we found that both the length of the ambiguous region and the plausibility of the ultimate interpretation affected the likelihood that such sentences would be fully reanalyzed. In Experiment 2, we compared garden path sentences with non-garden path sentences and compared performance on two different types of comprehension questions. In Experiments 3a and 3b, we constructed garden path sentences using a small class of syntactically unique verbs to provide converging evidence against the position that people employ some sort of "general reasoning" or pragmatic inference when faced with syntactically difficult garden paths. The results from these experiments indicate that reanalysis of such sentences is not always complete, so that comprehenders often derive an interpretation for the full sentence in which part of the initial misanalysis persists. We conclude that the goal of language processing is not always to create an idealized structure, but rather to create a representation that is "good enough" to satisfy the comprehender that an appropriate interpretation has been obtained.

Misinterpretations of garden-path sentences: implications for models of sentence processing and reanalysis

Theories of sentence comprehension have addressed both initial parsing processes and mechanisms responsible for reanalysis. Three experiments are summarized that were designed to investigate the reanalysis and interpretation of relatively difficult garden-path sentences (e.g., While Anna dressed the baby spit up on the bed). After reading such sentences, participants correctly believed that the baby spit up on the bed; however, they often confidently, yet incorrectly, believed that Anna dressed the baby. These results demonstrate that garden-path reanalysis is not an all-or-nothing process and that thematic roles initially assigned for the subordinate clause verb are not consistently revised. The implications of the partial reanalysis phenomenon for Fodor and Inoue's (1998) model of reanalysis and sentence processing are discussed. In addition, we discuss the possibility that language processing often creates "good enough" structures rather than ideal structures.

Crystallographic analysis of reversible metal binding observed in a mutant (Asp153-->Gly) of Escherichia coli alkaline phosphatase

Here we present the refined crystal structures of three different conformational states of the Asp153-->Gly mutant (D153G) of alkaline phosphatase (AP), a metalloenzyme from Escherichia coli. The apo state is induced in the crystal over a 3 month period by metal depletion of the holoenzyme crystals. Subsequently, the metals are reintroduced in the crystalline state in a time-dependent reversible manner without physically damaging the crystals. Two structural intermediates of the holo form based on data from a 2 week (intermediate I) and a 2 month soak (intermediate II) of the apo crystals with Mg2+ and Zn2+ have been identified. The three-dimensional crystal structures of the apo (R = 18.1%), intermediate I (R = 19.5%), and intermediate II (R = 19.9%) of the D153G enzyme have been refined and the corresponding structures analyzed and compared. Large conformational changes that extend from the mutant active site to surface loops, located 20 A away, are observed in the apo structure with respect to the holo structure. The structure of intermediate I shows the recovery of the entire enzyme to an almost native-like conformation, with the exception of residues Asp 51 and Asp 369 in the active site and the surface loop (406-410) which remains partially disordered. In the three-dimensional structure of intermediate II, both Asp 51 and Asp 369 are essentially in a native-like conformation, but the main chain of residues 406-408 within the loop is still not fully ordered. The D153G mutant protein exhibits weak, reversible, time dependent metal binding in solution and in the crystalline state.(ABSTRACT TRUNCATED AT 250 WORDS)

A molecular sensor system based on genetically engineered alkaline phosphatase

Binding and signaling proteins based on Escherichia coli alkaline phosphatase (AP; EC 3.1.3.1) were designed for the detection of antibodies. Hybrid proteins were constructed by using wild-type AP and point mutants of AP [Asp-101 --> Ser (D101S) and Asp-153 --> Gly (D153G)]. The binding function of the hybrid proteins is provided by a peptide epitope inserted between amino acids 407 and 408 in AP. Binding of anti-epitope antibodies to the hybrid proteins modulates the enzyme activity of the hybrids; upon antibody binding, enzyme activity can increase to as much as 300% of the level of activity in the absence of antibody or can decrease as much as 40%, depending on the presence or absence of the point mutations in AP. The fact that modulation is altered from inhibition to activation by single amino acid changes in the active site of AP suggests that the mechanism for modulation is due to structural alterations upon antibody binding. Modulation is a general phenomenon. The properties of the system are demonstrated by using two epitopes, one from the V3 loop of human immunodeficiency virus type 1 gp120 protein and one from hepatitis C virus core protein, and corresponding monoclonal antibodies. The trend of modulation is consistent for all hybrids; those in wild-type AP are inhibited by antibody, while those in the AP mutants are activated by antibody. This demonstrates that modulation of enzyme activity of the AP-epitope hybrid proteins is not specific to either a particular epitope sequence or a particular antibody-epitope combination.

Modulation of enzyme activity by antibody binding to an alkaline phosphatase-epitope hybrid protein

An epitope from the HIV-1 gp120 protein V3 loop has been inserted onto the surface of bacterial alkaline phosphatase at different positions in the vicinity of the enzyme active site, creating hybrid proteins that can bind to an anti-gp120 monoclonal antibody. One of the hybrid proteins, API1, has a 13 amino acid V3 loop sequence inserted between residues 407 and 408 of alkaline phosphatase. The enzymatic activity of this protein is modulated upon antibody binding. API1 maintains the full activity of the wild type alkaline phosphatase but in the presence of the anti-gp120 antibody, the enzyme activity is inhibited by 40-50%. Thus, the hybrid enzyme can be used to detect the presence of antibody in solution. The concept of signalling proteins may have a wide application. Two models for the mechanism of modulation, steric hindrance and allosteric regulation, are discussed.

Structural and biochemical differentiation of the guinea-pig colon during foetal development

We have studied some aspects of the morphological and biochemical differentiation of the foetal guinea-pig colonic epithelium. At day 40 the epithelium was organised in ridges and appeared pseudo-stratified. Folding of the epithelium, followed by villus formation, occurred between days 45 and 55, and by day 50 mucus-secreting goblet cells appeared at the bases of the colonic villi. By day 55 most epithelial cells, including goblet cells, possessed numerous microvilli which, by day 65, had become organised into well developed brush-borders. Between day 55 and term (day 65-68) mucosal depth increased markedly and the colon attained its final glandular morphology. Biochemical studies showed the specific activities of the microvillar hydrolases to be much lower in the washed colon than in either foetal meconium or small intestine at all times during development. Furthermore, a membrane fraction highly enriched in microvillus hydrolase activities was prepared from foetal colonic meconium using techniques originally devised to isolate the foetal small intestinal microvillus membrane. This meconial subfraction was almost identical in polypeptide composition to the highly-purified foetal small intestinal microvillus membrane. Identification of the colonic microvillus membrane was hampered by the absence of reliable membrane markers. Nevertheless, a fraction 14-fold enriched in aminopeptidase activity was prepared from day 40 foetal colon and its polypeptide composition compared by SDS-PAGE to that of the small intestinal microvillus membrane at the same age.