Finite Element Modelling of GFRP Reinforced Concrete Beams

The numerical modelling of twelve concrete beams reinforced with glass fibre reinforced polymer (GFRP) longitudinal and transverse bars was performed by the author using the finite element analysis (FEA) software ABAQUS. The experimental beam tests as performed by Krall (2014) were used to calibrate the Concrete Damaged Plasticity Model (CDPM) provided within ABAQUS. Recommendations were made regarding the modelling of concrete beams reinforced with and without GFRP stirrups. The analyses of beams without stirrups are presented first. The Hognestad Parabola was effective in modelling the compressive behaviour of the concrete. A fracture mechanics approach was used to model the post-cracking tensile behaviour of the concrete, with a bilinear stress-displacement response and a fracture energy of 90N/m providing the strongest accuracy. The use of discrete truss sections and smeared membrane sections to model the GFRP longitudinal reinforcement were both studied; both methods were effective, but the truss approach is recommended. Further modifications to the CDPM were necessary for the modelling of beams with stirrups. The presence of GFRP stirrups that do not exhibit the plastic behaviour that steel stirrups exhibit resulted in concrete-governed compression failures. To consider the confining effects that the stirrups had on the concrete, an increased dilation angle of 50 degrees was used in combination with an increased maximum concrete compressive strain. Truss reinforcement was again used for the longitudinal reinforcement, whereas membrane sections are recommended for the stirrups. A parametric study was performed by applying the proposed models to beams with slenderness ratios (a/d) ranging from 1.5 to 6.5. For a/d less than 2.5, further research is recommended to confirm the influence of the arch effect on the shear strength of deep members. For a/d = 2.5, the proposed ABAQUS models agree strongly with the shear model proposed by Nehdi et al. (2007). For larger ratios, the proposed models agree strongly with the flexural strength predictions. It was therefore shown that the proposed ABAQUS models are effective in accurately predicting the strength of beams with and without stirrups for various a/d ratios, and are able to produce reinforcement strain responses and crack patterns that agree strongly with the experimental data

The grey area : self-evaluation of performance in medical students at the University of Malta

Precise self-evaluation and a keen insight into one’s performance and limitations are essential in medical practice. We sought to assess the accuracy of medical students’ assessment of their own performance in a written clinical anatomy test.peer-reviewe

How much anatomy do medical students remember?

Pure anatomy teaching at the University of Malta is completed by the second year, and is not formally revisited later. This study aimed to determine the extent of anatomical knowledge retention in each year of medical school.peer-reviewe

Large-Area Atom Interferometry with Frequency-Swept Raman Adiabatic Passage

We demonstrate light-pulse atom interferometry with large-momentum-transfer atom optics based on stimulated Raman transitions and frequency-swept adiabatic rapid passage. Our atom optics have produced momentum splittings of up to 30 photon recoil momenta in an acceleration-sensitive interferometer for laser cooled atoms. We experimentally verify the enhancement of phase shift per unit acceleration and characterize interferometer contrast loss. By forgoing evaporative cooling and velocity selection, this method lowers the atom shot-noise-limited measurement uncertainty and enables large-area atom interferometry at higher data rates.Charles Stark Draper Laboratory (Fellowship

Environmental Differences between Migratory and Resident Ungulates—Predicting Movement Strategies in Rocky Mountain Mule Deer (Odocoileus hemionus) with Remotely Sensed Plant Phenology, Snow, and Land Cover

Migration is a valuable life history strategy for many species because it enables individuals to exploit spatially and temporally variable resources. Globally, the prevalence of species’ migratory behavior is decreasing as individuals forgo migration to remain resident year-round, an effect hypothesized to result from anthropogenic changes to landscape dynamics. Efforts to conserve and restore migrations require an understanding of the ecological characteristics driving the behavioral tradeoff between migration and residence. We identified migratory and resident behaviors of 42 mule deer (Odocoileus hemionus) based on GPS locations and correlated their locations to remotely sensed indicators of forage quality, land cover, snow cover, and human land use. The model classified mule deer seasonal migratory and resident niches with an overall accuracy of 97.8% and cross-validated accuracy of 81.2%. The distance to development was the most important variable in discriminating in which environments these behaviors occur, with resident niche space most often closer to developed areas than migratory niches. Additionally, snow cover in December was important for discriminating summer migratory niches. This approach demonstrates the utility of niche analysis based on remotely sensed environmental datasets and provides empirical evidence of human land use impacts on large-scale wildlife migrations

Robust Ramsey sequences with Raman adiabatic rapid passage

We present a method for robust timekeeping in which alkali-metal atoms are interrogated in a Ramsey sequence based on stimulated Raman transitions with optical photons. To suppress systematic effects introduced by differential ac Stark shifts and optical intensity gradients, we employ atom optics derived from Raman adiabatic rapid passage (ARP). Raman ARP drives coherent transfer between the alkali-metal hyperfine ground states via a sweep of the Raman detuning through the two-photon resonance. Our experimental implementation of Raman ARP reduced the phase sensitivity of Ramsey sequences to Stark shifts in [superscript 133]Cs atoms by about two orders of magnitude, relative to fixed-frequency Raman transitions. This technique also preserved Ramsey fringe contrast for cloud displacements reaching the 1/e[superscript 2] intensity radius of the laser beam. In a magnetically unshielded apparatus, second-order Zeeman shifts limited the fractional frequency uncertainty to ~3.5 × 10[superscript −12] after about 2500 s of averaging.Charles Stark Draper Laboratory (Fellowship Program)Charles Stark Draper Laborator

Abundance recovery error analysis using simulated AVIRIS data

Measurement noise and imperfect atmospheric correction translate directly into errors in the determination of the surficial abundance of materials from imaging spectrometer data. The effects of errors on abundance recovery were investigated previously using Monte Carlo simulation methods by Sabol et. al. The drawback of the Monte Carlo approach is that thousands of trials are needed to develop good statistics on the probable error in abundance recovery. This computational burden invariably limits the number of scenarios of interest that can practically be investigated. A more efficient approach is based on covariance analysis. The covariance analysis approach expresses errors in abundance as a function of noise in the spectral measurements and provides a closed form result eliminating the need for multiple trials. Monte Carlo simulation and covariance analysis are used to predict confidence limits for abundance recovery for a scenario which is modeled as being derived from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)

Particle Size Specific Magnetic Properties Across the Norwegian‐Greenland Seas: Insights Into the Influence of Sediment Source and Texture on Bulk Magnetic Records

We make fundamental observations of the particle size variability of magnetic properties from 71 core tops that span the southern Greenland and Norwegian Seas. These data provide the first detailed regional characterization of how bulk magnetic properties vary with sediment texture, sediment source, and sediment transport. Magnetic susceptibility (MS) and hysteresis parameters were measured on the bulk sediment and the five constituent sediment particle size fractions (clay, fine silt, medium silt, coarse silt, and sand). The median MS value of the medium silt size fraction is ~3–5 times higher than that of the sand and clay size fractions and results in a strong sensitivity of bulk MS to sediment texture. Hysteresis properties of the clay size fraction are relatively homogeneous and contrast that silt and sand size fractions which show regional differences across the study area. These coarser fractions are more transport limited and using medium silt hysteresis measurements and low temperature MS behavior we establish three endmembers that effectively explain the variability observed across the region. We model the response of bulk magnetic properties to changes in sediment texture and suggest that variations in sediment source are required to explain the bulk magnetic property variability observed in cores across the southern Greenland and Norwegian Seas. These findings imply that sediment source has a greater influence on driving bulk magnetic property variability across this region than has previously been assumed

Millennial-Scale Instability in the Geomagnetic Field Prior to the Matuyama-Brunhes Reversal

Changes in the Earth's magnetic field have global significance that reach from the outer core extending out to the uppermost atmosphere. Paleomagnetic records derived from sedimentary and volcanic sequences provide important insights into the geodynamo processes that govern the largest geomagnetic changes (polarity reversals), but dating uncertainties have hindered progress in this understanding. Here, we report a paleomagnetic record from multiple lava flows on Tahiti that bracket the Matuyama‐Brunhes (M‐B) polarity reversal ∼771,000 years ago. Our high‐precision ^(40)Ar/^(39)Ar ages constrain several rapid and short‐lived changes in field orientation up to 33,000 years prior to the M‐B reversal. These changes are similar to ones identified in other less well‐dated lava flows in Maui, Chile, and La Palma that occurred during an extended period of reduced field strength recorded in sediments. We use a simple stochastic model to show that these rapid polarity changes are highly attenuated in sediment records with low sedimentation rates. This prolonged 33,000 year period of reduced field strength and increased geomagnetic instability supports models that show frequent centennial‐to‐millennial‐scale polarity changes in the presence of a strongly weakened dipole field

Late quaternary paleomagnetic secular variation and chronostratigraphy from ODP sites 1233 and 1234

During Ocean Drilling Program Leg 202, detailed shipboard paleomagnetic measurements at Sites 1233 and 1234 identified a reproducible high-resolution record of paleomagnetic secular variation (PSV) at each site. These records also contained evidence for three magnetic field excursions. This paper summarizes the complete paleomagnetic record from Site 1233 and the paleomagnetic record for the uppermost 30 meters from Site 1234. We also establish a detailed PSV correlation between the two sites, located ~500 km apart. Twenty-seven accelerator mass spectrometry radiocarbon dates permit us to develop time-depth plots and detailed PSV time series for the last ~50,000 yr at both sites. Based on our chronostratigraphy, the most recent excursions occur at ~35,000 cal. yr before present (BP) (Excursion 3) and ~41,000 cal. yr BP (Excursion 3). The excursions were named for the oxygen isotope stages within which they occur. These two excursions are not significantly different in age from the Mono Lake Excursion and Laschamp Excursion. A third, older excursion, which has not yet been adequately dated, also occurs at Site 1233