Coaxial coil towed EMI sensor array for UXO detection and characterization

A new broadband electromagnetic induction (EMI) array sensor, GEM-5, for detecting and characterizing Unexploded Ordnance (UXO) has been developed in order to provide high production rates for EMI surveys. The sensor consists of a single rectangular loop transmitter around a linear array of seven pairs of coaxial receiver coils, with each coil in a pair located at the same vertical distance above and below the loop transmitter. The coil pairs are wired in an inverted series so that the signal consists of the difference between the voltage induced in the upper and lower coils. This particular configuration provides a high degree of primary field cancellation, dense spatial sampling rate due to simultaneous and continuous operation of all sensors, suppression of motion-induced and environmental noise, and strong source fields at typical UXO burial depths providing deep detection range. Our prototype tests indicate that the array yields a lower static and motion-induced noise over the critical low frequencies than that of existing sensors, and in particular, the signal-to-noise ratio at 90 Hz is 32 dB higher. Environmental noise can be largely removed from the difference measurements. The field test results from UXO test sites show that the prototype sensor has smoother background and appears to detect more seeded targets than the GEM-3 concentric sensor, however some of that gain can be attributed to higher power transmitter electronics.     

Controls on dissolved inorganic carbon and δC in cave waters from DeSoto Caverns: Implications for speleothem δC assessments

Unraveling the factors controlling the carbon chemistry and transport of carbon within extant karst systems has important implications concerning the assessment of time-series δ¹³C records of speleothems. Here we report the results of a 3-year study of total dissolved inorganic carbon [DIC] and δ¹³C_DIC from cave waters at DeSoto Caverns (Southeastern USA) that offer valuable insight on carbon transport and the accompanied isotope fractionations from end-member sources to speleothems.[DIC] and δ¹³C_DIC values of cave waters range from 0.2 to 6.0 mM and 2.7 to −12.9 (‰ VPDB), respectively. [DIC] and δ¹³C_DIC of “seasonal drips” show seasonal, albeit noisy, variability and are inversely related (δ¹³C_DIC = −2.49[DIC] + 0.64, r² = 0.84). A shallow pool fed by multiple drips shows a bimodal δ¹³C_DIC distribution with an isotopically heavier mode during winter (−4‰ to −5‰ VPDB) relative to summer months (−9‰ to −10‰ VPDB). A multi-year trend of decreasing water availability during the study period is not reflected in a response of cave water carbon chemistry suggesting that rainfall amount may not be a significant controlling factor of the carbon chemistry. Coupled cave air winter ventilation/summer stagnation and varying CO₂ fluxes through the soil horizon and epikarst exert the strongest influence on seasonal [DIC] and δ¹³C_DIC variability. Measured values of high [DIC] and low δ¹³C_DIC from cave waters collected during the summer/early fall closely approximate isotopic equilibrium conditions. Conversely, low [DIC] and high δ¹³C_DIC values during winter/early months indicate kinetically enhanced isotopic fractionations within the cave waters. The kinetically enhanced isotopic fractionation of partitioned between degassed CO₂ and precipitated CaCO₃(1000lnα_{[(CO2-HCO3)+(CaCO3(AR)-HCO3)]/2}) is greater by about a factor of two (−6.7 ± 0.3‰) relative to the same isotopic fractionation under equilibrium conditions (−3.1‰).On the basis of ¹⁴C mass balance and paired ¹⁴C-U/Th measurements we estimate that on average about ∼23% of C delivered annually by the drips to the aragonite stalagmites is derived from ¹⁴C-dead dolomite cap while the remainder of ∼77% is derived from ¹⁴C-live biomass. δ¹³C measurements of aragonite (n = 12) sampled from the tips of active speleothems during the summer months are consistent with theoretical aragonite δ¹³C values calculated using the shallow pool summer/early fall data thus confirming the δ¹³C seasonality in both drips and coeval aragonite. δ¹³C values of an active stalagmite section spanning the last 200 years show a normal distribution with a mean of −7.1 ± 1.2‰ (n = 81) and a mode of −7‰ to −8‰ that are statistically indistinguishable from the annual mean and mode of all dripwaters. Thus secular time-series δ¹³C records of stalagmites at DeSoto Caverns with resolving power >10⁻¹ year will likely carry the imprints of drip annual means that record climate-driven δ¹³C seasonal biases.     

Elemental damping formulation: an alternative modelling of inherent damping in nonlinear dynamic analysis

To date, nonlinear dynamic analysis for seismic engineering predominantly employs the classical Rayleigh damping model and its variations. Though earlier studies have identified issues with the use of this model in nonlinear seismic analysis, it still remains the popular choice for engineers as well as for software providers. In this paper a new approach to modelling damping is initiated by formulating the damping matrix at an elemental level. To this regard, two new elemental level discrete damping models adapted from their global counterparts are proposed for its application in nonlinear dynamic analysis. Implementation schemes for these newly proposed models using Newmark incremental method and revised Newmark total equilibrium method is outlined. The performance of these proposed models, compared to existing models, is illustrated by conducting nonlinear dynamic analyses on a four story RC frame designed to Eurocodes. The incremental dynamic analysis study presented in the paper illustrates the fact that both the proposed models seem to produce more reliable results from an engineering perspective in comparison to the global models. It is also shown that the proposed elemental damping models lead to smaller and more realistic damping moments in the plastic hinges. Furthermore, these models could be easily included in existing software frameworks without adding noticeably to the computational effort. The computation time required for these models is approximately equivalent to the one required when using the tangent Rayleigh damping matrix with constant coefficients.     

Microbiotic crusts as biomarkers for surface stability and wetness duration in the Negev Desert

Microbiotic crusts play an important role in arid and semi‐arid regions. Yet, very little information exists regarding the factors that impact their development. In an attempt to assess the main factors that may determine their growth, measurements of the amount of fines (silt and clay), rain, moisture content, wetness duration and wind erosion and deposition were carried out along a 12 station transect within a partially crusted dune field in the western Negev Desert and compared to the crust cover and chlorophyll content. Surface stability was the only variable that exhibited significant relationship with crust cover while daylight wetness duration exhibited strong positive relationship (r² = 0·92–0·99) with the crust's chlorophyll content. The data point out that microbiotic crusts may serve as a useful biomarker for surface stability. While wetness duration and wind will control crust cover and the crust chlorophyll content in semi‐stable habitats (with absolute annual change in sand level of 2–3 mm), stable habitats (absolute change <1 mm) will be controlled primarily by moisture, while habitats with low surface stability (absolute change of tens and hundreds of millimeters) will be primarily controlled by wind. Furthermore, owing to the strong positive relationship between daylight wetness duration and the crust's chlorophyll content, the crust may serve as a useful biomarker for the quantification of surface wetness duration. Copyright © 2009 John Wiley & Sons, Ltd.     

Simultaneous topology and sizing optimization of viscous dampers in seismic retrofitting of 3D irregular frame structures

A new methodology for performance‐based optimal seismic retrofitting using a limited number of size groups of viscous dampers is presented. The damping coefficient of each size group of dampers is taken as a continuous variable and is determined by the optimization algorithm. Furthermore, for each potential location, a damper of a single size group is optimally assigned, if any. Hence, the formulation presents a large step forward towards practical optimal design of dampers. The key for achieving an efficient optimization scheme is the incorporation of material interpolation techniques that were successfully applied in other structural optimization problems of discrete nature. This results in a very effective optimization methodology that is expected to be very efficient for large‐scale structures. The proposed approach is demonstrated on several example problems of 3D irregular frame structures. Copyright © 2014 John Wiley & Sons, Ltd.     

Radiocarbon deficiencies of US Gulf Coast lakes compromise paleo-hurricane records

Radiocarbon assays of sediments from Lake Shelby, US Gulf Coast, exhibit substantial ¹⁴C deficiencies of 9.3% and 4.7% for the limnic sapropel and associated fresh-water clams Rangia cuneata, respectively. Measured radiocarbon dates from the sapropel and clams require corrections of 785 ± 80 and 365 ± 90 ¹⁴C yr (1σ), respectively, in order to achieve consistency with the radiocarbon time scale. Lake sediments of the US Gulf Coast serve as unique repositories of pre-historic hurricane strikes. Previously unrecognized radiocarbon deficiencies likely render compromised chronologies of the paleo-hurricane records, and erroneous estimates of return period and landfall probability that are derived from the storm chronologies. The recalculated severe hurricane chronologies suggest that the annual landfall probabilities of the last millennium on the US Gulf Coast are equal to, or higher than, the preceding three millennia.     

Local deformation‐based design of minimal‐disturbance arm damper for retrofitting steel moment‐resisting frames

This paper presents a design approach for seismic rehabilitation of frames having a beam‐collapse mechanism using a technique termed minimal‐disturbance seismic rehabilitation. This technique pursues enhancing the seismic performance of buildings with the intention of improving the continuity of business. It minimizes obstruction of the visual and physical space of building users and the use of heavy construction equipment and work requiring fire permit (welding/cutting). The developed design approach is simple to use. Yet it leads to designs that limit the beams' plastic rotations to allowable values, while minimizing the number of locations where devices are installed and the devise dimensions. Furthermore, the effectiveness of the design approach and the rehabilitation technique is numerically studied through retrofitting a four‐story steel moment‐resisting frame. Copyright © 2017 John Wiley & Sons, Ltd.     

GENDER DIFFERENCES IN COMMUTING DISTANCE,RESIDENCE, AND EMPLOYMENT LOCATION: METROPOLITAN HAIFA 1972 AND 1983*

This paper highlights three major aspects of gender differences in employment in Haifa, Israel (1972 and 1983): commuting distance, place of residence, and employment location. In 1972 working womenaposs residences were more central-city-oriented, whereas in 1983 they were more suburbanized. Commuting distances increased between 1972 and 1983 for both sexes, but more for men than for women. This shorter “female'’distance is related to the location of employment and its occupational segregation. The lower commuting values in Haifa compared to other places relate to the size, housing patterns, and structure of the study area, and to its levels of suburbanization and automobile ownership.