Evaluating the psychometric properties of the Grit scale in Marine recruits using Rasch analysis

INTRODUCTION

Successful completion of initial military training has been suggested to be predicted by physical abilities, cognitive abilities and non-cognitive abilities such as hardiness and grit. This study aimed to assess the psychometric properties of a Dutch version of a grit measurement scale: the NL-Grit scale.

METHODS

We assessed the factor structure, unidimensionality of the subscales, discriminative quality of the rating scale and investigated to what extend the items together can reliably measure the entire range of grit levels in Dutch Marine recruits. We used data of Marine recruit training platoons of the Royal Netherlands Marine Corps.

RESULTS

Principal component analysis reflected two subscales: 'consistency of interests' and 'perseverance of effort'. Rasch analysis confirmed the unidimensionality of the intended subscales. Rasch rating scale analysis indicated that the five-point response scale was not used as intended by respondents. Disordered rating scale categories were collapsed to obtain ordered rating categories. The item and person parameters (grit levels) largely overlapped, indicating that the item spread was sufficient for measuring the entire range of grit trait levels. However, larger gaps between item location parameters suggested a low discriminative capacity of the NL-Grit scale for respondents with trait levels within the gaps.

CONCLUSION

Our evaluation of the NL-Grit scale suggests sound psychometric quality of the NL-Grit in Dutch Marine recruits. Reliability could be improved by adding items to fill the observed gaps in item content.

Fractionation of Sulfur and Carbon Isotopes in a Meromictic Lake

In the permanently stagnant depths of Green Lake (near Syracuse, N.Y.), sulfide made by bacteria is depleted in heavy sulfur (S(34)), and sulfate is enriched. The fractionation factor, 1.0575, is the greatest yet observed. Isotopic resemblance to salt-dome sulfur deposits is evident, and, like saltdome calcite, the lake's carbon dioxide is depleted in heavy carbon (C(13)).

Abyssal water carbon-14 distribution and the age of the world oceans

The carbon-14 distribution in the abyssal waters of the world oceans indicates replacement times for Pacific, Indian, and Atlantic ocean deep waters (more than 1500 meters deep) of approximately 510, 250, and 275 years, respectively. The deep waters of the entire world ocean are replaced on average every 500 years.

Cowpea mosaic virus infection induces a massive proliferation of endoplasmic reticulum but not Golgi membranes and is dependent on de novo membrane synthesis

Replication of cowpea mosaic virus (CPMV) is associated with small membranous vesicles that are induced upon infection. The effect of CPMV replication on the morphology and distribution of the endomembrane system in living plant cells was studied by expressing green fluorescent protein (GFP) targeted to the endoplasmic reticulum (ER) and the Golgi membranes. CPMV infection was found to induce an extensive proliferation of the ER, whereas the distribution and morphology of the Golgi stacks remained unaffected. Immunolocalization experiments using fluorescence confocal microscopy showed that the proliferated ER membranes were closely associated with the electron-dense structures that contain the replicative proteins encoded by RNA1. Replication of CPMV was strongly inhibited by cerulenin, an inhibitor of de novo lipid synthesis, at concentrations where the replication of the two unrelated viruses alfalfa mosaic virus and tobacco mosaic virus was largely unaffected. These results suggest that proliferating ER membranes produce the membranous vesicles formed during CPMV infection and that this process requires continuous lipid biosynthesis.

Permeation and gating properties of the novel epithelial Ca(2+) channel

The recently cloned epithelial Ca(2+) channel (ECaC) constitutes the Ca(2+) influx pathway in 1,25-dihydroxyvitamin D(3)-responsive epithelia. We have combined patch-clamp analysis and fura-2 fluorescence microscopy to functionally characterize ECaC heterologously expressed in HEK293 cells. The intracellular Ca(2+) concentration in ECaC-expressing cells was closely correlated with the applied electrochemical Ca(2+) gradient, demonstrating the distinctive Ca(2+) permeability and constitutive activation of ECaC. Cells dialyzed with 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid displayed large inward currents through ECaC in response to voltage ramps. The corresponding current-voltage relationship showed pronounced inward rectification. Currents evoked by voltage steps to potentials below -40 mV partially inactivated with a biexponential time course. This inactivation was less pronounced if Ba(2+) or Sr(2+) replaced Ca(2+) and was absent in Ca(2+)-free solutions. ECaC showed an anomalous mole fraction behavior. The permeability ratio P(Ca):P(Na) calculated from the reversal potential at 30 mM [Ca(2+)](o) was larger than 100. The divalent cation selectivity profile is Ca(2+) > Mn(2+) > Ba(2+) approximately Sr(2+). Repetitive stimulation of ECaC-expressing cells induced a decay of the current response, which was greatly reduced if Ca(2+) was replaced by Ba(2+) and was virtually abolished if [Ca(2+)](o) was lowered to 1 nM. In conclusion, ECaC is a Ca(2+) selective channel, exhibiting Ca(2+)-dependent autoregulatory mechanisms, including fast inactivation and slow down-regulation.

The Accumulation Record from the GISP2 Core as an Indicator of Climate Change Throughout the Holocene

A depth-age scale and an accumulation history for the Holocene have been established on the Greenland Ice Sheet Project 2 (GISP2) deep core, providing the most continuously dated record of annual layer accumulation currently available. The depth-age scale was obtained with the use of various independent techniques to count annual layers in the core. An annual record of surface accumulation during the Holocene was obtained by correcting the observed layer thicknesses for flow-thinning. Fluctuations in accumulation provide a continuous and detailed record of climate variability over central Greenland during the Holocene. Climate events, including "Little Ice Age" type events, are examined.

Oxygen Isotope Ratios in Trees Reflect Mean Annual Temperature and Humidity

Values of the oxygen isotope ratios (delta(18)O) in tree-ring cellulose closely reflect the delta(18)O values in atmospheric precipitation and hence mean annual temperature. The change in delta(18)O in cellulose is 0.41 per mil per degree Celsius for selected near-coastal stations. The values of delta(18)O in precipitation and cellulose also change with altitude, as demonstrated for Mount Rainier, Washington. A temperature lapse rate of 5.2 degrees +/- 0.5 degrees C per 1000 meters calculated from cellulose delta(18)O values agrees with the accepted mean annual lapse rate of 5 degrees C per 1000 meters for this region. Cellulose delta(18)O values and delta(18)O values of carbon dioxide equilibrated with leaf water differ by a fixed 16 per mil.

Late Wisconsin Climate of Northern Florida and the Origin of Species-Rich Deciduous Forest

Species-rich mesic forest covered northern Florida as early as 14,000 radiocarbon years before present. It probably originated in deciduous tree populations already present locally in conifer forest between 24,000 and 18,600 years before present. The cold, dry Late Wisconsin climate ended before 14,600 years before present. A transitional warm, dry phase preceded a precipitation increase at 14,000 years before present.

Changes in Atmospheric Carbon-14 Attributed to a Variable Sun

The (14)C production rate in the upper atmosphere changes with time because the galactic cosmic-ray flux responsible for (14)C production is modulated by the changes in solar wind magnetic properties. The resulting changes in the atmospheric (14)C level are recorded in tree rings and are used to calculate past (14)C production rates from a carbon reservoir model that describes terrestrial carbon exchange between the atmosphere, ocean, and biosphere. These past (14)C production rate changes are compared with (14)C production rates determined from 20th-century neutron flux measurements, and a theory relating (14)C production and solar variability, as given by geomagnetic Aa indices and sunspot numbers, is developed. This theory takes into account long-term solar changes that were previously neglected. The 860-year (14)C record indicates three episodes when sunspots apparently were absent: A.D. 1654 to 1714 (Maunder minimum), 1416 to 1534 (Spörer minimum), and 1282 to 1342 (Wolf minimum). A less precisely defined minimum occurred near A.D. 1040. The part of this record after A.D. 1645 correlates well with the basic features of the historical record of sunspot numbers. The magnitude of the calculated (14)C production rates points to a further increase in cosmic-ray flux when sunspots are absent. This flux was greatest during the Spörer minimum. A record of approximate sunspot numbers and Aa indices for the current millennium is also presented.

Carbon-14 Dating: A Comparison of Beta and Ion Counting

Accelerator ion counting compares favorably with conventional beta counting. The major advantage of ion counting is that milligram samples can be analyzed. When sample size is not limiting, ion counting complements beta counting for the more routine carbon-14 determinations. Further development is needed before ion counting can achieve the same high precision as beta counting for large samples (+/- 2 per mil). A solution to the background variability has to be found before ion counting can be used to date samples back to the 75,000-year limit of beta counting.

North American Glacial History Extended to 75,000 Years Ago

By concentrating carbon-14 through thermal diffusion, it is possible to extend the range of carbon-14 dating to 75,000 years ago. Samples with very low contamination levels have been encountered, and a reliable chronology appears possible. A Pacific Northwest climatic curve has been derived from palynological studies. The Pacific Northwest curve and the Great Lakes glacial history are age-calibrated by radiocarbon dating. The climatic patterns in the Pacific Northwest and Northwest Europe are similar in the early part of the last glaciation, with interstades near 60,000, 65,000, and 70,000 years ago. An age of 74,700 years for the St. Pierre interstade indicates a possible correlation with the previous interglacial.

Atmospheric Carbon Dioxide and Carbon Reservoir Changes

The net release of CO(2) from the biosphere to the atmosphere between 1850 and 1950 is estimated to amount to 1.2 x 10(9) tons of carbon per year. During this interval, changes in land use reduced the total terrestrial biomass by 7 percent. There has been a smaller reduction in biomass over the last few decades. In the middle 19th century the air had a CO(2) content of approximately 268 parts per millon, and the total increase in atmospheric CO(2) content since 1850 has been 18 percent. Major sinks for fossil fuel CO(2) are the thermocline regions of large oceanic gyres. About 34 percent of the excess CO(2) generated so far is stored in surface and thermocline gyre waters, and 13 percent has been advected into the deep sea. This leaves an airborne fraction of 53 percent.

Chronology of Hawaiian Glaciations

Both potassium/argon and carbon-14 ages of lava flows and tephra layers interstratified with glacial deposits on Mauna Kea, Hawaii, indicate that four episodes of ice cap glaciation culminated about 20,000, 55,000, 135,000, and 250,000 years ago. These episodes are correlated with marine isotope stages 2, 4, 6, and 8, marking times of high global ice volume.

Florida Submergence Curve Revised: Its Relation to Coastal Sedimentation Rates

New data substantiate as well as modify the south Florida submergence curve, which indicates that eustatic sea level has risen continuously, although at a generally decreasing rate, during the last 6500 to 7000 sidereal years (5500 standard radiocarbon years) to reach its present position. Accumulation rates of coastal deposits are similar to the rate of sea-level rise, thus supporting the generalization that submergence rates largely determine as well as limit rates of coastal sedimentation in lagoonal and estuarine areas.

Oxygen-18 content of atmospheric precipitation during last 11,000 years in the Great Lakes region

Freshwater lake marl and mollusks from Indiana show variations in ratios of oxygen-18 to oxygen-16 of a few per mil during the Postglacial. For the last 9000 years these variations are about 1 per mil for properly selected lake sediments. Thus the oxygen isotope composition of atmospheric precipitation appears relatively stable over this interval, indicating stationary atmospheric circulation patterns over the Great Lakes region. A reduction in oxygen-18 content around 10,000 years ago corresponds with the climate change indicated by pollen profiles. Large systematic differences were found between carbon-13 and oxygen-18 content of marl and mollusks.

Olmec Civilization, Veracruz, Mexico: Dating of the San Lorenzo Phase

Archeological excavations at San Lorenzo Tenochtitlan, Veracruz, show that the Olmec sculptures of this zone are associated with the San Lorenzo phase, which can be placed in the Early Formative period (1500-800 B.C.) on the basis of ceramic comparisons. Five of six radiocarbon dates for the San Lorenzo phase fall within the 1200-900 B.C. span. The San Lorenzo phase therefore marks the beginning of Olmec civilization, and the sites forming the San Lorenzo Tenochtitlan group represent the oldest civilized communities known in Mexico or Central America.