Spatial resolution requirements for active radiation detectors used beyond low earth orbit.

Measurements of the incident fluence of HZE particles, as a function of LET, are used to determine absorbed dose as well as Quality Factors for assigning risk estimates to astronauts during manned space missions. These data are often based on thin solid state detectors that measure energy deposition, dE, and the assumption that the trajectory of the particle, dx, is equivalent to the thickness of the detector. Heavy ions often fragment while penetrating shielding materials in vehicles or habitats. Projectile fragments can be clustered spatially and temporally at the location of the thin detector which are then misclassified as a single particle. Eliminating the confounding effects of coincident events is the first step in extending the reach of flight instruments to identify the charge and velocity of individual particles. Identification of individual particles, in a fragmentation spectrum, will require that detection systems have sufficient segmentation to eliminate coincident events. The objective of this study was to reduce coincident events while avoiding over-design and complexity. Monte Carlo simulations, using Geant4, were performed for 4He, 12C, 28Si and 56Fe ions at energies of 300, 900 and 2400 MeV/n incident upon aluminum shields having areal densities of 5.4, 13.5, and 54 g/cm2. The identity, energy and spatial distribution of all particles downstream from the shielding were analyzed using a novel approach based on proximity distributions. Results indicated that pixel dimensions on the order of 1 mm were sufficient to reduce errors caused by coincident events for active space radiation detectors.

Cross Cultural Indicators of Independent Learning in Young Children: A Jordanian Case.

This study attempts to explore the level of Independent Learning (IL) amongst a sample of Jordanian preschoolers. Behaviors of sixty preschool children aged 5-6 years old were observed and rated by their teachers against an Arabic version of the Children's Independent Learning Development (CHILD 3-5) observational instrument to explore the independent learning among young children according to their gender, engagement level, parental education and the size of their families. The results illustrated that preschoolers may show some aspects of behaviors particularly those related to pro-social and cognitive areas. It also indicated that children from high educated environments demonstrated IL behaviors more than those coming from low educated environments. Finally, children coming from larger family size showed less IL behaviors than those coming from smaller ones. Results and implications are discussed.

Cross cultural indicators of independent learning in young children: a jordanian case

This study attempts to explore the level of Independent Learning (IL) amongst a sample of Jordanian preschoolers. Behaviors of sixty preschool children aged 5-6 years old were observed and rated by their teachers against an Arabic version of the Children's Independent Learning Development (CHILD 3-5) observational instrument to explore the independent learning among young children according to their gender, engagement level, parental education and the size of their families. The results illustrated that preschoolers may show some aspects of behaviors particularly those related to pro-social and cognitive areas. It also indicated that children from high educated environments demonstrated IL behaviors more than those coming from low educated environments. Finally, children coming from larger family size showed less IL behaviors than those coming from smaller ones. Results and implications are discussed (AU)

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Neutron yields and effective doses produced by Galactic Cosmic Ray interactions in shielded environments in space.

In order to define the ranges of relevant neutron energies for the purposes of measurement and dosimetry in space, we have performed a series of Monte Carlo transport model calculations that predict the neutron field created by Galactic Cosmic Ray interactions inside a variety of simple shielding configurations. These predictions indicate that a significant fraction of the neutron fluence and neutron effective dose lies in the region above 20 MeV up to several hundred MeV. These results are consistent over thicknesses of shielding that range from very thin (2.7 g/cm(2)) to thick (54 g/cm(2)), and over both shielding materials considered (aluminum and water). In addition to these results, we have also investigated whether simplified Galactic Cosmic Ray source terms can yield predictions that are equivalent to simulations run with a full GCR source term. We found that a source using a GCR proton and helium spectrum together with a scaled oxygen spectrum yielded nearly identical results to a full GCR spectrum, and that the scaling factor used for the oxygen spectrum was independent of shielding material and thickness. Good results were also obtained using a GCR proton spectrum together with a scaled helium spectrum, with the helium scaling factor also independent of shielding material and thickness. Using a proton spectrum alone was unable to reproduce the full GCR results.

Quality factors for space radiation: A new approach.

NASA has derived new models for radiological risk assessment based on epidemiological data and radiation biology including differences in Relative Biological Effectiveness for leukemia and solid tumors. Comprehensive approaches were used to develop new risk cross sections and the extension of these into recommendations for risk assessment during space missions. The methodology relies on published data generated and the extensive research initiative managed by the NASA Human Research Program (HRP) and reviewed by the National Academy of Sciences. This resulted in recommendations for revised specifications of quality factors, QNASA(Z,ß) in terms of track structure concepts that extend beyond LET alone. The new paradigm for quality factors placed demands on radiation monitoring procedures that are not satisfied by existing dosimetry systems or particle spectrometers that are practical for space exploration where mass, volume, band width and power consumption are highly constrained. We have proposed a new definition of quality factors that relaxes the requirements for identifying charge, Z, and velocity, ß, of the incident radiation while still preserving the functional form of the inherent risk functions. The departure from the exact description of QNASA(Z,ß) is that the revised values are new functions of LET for solid cancers and leukemia. We present the motivation and process for developing the revised quality factors. We describe results of extensive simulations using GCR distributions in free space as well as the resulting spectra of primary and secondary particles behind aluminum shields and penetration through water. In all cases the revised dose averaged quality factors agreed with those based on the values obtained using QNASA(Z,ß). This provides confidence that emerging technologies for space radiation dosimetry can provide real time measurements of dose and dose equivalent while satisfying constraints on size, mass, power and bandwidth. The revised quality factors are sufficiently generalized to be applicable to radiation protection practices beyond space exploration.

TIMP-2 growth-stimulatory activity: a concentration- and cell type-specific response in the presence of insulin.

In addition to proteinase-inhibitory activities, growth-stimulatory activities have been described for all three known members of the tissue inhibitors of the metalloproteinase (TIMP) family, TIMP-1, TIMP-2, and ChIMP-3, believed to be the chicken homologue of TIMP-3. However, the mechanism by which the TIMPs stimulate cell growth is unclear. In this report we have demonstrated that rTIMP-2 was growth-stimulatory for human foreskin fibroblasts (HSF4, HSF43, HS68), lung adenocarcinoma cells (A549), human melanoma cells (WM115), and the Burkitt's lymphoma cell line RAMOS, and this stimulatory response was concentration-dependent, with the greatest stimulation occurring a 10-30 pM rTIMP-2 in [3H]thymidine incorporation assays and at 20-100 pM in cell growth assays. Normal human colon (18Co) and lung (37Lu) fibroblasts showed no response to rTIMP-2. [3H]Thymidine incorporation was inhibited by rTIMP-2 treatment in the nonadherent cell line HL60. These studies also demonstrated that for the cell types tested, TIMP-2 alone was insufficient for a growth stimulatory response requiring, at a minimum, the presence of insulin. In the absence of any "co-factor(s)," such as insulin, TIMP-2 treatment was inhibitory.