Assessment: Insights into Children\u27s Beliefs and Perceptions About Process Writing

How do children acquire knowledge about written language? Investigations of emergent literacy have shown that children\u27s written language knowledge reflects their cultural environment (Clay, 1982; Kastler, Roser, and Hoffman, 1987). At home, children observe their parents writing grocery lists, letters to friends and relatives, and telephone messages, thereby learning the functions of written language as they are used in daily life (Morgan, 1987; Purcell-Gates, 1986). Independently, children experiment with their own messages, incorporating scribble, pictures and random letters. Often their written products mirror the functional writing their parents modeled (Rowe, 1989). In school, additional opportunities to learn about written language are presented. Some tasks are inherent to the school setting, such as reports and labels, while others resemble those practices at home (Dyson, 1984). Children in classrooms where traditional writing instruction prevails find constraints placed upon their writing by their teacher, such as topic, length and purpose

Development of powder bed fusion–laser beam process for AISI 4140, 4340 and 8620 low-alloy steel

This study focuses on process development and mechanical property evaluation of AISI 4140, 4340 and 8620 low-alloy steel produced by powder bed fusion–laser beam (PBF-LB). Process development found that increasing the build plate preheating temperature to 180\ub0C improved processability, as it mitigated lack of fusion and cold cracking defects. Subsequent mechanical testing found that the low-alloy steels achieved a high ultimate tensile strength (4140:∼1400 MPa, 4340:∼1500 MPa, 8620:∼1100 MPa), impact toughness (4140:∼90–100 J, 4340:∼60–70 J, 8620:∼150–175 J) and elongation (4140:∼14%, 4340:∼14%, 8620:∼14–15%) that met or exceeded the ASTM standards. Mechanical testing also revealed limited directional anisotropy that was attributed to low levels of internal defects (< 0.1%), small grains with weak crystallographic texture and improved tempering due to build plate preheating and post PBF-LB stress relief. This indicates that with adequate process development, low-alloy steels produced by PBF-LB can meet or exceed the performance of conventionally produced alloys

Sintering anisotropy of binder jetted 316L stainless steel: part II–microstructure evolution during sintering

Green density of binder jetted parts are typically equal or lower than the powder tap density. Also, anisotropic green porosity distribution is expected because of the characteristics of the binder jetting (BJ) printing process. In this study, the microstructure evolution in terms of phases and porosity characteristics was studied. A transition from irregular-shape interconnected porosity in pre-sintered samples to closed quasi-spherical porosity for samples sintered at 1370\ub0C was observed. EBSD phase map showed ∼2.73% of δ-ferrite in sample sintered at 1370\ub0C. The anisotropic porosity distribution was revealed by a higher area fraction of aligned large pores (>35 \ub5m), within the cross-section perpendicular to the building direction. Chemical analysis showed an increase of C, O and N on the green sample, while a strong decrease was found after sintering when compared with the powder chemistry. δ-ferrite onset, from phase equilibrium calculations, varies from ∼1250\ub0C (sintered sample chemistry) to ∼1350\ub0C (powder chemistry)

Sintering anisotropy of binder jetted 316L stainless steel: part I–sintering anisotropy

In Binder Jetting (BJ) Additive Manufacturing (AM), green components are usually subjected to sintering process to reach required properties. Owing to the inherent low green density, binder jetted (BJ) parts undergo shrinkages up to 20%. In addition, anisotropic dimensional evolution during sintering is characteristic for BJ, generally caused by the specifics of the arrangement of particles during the printing process. In this study, the multi-axial dimensional evolution of 316L stainless steel cubic samples (10 7 10 7 10 mm3), manufactured using BJ, was characterised by dilatometry experiments. Dilatometry tests were conducted up to sintering temperatures of 1300\ub0C and 1370\ub0C, with a heating rate of 10\ub0C/min and 5\ub0C/min, respectively. Dilatometry results and final dimension measurements showed anisotropic shrinkage behaviour during sintering with about 15% larger shrinkage along the building direction. Shrinkages along the other two orthogonal directions were relatively similar, but a slightly larger final shrinkage along the printhead movement direction was observed. Relative density of 85.0% and 96.4% was obtained after sintering tests at 1300\ub0C and 1370\ub0C, respectively

Working with simple machines

A set of examples is provided that illustrate the use of work as applied to simple machines. The ramp, pulley, lever and hydraulic press are common experiences in the life of a student and their theoretical analysis therefore makes the abstract concept of work more real. The mechanical advantage of each of these systems is also discussed so that students can evaluate their usefulness as machines.Comment: 9 pages, 4 figure

Direct reaction measurements with a 132Sn radioactive ion beam

The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of 132Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the cross section. The magnitude of the nuclear effects was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p1/2 state expected above the N=82 shell closure. The data were analyzed using finite range adiabatic wave calculations and the results compared with the previous analysis using the distorted wave Born approximation. Angular distributions for the ground and first excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one neutron states beyond the benchmark doubly-magic nucleus 208Pb.Comment: 22 pages, 7 figure

Structure of 13^{13}Be probed via secondary beam reactions

The low-lying level structure of the unbound neutron-rich nucleus $^{13}$Be has been investigated via breakup on a carbon target of secondary beams of $^{14,15}$B at 35 MeV/nucleon. The coincident detection of the beam velocity $^{12}$Be fragments and neutrons permitted the invariant mass of the $^{12}$Be+$n$ and $^{12}$Be+$n$+$n$ systems to be reconstructed. In the case of the breakup of $^{15}$B, a very narrow structure at threshold was observed in the $^{12}$Be+$n$ channel. Contrary to earlier stable beam fragmentation studies which identified this as a strongly interacting $s$-wave virtual state in $^{13}$Be, analysis here of the $^{12}$Be+$n$+$n$ events demonstrated that this was an artifact resulting from the sequential-decay of the $^{14}$Be(2$^+$) state. Single-proton removal from $^{14}$B was found to populate a broad low-lying structure some 0.70 MeV above the neutron-decay threshold in addition to a less prominent feature at around 2.4 MeV. Based on the selectivity of the reaction and a comparison with (0-3)$\hbar\omega$ shell-model calculations, the low-lying structure is concluded to most probably arise from closely spaced J$^\pi$=1/2$^+$ and 5/2$^+$ resonances (E$_r$=0.40$\pm$0.03 and 0.85$^{+0.15}_{-0.11}$ MeV), whilst the broad higher-lying feature is a second 5/2$^+$ level (E$_r$=2.35$\pm$0.14 MeV). Taken in conjunction with earlier studies, it would appear that the lowest 1/2$^+$ and 1/2$^-$ levels lie relatively close together below 1 MeV.Comment: 14 pages, 13 figures, 2 tables. Accepted for publication in Physical Review

The magic nature of 132Sn explored through the single-particle states of 133Sn

Atomic nuclei have a shell structure where nuclei with 'magic numbers' of neutrons and protons are analogous to the noble gases in atomic physics. Only ten nuclei with the standard magic numbers of both neutrons and protons have so far been observed. The nuclear shell model is founded on the precept that neutrons and protons can move as independent particles in orbitals with discrete quantum numbers, subject to a mean field generated by all the other nucleons. Knowledge of the properties of single-particle states outside nuclear shell closures in exotic nuclei is important for a fundamental understanding of nuclear structure and nucleosynthesis (for example the r-process, which is responsible for the production of about half of the heavy elements). However, as a result of their short lifetimes, there is a paucity of knowledge about the nature of single-particle states outside exotic doubly magic nuclei. Here we measure the single-particle character of the levels in 133Sn that lie outside the double shell closure present at the short-lived nucleus 132Sn. We use an inverse kinematics technique that involves the transfer of a single nucleon to the nucleus. The purity of the measured single-particle states clearly illustrates the magic nature of 132Sn.Comment: 19 pages, 5 figures and 4 table