Neutron irradiation of Am-241 effectively produces curium

Computer study was made on the production of multicurie amounts of highly alpha-active curium 242 from americium 241 irradiation. The information available includes curium 242 yields, curium composition, irradiation data, and production techniques and safeguards

How Modify the Curriculum To Benefit the Academically Talented Student?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66896/2/10.1177_019263656104526448.pd

Structure/activity relationships applied to the hydrogenation of α,β-unsaturated carbonyls: The hydrogenation of 3-butyne-2-one over alumina-supported palladium catalysts

The gas phase hydrogenation of 3-butyne-2-one, an alkynic ketone, over two alumina-supported palladium catalysts is investigated using infrared spectroscopy in a batch reactor at 373 K. The mean particle size of the palladium crystallites of the two catalysts are comparable (2.4 ± 0.1 nm). One catalyst (Pd(NO3)2/Al2O3) is prepared from a palladium(II) nitrate precursor, whereas the other catalyst (PdCl2/Al2O3) is prepared using palladium(II) chloride as the Pd precursor compound. A three-stage sequential process is observed with the Pd(NO3)2/Al2O3 catalyst facilitating complete reduction all the way through to 2-butanol. However, hydrogenation stops at 2-butanone with the PdCl2/Al2O3 catalyst. The inability of the PdCl2/Al2O3 catalyst to reduce 2-butanone is attributed to the inaccessibility of edge sites on this catalyst, which are blocked by chlorine retention originating from the catalyst’s preparative process. The reaction profiles observed for the hydrogenation of this alkynic ketone are consistent with the site-selective chemistry recently reported for the hydrogenation of crotonaldehyde, an alkenic aldehyde, over the same two catalysts. Thus, it is suggested that a previously postulated structure/activity relationship may be generic for the hydrogenation of α,β-unsaturated carbonyl compounds over supported Pd catalysts

Probing Pair-Correlated Fermionic Atoms through Correlations in Atom Shot Noise

Pair-correlated fermionic atoms are created through dissociation of weakly bound molecules near a magnetic-field Feshbach resonance. We show that correlations between atoms in different spin states can be detected using the atom shot noise in absorption images. Furthermore, using time-of-Flight imaging we have observed atom pair correlations in momentum space

Null Distribution Of The Likelihood Ratio Statistic For Feed-Forward Neural Networks

Despite recent publications exploring model complexity with modern regression methods, their dimensionality is rarely quantified in practice and the distributions of related test statistics are not well characterized. Through a simulation study, we describe the null distribution of the likelihood ratio statistic for several different feed-forward neural network models

Gravitational Waves: Just Plane Symmetry

We present some remarkable properties of the symmetry group for gravitational plane waves. Our main observation is that metrics with plane wave symmetry satisfy every system of generally covariant vacuum field equations except the Einstein equations. The proof uses the homothety admitted by metrics with plane wave symmetry and the scaling behavior of generally covariant field equations. We also discuss a mini-superspace description of spacetimes with plane wave symmetry.Comment: 10 pages, TeX, uses IOP style file

Complementary Lenses: Using Theories of Situativity and Complexity to Understand Collaborative Learning as Systems-Level Social Activity

This article highlights possibilities for understanding challenges related to collaborative learning by bringing two complementary lenses into theoretical and empirical conversation—complexity and situativity. After presenting a theoretical comparison that characterizes complementarity between complexity and situativity in order to frame their relative contributions to a systems-level understanding of learning processes, we examine persistently unproductive social activity during a 14-session, collaborative engineering design project in a fifth-grade peer group from both perspectives. We do so in order to demonstrate the value of these complementary perspectives for understanding collaborative learning processes and to suggest different explanations of why unproductive social activity sometimes persists and possibilities for interrupting such dynamics. We thus suggest a shift from explanatory accounts of system processes to prospective processes for systems of action within social ecologies of change. Such a framework can resolve the social activity of collaborative learning around a systems-level orientation

The tip of the iceberg: a giant pelvic atypical lipoma presenting as a sciatic hernia

BACKGROUND: This case report highlights two unusual surgical phenomena: lipoma-like well-differentiated liposarcomas and sciatic hernias. It illustrates the need to be aware that hernias may not always simply contain intra-abdominal viscera. CASE PRESENTATION: A 36 year old woman presented with an expanding, yet reducible, right gluteal mass, indicative of a sciatic hernia. However, magnetic resonance imaging demonstrated a large intra- and extra-pelvic fatty mass traversing the greater sciatic foramen. The tumour was surgically removed through an abdomino-perineal approach. Subsequent pathological examination revealed an atypical lipomatous tumour (synonym: lipoma-like well-differentiated liposarcoma). The patient remains free from recurrence two years following her surgery. CONCLUSION: The presence of a gluteal mass should always suggest the possibility of a sciatic hernia. However, in this case, the hernia consisted of an atypical lipoma spanning the greater sciatic foramen. Although lipoma-like well-differentiated liposarcomas have only a low potential for recurrence, the variable nature of fatty tumours demands that patients require regular clinical and radiological review