Slip avalanches in crystal plasticity: scaling of the avalanche cutoff

Plastic deformation of crystals proceeds through a sequence of intermittent slip avalanches with scale-free (power-law) size distribution. On macroscopic scales, however, plastic flow is known to be smooth and homogeneous. In the present letter we use a recently proposed continuum model of slip avalanches to systematically investigate the nature of the cut-off which truncates scale-free behavior at large avalanche sizes. The dependence of the cut-off on system size, geometry, and driving mode, but also on intrinsic parameters such as the strain hardening rate is established. Implications for the observability of avalanche behavior in microscopic and macroscopic samples are discussed.Comment: 12 pages, 4 figure

Relativistic study of the nuclear anapole moment effects in diatomic molecules

Nuclear-spin-dependent (NSD) parity violating effects are studied for a number of diatomic molecules using relativistic Hartree-Fock and density functional theory and accounting for core polarization effects. Heavy diatomic molecules are good candidates for the successful measurement of the nuclear anapole moment, which is the dominant NSD parity violation term in heavy elements. Improved results for the molecules studied in our previous publication [Borschevsky et al., Phys. Rev. A 85, 052509 (2012)] are presented along with the calculations for a number of new promising candidates for the nuclear anapole measurements.Comment: 7 pages, 1 figure. arXiv admin note: substantial text overlap with arXiv:1209.4282, arXiv:1201.058

The Role of the Chief Instructional Officer within the California Community Colleges

California community colleges enroll one out of ten public college students in the United States. The Chief Instructional Officer (CIO) serves as leader within each college. Research examining CIOs in California is limited. This study investigates work performed by CIOs and the organizational factors which support or impede that work. Four questions guided this study. What is the role of the CIO—what do they do? What are the organizational factors which support or impede CIO effectiveness? How do the CIOs influence the enhancement of learning and instruction? What changes would CIOs suggest to become more effective leaders? This study relied upon interviews, literature review and job descriptions to answer these questions. California CIOs define their responsibilities similarly to CIOs in national studies. CIOs in California work within a mandated system of shared governance. CIOs working in shared governance experience benefits and frustrations from a slow decision making process. Budgets are uncertain and inequitable thus inhibiting planning. According to these CIOs, advocacy for community colleges is hindered by an ineffectual Chancellor\u27s Office. California CIOs have had little influence over policy and support strengthening their organizational influence. These CIOs affirm the central importance of communication skills. The ability to be persuasive and to possess interpersonal communication skills were linked to leadership. Effective persuasion requires honesty, integrity, and trustworthiness. These attributes are enhanced when CIOs build relationships with school personnel. Good relationships enhance authority and paradoxically the exercise of authority diminishes influence. Besides possessing good “people skills,” leadership requires the ability to “add value” in problem solving, that is, to be knowledgeable about community colleges and to share that information. Adding value and being able to plan for the future are leadership traits identified by the CIOs. California CIOs believe a philosophical shift emphasizing learning over instruction is occurring. This change is reflected in accreditation standards emphasizing assessment of learning. It is too soon to know the impact of this emphasis on learning and whether it will make significant differences in improving student success, but CIOs believe they have made changes and are responding to the new emphasis on learning

Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne

In the catalytic addition of water to propyne the Au(III) catalyst is not stable under non-relativistic conditions and dissociates into a Au(I) compound and Cl2. This implies that one link in the chain of events in the catalytic cycle is broken and relativity may well be seen as the reason why Au(III) compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl

Strain bursts in plastically deforming Molybdenum micro- and nanopillars

Plastic deformation of micron and sub-micron scale specimens is characterized by intermittent sequences of large strain bursts (dislocation avalanches) which are separated by regions of near-elastic loading. In the present investigation we perform a statistical characterization of strain bursts observed in stress-controlled compressive deformation of monocrystalline Molybdenum micropillars. We characterize the bursts in terms of the associated elongation increments and peak deformation rates, and demonstrate that these quantities follow power-law distributions that do not depend on specimen orientation or stress rate. We also investigate the statistics of stress increments in between the bursts, which are found to be Weibull distributed and exhibit a characteristic size effect. We discuss our findings in view of observations of deformation bursts in other materials, such as face-centered cubic and hexagonal metals.Comment: 14 pages, 8 figures, submitted to Phil Ma

The convergence of the ab-initio many-body expansion for the cohesive energy of solid mercury

A many-body expansion for mercury clusters of the form E = \sum_{i<j}\Delta \epsilon_{ij} + \sum_{i<j<k}\Delta \epsilon_{ijk} + ... \quad, does not converge smoothly with increasing cluster size towards the solid state. Even for smaller cluster sizes (up to n=6), where van der Waals forces still dominate, one observes bad convergence behaviour. For solid mercury the convergence of the many-body expansion can dramatically be improved by an incremental procedure within an embedded cluster approach. Here one adds the coupled cluster many-body electron correlation contributions of the embedded cluster to the bulk HF energy. In this way we obtain a cohesive energy (not corrected for zero-point vibration) of 0.79 eV in perfect agreement with the experimental value.Comment: 10 pages, 3 figures, accepted PR

Identification of the slow E3 transition 136mCs -> 136Cs with conversion electrons

We performed at ISOLDE the spectroscopy of the decay of the 8- isomer in 136Cs by and conversion-electron detection. For the first time the excitation energy of the isomer and the multipolarity of its decay have been measured. The half-life of the isomeric state was remeasured to T1/2 = 17.5(2) s. This isomer decays via a very slow 518 keV E3 transition to the ground state. In addition to this, a much weaker decay branch via a 413 keV M4 and a subsequent 105 keV E2 transition has been found. Thus we have found a new level at 105 keV with spin 4+ between the isomeric and the ground state. The results are discussed in comparison to shell model calculations.Comment: Phys. Rev. C accepted for publicatio