Picture-Hanging Puzzles

We show how to hang a picture by wrapping rope around n nails, making a polynomial number of twists, such that the picture falls whenever any k out of the n nails get removed, and the picture remains hanging when fewer than k nails get removed. This construction makes for some fun mathematical magic performances. More generally, we characterize the possible Boolean functions characterizing when the picture falls in terms of which nails get removed as all monotone Boolean functions. This construction requires an exponential number of twists in the worst case, but exponential complexity is almost always necessary for general functions.Comment: 18 pages, 8 figures, 11 puzzles. Journal version of FUN 2012 pape

Net Gain: Seeking better outcomes for local people when mitigating biodiversity loss from development

Economic development projects are increasingly applying the mitigation hierarchy to achieve No Net Loss, or even a Net Gain, of biodiversity. Because people value biodiversity and ecosystem services, this can affect the wellbeing of local people, however these types of social impacts from development receive limited consideration. We present ethical, practical and regulatory reasons why development projects applying the mitigation hierarchy should consider related social impacts. We highlight risks to local wellbeing where projects restrict access to biodiversity and ecosystem services in biodiversity offsets. We then present a framework laying out challenges and associated opportunities for delivering better biodiversity and local wellbeing outcomes. Greater coordination between social and biodiversity experts, and early and effective integration of local people in the process, will ensure that efforts to reduce the negative impacts of development on biodiversity can contribute to, rather than detract from, local people’s wellbeing

Agrobiodiversity and climate change: what do students need to know?

Key note paper presented at 2nd ANAFE International Symposium: ‘Mainstreaming climate change into agricultural education: tools, experiences and challenges’, Malawi, 2008. The paper informs that adaptation of production systems to climate change requires human capacity in agricultural biodiversity but a 2007 survey in African universities showed that education in this area is weak or absent. The authors argue that role of agricultural biodiversity in adaptation to climate change should be better understood, and that universities should seek to develop such competencies in their students. Universities should review curricula to include agricultural biodiversity dimensions through innovative, experiential teaching methods and active student participation

Inkjet-based biopatterning of bone morphogenetic protein-2 to spatially control calvarial bone formation

The purpose of this study was to demonstrate spatial control of osteoblast differentiation in vitro and bone formation in vivo using inkjet bioprinting technology and to create three-dimensional persistent bio-ink patterns of bone morphogenetic protein-2 (BMP-2) and its modifiers immobilized within microporous scaffolds. Semicircular patterns of BMP-2 were printed within circular DermaMatrix™ human allograft scaffold constructs. The contralateral halves of the constructs were unprinted or printed with BMP-2 modifiers, including the BMP-2 inhibitor, noggin. Printed bio-ink pattern retention was validated using fluorescent or 125I-labeled bio-inks. Mouse C2C12 progenitor cells cultured on patterned constructs differentiated in a dose-dependent fashion toward an osteoblastic fate in register to BMP-2 patterns. The fidelity of spatial restriction of osteoblastic differentiation at the boundary between neighboring BMP-2 and noggin patterns improved in comparison with patterns without noggin. Acellular DermaMatrix constructs similarly patterned with BMP-2 and noggin were then implanted into a mouse calvarial defect model. Patterns of bone formation in vivo were comparable with patterned responses of osteoblastic differentiation in vitro. These results demonstrate that three-dimensional biopatterning of a growth factor and growth factor modifier within a construct can direct cell differentiation in vitro and tissue formation in vivo in register to printed patterns. © 2010 Mary Ann Liebert, Inc

Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV

We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive Pi0 production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV. The cross section was measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be in good agreement with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T < 11 GeV/c and excludes a maximal positive gluon polarization in the proton. The mean transverse momentum fraction of Pi0's in their parent jets was found to be around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC