Energy transfer from an individual quantum dot to a carbon nanotube

A detailed understanding of energy transduction is crucial for achieving precise control of energy flow in complex, integrated systems. In this context, carbon nanotubes (CNTs) are intriguing model systems due to their rich, chirality-dependent electronic and optical properties. Here, we study the quenching of fluorescence from isolated quantum dots (QDs) upon approach of individual CNTs attached to atomic force microscope probes. Precision measurements of many different CNT/QD pairs reveal behavior consistent with resonant energy transfer between QD and CNT excitons via a Fohrster-like dipole-dipole coupling. The data reveal large variations in energy transfer length scales even though peak efficiencies are narrowly distributed around 96%. This saturation of efficiency is maintained even when energy transfer must compete with elevated intrinsic non-radiative relaxation rates during QD aging. These observations suggest that excitons can be created at different locations along the CNT length, thereby resulting in self-limiting behavior.Comment: 8 pages, 8 figures, with supplementary informatio

Implementing the Ahafo Benefit Agreements: Seeking Meaningful Community Participation at Newmont’s Ahafo Gold Mine in Ghana

In 2008, ten communities in the Brong Ahafo region of Ghana entered into agreements with Newmont Ghana to govern company-community relations, ensure local job creation, and share the benefits of the company’s mining operations. Ten years later, this report, co-authored by Canadian International Resources and Development Institute (CIRDI), African Center for Energy Policy (ACEP), CCSI, and ISP, looks at the communities’ experience of those agreements and suggests how the agreements might be improved. Though the agreements were celebrated for their attempts to include all stakeholders in decision-making, challenges remain around representation, consultation, and participation. New entities established to facilitate multi-stakeholder decision-making have led to the replication of existing power imbalances. And despite many improvements, the agreements have not fully stabilized company-community relations; tensions and grievances remain concerning employment, compensation, and resettlement, among other issues. The report makes research-informed recommendations for the communities, Newmont Ghana, and other stakeholders in the lead-up to the renegotiation of the agreements. While the negotiation of benefit agreements (sometimes called “Community Development Agreements”) have been the subject of wide-ranging research, academic literature on agreement implementation is still relatively sparse, and tends to focus on cases in Australia and Canada, with little information available from cases in low- or middle-income countries. This report therefore seeks to contribute to filling this gap, alongside other studies mentioned in the report. The report was published on July 25, 2018. On that day, ACEP presented the report and a Twi-translation of the executive summary to representatives and opinion leaders from the communities. ACEP also led a workshop both on the report and on benefit agreements more generally

Z boson decay to photon plus Kaluza-Klein graviton in large extra dimensions

In the large extra dimensional ADD scenario, Z bosons undergo a one-loop decay into a photon and Kaluza-Klein towers of gravitons/gravi-scalars. We calculate such a decay width, extending previous arguments about the general form of the four-dimensional on-shell amplitude. The amplitudes calculated are relevant to processes in other extra dimensional models where the Standard Model fields are confined to a 4-brane.Comment: 47 pages, uses feynmp for diagrams. v2: typographical corrections for letter-sized paper and to correct feynmf parsing error. v3: minor error in polarisation averaging and reference corrected. v4: reflects changes for published version; arithmetic error corrected and reference updated; section on transversality conditions not present in published version retaine

A Universal Method for Analysing Copolymer Growth

Polymers consisting of more than one type of monomer, known as copolymers, are vital to both living and synthetic systems. Copolymerisation has been studied theoretically in a number of contexts, often by considering a Markov process in which monomers are added or removed from the growing tip of a long copolymer. To date, the analysis of the most general models of this class has necessitated simulation. We present a general method for analysing such processes without resorting to simulation. Our method can be applied to models with an arbitrary network of sub-steps prior to addition or removal of a monomer, including non-equilibrium kinetic proofreading cycles. Moreover, the approach allows for a dependency of addition and removal reactions on the neighbouring site in the copolymer, and thermodynamically self-consistent models in which all steps are assumed to be microscopically reversible. Using our approach, thermodynamic quantities such as chemical work; kinetic quantities such as time taken to grow; and statistical quantities such as the distribution of monomer types in the growing copolymer can be derived either analytically or numerically directly from the model definition.Comment: 24 pages, 11 figure

High Harvest Yield, High Expansion, and Phenotype Stability of CD146 Mesenchymal Stromal Cells from Whole Primitive Human Umbilical Cord Tissue

Human umbilical cord blood is an excellent primitive source of noncontroversial stem cells for treatment of hematologic disorders; meanwhile, new stem cell candidates in the umbilical cord (UC) tissue could provide therapeutic cells for nonhematologic disorders. We show novel in situ characterization to identify and localize a panel of some markers expressed by mesenchymal stromal cells (MSCs; CD44, CD105, CD73, CD90) and CD146 in the UC. We describe enzymatic isolation and purification methods of different UC cell populations that do not require manual separation of the vessels and stroma of the coiled, helical-like UC tissue. Unique quantitation of in situ cell frequency and stromal cell counts upon harvest illustrate the potential to obtain high numerical yields with these methods. UC stromal cells can differentiate to the osteogenic and chondrogenic lineages and, under specific culturing conditions, they exhibit high expandability with unique long-term stability of their phenotype. The remarkable stability of the phenotype represents a novel finding for human MSCs, from any source, and supports the use of these cells as highly accessible stromal cells for both basic studies and potentially therapeutic applications such as allogeneic clinical use for musculoskeletal disorders

Overview and Guidance on Agile Development in Large Organizations

A continual debate surrounds the effectiveness of agile software development practices. Some organizations adopt agile practices to become more competitive, improve processes, and reduce costs. Other organizations are skeptical about whether agile development is beneficial. Large organizations face an additional challenge in integrating agile practices with existing standards and business processes. To examine the effects of agile development practices in large organizations, we review and integrate scientific literature and theory on agile software development. We further organize our theory and observations into a framework with guidelines for large organizations considering agile methodologies. Based on this framework, we present recommendations that suggest ways large organizations with established processes can successfully implement agile practices. Our analysis of the literature and theory provides new insight for researchers of agile software development and assists practitioners in determining how to adopt agile development in their organizations

Macroscopic Quantum Tunneling of Ferromagnetic Domain Walls

Quantum tunneling of domain walls out of an impurity potential in a mesoscopic ferromagnetic sample is investigated. Using improved expressions for the domain wall mass and for the pinning potential, we find that the cross-over temperature between thermal activation and quantum tunneling is of a different functional form than found previously. In materials like Ni or YIG, the crossover temperatures are around 5 mK. We also find that the WKB exponent is typically two orders of magnitude larger than current estimates. The sources for these discrepancies are discussed, and precise estimates for the transition from three-dimensional to one-dimensional magnetic behavior of a wire are given. The cross-over temperatures from thermal to quantum transitions and tunneling rates are calculated for various materials and sample sizes.Comment: 10 pages, 2 postscript figures, REVTe