160,423 research outputs found
Global hydrodynamic analysis of the molecular flexibility of galactomannans
In the past, intrinsic viscosity and sedimentation velocity analyses have been used separately to assess the conformation and flexibility of guar and locust bean gum galactomannans based on worm-like chain and semi-flexible coil models. Publication of a new global method combining data sets of both intrinsic viscosity and sedimentation coefficient with molecular weight, and minimising a target (error) function now permits a more robust analysis. Using this approach, values for the persistence length of (10 ± 2) nm for guar and (7 ± 1) nm for locust bean gum are returned if the mass per unit length ML is floated as a variable. Using a fixed mass per unit length based on the known compositional data of each galactomannan yields a similar value for Lp in both cases, (8 ± 1) nm for guar and (9 ± 1) nm for locust bean gum, with combined set of data yielding (9 ± 1) nm: within experimental error the flexibilities of both galactomannans are very similar. © 2007 Elsevier Ltd. All rights reserved
Transformational leadership can improve workforce competencies.
Staffing problems can arise because of poor delegation skills or a failure by leaders to respond appropriately to economic factors and patient demographics. Training dilemmas, meanwhile, can arise because of managers' confusion about what constitutes 'training' and what constitutes 'education', and where responsibility of provision lies, with the consequence that they neglect these activities. This article uses Kouzes and Posner's (2009) transformational leadership model to show how managers can respond. Leaders who challenge budgets, consider new ways of working and engage effectively with the workforce can improve productivity and care, while those who invest in appropriate learning will have a highly trained workforce. The author explains how integration of leadership roles and management functions can lead to innovative problem solving
Nanopores of carbon nanotubes as practical hydrogen storage media
We report on hydrogen desorption mechanisms in the nanopores of multiwalled carbon nanotubes (MWCNTs). The as-grown MWCNTs show continuous walls that do not provide sites for hydrogen storage under ambient conditions. However, after treating the nanotubes with oxygen plasma to create nanopores in the MWCNTs, we observed the appearance of a new hydrogen desorption peak in the 300–350 K range. Furthermore, the calculations of density functional theory and molecular dynamics simulations confirmed that this peak could be attributed to the hydrogen that is physically adsorbed inside nanopores whose diameter is approximately 1 nm. Thus, we demonstrated that 1 nm nanopores in MWCNTs offer a promising route to hydrogen storage media for onboard practical applications
Mechanically stacked 1 nm thick carbon nanosheets: Ultrathin layered materials with tunable optical, chemical and electrical properties
Carbon nanosheets are mechanically stable free-standing two-dimensional
materials with a thickness of ~1 nm and well defined physical and chemical
properties. They are made by radiation induced cross-linking of aromatic
self-assembled monolayers. Here we present a route to the scalable fabrication
of multilayer nanosheets with tunable electrical, optical and chemical
properties on insulating substrates. Stacks up to five nanosheets with sizes of
~1 cm^2 on oxidized silicon were studied. Their optical characteristics were
investigated by visual inspection, optical microscopy, UV/Vis reflection
spectroscopy and model calculations. Their chemical composition was studied by
X-ray photoelectron spectroscopy. The multilayer samples were then annealed in
ultra high vacuum at various temperatures up to 1100 K. A subsequent
investigation by Raman, X-ray photoelectron and UV/Vis reflection spectroscopy
as well as by electrical four-point probe measurements demonstrates that the
layered nanosheets transform into nanocrystalline graphene. This structural and
chemical transformation is accompanied by changes in the optical properties and
electrical conductivity and opens up a new path for the fabrication of
ultrathin functional conductive coatings.Comment: 36 pages, 7 Figure
Strong mobility degradation in ideal graphene nanoribbons due to phonon scattering
We investigate the low-field phonon-limited mobility in armchair graphene
nanoribbons (GNRs) using full-band electron and phonon dispersion relations. We
show that lateral confinement suppresses the intrinsic mobility of GNRs to
values typical of common bulk semiconductors, and very far from the impressive
experiments on 2D graphene. Suspended GNRs with a width of 1 nm exhibit a
mobility close to 500 cm^2/Vs at room temperature, whereas if the same GNRs are
deposited on HfO2 mobility is further reduced to about 60 cm^2/Vs due to
surface phonons. We also show the occurrence of polaron formation, leading to
band gap renormalization of ~118 meV for 1 nm-wide armchair GNRs.Comment: 11 pages, 4 figure
A Coaxially Integrated Photonic Orbital Angular Momentum Beam Multiplexer
We demonstrate an integrated photonic orbital angular momentum beam multiplexer consisting of four nested arc waveguide gratings. Well-defined OAM mode emissions over wide bandwidth of 1-nm enables simultaneous wavelength division multiplexing and OAM multiplexing
Electron Emission from Diamondoids: A Diffusion Quantum Monte Carlo Study
We present density-functional theory (DFT) and quantum Monte Carlo (QMC)
calculations designed to resolve experimental and theoretical controversies
over the optical properties of H-terminated C nanoparticles (diamondoids). The
QMC results follow the trends of well-converged plane-wave DFT calculations for
the size dependence of the optical gap, but they predict gaps that are 1-2 eV
higher. They confirm that quantum confinement effects disappear in diamondoids
larger than 1 nm, which have gaps below that of bulk diamond. Our QMC
calculations predict a small exciton binding energy and a negative electron
affinity (NEA) for diamondoids up to 1 nm, resulting from the delocalized
nature of the lowest unoccupied molecular orbital. The NEA suggests a range of
possible applications of diamondoids as low-voltage electron emitters
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