Methane cracking on single-wall carbon nanotubes studied by semi-empirical tight binding simulations

The catalytic properties of thermally distorted single wall carbon nanotubes for the methane dissociation reaction have been investigated in the framework of semi-empirical tight-binding molecular dynamics, electronic structure and total energy calculations. It is shown that, if methane molecules and the nanotube are allowed to get closer than the equilibrium physi-sorption distance, the next dissociation reaction step is characterized by a small enthalpy change. Moreover the reactivity hierarchy of the various carbon nanotubes considered is related to the electronic density of states originating from the axial components of the atomic orbitals.     

Dynamics of four-photon photoluminescence in gold nanoantennas

Two-pulse correlation is employed to investigate the temporal dynamics of both two-photon photoluminescence (2PPL) and four-photon photoluminescence (4PPL) in resonant and nonresonant nanoantennas excited at a wavelength of 800 nm. Both 2PPL and 4PPL data are consistent with the same two-step model already established for 2PPL, implying that the first excitation step in 4PPL is a three-photon sp → sp direct interband transition. Considering energy and parity conservation, we also explain why 4PPL behavior is favored over, for example, three- and five-photon photoluminescence in the power range below the damage threshold of our antennas. Since sizable 4PPL requires larger peak intensities of the local field, we are able to select either 2PPL or 4PPL in the same gold nanoantennas by choosing a suitable laser pulse duration. We thus provide a first consistent model for the understanding of multiphoton photoluminescence generation in gold nanoantennas, opening new perspectives for applications ranging from the characterization of plasmonic resonances to biomedical imaging.     

Skin breakdown in children and high-frequency oscillatory ventilation

OBJECTIVE: To investigate the relationship of high-frequency oscillatory ventilation (HFOV) to skin breakdown on the scalp and ears in mechanically ventilated children. STUDY DESIGN: Retrospective cohort study of 32 patients supported with HFOV paired with 32 patients supported with conventional mechanical ventilation (CV) in a pediatric intensive care unit (PICU). RESULTS: By univariate analysis, more HFOV patients had skin breakdown than did the CV patients (53% vs 12.5%, p=.001); HFOV patients also had greater severity of illness (Pediatric Risk of Mortality scores), higher mortality, and longer durations of neuromuscular blockade, low systolic blood pressure, and time exposed to risk. Life table analysis demonstrated no difference in the rate of skin breakdown between HFOV and CV patients. Multifactorial analysis showed that only PICU time at risk was a risk factor for skin breakdown. CONCLUSIONS: HFOV was not an independent risk factor for the development of skin breakdown. PICU time at risk was the sole risk factor for the development of skin breakdown in all mechanically ventilated patients in the PICU.     

The neuroscientific foundations of the exploration?exploitation dilemma.

What are the origins of the ability to continuously explore novel domains of activity while at the same time exploiting the current knowledge base with increasing efficacy? The conflicting objectives of exploration and exploitation compete for scarce resources, among which managerial attention is possibly the most critical. This paper integrates recent findings on the neuromodulation of attention to provide a foundational step in understanding how the mind of the manager handles the exploration?exploitation dilemma. Also, this paper proposes several possible ways to combine research in neuroscience, psychology, and management to advance our knowledge of the microfoundations of managerial decision-making. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A bio‐inspired approach for regulating and measuring visco‐elastic properties of a robot arm

This work focuses on interaction control of robot manipulators in unstructured environments, with special regard for situations of unpredictable contact/noncontact transitions. It is basically addressed to those environments where a high level of robot adaptability is required and no information on the geometry of the environment is available. By pointing out the main limitations of standard interaction control schemes in managing situations of contact/noncontact transitions, this paper proposes a new control solution that is inspired by the biological model of motor control in voluntary movements. It consists of a combination of a feedforward loop and a proportional‐derivative plus gravity compensation control in the feedback loop. The control law is named coactivation‐based compliance control in the joint space since a unique function, called coactivation function, is evaluated for regulating robot visco‐elasticity in an unpredictably variable environment. It resumes the mechanism of adjustable visco‐elastic properties acting on the agonist and antagonist muscles of a human arm. The work also proposes a methodology for evaluating performance of interaction control schemes that is based on stiffness graphical representation through ellipses. The method replicates the experimental setup used in neuroscience to measure stiffness in human limbs. It is regarded as a powerful tool for evaluating robot behavior over space and time, since it allows both a visual representation of stiffness variation during motion and a quantitative measure of robot performance. It is shown how the method can be used to evaluate a control scheme and how it can provide indications to improve a control law. In this paper, an application to the standard compliance control in the joint space and the coactivation‐based compliance control is presented. © 2005 Wiley Periodicals, Inc.