Polarization spectroscopy of an excited state transition.

We demonstrate polarization spectroscopy of an excited state transition in room-temperature cesium vapor. An anisotropy induced by a circularly polarized pump beam on the D2 transition is observed using a weak probe on the 6P3/2→7S1/2 transition. At high pump power, a subfeature due to Autler-Townes splitting is observed that theoretical modeling shows is enhanced by Doppler averaging. Polarization spectroscopy provides a simple modulation–free signal suitable for laser frequency stabilization to excited state transitions

Functionalized Nanoporous Carbon Scaffolds for Hydrogen Storage Applications

Recent efforts have demonstrated confinement in porous scaffolds at the nanoscale can alter the hydrogen sorption properties of metal hydrides, though not to an extent feasible for use in onboard hydrogen storage applications, proposing the need for a method allowing further modifications. The work presented here explores how the functionalization of nanoporous carbon scaffold surfaces with heteroatoms can modify the hydrogen sorption properties of confined metal hydrides in relation to non-functionalized scaffolds (FS). Investigations of nanoconfined LiBH4and NaAlH4indicate functionalizing the carbon scaffold surface with nitrogen can shift the activation energy of hydrogen desorption in excess of 20 kJ/mol from the activation energy decrease of greater than or equal to 40 kJ/mol obtained from confinement in non-FS. XPS measurements indicate a significant fraction of the nitrogen contained in the carbon scaffolds is pyridinic, suggesting interactions of the available lone electron pair with the confined hydride and decomposition products strongly influences the hydrogen sorption processes. TPD experiments demonstrate nitrogen-FS can stabilize the release of diborane by ~30 °C, and kinetically stabilize LiBH4against decomposition to higher temperatures. Increased reorientational activation energies measured for the systems with nitrogen-FS using quasielastic neutron scattering support the observed stabilization of LiBH4is connected with the surface chemistry of the scaffold. Peak rates of hydrogen release occur at higher temperature from NaAlH4in nitrogen-FS despite the lower measured activation energy, indicating the existence of a rate-limiting step that may be related to the level of scaffold nitrogen doping and the onset of NaAlH4melting

Cooperative Non-Equilibrium Dynamics in a Thermal Rydberg Ensemble

This thesis reports the investigation of cooperative non-equilibrium dynamics in a thermal Rydberg ensemble. Cooperative behaviour arises due to resonant dipole-dipole interactions between highly excited Rydberg atoms. In order to transfer atomic population from the ground state to the Rydberg state in a caesium vapour, a three-photon excitation scheme is developed. This scheme has a number of benefits over traditional two-photon Rydberg excitation as each transition utilises in- expensive high-power diode lasers. The process of developing the excitation scheme produces a number of important results, including an excited-state polarisation spectroscopy technique and the observation of coherent three-photon electromagnetically induced transparency. The optical response and atomic dynamics of the interacting ensemble can be separated into two distinct phases. When the Rydberg number density is low and the interactions are negligible, the system can be described by the behaviour of a single atom. However, when the Rydberg number density is high, resonant dipole-dipole interactions result in a significant modification of the ensemble properties. This cooperative many-body phase cannot be described by the behaviour of a single atom. In the frequency domain, the interactions produce an excitation-dependent cooperative energy shift that is observed using probe transmission spectroscopy. In the time domain, the interactions result in a cooperative enhancement of the atomic decay rate that is analysed using fluorescence spectroscopy. At the transition between the single-body and many-body phase, a first-order non-equilibrium phase transition occurs. This is observed spatially along the length of the excitation region as a sharp switch in the emitted fluorescence. The first-order phase transition is also observed in the temporal response of the ensemble through critical slowing down. The divergence of the switching time to steady state follows a universal scaling law for phase transitions and the determined critical exponent is in excellent agreement with previous work on non-equilibrium phase transitions

Factors Affecting U.S. Trade and Shipments of Information Technology Products: Computer Equipment, Telecommunications Equipment, and Semiconductors

Despite a recent downturn, the information technology (IT) products sector experienced a tremendous expansion in trade and shipments during the last decade and became an increasingly important component of the U.S. economy. This expansion was driven by a variety of factors such as the globalization of IT production, constant technological innovation, rapid growth in worldwide consumption, and global trade liberalization. This working paper will examine these factors, providing particular attention to the computer equipment, telecommunications equipment, and semiconductor industries.International Development,

Development of a Computational Methodology for Evaluating In Vivo Vertebral Mechanics in Subjects Having Various Conditions of the Lumbar Spine

Treating and evaluating the causes of low back pain (LBP) is difficult and not fully understood. However, assessing the in vivo motions and loading characteristics in the lumbar spine may provide important data for progressing the diagnosis and treatment of pathologies linked with LBP. This dissertation describes the development of a comprehensive approach for collecting both the kinematics and kinetics of the lumbar vertebrae under in vivo conditions. Forty-four subjects representing healthy, symptomatic, pathological, and surgically implanted (pre- and post-operative) conditions of the lumbar spine were evaluated using dynamic fluoroscopy and 3D-to-2D image registration to assess the motions of the five lumbar vertebrae while patients performed an active flexion-extension, lateral flexion, and axial rotation of the spine. 3D kinematics were extracted describing the relative in-plane and coupled out-of-plane motions of the intervertebral joints. A computational methodology was then utilized for the development of a multi-body, inverse mathematical model based on principles from Kane’s dynamics. The kinematics, as well as patient-specific bone geometries, recreated from CT, and ground reaction forces, collected using force plates, served as inputs to the model. Vertebral bones were defined as rigid bodies, while massless frames represented non-specific bone geometries for the lower body, torso and abdominal wall. Soft tissue attachment sites were selected on the vertebral bones allowing for ligaments to be defined for constraint and modeled as linear springs. Relevant muscle groups were also included and solved for using the pseudo-inverse algorithm, which enabled for decoupling of the derived resultant torques and ultimately defined the kinetic trajectory for the muscles. These methodologies allowed for the theoretical modeling of the entire lumbar region and prediction of joint reaction contact forces, ligament constraint forces, and applied musculotendon forces. Results from the model were validated for the prescribed motions using experimental loading data measured directly using telemetrized vertebral implants and intervertebral disc pressure sensors. A comparative analysis of the predicted forces from the model with experimentally collected data showed good agreement in the force profiles and an average combined error around 6.9%. This demonstrated the use of this methodology for in vivo analyses of the lumbar spine

EMSoD — A conceptual social framework that delivers KM values to corporate organizations

As social software is becoming increasingly disruptive to organizational structures and processes, Knowledge Management (KM) initiatives that have hitherto taken the form of a ‘knowledge repository’ now need redefining. With the emergence of Social Media (SM) platforms like Twitter, the hierarchical boundaries within the organization are broken down and a lateral flow of information is created. This has created a peculiar kind of tension between KM and SM, in which one is perceived as threatening the continued relevance of the other. Particularly, with the advances of social media and social software, KM is more in need of delivering measurable value to corporate organizations, if it is to remain relevant in the strategic planning and positioning of organizations. In view of this, this paper presents EMSoD — Enterprise Mobility and Social Data — a conceptual social framework which mediates between KM and SM to deliver actionable knowledge and employee engagement. Meanwhile, given that the main objective of this research is in the delivery of KM value to corporate organizations, this paper devises some mechanisms for measuring actionable knowledge and employee engagement, both as parameters of KM value