Measurements of atmospheric trace gases using open path differential UV absorption spectroscopy for urban pollution monitoring

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Investigation of electrospun fibrous scaffolds, locally delivered anti-inflammatory drugs, and neural stem cells for promoting nerve regeneration

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 79-82).The organization and intricacy of the central and peripheral nervous systems pose special criteria for the selection of a suitable scaffold to aid in regeneration. The scaffold must have sufficient mechanical strength while providing an intricate network of passageways for axons, Schwann cells, oligodendrocytes, and other neuroglia to populate. If neural regeneration is to occur, these intricate passageways must not be impeded by macrophages, neutrophils, or other inflammatory cells. Therefore it is imperative that the scaffold does not illicit a severe immune response. Biodegradable electrospun fibers are an appealing material for tissue engineering scaffolds, as they strongly resemble the morphology of extracellular matrix. In this study, electrospun fibers composed of poly(L-lactic acid) (PLLA) and polycaprolactone (PCL) were prepared with and without the steroid anti-inflammatory drug, dexamethasone, encapsulated. Histological analysis of harvested subcutaneous implants demonstrated the PLLA fibers encapsulating dexamethasone (PLLA/dex fibers) evoked a much less severe immune response than any other fiber. These findings were supported by in vitro drug release data showing a controlled release of dexamethasone from the PLLA/dex fibers and a burst release from the PCL/dex fibers. The ability of the PLLA/dex fibers to evade an immune response provides a very powerful tool for fabricating tissue engineering scaffolds, especially when the stringent demands of a neural tissue engineering scaffold are considered. Structural support and contact guidance are crucial for promoting peripheral nerve regeneration. A method to fabricate peripheral nerve guide conduits with luminal, axially aligned, electrospun fibers is described and implemented in this study. The method includes the functionalization of the fibers with the axonal outgrowth promoting protein, laminin, to further enhance regeneration. The implantation of stem cells at the. site of a spinal cord or peripheral nerve lesion has been shown to promote nerve regeneration. Preliminary work to isolate and culture pluripotent, adult neural stem cells for seeding on the above mentioned scaffold is also described here.by Nathaniel Vacanti.S.M

Acceptability and Feasibility of Virtual Reality to Promote Health Literacy in Primary Care from the Health Professional’s view: A Qualitative Study

ObjectiveThe development of health literacy is important in the management of chronic pain and virtual reality may be an effective medium for its development. This study aims to understand the usability and acceptability of a virtual reality-based pain education system for the facilitation of health literacy.MethodsSemi-structured interviews were conducted with health professionals who had used a VR-based pain education system within their clinical practice, to explore perceptions of feasibility. Data collection and analyses were informed by the Unified Theory of Acceptance and Use of Technology and the Integrated Model of Health Literacy.ResultsFrom 10 participants, the VR-based system was considered feasible in providing immersive experiential learning which addressed patient understanding and health-related communication.ConclusionVR appears to be perceived as an acceptable and feasible technology to support the development of health literacy in people with chronic pain. Its largest perceived benefit was its capacity to provide an immersive and entertaining alternative to conventional methods of pain education.Practice ImplicationsVirtual reality is considered as a feasible method of facilitating patient understanding and health-related communication related to chronic pain. Feasibility of such a tool relies clinically on time available, social expectations of VR, and the role of immersive and experiential learning within the management of chronic pain

Twisted Nano-optics: Manipulating Light at the Nanoscale with Twisted Phonon Polaritonic Slabs

Recent discoveries have shown that when two layers of van der Waals (vdW) materials are superimposed with a relative twist angle between their respective in-plane principal axes, the electronic properties of the coupled system can be dramatically altered. Here, we demonstrate that a similar concept can be extended to the optics realm, particularly to propagating polaritons, hybrid light-matter interactions. To do this, we fabricate stacks composed of two twisted slabs of a polar vdW crystal (MoO3) supporting low-loss anisotropic phonon polaritons (PhPs), and image the propagation of the latter when launched by localized sources (metal antennas). Our images reveal that under a critical angle the PhPs isofrequency curve (determining the PhPs momentum at a fixed frequency) undergoes a topological transition. Remarkably, at this angle, the propagation of PhPs is strongly guided along predetermined directions (canalization regime) with no geometrical spreading (diffraction-less). These results demonstrate a new degree of freedom (twist angle) for controlling the propagation of polaritons at the nanoscale with potential for nano-imaging, (bio)-sensing, quantum applications and heat management

Hepatic encephalopathy: a neurochemical, neuroanatomical, and neuropsychological study.

Hepatic encephalopathy (HE) is normally diagnosed by neuropsychological (NP) tests, which are not very specific and do not reveal the underlying pathology. Magnetic resonance imaging (MRI) and spectroscopy (MRS) of the brain offer alternative and possibly more specific markers for HE. These methods were applied in conjunction with NP testing in order to determine their usefulness in the identification of HE and to understand the pathogenesis of HE more clearly. MR imaging and spectroscopy examinations, in addition to a battery of 15 NP tests, were administered to investigate 31 patients awaiting liver transplantation and 23 healthy controls. MR image intensities from the globus pallidus region were calculated and normalized to those of the thalamus. Absolute concentrations and ratios with respect to creatine (Cr) of several metabolites were computed from MR spectra. The MR data were correlated with the results of NP tests. The patients showed impairment in NP tests of attention and visuospatial and verbal fluency. In T1-weighted MRI, the relative intensity of the globus pallidus with respect to that of the thalamus region was significantly elevated in patients and correlated(negatively) with three NP tests (Hooper, FAS, and Trails B). The absolute concentrations of myo-inositol (mI) and choline (Ch) were significantly reduced in three brain regions. In addition, the absolute concentrations of glutamine (Gln) and combined glutamate and glutamine (Glx) were increased in all three locations, with Gln increase being significant in all areas while that of Glx only in the occipital white matter. In summary, this study partially confirms a hypothesized mechanism of HE pathogenesis, an increased synthesis of glutamine by brain glutamate in astrocytes due to excessive blood ammonia, followed by a compensatory loss of myo-inositol to maintain astrocyte volume homeostasis. It also indicates that the hyperintensity observed in globus pallidus could be used as complementary to the NP test scores in evaluating the mental health of HE patients

Higher-Order Methods for Hamiltonian Engineering Pulse Sequence Design

We introduce a framework for designing Hamiltonian engineering pulse sequences that systematically accounts for the effects of higher-order contributions to the Floquet-Magnus expansion. Our techniques result in simple, intuitive decoupling rules, despite the higher-order contributions naively involving complicated, non-local-in-time commutators. We illustrate how these rules can be used to efficiently design improved Hamiltonian engineering pulse sequences for a wide variety of tasks, such as dynamical decoupling, quantum sensing, and quantum simulation.Comment: 12+10 pages, 6 figures, see accompanying paper "Robust Higher-Order Hamiltonian Engineering for Quantum Sensing with Strongly Interacting Systems" for application of these techniques to quantum sensin