Design and fabrication of a precision alignment system and package for a two-photon fluorescence imaging device

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaf 24).A compact, lightweight precision alignment system and package for an endomicroscope was designed and fabricated. The endomicroscope will consist of a millimeter-scale fiber resonator and a two-axis silicon optical bench. The alignment system provided five degrees of freedom and was designed to align the fiber resonator with the microchip with a resolution of one micron. The alignment system consisted of a system of ultra-fine screws and two compliant mechanisms to deamplify the motion of the screw. Finite element analysis was performed to optimize the compliant mechanisms for the desired transmission ratio of 20:1. The alignment system was fabricated and testing showed that the transmission ratios were lower than expected (18.6 for one compliant mechanism and 2.68 for the other). Testing also showed that the alignment system met the functional requirements for the ranges of motion.by Jean H. Chang.S.B

Semi-supervised linear spectral unmixing using a hierarchical Bayesian model for hyperspectral imagery

This paper proposes a hierarchical Bayesian model that can be used for semi-supervised hyperspectral image unmixing. The model assumes that the pixel reflectances result from linear combinations of pure component spectra contaminated by an additive Gaussian noise. The abundance parameters appearing in this model satisfy positivity and additivity constraints. These constraints are naturally expressed in a Bayesian context by using appropriate abundance prior distributions. The posterior distributions of the unknown model parameters are then derived. A Gibbs sampler allows one to draw samples distributed according to the posteriors of interest and to estimate the unknown abundances. An extension of the algorithm is finally studied for mixtures with unknown numbers of spectral components belonging to a know library. The performance of the different unmixing strategies is evaluated via simulations conducted on synthetic and real data

In-vitro toxoplasmacidal activity of cationic electron carriers

Exposing murine macrophages infected th the protozoan parasite Toxoplasma gondii to micromolar concentrations of some cationic electron carriers (dyes), resulted in complete killing of the intracellular parasites at concentrations at which these compounds did not seem toxic for the macrophages. The 50% inhibitory concentrations (with 95% confidence limits) were calculated as 0·26 (0·18-0·37), 1·35 (1-2·25), 0·45 (0·13-1·50), and 1·52 (0·91-2·53) μM for crystal violet, phenazine methosulphate, methylene blue and brilliant cresyl blue, respectively. The effects of these electron carriers did not appear to be the result of an enhancement of the natural antitoxoplasmic activity of the macrophages. None of the tested compounds was active against extracellular Tox. gondii as measured by ability to reinfect murine macrophages; thus, these dyes seem to act primarily on actively metabolizing, intracellular, Tox. gondii. Our data also suggest that the killing effect of the electron carriers was not related to the generation of reactive oxygen intermediates as judged by the inability of scavengers of these intermediates to block the activity against intracellular Tox. gondii. Further studies with related redox compounds would have an interesting chemotherapeutic perspective for treating toxoplasma infection

Late Cenozoic metamorphic evolution and exhumation of Taiwan

The Taiwan mountain belt is composed of a Cenozoic slate belt (Hsuehshan Range units, HR, and Backbone Slates, BS) and of accreted polymetamorphic basement rocks (Tananao Complex, TC). Ongoing crustal shortening has resulted from the collision between the Chinese continental margin and the Luzon volcanic arc, which initiated ~6.5 Ma ago. The grade and age of metamorphism and exhumation are a key record of the development of the orogenic wedge. Because the Taiwan mountain belt is mostly composed by accreted sediments lacking metamorphic index minerals, quantitative constraints on metamorphism are sparse. By contrast, these rocks are rich in carbonaceaous material (CM) and are therefore particularly appropriate for RSCM (Raman Spectroscopy of CM) thermometry. We apply this technique in addition to (U-Th)/He thermochronology on detrital zircons to assess peak metamorphic temperatures (T) and the late exhumational history respectively, along different transects in central and southern Taiwan. In the case of the HR units, we find evidence for high metamorphic T of at least 340°–350°C and locally up to 475°C, and for relative rapid exhumation with zircon (U-Th)/He ages in the range of 1.5–2 Ma. Farther east, the BS were only slightly metamorphosed (T < 330 °C), and zircons are not reset for (U-Th)/He. From the eastern BS to the inner TC schists, T gradually increases from ~350°C up to ~500°C following an inverted metamorphic gradient. Available geochronological constraints and the continuous thermal gradient from the BS to the basement rocks of the TC suggest that the high RSCM T of the TC were most probably acquired during the last orogeny, and were not inherited from a previous thermal event. Zircons yield (U-Th)/He ages of ~0.5–1.2 Ma. Peak metamorphic T and the timing of exhumation do not show along-strike variations over the TC in the studied area. In contrast, exhumation is laterally diachronous and decreases southward in the case of the HR units. In particular, our data imply that the HR units have been exhumed by a minimum of 15 km over the last few Ma. In the case of the BS, they show far less cumulated exhumation and much slower cooling rates. We propose that most of the deformation and exhumation of the Taiwan mountain belt is sustained through two underplating windows located beneath the Hsuehshan Range and the TC. Our data show significant departures from the predictions of the prevailing model in Taiwan, which assumes a homogeneous critical wedge with dominant frontal accretion. Our study sheds new light on how the mountain belt has grown as a possible result of underplating mostly

Character decomposition of Potts model partition functions. II. Toroidal geometry

We extend our combinatorial approach of decomposing the partition function of the Potts model on finite two-dimensional lattices of size L x N to the case of toroidal boundary conditions. The elementary quantities in this decomposition are characters K\_{l,D} labelled by a number of bridges l=0,1,...,L and an irreducible representation D of the symmetric group S\_l. We develop an operational method of determining the amplitudes of the eigenvalues as well as some of their degeneracies.Comment: 27 pages, 4 figure

Complex-temperature phase diagram of Potts and RSOS models

We study the phase diagram of Q-state Potts models, for Q=4 cos^2(PI/p) a Beraha number (p>2 integer), in the complex-temperature plane. The models are defined on L x N strips of the square or triangular lattice, with boundary conditions on the Potts spins that are periodic in the longitudinal (N) direction and free or fixed in the transverse (L) direction. The relevant partition functions can then be computed as sums over partition functions of an A\_{p-1} type RSOS model, thus making contact with the theory of quantum groups. We compute the accumulation sets, as N -> infinity, of partition function zeros for p=4,5,6,infinity and L=2,3,4 and study selected features for p>6 and/or L>4. This information enables us to formulate several conjectures about the thermodynamic limit, L -> infinity, of these accumulation sets. The resulting phase diagrams are quite different from those of the generic case (irrational p). For free transverse boundary conditions, the partition function zeros are found to be dense in large parts of the complex plane, even for the Ising model (p=4). We show how this feature is modified by taking fixed transverse boundary conditions.Comment: 60 pages, 16 figures, 2 table

The neuronal mechanisms underlying locomotion termination

It is critical for animals to be able to stop locomotion according to their external and internal needs. Limited studies show there are dedicated neuronal pathways responding to either sensory inputs or commands from higher brain areas to inhibit the locomotor circuit and actively terminate locomotion. Such neuronal mechanisms are clearly demonstrated by the quick ending of ongoing locomotor rhythms following the activation of “stop” cells in the brainstem. In contrast, some activity-dependent mechanisms intrinsic to the locomotor neuronal network are responsible for the spontaneous ending of locomotor episodes. Known autonomous mechanisms involve the release/accumulative production of adenosine or the mediation of long-lasting hyperpolarisation by Na+ pumps following locomotion. We discuss some recent studies that have led to these findings.PostprintPeer reviewe