A Volume Clearing Algorithm for Muon Tomography

The primary objective is to enhance muon-tomographic image reconstruction capability by providing distinctive information in terms of deciding on the properties of regions or voxels within a probed volume "V" during any point of scanning: threat type, non-threat type, or not-sufficient data. An algorithm (MTclear) is being developed to ray-trace muon tracks and count how many straight tracks are passing through a voxel. If a voxel "v" has sufficient number of straight tracks (t), then "v" is a non-threat type voxel, unless there are sufficient number of scattering points (p) in "v" that will make it a threat-type voxel. The algorithm also keeps track of voxels for which not enough information is known: where p and v both fall below their respective threshold parameters. We present preliminary results showing how the algorithm works on data collected with a Muon Tomography station based on gas electron multipliers operated by our group. The MTclear algorithm provides more comprehensive information to a human operator or to a decision algorithm than that provided by conventional muon-tomographic reconstruction algorithms, in terms of qualitatively determining the threat possibility from a probed volume. This is quite important because only low numbers of cosmic ray source muons are typically available in nature for tomography, while a quick determination of threats is essential.Comment: 3 pages, 3 figures, submitted to conf. record of 2014 IEEE Nucl. Sci. Symposium, Seattl

Adaptive Mesh Refinement for Hyperbolic Systems based on Third-Order Compact WENO Reconstruction

In this paper we generalize to non-uniform grids of quad-tree type the Compact WENO reconstruction of Levy, Puppo and Russo (SIAM J. Sci. Comput., 2001), thus obtaining a truly two-dimensional non-oscillatory third order reconstruction with a very compact stencil and that does not involve mesh-dependent coefficients. This latter characteristic is quite valuable for its use in h-adaptive numerical schemes, since in such schemes the coefficients that depend on the disposition and sizes of the neighboring cells (and that are present in many existing WENO-like reconstructions) would need to be recomputed after every mesh adaption. In the second part of the paper we propose a third order h-adaptive scheme with the above-mentioned reconstruction, an explicit third order TVD Runge-Kutta scheme and the entropy production error indicator proposed by Puppo and Semplice (Commun. Comput. Phys., 2011). After devising some heuristics on the choice of the parameters controlling the mesh adaption, we demonstrate with many numerical tests that the scheme can compute numerical solution whose error decays as $\langle N\rangle^{-3}$, where $\langle N\rangle$ is the average number of cells used during the computation, even in the presence of shock waves, by making a very effective use of h-adaptivity and the proposed third order reconstruction.Comment: many updates to text and figure

Experimental Spinal Cord Injury: Methodological and Neuroimmunological contributions with some Historical background

ABSTRACT Spinal cord injury (SCI) is an incurable neurotraumatic catastrophe that afflicts mostly young individuals with resultant functional impairment of varying degrees of severity. The single pharmacologic treatment option at present is systemic methylprednisolone administration within 8 hours postinjury oftentimes accompanied by neurosurgical interventions. As a rule, SCI becomes a chronic condition with significant handicap for the patient and socioeconomic repercussions for the affected families and health care system. Important discoveries in the field of central nervous system regeneration since the early 80’s have led to diverse potential therapeutic approaches for neuroprotection and repair. Unfortunately, most envisioned treatment apporaches would only be applicable at the acute and subacute stages of SCI, thereby excluding the large patient base with chronic SCI. In the first part of this thesis work the methodological aspects of a neurosurgical treatment protocol in a rat model of acute and chronic SCI were explored. In complete spinal cord transection experiments in rat, the acute and chronic spinal cord lesions were characterized with high-resolution magnetic resonance technology. A microneurosurgical ‘repair’ protocol was employed in both acute and chronic (at 2, 4 or 8 months postinjury) SCI. Behavioral evaluation of the operated animals with standard locomotor behavior tests and two novel behavioral tests, developed by the author, the Bipedal test and the Head-scratch test, demonstrated a statistically significant recovery for those animals that were subjected to the microsurgical reconstruction protocol. Partial functional recovery and histologically verifiable axonal regeneration was achieved in rats with both acute and chronic SCI. In the second part of this thesis work the neuroinflammatory and neuroimmunological correlates of peripheral and central nervous system injury were studied in mice. In one set of KO mice (TNFγ, STAT4, STAT6) and their corresponding wild type controls, behavioral recovery and axonal regeneration were evaluated after spinal cord overhemisection. In another set of KO mice (STAT4, STAT6, IFNγ, IFNγR and IRF1) and their corresponding wild type controls inflammatory and glial cell reactions were assessed after unilateral facial nerve transection lesions. The results suggest a positive role for the TH2 subset of the adaptive immune response in anatomic recovery after SCI. Finally, in this thesis work the historical origins of the ’inhibitory white matter hypothesis’ were researched shedding light on the pioneering work of Lugaro. Future treatments will have to address the complexity of SCI with a multipronged approach in order to effect the appropriate type and degree of immunomodulation, achieve neuroprotection, and promote collateral sprouting and axonal regeneration ultimately resulting in tissue repair and functional recovery. This thesis suggests: 1) that even complete, long-standing SCI can be amenable to therapy by demonstrating that the functional incapacity of experimental chronic paraplegia in rat is partially reversible, and 2) that judicious modulation of the immune response after SCI may have a role to play in axonal regeneration after SC

Reducing Streaking Artifacts in Quantitative Susceptibility Mapping

It is well known that reconstruction algorithms in quantitative susceptibility mapping often contain streaking artifacts. These are nondesirable objects that contaminate the image, and the possibility of removing or at least reducing them has a great practical interest. In [J. K. Choi, H. S. Park, S. Wang, Y. Wang, and J. K. Seo, SIAM J. Imaging Sci., 7 (2014), pp. 1669-1689], the cause of the artifacts is identified as propagation of singularities for a wave-type operator. In this work, we analyze such singularities using microlocal techniques and propose some strategies to reduce the artifacts.Peer reviewe

Order reconstruction for nematics on squares and hexagons:a Landau-de Gennes study

We construct an order reconstruction (OR-)type Landau-de Gennes critical point on a square domain of edge length 2λ, motivated by the well order reconstruction solution numerically reported in [S. Kralj and A. Majumdar, Proc. R. Soc. Lond. Ser. A Math. Phys. Eng. Sci., 470 (2014), 20140276]. The OR critical point is distinguished by a uniaxial cross with negative scalar order parameter along the square diagonals. The OR critical point is defined in terms of a saddle-type critical point of an associated scalar variational problem. The OR-type critical point is globally stable for small λ and undergoes a supercritical pitchfork bifurcation in the associated scalar variational setting. We consider generalizations of the OR-type critical point to a regular hexagon, accompanied by numerical estimates of stability criteria of such critical points on both a square and a hexagon in terms of material-dependent constants

Inverse Scattering of Dielectric Cylindrical Target Using Dynamic Differential Evolution and Self-Adaptive Dynamic Differential Evolution

[[abstract]]The inverse problem under consideration is to reconstruct the characteristic of scatterer from the scattering E field. Dynamic differential evolution (DDE) and self-adaptive dynamic differential evolution (SADDE) are stochastic-type optimization approach that aims to minimize a cost function between measurements and computer-simulated data. These algorithms are capable of retrieving the location, shape, and permittivity of the dielectric cylinder in a slab medium made of lossless materials. The finite-difference time-domain (FDTD) is employed for the analysis of the forward scattering. The comparison is carried out under the same conditions of initial population of candidate solutions and number of iterations. Numerical results indicate that SADDE outperforms the DDE a little in terms of reconstruction accuracy.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

Elementary structural building blocks encountered in silicon surface reconstructions

Driven by the reduction of dangling bonds and the minimization of surface stress, reconstruction of silicon surfaces leads to a striking diversity of outcomes. Despite this variety even very elaborate structures are generally comprised of a small number of structural building blocks. We here identify important elementary building blocks and discuss their integration into the structural models as well as their impact on the electronic structure of the surface

The reconstruction of Ni and Rh (001) surfaces upon Carbon, Nitrogen, or Oxygen adsorption

Nickel and Rhodium (001) surfaces display a similar - as from STM images - clock reconstruction when half a monolayer of C/Ni, N/Ni or O/Rh is adsorbed; no reconstruction is observed instead for O/Ni. Adsorbate atoms sit at the center of the black squares of a chess-board, $c(2\times 2)$, pattern and two different reconstructions are actually compatible with the observed STM images - showing a $(2\times 2)p4g$ pattern - according to whether a rotation of the black or white squares occurs. We report on a first - principles study of the structure of X/Ni(001) and X/Rh(001) surfaces (X=C,N,O) at half a monolayer coverage, performed using density-functional theory. Our findings are in agreement with all available experimental information and shed new light on the mechanisms responsible for the reconstructions. We show that the same substrate may display different reconstructions - or no reconstruction - upon adsorption of different atomic species, depending on the relative importance of the chemical and steric factors which determine the reconstruction.Comment: 18 pages, 5 figure