Microstructure and micromechanics of the sea urchin, Colobocentrotus atratus

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections."June 2011." Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 128-132).The purpose of this research is to study the porous microstructure and the micromechanics of the exoskeletal armor of the helmet urchin, Colobocentrotus atratus. Its unusual reduction in spines forms a smooth tiling of millimeter-sized, flattened polygonal protective aboral spines. Each aboral spine articulates with the underlying test via a ball-and-socket joint and the microstructure of each aboral spine is a porous network of single-crystal magnesium-doped calcite with a few percent of intercalated organic. Methods of microstructural characterization and simulation were developed through the investigation of the urchin's microstructure and the finite element model. With the high resolution scans from X-ray microcomputed tomography at the Advanced Photon Source at Argonne National Laboratory, Beamline 2BM, visualization and characterization of a complex porous network in three-dimensions was possible, providing a more quantitative insight into the geometry of the microstructure not characterized before in urchin biology literature. The galleried stereom of the individual spines were found to possess a gradient in volume fraction with distance from the socket ranging from 90% at the ball-and-socket joint to 50% at the outer surface. The axial direction of the galleried structure radiates outwardly from the socket and terminated perpendicular to the outer surface of the aboral spine. Additionally, with the microcomputed tomography results, an efficient and more accurate finite element model of an entire aboral spine along with the microstructural properties was created. The galleried mesh (average pore size ~ 15 microns) was modeled using three-dimensional elastic finite element analysis that consisted of a microstructurally-based parametric representative volume element with periodic boundary conditions. Various loading configurations were simulated to obtain anisotropic stiffness tensors and resulted in an orthotropic effective mechanical behavior with the stiffness in the plane transverse to the long axis of the galleried microstructure (E1, E2) approximately half the stiffness in the axial direction (E3). With parametric simulations, E3 was found to decrease linearly from 0.87 of the solid elastic modulus (Es) to 0.34 of Es as the volume fraction decreases from 0.88 to 0.46. In the transverse direction, E1 and E2 also decrease linearly from 0.49 of Es to 0.18 of Es within the same range of volume fraction. Spatial gradients in density were also modeled, corresponding to the gradient in porosity in the aboral spine. From simulation of blunt indentation by both a conical indenter and flat plate indenter, the graded porosity of the microstructure exhibits an expected lower overall stiffness and lower stress state than the solid material, but also serves to increase the strains near the exterior surface of the aboral spine while reducing the strains near the joint. This open-pore structure and trabeculae alignment results in a directional strengthening due to inhomogeneous deformations in the porous structure and provides resistance against blunt impacts and containment of penetration into the surface of the aboral spine.by Ting-Ting Chen.S.M

Theory of Transmission through disordered superlattices

We derive a theory for transmission through disordered finite superlattices in which the interface roughness scattering is treated by disorder averaging. This procedure permits efficient calculation of the transmission thr ough samples with large cross-sections. These calculations can be performed utilizing either the Keldysh or the Landauer-B\"uttiker transmission formalisms, both of which yield identical equations. For energies close to the lowest miniband, we demonstrate the accuracy of the computationally efficient Wannier-function approximation. Our calculations indicate that the transmission is strongly affected by interface roughness and that information about scale and size of the imperfections can be obtained from transmission data.Comment: 12 pages, 6 Figures included into the text. Final version with minor changes. Accepted by Physical Review

Vasorelaxant effect of a phenylethylamine analogue based on schwarzinicine A an alkaloid isolated from the leaves of Ficus schwarzii

N-Phenethyl-1-phenyl-pentan-3-amine (1) is a new compound synthesised as a simplified analogue of schwarzinicine A (2), a natural compound extracted from Ficus schwarzii. Compound 1 differs from compound 2 due to its structural simplification, featuring two phenyl rings without methoxy substitution, as opposed to compound 2, which possesses three 3,4-dimethoxy aromatic rings. Our previous research findings highlighted the calcium-inhibitory effects of compound 2, but the mechanism of action for compound 1 remains unexplored, serving as the primary focus of this study. Building upon our earlier research, this study aimed to elucidate compound 1's calcium-modulating potential by using rat-isolated aortae in an organ bath set-up and HEK cells expressing hTRPC channels with the fluorometric assay to measure calcium influx. Compound 1 elicited a vasorelaxation response (Emax 111.4%) similar to its parent compound 2 (Emax 123.1%), and inhibited hTRPC3-, hTRPC4-, hTRPC5-, and hTRPC6-mediated calcium influx into HEK cells with IC50 values of 6, 2, 2, 5 µM, respectively. Compound 1 has a similar pharmacological profile as its parent compound 2, whereby it exerts a vasorelaxant effect by attenuating calcium influx and inhibits multiple TRPC channels

TLR9- and CD40-Targeting Vaccination Promotes Human B Cell Maturation and IgG Induction via pDC-Dependent Mechanisms in Humanized Mice

Mice reconstituted with a human immune system (humanized mice) provide a robust model to study human immunology, vaccinology, and human infectious diseases. However, the development and function of B cells in humanized mice is impaired. B cells from humanized mice are immature and are impaired in IgM to IgG isotype switch in response to infection or vaccination. In the present study we report that Toll-like receptor 9 (TLR9) agonist CpG-B combined with CD40-targeting vaccination triggered human B cell immunoglobin class-switch from IgM+ to IgG+ B cells in humanized mice. Human B cells from mice vaccinated with CpG-B as adjuvant were more mature in phenotype and produced significant levels of both total IgG and antigen-specific IgG. We found that CpG-B treatment activated human pDCs (plasmacytoid dendritic cells) in vivo to induce interferon-alpha (IFN-α)expression in humanized mice. Pre-depletion of human pDC in vivo abrogated the adjuvant effect of CpG-B. Our results indicate that TLR9 and CD40-targeting vaccination triggers human B cell maturation and immunoglobulin class-switch in a pDC-dependent manner in humanized mice. The findings also shed light on induction of human IgG antibodies in humanized mouse models

Spin-Charge Separation in the t−Jt-J Model: Magnetic and Transport Anomalies

A real spin-charge separation scheme is found based on a saddle-point state of the $t-J$ model. In the one-dimensional (1D) case, such a saddle-point reproduces the correct asymptotic correlations at the strong-coupling fixed-point of the model. In the two-dimensional (2D) case, the transverse gauge field confining spinon and holon is shown to be gapped at {\em finite doping} so that a spin-charge deconfinement is obtained for its first time in 2D. The gap in the gauge fluctuation disappears at half-filling limit, where a long-range antiferromagnetic order is recovered at zero temperature and spinons become confined. The most interesting features of spin dynamics and transport are exhibited at finite doping where exotic {\em residual} couplings between spin and charge degrees of freedom lead to systematic anomalies with regard to a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic fluctuation with a small, doping-dependent energy scale is found, which is characterized in momentum space by a Gaussian peak at ($\pi/a$, $\pi/a$) with a doping-dependent width ($\propto \sqrt{\delta}$, $\delta$ is the doping concentration). This commensurate magnetic fluctuation contributes a non-Korringa behavior for the NMR spin-lattice relaxation rate. There also exits a characteristic temperature scale below which a pseudogap behavior appears in the spin dynamics. Furthermore, an incommensurate magnetic fluctuation is also obtained at a {\em finite} energy regime. In transport, a strong short-range phase interference leads to an effective holon Lagrangian which can give rise to a series of interesting phenomena including linear-$T$ resistivity and $T^2$ Hall-angle. We discuss the striking similarities of these theoretical features with those found in the high-$T_c$ cuprates and give aComment: 70 pages, RevTex, hard copies of 7 figures available upon request; minor revisions in the text and references have been made; To be published in July 1 issue of Phys. Rev. B52, (1995

Protons in near earth orbit

The proton spectrum in the kinetic energy range 0.1 to 200 GeV was measured by the Alpha Magnetic Spectrometer (AMS) during space shuttle flight STS-91 at an altitude of 380 km. Above the geomagnetic cutoff the observed spectrum is parameterized by a power law. Below the geomagnetic cutoff a substantial second spectrum was observed concentrated at equatorial latitudes with a flux ~ 70 m^-2 sec^-1 sr^-1. Most of these second spectrum protons follow a complicated trajectory and originate from a restricted geographic region.Comment: 19 pages, Latex, 7 .eps figure

Search for antihelium in cosmic rays

The Alpha Magnetic Spectrometer (AMS) was flown on the space shuttle Discovery during flight STS-91 in a 51.7 degree orbit at altitudes between 320 and 390 km. A total of 2.86 * 10^6 helium nuclei were observed in the rigidity range 1 to 140 GV. No antihelium nuclei were detected at any rigidity. An upper limit on the flux ratio of antihelium to helium of < 1.1 * 10^-6 is obtained.Comment: 18 pages, Latex, 9 .eps figure

A Study of Cosmic Ray Secondaries Induced by the Mir Space Station Using AMS-01

The Alpha Magnetic Spectrometer (AMS-02) is a high energy particle physics experiment that will study cosmic rays in the $\sim 100 \mathrm{MeV}$ to $1 \mathrm{TeV}$ range and will be installed on the International Space Station (ISS) for at least 3 years. A first version of AMS-02, AMS-01, flew aboard the space shuttle \emph{Discovery} from June 2 to June 12, 1998, and collected $10^8$ cosmic ray triggers. Part of the \emph{Mir} space station was within the AMS-01 field of view during the four day \emph{Mir} docking phase of this flight. We have reconstructed an image of this part of the \emph{Mir} space station using secondary $\pi^-$ and $\mu^-$ emissions from primary cosmic rays interacting with \emph{Mir}. This is the first time this reconstruction was performed in AMS-01, and it is important for understanding potential backgrounds during the 3 year AMS-02 mission.Comment: To be submitted to NIM B Added material requested by referee. Minor stylistic and grammer change

Comparative efficacy of exercise therapy and oral non-steroidal anti-inflammatory drugs and paracetamol for knee or hip osteoarthritis: a network meta-analysis of randomised controlled trials

Clinical guidelines recommend exercise as a core treatment for knee or hip osteoarthritis (OA). However, how its analgesic effect compares to analgesics, for example, oral non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol-the most commonly used analgesics for OA, remains unknown. Network meta-analysis. PubMed, Embase, Scopus, Cochrane Library and Web of Science from database inception to January 2022. Randomised controlled trials (RCTs) comparing exercise therapy with oral NSAIDs and paracetamol directly or indirectly in knee or hip OA. A total of n=152 RCTs (17 431 participants) were included. For pain relief, there was no difference between exercise and oral NSAIDs and paracetamol at or nearest to 4 (standardised mean difference (SMD)=-0.12, 95% credibility interval (CrI) -1.74 to 1.50; n=47 RCTs), 8 (SMD=0.22, 95% CrI -0.05 to 0.49; n=2 RCTs) and 24 weeks (SMD=0.17, 95% CrI -0.77 to 1.12; n=9 RCTs). Similarly, there was no difference between exercise and oral NSAIDs and paracetamol in functional improvement at or nearest to 4 (SMD=0.09, 95% CrI -1.69 to 1.85; n=40 RCTs), 8 (SMD=0.06, 95% CrI -0.20 to 0.33; n=2 RCTs) and 24 weeks (SMD=0.05, 95% CrI -1.15 to 1.24; n=9 RCTs). Exercise has similar effects on pain and function to that of oral NSAIDs and paracetamol. Given its excellent safety profile, exercise should be given more prominence in clinical care, especially in older people with comorbidity or at higher risk of adverse events related to NSAIDs and paracetamol. CRD42019135166

Measurement of W Polarisation at LEP

The three different helicity states of W bosons produced in the reaction e+ e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to measure the polarisation of W bosons, and its dependence on the W boson production angle. The fraction of longitudinally polarised W bosons is measured to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation