Biomimetic Design and Fabrication of Interior Architecture of Tissue Scaffolds Using Solid Freeform Fabrication

Modeling, design and fabrication of tissue scaffolds with intricate architecture, porosity and pore size for desired tissue properties presents a challenge in tissue engineering. This paper will present the details of our development in designing and fabrication of the interior architecture of scaffolds using a novel design approach. The Interior Architecture Design (IAD) approach seeks to generate scaffold layered freeform fabrication tool path without forming complicated 3D CAD scaffold models. This involves: applying the principle of layered manufacturing to determine the scaffold individual layered process planes and layered contour; defining the 2D characteristic patterns of the scaffold building blocks (unit cells) to form the Interior Scaffold Pattern; and the generation of process tool path for freeform fabrication of these scaffolds with the specified interior architecture. Feasibility studies applying the IAD algorithm to example models and the generation of fabrication planning instructions will be presented.Mechanical Engineerin

Medium: An exploratory study of PR professionals in Taiwan

This paper seeks to explore the attitudes and practices of public relations (PR) professionals in using the Internet as a PR medium in Taiwan. Specifically, the paper addresses three research questions: (1) What do PR professionals think about the function of the Internet and the roles of online communication in comparison with those of offline communication in Taiwan? (2) Will IT-related corporations be more likely to have a wider scope of Internet applications than non-IT related corporations? (3) Do IT corporations perceive the role of PR differently from non-IT related corporations? Using a semi-structured questionnaire, we conducted in-depth interviews with eight corporations’ PR and marketing department professionals in Taiwan from May 18- June 18, 2001. The findings show that (1) Although the Internet is widely used by PR professionals, it does not alter media strategies significantly; (2) PR professionals in IT corporations tend to practise more Internet communication functions than those in non-IT related corporations; (3) IT corporations are more likely to support the management role of PR professionals, as compared to those in non-IT related businesses. The study suggests that the applications of the Internet vary according to industry type, business strategies and roles of the PR professionals within an organisation

Direct Slicing of STEP Based NURBS Models for Solid Freeform Fabrication

Direct slicing of CAD models to generate process planning instructions for solid freeform fabrication may overcome inherent disadvantages of using STL format in terms of the process accuracy, ease of file management, and incorporation of multiple materials. This paper will present the results of our development of a direct slicing algorithm for layered freeform fabrication. The direct slicing algorithm was based on a neutral, international standard (ISO 10303) STEP-formatted NURBS geometric representation and is intended to be independent of any commercial CAD software. The following aspects of the development effort will be presented: 1) Determination of optimal build direction based upon STEP-based NURBS models; 2) Adaptive subdivision of NURBS data for geometric refinement; and 3) Ray-casting slice generation into sets of raster patterns. Feasibility studies applying the direct slicing algorithm to example models and the generation of fabrication planning instructions involving multi-material structures will also be presented.Mechanical Engineerin

Direct slicing of STEP based NURBS models for layered manufacturing

Abstract Direct slicing of CAD models to generate process planning instructions for solid freeform fabrication may overcome inherent disadvantages of using stereolithography format in terms of the process accuracy, ease of file management, and incorporation of multiple materials. This paper will present the results of our development of a direct slicing algorithm for layered freeform fabrication. The direct slicing algorithm was based on a neutral, international standard (ISO 10303) STEP-formatted non-uniform rational B-spline (NURBS) geometric representation and is intended to be independent of any commercial CAD software. The following aspects of the development effort will be presented: (1) determination of optimal build direction based upon STEP-based NURBS models; (2) adaptive subdivision of NURBS data for geometric refinement; and (3) ray-casting slice generation into sets of raster patterns. The development also provides for multi-material slicing and will provide an effective tool in heterogeneous slicing processes.

Radio Galaxy NGC 1265 unveils the Accretion Shock onto the Perseus Galaxy Cluster

We present a consistent 3D model for the head-tail radio galaxy NGC 1265 that explains the complex radio morphology and spectrum by a past passage of the galaxy and radio bubble through a shock wave. Using analytical solutions to the full Riemann problem and hydrodynamical simulations, we study how this passage transformed the plasma bubble into a toroidal vortex ring. Adiabatic compression of the aged electron population causes it to be energized and to emit low-surface brightness and steep-spectrum radio emission. The large infall velocity of NGC 1265 and the low Faraday rotation measure values and variance of the jet strongly argue that this transformation was due to the accretion shock onto Perseus situated roughly at R_200. Estimating the volume change of the radio bubble enables inferring a shock Mach number of M = 4.2_{-1.2}^{+0.8}, a density jump of 3.4_{-0.4}^{+0.2}, a temperature jump of 6.3_{-2.7}^{+2.5}, and a pressure jump of 21.5 +/- 10.5 while allowing for uncertainties in the equation of state of the radio plasma and volume of the torus. Extrapolating X-ray profiles, we obtain upper limits on the gas temperature and density in the infalling warm-hot intergalactic medium of kT < 0.4 keV and n < 5e-5 / cm^3. The orientation of the ellipsoidally shaped radio torus in combination with the direction of the galaxy's head and tail in the plane of the sky is impossible to reconcile with projection effects. Instead, this argues for post-shock shear flows that have been caused by curvature in the shock surface with a characteristic radius of 850 kpc. The energy density of the shear flow corresponds to a turbulent-to-thermal energy density of 14%. The shock-injected vorticity might be important in generating and amplifying magnetic fields in galaxy clusters. Future LOFAR observations of head-tail galaxies can be complementary probes of accretion shocks onto galaxy clusters.Comment: 14 pages, 4 figures, ApJ, in print; v3: typos corrected to match the published version; v2: improved presentation, added 2D numerical simulations and exact solution to the 1D Riemann problem of a shock overrunning a spherical bubble that gets transformed into a vortex rin

Differentiation and Protective Capacity of Virus-Specific CD8

Noroviruses can establish chronic infections with active viral shedding in healthy humans but whether persistence is associated with adaptive immune dysfunction is unknown. We used genetically engineered strains of mouse norovirus (MNV) to investigate CD8+ T cell differentiation during chronic infection. We found that chronic infection drove MNV-specific tissue-resident memory (Trm) CD8+ T cells to a differentiation state resembling inflationary effector responses against latent cytomegalovirus with only limited evidence of exhaustion. These MNV-specific Trm cells remained highly functional yet appeared ignorant of ongoing viral replication. Pre-existing MNV-specific Trm cells provided partial protection against chronic infection but largely ceased to detect virus within 72 hours of challenge, demonstrating rapid sequestration of viral replication away from T cells. Our studies revealed a strategy of immune evasion by MNV via the induction of a CD8+ T cell program normally reserved for latent pathogens and persistence in an immune-privileged enteric niche. Chronic infections often cause T cell dysfunction, but how noroviruses (NV) evade immunity is unknown. Tomov et al. show that gut-resident T cells against NV remain functional but ignorant of chronic viral replication, suggesting that NV persists in an immune-privileged enteric niche. © 2017 Elsevier Inc

Simultaneous planar measurements of gas and particle velocities in particle-laden flows: proof-of-concept

A laser-based technique is reported, employing simultaneous laser-induced fluorescence (LIF) and phosphorescence (LIP) to respectively mark the gas- and particle- phases and allow their simultaneous velocity measurement in a particle-laden flow. The technique discriminates the phases by optically separating the fluorescent and phosphorescent signals from each other and also from the scattering signals, thorough the novel use of optical filters and temporal separation. A proof-of-concept demonstration was conducted with using 250 μm PMMA spherical particles and 4 μm BAM:Eu²⁺ phosphorescent tracers, suspended in a water cuvette. Under 355 nm excitation (3rd harmonic of the Nd:YAG laser), both PMMA fluorescent and BAM:Eu²⁺ phosphorescent signals are shown to be sufficiently strong for imaging with CCD cameras, and sufficiently separable with using spectral filters and temporal profiles.Xiaopeng Bi, Zhiwei Sun, Timothy Lau, Zeyad Alwahabi and Graham Natha

Impact of Cluster Physics on the Sunyaev-Zel'dovich Power Spectrum

We use an analytic model to investigate the theoretical uncertainty on the thermal Sunyaev-Zel'dovich (SZ) power spectrum due to astrophysical uncertainties in the thermal structure of the intracluster medium. Our model accounts for star formation and energy feedback (from supernovae and active galactic nuclei) as well as radially dependent non-thermal pressure support due to random gas motions, the latter calibrated by recent hydrodynamical simulations. We compare the model against X-ray observations of low redshift clusters, finding excellent agreement with observed pressure profiles. Varying the levels of feedback and non-thermal pressure support can significantly change both the amplitude and shape of the thermal SZ power spectrum. Increasing the feedback suppresses power at small angular scales, shifting the peak of the power spectrum to lower ell. On the other hand, increasing the non-thermal pressure support has the opposite effect, significantly reducing power at large angular scales. In general, including non-thermal pressure at the level measured in simulations has a large effect on the power spectrum, reducing the amplitude by 50% at angular scales of a few arcminutes compared to a model without a non-thermal component. Our results demonstrate that measurements of the shape of the power spectrum can reveal useful information on important physical processes in groups and clusters, especially at high-redshift where there exists little observational data. Comparing with the recent South Pole Telescope measurements of the small-scale cosmic microwave background power spectrum, we find our model reduces the tension between the values of sigma_8 measured from the SZ power spectrum and from cluster abundances.Comment: 15 Pages, 9 Figures, updated to match version accepted by Ap

DFT Study of Planar Boron Sheets: A New Template for Hydrogen Storage

We study the hydrogen storage properties of planar boron sheets and compare them to those of graphene. The binding of molecular hydrogen to the boron sheet (0.05 eV) is stronger than that to graphene. We find that dispersion of alkali metal (AM = Li, Na, and K) atoms onto the boron sheet markedly increases hydrogen binding energies and storage capacities. The unique structure of the boron sheet presents a template for creating a stable lattice of strongly bonded metal atoms with a large nearest neighbor distance. In contrast, AM atoms dispersed on graphene tend to cluster to form a bulk metal. In particular the boron-Li system is found to be a good candidate for hydrogen storage purposes. In the fully loaded case this compound can contain up to 10.7 wt. % molecular hydrogen with an average binding energy of 0.15 eV/H2.Comment: 19 pages, 7 figures, and 3 table

Design of Force Fields from Data at Finite Temperature

We investigate the problem of how to obtain the force field between atoms of an experimentally determined structure. We show how this problem can be efficiently solved, even at finite temperature, where the position of the atoms differs substantially from the ground state. We apply our method to systems modeling proteins and demonstrate that the correct potentials can be recovered even in the presence of thermal noise.Comment: 10 pages, 1 postcript figure, Late