An Efficient Block-based Image Compression And Quality-Wise Decompression Algorithm

In this paper, we propose a block-based lossy image compression algorithm that makes use of spatial redundancies of neighboring pixels in image data. Compression is achieved by replacing a block of pixels with their statistical mean. The algorithm helps in decompressing the image at different quality levels. Quality matrices constructed from the quantization table of the JPEG baseline algorithm are used to achieve different qualities of the reconstructed data. Experimental results show that the proposed method outperforms existing polynomial-based algorithms both in computation time and complexity

Hierarchically porous 3D-printed akermanite scaffolds from silicones and engineered fillers

The present investigation is dedicated to the manufacturing of reticulated three-dimensional akermanite scaffolds, developed by direct reaction between silica, from the oxidation of a commercial silicone resin and oxide fillers, forming pastes for direct ink writing. Crack-free scaffolds, with dense and regular struts, were due to the use of CaCO3 (micro) and MgO nano-particles as reactive fillers. An excellent phase purity was obtained, with the help of the liquid phase provided by anhydrous sodium borate (Na2B4O7), upon firing. The structure of the scaffolds, finally, was successfully modified by using Mg(OH)2 and hydrated sodium borate: besides macro-porosity from direct ink writing, the new scaffolds exhibited homogenous \u2018spongy\u2019 struts (owing to water vapor release in the heating step), with no crack. Both types of scaffolds (with dense or porous struts) exhibited remarkable strength-to-density ratios

Glass powders and reactive silicone binder: Interactions and application to additive manufacturing of bioactive glass-ceramic scaffolds

A novel concept for the additive manufacturing of three-dimensional glass-ceramic scaffolds, to be used for tissue engineering applications, was based on fine glass powders mixed with a reactive binder, in the form of a commercial silicone. The powders consisted of ‘silica-defective glass’ specifically designed to react, upon firing in air, with the amorphous silica yielded by the binder. By silica incorporation, the glass was intended to reach the composition of an already known CaONa2OB2O3SiO2 system. Silica from the binder provided up to 15 wt% of the total silica. With the same overall formulation, silicone-glass powder mixtures led to nearly the same phase assemblage formed by the reference system, crystallizing into wollastonite (CaSiO3) and Ca-borate (CaB2O4). Samples from silicone-glass powder mixtures exhibited an excellent shape retention after firing, which was later exploited in highly porous reticulated scaffolds, obtained by means of direct ink writing (DIW)

STUDIES ON THE STRESS FLUCTUATIONS IN SHEARED STOKESIAN SUSPENSIONS USING CHAOS THEORY AND NONLINEAR DYNAMICS

The thesis report results obtained from a detailed analysis of the fluctuations of the rheological parameters viz. shear and normal stresses, simulated by means of the Stokesian Dynamics method, of a macroscopically homogeneous sheared suspension of neutrally buoyant non-Brownian suspension of identical spheres in the Couette gap between two parallel walls in the limit of vanishingly small Reynolds numbers using the tools of non-linear dynamics and chaos theory for a range of particle concentration and Couette gaps. The thesis used the tools of nonlinear dynamics and chaos theory viz. average mutual information, space-time separation plots, visual recurrence analysis, principal component analysis, false nearest-neighbor technique, correlation integrals, computation of Lyapunov exponents for a range of area fraction of particles and for different Couette gaps. The thesis observed that one stress component can be predicted using another stress component at the same area fraction. This implies a type of synchronization of one stress component with another stress component. This finding suggests us to further analysis of the synchronization of stress components with another stress component at the same or different area fraction of particles. The different model equations of stress components for different area fraction of particles hints at the possible existence a general formula for stress fluctuations with area fraction of particle as a paramete

3D Printing of Hierarchically Porous Lattice Structures Based on Åkermanite Glass Microspheres and Reactive Silicone Binder

The present study illustrates the manufacturing method of hierarchically porous 3D scaffolds based on åkermanite as a promising bioceramic for stereolithography. The macroporosity was designed by implementing 3D models corresponding to different lattice structures (cubic, diamond, Kelvin, and Kagome). To obtain micro-scale porosity, flame synthesized glass microbeads with 10 wt% of silicone resins were utilized to fabricate green scaffolds, later converted into targeted bioceramic phase by firing at 1100◦C in air. No chemical reaction between the glass microspheres, crystallizing into åkermanite, and silica deriving from silicone oxidation was observed upon heat treatment. Silica acted as a binder between the adjacent microspheres, enhancing the creation of microporosity, as documented by XRD, and SEM coupled with EDX analysis. The formation of ‘spongy’ struts was confirmed by infiltration with Rhodamine B solution. The compressive strength of the sintered porous scaffolds was up to 0.7 MPa with the porosity of 68–84%

Densification and rheological behaviors of 8YSZ powders for Vat photopolymerization-based additive manufacturing

Vat photopolymerization additive manufacturing technology allows the shaping of ceramic structures with limitless opportunities in terms of design freedom, structural resolution, and improving processing speed while reducing cost and wastage. The quality of a final product is influenced by the raw materials and processing routes. The particle size distribution of ceramic powders significantly affects ceramic slurry's rheology and cure behaviour as well as the densification process during sintering. This work studies the rheological properties of slurries prepared from 8 mol.% yttria-stabilized zirconia powders with various particle size distributions and densification of green bodies prepared from these suspensions. The suspension with a narrow particle size distribution showed a non-Newtonian behavior with a viscosity of >1 Pa s at a solid loading above 29 vol%, and a significant densification at a sintering temperature of 1400 °C. The viscosity of a suspension prepared from a powder with a wide particle size distribution was <1 Pa s in a solid loading range of 29–37 vol%. The higher cure depth at a lower exposure energy for slurry with coarse particles allowed a reduction of the printing time, while suspension with fine particles can be used for high-resolution printing with longer exposure time

\uc5kermanite glass microspheres: Preparation and perspectives of sinter-crystallization

Glass microspheres with the exact stoichiometry of \ue5kermanite (Ca2MgSi2O7), one of the most promising modern bioceramics, were produced by the flame synthesis method. The distinctive high cooling rate was found to prevent the crystallization; the size of amorphous microbeads could be correlated with the size of partially crystallized precursor powders, deriving from conventional melt quenching and milling. The glass microspheres were characterized in terms of crystallization and sintering behavior, in the perspective of applications in additive manufacturing of \ue5kermanite-based scaffolds. The results showed that merwinite (Ca3MgSi2O8) is the primary product of glass devitrification; only in a second stage, merwinite reacts with the residual glass and yields \ue5kermanite. The rapid crystallization, implying limited viscous flow sintering, was tested as an opportunity to create components with complex porosity distribution