Unidirectional Channels Research Articles

In vitro biodegradable and mechanical performance of biphasic calcium phosphate porous scaffolds with unidirectional macro-pore structure

In this study, porous biphasic calcium phosphate (BCP) scaffolds were fabricated by a freeze–gel casting technique using a tertiary-butyl alcohol (TBA) based slurry. After sintering, unidirectional macropore channels of scaffolds aligned regularly along the TBA ice growth direction were tailored simultaneously with micropores formed in the outer wall of the pore channels. The synthesized porous BCP scaffolds (two different sintering temperatures) exhibit compressive strength of 46.8MPa for 43.0% porosity and 33.1MPa for 45.9% porosity, respectively. After immersion in Hank's balanced salt solution (HBSS) for 1, 2, 4, 8 weeks, a precipitation started to be formed with individual small granules on the scaffolds surface. In the case of BCP scaffolds sintered at 1200°C, β-TCP were slowly degraded with increasing the immersing time; on the other hand, α-TCP (from BCP scaffolds sintered at 1300°C) was extremely degraded within 1 week of immersing. This behavior could be due to a fast hydrolysis (dissolution–reprecipitation) as a phase transformation from α-TCP to brushite or apatite compared to the β-TCP. After immersion in HBSS, overall the compressive strength of the scaffolds reduced by the gradual degradation in biological environment solution. This behavior is consistent with the degradation behavior of scaffolds after immersion in HBSS.

Porous hydroxyapatite scaffolds containing calcium phosphate glass-ceramics processed using a freeze/gel-casting technique

A freeze/gel-casting technique has been applied to produce porous ceramic composite scaffolds with tailored pore structures and improved compressive strength for tissue engineering applications. Tertiary-butyl alcohol (TBA)-based hydroxyapatite/calcium phosphate glass-ceramic suspensions with 5–15 vol.% solid loading were used in this study. Following sintering at 1050–1250 °C, the composite scaffolds were characterized in terms of microstructure, and physical and mechanical properties. The resulting scaffolds consisted of unidirectional pore channels (macro-sized) aligned in the solidification direction of the TBA solvent used in the freeze casting step and a few inter/intra-granular pores with small diameter (micron sized) remained in the wall structures of the pore channels by gel casting. With the addition of glass-ceramics (≤10 wt%), a liquid phase was formed mainly by the melting of calcium phosphate glasses at a given sintering temperature. The wall structures became more densified (less porous) aided by liquid phase sintering, possibly lending enhanced compressive strength.

동결-젤 주조 공정 기반 삼차부틸알코올을 이용한 단일방향 기공구조를 가지는 이상인산칼슘 세라믹 지지체의 제조 및 특성평가

Porous biphasic calcium phosphate scaffolds were fabricated by a freeze-gel casting technique using a tertiary-butyl alcohol (TBA)-based slurry. After sintering, unidirectional macropore channels of scaffolds aligned regularly along the TBA ice growth direction were tailored simultaneously with micropores formed in the outer wall of the pore channels. The crystallinity, micro structure, pore configuration, bulk density, and compressive strength for the scaffolds were investigated with X-ray diffractometery, scanning electron microscopy analysis, a water immersion method, and a universal test machine. The results revealed that the sintered porosity and pore size generally resulted in a high solid loading which resulted in low porosity and small pore size, which relatively increased the higher compressive strength. After being sintered at 1100-1300℃, the scaffolds showed an average porosity and compressive strength in the range 35.1-74.9% and 65.1-3.0 MPa, respectively, according to the processing conditions.

Limited Magnitude Error Detecting Codes over Z_{q}

The error detecting problem for limited magnitude errors over high radix channels is studied. In this error model, the error magnitude does not exceed a certain limited value and it is known beforehand. For asymmetric, unidirectional, and symmetric channels, both all and t error detecting codes are studied. In all these cases, close-to-optimal codes are proposed.

A supramolecular 2 : 1 guanidinium–carboxylate based building block for generation of water channels and clusters in organic materials

A bicyclic guanidine derivative is used here to generate a hydrogen-bonded 2 : 1 complex with bipyridine dicarboxylic acid. This supramolecule has numerous additional H-bond acceptors and is expected to display a high propensity for inclusion of water molecules in the solid state. Depending on the initial crystallization, it is in fact possible to utilize this property to build structures with water tetramers and unidirectional water channels.

Developing a power-efficient and low-cost 3D NoC using smart GALS-based vertical channels

Shorter global interconnects enable 3D NoC structures to offer higher performance, improved packaging density, and lower interconnect power consumption to CMPs and SoCs compared to their 2D counterparts. However, substantial challenges such as high peak temperatures, power densities and area footprints of vertical interconnects in each layer cannot be ignored. In this paper, a power and area efficient 3D NoC architecture based on power-aware Bidirectional Bisynchronous Vertical Channels (BBVC) is proposed as a solution to mitigate these challenges. Instead of using a pair of unidirectional channels for inter-layer communication, utilizing a dynamically self-configurable BBVC enables a system to benefit from low-latency nature of the vertical interconnects. In addition, based on the GALS implementation approach of the proposed channels, a forecasting-based dynamic frequency scaling technique for reducing the power consumption of the inter-layer communication is introduced. Simulation results show that the proposed architecture can reduce up to 47% through-silicon via (TSV) area footprint and up to 18% NoC power consumption with a slight performance degradation compared to a typical Symmetric 3D NoC.

An Efficient Monarchic Reconfiguration Protocol with Deadlock Freedom on Interconnection Networks

An Efficient Monarchic Reconfiguration Protocol with Deadlock Freedom on Interconnection Networks

Porous alumina/zirconia layered composites with unidirectional pore channels processed using a tertiary-butyl alcohol-based freeze casting

Symmetric three-layer porous alumina/zirconia composites with controlled “designer” pore structure have been prepared by a tertiary-butyl alcohol-based freeze casting and sintering at 1400–1500°C in air. Unidirectional aligned macropore channels were developed over a long range by controlling the solidification direction of tertiary-butyl alcohol solvent; in this case, they were surrounded by more dense structured walls. In layered composite, the bottom layer consisted of small sized pore channels (∼11μm in diameter) compared with the middle and the top layer, due to the comparatively rapid velocity of the TBA crystal growth during solidification. The compressive strength (63–376MPa) of the sintered porous layered composite remarkably increased as the porosity decreased (64–32%).

-Quantum-Dot Sensitized Metal Oxide Photoelectrodes: Photoelectrochemistry and Photoinduced Absorption Spectroscopy

TiO2, ZnO nanoparticulate(-np), and ZnO-nanorod(-nr) electrodes have been modified with FeS2 (pyrite) nanoparticles. Quantum size effect is manifested by a blue shift in both absorption and photocurrent action spectra. PIA (photoinduced absorption spectroscopy), a multipurpose tool in the study of dye-sensitized solar cells, is used to study quantum-dot modified metal oxide (MO) nanostructured electrodes. The PIA spectra showed an evidence for long-lived photoinduced charge separation. Time-resolved PIA showed that recombination between electrons and holes occurs on a millisecond timescale. Incident-photon-to-current efficiencies at 400 nm are ranged between 13% and 25%. The better solar cell performance of FeS2 on ZnO-nr over ZnO-np can be ascribed to the faster, unidirectional e-transport channels through the ZnO-nr as well as the longer electron lifetimes. The lower performances of electrodes can be explained by the presence of FeS2 phases other than the photoactive pyrite phase, as evidenced from XRD study.

Bioconjugated Fluorescent Zeolite L Nanocrystals as Labels in Protein Microarrays

Zeolite L nanocrystals, as inorganic host material containing hydrophobic fluorophore N,N'-bis(2,6-dimethylphenyl)perylene-3,4,9,10-tetracarboxylic diimide in the unidirectional channels, are developed as new labels for biosensor systems. The external surface of the particles is modified with carboxylic acid groups for conjugation to primary amines of biomolecules such as antibodies. Anti-digoxigenin (anti-DIG) is selected to be immobilized on zeolite L via N-hydroxysulfosuccinimide ester linker. Together with DIG, it serves as a good universal binding pair for diverse analyte detection owing to the high binding affinity and low background noise. The conjugates are characterized by the dynamic light scattering technique for their hydrodynamic diameters and by enzyme-linked immunosorbent assay for antigen-antibody binding behavior. The characterizations prove that anti-DIG antibodies are successfully immobilized on zeolite L with their binding activities maintained. The microarray fluorescent sandwich immunoassay based on such nanocrystalline labels shows high sensitivity in a thyroid-stimulating hormone assay with the lower detection limit down to the femtomolar range. These new fluorescent labels possess great potential for in vitro diagnostics applications.

Porous YSZ ceramics with unidirectionally aligned pore channel structure: Lowering thermal conductivity by silica aerogels impregnation

The previous report of this work has demonstrated the fabrication and properties of porous yttria-stabilized zirconia (YSZ) ceramics with unidirectionally aligned pore channels. As a follow-up study, the present work aims at lowering the thermal conductivity of the porous YSZ ceramics by silica aerogels impregnation. The porous YSZ ceramics were immersed in an about-to-gel silica sol. Both the unidirectionally aligned pore channels and the inter-grain pores by grain stacking in the channel-pore wall of the porous YSZ ceramics were impregnated with the silica sol. After aging and supercritical drying, silica aerogels formed in the macroporous network of the porous YSZ ceramics with unidirectionally aligned pore channels. The influences of silica aerogel impregnation on the microstructure and properties of porous YSZ ceramics with unidirectional aligned pore channels were investigated. The porosity decreased after impregnation with silica aerogels. Both microstructure observation and pore size distribution indicated that both channel-pore size and inter-grain pore-size decreased significantly after impregnation with silica aerogels. Impregnating porous YSZ ceramics with silica aerogels remarkably lowered the room-temperature thermal conductivity and enhanced the compressive strength. The as-fabricated materials are thus suitable for applications in bulk thermal isolators.

Fabrication of porous ceramic composites with improved compressive strength from coal fly ash

A freeze–gel casting method has been proposed to fabricate porous mullite–alumina composite with controlled ‘designer’ pore structure and improved compressive strength. In this work, a tertiary butyl alcohol–coal fly ash slurry system with appropriate addition of Al2O3 was used. Unidirectional aligned macropore channels were developed by controlling the solidification direction of the tertiary butyl alcohol solvent. Simultaneously, microsized pores formed in the walls of the pore channels; consequently, the inner section of the walls of the pore channels exhibited a more porous structure than the outer walls. The compressive strength of the sintered porous composite increased as the porosity decreased, i.e. the low porosity gave a high compressive strength. After sintering at 1500°C with 40 wt-% solid loading, the mullite–alumina composite with a porosity of 61·2% exhibited a compressive strength of ∼64·3 MPa.

Targeting complex embedded architectures by combining the multicore communications API (mcapi) with compile-time virtualisation

Within the domain of embedded systems, hardware architectures are commonly characterised by application-specific heterogeneity. Systems may contain multiple dissimilar processing elements, non-standard memory architectures, and custom hardware elements. The programming of such systems is a considerable challenge, not only because of the need to exploit large degrees of parallelism but also because hardware architectures change from system to system. To solve this problem, this paper proposes the novel combination of a new industry standard for communication across multicore architectures (MCAPI), with a minimal-overhead technique for targeting complex architectures with standard programming languages (Compile-Time Virtualisation). The Multicore Association have proposed MCAPI as an industry standard for on-chip communications. MCAPI abstracts the on-chip physical communication to provide the application with logical point-to-point unidirectional channels between nodes (software thread, hardware core, etc.). Compile-Time Virtualisation is used to provide an extremely lightweight implementation of MCAPI, that supports a much wider range of architectures than its specification normally considers. Overall, this unique combination enhances programmability by abstracting on-chip communication whilst also exposing critical parts of the target architecture to the programming language.

TBA-based freeze/gel casting of porous hydroxyapatite scaffolds

Porous ceramic scaffolds with a controlled “designer” pore structure have been prepared by the freeze/gel casting route using a TBA-based hydroxyapatite slurry system with 20–40 wt.% solid content. The products were characterized in terms of sintered microstructure, together with physical and mechanical properties. After sintering at 1050–1250 °C, the advantages of freeze casting and gel casting appeared in the pore structure and compressive strength of the ceramics, i.e., unidirectional aligned macro-pore channels developed by controlling the solidification direction of the TBA solvent used in the freeze casting together with small diameter (micron sized) isolated pores formed in the dense outer walls of the pore channels when processed by gel casting. The sintered porosity and pore size generally resulted in a high solid loading giving low porosity and small pore size, this leading to higher compressive strengths. The scaffolds obtained exhibited an average porosity and compressive strength in the range 41.9–79.3% and 35.1–2.7 MPa, respectively, depending on the processing conditions used.

A Bidirectional NoC (BiNoC) Architecture With Dynamic Self-Reconfigurable Channel

A bidirectional channel network-on-chip (BiNoC) architecture is proposed to enhance the performance of on-chip communication. In a BiNoC, each communication channel allows to be dynamically self-reconfigured to transmit flits in either direction. This added flexibility promises better bandwidth utilization, lower packet delivery latency, and higher packet consumption rate. Novel on-chip router architecture is developed to support dynamic self-reconfiguration of the bidirectional traffic flow. This area-efficient BiNoC router delivers better performance and requires smaller buffer size than that of a conventional network-on-chip (NoC). The flow direction at each channel is controlled by a channel direction control (CDC) algorithm. Implemented with a pair of finite state machines, this CDC algorithm is shown to be high performance, free of deadlock, and free of starvation. Extensive cycle-accurate simulations using synthetic and real-world traffic patterns have been conducted to evaluate the performance of the BiNoC. These results exhibit consistent and significant performance advantage over conventional NoC equipped with hard-wired unidirectional channels.

Control of pore channel size during freeze casting of porous YSZ ceramics with unidirectionally aligned channels using different freezing temperatures

Porous yttria-stabilized zirconia (YSZ) ceramics with unidirectionally aligned pore channels were prepared by freezing YSZ/tert-butyl alcohol (TBA) slurry under different freezing temperatures of −30, −78 and −196 °C, respectively. After removing the frozen TBA via freeze-drying in vacuum at −50 °C, the green samples were sintered at 1450 °C for 2 h in air. The results showed that the freezing temperature significantly influenced microstructure and properties of the porous YSZ ceramics. Both microstructure observation and pore size distribution indicated that the pore channel size decreased significantly with decreasing freezing temperature, regardless of microstructure variations in the individual sample. Both porosity and room-temperature thermal conductivity of the porous YSZ ceramics varied under different freezing temperatures. Regardless of microstructure variations in the samples under different freezing temperatures, all samples had unidirectional pore channels with increasing pore channel size along the freezing direction. The fabricated samples had remarkably low thermal conductivities both in directions perpendicular and parallel to the channel direction, thus rendering them suitable for applications in thermal insulations.

Fabrication and characterization of a porous multidomain hydroxyapatite scaffold for bone tissue engineering investigations

Tissue-engineering scaffold-based strategies have suffered from limited cell depth viability when cultured in vitro, with viable cells existing within the outer periphery of the fluid-scaffold interface. This is primarily believed to be due to the lack of nutrient delivery into and waste removal from the inner regions of the scaffold construct. This work develops a hydroxyapatite trimodal porous scaffold architecture (i.e., a scaffold providing a discrete domain for cell occupancy and a separate domain for nutrient delivery) through a freeze drying process. Unidirectional channels (500 microm diameter) were incorporated through CNC machining with total combined apparent porosities of 85.1% +/- 0.22%. Effective diffusion coefficients for the bimodal phase (consisting of micro- and meso-pores, without channels) were also determined (7.9 x 10(-10) m(2) s(-1)). Trimodal scaffolds also demonstrated enhanced permeability values (approximately 18-fold increase) compared with bimodal scaffold architectures. In vitro experiments were used to assess initial seeding efficiency and distribution as well as cell viability. The presence of unidirectional channels significantly enhanced initial cell seeding distribution throughout the scaffold depth, while maintaining relatively high seeding efficiencies (67.7% +/- 2.2% for trimodal, 79.1% +/- 2.1% for bimodal scaffolds). Numerical models demonstrated the effectiveness and efficacy of incorporating channels to increase the core oxygen concentration, with the accuracy of these models improved by using experimentally measured cellular oxygen consumption rates and effective diffusion coefficients. The presence of channels had a positive influence in minimizing the concentration gradients compared with bimodal scaffolds for the same cell density distributions.

석탄회의 재활용을 통한 다공질 뮬라이트 복합체의 제조

Porous mullite/alumina composites have been fabricated by a freeze casting technique using TBA-based coal fly ash/alumina slurry. After sintering, unidirectional macropore channels aligned regularly along the TBA ice growth direction were developed; simultaneously, small sized micropores fromed in the outer walls of the pore channels. The physical and mechanical properties (e.g. porosity and compressive strength) of the sintered porous composites were roughly dependant of processing conditions, due to the complexity of the factors affecting them. However, with increasing solid loading and sintering temperature, the compressive strength generally increased and the porosity decreased. After sintering 1500℃ for 2 h, the porous specimen (porosity: 52.1%) showed a maximum compressive strength of 70.0㎫.

Maintaining cell depth viability: on the efficacy of a trimodal scaffold pore architecture and dynamic rotational culturing

Tissue-engineering scaffold-based strategies have suffered from limited cell depth viability when cultured in vitro with viable cells typically existing at the fluid-scaffold interface. This is primarily believed to be due to the lack of nutrient delivery into and waste removal from the inner regions of the scaffold construct. This work focused on the assessment of a hydroxyapatite multi-domain porous scaffold architecture (i.e. a scaffold providing a discrete domain for cell occupancy and a separate domain for nutrient delivery). It has been demonstrated that incorporating unidirectional channels into a porous scaffold material significantly enhanced initial cell seeding distribution, while maintaining relatively high seeding efficiencies. In vitro static culturing showed that providing a discrete domain for nutrient diffusion and metabolic waste removal is insufficient to enhance or maintain homogeneous cell viability throughout the entire scaffold depth during a 7-day culture period. In contrast, scaffolds subjected to dynamic rotational culturing maintained uniform cell viability throughout the scaffold depth with increasing culturing time and enhanced the extent of cell proliferation (approximately 2-2.4-fold increase) compared to static culturing.

Porous mullite composite with controlled pore structure processed using a freeze casting of TBA-based coal fly ash slurries

Porous ceramic composite with controlled “designer” pore structure has been prepared by a freeze casting route using a tertiary-butyl alcohol (TBA)/coal fly slurry system. Unidirectional aligned macropore channels were developed by controlling the solidification direction. Simultaneously, small sized dendrite-like pores formed in the outer walls of the pore channels. The compressive strength of the sintered porous composite increased as the porosity decreased, i.e. low porosity gave a high compressive strength. After sintering at 1500 °C, the mullite composite with a porosity of 67% exhibited a compressive strength of ∼23 MPa.