Rectangular Blocks Research Articles

Ultra-broadband transmission absorption of the all-dielectric water-based metamaterial

In this paper, a structurally simple transmissive all-dielectric metamaterial absorber is designed, fabricated and measured. The unit cell consists of photosensitive resin and water, which the water layers composed of rectangle loop, rectangular block and traffic circle. It achieves over 90% absorption of electromagnetic waves in the frequency range between 11.0 and 27.3 GHz. Meanwhile, three absorption peaks are located at 12.5, 18.4, and 26.0 GHz, which the absorptive are 97.4%, 98.3%, and 98.5%, respectively. In addition, the characteristics of the designed metamaterial reveal wide-incident angle absorption and polarization-insensitive properties. The experimental sample is measured by using the free-space method, and the experimental results are verified to be in well agreement with the simulation data. Observing the distribution of electric and magnetic fields at different resonance frequencies, the physical mechanism of the absorption is attributed to strong magnetic resonance. Therefore, the proposed metamaterial has potential for widespread use in the fields of civilian and military.

Thermal Performance Analysis of Porous Foam-Assisted Flat-Plate Solar Collectors with Nanofluids

This study proposed a model of a porous media-assisted flat-plate solar collector (FPSC) using nanofluid flow. The heightened thermal efficiency of FPSC undergoes numerical scrutiny, incorporating various factors for analysis, including aspects like the configuration of the porous block introduced, Darcy number (Da = 10−5~10−2), types of nanoparticles, volume fraction (φ), and mixing ratio (φc). The numerical findings indicate that the dominant factor in the channel is the global Nusselt number (Nug). As the Darcy number rises, there is an improvement in the heat transfer performance within the channel. Simultaneously, for the case of Re = 234, φ = 3%, and φc = 100%, the Nug in the channel reaches a maximum value of 6.80, and the thermal efficiency can be increased to 70.5% with the insertion of rectangular porous blocks of Da = 10−2. Finally, the performance evaluation criteria (PEC) are employed for a comprehensive assessment of the thermal performance of FPSC. This analysis considers both the improved heat transfer and the pressure drop in the collector channel. The FPSC registered a maximum PEC value of 1.8 when rectangular porous blocks were inserted under conditions of Da = 10−2 and Re = 234 and the nanofluid concentrations of φ = 3% and φc = 100%. The findings can be provided to technically support the future commercial applications of FPSC. The findings may serve as a technical foundation for FPSC in upcoming porous media and support commercial applications.

Super-Rays Grouping Scheme and Novel Coding Architecture for Computational Time Reduction of Graph-Based Light Field Coding

Graph-based Light Field coding using the concept of super-rays is powerful to exploit signal redundancy along irregular shapes and achieves good energy compaction, compared to rectangular block -based approaches. However, its main limitation lies in the high time complexity for eigen-decomposition of each super-ray local graph, a high number of which can be found in a Light Field when segmented into super-rays. This paper examines a grouping scheme for super-rays in order to reduce the number of eigen-decomposition times, and proposes a novel coding architecture to handle the signal residual data arising for each super-ray group, as a tradeoff to achieve lower computational time. Experimental results have shown to reduce a considerable amount of decoding time for Light Field scenes, despite having a slight increase in the coding bitrates when compared with the original non-grouping super-ray-based approach. The proposal also remains to have competitive performance in Rate Distortion in comparison to HEVC-based and JPEG Pleno -based methods.

Effects of Different Chemical Disinfectants on Physical Properties of Denture Base Acrylic Resin Material

Statement of the problem: There is still a lack of data regarding the effects of exposure to different chemical disinfectants on the color stability, light translucency, and surface roughness of dentures is limited. Objective: This study aims to investigate the impact of six different chemical disinfectants on the color change, translucency, and surface roughness properties of heat-polymerized denture base acrylic resin. Material & Methods: Totally 70 rectangular blocks (10×10×2 mm) were polymerized from the heat-polymerized acrylic denture base resin material. The surfaces of the specimens polished with 600- and 1200-grit waterproof abrasive paper. Each specimen were immersed in six denture cleansers. The total immersion time of a specimen in selected chemical disinfectant was 36 hours. Color changes, translucency and, surface roughness were measured after immersion process. The results were statistically analyzed with 1-way ANOVA and the Tukey honestly significant difference (HSD) test (α=.05). Results: According to the results of the 1-way ANOVA test, significant differences were observed in the ∆E00, TP00 and Ra properties among the acrylic resin groups following immersion in chemical disinfectants (P<0.05). ΔE00 value of the CG group was significantly higher than that of the NS, SH, G, and E groups (P<0.05). The TP00 values of the NS and G groups were demonstrated significant differences compared with C group (P<0.05). The Ra values of the SH, SP, G, CG and, E groups were significantly increased after immersion process, in comparison with C and NS groups (P<0.05). Conclusions: Color stability, translucency and surface roughness of the denture base heat polymerized acrylic resin is influenced by chemical disinfectants.

IFM calculator: An algorithm for interfragmentary motion calculation in finite element analysis

BackgroundInterfragmentary motion (IFM) is a complex state that significantly impacts the healing process of fractures following implant placement. It is crucial to fully consider the IFM state after implantation in the design and biomechanical testing of implants. However, current finite element analysis software lacks direct tools for calculating IFM, and existing IFM tools do not offer a comprehensive solution in terms of accuracy, functionality, and visualization. MethodsIn our study, we developed a Python-based algorithm for calculating IFM that addresses limitations. Our algorithm automatically calculated IFM distances, sliding distances, gaps, as well as the angles and rotation of the two fracture surfaces using all nodes on both sides of the fracture ends. Researchers could input data and selected desired parameters in the interface. The algorithm then performed the necessary calculations and presented the results in a clear and concise manner. The algorithm also provided comprehensive data export capabilities, allowing researchers to customize analyses based on specific needs.To provide a more intuitive demonstration of the calculation process and usage of IFM-Cal, we conducted simulations in Ansys using two rectangular blocks to compare the accuracy and function of three different methods (Point based method, contact tool and IFM-Cal). ResultsThe point-based method and the contact tool could not accurately calculate IFA, while IFM-Cal could provide a comprehensive evaluation of IFA. In simulation 1, the IFM distances calculated using the point sampling method, contact tool, and IFM-Cal were 2.00 mm, 3.15 mm, and 2.00 mm, respectively. In simulation 2, both the point sampling method and contact tool failed to calculate the interfragmentary angle (IFA), while the IFM-Cal algorithm estimated an angle of -7.87°, which had a small error compared to the ground-truth value of 7.9°. ConclusionWe have developed an algorithm for computing IFM which can be utilized in finite element analysis and biomechanical experiments. By conducting comparative simulations with other existing algorithms, we have demonstrated the superior accuracy and expanded evaluation capabilities of our algorithm.

Self-Adaptive-Filling Deep Convolutional Neural Network Classification Method for Mountain Vegetation Type Based on High Spatial Resolution Aerial Images

The composition and structure of mountain vegetation are complex and changeable, and thus urgently require the integration of Object-Based Image Analysis (OBIA) and Deep Convolutional Neural Networks (DCNNs). However, while integration technology studies are continuing to increase, there have been few studies that have carried out the classification of mountain vegetation by combining OBIA and DCNNs, for it is difficult to obtain enough samples to trigger the potential of DCNNs for mountain vegetation type classification, especially using high-spatial-resolution remote sensing images. To address this issue, we propose a self-adaptive-filling method (SAF) to incorporate the OBIA method to improve the performance of DCNNs in mountain vegetation type classification using high-spatial-resolution aerial images. Using this method, SAF technology was employed to produce enough regular sample data for DCNNs by filling the irregular objects created by image segmenting using interior adaptive pixel blocks. Meanwhile, non-sample segmented image objects were shaped into different regular rectangular blocks via SAF. Then, the classification result was defined by voting combining the DCNN performance. Compared to traditional OBIA methods, SAF generates more samples for the DCNN and fully utilizes every single pixel of the DCNN input. We design experiments to compare them with traditional OBIA and semantic segmentation methods, such as U-net, MACU-net, and SegNeXt. The results show that our SAF-DCNN outperforms traditional OBIA in terms of accuracy and it is similar to the accuracy of the best performing method in semantic segmentation. However, it reduces the common pretzel phenomenon of semantic segmentation (black and white noise generated in classification). Overall, the SAF-based OBIA using DCNNs, which is proposed in this paper, is superior to other commonly used methods for vegetation classification in mountainous areas.

Development of stress block parameters for ultra high performance concrete

Extensive literature exists on mix design, production methods, and the structural behavior of ultra-high-performance concrete elements (UHPC). Numerous studies in these domains have significantly contributed to our comprehension of UHPC. Nevertheless, a notable research lacuna persists in formulating rectangular stress block parameters tailored specifically for UHPC. This gap arises from the predominant reliance on prevailing standard codes and guidelines, which are founded on experimental data derived from normal concrete, rendering them inadequately applicable to the design of UHPC structures. This paper addresses this research gap by proposing novel rectangular stress block parameters explicitly designed for UHPC. The compression stress block is derived by modeling the stress–strain response and evaluating the shape factor. Simultaneously, the tension stress block is developed by modeling responses during the linear elastic phase, fiber activation, and fiber activation stages using stress versus crack width relationships. The derived relationships considering strength, reinforcement index, and fiber efficiency satisfactorily predict the moment capacity of UHPC beams with varying fiber dosages and geometrical dimensions. The proposed stress block parameters, denoted as alpha and beta, are presented for compression strength ranging up to 200 MPa and found suitable for designing structural members using UHPC.

OPERATIONS ON BLOCK PREDICATE MATRICES

This article discusses the possibility of performing basic logical operations on matrices that are divided into rectangular blocks in an arbitrary manner. The results obtained are illustrated using the example of predicate logical matrices defined over a field of finite predicates of arbitrary arity. The possibility of extending the results obtained to Boolean matrices is also justified (they are considered to be defined over a field of finite predicates of zero arity). At the same time, using the apparatus of multivalued logic, starting from Boolean logical matrices, the results obtained can also be extended to the study of logical objects that are not Boolean. Block partitioning of matrices allows you to divide information specified in matrix form into parts, process these parts separately, and then combine them into a single whole, adhering to certain rules and restrictions described in this article. These methods can find their application in graph theory, in the theory of algorithms, programming and in other areas of theoretical and practical activity that are in one way or another related to mathematical logic.

Theoretical Investigation on Indirect Tensile Strength of Concrete with Rectangular Cross-Section under Locally Distributed Load.

The indirect tensile test plays a crucial role in experimental investigations of brittle material properties. In this study, a mechanical analysis model of the rectangular test block is established based on the theory of elastic mechanics for the characteristics of the indirect tensile test. The theoretical solution of the triangular series is derived for the rectangular test block under the locally distributed load. The finite element simulation results and splitting test results were compared with the theoretical results. The results of the study verify the accuracy of the theoretical solutions. Based on the proposed analytical solution, the effects of loading width and length-to-height ratio (h/l) of local loading on the measured tensile strength of test block are discussed. The results demonstrate that the tensile strength of the test block increases as the loading width expands, and the rate of growth in the recorded tensile strength gradually stabilizes. The variation in loading width affects the location of crack initiation points during the concrete test block splitting tests. When the loading width exceeds 6% of the side length of test block, the cracking point is positioned at the center of test block, ensuring the effectiveness of the splitting test. As the length-to-height ratio of the test block increases, there is a general upward trend in the measured tensile strength. When h/l < 0.6, the measured tensile strength initially increases before decreasing. However, when h/l > 0.6, the measured tensile strength consistently increases, with the rate of increase gradually diminishing until it stabilizes. The length-to-height ratio also significantly influences the location of the cracking point in the test block. As the length-to-height ratio increases, the cracking point initially shifts from around the center to the central point and then further from the center toward the edge. To ensure that the location of the crack initiation point is in the center of the specimen and that the tensile strength is close to the measured result, the length to height ratio can be chosen at around 0.85.

Multiresolution approximation for shallow water equations using summation-by-parts finite differences

Abstract We present spatial approximation for shallow water equations on a mesh of multiple rectangular blocks with different resolution in Cartesian geometry. The approximation is based on finite-difference operators that fulfill Summation By Parts (SBP) property – a discrete analogue of integration by parts. The solution continuity conditions between mesh blocks are imposed in a weak form using Simultaneous Approximation Terms (SAT) method.We show that the resulting discrete divergence and gradient operators are anti-conjugate. The important consequences are the discrete analogues for mass and energy conservation laws along with the proof of stability for linearized equations. The numerical shallow water equations model based on the presented spatial approximation is tested using problems with meteorological context. Test results prove high-order accuracy of SBP-SAT discretization. The interfaces between mesh blocks of different resolution produce no significant noise. The local mesh refinement is shown to have positive effect on the solution both locally inside the refined region and globally in the dynamically coupled areas.

Influence of Immediate and Delayed Dentin Sealing on Bonding Strength of Lithium Disilicate Glass Ceramic: An in vitro Study

Objective: To investigate the influence of immediate and delayed dentin sealing technique on shear bonding strength (SBS) of the lithium disilicate glass-ceramic on tooth structure with different depths.&#x0D; Methods: The buccal surfaces of 40 maxillary first premolars were prepared with two different depths (1mm and 1.5 mm) and two different timings for bonding (immediate and delayed dentin sealing). G1 (1 mm preparation) and G2 (1.5 mm preparation) were treated with bonding (Tetric N-Bond Universal, Ivoclar,2021, Schaan/Liechtenstein) two weeks after preparation, before cementation to the ceramic block with delayed dentin sealing (DDS), while G3 (1 mm preparation) and G4 (1.5 mm preparation) were treated immediately after preparation with bonding and immediate dentin sealing (IDS). All specimens were stored in artificial saliva (Biotene dry mouth, GSK goupe, Canada) for two weeks at 24℃. Forty lithium disilicate glass-ceramic rectangular blocks (Rosetta SM) (HASSBIO, Korea) with dimensions of (2 mm height, 2mm width and 3 mm thickness) were prepared. After preparation of the tooth surfaces, all prepared blocks were cemented to the prepared teeth in groups GI and G2 with phosphoric acid 37% for 15 seconds, and all ceramic fitting surfaces were treated with 10% hydroflouric acid for 20 seconds and coupling agent monobond, then aging was performed for 5000 cycles in artificial saliva from 5-55 °C for all specimens. A universal test machine was used to test the shear bond strength (SBS). The statistical analysis was done using a one-way ANOVA test followed by Tukey's post hoc test (p&lt;0.05).&#x0D; Results: The result revealed that IDS and minimum preparation depth had significantly higher bonding strength than DDS. Bonding strength in sequence was 15.50 ± 3.873 MPa in G3 and G4 8.25 ± 3.344 MPa, while for delayed dentin sealing the bonding strength was 7.75 ± 2.993 in G1 and 6.25 ± 2.125 MPa in G2.&#x0D; Conclusions: Teeth treated with IDS immediately after preparation showed significantly higher bonding strength than those treated with DDS for indirect ceramic restoration. Also, increase in the depth of the preparation toward the dentin led to a decrease in the bonding strength of the restoration.

Toward quantitative super-resolution microscopy: molecular maps with statistical guarantees.

Quantifying the number of molecules from fluorescence microscopy measurements is an important topic in cell biology and medical research. In this work, we present a consecutive algorithm for super-resolution (stimulated emission depletion (STED)) scanning microscopy that provides molecule counts in automatically generated image segments and offers statistical guarantees in form of asymptotic confidence intervals. To this end, we first apply a multiscale scanning procedure on STED microscopy measurements of the sample to obtain a system of significant regions, each of which contains at least one molecule with prescribed uniform probability. This system of regions will typically be highly redundant and consists of rectangular building blocks. To choose an informative but non-redundant subset of more naturally shaped regions, we hybridize our system with the result of a generic segmentation algorithm. The diameter of the segments can be of the order of the resolution of the microscope. Using multiple photon coincidence measurements of the same sample in confocal mode, we are then able to estimate the brightness and number of molecules and give uniform confidence intervals on the molecule counts for each previously constructed segment. In other words, we establish a so-called molecular map with uniform error control. The performance of the algorithm is investigated on simulated and real data.

A subdivision-stabilized B-spline mixed material point method

Subjected to external loadings, polymeric materials, e.g., biological tissues, hydrogels, and elastomers, may undergo extreme, nearly incompressible, (self-)contact deformations. For numerical modeling employing mesh-based techniques such as the finite element method (FEM), these deformations pose significant challenges due to large distortions in the deformed geometry, accuracy issues stemming from volumetric locking effects, and increased computational cost from complex contact searches. As an alternative to mesh-based methods, the material point method (MPM), a continuum-based particle technique, is gaining attention for its ability to handle extreme distortions and capture no-slip contact without added cost. For nearly incompressible material behaviors, while mixed formulations can address locking effects by treating displacements and pressure as independent fields, they can suffer from numerical instabilities close to the incompressibility limit due to the violation of the inf-sup condition, leading to inaccurate nodal pressure solutions. Here we propose an efficient and stable mixed B-spline material point method with highest achievable regularity for quasi-compressible polymeric materials. Using the two-scale relation of B-splines, we introduce a subdivision-stabilization for the two-field mixed MPM and obtain numerically stable, oscillation-free nodal solutions with equal-order interpolations with optimal regularity. Building on the Eulerian-Lagrangian nature of MPM, a previously-converged solution framework is adopted to mitigate issues related to cell-crossing and numerical fracture artifact present in standard MPM. We assess the stability and accuracy of the developed mixed MPM at large deformations for soft materials through the benchmark Cook’s membrane problem. Additionally, we test the robustness of the proposed MPM by modeling several examples, including the compression and indentation of a circular block into a quasi-compressible substrate and the twisting deformation of a rectangular block. The findings demonstrate the MPM’s capabilities for modeling practical soft material applications.

Synthesizing Non-Uniformly Excited Antenna Arrays Using Tiled Subarray Blocks

Conventionally, non-uniformly excited antenna arrays are synthesized by independently determining the excitation amplitude and phase of each single element. Such an approach is considered to be the most expensive and complex design method available. In this paper, the tilling technique is harnessed to synthesize non-uniformly excited antenna arrays. To apply this technique, the array elements are first divided into different subarray shapes, such as rectangles or squares known as tiles. The use of rectangular tile blocks instead of a single element architecture greatly simplifies the array design process and reduces array complexity. Next, the problem concerned with synthesizing sub-arrays comprising rectangular tile blocks is formulated and solved by using horizontal and vertical orientations of tiles having different shapes and sizes, and their larger integer expansions. The third approach to tiled design is a mixture of both previous tile architectures. A genetic algorithm is used to design such tiled arrays offering optimum sidelobe levels, beam width, directivity and taper efficiency. Simulation results demonstrated the effectiveness of the proposed tiled arrays.

Cucurbit[6]uril Hyperpolarized Chemical Exchange Saturation Transfer Pulse Sequence Parameter Optimization and Detectability Limit Assessment at 3.0T.

Molecular imaging is the future of personalized medicine; however, it requires effective contrast agents. Hyperpolarized chemical exchange saturation transfer (HyperCEST) can boost the signal of Hyperpolarized 129Xe MRI and render it a molecular imaging modality of high efficiency. Cucurbit[6]uril (CB6) has been successfully employed in vivo as a contrast agent for HyperCEST MRI, however its performance in a clinical MRI scanner has yet to be optimized. In this study, MRI pulse sequence parameter optimization was first performed in CB6 solutions in phosphate-buffered saline (PBS), and subsequently in whole sterile citrated bovine blood. The performance of four different depolarization pulse shapes (sinusoidal, 3-lobe sinc (3LS), rectangular (block), and hyperbolic secant (hypsec) was optimized. The detectability limits of CB6 in a clinical 3.0T MRI scanner was assessed using the optimized pulse sequences. The 3LS depolarization pulses performed best, and demonstrated 24% depletion in a 25µM solution of CB6 in PBS. It performed similarly in blood. The CB6 detectability limit was found to be 100µM in citrated bovine blood with a correspondent HyperCEST depletion of 30% ± 9%. For the first time, the HP 129Xe HyperCEST effect was observed in red blood cells (RBC) and had a similar strength as HyperCEST in plasma.

Experimental and Numerical Investigations on Flexible Paraffin/Fiber Composite Phase Change Material

Abstract A flexible paraffin/hollow fiber phase change composite was prepared using a simple impregnation method, and the thermal-release performance of a piece of woven paraffin/hollow fiber rectangular blocks was systematically investigated using experimental and numerical methods. The experimental results of the thermal-release performance were highly consistent with the numerical results. Consequently, the thermal-release performance, including the available energy and solidification time, of the paraffin/hollow fiber with different melting temperatures, mass fractions (corresponding to the enthalpy), specific heat, and thermal conductivity were numerically investigated. The available energy of the paraffin/hollow fiber completely depends on the mass fraction of the paraffin. The solidification time mainly depends on the mass fraction of the paraffin and secondarily on the thermal conductivity, while the specific heat has little effect on the solidification time. Therefore, the thermal-release performance of the paraffin/hollow fiber could be optimized through numerical simulation by altering the solidification temperature, mass fraction, thermal conductivity, and specific heat.

Large eddy simulation of enhanced heat transfer in grooved channel with pulsating flow corresponding to hydrodynamic frequency

This paper presents a numerical investigation on flow and heat transfer in a grooved channel formed by 9 rectangular blocks with steady and pulsating flow. Large eddy simulation is used to simulate the hydrodynamic instability in steady flow and heat transfer enhancement for pulsating flow. The simulations for steady flow at Re=700, 1500, 2500, are firstly conducted, showing that there are 23Hz, 70Hz and 130Hz natural frequencies fN induced by hydrodynamic instability (corresponding to Strouhal number StN=0.876, 1.243, 1.385) behind the first block, which disappear quickly with the flow development. A natural frequency fN of 34Hz (StN=1.295) is found only at Re=700 and it can be maintained and amplified by groove structures. Subsequently, a sinusoidal pulsating flow is applied, with the forcing frequency StF equal to the natural frequency StN in steady flow and the dimensionless amplitude A fixed at 0.2. Flow and thermal performance of the grooved channel is studied under the pulsating condition. A periodic process of vortex generation-shedding-fusion is found behind each block and the fluid in the channel has higher turbulent kinetic energy than that under the steady condition. Ultimately, compared with the thermal and pressure-drop performance between steady and pulsating flow, the enhancement of time-average Nusselt number ranges from 48.08%, 15.64%, 8.61% and time-average friction factor increases by about 40% at Re=700, 1500, 2500. The thermal performance factor is increased by 30.96% and 4.20% at Re=700, 1500 but is reduced slightly by 3.48% at Re=2500. It indicates that the augmentation of heat transfer through pulsating flow is significant at low Reynolds numbers.

Numerical investigation of hydraulic jumps with USBR and wedge-shaped baffle block basins for lower tailwater

Abstract The stilling basin of the Taunsa barrage is a modified form of the United States Bureau of Reclamation (USBR) Type-III basin, which consists of baffle and friction blocks. Studies revealed uprooting of baffle blocks due to their vertical face. Additionally, the literature highlighted issues of rectangular face baffle blocks: less drag, smaller wake area, and flow reattachment. In contrast, the use of wedge-shaped baffle blocks (WSBBs) is limited downstream of open-channel flows. Therefore, this study developed numerical models to investigate the effects of USBR and WSBB basins on the hydraulic jump (HJ) downstream of the Taunsa barrage under lower tailwater conditions. Surface profiles in WSBB and modified USBR basins showed agreement with previous studies, for which the coefficient of determination (R2) reached 0.980 and 0.970, respectively. The HJ efficiencies reached 57.9 and 58.6% in WSBB and modified USBR basins, respectively. The results of sequent depths, roller length, and velocity profiles in the WSBB basin were found more promising than the modified USBR basin, which further confirmed the suitability of the WSBB basin for barrages. Furthermore, WSBB improved flow behaviors in the basin, which showed no fluid reattachment on the sides of WSBB, increased wake regions, and decreased turbulent kinetic energies.

Heat transfer enhancement using combined microchannel with vertical rectangular micro fins

This paper focuses on the numerical optimisation of a combined hybrid microchannel heat sink with rectangular solid fins. The axial length and volume are fixed, and external structure is allowed to vary. The simulation was performed on an elemental unit cell of the microchannel heat sink . The purpose of the optimisation is to discover an optimal geometric arrangement in internal and external configurations that minimises peak temperature in the microchannel heat sink. A high-density uniform heat flux of 250 W/cm2 is assumed to be dissipated on the bottom wall of the unit cell by microelectronics circuit boards devices. Computational fluid dynamic code was used to discretized the fluid domain and solve a set of governing equations. The influence of hydraulic diameter, external structural shape and fluid velocity on peak temperature and global thermal resistance, is discussed. Coolant or water of Reynolds number range 400 to 500 in a forced convection laminar flow is introduced through the inlet of the computational domain to remove the heat at the bottom of the rectangular block microchannel. The results show that when the fluid velocity is increased from 9.8 to 12.3 m/s across the axial length of the micro heat sink, more heat is removed from the bottom of the combined heat sink. The results revealed that the pump power increased by 37.1% in combined microchannels with fins and from by 27.2% in finless micro heat sink. The result of the study is validated with what is documented in open literature for a traditional micro heat sink with circular flow channel and the trends agree.

The Effect of Femtosecond Laser Surface Patterns on the Effectiveness of Resin Composite to Zirconia Bonding.

This laboratory study aimed to evaluate the effect of different surface patterns using femtosecond laser treatment on the enclosed mold shear bond strength (EM-SBS) of resin composite to zirconia (ZrO2) surfaces and to contrast it with the widely used tribochemical silica coating (TBC) surface conditioning method. A set of fifteen rectangular ZrO2 blocks were randomly divided into five groups according to surface pretreatment: Control G0-no treatment; G1-TBC with silane application; G2-femtosecond laser irradiation with horizontal lines 30 µm apart; G3-femtosecond laser irradiation with horizontal lines 15 µm apart; and G4-femtosecond laser irradiation with cross lines 30 µm apart. The pretreated surfaces were characterized by a surface profilometer, tensiometer and scanning electron microscope. The EM-SBS of resin composite stubs to ZrO2 was measured followed by fractographic analysis. The surface roughness and water contact angle were observed to be statistically higher among the femtosecond laser groups compared to the TBC and control groups. The G4 group exhibited the highest EM-SBS among all the groups, irrespective of the ageing conditions used. At the end of 5000 thermocycles, G4 exhibited EM-SBS of 14.05 ± 4.21 MPa compared to 13.80 ± 3.01 MPa in G1 and 5.47 ± 0.97 MPa in G0. The two-way ANOVA revealed a significant effect of both study groups and ageing conditions on the EM-SBS (p < 0.001). Utilization of femtosecond laser technology holds promise as a potential and alternative mechanical retention approach for enhancing the bonding strength of the resin composite to ZrO2.