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The crystalline quality of GaN layer grown on 4H-SiC substrate using Metal Organic Chemical Vapor Deposition (MOCVD) has been improved by reducing the growth rate of GaN. Depth resolved CL (cathodoluminescence) study was also done to analyze the defects in the GaN layers. Two samples, one with fast growth rate (∼0.7 nm/s; Sample-A) of GaN and other with slower growth rate (∼0.2 nm/s; Sample-B) were grown. The surface morphology and crystalline quality of GaN epi-layers have been studied by Atomic Force Microscopy (AFM) and High Resolution X-Ray Diffraction (HRXRD), respectively. It was observed that growth rate of the GaN layer strongly influenced its crystalline quality and surface morphology. The GaN layer grown with slow growth rate exhibited improved surface morphology with lower rms roughness of ∼0.18 nm and lower surface pits density. X-ray rocking curve measurement for (0 0 2) and (1 0 2) planes showed that both screw and edge dislocation densities were reduced for the GaN grown with slow growth rate. Depth profiling by CL spectroscopy revealed intense Yellow (YL) and Blue luminescence (BL) band in Sample-A, while in Sample B, the YL and BL bands were much weaker. The higher yellow and blue luminescence in the GaN grown at higher growth rate may be correlated with nitrogen vacancies (VN) and two charged state of CN(−/0 and 0/+) acceptor.

Molybdenum Trioxide (MoO3) films are grown on Si(100) substrates by reactive RF magnetron sputtering in plasma containing a mixture of Argon and Oxygen, using a pure Molybdenum target. In this paper, we report the deposition of (MoO3) films on Si(100) substrates under varying gas flow (O2 + Ar gas) (20 sccm to 30 sccm with the duration of deposition~ 1hr) by RF reactive magnetron sputtering at room temperature. To get crystalline MoO3 films annealing in O2 environment at 500 °C for 4 h is done. Phase formation and orientation of the film is characterized by Glancing incidence X-ray diffraction (GIXRD). The identification of the orthorhombic MoO3 phase is investigated by XRD and Raman spectroscopy. Raman lines at 819 cm-1 and 995 cm-1 are due to the (A1g, B1g) symmetric stretching (Mo-O–Mo) bond and asymmetric stretching band (Mo=O) respectively. Surface morphology and cross-sectional image of the deposited thin films were investigated by FE-SEM image. UV-Visible reflectance and cross-sectional FE-SEM image confirm the thickness of the MoO3 films with oxygen-rich and oxygen deficient phase formation occur. Reverse leakage current density of 20 sccm 1hr sample is low (1×10-6 mA/cm2) as compared to 30 sccm 1hr sample (1×10-3 mA/cm2). The higher leakage is due to crack formation during the ex-situ annealing of MoO3 films. This MoO3 films can be used in Gas sensing and switching devices.

Generally, it is very difficult to grow large diameter 4H-SiC single crystal with single polytype by Physical Vapor Transport (PVT) growth method and mostly it ends up with the presence of some other polytypes (viz. 6H, 15R). This paper presents the various comprehensive polytype identification techniques in SiC wafer grown by PVT method. Characterization techniques, viz. X-Ray diffraction, Scanning electron microscopy, Cathodoluminescence (CL) and Raman spectroscopy, are used in the present study in order to identify the presence of 4H, 6H and 15R polytype region in SiC wafer. Raman mapping (using phonon frequencies at 150, 171, 203 cm−1 for 6H, 15R and 4H, respectively) and X-Ray Topography [using grazing incidence asymmetric plane (11–2 8) for 4H-SiC, (11–2 12) for 6H-SiC and (11–2 30) for 15H-SiC] and CL spectra (defect state peak positions at ~ 500 nm and 580 nm for 4H and 6H, respectively) are proposed to distinguish the switching of polytypes in a large area SiC wafer. The polytype switching in SiC ingot may occur because of temperature fluctuations during the sublimation growth process.

In this study, the GaN films were deposited in the multilayered structures under different growth conditions. SIMS analysis showed that intrinsic carbon incorporation around two orders can be controlled effectively by varying the growth parameters. Defects analysis by cross-sectional cathodoluminescence (X-CL) is demonstrated as a useful analytical technique for unambiguously understanding the effect of incorporation of the intrinsic carbon concentration on the yellow luminescence (YL) and blue luminescence (BL) band intensities. It was inferred from the experimental data that the observed BL and YL intensities are due to the electronic transitions through the isolated CN and CNON complex, respectively. This finding is in contrast to the theoretically published literature that two charged states of CN are responsible for both BL and YL which sought that the BL emission to be always smaller in comparison to YL emission. Our experimental data, for all different growth conditions showed the prominent BL in comparison to YL except for the growth at sufficiently lower temperature which is considered to be more conducive for higher oxygen incorporation into the stoichiometry. This increases the probability of CNON formation which is manifested in the enhancement of YL intensity over BL as the formation energy of CNON complex is lower than the CN defect. Thus, X-CL analysis method can be key to address the challenges of understanding the impurity character in multi-thin layered GaN structures.

This paper presents formation of interconnected mesoporous structure using low energy (50 keV) Ar+-ion irradiation normal to the GaSb surface for the ion fluence 1 × 1016 and 5 × 1017 ions/cm2. The...

Correlating hydrogen embrittlement phenomenon with the metallic microstructural features holds the key for developing metals resistant to hydrogen-based failures. In case of fatigue failure of hydrogen charged metals, in addition to the hydrogen-based failure mechanisms associated with monotonic loading such as HELP, HEDE etc., microstructural features such as grain size, type of grain boundary (special/random), fraction of special grain boundaries; their network and triple junctions can play a complex role. The probable sites for fatigue crack initiation in such metals can be identified as the sites of highest hydrogen concentration or accumulated plastic strain. To this end, we have developed an experimental framework based on in-situ fatigue crack initiation and propagation studies under scanning electron microscope (SEM) to identify the weakest link in the metallic microstructure leading to failure. In-situ fatigue experiments are performed on carefully designed polycrystalline nickel (99.95% pure) specimens (miniaturised, shallow-notched & electro-polished) using a 10 kN fatigue stage inside the SEM. Electron Back Scattering Diffraction (EBSD) map of the notched region surface helps identify the distribution of special/random grain boundaries, triple junctions and grain orientation. The specimen surface in the shallow notched region for both the hydrogen charged and un-charged specimens are then carefully studied to correlate the microstructural feature associated with fatigue crack initiation sites. Such correlation of the fatigue crack initiation site and microstructural feature is further corroborated with the knowledge of hydrogen trapping and grain’s elastic anisotropicity to be either the site of high hydrogen concentration, accumulated plastic slip or both.

Aim: This study aims to evaluate and compare the shear bond strength (SBS) of three different resin cements - total etch and rinse, self-etch and self-adhesive resin cements, used to bond the lithium disilicate restorations to human dentin. Settings and Design: Comparative -Invitro study design. Materials and Methods: Forty-five lithium disilicate (IPS E.max) discs (4 mm in diameter and 3 mm thick) were fabricated and randomly divided into three groups (n = 15). The occlusal surfaces of 45 extracted human maxillary premolars were ground flat. Fifteen specimens were luted, under a constant load, with each of the following resin cement: Variolink N (Group VN), Multilink N (Group MN), and Multilink Speed (Group MS). All cemented specimens were stored in distilled water for 1-week following which, they were tested under shear loading at a constant crosshead speed of 1 mm/min until fracture on a universal testing machine; the load at fracture was reported in megapascals (MPa) as the bond strength. Fractured specimens were also inspected by the scanning electron microscopy. Statistical analysis of the collected data was performed using one-way ANOVA test, post hoc Bonferroni test, and Chi-square test (α =0.05). Statistical Analysis Used: Oneway ANOVA test and post hoc Bonferroni test. Results: Mean SBS data of the groups in MPa were: Variolink N (Group VN): 14.19 ± 0.76; Multilink N (Group MN): 10.702 ± 0.75; and Multilink Speed (Group MS): 5.462 ± 0.66. Significant differences in SBS (P < 0.001) of the three resin cement were found. Intergroup comparison revealed statistically significant differences in SBS between Groups VN and MN (P < 0.001), Groups B and C (P < 0.001), and Groups VN and MS (P < 0.001). Chi-square test used to compare the distribution of mode of bond failure among the three groups delineated that the cohesive failure was significantly more among Group VN, whereas adhesive failure was significantly more among Group MN and MS. Conclusion: Total etch and rinse resin cement, i.e., Variolink N (Group VN) produced significantly higher bond strength of all-ceramics to dentin surfaces than did the self-etch and self-adhesive resin cements, i.e., Multilink N and Multilink Speed, respectively.

This paper presents an investigation on micropipe evolution from hexagonal voids in physical vapor transport-grown 4H-SiC single crystals using the cathodoluminescence (CL) imaging technique. Complementary techniques optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy (EDS) are also used to understand the formation mechanism of hexagonal voids along with the origin of pipes from these voids. The ability of CL to image variations along the depth of the sample provides new insights on how micropipes are attached to hexagonal voids that lie deep within the bulk single crystals. CL imaging confirms that multiple micropipes can originate from a single hexagonal void. EDS mapping shows that the inside of the micropipe walls exhibits higher levels of carbon. Investigation of the seed region by optical imaging shows that improper fixing of the seed to the crucible lid is the root cause for the formation of hexagonal voids that subsequently lead to micropipe formation.

Aim: The purpose of this study was to compare the marginal and internal adaptation of cobalt-chromium (Co-Cr) copings fabricated from conventional wax pattern, three-dimensional (3D)-printed resin pattern, and laser sintering technique. Materials and Methods: A total of thirty copings were made, out of which ten copings were made from 3D-printed resin pattern (Group A), ten from inlay wax pattern (Group B), and ten copings were obtained from direct metal laser sintering (DMLS) technique (Group C). All the thirty samples were seated on their respective dies and sectioned carefully using a laser jet cutter and were evaluated for marginal and internal gaps at the predetermined areas using a stereomicroscope. The values were then analyzed using one-way ANOVA test and post hoc Bonferroni test. Results: One-way ANOVA showed lowest mean marginal discrepancy for DMLS and highest value for copings fabricated from inlay wax. The values for internal discrepancy were highest for DMLS (169.38) and lowest for 3D-printed resin pattern fabricated copings (133.87). Post hoc Bonferroni test for both marginal and internal discrepancies showed nonsignificant difference when Group A was compared to Group B (P > 0.05) and significant when Group A was compared with Group C (P < 0.05). Group B showed significant difference (P < 0.05) when compared with Group C. Conclusion: Marginal and internal discrepancies of all the three casting techniques were within clinically acceptable values. Marginal fit of DMLS was superior as compared to other two techniques, whereas when internal fit was evaluated, conventional technique showed the best internal fit.

This paper reports two specific aspects of Si implantation in the molecular beam epitaxy grown p-type GaSb epilayer, namely, the evolution of nanoporosity and doping characteristics. The implantation is done with 100 keV Si ions at four different fluences, i.e., 5 × 1013, 1 × 1014, 5 × 1014, and 1 × 1015 ions/cm2. A field-emission scanning electron microscope (in-plane and cross-sectional view) shows a smooth nanoporous GaSb with a pore diameter of 10–20 nm for the higher fluences. The thickness of the porous film is enhanced from 235 nm (fluence: 1 × 1014 ions/cm2) to 515 nm (fluence: 1 × 1015 ions/ cm2). Development of smooth uniform porous GaSb using Si ion implantation is discussed from the viewpoint of displacement per atom and distribution of vacancies estimated through Stopping and Range of Ions in Matter simulation tool. Hall measurement shows conversion to n-type behavior after implantation and a variation in the sheet carrier concentration from 2.22 × 1014 to 8.52 × 1014 cm−2. There is a drastic change in the mobility with the onset of void formation by implantation.

Aim: This study aims to evaluate the flexural strength, hardness, and impact strength of heat-cured high-impact denture base resins with different polymer/monomer ratios. Materials and Methods: A total of 150 acrylic samples were prepared using high impact denture base resin (Travelon Hi). The samples were divided into five groups based on different powder/liquid ratios (g/ml) with 30 samples in each group. The P/L ratio in Group 1 (Ratio - 2.2:1) was the manufacturer's recommended ratio and was used as control. In Group 2, the ratio was 2.7:1, in Group 3, the ratio was 3.2:1, in Group 4, the ratio was 1.9:1, and Group 5 the ratio was 1.6:1. Each group with 30 samples was further subdivided into three different subgroups comprising 10 samples each, based on the properties to be evaluated, i.e., for flexural strength, hardness, and impact strength evaluation. The samples were tested for flexural strength, Vicker's hardness number (VHN) and impact strength. One-way ANOVA including post hoc-Tukey's tests was used to calculate the difference of means for quantitative variables and for intergroup comparison as well. Results: The results showed that the flexural strength values and VHN values showed a similar trend. The values decreased significantly as the ratio was increased or decreased from the control group. The results also showed that there was nonsignificant difference between the mean impact strength values for all the groups. Conclusion: For reinforced resins or high impact resins, the manufacturer's recommended polymer/monomer mixing ratio should be used to obtain the appropriate strength of the material.

Purpose: The purpose of this study was to evaluate the effect of incisal butt joint and incisal overlap design on the fracture resistance of ceramic veneers under two different loading conditions, i.e., 125° and 60° representing protrusive and intercuspal movements, respectively. Materials and Methods: Thirty-two maxillary central incisors were divided into two groups of sixteen specimens each and were prepared with incisal butt joint and incisal overlap design. Ceramic veneers were fabricated and cemented. Both the groups were further divided and mechanical testing to evaluate the fracture resistance were done using the universal testing machine. The values were recorded in Newton along with the assessment of the failure mode of both veneer and the tooth. Results: Unpaired t-test showed a significant difference (P < 0.05) with butt joint design having higher fracture resistance than palatal overlap design with the mean value of 409.50N at 60° angle and 473.37N at 125° angle. Paired t-test depicted a significant difference for both the designs at 125° than at 60° angle (P < 0.05). Chi-square analysis showed more number of intact veneers with butt joint design; however, there was no significant difference (P > 0.05). Failure mode of teeth showed more number of coronal fracture followed by cervical fracture and root fracture, but there was no significant difference between the two groups (P > 0.05). Conclusion: Butt joint design had higher fracture resistance than palatal overlap design. Under functional loads for both designs, fracture resistance was higher at 125° than at 60° angle.

The article presents design, analysis and development of a hyperelastic material based pneumatically driven soft bendingtype actuator as a viable actuation concept for enabling steering and navigation in a mechanized endoscopic device. The applications extend to rehabilitation and other non-medical field as well. This work introduces polylithic construction of a soft actuator using multiple grades of silicone. Developments of two types of actuators are presented, viz. one using single material in a monolithic (homogeneous) design and other utilizing combination of materials of different shore hardness in a polylithic (heterogeneous) construction. The behaviors of the developed actuators are studied using FEM modeling techniques with non-linear material models. Experiments are conducted with various end-point loading and blocked-tip conditions and corresponding simulation results are compared. It is observed that actuator built with softer actuation channel on the periphery and harder core manifests better deformation stability and uncompromised force capability at slightly higher actuation pressure than in homogenous construction.

Hydrogen is foreseen as a promising energy carrier that can control global warming by reducing CO2 emissions. However, hydrogen is associated with an embrittlement phenomenon that imparts substantial damage to the infrastructure by reducing the ductility, fracture strength, strength bearing capacity, etc., of metallic components. Therefore, understanding hydrogen-induced crack initiation mechanisms in metals are of prime importance. Greater insights into this critical phenomenon are expected if the hydrogen-induced crack initiation can be correlated with the local microstructure and corresponding stress-strain state towards their propensity for hydrogen accumulation. With this motivation, in this work, crack initiation is studied for the uncharged and hydrogen charged nickel specimens during in-situ tensile loading under the scanning electron microscope. By assuming the material to be elastic at low strains, a novel approach is implemented for generating the microstructural stress maps through strain and stiffness tensor extracted at each point in the region of interest on the specimen surface using high-resolution digital image correlation (HR-DIC) and Euler angles (given by electron backscattered diffraction data), respectively. Based on this analysis at low strain, the crack initiation sites for uncharged and hydrogen charged nickel specimens are correlated with microstructural maps of maximum Schmid factor, elastic modulus in the loading direction, hydrostatic stress, von Mises stress, and triaxiality factor. The analysis highlighted two independent factors responsible for hydrogen enhanced decohesion (HEDE) based intergranular failure observed only at the random grain boundaries, (i) strain localization due to hydrogen enhanced localized plasticity (HELP) mechanism of hydrogen embrittlement, and (ii) hydrostatic stress-based hydrogen diffusion to the crack initiation sites. These critical insights thus can help to design hydrogen embrittlement resistant metals. In addition, the novel experimental approach can be used to calibrate advance micromechanical models while providing quantitative estimate of the hydrogen distribution in realistic metallic microstructure responsible for hydrogen-assisted crack initiation with deformation.

The use of implants in the oral and maxillofacial skeleton continues to expand and since then implant surfaces have been modified in various ways to improve biocompatibility and accelerate osseointegration, which results in a shorter edentulous period for a patient. This article reviewed several methods that are widely used to modify the topography or chemistry of titanium surface, including blasting, acid etching, anodic oxidation, fluoride treatment, and calcium phosphate coating. Such modified surfaces demonstrate faster and stronger osseointegration than the turned commercially pure titanium surface.

Background or Statement of Problem: As, the longevity of provisional restorations is related to, a perfect adaptation and a strong, long-term union between restoration and teeth structures, therefore, evaluation of marginal leakage of provisional restorative materials luted with cements using the standardized procedures is essential. Aims and Objectives: To compare the marginal leakage of the provisional crowns fabricated from Autopolymerizing acrylic resin crowns and bisphenol A-glycidyl dimethacrylate (BIS-GMA) resin crowns. To compare the marginal leakage of the provisional crowns fabricated from autopolymerizing acrylic resin crowns and BIS-GMA resin crowns cemented with different temporary luting cements. To compare the marginal leakage of the provisional crowns fabricated from autopolymerizing acrylic resin (SC-10) crowns cemented with different temporary luting cements. To compare the marginal leakage of the provisional crowns fabricated from BIS-GMA resin crowns (Protemp 4) cemented with different temporary luting cements. Methodology: Freshly extracted 60 maxillary premolars of approximately similar dimensions were mounted in dental plaster. Tooth reduction with shoulder margin was planned to use a customized handpiece-holding jig. Provisional crowns were prepared using the wax pattern fabricated from computer aided designing/computer aided manufacturing milling machine following the tooth preparation. Sixty provisional crowns were made, thirty each of SC-10 and Protemp 4 and were then cemented with three different luting cements. Specimens were thermocycled, submerged in a 2% methylene blue solution, then sectioned and observed under a stereomicroscope for the evaluation of marginal microleakage. A five-level scale was used to score dye penetration in the tooth/cement interface and the results of this study was analyzed using the Chi-square test, Mann–Whitney U-test, Kruskal–Wallis H-test and the results were statistically significant P < 0.05 the power of study - 80%. Results: Marginal leakage was significant in both provisional crowns cemented with three different luting cements along the axial walls of teeth (P < 0.05) confidence interval - 95%. Conclusion: The temporary cements with eugenol showed more microleakage than those without eugenol. SC-10 crowns showed more microleakage compared to Protemp 4 crowns. SC-10 crowns cemented with Kalzinol showed maximum microleakage and Protemp 4 crowns cemented with HY bond showed least microleakage.

This article presents the design, fabrication and characterisation of an elastomeric flexible and stretchable strain sensor using a variable resistance fabric. This provides a viable alternative to the microfluid and nanoparticle based flexible strain sensors involving complex fabrication techniques. A nylon-spandex based stretchable fabric serves as the sensing element which is in turn embedded in an elastomeric substrate. The fabricated sensor is experimentally characterised for determining the linearity, hysteresis, stretchability and gauge factor. The Finite Element Method based simulations to predict the operational force range of the sensor corresponding to its strain sensing range has been validated with the experimental results. These sensors have a wide range of potential applications in the constantly developing field of compliant robotics and mechanisms. In future works, these sensors will be utilized in the biomechanical analysis of human movements to track the various joint parameters.

Hydrogen deteriorates the fatigue behaviour of metals by attacking their microstructure in different ways. For better clarity about hydrogen-based degradation of metals, it is vital to identify the microstructural configurations that promote fatigue crack initiation (FCI) in the presence of hydrogen. Intergranular regions in polycrystalline metals are more prone to hydrogen attack due to the prevailing atomic structure, elastic anisotropy, and plastic inhomogeneities causing increased hydrogen accumulation in this region. In this work, FCI is studied in a model material nickel in the uncharged and hydrogen charged state during in-situ strain controlled low cycle fatigue (LCF) testing under a scanning electron microscope (SEM). Crack initiation sites are characterized by investigating the elastic modulus in the loading direction as well as the maximum Schmid factor of the crack neighbouring grains extracted through the electron backscattered diffraction (EBSD) data. The crack frequency for the uncharged and hydrogen charged specimens is then analyzed using the difference in the elastic modulus ( Δ E ), the difference in the maximum Schmid factor ( Δ m ), and Δ E / Δ m ratio between the crack neighbouring grains. The comparison shows that for the hydrogen charged specimens, intergranular FCI sites show high values of Δ E / Δ m compared to the uncharged specimens. These findings provide a predictive model for hydrogen linked FCI in metals. In addition, the synergistic role of the Hydrogen Enhanced Local Plasticity (HELP) mediated Hydrogen Enhanced Decohesion (HEDE) mechanism responsible for FCI is also demonstrated.

Present work aims to unveil the mechanism of hydrogen embrittlement (HE) in SA508 Grade 3 Class I low alloy reactor pressure vessel (RPV) steel. In-situ tensile and low cycle fatigue (LCF) tests are performed on specially designed specimens using tensile/fatigue testing stage under scanning electron microscope (SEM). Electrochemical hydrogen charging resulted in localized void formation at prior austenite grain boundaries (PAGBs) during tensile loading. Alongside the hydrogen induced weakening of PAGBs due to synergetic HELP (hydrogen enhanced localized plasticity) and HEDE (hydrogen enhanced decohesion) mechanisms of HE, fish-eyes formation around Al2O3–SiO2 type inclusions are the primary factors for hydrogen enhanced tensile properties degradation in subject RPV steel. During LCF loading, crack initiation and propagation is facilitated by long rod inter-lath cementite particles distributed along the bainitic ferrite lath boundaries in the un-charged specimen. In case of hydrogen charged specimen, the edge crack formed during LCF loading propagated through the specimen by cleavage. Predominantly plasticity (slip) driven transgranular crack propagation occurred in un-charged specimen. In contrary, hydrogen charging resulted in LCF crack to propagate in mixed intergranular and transgranular manner during early stages of propagation, whereas once the crack length exceeded 5 to 6 grains, cleavage type transgranular crack propagation was observed.

AlGaN/GaN high electron mobility transistor (HEMT) epi-structures were grown on SiC substrate using MOVPE. In this paper, the growth of high-quality AlGaN epi-layer in AlGaN/GaN HEMT is reported. The optimization was carried out to improve surface morphology and quality of the AlGaN epi-layer to get high 2DEG (two-dimensional electron gas) properties of the HEMT structure. For this optimization, AlGaN epi-layers were grown with different V/III molar ratio. It was found that both lower and higher V/III molar ratios result in the step flow surface morphology of AlGaN. However, a higher V/III molar ratio results in reduced surface roughness, improved quality of AlGaN, and excellent 2DEG properties of HEMT epi-structure.

Context: Most of the maxillary complete dentures do not adapt accurately to the cast because of the changes in the resin during polymerization. The amount of heat associated with processing of polymethyl methacrylate has been correlated with the adaptation of the processed denture base to its supporting tissues. Aims: This study conducted to determine the effect of different curing temperatures on the accuracy of fit of a complete maxillary denture and to compare with that of fiber-reinforced acrylic resins. Materials and Methods : An ideal maxillary rubber mould used to make an edentulous cast. Forty-eight stone casts made from the ideal rubber mould. Out of 48 identical stone casts, 44 stone casts with wax adapted processed using simple acrylic resin. The remaining four stone casts were processed using fiber-reinforced acrylic resin. However, processing time for 12 hrs was maintained constant for all the samples. The variable to investigate was the temperature. Therefore, four denture bases processed at each temperature from 60°C to 80°C with two-degree increments for a total of 44 samples using simple acrylic resin. Remaining four samples processed at 70°C using fiber-reinforced acrylic resin. A traveling microscope used to measure the discrepancy between each cast and its denture base. Statistical analysis used: Analyzed with Student's unpaired t test. Results : Minimum distortion was observed at 70°C. Maximum distortion was observed for the denture bases processed at 80°C. Amount of distortion increases as the processing temperature increases which was highly significant. Distortion was significantly high from 60 to 68°C in the decreasing order. Conclusion: This study verified the observation that maxillary complete denture base show the greatest discrepancy at the central portion of the posterior palatal seal region as the processing temperature increases.

Acrylic resin denture teeth often exhibit rapid occlusal wear, which may lead to decrease in the chewing efficiency, loss of vertical dimension of occlusion, denture instability, temporomandibular joint disturbances, etc. There are various treatment options available like, use of highly cross linked acrylic teeth, amalgam or metal inserts on occlusal surface, use of composite, gold or metal occlusal surface, etc. Several articles have described methods to construct gold and metal occlusal surfaces, however, these methods are time-consuming, expensive and requires many cumbersome steps. These methods also requires the patient to be without the prosthesis for the time during which the laboratory procedures are performed. This article presents a quick, simple and relatively inexpensive procedure for construction of metal occlusal surfaces on complete dentures.

Short fatigue cracks, having dimension less than 1 mm, propagate at much faster rates (da/dN) even at lower stress intensity factor range (da/dN) as compared to the threshold stress intensity factor range obtained from long fatigue crack growth studies. These short cracks originate at the sub-grain level and some of them ultimately transit into critical long cracks over time. Therefore, designing the components subjected to fatigue loading merely on the long crack growth data and neglecting the short crack growth behavior can overestimate the component’s life. This aspect of short fatigue cracks become even more critical for materials used for safety critical applications such as reactor pressure vessel (RPV) steel in nuclear plants. In this work, the transition behaviour of short fatigue crack gowth into long fatigue crack is studied in SA508 Grade 3 Class I low alloy steel used in RPVs. In-situ characterization of initiation, propagation and transition of short fatigue cracks is performed using fatigue stage for Scanning Electron Microscope (SEM) in addition to digital microscopes fitted over a servo-hydraulic fatigue machine and correlated with the microtructural information obtained using electron backscatter diffraction (EBSD). SA508 steel having an upper bainitic microstructure have several microstructural interfaces such as phase and grain boundaries that play a significant role in controlling the short fatigue crack propagation. Specially designed and prepared short fatigue specimens (eletro-polished) with varying initial crack lengths of the order of tens of microns are used in this study. The transition of such short initial cracks into long cracks is then tracked to give detailed insight into the role of each phase and phase/grain boundary with an objective of establishing Kitagawa-Takahashi diagram for the given RPV steel. The behavior of the transited long cracks is then compared with the crack propagation behavior obtained using conventional CT specimens. The outcome of this research will enhance information on the integrity of the components made from RPV steel used in Indian nuclear power plants.

Nanostructured CdS thin films were deposited on glass substrates by chemical bath deposition technique. RBS and SEM analyses showed that the film surface was smooth, consisting of uniformly dispersed clusters. Absorption spectra of as prepared sample showed a blue shift in the absorption edge indicating quantum confinement effect. The band gap of the N + ion implanted samples decreased with increase in implantation fluence. Photoluminescence spectra showed a new peak (red band), in addition to the violet, blue and yellow emissions, due to surface states created during ion implantation. Raman peak appearing at 300 cm −1 for both as deposited and N + ion implanted samples was attributed to A 1 (LO) phonon of CdS. A new Raman peak which appeared at 250 cm −1 in the case of N + ion implanted samples was interpreted as E 1 (TO) mode resulting from the lattice disorder occurred due to ion implantation. The ratio of intensity of E 1 (TO) mode to that of A 1 (LO) mode showed conspicuous increase with increase in implantation fluence and the FWHM of both the modes increases with increase of implantation fluence.

(2004). Tungsten Heavy Alloy For Defence Applications. Materials Technology: Vol. 19, No. 4, pp. 210-215.

Background: Fewer studies were conducted on resistance form. This study evaluated the effect of different auxiliary features on inadequate resistance form. Aim: The aim of the study is to evaluate the resistance at 22° taper with reduced occluso-cervical height with different auxiliary features. Methodology: An ivorine tooth was prepared with computer-aided design-computer-aided manufacturing with total occlusal convergence (TOC) of 22°, shoulder finish line 0.9 mm wide, reduced occluso-cervical height, i.e., 2.5 mm, and reduced diameter. The crown preparation was subsequently modified to include interproximal grooves, interproximal boxes, and reduced TOC in the axial wall from 22° to 8° in the cervical 1.5 mm of the axial wall. A total of four groups with ten standardized metal dies were prepared for each design with the computer-aided milling machine. Standardized complete metal crowns using silicon mold were fabricated and cemented on metal dies with glass ionomer cement. The resistance of each specimen was evaluated when force was applied at a 45° angulation to the long axis of the die in a lingual to buccal direction by a universal testing machine. The values were then analyzed using one-way analysis of variance test and post hoc Bonferroni test. Results: The comparison of the mean resistance test values was done among all the groups, and there was a significant (P ≤ 0.001) difference found among the groups. Conclusion: The most effective method of enhancing resistance form preparation is to decrease the TOC of the cervical portion of the prepared axial walls. Two interproximal boxes significantly increased the resistance form. However, two interproximal grooves did not significantly increase the resistance form.

To compare the temperature changes in the pulpal chamber during fabrication of provisional restorations by direct method. A total of 108 three-unit FPD provisional restorations were fabricated on a study model and divided into three main groups according to the material used for the fabrication of matrix. Group A—Alginate impression index group, Group B—Polyvinylsiloxane putty impression index group, Group C—Vacuum formed template group. Each group comprising of 36 specimens, was subdivided into three subgroups based on the provisional restorative material used: polymethylmethacrylate (subgroup 1), polyethylmethacrylate (subgroup 2), bis-acryl composite resin (subgroup 3). Intrapulpal temperature changes were observed with the help of a thermocouple probe (connected to a digital microprocessor thermometer) inserted into the pulp chamber of an extracted mandibular second molar mounted on a study model, during the fabrication of provisional restorations by direct method. The subgroups mean temperature rise observed in Group A—A1, A2, A3 was 2.6250 ± 0.2491, 1.0500 ± 0.1382, 0.4083 ± 0.1165, respectively. The subgroups mean temperature rise observed in Group B—B1, B2, B3 was 4.6250 ± 0.2454, 3.3750 ± 0.3415, 2.5917 ± 0.2678, respectively. The subgroups mean temperature rise observed in Group C—C1, C2, C3 was 4.7694 ± 1.8361, 3.0611 ± 1.5767, 2.3806 ± 1.5713, respectively. The observations were statistically significant. The intrapulpal temperature rise during fabrication of a provisional restoration depended both on the type of provisional restorative material and the type of matrix used. The clinician should choose carefully the resin and the matrix material while fabricating provisional restorations with direct method.

The fractal geometries such as Koch curve, Sierpinsky gasket, and Hilbert curve, etc. have been widely studied and applied to design several microwave devices, such as antennas, frequency selective surfaces (FSS), and photonic band gap (PBG) devices. There are several advantages of these fractal devices including reduction of resonant frequencies, smaller size and broadband width. In this paper a critical study has been presented on application of fractal geometry to design the microstrip antenna, microstrip filters and frequency selective surfaces.

Purpose: This study was aimed to determine the effect of various tray spacer thickness and subsequent repeated pours on the accuracy and dimensional stability of the impression made from monophasic polyvinyl siloxane material. Materials and Methods: Custom trays with different spacer thickness (2, 4 and 6 mm) were used for making an impression of a master model simulating 3 unit fixed partial denture with monophasic polyvinyl siloxane material. These impressions were poured with die stone and repoured. Distance between the reference points were measured and subjected to statistical analysis. Result: Casts obtained from 1 st , 2 nd and 3 rd pour of the impression in 2, 4 and 6 mm spacer thickness tray have similar dimensional accuracy amongst each other and with the master model except in molar diameter and inter-abutment distances of cast obtained from 6 mm spacer thickness tray. Conclusion: The vertical distance of stone dies were decreased, whereas horizontal distance increased as the thickness of impression material is increased. There were statistically non-significant changes occurring among the repeated pours in 2, 4 and 6 mm spacer thickness. Clinical Implication: 2 and 4 mm spacer thickness are acceptable for making an impression for three unit fixed partial denture with monophasic polyvinyl siloxane material and it was not affected by two subsequent (1 st and 2 nd ) repeated pours.