Rekha Gupta

A modified Norde function for the measurement of the series resistance and the voltage‐dependent barrier height of triangular barrier diodes

The Norde function [J. Appl. Phys. 50, 5052 (1979)] used for measuring the barrier height, series resistance, and ideality factor of a Schottky barrier diode has been modified to obtain the same parameters for a triangular barrier diode (TBD). Unlike Schottky barrier diodes, the barrier height of a TBD depends upon the applied voltage and changes linearly with it. In order to calculate the additive term in the TBD barrier height, the modified function is therefore plotted for both reverse and forward bias cases. It is shown later that the modified Norde function enhances the accuracy of the results.

Measurement of barrier height and its controlling parameters in bulk barrier diodes

Bulk barrier diodes are majority carrier diodes, in which the current is given by the thermionic emission of carriers over a barrier present in the bulk of the material. The height of this barrier depends on the dopings of the various layers of the diode, which has a p+np or n+pn structure. In this paper, different ways to determine this barrier height and its controlling parameters, have been suggested by considering the effect of temperature on the current and the applied voltage of the device.

Engineering strain, densification, order parameter and magnetic properties of FePt thin films by dense electronic excitations

FePt films prepared by DC sputtering on Si ⟨100⟩ substrates when annealed at 600 °C for 1 h exhibited a structurally ordered and magnetically hard L10 phase. These FePt films were exposed to dense electronic excitations by using 100 MeV oxygen ions as a function of increasing fluences. Such excitations induce pressure and result in the enhancement of order parameter by increasing strain on the FePt films. Apart from this, the surface morphological images from field emission scanning electron microscopy reveal a densification of the films consequent to irradiation and are correlated with the details obtained from Rutherford back scattering analysis. The variation in the values of coercivity correlates well with the change in volume percentage of face centered tetragonal and face centered cubic phase. A coercivity of 14.7 kOe with order parameter 0.92 is achieved at a fluence of 5 × 1012 ions/cm2. The theoretical simulation of the demagnetization curve shows a strong correlation of coercivity and order para...

Control of the barrier height of triangular‐barrier diodes by doping their intrinsic layers

An analytic model for the control of the barrier height of a triangular‐barrier diode (TBD) is proposed. It is shown that an extra (p‐ or n‐type) doping given to the two intrinsic layers of a TBD changes its barrier height over a wide range (over all 40%). A simple closed‐form expression is derived to give the dependence of barrier height on the extra dopings. It is seen that the ideality of the diode is not affected in spite of a wide range of changes obtained in the barrier height. Furthermore, the differential resistance of the device is shown to exponentially decrease with the extra n‐type doping given to the structure. Such a strong dependence leads to an improvement in the forward‐bias cut‐off frequency of the device.

Optimality and duality in multiobjective programming involving support functions

In this paper a vector optimization problem (VOP) is considered where each component of objective and constraint function involves a term containing support function of a compact convex set. Weak and strong Kuhn−Tucker necessary optimality conditions for the problem are obtained under suitable constraint qualifications. Necessary and sufficient conditions are proved for a critical point to be a weak efficient or an efficient solution of the problem (VOP) assuming that the functions belong to different classes of pseudoinvex functions. Two Mond Weir type dual problems are considered for (VOP) and duality results are established.

Comparative evaluation of bonding strength of computer aided machined ceramic, pressable ceramic, and milled metal implant abutment copings and effect of surface conditioning on bonding strength: An in vitro study

Background/Purpose: The aim of this study was to compare the shear bond strength of computer aided design/computer aided machined ceramic (CAD/CAM), pressable ceramic, and milled metal implant copings on abutment and the effect of surface conditioning on bonding strength. Materials and Methods: A total of 90 test samples were fabricated on three titanium abutments. Among 90 test samples, 30 copings were fabricated by CAD/CAM, 30 by pressable, and 30 by milling of titanium metal. These 30 test samples in each group were further subdivided equally for surface treatment. Fifteen out of 30 test samples in each group were surface conditioned with airborne particle abrasion. All the 90 test samples were luted on abutment with glass ionomer cement. Bonding strength was evaluated for all the samples using universal testing machine at a crosshead speed of 5 mm/min. The results obtained were compared and evaluated using one-way ANOVA with post-hoc and unpaired t-test at a significance level of 0.05. Results: The mean difference for CAD/CAM surface conditioned subgroup was 1.28 ± 0.12, for nonconditioned subgroup was 1.20 ± 0.11. The mean difference for pressable surface conditioned subgroup was 1.18 ± 0.04, and for nonconditioned subgroup was 0.75 ± 0.28. The mean difference for milled metal surface conditioned subgroup was 2.57 ± 0.58, and for nonconditioned subgroup was 1.49 ± 0.15. Conclusions: On comparison of bonding strength, milled metal copings had an edge over the other two materials, and surface conditioning increased the bond strength.

Comparative evaluation of surface topography of tooth prepared using erbium, chromium: Yttrium, scandium, gallium, garnet laser and bur and its clinical implications

Background: Erbium, chromium: Yttrium, scandium, gallium, garnet (Er, Cr: YSGG) laser has been successfully used in the ablation of dental hard and soft tissues. It has been reported that this system is also useful for preparing tooth surfaces and etching, but no consensus exist in the literature regarding the advantage of lasers over conventional tooth preparation technique. Materials and Methods: Labial surfaces of 25 extracted human maxillary central incisors were divided into two halves. Right half was prepared with diamond bur and left half with Er, Cr; YSGG laser and a reduction of 0.3-0.5 mm was carried out. Topography of prepared surfaces of five teeth were examined under scanning electron microscope (SEM). The remaining samples were divided into 4 groups of 10 specimens each based on the surface treatment received: One group was acid etched and other was nonetched. Composite resin cylinders were bonded on prepared surfaces and shear bond strength was assessed using a universal testing machine. Results: The SEM observation revealed that the laser prepared surfaces were clean, highly irregular and devoid of a smear layer. Bur prepared surfaces were relatively smooth but covered with smear layer. Highest bond strength was shown by laser prepared acid etched group, followed by bur prepared the acid etched group. The bur prepared nonacid etched group showed least bond strength. Conclusions: Er, Cr: YSGG laser can be used for preparing tooth and bond strength value achieved by laser preparation alone without surface treatment procedure lies in the range of clinical acceptability.

Rehabilitation of resorbed mandibular ridges using mini implant retained overdentures: A case series with 3 year follow-up.

With the increasing average life expectancy of human beings, the need to cater geriatric patients is ever increasing. Complete dentures are an indispensable tool in this regard. The loose and unstable lower complete denture owing to residual ridge resorption is one of the most common problems faced by edentulous patients. Dental implant retained overdentures have emerged as an efficient treatment modality for such patients. Though useful, not every patient is a suitable candidate to go for conventional implant-borne prosthesis, limitation being the available bone width. In such cases, mini implants may be used for augmenting the retention of the dentures and improving the quality of life of patients. In this case series, rehabilitation of three compromised cases with mini implant retained overdentures have been described wherein patients are experiencing instability of lower denture due to thin resorbed mandibular ridges. In one of the cases, three mini implants placed in A, C, and E position were splinted using a cemented bar to retain the mandibular denture. The other two cases were rehabilitated using unsplinted ball type one piece mini implants placed in A, C, and E position in one case and B and D position in another case. Though splinted bar design should be preferred but the lack of available vertical space precluded the utilization of bar in other two cases. The results were found to be satisfactory with no complications reported during a follow-up period of over 3 years in all the cases.

Rehabilitation of a case of enucleated retinoblastoma

Retinoblastoma is one of the commonest malignant intraocular tumors in pediatric population, resulting in evisceration, enucleation or exenteration of orbital contents. An ocular prosthesis can boost the psychological wellbeing of a patient with an anophthalmic socket. Though the stock prosthesis for ocular defects can be used as an interim prosthesis but customized prosthesis is required for better fit, function, esthetics and tissue health of anophthalmic socket. The present case report describes the prosthetic rehabilitation of a surgically treated case of retinoblastoma.

A Novel Approach to Treat Traumatized Alveolar Ridges: Two Case Reports

Functional forces are transmitted to the basal seat mucosa through a hard denture base during mastication. Such hard base dentures are not comfortably tolerated in patients with fragile oral mucosa and will cause sore spots, masticatory pain, and further resorption of alveolar bone. Soft liners materials can be advocated successfully to manage such clinical situations. The soft liner material absorbs masticatory forces by means of the cushioning effect and distributes occlusal forces uniformly to prevent trauma to compromised residual ridges.