DISCREPANCY PARAMETERS OF APPROXIMATIONS OF DISCRETELY SPECIFIED DEPENDENCIES BY ANALYTICAL FUNCTIONS AND SEARCH CRITERIA FOR OPTIMAL VALUES OF THEIR COEFFICIENTS

Universal discrepancy parameters of approximations of discretely specified dependencies by analytical functions and search criteria for optimal values of their coefficients, as well as analysis of features of their application are described. Discrepancy parameters of approximations, which do not depend on the ranges of variation of the values of functions and the number of points of a discretely specified dependence, are proposed. They can be effective for objectively comparing the quality of approximations of any dependencies by any functions. Approximations of a discretely specified dependence of the mathematical expectation of the equivalent electrical resistance of a layer of aluminum granules during spark-erosion dispersion in water on the instantaneous values of the discharge current are carried out. As approximating functions, we chose a power function with an exponent factor –1 and a function based on exponential. Using the criteria of the least approximation error, the optimal values of the coefficients of both approximating functions are founded. It is shown in which cases it is advisable to use the combined search criteria for the optimal values of the coefficients of the approximating functions, and in which are enough simple one-component ones. Ref. 27, fig. 2, tables 2.

Prosthetic Management of a Posterior Ridge Defect Case with Fixed Removable Type of Hybrid Prosthesis - A Case Report

The main aim of prosthetic dentistry is restoring the form, function, comfort and appearance of the patient by the placement of a prosthesis replacing the missing teeth and contiguous tissues.1 Various prosthetic options for partially edentulous patients include an interim removable partial denture (RPD) to a cast partial denture, a fixed dental prosthesis (FDP), and a more implant-retained prosthesis. However, FDP and implant-retained prosthesis are not always feasible, particularly in patients with excessive residual ridge resorption and jaw defects due to trauma and / or surgical ablation. In such a situation, a dentist may resort to another option of fixed-RPD prosthesis, to restore the defective hard and soft tissues to achieve natural aesthetics, phonetics, comfort, and better hygiene. This hybrid prosthesis fulfils the objectives of the rehabilitation such as support, stability, and retention characteristics similar to a fixed prosthesis and aesthetics and hygiene maintenance of a removable prosthesis.2,3,4,5 Any prosthesis designed or fabricated should be based on the prosthetic principles of support, stability, retention, and preservation of remaining structures.1 From the patient's perspective, retention is one of the important factors for its acceptability. These retentive options range from simple bar and clip attachments to more sophisticated spark erosion overdentures.6,7 Spark erosion prosthesis is technique sensitive, bulky, and requires expensive equipment.6,7 On the other hand, precision attachments provide better vertical support and stimulation to the underlying tissue through intermittent vertical massage.8 Treatment with a hybrid denture is an affordable choice to fulfil the patient's aesthetic demands along with providing a good prognosis for the prosthesis and preservation of the remaining dentition. This article presents two case reports of prosthodontic rehabilitation of a patient with mandibular defects using an attachment-retained fixed-removable hybrid prosthesis.

An Investigation of Milling using a Combination of Electrical Discharge (ED) and Electrochemical (EC) Machining Techniques

This study investigate the machining operation perform by the combination of EDM and ECM process. Since in case of EDM the surface finish obtain is not as good as required so next machining operation is done by ECM. As we have, in EDM metal is removed from the workpiece through spark erosion and in ECM metal removed by anodic dissolution in the electrolyte. Both the process is done simultaneously in single machine changing the potential on anode and cathode and the medium. The EDM surface of 1μ mm Ra is improved to 0.2μ mm Ra by applying ECM. The surface roughness of a machined hole is improved to 0.07 mm Ra by applying 2 min of ECM lapping. Both the process is done simultaneously.

INFLUENCE OF THE CAPACITANCE OF THE CAPACITOR OF THE DISCHARGE CIRCUIT OF SEMI-CONDUCTOR ELECTRIC DISCHARGE INSTALLATIONS ON THEIR OUTPUT CURRENTS OF LIMITED DURATION

Based on the analysis of transient processes of oscillatory and aperiodic discharges of the storage capacitor of the electric discharge installation to the load, it is proved that an increase in its capacity always causes an increase in the value of the discharge current corresponding to a fixed duration of the discharge, less than the duration of reaching the maximum value of the discharge current. For the capacities of the discharge capacitor varied over a wide range, the change in the value of the discharge current in the load during its forced interruption at a certain time was studied. Based on this study, we proposed a method for increasing the rate of rising of impulse currents in the load, which consists in choosing a discharge capacitor with a larger capacity compared with a capacity sufficient to implement the desired technological mode, and forced interrupting the current in the load at a certain point in time, which corresponds to a certain fixed duration discharge (less than the duration of reaching the maximum value of the discharge current when the capacitor capacity is sufficient to implement the required technological mode). The forced limitation of the discharge duration is carried out by a fully controlled semiconductor switch. This method can be used as the basis for the production of spark erosion nano-sized powders of metals and alloys. Ref. 15, fig. 3, table .