Muhammad Sadiq

A study on the evaluation of the geoid-quasigeoid separation term over Pakistan with a solution of first and second order height terms

An attempt has been made to evaluate the geoid-quasigeoid separation term over Pakistan by using solutions of terms involving first and second order terrain heights. The first term, involving the Bouguer anomaly, has a significant value and requires being incorporated in any case for determination of the geoid from the quasigoidal solution. The results of the study show that the second term of separation, which involves the vertical gravity anomaly gradient, is significant only in areas with very high terrain elevations and reaches a maximum value of 2–3 cm. The integration radius of 18 km for the evaluation of the vertical gravity anomaly gradient was found to be adequate for the near zone contribution in the case of the vertical gravity anomaly gradient. The Earth Gravity Model EGM96 height anomaly gradient terms were evaluated to assess the magnitude of the model dependent part of the separation term. The density of the topographic masses was estimated with the linear operator of vertical gravity anomaly gradient using the complete Bouguer anomaly data with an initial arbitrary density of 2.67 g/cm3 to study the effect of variable Bouguer density on the geoid-quasigeoid separation. The density estimates seem to be reasonable except in the area of very high relief in the northern parts. The effect of variable density is significant in the value of the Bouguer anomaly-dependent geoid-quasigeoid separation and needs to be incorporated for its true applicability in the geoid-quasigeoid separation determination. The geoid height (N) was estimated from the geoid-quasigeoid separation term plus global part of height anomaly and terrain-dependant correction terms. The results were compared with the separation term computed from EGM96-derived gravity anomalies and terrain heights to estimate its magnitude and the possible amount of commission and omission effects.

Coherent states for a polynomial su(1,1) algebra and a conditionally solvable system

In a previous paper (2007 J. Phys. A: Math. Theor. 40 11105), we constructed a class of coherent states for a polynomially deformed su(2) algebra. In this paper, we first prepare the discrete representations of the nonlinearly deformed su(1, 1) algebra. Then we extend the previous procedure to construct a discrete class of coherent states for a polynomial su(1, 1) algebra which contains the Barut–Girardello set and the Perelomov set of the SU(1, 1) coherent states as special cases. We also construct coherent states for the cubic algebra related to the conditionally solvable radial oscillator problem.

Boron nitride-polymer composites: Mechanical properties evaluation at various strain ratios

Liquid phase exfoliation method is used to achieve three different sized (L≈0.4, 1, 1.9 µm) hexagonal Boron Nitride (hBN) nanosheets by changing the centrifugation rate. Mechanical properties of polymer composites are evaluated with hBN nanosheets utilized as reinforcement filler in polyvinylchloride (PVC) matrices. In an earlier work, uniaxial drawing (300%) was successfully employed to enhance the strength and modulus of these composites from 65–82 MPa and 1.45–1.8 GPa respectively. Here, we try to elaborate more the effect of uniaxial drawing on polymer nanocomposites (0.2 wt % for all three sizes BN) at various strain ratios (100–500%). The ultimate tensile strength (UTS) and Youngs modulus (Y) have experienced maximum increase at 450–500% strain are 3 GPa and 240 MPa respectively. Alignment and improved dispersion of hBN inside are the possible reasons for enhancement in mechanical properties; along with the strain induced delamination achieved with uniaxial drawing. The enhancement in mechanical characteristics of polymer composites is close to the theoretically predicted values of hBN.

Design and development of precision Astronomical North-finding system: A software and hardware perspective

Accurate and absolute north orientation at geographically isolated locations is usually the first challenge faced by planners, surveyors and civil engineers and is an indispensible requirement of many military applications. The Astronomical North is one of the key parameters used by basic navigation tools for attitude determination and trajectory verification. It has applications in geodetic surveying, mapping and topography. This work presents a system for accurate determination of the astronomical azimuth using Sun or Polaris at any time.

Outlier detection algorithm for satellite gravity gradiometry data using wavelet shrinkage de-noising

Abstract: On the basis of wavelet theory, we propose an outlier-detection algorithm for satellite gravity gradiometry by applying a wavelet-shrinkage-de-noising method to some simulation data with white noise and outliers. The result shows that this novel algorithm has a 97% success rate in outlier identification and that it can be efficiently used for pre-processing real satellite gravity gradiometry data.

A Comparative Study of Different Geodetic Boundary Value Solutions for Geoid with reference to its Calibration Using GPS/Leveling Data

The equipotential geoid of the gravity field of the Earth can be modeled with different formulation of the geodetic boundary value problems and their solutions. These techniques range from Helmerts 2nd method of condensation to Residual terrain modeling and then to the Molodenskij solution of the geodetic boundary value problem. The available data for gravity anomalies, elevation and their distribution within Pakistan requires careful study and selection from these solution methods. This study involves the comparison and discussion of different geoid modeling techniques with the geoid determined from GPS / Leveling data. Each of the above mentioned techniques has some advantages and drawbacks due to their data requirement, computational technique and validation of results. This calibration study will help to establish the selection of the suitable method for extended study of geoid model all over Pakistan. These techniques were implemented and tested in central area of Pakistan having diverse landscape with elevation range from 106m to 1522m above mean sea level. A statistical 3D regression model was developed for the compensation of offset between different geoidal solutions.