Muhammad Sabieh Anwar

Density functional theory and phytochemical study of Pistagremic acid.

We report here for the first time a comparative theoretical and experimental study of Pistagremic acid (P.A). We have developed a theoretical model for obtaining the electronic and spectroscopic properties of P.A. The simulated data showed nice correlation with the experimental data. The geometric and electronic properties were simulated at B3LYP/6-31 G (d, p) level of density functional theory (DFT). The optimized geometric parameters of P.A were found consistent with those from X-ray crystal structure. Differences of about 0.01 and 0.15 Å in bond length and 0.19-1.30° degree in the angles, respectively; were observed between the experimental and theoretical data. The theoretical vibrational bands of P.A were found to correlate with the experimental IR spectrum after a common scaling factor of 0.963. The experimental and predicted UV-Vis spectra (at B3LYP/6-31+G (d, p)) have 36 nm differences. This difference from experimental results is because of the condensed phase nature of P.A. Electronic properties such as Ionization Potential (I.P), Electron Affinities (E.A), co-efficient of highest occupied molecular orbital (HOMO), co-efficient of lowest unoccupied molecular orbital (LUMO) of P.A were estimated for the first time however, no correlation can be made with experiment. Inter-molecular interaction and its effect on vibrational (IR), electronic and geometric parameters were simulated by using Formic acid as model for hydrogen bonding in P.A.

Investigating viscous damping using a webcam

We describe an experiment involving a mass oscillating in a viscous fluid. The mechanical oscillator is tracked using a simple webcam, and an image processing algorithm records the position of the geometrical center as a function of time. Interesting information can be extracted from the displacement-time graphs, in particular, for the underdamped case. For example, we use these oscillations to determine the viscosity of the fluid. Our mean value of 1.08±0.07 mPa s for distilled water is in good agreement with the accepted value at 20 °C. The experiment has been successfully employed in an introductory laboratory setting.

Triethyl orthoformate mediated a novel crosslinking method for the preparation of hydrogels for tissue engineering applications: characterization and in vitro cytocompatibility analysis

This paper describes the development of a new crosslinking method for the synthesis of novel hydrogel films from chitosan and PVA for potential use in various biomedical applications. These hydrogel membranes were synthesized by blending different ratios of chitosan (CS) and poly(vinyl alcohol) (PVA) solutions and were crosslinked with 2.5% (w/v) triethyl orthoformate (TEOF) in the presence of 17% (w/v) sulfuric acid. The physical/chemical interactions and the presence of specific functional groups in the synthesized materials were evaluated by Fourier transform infrared (FT-IR) spectroscopy. The morphology, structure and pore size of the materials were investigated by scanning electron microscopy (SEM). Thermal gravimetric analysis (TGA) proved that these crosslinked hydrogel films have good thermal stability which was decreased as the CS ratio was increased. Differential scanning calorimetry (DSC) exhibited that CS and PVA were present in the amorphous form. The solution absorption properties were performed in phosphate buffer saline (PBS) solution of pH7.4. The 20% PVA-80% CS crosslinked hydrogel films showed a greater degree of solution absorption (183%) as compared to other compositions. The hydrogels with greater CS concentration (60% and 80%) demonstrated relatively more porous structure, better cell viability and proliferation and also revealed good blood clotting ability even after crosslinking. Based on the observed facts these hydrogels can be tailored for their potential utilization in wound healing and skin tissue engineering applications.

Complete Stokes polarimetry of magneto-optical Faraday effect in a terbium gallium garnet crystal at cryogenic temperatures

We report the complete determination of the polarization changes caused in linearly polarized incident light due to propagation in a magneto-optically active terbium gallium garnet (TGG) single crystal, at temperatures ranging from 6.3 to 300 K. A 28-fold increase in the Verdet constant of the TGG crystal is seen as its temperature decreases to 6.3 K. In contrast with polarimetry of light emerging from a Faraday material at room temperature, polarimetry at cryogenic temperatures cannot be carried out using the conventional fixed polarizer-analyzer technique because the assumption that ellipticity is negligible becomes increasingly invalid as temperature is lowered. It is shown that complete determination of light polarization in such a case requires the determination of its Stokes parameters, otherwise inaccurate measurements will result with negative implications for practical devices.

Video-based spatial portraits of a nonlinear vibrating string

The article describes a systematic experimental study of a string vibrating nonlinearly. The string is tracked in real time using strategically located cameras; the video tracking enables a remote observation of the oscillator without perturbing its inherent nonlinearities. We show that our technique can help probe the parametrically excited oscillations and study phenomena such as elliptical and circular trajectories near resonance, resonance fold-over, jump, hysteresis, and subharmonic resonance. The experiment has been successfully employed in the advanced physics laboratory.

Precise measurement of velocity dependent friction in rotational motion

Frictional losses are experimentally determined for a uniform circular disc exhibiting rotational motion. The clockwise and anticlockwise rotations of the disc, that result when a hanger tied to a thread is released from a certain height, give rise to vertical oscillations of the hanger as the thread winds and unwinds over a pulley attached to the disc. It is thus observed how the maximum height is achieved by the hanger decrements in every bounce. From the decrements, the rotational frictional losses are measured. The precision is enhanced by correlating vertical motion with the angular motion. This method leads to a substantial improvement in precision. Furthermore, the frictional torque is shown to be proportional to the angular speed. The experiment has been successfully employed in the undergraduate lab setting.

Ultralarge magneto-optic rotations and rotary dispersion in terbium gallium garnet single crystal.

We report systematically acquired data on the Verdet constant of terbium gallium garnet for wavelengths ranging from visible to near-infrared (405-830 nm) regime. Our experimental method of Stokes polarimetry is based on the Fourier decomposition of the received light intensity and allows unambiguous determination of both the Faraday rotation and the ellipticity of the emergent light. Temperature-dependent investigations in the range of 8-300 K extend earlier reports and verify the Verdets constant direct dependence on the magnetization, whose first-order approximation is simply a manifestation of the Curies law. Further, a least-squares fitting of the experimental data correlates well with theoretical predictions. At a wavelength of 405 nm and temperature of 8 K, the rotation is approximately 500°.

Accessing select properties of the electron with ImageJ: an open-source image-processing paradigm

This paper describes a way to measure the radii of curvature of electrons following a curved path in a magnetic field and the radii of the concentric rings resulting from the interference of the electrons inside an evacuated diffraction tube. High-resolution imaging dramatically increases the precision of measurements of physical distances, if they are along circular arcs. Digital photographs were taken and the free software ImageJ that comes with a multitude of image-processing routines and is widely used in life sciences research was employed for measurement and analysis.

Experimental determination of heat capacities and their correlation with theoretical predictions

We discuss an experiment for determining the heat capacities of various solids based on a calorimetric approach where the solid vaporizes a measurable mass of liquid nitrogen. We demonstrate our technique for copper and aluminum, and compare our data with Einstein’s model of independent harmonic oscillators and the more accurate Debye model. We also illustrate an interesting material property, the Verwey transition in magnetite.

Dielectric and magnetic investigations of mixed cubic spinel Co-ferrites with controlled Mg content

High temperature frequency dependent dielectric properties, and room temperature magnetic behavior of mixed ferrites with controlled content of Mg in Co 1−xMg xFe 2O4(x=0.0,0.1,0.3,0.5,0.7,0.9 and 1.0) compositions are studied. Single phase spinel structure with cubic symmetry, lattice parameters, crystallite size, magnetic and dielectric properties were substantiated with x-ray diffractometer, transmission electron microscope, vibrating sample magnetometer and impedance analysis, respectively. Due to interfacial polarization, dielectric behavior of all the compositions shows dispersion with increase in frequency. The dielectric data was investigated by comparing the tangent loss and electric modulus for assigning the type and mechanism of dielectric relaxation. Temperature dependent dielectric constant, tangent loss and AC conductivity increase due to thermal activation of charge carriers and drift mobility. Furthermore, room temperature weak ferromagnetic behavior is observed due to the incorporation of non-magnetic Mg ions.