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H Saleem

Publications and source records attributed to H Saleem.

15 recordsLinked to original sources
PubMed2006

FTIR, FT-Raman spectra and ab initio DFT vibrational analysis of 2-amino-5-chloropyridine.

The FTIR and FT-Raman spectra of 2-amino-5-chloropyridine (ACP) has been recorded in the region 4000-400 and 3500-100 cm-1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of ACP were obtained by the ab initio and density functional theory (DFT) levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311+G(2df,2p) basis sets. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.

Pyridines↗
PubMed2005

FTIR, FT-Raman spectra and ab initio DFT vibrational analysis of 2-bromo-4-methyl-phenylamine.

The FTIR and FT-Raman spectra of 2-bromo-4-methyl-phenylamine (BMP) have been recorded. From the standard geometrical parameters the geometry of BMP was optimized at ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-311+g(d,p) and 6-311+g(2df,2p) basis sets. Several thermodynamic parameters were also calculated for the minimum energy conformer at ab initio and DFT level of theories. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. Majority of the computed wavenumbers were found to be in good agreement with the experimental observations. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.

Aniline Compounds↗
PubMed2005

FT-Raman and FTIR spectra, assignments and ab initio calculations of 2-aminobenzyl alcohol.

The Fourier transform Raman and Fourier transform infrared spectra of 2-aminobenzyl alcohol (2ABA) were recorded in the solid phase. Geometry optimizations were done with out any constraint and harmonic vibrational wave numbers and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and DFT levels invoking 6-31g** and 6-311+g(2d, p) basis sets and the results were compared with the experimental values. With the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range and the error obtained was in general very low. The appropriate theoretical spectrograms for the Raman and IR spectra of 2ABA were also constructed.

Benzyl Alcohols↗
PubMed2004

FT-Raman and FT-IR spectra, vibrational assignments and density functional studies of 5-bromo-2-nitropyridine.

The Fourier transform Raman and Fourier transform infrared spectra of 5-bromo-2-nitropyridine were recorded in the solid phase. The equilibrium geometry, natural atomic charges, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were calculated by density functional B3LYP method with the 6-311++G(d,p) basis set. The scaled theoretical wavenumbers showed very good agreement with the experimental values. A detailed interpretations of the infrared and Raman spectra of 5-bromo-2-nitropyridine is reported on the basis of the calculated potential energy distribution (PED). The theoretical spectrograms for the Raman and IR spectra of the title molecule have been constructed.

Bromides↗
PubMed2004

Ion temperature gradient instability in a dusty plasma.

An analysis of the temperature-gradient-driven ( eta(i) ) instability of drift waves in dusty plasma is presented. Various limits that allow for the coupling of the drift wave with the dynamics of dust grains are discussed. In particular, the cases of tiny (magnetized) and relatively heavy (unmagnetized) grains are studied. It is shown that in both limits the behavior of the eta(i) mode is considerably affected by the dust dynamics. The growth rate turns out to be higher in the presence of dust, and the instability threshold is lower, resulting in a more unstable plasma.

Journal Article↗
PubMed2003

Nonlinear drift waves in electron-positron-ion plasmas.

It is suggested that low-frequency drift waves can play an important role in the dynamics of electron-positron plasmas comprising some concentration of ions. In the electromagnetic case the drift wave couples with the shear Alfvén wave in an electron-positron-ion plasma. The drift wave frequency can be very low in such plasmas depending on the concentration and density scale lengths of the plasma components. In the nonlinear regime these waves can give rise to dipolar vortices in both electrostatic and electromagnetic limits. The velocity of the nonlinear structure turns out to be different compared to the case of an electron-ion plasma.

Journal Article↗
PubMed2003

Vibrational spectra, assignments and normal coordinate analysis of 2-amino-5-bromopyridine.

The FTIR and laser Raman spectra of 2-amino-5-bromopyridine have been recorded. The observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate calculations, assuming C(s) point group symmetry. The potential energy distribution associated with normal modes is also reported here. The assignment of fundamental vibrations agrees well with the calculated frequencies.

4-Aminopyridine↗
PubMed2003

Vibrational spectra, assignments and normal coordinate analysis of 3-aminobenzyl alcohol.

The laser Raman and FTIR spectra of 3-aminobenzyl alcohol have been recorded. The observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate analysis, assuming C(s) point group symmetry. The potential energy distribution associated with normal modes is also reported here. The assignment of fundamental vibrations agrees well with the calculated frequencies.

Amino Alcohols↗
PubMed2002

Ion-acoustic envelope solitons in electron-positron-ion plasmas.

Ion-acoustic envelope solitons in a collisionless unmagnetized electron-positron-ion plasma are studied. The Krylov-Bogoliubov-Mitropolsky perturbative technique is used to obtain the nonlinear Schrödinger equation. The critical wave number for the modulational instability depends upon the concentration of different species and the temperature ratios of electrons and positrons. In the limiting case of zero positron concentration we recover the previous results of electron-ion plasma. It is found that a small concentration of ions in the electron-positron plasmas can change the dynamics of the system significantly. The ions can introduce slow time and long spatial scales in the plasmas. Thus the electron-positron plasmas become richer in linear and nonlinear wave dynamics.

Journal Article↗
PubMed2002

A comparison of three types of biopsy forceps in the endoscopic surveillance of Barrett's oesophagus.

BACKGROUND AND STUDY AIMS: Periodic endoscopic biopsy surveillance is recommended for selected patients with Barrett's oesophagus. A new angled swing-jaw forceps has become available which is said to facilitate tangential oesophageal biopsy sampling. We examined the size and quality of oesophageal biopsies obtained with the forceps of angled design in comparison with the large cup disposable forceps and the conventional reusable upper gastrointestinal forceps. PATIENTS AND METHODS: In this prospective comparative study, three biopsies were taken at each of three levels, using a different design of forceps at each level, in each of 48 patients undergoing endoscopic surveillance. The order in which the forceps were used was randomized. A pathologist assessed the size and quality of each set of biopsies obtained. RESULTS: The mean biopsy diameter was significantly greater at 3.00 mm with the angled forceps (P < 0.01), in comparison with 2.52 mm with the elliptical forceps and 2.07 mm with the conventional forceps. Fewer biopsies obtained with the angled forceps were graded as inadequate (8.3 %) compared with those obtained using the disposable large cup and conventional forceps (25 % and 22.9 %, respectively). CONCLUSIONS: The design of forceps used influences the size and quality of tissue obtained during endoscopic surveillance of Barrett's oesophagus. The angled swing-jaw forceps are recommended as the most suitable for this purpose.

Adult↗
PubMed2000

Electromagnetic instabilities in unmagnetized plasmas

It is shown that local perturbations in nonuniform unmagnetized plasmas can give rise to linearly growing electromagnetic fields on both electron and ion time scales. The plasma vorticity and compressibility couple due to density inhomogeneity, giving rise to instabilities with partially transverse and partially longitudinal characteristics in electron plasmas for omega(pe)</=omega and in electron-ion plasmas for omega(pe)</=omega as well as omega<<omega(pe) (where omega(pe) is the electron plasma oscillation frequency). It is reconfirmed that the pure transverse modes due to the thermoelectric term do not appear in nonuniform unmagnetized electron plasmas. Furthermore, it has been found that the thermal fluctuations in a collisionless inhomogeneous electron plasma happen on a slower time scale of the order of 1/c(s)k (where c(s) is the ion sound speed). It seems that in the presence of a steep density gradient the ion acoustic wave becomes electromagnetic. Since the curl of electric field becomes nonvanishing in the presence of a density gradient, any nonuniform plasma can have magnetic field fluctuations in the limit omega<<omega(pe) as well. It is suggested that in the limit omega<<omega(pe) the ion dynamics becomes important and a pure electron plasma model to study magnetic field instability is not useful. The estimate for the magnitude of slowly and rapidly growing magnetic fields using the electron-ion plasma model in a special range of parameters turns out to be of the order of megagauss, in good agreement with the experimental observations.

Journal Article↗
PubMed1999

Electron magnetohydrodynamic approximations and the magnetic drift wave.

It is shown that the approximations of electron magnetohydrodynamics (EMHD) are too restrictive to be realistic for at least plasmas of low-Z materials (for example, hydrogen and its isotopes). The simultaneously used assumptions of stationary ions and inertialess electrons are not self-consistent, especially within the framework of local theory. As a result the application of EMHD to describe the pure transverse magnetic drift wave suffers from weaknesses and such a mode does not seem to exist in magnetized plasmas.

Journal Article↗
PubMed1999

Electromagnetic convective cells in a nonuniform dusty plasma.

It is noticed that in the presence of a perturbed electron current parallel to an external magnetic field, the dispersion relation of the electrostatic convective cell and the magnetostatic modes are not modified, contrary to the result quoted in the literature. Instead, the electrostatic and magnetostatic modes are coupled if the propagation parallel to the magnetic field is taken into account in both dusty and electron-ion plasmas.

Journal Article↗