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A Salam

Publications and source records attributed to A Salam.

At least 19 recordsLinked to original sources
PubMed2006

On the effect of a radiation field in modifying the intermolecular interaction between two chiral molecules.

The change in the mutual energy of interaction between a pair of chiral molecules coupled via the exchange of a single virtual photon and in the presence of an electromagnetic field is calculated using nonrelativistic quantum electrodynamics. The particular viewpoint adopted is one that has an intuitive physical appeal and resembles a classical treatment. It involves the coupling of electric and magnetic dipole moments induced at each center by the incident radiation field to the resonant dipole-dipole interaction tensor. The energy shift is evaluated for fixed as well as random orientations of the molecular pair with respect to the direction of propagation of the field. A complete polarization analysis is carried out for the former situation by examining the effect of incident radiation that is linearly or circularly polarized and traveling in a direction that is parallel or perpendicular to the intermolecular distance vector. After tumble averaging, all polarization dependence of the energy shift vanishes. In both cases the interaction energy is directly proportional to the irradiance of the applied field, and is discriminatory, changing sign when one optically active species is replaced by its enantiomer. The asymptotic behavior of the energy shift at the limits of large and small separations is also studied.

Journal Article↗
PubMed2006

Unilateral hydrocephalus due to foramen of monro stenosis.

Unilateral lateral ventricular dilatation due to foramen of Monro stenosis or constriction can present with headache. Fundoscopy can be normal. This condition is congenital, radiological appraisal can disclose the diagnosis, and treatment depends upon the symptomatology. The condition can be treated well with insertion of a ventriculoperitoneal shunt.

Adolescent↗
PubMed2005

An ab initio and density functional theory study of keto-enol equilibria of hydroxycyclopropenone in gas and aqueous solution phase.

Keto-enol tautomerism in hydroxycyclopropenone (2-hydroxy-2-cyclopropen-1-one) has been studied using ab initio methods, the B3LYP functional of density functional theory, as well as complete basis set (CBS-QB3 and CBS-APNO) and G3 methods. Absolute and relative energies were calculated with each of the methods, whereas computations of geometries and harmonic frequencies for hydroxycyclopropenone and 1,2-cyclopropanedione were computed in the gas phase but were limited to HF, MP2 and CCSD levels of theory, and the B3LYP functional, in combination with the 6-31++G** basis set. Using the MP2/6-31++G** gas phase optimized structure, each species was then optimized fully in aqueous solution by employing the polarizable continuum model (PCM) self-consistent reaction field approach, in which HF, MP2 and B3LYP levels of theory were utilized, with the same 6-31++G** basis set. In both gas and aqueous solution phases, the keto form is higher in energy for all of the model chemistries considered. The presence of the solvent, however, is found to have very little effect on the bond lengths, angles and harmonic frequencies. From the B3LYP/6-31++G** Gibbs free energy, the keto-enol tautomeric equilibrium constant for 2-hydroxy-2-cyclopropen-1-one <==> 1,2-cyclopropanedione is computed to be K(T)(gas) = 2.35 x 10(-6), K(T)(aq) = 5.61 x 10(-14). It is concluded that the enol form is overwhelmingly predominant in both environments, with the effect of the solvent shifting the direction of equilibrium even more strongly in the favor of hydroxycyclopropenone. The almost exclusive nature of this species is attributed to stabilization resulting from aromaticity. Confirmation is provided by comparison of the simulated vibrational spectra of hydroxycyclopropenone with the measured infrared spectrum in an argon matrix.

Journal Article↗
PubMed2005

Resonant transfer of excitation between two molecules using Maxwell fields.

The matrix element for the resonant transfer of excitation between two molecules possessing electric and magnetic multipole moments of arbitrary order is calculated using quantum electrodynamical response theory. A prerequisite of the method is the functional form for the lth order linear electric and magnetic multipole dependent electric displacement and magnetic field operators in the neighborhood of a molecule, whose derivation is also given. The initially unexcited species is viewed as a test body accepting energy resonantly via coupling to the Maxwell fields of the excited multipole source molecule. The generalized electric-electric multipole contribution to the matrix element is shown to agree with an earlier calculation using time-dependent perturbation theory. As an application involving both electric and magnetic terms, the rate of excitation transfer between two chiral molecules is computed and found to depend on the handedness of each species.

Journal Article↗
PubMed2005

A general formula for the rate of resonant transfer of energy between two electric multipole moments of arbitrary order using molecular quantum electrodynamics.

A general expression is derived for the matrix element for the resonant transfer of energy between an initially excited donor species and an acceptor moiety in the ground state, with each entity possessing an electric multipole moment of arbitrary order. In the quantum electrodynamical framework employed, the coupling between the pair is mediated by the exchange of a single virtual photon. The probability amplitude found from second-order perturbation theory is a product of the electric moments located at each center and the resonant multipole-multipole interaction tensor. Using the Fermi golden rule, a general formula for the rate of energy transfer is obtained. As an illustration of the efficacy of the theory developed, rates of excitation energy exchange are calculated for systems interacting through dipole-quadrupole, dipole-octupole, quadrupole-quadrupole, and the familiar dipole-dipole coupling. For each of the cases examined, the near- and far-zone limits of the migration rate are calculated from the result valid for all donor-acceptor separations beyond wave function overlap. Expression of the octupole contribution to the transfer rate in terms of its irreducible components of weights 1 and 3 leads to new features. The octupole weight-1 term is found to contribute only when the interaction is retarded, while the dipole-octupole weight-1 contribution appears as a higher-order correction term to the dipole-dipole rate. Order of magnitude estimates are given for the contributions of dipole-quadrupole and dipole-octupole terms relative to the leading dipole-dipole rate for near-, intermediate-, and far-zone separations to further understand the role played by higher multipole moments in the transfer of excitation and the mechanism dominating the process.

Journal Article↗
PubMed2004

Quantum dynamics calculations using symmetrized, orthogonal Weyl-Heisenberg wavelets with a phase space truncation scheme. II. Construction and optimization.

In this paper, we extend and elaborate upon a wavelet method first presented in a previous publication [B. Poirier, J. Theo. Comput. Chem. 2, 65 (2003)]. In particular, we focus on construction and optimization of the wavelet functions, from theoretical and numerical viewpoints, and also examine their localization properties. The wavelets used are modified Wilson-Daubechies wavelets, which in conjunction with a simple phase space truncation scheme, enable one to solve the multidimensional Schrodinger equation. This approach is ideally suited to rovibrational spectroscopy applications, but can be used in any context where differential equations are involved.

Journal Article↗
PubMed2004

Quantum dynamics calculations using symmetrized, orthogonal Weyl-Heisenberg wavelets with a phase space truncation scheme. III. Representations and calculations.

In a previous paper [J. Theo. Comput. Chem. 2, 65 (2003)], one of the authors (B.P.) presented a method for solving the multidimensional Schrodinger equation, using modified Wilson-Daubechies wavelets, and a simple phase space truncation scheme. Unprecedented numerical efficiency was achieved, enabling a ten-dimensional calculation of nearly 600 eigenvalues to be performed using direct matrix diagonalization techniques. In a second paper [J. Chem. Phys. 121, 1690 (2004)], and in this paper, we extend and elaborate upon the previous work in several important ways. The second paper focuses on construction and optimization of the wavelength functions, from theoretical and numerical viewpoints, and also examines their localization. This paper deals with their use in representations and eigenproblem calculations, which are extended to 15-dimensional systems. Even higher dimensionalities are possible using more sophisticated linear algebra techniques. This approach is ideally suited to rovibrational spectroscopy applications, but can be used in any context where differential equations are involved.

Journal Article↗
PubMed2004

Features distinguishing amoebic from pyogenic liver abscess: a review of 577 adult cases.

Distinguishing amoebic from pyogenic liver abscesses is crucial because their treatments and prognoses differ. We retrospectively reviewed the medical records of 577 adults with liver abscess in order to identify clinical, laboratory, and radiographic factors useful in differentiating these microbial aetiologies. Presumptive diagnoses of amoebic (n = 471; 82%) vs. pyogenic (n = 106; 18%) abscess were based upon amoebic serology, microbiological culture results, and response to therapy. Patients with amoebic abscess were more likely to be young males with a tender, solitary, right lobe abscess (P = 0.012). Univariate analysis found patients with pyogenic abscess more likely to be over 50 years old, with a history of diabetes and jaundice, with pulmonary findings, multiple abscesses, amoebic serology titres <1:256 IU, and lower levels of serum albumin (P < 0.04). Multivariate logistic regression analysis confirmed that age >50 years, pulmonary findings on examination, multiple abscesses, and amebic serology titres <1:256 IU were predictive of pyogenic infection. Several clinical and laboratory parameters can aid in the differentiation of amebic and pyogenic liver abscess. In our setting, amebic abscess is more prevalent and, in most circumstances, can be identified and managed without percutaneous aspiration.

Adolescent↗
PubMed2004

Maximum tolerable dose of cyclophosphamide and azathioprine in Pakistani patients with primary renal disease.

OBJECTIVE: The immunosuppressive regimens, at present, mainly rely on western guidelines that were derived from studies conducted in western populations. No such study exists for South Asian population, which is home to almost two billion people different in both genetics and environment from west. Locally derived thresholds for side effects markedly different from western figures may warrant re-adjustment of current local immunosuppressive regimens that are at present based largely on western guidelines. In order to define optimum dose for Cyclophosphamide (CYC) and Azathioprine (AZA) based immunosuppressive therapy, we conducted this study to find out maximum tolerable doses of azathioprine (AZA) and cyclophosphamide (CYC) beyond which neutropenia and thrombocytepenia are most likely to occur in patients with primary renal pathology. METHOD: Patients with systemic vasculitis and idiopathic glomerulonephritis who were on CYC and AZA were identified through review of medical records at a tertiary care hospital in Pakistan (The Aga Khan University Hospital, Karachi). Patients were categorized under three principal diagnosis i.e. systemic lupus erythematosus (SLE), primary (idiopathic) glomerulonephritis (GN) and Wegener's granulomatosis (WG). The Receiver Operating Curve (ROC) was used to calculate the maximum tolerable dose for both CYC and AZA. RESULTS: We identified 94 patients aged 6-82 years (median 44.5 years) with primary renal disease (Wegener's granulomatosis n=13, Systemic lupus erythematosis n=62 and idiopathic glomerulonephritis n=19) who received CYC or AZA. Of these 94 patients, 36.2% (n=34) received CYC and 63.8% (n=60) received AZA. The mean dose of CYC was 1.54 +/- 0.50 mg/kg of body weight (range: 0.77-2.93). The mean dose of AZA was 1.64 +/- 0.59 mg/kg of body weight (range: 0.47-2.97). The maximum tolerable doses calculated for CYC and AZA were 1.25 mg/kg and 1.30 mg/kg of body weight respectively. The maximum tolerable dose for CYC and AZA among males could not be calculated, because of insufficient number of patients who developed neutropenia and thrombocytopenia. The maximum tolerable doses for CYC and AZA among females were 1.34 mg/kg and 1.03 mg/kg of body weight respectively. Also we found out that AZA was relatively more likely to cause neutropenia and thrombocytopenia (p=0.07). CONCLUSION: We thereby recommend that CYC should be initiated at a dose no more than 1 mg/kg of body weight and AZA at an initial dose of 0.75-1.0 mg/kg of body weight. The dose may be adjusted later on the basis of clinical response and laboratory reports.

Adolescent↗
PubMed2003

Outcome of adult acute lymphoblastic leukemia: a single center experience.

OBJECTIVE: To study the outcomes of adult patients with acute lymphoblastic leukemia. SETTING: Tertiary care hospital. STUDY DESIGN: Retrospective analysis. METHODS: Fifty eight adult patients (age >14 years) diagnosed as cases of acute lymphoblastic leukemia were studied with respect to their clinical, morphological and immunopathological features at presentation and their relationship with treatment outcomes. RESULTS: Forty five (77.5%) of the patients belonged to younger age group with male preponderance. The median age was 20 years and mean age was 25.1 years. Male to female ratio was 3:1. Common presenting signs were lymphadenopathy (17.2%), hepatomegaly (32.7%) and splenomegaly (62%). Laboratory features at presentation revealed: hemoglobin > or = 10 gm/dl in 18 (31%), WBC >50 x 10E9 / L in 18 (31%), LDH more than 1000 IU/L in 44 (75.8%) of patients. Morphology revealed that FAB L1 was seen in 21(37.2%) and L2 in 62 (32.7%). Immunophenotyping showed that 26 (61.9%) were early pre-B ALL, 6 (14.2%) were pre-B ALL and T-ALL were 10 (23.8%). Univariate analysis showed age more than 30 years, male gender, total leucocyte count >50 x 10(9)/L and hemoglobin more than 10 gm/dl to be risk factors for poor outcome. Multivariate analysis revealed age more than 30 years, male sex and total leucocyte count > 50 x 10(9)/L are independent risk factors for poor survival. Patients were treated according to the MRCUKX and XII adult protocols. Thirteen (22.4%) patients died during induction therapy secondary to sepsis and progressive disease whereas 42 (72.4%) patients achieved complete remission. Median survival was 18.6 months and 42% patients were alive at 5-years. CONCLUSION: Overall survival and disease free survival were comparable to those reported in literature. However, age more than 30 years, male gender and total leucocyte count >50 x 10(9)/L had an adverse impact on overall survival.

Adolescent↗
PubMed2002

Clinical, pathological and molecular factors predicting axillary node involvement in primary breast cancer in Pakistani women.

BACKGROUND: Axillary lymph node involvement in primary breast cancer is one of its most important prognostic features. Thus any factors that may predict axillary lymph node involvement in this setting could be potentially helpful in treatment planning and other interventions. OBJECTIVE: The objective of this study was to evaluate clinical, pathological and immuno-histochemical markers in univariate and multivariate analysis, which may be helpful predictors of axillary lymph node involvement in breast cancer. METHOD: A retrospective analysis of 555 cases. Of these 58% had axillary nodal positivity and 42% were negative. CONCLUSION: Factors of no significance included patient's age, height, weight, age of first pregnancy, parity, marital status, menopausal status, family history of breast cancer, side of tumor. In univariate analysis the age of menarche, duration of symptoms, tumor size, site in outer quadrant, S phase and skin and nipple involvement all predicted axillary nodal involvement. The length of breast-feeding, increased intraductal component and increased PCNA were inversely proportional to nodal involvement. In multiple regression analysis however only size of the tumor, involvement of the skin and nipple and disease in the outer quadrant of breast were the factors, which assumed significance.

Axilla↗
PubMed2002

Lack of benefit of granulocyte macrophage or granulocyte colony stimulating factor in patients with febrile neutropenia.

OBJECTIVES: To compare the clinical benefits of granulocyte-colony stimulating factor (G-CSF) or granulocyte macrophage-colony stimulating factor (GM-CSF) plus standard supportive care to supportive care alone among cancer patients with febrile neutropenia. METHODS: Clinical data were collected retrospectively from 148 consecutive cancer patients with neutropenia and fever. Patients had hematologic (i.e., acute leukemias or lymphoproliferative disorders) or non-hematologic malignancies (i.e., solid tumors including carcinoma of breast, lung, or colon). Clinical variables analyzed included: age and sex; underlying malignancies; chemotherapy regimens; symptoms at time of presentation; duration of fever prior to study enrollment; days from chemotherapy until administration of GM-CSF or G-CSF; number of previous neutropenic episodes; duration of fever and day of defervescence; absolute neutrophil count on day of defervescence; duration of neutropenia; number and types of antibiotics used; day amphotericin B begun; number of culture-documented infective episodes involving bloodstream, lung, pleura, urinary tract, gastrointestinal tract, intravenous cannulae, or skin; types of antimicrobial isolates; cost of cytokine therapy; length of hospital stay and clinical outcome. RESULTS: The use of myeloid growth factors increased the number of circulating peripheral white blood cells, but no significant effect was noted in terms of duration of neutropenia or fever, number of culture-proven infections (except pneumonia; p < 0.04), length of hospital stay, or survival. CONCLUSION: In areas with limited health care resources, expensive treatment with GM-CSF or G-CSF should be reserved for patients with complicated febrile neutropenia where the expected risk of infection is high and the duration of neutropenia is prolonged, or those with documented infections that are refractory to antibiotic treatment.

Adult↗
PubMed2001

Probing molecular conformations with electron momentum spectroscopy: the case of n-butane.

High-resolution (e,2e) measurements of the valence electronic structure and momentum-space electron density distributions of n-butane have been exhaustively reanalyzed in order to cope with the presence of two stable structures in the gas phase, namely the all-staggered and gauche conformers. The measurements are compared to a series of Boltzmann-weighted simulations based on the momentum-space form of Kohn-Sham (B3LYP) orbital densities, and to ionization spectra obtained from high-level [ADC(3)] one-particle Green's Function calculations. Indubitable improvements in the quality of the simulated (e,2e) ionization spectra and electron momentum profiles are seen when the contributions of the gauche form of n-butane are included. Both the one-electron binding energies and momentum distributions consistently image the distortions and topological changes that molecular orbitals undergo due to torsion of the carbon backbone, and thereby exhibit variations which can be traced experimentally. With regard to the intimate relation of (e,2e) cross sections with orbital densities, electron momentum spectroscopy can therefore be viewed as a very powerful, but up to now largely unexploited, conformational probe. The study also emphasizes the influence of thermal agitation in photoionization experiments of all kind.

Journal Article↗