PubMed Health⌕ Search

Biomedical subjects

M F Islam

Publications and source records attributed to M F Islam.

14 recordsLinked to original sources
PubMed2006

Structure of semidilute single-wall carbon nanotube suspensions and gels.

The microscopic network structure of surfactant-stabilized single-wall carbon nanotubes (SWNTs) in water was investigated as a function of SWNT concentration in the semidilute (overlapping) regime using small-angle neutron scattering (SANS). Most of the samples exhibit rigid rod behavior (i.e., Q(-1) intensity variation) at large scattering wavevector, Q, and a crossover to network behavior (i.e., approximately Q(-2) intensity variation) at low Q. The mesh size, xi, of the network was determined from the crossover of rigid rod to network behavior in the SANS intensity profile and was found to decrease with increasing SWNT concentration. When the dispersion quality of these associating rigid rods was degraded, only approximately Q(-2) intensity variation was observed at both high and low Q. Small-angle X-ray scattering measurements of the same stable dispersions were relatively insensitive to network structure because of poor contrast between SWNTs and surfactant.

Gels↗
PubMed2005

Cracks and topological defects in lyotropic nematic gels.

We report on the effects of the coupling of nematic order and elasticity in anisotropic lyotropic gels consisting of large nematic domains of surfactant coated single wall carbon nanotubes embedded in a cross-linked N-isopropyl acrylamide polymer matrix. We observe the following striking features: (i) undulations and then cusping of the gel sidewalls, (ii) a nematic director field that evolves as the gel sidewalls deform, (iii) networks of surface cracks that are orthogonal to the nematic director field, and (iv) fissures at the sidewall cusps and associated topological defects that would not form in liquid nematics.

Anisotropy↗
PubMed2005

Premelting at defects within bulk colloidal crystals.

Premelting is the localized loss of crystalline order at surfaces and defects at temperatures below the bulk melting transition. It can be thought of as the nucleation of the melting process. Premelting has been observed at the surfaces of crystals but not within. We report observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy. The crystals are equilibrium close-packed, three-dimensional colloidal structures made from thermally responsive microgel spheres. Particle tracking reveals increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. Our observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and atomic-scale crystals.

Journal Article↗
PubMed2004

Viscoelasticity of single wall carbon nanotube suspensions.

We investigate the viscoelastic properties of an associating rigid rod network: aqueous suspensions of surfactant stabilized single wall carbon nanotubes (SWNTs). The SWNT suspensions exhibit a rigidity percolation transition with an onset of solidlike elasticity at a volume fraction of 0.0026; the percolation exponent is 2.3+/-0.1. At large strain, the solidlike samples show volume fraction dependent yielding. We develop a simple model to understand these rheological responses and show that the shear dependent stresses can be scaled onto a single master curve to obtain an internanotube interaction energy per bond approximately 40k(B)T. Our experimental observations suggest SWNTs in suspension form interconnected networks with bonds that freely rotate and resist stretching. Suspension elasticity originates from bonds between SWNTs rather than from the stiffness or stretching of individual SWNTs.

Elasticity↗
PubMed2004

Direct measurement of the polarized optical absorption cross section of single-wall carbon nanotubes.

We determine optical absorption cross sections of single-wall carbon nanotubes for visible light copolarized and cross polarized with respect to the nanotube axis. The need for perfectly aligned ensembles in absorbance measurements is eliminated by using Raman scattering to measure the nematic order parameter in magnetically aligned nanotube suspensions. The absorbance data allow the first quantitative, spectral comparisons with theories of local field depolarization, and provide benchmark spectra for simple, rapid, and quantitative measurements of alignment within nanotube dispersions.

Journal Article↗
PubMed2004

Nematic nanotube gels.

We report the creation of nematic nanotube gels containing large domains of isolated, oriented, half-micron-long, single-wall carbon nanotubes (SWNTs). We make them by homogeneously dispersing surfactant coated SWNTs at low concentration in an N-isopropyl acrylamide gel and then inducing a volume-compression transition. These gels exhibit hallmark properties of a nematic: birefrigence, anisotropy in optical absorption, and disclination defects. We also investigate the isotropic-to-nematic transition of these gels, and we describe the physical properties of their ensuing nematic state, including a novel buckling of sample walls. Finally, we provide a simple model to explain our observations.

Journal Article↗
PubMed2003

Rheological microscopy: local mechanical properties from microrheology.

We demonstrate how tracer microrheology methods can be extended to study submicron scale variations in the viscoelastic response of soft materials; in particular, a semidilute solution of lambda-DNA. The polymer concentration is depleted near the surfaces of the tracer particles, within a distance comparable to the polymer correlation length. The rheology of this microscopic layer alters the tracers' motion and can be precisely quantified using one- and two-point microrheology. Interestingly, we found this mechanically distinct layer to be twice as thick as the layer of depleted concentration, likely due to solvent drainage through the locally perturbed polymer structure.

Bacteriophage lambda↗
PubMed2003

Field-induced structures in miscible ferrofluid suspensions with and without latex spheres.

We explore magnetic-field-induced ordering and microphase separation of aqueous ferrofluid and of aqueous mixtures of ferrofluid with nonmagnetic latex spheres. The ferrofluid is a surfactant stabilized aqueous suspension of magnetite (Fe3O4) particles with average diameter 20 nm (including the approximately 2.5-nm thick surfactant layer); the nonmagnetic latex spheres are charge stabilized polymethylmethacrylate (PMMA) particles with diameters of 42 nm, 108 nm, and 220 nm. In the presence of a uniform magnetic field, needlelike ferrofluid droplets formed that eventually grew to sample-traversing columns at fields of approximately 600 G; the two-dimensional structure of these columns was, however, glassy rather than hexagonal. In higher fields, approximately 1000 G, the columns stretched and coalesced into sheetlike striped liquids, but a true lamellar phase was not observed. The addition of nonmagnetic latex spheres to the ferrofluid suspension lowered substantially the critical field for the formation of columns, and induced lamellar (stripe) phases at relatively low applied fields. Image analysis was used to determine the spatial correlation functions, the average needle or column spacing, and the average lamellae spacing of these samples as a function of latex sphere size and concentration.

Journal Article↗
PubMed2002

Incidence and prognostic significance of right bundle branch block complicating acute myocardial infarction.

The incidence and hospital courseofacute myocardial infarction wereobserved among randomly selected 560 patients. The mean age of the patients was 53 +/- 6.67 years with male-female ratio 2.6:1. The incidence of right bundle branch block (RBBB) was 15% (84 out of 560 patients). New RBBB, old RBBB and RBBB of indeterminate age were observed in 33 (39.25%), 23 (27.40%) and 28 (33.25%) cases respectively. RBBB was isolated in 50 (60%) cases and bi-fascicular in remaining 34 (40%) cases. The rate of use of thrombolytic was greater in RBBB group than non-RBBB group (52% vs 30.67%, P < 0.05). The complications were more frequently observed in patients with RBBB: in-hospital mortality, 27.40% vs 10.90% (P < 0.01); use of temporary pacemaker, 15% vs 9% (P < 0.05); and heart failure, 50% vs 35% (P < 0.05). In sub-group analysis, in-hospital mortality rate was higher among bi-fascicular group than isolated RBBB group (P < 0.05). Thus it appeared from the results that the incidence of RBBB is relatively common i.e. 15% over all (84 out of 560) and 5.90% new (33 out of 560) and despite greater use of thrombolytics, some specific in-hospital complications were significantly higher in patients with RBBB than without, RBBB.

Adult↗
PubMed2001

Role of ultrasonography and urinary cytology in diagnosing recurrence of superficial urinary bladder cancer compared to cystoscopy.

Urinary cytology, ultrasonogram of the urinary bladder and cystoscopy were done in 99 cases of urinary bladder cancer patients in the department of urology of Dhaka Medical College Hospital (DMCH), Dhaka, during the period from January 1997 to December 1998. Pre transurethral resection of bladder tumour (TURBT), urinary cytology was positive in 20.20% cases and ultrasound scan was positive in 96.9% cases. Histopathological examination revealed 95.96% as transitional cell carcinoma:- Grade I (3.0%), Grade II (62.6%) and Grade III (34.4%). During follow-up urinary cytology was positive in only one case whereas ultrasound scan was positive in 53.5% cases of whom only 21.6% patients had actual recurrent bladder tumours proved by cystoscopy. Statistical analysis of the three tests and histopathology showed significant variation though by Chi-square test the ultrasound scan is found superior to urinary cytology. We conclude when ultrasonography of the urinary bladder shows any suspected lesion it should be examined by cystoscope and biopsy should be taken from the suspected area for confirmation. Neither urinary cytology nor ultrasound scan can replace cystoscopic examination.

Adult↗
PubMed2001

Fracture penis--a study of twenty cases.

During the period from June 1985 to December 1999 a total of 20 male patients of 17-52 years age group were managed for traumatic fracture of the penile shaft. Diagnosis in all cases was established by history and careful physical examination. All but one underwent early surgical intervention and repair of the fractured part. Twelve patients, who reported for treatment within 36 hrs. of injury had good results. Of the 7 patients, who reported after 36 hrs. of injury 4 had good and 3 had fair results. One patient who presented on the 7th day after injury didn't undergo surgery and developed fibrous chordee within next six months.

Accidental Falls↗
PubMed1975

Effect of ethanol on the metabolism of the white blood cells.

Ethanol at a concentration of 40 mg% in the medium was found to inhibit the respiratory uptake of oxygen by polymorphonuclear cells obtained from rat peritoneal fluid. The stimulated oxygen uptake by these cells under conditions of phagocytosis was also inhibited with this concentration of ethanol. The quantities of hydrogen peroxide produced by these cells were also found to have been diminished. The possible significance of these findings is discussed.

Animals↗