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Biomedical subjects

G Sinha

Publications and source records attributed to G Sinha.

At least 19 recordsLinked to original sources
PubMed2005

Dielectric spectroscopy of aerosil-dispersed liquid crystal embedded in Anopore membranes.

The complex dielectric permittivity epsilon* values are presented for aerosil-dispersed 4-pentyl-4-cyanobiphenyl (5CB) confined in Anopore membranes. The dielectric permittivities are measured in the frequency range from 10(-2) Hz to 1 GHz at temperatures ranging from 50 degrees C down to -20 degrees C. In bulk 5CB, which has only a nematic phase, there exist two main relaxation processes: one due to the rotation of molecules around their short axes for parallel orientation of the director to the probing field and another fast relaxation process due to the librational motion of molecules for perpendicular orientation. Inside Anopore membranes both these main relaxation processes can be observed, but with subtle differences. The relaxation process due to the rotation of molecules around the short axis is faster in Anopores at all temperatures in comparison with the bulk process. Hydrophilic aerosil particles, when dispersed in the liquid-crystal (LC) phase, attach to each other via hydrogen bonds and form a three-dimensional interconnecting aerosil network, thus dividing the LC phase into small domains. Dispersing 5CB with different concentrations of hydrophilic aerosils leads to a decrease in relaxation time with aerosil concentration. In these dispersed systems a slow additional relaxation process emerges. This slow process becomes stronger with higher concentrations of aerosil. From our experiments we conclude that this process is the relaxation of 5CB molecules homeotropically aligned to the surface of the aerosil particles. In the case of 5CB-aerosil dispersions enclosed in Anopore membranes this slow process still exists and increases also with aerosil concentration. The relaxation time of the rotation of the 5CB molecules around their short axis systematically increases in these 5CB-aerosil samples in Anopore membranes with aerosil concentration from the 5CB-Anopore behavior towards the behavior observed for 5CB-aerosil dispersions. We explain the evolution as resulting from opposing tendencies from size effects (in the Anopore membranes) and disorder effects (in the aerosil dispersions).

Journal Article↗
PubMed2005

Influence of nanosized confinements on 4-n-decyl-4'-cyanobiphenyl (10CB): a broadband dielectric study.

Real (epsilon') and imaginary (epsilon") parts of the complex dielectric permittivity (epsilon*) of the liquid crystal (LC) 4-n-decyl-4'-cyanobiphenyl (10CB) embedded in Anopore membranes and Vycor porous glass, as well as dispersed with hydrophilic aerosils, have been studied by means of broadband dielectric spectroscopy in the frequency range from 10(-2) Hz to 1 GHz . In bulk 10CB, which has a direct transition from an isotropic to a smectic- A phase, there exists one main relaxation process for the parallel orientation of the director with respect to the probing field and a faster one for the perpendicular orientation. All molecular relaxation processes in 10CB are of Debye type and have Arrhenius like temperature dependence. For 10CB embedded in untreated and surface treated cylindrical pores of Anopore membranes the dielectric spectra are similar to the bulk with the exception that both the rotation around the short axis and the libration motion are faster in the pores. In the case of 10CB dispersed with two different concentrations of hydrophilic aerosils an emergence of a slow relaxation process, which is stronger for the higher concentration, is additionally observed along with the bulklike processes. The slow process in the LC-hydrophilic aerosil system is attributed to the relaxation of the molecules that are homeotropically aligned close to the surfaces of the aerosil particles. This process also has an Arrhenius type of temperature dependence. For 10CB embedded in narrow channels of Vycor porous glass three relaxation processes are observed. Two of these processes are bulklike and are due to the librational motion of molecules and the rotation of molecules around their short axes. The slowest process seems to be a surface process, similar in origin to that observed for 10CB dispersed with hydrophilic aerosils, and is prominent amongst all. The material in the Vycor porous glass could be supercooled by at least 185 degrees below bulk crystallization temperature. The slow process has a Vogel-Fulcher-Tamman (VFT) type of temperature dependence typical for glass formers in this wide temperature range. In addition, the bulklike processes are found to be strongly modified and also have a VFT like temperature dependence from measurements done in a wide temperature range. This behavior is in contrast to other reports of glassy behavior in confined LC, where the glassy behavior as concluded from a slow relaxation process observed in a narrow temperature range.

Journal Article↗
PubMed2004

Broadband dielectric spectroscopy study of molecular dynamics in the glass-forming liquid crystal isopentylcyanobiphenyl dispersed with aerosils.

The glass-forming liquid crystal isopentylcyanobiphenyl (CB15) filled with different concentrations of hydrophilic and hydrophobic aerosils has been investigated by broadband dielectric spectroscopy in the frequency range from 10(-2) Hz to 10(7) Hz over a temperature range of 173 K-300 K. CB15 that consists of chiral molecules has a monotropic system of phases nematic (N*) and smectic-A upon supercooling and forms a glass further on. In the isotropic phase a single Davidson-Cole process exists in the substance, which is due to the rotation of the molecules around their short axes. In the supercooled N* phase a Cole-Cole process that is an order of magnitude faster is additionally present and is due to the rotation in a cone around the local director. The relaxation times of the process due to rotation around short axes obey the empirical Vogel-Fulcher-Tamman behavior typical for glass-forming systems. Filling of the liquid crystal (LC) with different concentrations of hydrophilic aerosils leads to the emergence of a slow relaxation process that grows with the increasing concentration of the aerosils. The aerosil particles, which form a three-dimensional network dividing the LC phase into domains, have little effect on the relaxation times of the bulk processes. As a consequence the glass transition temperature is merely affected. On the other hand, in LCs dispersed with hydrophobic aerosils the slow process is quite weak. The slow process is attributed to the relaxation of the molecules that are homeotropically attached at the surfaces of the aerosil particles. The LC-aerosil surface interaction leads to a considerable slowing down of the molecular rotation around their short axis. The process has an Arrhenius-like temperature dependence of the relaxation times with an activated type of dynamics, which can be explained by considering a nonincreasing rearranging region of cooperativity in surface layers.

Journal Article↗
PubMed2001

Extent of excision margin width required in breast conserving surgery for ductal carcinoma in situ.

BACKGROUND: Breast conserving surgery (BCS) is common practice for unifocal ductal carcinoma in situ (DCIS) less than 4 cm in size, but the extent of tumor free margin width around DCIS necessary to minimize recurrence is unclear. METHODS: Clinical and pathologic details were recorded from all patients with pure DCIS < 4 cm in size, treated with BCS between 1978 and 1997. Histologic margins were measured by using an ocular micrometer. Patients with clear margins (> 1 mm) were divided up into 3 groups for analysis based on margin of normal tissue excised: 1.1-5 mm, 5.1-10 mm, and 10.1-40 mm. RESULTS: There were 66 patients with close margins (< or = 1 mm), of which 25 cases (37.9%) recurred. The recurrence rates for the 3 clear margin groups ranged from 4.5-7.1%. Median followup was 47 months (range 12-197 mos). Risk of recurrence in the group with close margins was greater than the subgroups with clear margins (P < 0.001); no differences in recurrence was seen between the individual subgroups with clear margins. Nuclear Grade 3 was predictive of recurrence (P = 0.03). Following excision alone, the recurrence rate was 18.6%, compared with 11.1% when radiotherapy was given as adjuvant therapy. Women with clear margins following excision had a recurrence rate of only 8.1%. CONCLUSION: After BCS for DCIS, close margins were associated with a high risk of local recurrence. Radiotherapy did not compensate for inadequate surgical clearance.

Adult↗
PubMed1997

Comparison of image processing techniques (magnetic resonance imaging, computed tomography scan and ultrasound) for 3D modeling and analysis of the human bones.

Magnetic resonance imaging (MRI), computed tomography scanning (CT scan), and ultrasound imaging techniques (UI) were used for data acquisition to construct/develop a 3D solid model of the human tibia, femur, and skull. CT scan was found to be an acceptable technique for cadavers. CT scans are harmful to the human body in large doses, while MRIs and ultrasound are known to be safe. However, MRIs form a better tool in performing this image generation task for living beings because of its high resolution capacity when compared with images obtained using ultrasound techniques. High resolution poses to be a very important factor, as the consideration of various material properties of the bones was part of the emphasis of this research. MRIs have the capacity of displaying a distinct boundary between the muscles and the bone, in addition to the boundary between the cortical and the cancellous region within the bone. Ultrasound was found to be the cheapest technique and gave reasonably good results for just the outside boundaries of the bone. The models of the human bones were generated on a Computer Aided Design (CAD) system. The cross-sections obtained from (MRI, CT, or UI) were scanned into the computer. Image processing software was used to detect the boundaries of the bones. A C + + program was used to read the coordinates of the edges and construct a B-spline curve on the CAD system. The curves were converted to a B-rep solid using skinning. The solid models were meshed, constrained, and material properties were assigned to different regions of the models for Finite Element Analysis (FEM).

Anatomy, Cross-Sectional↗
PubMed1997

Prevalence and type of cerebral palsy in a British ethnic community: the role of consanguinity.

Little is known about the prevalence of cerebral palsy (CP) within ethnic subgroups born in Britain. The Yorkshire Regional Cerebral Palsy Register has ascertained all cases of CP in children born within the Regional Health Authority boundary in 1985 to 1987 inclusive and diagnosed by 5 years of age. Birth registrations recorded by ethnic subgroups allowed us to determine the prevalence of CP within the Bradford District Health Authority (BDHA) boundaries by Asian and non-Asian ethnic subgroups. All the children with CP in BDHA were examined by one individual and careful family pedigrees recorded. We noted that BDHA had a high prevalence of CP; 3.87 to 4.16 per 1000. The prevalences in the non-Asian and Asian populations were 3.18, and between 5.48 and 6.42, per 1000, respectively. This difference was statistically significant (P = 0.03). First cousin marriages occurred in 15 of the 39 Asian families (51.7%) and nine of these families had another first or second degree family member with a similar type of CP to the index child. There was no consanguinity in the non-Asian families. These data highlight the increased need for services in some ethnic populations living in Britain and the likely genetic aetiology of a significant proportion of cases of CP in Asian families.

Cerebral Palsy↗
PubMed1996

Primary pulmonary hypertension in HIV infection: an outcome determined by particular HLA class II alleles.

Primary pulmonary hypertension (PPH) may have an autoimmune basis that is influenced by host immunogenetics. The pathogenesis of primary pulmonary hypertension in human immunodeficiency virus (HIV) infection is unclear. The objective of this study was to determine whether patients with PPH and HIV infection have distinctive immunogenetic profiles. Ten racially mixed HIV-infected patients with PPH were typed for human leukocyte antigen (HLA) class II (DRB1, 3, 4, 5 and DQB1) by DNA-PCR sequence-specific oligonucleotide probes. Results were compared with two control groups: 128 HIV-negative Caucasians and a previously reported group of 97 HIV-positive, racially mixed control subjects. In those with PPH, there was a significantly increased frequency of HLA-DR6 (-DRB1*1301/2 subtypes) and of HLA-DR52 (DRB3*0301 subtype). These findings suggest that HIV-associated PPH reflects a host response to HIV-1 determined by one or more HLA-DR alleles located within the major histocompatibility complex. The same HLA-DR6 subtype found at increased frequency in our patients has previously been associated with the development of a CD8 lymphocytic host response to HIV-1, termed diffuse infiltrative lymphocytosis syndrome (DILS), which resembles autoimmune Sjogren's disease and is associated with prolonged survival. Together, these findings suggest that HIV-positive PPH may represent a clinical outcome that has similarities with that resulting from the immunogenetically determined host response present in DILS.

Adult↗
PubMed1995

The human insulin-like growth factor-II promoter P1 is not restricted to liver: evidence for expression of P1 in other tissues and for a homologous promoter in baboon liver.

The human insulin-like growth factor (IGF)-II gene (IGF2) contains 4 different promoters (P1-P4), three of which (P2-P4) are homologous to the 3 promoters found in murine IGF-II genes. IGF-II is abundantly expressed in adult humans and primates, but IGF2 is only expressed in brain in adult rat and mouse. Previously, promoter P1 had been found exclusively in human adult liver but not in other human tissues or in rat or mouse liver. Although mouse liver does not express a homologue of human P1 mRNA, 5' "pseudo-exons" which are homologues of human exons 2 and 3 have been identified in murine IGF2. Based on the published DNA sequences of human exon 2 and the homologous murine pseudo-exon psi 1, we designed a 5'-oligonucleotide common to both human and murine IGF2 and a 3'-oligonucleotide primer from coding exon 7. We amplified specific cDNA from human and baboon livers, but no specific band was seen in rat or mouse liver. Chain-termination DNA sequencing confirmed that the P1 mRNA sequence from baboon liver shares 90% homology with human P1 mRNA in the 5' noncoding region (exons 2 and 3). Mature baboon IGF-II peptide is identical to human IGF-II, but there are 7 amino acid differences in the E region of the IGF-II prohormone. In humans, IGF-II mRNA transcripts containing P1 were also found in human myometrium and myomas. Our results demonstrate that the P1 promoter of the IGF-II gene is present in human and baboon adult liver, although it is absent from murine liver. In humans, promoter P1 is also utilized in tissues other than adult liver. We speculate that promoter P1 may be an important factor in persistent IGF-II synthesis.

Adult↗
PubMed1993

A field trial of Billings' ovulation method for spacing and limitation of birth.

In spite of constant efforts by health and social workers, existing family planning measures are not used by a vast majority of eligible couples. This is because of the fear that the method may affect their health and happiness. Billings' ovulation method is based on the scientific observation that by noting the changes in cervical mucus, which is clear, slippery and copious in periovulatory period, it is possible to prevent pregnancy by avoiding intercourse during this period. As this method does not require the use of drugs or devices it was decided to promote this method in the urban areas and slums of Patna, Bihar where couples were not using other methods. This is not a comparative study of the cost-effectiveness of Billings' ovulation method versus other contraceptive measures at all. An analysis of 501 cases (267 in urban and 234 in slums) over a period of 2 1/2 years has been presented and it is gratifying to note that the couples from all religions and strata of the society (nearly 47% were slum dwellers) agreed to continue this method.

Adult↗
PubMed1993

Fertility and reproduction following inversion of uterus.

Puerperal inversion of the uterus is itself a rare occurrence. Records of fertility and reproduction following an episode of uterine inversion are even rarer. The reproductive outcome following correction of uterine inversion in 6 cases seen over a span of 35 years is being reported here. One case of acute inversion was managed by manual replacement and the remaining 5 of chronic inversion were corrected by Haultain's operation. The only patient managed by manual replacement conceived thrice. She aborted once, but delivered 2 healthy live babies subsequently by caesarean section done for uterine inertia each time. Out of the 5 patients treated by Haultain's technique, 3 conceived later. One did not come for follow-up after the 5th month. Each of the other 2 had full-term normal delivery of living baby under supervision. None of the cases had any complications. It is concluded that even after operative correction of inversion, uncomplicated delivery may be anticipated. Conservative surgical management is ideal even in apparently neglected and chronic cases, as most of these women were primipara or multipara with only one or 2 living children and had a desire of future child bearing.

Adult↗
PubMed1992

p53 and chromosome 3 abnormalities, characteristic of malignant lung tumours, are detectable in preinvasive lesions of the bronchus.

Bronchial epithelial dysplasia is believed to precede invasive squamous cell carcinoma of the lung. Six paired dysplasia and tumour samples were distinguished histologically in sections of formalin-fixed paraffin-embedded lung tissue from patients with lung cancer. Additionally, samples of dysplastic bronchial epithelium were obtained from patients without lung tumours. Microdissection of the unstained sections provided dysplastic and tumour samples from which DNA was prepared for comparison with the patients' constitutional genotype, using polymerase chain reaction-based restriction fragment length polymorphism analysis. All six samples of tumour and the paired adjacent samples of bronchial dysplasia showed loss of heterozygosity (LOH) at loci on the short arm of chromosome 3. Five of the six cases showed involvement of the p53 gene as assessed by LOH at the AccII site within the gene, and by immunoreactivity to CM-1, an antibody which recognizes the mutated form of the p53 protein in paraffin-embedded material. Of the dysplastic samples, obtained from patients without invasive tumours, all three showed LOH at 3p; one sample showed LOH at the AccII polymorphic locus within the p53 gene, and another sample, uninformative at this locus, stained positively with this antibody. These results indicate that somatic genetic changes are present in preinvasive lesions in the bronchus.

Base Sequence↗
PubMed1992

Neuromyotonia.

Explore the source record for details and available documents.

Adult↗
PubMed1988

Thoracoscopy: assessment of a physician service and comparison of a flexible bronchoscope used as a thoracoscope with a rigid thoracoscope.

The practicality of physicians performing thoracoscopy for diagnostic purposes was assessed in 30 patients with pleural effusions of unknown cause. A rigid thoracoscope was compared with a fibreoptic bronchoscope used as a flexible thoracoscope and the diagnostic adequacy of biopsy specimens obtained with the two instruments assessed. The two instruments were inserted by a physician in the bronchoscopy suite using local anaesthesia. The procedure proved safe, acceptable, and diagnostically effective. The rigid thoracoscope proved a more satisfactory instrument but the fibreoptic bronchoscope, with minor adaptations, may be used for thoracoscopy.

Biopsy↗