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Biomedical subjects

P Papadopoulos

Publications and source records attributed to P Papadopoulos.

At least 19 recordsLinked to original sources
PubMed2006

The role of temperature and density on the glass-transition dynamics of glass formers.

A correlation between the monomeric volume and the dynamic quantity E*(V)/H*, used to provide a quantitative measure of the role of temperature and density on the dynamics, is demonstrated for a series of polymers and glass-forming liquids. We show that monomeric volume and local packing play a key role in controlling the value of this ratio and thus the dynamics associated with the glass temperature.

Journal Article↗
PubMed2006

Mid term results of PlantTan plate in the treatment of proximal humerus fractures.

This prospective study evaluates the clinical efficacy of a special implant, PlantTan plate used for fixation of displaced proximal humerus fractures. The PlantTan plate was used for internal fixation of closed displaced proximal humeral fractures in 68 patients from September 1999 to June 2002, in a University Hospital. One of the surgeries was for a non-union, and five patients were lost to follow-up. The patients' ages ranged from 19 to 76 years (mean 61 years and median 66 years). Of the remaining 62 patients, 42 were female and 20 were male. As defined using the Neer classification 19 patients had two part, 37 three part and 6 had four part fractures. Median follow-up was 19 months (11-38). The outcome was assessed using radiographs, American Shoulder and Elbow Surgeons (ASES) score and Hospital for Special Surgery (HSS) scoring system. Fifty-two patients achieved union in a median of 8 weeks. The median cumulative score of activities of daily living of ASES was 20.4/30 (13-27). According to HSS, 11 scored excellent, 26 good, 14 fair and 11 scored poor. Eight patients had fixation failure and two developed avascular necrosis. Eleven patients developed an infection. Six patients developed an infection resulting in implant removal. One had a transient and one permanent axillary nerve palsy. Since the PlantTan plate provides stability, early active rehabilitation can be instituted. The implant is distally placed reducing impingement symptoms. However, the implant requires wide surgical exposure, is bulky and has an unacceptable infection rate. The fixation failure is high in patients with osteoporosis. In view of the above encountered problems, the implant has been discontinued in our hospital.

Adult↗
PubMed2006

Thermodynamic confinement and alpha-helix persistence length in poly(gamma-benzyl-L-glutamate)-b-poly(dimethyl siloxane)-b-poly(gamma-benzyl-L-glutamate) triblock copolymers.

The structure and the associated dynamics of a series of poly(gamma-benzyl-L-glutamate)-b-poly(dimethyl siloxane)-b-poly(gamma-benzyl-L-glutamate) (PBLG-b-PDMS-b-PBLG) triblock copolymers were investigated using small- and wide-angle X-ray scattering, NMR, transmission electron microscopy, and dielectric spectroscopy, respectively. The structural analysis revealed phase separation in the case of the longer blocks with defected alpha-helical segments embedded within the block copolymer nanodomains. The alpha-helical persistence length was found to depend on the degree of segregation; thermodynamic confinement and chain stretching results in the partial annihilation of helical defects.

Carbon Isotopes↗
PubMed2005

"Glass transition" in peptides: temperature and pressure effects.

We report on the origin of the liquid-to-glass transition in a series of oligopeptides of gamma-benzyl-L-glutamate up to the polymer (PBLG), and in Poly-Z-L-lysine (PZLL) and Polyglycine (PGly) using dielectric spectroscopy as a function of temperature and pressure. We show that temperature is the dominant control variable of the dynamics associated with the peptidic "glass transition." This is an intrinsic feature of the peptide dynamics, irrespective of the type of amino acid and of the peptide secondary structure. The influence of the type of secondary structure (alpha helix vs beta sheet) on the liquid-to-glass dynamics is discussed.

Journal Article↗
PubMed2004

Molecular dynamics of oligofluorenes: a dielectric spectroscopy investigation.

The molecular dynamics were investigated in a series of "defect-free" oligofluorenes up to the polymer by dielectric spectroscopy (DS). The method is very sensitive to the presence of keto "defects" that when incorporated on the backbone give rise to poor optical and electronic properties. Two dielectrically active processes were found (beta and alpha process). The latter process (alpha) displays strongly temperature dependent relaxation times and temperature- and molecular weight-dependent spectral broadening associated with intramolecular correlations. The glass temperature (Tg) obeys the Fox-Flory equation and the polymer Tg is obtained by DS at 332 K. The effective dipole moment associated with the alpha process is 0.27 +/- 0.03 D.

Journal Article↗
PubMed2001

A massive reservoir of low-excitation molecular gas at high redshift.

Molecular hydrogen (H2) is an important component of galaxies because it fuels star formation and the accretion of gas onto active galactic nuclei (AGN), the two processes that can generate the large infrared luminosities of gas-rich galaxies. Observations of spectral-line emission from the tracer molecule carbon monoxide (CO) are used to probe the properties of this gas. But the lines that have been studied in the local Universe-mostly the lower rotational transitions of J = 1 --> 0 and J = 2 --> 1-have hitherto been unobservable in high-redshift galaxies. Instead, higher transitions have been used, although the densities and temperatures required to excite these higher transitions may not be reached by much of the gas. As a result, past observations may have underestimated the total amount of molecular gas by a substantial amount. Here we report the discovery of large amounts of low-excitation molecular gas around the infrared-luminous quasar APM08279+5255 at redshift z = 3.91, using the two lowest excitation lines of 12 CO (J = 1 --> 0 and J = 2 --> 1). The maps confirm the presence of hot and dense gas near the nucleus, and reveal an extended reservoir of molecular gas with low excitation that is 10 to 100 times more massive than the gas traced by the higher-excitation observations. This raises the possibility that significant amounts of low-excitation molecular gas may exist in the environments of high-redshift (z > 3) galaxies.

Astronomical Phenomena↗
PubMed2000

Transcriptional activation of the granulocyte-macrophage colony-stimulating factor receptor gene in cell mutants.

Retroviral insertional mutagenesis has proven to be a powerful in vivo approach for identifying genetic mutations involved in tumorigenesis or developmental abnormalities. Applying this approach to an in vitro system, where experimental design can be readily manipulated, would greatly increase its efficacy. In this study, we sought to determine whether retroviral insertional mutagenesis could be used to isolate cell mutants, in which the transcriptional activation of a receptor gene has occurred. Cells of the myeloid progenitor cell line FDC-P1(M), which do not express the alpha receptor subunit (GMRalpha) for granulocyte-macrophage colony-stimulating factor (GM-CSF), were infected and selected for growth in GM-CSF. Over 100 mutants were isolated at a frequency up to ninefold higher than that of uninfected controls. Expression of GMRalpha in these mutants was confirmed by blocking proliferation with GM-CSF antibodies, detection of high-affinity receptors, and Northern blot analysis. Significantly, in 7/18 mutants analyzed, gross DNA rearrangements had occurred in the GMRalpha locus. These rearrangements were demonstrated to be due to intergenic rearrangements, juxtaposing an active enhancer/promoter upstream of the GMRalpha gene. In one mutant it could be demonstrated that the wild-type allele was also expressed, providing evidence that secondary mutations had occurred. The implications of these results for retroviral insertional mutagenesis are discussed.

Animals↗
PubMed2000

Classical information and distillable entanglement

We establish a quantitative connection between the amount of lost classical information about a quantum state and the concomitant loss of entanglement. Using methods that have been developed for the optimal purification of mixed states, we find a class of mixed states with known distillable entanglement. These results can be used to determine the quantum capacity of a quantum channel which randomizes the order of transmitted signals.

Journal Article↗
PubMed2000

Sheep poxvirus identification from clinical specimens by PCR, cell culture, immunofluorescence and agar gel immunoprecipitation assay.

Some 40 clinical specimens of skin lesions from sheep pox suspected cases were investigated by four different diagnostic assays: PCR, virus isolation in lamb testis cell cultures, direct immunofluorescent assay (DIFA) and antigen detecting agar gel immune precipitation test (AGIPT). All the specimens were positive by PCR and virus isolation, 29 were positive by DIFA and 16 by AGIPT. Using virus isolation on cell cultures as the gold standard, the PCR sensitivity was 100%, while that of DIFA and AGIPT was 73% and 40%, respectively. Skin samples with orf lesions or normal skin biopsies were PCR-negative. Cross-reactions with orf virus were observed in three samples only in the AGIPT assay. The PCR described combines high specificity and sensitivity with speed. PCR was therefore shown to be the method of choice for sheep poxvirus diagnosis directly from clinical specimens.

Animals↗
PubMed1997

Replacement of deficient acetabulum using Burch-Schneider cages. 22 patients followed for 2-10 years.

The absence of good bone stock with massive acetabular deficiency has been a major problem in both revision hip arthroplasty and in primary arthroplasty for congenital dislocation of the hip (CDH). 22 patients (24 hips; 21 revision and 3 primary replacements: mean age 58 years) with substantial bone loss underwent acetabular reinforcement with Burch-Schneider cages. Classification of acetabular deficiency was made according to the AAOS system. The surgical procedure involved preparation of acetabulum, filling the defect with bone autografts, placement of the cage with its flanges, fixation with screws on the lateral wall only and placement of a cement and plastic cup. Radiographic loosening with breakage of the screws was observed in only 1 patient. After a mean follow-up of 8 (2-10) years, good stability was achieved in all patients and no mechanical failure was observed. Satisfactory results were observed in all but one of the cases, indicating that effective support of the acetabulum can be achieved using Burch-Schneider cages.

Acetabulum↗
PubMed1995

The novel activation of ABL by fusion to an ets-related gene, TEL.

In human leukemia, activation of the ABL proto-oncogene locus on chromosome 9 most commonly occurs as a result of its fusion to the BCR locus on chromosome 22. The resulting chimeric protein displays an elevated tyrosine kinase activity. We have identified a novel activation of ABL which involves a gene located on chromosome 12, designated TEL. Like BCR, TEL is fused in-frame with ABL and produces a fusion protein with an elevated tyrosine kinase activity when assayed in an immune complex. The amino-terminal sequences of TEL encode a helix-loop-helix motif which may mediate dimerization.

Amino Acid Sequence↗
PubMed1995

The fusion of TEL and ABL in human acute lymphoblastic leukaemia is a rare event.

We have recently identified a common ALL patient which harboured a chromosomal fusion between the TEL gene on chromosome 12 and the ABL gene on chromosome 9. We designed an RT-PCR assay to screen 186 adult ALL and 30 childhood ALL patients for this novel translocation. We were unable to identify any additional cases with a TEL/ABL fusion product.

Adult↗
PubMed1994

Factors affecting the postoperative exercise capacity of patients with mitral stenosis and aortic regurgitation.

Factors affecting the exercise capacity of patients with mitral stenosis (MS) and aortic regurgitation (AR) are incompletely understood. Accordingly, exercise capacity was assessed in 13 patients with MS and in 13 with AR by means of cardiopulmonary exercise testing before as well as 3, 6 and 12 months after valve replacement. Left- and right-ventricular function were evaluated echocardiographically. Both in MS and in AR exercise capacity expressed by maximal oxygen consumption (VO2max) increased significantly after valve replacement and was directly related to right ventricular (RV) function assessed by the ratio of RV acceleration time to RV ejection time (r = 0.87, p < 0.001 and r = 0.74, p < 0.001, respectively) and inversely related to left atrial diameter (r = -0.72, p < 0.001 and r = -0.76, p < 0.001, respectively). No relation between VO2max and resting left-ventricular function was found. Thus, the postoperative improvement in the exercise capacity both in mitral stenosis and in aortic regurgitation is associated with an improvement in right-ventricular function and a decrease in left-atrial size.

Aortic Valve Insufficiency↗