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Biomedical subjects

A Kaminski

Publications and source records attributed to A Kaminski.

At least 19 recordsLinked to original sources
PubMed2003

Crossover from coherent to incoherent electronic excitations in the normal state of Bi(2)Sr(2)CaCu(2)O(8+delta).

Angle resolved photoemission spectroscopy (ARPES) and resistivity measurements are used to explore the overdoped region of the high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+delta). We find evidence for a new crossover line in the phase diagram between a coherent metal phase, for lower temperatures and higher doping, and an incoherent metal phase, for higher temperatures and lower doping. The former is characterized by two well-defined spectral peaks in ARPES due to coherent bilayer splitting and superlinear behavior in the resistivity, whereas the latter is characterized by a single broad spectral feature in ARPES and a linear temperature dependence of the resistivity.

Journal Article↗
PubMed2003

The origin of multiple superconducting gaps in MgB2.

Magnesium diboride, MgB2, has the highest transition temperature (T(c) = 39 K) of the known metallic superconductors. Whether the anomalously high T(c) can be described within the conventional BCS (Bardeen-Cooper-Schrieffer) framework has been debated. The key to understanding superconductivity lies with the 'superconducting energy gap' associated with the formation of the superconducting pairs. Recently, the existence of two kinds of superconducting gaps in MgB2 has been suggested by several experiments; this is in contrast to both conventional and high-T(c) superconductors. A clear demonstration of two gaps has not yet been made because the previous experiments lacked the ability to resolve the momentum of the superconducting electrons. Here we report direct experimental evidence for the two-band superconductivity in MgB2, by separately observing the superconducting gaps of the sigma and pi bands (as well as a surface band). The gaps have distinctly different sizes, which unambiguously establishes MgB2 as a two-gap superconductor.

Journal Article↗
PubMed2002

Burst fracture of the fifth lumbar vertebra: results of posterior internal fixation and transpedicular bone grafting.

Burst fractures of the fifth lumbar vertebra are rare, and there are only a few reports on this subject, which is characterised by its unique anatomical and biomechanical features. This retrospective analysis reports on ten patients whose fractures of L5 were stabilised with a short internal fixator in combination with a posterior fusion as well as transpedicular bone grafting. The average follow-up period was 22 months. Radiometric data were surveyed and compared to the functional results. The height of the fractured vertebra remained nearly unchanged throughout the course. Loss of lordosis of 4 degrees in the upper disc space and 4 degrees in the lower disc space were observed postoperatively. At the time of follow-up, the values of segmental lumbar lordosis were significantly below the preoperative level. The narrowing of the neural canal was reduced from 57% to 28% with the surgical intervention. However, there was no correlation between the functional and the radiological outcome. Neurological deficits were documented in two patients, which declined during the course. There were no severe postoperative complications. The results of the present study demonstrate that the described surgical procedure in fractures of the fifth lumbar vertebra does not promote an anatomic restoration of the fractured vertebra, nor of the segmental lordosis. However, the clinical results do not correlate with the radiological outcome. Nonoperative treatment with early mobilisation without external support seems to be the treatment of choice.

Adolescent↗
PubMed2002

Polaron percolation in diluted magnetic semiconductors.

We theoretically study the development of spontaneous magnetization in diluted magnetic semiconductors as arising from a percolation of bound magnetic polarons. Within the framework of a generalized percolation theory we derive analytic expressions for the Curie temperature and the magnetization in the limit of low carrier density, obtaining excellent quantitative agreement with Monte Carlo simulation results and good qualitative agreement with experimental results.

Journal Article↗
PubMed2002

Spontaneous breaking of time-reversal symmetry in the pseudogap state of a high-Tc superconductor.

A change in 'symmetry' is often observed when matter undergoes a phase transition-the symmetry is said to be spontaneously broken. The transition made by underdoped high-transition-temperature (high-Tc) superconductors is unusual, in that it is not a mean-field transition as seen in other superconductors. Rather, there is a region in the phase diagram above the superconducting transition temperature Tc (where phase coherence and superconductivity begin) but below a characteristic temperature T* where a 'pseudogap' appears in the spectrum of electronic excitations. It is therefore important to establish if T* is just a cross-over temperature arising from fluctuations in the order parameter that will establish superconductivity at Tc (refs 3, 4), or if it marks a phase transition where symmetry is spontaneously broken. Here we report that, for a material in the pseudogap state, left-circularly polarized photons give a different photocurrent from right-circularly polarized photons. This shows that time-reversal symmetry is spontaneously broken below T*, which therefore corresponds to a phase transition.

Journal Article↗
PubMed2001

Electron energy relaxation in the presence of magnetic impurities.

We study inelastic electron-electron scattering mediated by the exchange interaction of electrons with magnetic impurities and find the kernel of the corresponding two-particle collision integral. In a wide region of parameters, the kernel K is proportional to the inverse square of the transferred energy, K proportional to J4/E2. The exchange constant J is renormalized due to the Kondo effect. At small energy transfers, the 1/E2 divergence is cut off; the cutoff energy is determined by the dynamics of the impurity spins. The obtained results may provide a quantitative explanation of the experiments of Pothier et al. [Phys. Rev. Lett. 79, 3490 (1997)] on anomalously strong energy relaxation in short metallic wires.

Journal Article↗
PubMed2001

Renormalization of spectral line shape and dispersion below Tc in Bi2Sr2CaCu2O8+delta.

Angle-resolved photoemission data in the superconducting state of Bi2Sr2CaCu2O8+delta show a kink in the dispersion along the zone diagonal, which is related via a Kramers-Krönig analysis to a drop in the low energy scattering rate. As one moves towards (pi,0), this kink evolves into a spectral dip. The occurrence of these anomalies in the dispersion and line shape throughout the zone indicates the presence of a new energy scale in the superconducting state.

Journal Article↗
PubMed2001

Jejunal feeding, even when instituted late, improves outcomes in patients with severe pancreatitis and peritonitis.

This study assessed the feasibility and effectiveness of jejunal feeding (JF) after surgery due to secondary peritonitis or failed conservative therapy of severe pancreatitis. Of 60 patients, 30 were randomly assigned to receive postoperative JF and the remaining 30 constituted the control group. Acute Physiology and Chronic Health Evaluation II, nutritional intake, systemic inflammatory response syndrome, and outcomes were measured. Patients in JF group received the daily mean of 1294.6 (362.6) kcal including 830.6 (372.7.0) kcal enterally, versus 472.8 (155.8) kcal daily in the control group (P < 0.0001). There were fewer complications in the JF patients, with no significant difference; length of stay in the intensive care unit and in the hospital did not differ. The frequency of systemic inflammatory response syndrome was similar in both groups, but outcomes differed. The first surgical intervention resulted in 3.3% of relaparotomies in JF patients, caused by unresolved peritonitis, versus 26.7% in the control subjects (P = 0.03). Recovery of bowel transit took significantly less time in the JF patients (mean: 54.6 h versus 76.8 h in control subjects, P = 0.01). JF resulted in 3.3% mortality as opposed to 23.3% in the control group (P = 0.05). In conclusion, JF is feasible and effective in postoperative treatment of patients due to secondary peritonitis or severe pancreatitis. Improved bowel and peritoneal function could be the main impact of JF.

Adolescent↗
PubMed2000

Fermi surface of Bi2Sr2CaCu2O8

We study the Fermi surface of Bi2Sr2CaCu2O8 using angle resolved photoemission spectroscopy (ARPES) with a momentum resolution of approximately 0.01 of the Brillouin zone. We show that, contrary to recent suggestions, the ARPES derived Fermi surface is a large hole barrel centered at (pi,pi), independent of the incident photon energy. We caution that the photon energy and k dependence of the matrix elements, if not properly accounted for, can lead to misinterpretation of ARPES intensities.

Journal Article↗
PubMed2000

Quasiparticles in the superconducting state of Bi(2)Sr(2)CaCu(2)O(8+delta)

Recent improvements in momentum resolution lead to qualitatively new angle-resolved photoemission spectroscopy results on the spectra of Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) along the (pi,pi) direction, where there is a node in the superconducting gap. We now see the intrinsic line shape, which indicates the presence of true quasiparticles at all Fermi momenta in the superconducting state, and lack thereof in the normal state. The region of momentum space probed here is relevant for charge transport, motivating a comparison of our results to conductivity measurements by infrared reflectivity.

Journal Article↗
PubMed1999

Amnion allografts prepared in the Central Tissue Bank in Warsaw.

Applications of allogenic amnion grafts range from wound dressing of severe burns, dermabrasions and lower extremity ulcer treatments to plastic surgery, laryngology and ophthalmology. The aim of the present study was to elaborate the method of processing, preservation and sterilization of human amnion allografts prepared as wound dressing used mainly for burned patients. During the amniotic sac processing (after separation of chorion) special attention was paid to ensure that the epithelial side of amnion is placed directly on polyester net used as a support. After application on the wound, the epithelial side with the basement membrane is facing outwards; this will promote migration, attachment and spreading of the host cells encouraging epithelialization. Human amnion allografts were preserved by lyophilization or deep-freezing and subsequently radiation-sterilized with a dose of 35 kGy. It has been observed, however, that lyophilized irradiated allografts are resorbed within a few days, while frozen irradiated ones better adhere to wound and persist even 3 weeks after grafting, therefore, it has been decided to preserve amnion by deep-freezing. Since the beginning of 1998 over 400 preserved radiation-sterilized amnion allografts (with a total surface area over 40,000 cm2) have been prepared at the Central Tissue Bank in Warsaw and distributed to clinics and hospitals throughout the country.

Amnion↗
PubMed1998

The polypyrimidine tract binding protein (PTB) requirement for internal initiation of translation of cardiovirus RNAs is conditional rather than absolute.

Picornavirus RNAs are translated by an unusual mechanism of internal ribosome entry that requires a substantial segment of the viral 5'-untranslated region, generally known as the internal ribosome entry segment (IRES), and in some circumstances may require cellular trans-acting proteins, particularly polypyrimidine tract binding protein (PTB). It is shown here that for encephalomyocarditis virus (EMCV), the PTB dependence of IRES function in vitro is determined partly by the nature of the reporter cistron, and more especially by the size of an A-rich bulge in the IRES. With a wild-type EMCV IRES (which has a bulge of 6 As), translation is effectively independent of PTB provided the IRES is driving the synthesis of EMCV viral polyprotein. With an enlarged (7A) bulge and heterologous reporters, translation is highly dependent on PTB. Intermediate levels of PTB dependence are seen with a 7A bulge IRES driving viral polyprotein synthesis or a wild-type (6A) bulge IRES linked to a heterologous reporter. None of these parameters influenced the binding of PTB to the high-affinity site in the IRES. These results argue that PTB is not an essential and universal internal initiation factor, but, rather, that when it is required, its binding to the IRES helps to maintain the appropriate higher-order structure and to reverse distortions caused, for example, by an enlarged A-rich bulge.

Adenine Nucleotides↗
PubMed1998

Analysis of membrane protein cluster densities and sizes in situ by image correlation spectroscopy.

Communication between cells invariably involves interactions of a signalling molecule with a receptor at the surface of the cell. Typically, the receptor is imbedded in the membrane and it is hypothesized that the binding of the signalling molecule causes a change in the state of aggregation of the receptor which, in turn, initiates a biochemical signal within the cell. Subsequently, many of the occupied receptors bind to membrane-associated structures, called coated pits, which invaginate and pinch off to form coated vesicles, thereby removing the receptors from the cell surface. The state of aggregation of membrane receptors is obviously in constant flux. Any useful approach to measuring the state of aggregation must, therefore, allow for dynamic measurements in living cells. It is possible to use fluorescently labelled signalling molecules or antibodies directed at the receptor of interest to visualize the receptor on the cell surface with a fluorescence microscope. By employing a laser confocal microscope, high resolution images can be produced in which the fluorescence intensity is quantitatively imaged as a function of position across the surface of the cell. Calculations of autocorrelation functions of these images provide direct and accurate measures of the density of fluorescent particles on the surface. Combined with the average intensity in the image, which reflects the total average number of molecules, it is possible to estimate the degree of aggregation of the receptor molecules. We refer to this analysis as image correlation spectroscopy (ICS). We show how ICS can be used to measure the density of several receptors on a variety of cells and how it can be used to measure the density of coated pits and the number of molecules per coated pit. We also show how the technique can be used to monitor fusion of virus particles to cell membranes. Further, we illustrate that, by calculating cross-correlation functions between pairs of images, we can extend the analysis to measurements of the distributions as a function of time, on the second timescale, as well as to measurements of the movement of the receptor aggregates on the surface. Finally, we illustrate that, by this approach, we can measure the extent of interaction between two different receptors as a function of time. This represents the most quantitative measurement of the extent of co-localization of receptors available and is independent of the spatial resolution of the confocal microscope. The theory of ICS and image cross-correlation spectroscopy (ICCS), focussing on the interpretation of the data in terms of the biological phenomenon being probed, is discussed.

Animals↗
PubMed1997

Alteration of mineral crystallinity and collagen cross-linking of bones in osteopetrotic toothless (tl/tl) rats and their improvement after treatment with colony stimulating factor-1.

A common feature of various types of mammalian osteopetroses is a marked increase in bone mass accompanied by spontaneous bone fractures. The toothless (tl/tl) rat osteopetrotic mutation is characterized by drastically reduced bone resorption due to a profound deficiency of osteoclasts and their precursors. An altered bone morphology has also been observed. The mutants cannot be cured by bone marrow transplantation, but skeletal defects are greatly reduced after treatment with colony stimulating factor 1 (CSF-1). The objectives of this study were to characterize mineral and collagen matrices in cancellous and compact bone isolated from long bones of 6-week-old normal littermates, tl/tl osteopetrotic mutants and mutants (tl/tl) treated with CSF-1. There were no differences in bone mineral content, but a significant decrease in the crystallinity of mineral evaluated by the method based on electron paramagnetic resonance spectrometry was observed in all bones of tl/tl mutants as compared to that of controls. Within the collagen matrix, slight decreases in the labile cross-links, but significant increases in the content of the stable cross-links, pyridinoline, and deoxypyridinoline, were observed in both cancellous and compact bone of osteopetrotic mutants. In tl/tl mutants treated with human recombinant CSF-1, the normalization of the crystallinity of bone mineral as well as collagen cross-links was found. Our results indicate that remodeling of bone matrix in tl/tl mutants is highly suppressed, but that after treatment with CSF-1, this activity recovers significantly. Taken together, these data provide further support for the hypothesis that CSF-1 is an essential factor for normal osteoclast differentiation and bone remodelling.

Animals↗
PubMed1996

Chimaeric monoclonal antibodies encoded by the human VH26 gene from naïve transgenic mice display a wide range of antigen-binding specificities.

To elucidate the molecular basis for the ability of antibodies encoded by the human VH26 heavy-chain variable region gene to react with diverse antigens, we have generated 34 hybridomas secreting chimaeric monoclonal antibodies (human mu heavy chain/mouse light chains) from transgenic mice. The transgenic mice carry an immunoglobulin minilocus containing the human VH26 gene, human DH and JH gene segments, and genes encoding the human C mu region. The minilocus in these animals undergoes functional rearrangement resulting in the production of chimaeric antibodies in which human mu heavy chains utilizing the VH26 gene are paired with mouse kappa or lambda light chains. The hybridomas described in this study were generated from naïve animals and were selected solely on the basis of human mu-chain expression. The antibodies described have covalently attached mouse light chains and are multimeric in structure. The binding properties of the antibodies were examined using a panel of both self- and foreign antigens using enzyme-linked immunosorbent assays, agglutination or radio-immunoprecipitation assays and immunofluorescence. Chimaeric immunoglobulins from 21 of the 34 hybridoma clones (61.7%) reacted with one or more antigens, of which 13 (38.2%) reacted with more than two antigens. These studies demonstrate that the VH26 gene, in combination with human DH and JH gene segments, and mouse light-chain genes, is able to encode antibodies with a wide range of ligand-binding specificities. These findings have important implications in the context of the possible origins of autoantibodies encoded by VH26 which may play a role in the pathogenesis of a number of autoimmune conditions.

Animals↗
PubMed1996

Internal initiation of translation of hepatitis C virus RNA: the ribosome entry site is at the authentic initiation codon.

Hepatitis C viral (HCV) RNA includes an internal ribosome entry segment (IRES) that extends some 30 nt into the coding region and promotes internal initiation of translation at the authentic initiation codon at nt 342. The 5'-boundary of this IRES was mapped by in vitro translation and transfection assays and was found to lie between nt 42 and 71. Within these IRES boundaries there are, in most HCV strains, three AUG triplets upstream of the authentic initiation site. Although the first, 5'-proximal, of these is absolutely conserved, a mutational analysis showed that it is not a functional initiation codon. In particular, the G residue could be substituted provided compensatory mutations were made to maintain base pairing. The other two upstream AUGs are not absolutely conserved, and mutation of the third (5'-distal) had little effect on IRES activity. When an additional AUG codon was introduced by single-site mutation just upstream of the authentic initiation codon, it was found to be used when most of the IRES had been deleted to generate an RNA translated by the scanning ribosome mechanism, but was not used in the background of the full-length IRES when internal initiation is operative. These results argue that the IRES promotes direct ribosome entry immediately at, or indeed very close to, the authentic initiation codon, and that the upstream AUGs do not serve as ribosome entry sites.

Base Sequence↗