PubMed Health⌕ Search

Biomedical subjects

A Matulis

Publications and source records attributed to A Matulis.

15 recordsLinked to original sources
PubMed2006

Spectrum of classical two-dimensional Coulomb clusters.

The frequency spectrum of a system of classical charged particles interacting through a Coulomb repulsive potential and which are confined in a two-dimensional parabolic trap is studied. It is shown that, apart from the well-known center-of-mass and breathing modes, which are independent of the number of particles in the cluster, there are more "universal" modes whose frequencies depend only slightly on the number of particles. To understand these modes the spectrum of excitations as a function of the number of particles is compared with the spectrum obtained in the hydrodynamic approach. The modes are classified according to their averaged vorticity and it is shown that these "universal" modes have the smallest vorticity and follow the hydrodynamic behavior.

Journal Article↗
PubMed2004

Structure and spectrum of two-dimensional clusters confined in a hard wall potential.

The structural and dynamical properties of two-dimensional (2D) clusters of equally charged classical particles, which are confined in an external hard wall potential, are investigated through the Monte Carlo simulation technique. The ground-state configuration is investigated as a function of the interparticle interaction (Coulomb, dipole, logarithmic, and screened Coulomb). The excitation spectrum corresponding to the ground-state configuration of the system is discussed. The eigenmodes are investigated and the corresponding divergence and rotor are calculated, which indicates the "shearlike" and "compressionlike" aspects of the different modes. Both small and large clusters are considered.

Journal Article↗
PubMed2003

Structure and correlations in two-dimensional classical artificial atoms confined by a Coulomb potential.

The ordering of N equally charged particles (-e) moving in two dimensions and confined by a Coulomb potential, resulting from a displaced positive charge Ze is discussed. This is a classical model system for atoms. We obtain the configurations of charged particles which, depending on the value of N and Z, may result in ring structures, hexagonal-type configurations, and for N/Z approximately 1 in an inner structure of particles which is separated by an outer ring of particles. For N/Z<<1, the Hamiltonian of the parabolic confinement case is recovered. For N/Z approximately 1, the configurations are very different from those found in the case of a parabolic confinement potential. A hydrodynamic analysis is presented in order to highlight the correlations effects.

Journal Article↗
PubMed1996

Aberrant vascularity and von Willebrand factor distribution in inflamed synovial membrane.

OBJECTIVE: Von Willebrand factor (vWF) is an adhesive glycoprotein produced and secreted constitutively by endothelial cells. vWF is released upon endothelial stimulation and/or vascular injury, and mediates adhesion and aggregation of platelets. Our aim was to quantify synovial vasculature and to evaluate vWF distribution in situ in synovial membranes in various arthritides. METHODS: Immunohistochemical staining of vWF in synovial membranes from patients with rheumatoid arthritis (RA) (N = 9), psoriatic (PsA) (N = 3), and reactive (ReA) (N = 4) arthritis, and from 6 noninflammatory controls: osteoarthritis (N = 1), chondromatosis (N = 1), meniscus lesion (N = 4). Morphometric assessments were performed with an image analyzer. RESULTS: In RA, mean number of blood vessels/mm2 in the thickened synovium was relatively low (131 +/- 57 vs control 257 +/- 115, p = 0.0137, ReA 346 +/- 83, p = 0.0002, PsA 434 +/- 157, p = 0.0127). In particular, the superficial layer, corresponding to the thickness of normal synovial membrane (i.e., 56 +/- 5 microns), was sparsely vascularized (70 +/- 37 in the superficial vs 219 +/- 104 in the deeper layer, p = 0.0047). Synovial thickening was not seen in ReA and PsA. In accordance with its constitutive metabolism, vWF was found in the endothelial cells, inside the blood vessels, and in the subendothelium. In addition, RA was characterized by weak endothelial immunoreactivity and perivascular vWF. In ReA, perivascular vWF staining was visible in areas of inflammatory cell infiltrates. CONCLUSION: Morphometric findings indicate decreased vascularization of the superficial synovial membrane in RA. Second, vWF may play a role in the inflammatory/reparative responses in synovium in RA and ReA, which were characterized by vascular stimulation/injury and abnormal vWF distribution.

Adolescent↗
PubMed1980

Blood lymphocyte ultrastructure and deoxyribonucleic acid content in children with systemic lupus erythematosis.

Two varieties of peripheral blood lymphocytes have been disclosed in systemic lupus erythematosus (SLE) cases: one showing signs of degradation and nuclear chromatine elimination and the other one manifesting a state of biological activation, possibly of an immunologic nature. This karyostructural lymphocyte heterogeneity in SLE may cause a great scattering of these cells on histograms in respect to their nuclear deoxyribonucleic acid content determined by cytophotometry. On the other hand, the expressiveness of the scattering and the degree of predominance of negative tendency towards proliferation (with a shift to the left from 2 n) may thereby serve as a very objective quantitative indication of nuclear structure degradation and of loss by lymphocytes of chromatine with deoxyribonucleic acid during SLE.

Child↗
PubMed1980

[Intermittent disturbances of the atrial electrical activation in noncoronarogenic heart lesions].

The work discusses the results obtained in studying intermittent disorders of electrical activation of the atria by recording intracavitary "local" electrograms and additionally augmented ECG from the body surface of 42 patients with noncoronarogenic heart lesions. In 18 patients the intermittent changes in the atrial complex were due to impaired function of the sinus node and disturbance of sinoatrial conduction. In 12 patients functional block of the atrial conduction pathways was revealed, in 8 of them the rhythm was not changed, whereas in 4 the block was attended by Wenckebach's phenomenon. For correct diagnosis it is advisable to record "local" atrial electrograms or P wave of an additionally augmented ECG from the body surface.

Cardiac Catheterization↗