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D Arvanitis

Publications and source records attributed to D Arvanitis.

At least 19 recordsLinked to original sources
PubMed2005

Vanishing magnetic interactions in ferromagnetic thin films.

We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.

Journal Article↗
PubMed2001

Magnetisation reorientation in ultra-thin Fe films on Cu(100) upon deposition of Co.

Ultra thin films of Fe deposited on the (100) surface of a Cu single crystal exhibit a net perpendicular magnetic anisotropy. The addition of very low coverages of Co results in the easy magnetic direction reorienting into the film plane. This behavior is in contrast to the addition of similar amounts of Fe, whereupon the ferromagnetic response vanishes. This result is discussed in terms of the anisotropy energies derived from the spectroscopic data.

Journal Article↗
PubMed2001

Magnetic X-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces.

Epitaxic thin and ultrathin films on surfaces allow crystallographic phases that do not occur naturally in the bulk to be stabilized. They also offer new possibilities for an improved understanding of soft X-ray photoabsorption in magnetic systems. Data collected using the Elliptically Polarizing Undulator at BL 5.2 of the Stanford Synchrotron Radiation Laboratory are presented herein. Fe, Co and Ni films were prepared on Cu(100) surfaces. L2,3-edge spectra were recorded with circular and linear light. Fresnel diffractometry was used to quantify the degree of transverse beam coherence. A quantitative analysis of the spectral features indicates a correlation of the spectral intensities and the transverse beam coherence. Resonant reflectivity spectra for Co ultrathin films that exhibit strong dichroism are presented. The reflectivity data indicate that interference effects of the reflected beams at the two interfaces are of importance, even for ultrathin films.

Journal Article↗
PubMed2001

Immunohistochemical expression of p53, p21/waf1, rb, p16, cyclin D1, p27, Ki67, cyclin A, cyclin B1, bcl2, bax and bak proteins and apoptotic index in normal thymus.

The immunohistochemical expression of p53, p21, Rb, p16, cyclin D1, Ki67, cyclin A, cyclin B1, p27, bcl2, bax, and bak proteins and the apoptotic index (Al) were investigated in 20 normal thymuses (8 adults, 3 adolescents, 5 infants and 4 newborns). The expressions of Rb, Ki67, cyclin A and cyclin B1 were overlapping, being high in the cortex with a tendency for decreased expression toward the medulla. Apoptotic cells were mainly detected in the cortex and the corticomedullary junction, rarely being present in Hassall's corpuscles. The mean values of Ki67, cyclin A, and cyclin B1 expression in thymuses were 77.2%, 32.2% and 21.4% (newborns), 62.4%, 33.7% and 18.5% (infants), 56.9%, 23.4% and 18.9% (adolescents) and 38.7%, 21.7% and 14.6% (adults), respectively. The mean values of AI in thymuses from newborns, infants, adolescents and adults were 1.4%, 2.9%, 2.7% and 3.8%, respectively. This decrease in proliferation and increase in apoptosis may account for the process of thymic involution. P16 expression was widespread with most of Hassall's corpuscles being p16-positive. P16-positive cells and Hassall's corpuscles increased with the increase in age, in keeping with the suggested role of p16 in cellular senescence. P27 expression was undetectable in subcapsular thymocytes with a tendency for increased expression toward the medulla. The expressions of Ki67, cyclin A and cyclin B1 were inversly related with that of p27, consistent with previous evidence that p27 concentration is reduced when the cell-cycle progresses. P21 and much less frequently p53 proteins were mainly detected in a part of the subcapsular cortical epithelial cells. These findings suggest that a) in thymocytes, the apoptotic pathway is mostly p53-independent and the function of p21 as a negative regulator of the cell cycle must be redundant to other negative regulators, such as p16 and p27 which were abundantly detected in thymocytes and b) in some thymic epithelial cells, the p21 expression may be induced by p53, but in most of them seems to be p53-independent. Most of Hassall's corpuscles were p21-positive, consistent with previous evidence that these structures represent end stages of maturation of thymic medullary epithelium and that p21 protein is involved in the process of terminal differentiation. Cyclin D1 positivity was found in some macrophages. Bcl2 expression was mainly seen in medullary thymocytes, reflecting the surviving thymocytes in this region. The expressions of Bax and bak were more widespread in both the medulla and cortex, suggesting that these proteins play a broader role than bcl2 in the regulation of thymic apoptosis.

Adolescent↗
PubMed2000

Influence of source coherence on x-ray absorption spectroscopy.

Core-level x-ray absorption spectroscopy measurements have been performed at the L3,2 edges of Fe and Co thin films. The degree of source coherence was varied using soft x rays from five different beam lines. We observe an increase of the L edge resonance intensities relative to the continuum states which we propose is due to the presence of transverse coherence in the exciting radiation.

Journal Article↗
PubMed2000

Shape resonances of oriented molecules: ab initio theory and experiment on hydrocarbon molecules

We report ab initio calculations of the x-ray absorption cross section for the near edge x-ray absorption fine structure of C2H6, and C2H4, and C2H2 at the C K-edge, based on a full multiple scattering formalism. The angular dependence of the electric dipole transition in the calculations as well as the angular dependent experiments for the oriented molecules give a good opportunity to compare both. The resonance can be assigned to a sigma(*) shape resonance. The multiple scattering formalism and the experiment agree well and thereby support the existence of such features in the spectra.

Journal Article↗
PubMed2000

Analysis of eight polymorphic human genetic markers in a well-defined Greek population.

The use of DNA in forensic science has become a basic tool for person identification or parentage testing. The use of polymorphic markers permits the formation of a unique profile for each individual. The knowledge of allele frequencies in a given population allows the scientist to estimate the probability of a particular allele combination. For this task, allele databanks are essential. In this report, the authors estimate the frequencies of eight polymorphic markers (namely, HumFES, HumF13A1, HumTHO1, HumVWA, HumFABP2, HumLIPOL, D1S80, and D17S5) in a randomly selected sample from Crete, Greece. The allele profile of all markers, with the exception of D17S5 and HumFABP2, concurs with previous reports and international data.

Alleles↗
PubMed1999

Molecular epidemiology of a hepatitis C virus outbreak in a haemodialysis unit. Multicentre Haemodialysis Cohort Study on Viral Hepatitis.

BACKGROUND: Haemodialysis patients are at high risk of infection by hepatitis C virus. The aim of this study was to investigate a hepatitis C virus outbreak which occurred in a haemodialysis unit, using epidemiological and molecular methods. METHODS: Five seroconversions to hepatitis C virus antibody (anti-HCV) were observed over a 6 month period and these were added to the four previously recorded anti-HCV-positive patients. All nine patients involved in the outbreak were tested for HCV RNA by reverse transcription-polymerase chain reaction and hepatitis C genotype determination was accomplished by a reverse hybridization assay. Furthermore, part of the NS5 region of hepatitis C genome (nucleotide positions 7904-8304) was amplified and sequenced in all HCV RNA-positive patients. Then, phylogenetic analysis of the nucleotide sequences obtained was carried out in order to investigate any possible epidemiological linkage among patients. Detailed epidemiological records were also available for all haemodialysis patients. RESULTS: Samples from all five incident cases and three out of four prevalent HCV infections were found positive for HCV RNA. HCV genotyping studies revealed that all incident cases were classified as 4c/d, whereas one and two prevalent cases were 1a and 4c/d respectively. Sequence comparisons and phylogenetic tree analysis revealed that six of the patients harboured very similar strains and clustered together, including all incident and one prevalent case, which was implicated as index case. Further epidemiological analysis was consistent with patient to patient transmission. CONCLUSIONS: Molecular and epidemiological analysis suggested that horizontal nosocomial patient to patient transmission was the most likely explanation for the virus spread within the haemodialysis unit under study.

Base Sequence↗
PubMed1999

Long-term effects of small doses of calcitriol in hemodialysis patients with moderate secondary hyperparathyroidism.

Prevention of secondary hyperparathyroidism (SHPTH) and treatment of the moderate cases by small p.os doses of Vitamin D has not been thoroughly investigated on the long term, while large doses of Vitamin D have been successful in the short term treatment of this entity. We administered calcitriol p.os 0.5-1.0 microgram, according to iPTH levels, after each dialysis session, in 19 patients (group A) for 36 months. They were ten men and nine women, 63 years old (43-81), with iPTH levels > 4N (419 +/- 185 pg/mL). Seven adenomas were found in five of them (group A1). Serum Ca, phosphate (P) and alkaline phosphatase (AP) were measured every 15-30 days. Serum iPTH and aluminum as well as echogram or scanning of the parathyroid glands were checked every 6 months. Ten additional dialysis patients, seven men and three women, 54.5 years old (36-68), non-significantly different to group A in iPTH levels (290 +/- 225 pg/mL) with three adenomas in two of them (group B1) received no calcitriol and served as controls (group B). Calcitriol treatment significantly lowered serum iPTH levels in group A patients (from 419 +/- 185 to 173 +/- 142 pg/mL, p < 0.0001, delta iPTH: -246 +/- 161 pg/mL); iPTH remained stable in group B patients (delta iPTH: +7.9 +/- 116 pg/mL) with an intergroup significant difference at P < 0.0001. All other parameters measured did not show any significant change. No significant correlation of iPTH to Ca, P or AP was found in A. Initial iPTH levels were higher in A1 and B1 patients and decreased by calcitriol in A1 group. Adenomas in A1 patients did not change in number and size in contrast to B1 where new adenomas appeared (5 patients, 10 glands). Small doses of vitamin D lower high iPTH levels and prevent parathyroid gland hyperplasia. Existing hypertrophy is stabilized under calcitriol treatment both morphologically and biologically.

Administration, Oral↗
PubMed1997

Complete success of intradermal vaccination against hepatitis B in advanced chronic renal failure and hemodialysis patients.

Incomplete protection and response variability have been reported in chronic renal failure (CRF) and hemodialysis (HD) patients vaccinated against hepatitis B with the recombinant vaccine (rHBV). We vaccinated 12 consecutive patients (7 CRF and 5 HD), 7 males and 5 females, 61 years old (range 22-82); HD patients were on treatment from 1 to 12 months. CRF patients had a residual renal function (creatinine clearance) of 11 +/- 3 mL/min. Six patients had been already vaccinated unsuccessfully, as defined by the absence of detectable specific antibody S (Abs) 1 month after the completion of vaccination by the classical intramuscular method, with a median of 7 (range 3-18) doses of 20 micrograms. rHBV was given intradermally (i.d.) at the dose of 5 micrograms every fortnight up to 8 doses or until titers of Abs rose above 1000 mIU/mL. Levels above 10 mIU/mL were considered as protective. Abs titers were monitored during the whole vaccination period every 15 days and at the 1st, 3rd, and 6th month after its completion. Median number of i.d. doses given was 7 (range 4-8). Antibody titers rose gradually; surface antibodies (AbS) were detected as early as the end of the first month (2nd dose). Age and sex had no influence on the immune response, its duration, or antibody titers. i.d. administration of rHBV in repeated small injections was found to be absolutely effective, in both CRF and HD patients. AbS titers after multiple i.d. vaccination rose gradually in CRF and HD patients, and were protective for at least 6 months after the last injected dose. Protective levels were achieved even in patients not responding to multiple-double quantity intramuscular (i.m.) doses. Patients with stronger initial response to the vaccine (after the 4th dose) gave significantly higher AbS titers (at least in 50% of the follow-up measurements), although they received fewer injections and smaller total dose of vaccine.

Administration, Cutaneous↗
PubMed1996

Microsatellite instability in human atherosclerotic plaques.

The aetiopathology of atherosclerosis remains obscure. Although histologically the accumulation of lipids and the proliferation of the smooth muscle cells represents the main feature of the disease, little is known as regards the molecular alterations associated with the atherosclerotic lesions. In the present study we investigated whether an elevated mutational rate is detectable in human atheromatous plaques. Thirty specimens were assessed for microsatellite instability (MI) by 7 microsatellite markers and MI, in at least one marker, was apparent in 6 (20%) cases. Our data suggest that decreased fidelity in DNA replication and repair may be associated with the development of the disease.

Aged↗