Showing papers by "University of Crete published in 1997"

Similarity searching in medical image databases

Abstract: We propose a method to handle approximate searching by image content in medical image databases. Image content is represented by attributed relational graphs holding features of objects and relationships between objects. The method relies on the assumption that a fixed number of "labeled" or "expected" objects (e.g., "heart", "lungs", etc.) are common in all images of a given application domain in addition to a variable number of "unexpected" or "unlabeled" objects (e.g., "tumor", "hematoma", etc.). The method can answer queries by example, such as "find all X-rays that are similar to Smith's X-ray". The stored images are mapped to points in a multidimensional space and are indexed using state-of-the-art database methods (R-trees). The proposed method has several desirable properties: (a) Database search is approximate, so that all images up to a prespecified degree of similarity (tolerance) are retrieved. (b) It has no "false dismissals" (i.e., all images qualifying query selection criteria are retrieved). (c) It is much faster than sequential scanning for searching in the main memory and on the disk (i.e., by up to an order of magnitude), thus scaling-up well for large databases.

Tropospheric aerosol ionic composition in the Eastern Mediterranean region

Abstract: Concentrations of the major soluble ions: sulfate (SO 4 = ), nitrate (NO 3 − ), chloride (Cl − ), methanesulfonate (MSA), sodium (Na + ), ammonium (NH 4 + )), potassium (K + ), calcium (Ca ++ ) and magnesium (Mg ++ ), have been measured in 49 aerosol samples collected over a year period at a coastal site of the island of Crete in the Eastern Mediterranean. Significant correlations have been observed between nss-SO 4 = (nonsea salt sulfate) and NH 4 + and Cl – and NO 3 – . The NH 4 + /SO 4 = equivalent ratio was 0.32. Comparison between total measured concentrations of anions and cations shows a clear deficit of cations. Correlation observed between the cation deficit and the nss-SO 4 = concentrations suggests that H + is probably the missing cation. Taking into consideration MSA/nss-SO 4 = ratios, the contribution of biogenic sulfur in the Eastern Mediterranean was evaluated between 0.6 and 28.3%. The variations in the ion concentrations are discussed conjointly with meteorological data and 5-day back trajectories of air masses. DOI: 10.1034/j.1600-0889.49.issue3.7.x

The foraging ecology of two pairs of congeneric demersal fish species: Importance of morphological characteristics in prey selection

Abstract: The feeding habits of two sympatric species pairs of demersal fish (Mullus barbatus-Mullus surmuletus, Serranus cabrilla-Serranus hepatus) which occupy the shallow coastal area (25–30 m) in Iraklion Bay were investigated from samples collected on a monthly basis (August 1990 to August 1992). Stomach content analyses revealed that all of them were carnivores, feeding mainly on benthic invertebrates, and that each species consumed a narrow range of prey species with no significant dietary overlap. The morphology of their feeding apparatus was compared to examine the effect of any morphological differences on food selection and resource partitioning between the fish species. The species could be distinguished on the basis of the size of their mouth gape, the number of gill rakers and the length of their intestine. This study shows that each species pair follows a different strategy segregating along food niche dimensions. In particular, M. barbatus and M. surmuletus segregate their feeding niche consuming different prey taxa with similar sizes whereas S. cabrilla and S. hepatus differ considerably with respect to the degree to which prey species contribute to their diets coupled with differences in mean prey sizes.

Determination of normal splenic volume on computed tomography in relation to age, gender and body habitus

Abstract: The purpose of our study was to examine variations in normal splenic size in relation to age, gender and body habitus in vivo, and to determine normative data for splenic volume on CT. The width (W), length (L), thickness (Th), cross-sectional areas and volume (Vol) of the spleen were obtained from abdominal CT examinations of 140 patients who underwent CT for indications unrelated to splenic disease. Splenic volume did not vary significantly (–0.04 0.10) with the patient's age, gender, height, weight, body mass index or the diameter of the first lumbar vertebra, the latter considered as representative of body habitus on CT. The mean value of the measured splenic volume (S Vol) was 214.6 cm3 with a range from 107.2 to 314.5 cm3. S Vol correlated well with all the linear and the maximal cross-sectional area measurements and could be calculated using the formula: S Vol = 30 + 0.58 (W × L × Th.). Employing the same formula splenic volume was reliably assessed in 47 patients with clinically evident splenomegaly. Quantitative assessment of splenic volume might be of value in assessing mild variations in splenic size, because splenomegaly is the most common manifestation of splenic involvement in many disorders.

Intrapleural streptokinase versus urokinase in the treatment of complicated parapneumonic effusions: a prospective, double-blind study.

Abstract: Intrapleural administration of fibrinolytics has been shown in small numbers of patients with complicated parapneumonic effusions (CPE) and pleural empyema to be effective and relatively safe. Although streptokinase (SK) is recommended as the fibrinolytic of choice, there are no comparative studies among fibrinolytics. We therefore compared the efficacy, safety, and the cost of treatment two of the most used thrombolytics, SK and urokinase (UK). Fifty consecutive patients with CPE or empyema were randomly allocated to receive either SK (25 patients) or UK, in a double-blind fashion. All patients had inadequate drainage through chest tube ( 0.05). The SK instillations (mean +/- SD) were 6 +/- 2.16 (range, 3 to 10) and those of UK 5.92 +/- 2.05 (range, 3 to 8). High fever as adverse reaction to SK was observed in two patients. The total cost of the drug in the UK group was two times higher than that of SK ($180 +/- 47 for SK and $320 +/- 123 for UK). The mean total hospital stay after beginning fibrinolytic therapy was 11.28 +/- 2.44 d (range, 7 to 15) for the SK group and 10.48 +/- 2.53 d (range, 6 to 18) for the UK group (p = 0.32). We conclude that intrapleural SK or UK is an effective adjunct in the management of parapneumonic effusions and may reduce the need for surgery. UK could be the thrombolytic of choice given the potentially dangerous allergic reactions to SK and relatively little higher cost of UK.

Nuclear envelope breakdown in mammalian cells involves stepwise lamina disassembly and microtubule-drive deformation of the nuclear membrane

Abstract: We have studied nuclear envelope disassembly in mammalian cells by morphological methods. The first signs of nuclear lamina depolymerization become evident in early prophase as A-type lamins start dissociating from the nuclear lamina and diffuse into the nucleoplasm. While B-type lamins are still associated with the inner nuclear membrane, two symmetrical indentations develop on antidiametric sites of the nuclear envelope. These indentations accommodate the sister centrosomes and associated astral microtubules. At mid- to late prophase, elongating microtubules apparently push on the nuclear surface and eventually penetrate the nucleus. At this point the nuclear envelope becomes freely permeable to large ligands, as indicated by experiments with digitonin-treated cells and by the massive release of solubilized A-type lamins into the cytoplasm. At the prophase/prometaphase transition, the B-type lamina is fragmented, but 'islands' of lamin B polymer can still be discerned on the tips of congressing chromosomes. Finally, at metaphase, the lamin B polymer breaks down into small pieces, which tend to concentrate in the area of the mitotic spindle. Nuclear envelope breakdown is not prevented when the microtubules are depolymerized by nocodazole; however, the mode of nuclear lamina fragmentation in the absence of microtubules is markedly different from the normal one and involves multiple raffles and gaps, which develop rapidly along the entire surface of the nuclear envelope. These data suggest that nuclear envelope disassembly is a stepwise process in which the microtubules play an important part.

Male-dependent doubly uniparental inheritance of mitochondrial DNA and female-dependent sex-ratio in the mussel Mytilus galloprovincialis.

Abstract: We have investigated sex ratio and mitochondrial DNA inheritance in pair-matings involving five female and five male individuals of the Mediterranean mussel Mytilus galloprovincialis. The percentage of male progeny varied widely among families and was found to be a characteristic of the female parent and independent of the male to which it was mated. Thus sex-ratio in Mytilus appears to be independent of the nuclear genotype of the sperm. With a few exceptions, doubly uniparental inheritance (DUI) of mtDNA was observed in all families fathered by four of the five males: female and male progeny contained the mother's mtDNA (the F genome), but males contained also the father's paternal mtDNA (the M genome). Two hermaphrodite individuals found among the progeny of these crosses contained the F mitochondrial genome in the female gonad and both the F and M genomes in the male gonad. All four families fathered by the fifth male showed the standard maternal inheritance (SMI) of animal mtDNA: both female and male progeny contained only the maternal mtDNA. These observations illustrate the intimate linkage between sex and mtDNA inheritance in species with DUI and suggest different major roles for each gender. We propose a model according to which development of a male gonad requires the presence in the early germ cells of an agent associated with sperm-derived mitochondria, these mitochondria are endowed with a paternally encoded replicative advantage through which they overcome their original minority in the fertilized egg and this advantage (and, therefore, the chance of an early entrance into the germ line) is countered by a maternally encoded egg factor.

Comparison of corneal sensation following photorefractive keratectomy and laser in situ keratomileusis

Abstract: Purpose: To evaluate the effect of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) on corneal sensation. Setting: Eye Institute, Medical School of the University of Crete, Heraklion, Greece, and Orasis, Hellenic Eye Center of Athens, Greece. Methods: In a masked study, corneal sensation was measured with the CochetBonnet aesthesiometer in 40 consecutive patients 6 to 12 months following PRK and LASIK (60 mm constitutes normal reading and <40 mm, abnormal). Results: After 6 to 12 months, the mean corneal sensation following PRK was 39.2 mm (range 30 to 55 mm) (mean 9.5 months) and after LASIK, 53.6 mm (range 40 to 60 mm) (mean 9.3 months). The mean correction attempted for PRK was 7.05 diopters (D) (range 2.5 to 12.0 D) and for LASIK, 11.71 D (range 6.0 to 20.0 D). Conclusion: In this group of patients, with correction of primarily severe myopia, corneal sensation was significantly greater after LASIK than after PRK.

Invariant measures of full dimension for some expanding maps

Abstract: It is an open problem to determine for which maps , any compact invariant set carries an ergodic invariant measure of the same Hausdorff dimension as is conformal and expanding, then it is a known consequence of the thermodynamic formalism that such measures do exist. (We give a proof here under minimal smoothness assumptions.) If has the form and are conformal and expanding maps satisfying , then for a large class of invariant sets , we show that ergodic invariant measures of dimension arbitrarily close to the dimension of do exist. The proof is based on approximating by self-affine sets.

Uncommon locations of hydatid disease: CT appearances.

Abstract: Hydatid disease (HD), already known by Hippocrates, is prevalent and widespread in most sheep-raising countries in Asia, Australia, South America, Near East, and southern Europe. The disease is most commonly due to Echinococcus granulosus and may occur in any organ or tissue. The location is mostly hepatic (75 %) and pulmonary (15 %), and only 10 % occur in the rest of the body [1]. Imaging modalities such as US, CT, and MR imaging are helpful in diagnosing the disease. The reliability of each method depends on the cyst's location in the body [2-5]. The purpose of this essay is to illustrate the use of CT in depicting some unusual locations of HD besides the liver and lung.

The inner nuclear membrane protein LAP1 forms a native complex with B‐type lamins and partitions with spindle‐associated mitotic vesicles

Abstract: We have examined the in situ organization and nearest neighbours of the 'lamina-associated polypeptide-1' (LAP1), a type II membrane protein and a major constituent of the mammalian nuclear envelope. We show here that, during interphase, LAP1 forms multimeric assemblies which are suspended in the inner nuclear membrane and are specifically associated with B-type lamins. The LAP1-lamin B complex is distinct from analogous complexes formed by the 'lamina-associated polypeptide-2' (LAP2), another inner nuclear membrane protein, and includes a protein kinase. Upon nuclear envelope breakdown, LAP1 partitions with mitotic vesicles which carry nuclear lamin B. The LAP1 vesicles can be distinguished from fragments of the nuclear envelope containing LAP2 and exhibit a striking co-alignment with spindle microtubules. These observations suggest that the inner nuclear membrane comprises discrete territories which accommodate specific integral membrane proteins and are differentially disassembled during mitosis.

Non-Perturbative Models For The Quantum Gravitational Back-Reaction On Inflation

Abstract: We consider a universe in which inflation commences because of a positive cosmological constant, the effect of which is progressively screened by the interaction between virtual gravitons that become trapped in the expansion of spacetime. Perturbative calculations have shown that screening becomes non-perturbatively large at late times. In this paper we consider effective field equations which can be evolved numerically to provide a non-perturbative description of the process. The induced stress tensor is that of an effective scalar field which is a non-local functional of the metric. We use the known perturbative result, constrained by general principles and guided by a physical description of the screening mechanism, to formulate a class of ansatze for this functional. A scheme is given for numerically evolving the field equations which result from a simple ansatz, from the beginning of inflation past the time when it ends. We find that inflation comes to a sudden end, producing a system whose equation of state rapidly approaches that of radiation. Explicit numerical results are presented.

The fluctuation field of ferromagnetic materials

Abstract: Starting from the basic constitutive equation that describes the magnetic viscosity of a ferromagnetic material, under the single assumption of a constant external field H, a connection is shown between the different expressions used to determine experimentally the fluctuation field . The simplest method uses the relation . If is invariant during the viscous decay of the magnetization, the relation may also be employed. The relaxation curves obtained at different fields, in this case, superimpose onto a single curve on renormalizing the time. An alternative treatment that considers explicitly the demagnetizing field is also presented. The theory is then applied to magneto-optic thin films, where two activation mechanisms are involved, assuming the absence of dispersion in the energy barriers, and also to the common case of relaxation by a single activation mechanism in the presence of a dispersion of the energy barriers. In both situations, it is shown that the fluctuation field may vary in strength during magnetic reversal. A method of classification of the hard ferromagnetic materials, through experimental means, is suggested.

Viscoelastic properties of amorphous polymers. 5. A coupling model analysis of the thermorheological complexity of polyisobutylene in the glass‐rubber softening dispersion

Abstract: Isothermal data of high molecular weight polyisobutylene obtained by mechanical measurements with a spectral range over eight decades and additional photon correlation measurements have found that there are three distinct viscoelastic mechanisms in the glass-rubber transition zone. Theoretical considerations have helped to identify these three mechanisms to originate separately from local segmental (α) modes, sub-Rouse (sR) modes, and Rouse (R) modes. The temperature dependences of the shift factors of these mechanisms, aT,α, aT,sR and aT,R, determined over a common temperature range are found to be all different. The differences in temperature dependences are explained quantitatively by the coupling model. The local segmental motion contributes to compliances ranging from the glassy compliance, Jg, up to 10−8.5 Pa−1. The sub-Rouse modes contribute in the compliance range, 10−8.5 ≤ J(t) ≤ 10−7 Pa−1. The Rouse modes account for the compliances in the range of 10−7 Pa−1 ≤ J(t) ≤ Jplateau, where Jplateau is the plateau compliance. The magnitudes of the bounds given here are only rough estimates. Shift factors, aT, obtained by time-temperature superpositioning of viscoelastic data taken in the softening transition over a limited experimental window are shown to be a combination of the three individual shifts factors, aT,α, aT,sR, and aT,R. Consequently, care must be exercised in interpreting or using the WLF equation that fits the shift factors of the entire softening dispersion, because the latter do not describe the temperature dependence of any one of the three viscoelastic mechanisms. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 599–614, 1997

The neural integrators of the mammalian saccadic system

Abstract: The neural velocity to position integrators transform the saccade related signal of the burst generators into an eye position related tonic signal they convey to motoneurons. They are largely confined to three heavily interconnected midbrain structures: 1) The interstitial nucleus of Cajal (NIC), 2) The nucleus prepositus hypoglossi (NPH), 3) The vestibular nuclei (VN). Integration in the horizontal and vertical planes is accomplished largely independently by the NPH-VN and the NIC-VN complexes, respectively. Cells in these regions carry a more or less intense phasic signal related to saccades and a tonic signal related to eye position. Depending on the relationship between the rate of their discharge and the position of the eyes, these cells have been further subdivided into regular or irregular, more or less sensitive, and bi-directionally or uni-directionally modulated. The present review provides a brief description of their discharge pattern and that of burst neurons and extraocular motoneurons. Then, evidence concerning the input-output connections of relevant cell classes is summarized. Finally, several modelling attempts to simulate the neural velocity-to-position integrators are presented and their verisimilitude is evaluated in the light of psychophysical, anatomical, physiological and neurological evidence.