Showing papers by "Jožef Stefan Institute published in 2002"

Origin of apparent colossal dielectric constants

Abstract: Experimental evidence is provided that colossal dielectric constants ${\ensuremath{\varepsilon}}^{\ensuremath{'}}g~1000,$ sometimes reported to exist in a broad temperature range, can often be explained by Maxwell-Wagner-type contributions of depletion layers at the interface between sample and contacts or at grain boundaries. We demonstrate this on a variety of different materials. We speculate that the largest intrinsic dielectric constant observed so far in nonferroelectric materials is of order ${10}^{2}.$

Regulating cysteine protease activity: essential role of protease inhibitors as guardians and regulators.

Abstract: Cysteine proteases are widespread in nature. Their implication in numerous vital processes and pathologies make them highly attractive targets for drug design. The proper functioning and regulation of activity of cysteine proteases is a delicate balance of many factors, one of the most crucial being the protease inhibitors. In this review the basic principles of physiological protease inhibition by protein inhibitors are discussed with the focus on papain-like lysosomal cysteine proteases and the caspases, and their inhibitors.

Apoptotic pathways: involvement of lysosomal proteases.

Abstract: Apoptosis or programmed cell death is the major mechanism used by multicellular organisms to remove infected, excessive and potentially dangerous cells. Cysteine proteases from the caspase family play a crucial role in the process. However, there is increasing evidence that lysosomal proteases are also involved in apoptosis. In this review various lysosomal proteases and their potential contribution to propagation of apoptosis are discussed.

Amyloid-fibril formation: Proposed mechanisms and relevance to conformational disease

Abstract: The phenomenon of the transformation of proteins into amyloid-fibrils is of interest, firstly, because it is closely connected to the so-called conformational diseases, many of which are hitherto incurable, and secondly, because it remains to be explained in physical terms (energetically and structurally). The process leads to fibrous aggregates in the form of extracellular amyloid plaques, neuro-fibrillary tangles and other intracytoplasmic or intranuclear inclusions. In this review, basic principles common to the field of amyloid fibril formation and conformational disease are underlined. Existing models for the mechanism need to be tested by experiment. The kinetic and energetic bases of the process are reviewed. The main controversial issue remains the coexistence of more than one protein conformation. The possible role of oligomeric intermediates, and of domain-swapping is also discussed. Mechanisms for cellular defence and novel therapies are considered.

Expert-guided subgroup discovery: methodology and application

Abstract: This paper presents an approach to expert-guided subgroup discovery. The main step of the subgroup discovery process, the induction of subgroup descriptions, is performed by a heuristic beam search algorithm, using a novel parametrized definition of rule quality which is analyzed in detail. The other important steps of the proposed subgroup discovery process are the detection of statistically significant properties of selected subgroups and subgroup visualization: statistically significant properties are used to enrich the descriptions of induced subgroups, while the visualization shows subgroup properties in the form of distributions of the numbers of examples in the subgroups. The approach is illustrated by the results obtained for a medical problem of early detection of patient risk groups.

Proton decay in minimal supersymmetric SU(5)

Abstract: We systematically study proton decay in the minimal supersymmetric SU(5) grand unified theory We find that although the available parameter space of soft masses and mixings is quite constrained, the theory is still in accord with experiment

Sense Discrimination with Parallel Corpora

Abstract: This paper describes an experiment that uses translation equivalents derived from parallel corpora to determine sense distinctions that can be used for automatic sense-tagging and other disambiguation tasks. Our results show that sense distinctions derived from cross-lingual information are at least as reliable as those made by human annotators. Because our approach is fully automated through all its steps, it could provide means to obtain large samples of "sense-tagged" data without the high cost of human annotation.

The effect of dose calculation accuracy on inverse treatment planning.

Abstract: The effect of dose calculation accuracy during inverse treatment planning for intensity modulated radiotherapy (IMRT) was studied in this work. Three dose calculation methods were compared: Monte Carlo, superposition and pencil beam. These algorithms were used to calculate beamlets. which were subsequently used by a simulated annealing algorithm to determine beamlet weights which comprised the optimal solution to the objective function. Three different cases (lung, prostate and head and neck) were investigated and several different objective functions were tested for their effect on inverse treatment planning. It is shown that the use of inaccurate dose calculation introduces two errors in a treatment plan, a systematic error and a convergence error. The systematic error is present because of the inaccuracy of the dose calculation algorithm. The convergence error appears because the optimal intensity distribution for inaccurate beamlets differs from the optimal solution for the accurate beamlets. While the systematic error for superposition was found to be approximately 1% of Dmax in the tumour and slightly larger outside, the error for the pencil beam method is typically approximately 5% of Dmax and is rather insensitive to the given objectives. On the other hand, the convergence error was found to be very sensitive to the objective function, is only slightly correlated to the systematic error and should be determined for each case individually. Our results suggest that because of the large systematic and convergence errors, inverse treatment planning systems based on pencil beam algorithms alone should be upgraded either to superposition or Monte Carlo based dose calculations.

Reduced blood flow and oxygenation in SA-1 tumours after electrochemotherapy with cisplatin.

Abstract: Electrochemotherapy is an antitumour treatment that utilises locally delivered electric pulses to increase cytotoxicity of chemotherapeutic drugs. Besides increased drug delivery, application of electric pulses affects tumour blood flow. The aim of this study was to determine tumour blood flow modifying effects of electrochemotherapy with cisplatin, its effects on tumour oxygenation and to determine their relation to antitumour effectiveness. Electrochemotherapy of SA-1 subcutaneous tumours was performed by application of electric pulses to the tumours, following administration of cisplatin. Tumour blood flow modifying effects of electrochemotherapy were determined by measurement of tumour perfusion using the Patent blue staining technique, determination of tumour blood volume, and microvascular permeability using contrast enhanced magnetic resonance imaging, and tumour oxygenation using electron paramagnetic resonance oximetry. Antitumour effectiveness was determined by tumour growth delay and the extent of tumour necrosis and apoptosis. Tumour treatment by electrochemotherapy induced 9.4 days tumour growth delay. Tumour blood flow was reduced instantaneously and persisted for several days. This reduction in tumour blood flow was reflected in reduced tumour oxygenation. The maximal reduction in partial oxygen pressure (pO2) levels was observed at 2 h after the treatment, with steady recovery to the pretreatment level within 48 h. The reduced tumour blood flow and oxygenation correlated well with the extent of tumour necrosis and tumour cells apoptosis induced by electrochemotherapy with cisplatin. Therefore, the data indicate that antitumour effectiveness of electrochemotherapy is not only due to increased cytotoxicity of cisplatin due to electroporation of tumour cells, but also due to anti-vascular effect of electrochemotherapy, which resulted in reduced tumour blood flow and oxygenation.

Femtosecond snapshots of gap-forming charge-density-wave correlations in quasi-two-dimensional dichalcogenides 1 T − TaS 2 and 2 H − TaSe 2

Abstract: Time-resolved optical spectroscopy of collective and single-particle excitations of 1 T-TaS2 and 2H-TaSe2 reveals the presence of a large gap in the excitation spectrum on the femtosecond time scale, associated with the formation of various degrees of charge-density-wave order. In common with superconducting cuprates, excitations with energies less than the full gap show much slower relaxation. This separation of time scales cannot be explained in a quasi-two-dimensional Fermi-liquid picture with an anisotropic gap but rather suggests the formation of a fluctuating spatially inhomogeneous state eventually forming a long-range ordered state at low temperatures.

Uniaxial relaxor ferroelectrics: The ferroic random-field Ising model materialized at last

Abstract: Owing to their intrinsic charge disorder ferroelectric crystals of strontium-barium-niobate doped with Ce3+ materialize the three-dimensional ferroic random-field Ising model (RFIM) as evidenced by order paramenter and susceptibility criticalities with 93Nb NMR and dielectric spectroscopy, respectively. Upon cooling towards Tc, extreme critical slowing-down due to activated dynamic scaling gives rise to relaxor-like dispersion of the susceptibility and to a metastable ferroelectric nanodomain state with fractal size distribution as imaged by piezoelectric force microscopy.

Lysosomal enzymes, cathepsins in brain tumour invasion

Abstract: The expression patterns of different classes of peptidases in central nervous system (CNS) tumours have been most extensively studied in astrocytomas and meningiomas. Although the two types of tumours are very different in most respects, both may invade locally into normal brain. This process of invasion includes increased synthesis and secretion of lysosomal proteolytic enzymes – cathepsins. Aspartic endopeptidase cathepsin (Cat) D levels were found to be elevated in high-grade astrocytoma and partial inhibition of glioblastoma cell invasion by anti-Cat D antibody suggests that the enzyme activity is involved in the invasion process. Several studies on cysteine endopeptidase (CP) Cat B in gliomas agreed that transcript abundance, protein level and activity of Cat B increased in high-grade astrocytoma cultures compared with low-grade astrocytoma cultures and normal brain. Moreover, in glioma biopsies Cat B levels correlated with evidence of clinical invasion and it has been demonstrated that Cat B both in tumour cells and in endothelial cells can serve as a new biological marker for prognosis in glioblastoma patients. A high level of Cat B protein was also a diagnostic marker for invasive types of meningioma, distinguishing between histomorphologically benign, but invasive meningiomas and noninvasive, so-called clear–benign meningiomas. Cat L was also significantly increased in high-grade astrocytoma compared with low-grade astrocytoma and normal brain. Specific Cat L antibodies and antisense Cat L RNA transfection significantly lowered glioblastoma cell invasion. In meningioma, Cat L was a less-significant marker of invasion than Cat B. In contrast to cathepsins, the activities of endogenous cysteine peptidase inhibitors (CPIs), including stefins, cystatins and kininogens, were significantly higher in benign and atypical meningioma cell extracts than in malignant meningioma, and low-grade compared to high-grade astrocytoma. However, very low levels of stefins A and B were found in meningioma and glioblastoma tissues. Further studies on the expression levels and balance between cysteine endopeptidases (CPs) and CPIs would improve the clinical application of cathepsins in prognosis, which would lead to more-informed therapeutic strategies.

Kinematic control algorithms for on-line obstacle avoidance for redundant manipulators

Abstract: The paper deals with kinematic control algorithms for on-line obstacle avoidance which allow a kinematically redundant manipulator to move in an unstructured environment without colliding with obstacles. The presented approach is based on the redundancy resolution at the velocity level. The primary task is determined by the end-effector trajectories and for obstacle avoidance the internal motion of the manipulator is used. The obstacle avoiding motion is defined in one-dimensional operational space and, hence, the system has less singularities making implementation easier. Instead of the exact pseudoinverse solution we propose an approximate one which is computationally more efficient and allows us to consider many simultaneously active obstacles without any problems. The fast cycle times of the numerical implementation enable use of the algorithm in real-time control. For illustration, some simulation results of a highly redundant planar manipulator moving in an unstructured and time-varying environment and experimental results of a four link planar manipulator are given.

A Stoichiometric Model for Sillenites

Abstract: A critical review of crystallographic studies on sillenite compounds has allowed us to develop a general structural formula for the stoichiometric sillenites: Bi12(Bi4/5-nxMn+5x)O19.2+nx. We defined the stoichiometric sillenites as those with an oxygen sublattice that is fully occupied by either oxygen ions or lone electron pairs of Bi3+ ions. Nonstoichiometric groups of sillenites were identified as being either substoichiometric, with a deficient oxygen sublattice, or superstoichiometric, with an excess of oxygen. The compositions of the sillenites reported in the literature agree well with the proposed stoichiometric model. Two sillenites, Al and Zn, that were found to deviate from this model were experimentally investigated using X-ray diffraction, scanning electron microscopy, and wavelength-dispersive spectroscopy. The composition was found to be different from that reported previously and to correspond to the proposed stoichiometric model.

SPA-Based Adaptive Chosen-Ciphertext Attack on RSA Implementation

Abstract: We describe an adaptive chosen-ciphertext attack on a smart card implementation of the RSA decryption algorithm in the presence of side-channel information leakage. We studied the information leakage through power consumption variation. Simple power analysis (SPA) of the smart card that is widely used for secure Internet banking, Web access and remote access to corporate networks, revealed macro characteristics caused by improper implementation of Chinese remaindering. The findings can be used to eventually improve future implementations of fast RSA decryption.

Dielectric relaxation in ferroelectric PZT–PVDF nanocomposites

Abstract: Composites of electroactive ceramics and ferroelectric polymers are important for applications since they combine the most important features of the both phases and their properties can be easily tailored to various requirements. As the dielectric permittivity is involved in figures of merit of the quantities important for applications we studied dielectric response of Pb(Zr 0.5 Ti 0.5 )O 3 –polyvinylidene fluoride nanocomposites over a wide frequency and temperature range. It was found that though the permittivity value of the composites is high due to the high permittivity of the ceramics, the glass transition of the polymer and dielectric relaxation related to the wide-angle oscillation of polar groups attached to the main polymer chain determine the dielectric behaviour of the composites.

Liquid-phase sintering of Pb(Zr,Ti)O3 using PbO–WO3 additive

Abstract: The objective of this work was to lower the sintering temperature of lead zirconate titanate (PZT) without reducing the piezoelectric performance. PZT was sintered using PbO–WO3 additive of eutectic composition, which assists the densification process by liquid-phase formation. Sintering was carried out from 1075 to 1125 C between 1 and 4 h. Density, dielectric properties and piezoelectric properties were measured. Microstructure and fracture mechanism have been studied by SEM. At the mildest sintering conditions, the additive has a positive effect on dielectric and piezoelectric properties. The liquid-phase sintering leads to a denser material without additional grain growth. PZT with PbO–WO3 additive is mechanically weaker than pure PZT. The liquid phase leads to weaker grain boundaries and the material cracks in intergranular fracture, whereas pure PZT has a mixture of intergranular and transgranular fracture, and PZT sintered conventionally at 1260 C has transgranular fracture. # 2002 Elsevier Science Ltd. All rights reserved.

Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters

Abstract: The purpose of the present work was to develop a simple, rapid, sensitive and accurate method for the simultaneous determination of inorganic mercury (Hg2+) and monomethylmercury compounds (MeHg) in natural water samples at the pg L–1 level. The method is based on the simultaneous extraction of MeHg and Hg2+ dithizonates into an organic solvent (toluene) after acidification of about 300 mL of a water sample, followed by back extraction into an aqueous solution of Na2S, removal of H2S by purging with N2, subsequent ethylation with sodium tetraethylborate, room temperature precollection on Tenax, isothermal gas chromatographic separation (GC), pyrolysis and cold vapour atomic fluorescence spectrometric detection (CV AFS) of mercury. The limit of detection calculated on the basis of three times the standard deviation of the blank was about 0.006 ng L–1 for MeHg and 0.06 ng L–1 for Hg2+ when 300 mL of water was analysed. The repeatability of the results was about 5% for MeHg and 10% for Hg2+. Recoveries were 90–110% for both species.

The attainable superconducting Tc in a model of phase coherence by percolating

Abstract: The onset of macroscopic phase coherence in superconducting cuprates is considered to be determined by random percolating between mesoscopic Jahn-Teller pairs, stripes or clusters. The model is found to predict the onset of superconductivity near 6% doping, maximum Tc near 15% doping and Tc T* at optimum doping, and accounts for the destruction of superconductivity by Zn doping near 7%. The model also predicts a relation between the pairing (pseudogap) energy and Tc in terms of experimentally measurable quantities.

Comparison of structural and chemical properties of Cr-based hard coatings

Abstract: A series of chromium nitride, carbide and carbonitride coatings were prepared by ion plating using nitrogen and acetylene as reactive gases. The depositions were made at different partial pressures of the reactive gases while maintaining other parameters constant. The crystal structure and microstructure were studied by TEM. The CrN and Cr 2 N phases were detected in the chromium nitride coatings. In the carbide coatings, orthorhombic Cr 7 C 3 and the metastable cubic CrC phase were confirmed. For oxidation studies, the samples were annealed at 750 °C. Afterwards, the depth profile was measured by glow discharge optical emission spectrometry (GDOES). A complex diffusion was observed involving outdiffusion of nitrogen and segregation of carbon at the substrate-coating interface.

Enantiomeric excess dependence of the phase diagram of antiferroelectric liquid crystals.

Abstract: The phase diagram of the prototype antiferroelectric liquid crystal ${4\ensuremath{-}(1\ensuremath{-}\mathrm{m}\mathrm{e}\mathrm{t}\mathrm{h}\mathrm{y}\mathrm{l}\mathrm{h}\mathrm{e}\mathrm{p}\mathrm{t}\mathrm{y}\mathrm{l}\mathrm{o}\mathrm{x}\mathrm{y}\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{o}\mathrm{n}\mathrm{y}\mathrm{l})\mathrm{p}\mathrm{h}\mathrm{e}\mathrm{n}\mathrm{y}\mathrm{l}\ensuremath{-}4}^{\ensuremath{'}}$-octyloxybiphengl-4-carboxylate (MHPOBC) in dependence of enantiomeric excess was measured. It was shown that the $\mathrm{Sm}\ensuremath{-}{C}_{\ensuremath{\beta}}^{*}$ phase in very pure samples is the $\mathrm{Sm}\ensuremath{-}{C}_{\mathrm{FI}2}^{*}$ phase with a four-layer structure, and only after small racemization it transforms into the ferroelectric $\mathrm{Sm}\ensuremath{-}{C}^{*}$ phase. The phase diagram was theoretically explained by taking into account longer range bilinear and short range biquadratic interlayer interactions, that lead to the distorted clock structures and first-order transitions between them.