Showing papers by "Jožef Stefan Institute published in 2011"

Titanium dioxide in our everyday life; is it safe?

Abstract: Background. Titanium dioxide (TiO2) is considered as an inert and safe material and has been used in many applications for decades. However, with the development of nanotechnologies TiO2 nanoparticles, with numerous novel and useful properties, are increasingly manufactured and used. Therefore increased human and environmental exposure can be expected, which has put TiO2 nanoparticles under toxicological scrutiny. Mechanistic toxicological studies show that TiO2 nanoparticles predominantly cause adverse effects via induction of oxidative stress resulting in cell damage, genotoxicity, inflammation, immune response etc. The extent and type of damage strongly depends on physical and chemical characteristics of TiO2 nanoparticles, which govern their bioavailability and reactivity. Based on the experimental evidence from animal inhalation studies TiO2 nanoparticles are classified as "possible carcinogenic to humans" by the International Agency for Research on Cancer and as occupational carcinogen by the National Institute for Occupational Safety and Health. The studies on dermal exposure to TiO2 nanoparticles, which is in humans substantial through the use of sunscreens, generally indicate negligible transdermal penetration; however data are needed on long-term exposure and potential adverse effects of photo-oxidation products. Although TiO2 is permitted as an additive (E171) in food and pharmaceutical products we do not have reliable data on its absorption, distribution, excretion and toxicity on oral exposure. TiO2 may also enter environment, and while it exerts low acute toxicity to aquatic organisms, upon long-term exposure it induces a range of sub-lethal effects. Conclusions. Until relevant toxicological and human exposure data that would enable reliable risk assessment are obtained, TiO2 nanoparticles should be used with great care.

Ferri-liposomes as an MRI-visible drug-delivery system for targeting tumours and their microenvironment

Abstract: The tumour microenvironment regulates tumour progression and the spread of cancer in the body. Targeting the stromal cells that surround cancer cells could, therefore, improve the effectiveness of existing cancer treatments. Here, we show that magnetic nanoparticle clusters encapsulated inside a liposome can, under the influence of an external magnet, target both the tumour and its microenvironment. We use the outstanding T2 contrast properties (r2=573-1,286 s(-1) mM(-1)) of these ferri-liposomes, which are ∼95 nm in diameter, to non-invasively monitor drug delivery in vivo. We also visualize the targeting of the tumour microenvironment by the drug-loaded ferri-liposomes and the uptake of a model probe by cells. Furthermore, we used the ferri-liposomes to deliver a cathepsin protease inhibitor to a mammary tumour and its microenvironment in a mouse, which substantially reduced the size of the tumour compared with systemic delivery of the same drug.

Learning model trees from evolving data streams

Abstract: The problem of real-time extraction of meaningful patterns from time-changing data streams is of increasing importance for the machine learning and data mining communities. Regression in time-changing data streams is a relatively unexplored topic, despite the apparent applications. This paper proposes an efficient and incremental stream mining algorithm which is able to learn regression and model trees from possibly unbounded, high-speed and time-changing data streams. The algorithm is evaluated extensively in a variety of settings involving artificial and real data. To the best of our knowledge there is no other general purpose algorithm for incremental learning regression/model trees able to perform explicit change detection and informed adaptation. The algorithm performs online and in real-time, observes each example only once at the speed of arrival, and maintains at any-time a ready-to-use model tree. The tree leaves contain linear models induced online from the examples assigned to them, a process with low complexity. The algorithm has mechanisms for drift detection and model adaptation, which enable it to maintain accurate and updated regression models at any time. The drift detection mechanism exploits the structure of the tree in the process of local change detection. As a response to local drift, the algorithm is able to update the tree structure only locally. This approach improves the any-time performance and greatly reduces the costs of adaptation.

Left-Right Symmetry: from LHC to Neutrinoless Double Beta Decay

Abstract: The Large Hadron Collider has the potential to probe the scale of left-right symmetry restoration and the associated lepton number violation. Moreover, it offers the hope of measuring the right-handed leptonic mixing matrix. We show how this, together with constraints from lepton flavor violating processes, can be used to make predictions for neutrinoless double beta decay. We illustrate this connection in the case of the type-II seesaw.

Janus-faced influence of Hund's rule coupling in strongly correlated materials.

Abstract: We show that in multiband metals the correlations are strongly affected by Hund's rule coupling, which depending on the filling promotes metallic, insulating or bad-metallic behavior. The quasiparticle coherence and the proximity to a Mott insulator are influenced distinctly and, away from single- and half-filling, in opposite ways. A strongly correlated bad metal far from a Mott phase is found there. We propose a concise classification of $3d$ and $4d$ transition-metal oxides within which the ubiquitous occurrence of strong correlations in Ru- and Cr-based oxides, as well as the recently measured high N\'eel temperatures in Tc-based perovskites are naturally explained.

Plasma nanoscience : setting directions, tackling grand challenges

Abstract: This review paper presents historical perspectives, recent advances and future directions in the multidisciplinary research field of plasma nanoscience The current status and future challenges are presented using a three-dimensional framework The first and the largest dimension covers the most important classes of nanoscale objects (nanostructures, nanofeatures and nanoassemblies/nanoarchitectures) and materials systems, namely carbon nanotubes, nanofibres, graphene, graphene nanoribbons, graphene nanoflakes, nanodiamond and related carbon-based nanostructures; metal, silicon and other inorganic nanoparticles and nanostructures; soft organic nanomaterials; nano-biomaterials; biological objects and nanoscale plasma etching In the second dimension, we discuss the most common types of plasmas and plasma reactors used in nanoscale plasma synthesis and processing These include low-temperature non-equilibrium plasmas at low and high pressures, thermal plasmas, high-pressure microplasmas, plasmas in liquids and plasma–liquid interactions, high-energy-density plasmas, and ionized physical vapour deposition as well as some other plasma-enhanced nanofabrication techniques In the third dimension, we outline some of the 'Grand Science Challenges' and 'Grand Socio-economic Challenges' to which significant contributions from plasma nanoscience-related research can be expected in the near future The urgent need for a stronger focus on practical, outcome-oriented research to tackle the grand challenges is emphasized and concisely formulated as from controlled complexity to practical simplicity in solving grand challenges

Occurrence, fate and determination of cytostatic pharmaceuticals in the environment

Abstract: We review the literature on the analysis of pharmaceutically-derived cytostatic compounds in the environment. Cytostatics are a major class of chemotherapy drugs used extensively in the fight against cancer. They are a broad group of mostly organic compounds possessing a diverse range of physico-chemical parameters. Their differences and their presence in the environment in trace amounts make their determination in complex matrices a major challenge. Despite the good scientific foundations laid by those in the field, it is apparent that past research has focused mainly on hospital effluents and few have analyzed environmental samples. Importantly, no study has looked at environmental transformation products that, along with human metabolites, could contribute to overall toxicity. To improve understanding of the chemodynamics of cytostatics in natural waters, it is essential to have more data on the occurrence and the fate of these compounds, including their human metabolites and environmental transformation products. This approach will require advanced sampling techniques and state-of-the-art analytical tools, including the latest separation methods and cutting-edge instrumentation.

Finding the ciliary beating pattern with optimal efficiency.

Abstract: We introduce a measure for energetic efficiency of biological cilia acting individually or collectively and numerically determine the optimal beating patterns according to this criterion. Maximizing the efficiency of a single cilium leads to curly, often symmetric, and somewhat counterintuitive patterns. However, when looking at a densely ciliated surface, the optimal patterns become remarkably similar to what is observed in microorganisms like Paramecium. The optimal beating pattern then consists of a fast effective stroke and a slow sweeping recovery stroke. Metachronal coordination is essential for efficient pumping and the highest efficiency is achieved with antiplectic waves. Efficiency also increases with an increasing density of cilia up to the point where crowding becomes a problem. We finally relate the pumping efficiency of cilia to the swimming efficiency of a spherical microorganism and show that the experimentally estimated efficiency of Paramecium is surprisingly close to the theoretically possible optimum.

Quasi-two-dimensional Skyrmion lattices in a chiral nematic liquid crystal.

Abstract: Skyrmions are particle-like topological entities in a continuous field that have a role in various condensed matter systems. Here, numerical methods are used to show that a chiral nematic liquid crystal could be used as a model system to facilitate direct structural investigation of Skyrmions.

Accelerometer Placement for Posture Recognition and Fall Detection

Abstract: This paper presents an approach to fall detection with accelerometers that exploits posture recognition to identify postures that may be the result of a fall. Posture recognition as a standalone task was also studied. Nine placements of up to four sensors were considered: on the waist, chest, thigh and ankle. The results are compared to the results of a system using ultra wide band location sensors on a scenario consisting of events difficult to recognize as falls or non-falls. Three accelerometers proved sufficient to correctly recognize all the events except one(a slow fall). The location-based system was comparable to two accelerometers, except that it was able to recognize the slow fall because it resulted in lying outside the bed, whose location was known to the system. One accelerometer was able to recognize only the most clear-cut fall. Two accelerometers achieved over 90% accuracy of posture recognition, which was better than the location-based system. Chest and waist accelerometers proved best at both tasks, with the chest accelerometer having a slight advantage in posture recognition.

Coherence-Incoherence Crossover and the Mass-Renormalization Puzzles in Sr 2 RuO 4

Abstract: We calculate the electronic structure of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, treating correlations within dynamical mean-field theory. The approach successfully reproduces several experimental results and explains the key properties of this material: the anisotropic mass renormalization of quasiparticles and the crossover into an incoherent regime above a low temperature scale. While the orbital differentiation originates from the proximity of the van Hove singularity, strong correlations are caused by the Hund's coupling. The generality of this mechanism for other correlated materials is pointed out.

The Role of High-Altitude Platforms (HAPs) in the Global Wireless Connectivity

Abstract: Since 1990s, the investigations of aerospace communication segment have not only been concerned with satellites, but increasingly with lower altitude repeaters flying in the stratosphere. They are the so-called high-altitude platforms (HAPs) with important advantages with respect to satellites in terms of reduced cost of implementation, deployment, and launch. However, HAPs are characterized by a reduced coverage, as compared with satellites. Nevertheless, in recent literature, HAPs are not regarded as competitors of the satellite technology. On the contrary, the emphasis is on the effective and seamless integration among heterogeneous aerospace segments (GEO, LEO, and HAP) and aerospace segments with terrestrial wireless networks in order to globally extend the broadband wireless connectivity. This paper is focused on the role of HAPs in providing global connectivity in future communication systems and services. Potentialities, enabling technologies, and challenges are presented from the perspective of the integrated terrestrial/HAPs/satellite communications infrastructure.

Autophagy in protists

Abstract: Autophagy is the degradative process by which eukaryotic cells digest their own components using acid hydrolases within the lysosome. Originally thought to function almost exclusively in providing starving cells with nutrients taken from their own cellular constituents, autophagy is in fact involved in numerous cellular events including differentiation, turnover of macromolecules and organelles, and defense against parasitic invaders. During the last 10-20 years, molecular components of the autophagic machinery have been discovered, revealing a complex interactome of proteins and lipids, which, in a concerted way, induce membrane formation to engulf cellular material and target it for lysosomal degradation. Here, our emphasis is autophagy in protists. We discuss experimental and genomic data indicating that the canonical autophagy machinery characterized in animals and fungi appeared prior to the radiation of major eukaryotic lineages. Moreover, we describe how comparative bioinformatics revealed that this canonical machinery has been subject to moderation, outright loss or elaboration on multiple occasions in protist lineages, most probably as a consequence of diverse lifestyle adaptations. We also review experimental studies illustrating how several pathogenic protists either utilize autophagy mechanisms or manipulate host-cell autophagy in order to establish or maintain infection within a host. The essentiality of autophagy for the pathogenicity of many parasites, and the unique features of some of the autophagy-related proteins involved, suggest possible new targets for drug discovery. Further studies of the molecular details of autophagy in protists will undoubtedly enhance our understanding of the diversity and complexity of this cellular phenomenon and the opportunities it offers as a drug target.

DFT Study of Interaction of Azoles with Cu(111) and Al(111) Surfaces: Role of Azole Nitrogen Atoms and Dipole–Dipole Interactions

Abstract: Azoles and their derivatives are among the often used organic corrosion inhibitors for copper. For this reason, the adsorption of four azole molecules—imidazole, 1,2,3-triazole, tetrazole, and pent...

Coupled channel analysis of the rho meson decay in lattice QCD

Abstract: We employ a variational basis with a number of $\overline{q}q$ and $\ensuremath{\pi}\ensuremath{\pi}$ lattice interpolating fields with quantum numbers of the $\ensuremath{\rho}$ resonance to extract the discrete energy spectrum in a finite volume. In the elastic region, this spectrum is related to the phase shift of the continuum scattering amplitude by L\"uscher's formula, and the relation allows the extraction of resonance parameters from the spectrum calculation. The simulations are performed at three different total momenta of the coupled $\overline{q}q\ensuremath{-}\ensuremath{\pi}\ensuremath{\pi}$ system, which allows us to extract the $p$-wave scattering phase at five values of pion relative momenta near the resonance region. The effective range formula describes the phase-shift dependence nicely, and we extract the resonance mass ${m}_{\ensuremath{\rho}}=792(7)(8)\text{ }\text{ }\mathrm{MeV}$ and the coupling ${g}_{\ensuremath{\rho}\ensuremath{\pi}\ensuremath{\pi}}=5.13(20)$ at our ${m}_{\ensuremath{\pi}}\ensuremath{\simeq}266\text{ }\text{ }\mathrm{MeV}$. The coupling ${g}_{\ensuremath{\rho}\ensuremath{\pi}\ensuremath{\pi}}$ is directly related to the width of the $\ensuremath{\rho}$ meson, and our value is close to the value derived from the experimental width. The simulations are performed using dynamical gauge configurations with two mass-degenerate flavors of tree-level improved clover-Wilson fermions. Correlation functions are calculated using the recently proposed distillation method with Laplacian-Heaviside smearing of quarks, which enables flexible calculations, in many cases with unprecedented accuracy.

Search for light gauge bosons of the dark sector at the Mainz Microtron.

Abstract: A new exclusion limit for the electromagnetic production of a light U(1) gauge boson γ' decaying to e + e- was determined by the A1 Collaboration at the Mainz Microtron. Such light gauge bosons appear in several extensions of the standard model and are also discussed as candidates for the interaction of dark matter with standard model matter. In electron scattering from a heavy nucleus, the existing limits for a narrow state coupling to e + e- were reduced by nearly an order of magnitude in the range of the lepton pair mass of 210 MeV/c2}

First Limits on Left-Right Symmetry Scale from LHC Data

Abstract: We use the early Large Hadron Collider data to set the lower limit on the scale of left-right symmetry, by searching for the right-handed charged gauge boson ${W}_{R}$ via the final state with two leptons and two jets, for $33\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ integrated luminosity and 7 TeV center-of-mass energy This signal is kinematically observable for right-handed neutrino lighter than ${W}_{R}$ In the absence of a signal beyond the standard model background, we set the bound ${M}_{{W}_{R}}\ensuremath{\gtrsim}14\text{ }\text{ }\mathrm{TeV}$ at 95% CL This result is obtained for a range of right-handed neutrino masses of the order of few 100 GeV, assuming no accidental cancellation in right-handed lepton mixings

Controlled surface functionalization of silica-coated magnetic nanoparticles with terminal amino and carboxyl groups

Abstract: General and versatile methods for the functionalization of superparamagnetic, silica-coated, maghemite nanoparticles by surface amino and/or carboxyl groups have been established. The nanoparticles were synthesized using co-precipitation from aqueous solutions and coated with a thin layer of silica using the hydrolysis and condensation of tetraethoxysilane (TEOS). For the amino functionalization, 3-(2-aminoethylamino)propylmethyldimethoxysilane (APMS) was grafted onto the nanoparticle surfaces in their aqueous suspensions. The grafting process was followed by measurements of the ζ-potential and a determination of the concentration of the surface amino groups with conductometric titrations. The surface concentration of the amino groups could be varied by increasing the amount of APMS in the grafting process up to approximately 2.3 –NH2 groups per nm2. The carboxyl functionalization was obtained in two ways: (i) by a ring-opening linker elongation reaction of the surface amines at the functionalized nanoparticles with succinic anhydride (SA) in non-aqueous medium, and (ii) by reacting the APMS and SA first, followed by grafting of the carboxyl-terminated reagent onto the nanoparticle surfaces. Using the first method, the SA only reacted with the terminal primary amino groups (–NH2) of the surface-grafted APMS molecules. Infra-red spectroscopy (ATR FTIR) and mass spectrometry (HRMS) showed that the second method enables the bonding of up to two SA molecules per one APMS molecule, since the SA reacted with both the primary (–NH2) and secondary amino (–NH–) groups of the APMS molecule. When using both methods, the ratio between the surface amino and carboxyl groups can be controlled.

Energies and pressures in viruses: contribution of nonspecific electrostatic interactions

Abstract: We summarize some aspects of electrostatic interactions in the context of viruses. A simplified but, within well defined limitations, reliable approach is used to derive expressions for electrostatic energies and the corresponding osmotic pressures in single-stranded RNA viruses and double-stranded DNA bacteriophages. The two types of viruses differ crucially in the spatial distribution of their genome charge which leads to essential differences in their free energies, depending on the capsid size and total charge in a quite different fashion. Differences in the free energies are trailed by the corresponding characteristics and variations in the osmotic pressure between the inside of the virus and the external bathing solution.

Multiferroic magnetoelectric fluorides: why are there so many magnetic ferroelectrics?

Abstract: We review work on multiferroic magnetic fluorides with an aim to correct the popular opinion that magnetic ferroelectrics are rare in nature. After a qualitative summary describing the main families of magnetic fluorides that are piezoelectric and probably ferroelectric, we discuss in detail the most popular recent groups, namely the K(3)Fe(5)F(15) and Pb(5)Cr(3)F(19) families.

Surface Domain Structures and Mesoscopic Phase Transition in Relaxor Ferroelectrics

Abstract: Relaxor ferroelectrics are a prototypical example of ferroic systems in which interplay between atomic disorder and order parameters gives rise to emergence of unusual properties, including non-exponential relaxations, memory effects, polarization rotations, and broad spectrum of bias- and temperatureinduced phase transitions. Despite more than 40 years of extensive research following the original discovery of ferroelectric relaxors by the Smolensky group, the most basic aspect of these materials – the existence and nature of order parameter – has not been understood thoroughly. Using extensive imaging and spectroscopic studies by variable-temperature and time resolved piezoresponse force microscopy, we fithat the observed mesoscopic behavior is consistent with the presence of two effective order parameters describing dynamic and static parts of polarization, respectively. The static component gives rise to rich spatially ordered systems on the ∼ 100 nm length scales, and are only weakly responsive to electric fi eld. The surface of relaxors undergoes a mesoscopic symmetry breaking leading to the freezing of polarization fl uctuations and shift of corresponding transition temperature.