Serbian Academy of Science and Arts

Belgrade, Serbia

Serbian Academy of Science and Arts

Belgrade, Serbia
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Zivkovic I.S.,Serbian Academy of Science and Arts | Stanimirovic P.S.,University of Niš | Wei Y.,Fudan University
Neural Computation | Year: 2016

Two linear recurrent neural networks for generating outer inverses with prescribed range and null space are defined. Each of the proposed recurrent neural networks is based on the matrix-valued differential equation, a generalization of dynamic equations proposed earlier for the nonsingular matrix inversion, the Moore-Penrose inversion, as well as the Drazin inversion, under the condition of zero initial state. The application of the first approach is conditioned by the properties of the spectrum of a certain matrix; the second approach eliminates this drawback, though at the cost of increasing the number of matrix operations. The cases corresponding to the most common generalized inverses are defined. The conditions that ensure stability of the proposed neural network are presented. Illustrative examples present the results of numerical simulations. © 2016 Massachusetts Institute of Technology.

Stevanovic M.,Serbian Academy of Science and Arts
International journal of nanomedicine | Year: 2011

Highly stable dispersions of nanosized silver particles were synthesized using a straightforward, cost-effective, and ecofriendly method. Nontoxic glucose was utilized as a reducing agent and poly-α, γ, L-glutamic acid (PGA), a naturally occurring anionic polymer, was used as a capping agent to protect the silver nanoparticles from agglomeration and render them biocompatible. Use of ammonia during synthesis was avoided. Our study clearly demonstrates how the concentration of the capping agent plays a major role in determining the dimensions, morphology, and stability, as well as toxicity of a silver colloidal solution. Hence, proper optimization is necessary to develop silver colloids of narrow size distribution. The samples were characterized by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and zeta potential measurement. MTT assay results indicated good biocompatibility of the PGA-capped silver nanoparticles. Formation of intracellular reactive oxygen species was measured spectrophotometrically using 2,7-dichlorofluorescein diacetate as a fluorescent probe, and it was shown that the PGA-capped silver nanoparticles did not induce intracellular formation of reactive oxygen species.

Uskokovic V.,University of California at San Francisco | Uskokovic D.P.,Serbian Academy of Science and Arts
Journal of Biomedical Materials Research - Part B Applied Biomaterials | Year: 2011

The first part of this review looks at the fundamental properties of hydroxyapatite (HAP), the basic mineral constituent of mammalian hard tissues, including the physicochemical features that govern its formation by precipitation. A special emphasis is placed on the analysis of qualities of different methods of synthesis and of the phase transformations intrinsic to the formation of HAP following precipitation from aqueous solutions. This serves as an introduction to the second part and the main subject of this review, which relates to the discourse regarding the prospects of fabrication of ultrafine, nanosized particles based on calcium phosphate carriers with various therapeutic and/or diagnostic agents coated on and/or encapsulated within the particles. It is said that the particles could be either surface-functionalized with amphiphiles, peptides, proteins, or nucleic acids or injected with therapeutic agents, magnetic ions, or fluorescent molecules. Depending on the additive, they could be subsequently used for a variety of applications, including the controlled delivery and release of therapeutic agents (extracellularly or intracellularly), magnetic resonance imaging and hyperthermia therapy, cell separation, blood detoxification, peptide or oligonucleotide chromatography and ultrasensitive detection of biomolecules, and in vivo and in vitro gene transfection. Calcium phosphate nanoparticles as carriers of therapeutic agents that would enable a controlled drug release to treat a given bone infection and at the same be resorbed in the body so as to regenerate hard tissue lost to disease are emphasized hereby as one of the potentially attractive smart materials for the modern medicine. © 2010 Wiley Periodicals, Inc.

Kratica J.,Serbian Academy of Science and Arts
Computers and Industrial Engineering | Year: 2013

This paper deals with the uncapacitated multiple allocation p-hub median problem (UMApHMP). An electromagnetism-like (EM) method is proposed for solving this NP-hard problem. Our new scaling technique, combined with the movement based on the attraction-repulsion mechanism, directs the EM towards promising search regions. Numerical results on a battery of benchmark instances known from the literature are reported. They show that the EM reaches all previously known optimal solutions, and gives excellent results on large-scale instances. The present approach is also extended to solve the capacitated version of the problem. As it was the case in the uncapacitated version, EM also reached all previously known optimal solutions. © 2013 Elsevier Ltd. All rights reserved.

Calic J.,Serbian Academy of Science and Arts
Geomorphology | Year: 2011

Uvalas are a particular type of karst closed depression. While other types of closed depression - dolines and poljes - are regularly listed and relatively well defined in overviews of karst surface morphology, uvalas are either excluded or their vague identification is stressed. The leading idea of this paper is to obtain a clearer meaning of the term uvala and prevent its abandonment from karstology and general geomorphology. Within the study, 43 examples of uvalas have been selected. The studied uvalas are located in the Dinaric karst and karst of the Carpatho-Balkanides. All the case examples have been digitally processed in the same way. Creation of high-resolution digital elevation models enabled quantification of morphometric parameters, generation of inclination maps and cross-sections, as well as application of statistical analyses. Formation of the geographical information system of the studied uvalas was done using raster-based and vector-based GIS software packages. In 12 studied uvalas, detailed structural-geological mapping has been carried out, which revealed dominant development of uvalas along regional scale tectonically broken zones. A revised definition of the term uvala is suggested, leaving the opportunity for further discussion. © 2011 Elsevier B.V.

Jovanovic B.,Serbian Academy of Science and Arts
Archive for Rational Mechanics and Analysis | Year: 2013

In this article, we construct the Lax representations of the geodesic flow, the Jacobi-Rosochatius problem and its perturbations by means of separable polynomial potentials on an ellipsoid. We prove complete integrability in the case of a generic symmetric ellipsoid and describe analogous systems on complex projective spaces. Also, we consider billiards within an ellipsoid under the influence of the Hook and Rosochatius potentials between the impacts. A geometric interpretation of the integrability analogous to the classical Chasles and Poncelet theorems is given. © 2013 Springer-Verlag Berlin Heidelberg.

Zivaljevic R.T.,Serbian Academy of Science and Arts
Computational Geometry: Theory and Applications | Year: 2015

Illumination complexes are examples of 'flat polyhedral complexes' which arise if several copies of a convex polyhedron (convex body) Q are glued together along some of their common faces (closed convex subsets of their boundaries). A particularly nice example arises if Q is a Δ-zonotope (generalized rhombic dodecahedron), known also as the dual of the difference body Δ-Δ of a simplex Δ, or the dual of the convex hull of the root system An. We demonstrate that the illumination complexes and their relatives can be used as 'configuration spaces', leading to new 'fair division theorems'. Among the central new results is the 'polyhedral curtain theorem' (Theorem 3) which is a relative of both the 'ham sandwich theorem' and the 'splitting necklaces theorem'. © 2014 Elsevier B.V. All rights reserved.

Karan B.,Serbian Academy of Science and Arts
SISY 2013 - IEEE 11th International Symposium on Intelligent Systems and Informatics, Proceedings | Year: 2013

Recent advances in development of low-cost 3D sensors, such as Microsoft Kinect, bring attractive opportunities to robot system integrators. The accuracy provided by such sensors is generally unsatisfactory for many robotic applications, but it may be improved through calibration. This paper presents a calibration case study that is based on the sensor calibration procedure involving only a use of a simple checkerboard. It is shown that the calibration enables improving sensor accuracy 3 to 5 times, depending on the anticipated use of the sensor. Additionally, results obtained using different levels of complexity of calibration models reveal that depth measurement correction is an important component of calibration as it may reduce by 50% the errors in sensor reading. © 2013 IEEE.

Stankovic A.,Serbian Academy of Science and Arts | Dimitrijevic S.,University of Belgrade | Uskokovic D.,Serbian Academy of Science and Arts
Colloids and Surfaces B: Biointerfaces | Year: 2013

Metal oxide nanoparticles represent a new class of important materials that are increasingly being developed for use in research and health-related applications. Although the antibacterial activity and efficiency of bulk zinc oxide were investigated in vitro, the knowledge about the antibacterial activity of ZnO nanoparticles remains deficient. In this study, we have synthesized ZnO particles of different sizes and morphologies with the assistance of different types of surface stabilizing agents - polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA) and poly (α,γ, l-glutamic acid) (PGA) - through a low-temperature hydrothermal procedure. The characterization of the prepared powders was preformed using X-ray diffraction (XRD) method and field emission scanning electron microscopy (FE SEM), as well as Malvern's Mastersizer instrument for particle size distribution. The specific surface area (SSA) of the ZnO powders was measured by standard Brunauer-Emmett-Teller (BET) technique. The antibacterial behavior of the synthesized ZnO particles was tested against gram-negative and gram-positive bacterial cultures, namely Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), respectively. We compared the results of the antibacterial properties of the synthesized ZnO samples with those of the commercial ZnO powder. According to the obtained results, the highest microbial cell reduction rate was recorded for the synthesized ZnO powder consisting of nanospherical particles. In all of the examined samples, ZnO particles demonstrated a significant bacteriostatic activity. © 2012 Elsevier B.V.

News Article | September 28, 2016

Researchers at Brookhaven National Laboratory are all excited over a new discovery that they say could usher in the next generation of ultra-efficient electronic devices, batteries, and power grids. The key to the whole thing is a class of materials called cuprates, which can act as superconductors without requiring the super-cold temperatures that superconductors normally need. Health researchers have been casting a stinkeye on the habit of sitting with a hot laptop on your lap, so if the new Brookhaven research only gets that far it will make a huge difference. Superconductors don’t waste energy in the form of heat. The problem with the current crop of superconductors is that they require chilling, which adds weight, bulk and expense. As described by the Brookhaven team, if you could engineer a superconductor that can operate at room temperature, you’re golden: Picture power grids that never lose energy, more affordable mag-lev train systems, cheaper medical imaging machines like MRI scanners, and smaller yet powerful supercomputers. Conventional superconductors are efficient because they allow an electrical current to pass through without hitting any “roadblocks.” The challenge is replicate that phenomenon at room temperature using relatively inexpensive materials. To solve that problem, the Brookhaven team latched onto cuprates, a class of compounds characterized by layers of copper and oxygen atoms. When doctored with strontium and certain other elements, cuprates act as superconductors but they don’t require the extra-cold environment that other superconductors need: What makes cuprates so special is that they can achieve this “magical” state of matter at temperatures a hundred degrees or more above those required by standard superconductors. That makes them very promising for real-world, energy-saving applications. So, if you can figure out exactly how cuprates become superconductors, you’re one step closer to a room temperature superconductor. The new Brookhaven research stands the traditional understanding of superconductors on its head.  According to conventional theory, the temperature of the material is controlled by the strength of the interaction between pairs of electrons. The research team concluded that density, not strength, controls the temperature: In other words, it’s not the forces between objects that matter here, but the density of objects — in this case, electron pairs. Actually, it took a decade of work by lead researcher Ivan Bozovic and his team to get to that one-line summary. Here’s the rundown by Brookhaven science writer Ariana Tantillo: After 10 years of preparing and analyzing more than 2,000 samples of a cuprate with varying amounts of strontium, they found that the number of electron pairs within a given area (say, per cubic centimeter), or the density of electron pairs, controls the superconducting transition temperature. Our friends over at Science Daily add some details on the methodology: Bozovic and his research team grew their more than 2,500 LSCO samples by using a custom-designed molecular beam epitaxy system that places single atoms onto a substrate, layer by layer. This system is equipped with advanced surface-science tools, such as those for absorption spectroscopy and electron diffraction, that provide real-time information about the surface morphology, thickness, chemical composition, and crystal structure of the resulting thin films. Epitaxy refers to layering crystals onto a crystal base, btw. The award-winning system was actually developed by Bozovic and his team. The next step is to figure out why the electrons pair up to begin with, so stay tuned for that, however long it takes. Didn’t US Senator and former presidential candidate Ted Cruz (R-Texas) once famously say he would abolish the Energy Department, if elected? Yes, he did, and it appears that Republican presidential nominee Donald Trump is headed down the same track. Earlier this month, reports surfaced that Trump would give the old heave-ho to the Energy Department, among others. In that case, it would be bye-bye Brookhaven and all of the other laboratories under the Energy Department umbrella. Fortunately, the national laboratory system is still intact — for now — so US taxpayers (disclosure: that includes me) can go ahead and give themselves a nice group hug for supporting Brookhaven, Bozovic, and his research team. In 2014, Bozovic’s record of achievement garnered him a spot among the 2,800 members of Academia Europea, the European Academy of Humanities, Letters, and Sciences. That’s this: Among the members are fifty-two Nobel Laureates, several of whom were elected to the Academia before they received that prestigious prize. Invitations are made only after nomination by existing members followed by an extensive peer review to scrutinize and confirm each individual’s scholarship and eminence in their chosen field. Here’s a little more on Bozovic’s record: His research results have been published in more than 200 highly cited research papers, many in the highest-impact journals such as Nature, Science, and Nature Materials. Bozovic is a Fellow of the American Physical Society and of SPIE, the International Society for Optics and Photonics, and a Foreign Member of Serbian Academy of Science and Arts. Aside from pumping high-risk foundational research into the national economy, the Energy Department also directly supports the private sector through funding for startups (the SunShot Catalyst program is one good example) as well as loan guarantees for the big players. In one recent example, last summer the Energy Department announced $4.5 million in loan guarantees for Ford, GM, Nissan, Tesla and other stakeholders to expand the nation’s EV charging infrastructure. The goal is to enable “coast-to-coast, nationwide zero emissions travel” by 2020. Follow me on Twitter and Google+. Image: “This composite image offers a glimpse inside the custom system Brookhaven scientists used to create samples of materials that may pave the way for high-temperature superconductors” courtesy of Brookhaven National Laboratory. Buy a cool T-shirt or mug in the CleanTechnica store!   Keep up to date with all the hottest cleantech news by subscribing to our (free) cleantech daily newsletter or weekly newsletter, or keep an eye on sector-specific news by getting our (also free) solar energy newsletter, electric vehicle newsletter, or wind energy newsletter.

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