bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser modification of graphene oxide layers
Authors: Malinský Petr , Macková Anna , Cutroneo Mariapompea , Siegel Jakub , Bohačová Marie , Klímova Kateřina , Švorčík Václav , Sofer Zdenĕk
Published: January 2018

The effect of linearly polarized laser irradiation with various energy densities was successfully used for reduction of graphene oxide (GO). The ion beam analytical methods (RBS, ERDA) were used to follow the elemental composition which is expected as the consequence of GO reduction. The chemical composition analysis was accompanied by structural study showing changed functionalities in the irradiated GO foils using spectroscopy techniques including XPS, FTIR and Raman spectroscopy. The AFM was employed to identify the surface morphology and electric properties evolution were subsequently studied using standard two point method measurement. The used analytical methods report on reduction of irradiated graphene oxide on the surface and the decrease of surface resistivity as a growing function of the laser beam energy density.
α particle space distribution from fusion reactions in Boron irradiated by
mono-energetic protons
Authors: De Angelis Riccardo , Giulietti Danilo , Calcagnile Lucio , Quarta Gianluca , Andreoli Pierluigi , Cipriani Mattia , Consoli Fabrizio , Cristofari G. , Delle Side Domenico , Di Giorgio Giorgio , Ingenito Francesco , Maruccio Lucio
Published: January 2018

This work presents results regarding the p + 11B → 3α + 8.7MeV aneutronic fusion reaction. We obtained such results by directing a 0.675 MeV proton beam from a Tandetron accelerator to a solid Boron sample, varying the incidence angle. Three different detectors were used to reveal the alpha particles emitted during the experiments. The evidence obtained leads us to propose an innovative scheme to investigate the yield of the aneutronic reaction when the proton beam is directed against a 11B laser induced plasma.
Modification induced by laser irradiation on physical features of plastics materials filled with nanoparticles
Authors: Scolaro Cristina , Visco Annamaria , Torrisi Lorenzo , Restuccia Nancy , Pedullà Eugenio
Published: January 2018

The Thermal Laser Welding (TLW) process involves localized heating at the interface of two pieces of plastic that will be joined. Polymeric materials of Ultra High Molecular Weight Polyethylene (UHMWPE), both pure and containing nanostructures at different concentrations (titanium and silver nanoparticles), were prepared as thin foils in order to produce an interface between a substrate transparent to the infrared laser wavelength and an highly absorbent substrate, in order to be welded by the laser irradiation. The used diode laser operates at 970 nm wavelength, in continuum, with a maximum energy of 100 mJ, for times of the order of 1 -60 s, with a spot of 300 μm of diameter. The properties of the polymers and of nanocomposite sheets, before and after the laser welding process, were measured in terms of optical characteristics, wetting ability, surface roughness and surface morphology.
Physical investigations on the radiation damage of graphene oxide by IR pulsed laser
Authors: Silipigni Letteria , Torrisi Lorenzo , Cutroneo Mariapompea
Published: January 2018

Graphene oxide foils were irradiated by Nd:YAG laser at the moderated intensities of the order of 108 W/cm2 in vacuum. Measurements of atomic emission during the laser irradiation were performed with ion collectors and mass spectrometry, demonstrating a strong emission of carbon, oxygen and hydrogen atoms. Further investigations of the irradiated graphene oxide foils were carried out on pristine and laser irradiated samples by using Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. Results indicate that graphene oxide losses oxygen and hydrogen during the irradiation, changing its carbon content and its chemical and physical properties.
Cosmological Implications of Electroweak Monopole
Authors: Cho Y. M.
Published: January 2018

In this talk we review the basic features of the electroweak monopole, and estimate the remnant electroweak monopole density of the standard model in the present universe. We show that, although the electroweak phase transition is of the first order, the monopole production comes from the thermal fluctuations of the Higgs field after the phase transition, not the vacuum bubble collisions during the phase transition. Moreover, most of the monopoles produced initially are annihilated as soon as created, and this annihilation continues very long time, longer than the muon pair annihilation time. As the result the remnant monopole density at present universe becomes very small, of 10-11 of the critical density, too small to be the dark matter. We discuss the physical implications of our results on the ongoing monopole detection experiments.
SOGRO (Superconducting Omni-directional Gravitational Radiation Observatory)
Authors: Paik Ho Jung
Published: January 2018

Detection of gravitational waves (GWs) from merging binary black holes (BHs) by Advanced LIGO has ushered in the new era of GW astronomy. Many conceivable sources such as intermediate-mass BH binaries and white dwarf binaries, as well as stellar-mass BH inspirals, would emit GWs below 10 Hz. It is highly desirable to open a new window for GW astronomy in the infrasound frequency band. A low-frequency tensor detector could be constructed by combining six magnetically levitated superconducting test masses. Such a detector would be equally sensitive to GWs coming from anywhere in the sky, and would be capable of resolving the source direction and wave polarization. I will present the design concept of a new terrestrial GW detector, named SOGRO, which could reach a strain sensitivity of 10−19-10−21 Hz−1/2 at 0.1-10 Hz. Seismic and Newtonian gravity noises are serious obstacles in constructing terrestrial GW detectors at frequencies below 10 Hz. I will explain how these noises are rejected in SOGRO. I will also report the progress made in designing the platform and modelling its thermal noise.
New entropy formula for Kerr black holes
Authors: González Hernán A. , Grumiller Daniel , Merbis Wout , Wutte Raphaela
Published: January 2018

We introduce a new entropy formula for Kerr black holes inspired by recent results for 3-dimensional black holes and cosmologies with soft Heisenberg hair. We show that also Kerr–Taub–NUT black holes obey the same formula.
Stringy Gravity: Solving the Dark Problems at ‘short’ distance
Authors: Park Jeong-Hyuck
Published: January 2018

Dictated by Symmetry Principle, string theory predicts not General Relativity but its own gravity which assumes the entire closed string massless sector to be geometric and thus gravitational. In terms of R/(MG), i.e. the dimensionless radial variable normalized by mass, Stringy Gravity agrees with General Relativity toward infinity, but modifies it at short distance. At far short distance, gravitational force can be even repulsive. These may solve the dark matter and energy problems, as they arise essentially from small R/(MG) observations: long distance divided by much heavier mass. We address the pertinent differential geometry for Stringy Gravity, stringy Equivalence Principle, stringy geodesics and the minimal coupling to the Standard Model. We highlight the notion of ‘doubled-yet-gauged’ coordinate system, in which a gauge orbit corresponds to a single physical point and proper distance is defined between two gauge orbits by a path integral.
Scalar Dyon Production In Near Extremal Kerr-Newman Black Holes
Authors: Chen Chiang-Mei , Kim Sang Pyo , Sun Jia-Rui , Tang Fu-Yi
Published: January 2018

The pair production of charged scalar dyons is analytically studied in near-extremal Kerr-Newman (KN) dyonic black holes. The pair production rate and its thermal interpretation are given. Moreover, the absorption cross section ratio has been compared with the two-point function of the conformal field theories (CFTs) holographically dual to the near horizon geometry, namely warped AdS3, of the near extremal Kerr-Newman black holes to verify the threefold dyonic KN/CFTs correspondence.
Status of the GroundBIRD Telescope
Authors: Choi J. , Génova-Santos R. , Hattori M. , Hazumi M. , Ishitsuka H. , Kanno F. , Karatsu K. , Kiuchi K. , Koyano R. , Kutsuma H. , Lee K. , Mima S. , Minowa M. , Nagai M. , Nagasaki T. , Naruse M. , Oguri S. , Okada T. , Otani C. , Rebolo R. , Rubiño-Martín J. , Sekimoto Y. , Suzuki J. , Taino T. , Tajima O. , Tomita N. , Uchida T. , Won E. , Yoshida M.
Published: January 2018

Our understanding of physics at very early Universe, as early as 10−35 s after the Big Bang, relies on the scenario known as the inflationary cosmology. Inflation predicts a particular polarization pattern in the cosmic microwave background, known as the B-mode yet the strength of such polarization pattern is extremely weak. To search for the B-mode of the polarization in the cosmic microwave background, we are constructing an off-axis rotating telescope to mitigate systematic effects as well as to maximize the sky coverage of the observation. We will discuss the present status of the GroundBIRD telescope.
On the Induced Gravitational Collapse
Authors: M. Becerra Laura , Bianco Carlo , Fryer Chris , Rueda Jorge , Ruffini Remo
Published: January 2018

The induced gravitational collapse (IGC) paradigm has been applied to explain the long gamma ray burst (GRB) associated with type Ic supernova, and recently the Xray flashes (XRFs). The progenitor is a binary systems of a carbon-oxygen core (CO) and a neutron star (NS). The CO core collapses and undergoes a supernova explosion which triggers the hypercritical accretion onto the NS companion (up to 10-2 M⊙s-1). For the binary driven hypernova (BdHNe), the binary system is enough bound, the NS reach its critical mass, and collapse to a black hole (BH) with a GRB emission characterized by an isotropic energy Eiso > 1052 erg. Otherwise, for binary systems with larger binary separations, the hypercritical accretion onto the NS is not sufficient to induced its gravitational collapse, a X-ray flash is produced with Eiso < 1052 erg. We’re going to focus in identify the binary parameters that limits the BdHNe systems with the XRFs systems.
Oscillon in Einstein-scalar system with double well potential and its properties.
Authors: Ikeda Taishi , Yoo Chul-Moon , Cardoso Vitor
Published: January 2018

The dynamical evolution of self-interacting scalar field has many nontrivial behaviors, which tell us many lessons in a nonlinear dynamics. On Minkowski spacetime, the scalar field with double well potential has localized, non-singular, time-dependent, long-lived solutions, which are called oscillons. The lifetime of the oscillon depends on the initial conditions. Furthermore, when the initial parameter is fine-tuned, oscillons can be infinitely, and type I critical behavior is observed. Here, we investigate the Einstein-scalar system with double well potential. We show that oscillons exist in this system, and discuss the behavior when the initial parameter is fine-tuned. Our results suggests that a new type of critical behavior appears in this theory.
The orbital stability of a test body motion in the field of two massive bodies
Authors: Abishev Medeu , Toktarbay Saken , Abylayeva Aigerim , Talkhat Amanhan
Published: January 2018

We investigate the orbital stability of a test particle motion in the restricted three-body problem where all bodies have their own rotation. We have shown that it is possible to get some insight into the stability properties of the motion of test particles in restricted three-body problem, without knowing the exact solutions of the relativistic motion equations.
Multiphoton amplitude in a constant background field
Authors: Ahmad Aftab , Ahmadiniaz Naser , Corradini Olindo , Kim Sang Pyo , Schubert Christian
Published: January 2018

In this contribution, we present our recent compact master formulas for the multiphoton amplitudes of a scalar propagator in a constant background field using the worldline fomulation of quantum field theory. The constant field has been included nonperturbatively, which is crucial for strong external fields. A possible application is the scattering of photons by electrons in a strong magnetic field, a process that has been a subject of great interest since the discovery of astrophysical objects like radio pulsars, which provide evidence that magnetic fields of the order of 1012G are present in nature. The presence of a strong external field leads to a strong deviation from the classical scattering amplitudes. We explicitly work out the Compton scattering amplitude in a magnetic field, which is a process of potential relevance for astrophysics. Our final result is compact and suitable for numerical integration.
Gravitational waves from the first order electroweak phase transition in the Z3 symmetric singlet scalar model
Authors: Matsui Toshinori
Published: January 2018

Among various scenarios of baryon asymmetry of the Universe, electroweak baryogenesis is directly connected with physics of the Higgs sector. We discuss spectra of gravitational waves which are originated by the strongly first order phase transition at the electroweak symmetry breaking, which is required for a successful scenario of electroweak baryogenesis. In the Z3 symmetric singlet scalar model, the significant gravitational waves are caused by the multi-step phase transition. We show that the model can be tested by measuring the characteristic spectra of the gravitational waves at future interferometers such as LISA and DECIGO.
Event Rates of Gravitational Waves from merging Intermediate mass Black Holes: based on a Runaway Path to a SMBH
Authors: Shinkai Hisaaki
Published: January 2018

Based on a dynamical formation model of a supermassive black hole (SMBH), we estimate the expected observational profile of gravitational wave at ground-based detectors, such as KAGRA or advanced LIGO/VIRGO. Noting that the second generation of detectors have enough sensitivity from 10 Hz and up, we are able to detect the ring-down gravitational wave of a BH with the mass M < 2 × 103M⊙. This enables us to check the sequence of BH mergers to SMBHs via intermediate-mass BHs. We estimate the number density of galaxies from the halo formation model and estimate the number of BH mergers from the giant molecular cloud model assuming hierarchical growth of merged cores. At the designed KAGRA (and/or advanced LIGO/VIRGO), we find that the BH merger of its total mass M ∼ 60M⊙ is at the peak of the expected mass distribution. With its signal-to-noise ratio ρ = 10(30), we estimate the event rate R ∼ 200(20) per year in the most optimistic case, and we also find that BH mergers in the range M < 150M⊙ are R > 1 per year for ρ = 10. Thus, if we observe a BH with more than 100M⊙ in future gravitational-wave observations, our model naturally explains its source.
Flattening the inflaton potential beyond minimal gravity
Authors: Lee Hyun Min
Published: January 2018

We review the status of the Starobinsky-like models for inflation beyond minimal gravity and discuss the unitarity problem due to the presence of a large non-minimal gravity coupling. We show that the induced gravity models allow for a self-consistent description of inflation and discuss the implications of the inflaton couplings to the Higgs field in the Standard Model.
Inflationary attractors from nonminimal coupling
Authors: Yi Zhu , Gong Yungui
Published: January 2018

We show explicitly how the E model attractor is obtained from the general scalar-tensor theory of gravity with arbitrary conformal factors in the strong coupling limit. By using conformal transformations, any attractor with the observables ns and r can be obtained. The existence of attractors imposes a challenge to distinguish different models.
Brief History of Ultra-light Scalar Dark Matter Models
Authors: Lee Jae-Weon
Published: January 2018

This is a review on the brief history of the scalar field dark matter model also known as fuzzy
dark matter, BEC dark matter, wave dark matter, or ultra-light axion. In this model ultra-light scalar dark matter particles with mass m = O(10-22)eV condense in a single Bose-Einstein condensate state and behave collectively like a classical wave. Galactic dark matter halos can be described as a self-gravitating coherent scalar field configuration called boson stars. At the scale larger than galaxies the dark matter acts like cold dark matter, while below the scale quantum pressure from the uncertainty principle suppresses the smaller structure formation so that it can resolve the small scale crisis of the conventional cold dark matter model.
Atomki anomaly and the Secluded Dark Sector
Authors: Yamamoto Yasuhiro
Published: January 2018

The Atomiki anomaly can be interpreted as a new light vector boson. If such a new particle exists, it could be a mediator between the Standard Model sector and the dark sector including the dark matter. We discussed some simple effective models with these particles. In the models, the secluded dark matter models are good candidates to satisfy the thermal relic abundance. In particular, we found that the dark matter self-interaction can be large enough to solve the small scale structure puzzles if the dark matter is a
fermion.
SIMP dark matter and its cosmic abundances
Authors: Choi Soo-Min , Lee Hyun Min , Seo Min-Seok
Published: January 2018

We give a review on the thermal average of the annihilation cross-sections for 3 → 2 and general higher-order processes. Thermal average of higher order annihilations highly depend on the velocity of dark matter, especially, for the case with resonance poles. We show such examples for scalar dark matter in gauged Z3 models.
Forbidden Channels and SIMP Dark Matter
Authors: Choi Soo-Min , Kang Yoo-Jin , Lee Hyun Min
Published: January 2018

In this review, we focus on dark matter production from thermal freeze-out with forbidden channels and SIMP processes. We show that forbidden channels can be dominant to produce dark matter depending on the dark photon and / or dark Higgs mass compared to SIMP.
Thermodynamic Volume in AdS/CFT
Authors: Kim Kyung Kiu , Ahn Byoungjoon
Published: January 2018

In this note, we study on extended thermodynamics of AdS black holes by varying cosmological constant. We found and discussed pressure and volume of both bulk and boundary physics through AdS/CFT correspondence. In particular, we derive the relation between thermodynamic volume and a chemical potential for M2 brane dual to four dimensional AdS space. In addition, we show that thermodynamic volume of hyperbolic black hole is related to ‘entanglement pressure’ coming from a generalized first law of entanglement entropy.
Gravitational Scattering Amplitudes and Closed String Field Theory in the Proper-Time Gauge
Authors: Lee Taejin
Published: January 2018

We construct a covariant closed string field theory by extending recent works on the covariant open string field theory in the proper-time gauge. Rewriting the string scattering amplitudes generated by the closed string field theory in terms of the Polyakov string path integrals, we identify the Fock space representations of the closed string vertices. We show that the Fock space representations of the closed string field theory may be completely factorized into those of the open string field theory. It implies that the well known Kawai-Lewellen-Tye (KLT) relations of the first quantized string theory may be promoted to the second quantized closed string theory. We explicitly calculate the scattering amplitudes of three gravitons by using the closed string field theory in the proper-time gauge.
Conformal (In)Equality
Authors: Hyun Young-Hwan , Kim Yoonbai , Lee Seokcheon
Published: January 2018

The current accelerating expansion of the Universe is explained either by dark energy or by modified gravity theories. Both of them can explain exactly the same background evolution of the Universe, however this degeneracy may be broken when the observation of large scale structure formation is taken into account. Two observables are parameterized by the so-called dark energy equation of state, ω and the growth index parameter, γ. From these observed parameters, one may reconstruct the model parameters of the so-called scalar-tensor gravity theory, one of the modified gravity theories. Especially, the scalar-tensor gravity theory is described both in Jordan frame and in Einstein frame. If cosmological observations are interpreted in one frame, then all of the observables should also be interpreted in that frame. This explicitly shows conformal inequality of cosmological observables.
Quintessence in low-energy effective theory
Authors: Lee Tae Hoon
Published: January 2018

Considering a theory of Brans-Dicke gravity with general couplings of a heavy field, we derive the low-energy effective theory action in the universe of temperature much lower than the heavy field mass. Gravitational equations and the Brans-Dicke scalar field equation including an effective potential of the scalar field are obtained, which is induced through virtual interactions of the heavy field in the late-time universe. We find a deSitter cosmological solution stemming from the inverse power law effective potential of the scalar field and discuss the possibility that the late time acceleration of our universe can be described by means of the solution.
Upper Limit of Radiation from Coalescence of Rotating Hayward Black Holes
Authors: Gwak Bogeun
Published: January 2018

We review the upper limit of the gravitational radiation thermally allowed under the collision of two rotating Hayward black holes. The upper limit is dependent on the gravitational spin interaction between black holes and is useful to determine one of the parameters for consistency with Laser Interferometer Gravitational-Wave Observatory (LIGO) data.
Consideration of analogies between magnetic and quantum notices for molecular network
Authors: Piech Henryk , Jelonkiewicz Jerzy , Laskowski Lukasz , Laskowska Magdalena
Published: January 2018

Magnetic properties of spin glass materials [9,13] are close to quantum interpretation in their nature description [17]. Therefore, we can look for possible kinds of analogies in process of defining theoretic and practice conventions, rules and applications of the specific characteristics in elaboration quantum calculation strategies. We have not investigated possibilities to create directly quantum calculation units and practice calculation structures like qubits, registers, gates etc. [4,18], but dealing with spin and quantum definitions and descriptions we can try to involve these notices from different domains. Such a pragmatic approach only intuitively gives chances to create the transition theory and implement it even partially. Obviously, almost all of us have heard about quantum factorization, cryptography or teleportation but it is obtained as a result of exploration casually selected quantum properties and adapting them to mathematic problems. In our approach, we carefully investigate involutions among spin and quantum nature looking at possible implementation in molecular network.
CICT: New Eyes on Computational Competence in Computational Science
Authors: Fiorini Rodolfo A.
Published: January 2018

Science does not exists to enlighten people's minds only. It mainly exists to show the educated way from quanta to qualia. And that way starts from computational competence. In previous papers published elsewhere, we have already shown that traditionalQArithmetic can be regarded as a highly sophisticated open logic, powerful and flexible bidirectional formal language of languages, according to "Computational Information Conservation Theory" (CICT) new perspective. This new awareness can offer competitive approach to guide more effective and convenient algorithm development and application to arbitrary multiscale (AMS) biomedical system modeling and simulation. An articulated example on function computational modelling is presented and compared to standard, well-known and traditional approach. Results are critically discussed.
Performance comparison of model selection criteria by generated experimental data
Authors: Mavrevski Radoslav , Milanov Peter , Traykov Metodi , Pencheva Nevena
Published: January 2018

In Bioinformatics and other areas the model selection is a process of choosing a model from set of candidate models of different classes which will provide the best balance between goodness of fitting of the data and complexity of the model. There are many criteria for evaluation of mathematical models for data fitting. The main objectives of this study are: (1) to fitting artificial experimental data with different models with increasing complexity; (2) to test whether two known criteria as Akaike’s information criterion (AIC) and Bayesian information criterion (BIC) can correctly identify the model, used to generate the artificial data and (3) to assess and compare empirically the performance of AIC and BIC.
Computer modeling of Cannabinoid receptor type 1
Authors: Sapundzhi Fatima , Dzimbova Tatyana , Pencheva Nevena , Milanov Peter
Published: January 2018

Cannabinoid receptors are important class of receptors as they are involved in various physiological processes such as appetite, pain-sensation, mood, and memory. It is important to design receptor-selective ligands in order to treat a particular disorder. The aim of the present study is to model the structure of cannabinoid receptor CB1 and to perform docking between obtained models and known ligands. Two models of CBR1 were prepared with two different methods (Modeller of Chimera and MOE). They were used for docking with GOLD 5.2. It was established a high correlation between inhibitory constant Ki of CB1 cannabinoid ligands and the ChemScore scoring function of GOLD, which concerns both models. This suggests that the models of the CB1 receptors obtained could be used for docking studies and in further investigation and design of new potential, selective and active cannabinoids with the desired effects.
The Study of Permanent Magnets Synchronous Machine (PMSM) of the Autonomous Electric Power Supply System (ASE), compatible with the Concept of a More Electric Aircraft (MEA)
Authors: Setlak Lucjan , Kowalik Rafał
Published: January 2018

Based on the analysis and mathematical models of synchronous electric machines (motor/generator), basing on permanent magnets, presented in this paper, the main importance of alternator AC power sources in the form of starter/generator (for conventional aircraft) and in the form of integrated unit starter (motor)/AC synchronous generator S/G AC (with respect to advanced aircraft concept in terms of more electric aircraft) was highlighted. Additionally, through the analysis and selected simulations of the on-board autonomous power supply system of the modern aircrafts, sources of electrical energy (synchronous motor/generator, integrated unit starter/AC generator) were located in board autonomic power system ASE (EPS, PES). Main components of this system are the electro-energetic power system EPS and the energo-electronic power system PES. In addition, the analysis and exemplary simulations of main electricity sources based on mathematical models have contributed to highlighting the main practical applications in accordance with the concept of MEA.
Model and Simulation of Permanent Magnets Synchronous Machine (PMSM) of the Electric Power Supply System (EPS), in Accordance with the Concept of a More Electric Aircraft (MEA)
Authors: Setlak Lucjan , Kowalik Rafał
Published: January 2018

Based on the mathematical model of synchronous electric machine, basing on permanent magnets, presented in this paper, the key importance of alternator AC power sources in the form of generator (for conventional aircraft) and in the form of integrated unit starter/AC synchronous generator S/G AC (with respect to advanced aircraft concept in the field of more/all electric power MEA/AEA) was highlighted. In addition, through the analysis and selected simulations of the power supply system of a modern aircrafts, sources of onboard electrical energy (synchronous generator, integrated unit starter/AC generator) were located in board autonomic power system ASE (EPS, PES). Key components of this system are the electro-energetic power system EPS and the energo-electronic power system PES. Additionally, the analysis and exemplary simulations of key electricity sources based on mathematical models have contributed to highlighting the main practical applications in line with the trend of a more electric aircraft.
Simulations and experimental evaluation of an active orthosis for interaction in virtual environments
Authors: Tsveov Mihail , Venev Pavel , Chakarov Dimitar , Veneva Ivanka
Published: January 2018

In this work, the development of a human arm active orthosis is presented. The orthosis is designed primarily for training and rehabilitation in virtual environments.The orthosis system is intended for embodiment in virtual reality where it is allowing human to perceive forces at different body parts or the weight of lifted objects. In the paper the choice of a mechanical structure is shown equivalent to the structure of the human arm. A mechanical model of the orthosis arm as haptic device is built, where kinematic and dynamic parameters are evaluated. Impedance control scheme is selected as the most suitable for force refection at the hand or arm. An open-loop impedance controller is presented in the paper. Computer experiments are carried out using the dimensions of a real arm orthosis. Computer experiments have been carried out to provide force reflection by VR, according to virtual scenario. The conducted simulations show the range of the forces on the operator hand, orthosis can provide. The results of additional measurements and experimental evaluations of physical quantities in the interaction in a virtual environment are revealed in the paper.
On the effects from the simultaneous occurrence of the critical Casimir and dispersion forces between conical colloid particle and a thick plate immersed in nonpolar critical fluid
Authors: Valchev Galin
Published: January 2018

Here we study the interplay between the van der Waals (vdWF) and critical Casimir forces (CCF), as well as the total force (TF) between a conical colloid particle and a thick planar slab. We do that using general scaling arguments and mean-field type calculations utilizing the so-called “surface integration approach”, a generalization of the well known Derjaguin approximation. Its usage in the present research, requires knowledge on the forces between two parallel slabs, confining in between some fluctuating fluid medium characterized by its temperature T and chemical potential μ. The surfaces of the colloid particle and the slab are assumed coated by thin layers exerting strong preference to the liquid phase of a simple fluid, or one of the components of a binary mixture, modeled by strong adsorbing local surface potentials, ensuring the so-called (+,+) boundary conditions. On the other hand, the core region of the slab and the particle, influence the fluid by long-ranged competing dispersion potentials. We demonstrate that for a suitable set of colloid-fluid, slab-fluid, and fluid-fluid coupling parameters the competition between the effects due to the coatings and the core regions of the objects, result, when one changes T or μ, in sign change of the Casimir force (CF) and the TF acting between the colloid and the slab. Such an effect can provide a strategy for solving problems with handling, feeding, trapping and fixing of microparts in nanotechnology.
Theoretical-experimental method of multiscale modelling of two-component materials
Authors: Baltov Anguel , Yanakieva Ana
Published: January 2018

Modern mechano-mathematical models of materials are multilevel ones combining macro-, meso- and micro-level models. A major problem however is how to present a clear link between the levels. Moreover, structural models should be well verified, reflecting material behavior at meso-level and its microstructure. Hence, we propose a theoretical-experimental approach to multilevel modeling, treating discs which operate under plane stress. The approach comprises the following stages: I stage: Identify a system of characteristic points on the disc surface. Employing an appropriate optical method, find point displacements using time steps in the course of deformation. II stage: Based on displacement development in time, rationally find the variation of the strain tensor components using strains directed from the main point to the closest points of its vicinity. III stage: Define a meso-representative element in the disc plane as an ellipse with diameters related to the principal strains. IV stage: Having prepared metallographic micro-sections, define systems of characteristic structural elements in the meso-representative ellipses. V stage: Averaging the structural systems at meso-level, define macro-parameters involving material deformation parameters. VI stage: Find material macro-deformation parameters on the basis of an appropriate design of micro-representative elements and calculate the stressed-strained state of the latter applying representative loading. A test example is give in order to illustrate the approach.
A correlation between fracture toughness and cohesion strength of molybdenum thermal sprayed coatings
Authors: Paraschiv Alexandru , Matache Gheorghe , Puscasu Cristian , Grigorescu Mihaela
Published: January 2018

The Molydenum thermal sprayed coatings on steel substrate using electric arc, atmospheric plasma spray and high velocity oxy-fuel spray were investigated. The tensile bond strength tests were made in order to examine the degree of adhesion/cohesion strength of coatings. The Vickers indentation fracture toughness tests were made on parallel and perpendicular direction to the coating-substrate interface in order to examine the fracture toughness of the material in relationship with the microstructure, indentation direction, hardness and the length of microcracks developed under different loads. It was found that the fracture toughness is influenced by the direction and load of indentation. It was established a correlation between the fracture toughness and cohesion strength of Mo coatings and a general trend was described
Some specifics considering the urban territories river discharge determination
Authors: Chilikova-Lubomirova Mila , Constantin Diaconu Daniel
Published: January 2018

Urban territories are specific territories with a significant anthropogenic influence on the natural environment. As a result most of the existing natural conditions have been modified. Parts of them cover the natural forms of river beds and floodplains. Concerning to the humans safety, comfort and needs, while keeping ecosystems healthy function, different artificial structures also have been created. The process is connected to the well understanding and good quality data obtaining about the existing conditions and river flow behaviour, that are interconnected and relevant to the river discharge determination and its variations description – key issue for the entire river structures project, water extremes mitigation and maintaining a healthy state of the ecosystems. For the purpose various contact measurements and monitoring procedures are implemented. To clarify the process this material aims to present some specifics connected to the urban territories river discharge determination and the possibility for related monitoring networks creation. It is focused on the most used methods, their specifics and possible challenges for practical application. Main specifics connected to the related decision support systems creation and implementations are also presented. Main purpose is such state of the art dissemination, in help of decision makers and professionals in the area.
River Hydraulics during Flood Events: The Balkan Experiences
Authors: Chilikova-Lubomirova Mila , Zaimes George
Published: January 2018

Nowadays the appearances of water extremes are frequently observed mainly because of anthropogenic and climate change influences. These extremes cause various impacts on the environment. With respect to river systems, floods are such events that are characterized with increasingly untypical high water levels that overflow river beds. In many cases, they cause extremely harmful impacts to human societies, accompanied with serious environmental damages and modifications. This paper focus on the problems connected to flood appearances and some of their possible related impacts on river systems. To better understand these, phenomenon main specifics with regard to its occurrence, behavior and possible consequences are summarized. Most commonly used methods for flood assessments are presented. Some real case floods and their impacts on the river hydraulics from the Balkans are briefly presented. To better explain floods and the reason-outcome-mitigation nexus related recent required and adopted EC, Bulgarian and Greece policies and practices in the area are outlined concisely with regard to prevention measures in the form of early warning systems, river restoration etc. The presented information address the experts in regards to knowledge, practices dissemination and enhancement, and the connection between experts and responsible decision makers that deal with flood mitigation and prevention.
Experimental and numerical investigation of plasma parameters in the magnetosheath
Authors: Dobreva Polya , Kartalev Monio , Nitcheva Olga , Borodkova Natalia , Zastenker Georgy
Published: January 2018

We investigate the behaviour of the plasma parameters in the magnetosheath in a case when Interball-1 satellite stayed in the magnetosheath, crossing the tail magnetopause. In our analysis we apply the numerical magnetosheath-magnetosphere model as a theoretical tool. The bow shock and the magnetopause are self-consistently determined in the process of the solution. The flow in the magnetosheath is governed by the Euler equations of compressible ideal gas. The magnetic field in the magnetosphere is calculated by a variant of the Tsyganenko model, modified to account for an asymmetric magnetopause. Also, the magnetopause currents in Tsyganenko model are replaced by numericaly calulated ones. Measurements from WIND spacecraft are used as a solar wind monitor. The results demonstrate a good agreement between the model-calculated and measured values of the parameters under investigation.
Kamchia watershed groundwater recharge assessment by the CLM3 model
Authors: Nitcheva Olga , Milev Borislav , Trenkova Tanya , Philipova Nina , Dobreva Polya
Published: January 2018

Estimating groundwater recharge is an important part of the water resources evaluation. In spite of the numerous existing methods it continues to be not easy value to quantify. This is due to its dependence on many meteorological, hydrogeological, soil type and cover conditions and the impossibility for direct measurement. Employment of hydrological models in fact directly calculates the influence of the above cited natural factors. The Community Land Model (CLM3) being loaded with all land featuring data in global scale, including an adequate soil filtration process simulation by the Richards equation, together with the possibility for input of NCEP/NCAR Reanalyses database, featuring the meteorological effect, gives an opportunity to avoid to great extent the difficulties in groundwater (GW) recharge estimation. The paper presents the results from an experiment concerning GW recharge monthly estimation during 2013, worked out for the Kamchia river watershed in Bulgaria. The computed monthly and annual values are presented on GIS maps and are compared with existing assessments made by other methods. It is proved the good approach and the applicability of the method.
Effect of post type on the fracture resistance of endodontically treated premolars
Authors: Karteva Ekaterina , Manchorova Neshka , Pashkouleva Dessislava , Keskinova Donka , Vladimirov Stoyan
Published: January 2018

Endodontically treated teeth (ETT) are more susceptible to fracture during mastication. The aim of our study was to investigate the fracture resistance of premolars, restored with different techniques. Eighteen human premolars, extracted for orthodontic or periodontal reasons, were used. Mesio-occlusal cavities were prepared on all of them. They were divided into 3 groups according to the restoration method: with a cemented fiber post (FP), with a cemented metal post (MP) and without a post, but restored with a fiber reinforced composite core (FRC). After thermocycling, their fracture resistance was evaluated in a standard testing machine. The results were analyzed with one-way ANOVA and Tukey Honestly Significant Difference (HSD) tests (p<0.05). The fracture modes were also determined. The MP group showed the lowest fracture resistance rates and the highest number of unrestorable root fractures. In conclusion, teeth restored with FRC cores or FP show better survival rates than those restored with metal posts.
Biomechanical modelling of bile flow in the biliary system
Authors: Kuchumov Alex
Published: January 2018

The biliary system consists of the biliary tree, gallbladder and major duodenal papilla. Soft tissues compliance plays important role in the bio-fluids transport. Particularly, bile flow disturbances due to bile duct wall motor function changes in the extra-hepatic ducts, from medicine point of view are called dyscinesia of biliary tract. Fluid motion in the elastic and compliant ducts can be described by different models (for example, Windkessel model, peristaltic fluid motion, FSI algorithm). Our approach is decomposition of the biliary system into three compartments (extra-hepatic biliary tree, gallbladder, major duodenal papilla). Bile flow in the extra-hepatic ducts is simulated using FSI algorithm. Bile flow in the gallbladder can be described as flow in the reservoir with compliant ducts using Windkessel model. Bile flow in the major duodenal papilla is considered as peristaltic fluid motion, because the wall contraction is really important factor of fluid motion in that segment. The coupling of these compartments is performed by boundary conditions. The biliary system geometry was obtained using MRI patient-specific data. It was confirmed that normal bile can be modeled as Newtonian fluid and lithogenic bile can be modeled as non-Newtonian fluid (Carreau fluid). Bile ducts were modeled as hyperelastic material.
Studying the effect of elastic-plastic strain and hydrogen sulphide on the magnetic behaviour of pipe steels as applied to their testing
Authors: Povolotskaya Anna , Gorkunov Eduard , Zadvorkin Sergey , Veselov Igor
Published: January 2018

The paper reports results of magnetic measurements made on samples of the 12GB pipe steel (strength group X42SS) designed for producing pipes to be used in media with high hydrogen sulphide content, both in the initial state and after exposure to hydrogen sulphide, for 96, 192 and 384 hours under uniaxial elastic-plastic tension. At the stage of elastic deformation there is a unique correlation between the coercive force measured on a minor hysteresis loop in weak fields and tensile stress, which enables this parameter to be used for the evaluation of elastic stresses in pipes made of the 12 GB pipe steel under different conditions, including a hydrogen sulphide containing medium. The effect of the value of preliminary plastic strain, viewed as the initial stress-strain state, on the magnetic behaviour of X70 pipe steels under elastic tension and compression is studied. Plastic strain history affects the magnetic behaviour of the material during subsequent elastic deformation since plastic strain induces various residual stresses, and this necessitates taking into account the initial stress-strain state of products when developing magnetic techniques for the determination of their stress-strain parameters during operation.
High-speed deformation of copper samples with the use of magnetic pulse method
Authors: Krivosheev Sergey , Magazinov Sergey , Alekseev Dmitrii
Published: January 2018

The possibility of using the magnetic pulse method for studying the high-speed deformation modes of metals with strain rates up to 100,000 1/s without a preliminary phase of material compression under loading in the microsecond range of durations is shown. 3D calculation of the magnetic field and deformation modes has shown the possibility of creating loading schemes that are free of induced currents in the sample in the zone of maximum mechanical stresses. The first experiments show the need for verification of the Jones-Cook model at high deformation rates.
Application of Synthetic Aperture Focusing Technique for inspection of plate-like structures using EMAT generated Lamb waves
Authors: Mirchev Yordan , Staykov Krasimir , Ganchev Damyan
Published: January 2018

The main challenge for guided wave inspection is exact defect characterization and sizing. EMAT generated Lamb waves usually have low signal-to-noise ratio which reduces the defect detection, characterization and sizing capabilities. That's why in most cases the method is used only as a screening tool. The Synthetic Aperture Focusing Technique is a process that increases the signal-to-noise ratio by numerically focusing the acoustic fields. In this paper the application of SAFT is tested over EMAT generated Lamb waves. The improvement of lateral resolution and signal-to-noise ratio is evaluated. Results are presented as a comparison between standard B-scan and SAFT processed data.
Mechanical properties of composite coatings of chromium and nanodiamonds on aluminum
Authors: Gidikova Nelly , Sulowski Maciej , Madej Marcin , Valov Radoslav , Petkov Vladimir
Published: January 2018

Aluminum offers engineers weight saving advantages in their product design. However, aluminum has poor wear and friction properties. In addition, the surface oxide layer of this chemically active metal, which gives it the corrosion resistance, makes it a very difficult metal to plate [1]. Specific pre-treatment must be applied to remove the oxide layer from the aluminum surface. The nanodiamond particles additionally facilitates the process of chromium deposition. The object of this study is to evaluate the impact of nanodiamonds on the mechanical properties of the chromium coating plated on
Airborne sound insulation of new composite wall structures
Authors: Ivanova Yonka , Partalin Todor , Lakov Luben , Jivov Bojidar
Published: January 2018

Protection against noise is one of the essential requirements of the European Construction Product directive. In buildings, airborne sound insulation is used to define the acoustical quality between rooms. In order to develop wall structures with optimal sound insulation, an understanding of the physical origins of sound transmission is necessary. To develop a kind of knowledge that is applicable to the improvement of real walls and room barriers is the motive behind this study. The purpose of the work is to study the sound insulation of new composite wall structure.
Ageing management in NPP. Effectiveness of the methods for control, examination and monitoring in relation to mechanisms of degradation of mechanical properties
Authors: Dimova Galya
Published: January 2018

This paper describes ageing management activities for Long Term Operation (LTO) of components of Kozloduy NPP EAD. The stages of LTO Project are: Stage 1 - implementing a comprehensive assessment of the actual condition of the equipment; Stage 2 - providing of a Complex Analysis; Stage 3 – licensing of Plant Life Extension (PLEX) for long-term operation (LTO). The main activities are assessment of actual condition of the equipment and building; review of methods for control (non-destructive), examination and monitoring; assessment of effectiveness of methods; necessity of additional control/ examination/ service. The paper describes some mechanisms of degradation of mechanical properties, methods for control and criterions for their effectiveness.