bluuebunny/crossref_metadata_2025 huggingface dataset:
NON-DESTRUCTIVE EVALUATION OF MECHANICAL DAMAGE OF ADHESIVES USING MAGNETO-ELECTRIC NANOPARTICLES
Authors: SEISDEDOS GONZALO , HERNANDEZ BRIAN , DUBON JULIETTE , ONTIVEROS MARIANA , BOESL BENJAMIN , MCDANIEL DWAYNE
Published: November 2021

Adhesive bonding has been shown to successfully address some of the main problems with traditional fasteners, such as the reduction of the overall weight and a more uniformly distributed stress state. However, due to the unpredictability of failure of adhesive bonds, their use is not widely accepted in the aerospace industry. Unlike traditional fastening methods, it is difficult to inspect the health of an adhesive joint once it has been cured. For adhesive bonding to be widely accepted and implemented, there must be a better understanding of the fracture mechanism of the adhesive joints, as well as a way to monitor the health of the bonds nondestructively. Therefore, in-field structural health monitoring is an important tool to ensure optimal condition of the bond is present during its lifetime. This project focuses on the advancement of a non-invasive field instrument for evaluation of the health of the adhesive joints. The tool developed is based on a B-H looper system where coils are arranged into a noise-cancellation configuration to measure the magnetic susceptibility of the samples with a lock-in amplifier. The B-H looper system can evaluate the state of damage in an adhesive bond by detecting changes in surface charge density at the molecular level of an epoxy-based adhesive doped with magneto-electric nanoparticles (MENs). Epoxy-based adhesive samples were doped with MENs and then scanned using the B-H looper system. To evaluate the health of the adhesive joint, microindentation and tensile tests were performed on MENs-doped adhesive samples to understand the relationship between mechanical damage and magnetic signal. Correlations between magnetic signatures and mechanical damage were minimally observed, thus future studies will focus on refining the procedure and damaging methodology.
CLASSIFICATION OF BUCKLING MODES IN STIFFENED FUNCTIONALLY GRADED COMPOSITE TUBES SUBJECT TO BENDING
Authors: TRINH LUAN , WEAVER PAUL
Published: November 2021

Bamboo poles, and other one-dimensional thin-walled structures are usually loaded under compression, which may also be subject to bending arising from eccentric loading. Many of these structures contain diaphragms or circumferential stiffeners to prevent cross-sectional distortions and so enhance overall load-carrying response. Such hierarchical structures can compartmentalize buckling to local regions in addition to withstanding global buckling phenomena. Predicting the buckling mode shapes of such structures for a range of geometric parameters is challenging due to the interaction of these global and local modes. Abaqus finite element software is used to model thousands of circular hollow tubes with random geometric parameters such that the ratios of radius to periodic length range from 1/3-1/7, the ratio of wall thickness to radius varies from 1/4-1/10. The material used in this study is a type of bamboo, where the Young’s and shear moduli are point-wise orthotropic and gradually increase in magnitude in the radial direction. Under eccentric loads with varying eccentricity, the structures can buckle into a global mode or local modes within an internode, i.e. periodic unit. Moreover, the local modes may contain only one wave or multiple waves in the circumferential direction. As expected, numerical results show that the global mode is more likely to occur in small and thick tubes, whereas the local modes are observed in larger tubes with a smaller number of circumferential waves present in thicker walls. Also, greater eccentricity pushes the local mode domains towards smaller tubes. An efficient classification method is developed herein to identify the domains of each mode shape in terms of radius, wall thickness and eccentricity. Based on linear discriminant analysis, explicit boundary surfaces for the three domains are defined for the obtained data, which can help designers in predicting the mode shapes of tubular structures under axial bending.
EXPERIMENTAL EVALUATION OF COMPRESSIVE STRENGTH OF PAN-BASED CARBON MONOFILAMENT BY POISSON’S DEFORMATION IN CRUCIFORM SPECIMEN
Authors: ODAIRA, YUSUKE , SAITO HIROSHI , KIMPARA ISAO
Published: November 2021

Carbon fiber has relatively high anisotropy in tensile and compressive strength. Since, the diameter of carbon fiber is 5~10[μm], it is difficult to directly evaluate the compressive strength of monofilament. In this study, the compressive strength of carbon single fiber was evaluated using Poisson's deformation of Cruciform specimen. Using the Cruciform test method, the compressive strengths of monofilaments of PAN-based carbon fibers, T300B and T700SC, were experimentally and analytically evaluated. As a result, the compressive strengths of carbon single fibers was 5.12 [GPa] for T300/PA6 and 5.54 [GPa] for T700/PA6 in this study.
AERO-THERMO-DYNAMIC STUDY OF ULTRA-HIGH- TEMPERATURE CERAMIC COMPOSITES FOR THERMAL PROTECTION SYSTEMS AND ROCKET NOZZLES
Authors: MUNGIGUERRA STEFANO , CECERE ANSELMO , SAVINO RAFFAELE
Published: November 2021

The most extreme aero-thermo-dynamic conditions encountered in aerospace applications include those of atmospheric re-entry, characterized by hypersonic Mach numbers, high temperatures and a chemically reacting environment, and of rocket propulsion, in which a combusting, high-pressure, supersonic flow can severely attack the surfaces of the motor internal components (particularly nozzle throats), leading to thermo-chemical erosion and consequent thrust decrease. For these applications, Ultra-High-Temperature Ceramics (UHTC), namely transition metal borides and carbides, are regarded as promising candidates, due to their excellent high-temperature properties, including oxidation and ablation resistance, which are boosted by the introduction of secondary phases, such as silicon carbide and carbon fibers reinforcement (in the so-called Ultra-High- Temperature Ceramic Matrix Composites, UHTCMC). The recent European H2020 C3HARME research project was devoted to development and characterization of new-class UHTCMCs for near-zero ablation thermal protection systems for re-entry vehicles and near-zero erosion rocket nozzles. Within the frame of the project and in collaboration with several research institutions and private companies, research activities at the University of Naples “Federico II” (UNINA) focused on requirements definition, prototypes design and test conditions identification, with the aim to increase the Technology Readiness Level (TRL) of UHTCMC up to 6. Experimental tests were performed with two facilities: an arc-jet plasma wind tunnel, where small specimens were characterized in a relevant atmospheric re-entry environment (Fig.1a), and a lab-scale hybrid rocket engine, where material testing was performed with different setups, up to complete nozzle tests, in conditions representative of real propulsive applications (Fig.1b). The characterization of the aero-thermo-chemical response and ablation resistance of different UHTCMC formulations was supported by numerical computations of fluiddynamic flowfields and materials thermal behavior. The UNINA activities provided a large database supporting the achievement of the project objectives, with development and testing of full-scale TPS assemblies and a large-size solid rocket nozzle.
PROCESSING OF ULTRA-HIGH TEMPERATURE CERAMIC MATRIX COMPOSITES (UHTCMCS) THROUGH RF ENHANCED CHEMICAL VAPOUR INFILTRATION (RF-CVI)
Authors: VENKATACHALAM, VINOTHINI , BINNER JON , REIMER THOMAS , ESSER BUCKARD , MUNGIGUERRA STEFANO , SAVINO RAFFAELE
Published: November 2021

Carbon fibre (Cf) reinforced Ultra High Temperature Ceramic (UHTC) Matrix Composites (UHTCMCs) have proven to be excellent materials that can survive nearly 3000°C in highly oxidizing environments along with a good specific strength. Consequently, they have excellent potential for use in aerospace applications such as rocket nozzle throats and thermal protection systems (TPS). Due to the presence of the carbon fibres, UHTCMCs offer high strength and modulus combined with excellent thermal shock behaviour whilst the presence of the ultra-high temperature ceramic phase protects the carbon fibres at the application temperatures. High temperature oxidation, thermal ablation behaviour and mechanical properties of the UHTCMC’s relies heavily on the bonding between the carbon fibre and matrices especially the oxides formed to avoid any progressive failure and predict the life of the components. In the present investigation, a radio frequency assisted chemical vapor infiltration (RF-CVI) technique has been used to make the 2.5D Cf reinforced ZrB2, ZrB2/carbon matrices composites with various interphase materials. The advantage of RF heating is that it creates an inverse temperature profile in the sample, which means that the infiltration starts from inside and progresses outwards. This allows the time needed for processing to be reduced very significantly compared to the conventional CVI process. This presentation will report on the latest results from the research that has been undertaken at the University of Birmingham, including the results from a wide range of testing that has been undertaken at both DLR in Germany and the University of Naples in Italy.
FABRICATION AND CHARACTERIZATION OF UHTCMCS
Authors: VINCI ANTONIO , ZOLI LUCA , GALIZIA PIETRO , SILVESTRONI LAURA , GUTIÉRREZ CARLOS , RIVERA SERGIO , SCITI DILETTA
Published: November 2021

The materials currently used in aerospace and aviation, such as C/C and C/SiC composites, possess excellent mechanical properties but are limited to a maximum operational temperature of 1600°C (C/SiC) and poorly oxidizing environments (C/C). For more demanding applications, new materials able to withstand extreme temperatures without recession are required. In the framework of the C3harme project, a new class of materials labelled UHTCMCs, consisting of a UHTC matrix reinforced with carbon fibers, has been developed and characterized in order to overcome these challenges. Different fiber reinforcements and sintering parameters have been investigated from the microstructural point of view. The composites were fabricated via slurry infiltration of fiber, using a powder mixture of ZrB2 and SiC; the green pellets were then sintered via hot pressing. Extensive microstructural analysis was carried out on the sintered samples, showing how the sintering parameters and the choice of the fibers are crucial to obtain full densification without jeopardizing the fibers integrity and permit adequate load transfer.
EFFECT OF CURING TEMPERATURE OF EPOXY RESIN ON THE ELECTRICAL RESPONSE OF CARBON NANOTUBE YARN MONOFILAMENT COMPOSITES
Authors: RODRIGUEZ-UICAB OMAR , ABOT JANDRO L. , AVILÉS FRANCIS
Published: November 2021

The cyclic thermoresistive response of individual carbon nanotube yarns (CNTYs) embedded into epoxy resins is investigated. The influence of the temperature at which the epoxy resin cures on the thermoresistive response is investigated by using two epoxy resins, one that cures at room temperature and the other one that cures at 130 °C. Heating-cooling cycles ranging from room temperature (RT, 25 °C) to 80 °C, incremental cycles (RT to 40 °C, RT to 60 °C and RT to 80 °C) and incremental heating-dwell cycles are applied to monofilament composites, while their electrical resistance is simultaneously recorded. The monofilament composites showed a negative temperature coefficient of resistance during the heating-cooling cycles of -7.07x10-4 °C-1 for specimens cured at high temperature, and -5.93x10-4 °C-1 for specimens cured at room temperature. The hysteresis after the different heating-cooling cycles was slightly smaller for specimens cured at 130 °C, in comparison to specimens cured at room temperature. Several factors including the intrinsic thermoresistivity of CNTY, level of infiltration and the effect of curing temperature may explain the thermoresistive sensitivity of the monofilament composites.
HIERARCHICAL ELECTROSPUN VEILS AS POTENTIAL TOUGHENING MATERIALS FOR STRUCTURAL COMPOSITE LAMINATES
Authors: BAVASSO IRENE , SBARDELLA FRANCESCA , BRACCIALE MARIA PAOLA , TIRILLÒ JACOPO , PALMA LUCA DI , LAMPANI LUCA , SARASINI FABRIZIO
Published: November 2021

The use of fiber reinforced polymers (FRPs) as a replacement of traditional homogeneous materials is still hindered by their brittle behavior and poor interlaminar resistance. Interleaving veils in polymer matrix, especially with fibers at the nanoscale dimension, is considered as one of the most promising toughening methods. By considering the hierarchical nature of the resulting laminated composites, their properties are intrinsically dependent on the interaction between the nanofibrous veils and the thermosetting resin and, in an attempt to tailor the interfacial adhesion between the electrospun fibers and matrix, surface modification of the fibers with the integration of inorganic nanostructures could be a solution. This work is an investigation on the use of commercially available electrospun nylon nanofibers decorated with ZnO nanorods obtained by three-step chemical synthesis. The modified veils were interleaved in carbon/epoxy prepreg composites and their mechanical properties were evaluated under Low Velocity Impact (LVI) tests at different energy levels (5 J and 7.5 J). Although the presence of ZnO nanorods did not limit the extension of the delaminated area in case of high energy level test (7.5 J), nanomaterials contributed positively to reduce the extent of the damaged area when a low energy impact was adopted (5 J). A beneficial effect of ZnO-functionalized commercial electrospun veils was observed in the flexural strength of laminated composites. After LVI tests at 5 J and 7.5 J, the flexural strength resulted higher compared to that observed in the same tests on specimens with non-decorated veils (NY4M), thus suggesting a positive role played by ZnO nanorods in hindering delamination propagation.
MODE-I FATIGUE CRACK HEALING IN CFRP COMPOSITES USING THERMOPLASTIC HEALANT
Authors: VISHE NILESH J. , MULANI SAMEER B. , ROY SAMIT
Published: November 2021

Mode-I fatigue crack healing in carbon fiber-reinforced polymer (CFRP) composites subjected to fatigue loading is investigated in this study. Laminated composites are highly susceptible to delamination, and delamination due to fatigue loading is one of the most critical damage modes in composite structures that may lead to a catastrophic failure. Hence, it is paramount to investigate and quantify the delamination crack growth behavior due to fatigue loading and explore methods to heal the delamination. Therefore, double cantilever beam (DCB) specimens of a carbon fiber-reinforced thermoset polymer (CFRP) composite containing thermoplastic healants were manufactured. Mode- I fatigue delamination experiments were carried out for virgin (initial case) and up to seven repeated healing cycles. The main objective of using thermoplastic healants, i.e., polycaprolactone (PCL) and shape memory polymer (SMP), was to close and then heal the cracks formed during fatigue loading and retain the fatigue life of the DCB specimen. The in-situ healing was achieved by activating macro fiber composite (MFC) actuators bonded to the DCB specimen, where the high frequency vibration of the actuator provides the heat necessary to close the cracks using thermoplastic healants. The insitu healing was triggered using MFCs after 5000 cycles of initial loading to allow initial crack extension. The DCB specimen was then loaded up to half a million cycles to study the effect of healing on fatigue life. From the experimental data of the virgin and healed specimens, the Paris law parameters were extracted, and the results obtained were repeatable. Significant increase in maximum Mode-I strain energy release rate (G ) observed after in-situ healing is likely due to the increase in the bond stiffness of the DCB specimen material of the healed zone. More research is needed to investigate the exact mechanism for the increase of G . Mode-I fatigue life improvement of up to a factor of 2 was observed after in-situ healing for the same delamination crack growth with respect to the virgin cycle prior to healing. We envision that these findings will be helpful in extending the service life of composites and result in significant repair cost savings.
RESIDUAL PLASTIC STRAIN STATE AND DELAMINATION PATTERN OF COMPOSITE LAMINATES WITH AUTOMATED INDUCED-GAP SUBJECTED TO HEMI-SPHERICAL IMPACT LOADING
Authors: GHAYOUR MOHAMMADHOSSEIN , HOJJATI MEHDI , GANESAN RAJAMOHAN
Published: November 2021

Automated manufacturing defects are types of composite structure defects that occur during fiber deposition by advanced robots. The induced gap is the most probable type of defect in the Automated Fiber Placement (AFP) technique. This defect can affect the mechanical performance of the composite structures at both material level by inducing the material inhomogeneity and the structural level by introducing the consolidation effect in the structure during the curing process. The current study investigates the effect of induced-gaps on the damage assessment of thin composite plates under Low-Velocity Impact (LVI) loading. The paper focuses on the delamination initiation and propagation and the residual plastic strain state of the impacted plates. The primary application of this study is to understand the interaction of induced gaps on the delamination pattern of composite samples subjected to LVI. For this purpose, a series of LVI tests are performed. Ultrasonic C-scan analysis and microscopic observation are implied to evaluate the internal damage due to impact loading. Finite Element (FE) analyses are then performed to evaluate the residual strain of the composite plates under Impact Energy (IE) loading less than 15 J. Then, the residual plastic strain in the impact zone is evaluated using a meso-macro method, and the effect of the local plasticity that occurs in the gap zones on the delamination initiation and propagation is studied. Results show that the stress relaxation due to the resin plasticity at the gap areas can affect the delamination pattern of the impacted composite plates. It is also shown that the residual strain of the impacted plates at the gap areas are new sources of the damages that need to be considered in the LVI analysis of the composite plates manufactured by the AFP technique.
EFFICIENT NUMERICAL ANALYSIS BASED ON PERTURBATION METHOD FOR THE EFFECT OF WAVINESS IN CFRP
Authors: SUGIURA TAKANORI , YOSHIMURA AKINORI , ARAI MASAHIRO , GOTO KEITA
Published: November 2021

The paper proposes a numerical multiscale homogenization method for carbon fiber reinforced composites, where fiber alignment is disturbed due to unintended imperfections (fiber waviness). Imperfection is introduced as input to the calculation, and the calculation is always done using idealized perfect geometry. This has a distinct advantage in numerical calculations where the same mesh can be used for a series of imperfect geometries. The calculation is based on second-order perturbation method in order to capture the anisotropy which is the feature of CFRP. The proposed method is validated by comparing the results to those of a conventional calculation. The results demonstrate that the proposed method can accurately capture the stress distribution when the amplitude of the imperfection is small.
MICROSTRUCTURAL SIMULATION OF SUPERELASTIC ZIRCONIA-REINFORCED METAL COMPOSITE FOR ENERGY DISSIPATION APPLICATIONS
Authors: YACOUTI, MARWA , SHAKIBA MARYAM
Published: November 2021

This paper studies the mechanical properties of superelastic zirconia-reinforced aluminum-matrix composites through finite element simulations of microstructural representations. The objective of this study is to exploit the reversible phase transformation of zirconia to develop a composite with improved strength and energy dissipation capacity. Zirconia is a shape memory ceramic with promising potential in actuation, energy damping, and fatigue applications. Compared to the most commonly used shape memory alloys, zirconia is distinguished by a wider operational temperature range, higher recoverable strains, and a larger energy dissipation. The two-phase composite studied in this work consists of 16 mol% ceria-doped zirconia particles embedded in an aluminum matrix. The behavior of zirconia is simulated using the isothermal superelastic constitutive relationship proposed by Auricchio and Taylor. A series of numerical simulations is conducted to examine the effects of the matrix yield stress as well as the particles’ diameter and volume fraction on the evolution of the phase transformation, the strength, and the energy dissipation of the composite. A random generating algorithm is used to produce the locations of zirconia reinforcing particles. The results indicate that zirconia-reinforced aluminum-matrix composite exhibits enhanced strength and energy dissipation. The incorporation of 50% zirconia volume fraction improves the maximum stress by 50% while the amount of energy dissipation is increased by 24%. This paper provides insight into the potential application of zirconia-based composites for an efficient damping response.
EXPERIMENTAL INVESTIGATION OF HIGH VELOCITY IMPACT ON CNT REINFORCED COMPOSITES EMPLOYING SINGLE STAGE GAS GUN
Authors: MUNIRAJ D. , MUGHILARASAN S. , SREEHARI V. M.
Published: November 2021

Composite plays a significant role in the field of aerospace due to its excellent mechanical properties, nevertheless, they are highly susceptible to out-of-plane impact load. Fibre-reinforced composite fails effortlessly under impact load and absorb energy through damage mechanics rather than deformation. The present study investigates the damage behaviour of the CNT reinforced carbon fibre-epoxy composite under high velocity impact using single stage gas gun. Composite plates were fabricated with 0 to 0.6 weight percentage content of CNT as reinforcement using vacuum assisted resin transfer moulding. A series of impact test with various impact energy was carried out on carbon/epoxy composite plate to study the impact performance. From the experimentation it was observed that the 0.3 weight percentage CNT addition provides the optimum impact performance. Damage characterization was performed for various impact velocity based on the micro and macro scale damage area. Knowledge of the damage behaviour of CNT reinforced carbon fibreepoxy composite plate under high velocity impact loads is essential for both the product development and material selection in the aerospace application.
STRAIN RATE-DEPENDENT CHARACTERIZATION OF THE IN-PLANE SHEAR RESPONSE OF A UNIDIRECTIONAL NON-CRIMP FABRIC CARBON FIBER/SNAP-CURE EPOXY COMPOSITE
Authors: ROUF KHIZAR , WORSWICK MICHAEL J. , MONTESANO JOHN
Published: November 2021

The dynamic in-plane shear stress-strain response of a unidirectional non- crimp fabric carbon fiber/snap-cure epoxy composite was studied by subjecting 30° and 45° off-axis specimens to compression loading at high strain rates. Tests were performed using a compression split-Hopkinson pressure bar apparatus where an approximate axial strain rate of 305 s-1 was achieved. Images of the deformed specimen surfaces were captured with high-speed cameras and digital image correlation used to obtain a strain map. Pulse shaping was performed using a copper pulse shaper to achieve dynamic equilibrium during the high-rate tests. The results demonstrated that the in-plane shear yield stress and strength increased by 53% and 68%, respectively, when the strain rate increased from quasi-static to 305 s-1.
HIGH ENERGY WIDE AREA BLUNT IMPACT OF COMPOSITE AIRCRAFT STRUCTURES PART B: TESTING AND INTERNAL DAMAGE MODES
Authors: NAM MOONHEE , SOUZA CHAIANE WIGGERS DE , KIM HYONNY
Published: November 2021

Modern aircraft structures constructed from high strength laminated composite materials present a challenge in the detection of damage resulting from impact events. Broad-area contact from large sized or blunt radius objects furthermore create conditions in which significant internal damage can result, while leaving low (or even no) externally visible indications of damage being present. Composite fuselage structures subjected to high energy wide area blunt impact (HEWABI) sources have been studied. These impact sources act over a wide area and can possibly damage multiple internal structural elements. HEWABI sources of concern are generally heavy ground service equipment (GSE) such as belt loaders, cargo loaders, catering trucks, etc., which have soft rubber/elastomeric bumper-type pads mounted at locations where the GSE could contact the aircraft. Of particular interest in this study is the formation of damage in composite frame and shear tie components during HEWABI events occurring near the passenger floor joint. Carbon/epoxy composite test specimens reflecting modern composite fuselage features were designed and fabricated having continuous shear ties and representative stiffness interaction between the floor beam and circumferential frame members. Quasi-static and slow speed tests (representing impact) conducted using rubber bumper faced indentors developed significant internal damage to internal components. Specifically, fiber failures and large-size crack formation in shear ties, frames, and stringers occurred with low/no external observability in the external skin. A clear quantitative understanding of damage modes and damage location that could result from HEWABI events is important for establishing damage size criteria in the evaluation of a structure’s residual strength and damage tolerance capability.
DYNAMIC FACTURE OF HYDROTHERMALLY DEGRADED CARBON-EPOXY COMPOSITES
Authors: PITTMAN EMILY , KOUMLIS STYLIANOS , LAMBERSON LESLIE
Published: November 2021

Structures used in naval applications are often subjected to marine or other aqueous environments during their work-life. It has been observed that many composites absorb moisture when exposed to such environments, which can lead to material damage and degradation of mechanical properties. The addition of salt to the water solution may have additional impacts on the material degradation over time. Furthermore, many of these applications require that the material be subject to stresswave loading environments like impact that may cause dynamic fracture. In this experimental study, the effect of water absorption on the Mode-I dynamic fracture behavior of carbon-epoxy composites is investigated. Specifically, the effects of moisture uptake and the role of saline on the critical dynamic SIF are investigated. Samples were hygrothermally soaked in an elevated temperature bath (70 °C) of either ASTM standard sea water or distilled water. The elevated temperature accelerates mass absorption, making experimental observation possible on a more reasonable timeline than natural aging. Soaking durations varied between 3.5 hours to excess of 4 months to explore the role of soak time on dynamic fracture behavior. Pre-cracked specimens were impacted using a unique long-bar striker device at 4 m/s, and the resulting Mode-I (opening mode) fracture behavior investigated. Digital image correlation (DIC) was used in conjunction with ultra-high-speed imaging to track the crack tip surface displacements, and an elastodynamic solution was leveraged to extract the stress intensity factors (SIF) at fracture initiation. The dynamic fracture toughness of the soaked samples was compared with results from a group of unsoaked, ambient condition samples. The results indicated that the ambient condition samples had a consistently higher Mode-I SIF than any of the soaked conditions. The difference between the ambient condition SIF and the soaked conditions was observed to be approximately 60% for the 3.5 hour soaks, 40% for the 2 day soaks, 50% for the 2 week soaks, and 80% for the samples soaked for longer than 4 months. The SIF reduction is thought to be due primarily to matrix and interface degradation. No statistically significant difference in the SIF was observed between samples soaked in DI water versus salt water.
Archives and planning for sustainable development models of reality: case study in the archival service of the wilaya of Constantine
Authors: Abada Chahrazed , Delhoum Intissar
Published: November 2021

Interest in archives emerged mainly since the French Revolution. Much more attention was paid to historical documents, especially for their cultural and historical role. In the United States, during the Second World War, attention was much more focused on administrative archives, thanks to Schellenberg's theory of the three ages (1956), which gave a wider opportunity to the application of Archives.In addition, the archive centers have an important role in the administrative processes and in the planning of the various development projects based on the new technologies.On the other hand, sustainable development is defined as development that meets the needs of the present without compromising the ability of future generations to meet their own needs. It is based on a long-term vision that takes into account the indivisibility of the environmental, social and economic dimensions of development activities. And archives are an indispensable tool for improving the political, economic and administrative management of a country.The adoption of good archival management systems makes it possible to quickly find the documents needed to make decisions in an appropriate time, thus improving the efficiency of the administration. Accordingly, the good management of archival documents has a financial impact on administrative efficiency, highlighting the studies and experiments already carried out, rather than repeating them. This saves time, money and work. In contrast, Loss or destruction of archival documents can cause political, administrative, or legal management difficulties and thus harm the state.We adopted the descriptive method in addition to conducting interviews with officials in the department in the purpose of collecting the necessary data to discover the extent to which archives contribute in planning sustainable development. We reached,at the end, the conviction that the creation of guidance documents is vital to activate the role of archives in this context.
COVID-19 and Hotel Productivity Changes: An Empirical Analysis Using Malmquist Productivity Index
Authors: Kim Changhee , Kang Hee Jay , Chung Kyunghwa , Choi Kanghwa
Published: November 2021

This research investigates the impact of COVID-19 on hotel productivity change using the Malmquist Productivity Index (MPI). For 26 U.S. hotel brands, productivity changes over 10 quarters from the first quarter of 2018 to the second quarter of 2020 were analyzed. After the COVID-19 outbreak, the investigated hotels’ productivity deteriorated. Decomposition revealed that, whereas technical efficiency change (EC) improved, technological change (TC) regressed, resulting in deterioration of the MPI. The investigated hotels’ EC-related practices included enhanced cleaning operations, partnering with a hygiene brand, cutting the workforce, and pay cuts. Practices related to TC included the adoption of new hygiene technology and setting a new standard at the organizational level through the formation of a global council and accreditation related to disinfection and hygiene. Our results show that though U.S. hotels are trying to improve their productivity by efficiently utilizing resources, frontier technology’s regress is decreasing productivity. Our results support the importance of investment in technology for productivity management. This research provides empirical evidence for the need for hotels to pursue technological advances to overcome the pandemic.
MANAGING RISK WITH THE USE OF COMPUTER SIMULATION
Authors: Bučková Monika , Fusko Miroslav , Gabajová Gabriela , Gašo Martin , Mičieta Branislav , Martinkovič Milan
Published: November 2021

Internal and external risk management has become an important issue in today's global business environment, which is fraught with health, natural, political, economic and technical threats. This article deals with the design of a methodology for problem-solving and risk management in connection with computer simulation. The risk management methodology proposed by us consists of individual steps, which are summarized into three stages - risk assessment, risk analysis and risk management. The proposed computer simulation methodology consists of several steps, for example creating a parametric simulation model, designing experiments, analysis of the simulation model results or the evaluation of the simulation results. These steps are described in the article. After completing the previous steps, we describe the points of an action plan and what it must contain to avoid consequences and the impact of risks at the lowest possible level. An example of the use of computer simulation is the risk situation associated with the fluctuation of employees. In the end, the proposed methodology is supported by the results of our research and its further direction.
ASSESSMENT OF SELECTED DETERMINANTS OF BURNOUT SYNDROME AND COPING STRATEGIES IN TERMS OF GENDER IN ENTREPRENEURS
Authors: Čigarská Barbara Nicole , Birknerová Zuzana
Published: November 2021

Nowadays, the issue of burnout syndrome is relatively extensive and increasingly manifested. Although burnout syndrome can affect anyone, certain differences in its occurrence are noticeable, especially in personality traits, gender, or the character of work. This article aims to assess the signals of burnout syndrome and coping strategies in terms of gender. The main determinants of burnout syndrome are Emotional Exhaustion, Depersonalization, and Personal Accomplishment and are included in the Maslach Burnout Inventory, consisting of twenty-two questions, separately dealing with mentioned individual determinants. The Brief Cope inventory, which outlines fourteen strategies about how to cope with stress, was used to find out which coping strategies entrepreneurs used in difficult situations. The research was carried on a representative sample of entrepreneurs (N = 113) in the Slovak Republic by online questionary. The result of the analysis reported the existence of statistically significant differences (p < .05) between determinants of burnout syndrome and coping strategies in terms of gender among entrepreneurs in the assessment of selected determinants. Entrepreneurs used mostly problem-focused coping strategies like Active coping and Planning, an emotion-focused coping strategy of Humor, a dysfunctional coping strategy of Venting to mitigate the influence of difficult situations. The research assumed the existence of positive differences between the assessment of determinants of burnout syndrome in terms of gender. The results reported a higher tendency of female entrepreneurs to be more often emotionally exhausted than males. Personal Accomplishment and Depersonalization did not report any statistically significant differences in terms of gender.
AUGMENTED REALITY AS A POWERFUL MARKETING TOOL
Authors: Gabajová Gabriela , Krajčovič Martin , Furmannová Beáta , Matys Marián , Biňasová Vladimíra , Stárek Marián
Published: November 2021

Today's market is oversaturated with new technologies that are slowly moving through our daily routine. Businesses often have to pursue new strategies to reach new customers and retain existing ones. Popular technologies of today undoubtedly include virtual reality (VR) and augmented reality (AR). The application of augmented reality in the field of trade, marketing, promotion of products and services has its own potential and justification. A questionnaire survey of the current state of  AR utilization in companies of Central Slovakia shows that the interest in the use of this technology exists in this area, although in practice it is implemented rather rarely. However, a suitable design solution and the worldwide trend of smartphone use can help to achieve the goal of greater implementation. The design of the methodology for the use of AR in the field of marketing consist of a sequence of several basic steps. Verification of the proposed methodology is carried out on a practical example by creating a real mobile application using augmented reality to promote the selected product. The final mobile application includes several attractive features for the end-user which can be accessed through a smartphone and displayed in augmented reality. Such a mobile application in augmented reality provides the company with a powerful marketing tool, but it also has its limitations.
WILLINGNESS OF PROFESSIONALS WORKING IN SPECIALIZED HOSPITALS AND SOCIAL SERVICES TO WORK WITH PATIENTS AND CONSUMERS SUFFERING FROM MENTAL ILLNESSES
Authors: Konstantinova Draganova Daniela , Stancheva Angelova-Barbolova Nikolina
Published: November 2021

At the current level of development in psychiatry, in the conditions of deinstitutionalization of mental health services and increased opportunities for control of the symptoms of mental disorders, the problem related to the socialization of patients is becoming more and more relevant. More than 50% of patients with schizophrenia are in a socially active age, which gives rise to the social significance of their rehabilitation.

International practice shows that all specialists dealing with the rehabilitation of patients with mental disorders need to undergo training, which includes the adoption of special methods and techniques. Their work is complex, long and creative.

In Bulgaria there are many national strategies that present different programs for long-term care or only analyze the current situation and care needs. There is no clear vision of how exactly in the future and with what means and specialists this process will take place. The development of psychiatric care lags far behind the needs of the population. There is a serious risk that the lack of trained specialists can ruin the good intentions for deinstitutionalization.

The goal of the present study is to examine the readiness of specialists working in specialized medical institutions and social services to work with patients and users suffering from mental illness.

A survey method was used among specialists from medical institutions and social services for patients with mental and behavioral disorders.

Most of the specialists in psychiatric hospitals in Bulgaria feel prepared to work with the mentally ill - 88.9%;

Almost everyone believes that they need additional training.
THE IMMUNE RESPONSE AGAINST RABIES VIRUS AMONG CANINE DONORS IN A ROMANIAN BLOOD BANK
Authors: Ionescu Teodor-Stefan , Dan Marius , Cobzariu Dragos , Baraitareanu Stelian , Danes Doina
Published: November 2021

INTRODUCTION: Seventy-six samples were collected from sixteen canine blood donors at every blood donation performed in accord with the canine donor selection guidelines. Statistical analysis of ELISA OD values revealed no significant variation of anti-rabies antibodies values during repeat donations. Our results support the statement that blood donation does not affect the immune status of donors.

OBJECTIVES: The study aimed to assess the immune status against rabies among the canine blood donors in a Romanian canine blood bank

METHODS: Serum samples (n=76) were collected from pet owned dogs (n=16) recorded in the blood bank register of a Romanian blood bank were performed with the immunological status of the investigated canine blood donors was evaluated using the indirect ELISA commercial kit PLATELIA RABIES II (BIO-RAD, France) as per the manufacturer's instructions

RESULTS: The overall picture of ELISA OD results revealed non-significant variation between and within D1-D6 groups of values (p>0.05, F<Fcrit).

CONCLUSION: The next studies topic would be to compare the results provided by the ELISA technology with FAVN.
AZADIRACHTA INDICA OIL AS PROTECTOR OF CHRONIC OCHRATOXIN-INDUCED NEPHROTOXICITY
Authors: Koleva-Korkelia Iliana , Karamalakova Yanka , Nikolova Galina
Published: November 2021

Ochratoxin A (OTA) mycotoxin affects protein synthesis, metabolic oxidative pathways and ROS mediation. In the present study, we investigate the antioxidative-therapeutic potential of Azadirachta Indica Oil (A. indica) against chronic (28 days) OTA-induced nephrotoxicity. Balb/c male mice were exposed to i.e., (1) controls; (2) A. indica treated (120 mg/kg b. wt. i.p., given every two days); (3) c) OTA treated (Isolate D2306, 1.25 mg/kg b.wt., i.p., given every two days); d) A. indica (120 mg/kg b.wt., i.p.) administered 2h prior to OTA-administration. Till the end of the 28 experimental days of chronic OTA-nephrotoxicity, the mortality rate (±0) was not observed in mice. Kidney tissue was subjected for the determination of biochemical indexes (the MDA ratio, and antioxidant capability of SOD, and GSH) and EPR- ROS productions. OTA-exposure resulted in twofold significant increases in SOD (p<0.004), GSH (p<0.05) and malondialdehyde (MDA) levels (p<0.00), compared to controls. Further, a nephro-cells experiment was performed to investigate the oxidative stress-protective action of A. indica. Our results showed that A. indica oil and A. indica +OTA combination inhibited OTA-induced nephrotoxicity via a significant reduction of lipid peroxidation (p<0.003), ROS production (p<0.005), and endogenous antioxidant activation. Thus, it can be concluded that A. indica treatment neutralized chronic OTA-induced nephrotoxicity, not only by reducing lipid peroxidation but also by improving antioxidant status. Through the present experiments, it was demonstrated that A. indica has protective potential in nephron-inflammations.
C-REACTIVE PROTEIN LEVELS - INDICATOR FOR PROGNOSIS OF SPONTANEOUS PRETERM BIRTH IN BULGARIAN WOMEN
Authors: Koleva-Korkelia Iliana , Karamalakova Yanka
Published: November 2021

It is estimated that every year fifteen million premature babies are born worldwide mainly due to spontaneous preterm birth (sPTB). Furthermore, in clinical settings, there still are no reliable and accurate tools to predict preterm labor. Hence, the aim of this pioneering research was to estimate the relationship between the maternal inflammatory indicator and sPTB in a case-control study between 220 South Bulgarian women. The study was conducted at UMBAL, Stara Zagora, Bulgaria (2017-2020) and enrolled a total of 220 women, determined into two groups: 1) TB (n = 110), who were to give birth at term ≥ 37 to ≤ 39 + 6 gestation weeks with active labor at the time of hospitalization; and 2) sPTB (n = 110), women with preterm birth ≤ 32–34 + 6 gestation weeks and declared active labor, who were to give birth within 5-24 hrs. The inflammatory indicators/CRP concentration was quantified in plasma by immunoturbidimetric methods within 2 hrs. in mg/l. The median maternal CRP (8.77 ± 3.91), with cutoff = 4.9 mg/l was identified as optimal inflammation with highest risk of sPTB (sensitivity = 86.6%; specificity = 53.7%, р < 0.0001). Moreover, a cutoff CRP = 4.9 mg/l was found to be most effective in determining maternal age ≤ 19 years, the sensitivity of 68.6%, and positively correlated OR = 8.122 vs. OR = 2.354, with increased total sPTB risk at ≤ 32-34 + 6 weeks, respectively (p < 0.001).

In conclusion, increased CRP concentrations and a decreased maternal age were associated with increased risks of sPTB, before ≤ 32-34 + 6 weeks. Minimal inflammation and other factors in combination may also act as sPTB prognosis.
PREVALENCE OF PREMENSTRUAL SYMPTOMS AMONG BULGARIAN WOMEN
Authors: Popova-Dobreva Diana
Published: November 2021

INTRODUCTION: Premenstrual symptoms are common and can worsen women's quality of life. This study examines the prevalence of premenstrual symptoms such as weight gain; swelling of ankles, feet, and hands; frequent change of mood; fatigue; difficulty concentrating; depression; nervousness and irritability; and nausea.

OBJECTIVES: The objectives of this study are: (1) to reveal the prevalence of premenstrual symptoms among Bulgarian women and (2) to establish how the presence of premenstrual symptoms affects the Emotional well-being of women.

METHODS: The applied methodology includes an online-based anonymous study, which focuses on the prevalence of premenstrual symptoms among Bulgarian women and their emotional health. A characteristic of the studied contingent on age, BMI, and physical activity was made.

RESULTS:  The results of 126 women surveyed were analyzed. Of these, 96.8% have at least one premenstrual symptom. 30.2% have one or two symptoms, 43.7% have 3-4 symptoms and 23% have 5-8 symptoms. 14.8% of women with symptoms reported worsening of their symptoms because of increased stress associated with COVID-19. There is a statistically significant correlation between the number of symptoms and the emotional well-being of women.

CONCLUSION: The prevalence of premenstrual symptoms is common among the studied Bulgarian women. A greater number of symptoms has a negative effect on women's emotional well-being. We consider it appropriate to introduce the application of physiotherapeutic methods as well as alternative therapies for the treatment and prevention of premenstrual syndrome.
DATAFICATION AS A NECESSARY STEP IN THE PROCESSING OF BIG DATA IN DECISION-MAKING TASKS OF BUSINESS
Authors: Misut Martin , Jurik Pavol
Published: November 2021

The digital transformation of business in the light of opportunities and focusing on the challenges posed by the introduction of Big Data in enterprises allows for a more accurate reflection of the internal and external environmental stimuli. Intuition ceases to be present in the decision-making process, and decision-making becomes strictly data-based. Thus, the precondition for data-based decision-making is relevant data in digital form, resulting from data processing. Datafication is the process by which subjects, objects and procedures are transformed into digital data. Only after data collection can other natural steps occur to acquire knowledge to improve the company's results if we move in the industry's functioning context. The task of finding a set of attributes (selecting attributes from a set of available attributes) so that a suitable alternative can be determined in its decision-making is analogous to the task of classification. Decision trees are suitable for solving such a task. We verified the proposed method in the case of logistics tasks. The analysis subject was tasks from logistics and 80 well-described quantitative methods used in logistics to solve them. The result of the analysis is a matrix (table), in which the rows contain the values of individual attributes defining a specific logistic task. The columns contain the values of the given attribute for different tasks. We used Incremental Wrapper Subset Selection IWSS package Weka 3.8.4 to select attributes. The resulting classification model is suitable for use in DSS. The analysis of logistics tasks and the subsequent design of a classification model made it possible to reveal the contours of the relationship between the characteristics of a logistics problem explicitly expressed through a set of attributes and the classes of methods used to solve them.