29 results on '"Adrian, Victor"'
Search Results
2. POSSIBILITIES OF USING WASTE GLASS IN CEMENTITIOUS COMPOSITES.
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LĂZĂRESCU, Adrian-Victor, FLOREAN, Carmen Teodora, and HEGYI, Andreea
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GLASS waste , *CEMENT composites , *GLASS composites , *COMPOSITE materials , *MORTAR , *SUSTAINABLE construction - Abstract
For sustainable development in construction, the concrete industry is exploring various alternatives for producing new composite materials that contribute to sustainable development. In this context, eco-innovative and low environmental impact (eco-friendly) materials such as cementitious composites, in which aggregates are substituted with waste glass, represent a future alternative. This paper presents several types of composite materials with different proportions of waste glass that can successfully replace conventional masonry mortars. [ABSTRACT FROM AUTHOR]
- Published
- 2023
3. Study on the Possibilities of Developing Cementitious or Geopolymer Composite Materials with Specific Performances by Exploiting the Photocatalytic Properties of TiO 2 Nanoparticles.
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Hegyi, Andreea, Lăzărescu, Adrian-Victor, Ciobanu, Adrian Alexandru, Ionescu, Brăduţ Alexandru, Grebenişan, Elvira, Chira, Mihail, Florean, Carmen, Vermeşan, Horaţiu, and Stoian, Vlad
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CEMENT composites , *COMPOSITE materials , *SELF-healing materials , *TITANIUM dioxide , *CIRCULAR economy , *CONSTRUCTION materials - Abstract
Starting from the context of the principles of Sustainable Development and Circular Economy concepts, the paper presents a synthesis of research in the field of the development of materials of interest, such as cementitious composites or alkali-activated geopolymers. Based on the reviewed literature, the influence of compositional or technological factors on the physical-mechanical performance, self-healing capacity and biocidal capacity obtained was analyzed. The inclusion of TiO2 nanoparticles in the matrix increase the performances of cementitious composites, producing a self-cleaning capacity and an anti-microbial biocidal mechanism. As an alternative, the self-cleaning capacity can be achieved through geopolymerization, which provides a similar biocidal mechanism. The results of the research carried out indicate the real and growing interest for the development of these materials but also the existence of some elements still controversial or insufficiently analyzed, therefore concluding the need for further research in these areas. The scientific contribution of this study consists of bringing together two apparently distinct research directions in order to identify convergent points, to create a favorable framework for the development of an area of research little addressed so far, namely, the development of innovative building materials by combining improved performance with the possibility of reducing environmental impact, awareness and implementation of the concept of a Circular Economy. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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4. Phase Behavior of Carbon Dioxide + Isobutanol and Carbon Dioxide + tert -Butanol Binary Systems.
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Sima, Sergiu, Crişciu, Adrian Victor, and Secuianu, Catinca
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CARBON dioxide , *LIQUID-liquid equilibrium , *VAPOR-liquid equilibrium , *STRUCTURAL isomers , *EQUATIONS of state , *SAPPHIRES , *ISOBUTANOL - Abstract
In recent years, the dramatic increase of greenhouse gases concentration in atmosphere, especially of carbon dioxide, determined many researchers to investigate new mitigation options. Thermodynamic studies play an important role in the development of new technologies for reducing the carbon levels. In this context, our group investigated the phase behavior (vapor–liquid equilibrium (VLE), vapor–liquid–liquid equilibrium (VLLE), liquid–liquid equilibrium (LLE), upper critical endpoints (UCEPs), critical curves) of binary and ternary systems containing organic substances with different functional groups to determine their ability to dissolve carbon dioxide. This study presents our results for the phase behavior of carbon dioxide + n-butanol structural isomers binary systems at high-pressures. Liquid–vapor critical curves are measured for carbon dioxide + isobutanol and carbon dioxide + tert-butanol binary systems at pressures up to 147.3 bar, as only few scattered critical points are available in the literature. New isothermal vapor–liquid equilibrium data are also reported at 363.15 and 373.15 K. New VLE data at higher temperature are necessary, as only another group reported some data for the carbon dioxide + isobutanol system, but with high errors. Phase behavior experiments were performed in a high-pressure two opposite sapphire windows cell with variable volume, using a static-analytical method with phases sampling by rapid online sample injectors (ROLSI) coupled to a gas chromatograph (GC) for phases analysis. The measurement results of this study are compared with the literature data when available. The new and all available literature data for the carbon dioxide + isobutanol and carbon dioxide + tert-butanol binary systems are successfully modeled with three cubic equations of state, namely, General Equation of State (GEOS), Soave–Redlich–Kwong (SRK), and Peng–Robinson (PR), coupled with classical van der Waals mixing rules (two-parameter conventional mixing rules, 2PCMR), using a predictive method. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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5. ZINNOVATIVE THERMAL INSULATION PRODUCTS OBTAINED BY RECYCLING AND REUSING POSTINDUSTRIAL TEXTILE WASTE.
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LĂZĂRESCU, Adrian-Victor, BULACU, Cezar, HEGYI, Andreea-Cristina, CĂLĂTAN, Gabriela, and FLOREAN, Carmen
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THERMAL insulation , *TEXTILE waste , *WASTE recycling , *NONRENEWABLE natural resources , *WATER vapor , *RENEWABLE natural resources - Published
- 2021
6. INFLUENCE OF NAOH SOLUTION CONCENTRATION ON THE COMPRESSIVE STRENGTH OF ALKALI-ACTIVATED FLY ASH-BASED GEOPOLYMER BINDERS.
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LĂZĂRESCU, Adrian-Victor, IONESCU, Brăduţ Alexandru, CHIRA, Mihail, and FLOREAN, Carmen
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COMPRESSIVE strength , *APPLIED sciences , *KAOLIN , *CRUMB rubber , *HEAT treatment , *BIOENGINEERING , *SOLUBLE glass , *FLY ash - Published
- 2021
7. INFLUENCE OF THE HEAT TREATMENT PROCEDURE ON THE GEOPOLYMER MATERIALS PROPERTIES – A REVIEW.
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IONESCU, Brăduț Alexandru, LĂZĂRESCU, Adrian-Victor, and HEGYI, Andreea
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HEAT treatment , *INORGANIC polymers , *ALUMINUM silicates - Abstract
The term “geopolymer” was originally introduced by the French chemist Davidovits, representing a wide range of anorganic materials. According to him, among the nine different classes of geopolymers, geopolymer concrete is of particular interest, consisting of materials containing aluminosilicates that could be used to completely replace the amount of Portland cement in ordinary concrete. The aim of this study is to present relevant data in the field of alkali-activated geopolymer materials regarding the production of this type of materials using both ambiental and heat curing and studying the differences between the two procedures. [ABSTRACT FROM AUTHOR]
- Published
- 2020
8. FLY ASH BASED GEOPOLYMER PASTE USING ROMANIAN LOCAL SOURCE MATERIALS - PRELIMINARY RESULTS.
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Szilagyi, Henriette, Lăzărescu, Adrian-Victor, Baeră, Cornelia, and Ioani, Adrian
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INDUSTRIAL waste management , *FLY ash , *SUSTAINABLE development , *POLYMER-impregnated concrete , *WASTE recycling - Abstract
The benefit of recycling industrial by-products in the construction industry led to growing interest in exploring and potentially exploiting these by-products, in the context of sustainable development, and in creating new materials. Fly ash is a type of byproduct waste, having enjoyed considerable attention, especially from the perspective of creating and perfecting fly ash based geopolymer concrete. In Romania, over 80% of industrial waste is deposited, this being the most widely used method of waste disposal. This creates the premises of potentially using this waste as a source material in producing fly ash based geopolymer concrete. In order to obtain a material with desirable compressive strength, the mix design of geopolymers needs to be carefully studied and much research remains to be conducted. The aim of this paper is to present the preliminary results for producing fly ash-based geopolymer paste, using Romanian local source materials and to open new perspectives on the global existing research agenda about the production of fly ash-based geopolymer concrete. Preliminary results shown a compressive strength of the fly ash-based geopolymer paste between 7 and 25 MPa, at 2, and 7 days, respectively when keeping the fly ash/alkaline liquid ratio constant and different Na2SiO3 solution/NaOH solution ratios, with NaOH solution concentration of 8M. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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9. UNBURNED CLAY AND INDUSTRIAL WASTE - ECOLOGICAL CONSTRUCTION MATERIALS.
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LĂZĂRESCU, Adrian-Victor, CĂLĂTAN, Gabriela, TOADER, Tudor Panfil, LUPAN, Lidia Maria, and FLOREAN, Carmen
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INDUSTRIAL wastes , *CONSTRUCTION materials , *CLAY , *SLURRY , *BRICKS - Published
- 2021
10. Morphologic and ultrasound survey in type 2 diabetic placenta.
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Tetileanu, Adrian Victor, Berceanu, Costin, Brătilă, Elvira, Navolan, Dan, Ciortea, Răzvan, Berceanu, Sabina, Cîrstoiu, Monica Mihaela, Ofițeru, Anca-Maria, Bohîlțea, Roxana Elena, Stepan, Alex Emilian, and Mehedințu, Claudia
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TYPE 2 diabetes diagnosis , *DIABETIC neuropathies , *GLYCEMIC control , *PREECLAMPSIA , *FIBRIN - Abstract
The aim of this study is to establish morphological, histological and ultrasonographic (US) correlations in the placenta of type 2 diabetes. This is a multicenter case-control study conducted on a lot of 21 selected cases diagnosed with type 2 diabetes, analyzed over a two year period. The clinical characteristics of the patients in the study group are represented by the average age of 34 years and diabetes associated with preeclampsia, hypertension, diabetic neuropathy, urinary infections, obesity or history of infertility. All the patients in the study group are Caucasian. US assessment of placental characteristics in our series revealed increased placental thickness from the second trimester and placentomegaly at the end of the third trimester. Immature appearance of placenta has been observed. Gross analysis of maternal and fetal surfaces of the placentas revealed basal plate and subchorionic fibrin depositions, placental infarction or intervillous thrombosis. Preconceptional glycemic control and its support during gestation are essential for pregnancy outcome. US findings have as a background the morphological changes. From morphological perspective there is about a combination of anomalies, otherwise unspecific which, in terms of association with various comorbidities could define a placental diabetic pattern. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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11. A Noise-Shaped Randomized Modulation for Switched-Mode DC-DC Converters.
- Author
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Cui, Keer, Adrian, Victor, Gwee, Bah-Hwee, and Chang, Joseph S.
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DC-to-DC converters , *ELECTRONIC modulation , *ELECTRONIC noise - Abstract
We propose a novel low-harmonics low-noise modulation scheme for switched-mode dc–dc converters. The proposed scheme is a hybrid of a randomized modulation scheme, namely, the randomized wrapped-around pulse position modulation scheme (RWAPPM), and a noise-shaper. The RWAPPM mitigates the switching-frequency harmonics in the input current, whereas the noise-shaper mitigates the low-frequency noise therein. We derive an analytical expression for the input current spectrum of the hybrid scheme. We benchmark the hybrid scheme against the conventional pulse width modulation scheme (PWM) and the RWAPPM without the noise-shaper. At 0.5 duty cycle, 3.3-V input voltage, 100-kHz average switching frequency, and with the second-order noise-shaper, the peak spectral power in the input current spectrum of the hybrid scheme is 18.1 dB lower than the PWM. Other randomized and spread-spectrum modulation schemes, in general, have undesirably higher input noise current than that of the PWM. However, the input noise current of the proposed hybrid scheme, obtained at ~73-mA rms (integrated over a 200-kHz bandwidth without an input filter), is comparable with that of the PWM, and is lower by ~16-mA rms compared with that of the RWAPPM without the noise-shaper. We also benchmark the hybrid scheme against other well known randomized and spread-spectrum modulation schemes. We further propose a novel pulse generator structure that embodies the hybrid scheme. We realize a dc–dc converter employing the pulse generator, and measure the converter to verify the derived expression and the characteristics of the hybrid scheme. We also measure the output voltage spectrum, the transient-response, and the operating range of the converter. [ABSTRACT FROM PUBLISHER]
- Published
- 2018
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12. Influence of TiO 2 Nanoparticles on the Physical, Mechanical, and Structural Characteristics of Cementitious Composites with Recycled Aggregates.
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Florean, Carmen Teodora, Vermeșan, Horațiu, Gabor, Timea, Neamțu, Bogdan Viorel, Thalmaier, Gyorgy, Hegyi, Andreea, Csapai, Alexandra, and Lăzărescu, Adrian-Victor
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MORTAR , *CEMENT composites , *ELECTRONIC waste , *ENERGY dispersive X-ray spectroscopy , *TITANIUM dioxide , *SUSTAINABILITY - Abstract
The aim of this study is to analyze the effect of the addition of TiO2 nanoparticles (NTs) on the physical and mechanical properties, as well as the microstructural changes, of cementitious composites containing partially substituted natural aggregates (NAs) with aggregates derived from the following four recycled materials: glass (RGA), brick (RGB), blast-furnace slag (GBA), and recycled textolite waste with WEEE (waste from electrical and electronic equipment) as the primary source (RTA), in line with sustainable construction practices. The research methodology included the following phases: selection and characterization of raw materials, formulation design, experimental preparation and testing of specimens using standardized methods specific to cementitious composite mortars (including determination of apparent density in the hardened state, mechanical strength in compression, flexure, and abrasion, and water absorption by capillarity), and structural analysis using specialized techniques (scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS)). The analysis and interpretation of the results focused primarily on identifying the effects of NT addition on the composites. Results show a decrease in density resulting from replacing NAs with recycled aggregates, particularly in the case of RGB and RTA. Conversely, the introduction of TiO2 nanoparticles resulted in a slight increase in density, ranging from 0.2% for RTA to 7.4% for samples containing NAs. Additionally, the introduction of TiO2 contributes to improved compressive strength, especially in samples containing RTA, while flexural strength benefits from a 3–4% TiO2 addition in all composites. The compressive strength ranged from 35.19 to 70.13 N/mm2, while the flexural strength ranged from 8.4 to 10.47 N/mm2. The abrasion loss varied between 2.4% and 5.71%, and the water absorption coefficient varied between 0.03 and 0.37 kg/m2m0.5, the variations being influenced by both the nature of the aggregates and the amount of NTs added. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) analysis showed that TiO2 nanoparticles are uniformly distributed in the cementitious composites, mainly forming CSH gel. TiO2 nanoparticles act as nucleating agents during early hydration, as confirmed by EDS spectra after curing. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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13. Influence of TiO 2 Nanoparticles on the Resistance of Cementitious Composite Materials to the Action of Bacteria.
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Hegyi, Andreea, Lăzărescu, Adrian-Victor, Szilagyi, Henriette, Grebenişan, Elvira, Goia, Jana, Mircea, Andreea, and Lettieri, Stefano
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COMPOSITE materials , *GRAM-positive bacteria , *NANOPARTICLES , *MAINTENANCE costs , *GRAM-negative bacteria - Abstract
The formation of biofilms on cementitious building surfaces can cause visible discoloration and premature deterioration, and it can also represent a potential health threat to building occupants. The use of embedded biofilm-resistant photoactivated TiO2 nanoparticles at low concentrations in the cementitious composite matrix is an effective method to increase material durability and reduce maintenance costs. Zone of inhibition studies of TiO2-infused cementitious samples showed efficacy toward both Gram-negative and Gram-positive bacteria. [ABSTRACT FROM AUTHOR]
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- 2021
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14. A Randomized Wrapped-Around Pulse Position Modulation Scheme for DC–DC Converters.
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Adrian, Victor, Chang, Joseph S., and Gwee, Bah-Hwee
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ELECTRONIC modulation , *ANALOG-to-digital converters , *PULSE frequency modulation , *SWITCHING circuits , *DIGITAL electronics - Abstract
We present a novel randomized wrapped-around pulse position modulation (RWAPPM) scheme for digital modulators of dc–dc converters. Unlike the reported modulation schemes that require a varying switching period (thereby resulting in high attenuation or complete elimination of discrete harmonics), the proposed RWAPPM conversely requires only a constant switching period (thereby advantageous in terms of easy realization in hardware), and yet, its discrete harmonics are negligible. We derive an expression for the spectrum of the RWAPPM scheme to analytically obtain the peak spectral power and ripple noise voltage of RWAPPM. This expression further provides insight to the parameters that influence the RWAPPM spectrum. We benchmark the RWAPPM scheme against the ubiquitous conventional pulsewidth modulation scheme and six reported (randomized and frequency modulation) schemes. The RWAPPM scheme features negligible discrete harmonics [\leq -158 dB relative to full scale (dBFS)], and among the modulation schemes, it features the lowest peak spectral power at -26.6 dBFS (before low-pass filtering) and relatively low ripple noise at 2 mVrms (after low-pass filtering) for a 3.6–2.5-V conversion and an effective switching frequency of 120 kHz. We verify the derived expression and attributes of the RWAPPM spectrum by computer simulations and on the basis of experimental measurements on a dc–dc converter. [ABSTRACT FROM PUBLISHER]
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- 2010
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15. A Low-Voltage Micropower Digital Class-D Amplifier Modulator for Hearing Aids.
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Adrian, Victor, Chang, Joseph S., and Bah-Hwee Gwee
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ELECTRONIC modulators , *HEARING aid design & construction , *PULSE amplifiers , *ELECTRONIC pulse techniques , *DIGITAL electronics , *DIGITAL technology , *ELECTRONIC modulation - Abstract
We present a micropower digital modulator for class-D amplifiers for power-critical digital hearing aids. The modulator design embodies a proposed Lagrange interpolation (a combined first- and second-order Lagrange) algorithmic pulsewidth modulation (PWM) and a third-order ΔΣE noise shaper. By means of double-Fourier-series analysis, we analyze and determine the harmonic nonlinearities of the proposed algorithmic PWM. At 48-kHz sampling, 96-kHz PWM output, 997-Hz input, and input modulation index = 0.9, the modulator circuit achieves a total harmonic distortion + noise (THD + N) of -74 dB (0.02%) over an 8-kHz voice bandwidth-a 12-dB THD + N improvement over a reported design and yet dissipates only ∼50% of the power. The proposed modulator dissipates the lowest power dissipation of all modulators compared, and by means of a proposed figure of merit, the proposed modulator exhibits very competitive performance. The modulator IC is fabricated in a 0.35-μm digital CMOS process with a core area of 0.46 mm². [ABSTRACT FROM AUTHOR]
- Published
- 2009
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16. SHEEP WOOL HEAT INSULATION SUSTAINABILITY.
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Hegyi, Andreea, Szilagyi, Henriette, Lăzărescu, Adrian-Victor, Meiţă, Vasile, and Sandu, Mihaela
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WOOL , *THERMAL insulation , *NONRENEWABLE natural resources , *SHEEP , *CONSTRUCTION materials , *QUALITY of life , *INDOOR air quality , *RENEWABLE natural resources - Abstract
Sustainability is a criterion defined since the 1980s, essential in all areas of activity, without which development cannot be acheived. Thermal insulation mattresses produced using sheep wool, successfully meet the conditions imposed by this criterion. This type of building material ensures the responsible use of non-renewable natural resources, the possibility of reuse and recycling of materials, contributes to environmental protection and pollution reduction, energy saving and provides a hygienic and healthy living climate. This paper analyzes how sheep wool mattresses meet sustainability requirements, simultaneously with compliance with specific requirements in construction based on the criteria of regulation (EU) no. 305/2011 of the European Parliament and of the Council of 9 March 2011 laying down harmonised conditions for the marketing of construction products. At the same time, the physical and mechanical performances of 20 types of sheep wool mattresses, from 7 manufacturers, available on the international market, are presented. This identifies the strengths of these products (thermal insulation performance, low overload of the structural strength of buildings due to low density, low environmental impact and contribution to improving indoor air quality), as well as weaknesses (high water absorption, low mechanical strength, which make it difficult to use outside buildings, requiring either indoor location, additional protection measures for outdoor location). However, cumulating all these aspects, it can be said that sheep wool mattresses are a good heat-insulating material, which successfully meets the requirements of sustainable development, the benefits in terms of environmental impact and quality of life recommending them as a possible substitute for some sintering heat-insulating materials, highly polluting and hardly or not at all biodegradable. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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17. INFLUENCE OF TIO2 NANOPARTICLES ON THE PHYSICO-MECHANICAL PROPERTIES OF CEMENTITIOUS COMPOSITES – EXPERIMENTAL RESULTS.
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GREBENIȘAN, Elvira, HEGYI, Andreea, and LĂZĂRESCU, Adrian-Victor
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NANOPARTICLES , *COMPOSITE materials - Abstract
Urban constructions are subject to deterioration and degradation due to the action of external factors, pollutants from air, water, compounds resulting from the combustion of fuels used for heating and transport, etc. currently, worldwide, the possibility of building cementitious composite materials with self-cleaning properties is reported due to the photocatalytic capacity of TiO2 nanoparticles, used as an addition or as a substitute for a part of cement. The aim of this paper is to present experimental research on the influence of the introduction of titanium dioxide nanoparticles (TiO2) on some physicomechanical properties of cementitious composites. Experimental research has been carried out on cementitious composite material containing TiO2 nanoparticles respectively the evolution of the following parameters was analysed: setting time, apparent density, absolute density, porosity, water absorption, water absorption by capillarity and white degree. The main objective of this study was to analyse the influence of the presence of titanium dioxide (TiO2) nanoparticles on the physico-mechanical properties of cementitious composites. [ABSTRACT FROM AUTHOR]
- Published
- 2020
18. Influence of the Extraction Solution on the Removal of Heavy Metals from Polluted Soils.
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Sur, Ioana Monica, Hegyi, Andreea, Micle, Valer, Gabor, Timea, and Lăzărescu, Adrian-Victor
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METAL content of soils , *HEAVY metals , *COPPER , *HEAVY metal toxicology , *SOILS , *GLUCONIC acid - Abstract
Soil pollution with heavy metals is a problem for the whole geosystem. The aim of the research is to identify new solutions for extracting heavy metals from polluted soils so that they can be further exploited. To this end, investigations of the physicochemical characteristics of the soil sample under study were carried out. Following the analyses, the soil was characterised as lute-coarse sand (UG) with a strongly acidic pH (4.67), a hygroscopicity coefficient (CH = 4.8% g/g), and a good supply of nutrients: nitrogen (Nt): 0.107%; mobile phosphorus (PAL): 6 mg kg−1 and mobile potassium (KAL): 26 mg kg−1, but is low in humus (2.12%). The metal content of the soil was determined by atomic absorption spectrometry (AAS), and the analyses showed high concentrations of metals (Pb: 27,660 mg kg−1; Cu: 5590 mg kg−1; Zn: 2199 mg kg−1; Cd: 11.68 mg kg−1; Cr: 146 mg kg−1). The removal of metals (Pb, Cu, Zn, Cd, and Cr) from polluted soil by different extraction agents (water, humus, malic acid, chitosan, and gluconic acid) was investigated. Metal extraction experiments were carried out in a continuous orbital rotation-oscillation stirrer at a solid/liquid/ (S/L ratio; g:mL) of 1:4, at two concentrations of extraction solution (1% and 3%), and at different stirring times (2, 4, 6, and 8 h). The yield of the extraction process is very low for all proposed extraction solutions. The maximum values of extraction efficiency are: 0.5% (Pb); 3.28% (Zn); and 5.72% (Cu). Higher values were obtained in the case of Cr (11.97%) in the variant of using humus 3% as an extraction solution at a stirring time of 6 h. In the investigated experimental conditions, the best removal efficiencies were obtained in the case of cadmium (26.71%) when using a 3% malic acid solution. In conclusion, it is considered that, from case to case, the type of extraction solution as well as the nature of the metal influence the mechanism of the depollution process, i.e., the capacity of the fine soil granules to free themselves from the pollutant metal that has adhered to them, and further research is considered necessary in the future. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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19. Thermophysical Characteristics of Clay for Efficient Rammed Earth Wall Construction.
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Petcu, Cristian, Dobrescu, Cornelia Florentina, Dragomir, Claudiu Sorin, Ciobanu, Adrian Alexandru, Lăzărescu, Adrian Victor, and Hegyi, Andreea
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SPECIFIC heat capacity , *THERMAL diffusivity , *CLAY , *SPECIFIC heat , *CONSTRUCTION materials , *CLAY soils , *THERMAL conductivity - Abstract
This case study focuses on twelve compacted clay soil samples to understand their fundamental physical and thermal properties. For each sample, the density, thermal conductivity, thermal diffusivity, specific heat, and drying shrinkage were assessed. The identification and characterisation of the materials were also carried out by positioning them into the ternary diagram based on the percentage of sand, silt, and clay. These properties are definitive for the performance characteristics of materials used in rammed earth wall construction. The aim is to provide information for better knowledge and prediction regarding the dynamic heat flow in rammed earth walls. Experimental results show a relatively wide range of values for each property, reflecting the diverse properties of the sampled clays. The thermophysical characteristics of the 12 types of earth analysed showed correlations with reports in the literature in terms of density (1490–2150 kg/m3), porosity (23.22–39.99%), specific heat capacity (701–999 J/kgK), and thermal conductivity (0.523–1.209 W/mK), which indicates them as materials suitable for use in the construction of rammed earth walls. Using test data, a dynamic assessment of heat flow through simulated rammed earth walls was performed. For a better understanding of the results obtained, they were compared with results obtained for simulations where the building element would be made of concrete, i.e., a mineral wool core composite. Thus, heat flux at the wall surface and mass flux, respectively, during the 16 years of operation showed similar evolution for all 12 types of clay material analysed, with small variations explained by differences in thermophysical characteristics specific to each type of S1–S12 earth. In the case of walls made from clay material, there is a stabilisation in the evolution of the water content phenomenon by the 5th year of simulation. This contrasts with walls made of concrete, where the characteristic water content appears to evolve continuously over the 16-year period. Therefore, it can be said that in the case of the construction elements of existing buildings, which have already gone through a sufficient period for the maturation of the materials in their construction elements, the rammed earth wall quickly develops a moisture buffer function. In the case of simulating a mineral wool core composite wall, it cannot perform as a temperature or humidity buffer, exhibiting an enthalpy exchange with indoor air that is only 4% of that of the rammed earth walls; consequently, it does not play a significant role in regulating indoor comfort conditions. Overall, there is confirmation of the temperature and moisture buffering capabilities of rammed earth walls during both warm and cold periods of the year, which is consistent with other reports in the literature. The findings of this research provide a better insight into clay as a material for rammed earth walls for more efficient design and construction, offering potential improvements regarding indoor comfort, energy efficiency, and sustainability. The data also provides useful information in the fields of architecture and civil engineering regarding the use of clay as an eco-friendly building material. The results emphasise the importance of thoroughly understanding the thermophysical properties of clay to ensure the efficiency of rammed earth construction. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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20. Research on Thermal Insulation Performance and Impact on Indoor Air Quality of Cellulose-Based Thermal Insulation Materials.
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Petcu, Cristian, Hegyi, Andreea, Stoian, Vlad, Dragomir, Claudiu Sorin, Ciobanu, Adrian Alexandru, Lăzărescu, Adrian-Victor, and Florean, Carmen
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INDOOR air quality , *THERMAL insulation , *INSULATING materials , *WASTE paper , *CIGARETTE filters , *CONSTRUCTION materials , *RAW materials - Abstract
Worldwide, the need for thermal insulation materials used to increase the energy performance of buildings and ensure indoor thermal comfort is constantly growing. There are several traditional, well-known and frequently used thermal insulation materials on the building materials market, but there is a growing trend towards innovative materials based on agro-industrial waste. This paper analyses the performance of 10 such innovative thermal insulation materials obtained by recycling cellulosic and/or animal waste, using standardised testing methods. More precisely, thermal insulation materials based on the following raw materials were analysed: cellulose acetate, cigarette filter manufacturing waste; cellulose acetate, cigarette filter manufacturing waste and cigarette paper waste; cellulose acetate, waste from cigarette filter manufacturing, waste cigarette paper and waste aluminised paper; cellulose from waste paper (two types made by two independent manufacturers); wood fibres; cellulose from cardboard waste; cellulose from waste cardboard, poor processing, inhomogeneous product; rice husk waste and composite based on sheep wool, recycled PET fibres and cellulosic fibres for the textile industry. The analysis followed the performance in terms of thermal insulating quality, evidenced by the thermal conductivity coefficient (used as a measurable indicator) determined for both dry and conditioned material at 50% RH, in several density variants, simulating the subsidence under its own weight or under various possible stresses arising in use. The results showed in most cases that an increase in material density has beneficial effects by reducing the coefficient of thermal conductivity, but exceptions were also reported. In conjunction with this parameter, the analysis of the 10 types of materials also looked at their moisture sorption/desorption capacity (using as a measurable indicator the amount of water stored by the material), concluding that, although they have a capacity to regulate the humidity of the indoor air, under low RH conditions the water loss is not complete, leaving a residual quantity of material that could favour the development of mould. Therefore, the impact on indoor air quality was also analysed by assessing the risk of mould growth (using as a measurable indicator the class and performance category of the material in terms of nutrient content conducive to the growth of microorganisms) under high humidity conditions but also the resistance to the action of two commonly encountered moulds, Aspergillus niger and Penicillium notatum. The results showed a relative resistance to the action of microbiological factors, indicating however the need for intensified biocidal treatment. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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21. DYNAMIC BEHAVIOURAL DECISION SYSTEMS.
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Badescu, Adrian Victor and Cristea, Radu Nicolae
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FUZZY algorithms , *INVESTMENTS , *GAME theory , *MERGERS & acquisitions , *FUZZY logic - Abstract
This paper explains mathematically the concept of investment agent's bounded rationality to bring a new perspective on the use of threats as means of analyzing competition. The paper thus blends together two approaches: strong efficiency economics and behavioral economics. Further we construct a dynamic situation and considering a two step duopoly we develop a new type of equilibrium - a fuzzy equilibrium - that is better suited for real decision situations. [ABSTRACT FROM AUTHOR]
- Published
- 2011
22. Influence of Fe 2 O 3 , MgO and Molarity of NaOH Solution on the Mechanical Properties of Fly Ash-Based Geopolymers.
- Author
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Ionescu, Brăduț Alexandru, Chira, Mihail, Vermeșan, Horațiu, Hegyi, Andreea, Lăzărescu, Adrian-Victor, Thalmaier, Gyorgy, Neamțu, Bogdan Viorel, Gabor, Timea, and Sur, Ioana Monica
- Subjects
- *
FLY ash , *FERRIC oxide , *MOLARITY , *MAGNESIUM oxide , *PASTE - Abstract
The use of waste from industrial activities is of particular importance for environmental protection. Fly ash has a high potential in the production of construction materials. In the present study, the use of fly ash in the production of geopolymer paste and the effect of Fe2O3, MgO and molarity of NaOH solution on the mechanical strength of geopolymer paste are presented. Samples resulting from the heat treatment of the geopolymer paste were subjected to mechanical tests and SEM, EDS and XRD analyses. Samples were obtained using 6 molar and 8 molar NaOH solution with and without the addition of Fe2O3 and MgO. Samples obtained using a 6 molar NaOH solution where Fe2O3 and MgO were added had higher mechanical strengths compared to the other samples. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
23. Extraction of Metals from Polluted Soils by Bioleaching in Relation to Environmental Risk Assessment.
- Author
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Sur, Ioana Monica, Micle, Valer, Hegyi, Andreea, and Lăzărescu, Adrian-Victor
- Subjects
- *
ENVIRONMENTAL risk assessment , *BACTERIAL leaching , *ENVIRONMENTAL health , *SOIL testing , *SOILS - Abstract
Environmental pollution has particular implications for the whole geosystem and increases the global risk to human and ecological health. In this regard, investigations were carried out on soil samples to perform the quality status assessment by determining: pH, texture, structure and metal concentration, as well as carrying out an assessment of anthropogenic activity by determining pollution indices: Cf (contamination factor), Cd (degree of contamination), PLI (pollution load index), Er (ecological risk index) and PERI (potential ecological risk index). Analyses on soil samples showed high concentrations of metals (Cu: 113–2996 mg kg−1; Pb: 665–5466 mg kg−1; Cr: 40–187 mg kg−1; Ni: 221–1708 mg kg−1). The metal extraction experiments were carried out by bioleaching using Thiobacillusferrooxidans, microorganisms at different amounts of bioleaching solution (20 mL and 40 mL 9K medium) and a stirring time of up to 12 h. The results on the degree of contamination, pollution loading index PLI (2.03–57.23) and potential ecological risk index PERI (165–2298) indicate that the soils in the studied area have a very high degree of pollution. The decontamination procedure by bioleaching showed a decrease, but at the end of the test (12 h), the followed indices indicate high values, suggesting that bioleaching should continue. The depollution yield after 12 h of treatment is, however, encouraging: Cu 29–76%, Pb: 10–32%, Cr: 39–72% and Ni 44–68%. The use of yield–time correlation equations allows the identification of the optimal exposure time on the bioleaching extraction process to obtain optimal results. The aim of the research is to determine the soil quality, soil environmental risk, extraction of metals from polluted soils by bioleaching and to identify influencing factors in achieving high remediation yields. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
24. Thermal Insulation Mattresses Based on Textile Waste and Recycled Plastic Waste Fibres, Integrating Natural Fibres of Vegetable or Animal Origin.
- Author
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Hegyi, Andreea, Vermeșan, Horațiu, Lăzărescu, Adrian-Victor, Petcu, Cristian, and Bulacu, Cezar
- Subjects
- *
NATURAL fibers , *WASTE recycling , *PLASTIC recycling , *WOOL , *TEXTILE waste , *THERMAL insulation , *FIBERS , *PLASTIC scrap - Abstract
The current context provides, worldwide, the need to identify solutions for the thermal efficiency of constructions, through sustainable and innovative methods and products. A viable solution is to produce thermal insulating products by carding-folding technology, using natural fibres and recycled polyethylene terephthalate (rPET) and polyester (rPES) waste, converted to fibres. This paper presents experimental results obtained after testing several thermal insulation composite products produced using a mix of sheep wool, cellulose, rPET and rPES fibres. The results of the research demonstrate the thermal insulation properties but, at the same time, identify the benefits of using such materials on the quality of the air in the interior space (the ability to adjust humidity and reduce the concentration of harmful substances). At the same time, the advantages of using sheep wool composite mattresses concerning their resistance to insect attack is demonstrated when compared with ordinary thermal insulation materials. Finally, sensitivity elements of these composites are observed in terms of sensitivity to mould, and to contact with water or soil, drawing future research directions in the development of this type of materials. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
25. Influence of TiO 2 Nanoparticles on the Resistance of Cementitious Composite Materials to the Action of Fungal Species.
- Author
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Hegyi, Andreea, Grebenişan, Elvira, Lăzărescu, Adrian-Victor, Stoian, Vlad, and Szilagyi, Henriette
- Subjects
- *
COMPOSITE materials , *NANOSTRUCTURED materials , *CEMENT composites , *NANOPARTICLES , *ULTRAVIOLET radiation , *CAPACITY building - Abstract
The development of mold films on the cement surfaces of buildings is a health and safety problem for the population, aesthetic but also in terms of their durability. The use of specific performance of cementitious composites containing TiO2 nanoparticles, photoactivated by UV radiation, can be a viable solution to mitigate to eliminate these problems. The experimental studies presented aim to analyze the capacity to inhibit the development of mold type Aspergillus and Penicillium on the surface of composite materials with nano-TiO2 content and the identification of the optimal range of nanomaterial addition. The identification and analysis of the inhibition halo (zone with a biological load of maximum 1–10 colonies of microorganisms) confirmed the biocidal capacity of the cementitious composites, but also indicated the possibility that an excess of TiO2 nanoparticles in the mixture could induce a development of cell resistance, which would be unfavorable both in terms of behavior and in terms of cost. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
26. Highly homogeneous nanostructured templates based on environmental friendly microemulsion for nanomaterials processing.
- Author
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Rogozea, Elena Adina, Olteanu, Nicoleta Liliana, Crisciu, Adrian Victor, Petcu, Adina Roxana, and Mihaly, Maria
- Subjects
- *
NANOSTRUCTURED materials , *CHEMICAL templates , *MICROEMULSIONS , *POLYETHYLENE glycol , *WATER , *PHASE transitions , *ALCOHOL - Abstract
Highly homogeneous nanostructured templates in the system Water/Polyoxyethylene(4)lauryl ether (Brij 30)/Pinus Oil have been designed for nanomaterials processing by studying the phase behaviour and influence of several physico-chemical parameters such as water/oil ratio (R), water/alcohol ratio (r), temperature, surfactant concentration and nickel salt on the phase transition. A Winsor I→III→II inversion was promoted by using isopropanol cosolvent, at different r, from 1 to 10. For r=4, as the temperature is increased the Winsor II domain is enhanced subsequently, but no phase transition by temperature change has been revealed. While a narrowing of Winsor II microemulsion region has been noticed, as a result of Ni(II) salt addition by increasing the concentration, still no phase transitions promoted by their presence have been obtained. The Water/Isopropanol/Brij 30/Pinus Oil formulations are promoted as potential synthesis templates for both inorganic and organic materials or as an efficient extraction system for pollutants removal from aqueous media. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
27. A Micropower Low-Distortion Digital Class-D Amplifier Based on an Algorithmic Pulsewidth Modulator.
- Author
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Gwee, Bah-Hwee, Joseph S. Chang, and Adrian, Victor
- Subjects
- *
ELECTRONIC amplifiers , *SIGNAL generators , *DATA transmission systems , *DIGITAL communications , *SIMULATION methods & models , *NUMERICAL analysis - Abstract
A digital Class-D amplifier comprises a pulsewidth modulator (PWM) and an output stage. In this paper, we simplify the time-domain expression for the algorithmic PWM linear interpolation (LI) sampling process and analytically derive its double Fourier series expression. By means of our derivation, we show that the nonlinearities of the LI process are very low, especially given its modest computation complexity and low sampling frequency. In particular, the total-harmonic distortion (THD) ≈0.02 % and fold-back distortion is -98.4 dB (averaged from modulation indexes M = 0.1 to 0.9) for the 4-kHz voiceband bandwidth @1-kHz input, 48-kHz sampling. We also describe a simple hardware for realizing the LI process. We propose a frequency doubler (with small overheads) for the pulse generator for the PWM, thereby reducing the counter clock rate by 2, leading to a substantial r.∼47% power dissipation reduction for the Class-D amplifier. By means of computer simulations and on the basis of experimental measurements, we verify our double Fourier series derivation and show the attractive attributes of a Class-D amplifier embodying our simplified LI sampling expression and reduced clock rate pulse generator. We show that our Class-D amplifier design is micropower (∼60 μW @1.1 V and 48-kHz sampling rate, and THD ≈0.03%) and is suit- able for practical power-critical portable audio devices, including digital hearing aids. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
28. Physical–chemical parameters promoting phase changes in non-ionic environmental-friendly microemulsions
- Author
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Fleancu, Madalina Camelia, Olteanu, Nicoleta Liliana, Rogozea, Adina Elena, Crisciu, Adrian Victor, Pincovschi, Irina, and Mihaly, Maria
- Subjects
- *
NONIONIC surfactants , *PHASE transitions , *MICROEMULSIONS , *AQUEOUS solutions , *SURFACE active agents , *PHYSICAL & theoretical chemistry , *HYDROPHILIC compounds , *ETHYL acetate , *METAL ions , *LIQUID-liquid extraction - Abstract
Abstract: A series of influencing parameters (water/oil ratio, cosolvent, temperature, surfactant concentration, metallic salt and dye concentration) on the phase transitions in Water/polyoxietilen(4)laurylether/Ethyl acetate ternary system have been studied in order to optimize the extraction of pollutants (metallic cations and dyes) from aqueous media by non-ionic microemulsions. This system presents a phase inversion temperature (PIT) around 15°C, corresponding for WI to WII phase transition. While there is an extending tendency of WII areas with increasing temperature over 40°C, the opposite effect is noticed by adding Ni(II) and Crystal Violet dye into the water phase. No effect was registered at small amounts of Crystal Violet dye addition. Based on evaluation of distribution coefficient in liquid–liquid Ni(II) extraction system and the load capacity of microemulsion with the two pollutants (Ni(II) and Crystal Violet dye), the optimum extraction conditions for this system would correspond to water/microemulsion volumetric ratio, F =8, no added co-solvent, and surfactant concentration around 20% (w/w), resulting in extraction efficiencies around 90%. The pollutants extraction from an aqueous phase by WII microemulsions is based on their diffusion from diluted water phase in the interfacial film of surfactant (CV dye) or into the micelles (Ni(II)) according to the equilibrium constant and rate constant data. By a simple control of surfactant concentration, the non-ionic microemulsions Water/polyoxietilen(4)laurylether (Brij 30)/Ethyl acetate (EtOAc) system can be an efficient solution for extraction of hydrophilic pollutants sensitive to heat from aqueous media at environment temperature. [Copyright &y& Elsevier]
- Published
- 2013
- Full Text
- View/download PDF
29. Improving Indoor Air Quality by Using Sheep Wool Thermal Insulation.
- Author
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Hegyi, Andreea, Bulacu, Cezar, Szilagyi, Henriette, Lăzărescu, Adrian-Victor, Meiţă, Vasile, Vizureanu, Petrică, Sandu, Mihaela, Milani, Gabriele, and Sandu, Andrei Victor
- Subjects
- *
WOOL , *THERMAL insulation , *WATER vapor , *INDOOR air quality , *SHEEP , *AIR quality , *HUMIDITY control , *THERMAL conductivity - Abstract
Currently, the need to ensure adequate quality of air inside the living space but also the thermal efficiency of buildings is pressing. This paper presents the capacity of sheep wool heat-insulating mattresses to simultaneously provide these needs, cumulatively analyzing efficiency indicators for thermal insulation and indicators of improving air quality. Thus, the values obtained for the coefficient of thermal conductivity, and its resistance to heat transfer, demonstrate the suitability of their use for thermal insulation. The results of the permeability to water vapor characteristics on the sorption/desorption of water, air, demonstrate the ability to control the humidity of the indoor air and the results on the reduction of the concentration of formaldehyde, demonstrating their contribution to the growth of the quality of the air, and to reduce the risk of disease in the population. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
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