Dan Savastru - Academia.edu (original) (raw)

Papers by Dan Savastru

A new method of detecting how a crack appears and grows, as a damage, in fiber reinforced polymer... more A new method of detecting how a crack appears and grows, as a damage, in fiber reinforced polymer composite material using embedded Fiber Bragg Grating (FBG) and/or Long Period Grating Fiber Sensors (LPGFS) is presented. Different features of the crack mechanism that induce a change in the FBG sensor or LPGFS response are identified. The response of FBG sensor or LPGFS under host composite material host crack action is investigated and simulated for defining the functional limits of the composite material. FBG sensor or LPGFS are considered as embedded in polymer matrix of composite material.

Surface plasmon propagation in a multilayer planar waveguide structure was studied. We are propos... more Surface plasmon propagation in a multilayer planar waveguide structure was studied. We are proposing an algorithm for solving the characteristic equation in order to determine the complex effective refractive index n eff. The absolute minimum of the complex characteristic equation is determined in three steps considering the nodes of an increasingly refined mesh. After each step a new mesh is created around the node of the previous mesh in which the minimum was found. Tests on a 4-layer structure proved that the algorithm is convergent, rapid and accurate.

In this paper we evaluated the efficacy of photodynamic treatment of infected wounds on pig anima... more In this paper we evaluated the efficacy of photodynamic treatment of infected wounds on pig animal model by diffuse reflectance spectrometry. The study was conducted on fifteen wounds contaminated with Staphylococcus aureus bacteria that were incubated for 30 min with methylene blue solution (c = 3.3 x 10-3 M) and exposed to laser radiations (λ = 670 nm, P = 15 mW) for 15 min. The efficiency of photodynamic inactivation of bacteria was evaluated by microbiological exams and diffuse reflectance spectrometry. The results of the microbiological exams showed that the bacterial concentration has decreased from 6.93±0.138 logCFU/ml to 3.12±0.108 logCFU/ml. The spectral examination showed that the diffuse reflectance of wounds contaminated with Staphylococcus aureus has decreased from 5.06±0.036 % to 3.36±0.025 %. In conclusion, photodynamic therapy is an effective method for the treatment of infected wounds and there is a correlation between the CFU count and diffuse reflectance.

Among copper oxides, Cu 2 O is intensively studied due to its high optical absorption coefficient... more Among copper oxides, Cu 2 O is intensively studied due to its high optical absorption coefficient and relatively good electrical properties. Copper oxide thin films properties depend on the deposition method as an effect of detailed arrangement of Cu and O atoms that induce different physical properties. Cu 2 O is a p-type semiconductor having a band gap sufficiently close to the optimal band gap under AM1.5 radiation spectrum, which makes it an attractive material for photovoltaic applications and solar cells. The structural and morphological properties of deposited thin films were investigated by S canning Electron Microscopy (S EM) and Atomic Force Microscopy (AFM). The thin film thickness and optical constants were determined by S pectroscopic Ellipsometry (S E). The purpose of the paper was to study the technological possibilities of preparing high quality Cu 2 O thin films, used in photovoltaic applications. The sputter-deposited Cu 2 O thin films presented in this work show g...

Knowing the noise level measured in saline medium of-118dBm we designed and constructed a complex... more Knowing the noise level measured in saline medium of-118dBm we designed and constructed a complex antenna system with which we measured the signals injected from a generator in this environment. Measurements made with the antenna system in saline environment, have highlighted the signal level of-61.5dBm, much lower than until now. Thus, the attenuation of the saline medium was determined for the horizontal plane compared to the previous measurements made for the vertical plane.

Fifth International Conference on Remote Sensing and Geoinformation of the Environment (RSCy2017), 2017

The aim of this study is to evaluate the human impact, in terms of organic matter distribution an... more The aim of this study is to evaluate the human impact, in terms of organic matter distribution and chlorophyll found in representative lakes from Bucharest city. The water quality of these lakes was evaluated using fluorescence spectroscopy together with conductivity and pH. Fluorescence data, in the form tryptophan/humic acid ratio, was used to evaluate the humification degree and to evidence the level of microbial contaminations of water lakes. Graphical representation of fluorescence ratio, Chl-a intensity, conductivity and pH was used to divide the analyzed samples in two groups. A quality score of 0 or 1 was introduced to delimitate between good or poor water quality using threshold values. The use of quality scores was helpful in realisation of a water quality map with Bucharest’s lakes, indicating the limnological systems’ ecological state. The results showed that the analysis of chromophoric organic matter can be useful in identifying the negative human influence on urban la...

In this paper we present theoretical and experimental results regarding the analysis of optimum c... more In this paper we present theoretical and experimental results regarding the analysis of optimum conditions to couple the light within a BK7-Au-As2S3-Air plasmonic compound. We first determined the characteristic equation for the plasmonic waveguide structure consisting in four thin layers by solving the system of Helmholtz equations and applying continuity conditions at the three interfaces of the structure. Subsequently, numerical calculations have been done to obtain the propagation constant and the field distribution within the structure layers. The plasmonic mode confined to the metal interface corresponds to TM0 waveguide mode. The structure supports higher order waveguide modes which can be exited, for several dielectric thicknesses, using low refractive index prism. The investigations emphasize that the value of the resonance angle is in very good accordance with our theoretical findings. Plasmonic waveguide which contains As2S3 as active optical material is a promising confi...

Rock microfracturing in the Earth’s crust preceding a seismic rupture may cause local surface def... more Rock microfracturing in the Earth’s crust preceding a seismic rupture may cause local surface deformation fields, rock dislocations, charged particle generation and motion, electrical conductivity changes, radon and other gases emission, fluid diffusion, electrokinetic, piezomagnetic and piezoelectric effects as well as climate fluctuations. Space-time anomalies of radon gas emitted in underground water, soil and near the ground air weeks to days in the epicentral areas can be associated with the strain stress changes that occurred before the occurrence of medium and strong earthquakes. This paper presents some results of continuous monitoring of radon in air near the ground with short term (ten days exposure time) solid state nuclear track detectors (SSNTD) CR-39 at seismic stations Plostina (Vrancea), and Bucharest Magurele, Romania. During 2012–2016 periods, radon concentration anomalies along with meteorological parameters were found to be statistically significant for the seism...

Sensors (Basel, Switzerland), 2021

The neutrinos of cosmic radiation, due to interaction with any known medium in which the Cherenko... more The neutrinos of cosmic radiation, due to interaction with any known medium in which the Cherenkov detector is used, produce energy radiation phenomena in the form of a Cherenkov cone, in very large frequency spectrum. These neutrinos carry with them the information about the phenomena that produced them and by detecting the electromagnetic energies generated by the Cherenkov cone, we can find information about the phenomena that formed in the universe, at a much greater distance, than possibility of actually detection with current technologies. At present, a very high number of sensors for detection electromagnetic energy is required. Thus, some sensors may detect very low energy levels, which can lead to the erroneous determination of the Cherenkov cone, thus leading to information errors. As a novelty, we propose, to use these sensors for determination of the dielectrically permittivity of any known medium in which the Cherenkov detector is used, by preliminary measurements, the ...

Journal of Optoelectronics and Advanced Materials, 2010

This paper is the second of a series on numerical simulation of distributed feedback fiber laser ... more This paper is the second of a series on numerical simulation of distributed feedback fiber laser (DFB-FL) sensors and their applications, especially in aeronautics. Here the developed numerical analysis of a DFB-FL air acoustic sensor is presented. The main purpose of the performed theoretical analysis consists into a better understanding of DFB-FL itself and of its intereaction with environment in order to be operated as an air acoustic sensor.

Journal of Optoelectronics and Advanced Materials, 2005

Arsenic chalcogenide microlenses (As 2 S 3 ) produced by an original procedure have been used for... more Arsenic chalcogenide microlenses (As 2 S 3 ) produced by an original procedure have been used for focusing the red - infrared laser light direct through an optical fiber. The microlenses with diameter in the range 150 - 400μm were glued on the optical single-mode fiber ends by Canada balm under optical microscope. The focusing effect of the microlenses was investigated in a stereomicroscope, and the focusing quality was studied with the radiation of a He-Ne laser.

Journal of Optoelectronics and Advanced Materials, 2010

Mining waste impacts on the environment are related to the biophysical and spectral footprints ch... more Mining waste impacts on the environment are related to the biophysical and spectral footprints changes in the waste disposal areas and resulting loss of land productivity, direct and indirect effects on different agroforest, urban and aquatic ecosystems. The aim of this paper was to evaluate and characterize selected hazardous waste disposal sites in Baia Mare region, Romania. Use of Landsat TM, ETM and IKONOS satellite data over 1989- 2007 period stressed land cover changes in some mining industry test areas. Accuracy of image processing results (mineralogical classification) was confirmed through ground sampling and analysis of reflectance spectra with portable GER 2600 spectroradiometer.

Journal of Optoelectronics and Advanced Materials, 2008

Land Survey is the backbone for any civil engineering planning and realisation. This is true both... more Land Survey is the backbone for any civil engineering planning and realisation. This is true both for Cartography at large scale (1:5000 and higher) and for studying and solve problems associated to soil movements and territorial disasters. Buildings located on (or close to) a risk area like landslide, etc. are a sensible problem that Public Administration in general, have to take into account. The needs of monitoring part of the territory, in particular sensible public buildings such schools, hospitals, etc. leads to the use of GNSS technologies in addition to classical instruments.

Climate changes and rapid urbanization are the main factors affecting forest vegetation land cove... more Climate changes and rapid urbanization are the main factors affecting forest vegetation land cover around the globe. Satellite remote sensing data provide important information to detect changes in forest landscapes over long time periods in contrast to conventional approaches. Satellite remote sensing provides a useful tool to capture the temporal dynamics of forest vegetation change in response to climate shifts, at spatial resolutions fine enough to capture the spatial heterogeneity. In this paper, we present an integrated, standardized approach that aims at combining remote sensing data provided by different sensors, available for a long-term period (2000-2018). This multi-sensor and multi-temporal approach detects Cernica-Branesti periurban forest vegetation dynamics based on derived biophysical parameters within the highly dynamic city of Bucharest, as a test case. Landsat TM/ETM/OLI, MODIS Terra/Aqua, and Sentinel 2 data are combined in an integrated procedure to locate fores...

During last decade, due to fast progress of geospatial technology development, all weather, high-... more During last decade, due to fast progress of geospatial technology development, all weather, high-resolution and highdynamic range, a huge time-series data base is available for earthquake precursors anomalies monitoring in active geotectonic areas. In this paper, changes before and after the Vrancea earthquakes in the crustal dynamics as well as in the land and atmospheric parameters (land surface temperature LST, surface latent heat flux -SLHF, and air surface temperature- AT anomalies, have been investigated on the basis of time-series geospatial (NOAA AVHRR and MODIS Terra/Aqua) and field data analysis for January 2012- January 2020 period. For some analyzed earthquakes, starting with ten days up to one week prior to a moderate or earthquakes a transient thermal infrared rise appeared in LST (5-10 K° ), SLHF (tens of W/m2 ), and AT (2-10 C° ) values higher than the normal, function of the magnitude and focal depth, which disappeared after the main shock. The joint analysis of geo...

This paper is pointing to an investigation of various aspects of distributed feedback fiber laser... more This paper is pointing to an investigation of various aspects of distributed feedback fiber laser sensors and their interaction with environment and of possible applications by numerically solving coupled-mode equations system describing the laser field propagation. The developed numerical analysis has the aim of a better understanding of DFB-FL itself and of its interaction with environment in order to be operated as a sensor. The main idea of the paper consists into investigating how various environment parameters modify the coefficients of coupled-mode equations describing laser field propagation through the DFB-FL structure. Basically, this is the key of understanding operation of DFB-FL sensors.

The Insulator-Metal-Insulator-Insulator (IMII) plasmonic structures present a great interest for ... more The Insulator-Metal-Insulator-Insulator (IMII) plasmonic structures present a great interest for the optical photonics devices. In this paper we present an analyze for coupling of light into plasmonic structures which contains a dielectric waveguide. We obtained the characteristic equation for the wave guides in the IMII structure by solving the Helmholtz equations in four homogeneous media. The characteristic equations for three and four layers have similar forms as established. Subsequently, the numerical simulations for TM waveguide modes and the coupling by a prism with the refractive index lower then waveguide were done. It was showed that, the TM0 mode is confined to the metal interface and can’t be exited. Resonance coupling into higher waveguide modes may be realized for some film thicknesses.

A new method of detecting how a crack appears and grows, as a damage, in fiber reinforced polymer... more A new method of detecting how a crack appears and grows, as a damage, in fiber reinforced polymer composite material using embedded Fiber Bragg Grating (FBG) and/or Long Period Grating Fiber Sensors (LPGFS) is presented. Different features of the crack mechanism that induce a change in the FBG sensor or LPGFS response are identified. The response of FBG sensor or LPGFS under host composite material host crack action is investigated and simulated for defining the functional limits of the composite material. FBG sensor or LPGFS are considered as embedded in polymer matrix of composite material.

Surface plasmon propagation in a multilayer planar waveguide structure was studied. We are propos... more Surface plasmon propagation in a multilayer planar waveguide structure was studied. We are proposing an algorithm for solving the characteristic equation in order to determine the complex effective refractive index n eff. The absolute minimum of the complex characteristic equation is determined in three steps considering the nodes of an increasingly refined mesh. After each step a new mesh is created around the node of the previous mesh in which the minimum was found. Tests on a 4-layer structure proved that the algorithm is convergent, rapid and accurate.

In this paper we evaluated the efficacy of photodynamic treatment of infected wounds on pig anima... more In this paper we evaluated the efficacy of photodynamic treatment of infected wounds on pig animal model by diffuse reflectance spectrometry. The study was conducted on fifteen wounds contaminated with Staphylococcus aureus bacteria that were incubated for 30 min with methylene blue solution (c = 3.3 x 10-3 M) and exposed to laser radiations (λ = 670 nm, P = 15 mW) for 15 min. The efficiency of photodynamic inactivation of bacteria was evaluated by microbiological exams and diffuse reflectance spectrometry. The results of the microbiological exams showed that the bacterial concentration has decreased from 6.93±0.138 logCFU/ml to 3.12±0.108 logCFU/ml. The spectral examination showed that the diffuse reflectance of wounds contaminated with Staphylococcus aureus has decreased from 5.06±0.036 % to 3.36±0.025 %. In conclusion, photodynamic therapy is an effective method for the treatment of infected wounds and there is a correlation between the CFU count and diffuse reflectance.

Among copper oxides, Cu 2 O is intensively studied due to its high optical absorption coefficient... more Among copper oxides, Cu 2 O is intensively studied due to its high optical absorption coefficient and relatively good electrical properties. Copper oxide thin films properties depend on the deposition method as an effect of detailed arrangement of Cu and O atoms that induce different physical properties. Cu 2 O is a p-type semiconductor having a band gap sufficiently close to the optimal band gap under AM1.5 radiation spectrum, which makes it an attractive material for photovoltaic applications and solar cells. The structural and morphological properties of deposited thin films were investigated by S canning Electron Microscopy (S EM) and Atomic Force Microscopy (AFM). The thin film thickness and optical constants were determined by S pectroscopic Ellipsometry (S E). The purpose of the paper was to study the technological possibilities of preparing high quality Cu 2 O thin films, used in photovoltaic applications. The sputter-deposited Cu 2 O thin films presented in this work show g...

Knowing the noise level measured in saline medium of-118dBm we designed and constructed a complex... more Knowing the noise level measured in saline medium of-118dBm we designed and constructed a complex antenna system with which we measured the signals injected from a generator in this environment. Measurements made with the antenna system in saline environment, have highlighted the signal level of-61.5dBm, much lower than until now. Thus, the attenuation of the saline medium was determined for the horizontal plane compared to the previous measurements made for the vertical plane.

Fifth International Conference on Remote Sensing and Geoinformation of the Environment (RSCy2017), 2017

The aim of this study is to evaluate the human impact, in terms of organic matter distribution an... more The aim of this study is to evaluate the human impact, in terms of organic matter distribution and chlorophyll found in representative lakes from Bucharest city. The water quality of these lakes was evaluated using fluorescence spectroscopy together with conductivity and pH. Fluorescence data, in the form tryptophan/humic acid ratio, was used to evaluate the humification degree and to evidence the level of microbial contaminations of water lakes. Graphical representation of fluorescence ratio, Chl-a intensity, conductivity and pH was used to divide the analyzed samples in two groups. A quality score of 0 or 1 was introduced to delimitate between good or poor water quality using threshold values. The use of quality scores was helpful in realisation of a water quality map with Bucharest’s lakes, indicating the limnological systems’ ecological state. The results showed that the analysis of chromophoric organic matter can be useful in identifying the negative human influence on urban la...

In this paper we present theoretical and experimental results regarding the analysis of optimum c... more In this paper we present theoretical and experimental results regarding the analysis of optimum conditions to couple the light within a BK7-Au-As2S3-Air plasmonic compound. We first determined the characteristic equation for the plasmonic waveguide structure consisting in four thin layers by solving the system of Helmholtz equations and applying continuity conditions at the three interfaces of the structure. Subsequently, numerical calculations have been done to obtain the propagation constant and the field distribution within the structure layers. The plasmonic mode confined to the metal interface corresponds to TM0 waveguide mode. The structure supports higher order waveguide modes which can be exited, for several dielectric thicknesses, using low refractive index prism. The investigations emphasize that the value of the resonance angle is in very good accordance with our theoretical findings. Plasmonic waveguide which contains As2S3 as active optical material is a promising confi...

Rock microfracturing in the Earth’s crust preceding a seismic rupture may cause local surface def... more Rock microfracturing in the Earth’s crust preceding a seismic rupture may cause local surface deformation fields, rock dislocations, charged particle generation and motion, electrical conductivity changes, radon and other gases emission, fluid diffusion, electrokinetic, piezomagnetic and piezoelectric effects as well as climate fluctuations. Space-time anomalies of radon gas emitted in underground water, soil and near the ground air weeks to days in the epicentral areas can be associated with the strain stress changes that occurred before the occurrence of medium and strong earthquakes. This paper presents some results of continuous monitoring of radon in air near the ground with short term (ten days exposure time) solid state nuclear track detectors (SSNTD) CR-39 at seismic stations Plostina (Vrancea), and Bucharest Magurele, Romania. During 2012–2016 periods, radon concentration anomalies along with meteorological parameters were found to be statistically significant for the seism...

Sensors (Basel, Switzerland), 2021

The neutrinos of cosmic radiation, due to interaction with any known medium in which the Cherenko... more The neutrinos of cosmic radiation, due to interaction with any known medium in which the Cherenkov detector is used, produce energy radiation phenomena in the form of a Cherenkov cone, in very large frequency spectrum. These neutrinos carry with them the information about the phenomena that produced them and by detecting the electromagnetic energies generated by the Cherenkov cone, we can find information about the phenomena that formed in the universe, at a much greater distance, than possibility of actually detection with current technologies. At present, a very high number of sensors for detection electromagnetic energy is required. Thus, some sensors may detect very low energy levels, which can lead to the erroneous determination of the Cherenkov cone, thus leading to information errors. As a novelty, we propose, to use these sensors for determination of the dielectrically permittivity of any known medium in which the Cherenkov detector is used, by preliminary measurements, the ...

Journal of Optoelectronics and Advanced Materials, 2010

This paper is the second of a series on numerical simulation of distributed feedback fiber laser ... more This paper is the second of a series on numerical simulation of distributed feedback fiber laser (DFB-FL) sensors and their applications, especially in aeronautics. Here the developed numerical analysis of a DFB-FL air acoustic sensor is presented. The main purpose of the performed theoretical analysis consists into a better understanding of DFB-FL itself and of its intereaction with environment in order to be operated as an air acoustic sensor.

Journal of Optoelectronics and Advanced Materials, 2005

Arsenic chalcogenide microlenses (As 2 S 3 ) produced by an original procedure have been used for... more Arsenic chalcogenide microlenses (As 2 S 3 ) produced by an original procedure have been used for focusing the red - infrared laser light direct through an optical fiber. The microlenses with diameter in the range 150 - 400μm were glued on the optical single-mode fiber ends by Canada balm under optical microscope. The focusing effect of the microlenses was investigated in a stereomicroscope, and the focusing quality was studied with the radiation of a He-Ne laser.

Journal of Optoelectronics and Advanced Materials, 2010

Mining waste impacts on the environment are related to the biophysical and spectral footprints ch... more Mining waste impacts on the environment are related to the biophysical and spectral footprints changes in the waste disposal areas and resulting loss of land productivity, direct and indirect effects on different agroforest, urban and aquatic ecosystems. The aim of this paper was to evaluate and characterize selected hazardous waste disposal sites in Baia Mare region, Romania. Use of Landsat TM, ETM and IKONOS satellite data over 1989- 2007 period stressed land cover changes in some mining industry test areas. Accuracy of image processing results (mineralogical classification) was confirmed through ground sampling and analysis of reflectance spectra with portable GER 2600 spectroradiometer.

Journal of Optoelectronics and Advanced Materials, 2008

Land Survey is the backbone for any civil engineering planning and realisation. This is true both... more Land Survey is the backbone for any civil engineering planning and realisation. This is true both for Cartography at large scale (1:5000 and higher) and for studying and solve problems associated to soil movements and territorial disasters. Buildings located on (or close to) a risk area like landslide, etc. are a sensible problem that Public Administration in general, have to take into account. The needs of monitoring part of the territory, in particular sensible public buildings such schools, hospitals, etc. leads to the use of GNSS technologies in addition to classical instruments.

Climate changes and rapid urbanization are the main factors affecting forest vegetation land cove... more Climate changes and rapid urbanization are the main factors affecting forest vegetation land cover around the globe. Satellite remote sensing data provide important information to detect changes in forest landscapes over long time periods in contrast to conventional approaches. Satellite remote sensing provides a useful tool to capture the temporal dynamics of forest vegetation change in response to climate shifts, at spatial resolutions fine enough to capture the spatial heterogeneity. In this paper, we present an integrated, standardized approach that aims at combining remote sensing data provided by different sensors, available for a long-term period (2000-2018). This multi-sensor and multi-temporal approach detects Cernica-Branesti periurban forest vegetation dynamics based on derived biophysical parameters within the highly dynamic city of Bucharest, as a test case. Landsat TM/ETM/OLI, MODIS Terra/Aqua, and Sentinel 2 data are combined in an integrated procedure to locate fores...

During last decade, due to fast progress of geospatial technology development, all weather, high-... more During last decade, due to fast progress of geospatial technology development, all weather, high-resolution and highdynamic range, a huge time-series data base is available for earthquake precursors anomalies monitoring in active geotectonic areas. In this paper, changes before and after the Vrancea earthquakes in the crustal dynamics as well as in the land and atmospheric parameters (land surface temperature LST, surface latent heat flux -SLHF, and air surface temperature- AT anomalies, have been investigated on the basis of time-series geospatial (NOAA AVHRR and MODIS Terra/Aqua) and field data analysis for January 2012- January 2020 period. For some analyzed earthquakes, starting with ten days up to one week prior to a moderate or earthquakes a transient thermal infrared rise appeared in LST (5-10 K° ), SLHF (tens of W/m2 ), and AT (2-10 C° ) values higher than the normal, function of the magnitude and focal depth, which disappeared after the main shock. The joint analysis of geo...

This paper is pointing to an investigation of various aspects of distributed feedback fiber laser... more This paper is pointing to an investigation of various aspects of distributed feedback fiber laser sensors and their interaction with environment and of possible applications by numerically solving coupled-mode equations system describing the laser field propagation. The developed numerical analysis has the aim of a better understanding of DFB-FL itself and of its interaction with environment in order to be operated as a sensor. The main idea of the paper consists into investigating how various environment parameters modify the coefficients of coupled-mode equations describing laser field propagation through the DFB-FL structure. Basically, this is the key of understanding operation of DFB-FL sensors.

The Insulator-Metal-Insulator-Insulator (IMII) plasmonic structures present a great interest for ... more The Insulator-Metal-Insulator-Insulator (IMII) plasmonic structures present a great interest for the optical photonics devices. In this paper we present an analyze for coupling of light into plasmonic structures which contains a dielectric waveguide. We obtained the characteristic equation for the wave guides in the IMII structure by solving the Helmholtz equations in four homogeneous media. The characteristic equations for three and four layers have similar forms as established. Subsequently, the numerical simulations for TM waveguide modes and the coupling by a prism with the refractive index lower then waveguide were done. It was showed that, the TM0 mode is confined to the metal interface and can’t be exited. Resonance coupling into higher waveguide modes may be realized for some film thicknesses.