In this article, we present a study on the microwave frequency properties of poly(vinyl chloride)... more In this article, we present a study on the microwave frequency properties of poly(vinyl chloride)/Fe composite nanofibers, with different concentrations of iron particles incorporated in poly(vinyl chloride) matrix. Using electrospinning, composite nanofibers were obtained with size ranging between 100 and 500 nm. The absorption properties of synthesized nanofibers were measured between two open-end rectangular waveguides in the 8-12 GHz frequency domain. The transmission loss measurements for poly(vinyl chloride)/Fe composite nanofibers demonstrated that this material can be used as protection material in X-band frequency domain. The applied magnetic field significantly modifies the measured scattering parameters in our samples case in a rather large domain of values for the field.
During the preparation of Fe3O4/PVC composite nanofibers by electrospinning of FeCl3 solutions in... more During the preparation of Fe3O4/PVC composite nanofibers by electrospinning of FeCl3 solutions in PVC/THF/DMF system was observed a strong dependence of the formation mechanism of Fe3O4 nanoparticles on FeCl3 concentration, with an optimum at 2.91% FeCl3 in PVC. To explain the existence of this optimum is proposed for the first time an original mechanism, well supported by the results of
... VMFV method has been used to study the dynamics of MVs development in the polymer ... Owing t... more ... VMFV method has been used to study the dynamics of MVs development in the polymer ... Owing to horizontal orientation and small spacer thickness, the gas-phase mass transfer was ... themembrane is also an important parameter, which strongly affects the final morphology of the ...
Chitosan films obtained by dry phase inversion were prepared from an aqueous solution of chitosan... more Chitosan films obtained by dry phase inversion were prepared from an aqueous solution of chitosan in acetic acid. The films, of thickness less than 20 μm, were transparent, very flexible and had smooth surfaces. Increasing the film thickness induced an increase of the internal tensions and the consequent formation of a rough surface. Structural investigations by X-ray diffraction and Fourier transform IR analysis, showed that the chitosan films, as prepared, are amorphous. Further annealing to evaporate acetic acid and water traces, changed the amorphous phase into a more ordered phase, characterized by diffraction peaks at 2θ values of 9, 17, 20 and 23 degrees. Thermal investigations by TG, DTG, and DTA revealed that the decomposition of the chitosan films as prepared proceeds in two stages, starting from 180°C and 540°C.
In this work, we present a study on the microwave frequency absorption of PVC/ -Fe 2 O 3 , PVC/Fe... more In this work, we present a study on the microwave frequency absorption of PVC/ -Fe 2 O 3 , PVC/Fe 3 O 4 , and PVC/CoFe 2 O 4 /CoO nanofibers. The composite nanofibers with size ranging between 100 nm and 1 m where obtained by electrospinning technique. The absorption properties of synthesized nanofibers were measured between two open-end rectangular waveguides in the 8-12 GHz frequency domain. The value of the transmission loss was found to be below 10 dB for PVC/Fe 3 O 4 composite nanofibers demonstrating that this material can be used as absorber of electromagnetic radiation in the mentioned frequency range.
ABSTRACT In this paper we present a study on the microwave frequency properties of PVC/Fe 3 O 4 c... more ABSTRACT In this paper we present a study on the microwave frequency properties of PVC/Fe 3 O 4 composite nanofibers, with different amounts of iron oxide nanoparticles incorporate in PVC matrix. Using electrospinning where obtained composite nanofibers with diameters ranging between 100 nm and 600 nm. The transmission loss of PVC/Fe 3 O 4 composites measured in the microwave frequency range of X-band were found to be below −15 dB demonstrating that these materials can be used as protection material of electromagnetic radia-tion. The applied magnetic field significantly modifies the measured scattering parameters in our samples case in a rather large domain of values for the field.
Cancer is one of the most serious and merciless health problems of the mankind, about seven milli... more Cancer is one of the most serious and merciless health problems of the mankind, about seven million people dying of cancer every year. Two of the most important and promising targets in cancer chemotherapy include DNA alkylating agents and DNA intercalators. The emphasis of this work was to design, synthetize and formulate a mechanism of action for a new class of dual DNA intercalators. The dual DNA intercalators have three main parts: an alkylating unit (represented by two halo-alkyl-ester chains), an intercalator unit (five-or six-membered ring nitrogen heterocycle) and an acetophenone skeleton linker. As mechanism of action, we consider that these compounds act as dual DNA intercalators, the alkylating unit realizing a covalent bonding via DNA protein ''cross-linking effect" while nitrogen heterocycles will realize noncovalent bonding via DNA intercalation with purine and pyrimidine bases from DNA and the amino acids from topoisomerases enzymes. Our hypothesis was confirmed by in vitro anticancer tests against HeLa cell lines, where the newly obtained compounds demonstrated a very good activity.
During the preparation of Fe 3 O 4 /PVC composite nanofibers by electrospinning of FeCl 3 solutio... more During the preparation of Fe 3 O 4 /PVC composite nanofibers by electrospinning of FeCl 3 solutions in PVC/THF/DMF system was observed a strong dependence of the formation mechanism of Fe 3 O 4 nanoparticles on FeCl 3 concentration, with an optimum at 2.91% FeCl 3 in PVC. To explain the existence of this optimum is proposed for the first time an original mechanism, well supported by the results of structural analysis of the composite nanofibers by XRD, FTIR and SEM.
The switching properties of (Nb, Co)-doped BaTiO3 ceramics were studied in the range of temperatu... more The switching properties of (Nb, Co)-doped BaTiO3 ceramics were studied in the range of temperatures between 0° and 140°C. Experimental dependences of switching current density j(t) and electric displacement D(t) are compared to those predicted by the extended Avrami theory. The effective dimension of nucleation is noninteger d∈(2,3), irrespective of the temperatures and amplitudes of field strength.
The experimental switching currents obtained in (Nb, Co)-doped BaTiO3 ceramics at various field a... more The experimental switching currents obtained in (Nb, Co)-doped BaTiO3 ceramics at various field amplitudes and frequencies are compared to those computed from the extended Kolmogorov-Avrami theory, using the method of Fourier spectral analysis. For improving the agreement between data and model, a nonlinear correction in the manner proposed by Hatano et al. was used. The pure switching currents were numerically
A detailed analysis of polarization reversal in ferroelectrics has been performed, in the framewo... more A detailed analysis of polarization reversal in ferroelectrics has been performed, in the framework of the Landau model for phase transitions. Some important characteristics of homogeneous switching have been emphasized and later used in studying the more general case of inhomogeneous switching. The two extremes of switching current correspond to the inflexion points of the dielectric hysteresis loop. Hysteresis loops of poled ferroelectric samples are expected to include negative-susceptibility regions, for high-frequency applied electric fields. The switching current minimum is eliminated by the experimental method used for recording the switching responses. Equivalent Landau coefficients and electric fields have been defined, in order to integrate the size effects and inhomogeneity contribution to switching of the global order parameter. We correlated the size effects on the critical parameters of the switching (the coercive field) and the ferroelectric-to-paraelectric phase transition (the Curie temperature). Polarization reversal in small-size ferroelectrics can be regarded as a diffuse phase transition, whereas its character is closer to normal for large-size samples. The size dependencies of the reversal speed and maximum current result from the size dependencies of the equivalent Landau coefficients and electric field inducing reversal.
... l 196 ( 1994) 2722ii0 Switching currents in (Nb, Co)doped BaTi03 ceramics in the presence of ... more ... l 196 ( 1994) 2722ii0 Switching currents in (Nb, Co)doped BaTi03 ceramics in the presence of a sinusoidal electric field Liliana Mitoseriu, Vasile Tura, Alexandru Stancu . ... C(t,t')2o [cos(wt')cos(cot)] (A.3) and the volume fraction of the reversed area, q(t)=1expC 4a oNo sin2(' ...
The real part of the complex dielectric permittivity (e:) and the dielectric loss angle (tan 6) a... more The real part of the complex dielectric permittivity (e:) and the dielectric loss angle (tan 6) are measured for ferroelectric NaN02 pressed powders. The effects of manufacturing pressures on the Curie temperature and thermal hysteresis are analysed.
The nonlinear response of a one multilayer capacitor with (Nb, Co)doped BaTiO, ceramics to a sing... more The nonlinear response of a one multilayer capacitor with (Nb, Co)doped BaTiO, ceramics to a single-pulse voltage is analyzed. The dependences ofjm, tl;l' , log j, and j,t, upon the electric field E are compared to those of the barium titanate singlecrystal. The experimental results are compared with some theoretical models. 0375-9601/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDlO375-9601(94)00309-D
Barium titanate ceramics having grain sizes between 0.5μm and 20μm were used in a comparative inv... more Barium titanate ceramics having grain sizes between 0.5μm and 20μm were used in a comparative investigation of the ferro-para phase transition, by recording the temperature dependencies of the heat capacity and pyrocharge. The experimental results and the theoretical approach suggest that internal stresses are the main cause of the observed grain size effects
The field and temperature dependence of the switching parameters in ferroelectric media are obtai... more The field and temperature dependence of the switching parameters in ferroelectric media are obtained using a discreet lattice model developped by Ishibashi. Partial switching process has been simulated using both pulse frequency modulation (PFM) and pulse with modulation (PWM). A new interpretation of the differences between the switching and non-switching responses of the ferroelectric has been obtained on the basis of dipole kinetics described by the proposed model.
Grain size dependence of the initial dielectric constant and Rayleigh coefficients of BaTiO3 cera... more Grain size dependence of the initial dielectric constant and Rayleigh coefficients of BaTiO3 ceramics with grain sizes from 0.5μm to 20μm have been studied. A region of Rayleigh law validity was observed for each grain size. The initial dielectric constant show a maximum for the ceramic with 2.5μm grain size and the Rayleigh coefficient increases with increasing the grain size.
In this article, we present a study on the microwave frequency properties of poly(vinyl chloride)... more In this article, we present a study on the microwave frequency properties of poly(vinyl chloride)/Fe composite nanofibers, with different concentrations of iron particles incorporated in poly(vinyl chloride) matrix. Using electrospinning, composite nanofibers were obtained with size ranging between 100 and 500 nm. The absorption properties of synthesized nanofibers were measured between two open-end rectangular waveguides in the 8-12 GHz frequency domain. The transmission loss measurements for poly(vinyl chloride)/Fe composite nanofibers demonstrated that this material can be used as protection material in X-band frequency domain. The applied magnetic field significantly modifies the measured scattering parameters in our samples case in a rather large domain of values for the field.
During the preparation of Fe3O4/PVC composite nanofibers by electrospinning of FeCl3 solutions in... more During the preparation of Fe3O4/PVC composite nanofibers by electrospinning of FeCl3 solutions in PVC/THF/DMF system was observed a strong dependence of the formation mechanism of Fe3O4 nanoparticles on FeCl3 concentration, with an optimum at 2.91% FeCl3 in PVC. To explain the existence of this optimum is proposed for the first time an original mechanism, well supported by the results of
... VMFV method has been used to study the dynamics of MVs development in the polymer ... Owing t... more ... VMFV method has been used to study the dynamics of MVs development in the polymer ... Owing to horizontal orientation and small spacer thickness, the gas-phase mass transfer was ... themembrane is also an important parameter, which strongly affects the final morphology of the ...
Chitosan films obtained by dry phase inversion were prepared from an aqueous solution of chitosan... more Chitosan films obtained by dry phase inversion were prepared from an aqueous solution of chitosan in acetic acid. The films, of thickness less than 20 μm, were transparent, very flexible and had smooth surfaces. Increasing the film thickness induced an increase of the internal tensions and the consequent formation of a rough surface. Structural investigations by X-ray diffraction and Fourier transform IR analysis, showed that the chitosan films, as prepared, are amorphous. Further annealing to evaporate acetic acid and water traces, changed the amorphous phase into a more ordered phase, characterized by diffraction peaks at 2θ values of 9, 17, 20 and 23 degrees. Thermal investigations by TG, DTG, and DTA revealed that the decomposition of the chitosan films as prepared proceeds in two stages, starting from 180°C and 540°C.
In this work, we present a study on the microwave frequency absorption of PVC/ -Fe 2 O 3 , PVC/Fe... more In this work, we present a study on the microwave frequency absorption of PVC/ -Fe 2 O 3 , PVC/Fe 3 O 4 , and PVC/CoFe 2 O 4 /CoO nanofibers. The composite nanofibers with size ranging between 100 nm and 1 m where obtained by electrospinning technique. The absorption properties of synthesized nanofibers were measured between two open-end rectangular waveguides in the 8-12 GHz frequency domain. The value of the transmission loss was found to be below 10 dB for PVC/Fe 3 O 4 composite nanofibers demonstrating that this material can be used as absorber of electromagnetic radiation in the mentioned frequency range.
ABSTRACT In this paper we present a study on the microwave frequency properties of PVC/Fe 3 O 4 c... more ABSTRACT In this paper we present a study on the microwave frequency properties of PVC/Fe 3 O 4 composite nanofibers, with different amounts of iron oxide nanoparticles incorporate in PVC matrix. Using electrospinning where obtained composite nanofibers with diameters ranging between 100 nm and 600 nm. The transmission loss of PVC/Fe 3 O 4 composites measured in the microwave frequency range of X-band were found to be below −15 dB demonstrating that these materials can be used as protection material of electromagnetic radia-tion. The applied magnetic field significantly modifies the measured scattering parameters in our samples case in a rather large domain of values for the field.
Cancer is one of the most serious and merciless health problems of the mankind, about seven milli... more Cancer is one of the most serious and merciless health problems of the mankind, about seven million people dying of cancer every year. Two of the most important and promising targets in cancer chemotherapy include DNA alkylating agents and DNA intercalators. The emphasis of this work was to design, synthetize and formulate a mechanism of action for a new class of dual DNA intercalators. The dual DNA intercalators have three main parts: an alkylating unit (represented by two halo-alkyl-ester chains), an intercalator unit (five-or six-membered ring nitrogen heterocycle) and an acetophenone skeleton linker. As mechanism of action, we consider that these compounds act as dual DNA intercalators, the alkylating unit realizing a covalent bonding via DNA protein ''cross-linking effect" while nitrogen heterocycles will realize noncovalent bonding via DNA intercalation with purine and pyrimidine bases from DNA and the amino acids from topoisomerases enzymes. Our hypothesis was confirmed by in vitro anticancer tests against HeLa cell lines, where the newly obtained compounds demonstrated a very good activity.
During the preparation of Fe 3 O 4 /PVC composite nanofibers by electrospinning of FeCl 3 solutio... more During the preparation of Fe 3 O 4 /PVC composite nanofibers by electrospinning of FeCl 3 solutions in PVC/THF/DMF system was observed a strong dependence of the formation mechanism of Fe 3 O 4 nanoparticles on FeCl 3 concentration, with an optimum at 2.91% FeCl 3 in PVC. To explain the existence of this optimum is proposed for the first time an original mechanism, well supported by the results of structural analysis of the composite nanofibers by XRD, FTIR and SEM.
The switching properties of (Nb, Co)-doped BaTiO3 ceramics were studied in the range of temperatu... more The switching properties of (Nb, Co)-doped BaTiO3 ceramics were studied in the range of temperatures between 0° and 140°C. Experimental dependences of switching current density j(t) and electric displacement D(t) are compared to those predicted by the extended Avrami theory. The effective dimension of nucleation is noninteger d∈(2,3), irrespective of the temperatures and amplitudes of field strength.
The experimental switching currents obtained in (Nb, Co)-doped BaTiO3 ceramics at various field a... more The experimental switching currents obtained in (Nb, Co)-doped BaTiO3 ceramics at various field amplitudes and frequencies are compared to those computed from the extended Kolmogorov-Avrami theory, using the method of Fourier spectral analysis. For improving the agreement between data and model, a nonlinear correction in the manner proposed by Hatano et al. was used. The pure switching currents were numerically
A detailed analysis of polarization reversal in ferroelectrics has been performed, in the framewo... more A detailed analysis of polarization reversal in ferroelectrics has been performed, in the framework of the Landau model for phase transitions. Some important characteristics of homogeneous switching have been emphasized and later used in studying the more general case of inhomogeneous switching. The two extremes of switching current correspond to the inflexion points of the dielectric hysteresis loop. Hysteresis loops of poled ferroelectric samples are expected to include negative-susceptibility regions, for high-frequency applied electric fields. The switching current minimum is eliminated by the experimental method used for recording the switching responses. Equivalent Landau coefficients and electric fields have been defined, in order to integrate the size effects and inhomogeneity contribution to switching of the global order parameter. We correlated the size effects on the critical parameters of the switching (the coercive field) and the ferroelectric-to-paraelectric phase transition (the Curie temperature). Polarization reversal in small-size ferroelectrics can be regarded as a diffuse phase transition, whereas its character is closer to normal for large-size samples. The size dependencies of the reversal speed and maximum current result from the size dependencies of the equivalent Landau coefficients and electric field inducing reversal.
... l 196 ( 1994) 2722ii0 Switching currents in (Nb, Co)doped BaTi03 ceramics in the presence of ... more ... l 196 ( 1994) 2722ii0 Switching currents in (Nb, Co)doped BaTi03 ceramics in the presence of a sinusoidal electric field Liliana Mitoseriu, Vasile Tura, Alexandru Stancu . ... C(t,t')2o [cos(wt')cos(cot)] (A.3) and the volume fraction of the reversed area, q(t)=1expC 4a oNo sin2(' ...
The real part of the complex dielectric permittivity (e:) and the dielectric loss angle (tan 6) a... more The real part of the complex dielectric permittivity (e:) and the dielectric loss angle (tan 6) are measured for ferroelectric NaN02 pressed powders. The effects of manufacturing pressures on the Curie temperature and thermal hysteresis are analysed.
The nonlinear response of a one multilayer capacitor with (Nb, Co)doped BaTiO, ceramics to a sing... more The nonlinear response of a one multilayer capacitor with (Nb, Co)doped BaTiO, ceramics to a single-pulse voltage is analyzed. The dependences ofjm, tl;l' , log j, and j,t, upon the electric field E are compared to those of the barium titanate singlecrystal. The experimental results are compared with some theoretical models. 0375-9601/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDlO375-9601(94)00309-D
Barium titanate ceramics having grain sizes between 0.5μm and 20μm were used in a comparative inv... more Barium titanate ceramics having grain sizes between 0.5μm and 20μm were used in a comparative investigation of the ferro-para phase transition, by recording the temperature dependencies of the heat capacity and pyrocharge. The experimental results and the theoretical approach suggest that internal stresses are the main cause of the observed grain size effects
The field and temperature dependence of the switching parameters in ferroelectric media are obtai... more The field and temperature dependence of the switching parameters in ferroelectric media are obtained using a discreet lattice model developped by Ishibashi. Partial switching process has been simulated using both pulse frequency modulation (PFM) and pulse with modulation (PWM). A new interpretation of the differences between the switching and non-switching responses of the ferroelectric has been obtained on the basis of dipole kinetics described by the proposed model.
Grain size dependence of the initial dielectric constant and Rayleigh coefficients of BaTiO3 cera... more Grain size dependence of the initial dielectric constant and Rayleigh coefficients of BaTiO3 ceramics with grain sizes from 0.5μm to 20μm have been studied. A region of Rayleigh law validity was observed for each grain size. The initial dielectric constant show a maximum for the ceramic with 2.5μm grain size and the Rayleigh coefficient increases with increasing the grain size.
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