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Mercouri G Kanatzidis - One of the best experts on this subject based on the ideXlab platform.
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high temperature charge and thermal transport properties of the n type thermoelectric material pbse
Physical Review B, 2011Co-Authors: John Androulakis, Duck Young Chung, Li Zhang, Ctirad Uher, Thomas C Hasapis, E Hatzikraniotis, K M Paraskevopoulos, Mercouri G KanatzidisAbstract:We present a detailed study of the charge transport, infrared optical reflectivity, and thermal transport properties of n-type PbSe crystals. A strong scattering, mobility-limiting mechanism was revealed to be at play at temperatures above 500 K. The mechanism is indicative of complex electron-phonon interactions that cannot be explained by conventional acoustic phonon scattering alone. We applied the first-order nonparabolicity approximation to extract the density-of-states effective mass as a function of doping both at room temperature and at 700 K. The results are compared to those of a parabolic band model and in light of doping-dependent studies of the infrared optical reflectivity. The thermal conductivity behavior as a function of temperature shows a strong deviation from the expected Debye-Peierls high-temperature behavior (umklapp dominated) indicating an additional heat-Carrying Channel, which we associate with optical phonon excitations. The correlation of the thermal conductivity observations to the high-temperature carrier mobility behavior is discussed. The thermoelectric figure of merit exhibits a promising value of {approx} 0.8 at 700 K at {approx} 1.5 x 10{sup 19} cm{sup -3}.
Shlomo Zach - One of the best experts on this subject based on the ideXlab platform.
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demonstrating the use of oam modes to facilitate the networking functions of Carrying Channel header information and orthogonal Channel coding
Optics Letters, 2020Co-Authors: Ahmed Almaiman, Haoqian Song, Kai Pang, Runzhou Zhang, Zhe Zhao, Hao Song, Cong Liu, Karapet Manukyan, Kaiheng Zou, Shlomo ZachAbstract:We experimentally demonstrate the use of orbital angular momentum (OAM) modes as a degree of freedom to facilitate the networking functions of Carrying header information and orthogonal Channel coding. First, for Carrying Channel header information, we transmit a 10 Gb/s on-off keying (OOK) data Channel as a Gaussian beam and add to it a 10 Mb/s OOK header carried by an OAM beam with the mode order l=3. We recover the header and use it to drive a switch and select the output port. Secondly, for orthogonal Channel coding, we configure transmitters to generate orthogonal spatial codes (orthogonal spatial beam profiles of OAM modes), each Carrying an independent data stream. We measure the correlation between the OAM codes and demonstrate their use in a multiple access system Carrying two 10 Gb/s OOK data Channels. At the end of this Letter, we combine the concepts of using OAM modes for Carrying Channel header information and orthogonal Channel coding in one experiment. We transmit a 10 Gb/s OOK data Channel as a Gaussian beam and add to it two 10 Mb/s OOK header waveforms carried by different OAM codes. In the routing node, we recover one of the headers to drive the switch.
Li Zhang - One of the best experts on this subject based on the ideXlab platform.
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high temperature charge and thermal transport properties of the n type thermoelectric material pbse
Physical Review B, 2011Co-Authors: John Androulakis, Duck Young Chung, Li Zhang, Ctirad Uher, Thomas C Hasapis, E Hatzikraniotis, K M Paraskevopoulos, Mercouri G KanatzidisAbstract:We present a detailed study of the charge transport, infrared optical reflectivity, and thermal transport properties of n-type PbSe crystals. A strong scattering, mobility-limiting mechanism was revealed to be at play at temperatures above 500 K. The mechanism is indicative of complex electron-phonon interactions that cannot be explained by conventional acoustic phonon scattering alone. We applied the first-order nonparabolicity approximation to extract the density-of-states effective mass as a function of doping both at room temperature and at 700 K. The results are compared to those of a parabolic band model and in light of doping-dependent studies of the infrared optical reflectivity. The thermal conductivity behavior as a function of temperature shows a strong deviation from the expected Debye-Peierls high-temperature behavior (umklapp dominated) indicating an additional heat-Carrying Channel, which we associate with optical phonon excitations. The correlation of the thermal conductivity observations to the high-temperature carrier mobility behavior is discussed. The thermoelectric figure of merit exhibits a promising value of {approx} 0.8 at 700 K at {approx} 1.5 x 10{sup 19} cm{sup -3}.
Xing Hongyan - One of the best experts on this subject based on the ideXlab platform.
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Electromagnetic Fields Associated With the M‐Component Mode of Charge Transfer
'American Geophysical Union (AGU)', 2019Co-Authors: He Lixia, Azadifar Mohammad, Rubinstein Marcos, Rachidi Farhad, Rakov, Vladimir A., Cooray Vernon, Pavanello Davide, Xing HongyanAbstract:In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-component or leader/return-stroke like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created Channel connected to the ICC-Carrying Channel at relatively short distance from the tower top, resulting in the so-called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M-component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with the M-component charge transfer mode (including classical M-component pulses and M-component-type pulses superimposed on the initial continuous current) is analyzed, and compared with its effect on the fields associated with the return-stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2D FDTD (2-Dimentional Finite-Difference Time-Domain) method, in which the M-component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning Channel (Rakov et al. 1995 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for ‘classical’ M-component and M-component-type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of the M-component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster travelling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M-component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component which mainly depends on the overall transferred charge. The contribution of the radiation component to the M-component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch-to-Channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E-field and 1.9 for the H-field. For a junction height greater than 6 km, the E-field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li et al. (2016b) in which an electric field propagation factor of 1.8 was inferred for return strokes and mixed mode pulses, considering that junction points lower than 1 km or so would result in a mixed-mode of charge transfer, in which a downward leader/return-stroke like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 s or so) for which the tendency reverses. Finally, model-predicted fields associated with different charge transfer modes, namely return stroke, mixed mode, classical M-component, and M-component-type ICC pulse are compared with experimental observations at the Säntis tower. It is found that the vertical electric field waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed mode models (1.0 km for the return stroke and 0.8 km for the mixed-mode pulse) are lower than the value of 2.0 km typically used in the literature
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Electromagnetic fields associated with the M‐component mode of charge transfer
'American Geophysical Union (AGU)', 2019Co-Authors: He Lixia, Azadifar Mohammad, Rubinstein Marcos, Rachidi Farhad, Rakov, Vladimir A., Cooray Vernon, Pavanello Davide, Xing HongyanAbstract:In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-component or leader/return‐stroke‐like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created Channel connected to the ICC‐Carrying Channel at relatively short distance from the tower top, resulting in the so‐called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M‐component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with theM‐component charge transfer mode (including classical M‐component pulses and M‐component‐type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2‐Dimentional Finite‐Difference Time Domain method, in which the M‐component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning Channel (Rakov et al., 1995, https://doi.org/10.1029/95JD01924 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M‐component and M‐component‐type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of theM‐component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M‐component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component, which mainly depends on the overall transferred charge. The contribution of the radiation component to the M‐component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch‐to‐Channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E‐field and 1.9 for the H‐field. For a junction height greater than 6 km, the E‐field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li, Azadifar, Rachidi, Rubinstein, Paolone, et al. (2016, https://doi.org/10.1109/TEMC.2015.2483018) in which an electric field propagation factor of 1.8 was inferred for return strokes and mixed‐mode pulses, considering that junction points lower than 1 km or so would result in a mixed mode of charge transfer, in which a downward leader/return‐stroke‐like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 μs or so) for which the tendency reverses. Finally, model‐predicted fields associated with different charge transfer modes, namely, return stroke, mixed‐mode, classical M‐component, and M‐component‐type ICC pulse are compared with experimental observations at the Säntis Tower. It is found that the vertical electric field waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed‐mode models (1.0 km for the return stroke and 0.8 km for the mixed‐mode pulse) are lower than the value of 2.0 km typically used in the literature
Ahmed Almaiman - One of the best experts on this subject based on the ideXlab platform.
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demonstrating the use of oam modes to facilitate the networking functions of Carrying Channel header information and orthogonal Channel coding
Optics Letters, 2020Co-Authors: Ahmed Almaiman, Haoqian Song, Kai Pang, Runzhou Zhang, Zhe Zhao, Hao Song, Cong Liu, Karapet Manukyan, Kaiheng Zou, Shlomo ZachAbstract:We experimentally demonstrate the use of orbital angular momentum (OAM) modes as a degree of freedom to facilitate the networking functions of Carrying header information and orthogonal Channel coding. First, for Carrying Channel header information, we transmit a 10 Gb/s on-off keying (OOK) data Channel as a Gaussian beam and add to it a 10 Mb/s OOK header carried by an OAM beam with the mode order l=3. We recover the header and use it to drive a switch and select the output port. Secondly, for orthogonal Channel coding, we configure transmitters to generate orthogonal spatial codes (orthogonal spatial beam profiles of OAM modes), each Carrying an independent data stream. We measure the correlation between the OAM codes and demonstrate their use in a multiple access system Carrying two 10 Gb/s OOK data Channels. At the end of this Letter, we combine the concepts of using OAM modes for Carrying Channel header information and orthogonal Channel coding in one experiment. We transmit a 10 Gb/s OOK data Channel as a Gaussian beam and add to it two 10 Mb/s OOK header waveforms carried by different OAM codes. In the routing node, we recover one of the headers to drive the switch.