Samples of chromium doped ZnO were synthesized using co-precipitation technique at room temperature. Structural and optical properties of Cr doped ZnO samples were investigated by X-ray diffraction technique (XRD and ...Samples of chromium doped ZnO were synthesized using co-precipitation technique at room temperature. Structural and optical properties of Cr doped ZnO samples were investigated by X-ray diffraction technique (XRD and UV-Visible spectroscopy (UV-Vis) respectively. X-ray diffraction (XRD) patterns confirm that the samples have hexagonal (wurtzite) structure with no additional peak which suggests that Cr ions go to the regular Zn sites in the ZnO crystal structure. The lattice constants were calculated using X-ray diffraction data and it is found that lattice parameters decrease with increasing Cr content. The average grain size was calculated using Scherrer’s formula for pure and Cr doped ZnO samples and it is observed that grain size is in the range 11 to17 nm. Band gap of Zn1–xCrxO samples has been evaluated using UV-Vis spectrometer. It is found that the band gap decreases as Cr increases;it is attributed to the s-d and p interactions and the smaller average grain size. It indicates that incorporation of Cr ions into the ZnO matrix. The chemical species of the grown crystals were identified by Fourier transform infrared spectroscopy (FTIR). From FTIR spectra it is observed that IR peaks corresponding to the Zn-O bands. Such results are presented in this paper quantitatively and qualitatively.展开更多
Semiconductor solar cell (PV cell) has been widely used for generating solar electricity. However, the high cost and severe pollution limits its application. Recently the discovery of graphene may open a door to fabri...Semiconductor solar cell (PV cell) has been widely used for generating solar electricity. However, the high cost and severe pollution limits its application. Recently the discovery of graphene may open a door to fabricate a novel solar cell with lower cost and more environmentally friendly. Our proposed solar cell device consists of a graphene strip and two semiconductor strips with different energy gaps attached to the two edges of the graphene strip on a flat plane. This structure is a two-dimensional quantum well. The energy bands of graphene can be described by a two-dimensional Dirac equation centered on hexagonal corners (Dirac points) of the honeycomb lattice Brillouin zone. The 2 D Dirac equation has been solved numerically in this paper. The results indicate that the graphene quantum well possesses very dense quantum energy states which imply that quantum well of this type can absorb sun light with more different frequencies. If we use graphene quantum well to fabricate the photo voltaic cell, the efficiency of converting solar energy to electricity will be enhanced.展开更多
Presented here are the Generalized BCS Equations incorporating Fermi Energy for the study of the {Δ, Tc, jc(T)} values of both elemental and composite superconductors (SCs) for all T ≤ Tc, where Δ, Tc and jc(T) den...Presented here are the Generalized BCS Equations incorporating Fermi Energy for the study of the {Δ, Tc, jc(T)} values of both elemental and composite superconductors (SCs) for all T ≤ Tc, where Δ, Tc and jc(T) denote, respectively, one of the gap values, the critical temperature and the T-dependent critical current density. This framework, which extends our earlier study that dealt with the {Δ0, Tc, jc(0)} values of an SC, is also shown to lead to T-dependent values of several other related parameters such as the effective mass of electrons, their number density, critical velocity, Fermi velocity (VF), coherence length and the London penetration depth. The extended framework is applied to the jc(T) data reported by Romijn et al. for superconducting Aluminium strips and is shown not only to provide an alternative to the explanation given by them, but also to some novel features such as the role of the Sommerfeld coefficient γ(T) in the context of jc(T) and the role of VF(T) in the context of a recent finding by Plumb et al. about the superconductivity of Bi-2212.展开更多
The paper suggests that E = mc<sup>2</sup> may be open to misinterpretation and that in this form it is not what Einstein advanced first. It is further suggested to return to the slightly less compact form...The paper suggests that E = mc<sup>2</sup> may be open to misinterpretation and that in this form it is not what Einstein advanced first. It is further suggested to return to the slightly less compact formula E = Kmc<sup>2</sup> where a < K < 1 which has the merit of accounting for the measured ordinary energy density of the cosmos (K = 1/22) and the conjectured missing dark energy density of the universe (K = 21/22) from the view point of economical notation.展开更多
Model of hole-pairs in electrical transport along ab plane in cuprate superconductors has already been proposed. It has been found to be in the shape of 3dx2–y2 orbital of an electron in an atom. This time, model of ...Model of hole-pairs in electrical transport along ab plane in cuprate superconductors has already been proposed. It has been found to be in the shape of 3dx2–y2 orbital of an electron in an atom. This time, model of hole-pairs in transport along c-axis in cuprate superconductors is proposed. In ab-plane, hole-pairs are formed along CuO2 plane;one hole-pair covering 9 - 10 two dimensional CuO2 unit cells in 3dx2–y2 configuration. In the investigation of c-axis hole-pairs, cuprate superconductors have been sub-divided into three categories depending on the number of CuO2 planes/formula unit. There is a little different treatment for finding out the order parameter in each category. Coherence lengths along ab-planes are of the order of a few tens of Angstroms, whereas along c-axis, they are less than even their a-, b-lattice constants. In cuprates with 2 or 3 CuO2 planes, the order parameter is of 3dz2–x2 type in zx-plane with lobes along both the axes much constrained. For cuprates with a single CuO2 layer, the order parameter is of 3dx2–y2 type, but its dimensions are less than a-, b-lattice constants.展开更多
Increase of Tc in Al1−x(SiO2)x cermets with increasing x is caused by electron transfer from the Al grains to the SiO2 phase occupying surface states, expressed by Tc/Tc,max=1−γ⋅n2(*), where n is the electron density...Increase of Tc in Al1−x(SiO2)x cermets with increasing x is caused by electron transfer from the Al grains to the SiO2 phase occupying surface states, expressed by Tc/Tc,max=1−γ⋅n2(*), where n is the electron density in the Al phase and γa characteristic parameter. Decrease of Tc in Pb-Cu-sandwiches is attributed to the electron transfer from the Cu film to the Pb film. γand Tc,maxin equation (*) stands for the influence of the electron-phonon interaction and n2for the influence of the electron-electron Coulomb repulsion on Tc. The result that equation (*) holds for both hole-doped cuprate high-temperature superconductivity (HTSC) and Al1−x(SiO2)x cermets is an important indication that common mechanisms underlie HTSC and classical superconductors. The difference between the two is that in HTSC, electron transfer occurs between different electronic bands, but in Al1−x(SiO2)x cermets between different phases.展开更多
Experimental confirmation discussed the effect of the immediate surroundings of a pulse-powered toroidal coil on biological material which was placed in an environment without the influence of electromagnetic force.
This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% im...This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% impurity concentration. Our comprehensive analysis encompasses structural properties, electronic band structures, and charge density distributions. The optimized lattice constant and band gap energy of 3C-SiC were found to be 4.373 Å and 1.36 eV respectively, which is in agreement with previous research (Bui, 2012;Muchiri et al., 2018). Our results show that B doping narrows the band gap, enhances electrical conductivity, and influences charge transfer interactions. The charge density analysis reveals substantial interactions between B dopants and surrounding carbon atoms. This work not only enhances our understanding of the material’s electronic properties, but also highlights the importance of charge density analysis for characterizing charge transfer mechanisms and their implications in the 3C-SiC semiconductors.展开更多
It is common experience that our eyes do not perceive significant changes in color when we observe for long time an object continuously exposed to light. We always see plants to be green in summer until in autumn fact...It is common experience that our eyes do not perceive significant changes in color when we observe for long time an object continuously exposed to light. We always see plants to be green in summer until in autumn factors external to our vision, such as changes in the length of daylight and temperature, cause the break-down of chlorophyll and, in turn, spectacular changes in plant’s colors. Likewise, the photocurrent produced in solar panels or field effect transistors achieves a steady state magnitude shortly after the start of the illumination. The steady state photocurrent lasts until the illumination stops. Understanding the origin of the steady state response of a device or light harvesting (LH) system to illumination with electromagnetic (EM) waves motivates the research presented in this work. In our experiments, we used capacitors as LH systems and illuminated them with infrared (IR) light over an 80 hours time period. We investigated the interaction between light and matter by monitoring versus time the voltage output of the capacitors. By combining modeling and experimental observations, we concluded that the steady state voltage is established soon after the start of the illumination as the consequence of the law of conservation of energy. We also found that the magnitude of the voltage in the steady state depends on the power and period of the illuminating IR light, and on the capacitance of the capacitor. When light’s power undergoes fluctuations, also the voltage produced by the capacitor and the surface charge density on the capacitors do so. These findings suggest that the law of conservation of energy has a significant repercussion when light is absorbed by matter in the steady state, for example in the mechanism of vision in vertebrates. Likewise, these findings are true when light is emitted from matter, for example in the mechanism of formation of the Cosmic Microwave Background (CMB).展开更多
Based on the density functional theory within the local density approximation (LDA), we studied the electronic, elastic, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> compou...Based on the density functional theory within the local density approximation (LDA), we studied the electronic, elastic, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> compounds under pressure. The elastic constants, optic and static dielectric constants, born effective charges, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> in cubic phase were studied as pressure dependences with the ab initio method. For these compounds, we have also calculated the bulk modulus, Young’s modulus, shear modulus, Vickers hardness, Poisson’s ratio, anisotropy factor, sound velocities, and Debye temperature from the obtained elastic constants. In addition, the brittleness and ductility properties of these compounds were estimated from Poisson’s ratio and Pugh’s rule (G/B). Our calculated values also show that AgNbO<sub>3</sub> (0.37) and AgTaO<sub>3</sub> (0.39) behave as ductile materials and steer away from brittleness by increasing pressure. The calculated values of Vicker hardness for both compounds indicate that they are soft materials. The results show that band gaps, elastic constants, elastic modules, and dynamic properties for both compounds are sensitive to pressure changes. We have also made some comparisons with related experimental and theoretical data that is available in the literature.展开更多
As pointed out in the paper preceding this one, in the case of functionals whose independent variable must obey conditions of integral normalization, conventional functional differentiation, defined in terms of an arb...As pointed out in the paper preceding this one, in the case of functionals whose independent variable must obey conditions of integral normalization, conventional functional differentiation, defined in terms of an arbitrary test function, is generally inapplicable and functional derivatives with respect to the density must be evaluated through the alternative and widely used limiting procedure based on the Dirac delta function. This leads to the determination of the rate of change of the dependent variable with respect to its independent variable at each isolated pair, , that may not be part of a functional (a set of ordered pairs). This extends the concept of functional derivative to expectation values of operators with respect to wave functions leading to a density even if the wave functions (and expectation values) do not form functionals. This new formulation of functional differentiation forms the basis for the study of the mathematical integrity of a number of concepts in density functional theory (DFT) such as the existence of a universal functional of the density, of orbital-free density functional theory, the derivative discontinuity of the exchange and correlation functional and the extension of DFT to open systems characterized by densities with fractional normalization. It is shown that no universal functional exists but, rather, a universal process based only on the density and independent of the possible existence of a potential, leads to unique functionals of the density determined through the minimization procedure of the constrained search. The mathematical integrity of two methodologies proposed for the treatment of the Coulomb interaction, the self-interaction free method and the optimized effective potential method is examined and the methodologies are compared in terms of numerical calculations. As emerges from this analysis, the optimized effective potential method is found to be numerically approximate but formally invalid, contrary to the rigorously exact results of the self-interaction-free method.展开更多
The heat capacity of some ferrimagnets has additional structures like a shoulder in the Schottky-like peak, or emergence of a second peak when an external magnetic field is applied. It is shown here that the ferromagn...The heat capacity of some ferrimagnets has additional structures like a shoulder in the Schottky-like peak, or emergence of a second peak when an external magnetic field is applied. It is shown here that the ferromagnetic and anti-ferromagnetic elementary excitation spectra give rise to two independent heat capacity peaks, one enveloped by the other, which add up to give the peak for the total system. Taking this into account helps understand the additional structures in the peaks. Moreover, the classification of ferrimagnets into predominantly antiferromagnetic, ferromagnetic, or a mixture of the two is shown to be validated by studying them under additional influences like dimerization and frustration. Because these two are shown to influence the ferromagnetic and antiferromagnetic dispersion rela tions—and hence the quantities like heat capacity and magnetic susceptibility—by different amounts, the characterization of ferrimagnetic systems (1,1/2), (3/2,1) and (3/2,1/2) is brought out more clearly. Both these influences enhance antiferromagnetic character. PACS numbers: 75.10.Jm, 75.50.Ge.展开更多
In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition met...In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.展开更多
Results of experimental investigation of detection (rectification) of high power X-band microwave signal in diodes of various design (semiconductor p-n-junction, point-contact, Schottky, Metal-Isolator-Metal—MIM) are...Results of experimental investigation of detection (rectification) of high power X-band microwave signal in diodes of various design (semiconductor p-n-junction, point-contact, Schottky, Metal-Isolator-Metal—MIM) are reported. The maximum of the detected direct voltage V vs. power P of microwave signal and subsequent polarity reversal, previously found in MIM diodes in the optical and microwave bands, have found to be characteristic of all investigated diodes as well. After the reversal of polarity, this dependence comes linear, and the sign of the voltage corresponds to thermoEMF. In some diodes, the hysteresis on V(P) was observed. All 5 types of V(P) of MIM diodes (have made from different pairs of metals), reported earlier, were reproduced on same p-n-junction diode by variable external DC bias. These results joined with abnormal frequency cutoff forced to suggest that there is an unknown mechanism for direct flow of charge carriers (and for generate direct current) in the high-frequency electrical field, which differs from the conventional rectification.展开更多
The present short paper is concerned with accurate explanation as well as quantification of the so called missing dark energy of the cosmos. It was always one of the main objectives of any successful general theory of...The present short paper is concerned with accurate explanation as well as quantification of the so called missing dark energy of the cosmos. It was always one of the main objectives of any successful general theory of high energy particle physics and quantum cosmology to keep non-physical negative norms, the so called ghosts completely out of that theory. The present work takes the completely contrary view by admitting these supposedly spurious states as part of the physical Hilbert space. It is further shown that rethinking the ghost free condition with the two critical spacetime dimensions D<sub>1</sub> = 26 and D<sub>2</sub> = 25 together with the corresponding intercept a<sub>1</sub> = 1 and a<sub>2</sub> ≤ 1 respectively and in addition imposing, as in Gross et al. heterotic superstrings, an overall 496 dimensional exceptional Lie symmetry group, then one will discover that there are two distinct types of energy. The first is positive norm ordinary energy connected to the zero set quantum particles which is very close to the measured ordinary energy density of the cosmos, namely E(O) = mc<sup>2</sup>/22. The second is negative norm (i.e. ghost) energy connected to the empty set quantum wave and is equal to the conjectured dark energy density of the cosmos E(D) = mc<sup>2</sup> (21/22) presumed to be behind the observed accelerated cosmic expansion. That way we were able to not only explain the physics of dark energy without adding any new concepts or novel additional ingredients but also we were able to compute the dark energy density accurately and in full agreement with measurements and observations.展开更多
It is invited statistical explanation of the frequency and temperature dependence of the absorption coefficients of semiconductors on the long-wave edge of the fundamental absorption. With the help of mathematical mod...It is invited statistical explanation of the frequency and temperature dependence of the absorption coefficients of semiconductors on the long-wave edge of the fundamental absorption. With the help of mathematical modeling, it shows that the thermal broadening of the energy states of the conduction band and the discrete states in the band gap can cause long-wave decline according to the Urbach rule.展开更多
The change in electron mobility of n-Si with increasing the temperature which may be due to the inclusion of gLOphonon energy of 720 K, is presented. Under orientation of the uniaxial pressure X//[110]//J, g-transitio...The change in electron mobility of n-Si with increasing the temperature which may be due to the inclusion of gLOphonon energy of 720 K, is presented. Under orientation of the uniaxial pressure X//[110]//J, g-transitions are attached in the directions [100] and [010]. The f-transitions are not completely removed from valleys located in the plane (100). In this case, there is no change in the slope of the dependence logρ vs. logT for the temperature range 77 to 450 K. So, no appreciable contribution of g-transitions to intervalley scattering occurs, while the observed is the decisive role of f-transitions to intervalley scattering. The results of measuring of the tensoresistivity effect for n-Si crystals under X//[001]//J are presented at these temperatures too.展开更多
Nanocrystalline Al doped nickel-cobalt ferrite [Ni0.6Co0.4Fe2-xAlxO4 (x = 0.0, 0.1, 0.3, 0.5 and 0.7)] powders have been synthesized by sol-gel auto-ignition method and the effect of non-magnetic aluminum content on t...Nanocrystalline Al doped nickel-cobalt ferrite [Ni0.6Co0.4Fe2-xAlxO4 (x = 0.0, 0.1, 0.3, 0.5 and 0.7)] powders have been synthesized by sol-gel auto-ignition method and the effect of non-magnetic aluminum content on the nanosize particles and magnetic properties has been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with inverse spinel structure. The calculated grain size from XRD data have been verified using transmission electron microscopy (TEM). TEM photograph shows that the powders consist of nano meter sized grain. The size of nanoparticles decreases as the non magnetic Al content increases. Magnetic hysteresis loops were measured at room temperature with maximum applied magnetic field of 20 KOe. As aluminum content increases, the measured magnetic hysteresis curves became narrow and saturation magnetization (Ms), and coercive force (Hc) decreased. The reduction of magnetization with the increase of aluminum content is caused by non-magnetic Al3+ ions and weakened interaction between sub-lattices.展开更多
Quantum confinement effect in semiconductor quantum dots (QD's) of CdSe, ZnS and GaAs has been studied using the Brus Equation. It is found that the simple models obtained for the three different semiconductor nan...Quantum confinement effect in semiconductor quantum dots (QD's) of CdSe, ZnS and GaAs has been studied using the Brus Equation. It is found that the simple models obtained for the three different semiconductor nanocrystals exhibit the size dependence predicted by the particle-in-a-box model. The result shows that ground state confinement energy is inversely proportional to the size (radius). Thus, as one increases the radius (size), the confinement energy decreases, but never reaches zero. i.e., the lowest possible energy for the quantum dot sample is not zero.展开更多
We propose an improved finite temperature Lanczos method using the stochastic state selection method. In the finite temperature Lanczos method, we generate Lanczos states and calculate the eigenvalues. In addition we ...We propose an improved finite temperature Lanczos method using the stochastic state selection method. In the finite temperature Lanczos method, we generate Lanczos states and calculate the eigenvalues. In addition we have to calculate matrix elements that are the values of an operator between two Lanczos states. In the calculations of the matrix elements we have to keep the set of Lanczos states on the computer memory. Therefore the memory limits the system size in the calculations. Here we propose an application of the stochastic state selection method in order to weaken this limitation. This method is to select some parts of basis states stochastically and to abandon other basis state. Only by the selected basis states we calculate the inner product. After making the statistical average, we can obtain the correct value of the inner product. By the stochastic state selection method we can reduce the number of the basis states for calculations. As a result we can relax the limitation on the computer memory. In order to study the Higgs mode at finite temperature, we calculate the dynamical correlations of the two spin operators in the spin-1/2 Heisenberg antiferromagnet on the square lattice using the improved finite temperature Lanczos method. Our results on the lattices of up to 32 sites show that the Higgs mode exists at low temperature and it disappears gradually when the temperature becomes large. At high temperature we do not find this mode in the dynamical correlations.展开更多
文摘Samples of chromium doped ZnO were synthesized using co-precipitation technique at room temperature. Structural and optical properties of Cr doped ZnO samples were investigated by X-ray diffraction technique (XRD and UV-Visible spectroscopy (UV-Vis) respectively. X-ray diffraction (XRD) patterns confirm that the samples have hexagonal (wurtzite) structure with no additional peak which suggests that Cr ions go to the regular Zn sites in the ZnO crystal structure. The lattice constants were calculated using X-ray diffraction data and it is found that lattice parameters decrease with increasing Cr content. The average grain size was calculated using Scherrer’s formula for pure and Cr doped ZnO samples and it is observed that grain size is in the range 11 to17 nm. Band gap of Zn1–xCrxO samples has been evaluated using UV-Vis spectrometer. It is found that the band gap decreases as Cr increases;it is attributed to the s-d and p interactions and the smaller average grain size. It indicates that incorporation of Cr ions into the ZnO matrix. The chemical species of the grown crystals were identified by Fourier transform infrared spectroscopy (FTIR). From FTIR spectra it is observed that IR peaks corresponding to the Zn-O bands. Such results are presented in this paper quantitatively and qualitatively.
文摘Semiconductor solar cell (PV cell) has been widely used for generating solar electricity. However, the high cost and severe pollution limits its application. Recently the discovery of graphene may open a door to fabricate a novel solar cell with lower cost and more environmentally friendly. Our proposed solar cell device consists of a graphene strip and two semiconductor strips with different energy gaps attached to the two edges of the graphene strip on a flat plane. This structure is a two-dimensional quantum well. The energy bands of graphene can be described by a two-dimensional Dirac equation centered on hexagonal corners (Dirac points) of the honeycomb lattice Brillouin zone. The 2 D Dirac equation has been solved numerically in this paper. The results indicate that the graphene quantum well possesses very dense quantum energy states which imply that quantum well of this type can absorb sun light with more different frequencies. If we use graphene quantum well to fabricate the photo voltaic cell, the efficiency of converting solar energy to electricity will be enhanced.
文摘Presented here are the Generalized BCS Equations incorporating Fermi Energy for the study of the {Δ, Tc, jc(T)} values of both elemental and composite superconductors (SCs) for all T ≤ Tc, where Δ, Tc and jc(T) denote, respectively, one of the gap values, the critical temperature and the T-dependent critical current density. This framework, which extends our earlier study that dealt with the {Δ0, Tc, jc(0)} values of an SC, is also shown to lead to T-dependent values of several other related parameters such as the effective mass of electrons, their number density, critical velocity, Fermi velocity (VF), coherence length and the London penetration depth. The extended framework is applied to the jc(T) data reported by Romijn et al. for superconducting Aluminium strips and is shown not only to provide an alternative to the explanation given by them, but also to some novel features such as the role of the Sommerfeld coefficient γ(T) in the context of jc(T) and the role of VF(T) in the context of a recent finding by Plumb et al. about the superconductivity of Bi-2212.
文摘The paper suggests that E = mc<sup>2</sup> may be open to misinterpretation and that in this form it is not what Einstein advanced first. It is further suggested to return to the slightly less compact formula E = Kmc<sup>2</sup> where a < K < 1 which has the merit of accounting for the measured ordinary energy density of the cosmos (K = 1/22) and the conjectured missing dark energy density of the universe (K = 21/22) from the view point of economical notation.
文摘Model of hole-pairs in electrical transport along ab plane in cuprate superconductors has already been proposed. It has been found to be in the shape of 3dx2–y2 orbital of an electron in an atom. This time, model of hole-pairs in transport along c-axis in cuprate superconductors is proposed. In ab-plane, hole-pairs are formed along CuO2 plane;one hole-pair covering 9 - 10 two dimensional CuO2 unit cells in 3dx2–y2 configuration. In the investigation of c-axis hole-pairs, cuprate superconductors have been sub-divided into three categories depending on the number of CuO2 planes/formula unit. There is a little different treatment for finding out the order parameter in each category. Coherence lengths along ab-planes are of the order of a few tens of Angstroms, whereas along c-axis, they are less than even their a-, b-lattice constants. In cuprates with 2 or 3 CuO2 planes, the order parameter is of 3dz2–x2 type in zx-plane with lobes along both the axes much constrained. For cuprates with a single CuO2 layer, the order parameter is of 3dx2–y2 type, but its dimensions are less than a-, b-lattice constants.
文摘Increase of Tc in Al1−x(SiO2)x cermets with increasing x is caused by electron transfer from the Al grains to the SiO2 phase occupying surface states, expressed by Tc/Tc,max=1−γ⋅n2(*), where n is the electron density in the Al phase and γa characteristic parameter. Decrease of Tc in Pb-Cu-sandwiches is attributed to the electron transfer from the Cu film to the Pb film. γand Tc,maxin equation (*) stands for the influence of the electron-phonon interaction and n2for the influence of the electron-electron Coulomb repulsion on Tc. The result that equation (*) holds for both hole-doped cuprate high-temperature superconductivity (HTSC) and Al1−x(SiO2)x cermets is an important indication that common mechanisms underlie HTSC and classical superconductors. The difference between the two is that in HTSC, electron transfer occurs between different electronic bands, but in Al1−x(SiO2)x cermets between different phases.
文摘Experimental confirmation discussed the effect of the immediate surroundings of a pulse-powered toroidal coil on biological material which was placed in an environment without the influence of electromagnetic force.
文摘This study delves into the charge transfer mechanism of boron (B)-doped 3C-SiC through first-principles investigations. We explore the effects of B doping on the electronic properties of 3C-SiC, focusing on a 12.5% impurity concentration. Our comprehensive analysis encompasses structural properties, electronic band structures, and charge density distributions. The optimized lattice constant and band gap energy of 3C-SiC were found to be 4.373 Å and 1.36 eV respectively, which is in agreement with previous research (Bui, 2012;Muchiri et al., 2018). Our results show that B doping narrows the band gap, enhances electrical conductivity, and influences charge transfer interactions. The charge density analysis reveals substantial interactions between B dopants and surrounding carbon atoms. This work not only enhances our understanding of the material’s electronic properties, but also highlights the importance of charge density analysis for characterizing charge transfer mechanisms and their implications in the 3C-SiC semiconductors.
文摘It is common experience that our eyes do not perceive significant changes in color when we observe for long time an object continuously exposed to light. We always see plants to be green in summer until in autumn factors external to our vision, such as changes in the length of daylight and temperature, cause the break-down of chlorophyll and, in turn, spectacular changes in plant’s colors. Likewise, the photocurrent produced in solar panels or field effect transistors achieves a steady state magnitude shortly after the start of the illumination. The steady state photocurrent lasts until the illumination stops. Understanding the origin of the steady state response of a device or light harvesting (LH) system to illumination with electromagnetic (EM) waves motivates the research presented in this work. In our experiments, we used capacitors as LH systems and illuminated them with infrared (IR) light over an 80 hours time period. We investigated the interaction between light and matter by monitoring versus time the voltage output of the capacitors. By combining modeling and experimental observations, we concluded that the steady state voltage is established soon after the start of the illumination as the consequence of the law of conservation of energy. We also found that the magnitude of the voltage in the steady state depends on the power and period of the illuminating IR light, and on the capacitance of the capacitor. When light’s power undergoes fluctuations, also the voltage produced by the capacitor and the surface charge density on the capacitors do so. These findings suggest that the law of conservation of energy has a significant repercussion when light is absorbed by matter in the steady state, for example in the mechanism of vision in vertebrates. Likewise, these findings are true when light is emitted from matter, for example in the mechanism of formation of the Cosmic Microwave Background (CMB).
文摘Based on the density functional theory within the local density approximation (LDA), we studied the electronic, elastic, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> compounds under pressure. The elastic constants, optic and static dielectric constants, born effective charges, and dynamic properties of AgNbO<sub>3</sub> and AgTaO<sub>3</sub> in cubic phase were studied as pressure dependences with the ab initio method. For these compounds, we have also calculated the bulk modulus, Young’s modulus, shear modulus, Vickers hardness, Poisson’s ratio, anisotropy factor, sound velocities, and Debye temperature from the obtained elastic constants. In addition, the brittleness and ductility properties of these compounds were estimated from Poisson’s ratio and Pugh’s rule (G/B). Our calculated values also show that AgNbO<sub>3</sub> (0.37) and AgTaO<sub>3</sub> (0.39) behave as ductile materials and steer away from brittleness by increasing pressure. The calculated values of Vicker hardness for both compounds indicate that they are soft materials. The results show that band gaps, elastic constants, elastic modules, and dynamic properties for both compounds are sensitive to pressure changes. We have also made some comparisons with related experimental and theoretical data that is available in the literature.
文摘As pointed out in the paper preceding this one, in the case of functionals whose independent variable must obey conditions of integral normalization, conventional functional differentiation, defined in terms of an arbitrary test function, is generally inapplicable and functional derivatives with respect to the density must be evaluated through the alternative and widely used limiting procedure based on the Dirac delta function. This leads to the determination of the rate of change of the dependent variable with respect to its independent variable at each isolated pair, , that may not be part of a functional (a set of ordered pairs). This extends the concept of functional derivative to expectation values of operators with respect to wave functions leading to a density even if the wave functions (and expectation values) do not form functionals. This new formulation of functional differentiation forms the basis for the study of the mathematical integrity of a number of concepts in density functional theory (DFT) such as the existence of a universal functional of the density, of orbital-free density functional theory, the derivative discontinuity of the exchange and correlation functional and the extension of DFT to open systems characterized by densities with fractional normalization. It is shown that no universal functional exists but, rather, a universal process based only on the density and independent of the possible existence of a potential, leads to unique functionals of the density determined through the minimization procedure of the constrained search. The mathematical integrity of two methodologies proposed for the treatment of the Coulomb interaction, the self-interaction free method and the optimized effective potential method is examined and the methodologies are compared in terms of numerical calculations. As emerges from this analysis, the optimized effective potential method is found to be numerically approximate but formally invalid, contrary to the rigorously exact results of the self-interaction-free method.
文摘The heat capacity of some ferrimagnets has additional structures like a shoulder in the Schottky-like peak, or emergence of a second peak when an external magnetic field is applied. It is shown here that the ferromagnetic and anti-ferromagnetic elementary excitation spectra give rise to two independent heat capacity peaks, one enveloped by the other, which add up to give the peak for the total system. Taking this into account helps understand the additional structures in the peaks. Moreover, the classification of ferrimagnets into predominantly antiferromagnetic, ferromagnetic, or a mixture of the two is shown to be validated by studying them under additional influences like dimerization and frustration. Because these two are shown to influence the ferromagnetic and antiferromagnetic dispersion rela tions—and hence the quantities like heat capacity and magnetic susceptibility—by different amounts, the characterization of ferrimagnetic systems (1,1/2), (3/2,1) and (3/2,1/2) is brought out more clearly. Both these influences enhance antiferromagnetic character. PACS numbers: 75.10.Jm, 75.50.Ge.
文摘In search of an experimental route to produce linear arrays of spins without the use of nanotechnological tools, we have doped Nb<sub>28</sub>O<sub>70</sub> with small amounts of transition metal oxides (TM;in this case Fe<sub>2</sub>O<sub>3</sub>) or rare-earth oxides<sub>3</sub>, and investigated the location of the alien metal (Fe in this case) in the structure. Previous AC magnetic susceptibility measurements at low temperatures have been consistent with the formation of arrays of TM magnetic moments along the widely spaced columns parallel to the crystallographic b-axis in the Nb<sub>28</sub>O<sub>70</sub> structure. To obtain further details about the TM distribution, the previous investigation has been extended now to include a room-temperature Mössbauer spectroscopic analysis of the Fe-doped material. The data are consistent with the presence of low-spin Fe<sup>3+</sup> ions in both octahedral and tetrahedral coordinations of oxygens, and confirm (as suggested in the previous work) that Fe also interchanges positions with Nb ions located at tetrahedrally coordinated sites in the columns of the structure.
文摘Results of experimental investigation of detection (rectification) of high power X-band microwave signal in diodes of various design (semiconductor p-n-junction, point-contact, Schottky, Metal-Isolator-Metal—MIM) are reported. The maximum of the detected direct voltage V vs. power P of microwave signal and subsequent polarity reversal, previously found in MIM diodes in the optical and microwave bands, have found to be characteristic of all investigated diodes as well. After the reversal of polarity, this dependence comes linear, and the sign of the voltage corresponds to thermoEMF. In some diodes, the hysteresis on V(P) was observed. All 5 types of V(P) of MIM diodes (have made from different pairs of metals), reported earlier, were reproduced on same p-n-junction diode by variable external DC bias. These results joined with abnormal frequency cutoff forced to suggest that there is an unknown mechanism for direct flow of charge carriers (and for generate direct current) in the high-frequency electrical field, which differs from the conventional rectification.
文摘The present short paper is concerned with accurate explanation as well as quantification of the so called missing dark energy of the cosmos. It was always one of the main objectives of any successful general theory of high energy particle physics and quantum cosmology to keep non-physical negative norms, the so called ghosts completely out of that theory. The present work takes the completely contrary view by admitting these supposedly spurious states as part of the physical Hilbert space. It is further shown that rethinking the ghost free condition with the two critical spacetime dimensions D<sub>1</sub> = 26 and D<sub>2</sub> = 25 together with the corresponding intercept a<sub>1</sub> = 1 and a<sub>2</sub> ≤ 1 respectively and in addition imposing, as in Gross et al. heterotic superstrings, an overall 496 dimensional exceptional Lie symmetry group, then one will discover that there are two distinct types of energy. The first is positive norm ordinary energy connected to the zero set quantum particles which is very close to the measured ordinary energy density of the cosmos, namely E(O) = mc<sup>2</sup>/22. The second is negative norm (i.e. ghost) energy connected to the empty set quantum wave and is equal to the conjectured dark energy density of the cosmos E(D) = mc<sup>2</sup> (21/22) presumed to be behind the observed accelerated cosmic expansion. That way we were able to not only explain the physics of dark energy without adding any new concepts or novel additional ingredients but also we were able to compute the dark energy density accurately and in full agreement with measurements and observations.
文摘It is invited statistical explanation of the frequency and temperature dependence of the absorption coefficients of semiconductors on the long-wave edge of the fundamental absorption. With the help of mathematical modeling, it shows that the thermal broadening of the energy states of the conduction band and the discrete states in the band gap can cause long-wave decline according to the Urbach rule.
文摘The change in electron mobility of n-Si with increasing the temperature which may be due to the inclusion of gLOphonon energy of 720 K, is presented. Under orientation of the uniaxial pressure X//[110]//J, g-transitions are attached in the directions [100] and [010]. The f-transitions are not completely removed from valleys located in the plane (100). In this case, there is no change in the slope of the dependence logρ vs. logT for the temperature range 77 to 450 K. So, no appreciable contribution of g-transitions to intervalley scattering occurs, while the observed is the decisive role of f-transitions to intervalley scattering. The results of measuring of the tensoresistivity effect for n-Si crystals under X//[001]//J are presented at these temperatures too.
文摘Nanocrystalline Al doped nickel-cobalt ferrite [Ni0.6Co0.4Fe2-xAlxO4 (x = 0.0, 0.1, 0.3, 0.5 and 0.7)] powders have been synthesized by sol-gel auto-ignition method and the effect of non-magnetic aluminum content on the nanosize particles and magnetic properties has been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with inverse spinel structure. The calculated grain size from XRD data have been verified using transmission electron microscopy (TEM). TEM photograph shows that the powders consist of nano meter sized grain. The size of nanoparticles decreases as the non magnetic Al content increases. Magnetic hysteresis loops were measured at room temperature with maximum applied magnetic field of 20 KOe. As aluminum content increases, the measured magnetic hysteresis curves became narrow and saturation magnetization (Ms), and coercive force (Hc) decreased. The reduction of magnetization with the increase of aluminum content is caused by non-magnetic Al3+ ions and weakened interaction between sub-lattices.
文摘Quantum confinement effect in semiconductor quantum dots (QD's) of CdSe, ZnS and GaAs has been studied using the Brus Equation. It is found that the simple models obtained for the three different semiconductor nanocrystals exhibit the size dependence predicted by the particle-in-a-box model. The result shows that ground state confinement energy is inversely proportional to the size (radius). Thus, as one increases the radius (size), the confinement energy decreases, but never reaches zero. i.e., the lowest possible energy for the quantum dot sample is not zero.
文摘We propose an improved finite temperature Lanczos method using the stochastic state selection method. In the finite temperature Lanczos method, we generate Lanczos states and calculate the eigenvalues. In addition we have to calculate matrix elements that are the values of an operator between two Lanczos states. In the calculations of the matrix elements we have to keep the set of Lanczos states on the computer memory. Therefore the memory limits the system size in the calculations. Here we propose an application of the stochastic state selection method in order to weaken this limitation. This method is to select some parts of basis states stochastically and to abandon other basis state. Only by the selected basis states we calculate the inner product. After making the statistical average, we can obtain the correct value of the inner product. By the stochastic state selection method we can reduce the number of the basis states for calculations. As a result we can relax the limitation on the computer memory. In order to study the Higgs mode at finite temperature, we calculate the dynamical correlations of the two spin operators in the spin-1/2 Heisenberg antiferromagnet on the square lattice using the improved finite temperature Lanczos method. Our results on the lattices of up to 32 sites show that the Higgs mode exists at low temperature and it disappears gradually when the temperature becomes large. At high temperature we do not find this mode in the dynamical correlations.