The paper approaches the problem of the command functions of galvanometer-based scanners （GS） that are necessary to produce the linear plus parabolic scanning function of the GS, which we have proved previously to p...The paper approaches the problem of the command functions of galvanometer-based scanners （GS） that are necessary to produce the linear plus parabolic scanning function of the GS, which we have proved previously to produce the highest possible duty cycle （i.e., time efficiency） of the device. We have completed this theoretical aspect （which contradicted what has been stated previously in the literature, where it has been considered that the linear plus sinusoidal scanning function was the best） with the experimental study of the most used scanning functions of the GSs （sawtooth, sinusoidal and triangular）, with applications in biomedical imaging, in particular in optical coherence tomography, demonstrating that the triangular function is always the best one to be applied, from both an optical and a mechanical point of view. In the present study the input voltage/command function which should be applied to the GS to produce the desired triangular scanning function （with controlled non-linearity for the fastest possible stop-and-turn portions） was determined analytically, in relationship with the active torque that drives the device. This command function is analyzed with regard to the specific, respectively required parameters of the GS： natural frequency and damping factor, respectively scan speed and amplitude. The modeling in an open loop control structure of the GS is finally discussed as a trade-off between using the highest possible duty cycle and minimizing the maximum peaks of the input voltage.展开更多
The double perovskites Sr_(2)SmNbO_(6),Sr_(2)CoNbO_(6)and Ba2CoNbO_(6)were investigated with first principles computations based on the density functional theory and plus U treatment.Firstly,different calculation meth...The double perovskites Sr_(2)SmNbO_(6),Sr_(2)CoNbO_(6)and Ba2CoNbO_(6)were investigated with first principles computations based on the density functional theory and plus U treatment.Firstly,different calculation methods were examined in order to quantitatively approach the exact band gap.It was found that neither the strongly constrained and appropriately normed(SCAN)semilocal density functional nor the hybrid HSE06 functional can well address the semiconducting nature of the investigated double perovskites,while PBEþU or SCANþU with appropriately determining the U value can have good performance,which paves the way for future studies of double perovskites.With self-consistently calculated electron correlation strength,the magnetic states and the band gaps of the Sr_(2)CoNbO_(6)and Ba_(2)CoNbO_(6)were more precisely determined.The electronic,optical and thermoelectric properties were then investigated and discussed for possible applications.展开更多
Cognitive disturbances with neglect-like features have been reported occasionally in patients with chiasmal disorders, so far however with no obvious substrate by conventional brain imaging. Thus, there were no right ...Cognitive disturbances with neglect-like features have been reported occasionally in patients with chiasmal disorders, so far however with no obvious substrate by conventional brain imaging. Thus, there were no right hemisphere lesions that could explain the lateralised visual inattention as observed in particular during monocular visual acuity testing. On this background, we further examined four adult patients who consented to functional 18F-fluoro-deoxyglucose (FDG) positron emission tomography (PET) scan. In three there were no significant findings. The fourth patient, a 26-year-old male with cognitive defects after surgery for craniopharyngioma, will be discussed in more detail. His PET scan demonstrated a widespread reduction of regional metabolic activity in left hemisphere primary visual cortex and higher order visual areas, despite absence of explanatory pathological signal changes on MRI. As present in only one out of four patients, however, the findings do not allow specific pathogenetic mechanisms to be suggested, nor generally to substantiate involvement of higher cerebral circuits. Obviously, even developed imaging has its limits, and in the very theory the visual dysfunctions observed might still depend on higher brain centres’ faulty adaptation to loss of pre-geniculate visual information.展开更多
Work function plays a significant role in surface chemistry. Local work function provides the information of local d/pole-d/pole interaction and charge distribution between adsorbates and substrate, highlighting the l...Work function plays a significant role in surface chemistry. Local work function provides the information of local d/pole-d/pole interaction and charge distribution between adsorbates and substrate, highlighting the local charge effect of the targeted spot which is normally smeared out in conventional average work function measurements. Chloroaluminum phthalocyanine （CIA1Pc）, an important optoelectronic molecule with a permanent dipole moment pointing from the Pc ring to the ending CI atom, adsorbed on Au（111） in either Cl-up or Cl-down configuration. Scanning tunneling microscopy/spectroscopy measurements revealed that at the centers of Cl-up and CI-down molecules, the local work functions changed oppositely with respect to the Au（111） substrate. At their Pc lobes, however, the local work functions unanimously increased due to charging effect of the indole lobes in the CIAIPc molecule.展开更多
Hydrated ions play essential roles in diverse chemical and biological processes,yet accurately characterizing their hydration structures remains challenging due to the delicate interplay of ion–water and water–water...Hydrated ions play essential roles in diverse chemical and biological processes,yet accurately characterizing their hydration structures remains challenging due to the delicate interplay of ion–water and water–water interactions.Here,we use ab initio molecular dynamics(AIMD)simulations based on the strongly constrained and appropriately normed(SCAN)exchange–correlation functional to systematically investigate the hydration structures of eight representative ions(Mg^(2+),Ca^(2+),Li^(+),Na^(+),K^(+),F^(-),Cl^(-),Br^(-))in aqueous solution.Compared to the widely used Perdew–Burke–Ernzerhof(PBE)functional,SCAN substantially improves the description of solvent water by weakening the hydrogen-bond network and enhancing structural disorder,yielding results in closer agreement with experiments.SCAN modifies ionic hydration shells in an ion-specific manner,governed by ionic size and charge,and reproduces experimental hydration geometries especially well for intermediate-size monovalent ions(Na^(+),Cl^(-)).Moreover,SCAN consistently reduces the overpolarization of water molecules near ions.These improvements lead to more accurate and physically consistent hydration structures,highlighting SCAN's utility for modeling complex aqueous systems and offering guidance for future studies of ionic solvation.展开更多
In optical scanning holography, one pupil produces a spherical wave and another produces a plane wave. They interfere with each other and result in a fringe pattern for scanning a three-dimensional object. The resolut...In optical scanning holography, one pupil produces a spherical wave and another produces a plane wave. They interfere with each other and result in a fringe pattern for scanning a three-dimensional object. The resolution of the hologram reconstruction is affected by the point spread function(PSF) of the optical system. In this paper, we modulate the PSF by a spiral phase plate, which significantly enhances the lateral and depth resolution. We explain the theory for such resolution enhancement and show simulation results to verify the efficacy of the approach.展开更多
Si dangling bonds at the interface of quasi-free-standing monolayer graphene （QFMLG） are known to act as scattering centers that can severely affect carrier mobility Herein, we investigate the atomic and electronic ...Si dangling bonds at the interface of quasi-free-standing monolayer graphene （QFMLG） are known to act as scattering centers that can severely affect carrier mobility Herein, we investigate the atomic and electronic structure of Si dangling bonds in QFMLG using low-temperature scanning tunneling microscopy/ spectroscopy （STM/STS）, atomic force microscopy （AFM）, and density functional theory （DFT） calculations. Two types of defects with different contrast were observed on a flat graphene terrace by STM and AFM; in particular, their STM contrast varied with the bias voltage. Moreover, these defects showed characteristic STS peaks at different energies, 1.1 and 1.4 eV. The comparison of the experimental data with the DFT calculations indicates that the defects with STS peak energies of 1.1 and 1.4 eV consist of clusters of three and four Si dangling bonds, respectively. The relevance of the present results for the optimization of graphene synthesis is discussed.展开更多
基金the support of the US Department of State through Fulbright Scholar Grant 474/2009
文摘The paper approaches the problem of the command functions of galvanometer-based scanners （GS） that are necessary to produce the linear plus parabolic scanning function of the GS, which we have proved previously to produce the highest possible duty cycle （i.e., time efficiency） of the device. We have completed this theoretical aspect （which contradicted what has been stated previously in the literature, where it has been considered that the linear plus sinusoidal scanning function was the best） with the experimental study of the most used scanning functions of the GSs （sawtooth, sinusoidal and triangular）, with applications in biomedical imaging, in particular in optical coherence tomography, demonstrating that the triangular function is always the best one to be applied, from both an optical and a mechanical point of view. In the present study the input voltage/command function which should be applied to the GS to produce the desired triangular scanning function （with controlled non-linearity for the fastest possible stop-and-turn portions） was determined analytically, in relationship with the active torque that drives the device. This command function is analyzed with regard to the specific, respectively required parameters of the GS： natural frequency and damping factor, respectively scan speed and amplitude. The modeling in an open loop control structure of the GS is finally discussed as a trade-off between using the highest possible duty cycle and minimizing the maximum peaks of the input voltage.
基金supported by the Research Start-up Fund of Southwest Jiaotong University(No.~2019KY23)the Fundamental Research Funds for the Central Universities,China(No.2682019CX06)+1 种基金the National Natural Sciences Foundation of China(No.52204227,No.52072311)the Outstanding Young Scientific and Technical Talents in Sichuan Province,China(2019JDJQ0009).
文摘The double perovskites Sr_(2)SmNbO_(6),Sr_(2)CoNbO_(6)and Ba2CoNbO_(6)were investigated with first principles computations based on the density functional theory and plus U treatment.Firstly,different calculation methods were examined in order to quantitatively approach the exact band gap.It was found that neither the strongly constrained and appropriately normed(SCAN)semilocal density functional nor the hybrid HSE06 functional can well address the semiconducting nature of the investigated double perovskites,while PBEþU or SCANþU with appropriately determining the U value can have good performance,which paves the way for future studies of double perovskites.With self-consistently calculated electron correlation strength,the magnetic states and the band gaps of the Sr_(2)CoNbO_(6)and Ba_(2)CoNbO_(6)were more precisely determined.The electronic,optical and thermoelectric properties were then investigated and discussed for possible applications.
文摘Cognitive disturbances with neglect-like features have been reported occasionally in patients with chiasmal disorders, so far however with no obvious substrate by conventional brain imaging. Thus, there were no right hemisphere lesions that could explain the lateralised visual inattention as observed in particular during monocular visual acuity testing. On this background, we further examined four adult patients who consented to functional 18F-fluoro-deoxyglucose (FDG) positron emission tomography (PET) scan. In three there were no significant findings. The fourth patient, a 26-year-old male with cognitive defects after surgery for craniopharyngioma, will be discussed in more detail. His PET scan demonstrated a widespread reduction of regional metabolic activity in left hemisphere primary visual cortex and higher order visual areas, despite absence of explanatory pathological signal changes on MRI. As present in only one out of four patients, however, the findings do not allow specific pathogenetic mechanisms to be suggested, nor generally to substantiate involvement of higher cerebral circuits. Obviously, even developed imaging has its limits, and in the very theory the visual dysfunctions observed might still depend on higher brain centres’ faulty adaptation to loss of pre-geniculate visual information.
基金supported by National Natural Science Foundation of China(Nos. 91527303, 21333001,21373020, 61321001)MOST(Nos.2013CB933404,2014CB239302),China
文摘Work function plays a significant role in surface chemistry. Local work function provides the information of local d/pole-d/pole interaction and charge distribution between adsorbates and substrate, highlighting the local charge effect of the targeted spot which is normally smeared out in conventional average work function measurements. Chloroaluminum phthalocyanine （CIA1Pc）, an important optoelectronic molecule with a permanent dipole moment pointing from the Pc ring to the ending CI atom, adsorbed on Au（111） in either Cl-up or Cl-down configuration. Scanning tunneling microscopy/spectroscopy measurements revealed that at the centers of Cl-up and CI-down molecules, the local work functions changed oppositely with respect to the Au（111） substrate. At their Pc lobes, however, the local work functions unanimously increased due to charging effect of the indole lobes in the CIAIPc molecule.
基金supported by the National Natural Science Foundation of China(Grant Nos.12535001,11935002,and 11525520)the National Key Research and Development Program of China(Grant No.2021YFA1400500)。
文摘Hydrated ions play essential roles in diverse chemical and biological processes,yet accurately characterizing their hydration structures remains challenging due to the delicate interplay of ion–water and water–water interactions.Here,we use ab initio molecular dynamics(AIMD)simulations based on the strongly constrained and appropriately normed(SCAN)exchange–correlation functional to systematically investigate the hydration structures of eight representative ions(Mg^(2+),Ca^(2+),Li^(+),Na^(+),K^(+),F^(-),Cl^(-),Br^(-))in aqueous solution.Compared to the widely used Perdew–Burke–Ernzerhof(PBE)functional,SCAN substantially improves the description of solvent water by weakening the hydrogen-bond network and enhancing structural disorder,yielding results in closer agreement with experiments.SCAN modifies ionic hydration shells in an ion-specific manner,governed by ionic size and charge,and reproduces experimental hydration geometries especially well for intermediate-size monovalent ions(Na^(+),Cl^(-)).Moreover,SCAN consistently reduces the overpolarization of water molecules near ions.These improvements lead to more accurate and physically consistent hydration structures,highlighting SCAN's utility for modeling complex aqueous systems and offering guidance for future studies of ionic solvation.
基金supported in part by the Research Grants Council of the Hong Kong Special Administrative Region,China, under project 7131–12Ethe NSFC RGC grant under project N–HKU714–13
文摘In optical scanning holography, one pupil produces a spherical wave and another produces a plane wave. They interfere with each other and result in a fringe pattern for scanning a three-dimensional object. The resolution of the hologram reconstruction is affected by the point spread function(PSF) of the optical system. In this paper, we modulate the PSF by a spiral phase plate, which significantly enhances the lateral and depth resolution. We explain the theory for such resolution enhancement and show simulation results to verify the efficacy of the approach.
文摘Si dangling bonds at the interface of quasi-free-standing monolayer graphene （QFMLG） are known to act as scattering centers that can severely affect carrier mobility Herein, we investigate the atomic and electronic structure of Si dangling bonds in QFMLG using low-temperature scanning tunneling microscopy/ spectroscopy （STM/STS）, atomic force microscopy （AFM）, and density functional theory （DFT） calculations. Two types of defects with different contrast were observed on a flat graphene terrace by STM and AFM; in particular, their STM contrast varied with the bias voltage. Moreover, these defects showed characteristic STS peaks at different energies, 1.1 and 1.4 eV. The comparison of the experimental data with the DFT calculations indicates that the defects with STS peak energies of 1.1 and 1.4 eV consist of clusters of three and four Si dangling bonds, respectively. The relevance of the present results for the optimization of graphene synthesis is discussed.
