16 research outputs found
Investigation of the topography-dependent current in conductive AFM and the calibration method
The topography and the electrical properties of materials are two crucial
characteristics in determining their functionalities. Conductive atomic force
microscopy (CAFM) is widely recognized for its ability to independently measure
the topology and conductivity of the sample surface. The increasing trend
towards miniaturization in electrical devices and sensors has led to an urgent
demand for enhancing the accuracy of CAFM characterization. However, the
sample's topography may affect the current measured by CAFM, leading to an
inaccurate estimation of the sample's conductivity. Herein, we investigated the
existence of topography-dependent current that originates from changes in
capacitance between the probe and sample in CAFM testing. A linear correlation
between the current and topography has been established using both experimental
and theoretical methods. A calibration method based on this linear correlation
has been proposed to eliminate the current error induced by the uneven surface
of both insulators and conductors. This work will yield substantial advantages
for research requiring high-precision CAFM testing.Comment: Corrected typo
Bifurcation of Safe Basins and Chaos in Nonlinear Vibroimpact Oscillator under Harmonic and Bounded Noise Excitations
The erosion of the safe basins and chaotic motions of a nonlinear vibroimpact oscillator under both harmonic and bounded random noise is studied. Using the Melnikov method, the system’s Melnikov integral is computed and the parametric threshold for chaotic motions is obtained. Using the Monte-Carlo and Runge-Kutta methods, the erosion of the safe basins is also discussed. The sudden change in the character of the stochastic safe basins when the bifurcation parameter of the system passes through a critical value may be defined as an alternative stochastic bifurcation. It is founded that random noise may destroy the integrity of the safe basins, bring forward the occurrence of the stochastic bifurcation, and make the parametric threshold for motions vary in a larger region, hence making the system become more unsafely and chaotic motions may occur more easily
Polyimides Crosslinked by Aromatic Molecules and Nanocomposites for High Temperature Capacitive Energy Storage
High temperature polymer-based dielectric capacitors are crucial for
application in electronic power systems. However, the storage performance of
conventional dielectrics polymer dramatically deteriorates due to the thermal
breakdown under concurrent high temperatures and electric fields, and there are
hardly reports on the causes of thermal breakdown from the aspects of the high
temperature conduction loss and Joule heat dissipation. Herein, a combined
strategy of crosslinking and compositing for polyimide-based nanocomposites is
proposed, which minimizes the thermal breakdown by significantly inhibiting the
high-temperature conduction loss and enhancing the high thermal conductivity.
Furthermore, the rationale of the strategy was theoretically and experimentally
verified from multiple perspectives. The charge-trapping effect is directly
observed and quantitatively probed by Kelvin probe force microscopy with nano
level resolution, indicating that the crosslinking network introduces local
deep traps and effectively suppresses the charge transport. The thermal
conductivity of the nanocomposites inhibits the high temperature thermal
breakdown, which is confirmed by phase field simulations. Consequently, the
optimized nanocomposites possess an ultra high discharge energy density(Ud) of
5.45 J/cm3 and 3.54 J/cm3 with a charge discharge efficiency, respectively,
which outperforms the reported polyimide based dielectric nanocomposites. This
work provides a scalable direction for high temperature polymer based
capacitors with excellent performance
Moment Stability of Linear Vibro-impact System to Boundary Random Parametrical Excitation
Abstract The resonance response and moment stability of a single-degree-of-freedom linear vibro-impact oscillator with a one-sided barrier to a boundary random parametrical excitation are investigated. The analysis is based on a special Zhuravlev transformation, which reduces the system to one without impacts or velocity jumps, thereby permitting the applications of asymptotic averaging over the period for slowly varying random process. By using the ItĂ´'s differential rule, differential equations ruling the time evolution of the first and second order response moments are obtained. The necessary and sufficient conditions of stability in the moments are that the coefficients matrix of the differential equations ruling the moments have complex eigenvalues with negative real parts. The analytical expression of the stability condition in the first order moments is obtained, while results of the second order moments are given numerically. Some numerical simulations and graphs are presented for representative cases. It is founded that when the amplitude of the parametrical excitation increase, the stability regions will reduce whether in the first order moments or the second order moments. The stability regions will reduce to the minimum value in the principal resonance case. The stability regions based on different order moments will become identical when the intensity of the random disorder increases to zero. The stochastic excitation stabilizes the system in some cases
Whole-Tree Response of Non-Structural Carbohydrates, Carbon and Nitrogen Concentrations in Two Temperate Tree Species to 10-Year Nitrogen Fertilization
This study aimed to investigate the effects of long-term nitrogen fertilization on non-structural carbohydrates (NSC) and nitrogen (N) status and their interaction in mature trees at the whole-tree scale. Ten g N m(-2) yr(-1) of ammonium nitrate fertilizer were applied to 26-year-old Larix gmelinii Rupr. (larch) and Fraxinus mandschurica Rupr. (ash) trees in Northeastern China from 2002 to 2012. NSC, total carbon (C) and total N concentrations in different compartments were examined. For both species, concentrations of NSC and their components (soluble sugars and starch) tended to increase in aboveground organs but decrease in fine roots following N fertilization, with significant (p < 0.05) changes only observed in ash stems and larch roots. N fertilization increased N concentrations and decreased the C:N ratio in all organs, especially in foliage and roots, while the effects of fertilization on total C concentrations varied with tree species and organs. Concentrations of NSC (mainly reflected in soluble sugar) were generally negatively correlated with N concentration in fine roots but positively related to N concentration in aboveground woody organs in both control and fertilized treatments. However, fertilization strengthened this correlation in fine roots and weakened this relationship in aboveground organs. This study provides a decade-long insight into the effect of currently increasing N deposition on tree growth and function
Concurrent Harvesting of Ambient Energy by Hybrid Nanogenerators for Wearable Self-Powered Systems and Active Remote Sensing
Harvesting
energy available from ambient environment is highly desirable for
powering personal electronics and health applications. Due to natural
process and human activities, steam can be produced by boilers, human
perspiration, and the wind exists ubiquitously. In the outdoor environment,
these two phenomena usually exist at the same place, which contain
heat and mechanical energies simultaneously. However, previous studies
have isolated them as separate sources of energy to harvest and hence
failed to utilize them effectively. Herein, we present unique hybrid
nanogenerators for individually/simultaneously harvesting thermal
energy from water vapors and mechanical energy from intermittent wind
blowing from the bottom side, which consist of a wind-driven triboelectric
nanogenerator (TENG) and pyroelectric–piezoelectric nanogenerators
(PPENGs). The output power of the PPENG and the TENG can be up to
about 184.32 ÎĽW and 4.74 mW, respectively, indicating the TENG
plays the dominant role. Our hybrid nanogenerators could provide different
applications such as to power digital watch and enable self-powered
sensing with wireless transmission. The device could also be further
integrated into a face mask for potentially wearable applications.
This work not only provides a promising approach for renewable energy
harvesting but also enriches potential applications for self-powered
systems and wireless sensors
Concurrent Harvesting of Ambient Energy by Hybrid Nanogenerators for Wearable Self-Powered Systems and Active Remote Sensing
Harvesting
energy available from ambient environment is highly desirable for
powering personal electronics and health applications. Due to natural
process and human activities, steam can be produced by boilers, human
perspiration, and the wind exists ubiquitously. In the outdoor environment,
these two phenomena usually exist at the same place, which contain
heat and mechanical energies simultaneously. However, previous studies
have isolated them as separate sources of energy to harvest and hence
failed to utilize them effectively. Herein, we present unique hybrid
nanogenerators for individually/simultaneously harvesting thermal
energy from water vapors and mechanical energy from intermittent wind
blowing from the bottom side, which consist of a wind-driven triboelectric
nanogenerator (TENG) and pyroelectric–piezoelectric nanogenerators
(PPENGs). The output power of the PPENG and the TENG can be up to
about 184.32 ÎĽW and 4.74 mW, respectively, indicating the TENG
plays the dominant role. Our hybrid nanogenerators could provide different
applications such as to power digital watch and enable self-powered
sensing with wireless transmission. The device could also be further
integrated into a face mask for potentially wearable applications.
This work not only provides a promising approach for renewable energy
harvesting but also enriches potential applications for self-powered
systems and wireless sensors
Concurrent Harvesting of Ambient Energy by Hybrid Nanogenerators for Wearable Self-Powered Systems and Active Remote Sensing
Harvesting
energy available from ambient environment is highly desirable for
powering personal electronics and health applications. Due to natural
process and human activities, steam can be produced by boilers, human
perspiration, and the wind exists ubiquitously. In the outdoor environment,
these two phenomena usually exist at the same place, which contain
heat and mechanical energies simultaneously. However, previous studies
have isolated them as separate sources of energy to harvest and hence
failed to utilize them effectively. Herein, we present unique hybrid
nanogenerators for individually/simultaneously harvesting thermal
energy from water vapors and mechanical energy from intermittent wind
blowing from the bottom side, which consist of a wind-driven triboelectric
nanogenerator (TENG) and pyroelectric–piezoelectric nanogenerators
(PPENGs). The output power of the PPENG and the TENG can be up to
about 184.32 ÎĽW and 4.74 mW, respectively, indicating the TENG
plays the dominant role. Our hybrid nanogenerators could provide different
applications such as to power digital watch and enable self-powered
sensing with wireless transmission. The device could also be further
integrated into a face mask for potentially wearable applications.
This work not only provides a promising approach for renewable energy
harvesting but also enriches potential applications for self-powered
systems and wireless sensors
Concurrent Harvesting of Ambient Energy by Hybrid Nanogenerators for Wearable Self-Powered Systems and Active Remote Sensing
Harvesting
energy available from ambient environment is highly desirable for
powering personal electronics and health applications. Due to natural
process and human activities, steam can be produced by boilers, human
perspiration, and the wind exists ubiquitously. In the outdoor environment,
these two phenomena usually exist at the same place, which contain
heat and mechanical energies simultaneously. However, previous studies
have isolated them as separate sources of energy to harvest and hence
failed to utilize them effectively. Herein, we present unique hybrid
nanogenerators for individually/simultaneously harvesting thermal
energy from water vapors and mechanical energy from intermittent wind
blowing from the bottom side, which consist of a wind-driven triboelectric
nanogenerator (TENG) and pyroelectric–piezoelectric nanogenerators
(PPENGs). The output power of the PPENG and the TENG can be up to
about 184.32 ÎĽW and 4.74 mW, respectively, indicating the TENG
plays the dominant role. Our hybrid nanogenerators could provide different
applications such as to power digital watch and enable self-powered
sensing with wireless transmission. The device could also be further
integrated into a face mask for potentially wearable applications.
This work not only provides a promising approach for renewable energy
harvesting but also enriches potential applications for self-powered
systems and wireless sensors