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  • Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences  (30)
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  • Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences  (30)
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  • 1
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 49, No. 10 ( 2000), p. 2007-
    Abstract: The changes of defects in PbWO4 crystal caused by La dopant have been studied by means of positron annihilation lifetime and X-ray photoelectron spec trum (XPS).The results show that La dopant enhance the concentration of lead vac ancy (VPb) which can be described as the positron capture center in PbWO4 crystal,and lead vacancy will furthermore introduce low-valent oxygen center.We discuss the mechanism of La doped in PbWO4,and consi der that oxygen vacancy is restrained by doping of La,while lead vacancy density is increased by La dopant.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2000
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  • 2
    Online Resource
    Online Resource
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2016
    In:  Acta Physica Sinica Vol. 65, No. 24 ( 2016), p. 240701-
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 65, No. 24 ( 2016), p. 240701-
    Abstract: In recent years,the modeling and application of biological neurons have gained more and more attention.By now, the research on neuron models has become one of the most important branches of neuroscience.Neuron models can be used in various areas,such as biomimetic applications,memory design,logical computing,and signal processing. Furthermore,it is significant to study the dynamic characteristics of neural system by using neuron models.In this paper,the historical development of neuron models is reviewed.The neuron models have experienced three development stages.In the pioneering stage,a group of scientists laid the experimental and theoretical foundation for later research. Then,the whole study started to blossom after the publication of Hodgkin-Huxley model.In the 1970s and 1980s,various models were proposed.One of the research focuses was the simulation of neural repetitive spiking.Since the 1990s, researchers have paid more attention to setting up models that are both physiologically meaningful and computationally effective.The model put forward by Izhikevich E M has been proved to solve the problem successfully.Recently,IBM presented a versatile spiking neuron model based on 1272 ASIC gates.The model,both theoretically understandable and physically implementable,has been used as a basic building block in IBM's neuro-chip TrueNorth.In the paper, seventeen neuron models worth studying are listed.To give a more explicit explanation,these models are classified as two groups,namely conductance-dependent and conductance-independent models.The former group's goal is to model the electrophysiology of neuronal membrane,while the latter group is only to seek for capturing the input-output behavior of a neuron by using simple mathematical abstractions.The complexity and features of each model are illustrated in a chart,while the prominent repetitive spiking curves of each model are also exhibited.Five of the models are further detailed,which are the Hodgkin-Huxley model,the Integrate-and-fire model,the Fitzhugh-Nagumo model,the Izhikevich model,and the most recent model used by IBM in its neuro-chip TrueNorth.Finally,three questions are put forward at the end of the paper,which are the most important problems that today's researchers must consider when setting up new neuron models.In conclusion,the feasibility of physical implementation remains to be a challenge to all researchers. Through the aforementioned work,the authors aim to provide a reference for the study that follows,helping researchers to compare those models in order to choose the properest one.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2016
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  • 3
    Online Resource
    Online Resource
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2012
    In:  Acta Physica Sinica Vol. 61, No. 13 ( 2012), p. 135204-
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 61, No. 13 ( 2012), p. 135204-
    Abstract: The quasi-isentropic compression of material with high strain rate can be obtained by the ramp wave loading of plasma jet produced by laser-driven reservoir target. The quasi-isentropic compression experiments of aluminum are carried out on the high power laser facility of SG-III prototype. The smooth and continuous speed history of free surface of specimen is recorded with a line-imaging velocity interferometer (VISAR). The peak pressure (60 GPa), the rise time of the load (~ 10 ns) and the strain (~ 108 s-1) are derived by the back-integrating method, and the reverberation of compression wave at the rear surface of the sample is observed.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2012
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  • 4
    Online Resource
    Online Resource
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2006
    In:  Acta Physica Sinica Vol. 55, No. 10 ( 2006), p. 5375-
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 55, No. 10 ( 2006), p. 5375-
    Abstract: Stable square emission patterns are observed in argon discharge at atmospheric pressure by using a dielectric barrier discharge device with different lateral boundary conditions. The spatio-temporal dynamics of square pattern in nanosecond time scale is investigated. It is found that the square pattern is an interlacing of two oscillating square sublattices, which have time sequence inversion behavior. The influence of the wall charge distribution on the forming process and the spatio-temporal dynamics of the emission patterns is discussed.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2006
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  • 5
    Online Resource
    Online Resource
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2018
    In:  Acta Physica Sinica Vol. 67, No. 23 ( 2018), p. 235201-
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 67, No. 23 ( 2018), p. 235201-
    Abstract: In indirect-drive inertial confinement fusion (ICF), laser beams are injected into a high-Z hohlraum and the laser energy is converted into intense X-ray radiation, which ablates a capsule located in the center of the hohlraum, and thus making it implode. To achieve high implosion efficiency, it is required that the hohlraum inner wall plasma movement, which will block further laser injection through the laser entrance hole (LEH), be suppressed. Evolution of hohlraum radiation nonuniformity caused by the plasma movement will result in implosion asymmetry which will prevent the ignition from happening. Therefore it is very important to study the hydrodynamic movement of high-Z plasma in ICF experiment.〈br/〉In ICF hohlraum, various plasmas of laser spots, corona, radiation ablation and jets move in different ways driven by laser ablation and X-ray radiation ablation, which is hard to observe and study. An X-ray dual spectral band time-resolved imaging method is developed to clearly observe the motion of various plasmas in hohlraum. Based on the time-resolved X-ray framing camera, using the typical gold plasma emission spectrum, the gold microstrip MCP response spectrum, and the 1.5 μm Al or 3 μm Ti filter transmittance spectrum, the two narrow-band X-ray peaks at 0.8 keV and 2.5 keV are highlighted. The 0.8 keV X-ray shows the Planck spectrum of gold plasma, and 2.5 keV X-ray indicates the M-band of gold plasma.〈br/〉In the vacuum hohlraum, jets are observed clearly, which are verified to be 4 times the sound speed experimentally. The generation mechanism of gold plasma jets in the ICF hohlraum is mainly due to collision rather than magnetic field, because it is estimated that thermal pressure is much bigger than magnetic pressure. In the gas-filled hohlraum, low-Z C〈sub〉5〈/sub〉H〈sub〉12〈/sub〉 gas can effectively eliminate high-Z gold jets and suppress the high-Z gold coronal plasma movement. The interface between the low-Z and high-Z substance is observed clearly, and gold plasma is accumulated obviously in the later period at the interface. Moreover, spike and filamentous structure occur at the interface between the two substances, which is probably caused by the hydrodynamic instability. The 0.8 keV rather than 2.5 keV X-ray is observed around inner wall, which originates from the low-temperature plasma driven by radiation ablation and is predicted by simulation code. Furthermore, the pressure balance between the two substances and the density steepness at the interface are also analyzed.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2018
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  • 6
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 59, No. 12 ( 2010), p. 8471-
    Abstract: The velocity distribution of emission electrons in the transfer ionization process of 70keV He2+ colliding on He has been studied with a reaction microscope. These distributions show that the electrons lie mainly in the scattering plane which are observed to be emitted preferentially in the forward direction, lying between 0 and projectile velocity Vp. The distributions also display a typical two-fingered structure with a local minimum on internuclear axis. This characteristic can be qualitatively explained as being due to the interference between σ amplitude and π amplitude of electrons final wavefunction. It depends also on the impact parameters; the π amplitude contribution is dominant at small impact parameters, which leads to a symmetric velocity distribution around the internuclear axis. However, at large impact parameters the σ amplitude contribution increases relatively obviously, resulting in an asymmetric electrons velocity distribution around the internuclear axis.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2010
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  • 7
    Online Resource
    Online Resource
    Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences ; 2011
    In:  Acta Physica Sinica Vol. 60, No. 9 ( 2011), p. 095202-
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 60, No. 9 ( 2011), p. 095202-
    Abstract: To accelerate the electrons efficiently in the laser wake-field accelerator, it is necessary to suppress the instability induced by the diffraction and the defocusing of the laser pulse. The gas-filled capillary discharge waveguide can generate an approximately parabolic density distribution, which can guide the laser pulse efficiently and suppress the instability. Using the Stark effect, this plasma density distribution is measured in this paper, and the relationship between plasma density and filled pressure is presented. By using the MHD code CRMHA, the formation of the capillary waveguide is simulated and researched in detail.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2011
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  • 8
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 62, No. 1 ( 2013), p. 014206-
    Abstract: In order to explore the proper working voltage for the third-generation low light level image intensifier, the influence of pro-proximity pulse voltage on image intensifier halo effect is investigated. The pulse voltage is applied to photocathode of image intensifier. Respectively change the high and low level voltage and duty ratio, image intensifier halo images are collected by high-resolution charge-coupled device (CCD). The gray distributions for pixel points on halo image central line are given and comparatively analyzed. The results show that as high level voltage and duty ratio increase, the number of pixel points whose gray value is 255 increases and the border between signal and background becomes clear. When high level voltage is above 200 V and duty ratio is above 60%, the pro-proximity voltage has not great influence on image intensifier halo effect. When low level voltage is above 2 V, photoelectrons escaping from photocathode cannot reach microchannel plate under low level voltage stage. The present investigation is beneficial to the exploration of the optimal working voltage for image intensifier and energy range of photoelectrons escaping from photocathode, and provides an experimental support for the improvement of the third-generation low light level image intensifier performance.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2013
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  • 9
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 65, No. 18 ( 2016), p. 188101-
    Abstract: Graphene has been a superstar in the fields ranging from materials science to condensed-matter physics since 2004. Graphene possesses good thermal and mechanical properties, high electron transfer capability and relatively low production cost. As a consequence, graphene has been used in the areas of multi-functional advanced materials and electronics. A direct disperse method has been widely applied to polymers to improve their dielectric properties. Recently, graphene/polymer composites have received much attention. Graphene nanosheets can significantly improve the physical properties of the host polymer at a very low content of conductive filler loading. Poly vinylidene fluoride (PVDF) is a semicrystalline thermoplastic polymer with remarkably high piezo-/pyroelectric coefficient, and excellent thermal stability and chemical resistance. More efforts have been recently devoted to the preparations of high-' composites based on PVDF. In this work, a graphene/PVA/PVDF nanocomposite film composed of poly(vinyl alcohol) (PVA), reduced graphene oxide (RGO), and poly (vinylidene fluoride) (PVDF) is fabricated. First of all, graphene oxide (GO) is prepared by the modified Hummers method. GO and PVA are successively dissolved in the dimethyl sulfoxide (DMSO) solution, in order to obtain PVA functionalized GO which is formed via non-covalent bonds. Then PVDF is added into this solution to form a homogeneous three-phase aqueous mixture. According to the solution-casting and thermal reduction processes, the three-phase nanocomposite films are formed. The thickness values of the films are in a range of 0.3-0.4 mm. The square specimens are coated with a silver paste prior to electrical measurements. The obtained products are characterized using X-ray diffraction, UV Vis absorption spectrum, Fourier transform infrared absorption spectrum, and atomic force microscopy. The morphologies of PVDF and RGO/PVA/PVDF films are investigated by a scanning electron microscope. Electrical measurements are conducted in a frequency range from 102 to 104 Hz. Results suggest that GO can be reduced to RGO and phase transition of PVDF from to phases is effectively promoted at 120 ℃. The dielectric properties of the polymer matrix are improved. Furthermore, PVA modified RGO is easier to disperse in the PVDF substrate than the original one, which strongly reduces the spherulite size of PVDF and improves the dielectric property of the composite film. The percolation threshold (fvol*) of RGO/PVA/PVDF film is estimated to be 8.45 vol.%, and the dielectric constant of the film is 238 times as large as that of the pure PVDF films at 102 Hz. In addition, the dielectric constant increases rapidly near the percolation threshold and depends on frequency, which is mainly ascribed to the Maxwell-Wagner-Sillars polarization in the low frequency range. This study provides a low-cost and simple method of preparing polymer nanocomposites with high dielectric properties.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2016
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  • 10
    In: Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 69, No. 7 ( 2020), p. 078501-
    Abstract: In this paper, the total dose effect on AlGaN/GaN high-electron-mobility transistor (HEMT) devices after 〈sup〉60〈/sup〉Co γ-ray irradiation with a total dose of 1 Mrad(Si) was investigated at different biases (〈i〉V〈/i〉〈sub〉GS〈/sub〉 = –3 V, 〈i〉V〈/i〉〈sub〉DS〈/sub〉〈italic/〉 = 0.5 V; 〈i〉V〈/i〉〈sub〉GS〈/sub〉 = –1.9 V, 〈i〉V〈/i〉〈sub〉DS〈/sub〉 = 0.5 V; 〈i〉V〈/i〉〈sub〉GS〈/sub〉 = 0 V, 〈i〉V〈/i〉〈sub〉DS〈/sub〉 = 0 V). The experimental results were analyzed using 1/〈i〉f〈/i〉 low-frequency noise and direct current electrical characteristics. The electrical parameters degraded mostly under zero bias condition because of the radiation-induced defect charge of the oxide layer and the interface state. Wherein, the saturation drain current was reduced by 36.28%, and the maximum transconductance was reduced by 52.94%. The reason was that the oxide dielectric layer of AlGaN/GaN HEMT devices generated electron-hole pairs under γ-ray irradiation, and most of the electrons were quickly swept out of the oxide region corresponding to the gate-source and gate-drain spacer regions, and most of the holes remained in the oxide. Under the action of the built-in electric field, holes slowly moved towards the interface between the oxide and AlGaN, which depleted the two-dimensional electron gas of the channel.According to the McWhorter model, the low-frequency noise in the AlGaN/GaN HEMT devices results from random fluctuations of carriers, which are caused by the capture and release processes of carriers by traps and defect states in the barrier layer. The extracted defect densities in AlGaN/GaN HEMT devices increased from 4.080 × 10〈sup〉17 〈/sup〉cm〈sup〉–3〈/sup〉·eV〈sup〉–1〈/sup〉 to 6.621 × 10〈sup〉17 〈/sup〉cm〈sup〉–3〈/sup〉·eV〈sup〉–1〈/sup〉 under the condition of zero bias, and the result was in good agreement with test results of the direct currentelectrical characteristics. The damage mechanism was the radiation-induced defect charge in the oxide layer and the interface state, which increased the flat-band voltage noise power spectral density of the AlGaN/GaN HEMT devices. According to the charge tunneling mechanism, the spatial distribution of defect in the barrier layer was extracted, and the result also proved that the densities of radiation-induced defect charges under zero bias were more than the other biases. The experimental results showed that zero bias was the worst bias for AlGaN/GaN HEMT devices irradiation.
    Type of Medium: Online Resource
    ISSN: 1000-3290 , 1000-3290
    Language: Unknown
    Publisher: Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
    Publication Date: 2020
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