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1.
李春宏周信达韩伟冯斌朱启华郑万国 《高压物理学报》2016,(5):392-398
采用化学气相沉积法在铜箔基底上生长单层石墨烯,利用湿化学方法将单层石墨烯转移到石英玻璃基底,获得石英基单层石墨烯样品。利用相衬显微镜和扫描电子显微镜,实验研究了单层石墨烯样品在紫外纳秒脉冲激光辐照下的损伤阈值和损伤概率,以及不同辐照通量下的典型微观结构。实验结果表明,单层石墨烯样品对550nm波长光的吸收率约为2.38%,与理论值2.3%接近。在波长为355nm、脉宽为5.8ns的条件下测得激光损伤阈值为78mJ/cm2。当辐照通量低于损伤阈值时,石墨烯样品表面有纳米碳球和碳花形成;当辐照通量等于损伤阈值时,石墨烯样品表面产生明显的多孔碳骨架烧蚀痕迹;当辐照通量高于损伤阈值时,则形成了特定的周期性折叠碳结构。 相似文献
2.
提出了一个含崩塌概率的一维沙堆模型,并用元胞自动机方法对该模型进行计算机模拟. 结果表明在崩塌概率p从0到1的变化过程中存在两个临界点p1和p2. 当p12时模型具有自组织临界行为,并且系统在从平凡行为到自组织临界行为之间有一个快速的转变. 当模型具有自组织临界性时,这种自组织临界行为具有普适性,两个临界指数分别是1.50±0.02和1.58±0.15. 该模型能够较好地解释一维米粒堆实验中出现的自组织临界现象
关键词:
自组织临界性
BTW模型
崩塌概率 相似文献
3.
《高压物理学报》2016,(5)
采用化学气相沉积法在铜箔基底上生长单层石墨烯,利用湿化学方法将单层石墨烯转移到石英玻璃基底,获得石英基单层石墨烯样品。利用相衬显微镜和扫描电子显微镜,实验研究了单层石墨烯样品在紫外纳秒脉冲激光辐照下的损伤阈值和损伤概率,以及不同辐照通量下的典型微观结构。实验结果表明,单层石墨烯样品对550nm波长光的吸收率约为2.38%,与理论值2.3%接近。在波长为355nm、脉宽为5.8ns的条件下测得激光损伤阈值为78mJ/cm2。当辐照通量低于损伤阈值时,石墨烯样品表面有纳米碳球和碳花形成;当辐照通量等于损伤阈值时,石墨烯样品表面产生明显的多孔碳骨架烧蚀痕迹;当辐照通量高于损伤阈值时,则形成了特定的周期性折叠碳结构。 相似文献
4.
实验研究了高功率纳秒量级激光脉冲在空气中聚焦时的能量透过率随输入激光脉冲能量变化的规律,发现在纳秒激光脉冲聚焦半径相同的情况下,激光脉冲的能量透过率随入射激光脉冲能量的变化可分为三种情况:当入射激光脉冲能量较低时,激光脉冲能量全部通过;当入射激光脉冲能量增大后,激光脉冲的能量透过率由近100%迅速减小;当入射激光脉冲的能量进一步增加时,激光脉冲的能量透过率继续缓慢变小.用临界自由电子密度以及所对应的临界时间点对上述实验现象进行了理论分析得到了如下结论:当自由电子密度未达到临界自由电子密度时,多光子电离过程起主要作用,而当自由电子密度超过临界自由电子密度后,逆韧致吸收过程起主要作用,临界时间点是入射激光脉冲与空气作用过程中自由电子密度达到临界自由电子密度的时刻.入射激光脉冲能量决定了临界时间点在脉冲作用时间上的位置,临界时间点的位置决定了激光脉冲的能量透过率.可以通过测量激光脉冲的能量透过率来计算出临界自由电子密度,从而确定出激光脉冲在空气中聚焦时的能量透过特性.
关键词:
临界自由电子密度
临界时间点
多光子电离
逆韧致吸收 相似文献
5.
在复合波长(波长分别为1053、527、351nm)情况下,利用激光近场对熔石英样品进行损伤实验。设计了一种基于激光近场辐照的损伤阈值定义方法,并利用带有灰度抑制的分水岭标记算法对损伤图像进行损伤区域提取,通过对比损伤图像与相应光束近场能量分布,计算出损伤区域与非损伤区域临界处的光能量密度,即为熔石英样品的损伤阈值。实验结果表明,复合波长激光诱导熔石英损伤是3种波长激光共同作用的结果,但351nm激光对损伤起主要作用,初始损伤阈值为8.22J/cm2;在复合波长激光多次辐照样品的情况下,熔石英样品后表面的损伤成指数形式增长,损伤增长系数为0.59。 相似文献
6.
本主要报道了对烧结样品YBa2Cu3O7—δ(Y-123)进行部分元素替代的初步实验结果.用Ca^2 部分替代Y^3 形成的Y1-xCaxBa2Cu3O7—δ(YCBCO)样品呈现出如下特征:样品的正常态电阻率ρ随Ca的替代浓度增加而依次降低,而超导临界温度Tc也依次下降.这一现象与通常情况下对铜氧化物超导材料进行元素替代所引起的行为截然不同.实验还显示:样品在低温下的临界电流密度Jc得到明显提高,掺Ca后烧结样品的临界电流受外磁场的影响明显减小.在弱磁场下,不同掺杂浓度样品的临界电流Ic随外磁场呈不同比例地线性下降,与一般颗粒多晶高温超导体临界电流Ic随外磁场行为明显不同. 相似文献
7.
本文主要研究了在77K温度下,拉伸应变和弯曲应变对Bi-2223/Ag超导带材临界电流的影响,得到了超导带材的临界电流随拉伸强度、曲率半径变化规律.实验结果显明,拉伸作用在超导带材上产生的形变对其临界电流(Ic)的影响存在一个临界值εirr=0.3%.形变小于此临界值,Ic变化较小,超过此临界值,临界电流急剧下降.弯曲实验同样存在类似关系.同步辐射光源对超导带材检测表明,在形变情况下,超导氧化物陶瓷芯的微裂纹迅速增加和交织是Ic降低的主要原因. 相似文献
8.
掺入BaCuO2杂相的YBa2Cu3O7-δ(YBCO)粉末样品采用固相反应方法制备获得。XRD的Rietveld精修显示BaCuO2杂相和YBCO并存。在YBCO+xBaCuO2(x=0,0.05,0.1,0.2,0.3)的一系列样品中,当x=0.05时,样品的临界电流密度最大。在磁场中,微量BaCuO2杂相的添加,使YBCO的临界电流(Jc)提高了,但超导转变温度(Tc)稍微有所下降。临界电流密度的这些特征行为来自于两方面的共同作用,一方面是超导性的变化,另一方面纳米尺寸范围内的空间分布的非均匀性。 相似文献
9.
采用X射线衍射仪,扫描电镜,超导量子干涉仪等仪器对纳米C和SiC掺杂的MgB2带材进行了表征,并采用标准四引线法对样品的临界电流进行了测试. 实验表明,C和SiC掺杂在提高MgB2带材高场下的临界电流密度方面具有显著效果. 在温度为4.2 K、磁场大于9 T条件下,C和SiC掺杂样品的临界电流密度与未掺杂样品相比均提高一个数量级以上. 掺杂样品高磁场下良好的临界电流性能主要归因于C对B的替代所产生的晶格畸变、位错等缺陷和局部成分变化而导致的有效晶内钉扎作用. 实验结果表明,SiC掺杂的MgB2带材之所以具有非常好的高场电流特性,和C掺杂的样品一样, C对B的替代起到十分关键的作用.
关键词:
2带材')" href="#">MgB2带材
C掺杂
SiC掺杂
临界电流性能 相似文献
10.
11.
M. A. Zelikman 《Physics of the Solid State》1997,39(11):1751-1755
A system of pancake vortices formed near the boundary of a sample in a monotonically increasing external magnetic field is
calculated with allowance for pinning due to the cellular structure of the medium for various values of the pinning parameter
I, which is proportional to the critical current of the junction and the cell diameter. The shortest distance from the outermost
vortex to the nearest neighbor is proportional to I
−11. It is shown that the pinning parameter has a critical value I
c separating two regimes with different types of critical states. For I<I
c the external magnetic field has a threshold value H
t(I), above which the field immediately penetrates the interior of the junction to an infinite distance. For I>I
c the magnetic field decays linearly from the boundary into the interior of the junction. The value obtained in the study,
I
c=3.369, differs from the value of 0.9716 postulated by other authors. The dependence of the slope of the magnetic field profile
near the boundary on I is determined. It is shown that the slope is independent of I in intervals 2πk<I<2πk+π.
Fiz. Tverd. Tela (St. Petersburg) 39, 1958–1963 (November 1997) 相似文献
12.
Based on a damage evolution equation and a critical damage
function model, this paper has completed the numerical simulation of
ductile spall fracture. The free-surface velocity and damage
distribution have been used to determine jointly the physical
parameters Dl (the critical linking damage), Df
(the critical fracturing damage) and k (the softening rate of
critical damage function model)of the critical damage function
model, which are 0.11, 0.51 and 0.57 respectively. Results indicate
that the parameters determined by any of shots could be applicable
to the rest of other shots, which is convincing proof for the
universal property of critical damage function. In our experiments,
the shock pressure is about 1~GPa to 2.5~GPa. For the reason of
limited pressure range, there are still some limitations in the
methods of present analysis. Moreover, according to the damage
evolution characteristic of pure aluminum obtained by experiments,
two critical damages are obtained, which are 0.11 and 0.51
respectively. The results are coincident with the experimental ones,
which indicate that the critical growth behaviour of damage occurs
in the plastic metal under dynamic loading. 相似文献
13.
M. A. Zelikman 《Technical Physics》2009,54(2):197-203
A new approach to magnetic field profiling inside a Josephson contact is suggested. Its essence consists in analyzing continuous
variation of a current configuration leading to a decrease in the Gibbs potential. With this approach, one can find a configuration
into which the Meissner state turns when an external field slightly exceeds the upper boundary of the Meissner regime and
trace the evolution of this configuration with increasing field. Calculations show that there exists critical value I
c of the pinning parameter in the range 0.95–1.00. This critical value separates two possible conditions of magnetic field
penetration into the contact. At I > I
c, a near-boundary current configuration completely compensating for the external field inside the contact arises irrespective
of the external field strength. At I < I
c, such a situation is observed only until the external field strength exceeds certain value H
max. Higher fields penetrate into the contact indefinitely deep. In nearboundary configurations, the magnetic field drops with
increasing depth almost linearly. Its slope k has rational values, which remain constant within finite intervals of I. As I goes beyond a given interval, k rises stepwise and takes on another rational value. When an external magnetic field is switched on adiabatically, configurations
with a maximal growth rate of the magnetic field are observed. 相似文献
14.
M. A. Zelikman 《Technical Physics》2005,50(8):967-975
A method is proposed for solving the nonlinear system of equations of fluxoid quantization for two interacting linear vortices.
It is shown that the centers of the vortices may lie in adjacent cells only if the pinning parameter I > 0.91, in alternate cells if I > 0.44, and in each third cell if I > 0.25. These critical values are substantially lower than analogous values for planar vortices. It is shown that, as the
value of I tends to zero, the minimal spacing between linear vortices does not increase indefinitely, but attains a certain finite value
and then remains unchanged. This means that pinning of linear vortices cannot be ignored even for values of I quite close to zero. It is shown that two linear vortices with centers in the neighboring cells along a diagonal may coexist
for indefinitely small values of I. 相似文献
15.
The steady-state fluorescence technique was used to study coil-helix (sol-gel) and helix-coil (gel-sol) transitions of the kappa carrageenan-water system with various carrageenan contents. Fluorescence (I) and scattered light (Isc ) intensities were measured against temperature to determine critical phase transition temperatures and exponents. It was observed that the coil-helix transition temperatures, Tch were much lower than the helix-coil (Thc ) transition temperatures due to the hysteresis of the phase transition loops. The gel fraction exponent (β) was measured and found to be in accord with the classical Flory-Stockmayer model. 相似文献
16.
Electrical resistivity (ρ) of the amorphous (a-)Fe100−c
Zr
c
(c=8.5, 9.5 and 10) alloys has been measured in the temperature range 77 to 300 K, which embraces the second-order magnetic
phase transition at the Curie temperature point T
c. Analysis of the resistivity data particularly in the critical region reveals that these systems have a much wider range
of critical region compared to other crystalline ferromagnetic materials. The value of T
c and specific heat critical exponent, α has the same values as those determined from our earlier magnetic measurements. The value of α for all the present investigated alloys are in close agreement with the values predicted for three-dimensional (3D) Heisenberg
ferromagnet systems, which gives contradiction to the earlier results on similar alloys. It is observed from the analysis
that the presence of quenched disorder does not have any influence on critical behavior. 相似文献
17.
M. A. Zelikman 《Technical Physics》2009,54(9):1290-1300
A new approach based on analysis of continuous configurational modification in the direction of a decrease in the Gibbs potential
is proposed for computing the penetration of an external magnetic field in an ordered 3D Josephson medium. The configuration
to which the Meissner state passes when the external field slightly exceeds the Meissner stability threshold is determined.
This configuration contains a periodic sequence of linear vortices with centers lying in an alternating cell, parallel to
the boundary, and located at a certain distance from it. A further increase in the field reveals that the 3D medium behaves
like a long periodically modulated Josephson junction. However, the critical value I
C
of the pinning parameter for a 3D medium, which lies in the interval 0.7–0.8, is lower than the analogous value I
C
= 0.9716 for a long junction. The values of H
max for I < I
C
, as well as the steepness of the decrease in the magnetic field at the boundary for I > I
C
, are higher in the 3D medium than in a long junction. For very large values of I, the field penetrates the boundary region not as a 2D lattice of linear vortices, but as a 1D lattice of plane vortices,
which are mathematically equivalent to the vortices in a long junction. 相似文献
18.
M. Sato 《等离子体物理论文集》1981,21(2):77-86
Influences of an axial magnetic field on the ionization wave and the positive column in rare gas discharges are studied experimentally. The upper critical current Ic for the appearance of ionization waves in the magnetic field B is newly found. As B is gradually increased, the value of Ie slightly increases from the Pupp's value and after passing a prominent maximum, finally become very small. In addition an anomaly takes place in the axial electric field E of the positive column stable for helical instabilities. With increasing the magnetic field the value of E goes through a weak maximum before decreasing. It is concluded that this anomaly, apparently incompatible with classical diffusion theory, is closely related to the appearance of ionization waves in the positive column. 相似文献
19.
M. A. Zelikman 《Technical Physics》2008,53(8):971-977
The stability of the Meissner state of a 3D Josephson medium against combinations of phase jump small fluctuations at contacts
is considered. Expressions for the elements of the quadratic form matrix for the second variation of the Gibbs potential are
derived. Overheat field values and forms of fluctuations causing instabilities are found. Ratio H
S1/H
S2, where H
S1 is the overheat field and H
S2 is the maximal field at which the Meissner state still exists, grows with increasing pinning parameter I, varying between 0.84 and 1. Almost at all pinning parameters, critical fluctuations represent rapidly decreasing (inward
to the sample) periodic alternating-sign structures one cell wide. When the pinning parameter is very small (I < 0.1), such an instability is absent. In this range of I, ratio H
S1/H
S2 is close to unity. 相似文献
20.
《Journal of Macromolecular Science: Physics》2013,52(3-4):421-430
The molecular weight (MW) dependence of the primary nucleation rate (I) was studied for poly(ethylene succinate). The primary nucleation rate was measured in a wide range of temperatures. It has a bell shape with a maximum nucleation rate (I max ) that showed a remarkable MW dependence. I max decreased first with MW to about 3000 and then increased. The MW of about 3000 was attributed to the transition from intermolecular nucleation to intramolecular nucleation. The MW dependence of I max was expressed as I max ∝MWα. The value of α was negative unity for intermolecular nucleation and positive unity for intramolecular nucleation. 相似文献