We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the...We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.展开更多
This paper reports the performances of Ti/Al based ohmic contacts fabricated on highly doped p-type 4H-SiC epitaxial layer which has a severe step-bunching surface. Different contact schemes are investigated based on ...This paper reports the performances of Ti/Al based ohmic contacts fabricated on highly doped p-type 4H-SiC epitaxial layer which has a severe step-bunching surface. Different contact schemes are investigated based on the AI：Ti composition with no more than 50 at.% Al. The specific contact resistance （SCR） is obtained to be as low as 2.6 × 10-6Ωcm2 for the bilayered Ti（100 nm）/Al（100 nm） contact treated with 3 rain rapid thermal annealing （RTA） at 1000 ℃. The microstructure analyses examined by physical and chemical characterization techniques reveal an alloy-assisted ohmic contact formation mechanism, i.e., a high degree of alloying plays a decisive role in forming the interfacial ternary Ti3SiC2 dominating the ohmic behavior of the Ti/Al based contact. Furthermore, a globally covered Ti3 SiC2 layer with （0001）-oriented texture can be formed, regardless of the surface step bunching as well as its structural evolution during the metallization annealing.展开更多
We report on the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the Pd/Ti/n-InP Schottky barrier diodes (SBDs) in the temperature range 160-400 K in steps of 40 K. The barrier heights and ideal...We report on the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the Pd/Ti/n-InP Schottky barrier diodes (SBDs) in the temperature range 160-400 K in steps of 40 K. The barrier heights and ideality factors of Schottky contact are found in the range 0.35 eV (I-V), 0.73 eV (C-V) at 160 K and 0.63 eV (I-V), 0.61 eV (C-V) at 400 K, respectively. It is observed that the zero-bias barrier height decreases and ideality factor n increase with a decrease in temperature, this behaviour is attributed to barrier inhomogeneities by assuming Gaussian distribution at the interface. The calculated value of series resistance (Rs) from the forward I-V characteristics is decreased with an increase in temperature. The homogeneous barrier height value of approximately 0.71 eV for the Pd/Ti Schottky diode has been obtained from the linear relationship between the temperature-dependent experimentally effective barrier heights and ideality factors. The zero-bias barrier height ( ) versus 1/2kT plot has been drawn to obtain evidence of a Gaussian distribution of the barrier heights and values of = 0.80 eV and = 114 mV for the mean barrier height and standard deviation have been obtained from the plot, respectively. The modified Richardson ln(I0/T2)- ( ) versus 1000/T plot has a good linearity over the investigated temperature range and gives the mean barrier height ( ) and Richardson constant (A*) values as 0.796 eV and 6.16 Acm-2K-2 respectively. The discrepancy between Schottky barrier heights obtained from I-V and C-V measurements is also interpreted.展开更多
Vertical rigidity of the space self adaptive 530 high rigidity mill is calculated by applying the boundary element method (BEM) of three dimension elastic contact problem,which can update the existed deforming s...Vertical rigidity of the space self adaptive 530 high rigidity mill is calculated by applying the boundary element method (BEM) of three dimension elastic contact problem,which can update the existed deforming separation calculating theory and corresponding methods of material mechanics,elastic mechanics and finite element method.The method has less hypotheses and stronger synthesis in contact type calculating model.The advantages of the method are high calculating rate,high calculating accuracy,etc..展开更多
Let C be a closed convex weakly Cauchy subset of a normed space X. Then we define a new {a,b,c} type nonexpansive and {a,b,c} type contraction mapping T from C into C. These types of mappings will be denoted respectiv...Let C be a closed convex weakly Cauchy subset of a normed space X. Then we define a new {a,b,c} type nonexpansive and {a,b,c} type contraction mapping T from C into C. These types of mappings will be denoted respectively by {a,b,c}-ntype and {a,b,c}-ctype. We proved the following： 1. If T is {a,b,c}-ntype mapping, then inf{ ｜｜ T（x）-x｜｜ ：x C C} =0, accordingly T has a unique fixed point. Moreover, any sequence {Xn}n∈NN in C with limn→∞｜｜T（xn） - Xn｜｜ = 0 has a subsequence strongly convergent to the unique fixed point of T. 2. If T is {a,b,c}-ctype mapping, then T has a unique fixed point. Moreover, for any x∈C the sequence of iterates {Tn （x）}n∈N has subsequence strongly convergent to the unique fixed point of T. This paper extends and generalizes some of the results given in [2,4, 7] and [13].展开更多
The influence of a deep-level-defect（DLD） band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN（p^＋＋-GaN） contact layer w...The influence of a deep-level-defect（DLD） band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN（p^＋＋-GaN） contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I–V measurement shows that the variable-range hopping（VRH） transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p^＋＋-GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p^＋＋-GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97×10^-4Ω·cm^2 is achieved.展开更多
It is well documented that dietary restriction can prevent many different diseases and extend the life spans of different rodent species. In the previous study, we reported that intermittent fasting (IF) as well as mo...It is well documented that dietary restriction can prevent many different diseases and extend the life spans of different rodent species. In the previous study, we reported that intermittent fasting (IF) as well as moderate dietary restriction ameliorated the allergic dermatitis in ICR mice. In the present study, we demonstrated the ameliorative effects of IF on allergic dermatitis in NC/Nga mice, a strain known as a model for atopic dermatitis. Interestingly, the total number of CD4+CD8+ double positive thymocyte in mice after IF significantly decreased in comparison to that in mice fed ad libitum. Although it was reported that an immunosuppressive compound inhibited the contact allergic response by inducing the CD4+CD25+ regulatory T-cells, IF did not affect regulatory T cells in the present study. These results suggested that CD4+CD8+ double positive thymocytes play an important role in the regulation of allergy by IF in NC/Nga mice.展开更多
We report on the effect of annealing temperature on electrical, interfacial reactions and surface morphological properties of Ni/Cu Schottky contacts on n-type InP. The extracted barrier height of as-deposited Ni/Cu S...We report on the effect of annealing temperature on electrical, interfacial reactions and surface morphological properties of Ni/Cu Schottky contacts on n-type InP. The extracted barrier height of as-deposited Ni/Cu Schottky contact is 0.59 eV (I-V) respectively. The high-quality Schottky contact with barrier height and ideality factor of 0.65 eV (I-V) and 1.15 respectively, can be obtained after annealing at 300℃ for 1 min in a nitrogen atmosphere. However, annealing at 400℃, results the decrease in the barrier height to 0.54 eV (I-V). From the above observations, it is observed that Ni/Cu Schottky contact exhibited excellent electrical properties after annealing at 300℃. Hence, the optimum annealing temperature for the Ni/Cu Schottky contact is 300℃. Furthermore, Cheung’s functions is used to extract the diode parameters including ideality factor, barrier height and series resistance. According to the XRD analysis, the formation of the indium phases at the Ni/Cu/n-InP interface could be the reason for the increase in the barrier height at annealing temperature 300℃. Further, the degradation of the barrier heights after annealing at 400℃ may be due to the formation of phosphide phases at the Ni/Cu/n-InP interface. Scanning electron microscopy (SEM) results show that the overall surface morphology of the Ni/Cu Schottky contact is reasonably smooth.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774377 and 11574343)。
文摘We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.
基金supported by the Key Specific Projects of Ministry of Education of China(Grant No.625010101)the National Natural Science Foundation of China(Grant No.61234006)+2 种基金the Natural Science Foundation of Shaan Xi Province,China(Grant No.2013JQ8012)the Doctoral Fund of Ministry of Education of China(Grant No.20130203120017)the Specific Project of the Core Devices,China(Grant No.2013ZX0100100-004)
文摘This paper reports the performances of Ti/Al based ohmic contacts fabricated on highly doped p-type 4H-SiC epitaxial layer which has a severe step-bunching surface. Different contact schemes are investigated based on the AI：Ti composition with no more than 50 at.% Al. The specific contact resistance （SCR） is obtained to be as low as 2.6 × 10-6Ωcm2 for the bilayered Ti（100 nm）/Al（100 nm） contact treated with 3 rain rapid thermal annealing （RTA） at 1000 ℃. The microstructure analyses examined by physical and chemical characterization techniques reveal an alloy-assisted ohmic contact formation mechanism, i.e., a high degree of alloying plays a decisive role in forming the interfacial ternary Ti3SiC2 dominating the ohmic behavior of the Ti/Al based contact. Furthermore, a globally covered Ti3 SiC2 layer with （0001）-oriented texture can be formed, regardless of the surface step bunching as well as its structural evolution during the metallization annealing.
文摘We report on the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the Pd/Ti/n-InP Schottky barrier diodes (SBDs) in the temperature range 160-400 K in steps of 40 K. The barrier heights and ideality factors of Schottky contact are found in the range 0.35 eV (I-V), 0.73 eV (C-V) at 160 K and 0.63 eV (I-V), 0.61 eV (C-V) at 400 K, respectively. It is observed that the zero-bias barrier height decreases and ideality factor n increase with a decrease in temperature, this behaviour is attributed to barrier inhomogeneities by assuming Gaussian distribution at the interface. The calculated value of series resistance (Rs) from the forward I-V characteristics is decreased with an increase in temperature. The homogeneous barrier height value of approximately 0.71 eV for the Pd/Ti Schottky diode has been obtained from the linear relationship between the temperature-dependent experimentally effective barrier heights and ideality factors. The zero-bias barrier height ( ) versus 1/2kT plot has been drawn to obtain evidence of a Gaussian distribution of the barrier heights and values of = 0.80 eV and = 114 mV for the mean barrier height and standard deviation have been obtained from the plot, respectively. The modified Richardson ln(I0/T2)- ( ) versus 1000/T plot has a good linearity over the investigated temperature range and gives the mean barrier height ( ) and Richardson constant (A*) values as 0.796 eV and 6.16 Acm-2K-2 respectively. The discrepancy between Schottky barrier heights obtained from I-V and C-V measurements is also interpreted.
文摘Vertical rigidity of the space self adaptive 530 high rigidity mill is calculated by applying the boundary element method (BEM) of three dimension elastic contact problem,which can update the existed deforming separation calculating theory and corresponding methods of material mechanics,elastic mechanics and finite element method.The method has less hypotheses and stronger synthesis in contact type calculating model.The advantages of the method are high calculating rate,high calculating accuracy,etc..
文摘Let C be a closed convex weakly Cauchy subset of a normed space X. Then we define a new {a,b,c} type nonexpansive and {a,b,c} type contraction mapping T from C into C. These types of mappings will be denoted respectively by {a,b,c}-ntype and {a,b,c}-ctype. We proved the following： 1. If T is {a,b,c}-ntype mapping, then inf{ ｜｜ T（x）-x｜｜ ：x C C} =0, accordingly T has a unique fixed point. Moreover, any sequence {Xn}n∈NN in C with limn→∞｜｜T（xn） - Xn｜｜ = 0 has a subsequence strongly convergent to the unique fixed point of T. 2. If T is {a,b,c}-ctype mapping, then T has a unique fixed point. Moreover, for any x∈C the sequence of iterates {Tn （x）}n∈N has subsequence strongly convergent to the unique fixed point of T. This paper extends and generalizes some of the results given in [2,4, 7] and [13].
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61474110,61377020,61376089,61223005,and 61176126)the National Science Fund for Distinguished Young Scholars of China(Grant No.60925017)+1 种基金One Hundred Person Project of the Chinese Academy of Sciencesthe Basic Research Project of Jiangsu Province,China(Grant No.BK20130362)
文摘The influence of a deep-level-defect（DLD） band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN（p^＋＋-GaN） contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I–V measurement shows that the variable-range hopping（VRH） transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p^＋＋-GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p^＋＋-GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97×10^-4Ω·cm^2 is achieved.
文摘It is well documented that dietary restriction can prevent many different diseases and extend the life spans of different rodent species. In the previous study, we reported that intermittent fasting (IF) as well as moderate dietary restriction ameliorated the allergic dermatitis in ICR mice. In the present study, we demonstrated the ameliorative effects of IF on allergic dermatitis in NC/Nga mice, a strain known as a model for atopic dermatitis. Interestingly, the total number of CD4+CD8+ double positive thymocyte in mice after IF significantly decreased in comparison to that in mice fed ad libitum. Although it was reported that an immunosuppressive compound inhibited the contact allergic response by inducing the CD4+CD25+ regulatory T-cells, IF did not affect regulatory T cells in the present study. These results suggested that CD4+CD8+ double positive thymocytes play an important role in the regulation of allergy by IF in NC/Nga mice.
文摘We report on the effect of annealing temperature on electrical, interfacial reactions and surface morphological properties of Ni/Cu Schottky contacts on n-type InP. The extracted barrier height of as-deposited Ni/Cu Schottky contact is 0.59 eV (I-V) respectively. The high-quality Schottky contact with barrier height and ideality factor of 0.65 eV (I-V) and 1.15 respectively, can be obtained after annealing at 300℃ for 1 min in a nitrogen atmosphere. However, annealing at 400℃, results the decrease in the barrier height to 0.54 eV (I-V). From the above observations, it is observed that Ni/Cu Schottky contact exhibited excellent electrical properties after annealing at 300℃. Hence, the optimum annealing temperature for the Ni/Cu Schottky contact is 300℃. Furthermore, Cheung’s functions is used to extract the diode parameters including ideality factor, barrier height and series resistance. According to the XRD analysis, the formation of the indium phases at the Ni/Cu/n-InP interface could be the reason for the increase in the barrier height at annealing temperature 300℃. Further, the degradation of the barrier heights after annealing at 400℃ may be due to the formation of phosphide phases at the Ni/Cu/n-InP interface. Scanning electron microscopy (SEM) results show that the overall surface morphology of the Ni/Cu Schottky contact is reasonably smooth.
