Patients living with chronic kidney disease (CKD) are at high risk of cardiovascular events. Our aim in this study was to assess the cut-off value for lipoprotein (a) (Lp(a)) in CKD patients with a history of cardiova...Patients living with chronic kidney disease (CKD) are at high risk of cardiovascular events. Our aim in this study was to assess the cut-off value for lipoprotein (a) (Lp(a)) in CKD patients with a history of cardiovascular disease (CVD). This was a cross-sectional study. Variables including age, sex, history of CVD, body mass index and CKD stage, were collected during CKD patient’s first admission in the nephrology dialysis department. Blood samples were collected for quantitative determination of Lp(a) by immunoturbidimetric method. They were divided into two groups: CKD patients without history of CVD and CKD patients with history of CVD. Fisher’s exact test was used to assess associations with a significance level of 0.05%. Area under the curve (AUC) and new cut-off value for Lp(a) were identified by drawing Receiver Operating Characteristic (ROC) curve. A total of seventy CKD patients with median age of 43 years [minimum-maximum = 15 - 78 years] were included. Patients with history of CVD were 65.71% (46/70). New Lp(a) cut-off point in CKD patients with history of CVD was 66.50 nmol/L [sensitivity, 87.00%;specificity, 58.30%;AUC = 0.727;p = 0.000]. ROC curve demonstrated good performance of Lp(a) to screen CKD patients with history of CVD. Further research is needed to determine an LPA gene polymorphism’s contribution to increasing risk for CVD at each kidney disease stage.展开更多
The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden laye...The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.展开更多
This study examines a Kuroshio main path(KMP) cut-off event east of Taiwan Island occurred in fall-winter2013–2014 and its impacts on the South China Sea(SCS) by analyzing satellite altimetry and mooring observations...This study examines a Kuroshio main path(KMP) cut-off event east of Taiwan Island occurred in fall-winter2013–2014 and its impacts on the South China Sea(SCS) by analyzing satellite altimetry and mooring observations. Satellite altimeter sea level anomaly(SLA) images reveal a complete process that a huge cyclonic eddy(CE) from the Pacific collided with the Kuroshio and the western boundary from 15 October 2013 to 15 January 2014. Mooring observations evidenced that the Kuroshio upper ocean volume transport was cut off more than 82% from 17×106 m^3/s in September to 3×106 m^3/s in November 2013. The KMP cut-off event caused the Kuroshio branching and intruding into the SCS and strengthened the eddy kinetic energy in the northern SCS west of the Luzon Strait. Using the total momentum as a dynamic criterion to determine the role of eddy collision with the Kuroshio reasonably explains the KMP cut-off event.展开更多
The aim of this study was to evaluate the effects of low-dose tibolone therapy on ovarian area, uterine volume and endometrial thickness, and define the cut-off value of endometrial thickness for curettage during uter...The aim of this study was to evaluate the effects of low-dose tibolone therapy on ovarian area, uterine volume and endometrial thickness, and define the cut-off value of endometrial thickness for curettage during uterine bleeding. We followed 619 postmenopausal women, aged 40-60 years, for two years. There were 301 subjects in the low-dose tibolone treatment group and 318 subjects in the control group. The ovarian area, uterine volume and endometrial thickness in all participants were measured by transvaginal ultrasound prior to, one and two years post enrollment, respectively. Endometrial specimens were collected from all subjects with abnormal uterine bleeding during the follow-up period. We found that the uterine volume in the treatment group was greater than that in the control group, and the difference was significant (P〈0.05), but there were no significant differences in ovarian area and endometrial thickness between the two groups (P〉0.05). When the cut-off value for endometrial thickness was 7.35 ram, the sensitivity and specificity were 100% and 79.07%, respectively, and 85.71% and 93.02% when 7.55 mm was set as the cut-offduring tibolone therapy. The results indicate that low-dose tibolone therapy may postpone uterine atrophy and the cut-off value of endometrial thickness may be appropriately adjusted for curettage.展开更多
With the rapid increase of water contamination,membrane separation technology and their corresponding molecular weight cut-off(MWCO) evaluation method become more necessary.In this study,Panax notoginseng saponins was...With the rapid increase of water contamination,membrane separation technology and their corresponding molecular weight cut-off(MWCO) evaluation method become more necessary.In this study,Panax notoginseng saponins was used as a new standard marker to determinate ultrafiltration(UF) membrane MWCOs,series of Millipore membranes were selected as control group to analyze and calculate the relationship between retention rate and MWCOs with exponential or logarithmic equation.A new and convenient method was provided for determining the membrane MWCO by modeling analysis retention rate with MWCOs,and the regression coefficients >0.990.The feasibility and practicability of established method was verified by different manufactures' membrane and dextrans.In the detection progress,as the main ingredient of Panax notoginseng saponins,Notoginsenoside R_1,Ginsenoside Rg_1,Ginsenoside Rb_1 and Ginsenoside Rd with different surface activity,the MWCO range of UF membranes can be divided into two zones mainly due to the retention rate difference among Notoginsenoside R_1,Ginsenoside Rg_1,Ginsenoside Rb_1 and Ginsenoside Rd.Zone 1,1000-10000;and Zone II,10000-100000.Thus,the new method would be helpful to improve the applicability of UF membrane in separation technology.展开更多
Determining the hydrometallurgical cut-off grades specifies the destination of low grade materials and this is subjected to more benefits in mining. Copper production rate is considered as one of the fundamental issue...Determining the hydrometallurgical cut-off grades specifies the destination of low grade materials and this is subjected to more benefits in mining. Copper production rate is considered as one of the fundamental issues in hydrometallurgical cut-off grades determination. Slags are remarked as one of the main sources of copper. It is not only regarded as a waste but also identified as another resource extracting base metals. Slags are characterized by copper high grade. Thus, slag copper recovery can be led to different cut-off grades and net present value(NPV). The current research scrutinizes the effect of slag recovery by both flotation and hydrometallurgical methods on the hydrometallurgical cut-off grades. For this purpose, the optimum cut-off grade algorithms of hydrometallurgical methods are developed by considering associated environmental parameters, incomes and also the costs. Then, their optimum amounts are calculated with NPV maximization as an objective function. The results indicate that considering slag copper recovery in the hydrometallurgical cut-off grade algorithms reduces the environmental costs caused by slag dumping and leads to more NPV by 9%.展开更多
In situ measurements of the vertical structure of ozone were made in Changchun (43.53°N, 125.13°E), China, by the Institute of Atmosphere Physics, in the summers of 2010-13. Analysis of the 89 validated oz...In situ measurements of the vertical structure of ozone were made in Changchun (43.53°N, 125.13°E), China, by the Institute of Atmosphere Physics, in the summers of 2010-13. Analysis of the 89 validated ozone profiles shows the vari- ation of ozone concentration in the upper troposphere and lower stratosphere (UTLS) caused by cut-off lows (COLs) over Changchun. During the COL events, an increase of the ozone concentration and a lower height of the tropopause are observed. Backward simulations with a trajectory model show that the ozone-rich airmass brought by the COL is from Siberia. A case study proves that stratosphere-troposphere exchange (STE) occurs in the COL. The ozone-rich air mass transported from the stratosphere to the troposphere first becomes unstable, then loses its high ozone concentration. This process usually happens during the decay stage of COLs. In order to understand the influence of COLs on the ozone in the UTLS, statistical analysis of the ozone profiles within COLs, and other profiles, are employed. The results indicate that the ozone concentrations of the in-COL profiles are significantly higher than those of the other profiles between ±4 km around the tropopause. The COLs induce an increase in UTLS column ozone by 32% on average. Meanwhile, the COLs depress the lapse-rate tropopause (LRT)/dynamical tropopause height by 1.4/1.7 km and cause the atmosphere above the tropopause to be less stable. The influence of COLs is durable because the increased ozone concentration lasts at least one day after the COL has passed over Changchun. Furthermore, the relative coefficient between LRT height and lower stratosphere (LS) column ozone is -0.62, which implies a positive correlation between COL strength and LS ozone concentration.展开更多
As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor (HBT). In this paper, this tradeoff is alleviated by collec...As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor (HBT). In this paper, this tradeoff is alleviated by collector doping engineering in the SiGe HBT by utilizing a novel composite of P+ and N- doping layers inside the collector-base (CB) space-charge region (SCR). Compared with the single N-type collector, the introduction of the thin P+ layers provides a reverse electric field weakening the electric field near the CB metallurgical junction without changing the field direction, and the thin N layer further effectively lowers the electric field near the CB metallurgical junction. As a result, the electron temperature near the CB metallurgical junction is lowered, consequently suppressing the impact ionization, thus BVcEO is improved with a slight degradation in fT. The results show that the product of fTXBVcEo is improved from 309.51 GHz.V to 326.35 GHz.V.展开更多
The photoassociation dynamics of ultracold lithium atoms controlled by a cut-off pulse has been investigated theoretically by solving numerically the time-dependent Schr6dinger equation using the mapped Fourier grid m...The photoassociation dynamics of ultracold lithium atoms controlled by a cut-off pulse has been investigated theoretically by solving numerically the time-dependent Schr6dinger equation using the mapped Fourier grid method. The frequency components of the laser pulse close to the atomic resonance are partly cut off. Compared with the typical Gauss-type pulses, the cut-off pulse is helpful to suppress efficiently the weakly bound states and prepare the associated molecules in the lower vibrational states. Especially, the dependence of photoassociation probability on the cut-off position of the laser pulse is explored.展开更多
In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an...In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm<sup>-1</sup> was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm<sup>-1</sup> cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm<sup>-1</sup> cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm<sup>-1</sup> cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.展开更多
本文使用三维非绝热朗格朗日轨迹模式OFFLINE3,对春末夏初东亚地区的切断低压所主导的双向平流层-对流层交换(STE)进行定量计算。通过对10个东亚地区切断低压的识别、计算、分析,发现切断低压附近发生平流层向对流层质量通量(STT)与对...本文使用三维非绝热朗格朗日轨迹模式OFFLINE3,对春末夏初东亚地区的切断低压所主导的双向平流层-对流层交换(STE)进行定量计算。通过对10个东亚地区切断低压的识别、计算、分析,发现切断低压附近发生平流层向对流层质量通量(STT)与对流层向平流层质量通量(TST)量级相当,但是分布范围不同:STT出现在低压中心西南部,最大通量位置出现在低压中心东南,TST最大值出现在槽前,并且从低压中心向外STT与TST交替分布。从本文所取的切断低压个例而言,切断低压产生的STT质量通量量级为10-4 kg m-2 s-1,促成的STE的净输送方向为从平流层向对流层,量级为10-4 kg m-2 s-1,比全球平均STE质量通量大1–2个量级。展开更多
The spin cut-off parameter of the nuclear level density and effective moment of inertia for a large number of nuclei have been determined from analysis of the experimental data on S-wave neutron resonances and spins o...The spin cut-off parameter of the nuclear level density and effective moment of inertia for a large number of nuclei have been determined from analysis of the experimental data on S-wave neutron resonances and spins of lowlying levels. Contrary to claims made before, it is shown the spin cut-off parameter differs considerably from their corresponding rigid body values, and the energy dependence of the effective moment of inertia confirms the interacting fermion model prediction.展开更多
We calculate the Casimir force at a finite cut-off Λ by summing the forces induced by the all fluctuationmodes.We show that the Casimir force is independent of the cut-off function in the limit LΛ→∞.There is a cor...We calculate the Casimir force at a finite cut-off Λ by summing the forces induced by the all fluctuationmodes.We show that the Casimir force is independent of the cut-off function in the limit LΛ→∞.There is a correctionin the order of(LΛ)^(-2),when LΛ is finite and large.This correction becomes remarkable when L is comparable withthe microscopic length scale Λ^(-1).It has been demonstrated that the Casimir force at a finite cut-off should be definedby summing forces of all fluctuation modes,instead of the derivative of Casimir energy with respect to L where anadditional derivative of the cut-off function has been introduced.展开更多
In order to quickly explore the quality of cut-off wall in dams, a new method of high-density seismic image was adopted and estimated by model and in-situ wall tests.The vibration exciter was employed and several para...In order to quickly explore the quality of cut-off wall in dams, a new method of high-density seismic image was adopted and estimated by model and in-situ wall tests.The vibration exciter was employed and several parameters such as hypocentral distance, length of signal record and sampling space in signal collection were determined, which are 8 m, 0.25 ms and 128 ms respectively. Through time and frequency field signal analyses, it is concluded that, the smaller arrival times of reflected longitudinal and surface waves, and the higher their main frequencies, the higher the strength of the wall, vice versa. Accordingly the construction quality of the wall can be evaluated quickly by high-density seismic image.展开更多
文摘Patients living with chronic kidney disease (CKD) are at high risk of cardiovascular events. Our aim in this study was to assess the cut-off value for lipoprotein (a) (Lp(a)) in CKD patients with a history of cardiovascular disease (CVD). This was a cross-sectional study. Variables including age, sex, history of CVD, body mass index and CKD stage, were collected during CKD patient’s first admission in the nephrology dialysis department. Blood samples were collected for quantitative determination of Lp(a) by immunoturbidimetric method. They were divided into two groups: CKD patients without history of CVD and CKD patients with history of CVD. Fisher’s exact test was used to assess associations with a significance level of 0.05%. Area under the curve (AUC) and new cut-off value for Lp(a) were identified by drawing Receiver Operating Characteristic (ROC) curve. A total of seventy CKD patients with median age of 43 years [minimum-maximum = 15 - 78 years] were included. Patients with history of CVD were 65.71% (46/70). New Lp(a) cut-off point in CKD patients with history of CVD was 66.50 nmol/L [sensitivity, 87.00%;specificity, 58.30%;AUC = 0.727;p = 0.000]. ROC curve demonstrated good performance of Lp(a) to screen CKD patients with history of CVD. Further research is needed to determine an LPA gene polymorphism’s contribution to increasing risk for CVD at each kidney disease stage.
基金the National Natural Science Foundation of China (Grant No.51379066)the Fundamental Research Funds for the Central Universities (Grant No.2016B03514)+1 种基金the National Key Technology Support Program (Grant No.2015BAB07B05)the Key Laboratory of Earth-Rock Dam Failure Mechanism and Safety Control Techniques (Grant No.YK913007).
文摘The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.
基金The National Natural Science Foundation of China under contract No.41776034the Ministry of Science and Technology of Taiwan under contract Nos MOST 105-2611-M-019-001 and MOST 106-2611-M-019-015+1 种基金the GASI Project under contract Nos GASI-IPOVAI-01-02 and GASI-02-SCS-YGST2-02the Foundation of Guangdong Province for Outstanding Young Teachers in University under contract No.YQ201588
文摘This study examines a Kuroshio main path(KMP) cut-off event east of Taiwan Island occurred in fall-winter2013–2014 and its impacts on the South China Sea(SCS) by analyzing satellite altimetry and mooring observations. Satellite altimeter sea level anomaly(SLA) images reveal a complete process that a huge cyclonic eddy(CE) from the Pacific collided with the Kuroshio and the western boundary from 15 October 2013 to 15 January 2014. Mooring observations evidenced that the Kuroshio upper ocean volume transport was cut off more than 82% from 17×106 m^3/s in September to 3×106 m^3/s in November 2013. The KMP cut-off event caused the Kuroshio branching and intruding into the SCS and strengthened the eddy kinetic energy in the northern SCS west of the Luzon Strait. Using the total momentum as a dynamic criterion to determine the role of eddy collision with the Kuroshio reasonably explains the KMP cut-off event.
基金supported by the Sci-tech Research Development Program of Shaanxi Province (No.2015SF015)
文摘The aim of this study was to evaluate the effects of low-dose tibolone therapy on ovarian area, uterine volume and endometrial thickness, and define the cut-off value of endometrial thickness for curettage during uterine bleeding. We followed 619 postmenopausal women, aged 40-60 years, for two years. There were 301 subjects in the low-dose tibolone treatment group and 318 subjects in the control group. The ovarian area, uterine volume and endometrial thickness in all participants were measured by transvaginal ultrasound prior to, one and two years post enrollment, respectively. Endometrial specimens were collected from all subjects with abnormal uterine bleeding during the follow-up period. We found that the uterine volume in the treatment group was greater than that in the control group, and the difference was significant (P〈0.05), but there were no significant differences in ovarian area and endometrial thickness between the two groups (P〉0.05). When the cut-off value for endometrial thickness was 7.35 ram, the sensitivity and specificity were 100% and 79.07%, respectively, and 85.71% and 93.02% when 7.55 mm was set as the cut-offduring tibolone therapy. The results indicate that low-dose tibolone therapy may postpone uterine atrophy and the cut-off value of endometrial thickness may be appropriately adjusted for curettage.
基金Supported by the National Natural Science Foundation of China(No.81503258,No.81373980)Youth Natural Science Foundation of Jiangsu Province(No.BK20151005)Science and Technology Project of Jiangsu Traditional Chinese Medicine Administration(No.YB2015009)
文摘With the rapid increase of water contamination,membrane separation technology and their corresponding molecular weight cut-off(MWCO) evaluation method become more necessary.In this study,Panax notoginseng saponins was used as a new standard marker to determinate ultrafiltration(UF) membrane MWCOs,series of Millipore membranes were selected as control group to analyze and calculate the relationship between retention rate and MWCOs with exponential or logarithmic equation.A new and convenient method was provided for determining the membrane MWCO by modeling analysis retention rate with MWCOs,and the regression coefficients >0.990.The feasibility and practicability of established method was verified by different manufactures' membrane and dextrans.In the detection progress,as the main ingredient of Panax notoginseng saponins,Notoginsenoside R_1,Ginsenoside Rg_1,Ginsenoside Rb_1 and Ginsenoside Rd with different surface activity,the MWCO range of UF membranes can be divided into two zones mainly due to the retention rate difference among Notoginsenoside R_1,Ginsenoside Rg_1,Ginsenoside Rb_1 and Ginsenoside Rd.Zone 1,1000-10000;and Zone II,10000-100000.Thus,the new method would be helpful to improve the applicability of UF membrane in separation technology.
文摘Determining the hydrometallurgical cut-off grades specifies the destination of low grade materials and this is subjected to more benefits in mining. Copper production rate is considered as one of the fundamental issues in hydrometallurgical cut-off grades determination. Slags are remarked as one of the main sources of copper. It is not only regarded as a waste but also identified as another resource extracting base metals. Slags are characterized by copper high grade. Thus, slag copper recovery can be led to different cut-off grades and net present value(NPV). The current research scrutinizes the effect of slag recovery by both flotation and hydrometallurgical methods on the hydrometallurgical cut-off grades. For this purpose, the optimum cut-off grade algorithms of hydrometallurgical methods are developed by considering associated environmental parameters, incomes and also the costs. Then, their optimum amounts are calculated with NPV maximization as an objective function. The results indicate that considering slag copper recovery in the hydrometallurgical cut-off grade algorithms reduces the environmental costs caused by slag dumping and leads to more NPV by 9%.
基金jointly supported by the National Basic Research Program of China (Grant No.2010CB428602)the National Natural Science Foundation of China (Grant Nos.41275046 and 41025017)
文摘In situ measurements of the vertical structure of ozone were made in Changchun (43.53°N, 125.13°E), China, by the Institute of Atmosphere Physics, in the summers of 2010-13. Analysis of the 89 validated ozone profiles shows the vari- ation of ozone concentration in the upper troposphere and lower stratosphere (UTLS) caused by cut-off lows (COLs) over Changchun. During the COL events, an increase of the ozone concentration and a lower height of the tropopause are observed. Backward simulations with a trajectory model show that the ozone-rich airmass brought by the COL is from Siberia. A case study proves that stratosphere-troposphere exchange (STE) occurs in the COL. The ozone-rich air mass transported from the stratosphere to the troposphere first becomes unstable, then loses its high ozone concentration. This process usually happens during the decay stage of COLs. In order to understand the influence of COLs on the ozone in the UTLS, statistical analysis of the ozone profiles within COLs, and other profiles, are employed. The results indicate that the ozone concentrations of the in-COL profiles are significantly higher than those of the other profiles between ±4 km around the tropopause. The COLs induce an increase in UTLS column ozone by 32% on average. Meanwhile, the COLs depress the lapse-rate tropopause (LRT)/dynamical tropopause height by 1.4/1.7 km and cause the atmosphere above the tropopause to be less stable. The influence of COLs is durable because the increased ozone concentration lasts at least one day after the COL has passed over Changchun. Furthermore, the relative coefficient between LRT height and lower stratosphere (LS) column ozone is -0.62, which implies a positive correlation between COL strength and LS ozone concentration.
基金supported by the National Natural Science Foundation of China(Grant Nos.60776051,61006059,and 61006044)the Beijing Municipal Natural Science Foundation,China(Grant Nos.4142007,4143059,4082007,and 4122014)the Beijing Municipal Education Committee,China(Grant Nos.KM200710005015 and KM200910005001)
文摘As is well known, there exists a tradeoff between the breakdown voltage BVcEO and the cut-off frequency fT for a standard heterojunction bipolar transistor (HBT). In this paper, this tradeoff is alleviated by collector doping engineering in the SiGe HBT by utilizing a novel composite of P+ and N- doping layers inside the collector-base (CB) space-charge region (SCR). Compared with the single N-type collector, the introduction of the thin P+ layers provides a reverse electric field weakening the electric field near the CB metallurgical junction without changing the field direction, and the thin N layer further effectively lowers the electric field near the CB metallurgical junction. As a result, the electron temperature near the CB metallurgical junction is lowered, consequently suppressing the impact ionization, thus BVcEO is improved with a slight degradation in fT. The results show that the product of fTXBVcEo is improved from 309.51 GHz.V to 326.35 GHz.V.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10974024)the SRFDP, China (Grant No. 20090041110025)
文摘The photoassociation dynamics of ultracold lithium atoms controlled by a cut-off pulse has been investigated theoretically by solving numerically the time-dependent Schr6dinger equation using the mapped Fourier grid method. The frequency components of the laser pulse close to the atomic resonance are partly cut off. Compared with the typical Gauss-type pulses, the cut-off pulse is helpful to suppress efficiently the weakly bound states and prepare the associated molecules in the lower vibrational states. Especially, the dependence of photoassociation probability on the cut-off position of the laser pulse is explored.
文摘In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm<sup>-1</sup> was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm<sup>-1</sup> cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm<sup>-1</sup> cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm<sup>-1</sup> cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.
基金supported by the Special Fund for Strategic Pilot Technology,Chinese Academy of Sciences[grant number XDA05040300]
文摘本文使用三维非绝热朗格朗日轨迹模式OFFLINE3,对春末夏初东亚地区的切断低压所主导的双向平流层-对流层交换(STE)进行定量计算。通过对10个东亚地区切断低压的识别、计算、分析,发现切断低压附近发生平流层向对流层质量通量(STT)与对流层向平流层质量通量(TST)量级相当,但是分布范围不同:STT出现在低压中心西南部,最大通量位置出现在低压中心东南,TST最大值出现在槽前,并且从低压中心向外STT与TST交替分布。从本文所取的切断低压个例而言,切断低压产生的STT质量通量量级为10-4 kg m-2 s-1,促成的STE的净输送方向为从平流层向对流层,量级为10-4 kg m-2 s-1,比全球平均STE质量通量大1–2个量级。
文摘The spin cut-off parameter of the nuclear level density and effective moment of inertia for a large number of nuclei have been determined from analysis of the experimental data on S-wave neutron resonances and spins of lowlying levels. Contrary to claims made before, it is shown the spin cut-off parameter differs considerably from their corresponding rigid body values, and the energy dependence of the effective moment of inertia confirms the interacting fermion model prediction.
基金National Natural Science Foundation of China under Grant No.10325418
文摘We calculate the Casimir force at a finite cut-off Λ by summing the forces induced by the all fluctuationmodes.We show that the Casimir force is independent of the cut-off function in the limit LΛ→∞.There is a correctionin the order of(LΛ)^(-2),when LΛ is finite and large.This correction becomes remarkable when L is comparable withthe microscopic length scale Λ^(-1).It has been demonstrated that the Casimir force at a finite cut-off should be definedby summing forces of all fluctuation modes,instead of the derivative of Casimir energy with respect to L where anadditional derivative of the cut-off function has been introduced.
文摘In order to quickly explore the quality of cut-off wall in dams, a new method of high-density seismic image was adopted and estimated by model and in-situ wall tests.The vibration exciter was employed and several parameters such as hypocentral distance, length of signal record and sampling space in signal collection were determined, which are 8 m, 0.25 ms and 128 ms respectively. Through time and frequency field signal analyses, it is concluded that, the smaller arrival times of reflected longitudinal and surface waves, and the higher their main frequencies, the higher the strength of the wall, vice versa. Accordingly the construction quality of the wall can be evaluated quickly by high-density seismic image.