A novel programmable gain amplifier（ PGA） based on a signal-summing topology is proposed. Different from conventional signal-summing variable gain amplifiers（ VGA）,a binary-weighted switching technique is employed...A novel programmable gain amplifier（ PGA） based on a signal-summing topology is proposed. Different from conventional signal-summing variable gain amplifiers（ VGA）,a binary-weighted switching technique is employed to vary the current-steering transistors＇ aspect ratio to change their transconductance, and hence, an accurate gain step size of 6dB is achieved. The constant-g_m biasing technique and the matching of the transistors and resistors ensures that the gain of the proposed topology is independent of the variation of process, voltage and temperature（ PVT）. P-well NMOS（ Nmetal oxide semiconductor） transistors are utilized to eliminate the influence of back-gate effect which will induce gain error.The source-degeneration technique ensures good linearity performance at a low gain. The proposed PGA is fabricated in a0.18 μm CMOS（ complementary metal oxide semiconductor）process. The measurement results show a variable gain ranging from 0 to24 dB with a step size of 6 dB and a maximum gain error of 0. 3dB. A constant 3dB bandwidth of 210 MHz is achieved at different gain settings. The measured output 3rd intercept point（OIP3） and minimum noise figure（ NF） are20. 9 dBm and 11.1 dB, respectively. The whole PGA has a compact layout of 0.068 mm^2. The total power consumption is4. 8 mW under a 1. 8 V supply voltage.展开更多
Experimental investigation was carried out in an elliptical based stirred tank with a diameter of 0.48 m to explore the power demand and mixing performance of coaxial mixers.Syrup and CMC solution(sodium carboxy methy...Experimental investigation was carried out in an elliptical based stirred tank with a diameter of 0.48 m to explore the power demand and mixing performance of coaxial mixers.Syrup and CMC solution(sodium carboxy methyl cellulose)were used as the Newtonian and non-Newtonian fluids,respectively.Four different coaxial mixers were combined with either CBY or Pfaudler impeller as the inner one,and anchor or helical ribbon(HR)as the outer one.Results show that Pfaudler-HR is the optimized combination among four coaxial mixers in this work,which provides the shortest mixing time given the same power consumption.Compared with the syrup solution,the increase of power input can make the mixing time decreasing more obviously in the CMC solution.The quantitative correlations for both syrup and CMC solutions were established to calculate the power draw and the mixing time of four coaxial mixers.展开更多
The B-meson decay constant fB is an important component for studying the B-meson decays, which can be studied through QCD sum rules. We make a detailed discussion on f B from two sum rules up to next-to- leading order...The B-meson decay constant fB is an important component for studying the B-meson decays, which can be studied through QCD sum rules. We make a detailed discussion on f B from two sum rules up to next-to- leading order, i.e. sum rules I and II, which are derived from the conventional correlator and the correlator with chiral currents respectively. It is found that these two sum rules are consistent with each other. The sum rules H involves less non-perturbative condensates as that of sum rules I, and in principle, it can be more accurate if we know the dimensionfour gluon condensate well. It is found that fB decreases with the increment of mb, and to compare with the Belle experimental data on fB, both sum rules I and H prefer smaller pole b-quark mass, mb= 4.68 ± 0.07 GeV. By varying all the input parameters within their reasonable regions and by adding all the uncertainties in quadrature, we obtain fB=172-25^＋23 MeV for sum rules I and fB =214-34^26 MeV for sum rules П.展开更多
A numerical model of two-dimensional soil water movement under surface drip irrigation condition was developed. The physical process of soil water movement is described by 2D Richards equation,and the upper boundary c...A numerical model of two-dimensional soil water movement under surface drip irrigation condition was developed. The physical process of soil water movement is described by 2D Richards equation,and the upper boundary condition is depicted by the improved moving ponded area boundary. The partial differential equation(PDE) is transformed into ordinary differential equations(ODEs) through spatial semi-discretization and numerically solved by an ordinary differential equation solver(CVODE) . The numerical and field experiments indicate the good performance of the model in terms of accuracy and efficiency. The model provides a useful tool for long-term simulation of soil water movement under surface drip irrigation. Also,the model can serve as a general 2D Richards equation solver for variably saturated soil water movement,which is named as TIVS model(Tsinghua Integrated Variably Saturated soil water movement model).展开更多
基金The National Natural Science Foundation of China(No.61306069)
文摘A novel programmable gain amplifier（ PGA） based on a signal-summing topology is proposed. Different from conventional signal-summing variable gain amplifiers（ VGA）,a binary-weighted switching technique is employed to vary the current-steering transistors＇ aspect ratio to change their transconductance, and hence, an accurate gain step size of 6dB is achieved. The constant-g_m biasing technique and the matching of the transistors and resistors ensures that the gain of the proposed topology is independent of the variation of process, voltage and temperature（ PVT）. P-well NMOS（ Nmetal oxide semiconductor） transistors are utilized to eliminate the influence of back-gate effect which will induce gain error.The source-degeneration technique ensures good linearity performance at a low gain. The proposed PGA is fabricated in a0.18 μm CMOS（ complementary metal oxide semiconductor）process. The measurement results show a variable gain ranging from 0 to24 dB with a step size of 6 dB and a maximum gain error of 0. 3dB. A constant 3dB bandwidth of 210 MHz is achieved at different gain settings. The measured output 3rd intercept point（OIP3） and minimum noise figure（ NF） are20. 9 dBm and 11.1 dB, respectively. The whole PGA has a compact layout of 0.068 mm^2. The total power consumption is4. 8 mW under a 1. 8 V supply voltage.
文摘Experimental investigation was carried out in an elliptical based stirred tank with a diameter of 0.48 m to explore the power demand and mixing performance of coaxial mixers.Syrup and CMC solution(sodium carboxy methyl cellulose)were used as the Newtonian and non-Newtonian fluids,respectively.Four different coaxial mixers were combined with either CBY or Pfaudler impeller as the inner one,and anchor or helical ribbon(HR)as the outer one.Results show that Pfaudler-HR is the optimized combination among four coaxial mixers in this work,which provides the shortest mixing time given the same power consumption.Compared with the syrup solution,the increase of power input can make the mixing time decreasing more obviously in the CMC solution.The quantitative correlations for both syrup and CMC solutions were established to calculate the power draw and the mixing time of four coaxial mixers.
基金Supported by Natural Science Foundation Project of CQ CSTC under Grant No.2008BB0298by Natural Science Foundation of China under Grant Nos.10805082 and 11075225by the Fundamental Research Funds for the Central Universities under Grant No.CDJZR101000616
文摘The B-meson decay constant fB is an important component for studying the B-meson decays, which can be studied through QCD sum rules. We make a detailed discussion on f B from two sum rules up to next-to- leading order, i.e. sum rules I and II, which are derived from the conventional correlator and the correlator with chiral currents respectively. It is found that these two sum rules are consistent with each other. The sum rules H involves less non-perturbative condensates as that of sum rules I, and in principle, it can be more accurate if we know the dimensionfour gluon condensate well. It is found that fB decreases with the increment of mb, and to compare with the Belle experimental data on fB, both sum rules I and H prefer smaller pole b-quark mass, mb= 4.68 ± 0.07 GeV. By varying all the input parameters within their reasonable regions and by adding all the uncertainties in quadrature, we obtain fB=172-25^＋23 MeV for sum rules I and fB =214-34^26 MeV for sum rules П.
基金supported by the "Eleventh Five-year Plan" Project (Grant No.2007BAD38B01)
文摘A numerical model of two-dimensional soil water movement under surface drip irrigation condition was developed. The physical process of soil water movement is described by 2D Richards equation,and the upper boundary condition is depicted by the improved moving ponded area boundary. The partial differential equation(PDE) is transformed into ordinary differential equations(ODEs) through spatial semi-discretization and numerically solved by an ordinary differential equation solver(CVODE) . The numerical and field experiments indicate the good performance of the model in terms of accuracy and efficiency. The model provides a useful tool for long-term simulation of soil water movement under surface drip irrigation. Also,the model can serve as a general 2D Richards equation solver for variably saturated soil water movement,which is named as TIVS model(Tsinghua Integrated Variably Saturated soil water movement model).
