A 10-bit 50-MS/s sample-and-hold circuit with low distortion sampling switches

A fully-differential switched-capacitor sample-and-hold (S/H) circuit used in a 10-bit 50-MS/s pipeline analog-to-digital converter (ADC) was designed and fabricated using a 0.35-μm CMOS process. Capacitor fliparound architecture was used in the S/H circuit to lower the power consumption. In addition, a gain-boosted operational transconductance amplifier (OTA) was designed with a DC gain of 94 dB and a unit gain bandwidth of 460 MHz at a phase margin of 63 degree, which matches the S/H circuit. A novel double-side bootstrapped switch was used, improving the precision of the whole circuit. The measured results have shown that the S/H circuit reaches a spurious free dynamic range (SFDR) of 67 dB and a signal-to-noise ratio (SNR) of 62.1 dB for a 2.5 MHz input signal with 50 MS/s sampling rate. The 0.12 mm~2 S/H circuit operates from a 3.3 V supply and consumes 13.6 mW.

A Monolithic Integrated Logic Circuit of Resonant Tunneling Diodes and a HEMT

A technology for the monolithic integration of resonant tunneling diodes (RTDs) and high electron mobility transistors (HEMTs) is developed. Molecular beam epitaxy is used to grow an RTD on a HEMT structure on GaAs substrate. The RTD has a room temperature peak-to-valley ratio of 5.2:1 with a peak current density of 22.5kA/cm~2. The HEMT has a 1μm gate length with a-1V threshold voltage. A logic circuit called a monostableto-bistable transition logic element (MOBILE) circuit is developed. The experimental result confirms that the fabricated logic circuit operates successfully with frequency operations of up to 2GHz.

Electro-mass multi odor sensor

For an olfactory sensor or electronic nose the task is not only to detect the object concentration, but also to recognize it. It is well known that all the elements can be identified by their charge to mass ratio e+/m. We tried to use this principle for molecular recognition. Two kinds of sensors are used simultaneously in testing. One is Quartz Crystal Microbalance (QCM) for detecting the change in mass, the other is Interdigital Electrode (IE) for detecting the change in conduction. In this paper the principle and the feasibility of this method are reported. The preliminary results on the recognition of alcohols are presented. The multisensor can be used as an instrument for research on material properties and kinetic process as well.

Electro-mass olfactory multi-sensor (EMMS)

For an olfactory sensor or electronic nose, the task is not only to detect the object concentration, but also to recognize it. It is well known that all the elements can be identified by their charge to mass ratio e(+)/m. We tried to imitate this principle for molecular recognition. Two kinds of sensors are used simultaneously in testing. One is quartz crystal microbalance (QCM) for detecting the change in mass, the other is interdigital electrode (IE) for detecting the change in conduction, as an electro-mass multi-sensor (EMMS). in this paper, the principle and the feasibility of this method are discussed. The preliminary results on the recognition of alcohol by EMMS coated with lipids are presented. Meanwhile, the multi-sensor can also be used as an instrument for research on some physico-chemistry problems. The change in conduction of coated membrane caused by one absorbed molecule is reported. It is found that when a QCM is coated with membrane, it still obeys the relationship Delta F (frequency change of QCM) = K Delta m (mass change of absorbed substance) and the proportional coefficient, K, depends not only on quartz properties but also on membrane characteristics as well. (C) 2000 Elsevier Science S.A. All rights reserved.

Observation of N-Shaped Negative Differential Resistance in GaAs-Based Modulation-Doped Field Effect Transistor with InAs Quantum Dots

N-shaped negative differential resistance (NDR) with a high peak-to-valley ratio (PVR) is observed in a GaAs-based modulation-doped field effect transistor (MODFET) with InAs quantum dots (QDs) in the barrier layer (QDFET) compared with a GaAs MODFET. The NDR is explained as the real-space transfer (RST) of high-mobility electrons in a channel into nearby barrier layers with low mobility, and the PVR is enhanced dramatically upon inserting the QD layer. It is also revealed that the QD layer traps holes and acts as a positively charged nano-floating gate after a brief optical illumination, while it acts as a negatively charged nano-floating gate and depletes the adjacent channel when charged by the electrons. The NDR suggests a promising application in memory or high-speed logic devices for the QDFET structure.

40 Gbits/s all-optical clock recovery for degraded signals using an amplified feedback laser

All-optical clock recovery for the return-to-zero modulation format is demonstrated experimentally at 40 Gbits/s by using an amplified feedback laser. A 40 GHz optical clock with a root-mean-square (rms) timing jitter of 130 fs and a carrier-to-noise ratio of 42 dB is obtained. Also, a 40 GHz optical clock with timing jitter of 137 fs is directly recovered from pseudo-non-return-to-zero signals degraded by polarization-mode dispersion (PMD). No preprocessing stage to enhance the clock tone is used. The rms timing jitter of the recovered clock is investigated for different values of input power and for varying amounts of waveform distortion due to PMD.

Improved digital processing method used for image motion measurement based on hybrid opto-digital joint transform correlator

Hybrid opto-digital joint transform correlator (HODJTC) is effective for image motion measurement, but it is different from the traditional joint transform correlator because it only has one optical transform and the joint power spectrum is directly input into a digital processing unit to compute the image shift. The local cross-correlation image can be directly obtained by adopting a local Fourier transform operator. After the pixel-level location of cross-correlation peak is initially obtained, the up-sampling technique is introduced to relocate the peak in even higher accuracy. With signal-to-noise ratio >= 20 dB, up-sampling factor k >= 10 and the maximum image shift <= 60 pixels, the root-mean-square error of motion measurement accuracy can be controlled below 0.05 pixels.

Extracting nanobelt mechanical properties from nanoindentation

A three-spring-in-series model is proposed for the nanobelt (NB) indentation test. Compared with the previous two-spring-in-series model, which considers the bending stiffness of atomic force microscope cantilever and the indenter/NB contact stiffness, this model adds a third spring of the NB/substrate contact stiffness. NB is highly flexural due to its large aspect ratio of length to thickness. The bending and lift-off of NB form a localized contact with substrate, which makes the Oliver-Pharr method [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)] and Sneddon method [I. N. Sneddon, Int. J. Eng. Sci. 3, 47 (1965)] inappropriate for NB indentation test. Because the NB/substrate deformation may have significant impact on the force-indentation depth data obtained in experiment, the two-spring-in-series model can lead to erroneous predictions on the NB mechanical properties. NB in indentation test can be susceptible to the adhesion influence because of its large surface area to volume ratio. NB/substrate contact and adhesion can have direct and significant impact on the interpretation of experimental data. Through the three-spring-in-series model, the influence of NB/substrate contact and adhesion is analyzed and methods of reducing such influence are also suggested. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432748]

U-transformation-finite element method in 3-dimensional analysis of orthotropic laminates

For an orthotropic laminate, an equivalent system with doubly cyclic periodicity is introduced. Then a 3-dimensional finite element model for the equivalent system is transformed into the unitary space, where the large finite element matrix equation is decoupled into some small matrix equations. Such a decoupling very efficiently reduces the computational effort. For an orthotropic laminate with four clamped edges, no exact elasticity solution is available, and the deflection values predicted by different methods have a considerable difference each other for a small length-to-thickness ratio. The present predictions are the largest because the present method is a full 3-dimensional finite element analysis without superfluous constraints. Illustrative numerical examples are presented to observe the distributions of stresses through the thickness of the laminates. (C) 2010 Elsevier Ltd. All rights reserved.

FLOW-PIPE-SEEPAGE COUPLING ANALYSIS OF SPANNING INITIATION OF A PARTIALLY-EMBEDDED PIPELINE

The initiation of pipeline spanning involves the coupling between the flow over the pipeline and the seepage-flow in the soil underneath the pipeline. The pipeline spanning initiation is experimentally observed and discussed in this article. It is qualitatively indicated that the pressure-drop induced soil seepage failure is the predominant cause for pipeline spanning initiation. A flow-pipe-seepage sequential coupling Finite Element Method (FEM) model is proposed to simulate the coupling between the water flow-field and the soil seepage-field. A critical hydraulic gradient is obtained for oblique seepage failure of the sand in the direction tangent to the pipe. Parametric study is performed to investigate the effects of inflow velocity, pipe embedment on the pressure-drop, and the effects of soil internal friction angle and pipe embedment-to-diameter ratio on the critical flow velocity for pipeline spanning initiation. It is indicated that the dimensionless critical flow velocity changes approximately linearly with the soil internal friction angle for the submarine pipeline partially-embedded in a sandy seabed.

大气CO2浓度升高对红桦碳水化合物含量和分配的影响

碳水化合物按其存在的形式可分为结构性碳水化合物和非结构性碳水化合物两种。前者主要用于植物体的形态建成；后者是参与植物生命代谢的重要物质。迄今为止，有关CO2浓度升高对植物叶片中的碳水化合物含量的研究较多，而对其它器官中碳水化合物含量以及碳水化合物在植物体内的分配响应研究较少。碳水化合物含量在植物各器官中的变化能够反映光合同化产物在叶和茎、枝和根中的转运情况；碳水化合物的分配与植物的生长模式相关，它的变化会对植物的生长情况产生影响。因此，为全面认识植物生理生化与生长过程对大气CO2浓度升高响应情况，需要对CO2浓度升高条件下植物体内碳水化合物的含量及分配变化进行深入的研究与探讨。本文应用自控、独立、封闭的生长室系统，研究了红桦幼苗根、茎、叶和枝的碳水化合物含量以及分配格局对大气CO2浓度升高(环境CO2浓度+350 µmol·mol-1) 的响应。研究结果表明：1) CO2浓度升高使红桦幼苗叶片中的非结构性碳水化合物含量显著增加。这可能会对光合作用造成反馈抑制，降低光合速率。2) CO2浓度升高使红桦幼苗根、茎和枝中的还原糖、蔗糖、总可溶性糖、淀粉和总的非结构性碳水化合物(TNC) 含量显著增加。说明CO2浓度升高促进了碳水化合物由叶片向枝、茎和根中的运输转移，支持了Finn和Brun的假设。3) 在总的非结构性碳水化合物(TNC) 中，淀粉所占比例最大。同样地，CO2浓度升高使TNC含量增加的部分中，淀粉所占的比例也最大。在叶片、枝、茎和根中淀粉含量增加部分占TNC含量增加部分的91.45%、88.23%、83.23%和82.01%。4) CO2浓度升高使红桦幼苗根、茎、叶和枝内的纤维素含量有增加的趋势，但未达到显著水平。需要进一步研究长期CO2浓度升高下，纤维素含量的响应程度。5) CO2浓度升高使碳水化合物在红桦幼苗体内的分配发生了改变。红桦幼苗体内碳水化合物分配变化的一致趋势是由地上部分向地下部分分配转移。其中，测定的所有碳水化合物均向根中分配增多。同时，CO2浓度升高使红桦幼苗的根冠比显著增大；根系干重显著增加。这些结果支持了Gorissen 和Cotrufo的假设，即碳水化合物向根中分配增多是根冠比增大的主要原因。6) CO2浓度升高使红桦幼苗体内的氮含量显著下降。氮含量的下降可能主要是由生长的加快和TNC (主要是淀粉) 含量的增加对氮的稀释造成的。Carbohydrates found in plants are frequently grouped into two different classes:structural carbohydrates and non-structural carbohydrates. The former mainlyconstruct the plant basic framework, while the latter are essential for plant growth andmetabolism. As yet there is lack of information on the effects of elevated CO2concentration on carbohydrate contents in stem, branch and root of plant, and oncarbohydrate allocation in organs of plant although there have been many reports onthe responses of carbohydrate contents to elevated CO2 concentration in plant foliages.A shift of carbohydrate contents in plant reflects a change in transporting ofphotosynthetic production from leaf to stem, branch and root of plant. The allocationof carbohydrates that is correlated to plant growth patterns affects plant growth. Thus,in order to understand the influences of elevated CO2 on biochemical process,physiological change and plant growth well, the response of carbohydrate contentsand allocation in plant to elevated CO2 should be further investigated. In our study, theeffects of elevated CO2 on carbohydrate contents and their allocation between leaf,stem, branch and root tissue of Betula albosinensis seedlings were determined. Theseedlings were grown in independent and enclosed-top chambers. Chambers werecontrolled to reproduce ambient (CK) and ambient + 350 µmol·mol-1 CO2 (EC)concentration for 1 year. The results here showed that,1) Elevated CO2 significantly increased non-structural carbohydrate contents in leafof red birch seedlings. This will reduce photosynthetic rate.2) Elevated CO2 also significantly increased non-structural carbohydrate contentsin root, stem and branch of red birch seedlings. These findings supported thehypothesis that elevated CO2 accelerated carbohydrates from leaf to branch, stem androot.3) Starch makes up the largest parts of total non-structural carbohydrate. In thesame way, the increase of starch plays a main role in the increase of totalnon-structural carbohydrate under elevated CO2. In leaf, branch, stem and root, theincrements of starch contents comprised 91.45%, 88.23%, 83.23% and 82.01% of theincrements of total non-structural carbohydrate contents.4) Under elevated CO2 the cellulose contents have an increasing tendency in redbirch seedlings. It is needed to investigate the effects of long-term elevated CO2 oncellulose contents in plant.5) There are significant CO2 effects on the allocation of carbohydrate in organs ofred birch seedlings. Under elevated CO2 more carbohydrates were allocated to root.Moreover, CO2 enrichment significantly increased the root to shoot ratio of red birchseedlings and the dry weight of roots. These results supported Gorissen and Cotrufo ‘shypothesis that increase of carbohydrate allocation to root mostly contributed to theincrease of root to shoot ratio.6) Elevated CO2 brought about a reduction in the nitrogen contents of leaf, stem,branch and root. The decline of nitrogen contents under elevated CO2 is mainlycaused by the dilution effects of increasing starch level and growth of red birchseedlings.

Effect of entrance-channel asymmetry on the isospin dependence of nucleon emission in heavy ion collisions

Using the isospin- and momentum-dependent hadronic transport model 1BUU04, we have investigated the influence of the entrance-channel isospin asymmetry on the sensitivity of the pre-equilibrium neutron/proton ratio to symmetry energy in central heavy-ion collisions induced by high-energy radioactive beams. Our analysis and discussion are based on the dynamical simulations of the three isotopic reaction Systems Sn-132+Sn-124, Sn-124+Sn-112 and Sn-112+(112)Su which are of the same total proton number but, different isospin asymmetry. We find that, the kinetic-energy distributions of the pre-equilibrium neutron/proton ratio are quite sensitive to the density-dependence of symmetry energy at incident beam energy E/A = 400 MeV, and the sensitivity increases as the isospin asymmetry of the reaction system increases.

Fast simulation of the forward tracking detector of HPLUS

The necessity of installing a forward tracking detector stack is discussed for the Hadron Physics LanzhoU Spectrometer(HPLUS). A local tracker is developed to solve the multi-track finding problem. The track candidates are searched iteratively via Hough Transform. The fake tracks are removed by a least square fitting process. With this tracker we have studied the feasibility of pp -> pp + phi(-> K+K-), a typical physical channel proposed on HPLUS. The single track momentum resolution due to the uncertainty of the positioning in FTD is 1.3%. The multiple scattering effect contributes about 20% to the momentum resolution in the FTD coverage. The width and the signal-to-background ratio of the reconstructed phi are 1.51 MeV and 4.36, respectively, taking into account the direct Kaon channel pp -> pp + K+K- as background. The geometry coverage of FTD for phi events is about 85.4%. Based on the current fast simulation and estimation, the geometrical configuration of FTD meets the physical requirement of HPLUS under the current luminosity and multiplicity conditions. The tracker is applicable in the full simulation coming next and is extendable to other tracking component of HPLUS.

Flipped symmetry potential in heavy-ion collisions

Within the IBUU transport model, flipping of the symmetry potential in heavy-ion collisions is studied. It is found that there exist flipping of the symmetry potential in the isospin fractionation, the single neutron to proton ratio, the double neutron to proton ratio and the neutron-proton differential flow from lower to higher incident energies. The flipping of the symmetry potential results from the change of the relative magnitude of the hard and soft symmetry energies at lower and higher densities. Future observations of the flipped symmetry potential in experiment will help the study of the density-dependent symmetry energy.