植物结构专题研究

1． 裸子植物次生韧皮部中晶体的分布类型及其意义 应用偏光镜检术和扫描电境一一能谱分析等手段对1 1科30种裸子植物次生韧皮部中晶体的形状、大小、分布类型和化学成分进行了系统研究。结果发现，所有的观察种类都具有晶体，钙是晶体的主要成分。在苏铁科、银杏科和松科，晶体存在于韧皮薄壁组织细胞的胞腔中：在其他各科，晶体则主要存在于韧皮细胞的胞壁上;通常胞腔中的晶体通常比胞壁上的大．苏铁科、银杏科和松科的晶体形状分别足棱形晶体、晶簇和柱状晶体或方形晶体．其他各科的晶体形状均为沙晶，但分布的部位各不相同。在杉科、柏科、和罗汉松科的韧皮部中，品体主要嵌埋在各类细胞的径向壁上：在三尖杉科的韧皮部，晶体主要存在于部分薄壁组织细胞的弦向壁上：在红豆杉科（澳洲红豆杉属除外），晶体嵌埋在韧皮纤维的外侧壁上;在麻黄科、买麻藤科，晶体主要存在于薄壁细胞间的胞间隙中，偶尔也在薄壁组织细胞的内侧，但在裸子植物的韧皮部，未见典型的针晶。根据晶体的上述变化，将晶体分布类型分成棱形晶体在薄壁组织细胞腔内、簇晶在溥壁组织细胞腔内、柱形晶体在薄壁组织细胞腔内、沙品在韧皮细胞壁上、沙品在韧皮纤维壁上和沙晶在韧皮薄壁组织细胞间的胞间隙内等六大类型，并依此讨论了它们在裸予植物各类群中的分类意义． 在红豆杉科中，晶体仪存在于厚壁组织细胞类的韧皮纤维上。根据该五属韧皮纤维．L晶体的比较观察，发现红豆杉属、白豆杉属的韧皮纤维具六角形和方形两种晶体，穗花杉属和榧树属仅具方形一种晶体，澳洲红豆杉属不具晶体．从晶体的有无和晶体的类型，讨论了它们在红豆杉科各属间的分类意义． 2． 长苞铁杉的结构及其系统发育的研究 长苞铁杉足我国特有的珍稀濒危植物。自发现以来，其分类位置曾几度变迁．1931年，郑万钧将其归属于铁杉属。1948年，Gaussen ＆van Campo-Duplan认为它是云南油杉和铁杉的杂交种，主张建立铁油杉属(Ts uga -Keteleeria). 1951年，胡先驌认为长苞铁杉与其他铁杉区别明显，提出建立新属- Nothotsuga. 1957年，喻诚鸿根据木材解剖的结果，认为长苞铁杉木质部缺乏正常树脂道，与铁杉属没有本质上的区别，建议将它归人铁杉属．<<中国植物志>>第七卷设长苞铁杉组(Sect. Heopeuce)，与铁杉组(Sect. Tsuga)平行，同归于铁杉属。 本课题对长苞铁杉营养器官的结构做了研究，发现长苞铁杉成熟部位的次生木质部具正常树脂道，创伤树脂道除切向连续分布外还有单个独生的现象，早晚材过渡不明显，射线管胞不发达，交叉场纹孔以杉木型为主，韧皮部中具树脂腔(Resin caviLy)。叶片气孔雨面生，维管束鞘明显，细胞大小均匀，树脂道1个边生。 上述特征都与铁杉属存在明显区别，因而作者支持胡先驌(1951)、Frankis(1989)、Faljon(1990)等关于建立长苞铁杉属的主张。 3． 白皮松的结构及其系统发育的研究 按<<中国植物志>>第七卷的分类系统，白皮松隶属单维管束亚属白皮松组，但其对分类位置曾有不同看法． 本课题通过白皮松营养体结构的研究，发现它在许多方面与单维管束亚属的其他种类有显著差异，白皮松针叶的气孔分布于背腹雨面，气孔间连结细胞的雨侧具石细胞，副卫细胞为近四方形且数目比较恒定，角质层内表面具深波浪状的胞间凸缘：次生木质部的射线管胞内壁具微锯齿状突起，交叉场纹孔松木型，管胞内表面及纹孔部分具明显的瘤层结构;树皮薄，其最外侧仅保留一层周皮，无内皮外皮之分，外侧的韧皮薄壁组织细胞与射线有明显的扩展与弯曲现象，韧皮薄壁组织细胞中的晶体有长柱形和短柱形雨种类型．依据上述结构特征结合前人从染色体、心边材抽提物化学成分析的研究结果，作者支持将白皮松从单维管束亚属中独立出来，成立白皮松亚属的主张。 4． C02浓度升高对植物生长的影响 大气中C02浓度的升高以及所引起的温室效应已成为了人们普遍关注的焦点。预计到21世纪下半叶，C02浓度将增加一倍(Gates���1983).由于C02是植物光合作用的重要原料， 它的变化将直接影响植物的生长和发育，进而引起生物圈乃至整个生态系统的变化。 本项目通过在人工气候室内增加C02浓度，观察大豆与黄麻的生长及其内部结构的影响。结果表明：在短期内，C02浓度升高对两种植物的生长有促进作用，对植物内部结构也有较明显的影响。其中包括种子的发芽率提高，幼苗生长加快，植株明显增高，叶面积增大，叶片加厚（栅栏组织层数增加），根系数量增多，气孔数量减少，茎干增粗、生长轮加宽，韧皮纤维和木纤维增长、大豆结实率增高。但C02浓度升高对两种植物的长期作用仍有待于进一步研究。 本项目还在进行之中。

Ballistic Single-Electron Quputer

We propose a new solid state implementation of a quantum computer (quputer) using ballistic single electrons as flying qubits in 1D nanowires. We use a single electron pump (SEP) to prepare the initial state and a single electron transistor (SET) to measure the final state. Single qubit gates are implemented using quantum dots as phase shifters and electron waveguide couplers as beam splitters. A Coulomb coupler acts as a 2-qubit gate, using a mutual phase modulation effect. Since the electron phase coherence length in GaAs/AlGaAs heterostructures is of the order of 30$\mu$m, several gates (tens) can be implemented before the system decoheres.

An ecodesign model based on industry experience

With the increase in environmental legislation facing many industrial sectors organisations are now looking for ways to improve their environmental performance. To a large extent organisations have tended to concentrate on their operations inside the "factory gates" with little regard to the environmental performance of the products they produce. However, this is now changing and some organisations are beginning to take a close look at their products and their effects on the environment during its use phase as well as during the manufacture and disposal phases. At Cranfield University we have carried out a 3 year survey of US, Central European and UK companies claiming to practice ecodesign has been undertaken. Thirty electrical and electronic manufacturers were studied, some through in-depth observation of design programmes, most through semi-structured interviews. The survey and action research sought to understand the way in which these companies practised ecodesign and how they .had implemented ecodesign. A common pattern emerged from the data which suggests that companies successfully implementing ecodesign have many similar experiences. The resulting ecodesign model is presented and discussed, and the factors critical to successful implementation at various stages are explored. The factors cover a range of topics including design management, motivation, design tools, design phases, communication and the designers perspective.

Low on-resistance SOI dual-trench-gate MOSFET

A low specific on-resistance (R-{{\rm on}, {\rm sp}}) integrable silicon-on-insulator (SOI) MOSFET is proposed, and its mechanism is investigated by simulation. The SOI MOSFET features double trenches and dual gates (DTDG SOI): an oxide trench in the drift region, a buried gate inset in the oxide trench, and another trench gate (TG) extended to a buried oxide layer. First, the dual gates form dual conduction channels, and the extended gate widens the vertical conduction area; both of which sharply reduce R-{{\rm on}, {\rm sp}}. Second, the oxide trench folds the drift region in the vertical direction, resulting in a reduced device pitch and R-{{\rm on}, {\rm sp}}. Third, the oxide trench causes multidirectional depletion. This not only enhances the reduced surface field effect and thus reshapes the electric field distribution but also increases the drift doping concentration, leading to a reduced R-{{\rm on}, {\rm sp}} and an improved breakdown voltage (BV). Compared with a conventional SOI lateral Double-diffused metal oxide semiconductor (LDMOS), the DTDG MOSFET increases BV from 39 to 92 V at the same cell pitch or decreases R-{{\rm on}, { \rm sp}} by 77% at the same BV by simulation. Finally, the TG extended synchronously acts as an isolation trench between the high/low-voltage regions in a high-voltage integrated circuit, saving the chip area and simplifying the isolation process. © 2006 IEEE.

Device and circuit-level performance of carbon nanotube field-effect transistor with benchmarking against a nano-MOSFET

The performance of a semiconducting carbon nanotube (CNT) is assessed and tabulated for parameters against those of a metal-oxide-semiconductor field-effect transistor (MOSFET). Both CNT and MOSFET models considered agree well with the trends in the available experimental data. The results obtained show that nanotubes can significantly reduce the drain-induced barrier lowering effect and subthreshold swing in silicon channel replacement while sustaining smaller channel area at higher current density. Performance metrics of both devices such as current drive strength, current on-off ratio (Ion/Ioff), energy-delay product, and power-delay product for logic gates, namely NAND and NOR, are presented. Design rules used for carbon nanotube field-effect transistors (CNTFETs) are compatible with the 45-nm MOSFET technology. The parasitics associated with interconnects are also incorporated in the model. Interconnects can affect the propagation delay in a CNTFET. Smaller length interconnects result in higher cutoff frequency. © 2012 Tan et al.

Electron spin resonance signature of the oxygen vacancy in HfO 2

The oxygen vacancy has been inferred to be the critical defect in HfO 2, responsible for charge trapping, gate threshold voltage instability, and Fermi level pinning for high work function gates, but it has never been conclusively identified. Here, the electron spin resonance g tensor parameters of the oxygen vacancy are calculated, using methods that do not over-estimate the delocalization of the defect wave function, to be g xx = 1.918, g yy = 1.926, g zz = 1.944, and are consistent with an observed spectrum. The defect undergoes a symmetry lowering polaron distortion to be localized mainly on a single adjacent Hf ion. © 2012 American Institute of Physics.

Three-dimensional distribution of Al in high-k metal gate: Impact on transistor voltage threshold

The three-dimensional spatial distribution of Al in the high-k metal gates of metal-oxide-semiconductor field-effect-transistors is measured by atom probe tomography. Chemical distribution is correlated with the transistor voltage threshold (VTH) shift generated by the introduction of a metallic Al layer in the metal gate. After a 1050 °C annealing, it is shown that a 2-Å thick Al layer completely diffuses into oxide layers, while a positive VTH shift is measured. On the contrary, for thicker Al layers, Al precipitation in the metal gate stack is observed and the VTH shift becomes negative. © 2012 American Institute of Physics.

Unified compression model for venice lagoon natural silts

Over the last 50 years, the city of Venice, Italy, has observed a significant increase in the frequency of flooding. Numerous engineering solutions have been proposed, including the use of movable gates located at the three lagoon inlets. A key element in the prediction of performance is the estimation of settlements of the foundation system of the gates. The soils of Venice Lagoon are characterized by very erratic depositional patterns of clayey silts, resulting in an extremely heterogeneous stratigraphy with discontinuous layering. The soils are also characterized by varying contents of coarse and fine-grained particles. In contrast, the mineralogical composition of these deposits is quite uniform, which allows us to separate the influence of mineralogy from that of grain size distribution. A comprehensive geotechnical testing program was performed to assess the one-dimensional compression of Venice soils and examine the factors affecting the response in the transition from one material type to another. The compressibility of these natural silty clayey soils can be described by a single set of constitutive laws incorporating the relative fraction of granular to cohesive material. © 2007 ASCE.

Cryogenic on-chip multiplexer for the study of quantum transport in 256 split-gate devices

We present a multiplexing scheme for the measurement of large numbers of mesoscopic devices in cryogenic systems. The multiplexer is used to contact an array of 256 split gates on a GaAs/AlGaAs heterostructure, in which each split gate can be measured individually. The low-temperature conductance of split-gate devices is governed by quantum mechanics, leading to the appearance of conductance plateaux at intervals of 2e^2/h. A fabrication-limited yield of 94% is achieved for the array, and a "quantum yield" is also defined, to account for disorder affecting the quantum behaviour of the devices. The quantum yield rose from 55% to 86% after illuminating the sample, explained by the corresponding increase in carrier density and mobility of the two-dimensional electron gas. The multiplexer is a scalable architecture, and can be extended to other forms of mesoscopic devices. It overcomes previous limits on the number of devices that can be fabricated on a single chip due to the number of electrical contacts available, without the need to alter existing experimental set ups.

Depicting the future strategic plans of the Royal Australian Navy using a roadmapping framework as a visual composite canvas

Strategic planning can be an arduous and complex task; and, once a plan has been devised, it is often quite a challenge to effectively communicate the principal missions and key priorities to the array of different stakeholders. The communication challenge can be addressed through the application of a clearly and concisely designed visualisation of the strategic plan - to that end, this paper proposes the use of a roadmapping framework to structure a visual canvas. The canvas provides a template in the form of a single composite visual output that essentially allows a 'plan-on-a-page' to be generated. Such a visual representation provides a high-level depiction of the future context, end-state capabilities and the system-wide transitions needed to realise the strategic vision. To demonstrate this approach, an illustrative case study based on the Australian Government's Defence White Paper and the Royal Australian Navy's fleet plan will be presented. The visual plan plots the in-service upgrades for addressing the capability shortfalls and gaps in the Navy's fleet as it transitions from its current configuration to its future end-state vision. It also provides a visualisation of project timings in terms of the decision gates (approval, service release) and specific phases (proposal, contract, delivery) together with how these projects are rated against the key performance indicators relating to the technology acquisition process and associated management activities. © 2013 Taylor & Francis.

Tunable Rashba effect in two-dimensional LaOBiS2 films: Ultrathin candidates for spin field effect transistors

Rashba spin splitting is a two-dimensional (2D) relativistic effect closely related to spintronics. However, so far there is no pristine 2D material to exhibit enough Rashba splitting for the fabrication of ultrathin spintronic devices, such as spin field effect transistors (SFET). On the basis of first-principles calculations, we predict that the stable 2D LaOBiS2 with only 1 nm of thickness can produce remarkable Rashba spin splitting with a magnitude of 100 meV. Because the medium La2O2 layer produces a strong polar field and acts as a blocking barrier, two counter-helical Rashba spin polarizations are localized at different BiS 2 layers. The Rashba parameter can be effectively tuned by the intrinsic strain, while the bandgap and the helical direction of spin states sensitively depends on the external electric field. We propose an advanced Datta-Das SFET model that consists of dual gates and 2D LaOBiS2 channels by selecting different Rashba states to achieve the on-off switch via electric fields. © 2013 American Chemical Society.

Compact Reconfigurable Binary-Decision-Diagram Logic Circuit on a GaAs Nanowire Network

We describe a reconfigurable binary-decision-diagram logic circuit based on Shannon's expansion of Boolean logic function and its graphical representation on a semiconductor nanowire network. The circuit is reconfigured by using programmable switches that electrically connect and disconnect a small number of branches. This circuit has a compact structure with a small number of devices compared with the conventional look-up table architecture. A variable Boolean logic circuit was fabricated on an etched GaAs nanowire network having hexagonal topology with Schottky wrap gates and SiN-based programmable switches, and its correct logic operation together with dynamic reconfiguration was demonstrated.

Compact voltage-mode multi-valued literal gate using nanoscale ballistic MOSFETs

A CMOS voltage-mode multi-valued literal gate is presented. The ballistic electron transport characteristic of nanoscale MOSFETs is smartly used to compactly achieve universal radix-4 literal operations. The proposed literal gates have small numbers of transistors and low power dissipations, which makes them promising for future nanoscale multi-valued circuits. The gates are simulated by HSPICE.

Fabrication and characterization of active and sequential circuits utilizing Schottky-wrap-gate-controlled GaAs hexagonal nanowire network structures

For realization of hexagonal BDD-based digital systems, active and sequential circuits including inverters, flip flops and ring oscillators are designed and fabricated on GaAs-based hexagonal nanowire networks controlled by Schottky wrap gates (WPGs), and their operations are characterized. Fabricated inverters show comparatively high transfer gain of more than 10. Clear and correct operation of hexagonal set-reset flip flops (SR-FFs) is obtained at room temperature. Fabricated hexagonal D-type flip flop (D-FF) circuits integrating twelve WPG field effect transistors (FETs) show capturing input signal by triggering although the output swing is small. Oscillatory output is successfully obtained in a fabricated 7-stage hexagonal ring oscillator. Obtained results confirm that a good possibility to realize practical digital systems can be implemented by the present circuit approach.

Resonant tunneling through S- and U-shaped graphene nanoribbons

We theoretically investigate resonant tunneling through S- and U-shaped nanostructured graphene nanoribbons. A rich structure of resonant tunneling peaks is found emanating from different quasi-bound states in the middle region. The tunneling current can be turned on and off by varying the Fermi energy. Tunability of resonant tunneling is realized by changing the width of the left and/or right leads and without the use of any external gates.