区域景观结构动态变化的趋势分析及其应用研究

根据景观生态学原理,对区域内的景观进行分类,应用向量空间理论,提出并确定了相应的景观结构向量及其区域景观结构动态转移模型.对景观结构动态变化趋势的推理和分析结果表明,在一定的区域内,景观类型之间无论按照何种方式、以何种概率进行转移,如果转移概率不发生变化,则经过长期的动态变化后,景观结构将趋向一种稳定的状态,景观生态系统具有自稳定性.实例应用结果也表明,区域景观经有限次转移后将稳定在若干种景观类型上.因此,在区域景观结构管理中,关键在于对景观类型之间的转移概率作合理调控与管理.     

Coherent optical spectroscopy of a strongly driven quantum dot

Quantum dots are typically formed from large groupings of atoms and thus may be expected to have appreciable many-body behavior under intense optical excitation. Nonetheless, they are known to exhibit discrete energy levels due to quantum confinement effects. We show that, like single-atom or single-molecule two- and three-level quantum systems, single semiconductor quantum dots can also exhibit interference phenomena when driven simultaneously by two optical fields. Probe absorption spectra are obtained that exhibit Autler-Townes splitting when the optical fields drive coupled transitions and complex Mollow-related structure, including gain without population inversion, when they drive the same transition. Our results open the way for the demonstration of numerous quantum level-based applications, such as quantum dot lasers, optical modulators, and quantum logic devices.     

Quantum register based on individual electronic and nuclear spin qubits in diamond

The key challenge in experimental quantum information science is to identify isolated quantum mechanical systems with long coherence times that can be manipulated and coupled together in a scalable fashion. We describe the coherent manipulation of an individual electron spin and nearby individual nuclear spins to create a controllable quantum register. Using optical and microwave radiation to control an electron spin associated with the nitrogen vacancy (NV) color center in diamond, we demonstrated robust initialization of electron and nuclear spin quantum bits (qubits) and transfer of arbitrary quantum states between them at room temperature. Moreover, nuclear spin qubits could be well isolated from the electron spin, even during optical polarization and measurement of the electronic state. Finally, coherent interactions between individual nuclear spin qubits were observed and their excellent coherence properties were demonstrated. These registers can be used as a basis for scalable, optically coupled quantum information systems.     

Quantum criticality without tuning in the mixed valence compound beta-YbAlB4

Fermi liquid theory, the standard theory of metals, has been challenged by a number of observations of anomalous metallic behavior found in the vicinity of a quantum phase transition. The breakdown of the Fermi liquid is accomplished by fine-tuning the material to a quantum critical point by using a control parameter such as the magnetic field, pressure, or chemical composition. Our high-precision magnetization measurements of the ultrapure f-electron-based superconductor β-YbAlB(4) demonstrate a scaling of its free energy that is indicative of zero-field quantum criticality without tuning in a metal. The breakdown of Fermi liquid behavior takes place in a mixed-valence state, which is in sharp contrast with other known examples of quantum critical f-electron systems that are magnetic Kondo lattice systems with integral valence.     

A 2D quantum walk simulation of two-particle dynamics

Multidimensional quantum walks can exhibit highly nontrivial topological structure, providing a powerful tool for simulating quantum information and transport systems. We present a flexible implementation of a two-dimensional (2D) optical quantum walk on a lattice, demonstrating a scalable quantum walk on a nontrivial graph structure. We realized a coherent quantum walk over 12 steps and 169 positions by using an optical fiber network. With our broad spectrum of quantum coins, we were able to simulate the creation of entanglement in bipartite systems with conditioned interactions. Introducing dynamic control allowed for the investigation of effects such as strong nonlinearities or two-particle scattering. Our results illustrate the potential of quantum walks as a route for simulating and understanding complex quantum systems.     

Conditional dynamics of interacting quantum dots

Conditional quantum dynamics, where the quantum state of one system controls the outcome of measurements on another quantum system, is at the heart of quantum information processing. We demonstrate conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot. Interaction between the dots is mediated by the tunnel coupling between optically excited states and can be optically gated by applying a laser field of the right frequency. Our results represent substantial progress toward realization of an optically effected controlled-phase gate between two solid-state qubits.     

Restricting dislocation movement in transition metal carbides by phase stability tuning

A mechanism to enhance hardness in multilayer coatings is proposed. Using the technologically important hard transition metal carbides as prototypes, although the principle is transferable also to other systems, we demonstrate, from first-principles calculations, that by suitable alloying the energy difference between several competing structures in the transition metal carbides is small or tunable. This creates multiphase/polytypic compounds with a random or controllable layer stacking sequence, systems in which the propagation of dislocations can be strongly suppressed by a large number of interfaces between structures with different glide systems, accordingly allowing the possibility of a greatly enhanced hardness. With modern thin-film technologies, it should therefore be possible to deposit such materials that will express multilayer characteristics with only minor changes in the chemical constitution of the material, which is in contrast to conventional superlattices.     

Ultrastrong coupling of the cyclotron transition of a 2D electron gas to a THz metamaterial

Artificial cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems because of the possibility of manipulating the cavity quantum electrodynamic ground state with controllable physical properties. We report here experiments showing ultrastrong light-matter coupling in a terahertz (THz) metamaterial where the cyclotron transition of a high-mobility two-dimensional electron gas (2DEG) is coupled to the photonic modes of an array of electronic split-ring resonators. We observe a normalized coupling ratio, Ω/ω(c) = 0.58, between the vacuum Rabi frequency, ?, and the cyclotron frequency, ω(c). Our system appears to be scalable in frequency and could be brought to the microwave spectral range with the potential of strongly controlling the magnetotransport properties of a high-mobility 2DEG.     

主伐对森林景观结构和空间分布格局影响的研究

本文用不同尺度分析了采伐对森林景观的影响。通过对景观组成单元的类型、总体景观比例随海拔梯度的分布格局、景观内各组份水平分布的隔离度等比较表明，采伐后自然重建的景观与原生景观无显著差异，森林景观对采伐干扰具有渐进稳定性。各景观单元均属聚集性分布。景观内部结构的多样性、均匀度有一定提高，景观优势度有所降低。采伐使景观单元破碎化，出现重组现象。采伐引发的景观单元转移概率因类型不同而异；松栎混交林景观单元在其生态区位内稳定性强，对采伐有负反馈效应；华山松为优势的景观单元采伐后明显扩大，以铁杉为主的景观单元也有类似情况；弱度干扰的红桦、云、冷杉景观单元结构稳定并有所扩展。     

Quantum phase transition in organic charge-transfer complexes

A phase transition in an organic charge-transfer complex, which originates from the neutral-ionic valence instability, can be tuned toward zero kelvin with use of external pressure or chemical modification as a control parameter. The phase diagram and observed dielectric behaviors are typical of quantum paraelectricity, yet this zero-kelvin transition point namely, the quantum critical point, accompanies large quantum fluctuation of the molecular charge, as demonstrated by the molecular vibrational mode spectra. The result indicates that the pi-electron transfer between donor and acceptor molecules is coupled with the zero-point lattice dynamics around the quantum critical point.     

基于CA-Markov景观格局预测模型的建构研究

为预测景观格局变化,将CA模型与Markov模型相结合,构建具有空间和数量双重优势的CA—Markov预测模型,并以黑龙江省宝清县1996—2004年土地利用类型图为基础,建立转移概率矩阵和土地利用适宜性图像集,预测2012年该县的景观分布状态。将预测结果与真实值比较,Kappa系数迭0．89,符合精度要求。最终预测该县2020年景观格局的变化情况。通过预测结果及对比表明该区域湿地面积明显减少,景观破碎度正不断加深,望有关部门加以重视并采取相应补救措施。     

Symmetrized characterization of noisy quantum processes

A major goal of developing high-precision control of many-body quantum systems is to realize their potential as quantum computers. A substantial obstacle to this is the extreme fragility of quantum systems to "decoherence" from environmental noise and other control limitations. Although quantum computation is possible if the noise affecting the quantum system satisfies certain conditions, existing methods for noise characterization are intractable for present multibody systems. We introduce a technique based on symmetrization that enables direct experimental measurement of some key properties of the decoherence affecting a quantum system. Our method reduces the number of experiments required from exponential to polynomial in the number of subsystems. The technique is demonstrated for the optimization of control over nuclear spins in the solid state.     

厦门城市绿地生态系统景观结构与异质性分析

对厦门城区绿地生态系统景观结构和异质性进行分析的结果表明：在厦门城区绿地生态系统中，单位绿地斑块最多，占城区绿地系统总斑块数的32％，而居住区所占面积较少，但斑块数却占总斑块数的28％。风景林地的斑块数最小，仅为1.3％，但其面积却在城区绿地系统中占的比例最大，达32．2％。公共绿地景观斑块不多，只占12％，而绿地面积较大，占总面积的24．6％。厦门本岛城市绿地景观多样性指数为1.243，绿地整体的多样性指数较低；景观优势度为0．914，均匀度为0.642，整体绿地景观格局分布不均匀，存在看少数绿地景观控制着整个绿地格局；绿地廊道密度为0.549，分布密度较低，不能很好地发挥生态防护功能。同时，根据分析结果提出了相应的对策和建议．     

基于Markov的福建省溪南半岛植被景观动态变化预测

在遥感和地理信息系统技术的支持下,利用1994和2008年两个时期的影像图作为信息源,获取福建省溪南半岛各景观要素类型的转化数据,确定相应的转移概率矩阵,并应用马尔科夫模型原理,运用MATLAB7.0软件定量预测出未来2022、2036、2050、2064年植被景观情况。结果表明,溪南半岛林地的恢复状况形势好转,生态条件将有所提高,溪南半岛的植被景观生态将向着和谐的方向发展,为"海西宁德工业区"的规划、管理及其资源使用与保护提供科学的指导。     

Experimental verification of decoherence-free subspaces

Using spontaneous parametric down-conversion, we produce polarization-entangled states of two photons and characterize them using two-photon tomography to measure the density matrix. A controllable decoherence is imposed on the states by passing the photons through thick, adjustable birefringent elements. When the system is subject to collective decoherence, one particular entangled state is seen to be decoherence-free, as predicted by theory. Such decoherence-free systems may have an important role for the future of quantum computation and information processing.     

Dipolar antiferromagnetism and quantum criticality in LiErF₄

Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF(4), establishing it as a model dipolar-coupled antiferromagnet with planar spin-anisotropy and a quantum phase transition in applied field H(c|| = 4.0 ± 0.1 kilo-oersteds. We discovered non-mean-field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two-dimensional XY/h(4) universality class; in accord with this, the quantum phase transition at H(c) exhibits three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations.     

森林景观组成结构动态模拟及预测方法研究

以关帝林区 4个时期的航空像片和地形图为基础资料 ,通过地形斑块图层和植被斑块图层叠加建立景观要素斑块图层及相应数据库 ,在ARC/INFO支持下采用加密的公里网格样点取样的方法 ,成功地确立了森林景观转移概率矩阵 ,并应用马尔可夫模型对研究地区森林景观格局的变化趋势进行了分析、模拟和动态预测。结果表明该地区森林景现在现有经营方针和干扰状况下 ,将在 2 0 2 4年左右达到一个稳定状态。景观总体质量提高 ,有林地面积增加 ,其中寒温性针叶林和温性针叶林面积增大 ,落叶阔叶林面积略有减少。预示着关帝林区最终将趋于一种经济发展与森林资源管理、生态环境保护相协调的森林景观格局。     

基于VR全景图技术的乡村景观视觉评价偏好研究

乡村景观评价是乡村景观规划的基础。为了更好地了解和研究乡村景观视觉环境的影响因素,本文首次将VR全景图技术应用于景观评价的研究中,进行了新技术应用于风景园林领域的实践尝试。利用VR全景图技术对空间、场景高度还原仿真的特点,改进传统的SBE法,以城市青年人群为例,通过观测实验并进行打分,从而得出原始数据,对乡村景观视觉评价及景观要素偏好进行研究。首先,使用改进后的SBE法与SD法构建了乡村景观视觉评价模型,并确定了4个显著影响指标(建筑肌理感、植物种类、道路形态和卫生状况)。其次,根据VR全景图场景中偏好视域截图,进而从截图中归纳提取出9个景观偏好指标。利用线性回归的方法,分别研究这9个景观偏好指标的偏好概率与该指标价值分数、所在场景SBE得分之间是否存在函数关系,并得出三者之间互相作用的模型。得出建筑特色指标与水环境指标的偏好概率与其自身的价值分数有显著关系;建筑肌理感、农田肌理感的偏好概率受其价值分数与场景SBE值共同影响;自然视野与其他视觉焦点的偏好概率受到场景SBE值影响更为显著;道路形态、道路材料和植物种类偏好概率与其自身价值分数、场景SBE值并无明显关系。最后,分析出城市青年人群会产生此种偏好的原因,并希望能够对未来乡村景观建设起到指导作用。      

Doped nanocrystals

The critical role that dopants play in semiconductor devices has stimulated research on the properties and the potential applications of semiconductor nanocrystals, or colloidal quantum dots, doped with intentional impurities. We review advances in the chemical synthesis of doped nanocrystals, in the theoretical understanding of the fundamental mechanisms that control doping, and in the creation of highly conducting nanocrystalline films. Because impurities can be used to alter the properties of nanoscale materials in desirable and controllable ways, doped nanocrystals can address key problems in applications from solar cells to bioimaging.     

植物多样性理论在城市广场景观评价中的应用——以怀化市五溪文化广场为例

在研究现行的几种景观评价方法的基础上,指出植物多样性理论在景观评价中的作用。植物多样性指数能在一定程度上反映场景中的植物种类、植物个体数量,但它却不适于做为评价景观效果的直接指标;植物多样性指数在一定程度上反映了场景的客容量、景观场景供游人参与园林活动的机率:D→0或D→1,游人参与园林活动的机率低,D→0.5,游人参与园林活动的机率高;D值越大,景观场景中植物种类与个体数量越少,乔木类所占比例越低。为使景观评价方法更客观、科学,对园林景观场景中野生杂草与人工疏林中的耐践踏草种类多样性统计问题进行更深入地研究。