Repeated and sudden reversals of the dipole field generated by a spherical dynamo action

Using long-duration, three-dimensional magnetohydrodynamic simulation, we found that the magnetic dipole field generated by a dynamo action in a rotating spherical shell repeatedly reverses its polarity at irregular intervals (that is, punctuated reversal). Although the total convection energy and magnetic energy alternate between a high-energy state and a low-energy state, the dipole polarity can reverse only at high-energy states where the north-south symmetry of the convection pattern is broken and the columnar vortex structure becomes vulnerable. Another attractive finding is that the quadrupole mode grows, exceeding the dipole mode before the reversal; this may help to explain how Earth's magnetic field reverses.     

Direct spectroscopic detection of a zwitterionic excited state

Two electrons in two weakly coupled orbitals give rise to two states (diradical) with electrons residing in separate orbitals and two states (zwitterionic) with both electrons paired in one orbital or the other. This two-electron, two-orbital state manifold has eluded experimental confirmation because the zwitterionic states have been difficult to locate. Two-photon excitation of fluorescence from Mo(2)CI(4)(PMe(3))(4) (D2d) has been measured with linearly and circularly polarized light. From the polarization ratio and the energy of the observed transition, the 2(1)A(1) (delta*delta*) excited state has been located and characterized. In conjunction with the one-photon allowed (1)B(2) (deltadelta*) excited state, the zwitterionic state manifold for the quadruply bonded metal-metal class of compounds is thus established.     

Transition-State Spectroscopy of Cyclooctatetraene

The 351-nanometer photoelectron spectrum of the planar cyclooctatetraene radical anion (COT·-) shows transitions to two electronic states of cyclooctatetraene (COT). These states correspond to the D4h 1A1g state, which is the transition state for COT ring inversion, and the D8h 3A2u state. The electron binding energy of the 1A1g transition state is 1.099 ± 0.010 electron volts, which is lower by 12.1 ± 0.3 kilocalories per mole than that of the 3A2u state. The photoelectron spectrum shows that the singlet lies well below the triplet in D8h COT and confirms ab initio predictions that the molecule violates Hund's rule. Vibrational structure is observed for both features and is readily assigned by use of a simple potential energy surface.     

Managing state energy conservation programs: the Minnesota experience

In fiscal year 1980, the Department of Energy awarded grants for state energy conservation programs that totaled more than $400 million; the proposed figure for fiscal year 1981 is almost $600 million. Many states provide additional funds to implement conservation programs. This suggests that state governments play a major role in delivering conservation services to their citizens and are key agents in the nation's conservation efforts. This article discusses the energy conservation activities and responsibilities of one state energy office, the Minnesota Energy Agency, and the obstacles and constraints it faces in delivering its services. Suggestions are presented for resolving these difficulties and for improving the efficiency with which the agency manages its programs.     

Crystal structure of the maltose transporter in a pretranslocation intermediate state

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters convert chemical energy from ATP hydrolysis to mechanical work for substrate translocation. They function by alternating between two states, exposing the substrate-binding site to either side of the membrane. A key question that remains to be addressed is how substrates initiate the transport cycle. Using x-ray crystallography, we have captured the maltose transporter in an intermediate step between the inward- and outward-facing states. We show that interactions with substrate-loaded maltose-binding protein in the periplasm induce a partial closure of the MalK dimer in the cytoplasm. ATP binding to this conformation then promotes progression to the outward-facing state. These results, interpreted in light of biochemical and functional studies, provide a structural basis to understand allosteric communication in ABC transporters.     

Determining transition-state geometries in liquids using 2D-IR

Many properties of chemical reactions are determined by the transition state connecting reactant and product, yet it is difficult to directly obtain any information about these short-lived structures in liquids. We show that two-dimensional infrared (2D-IR) spectroscopy can provide direct information about transition states by tracking the transformation of vibrational modes as a molecule crossed a transition state. We successfully monitored a simple chemical reaction, the fluxional rearrangement of Fe(CO)5, in which the exchange of axial and equatorial CO ligands causes an exchange of vibrational energy between the normal modes of the molecule. This energy transfer provides direct evidence regarding the time scale, transition state, and mechanism of the reaction.     

Simulations of jets driven by black hole rotation

The origin of jets emitted from black holes is not well understood; however, there are two possible energy sources: the accretion disk or the rotating black hole. Magnetohydrodynamic simulations show a well-defined jet that extracts energy from a black hole. If plasma near the black hole is threaded by large-scale magnetic flux, it will rotate with respect to asymptotic infinity, creating large magnetic stresses. These stresses are released as a relativistic jet at the expense of black hole rotational energy. The physics of the jet initiation in the simulations is described by the theory of black hole gravitohydromagnetics.     

低维周期量子点中极化子压缩效应

研究了低维周期对称量子点中极化子的压缩效应。通过引入单模压缩态,改进了Lee-Low-Pines和Huybrechts(LLP-H)方法,并计算了压缩态下极化子的能量。该计算方法不仅适用于所有的耦合常数范围,而且还可以考虑LLP-H方法中忽略了的哈密顿量中声子算符的线形项以及双线形项。将该计算方法所得到的低维周期对称量子点中极化子基态下极化子结合能和势能与LLP-H方法的计算结果相比较,计算结果更加精确。     

Correlations between ground and excited state spectra of a quantum Dot

The ground and excited state spectra of a semiconductor quantum dot with successive electron occupancy were studied with linear and nonlinear magnetoconductance measurements. A direct correlation was observed between the mth excited state of the N-electron system and the ground state of the (N + m)-electron system for m up to 4. The results are consistent with a single-particle picture in which a fixed spectrum of energy levels is successively filled, except for a notable absence of spin degeneracy. Further departures from the single-particle picture due to electron-electron interaction were also observed. Magnetoconductance fluctuations of ground states show anticrossings where wave function characteristics are exchanged between adjacent levels.     

Dephosphorylation of the calcium pump coupled to counterion occlusion

P-type ATPases extract energy by hydrolysis of adenosine triphosphate (ATP) in two steps, formation and breakdown of a covalent phosphoenzyme intermediate. This process drives active transport and countertransport of the cation pumps. We have determined the crystal structure of rabbit sarcoplasmic reticulum Ca2+ adenosine triphosphatase in complex with aluminum fluoride, which mimics the transition state of hydrolysis of the counterion-bound (protonated) phosphoenzyme. On the basis of structural analysis and biochemical data, we find this form to represent an occluded state of the proton counterions. Hydrolysis is catalyzed by the conserved Thr-Gly-Glu-Ser motif, and it exploits an associative nucleophilic reaction mechanism of the same type as phosphoryl transfer from ATP. On this basis, we propose a general mechanism of occluded transition states of Ca2+ transport and H+ countertransport coupled to phosphorylation and dephosphorylation, respectively.     

Resonating valence-bond ground state in a phenalenyl-based neutral radical conductor

An organic material composed of neutral free radicals based on the spirobiphenalenyl system exhibits a room temperature conductivity of 0.3 siemens per centimeter and a high-symmetry crystal structure. It displays the temperature-independent Pauli paramagnetism characteristic of a metal with a magnetic susceptibility that implies a density of states at the Fermi level of 15.5 states per electron volt per mole. Extended Hückel calculations indicate that the solid is a three-dimensional organic metal with a band width of approximately 0.5 electron volts. However, the compound shows activated conductivity (activation energy, 0.054 electron volts) and an optical energy gap of 0.34 electron volts. We argue that these apparently contradictory properties are best resolved in terms of the resonating valence-bond ground state originally suggested by Pauling, but with the modifications introduced by Anderson.     

扶手椅型石墨烯纳米带边缘的硼掺杂

利用第一性原理研究了2种边缘掺杂硼方式的扶手椅型石墨烯纳米带.结果表明：硼掺杂使得沿纳米带方向的晶格常数发生改变,并且在能带隙中出现新的能带.对于原胞中添加4个硼原子的掺杂方式（B1-7AGNR）,沿纳米带方向的晶格常数有所增加,在带隙中出现了4条能带,其中2条能带来自于硼的2pz轨道,其余2条能带主要来自于硼的2ps和2py轨道.对于原胞中添加2个硼原子的掺杂方式（B2-7AGNR）,沿纳米带方向的晶格常数有所减小,在带隙中出现了2条能带,其来自于硼的2pz轨道.     

单片微机电力网无功自动补偿节能装置的研制

针对式农业电力网感性负载较多，功率因数较低的情况，研制出一种电力网无功补偿装置，可根据电力网功率因数的高低，采用单片微机进行相应的数据处理得到电网我最佳无功补偿量，从而投入或切除相应容量的并联电容器。使电网我运行在最佳功率因数状态，实现电网的运行，同时对该装置了智能化设计。     

Radiative-capture studies of the giant dipole resonance. Gamma-ray yields from capture of protons and alpha-particles give finer details than studies of gamma-ray absorption

The data on radiative capture through the giant resonance have led to a model in which the capture is pictured as proceeding through a single broad (and therefore short-lived) state that can be called the giant-resonance state. This state is the one formed directly upon capture of a proton, and hence most of the capture radiation is emitted quickly in the direct-interaction mode. Some of the energy that is contained in the giant-resonance state is shared with the more-complicated states of the compound nucleus (that is, with states having many excited nucleons). This sharing, in turn, gives rise to the fine structure that is observed within the giant-resonance envelope. The constant angular distributions that are observed throughout the giant-resonance region support the single-state picture of the giant resonance.     

Capturing a photoexcited molecular structure through time-domain x-ray absorption fine structure

The determination of the structure of transient molecules, such as photoexcited states, in disordered media (such as in solution) usually requires methods with high temporal resolution. The transient molecular structure of a reaction intermediate produced by photoexcitation of NiTPP-L2 (NiTPP, nickeltetraphenylporphyrin; L, piperidine) in solution was determined by x-ray absorption fine structure (XAFS) data obtained on a 14-nanosecond time scale from a third-generation synchrotron source. The XAFS measurements confirm that photoexcitation leads to the rapid removal of both axial ligands to produce a transient square-planar intermediate, NiTPP, with a lifetime of 28 nanoseconds. The transient structure of the photodissociated intermediate is nearly identical to that of the ground state NiTPP, suggesting that the intermediate adopts the same structure as the ground state in a noncoordinating solvent before it recombines with two ligands to form the more stable octahedrally coordinated NiTPP-L2.     

Quantum criticality: competing ground states in low dimensions

Small changes in an external parameter can often lead to dramatic qualitative changes in the lowest energy quantum mechanical ground state of a correlated electron system. In anisotropic crystals, such as the high-temperature superconductors where electron motion occurs primarily on a two-dimensional square lattice, the quantum critical point between two such lowest energy states has nontrivial emergent excitations that control the physics over a significant portion of the phase diagram. Nonzero temperature dynamic properties near quantum critical points are described, using simple theoretical models. Possible quantum phases and transitions in the two-dimensional electron gas on a square lattice are discussed.     

球与定轴转动杆在完全弹性碰撞过程中的能量转换(b)

通过求解球与定轴转动杆完全弹性碰撞过程的非线笥动力学微分方程组,研究了碰撞过程中动能与压缩变形能之间的相互转换。得出了碰撞始末球的平动动能与杆绕定轴的转动动能之和明显不守恒的结论。     

Probing the carrier capture rate of a single quantum level

The performance of many semiconductor quantum-based structures is governed by the dynamics of charge carriers between a localized state and a band of electronic states. Using scanning tunneling spectroscopy, we studied the transport of inelastic tunneling electrons through a prototypical localized state: an isolated dangling-bond state on a Si(111) surface. From the saturation of the current at an energy resonant with this state, the hole capture rate by the dangling bond was determined. By further mapping the spatial extension of its wave function, the localized nature of the level was found to be consistent with the small magnitude of its cross section. This approach illustrates how the microscopic environment of a single defect critically affects its carrier dynamics.     

Persistent cultural systems

I have indicated here some features of a kind of entity which I have called a cultural identity system, and I have focused on a variety of this general type-the persistent system. In general terms it is best described as a system of beliefs and sentiments concerning historical events. I suggest using the term "a people" for the human beings who, at any given time, hold beliefs of this kind. These are phenomena with which we have been long familiar, but they have not been systematically studied by any but a few investigators. I have emphasized that a persistent system is a cumulative cultural phenomenon, an open-ended system that defines a course of action for the people believing in it. Such peoples are able to maintain continuity in their experience and their conception of themselves in a wide variety of sociocultural environments. I hold that certain kinds of identifiable conditions give rise to this type of cultural system. These may best be summarized as an oppositional process involving the interactions of individuals in the environment of a state or a similar large-scale organization. The oppositional process frequently produces intense collective consciousness and a high degree of internal solidarity. This is accompanied by a motivation for individuals to continue the kind of experience that is "stored" in the identity system in symbolic form. The persistent identity system is more stable as a cultural structure than are large-scale political organizations. When large-scale states disintegrate, they often appear to decompose into cultural systems of the persistent type. Large-scale organizations also give rise to the kind of environment that can result in the formation of new persistent systems. It is possible that, while being formed, states depend for their impetus on the accumulated energy of persistent peoples. A proposition for consideration is that states tend to dissipate the energy of peoples after transforming that energy into state-level integrations, and then regularly break down in the absence of mechanisms for maintaining human motivations in the large-scale organizations that they generate.     

Countercurrent chromatography with flow-through coil planet centrifuge

We have developed a new method of countercurrent chromatography which employs a vertical helical tube in the centrifugal field. The helical tube is arranged so that it does not rotate as it revolves, thus eliminating the need for rotating seals. When the gyrating tube is filled with either phase and the other phase is introduced into the tube in the proper direction, an equilibrium state results in which the two phases are split into multiple alternating segments within the coil. Each phase oscillates to and fro with the rotation as the moving phase is steadily eluted out through the other end of the tube. Consequently, solutes introduced into the tube are subjected to a rapid partition process, resulting in an efficient chromatographic separation without the complications arising from solid supports. The method is illustrated by the microanalytical separation of dinitrophenyl amino acids and can be used on a preparative scale.