Sample Size Dependence of Second Magnetizaion Peak in Type-ⅡSuperconductors

We show that the second magnetization peak(SMP),i.e.,an increase in the magnetization hysteresis loop width in type-11 superconductors,vanishes for samples smaller than a critical size,We argue that the SMP is not related to the critical current enhancement but can be well explainde within a frameword of the thermomagenetic flux-jump in stability theory,where flux jumps reduce the absolute irreversible magnetization relative to the isothermal critical state value at low enough magnetic fields.The recovering of the isothermal critical sate with increasing field leads to the SMP.The low-field SMP takes place in both low-T.conventional and high*t.unconventional superconductors.Our results show that the rsstoration of the isothermal critical state is rsponsible for the SMP occurrence in both cases.     

SELF-LEARNING FUZZY CONTROL RULES USING GENETIC ALGORITHMS

This papcr presents a new genetic algorithms(GAs)-based method for self-learniag fuzzy control rules. An improved GA is used to learn to optimally select the fuzzy membership functions of the linguistic labels in the condition portion of each rule, and to automatically generate fuzzy control actions under each condition. The dynamics of the controlled system is unknown to the GA. The only information for evaluating performance is a failure signal indicating that the controlled system is out of control. We compare its performance with that of other learning methods for the same problem. We also examine the ability of the algorithm to adapt to changing conditions. Simulation results show that such an approach for self-learning fuzzy control rules is both effective and robust.     

Influence of magnetic current on the ground state entanglement in an isotropic transverse XY chain

We study the ground state entanglement in a three-qubit XY chain under the influence of a magnetization current. It is found that the ground state changes from a W state to a disentangled state as the magnetic field varies. When the Lagrange multiplier λ> , namely under a strong magnetic current, the ground state holds onto a W state for a large range of the magnetic field strength. A phase transition to the magnetization-current phase occurs under a certain condition.     

Influence of magnetic current on the ground state entanglement in an isotropic transverse XY chain

We study the ground state entanglement in a three-qubit XY chain under the influence of a magnetization current. It is found that the ground state changes from a W state to a disentangled state as the magnetic field varies. When the Lagrange multiplier λ> , namely under a strong magnetic current, the ground state holds onto a W state for a large range of the magnetic field strength. A phase transition to the magnetization-current phase occurs under a certain condition.     

The bubble leakage mechanism for vertical upflows by the phase separation concept

Recently,our research group proposed the phase separation condenser tube,in which a mesh cylinder was inserted to form the flow structure of‘‘gas near the tube wall and liquid in the tube core’’,significantly enhance the condensation heat transfer.But the bubble leakage towards the core region may worsen the heat transfer enhancement.In order to prevent the bubble leakage,the critical criterion was proposed based on the Young–Laplace equation,considering the inertia force,viscous force and pulsating flow.It was found that the critical criterion depends on the dimensionless parameter G*,the We number and a coefficient C.The numerical model was developed in terms of the volume of fluid method to predict the two-phase laminar flow in the phase separation condenser tube.The results show that the bubble leakage takes place at the bubble tip,which is agreed with the experimental observations.The critical curve distinguishing the non-bubble-breaking and bubble-breaking was obtained by comparing the bubble dynamics at different G*and We.The coefficient C was determined.The critical criterion for the bubble leakage is given as G We0:22We0:99349 G4:7 103 We0:00651t196:39We0:006514cosa DHW,providing the design and operation guidance for the phase separation condenser tube.     

A comparison of transition state of phenol in H-atom abstraction by methyl and methylperoxyl radicals

DFT method was employed to locate transition state for H-atom transfer from phenol by methyl radical and methylperoxyl radical. The reaction pathway energy profiles and the structure of transition state show that a common feature is the out-of-plane structure of the transition state: in contrast to the en- ergetic minima of a hydrogen-bonded intermediate, the hydrogen bond in transition structures is con- siderably twisted out of the aromatic ring. From the values of enthalpy (△H) and activation energy (Ea) obtained, it is found that the rate of the reaction of peroxyl radical with phenolic antioxidant is higher than that of alkyl radical with antioxidant. Spin density distributions show that the electron transmis- sion is between methyl (methylperoxyl) radical and phenol.     

A new method for detecting line spectrum of ship-radiated noise using Duffing oscillator

A detection scheme for line spectrum of ship-radiated noise is proposed using Duffing oscillator. The chaotic trajectory of Duffing oscillator is analyzed and the state equation of the system is improved to detect weak periodic signals in different frequencies. According to the simulation results, the phase transforms of Duffing oscillator are sensitive to periodic signals and immune to the random noise and the periodic interference signals which have larger angular frequency difference from the referential signal. By employing Lyapunov exponents in the field of detection as the criteria for chaos, the phase transforms of dynamic behaviors in quantity are successfully determined. Meanwhile, the threshold value in critical state has been evaluated more accurately. Based on the phase transforms of Duffing oscillator, a new method for detecting line spectrum of ship-radiated noise is given. Three types of ship-radiated noise signals are analyzed and the values of line spectrum are acquired successfully by this method. The experimental results show that this method has high sensitivity and high resolution.     

A comparison study on the melt crystallization kinetics of long chain branched and linear isotactic polypropylenes

The isothermal and non-isothermal crystallization kinetics of LCBPP and linear-iPP was investigated by optical microscopy and differential scanning calorimetry （DSC）. The optical microscopy results in the isothermal crystallization process show that the crystals of LCBPP grow slower than the crystals of the linear-iPP. This originates from the low chain mobility, or in other words, the lower chain diffusion rate of LCBPP due to the existence of long side chains. The DSC results in the isothermal crystallization process show that the LCBPP exhibits, however, a higher overall crystallization rate with respect to the linear-iPP. This is related to the higher nucleation ability of LCBPP since the isothermal crystallization process of both LCBPP and linear-iPP are nucleation-dominated. Avrami analysis indicates that the nucleation nature and crystal growth manner of LCBPP and linear-iPP are about the same. The analyses of the non-isothermal crystallization processes indicate an increment in crystallization rate with increasing cooling rate. But at any cooling rate, the linear-iPP crystallizes more quickly than the LCBPP. This implies that the non-isothermal crystallization processes of LCBPP and linear-iPP are diffusion-dominated, in which the lower chain diffusion rate of LCBPP results in the slower crystallization of it.     

Convex Duality in Portfolio Optimization under Constraints and with Higher Interest Rate for Borrowing

We study the stochastic control problem of maximizing expected utility from terminal wealth and/or consumption, when the portfolio is constrained to take values in a given closed, convex subset of Rd, and in the presence of a higher interest rate for borrowing. The setting is that of a continuous-time, Ito process model for the underlying asset prices. The solution of the unconstrained problem is given. In addition to the original constrained optimization problem, a so-called combined dual problem is introduced. Finally, the existence question of optimal processes for both the dual and the primal problem is settled.     

A P2P load balancing-supported ID management algorithm

Load balancing is a critical issue in peer-to-peer networks. DHT (distributed hash tables) do not evenly partition the hash-function range, and some nodes get a larger portion of it. The loads of some nodes are as much as O(log n) times the average. In this paper, a low-cost, decentralized algorithm for ID allocation with complete knowledge in DHT-based system is proposed. It can adjust system load on nodes’ departure. It is proved that the ratio of longest arc to shortest arc is no more than 4 with high probability when network scale increases non-strictly. When network scale decreases from one stable state to another, algorithm can repair the unevenness of nodes distribution. The performance is analyzed in simulation. Simulating results show that updating messages only occupy a little of network bandwidth.     

Electron-spin domains: magnetic enhancement of superconductivity

An inhomogeneous superconducting state, not yet conclusively identified, was predicted by Fulde and Ferrell and Larkin and Ovchinnikov (FFLO) to arise in superconductors with strong Pauli limiting, a consequence of the electrons' Zeeman (spin) energy in a magnetic field. Radovan et al. propose that the observed cascades of steps in magnetization of the heavy fermion superconductor CeCoIn5, within the recently discovered second low-temperature state, are due to transitions between Landau-level (LL) states with different m-quanta vortices, expected under certain conditions when the magnetic field is swept within the FFLO state. The authors then conclude that the observed steps in magnetization constitute a proof that the low-temperature state in CeCoIn5 is indeed an FFLO state. We argue that this interpretation of the observed steps in magnetization cannot be supported on either quantitative or qualitative grounds.     

Superinsulator and quantum synchronization

Synchronized oscillators are ubiquitous in nature, and synchronization plays a key part in various classical and quantum phenomena. Several experiments have shown that in thin superconducting films, disorder enforces the droplet-like electronic texture--superconducting islands immersed into a normal matrix--and that tuning disorder drives the system from superconducting to insulating behaviour. In the vicinity of the transition, a distinct state forms: a Cooper-pair insulator, with thermally activated conductivity. It results from synchronization of the phase of the superconducting order parameter at the islands across the whole system. Here we show that at a certain finite temperature, a Cooper--air insulator undergoes a transition to a superinsulating state with infinite resistance. We present experimental evidence of this transition in titanium nitride films and show that the superinsulating state is dual to the superconducting state: it is destroyed by a sufficiently strong critical magnetic field, and breaks down at some critical voltage that is analogous to the critical current in superconductors.     

Magnetic enhancement of superconductivity from electron spin domains

Since the discovery of superconductivity, there has been a drive to understand the mechanisms by which it occurs. The BCS (Bardeen-Cooper-Schrieffer) model successfully treats the electrons in conventional superconductors as pairs coupled by phonons (vibrational modes of oscillation) moving through the material, but there is as yet no accepted model for high-transition-temperature, organic or 'heavy fermion' superconductivity. Experiments that reveal unusual properties of those superconductors could therefore point the way to a deeper understanding of the underlying physics. In particular, the response of a material to a magnetic field can be revealing, because this usually reduces or quenches superconductivity. Here we report measurements of the heat capacity and magnetization that show that, for particular orientations of an external magnetic field, superconductivity in the heavy-fermion material CeCoIn(5) is enhanced through the magnetic moments (spins) of individual electrons. This enhancement occurs by fundamentally altering how the superconducting state forms, resulting in regions of superconductivity alternating with walls of spin-polarized unpaired electrons; this configuration lowers the free energy and allows superconductivity to remain stable. The large magnetic susceptibility of this material leads to an unusually strong coupling of the field to the electron spins, which dominates over the coupling to the electron orbits.     

Quantum critical behaviour in a high-T(c) superconductor

Quantum criticality is associated with a system composed of a nearly infinite number of interacting quantum degrees of freedom at zero temperature, and it implies that the system looks on average the same regardless of the time- and length scale on which it is observed. Electrons on the atomic scale do not exhibit such symmetry, which can only be generated as a collective phenomenon through the interactions between a large number of electrons. In materials with strong electron correlations a quantum phase transition at zero temperature can occur, and a quantum critical state has been predicted, which manifests itself through universal power-law behaviours of the response functions. Candidates have been found both in heavy-fermion systems and in the high-transition temperature (high-T(c)) copper oxide superconductors, but the reality and the physical nature of such a phase transition are still debated. Here we report a universal behaviour that is characteristic of the quantum critical region. We demonstrate that the experimentally measured phase angle agrees precisely with the exponent of the optical conductivity. This points towards a quantum phase transition of an unconventional kind in the high-T(c) superconductors.     

A one-dimensional chain state of vortex matter.

Magnetic flux penetrates isotropic type II superconductors in flux-quantized vortices, which arrange themselves into a lattice structure that is independent of the direction of the applied field. In extremely anisotropic high-transition-temperature (high-Tc) superconductors, a lattice of stacks of circular 'pancake' vortices forms when a magnetic field is applied perpendicular to the copper oxide layers, while an orthogonal elongated lattice of elliptical Josephson vortices forms when the applied field is parallel to the layers. Here we report that when a tilted magnetic field is applied to single crystals of Bi2Sr2CaCu2O8+delta, these lattices can interact to form a new state of vortex matter in which all stacks of pancake vortices intersect the Josephson vortices. The sublattice of Josephson vortices can therefore be used to manipulate the sublattice of pancake vortices. This result explains the suppression of irreversible magnetization by in-plane fields as seen in Bi2Sr2CaCu2O8+delta crystals, a hitherto mysterious observation. The ability to manipulate sublattices could be important for flux-logic devices, where a 'bit' might be represented by a pancake vortex stack, and the problem of vortex positioning is overcome through sublattice interactions. This also enables the development of flux transducers and amplifiers, considerably broadening the scope for applications of anisotropic high-Tc superconductors.     

A hidden pseudogap under the 'dome' of superconductivity in electron-doped high-temperature superconductors

The ground state of superconductors is characterized by the long-range order of condensed Cooper pairs: this is the only order present in conventional superconductors. The high-transition-temperature (high-T(c)) superconductors, in contrast, exhibit more complex phase behaviour, which might indicate the presence of other competing ground states. For example, the pseudogap--a suppression of the accessible electronic states at the Fermi level in the normal state of high-T(c) superconductors-has been interpreted as either a precursor to superconductivity or as tracer of a nearby ground state that can be separated from the superconducting state by a quantum critical point. Here we report the existence of a second order parameter hidden within the superconducting phase of the underdoped (electron-doped) high-T(c) superconductor Pr2-xCe(x)CuO4-y and the newly synthesized electron-doped material La2-xCe(x)CuO4-y (ref. 8). The existence of a pseudogap when superconductivity is suppressed excludes precursor superconductivity as its origin. Our observation is consistent with the presence of a (quantum) phase transition at T = 0, which may be a key to understanding high-T(c) superconductivity. This supports the picture that the physics of high-T(c) superconductors is determined by the interplay between competing and coexisting ground states.     

Nanoengineering of Flux Pinning Sites in High-Tc Superconductors

Volume pinning forces were determined for a variety of bulk high-Tc superconductors of the 123-type from magnetization measurements. By means of scaling of the pinning forces, the acting pinning mechanisms in various temperature ranges were identified. The Nd-based superconductors and some YBCO crystals exhibited a dominating pinning of the δTc-type (i.e. , small, superconducting pinning sites). In contrast to this, the addition of insulating 211 particles provided pinning of the δ/-type; providing effective pinning in the entire temperature range acting as a "background" pinning mechanism for the peak effect. Due to the small coherence lengths of the high-Tc compounds, effective pinning sites are defects or particles of nanometer size relative to ζ3. Integral magnetic measurements of the magnetization as a function of temperature in large applied magnetic fields (up to 7 T) revealed that practically all high-Tc compounds were spatially inhomogeneous, which could be caused by oxygen deficiency (YBCO)     

A Bragg glass phase in the vortex lattice of a type II superconductor

Although crystals are usually quite stable, they are sensitive to a disordered environment: even an infinitesimal amount of impurities can lead to the destruction of crystalline order. The resulting state of matter has been a long-standing puzzle. Until recently it was believed to be an amorphous state in which the crystal would break into 'crystallites'. But a different theory predicts the existence of a novel phase of matter: the so-called Bragg glass, which is a glass and yet nearly as ordered as a perfect crystal. The 'lattice' of vortices that contain magnetic flux in type II superconductors provide a good system to investigate these ideas. Here we show that neutron-diffraction data of the vortex lattice provides unambiguous evidence for a weak, power-law decay of the crystalline order characteristic of a Bragg glass. The theory also predicts accurately the electrical transport properties of superconductors; it naturally explains the observed phase transitions and the dramatic jumps in the critical current associated with the melting of the Bragg glass. Moreover, the model explains experiments as diverse as X-ray scattering in disordered liquid crystals and the conductivity of electronic crystals.     

Resonance as a measure of pairing correlations in the high-Tc superconductor YBa2Cu3O6.6

One of the most striking properties of the high-transition-temperature (high-Tc) superconductors is that they are all derived from insulating antiferromagnetic parent compounds. The intimate relationship between magnetism and superconductivity in these copper oxide materials has intrigued researchers from the outset, because it does not exist in conventional superconductors. Evidence for this link comes from neutron-scattering experiments that show the unambiguous presence of short-range antiferromagnetic correlations (excitations) in the high-Tc superconductors. Even so, the role of such excitations in the pairing mechanism for superconductivity is still a subject of controversy. For YBa2Cu3O(6+x), where x controls the hole-doping level, the most prominent feature in the magnetic excitation spectrum is a sharp resonance (refs 6-11). Here we show that for underdoped YBa2Cu3O6.6, where x and Tc are below their optimal values, modest magnetic fields suppress the resonance significantly, much more so for fields approximately perpendicular to the CuO2 planes than for parallel fields. Our results indicate that the resonance measures pairing and phase coherence, suggesting that magnetism plays an important role in high-Tc superconductivity. The persistence of a field effect above Tc favours mechanisms in which the superconducting electron pairs are pre-formed in the normal state of underdoped copper oxide superconductors, awaiting transition to the superconducting state.