Multi-level Transition Research Articles

Mechanism and thermodynamics of multilevel structural transitions in liquid crystals under external actions

The temperature dependence of the viscosity η and electric conductivity σ of high-, low- and very-low-density blood serum lipoproteins and apolipoprotein A-I is studied. The study reveals an anomalous range of T c at (35–38) ± 0.5 °C. The width of the transition is 2 °C. The viscous flow enthalpy, the activation energy Δ H, the transition enthalpy Δ H tr and the temperature coefficients Δη / Δ T and Δ σ/ Δ T on either side of T c are calculated. For all lipoprotein classes, the observed anomalous changes in viscosity and electric conductivity are due to structural phase transitions in the physiological temperature range. They are observed in both lipid and protein components of lipoproteins. Because Δ H tr in high-density lipoproteins is low, it is thought that phospholipids feature an oriented A ↔ C smectic transition referring to the second-order transition. The structural transition in apolipoprotein A-I, because of its very low enthalpy, can also be referred to the second-order transition. This transition results from the change in symmetry in response to a change in the secondary protein structure (coil ↔ β-structure transition). In very-low-density lipoproteins, the transition is likely to be of the smectic → cholesteric type. Similar structural transitions were detected in erythrocyte membranes of participants of a Soviet-Canadian transarctic ski expedition as the result of extreme conditions. The findings suggest that liquid crystalline biostructures (lipoproteins, cell membranes) can assume various thermo-dynamic states that affect their properties. This fact makes liquid crystalline biostructures similar in behavior to solid crystals in external force fields.

Multilevel Transitions of Closely Arranged Spin Valve Pillars Using Spin Transfer Switching

Two closely arranged spin valve pillars sharing a pair of top and bottom electrodes were fabricated and their spin transfer switching (STS) characteristics were investigated. Each pillar was a 300 times 100 nm rectangle, such that the distance d between two pillars was varied up to 1 mum . The STS curves of a single pillar and closely arranged pillars with the distance d of 1 mum showed single-step transitions, but the STS curves of closely arranged pillars with the distance d of 0.3 mum showed clear two-step transitions. We found that the plateau width of the intermediate resistive state of the two-step transitions can be controlled by the distance >d . The basis for this stable intermediate resistive state seemed to be magnetic interactions and the intrinsic switching mode of STS.

Multimode entanglement of light and atomic ensembles via off-resonant coherent forward scattering

Quantum theoretical treatment of coherent forward scattering of light in a polarized atomic ensemble with an arbitrary angular momentum is developed. We consider coherent forward scattering of a weak radiation field interacting with a realistic multilevel atomic transition. Based on the concept of an effective Hamiltonian and on the Heisenberg formalism, we discuss the coupled dynamics of the quantum fluctuations of the polarization Stokes components of propagating light and of the collective spin fluctuations of the scattering atoms. We show that in the process of coherent forward scattering, this dynamics can be described in terms of a polariton-type spin wave created in the atomic sample. Our work presents a general example of an entangling process in the system of collective quantum states of light and atomic angular momenta, previously considered only for the case of spin-$\frac{1}{2}$ atoms. We use the developed general formalism to test the applicability of the spin-$\frac{1}{2}$ approximation for modeling the quantum nondemolishing measurement of atoms with a higher angular momentum.

Coarse-grained Picture for Controlling Complex Quantum Systems

Controlling atomic and molecular processes by laser fields is one of current topics in physics and chemistry, and there are various control schemes applied to such processes. These strategies are known to work when the system to be controlled is rather simple or small. However, in reality, the system can become ‘‘complex,’’ where the dynamics will be described by multi-level–multi-level transitions with a random interaction. Although the laser field can be obtained by optimal control theory (OCT) even for such complex systems, it is difficult to analyze the controlled dynamics because such a field obtained numerically is often too complicated to interpret. Hence it is desirable to have a more analytical point of view. It is well known that the pulse or its generalizations can be employed to control few-level problems. Recently, an analytic result for multi-level control problems between general quantum states has been reported. The scheme is based on STIRAP, and assumes an intermediate state coupled to the initial and target states. Though the scheme can accomplish perfect control, it relies on the energy level picture of a quantum system, so it is difficult to apply the scheme to large systems. In this short note, we propose a new approach to obtain an analytic optimal field for complex quantum systems. Under a ‘‘coarse-grained picture’’ with OCT, which is valid for such a complex system, we derive an analytic expression for the optimal field which steers initial states to target states in a certain limit. By numerically solving Schrodinger equations, we confirm that perfect control is actually achieved. This point is important because the zeroth-order solutions of OCT, which look similar to our result, are not guaranteed to achieve perfect control. Another point is that our final expression does not require detailed information from the energy level picture, so that it is easy to apply to large quantum systems, in principle. We use OCT as a theoretical vehicle. The aim of OCT is to obtain an optimal field ðtÞ which guides the system from an initial state j ii at t 1⁄4 0 to a target state j f i at some specific time t 1⁄4 T . According to the OCT scheme by Zhu et al., the optimal field for the Hamiltonian H1⁄2 ðtÞ 1⁄4 H0 þ ðtÞV is given by

Phase-coherent multilevel two-photon transitions in cold Rb atoms: Ultrahigh-resolution spectroscopy via frequency-stabilized femtosecond laser

A two-photon transition in cold Rb atoms will be probed with a phase-coherent wide bandwidth femtosecond laser comb. Frequency domain analysis yields a high-resolution picture where phase coherence among various transition pathways through different intermediate states produces interference effects on the resonantly enhanced transition probability. This result is supported by the time domain Ramsey interference effect. The two-photon transition spectrum is analyzed in terms of the pulse repetition rate and carrier frequency offset, leading to a cold-atom-based frequency stabilization scheme for both degrees of freedom of the femtosecond laser.

Simulation of land development through the integration of cellular automata and multicriteria evaluation

Cellular automata (CA) simulation has become a popular method of exploring the behaviour of all kinds of self-organising systems. The city may clearly be viewed as such a system but one with a particularly complex set of transition rules. Many natural processes such as the spread of fire or vegetation can be modelled by a simple set of local rules. Insofar as the development of a piece of land depends on the neighbourhood situation as well as on the characteristics of a site, urban evolution can be treated in much the same way, with transition rules translating the evaluation of the location into a land conversion outcome. If this modelling paradigm is to be used to gain insight into real-world urban development processes, there is a need to discover ways of capturing the richness of land conversion behaviour in the simplifying mechanisms of CA. Our paper contributes to this research agenda by integrating multicriteria evaluation (MCE) into a CA simulation in order to define nondeterministic, multidimensional, and multilevel transition rules. An analytical hierarchy process is used to implement MCE-derived transition rules. The integrated MCE – CA model may be used in a gaming mode to explore how urban form evolves under different development regimes caricatured by the set of multicriteria weights. We use it to test loosely hypotheses about the nature of the regimes that have governed the expansion of a fast-growing southern Chinese city.

Multilevel rotational transitions in the intermediate stage of three-photon ionization of molecules

Ionization and dissociation of diatomic molecules induced by a weak field (after preliminarily populating an intermediate level) and by intense, linearly polarized monochromatic radiation have been studied. Field-induced mixing of rotational components of various electronic-vibrational states of molecules (such as CO, NO, etc.) at field strength f∼10−4–10−5 atomic units can lead to migration among states with different angular momenta J. Therefore, ions with rotational momenta J+ much higher than those prescribed by selection rules for three-photon absorption can be formed from molecules in the ground state. The possibility of selective formation of ions with J+≫1 and zero projection of the angular momentum on the polarization vector of the external electromagnetic radiation has been investigated.

原子炉診断への応用を目的とした故障生起汎化知識の表現

A new method for diagnostic knowledge acquisition based on the generalized failure mechanism knowledge (GFMK) has been proposed in order to solve the problem of incompleteness of the diagnostic knowledgebase. The present study consists of two main issues; derivation of the GFMK from actually experienced events and the failure mode estimation based on the plant model. Failure events and objective plant are described by multi-level state transition model and multi-level, multi-attribute model, respectively. A systematic knowledge representation has been obtained through combined use of these two methods. The validity of the failure events representation method and the capability of the GFMK extraction from failure events have been demonstrated by applying proposed methodology to the actually experienced failure events. The failure mode estimation capability has been demonstrated by applying the GFMK to the primary loop recirculation system of boiling water reactor represented by the proposed model.

Mean detector for slow fluctuations

Detectors for noise measurements at low frequencies need to be capable of integrating over long periods and should also be immune from drifts of datum level. A circuit satisfying these requirements is described and its performance is quoted. The technique employs a combination of integration and a multilevel transit counting circuit.

Flux Jumping in Nb +25% Zr Wire

Flux jumping has been investigated in both cold-worked and heat-treated (1 h at 700°C) 0.025-cm-diam Nb+25% Zr wire wound into solenoids and noninductive coils of approximate dimensions: i.d.=0.3 cm, o.d.=1.2 cm, length=2.6 cm. The measurements taken at 4.2°K were: (1) The induced voltage pulses vs applied magnetic field with both I=0 and a preset transport current. (2) The induced voltage pulses vs coil current for H=0 and with a preset uniform external field. For the case with no transport current in the coil (I=0) when the external field was increased smoothly from zero, a squence of very sharp voltage pulses (flux jumps) were induced in the coil, and recorded simultaneously on both an X-Y recorder and an oscilloscope. These flux jumps had the following general characteristics for all the cases discussed in this paper: (1) Starting from well defined initial conditions, the pulse always appeared at about the same place in the field sweeping cycle. (2) The polarity of the pulses is reversed when the direction of field change is reversed. (3) The pattern of these pulses was essentially unchanged when the field sweep rate was increased from 7 to 340 G/sec. As a result of these measurements, we have obtained new insight into both the multilevel transitions of noninductive coils and the phenomenon known as degradation of solenoids. Two successful methods are described for partially overcoming the excessive degradation of a solenoid made from heat treated wire. The flux jumps are interpreted according to an extension of a model proposed by both Bean and London.