Behavior of the Hamiltonian's Eigenstates Around the Avoided Level Crossing

We numerically show the changing of eigenstates of the Hamiltonian as a function of a control parameter governing the strength of a non-integrable perturbation. The eigenstates change abruptly at avoided level crossing. After the avoided level crossing, they tend to restore their original form before the avoided level crossing, and exchange their distribution, especially for those which can be treated as isolated two-body collisions. But in general, the eigenstates have some changings after the avoided crossing, and the symmetries of the system are broken down locally at this kind of avoided level crossings.     

Muon level crossing resonance in diamagnetic systems-general considerations

This paper is a general discussion of the nature of the level crossing phenomena in diamagnetic systems, with particular emphasis on the quadrupolar LCR as evidenced in Cu. The system exhibits some surprises at higher temperatures which indicate that the level crossing technique contains hitherto unsuspected capabilities for μSR.     

Butterfly hysteresis loop at nonzero bias field in antiferromagnetic molecular rings: cooling by adiabatic magnetization

At low temperatures, the magnetization of the molecular ferric wheel NaFe6 exhibits a step at a critical field B(c) due to a field-induced level crossing. By means of high-field torque magnetometry we observed a hysteretic behavior at the level crossing with a characteristic butterfly shape which is analyzed in terms of a dissipative two-level model. Several unusual features were found. The nonzero bias field of the level crossing suggests the possibility of cooling by adiabatic magnetization.     

Optical potentials for elastic heavy ion scattering

The zero-field level crossing effect in selective reflection from an atomic vapour is calculated for normally incident radiation using a theory which, unlike the conventional dispersion theory, includes the effect of transient polarization behaviour due to diffuse wall collisions of vapour atoms. Both longitudinal and transverse magnetic fields are considered. At low vapour densities we find a narrowing of the level crossing curve in selective reflection relative to its width in the conventional dispersion theory. The narrowing is calculated as a function of the ratio of the homogeneous and inhomogeneous line width of the vapour for a Maxwellian velocity distribution of the vapour atoms and spectrally uniform incident radiation. The theory of this paper offers an explanation for recent observations of narrowing of level crossing curves in selective reflection.     

Model for Risk Calculation and Reliability Comparison of Level Crossings

There is not a single country in the world that is so rich that it can remove all level crossings or provide their denivelation in order to absolutely avoid the possibility of accidents at the intersections of railways and road traffic. In the Republic of Serbia alone, the largest number of accidents occur at passive crossings, which make up three-quarters of the total number of crossings. Therefore, it is necessary to constantly find solutions to the problem of priorities when choosing level crossings where it is necessary to raise the level of security, primarily by analyzing the risk and reliability at all level crossings. This paper presents a model that enables this. The calculation of the maximal risk of a level crossing is achieved under the conditions of generating the maximum entropy in the virtual operating mode. The basis of the model is a heterogeneous queuing system. Maximum entropy is based on the mandatory application of an exponential distribution. The system is Markovian and is solved by a standard analytical concept. The basic input parameters for the calculation of the maximal risk are the geometric characteristics of the level crossing and the intensities and structure of the flows of road and railway vehicles. The real risk is based on statistical records of accidents and flow intensities. The exact reliability of the level crossing is calculated from the ratio of real and maximal risk, which enables their further comparison in order to raise the level of safety, and that is the basic idea of this paper.     

Optical resolution beyond the natural linewidth: A level-crossing experiment on the 32 P 3/2 level of sodium using a tunable dye laser

A level crossing experiment on the hyperfine structure of the 3² P _3/2 level of Na²³ was performed using a nitrogen laser pumped dye laser for the excitation of the Na atoms. The fluorescent light was observed in time intervals which were initiated up to seven lifetimes after excitation. Therefore the signal was only determined by atoms having survived in the excited state up to the initiating time. The minimum linewidth observed was 6 times smaller than the natural width. Neighbouring crossing signals, which overlap in a level crossing experiment using time integral observation of the fluorescent light, could be resolved. The accuracy of the hyperfine constants of the 3² P _3/2 level could be improved.     

Trace Distance and Level Crossing in Spin-Bosen Model with Added Classical Driving Fields

By making use of the trace distance as a measure we investigate the influence of classical driving fields on a open quantum system when the system and its environment are initially in a correlated state. It is shown that the amount of trace distance is sensitive to the classical driving fields which implies that the information flowing between open system and its environment can be controlled by the classical driving fields. Furthermore, we also explore the dependence of the trace distance on the initial parameters when the total system is considered in the thermal equilibrium state. We find that the trace distance on the coupling strength can be used to demonstrate the level crossing of the ground state of the system. In particular, the classical driving fields have significant effect on the level crossing of the ground state.     

Level mixing resonances on oriented nuclei

The level crossing and level mixing resonance methods have been developed in order to enable the measurement of quadrupole interaction frequencies of nuclei with lifetimes between microseconds and minutes in solids. Both methods are shown to be better suited for application 1n this lifetime region than the existing ones. Only the level mixing resonance method can be applied to nuclei with lifetimes up to several minutes. A review of our level crossing and level mixing experiments is also given in this paper.     

Partial Wave Crossing Relations for Meson-Baryon Scattering

Three different types of relations for meson-baryon partial wave amplitudes following from the s ↔ u crossing symmetry of the invariant amplitudes are investigated: i) the partial wave crossing relations directly derived from the s ↔ u crossing symmetry and the partial wave projection, ii) the partial wave crossing relations following from a combined use of s ↔ u crossing symmetry and analyticity, and iii) the crossing sum rules, which are a direct consequence of the s ↔ u crossing symmetry. The kernels entering the crossing relations i) and ii) are given in an analytic form, valid for arbitrary angular momentum. Their properties are studied in detail. By means of the partial wave crossing relations ii) it is demonstrated that u-channel exchange of a resonance leads to a resonance-like behaviour of the partial wave amplitudes on the crossed physical cut. This phenomenon is described in terms of “pseudoresonances”. Finally the crossing sum rules iii) and their practical use are thoroughly discussed, and they are compared with the partial wave crossing relations i) and ii). Special attention is paid to the crossing symmetry constraints on the S-wave amplitudes. As a result of these investigations we present a crossing symmetric ansatz for these amplitudes which gives a more reliable parametrization than the usual effective range approximation.     

Magnetic field effect on the luminescence of the paired Ag- ions in alkali halides (II)

The fine structure of the relaxed excited state of paired Ag^- ions in KBr and RbBr is studied by measuring the magnetic field effects on the decay time of the luminescence at about 2 K. The experimental results obtained are found to be well explained theoretically by assuming thermal equilibrium, with the exception of an anomalous change at about 43 kG(KBr) or at about 34 kG(RbBr). The anomalous change exhibits a level crossing and also shows that the Zeeman levels do not reach the thermal equilibrium at least in the neighborhood of the level crossing.     

Gate adjustable coherent three and four level mixing in a vertical quantum dot molecule

We study level mixing in the single-particle energy spectrum of one of the constituent quantum dots in a vertical double quantum dot by performing magneto-resonant-tunneling spectroscopy. The device used in this study differs from previous vertical double quantum dot devices in that the single side gate is now split into four separate gates. Because of the presence of natural perturbations caused by anharmonicity and anisotropy, applying different combinations of voltages to these gates allows us to alter the effective potential landscape of the two dots and hence influence the level mixing. We present here preliminary results from one three level crossing and one four level crossing high up in the energy spectrum of one of the probed quantum dots, and demonstrate that we are able to change significantly the energy dispersions with magnetic field in the vicinity of the crossing regions.     

简并四波混频中的能级交叉效应

我们用微扰方法计算了近简并准二能级系统的三阶非线性极化率x⁽³⁾(-ω;ω,ω,-ω)。研究了简并四波混频的能级交叉效应,并与共振荧光的能级交叉效应比较。指出简并四波混频的能级交叉效应可用来测量上能级及下能级的弛豫速率。 关键词：     

A Critical Look at 50 Years Particle Theory from the Perspective of the Crossing Property

The crossing property is perhaps the most subtle aspect of the particle-field relation. Although it is not difficult to state its content in terms of certain analytic properties relating different matrixelements of the S-matrix or formfactors, its relation to the localization- and positive energy spectral principles requires a level of insight into the inner workings of QFT which goes beyond anything which can be found in typical textbooks on QFT. This paper presents a recent account based on new ideas derived from “modular localization” including a mathematic appendix on this subject. Its main achievement is the proof of the crossing property from a two-algebra generalization of the KMS condition.     

Repulsion of resonance states and exceptional points

Level repulsion is associated with exceptional points which are square root singularities of the energies as functions of a (complex) interaction parameter. This is also valid for resonance state energies. Using this concept it is argued that level anticrossing (crossing) must imply crossing (anticrossing) of the corresponding widths of the resonance states. Further, it is shown that an encircling of an exceptional point induces a phase change of one wave function but not of the other. An experimental setup is discussed where this phase behavior, which differs from the one encountered at a diabolic point, can be observed.     

Level crossing in microwave spectroscopy of CH3F

Stark tuned level crossing resonances have been detected in CH₃F through non-linear microwave absorption. In our experiments, the level crossing width is about ten times smaller than the Doppler width.     

Characteristics of Level Anticrossing in Parallel Electric and Magnetic Fields

Using the matrix diagonalization method, we have studied two kinds of level anticrosing of Rydberg cesium atom in parallel electric and magnetic fields. Our numerical results reveal that in the vicinity position of level crossing between different parity states in a magnetic field, the energy levels and other behaviors of the states are quite sensitive to the electric field. We tabulate some features which may be as a guide in experimental verification.     

Simulation of pedestrian flow based on cellular automata: A case of pedestrian crossing street at section in China

One of the purposes of pedestrian studies is to evaluate the effects of a proposed program on the pedestrian facilities before its implementation. In order to evaluate the level of service (LOS) of a pedestrian facility, a microscopic model is built to simulate the process of pedestrian crossing street. Most of the existing models focus on the occupant evacuation flow in buildings; however, they are not appropriate for pedestrians in the traffic. According to the characteristics of pedestrian crossing street at signalized crosswalks, we build a model based on cellular automata. Both of the system size and cell size are coordinate with the reality. Depending on the contrast of three parameters of pedestrian flow between simulation data and the reality data, we found that this model is analogous to the real process of pedestrian crossing street at signalized sections. Finally, simulation and its results can provide guidance for evaluating the effects of pedestrian facilities before their implementation.     

B-type delayed fluorescence of rubreneperoxide in solution.

B-type of delayed fluorescence was observed for the first time for rubreneperoxide. Rubreneperoxide molecules were excited in a two step process. In the first step an excited singlet S₁ is created, which undergoes intersystem crossing to T₁; then T-T absorption creates an excited triplet rubreneperoxide molecule, which returns to the first excited singlet level by intersystem crossing. The recreated first excited singlet of rubreneperoxide decays back to the ground state by emitting B-type of delayed fluorescence.     

类In离子的能级结构参数的研究

在全相对论理论框架下,研究了类In等电子序(Ba VIII-Nd XII)低激发态组态5s~24f和5s`25p间的光谱性质.系统地研究了Breit相互作用和量子电动力学(QED)效应对能级的影响.离子Pr~(~(10+))附近出现相对论轨道4f-5p能级交叉,窄的能级间隔可以使得跃迁波长在现代激光范围,这可能设计成原子钟.计算得到Pr~(10+)基态和激发态磁偶极和电四极超精细结构常数.目前的计算结果可以为实验测量提供理论依据.