Extra Transitions Research Articles

Molecular beam epitaxy, photoluminescence from Mn2+ multiplets and self-trapped exciton states of γ-MnTe single-crystalline thin films

Single-crystalline γ-MnTe thin films with zinc-blende structure were grown epitaxially on InP(111) by molecular beam epitaxy. Two-dimensional growth regime and atomic surface flatness are achieved, and appearance of Laue’s oscillation peaks illustrates the superior crystalline quality and interface of γ-MnTe films. A pseudocrystalbuffer layer is formed at interface releasing the strain led by the large lattice mismatch between γ-MnTe and InP, and then growth of γ-MnTe films with a perfect lattice evidences the high-quality crystallinity in a fully relaxed state. Photoluminescence (PL) emissions from 4T1g(4G) and 4T1(4G) related to Mn2+ ions d-d multiplets are observed with their respective activation energies of ∼142.5 meV and ∼323.5 meV. Such high potentials reflecting the nonradiative recombination indicate the thermal stability of these PL. Moreover, two extra PL transitions assigned to be the emissions from self-trapped exciton (STE) states are found below TN. Time-resolved PL (TRPL) spectra at various temperatures indicate that the relaxation dynamics of photoexcited d-electrons is strongly correlated to the antiferromagnetic ordering transition due to the synergy of magnon, phonon and STE states. These findings suggest that introduction of STE states in a material by controlling its magnetic ordering qualifies the competition in optoelectronics devices.

Absorbing–reflecting factorizations for birth–death chains on the integers and their Darboux transformations

We consider a new way of factorizing the transition probability matrix of a discrete-time birth–death chain on the integers by means of an absorbing and a reflecting birth–death chain to the state 0 and viceversa. First we will consider reflecting–absorbing factorizations of birth–death chains on the integers. We give conditions on the two free parameters such that each of the factors is a stochastic matrix. By inverting the order of the factors (also known as a Darboux transformation) we get new families of “almost” birth–death chains on the integers with the only difference that we have new probabilities going from the state 1 to the state −1 and viceversa. On the other hand an absorbing–reflecting factorization of birth–death chains on the integers is only possible if both factors are split into two separated birth–death chains at the state 0. Therefore it makes more sense to consider absorbing–reflecting factorizations of “almost” birth–death chains with extra transitions between the states 1 and −1 and with some conditions. This factorization is now unique and by inverting the order of the factors we get a birth–death chain on the integers. In both cases we identify the spectral matrices associated with the Darboux transformation, the first one being a Geronimus transformation and the second one a Christoffel transformation of the original spectral matrix. We also study the probabilistic implications of both transformations. Finally, we apply our results to examples of chains with constant transition probabilities.

Low‐loss and broadband coaxial line to air‐filled substrate integrated waveguide transition

This Letter introduces a low-loss and broadband coaxial line to air-filled substrate integrated waveguide (AFSIW) transition for the first time. The fabrication of this transition involves three substrate layers. The inner conductor of the coaxial line is connected to the metal layer of the lower substrate and its outer conductor is connected to the metal layer of the upper substrate. This transition uses a taper-shaped configuration at the end of the line to achieve the better impedance matching and wider matching bandwidth. In the previously reported AFSIW components, several transitions are used to transform the transverse electromagnetic mode of the coaxial line to the TE 10 mode of the AFSIW structure. By using the proposed transition, these extra transitions are eliminated, which leads to the size and loss reduction of the structure. For validation purposes, a prototype of the back-to-back coaxial line to AFSIW transition is fabricated and measured for the entire C-band. The simulated and measured results are in good agreement. The proposed transition achieves the measured insertion loss of 0.55 ± 0.5 dB (0.28 ± 0.25 dB for the transition) and return loss of better than -11 dB from 4 to 8 GHz.

Online monitoring for diagnosis of violations of constraints in Petri net models

Abstract Fault diagnosis in partially-observed discrete-event systems requires modelling faults as unobservable events within the system. Representing faults as events is not always realistic. For example, some classes of fault are in form of violations of constraints such as service-level agreement (SLA) and Quality of Service (QoS). To model such faults, we need to modify the plant model which is not always acceptable. Firstly, this may make the models large. Secondly, adding extra transitions is not always preferable from engineers’ prospective as every modification of the constraint will modify the model of the plant. This paper applies integer Fourier-Motzkin elimination (IFME) approach to address this issue. Since the constraints and their violations can be written as inequalities, we show that starting from a Petri net two sets of inequalities (diagnoser) are obtained. These sets are used to judge whether an observed sequence may satisfy (violate) these inequalities. The correctness of the proposed approach has also been proved.

Microscopic model calculations for the magnetization process of layered triangular-lattice quantum antiferromagnets.

Magnetization processes of spin-1/2 layered triangular-lattice antiferromagnets (TLAFs) under a magnetic field H are studied by means of a numerical cluster mean-field method with a scaling scheme. We find that small antiferromagnetic couplings between the layers give rise to several types of extra quantum phase transitions among different high-field coplanar phases. Especially, a field-induced first-order transition is found to occur at H≈0.7H_{s}, where H_{s} is the saturation field, as another common quantum effect of ideal TLAFs in addition to the well-established one-third plateau. Our microscopic model calculation with appropriate parameters shows excellent agreement with experiments on Ba_{3}CoSb_{2}O_{9} [T. Susuki etal., Phys. Rev. Lett. 110, 267201 (2013)]. Given this fact, we suggest that the Co^{2+}-based compounds may allow for quantum simulations of intriguing properties of this simple frustrated model, such as quantum criticality and supersolid states.

Inelastic Neutron Scattering Studies on the Crystal Field Excitations in Superconducting NdFeAsO0.85F0.15

Inelastic neutron scattering experiments were performed on polycrystalline samples of NdFeAsO0.85F0.15over a wide temperature range (3 K–250 K). Based on the analysis of the experimental data, a Nd3+CF energy level scheme is proposed to give a consistent explanation about the observed CF transitions. The observed extra ground-state CF transitions could not be simply explained by the transitions between five Kramers doublets split from the Nd3+ 4I9/2ground state in theC4vpoint symmetry. A reliable explanation would be a superposition of crystal fields due to different local symmetries around the Nd3+ions induced by the fluorine doping.

Intermediate Band to Conduction Band Optical Absorption in ZnTeO

ZnTe doped with high concentrations of oxygen has been proposed in previous works as an intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this study, we present the first measurement of the absorption coefficient associated with transitions from the IB to the conduction band (CB) in ZnTeO. The samples used are 4-μm-thick ZnTe layers with or without O in a concentration ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , which have been grown on semiinsulating GaAs substrates by molecular beam epitaxy (MBE). The IB-CB absorption coefficient peaks for photon energies ~0.4 eV. It is extracted from reflectance and transmittance spectra measured using Fourier transform infrared (FTIR) spectroscopy. Under typical FTIR measurement conditions (low light intensity, broadband spectrum), the absorption coefficient in IB-to-CB transitions reaches 700 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . This is much weaker than the one observed for VB-IB absorption. This result is consistent with the fact that the IB is expected to be nearly empty of electrons under equilibrium conditions in ZnTe(O).

An ultra-high vacuum electrochemical flow cell for in situ/operando soft X-ray spectroscopy study.

An in situ flow electrochemical cell has been designed and fabricated to allow better seal under UHV chamber thus to achieve a good signal to noise ratio in fluorescence yield detection of X-ray absorption spectra for spectroelectrochemical study. The cell also stabilizes the thin silicon nitride membrane window in an effective manner so that the liquid cell remains intact during X-ray absorption experiments. With the improved design of the liquid cell, electrochemical experiments such as cyclic voltammetry have been performed for 10 cycles with a good stability of sample window. Also an operando electrochemical experiment during photoelectrochemistry has been performed on n-type hematite electrode deposited on silicon nitride window. The experiment allows us to observe the formation of two extra electronic transitions before pre edge of O K-edge spectra.

Invariant measure of the stochastic Allen-Cahn equation: the regime of small noise and large system size

We study the invariant measure of the one-dimensional stochastic Allen-Cahn equation for a small noise strength and a large but finite system. We endow the system with inhomogeneous Dirichlet boundary conditions that enforce at least one transition from -1 to 1. (Our methods can be applied to other boundary conditions as well.) We are interested in the competition between the energy that should be minimized due to the small noise strength and the entropy that is induced by the large system size. Our methods handle system sizes that are exponential with respect to the inverse noise strength, up to the critical exponential size predicted by the heuristics. We capture the competition between energy and entropy through upper and lower bounds on the probability of extra transitions between -1 and 1. These bounds are sharp on the exponential scale and imply in particular that the probability of having one and only one transition from -1 to +1 is exponentially close to one. In addition, we show that the position of the transition layer is uniformly distributed over the system on scales larger than the logarithm of the inverse noise strength. Our arguments rely on local large deviation bounds, the strong Markov property, the symmetry of the potential, and measure-preserving reflections.

Conflict-preserving abstraction of discrete event systems using annotated automata

This paper proposes to enhance compositional verification of the nonblocking property of discrete event systems by introducing annotated automata. Annotations store nondeterministic branching information, which would otherwise be stored in extra states and transitions. This succinct representation makes it easier to simplify automata and enables new efficient means of abstraction, reducing the size of automata to be composed and thus the size of the synchronous product state space encountered in verification. The abstractions proposed are of polynomial complexity, and they have been successfully applied to model check the nonblocking property of the same set of large-scale industrial examples as used in related work.

Anisotropy of Photoluminescence in Layered Semiconductors ReS&lt;sub&gt;2&lt;/sub&gt; and ReS&lt;sub&gt;2&lt;/sub&gt;:Au

The optical anisotropy properties of rhenium disulphide (ReS2) and Au-doped rhenium disulphide (ReS2:Au) have been investigated by polarization-dependent photoluminescence (PL). Because the excitonic transitions show strong polarization dependences in the near-infrared region, we used polarization-dependent PL measurements in the range between 0° and 180° to characterize the unique polarization property of ReS2 and ReS2:Au, and identify the origin of the excitonic transitions. It was observed that the variation in the amplitude of PL excitonic transitions with different polarization characteristics follows the Malus rule. In comparison with the undoped ReS2, the PL spectra of Au-doped sample show not only the main excitonic transitions near the direct band edge but also some extra transitions owing to the doping effects.

On the origin and evolution of life in the Galaxy

AbstractA simple stochastic model for evolution, based upon the need to pass a sequence of n critical steps is applied to both terrestrial and extraterrestrial origins of life. In the former case, the time at which humans have emerged during the habitable period of Earth suggests a value of n=4. Progressively adding earlier evolutionary transitions gives an optimum fit when n=5, implying either that their initial transitions are not critical or that habitability began around 6 Ga ago. The origin of life on Mars or elsewhere within the Solar System is excluded by the latter case and the simple anthropic argument is that extraterrestrial life is scarce in the Universe because it does not have time to evolve. Alternatively, the timescale can be extended if the migration of basic progenotic material to Earth is possible. If extra transitions are included in the model to allow for Earth migration, then the start of habitability needs to be even earlier than 6 Ga ago. Our present understanding of Galactic habitability and dynamics does not exclude this possibility. We conclude that Galactic punctuated equilibrium, proposed as a way round the anthropic problem, is not the only way of making life more common in the Galaxy.

Deperturbation study of the [formula omitted] state of C 2 by applying degenerate and two-color resonant four-wave mixing

The potential of four-wave mixing spectroscopy in combination with a discharge slit-jet source is explored by performing an analysis of the perturbations occurring between vibronic levels of the d 3 Π g , v ′ = 4 and b 3 Σ g - , v ′ = 16 states of C 2. Unambiguous assignments of perturbed transitions are achieved by intermediate level labeling in the a 3 Π u state of the Swan system and results in the re-assignment of several line positions found in the literature. Furthermore, extra transitions are observed and assigned in a straightforward manner that originate from the perturbing b 3 Σ g - , v ′ = 16 electronic state. Significantly perturbed rotational transitions in the (4, 3) band of the Swan system are reported for the first time. A least-squares fit to 35 perturbed and perturbing transitions yields the vibronic origin, rotational and spin-spin coupling constant of the b 3 Σ g - , v ′ = 16 state as well as the spin-orbit and L-uncoupling parameters for the interaction between the d 3 Π g , v ′ = 4 and b 3 Σ g - , v ′ = 16 states.

Compositional Nonblocking Verification Using Annotated Automata

This paper proposes to enhance compositional verification of the nonblocking property of discrete event systems by introducing annotated automata. Annotations store nondeterministic branching information, which would otherwise be stored in extra states and transitions. This more succinct representation makes it easier to simplify automata and enables new efficient means of abstraction, further reducing the size of automata to be composed and thus the size of the synchronous product state space encountered in verification. The abstractions proposed are of polynomial complexity, and they have been successfully applied for nonblocking verification of the same set of large-scale industrial examples as used in related work.

Extra electroweak phase transitions from strong dynamics

We show that models of dynamical electroweak symmetry breaking can possess an extremely rich finite temperature phase diagram. We suggest that early-universe extra electroweak phase transitions can appear in these models.

Piezoreflectance Study of Band-Edge Excitons of ReS2:Au

The optical properties of Au-doped rhenium disulphide (ReS2:Au) have been investigated by temperature- and polarization-dependent piezoreflectance (PzR) measurements. In comparison with the undoped ReS2, ReS2:Au shows not only the main excitonic transitions of E1ex, E2ex, E3ex, and E4ex near the direct band edge but also two extra transitions EAex and EBex owing to the doping effects. From temperature-dependent PzR spectra in the temperature range from 40 to 300 K, the least-squares fits are used to extract the parameters that describe the temperature variations of the band-edge excitonic transitions. The excitonic transitions show a strong polarization dependence in the near-infrared region. The polarization-dependent PzR measurement in the range between 0 and 180° was used to characterize the unique polarization property of ReS2:Au, and identify the origin of the excitonic transitions. However, the variation in the amplitude of PzR excitonic transitions with different polarization characteristics follows the Malus rule.

The effect of forbidden transitions on cosmological hydrogen and helium recombination

More than half of the atoms in the Universe recombined via forbidden transitions, so that accurate treatment of the forbidden channels is important in order to follow the cosmological recombination process with the level of precision required by future microwave anisotropy experiments. We perform a multilevel calculation of the recombination of hydrogen (H) and helium (He) with the addition of the 2 3 P 1 -1 1 S 0 spin-forbidden transition for neutral helium (He I), plus the nS-1S and nD-1S two-photon transitions for H (up to n = 40) and among singlet states of He I (n ≤ 10 and e ≤ 7). The potential importance of such transitions was first proposed by Dubrovich & Grachev using an effective three-level atom model. Here, we relax the thermal equilibrium assumption among the higher excited states to investigate the effect of these extra forbidden transitions on the ionization fraction Χ e and the cosmic microwave background (CMB) angular power spectrum C e . The spin-forbidden transition brings more than 1 per cent change in Χ e . The two-photon transitions may also give non-negligible effects, but currently accurate rates exist only for n ≤ 3. We find that changes in both Χ e and C e . would be at about the per cent level with the approximate rates given by Dubrovich & Grachev. However, the two-photon rates from 3S to IS and 3D to IS of H appear to have been overestimated, and our best numerical calculation puts the effect on Χ e and C e at below the per cent level. Nevertheless, we do not claim that we have the definite answer, since several issues remain open; sub-per cent level computation of the C e values requires improved calculations of atomic transition rates as well as increasingly complex multilevel atom calculations.

Understanding the luminescence of rare-earth-doped crystals through electron paramagnetic resonance spectroscopy

Optical transitions of rare-earth ions in condensed matter, even at very low doping levels, often exhibit complex structures in absorption and emission spectra. These extra transitions can be due to different rare-earth ions sites or due to interacting ions. Electron paramagnetic resonance spectroscopy of Kramers’ ions is a powerful tool to analyze this multisite character. Moreover, it can give information about the interactions between two rare-earth ions in pairs. We illustrate these different points with some results obtained in our group with vanadates crystals and with a general analysis of rare-earth pairs spectra in single crystals.

Physical properties of SmMIn 5 ( [formula omitted], Rh, Ir)

SmMIn 5 ( M = Co , Rh , Ir ) crystallizes in the tetragonal HoCoGa 5-type structure. This type of crystal structure is noticed as tetragonal variants of the AuCu 3 -structure, in which new superconductors were discovered. PuCoGa 5 and PuRhGa 5 are also the interesting superconductors. On the other hand, it is expected that Sm has a ground state similar to Pu compounds. We have succeeded in growing single crystals of SmMIn 5 by the flux method. SmRhIn 5 and SmIrIn 5 showed the antiferromagnetic ordering and extra transitions below T N , which is almost same as the results in the previous report. We have succeeded in growing single crystals of SmCoIn 5. It also showed the antiferromagnetic ordering and extra transitions below T N = 11.9 K . The temperatures of these anomalies are 6, 7.6 and 11.9 K and lowest found in SmMIn 5 compounds.

Fourier Transform Emission Spectra of the (000)–(000) Band of the λ4051.6 Band of C3

The (000)–(000) band of the 4051.6 8 group ( ˜ A 1 � u ˜ X 1 � þ )o f C3 was recorded in emission with a Bruker IFS 120HR Fourier transform (FT) spectrometer at the University of Waterloo. The band was excited by a microwave discharge in isopropanol (less than a few mtorr) diluted in helium (2 torr). Our new FT data provide more reliable and accurately calibrated transition wavenumbers than those from the grating spectra given by Gausset and coworkers. Analysis of our new spectrum combined with the data by McCall and coworkers confirmed that the lower J levels in the ˜ A state were strongly perturbed, as reported by Gausset and coworkers. The unidentified lines observed by McCall and coworkers could be attributed to extra transitions to an unknown perturbing state. Subject heading gs: astrochemistry — ISM: clouds — ISM: molecules — methods: laboratory — molecular data