Excited Ones Research Articles

Surface energy and elementary excitations of the XYZ spin chain with integrable open boundary fields

We study the thermodynamic limit of the anisotropic XYZ spin chain with non-diagonal integrable open boundary conditions. Although the U(1)-symmetry is broken, by using the new parametrization scheme, we exactly obtain the surface energy and the excitation energy of the system, which has solved the difficulty in the inhomogeneous T − Q relation. With the boundary parameters in the regions making the Hamiltonian Hermitian, we have obtained the distribution patterns of the zeros of the eigenvalue of the transfer matrix for the ground state and the excited ones. We find that the surface and excitation energies depend on the parities of sites number N, due to the long-range Neel order in the bulk. The easy-axis and thermodynamic limit for all the regions of boundary parameters are studied. We also obtain the physical quantities in the thermodynamic limit of boundary XXZ model by taking the trigonometric limit.

Relativistic Correction from the Four-Body Nonadiabatic Exponential Wave Function.

We present a method for calculating the relativistic correction in hydrogen molecules that significantly exceeds the accuracy of all the previous literature results. This method utilizes the explicitly correlated nonadiabatic exponential wave function, and thus treats electrons and nuclei equivalently. The proposed method can be applied to any rovibrational state, including highly excited ones. The numerical precision of the relativistic correction reaches several kHz (∼10-7 cm-1), which is below the best experimental accuracy.

Spectral and optical properties of a [formula omitted] molecular complex confined in InAs/GaAs Quantum Camels: A spatial finite element method treatment

The evolution of eigenstates and related optical absorption (sum of linear and nonlinear contributions) of a singly ionized double donor (D2+) confined in InAs/GaAs (quantum-well-dot nanostructure) quantum camels were theoretically investigated. Within the effective mass and the compact density matrix approximations, the energy levels and optical absorption were characterized as a function of a hydrostatic pressure field applied, the sample temperature, and the wetting layer thickness via a spatial finite element method analysis. Results show that an increase of hydrostatic pressure (sample temperature) between 0 to 30 kbar (4 to 300 K) leads to a stabilization (destabilization) of the energy levels and a decrease (increase) of the absorption peak value with a red-shift (blue-shift). On the other hand, an increase in the wetting layer thickness leads to a reduction in the energy levels, and a monotonous evolution from quantum-dot states to wetting-layer states, especially in the excited ones, is seen. In addition, an increase in the absorption peak value is reported, which can be intended as an electron mobility enhancement. The donor-electron interactions reduce the wavefunction’s spatially-extended feature, enhancing the absorption peak in the analyzed |1〉→|6〉 transition. In the |1〉→|2〉 optical transition, the resonant peak can be tuned within the band ≈25–48 meV, slightly beyond the Terahertz frequency range.

FDevelopment of Self-Activated Photosensitizers based on the Chemiluminescent System of Marine Coelenterazine

IntroductionPhotodynamic therapy (PDT) of cancer possesses advantageous features, such as a minimally invasive nature and few side-effect [1]. However, its use can be restricted to more surface tumors, due to its dependance on light-irradiation. To overcome this problem, we propose the development of single-molecule photosensitizers (PSs), based on chemiluminescent (CL) marine Coelenterazine (Clz) [2-6], which can be self-activated in the absence of light. ApproachClz analogs were synthesized via routes optimized by our team [2-6], and their structure was characterized by HR-MS, NMR and FTIR spectroscopy. They were subjected to a through luminometric and photophysical characterization, to determine their CL features and singlet oxygen sensitization [2-6]. Their toxicity was investigated in vitro toward different cancer (breast, prostate, neuroblastoma, lung and gastric) and noncancer (breast and keratinocytes) cell lines, via the MTT assay in the absence of light [2-6]. ResultsThe obtained Clz analogs were designed so their CL reaction generate mainly triplet states, instead of singlet excited ones [2-6]. They were shown to indeed be able to sensitize the highly cytotoxic singlet oxygen, without light-irradiation, due to a CL reaction triggered solely by molecule overexpressed in cancer cells (superoxide anion) [2-6]. In vitro assays showed that these analogs present cytotoxicity toward all the different studied cancer cell lines [2-6]. Moreover, some of them even showed comparable or even better activity than a reference chemotherapeutic drug [3,4]. Finally, a promising profile of safety was observed in testing with noncancer cells [3]. ConclusionsDifferent single-molecule PSs were developed, which are capable of intracellular self-activation without light-irradiation [2-6]. Namely, they are directly chemiexcited to triplet excited states via a CL reaction triggered by a molecule overexpressed in cancer cells, which generates singlet oxygen without light-irradiation. This new approach was found to induce toxicity toward different cancer cell lines, while possessing a promising profile of safety for noncancer cells. Thus, these PSs can provide a pathway for eliminating the light-related restrictions of PDT, while maintaining its advantages.

Medium inhomogeneities modulate emerging spiral waves

We study the spatiotemporal dynamics of spiral waves in a lattice of chemically coupled memristive FitzHugh–Nagumo neurons. We also introduce local and global functional inhomogeneities by means of variations in nodal action potentials that are distributed in different ways. We find that, in the presence of globally distributed random inhomogeneity, increasing the maximum threshold for excitability generates neurons with reduced depolarization capacity. Although such a setup makes the entire medium less excitable and thus challenges the robustness of emerging spiral waves, highly excitable neurons can compensate for the less excitable ones, thereby nonetheless preserving the spiral wave pattern. However, this compensatory mechanism has limitations, which can ultimately lead to the elimination of spiral waves under specific conditions. When inhomogeneities are local, two different scenarios are possible. If the distribution is random, the spiral tip cannot penetrate the inhomogeneous region but remains resilient against it. The tip is consistently anchored to the inhomogeneity, meandering around its boundary. As the inhomogeneity size increases, the curvature of the spiral tip and the propagation speed of the circular wavefronts decrease. If the distribution is uniform, inhomogeneities are analogous to semi-conducting barriers, thus permitting the spiral rotor to penetrate while sacrificing the strength of its wavefronts.

Reactive collisions between electrons and BeH+ above dissociation threshold.

Our previous studies of dissociative recombination and vibrational excitation/de-excitation of the BeH+ ion, based on the multichannel quantum defect theory, are extended to collision energies above the dissociation threshold, taking into account the vibrational continua of the BeH+ ion and, consequently, its dissociative excitation. We have also significantly increased the number of dissociative states of 2Π, 2Σ+ and 2Δ symmetry included in our cross section calculations, generating the most excited ones by using appropriate scaling laws. Our results are suitable for modeling the kinetics of BeH+ in edge fusion plasmas for collision energies up to 12 eV.

Enhanced Total Vibrational Excitation Yield in a Slow Narrow-Pulsed Hydrogen Molecular Beam.

High-efficiency excitation of a molecular beam is critical for investigating state-selected chemistry. However, achieving vibrational excitation of the entire beam for Raman-active molecules such as H2 proves extremely challenging, primarily because laser pulses are much shorter than the molecular beam. In this study, we achieve a total excitation efficiency of over 20% by employing stimulated Raman pumping (SRP) in a slow, narrow-pulsed molecular beam. Through optimizing the intensity and spot shape of the SRP lasers, we attain saturated excitation within the laser crossing region. Furthermore, by reducing the beam velocity and narrowing the beam pulse using a cold valve and a fast chopper, we significantly enhance the total excitation yield. COMSOL simulation and a newly developed model reveal that a critical velocity allows the chopper to block unexcited molecules and reserve most of the excited ones from the beam, resulting in the highest overall excitation yield. This innovative setup opens new possibilities for state-selected experiments in surface science and ion-molecule reaction dynamics, particularly involving weak transitions and pulsed lasers.

Many body density of states of a system of non interacting spinless fermions

The modeling of out-of-equilibrium many-body quantum systems requires to go beyond low-energy physics and single or few bodies densities of states. Many-body localization, presence or lack of thermalization and quantum chaos are examples of phenomena in which states at different energy scales, including highly excited ones, contribute to dynamics and therefore affect the system’s properties. Quantifying these contributions requires the many-body density of states (MBDoS), a function whose calculation becomes challenging even for non-interacting identical particles due to the difficulty to enumerate accessible states while enforcing the exchange symmetry. In the present work, we introduce a new approach to evaluate the MBDoS in the general case of non-interacting systems of identical quantum particles. The starting point of our method is the principal component analysis of a filling matrix F describing how N particles can be distributed into L single-particle energy levels. We show that the many body spectrum can be expanded as a weighted sum of singular vectors of the filling matrix. The weighting coefficients only involve renormalized energies obtained from the single body spectrum. We illustrate our method in two classes of problems that are mapped into spinless fermions : (i) non-interacting electrons in a homogeneous tight-binding model in 1D and 2D, and (ii) interacting spins in a chain under a transverse field.

Two-dimensional fractional [formula omitted]-symmetric cubic–quintic NLS equation: Double-loop symmetry breaking bifurcations, ghost states and dynamics

In this paper, we address the double-loop symmetry breaking bifurcations of optical vortex solitons in the two-dimensional (2D) fractional cubic–quintic nonlinear Schrödinger (FCQNLS) equation with an imprinted partially parity-time (PPT) symmetric complex potential. The continuous branches of asymmetric solitons bifurcate from the fundamental one as the power exceeds some critical value. It is found that the symmetry breaking point is exactly the point at which the fundamental symmetric soliton is destabilized. Intriguingly, the branches of asymmetry solitons (alias ghost states) are existing with complex conjugate propagation constants, which is solely in fractional media. Moreover, the branch of asymmetric solitons crosses the branch of fundamental symmetric ones when it reaches the second critical value, and eventually merges back into it at the third critical power point. The imaginary part of the propagation constant also exhibits a circular shape. And the stability of the fundamental symmetric soliton is restored. In addition, the stability of two branches of asymmetric solitons differs from each other. The reason generating this phenomenon is analyzed in detail. Besides, the branch of dipole solitons for the first excited state is also discussed numerically, which is always stable in the process of symmetry breaking. The stability and dynamics of symmetric (fundamental and the first excited ones) and asymmetric solitons are explored via the linear stability analysis, direct simulation, modulation as well as adiabatic excitation. These results will provide some theoretical basis for the study of spontaneous symmetry breaking phenomena and related experiments in fractional media with PPT-symmetric potentials.

The worst II – eight days a week

The worst II – eight days a week

Doping effect on the light absorption and photoluminescence of Ge/Si quantum dots in the infrared spectral range

The results of comprehensive studies of near-infrared photoluminescence and mid-infrared equilibrium and photoinduced absorption spectra in structures with Ge/Si quantum dots with different doping levels at different optical pumping intensities and different temperatures are presented. Obtained dependences of interband photoluminescence spectra on temperature and optical pumping intensity are explained by the change in the intensities of direct and indirect in real space electron-hole recombination in Ge/Si quantum dots. The spectra of equilibrium and photoinduced absorption of polarized mid-infrared radiation demonstrate peaks associated with transitions of holes from the ground and excited states to continuum states above quantum dots and with optical transitions from the ground states to excited ones.

Power-law holographic dark energy and cosmology

We formulate power-law holographic dark energy, which is a modified holographic dark energy model based on the extended entropy relation arising from the consideration of state mixing between the ground and the excited ones in the calculation of the entanglement entropy. We construct two cases of the scenario, imposing the usual future event horizon choice, as well as the Hubble one. Thus, the former model is a one-parameter extension of standard holographic dark energy, recovering it in the limit where power-law extended entropy recovers Bekenstein–Hawking one, while the latter belongs to the class of running vacuum models, a feature that may reveal the connection between holography and the renormalization group running. For both models we extract the differential equation that determines the evolution of the dark-energy density parameter and we provide the expression for the corresponding equation-of-state parameter. We find that the scenario can describe the sequence of epochs in the Universe evolution, namely the domination of matter followed by the domination of dark energy. Moreover, the dark-energy equation of state presents a rich behavior, lying in the quintessence regime or passing into the phantom one too, depending on the values of the two model parameters, a behavior that is richer than the one of standard holographic dark energy.

Терагерцовая спектроскопия магнитоэлектрика HoAl-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-

Experimental and theoretical study of submillimeter (terahertz) spectroscopic and magnetic properties of the rare-earth aluminum borate HoAl3(BO3)4 were performed at temperatures 3–300 K. In the transmittance spectra a number of resonance lines were detected at frequencies 2–35 cm–1 for different radiation polarizations. These modes were identified as transitions between the lower levels of the ground multiplet of the Ho3+ ion split by the crystal field, including both transitions from the ground state to the excited ones and transitions between the excited states. The established excitation conditions of the observed modes and the simulation of the spectra made it possible to separate the magnetic and electric dipole transitions and to determine the energies of the corresponding states, their symmetry, and the matrix elements of the transitions. Low-frequency lines that do not fit into the established picture of the electron states of Ho3+ were also found; these lines, apparently, correspond to the ions with the distorted by defects local symmetry of the crystal field.

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Experimental and theoretical study of submillimeter (terahertz) spectroscopic and magnetic properties of the rare-earth aluminum borate HoAl3(BO3)4 were performed at temperatures 3–300 K. In the transmittance spectra a number of resonance lines were detected at frequencies 2–35 cm–1 for different radiation polarizations. These modes were identified as transitions between the lower levels of the ground multiplet of the Ho3+ ion split by the crystal field, including both transitions from the ground state to the excited ones and transitions between the excited states. The established excitation conditions of the observed modes and the simulation of the spectra made it possible to separate the magnetic and electric dipole transitions and to determine the energies of the corresponding states, their symmetry, and the matrix elements of the transitions. Low-frequency lines that do not fit into the established picture of the electron states of Ho3+ were also found; these lines, apparently, correspond to the ions with the distorted by defects local symmetry of the crystal field.

Quasi-doublets of non-Kramers Ho3+ ion and magnetic ordering of holmiumfrancisite-analog Cu3Ho(SeO3)2O2Cl

Optical spectroscopy of the f-f transitions in the non-Kramers Ho3+ ion was performed in a wide temperature range, from 4 K to room temperature, to study magnetic properties of the francisite-like holmium compound Cu3Ho(SeO3)2O2Cl. Despite the absence of symmetry doublets of the Ho3+ ion, its quasi-doublets were found, which are split in the exchange field acting on holmium ions in the magnetically ordered state of the crystal under study. From the splittings, the temperature of magnetic ordering was found, TN = 38 K. Two quasi-doublets of Ho3+ ion, namely, the ground and the first excited ones, with the energy gap 25 cm−1, contribute to the low-temperature magnetism of Cu3Ho(SeO3)2O2Cl. The energy structure of crystal-field levels of the ground multiplet 5I8 of the holmium ion was investigated, and the contribution of the rare-earth ion to the heat capacity of Cu3Ho(SeO3)2O2Cl was calculated.

Photophysical properties of push-π-pull type chromophores of aryl-substituted bipyridines in different solvents

Photophysical studies of 4′-methyl-2,2′-bipyridine derivatized with the polycyclic aromatic hydrocarbons (PAHs) anthracene (mbpy-anth), naphthalene (mbpy-naph), and pyrene (mbpy-pyr) were acquired in different solvents. While the absorption spectra were not affected by the solvent nature, the emission ones showed red shifts with increase polarity consistent with an intramolecular charge-transfer (ICT) character. Theoretical calculations found a dominant “Hole” → “Particle” contribution for the first five transitions involving local excited-state (LE) and ICT transitions, with the latter being dominant at higher wavelengths (S0 → 1CT). The fluorescence solvatochromic data suggested a hybridized local and charge transfer (HLCT) state for the mbpy-R compounds with the CT contribution prevailing in high polar solvents; a result that was corroborated by the monoexponential decay lifetimes. The Stokes shifts difference between heptane and dimethylsulphoxide, the most and least polar solvents used in this work, was calculated as 1315, 2969, and 808 cm−1 for mbpy-naph, mbpy-anth, and mbpy-pyr, respectively. The increase of the solvent polarity results in a red shift and a broadening of the emission and excitation bands for mbpy-anth and mbpy-naph with the spectra of the latter being the most affected. For mbpy-pyr, on the contrary, the emission spectra were narrower than the excitation ones indicating the La transitions lie at lower energy than the Lb. For this species, the results indicated an effective mixing of LE and CT states in the moderately polar solvents being in accordance with the observed single exponential decay which is likely related to one hybridized state.

Robust equilibrium optimization of structural dynamic characteristics considering different working conditions

In the design of complex products such as turbo-generators and compressors, it is very important to optimize the dynamic characteristics of the key components by moving their natural frequencies away from the excitation ones as well as their multiples to avoid resonances and resultant malfunctions. At the same time, the uncertainties such as the fluctuations of material properties inherent in the manufacture of key components will inevitably cause the variation of their structural dynamic characteristics and thus need to be fully considered in the optimization process. Considering that the robustness requirement of structures with uncertain material properties (specifically, uncertain elastic modulus and density) usually varies under different working conditions, the robust equilibrium optimization of structural dynamic characteristics considering different working conditions is investigated in this paper for the first time. Firstly, the robust optimization model for the dynamic characteristics of uncertain structures is constructed with the uncertainties described as interval variables. Subsequently, a novel robust equilibrium optimization algorithm is proposed to solve the constructed robust optimization model. Specifically, a new concept of overlap coefficient between interval boundary angles (OCBA) is proposed with the introduction of an overlap sensitivity factor, based on which the constraint robustness considering the requirements of different working conditions can be flexibly assessed. Then, the robust equilibrium strategy for all structural performance indices are proposed for the direct ranking of various design vectors, based on which the robust equilibrium optimization algorithm is developed. The validity and effectiveness of the proposed robust equilibrium optimization approach are demonstrated by realistic engineering examples including the cone ring fixture of a large turbo-generator and the compressor shell of a refrigerator.

Borehole Sonic Data Dispersion Analysis With a Modified Differential-Phase Semblance Method

Ruijia Wang, Richard Coates, and Jiajun Zhao The sonic wave fields produced by wireline and logging-while-drilling (LWD) monopole, dipole, and quadrupole tools often consist of multiple borehole modes. Classic frequency-slowness semblance-map methods used to process this data often detect only strongly excited modes and overlook weak ones, and erroneously detect some modes. Conventional dispersion processing methods can be separated into two groups: single-mode and multimode extraction algorithms. Single-mode methods are stable but only return one mode, the most energetic one, at each frequency. Single-mode methods include the differential-phase frequency-semblance (DPFS) method and the weighted spectral-semblance method. Multimode methods can return multiple modes at each frequency but may be unstable in some cases. Due to their assumptions about signal models, multimode methods are often sensitive to unbalanced receiver arrays, poor data quality, and formation heterogeneity. For example, in some extreme cases, such as a formation with strong heterogeneity, multimode methods may yield erroneous ghost modes or discontinuous dispersion curves for each mode. Borehole modes with different slowness have different arrival times. Converting the data to the frequency domain can obscure this critical information or encode these time differences into phase differences between adjacent frequencies. Conventional frequency-semblance approaches, which use only a single frequency independently from adjacent ones, ignore this phase information. In this paper, we propose employing the phase differences between adjacent frequencies to facilitate multimode dispersion analysis. We modify one conventional method to incorporate the arrival time of modes or the phase difference between adjacent frequencies. We validate the proposed approach with synthetic, laboratory, and field data. The results suggest the method can extract a much more comprehensive representation of modes present in the sonic data. Additionally, the method provides reliable estimates, even when the number of receivers is small. Unlike the Prony and matrix-pencil methods based on assumed signal models, the proposed approach, which we denote “Modified Differential-Phase Frequency Semblance” (MDPFS), is a modification of the single-mode differential phase approach. The MDPFS is still a semblance-based approach, and as with other semblance-based processing, it is expected to be less sensitive to unbalanced receiver arrays, poor data quality, and formation heterogeneity than other multimode algorithms.

Effect of the ketogenic diet in excitable tissues.

In the past decade, ketogenic diet (KD) has gained some popularity as a potential treatment for a wide range of diseases, including neurological and metabolic disorders, thanks to a beneficial role mainly related to its anti-inflammatory properties. The high-fat and carbohydrate-restricted regimen causes changes in the metabolism, leading, through the β-oxidation of fatty acids, to the hepatic production of ketone bodies (KBs), which are used by many extrahepatic tissues as energy fuels. Once synthetized, KBs are delivered through the systemic circulation to all the tissues of the organism, where they play pleiotropic roles acting directly and indirectly on various targets, and among them ion channels and neurotransmitters. Moreover, they can operate as signaling metabolites and epigenetic modulators. Therefore, it is inappropriate to consider that the KD regimen can improve the patients' clinical condition simply by means of specific and localized effects; rather, it is more correct to think that KBs affect the organism as a whole. In this review, we tried to summarize the recent knowledge of the effects of KBs on various tissues, with a particular attention on the excitable ones, namely the nervous system, heart, and muscles.

Analysis of Steady-State Oscillations in an Autonomous Oscillator under Multi-Frequency Excitation

The analysis of the behavior of an oscillator under multi-frequency excitation is considered in the paper. The investigation is based on the phase macromodel. The paper shows that three steady-state modes can exist in oscillator under multi-frequency excitation. The synchronized (locked) mode can be defined as the coincidence of the oscillator fundamentals with the excitation fundamentals in the region of sufficiently large excitation magnitude. The unsynchronized (unlocked) mode exists outside the synchronized region and its spectrum contains additional intrinsic fundamental besides the excitation ones. Singular points mode in some isolated points outside the synchronized region is characterized by the equality of the number of the oscillator fundamentals with the number of the excitation fundamentals. Performed numerical experiments confirmed the appearance of bifurcation points while transition of oscillator into the synchronization mode. The existence of singular points outside the synchronization region and their isolated character was also experimentally demonstrated. The problems of finding a steady-state solution of the phase equation of an excited oscillator by the Harmonic Balance (HB) method are considered. It is shown that main difficulties are connected with the presence of linear term in the steady-state solution. A transformation is proposed to provide the formation of HB equations for the phase micromodel in a standard form. Additional difficulties of HB simulations of synchronized oscillator phase equations are discussed.