Pairing Vibrations Research Articles

A quantum chemistry study for 1-ethyl-3-Methylimidazolium ion liquids with aprotic heterocyclic anions applied to carbon dioxide absorption

Flue gas is largely responsible for acid rain and global warming. A special class of imidazolium-based ionic liquids (ILs) has been given a great deal of attention as holding a high absorptivity for the acid gas component, such as CO2. We simulate a class of novel ionic liquids (ILs) formed between the 1-ethyl-3-methylimidazolium cation ([emim]+) and the aprotic heterocyclic anions (AHA), and present a molecular-level description of the interactions of ILs with CO2. The covalent bonds are found between anions and CO2 in the calculated minimum energy structures at B3LYP/6-311++G (d,p) level. And also the basicity of anion is found to have a promotional effect on the solubility of CO2 in ILs. The energy barriers of proton transfer show that [emim][Ind], [emim][4-Triaz] and [emim][3-Triaz] will produce imidazolium carbonates during the proton transfer process because of their high basicities. Both [emim][Tetz] and [emim][Bentri], however, can not prompt the formation of the intermolecular carbene because their basicities are too weak to do so. This implies that the formation of N-heterocyclic carbine complexes can be effectively tuned by varying the basifies of counteractions. Additionally, the infrared spectra are presented to investigate the ion pair vibration characteristics. And the further natural bond orbital (NBO) method is applied to reveal the mechanism of hydrogen bonding interactions.

Spectrally resolved infrared microscopy and chemometric tools to reveal the interaction between blue light (470 nm) and methicillin-resistant Staphylococcus aureus

Blue light inactivates methicillin-resistant Staphylococcus aureus (MRSA), a Gram-positive antibiotic resistant bacterium that leads to fatal infections; however, the mechanism of bacterial death remains unclear. In this paper, to uncover the mechanism underlying the bactericidal effect of blue light, a combination of Fourier transform infrared (FTIR) spectroscopy and chemometric tools is employed to detect the photoreactivity of MRSA and its distinctive pathway toward apoptosis after treatment. The mechanism of action of UV light and vancomycin against MRSA is also investigated to support the findings. Principal component analysis followed by linear discriminant analysis (PCA- LDA) is employed to reveal clustering of five groups of MRSA samples, namely untreated (control I), untreated and incubated at ambient air (control II), irradiated with 470nm blue light, irradiated with 253.5 UV light, and vancomycin-treated MRSA. Loadings plot from PCA-LDA analysis reveals important functional groups in proteins (1683, 1656, 1596, 1542cm−1), lipids (1743, 1409cm−1), and nucleic acids region of the spectrum (1060, 1087cm−1) that are responsible for the classification of blue light irradiated spectra and control spectra. Cluster vector plots and scores plot reveals that UV light-irradiated spectra are the most biochemically similar to blue light- irradiated spectra; however, some wavenumbers experience a shift. The shifts between blue light and UV light irradiated loadings plot at νasym PO2− band (from 1228 to 1238cm−1), DNA backbone (from 970 to 966cm−1) and base pairing vibration of DNA (from 1717 to 1712cm−1) suggest distinctive changes in DNA conformation in response to irradiation. Our findings indicate that irradiation of MRSA with 470nm light induces A-DNA cleavage and that B-DNA is more resistant to damage by blue light. Blue light and UV light treatment of MRSA are complementary and distinct from the known antimicrobial effect of vancomycin. Moreover, it is known that UV-induced cleavage of DNA predominantly targets B-DNA, which is in agreement with the FTIR findings. Overall the results suggest that the combination of light and vancomycin could be a more robust approach in treating MRSA infections

Elastic response of the atomic nucleus in gauge space: Giant Pairing Vibrations

Due to quantal fluctuations, the ground state of a closed shell system $ A_{0}$ can become virtually excited in a state made out of the ground state of the neighbour nucleus $ \vert gs(A_0+2) \rangle $ ( $ \vert gs(A_0-2) \rangle $ ) and of two uncorrelated holes (particles) below (above) the Fermi surface. These $ J^{\pi} = 0^{+}$ pairing vibrational states have been extensively studied with two-nucleon transfer reactions. Away from closed shells, these modes eventually condense, leading to nuclear superfluidity and thus to pairing rotational bands with excitation energies much smaller than $ \hbar\omega_{0}$ , the energy separation between major shells. Pairing vibrations are the plastic response of the nucleus in gauge space, in a similar way in which low-lying quadrupole vibrations, i.e. surface vibrations with energies much smaller than $ \hbar\omega_{0}$ whose eventual condensation leads to quadrupole deformed nuclei, provide an example of the plastic nuclear response in 3D space. While much is known, in particular concerning its damping, regarding the counterpart of quadrupole plastic modes, i.e. regarding the giant quadrupole resonances (GQR), $ J^{\pi} = 2^{+}$ elastic response of the nucleus with energies of the order of $ \hbar\omega_{0}$ , little is known regarding this subject concerning pairing modes (giant pairing vibrations, GPV). Consequently, the recently reported observation of L = 0 resonances, populated in the reactions 12C(18O,16O)14C and 13C(18O,16O)15C and lying at an excitation energy of the order of $ \hbar\omega_{0}$ , likely constitutes the starting point of a new field of research, that of the study of the elastic response of nuclei in gauge space. Not only that, but also the fact that the GPV have likely been serendipitously observed in these light nuclei when it has failed to show up in more propitious nuclei like Pb, provides unexpected and fundamental insight into the relation existing between basic mechanisms --Landau, doorway, compound damping-- through which giant resonances acquire a finite lifetime, let alone the radical difference regarding these phenomena displayed by correlated (ph) and (pp) modes.

Neutron decay ofC15resonances by measurements of neutron time-of-flight

The neutron decay of the resonant states of light neutron-rich nuclei is an important and poorly explored property, useful to extract valuable nuclear structure information. In the present paper the neutron decay of the C15 resonances populated via the two-neutron transfer reaction C13(O18,O16n) at 84-MeV incident energy is reported for the first time using an innovative technique which couples the MAGNEX magnetic spectrometer and the EDEN neutron detector array. Experimental data show that the resonances below the one-neutron emission threshold decay to the C14 ground state via one-neutron emission with an almost 100% total branching ratio, whereas the recently observed C15 giant pairing vibration at 13.7 MeV mainly decays via two-neutron emission.

Population of the giant pairing vibration

Background: The giant pairing vibration (GPV), a correlated two-nucleon mode in the second shell above the Fermi surface, has long been predicted and expected to be strongly populated in two-nucleon transfer cross sections similar to those of the normal pairing vibration. Recent experiments have provided evidence for this mode in $^{14,15}\text{C}$ but, despite sensitive studies, it has not been definitively identified in either Sn or Pb nuclei where pairing correlations are known to play a crucial role.Purpose: Our aim is to test whether features inherent to the mixing of bound and unbound levels might account for this and to study the effect in a simple and intuitively clear approach.Method: We study the mixing of unbound levels in a set of toy models that capture the essential physics of the GPV, along with a more realistic calculation including distorted-wave Born approximation transfer amplitudes.Results: The calculated (relative) cross section to populate a simulated GPV state is effectively low, compared to the case of bound levels with no widthsConclusions: The mixing turns out to be only a minor contributor to the weak population. Rather, the main reason is the melting of the GPV peak due to the width it acquires from the low orbital angular momentum single-particle states playing a dominant role in two-nucleon transfer amplitudes. This effect, in addition to a severe $Q$-value mismatch, may account for the elusive nature of this mode in $(t,p)$ and $(p,t)$ reactions.

Two more or less

A recent experiment has provided tantalizing evidence in favour of the elusive 'giant pairing vibration' — an exotic excitation of the atomic nucleus.

On the absence of rotational levels for J π K = 0+02 and 2+22 nonrotational states in 164Dy and 166Er

Various reasons for the absence of rotational levels for JπK = 0+02 and 2+22 nonrotational states in 164Dy and 166Er are considered. Preference is given to the effect of the excitation of an anharmonic two-phonon state in pair vibrations of the superconducting type.

Large-amplitude pairing fluctuations in atomic nuclei

Pairing fluctuations are self-consistently incorporated on the same footing as the quadrupole deformations in present state-of-the-art calculations including particle-number and angular-momentum conservation as well as configuration mixing. The approach is complemented by the use of the finite-range density-dependent Gogny force which, with a unique source for the particle-hole and particle-particle interactions, guarantees a self-consistent interplay in both channels. We have applied our formalism to study the role of the pairing degree of freedom in the description of the most relevant observables like spectra, transition probabilities, separation energies, etc. We find that the inclusion of pairing fluctuations mostly affects the description of excited states, depending on the excitation energy and the angular momentum. $E0$ transition probabilities experience rather big changes while $E2$'s are less affected. Genuine pairing vibrations are thoroughly studied with the conclusion that deformations strongly inhibits their existence. These studies have been performed for a selection of nuclei: spherical, deformed, and with different degrees of collectivity.

Di-neutron correlation in monopole two-neutron transfer modes in the Sn isotope chain

We study microscopic structures of monopole pair vibrational modes and associated two-neutron transfer amplitudes in neutron-rich Sn isotopes by means of the linear response formalism of the quasiparticle random phase approximation (QRPA). For this purpose we introduce a method to decompose the transfer amplitudes with respect to two-quasiparticle components of the QRPA eigenmode. It is found that pair-addition vibrational modes in neutron-rich ${}^{132--140}$Sn and the pair rotational modes in ${}^{142--150}$Sn are commonly characterized by coherent contribution of quasaiparticle states having high orbital angular momenta $l\ensuremath{\gtrsim}5$, which suggests transfer of a spatially correlated neutron pair. The calculation also predicts a high-lying pair vibration, the giant pair vibration, emerging near the one-neutron separation energy in ${}^{110--130}$Sn, and we find that they have the same di-neutron characters as that of the low-lying pair vibration in ${}^{132--140}$Sn.

Proton pair correlations and the neutrinoless double-βdecay of76Ge

Proton pair correlations relevant for the neutrinoless double-$\ensuremath{\beta}$ decay of ${}^{76}$Ge have been probed via the ${}^{74,76}$Ge(${}^{3}$He,$n$) reactions at 16 MeV. No evidence for pairing vibrations in either nucleus is observed at sensitivity limits of $\ensuremath{\sim}$6$%$ and $\ensuremath{\sim}$19$%$ of the ground-state strength in ${}^{76}$Se and ${}^{78}$Se, respectively. These results are relevant for the understanding of matrix elements for neutrinoless double-$\ensuremath{\beta}$ decay. The lack of pairing vibrations is consistent with a simple BCS structure for the ground states of ${}^{76}$Ge and ${}^{76}$Se, assumed in quasiparticle random phase approximation (QRPA) models of the process.

Quantitative study of coherent pairing modes with two-neutron transfer: Sn isotopes

Pairing rotations and pairing vibrations are collective modes associated with a field, the pair field, which changes the number of particles by two. Consequently, they can be studied at profit with the help of two-particle transfer reactions on superfluid and in normal nuclei, respectively. The advent of exotic beams has opened, for the first time, the possibility to carry out such studies in medium heavy nuclei, within the same isotopic chain. In the case studied in the present paper that of the Sn-isotopes (essentially from closed (Z=N=50) to closed (Z=50,N=82) shells). The static and dynamic off-diagonal, long range order phase coherence in gauge space displayed by pairing rotations and vibrations respectively, leads to coherent states which behave almost classically. Consequently, these modes are amenable to an accurate nuclear structure description in terms of simple models containing the right physics, in particular BCS plus QRPA and HF mean field plus RPA respectively. The associated two- nucleon transfer spectroscopic amplitudes predicted by such model calculations can thus be viewed as essentially "exact". This fact, together with the availability of optical potentials for the different real and virtual channels involved in the reactions considered, namely (A+2)Sn+p, (A+1)Sn+d and (A)Sn+t, allows for the calculation of the associated absolute cross sections without, arguably, free parameters. The numerical predictions of the absolute differential cross sections, obtained making use of the above mentioned nuclear structure and optical potential inputs, within the framework of second order DWBA, taking into account simultaneous, successive and non-orthogonality contributions provide, within experimental errors an overall account of the experimental findings for all of the measured (A+2)Sn(p,t)(A)Sn(gs) reactions, for which absolute cross sections have been reported to date.

Description of two-particle transfer in superfluid systems

Exact results of pair transfer probabilities for the Richardson model with equidistant or random level spacing are presented. The results are then compared either to particle-particle random-phase approximation (ppRPA) in the normal phase or quasiparticle random-phase approximation (QRPA) in the superfluid phase. We show that both ppRPA and QRPA are globally well reproducing the exact case although some differences are seen in the superfluid case. In particular, the QRPA overestimates the pair transfer probabilities to excited states in the vicinity of the normal-superfluid phase transition, which might explain the difficulty in detecting collective pairing phenomena as, for example, the giant pairing vibration. The shortcoming of QRPA can be traced back to the breaking of particle number that is used to incorporate pairing. A method based on direct diagonalization of the Hamiltonian in the space of two quasiparticles projected onto good particle number is shown to improve the description of pair transfer probabilities in superfluid systems.

Nuclear quantum many-body dynamics

A summary of recent researches on nuclear dynamics with realistic microscopic quantum approaches is presented. The Balian-V\'en\'eroni variational principle is used to derive the time-dependent Hartree-Fock (TDHF) equation describing the dynamics at the mean-field level, as well as an extension including small-amplitude quantum fluctuations which is equivalent to the time-dependent random-phase approximation (TDRPA). Such formalisms as well as their practical implementation in the nuclear physics framework with modern three-dimensional codes are discussed. Recent applications to nuclear dynamics, from collective vibrations to heavy-ion collisions are presented. A particular attention is devoted to the interplay between collective motions and internal degrees of freedom. For instance, the harmonic nature of collective vibrations is questioned. Nuclei are also known to exhibit superfluidity due to pairing residual interaction. Extensions of the theoretical approach to study such pairing vibrations are now available. Large amplitude collective motions are investigated in the framework of heavy-ion collisions leading, for instance, to the formation of a compound system. How fusion is affected by the internal structure of the collision partners, such as their deformation, is discussed. Other mechanisms in competition with fusion, and responsible for the formation of fragments which differ from the entrance channel (transfer reactions, deep-inelastic collisions, and quasi-fission) are investigated. Finally, studies of actinide collisions forming, during very short times of few zeptoseconds, the heaviest nuclear systems available on Earth, are presented.

Pair correlation and pair collectivity in neutron-rich nuclei

We describe the neutron Cooper pair, the pair vibrational states and the associated two-neutron transfer strength by applying the Skyrme–Hartree–Fock–Bogoliubov mean-field model and the quasiparticle random phase approximation to neutron-rich Sn isotopes. The wave function of the Cooper pair exhibits a strong spatial correlation favoring short relative distances smaller than a few fm, in contrast to the case of the single-j Cooper pair. The model also predicts an anomalous pair vibration in neutron-rich isotopes beyond the N = 82 magic number, which originates from the weak binding of the last neutrons.

Soft spin-dipole resonances in 40Ca

High resolution experimental data has been obtained for the 40,42,44,48Ca(3He,t)Sc charge exchange reaction at 420 MeV beam energy, which favors the spin-isospin excitations. The measured angular distributions were analyzed for each state separately, and the relative spin dipole strength has been extracted for the first time. The low-lying spin-dipole strength distribution in 40Sc shows some interesting periodic gross feature. It resembles to a soft, damped multi-phonon vibrational band with ℏω= 1.8 MeV, which might be associated to pairing vibrations around 40Ca.

Specific shear viscosity in hot rotating systems of paired fermions

The specific shear viscosity $\bar\eta$ of a classically rotating system of nucleons that interact via a monopole pairing interaction is calculated including the effects of thermal fluctuations and coupling to pair vibrations within the selfconsistent quasiparticle random-phase approximation. It is found that $\bar\eta$ increases with angular momentum $M$ at a given temperature $T$. In medium and heavy systems, $\bar\eta$ decreases with increasing $T$ at $T\geq$ 2 MeV and this feature is not affected much by angular momentum. But in lighter systems (with the mass number $A\leq$ 20), $\bar\eta$ increases with $T$ at a value of $M$ close to the maximal value $M_{max}$, which is defined as the limiting angular momentum for each system. The values of $\bar\eta$ obtained within the schematic model as well as for systems with realistic single-particle energies are always larger than the universal lower-bound conjecture $\hbar/(4\pi k_B)$ up to $T$=5 MeV.

Experimental Study on Active Vibration Control of a Gear Pair System Based on FxLMS Algorithm

To treat gear pair vibration due to internal excitation, an active internal gearbox structure near the gear pair is developed based on an active shaft transverse vibration control concept in the effort to tackle the gear excitation problem more directly. A controller of the FxLMS algorithm combined with frequency estimation technique is designed. And it is evaluated based on the experimental setup of the active gearbox vibration control system in contrast to fuzzy-PD controller. The experimental results show that 9.94dB attenuation in the gearbox housing vibration response can be achieved at the first gear mesh frequency by FxLMS controller, but only 5.62dB attenuation by fuzzy-PD controller. Besides, the insufficient effect at 210.8Hz and 216.2Hz is caused by typical out-of-band overshoot.

Tooth Profile Modification and its Effect on Spur Gear Pair Vibration in Presence of Localized Tooth Defect

AbstractVibration induced by gears includes important data about gearbox condition. We can use dynamic modeling of gear vibration for increasing our information about vibration generating mechanisms in gearboxes and dynamic behavior of gearbox in the presence of some kind of gear defects. In this paper a six degree-of-freedom nonlinear dynamic model including different gear errors and defects is developed for investigation of effects of tooth localized defect and profile modifications on overall gear dynamics. Interactions between tooth modifications and profile error are studied and the role of profile modification in dynamic response when a localized defect is incurred by a tooth is shown. It is indicated that although profile modifications and profile errors are micro-geometrical, they have considerable effects on vibrations of gear pair. Especially for the case of root relieved teeth that is shown to be more effective in reduction of vibration in the presence of tooth localized defect. Finally, the simulation results are compared with results from literature and the model is verified.

Density response of a trapped Fermi gas: A crossover from the pair vibration mode to the Goldstone mode

We consider the density response of a trapped two-component Fermi gas. Combining the Bogoliubov-deGennes method with the random phase approximation allows the study of both collective and single-particle excitations. Calculating the density response across a wide range of interactions, we observe a crossover from a weakly interacting pair vibration mode to a strongly interacting Goldstone mode. The crossover is associated with a depressed collective mode frequency and an increased damping rate, in agreement with density response experiments performed in strongly interacting atomic gases.

Active Gear Pair Vibration Control Based on Filtered-X RLS Algorithm

Based on the investigation of active gear pair vibration control system, an adaptive controller combined with Filtered-X method and RLS algorithm is developed to reduce the periodic vibration of gear driven shaft. The active control of the gear shaft transverse vibration is simulated to validate the efficiency of the proposed Filtered-X RLS algorithm (FXRLS). The results indicate that the FXRLS is significantly better in convergence speed and stability than the commonly used Filtered-X LMS algorithm (FXLMS), and the stability and convergence are more robust.