Effects of arbitrarily directed field on spin phase oscillations in biaxial molecular magnets

Quantum phase interference and spin-parity effects are studied in biaxial molecular magnets in a magnetic field at an arbitrarily directed angle. The calculations of the ground-state tunnel splitting are performed on the basis of the instanton technique in the spin-coherent-state path-integral representation, and complemented by exactly numerical diagonalization. Both the Wentzel-Kramers-Brillouin exponent and the preexponential factor are obtained for the entire region of the direction of the field. Our results show that the tunnel splitting oscillates with the field for the small field angle, while for the large field angle the oscillation is completely suppressed. This distinct angular dependence, together with the dependence of the tunnel splitting on the field strengh, provide an independent test for spin-parity effects in biaxial molecular magnets. The analytical results for the molecular Fe$_{8}$ magnet, are found to be in good areement with the numerical simulations, which suggests that even the molecular magnet with total spin S=10 is large enough to be treated as a giant spin system.Comment: 19 pages, 5 figure

Spin tunneling properties in mesoscopic magnets: effects of a magnetic field

The tunneling of a giant spin at excited levels is studied theoretically in mesoscopic magnets with a magnetic field at an arbitrary angle in the easy plane. Different structures of the tunneling barriers can be generated by the magnetocrystalline anisotropy, the magnitude and the orientation of the field. By calculating the nonvacuum instanton solution explicitly, we obtain the tunnel splittings and the tunneling rates for different angle ranges of the external magnetic field ($\theta_{H}=\pi/2$ and $\pi/2<\theta_{H}<\pi$). The temperature dependences of the decay rates are clearly shown for each case. It is found that the tunneling rate and the crossover temperature depend on the orientation of the external magnetic field. This feature can be tested with the use of existing experimental techniques.Comment: 27 pages, 4 figures, accepted by Euro. Phys. J.

Resonant quantum coherence of magnetization at excited states in nanospin systems with different crystal symmetries

The quantum interference effects induced by the Wess-Zumino term, or Berry phase are studied theoretically in resonant quantum coherence of magnetization vector between degenerate excited states in nanometer-scale single-domain ferromagnets in the absence of an external magnetic field. By applying the periodic instanton method in the spin-coherent-state path integral, we evaluate the low-lying tunnel splittings between degenerate excited states of neighboring wells. And the low-lying energy level spectrum of m-th excited states are obtained with the help of the Bloch theorem in one-dimensional periodic potential.Comment: 23 pages, final version and accepted by Eur. Phys. J.

Quasinormal modes and stability of higher dimensional rotating black holes under massive scalar perturbations

We consider the stability of six-dimensional singly rotating Myers-Perry black holes under massive scalar perturbations. Using Leaver's continued fraction method, we compute the quasinormal modes of the massive scalar fields. All modes found are damped under the quasinormal boundary conditions. It is also found that long-living modes called quasiresonances exist for large scalar masses as in the four-dimensional Kerr black hole case. Our numerical results provide a direct and complement evidence for the stability of six-dimensional MP black holes under massive scalar perturbation.Comment: 11 pages,9 figure

Postoperative vomiting/nausea in Chinese patients undergoing bariatric surgery

Purpose: To assess the incidence of post-operative vomiting/nausea (PVN), as well as usage and effectiveness of PVN prophylaxis in Chinese patients receiving bariatric surgery. Methods: This prospective observational study included 82 patients subjected to bariatric surgery using total intravenous (IV) anesthesia. Patients were given PVN prophylactic treatment as per the local practice depending on Apfel et al criterion for simplified risk score useful for PVN prediction. Postsurgery, the patients were evaluated at 2, 4, 6, 24, 48 and 72 h using a questionnaire. Univariate analysis of risk factors associated with PVN was carried conducted with Pearson’s Chi-squared test for category variables and Mann–Whitney–Wilcoxon test for a continuous variable. Results: About 69 % of the patients developed PVN within 24 h post-surgery, and the risk increased with increase in the number of PVN risk factors. Significant contrasts were seen with respect to PVN, with higher occurrence in females (81.36 %), when compared to males (39.13 %) within the first 24 h (p &lt; 0.05). Two patients got sub-optimum PVN prophylactic therapy as per guidelines, 19 patients had optimum therapy, while 61 patients had supra-optimum therapy. Moreover, 63.94 % of patients who obtained supra-optimum PVN prophylactic therapy experienced PVN within 24 h post-surgery, while 84.21 % of patients with optimum PVN prophylactic therapy experienced PVN within the same period (p &lt; 0.05). Overall, 35.37 % of patients experienced serious nausea 24 h post-surgery. Conclusion: PVN incidence is high, notwithstanding the fact that almost all the patients received optimum or supra-optimum prophylactic therapy. These findings raise dubiety regarding the viability and significance of using risk-based PVN prophylactic therapy in patients under bariatric surgery. Thus, further research is needed in this regard

Stability of five-dimensional Myers-Perry black holes under massive scalar perturbation: bound states and quasinormal modes

The stability of five-dimensional singly rotating Myers-Perry Black Holes against massive scalar perturbations is studied. Both the quasibound states and quasinormal modes of the massive scalar field are considered. For the quasibound states, we use an analytical method to discuss the effective potential felt by the scalar field, and found that there is no potential well outside the event horizon. Thus, singly rotating Myers-Perry Black Holes are stable against the perturbation of quasibound states of massive scalar fields. Then, We use continued fraction method based on solving a seven-term recurrence relations to compute the spectra of the quasinormal modes. For different values of the black hole rotation parameter $a$, scalar mass parameter $\mu$ and angular quantum numbers, all found quasinormal modes are damped. So singly rotating Myers-Perry Black Holes are also stable against the perturbation of quasinormal modes of massive scalar fields. Besides, when the scalar mass $\mu$ becomes relatively large, the long-living quasiresonances are also found as in other rotating black hole models. Our results complement previous arguments on the stability of five-dimensional singly rotating Myers-Perry black holes against massive scalar perturbations.Comment: references adde

Bis(nitrato-κO)(3-oxapentane-1,5-diamine-κ3 N,O,N′)zinc(II)

In the title compound, [Zn(NO3)2(C4H12N2O)], the ZnII atom is N,O,N′-chelated by a 3-oxapentane-1,5-diamine ligand and is further coordinated by two nitrate anions in a distorted trigonal–bipyramidal geometry. Inter­molecular N—H⋯O hydrogen bonding is present in the crystal structure. A short O⋯O contact of 2.816 (8) Å is observed between the nitrate anions of adjacent mol­ecules