Two-level interacting boson models beyond the mean field

The phase diagram of two-level boson Hamiltonians, including the Interacting Boson Model (IBM), is studied beyond the standard mean field approximation using the Holstein-Primakoff mapping. The limitations of the usual intrinsic state (mean field) formalism concerning finite-size effects are pointed out. The analytic results are compared to numerics obtained from exact diagonalizations. Excitation energies and occupation numbers are studied in different model space regions (Casten triangle for IBM) and especially at the critical points.Comment: 14 pages, 13 figure

Phase diagram for a Cubic Consistent-Q Interacting Boson Model Hamiltonian: signs of triaxiality

An extension of the Consistent-Q formalism for the Interacting Boson Model that includes the cubic QxQxQ term is proposed. The potential energy surface for the cubic quadrupole interaction is explicitly calculated within the coherent state formalism using the complete chi-dependent expression for the quadrupole operator. The Q-cubic term is found to depend on the asymmetry deformation parameter gamma as a linear combination of cos(3gamma) and cos^2(3\gamma) terms, thereby allowing for triaxiality. The phase diagram of the model in the large N limit is explored, it is described the order of the phase transition surfaces that define the phase diagram, and moreover, the possible nuclear equilibrium shapes are established. It is found that, contrary to expectations, there is only a very tiny region of triaxiality in the model, and that the transition from prolate to oblate shapes is so fast that, in most cases, the onset of triaxiality might go unnoticed.Comment: 18 pages, 19 figure

On the relation between E(5)−E(5)-models and the interacting boson model

The connections between the $E(5)-$models (the original E(5) using an infinite square well, $E(5)-\beta^4$, $E(5)-\beta^6$ and $E(5)-\beta^8$), based on particular solutions of the geometrical Bohr Hamiltonian with $\gamma$-unstable potentials, and the interacting boson model (IBM) are explored. For that purpose, the general IBM Hamiltonian for the $U(5)-O(6)$ transition line is used and a numerical fit to the different $E(5)-$models energies is performed, later on the obtained wavefunctions are used to calculate B(E2) transition rates. It is shown that within the IBM one can reproduce very well all these $E(5)-$models. The agreement is the best for $E(5)-\beta^4$ and reduces when passing through $E(5)-\beta^6$, $E(5)-\beta^8$ and E(5), where the worst agreement is obtained (although still very good for a restricted set of lowest lying states). The fitted IBM Hamiltonians correspond to energy surfaces close to those expected for the critical point. A phenomenon similar to the quasidynamical symmetry is observed

Relationship between X(5)-models and the interacting boson model

The connections between the X(5)-models (the original X(5) using an infinite square well, X(5)-$\beta^8$, X(5)-$\beta^6$, X(5)-$\beta^4$, and X(5)-$\beta^2$), based on particular solutions of the geometrical Bohr Hamiltonian with harmonic potential in the $\gamma$ degree of freedom, and the interacting boson model (IBM) are explored. This work is the natural extension of the work presented in [1] for the E(5)-models. For that purpose, a quite general one- and two-body IBM Hamiltonian is used and a numerical fit to the different X(5)-models energies is performed, later on the obtained wave functions are used to calculate B(E2) transition rates. It is shown that within the IBM one can reproduce well the results for energies and B(E2) transition rates obtained with all these X(5)-models, although the agreement is not so impressive as for the E(5)-models. From the fitted IBM parameters the corresponding energy surface can be extracted and it is obtained that, surprisingly, only the X(5) case corresponds in the moderate large N limit to an energy surface very close to the one expected for a critical point, while the rest of models seat a little farther.Comment: Accepted in Physical Review

The U(5)-O(6) transition in the Interacting Boson Model and the E(5) critical point symmetry

The relation of the recently proposed E(5) critical point symmetry with the interacting boson model is investigated. The large-N limit of the interacting boson model at the critical point in the transition from U(5) to O(6) is obtained by solving the Richardson equations. It is shown explicitly that this algebraic calculation leads to the same results as the solution of the Bohr differential equation with a $\beta^4$ potential.Comment: Accepted in PR

Effect of exercise on sleep quality and insomnia in middle-aged women: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVE: We assessed the effects of programmed exercise (PE) on sleep quality and insomnia in middle-aged women (MAW). METHODS: Searches were conducted in five databases from inception through December 15, 2016 for randomized controlled trials (RCTs) evaluating the effects of PE versus a non-exercising control condition on sleep quality, sleep disturbance and/or insomnia in MAW. Interventions had to last at least 8 weeks. Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI) and insomnia with the Insomnia Severity Index (ISI). Random effects models were used for meta-analyses. The effects on outcomes were expressed as mean differences (MDs) and their 95% confidence intervals (CI). RESULTS: Five publications reported data from four RCTs on PE effects during 12-16 weeks on sleep quality (n=4 studies reporting PSQI results) and/or insomnia (n=3 studies reporting ISI results), including 660 MAW. Low-moderate levels of exercise significantly lowered the PSQI score (MD=-1.34; 95% CI -2.67, 0.00; p=0.05) compared with controls. In a subgroup analysis, moderate PE (aerobic exercise) had a positive effect on sleep quality (PSQI score MD=-1.85; 95% CI -3.62, -0.07; p=0.04), while low levels of physical activity (yoga) did not have a significant effect (MD-0.46, 95% CI -1.79, 0.88, p=0.50). In three studies (two studies of yoga, one study of aerobic exercise), there was a non-significant reduction in the severity of insomnia measured with the ISI score (MD -1.44, 95% CI -3.28, 0. 44, p=0.13) compared with controls. Heterogeneity of effects among studies was moderate to high. CONCLUSION: In middle-aged women, programmed exercise improved sleep quality but had no significant effect on the severity of insomnia.Actividad Física y Deport

Medium-modified evolution of multiparticle production in jets in heavy-ion collisions

The energy evolution of medium-modified average multiplicities and multiplicity fluctuations in quark and gluon jets produced in heavy-ion collisions is investigated from a toy QCD-inspired model. In this model, we use modified splitting functions accounting for medium-enhanced radiation of gluons by a fast parton which propagates through the quark gluon plasma. The leading contribution of the standard production of soft hadrons is found to be enhanced by the factor $\sqrt{N_s}$ while next-to-leading order (NLO) corrections are suppressed by $1/\sqrt{N_s}$, where the nuclear parameter $N_s>1$ accounts for the induced-soft gluons in the hot medium. The role of next-to-next-to-leading order corrections (NNLO) is studied and the large amount of medium-induced soft gluons is found to drastically affect the convergence of the perturbative series. Our results for such global observables are cross-checked and compared with their limits in the vacuum and a new method for solving the second multiplicity correlator evolution equations is proposed.Comment: 21 pages and 8 figures, typo corrections, references adde

Emissions from a Euro 6 engine using polyoxymethylene dimethyl ethers: Chemical effects vs mapping strategy

New fuel technologies, such as electrofuels, are an attractive alternative to meet the energy demand and emission regulations, with sustainable electricity being the primary source of energy. Recently, there is increasing interest in using polyoxymethylene dimethyl ether (OME) as a diesel substitute. This study investigated the effect of a diesel fuel blend with 20% of OME (OME20) with 3–5 oxymethylene groups, on the performance, combustion characteristics, regulated emissions, particle number (PN), and particle size distribution in a compression ignition Euro 6 engine following the Worldwide harmonized Light vehicle Test Cycle (WLTC). Regulated emissions were measured downstream of the aftertreatment system, while PN emissions were measured upstream of the particulate filter. The results showed that OME20 increased the peaks of pressure and heat released rate, causing an increase in the combustion speed compared to diesel. OME20 reduced CO and THC accumulated emissions by 52% and 17%, respectively, and the PN exhibited a dramatic reduction close to 61%. Such reductions were influenced by both the fuel formulation and the engine settings induced by the fuel. With OME20, the engine requires higher fueling to maintain the same power output. Therefore, the accelerator pedal position was higher compared to diesel, leading a decrease in exhaust gas recirculation (EGR) rate to increase the air mass flow. Consequently, PN, CO and THC emissions were reduced, and conversely, accumulated NOx emissions increased up to 42%. OME20 decreased the peak number concentrations of accumulation-mode particles at all driving cycle phases and caused a slight shift of the particles toward smaller size compared to diesel fuel. From the results, it can be concluded that PN and regulated emissions, despite being strongly affected by the fuel properties, are very sensitive to the EGR rate and the equivalence ratio, which are established in the engine mapping.Las nuevas tecnologías de combustibles, como los electrocombustibles, son una alternativa atractiva para cumplir con la demanda energética y las regulaciones de emisiones, siendo la electricidad sustentable la principal fuente de energía. Recientemente, existe un interés creciente en el uso de polioximetilen dimetil éter (OME) como sustituto del diesel. Este estudio investigó el efecto de una mezcla de combustible diésel con un 20 % de OME (OME20) con 3–5 grupos oximetileno sobre el rendimiento, las características de combustión, las emisiones reguladas, el número de partículas (PN) y la distribución del tamaño de las partículas en un motor Euro de encendido por compresión. 6 siguiendo el ciclo de prueba de vehículos ligeros armonizados a nivel mundial (WLTC). Las emisiones reguladas se midieron aguas abajo del sistema de postratamiento, mientras que las emisiones de PN se midieron aguas arriba del filtro de partículas. Los resultados mostraron que OME20 aumentó los picos de presión y la tasa de liberación de calor, lo que provocó un aumento en la velocidad de combustión en comparación con el diésel. OME20 redujo las emisiones acumuladas de CO y THC en un 52 % y un 17 %, respectivamente, y el PN exhibió una reducción drástica cercana al 61 %. Tales reducciones fueron influenciadas tanto por la formulación del combustible como por los ajustes del motor inducidos por el combustible. Con OME20, el motor requiere una mayor carga de combustible para mantener la misma potencia de salida. Por lo tanto, la posición del pedal del acelerador era más alta en comparación con el diésel, lo que provocó una disminución en la tasa de recirculación de gases de escape (EGR) para aumentar el flujo de masa de aire. En consecuencia, se redujeron las emisiones de PN, CO y THC y, por el contrario, NO acumulado respectivamente, y la PN exhibió una drástica reducción cercana al 61%. Tales reducciones fueron influenciadas tanto por la formulación del combustible como por los ajustes del motor inducidos por el combustible. Con OME20, el motor requiere una mayor carga de combustible para mantener la misma potencia de salida. Por lo tanto, la posición del pedal del acelerador era más alta en comparación con el diésel, lo que provocó una disminución en la tasa de recirculación de gases de escape (EGR) para aumentar el flujo de masa de aire. En consecuencia, se redujeron las emisiones de PN, CO y THC y, por el contrario, NO acumulado respectivamente, y la PN exhibió una drástica reducción cercana al 61%. Tales reducciones fueron influenciadas tanto por la formulación del combustible como por los ajustes del motor inducidos por el combustible. Con OME20, el motor requiere una mayor carga de combustible para mantener la misma potencia de salida. Por lo tanto, la posición del pedal del acelerador era más alta en comparación con el diésel, lo que provocó una disminución en la tasa de recirculación de gases de escape (EGR) para aumentar el flujo de masa de aire. En consecuencia, se redujeron las emisiones de PN, CO y THC y, por el contrario, NO acumulado provocando una disminución en la tasa de recirculación de gases de escape (EGR) para aumentar el flujo de masa de aire. En consecuencia, se redujeron las emisiones de PN, CO y THC y, por el contrario, NO acumulado provocando una disminución en la tasa de recirculación de gases de escape (EGR) para aumentar el flujo de masa de aire. En consecuencia, se redujeron las emisiones de PN, CO y THC y, por el contrario, NO acumuladox las emisiones aumentaron hasta un 42%. OME20 disminuyó las concentraciones máximas de partículas en modo de acumulación en todas las fases del ciclo de conducción y provocó un ligero cambio de las partículas hacia un tamaño más pequeño en comparación con el combustible diésel. De los resultados se puede concluir que la PN y las emisiones reguladas, a pesar de estar fuertemente afectadas por las propiedades del combustible, son muy sensibles a la tasa de EGR y la relación de equivalencia, las cuales se establecen en el mapeo del motor

Quantum quench influenced by an excited-state phase transition

We analyze excited-state quantum phase transitions (ESQPTs) in three schematic (integrable and nonintegrable) models describing a single-mode bosonic field coupled to a collection of atoms. It is shown that the presence of the ESQPT in these models affects the quantum relaxation processes following an abrupt quench in the control parameter. Clear cut evidence of the ESQPT effects is presented in integrable models, while in the nonintegrable model the evidence is blurred due to chaotic behavior of the system in the region around the critical energy.Comment: submitted to Physical Review

Anharmonic double-phonon excitations in the interacting boson model

Double-$\gamma$ vibrations in deformed nuclei are analyzed in the context of the interacting boson model. A simple extension of the original version of the model towards higher-order interactions is required to explain the observed anharmonicities of nuclear vibrations. The influence of three- and four-body interactions on the moments of inertia of ground- and $\gamma$-bands, and on the relative position of single-$\gamma$ and double-$\gamma$ bands is studied in detail. As an example of a realistic calculation, spectra and transitions of the highly $\gamma$-anharmonic nuclei $^{164}$Dy, $^{166}$Er, and $^{168}$Er are interpreted in this approach.Comment: 38 pages, TeX (ReVTeX). 15 ps figures. Submitted to Phys. Rev.