Ultrabroadband conical emission generated from the ultraviolet up to the far-infrared during the optical filamentation in air

Ultraviolet and infrared conical emissions were observed during the filamentation in air of powerful femtosecond laser pulses produced by a portable terawatt laser system. The broadband spectrum was measured from 200 nm up to 14 microm and covered the complete optical transmission window of the atmosphere. The angularly resolved spectrum showed some X-wave structure across the frequency range analyzed. However, we demonstrated that the strong conical emission observed in the mid- and far-infrared is mainly owing to the four-wave mixing between the pump pulse and its blueshifted conical emission.     

Modeling the sound transmission between rooms coupled through partition walls by using a diffusion model

In this paper, a modification of the diffusion model for room acoustics is proposed to account for sound transmission between two rooms, a source room and an adjacent room, which are coupled through a partition wall. A system of two diffusion equations, one for each room, together with a set of two boundary conditions, one for the partition wall and one for the other walls of a room, is obtained and numerically solved. The modified diffusion model is validated by numerical comparisons with the statistical theory for several coupled-room configurations by varying the coupling area surface, the absorption coefficient of each room, and the volume of the adjacent room. An experimental comparison is also carried out for two coupled classrooms. The modified diffusion model results agree very well with both the statistical theory and the experimental data. The diffusion model can then be used as an alternative to the statistical theory, especially when the statistical theory is not applicable, that is, when the reverberant sound field is not diffuse. Moreover, the diffusion model allows the prediction of the spatial distribution of sound energy within each coupled room, while the statistical theory gives only one sound level for each room.     

Modeling urban street patterns

Urban street patterns form planar networks whose empirical properties cannot be accounted for by simple models such as regular grids or Voronoi tesselations. Striking statistical regularities across different cities have been recently empirically found, suggesting that a general and detail-independent mechanism may be in action. We propose a simple model based on a local optimization process combined with ideas previously proposed in studies of leaf pattern formation. The statistical properties of this model are in good agreement with the observed empirical patterns. Our results thus suggest that in the absence of a global design strategy, the evolution of many different transportation networks indeed follows a simple universal mechanism.     

A Geometric Approach to Integrability of Abel Differential Equations

A geometric approach is used to study the Abel first-order differential equation of the first kind. The approach is based on the recently developed theory of quasi-Lie systems which allows us to characterise some particular examples of integrable Abel equations. Second order Abel equations will be discussed and the inverse problem of the Lagrangian dynamics is analysed: the existence of two alternative Lagrangian formulations is proved, both Lagrangians being of a non-natural class. The study is carried out by means of the Darboux polynomials and Jacobi multipliers.     

Effects of temperature and dissolved CO<Subscript>2</Subscript> on the scaling of water in the presence of copper and zinc

In this study, through the method of rapid controlled precipitation (RCP), the influence of temperature and dissolved CO₂ on the scaling capacity of mineral water in the presence of copper and zinc ions was studied in laboratory experiments. The results indicated that with a rise in temperature or concentration of dissolved CO₂, the scaling time of Salvetat water greatly decreased and the rate of precipitation considerably increased; therefore, the minimum dosage of copper or zinc ion for achieving total inhibition of scaling needed to be increased, which would provide better guidance for practical use of metal ions in inhibiting the scaling of drinking water.     

Experimental estimate of a classicality witness via a single measurement

The perception that quantum correlations can still appear in separable states has opened exciting new possibilities regarding their use as a resource in quantum information science. Quantifying such quantum correlations involves the complete knowledge of the system's state and numerical optimization procedures. Thus, it is natural to seek methods involving fewer measurements that indicate the nature of the correlations in a system. Here we propose a classicality witness that can be accurately estimated via statistics from a single measurement and perform an experiment to explore the utility of this witness for quantum states with different types of correlations.     

Structure of polymeric carbon dioxide CO2-V

The structure of polymeric carbon dioxide (CO2-V) has been solved using synchrotron x-ray powder diffraction, and its evolution followed from 8 to 65 GPa. We compare the experimental results obtained for a 100% CO2 sample and a 1 mol?% CO2/He sample. The latter allows us to produce the polymer in a pure form and study its compressibility under hydrostatic conditions. The high quality of the x-ray data enables us to solve the structure directly from experiments. The latter is isomorphic to the β-cristobalite phase of SiO2 with the space group I42d. Carbon and oxygen atoms are arranged in CO4 tetrahedral units linked by oxygen atoms at the corners. The bulk modulus determined under hydrostatic conditions, B0=136(10) GPa, is much smaller than previously reported. The comparison of our experimental findings with theoretical calculations performed in the present and previous studies shows that density functional theory very well describes polymeric CO2.     

Scattering forces and electromagnetic momentum density in crossed circularly polarized standing waves

We analyze the forces on a small dipolar particle and the electromagnetic momentum density in a configuration consisting in two perpendicular circularly polarized stationary waves. The field distribution shows regions in which the electric and magnetic fields are parallel corresponding to a null Poynting vector. Although the average value of the momentum density, proportional to the Poynting vector, is zero in these regions, there are scattering forces acting on small particles due to light's spin force. The total scattering force suggests a new definition of the average value of the momentum density for free propagating electromagnetic fields.     

Modeling hyperfine parameters observed from the charge-ordered to valence-mixed state of NdBaFe(2)O(5)

Orbital populations of the minority-spin Fe(2+) electron in NdBaFe(2)O(5) are extracted from electric and magnetic hyperfine parameters of (57)Fe M?ssbauer spectra across the temperature interval where charge ordering of the valence state 2.5?+ of iron occurs. The previously used approach that assigns the minority-spin population to a single lowest-energy d orbital is expanded to three orbitals by setting up a system of equations in terms of the Fe(2+)/Fe(3+) balance from isomer shift, a point-charge model for the valence and ligand contributions to the electric-field gradient, a point-dipole model for the dipolar contribution and an iterative scheme for small orbital contributions to the internal magnetic field. This allows us to model the hyperfine fields (electric and magnetic) in the intermediate temperature range of partial charge ordering between T(V )?≈?210?K and T(p)?≈?285?K, for which the one-orbital model was insufficient.     

Modulated spin liquid: a new paradigm for URu2Si2

We argue that near a Kondo breakdown critical point, a spin liquid with spatial modulations can form. Unlike its uniform counterpart, we find that this occurs via a second order phase transition. The amount of entropy quenched when ordering is of the same magnitude as for an antiferromagnet. Moreover, the two states are competitive, and at low temperatures are separated by a first order phase transition. The modulated spin liquid we find breaks Z4 symmetry, as recently seen in the hidden order phase of URu2Si2. Based on this, we suggest that the modulated spin liquid is a viable candidate for this unique phase of matter.