Loschmidt echo and fidelity decay near an exceptional point

Non-Hermitian classical and open quantum systems near an exceptional point (EP) are known to undergo strong deviations in their dynamical behavior under small perturbations or slow cycling of parameters as compared to Hermitian systems. Such a strong sensitivity is at the heart of many interesting phenomena and applications, such as the asymmetric breakdown of the adiabatic theorem, enhanced sensing, non-Hermitian dynamical quantum phase transitions and photonic catastrophe. Like for Hermitian systems, the sensitivity to perturbations on the dynamical evolution can be captured by Loschmidt echo and fidelity after imperfect time reversal or quench dynamics. Here we disclose a rather counterintuitive phenomenon in certain non-Hermitian systems near an EP, namely the deceleration (rather than acceleration) of the fidelity decay and improved Loschmidt echo as compared to their Hermitian counterparts, despite large (non-perturbative) deformation of the energy spectrum introduced by the perturbations. This behavior is illustrated by considering the fidelity decay and Loschmidt echo for the single-particle hopping dynamics on a tight-binding lattice under an imaginary gauge field.Comment: 11 pages, 6 figures, to appear in Annalen der Physi

Dynamic facial expressions of emotions are discriminated at birth

The ability to discriminate between different facial expressions is fundamental since the first stages of postnatal life. The aim of this study is to investigate whether 2-days-old newborns are capable to discriminate facial expressions of emotions as they naturally take place in everyday interactions, that is in motion. When two dynamic displays depicting a happy and a disgusted facial expression were simultaneously presented (i.e., visual preference paradigm), newborns did not manifest any visual preference (Experiment 1). Nonetheless, after being habituated to a happy or disgusted dynamic emotional expression (i.e., habituation paradigm), newborns successfully discriminated between the two (Experiment 2). These results indicate that at birth newborns are sensitive to dynamic faces expressing emotions

Nitrogen balance and fate in a heavily impacted watershed (Oglio River, Northern Italy): in quest of the missing sources and sinks

We present data from a comprehensive investigation carried out from 2007 to 2010, focussing on nitrogen pollution in the Oglio River basin (3800 km², Po Plain, Northern Italy). Nitrogen mass balances, computed for the whole basin with 2000 and 2008 data, suggest a large N surplus in this area, over 40 000 t N yr⁻¹, and increasing between 2000 and 2008. Calculations indicate a very large impact of animal husbandry and agricultural activities in this watershed, with livestock manure and synthetic fertilizers contributing 85% of total N inputs (about 100 000 t N yr⁻¹) and largely exceeding crop uptake and other N losses (about 60 000 t N yr⁻¹). Nitrogen from domestic and industrial origin is estimated as about 5800 and 7200 t N yr⁻¹, respectively, although these loads are overestimated, as denitrification in treatment plants is not considered; nonetheless, they represent a minor term of the N budget. Annual export of nitrogen from the basin, calculated from flow data and water chemistry at the mouth of the Oglio River, is estimated at 13 000 t N yr⁻¹, and represents a relatively small fraction of N inputs and surplus (∼12% and 34%, respectively). After considering N sinks in crop uptake, soil denitrification and volatilization, a large excess remains unaccounted (∼26 000 t N yr⁻¹) in unknown temporary or permanent N sinks. Nitrogen removal via denitrification was evaluated in the Oglio riverbed with stable isotope techniques (δ¹⁵N and δ¹⁸O in nitrate). The downstream final segment of the river displays an enriched nitrate stable isotope composition but calculations suggest a N removal corresponding to at most 20% of the unaccounted for N amount. Denitrification was also evaluated in riverine wetlands with the isotope pairing technique. Areal rates are elevated but overall N removal is low (about 1% of the missing N amount), due to small wetland surfaces and limited lateral connectivity. The secondary drainage channel network has a much higher potential for nitrogen removal via denitrification, due to its great linear development, estimated in over 12 500 km, and its capillary distribution in the watershed. In particular, we estimated a maximum N loss up to 8500 t N yr⁻¹, which represents up to 33% of the unaccounted for N amount in the basin. Overall, denitrification in surface aquatic habitats within this basin can be responsible for the permanent removal of about 12 000 t N yr⁻¹; but the fate of some 14 000 t remains unknown. Available data on nitrate concentration in wells suggest that in the central part of the watershed groundwater accumulates nitrogen. Simultaneously, we provide evidences that part of the stored nitrate can be substantially recycled via springs and can pollute surface waters via river-groundwater interactions. This probably explains the ten fold increase of nitrate concentration in a reach of the Oglio River where no point pollutions sources are present

Nitrogen balance and fate in a heavily impacted watershed (Oglio River, Northern Italy): in quest of the missing sources and sinks

Abstract. We present data from a comprehensive investigation carried out from 2007 to 2010, focussing on nitrogen pollution in the Oglio River basin (3800 km2, Po Plain, Northern Italy). Nitrogen mass balances, computed for the whole basin with 2000 and 2008 data, suggest a large N surplus in this area, over 40 000 t N yr−1, and increasing between 2000 and 2008. Calculations indicate a very large impact of animal husbandry and agricultural activities in this watershed, with livestock manure and synthetic fertilizers contributing 85% of total N inputs (about 100 000 t N yr−1) and largely exceeding crop uptake and other N losses (about 60 000 t N yr−1). Nitrogen from domestic and industrial origin is estimated as about 5800 and 7200 t N yr−1, respectively, although these loads are overestimated, as denitrification in treatment plants is not considered; nonetheless, they represent a minor term of the N budget. Annual export of nitrogen from the basin, calculated from flow data and water chemistry at the mouth of the Oglio River, is estimated at 13 000 t N yr−1, and represents a relatively small fraction of N inputs and surplus (∼12% and 34%, respectively). After considering N sinks in crop uptake, soil denitrification and volatilization, a large excess remains unaccounted (∼26 000 t N yr−1) in unknown temporary or permanent N sinks. Nitrogen removal via denitrification was evaluated in the Oglio riverbed with stable isotope techniques (δ15N and δ18O in nitrate). The downstream final segment of the river displays an enriched nitrate stable isotope composition but calculations suggest a N removal corresponding to at most 20% of the unaccounted for N amount. Denitrification was also evaluated in riverine wetlands with the isotope pairing technique. Areal rates are elevated but overall N removal is low (about 1% of the missing N amount), due to small wetland surfaces and limited lateral connectivity. The secondary drainage channel network has a much higher potential for nitrogen removal via denitrification, due to its great linear development, estimated in over 12 500 km, and its capillary distribution in the watershed. In particular, we estimated a maximum N loss up to 8500 t N yr−1, which represents up to 33% of the unaccounted for N amount in the basin. Overall, denitrification in surface aquatic habitats within this basin can be responsible for the permanent removal of about 12 000 t N yr−1; but the fate of some 14 000 t remains unknown. Available data on nitrate concentration in wells suggest that in the central part of the watershed groundwater accumulates nitrogen. Simultaneously, we provide evidences that part of the stored nitrate can be substantially recycled via springs and can pollute surface waters via river-groundwater interactions. This probably explains the ten fold increase of nitrate concentration in a reach of the Oglio River where no point pollutions sources are present

Low power GaAs digital and analog functionalities for microwave signal conditioning in AESA systems

A MMIC demonstrator for RF phase and amplitude control with on board 18-bit serial to parallel conversion (Multi-Functional Chip) is presented. Thanks to an alternative digital building block topology, the DC power consumption of the digital serial to parallel converter is noteworthy: less than 43 mW (2 mW/bit). The main RF performances are 0° - 360° phase coverage and 0 dB - 31.5 dB attenuation setting, in the 7.6 GHz - 9.1 GHz operating bandwidth. The circuit, whose area is 6 mm2, is realised in an industrial and commercially available GaAs technology. This component can be used in active electronically scanned arrays for beam steering

Beam heat load analysis with COLDDIAG: a cold vacuum chamber for diagnostics

The knowledge of the heat intake from the electron beam is essential to design the cryogenic layout of superconducting insertion devices. With the aim of measuring the beam heat load to a cold bore and understanding the responsible mechanisms, a cold vacuum chamber for diagnostics (COLDDIAG) has been built. The instrumentation comprises temperature sensors, pressure gauges, mass spectrometers and retarding field analyzers, which allow to study the beam heat load and the influence of the cryosorbed gas layer. COLDDIAG was installed in the storage ring of the Diamond Light Source from September 2012 to August 2013. During this time measurements were performed for a wide range of machine conditions, employing the various measuring capabilities of the device. Here we report on the analysis of the measured beam heat load, pressure and gas content, as well as the low energy charged particle flux and spectrum as a function of the electron beam parameters

Polarisation Patterns and Vectorial Defects in Type II Optical Parametric Oscillators

Previous studies of lasers and nonlinear resonators have revealed that the polarisation degree of freedom allows for the formation of polarisation patterns and novel localized structures, such as vectorial defects. Type II optical parametric oscillators are characterised by the fact that the down-converted beams are emitted in orthogonal polarisations. In this paper we show the results of the study of pattern and defect formation and dynamics in a Type II degenerate optical parametric oscillator for which the pump field is not resonated in the cavity. We find that traveling waves are the predominant solutions and that the defects are vectorial dislocations which appear at the boundaries of the regions where traveling waves of different phase or wave-vector orientation are formed. A dislocation is defined by two topological charges, one associated with the phase and another with the wave-vector orientation. We also show how to stabilize a single defect in a realistic experimental situation. The effects of phase mismatch of nonlinear interaction are finally considered.Comment: 38 pages, including 15 figures, LATeX. Related material, including movies, can be obtained from http://www.imedea.uib.es/Nonlinear/research_topics/OPO

Centers of Mass and Rotational Kinematics for the Relativistic N-Body Problem in the Rest-Frame Instant Form

In the Wigner-covariant rest-frame instant form of dynamics it is possible to develop a relativistic kinematics for the N-body problem. The Wigner hyperplanes define the intrinsic rest frame and realize the separation of the center-of-mass. Three notions of {\it external} relativistic center of mass can be defined only in terms of the {\it external} Poincar\'e group realization. Inside the Wigner hyperplane, an {\it internal} unfaithful realization of the Poincar\'e group is defined. The three concepts of {\it internal} center of mass weakly {\it coincide} and are eliminated by the rest-frame conditions. An adapted canonical basis of relative variables is found. The invariant mass is the Hamiltonian for the relative motions. In this framework we can introduce the same {\it dynamical body frames}, {\it orientation-shape} variables, {\it spin frame} and {\it canonical spin bases} for the rotational kinematics developed for the non-relativistic N-body problem.Comment: 78 pages, revtex fil

Use of Equivalent Hermitian Hamiltonian for PTPT-Symmetric Sinusoidal Optical Lattices

We show how the band structure and beam dynamics of non-Hermitian $PT$-symmetric sinusoidal optical lattices can be approached from the point of view of the equivalent Hermitian problem, obtained by an analytic continuation in the transverse spatial variable $x$. In this latter problem the eigenvalue equation reduces to the Mathieu equation, whose eigenfunctions and properties have been well studied. That being the case, the beam propagation, which parallels the time-development of the wave-function in quantum mechanics, can be calculated using the equivalent of the method of stationary states. We also discuss a model potential that interpolates between a sinusoidal and periodic square well potential, showing that some of the striking properties of the sinusoidal potential, in particular birefringence, become much less prominent as one goes away from the sinusoidal case.Comment: 11 pages, 8 figure