A revisitation of the 1888 H.Hertz experiment

We propose a revisitation of the original experiment performed by H. Hertz in 1888. With a simple setup it is possible to produce electromagnetic waves with a frequency in the range of 3 MHz. By performing Fourier analysis of the signal captured by a resonant antenna it is possible to study the behaviour of the RLC series circuit, frequency splitting of coupled resonances and finally the characteristics of the near-field emitted by the loop antenna

Phase-Insensitive Scattering of Terahertz Radiation

The nonlinear interaction between Near-Infrared (NIR) and Terahertz pulses is principally investigated as a means for the detection of radiation in the hardly accessible THz spectral region. Most studies have targeted second-order nonlinear processes, given their higher efficiencies, and only a limited number have addressed third-order nonlinear interactions, mainly investigating four-wave mixing in air for broadband THz detection. We have studied the nonlinear interaction between THz and NIR pulses in solid-state media (specifically diamond), and we show how the former can be frequency-shifted up to UV frequencies by the scattering from the nonlinear polarisation induced by the latter. Such UV emission differs from the well-known electric-field-induced second harmonic (EFISH) one, as it is generated via a phase-insensitive scattering, rather than a sum- or difference-frequency four-wave-mixing process

Experimental characterization of lithium-ion cell strain using laser sensors

The characterization of thickness change during operation of LFP/Graphite prismatic batteries is presented in this work. In this regard, current rate dependence, hysteresis behaviour between charge and discharge and correlation with phase changes are deepened. Experimental tests are carried out with a battery testing equipment correlated with optical laser sensors to evaluate swelling. Furthermore, thickness change is computed analytically with a mathematical model based on lattice parameters of the crystal structures of active materials. The results of the model are validated with experimental data. Thickness change is able to capture variations of the internal structure of the battery, referred to as phase change, characteristic of a certain state of charge. Furthermore, phase change shift is a characteristic of battery ageing. Being able to capture these properties with sensors mounted on the external surface the cell is a key feature for improving state of charge and state of health estimation in battery management system

Geometrical optics design of a compact range Gregorian subreflector system by the principle of the central ray

In recent years, the compact range has become very popular for measuring Radar Cross Section (RCS) and antenna patterns. The compact range, in fact, offers several advantages due to reduced size, a controlled environment, and privacy. On the other hand, it has some problems of its own, which must be solved properly in order to achieve high quality measurement results. For example, diffraction from the edges of the main reflector corrupts the plane wave in the target zone and creates spurious scattering centers in RCS measurements. While diffraction can be minimized by using rolled edges, the field of an offset single reflector compact range is corrupted by three other errors: the taper of the reflected field, the cross polarization introduced by the tilt of the feed and the aperture blockage introduced by the feed itself. These three errors can be eliminated by the use of a subreflector system. A properly designed subreflector system offers very little aperture blockage, no cross-polarization introduced and a minimization of the taper of the reflected field. A Gregorian configuration has been adopted in order to enclose the feed and the ellipsoidal subreflector in a lower chamber, which is isolated by absorbers from the upper chamber, where the main parabolic reflector and the target zone are enclosed. The coupling between the two rooms is performed through a coupling aperture. The first cut design for such a subreflector system is performed through Geometrical Optics ray tracing techniques (GO), and is greatly simplified by the use of the concept of the central ray introduced by Dragone. The purpose of the GO design is to establish the basic dimensions of the main reflector and subreflector, the size of the primary and secondary illuminating surfaces, the tilt angles of the subreflector and feed, and estimate the feed beamwidth. At the same time, the shape of the coupling aperture is initially determined

Reply to Comment on: Hawking radiation from ultrashort laser pulse filaments

A comment by R. Schutzhold et al. raises possible concerns and questions regarding recent measurements of analogue Hawking radiation. We briefly reply to the opinions expressed in the comment and sustain that the origin of the radiation may be understood in terms of Hawking emission

The breakdown of the cytokine network subsequent to human immunodeficiency virus infection

The acquired immunodeflciency syndrome (AIDS) is a clinically multifaceted disease induced by infection with the human immunodeficiency virus (HIV). HIV infection results in a complex pattern of immunologic alterations that leads to the development of AIDS in the majority of HIV seropositive (HIV+) individuals. The reduction in CD4 T lymphocyte counts is the hallmark of HIV infection; nevertheless, long before the reduction in CD4 counts reaches critical levels, a series of profound and complex defects that impair the function of CD4 T lymphocytes can be detected. Thus, HIV infection is characterized by quantitative and qualitative defects affecting CD4 T lymphocytes. It was suggested recently that programmed cell death (PCD) is an important mechanism leading to CD4 depletion in HIV infection, and that susceptibility of peripheral lymphocytes to PCD is differentially regulated by diverse cytokines. Thus, type 1 cytokines would protect CD4 lymphocytes against PCD, whereas type 2 cytokines would not protect against, and could augment, PCD. We suggest that the qualitative alterations of the immune response provoke the CD4 depletion characteristic of HIV disease via type 2 cytokinemediated augmentation of PCD, and are therefore ultimately responsible for the progression of HIV infection. Finally, we summarize recent data showing that three correlates of disease progression: emergence of HIV strains with syncitium-inducing ability (SI), type 1-to-type 2 cytokine shift, and CD4 depletion, are significantly associated, suggesting a complex interconnected virologic-immunologic pathogenesis of HIV infection

Emergence of X-shaped spatiotemporal coherence in optical waves

Considering the problem of parametric nonlinear interaction, we report the experimental observation of electromagnetic waves characterized by an X-shaped spatiotemporal coherence; i.e., coherence is neither spatial nor temporal, but skewed along specific spatiotemporal trajectories. The application of the usual, purely spatial or temporal, measures of coherence would erroneously lead to the conclusion that the field is fully incoherent. Such hidden coherence has been identified owing to an innovative diagnostic technique based on simultaneous analysis of both the spatial and temporal spectra

Laser-assisted guiding of electric discharges around objects

Electric breakdown in air occurs for electric fields exceeding 34 kV/cm and results in a large current surge that propagates along unpredictable trajectories. Guiding such currents across specific paths in a controllable manner could allow protection against lightning strikes and high-voltage capacitor discharges. Such capabilities can be used for delivering charge to specific targets, for electronic jamming, or for applications associated with electric welding and machining. We show that judiciously shaped laser radiation can be effectively used to manipulate the discharge along a complex path and to produce electric discharges that unfold along a predefined trajectory. Remarkably, such laser-induced arcing can even circumvent an object that completely occludes the line of sight

X-shaped space-time coherence in optical parametric generation

We study the spatiotemporal coherence properties of superfluorescence radiation generated in optical parametric amplification of quantum noise. We show that the angular dispersion properties of the spatiotemporal spectra, measured in different phase-matching conditions, lead to a clear X-shaped structure of the mutual correlation function of the radiation. Within a statistical picture, we interpret the generated superfluorescence as a stochastic \u201cgas\u201d of quasistationary modes characterized by a skewed correlation in the spatiotemporal domain, with characteristics similar to linear and nonlinear X waves not describable within a separable approach in space and time

Spatiotemporal Amplitude and Phase Retrieval of Bessel-X pulses using a Hartmann-Shack Sensor

We propose a new experimental technique, which allows for a complete characterization of ultrashort optical pulses both in space and in time. Combining the well-known Frequency-Resolved-Optical-Gating technique for the retrieval of the temporal profile of the pulse with a measurement of the near-field made with an Hartmann-Shack sensor, we are able to retrieve the spatiotemporal amplitude and phase profile of a Bessel-X pulse. By following the pulse evolution along the propagation direction we highlight the superluminal propagation of the pulse peak