Ion kinetic energy conservation and magnetic field strength constancy in multi-fluid solar wind Alfv\'enic turbulence

We investigate properties of the plasma fluid motion in the large amplitude low frequency fluctuations of highly Alfv\'enic fast solar wind. We show that protons locally conserve total kinetic energy when observed from an effective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame can be reasonably identified by alpha particles, which, owing to their drift with respect to protons at about the Alfv\'en speed along the magnetic field, do not partake in the fluid low frequency fluctuations. Using their velocity to transform proton velocity into the frame of Alfv\'enic turbulence, we demonstrate that the resulting plasma motion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity and magnetic field vectors as expected for unidirectional Alfv\'enic fluctuations in equilibrium. We propose that this constraint, via the correlation between velocity and magnetic field in Alfv\'enic turbulence, is at the origin of the observed constancy of the magnetic field: while the constant velocity corresponding to constant energy can be only observed in the frame of the fluctuations, the correspondingly constant total magnetic field, invariant for Galilean transformations, remains the observational signature, in the spacecraft frame, of the constant total energy in the Alfv\'en turbulence frame.Comment: 6 pages, 6 figures, Accepted for publication in The Astrophysical Journa

Nonlinear motion and mechanical mixing in as-grown GaAs nanowires

We report nonlinear behavior in the motion of driven nanowire cantilevers. The nonlinearity can be described by the Duffing equation and is used to demonstrate mechanical mixing of two distinct excitation frequencies. Furthermore, we demonstrate that the nonlinearity can be used to amplify a signal at a frequency close to the mechanical resonance of the nanowire oscillator. Up to 26 dB of amplitude gain are demonstrated in this way

Magnetization reversal of an individual exchange biased permalloy nanotube

We investigate the magnetization reversal mechanism in an individual permalloy (Py) nanotube (NT) using a hybrid magnetometer consisting of a nanometer-scale SQUID (nanoSQUID) and a cantilever torque sensor. The Py NT is affixed to the tip of a Si cantilever and positioned in order to optimally couple its stray flux into a Nb nanoSQUID. We are thus able to measure both the NT's volume magnetization by dynamic cantilever magnetometry and its stray flux using the nanoSQUID. We observe a training effect and temperature dependence in the magnetic hysteresis, suggesting an exchange bias. We find a low blocking temperature $T_B = 18 \pm 2$ K, indicating the presence of a thin antiferromagnetic native oxide, as confirmed by X-ray absorption spectroscopy on similar samples. Furthermore, we measure changes in the shape of the magnetic hysteresis as a function of temperature and increased training. These observations show that the presence of a thin exchange-coupled native oxide modifies the magnetization reversal process at low temperatures. Complementary information obtained via cantilever and nanoSQUID magnetometry allows us to conclude that, in the absence of exchange coupling, this reversal process is nucleated at the NT's ends and propagates along its length as predicted by theory.Comment: 8 pages, 4 figure

MULTIPLE CURRENT SHEET SYSTEMS IN THE OUTER HELIOSPHERE: ENERGY RELEASE AND TURBULENCE

Accepted for publication in The Astrophysical Journal, March 21, 201

THE THREE-DIMENSIONAL EVOLUTION OF ION-SCALE CURRENT SHEETS: TEARING AND DRIFT-KINK INSTABILITIES IN THE PRESENCE OF PROTON TEMPERATURE ANISOTROPY

We present the first three-dimensional hybrid simulations of the evolution of ion-scale current sheets, with an investigation of the role of temperature anisotropy and associated kinetic instabilities on the growth of the tearing instability and particle heating. We confirm the ability of the ion cyclotron and firehose instabilities to enhance or suppress reconnection, respectively. The simulations demonstrate the emergence of persistent three-dimensional structures, including patchy reconnection sites and the fast growth of a narrow-band drift-kink instability, which suppresses reconnection for thin current sheets with weak guide fields. Potential observational signatures of the three-dimensional evolution of solar wind current sheets are also discussed. We conclude that kinetic instabilities, arising from non-Maxwellian ion populations, are significant to the evolution of three-dimensional current sheets, and two-dimensional studies of heating rates by reconnection may therefore over-estimate the ability of thin, ion-scale current sheets to heat the solar wind by reconnection

On the competition between radial expansion and Coulomb collisions in shaping the electron velocity distribution function: Kinetic simulations

International audienc

Bio-nanotechnology application in wastewater treatment

The nanoparticles have received high interest in the field of medicine and water purification, however, the nanomaterials produced by chemical and physical methods are considered hazardous, expensive, and leave behind harmful substances to the environment. This chapter aimed to focus on green-synthesized nanoparticles and their medical applications. Moreover, the chapter highlighted the applicability of the metallic nanoparticles (MNPs) in the inactivation of microbial cells due to their high surface and small particle size. Modifying nanomaterials produced by green-methods is safe, inexpensive, and easy. Therefore, the control and modification of nanoparticles and their properties were also discussed

Experimental Durability Analysis of Historical Ferrocement

The paper presents the results of a recent testing campaign carried out on the ferrocement elements built by Pier Luigi Nervi in the structures of Torino Esposizioni. These pavilions, built between 1947-1953, allowed Nervi to apply for the first time in a large structure his advances in the use of ferrocement in civil construction that he had pioneered during the war. The results obtained by Nervi were patented immediately after the end of the construction site and would have characterized Nervi’s technique for his whole career. Before Nervi’s civil applications, ferrocement was mainly used to build boats. The material is characterized by the multiple layers of mesh or fine rods completely impregnated with cement mortar, which Nervi noted could be applied to build slabs and roofing elements by using a very low amount of material. Considering the historical value of the structures and since the ferrocement elements are extremely thin, to investigate the durability of this material, small-scale ferrocement mockups were built in the laboratory, starting from a small sample collected on-site. A detailed testing program was developed, which included applying different treatments to the specimens before subjecting the samples to an accelerated weathering procedure to test the effects of each (mixed-in corrosion inhibitor, surface-applied inhibitor, etc.). The analysis of the ferrocement developed by Nervi in his constructions is a mandatory step for evaluating the health state of these elements and will help define the guidelines for their conservation. Moreover, it will help to expand the knowledge of Nervi’s system