Dynamics of Hyperbolically Symmetric Fluids

We study the general properties of dissipative fluid distributions endowed with hyperbolical symmetry. Their physical properties are analyzed in detail. It is shown that the energy density is necessarily negative, and the central region cannot be attained by any fluid element. We describe this inner region by a vacuum cavity around the center. By assuming a causal transport equation some interesting thermodynamical properties of these fluids are found. Several exact analytical solutions, which evolve in the quasi–homologous regime and satisfy the vanishing complexity factor condition, are exhibited.

A Low Temperature Drifting Acoustic Wave Pressure Sensor with an Integrated Vacuum Cavity for Absolute Pressure Sensing

In this paper we demonstrate a novel acoustic wave pressure sensor, based on an aluminum nitride (AlN) piezoelectric thin film. It contains an integrated vacuum cavity, which is micro-fabricated using a cavity silicon-on-insulator (SOI) wafer. This sensor can directly measure the absolute pressure without the help of an external package, and the vacuum cavity gives the sensor a very accurate reference pressure. Meanwhile, the presented pressure sensor is superior to previously reported acoustic wave pressure sensors in terms of the temperature drift. With the carefully designed dual temperature compensation structure, a very low temperature coefficient of frequency (TCF) is achieved. Experimental results show the sensor can measure the absolute pressure in the range of 0 to 0.4 MPa, while the temperature range is from 20 °C to 220 °C with a TCF of −14.4 ppm/°C. Such a TCF is only about half of that of previously reported works.

Bounds on ortho-positronium and J/ψ–Υ quarkonia invisible decays and constraints on hidden braneworlds in a SO(3,1)-broken 5D bulk

While our visible Universe could be a 3-brane, some cosmological scenarios consider that other 3-branes could be hidden in the extra-dimensional bulk. Matter disappearance toward a hidden brane is mainly discussed for neutron — both theoretically and experimentally — but other particles are poorly studied. Recent experimental results offer new constraints on positronium or quarkonium invisible decays. In the present work, we show how a two-brane Universe allows for such invisible decays. We put this result in the context of the recent experimental data to constrain the brane energy scale [Formula: see text] (or effective brane thickness [Formula: see text]) and the interbrane distance [Formula: see text] for a relevant two-brane Universe in a [Formula: see text]-broken 5D bulk. Quarkonia present poor bounds compared to the results deduced from previous passing-through-walls-neutron experiments for which scenarios with [Formula: see text] GeV and [Formula: see text] fm are excluded. By contrast, positronium experiments can compete with neutron experiments depending on the matter content of each brane. To constrain scenarios up to the Planck scale, positronium experiments in vacuum cavity should be able to reach [Formula: see text].

Fabrication of a Piezoresistive Barometric Pressure Sensor by a Silicon-on-Nothing Technology

This paper presents a piezoresistive barometric pressure sensor fabricated by using a Silicon-on-Nothing (SON) technology. Array of silicon trenches were annealed in hydrogen environment to form continuing crystalline silicon membrane over a vacuum cavity. Epitaxial growth on the silicon membrane is then completed for the desired thickness. All processes are CMOS compatible and performed on the front side of the silicon wafer. The piezoresistive barometric pressure sensor has been demonstrated with pressure hysteresis as low as 0.007%.