The physics of rotational flattening and the point core model

A point mass at the center of an ellipsoidal homogeneous fluid is used as a simple model to study the effect of rotation on the shape and external gravitational field of planets and stars. Maclaurin's analytical result for a homogenous body is generalized to this model. The absence of a third order term in the Taylor expansion of the Maclaurin function leads to further simple but very accurate analytical results connecting the three observables: oblateness ($\epsilon$), gravitational quadrupole ($J_{2}$), and angular velocity parameter ($q$). These are compared to observational data for the planets. The moments of inertia of the planets are calculated and compared to published values. The oblateness of the Sun is estimated. Oscillations near equilibrium are studied within the model.Comment: 23 pages, 2 figures, one tabl

On the different ways of being a bi-dialectal immigrant. From speech isolation through code-switching to full integration. The case of Argentineans in Malaga (Spain).

In this paper we analyse the accommodation (convergence) or divergence of young immigrants born in Buenos Aires, Argentina but living in Malaga, Spain (n = 22). For analysing this community, we took advantage of previous studies on dialects in contact such as Auer et. al. (2000), Hinskens et. al. (2016), Kerswill & Williams (2000), or Trudgill (1986), among others. We have focused our attention on a very salient feature of the variety of Buenos Aires: the realization patterns of the voiced palatal fricative /ʝ/ (n = 1176) by young immigrant speakers. In such an immigration context, different realizations of /ʝ/ are observable, from open [j] to voiceless fricative realizations [ʃ]. An acoustic analysis based on standardised zero crossings rate, relative intensity, and other complementary measurements allows us to set the acoustic parameters underlying palatal /ʝ/ allophones, and to reveal a clear recession in the use of the native closed – and even voiceless – allophones by the Buenos Aires young immigrant speakers.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Capacitive MEMS-based sensors : thermo-mechanical stability and charge trapping

Micro-Electro Mechanical Systems (MEMS) are generally characterized as miniaturized systems with electrostatically driven moving parts. In many cases, the electrodes are capacitively coupled. This basic scheme allows for a plethora of specifications and functionality. This technology has presently matured and is widely employed in industry. \ud A voltage across the electrodes will attract the movable part. This relation between electric field and separation (or capacitance) can be conveniently employed to sense tiny displacements (less than 1 pm) or for example as a through sensor for electromagnetic power through a coplanar waveguide (CPW).\ud The design involves often dielectric layers, whether accidental (native oxide) or intentional. During fabrication and / or operation of the device, trapped charge can uncontrollably accumulate and decumulate in these layers, causing parasitic forces on the device. These parasitic forces can influence the device beyond acceptable limits. The research described in this thesis approaches this phenomenon in two ways: a) device level and b) fundamental level. \ud a) Device level: Complete MEMS structures. The thesis contains theory of capacitive MEMS, including amongst others pull-in voltage, electrostatically loaded clamped-clamped beams, and electro-mechanical resonance, as well as the origin, dynamics and influence of trapped charges, in conjunction with built-in voltage. A cryogenic experimental study has been done on the effect of charge trapping on two types of MEMS-based RF power sensors. New structures have been realized with far better thermo-mechanical immunity. These structures are the first to involve double beam springs, which are fabricated by wet KOH etching of silicon. It is demonstrated that even an ultrathin aluminum oxide (native, ~ 2 nm) can harbor significant charge trapping. The dynamics are found to slow down considerably at cryogenic temperatures. At last, a study is done on when charge trapping actually limit the performance of real MEMS devices: a gravity gradiometer and an RF power sensor. \ud b) Fundamental level. Existing measurements and imaging of local trapped charges by conducting atomic force microscopy (AFM) are reinterpreted by a new model. This multi mirror model calculates the electrostatic interaction (force, gradient and contact potential difference) between the sample surface containing the trapped charge and the tip of the AFM, represented by a conducting sphere. This model improves drastically over existing calculations. Some interesting theoretical approximations of quantities describing this interaction have been found

Conclusions

One of the basic problems in local organic food systems seems to be connected to food chains. The range of creative initiatives covers all thinkable fields: information about ecology, farmers' own activities in creating brands and labels, associations, developing ordering and delivery systems, processing, municipal help, marketing campaigns and so on

Images of Locally Finite Derivations of Polynomial Algebras in Two Variables

In this paper we show that the image of any locally finite $k$-derivation of the polynomial algebra $k[x, y]$ in two variables over a field $k$ of characteristic zero is a Mathieu subspace. We also show that the two-dimensional Jacobian conjecture is equivalent to the statement that the image $Im D$ of every $k$-derivation $D$ of $k[x, y]$ such that $1\in Im D$ and $div D=0$ is a Mathieu subspace of $k[x, y]$.Comment: Minor changes and improvements. Latex, 9 pages. To appear in J. Pure Appl. Algebr