Sobre el tiempo: primeras aproximaciones entre el pensamiento físico y el pensamiento sociológico de Norbert Elias

The fundamental concept of time used by Physics was built by Galileo, through the observation of the apparent pendulum isochronism and establishing the possibility of using an instrument as a generator of temporal intervals to investigate natural phenomena occurring around them. At that time, a religious conception of time was dominant: according to this, the celestial objects, infallible and without the imperfections of the common world, dictated the temporal evolution of every phenomena. Thanks to Galileo, we are able to measure time and, consequently, we started to measure the world. With Newton, we return to a divine conception of time: evolution is an absolute space and time which can be understood as a divine sensation. The absolute time permeates everything that happens in our universe; it does not matter where the clock is because it is always capable of measuring uniformly time intervals. The three-dimensional space is Euclidean, meanwhile time is completely independent. For Elias, beyond the three physical and classical dimensions, it is needed to add are two other dimensions which are built in the context of human interdependency, namely, time and symbol. Time is an relevant dimension of Elias thought, time as an experience of duration, reference, and as a measurable change; time, simultaneously, as a physical and social entity. Clocks play a key role in the way we investigate the world and as instruments of time measurement produce a new time dimensions. But they are not built just for this purpose; their accuracy is closely related to the great voyages. Accuracy in time measurement provides a more exact position of a ship's longitude on the globe. With Einstein, this absolute synchronicity of two clocks loses its meaning: from this moment, clocks measure different time intervals according to their location and spatial movement. The time is "spatialized" and space-time is now a locating system of any event in our universe. The purpose of this article is to explore the possibilities of a dialogue on concepts of time, between a natural science, Physics, and the multiple faces offered by figurational approach.La concepción fundamental del tiempo en la Física es aquella construida por Galileo,  al observar el aparente isocronismo de un péndulo,  instrumento empleado como generador de intervalos temporales para investigar los fenómenos naturales que ocurrían en la órbita de los satélites de Júpiter. En aquel momento prevalecía una concepción divina del tiempo, en la que los objetos celestes, infalibles y sin las imperfecciones del mundo cotidiano, regían  la evolución temporal de todos los fenómenos: con Galileo medimos el tiempo y a partir de él comenzamos a medir el mundo. Con Newton se produce un retorno a la concepción divina del tiempo: toda evolución es un espacio y tiempo absolutos entendidos en última instancia como sensación divina. El tiempo absoluto permea todo lo que ocurre en nuestro universo. No importa donde se encuentre el reloj ya que éste es capaz de medir los intervalos de tiempo de forma uniforme. El espacio tridimensional es euclidiano, y el tiempo totalmente independiente. Para Elias, a las tres dimensiones físicas, se le añaden otras dos construidas con base en las relaciones interdependientes entre los seres humanos: tiempo y símbolo. El tiempo es una dimensión relevante en el pensamiento de Elias, tiempo como experiencia de duración, con referencia mensurable y perspectiva de cambio que se bifurca en tiempo físico y tiempo social. El perfeccionamiento de los relojes desempeña un papel fundamental en nuestro conocimiento del mundo: en tanto instrumentos de medición, ellos mismos son productores de una dimensión del  tiempo. Sin embargo no se construyeron con ese único propósito pues su precisión esta también íntimamente relacionada con las grandes navegaciones. La exactitud en la medición del tiempo ofrece mayor precisión a la hora de determinar la posición  de un barco en el globo terráqueo. Con Einstein la sincronía absoluta de los relojes pierde significado: éstos medirán a partir de ahora intervalos de tiempo diferentes de acuerdo con su localización y su movimiento en el espacio. El tiempo se ha “especializado” y disponemos de un espacio como tiempo encargado de la localización de cualquier evento en nuestro universo. El propósito de este artículo es explorar las posibilidades de diálogo pertinentes en las concepciones del tiempo que maneja una ciencia natural, la Física, y las que derivan de un abordaje sociológico figuracional

Asteroid taxonomic signatures from photometric phase curves

We explore the correlation between an asteroid's taxonomy and photometric phase curve using the H, G12 photometric phase function, with the shape of the phase function described by the single parameter G12. We explore the usability of G12 in taxonomic classification for individual objects, asteroid families, and dynamical groups. We conclude that the mean values of G12 for the considered taxonomic complexes are statistically different, and also discuss the overall shape of the G12 distribution for each taxonomic complex. Based on the values of G12 for about half a million asteroids, we compute the probabilities of C, S, and X complex membership for each asteroid. For an individual asteroid, these probabilities are rather evenly distributed over all of the complexes, thus preventing meaningful classification. We then present and discuss the G12 distributions for asteroid families, and predict the taxonomic complex preponderance for asteroid families given the distribution of G12 in each family. For certain asteroid families, the probabilistic prediction of taxonomic complex preponderance can clearly be made. The Nysa-Polana family shows two distinct regions in the proper element space with different G12 values dominating in each region. We conclude that the G12-based probabilistic distribution of taxonomic complexes through the main belt agrees with the general view of C complex asteroid proportion increasing towards the outer belt. We conclude that the G12 photometric parameter cannot be used in determining taxonomic complex for individual asteroids, but it can be utilized in the statistical treatment of asteroid families and different regions of the main asteroid belt.Comment: submitted to Icaru

Vasodilator response to galvanic current stimulation of the skin accurately detects acetylsalicylic acid intake: A study in 400 vascular patients

Background and aims The first cause of low-dose acetylsalicylic-acid (ASA) inefficacy is poor adherence to treatment. No non-invasive technique is available to assess ASA intake. Current-induced vasodilation (CIV) was found abolished in healthy volunteers after low-dose ASA intake. We tested clinical characteristics, treatments, and comorbid conditions influencing CIV amplitude in vascular patients. Methods CIV was tested in 400 patients (277 males and 123 females, aged 65.4 ± 13.4 years). We focused on clinical characteristics, treatments, and comorbid conditions as covariates of CIV amplitude. We studied the CIV amplitude to covariate relationships with multivariate linear regression and receiver operating characteristics (ROC). Results The multivariate linear model determined that ASA intake within the last 48 h and the interaction between ASA intake and body mass index (BMI) were the sole covariates associated with CIV amplitude. For the whole population, the area under the ROC curve (AUC) for CIV to predict ASA intake was 0.853 [95% confidence interval (CI): 0.814–0.892]. Considering separately the areas observed for non-obese (BMI ≤30, n = 303) and obese (BMI>30, n = 93) patients, the AUC [95% CI] was 0.873 [0.832–0.915] and 0.776 [0.675–0.878], respectively (p = 0.083). Conclusions ASA is the only drug that affects the amplitude of CIV response observed after galvanic current application to the skin of vascular patients. CIV depends on BMI but not age or gender. As such, CIV appears to be a potential objective marker of ASA intake and could facilitate future non-invasive assessments of adherence to ASA treatment

The predictive power of magnetospheric models for estimating ground magnetic field variation in the United Kingdom

Space weather events can have damaging effects on ground-based infrastructure. Geomagnetically induced currents (GIC) caused by rapid magnetic field fluctuations during geomagnetic storms can negatively affect power networks, railways as well as navigation systems. To reduce such negative impacts, good forecasting capability is essential. In this study we assess the performance of contemporary magnetohydrodynamic (MHD) models in predicting the external-only ground magnetic field perturbations at three United Kingdom observatories during two severe space weather events: September 2017 and March 2015. Simulated magnetic data were acquired via Community Coordinated Modeling Center (CCMC), using the following models: Space Weather Modeling Framework (SWMF), Open Geospace General Circulation Model (Open GGCM) and Lyon–Fedder–Mobarry (LFM) combined with the Rice Convection Model (RCM). All simulations use spacecraft measurements at L1 as their solar wind input in calculating ground perturbations. Qualitative and quantitative comparison between measured and modelled values suggest that the performance of MHD models vary with latitude, the magnetic component and the characteristics of the storm analysed. Most models tend to exaggerate the magnitude of disturbances at lower latitudes but better capture the fluctuations at the highest latitude. For the two storms investigated, the addition of RCM tends to result in overestimation of the amplitude of ground perturbations. The observed data-model discrepancies most likely arise due to the many approximations required in MHD modelling, such as simplified solar wind input or shift in location of the electrojets in the simulated magnetospheric and ionospheric currents. It was found that no model performs consistently better than any other, implying that each simulation forecasts different aspects of ground perturbations with varying level of accuracy. Ultimately, the decision of which model is most suitable depends on specific needs of the potential end user

Magnetization reversal processes in epitaxial Fe/GaAs(001) films

Copyright © 1994 American Institute of PhysicsIn this article we present the results of a detailed study of the switching behavior observed in epitaxial single Fe films of thickness between 30 and 450 Å, and a wedge shaped Fe film with a thickness range of 10–60 Å grown on GaAs (001). These films have cubic and uniaxial anisotropies which change with film thickness. For the fixed thickness films the values of the anisotropy constants were accurately determined by Brillouin light scattering (BLS) measurements together with polar magneto‐optic Kerr effect (MOKE) measurements that gave the value of the magnetization. The switching behavior of these samples was observed with in‐plane MOKE magnetometry as a function of the angle between the applied field and the in‐plane crystallographic axes. Measurements of the component of magnetization perpendicular to the applied field allow a precise determination of the relative orientation of the hard and easy in‐plane anisotropy axes. This can be used to accurately determine the ratio of uniaxial to cubic anisotropy constants, when this ratio is less than one. The ratios obtained from MOKE agree well with those obtained from BLS. Minimum energy calculations predict that the reversal process should proceed by a continuous rotation of the magnetization vector with either one or two irreversible jumps, depending on the applied field orientation and the nature of the anisotropy of the film. The calculations provide a good qualitative description of the observed reversal process, although the magnetic microstructure influences the exact values of the switching fields

Exchange Anisotropy in Epitaxial and Polycrystalline NiO/NiFe Bilayers

(001) oriented NiO/NiFe bilayers were grown on single crystal MgO (001) substrates by ion beam sputtering in order to determine the effect that the crystalline orientation of the NiO antiferromagnetic layer has on the magnetization curve of the NiFe ferromagnetic layer. Simple models predict no exchange anisotropy for the (001)-oriented surface, which in its bulk termination is magnetically compensated. Nonetheless exchange anisotropy is present in the epitaxial films, although it is approximately half as large as in polycrystalline films that were grown simultaneously. Experiments show that differences in exchange field and coercivity between polycrystalline and epitaxial NiFe/NiO bilayers couples arise due to variations in induced surface anisotropy and not from differences in the degree of compensation of the terminating NiO plane. Implications of these observations for models of induced exchange anisotropy in NiO/NiFe bilayer couples will be discussed.Comment: 23 pages in RevTex format, submitted to Phys Rev B

P/2010A2 LINEAR - I: An impact in the Asteroid Main Belt

Comet P/2010A2 LINEAR is a good candidate for membership with the Main Belt Comet family. It was observed with several telescopes (ESO NTT, La Silla; Gemini North, Mauna Kea; UH 2.2m, Mauna Kea) from 14 Jan. until 19 Feb. 2010 in order to characterize and monitor it and its very unusual dust tail, which appears almost fully detached from the nucleus; the head of the tail includes two narrow arcs forming a cross. The immediate surroundings of the nucleus were found dust-free, which allowed an estimate of the nucleus radius of 80-90m. A model of the thermal evolution indicates that such a small nucleus could not maintain any ice content for more than a few million years on its current orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up and electrostatic dust levitations were also rejected, leaving an impact with a smaller body as the favoured hypothesis, and ruling out the cometary nature of the object. The impact is further supported by the analysis of the tail structure. Finston-Probstein dynamical dust modelling indicates the tail was produced by a single burst of dust emission. More advanced models, independently indicate that this burst populated a hollow cone with a half-opening angle alpha~40degr and with an ejection velocity v_max ~ 0.2m/s, where the small dust grains fill the observed tail, while the arcs are foreshortened sections of the burst cone. The dust grains in the tail are measured to have radii between a=1-20mm, with a differential size distribution proportional to a^(-3.44 +/- 0.08). The dust contained in the tail is estimated to at least 8x10^8kg, which would form a sphere of 40m radius. Analysing these results in the framework of crater physics, we conclude that a gravity-controlled crater would have grown up to ~100m radius, i.e. comparable to the size of the body. The non-disruption of the body suggest this was an oblique impact.Comment: 15 pages, 11 figures, in pres

On the V-type asteroids outside the Vesta family. I. Interplay of nonlinear secular resonances and the Yarkovsky effect: the cases of 956 Elisa and 809 Lundia

Among the largest objects in the main belt, asteroid 4 Vesta is unique in showing a basaltic crust. It is also the biggest member of the Vesta family, which is supposed to originate from a large cratering event about 1 Gyr ago (Marzari et al. 1996). Most of the members of the Vesta family for which a spectral classification is available show a V-type spectra. Before the discovery of 1459 Magnya (Lazzaro et al. 2000) and of several V-type NEA (Xu 1995), all the known V-type asteroids were members of the Vesta family. Recently two V-type asteroids, 809 Lundia and 956 Elisa, (Florczak et al. 2002) have been discovered well outside the limits of the family, near the Flora family. We currently know 22 V-type asteroids outside the family, in the inner asteroid belt. In this work we investigate the possibility that these objects are former family members that migrated to their current positions via the interplay of Yarkovsky effect and nonlinear secular resonances. The main dynamical feature of 956 Elisa and 809 Lundia is that they are currently inside the 2(g-g6)+s-s6 (z2 by Milani and Knezevic, 1993) secular resonance. Our investigations show that members of the Vesta dynamical family may drift in three-body and weak secular resonances until they are captured in the strong z2 secular resonance. Only asteroids with diameters larger than 16 km can remain in one of the three-body or secular resonances long enough to reach the region of the z2 resonance. This two-step mechanism of capture into the z2 resonance could explain: i) the current resonant orbits of 956 Elisa and 809 Lundia, ii) why their size is significantly larger than that of the typical member of the Vesta family, and iii) provide a lower limit on the Vesta family age.Comment: 14 pages, 10 figures, 3 tables. Accepted for publication in A&