Nach oben pdf A Combined Entropy/Phase-Field Approach to Gravity

A Combined Entropy/Phase-Field Approach to Gravity

A Combined Entropy/Phase-Field Approach to Gravity

4. Lagrange Formalism Similar to entropy, the Lagrange formalism also plays a significant role in many areas of physics. In addition to the derivation of the Boltzmann factor depicted above, the Lagrange formalism is a major foundation for quantum mechanics and, in particular, has been used to derive relations between symmetries and conservation laws. The Noether theorems, which were derived using the Lagrange formalism, showed that invariance of physical laws subject to a translation implies the conservation of momentum and invariance subject to translation in time implies the conservation of energy. A further striking observation is that major physical laws all contain a Laplacian operator (that is, are a Poisson-type equation) somehow suggesting a common ground of all these models, which comprise all different length scales like gravitation, electrostatics, thermal conductivity, diffusion, flow, phase-field, Schrödinger equations, density functional equations and many others. Some operators present in the Lagrange scheme have the property of generating Laplacian operators. The basic concept of the Lagrange formalism is based on a functional being a scalar function F of a variable Φ i which, itself, is a function of space and time Φ i = Φ i ( r, t ) , and being an integral of a density function f.
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Bandwidth correction of Swarm GPS carrier phase observations for improved orbit and gravity field determination

Bandwidth correction of Swarm GPS carrier phase observations for improved orbit and gravity field determination

Gravity fields derived from GPS tracking of the three Swarm satellites have shown artifacts near the geomagnetic equa- tor, where the carrier phase tracking on the L2 frequency is unable to follow rapid ionospheric path delay changes due to a limited tracking loop bandwidth of only 0.25 Hz in the early years of the mission. Based on the knowledge of the loop filter design, an analytical approach is developed to recover the original L2 signal from the observed carrier phase through inversion of the loop transfer function. Precise orbit determination and gravity field solutions are used to assess the quality of the correction. We show that the a posteriori RMS of the ionosphere-free GPS phase observations for a reduced-dynamic orbit determination can be reduced from 3 to 2 mm while keeping up to 7% more data in the outlier screening compared to uncorrected observations. We also show that artifacts in the kinematic orbit and gravity field solution near the geomagnetic equator can be substantially reduced. The analytical correction is able to mitigate the equatorial artifacts. However, the ana- lytical correction is not as successful compared to the down-weighting of problematic GPS data used in earlier studies. In contrast to the weighting approaches, up to 9–10% more kinematic positions can be retained for the heavily disturbed month March 2015 and also stronger signals for gravity field estimation in the equatorial regions are obtained, as can be seen in the reduced error degree variances of the gravity field estimation. The presented approach may also be applied to other low earth orbit missions, provided that the GPS receivers offer a sufficiently high data rate compared to the tracking loop bandwidth, and provided that the basic loop-filter parameters are known.
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Regional Gravity Field Modeling with Adjusted Spherical Cap Harmonics in an Integrated Approach

Regional Gravity Field Modeling with Adjusted Spherical Cap Harmonics in an Integrated Approach

The calculation of the SH coefficients can only be solved by means of global data coverage. This could only be achieved after the first geodetic satellite missions (like the LAGEOS, GRACE, GOCE and CHAMP missions). The satellite missions are utilizing different types of measurement principles. The LAGEOS satellites apply the principle of Satellite Laser Ranging (SLR), while the CHAMP mission uses the principle of Satellite-to-Satellite tracking in high- low mode, where the residual gravity accelerations are additionally measured by means of an accelerometer. The GRACE Satellite mission uses the principle of Satellite-to-Satellite tracking in low-low mode, where the gravity differences between two satellites separated by hundreds of kilometers are observed. The most modern GOCE mission uses the principle of gravity gradiometry using a group of accelerometers fixed on the three axes of the satellite. The combination of satellite observations with terrestrial measurements led to the combined gravity models (e.g. EGM98A, EGM96, EIGEN06c and EGM2008). The SH can be calculated by two methods: the first is the integration method that keeps the orthogonality conditions of the SH, and second is the least squares estimation (Fan, 2004).
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Collective quantum effects in field theory and gravity

Collective quantum effects in field theory and gravity

system as a toy model and studied its phase transition. At the quantum crit- ical point, the first Bogoliubov mode becomes light, increasing the density of states. The number of nearly degenerate states is not excessive, however, be- cause the minimal mass gap scales like N −1/3 , a far cry from the exponential degeneracy of black holes. It is still one of the important unsolved questions of the graviton condensate picture to plausibly explain the black hole entropy. Simply replacing the Lieb-Liniger coupling α with a momentum dependent term proportional to k 2 looks somewhat plausible with the graviton interac- tion in mind and would hint at many more Bogoliubov modes becoming light in (2.24). Whether the resulting model is viable, however, is a completely separate question. A momentum dependent coupling was already introduced in [BM+13] and analyzed more closely with the black hole entropy in mind in [DF+15]. More investigations regarding the entropy are, however, clearly mandated, especially as BMS transformations at the horizon [HPS16] have also been considered to provide the required states in the graviton condensate model [AD+16].
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Non-perturbative effects in field
theory and gravity

Non-perturbative effects in field theory and gravity

After discussing non perturbative physics in the context of nonabelian gauge theories we will now discuss aspects of gravity. The most puzzling object in gravity is certainly a black hole with two of the big open questions being the origin of black hole entropy and the so called information paradox. Accord- ing to an argument by Bekenstein black holes should have an entropy [3–5], which is proportional to the horizon area of the black hole measured in planck units. A clear microscopic interpretation of this entropy has not been found so far. There have been microscopic computations of the degeneracy of ex- tremal black holes in the context of string theory, which provides an ultra- violet completion to general relativity. This approach has been pioneered in a seminal paper by Strominger and Vafa [6], where they compute the degeneracy of BPS black holes using an intricate series of very indirect ar- guments. However due to their indirect nature, these computations do not give a clear interpretation of the degeneracy, however they provide a clear check as to the correctness of associating an entropy to black holes. It is not clear whether these arguments can be extended to Schwarzschild black holes. The information paradox [7] arises when quantizing a field theory on a black hole background. Hawking has shown [8], that due to quantum fluctuations a black hole will emit particles with a thermal spectrum with a temperature proportional to the inverse Schwarzschild radius T H ∼ R −1 . The information
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Quantum corpuscular approach to solutions in gravity and field theory

Quantum corpuscular approach to solutions in gravity and field theory

In order to make our ideas transparent, we applied these constructions to concrete physical systems. In the case of the auxiliary current description, we were mostly inter- ested in black hole physics. Understanding the black hole quantum state in terms of a multi-graviton state on flat space-time, we were able to compute observables connected to the black hole interior such as the density of gravitons in momentum space or their energy density at the parton level and in the large mass limit. Consistency of our results then implied that the total mass of the black hole must scale as the number of fields composing the auxiliary current. We found that the distribution of gravitons in the black hole is dominated by quanta of large wavelength which resonates with the ideas put forward in the Black Hole Quantum N Portrait. Based on these results, we explained that the distri- bution function of gravitons is directly accessible in S-matrix processes. As a consequence, an outside observer can in principle reconstruct the internal structure of the black hole. Thus, no loss of information as well as the existence of quantum hair are expected in our approach. Finally, we showed how the Schwarzschild metric emerges from our approach. The basic insight was to replace a classical black hole source characterized by the mass by the corresponding microscopic quantum source. This quantum source was identified with the energy density of gravitons inside the black hole. On the one hand, the mass arises as a collective effect of N gravitons. On the other hand, for any finite N , we argued that there are corrections to the classical notion of mass which can be absorbed in a wave function renormalization. Using this result combined with the finding of [67] it was straightforward to show that in our description, classical geometry indeed emerges in the limit N → ∞.
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Strain Rate Sensitivity of a TRIP-Assisted Dual-Phase High-Entropy Alloy

Strain Rate Sensitivity of a TRIP-Assisted Dual-Phase High-Entropy Alloy

As discussed above, the recently developed TRIP-assisted DP- HEAs show comparable strengthening mechanisms and hence mechanical properties found also in many advanced steels, e.g., DP and TRIP steels ( Hadfield, 1888; Curtze et al., 2009; Raabe et al., 2013 ). Many of these steels show positive and strong strain rate sensitivity upon deformation ( Curtze et al., 2009 ). This feature has been attributed to the rationale that at higher strain rates the time for a dislocation to be rendered immobile in front of an obstacle (e.g., grain boundaries, twin boundaries and phase interfaces) before it can propagate upon gaining additional thermal energy is shorter than that at lower strain rates ( Meyers, 1994; Curtze et al., 2009 ). For instance, high manganese containing TRIP/TWIP steels usually undergo deformation driven transformations involving formation of ε and α martensite as well as mechanical twins ( Grässel et al., 2000; Gutierrez-Urrutia and Raabe, 2011; Wong et al., 2016 ). The transformation paths could be affected by strain rate as the adiabatic heating modifies the phase transformation rate, leading to change in mechanical properties such as ultimate strength, uniform and total elongations ( Sato et al., 1989; Grässel et al., 2000 ). Also, DP steels with a ferritic-martensitic microstructure ( Fu et al., 2012; Tasan et al., 2015 ) are generally more sensitive to strain rate changes compared to TRIP steels consisting of bainite, martensite, retained austenite and ferrite matrix ( Grässel et al., 2000; Huh et al., 2008 ).
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A theoretical approach to the formation of glycine in the interstellar gas phase

A theoretical approach to the formation of glycine in the interstellar gas phase

I awoke the next day to a sound like sizzling bacon, the noise made by ice melting in a pan on a primus. In the months after Antarctica, I often heard it in the boneless moments between sleep and consciousness; then memories ached like an old wound. Sunshine was pouring through the window. Steve brought tea to our bunks. Some of the ice must have been brackish, as it was salty. I made up a jug of milk for our breakfast cereal, and that was salty too. I wasn’t having much luck with breakfasts. But it didn’t matter. Nothing mattered. We basked on our veranda, and a flock of Antarctic terns flew by, their high-pitched chirp exotically foreign after the coarse squawk of the skuas. Later, we took the boats out and followed a minke whale around the bergs, sailing through Daliesque arches and poking into cold blue grottoes. The sun was low, and the honeyed air was so still that the growlers and bergy bits were barely moving. It was a golden evening. A day like that made everything worthwhile.
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Impacts of EU Enlargement Process: A Gravity Model Approach

Impacts of EU Enlargement Process: A Gravity Model Approach

457 of the European Union and zero otherwise. The estimated coefficient EU membership is positive and has a very high estimated value. The coefficient is also statistically significant at the 5% level. The impacts of EU membership are all positively significant. The intra-EU trade volumes were positively affected by the enlargement of the European Community with the accession of new member states .In estimating the bilateral trade within the EU seven models were set up according to the panel analysis between 2000 and 2010 (OLS, Random effects (RE) fixed effects (FE)).Dependent variable is log bilateral exports. Country pair fixed effects, exporter- year and importer-year dummies included. According to the panel fixed effect estimation the exporter GDP and importer GDP are positive as expected and significant at 5% (any unit increase of a country’s GDP raises its exports to other EU countries by 1.535% more). When one country of the country pair is the member of EU and the other is not then the export raises with exp (0. 23) =25.6%. When both the countries are members of the EU, the estimated coefficient EU membership is positive and has a very high estimated value of exp (0.38) =1.462.The EU dummy is 0.545.
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A combined FSTRA-shotgun proteomics approach to identify molecular changes in zebrafish upon chemical exposure

A combined FSTRA-shotgun proteomics approach to identify molecular changes in zebrafish upon chemical exposure

The fish short-term reproduction assay (FSTRA) is a common in vivo screening assay for assessing endocrine effects of chemicals on reproduction in fish. However, the current reliance on measures such as egg number, plasma vitellogenin concentration and morphological changes to determine endocrine effects can lead to false labelling of chemicals with non-endocrine modes- of-action. Here, we integrated quantitative liver and gonad shotgun proteomics into the FSTRA in order to investigate the causal link between an endocrine mode-of-action and adverse effects assigned to the endocrine axis. Therefore, we analyzed the molecular effects of fadrozole-induced aromatase inhibition in zebrafish (Danio rerio). We observed a concentration-dependent decrease in fecundity, a reduction in plasma vitellogenin concentrations and a mild oocyte atresia with oocyte membrane folding in females. Consistent with these apical measures, proteomics revealed a significant dysregulation of proteins involved in steroid hormone secretion and estrogen stimulus in the female liver. In the ovary, the deregulation of estrogen synthesis and binding of sperm to zona pellucida were among the most significantly perturbed pathways. A significant deregulation of proteins targeting the transcriptional activity of estrogen receptor (esr1) was observed in male liver and testis. Our results support that organ- and sex-specific quantitative proteomics represent a promising tool for identifying early gene expression changes preceding chemical-induced adverse outcomes. these data can help to establish consistency in chemical classification and labelling.
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Dual approach to lattice field theories / Thomas Kloiber

Dual approach to lattice field theories / Thomas Kloiber

These shortcomings ultimately led to the advent of quantum field theory (although previous attempts date back to the early days of quantum me- chanics, cf. [2] and [3]). Starting from classical field theory – which does not account for quantum aspects, e. g., like the particle nature of the photon – one promotes the infinity of classical oscillators representing the modes of the classical fields to quantum harmonic oscillators and therefore quantizing the theory. In this so-called canonical quantization approach, the fields be- come operator valued distributions labeled by a space-time coordinate and particles emerge as excited states of these fields, the so called field quanta. Thus, a (relativistic) quantum field theory unifies the concepts of classical field theory, quantum mechanics and special relativity. The first major the- ory of that kind and the prototype of a successful quantum field theory was quantum electrodynamics (QED) which proved to be extraordinarily success- ful in describing electromagnetic interactions. In the early days QED was plagued by the so called problem of infinities, i. e., basic physical properties like the electron self-energy diverged. The techniques of renormalization and regularization overcame this problem and QED was brought into its final form most notably by Richard Feynman, Julian Schwinger and Shin’ichir¯o Tomonaga. QED is an example of an abelian gauge theory. In simple terms, a gauge theory is a theory which is invariant under some local, continuous symme- try transformations in an internal space which form a Lie group (the gauge group), in the case of QED it is the commutative circle group U(1). Thus, one of the four fundamental forces of nature, namely the electromagnetic force, could be described in a satisfactory way within the framework of gauge theories, where the photon is the carrier of this force and in this context is termed gauge boson. Since the corresponding symmetries constrain and dictate the form of
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Strain Rate Sensitivity of a TRIP-Assisted Dual-Phase High-Entropy Alloy

Strain Rate Sensitivity of a TRIP-Assisted Dual-Phase High-Entropy Alloy

samples were subjected to ultrasonic cleaning with ethanol before proceeding to next step. Microstructural characterization was carried out using electron backscattered diffraction (EBSD) and electron channeling contrast imaging (ECCI). EBSD measurements were performed in a dual-beam Zeiss-crossbeam XB1560 scanning electron microscope (SEM) equipped with the TSL OIM data collection software. ECCI analysis was conducted using a Zeiss-Merlin instrument ( Gutierrez-Urrutia et al., 2009 ). For the tensile tested samples, the deformation microstructures were analyzed via EBSD and ECCI at sample regions which had experienced different local strain levels. For the un-deformed samples, the compositional homogeneity was also analyzed by energy dispersive X-ray spectroscopy (EDS) using the Zeiss-Merlin instrument.
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European Gravity Service for Improved Emergency Management - a new Horizon 2020 project to serve the international community and improve the accessibility to gravity field products

European Gravity Service for Improved Emergency Management - a new Horizon 2020 project to serve the international community and improve the accessibility to gravity field products

Adopting rigorous and independent processing approaches, each AC will deliver consistent gravity field solutions. For the first time, a meaningful combination by the Analysis Center Coordinator (ACC) will be possible. This task will be coordinated by AIUB, it includes

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Modeling of Martensitic Transformations in Pure Iron by a Phase Field Approach Using Information from Atomistic Simulation

Modeling of Martensitic Transformations in Pure Iron by a Phase Field Approach Using Information from Atomistic Simulation

Iron is an example for an allotropic material. In this paper two allotrops are of interest. At room temperature and ambient pressure α-iron is the stable phase. It has a body centered cubic (bcc) crystal structure. If the temperature is increased, it transforms into the γ-iron, also called austenite. The austenitic crystal lattice consists of face cen- tered cubic (fcc) elementary cells. The change from austenite to α-iron depends on the cooling rate. If the probe is cooled slowly, the transformation is diffuse. For a sufficiently high cooling rate, a diffusionless transformation from the fcc to the bcc phase takes place, which is known as martensitic transformation in iron (Sandoval et al. (2009a)). The change of structure can be described by the Bain model (Bain (1924)) which defines a preexisting bcc unit cell within two fcc cells (Figure 2). To attain the martensitic bcc cell, a distortion of the preexisting bcc cell is necessary. The Bain model demonstrates that due to the crystallographic misfit an eigenstrain in the martensitic phase exits, which is considered in the proposed model for martensitic transformations.
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Foreign direct investment and trade: A bi-directional gravity approach

Foreign direct investment and trade: A bi-directional gravity approach

2. Theoretical Framework A large literature regarding international trade and FDI shows that the relationship of inward FDI and the exports of host countries mainly concentrate on complementarity and substitution, usually with exports regressed on some measure of FDI and some other control variables. FDI can also affect the breakdown of exports by industry and geographical area. The main analysis on the effects of FDI on exports is based on the Heckscher (1919)-Ohlin (1933) model and it’s extensions (Mundell (1968); Kojima (1975, 1977, 1982); Krugman (1983); Helpman (1984); Horstmann and Markusen (1984); Helpman and Krugman (1985); Blomström (1990); Markusen (1992); Brian, Hanson, and Harrison (1997); Lipsey (1998, 2000, 2002); Helpman, Melitz, and Yeaple (2003); Barrios, Görg and Strobl (2005)).
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A Spatial-Filtering Zero-Inflated Approach to the Estimation of the Gravity Model of Trade

A Spatial-Filtering Zero-Inflated Approach to the Estimation of the Gravity Model of Trade

2 1. Introduction A traditional gravity model describing trade in its simple form (Linnemann 1966; Tinbergen 1962) asserts that the volume of trade between a country pair is proportional to the product of their gross domestic products and inversely related to a measure of distance separating them, where distance is broadly defined as a function of several variables that can be viewed as trade resistance factors. The log-linear specification of the gravity model along with ordinary least squares (OLS) estimation has been widely used in the empirical literature (Egger 2002; Frankel and Rose 2002; Rose 2000), mostly because of its good empirical performance and, in later years, for the strong theoretical foundations provided in papers such as Anderson (1979) and Anderson and van Wincoop (2003). However, most recent contributions stress that null trade flows are to be specifically taken into account. Helpman et al. (2008) prove that disregarding countries that do not trade with each other generates biased estimates. Moreover, Santos Silva and Tenreyro (2006) show that log-linearization of the gravity model leads to inconsistent estimates in the presence of heteroscedasticity in trade levels. They propose a Poisson-type specification of the gravity model along with the Poisson pseudo-maximum likelihood (PPML) estimator, somehow similarly to the Poisson approach initially proposed by Flowerdew and Aitkin (1982). Santos Silva and Tenreyro (2006; 2011) also provide simulation evidence that the PPML estimator is well behaved, even when the conditional variance is far from being proportional to the conditional mean. Several empirical studies of trade have applied the PPML estimator (see Burger et al. 2009; Linders et al. 2008; Martin and Pham 2015; Martínez-Zarzoso 2013). Alternatively, in order to correct for overdispersion, a negative binomial (NB) regression model, which belongs to the family of Poisson models, and allows for the dispersion parameter to differ from 1, is employed. A wider discussion regarding the choice between Poisson and NB estimators (for the pseudo-ML case in particular), can be found, for example, in Bosquet and Boulhol (2014) and Head and Mayer (2015).
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A spatial-filtering zero-inflated approach to the estimation of the gravity model of trade

A spatial-filtering zero-inflated approach to the estimation of the gravity model of trade

A further aspect stressed in recent contributions is the one of null trade flows and the necessity to specifically take them into account in regression modelling. Helpman et al. ( 2008 ) prove that disregarding countries that do not trade with each other generates biased estimates. Zero-inflated specifications of Poisson models (ZIP) ( Lambert 1992 ; Greene 1994 ; Long 1997 ) permit to explicitly model the presence of a large number of zero flows, because it considers the existence of two groups within the population: one having strictly zero counts, and another having a non-zero probability of having a trade flow greater than zero. In this framework, a relevant question is whether the determinants of zero flows are the same as the ones of trade counts. Indeed, Burger et al. ( 2009 ) stress that some variables (such as common language, institutional and geographical distance) may be more important in determining the profitability of bilateral trade (decision to trade) rather than the potential volume of bilateral trade. Nordås ( 2008 ), on the other hand, employed the same variables in both model parts, in an empirical application focusing on trade liberalization. However, so far, which variables determine the decision to trade is not so clear, and models may suffer from omitted variables bias in either one of model parts, or both.
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Modelling flow through a permeable bed: a combined physical-numerical approach

Modelling flow through a permeable bed: a combined physical-numerical approach

Developing numerical models capable of simulat- ing the hydrodynamics of open-channel flows over rough and permeable beds is crucial for pre- dicting the morphodynamic evolution of alluvial channels and the complex physical-chemical processes occurring within the subsurface (hypor- heic zone) of river beds. However, most current numerical models assume that alluvial streams have an impermeable channel bed (Raudkivi, 1998). This represents a significant issue as ex- perimental observations have shown that such as- sumptions are erroneous as turbulence within gravel-beds can be significant (Bencala and Wal- ters, 1983). Thus, Darcian theory, suitable for low-conductivity porous media, should not be ap- plied within cohesionless gravel-bed rivers. The Navier Stokes (NS) equations can be used to model flow through a porous media if the internal morphology is known. However, this is rarely the case and the complexity of the internal morphol- ogy of the bed has meant that the normal approach to this problem is to volume-average the NS equa- tions and close them with the Hazen-Dupui-Darcy (HDD) model (Lage et al., 2002). However, if the internal morphology of the bed is known, a mass flux scaling algorithm that has been developed to include complex bed topography into a stable dis-
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Topological defects in conformal field theories, entanglement entropy and indices

Topological defects in conformal field theories, entanglement entropy and indices

These defects describe critical impurities of low dimensional quantum systems. For two dimensional CFTs defects can be thought of as lines separating two (possibly different) CFTs on each side of the defect. Thereby the defect, or also called interface, acts as a map from one CFT to the other and vice versa. Folding the CFTs along the defect line result in a tensor theory of the two CFTs with the defect representing a boundary condition [39]. In this way the notion of defects can be related to the area of determining boundary states in a CFT. As it turned out the defects generalize in a natural way the notion of boundary conditions by setting local gluing conditions along the defect line. Interfaces and their properties such as their transmissivity and reflectivity [49] or their implementation of symmetries [54] have been studied in various contexts and many of their properties have been discovered [50–54]. For example it has be shown that special defects can implement symmetries or dualities [45, 46] between the various CFTs.
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Conducting field research abroad: a socioanthropological approach

Conducting field research abroad: a socioanthropological approach

My sociological study gave me a different perspective on banlieues. In this context, I entered the suburbs through meeting families and spending time with them. I didn’t have to worry about pointing out problems or trying to sup- port people, but only about trying to understand their living situations. I par- ticipated in their daily activities or special family events such as weddings or engagement celebrations. I had meals with them and felt like a family friend, sometimes even as a family member. I also participated in activities organized for women such as sewing lessons or French and Arab classes. The families I met told me about their life stories and their daily life. They were just like any other family I had met in other contexts. I met their neighbors and saw the ways in which they were close to each other. This solidarity had also been visi- ble when I was in the social work field, but in a different way, more from the outside. Being inside the families gave me an entirely new perspective on the banlieues. Of course, I also saw social problems there. The families I visited for example were always worried my bike would get stolen while I was at their home. They took it to their basement and locked it there. They insisted on the fact however that even if it did get stolen, they would find it within a short pe- riod of time through the friends of their sons. Delinquency and social problems were present, but not in the overwhelming and sometimes threatening way I had experienced them in the context of social work. What was dominant was the normal daily life of the inhabitants with their difficulties, for example, higher unemployment rates than in other parts of the city and their strengths, for example, an intense solidarity through the family and neighborhood. I real- ized how different one and the same field can be according to one’s entry into it.
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