Статті в журналах з теми "Quasi-rigid domains"

The reflection of internal gravity waves at sloping boundaries leads to focusing or defocusing. In closed domains, focusing typically dominates and projects the wave energy onto ‘wave attractors’. For small-amplitude internal waves, the projection of energy onto higher wavenumbers by geometric focusing can be balanced by viscous dissipation at high wavenumbers. Contrary to what was previously suggested, viscous dissipation in interior shear layers may not be sufficient to explain the experiments on wave attractors in the classical quasi-two-dimensional trapezoidal laboratory set-ups. Applying standard boundary layer theory, we provide an elaborate description of the viscous dissipation in the interior shear layer, as well as at the rigid boundaries. Our analysis shows that even if the thin lateral Stokes boundary layers consist of no more than 1 % of the wall-to-wall distance, dissipation by lateral walls dominates at intermediate wave numbers. Our extended model for the spectrum of three-dimensional wave attractors in equilibrium closes the gap between observations and theory by Hazewinkel et al. (J. Fluid Mech., vol. 598, 2008, pp. 373–382).

It is known that a quasi-rigid-body mode (QR mode) exists in hard disk drives (HDDs) in the frequency range from 3 to 5 kHz and that it is caused by the flexibility of the pivot and the mass and structure of the head actuator assembly (HAA). This mode hinders performance improvement of the servo system in this bandwidth and thus limits the area density growth of HDDs. In this paper, a novel tuned damping device is proposed to suppress the QR mode and to reduce the residual vibration in head positioning in order to improve the servo system performance. The damping device is to be installed on the arm and hollow space within the voice coil motor (VCM) on the HDDs. The dynamic characteristics of the HAA with the tuned damping device are measured in both the frequency and the time domain and are analysed by finite element modelling (FEM). It is shown that the tuned damping device can work effectively to suppress quasi-rigid body vibration of the HAA and minimize the residual vibration in head positioning.

We study, both theoretically and numerically, the equilibrium of a hinged rigid leaflet with an attached rotational spring, immersed in a stationary incompressible fluid within a rigid channel. Through a careful investigation of the properties of the domain functional describing the angular momentum exerted by the fluid on the leaflet (which depends on both the leaflet angular position and its thickness), we identify sufficient conditions on the spring stiffness function for the existence (and uniqueness) of equilibrium positions. This study resorts to techniques from shape differential calculus. We propose a numerical technique that exploits the mesh flexibility of the Virtual Element Method (VEM). A (polygonal) computational mesh is generated by cutting a fixed background grid with the leaflet geometry, and the problem is then solved with stable VEM Stokes elements of degrees [Formula: see text] and [Formula: see text] combined with a bisection algorithm. We prove quasi-optimal error estimates and present a large array of numerical experiments to document the accuracy and robustness with respect to degenerate geometry of the proposed methodology.

Abstract. An experimental study on the instability of a detached Stewartson layer, using an annular, rotating tank with flat, rigid upper and lower boundaries, showed an instability to steady vortices at a critical Reynolds number, arranged in a global mode structure along the shear layer. Increasing the Reynolds number resulted in successive transitions to lower modes where time-dependent behaviour was only found for flows with three or less vortices. Previous numerical simulations of a related experiment, using a two-dimensional spectral model of the quasi-geostrophic vorticity equation incorporating Ekman forcing and viscous dissipation, suggested that the boundary conditions at the inner cylinder of the domain could significantly affect the interior flow by the generation and shedding of vorticity at this inner boundary. A comparison of the numerical results with experimental data suggests that the rise of time-dependent behaviour is due to vorticity generation at the inner domain boundary.

The effects of dynamic soil–structure interaction (SSI) have been extensively studied in the last few decades, and proper analysis for the linear elastic case in frequency domain has been established successfully. However, SSI is rarely considered in the design of building structures, and instead, buildings are frequently analyzed using a rigid base assumption and quasi-static loading conditions that ignore SSI and its dynamic nature. Acknowledging these shortcomings, the National Institute of Standards and Technology (NIST) published in 2012 a set of recommendations on time-domain analyses of SSI for building structures compatible with standard finite element packages for consideration in engineering design. The so-called NIST GCR 12-917-21 report introduced a major simplification to enable frequency domain tools to be implemented in time domain analyses. That is, replacing the frequency-dependent soil impedance functions by a single-valued functions read at the flexible-base structure frequency; This work seeks to quantify the accuracy of this simplification considering fully coupled two-dimensional (2D) finite element models (FEM) as the reference. Using a Bayesian approach based on ensemble Kalman inversion (EnKI) and a range of numerical simulations of soil–foundation–building interaction, we estimate the optimal frequency that can be used to estimate soil impedance for time domain analyses; and we evaluate the improvement that the corresponding impedance offers relative to the full FEM results when compared to time domain analyses performed in accordance to the NIST recommendations outlined above.

In this study we give a characterization of semi-geostrophic turbulence by performing freely decaying simulations for the case of constant uniform potential vorticity, a set of equations known as the surface semi-geostrophic approximation. The equations are formulated as conservation laws for potential temperature and potential vorticity, with a nonlinear Monge–Ampère type inversion equation for the streamfunction, expressed in a transformed coordinate system that follows the geostrophic flow. We perform model studies of turbulent surface semi-geostrophic flows in a domain doubly periodic in the horizontal and limited in the vertical by two rigid lids, allowing for variations of potential temperature at one of the boundaries, and we compare the results with those obtained in the corresponding surface quasi-geostrophic case. The results show that, while the surface quasi-geostrophic dynamics is dominated by a symmetric population of cyclones and anticyclones, the surface semi-geostrophic dynamics features a more prominent role of fronts and filaments. The resulting distribution of potential temperature is strongly skewed and peaked at non-zero values at and close to the active boundary, while symmetry is restored in the interior of the domain, where small-scale frontal structures do not penetrate. In surface semi-geostrophic turbulence, energy spectra are less steep than in the surface quasi-geostrophic case, with more energy concentrated at small scales for increasing Rossby number. The energy related to frontal structures, the lateral strain rate and the vertical velocities are largest close to the active boundary. These results show that the semi-geostrophic model could be of interest for studying the lateral mixing of properties in geophysical flows.

Abstract. The disruptive potential of floating wind turbines has attracted the interest of both the industry and the scientific community. Lacking a rigid foundation, such machines are subject to large displacements whose impact on aerodynamic performance is not yet fully explored. In this work, the unsteady aerodynamic response to harmonic-surge motion of a scaled version of the DTU 10 MW turbine is investigated in detail. The imposed displacements have been chosen representative of typical platform motion. The results of different numerical models are validated against high-fidelity wind tunnel tests specifically focused on the aerodynamics. Also, a linear analytical model relying on the quasi-steady assumption is presented as a theoretical reference. The unsteady responses are shown to be dominated by the first surge harmonic, and a frequency domain characterization, mostly focused on the thrust oscillation, is conducted involving aerodynamic damping and mass parameters. A very good agreement among the codes, the experiments, and the quasi-steady theory has been found, clarifying some literature doubts. A convenient way to describe the unsteady results in a non-dimensional form is proposed, hopefully serving as a reference for future works.

A wind tunnel test on a large-span cantilevered elliptical annular roof was carried out. The time series of wind pressures were tested simultaneously on the upper and lower surfaces of a roof structure rigid model, that was exposed to open and suburban boundary layer air flows in various wind directions. The spatial correlation characteristics of fluctuating pressures on the roof structure were analyzed. Both the analyzing results of the correlation coefficient in time domain and the coherence function in frequency domain indicated that the correlation structure of the fluctuating pressure of a large-span roof is sensitive to the location of the investigated taps, the roof geometry, the wind direction, and the inflow turbulence. Therefore, the simulation methodology, using a single coherence function, based on the spatial interval of two taps, ignoring the geometry characteristics and the particular tap locations on the roof, a method commonly used in wind load simulations for high-rise and flat roof structures, is shown to not be appropriate for large-span cantilevered roof structures. This quasi-steady approach cannot be employed to evaluate large-span roof structures.

Recent research has attempted to use role-based approaches to recommend mobile services to other members among the same group in a context dependent manner. However, the traditional role mining approaches originated from the domain of security control tend to be rigid and may not be able to capture human behaviors adequately. In particular, during the course of role mining process, these approaches easily result in over-fitting, i.e., too many roles with slightly different service consumption patterns are found. As a result, they fail to reveal the true common preferences within the user community. This paper proposes an online role mining algorithm with a residual term and an error term, that automatically group users according to their interests and habits without losing sight of their individual preferences and random errors. Moreover, to resolve the over-fitting problem, the authors relax the role definition in role mining mechanism by introducing quasi-roles based on the concept of quasi-bicliques. Most importantly, the new concept allows us to propose a monitoring framework to detect and correct over-fitting in online role mining such that recommendations can be made based on the latest and genuine common preferences. To the best of the authors’ knowledge, this is a new area in service recommendation that is yet to be fully explored.

The stability of elliptically perturbed circular vortices is investigated in a two-layer shallow-water model, with constant background rotation. The fluid is bounded above and below by rigid and at surfaces. The linear stability analysis shows that elliptical perturbations are most unstable for moderate Burger numbers and vorticity shears. Shorter waves dominate for more sheared vortices. Shallow-water and quasi-geostrophic growth rates exhibit a striking similarity, except at each end of the Burger number domain. There, cyclones (anticyclones) with finite Rossby numbers are more (less) unstable than their quasi-geostrophic counterparts. A simple model gives a first-order trend for this bias.Nonlinear model runs with initially perturbed vortices also show the similarity between the two dynamics. In these runs, elliptically deformed vortices stabilize as stationary rotating tripoles for moderate linear instability; on the other hand, strongly unstable vortices break as dipoles. During these nonlinear processes, energy transfers indicate that barotropic instability is at least as active as the baroclinic one. For tripole formation, the modal analysis of the perturbation exhibits a dominant contribution of the original wave and of the mean flow correction. The ageostrophic and divergent parts of the flow are respectively weak and negligible. The Lighthill equation proves that few internal gravity waves are generated during tripole formation or dipolar breaking. Finally, the effects of triangular perturbations on circular vortices and the formation of quadrupoles are briefly addressed.

This paper introduces MBSymba, an object-oriented language for the modeling of multibody systems and the automatic generation of equations of motion in symbolic form. MBSymba has built upon the general-purpose computer algebra software Maple and it is freely available for teaching and research purposes. With MBSymba, objects such as points, vectors, rigid bodies, forces and torques, and the relationships among them may be defined and manipulated both at high and low levels. Absolute, relative or mixed coordinates may be used, as well as combination of infinitesimal and noninfinitesimal variables. Once the system has been modeled, Lagrange’s and/or Newton’s equations can be derived in a quasi-automatic way, either in an inertial or noninertial reference frame. Equations can be automatically converted into Matlab, C/C++ or Fortan code to produce stand alone, numerically optimized simulation code. MBSymba is particularly suited for the modeling of ground, water or air vehicles; therefore, the mathematical model of a passenger car with trailer is illustrated as a case study. Time domain simulations, steady state analysis and stability results are also presented.

Many urologists are currently studying new designs of ureteral stents to improve the quality of their operations and the subsequent recovery of the patient. In order to help during this design process, many computational models have been developed to simulate the behaviour of different biological tissues and provide a realistic computational environment to evaluate the stents. However, due to the high complexity of the involved tissues, they usually introduce simplifications to make these models less computationally demanding. In this study, the interaction between urine flow and a double-J stented ureter with a simplified geometry has been analysed. The Fluid-Structure Interaction (FSI) of urine and the ureteral wall was studied using three models for the solid domain: Mooney-Rivlin, Yeoh, and Ogden. The ureter was assumed to be quasi-incompressible and isotropic. Data obtained in previous studies from ex vivo and in vivo mechanical characterization of different ureters were used to fit the mentioned models. The results show that the interaction between the stented ureter and urine is negligible. Therefore, we can conclude that this type of models does not need to include the FSI and could be solved quite accurately assuming that the ureter is a rigid body and, thus, using the more simple Computational Fluid Dynamics (CFD) approach.

Many classical problems of Mechanics can be studied regarding them as perturbations of integrable systems; this is the case of the fast rotations of the rigid body in an arbitrary potential, the restricted three body problem with small values of the mass-ratio, and others. However, the application of the classical results of Hamiltonian Perturbation Theory to these systems encounters difficulties due to the presence of the so-called ‘degeneracy’. More precisely, the Hamiltonian of a quasi-integrable degenerate system looks likewhere (I, φ) є U × Tn, U ⊆ Rn, are action-angle type coordinates, while the degeneracy of the system manifests itself with the presence of the ‘degenerate’ variables (p, q) є B ⊆ R2m. The KAM theorem has been applied under quite general assumptions to degenerate Hamiltonians (Arnold, 1963), while the Nekhoroshev theorem (Nekhoroshev, 1977) provides, if h is convex, the following bounds: there exist positive ε0, a0, t0 such that if ε < ε0 then if where Te is the escape time of the solution from the domain of (1). An escape is possible because the motion of the degenerate variables can be bounded in principle only by , and so over the time they can experience large variations. Therefore, there is the problem of individuating which assumptions on the perturbation and on the initial data allow to control the motion of the degenerate variables over long times.

Abstract Lifting-line based solvers could supersede the blade element momentum (BEM) method as the industry standard in the near future as rotor sizes of modern wind turbines and computational resources continue to increase. A comparison study between both methods is presented where the IEA 10 MW wind turbine is evaluated in the aero-servo-elastic simulation tool QBlade, comparing the lifting-line free vortex wake method to an unsteady blade element momentum solver. Besides the baseline rotor of the IEA 10 MW turbine, the comparison includes several blade tip extensions, including a swept and a dihedral geometry, to further differentiate capabilities between both methods in aerodynamically complex flow fields. As a reference serve results from equivalent simulations performed with multiple fidelity solvers of the simulation tool HAWC2. Results of a rigid load case demonstrate considerable improvement regarding the aerodynamic accuracy of lifting-line based methods in below rated conditions over BEM codes. The aerodynamic loads on geometrically complex tip extensions in steady conditions prove good capabilities of lower fidelity codes to predict out-of-plane bend shapes but also clear limitations regarding loads on swept geometries. A quasi-steady aeroelastic load case further demonstrates the capability of both QBlade codes to produce comparable results to similar fidelity solvers of the HAWC2 tool on an integral level. A detailed comparison in the time domain shows a larger dependency of the results on the type of structural solver that is used in contrast to the fidelity level of the aerodynamic method.

In this paper, we consider the dynamical description of a pendulum model consists of a heavy solid connection to a nonelastic string which suspended on an elliptic path in a vertical plane. We suppose that the dimensions of the solid are large enough to the length of the suspended string, in contrast to previous works which considered that the dimensions of the body are sufficiently small to the length of the string. According to this new assumption, we define a large parameter ε and apply Lagrange’s equation to construct the equations of motion for this case in terms of this large parameter. These equations give a quasi-linear system of second order with two degrees of freedom. The obtained system will be solved in terms of the generalized coordinates θ and φ using the large parameter procedure. This procedure has an advantage over the other methods because it solves the problem in a new domain when fails all other methods for solving the problem in such a domain under these conditions. It is one of the most important applications, when we study the slow spin motion of a rigid body in a Newtonian field of force under an external moment or the rotational motion of a heavy solid in a uniform gravity field or the gyroscopic motions with a sufficiently small angular velocity component about the major or the minor axis of the ellipsoid of inertia. There are many applications of this technique in aerospace science, satellites, navigations, antennas, and solar collectors. This technique is also useful in all perturbed problems in physics and mechanics, for example, the perturbed pendulum motions and the perturbed mechanical systems. The results of this paper also are useful in moving bridges and the swings. For satisfying the validation of the obtained solutions, we consider numerical considerations by one of the numerical methods and compare the obtained analytical and numerical solutions.

AbstractSince quasi-phase-matching of nonlinear optics was proposed in 1962, nonlinear photonic crystals were rapidly developed by ferroelectric domain inversion induced by electric or light poling. The three-dimensional (3D) periodical rotation of ferroelectric domains may add feasible modulation to the nonlinear coefficients and break the rigid requirements for the incident light and polarization direction in traditional quasi-phase-matching media. However, 3D rotating ferroelectric domains are difficult to fabricate by the direct external poling technique. Here, we show a natural potassium–tantalate–niobate (KTN) perovskite nonlinear photonic crystal with spontaneous Rubik’s cube-like domain structures near the Curie temperature of 40 °C. The KTN crystal contains 3D ferroelectric polarization distributions corresponding to the reconfigured second-order susceptibilities, which can provide rich reciprocal vectors to compensate for the phase mismatch along an arbitrary direction and polarization of incident light. Bragg diffraction and broadband second-harmonic generation are also presented. This natural nonlinear photonic crystal directly meets the 3D quasi-phase-matching condition without external poling and establishes a promising platform for all-optical nonlinear beam shaping and enables new optoelectronic applications for perovskite ferroelectrics.

AbstractVertical ferroelectricity where a net dipole moment appears as a result of in-plane ionic displacements has gained enormous attention following its discovery in transition metal dichalcogenides. Based on first-principles calculations, we report on the evidence of robust vertical ferroelectricity upon interlayer sliding in layered semiconducting β-ZrI2, a sister material of polar semimetals MoTe2 and WTe2. The microscopic origin of ferroelectricity in ZrI2 is attributed to asymmetric shifts of electronic charges within a trilayer, revealing a subtle interplay of rigid sliding displacements and charge redistribution down to ultrathin thicknesses. We further investigate the variety of ferroelectric domain boundaries and predict a stable charged domain wall with a quasi-two-dimensional electron gas and a high built-in electric field that can increase electron mobility and electromechanical response in multifunctional devices. Semiconducting behaviour and a small switching barrier of ZrI2 hold promise for various ferroelectric applications, and our results provide important insights for further development of slidetronics ferroelectricity.

AbstractA space-time adaptive algorithm to solve the motion of a rigid disk in an incompressible Newtonian fluid is presented, which allows collision or quasi-collision processes to be computed with high accuracy. In particular, we recover the theoretical result proven in [M. Hillairet, Lack of collision between solid bodies in a 2D incompressible viscous flow, Comm. Partial Differential Equations 32 2007, 7–9, 1345–1371], that the disk will never touch the boundary of the domain in finite time. Anisotropic, continuous piecewise linear finite elements are used for the space discretization, the Euler scheme for the time discretization. The adaptive criteria are based on a posteriori error estimates for simpler problems.

Coupled dynamic analysis of a floating offshore wind turbine (FOWT) is predicted with in-house ITU-WAVE computational tool. The hydrodynamic parameters are approximated with time marching of boundary integral equation whilst aerodynamic parameters are solved with unsteady blade element momentum method. In addition, forces on FOWT due to mooring lines are predicted with quasi-static analysis whilst hydrodynamic viscous effects are included with Morison equation. FOWT’s blades are considered as an elastic structure whilst tower is considered as a rigid structure. The effects of steady wind speed on surge motion spectrum decrease the spectrum amplitude over wave frequency ranges, but this effect is not significant. The duration of time domain simulation plays significant role in the region of surge and pitch resonant frequencies. The numerical results of in-house ITU-WAVE computational code for eigenfrequencies of blades, aerodynamics and hydrodynamics parameters are validated against other numerical results which shows satisfactory agreements.

ABSTRACT Numerical modeling of earthquake dynamics and derived insight for seismic hazard relies on credible, reproducible model results. The sequences of earthquakes and aseismic slip (SEAS) initiative has set out to facilitate community code comparisons, and verify and advance the next generation of physics-based earthquake models that reproduce all phases of the seismic cycle. With the goal of advancing SEAS models to robustly incorporate physical and geometrical complexities, here we present code comparison results from two new benchmark problems: BP1-FD considers full elastodynamic effects, and BP3-QD considers dipping fault geometries. Seven and eight modeling groups participated in BP1-FD and BP3-QD, respectively, allowing us to explore these physical ingredients across multiple codes and better understand associated numerical considerations. With new comparison metrics, we find that numerical resolution and computational domain size are critical parameters to obtain matching results. Codes for BP1-FD implement different criteria for switching between quasi-static and dynamic solvers, which require tuning to obtain matching results. In BP3-QD, proper remote boundary conditions consistent with specified rigid body translation are required to obtain matching surface displacements. With these numerical and mathematical issues resolved, we obtain excellent quantitative agreements among codes in earthquake interevent times, event moments, and coseismic slip, with reasonable agreements made in peak slip rates and rupture arrival time. We find that including full inertial effects generates events with larger slip rates and rupture speeds compared to the quasi-dynamic counterpart. For BP3-QD, both dip angle and sense of motion (thrust versus normal faulting) alter ground motion on the hanging and foot walls, and influence event patterns, with some sequences exhibiting similar-size characteristic earthquakes, and others exhibiting different-size events. These findings underscore the importance of considering full elastodynamics and nonvertical dip angles in SEAS models, as both influence short- and long-term earthquake behavior and are relevant to seismic hazard.

Natural and engineered surfaces are never smooth, but irregular, rough at different scales, compliant, possibly porous, liquid impregnated or superhydrophobic. The correct numerical modelling of fluid flowing through and around them is important but poses problems. For media characterized by a periodic or quasi-periodic microstructure of characteristic dimensions smaller than the relevant scales of the flow, multiscale homogenization can be used to study the effect of the surface, avoiding the numerical resolution of small details. Here, we revisit the homogenization strategy using adjoint variables to model the interaction between a fluid in motion and regularly micro-textured, permeable or impermeable walls. The approach described allows for the easy derivation of auxiliary/adjoint systems of equations which, after averaging, yield macroscopic tensorial properties, such as permeability, elasticity, slip, transpiration, etc. When the fluid in the neighbourhood of the microstructure is in the Stokes regime, classical results are recovered. Adjoint homogenization, however, permits simple extension of the analysis to the case in which the flow displays nonlinear effects. Then, the properties extracted from the auxiliary systems take the name of effective properties and do not depend only on the geometrical details of the medium, but also on the microscopic characteristics of the fluid motion. Examples are shown to demonstrate the usefulness of adjoint homogenization to extract effective tensor properties without the need for ad hoc parameters. In particular, notable results reported herein include:(i)an original formulation to describe filtration in porous media in the presence of inertial effects;(ii)the microscopic and macroscopic equations needed to characterize flows through poroelastic media;(iii)an extended Navier’s condition to be employed at the boundary between a fluid and an impermeable rough wall, with roughness elements which can be either rigid or linearly elastic;(iv)the microscopic problems needed to define the relevant parameters for a Saffman-like condition at the interface between a fluid and a porous substrate; and(v)the macroscopic equations which hold at the dividing surface between a free-fluid region and a fluid-saturated poroelastic domain.

Introduction Nun habe ich Euch genug geschrieben, diesen Brief wenn sei [sic] lesen würden, dann würde ich den Genickschuß bekommen.Now I have written you enough, this letter if they would read it, I would get the neck shot. (M., all translations from German sources and quotations by the author) When the German soldier Otto M. wrote these lines from Russia to his family on 3 September 1943 during the Second World War, he knew that his war letter would not be subject to the National Socialist censorship apparatus. The letter contains, inter alia, detailed information about the course of the war on the front, troop locations, and warnings about the Nazi regime. M., as he wrote in the letter, smuggled it past the censorship via a “comrade”. As a German soldier, M. was a member of the Volksgemeinschaft—a National Socialist concept that drew a “racist and anti-Semitic borderline” (Wildt 48)—and was thus not socially excluded due to his status. Nevertheless, in the sentence quoted above, M. anticipates possible future consequences of his deviant actions, which would be carried out by “them”—potentially leading to his violent death. This article investigates how social and societal exclusion is brought forth by everyday media practices such as writing letters. After an introduction to the thesis under discussion, I will briefly outline the linguistic research on National Socialism that underlies the approach presented. In the second section, the key concepts of agency and dispositif applied in this work are discussed. This is followed by two sections in which infrastructural and interactional practices of exclusion are analysed. The article closes with some concluding remarks. During the Second World War, Wehrmacht soldiers and their relatives could not write and receive letters that were not potentially subject to controls. Therefore, the blunt openness with which M. anticipated the brutal sanctions of behavioural deviations in the correspondence quoted above was an exception in the everyday practice of war letter communication. This article will thus pursue the following thesis: private communication in war letters was subject to specific discourse conditions under National Socialism, and this brought forth excluding agency, which has two intertwined readings. Firstly, “excluding” is to be understood as an attribute of “agency” in the sense of an acting entity that either is included and potentially excludes or is excluded due to its ascribed agency. For example, German soldiers who actively participated in patriotic service were included in the Volksgemeinschaft. By contrast, Jews or Communists, to name but a few groups that, from the perspective of racist Nazi ideology, did not contribute to the community, were excluded from it. Such excluding agencies are based on specific practices of dispositional arrangement, which I refer to as infrastructural exclusion of agency. Secondly, excluding agency describes a linguistic practice that developed under National Socialism and has an equally stabilising effect on it. Excluding agency means that agents, and hence protagonists, are excluded by means of linguistic mitigation and omission. This second reading emphasises practices of linguistic construction of agency in interaction, which is described as interactional exclusion of agency. In either sense, exclusion is inextricably tied to the notion of agency, which is illustrated in this article by using data from field post letters of the Second World War. Social exclusion, along with its most extreme manifestations under fascism, is both legitimised and carried out predominantly through discursive practices. This includes for the public domain, on the one hand, executive language use such as in laws, decrees, orders, court hearings, and verdicts, and on the other hand, texts such as ideological writings, speeches, radio addresses, folk literature, etc. Linguistic research on National Socialism and its mechanisms of inclusion and exclusion has long focussed on the power of a regulated public use of language that seemed to be shaped by a few protagonists, most notably Hitler and Goebbels (Schlosser; Scholl). More recent works, however, are increasingly devoted to the differentiation of heterogeneous communities of practice, which were primarily established through discursive practices and are manifested accordingly in texts of that time (Horan, Practice). Contrary to a justifiably criticised “exculpation of the speakers” (Sauer 975) by linguistic research, which focusses on language but not on situated, interactional language use, such a perspective is increasingly interested in “discourse in National Socialism, with a particular emphasis on language use in context as a shared, communicative phenomenon” (Horan, Letter 45). To understand the phenomenon of social and societal exclusion, which was constitutive for National Socialism, it is also necessary to analyse those discursive practices of inclusion and exclusion through which the speakers co-constitute everyday life. I will do this by relating the discourse conditions, based on Foucault’s concept of dispositif (Confessions 194), to the agency of the correspondents of war letters, i.e. field post letters. On Agency and Dispositif Agency and dispositif are key concepts for the analysis of social exclusion, because they can be applied to analyse the situated practices of exclusion both in terms of the different capacities for action of various agents, i.e. acting entities, and the inevitably asymmetrical arrangement within which actions are performed. Let me first, very briefly, outline some linguistic conceptions of agency. While Ahearn states that “agency refers to the socioculturally mediated capacity to act” (28) and thus conceives agency as a potential, Duranti understands agency “as the property of those entities (i) that have some degree of control over their own behavior, (ii) whose actions in the world affect other entities’ (and sometimes their own), and (iii) whose actions are the object of evaluation (e.g. in terms of their responsibility for a given outcome)” (453). Deppermann considers agency to be a means of social and situational positioning: “‘agency’ is to capture properties of the subject as agent, that is, its role with respect to the events in which it is involved” (429–30). This is done by linguistic attribution. Following Duranti, this analysis is based on the understanding that agency is established by the ascription of action to an entity which is thereby made or considered accountable for the action. This allows a practice-theoretical reference to Garfinkel’s concept of accountability and identifies agentive practices as “visibly-rational-and-reportable-for-all-practical purposes” (7). The writing of letters in wartime is one such reflexive discursive practice through which agents constitute social reality by means of ascribing agency. The concept of semantic roles (Fillmore; von Polenz), offers another, distinctly linguistic access to agency. By semantic roles, agency in situated interaction is established syntactically and semantically. Put simply, a distinction is made between an Agent, as someone who performs an action, and a Patient, as someone to whom an action occurs (von Polenz 170; semantic roles such as Agent, Patient, Experiencer, etc. are capitalised by convention). Using linguistic data from war letters, this concept is discussed in more detail below. In the following, “field post” is considered as dispositif, by which Foucault means a thoroughly heterogeneous ensemble consisting of discourses, institutions, architectural forms, regulatory decisions, laws, administrative measures, scientific statements, philosophical, moral and philanthropic propositions – in short, the said as much as the unsaid. Such are the elements of the apparatus [dispositif]. The apparatus [dispositif] itself is the system of relations that can be established between these elements. (Foucault, Confessions 194) The English translation of the French “dispositif” as “apparatus” encourages an understanding of dispositif as a rather rigid structure. In contrast, the field post service of the Second World War will be used here to show how such dispositifs enable practices of exclusion or restrict access to practices of inclusion, while these characteristics themselves are in turn established by practices or, as Foucault calls them, procedures (Foucault, Discourse). An important and potentially enlightening notion related to dispositif is that of agencement, which in turn is borrowed from Deleuze and Guattari and was further developed in particular in actor-network theory (Çalışkan and Callon; Gherardi). What Çalışkan and Callon state about markets serves as a general description of agencement, which can be defined as an “arrangement of heterogeneous constituents that deploys the following: rules and conventions; technical devices; metrological systems; logistical infrastructures; texts, discourses and narratives …; technical and scientific knowledge (including social scientific methods), as well as the competencies and skills embodied in living beings” (3). This resembles Foucault’s concept of dispositif (Foucault, Confessions; see above), which “denotes a heterogeneous ensemble of discursive and nondiscursive elements with neither an originary subject not [sic] a determinant causality” (Coté 384). Considered morphosemantically, agencement expresses an important interrelation: in that it is derived from both the French agencer (to construct; to arrange) and agence (agency; cf. Hardie and MacKenzie 58) and is concretised and nominalised by the suffix -ment, agencement elegantly integrates structure and action according to Giddens’s ‘duality of structure’. While this tying aspect certainly contributes to a better understanding of dispositional arrangements and should therefore be considered, agencement, as applied in actor-network theory, emphasises above all “the fact that agencies and arrangements are not separate” (Çalışkan and Callon) and is, moreover, often employed to ascribe agency to material objects, things, media, etc. This approach has proven to be very fruitful for analyses of socio-technical arrangements in actor-network theory and practice theory (Çalışkan and Callon; Gherardi). However, within the presented discourse-oriented study on letter writing and field post in National Socialism, a clear analytical differentiation between agency and arrangement, precisely in order to point out their interrelation, is essential to analyse practices of exclusion. This is why I prefer dispositif to agencement as the analytical concept here. Infrastructural Exclusion of Agency in Field Post Letters In the Second World War, writing letters between the “homeland” and the “frontline” was a fundamental everyday media practice with an estimated total of 30 to 40 billion letters in Germany (Kilian 97). War letters were known as field post (Feldpost), which was processed by the field post service. The dispositif “field post” was, in opposition to the traditional postal service, subject to specific conditions regarding charges, transport, and above all censorship. No transportation costs arose for field post letters up to a weight of 250 grams. Letters could only be sent by or to soldiers with a field post number that encoded the addresses of the field post offices. Only soldiers who were deployed outside the Reich’s borders received a field post number (Kilian 114). Thus, the soldiers were socially included as interactants due to their military status. The entire organisation of the field post was geared towards enabling members of the Volksgemeinschaft to communicatively shape, maintain, and continue their social relationships during the war (Bergerson et al.). Applying Foucault, the dispositif “field post” establishes selection and exclusion mechanisms in which “procedures of exclusion” (Discourse 52) become manifest, two of which are to be related to the field post: “exclusion from discourse” and “scarcity of speaking subjects” (Spitzmüller and Warnke 73). Firstly, “procedures of exclusion ensure that only certain statements can be made in discourse” (Spitzmüller and Warnke 73). This exclusion procedure ought to be implemented by controlling and, ultimately, censoring field post letters. Reviews were carried out by censorship offices (Feldpostprüfstellen), which were military units independent of the field post offices responsible for delivery. Censorship initially focussed on military information. However, “in the course of the war, censorship shifted from a control measure aimed at defence towards a political-ideological review” (Kilian 101). Critical remarks could be legally prosecuted and punished with prison, penitentiary, or death (Kilian 99). Hence, it is assumed that self-censorship played a role not only for public media, such as newspapers, but also for writing private letters (Dodd). As the introductory quotation from Otto M. shows, writers who spread undesirable information in their letters anticipated the harshest consequences. In this respect, randomised censorship—although only a very small proportion of the high volume of mail was actually opened by censors (Kilian)—established a permanent disposition of control that resulted in a potentially discourse-excluding social stratification of private communication. Secondly, the dispositif “field post” was inherently exclusive and excluding, as those who did not belong to the Volksgemeinschaft could not use the service and thus could not acquire agentive capacity. The “scarcity of speaking subjects” (Spitzmüller and Warnke 73) was achieved by restricting participation in the field post system to members of the Volksgemeinschaft. Since agency is based on the most basic prerequisite, namely the ability to act linguistically at all, the mere possibility of exercising agency was infrastructurally restricted by the field post system. Excluding people from “agency-through-language” means excluding them from an “agency of an existential sort” (Duranti 455), which is described here, regarding the field post system, as infrastructural exclusion of agency. Interactional Exclusion of Agency in Field Post Letters In this section, I will elaborate how agency is brought forth interactionally through linguistic means on the basis of data from a field post corpus that was compiled in the project “Linguistic Social History 1933 to 1945” (Kämper). The aim of the project is an actor-based description of discursive practices and patterns at the time of National Socialism, which takes into account the fact that society in the years 1933 to 1945 consisted of heterogeneous communities of practice (Horan, Practice). Letter communication is considered to be an interaction that is characterised by mediated indexicality, accountability, reflexivity, sequentiality, and reciprocity (Dang-Anh) and is performed as situated social practice (Barton and Hall). The corpus of field letters examined here provides access to the everyday communication of members of the ‘integrated society’, i.e. those who were neither high-ranking members of the Nazi apparatus nor exposed to the repressions of the fascist dictatorship. The corpus consists of about 3,500 letters and about 2.5 million tokens. The data were obtained by digitising letter editions using OCR scans and in cooperation with the field post archive of the Museum for Communication Berlin (cf. sources below). We combine qualitative and quantitative methods, the latter providing heuristic indicators for in-depth hermeneutical analysis (Felder; Teubert). We apply corpus linguistic methods such as keyword, collocation and concordance analysis to the digitised full texts in order to analyse the data intersubjectively by means of corpus-based hermeneutic discourse analysis (Dang-Anh and Scholl). However, the selected excerpts of the corpus do not comprise larger data sets or complete sequences, but isolated fragments. Nevertheless, they illustrate the linguistic (non-)constitution of agency and thus distinctively exemplify exclusionary practices in field post letter writing. From a linguistic point of view, the exclusion of actors from action is achieved syntactically and semantically by deagentivisation (Bernárdez; von Polenz 186), as will be shown below. The following lines were written by Albert N. to his sister Johanna S. and are dated 25 June 1941, shortly after the beginning of the German Wehrmacht’s military campaign in Russia (Russlandfeldzug) a few days earlier. Vor den russ. Gefangenen bekommt man einen Ekel, d.h. viele Gefangene werden nicht gemacht.One gets disgusted by the Russian prisoners, i.e. many prisoners are not made. (N.) In the first part of the utterance, “mitigation of agency” (Duranti 465) is carried out using the impersonal pronoun “man” (“one”) which does not specify its referent. Instead, by means of deagentivisation, the scope of the utterance is generalised to an indefinite in‑group of speakers, whereby the use of the impersonal pronoun implies that the proposition is valid or generally accepted. Moreover, the use of “one” generalises the emotional expression “disgust”, thus suggesting that the aversive emotion is a self-evident affect experienced by everyone who can be subsumed under “one”. In particular, this includes the author, who is implicitly displayed as primarily perceiving the emotion in question. This reveals a fundamental practice of inclusion and exclusion, the separating distinction between “us”/“we” and “them”/“the others” (Wodak). In terms of semantic roles, the inclusive and generalised formal Experiencer “one” is opposed to the Causative “Russian prisoner” in an exclusionary manner, implicitly indicating the prisoners as the cause of disgust. The subsequent utterance is introduced by “i.e.”, which marks the causal link between the two phrases. The wording “many prisoners are not made” strongly suggests that it refers to homicides, i.e. executions carried out at the beginning of the military campaign in Russia by German troops (Reddemann 222). The depiction of a quasi-universal disgust in the first part establishes a “negative characterization of the out-group” (Wodak 33) which, in the expressed causal relation with the second phrase, seems to morally legitimise or at least somehow justify the implied killings. The passive form entirely omits an acting entity. Here, deagentivisation obscures the agency of the perpetrators. However, this is not the only line between acting and non-acting entities the author draws. The omission of an agent, even the impersonal “one”, in the second part, and the fact that there is no talk of self-experienceable emotions, but war crimes are hinted at in a passive sentence, suggest the exclusion of oneself as a joint agent of the indicated actions. As further data from the corpus indicate, war crimes are usually not ascribed to the writer or his own unit as the agents but are usually attributed to “others” or not at all. Was Du von Juden schreibst, ist uns schon länger bekannt. Sie werden im Osten angesiedelt.What you write about Jews is already known to us for some time. They are being settled in the East. (G.) In this excerpt from a letter, which Ernst G. wrote to his wife on 22 February 1942, knowledge about the situation of the Jews in the war zone is discussed. The passage appears quite isolated with its cotext in the letter revolving around quite different, trivial, everyday topics. Apparently, G. refers in his utterance to an earlier letter from his wife, which has not been preserved and is therefore not part of the corpus. “Jews” are those about whom the two agents, the soldier and his wife, write, whereas “us” refers to the soldiers at the front. In the second part, agency is again obscured by deagentivisation. While “they” anaphorically refers to “Jews” as Patients, the agents of their alleged resettlement remain unnamed in this “agent-less passive construction” (Duranti 466). Jews are depicted here as objects being handled—without any agency of their own. The persecution of the Jews and the executions carried out on the Russian front (Reddemann 222), including those of Jews, are euphemistically played down here as “settlements”. “Trivialization” and “denial” are two common discursive practices of exclusion (Wodak 134) and emerge here, as interactional exclusion of agency, in one of their most severe manifestations. Conclusion Social and societal exclusion, as has been shown, are predominantly legitimised as well as constituted, maintained, and perpetuated by discursive practices. Field post letters can be analysed both in terms of the infrastructure—which is itself constituted by infrastructuring practices and is thus not rigid but dynamic—that underlies excluding letter-writing practices in times of war, and the extent to which linguistic excluding practices are performed in the letters. It has been shown that agency, which is established by the ascription of action to an entity, is a central concept for the analysis of practices of exclusion. While I propose the division into infrastructural and interactional exclusion of agency, it must be pointed out that this can only be an analytical distinction and both bundles of practices, that of infrastructuring and that of interacting, are intertwined and are to be thought of in relation to each other. Bringing together the two concepts of agency and dispositif, despite the fact that they are of quite different origins, allows an analysis of exclusionary practices, which I hope does justice to the relation of interaction and infrastructure. By definition, exclusion occurs against the background of an asymmetrical arrangement within which exclusionary practices are carried out. Thus, dispositif is understood as an arranged but flexible condition, wherein agency, as a discursively ascribed or infrastructurally arranged property, unfolds. Social and societal exclusion, which were constitutive for National Socialism, were accomplished not only in public media but also in field post letters. Writing letters was a fundamental everyday media practice and the field post was a central social medium during the National Socialist era. However, exclusion occurred on different infrastructural and interactional levels. As shown, it was possible to be excluded by agency, which means exclusion by societal status and role. People could linguistically perform an excluding agency by constituting a division between “us” and “them”. Also, specific discourses were excluded by the potential control and censorship of communication by the authorities, and those who did not suppress agency, for example by self-censoring, feared prosecution. Moreover, the purely linguistic practices of exclusion not only constituted or legitimised the occasionally fatal demarcations drawn under National Socialism, but also concealed and trivialised them. As discussed, it was the perpetrators whose agency was excluded in war letters, which led to a mitigation of their actions. In addition, social actors were depreciated and ostracised through deagentivisation, mitigation and omission of agency. In extreme cases of social exclusion, linguistic deagentivisation even prepared or resulted in the revocation of the right to exist of entire social groups. The German soldier Otto M. feared fatal punishment because he did not communicatively act according to the social stratification of the then regime towards a Volksgemeinschaft in a field post letter. This demonstrates how thin the line is between inclusion and exclusion in a fascist dictatorship. 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