704 resultados para Conical mirrors


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BACKGROUND AND PURPOSE: Computer-assisted navigation is increasingly used in functional endoscopic sinus surgery (FESS) to prevent injury to vital structures, necessitating preparative CT and, thus, radiation exposure. The purpose of our study was to investigate currently used radiation doses for CT in computer-assisted navigation in sinus surgery (CAS-CT) and to assess minimal doses required. MATERIALS AND METHODS: A questionnaire inquiring about dose parameters used for CAS-CT was sent to 30 radiologic institutions. The feasibility of low-dose registration was tested with a phantom. The influence of CAS-CT dose on technical accuracy and on the practical performance of 5 ear, nose, and throat (ENT) surgeons was evaluated with cadaver heads. RESULTS: The questionnaire response rate was 63%. Variation between minimal and maximal dose used for CAS-CT was 18-fold. Phantom registration was possible with doses as low as 1.1 mGy. No dose dependence on technical accuracy was found. ENT surgeons were able to identify anatomic landmarks on scans with a dose as low as 3.1 mGy. CONCLUSIONS: The vast dose difference between institutions mirrors different attitudes toward image quality and radiation-protection issues rather than being technically founded, and many patients undergo CAS-CT at higher doses than necessary. The only limit for dose reduction in CT for computer-assisted endoscopic sinus surgery is the ENT surgeon's ability to cope with impaired image quality, whereas there is no technically justified lower dose limit. We recommend, generally, doses used for the typical diagnostic low-dose sinus CT (120 kV/20-50 mAs). When no diagnostic image quality is needed, even a reduction down to a third is possible.

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Direct imaging of extra-solar planets in the visible and infrared region has generated great interest among scientists and the general public as well. However, this is a challenging problem. Diffculties of detecting a planet (faint source) are caused, mostly, by two factors: sidelobes caused by starlight diffraction from the edge of the pupil and the randomly scattered starlight caused by the phase errors from the imperfections in the optical system. While the latter diffculty can be corrected by high density active deformable mirrors with advanced phase sensing and control technology, the optimized strategy for suppressing the diffraction sidelobes is still an open question. In this thesis, I present a new approach to the sidelobe reduction problem: pupil phase apodization. It is based on a discovery that an anti-symmetric spatial phase modulation pattern imposed over a pupil or a relay plane causes diffracted starlight suppression sufficient for imaging of extra-solar planets. Numerical simulations with specific square pupil (side D) phase functions, such as ... demonstrate annulling in at least one quadrant of the diffraction plane to the contrast level of better than 10^12 with an inner working angle down to 3.5L/D (with a = 3 and e = 10^3). Furthermore, our computer experiments show that phase apodization remains effective throughout a broad spectrum (60% of the central wavelength) covering the entire visible light range. In addition to the specific phase functions that can yield deep sidelobe reduction on one quadrant, we also found that a modified Gerchberg-Saxton algorithm can help to find small sized (101 x 101 element) discrete phase functions if regional sidelobe reduction is desired. Our simulation shows that a 101x101 segmented but gapless active mirror can also generate a dark region with Inner Working Distance about 2.8L/D in one quadrant. Phase-only modulation has the additional appeal of potential implementation via active segmented or deformable mirrors, thereby combining compensation of random phase aberrations and diffraction halo removal in a single optical element.

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This dissertation presents a detailed study in exploring quantum correlations of lights in macroscopic environments. We have explored quantum correlations of single photons, weak coherent states, and polarization-correlated/polarization-entangled photons in macroscopic environments. These included macroscopic mirrors, macroscopic photon number, spatially separated observers, noisy photons source and propagation medium with loss or disturbances. We proposed a measurement scheme for observing quantum correlations and entanglement in the spatial properties of two macroscopic mirrors using single photons spatial compass state. We explored the phase space distribution features of spatial compass states, such as chessboard pattern by using the Wigner function. The displacement and tilt correlations of the two mirrors were manifested through the propensities of the compass states. This technique can be used to extract Einstein-Podolsky-Rosen correlations (EPR) of the two mirrors. We then formulated the discrete-like property of the propensity Pb(m,n), which can be used to explore environmental perturbed quantum jumps of the EPR correlations in phase space. With single photons spatial compass state, the variances in position and momentum are much smaller than standard quantum limit when using a Gaussian TEM00 beam. We observed intrinsic quantum correlations of weak coherent states between two parties through balanced homodyne detection. Our scheme can be used as a supplement to decoy-state BB84 protocol and differential phase-shift QKD protocol. We prepared four types of bipartite correlations ±cos2(θ12) that shared between two parties. We also demonstrated bits correlations between two parties separated by 10 km optical fiber. The bits information will be protected by the large quantum phase fluctuation of weak coherent states, adding another physical layer of security to these protocols for quantum key distribution. Using 10 m of highly nonlinear fiber (HNLF) at 77 K, we observed coincidence to accidental-coincidence ratio of 130±5 for correlated photon-pair and Two-Photon Interference visibility >98% entangled photon-pair. We also verified the non-local behavior of polarization-entangled photon pair by violating Clauser-Horne-Shimony-Holt Bell’s inequality by more than 12 standard deviations. With the HNLF at 300 K (77 K), photon-pair production rate about factor 3(2) higher than a 300 m dispersion-shifted fiber is observed. Then, we studied quantum correlation and interference of photon-pairs; with one photon of the photon-air experiencing multiple scattering in a random medium. We observed that depolarization noise photon in multiple scattering degrading the purity of photon-pair, and the existence of Raman noise photon in a photon-pair source will contribute to the depolarization affect. We found that quantum correlation of polarization-entangled photon-pair is better preserved than polarization-correlated photon-pair as one photon of the photon-pair scattered through a random medium. Our findings showed that high purity polarization-entangled photon-pair is better candidate for long distance quantum key distribution.

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PURPOSE: This retrospective study reports the clinical outcome following placement of extraoral implants in severely resorbed posterior ridges to support distal-extension removable dentures. MATERIAL AND METHODS: Consecutively treated patients with partially or completely edentulous ridges, with available bone height in the posterior region of 6 mm or less, were included in the study. Implants originally intended for extraoral use (Straumann) were placed in second molar regions and allowed to heal for 4 to 6 months before abutment connection. At recall appointments, the peri-implant hard and soft tissues were evaluated. Complications with implant components, as well as mechanical and structural failures of the prostheses, were recorded. Two-year survival rates were calculated and life table analyses undertaken. RESULTS: Twenty-nine patients (19 women and 10 men; average age 61.2 years, range, 44 to 75 years) were included in the study. Forty-seven extraoral implants in 26 patients were placed in the second molar site of the mandible. Two extraoral implants in 2 patients failed during the osseointegration phase, yielding an 8-year cumulative success rate of 91.8%. The mean distance from the extraoral implants to the most distal tooth/implant was 28.1 mm (range, 16.7 to 39.2 mm). Twenty-three extraoral implants were restored with magnets, 18 with ball anchors, and 4 with conical cylinders. Replacement of abutments and retention elements was necessary in 2 patients. Four abutments in 2 patients were disconnected from the restorations. CONCLUSIONS: Within the limits of the employed research design, extraoral implants may be used successfully to provide support for distal-extension removable dentures in severely resorbed posterior alveolar ridges.

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Nonlinear computational analysis of materials showing elasto-plasticity or damage relies on knowledge of their yield behavior and strengths under complex stress states. In this work, a generalized anisotropic quadric yield criterion is proposed that is homogeneous of degree one and takes a convex quadric shape with a smooth transition from ellipsoidal to cylindrical or conical surfaces. If in the case of material identification, the shape of the yield function is not known a priori, a minimization using the quadric criterion will result in the optimal shape among the convex quadrics. The convexity limits of the criterion and the transition points between the different shapes are identified. Several special cases of the criterion for distinct material symmetries such as isotropy, cubic symmetry, fabric-based orthotropy and general orthotropy are presented and discussed. The generality of the formulation is demonstrated by showing its degeneration to several classical yield surfaces like the von Mises, Drucker–Prager, Tsai–Wu, Liu, generalized Hill and classical Hill criteria under appropriate conditions. Applicability of the formulation for micromechanical analyses was shown by transformation of a criterion for porous cohesive-frictional materials by Maghous et al. In order to demonstrate the advantages of the generalized formulation, bone is chosen as an example material, since it features yield envelopes with different shapes depending on the considered length scale. A fabric- and density-based quadric criterion for the description of homogenized material behavior of trabecular bone is identified from uniaxial, multiaxial and torsional experimental data. Also, a fabric- and density-based Tsai–Wu yield criterion for homogenized trabecular bone from in silico data is converted to an equivalent quadric criterion by introduction of a transformation of the interaction parameters. Finally, a quadric yield criterion for lamellar bone at the microscale is identified from a nanoindentation study reported in the literature, thus demonstrating the applicability of the generalized formulation to the description of the yield envelope of bone at multiple length scales.

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Prevention and treatment of osteoporosis rely on understanding of the micromechanical behaviour of bone and its influence on fracture toughness and cell-mediated adaptation processes. Postyield properties may be assessed by nonlinear finite element simulations of nanoindentation using elastoplastic and damage models. This computational study aims at determining the influence of yield surface shape and damage on the depth-dependent response of bone to nanoindentation using spherical and conical tips. Yield surface shape and damage were shown to have a major impact on the indentation curves. Their influence on indentation modulus, hardness, their ratio as well as the elastic-to-total work ratio is well described by multilinear regressions for both tip shapes. For conical tips, indentation depth was not statistically significant (p<0.0001). For spherical tips, damage was not a significant parameter (p<0.0001). The gained knowledge can be used for developing an inverse method for identification of postelastic properties of bone from nanoindentation.

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A new species of Cladorhizidac, front the Aleutian Islands is described and compared with all known species of Cladorhizza worldwide. Cladorhiza corona sp. now has a unique growth form with two planes of differently shaped appendages. Appendages are Inserted directly at the stalk; a spherical or conical body at the stalk is lacking. It is the only species reported where different spicule types occur in three morphologically different areas of the sponge. The spiculation of the basal plate is characterized by the occurrence of short, thick anisoxcas and the lack of anisochelae. Anisochelac arc found in the stalk and the basal appendages only. Flattened sigmancistras and (sub-)tylostyles are restricted to the crown. The arrangement of spicules is different in the basal plate, the stalk with the basal appendages, and in the distal append ages. The dimensions and combination of spicule types separate C. corona sp. nov. from all known members of the genus.

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High reflective materials in the microwave region play a very important role in the realization of antenna reflectors for a broad range of applications, including radiometry. These reflectors have a characteristic emissivity which needs to be characterized accurately in order to perform a correct radiometric calibration of the instrument. Such a characterization can be performed by using open resonators, waveguide cavities or by radiometric measurements. The latter consists of comparative radiometric observations of absorbers, reference mirrors and the sample under test, or using the cold sky radiation as a direct reference source. While the first two mentioned techniques are suitable for the characterization of metal plates and mirrors, the latter has the advantages to be also applicable to soft materials. This paper describes how, through this radiometric techniques, it is possible to characterize the emissivity of the sample relative to a reference mirror and how to characterize the absolute emissivity of the latter by performing measurements at different incident angles. The results presented in this paper are based on our investigations on emissivity of a multilayer insulation material (MLI) for space mission, at the frequencies of 22 and 90 GHz.

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Chapter 2 by Luca Di Blasi (...) gives us an insight into the history of nihilism, specifically by exposing a continuity (or else a cycle or repetition) between the earliest debates on the subject in the turn of the nineteenth century and latest ones in the turn of the twenty-first Di Blasi emphasizes the fact that the struggle between philosophy and religion, reason and faith, was a pertinent motif in Jacobi’s critique of Fichte’s philosophy and in Hegel’s response to this critique. A similar problematic, and similar dynamic, recurs two centuries later, where debates around the concept of nihilism among thinkers like Vattimo, Derrida, Habermas, and Žižek again revolve around the relation between religion, science, secularism, and “post-secularism.” Beginning with Hegel, Di Blasi’s chapter ends with a focus on Žižek as a “neo-Hegelian” showing how, in attacking his contemporaries, Žižek mirrors and revives Hegel’s approach in his critique of Jacobi and Fichte. Suggestively, Žižek informs us that now “the circle is closed” and that “to be a Hegelian today does not mean to assume the superfluous burden of some metaphysical past, but to regain the ability to begin from the beginning...”

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Aging societies suffer from an increasing incidence of bone fractures. Bone strength depends on the amount of mineral measured by clinical densitometry, but also on the micromechanical properties of the bone hierarchical organization. A good understanding has been reached for elastic properties on several length scales, but up to now there is a lack of reliable postyield data on the lower length scales. In order to be able to describe the behavior of bone at the microscale, an anisotropic elastic-viscoplastic damage model was developed using an eccentric generalized Hill criterion and nonlinear isotropic hardening. The model was implemented as a user subroutine in Abaqus and verified using single element tests. A FE simulation of microindentation in lamellar bone was finally performed show-ing that the new constitutive model can capture the main characteristics of the indentation response of bone. As the generalized Hill criterion is limited to elliptical and cylindrical yield surfaces and the correct shape for bone is not known, a new yield surface was developed that takes any convex quadratic shape. The main advantage is that in the case of material identification the shape of the yield surface does not have to be anticipated but a minimization results in the optimal shape among all convex quadrics. The generality of the formulation was demonstrated by showing its degeneration to classical yield surfaces. Also, existing yield criteria for bone at multiple length scales were converted to the quadric formulation. Then, a computational study to determine the influence of yield surface shape and damage on the in-dentation response of bone using spherical and conical tips was performed. The constitutive model was adapted to the quadric criterion and yield surface shape and critical damage were varied. They were shown to have a major impact on the indentation curves. Their influence on indentation modulus, hardness, their ratio as well as the elastic to total work ratio were found to be very well described by multilinear regressions for both tip shapes. For conical tips, indentation depth was not a significant fac-tor, while for spherical tips damage was insignificant. All inverse methods based on microindentation suffer from a lack of uniqueness of the found material properties in the case of nonlinear material behavior. Therefore, monotonic and cyclic micropillar com-pression tests in a scanning electron microscope allowing a straightforward interpretation comple-mented by microindentation and macroscopic uniaxial compression tests were performed on dry ovine bone to identify modulus, yield stress, plastic deformation, damage accumulation and failure mecha-nisms. While the elastic properties were highly consistent, the postyield deformation and failure mech-anisms differed between the two length scales. A majority of the micropillars showed a ductile behavior with strain hardening until failure by localization in a slip plane, while the macroscopic samples failed in a quasi-brittle fashion with microcracks coalescing into macroscopic failure surfaces. In agreement with a proposed rheological model, these experiments illustrate a transition from a ductile mechanical behavior of bone at the microscale to a quasi-brittle response driven by the growth of preexisting cracks along interfaces or in the vicinity of pores at the macroscale. Subsequently, a study was undertaken to quantify the topological variability of indentations in bone and examine its relationship with mechanical properties. Indentations were performed in dry human and ovine bone in axial and transverse directions and their topography measured by AFM. Statistical shape modeling of the residual imprint allowed to define a mean shape and describe the variability with 21 principal components related to imprint depth, surface curvature and roughness. The indentation profile of bone was highly consistent and free of any pile up. A few of the topological parameters, in particular depth, showed significant correlations to variations in mechanical properties, but the cor-relations were not very strong or consistent. We could thus verify that bone is rather homogeneous in its micromechanical properties and that indentation results are not strongly influenced by small de-viations from the ideal case. As the uniaxial properties measured by micropillar compression are in conflict with the current literature on bone indentation, another dissipative mechanism has to be present. The elastic-viscoplastic damage model was therefore extended to viscoelasticity. The viscoelastic properties were identified from macroscopic experiments, while the quasistatic postelastic properties were extracted from micropillar data. It was found that viscoelasticity governed by macroscale properties has very little influence on the indentation curve and results in a clear underestimation of the creep deformation. Adding viscoplasticity leads to increased creep, but hardness is still highly overestimated. It was possible to obtain a reasonable fit with experimental indentation curves for both Berkovich and spherical indenta-tion when abandoning the assumption of shear strength being governed by an isotropy condition. These results remain to be verified by independent tests probing the micromechanical strength prop-erties in tension and shear. In conclusion, in this thesis several tools were developed to describe the complex behavior of bone on the microscale and experiments were performed to identify its material properties. Micropillar com-pression highlighted a size effect in bone due to the presence of preexisting cracks and pores or inter-faces like cement lines. It was possible to get a reasonable fit between experimental indentation curves using different tips and simulations using the constitutive model and uniaxial properties measured by micropillar compression. Additional experimental work is necessary to identify the exact nature of the size effect and the mechanical role of interfaces in bone. Deciphering the micromechanical behavior of lamellar bone and its evolution with age, disease and treatment and its failure mechanisms on several length scales will help preventing fractures in the elderly in the future.

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Glacier fluctuations are a key indicator of changing climate. Their reconstruction beyond historical times unravels glacier variability and its forcing factors on long time scales, which can considerably improve our understanding of the climate–glacier relationship. Here, we present a 2250-year-long reconstruction of particle-mass accumulation rates recorded in the lacustrine sediments of Lake Trüebsee (Central Swiss Alps) that are directly related to glacier extent, thus reflecting a continuous record of fluctuations of the upstream-located Titlis Glacier. Mass accumulation rate values show strong centennial to multi-centennial fluctuations and reveal 12 well-pronounced periods of enhanced values corresponding to times of maximum extent of the neighboring Lower Grindelwald Glacier. This result supports previous studies of proglacial lake sediments that documented high mass accumulation rate values during glacier advances. The strong variability in the Lake Trüebsee mass accumulation rate record thus represents a highly sensitive paleoclimatic archive, which mirrors rapid and pronounced feedbacks of Titlis Glacier to climatic changes over the past 2250years. The comparison of our data with independent paleo-temperature reconstructions from tree rings suggests that variations in mean summer temperature were the primary driving factor of fluctuations of Titlis Glacier. Also, advances of Titlis Glacier occurred during the grand solar minima (Dalton, Maunder, Spörer, Wolf) of the last millennium. This relation of glacier extent with summer temperature reveals strong evidence that the mass balance of this Alpine glacier is primarily controlled by the intensity of glacier melting during summer.

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AIM The aim of this prospective, randomized, controlled multicenter study was to determine the 3-year efficacy and stability of the soft and hard tissues at implants with a different geometry that were placed in fresh extraction sockets. MATERIAL AND METHODS Implants with two different configurations, cylindrical (Group A) or conical/cylindrical (Group B) were installed, and healing abutments were attached. Sixteen weeks after implant placement, subjects returned for a re-entry procedure. Prosthetic restorations were delivered 22 weeks after implant placement. Each subject was placed in a 3-year follow-up program, including examinations at yearly visits including various soft tissue and bone level parameters. RESULTS The percentage of sites that were considered inflamed during the follow-up period was stable and varied between 8.8% and 10.2%. The radiographic examinations documented improved bone levels at the final examination and the mean improvement from baseline (placement of permanent restoration; PR) amounted to 0.17 ± 0.67 mm. More than 70% (54 of 76) of the implants monitored in this study suffered no bone loss during the maintenance period. Moreover, there was an obvious "gain" of interproximal soft tissue volume and at the 3-year examination around 25% of all embrasure gaps were completely filled with "papillae". CONCLUSIONS Both conical/cylindrical and cylindrical implants placed in fresh extraction sockets allowed proper soft and hard tissue healing to occur. At both types of implants, mucosal inflammation was infrequent, marginal bone levels were maintained, and soft tissue volume increased gradually after the placement of the permanent restoration.

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OBJECTIVES To evaluate the location and morphologic characteristics of supernumerary teeth and to assess the frequency and extent of root resorption of adjacent teeth using cone beam computed tomography (CBCT). MATERIALS AND METHODS CBCT scans of 82 patients with supernumerary teeth in the maxilla and mandible were evaluated by two orthodontists independently. Data regarding the type, shape, and three-dimensional (3D) location of the supernumeraries including the frequency and extent of root resorption of adjacent teeth were recorded and evaluated for possible associations. RESULTS The study comprised a total of 101 supernumerary teeth. Most of the patients (80.5 per cent) exhibited one single supernumerary tooth, while 15.8 per cent had two and 3.7 per cent had three supernumeraries. Males were affected more than females with a ratio of 1.65:1. Mesiodentes were the most frequently diagnosed type of supernumerary teeth (48.52 per cent), followed by supernumerary premolars (23.76 per cent) and lateral incisors (18.81 per cent). Supernumeraries were most commonly conical in shape (42.6 per cent) with a normal or inclined vertical position (61.4 per cent). Root resorption of adjacent teeth was detected for 22.8 per cent of the supernumerary teeth, most frequently for supernumerary premolars. There was a significant association between root resorption of adjacent teeth and type and shape of tooth. Interrater agreement for the measurements performed showed kappa values ranging from 0.55 to 1 with a kappa value of 1 for type and shape of the supernumerary teeth. CONCLUSIONS CBCT provides 3D information about location and shape of supernumerary teeth as well as prevalence and degree of root resorption of neighbouring teeth with moderate to high interrater correlation.

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The S0 → S1 vibronic spectrum and S1 state nonradiative relaxation of jet-cooled keto-amino 5-fluorocytosine (5FCyt) are investigated by two-color resonant two-photon ionization spectroscopy at 0.3 and 0.05 cm–1 resolution. The 000 rotational band contour is polarized in-plane, implying that the electronic transition is 1ππ*. The electronic transition dipole moment orientation and the changes of rotational constants agree closely with the SCS-CC2 calculated values for the 1ππ* (S1) transition of 5FCyt. The spectral region from 0 to 300 cm–1 is dominated by overtone and combination bands of the out-of-plane ν1′ (boat), ν2′ (butterfly), and ν3′ (HN–C6H twist) vibrations, implying that the pyrimidinone frame is distorted out-of-plane by the 1ππ* excitation, in agreement with SCS-CC2 calculations. The number of vibronic bands rises strongly around +350 cm–1; this is attributed to the 1ππ* state barrier to planarity that corresponds to the central maximum of the double-minimum out-of-plane vibrational potentials along the ν1′, ν2′, and ν3′ coordinates, which gives rise to a high density of vibronic excitations. At +1200 cm–1, rapid nonradiative relaxation (knr ≥ 1012 s–1) sets in, which we interpret as the height of the 1ππ* state barrier in front of the lowest S1/S0 conical intersection. This barrier in 5FCyt is 3 times higher than that in cytosine. The lifetimes of the ν′ = 0, 2ν1′, 2ν2′, 2ν1′ + 2ν2′, 4ν2′, and 2ν1′ + 4ν2′ levels are determined from Lorentzian widths fitted to the rotational band contours and are τ ≥ 75 ps for ν′ = 0, decreasing to τ ≥ 55 ps at the 2ν1′ + 4ν2′ level at +234 cm–1. These gas-phase lifetimes are twice those of S1 state cytosine and 10–100 times those of the other canonical nucleobases in the gas phase. On the other hand, the 5FCyt gas-phase lifetime is close to the 73 ps lifetime in room-temperature solvents. This lack of dependence on temperature and on the surrounding medium implies that the 5FCyt nonradiative relaxation from its S1 (1ππ*) state is essentially controlled by the same ∼1200 cm–1 barrier and conical intersection both in the gas phase and in solution.

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In the wake of the financial crisis, budgetary discipline has taken centre stage in politics. More than ever a country's budget mirrors the true policy preferences of the legislative majority beyond all political discourse and cheap talk. The paper sheds light on mandate fulfilment in the field of public spending and fiscal policy in general. Based on previous work on pledge fulfilment in Switzerland the paper compares publicised pre-electoral statements of MPs on public spending and the development of the public finances with their post-electoral legislative behaviour during budget debates and votes. The findings of the paper confirm the results of the aforementioned earlier studies and point to the potential of budgetary statements for future mandate fulfilment research.