Regulation of Oscillatory Systems Subjected to Viability Constraints

Regarding forcing terms of oscillatory systems of second-order differential equations as controls, we look for feedback (set-valued) maps governing the evolution of solutions satisfying viability of state constraints. We give a condition ensuring the existence of minimally forced solutions: the oscillation is unforced as long as viability is not at stake. Finally we compare "minimally forced oscillations" with free oscillations

Viability in a Keynesian Model: A Preliminary Approach

The purpose of this paper is to study an elementary dynamic Keynesian model by means of the viability approach. The mathematical theory of viability allows one to raise and answer questions which cannot be solved with usual dynamic tools. It deals with the question whether for a given dynamical system, there can be found solutions which satisfy some a priori given constraints, and with the analysis of subsets of the phase space where viable evolutions, i.e., evolutions satisfying the given constraints, are possible. Equilibria are examples of such viable sets, but the viability approach is much more general then the equilibrium approach. In contrast to traditional ecodynamics where local stability and asymptotic properties of models are the heart of the matter, the viability approach is concerned with contingent evolutions over time of dynamic systems. In section 2 we describe an elementary dynamic Keynesian model. Viability questions are evoked in section 3 along with some intuitive answers, and rigorous results and developments will be found in section 4

Compensation of Non-Linear Shrinkage of Polymer Materials in Selective Laser Sintering

Inaccuracies in the selective laser sintering (SLS) process using polymer materials are typically caused by inhomogeneous shrinkage due to inhomogeneous temperature distribution in the powder bed of the SLS machine. These shrinking effects lead to stress in the sintered parts, causing the part to distort. The inhomogeneous shrinkage of benchmark parts has been compensated empirically in a former work. The results cannot been transferred to all geometries, because each geometry requires a specific temperature for laser sintering and, thus, has its own related shrinkage distribution. In a new theoretical approach, shrinkage behavior is to be integrated in a thermal simulation of the SLS process and the thermal shrinkage calculated prior to the building process. In the following, experimental data of the temperature- and pressuredependent shrinkage of laser-sintered powder samples is presented. Possible theories for a physical model of thermal shrinkage are discussed. In particular, these models have to consider granular characteristics such as internal friction, particle sliding, and powder compaction.Mechanical Engineerin

The Simulation of the SLS Process as the Basis of a Process Optimization 377

In this work, a new model of the SLS process is introduced, offering the chance of analytically optimizing Selective Laser Sintering. The laser energy input is calculated by considering multiple scattering in the powder bed. The heat transfer is described by a new model which considers the heat flow through the growing sintering neck, and the sintering dynamics are determined by a new viscoelastic sintering model. All theoretical models are verified through experiments at near SLS conditions and are implemented in an enhanced FEM simulation of the process. Through this simulation, the major problems of the Selective Laser Sintering are illustrated and approaches for optimization of the SLS process are shown.Mechanical Engineerin

Synthesis of <i>N</i>‑Substituted Sulfamate Esters from Sulfamic Acid Salts by Activation with Triphenylphosphine Ditriflate

A general approach to access sulfamate esters through preparation of sulfamic acid salts, subsequent activation with triphenylphosphine ditriflate, and nucleophilic trapping is disclosed. The method proceeds in modest to excellent yields to incorporate nucleophiles derived from aliphatic alcohols and phenols. This approach can be employed to furnish differentially substituted sulfamides

Structure of a spumaretrovirus gag central domain reveals an ancient retroviral capsid

The Spumaretrovirinae, or foamy viruses (FVs) are complex retroviruses that infect many species of monkey and ape. Despite little sequence homology, FV and orthoretroviral Gag proteins perform equivalent functions, including genome packaging, virion assembly, trafficking and membrane targeting. However, there is a paucity of structural information for FVs and it is unclear how disparate FV and orthoretroviral Gag molecules share the same function. To probe the functional overlap of FV and orthoretroviral Gag we have determined the structure of a central region of Gag from the Prototype FV (PFV). The structure comprises two all α-helical domains NtDCEN and CtDCEN that although they have no sequence similarity, we show they share the same core fold as the N- (NtDCA) and C-terminal domains (CtDCA) of archetypal orthoretroviral capsid protein (CA). Moreover, structural comparisons with orthoretroviral CA align PFV NtDCEN and CtDCEN with NtDCA and CtDCA respectively. Further in vitro and functional virological assays reveal that residues making inter-domain NtDCEN—CtDCEN interactions are required for PFV capsid assembly and that intact capsid is required for PFV reverse transcription. These data provide the first information that relates the Gag proteins of Spuma and Orthoretrovirinae and suggests a common ancestor for both lineages containing an ancient CA fold

Momentum dependence of the imaginary part of the omega- and eta`-nucleus optical potential

The photoproduction of ω and η′ mesons off carbon and niobium nuclei has been measured as a function of the meson momentum for incident photon energies of 1.2-2.9GeV at the electron accelerator ELSA. The mesons have been identified via the ω→π0γ→3γ and η′→π0π0η→6γ decays, respectively, registered with the CBELSA/TAPS detector system. From the measured meson momentum distributions the momentum dependence of the transparency ratio has been determined for both mesons. Within a Glauber analysis the in-medium ω and η′ widths and the corresponding absorption cross sections have been deduced as a function of the meson momentum. The results are compared to recent theoretical predictions for the in-medium ω width and η′-N absorption cross sections. The energy dependence of the imaginary part of the ω- and η′-nucleus optical potential has been extracted. The finer binning of the present data compared to the existing data allows a more reliable extrapolation towards the production threshold. The modulus of the imaginary part of the η′-nucleus potential is found to be about three times smaller than recently determined values of the real part of the η′-nucleus potential, which makes the η′ meson a suitable candidate for the search for meson-nucleus bound states. For the ω meson, the modulus of the imaginary part near threshold is comparable to the modulus of the real part of the potential. As a consequence, only broad structures can be expected, which makes the observation of ω mesic states very difficult experimentally

Observation of a structure in the M-p eta invariant mass distribution near 1700 MeV/c(2) in the gamma p -> p pi(0)eta reaction

The reaction gamma p -> p pi(0)eta has been studied with the CBELSA/TAPS detector at the electron stretcher accelerator ELSA in Bonn for incident photon energies from threshold up to 3.1 GeV. This paper has been motivated by the recently claimed observation of a narrow structure in the MN n invariant mass distribution at a mass of 1678 MeV/c(2). The existence of this structure cannot be confirmed in the present work. Instead, for E-gamma = 1400-1500 MeV and the cut M-P pi(0) pa(0) -> p pi(0)eta reaction