Numerical Results for the System Noise Temperature of an Aperture Array Tile and Comparison with Measurements

The purpose of this report is to document the noise performance of a complex beamforming array antenna system and to characterize the recently developed noise measurement facility called THACO, which was developed at ASTRON. The receiver system includes the array antenna of strongly coupled 144 TSA elements, 144 Low Noise Amplifiers (LNAs) (Tmin =35-40K) and the data recording/storing facilities of the initial test station that allow for off-line digital beamforming. The primary goal of this study is to compare the measured receiver noise temperatures with the simulated values for several practical beamformers, and to predict the associated receiver noise coupling contribution, antenna thermal noise and ground noise pick-up (due to the back radiation).Comment: ASTRON repor

Variability and nature of the binary in the Red Rectangle Nebula

We present new observations of the central binary inside the Red Rectangle nebula. The detection of zinc in the optical spectrum confirms that the peculiar photospheric abundances are due to accretion of circumstellar gas. Grey brightness variations with the orbital period are observed. They are interpreted as being due to the variation of the scattering angle with orbital phase. The small orbital separation of the system is not compatible with previous normal evolution of the primary on the AGB. We point out the similarity of the orbital history of this and other similar systems with those of some close Barium stars and suggest that the nonzero eccentricity of the orbit is the result of tidal interaction with the circumbinary disk.Comment: 4 pages, 3 figures, A&A Letters accepte

Transition Form Factors between Pseudoscalar and Vector Mesons in Light-Front Dynamics

We study the transition form factors between pseudoscalar and vector mesons using a covariant fermion field theory model in $(3+1)$ dimensions. Performing the light-front calculation in the $q^+ =0$ frame in parallel with the manifestly covariant calculation, we note that the suspected nonvanishing zero-mode contribution to the light-front current $J^+$ does not exist in our analysis of transition form factors. We also perform the light-front calculation in a purely longitudinal $q^+ > 0$ frame and confirm that the form factors obtained directly from the timelike region are identical to the ones obtained by the analytic continuation from the spacelike region. Our results for the $B \to D^* l \nu_l$ decay process satisfy the constraints on the heavy-to-heavy semileptonic decays imposed by the flavor independence in the heavy quark limit.Comment: 20 pages, 14 figure

The Vector Meson Form Factor Analysis in Light-Front Dynamics

We study the form factors of vector mesons using a covariant fermion field theory model in $(3+1)$ dimensions. Performing a light-front calculation in the $q^+ =0$ frame in parallel with a manifestly covariant calculation, we note the existence of a nonvanishing zero-mode contribution to the light-front current $J^+$ and find a way of avoiding the zero-mode in the form factor calculations. Upon choosing the light-front gauge (\ep^+_{h=\pm}=0) with circular polarization and with spin projection $h=\uparrow\downarrow=\pm$, only the helicity zero to zero matrix element of the plus current receives zero-mode contributions. Therefore, one can obtain the exact light-front solution of the form factors using only the valence contribution if only the helicity components, $(h'h)=(++),(+-)$, and $(+0)$, are used. We also compare our results obtained from the light-front gauge in the light-front helicity basis (i.e. $h=\pm,0$) with those obtained from the non-LF gauge in the instant form linear polarization basis (i.e. $h=x,y,z$) where the zero-mode contributions to the form factors are unavoidable.Comment: 33 pages; typo in Eq.(15) is corrected; comment on Ref.[9] is corrected; version to appear in Phys. Rev.

Parameter Study for First-Generation Sheeting Failure using a Theoretical and FE Model

First-generation sheeting is sheeting without longitudinal and transversal stiffeners. For the prediction of failure of this sheeting type, if loaded by j concentrated load and bending moment, several theoretical models and design codes exist. One of these theoretical models was developed recently and predicts failure by using a derivative of the web-crippling deformation due to the concentrated load as an imperfection for the compressed flange for which the behaviour is predicted by Marguerre's simultaneous differential plate equations. The quality of the model has been checked with a whole range of experiments, however, the experiments did not have such a variation of variables that the model could be checked systematically. In this paper, a FE model is used to predict failure for a systematic variation of sheeting variables and the failure loads are used to check the theoretical model. For varying web width, angle between web and flange, corner radius, yield strength, plate thickness, and span length, the theoretical model performs well, qualitatively and quantitatively, compared to the finite element model. For the compressed flange width and load bearing plate width, the theoretical model results show some divergence from the FE model results, although absolute differences remain acceptable

Elastic post-buckling behaviour of uniformly compressed plates

In this paper it is discussed how existing analytical and semi-analytical formulas for describing the elastic-post-buckling behavior of uniformly compressed square plates with initial imperfections, for loads up to three times the buckling load can be simplified and improved. For loads larger than about twice the buckling load the influence of changes in the buckling shape, assumed sinusoidal, cannot be neglected anymore. These changes can be taken into account by using the perturbation approach. The existing and improved formulas are compared to the results of finite element simulations

Ultimate Failure Behaviour of Second-generation Sheeting Subjected to Combined Bending Moment and Concentrated Load

Second-generation sheeting is widely used for cladding and roof construction. At interior supports, it is subjected to combined bending moment and concentrated load. Unfortunately, design rules for this loading are complicated and do not provide insight in the sheeting\u27s failure behaviour. This means there is a need for a new, insight providing design rule. For first-generation sheeting, a similar problem did exist. The Technische Universiteit Eindhoven (TUE) carried out three research projects [Bakk92a,Vaes95a,Hofm00a] that provided insight in the first-generation sheeting behaviour and resulted in a new, insight providing design rule. The TUE now uses the strategy of these three research projects for a new project on second-generation sheeting [Kasp01a], with the final aim of a new design rule for second-generation sheeting. In this new project, experiments on commonly used (in the Netherlands) second-generation sheeting were carried out. Second-generation sheeting behaviour was compared with first-generation sheeting behaviour. For sheeting with only stiffeners in flange, load falls occur before ultimate load. Stiffeners in the web only result in load falls after the ultimate load. For an experiment with only stiffeners in the web, a finite element simulation was made. The simulation predicts the sheeting behaviour fairly well and indicates how a stiffener affects the sheeting behaviour