Is a top-heavy initial mass function needed to reproduce the submillimeter galaxy number counts?

Matching the number counts and redshift distribution of submillimeter galaxies (SMGs) without invoking modifications to the initial mass function (IMF) has proved challenging for semi-analytic models (SAMs) of galaxy formation. We adopt a previously developed SAM that is constrained to match the z=0 galaxy stellar mass function and makes various predictions that agree well with observational constraints; we do not recalibrate the SAM for this work. We implement three prescriptions to predict the submillimeter flux densities of the model galaxies; two depend solely on star formation rate, whereas the other also depends on the dust mass. By comparing the predictions of the models, we find that taking into account the dust mass, which affects the dust temperature and thus influences the far-infrared spectral energy distribution, is crucial for matching the number counts and redshift distribution of SMGs. Moreover, despite using a standard IMF, our model can match the observed SMG number counts and redshift distribution reasonably well, which contradicts the conclusions of some previous studies that a top-heavy IMF, in addition to taking into account the effect of dust mass, is needed to match these observations. Although we have not identified the key ingredient that is responsible for our model matching the observed SMG number counts and redshift distribution without IMF variation- which is challenging given the different prescriptions for physical processes employed in the SAMs of interest-our results demonstrate that in SAMs, IMF variation is degenerate with other physical processes, such as stellar feedback.Comment: 6 pages, 3 figures, Accepted for publication in MNRA

Mid-Lift-To-Drag Ratio Rigid Vehicle 6-DOF EDL Performance Using Tunable Apollo Powered Guidance

The Mid-Lift-to-Drag ratio Rigid Vehicle (MRV) is a candidate in the NASA multi-center effort to determine the most cost effective vehicle to deliver a large-mass payload to the surface of Mars for a human mission. Products of this effort include six-degree-of-freedom (6DoF) entry-to-landing trajectory performance studies for each candidate vehicle. These high fidelity analyses help determine the best guidance and control (G&C) strategies for a feasible, robust trajectory. This paper presents an analysis of the MRV's G&C design by applying common entry and descent associated uncertainties using a Fully Numerical Predictor-corrector Entry Guidance (FNPEG) and tunable Apollo powered descent guidance

Electro-thermal modelling of multi chip power modules for high power converter application

In a compact power electronics systems such as converters, thermal interaction between components is inevitable. Traditional RC lumped modelling method does not take that into account and this would cause inaccuracy in the predicted temperature in the components of the systems. In this work, numerical simulation have been used to obtain detailed temperature distribution in power devices and the parameters for a Foster network behavior thermal model are extracted so that the thermal interaction can be accounted for and the model can be used to predict temperatures at all critical layers of the components. An ad-hoc conventional three-phase voltage source inverter (DC to AC converter) with a rating of 7.8 KW has been studied in this work as an example of the application of the proposed framework. The key component in the converter is a 75A11200V rated IGBT module. A power electronics circuit simulator is used to predict the power losses in the IGBT module and a Finite Element Analysis software is used to obtain the transient temperature profile in the module and the behaviour thermal model parameters are extracted using curve-fit approach. The resulting combined electro-thermal model is analysed using the circuit simulator again to obtain the temperature for various loading conditions. The results show that the proposed method can significantly improve the accuracy of predicted temperatures in the IGBT modules

Quantum Layers over Surfaces Ruled Outside a Compact Set

In this paper, we proved the quantum layer over a surface which is ruled outside a compact set, asymptotically flat but not totally geodesic admits ground states