Decomposition in HTPB bonded HMX followed by heat generation rate and chemiluminescence

The decomposition in HTPB bonded HMX was characterized with two highly sensitive methods: heat flow microcalorimetry (HFMC) and Chemiluminescence (CL). The material is stabilized with a phenolic antioxidant. The heat generation (HFMC) rate was determined from 120 to 150°C using a TAM™ microcalorimeter and the oxidation of the substance was followed by the CL emission between 100 and 140°C directly from the solid state sample. The end of antioxidant activity results in both measurements sets in characteristic changes in the curves. Kinetic parameters were calculated applying Arrhenius parameterization for the times to the end of antioxidant activity and by applying modelling with an autocatalytic model extended by a side reaction, which is assigned to the antioxidant consumption. The evaluation with the characteristic times gives good agreement between the two methods; the modelling represents the different but supplementing probing of the two measurement method

Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films

We investigate the magnetization dynamics through the magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance response is dependent on the thickness of the non-magnetic Cu spacer material, a fact associated to the kind of the magnetic interaction between the ferromagnetic layers. Thus, we present an experimental study on asymmetric magnetoimpedance in ferromagnetic films with biphase magnetic behavior and explore the possibility of tuning the linear region of the magnetoimpedance curves around zero magnetic field by varying the thickness of the non-magnetic spacer material, and probe current frequency. We discuss the experimental magnetoimpedance results in terms of the different mechanisms governing the magnetization dynamics at distinct frequency ranges, quasi-static magnetic properties, thickness of the non-magnetic spacer material, and the kind of the magnetic interaction between the ferromagnetic layers. The results place ferromagnetic films with biphase magnetic behavior exhibiting asymmetric magnetoimpedance effect as a very attractive candidate for application as probe element in the development of auto-biased linear magnetic field sensors.Comment: 5 figure

Pair Wave Functions in Atomic Fermi Condensates

Recent experiments have observed condensation behavior in a strongly interacting system of fermionic atoms. We interpret these observations in terms of a mean-field version of resonance superfluidity theory. We find that the objects condensed are not bosonic molecules composed of bound fermion pairs, but are rather spatially correlated Cooper pairs whose coherence length is comparable to the mean spacing between atoms. We propose experiments that will help to further probe these novel pairs

The role of elastic stresses on leaf venation morphogenesis

We explore the possible role of elastic mismatch between epidermis and mesophyll as a driving force for the development of leaf venation. The current prevalent 'canalization' hypothesis for the formation of veins claims that the transport of the hormone auxin out of the leaves triggers cell differentiation to form veins. Although there is evidence that auxin plays a fundamental role in vein formation, the simple canalization mechanism may not be enough to explain some features observed in the vascular system of leaves, in particular, the abundance of vein loops. We present a model based on the existence of mechanical instabilities that leads very naturally to hierarchical patterns with a large number of closed loops. When applied to the structure of high order veins, the numerical results show the same qualitative features as actual venation patterns and, furthermore, have the same statistical properties. We argue that the agreement between actual and simulated patterns provides strong evidence for the role of mechanical effects on venation development.Comment: 10 figures, published in PLoS Computational Biolog

Field emission microscope for a single fullerene molecule

Applying strong direct current (DC) electric fields on the apex of a sharp metallic tip, electrons can be radially emitted from the apex to vacuum. Subsequently, they magnify the nanoscopic information on the apex, which serves as a field emission microscope (FEM). When depositing molecules on such a tip, peculiar electron emission patterns such as clover leaves appear. These phenomena were first observed seventy years ago. However, the source of these emission patterns has not yet been identified owing to the limited experimental information about molecular configurations on a tip. Here, we used fullerene molecules and characterized the molecule-covered tip by an FEM. In addition to the experiments, simulations were performed to obtain optimized molecular configurations on a tip. Both results indicate that the molecules, the source of the peculiar emission patterns, appear on a molecule layer formed on the tip under strong DC electric fields. Furthermore, the simulations revealed that these molecules are mostly isolated single molecules forming single-molecule-terminated protrusions. Upon the excellent agreements in both results, we concluded that each emission pattern originates from a single molecule. Our work should pave the way to revive old-fashioned electron microscopy as a powerful tool for investigating a single molecule

Fermionization of two distinguishable fermions

In this work we study a system of two distinguishable fermions in a 1D harmonic potential. This system has the exceptional property that there is an analytic solution for arbitrary values of the interparticle interaction. We tune the interaction strength via a magnetic offset field and compare the measured properties of the system to the theoretical prediction. At the point where the interaction strength diverges, the energy and square of the wave function for two distinguishable particles are the same as for a system of two identical fermions. This is referred to as fermionization. We have observed this phenomenon by directly comparing two distinguishable fermions with diverging interaction strength with two identical fermions in the same potential. We observe good agreement between experiment and theory. By adding one or more particles our system can be used as a quantum simulator for more complex few-body systems where no theoretical solution is available

Young Suns Exoplanet Survey: Detection of a wide-orbit planetary-mass companion to a solar-type Sco-Cen member

The Young Suns Exoplanet Survey consists of a homogeneous sample of 70 young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association with an average age of 15 ± 3 Myr. We report the detection of a co-moving companion around the K3IV star TYC 8998-760-1 (2MASSJ13251211–6456207) that is located at a distance of 94.6 ± 0.3 pc using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER constrain the mass of the star to 1.00±0.02M⊙ and an age of 16.7±1.4 Myr. The companion TYC 8998-760-1 b is detected at a projected separation of 1.71″, which implies a projected physical separation of 162 au. Photometric measurements ranging from Y to M band provide a mass estimate of 14±3 M_(jup) by comparison to BT-Settl and AMES-dusty isochrones, corresponding to a mass ratio of q = 0.013 ± 0.003 with respect to the primary. We rule out additional companions to TYC 8998-760-1 that are more massive than 12 M_(jup) and farther than 12 au away from the host. Future polarimetric and spectroscopic observations of this system with ground and space based observatories will facilitate testing of formation and evolution scenarios shaping the architecture of the circumstellar environment around this ‘young Sun’

Automated Point-based Tolerance Analysis Model Creation for Sheet Metal Parts

AbstractThis paper focuses on a concept that shows a way to automatically create a point-based tolerance analysis model out of existing development data. Nowadays solutions for an automated tolerance simulation model creation are using a static approach for the model build-up. For this purpose product-/ production- development data are automatically mapped on preexisting models (e.g. skeleton models). If chances during development process occur, the tolerance simulation models have to be reworked. Today only simple changes in the model can be automated (e.g. change of distribution, tolerance range etc.). A complete new tolerance simulation model build-up process for dynamically changing product-/ production- development information is not possible. To give an application example, tolerance simulation models for sheet metal parts in automotive industry are based on different development data. Before the first simulation model is created (to secure the tolerance concepts etc.), all necessary information have already been developed, e.g. in the automotive industry's development process: part geometry, tolerance information, assembly graph, jig and fixture concept, joining location and measurement points. Thus the automated simulation generation should be possible.First step is to describe an interface for a dynamic model creation in tolerance simulation systems. In a second step preprocessing of development data is necessary to map them into tolerance simulation software restrictions. This delivers a solution to fill the gap between the PDM-/ CAD and the CAT-system. The considered approach for automated tolerance simulation model creation provides the opportunity to build-up the tolerance analysis models highly efficient and almost automatically. Tolerance analysis can then be used to rapidly calculate several options. This offers the possibility to increase the product maturity level at a very early stage of the development process