Comparison of different failure criteria for fiber-reinforced plastics in terms of fracture curves for arbitrary stress combinations

For fiber-reinforced plastics exists a big number of different criteria for the failure prediction. The intention of this paper is to compare the TSAI-HIL-, the LaRC04- and PUCK’s criterion in terms of their fracture curves for a unidirectional glass-fiber reinforced composite layer. Therefore after the implementation of these three criteria, the two-dimensional fracture curves for all possible stress combinations, which can be derived from a general spatial stress tensor, are computed. In this way, the characteristics of the criteria, similarities and differences and possible weak points become obvious.     

Multiscale Nanoparticle Assembly: From Particulate Precise Manufacturing to Colloidal Processing

Nanoparticle assembly and colloidal processing are two techniques with the goal to fabricate materials and devices from preformed particles. While colloidal processing has become an integral part of ceramic processing, nanoparticle assembly is still mainly limited to academic interests. It typically starts with the precise synthesis of building blocks, which are generally not only considerably smaller than those used for colloidal processing, but also better defined in terms of size, shape, and size distribution. Their arrangement into 1D, 2D, and 3D architectures is performed with great accuracy well beyond what is achieved by colloidal processing. At the same time, the final assembly is not sintered such that the intrinsic, nanospecific properties of the initial building blocks are preserved or even lead to collective behavior. However, in contrast to colloidal processing the structures accessible by nanoparticle assembly are often limited to a small length scale. The review presents selected examples of nanoparticle assembly and colloidal processing with the goal to reveal the capabilities of these two techniques to fabricate novel materials from preformed building blocks, and also to demonstrate the immense opportunities that would arise if the two methods could be combined with each other.     

Cryptanalysis of the Tillich�CZ��mor Hash Function

At CRYPTO ’94, Tillich and Zémor proposed a family of hash functions, based on computing a suitable matrix product in groups of the form SL₂(\mathbbF_2ⁿ)SL_{2}(\mathbb{F}_{2^{n}}). We show how to construct collisions between palindromic bit strings of length 2n+2 for Tillich and Zémor’s construction. The approach also yields collisions for related proposals by Petit et al. from ICECS ’08 and CT-RSA ’09.     

Characterization and Modeling of Broad Spectrum InAs–GaAs Quantum-Dot Superluminescent Diodes Emitting at 1.2–1.3 μm

High-power broadband superluminescent diodes (SLDs) emitting in the 1.2-1.3-mum region are demonstrated using InAs-GaAs quantum dots (QDs). The highest output powers of ~30-50 mW are achieved using 18 QD layers with p-doped GaAs spacers. At these high powers the device operates in a regime of broad bandwidth (~100 nm) with a spectral dip of ~5 dB between two separate peaks originated by the QD ground and excited states. Spectral calculations performed with a traveling-wave rate equation model show excellent agreement with the experimental data and provide design rules for optimizing the output spectrum. SLD characteristics are presented for two different device structures consisting of tilted and bent waveguides. The latter allows the achievement of higher output powers at lower currents. The coherence properties and the temperature characteristics are also discussed in detail.     

Synergistic Roll‐to‐Roll Transfer and Doping of CVD‐Graphene Using Parylene for Ambient‐Stable and Ultra‐Lightweight Photovoltaics

A roll‐to‐roll (R2R) transfer technique is employed to improve the electrical properties of transferred graphene on flexible substrates using parylene as an interfacial layer. A layer of parylene is deposited on graphene/copper (Cu) foils grown by chemical vapor deposition and are laminated onto ethylene vinyl acetate (EVA)/poly(ethylene terephthalate). Then, the samples are delaminated from the Cu using an electrochemical transfer process, resulting in flexible and conductive substrates with sheet resistances of below 300 Ω sq^?1, which is significantly better (fourfold) than the sample transferred by R2R without parylene (1200 Ω sq^?1). The characterization results indicate that parylene C and D dope graphene due to the presence of chlorine atoms in their structure, resulting in higher carrier density and thus lower sheet resistance. Density functional theory calculations reveal that the binding energy between parylene and graphene is stronger than that of EVA and graphene, which may lead to less tear in graphene during the R2R transfer. Finally, organic solar cells are fabricated on the ultrathin and flexible parylene/graphene substrates and an ultra‐lightweight device is achieved with a power conversion efficiency of 5.86%. Additionally, the device shows a high power per weight of 6.46 W g^?1 with superior air stability.     

A 60 GHz phased array with measurement and de-embedding techniques

We present a 60 GHz phased array system that combines several key technologies to realize 10 GHz bandwidth coverage. Particularly, a tightly coupled dipole array centered at 60 GHz is designed and tested for its wideband performance. The tightly coupled dipole elements offer excellent wideband behavior of 10 GHz with voltage standing wave ratio?<?3 with scanning to 45°, as well as low cost printed circuit board fabrication. Additionally, we demonstrate a measurement setup with de-embedding procedure to measure gain at the antenna feed point. A feeding structure was designed and fabricated for de-embedding gain pattern measurements. Recovered measurements are shown to be in agreement with simulation.     

Combining Scan Test and Built-in Self Test

For digital chips containing functional logic and embedded memories, these are usually tested separately: Scan test is used for testing functional logic; Memory Built-in Self Test (MBIST) is run for embedded memories. A new approach is proposed to exercise scan test and MBIST in parallel in order to reduce production test time and improve stress tests. It requires only small additional logic and allows to simultaneously run both test modes. In general, the approach can be used to control simultaneously scan test and any Built-in Self Test (BIST) providing a simple pass/fail result.     

On the reliability of scanning probe based electrostatic force measurements

The dimensions of semiconductor devices rapidly decreasing, the detection and control of spatial inhomogeneities of material properties on a sub-μm scale becomes essential.For mapping various electrical properties with nearly nm-resolution, scanning probe techniques appear to be ideally suited. However, data evaluation always involves a transfer from measured to real properties by a device depending convolution procedure.We report on our results for different modes of electrical measurements, namely scanning Kelvin probe microscopy (SKM) and scanning capacitance microscopy (SCM) on various sample systems discussing the influence of experimental parameters. In addition, results of finite element simulations on this topic are presented.It turns out that the averaging function correlating real and measured data may appear quite simple, thus making a reliable reconstruction possible. On the other hand, the existence of surface charges can drastically change the results.     

An overview of state of the art and research in the fields of sensible, latent and thermo-chemical thermal energy storage

Due to the increase in volatile renewable power and heat generation (wind or solar), thermal energy storage (TES) has obtained growing importance and interest. The technology can be distinguished into three main types: sensible, latent and thermochemical storage. Apart from low and medium temperature heat applications, high temperature TES also is an attractive means to store power in the form of heat (before the thermodynamic transformation process). Thermochemical storage allows for long duration seasonal storage of energy.