Nanogranular packing of C-S-H at substochiometric conditions

Herein, we present a comprehensive nanoindentation investigation of cement pastes prepared at substoichiometric water-to-cement (w/c) mass ratios between 0.15 and 0.4 with and without heat treatment. Based on a statistical indentation technique, we provide strong evidence of the existence of a statistically significant third hydrated mechanical phase in addition to the already known Low-Density (LD) and High-Density (HD) C-S-H phases. The nanomechanical properties of this third phase are found to follow similar packing density scaling relations as LD C-S-H and HD C-S-H, while being significantly greater. This third phase, whose nano-packing density is measured at 0.83 ± 0.01, is therefore termed Ultra-High-Density (UHD) phase. All three phases are present in concrete materials in different volume proportions: LD dominates cement-based materials prepared at high w/c mass ratios; HD and UHD control the microstructure of low w/c ratio materials. In addition, heat treatment favors the formation of HD and UHD. The insight thus gained into the link between composition, processing and microstructure makes it possible to monitor packing density distributions of the hydration products at the nanoscale.     

Statistical Indentation Techniques for Hydrated Nanocomposites: Concrete, Bone, and Shale

Concrete, bone and shale have one thing in common: their load-bearing mineral phase is a hydrated nanocomposite. Yet the link between material genesis, microstructure, and mechanical performance for these materials is still an enigma that has deceived many decoding attempts. In this article, we advance statistical indentation analysis techniques that make it possible to assess, in situ , the nanomechanical properties, packing density distributions, and morphology of hydrated nanocomposites. These techniques are applied to identify intrinsic and structural sources of anisotropy of hydrated nanoparticles: calcium–silicate–hydrate (C–S–H), apatite, and clay. It is shown that C–S–H and apatite, the binding phase in, respectively, cement-based materials and bone, are intrinsically isotropic; this is most probably due to a random precipitation and growth process of particles in calcium oversaturated pore solutions, which can also explain the nonnegligible internanoparticle friction. In contrast, the load-bearing clay phase in shale, the sealing formation of most hydrocarbon reservoirs, is found to be intrinsically anisotropic and frictionless. This is indicative of a 'smooth' deposition and compaction history, which, in contrast to mineral growth in confined spaces, minimizes nanoparticle interlocking. In all cases, the nanomechanical behavior is governed by packing density distributions of elementary particles delimitating macroscopic diversity.     

The nano-mechanical signature of Ultra High Performance Concrete by statistical nanoindentation techniques

Advances in engineering the microstructure of cementitious composites have led to the development of fiber reinforced Ultra High Performance Concretes (UHPC). The scope of this paper is twofold, first to characterize the nano-mechanical properties of the phases governing the UHPC microstructure by means of a novel statistical nanoindentation technique; then to upscale those nanoscale properties, by means of continuum micromechanics, to the macroscopic scale of engineering applications. In particular, a combined investigation of nanoindentation, scanning electron microscope (SEM) and X-ray Diffraction (XRD) indicates that the fiber-matrix transition zone is relatively defect free. On this basis, a four-level multiscale model with defect free interfaces allows to accurately determine the composite stiffness from the measured nano-mechanical properties. Besides evidencing the dominant role of high density calcium silicate hydrates and the stiffening effect of residual clinker, the suggested model may become a useful tool for further optimizing cement-based engineered composites.     

Flexible Universal Networks—A New Approach to Telecommunication Services?

GPRS, WLAN integration, Mobile Number Portability and UMTS are some of the new technologies which are foreseen to carry many new service applications. In the near future, it is expected that mobile networks will go beyond connecting people and will connect an increasing number of machines, appliances, consumer devices, sensors and actuators. Also, users will connect through personal area networks and the importance of user profiles and service profiles will grow. Given the current strictness of network design, those services will further increase the complexity of today's networks. The reason is established design principles, which require new, dedicated network elements for new service applications. In addition, the applications contain their own subscriber data, usually stored locally in the application's database (distributed across the network), managed from their own management systems and with their own interfaces to Subscriber Care and Accounting Systems. In current designs, databases like home location register, AAA-Servers, MMS, Number Portability and others keep a significant amount of identical data that have to be kept consistent across all applications. For Network Operators, the effort to plan, to administrate and to introduce new services in those networks increases dramatically. This paper presents a concept to simplify current and future telecommunication networks. The concept contains a number of measures that complement each other but can be implemented independently one from another. In addition, a Telco project is presented (Evolute) where some of the ideas presented in the paper have been implemented.     

Deconvolution am Beispiel von Infrarotspektren verschiedener Milcheiwei?stoffe

Zusammenfassung Die Theorie der Deconvolution von IR-Spektren wird dargestellt and an Milcheiweißspektren veranschaulicht. An einem einfachen Beispiel aus der milchwirtschaftlichen Praxis (Kühlung von Milch) werden die Vorteile der Deconvolution demonstriert. Es wird jedoch ausdrücklich darauf hingewiesen, daß die Deconvolution sinnvoll dosiert eingesetzt werden muß, damit keine unphysikalischen Effekte verstärkt werden, welche zu Fehlinterpretationen führen können.

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Deconvolution of milk protein infra-red spectra

Summary The theory of deconvolution of infra-red spectra is presented and illustrated using milk protein spectra. The advantage of this method is impressively demonstrated and its relevance for dairy farming shown using a simple example, the cooling of milk.

     

Multiple equality sets and post machines

Equality sets of finite sets of homomorphisms are studied as part of formal language theory. Some particular equality sets, called Merge_k(k-COPY), are investigated. These languages are combinatorially difficult, and are full semiAFL generators of the recursively enumerable sets, and are semiAFL generators of the class MULTI-RESET, provided k ? 3. To accomplish this characterization, equality sets are related to multihead and multitape Post machines operating in real time. A Post machine has a one-way input tape and Post tapes as storage tapes, which in the multihead version are scanned from left to right by a write head and several read heads. By simulating Post machines by multiple reset machines, and vice versa, several new characterisations of the class MULTI-RESET are obtained, and it is shown that for multihead and multitape Post machines linear time is no more powerful than real time, and two Post tapes or, alternatively, three heads on one Post tape are as powerful as any finite number of heads or tapes. Finally, some complexity bounds for equality sets and Post machines are discussed.     

The scratch test for strength and fracture toughness determination of oil well cements cured at high temperature and pressure

Recent advances in scratch test analysis provide new ways to relate measured scratch test properties not only to strength properties but fracture properties of materials as well. Herein, we present an application of such tools to oil well cements cured at high temperatures and pressures. We find a concurrent increase of strength and toughness of different oil well cement baseline formulations which we relate to the water-to-binder ratio for a series of cementitious materials prepared with cement and silica flour. The scratch test thus emerges as a self-consistent technique for both cohesive–frictional strength and fracture properties that is highly reproducible, almost non-destructive, and not more sophisticated than classical compression tests, which makes this ‘old’ test highly attractive for performance-based field applications.     

Modeling of Early-Age Creep of Shotcrete. I: Model and Model Parameters

In this paper, creep and viscous flow are revisited from the standpoint of constitutive modeling of thermo-chemo-mechanical couplings in early-age concrete. Within the framework of closed reactive porous media, creep is modeled by means of two mechanisms: a stress-induced water movement within the macropores and a relaxation mechanism in the micropores of cement gel, both of which lead to aging effects on creep and viscous flow of concrete. Regarding the first creep mechanism, aging results from chemomechanical couplings. Concerning the second mechanism, long-term aging is attributed to the relaxation of microprestresses in the micropores. Following the formulation of the model, it is shown how the material parameters can be identified from creep tests performed at different ages of loading. Finally, the model is applied to shotcrete, for which proper experimental data are missing.     

Surface-recombination-free InGaAs/InP HBTs and the base contact recombination

Surface-recombination-free InGaAs/InP HBTs with graded base have been demonstrated. The HBTs were passivated by ammonium sulfide. The current gain of the nonself-aligned HBTs was independent of the emitter periphery, indicating that the surface recombination was removed by the passivation. For the self-aligned HBTs, the current gain was still dependent on the emitter periphery after the passivation due to the base contact recombination. A surface leakage channel has been identified to result in a significant increase in the base contact recombination. The passivation has two effects: one is the surface recombination velocity reduction and the other is the surface leakage channel elimination.