Showing papers by "Karlsruhe Institute of Technology published in 1980"

Shear band inclination and shear modulus of sand in biaxial tests

Abstract: The spontaneous shear band formation in the biaxial test on dry sand samples with constant cell pressure is treated as a bifurcation problem. The constitutive response of sand is described in terms of mobilized friction and dilatancy. Dilatancy is looked upon as an internal constraint and the hardening rule is expressed in terms of an adequate dimensionless stress measure. Owing to fail of normality in sand, localization always occurs in the hardening regime. The theoretical solution of the shear band inclination is a geometrical mean of the classical Coulomb and Roscoe solutions and is in good agreement with the experimental data. The incipient shear modulus is proportional to the stress level and can be estimated to be also proportional to these cant modulus.

Interval Analysis in the Extended Interval Space IR

Abstract: This paper shows, how the extended Interval Space IR can be used to write formulas, theorems, and proofs in a closed form, ie without using the left and right interval bounds So a basic generalization and moreover a simplification and improvement of the theorems and proofs is achieved

Ordered attributed grammars

Abstract: Ordered attributed grammars are defined as a large subclass of semantically well-defined attributed grammars proposed by Knuth. An attributed grammar is ordered if for each symbol a partial order over the associated attributes can be given, such that in any context of the symbol the attributes are evaluable in an order which includes that partial order. The definition does not refer to a predefined strategy for attribute evaluation, e.g. several passes from left to right. For each attributed grammar evaluable by any predefined evaluation strategy such an order exists. The ordering property can be checked by an algorithm, which depends polynomially in time on the size of the input grammar. "Visit-sequences" are computed from the attribute dependencies given by an ordered attributed grammar. They describe the control flow of an algorithm for attribute evaluation which can be part of an automatically generated compiler.

Upper limit for the conversion of solar energy

Abstract: A semiconductor in the solar radiation field acts as a thermal electronic engine. It converts absorbed radiation heat into chemical energy of the excited electron-hole gas. In flow equilibrium, a homogeneous semiconductor gives off this chemical energy by radiative recombination to the surroundings. If provision is made, as by a p-n junction, to divert the excited electrons and holes, before they recombine, from their point of generation, their chemical energy may be converted into electrical energy. The ratio of this chemical energy current, which constitutes an upper limit for the obtainable electrical energy current, to the absorbed heat current is computed as a function of the value of the bandgap of the semiconductor. Under the assumption that the absorptivity of the electron-hole system of the semiconductor is unity for photon energies larger than the bandgap and zero for smaller photon energies, the conversion efficiency for unfocussed sunlight has a maximum of 30 percent for a bandgap of 1:3 eV.

The Static Dielectric Constant of Water at High Pressures and Temperatures to 500 MPa and 550°C

Abstract: Measurements of the static dielectric constant (permittivity) of water have been made between 100 and 550°C to a maximum pressure of 500 MPa A capacitor within a high-pressure vessel and a transformer ratio bridge at a frequency of 100 kHz were used The capacitor was made of two coaxial half-cylinders, which could be rotated against each other to eliminate lead capacities At 200°C and 100 and 500 MPa resp values of 380 and 458 and at 500°C and at the same pressures values of 93 and 188 were found for the dielectric constant Using the experimental data Kirkwood correlation factors were calculated and presented in dependence of temperature and density

X-ray yields in protonium and mesic hydrogen

Abstract: Recent experimental investigations of atomic x rays in protonium have revived interest in the atomic cascade process. Following a calculation of Leon and Bethe, which includes chemical and Auger deexcitation, Stark mixing and annihilation, as well as radiative transitions, we investigate the dependence of the yields of $K$ and $L$ x rays on the target density, and on the hadronic shifts and widths of the $1s$ and $2p$ levels. Numerical results are also given for kaonic, pionic, and muonic hydrogen.

Gain and Reflection Spectroscopy and the Present Understanding of the Electron-Hole Plasma in II-VI Compounds

Abstract: The reflection and gain spectra of CdS and ZnO are investigated as a function of excitation intensity and temperature. For the gain spectroscopy the two beam method and the variation of the excitation strip length are used. The results indicate, that an electron–hole plasma is formed under high excitation, preferentially if small excitation spots are used. The electron–hole plasma comes close to its thermal equilibrium only in especially favourable cases. Excitonic recombination processes are predominant, if larger excitation spots are used. Die Spektren der Reflexion und der optischen Verstarkung werden an CdS und ZnO in Abhangigkeit von der Anregungsintensitat und der Temperatur untersucht. Fur die Messung der optischen Verstarkung werden die Zweistrahl- und die Strichlangenmethode eingesetzt. Die Ergebnisse zeigen, das sich bei hoher Anregung ein Elektron–Loch-Plasma bildet, besonders bei Verwendung kleiner angeregter Gebiete. Es nahert sich aber nur in besonders gunstigen Fallen dem thermischen Gleichgewicht an. Bei groseren angeregten Gebieten uberwiegen exzitonische Rekombinations-prozesse.

The Importance of Blue Light for the Development of Sun-Type Chloroplasts

Abstract: Depending on environmental factors, the development of chloroplasts from either pro-plastids or etioplasts will lead to two distinctive types of chloroplast, which are different in composition, ultrastructure, and photosynthetic activity [1, 8]. At low light intensities and in shade leaves the shade-type chloroplast with high grana stacks, lower Hill activity rates and a higher level of chlorophyll b is formed, indicating more light-harvesting complex CPII [6, 10]. Sun leaves and plants grown at high light intensities, in turn, develop sun-type chloroplasts with less lamellar material and only few and low grana stacks. Their higher Hill activity is correlated with a higher level of prenylquinones, which function as potential photosynthetic electron carriers, and can also be seen in a changed chlorophyll (higher a/b ratios) and carotenoid composition (lower x/c ratios) [6].

Upper limit of thermophotovoltaic solar-energy conversion

Abstract: The efficiency of the conversion of solar energy into electrical energy by solar cells is improved if the incident solar radiation is first absorbed by an intermediate absorber. The reemitted radiation is directed onto the solar cell. This mode of operation is known as thermophotovoltaic energy conversion. A black-body intermediate absorber is advantageous for small-bandgap solar cells. An even higher improvement is, however, achieved by a selective intermediate absorber with an absorption edge at the energy of the bandgap of the solar cell. Furthermore, if only a narrow spectral interval of radiation near the absorption edge is transmitted through a filter from the intermediate absorber to the solar cell, a maximum efficiency of 65 percent is obtained for a solar cell and absorber with a bandgap of 0.8 eV.

Structure and dynamics of liquid carbon tetrachloride.

Abstract: The structure and dynamics of liquid CCl4 are analysed on the basis of a molecular dynamics experiment involving 64 particles and lasting 10 ps. CCl4 molecules are modelled as rigid tetrahedra interacting by a 4CLJ potential. The resulting spatial and time correlation functions are compared to X-ray, neutron and light scattering data. Selected expansion coefficients of g(r, Θ1, Θ2) are used in a critical examination of various orientational models.

Results of the search for K-series X-rays from kaonic hydrogen

Abstract: The X-ray spectrum associated withK− stopping in liquid hydrogen was measured with high resolution Si(Li) detectors. The totalK X-ray yield is not larger than 8×10−4 per stoppedK− assuming no line broadening. A weak line pattern was found, which was tentatively ascribed to theK− HK-series X-rays. The shift and width of the 1s level, deduced from this pattern, are e1s=+270±80 eV andΓ=560±260 eV, respectively.

Two Simple Time-Shear Rate Relations Combining Viscosity and First Normal Stress Coefficient in the Linear and Non-Linear Flow Range

Abstract: The theory of linear viscoelasticity is able to describe the time dependent flow behaviour of viscoelastic liquids in the range of small shear rates K. Using a memory function, defined for example in 1, with a suitable set of constants the transient zero viscosity ηo(t,K→O) can be calculated. The theory of linear viscoelasticity however, predicts no shear rate dependency of the viscosity as aobserved for nearly all polymers at higher shear rates.

Sensor Fault Detection in a System with Random Disturbances

Abstract: Sensor faults are detected in an operating automatic system by a simplified version of the dedicated observer scheme Control inputs are augmented by a random disturbance of moderate intensity The dedicated observer in this case is a Kalman filter, driven by a single sensor This filter provides estimates of the outputs from the other, nonredundant, sensors A logical combination of these functionally redundant signals with the actual sensor signals provides prompt detection of incipient faults on all instruments without false alarms The scheme is applied to a simulation of the lateral axis control system of a hydrofoil boat in which four sensors are to be covered by the fault detection scheme Tests indicate that the scheme is robust with respect to variations in the intensity of the random disturbance

Potential curves for the ground and excited states of the NaN2 system

Abstract: The potential curves for the ground and excited states of the NaN 2 system are calculated in C ∞v , C 2v , C S -symmetry, using a modified HF-method. The results explain the quenching and excitation of Na atoms colliding with N 2 molecules observed in scattering experiments, with particular reference to the population of the final vibrational levels in N 2 , and to the possibility of rotational excitation.