Dynamic crack propagation with cohesive elements: a methodology to address mesh dependency

In this paper, two brittle fracture problems are numerically simulated: the failure of a ceramic ring under centrifugal loading and crack branching in a PMMA strip. A three‐dimensional finite element package in which cohesive elements are dynamically inserted has been developed. The cohesive elements' strength is chosen to follow a modified weakest link Weibull distribution. The probability of introducing a weak cohesive element is set to increase with the cohesive element size. This reflects the physically based effect according to which larger elements are more likely to contain defects. The calculations illustrate how the area dependence of the Weibull model can be used to effectively address mesh dependency. On the other hand, regular Weibull distributions have failed to reduce mesh dependency for the examples shown in this paper. The ceramic ring calculations revealed that two distinct phenomena appear depending on the magnitude of the Weibull modulus. For low Weibull modulus, the fragmentation of the ring is dominated by heterogeneities. Whereas many cracks were generated, few of them could propagate to the outer surface. Monte Carlo simulations revealed that for highly heterogeneous rings, the number of small fragments was large and that few large fragments were generated. For high Weibull modulus, signifying that the ring is close to being homogeneous, the fragmentation process was very different. Monte Carlo simulations highlighted that a larger number of large fragments are generated due to crack branching. Copyright © 2003 John Wiley & Sons, Ltd.     

On the role of high-energy electrons in the formation of a plasma-beam discharge structure in a diode with a slit cathode

The spatial structure of visible emission from plasma of a transverse nanosecond pulsed electric discharge in a gas-filled diode with a hollow (slit) cathode has been experimentally studied. A relation is established between the regime of electron energy relaxation and the plasma-beam discharge structure formation. High values of the electron emission coefficient are observed in the experiment, which cannot be explained using the notion of electron emission from a cathode bombarded by fast heavy particles.     

Increasing the efficiency of metal-air current sources operating in a pulse-train mode

A considerable (～1.4-fold) increase in the average output power of a chemical current source has been achieved by means of a periodic pulsed manipulation of the load. A scheme used for the pulse-train loading is presented and mechanisms ensuring an increase in the average output power of the current source are considered.     

Workplane illuminance prediction method for daylighting control systems

A new prediction method with an interior light sensor for the workplane illuminance in daylighting control systems is introduced. Based on radiosity theory, the spatial distributions of daylight and electric light in the space are discussed and the prediction method is developed. An experimental verification of the technique is performed in an outdoor test-room for a double-glazed window system with a motorized venetian blind integrated between the two glazings. Electric light and daylight predictions were performed in accordance with the proposed method. The results showed that the electric light workplane illuminance can be predicted with high accuracy (±5 lux error with a linear correlation) and that the daylight workplane illuminance can be predicted within ±20 lux (with a linear correlation) for any sky conditions (overcast, clear sky, or variable) with the window system controlled to prevent direct daylight transmission. This method is useful for integrated control of motorized daylighting devices and dimmable electric lights.     

The structure and thermo EMF of a nanotubular carbon deposit formed in electric discharge plasma

We have studied the structure and thermo emf of a nanotubular carbon deposit formed in electric arc discharge plasma. The deposit contains flocky granules with dimensions of 15–20 μm within a 20–60 μm-thick layer on the substrate surface. This deposit is characterized by a sufficiently high thermo emf (60 μV/K) and electric conductivity (600 Ω⁻¹ m⁻¹).     

Results of benchmark calculations based on OLHF-1 test

The subject of this paper is to compare the results of the different calculations performed by the benchmark participants in the framework of the OECD Lower Head Failure (OLHF) program. The benchmark consists in the finite element (FE) calculation or in analytical calculations of the mechanical behavior of the OLHF-1 experiment. Seven participants from six countries and seven companies or organizations (AVN, VTT, GRS, UJV, SNL, IPSN and CEA) have performed the benchmark.The OLHF experiment program extends the NRC-sponsored SNL LHF program (NUREG/CR-5582) completed in 1998: these experiments where intended to simulate the thermal/mechanical loads to a 1/4.85-scale model of a reactor pressure vessel. The pressure vessel material (SA533B1 steel) used in these experiments is prototypic of reactor PWR vessel material and has been well characterized by material property testing as part of this program. The OLHF tests advance the results of the previous testing program by examining the effects of large temperature differences across the vessel wall. Large temperature differences in excess of 150–400 K are more prototypic of accident conditions.Most of the participants performed 2-D axisymmetric analyses and doesn’t study the crack opening. The global mechanical behaviour of OLHF-1 experiment is well represented but prediction of the maximum vertical displacement is not in good agreement with the experimental value. Failure time and location are in quite good agreement with experimental results but large discrepancies are observed on the mode of failure: creep or plasticity. To improve predictions, more investigation and work is needed on the choice of the failure criteria and failure mode.     

A personal computer based system used in electromyography for interpretation and reporting

Programs for rule based electromyography (EMG) interpretation and reporting are described. A number of parameters are obtained during an EMG investigation. The combination of these data leads to a neurophysiological conclusion. Knowledge from the literature, research and experience is the basis for rule development. Rules have been developed for 14 of the most commonly used classifications of an EMG. The syntax is relatively easy and the user may change the rules, add rules or apply the system for other types of data. The results are displayed in a new graphical way. The system presented here is part of an integrated EMG laboratory with administrative routines, distributed databases for storage of results and routines for automatic report generation.     

High-gain pseudomorphic InGaAs base ballistic hot-electron device

A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In _0.12Ga_0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In_0.12Ga_0.88As was estimated to be about 380 meV     

Phase relations in the ternary system Cu-In-Se

The phase relations of the ternary system Cu-In-Se were studied at 750° C by quenching experiments. Special attention was given to the region CuInSe₂In₂Se₃-In₄Se₃. Only four ternary phases with extended homogeneity ranges were found to exist. They were characterized by X-ray powder diffraction, electron microprobe analysis (EK8PA)' end optical microscopy. Differential thermal analysis (DTA) investigations allowed us to construct theT-x diagram of the Cu₂Se-In₂Se₃. out between 47 and 100 mol% In₂Se₃. Besides, it was also possible to give a tentative diagram of the solid-liquid equilibria at 750° C and to get some information on the sub-solid existence fields beside the Cu₂Se-In₂Se₃ cut.     

Scientific co-operation in Europe and the citation of multinationally authored papers

Under the sponsorship of the U.S. National Science Foundation, CHI Research, Inc. developed the bibliometric indicators for the U.S. National Science Board'sScience Indicators Reports starting withScience Indicators 1972. In the work reported here, for the Commission of the European Communities, CHI has extended the Science Indicators techniques and database to a study of publication, coauthorship and citation within 28 scientific fields related to various European Community programs.Perhaps the most important finding of the research was that internationally coauthored papers — papers authored by scientists affiliated with institutions in more than one EC country — were cited two times as highly as papers authored by scientists working at a single institution within a single country. These EC-EC internationally coauthored papers were cited as highly as EC-Non EC and Non-EC papers. This indicates that the internationally linked European science is of as high impact as any other science in the world.A second key finding was that, after compensating for national scientific size, the degree of international coauthorship did not appear to be particularly dependent upon size. However, linguistic and cultural factors were found to be very strong. The patterns of coauthorship amongst the European countries are far from homogeneous, and are quite heavily affected by linguistic, historical, and cultural factors.Finally, it was found that international coauthorship is increasing steadily, both within and outside of the Community, with some evidence that international cooperation is increasing more rapidly in scientific fields that have been targeted by the Commission.This work has been sponsored by the MONITOR programme of the Commission of the European Communities.