We calculate the lateral distribution of Cherenkov light at different levels of shower development. The calculations use the universal characteristics of large showers. We derive that the angular and ...lateral distributions of Cherenkov photons emitted by a shower path element depend only on the shower age and height in the atmosphere of this element. The width of a shower image in the Cherenkov scattered light also depends, however, on the zenith angle and
X
max
. We also show that below shower maximum it is considerably wider than the width in the fluorescence light.
In this contribution, some aspects of fractography are discussed, arguably the failure analysts' most potent analytical tool in metallurgical failure analyses. The characterisation of fracture ...surfaces is indispensable when it comes to getting to the bottom of things in regards to component failures. When machine parts or entire assemblies fail by fracture of individual members, the fracture surface contains the data that tells the failure analyst about the history of the failed component, and hopefully will also shed some light on the exact failure mode that eventually lead to fracture. That makes fractography, the art of reading fracture surfaces, so valuable. This applies to all material classes, i. e. metals, ceramics, and plastics alike. This paper, however, focuses on failures of metallic components only. When there is no fracture surface in a failed part, one is produced by forcing open cracks or other imperfections that might be suitable for this purpose. Once this is achieved, the failure analyst will open his or her toolset of macro- and microfractographic analysis equipment. It is not exaggerated to say that the scanning electron microscope (SEM) revolutionised the art of microfractography from the early 1960 s on. In this paper, a number of examples for this are given.
Departments of Neurological Surgery and Radiology,
University of Texas Southwestern Medical Center, Dallas, Texas
75235-8855
The
response of the cerebral circulation to exercise has been studied with
...transcranial Doppler ultrasound (TCD) because this modality provides
continuous measurements of blood velocity and is well suited for the
exercise environment. The use of TCD as an index of cerebral blood
flow, however, requires the assumption that the diameter of the
insonated vessel is constant. Here, we examine this assumption for
rhythmic handgrip using a spectral index designed to measure trends in
vessel flow. Nineteen normal subjects were studied during 5 min of
volitional maximum rhythmic right handgrip at 1 Hz. TCD velocities from
both middle arteries (left and right), blood pressure, and end-tidal
P CO 2 were recorded every 10 s. A spectral
weighted sum was also calculated as a flow index (FI). Averages were
computed from the last 2 min of handgrip. Relative changes in velocity,
FI, and pressure were calculated. The validity of FI was tested by
comparing the change in diameter derived from equations relating flow
and diameter. Mean blood pressure increased 23.8 ± 17.8% (SD), and
velocity increased 13.3 ± 9.8% (left) and 9.6 ± 8.3% (right).
Although the mean change in FI was small 2.0 ± 18.2% (left)
and 4.7 ± 29.7% (right), the variation was high: some
subjects showed a significant increase in FI and others a significant
decrease. Diameter estimates from two equations relating flow and
luminal area were not significantly different. Decreases in FI were
associated with estimated diameter decreases of 10%. Our data suggest
that the cerebral blood flow (CBF) response to rhythmic handgrip is
heterogeneous and that middle cerebral artery flow can decrease in some
subjects, in agreement with prior studies using the Kety-Schmidt
technique. We speculate that the velocity increase is due to
sympathetically mediated vasoconstriction rather than a ubiquitous flow
increase. Our data suggest that the use of ordinary TCD velocities to
interpret the CBF response during exercise may be invalid.
transcranial Doppler; exercise; cerebral blood flow
This paper is related to 16Mo3, a low-alloy steel typical in the manufacture of large welded steel casings of heavy-duty gas turbine engines. The usual practice in manufacturing is to stress relieve ...these housings after fabrication welding. If, however, weld imperfections are detected by non-destructive testing, weld repairs are performed, followed by additional stress-relief heat treatments. The methods applied were used to detect possible embrittlement by secondary carbide precipitation and to finally draw conclusions on material changes. The critical area of a weld is the heat affected zone. In this area a worsening of the stress condition in connection with a change in carbide precipitation and thus a decrease in creep rupture strength occurs. A concrete alloy composition and heat treatment adapted to the precipitation behavior are important, because they determine the type, amount and distribution of the resulting carbides 1, 2.
Abstract
This paper is a compilation of failure analysis case studies exploring the subject of inadequate heat treatment. As with other papers in this series, the presented failure cases are rather ...simple and may appear trivial to the experienced failure analyst. The authors can guarantee however, that minor heat treatment errors are committed easily and have a considerable damage potential which may entail heavy financial losses. Therefore, cases of inadequate heat treatment or a complete lack of necessary heat treatment belong by all means in the column
Failure Analysis
. The metallurgical subject of these failure cases are low-alloy hardenable steels without exception. Common heat treatment processes such as induction hardening, case hardening, nitriding as well as through-hardening and tempering will be touched upon.
Abstract
The failure of fastening elements in electrical terminal blocks was attributed to various material-related causes. While the casehardened terminal screws broke due to hydrogen embrittlement, ...the material-related cause of the plastic deformations of the roof-shaped washers and the stripping of the threads of the square nuts are undersizing and an insufficient strength for this particular application.
Este artículo presenta un breve panorama descriptivo de la historia del jazz en Brasil, destacando los principales personajes y modificaciones estético-culturales que ocurrieron en el marco de su ...proceso de absorción por parte de la sociedad brasileña a lo largo del siglo XX e inicios del siglo XXI. Dividido en cuatro fases, el primer período, al que dedicamos más páginas, presenta el desarrollo del jazz como una música popular para bailar en clubes y sociedades, entre géneros musicales extranjeros y brasileños, animados por las jazz bands. El segundo momento aborda al jazz diseminado gracias a las innovaciones tecnológicas, absorbido por un segmento de la élite urbana, y generalmente ejecutado por grupos musicales en formación de big band. La tercera fase trata del momento en que los músicos brasileños mezclan músicas locales con los recursos sonoros del jazz, amalgamándolos en la bossa nova y en el samba-jazz. Y un cuarto periodo, cuando el jazz brasileño se desarrolla a partir de diversas concepciones, y pasa a ser reconocido como Música Instrumental Brasileña.
Abstract
Protector tubes for temperature sensors were welded onto experimental gas turbine compressor blades. While the blades were made of a high alloy hard-martensitic stainless chromium steel, a ...high alloy metastable austenitic stainless steel was used for the tiny protector tubes. The dissimilar weld joint was applied using manual GTAW. A large amount of blocky delta ferrite formed in the HAZ immediately adjacent to the fusion line, on the side of the martensitic steel. Delta ferrite in such dissimilar welds might detrimentally affect the mechanical properties of the weld joint. It was therefore recommended not to use the affected experimental blades in test engine service. Even though no failure occurred in this case, one was prevented by declaring the subject instrumented parts unfit for test engine service.
Linear Friction Welding (LFW) is a rarely used joining technology. To test the suitability of this solid-state process for hot cracking-sensitive nickel base superalloys, tests were performed using ...conventionally and directionally cast slabs of Alloy 247. Since LFW does not involve melting of the weld flanks, there were some expectations that this special welding technique could overcome the poor weldability of Alloy 247. However, all tested specimens failed by liquation cracking (LC) within the Weld Center Zone (WCZ) at the directionally cast side.
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