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- Englisch (2)
Schlagworte
- A. versicolor (1)
- Aspergillus sydowii (1)
- Chad (1)
- Co-firing (1)
- Desert sand (1)
- Ferrite (1)
- LTCC (1)
- Sterigmatocystin (1)
Desert dust seeds distant lands and waters
with minerals as well as micro-organisms raising the
question of whether this ancient phenomenon also
spreads pathogens across the globe. Severe dust
storms require strong winds blowing over land-masses
that are largely devoid of vegetation, effectively
limiting the scope for winds to raise pathogens into
the air. Nevertheless, changing patterns of land-use,
often driven by belligerency, result in refugees
spreading to areas that were previously deemed barely
habitable. With the help of the International Committee
of the Red Cross, a number of sand/dust samples
were collected from the Republic of Chad, some near
refugee camps, others further removed from human
influence. In parallel studies, we documented the
micro-organisms present in these samples and used a
number of the isolates here to test the effect of
environmental constraints on their ability to survive
intercontinental flight. We also added traditional
pathogens to the palette of microbes and tested the
effects of UV irradiation, desiccation and temperature
on survival of both bacteria and fungi. A clear trend
was obvious—those microbes that are coloured or able
to form conidia or spores (in other words, those that
are native to deserts) were well able to resist the
imposed stresses. On the other hand, most pathogens
were more sensitive to stresses than the environmental
isolates. Toxin production in two species of Aspergillus
was also investigated. Short-term desiccation
(simulating environmental conditions during intercontinental
travel) of sand amended with fungal spores
containing sterigmatocystin leads to increased mycotoxin
contents, but significant mycotoxin production
was only possible under growth-permissive conditions,
e.g. at higher humidity. It thus seems likely that an ever-decreasing fraction of the initial pathogen load
survives as the dust recedes from its desert source and
that those organisms that land on other continents are
highly enriched in desert dwellers.
Further miniaturization of electronic packaging calls for integration of magnetic functional components into LTCC modules. For integration of magnetic function into LTCC, low fired MnZn- and NiCuZn-ferrites which can be fully densified at the standard LTCC sintering temperature of 900°C were developed. To co-fire these ferrite tapes with dielectric tapes the sintering shrinkage and the coefficient of thermal expansion of ferrite and dielectric tapes must be matched. For each ferrite material a new LTCC dielectric material was designed. The embedded ferrite tapes into new LTCC dielectric tapes can be sufficiently densified during co-firing at 900°C without any cracking. Compared to separately sintered ferrites the permeability of embedded ferrite tapes is reduced. For embedded NiCuZn ferrites permeabilities between 230 and 570 (at 2 MHz) according to the thickness of the embedded ferrite layer were measured. For embedded MnZn ferrites a permeability of 300 was measured.