100 research outputs found
Magetoresistance of RuO_2-based resistance thermometers below 0.3 K
We have determined the magnetoresistance of RuO_2-based resistors (Scientific
Instruments RO-600) between 0.05 K and 0.3 K in magnetic fields up to 8 T. The
magnetoresistance is negative around 0.5 T and then becomes positive at larger
fields. The magnitude of the negative magnetoresistance increases rapidly as
the temperature is lowered, while that of the positive magnetoresistance has
smaller temperature dependence. We have also examined the temperature
dependence of the resistance below 50 mK in zero magnetic field. It is
described in the context of variable-range-hopping conduction down to 15 mK.
Hence, the resistors can be used as thermometers down to at least 15 mK.Comment: 6 pages with 7 embedded figures. Published version (very minor
changes
Gauge factor of thick film resistors: outcomes of the variable range hopping model
Despite a large amount of data and numerous theoretical proposals, the
microscopic mechanism of transport in thick film resistors remains unclear.
However, recent low temperature measurements point toward a possible variable
range hopping mechanism of transport. Here we examine how such a mechanism
affects the gauge factor of thick film resistors. We find that at sufficiently
low temperatures , for which the resistivity follows the Mott's law
, the gauge factor GF is proportional to
. Moreover, the inclusion of Coulomb gap effects leads to at lower temperatures. In addition, we study a simple
model which generalizes the variable range hopping mechanism by taking into
account the finite mean inter-grain spacing. Our results suggest a possible
experimental verification of the validity of the variable range hopping in
thick film resistors.Comment: 7 pages, 3 eps figures, submitted to Journal of Applied Physic
Patterns and Risk Factors of Helminthiasis and Anemia in a Rural and a Peri-urban Community in Zanzibar, in the Context of Helminth Control Programs
In many parts of the developing world, parasitic worms and anemia are of considerable public health and economic importance. We studied the patterns and risk factors of parasitic worm infections in a rural and a peri-urban community on Zanzibar Island, Tanzania, in the context of national deworming programs. We invited 658 individuals aged between 5 and 100 years and examined their stool and urine for the presence of parasitic worm eggs. Additionally, we obtained a finger-prick blood sample to estimate the level of anemia and to assess for specific immune reactions against parasitic worm infections. We found that, despite large-scale deworming efforts in Zanzibar over the past 15 years, three-quarter of the rural participants and half of the peri-urban residents were infected with parasitic worms. Every second participant was anemic. Risk factors for a parasitic worm infection were age, sex, consumption of raw vegetables or salad, recent travel history, and socio-economic status. For a sustainable control of parasitic worm infections and prevention of anemia, access to safe and efficacious drugs, complemented with health education and improvements in water supply and adequate sanitation are necessary
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