RESUMO

We report the resistivity of 5 Cu films approximately 65 nm thick, measured between 5 and 290 K, and the transverse magnetoresistance and Hall effect measured at temperatures 5 K < T < 50 K. The mean grain diameters are D = (8.9, 9.8, 20.2, 31.5, 34.7) nm, respectively. The magnetoresistance signal is positive in samples where D > L/2 (where L = 39 nm is the electron mean free path in the bulk at room temperature), and negative in samples where D < L/2. The sample where D = 20.2 nm exhibits a negative magnetoresistance at B < 2 Tesla and a positive magnetoresistance at B > 3 Tesla. A negative magnetoresistance in Cu films has been considered evidence of charge transport involving weak Anderson localization. These experiments reveal that electron scattering by disordered grain boundaries found along L leads to weak Anderson localization, confirming the localization phenomenon predicted by the quantum theory of resistivity of nanometric metallic connectors. Anderson localization becomes a severe obstacle for the successful development of the circuit miniaturization effort pursued by the electronic industry, for it leads to a steep rise in the resistivity of nanometric metallic connectors with decreasing wire dimensions (D < L/2) employed in the design of Integrated Circuits.

RESUMO

Here we describe clinical and pathologic evidence of Chagas disease caused in dogs by circulating Trypanosoma cruzi from a newly recognized endemic area in Mexico. We show that the Zumpahuacan isolate, although less virulent than the Sylvio-X10 reference strain that caused acute myocarditis and death, was pathogenic in dogs. Dogs infected with the Zumpahuacan isolate exhibited electrocardiographic alterations, left- and right-ventricle dilation, and hydropericardium. Histologically, diffused perimysial and endomysial lymphoplasmacytic cell infiltration, cardiomyocyte necrosis, and amastigote nests were noted in Zumpahuacan-infected dogs. These findings suggest that the risk of T. cruzi infection and Chagas disease is present in the State of Mexico, and further research is needed to identify the T. cruzi bio-types circulating in southern State of Mexico.

Assuntos

Doença de Chagas/veterinária , Doenças do Cão/parasitologia , Trypanosoma cruzi/patogenicidade , Animais , Cardiomiopatia Chagásica/epidemiologia , Cardiomiopatia Chagásica/parasitologia , Cardiomiopatia Chagásica/veterinária , Doença de Chagas/epidemiologia , Doença de Chagas/parasitologia , Doença de Chagas/patologia , Modelos Animais de Doenças , Reservatórios de Doenças/veterinária , Doenças do Cão/epidemiologia , Doenças do Cão/patologia , Cães , México/epidemiologia , Camundongos , Camundongos Endogâmicos BALB C , Miocárdio/patologia , Virulência

RESUMO

We report measurements of the Hall effect performed on 4 gold films evaporated onto mica substrates where the signal arises primarily from electron-surface scattering. The measurements were performed at low temperatures T (4 K < or = T < or = 50 K) under high magnetic field strengths B (1.5 T < or = B < or = 9 T), with B oriented perpendicular to the films.