Jose Pizarro

Characterization of rotavirus electropherotypes excreted by symptomatic and asymptomatic infants.

Human rotavirus isolates from 1100 stool samples were analyzed by polyacrylamide gel electrophoresis, and 48 different migration patterns were detected. Heterogeneity in the migration of segment 10 was observed in both long and short electropherotypes in which three long and two short patterns were identified. In spite of these variations all short and long electropherotypes were subgrouped by enzyme immunoassay as subgroups I and II respectively. Mixed infections were detected in 17% of cases and the subgrouping correlated with the corresponding electropherotypes. The same electropherotypes were present in severe, mild and asymptomatic cases and no electropherotype was particularly associated with greater virulence. Furthermore, the electropherotypes isolated from nosocomial asymptomatic cases were the same as those detected from those admitted with severe diarrhea. It seems unlikely that electropherotyping can be used to identify more virulent strains of rotavirus.

ALMA band 1 development at Universidad de Chile

The lowest spectroscopic band devised for the Atacama Large Millimeter Array (ALMA), the so-called Band 1, covers the frequency range from 31 to 45 GHz. This band was not implemented during the rst construction phase of the telescope, but will be included during a second ALMA development phase. During the past 4 years our group has been working on the development of technology to cover this band, complying with the demanding ALMA specications. Among the most burdensome challenges are the stringent specications on noise temperature, the large required bandwidth, and the limited space available for this receiver within the ALMA cryostat. In this paper we present some of the technologies we have developed, including the design of key components like horn, lens, ortho-mode transducer, and low noise ampliers. We also present an evaluation of third-party components which can be used in the receiver. The work is used to present a preliminary layout of the Band 1 receiver.

Amplification system of ALMA Band 1

At Universidad de Chile we have started a program for the development of a prototype receiver for Band 1 (31-45 GHz) of the Atacama Large Millimeter Array. This receiver will use a low-noise amplifier which is specified to have 5 times the quantum limit (~10 K). Here we present the first efforts and results towards reaching that goal.

Magnetic structures of the B and C type Cr(PO3)3 metaphosphatesElectronic supplementary information (ESI) available: experimental, calculated and difference neutron powder profiles; final refined positional and thermal parameters; main interatomic distances and angles. See http://www.rsc.org/suppdata/jm/b3/b313895j/

The B and C type Cr(PO3)3 metaphosphates were synthesised by ceramic methods with control of the Cr/P ratio in the reaction medium. Neutron powder diffraction experiments and heat-capacity measurements were carried out on polycrystalline samples. The C-type [Cr(PO3)3] compound is ordered as a three-dimensional Heisenberg antiferromagnet with a J/k value of 0.3 K whereas the B-type [Cr2P6O18] phase shows that the magnetic susceptibility depends strongly on the magnetic field at temperatures less than 4 K suggesting the presence of some ferromagnetic contributions in the ordered state. The heat-capacity measurements of C-type Cr(PO3)3 exhibit a three-dimensional magnetic ordering (λ-type) peak at 4.2 K. The absence of an appreciable anomaly in the magnetic heat capacity obtained above TN suggests a small short-range order in this Cr(PO3)3 metaphosphate. The magnetic structures of both compounds are consistent with the existence of predominant antiferromagnetic superexchange interactions via |PO4| tetrahedra between the Cr(III) ions. In the C-type phase, the magnetic moments arranged in (100) ferromagnetic layers are antiparallel with those of the neighbouring layers stabilising an antiferromagnetic structure. The magnetic moments lie in the xz plane pointing 13° out of the x axis. In the B-type phase, the presence of a weak ferromagnetic component is observed. Magnetostructural correlations in both chromium compounds indicate that only super-superexchange interactions via one or two phosphate groups are present. The [Cr–O–P and O–P–O] angles of the magnetic exchange pathways show typical values of antiferromagnetic couplings. The competition between different magnetic interactions in Cr(PO3)3 through super-superexchange pathways is not strong enough to cause magnetic frustration as observed in other metaphosphates.