758 research outputs found
Non-collinear long-range magnetic ordering in HgCr2S4
The low-temperature magnetic structure of \HG has been studied by
high-resolution powder neutron diffraction. Long-range incommensurate magnetic
order sets in at T22K with propagation vector
\textbf{k}=(0,0,0.18). On cooling below T, the propagation vector
increases and saturates at the commensurate value \textbf{k}=(0,0,0.25). The
magnetic structure below T consists of ferromagnetic layers in the
\textit{ab}-plane stacked in a spiral arrangement along the \textit{c}-axis.
Symmetry analysis using corepresentations theory reveals a point group symmetry
in the ordered magnetic phase of 422 (D), which is incompatible with
macroscopic ferroelectricity. This finding indicates that the spontaneous
electric polarization observed experimentally cannot be coupled to the magnetic
order parameter
Mechanochemical generation of perchlorate
Perchlorate (ClO4−) is widespread in the solar system having been detected on Earth, on Mars, in chondrite meteorites and in lunar samples. On Mars, perchlorates expand the potential for habitable conditions by lowering the freezing point of liquid water in the formation of brines. In future manned space exploration their presence poses a hazard to human health, however, it also represents opportunities as a source of oxygen and fuel. Despite their prevalence, the mechanism(s) of perchlorate formation in different solar system environments are poorly understood. Here we demonstrate that perchlorate can be generated through the mechanical activation of silicates in the presence of chloride
Spin and orbital moments of ultra-thin Fe films on various semiconductor surfaces
The magnetic moments of ultrathin Fe films on three different III-V semiconductor substrates, namely GaAs, InAs and In0.2Ga0.8As have been measured with X-ray magnetic circular dichroism at room temperature to assess their relative merits as combinations suitable for next-generation spintronic devices. The results revealed rather similar spin moments and orbital moments for the three systems, suggesting the relationship between film and semiconductor lattice parameters to be less critical to magnetic moments than magnetic anisotropy
Seasonal changes of ice surface characteristics and productivity in the ablation zone of the Greenland Ice Sheet
Field and remote sensing observations in the ablation zone of the Greenland
Ice Sheet have revealed a diverse range of ice surface characteristics,
primarily reflecting the variable distribution of fine debris (cryoconite).
This debris reduces the surface albedo and is therefore an important control
on melt rates and ice sheet mass balance. Meanwhile, studies of ice sheet
surface biological processes have found active microbial communities
associated with the cryoconite debris, which may themselves modify the
cryoconite distribution. Due to the considerable difficulties involved with
collecting ground-based observations of the ice surface, our knowledge of
the physical and biological surface processes, and their links, remains very
limited. Here we present data collected at a field camp established in the
ice sheet ablation zone at 67° N, occupied for almost the entire
melt season (26 May–10 August 2012), with the aim of gaining a much more
detailed understanding of the physical and biological processes occurring on
the ice surface. These data sets include quadrat surveys of surface type,
measurements of ice surface ablation, and in situ biological oxygen demand
incubations to quantify microbial activity. In addition, albedo at the site
was retrieved from AVHRR (Advanced Very High Resolution Radiometer) remote sensing data. Observations of the areal
coverage of different surface types revealed a rapid change from complete
snow cover to the "summer" (summer study period) ice surface of patchy debris ("dirty ice") and
cryoconite holes. There was significant correlation between surface albedo,
cryoconite hole coverage and surface productivity during the melt season,
but microbial activity in "dirty ice" was not correlated with albedo and
varied widely throughout the season. While this link suggests the potential
for a remote-sensing approach to monitoring cryoconite hole biological
processes, very wide seasonal and spatial variability in net surface
productivity demonstrates the need for caution when extrapolating point
measurements of biological processes to larger temporal or spatial scales
Hydrogeological controls on microbial activity and habitability in the Precambrian continental crust
Ice sheets as a significant source of highly reactive nanoparticulate iron to the oceans
The Greenland and Antarctic Ice Sheets cover ~\n10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40–2.54?Tg per year in Greenland and 0.06–0.17?Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting
The potential of magnetic hyperthermia for triggering the differentiation of cancer cells
Magnetic hyperthermia is a potential technique for cancer therapy that exploits heat generated by magnetic nanoparticles to kill cancerous cells. Many studies have shown that magnetic hyperthermia is effective at killing cancer cells both in vitro and in vivo, however little attention has been paid to the cellular functioning of the surviving cells. We report here new evidence demonstrating the onset of thermally triggered differentiation in osteosarcoma cancer cells that survive magnetic hyperthermia treatment. This raises the possibility that in addition to causing cell death, magnetic hyperthermia could induce surviving cancer cells to form more mature cell types and thereby inhibit their capacity to self-renew. Such processes could prove to be as important as cell death when considering magnetic hyperthermia for treating cancer
- …