275 research outputs found
Bats Use Magnetite to Detect the Earth's Magnetic Field
While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a “compass organelle” containing the iron oxide particles magnetite (Fe3O4). Bats have recently been shown to use magnetic cues for compass orientation but the method by which they detect the Earth's magnetic field remains unknown. Here we use the classic “Kalmijn-Blakemore” pulse re-magnetization experiment, whereby the polarity of cellular magnetite is reversed. The results demonstrate that the big brown bat Eptesicus fuscus uses single domain magnetite to detect the Earths magnetic field and the response indicates a polarity based receptor. Polarity detection is a prerequisite for the use of magnetite as a compass and suggests that big brown bats use magnetite to detect the magnetic field as a compass. Our results indicate the possibility that sensory cells in bats contain freely rotating magnetite particles, which appears not to be the case in birds. It is crucial that the ultrastructure of the magnetite containing magnetoreceptors is described for our understanding of magnetoreception in animals
On the Energy Transfer Performance of Mechanical Nanoresonators Coupled with Electromagnetic Fields
We study the energy transfer performance in electrically and magnetically
coupled mechanical nanoresonators. Using the resonant scattering theory, we
show that magnetically coupled resonators can achieve the same energy transfer
performance as for their electrically coupled counterparts, or even outperform
them within the scale of interest. Magnetic and electric coupling are compared
in the Nanotube Radio, a realistic example of a nano-scale mechanical
resonator. The energy transfer performance is also discussed for a newly
proposed bio-nanoresonator composed of a magnetosomes coated with a net of
protein fibers.Comment: 9 Pages, 3 Figure
No alignment of cattle along geomagnetic field lines found
This paper presents a study of the body orientation of domestic cattle on
free pastures in several European states, based on Google satellite
photographs. In sum, 232 herds with 3412 individuals were evaluated. Two
independent groups participated in our study and came to the same conclusion
that, in contradiction to the recent findings of other researchers, no
alignment of the animals and of their herds along geomagnetic field lines could
be found. Several possible reasons for this discrepancy should be taken into
account: poor quality of Google satellite photographs, difficulties in
determining the body axis, selection of herds or animals within herds, lack of
blinding in the evaluation, possible subconscious bias, and, most importantly,
high sensitivity of the calculated main directions of the Rayleigh vectors to
some kind of bias or to some overlooked or ignored confounder. This factor
could easily have led to an unsubstantiated positive conclusion about the
existence of magnetoreception.Comment: Added electronic supplement with source dat
Carbon and climate system coupling on timescales from the Precambrian to the Anthropocene
Author Posting. © Annual Reviews, 2007. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 32 (2007): 31-66, doi:10.1146/annurev.energy.32.041706.124700.The global carbon and climate systems are closely intertwined, with
biogeochemical processes responding to and driving climate variations. Over a range of
geological and historical time-scales, warmer climate conditions are associated with
higher atmospheric levels of CO2, an important climate-modulating greenhouse gas. The
atmospheric CO2-temperature relationship reflects two dynamics, the planet’s climate
sensitivity to a perturbation in atmospheric CO2 and the stability of non-atmospheric
carbon reservoirs to evolving climate. Both exhibit non-linear behavior, and coupled
carbon-climate interactions have the potential to introduce both stabilizing and
destabilizing feedback loops into the Earth System. Here we bring together evidence
from a wide range of geological, observational, experimental and modeling studies on the
dominant interactions between the carbon cycle and climate. The review is organized by
time-scale, spanning interannual to centennial climate variability, Holocene millennial
variations and Pleistocene glacial-interglacial cycles, and million year and longer
variations over the Precambrian and Phanerozoic. Our focus is on characterizing and,
where possible quantifying, the emergent behavior internal to the coupled carbon-climate
system as well as the responses of the system to external forcing from tectonics, orbital
dynamics, catastrophic events, and anthropogenic fossil fuel emissions. While there are
many unresolved uncertainties and complexity in the carbon cycle, one emergent
property is clear across time scales: while CO2 can increase in the atmosphere quickly,
returning to lower levels through natural processes is much slower, so the consequences
of the human perturbation will far outlive the emissions that caused them.S. Doney acknowledges support from the NSF Geosciences Carbon and Water program
(NSF ATM-0628582) and the WHOI W. Van Alan Clark Sr. Chair. D. Schimel
acknowledges support from the NSF Biocomplexity in the Environment program (NSF
EAR-0321918)
Information storing by biomagnetites
Since the discovery of the presence of biogenic magnetites in living
organisms, there have been speculations on the role that these biomagnetites
play in cellular processes. It seems that the formation of biomagnetite
crystals is a universal phenomenon and not an exception in living cells. Many
experimental facts show that features of organic and inorganic processes could
be indistinguishable at nanoscale levels. Living cells are quantum "devices"
rather than simple electronic devices utilizing only the charge of conduction
electrons. In our opinion, due to their unusual biophysical properties, special
biomagnetites must have a biological function in living cells in general and in
the brain in particular. In this paper we advance a hypothesis that while
biomagnetites are developed jointly with organic molecules and cellular
electromagnetic fields in cells, they can record information about the Earth's
magnetic vector potential of the entire flight in migratory birds.Comment: 17 pages, 3 figure
Safety Implications of High-Field MRI: Actuation of Endogenous Magnetic Iron Oxides in the Human Body
Background: Magnetic Resonance Imaging scanners have become ubiquitous in hospitals and high-field systems (greater than 3 Tesla) are becoming increasingly common. In light of recent European Union moves to limit high-field exposure for those working with MRI scanners, we have evaluated the potential for detrimental cellular effects via nanomagnetic actuation of endogenous iron oxides in the body.Methodology: Theoretical models and experimental data on the composition and magnetic properties of endogenous iron oxides in human tissue were used to analyze the forces on iron oxide particles.Principal Finding and Conclusions: Results show that, even at 9.4 Tesla, forces on these particles are unlikely to disrupt normal cellular function via nanomagnetic actuation
Magnetism, FeS colloids, and Origins of Life
A number of features of living systems: reversible interactions and weak
bonds underlying motor-dynamics; gel-sol transitions; cellular connected
fractal organization; asymmetry in interactions and organization; quantum
coherent phenomena; to name some, can have a natural accounting via
interactions, which we therefore seek to incorporate by expanding the horizons
of `chemistry-only' approaches to the origins of life. It is suggested that the
magnetic 'face' of the minerals from the inorganic world, recognized to have
played a pivotal role in initiating Life, may throw light on some of these
issues. A magnetic environment in the form of rocks in the Hadean Ocean could
have enabled the accretion and therefore an ordered confinement of
super-paramagnetic colloids within a structured phase. A moderate H-field can
help magnetic nano-particles to not only overcome thermal fluctuations but also
harness them. Such controlled dynamics brings in the possibility of accessing
quantum effects, which together with frustrations in magnetic ordering and
hysteresis (a natural mechanism for a primitive memory) could throw light on
the birth of biological information which, as Abel argues, requires a
combination of order and complexity. This scenario gains strength from
observations of scale-free framboidal forms of the greigite mineral, with a
magnetic basis of assembly. And greigite's metabolic potential plays a key role
in the mound scenario of Russell and coworkers-an expansion of which is
suggested for including magnetism.Comment: 42 pages, 5 figures, to be published in A.R. Memorial volume, Ed
Krishnaswami Alladi, Springer 201
Genomic Expansion of Magnetotactic Bacteria Reveals an Early Common Origin of Magnetotaxis with Lineage-specific Evolution
The origin and evolution of magnetoreception, which in diverse prokaryotes and protozoa is known as magnetotaxis and enables these microorganisms to detect Earth’s magnetic field for orientation and navigation, is not well understood in evolutionary biology. The only known prokaryotes capable of sensing the geomagnetic field are magnetotactic bacteria (MTB), motile microorganisms that biomineralize intracellular, membrane-bounded magnetic single-domain crystals of either magnetite (Fe3O4) or greigite (Fe3S4) called magnetosomes. Magnetosomes are responsible for magnetotaxis in MTB. Here we report the first large-scale metagenomic survey of MTB from both northern and southern hemispheres combined with 28 genomes from uncultivated MTB. These genomes expand greatly the coverage of MTB in the Proteobacteria, Nitrospirae, and Omnitrophica phyla, and provide the first genomic evidence of MTB belonging to the Zetaproteobacteria and “Candidatus Lambdaproteobacteria” classes. The gene content and organization of magnetosome gene clusters, which are physically grouped genes that encode proteins for magnetosome biosynthesis and organization, are more conserved within phylogenetically similar groups than between different taxonomic lineages. Moreover, the phylogenies of core magnetosome proteins form monophyletic clades. Together, these results suggest a common ancient origin of iron-based (Fe3O4 and Fe3S4) magnetotaxis in the domain Bacteria that underwent lineage-specific evolution, shedding new light on the origin and evolution of biomineralization and magnetotaxis, and expanding significantly the phylogenomic representation of MTB
Protistan Diversity in the Arctic: A Case of Paleoclimate Shaping Modern Biodiversity?
The impact of climate on biodiversity is indisputable. Climate changes over geological time must have significantly influenced the evolution of biodiversity, ultimately leading to its present pattern. Here we consider the paleoclimate data record, inferring that present-day hot and cold environments should contain, respectively, the largest and the smallest diversity of ancestral lineages of microbial eukaryotes.We investigate this hypothesis by analyzing an original dataset of 18S rRNA gene sequences from Western Greenland in the Arctic, and data from the existing literature on 18S rRNA gene diversity in hydrothermal vent, temperate sediments, and anoxic water column communities. Unexpectedly, the community from the cold environment emerged as one of the richest observed to date in protistan species, and most diverse in ancestral lineages.This pattern is consistent with natural selection sweeps on aerobic non-psychrophilic microbial eukaryotes repeatedly caused by low temperatures and global anoxia of snowball Earth conditions. It implies that cold refuges persisted through the periods of greenhouse conditions, which agrees with some, although not all, current views on the extent of the past global cooling and warming events. We therefore identify cold environments as promising targets for microbial discovery
- …