5,636 research outputs found
Cell bystander effect induced by radiofrequency electromagnetic fields and magnetic nanoparticles
Induced effects by direct exposure to ionizing radiation (IR) are a central
issue in many fields like radiation protection, clinic diagnosis and
oncological therapies. Direct irradiation at certain doses induce cell death,
but similar effects can also occur in cells no directly exposed to IR, a
mechanism known as bystander effect. Non-IR (radiofrequency waves) can induce
the death of cells loaded with MNPs in a focused oncological therapy known as
magnetic hyperthermia. Indirect mechanisms are also able to induce the death of
unloaded MNPs cells. Using in vitro cell models, we found that colocalization
of the MNPs at the lysosomes and the non-increase of the temperature induces
bystander effect under non-IR. Our results provide a landscape in which
bystander effects are a more general mechanism, up to now only observed and
clinically used in the field of radiotherapy.Comment: 16 pages, 4 figures, submitted to International Journal of Radiation
Biolog
Probing the stability of superheavy dark matter particles with high-energy neutrinos
Two of the most fundamental properties of the dark matter particle, the mass
and the lifetime, are only weakly constrained by the astronomical and
cosmological evidence of dark matter. We derive in this paper lower limits on
the lifetime of dark matter particles with masses in the range 10 TeV-10^15 TeV
from the non-observation of ultrahigh energy neutrinos in the AMANDA, IceCube,
Auger and ANITA experiments. For dark matter particles which produce neutrinos
in a two body or a three body decay, we find that the dark matter lifetime must
be longer than O(10^26-10^28) s for masses between 10 TeV and the Grand
Unification scale. Finally, we also calculate, for concrete particle physics
scenarios, the limits on the strength of the interactions that induce the dark
matter decay.Comment: 17 pages, 6 figures; v2: references added, discussion improved,
matches the version published at JCA
Protein adsorption onto Fe3O4 nanoparticles with opposite surface charge and its impact on cell uptake
Nanoparticles (NPs) engineered for biomedical applications are meant to be in
contact with protein-rich physiological fluids. These proteins are usually
adsorbed onto the NP surface, forming a swaddling layer called protein corona
that influences cell internalization. We present a study on protein adsorption
onto different magnetic NPs (MNPs) when immersed in cell culture medium, and
how these changes affect the cellular uptake. Two colloids with magnetite cores
of 25 nm, same hydrodynamic size and opposite surface charge were in situ
coated with (a) positive polyethyleneimine (PEI-MNPs) and (b) negative
poly(acrylic acid) (PAA-MNPs). After few minutes of incubation in cell culture
medium the wrapping of the MNPs by protein adsorption resulted in a 5-fold size
increase. After 24 h of incubation large MNP-protein aggregates with
hydrodynamic sizes 1500 to 3000 nm (PAA-MNPs and PEI-MNPs respectively) were
observed. Each cluster contained an estimated number of magnetic cores between
450 and 1000, indicating the formation of large aggregates with a "plum
pudding" structure of MNPs embedded into a protein network of negative surface
charge irrespective of the MNP_core charge. We demonstrated that PEI-MNPs are
incorporated in much larger amounts than the PAA-MNPs units. Quantitative
analysis showed that SH-SY5Y cells can incorporate 100 per cent of the added
PEI-MNPs up to about 100 pg per cell, whereas for PAA-MNPs the uptake was less
than 50 percent. The final cellular distribution showed also notable
differences regarding partial attachment to the cell membrane. These results
highlight the need to characterize the final properties of MNPs after protein
adsorption in biological media, and demonstrate the impact of these properties
on the internalization mechanisms in neural cells.Comment: 32 pages, 10 figure
Computing with cells: membrane systems - some complexity issues.
Membrane computing is a branch of natural computing which abstracts computing models from the structure and the functioning of the living cell. The main ingredients of membrane systems, called P systems, are (i) the membrane structure, which consists of a hierarchical arrangements of membranes which delimit compartments where (ii) multisets of symbols, called objects, evolve according to (iii) sets of rules which are localised and associated with compartments. By using the rules in a nondeterministic/deterministic maximally parallel manner, transitions between the system configurations can be obtained. A sequence of transitions is a computation of how the system is evolving. Various ways of controlling the transfer of objects from one membrane to another and applying the rules, as well as possibilities to dissolve, divide or create membranes have been studied. Membrane systems have a great potential for implementing massively concurrent systems in an efficient way that would allow us to solve currently intractable problems once future biotechnology gives way to a practical bio-realization. In this paper we survey some interesting and fundamental complexity issues such as universality vs. nonuniversality, determinism vs. nondeterminism, membrane and alphabet size hierarchies, characterizations of context-sensitive languages and other language classes and various notions of parallelism
On the Progenitor System of Nova V2491 Cygni
Nova V2491 Cyg is one of just two detected pre-outburst in X-rays. The light
curve of this nova exhibited a rare "re-brightening" which has been attributed
by some as the system being a polar, whilst others claim that a magnetic WD is
unlikely. By virtue of the nature of X-ray and spectroscopic observations the
system has been proposed as a recurrent nova, however the adoption of a 0.1 day
orbital period is generally seen as incompatible with such a system. In this
research note we address the nature of the progenitor system and the source of
the 0.1 day periodicity. Through the combination of Liverpool Telescope
observations with published data and archival 2MASS data we show that V2491
Cyg, at a distance of 10.5 - 14 kpc, is likely to be a recurrent nova of the U
Sco-class; containing a sub-giant secondary and an accretion disk, rather than
accretion directly onto the poles. We show that there is little evidence, at
quiescence, supporting a ~ 0.1 day periodicity, the variation seen at this
stage is likely caused by flickering of a re-established accretion disk. We
propose that the periodicity seen shortly after outburst is more likely related
to the outburst rather than the - then obscured - binary system. Finally we
address the distance to the system, and show that a significantly lower
distance (~ 2 kpc) would result in a severely under-luminous outburst, and as
such favour the larger distance and the recurrent nova scenario.Comment: 5 pages, 3 images, accepted for publication in A&A as a research not
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