740 research outputs found
THE TURNING MOTION AND FORCES INVOLVED IN THE BACKSTROKE FLIP TURN
This study examined the backstroke turning motion. Twelve male and female subjects, including beginners and trained swimmers, performed backstroke flipturns. The time taken from 5m turn in to 2.5m turn out ranged from 4.25sec to 6.31sec. There was a significant difference between the beginners and trained subjects during the preparation and beginning of turn phases. The forces during the push off phase ranged from 1040.6N - 321.9N. Values for trained backstroke swimmers were approximately equal to 50% of the values for trained crawl swimmers (Takahashi 1983), and 100% for semi-trained crawl swimmers (Goya 1997). This study revealed that the streamlined position after push off might be a very important factor influencing the magnitude of kick off force and direction
Cell death induced by the application of alternating magnetic fields to nanoparticle-loaded dendritic cells
In this work, the capability of primary, monocyte-derived dendritic cells
(DCs) to uptake iron oxide magnetic nanoparticles (MNPs) is assessed and a
strategy to induce selective cell death in these MNP-loaded DCs using external
alternating magnetic fields (AMFs) is reported. No significant decrease in the
cell viability of MNP-loaded DCs, compared to the control samples, was observed
after five days of culture. The amount of MNPs incorporated into the cytoplasm
was measured by magnetometry, which confirmed that 1 to 5 pg of the particles
were uploaded per cell. The intracellular distribution of these MNPs, assessed
by transmission electron microscopy, was found to be primarily inside the
endosomic structures. These cells were then subjected to an AMF for 30 min, and
the viability of the blank DCs (i.e., without MNPs), which were used as control
samples, remained essentially unaffected. However, a remarkable decrease of
viability from approximately 90% to 2-5% of DCs previously loaded with MNPs was
observed after the same 30 min exposure to an AMF. The same results were
obtained using MNPs having either positive (NH2+) or negative (COOH-) surface
functional groups. In spite of the massive cell death induced by application of
AMF to MNP-loaded DCs, the amount of incorporated magnetic particles did not
raise the temperature of the cell culture. Clear morphological changes at the
cell structure after magnetic field application were observed using scanning
electron microscopy. Therefore, local damage produced by the MNPs could be the
main mechanism for the selective cell death of MNP-loaded DCs under an AMF.
Based on the ability of these cells to evade the reticuloendothelial system,
these complexes combined with an AMF should be considered as a potentially
powerful tool for tumour therapy.Comment: In Press. 33 pages, 11 figure
Application of magnetically induced hyperthermia on the model protozoan Crithidia fasciculata as a potential therapy against parasitic infections
Magnetic hyperthermia is currently an EU-approved clinical therapy against
tumor cells that uses magnetic nanoparticles under a time varying magnetic
field (TVMF). The same basic principle seems promising against trypanosomatids
causing Chagas disease and sleeping sickness, since therapeutic drugs available
display severe side effects and drug-resistant strains. However, no
applications of this strategy against protozoan-induced diseases have been
reported so far. In the present study, Crithidia fasciculata, a widely used
model for therapeutic strategies against pathogenic trypanosomatids, was
targeted with Fe_{3}O_{4} magnetic nanoparticles (MNPs) in order to remotely
provoke cell death using TVMFs. The MNPs with average sizes of d approx. 30 nm
were synthesized using a precipitation of FeSO_{4}4 in basic medium. The MNPs
were added to Crithidia fasciculata choanomastigotes in exponential phase and
incubated overnight. The amount of uploaded MNPs per cell was determined by
magnetic measurements. Cell viability using the MTT colorimetric assay and flow
cytometry showed that the MNPs were incorporated by the cells with no
noticeable cell-toxicity effects. When a TVMF (f = 249 kHz, H = 13 kA/m) was
applied to MNP-bearing cells, massive cell death was induced via a
non-apoptotic mechanism. No effects were observed by applying a TVMF on control
(without loaded MNPs) cells. No macroscopic rise in temperature was observed in
the extracellular medium during the experiments. Scanning Electron Microscopy
showed morphological changes after TVMF experiments. These data indicate (as a
proof of principle) that intracellular hyperthermia is a suitable technology to
induce the specific death of protozoan parasites bearing MNPs. These findings
expand the possibilities for new therapeutic strategies that combat parasitic
infections.Comment: 9 pages, four supplementary video file
Numerical Simulation of Magnetic Interactions in Polycrystalline YFeO3
The magnetic behavior of polycrystalline yttrium orthoferrite was studied
from the experimental and theoretical points of view. Magnetization
measurements up to 170 kOe were carried out on a single-phase YFeO3 sample
synthesized from heterobimetallic alkoxides. The complex interplay between
weak-ferromagnetic and antiferromagnetic interactions, observed in the
experimental M(H) curves, was successfully simulated by locally minimizing the
magnetic energy of two interacting Fe sublattices. The resulting values of
exchange field (H_E = 5590 kOe), anisotropy field (H_A = 0.5 kOe) and
Dzyaloshinsky-Moriya antisymmetric field (H_D = 149 kOe) are in good agreement
with previous reports on this system.Comment: 26 pages, 9 figure
Trajectories of objectively measured physical activity in free-living older men.
BACKGROUND: The steep decline in physical activity (PA) among the oldest old is not well understood; there is little information about the patterns of change in PA and sedentary behaviour (SB) in older people. Longitudinal data on objectively measured PA data can give insights about how PA and SB change with age.
METHODS: Men age 70-90 yr, from a United Kingdom population-based cohort wore a GT3X accelerometer over the hip annually on up to three occasions (56%, 50%, and 51% response rates) spanning 2 yr. Multilevel models were used to estimate change in activity. Men were grouped according to achieving ≥150 min·wk of MVPA in bouts of ≥10 min (current guidelines) at two or three time points.
RESULTS: A total of 1419 ambulatory men had ≥600 min wear time on ≥3 d at ≥2 time points. At baseline, men took 4806 steps per day and spent 72.5% of their day in SB, 23.1% in light PA, and 4.1% in moderate-to-vigorous PA (MVPA). Mean change per year was -341 steps, +1.1% SB, -0.7% light PA, and -0.4% MVPA each day (all P 30 min increased from 5.1 by 0.1 per year (P = 0.02).
CONCLUSIONS: Among older adults, the steep decline in total PA occurred because of reductions in MVPA, while light PA is relatively spared and sedentary time and long sedentary bouts increase
Validity of the N\'{e}el-Arrhenius model for highly anisotropic Co_xFe_{3-x}O_4 nanoparticles
We report a systematic study on the structural and magnetic properties of
Co_{x}Fe_{3-x}O_{4} magnetic nanoparticles with sizes between to nm,
prepared by thermal decomposition of Fe(acac)_{3} and Co(acac)_{2}. The large
magneto-crystalline anisotropy of the synthesized particles resulted in high
blocking temperatures ( K \leqq K for d nm ) and large coercive fields ( kA/m for K).
The smallest particles ( nm) revealed the existence of a magnetically
hard, spin-disordered surface. The thermal dependence of static and dynamic
magnetic properties of the whole series of samples could be explained within
the N\'{e}el-Arrhenius relaxation framework without the need of ad-hoc
corrections, by including the thermal dependence of the magnetocrystalline
anisotropy constant through the empirical Br\"{u}khatov-Kirensky
relation. This approach provided values very similar to the bulk
material from either static or dynamic magnetic measurements, as well as
realistic values for the response times ( s).
Deviations from the bulk anisotropy values found for the smallest particles
could be qualitatively explained based on Zener\'{}s relation between
and M(T)
Superconductivity and Magnetism in REFeAsO1-xFx (RE=Rare Earth Elements)
Fluoride-doped iron-based oxypnictides containing rare-earth gadolinium
(GdFeAsO0.8F0.2) and co-doping with yttrium (Gd0.8Y0.2FeAsO0.8F0.2) have been
prepared via conventional solid state reaction at ambient pressure. The
non-yttrium substituted oxypnictide show superconducting transition as high as
43.9 K from temperature dependent resistance measurements with the Meissner
effect observed at a lower temperature of 40.8 K from temperature dependent
magnetization measurements. By replacing a small amount of gadolinium with
yttrium Tc was observed to be lowered by 10 K which might be caused by a change
in the electronic or magnetic structures since the crystal structure was not
altered.Comment: 4 pages, 4 figures, Journal of Physics: Conference Series
(Proceedings in the LT25 Low Temperature Physics Conference) Submitte
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