940 research outputs found
Effects of radio-frequency fields on bacterial cell membranes and nematode temperature-sensitive mutants
Membrane-related bioeffects have been reported in response to both radio-frequency (RF) and extremely low-frequency (ELF) electromagnetic fields (EMFs), particularly in neural cells. We have tested whether RF fields might cause inner membrane leakage in ML35 E. coli cells, which express β-galactosidase (lacZ) constitutively, but lack the lacY permease required for substrate entry. The activity of lacZ (indicating substrate leakage through the inner cell membrane) was increased only slightly by RF exposure (1 GHz, 0.5 W) over 45 min. Since lacZ activity showed no further increase with a longer exposure time of 90 min, this suggests that membrane permeability per se is not significantly affected by RF fields, and that slight heating (≤ 0.1°C) could account for this small difference. Temperature-sensitive (ts) mutants of the nematode, Caenorhabditis elegans, are wild-type at 15°C but develop the mutant phenotype at 25°C; an intermediate temperature of 21°C results in a reproducible mixture of both phenotypes. For two ts mutants affecting transmembrane receptors (TRA-2 and GLP-1), RF exposure for 24 h during the thermocritical phase strongly shifts the phenotype mix at 21°C towards the mutant end of the spectrum. For ts mutants affecting nuclear proteins, such phenotype shifts appear smaller (PHA-1) or non-significant (LIN-39), apparently confirming suggestions that RF power is dissipated mainly in the plasma membrane of cells. However, these phenotype shifts are no longer seen when microwave treatment is applied at 21°C in a modified exposure apparatus that minimises the temperature difference between sham and exposed conditions. Like other biological effects attributed to microwaves in the C. elegans system, phenotype shifts in ts mutants appear to be an artefact caused by very slight heating
Is utilization of health services for HIV patients equal by socioeconomic status? Evidence from the Basque country
Access to ART and health services is guaranteed under universal coverage to improve life expectancy and quality of life for HIV patients. However, it remains unknown whether patients of different socioeconomic background equally use different types of health services
Damping of long-wavelength collective excitations in quasi-onedimensional Fermi liquids
The imaginary part of the exchange-correlation kernel in the longitudinal
current-current response function of a quasi-onedimensional Fermi liquid is
evaluated by an approximate decoupling in the equation of motion for the
current density, which accounts for processes of excitation of two
particle-hole pairs. The two-pair spectrum determines the intrinsic damping
rate of long-wavelength collective density fluctuations, which is calculated
and contrasted with a result previously obtained for a clean Luttinger liquid.Comment: 9 pages, no figures, Physica B in pres
Far-infrared absorption in parallel quantum wires with weak tunneling
We study collective and single-particle intersubband excitations in a system
of quantum wires coupled via weak tunneling. For an isolated wire with
parabolic confinement, the Kohn's theorem guarantees that the absorption
spectrum represents a single sharp peak centered at the frequency given by the
bare confining potential. We show that the effect of weak tunneling between two
parabolic quantum wires is twofold: (i) additional peaks corresponding to
single-particle excitations appear in the absorption spectrum, and (ii) the
main absorption peak acquires a depolarization shift. We also show that the
interplay between tunneling and weak perpendicular magnetic field drastically
enhances the dispersion of single-particle excitations. The latter leads to a
strong damping of the intersubband plasmon for magnetic fields exceeding a
critical value.Comment: 18 pages + 6 postcript figure
First V-notching experiment in the spiny lobster Palinurus elephas
V-notching tagging has been practiced for decades in juveniles and ovigerous females of the clawed lobsters Homarus americanus and H. gammarus as an effective conservation strategy in several European and US fisheries. For the first time a V-notch experimental study was conducted with the spiny lobster Palinurus elephas with the aims of: 1) assess survival of notched versus unnotched lobsters, 2) assess differences in the incidence of shell disease of notched and unnotched lobsters, and 3) assess the rate of notch loss (tag retention) with respect to molt frequency. A total of 36 wild young adults were housed in a tank of 10000 litres separated in three replicates of 12 lobsters each one. Half of individuals of each replicate were marked with a v-notch (side 1 cm long). Tank environmental conditions (temperature, salinity and dissolved oxygen) were controlled to mimic conditions in the wild. The experiment lasted 20 months. There were no significant differences in survival or health conditions of notched and unnotched specimens. After 15 months, all the indivudals had completed two molts and five of them have undergone the third one. After the second molt on average 25% of the notched area has been overgrown and lobsters with the third molt have overgrown 45% of the notched area. The performance of area, width and height of the V-notch tab for regulatory purposes are discusse
Practical recommendations for measuring rates of visual field change in glaucoma
To date, there has been a lack of evidence-based guidance on the frequency of visual field examinations required to identify clinically meaningful rates of change in glaucoma. The objective of this perspective is to provide practical recommendations for this purpose. The primary emphasis is on the period of time and number of examinations required to measure various rates of change in mean deviation (MD) with adequate statistical power. Empirical data were used to obtain variability estimates of MD while statistical modelling techniques derived the required time periods to detect change with various degrees of visual field variability. We provide the frequency of examinations per year required to detect different amounts of change in 2, 3 and 5 years. For instance, three examinations per year are required to identify an overall change in MD of 4 dB over 2 years in a patient with average visual field variability. Recommendations on other issues such as examination type, strategy and quality are also made
Generative models of the human connectome
The human connectome represents a network map of the brain's wiring diagram
and the pattern into which its connections are organized is thought to play an
important role in cognitive function. The generative rules that shape the
topology of the human connectome remain incompletely understood. Earlier work
in model organisms has suggested that wiring rules based on geometric
relationships (distance) can account for many but likely not all topological
features. Here we systematically explore a family of generative models of the
human connectome that yield synthetic networks designed according to different
wiring rules combining geometric and a broad range of topological factors. We
find that a combination of geometric constraints with a homophilic attachment
mechanism can create synthetic networks that closely match many topological
characteristics of individual human connectomes, including features that were
not included in the optimization of the generative model itself. We use these
models to investigate a lifespan dataset and show that, with age, the model
parameters undergo progressive changes, suggesting a rebalancing of the
generative factors underlying the connectome across the lifespan.Comment: 38 pages, 5 figures + 19 supplemental figures, 1 tabl
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