207 research outputs found
Probing the truncation of galaxy dark matter halos in high density environments from hydrodynamical N-body simulations
We analyze high resolution, N-body hydrodynamical simulations of fiducial
galaxy clusters to probe tidal stripping of the dark matter subhalos. These
simulations include a prescription for star formation allowing us to track the
fate of the stellar component as well. We investigate the effect of tidal
stripping on cluster galaxies hosted in these dark matter subhalos as a
function of cluster-centric radius. To quantify the extent of the dark matter
halos of cluster galaxies, we introduce the half mass radius r_half as a
diagnostic, and study its evolution with projected cluster-centric distance R
as a function of redshift. We find a well defined trend for (r_half,R): the
closer the galaxies are to the center of the cluster, the smaller the half mass
radius. Interestingly, this trend is inferred in all redshift frames examined
in this work ranging from z=0 to z=0.7. At z=0, galaxy halos in the central
regions of clusters are found to be highly truncated, with the most compact
half mass radius of 10 kpc. We also find that r_half depends on luminosity and
we present scaling relations of r_half with galaxy luminosity. The
corresponding total mass of the cluster galaxies is also found to increase with
projected cluster-centric distance and luminosity, but with more scatter than
the (r_half,R) trend. Comparing the distribution of stellar mass to total mass
for cluster galaxies, we find that the dark matter component is preferentially
stripped, whereas the stellar component remains protected by the halo and is
much less affected by tidal forces. We compare these results with galaxy-galaxy
lensing probes of r_half and find qualitative agreement. (Abridged)Comment: Accepted for publication in Ap
Comparison of photosensitivity in germanium doped silica fibers using 244 nm and 266 nm continuous wave lasers
Repetitive Activation of the Corticospinal Pathway by Means of rTMS may Reduce the Efficiency of Corticomotoneuronal Synapses
Low-frequency rTMS applied to the primary motor cortex (M1) may produce depression of motor-evoked potentials (MEPs). This depression is commonly assumed to reflect changes in cortical circuits. However, little is known about rTMS-induced effects on subcortical circuits. Therefore, the present study aimed to clarify whether rTMS influences corticospinal transmission by altering the efficiency of corticomotoneuronal (CM) synapses. The corticospinal transmission to soleus Îą-motoneurons was evaluated through conditioning of the soleus H-reflex by magnetic stimulation of either M1 (M1-conditioning) or the cervicomedullary junction (CMS-conditioning). The first facilitation of the H-reflex (early facilitation) was determined after M1- and CMS-conditioning. Comparison of the early facilitation before and after 20-min low-frequency (1 Hz) rTMS revealed suppression with M1- (â17 Âą 4%; P = 0.001) and CMS-conditioning (â6 Âą 2%; P = 0.04). The same rTMS protocol caused a significant depression of compound MEPs, whereas amplitudes of H-reflex and M-wave remained unaffected, indicating a steady level of motoneuronal excitability. Thus, the effects of rTMS are likely to occur at a premotoneuronal siteâeither at M1 and/or the CM synapse. As the early facilitation reflects activation of direct CM projections, the most likely site of action is the synapse of the CM neurons onto spinal motoneuron
Illusory Sensation of Movement Induced by Repetitive Transcranial Magnetic Stimulation
Human movement sense relies on both somatosensory feedback and on knowledge of the motor commands used to produce the movement. We have induced a movement illusion using repetitive transcranial magnetic stimulation over primary motor cortex and dorsal premotor cortex in the absence of limb movement and its associated somatosensory feedback. Afferent and efferent neural signalling was abolished in the arm with ischemic nerve block, and in the leg with spinal nerve block. Movement sensation was assessed following trains of high-frequency repetitive transcranial magnetic stimulation applied over primary motor cortex, dorsal premotor cortex, and a control area (posterior parietal cortex). Magnetic stimulation over primary motor cortex and dorsal premotor cortex produced a movement sensation that was significantly greater than stimulation over the control region. Movement sensation after dorsal premotor cortex stimulation was less affected by sensory and motor deprivation than was primary motor cortex stimulation. We propose that repetitive transcranial magnetic stimulation over dorsal premotor cortex produces a corollary discharge that is perceived as movement
Changes in corticospinal drive to spinal motoneurones following tablet-based practice of manual dexterity
The use of touch screens, which require a high level of manual dexterity, has exploded since the development of smartphone and tablet technology. Manual dexterity relies on effective corticospinal control of finger muscles, and we therefore hypothesized that corticospinal drive to finger muscles can be optimized by tabletâbased motor practice. To investigate this, sixteen ableâbodied females practiced a tabletâbased game (3Â ĂÂ 10Â min) with their nondominant hand requiring incrementally fast and precise pinching movements involving the thumb and index fingers. The study was designed as a semirandomized crossover study where the participants attended one practiceâ and one control session. Before and after each session electrophysiological recordings were obtained during three blocks of 50 precision pinch movements in a standardized setup resembling the practiced task. Data recorded during movements included electroencephalographic (EEG) activity from primary motor cortex and electromyographic (EMG) activity from first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles. Changes in the corticospinal drive were evaluated from coupling in the frequency domain (coherence) between EEGâEMG and EMGâEMG activity. Following motor practice performance improved significantly and a significant increase in EEGâEMG(APB) and EMG(APB)âEMG(FDI) coherence in the beta band (15â30Â Hz) was observed. No changes were observed after the control session. Our results show that tabletâbased motor practice is associated with changes in the common corticospinal drive to spinal motoneurons involved in manual dexterity. Tabletâbased motor practice may be a motivating training tool for stroke patients who struggle with loss of dexterity
Er naturzonen vÌrd at investere i - de sidste 25 ürs miljøøkonomiske vÌrdisÌtningsstudier i DK
Danskerne og velgørenhed anno 2013
Der synes at vĂŚre en regulĂŚr støjmur i det offentlige rum, som kommer til udtryk gennem øget kommunikation og markedsføring for at fĂĽ âtaletidâ hos forbrugerne.
Forbrugerne udvikler som en reaktion pĂĽ dette en stigende reklamelede og opbygger et âteflonâ lag, der gør at kommunikations- og marketingbudskaber har vanskeligt ved at bide sig fast i forbrugernes bevidsthed. Resultatet er, at det er blevet vanskeligere og dyrere at fĂĽ taletid hos forbrugeren, og samtidig opleves en faldende virkningsgrad af indsatsen.
Denne analyse ønsker at belyse de udfordringer og mulighed dette giver i relation til velgørenhed. Men lad os først starte med at definere begrebet âvelgørenhedâ, sĂĽ vi alle taler samme sprog
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