Metallic magnetic nanoparticles

In this paper, we reviewed some relevant aspects of the magnetic properties of metallic nanoparticles with small size ( below 4 nm), covering the size effects in nanoparticles of magnetic materials, as well as the appearance of magnetism at the nanoscale in materials that are nonferromagnetic in bulk. These results are distributed along the text that has been organized around three important items: fundamental magnetic properties, different fabrication procedures, and characterization techniques. A general introduction and some experimental results recently obtained in Pd and Au nanoparticles have also been included. Finally, the more promising applications of magnetic nanoparticles in biomedicine are indicated. Special care was taken to complete the literature available on the subject

Two dimensional electron gas confined over a spherical surface: Magnetic moment

Magnetism of capped nanoparticles, NPs, of non- magnetic substances as Au and ZnO is briefly reviewed. The source of the magnetization is discussed on the light of recent X-ray magnetic circular dichroism experiments. As magnetic dichroism analysis has pointed out impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. It is proposed that mesoscopic collective orbital magnetic moments induced at the surface states can account for the experimental magnetism characteristic of these nanoparticles. The total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 10(2) or 10(3) Bohr magnetons

Punishment Feedback Impairs Memory and Changes Cortical Feedback-Related Potentials During Motor Learning

© Copyright © 2020 Hill, Stringer, Waddell and Del Arco. Reward and punishment have demonstrated dissociable effects on motor learning and memory, which suggests that these reinforcers are differently processed by the brain. To test this possibility, we use electroencephalography to record cortical neural activity after the presentation of reward and punishment feedback during a visuomotor rotation task. Participants were randomly placed into Reward, Punishment, or Control groups and performed the task under different conditions to assess the adaptation (learning) and retention (memory) of the motor task. These conditions featured an incongruent position between the cursor and the target, with the cursor trajectory, rotated 30° counterclockwise, requiring the participant to adapt their movement to hit the target. Feedback based on error magnitude was provided during the Adaptation condition in the form of a positive number (Reward) or negative number (Punishment), each representing a monetary gain or loss, respectively. No reinforcement or visual feedback was provided during the No Vision condition (retention). Performance error and event-related potentials (ERPs) time-locked to feedback presentation were calculated for each participant during both conditions. Punishment feedback reduced performance error and promoted faster learning during the Adaptation condition. In contrast, punishment feedback increased performance error during the No Vision condition compared to Control and Reward groups, which suggests a diminished motor memory. Moreover, the Punishment group showed a significant decrease in the amplitude of ERPs during the No Vision condition compared to the Adaptation condition. The amplitude of ERPs did not change in the other two groups. These results suggest that punishment feedback impairs motor retention by altering the neural processing involved in memory encoding. This study provides a neurophysiological underpinning for the dissociative effects of punishment feedback on motor learning

Shearwater Eggs in Lobos 3, a Holocene Site of Fuerteventura (Canary Islands)

Two eggs (L29 and N28) were recovered in the Holocene site of Lobos 3, (Islote de Lobos, north Fuerteventura, Canary Islands), the site has been interpreted as a purple dye workshop from the Early Roman Empire Epoch. For the first time, eggs from a Holocene deposit of the Canary Islands have been analyzed in terms of size, shape, and biomineral structure, and studied on the basis of several thin sections and SEM analysis. The analysis of the remains allowed the assignation of both eggs to Procellariidae birds, thanks to the relative proportion of the eggshell layers and the vesiculation patterns. The size of the eggs allowed the assignation of L29 to cf. Calonectris/Puffinus, and to cf. Puffinus for N28. The absence of more structural analysis on Procellariiformes eggshells prevent a more specific assignation. The accumulation pattern of the eggs is compatible with a seasonal occupation pattern of the Roman site

Spin-wave excitations in ribbon-shaped Fe nanoparticles

It has been found that in highly anisometric ribbon-shaped Fe particles with nanoscale dimensions that the magnetization decreases with temperature markedly faster than in bulk bcc Fe. This anomalous dependence, which becomes more remarkable as the length-to-cross section ratio increases, arises from the elongated shape of the particles. The analytical approximation performed on the thermal spectrum of magnons, compatible with the sample dimensions, unravels the correlated influences of shape and size on the thermal decreasing rate of magnetization

Mechanically driven alloying of immiscible elements (Comment)

In conclusion we have proven that the fact that both fcc FeCu and bcc Fe magnetization agree at 300 K is simply an accident and our data at low temperature show clearly that the Fe contribution after precipitation from the metastable phase has a deficiency in magnetization of at least 20% with respect to the Fe state in fcc FeCu metastable solid solution