ABSTRACT
Sources of magnetic fields-magnetic monopoles-have so far proven elusive as elementary particles. Condensed-matter physicists have recently proposed several scenarios of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin-ice state is argued to be well described by networks of aligned dipoles resembling solenoidal tubes-classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defects look like magnetic monopoles. We demonstrated, by diffuse neutron scattering, the presence of such strings in the spin ice dysprosium titanate (Dy2Ti2O7). This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate the density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.
ABSTRACT
Two experiments examined the effects of disrupting the temporal patterns that develop during sentence reading and listening. Sentences were presented either visually, one word at a time (Experiment 1) or as natural speech (Experiment 2). Half of the sentences were familiar (proverbs or idioms) while the other half were constructed anew for these experiments. Within half the sentences, there was an unexpected 600-ms delay between the final two words. In both modalities, the amplitude of the N400 component of the event-related brain potential (ERP) to sentence final words was larger for unfamiliar than familiar sentences. The results in the two modalities differed, however, in that a Contingent Negative Variation (CNV) developed during the delay interval in the visual modality, whereas in the auditory modality the delay was marked by an emitted potential. The present results show that temporal patterns are processed differently in natural speech and in reading words presented one at a time in the center of a computer screen.
