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We consider a model of two driven and collectively damped atoms with different quantum feedbacks. We find that the steady entanglement depends on the initial condition in the case of symmetric feedback but is independent of the initial condition in the case of nonsymmetric feedback. We also find that in the process of the transition from the symmetric feedback to the nonsymmetric feedback, the entanglement between the two atoms is discontinuous. Without the feedback ͑symmetric case͒, in the symmetric subspace the steady entanglement between the two atoms will be very small; then we apply a feedback just to one of the atoms ͑nonsymmetric case͒, the steady entanglement will increase greatly, which can reach C Ϸ 0.82. It is very interesting that if we withdraw the feedback, the strong steady entanglement will remain, i.e., the whole process is irreversible, and reminds us of the hysteresis phenomena.

Yttria-stabilized cubic zirconia has been studied at 300 K by use of Raman spectroscopy under uniaxial stress along the [001] and [111] directions. The main effects observed are the frequency shifts of the F2g-type Raman band at ∼610 cm−1 which vary linearly with the applied stress and tend to increase with Y2O3 concentration. Effective deformation potentials are determined for the F2g band. These potentials are necessary for strain characterization of stabilized cubic zirconia, in buffer or epitaxial film configurations. Polycrystalline yttria-stabilized tetragonal zirconia is likewise studied.

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Vision plays a critical role in guiding spatial navigation. A traditional view of the visual cortex is to compute a world-centered map of visual space, and visual neurons exhibit diverse tunings to simple or complex visual features. The neural representation of spatio-visual map in the visual cortex is thought to be transformed from spatial modulation signals at the hippocampal-entorhinal system. Although visual thalamic and cortical neurons have been shown to be modulated by spatial signals during navigation, the exact source of spatially modulated neurons within the visual circuit has never been identified, and the neural correlate underpinning a visuospatial or spatio-visual map remains elusive. To search for direct visuospatial and visuodirectional signals, here we record in vivo extracellular spiking activity in the secondary visual cortex (V2) from freely foraging rats in a naturalistic environment. We identify that V2 neurons forms a complete spatio-visual map with a wide range of spatial tunings, which resembles the classical spatial map that includes the place, head-direction, border, grid and conjunctive cells reported in the hippocampal-entorhinal network. These spatially tuned V2 neurons display stable responses to external visual cues, and are robust with respect to non-spatial environmental changes. Spatially and directionally tuned V2 neuronal firing persists in darkness, suggesting that this spatio-visual map is not completely dependent on visual inputs. Identification of functionally distinct spatial cell types in visual cortex expands its classical role of information coding beyond a retinotopic map of the eye-centered world.