Phase diagrams of the transverse Ising antiferromagnet in the presence of the longitudinal magnetic field

In this paper we study the critical behavior of the two-dimensional antiferromagnetic Ising model in both uniform longitudinal (H$H$) and transverse (Ω$\Omega$) magnetic fields. Using the effective-field theory (EFT) with correlation in single site clusters we calculate the phase diagrams in the H−T$H-T$ and Ω−T$\Omega -T$ planes for the square lattice. We have only found second order phase transitions for all values of fields and reentrant behavior was not observed.     

Standstill Electric Charge Generates Magnetostatic Field under Born-Infeld Electrodynamics

The Abelian Born-Infeld classical non-linear Electrodynamic has been used to investigate the electric and magnetostatic fields generated by a point-like electric charge at rest in an inertial frame. The results show a rich internal structure for the charge. Analytical solutions have also been found. Such fields configurations have been interpreted in terms of vacuum polarization and magnetic-like charges produced by the very high strengths of the electric field considered. Apparently non-linearity is responsible for the emergence of an anomalous magnetostatic field suggesting a possible connection to that created by a magnetic dipole composed of two magnetic charges with opposite signs. Consistently in situations where the Born-Infeld field strength parameter is free to become infinite, Maxwell’s regime takes over, the magnetic sector vanishes and the electric field assumes a Coulomb behavior with no trace of a magnetic component. The connection to other monopole solutions, like Dirac’s and ’tHooft’s Poliakov’s types are also discussed. Finally, some speculative remarks are presented in an attempt to explain such fields.     

Probing quantum-vacuum geometrical effects with cold atoms

The lateral Casimir-Polder force between an atom and a corrugated surface should allow one to study experimentally nontrivial geometrical effects in the electromagnetic quantum vacuum. Here, we derive the theoretical expression of this force in the scattering approach. We show that large corrections to the "proximity force approximation" could be measured using present-day technology with a Bose-Einstein condensate used as a vacuum field sensor.     

Vortex condensation in the dual Chern–Simons–Higgs model

The contribution of nontrivial vacuum (topological) excitations, more specifically vortex configurations of the self-dual Chern–Simons–Higgs model, to the functional partition function is considered. By using a duality transformation, we arrive at a representation of the partition function in terms of which explicit vortex degrees of freedom are coupled to a dual gauge field. By matching the obtained action to a field theory for the vortices, the physical properties of the model in the presence of vortex excitations are then studied. In terms of this field theory for vortices in the self-dual Chern–Simons–Higgs model, we determine the location of the critical value for the Chern–Simons parameter below which vortex condensation can happen in the system. The effects of self-energy quantum corrections to the vortex field are also considered.     

Effect of the ytterbium concentration on the upconversion luminescence of Yb3+/Er3+ co-doped PbO–GeO2–Ga2O3 glasses

The effect of Yb³⁺ concentration on the frequency upconversion (UPC) of Er³⁺ in PbO–GeO₂–Ga₂O₃ glasses is reported for the first time. Samples were prepared with 0.5 wt% of Er₂O₃ and different concentrations of Yb₂O₃ (1.0–5.0 wt%). The green (523 and 545 nm) and red (657 nm) emissions are observed under 980 nm diode laser excitation. The dependence of the frequency UPC emission intensity upon the excitation power was examined and the UPC mechanisms are discussed. An interesting characteristic of these glasses is the increase of the ratio of red to green emission, through an increase of the Yb³⁺ concentration due to an efficient energy transfer from Yb³⁺ to Er³⁺.     

Carbon Dots (C‐dots) from Cow Manure with Impressive Subcellular Selectivity Tuned by Simple Chemical Modification

Improved cellular selectivity for nucleoli staining was achieved by simple chemical modification of carbon dots (C‐dots) synthesized from waste carbon sources such as cow manure (or from glucose). The C‐dots were characterized and functionalized (amine‐passivated) with ethylenediamine, affording amide bonds that resulted in bright green fluorescence. The new modified C‐dots were successfully applied as selective live‐cell fluorescence imaging probes with impressive subcellular selectivity and the ability to selectively stain nucleoli in breast cancer cell lineages (MCF‐7). The C‐dots were also tested in four other cellular models and showed the same cellular selection in live‐cell imaging experiments.