Monitoring and analysis of anomalous refraction using a digital zenith camera system

Context. Anomalous refraction is considered to be a limiting factor for ground-based astrometry in general and astrogeodetic observations in particular. Typical characteristics of anomalous refraction are basically known by means of spot-check-data, however the fluctuation is rather little studied. Aims. The goal of this study is to derive empirical knowledge on the fluctuation of anomalous refraction in the optical domain. Methods. A Digital Zenith Camera System usually applied for the astrogeodetic determination of the Earth's gravity field has been used for continuously monitoring anomalous refraction. With a sample frequency of about 2 observations per minute, about 7300 single observation epochs were collected during 6 nights. Residuals of the observations with respect to reference data show how anomalous refraction behaves. Results. The analysis of approximately 70 h of observational data reveals heterogeneous fluctuation patterns of anomalous refraction at the zenith. Wave-like and bump-like variations appear as well as slowly-changing, drift-like structures. With respect to its magnitude, the effect reaches from 0."05 up to about 0."2 at frequencies of some hours. Even much lower frequencies of anomalous refraction are indicated in the data sets causing an offset of about 0."04. The accuracy of the filtered data has been found to be about 0."05- 0."08. Conclusions. The study indicates how anomalous refraction may fluctuate. The results are considered to give an estimate of the accuracy limit for astrogeodetic and other absolute ground-based astrometric observations

An SU(N) Mott insulator of an atomic Fermi gas realized by large-spin Pomeranchuk cooling

The Hubbard model, containing only the minimum ingredients of nearest neighbor hopping and on-site interaction for correlated electrons, has succeeded in accounting for diverse phenomena observed in solid-state materials. One of the interesting extensions is to enlarge its spin symmetry to SU(N>2), which is closely related to systems with orbital degeneracy. Here we report a successful formation of the SU(6) symmetric Mott insulator state with an atomic Fermi gas of ytterbium (173Yb) in a three-dimensional optical lattice. Besides the suppression of compressibility and the existence of charge excitation gap which characterize a Mott insulating phase, we reveal an important difference between the cases of SU(6) and SU(2) in the achievable temperature as the consequence of different entropy carried by an isolated spin. This is analogous to Pomeranchuk cooling in solid 3He and will be helpful for investigating exotic quantum phases of SU(N) Hubbard system at extremely low temperatures.Comment: 20 pages, 6 figures, to appear in Nature Physic

Effect of a Transverse D.C. Electric Fields on Electrostatic lon-Cyclotron Wave Instability

Abstract The temporal evolution of the current-driven electrostatic ion-cyclotron (CDEIC) instability is investigated in presence of a transverse d.c. electric fields in a collisional magnetized plasma. The growth rate of the instability has the largest value at the mode frequency for the appropriate magnetic field (where the effect of a transverse d.c. electric fields is larger) when the electron drift velocity is less than the critical value for the CDEIC instability. The growth rate is also a sensitive function of electron collision frequency

Erythropoietin (EPO) increases myelin gene expression in CG4 oligodendrocyte cells through the classical EPO receptor

Erythropoietin (EPO) has protective effects in neurodegenerative and neuroinflammatory diseases, including in animal models of multiple sclerosis, where EPO decreases disease severity. EPO also promotes neurogenesis and is protective in models of toxic demyelination. In this study, we asked whether EPO could promote neurorepair by also inducing remyelination. In addition, we investigated whether the effect of EPO could be mediated by the classical erythropoietic EPO receptor (EPOR), since it is still questioned if EPOR is functional in non-hematopoietic cells. Using CG4 cells, a line of rat oligodendrocyte precursor cells, we found that EPO increases the expression of myelin genes (myelin oligodendrocyte glycoprotein (MOG) and myelin basic protein (MBP)). EPO had no effect in wild-type CG4 cells, which do not express EPOR, whereas it increased MOG and MBP expression in cells engineered to overexpress EPOR (CG4-EPOR). This was reflected in a marked increase in MOG protein levels, as detected by western blot. In these cells, EPO induced by 10-fold the early growth response gene 2 (Egr2), which is required for peripheral myelination. However, Egr2 silencing with a siRNA did not reverse the effect of EPO, indicating that EPO acts through other pathways. In conclusion, EPO induces the expression of myelin genes in oligodendrocytes and this effect requires the presence of EPOR. This study demonstrates that EPOR can mediate neuroreparative effects

Caloric Curves and Nuclear Expansion

Nuclear caloric curves have been analyzed using an expanding Fermi gas hypothesis to extract average nuclear densities. In this approach the observed flattening of the caloric curves reflects progressively increasing expansion with increasing excitation energy. This expansion results in a corresponding decrease in the density and Fermi energy of the excited system. For nuclei of medium to heavy mass apparent densities ~ 0.4 rho_0 are reached at the higher excitation energies.Comment: 4 pages, 3 figure

Quantum Computing and Quantum Simulation with Group-II Atoms

Recent experimental progress in controlling neutral group-II atoms for optical clocks, and in the production of degenerate gases with group-II atoms has given rise to novel opportunities to address challenges in quantum computing and quantum simulation. In these systems, it is possible to encode qubits in nuclear spin states, which are decoupled from the electronic state in the $^1$S$_0$ ground state and the long-lived $^3$P$_0$ metastable state on the clock transition. This leads to quantum computing scenarios where qubits are stored in long lived nuclear spin states, while electronic states can be accessed independently, for cooling of the atoms, as well as manipulation and readout of the qubits. The high nuclear spin in some fermionic isotopes also offers opportunities for the encoding of multiple qubits on a single atom, as well as providing an opportunity for studying many-body physics in systems with a high spin symmetry. Here we review recent experimental and theoretical progress in these areas, and summarise the advantages and challenges for quantum computing and quantum simulation with group-II atoms.Comment: 11 pages, 7 figures, review for special issue of "Quantum Information Processing" on "Quantum Information with Neutral Particles

Caloric curves and critical behavior in nuclei

Data from a number of different experimental measurements have been used to construct caloric curves for five different regions of nuclear mass. These curves are qualitatively similar and exhibit plateaus at the higher excitation energies. The limiting temperatures represented by the plateaus decrease with increasing nuclear mass and are in very good agreement with results of recent calculations employing either a chiral symmetry model or the Gogny interaction. This agreement strongly favors a soft equation of state. Evidence is presented that critical excitation energies and critical temperatures for nuclei can be determined over a large mass range when the mass variations inherent in many caloric curve measurements are taken into account.Comment: In response to referees comments we have improved the discussion of the figures and added a new figure showing the relationship between the effective level density and the excitation energy. The discussion has been reordered and comments are made on recent data which support the hypothesis of a mass dependence of caloric curve