Higher dimensional Calabi-Yau manifolds of Kummer type

Based on Cynk-Hulek method we construct complex Calabi-Yau varieties of arbitrary dimensions using elliptic curves with automorphism of order 6. Also we give formulas for Hodge numbers of varieties obtained from that construction. We shall generalize result of Katsura and Sch\"utt to obtain arbitrarily dimensional Calabi-Yau manifolds which are Zariski in any characteristic $p\not\equiv 1\pmod{12}.$Comment: 13 pages, 2 figure

Optically probing the fine structure of a single Mn atom in an InAs quantum dot

We report on the optical spectroscopy of a single InAs/GaAs quantum dot (QD) doped with a single Mn atom in a longitudinal magnetic field of a few Tesla. Our findings show that the Mn impurity is a neutral acceptor state A^0 whose effective spin J=1 is significantly perturbed by the QD potential and its associated strain field. The spin interaction with photo-carriers injected in the quantum dot is shown to be ferromagnetic for holes, with an effective coupling constant of a few hundreds of micro-eV, but vanishingly small for electrons.Comment: 5 pages, 3 figure

Efficient dynamical nuclear polarization in quantum dots: Temperature dependence

We investigate in micro-photoluminescence experiments the dynamical nuclear polarization in individual InGaAs quantum dots. Experiments carried out in an applied magnetic field of 2T show that the nuclear polarization achieved through the optical pumping of electron spins is increasing with the sample temperature between 2K and 55K, reaching a maximum of about 50%. Analysing the dependence of the Overhauser shift on the spin polarization of the optically injected electron as a function of temperature enables us to identify the main reasons for this increase.Comment: 5 pages, 3 figure

IMMUNE STATUS OF MICE TOLERANT OF LIVING CELLS : II. CONTINUOUS PRESENCE AND NATURE OF FACILITATION-ENHANCING ANTIBODIES IN TOLERANT ANIMALS

CBA mice were rendered highly tolerant to A/Jax cells by neonatal intravenous injections of (CBA x A)F1 spleen cells. The high degree of tolerance was ascertained by the absence of circulating antibodies detected in the sera by the usual tests and by the perfect state of A skin grafts during all the experiments. Tolerant sera (sera from tolerant animals) were studied at three periods of tolerance: before skin test grafting, from 2 to 11 wk after grafting, and at time of sacrifice at almost 6 months of age. The tolerant sera were shown to have specific facilitation-enhancing properties promoting the take and growth of A/Jax sarcoma (SaI and /Sa 15091a grafted on normal CBA mice. These properties were present throughout the duration of the experiments, showing that they were not the result of a beginning interruption of tolerance. The tolerant sera, although lacking the usual serological properties (hemagglutination, hemolysis, cytotoxicity, passive cutaneous anaphylaxis) had, however, specific synergistic hemagglutinating properties (increasing the hemagglutinating titer of a reference immune serum). Antibodies giving direct specific hemagglutination could be extracted from spleens of 20% of highly tolerant mice. The tolerant sera were also found to contain more IgG1 and more IgA than normal sera while they contained normal quantities of the complement-fixing immunoglobulins IgG2 and IgM. Fractionation of tolerant sera on DEAE chromatography column confirmed the data concerning immunoglobulin classes and demonstrated direct specific serological activities undetected in unfractionated sera: a weak hemolysis in the most cationic fractions and a weak hemagglutination in the middle fractions. Synergistic hemagglutination, detected in unfractionated serum, was localized in fast anionic fractions containing high IgA concentration, along with facilitation-enhancing activity, thus confirming a link suggested previously between these three properties. The relation between immunological tolerance and facilitating antibodies was discussed in the light of the fact that antibodies, possibly of a particular class continuously present at low dose in the sera of highly tolerant animals, are able to transfer (at least partly) this state of tolerance provided a sensitive test system is utilized

A hybrid metal/semiconductor electron pump for quantum metrology

Electron pumps capable of delivering a current higher than 100pA with sufficient accuracy are likely to become the direct mise en pratique of the possible new quantum definition of the ampere. Furthermore, they are essential for closing the quantum metrological triangle experiment which tests for possible corrections to the quantum relations linking e and h, the electron charge and the Planck constant, to voltage, resistance and current. We present here single-island hybrid metal/semiconductor transistor pumps which combine the simplicity and efficiency of Coulomb blockade in metals with the unsurpassed performances of silicon switches. Robust and simple pumping at 650MHz and 0.5K is demonstrated. The pumped current obtained over a voltage bias range of 1.4mV corresponds to a relative deviation of 5e-4 from the calculated value, well within the 1.5e-3 uncertainty of the measurement setup. Multi-charge pumping can be performed. The simple design fully integrated in an industrial CMOS process makes it an ideal candidate for national measurement institutes to realize and share a future quantum ampere

Effective algebraic degeneracy

We prove that any nonconstant entire holomorphic curve from the complex line C into a projective algebraic hypersurface X = X^n in P^{n+1}(C) of arbitrary dimension n (at least 2) must be algebraically degenerate provided X is generic if its degree d = deg(X) satisfies the effective lower bound: d larger than or equal to n^{{(n+1)}^{n+5}}

Optical properties of an ensemble of G-centers in silicon

We addressed the carrier dynamics in so-called G-centers in silicon (consisting of substitutional-interstitial carbon pairs interacting with interstitial silicons) obtained via ion implantation into a silicon-on-insulator wafer. For this point defect in silicon emitting in the telecommunication wavelength range, we unravel the recombination dynamics by time-resolved photoluminescence spectroscopy. More specifically, we performed detailed photoluminescence experiments as a function of excitation energy, incident power, irradiation fluence and temperature in order to study the impact of radiative and non-radiative recombination channels on the spectrum, yield and lifetime of G-centers. The sharp line emitting at 969 meV ($\sim$1280 nm) and the broad asymmetric sideband developing at lower energy share the same recombination dynamics as shown by time-resolved experiments performed selectively on each spectral component. This feature accounts for the common origin of the two emission bands which are unambiguously attributed to the zero-phonon line and to the corresponding phonon sideband. In the framework of the Huang-Rhys theory with non-perturbative calculations, we reach an estimation of 1.6$\pm$0.1 \angstrom for the spatial extension of the electronic wave function in the G-center. The radiative recombination time measured at low temperature lies in the 6 ns-range. The estimation of both radiative and non-radiative recombination rates as a function of temperature further demonstrate a constant radiative lifetime. Finally, although G-centers are shallow levels in silicon, we find a value of the Debye-Waller factor comparable to deep levels in wide-bandgap materials. Our results point out the potential of G-centers as a solid-state light source to be integrated into opto-electronic devices within a common silicon platform