Spectrally pure heralded single photons by spontaneous four-wave mixing in a fiber: reducing impact of dispersion fluctuations

We model the spectral quantum-mechanical purity of heralded single photons from a photon-pair source based on nondegenerate spontaneous four-wave mixing taking the impact of distributed dispersion fluctuations into account. The considered photon-pair-generation scheme utilizes pump-pulse walk-off to produce pure heralded photons and phase matching is achieved through the dispersion properties of distinct spatial modes in a few-mode silica step-index fiber. We show that fiber-core-radius fluctuations in general severely impact the single-photon purity. Furthermore, by optimizing the fiber design we show that generation of single photons with very high spectral purity is feasible even in the presence of large core-radius fluctuations. At the same time, contamination from spontaneous Raman scattering is greatly mitigated by separating the single-photon frequency by more than 32 THz from the pump frequency

Quantitative Convergent Beam Electron Diffraction and Charge Density Studies

Very accurate low-order structure factors have been measured in copper, magnesium and strontium titanate using quantitative convergent beam electron diffraction (QCBED). The charge density distribution in these materials has been studied using the measured structure factors. The results have also been compared to ab initio density functional theory (DFT) calculations. In the case of copper, we combined our low-order structure factors with higher order γ-ray structure factors, in order to obtain a larger experimental data set for maximum entropy and multipole analysis. The results show that bond formation induces a large change in the 3d orbital radial function. As expected for metallic bonding, no asphericity of the orbitals has been observed. These results are in perfect agreement with DFT calculations. For magnesium it was shown that the anisotropic displacement parameters could be determined accurately from the low order QCBED data, if structure factors from DFT calculations were used as a static lattice reference. This data set was combined with X-ray structure factor measurements and used to test some commonly used DFT functionals and self interaction correction (SIC) schemes. It was found that the local density approximation combined with the SIC of Lundin and Eriksson (2001) gave the best agreement with experiments. Using this functional no non-nuclear maximum was found in beryllium, but not in magnesium.dr.ing.dr.ing

Cancer risk in long-term users of valproate: a population-based case-control study

Udgivelsesdato: 2009-JunBACKGROUND: Inhibitors of histone deacetylases (HDAC) have shown promise as targeted cancer therapy. Valproate, an older anticonvulsant, has been shown to possess HDAC inhibitory activity. We undertook this case-control study to clarify whether long-term users of valproate had a reduced cancer incidence. If so, it would support HDAC inhibition as a pharmacologic principle in chemoprevention. METHODS: We identified 149,417 incident cancer cases in Denmark during the study period 2000 through 2005, and 597,668 age- and gender-matched controls. Data on history of cancer, past hospital admission diagnoses, and prescription history were obtained from the Danish Cancer Registry, the Danish National Patient Registry, and the Danish Prescription Registry. Primary exposure to valproate was defined as a cumulative dose of minimum 1,500 g within the past 5 years. Confounders were controlled by conditional logistic regression. RESULTS: Among the cases and controls, 81 (0.05%) and 260 (0.04%), respectively, were long-term users of valproate. For cancer overall, the crude and adjusted odds ratios were 1.25 [95% confidence interval (95% CI), 0.97-1.60] and 1.21 (95% CI, 0.95-1.56), respectively. Subgroup analyses revealed no dose or duration effect for overall cancer incidence, and no specific cancer site was found to be inversely associated with long-term use of valproate. For lung cancer, we found a positive but imprecise association (adjusted odds ratio, 2.32; 95% CI, 1.12-4.79). CONCLUSION: Long-term valproate use is not associated with a reduced cancer risk. Our study does not support HDAC inhibition as a pharmacologic principle for general chemoprevention

An azumamide C analogue without the zinc-binding functionality

Histone deacetylase (HDAC) inhibitors have attracted considerable attention due to their promise as therapeutic agents.</p