Stable operation of a synchronously pumped colliding-pulse mode-locked ring dye laser

Pulses of 100-fsec duration are obtained by synchronous pumping of a colliding-pulse ring dye laser with a mode-locked Ar+-ion laser. Stable operation of the synchronously pumped colliding-pulse mode-locked laser over hours was obtained by a suitable choice of the distance between the gain and the absorber in combination with an appro-priate pump-pulse sequence. Passive mode locking of a ring dye laser by the inter-action of two counterpropagating pulses in a thin sat-urable absorber (colliding-pulse mode locking) yields femtosecond laser pulses. ' In these lasers the gain medium (Rhodamine 6G) is pumped by a cw Ar+-ion laser. The saturable absorber (DODCI, 3,3-diethyl-oxadicarbocyanine iodide) synchronizes two counter-propagating pulses meeting in the absorber jet stream. The colliding pulses form a transient grating, which synchronizes and stabilizes the pulses.2 In order to ensure equal amplification for both counterpropagatin

Terahertz beats of vibrational modes studied by femtosecond coherent Raman spectroscopy

A recently developed femtosecond coherent Raman technique allows the measurement of Fourier transform coherent Raman spectra with high-frequency differences. The simultaneous excitation of different vibrational modes with a broad-band tunable driving force leads to a strong beating of the coherent Raman probe scattering. The high time resolution of the experimental set-up allows one to measure beat frequencies of more than 10 THz with high precision

Np95 interacts with de novo DNA methyltransferases, Dnmt3a and Dnmt3b, and mediates epigenetic silencing of the viral CMV promoter in embryonic stem cells

Recent studies have indicated that nuclear protein of 95 kDa (Np95) is essential for maintaining genomic methylation by recruiting DNA methyltransferase (Dnmt) 1 to hemi-methylated sites. Here, we show that Np95 interacts more strongly with regulatory domains of the de novo methyltransferases Dnmt3a and Dnmt3b. To investigate possible functions, we developed an epigenetic silencing assay using fluorescent reporters in embryonic stem cells (ESCs). Interestingly, silencing of the cytomegalovirus promoter in ESCs preceded DNA methylation and was strictly dependent on the presence of either Np95, histone H3 methyltransferase G9a or Dnmt3a and Dnmt3b. Our results indicate a regulatory role for Np95, Dnmt3a and Dnmt3b in mediating epigenetic silencing through histone modification followed by DNA methylation

Spectral structure and decompositions of optical states, and their applications

We discuss the spectral structure and decomposition of multi-photon states. Ordinarily `multi-photon states' and `Fock states' are regarded as synonymous. However, when the spectral degrees of freedom are included this is not the case, and the class of `multi-photon' states is much broader than the class of `Fock' states. We discuss the criteria for a state to be considered a Fock state. We then address the decomposition of general multi-photon states into bases of orthogonal eigenmodes, building on existing multi-mode theory, and introduce an occupation number representation that provides an elegant description of such states that in many situations simplifies calculations. Finally we apply this technique to several example situations, which are highly relevant for state of the art experiments. These include Hong-Ou-Mandel interference, spectral filtering, finite bandwidth photo-detection, homodyne detection and the conditional preparation of Schr\"odinger Kitten and Fock states. Our techniques allow for very simple descriptions of each of these examples.Comment: 12 page

Induction of severe hypoxemia and low lung recruitability for the evaluation of therapeutic ventilation strategies: a translational model of combined surfactant-depletion and ventilator-induced lung injury

Background: Models of hypoxemic lung injury caused by lavage-induced pulmonary surfactant depletion are prone to prompt recovery of blood oxygenation following recruitment maneuvers and have limited translational validity. We hypothesized that addition of injurious ventilation following surfactant-depletion creates a model of the acute respiratory distress syndrome (ARDS) with persistently low recruitability and higher levels of titrated "best" positive end-expiratory pressure (PEEP) during protective ventilation. Methods: Two types of porcine lung injury were induced by lung lavage and 3 h of either protective or injurious ventilation, followed by 3 h of protective ventilation (N = 6 per group). Recruitment maneuvers (RM) and decremental PEEP trials comparing oxygenation versus dynamic compliance were performed after lavage and at 3 h intervals of ventilation. Pulmonary gas exchange function, respiratory mechanics, and ventilator-derived parameters were assessed after each RM to map the course of injury severity and recruitability. Results: Lung lavage impaired respiratory system compliance (C-rs) and produced arterial oxygen tensions (PaO2) of 84 +/- 13 and 80 +/- 15 (FIO2 = 1.0) with prompt increase after RM to 270-395 mmHg in both groups. After subsequent 3 h of either protective or injurious ventilation, PaO2/FIO2 was 104 +/- 26 vs. 154 +/- 123 and increased to 369 +/- 132 vs. 167 +/- 87 mmHg in response to RM, respectively. After additional 3 h of protective ventilation, PaO2/FIO2 was 120 +/- 15 vs. 128 +/- 37 and increased to 470 +/- 68 vs. 185 +/- 129 mmHg in response to RM, respectively. Subsequently, decremental PEEP titration revealed that C-rs peaked at 36 +/- 10 vs. 25 +/- 5 ml/cm H2O with PEEP of 12 vs. 16 cmH(2)O, and PaO2/FIO2 peaked at 563 +/- 83 vs. 334 +/- 148 mm Hg with PEEP of 16 vs. 22 cmH(2)O in the protective vs. injurious ventilation groups, respectively. The large disparity of recruitability between groups was not reflected in the C-rs nor the magnitude of mechanical power present after injurious ventilation, once protective ventilation was resumed. Conclusion: Addition of transitory injurious ventilation after lung lavage causes prolonged acute lung injury with diffuse alveolar damage and low recruitability yielding high titrated PEEP levels. Mimicking lung mechanical and functional characteristics of ARDS, this porcine model rectifies the constraints of single-hit lavage models and may enhance the translation of experimental research on mechanical ventilation strategies

Turbulent transport in the scrape-off layer of Wendelstein 7-X

Turbulent transport is widely considered to be the main driver for cross-field transport in the scrape-off layer (SOL) of toroidal magnetized plasmas. Here, reciprocating Langmuir probes are employed to measure both the plasma profiles and the turbulent particle transport in the SOL of the Wendelstein 7-X stellarator. The relation between turbulent radial particle flux Γr and the local pressure gradient is often approximately linear across the entire SOL width, indicating that radial turbulence spreading is absent. This observation holds across a wide range of magnetic configurations and different plasma heating and density scenarios. The magnitude of the turbulent transport for a given gradient reveals a dependence on the magnetic configuration and the position in the SOL, which we relate to the cross-spectral characteristics of multi-tip floating potential measurements. Magnetic islands can add further complexity due to non-monotonic SOL profiles and the breaking of the transport-gradient relation. Finally, anomalous diffusion coefficients are determined from the probe measurements