Optomechanical Stochastic Resonance in a Macroscopic Torsion Oscillator

Linear mechanical oscillators have been applied to measure very small forces, mostly with the help of noise suppression. In contrast, adding noise to non-linear oscillators can improve the measurement conditions. Here, this effect of stochastic resonance is demonstrated in a macroscopic torsion oscillator, for an optomechanical non-linear potential. The signal output is enhanced for a sub-threshold electronic signal. This non-linear oscillator serves as a model system for the enhancement of signal-to-noise ratio in high precision optomechanical experiments.Comment: 4 pages (double column), 3 figure

Eddington limited starbursts in the central 10pc of AGN, and the Torus in NGC1068

We present results from a survey of nearby AGN using the near infrared adaptive optics integral field spectrograph SINFONI. These data enable us to probe the distribution and kinematics of the gas and stars at spatial resolutions as small as 0.085arcsec. We find strong evidence for recent but short lived starbursts residing in very dense nuclear disks. On scales of less than 10pc these would have reached Eddington-limited luminosities when active, perhaps accounting for their short duration. In addition, for NGC1068 at a resolution of 6pc, we present direct observations of molecular gas close around the AGN which we identify with the obscuring torus.Comment: Conference proceedings to appear in "The Central Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: ASP

Fine Structure of the 1s3p ^3P_J Level in Atomic ^4He: Theory and Experiment

We report on a theoretical calculation and a new experimental determination of the 1s3p ^3P_J fine structure intervals in atomic ^4He. The values from the theoretical calculation of 8113.730(6) MHz and 658.801(6) MHz for the nu_{01} and nu_{12} intervals, respectively, disagree significantly with previous experimental results. However, the new laser spectroscopic measurement reported here yields values of 8113.714(28) MHz and 658.810(18) MHz for these intervals. These results show an excellent agreement with the theoretical values and resolve the apparent discrepancy between theory and experiment.Comment: 9 pages, 3 figure

Low Energy States of 3181Ga50^{81}_{31} Ga_{50} : Elements on the Doubly-Magic Nature of 78^{78}Ni

Excited levels were attributed to $^{81}_{31}$Ga$_{50}$ for the first time which were fed in the $\beta$-decay of its mother nucleus $^{81}$Zn produced in the fission of $^{nat}$U using the ISOL technique. We show that the structure of this nucleus is consistent with that of the less exotic proton-deficient N=50 isotones within the assumption of strong proton Z=28 and neutron N=50 effective shell effects.Comment: 4 pages, REVTeX 4, 5 figures (eps format

Lausannevirus Encodes a Functional Dihydrofolate Reductase Susceptible to Proguanil.

Lausannevirus belongs to the family Marseilleviridae within the group of nucleocytoplasmic large DNA viruses (NCLDVs). These giant viruses exhibit unique features, including a large genome, ranging from 100 kb to 2.5 Mb and including from 150 to more than 2,500 genes, as well as the presence of genes coding for proteins involved in transcription and translation. The large majority of Lausannevirus open reading frames have unknown functions. Interestingly, a bifunctional dihydrofolate reductase-thymidylate synthase (DHFR-TS) is encoded in the Lausannevirus genome. The enzyme plays central roles in DNA precursor biosynthesis. DHFR is the pharmacological target of antifolates, such as trimethoprim, pyrimethamine, and proguanil. First, the functionality of Lausannevirus DHFR-TS was demonstrated by the successful complementation of a DHFR-deficient Saccharomyces cerevisiae strain with a plasmid expressing the heterologous gene. Additionally, using this heterologous expression system, we demonstrated the in vitro susceptibility of Lausannevirus DHFR-TS to proguanil and its resistance to pyrimethamine and trimethoprim. Proguanil may provide a unique and useful treatment if Lausannevirus proves to be a human pathogen. To our knowledge, this is the first time that a DHFR-TS has been described and characterized in an NCLDV

Observation of opto-mechanical multistability in a high Q torsion balance oscillator

We observe the opto-mechanical multistability of a macroscopic torsion balance oscillator. The torsion oscillator forms the moving mirror of a hemi-spherical laser light cavity. When a laser beam is coupled into this cavity, the radiation pressure force of the intra-cavity beam adds to the torsion wire's restoring force, forming an opto-mechanical potential. In the absence of optical damping, up to 23 stable trapping regions were observed due to local light potential minima over a range of 4 micrometer oscillator displacement. Each of these trapping positions exhibits optical spring properties. Hysteresis behavior between neighboring trapping positions is also observed. We discuss the prospect of observing opto-mechanical stochastic resonance, aiming at enhancing the signal-to-noise ratio (SNR) in gravity experiments.Comment: 4 pages, 5 figure