Enhanced cosmic-ray flux toward zeta Persei inferred from laboratory study of H3+ - e- recombination rate

The H3+ molecular ion plays a fundamental role in interstellar chemistry, as it initiates a network of chemical reactions that produce many interstellar molecules. In dense clouds, the H3+ abundance is understood using a simple chemical model, from which observations of H3+ yield valuable estimates of cloud path length, density, and temperature. On the other hand, observations of diffuse clouds have suggested that H3+ is considerably more abundant than expected from the chemical models. However, diffuse cloud models have been hampered by the uncertain values of three key parameters: the rate of H3+ destruction by electrons, the electron fraction, and the cosmic-ray ionisation rate. Here we report a direct experimental measurement of the H3+ destruction rate under nearly interstellar conditions. We also report the observation of H3+ in a diffuse cloud (towards zeta Persei) where the electron fraction is already known. Taken together, these results allow us to derive the value of the third uncertain model parameter: we find that the cosmic-ray ionisation rate in this sightline is forty times faster than previously assumed. If such a high cosmic-ray flux is indeed ubiquitous in diffuse clouds, the discrepancy between chemical models and the previous observations of H3+ can be resolved.Comment: 6 pages, Nature, in pres

Cdc28/Cdk1 Regulates Spindle Pole Body Duplication through Phosphorylation of Spc42 and Mps1

AbstractDuplication of the Saccharomyces cerevisiae spindle pole body (SPB) once per cell cycle is essential for bipolar spindle formation and accurate chromosome segregation during mitosis. We have investigated the role that the major yeast cyclin-dependent kinase Cdc28/Cdk1 plays in assembly of a core SPB component, Spc42, to better understand how SPB duplication is coordinated with cell cycle progression. Cdc28 is required for SPB duplication and Spc42 assembly, and we found that Cdc28 directly phosphorylates Spc42 to promote its assembly into the SPB. The Mps1 kinase, previously shown to regulate Spc42 phosphorylation and assembly, is also a Cdc28 substrate, and Cdc28 phosphorylation of Mps1 is needed to maintain wild-type levels of Mps1 in cells. Analysis of nonphosphorylatable mutants in SPC42 and MPS1 indicates that direct Spc42 phosphorylation and indirect regulation of Spc42 through Mps1 are two overlapping pathways by which Cdc28 regulates Spc42 assembly and SPB duplication during the cell cycle

INFRARED CAVITY RINGDOWN SPECTROSCOPY OF JET-COOLED PAHS: A COMPARISON WITH MATRIX SPECTRA

Author Institution: Department of Chemistry, University of California; Department of Chemistry, National Tsing Hua UniversityInfrared absorption spectra of the CH stretching region were observed for naphthalene, anthracene, phenanthrene, pyrene, and perylene using a heated supersonic slit source and cavity ringdown spectroscopy. Results are compared closely with 10 K Ar matrix spectra to detemine general matrix perturbation effects for this class of molecules. Fundamental transitions in the matrix spectra were subject to spectral shifts of up to $3.0 cm^{-1}$ and band widths were generally broader than the jet-cooled spectra by up to 80%. Weak features not predicted by theory were observed in both Ar matrix and gas-phase spectra with similar relative intensities which suggest assignment to overtones and combination bands

The "Myth" of the Minimum SAR Antenna Area Constraint

A design constraint traceable ot the early days of spaceborne Synthetic Aperture Radar (SAR) is known as the minimum antenna area constraint for SAR. In this paper, it is confirmed that this constraint strictly applies only to the case where both the best possible resolution and the widest possible swath are the design goals. SAR antennas with area smaller than the constraint allows are shown to be possible, have been used on spaceborne SAR missions in the past, and should permit further, lower-cost SAR mission in the future

GENERATION OF INFRARED RADIATION BY STIMULATED RAMAN SCATTERING IN LIQUID AND SOLID PARAHYDROGEN

$^{a}$email: [email protected] Institution: Department of Chemistry, University of California at Berkeley; Department of Chemistry, University of Chicago; Division of Chemistry, Graduate School of Science, Kyoto UniversityWe report the results of our preliminary investigations into the suitability of condensed phase parahydrogen as a Raman-shifting medium for the generation of tunable infrared radiation for cavity ringdown laser absorption spectroscopy (CR-LAS). We have observed the conversion of $\sim 10$ ns pulses of 532 nm radiation into first-, second-, and third-order vibrational Stokes radiation in bulk liquid and solid parahydrogen after a single 11-cm pass. Surprisingly, we find that liquid-$H_{2}$ yields more efficient conversion than solid-$H_{2}$ with certain focal geometries, and that in the case of the solid, a collimated or loosely focused pump geometry is more efficient than a tight focus. We also will discuss our more recent studies of Raman shifting using the longer $({\sim} 100 ns)$ pulses of an alexandrite laser

Thermodynamic treatment of oligonucleotide duplex–simplex equilibria

Thermodynamic formulations have been devised to obtain ΔG° values directly from spectroscopic data at a fixed common temperature in nucleic acid duplex–simplex melting curves. In addition, the dependence of melting on salt concentration has been expressed in terms of a stepwise stoichiometric representation, which leads to a specific equation for the partition of the added sodium ions between the different oligonucleotide forms

ENHANCED COSMIC-RAY FLUX TOWARD ζ\zeta PERSEI INFERRED FROM STORAGE RING MEASUREMENT OF DISSOCIATIVE RECOMBINATION RATE OF ROTATIONALLY COLD H3+H^{+}_{3}

$^{a}$email: [email protected] Institution: Department of Chemistry, University of California at Berkeley; Department of Chemistry, Gemini Observatory; Department of Chemistry, JILA, University of Colorado and NIST; Department of Chemistry, Institute of Physics, \'{S}wietokrzyska Academy; Department of Physics, SCFAB, Stockholm University; Manne Siegbahn Laboratory, Stockholm University; Department of Physics, SCFAB, Stockholm UniversityThe $H^{+}_{3}$ molecular ion plays a fundamental role in interstellar chemistry, as it initiates a network of chemical reactions that produce many interstellar molecules. In dense clouds, the $H_{3}^{+}$ abundance is understood using a simple chemical model, from which observations of $H_{3}^{+}$ yield valuable estimates of cloud path length, density, and temperature. On the other hand, observations of diffuse clouds have suggested that $H_{3}^{+}$ is considerably more abundant than expected from the chemical models. However, diffuse cloud models have been hampered by the uncertain values of three key parameters: the rate of $H_{3}^{+}$ destruction by electrons, the electron fraction, and the cosmic-ray ionization rate. Here we report a direct experimental measurement of the $H_{3}^{+}$ dissociative recombination rate under nearly interstellar conditions, using a supersonic expansion discharge source that has been shown (using cavity ringdown spectroscopy) to produce rotationally cold $H_{3}^{+}$ ions. We also report the observation of $H_{3}^{+}$ in a diffuse cloud (towards $\zeta$ Persei) where the electron fraction is already known from ultraviolet spectroscopy. Taken together, these results allow us to derive the value of the third uncertain model parameter: we find that the cosmic-ray ionization rate in this sightline is forty times faster than previously assumed. If such a high cosmic-ray flux is indeed ubiquitous in diffuse clouds, the discrepancy between chemical models and the previous observations of $H_{3}^{+}$ can be resolved