On bi-integrable natural Hamiltonian systems on the Riemannian manifolds

We introduce the concept of natural Poisson bivectors, which generalizes the Benenti approach to construction of natural integrable systems on the Riemannian manifolds and allows us to consider almost the whole known zoo of integrable systems in framework of bi-hamiltonian geometry.Comment: 24 pages, LaTeX with AMSfonts (some new references were added

Probing structural relaxation in complex fluids by critical fluctuations

Complex fluids, such as polymer solutions and blends, colloids and gels, are of growing interest in fundamental and applied soft-condensed-matter science. A common feature of all such systems is the presence of a mesoscopic structural length scale intermediate between atomic and macroscopic scales. This mesoscopic structure of complex fluids is often fragile and sensitive to external perturbations. Complex fluids are frequently viscoelastic (showing a combination of viscous and elastic behaviour) with their dynamic response depending on the time and length scales. Recently, non-invasive methods to infer the rheological response of complex fluids have gained popularity through the technique of microrheology, where the diffusion of probe spheres in a viscoelastic fluid is monitored with the aid of light scattering or microscopy. Here we propose an alternative to traditional microrheology that does not require doping of probe particles in the fluid (which can sometimes drastically alter the molecular environment). Instead, our proposed method makes use of the phenomenon of "avoided crossing" between modes associated with the structural relaxation and critical fluctuations that are spontaneously generated in the system.Comment: 4 pages, 4 figure

Measurements of Isotope Effects in the Photoionization of N_2 and Implications for Titan's Atmosphere

Isotope effects in the non-dissociative photoionization of molecular nitrogen (N_2 + hν → N_2^+ + e^−) may play a role in determining the relative abundances of isotopic species containing nitrogen in interstellar clouds and planetary atmospheres but have not been previously measured. Measurements of the photoionization efficiency spectra of ^(14)N^2, ^(15)N^(14)N, and ^(15)N_2 from 15.5 to 18.9 eV (65.6–80.0 nm) using the Advanced Light Source at Lawrence Berkeley National Laboratory show large differences in peak energies and intensities, with the ratio of the energy-dependent photoionization cross sections, σ(^(14)N_2)/σ (^(15)N^(14)N), ranging from 0.4 to 3.5. Convolving the cross sections with the solar flux and integrating over the energies measured, the ratios of photoionization rate coefficients are J(^(15)N^(14)N)/J(^(14)N_2) = 1.00 ± 0.02 and J(^(15)N_2)/J(^(14)N_2) = 1.00 ± 0.02, suggesting that isotopic fractionation between N_2 and N_2^+ should be small under such conditions. In contrast, in a one-dimensional model of Titan’s atmosphere, isotopic self-shielding of ^(14)N_2 leads to values of J(^(15)N^(14)N)/J(^(14)N_2) as large as ~1.17, larger than under optically thin conditions but still much smaller than values as high as ~29 predicted for N_2 photodissociation. Since modeled photodissociation isotope effects overpredict the HC^(15)N/HC^(14)N ratio in Titan’s atmosphere, and since both N atoms and N_2^+ ions may ultimately lead to the formation of HCN, estimates of the potential of including N_2 photoionization to contribute to a more quantitative explanation of ^(15)N/^(14)N for HCN in Titan’s atmosphere are explored

Watson–Crick and Sugar-Edge Base Pairing of Cytosine in the Gas Phase: UV and Infrared Spectra of Cytosine·2-Pyridone

While keto-amino cytosine is the dominant species in aqueous solution, spectroscopic studies in molecular beams and in noble gas matrices show that other cytosine tautomers prevail in apolar environments. Each of these offers two or three H-bonding sites (Watson–Crick, wobble, sugar-edge). The mass- and isomer-specific S1 ← S0 vibronic spectra of cytosine·2-pyridone (Cyt·2PY) and 1-methylcytosine·2PY are measured using UV laser resonant two-photon ionization (R2PI), UV/UV depletion, and IR depletion spectroscopy. The UV spectra of the Watson–Crick and sugar-edge isomers of Cyt·2PY are separated using UV/UV spectral hole-burning. Five different isomers of Cyt·2PY are observed in a supersonic beam. We show that the Watson–Crick and sugar-edge dimers of keto-amino cytosine with 2PY are the most abundant in the beam, although keto-amino-cytosine is only the third most abundant tautomer in the gas phase. We identify the different isomers by combining three different diagnostic tools: (1) methylation of the cytosine N1–H group prevents formation of both the sugar-edge and wobble isomers and gives the Watson–Crick isomer exclusively. (2) The calculated ground state binding and dissociation energies, relative gas-phase abundances, excitation and the ionization energies are in agreement with the assignment of the dominant Cyt·2PY isomers to the Watson–Crick and sugar-edge complexes of keto-amino cytosine. (3) The comparison of calculated ground state vibrational frequencies to the experimental IR spectra in the carbonyl stretch and NH/OH/CH stretch ranges strengthen this identification

Vacuum-Ultraviolet Photoionization and Mass Spectrometric Characterization of Lignin Monomers Coniferyl and Sinapyl Alcohols

The fragmentation mechanisms of monolignols under various energetic processes are studied with jet-cooled thermal desorption molecular beam (TDMB) mass spectrometry (MS), 25 keV Bi3+ secondary ion MS (SIMS), synchrotron vacuum-ultraviolet secondary neutral MS (VUV-SNMS) and theoretical methods. Experimental and calculated appearance energies of fragments observed in TDMB MS indicate that the coniferyl alcohol photoionization mass spectra contain the molecular parent and several dissociative photoionization products. Similar results obtained for sinapyl alcohol are also discussed briefly. Ionization energies of 7.60 eV ? 0.05 eV for coniferyl alcohol and<7.4 eV for both sinapyl and dihydrosinapyl alcohols are determined. The positive ion SIMS spectrum of coniferyl alcohol shares few characteristic peaks (m/z = 137 and 151) with the TDMB mass spectra, shows extensive fragmentation, and does not exhibit clear molecular parent signals. VUV-SNMS spectra, on the other hand, are dominated by the parent ion and main fragments also present in the TDMB spectra. Molecular fragmentation in VUV-SNMS spectra can be reduced by increasing the extraction delay time. Some features resembling the SIMS spectra are also observed in the desorbed neutral products. The monolignol VUV-SNMS peaks shared with the TDMB mass spectra suggest that dissociative photoionization of ion-sputtered neutral molecules predominate in the VUV-SNMS mass spectra, despite the extra internal energy imparted in the initial ion impact. The potential applications of these results to imaging mass spectrometry of bio-molecules are discussed

Soft Ionization of Thermally Evaporated Hypergolic Ionic Liquid Aerosols

Isolated ion pairs of a conventional ionic liquid, 1-Ethyl-3-Methyl-Imidazolium Bis(trifluoromethylsulfonyl)imide ([Emim+][Tf2N?]), and a reactive hypergolic ionic liquid, 1-Butyl-3-Methyl-Imidazolium Dicyanamide ([Bmim+][Dca?]), are generated by vaporizing ionic liquid submicron aerosol particles for the first time; the vaporized species are investigated by dissociative ionization with tunable vacuum ultraviolet (VUV) light, exhibiting clear intact cations, Emim+ and Bmim+, presumably originating from intact ion pairs. Mass spectra of ion pair vapor from an effusive source of the hypergolic ionic liquid show substantial reactive decomposition due to the internal energy of the molecules emanating from the source. Photoionization efficiency curves in the near threshold ionization region of isolated ion pairs of [Emim+][Tf2N?]ionic liquid vapor are compared for an aerosol source and an effusive source, revealing changes in the appearance energy due to the amount of internal energy in the ion pairs. The aerosol source has a shift to higher threshold energy (~;;0.3 eV), attributed to reduced internal energy of the isolated ion pairs. The method of ionic liquid submicron aerosol particle vaporization, for reactive ionic liquids such as hypergolic species, is a convenient, thermally ?cooler? source of isolated intact ion pairs in the gas phase compared to effusive sources

Tunable Lattice-Form Mach-Zehnder Interferometer For Arbitrary Binary Code Generation At 40 Ghz

We use the direct temporal domain approach to design spectrally periodic optical filters for pulse repetition rate multiplication (PRRM) with envelope shaping. In particular, we demonstrate a tunable lattice-form MachZehnder interferometer using Silica-based planar lightwave circuit (PLC) for arbitrary 4-bit binary amplitude code generation at 40 GHz and to increase the repetition rate of a 10 GHz input pulse train to 20 GHz or 40 GHz. In addition to PRRM and envelope shaping, the device also has the capability of arbitrary phase coding. © 2006 IEEE

Tunable Lattice-Form Mach-Zehnder Interferometer For Arbitrary Binary Code Generation At 40 Ghz

We use the direct temporal domain approach to design spectrally periodic optical filters for pulse repetition rate multiplication (PRRM) with envelope shaping. In particular, we demonstrate a tunable lattice-form Mach-Zehnder interferometer using Silica-based planar lightwave circuit (PLC) for arbitrary 4-bit binary amplitude code generation at 40 GHz and to increase the repetition rate of a 10 GHz input pulse train to 20 GHz or 40 GHz. In addition to PRRM and envelope shaping, the device also has the capability of arbitrary phase coding. © 2010 IEEE