Injection and flow control system for microchannels

In spite of considerable efforts, flow control in micro-channels remains a challenge owing to the very small ratio of channel/supply-system volumes, as well as the induction of spurious flows by extremely small pressure or geometry changes. We present here an inexpensive and robust system for flow control in a microchannel system, based on a dynamic control of reservoir pressures at the end of each channel. This system allows flow equilibration with a time constant smaller than one second, and is also able to maintain stable flux from stopped flow to many microl min(-1) range over several hours. It is robust to changes in ambient pressure and temperature. This system further includes a feature for sub-microliter sample injection during the experiment. We quantify flow control in elastomer and thermoplastic channels, and demonstrate the impact on one application of the system, namely the reproducible, automated separation of large DNA by electrophoresis in a self-organized magnetic bead matrix in a microchannel.     

Nuclear spin conversion of molecular hydrogen on amorphous solid water in the presence of O2 traces

Nuclear spin conversion (NSC) of ortho- to para-H(2) and para- to ortho-D(2) has been investigated on an amorphous solid water (ASW) surface at 10 K, in the presence of co-adsorbed O(2). The dynamics of the nuclear spin conversion could be revealed by combination of resonance enhanced multiphoton ionization spectroscopy (REMPI) with temperature programmed desorption (TPD) experiments. The conversion rates are consistent with a diffusion of molecular hydrogen inducing a nuclear spin conversion enhanced in the vicinity of molecular oxygen. The conversion times were found to increase with decreasing O(2) and H(2) coverage. Finally, on oxygen free ASW surface, the extremely long conversion characteristic times measured showed that such surface is not an efficient catalyst for NSC, in contradiction with hypothesis commonly made for interstellar medium.     

Spectral properties of topical retinoids prevent DNA damage and apoptosis after acute UV-B exposure in hairless mice

We showed in a recent study that topical retinyl palmitate prevented UV-B-induced DNA damage and erythema in humans. Given that retinyl palmitate is a precursor of retinoic acid, the biological form of vitamin A that acts through nuclear receptors, we wondered whether these protective effects toward UV-B exposure were either receptor dependent or linked to other properties of the retinoid molecule such as its spectral properties. We determined the epidermal retinoid profile induced by topical retinoic acid in hairless mice and analyzed its effect on markers of DNA photodamage (thymine dimers) and apoptosis following acute UV-B exposure; we compared these effects to those induced by other natural topical retinoids (retinaldehyde, retinol and retinyl palmitate) which do not directly activate the retinoid receptors. We then analyzed the direct action of these retinoids on UV-B-induced DNA damage and apoptosis in cultured A431 keratinocytes. Topical retinoic acid significantly decreased (approximately 50%) the number of apoptotic cells, as well as the formation of thymine dimers in the epidermis of mice exposed to acute UV-B. Interestingly, the other topical retinoids decreased apoptosis and DNA damage in a similar way. On the other hand, neither retinoic acid nor the other retinoids interfered with the apoptotic process in A431 keratinocytes exposed to UV-B, whereas DNA photodamage was slightly decreased. We conclude that the decrease of apoptotic cells in hairless mouse epidermis following topical retinoids and UV-B irradiation reflects a protection of the primary targets of UV-B (DNA) by a mechanism independent of the activation of retinoid nuclear receptors, rather than a direct inhibition of apoptosis.     

Rydberg transitions in neon observed by optogalvanic effect in the 830-870 and 380-420 nm regions

New optogalvanic (OG) Rydberg-Rydberg transitions of neon have been observed in the near-infrared region (830-870 nm), using a commercial Fe-Ne hollow cathode. They involve transitions from the 3d[3/2] J=1 and 3d[7/2] J=3,4 levels to high-lying nf levels. In addition, other OG transitions, observed in the blue range, have been completely assigned to ns, nd, ns′ and nd′ Rydberg series excited from the 3p[1/2] J=1 and 3p[5/2] J=2,3 levels of neon. These transitions and assignments allowed us to extend the range of tunable laser calibration on the two edges of the visible range, where there is a lack of available calibration lines, i.e. the near-infrared and the far-blue range, with a 0.01 nm absolute accuracy.     

High resolution photoabsorption and photofragment fluorescence spectroscopy of water between 10.9 and 12 eV

This work presents absorption and photofragment fluorescence spectra of water (H2O and D2O) simultaneously recorded at rotational resolution and at room temperature, by means of a synchrotron radiation source in the range 10.9-12 eV, covering the nd intense series from n=3 to 8. The Rydberg states observed are assigned in the light of the most advanced theoretical work available [M. S. Child, Philos. Trans. R. Soc. London, Ser. A 355, 1623 (1997)], and by reference to the stretching and bending mode progressions. Comparison between absorption and fluorescence spectra is shown to reveal a fast predissociation mechanism involving the linear 3pb2 1B2 state, and permits the identification of its (0,14,0) vibrational level observed in the absorption spectra.     

Coupled magnetic cycloids in multiferroic TbMnO3 and Eu3/4Y1/4MnO3

Based on the detailed Mn L(2,3)-edge x-ray resonant scattering results, we report a new complexity in the magnetic order of multiferroic orthomangnites, which has been considered as the simple A-type cycloid order inducing ferroelectricity. The Dzyaloshinskii-Moriya interaction involved in the orthorhombic distortion brings on F-type canting from the A type, and the ordering type becomes the off-phase synchronized bc cycloid in TbMnO(3) or the tilted antiphase ab cycloid in Eu(3/4)Y(1/4)MnO(3). The F-type canting is responsible for the magnetic field-driven multiferroicity to weak ferromagnetism transition.     

X-Ray spectra and electronic correlations of FeSe(1-x)Te(x)

Critical issues concerning emerging Fe-based superconductors include the degree of electron correlation and the origin of the superconductivity. X-Ray absorption spectra (XAS) and resonant inelastic X-ray scattering spectra (RIXS) of FeSe(1-x)Te(x) (x = 0-1) single crystals were obtained to study their electronic properties that relate to electron correlation and superconductivity. The linewidth of Fe L(2,3)-edges XAS of FeSe(1-x)Te(x) is narrower than that of Fe-pnictides, revealing the difference between their hybridization effects and localization character and those of other Fe-pnictides. While no significant differences exist between the Fe L-edge XAS and RIXS of FeSe(1-x)Te(x) and those of Fe-pnictides, Se K-edge and Te K-edge XAS exhibit substantial edge shift, suggesting that the superconductivity in an Fe-Se superconductor is strongly associated with the ligand states. A comparison of the Se K-edge and Te K-edge spectra reveals that the charge transfer may occur between Se and Te. Given the Coulomb interaction and the bandwidth, the spectral results indicate that FeSe(1-x)Te(x) is unlikely to be a weakly correlated system unlike the Fe-pnictides of the "1111" and "122" families. The spectral results further demonstrate that superconductivity in this class of Fe-based compounds is strongly associated with the ligand 4p hole state.     

Interaction of atomic and molecular deuterium with a nonporous amorphous water ice surface between 8 and 30 K

Molecular and atomic interactions of hydrogen on dust grains covered with ice at low temperatures are key mechanisms for star formation and chemistry in dark interstellar clouds. We have experimentally studied the interaction of atomic and molecular deuterium on nonporous amorphous water ice surfaces between 8 and 30 K, in conditions compatible with an extrapolation to an astrophysical context. The adsorption energy of D(2) presents a wide distribution, as already observed on porous water ice surfaces. At low coverage, the sticking coefficient of D(2) increases linearly with the number of deuterium molecules already adsorbed on the surface. Recombination of atomic D occurs via a prompt reaction that releases molecules into the gas phase. Part of the newly formed molecules are in vibrationally excited states (v=1-7). The atomic recombination efficiency increases with the presence of D(2) molecules already adsorbed on the water ice, probably because these increase the sticking coefficient of the atoms, as in the case of incident D(2). We have measured the atomic recombination efficiency in the presence of already absorbed D(2), as it is expected to occur in the interstellar medium. The recombination efficiency decreases rapidly with increasing temperature and is zero at 13 K. This allows us to estimate an upper limit to the value of the atom adsorption energy E(a) approximately 29 meV, in agreement with previous calculations.     

Wrinkle-Based Measurement of Elastic Modulus of Nano-Scale Thin Pt Film Deposited on Polymeric Substrate: Verification and Uncertainty Analysis

Wrinkle-based measurement of elastic modulus for a nano-scale thin film was analyzed. As a demonstrative example, the wrinkles of Pt films on a Polydimethylsiloxane (PDMS) substrate under compressive loading were formed with a well-defined wavelength, corresponding to the difference of elastic moduli between the films and substrates. The elastic modulus of the Pt nano-scale thin film measured with the wrinkle-based measurement was found to be consistent with that independently measured with micro-tensile test. Uncertainty of the wrinkle-based measurement was analyzed to figure out the main uncertainty components for the evaluation of elastic modulus measurement, and guidelines for the reliable wrinkle-based measurement were suggested.