674 research outputs found
Nuclear Wavepacket Dynamics of Alkali Adsorbates on Metal Surfaces Studied by Time-Resolved Second Harmonic Generation
This paper reviews recent efforts to understand the dynamics of coherent surface vibrations of alkali atoms adsorbed on metal surfaces. Time-resolved second harmonic generation is used for the coherent excitation and detection of the nuclear wavepacket dynamics of the surface modes. The principles of the measurement and the experimental details are described. The main focus is on coverage and excitation photon energy dependences of the coherent phonon dynamics for Na-, K-, and Cs-covered Cu(111). The excitation mechanism of the coherent phonon has been revealed by the ultrafast time-domain technique and theoretical modelings
Photodynamic Inactivation of <em>Escherichia coli</em> with Cationic Porphyrin Sensitizers
The activity of singlet-oxygen sensitizers for photodynamic inactivation (PDI) of microorganisms and photodynamic therapy of tumor cells has been evaluated using Escherichia coli, Saccharomyces cerevisiae, and human cancer cell lines. In this chapter, drug resistance of E. coli was examined based on the PDI activity of a variety of RPy-P-porphyrin sensitizers with different number of ionic valence and different hydrophobic characters. The PDI activities toward E. coli were evaluated using the minimum effective concentrations ([P]) of the porphyrin sensitizers. It was found that the [P] value for E. coli was larger than that for S. cerevisiae. E. coli has drug-resistance toward hydrophobic and mono-cationic porphyrins. However, E. coli has weak drug-resistance toward the porphyrins with both polycationic character and hydrophobicity. Since the outer membrane mainly consists of lipopolysaccharides and phospholipids that are negatively charged, cationic porphyrins are able to adsorb to the outer leaflet. Then the cationic porphyrins with hydrophobic character can interact with not only the outer leaflet but also inner leaflet of the outer membrane and the plasma membrane. Thus, porphyrins may be incorporated inside E. coli cells via the self-promoted uptake pathway. Moreover, polycationic porphyrins can interact with DNA and proteins by strong binding affinities
Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5
Either bulk rotation or local turbulence is widely invoked to drive
fragmentation in collapsing cores so as to produce multiple star systems. Even
when the two mechanisms predict different manners in which the stellar spins
and orbits are aligned, subsequent internal or external interactions can drive
multiple systems towards or away from alignment thus masking their formation
process. Here, we demonstrate that the geometrical and dynamical relationship
between the binary system and its surrounding bulk envelope provide the crucial
distinction between fragmentation models. We find that the circumstellar disks
of the binary protostellar system L1551 IRS 5 are closely parallel not just
with each other but also with their surrounding flattened envelope.
Measurements of the relative proper motion of the binary components spanning
nearly 30 yr indicate an orbital motion in the same sense as the envelope
rotation. Eliminating orbital solutions whereby the circumstellar disks would
be tidally truncated to sizes smaller than are observed, the remaining
solutions favor a circular or low-eccentricity orbit tilted by up to
25 from the circumstellar disks. Turbulence-driven fragmentation
can generate local angular momentum to produce a coplanar binary system, but
which bears no particular relationship with its surrounding envelope. Instead,
the observed properties conform with predictions for rotationally-driven
fragmentation. If the fragments were produced at different heights or on
opposite sides of the midplane in the flattened central region of a rotating
core, the resulting protostars would then exhibit circumstellar disks parallel
with the surrounding envelope but tilted from the orbital plane as is observed.Comment: Accepted for publication in Ap
Iodo-Nonoxynol-9-Derivatives and Methods for Their Use
Mono- and di-iodinated nonoxynol-9-derivatives and methods for their use are disclosed
Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE
We report the ALMA observation of the Class I binary protostellar system
L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6
times higher resolution and a ~6 times higher sensitivity than those of our
previous SMA observations, which revealed a r ~300 AU-scale circumbinary disk
in Keplerian rotation. The 0.9-mm continuum shows two opposing U-shaped
brightenings in the circumbinary disk, and exhibits a depression between the
circumbinary disk and the circumstellar disk of the primary protostar. The
molecular lines trace non-axisymmetric deviations from Keplerian rotation in
the circumbinary disk at higher velocities relative to the systemic velocity,
where our previous SMA observations could not detect the lines. In addition, we
detect inward motion along the minor axis of the circumbinary disk. To explain
the newly-observed features, we performed a numerical simulation of gas orbits
in a Roche potential tailored to the inferred properties of L1551 NE. The
observed U-shaped dust features coincide with locations where gravitational
torques from the central binary system are predicted to impart angular momentum
to the circumbinary disk, producing shocks and hence density enhancements seen
as a pair of spiral arms. The observed inward gas motion coincides with
locations where angular momentum is predicted to be lowered by the
gravitational torques. The good agreement between our observation and model
indicates that gravitational torques from the binary stars constitute the
primary driver for exchanging angular momentum so as to permit infall through
the circumbinary disk of L1551 NE.Comment: 38 pages, 11 figures, accepted for publication in Ap
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