557 research outputs found
Photoionization and dynamic solvation of the excited states of 7-azaindole
The excited-state photophysics of the biological probe, 7-azaindole, are examined in water and methanol. Electrons in a presolvated state absorbing in the infrared appear within the excitation pulse width of 130 fs. 330 i 100 fs is required for the presolvated electron to achieve the spectrum characteristic of the completely solvated electron. An excited-state transient absorbance decays in -350 fs for 7-azaindole and its methylated analog, N1-methyl-7-azaindole (1M7AI), in the region 400-450 nm in water and methanol. The instantaneous appearance of the electron in the infrared is attributed to the decay of the lLb excited-state that overlaps the \u27La excited state of 7-azaindole. The rapid decay of the excited-state transient absorbance is attributed to preferential, dynamic solvation of the \u27La state. 7-Azaindole thus provides an interesting example of a molecule whose excited state is continuously and dynamically solvated but which also produces a species, e,,-, whose solvation appears to occur in a stepwise process
Photophysics and Biological Applications of 7-Azaindole and Its Analogs
7-Azaindole is the chromophoric moiety of 7-azatryptophan, which is an alternative to tryptophan as an optical probe of protein structure and dynamics. The great power of the 7-azaindole chromophore is that it is red shifted both in absorption and emission from tryptophan, that its fluorescence decay is single exponential in water under appropriate conditions, and that its emission is sensitive to solvent. In addition, 7-azatryptophan can be incorporated into synthetic peptides and bacterial protein. In this article, the interactions of 7-azaindole with its environment are discussed. Special attention is directed to the difference in its fluorescence properties in water as opposed to nonaqueous solvents. The sensitivity of 7-azaindole to its environment is demonstrated and then exploited by studying it and its analogs in peptides and in complexes with larger proteins containing many tryptophan residues
Critical collapse of collisionless matter - a numerical investigation
In recent years the threshold of black hole formation in spherically
symmetric gravitational collapse has been studied for a variety of matter
models. In this paper the corresponding issue is investigated for a matter
model significantly different from those considered so far in this context. We
study the transition from dispersion to black hole formation in the collapse of
collisionless matter when the initial data is scaled. This is done by means of
a numerical code similar to those commonly used in plasma physics. The result
is that for the initial data for which the solutions were computed, most of the
matter falls into the black hole whenever a black hole is formed. This results
in a discontinuity in the mass of the black hole at the onset of black hole
formation.Comment: 22 pages, LaTeX, 7 figures (ps-files, automatically included using
psfig
Dynamic Solvation in Room-Temperature Ionic Liquids
The dynamic solvation of the fluorescent probe, coumarin 153, is measured in five room-temperature ionic liquids using different experimental techniques and methods of data analysis. With time-resolved stimulated-emission and time-correlated single-photon counting techniques, it is found that the solvation is comprised of an initial rapid component of âŒ55 ps. In all the solvents, half or more of the solvation is completed within 100 ps. The remainder of the solvation occurs on a much longer time scale. The emission spectra of coumarin 153 are nearly superimposable at all temperatures in a given solvent unless they are obtained using the supercooled liquid, suggesting that the solvents have an essentially glassy nature. The physical origin of the two components is discussed in terms of the polarizability of the organic cation for the faster one and the relative diffusional motion of the cations and the anions for the slower one. A comparison of the solvation response functions obtained from single-wavelength and from spectral-reconstruction measurements is provided. Preliminary fluorescence-upconversion measurements are presented against which the appropriateness of the single-wavelength method for constructing solvation correlation functions and the use of stimulated-emission measurements is considered. These measurements are consistent with the trends mentioned above, but a comparison indicates that the presence of one or more excited states distorts the stimulated-emission kinetics such that they do not perfectly reproduce the spontaneous emission data. Fluorescence-upconversion results indicate an initial solvation component on the order of âŒ7 ps
Introduction
Les mouvements migratoires des Latino-amĂ©ricains ne sont pas un phĂ©nomĂšne nouveau. Quâils remontent au dĂ©but, au milieu ou Ă la fin du vingtiĂšme siĂšcle, ou quâils soient encore plus rĂ©cents, quâils se dirigent vers les pays du Nord (les Etats-Unis et lâEspagne principalement) ou vers le Sud (massivement vers lâensemble du continent latino-amĂ©ricain), ces mouvements migratoires ont modifiĂ© en profondeur les sociĂ©tĂ©s de dĂ©part et dâaccueil (et lâon songera au fait que, en 2030, un quart de la p..
Possible direct method to determine the radius of a star from the spectrum of gravitational wave signals
We computed the spectrum of gravitational waves from a dust disk star of
radius R inspiraling into a Kerr black hole of mass M and specific angular
momentum a. We found that when R is much larger than the wave length of the
quasinormal mode, the spectrum has several peaks and the separation of peaks
is proportional to irrespective of M and a. This
suggests that the radius of the star in coalescing binary black hole - star
systems may be determined directly from the observed spectrum of gravitational
wave. This also suggests that the spectrum of the radiation may give us
important information in gravitational wave astronomy as in optical astronomy.Comment: 4 pages with 3 eps figures, revtex.sty, accepted for publication in
Phys. Rev. Let
Observation of critical phenomena and self-similarity in the gravitational collapse of radiation fluid
We observe critical phenomena in spherical collapse of radiation fluid. A
sequence of spacetimes is numerically computed, containing
models () that adiabatically disperse and models () that
form a black hole. Near the critical point (), evolutions develop a
self-similar region within which collapse is balanced by a strong,
inward-moving rarefaction wave that holds constant as a function of a
self-similar coordinate . The self-similar solution is known and we show
near-critical evolutions asymptotically approaching it. A critical exponent
is found for supercritical () models.Comment: 10 pages (LaTeX) (to appear in Phys. Rev. Lett.), TAR-039-UN
Filifactor alocis - involvement in periodontal biofilms
<p>Abstract</p> <p>Background</p> <p>Bacteria in periodontal pockets develop complex sessile communities that attach to the tooth surface. These highly dynamic microfloral environments challenge both clinicians and researchers alike. The exploration of structural organisation and bacterial interactions within these biofilms is critically important for a thorough understanding of periodontal disease. In recent years, <it>Filifactor alocis</it>, a fastidious, Gram-positive, obligately anaerobic rod was repeatedly identified in periodontal lesions using DNA-based methods. It has been suggested to be a marker for periodontal deterioration. The present study investigated the epidemiology of <it>F. alocis </it>in periodontal pockets and analysed the spatial arrangement and architectural role of the organism in <it>in vivo </it>grown subgingival biofilms.</p> <p>Results</p> <p>A species-specific oligonucleotide probe, FIAL, was designed and evaluated. A total of 490 subgingival plaque samples were submitted to PCR and subsequent dot blot hybridization to compare the prevalence of <it>F. alocis </it>in patients suffering from generalized aggressive periodontitis (GAP), chronic periodontitis (CP), and control subjects resistant to periodontitis. Moreover, a specially designed carrier system was used to collect <it>in vivo </it>grown subgingival biofilms from GAP patients. Subsequent topographic analysis was performed using fluorescence in situ hybridization.</p> <p>While the majority of patients suffering from GAP or CP harboured <it>F. alocis</it>, it was rarely detected in the control group. In the examined carrier-borne biofilms the organism predominantly colonized apical parts of the pocket in close proximity to the soft tissues and was involved in numerous structures that constitute characteristic architectural features of subgingival periodontal biofilms.</p> <p>Conclusions</p> <p><it>F. alocis </it>is likely to make a relevant contribution to the pathogenetic structure of biofilms accounting for periodontal inflammation and can be considered an excellent marker organism for periodontal disease.</p
Improved numerical stability of stationary black hole evolution calculations
We experiment with modifications of the BSSN form of the Einstein field
equations (a reformulation of the ADM equations) and demonstrate how these
modifications affect the stability of numerical black hole evolution
calculations. We use excision to evolve both non-rotating and rotating
Kerr-Schild black holes in octant and equatorial symmetry, and without any
symmetry assumptions, and obtain accurate and stable simulations for specific
angular momenta J/M of up to about 0.9M.Comment: 13 pages, 11 figures, 1 typo in Eq. (20) correcte
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