1,223 research outputs found
A Midsummer Knot's Dream
In this paper, we introduce playing games on shadows of knots. We demonstrate
two novel games, namely, To Knot or Not to Knot and Much Ado about Knotting. We
also discuss winning strategies for these games on certain families of knot
shadows. Finally, we suggest variations of these games for further study.Comment: 11 pages, 8 figures. To appear, College Mathematics Journal
Time-resolved photoelectron imaging of excited state relaxation dynamics in phenol, catechol, resorcinol and hydroquinone
Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S1 (\u3c0\u3c0*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S1potential surface. In catechol, the overall S1 state lifetime was observed to be 12.1 ps, which is 1\u20132 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S1 state and the close lying S2 (\u3c0\u3c3*) state, which is dissociative along the O\u2013H stretching coordinate. Further evidence of this S1/S2 interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.Peer reviewed: YesNRC publication: Ye
Undersampling raster scans in spectromicroscopy for a reduced dose and faster measurements
Combinations of spectroscopic analysis and microscopic techniques are used
across many disciplines of scientific research, including material science,
chemistry and biology. X-ray spectromicroscopy, in particular, is a powerful
tool used for studying chemical state distributions at the micro and nano
scales. With the beam fixed, a specimen is typically rastered through the probe
with continuous motion and a range of multimodal data is collected at fixed
time intervals.
The application of this technique is limited in some areas due to: long
scanning times to collect the data, either because of the area/volume under
study or the compositional properties of the specimen; and material degradation
due to the dose absorbed during the measurement. In this work, we propose a
novel approach for reducing the dose and scanning times by undersampling the
raster data. This is achieved by skipping rows within scans and reconstructing
the x-ray spectromicroscopic measurements using low-rank matrix completion. The
new method is robust and allows for x 5-6 reduction in sampling. Experimental
results obtained on real data are illustrated.Comment: 22 pages,11 figure
Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy
Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright 1La and 1Lb electronic states of 1\u3c0\u3c0* character and spectroscopically dark and dissociative 1\u3c0\u3c3* states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited 1La state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived 1Lb state or the 1\u3c0\u3c3* state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the 1\u3c0\u3c3* state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied.Peer reviewed: YesNRC publication: Ye
West Nile virus in the New World: potential impacts on bird species
The past five years have seen the arrival and extremely rapid expansion of West Nile virus
(WNV) in the Western Hemisphere. The rapid sweep across North America has permitted
little time for developing knowledge of the virus’s potential impacts on wildlife in
the New World. Given this information gap, we here summarize for the ornithological
community what is known or can be anticipated for WNV’s effect on bird communities in
coming years. Our particular focus is on impacts of WNV on the conservation status of
birds, the principal vertebrate reservoir for the virus
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