27 research outputs found
Enhancement of Vibronic and Ground-State Vibrational Coherences in 2D Spectra of Photosynthetic Complexes
A vibronic-exciton model is applied to investigate the mechanism of
enhancement of coherent oscillations due to mixing of electronic and nuclear
degrees of freedom recently proposed as the origin of the long-lived
oscillations in 2D spectra of the FMO complex [Christensson et al. J. Phys.
Chem. B 116 (2012) 7449]. We reduce the problem to a model BChl dimer to
elucidate the role of resonance coupling, site energies, nuclear mode and
energy disorder in the enhancement of vibronic-exciton and ground-state
vibrational coherences, and to identify regimes where this enhancement is
significant. For a heterodimer representing the two coupled BChls 3 and 4 of
the FMO complex, the initial amplitude of the vibronic-exciton and vibrational
coherences are enhanced by up to 15 and 5 times, respectively, compared to the
vibrational coherences in the isolated monomer. This maximum initial amplitude
enhancement occurs when there is a resonance between the electronic energy gap
and the frequency of the vibrational mode. The bandwidth of this enhancement is
about 100 cm-1 for both mechanisms. The excitonic mixing of electronic and
vibrational DOF leads to additional dephasing relative to the vibrational
coherences. We evaluate the dephasing dynamics by solving the quantum master
equation in Markovian approximation and observe a strong dependence of the
life-time enhancement on the mode frequency. Long-lived vibronic-exciton
coherences are found to be generated only when the frequency of the mode is in
the vicinity of the electronic resonance. Although the vibronic-exciton
coherences exhibit a larger initial amplitude compared to the ground-state
vibrational coherences, we conclude that both type have a similar magnitude at
long time for the present model. The ability to distinguish between
vibronic-exciton and ground-state vibrational coherences in the general case of
molecular aggregate is discussed.Comment: 16 pages, 6 figure
Ultrafast Photo-Induced Charge Transfer Unveiled by Two-Dimensional Electronic Spectroscopy
The interaction of exciton and charge transfer (CT) states plays a central
role in photo-induced CT processes in chemistry, biology and physics. In this
work, we use a combination of two-dimensional electronic spectroscopy (2D-ES),
pump-probe measurements and quantum chemistry to investigate the ultrafast CT
dynamics in a lutetium bisphthalocyanine dimer in different oxidation states.
It is found that in the anionic form, the combination of strong CT-exciton
interaction and electronic asymmetry induced by a counter-ion enables CT
between the two macrocycles of the complex on a 30 fs timescale. Following
optical excitation, a chain of electron and hole transfer steps gives rise to
characteristic cross-peak dynamics in the electronic 2D spectra, and we monitor
how the excited state charge density ultimately localizes on the macrocycle
closest to the counter-ion within 100 fs. A comparison with the dynamics in the
radical species further elucidates how CT states modulate the electronic
structure and tune fs-reaction dynamics. Our experiments demonstrate the unique
capability of 2D-ES in combination with other methods to decipher ultrafast CT
dynamics.Comment: 14 pages, 11 figures, and Supporting informatio
Morphology and kinematics of the ionised gas in early-type galaxies
We present results of our ongoing study of the morphology and kinematics of
the ionised gas in 48 representative nearby elliptical and lenticular galaxies
using the SAURON integral-field spectrograph on the 4.2m William Herschel
Telescope. Making use of a recently developed technique, emission is detected
in 75% of the galaxies. The ionised-gas distributions display varied
morphologies, ranging from regular gas disks to filamentary structures.
Additionally, the emission-line kinematic maps show, in general, regular
motions with smooth variations in kinematic position angle. In most of the
galaxies, the ionised-gas kinematics is decoupled from the stellar counterpart,
but only some of them present signatures of recent accretion of gaseous
material. The presence of dust is very common in our sample and is usually
accompanied by gas emission. Our analysis of the [OIII]/Hbeta emission-line
ratios, both across the whole sample as well as within the individual galaxies,
suggests that there is no unique mechanism triggering the ionisation of the
gas.Comment: 8 pages, 2 figures, submitted to "Adaptive Optics-Assisted
Integral-Field Spectroscopy", Rutten R.G.M., Benn C.R., Mendez J., eds., May
2005, La Palma (Spain), New Astr. Rev. For full resolution PS, see
http://www.strw.leidenuniv.nl/~jfalcon/JFB_AOmeeting_color_hires.ps.g
Formation and evolution of S0 galaxies: a SAURON case study of NGC7332
We present SAURON integral-field observations of the S0 galaxy NGC7332.
Existing broad-band ground-based and HST photometry reveals a double disk
structure and a boxy bulge interpreted as a bar viewed close to edge-on. The
SAURON two-dimensional stellar kinematic maps confirm the existence of the bar
and inner disk but also uncover the presence of a cold counter-rotating stellar
component within the central 250 pc. The Hbeta and [OIII] emission line maps
show that the ionised gas has a complex morphology and kinematics, including
both a component counter-rotating with respect to the stars and a fainter
co-rotating one. Analysis of the absorption line-strength maps show that
NGC7332 is young everywhere. The presence of a large-scale bar can explain most
of those properties, but the fact that we see a significant amount of unsettled
gas, together with a few peculiar features in the maps, suggest that NGC7332 is
still evolving. Interactions as well as bar-driven processes must thus have
played an important role in the formation and evolution of NGC7332, and
presumably of S0 galaxies in general.Comment: 12 pages, 12 figures, accepted for publication in MNRA
The ATLAS3D project - XXVII : Cold gas and the colours and ages of early-type galaxies
Date of Acceptance: 16/12/2013We present a study of the cold gas contents of the ATLAS3D early-type galaxies, in the context of their optical colours, near-ultraviolet colours and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas poor as previously thought, and at least 40 per cent of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation) and removal. Molecular and atomic gas detection rates range from 10 to 34 per cent in red sequence early-type galaxies, depending on how the red sequence is defined, and from 50 to 70 per cent in blue early-type galaxies. Notably, massive red sequence early-type galaxies (stellar masses >5 × 1010 M⊙, derived from dynamical models) are found to have H I masses up to M(H I)/M* ∼ 0.06 and H2 masses up to M(H2)/M* ∼ 0.01. Some 20 per cent of all massive early-type galaxies may have retained atomic and/or molecular gas through their transition to the red sequence. However, kinematic and metallicity signatures of external gas accretion (either from satellite galaxies or the intergalactic medium) are also common, particularly at stellar masses ≤5 × 1010 M⊙, where such signatures are found in ∼50 per cent of H2-rich early-type galaxies. Our data are thus consistent with a scenario in which fast rotator early-type galaxies are quenched former spiral galaxies which have undergone some bulge growth processes, and in addition, some of them also experience cold gas accretion which can initiate a period of modest star formation activity. We discuss implications for the interpretation of colour–magnitude diagramsPeer reviewedFinal Accepted Versio
Origin of Long Lived Coherences in Light-Harvesting Complexes
A vibronic exciton model is developed to investigate the origin of long lived
coherences in light-harvesting complexes. Using experimentally determined
parameters and uncorrelated site energy fluctuations, the model predicts
oscillations in the nonlinear spectra of the Fenna-Matthews-Olson (FMO) complex
with a dephasing time of 1.3 ps at 77 K. These oscillations correspond to the
coherent superposition of vibronic exciton states with dominant contributions
from vibrational excitations on the same pigment. Purely electronic coherences
are found to decay on a 200 fs timescale.Comment: 4 pages, 2 figure
Elective Cancer Surgery in COVID-19-Free Surgical Pathways During the SARS-CoV-2 Pandemic: An International, Multicenter, Comparative Cohort Study.
PURPOSE: As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19-free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS: This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19-free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS: Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19-free surgical pathways. Patients who underwent surgery within COVID-19-free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19-free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score-matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19-free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION: Within available resources, dedicated COVID-19-free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks
Elective cancer surgery in COVID-19-free surgical pathways during the SARS-CoV-2 pandemic: An international, multicenter, comparative cohort study
PURPOSE As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19–free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19–free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19–free surgical pathways. Patients who underwent surgery within COVID-19–free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19–free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score–matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19–free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION Within available resources, dedicated COVID-19–free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks