From Torsional Spectra to Hamiltonians and Dynamics: Effects of Coupled Bright and Dark States of 9-(N-Carbazolyl) Anthracene

The torsional dynamics of the 9-(N-carbazolyl)-anthracene (C9A) molecule is investigated by means of time-independent (1) and time-dependent (2) quantum-mechanical simulations in a diabatic representation. The study includes effects of surface crossing of the bright S1 state with a dark state. The intensity pattern of the S0->S1 fluorescence excitation spectrum is used to fit an effective one-dimensional Hamiltonian with a single-minimum potential for the dark state together with diabatic couplings to the double well potential of the bright state. Based on this Hamiltonian, first predictions for a pump-probe scheme are made. In the pump process the molecules are excited to the S1 state followed by competing torsions in the bright state and diabatic curve crossings to the dark state, depending on the pump frequency. Assuming the probe process to be an ionization from the bright state, the interfering effects of the dark state on the dynamics in the bright state can be monitored in a directly time-dependent way on a fs - ps time scale

Flexibility in Animal Signals Facilitates Adaptation to Rapidly Changing Environments

Charles Darwin posited that secondary sexual characteristics result from competition to attract mates. In male songbirds, specialized vocalizations represent secondary sexual characteristics of particular importance because females prefer songs at specific frequencies, amplitudes, and duration. For birds living in human-dominated landscapes, historic selection for song characteristics that convey fitness may compete with novel selective pressures from anthropogenic noise. Here we show that black-capped chickadees (Poecile atricapillus) use shorter, higher-frequency songs when traffic noise is high, and longer, lower-frequency songs when noise abates. We suggest that chickadees balance opposing selective pressures by use low-frequency songs to preserve vocal characteristics of dominance that repel competitors and attract females, and high frequency songs to increase song transmission when their environment is noisy. The remarkable vocal flexibility exhibited by chickadees may be one reason that they thrive in urban environments, and such flexibility may also support subsequent genetic adaptation to an increasingly urbanized world

Anthropogenic noise is associated with changes in acoustic but not visual signals in red-winged blackbirds

Some birds in noisy areas produce songs with higher frequency and/or amplitude and altered timing compared to individuals in quiet areas. These changes may function to increase the efficacy of acoustic signals by reducing masking by noise. We collected audio recordings of red-winged blackbirds and measured noise levels. We found that males in noisier places produced songs with fewer syllables and slower repeat rate of elements in some components (rattles). Birds may also improve the efficacy of communication in noise by increasing usage of other signaling modalities. Red-winged blackbirds also perform a visual display in different intensities while singing. We also tested whether this species performs the visual display in different intensities according to current noise levels, and predicted that if the efficacy of songs is impaired in noisy places, males would compensate by performing a more intense visual display. For this, we also collected visual recordings from the same males from which we obtained acoustic recordings. We found no association between acoustic noise and the intensity of the visual display; thus, our results do not support the idea that males are using the visual display as a backup signal to communicate under acoustic noise. We discuss some possible explanations of this negative finding and for the observed noise-related changes in song length and rattle rate in the context of communication under noise

Time-Resolved Dual Fluorescence of 1-Phenylpyrrole in Acetonitrile: Molecular Dynamics Symulations of Solvent Response to Twisted Intramolecular Charge Transfer

The real time dynamics of solvation of 1-phenylpyrrole (PhPy) in acetonitrile (ACN) upon electronic excitation is investigated by means of non-equilibrium molecular dynamics simulations. The interaction is modeled by empirical intermolecular pair potentials using partial charges and intramolecular torsional potentials from high level ab initio calculations of ground and excited states of PhPy. The intramolecular torsional motion following sudden excitation from the twisted ground state to the 21B charge transfer state is strongly damped by the viscous ACN solvent leading to a near-exponential approach of the perpendicular conformation on a timescale of about 5...10 ps. The intermolecular dynamics is characterized by rapid reorientation of the solvent molecules on a time scale of 100 fs followed by weak quasi-coherent librations. The solvatochromatic red shift of the charge transfer state with respect to the locally excited 11B state results in dual fluorescence thus supporting the twisted intramolecular charge transfer (TICT) mechanism for PhPy in a polar solvent

Noise, avian abundance, and productivity at banding stations across the Continental United States

Noise is an increasingly common component of the natural world, due in large part to human activity. Anthropogenic noise negatively impacts abundance, health, and reproduction in many songbird populations. A few studies have reported altered abundance at larger scales. But whether continental trends are being detected at banding stations, which also offer data on productivity and survivorship, is unknown. Further, it is not known whether localized trends correlate with population trends observed at larger scales. We used breeding season data from 1160 constant-effort banding stations (Monitoring Avian Productivity and Survivorship; MAPS) and a spatially explicit noise model to determine whether abundance and productivity were related to mean noise level or spatial heterogeneity (SD) in noise within a 1-km station radius for 72 passerine species. We also determined whether particular life history traits were predictive of noise responses, and compared continental results to those from local studies. Increasing mean noise level was associated with declines in abundance for 27.1% of species and productivity in 22.1% species. Increasing heterogeneity was associated with declines in abundance for 14.3% species and productivity in 14.7% species. The relationship between noise and abundance was not correlated with the relationship between noise and productivity, and acoustic and life history traits were not related to noise responses. Continental results were similar to localized data in 43.1% and 21.4% of species for abundance and productivity, respectively. Although some patterns differed between the local and continental scale, our results indicate that the MAPS banding dataset is capable of detecting noise-associated impacts on abundance and productivity. This is currently the only large-scale dataset capable of quantifying the relationship between noise and productivity in the continental USA, although other datasets exist elsewhere that may also contribute to our understanding of noise impacts at the larger scale

Relationship between song duration and instantaneous noise.

<p>The line predicting song duration is derived from a general linear mixed model and data points correspond to the observed mean song duration at each decibel (±1 SE) averaged for all songs in all sites on weekend (black circles) and weekday (grey triangles) recordings.</p

Relationship between <i>bee</i> note peak frequency and average ambient noise levels.

<p>The line predicting <i>bee</i> note peak frequency is derived from a general linear mixed model and data points correspond to the observed mean <i>bee</i> note peak frequency at each decibel (±1 SE) averaged for all songs in all sites on weekend (black circles) and weekday (grey triangles) recordings.</p