Telling the Seasons Underground: The Circadian Clock and Ambient Temperature Shape Light Exposure and Photoperiodism in a Subterranean Rodent

Living organisms anticipate the seasons by tracking the proportion of light and darkness hours within a day—photoperiod. The limits of photoperiod measurement can be investigated in the subterranean rodents tuco-tucos (Ctenomys aff. knighti), which inhabit dark underground tunnels. Their exposure to light is sporadic and, remarkably, results from their own behavior of surface emergence. Thus, we investigated the endogenous and exogenous regulation of this behavior and its consequences to photoperiod measurement. In the field, animals carrying biologgers displayed seasonal patterns of daily surface emergence, exogenously modulated by temperature. In the laboratory, experiments with constant lighting conditions revealed the endogenous regulation of seasonal activity by the circadian clock, which has a multi-oscillatory structure. Finally, mathematical modeling corroborated that tuco-tuco’s light exposure across the seasons is sufficient for photoperiod encoding. Together, our results elucidate the interrelationship between the circadian clock and temperature in shaping seasonal light exposure patterns that convey photoperiod information in an extreme photic environment.

Sleep spindles comprise a subset of a broader class of electroencephalogram events

Study Objectives Sleep spindles are defined based on expert observations of waveform features in the electroencephalogram traces. This is a potentially limiting characterization, as transient oscillatory bursts like spindles are easily obscured in the time-domain by higher amplitude activity at other frequencies or by noise. It is therefore highly plausible that many relevant events are missed by current approaches based on traditionally-defined spindles. Given their oscillatory structure, we reexamine spindle activity from first principles, using time-frequency activity in comparison to scored spindles. Methods Using multitaper spectral analysis, we observe clear time-frequency peaks in the sigma (10-16 Hz) range (TFσ peaks). While nearly every scored spindle coincides with a TFσ peak, numerous similar TFσ peaks remain undetected. We therefore perform statistical analyses of spindles and TFσ peaks using manual and automated detection methods, comparing event co-occurrence, morphological similarities, and night-to-night consistency across multiple datasets. Results On average, TFσ peaks have more than 3 times the rate of spindles (mean rate: 9.8 vs. 3.1 events/min). Moreover, spindles subsample the most prominent TFσ peaks with otherwise identical spectral morphology. We further demonstrate that detected TFσ peaks have stronger night-to-night rate stability (rho = 0.98) than spindles (rho = 0.67), while covarying with spindle rates across subjects (rho = 0.72). Conclusions These results provide compelling evidence that traditionally-defined spindles constitute a subset of a more generalized class of electroencephalogram events. TFσ peaks are therefore a more complete representation of the underlying phenomenon, providing a more consistent and robust basis for future experiments and analyses.

Synchrotron spectroscopy of the CSH-bending and CH3-rocking bands of methyl mercaptan

The CSH-bending and CH3-rocking infrared bands of CH3SH have been investigated in Fourier transform spectra recorded at 0.001 cm−1 resolution employing synchrotron radiation at the Canadian Light Source in Saskatoon. The relative band strengths and structures are quite different from those of the CH3OH methanol analogue, with the CSH bend being very weak and both the in-plane and out-of-plane CH3 rocks being strong with intensities greater than the C–S stretch. The CSH bend has parallel a-type character with no detectable b-type component. The out-of-plane CH3 rock is a purely c-type perpendicular band, whereas the in-plane rock is of mixed a/b character. Sub-bands have been assigned for A and E torsional species up to about K = 10 for each vibrational mode, providing upper-state term values from which K-reduced substate origins were determined. For the CSH bend, the origins follow the customary oscillatory torsional pattern as a function of K with a sharply reduced amplitude of 0.362 cm−1 compared to the 0.653 cm−1 for the ground state. The torsional energy curves for the out-of-plane rock are also well-behaved but have inverted ordering of the A–E torsional splitting components and a larger amplitude of 1.33 cm−1. In contrast, the substate origins for the in-plane rock are scattered over a range of about 2 cm−1 without clear oscillatory structure. Several instances of coupling among the lower modes and the ground state via resonances between accidentally near-degenerate levels have been observed and characterized. Ab initio calculations are found to give a good representation of the frequency and relative intensity patterns for the lower vibrational modes.

Photodetachment of H– ion in perpendicular electric and magnetic fields near a metal surface

The photodetachment of the H– ion in perpendicular electric and magnetic fields near a metal surface has been investigated on the basis of the semiclassical closed-orbit theory. Firstly, we give a clear physical picture of the detached electron’s movement and find out the closed orbits of this system. Then we put forward an analytical formula for calculating the photodetachment cross section. It is found that the perpendicular electric and magnetic fields can produce some interesting effects. As the magnetic field is relatively weak, the influence of the electric field and the electrostatic potential dominates and the oscillatory structure in the photodetachment cross section exhibits a smoothly oscillating curve. As we keep the electric field and the ion–surface distance unchanged, with the increase of the magnetic field strength, the number of closed orbits is increased and the oscillatory structure in the photodetachment cross section is characterized by broad Landau level envelops. Therefore, we can use the perpendicular electric and magnetic fields to control the photodetachment of H– near a metal surface. Our study may guide future experimental research on the photodetachment microscopy of negative ion in external fields near surfaces.