Humans and mice fluctuate between external and internal modes of sensory processing

Perception cycles through periods of enhanced and reduced sensitivity to external information. Here, we asked whether such infra-slow oscillations arise as a noise-related epiphenomenon of limited processing capacity or, alternatively, represent a structured mechanism of perceptual inference. Using two large-scale datasets, we found that humans and mice waver between alternating intervals of externally- and internally-oriented modes of sensory analysis. During external mode, perception was more sensitive to external sensory information, whereas internal mode was characterized by enhanced biases toward perceptual history. Computational modeling indicated that dynamic changes in mode are governed by two interlinked factors: (i), the integration of subsequent stimuli over time and, (ii), infra-slow anti-phase oscillations in the perceptual impact of external sensory information versus internal predictions that are provided by perceptual history. Between-mode fluctuations may benefit perception by enabling the generation of stable representations of the environment despite an ongoing stream of noisy sensory inputs.

Elements of the dynamical response to climate change over the Mediterranean

Future climate simulations indicate that the Mediterranean Basin will experience large low-level circulation changes during winter, characterized by a strong anomalous ridge that drives a regional precipitation decline. Previous research highlighted how shifts in stationary wave structure and the atmospheric response to reduced warming of the Mediterranean Sea compared to land could explain the development of this anomalous pressure high. Here, we expand on these results and provide new arguments for why and how the Mediterranean is projected to experience large circulation changes during winter. First, we find that zonal asymmetries in the vertical structure of stationary waves are important to explain the enhanced circulation response in the region, and that these asymmetries are related through the external mode to the vertical structure of the mean zonal wind. Second, in winter, the Mediterranean is located just to the north of the Hadley cell edge and consequently relatively free of large-scale descent; together with low near-surface static stability above the sea, this allows the weaker warming trend above the sea to propagate to the low troposphere and trigger a major circulation response. During summer, however, remotely-forced descent and strong static stability prevent the cooling anomaly from expanding upwards. Most of the inter-model scatter in the projected low-level circulation response is related to the spread in upper-tropospheric dynamical trends. Importantly, because climate models exhibit too much vertical coherence over the Mediterranean, our results suggest they overestimate the sensitivity of Mediterranean near-surface circulation to large-scale dynamical changes.

STABILITY CHARACTERISTICS OF COMPRESSIBLE BINARY PLANAR JETS

The present work investigates the stability of compressible binary planar jets. Different from a homogeneous jet, where a single chemical species is present, the binary jet may have strong density gradients due to the choice of the chemical species considered in each stream. The goal is to identify the possible instability modes for simple and co-flowing jets and investigate the effect of density gradients on the flow structure, growth rates, unstable frequency range and disturbance phase speed for each mode. The effect of species concentration on free shear layer stability has been reported previously in the literature, but detailed comparisons between stability modes and characteristics for a range of density ratios typical of oxygen and hydrogen mixtures as well as the identification of inner and outer sinuous and varicose modes are new. Linear stability theory is used to determine the stability characteristics of the different configurations. For the co-flowing jet four different modes are found, the inner and outer shear layers both have sinuous and varicose modes. Both for the sinuous and varicose modes the simple jet is more unstable when the fluid with the highest density is at the inner jet, with amplification rates twice as high as the lowest density ratio considered, but the range of unstable frequencies can be four times lower. The sinuous mode is less dispersive than the varicose and the disturbance speeds may vary by one order of magnitude with density ratio. For co-flowing jets the external mode is up to seven times more unstable, but this is due to the choice of the velocity ratio considered. For the inner mode the density gradient has a stabilizing effect regardless of which species is at the center. The co-flowing jet is more dispersive, except for the varicose inner mode. The variation of phase speed with density gradient is not as strong as in the simple jet. The ratio of larges to lower phase speeds are of the order of 2 for the co-flowing jet and 4 for the simple jet.

Overtransmission of Rossby Waves at a Lower-Layer Critical Latitude in the Two-Layer Model

Rossby waves, propagating from the midlatitudes toward the tropics, are typically absorbed by critical latitudes (CLs) in the upper troposphere. However, these waves typically encounter CLs in the lower troposphere first. We study a two-layer linear scattering problem to examine the effects of lower CLs on these waves. We begin with a review of the simpler barotropic case to orient the reader. We then progress to the baroclinic case using a two-layer quasigeostrophic model in which there is vertical shear in the mean flow on which the waves propagate, and in which the incident wave is assumed to be an external-mode Rossby wave. We use linearized equations and add small damping to remove the critical-latitude singularities. We consider cases in which either there is only one CL, in the lower layer, or there are CLs in both layers, with the lower-layer CL encountered first. If there is only a CL in the lower layer, the wave’s response depends on the sign of the mean potential vorticity gradient at this lower-layer CL: if the PV gradient is positive, then the CL partially absorbs the wave, as in the barotropic case, while for a negative PV gradient, the CL is a wave emitter, and can potentially produce overreflection and/or overtransmission. Our numerical results indicate that overtransmission is by far the dominant response in these cases. When an upper-layer absorbing CL is encountered, following the lower-layer encounter, one can still see the signature of overtransmission at the lower-layer CL.

Sperm Lipid Composition in Early Diverged Fish Species: Internal vs. External Mode of Fertilization

The lipid composition of sperm membranes is crucial for fertilization and differs among species. As the evolution of internal fertilization modes in fishes is not understood, a comparative study of the sperm lipid composition in freshwater representatives of externally and internally fertilizing fishes is needed for a better understanding of taxa-specific relationships between the lipid composition of the sperm membrane and the sperm physiology. The lipidomes of spermatozoa from stingray, a representative of cartilaginous fishes possessing internal fertilization, and sterlet, a representative of chondrostean fishes with external fertilization, have been studied by means of nuclear magnetic resonance (NMR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), electrospray MS, gas chromatography-(GC) MS, and thin-layer chromatography (TLC). NMR experiments revealed higher cholesterol content and the presence of phosphatidylserine in stingray compared to sterlet sperm. Unknown MS signals could be assigned to different glycosphingolipids in sterlet (neutral glycosphingolipid Gal-Cer(d18:1/16:0)) and stingray (acidic glycosphingolipid sulpho-Gal-Cer(d18:1/16:0)). Free fatty acids in sterlet sperm indicate internal energy storage. GC-MS experiments indicated a significant amount of adrenic acid, but only a low amount of docosahexaenoic acid in stingray sperm. In a nutshell, this study provides novel data on sperm lipid composition for freshwater stingray and sterlet possessing different modes of fertilization.

Regional study hubs: Increasing student engagement to support regional students facing high first-year attrition risk factors

The Country Universities Centre (CUC) network of regional study hubs are an emerging tool for supporting regional students to achieve success in higher education. The CUC cohort of students, and regional students more generally, face several risk factors for first-year attrition including: external mode of study, over 25 years of age, part-time study load, alternative pathways to admission, and medium to low SES. In addition, work-life balance, financial considerations, and access to technology all create barriers to study for these students. The CUC facilities and staff provide academic, administrative and pastoral support to students, as well as creating a learning community to facilitate student-to-student interactions. The positive effect of the CUC support is shown by means of a survey and student case-studies.

Pacific Influences on the Meridional Temperature Transport of the Indian Ocean

In this study, low-frequency variability of the meridional temperature transport in the Indian Ocean is examined using a mesoscale-eddy-resolving global ocean circulation model for the period 1979–2014. The dominant empirical orthogonal function (EOF) of the meridional temperature transport is found to be highly influenced by Pacific El Niño–Southern Oscillation (ENSO) through both oceanic and atmospheric waveguides, with the southward temperature transport being stronger during La Niña and weaker during El Niño. A dynamical decomposition of the meridional streamfunction and temperature transport shows that the relative importance of different dynamic modes varies with latitude; these modes act together to contribute to the coherent ENSO response. The Ekman mode explains a larger part of low-frequency variability in overturning and temperature transport north of the equator. Between 25° and 3°S, variations associated with vertical shear mode are of greater importance. The external mode has an important contribution between 30° and 25°S where the western boundary currents impinge on topography. South of 25°S, the variability of the external mode contribution has significant negative correlations with the vertical shear mode, suggesting that the large variability of external mode depends on the joint effects of baroclinicity and topography, such that hydrographic sections alone may not be suitable for deducing changes in the meridional temperature transport at these latitudes.