Energy transfers between multidecadal and turbulent variability

One of the proposed mechanisms to explain the multidecadal variability observed in sea surface temperature of the North Atlantic consists of a large-scale low-frequency internal mode spontaneously developing because of the large-scale baroclinic instability of the time-mean circulation. Even though this mode has been extensively studied in terms of the buoyancy variance budget, its energetic properties remain poorly known. Here we perform the full mechanical energy budget including available potential energy (APE) and kinetic energy (KE) of this internal mode and decompose the budget into three frequency bands: mean, low frequency (LF) associated with the large-scale mode and high frequency (HF) associated with mesocale eddy turbulence. This decomposition allows us to diagnose the energy fluxes between the different reservoirs and to understand the sources and sinks. Due to the large-scale of the mode, most of its energy is contained in the APE. In our configuration, the only source of LF APE is the transfer from mean APE to LF APE that is attributed to the large-scale baroclinic instability. In return the sinks of LF APE are the parameterized diffusion, the flux toward HF APE and to a much lesser extent toward LF KE. The presence of an additional wind-stress component weakens multidecadal oscillations and modifies the energy fluxes between the different energy reservoirs. The KE transfer appears to only have a minor influence on the multidecadal mode compared to the other energy sources involving APE, in all experiments. These results highlight the utility of the full APE/ KE budget.

Health Promotion and Sexology Student and Teaching Staff Perspectives of Online Learning and Teaching During COVID-19: A Mixed Methods Study

Universities are undergoing rapid and unprecedented changes due to the COVID-19 pandemic, and the needs of learners during this transition are not necessarily well understood or addressed. This study aimed to examine the impact of the “remote internal” unit delivery in a large Western Australian university, as experienced by students and teaching staff within a department of health promotion and sexology (DHPS). In the remote internal mode, previously “internal” (face-to-face) students received prerecorded lectures and attended workshops and seminars in real time through use of the learning platforms. The mixed methods study was conducted across three phases in 2020. A quantitative online student survey was followed by student and teaching staff focus groups and document analysis. Six themes were uncovered regarding the student experience of the remote internal mode: (1) face-to-face contact provides a sense of community, (2) online learning is better when it is interactive, (3) online learning is convenient, (4) delivery mode affects student willingness to contribute to discussions, (5) students enjoy a mixture of teaching patterns, and (6) technological issues create barriers to effective learning. Five themes were revealed regarding teaching staff experience of the remote internal mode: (1) connections matter, (2) face-to-face delivery enhances engagement, (3) learning outcomes are a priority for teaching staff, (4) online delivery needs effective supports, and (5) students have online privacy concerns. Considerations for course modalities, methods to enhance interactivity, and supportive technology and infrastructure are recommended to ensure that the technological, demographic, and socio-environmental needs of students are adequately met.

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.

Direct observation of chaotic resonances in optical microcavities

Optical microcavities play a significant role in the study of classical and quantum chaos. To date, most experimental explorations of their internal wave dynamics have focused on the properties of their inputs and outputs, without directly interrogating the dynamics and the associated mode patterns inside. As a result, this key information is rarely retrieved with certainty, which significantly restricts the verification and understanding of the actual chaotic motion. Here we demonstrate a simple and robust approach to directly and rapidly map the internal mode patterns in chaotic microcavities. By introducing a local index perturbation through a pump laser, we report a spectral response of optical microcavities that is proportional to the internal field distribution. With this technique, chaotic modes with staggered mode spacings can be distinguished. Consequently, a complete chaos assisted tunneling (CAT) and its time-reversed process are experimentally verified in the optical domain with unprecedented certainty.

A Numerical Solution for the Coexisting Field of Surface and Internal Solitary Waves

The numerical solutions for the coexisting fields of surface and internal solitary waves have been obtained, where the set of nonlinear equations based on the variational principle for steady waves are solved using the Newton- Raphson method. The relative phase velocity of surface-mode solitary waves is smaller in the coexisting fields of surface and internal solitary waves than in the cases without the coexistence of internal waves. The relative phase velocity of internal-mode solitary waves is also smaller in the coexisting fields of surface and internal solitary waves than in the cases without surface waves. The interfacial position of an internal mode internal solitary wave in a coexisting field of surface and internal waves can exceed the critical level determined in the corresponding case without a surface wave. The wave height ratio between internal-mode surface and internal solitary waves is smaller than the corresponding linear shallow water wave solution, and the difference increases, as the relative wave height of internal-mode internal solitary waves is increased.