Resonance-enhanced spectral funneling in Fabry–Perot resonators with a temporal boundary mirror

A temporal boundary refers to a specific time at which the properties of an optical medium are abruptly changed. When light interacts with the temporal boundary, its spectral content can be redistributed due to the breaking of continuous time-translational symmetry of the medium where light resides. In this work, we use this principle to demonstrate, at terahertz (THz) frequencies, the resonance-enhanced spectral funneling of light coupled to a Fabry–Perot resonator with a temporal boundary mirror. To produce a temporal boundary effect, we abruptly increase the reflectance of a mirror constituting the Fabry–Perot resonator and, correspondingly, its quality factor in a step-like manner. The abrupt increase in the mirror reflectance leads to a trimming of the coupled THz pulse that causes the pulse to broaden in the spectral domain. Through this dynamic resonant process, the spectral contents of the input THz pulse are redistributed into the modal frequencies of the high-Q Fabry–Perot resonator formed after the temporal boundary. An energy conversion efficiency of up to 33% was recorded for funneling into the fundamental mode with a Fabry–Perot resonator exhibiting a sudden Q-factor change from 4.8 to 48. We anticipate that the proposed resonance-enhanced spectral funneling technique could be further utilized in the development of efficient mechanically tunable narrowband terahertz sources for diverse applications.

Tempos do passado e tempos do futuro em confronto: diferenças e paralelismos

This paper deals with the main similarities and differences that arise between past and future tenses. In particular, we argue that, while the propositions associated with past tenses are completely settled and their truth-value can be evaluated at the speech time, the propositions described by future tenses cannot be seen as true or false at the utterance time since these linguistic forms are ramifying, in that they typically point to a variety of inertia histories or inertia worlds. Nevertheless, if we consider more closely some particular tenses in European Portuguese – namely the Pretérito Imperfeito (Imperfect) and the Pretérito Perfeito do Indicativo (simple past), as representatives of the past tenses, and the Futuro Simples (simple future) and the structure ir (‘go’) + Infinitive, as representatives of the future ones, we conclude that there are also some important parallels across the two temporal domains. We claim that both the Imperfeito and the Futuro Simples merely locate the situations in a past or future interval, respectively, and that the final interpretation of the sentences in which they occur is the result of the interaction of their temporal characteristics with aspectual and modal features. The Pretérito Perfeito and the structure ir (‘go’) + Infinitive, on the other hand, share the common property of imposing an additional temporal boundary beyond which the eventualities cannot take place; as a result, aspectual effects and modal readings are much more conditioned and pure temporal interpretations – both in the past and in the future – become greatly predominant.

Transcending time and place in the context of Covid-19

During 2020, because of Covid-related restrictions, opportunities to travel to sacred heritage sites dramatically decreased and Pagans’ and shamans’ gatherings and rituals necessarily moved online. This article picks up from an earlier paper (Rountree, 2006) to reconsider relationships between time, place, imagination and ritual performance in the online context. It argues that whereas in the context of “real” heritage sites, the temporal boundary between past and present seems to blur or dissolve as a result of Pagans’ embodied, material connections with a sacred place, in the online ritual context boundaries of place blur or dissolve because of synchronous temporal connections with likeminded others in sacred space. Two case studies are explored: the responses of those who gathered online to witness English Heritage’s livestreaming of Summer Solstice 2020 at Stonehenge, and the experiences of a group of modern Western shamans, mostly living in Malta, whose regular meetings shifted from members’ homes, places in nature and sacred heritage sites to Zoom in early 2020.

Self-Supervised Video Action Localization with Adversarial Temporal Transforms

Weakly-supervised temporal action localization aims to locate intervals of action instances with only video-level action labels for training. However, the localization results generated from video classification networks are often not accurate due to the lack of temporal boundary annotation of actions. Our motivating insight is that the temporal boundary of action should be stably predicted under various temporal transforms. This inspires a self-supervised equivariant transform consistency constraint. We design a set of temporal transform operations, including naive temporal down-sampling to learnable attention-piloted time warping. In our model, a localization network aims to perform well under all transforms, and another policy network is designed to choose a temporal transform at each iteration that adversarially brings localization result inconsistent with the localization network's. Additionally, we devise a self-refine module to enhance the completeness of action intervals harnessing temporal and semantic contexts. Experimental results on THUMOS14 and ActivityNet demonstrate that our model consistently outperforms the state-of-the-art weakly-supervised temporal action localization methods.

Quenched topological boundary modes can persist in a trivial system

Topological boundary modes can occur at the spatial interface between a topological and gapped trivial phase and exhibit a wavefunction that exponentially decays in the gap. Here we argue that this intuition fails for a temporal boundary between a prequench topological phase that possess topological boundary eigenstates and a postquench gapped trivial phase that does not possess any eigenstates in its gap. In particular, we find that characteristics of states (e.g., probability density) prepared in a topologically non-trivial system can persist long after it is quenched into a gapped trivial phase with spatial profiles that appear frozen over long times postquench. After this near-stationary window, topological boundary mode profiles decay albeit, slowly in a power-law fashion. This behavior highlights the unusual features of nonequilibrium protocols enabling quenches to extend and control localized states of both topological and non-topological origins.

Temporal certainty of material civil legal relations. Some problematic issues

This article is devoted to the study of the scientific question of the temporal parameters of the certainty of the protection and legal relationship that arises in the case of violation of the subjective civil rights of the person. The author’s vision of the time of existence of the law is given, in this context the fundamental difference between the concepts of "duration of the legal relationship" and "time of exercise of subjective right" is substantiated. It is substantiated that the duration of the behavior of the contractors is not always equal to the duration of the legal relationship, because the moment of the relationship does not always coincide with the moment of its implementation. Along with the legal relationship arises not the behavior itself, but only the legal means of ensuring such behavior – a subjective right and legal obligation. So, on the other hand, the time for the exercise of a subjective right coincides with the period of its existence. Given that the temporal factors in the protection of law have a significant specificity of regulation, a fundamental separation of protective and regulatory material relations. The fact is that it is not always easy to establish a temporal boundary when an intact right passes to a disturbed state. This means that there are certain problems in accessing the appropriate protective tools. Examples of such substitution of concepts and criteria for their elimination are given. The paper also provides a scientific definition of the real essence of the protective relationship, which is that in the case of violation of subjective substantive law there is a different than before, the interaction, which is protective and legal in nature. It includes the material claim of the right holder to the infringer and the corresponding obligation of the latter. It is noted that the forms of implementation of the protection requirement of the holder of the new right may be different, each of them has its own time regulators. For example, a lawsuit is filed for a limited period of time – a statute of limitations, while for operational measures or other out–of–court claims there are special deadlines, or no time limit at all. Therefore, the need for a separate temporal mediation of each of these methods of protective response is emphasized.