Delayed sleep phase disorder

Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep–wake phase disorder, is the delaying of a person's circadian rhythm (biological clock) compared to those of societal norms. The disorder affects the timing of biological rhythms including sleep, peak period of alertness, core body temperature, and hormonal cycles. The diagnosis of this disorder is currently a point of contention among specialists of sleep disorders. Many insomnia-related disorders can present significantly differently between patients, and circadian rhythm disorders and melatonin related disorders are not well understood by modern medical science. The orexin system was identified only in 1998, yet it appears intimately implicated in human sleep-wake systems. Evidence for the plasticity of human circadian rhythm cycles has been provided by multiple studies. In one example, several dozen volunteers spent many months underground in a French cave, while researchers monitored their periods of waking and sleeping. Their results found significant divergence between individuals, with most participants settling upon a rhythm of 30 +/- 4 hours. Researchers have speculated that the lack of exposure to natural sunrise/sunset cycles relates many of the symptoms of these circadian disorders to modern habits of humans spending extended periods indoors, without sunlight exposure and with artificial light. Symptom management may be possible with therapeutic drugs such as orexin antagonists or melatonin receptor agonists, as well as regular outdoor exercise. There may be a genetic component to the syndrome. DSPD was first formally described in 1981 by Elliot D. Weitzman and others at Montefiore Medical Center. It is responsible for 7–13% of patient complaints of chronic insomnia. However, since many doctors are unfamiliar with the condition, it often goes untreated or is treated inappropriately; DSPD is often misdiagnosed as primary insomnia or as a psychiatric condition.

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Delayed sleep phase disorder

Circadian rhythm sleep disorder

Circadian rhythm sleep disorders (CRSD), also known as circadian rhythm sleep-wake disorders (CRSWD), are a family of sleep disorders which affect the timing of sleep. CRSDs arise from a persistent pattern of sleep/wake disturbances that can be caused either by dysfunction in one's biological clock system, or by misalignment between one's endogenous oscillator and externally imposed cues. As a result of this mismatch, those affected by circadian rhythm sleep disorders have a tendency to fall asleep at unconventional time points in the day.

Non-24-hour sleep–wake disorder

Non-24-hour sleep–wake disorder (non-24 or N24SWD) is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in a society". Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light–dark cycle in nature. Although this sleep disorder is more common in blind people, affecting up to 70% of the totally blind, it can also affect sighted people.

Superior robustness of anomalous non-reciprocal topological edge states

Romain Christophe Rémy Fleury, Zhechen Zhang, Pierre Delplace

Robustness against disorder and defects is a pivotal advantage of topological systems, manifested by the absence of electronic backscattering in the quantum-Hall and spin-Hall effects, and by unidirectional waveguiding in their classical analogues. Two-dimensional (2D) topological insulators, in particular, provide unprecedented opportunities in a variety of fields owing to their compact planar geometries, which are compatible with the fabrication technologies used in modern electronics and photonics. Among all 2D topological phases, Chern insulators are currently the most reliable designs owing to the genuine backscattering immunity of their non-reciprocal edge modes, brought via time-reversal symmetry breaking. Yet such resistance to fabrication tolerances is limited to fluctuations of the same order of magnitude as their bandgap, limiting their resilience to small perturbations only. Here we investigate the robustness problem in a system where edge transmission can survive disorder levels with strengths arbitrarily larger than the bandgap—an anomalous non-reciprocal topological network. We explore the general conditions needed to obtain such an unusual effect in systems made of unitary three-port non-reciprocal scatterers connected by phase links, and establish the superior robustness of anomalous edge transmission modes over Chern ones to phase-link disorder of arbitrarily large values. We confirm experimentally the exceptional resilience of the anomalous phase, and demonstrate its operation in various arbitrarily shaped disordered multi-port prototypes. Our results pave the way to efficient, arbitrary planar energy transport on 2D substrates for wave devices with full protection against large fabrication flaws or imperfections.

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