Clock Phase Research Articles

Telemedicine through social media to enhance guideline-directed revascularization in STEMI: a five-year analysis in a developing nation

Abstract Background Timely reperfusion reduces mortality in ST segment Elevation Myocardial infarction (STEMI). Telemedicine and social media have been variably used to improve STEMI care in community settings. We established a new care system for STEMI in a public health setting serving a population of over 80 million, in a state with from a developing nation. Purpose To enhance guideline directed revascularisation (GDR) in STEMI by networking non-percutaneous coronary intervention (PCI) capable hospitals to PCI capable hospitals in a hub-and-spoke model and implementing telemedicine via social media platforms (Whatsapp) over five years(2019-2023). Methods Eighteen Government medical college hospitals were identified as hubs and were provided with cardiac catheterisation laboratories and empowered to provide either round the clock (Phase I hubs) or office hour primary PCI (Phase II hubs). They were linked to 188 Taluk or District-level, non-PCI capable Government hospitals identified as spokes to form 18 STEMI clusters. Separate social media groups on WhatsApp were created for each of the clusters, facilitating the sharing of de-identified ECGs and clinical data from spokes for guidance on diagnosis and management by hub hospital cardiologists. Transfer to hub hospitals for catheter based therapies were coordinated through prior intimation in the cluster WhatsApp group to ensure timely arrival and treatment. A customised uniform protocol for STEMI management was developed and health care personnel were trained accordingly. Human resource support was provided to collect and submit cumulative daily data on the number of STEMIs, the revascularisation provided and mortality through online free web forms. Annual cumulative data on STEMI volumes and GDR were analysed. Results 71,907 STEMI patients were treated from 2019 to 2023. We observed a 67% increase in STEMIs treated per year from over five years (11,363 in 2019 to 18565 in 2023). Use of pharmaco-invasive therapy increased from 7.9% to 31.7% (Figure-1). There was a marginal increase in use of primary PCI. The count of patients without GDR decreased by 20%. There was a 6.7 fold (672 in 2019 to 4,535 in 2023) rise in patients referred from spoke to hub hospitals for catheter-based revascularization. Over five years, there was an increase in the proportion of patients receiving GDR. This increase was more evident in Phase II hubs (52% in 2019 to 87.1% in 2023). Commensurate with the increase in GDR, phase II hubs demonstrated a tangible decrease in mortality (Figure-2). Conclusion We have shown that networking of non-PCI-capable hospitals with PCI-capable hospitals in a hub and spoke model using social media groups, facilitates telemedicine, leading to improved GDR in STEMI. This innovative approach not only enhances connectivity but also contributes to more efficient and timely cardiac care in resource-constrained settings.Figure 1. Revascularisation in STEMIFigure 2.Mortality Trends in STEMI (hubs)

Exenatide administration time-dependently affects the hepatic circadian clock through glucagon-like peptide-1 receptors in the central nervous system

Accumulating evidence indicates that disruption of the circadian clock contributes to the development of lifestyle-related diseases. We have previously shown that exenatide, a glucagon-like peptide-1 (GLP-1) receptor agonist, can strongly affect the molecular clocks in the peripheral tissues. This study aimed to investigate the effects of its dosing time and the central nervous system-specific GLP-1 receptor knockdown (GLP1RKD) on the hepatic clock in mice treated with exenatide. Male C57BL/6J and GLP1RKD mice were housed under a 12-h/12-h light/dark cycle, and feeding was restricted to either the light period (L-TRF) or the first 4 h in the dark period (D-TRF). In parallel, exenatide was administered 4–5 times, once daily either at the beginning of the dark (ZT 12) or light period (ZT 0), and we assessed the mRNA expression rhythms of clock genes in the liver thereafter. Exenatide administration at ZT 12 counteracted the phase shift effect of the L-TRF on the hepatic clock of wild-type mice, whereas the dosing at ZT 0 enhanced its effect. However, exenatide did not influence the phase of the hepatic clock under D-TRF regardless of the dosing time. The effect of exenatide in wild-type mice weakened in GLP1RKD mice. These results showed that exenatide dosing time-dependently affects the hepatic circadian clock through the central GLP-1 system. Exenatide administration at the beginning of the active period (i.e., in the morning for humans) might prevent disruption of the peripheral clocks caused by irregular eating habits.

An efficient nano-design of image processor circuits for morphology operations based on quantum dots

Quantum-dot cellular automata (QCA) are one of the most promising alternatives to traditional VLSI technology despite significant current obstacles. The QCA has the advantages of very low power dissipation, faster switching speed, and extremely low circuit area, which can be used in designing nano-scale image processing circuits. Morphological operations and processing of digital image processing is a significant topic for researchers because it is widely used for analyzing, enhancing, and modifying images to extract meaningful information or improve their visual quality. Image processing is also used for image retrieval and enhancement, image compression, object recognition, machine vision, and medical applications. QCA technology, as a new and leading technology with great potential, can play a fundamental role in morphological operations, processing digital images, image editing, medical imaging, facial recognition, and autonomous vehicles. In recent years, researchers in this field have presented many circuits, but they have many flaws in terms of speed, accuracy, and area consumption, and the need to create more efficient circuits is felt more than ever. Therefore, in this article, a new design for morphological operations and processing digital images is presented using QCA technology. This paper presents a new efficient QCA-based implementation of image processing based on the direct interactions between the QCA cells. This circuit uses two majority gates of five new inputs to produce the output and produces the desired output. In addition, a comparison and analysis of the area and clocking complexity, design cost, and energy dissipation through simulation using QCADesigner and QCADesigner-E are done. The results show that the presented circuit produces the expected and correct output results in 0.75 clock phases, and the obtained results show the high speed and low consumption space of the presented circuit. In addition, the presented circuit performs better than the previous best circuits in terms of quantum cost and delay, and according to the mentioned advantages, it can be used to improve and expand other circuits in image processing.

Reversible arithmetic and logic unit using a novel reversible NRRG gate in quantum dot technology

Quantum-dot Cellular Automata (QCA) has become one of the promising studies for nano-scale computing. QCA is one of the candidate technologies to be replaced with CMOS technology. QCA technology not only reduces power consumption and delay but also increases operating frequency and speed. The arithmetic logic unit is the essential component in a processor that performs arithmetic and logical operations. This paper presents a novel 5 × 5 reversible logic gate called the NRRG (Norouzi_Rasouli Reversible Gate) which can be used as the basic building block of 4:1 and 8:1 reversible multiplexers. Then, we have designed a RALU (reversible arithmetic and logic unit) using this gate. Our design can perform 20 operations such as AND, NAND, OR, XOR, XNOR, COPY, addition, and increment. The proposed QCA RALU requires 0.44 μm2 area, 480 QCA cells, and 10 clock phases. The proposed design needs less cell count, delay, and cost of QCA compared to previous works. The structure is implemented without any rotated cells and only uses one layer which improves the manufacturability of the design. The architectures are designed and simulated using QCA Designer 2.0.3.

An efficient new design of nano-scale comparator circuits using quantum-dot technology

Traditional semiconductor-based technology has recently faced many issues, such as physical scalability constraints and short-channel properties. Much research on nano-scale designs has resulted in these flaws. Quantum-dot Cellular Automata (QCA) is a promising nanotechnology solution for solving CMOS-related issues. The 4-dot squared cell is identified as the main feature of this technology. Also, a comparator is an essential electronic device that compares 2 voltages or currents. It is frequently employed to confirm whether an input has achieved a predefined value or not. So, the design of the QCA-based comparator is one of the interesting lines in recent studies. However, cell and area consumption limits the circuit design in the most relevant research. As a result, two efficient comparator circuits based on the inherent rules of quantum dots have been presented in this work. The proposed 1-bit design employs 35 quantum cells in a 0.04 μm2 compact layout space. Also, the proposed 2-bit design uses 173 cells in a 0.19 μm2 compact layout area. These circuits, which are built across three layers of 90-degree cells, remove the need for coplanar crossovers, ensuring accessible inputs and outputs. The presented 1-bit comparator circuit uses 3 majority gates with three inputs. The first output signal in 1-bit comparator is generated after 0.75 clock phases and in 2-bit design after 1.25 clock phases. QCADesigner-E evaluated the suggested circuits' practical accuracy, cost, and power. The results showed that the proposed designs are extremely efficient in cell and area consumption compared to the state-of-the-art designs.

Practical Advice on Measuring and Applying Light for Laboratory Mammals.

Light is recognized as an important component of the environment for laboratory animals. It supports vision, sets the phase of circadian clocks, and drives wide-ranging adjustments in physiological and behavioral state. Manipulating light is meanwhile a key experimental approach in the fields of vision science and chronobiology. Nevertheless, until recently, there has been no consensus on methods for quantifying light as experienced by laboratory animals. Widely adopted practices employ metrics such as illuminance (units = lux) that are designed to quantify light as experienced by human observers. These weight energy across the spectrum according to a spectral sensitivity profile for human vision that is not widely replicated for non-human species. Recently, a Consensus View was published that proposes methods of light measurement and standardization that take account of these species-specific differences in wavelength sensitivity. Here, we draw upon the contents of that consensus to provide simplified advice on light measurement in laboratory mammal experimentation and husbandry and quantitative guidance on what constitutes appropriate lighting for both visual and circadian function.

Readjustment of circadian clocks by exercise intervention is a potential therapeutic target for sleep disorders: a narrative review.

Circadian clocks are evolved endogenous biological systems that communicate with environmental cues to optimize physiological processes, such as the sleep-wake cycle, which is nearly related to quality of life. Sleep disorders can be treated using pharmacological strategies targeting melatonin, orexin, or core clock genes. Exercise has been widely explored as a behavioral treatment because it challenges homeostasis in the human body and affects the regulation of core clock genes. Exercise intervention at the appropriate time of the day can induce a phase shift in internal clocks. Although exercise is a strong external time cue for resetting the circadian clock, exercise therapy for sleep disorders remains poorly understood. This review focused on exercise as a potential treatment for sleep disorders by tuning the internal circadian clock. We used scientific paper depositories, including Google Scholar, PubMed, and the Cochrane Library, to identify previous studies that investigated the effects of exercise on circadian clocks and sleep disorders. The exercise-induced adjustment of the circadian clock phase depended on exercise timing and individual chronotypes. Adjustment of circadian clocks through scheduled morning exercises can be appropriately prescribed for individuals with delayed sleep phase disorders. Individuals with advanced sleep phase disorders can synchronize their internal clocks with their living environment by performing evening exercises. Exercise-induced physiological responses are affected by age, sex, and current fitness conditions. Personalized approaches are necessary when implementing exercise interventions for sleep disorders.

Research on Clock Synchronization of Data Acquisition Based on NoC

Data acquisition based on network-on-chip (NoC) technology is a high-sampling-rate data acquisition scheme using low-sampling-rate analog–digital conversion (ADC) chips. It has the characteristics of multi-task parallel communication, being global asynchronous, local synchronous clock distribution, high throughput, low transmission latency, and strong scalability. High-speed data acquisition is realized through the combination of an on-chip network and time-interleaved data acquisition technology. In the time-interleaved sampling technique, the precision of clock synchronization directly affects the precision of sampling. Based on the proposed NOC data acquisition scheme, an improved White Rabbit clock synchronization protocol is applied to high-speed data acquisition to achieve high-precision synchronization of multi-channel time-interleaved sampling clocks. Firstly, the offset of the master clock and slave clock is determined by the PTP protocol, and the offset is corrected to achieve rough synchronization between the master clock and slave clock. Secondly, a digital dual-mixer time difference (DDMTD) is used to measure the phases of the master and slave clocks. After that, the phase of the slave clock is corrected through the dynamic phase-shift function of the clock’s phase-locked loop (PLL). Finally, according to the simulation results in Modelsim, the average absolute error of a TI-ADC sampling clock can be less than 20 ps.

A clock synchronization and trigger distribution scheme for China Spallation Neutron Source

China Spallation Neutron Source (CSNS) is a complex system engineering composed of particle accelerators, a target station, and neutron spectrometers with various equipment types and distribution. The collaborative operation of the equipment requires accurate clock synchronization and trigger distribution. Currently, to meet the requirements of different system devices, clock synchronization and trigger distribution in CSNS are implemented based on different methods, resulting in complex clock and trigger networks, demanding upgrades, and a lack of unified timestamps. This paper proposes a clock synchronization and trigger distribution scheme based on the field-programmable gate array (FPGA) and single-mode dual-core fiber link. The decoupling of clock phase synchronization and time base synchronization improves the frequency of phase compensation. Benefiting from the phase interpolator (PI) in the FPGA transceivers, high-precision phase compensation and phase deterministic control are realized, achieving picoseconds synchronization precision and stability in the four-level network. Based on the custom lightweight link layer protocol, by optimizing the routing method of data frames and adopting priority control, the transmission of multiple data is realized, and the hardware delay of the critical data, such as interlock, is guaranteed to be less than 1.5 μs in the four-level system. The scheme provides a general precise clock synchronization and distributed trigger method for CSNS devices, simplifies the system complexity, and is conducive to the system upgrade in the second stage.

Transcriptional rewiring of an evolutionarily conserved circadian clock

Circadian clocks temporally coordinate daily organismal biology over the 24-h cycle. Their molecular design, preserved between fungi and animals, is based on a core-oscillator composed of a one-step transcriptional-translational-negative-feedback-loop (TTFL). To test whether this evolutionarily conserved TTFL architecture is the only plausible way for achieving a functional circadian clock, we adopted a transcriptional rewiring approach, artificially co-opting regulators of the circadian output pathways into the core-oscillator. Herein we describe one of these semi-synthetic clocks which maintains all basic circadian features but, notably, it also exhibits new attributes such as a “lights-on timer” logic, where clock phase is fixed at the end of the night. Our findings indicate that fundamental circadian properties such as period, phase and temperature compensation are differentially regulated by transcriptional and posttranslational aspects of the clockworks.

Current status and applications of time-to-digital converters

Time-to-Digital Converter (TDC) is widely used to realize time interval measurement. The high-precision time measurement technique has important applications in the fields of laser ranging, particle identification, and radioactive nuclear medicine engineering. Based on the existing literature research and data, this paper studies the application areas of TDC in the present development and analyzes the future prospects of TDC applications. The research results showed that: TDC, based on signal screening, realizes time interval measurement as the ultimate purpose of building the system and, at the same time, completes the function of multi-pulse time interval measurement, which can meet the needs of more diversified measurements in the experiments. In the circuit structure, it can identify the feedback output in the all-digital phase-locked loop (ADPLL) and the reference clock phase and frequency information between the feedback output and the reference clock in an ADPLL. It is also promising for use in other areas of high-precision time measurement and processing of circuit signals.

Multi-phase time-zooming high-precision ultrasonic water flow meter

In this study, we have developed a high-precision ultrasonic water flow meter with a 0.18 μm standard CMOS technology. Three methods are proposed to improve the performance: implementation of an active bandpass filter, threshold voltage optimization, and integration of a multi-phase time-zooming technique. The active bandpass filter effectively reduces noise in the received signal, thereby contributing to the overall accuracy of propagation measurements. Based on a threshold voltage generator, our proposed system identifies the optimum threshold voltage, ensuring robust noise durability. Furthermore, we have extended the conventional time-zooming technique by incorporating multiple phases of internal clocks. This innovative multiphase time-zooming technique offers a theoretical improvement in time resolution. The results demonstrate a remarkable suppression of flow rate measurement variations, achieving an impressive reduction to 1/10 of the original values. This affirms the effectiveness of the developed ultrasonic water flow meter in ensuring precise and reliable flow rate measurements.

Implementation of field-programmable Gate array-based clock synchronization in the fiber channel communication system.

A sub-nanosecond clock synchronization scheme based on the field programmable gate array (FPGA) is proposed for the Fiber Channel (FC) communication system in this paper. The counter value of the slave node is synchronized to that of the master node through the embedded IEEE 1588 protocol over the communication link. In order to ensure the counter clocks have the same frequency in both nodes, which is recovered from the FC communication link, the clock phase difference is measured by the digital dual mixer time difference technique and the data recovery technique in the Gigabyte Transceiver, and then it is compensated by the mixed-mode clock manager in FPGAs. The proposed clock synchronization approach is evaluated with an FC communication system that has a serial rate of 12.5 Gbps, and the reported experimental results show that the proposed clock synchronization module can achieve a time difference lower than 1ns.

A Cellular Potts Model of the interplay of synchronization and aggregation.

We investigate the behavior of systems of cells with intracellular molecular oscillators ("clocks") where cell-cell adhesion is mediated by differences in clock phase between neighbors. This is motivated by phenomena in developmental biology and in aggregative multicellularity of unicellular organisms. In such systems, aggregation co-occurs with clock synchronization. To account for the effects of spatially extended cells, we use the Cellular Potts Model (CPM), a lattice agent-based model. We find four distinct possible phases: global synchronization, local synchronization, incoherence, and anti-synchronization (checkerboard patterns). We characterize these phases via order parameters. In the case of global synchrony, the speed of synchronization depends on the adhesive effects of the clocks. Synchronization happens fastest when cells in opposite phases adhere the strongest ("opposites attract"). When cells of the same clock phase adhere the strongest ("like attracts like"), synchronization is slower. Surprisingly, the slowest synchronization happens in the diffusive mixing case, where cell-cell adhesion is independent of clock phase. We briefly discuss potential applications of the model, such as pattern formation in the auditory sensory epithelium.

Synchronized measurement method for urban distribution networks based on proportional-integral control

In the context of the rising prevalence of renewable energy, the need for precise and synchronized measurements in urban distribution networks has become increasingly critical. Conventional synchronization techniques, which predominantly depend on Global Navigation Satellite System (GNSS) timing signals, are often plagued by significant sampling time errors. Addressing this challenge, this study introduces an innovative automatic synchronization measurement method employing proportional-integral (PI) control. This method is composed of three integral components: the monitoring of local clock phases via pulses per second (PPS) signals, modulation of the clock phase through a PI controller, and the estimation of grid phasors from the synchronized sampled data. The test results of this method on a hardware platform demonstrate its capability to significantly reduce the sampling error from 2 × 10−3 V to an impressive 1 × 10−5 V, while also meeting the requirements of the synchronized phasor measurement standards outlined in C37.118.1. These advancements underscore the significant potential of PI-controlled simultaneous sampling in enhancing the operational efficiency and reliability of urban distribution networks, particularly in environments with a high integration of renewable energy sources.

Modeling the interplay of oscillatory synchronization and aggregation via cell–cell adhesion

We present a model of systems of cells with intracellular oscillators (‘clocks’). This is motivated by examples from developmental biology and from the behavior of organisms on the threshold to multicellularity. Cells undergo random motion and adhere to each other. The adhesion strength between neighbors depends on their clock phases in addition to a constant baseline strength. The oscillators are linked via Kuramoto-type local interactions. The model is an advection-diffusion partial differential equation with nonlocal advection terms. We demonstrate that synchronized states correspond to Dirac-delta measure solutions of a weak version of the equation. To analyze the complex interplay of aggregation and synchronization, we then perform a linear stability analysis of the incoherent, spatially uniform state. This lets us classify possibly emerging patterns depending on model parameters. Combining these results with numerical simulations, we determine a range of possible far-from equilibrium patterns when baseline adhesion strength is zero: There is aggregation into separate synchronized clusters with or without global synchrony; global synchronization without aggregation; or unexpectedly a ‘phase wave’ pattern characterized by spatial gradients of clock phases. A 2D Lattice-Gas Cellular Automaton model confirms and illustrates these results.

Abstract WP9: Ischemic Stroke Progression After Witnessed Onset in Daytime vs Night-Time

Introduction: Early neurologic deterioration (END) and poor functional outcomes are more frequent with night than daytime onset of ischemic stroke. This variation may be related to: 1) circadian variation endogenous bodily rhythms and/or 2) extrinsic environmental time cues. Methods: To assess the contribution of extrinsic environmental time to ischemic stroke course, we evaluated patients with acute cerebral ischemia (ACI) onset within last 2h, enrolled in the NIH FAST-MAG trial of prehospital neuroprotection, consisting of patients with witnessed/wake onset. Results: Among 1235 ACI patients (ischemic stroke 1033, TIA 202), age was 70.8 [±13.2], 45.3% female, initial NIHSS 7 (IQR 2-15), LKW to randomization 59 mins (IQR 46-80), and 473 (38%) treated with IV lytics. Onset occurred during clock daytime (07:00-22:59) in 1147 (92.9%) and night-time (23:00-06:59) in 88 (7.1%). Patients were similar in 18 baseline characteristics, but night-onset had higher initial SBP (162 vs 155, p=0.01) and longer onset to paramedic times (33m vs 23m, p = 0.0002). Among non-lytic patients, both unadjusted and adjusted clinical outcomes were similar in night vs daytime patients, including END (13.6% vs 16.4%), 90d mRS 0-2 (63.6% vs 58.5%), and 90d mortality (10.2% vs 12.8%). Among lytic patients, clinical outcomes were also similar in night vs daytime onset patients, including unadjusted END (36% vs 21.7%), 90d mRS 0-2 (52% vs 46.9%), and 90d mortality (12% vs 17.4%). Night vs daytime onset did not modify the effect of magnesium vs placebo on outcome among either non-thrombolytic or thrombolytic-treated patients (Figure). Conclusion: Among acute cerebral ischemia patients, efficacy, safety, and neuroprotective agent response outcomes were not modified by witnessed onset during active versus inactive phase clock times. These findings suggest biological wake-sleep state rather than chronologic clock time is the driver of known circadian rhythmicity in stroke course.

Melanopsin DNA aptamers can regulate input signals of mammalian circadian rhythms by altering the phase of the molecular clock.

DNA aptamers can bind specifically to biomolecules to modify their function, potentially making them ideal oligonucleotide therapeutics. Herein, we screened for DNA aptamer of melanopsin (OPN4), a blue-light photopigment in the retina, which plays a key role using light signals to reset the phase of circadian rhythms in the central clock. Firstly, 15 DNA aptamers of melanopsin (Melapts) were identified following eight rounds of Cell-SELEX using cells expressing melanopsin on the cell membrane. Subsequent functional analysis of each Melapt was performed in a fibroblast cell line stably expressing both Period2:ELuc and melanopsin by determining the degree to which they reset the phase of mammalian circadian rhythms in response to blue-light stimulation. Period2 rhythmic expression over a 24-h period was monitored in Period2:ELuc stable cell line fibroblasts expressing melanopsin. At subjective dawn, four Melapts were observed to advance phase by >1.5 h, while seven Melapts delayed phase by >2 h. Some Melapts caused a phase shift of approximately 2 h, even in the absence of photostimulation, presumably because Melapts can only partially affect input signaling for phase shift. Additionally, some Melaps were able to induce phase shifts in Per1::luc transgenic (Tg) mice, suggesting that these DNA aptamers may have the capacity to affect melanopsin in vivo. In summary, Melapts can successfully regulate the input signal and shifting phase (both phase advance and phase delay) of mammalian circadian rhythms in vitro and in vivo.

Clock synchronizing radio access networks to picosecond precision using optical clock distribution and clock phase caching

Performing positioning of future mobile devices using trilateration through radio access networks would provide a robust alternative to currently used global navigation satellite systems. However, the positioning accuracy is strongly dependent on the time synchronization accuracy of the antennas used as location reference points. Consequently, achieving sub-30 cm positioning accuracies requires the synchronization of radio access network antennas to sub-nanosecond accuracy. Here we show a clock phase synchronization and optical clock signal distribution approach to clock synchronization in radio access networks that achieves 0.98-ps root-mean-square precision clock synchronization, in a real-time field-trial demonstration on 37.6-km dark fiber, with optical clock frequency synchronization and clock phase caching operating using 25.6-Gb/s commercial transceivers. We quantify the clock synchronization performance of our approach using standard metrics, including time deviation (TDEV) and mean time interval error (MTIE). Furthermore, we estimate the impact of varying the phase update rate used in clock phase caching on the clock synchronization performance of our approach. Through our two combined approaches, we explore a route towards achieving sub-nanosecond clock synchronization in radio access networks.

Reaction of the endogenous regulatory mechanisms to early weekday wakeups: a review of its popular explanations in light of model-based simulations.

Introduction: Several widely held explanations of the mechanisms underlying the responses of endogenous sleep-wake-regulating processes to early weekday wakeups have been proposed. Here, they were briefly reviewed and validated against simulations based on the rhythmostatic version of a two-process model of sleep-wake regulation. Methods: Simulated sleep times on weekdays and weekends were compared with the times averaged over 1,048 samples with either earlier or later weekday risetimes. In total, 74 paired samples were collected before and during lockdown, and 93 paired samples were collected during early and later school start times. Results: The counterintuitive predictions of the simulations included the following: 1) only one night of ad lib sleep is sufficient to restore the endogenously determined sleep times after 1day/5 days of larger/smaller reduction/extension of the sleep/wake phase of the circadian sleep-wake cycle; 2) sleep loss on weekdays is irrecoverable; 3) irrespective of the amount of such deadweight loss, sleep on weekends is not prolonged; and 4) the control of the circadian clocks over the sleep-wake cyclicity is not disrupted throughout the week. Discussion: The following popular explanations of the gaps between weekends and weekdays in sleep timing and duration were not supported by these simulations: 1) early weekday wakeups cause "social jetlag," viewed as the weekend and weekday (back and forth) shifts of the sleep phase relative to the unchanged phase of the circadian clocks, and 2) early weekday wakeups cause an accumulation of "sleep debt paid back" on weekends, or, in other terms, people can "catch-up" or "compensate" sleep on weekends.