Full Entrainment Research Articles

The Role of Coherent Airflow Structures on the Incipient Aeolian Entrainment of Coarse Particles

AbstractThe role of coherent airflow structures capable of setting gravel‐sized particles in motion is studied theoretically and experimentally. Specifically, a micromechanical model based on energy conservation is proposed to describe the incipient motion of large‐particles ranging from rocking (incomplete entrainment) to incipient rolling (full entrainment). Wind tunnel experiments were conducted on an aerodynamically rough bed surface under near‐threshold airflow conditions. Synchronous signals of airflow velocities upwind of the test particles and particle displacement are measured using a hot film anemometer and a laser distance sensor, respectively, from which coherent airflow structures (extracted via quadrant analysis) and particle movements are interlinked. It is suggested that the incipient motion of gravel‐sized particles (rocking and rolling) may result from sufficiently energetic sweep events corresponding to aerodynamic drag forces in excess of the local micro‐topography resistance. However, full entrainment in rolling mode should satisfy the presented work‐based criterion. Furthermore, using an appropriate probabilistic frame, the proposed criterion may be suitable for describing processes of energy transfer from the wind to the granular soil surface, ranging from the creep transport of gravels to the “mechanical sieving” of mega‐ripples, as well as the transport of light anthropogenic debris (such as plastics).

Divisive gain modulation enables flexible and rapid entrainment in a neocortical microcircuit model.

Neocortical circuits exhibit a rich dynamic repertoire, and their ability to achieve entrainment (adjustment of their frequency to match the input frequency) is thought to support many cognitive functions and indicate functional flexibility. Although previous studies have explored the influence of various circuit properties on this phenomenon, the role of divisive gain modulation (or divisive inhibition) is unknown. This gain control mechanism is thought to be delivered mainly by the soma-targeting interneurons in neocortical microcircuits. In this study, we use a neural mass model of the neocortical microcircuit (extended Wilson–Cowan model) featuring both soma-targeting and dendrite-targeting interneuronal subpopulations to investigate the role of divisive gain modulation in entrainment. Our results demonstrate that the presence of divisive inhibition in the microcircuit, as delivered by the soma-targeting interneurons, enables its entrainment to a wider range of input frequencies. Divisive inhibition also promotes a faster entrainment, with the microcircuit needing less time to converge to the fully entrained state. We suggest that divisive inhibition, working alongside subtractive inhibition, allows for more adaptive oscillatory responses in neocortical circuits and, thus, supports healthy brain functioning.NEW & NOTEWORTHY We introduce a computational neocortical microcircuit model that features two inhibitory neural populations, with one providing subtractive and the other divisive inhibition to the excitatory population. We demonstrate that divisive inhibition widens the range of input frequencies to which the microcircuit can become entrained and diminishes the time needed to reach full entrainment. We suggest that divisive inhibition enables more adaptive oscillatory activity, with important implications for both normal and pathological brain function.

Liquid entrainment behavior at the nozzle exit in coaxial gas–liquid jets

The near-field flow behavior of coaxial gas–liquid jets has a significant influence on the atomization performance and life cycle of atomizers, and the present study focused on this issue. The flow visualization technique was employed to examine liquid entrainment behavior near the nozzle. The thick central tube affected both gas and liquid flow fields. Liquid entrainment could be observed in the near-field with the increase in gas velocity, and a liquid “bulge” structure was induced on the surface of the near-field liquid jet for the first time. The formation mechanism and dynamic characteristics of the “bulge” were studied. Two critical situations in the liquid entrainment process to the surface of the central tube were identified as “initial entrainment” and “full entrainment”. The two critical situations were studied in a convective gas–liquid layer in the recirculation region based on total pressure conservation theory. The theoretical models for the two situations were obtained, and these models agreed well with the experimental results.

The Comparison between Circadian Oscillators in Mouse Liver and Pituitary Gland Reveals Different Integration of Feeding and Light Schedules

The mammalian circadian system is composed of multiple peripheral clocks that are synchronized by a central pacemaker in the suprachiasmatic nuclei of the hypothalamus. This system keeps track of the external world rhythms through entrainment by various time cues, such as the light-dark cycle and the feeding schedule. Alterations of photoperiod and meal time modulate the phase coupling between central and peripheral oscillators. In this study, we used real-time quantitative PCR to assess circadian clock gene expression in the liver and pituitary gland from mice raised under various photoperiods, or under a temporal restricted feeding protocol. Our results revealed unexpected differences between both organs. Whereas the liver oscillator always tracked meal time, the pituitary circadian clockwork showed an intermediate response, in between entrainment by the light regimen and the feeding-fasting rhythm. The same composite response was also observed in the pituitary gland from adrenalectomized mice under daytime restricted feeding, suggesting that circulating glucocorticoids do not inhibit full entrainment of the pituitary clockwork by meal time. Altogether our results reveal further aspects in the complexity of phase entrainment in the circadian system, and suggest that the pituitary may host oscillators able to integrate multiple time cues.

Olfactory cues accelerate reentrainment following phase shifts and entrain free-running rhythms in female Octodon degus (Rodentia).

Social interactions between conspecifics is a type of nonphotic zeitgeber common to several species. In the diurnal rodent Octodon degus, social interactions enhance reentrainment after phase shifts and can act as a weak zeitgeber. Olfactory stimuli appear necessary for these effects since bulbectomy eliminates socially enhanced reentrainment. In Experiment 1, the authors examined whether stimulation of the main olfactory system was sufficient to enhance reentrainment after 6-h phase advances and delays in the adult female O. degus. When test animals received conspecific odor cues during reentrainment, they entrained 39% faster after phase advances (p < 0.05) and 33% faster after phase delays (p < 0.001) than when they did not receive odor cues. Thus, olfactory cues from distant female donors were sufficient to enhance rates of entrainment in female O. degus and provided results equivalent to earlier studies with donors and shifters housed in the cages together. In Experiment 2, the authors examined whether discrete 3-h and 1-h daily pulses of airborne odors from a group of 5 entrained female degus would be sufficient to produce entrainment of wheel-running activity in adult female conspecifics. During the period of exposure to 3-h pulses, 50% (4/8) of the subjects temporarily entrained to a 24-h cycle, while 12.5% (1/8) of the subjects fully entrained. Exposure to 1-h pulses allowed 37.5% (3/8) of the subjects to temporarily entrain and 12.5% (1/8) of the subjects to fully entrain. Duration of entrained episodes was positively correlated with psi, daily onset of activity with respect to the timing of odor exposure (Pearson r = 0.731; p < 0.05), such that animals with the entraining odor pulse beginning during subjective day (psi = 7.8 h, CT 7.8 +/- 1.4) had longer periods of entrainment (22.2 +/- 5.6 days) than animals with the entraining pulse occurring during subjective night (psi = -4.6 h; CT 19.4 +/- 0.9; 5.6 +/- 0.9 days; p < 0.001). In addition, for each animal, the combined duration of all episodes of 24-h entrainment correlated with increased period length (tau) of free-running rhythms (Pearson r = 0.733; p < 0.05). Thus, daily discrete pulses of odors with durations of either 1 or 3 h from female conspecifics were sufficient to produce both temporary and full entrainment to a 24-h cycle in the majority of female O. degus, and the likelihood of long periods of entrainment correlated with long taus and coordination of the odor pulse with mid subjective day.

Amplitude dropout in coupled lasers

We study the entrainment of coupled solid-state lasers by an external injected field. We show that the total output intensity exhibits unexpected nonmonotonic behavior as a function of the injected field and find the critical amplitude marking the transition to the low-intensity branch. In addition, we also show that substantial partial entrainment can be achieved for injected fields much weaker than that required for full entrainment.

Phase model analysis of two lasers with injected field

We study the dynamics of two coupled solid state lasers subject to an injected field. A singular perturbation technique is used to reduce the full set of rate equations; we present a comprehensive bifurcation analysis of the resulting phase model. We find four distinct routes to full entrainment as the injected field amplitude increases; bifurcation diagram predicts that the entrainment (reflected in the total intensity) does not monotonically improve with the injected field strength. Our numerical simulations suggest that the reduced phase model captures the relevant dynamics well beyond the asymptotic regime in which it is derived.

Social cues modulate free-running circadian activity rhythms in the diurnal rodent, Octodon degus.

Two experiments assessed the effects of social cues and daily disturbance on the circadian locomotor activity rhythms of Octodon degus housed in constant darkness. In experiment 1, females in free-running conditions were housed alone or with entrained female partners ("donors") in cages on either side of a mesh barrier. Donors were removed daily and entrained to 1 h of light, and as a control, the cages of singly housed animals were rustled daily coincident with donor removal and replacement. None of the animals housed alone entrained to daily disturbances presented during the active phase, and seven of eight degus failed to show changes in the circadian period (tau) or phase of their rhythms. In contrast, although the presence of entrained donors did not elicit full entrainment of free-running rhythms, five of six animals demonstrated partial entrainment for 5-12 days (of 30 days), four of six altered phase of activity onset, and six of six lengthened tau of circadian rhythms. In experiment 2, females whose free-running circadian activity rhythms were at least 10 h out of phase were housed together in pairs. None of the pairs demonstrated mutual synchronization of their activity rhythms, although 8 of 12 degus modified phase of activity onset and 9 of 12 animals altered tau. We conclude social information in the absence of light, is sufficient for partial entrainment and for changes in tau and phase of free-running rhythms in this diurnal rodent.

Entrainment of solid-state laser arrays.

We find that the natural antiphasing tendency in linear solid-state laser arrays can be overcome by an injected field, even if the N elements are not identical. We derive a condition for full entrainment that agrees well with numerical simulations using experimentally accessible parameters. The resulting output intensity saturates near the maximum coherent value of ${\mathit{N}}^{2}$ times that of a single laser. We find that the entrained output can be modulated in a prescribed manner by a suitable choice of the injected field.

Entrainment of the Swimmeret Rhythm of the Crayfish to Controlled Movements of Some of the Appendages

ABSTRACT A machine was used to impose controlled movements, closely resembling natural movements, on some of the swimmerets of crayfish with their ventral nerve cords cut between thorax and abdomen. The rhythm of the unrestrained swimmerets could be entrained to the imposed frequency. Full entrainment occurred most readily when three or four swimmerets were controlled and was uncommon with two. When one was controlled, only partial entrainment was seen. A small proportion of preparations could not be entrained irrespective of the number of swimmerets controlled. Entrainment of the neural rhythm also occurred when movement was imposed on one or more swimmerets attached to an otherwise isolated nerve cord. This is the first demonstration that sensory input affects the periodicity of the swimmeret rhythm. In the light of this result, the hypothesis that swimmeret rhythm is largely controlled by a central pattern generator should be viewed with caution. It now appears that there is also an influential sensory component responsible for stabilizing and adjusting the timing of the swimmeret rhythm.

Entrainment and chaos in a discrete map with commensurate external forcing

The behaviour of a discrete map under an external forcexn+1 = 1 - λxn2 + σsn is studied, where sn is a sequence of integer periodT representing an external force with a commensurate period. Many properties of self-oscillating systems in the presence of an external force are recovered. In particular, the region of full entrainment at periodT at moderately large values of the force magnitudeσ and the region of natural (unforced,σ = 0) periodT on theλ-axis are found to be topologically connected in parameter space.

The relative importance of sunrise and sunset for entrainment of oviposition in the fowl.

1. A series of four "sunset" signals, without associated sunrises, was given to laying hens by reducing light intensity in steps from 190 lx to 63, 21, 7 and 2 lx at 24-h intervals. Four "sunrises" were given by reversing the process. Treatments involving single "sunrises", single "sunsets" and combinations of sunrises and sunsets at 12-h intervals were also tested. 2. Only treatments which included one or more sunset signals were found to give full entrainment of oviposition, as judged by the proportion of eggs laid in a modal 8-h segment of each 24-h cycle. Full entrainment was achieved if the sunset occurred between 16.00 h and midnight, but not if the sunset occurred in the morning hours. Treatments involving only sunrise signals did not fully entrain oviposition but did have effect on the timing and distribution of ovipositions. Sunrises given in association with sunsets increased the degree of entrainment achieved, as compared with the sunset signal alone. 3. This study indicates that sunset is a potent synchronising agent for phase setting oviposition and, presumably, for phase setting the endogenous circadian rhythm of the fowl. Sunrise can also exert a modifying influence.

Entrainment of oviposition in the fowl using light-dark cycles.

1. Fourteen experiments were performed to determine the minimum photoperiod and minimum scotoperiod needed for entrainment of oviposition in hens exposed to 21-h, 24-h and 30-h cycles. Entrainment was measured by the proportion of total eggs laid in a modal 8-h segment of each cycle. 2. In a 24-h light and dark cycle, a 15-min photoperiod or a 5-h scotoperiod produced essentially the same degree of entrainment as 6 h light, 18 h darkness (6L : 18D) or 14L : 10D, which were used as control treatments. Under 21-h light and dark cycles a minimum 3-h photoperiod or a minimum 9-h scotoperiod was needed to achieve full phase setting. When the cycle length was increased to 30 h a minimum 8-h photoperiod or a minimum 12-h scotoperiod was required for full entrainment. 3. This study demonstrates that photoperiod is a stronger signal than scotoperiod for the purpose of phase setting oviposition. It also shows that a stronger signal is required to achieve entrainment when the length of the light-dark cycle is several hours shorter or longer than the natural period of 24 h.

Entrainment of oviposition in the fowl using bright and dim light cycles.

1. Nine short trial, involving 96 different treatments, were used to investigate the critical intensities and duration of bright and dim periods of lighting needed to entrain oviposition in cycles ranging from 21 to 30 h. 2. Entrainment was shown to depend upon the contrast between bright and dim lighting, and to be independent of the absolute light intensity. 3. A bright: dim ratio of 13:1 fully entrained oviposition in cycles of 25 h and 27 h. For 23-h and 28-h cycles a 30:1 ratio was required. Twenty-one-hour cycles required a ratio of 300:1 and with 30-h cycles a ratio of 1000:1 was needed to achieve full entrainment of oviposition. 4. In 24-h cycles, 1 h of bright lighting at 02.00 h was sufficient to override other environmental signals and cause eggs to be laid in the late evening, but a minimum bright period of 6 h was needed to cause full phase setting with 21-h cycles. 5. Circadian periodicity can easily be imposed on hens by providing a short exposure to bright light with a background of continuous dim light; but the signal must be increased (by providing a greater contrast between bright and dim lights and/or a longer period of bright lighting) to entrain oviposition when the cycle deviates markedly from the natural period of 24 h.

Vaporization Rate Limited Combustion in Bipropellant Rocket Chambers

A one-dimensional model of the bipropellant rocket combustion chamber is analyzed on the as­ sumption that vaporization of liquid droplets is the rate controlling step in the combustion process. The dependence of the gas flow variables on position coordinate in the chamber is determined in elementary analytic form subject to the assumptions that the vaporized propellants are instan­ taneously mixed and reacted in stoichiometri c ratio, and that droplet motion is governed by full entrainment in the product gas flow; i.e., droplet velocity is equal to local gas velocity. The formal solutions obtained permit comparison and contrast with the more fundamental case of monopro­ pellant combustion. It is concluded that in the bipropellant system gas velocity distribution is de­ termined primarily by the droplet spectrum and volatility of the more slowly vaporizing species, and that the temperature distribution is strongly dependent on the droplet size spectrum and volatility of the more rapidly vaporizing species. Depression of the temperature levels associated with the presence of excess unreacted propellant gas near the injector implies the existence of flameholding stability limits due to excessive mismatch in the local vaporization rates. The possible scope of applications and limitations of the vaporization rate controlled combustion model is dis­ cussed on the basis of relevant data available in the literature on combustion in rockets.