Free running period affected by network structures of suprachiasmatic nucleus neurons exposed to constant light

Exposed to the natural light-dark cycle,24 h rhythms exist in behavioral and physiological processes of living beings.Interestingly,under constant darkness or constant light,living beings can maintain a robust endogenous rhythm with a free running period(FRP)close to 24 h.In mammals,the circadian rhythm is coordinated by a master clock located in the suprachiasmatic nucleus(SCN)of the brain,which is composed of about twenty thousand self-oscillating neurons.These SCN neurons form a heterogenous network to output a robust rhythm.Thus far,the exact network topology of the SCN neurons is unknown.In this article,we examine the effect of the SCN network structure on the FRP when exposed to constant light by a Poincare model.Four typical network structures are considered,including a nearest-neighbor coupled network,a Newman-Watts small world network,an Erd¨os-Renyi random network and a Barabasi-Albert(BA)scale free network.The results show that the FRP is longest in the BA network,because the BA network is characterized by the most heterogeneous structure among these four types of networks.These findings are not affected by the average node degree of the SCN network or the value of relaxation rate of the SCN neuronal oscillators.Our findings contribute to the understanding of how the network structure of the SCN neurons influences the FRP.

Joint MAP channel estimation and data detection for OFDM in presence of phase noise from free running and phase locked loop oscillator

This paper addresses a computationally compact and statistically optimal joint Maximum a Posteriori(MAP)algorithm for channel estimation and data detection in the presence of Phase Noise(PHN)in iterative Orthogonal Frequency Division Multiplexing(OFDM)receivers used for high speed and high spectral efficient wireless communication systems.The MAP cost function for joint estimation and detection is derived and optimized further with the proposed cyclic gradient descent optimization algorithm.The proposed joint estimation and detection algorithm relaxes the restriction of small PHN assumptions and utilizes the prior statistical knowledge of PHN spectral components to produce a statistically optimal solution.The frequency-domain estimation of Channel Transfer Function(CTF)in frequency selective fading makes the method simpler,compared with the estimation of Channel Impulse Response(CIR)in the time domain.Two different time-varying PHN models,produced by Free Running Oscillator(FRO)and Phase-Locked Loop(PLL)oscillator,are presented and compared for performance difference with proposed OFDM receiver.Simulation results for joint MAP channel estimation are compared with Cramer-Rao Lower Bound(CRLB),and the simulation results for joint MAP data detection are compared with“NO PHN"performance to demonstrate that the proposed joint MAP estimation and detection algorithm achieve near-optimum performance even under multipath channel fading.

Diagnostic values of combination of free running asthma screening test and total serum allergen IgE level in children with asthma

Background A free running asthma screening test is usually used for screening exercise-induced bronchoconstriction.The total serum allergen IgE level can reveal the patient＇s atopy characteristics.Our study is to evaluate the diagnostic values of the combination of the two tests in asthmatic children and compare this new diagnostic method with the Intemational Study of Asthma and Allergies in Childhood （ISSAC） questionnaires and the bronchial provocation test,which are popular diagnostic tool for pediatric asthma.Methods A total of 773 school children were recruited in this study.The children＇s asthma was diagnosed by means of a combination of the free running asthma screening test and total serum allergen IgE level.The new diagnostic method value was assessed using receiver operating characteristic （ROC） curves and compared with other diagnostic tools such as ISSAC questionnaires and the bronchial provocation test.Results The AUC of this new diagnostic method was higher than 0.9.When the cut-off value of total serum allergen IgE level was ≥47 KU/L,the sensitivity and the specificity were 71.4％ and 85.1％,respectively,which were better than those of either the ISSAC questionnaires or bronchial provocation test.Conclusion The combination of the free running asthma screening test and total serum allergen IgE level may be an effective diagnostic tool for children＇s asthma.

Collective behaviors of suprachiasm nucleus neurons under different light–dark cycles

The principal circadian clock in the suprachiasm nucleus （SCN） regulates the circadian rhythm of physiological and behavioral activities of mammals. Except for the normal function of the circadian rhythm, the ensemble of SCN neurons may show two collective behaviors, i.e., a free running period in the absence of a light-dark cycle and an entrainment ability to an external T cycle. Experiments show that both the free running periods and the entrainment ranges may vary from one species to another and can be seriously influenced by the coupling among the SCN neurons. We here review the recent progress on how the heterogeneous couplings influence these two collective behaviors. We will show that in the case of homogeneous coupling, the free running period increases monotonically while the entrainment range decreases monotonically with the increase of the coupling strength. While in the case of heterogenous coupling, the dispersion of the coupling strength plays a crucial role. It has been found that the free running period decreases with the increase of the dispersion while the entrainment ability is enhanced by the dispersion. These findings provide new insights into the mechanism of the circadian clock in the SCN.