Summer activity patterns among teenage girls: harmonic shape invariant modeling to estimate circadian cycles

Background

Physical activity as measured by activity counts over short time intervals across a 24 h period are often used to assess circadian variation. We are interested in characterizing circadian patterns in activity among adolescents and examining how these patterns vary by obesity status. New statistical approaches are needed to examine how factors affect different features of the circadian pattern and to make appropriate covariate adjustments when the outcomes are longitudinal count data.

Methods

We develop a statistical model for longitudinal or repeated activity count data that is used to examine differences in the overall activity level, amplitude (defined as the difference between the lowest and highest activity level over a 24 hour period), and phase shift. Using seven days of continuous activity monitoring, we characterize the circadian patterns and compare them between obese and non-obese adolescent girls.

Results

We find a statistically significant phase delay in adolescent girls who were obese compared with their non-obese counterparts. After the appropriate adjustment for measured potential confounders, we did not find differences in mean activity level between the two groups.

Conclusion

New statistical methodology was developed to identify a phase delay in obese compared with non-obese adolescents. This new approach for analyzing longitudinal circadian rhythm count data provides a useful statistical technique to add to the repertoire for those analyzing circadian rhythm data.     

Circadian light

The present paper reflects a work in progress toward a definition of circadian light, one that should be informed by the thoughtful, century-old evolution of our present definition of light as a stimulus for the human visual system. This work in progress is based upon the functional relationship between optical radiation and its effects on nocturnal melatonin suppression, in large part because the basic data are available in the literature. Discussed here are the fundamental differences between responses by the visual and circadian systems to optical radiation. Brief reviews of photometry, colorimetry, and brightness perception are presented as a foundation for the discussion of circadian light. Finally, circadian light (CL_A) and circadian stimulus (CS) calculation procedures based on a published mathematical model of human circadian phototransduction are presented with an example.     

To sleep or not to sleep: the ecology of sleep in artificial organisms

Background  

All animals thus far studied sleep, but little is known about the ecological factors that generate differences in sleep characteristics across species, such as total sleep duration or division of sleep into multiple bouts across the 24-hour period (i.e., monophasic or polyphasic sleep activity). Here we address these questions using an evolutionary agent-based model. The model is spatially explicit, with food and sleep sites distributed in two clusters on the landscape. Agents acquire food and sleep energy based on an internal circadian clock coded by 24 traits (one for each hour of the day) that correspond to "genes" that evolve by means of a genetic algorithm. These traits can assume three different values that specify the agents' behavior: sleep (or search for a sleep site), eat (or search for a food site), or flexibly decide action based on relative levels of sleep energy and food energy. Individuals with higher fitness scores leave more offspring in the next generation of the simulation, and the model can therefore be used to identify evolutionarily adaptive circadian clock parameters under different ecological conditions.     

CERES-Rice模型区域应用中遗传参数升尺度的一种方法

 为了提升CERES Rice模型中遗传参数的空间尺度,以适应区域性研究需要,以江苏省为例,在具有不同水稻品种生态类型的4个稻区各选5~6个样点,以稻区为空间尺度,利用每个样点4年（2001-2004年）县级统计水稻单产资料及同期同地的气象和土壤资料,结合江苏省各地的水稻品种区域试验资料,采用试错法对CERES Rice中8个遗传参数,特别是4个与产量相关的遗传参数分别进行了调试与确定（方法1,简称稻区尺度调试法）,并与传统的其他3种升尺度方法,即代表性品种单点调试法（方法2）、县级尺度调试法（方法3）和超大尺度调试法（方法4）的模拟效果进行了比较。结果显示,方法1的模拟效果较为理想,各稻区模拟产量与统计产量的相关系数均达到显著或极显著水平,均方根差值均小于9％。而其他3种方法的模拟效果均明显不如方法1。研究提出的遗传参数升尺度方法不仅适用于气候变化影响评价研究,也可为作物生长模型在其他区域研究中的应用提供方法上的借鉴。     

Modeling and experimental validation of tensile properties of sugar palm fiber reinforced high impact polystyrene composites

Sugar palm fiber is one of the most abundant natural fibers used in biocomposites. However, prediction of the mechanical properties of such natural fiber reinforced composites is still challenging. Most of the theoretical modelings are based the micromechanical method. There have been little studies involving statistical approach for prediction of mechanical properties of natural fiber reinforced composites. In this study, the tensile properties of short sugar palm fiber-reinforced high impact polystyrene (SPF-HIPS) composites obtained by means of statistical approach were investigated and compared with the experimental observations and with micromechanical models available in the literature. Statistical approach was used to predict the performance of the composite part with different fiber loadings. A two-parameter Weibull distribution function was used to model the fiber length distribution in the composite. For the experimental validation, the composites were prepared by hot compression technique for different fiber loadings (10 %, 20 %, 30 %, 40 % and 50 % by weight). Tensile testing of the composites was carried out according to ASTM D638 to obtain the composites tensile strength and modulus of elasticity. Experimental results showed that the tensile strength of the composite reduced due to the addition of sugar palm fibers, whereas the elastic modulus increased by a factor of up to 1.34. The current statistical model predicted the tensile properties of SPF-HIPS composite close to the experimental values. It was found that statistical approach with standard micromechanical models can be used to predict the mechanical properties of sugar palm fiber reinforced HIPS composites. Hence, this study could assist in decisions regarding the design of natural fiber reinforced composite products.     

Evolution of temporal order in living organisms

Circadian clocks are believed to have evolved in parallel with the geological history of the earth, and have since been fine-tuned under selection pressures imposed by cyclic factors in the environment. These clocks regulate a wide variety of behavioral and metabolic processes in many life forms. They enhance the fitness of organisms by improving their ability to efficiently anticipate periodic events in their external environments, especially periodic changes in light, temperature and humidity. Circadian clocks provide fitness advantage even to organisms living under constant conditions, such as those prevailing in the depth of oceans or in subterranean caves, perhaps by coordinating several metabolic processes in the internal milieu. Although the issue of adaptive significance of circadian rhythms has always remained central to circadian biology research, it has never been subjected to systematic and rigorous empirical validation. A few studies carried out on free-living animals under field conditions and simulated periodic and aperiodic conditions of the laboratory suggest that circadian rhythms are of adaptive value to their owners. However, most of these studies suffer from a number of drawbacks such as lack of population-level replication, lack of true controls and lack of adequate control on the genetic composition of the populations, which in many ways limits the potential insights gained from the studies. The present review is an effort to critically discuss studies that directly or indirectly touch upon the issue of adaptive significance of circadian rhythms and highlight some shortcomings that should be avoided while designing future experiments.     

A Method for Upscaling Genetic Parameters of CERES-Rice in Regional Applications

To upscale the genetic parameters of CERES-Rice in regional applications, Jiangsu Province, the second largest rice producing province in China, was taken as an example. The province was divided into four rice regions with different rice variety types, and five to six sites in each region were selected. Then the eight genetic parameters of CERES-Rice, particularly the four parameters related to the yield, were modified and validated using the Trial and Error Method and the local statistical data of rice yield at a county level from 2001 to 2004, combined with the regional experiments of rice varieties in the province as well as the local meteorological and soil data (Method 1). The simulated results of Method 1 were compared with those of other three traditional methods upscaling the genetic parameters, i.e., using one-site experimental data from a local representative rice variety (Method 2), using local long-term rice yield data at a county level after deducting the trend yield due to progress of science and technology (Method 3), and using rice yield data at a super scale, such as provincial, ecological zone, country or continent levels (Method 4). The results showed that the best fitness was obtained by using the Method 1. The coefficients of correlation between the simulated yield and the statistical yield in the Method 1 were significant at 0.05 or 0.01 levels and the root mean squared error (RMSE) values were less than 9% for all the four rice regions. The method for upscaling the genetic parameters of CERES-Rice presented is not only valuable for the impact studies of climate change, but also favorable to provide a methodology for reference in crop model applications to the other regional studies.     

A Statistical Framework for Selecting Natural Fibre Reinforced Polymer Composites Based on Regression Model

Material selection is an important stage in the development of products from composites process of automotive component application. Numerious different Multi-Criteria Decision-Making tools have their own strenghts and limitations. This paper presents a framework for material selection of natural fibre reinforced polymer composites by using statistical approach. The framework is developed using statistical methods which are simple, multiple and stepwise regression for the material selection process. The performance of potential material is investigated by a statistical analysis such as coefficient of correlation, coefficient of determination and analysis of variance. A case study to select the best composite of parking brake lever is applied to this framework. End results revealed that kenaf reinforced polypropylene is the best candidate for construction of automotive parking brake lever component. The best possible of statistical model for material selection of the composite can be referred by design engineer in composite industry for a multiple application. Moreover, the proposed framework is an aid to help engineers and designers to choose most suitable material.     

Larval instars determination for the European Grapevine Moth (Lepidoptera: Tortricidae) based on the frequency distribution of head-capsule widths

Morphological measurements such as head-capsule (HC) width can be very useful and accessible tools that may be employed for classifying Lepidopteran larval instars according to stage of life history. The availability of such measures is crucial in the management of larval pests, because their control relies upon making accurate assessment of the life history stage at which larvae has reached in various environmental conditions. Such forecasts are then used in order to estimate the timing of emergence for future adult populations. Previous studies investigated the use of head-capsule widths from field larvae of European Grapevine Moth (EGVM), Lobesia botrana Den. and Schiff., to describe the distributions of the five instars during three generations of the insect. The observations were performed in 1998 and 2002 in a vineyard near Bordeaux. The results presented here increase the scope of earlier methods by providing statistical confidence. Our method was calibrated on a large number of individuals (N = 552) issued from our insect culture and uses a nonlinear least-squares parameter estimation to describe the distribution of each larval instar inside each generation. The model was tested on a wild larval population (n = 3007) occurring in our experimental vineyard during two complete years. The instar class ranges and boundaries were characterized with the associated probabilities of misclassification. A final classification statistical model is developed for each instar and each generation. From this study, we conclude that larval HC sizes increase statistically according to the generation of the year, and thus is influenced by grape phenology.     

Circadian rhythm and its role in malignancy

Circadian rhythms are daily oscillations of multiple biological processes directed by endogenous clocks. The circadian timing system comprises peripheral oscillators located in most tissues of the body and a central pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Circadian genes and the proteins produced by these genes constitute the molecular components of the circadian oscillator which form positive/negative feedback loops and generate circadian rhythms. The circadian regulation extends beyond clock genes to involve various clock-controlled genes (CCGs) including various cell cycle genes. Aberrant expression of circadian clock genes could have important consequences on the transactivation of downstream targets that control the cell cycle and on the ability of cells to undergo apoptosis. This may lead to genomic instability and accelerated cellular proliferation potentially promoting carcinogenesis. Different lines of evidence in mice and humans suggest that cancer may be a circadian-related disorder. The genetic or functional disruption of the molecular circadian clock has been found in various cancers including breast, ovarian, endometrial, prostate and hematological cancers. The acquisition of current data in circadian clock mechanism may help chronotherapy, which takes into consideration the biological time to improve treatments by devising new therapeutic approaches for treating circadian-related disorders, especially cancer.     

Statistical analysis of the effect of multi-stage hot drawing on the thermal shrinkage and crystallographic order of biodegradable aliphatic-aromatic co-polyester fibres

Using statistical experimental design, the effects of multi-stage hot drawing process on thermal shrinkage and crystallographic order of linear aliphatic-aromatic co-polyester fibres were statistically analyzed. Thermal shrinkage and fullwidth half-maximum (FWHM) of an X-ray scattering profile of the fibres have been quantitatively assessed, and the direction of increasing or decreasing the significant process parameters has been characterized. It has been found that the number of drawing stages, drawing temperature and relaxing stage ratio affect the shrinkage and crystallographic order together. Plate temperature and the interaction between drawing stages and drawing temperature or drawing ratio have an effect on thermal shrinkage; Spin finish application and relaxing temperature have an effect on crystallographic order. The data analysis has been characterized with regard to the relationship between the studied factors statistically analyzed and the scientific reasons suggested. Factorial statistical analysis simulates the combination of drawing process parameters and the selected as-spun environmentally friendly biodegradable fibre.     

Fiber formation model for PVP (polyvinyl pyrrolidone) electrospinning. I. Critical voltage

The major concern in electrospinning process is the occurrence of jet formation. In order to study the physical properties of the solution and process parameters, critical voltage models in electrospinning are presented. Critical voltage models are developed to predict the onset of electrospinning. Rayleigh’s instability phenomena at the moment of droplet shape change, Zeleny’s research for relationship between surface tension and electric field, and Taylor’s critical voltage model are the theoretical backgrounds of this proposition. SIC 1, SIC 2, GSP models are suggested to calculate the critical voltage according to the shapes of polymer drop. This newly developed critical voltage model for polymer jet during electrospinning could predict other processing parameters, such as, TCD, radius and length of nozzle, and is verified by comparing experimental values using polyvinyl pyrrolidone (PVP) solution through electrospinning.     

Effects of saliva collection using cotton swabs on melatonin enzyme immunoassay

Background  

Although various acceptable and easy-to-use devices have been used for saliva collection, cotton swabs are among the most common ones. Previous studies reported that cotton swabs yield a lower level of melatonin detection. However, this statistical method is not adequate for detecting an agreement between cotton saliva collection and passive saliva collection, and a test for bias is needed. Furthermore, the effects of cotton swabs have not been examined at lower melatonin level, a level at which melatonin is used for assessment of circadian rhythms, namely dim light melatonin onset (DLMO). In the present study, we estimated the effect of cotton swabs on the results of salivary melatonin assay using the Bland-Altman plot at lower level.     

Standards of evidence in chronobiology: A response

A number of recent studies have debated the existence and nature of clocks outside the suprachiasmatic nucleus that may underlie circadian rhythms in conditions of food entrainment or methamphetamine administration. These papers claim that either the canonical clock genes, or the circuitry in the dorsomedial nucleus of the hypothalamus, may not be necessary for these forms of entrainment. In this paper, we review the evidence necessary to make these claims. In particular, we point out that it is necessary to remove classical conditioning stimuli and interval timer (homeostatic) effects to insure that the remaining entrainment is due to a circadian oscillator. None of these studies appears to meet these criteria for demonstrating circadian entrainment under these conditions. Our own studies, which were discussed in detail by a recent Review in these pages by Mistlberger and colleagues, came to an opposite conclusion. However, our studies were designed to meet these criteria, and we believe that these methodological differences explain why we find that canonical clock gene Bmal1 and the integrity of the dorsomedial nucleus are both required to produce true circadian entrainment under conditions of restricted feeding.     

Ischemic stroke destabilizes circadian rhythms

Background  

The central circadian pacemaker is a remarkably robust regulator of daily rhythmic variations of cardiovascular, endocrine, and neural physiology. Environmental lighting conditions are powerful modulators of circadian rhythms, but regulation of circadian rhythms by disease states is less clear. Here, we examine the effect of ischemic stroke on circadian rhythms in rats using high-resolution pineal microdialysis.     

A mechanical model for felt in impulse drying: A cellular materials approach. II. Experimental validation

High-intensity paper drying processes involve the complex phenomena of multiphase transport in porous media. Impulse drying is such a process, in which enhanced liquid water removal is the key to energy savings. This paper concerns the study of the mechanical behavior of felts used in the papermaking industry, namely those applied in the press section of the paper machine. Here, a viscoelastoplastic model based on the cellular solids theory is presented, and its range of adequacy explored using data from uniaxial laboratory experiments. The model predictions show some agreement with the experiments but accurate documentation of multiphase-flow parameters and a proper heat and mass transport model, able to describe the multiphase transport in the course of the pressing event, would certainly improve the performance of the model.     

A physically based FVM watershed model fully coupling surface and subsurface water flows

A sophisticated modeling approach for simulating-coupled surface and subsurface flows in a watershed is presented. The watershed model developed is a spatially distributed physically based model of composite dimension, consisting of 3-D variably saturated groundwater flow submodel, 2-D overland flow submodel and 1-D river flow submodel. The 3-D subsurface flow is represented by the complete Richards equation, while the 2-D and 1-D surface flows by the diffusive approximations of their complete dynamic equations. For piecewise integration of these equations, the finite volume method (FVM) is employed assuming unknown variables such as the water depth and the pressure head to be volume-averaged state ones. Problem plane geometry is meshed with the unstructured cells of triangular shape which conforms to external as well as internal irregular boundaries such as those between 1-D and 2-D flows. A cell size controlling scheme, referred to as quasi-adaptive meshing scheme, is introduced to keep the local discretization errors caused by topographic elevation gradient even over the entire-meshed geometry. Performance of the model is tested through its practical application to a rugged intermountain watershed. Tuning the values of the three key parameters ensures successful calibration of the model. Once the model is so calibrated, it could reproduce satisfactory runoff response to any rainfall event. Expansion and shrinkage of the contributing area importantly affecting the direct runoff, caused by the vicissitude of rainfall during its total duration, are well reproduced, like what the commonly accepted runoff theory argues. It is thus concluded that the model developed could serve as a powerful watershed simulator usable for investigating and assessing the hydrological aspect of a watershed.     

Analysis of two soft computing modeling methodologies for predicting thickness loss of persian hand-knotted carpets

Thickness loss caused by static and dynamic loads is one of the most important quality factors in carpets. This property is influenced by pile yarn characteristics and carpet construction parameters. Exploring the relationship between thickness loss and effective factors is highly significant to optimize the selection of the variables. Soft computing approaches, which are potent data-modeling tools in capturing complex input-output relationships, seem to be the powerful technique to decipher the above-mentioned relationship. This paper presents two different modeling methodologies for predicting thickness loss of Persian hand-knotted carpets. At first, several topologies with different architectures were used to get the best neural-network model. Since, ANN model is a black box and did not succeed in indicating inter-relationship between input and output parameters, gene expression programming (GEP) is presented here as another intelligent algorithm to predict thickness loss of the carpets. Our study showed that, GEP model has a significant priority over the ANN. The correlation coefficient (R-value) and mean square error (MSE) for GEP model were 0.950 and 0.219 respectively, while these parameters were 0.707 and 0.510 for ANN model. This indicates the desirable predictive power of GEP algorithm. Based on the proposed models, the dominant parameter on thickness loss found to be knot density and content of slipe wool.