Low-level Perturbations Research Articles

Developmental thyroid hormone disruption: Prevalence, environmental contaminants and neurodevelopmental consequences

Thyroid hormones (TH) are critical for growth and development and particularly brain development. There are numerous environmental agents that lead to marginal reductions of circulating TH. Although it is clear that severe developmental hypothyroidism is profoundly detrimental to neurodevelopment, there is less information regarding the consequences of modest degrees of thyroid. The impact of low level TH disruptions induced by environmental contaminants has not been defined. This paper is a synopsis from four invited speakers who presented at the 13th International Neurotoxicology Association meeting held in Xi’an, China during the summer of 2011. An overview of the role of TH in brain development and a review of human and animal data on the neurological sequelae of disruption of the thyroid axis in the pre- and early post-natal periods were presented by Mary Gilbert and Joanne Rovet. Iodine deficiency, a common cause of TH insufficiency and mental retardation in many countries, including China, was addressed by Zupei Chen. In this presentation the current incidence of iodine deficiency and neurological outcome in China and the efficacy of recently implemented iodinization programs to eliminate this cause of mental retardation were reviewed. Joanne Rovet described the impact of TH disruption during pregnancy and under conditions of congenital hypothyroidism. Children born with normal thyroid function, but who experienced TH insufficiency in the womb, display subtle cognitive impairments and abnormalities in brain imaging. Despite early detection and treatment, deficiencies also exist in children born with thyroid disorders. Different patterns of cognitive effects result from prenatal versus postnatal TH insufficiency. Mary Gilbert reported on the effects of environmental contaminants with thyroid disrupting action on brain development in animals. Results of neurophysiological, behavioral, structural and molecular alterations that accompany modest perturbations of the thyroid axis were reviewed. Noriyuki Koibuchi described molecular targets of TH-mediated signalling accompanying exposure to persistent organic pollutants. Both polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are prevalent environmental contaminants that disrupt TH signalling at the receptor level. This action by these chemical classes could contribute to the negative impact of these chemicals on brain function. In summary, epidemiological, preclinical and animal research has clearly identified the critical role of TH in brain development. Additional work is required to understand the impact of low level perturbations of the thyroid axis to evaluate the risk associated with environmental contaminants with thyroid action.

Mesoscale moist adjoint sensitivity study of a mei-yu heavy rainfall event

The mesoscale moist adjoint sensitivities related to the initiation of mesoscale convective systems (MCSs) are evaluated for a mei-yu heavy rainfall event. The sensitivities were calculated on a realistic background gained from a four-dimensional variational data assimilation of precipitation experiment to make the sensitivity computation possible and reasonable within a strong moist convective event at the mesoscale. The results show that the computed sensitivities at the mesoscale were capable of capturing the factors affecting MCS initiation. The sensitivities to the initial temperature and moisture are enhanced greatly by diabatic processes, especially at lower levels, and these sensitivities are much larger than those stemming from the horizontal winds, which implies that initiation of MCSs is more sensitive to low-level temperature and moisture perturbations rather than the horizontal winds. Moreover, concentration of sensitivities at low levels reflects the characteristics of the mei-yu front. The results provide some hints about how to improve quantitative precipitation forecasts of mei-yu heavy rainfall, such as by conducting mesoscale targetted observations via the adjoint-based method to reduce the low-level errors in the initial temperature and moisture.

Transient Environmental Sensitivities of Explicitly Simulated Tropical Convection

Abstract A three-dimensional cloud-resolving model, maintained in a statistically steady convecting state by tropics-like forcing, is subjected to sudden (10 min) stimuli consisting of horizontally homogeneous temperature and/or moisture sources with various profiles. Ensembles of simulations are used to increase the statistical robustness of the results and to assess the deterministic nature of the model response for domain sizes near contemporary global model resolution. The response to middle- and upper-tropospheric perturbations is predominantly local in the vertical: convection damps the imposed stimulus over a few hours. Low-level perturbations are similarly damped, but also produce a vertically nonlocal response: enhancement or suppression of new deep convective clouds extending above the perturbed level. Experiments show that the “effective inhibition layer” for deep convection is about 4 km deep, far deeper than traditional convective inhibition defined for undilute lifted parcels. Both the local and nonlocal responses are remarkably linear but can be highly stochastic, especially if deep convection is only intermittently present (small domains, weak forcing). Quantitatively, temperature-versus-moisture perturbations in a ratio corresponding to adiabatic vertical displacements produce responses of roughly equal magnitude. However, moisture perturbations seem to provoke the nonlocal (upward spreading) type of response more effectively. This nonlocal part of the response is also more effective when background forcing intensity is weak. Only at very high intensity does the response approach the limits of purely local damping and pure determinism that would be most convenient for theory and parameterization.

Damage propagation in complex biological systems following exposure to low doses of ionising radiation

Biological organisms present hierarchical levels of organisation capable of maintaining homeostasis at low-level perturbations through intricate signalling between cells. Ionising radiation may damage DNA and other molecular components. This primary risk rises linearly with dose over a certain dose range. A second risk describes the probability of the initial DNA and other damage to propagate in the body to cause disease, such as cancer. The homeostatic control of the second risk does not function in a linear fashion. Moreover, low-dose irradiation may adaptively up-regulate protective responses at different organisational levels genetically controlled. Such adaptive protections (APs) usually defend also against the inevitable abundant non-radiogenic perturbations. Below ≅0.1Gy, APs are potentially beneficial in outweighing the consequences of the relatively rare radiogenic damage at low doses. The balance between health risk and benefit of low-level irradiation of an individual may become predictable by gene-expression profiles also for eventually treating disease.

Rapporteur report: interaction mechanisms.

Three papers were presented in the session on the interaction mechanisms of weak electric fields induced in the body by exposure to extremely low frequency electromagnetic fields with biological systems, particularly the central nervous system. The first paper considered the plausibility of various interaction mechanisms. The second paper dealt with voltage gated ion channels and the way in which they could be involved in the generation of biological effects. The final paper described a kinetic proofreading mechanism, sensitive, in theory, to very low level perturbations. These papers were discussed in a plenary session and in one breakout group, all of which are briefly summarised in this report.

Current technology in newborn universal hearing detection: Jacobson J.; Jacobson C.A.Semin. Hear. (USA) (1996) 17/2 (125–138)

Thyroid hormones (TH) are critical for growth and development and particularly brain development. There are numerous environmental agents that lead to marginal reductions of circulating TH. Although it is clear that severe developmental hypothyroidism is profoundly detrimental to neurodevelopment, there is less information regarding the consequences of modest degrees of thyroid. The impact of low level TH disruptions induced by environmental contaminants has not been defined. This paper is a synopsis from four invited speakers who presented at the 13th International Neurotoxicology Association meeting held in Xi’an, China during the summer of 2011. An overview of the role of TH in brain development and a review of human and animal data on the neurological sequelae of disruption of the thyroid axis in the pre- and early post-natal periods were presented by Mary Gilbert and Joanne Rovet. Iodine deficiency, a common cause of TH insufficiency and mental retardation in many countries, including China, was addressed by Zupei Chen. In this presentation the current incidence of iodine deficiency and neurological outcome in China and the efficacy of recently implemented iodinization programs to eliminate this cause of mental retardation were reviewed. Joanne Rovet described the impact of TH disruption during pregnancy and under conditions of congenital hypothyroidism. Children born with normal thyroid function, but who experienced TH insufficiency in the womb, display subtle cognitive impairments and abnormalities in brain imaging. Despite early detection and treatment, deficiencies also exist in children born with thyroid disorders. Different patterns of cognitive effects result from prenatal versus postnatal TH insufficiency. Mary Gilbert reported on the effects of environmental contaminants with thyroid disrupting action on brain development in animals. Results of neurophysiological, behavioral, structural and molecular alterations that accompany modest perturbations of the thyroid axis were reviewed. Noriyuki Koibuchi described molecular targets of TH-mediated signalling accompanying exposure to persistent organic pollutants. Both polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are prevalent environmental contaminants that disrupt TH signalling at the receptor level. This action by these chemical classes could contribute to the negative impact of these chemicals on brain function. In summary, epidemiological, preclinical and animal research has clearly identified the critical role of TH in brain development. Additional work is required to understand the impact of low level perturbations of the thyroid axis to evaluate the risk associated with environmental contaminants with thyroid action.

The effect of double bends out of plane on turbine meters

Gas turbine meters are widely used for custody transfer. Under the ISO Work Group ISO TC30/SC10, the DIS version of the Standard 9951 for gas turbine meters has recently been sent out. This standard gives test configurations for testing turbine meters for installation effects, through high and low level perturbations. This paper describes those perturbation tests on a 300 mm turbine meter in both atmospheric air and high pressure gas. The main conclusions for this meter are that: the test for atmospheric conditions predicts the effects at higher pressure well; the high level perturbation test does not cause additional shifts to the low level test, which leads to the question as to whether the high perturbation test should be modified; the meter stays within the allowable ISO shift limits without any additional straighteners with 10D free upstream length. The effect of swirl on turbine meters is much smaller than on other measurement principles, like orifice plate installations, especially with 15D free upstream length.

Electrochemical Laplace-plane impedance analysis of coated electrodes containing redox systems

The impedance function in the real-axis Laplace plane (the “operational impedance” or “ transient impedance”) of a thin-layer electrochemical cell containing a quasi-reversible redox system is derived. It allows the analysis of low-level perturbations from equilibrium conditions. To demonstrate the method, the real-axis impedance of an electrode coated with a redox-active polymer film is determined by small-amplitude potential step experiments, and analysed.

Controlled environment experiments in pollution studies

Abstract In the last decade society has become aware of the increasing negative effects of human waste products introduced to the oceans. There is proof evidence, at least for some areas of the world ocean, that the marine environment is seriously in danger. The scientific community is very concerned, arguing that there is an urgent need for basic research in this field because too little is known on the harzardous effects of man-made pollutants on the structure and functioning of marine ecosystems. There are two ways to perform experiments under controlled environment conditions: (1) in the laboratory; (2) in in-situ experiments with enclosures. Most laboratory experiments are designed to study the influence and the tolerance spectrum of specific pollutants, e.g. copper or DDT, on any specific organism, e.g. a mussel or a fish. In these experiments it is fairly difficult to simulate natural conditions. The concentrations of the pollutants are generally fairly high, often several orders of magnitude higher than in the ocean. It is questionable, if the results from these experiments can be extrapolated to nature. The second approach to obtain reliable data on the influence of perturbations on marine organisms is to use enclosures of various sizes in-situ or in landbased facilities. Fibre-glass containers and plastic bags have been used successfully in the last years, e.g. in the U.K., U.S.A., Canada, France and W. Germany. The main goal of these experiments is to study the long-term effect of low-level perturbations on natural populations of the pelagic or benthic ecosystem. In the paper examples of recent results will be discussed in detail.

Experiences with Identification of Power Plant Dynamics

Dynamic testing was performed on three nuclear power plants and one coal fueled power plant. Low level perturbations were used so as to cause insignificant disturbance to normal power generation and tests were designed to use standard plant hardware and instrumentation in order to minimize costs. The test results were used in identification work that included estimation of parameters in physical models and construction of empirical (black box) models.It was found that certain important performance-related parameters can be identified using physical models if appropriate identifiability conditions are satisfied. Empirical models were found to be simple to generate and low order models were found to be suprisingly capable of predicting plant behavior.

DEVELOPMENT OF TROPICAL CYCLONES IN RELATION TO CIRCULATION PATTERNS AT THE 200-MILLIBAR LEVEL*

Abstract The 200-mb. flow existing above low-level perturbations at the time of development into tropical storm or hurricane intensity was studied. On the basis of observations in a sample of 40 cases, it is concluded that poleward flow aloft, such as is found in the eastern side of troughs in the westerlies and tropical upper-level cold Lows or in the western side of anticyclones, is more favorable for development of low-level perturbations underneath than equatorward flow. It is also shown that flow aloft with anticyclonic vorticity is more favorable than flow with cyclonic vorticity.