Effects Of Transient Disturbances Research Articles

Effects of transient unilateral functional brain disruption on global neural network status in rats: a methods paper.

Permanent focal brain damage can have critical effects on the function of nearby as well as remote brain regions. However, the effects of transient disturbances on global brain function are largely unknown. Our goal was to develop an experimental in vivo model to map the impact of transient functional brain impairment on large-scale neural networks in the absence of structural damage. We describe a new rat model of transient functional hemispheric disruption using unilateral focal anesthesia by intracarotid pentobarbital injection. The brain's functional status was assessed with resting-state fMRI (rs-fMRI) and electroencephalography (EEG). We performed network analysis to identify and quantify highly connected network hubs, i.e., “rich-club organization,” in pre- and postbarbital functional networks. Perfusion MRI data demonstrated that the catheterized carotid artery predominantly supplied the ipsilateral hemisphere, allowing for selective hemispheric brain silencing. The prebarbital baseline network displayed strong functional connectivity (FC) within and between hemispheres. Following pentobarbital injection, the disrupted hemisphere revealed increased intrahemispheric FC with concomitant decrease of interhemispheric connectivity. The bilateral functional network was characterized by a strong positive rich-club effect, which was not affected by ipsilateral disruption. Nevertheless, the rich-club value was significantly decreased in the ipsilateral hemisphere and to a lesser extent contralaterally. Loss of interhemispheric EEG synchronization supported the rs-fMRI findings. Our data support the concept that densely connected rich-club regions play a central role in global brain communication, and show that network hub configurations can be significantly affected by focal temporary functional hemispheric disruption without structural neuronal damage. Further studies with this rat model will provide essential additional insights into network reorganization patterns in response to transient functional brain disruption.

Traceable magnetic field strength measurements to 120 kHz

With the advent of a series of reports on studies of the effects of magnetic fields on human health there has been a demand for traceable calibrations of the plethora of instruments produced for this type of measurement. To meet this and ongoing requirements, a facility has been established at the National Physical Laboratory (NPL) for low AC magnetic field calibrations up to a frequency of 120 kHz and for improved DC calibrations, made possible by an ambient field cancellation system. A prime consideration for low magnetic field calibrations is the level of the ambient field and the field gradient. The paper describes the surveys carried out which highlight the significant effect of transient disturbances from the electric train service, choice of materials for fitting out the laboratory, and the means of cancelling the ambient magnetic field using a triaxial Helmholtz coil and servo system. Details of the design, construction and calibration of a Helmholtz coil system for producing magnetic field strengths at high frequencies are given together with the requirements of the key circuit elements (power supply, current measurement system). An outline of the design, construction and calibration of a NPL triaxial Helmholtz coil system is also given.

Response to sudden shifts in a two-nation arms race

This article concerns living systems at the international or supranational level. Control theoretic techniques may be used to obtain information about the behavior of formal arms race models that cannot be gained by alternative methods. A two-nation, Richardson linear reaction process arms race model is treated as a second-order linear control system in order to determine its response to a sudden parameter shift represented as a step function disturbance. In contrast to the equilibrium oriented techniques generally used in the study of arms race models, control theoretic methods allow detailed analysis of both long-term and short-term effects of transient disturbances, including the way in which the system moves to a new equilibrium. The Routh-Hurwitz criteria and root-locus plot are compared to the more traditional stability criteria. System response is analyzed in detail for both the critically damped and the over- or under-damped cases. State space solution concepts that allow treatment of many-nation systems are examined. The techniques here applied to the arms expenditures of two nations isolated from or only loosely coupled to the rest of the world are also applicable to other reaction processes, such as two-party or intergroup conflicts, and this treatment may be extended both to higher-order differential equation models and to a large class of nonlinear models. Some methods are suggested for governments to use in managing their behavior so as to bring sudden shifts in arms races under greater control.

Perturbation equations for the time-average state of the atmosphere including the effects of transient disturbances

The time-average, or «stationary», state of the atmosphere can be regarded as a forced response to large-scale transient eddy transports of heat and momentum, as well as to fixed sources and sinks of heat and momentum resulting from small-scale transient eddy processes, non-adiabatic processes (e. g., radiation and phase transformations), topography, and friction. Perturbation equations governing this response are derived and a program of research based on the equations is proposed.