Occurrence Of Lag Research Articles

Bilateral motor coordination during upper limb symmetric pushing movements at two levels of force resistance in healthy and post-stroke individuals.

Impairments of the upper limb (UL) are common after a stroke and may affect bilateral coordination. A better understanding of UL bilateral coordination is required for designing innovative rehabilitation strategies. To assess bilateral coordination after stroke using time-distance, velocity and force parameters during an UL bilateral task performed by simultaneously pushing handles on a bilateral exerciser at two levels of force. Two groups were included to assess bilateral coordination on a newly designed bimanual exerciser- One group of individuals at least 3months post-stroke (n=19) with moderate impairment and one group of healthy individuals (n=20). Participants performed linear movements by pushing simultaneously with both hands on instrumented handles. The task consisted of two one-minute trials performed in sitting at two levels of participants' maximum force (MF): 30% and 15%, with visual feedback. Time-distance parameters, spatial, velocity and force profiles were compared between groups, between levels of resistance and the first part (0-50%) and entire duration of the pushing cycles (0-100%). The mean pushing time was longer at 30% MF compared to 15% MF in the stroke group. Spatial profiles, represented by hand positions on the rail, revealed that the paretic hand lagged slightly behind throughout the cycle. For velocity, both groups displayed good coordination. It was less coupled at 30% than 15% MF and a trend was observed toward more lag occurrence in the stroke group. Except for lower forces on the paretic side in the stroke group, the shape of the force profiles was similar between groups, sides and levels of resistance. For all parameters, the coordination was good up to 75% of the pushing cycle and decreased toward the end of the cycle. Individuals after stroke presented with overall spatial and temporal coupling of the UL during bilateral pushing movements. The relay of information at different levels of the nervous system might explain the coordinated pushing movements and might be interesting for training UL coordination.

On the distribution of multicomponent mixtures over generalized exposure time in subsurface flow and reactive transport: Foundations, and formulations for groundwater age, chemical heterogeneity, and biodegradation

The fate of materials undergoing transport and reactions in natural porous media sometimes depends on the time of exposure of the conveyed material to other materials present in the system. The distribution of groundwater age, the effects of mineral chemical heterogeneity on reactive solute transport, and the occurrence of lag in reaction systems are some areas of hydrogeology that involve exposure time in an important way. A general balance equation for accounting for such effects is provided through an extended transport operator that incorporates generalized exposure time as an additional independent coordinate. Evolution of material distributions over exposure time appears within this transport operator as a convective process that represents space‐ and time‐dependent generalized exposure of material constituents undergoing physical transport and nonequilibrium chemical and microbiological mass transformations. The general equation is derived from basic mass balance arguments by treating the constituents as a mixture of overlapping continua and developing evolution equations for the mixture material densities in the new dimensions of space, time, and exposure time. Example applications of the approach to each of the three examples above are described.

Changes in sap exudation of maize and occurrence of lags in exudation during the growing season

1. A method of “measuring strips” for the investigation of the sap exudation of crops under field conditions is described. The quantity of liquid exuded from the detopped stem stump is determined from the length of a wetted zone of a narrow strip of filter paper protected against evaporation of the liquid by a polyethylene cover bag. The strips with the cover bags can be used even to collect greater amounts of exudated liquid. 2. Using this method, the sap exudation of detopped maize plants was observed during the whole growing season. On typical curves illustrating the course of the wetting of the measuring strips, the temporary absorption of the sap from the cells and conducting elements severed by the cut, the lag in exudation and the actual sap exudation can be distinguished. 3. The length of the lag period indicates the magnitude of the momentary water deficit of the investigated plant and the rate of sap exudation indicates the availability of soil moisture. 4. The rate of sap exudation reached its maximum at the end of June and then decreased gradually. In this period also the distinct lag periods were first observed. The occurence of shorter lag periods between the 5th and 29th July, i.e. in the shooting stage which from the standpoint of precipitation is critical for the height of yield, signifies that the critical stage probably coincides with the period in which the natural disproportion between available soil moisture and transpiration may become important. 5. During the period of long lags towards the end of the growing season, the measuring strips were fastened upon the plant stumps 24 hours after the decapitation. The “exudation after 24 hours” determined in this way indicates a significant decrease at the end of August when the soil moisture dropped to a value approaching the permanent wilting percentage. 6. The results have shown that the method of “measuring strips” permits an easy and sensitive evaluation of the water relations of maize plants growing under field conditions.