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No description available.

No description available.

In traditional Chinese herb medicine, Alismatis rhizoma has been used in treating edema, inflammation and increasing urine flow. Mechanism of Alismatis rhizoma¡¦s effect on these functions has not been elucidated. Since diuresis has been considered closely related to the reabsorption of sodium ion via the epithelium of tubule and collecting duct in kidney, we suspected that Alismatis rhizoma may influence transportation of salt and water. The measurement of short circuit current ( Isc ) has been used widely to estimate the ion transportation between mucosal and serosal side of epithelium. In the present experiment, we used the voltage ¡V clamp technique to demonstrate the effect of Alismatis rhizoma¡¦s extracts ( ARE ) on Isc and sodium ion conductance in frog skin. Our result showed that in control stage, the potential difference ( PD ) of frog skin is 64.81 ¡Ó 2.44 mV, the Isc is 59.82 ¡Ó 3.58 £gA / cm2 and the conductance is 1.09 ¡Ó 0.18 £gA / cm2 / mV. After ARE was applied to mucosal side of the frog skin, its Isc decrease from 62.63 ¡Ó 5.31 £gA / cm2 to 47.92 ¡Ó 5.41 £gA / cm2, which could further go down to 3.36 ¡Ó 1.06 £gA/cm2 by adding amiloride. Treating serosal side of frog skin with ARE decreased approximately 10% of its Isc. No apparent changes in conductance were observed by adding ARE to mucosal ( 0.98 ¡Ó 0.24 £gA / cm2 / mV ) or serosal side ( 0.96 ¡Ó 0.23 £gA / cm2 / mV ). Adding L-arginine ( the precursor of nitric oxide ) to the serosal side of the skin epithelium elevated the Isc for 17.10 ¡Ó 9.30 £gA/cm2. This effect can be inhibited by applying ARE or NG-L-nitro-arginine methyl ester ( L-NAME, NO synthase inhibitor ) before application of L-arginine. In summary, Alismatis rhizoma could affect Isc on both mucosal and serosal sides of the frog skin. Its effect on lowering Isc was more obvious when applied to the mucosal side than to the serosal side. The ARE may exert its effect on mucosal side by affecting amiloride¡Vsensitive sodium channel and on serosal side by affecting the NO signal transduction pathway.

Rhei Rhizoma, also named as rhubarb or Da Huang, has been used widely in oriental traditional medicine in treating constipation and edema. However, though much affection has been paid to the make of components on pharmaceutical mechanisms, few studies have been conducted to reveal chemical and physical mechanism of these effects. Studies have shown that diarrhea causes imbalance of chloride and sodium ion movements via epithelium, we wondered if similar mechanism may apply to Rhei Rhizoma, a herbal drug which has been used to treat constipation in oriental medicine for thousands of years. The measurement of short-circuit current (Isc) has been used widely to estimate the ion transportation between mucosal and serosal side of epithelium. In this study, we used Ussing chamber technique to examine the alternation in membrane potential and short-circuit currents. The result shows, at default, the Isc of frog skin we used was at 59.23¡Ó5.58£gA/cm², and the conductance was at 1.11¡Ó0.50£gA/cm²¡EmV. The lnjection of 1ml RRE to mucosal side of the frog skin leaded to a 90% elevation of the Isc. Followed by the application of Amiloride (sodium channel inhibitor) and Chlorothiazide (chloride channel inhibitor) to mucosal side of the epithelial skin, the observed Isc were then reduced 136% and 33% respectively. If RRE were applied after the adding of Amiloride or Chlorothiazide to the frog skin, then the Isc of the skin elevated only 24% and 70% respectively. These results show that Rhei Rhizoma Extract (RRE) significantly increases Isc upon application to the mucosal side of the skin epithelium. Amiloride and Chlorothiazide will both inhibit the Isc induced by RRE, indicating activation of chloride channel and Amiloride-sensitive sodium channel of the epithelial tissue by RRE. After the regular Ringer solution used in the preparation was replaced by Na-free and Cl-free Ringer solution, the inhibition of Isc by RRE application could still be observed although the inhibition was trivia. These results indicate that RRE acts dominantly on mucosa side of the epithelium and can be used to enhance sodium transport and to stimulate the secretion of Cl- in the epithelium.

No description available.

Summary Clmatis Armandi has been used frequently in traditional Chinese medicine for the treatment of diuretic symptoms. The mechanism of its action is unclear. Possible action of this substance may involve alternation of electrolyte transport through the epithelia membranes. In this study¡Atransepithelial conductance of frog skin was measured in vitro in voltage-clamped Ussing chambers. Adding Clematis Armandi extracts to apical surface induced a conductance increment of 1.21 £gS and an apical to serosal Isc of 28.78 £gA/cm2. The Isc can not be completely blocked by apical application of amiloride. Nifedipine and TEA had no effect on Clematis Armandi induced Isc decrease. These data indicate that frog skin is highly responsive to the concentrated Clematis Armandi extracts. The increase in Isc reflects changes in transepithelial transport of Na+ ions modulated at apical membrane. The enormous increase in transepithelial conductance suggests that in additional to enhancement of amiloride-sensitive Na+ channels, Clematis Armandi may also modulate other pathways, such as Cl- ion channel modulation, which needs further investigation.

Popularly used impedance-based methods need voltage and current waveform as well as line impedance per unit length to estimate distance to fault location. For a non-homogenous system with different line configuration, these methods assume that the system is homogenous and use the line impedance of the most frequently occurring line configuration. Load present in the system before fault is an important parameter which affects fault location accuracy. Impedance-based methods like Takagi and positive-sequence method assume that the load is lumped beyond the fault point which may not be true for a typical distribution system. As a result, accuracy of the impedance-based methods in estimating distance to fault is affected. Another short-coming of impedance-based methods are that they are unable to identify the branch in which the fault may be located. To minimize these errors, this thesis proposes a short-circuit fault current profile approach to complement impedance-based algorithms. In the short-circuit fault current profile approach, circuit model of the distribution feeder is used to place faults at every bus and the corresponding short-circuit fault current is plotted against reactance or distance to fault. When a fault occurs in the distribution feeder, fault current recorded by relay is extrapolated on the current profile to get location estimates. Since the circuit model is directly used in building the current profile, this approach takes into account load and non-uniform line impedance. Using the estimates from short-circuit fault current profile approach and impedance-based methods, the path on which the fault is located is identified. Next to improve fault location estimates, a median value of the estimates is computed. The median is a more robust estimate since it is not affected by outliers. The strategy developed above is tested using modified IEEE 34 Node Test Feeder and validated against field data provided by utilities. For the IEEE 34 Node Test Feeder, it is observed that the median estimate computed from impedance-based methods and the short-circuit fault current profile approach is very close to the actual fault location. Error in estimation is within 0.58 miles. It was also observed that if a 0.6 mile radius is built around the median estimate, the fault will lie within that range. Now the IEEE 34 Node Test Feeder represents a typical distribution feeder and has also been modeled to represent the worst case scenario, i.e. load current is around 51% of the fault current for the farthest bus. Hence the 0.6 mile radius around the median estimate will hold true for most distribution feeders and will be used when computing the fault range for field case events. For the field events, it was seen that the actual faults indeed lie within the 0.6 mile radius built around the median estimate and the path of the fault location has also been accurately estimated. For certain events, voltage waveform was not useful for analysis. In such situations, short-circuit fault current profile alone could be used to estimate fault location. Error in estimation is within 0.1 miles, provided the circuit model closely represents the distribution feeder. / text

This research attempts to quantify the complex interactions between HVDC transmission schemes in a multi-infeed configuration, particularly with regard to the voltage interactions and the commutation failure phenomena. The in-depth analysis of multi-infeed HVDC systems discussed in this research shows the application of several indices such as the MIIF, MIESCR, and CFII, that can provide researchers and planning engineers in the area of HVDC transmission with the necessary tools for their system studies. It shows that these indices are applicable in a multi-infeed system comprising HVDC schemes with different ratings. The Multi-Infeed Interaction Factor (MIIF) quantifies the level of voltage interactions between converter ac buses. The Multi-Infeed Effective Short Circuit Ratio (MIESCR) index is an indicator of ac system strengths with regard to the assessment of the transient overvoltage (TOV) and the power-voltage stability of multi-infeed HVDC systems. The Commutation Failure Immunity Index (CFII) utilizes electromagnetic transient simulation programs to evaluate the immunity of an HVDC converter to commutation failures. The CFII takes into account the ac system strength and the HVDC controls and evaluates their impact on the commutation process. The immunity of both single-infeed and multi-infeed systems to commutation failure phenomena are accurately evaluated and quantified by the CFII. Using the CFII, it is shown that the current commutation in multi-infeed HVDC schemes could fail under circumstances in which the probability of failure had been perceived to be low. The causes of, the effects of, and the remedial actions needed to deal with such anomalous commutation failures are discussed in this thesis. The capability of the new indices to provide an insight into the interactions phenomena in multi-infeed systems are clearly demonstrated by examples that show their application in the analysis of an actual multi-infeed HVDC system that is in the planning phase in the province of Alberta in Canada.

This research attempts to quantify the complex interactions between HVDC transmission schemes in a multi-infeed configuration, particularly with regard to the voltage interactions and the commutation failure phenomena. The in-depth analysis of multi-infeed HVDC systems discussed in this research shows the application of several indices such as the MIIF, MIESCR, and CFII, that can provide researchers and planning engineers in the area of HVDC transmission with the necessary tools for their system studies. It shows that these indices are applicable in a multi-infeed system comprising HVDC schemes with different ratings. The Multi-Infeed Interaction Factor (MIIF) quantifies the level of voltage interactions between converter ac buses. The Multi-Infeed Effective Short Circuit Ratio (MIESCR) index is an indicator of ac system strengths with regard to the assessment of the transient overvoltage (TOV) and the power-voltage stability of multi-infeed HVDC systems. The Commutation Failure Immunity Index (CFII) utilizes electromagnetic transient simulation programs to evaluate the immunity of an HVDC converter to commutation failures. The CFII takes into account the ac system strength and the HVDC controls and evaluates their impact on the commutation process. The immunity of both single-infeed and multi-infeed systems to commutation failure phenomena are accurately evaluated and quantified by the CFII. Using the CFII, it is shown that the current commutation in multi-infeed HVDC schemes could fail under circumstances in which the probability of failure had been perceived to be low. The causes of, the effects of, and the remedial actions needed to deal with such anomalous commutation failures are discussed in this thesis. The capability of the new indices to provide an insight into the interactions phenomena in multi-infeed systems are clearly demonstrated by examples that show their application in the analysis of an actual multi-infeed HVDC system that is in the planning phase in the province of Alberta in Canada.