The phenomena associated with the performance of newly listed companies has increased the interest of many researchers who have developed a vast literature on long-term underpricing and underperformance, which togethe...The phenomena associated with the performance of newly listed companies has increased the interest of many researchers who have developed a vast literature on long-term underpricing and underperformance, which together with hot and cold issue markets, represent the three anomalies that have always accompanied with Initial Public Offerings （IPOs）. The objective of this work is to investigate the long-run performance of IPOs of venture and non-venture-backed companies. The analysis of a sample of 102 IPOs carried out in Italy in 1998-2005 revealed that both companies （venture-backed and non-venture-backed） showed negative values, thus, confirming the phenomenon of underperformance. During the 36 months following their listing, venture-backed companies seemed to register negative and statistically significant values both with the CARsVB methodology （-93.99%） and the Buy and Hold Abnormal Returns methodology （BHARsVB -88.37%）. Venture-backed companies, unlike non- venture-backed companies, seem to be able to restrain the losses, measured by both methods, in the first 12 months （CARsB - 12.38% -20.15% CARSNNVB; BHARsVB - 10.17%; BHARsNVB - 15.51%）. During the 36 months, however, the IPOs showed negative and statistically significant values regardless of whether they were venture or non-venture-backed. The test on the difference between the average abnormal returns of the two methodologies （CAARS and BHAARs） did not produce statistically significant results. The Wealth Relative was calculated and from the results it would appear that the portfolio of venture-backed IPOs does not register ＂brilliant＂ performances. The portfolio of 102 IPOs does not seem to beat the ＂market portfolio＂. In conclusion, therefore, the phenomenon of underperformance seems to be real in our country and is documented by strongly negative and statistically significant values obtained from the samples of IPOs analyzed.展开更多
This work presents an advanced and detailed analysis of the mechanisms of hepatitis B virus(HBV)propagation in an environment characterized by variability and stochas-ticity.Based on some biological features of the vi...This work presents an advanced and detailed analysis of the mechanisms of hepatitis B virus(HBV)propagation in an environment characterized by variability and stochas-ticity.Based on some biological features of the virus and the assumptions,the corresponding deterministic model is formulated,which takes into consideration the effect of vaccination.This deterministic model is extended to a stochastic framework by considering a new form of disturbance which makes it possible to simulate strong and significant fluctuations.The long-term behaviors of the virus are predicted by using stochastic differential equations with second-order multiplicative α-stable jumps.By developing the assumptions and employing the novel theoretical tools,the threshold parameter responsible for ergodicity(persistence)and extinction is provided.The theoretical results of the current study are validated by numerical simulations and parameters estimation is also performed.Moreover,we obtain the following new interesting findings:(a)in each class,the average time depends on the value ofα;(b)the second-order noise has an inverse effect on the spread of the virus;(c)the shapes of population densities at stationary level quickly changes at certain values of α.The last three conclusions can provide a solid research base for further investigation in the field of biological and ecological modeling.展开更多
文摘The phenomena associated with the performance of newly listed companies has increased the interest of many researchers who have developed a vast literature on long-term underpricing and underperformance, which together with hot and cold issue markets, represent the three anomalies that have always accompanied with Initial Public Offerings （IPOs）. The objective of this work is to investigate the long-run performance of IPOs of venture and non-venture-backed companies. The analysis of a sample of 102 IPOs carried out in Italy in 1998-2005 revealed that both companies （venture-backed and non-venture-backed） showed negative values, thus, confirming the phenomenon of underperformance. During the 36 months following their listing, venture-backed companies seemed to register negative and statistically significant values both with the CARsVB methodology （-93.99%） and the Buy and Hold Abnormal Returns methodology （BHARsVB -88.37%）. Venture-backed companies, unlike non- venture-backed companies, seem to be able to restrain the losses, measured by both methods, in the first 12 months （CARsB - 12.38% -20.15% CARSNNVB; BHARsVB - 10.17%; BHARsNVB - 15.51%）. During the 36 months, however, the IPOs showed negative and statistically significant values regardless of whether they were venture or non-venture-backed. The test on the difference between the average abnormal returns of the two methodologies （CAARS and BHAARs） did not produce statistically significant results. The Wealth Relative was calculated and from the results it would appear that the portfolio of venture-backed IPOs does not register ＂brilliant＂ performances. The portfolio of 102 IPOs does not seem to beat the ＂market portfolio＂. In conclusion, therefore, the phenomenon of underperformance seems to be real in our country and is documented by strongly negative and statistically significant values obtained from the samples of IPOs analyzed.
基金supported by the NSFC(12201557)the Foundation of Zhejiang Provincial Education Department,China(Y202249921).
文摘This work presents an advanced and detailed analysis of the mechanisms of hepatitis B virus(HBV)propagation in an environment characterized by variability and stochas-ticity.Based on some biological features of the virus and the assumptions,the corresponding deterministic model is formulated,which takes into consideration the effect of vaccination.This deterministic model is extended to a stochastic framework by considering a new form of disturbance which makes it possible to simulate strong and significant fluctuations.The long-term behaviors of the virus are predicted by using stochastic differential equations with second-order multiplicative α-stable jumps.By developing the assumptions and employing the novel theoretical tools,the threshold parameter responsible for ergodicity(persistence)and extinction is provided.The theoretical results of the current study are validated by numerical simulations and parameters estimation is also performed.Moreover,we obtain the following new interesting findings:(a)in each class,the average time depends on the value ofα;(b)the second-order noise has an inverse effect on the spread of the virus;(c)the shapes of population densities at stationary level quickly changes at certain values of α.The last three conclusions can provide a solid research base for further investigation in the field of biological and ecological modeling.
