A study of blow-ups in the Keller-Segel model of chemotaxis

We study the Keller-Segel model of chemotaxis and develop a composite particle-grid numerical method with adaptive time stepping which allows us to accurately resolve singular solutions. The numerical findings (in two dimensions) are then compared with analytical predictions regarding formation and interaction of singularities obtained via analysis of the stochastic differential equations associated with the Keller-Segel model

First report of two ichneumonid wasp species from Iran

طی بررسـی‌های انجام‌شده جهت شناسایی پارازیتوئیدهای لارو شب‌پره‌ی کرم گلوگاه انار،Ectomyelois ceratoniae Zeller (Lep.: Pyralidae)، در باغات انار استان قم‌، منطقه‌ی قله‌چم واقع در 15 کیلومتری جنوب غربی شهر قم و استان مرکزی‌، منطقه‌ی ساوه‌، که در طی سال‌های 86-1385 صورت گرفت‌، 2 گونه زنبور پارازیتوئید از خانواده‌ی Ichneumonidae از روی لاروهای شب‌پره‌ی فوق جمع‌آوری گردید که برای اولین بار از ایران گزارش می‌شوند

Agency Contracts with Long-Term Customer Relationships

In certain types of industries contracts for sales agents include both commission payments for sales and clawbacks of these payments if existing clients are not retained. This paper provides a model that shows that contracts with these features arise in equilibrium in environments having: i) up-front selling costs that are re-couped from on-going sales ii) heterogeneous customers iii) limited sales agent access to capital markets and iv) imperfect commitment by customers and agents to long-term contracts. We test the model using information on insurance sales agent contracts in New Zealand prior to and after bank entry into the insurance sales market. Increased policy lapse rates for traditional insurances post bank entry indicate that banks were cream-skimming customers. Our model predicts that in this case bank entry should reduce the value of both initial commissions paid for sales and the clawback for policy lapses. The data support this prediction