Analysis of splenic and thymic lymphocyte subpopulations in chickens infected with Salmonella enteritidis

Lymphocytes expressing CD3, CD4, CD8, pan lymphocyte, IgA, IgG and IgM cell surface antigens were assessed by in the spleen and thymus of chickens following infection with Salmonella enteritidis using flow cytometric analysis. At 6 days post primary infection and 2 days post secondary infection with S. enteritidis, the percentages of IgA+ and IgM+ lymphocytes in the spleen were significantly increased (P < 0.05). At 2 days post secondary infection with S. enteritidis, the percentage of CD4+ T lymphocyte in the spleen and CD8+ T lymphocyte percentage in the thymus were significantly increased (P < 0.05). These results indicate that S. enteritidis infection induces changes in the spleen and thymus that reflect the dynamics of the host protective immune response.     

Optimisation of the number of IGBT devices in a series-parallel string

High-power semiconductor switches can be realised by connecting existing devices in series and parallel. The number of devices in series depends on the operating voltage of an application and the individual device voltage rating. For a given application, the use of higher voltage rated IGBTs leads to a fewer number of devices and vice versa. The total power loss of the series string equals to the sum of individual IGBT power losses and total loss increases with the increase in operating frequency. The level of increase in power loss depends on the device characteristics. For high current operation, the minimum number of devices depends on the current rating of individual device. In this paper, series IGBT string of six 1.2 kV, four 1.7 kV, two 3.3 kV and a single 6.5 kV IGBTs are simulated for a 4.5 kV/100 A application and power losses are analysed for different frequencies and duty cycles. This power loss analysis is extended for commercial IGBTs to compare the simulation results. The number of devices for minimum power loss depends on operating frequencies and power savings are significant both at low and high frequencies. In addition to the power losses, the other important issues in optimising the number of IGBTs are described in this paper. When IGBT modules are connected in parallel the principle of derating is applied to obtained reliable operation. This is explained with some examples.