Transgenic expression of the Ly49A natural killer cell receptor confers class I major histocompatibility complex (MHC)-specific inhibition and prevents bone marrow allograft rejection.

Natural killer (NK) cells and some T cells are endowed with receptors specific for class I major histocompatibility complex (MHC) molecules that can inhibit cellular effector functions. The function of the Ly49 receptor family has been studied in vitro, but no gene transfer experiments have directly established the role of these receptors in NK cell functions. We show here that transgenic expression of the H-2Dd-specific Ly49A receptor in all NK cells and T cells conferred class I-specific inhibition of NK cell-mediated target cell lysis as well as of T cell proliferation. Furthermore, transgene expression prevented NK cell-mediated rejection of allogeneic H-2d bone marrow grafts by irradiated mice. These results demonstrate the function and specificity of Ly49 receptors in vivo, and establish that their subset-specific expression is necessary for the discrimination of MHC-different cells by NK cells in unmanipulated mice

Elements of a theory of global governance

In the aftermath of the Second World War the international institutional breakthroughs that occurred provided the momentum for decades of sustained economic growth and geopolitical stability sufficient for the transformation of the world economy, the shift from the cold war to a multipolar order, and the rise of new communication and network societies. However, what worked then does not work as well now, as gridlock freezes problem-solving capacity in global governance. The search for pathways through and beyond gridlock is a hugely significant task – nationally and globally – if global governance is to be once again effective, responsive and fit for purpose. This article explores these issues and provides elements of a theory of global governance in order to begin to understand the challenges of the 21st century and how to surmount them

Modeling and control of a silicon substrate heater for carbon nanotube growth experiments

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaf 26).The precision engineering research group at MIT is working on carbon nanotube growth experiments on silicon substrates and in microfabricated silicon devices, to try to produce improved bulk nanotube growth. For this thesis, a heating control system was designed and implemented for eventual use in CNT growth experiments. The computer program that controls the heater is user-adaptable, so that an experimenter can easily change the desired temperatures at various points of the process. Later, this heating system will become part of a much larger system that also incorporates a controlled flow rate. The goal of the system is to achieve high-bandwidth control of reaction conditions. In the heating control system designed, a computer controls a power supply attached to a wire-wrapped silicon chip, which is used to heat up the system, and the temperature is measured by a thermocouple. The control algorithm uses proportional gain, and the output is a PWM voltage. For accurate control of the system, a goal was set out to achieve an error of within 10%. For gains above 5, the computer can accurately control the temperature to less than 5.5% of the desired values in steady state, and an error of 0.75% was achieved with a gain of 50.(cont.) Thus the system meets the desired specification of error. Also, while the error drops dramatically with increasing gain, the overshoot increases much more slowly, making a higher gain desirable. Also, the system still has only reached temperatures of 650 degrees Celsius, although temperatures of 1000 degrees Celsius are required for nanotube growth. In order to achieve this, further tests will be performed with thicker wire and more voltage. Also, contact resistances within the chromel decrease with increasing temperatures, which reduce the percentage of power dissipated in the chromel compared to the lead wires. If the system is modified to eliminate this effect, by wrapping the wire differently or by using doped silicon, higher temperatures can be achieved. This will also make the system more predictable, leading to a better model and better control. Finally, to improve overall performance, one can experiment with changes to the switching time, using a PI or PID controller, and active cooling.by David Held.S.B

The Politics of Citizenship

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