On the formation of nodules in the cortex of Hevea brasiliensis

1. Nodules are produced in the cortex of Hevea brasiliensis as the result of an alteration in the latex vessel content.2. This alteration has not been connected with the attack of any parasitic organism, b ut appears rather to be due to physiological changes in the latex.3. The tendency to suffer alteration in the latex vessel content appears to be confined to certain individual trees which have a predisposition to develop this condition.4. Four types of nodule have been distinguished :— (a) Nodules formed round altered latex vessels. (b) Nodules formed round lesions in the cortex into which latex has oozed and coagulated. May occur in any Hevea tree. (c) Nodules formed round areas into which latex has oozed and coagulated ; the coagulated latex occupies the intercellular spaces without lesion of tissue. May occur in any Hevea tree. ('d) Nodules formed under unknown conditions round areas of cortex from which latex m ay be entirely absent. Rare

Output power limitations and improvements in passively mode locked GaAs/AlGaAs quantum well lasers

We report a novel approach for increasing the output power in passively mode locked semiconductor lasers. Our approach uses epitaxial structures with an optical trap in the bottom cladding that enlarges the vertical mode size to scale the pulse saturation energy. With this approach we demonstrate a very high peak power of 9.8 W per facet, at a repetition rate of 6.8 GHz and with pulse duration of 0.71 ps. In particular, we compare two GaAs/AlGaAs epilayer designs, a double quantum well design operating at 830 nm and a single quantum well design operating at 795 nm, with vertical mode sizes of 0.5 and 0.75 μm, respectively. We show that a larger mode size not only shifts the mode locking regime of operation toward higher powers, but also produces other improvements with respect to two main failure mechanisms that limit the output power, catastrophic optical mirror damage and catastrophic optical saturable absorber damage. For the 830-nm material structure, we also investigate the effect of nonabsorbing mirrors on output power and mode locked operation of colliding pulse mode locked lasers

An Analytical Investigation of Vortex Breakdown

It is well-known that the separation of flow from the leading edges of a highly swept wing at a high angle of attack results in the creation of a well-ordered vortical flowfield above the upper surface of the wing; the sudden disruption of this flowfield that occurs at a critical angle of attack limits the flight regime for such a wing. Although considerable research effort has been directed towards this "vortex breakdown" phenomenon, there is as yet no widely accepted explanation for its occurrence, nor a consistently effective means for its prevention or control