Fabrication of the 23-ft Collimating Mirror for the JPL 25-ft Space Simulator

Optical, structural, and thermal design criteria and fabrication techniques for collimating mirror in space simulato

Reentrant stability of BEC standing wave patterns

We describe standing wave patterns induced by an attractive finite-ranged external potential inside a large Bose-Einstein Condensate (BEC). As the potential depth increases, the time independent Gross-Pitaevskii equation develops pairs of solutions that have nodes in their wavefunction. We elucidate the nature of these states and study their dynamical stability. Although we study the problem in a two-dimensional BEC subject to a cylindrically symmetric square-well potential of a radius that is comparable to the coherence length of the BEC, our analysis reveals general trends, valid in two and three dimensions, independent of the symmetry of the localized potential well, and suggestive of the behavior in general, short- and large-range potentials. One set of nodal BEC wavefunctions resembles the single particle n node bound state wavefunction of the potential well, the other wavefunctions resemble the n-1 node bound-state wavefunction with a kink state pinned by the potential. The second state, though corresponding to the lower free energy value of the pair of n node BEC states, is always unstable, whereas the first can be dynamically stable in intervals of the potential well depth, implying that the standing wave BEC can evolve from a dynamically unstable to stable, and back to unstable status as the potential well is adiabatically deepened, a phenomenon that we refer to as "reentrant dynamical stability".Comment: 13 pages, 9 figures; revised discussion in Sec.

The University of Edinburgh natural history class lists 1782-1800

In 1779 Revd Dr John Walker was appointed to be the University of Edinburgh’s Professor of Natural History. Because of the institutional structure of the university, he took care to keep detailed class lists from 1782 to 1800. These are extant in the University of Edinburgh’s Special Collections Department. As many of the students on the lists would go on to have a profound impact on the practice of nineteenth century natural history, I have compiled them into a table so that they can be used as a reference tool for those interested in the study of natural history in Edinburgh during the late eighteenth century. The table is arranged into columns that state the student’s name, degree, year of attendance and geographic origin. To help the reader better understand the table, I have written a brief introductory essay that addresses Walker’s organisation of the course and the types of students who attended the lectures. It also identifies the prominent role played by chemistry in Edinburgh’s natural history community and discusses the foundation of the Student Natural History Society of Edinburgh