Tight Trap Research Articles

Bosonic Clouds with Attractive Interaction Beyond the Local Interaction Approximation

We study the properties of a Bose–Einstein condensed cloud of atoms with negative scattering length confined in a harmonic trap. When a realistic non local (finite range) effective interaction is taken into account, we find that, besides the known low density metastable solution, a new branch of Bose condensate appears at higher density. This state is self–bound but its density can be quite low if the number N of atoms is not too big. The transition between the two classes of solutions as a function of N can be either sharp or smooth according to the ratio between the range of the attractive interaction and the length of the trap. A tight trap leads to a smooth transition. In addition to the energy and the shape of the cloud we study also the dynamics of the system. In particular, we study the frequencies of collective oscillation of the Bose condensate as a function of the number of atoms both in the local and in the non local case. Moreover, we consider the dynamics of the cloud when the external trap is switched off.

Ground state of a weakly interacting Bose gas of atoms in a tight trap.

We study properties of the ground state of a bosonic gas of atoms in a tight trap. The atoms interact via model molecular potentials that may have either positive or negative scattering lengths. We discuss the possibility of Bose-Einstein condensation in such a system. We show that when the size of the trap becomes comparable to the correlation length of the condensate, stable Bose-Einstein condensation might occur independent of the sign of the scattering length. \textcopyright{} 1996 The American Physical Society.

Partial degradation of the extrinsic 23-kDa protein of the Photosystem II complex of spinach

Chymotrypsin eliminated nine amino acid residues at the amino-terminal side of the extrinsic 23-kDa protein of the oxygen-evolving Photosystem II complex of spinach. The resultant 22-kDa fragment was able to bind to the Photosystem II complex but with lowered binding affinity. However, once the 22-kDa fragment bound to the complex, it retained most functions of the 23-kDa protein; the fragment provided a binding site for the extrinsic 18-kDa protein, preserved a tight trap for Ca 2+ in the complex, and shifted the optimum Cl − concentration for oxygen evolution from 30 to 10 mM, although it was less effective in sustaining oxygen evolution at Cl − concentrations below 10 mM. These observations suggest that the elimination of nine amino acid residues at the amino-terminal region of the 23-kDa protein does not significantly alter the conformation of the protein, except for partial modification of its binding site and its interaction with Cl −.

Porosity Styles of the Midale Field in Williston Basin of Southeastern Saskatchewan: ABSTRACT

The Midale oil field, southeastern Saskatchewan, lies on the northeastern flank of the Williston basin. The reservoir is in limestones, dolomites, and evaporites (mainly anhydrite) of the Midale Beds (Mississippian), that were deposited during a predominantly regressive episode on a shallow shelf. The Midale Beds are divided into a lower, middle, and upper zone. Many of the characteristic pore types in these zones, as observed in thin section and under SEM, can be related to both original depositional environment and postdepositional diagenetic modifications. The dominant styles of porosity in the fine-grained argillaceous limestones of the lower zone are secondary intraparticle, moldic, or microvuggy. These fabrics result from the preferential dissolution of cement or very fine shell debris. A lack of pore interconnections precludes these sediments from being effective reservoir rocks. The most significant pore type in the middle zone is secondary intercrystalline porosity within fine-grained dolomite. This fabric is the result of solution of calcite or aragonite from between rhombs after incomplete dolomitization. A crinoidal grainstone with pervasive early diagenetic syntaxial rim cement forms a tight trap in the middle zone. The upper zone consists of fractured calcareous microcrystalline dolomite. The main pore type is a non-fabric selective system of oblique to vertical microfractures, which may be associated with regional uplift or local salt solution. The presence of dolomite rhombs on fracture surfaces indicates that dolomitization was relatively late, postdating fracturing. The microfractures in the upper zone counteract the porosity-occluding effects of stylolitization and secondary anhydritization. End_of_Article - Last_Page 587------------