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We propose a model that realistically describes the experimental noise curves of GaAs/AlGaAs quantum-well intersubband photodetectors and that, additionally, allows the determination of some important transport parameters of these devices. The analysis was based on the quantum mechanical calculation of the capture lifetime in a quantum well and on the assumption that the capture probability can be explicitly expressed as a function of the electronic thermal velocity at zero bias and of the saturation velocity at large bias. Our experimental and theoretical results point out that the plateau observed in the noise measurements at low temperature and low electric field is due to an extra conduction path through the miniband of the superlattice formed by the ground states of all the wells. [ABSTRACT FROM AUTHOR]

The title compound, C21H32O4 crystallizes in a triclinic unit cell, which is very unusual for steroids. The asymmetric unit contains two independent mol­ecules with almost identical geometry, although they are slighly twisted in opposite directions. These mol­ecules form a dimer inter­connected via hydrogen bonds. Both mol­ecules have a cis A/ B ring junction characteristic of a 5β-configuration, but differ in the orientation of their hydroxyl groups. [ABSTRACT FROM AUTHOR]

The title compounds, both C23H34O5, are the 5α and 5β configurations of two diacetate epimers. The 5β-diacetate crystallizes in an hexagonal structure, unusual for steroid molecules. The unit cell has an accessible solvent volume of 358 Å3, responsible for clathrate behaviour. The 5β-epimer also features some shorter than average bond lengths in the 3α,4β-acetoxy groups. The conformations of the molecules of both epimers are compared with those obtained through ab initio quantum chemistry calculations. Cohesion of the crystals can be attributed to van der Waals and weak molecular C—H…O interactions. [ABSTRACT FROM AUTHOR]

The article presents information on Pentafluorophenyl 3-phenylprop-2-enoate. The compound was synthesized to study the reactivity of cinnamic acid towards pentafluorophenol and pentafluorothiophenol. In the compound, the regular geometry of the carbon skeleton of the phenyl ring is slightly modified, and the deformation is due to hybridization and conjugation effects. An intermolecular hydrogen bond results in the formation of a dimer. In an experiment, the compound was prepared by treating 3-phenyl-2-propenoic acid with dicyclohexylcarbodiimide and pentafluorophenol in anhydrous dioxane.

Examines the structures of synthetic receptors and their synthetic intermediates on a crystallographic basis. Improvement in the understanding of molecular-recognition principles; Construction of steroid-based synthetic receptor; Assessment of the cholic acid derivative.

The title compound, C26H38O6, has a cis junction between two of the six-membered rings ( A and B). All three of the six-membered rings have chair conformations that are slightly flattened and the five-membered ring has an unusual 13β-envelope conformation. The 7α and 12α ring substituents are both axial and the 3α and 17β groups are equatorial and pseudo-equatorial, respectively. The 3α-form­yloxy group is involved in one weak inter­molecular C—H⋯O bond, which links the mol­ecules into dimers in a head-to-head fashion. [ABSTRACT FROM AUTHOR]