Hydrolysis products of diorganotin dihalides. I. Bis[1,3‐dihydroxo‐1,1,3,3‐tetrakis(2‐methyl‐2‐phenylpropyl)­distannoxane]

In the solid state, the title compound, di‐μ‐hydroxo‐1:2κ²O;‐3:4κ²O‐dihydroxo‐1κO,4κO‐octakis(2‐methyl‐2‐phenyl­propyl)‐1κ²C,2κ²C,3κ²C,4κ²C‐di‐μ₃‐oxo‐1:2:3κ³O;2:3:4κ³O‐tetratin(IV), [Sn₄O₂(OH)₄(C₁₀H₁₃)₈], forms centrosymmetric dimeric [(Neophyl₂SnOH)(Neophyl₂SnOH)O]₂ mol­ecules (Neophyl = 2‐methyl‐2‐phenylpropyl), with an almost planar Sn–O framework that adopts a ladder‐type structure consisting of three four‐membered rings. The hydroxyl groups are shielded by the organic groups, which prevent them from further condensation and from the formation of hydrogen bonds.     

In-plane and perpendicular tunneling through InAs quantum dots

A Schottky diode with InAs dots in the intrinsic GaAs region was used to investigate perpendicular tunneling (in growth direction) through InAs quantum dots (QDs). At forward bias conditions electrons tunnel from the ohmic back contact into the metal Schottky gate. Peaks appear in the differential conductance when a QD level comes into resonance with the Fermi-level of the n-doped region. The observed tunneling features are attributed to electron transport through the s- and p-shell of the InAs islands. In our in-plane tunneling experiments the islands were embedded in the channel region of an n-doped GaAs/AlGaAs HEMT-structure. In order to study tunneling through single InAs islands, a quantum point contact was defined by lithography with an atomic force microscope and subsequent wet-chemical etching. In contrast to unpatterned devices sharp peaks appear in the I–V characteristic of our samples reflecting the transport of electrons through the p-shell of a single InAs QD.     

SIMS Analysis of the wear of boron nitride tools for the machining of compacted graphite iron and grey cast iron

Cubic boron nitride (cBN) is a common material for tools for the machining of cast irons at high cutting speed. During the machining of compacted graphite iron (CGI) in continuous cutting the wear of the cBN tools was found to be significantly higher compared to the machining of grey cast iron. This is possibly a result of a heating of the tool surface during the cutting of CGI. One possible reason for the wear is diffusion of some elements from the cutting tool into the CGI or from the CGI into the cutting tool. SIMS measurements were carried out which prove the existence of such diffusion processes. A static model experiment has been performed by heating cBN tools to 700 °C while in contact with CGI or cast iron (CI). SIMS depth profiles of the cBN tools and of CGI/CI show that there is a diffusion of several elements in both directions (B, W and Ti from the cBN tools into the CGI or CI, Fe and Si from the CGI or CI samples into the cBN) up to a depth of 20 μm. Received: 18 March 1999 / Revised: 16 June 1999 / Accepted: 18 June 1999     

How small can a lattice of order-dimension n be?

The aim of this paper is to study the order-dimension of partition lattices and linear lattices. Our investigations were motivated by a question due to Bill Sands: For a lattice L, does dim L=n always imply |L|≥2 ⁿ ? We will answer this question in the negative since both classes of lattices mentioned above form counterexamples. In the case of the partition lattices, we will determine the dimension up to an absolute constant. For the linear lattice over GF(2), L _n , we determine the dimension up to a factor C/n for an absolute constant C.     

Development of a 4–15 μm infrared GaAs hyperspectral QWIP imager

In the on-going evolution of GaAs quantum well infrared photodetectors (QWIPs) we have developed a four band, 640 × 512, 23 μm × 23 μm pixel array which we have subsequently integrated with a linear variable etalon (LVE) filter providing over 200 spectral bands across the 4–15.4 μm wavelength region. This effort was a collaboration between NASA’s Goddard Space Flight Center (GSFC), the Jet Propulsion Laboratory (JPL) and the Army Research Laboratory (ARL) sponsored by the Earth Science Technology Office of NASA. The QWIP array was fabricated by graded molecular beam epitaxial (MBE) growth that was specifically tailored to yield four distinct bands (FWHM): Band 1; 4.5–5.7 μm, Band 2; 8.5–10 μm, Band 3; 10–12 μm and Band 4; 13.3–14.8 μm. Each band occupies a swath that comprises 128 × 640 elements. The addition of the LVE (which is placed directly over the array) further divides the four “broad” bands into 209 separate spectral bands ranging in width from 0.02 μm at 5 μm to 0.05 μm at 15 μm. The detector is cooled by a mechanical cryocooler to 46 K. The camera system is a fully reflective, f/4.2, 3-mirror system with a 21° × 25° field of view. The project goals were: (1) develop the 4 band GaAs QWIP array; (2) develop the LVE and; (3) implement a mechanical cryocooler. This paper will describe the efforts and results of this undertaking with emphasis on the overall system characteristics.     

Zur präparativen Bildung des Tri-tert.-butyl-nonaphosphans(3); P9(CMe3)3

Formation of Tri-tert.-butyl-nonaphosphane (3); P₉(CMe₃)₃ P₉(CMe₃)₃ 1 is formed by the reaction of “Na₃P/K₃P” with (Me₃C)PCl₂ [maximum yield 20% with regard to (Me₃C)PCl₂]. The molar ratio of the reactants used on this synthesis is Na/K:P₄:(Me₃C)PCl₂ is 4:1:2. The method of preparation is described.     

A constructive method for solving the displacement boundary-value problem of elastostatics by use of global basis systems

In this paper we are concerned with the three-dimensional homogeneous isotropic elastostatic boundary-value problem. Global basis vector fields are shown to be constructive structures for approximating the solution. The theoretical tool is a regularity condition developed from the classical integral equation approach. The paper ends with some reflections on the practical computability and numerical applicability.