Identification of two distinct properties of class II major histocompatibility complex-associated peptides

We have examined the interactions of various peptides with the mouse class II major histocompatibility complex molecule I-Ak. The peptides were derived from the model protein hen egg white lysozyme (HEL). The immunodominant peptide of HEL is a 10-mer, residues 52-61. Our previous work established that this sequence contains the key residues for binding and presentation to T cells. Now we show that the binding of this 10-mer sequence resulted in complexes of I-Ak and peptide that, in SDS/PAGE (without boiling the protein), rapidly dissociated from the component alpha and beta chains. The binding interactions were studied in vitro, by incubating purified I-Ak and radiolabeled peptide, or ex vivo, by using antigen-presenting cells incubated with peptides. Peptides with additional residues at either the amino or carboxyl terminus behaved dramatically differently. Complexes of I-Ak with the longer peptides were stable to SDS/PAGE. Very few amino acid additions result in the change from unstable to stable complexes. The important issue here is that when cultured with HEL, antigen-presenting cells selected the HEL peptides containing the 52-61 sequences that favored stability [Nelson, C. A., Roof, R. W., McCourt, D. W. & Unanue, E. R. (1992) Proc. Natl., Acad. Sci. USA 89, 7380-7383]. Also, from other studies, such sequences correlate with a high immunogenicity of the peptide. We conclude that there are structural features of peptides that change the stability of the class II molecule and that are independent of the "core" peptide seen by the T cells.     

A new approach for handling and transferring of thin semiconductor materials

 Based on the fracture mechanics analysis of crack propagation, the phenomenon of subcritical crack growth was utilized for a controlled debonding of directly wafer-bonded interfaces. The approach allowed the well-defined separation of bonded wafers although the bond strength was high due to thermal annealing. The achieved splitting velocity depended on the wafer material, the wafer thickness ratio, the bonding process parameters, and the environmental conditions during cleaving. In combination with wafer bonding, the method can be used for a temporary stiffening and handling of thin and brittle wafers during fabrication, even if the wafers are exposed to high process temperatures. The approach can also be applied to fabricate micromechanical systems (MEMS). Received: 12 July 2001/Accepted: 26 February 2002 This paper was presented at the Conference of Micro System Technologies 2001 in March 2001.     

Improvement of Centrifugal Cryoconcentration by Ice Recovery Applied to Orange Juice

Centrifugal cryoconcentration, a concentration technique employed for fruit juices, involves challenges that still have to be overcome. The improvement of centrifugal cryoconcentration by recovery of ice fractions applied to orange juice is evaluated. The concentration process was performed with three consecutive cryoconcentration cycles and two recirculated ices. The solutes in the concentrated samples increased progressively six times after three cycles compared to the initial concentration of solids. The ice recovery samples increase the overall efficiency of the centrifugal cryoconcentration technique applied to orange juice.     

High-Performance Directional Metallopolyamides. II. Optical Spectroscopic Studies of Metal Chelation

The chelating interaction between metal ions and 4,4-disubstituted-2,2-bipyridyl-containing high-performance polymeric ligands prepared from 2,2-bipyridyl-4,4-dicarboxylic acid and a series of primary aromatic diamines was investigated by optical spectroscopy. Optical spectroscopic studies of the chelation of ruthenium ions by the 2,2-bipyridyl-containing polyamides revealed the formation of distinct ruthenium(II) complexes [Ru^II(poly)L₄] ( _max=530 nm), [Ru^II(poly)₂L₂] ( _max=584 nm), and [Ru^II(poly)₃]²⁺ ( _max=476 nm), while iron(II) ions formed only one complex ( _max=569 nm). The diverse functional features of the polymer repeat unit directly influences the chelation of metal ions.     

A linear statistical FET model using principal component analysis

An important issue in statistical circuit design, other than the algorithms themselves, is the development of efficient, statistically valid element models. The authors first discuss what features are needed for a good statistical model. The standard FET model is shown to be difficult to use in a statistical simulation, due to the nonlinear relation between FET S-parameters and model parameters. A linear statistical FET model is then proposed that is based on principal component analysis. This linear model gives uncorrelated model parameters. In an example using measured S-parameter data from ninety 0.5-μm GaAs FETs, 13 uncorrelated model parameters were needed to model the data from 1 to 11 GHz and at one bias. Simulation using this linear model and issues relating to bias are discussed