Search

Presents a study that investigated the implantation of selenium ion on gallium arsenide/(aluminum, gallium) arsenic quantum well. Analysis of the interface diffuseness; Examination of the loss of surface material; Determination of the occurrence of crystallographic defects.

We studied the magnetic excitations from the S=1/2 two-leg ladders in La[sub 6]Ca[sub 8]Cu[sub 24]O[sub 41]. In order to understand the full dispersion of the magnon branch for the lowest triplet excitation, effects of the four-spin and the next-nearest-neighbor (diagonal) exchange interactions are analyzed. We also compare the parameters obtained from the fit to the full dispersion curve with those obtained in the related compounds. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Low-temperature specific heat measurements on NdNiO[sub 3] evidence the onset of Nd cooperative ordering at T[sub N2]=0.77 K. Because of the particular arrangement of the Ni magnetic moments, half of the Nd ions have an antiferromagnetically compensated environment while the other half have a noncompensated one. We show that both types of Nd ions are affected by a different but non-negligible Nd–Ni exchange field, in contrast with the current model used in literature.© 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

T lymphocytes are stimulated when they recognize short peptides bound to class I proteins of the major histocompatibility complex (MHC) protein, as peptide-MHC complexes. Due to the diversity in T-cell receptor (TCR) molecules together with both the peptides and MHC proteins they bind to, it has been difficult to design vaccines and treatments based on these interactions. Machine learning has made some progress in trying to predict the immunogenicity of peptide sequences in the context of specific MHC class I alleles but, as such approaches cannot integrate temporal information and lack explanatory power, their scope will always be limited. Here, we advocate a mechanistic description of antigen presentation and TCR activation which is explanatory, predictive, and quantitative, drawing on modeling approaches that collectively span several length and time scales, being capable of furnishing reliable biological descriptions that are difficult for experimentalists to provide. It is a form of multiscale systems biology. We propose the use of chemical rate equations to describe the time evolution of the foreign and host proteins to explain how the original proteins end up being presented on the cell surface as peptide fragments, while we invoke molecular dynamics to describe the key binding processes on the molecular level, including those of peptide-MHC complexes with TCRs which lie at the heart of the immune response. On each level, complementary methods based on machine learning are available, and we discuss the relationship between these divergent approaches. The pursuit of predictive mechanistic modeling approaches requires experimentalists to adapt their work so as to acquire, store, and expose data that can be used to verify and validate such models. [ABSTRACT FROM AUTHOR]

A special Microsymposium on polarized neutron methods and technologies on existing and future pulsed neutron sources was held at PNCMI-2002. We present the recommendations formulated by three working groups on “Diffraction,” “Inelastic Scattering” and “Reflectometry.” Needs for method development as well as opportunities for novel polarized neutron instrumentation are identified. [Copyright &y& Elsevier]

The existence of a wide distribution of low energy excess magnetic states due to topological disorder in a magnetic glass is confirmed experimentally for terbium metaphosphate glasses with compositions in the vicinity of (Tb[sub 2]O[sub 3)0:25](P[sub 2]O[sub 5)0:75]. A broad peak with a maximum at 7.5K is found in the magnetic contribution to the specific heat; this has its origin in the excess magnetic states. A strong magnetic contribution to the inelastic neutron scattering, isolated by subtraction of the vibrational contribution, arises from a complex of states of higher energies than those responsible for the magnetic contribution to the specific heat. [ABSTRACT FROM AUTHOR]

Position sensitive detectors at the ISIS facility largely comprise of a mixture of 3He proportional counters and fibre-coded scintillation detectors based on ZnS/6LiF. The latest developments of these devices at ISIS will be discussed with reference to three ISIS instruments, MERLIN, GEM and ENGIN-X. MERLIN is the new chopper spectrometer now being developed at ISIS and features a large 2D detector array covering more than 20 m2 with a requirement in position resolution of 25×25 mm2. Resistive wire detectors are proposed for this detector, but to minimise gaps in the solid angle, detectors with active lengths of 2.9 m are being proposed. Initial results from prototype detectors will be presented. GEM is a general materials diffractometer now nearing completion and ENGIN-X is the engineering instrument, which became operational in November 2002. Detectors for both these instruments use linear arrays of fibre optic-encoded ZnS/6Li scintillator, with position resolutions of 5 and 3 mm, respectively. Work has now started on the construction of the ISIS second target station, TS-2. This facility will be tailored to the production of lower-energy neutrons compared with target station 1, with applications predominantly in soft condensed matter, bio-molecular sciences and advanced materials. The challenges this presents for future neutron detector development at ISIS will be reviewed together with some potential lines of detector development. [Copyright &y& Elsevier]