2,610 research outputs found
VH-RELATED IDIOTOPES DETECTED BY SITE-DIRECTED MUTAGENESIS
The function of the CD4 cell surface protein as
coreceptor on T helper lymphocytes and as receptor
for HIV makes this glycoprotein a prime target for
an immune intervention with mAb. A detailed understanding
of the structural determinants on the
therapeutic CD4 mAb that are involved in Ag binding
or are recognized by anti-idiotypic mAb (anti-Id)
may be important for designing antibodies with optimal
therapeutic efficacy. Seven anti-Id raised
against the CD4 mAb M-T310 were selected from a
large panel with the intention to obtain CD4 mimicking
structures with specificity foHr IV gp120. The
selected anti-Id did not reacwt ith other CDCspecific
mAb cross-blocking M-T310. Among these, mAb MT404,
although having the same L chain as M-T310
and a VH region sequence differing onlya t 14 amino
acid positions, was not recognized by the anti-Id. MT310
H chain complexed with the J558L L chain
reacted with all anti-Id, thus demonstrating that the
recognized idiotopes are located within the VH region.
To identify the idiotopes of M-T310 seen by
the anti-Id, variants of M-T404 containing one or
more of the M-T3 1 O-derived substitutions were generated
by oligonucleotide-directed mutagenesis.
The reactivity pattern of the mutant proteins with
the anti-Id demonstrated that the idiotopes reside
within the complementarity determining region
(CDR) 2 and CDR3 loops of the VH region. A major
idiotope was definebdy a single amino acid in CDR2
that was recognized by three anti-Id, whereas the
four other anti-Id reacted with determinants of
CDR3. Although the performed amino acid substitutions
did influence the Id recognition, Ag binding
was not significantly affected, suggesting that none
of the anti-Id can be considered as a mimicry of the
CD4 A
Comment on Decay
We calculate the rate for decay using Chiral
Perturbation Theory. This isospin violating process results from -
mixing, and its amplitude is proportional to . Experimental information on the branching
ratio for can provide insight into the pattern of
violation in radiative decays.Comment: 7 pages with 2 figures not included but available upon request,
CALT-68-191
Advanced aeroservoelastic stabilization techniques for hypersonic flight vehicles
Advanced high performance vehicles, including Single-Stage-To-Orbit (SSTO) hypersonic flight vehicles, that are statically unstable, require higher bandwidth flight control systems to compensate for the instability resulting in interactions between the flight control system, the engine/propulsion dynamics, and the low frequency structural modes. Military specifications, such as MIL-F-9490D and MIL-F-87242, tend to limit treatment of structural modes to conventional gain stabilization techniques. The conventional gain stabilization techniques, however, introduce low frequency effective time delays which can be troublesome from a flying qualities standpoint. These time delays can be alleviated by appropriate blending of gain and phase stabilization techniques (referred to as Hybrid Phase Stabilization or HPS) for the low frequency structural modes. The potential of using HPS for compensating structural mode interaction was previously explored. It was shown that effective time delay was significantly reduced with the use of HPS; however, the HPS design was seen to have greater residual response than a conventional gain stablized design. Additional work performed to advance and refine the HPS design procedure, to further develop residual response metrics as a basis for alternative structural stability specifications, and to develop strategies for validating HPS design and specification concepts in manned simulation is presented. Stabilization design sensitivity to structural uncertainties and aircraft-centered requirements are also assessed
Microscopic investigation of phonon modes in SiGe alloy nanocrystals
Phonon modes in spherical silicon germanium alloy (SiGe) nanocrystals containing up to 1147 atoms (3.6 nm) have been investigated as a function of the Si concentration. Microscopic details of phonon modes, including phonon frequencies and vibrational amplitudes, phonon density-of-states are calculated directly from the dynamic matrices. In particular, the dependence of phonon frequency on the configuration (such as a different ratio of Si to Ge atoms), and location (surface or interior) of clusters of atoms in SiGe alloy nanocrystals have been investigated. Low frequency surface phonons that are related to the spheroidal and torsional modes of a continuum sphere are identified and their frequency dependence on alloy concentration elucidated. The calculated results are compared with measured Raman spectra in bulk, thin films, and superlattices of SiGe alloy reported in the literature. Insights into the behavior of Raman peaks usually identified as Ge-Ge, Si-Si, and Ge-Si optical phonon modes are presented
Theoretical investigation of the surface vibrational modes in germanium nanocrystals
We have used a microscopic lattice dynamical model to study phonon modes in germanium (Ge) NC with size varying between 47 to 7289 atoms (diametersimilar to6.8 nm). By separating these atoms into bulk and surface atoms we have found that surface modes can exist in Ge NC both at low frequencies (\u3c50\u3ecm(-1)) and at high frequency (similar to260 cm(-1)). The latter mode is a resonant mode which occurs in the pseudogap between the acoustic and optical phonon branches in bulk Ge. From the low frequency surface modes we have been able to reconstruct the spheroidal and torsional Lamb modes which have been used to interpret experimental results. Finally, we found that the Lamb model starts to deviate from the lattice dynamical results for Ge NC with diameternm
Chiral transition and deconfinement transition in QCD with the highly improved staggered quark (HISQ) action
We report preliminary results on the chiral and deconfinement aspects of the
QCD transition at finite temperature using the Highly Improved Staggered Quark
(HISQ) action on lattices with temporal extent of N_{\tau}=6 and 8. The chiral
aspects of the transition are studied in terms of quark condensates and the
disconnected chiral susceptibility. We study the deconfinement transition in
terms of the strange quark number susceptibility and the renormalized Polyakov
loop. We made continuum estimates for some quantities and find reasonably good
agreement between our results and the recent continuum extrapolated results
obtained with the stout staggered quark action.Comment: Talk presented by P. Petreczky at workshop Dense Matter 2010, April
6-9, Stellenbosch, South Africa, to be published in the proceeding
Strong and Electromagnetic Decays of Two New Baryons
Two recently discovered excited charm baryons are studied within the
framework of Heavy Hadron Chiral Perturbation Theory. We interpret these new
baryons which lie 308 \MeV and 340 \MeV above the as
members of a P-wave spin doublet. Differential and total decay rates for their
double pion transitions down to the ground state are calculated.
Estimates for their radiative decay rates are also discussed. We find that the
experimentally determined characteristics of the baryons may be
simply understood in the effective theory.Comment: 16 pages with 4 figures not included but available upon request,
CALT-68-191
Chiral Estimates of Strong CP Violation Revisited
The effects of the CP violating term in the QCD Lagrangian upon low
energy hadronic phenomenology are reconsidered. Strong CP violating
interactions among Goldstone bosons and octet baryons are incorporated into an
effective chiral Lagrangian framework. The term's impact upon the
decays and is then investigated but
found to be extremely small. A refined model independent estimate of
nonanalytic contributions to the neutron electric dipole moment is also
determined using velocity dependent Baryon Chiral Perturbation Theory. We
obtain the approximate upper bound .Comment: 11 pages with 3 figures not included but available upon request,
CALT-68-184
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