466 research outputs found
Symmetry Scheme for Amino Acid Codons
Group theoretical concepts are invoked in a specific model to explain how
only twenty amino acids occur in nature out of a possible sixty four. The
methods we use enable us to justify the occurrence of the recently discovered
twenty first amino acid selenocysteine, and also enables us to predict the
possible existence of two more, as yet undiscovered amino acids.Comment: 18 pages which include 4 figures & 3 table
Z', new fermions and flavor changing processes, constraints on E models from --> eee
We study a new class of flavor changing interactions, which can arise in
models based on extended gauge groups (rank 4) when new charged fermions are
present together with a new neutral gauge boson. We discuss the cases in which
the flavor changing couplings in the new neutral current coupled to the
are theoretically expected to be large, implying that the observed
suppression of neutral flavor changing transitions must be provided by heavy
masses together with small - mixing angles.
Concentrating on E models, we show how the tight experimental limit on implies serious constraints on the mass and mixing
angle. We conclude that if the value of the flavor changing parameters is
assumed to lie in a theoretically natural range, in most cases the presence of
a much lighter than 1 TeV is unlikely.Comment: plain tex, 22 pages + 2 pages figures in PostScript (appended after
`\bye'), UM-TH 92-1
RADIOACTIVE WASTE DISPOSAL PROJECTS. IDAHO CHEMICAL PROCESSING PLANT TECHNICAL PROGRESS REPORT FOR JULY-SEPTEMBER 1959
The progress of extensive laboratory and pilot plant investigations on the fluidized bed process for the con version of radioactive liquid wastes to solids is reported. These studies are directed toward obtaining information on the dynamics of fluidized bed operation, the removal of volatile fission products and solids particles from gases, the development of equipment and operating techniques, and the various long term disposal aspects of all radioactive wastes. Laboratory studies on the removal of volatile ruthenium from a simulated calciner off-gas showed the removal efficiency of silica gel to decrease with successive wetting and drying cycles. Electrostatic precipitators were found to have a higher removal efficiency for solid particles (alumina) when a wetted wall rather than a dry wall type was used. Tests to determine the distribution of ruthenium in a pilot plant calciner were performed. Pilot plant data on particle growth in a fluidized bed were compared with theoretical equations. Operating experience with a NaK heat transfer system, and with liquid flow controllers is reported. The results of a series of qualitative tests to determine the likelihood of an explosive reaction should NaK leak into a fluidized bed calciner indicated that such a reaction is unlikely. A NaK leak that occurred at a welded junction was attributed to thermal overstressing of the metal and not due to corrosion. Calcium fluoride-impregnated Teflon was found to be a superior gasketing material, both chemically and mechanically, to pure Teflon. A literature survey on the chemistry of zirconium in a calcination process suggested the possibility of calcination in contact with silica and a laboratory unit is being installed to study the process. The hydraulics of a pulsed plate solids-liquid contactor and its associated equipment were determined. A preliminary investigation was started of the possibility of using metallizing techniques to surface coat solid particles and thereby reduce the leaching of fission products when contacted with ground water. Construction of a demonstrational fluidized bed calciner was approximately half completed; however, the national steel strike has slowed the construction schedule and the completion date cannot be estimated until the strike is settled. Process and equipment reviews of the facility and the results of thermal conductivity measurements on Idaho sands are reported. (auth
Spontaneous parity violation and minimal Higgs models
In this paper we present a model for the spontaneous breaking of parity with
two Higgs doublets and two neutral Higgs singlets which are even and odd under
D-parity. The condition can be satisfied without introducing
bidoublets and it is induced by the breaking of D-parity through the vacuum
expectation value of the odd Higgs singlet. Examples of left-right symmetric
and mirror fermions models in grand unified theories are presented.Comment: Revised version. Accepted in Eur. Phys. Journal
Maximal atmospheric neutrino mixing and the small ratio of muon to tau mass
We discuss the problem of the small ratio of muon mass to tau mass in a class
of seesaw models where maximal atmospheric neutrino mixing is enforced through
a -- interchange symmetry. We introduce into those models an
additional symmetry such that in the case of exact
invariance. The symmetry may be softly broken in the Higgs potential, and
one thus achieves in a technically natural way. We speculate
on a wider applicability of this mechanism.Comment: 10 pages, plain LaTeX, no figures, minor changes, final version for
J. Phys.
Implications of LEP Results for SO(10) Grandunification with Two Intermediate Stages
We consider the breaking of the grand unification group to the
standard model gauge group through several chains containing two intermediate
stages. Using the values of the gauge coupling constants at scale derived
from recent LEP data, we determine the range of their intermediate and
unification scales. In particular, we identify those chains that permit new
gauge structure at relatively low energy .Comment: (LATEX, 9 pages + 3 pages of figures not included) OITS-48
The Relative Composition of the Inflammatory Infiltrate as an Additional Tool for Synovial Tissue Classification
10.1371/journal.pone.0072494PLoS ONE88-POLN
Enhanced Antigen-Specific Antitumor Immunity with Altered Peptide Ligands that Stabilize the MHC-Peptide-TCR Complex
AbstractT cell responsiveness to an epitope is affected both by its affinity for the presenting MHC molecule and the affinity of the MHC-peptide complex for TCR. One limitation of cancer immunotherapy is that natural tumor antigens elicit relatively weak T cell responses, in part because high-affinity T cells are rendered tolerant to these antigens. We report here that amino acid substitutions in a natural MHC class I–restricted tumor antigen that increase the stability of the MHC-peptide-TCR complex are significantly more potent as tumor vaccines. The improved immunity results from enhanced in vivo expansion of T cells specific for the natural tumor epitope. These results indicate peptides that stabilize the MHC-peptide-TCR complex may provide superior antitumor immunity through enhanced stimulation of specific T cells
Possible Origin of Fermion Chirality and Gut Structure From Extra Dimensions
The fundamental chiral nature of the observed quarks and leptons and the
emergence of the gauge group itself are most puzzling aspects of the standard
model. Starting from general considerations of topological properties of gauge
field configurations in higher space-time dimensions, it is shown that the
existence of non-trivial structures in ten dimensions would determine a class
of models corresponding to a grand unified GUT structure with complex fermion
representations with respect to . The
discussion is carried out within the framework of string theories with
characteristic energy scales below the Planck mass. Avoidance of topological
obstructions upon continuous deformation of field configurations leads to
global chiral symmetry breaking of the underlying fundamental theory, imposes
rigorous restrictions on the structure of the vacuum and space-time itself and
determines uniquely the gauge structure and matter content.Comment: final version to appear in Phys. Rev.
SO(10) Cosmic Strings and Baryon Number Violation
SO(10) cosmic strings formed during the phase transition Spin(10)
SU(5) are studied. Two types of strings ---
one effectively Abelian and one non-Abelian --- are constructed and the string
solutions are calculated numerically. The non-Abelian string can catalyze
baryon number violation via the ``twisting'' of the scalar field which causes
mixing of leptons and quarks in the fermion multiplet. The non-Abelian string
is also found to have the lower energy possibly for the entire range of the
parameters in the theory. Scattering of fermions in the fields of the strings
is analyzed, and the baryon number violation cross section is calculated. The
role of the self-adjoint parameters is discussed and the values are computed.Comment: LaTex (RevTex), 36 pages, 6 figures (available upon request),
MIT-CTP#215
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