549 research outputs found
Two-User Gaussian Interference Channel with Finite Constellation Input and FDMA
In the two-user Gaussian Strong Interference Channel (GSIC) with finite
constellation inputs, it is known that relative rotation between the
constellations of the two users enlarges the Constellation Constrained (CC)
capacity region. In this paper, a metric for finding the approximate angle of
rotation (with negligibly small error) to maximally enlarge the CC capacity for
the two-user GSIC is presented. In the case of Gaussian input alphabets with
equal powers for both the users and the modulus of both the cross-channel gains
being equal to unity, it is known that the FDMA rate curve touches the capacity
curve of the GSIC. It is shown that, with unequal powers for both the users
also, when the modulus of one of the cross-channel gains being equal to one and
the modulus of the other cross-channel gain being greater than or equal to one,
the FDMA rate curve touches the capacity curve of the GSIC. On the contrary, it
is shown that, under finite constellation inputs, with both the users using the
same constellation, the FDMA rate curve strictly lies within (never touches)
the enlarged CC capacity region throughout the strong-interference regime. This
means that using FDMA it is impossible to go close to the CC capacity. It is
well known that for the Gaussian input alphabets, the FDMA inner-bound, at the
optimum sum-rate point, is always better than the simultaneous-decoding
inner-bound throughout the weak-interference regime. For a portion of the weak
interference regime, it is shown that with identical finite constellation
inputs for both the users, the simultaneous-decoding inner-bound, enlarged by
relative rotation between the constellations, is strictly better than the FDMA
inner-bound.Comment: 12 pages, 10 figure
Resonance Raman Spectroscopy of the Oxygenated Intermediates of Human CYP19A1 Implicates a Compound I Intermediate in the Final Lyase Step
CYP19A1, or aromatase, a cytochrome P450 responsible for estrogen biosynthesis in humans, is an important therapeutic target for the treatment of breast cancer. There is still controversy surrounding the identity of reaction intermediate that catalyzes carbon–carbon scission in this key enzyme. Probing the oxy-complexes of CYP19A1 poised for hydroxylase and lyase chemistries using resonance Raman spectroscopy and drawing a comparison with CYP17A1, we have found no significant difference in the frequencies or isotopic shifts for these two steps in CYP19A1. Our experiments implicate the involvement of Compound I in the terminal lyase step of CYP19A1 catalysis
The quantization of exotic states in SU(3) soliton models: A solvable quantum mechanical analog
The distinction between the rigid rotor and Callan-Klebanov approaches to the
quantization of SU(3) solitons is considered in the context of exotic baryons.
A numerically tractable quantum mechanical analog system is introduced to test
the reliability of the two quantization schemes. We find that in the equivalent
of the large N_c limit of QCD, the Callan-Klebanov approach agrees with a
numerical solution of the quantum mechanical analog. Rigid rotor quantization
generally does not. The implications for exotic baryons are briefly discussed.Comment: 8 pages; 3 figures; minor corrections; reference adde
Neutrino Masses from Non-minimal Gravitational Interactions of Massive Neutral Fermions
A new mechanism is proposed for generating neutrino masses radiatively
through a non-minimal coupling to gravity of fermionic bilinears involving
massive neutral fermions. Such coupling terms can arise in theories where the
gravity sector is augmented by a scalar field. They necessarily violate the
principle of equivalence, but such violations are not ruled out by present
experiments. It is shown that the proposed mechanism is realised most
convincingly in theories of the Randall- Sundrum type, where gravity couples
strongly in the TeV range. The mechanism has the potential for solving both the
solar and atmospheric neutrino problems. The smallness of neutrino masses in
this scenario is due to the fact that the interaction of the massive neutral
fermions arises entirely from higher-dimensional operators in the effective
Lagrangian.Comment: 7 page Latex 2e file, axodraw needed. Discussion and references
added. Version to appear in MPL
Three generations of colored fermions with family symmetry from Cayley-Dickson sedenions
An algebraic representation of three generations of fermions with
color symmetry based on the Cayley-Dickson algebra of sedenions is
constructed. Recent constructions based on division algebras convincingly
describe a single generation of leptons and quarks with Standard Model gauge
symmetries. Nonetheless, an algebraic origin for the existence of exactly three
generations has proven difficult to substantiate. We motivate as a
natural algebraic candidate to describe three generations with gauge
symmetry. We initially represent one generation of leptons and quarks in terms
of two minimal left ideals of , generated from a subset of
all left actions of the complex sedenions on themselves. Subsequently we employ
the finite group , which are automorphisms of but not of
to generate two additional generations. Given the relative
obscurity of sedenions, efforts have been made to present the material in a
self-contained manner.Comment: 18 pages, 1 figur
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