468 research outputs found
Deformations of the fermion realization of the sp(4) algebra and its subalgebras
With a view towards future applications in nuclear physics, the fermion
realization of the compact symplectic sp(4) algebra and its q-deformed versions
are investigated. Three important reduction chains of the sp(4) algebra are
explored in both the classical and deformed cases. The deformed realizations
are based on distinct deformations of the fermion creation and annihilation
operators. For the primary reduction, the su(2) sub-structure can be
interpreted as either the spin, isospin or angular momentum algebra, whereas
for the other two reductions su(2) can be associated with pairing between
fermions of the same type or pairing between two distinct fermion types. Each
reduction provides for a complete classification of the basis states. The
deformed induced u(2) representations are reducible in the action spaces of
sp(4) and are decomposed into irreducible representations.Comment: 28 pages, LaTeX 12pt article styl
Deformations of the Boson Representation and its Subalgebras
The boson representation of the sp(4,R) algebra and two distinct deformations
of it, are considered, as well as the compact and noncompact subalgebras of
each. The initial as well as the deformed representations act in the same Fock
space.
One of the deformed representation is based on the standard q-deformation of
the boson creation and annihilation operators. The subalgebras of sp(4,R)
(compact u(2) and three representations of the noncompact u(1,1) are also
deformed and are contained in this deformed algebra. They are reducible in the
action spaces of sp(4,R) and decompose into irreducible representations.
The other deformed representation, is realized by means of a transformation
of the q-deformed bosons into q-tensors (spinor-like) with respect to the
standard deformed su(2). All of its generators are deformed and have
expressions in terms of tensor products of spinor-like operators. In this case,
an other deformation of su(2) appears in a natural way as a subalgebra and can
be interpreted as a deformation of the angular momentum algebra so(3). Its
representation is reducible and decomposes into irreducible ones that yields a
complete description of the same
Generalized q-Deformed Symplectic sp(4) Algebra for Multi-shell Applications
A multi-shell generalization of a fermion representation of the q-deformed
compact symplectic sp_q(4) algebra is introduced. An analytic form for the
action of two or more generators of the Sp_q(4) symmetry on the basis states is
determined and the result used to derive formulae for the overlap between
number preserving states as well as for matrix elements of a model Hamiltonian.
A second-order operator in the generators of Sp_q(4) is identified that is
diagonal in the basis set and that reduces to the Casimir invariant of the
sp(4) algebra in the non-deformed limit of the theory. The results can be used
in nuclear structure applications to calculate beta-decay transition
probabilities and to provide for a description of pairing and higher-order
interactions in systems with nucleons occupying more than a single-j orbital.Comment: 10 page
Coherent pairing states for the Hubbard model
We consider the Hubbard model and its extensions on bipartite lattices. We
define a dynamical group based on the -pairing operators introduced by
C.N.Yang, and define coherent pairing states, which are combinations of
eigenfunctions of -operators. These states permit exact calculations of
numerous physical properties of the system, including energy, various
fluctuations and correlation functions, including pairing ODLRO to all orders.
This approach is complementary to BCS, in that these are superconducting
coherent states associated with the exact model, although they are not
eigenstates of the Hamiltonian.Comment: 5 pages, RevTe
Challenges to support edge-as-a-service
A new era in telecommunications is emerging. Virtualized networking functions and resources will offer network operators a way to shift the balance of expenditure from capital to operational, opening up networks to new and innovative services. This article introduces the concept of edge as a service (EaaS), a means of harnessing the flexibility of virtualized network functions and resources to enable network operators to break the tightly coupled relationship they have with their infrastructure and enable more effective ways of generating revenue. To achieve this vision, we envisage a virtualized service access interface that can be used to programmatically alter access network functions and resources available to service providers in an elastic fashion. EaaS has many technically and economically difficult challenges that must be addressed before it can become a reality; the main challenges are summarized in this article
Quantitative SPECT/CT parameters of myocardial 99mTechnetium-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD) uptake in suspected cardiac transthyretin amyloidosis
Background: 99mTc-labelled bisphosphonates are used for imaging assessment of patients with transthyretin cardiac amyloidosis (ATTR). Present study evaluates whether quantitative SPECT/CT measurement of absolute myocardial 99mTc-labelled 3,3-diphosphono-1,2-propanodicarboxylic acid (Tc-DPD) uptake can diagnose patients with suspected ATTR. / Methods: Twenty-eight patients (25 male, age 80.03 ± 6.99 years) with suspected ATTR referred for Tc-DPD imaging had planar and SPECT/CT imaging of the chest. Three operators independently obtained Tc-DPD myocardial SUVmax and SUVmean above threshold (SMaT) (20, 40 and 60% of SUVmax), using a semi-automated threshold segmentation method. Results were compared to visual grading (0–3) of cardiac uptake. / Results: Twenty-two patients (78%) had cardiac uptake (2 grade 1, 15 grade 2, 5 grade 3). SUVmax and SMaT segmentation thresholds enabled separating grades 2/3 from 0/1 with excellent inter- and intra-reader correlation. Cut-off values 6.0, 2.5, 3 and 4 for SUVmax, SMaT20,40,60, respectively, separated between grades 2/3 and 0 /1 with PPV and NPV of 100%. SMaT20,40,60(cardiac)/SUVmean (liver) and SMaT20,40,60(cardiac)/SUVmean(liver/lung) separated grades 2 and 3. / Conclusion: Quantitative SPECT/CT parameters of cardiac Tc-DPD uptake are robust, enabling separation of patients with grades 2 and 3 cardiac uptake from grades 0 and 1. Larger patient cohorts will determine the incremental value of SPECT/CT quantification for ATTR management
Small oscillations of a chiral Gross-Neveu system
We study the small oscillations regime (RPA approximation) of the
time-dependent mean-field equations, obtained in a previous work, which
describe the time evolution of one-body dynamical variables of a uniform Chiral
Gross-Neveu system. In this approximation we obtain an analytical solution for
the time evolution of the one-body dynamical variables. The two-fermion physics
can be explored through this solution. The condition for the existence of bound
states is examined.Comment: 21pages, Latex, 1postscript figur
On the use of the group SO(4,2) in atomic and molecular physics
In this paper the dynamical noninvariance group SO(4,2) for a hydrogen-like
atom is derived through two different approaches. The first one is by an
established traditional ascent process starting from the symmetry group SO(3).
This approach is presented in a mathematically oriented original way with a
special emphasis on maximally superintegrable systems, N-dimensional extension
and little groups. The second approach is by a new symmetry descent process
starting from the noninvariance dynamical group Sp(8,R) for a four-dimensional
harmonic oscillator. It is based on the little known concept of a Lie algebra
under constraints and corresponds in some sense to a symmetry breaking
mechanism. This paper ends with a brief discussion of the interest of SO(4,2)
for a new group-theoretical approach to the periodic table of chemical
elements. In this connection, a general ongoing programme based on the use of a
complete set of commuting operators is briefly described. It is believed that
the present paper could be useful not only to the atomic and molecular
community but also to people working in theoretical and mathematical physics.Comment: 31 page
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