321 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
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
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
Barriers and shortcomings in access to cardiovascular management and prevention for familial hypercholesterolemia during the COVID-19 pandemic
Familial hypercholesterolemia (FH) is a hereditary condition caused by mutations in the lipid pathway. The goal in managing FH is to reduce circulating low-density lipoprotein cholesterol and, therefore, reduce the risk of developing atherosclerotic cardiovascular disease (ASCVD). Because FH patients were considered high risk groups due to an increased susceptible for contracting COVID-19 infection, we hypothesized whether the effects of the pandemic hindered access to cardiovascular care. In this review, we conducted a literature search in databases Pubmed/Medline and ScienceDirect. We included a comprehensive analysis of findings from articles in English related and summarized the effects of the pandemic on cardiovascular care through direct and indirect effects. During the COVID-19 pandemic, FH patients presented with worse outcomes and prognosis, especially those that have suffered from early ASCVD. This caused avoidance in seeking care due to fear of transmission. The pandemic severely impacted consultations with lipidologists and cardiologists, causing a decline in lipid profile evaluations. Low socioeconomic communities and ethnic minorities were hit the hardest with job displacements and lacked healthcare coverage respectively, leading to treatment nonadherence. Lock-down restrictions promoted sedentary lifestyles and intake of fatty meals, but it is unclear whether these factors attenuated cardiovascular risk in FH. To prevent early atherogenesis in FH patients, universal screening programs, telemedicine, and lifestyle interventions are important recommendations that could improve outcomes in FH patients. However, the need to research in depth on the disproportionate impact within different subgroups should be the forefront of FH research
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
An Algebraic Pairing Model with Sp(4) Symmetry and its Deformation
A fermion realization of the compact symplectic sp(4) algebra provides a
natural framework for studying isovector pairing correlations in nuclei. While
these correlations manifest themselves most clearly in the binding energies of
0^+ ground states, they also have a large effect on the energies of excited
states, including especially excited 0^+ states. In this article we consider
non-deformed as well as deformed algebraic descriptions of pairing through the
reductions of sp_{(q)}(4) to different realizations of u_{(q)}(2) for single-j
and multi-j orbitals. The model yields a classification scheme for completely
paired 0^{+} states of even-even and odd-odd nuclei in the 1d_{3/2}, 1f_{7/2},
and 1f_{5/2}2p_{1/2}2p_{3/2}1g_{9/2} shells. Phenomenological non-deformed and
deformed isospin-breaking Hamiltonians are expressed in terms of the generators
of the dynamical symmetry groups Sp(4) and Sp_{q}(4). These Hamiltonians are
related to the most general microscopic pairing problem, including isovector
pairing and isoscalar proton-neutron interaction along with non-linear
interaction in the deformed extension. In both the non-deformed and deformed
cases the eigenvalues of the Hamiltonian are fit to the relevant Coulomb
corrected experimental 0^{+} energies and this, in turn, allows us to estimate
the interaction strength parameters, to investigate isovector-pairing
properties and symmetries breaking, and to predict the corresponding energies.
While the non-deformed theory yields results that are comparable to other
theories for light nuclei, the deformed extension, which takes into account
higher-order interactions between the particles, gives a better fit to the
data. The multi-shell applications of the model provide for reasonable
predictions of energies of exotic nuclei.Comment: 19 pages, 5 figures minor changes; improvements to achieve a better
and clearer presentation of our messages and idea
Risk-shifting Through Issuer Liability and Corporate Monitoring
This article explores how issuer liability re-allocates fraud risk and how risk allocation may reduce the incidence of fraud. In the US, the apparent absence of individual liability of officeholders and insufficient monitoring by insurers under-mine the potential deterrent effect of securities litigation. The underlying reasons why both mechanisms remain ineffective are collective action problems under the prevailing dispersed ownership structure, which eliminates the incentives to moni-tor set by issuer liability. This article suggests that issuer liability could potentially have a stronger deterrent effect when it shifts risk to individuals or entities holding a larger financial stake. Thus, it would enlist large shareholders in monitoring in much of Europe. The same risk-shifting effect also has implications for the debate about the relationship between securities litigation and creditor interests. Credi-tors’ claims should not be given precedence over claims of defrauded investors (e.g., because of the capital maintenance principle), since bearing some of the fraud risk will more strongly incentivise large creditors, such as banks, to monitor the firm in jurisdictions where corporate debt is relatively concentrated
Veterinary decision making in relation to metritis - a qualitative approach to understand the background for variation and bias in veterinary medical records
<p>Abstract</p> <p>Background</p> <p>Results of analyses based on veterinary records of animal disease may be prone to variation and bias, because data collection for these registers relies on different observers in different settings as well as different treatment criteria. Understanding the human influence on data collection and the decisions related to this process may help veterinary and agricultural scientists motivate observers (veterinarians and farmers) to work more systematically, which may improve data quality. This study investigates qualitative relations between two types of records: 1) 'diagnostic data' as recordings of metritis scores and 2) 'intervention data' as recordings of medical treatment for metritis and the potential influence on quality of the data.</p> <p>Methods</p> <p>The study is based on observations in veterinary dairy practice combined with semi-structured research interviews of veterinarians working within a herd health concept where metritis diagnosis was described in detail. The observations and interviews were analysed by qualitative research methods to describe differences in the veterinarians' perceptions of metritis diagnosis (scores) and their own decisions related to diagnosis, treatment, and recording.</p> <p>Results</p> <p>The analysis demonstrates how data quality can be affected during the diagnostic procedures, as interaction occurs between diagnostics and decisions about medical treatments. Important findings were when scores lacked consistency within and between observers (variation) and when scores were adjusted to the treatment decision already made by the veterinarian (bias). The study further demonstrates that veterinarians made their decisions at 3 different levels of focus (cow, farm, population). Data quality was influenced by the veterinarians' perceptions of collection procedures, decision making and their different motivations to collect data systematically.</p> <p>Conclusion</p> <p>Both variation and bias were introduced into the data because of veterinarians' different perceptions of and motivations for decision making. Acknowledgement of these findings by researchers, educational institutions and veterinarians in practice may stimulate an effort to improve the quality of field data, as well as raise awareness about the importance of including knowledge about human perceptions when interpreting studies based on field data. Both recognitions may increase the usefulness of both within-herd and between-herd epidemiological analyses.</p
A hippocampal circuit linking dorsal CA2 to ventral CA1 critical for social memory dynamics
Recent results suggest that social memory requires the dorsal hippocampal CA2 region as well as a subset of ventral CA1 neurons. However, it is unclear whether dorsal CA2 and ventral CA1 represent parallel or sequential circuits. Moreover, because evidence implicating CA2 in social memory comes largely from long-term inactivation experiments, the dynamic role of CA2 in social memory remains unclear. Here, we use pharmacogenetics and optogenetics in mice to acutely and reversibly silence dorsal CA2 and its projections to ventral hippocampus. We show that dorsal CA2 activity is critical for encoding, consolidation, and recall phases of social memory. Moreover, dorsal CA2 contributes to social memory by providing strong excitatory input to the same subregion of ventral CA1 that contains the subset of neurons implicated in social memory. Thus, our studies provide new insights into a dorsal CA2 to ventral CA1 circuit whose dynamic activity is necessary for social memory.We thank David H. Brann and the other members of the Siegelbaum laboratory for
helpful discussions and João Cerqueira for critical input. This work was supported by
R01 MH104602 and R01 MH106629 from the NIH (S.A.S.), by PD/BD/113700/2015
from the Portuguese Foundation for Science and Technology (T.M.) and by the European Molecular Biology Organization (A.O.)
Cancer-associated fibroblasts promote aggressive gastric cancer phenotypes via heat shock factor 1-mediated secretion of extracellular vesicles
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