60 research outputs found
Realization of compact Lie algebras in K\"ahler manifolds
The Berezin quantization on a simply connected homogeneous K\"{a}hler
manifold, which is considered as a phase space for a dynamical system, enables
a description of the quantal system in a (finite-dimensional) Hilbert space of
holomorphic functions corresponding to generalized coherent states. The Lie
algebra associated with the manifold symmetry group is given in terms of
first-order differential operators. In the classical theory, the Lie algebra is
represented by the momentum maps which are functions on the manifold, and the
Lie product is the Poisson bracket given by the K\"{a}hler structure. The
K\"{a}hler potentials are constructed for the manifolds related to all compact
semi-simple Lie groups. The complex coordinates are introduced by means of the
Borel method. The K\"{a}hler structure is obtained explicitly for any unitary
group representation. The cocycle functions for the Lie algebra and the Killing
vector fields on the manifold are also obtained
Analytic representations based on SU(1,1) coherent states and their applications
We consider two analytic representations of the SU(1,1) Lie group: the
representation in the unit disk based on the SU(1,1) Perelomov coherent states
and the Barut-Girardello representation based on the eigenstates of the SU(1,1)
lowering generator. We show that these representations are related through a
Laplace transform. A ``weak'' resolution of the identity in terms of the
Perelomov SU(1,1) coherent states is presented which is valid even when the
Bargmann index is smaller than one half. Various applications of these
results in the context of the two-photon realization of SU(1,1) in quantum
optics are also discussed.Comment: LaTeX, 15 pages, no figures, to appear in J. Phys. A. More
information on http://www.technion.ac.il/~brif/science.htm
Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world
Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic.
Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality.
Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States.
Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis.
Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection
- …