A study of local and non-local spatial densities in quantum field theory

We use a one-dimensional model system to compare the predictions of two different 'yardsticks' to compute the position of a particle from its quantum field theoretical state. Based on the first yardstick (defined by the Newton-Wigner position operator), the spatial density can be arbitrarily narrow and its time-evolution is superluminal for short time intervals. Furthermore, two spatially distant particles might be able to interact with each other outside the light cone, which is manifested by an asymmetric spreading of the spatial density. The second yardstick (defined by the quantum field operator) does not permit localized states and the time evolution is subluminal.Comment: 29 pages, 3 figure

Genetics and Genetic Testing in Congenital Heart Disease

Congenital heart defects (CHDs) are structural abnormalities of the heart and great vessels that are present from birth. The presence or absence of extra-cardiac anomalies has historically been used to identify patients with possible monogenic, chromosomal, or teratogenic CHD etiologies. These distinctions remain clinically relevant, particularly with regard to management; however, identification of genetic causes in patients with presumably non-syndromic CHD indicates that isolated CHD can also be genetic in origin. In recent years, the field of cardiac genetics has benefited from a growing understanding of the complex molecular mechanisms underpinning heart development, and the extreme genetic heterogeneity of CHD is increasingly appreciated. Progress has been largely supported by improvements in genetic testing technology derived from worldwide efforts to accurately and economically characterize the full breadth of human genomic variation. The last fifteen years in particular have witnessed emergence and refinement of novel cytogenetic and sequencing technologies, which have proven to be enormously effective tools for both diagnosis and identification of novel CHD-causing genes. These advancements have led to an increasing need for cardiac care providers to be well versed in the molecular genetic origins of CHD and to have working knowledge of the benefits and limitations of available testing methods. In this review, we provide a general overview of key morphologic, molecular, and signaling mechanisms relevant to heart development before summarizing overall progress in the molecular genetic analyses of CHDs and current recommendations for clinical application of genetic testing. Particular emphasis is placed on the utility and limitations of chromosomal microarray analyses (CMAs) and on emerging clinical roles for whole exome sequencing (WES) and other next-generation sequencing (NGS) technologies

Supersonic performance, stability and control characteristics of a 0.01875 scale model Rockwell International 089B-139B orbiter configuration (LA8C)

An investigation was made in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.9 and 2.86 to study the supersonic aerodynamic characteristics of a Rockwell International shuttle orbiter configuration. Tests were made at a Reynolds number of 1.5 million per foot with an angle-of-attack range of minus 4 to 28 deg and sideslip variations of minus 6 to 8 deg. The effects of elevon and aileron deflections were investigated

Bosonic analog of the Klein paradox

The standard Klein paradox describes how an incoming electron scatters off a supercritical electrostatic barrier that is so strong that it can generate electron- positron pairs. This fermionic system has been widely discussed in textbooks to illustrate some of the discrepancies between quantum mechanical and quantum field theoretical descriptions for the pair creation process. We compare the fermionic dynamics with that of the corresponding bosonic system. We point out that the direct counterpart of the Pauli exclusion principle (the central mechanism to resolve the fermionic Klein paradox) is stimulated emission, which leads to the resolution of the analogous bosonic paradox

Space-time properties of a boson-dressed fermion for the Yukawa model

We analyze the interaction of fermions and bosons through a one-dimensional Yukawa model. We numerically compute the energy eigenstates that represent a physical fermion, which is a superposition of bare fermionic and bosonic eigenstates of the uncoupled Hamiltonian. It turns out that even fast bare fermions require only low-momentum dressing bosons, which attach themselves to the fast fermion through quantum correlations. We compare the space-time evolution of a physical fermion with that of its bare counterpart and show the importance of using dressed observables. The time evolution of the center of mass as well as the wave packet\u27s spatial width suggests that the physical particle has a lower mass than the sum of the masses of its bare constituents. The numerically predicted dressed mass agrees with that from lowest-order perturbation theory as well as with the renormalized mass obtained from the corresponding Feynman graphs. For a given momentum, this lower mass leads to a faster physical particle and a different relativistic spreading behavior of the wave packet

Exponential enhancement of field-induced pair creation from the bosonic vacuum

Using numerical solutions to quantum field theory, the creation of boson-antiboson pairs from the vacuum under a very strong localized external electric field is explored. The simulations reveal that the initial linear increase of the number of particles turns into an exponential growth. This self-amplification can be understood as the result of the interaction of the previously generated particles with the creation process. While the number of particles keeps increasing, the spatial shape of the (normalized) charge density of the created particles reaches a universal form that can be related to the bound states of the supercritical potential well. We accompany the space-time resolved quantum field theoretical simulations with a model calculation that allows us to interpret the numerical simulations in terms of simple classical mechanical concepts