Safe domain and elementary geometry

A classical problem of mechanics involves a projectile fired from a given point with a given velocity whose direction is varied. This results in a family of trajectories whose envelope defines the border of a 'safe' domain. In the simple cases of a constant force, harmonic potential and Kepler or Coulomb motion, the trajectories are conic curves whose envelope in a plane is another conic section which can be derived either by simple calculus or by geometrical considerations. The case of harmonic forces reveals a subtle property of the maximal sum of distances within an ellipse.Comment: Also available from http://democrite.in2p3.fr/democrite-0002317

Historical Survey of the Quasi-Nuclear Baryonium

We review ideas and speculations concerning possible bound states or resonances of the nucleon--antinucleon system.Comment: 12 pages, Talk at the Workshop on Hadron Spectroscopy, Frascati, Italy, march 199

Recent issues in hadron spectroscopy

A brief survey is presented of recently discovered hadrons, some of them presumably demonstrating a new kind of internal structure. This includes : spin-singlet quarkonium, mesons with unexpected mass or width, baryons with two heavy quarks, and pentaquark candidates. Flavour configurations with a combination of light and heavy quarks appear as particularly promising.Comment: Based on an invited talk at the session on Subnucleon degrees of freedo

Stability of multiquarks in a simple string model

A simple string model inspired by the strong-coupling regime of Quantum ChromoDynamics is used as a potential for studying the spectrum of multiquark systems with two quarks and two antiquarks, with a careful treatment of the four-body problem. It is found that the ground state is stable, lying below the threshold for dissociation into two isolated mesons.Comment: 4 pages, 2 figures, Refs. added, typos corrected, discussion improved, to appear in Phys. Rev.

Positivity domains for pairs of triples of spin observables

Positivity restrains the allowed domains for pairs or triples of spin observables in polarised reactions. Various domain shapes in ${1\over2}+{1\over2}\to{1\over2}+{1\over2}$ reactions are displayed. Some methods to determine these domains are mentioned and a new one based on the anticommutation between two observables is presented.Comment: Talk given by Xavier Artru at "DSPIN-07", XII Workshop on High-Energy Spin Physics, Dubna, Sept. 3-7, 2007, to appear in the Proceeding

Graph Laplacians and Stabilization of Vehicle Formations

Control of vehicle formations has emerged as a topic of significant interest to the controls community. In this paper, we merge tools from graph theory and control theory to derive stability criteria for formation stabilization. The interconnection between vehicles (i.e., which vehicles are sensed by other vehicles) is modeled as a graph, and the eigenvalues of the Laplacian matrix of the graph are used in stating a Nyquist-like stability criterion for vehicle formations. The location of the Laplacian eigenvalues can be correlated to the graph structure, and therefore used to identify desirable and undesirable formation interconnection topologies

Comments on "Observation of Long-Range, Near-Side Angular Correlations in Proton-Proton Collisions at the LHC" by the CMS collaboration(arXiv:1009.4122v1 [hep-ex])"

It is the purpose of this note to point out that the CMS observation is in line with previous observations in particle physics at large transverse momenta and/or high multiplicities at lower energies, which were interpreted as possible evidence for quark-gluon plasma (QGP), and to suggest other features of the QGP observed in A+A collisions such as radial flow and jet quenching, which should be investigated in p-p collisions in order to provide further evidence for QGP production

Spiritual Well-Being, Self-Esteem and Intimacy Among Couples Using Natural Family Planning

Making decisions about achieving and avoiding pregnancy and the methods used to attain those ends are some of the most central decisions during a couple\u27s reproductive life. Health professionals (especially professional nurses) are often consulted to aid couples in their reproductive decisions and provide couples with choices of reproductive control. Information provided on family planning choices, however, is often limited and usually involves issues of effectiveness to avoid pregnancy, convenience, health risks, and life-style preferences.1,2 Little information is provided on how family planning methods compare on psychological, spiritual, and social well-being variables. One method of family planning that needs further study on these variables is Natural Family Planning (NFP). The purpose of this study was to describe how NFP influenced the intimacy, self-esteem, and the spiritual well-being of couples who used NFP to avoid pregnancy for at least a one year period. A secondary purpose was to describe and compare the intimacy, self-esteem and spiritual well-being of couples who stopped using NFP and who have used contraception for at least a year

Evaluation of Pit-trap Transects With Varied Trap Spacing in a Northern Michigan Forest

The study compared effects of four distances between traps (range 0.5-4.0 m) on arthropod captures. Twelve traps were aligned in each of four transects, and 20 samples. trap were obtained during summer and fall in a northern Michigan deciduous forest. Catches proved to be unaffected by trap spacing. Rather, they reflected local within-site differences in abundance of dominant species

Reassessment of the evidence for postcranial skeletal pneumaticity in Triassic archosaurs, and the early evolution of the avian respiratory system.

Uniquely among extant vertebrates, birds possess complex respiratory systems characterised by the combination of small, rigid lungs, extensive pulmonary air sacs that possess diverticula that invade (pneumatise) the postcranial skeleton, unidirectional ventilation of the lungs, and efficient crosscurrent gas exchange. Crocodilians, the only other living archosaurs, also possess unidirectional lung ventilation, but lack true air sacs and postcranial skeletal pneumaticity (PSP). PSP can be used to infer the presence of avian-like pulmonary air sacs in several extinct archosaur clades (non-avian theropod dinosaurs, sauropod dinosaurs and pterosaurs). However, the evolution of respiratory systems in other archosaurs, especially in the lineage leading to crocodilians, is poorly documented. Here, we use µCT-scanning to investigate the vertebral anatomy of Triassic archosaur taxa, from both the avian and crocodilian lineages as well as non-archosaurian diapsid outgroups. Our results confirm previous suggestions that unambiguous evidence of PSP (presence of internal pneumatic cavities linked to the exterior by foramina) is found only in bird-line (ornithodiran) archosaurs. We propose that pulmonary air sacs were present in the common ancestor of Ornithodira and may have been subsequently lost or reduced in some members of the clade (notably in ornithischian dinosaurs). The development of these avian-like respiratory features might have been linked to inferred increases in activity levels among ornithodirans. By contrast, no crocodile-line archosaur (pseudosuchian) exhibits evidence for unambiguous PSP, but many of these taxa possess the complex array of vertebral laminae and fossae that always accompany the presence of air sacs in ornithodirans. These laminae and fossae are likely homologous with those in ornithodirans, which suggests the need for further investigation of the hypothesis that a reduced, or non-invasive, system of pulmonary air sacs may be have been present in these taxa (and secondarily lost in extant crocodilians) and was potentially primitive for Archosauria as a whole