2,177,907 research outputs found
Unstable Galaxy Models
The dynamics of collisionless galaxy can be described by the Vlasov-Poisson
system. By the Jean's theorem, all the spherically symmetric steady galaxy
models are given by a distribution of {\Phi}(E,L), where E is the particle
energy and L the angular momentum. In a celebrated Doremus-Feix-Baumann
Theorem, the galaxy model {\Phi}(E,L) is stable if the distribution {\Phi} is
monotonically decreasing with respect to the particle energy E. On the other
hand, the stability of {\Phi}(E,L) remains largely open otherwise. Based on a
recent abstract instability criterion of Guo-Lin, we constuct examples of
unstable galaxy models of f(E,L) and f(E) in which f fails to be monotone in E
Signatures of Stripe Phases in Hole Doped
We study nickelate-centered and oxygen-centered stripe phases in doped
LaNiO materials. We use an inhomogeneous Hartree-Fock and
random-phase approximation approach including both electron-electron and
electron-lattice(e-l) coupling for a layer of LaNiO. We find that
whether the ground state after commensurate hole doping comprises Ni-centered
or O-centered charge-localized stripes depends sensitively on the e-l
interaction. With increasing e-l interaction strength, a continuous transition
from an O-centered stripe phase to a Ni-centered one is found. Various low- and
high-energy signatures of these two kinds of stripe phases are predicted, which
can clearly distinguish them. These signatures reflect the strongly correlated
spin-charge-lattice features in the vicinity of Ni-centered or O-centered
stripe domains. The importance of e-l interaction for recent experiments on
stripe phases is discussed.Comment: 11 pages, 12 figures, to appear in Phys.Rev.B(July 1,1998
Saraband: The Memoirs of E L Mascall
Reviewed Book: Mascall, Eric Lionel. Saraband: The Memoirs of E L Mascall. Leominster, England: Gracewing, 1992
Theoretical Expectations For High Mass Photon Pairs in L+ L- Gamma Gamma Events at LEP/SLC
Recently, the L3 collaboration has reported the observation of four events in
the reactions e+ e- --> L+ L- + (2 Photons), L = e, mu, tau, with the invariant
photon pair mass near 60 GeV in a data sample collected in the L3 detector
corresponding to 950,000 produced Z0's. More recently, more data from the other
LEP collaborations have become available. In this paper, we use the Monte Carlo
genrator YFS3 and our recent exact results on e+ e- --> L+ L- + (2 Photons) to
assess the QED expectations for such L3-type high mass photon pair events in e+
e- --> L+ L- + (n Photons) near the Z0 resonance.Comment: 9 pages (LaTeX + 6 uu-encoded figures), UTHEP-93-1002 (version with
corrected preprint number
Global weak solution and blow-up criterion of the general Ericksen-Leslie system for nematic liquid crystal flows
In this paper we investigate the three dimensional general Ericksen-Leslie
(E--L) system with Ginzburg-Landau type approximation modeling nematic liquid
crystal flows. First, by overcoming the difficulties from lack of maximum
principle for the director equation and high order nonlinearities for the
stress tensor, we prove existence of global-in-time weak solutions under
physically meaningful boundary conditions and suitable assumptions on the
Leslie coefficients, which ensures that the total energy of the E--L system is
dissipated. Moreover, for the E--L system with periodic boundary conditions, we
prove the local well-posedness of classical solutions under the so-called
Parodi's relation and establish a blow-up criterion in terms of the temporal
integral of both the maximum norm of the curl of the velocity field and the
maximum norm of the gradient of the liquid crystal director field
Sustainable restorative environments : consideration of social, ecological and economic sustainability provides more ecosystem services
Den hĂ€r studien belyser hur man kan planera för vĂ€xtval i restorativa miljöer (platser som frĂ€mjar Ă„terhĂ€mtning) pĂ„ ett sĂ€tt som bidrar till social, ekologisk samt ekonomisk hĂ„llbarhet. En fallstudie i HĂ€lsotrĂ€dgĂ„rden i Kristianstad och Fyra Ă
rstiders park i Sölvesborg med restorativa kvaliteter samt en litteraturstudie har gjorts och erfarenheterna frÄn detta utmynnar i en checklista, med nÄgra av de aspekter och frÄgestÀllningar man kan ha i Ätanke dÄ man planerar för restorativa miljöer. Förutom FN:s hÄllbarhetsmÄl Àr de kulturella, stödjande, försörjande samt reglerande ekosystemtjÀnsterna nÄgot som Àr viktigt dÄ man planerar planteringar för framtiden. Studien tydliggör att med hÄllbara val i en naturlik plantering med trÀd, buskar och perenner, kan bÄde restorativa kvaliteter och ekosystemtjÀnster nÄs. I urbana ekosystem kan en artrik biotop skapas som ger bÀttre stadsklimat och en attraktivare miljö.This study illuminates how to plan for plant selection in restorative environments (places that promote recovery) in a way that contributes to social, ecological and economic sustainability. A case study in The Health Garden in Kristianstad and Four Seasons Park in Sölvesborg with restorative qualities and a literature study have been carried out, resulting in a checklist with some of the aspects and problems to keep in mind when planning for restorative environments. In addition to the UN's sustainability goals, the cultural, supporting, supplying and regulating ecosystem services are important when planning plantations for the future. The result of the study shows that using sustainable choices in a natural planting with trees, shrubs and perennials, both restorative qualities and ecosystem services can be reached. Species rich biotopes can be created in urban ecosystems that provides a better urban climate and a more attractive environment
Nature and digitalisation challenging the traditional playground
Playing outdoors in nature with peers has been attributed most importance for childrenâs healthy development but is increasingly marginalized because of the attractiveness of screen-based play. Careful merging of digital technology into outdoor play environments rich on nature elements could potentially help bridge digital play with more traditional play activities outdoors. A systematic comparison was made of outdoor play in more or less green settings, with and without digital installations or traditional play equipment. The separate and combined role of digital artefacts, play equipment and natural elements, were investigated, with particular focus on the effects of merging digital materials into nature. A group of children aged 6â8 were involved in a field study in a three-week period playing in a traditional playground, a forest and in a forest with digitally enhanced play artefacts. ChildrenÂŽs play behavior was evaluated using a behavioral tracking method, a questionnaire and a contextual interview with the children, and a physical activity measure, in combination with inventories including maps to document the design, and the ecological and physical status of the settings. The study documents differences in childrenâs play behavior across the three settings. It differs most between the digital forest setting and the forest setting regarding the play categories imaginative play, physical play and rule play and the digital forest setting stands out when it comes to expressive play. It is discussed how particular attributes in the physical environment influence the overall play flow and the interactive effects of natural material and digital material. Ecologically, the forest and the forest with digitally enhanced artefacts were more diverse than the traditional playground, but the natural material present was important for play in all settings
Nature of the glassy phase of RNA secondary structure
We characterize the low temperature phase of a simple model for RNA secondary
structures by determining the typical energy scale E(l) of excitations
involving l bases. At zero temperature, we find a scaling law E(l) \sim
l^\theta with \theta \approx 0.23, and this same scaling holds at low enough
temperatures. Above a critical temperature, there is a different phase
characterized by a relatively flat free energy landscape resembling that of a
homopolymer with a scaling exponent \theta=1. These results strengthen the
evidence in favour of the existence of a glass phase at low temperatures.Comment: 7 pages, 1 figur
- âŠ