14,319 research outputs found

### The Resonance Overlap and Hill Stability Criteria Revisited

We review the orbital stability of the planar circular restricted three-body
problem, in the case of massless particles initially located between both
massive bodies. We present new estimates of the resonance overlap criterion and
the Hill stability limit, and compare their predictions with detailed dynamical
maps constructed with N-body simulations. We show that the boundary between
(Hill) stable and unstable orbits is not smooth but characterized by a rich
structure generated by the superposition of different mean-motion resonances
which does not allow for a simple global expression for stability.
We propose that, for a given perturbing mass $m_1$ and initial eccentricity
$e$, there are actually two critical values of the semimajor axis. All values
$a a_{\rm unstable}$ are
unstable in the Hill sense. The first limit is given by the Hill-stability
criterion and is a function of the eccentricity. The second limit is virtually
insensitive to the initial eccentricity, and closely resembles a new resonance
overlap condition (for circular orbits) developed in terms of the intersection
between first and second-order mean-motion resonances.Comment: 33 pages, 14 figures, accepte

### As diversity increases, people paradoxically perceive social groups as more similar

With globalization and immigration, societal contexts differ in sheer variety of resident social groups. Social diversity challenges individuals to think in new ways about new kinds of people and where their groups all stand, relative to each other. However, psychological science does not yet specify how human minds represent social diversity, in homogeneous or heterogenous contexts. Mental maps of the array of societyâ€™s groups should differ when individuals inhabit more and less diverse ecologies. Nonetheless, predictions disagree on how they should differ. Confirmation bias suggests more diversity means more stereotype dispersion: With increased exposure, perceiversâ€™ mental maps might differentiate more among groups, so their stereotypes would spread out (disperse). In contrast, individuation suggests more diversity means less stereotype dispersion, as perceivers experience within-group variety and between-group overlap. Worldwide, nationwide, individual, and longitudinal datasets (n = 12,011) revealed a diversity paradox: More diversity consistently meant less stereotype dispersion. Both contextual and perceived ethnic diversity correlate with decreased stereotype dispersion. Countries and US states with higher levels of ethnic diversity (e.g., South Africa and Hawaii, versus South Korea and Vermont), online individuals who perceive more ethnic diversity, and students who moved to more ethnically diverse colleges mentally represent ethnic groups as more similar to each other, on warmth and competence stereotypes. Homogeneity shows more-differentiated stereotypes; ironically, those with the least exposure have the most-distinct stereotypes. Diversity means less-differentiated stereotypes, as in the melting pot metaphor. Diversity and reduced dispersion also correlate positively with subjective wellbeing.info:eu-repo/semantics/publishedVersio

### Gauge transformations for higher-order lagrangians

Noether's symmetry transformations for higher-order lagrangians are studied.
A characterization of these transformations is presented, which is useful to
find gauge transformations for higher-order singular lagrangians. The case of
second-order lagrangians is studied in detail. Some examples that illustrate
our results are given; in particular, for the lagrangian of a relativistic
particle with curvature, lagrangian gauge transformations are obtained, though
there are no hamiltonian gauge generators for them.Comment: 22 pages, LaTe

### Atomistic simulations of self-trapped exciton formation in silicon nanostructures: The transition from quantum dots to nanowires

Using an approximate time-dependent density functional theory method, we
calculate the absorption and luminescence spectra for hydrogen passivated
silicon nanoscale structures with large aspect ratio. The effect of electron
confinement in axial and radial directions is systematically investigated.
Excited state relaxation leads to significant Stokes shifts for short nanorods
with lengths less than 2 nm, but has little effect on the luminescence
intensity. The formation of self-trapped excitons is likewise observed for
short nanostructures only; longer wires exhibit fully delocalized excitons with
neglible geometrical distortion at the excited state minimum.Comment: 10 pages, 4 figure

### Fast-ion redistribution and loss due to edge perturbations in the ASDEX Upgrade, DIII-D and KSTAR tokamaks

The impact of edge localized modes (ELMs) and externally applied resonant and non-resonant magnetic perturbations
(MPs) on fast-ion confinement/transport have been investigated in the ASDEX Upgrade (AUG), DIII-D and KSTAR
tokamaks. Two phases with respect to the ELM cycle can be clearly distinguished in ELM-induced fast-ion losses.
Inter-ELM losses are characterized by a coherent modulation of the plasma density around the separatrix while
intra-ELM losses appear as well-defined bursts. In high collisionality plasmas with mitigated ELMs, externally
applied MPs have little effect on kinetic profiles, including fast-ions, while a strong impact on kinetic profiles is
observed in low-collisionality, low q95 plasmas with resonant and non-resonant MPs. In low-collisionality H-mode
plasmas, the large fast-ion filaments observed during ELMs are replaced by a loss of fast-ions with a broad-band
frequency and an amplitude of up to an order of magnitude higher than the neutral beam injection prompt loss signal without MPs. A clear synergy in the overall fast-ion transport is observed between MPs and neoclassical tearing modes. Measured fast-ion losses are typically on banana orbits that explore the entire pedestal/scrape-off layer. The fast-ion response to externally applied MPs presented here may be of general interest for the community to better
understand the MP field penetration and overall plasma response.Marie Curie FP7 Integration PCIG11-GA2012-321455Ministerio de EconomÃa y Competitividad RYC-2011-09152, ENE2012-31087US Department of Energy DE-FC02-04ER54698, SC-G903402, DEFG02- 04ER54761, DE-AC02-09CH11466, DE-FG02- 08ER54984NRF Korea 2009-008201

### Medium-modified evolution of multiparticle production in jets in heavy-ion collisions

The energy evolution of medium-modified average multiplicities and
multiplicity fluctuations in quark and gluon jets produced in heavy-ion
collisions is investigated from a toy QCD-inspired model. In this model, we use
modified splitting functions accounting for medium-enhanced radiation of gluons
by a fast parton which propagates through the quark gluon plasma. The leading
contribution of the standard production of soft hadrons is found to be enhanced
by the factor $\sqrt{N_s}$ while next-to-leading order (NLO) corrections are
suppressed by $1/\sqrt{N_s}$, where the nuclear parameter $N_s>1$ accounts for
the induced-soft gluons in the hot medium. The role of next-to-next-to-leading
order corrections (NNLO) is studied and the large amount of medium-induced soft
gluons is found to drastically affect the convergence of the perturbative
series. Our results for such global observables are cross-checked and compared
with their limits in the vacuum and a new method for solving the second
multiplicity correlator evolution equations is proposed.Comment: 21 pages and 8 figures, typo corrections, references adde

### The Single-Particle Spectral Function of $^{16}{\rm O}$

The influence of short-range correlations on the $p$-wave single-particle
spectral function in $^{16}{\rm O}$ is studied as a function of energy. This
influence, which is represented by the admixture of high-momentum components,
is found to be small in the $p$-shell quasihole wave functions. It is therefore
unlikely that studies of quasihole momentum distributions using the $(e,e'p)$
reaction will reveal a significant contribution of high momentum components.
Instead, high-momentum components become increasingly more dominant at higher
excitation energy. The above observations are consistent with the energy
distribution of high-momentum components in nuclear matter.Comment: 5 pages, RevTeX, 3 figure

- â€¦