35,386 research outputs found
Effective field theory description of halo nuclei
Nuclear halos emerge as new degrees of freedom near the neutron and proton
driplines. They consist of a core and one or a few nucleons which spend most of
their time in the classically-forbidden region outside the range of the
interaction. Individual nucleons inside the core are thus unresolved in the
halo configuration, and the low-energy effective interactions are short-range
forces between the core and the valence nucleons. Similar phenomena occur in
clusters of He atoms, cold atomic gases near a Feshbach resonance, and some
exotic hadrons. In these weakly-bound quantum systems universal scaling laws
for s-wave binding emerge that are independent of the details of the
interaction. Effective field theory (EFT) exposes these correlations and
permits the calculation of non-universal corrections to them due to
short-distance effects, as well as the extension of these ideas to systems
involving the Coulomb interaction and/or binding in higher angular-momentum
channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo
nuclei, has been used to compute the properties of single-neutron, two-neutron,
and single-proton halos of s-wave and p-wave type. This review summarizes these
results for halo binding energies, radii, Coulomb dissociation, and radiative
capture, as well as the connection of these properties to scattering
parameters, thereby elucidating the universal correlations between all these
observables. We also discuss how Halo EFT's encoding of the long-distance
physics of halo nuclei can be used to check and extend ab initio calculations
that include detailed modeling of their short-distance dynamics.Comment: 104 pages, 31 figures. Topical Review for Journal of Physics G. v2
incorporates several modifications, particularly to the Introduction, in
response to referee reports. It also corrects multiple typos in the original
submission. It corresponds to the published versio
Period halving of Persistent Currents in Mesoscopic Mobius ladders
We investigate the period halving of persistent currents(PCs) of
non-interacting electrons in isolated mesoscopic M\"{o}bius ladders without
disorder, pierced by Aharonov-Bhom flux. The mechanisms of the period halving
effect depend on the parity of the number of electrons as well as on the
interchain hopping. Although the data of PCs in mesoscopic systems are
sample-specific, some simple rules are found in the canonical ensemble average,
such as all the odd harmonics of the PCs disappear, and the signals of even
harmonics are non-negative. {PACS number(s): 73.23.Ra, 73.23.-b, 68.65.-k}Comment: 6 Pages with 3 EPS figure
Spin-lattice order in frustrated ZnCr2O4
Using synchrotron X-rays and neutron diffraction we disentangle spin-lattice
order in highly frustrated ZnCrO where magnetic chromium ions occupy
the vertices of regular tetrahedra. Upon cooling below 12.5 K the quandary of
anti-aligning spins surrounding the triangular faces of tetrahedra is resolved
by establishing weak interactions on each triangle through an intricate lattice
distortion. The resulting spin order is however, not simply a N\'{e}el state on
strong bonds. A complex co-planar spin structure indicates that antisymmetric
and/or further neighbor exchange interactions also play a role as ZnCrO
resolves conflicting magnetic interactions
Local‐Regional Similarity in Drylands Increases During Multiyear Wet and Dry Periods and in Response to Extreme Events
Climate change is predicted to impact ecosystems through altered precipitation (PPT) regimes. In the Chihuahuan Desert, multiyear wet and dry periods and extreme PPT pulses are the most influential climatic events for vegetation. Vegetation responses are most frequently studied locally, and regional responses are often unclear. We present an approach to quantify correlation of PPT and vegetation responses (as Normalized Difference Vegetation Index [NDVI]) at the Jornada ARS‐LTER site (JRN; 550 km2 area) and the surrounding dryland region (from 0 to 500 km distance; 400,000 km2 study area) as a way to understand regional similarity to locally observed patterns. We focused on fluctuating wet and dry years, multiyear wet or dry periods of 3–4 yr, and multiyear wet periods that contained one or more extreme high PPT pulses or extreme low rainfall. In all but extreme high PPT years, JRN PPT was highly correlated... (See article for full abstract)
A Temperature Analysis of High-power AlGaN/GaN HEMTs
Galliumnitride has become a strategic superior material for space, defense
and civil applications, primarily for power amplification at RF and mm-wave
frequencies. For AlGaN/GaN high electron mobility transistors (HEMT), an
outstanding performance combined together with low cost and high flexibility
can be obtained using a System-in-a-Package (SIP) approach. Since thermal
management is extremely important for these high power applications, a hybrid
integration of the HEMT onto an AlN carrier substrate is proposed. In this
study we investigate the temperature performance for AlGaN/GaN HEMTs integrated
onto AlN using flip-chip mounting. Therefore, we use thermal simulations in
combination with experimental results using micro-Raman spectroscopy and
electrical dc-analysis.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Motion of a Solitonic Vortex in the BEC-BCS Crossover
We observe a long-lived solitary wave in a superfluid Fermi gas of Li
atoms after phase-imprinting. Tomographic imaging reveals the excitation to be
a solitonic vortex, oriented transverse to the long axis of the cigar-shaped
atom cloud. The precessional motion of the vortex is directly observed, and its
period is measured as a function of the chemical potential in the BEC-BCS
crossover. The long period and the correspondingly large ratio of the inertial
to the bare mass of the vortex are in good agreement with estimates based on
superfluid hydrodynamics that we derive here using the known equation of state
in the BEC-BCS crossover
Ground state of spin-1 Bose-Einstein condensates with spin-orbit coupling in a Zeeman field
We systematically investigate the weakly trapped spin-1 Bose-Einstein
condensates with spin-orbit coupling in an external Zeeman field. We find that
the mean-field ground state favors either a magnetized standing wave phase or
plane wave phase when the strength of Zeeman field is below a critical value
related to the strength of spin-orbit coupling. Zeeman field can induce the
phase transition between standing wave and plane wave phases, and we determine
the phase boundary analytically and numerically. The magnetization of these two
phases responds to the external magnetic field in a very unique manner, the
linear Zeeman effect magnetizes the standing wave phase along the direction of
the magnetic field, but the quadratic one demagnetizes the plane wave phase.
When the strength of Zeeman field surpasses the critical value, the system is
completely polarized to a ferromagnetic state or polar state with zero
momentum
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