214,319 research outputs found
Vortex Structures Formed by the Interference of Sliced Condensates
We study the formation of vortices, vortex necklaces and vortex ring
structures as a result of the interference of higher-dimensional Bose-Einstein
condensates (BECs). This study is motivated by earlier theoretical results
pertaining to the formation of dark solitons by interfering quasi
one-dimensional BECs, as well as recent experiments demonstrating the formation
of vortices by interfering higher-dimensional BECs. Here, we demonstrate the
genericity of the relevant scenario, but also highlight a number of additional
possibilities emerging in higher-dimensional settings. A relevant example is,
e.g., the formation of a "cage" of vortex rings surrounding the
three-dimensional bulk of the condensed atoms. The effects of the relative
phases of the different BEC fragments and the role of damping due to coupling
with the thermal cloud are also discussed. Our predictions should be
immediately tractable in currently existing experimental BEC setups.Comment: 8 pages, 6 figures (low res). To appear in Phys. Rev. A. Full
resolution preprint available at:
http://www-rohan.sdsu.edu/~rcarrete/publications
Anomalous strength of membranes with elastic ridges
We report on a simulational study of the compression and buckling of elastic
ridges formed by joining the boundary of a flat sheet to itself. Such ridges
store energy anomalously: their resting energy scales as the linear size of the
sheet to the 1/3 power. We find that the energy required to buckle such a ridge
is a fixed multiple of the resting energy. Thus thin sheets with elastic ridges
such as crumpled sheets are qualitatively stronger than smoothly bent sheets.Comment: 4 pages, REVTEX, 3 figure
Study of Innovative Built-up Cold-formed Beams
In the present work innovative built-up cold-formed steel beams are presented. These are obtained by combining the pressing and cold-rolling forming techniques of steel sheets, along with the use of suitable connecting systems. Firstly, the beam shape features and the possible application fields, as well as the research project devoted to the assessment of their structural behaviour, are discussed. Then, experimental results concerning the characterization of both sheet material properties and connecting system performances are shown. In particular, the study of the sheet material is carried out by using an appropriate methodology of analysis, aiming at evaluating both mechanical and geometrical imperfections arising from the whole manufacturing process. At the same time, the mechanical behaviour of different connecting systems is investigated by means of several lap shear tests. The obtained results have provided useful design information and will be subsequently used to calibrate the numerical and theoretical models, addressing the prediction of the structural response of these innovative cold-formed beams
Enhancing the superconducting transition temperature of BaSi2 by structural tuning
We present a joint experimental and theoretical study of the superconducting
phase of the layered binary silicide BaSi2. Compared with the layered AlB2
structure of graphite or diboride-like superconductors, in the hexagonal
structure of binary silicides the sp3 arrangement of silicon atoms leads to
corrugated sheets. Through a high-pressure synthesis procedure we are able to
modify the buckling of these sheets, obtaining the enhancement of the
superconducting transition temperature from 4 K to 8.7 K when the silicon
planes flatten out. By performing ab-initio calculations based on density
functional theory we explain how the electronic and phononic properties of the
system are strongly affected by changes in the buckling. This mechanism is
likely present in other intercalated layered superconductors, opening the way
to the tuning of superconductivity through the control of internal structural
parameters.Comment: Submitte
Superlattice formed by quantum-dot sheets: density of states and IR absorption
Low-energy continuous states of electron in heterosrtucture with periodically
placed quantum-dot sheets are studied theoretically. The Green's function of
electron is governed by the Dyson equation with the self-energy function which
is determined the boundary conditions at quantum-dot sheets with weak damping
in low-energy region. The parameters of superlattice formed by quantum-dot
sheets are determined using of the short-range model of quantum dot. The
density of states and spectral dependencies of the anisotropic absorption
coefficient under mid-IR transitions from doped quantum dots into miniband
states of superlattice strongly depend on dot concentration and on period of
sheets. These dependencies can be used for characterization of the multi-layer
structure and they determine parameters of different optoelectronic devices
exploiting vertical transport of carriers through quantum-dot sheets.Comment: 7 pages and 5 figure
Optical elements formed by compressed gases: Analysis and potential applications
Spherical, cylindrical, and conical shock waves are optically analogous to gas lenses. The geometrical optics of these shock configurations are analyzed as they pertain to flow visualization instruments, particularly the rainbow schlieren apparatus and single-pass interferometers. It is proposed that a lens or mirror formed by gas compressed between plastic sheets has potential as a fluid visualization test object; as the objective mirror in a very large space-based telescope, communication antenna, or energy collector; as the objective mirror in inexpensive commercial telescopes; and as a component in fluid visualization apparatuses
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