32,540 research outputs found
Pinning quantum phase transition of photons in a hollow-core fiber
We show that a pinning quantum phase transition for photons could be observed
in a hollow-core one-dimensional fiber loaded with a cold atomic gas. Utilizing
the strong light confinement in the fiber, a range of different strongly
correlated polaritonic and photonic states, corresponding to both strong and
weak interactions can be created and probed. The key ingredient is the creation
of a tunable effective lattice potential acting on the interacting polaritonic
gas which is possible by slightly modulating the atomic density. We analyze the
relevant phase diagram corresponding to the realizable Bose-Hubbard (weak) and
sine-Gordon (strong) interacting regimes and conclude by describing the
measurement process. The latter consists of mapping the stationary excitations
to propagating light pulses whose correlations can be efficiently probed once
they exit the fiber using available optical technologiesComment: 4 pages, 4 figures. Comments welcome
An collider based on proton-driven plasma wakefield acceleration
Recent simulations have shown that a high-energy proton bunch can excite
strong plasma wakefields and accelerate a bunch of electrons to the energy
frontier in a single stage of acceleration. This scheme could lead to a future
collider using the LHC for the proton beam and a compact electron
accelerator of length 170 m, producing electrons of energy up to 100 GeV. The
parameters of such a collider are discussed as well as conceptual layouts
within the CERN accelerator complex. The physics of plasma wakefield
acceleration will also be introduced, with the AWAKE experiment, a proof of
principle demonstration of proton-driven plasma wakefield acceleration, briefly
reviewed, as well as the physics possibilities of such an collider.Comment: 6 pages, 2 figures, to appear in the proceedings of the DIS 2014
Workshop, 28 April - 2 May, Warsaw, Polan
Collider design issues based on proton-driven plasma wakefield acceleration
Recent simulations have shown that a high-energy proton bunch can excite
strong plasma wakefields and accelerate a bunch of electrons to the energy
frontier in a single stage of acceleration. It therefore paves the way towards
a compact future collider design using the proton beams from existing
high-energy proton machines, e.g. Tevatron or the LHC. This paper addresses
some key issues in designing a compact electron-positron linear collider and an
electron-proton collider based on existing CERN accelerator infrastructure
Strong ExB shear flows in the pedestal region in H-mode plasma
We report the first experimental observation of stationary zonal flows in the
pedestal region of the H-mode plasma in the H-1 toroidal heliac. Strong peaks
in E_r shear mark the top and foot of the density pedestal. Strong m=n=0
low-frequency (f < 0.6 kHz) zonal flows are observed in regions of increased
E_r, suggesting substantial contribution of zonal flows to the spatial
modulation of E_r radial profiles. Radial localization of zonal flows is
correlated with a region of zero magnetic shear and low-order (7/5) rational
surfaces.Comment: 4 pages, 5 figure
Explosive events on sub-arcsecond scale in IRIS observations: a case study
We present study of a typical explosive event (EE) at sub-arcsecond scale
witnessed by strong non-Gaussian profiles with blue- and red-shifted emission
of up to 150 km/s seen in the transition-region Si IV 1402.8 \AA, and the
chromospheric Mg II k 2796.4 \AA\ and C II 1334.5 \AA\ observed by the
Interface Region Imaging Spectrograph at unprecedented spatial and spectral
resolution. For the first time a EE is found to be associated with very
small-scale (120 km wide) plasma ejection followed by retraction in the
chromosphere. These small-scale jets originate from a compact bright-point-like
structure of 1.5" size as seen in the IRIS 1330 \AA\ images. SDO/AIA and
SDO/HMI co-observations show that the EE lies in the footpoint of a complex
loop-like brightening system. The EE is detected in the higher temperature
channels of AIA 171 \AA, 193 \AA\ and 131 \AA\ suggesting that it reaches a
higher temperature of log T (K). Brightenings observed in the AIA
channels with durations 90--120 seconds are probably caused by the plasma
ejections seen in the chromosphere. The wings of the C II line behave in a
similar manner as the Si IV's indicating close formation temperatures, while
the Mg II k wings show additional Doppler-shifted emission. Magnetic
convergence or emergence followed by cancellation at a rate of
Mx s is associated with the EE region. The combined changes of the
locations and the flux of different magnetic patches suggest that magnetic
reconnection must have taken place. Our results challenge several theories put
forward in the past to explain non-Gaussian line profiles, i.e. EEs. Our case
study on its own, however, cannot reject these theories, thus further in-depth
studies on the phenomena producing EEs are required.Comment: 16 figures, accepted for publication in Ap
Toughening and asymmetry in peeling of heterogeneous adhesives
The effective adhesive properties of heterogeneous thin films are
characterized through a combined experimental and theoretical investigation. By
bridging scales, we show how variations of elastic or adhesive properties at
the microscale can significantly affect the effective peeling behavior of the
adhesive at the macroscale. Our study reveals three elementary mechanisms in
heterogeneous systems involving front propagation: (i) patterning the elastic
bending stiffness of the film produces fluctuations of the driving force
resulting in dramatically enhanced resistance to peeling; (ii) optimized
arrangements of pinning sites with large adhesion energy are shown to control
the effective system resistance, allowing the design of highly anisotropic and
asymmetric adhesives; (iii) heterogeneities of both types result in front
motion instabilities producing sudden energy releases that increase the overall
adhesion energy. These findings open potentially new avenues for the design of
thin films with improved adhesion properties, and motivate new investigation of
other phenomena involving front propagation.Comment: Physical Review Letters (2012)
Giant viscosity enhancement in a spin-polarized Fermi liquid
The viscosity is measured for a Fermi liquid, a dilute He-He mixture,
under extremely high magnetic field/temperature conditions ( T, mK). The spin splitting energy is substantially greater than
the Fermi energy ; as a consequence the polarization tends to unity
and s-wave quasiparticle scattering is suppressed for . Using a
novel composite vibrating-wire viscometer an enhancement of the viscosity is
observed by a factor of more than 500 over its low-field value. Good agreement
is found between the measured viscosity and theoretical predictions based upon
a -matrix formalism.Comment: 4 pages, 4 figure
Luminous Infrared Galaxies in the Local Universe
We study the morphology and star formation properties of 159 local luminous
infrared galaxy (LIRG) using multi-color images from Data Release 2 (DR2) of
the Sloan Digital Sky Survey (SDSS). The LIRGs are selected from a
cross-correlation analysis between the IRAS survey and SDSS. They are all
brighter than 15.9 mag in the r-band and below redshift ~ 0.1, and so can be
reliably classified morphologically. We find that the fractions of
interacting/merging and spiral galaxies are ~ 48% and ~ 40% respectively. Our
results complement and confirm the decline (increase) in the fraction of spiral
(interacting/merging) galaxies from z ~1 to z ~ 0.1, as found by Melbourne, Koo
& Le Floc'h (2005). About 75% of spiral galaxies in the local LIRGs are barred,
indicating that bars may play an important role in triggering star formation
rates > 20 M_{sun}/yr in the local universe. Compared with high redshift LIRGs,
local LIRGs have lower specific star formation rates, smaller cold gas
fractions and a narrower range of stellar masses. Local LIRGs appear to be
either merging galaxies forming intermediate mass ellipticals or spiral
galaxies undergoing high star formation activities regulated by bars.Comment: 22 pages, 5 figures, accepted for publication in ApJ, title changed,
typos corrected,major revisions following referee's comments,updated
reference
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