18,827 research outputs found
Distributions of Upper PAPR and Lower PAPR of OFDM Signals in Visible Light Communications
Orthogonal frequency-division multiplexing (OFDM) in visible light
communications (VLC) inherits the disadvantage of high peak-to-average power
ratio (PAPR) from OFDM in radio frequency (RF) communications. The upper peak
power and lower peak power of real-valued VLC-OFDM signals are both limited by
the dynamic constraints of light emitting diodes (LEDs). The efficiency and
transmitted electrical power are directly related with the upper PAPR (UPAPR)
and lower PAPR (LPAPR) of VLC-OFDM. In this paper, we will derive the
complementary cumulative distribution function (CCDF) of UPAPR and LPAPR, and
investigate the joint distribution of UPAPR and LPAPR.Comment: acceptted by IEEE ICASSP 2014. arXiv admin note: text overlap with
arXiv:1304.019
Enhanced heat transport by turbulent two-phase Rayleigh-B\'enard convection
We report measurements of turbulent heat-transport in samples of ethane
(CH) heated from below while the applied temperature difference straddled the liquid-vapor co-existance curve . When the sample
top temperature decreased below , droplet condensation occurred
and the latent heat of vaporization provided an additional heat-transport
mechanism.The effective conductivity increased linearly with
decreasing , and reached a maximum value that was an
order of magnitude larger than the single-phase . As
approached the critical pressure, increased dramatically even
though vanished. We attribute this phenomenon to an enhanced
droplet-nucleation rate as the critical point is approached.Comment: 4 gages, 6 figure
Evaluation of structural analysis methods for life prediction
The utility of advanced constitutive models and structural analysis methods are evaluated for predicting the cyclic life of an air-cooled turbine blade for a gas turbine aircraft engine. Structural analysis methods of various levels of sophistication were exercised to obtain the cyclic stress-strain response at the critical airfoil location. Calculated strain ranges and mean stresses from the stress-strain cycles were used to predict crack initiation lives by using the total strain version of the strain range partitioning life prediction method. The major results are given and discussed
Magnetic Catalysis in AdS4
We study the formation of fermion condensates in Anti de Sitter space. In
particular, we describe a novel version of magnetic catalysis that arises for
fermions in asymptotically AdS4 geometries which cap off in the infra-red with
a hard wall. We show that the presence of a magnetic field induces a fermion
condensate in the bulk that spontaneously breaks CP symmetry. From the
perspective of the dual boundary theory, this corresponds to a strongly coupled
version of magnetic catalysis in d=2+1.Comment: 22 pages, 4 figures. v2: References added, factors of 2 corrected,
extra comments added in appendix. v3: extra comments about fermion modes in a
hard wall background. v4: A final factor of
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Morphology and reactivity of size-selected titanium oxide nanoclusters on Au(111).
The morphology and reactivity of mass-selected titania clusters, Ti3O6 and Ti3O5, deposited onto Au(111) were studied by scanning tunneling microscopy and temperature programmed desorption. Despite differing by only one oxygen atom, the stoichiometric Ti3O6 and the sub-stoichiometric ("reduced") Ti3O5 clusters exhibit very different structures and preferred binding sites. The Ti3O6 clusters bind at step edges and form small assemblies (2-4 clusters) on Au terraces, while the "reduced" Ti3O5 clusters form much larger fractal-like assemblies that can extend across step boundaries. Annealing the Ti3O5,6/Au(111) systems to higher temperatures causes changes in the size-distributions of cluster assemblies, but does not lead to the formation of TiOx nanoislands for temperatures ≤700 K. Reactivity studies show that the reduced Ti3O5 cluster has higher activity than Ti3O6 for 2-propanol dehydration, although both clusters exhibit substantial activity for dehydrogenation to acetone. Calculations using DFT+U suggest that the differences in aggregate morphology and reactivity are associated with the number of undercoordinated Ti3c sites in the supported clusters
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