2,126 research outputs found
Tree-chromatic number is not equal to path-chromatic number
For a graph and a tree-decomposition of , the
chromatic number of is the maximum of , taken
over all bags . The tree-chromatic number of is the
minimum chromatic number of all tree-decompositions of .
The path-chromatic number of is defined analogously. In this paper, we
introduce an operation that always increases the path-chromatic number of a
graph. As an easy corollary of our construction, we obtain an infinite family
of graphs whose path-chromatic number and tree-chromatic number are different.
This settles a question of Seymour. Our results also imply that the
path-chromatic numbers of the Mycielski graphs are unbounded.Comment: 11 pages, 0 figure
Multi-layer Unmanned Aerial Vehicle Networks: Modeling and Performance Analysis
Since various types of unmanned aerial vehicles (UAVs) with different
hardware capabilities are introduced, we establish a foundation for the
multi-layer aerial network (MAN). First, the MAN is modeled as K layer ANs, and
each layer has UAVs with different densities, floating altitudes, and
transmission power. To make the framework applicable for various scenarios in
MAN, we consider the transmitter- and the receiver-oriented node association
rules as well as the air-to-ground and air-to-air channel models, which form
line of sight links with a location-dependent probability. We then newly
analyze the association probability, the main link distance distribution,
successful transmission probability (STP), and area spectral efficiency (ASE)
of MAN. The upper bounds of the optimal densities that maximize STP and ASE are
also provided. Finally, in the numerical results, we show the optimal UAV
densities of an AN that maximize the ASE and the STP decrease with the altitude
of the network. We also show that when the total UAV density is fixed for two
layer AN, the use of single layer in higher(lower) altitude only for all UAVs
can achieve better performance for low(high) total density case, otherwise,
distributing UAVs in two layers, i.e., MAN, achieves better performance
Surface-electrode ion trap with integrated light source
An atomic ion is trapped at the tip of a single-mode optical fiber in a
cryogenic (8 K) surface-electrode ion trap. The fiber serves as an integrated
source of laser light, which drives the quadrupole qubit transition of
Sr. Through \emph{in situ} translation of the nodal point of the
trapping field, the Gaussian beam profile of the fiber output is imaged, and
the fiber-ion displacement, in units of the mode waist at the ion, is optimized
to within of the mode center despite an initial offset of
. Fiber-induced charging at W is observed to be
V/m at an ion height of m, with charging and discharging
time constants of s and s respectively. This work is of
importance to large-scale, ion-based quantum information processing, where
optics integration in surface-electrode designs may be a crucial enabling
technology.Comment: 4 pages, 4 figure
Cooling of photoexcited carriers in graphene by internal and substrate phonons
We investigate the energy relaxation of hot carriers produced by
photoexcitation of graphene through coupling to both intrinsic and remote
(substrate) surface polar phonons using the Boltzmann equation approach. We
find that the energy relaxation of hot photocarriers in graphene on commonly
used polar substrates, under most conditions, is dominated by remote surface
polar phonons. We also calculate key characteristics of the energy relaxation
process, such as the transient cooling time and steady state carrier
temperatures and photocarriers densities, which determine the thermoelectric
and photovoltaic photoresponse, respectively. Substrate engineering can be a
promising route to efficient optoelectronic devices driven by hot carrier
dynamics.Comment: related papers at http://tonylow.info
Understanding Contraflow Pop-Culture Tourism: The Case of Transnational Fandom of South Korean Pop-Culture and the “Hallyu” Tourism
Pop-culture tourism has continuously grown its market among those who are fanatic of pop-culture, and destination marketers have noticed pop-culture as an effective marketing tool to attract more visitors. Pop-culture has been dominant by the US, but interestingly, a recent phenomenon sees a contra-cultural flow. This paper explores contraflow pop-culture tourism and guides the reader to how to understand this new tourism niche. Reviewing the case of transnational fandom of South Korean pop-culture, so called “Korean Wave” or “Hallyu” and its impact on inbound tourism, this paper suggests digital mediation as a key driver of contraflow pop-culture and transnational fandom, pop-culture as a vehicle for change destination image, and pop-culture tourism as a driving force of creative economy
Cervial cancer screening among HIV-positive women in rural Cambodia: a pilot programme
Mexico AIDS Conference 200
A surface electrode point Paul trap
We present a model as well as experimental results for a surface electrode
radio-frequency Paul trap that has a circular electrode geometry well-suited
for trapping of single ions and two-dimensional planar ion crystals. The trap
design is compatible with microfabrication and offers a simple method by which
the height of the trapped ions above the surface may be changed \emph{in situ}.
We demonstrate trapping of single and few Sr+ ions over an ion height range of
200-1000 microns for several hours under Doppler laser cooling, and use these
to characterize the trap, finding good agreement with our model.Comment: 10 pages, 11 figures, 1 tabl
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