313 research outputs found
Dense Stellar Matter with Strange Quark Matter Driven by Kaon Condensation
The core of neutron-star matter is supposed to be at a much higher density
than the normal nuclear matter density for which various possibilities have
been suggested such as, for example, meson or hyperon condensation and/or
deconfined quark or color-superconducting matter. In this work, we explore the
implication on hadron physics of a dense compact object that has three
"phases", nuclear matter at the outer layer, kaon condensed nuclear matter in
the middle and strange quark matter at the core. Using a drastically simplified
but not unreasonable model, we develop the scenario where the different phases
are smoothly connected with the kaon condensed matter playing a role of
"doorway" to a quark core, the equation of state (EoS) of which with parameters
restricted within the range allowed by nature could be made compatible with the
mass vs. radius constraint given by the 1.97-solar mass object PSR J1614-2230
recently observed.Comment: 18 pages, 18 figure
Triple layered compact star with strange quark matter
We explore the possibility of three phases in the core of neutron star in a
form of triple layers. From the center, strange quark matter, kaon condensed
nuclear matter and nuclear matter form a triple layer. We discuss how the phase
of strange quark matter is smoothly connected to kaon condensed nuclear matter
phase. We also demonstrate that the compact star with triple layered structure
can be a model compatible with the 1.97-solar-mass object PSR J1614-2230
recently observed.Comment: 8 pages, 2 figures, to appear in the Proceedings of the Symposium on
Cosmology and Particle Astrophysics (CosPA2011), October 28-31, 2011,
Beijing, Chin
Signatures of unconventional pairing in near-vortex electronic structure of LiFeAs
A major question in Fe-based superconductors remains the structure of the
pairing, in particular whether it is of unconventional nature. The electronic
structure near vortices can serve as a platform for phase-sensitive
measurements to answer this question. By solving Bogoliubov-de Gennes equations
for LiFeAs, we calculate the energy-dependent local electronic structure near a
vortex for different nodeless gap-structure possibilities. At low energies, the
local density of states (LDOS) around a vortex is determined by the
normal-state electronic structure. However, at energies closer to the gap
value, the LDOS can distinguish an anisotropic from a conventional isotropic
s-wave gap. We show within our self-consistent calculation that in addition,
the local gap profile differs between a conventional and an unconventional
pairing. We explain this through admixing of a secondary order parameter within
Ginzburg-Landau theory. In-field scanning tunneling spectroscopy near vortices
can therefore be used as a real-space probe of the gap structure
Improving Usability of Mobile Applications Through Speculation and Distraction Minimization
We live in a world where mobile computing systems are increasingly integrated with our day-to-day activities. People use mobile applications virtually everywhere they go, executing them on mobile devices such as smartphones, tablets, and smart watches. People commonly interact with mobile applications while performing other primary tasks such as walking and driving (e.g., using turn-by-turn directions while driving a car). Unfortunately, as an application becomes more mobile, it can experience resource scarcity (e.g., poor wireless connectivity) that is atypical in a traditional desktop environment. When critical resources become scarce, the usability of the mobile application deteriorates significantly.
In this dissertation, I create system support that enables users to interact smoothly with mobile applications when wireless network connectivity is poor and when the userās attention is limited. First, I show that speculative execution can mitigate user-perceived delays in application responsiveness caused by high-latency wireless network connectivity. I focus on cloud-based gaming, because the smooth usability of such application is highly dependent on low latency. User studies have shown that players are sensitive to as little as 60 ms of additional latency and are aggravated at latencies in excess of 100ms. For cloud-based gaming, which relies on powerful servers to generate high-graphics quality gaming content, a slow network frustrates the user, who must wait a long time to see input actions reflected in the game. I show that by predicting the userās future gaming inputs and by performing visual misprediction compensation at the client, cloud-based gaming can maintain good usability even with 120 ms of network latency.
Next, I show that the usability of mobile applications in an attention-limited environment (i.e., driving a vehicle) can be improved by automatically checking whether interfaces meet best-practice guidelines and by adding attention-aware scheduling of application interactions. When a user is driving, any application that demands too much attention is an unsafe distraction. I first develop a model checker that systematically explores all reachable screens for an application and determines whether the application conforms to best-practice vehicular UI guidelines. I find that even well- known vehicular applications (e.g., Google Maps and TomTom) can often demand too much of the driverās attention. Next, I consider the case where applications run in the background and initiate interactions with the driver. I show that by quantifying the driverās available attention and the attention demand of an interaction, real-time scheduling can be used to prevent attention overload in varying driving conditions.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136989/1/kyminlee_1.pd
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