5,203 research outputs found
Approximation for Maximum Surjective Constraint Satisfaction Problems
Maximum surjective constraint satisfaction problems (Max-Sur-CSPs) are
computational problems where we are given a set of variables denoting values
from a finite domain B and a set of constraints on the variables. A solution to
such a problem is a surjective mapping from the set of variables to B such that
the number of satisfied constraints is maximized. We study the approximation
performance that can be acccchieved by algorithms for these problems, mainly by
investigating their relation with Max-CSPs (which are the corresponding
problems without the surjectivity requirement). Our work gives a complexity
dichotomy for Max-Sur-CSP(B) between PTAS and APX-complete, under the
assumption that there is a complexity dichotomy for Max-CSP(B) between PO and
APX-complete, which has already been proved on the Boolean domain and 3-element
domains
From high-scale leptogenesis to low-scale one-loop neutrino mass generation
We show that a high-scale leptogenesis can be consistent with a low-scale
one-loop neutrino mass generation. Our models are based on the SU(3)_c\times
SU(2)_L\times U(1)_Y\times U(1)_{B-L} gauge groups. Except a complex singlet
scalar for the U(1)_{B-L} symmetry breaking, the other new scalars and fermions
(one scalar doublet, two or more real scalar singlets/triplets and three
right-handed neutrinos) are odd under an unbroken Z_2 discrete symmetry. The
real scalar decays can produce an asymmetry stored in the new scalar doublet
which subsequently decays into the standard model lepton doublets and the
right-handed neutrinos. The lepton asymmetry in the standard model leptons then
can be partially converted to a baryon asymmetry by the sphaleron processes. By
integrating out the heavy scalar singlets/triplets, we can realize an effective
theory to radiatively generate the small neutrino masses at the TeV scale.
Furthermore, the lightest right-handed neutrino can serve as a dark matter
candidate.Comment: 8 pages, 4 figure
El camino del 'desarrollo armonioso' de China
Las dos cuestiones esenciales que se plantean en este programa, tanto el crecimiento de la economía como la armonía interna en la sociedad necesaria para conseguirlo, se han convertido en el foco del futuro desarrollo social chino. La aparición de la 'armonía' como condición previa por primera vez en el diseño de camino de este país socialista atraído la atención de los estudiosos
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Redevelopment of Urban Village in Shenzhen
Urban Villages are a specific phenomenon raised in modern China due to the high-speed economic development and urbanization in recent three decades. And there are social, economic, cultural and architectural transformations happened in these villages during these years. They appear on both the outskirts and the downtown segments of major cities, and surrounded by skyscrapers, transportation infrastructures, and other modern urban constructions. They are commonly inhabited by the poor and transient.
Most of Urban Villages are heavily populated, overdeveloped, and lack of basic infrastructure. Some villages\u27 building density is higher than 70%. They are composed of overcrowded multi-story buildings from three to five (or more) floors, also with narrow alleys, which are difficult for vehicles to pass through. Inside these villages, it is dark and damp year round and the lights have to be kept on during daytime. However, they are also among the liveliest areas in some cities and are notable for affording economic opportunity for newcomers to the city.
However, Urban Villages are rejected by the governor and face demolition–redevelopment programs in order to replace them with formal urban neighborhoods. But the demolition-redevelopment approach would be devastating not only for the rural migrants, but also for the city’s economy which is largely based on labor-intensive sectors.
In my study, I take Gangsha Village, a typical urban village in Shenzhen City, as a study case, to explore an appropriate reformation approach that combines urban design and architectural strategy to solve social, economic and cultural problems in Urban Village. To provide them a better living condition, and make the village better serves the city
Quasi-degenerate dark photon and dark matter
We introduce an dark sector without any fermions and then
realize a non-abelian kinetic mixing between the dark gauge fields
and the standard model gauge fields. While one of
the dark gauge bosons becomes a dark photon, the others can keep stable to form
a dark matter particle. The nearly degenerate masses of dark photon and dark
matter could be tested if the dark photon and the dark matter are both observed
in the future.Comment: 5 page
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