27,059 research outputs found
Top-N Recommendation on Graphs
Recommender systems play an increasingly important role in online
applications to help users find what they need or prefer. Collaborative
filtering algorithms that generate predictions by analyzing the user-item
rating matrix perform poorly when the matrix is sparse. To alleviate this
problem, this paper proposes a simple recommendation algorithm that fully
exploits the similarity information among users and items and intrinsic
structural information of the user-item matrix. The proposed method constructs
a new representation which preserves affinity and structure information in the
user-item rating matrix and then performs recommendation task. To capture
proximity information about users and items, two graphs are constructed.
Manifold learning idea is used to constrain the new representation to be smooth
on these graphs, so as to enforce users and item proximities. Our model is
formulated as a convex optimization problem, for which we need to solve the
well-known Sylvester equation only. We carry out extensive empirical
evaluations on six benchmark datasets to show the effectiveness of this
approach.Comment: CIKM 201
Multipole Gravitational Lensing and High-order Perturbations on the Quadrupole Lens
An arbitrary surface mass density of gravitational lens can be decomposed
into multipole components. We simulate the ray-tracing for the multipolar mass
distribution of generalized SIS (Singular Isothermal Sphere) model, based on
the deflection angles which are analytically calculated. The magnification
patterns in the source plane are then derived from inverse shooting technique.
As have been found, the caustics of odd mode lenses are composed of two
overlapping layers for some lens models. When a point source traverses such
kind of overlapping caustics, the image numbers change by \pm 4, rather than
\pm 2. There are two kinds of images for the caustics. One is the critical
curve and the other is the transition locus. It is found that the image number
of the fold is exactly the average value of image numbers on two sides of the
fold, while the image number of the cusp is equal to the smaller one. We also
focus on the magnification patterns of the quadrupole (m = 2) lenses under the
perturbations of m = 3, 4 and 5 mode components, and found that one, two, and
three butterfly or swallowtail singularities can be produced respectively. With
the increasing intensity of the high-order perturbations, the singularities
grow up to bring sixfold image regions. If these perturbations are large enough
to let two or three of the butterflies or swallowtails contact, eightfold or
tenfold image regions can be produced as well. The possible astronomical
applications are discussed.Comment: 24 pages, 6 figure
Origins of the Isospin Violation of Dark Matter Interactions
Light dark matter (DM) with a large DM-nucleon spin-independent cross section
and furthermore proper isospin violation (ISV) may provide
a way to understand the confusing DM direct detection results. Combing with the
stringent astrophysical and collider constraints, we systematically investigate
the origin of ISV first via general operator analyses and further via
specifying three kinds of (single) mediators: A light from chiral
, an approximate spectator Higgs doublet (It can explain the
anomaly simultaneously) and color triplets. In addition, although from an
exotic mixing with generating , we can combine it with
the conventional Higgs to achieve proper ISV. As a concrete example, we propose
the model where the charged light sneutrino is the inelastic
DM, which dominantly annihilates to light dark states such as with sub-GeV
mass. This model can address the recent GoGeNT annual modulation consistent
with other DM direct detection results and free of exclusions.Comment: References added and English greatly improve
Thermodynamics of Ion Separation by Electrosorption
We present a simple, top-down approach for the calculation of minimum energy
consumption of electrosorptive ion separation using variational form of the
(Gibbs) free energy. We focus and expand on the case of electrostatic
capacitive deionization (CDI), and the theoretical framework is independent of
details of the double-layer charge distribution and is applicable to any
thermodynamically consistent model, such as the Gouy-Chapman-Stern (GCS) and
modified Donnan (mD) models. We demonstrate that, under certain assumptions,
the minimum required electric work energy is indeed equivalent to the free
energy of separation. Using the theory, we define the thermodynamic efficiency
of CDI. We explore the thermodynamic efficiency of current experimental CDI
systems and show that these are currently very low, less than 1% for most
existing systems. We applied this knowledge and constructed and operated a CDI
cell to show that judicious selection of the materials, geometry, and process
parameters can be used to achieve a 9% thermodynamic efficiency (4.6 kT energy
per removed ion). This relatively high value is, to our knowledge, by far the
highest thermodynamic efficiency ever demonstrated for CDI. We hypothesize that
efficiency can be further improved by further reduction of CDI cell series
resistances and optimization of operational parameters
CP violation in neutrino oscillation and leptogenesis
We study the correlation between CP violation in neutrino oscillations and
leptogenesis in the framework with two heavy Majorana neutrinos and three light
neutrinos. Among three unremovable CP phases, a heavy Majorana phase
contributes to leptogenesis. We show how the heavy Majorana phase contributes
to Jarlskog determinant as well as neutrinoless double decay by
identifying a low energy CP violating phase which signals the CP violating
phase for leptogenesis. For some specific cases of the Dirac mass term of
neutrinos, a direct relation between lepton number asymmetry and is
obtained. For the most general case of the framework, we study the effect on coming from the phases which are not related to leptogenesis, and also show
how the correlation can be lost in the presence of those phases.Comment: 4 pages and 3 figure
Identification of nonlinearity in conductivity equation via Dirichlet-to-Neumann map
We prove that the linear term and quadratic nonlinear term entering a
nonlinear elliptic equation of divergence type can be uniquely identified by
the Dirichlet to Neuman map. The unique identifiability is proved using the
complex geometrical optics solutions and singular solutions
Supersymmetry in Slow Motion
We construct new theories of electroweak symmetry breaking that employ a
combination of supersymmetry and discrete symmetries to stabilize the weak
scale up to and beyond the energies probed by the LHC. These models exhibit
conventional supersymmetric spectra but the fermion-sfermion-gaugino vertices
are absent. This closes many conventional decay channels, thereby allowing
several superpartners to be stable on collider time scales. This opens the door
to the possibility of directly observing R-hadrons and three flavors of
sleptons inside the LHC detectors.Comment: A reference added. The discussion on the Higgs sector expanded. The
version accepted for publication in JHE
A metawindow with optimised acoustic and ventilation performance
Crucial factors in window performance, such as natural ventilation and noise control, are generally conceived separately, forcing users to choose one over the other. To solve this dualism, this study aimed to develop an acoustic metamaterial (AMM) ergonomic window design to allow noise control without dependence on the natural ventilation duration and vice versa. First, the finite element method (FEM) was used to investigate the noise control performance of the acoustic metawindow (AMW) unit, followed by anechoic chamber testing, which also served as the validation of the FEM models. Furthermore, FEM analysis was used to optimise the acoustic performance and assess the ventilation potential. The numerical and experimental results exhibited an overall mean sound reduction of 15 dB within a bandwidth of 380 to 5000 Hz. A good agreement between the measured and numerical results was obtained, with a mean variation of 30%. Therefore, the AMW unit optimised acoustic performance, resulting in a higher noise reduction, especially from 50 to 500 Hz. Finally, most of the AMW unit configurations are suitable for natural ventilation, and a dynamic tuned ventilation capacity can be achieved for particular ranges by adjusting the window’s ventilation opening. The proposed designs have potential applications in building acoustics and engineering where natural ventilation and noise mitigation are required to meet regulations simultaneously
One-Loop QCD Mass Effects in the Production of Polarized Bottom and Top Quarks
The analytic expressions for the production cross sections of polarized
bottom and top quarks in annihilation are explicitly derived at the
one-loop order of strong interactions. Chirality-violating mass effects will
reduce the longitudinal spin polarization for the light quark pairs by an
amount of , when one properly considers the massless limit for the final
quarks. Numerical estimates of longitudinal spin polarization effects in the
processes and are presented.Comment: 17 p. (5 figs available upon request), LaTeX, MZ-TH/93-30, RAL/93-81,
FTUV/93-4
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