195,814 research outputs found
Recent progress in random metric theory and its applications to conditional risk measures
The purpose of this paper is to give a selective survey on recent progress in
random metric theory and its applications to conditional risk measures. This
paper includes eight sections. Section 1 is a longer introduction, which gives
a brief introduction to random metric theory, risk measures and conditional
risk measures. Section 2 gives the central framework in random metric theory,
topological structures, important examples, the notions of a random conjugate
space and the Hahn-Banach theorems for random linear functionals. Section 3
gives several important representation theorems for random conjugate spaces.
Section 4 gives characterizations for a complete random normed module to be
random reflexive. Section 5 gives hyperplane separation theorems currently
available in random locally convex modules. Section 6 gives the theory of
random duality with respect to the locally convex topology and in
particular a characterization for a locally convex module to be
prebarreled. Section 7 gives some basic results on convex
analysis together with some applications to conditional risk measures. Finally,
Section 8 is devoted to extensions of conditional convex risk measures, which
shows that every representable type of conditional convex risk
measure and every continuous type of convex conditional risk measure
() can be extended to an type
of lower semicontinuous conditional convex risk measure and an
type of continuous
conditional convex risk measure (), respectively.Comment: 37 page
Nuclear spin relaxation rates in two-leg spin ladders
Using the transfer-matrix DMRG method, we study the nuclear spin relaxation
rate 1/T_1 in the two-leg s=1/2 ladder as function of the inter-chain
(J_{\perp}) and intra-chain (J_{|}) couplings. In particular, we separate the
q_y=0 and \pi contributions and show that the later contribute significantly to
the copper relaxation rate ^{63}(1/T_1) in the experimentally relevant coupling
and temperature range. We compare our results to both theoretical predictions
and experimental measures on ladder materials.Comment: Few modifications from the previous version 4 pages, 5 figures,
accepted for publication in PR
Topological String Defect Formation During the Chiral Phase Transition
We extend and generalize the seminal work of Brandenberger, Huang and Zhang
on the formation of strings during chiral phase transitions(berger) and discuss
the formation of abelian and non-abelian topological strings during such
transitions in the early Universe and in the high energy heavy-ion collisions.
Chiral symmetry as well as deconfinement are restored in the core of these
defects. Formation of a dense network of string defects is likely to play an
important role in the dynamics following the chiral phase transition. We
speculate that such a network can give rise to non-azimuthal distribution of
transverse energy in heavy-ion collisions.Comment: 10 pages, 4 figures, minor correction
Neural Collaborative Filtering
In recent years, deep neural networks have yielded immense success on speech
recognition, computer vision and natural language processing. However, the
exploration of deep neural networks on recommender systems has received
relatively less scrutiny. In this work, we strive to develop techniques based
on neural networks to tackle the key problem in recommendation -- collaborative
filtering -- on the basis of implicit feedback. Although some recent work has
employed deep learning for recommendation, they primarily used it to model
auxiliary information, such as textual descriptions of items and acoustic
features of musics. When it comes to model the key factor in collaborative
filtering -- the interaction between user and item features, they still
resorted to matrix factorization and applied an inner product on the latent
features of users and items. By replacing the inner product with a neural
architecture that can learn an arbitrary function from data, we present a
general framework named NCF, short for Neural network-based Collaborative
Filtering. NCF is generic and can express and generalize matrix factorization
under its framework. To supercharge NCF modelling with non-linearities, we
propose to leverage a multi-layer perceptron to learn the user-item interaction
function. Extensive experiments on two real-world datasets show significant
improvements of our proposed NCF framework over the state-of-the-art methods.
Empirical evidence shows that using deeper layers of neural networks offers
better recommendation performance.Comment: 10 pages, 7 figure
Two-Level Systems in Evaporated Amorphous Silicon
In -beam evaporated amorphous silicon (-Si), the densities of two-level
systems (TLS), and , determined from specific heat
and internal friction measurements, respectively, have been shown to
vary by over three orders of magnitude. Here we show that and
are proportional to each other with a constant of
proportionality that is consistent with the measurement time dependence
proposed by Black and Halperin and does not require the introduction of
additional anomalous TLS. However, and depend strongly
on the atomic density of the film () which depends on both film
thickness and growth temperature suggesting that the -Si structure is
heterogeneous with nanovoids or other lower density regions forming in a dense
amorphous network. A review of literature data shows that this atomic density
dependence is not unique to -Si. These findings suggest that TLS are not
intrinsic to an amorphous network but require a heterogeneous structure to
form
Relativistic cosmological perturbation scheme on a general background: scalar perturbations for irrotational dust
In standard perturbation approaches and N-body simulations, inhomogeneities
are described to evolve on a predefined background cosmology, commonly taken as
the homogeneous-isotropic solutions of Einstein's field equations
(Friedmann-Lema\^itre-Robertson-Walker (FLRW) cosmologies). In order to make
physical sense, this background cosmology must provide a reasonable description
of the effective, i.e. spatially averaged, evolution of structure
inhomogeneities also in the nonlinear regime. Guided by the insights that (i)
the average over an inhomogeneous distribution of matter and geometry is in
general not given by a homogeneous solution of general relativity, and that
(ii) the class of FLRW cosmologies is not only locally but also globally
gravitationally unstable in relevant cases, we here develop a perturbation
approach that describes the evolution of inhomogeneities on a general
background being defined by the spatially averaged evolution equations. This
physical background interacts with the formation of structures. We derive and
discuss the resulting perturbation scheme for the matter model `irrotational
dust' in the Lagrangian picture, restricting our attention to scalar
perturbations.Comment: 18 pages. Matches published version in CQ
Experimental observation of an enhanced anisotropic magnetoresistance in non-local configuration
We compare non-local magnetoresistance measurements in multi-terminal Ni
nanostructures with corresponding local experiments. In both configurations,
the measured voltages show the characteristic features of anisotropic
magnetoresistance (AMR). However, the magnitude of the non-local AMR signal is
up to one order of magnitude larger than its local counterpart. Moreover, the
non-local AMR increases with increasing degree of non-locality, i.e., with the
separation between the region of the main current flow and the voltage
measurement region. All experimental observations can be consistently modeled
in terms of current spreading in a non-isotropic conductor. Our results show
that current spreading can significantly enhance the magnetoresistance signal
in non-local experiments
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