11,754 research outputs found
Sparsely Aggregated Convolutional Networks
We explore a key architectural aspect of deep convolutional neural networks:
the pattern of internal skip connections used to aggregate outputs of earlier
layers for consumption by deeper layers. Such aggregation is critical to
facilitate training of very deep networks in an end-to-end manner. This is a
primary reason for the widespread adoption of residual networks, which
aggregate outputs via cumulative summation. While subsequent works investigate
alternative aggregation operations (e.g. concatenation), we focus on an
orthogonal question: which outputs to aggregate at a particular point in the
network. We propose a new internal connection structure which aggregates only a
sparse set of previous outputs at any given depth. Our experiments demonstrate
this simple design change offers superior performance with fewer parameters and
lower computational requirements. Moreover, we show that sparse aggregation
allows networks to scale more robustly to 1000+ layers, thereby opening future
avenues for training long-running visual processes.Comment: Accepted to ECCV 201
Robust pricing--hedging duality for American options in discrete time financial markets
We investigate pricing-hedging duality for American options in discrete time
financial models where some assets are traded dynamically and others, e.g. a
family of European options, only statically. In the first part of the paper we
consider an abstract setting, which includes the classical case with a fixed
reference probability measure as well as the robust framework with a
non-dominated family of probability measures. Our first insight is that by
considering a (universal) enlargement of the space, we can see American options
as European options and recover the pricing-hedging duality, which may fail in
the original formulation. This may be seen as a weak formulation of the
original problem. Our second insight is that lack of duality is caused by the
lack of dynamic consistency and hence a different enlargement with dynamic
consistency is sufficient to recover duality: it is enough to consider
(fictitious) extensions of the market in which all the assets are traded
dynamically. In the second part of the paper we study two important examples of
robust framework: the setup of Bouchard and Nutz (2015) and the martingale
optimal transport setup of Beiglb\"ock et al. (2013), and show that our general
results apply in both cases and allow us to obtain pricing-hedging duality for
American options.Comment: 29 page
Robustness of Random Graphs Based on Natural Connectivity
Recently, it has been proposed that the natural connectivity can be used to
efficiently characterise the robustness of complex networks. Natural
connectivity quantifies the redundancy of alternative routes in a network by
evaluating the weighted number of closed walks of all lengths and can be
regarded as the average eigenvalue obtained from the graph spectrum. In this
article, we explore the natural connectivity of random graphs both analytically
and numerically and show that it increases linearly with the average degree. By
comparing with regular ring lattices and random regular graphs, we show that
random graphs are more robust than random regular graphs; however, the
relationship between random graphs and regular ring lattices depends on the
average degree and graph size. We derive the critical graph size as a function
of the average degree, which can be predicted by our analytical results. When
the graph size is less than the critical value, random graphs are more robust
than regular ring lattices, whereas regular ring lattices are more robust than
random graphs when the graph size is greater than the critical value.Comment: 12 pages, 4 figure
Merits and Qualms of Work Fluctuations in Classical Fluctuation Theorems
Work is one of the most basic notion in statistical mechanics, with work
fluctuation theorems being one central topic in nanoscale thermodynamics. With
Hamiltonian chaos commonly thought to provide a foundation for classical
statistical mechanics, here we present general salient results regarding how
(classical) Hamiltonian chaos generically impacts on nonequilibrium work
fluctuations. For isolated chaotic systems prepared with a microcanonical
distribution, work fluctuations are minimized and vanish altogether in
adiabatic work protocols. For isolated chaotic systems prepared at an initial
canonical distribution at inverse temperature , work fluctuations
depicted by the variance of are also minimized by adiabatic work
protocols. This general result indicates that if the variance of
diverges for an adiabatic work protocol, then it diverges for all nonadiabatic
work protocols sharing the same initial and final Hamiltonians. How such
divergence explicitly impacts on the efficiency of using the Jarzynski's
equality to simulate free energy differences is studied in a Sinai model. Our
general insights shall boost studies in nanoscale thermodynamics and are of
fundamental importance in designing useful work protocols.Comment: 11 pages, 5 figures, close to published versio
Assessment of natural ventilation potential for residential buildings across different climate zones in Australia
In this study, the natural ventilation potential of residential buildings was numerically investigated based on a typical single-story house in the three most populous climate zones in Australia. Simulations using the commercial simulation software TRNSYS (Transient System Simulation Tool) were performed for all seasons in three representative cities, i.e., Darwin for the hot humid summer and warm winter zone, Sydney for the mild temperate zone, and Melbourne for the cool temperate zone. A natural ventilation control strategy was generated by the rule-based decision-tree method based on the local climates. Natural ventilation hour (NVH) and satisfied natural ventilation hour (SNVH) were employed to evaluate the potential of natural ventilation in each city considering local climate and local indoor thermal comfort requirements, respectively. The numerical results revealed that natural ventilation potential was related to the local climate. The greatest natural ventilation potential for the case study building was observed in Darwin with an annual 4141 SNVH out of 4728 NVH, while the least natural ventilation potential was found in the Melbourne case. Moreover, summer and transition seasons (spring and autumn) were found to be the optimal periods to sustain indoor thermal comfort by utilising natural ventilation in Sydney and Melbourne. By contrast, natural ventilation was found applicable over the whole year in Darwin. In addition, the indoor operative temperature results demonstrated that indoor thermal comfort can be maintained only by utilising natural ventilation for all cases during the whole year, except for the non-natural ventilation periods in summer in Darwin and winter in Melbourne. These findings could improve the understanding of natural ventilation potential in different climates, and are beneficial for the climate-conscious design of residential buildings in Australia
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