13,675 research outputs found
A Memory-Efficient Sketch Method for Estimating High Similarities in Streaming Sets
Estimating set similarity and detecting highly similar sets are fundamental
problems in areas such as databases, machine learning, and information
retrieval. MinHash is a well-known technique for approximating Jaccard
similarity of sets and has been successfully used for many applications such as
similarity search and large scale learning. Its two compressed versions, b-bit
MinHash and Odd Sketch, can significantly reduce the memory usage of the
original MinHash method, especially for estimating high similarities (i.e.,
similarities around 1). Although MinHash can be applied to static sets as well
as streaming sets, of which elements are given in a streaming fashion and
cardinality is unknown or even infinite, unfortunately, b-bit MinHash and Odd
Sketch fail to deal with streaming data. To solve this problem, we design a
memory efficient sketch method, MaxLogHash, to accurately estimate Jaccard
similarities in streaming sets. Compared to MinHash, our method uses smaller
sized registers (each register consists of less than 7 bits) to build a compact
sketch for each set. We also provide a simple yet accurate estimator for
inferring Jaccard similarity from MaxLogHash sketches. In addition, we derive
formulas for bounding the estimation error and determine the smallest necessary
memory usage (i.e., the number of registers used for a MaxLogHash sketch) for
the desired accuracy. We conduct experiments on a variety of datasets, and
experimental results show that our method MaxLogHash is about 5 times more
memory efficient than MinHash with the same accuracy and computational cost for
estimating high similarities
Dissipation and detonation of shock waves in lipid monolayers
Lipid interfaces not only compartmentalize but also connect different
reaction centers within a cell architecture. These interfaces have well defined
specific heats and compressibilities, hence energy can propagate along them
analogous to sound waves. Lipid monolayers prepared at the air-water interface
of a Langmuir trough present an excellent model system to study such
propagations. Here we propose that recent observations of two-dimensional shock
waves observed in lipid monolayers also provide the evidence for the detonation
of shock waves at such interfaces, i.e. chemical energy stored in the interface
can be absorbed by a propagating shock front reinforcing it in the process. To
this end, we apply the classical theory in shock waves and detonation in the
context of a lipid interface and its thermodynamic state. Based on these
insights it is claimed that the observed self-sustaining waves in lipid
monolayers represent a detonation like phenomena that utilizes the latent heat
of phase transition of the lipids. However, the general nature of these
equations allows that other possible sources of chemical energy can contribute
to the propagating shock wave in a similar manner. Consequently, the
understanding is applied to the nerve pulse propagation that is believed to
represent a similar phenomenon, to obtain a qualitative understanding of the
pressure and temperature dependence of amplitude and threshold for action
potentials. While we mainly discuss the case of a stable detonation, the
problem of initiation of detonation at interfaces and corresponding heat
exchange is briefly discussed, which also suggests a role for thunder like
phenomena in pulse initiation.Comment: 6 Figure
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