1,870 research outputs found
An Estimate of the Vibrational Frequencies of Spherical Virus Particles
The possible normal modes of vibration of a nearly spherical virus particle
are discussed. Two simple models for the particle are treated, a liquid drop
model and an elastic sphere model. Some estimates for the lowest vibrational
frequency are given for each model. It is concluded that this frequency is
likely to be of the order of a few GHz for particles with a radius of the order
of 50 nm.Comment: 6 pages, 1 figur
Runtime Optimizations for Tree-Based Machine Learning Models
Tree-based models have proven to be an effective solution for web ranking as well as other machine learning problems in diverse domains. This paper focuses on optimizing the runtime performance of applying such models to make predictions, specifically using gradient-boosted regression trees for learning to rank. Although exceedingly simple conceptually, most implementations of tree-based models do not efficiently utilize modern superscalar processors. By laying out data structures in memory in a more cache-conscious fashion, removing branches from the execution flow using a technique called predication, and micro-batching predictions using a technique called vectorization, we are able to better exploit modern processor architectures. Experiments on synthetic data and on three standard learning-to-rank datasets show that our approach is significantly faster than standard implementations
Bound states of neutral particles in external electric fields
Neutral fermions of spin with magnetic moment can interact with
electromagnetic fields through nonminimal coupling. The Dirac--Pauli equation
for such a fermion coupled to a spherically symmetric or central electric field
can be reduced to two simultaneous ordinary differential equations by
separation of variables in spherical coordinates. For a wide variety of central
electric fields, bound-state solutions of critical energy values can be found
analytically. The degeneracy of these energy levels turns out to be numerably
infinite. This reveals the possibility of condensing infinitely many fermions
into a single energy level. For radially constant and radially linear electric
fields, the system of ordinary differential equations can be completely solved,
and all bound-state solutions are obtained in closed forms. The radially
constant field supports scattering solutions as well. For radially linear
fields, more energy levels (in addition to the critical one) are infinitely
degenerate. The simultaneous presence of central magnetic and electric fields
is discussed.Comment: REVTeX, 14 pages, no figur
Cumulative Citation Recommendation: A Feature-aware Comparisons of Approaches
In this work, we conduct a feature-aware comparison of approaches to Cumulative Citation Recommendation (CCR), a task that aims to filter and rank a stream of documents according to their relevance to entities in a knowledge base. We conducted experiments starting with a big feature set, identified a powerful subset and applied it to comparing classification and learning to rank algorithms. With few set of powerful features, we achieve better performance than the state-of-the-art. Surprisingly, our findings challenge the previously known preference of learning-to-rank over classification: in our study, the CCR performance of the classification approach outperforms that using learning-to-rank. This indicates that comparing two approaches is problematic due to the interplay between the approaches themselves and the feature sets one chooses to use
Column Stores as an IR Prototyping Tool
. We make the suggestion that instead of implementing custom
index structures and query evaluation algorithms, IR researchers should
simply store document representations in a column-oriented relational
database and write ranking models using SQL. For rapid prototyping, this
is particularly advantageous since researchers can explore new ranking
functions and features by simply issuing SQL queries, without needing to
write imperative code. We demonstrate the feasibility of this approach
by an implementation of conjunctive BM25 using MonetDB on a part of
the ClueWeb12 collection
The anomaly of the oxygen bond-bending mode at 320 cm and the additional absorption peak in the c-axis infrared conductivity of underdoped YBaCuO single crystals revisited by ellipsometricmeasurements
We have performed ellipsometric measurements of the far-infrared c-axis
dielectric response of underdoped YBaCuO single
crystals. Here we report a detailed analysis of the temperature-dependent
renormalization of the oxygen bending phonon mode at 320 cm and the
formation of the additional absorption peak around 400-500 cm. For a
strongly underdoped YBaCuO crystal with T=52 K we
find that, in agreement with previous reports based on conventional reflection
measurements, the gradual onset of both features occurs well above T at
T*150 K. Contrary to some of these reports, however, our data establish
that the phonon anomaly and the formation of the additional peak exhibit very
pronounced and steep changes right at T. For a less underdoped
YBaCuO crystal with T=80 K, the onset temperature of
the phonon anomaly almost coincides with T. Also in contrast to some
previous reports, we find for both crystals that a sizeable fraction of the
spectral weight of the additional absorption peak cannot be accounted for by
the spectral-weight loss of the phonon modes but instead arises from a
redistribution of the electronic continuum. Our ellipsometric data are
consistent with a model where the bilayer cuprate compounds are treated as a
superlattice of intra- and inter-bilayer Josephson-junctions
Therapeutic capsule endoscopy: Opportunities and challenges
10.1260/2040-2295.2.4.459Journal of Healthcare Engineering24459-47
AdS spacetimes from wrapped M5 branes
We derive a complete geometrical characterisation of a large class of
, and supersymmetric spacetimes in eleven-dimensional
supergravity using G-structures. These are obtained as special cases of a class
of supersymmetric , and
geometries, naturally associated to M5-branes wrapping calibrated cycles in
manifolds with , SU(3) or SU(2) holonomy. Specifically, the latter class
is defined by requiring that the Killing spinors satisfy the same set of
projection conditions as for wrapped probe branes, and that there is no
electric flux. We show how the R-symmetries of the dual field theories appear
as isometries of the general AdS geometries. We also show how known solutions
previously constructed in gauged supergravity satisfy our more general
G-structure conditions, demonstrate that our conditions for half-BPS
geometries are precisely those of Lin, Lunin and Maldacena, and construct some
new singular solutions.Comment: 1+56 pages, LaTeX; v2, references added; v3, minor corrections, final
version to appear in JHE
Semileptonic decays of , , and
Stimulated by recent observations of the excited bottom-strange mesons
and , we calculate the semileptonic decays , which is relevant for the exploration of the
potential of searching these semileptonic decays in experiment.Comment: 11 pages, 3 figures, 9 tables. More discussion added, some
descriptions changed. The version to appear in EPJ
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