1,186 research outputs found
Gene duplication in an African cichlid adaptive radiation
Background Gene duplication is a source of evolutionary innovation and can contribute to the divergence of lineages; however, the relative importance of this process remains to be determined. The explosive divergence of the African cichlid adaptive radiations provides both a model for studying the general role of gene duplication in the divergence of lineages and also an exciting foray into the identification of genomic features that underlie the dramatic phenotypic and ecological diversification in this particular lineage. We present the first genome-wide study of gene duplication in African cichlid fishes, identifying gene duplicates in three species belonging to the Lake Malawi adaptive radiation (Metriaclima estherae, Protomelas similis, Rhamphochromis “chilingali”) and one closely related species from a non-radiated riverine lineage (Astatotilapia tweddlei). Results Using Astatotilapia burtoni as reference, microarray comparative genomic hybridization analysis of 5689 genes reveals 134 duplicated genes among the four cichlid species tested. Between 51 and 55 genes were identified as duplicated in each of the three species from the Lake Malawi radiation, representing a 38%–49% increase in number of duplicated genes relative to the non-radiated lineage (37 genes). Duplicated genes include several that are involved in immune response, ATP metabolism and detoxification. Conclusions These results contribute to our understanding of the abundance and type of gene duplicates present in cichlid fish lineages. The duplicated genes identified in this study provide candidates for the analysis of functional relevance with regard to phenotype and divergence. Comparative sequence analysis of gene duplicates can address the role of positive selection and adaptive evolution by gene duplication, while further study across the phylogenetic range of cichlid radiations (and more generally in other adaptive radiations) will determine whether the patterns of gene duplication seen in this study consistently accompany rapid radiation
The formative years of relativity : the history and meaning of Einstein's Princeton Lectures
TABLE OF CONTENTS: Foreword Diana Kormos Buchwald ix Preface xiii I Preliminaries 1 1 Introduction 3 2 Einstein's First Trip to America 11 3 Structure and Contents of The Meaning of Relativity 17 II The Emerging World of General Relativity 23 1 Physics and Geometry 25 2 The Principles of General Relativity 34 3 The First Solutions and the Challenge of Their Interpretation 46 4 Einstein and the Astronomers 52 5 The Genesis of Relativistic Cosmology 69 6 The Controversy over Gravitational Waves 94 7 Philosophical Debates on General Relativity 106 8 The Quest for a Unified Field Theory 122 9 Early Monographs on Relativity 140 10 Beyond the Formative Years 155 III Einstein's Book with the Appendixes 159 1 Space and Time in Pre-relativity Physics 161 2 The Theory of Special Relativity 184 3 The General Theory of Relativity 215 4 The General Theory of Relativity (Continued) 239 5 Appendix for the Second Edition: On the "Cosmologic Problem" 269 6 Appendix II (PUP 4th edition, 1953): Generalization of Gravitation Theory 293 7 Appendix II (PUP 5th edition, 1956): Relativistic Theory of the Non-symmetric Field 326 IV The Popular Lectures 361 1 Introductory Remarks 363 2 Einstein's Lectures 366 V Biographical Notes on the Protagonists of the Formative Years 387 Index 40
A scanning microcavity for in-situ control of single-molecule emission
We report on the fabrication and characterization of a scannable Fabry-Perot
microcavity, consisting of a curved micromirror at the end of an optical fiber
and a planar distributed Bragg reflector. Furthermore, we demonstrate the
coupling of single organic molecules embedded in a thin film to well-defined
resonator modes. We discuss the choice of cavity parameters that will allow
sufficiently high Purcell factors for enhancing the zero-phonon transition
between the vibrational ground levels of the electronic excited and ground
states.Comment: 8 page
Navigation/traffic control satellite mission study. Volume 3 - System concepts
Satellite network for air traffic control, solar flare warning, and collision avoidanc
A planar dielectric antenna for directional single-photon emission and near-unity collection efficiency
Single emitters have been considered as sources of single photons in various
contexts such as cryptography, quantum computation, spectroscopy, and
metrology. The success of these applications will crucially rely on the
efficient directional emission of photons into well-defined modes. To
accomplish a high efficiency, researchers have investigated microcavities at
cryogenic temperatures, photonic nanowires, and near-field coupling to metallic
nano-antennas. However, despite an impressive progress, the existing
realizations substantially fall short of unity collection efficiency. Here we
report on a theoretical and experimental study of a dielectric planar antenna,
which uses a layered structure for tailoring the angular emission of a single
oriented molecule. We demonstrate a collection efficiency of 96% using a
microscope objective at room temperature and obtain record detection rates of
about 50 MHz. Our scheme is wavelength-insensitive and can be readily extended
to other solid-state emitters such as color centers and semiconductor quantum
dots
Phase Transition between the Cholesteric and Twist Grain Boundary C Phases
The upper critical temperature Tc2 for the phase transition between the
Cholesteric phase (N*) and the Twist Grain Boundary C phase with the layer
inclination tilted to the pitch axis (TGBct) in thermotropic liquid crystals is
determined by the mean field Chen-Lubensky approach. We show that the N*-TGBct
phase transition is split in two with the appearance of either the TGBA or the
TGB2q phase in a narrow temperature interval below Tc2. The latter phase is
novel in being superposed from two degenerate
TGBct phases with different (left and right) layers inclinations to the pitch
axis.Comment: Phys. Rev. E, to be publ; 24 pages, RevTeX + 3 ps figure
Photonic crystal optical waveguides for on-chip Bose-Einstein condensates
We propose an on-chip optical waveguide for Bose-Einstein condensates based
on the evanescent light fields created by surface states of a photonic crystal.
It is shown that the modal properties of these surface states can be tailored
to confine the condensate at distances from the chip surface significantly
longer that those that can be reached by using conventional index-contrast
guidance. We numerically demonstrate that by index-guiding the surface states
through two parallel waveguides, the atomic cloud can be confined in a
two-dimensional trap at about 1m above the structure using a power of
0.1mW.Comment: 5 pages, 4 figure
Boundary Effects in Chiral Polymer Hexatics
Boundary effects in liquid-crystalline phases can be large due to long-ranged
orientational correlations. We show that the chiral hexatic phase can be locked
into an apparent three-dimensional N+6 phase via such effects. Simple numerical
estimates suggest that the recently discovered "polymer hexatic" may actually
be this locked phase.Comment: 4 pages, RevTex, 3 included eps figure
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