445 research outputs found
Unified model of ultracold molecular collisions
A scattering model is developed for ultracold molecular collisions, which
allows inelastic processes, chemical reactions, and complex formation to be
treated in a unified way. All these scattering processes and various
combinations of them are possible in ultracold molecular gases, and as such
this model will allow the rigorous parametrization of experimental results. In
addition we show how, once extracted, these parameters can be related to the
physical properties of the system, shedding light on fundamental aspects of
molecular collision dynamics.Comment: 16 Pages, 5 Figure
Electro-association of ultracold dipolar molecules into tetramer field-linked states
The presence of electric or microwave fields can modify the long-range forces
between ultracold dipolar molecules in such a way as to engineer weakly-bound
states of molecule pairs. These so-called field-linked states [Avdeenkov et
al., Phys. Rev. Lett. 90, 043006 (2003), Lassabli\`ere et al., Phys. Rev. Lett.
121, 163402 (2018)], in which the separation between the two bound molecules
can be orders of magnitude larger than the molecules themselves, have been
observed as resonances in scattering experiments [Chen et al., Nature 614, 59
(2023)]. Here, we propose to use them as tools for the assembly of weakly-bound
tetramer molecules, by means of ramping an electric field, the electric-field
analog of magneto-association in atoms. This ability would present new
possibilities for constructing ultracold polyatomic molecules
The Baryon Oscillation Spectroscopic Survey of SDSS-III
The Baryon Oscillation Spectroscopic Survey (BOSS) is designed to measure the
scale of baryon acoustic oscillations (BAO) in the clustering of matter over a
larger volume than the combined efforts of all previous spectroscopic surveys
of large scale structure. BOSS uses 1.5 million luminous galaxies as faint as
i=19.9 over 10,000 square degrees to measure BAO to redshifts z<0.7.
Observations of neutral hydrogen in the Lyman alpha forest in more than 150,000
quasar spectra (g<22) will constrain BAO over the redshift range 2.15<z<3.5.
Early results from BOSS include the first detection of the large-scale
three-dimensional clustering of the Lyman alpha forest and a strong detection
from the Data Release 9 data set of the BAO in the clustering of massive
galaxies at an effective redshift z = 0.57. We project that BOSS will yield
measurements of the angular diameter distance D_A to an accuracy of 1.0% at
redshifts z=0.3 and z=0.57 and measurements of H(z) to 1.8% and 1.7% at the
same redshifts. Forecasts for Lyman alpha forest constraints predict a
measurement of an overall dilation factor that scales the highly degenerate
D_A(z) and H^{-1}(z) parameters to an accuracy of 1.9% at z~2.5 when the survey
is complete. Here, we provide an overview of the selection of spectroscopic
targets, planning of observations, and analysis of data and data quality of
BOSS.Comment: 49 pages, 16 figures, accepted by A
The \u3cem\u3eChlamydomonas\u3c/em\u3e Genome Reveals the Evolution of Key Animal and Plant Functions
Chlamydomonas reinhardtii is a unicellular green alga whose lineage diverged from land plants over 1 billion years ago. It is a model system for studying chloroplast-based photosynthesis, as well as the structure, assembly, and function of eukaryotic flagella (cilia), which were inherited from the common ancestor of plants and animals, but lost in land plants. We sequenced the ∼120-megabase nuclear genome of Chlamydomonas and performed comparative phylogenomic analyses, identifying genes encoding uncharacterized proteins that are likely associated with the function and biogenesis of chloroplasts or eukaryotic flagella. Analyses of the Chlamydomonas genome advance our understanding of the ancestral eukaryotic cell, reveal previously unknown genes associated with photosynthetic and flagellar functions, and establish links between ciliopathy and the composition and function of flagella
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