12,790 research outputs found
Exothermic isospin-violating dark matter after SuperCDMS and CDEX
We show that exothermic isospin-violating dark matter (IVDM) can make the
results of the latest CDMS-Si experiment consistent with recent null
experiments, such as XENON10, XENON100, LUX, CDEX, and SuperCDMS, whereas for
the CoGeNT experiment, a strong tension still persists. For CDMS-Si, separate
exothermic dark matter or isospin-violating dark matter cannot fully ameliorate
the tensions among these experiments; the tension disappears only if exothermic
scattering is combined with an isospin-violating effect of f_n/f_p=-0.7. For
such exothermic IVDM to exist, at least a new vector gauge boson (dark photon
or dark Z') that connects SM quarks to Majorana-type DM particles is required.Comment: 12 pages, 6 figure
Stringent Nucleotide Recognition by the Ribosome at the Middle Codon Position.
Accurate translation of the genetic code depends on mRNA:tRNA codon:anticodon base pairing. Here we exploit an emissive, isosteric adenosine surrogate that allows direct measurement of the kinetics of codon:anticodon University of California base formation during protein synthesis. Our results suggest that codon:anticodon base pairing is subject to tighter constraints at the middle position than at the 5'- and 3'-positions, and further suggest a sequential mechanism of formation of the three base pairs in the codon:anticodon helix
Controllability Canonical Forms of Linear Ensemble Systems
Ensemble control, an emerging research field focusing on the study of large
populations of dynamical systems, has demonstrated great potential in numerous
scientific and practical applications. Striking examples include pulse design
for exciting spin ensembles in quantum physics, neurostimulation for relieving
neurological disorder symptoms, and path planning for steering robot swarms.
However, the control targets in such applications are generally large-scale
complex and severely underactuated ensemble systems, research into which
stretches the capability of techniques in classical control and dynamical
systems theory to the very limit. This paper then devotes to advancing our
knowledge about controllability of linear ensemble systems by integrating tools
in modern algebra into the technique of separating points developed in our
recent work. In particular, we give an algebraic interpretation of the dynamics
of linear systems in terms of actions of polynomials on vector spaces, and this
leads to the development of the functional canonical form of matrix-valued
functions, which can also be viewed as the generalization of the rational
canonical form of matrices in linear algebra. Then, leveraging the technique of
separating points, we achieve a necessary and sufficient characterization of
uniform ensemble controllability for time-invariant linear ensemble systems as
the ensemble controllability canonical form, in which the system and control
matrices are in the functional canonical and block diagonal form, respectively.
This work successfully launches a new research scheme by adopting and tailoring
finite-dimensional methods to tackle control problems involving
infinite-dimensional ensemble systems, and lays a solid foundation for a more
inclusive ensemble control theory targeting a much broader spectrum of control
and learning problems in both scientific research and practice
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