96,730 research outputs found
Accessibility of the lowest quintet state of organic molecules through triplet-triplet annihilation; an INDO CI study
By the spin-allowed annihilation of two metastable triplet states (triplet-triplet annihilation-TTA) one electronic ground state (S0) and one electronically excited singlet (Si) or triplet (Ti) or quintet (Qk) state are created, provided the sum of the excitation energies of the two metastable triplet states is sufficient for the creation of the particular excited state. On the basis of semi-empirical calcns. of the excitation energies of T1 and Q1 of forty-six conjugated org. compds. it is shown that Q1 of benzene and some other compds. should be accessible through annihilation of like triplets (homo-TTA), and that Q1 of many compds. should be accessible through annihilation of unlike triplets (hetero-TTA). The population of Q1, competing with that of S1, should cause an unusual magnetic-field dependence of the delayed fluorescence S1 -> S0. In favorable cases, the population of Q1 should lead to an inverse (pos.) magnetic high-field effect on the delayed fluorescence
Synchronization Strings: Codes for Insertions and Deletions Approaching the Singleton Bound
We introduce synchronization strings as a novel way of efficiently dealing
with synchronization errors, i.e., insertions and deletions. Synchronization
errors are strictly more general and much harder to deal with than commonly
considered half-errors, i.e., symbol corruptions and erasures. For every
, synchronization strings allow to index a sequence with an
size alphabet such that one can efficiently transform
synchronization errors into half-errors. This powerful new
technique has many applications. In this paper, we focus on designing insdel
codes, i.e., error correcting block codes (ECCs) for insertion deletion
channels.
While ECCs for both half-errors and synchronization errors have been
intensely studied, the later has largely resisted progress. Indeed, it took
until 1999 for the first insdel codes with constant rate, constant distance,
and constant alphabet size to be constructed by Schulman and Zuckerman. Insdel
codes for asymptotically large or small noise rates were given in 2016 by
Guruswami et al. but these codes are still polynomially far from the optimal
rate-distance tradeoff. This makes the understanding of insdel codes up to this
work equivalent to what was known for regular ECCs after Forney introduced
concatenated codes in his doctoral thesis 50 years ago.
A direct application of our synchronization strings based indexing method
gives a simple black-box construction which transforms any ECC into an equally
efficient insdel code with a slightly larger alphabet size. This instantly
transfers much of the highly developed understanding for regular ECCs over
large constant alphabets into the realm of insdel codes. Most notably, we
obtain efficient insdel codes which get arbitrarily close to the optimal
rate-distance tradeoff given by the Singleton bound for the complete noise
spectrum
Interactive Channel Capacity Revisited
We provide the first capacity approaching coding schemes that robustly
simulate any interactive protocol over an adversarial channel that corrupts any
fraction of the transmitted symbols. Our coding schemes achieve a
communication rate of over any
adversarial channel. This can be improved to for
random, oblivious, and computationally bounded channels, or if parties have
shared randomness unknown to the channel.
Surprisingly, these rates exceed the interactive channel capacity bound
which [Kol and Raz; STOC'13] recently proved for random errors. We conjecture
and to be the optimal rates for their respective settings
and therefore to capture the interactive channel capacity for random and
adversarial errors.
In addition to being very communication efficient, our randomized coding
schemes have multiple other advantages. They are computationally efficient,
extremely natural, and significantly simpler than prior (non-capacity
approaching) schemes. In particular, our protocols do not employ any coding but
allow the original protocol to be performed as-is, interspersed only by short
exchanges of hash values. When hash values do not match, the parties backtrack.
Our approach is, as we feel, by far the simplest and most natural explanation
for why and how robust interactive communication in a noisy environment is
possible
Precision Studies of Light Mesons at COMPASS
The COMPASS experiment at CERN's SPS investigates the structure and
excitations of strongly interacting systems. Using reactions of 190 GeV/c pions
with protons and nuclear targets, mediated by the strong and electromagnetic
interaction, an unprecedented statistical precision has been reached allowing
new insight into the properties of light mesons. For the first time the
diffractively produced 3pi final state has been analyzed simultaneously in bins
of invariant mass and four-momentum transfer using a large set of 88 waves up
to a total angular momentum of 6. In addition to a precise determination of the
properties of known resonances and including a model-indepedent analysis of the
pi pi S-wave isobar, a new narrow axial-vector state coupling strongly to
f0(980)pi has been found in previously unchartered territory. By selecting
reactions with very small four-momentum transfer COMPASS is able to study
processes involving the exchange of quasi-real photons. These provide clean
access to low-energy quantities such as radiative couplings and
polarizabilities of mesons, and thus constitute a test of model predictions
such as chiral perturbation theory.Comment: Proceedings of the XV International Conference on Hadron Spectroscopy
(Hadron 2013). 9 pages, 5 figure
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