3,192 research outputs found
Amino acid substitution during functionally constrained divergent evolution of protein sequences
In aligning homologous protein sequences, it is generally assumed that amino acid substitutions subsequent in time occur independently of amino acid substitutions previous in time, i.e. that patterns of mulation are similar at low and high sequence divergence. This assumption is examined here and shown to be incorrect in an interesting way. Separate mutation matrices were constructed for aligned protein sequence pairs at divergences ranging from 5 to 100 PAM units (point accepted mutations per 100 aligned positions). From these, the corresponding log-odds (Day-hoff) matrices, normalized to 250 PAM units, were constructed. The matrices show that the genetic code influences accepted point mutations strongly at early stages of divergence, while the chemical properties of the side chains dominate at more advanced stage
Distribution of sound pressure around a singing cricket: radiation pattern and asymmetry in the sound field
Male field crickets generate calls to attract distant females through tegminal stridulation: the
rubbing together of the overlying right wing which bears a file of cuticular teeth against the
underlying left wing which carries a sclerotised scraper. During stridulation, specialised areas of
membrane on both wings are set into oscillating vibrations to produce acoustic radiation. The
location of females is unknown to the calling males and thus increasing effective signal range in all
directions will maximise transmission effectiveness. However, producing an omnidirectional sound
field of high sound pressure levels may be problematic due to the mechanical asymmetry found in
this sound generation system. Mechanical asymmetry occurs by the right wing coming to partially
cover the left wing during the closing stroke phase of stridulation. As such, it is hypothesised that the
sound field on the left-wing side of the animal will contain lower sound pressure components than
on the right-wing side as a result of this coverage. This hypothesis was tested using a novel method
to accurately record a high resolution, three dimensional mapping of sound pressure levels around
restrained Gryllus bimaculatus field crickets singing under pharmacological stimulation. The results
indicate that a bilateral asymmetry is present across individuals, with greater amplitude components
present in the right wing side of the animal. Individual variation in sound pressure to either the right
or left-wing side is also observed. However, statistically significant differences in bilateral sound field
asymmetry as presented here may not affect signalling in the field
More on Tachyon Cosmology in De Sitter Gravity
We aim to study rolling tachyon cosmological solutions in de Sitter gravity.
The solutions are taken to be flat FRW type and these are not time-reversal
symmetric. We find that cosmological constant of our universe has to be
fine-tuned at the level of the action itself, as in KKLT string
compactification. The rolling tachyon can give rise to required inflation with
suitable choice of the initial conditions which include nonvanishing Hubble
constant. We also determine an upper bound on the volume of the
compactification manifold.Comment: 15pp, 3 figures; references adde
Graviton mass and total relative density of mass Omega_tot in Universe
It is noticed that the total relative density of mass in the Universe
Omega_tot should exceed 1, i.e. Omega_tot=1+f^2/6 according to the field
relativistic theory of gravity (RTG), which is free of the cosmological
singularity and which provides the Euclidean character for the 3-dimensional
space. Here f is the ratio of the graviton mass m_g to the contemporary value
of the ``Hubble mass'' m^0_H=\hbar H_0/c^2\simeq 3,8\cdot 10^{-66}h(g)
(h=0,71\pm0,07). Applying results of the experimental data processing presented
in [1] an upper limit for the graviton mass is established as m_g\leq 3,2\cdot
10^{-66}g at the 95% confidence level.Comment: 8 pages, latex fil
Quantum Cryptography Based on the Time--Energy Uncertainty Relation
A new cryptosystem based on the fundamental time--energy uncertainty relation
is proposed. Such a cryptosystem can be implemented with both correlated photon
pairs and single photon states.Comment: 5 pages, LaTex, no figure
Entangled photon pairs produced by a quantum dot strongly coupled to a microcavity
We show theoretically that entangled photon pairs can be produced on demand
through the biexciton decay of a quantum dot strongly coupled to the modes of a
photonic crystal. The strong coupling allows to tune the energy of the mixed
exciton-photon (polariton) eigenmodes, and to overcome the natural splitting
existing between the exciton states coupled with different linear polarizations
of light. Polariton states are moreover well protected against dephasing due to
their lifetime ten to hundred times shorter than that of a bare exciton. Our
analysis shows that the scheme proposed can be achievable with the present
technology
Interpolation of Hilbert and Sobolev Spaces: Quantitative Estimates and Counterexamples
This paper provides an overview of interpolation of Banach and Hilbert
spaces, with a focus on establishing when equivalence of norms is in fact
equality of norms in the key results of the theory. (In brief, our conclusion
for the Hilbert space case is that, with the right normalisations, all the key
results hold with equality of norms.) In the final section we apply the Hilbert
space results to the Sobolev spaces and
, for and an open . We exhibit examples in one and two dimensions of sets
for which these scales of Sobolev spaces are not interpolation scales. In the
cases when they are interpolation scales (in particular, if is
Lipschitz) we exhibit examples that show that, in general, the interpolation
norm does not coincide with the intrinsic Sobolev norm and, in fact, the ratio
of these two norms can be arbitrarily large
Environment and classical channels in categorical quantum mechanics
We present a both simple and comprehensive graphical calculus for quantum
computing. In particular, we axiomatize the notion of an environment, which
together with the earlier introduced axiomatic notion of classical structure
enables us to define classical channels, quantum measurements and classical
control. If we moreover adjoin the earlier introduced axiomatic notion of
complementarity, we obtain sufficient structural power for constructive
representation and correctness derivation of typical quantum informatic
protocols.Comment: 26 pages, many pics; this third version has substantially more
explanations than previous ones; Journal reference is of short 14 page
version; Proceedings of the 19th EACSL Annual Conference on Computer Science
Logic (CSL), Lecture Notes in Computer Science 6247, Springer-Verlag (2010
Geometry of the 3-Qubit State, Entanglement and Division Algebras
We present a generalization to 3-qubits of the standard Bloch sphere
representation for a single qubit and of the 7-dimensional sphere
representation for 2 qubits presented in Mosseri {\it et
al.}\cite{Mosseri2001}. The Hilbert space of the 3-qubit system is the
15-dimensional sphere , which allows for a natural (last) Hopf
fibration with as base and as fiber. A striking feature is, as in
the case of 1 and 2 qubits, that the map is entanglement sensitive, and the two
distinct ways of un-entangling 3 qubits are naturally related to the Hopf map.
We define a quantity that measures the degree of entanglement of the 3-qubit
state. Conjectures on the possibility to generalize the construction for higher
qubit states are also discussed.Comment: 12 pages, 2 figures, final versio
Entanglement and the SU(2) phase states in atomic systems
We show that a system of 2n identical two-level atoms interacting with n
cavity photons manifests entanglement and that the set of entangled states
coincides with the so-called SU(2) phase states. In particular, violation of
classical realism in terms of the GHZ and GHSH conditions is proved. We discuss
a new property of entanglement expressed in terms of local measurements. We
also show that generation of entangled states in the atom-photon systems under
consideration strongly depends on the choice of initial conditions and that the
parasitic influence of cavity detuning can be compensated through the use of
Kerr medium.Comment: 10 pages, 1 figur
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