11,383 research outputs found
Synchronous Behavior of Two Coupled Electronic Neurons
We report on experimental studies of synchronization phenomena in a pair of
analog electronic neurons (ENs). The ENs were designed to reproduce the
observed membrane voltage oscillations of isolated biological neurons from the
stomatogastric ganglion of the California spiny lobster Panulirus interruptus.
The ENs are simple analog circuits which integrate four dimensional
differential equations representing fast and slow subcellular mechanisms that
produce the characteristic regular/chaotic spiking-bursting behavior of these
cells. In this paper we study their dynamical behavior as we couple them in the
same configurations as we have done for their counterpart biological neurons.
The interconnections we use for these neural oscillators are both direct
electrical connections and excitatory and inhibitory chemical connections: each
realized by analog circuitry and suggested by biological examples. We provide
here quantitative evidence that the ENs and the biological neurons behave
similarly when coupled in the same manner. They each display well defined
bifurcations in their mutual synchronization and regularization. We report
briefly on an experiment on coupled biological neurons and four dimensional ENs
which provides further ground for testing the validity of our numerical and
electronic models of individual neural behavior. Our experiments as a whole
present interesting new examples of regularization and synchronization in
coupled nonlinear oscillators.Comment: 26 pages, 10 figure
Fourier transform spectroscopy and coupled-channel deperturbation treatment of the A1Sigma+ ~ b3Pi complex of KCs molecule
The laser induced fluorescence (LIF) spectra A1Sigma ~ b3Pi --> X1Sigma+ of
KCs dimer were recorded in near infrared region by Fourier Transform
Spectrometer with a resolution of 0.03 cm-1. Overall more than 200 LIF spectra
were rotationally assigned to 39K133Cs and 41K133Cs isotopomers yielding with
the uncertainty of 0.003-0.01 cm-1 more than 3400 rovibronic term values of the
strongly mixed singlet A1Sigma+ and triplet b3Pi states. Experimental data
massive starts from the lowest vibrational level v_A=0 of the singlet and
nonuniformly cover the energy range from 10040 to 13250 cm-1 with rotational
quantum numbers J from 7 to 225. Besides of the dominating regular A1Sigma+ ~
b3P Omega=0 interactions the weak and local heterogenous A1S+ ~ b3P Omega=1
perturbations have been discovered and analyzed. Coupled-channel deperturbation
analysis of the experimental 39K133Cs e-parity termvalues of the A1S+ ~ b3P
complex was accomplished in the framework of the phenomenological 4 x 4
Hamiltonian accounting implicitly for regular interactions with the remote
states manifold. The resulting diabatic potential energy curves of the
interacting states and relevant spin-orbit coupling matrix elements defined
analytically by Expanded Morse Oscillators model reproduce 95% of experimental
data field of the 39K133Cs isotopomer with a standard deviation of 0.004 cm-1
which is consistent with the uncertainty of the experiment. Reliability of the
derived parameters was additionally confirmed by a good agreement between the
predicted and experimental termvalues of 41K133Cs isotopomer. Calculated
intensity distributions in the A ~ b --> X LIF progressions are also consistent
with their experimental counterparts.Comment: 17 pages, 14 figure
Stopping power of hot QCD plasma
The partonic energy loss has been calculated taking both the hard and soft
contributions for all the processes, revealing the importance of the
individual channels. Cancellation of the intermediate separation scale has been
exhibited. Subtleties related to the identical final state partons have
properly been taken into account. The estimated collisional loss is compared
with its radiative counter part. We show that there exists a critical energy
() below which the collisional loss is more than its radiative
counterpart. In addition, we present closed form formulas for both the
collision probabilities and the stopping power ()Comment: revised version, section added, 9pages with 5 figure
A long, nontranslatable poly(A) RNA stored in the egg of the sea urchin Strongylocentrotus purpuratus
Nontranslatable transcripts containing interspersed repetitive sequence elements constitute a major fraction of the poly(A) RNA stored in the cytoplasm of both the sea urchin egg and the amphibian oocyte. We report the first complete sequence of a representative interspersed maternal RNA transcript, called ISp1. The transcript is about 3.7 kb in length [including poly(A) tail]; and the 5' half consists of a cluster of repetitive sequences, whereas the 3' half is single copy. Other repetitive sequences occur in the 5' and 3' regions flanking the transcription unit. In several cloned alleles, the flanking repetitive and single-copy sequences differ, indicating a high degree of insertional and deletional rearrangement around, as well as within, the transcription unit. No significant open reading frames exist in any region of the ISp1 transcript, nor is it spliced to give rise to translatable mRNA in egg or embryo. A 620-nucleotide repetitive sequence element at the 5' end of the ISp1 transcript is also represented in a large number of other long interspersed maternal poly(A) RNAs. In addition, this sequence appears in a prevalent set of small polyadenylated RNAs about 600-nucleotides in length, which disappear almost completely by the gastrula stage of development. The structural features of the ISp1 RNA uncovered in this work exclude several hypotheses of interspersed maternal poly(A) RNA origin and function
Z_3-graded exterior differential calculus and gauge theories of higher order
We present a possible generalization of the exterior differential calculus,
based on the operator d such that d^3=0, but d^2\not=0. The first and second
order differentials generate an associative algebra; we shall suppose that
there are no binary relations between first order differentials, while the
ternary products will satisfy the cyclic relations based on the representation
of cyclic group Z_3 by cubic roots of unity. We shall attribute grade 1 to the
first order differentials and grade 2 to the second order differentials; under
the associative multiplication law the grades add up modulo 3. We show how the
notion of covariant derivation can be generalized with a 1-form A, and we give
the expression in local coordinates of the curvature 3-form. Finally, the
introduction of notions of a scalar product and integration of the Z_3-graded
exterior forms enables us to define variational principle and to derive the
differential equations satisfied by the curvature 3-form. The Lagrangian
obtained in this way contains the invariants of the ordinary gauge field tensor
F_{ik} and its covariant derivatives D_i F_{km}.Comment: 13 pages, no figure
Mesoscopic molecular ions in Bose-Einstein condensates
We study the possible formation of large (mesoscopic) molecular ions in an
ultracold degenerate bosonic gas doped with charged particles (ions). We show
that the polarization potentials produced by the ionic impurities are capable
of capturing hundreds of atoms into loosely bound states. We describe the
spontaneous formation of these hollow molecular ions via phonon emission and
suggest an optical technique for coherent stimulated transitions of free atoms
into a specific bound state. These results open up new interesting
possibilities for manipulating tightly confined ensembles.Comment: 4 pages (two-columns), 2 figure
Photoassociative Production and Trapping of Ultracold KRb Molecules
We have produced ultracold heteronuclear KRb molecules by the process of
photoassociation in a two-species magneto-optical trap. Following decay of the
photoassociated KRb*, the molecules are detected using two-photon ionization
and time-of-flight mass spectroscopy of KRb. A portion of the metastable
triplet molecules thus formed are magnetically trapped. Photoassociative
spectra down to 91 cm below the K(4) + Rb (5) asymptote have
been obtained. We have made assignments to all eight of the attractive Hund's
case (c) KRb* potential curves in this spectral region.Comment: 4 pages, 4 figure
Sirtuin 3 deficiency does not alter host defenses against bacterial and fungal infections.
Sirtuin 3 (SIRT3) is the main mitochondrial deacetylase. SIRT3 regulates cell metabolism and redox homeostasis, and protects from aging and age-associated pathologies. SIRT3 may drive both oncogenic and tumor-suppressive effects. SIRT3 deficiency has been reported to promote chronic inflammation-related disorders, but whether SIRT3 impacts on innate immune responses and host defenses against infections remains essentially unknown. This aspect is of primary importance considering the great interest in developing SIRT3-targeted therapies. Using SIRT3 knockout mice, we show that SIRT3 deficiency does not affect immune cell development and microbial ligand-induced proliferation and cytokine production by splenocytes, macrophages and dendritic cells. Going well along with these observations, SIRT3 deficiency has no major impact on cytokine production, bacterial burden and survival of mice subjected to endotoxemia, Escherichia coli peritonitis, Klebsiella pneumoniae pneumonia, listeriosis and candidiasis of diverse severity. These data suggest that SIRT3 is not critical to fight infections and support the safety of SIRT3-directed therapies based on SIRT3 activators or inhibitors for treating metabolic, oncologic and neurodegenerative diseases without putting patients at risk of infection
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