2,868 research outputs found
Invariants of solvable rigid Lie algebras up to dimension 8
The invariants of all complex solvable rigid Lie algebras up to dimension
eight are computed. Moreover we show, for rank one solvable algebras, some
criteria to deduce to non-existence of non-trivial invariants or the existence
of fundamental sets of invariants formed by rational functions of the Casimir
invariants of the associated nilradical.Comment: 16 pages, 7 table
Interstellar nitrile anions: Detection of C3N- and C5N- in TMC-1
We report on the first detection of C3N- and C5N- towards the cold dark core
TMC-1 in the Taurus region, using the Yebes 40 m telescope. The observed
C3N/C3N- and C5N/C5N- abundance ratios are 140 and 2, respectively; that is
similar to those found in the circumstellar envelope of the carbon-rich star
IRC+10216. Although the formation mechanisms for the neutrals are different in
interstellar (ion-neutral reactions) and circumstellar clouds
(photodissociation and radical-neutral reactions), the similarity of the
C3N/C3N- and C5N/C5N- abundance ratios strongly suggests a common chemical path
for the formation of these anions in interstellar and circumstellar clouds. We
discuss the role of radiative electronic attachment, reactions between N atoms
and carbon chain anions Cn-, and that of H- reactions with HC3N and HC5N as
possible routes to form CnN-. The detection of C5N- in TMC-1 gives strong
support for assigning to this anion the lines found in IRC+10216, as it
excludes the possibility of a metal-bearing species, or a vibrationally excited
state. New sets of rotational parameters have been derived from the observed
frequencies in TMC-1 and IRC+10216 for C5N- and the neutral radical C5N.Comment: Accepted for publication in A&A Letter
The mitochondrial elongation factor LeEF-Tsmt is regulated during tomato fruit ripening and upon wounding and ethylene treatment.
A gene encoding an elongation factor LeEF-Tsmt that participates in the protein synthesis process in mitochondria shows strong expression in ripening fruit as compared to other organs. It is strongly up-regulated during the first stages of the ripening process in parallel with the climacteric rise in respiration. LeEF-Tsmt expression is stimulated by ethylene, wounding and high temperature but ethylene-insensitive mutants exhibit normal expression. Transgenic fruit have been generated in which LeEF-Tsmt has been constitutively up- and down-regulated. Surprisingly, altering the expression of the gene by genetic transformation with antisense and sense LeEF-Tsmt constructs did not affect the pattern of respiration and ethylene production during ripening and upon wounding. In addition, expression of the alternative oxidase gene which is known to play an important role in respiratory climacteric was not affected. Possible reasons for the absence of effect on respiration of variations of LeEF-Tsmt gene expression are discussed
Interaction-dependent photon-assisted tunneling in optical lattices: a quantum simulator of strongly-correlated electrons and dynamical gauge fields
We introduce a scheme that combines photon-assisted tunneling by a moving optical lattice with strong Hubbard interactions, and allows for the quantum simulation of paradigmatic quantum many-body models. We show that, in a certain regime, this quantum simulator yields an effective Hubbard Hamiltonian with tunable bond-charge interactions, a model studied in the context of strongly-correlated electrons. In a different regime, we show how to exploit a correlated destruction of tunneling to explore Nagaoka ferromagnetism at finite Hubbard repulsion. By changing the photon-assisted tunneling parameters, we can also obtain a t-J model with independently controllable tunneling t, super-exchange interaction J, and even a Heisenberg-Ising anisotropy. Hence, the full phase diagram of this paradigmatic model becomes accessible to cold-atom experiments, departing from the region t _ J allowed by standard single-band Hubbard Hamiltonians in the strong-repulsion limit. We finally show that, by generalizing the photon-assisted tunneling scheme, the quantum simulator yields models of dynamical Gauge fields, where atoms of a given electronic state dress the tunneling of the atoms with a different internal state, leading to Peierls phases that mimic a dynamical magnetic field
Discovery of HC4NC in TMC-1: A study of the isomers of HC3N, HC5N, and HC7N
We present a study of the isocyano isomers of the cyanopolyynes HC3N, HC5N,
and HC7N in TMC-1 and IRC+10216 carried out with the Yebes 40m radio telescope.
This study has enabled us to report the detection, for the first time in space,
of HCCCCNC in TMC-1 and to give upper limits for HC6NC in the same source. In
addition, the deuterated isotopologues of HCCNC and HNCCC were detected, along
with all 13C substitutions of HCCNC, also for the first time in space. The
abundance ratios of HC3N and HC5N, with their isomers, are very different in
TMC-1 and IRC+10216, namely, N(HC5N)/N(HC4NC) is 300 and >2100, respectively.
We discuss the chemistry of the metastable isomers of cyanopolyynes in terms of
the most likely formation pathways and by comparing observational abundance
ratios between different sources.Comment: This article was submitted to A&A on 27/08/2020 and accepted for
publication on 11/09/202
Spectral and localization properties of random bipartite graphs
Bipartite graphs are often found to represent the connectivity between the
components of many systems such as ecosystems. A bipartite graph is a set of
nodes that is decomposed into two disjoint subsets, having and
vertices each, such that there are no adjacent vertices within the same set.
The connectivity between both sets, which is the relevant quantity in terms of
connections, can be quantified by a parameter that equals the
ratio of existent adjacent pairs over the total number of possible adjacent
pairs. Here, we study the spectral and localization properties of such random
bipartite graphs. Specifically, within a Random Matrix Theory (RMT) approach,
we identify a scaling parameter that fixes the
localization properties of the eigenvectors of the adjacency matrices of random
bipartite graphs. We also show that, when ) the
eigenvectors are localized (extended), whereas the
localization--to--delocalization transition occurs in the interval
. Finally, given the potential applications of our findings, we
round off the study by demonstrating that for fixed , the spectral
properties of our graph model are also universal.Comment: 17 pages, 10 figure
Discovery of HC3O+ in space: The chemistry of O-bearing species in TMC-1
Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of
harmonically related lines with a rotational constant B0=4460.590 +/- 0.001 MHz
and a distortion constant D0=0.511 +/- 0.005 kHz towards the cold dense core
TMC-1. High-level-of-theory ab initio calculations indicate that the best
possible candidate is protonated tricarbon monoxide, HC3O+. We have succeeded
in producing this species in the laboratory and observed its J = 2-1 and 3-2
rotational transitions. Hence, we report the discovery of HC3O+ in space based
on our observations, theoretical calculations, and laboratory experiments. We
derive an abundance ratio N(C3O)/N(HC3O+) = 7. The high abundance of the
protonated form of C3O is due to the high proton affinity of the neutral
species. The chemistry of O-bearing species is modelled, and predictions are
compared to the derived abundances from our data for the most prominent
O-bearing species in TMC-1.Comment: Accepted for publication in A&A Letter
Surface Enhanced Second Harmonic Generation from Macrocycle, Catenane, and Rotaxane Thin Films: Experiments and Theory
Surface enhanced second harmonic generation (SE SHG) experiments on molecular structures, macrocycles, catenanes, and rotaxanes, deposited as monolayers and multilayers by vacuum sublimation on silver, are reported. The measurements show that the molecules form ordered thin films, where the highest degree of order is observed in the case of macrocycle monolayers and the lowest in the case of rotaxane multilayers. The second harmonic generation activity is interpreted in terms of electric field induced second harmonic (EFISH) generation where the electric field is created by the substrate silver atoms. The measured second order nonlinear optical susceptibility for a rotaxane thin film is compared with that obtained by considering only EFISH contribution to SHG intensity. The electric field on the surface of a silver layer is calculated by using the Delphi4 program for structures obtained with TINKER molecular mechanics/dynamics simulations. An excellent agreement is observed between the calculated and the measured SHG susceptibilities.
Seleção genômica ampla para os componentes da eficiência no uso de fósforo em milho.
O objetivo deste trabalho foi verificar a eficácia do método da seleção genomica ampla (GWS) no melhoramentode milho para os componentes da eficiência no uso de fósforo (EUP). Para isto, foram avaliadas 41 combinações hÃbridas de milho, em alta e baixa disponibilidade de P, em casa de vegetação pertencente ao Departamento de Fitotecnia da Universidade Federal de Viçosa, em outubro de 2010. As plantas foram coletadas no estádio V6. Foram estimados os dois componentes da EUP, que são as eficiências de absorção e de utilização de N. Os dados obtidos foram submetidos a análises estatÃsticas via metodologia REML/BLUP. Na genotipagem da população de estimação, foram utilizados 80 marcadores microssatélites (SSR). A predição dos valores genéticos genômicos dos hÃbridos foi obtida via RR-BLUP/GWS. Para os caracteres em que a GWS apresentou altos valores de acurácia seletiva, ela foi comparada com a seleção recorrente intrapopulacional. Com o uso da GWS houve um aumento significativo na acurácia seletiva, nos ganhos estimados por unidade de tempo
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