1,682 research outputs found
Simultaneous structural and control optimization via linear quadratic regulator eigenstructure assignment
A method for simultaneous structural and control design of large flexible space structures (LFSS) to reduce vibration generated by disturbances is presented. Desired natural frequencies and damping ratios for the closed loop system are achieved by using a combination of linear quadratic regulator (LQR) synthesis and numerical optimization techniques. The state and control weighing matrices (Q and R) are expressed in terms of structural parameters such as mass and stiffness. The design parameters are selected by numerical optimization so as to minimize the weight of the structure and to achieve the desired closed-loop eigenvalues. An illustrative example of the design of a two bar truss is presented
Trion induced negative photoconductivity in monolayer MoS2
Optical excitation typically enhances electrical conduction and low-frequency
radiation absorption in semiconductors. We have, however, observed a pronounced
transient decrease of conductivity in doped monolayer molybdenum disulfide
(MoS2), a two-dimensional (2D) semiconductor, under femtosecond laser
excitation. In particular, the conductivity is reduced dramatically down to
only 30% of its equilibrium value with high pump fluence. This anomalous
phenomenon arises from the strong many-body interactions in the system, where
photoexcited electron-hole pairs join the doping-induced charges to form
trions, bound states of two electrons and one hole. The resultant increase of
the carrier effective mass substantially diminishes the carrier conductivity
Variabilidade genética entre javalis (sus scrofa scrofa), híbridos e suínos por meio de marcadores microssatélites.
Os híbridos entre javalis e suínos é bastante comum. Assim, tem-se detectado polimorfismo em javalis, variando o número de cromossomos de 36 a 38. No experimento foram utilizados os animais agrupados em 5 grupos genéticos: grupo I - 59 suínos domésticos com 2n = 38; grupo II - 46 javalis puros de origem (PO) com 2n = 36; grupo III - 6 híbridos, com 2n=36; grupo IV - 30 híbridos com 2n=37 e grupo V - 10 híbridos com 2n=38. O DNA genômico foi extraído e, posteriormente, amplificou-se, pela técnica de PCR, os fragmentos desses microssatélites - IGF1, ACTG2, TNFB -, os quais foram desenvolvidos para a subespécie Sus scrofa domestica. O objetivo do presente trabalho foi avaliar a heterozigosidade esperada (He) e observada (Ho) e o coeficiente de endogamia (FIS) dentro de cada população e testar as relações existentes entre os cinco grupos genéticos para estabelecer a distância genética entre eles. Os valores médios de heterozigosidades variaram 0,537-0,7871 e apresentam-se inferiores aos valores médios de heterozigosidades esperadas (0,6749-0,8279).Os valores de FIS para os Grupos II e III foram negativos, -0,005 e -0,037 respectivamente nestas populações. Nos demais grupos os valores de FIS foram positivos
Suppression of type I and type III interferon signalling by NSs protein of severe fever-with-thrombocytopenia syndrome virus through inhibition of STAT1 phosphorylation and activation
Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne pathogen causing significant morbidity and mortality in Asia. NSs protein of SFTSV is known to perturb type I IFN induction and signalling, but the mechanism remains to be fully understood. Here, we showed the suppression of both type I and type III IFN signalling by SFTSV NSs protein is mediated through inhibition of STAT1 phosphorylation and activation. Infection with live SFTSV or expression of NSs potently suppressed IFN-stimulated genes but not NFκB activation. NSs was capable of counteracting the activity of IFN-α1, IFN-β, IFN-λ1 and IFN-λ2. Mechanistically, NSs associated with STAT1 and STAT2, mitigated IFN-β-induced phosphorylation of STAT1 at S727, and reduced the expression and activity of STAT1 protein in IFN-β-treated cells, resulting in the inhibition of STAT1 and STAT2 recruitment to IFN-stimulated promoters. Taken together, SFTSV NSs protein is an IFN antagonist that suppresses phosphorylation and activation of STAT1.postprin
Pair production of the T-odd leptons at the LHC
The T-odd leptons predicted by the littlest model with T-parity can
be pair produced via the subprocesses ,
, and (= or
) at the Large Hadron Collider . We estimate the hadronic
production cross sections for all of these processes and give a simply
phenomenology analysis. We find that the cross sections for most of the above
processes are very small. However, the value of the cross section for the
process can reach .Comment: 12 pages, 2 figure
Spin-charge separation in the single hole doped Mott antiferromagnet
The motion of a single hole in a Mott antiferromagnet is investigated based
on the t-J model. An exact expression of the energy spectrum is obtained, in
which the irreparable phase string effect [Phys. Rev. Lett. 77, 5102 (1996)] is
explicitly present. By identifying the phase string effect with spin backflow,
we point out that spin-charge separation must exist in such a system: the doped
hole has to decay into a neutral spinon and a spinless holon, together with the
phase string. We show that while the spinon remains coherent, the holon motion
is deterred by the phase string, resulting in its localization in space. We
calculate the electron spectral function which explains the line shape of the
spectral function as well as the ``quasiparticle'' spectrum observed in
angle-resolved photoemission experiments. Other analytic and numerical
approaches are discussed based on the present framework.Comment: 16 pages, 9 figures; references updated; to appear in Phys. Rev.
The Static and Dynamic Lattice Changes Induced by Hydrogen Adsorption on NiAl(110)
Static and dynamic changes induced by adsorption of atomic hydrogen on the
NiAl(110) lattice at 130 K have been examined as a function of adsorbate
coverage. Adsorbed hydrogen exists in three distinct phases. At low coverages
the hydrogen is itinerant because of quantum tunneling between sites and
exhibits no observable vibrational modes. Between 0.4 ML and 0.6 ML, substrate
mediated interactions produce an ordered superstructure with c(2x2) symmetry,
and at higher coverages, hydrogen exists as a disordered lattice gas. This
picture of how hydrogen interacts with NiAl(110) is developed from our data and
compared to current theoretical predictions.Comment: 36 pages, including 12 figures, 2 tables and 58 reference
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