Ultrasensitive Displacement Noise Measurement of Carbon Nanotube Mechanical Resonators

Mechanical resonators based on a single carbon nanotube are exceptional sensors of mass and force. The force sensitivity in these ultra-light resonators is often limited by the noise in the detection of the vibrations. Here, we report on an ultra-sensitive scheme based on a RLC resonator and a low-temperature amplifier to detect nanotube vibrations. We also show a new fabrication process of electromechanical nanotube resonators to reduce the separation between the suspended nanotube and the gate electrode down to $\sim 150$~nm. These advances in detection and fabrication allow us to reach $0.5~\mathrm{pm}/\sqrt{\mathrm{Hz}}$ displacement sensitivity. Thermal vibrations cooled cryogenically at 300~mK are detected with a signal-to-noise ratio as high as 17~dB. We demonstrate $4.3~\mathrm{zN}/\sqrt{\mathrm{Hz}}$ force sensitivity, which is the best force sensitivity achieved thus far with a mechanical resonator. Our work is an important step towards imaging individual nuclear spins and studying the coupling between mechanical vibrations and electrons in different quantum electron transport regimes.Comment: 9 pages, 5 figure

Interacting holographic tachyon model of dark energy

We propose a holographic tachyon model of dark energy with interaction between the components of the dark sector. The correspondence between the tachyon field and the holographic dark energy densities allows the reconstruction of the potential and the dynamics of the tachyon scalar field in a flat Friedmann-Robertson-Walker universe. We show that this model can describe the observed accelerated expansion of our universe with a parameter space given by the most recent observational results.Comment: 7 pages, 8 figures, accepted for publication in IJMP

Applicability of TRMM Precipitation for Hydrologic Modeling in a Basin in the Northeast Brazilian Agreste.

<div><p>Abstract Determining precipitation using remote sensing is gaining space in hydrologic studies, helping make up for the lack of data in many regions of Brazil. The products from satellite TRMM (Tropical Rainfall Measuring Mission) are widely applied in studies in Brazil, but there are still few results about their applicability for hydrologic modeling in the Northeast Region, which is characterized by an irregular precipitation regime. The objective of this study is to evaluate the feasibility of using the TRMM 3B42 V7 data for hydrologic modeling in the Japaratuba river basin in Sergipe at three timescales: daily, every ten days, and monthly. The comparative analysis between the rainfall data from rain gauges and TRMM did not indicate satisfactory adequacy at these studied scales, since the TRMM data underestimated the total rainfall for all stations used in the study. However, for the hydrologic modeling, acceptable values were obtained for the efficiency coefficients evaluated only for the ten-day and monthly scales.</p></div

Robust Ferroelectric State in Multiferroic Mn1−x_{1-x}Znx_xWO4_4

We report the remarkably robust ferroelectric state in the multiferroic compound Mn$_{1-x}$Zn$_x$WO$_4$. The substitution of the magnetic Mn$^{2+}$ with nonmagnetic Zn$^{2+}$ reduces the magnetic exchange and provides control of the various magnetic and multiferroic states of MnWO$_4$. Only 5 % of Zn substitution results in a complete suppression of the frustrated collinear (paraelectric) low temperature phase. The helical magnetic and ferroelectric phase develops as the ground state. The multiferroic state is stable up to a high level of substitution of more than 50 %. The magnetic, thermodynamic, and dielectric properties as well as the ferroelectric polarization of single crystals of Mn$_{1-x}$Zn$_x$WO$_4$ are studied for different substitutions up to x=0.5. The magnetic phases have been identified in single crystal neutron scattering experiments. The ferroelectric polarization scales with the neutron intensity of the incommensurate peak of the helical phase.Comment: 6 pages, 8 figure

Flutuação populacional de Rhynchophorus palmarum (L.) (Coleoptera: Curculionidae) em palmeiras oleíferas no Amazonas.

As coleobrocas são umas das principais pragas das palmeiras devido aos seus danos diretos e indiretos resultarem na morte de diversas plantas. O levantamento populacional destes insetos é de extrema importância, visto a necessidade de se manejar adequadamente o controle realizado na área. Este estudo teve como objetivo monitorar a flutuação populacional de Rhynchophorus palmarum em plantios comerciais de Elaeis guineensis Jacq. e E. oleífera (HBK) Cortes, no estado do Amazonas

Effects of substituting ytterbium for scandium on corrosion behaviour of Al-Sc alloy

The localized corrosion and electrochemical behaviour of Al-0.28 wt.% Sc and Al-0.24 wt.% Sc-0.07 wt.% Yb alloys have been studied in 3.5 wt.% NaCl solution. The results showed that the impurity intermetallic phases containing Fe can act as cathodes and promote localized corrosion in the surrounding matrix. Yb had strong effect on the polarization behaviour in the anodic domain of Al-Sc alloy by improving the pitting corrosion resistance of this alloy. It has been deduced that a high number density of fully coherent nano-sized Al3Sc or Al-3(Sc, Yb) precipitates in heat treated alloys can enhance the passivation tendency of these alloys.This research was supported by The Project Bridging The Gap, funded by the Erasmus Mundus External Cooperation Window Program. Acknowledgements also to the University of Minho, for the provision of research facilitiesinfo:eu-repo/semantics/publishedVersio

Persistência e uniformidade da cor verde em grãos de feijão-caupi.

O parental GV10-91-11, selecionado de uma população introduzida dos Estados Unidos, e que apresenta tegumento e cotilédones verdes, com genótipo gtgtgcgc, foi cruzado com três parentaisbrasileiros, BR2-Bragança, BRS Guariba e TE93-222-11F, todos com genótipo GTGTGCGC. As gerações segregantes foram avançadas pelo método da descendência de vagem única até F5. Foram selecionadas62 linhagens F5:6 para a avaliação da persistência e da uniformidade da cor dos grãos. Foi utilizado o delineamento de blocos causalizados com duas repetições. Cada parcela foi constituída de uma amostra de 36 g de grãos acondicionados em sacos plásticos transparentes. Foram realizadas avaliações, por meio de escalas de notas de 1 a 5, aos 0, 30, 60, 90 e 120 dias de exposição em prateleira. A cada avaliação foi retirada uma sub-amostra para referência, que foi armazenada em câmara fria, na ausência de luz. A análise dos dados foi feita pelo teste de Quade. Os resultados mostraram que em algumas linhagens a cor e a uniformidade da cor persistiram até 90 dias e, embora com forte perda da cor, a uniformidade se estendeu até 120 dias. As linhagens MNC 00-595F-2 e MNC 00-595F-26 se destacaram em ambos os caracteres