Spin nematic ground state of the triangular lattice S=1 biquadratic model

Motivated by the spate of recent experimental and theoretical interest in Mott insulating S=1 triangular lattice magnets, we consider a model S=1 Hamiltonian on a triangular lattice interacting with rotationally symmetric biquadratic interactions. We show that the partition function of this model can be expressed in terms of configurations of three colors of tightly-packed, closed loops with {\em non-negative} weights, which allows for efficient quantum Monte Carlo sampling on large lattices. We find the ground state has spin nematic order, i.e. it spontaneously breaks spin rotation symmetry but preserves time reversal symmetry. We present accurate results for the parameters of the low energy field theory, as well as finite-temperature thermodynamic functions

Turbulent atmospheric flow over a backward-facing step

The phenomenon of atmospheric shear layer separation over a man-made structure such as a building (modeled as a backward-facing step) has been analyzed theoretically by (1) solving the two-dimensional equations of motion in the two variables, stream function and vorticity, and by (2) employing an approximate integral technique. Boundary conditions for the undisturbed flow are that of the turbulent atmospheric shear flow over a rough terrain. In the first approach a two-equation model of turbulence was used. In the second approach an approximate technique was utilized in an attempt to describe the details of the flow in the recirculation zone behind the step. The results predict velocity profiles in sufficient detail that the presence of the corner eddy in the region of negative surface pressure gradient is evident. The magnitude of the reversed flow velocity in the recirculation eddy has been found to agree with that found from experiments. Also, a surface eddy viscosity distribution has been an outgrowth of the method which realistically follows the magnitude of the surface pressure gradient distribution as found experimentally

Metals get an awkward cousin

A newly predicted state of matter is a simple theoretical example of a phase that conducts electricity but is not smoothly connected to our conventional model of metals. A viewpoint on arXiv:1201.5998.Comment: Physics 5, 82 (2012

Statistical analysis of service stresses in aircraft wings

On the wing structures of modern high speed aircraft, in particular, the comparatively high-service stresses and the consistently increasing number of hours of operation during the life of the separate airplane parts make the studies of strength requirement under recurrent stresses appear of major concern. The DVL has therefore made exhaustive studies for this structural group of airplanes, some results of which are reported here

The stress criterion of a tension member with graded flexural stiffness : contribution to the problem of "clamping effect" outside of the elastic range

The approximate size of the stress criterion of a bar on two supports stressed beyond the elastic range is assessed by an approximation. The calculation proceeds from the premise of "substitute flexural stiffness" so defined that the part stressed beyond the elastic range may be considered as following Hooke's law when determining the flexural deformation quantities. For the determination of the substitute flexural stiffness, it is presumed that the material is already stressed so much beyond the yield point as to be strain-hardened. The data are directly applicable to materials having no definite yield point. For the rest, von Karman's method for compressed and subsequently deflected bars serves as basis for the calculation

Concentrations and uptake of macro and micronutrients by chickpea compared to pea, barley and oat in Central Europe

Ein zweijähriger Feldversuch wurde im Osten Österreichs durchgeführt, um die Konzentrationen und die Aufnahme von Makro- (Ca, K, Mg, P) und Mikronährstoffen (Cu, Mn, Zn) durch Kichererbse (Cicer arietinum) im Vergleich zu Erbse, Gerste und Hafer zu erheben, um so Informa­tionen für die mögliche Einführung von Kicher­erbse in zentraleuropäische Agrarsysteme zu gewinnen. Die Körner von Kichererbse wiesen höhere Nährstoffkonzentrationen (mit Ausnahme von Mn) auf als jene der beiden Getreidearten. In einem Jahr mit durchschnittlichen klimatischen Verhältnissen konnte die Kichererbse eine geringe Aufnahme von Mg und P ins Korn pro Fläche erreichen, während der K-, Cu- und Zn-Kornertrag ähnlich jenem von Gerste und Hafer war, da die Kichererbse den geringeren Kornertrag durch höhere Nährstoffkonzentrationen kompensieren konnte. Indessen konnte die Kichererbse in einem Jahr mit starker Trockenheit die anderen Kulturpflanzen im Kornertrag der Makronährstoffe Ca, K, Mg und P und des Mikronährstoffes Cu übertreffen, und zwar aufgrund des mit den weiteren Kulturpflanzen ähnlichen Kornertrages und den höheren Kornkonzentrationen dieser Elemente im Vergleich zu Gerste und Hafer. DOI: 10.5073/JfK.2015.12.02, https://doi.org/10.5073/JfK.2015.12.02Chickpea (Cicer arietinum) could be a promising new crop in Central Europe for contributing to agro-system diversification and reducing the substantial deficit of vegetable protein sources in the European Union. A two-year field experiment was conducted in eastern Austria to assess concentrations and uptake of macro (Ca, K, Mg, P) and micronutrients (Cu, Mn, Zn) of chickpea as compared to pea, barley and oat to gain information for a possible introduction of chickpea to Central European agro-system with regard to its contribution to human and livestock nutrition and its nutrient demand. Chickpea grain had higher concentrations of all analysed nutrients (except of Mn) than cereal grains. In year with average climatic conditions, chickpea had a lower grain nutrient uptake of Mg and P than pea, barley and oat but a similar one to barley and oat for K, Cu and Zn as higher grain concentrations of chickpea could compensate its lower grain yield. Whereas, chickpea could outperform the other crops in a year with drought conditions regarding the uptake of macronutrients Ca, K, Mg and P and micronutrient Cu due to both a similar grain yield with the other crops and higher grain concentrations of these elements as compared to barley and oat. DOI: 10.5073/JfK.2015.12.02, https://doi.org/10.5073/JfK.2015.12.0

Artificial Neural Network-based error compensation procedure for low-cost encoders

An Artificial Neural Network-based error compensation method is proposed for improving the accuracy of resolver-based 16-bit encoders by compensating for their respective systematic error profiles. The error compensation procedure, for a particular encoder, involves obtaining its error profile by calibrating it on a precision rotary table, training the neural network by using a part of this data and then determining the corrected encoder angle by subtracting the ANN-predicted error from the measured value of the encoder angle. Since it is not guaranteed that all the resolvers will have exactly similar error profiles because of the inherent differences in their construction on a micro scale, the ANN has been trained on one error profile at a time and the corresponding weight file is then used only for compensating the systematic error of this particular encoder. The systematic nature of the error profile for each of the encoders has also been validated by repeated calibration of the encoders over a period of time and it was found that the error profiles of a particular encoder recorded at different epochs show near reproducible behavior. The ANN-based error compensation procedure has been implemented for 4 encoders by training the ANN with their respective error profiles and the results indicate that the accuracy of encoders can be improved by nearly an order of magnitude from quoted values of ~6 arc-min to ~0.65 arc-min when their corresponding ANN-generated weight files are used for determining the corrected encoder angle.Comment: 16 pages, 4 figures. Accepted for Publication in Measurement Science and Technology (MST

Carbon Nanofiber-Based, High-Frequency, High-Q, Miniaturized Mechanical Resonators

High Q resonators are a critical component of stable, low-noise communication systems, radar, and precise timing applications such as atomic clocks. In electronic resonators based on Si integrated circuits, resistive losses increase as a result of the continued reduction in device dimensions, which decreases their Q values. On the other hand, due to the mechanical construct of bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators, such loss mechanisms are absent, enabling higher Q-values for both BAW and SAW resonators compared to their electronic counterparts. The other advantages of mechanical resonators are their inherently higher radiation tolerance, a factor that makes them attractive for NASA s extreme environment planetary missions, for example to the Jovian environments where the radiation doses are at hostile levels. Despite these advantages, both BAW and SAW resonators suffer from low resonant frequencies and they are also physically large, which precludes their integration into miniaturized electronic systems. Because there is a need to move the resonant frequency of oscillators to the order of gigahertz, new technologies and materials are being investigated that will make performance at those frequencies attainable. By moving to nanoscale structures, in this case vertically oriented, cantilevered carbon nanotubes (CNTs), that have larger aspect ratios (length/thickness) and extremely high elastic moduli, it is possible to overcome the two disadvantages of both bulk acoustic wave (BAW) and surface acoustic wave (SAW) resonators. Nano-electro-mechanical systems (NEMS) that utilize high aspect ratio nanomaterials exhibiting high elastic moduli (e.g., carbon-based nanomaterials) benefit from high Qs, operate at high frequency, and have small force constants that translate to high responsivity that results in improved sensitivity, lower power consumption, and im - proved tunablity. NEMS resonators have recently been demonstrated using topdown, lithographically fabricated ap - proaches to form cantilever or bridgetype structures. Top-down approaches, however, rely on complicated and expensive e-beam lithography, and often require a release mechanism. Reso - nance effects in structures synthesized using bottom-up approaches have also recently been reported based on carbon nanotubes, but such approaches have relied on a planar two-dimensional (2D) geometry. In this innovation, vertically aligned tubes synthesized using a bottom- up approach have been considered, where the vertical orientation of the tubes has the potential to increase integration density even further. The simulation of a vertically oriented, cantilevered carbon nanotube was performed using COMSOL Multi - physics, a finite element simulation package. All simulations were performed in a 2D geometry that provided consistent results and minimized computational complexity. The simulations assumed a vertically oriented, cantilevered nanotube of uniform density (1.5 g/cu cm). An elastic modulus was assumed to be 600 GPa, relative permittivity of the nanotube was assumed to be 5.0, and Poisson s ratio was assumed to be 0.2. It should be noted that the relative permittivity and Poisson s ratio for the nanotubes of interest are not known accurately. However, as in previous simulations, the relative permittivity and Poisson s ratios were treated as weak variables in the simulation, and no significant changes were recognized when these variables were varied

Applications and Methods of Operating a Three-dimensional Nano-electro-mechanical Resonator and Related Devices

Carbon nanofiber resonator devices, methods for use, and applications of said devices are disclosed. Carbon nanofiber resonator devices can be utilized in or as high Q resonators. Resonant frequency of these devices is a function of configuration of various conducting components within these devices. Such devices can find use, for example, in filtering and chemical detection