Square root meadows

Let Q_0 denote the rational numbers expanded to a meadow by totalizing inversion such that 0^{-1}=0. Q_0 can be expanded by a total sign function s that extracts the sign of a rational number. In this paper we discuss an extension Q_0(s ,\sqrt) of the signed rationals in which every number has a unique square root.Comment: 9 page

Exotic branes and non-geometric backgrounds

When string/M-theory is compactified to lower dimensions, the U-duality symmetry predicts so-called exotic branes whose higher dimensional origin cannot be explained by the standard string/M-theory branes. We argue that exotic branes can be understood in higher dimensions as non-geometric backgrounds or U-folds, and that they are important for the physics of systems which originally contain no exotic charges, since the supertube effect generically produces such exotic charges. We discuss the implications of exotic backgrounds for black hole microstate (non-)geometries.Comment: 4 pages. v2: journal version. The discussion on "double puff-up" revise

Surface plasma resonance in small rare gas clusters by mixing IR and VUV laser pulses

The ionization dynamics of a Xenon cluster with 40 atoms is analyzed under a pum p probe scenario of laser pulses where an infrared laser pulse of 50 fs length follows with a well defined time delay a VUV pulse of the same length and peak intensity. The mechanism of resonant energy absorption due to the coinc idence of the IR laser frequency with the frequency of collective motion of quasi free electrons in the cluster is mapped out by varying the time delay between the pulses

Next-to-next-to-leading logarithmic resummation for transverse thrust

We obtain a prediction for the hadron-collider event-shape variable transverse thrust in which the terms enhanced in the dijet limit are resummed to next-to-next-to-leading logarithmic accuracy. Our method exploits universality properties made manifest in the factorized expression for the cross section and only requires one-loop calculations. The necessary two-loop ingredients are extracted using known results and existing numerical codes. Our technique is general and applicable to other observables as well.Comment: 6 pages, 2 figures. v2: Corrected values in Eq.(15); updated Figure 2 accordingl

Single-Frequency, Thin-Film-Tuned, 0.6W, Diode-Pumped Nd:YVO\u3csub\u3e4\u3c/sub\u3e Laser

Application of a metallic thin-film selector to the single-frequency oscillation of a diode-pumped Nd:YVO4 laser has been investigated theoretically and experimentally. We show that a chromium thin-film selector with a thickness between 8 and 9 nm provides single-frequency output within a power range of 0.6W. Single-frequency operation, slow smooth turning, or chirping was realized by the output coupler movement with a piezoceramic transducer. Chuirping at a repetition rate of 0.5 kHz in the 0.5-10-GHz range was achieved. Physical and technical limitations caused by the wide-gain bandwidith, thermal effects, and mechanical vibrations of cavity elements are discussed

Neural network modeling of nonlinear systems based on Volterra series extension of a linear model

A Volterra series approach was applied to the identification of nonlinear systems which are described by a neural network model. A procedure is outlined by which a mathematical model can be developed from experimental data obtained from the network structure. Applications of the results to the control of robotic systems are discussed

Disk wind feedback from high-mass protostars

We perform a sequence of 3D magnetohydrodynamic (MHD) simulations of the outflow-core interaction for a massive protostar forming via collapse of an initial cloud core of $60~{M_\odot}$. This allows us to characterize the properties of disk wind driven outflows from massive protostars, which can allow testing of different massive star formation theories. It also enables us to assess quantitatively the impact of outflow feedback on protostellar core morphology and overall star formation efficiency. We find that the opening angle of the flow increases with increasing protostellar mass, in agreement with a simple semi-analytic model. Once the protostar reaches $\sim24~{M_\odot}$ the outflow's opening angle is so wide that it has blown away most of the envelope, thereby nearly ending its own accretion. We thus find an overall star formation efficiency of $\sim50\%$, similar to that expected from low-mass protostellar cores. Our simulation results therefore indicate that the MHD disk wind outflow is the dominant feedback mechanism for helping to shape the stellar initial mass function from a given prestellar core mass function.Comment: Accepted for publication in Ap