The Scattering Variety

The so-called Scattering Equations which govern the kinematics of the scattering of massless particles in arbitrary dimensions have recently been cast into a system of homogeneous polynomials. We study these as affine and projective geometries which we call Scattering Varieties by analyzing such properties as Hilbert series, Euler characteristic and singularities. Interestingly, we find structures such as affine Calabi-Yau threefolds as well as singular K3 and Fano varieties

Optimization in random field Ising models by quantum annealing

We investigate the properties of quantum annealing applied to the random field Ising model in one, two and three dimensions. The decay rate of the residual energy, defined as the energy excess from the ground state, is find to be $e_{res}\sim \log(N_{MC})^{-\zeta}$ with $\zeta$ in the range $2...6$, depending on the strength of the random field. Systems with ``large clusters'' are harder to optimize as measured by $\zeta$. Our numerical results suggest that in the ordered phase $\zeta=2$ whereas in the paramagnetic phase the annealing procedure can be tuned so that $\zeta\to6$.Comment: 7 pages (2 columns), 9 figures, published with minor changes, one reference updated after the publicatio

Elastic lines on splayed columnar defects studied numerically

We investigate by exact optimization method properties of two- and three-dimensional systems of elastic lines in presence of splayed columnar disorder. The ground state of many lines is separable both in 2d and 3d leading to a random walk -like roughening in 2d and ballistic behavior in 3d. Furthermore, we find that in the case of pure splayed columnar disorder in contrast to point disorder there is no entanglement transition in 3d. Entanglement can be triggered by perturbing the pure splay system with point defects.Comment: 9 pages, 11 figures. Accepted for publication in PR

Spin(7) compactifications and 1/4-BPS vacua in heterotic supergravity.

We continue the investigation into non-maximally symmetric compactifications of the heterotic string. In particular, we consider compactifications where the internal space is allowed to depend on two or more external directions. For preservation of supersymmetry, this implies that the internal space must in general be that of a Spin(7) manifold, which leads to a 1/4-BPS four-dimensional supersymmetric perturbative vacuum breaking all but one supercharge. We find that these solutions allow for internal geometries previously excluded by the domain-wall-type solutions, and hence the resulting four-dimensional superpotential is more generic. In particular, we find an interesting resemblance to the superpotentials that appear in non-geometric flux compactifications of type II string theory. If the vacua are to be used for phenomenological applications, they must be lifted to maximal symmetry by some non-perturbative or higher-order effect.NCS201

Collision effects in velocity-selective optical pumping of sodium

We report on a quantitative experimental investigation of velocity-changing collisions by means of velocity-selective optical pumping (VSOP). We have calculated the VSOP line shape for an atom with hyperfine structure with the use of two phenomenological kernels for the collision effects: the Keilson-Storer kernel, and a two-term kernel consisting of a broad Keilson-Storer part and a narrower Gaussian component. Corrections were included to account for the finite absorption in the sample and the backward reflection of the pumping beam. The experiments were carried out in sodium vapor with neon as the perturber gas. The D1 line of sodium was used for optical pumping, and the orientation of the ground state was detected. Free parameters of the theory were determined by fitting the predicted line shapes to experimental curves. The Keilson-Storer kernel proved unsatisfactory, but the two-term kernel reproduced well the observed line shapes over the entire collision profiles in the neon pressure range 0-57 mtorr. In an independent experiment using rapidly modulated VSOP we also measured directly the cross section of velocity-changing collisions: σ=(1.13±0.10)×10exp−14 cm2. The large weight obtained for the narrow Gaussian from the fits, as well as the collision cross section which is three times as large as the cross section deduced from tabulated gas kinetic radii, may indicate the presence of collisions with relatively small velocity changes in addition to hard-sphere encounters.Peer reviewe

Pseudopeptidic ligands: exploring the self-assembly of isopthaloylbisglycine (H2IBG) and divalent metal ions

No description supplie

Noise-induced strong stabilization

We consider a 2-dimensional stochastic differential equation in polar coordinates depending on several parameters. We show that if these parameters belong to a specific regime then the deterministic system explodes in finite time, but the random dynamical system corresponding to the stochastic equation is not only strongly complete but even admits a random attractor

Natural quantitative genetic variance in plant growth differs in response to ecologically relevant temperature heterogeneity

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Winter precipitation trends for two selected European regions over the last 500 years and their possible dynamical background

Summary: We analyse winter (DJF) precipitation over the last 500 years on trends using a spatially and temporally highly resolved gridded multi-proxy reconstruction over European land areas. The trends are detected applying trend matrices, and the significance is assessed with the Mann-Kendall-trend test. Results are presented for southwestern Norway and southern Spain/northern Morocco, two regions that show high reconstruction skill over the entire period. The absolute trend values found in the second part of the 20th century are unprecedented over the last 500 years in both regions. During the period 1715-1765, the precipitation trends were most pronounced in southwestern Norway as well as southern Spain/northern Morocco, with first a distinct negative trend followed by a positive countertrend of similar strength. Relating the precipitation time series to variations of the North Atlantic Oscillation Index (NAOI) and the solar irradiance using running correlations revealed a couple of instationarities. Nevertheless, it appears that the NAO is responsible in both regions for most of the significant winter precipitation trends during the earlier centuries as well as during recent decades. Some of the significant winter precipitation trends over southwestern Norway and southern Spain/northern Morocco might be related to changes in the solar irradianc