A First Glimpse of String Theory in the Sky?

We propose a new method for identifying new physics imprints on present observational data in cosmology whereby signatures of string theory are clearly distinguished from imprints of possible features on the inflaton potential. Our method relies on the cross-correlations spectra of cosmic shear from large scale structure (LSS) with the CMB temperature anisotropies and E-mode polarization, by using the following properties: inflationary cosmology provides only one source term for all CMB spectra and LSS which highly constrains any deviations from the standard predictions; string theory can add new non-inflationary channels to the source of perturbations as well as modify clustering properties at large scales. Discrepancies in the source terms of correlations and clustering properties provide the evidence for new physics. Models of single-field inflation with a feature are disfavored even with present data. Upcoming WMAP results and future data from weak lensing of LSS will further improve our ability to probe new physics in this manner and could open the first direct window to string theory.Comment: 14 pages, 7 figures, Revtex, typos corrected and references adde

Non-Gaussianity from Axion Monodromy Inflation

We study the primordial non-Gaussinity predicted from simple models of inflation with a linear potential and superimposed oscillations. This generic form of the potential is predicted by the axion monodromy inflation model, that has recently been proposed as a possible realization of chaotic inflation in string theory, where the monodromy from wrapped branes extends the range of the closed string axions to beyond the Planck scale. The superimposed oscillations in the potential can lead to new signatures in the CMB spectrum and bispectrum. In particular the bispectrum will have a new distinct shape. We calculate the power spectrum and bispectrum of curvature perturbations in the model, as well as make analytic estimates in various limiting cases. From the numerical analysis we find that for a wide range of allowed parameters the model produces a feature in the bispectrum with fnl ~ 50 or larger while the power spectrum is almost featureless. This model is therefore an example of a string-inspired inflationary model which is testable mainly through its non-Gaussian features. Finally we provide a simple analytic fitting formula for the bispectrum which is accurate to approximately 5% in all cases, and easily implementable in codes designed to provide non-Gaussian templates for CMB analyses.Comment: 14 pages, 4 figures, added references, and a new figure with the general shap

Is scientific misconduct increasing? Retraction rates may present more questions than answers.

Drawing on the research from his recent study into rising retraction rates R. Grant Steen argues retractions alone may be a poor surrogate measure of scientific misconduct. Science cultures are shifting to become more aware of certain “crimes” and publishing cultures may also be more willing to take immediate action. Nevertheless, there is reason to suspect that misconduct may really be increasing in prevalence and it is important to consider how best the community can measure and address this

R. E. Steen to Mrs. McKellar, 24 March 1941

Professional correspondenc

Relationship of film optical density to yield indicators

Relationship between preharvest yield indicators and film densities of aerial infrared film in microexperiment

Fat Deposition in Spitzbergen Ptarmigan (Lagopus mutus hyperboreus)

Fat depots and muscle lipids were measured in ptarmigan shot at Longyearbyen in fall and in spring. In the fall the ptarmigan weighed 740 g of which l00 g was dissectable fat and 11.5% of the pectoralis dry weight was lipid. In the spring the fat depots were almost absent and muscle lipid was halved. Neither Alaskan nor Scandinavian rock or willow ptarmigan show comparable fat depots, but the muscle lipid levels compare favourably with values obtained for Spitzbergen ptarmigan. Even larger fat depots were found in the Spitzbergen reindeer and fall fat deposition is most likely an important metabolic adaptation in high-arctic herbivores

Enhanced friction modeling for steady-state rolling tires

Tire modeling is nowadays a necessary tool in the tire industry. Car manufacturers, governments and consumers demand better traction under all circumstances, less wear and more recently less noise and a lower rolling resistance. Therefore finite element analysis is adopted in the design process of new tires to cope with these, often conflicting, demands. Finite element tire modeling can increase the insight on specific properties of a tire, decrease the development time and reduce development costs of new tires. However in practice most finite element models are still not able to match outdoor experiments. Both the static deformation and the dynamic response of the tire rolling on the road should be accurately predicted. The cornering, braking and traction of a tire depend on the generated friction forces. Friction depends not only on the tread properties of the tire, but also on the road surface and environmental conditions. The main goal of this thesis is to develop a robust and numerically efficient friction model for finite element tire simulations and to create a framework for the identification and implementation of friction related parameters. The numerical modeling of a tire in combination with its environment is a challenging task, since different physical phenomena play a role. Typically the techanical, thermal and fluid domains contribute to the tire response. This research is restricted to the mechanical domain, where a numerical modeling framework for steady-state rolling tire simulations is defined. In future developments of the model other effects can be included using this framework as a base. One of the objectives of this thesis is to develop and validate a tire friction model for finite element analysis, which captures observed effects of dry friction on the handling characteristics of rolling tires. Friction by itself is a highly complex interaction phenomenon between contacting materials and can be modeled on many different length scales, applying different numerical techniques. This can however lead to an enormous computational burden and as a result it can be impractical for an industrial application. To provide a numerically feasible and relatively fast solution a phenomenological friction model is chosen, where the parameters are identified using a two step experimental / numerical approach. Firstly, friction experiments are performed on a laboratory abrasion and skid tester to investigate the influence of contact pressure on the frictional force. In this experimental setup a small solid tire, with adjustable side slip angle, is pressed on an abrasive disk. The friction present between the abrasive disk and solid tire drives the tire and the resulting forces are measured with a force sensor. Several experiments under different normal loads and side slip angles of the tire are conducted. These measurements, under low rolling velocity, are used to identify contact pressure dependent friction parameters. The relevant parts of this setup are modeled in the commercial finite element package ABAQUS and the steady-state performance of the small tire under different slip angles is evaluated and compared with experiments. It is shown that the present turn slip, which has great impact on the slip velocity field at the trailing edge of the contact area, is captured well with the model. Furthermore, the calculated cornering stiffness is in good agreement with the experiments. Secondly, outdoor braking experiments at different velocities with a full scale tire are conducted to obtain a velocity dependent parameter set for the tire friction model. The derived friction model is then coupled to a finite element model of this full scale tire, which is also constructed in the software package ABAQUS. The finite element model is validated statically using measurements of the contact pressure distribution, contact area and of the radial and axial stiffness of the tire. The steady-state transport approach in ABAQUS is used to efficiently compute steady-state solutions at different forward velocities as used in the outdoor experiments. Finally, the predictive capability of the FE tire model in combination with the proposed friction model is assessed. The basic handling characteristics, such as pure braking, pure cornering, and combined slip under different loads, inflation pressures and velocities are evaluated and validated with experiments. Based on this comparison, it can be concluded that all three basic handling characteristics are adequately predicted