Towards a Re-definition of the Second Based on Optical Atomic Clocks

The rapid increase in accuracy and stability of optical atomic clocks compared to the caesium atomic clock as primary standard of time and frequency asks for a future re-definition of the second in the International System of Units (SI). The status of the optical clocks based on either single ions in radio-frequency traps or on neutral atoms stored in an optical lattice is described with special emphasis of the current work at the Physikalisch-Technische Bundesanstalt (PTB). Besides the development and operation of different optical clocks with estimated fractional uncertainties in the 10^-18 range, the supporting work on ultra-stable lasers as core elements and the means to compare remote optical clocks via transportable standards, optical fibers, or transportable clocks is reported. Finally, the conditions, methods and next steps are discussed that are the prerequisites for a future re-definition of the second

A Dual Model of Open Source License Growth

Every open source project needs to decide on an open source license. This decision is of high economic relevance: Just which license is the best one to help the project grow and attract a community? The most common question is: Should the project choose a restrictive (reciprocal) license or a more permissive one? As an important step towards answering this question, this paper analyses actual license choice and correlated project growth from ten years of open source projects. It provides closed analytical models and finds that around 2001 a reversal in license choice occurred from restrictive towards permissive licenses.Comment: 14 pages, 6 figure

Russia and Information Power

On November 23, 2021, Dr. Kevin Riehle, Associate Professor at the University of Mississippi, presented on Russia and Information Power at the 2021 CASIS West Coast Security Conference. The presentation was followed by a question and answer period with questions from the audience and CASIS Vancouver executives. The key points discussed were Russia’s foreign policy goals in its information warfare campaign, as well as how Russia exploits information and wields military and diplomatic power as levers to accomplish its political and strategic goals

JOINTS - NATURE'S HIGH-TECH? - Biomechanical Methods, Instruments and Models for the Analysis of Load and Strain Imposed on Human Joints by Participation in Sport Activities

Are joints nature's high-tech development? Are they anatomical marvels moved and steadied by muscles, cartilage and tendons, incomparable in their precision and durability? Or are they - due to a phylogenetic development from quadrupedal to bipedal locomotion - rather more to be viewed as faulty constructions whose complicated mechanisms are highly injury-prone and whose structures fairly rapidly begin to show signs of war and tear caused by the stress of everyday usage or sport activities? In this contribution the dynamic aspects of the functional anatomy of the large joints (shoulder, elbow, hand, hip, knee and ankle, as well as the vertebral column) are briefly presented, along with an overview of biomechanical methods, instruments and models for the analysis of loads and strains imposed on human joints by participation in sports. Special methods for the calculation of the forces and torques of human joints were developed using SDS software (Solid Dynamic System. France) employing 39 anthropometric measurements of each athlete. These were processed using the program ANT, which we developed for general use. ANT calculates the 15 segments of the Hanavan model by using the mass density given by Dempster et al. (1967), whereby X-ray-kinematographic and magnetic-resonance tomographic studies of the knee joint (15 subjects in vivo, 3 joints in vitro), ankle joint (20 subjects in vivo) and vertebral column (5 subjects in vivo) supplemented the model parameter for anthropometry. As examples analyses of trampoline gymnasts (see graphics) and runners are presented, carried out with the assistance of the 30 Peak Performance System and supplemented by measurements made using Kistler measurement platforms and the Novel- Pedar System (pressure distribution). Clinical and X-ray-genological long-term studies of the vertebral columns of trampoline gymnasts, along with comparative studies by other authors, provide a concluding overview of the effects of strain on human joints

Wavelength dependent ac-Stark shift of the 1S0 - 3P1 transition at 657 nm in Ca

We have measured the ac-Stark shift of the 4s2 1S0 - 4s4p 3P1 line in 40Ca for perturbing laser wavelengths between 780 nm and 1064 nm with a time domain Ramsey-Borde atom interferometer. We found a zero crossing of the shift for the mS = 0 - mP = 0 transition and \sigma polarized perturbation at 800.8(22) nm. The data was analyzed by a model deriving the energy shift from known transition wavelengths and strengths. To fit our data, we adjusted the Einstein A coefficients of the 4s3d 3D - 4s4p 3P and 4s5s 3S - 4s4p 3P fine structure multiplets. With these we can predict vanishing ac-Stark shifts for the 1S0 m = 0 - 3P1 m = 1 transition and \sigma- light at 983(12) nm and at 735.5(20) nm for the transition to the 3P0 level.Comment: 8 pages, 5 figures, 2 table