Does Okun’s law still hold today?

Arthur Okun claimed that when a country’s unemployment rate fell, the GDP expanded. This paper investigates the claim of Arthur Okun and the effect of unemployment rates and GDP of a country on each other. Data from three countries, namely, USA, Japan, and France, were tested to see if there was a causal link between the two variables. It was found that the proposed law of Arthur Okun did not hold. In the USA, there was a two way causality link but different directions of effect. France and Japan did not have a causal link between the two variables

Bending loss improvement and twisting loss studies of flexible multimode polymer waveguides

© 2020 SPIE. Multimode polymer waveguides have attracted considerable interest for use in high-speed on-board communication links as they provide low loss (40 GHz×m) and can be cost-effectively integrated onto standard PCBs. The fabrication of such waveguides on flexible substrates can provide additional advantages: shape flexibility, lightweight and reduced thickness which are particularly important in the aviation and automotive industries. Such flexible and lightweight optical connections will play an important role in next-generation airplanes and driverless cars connecting the multitude of peripheral sensors with the central processing unit at high speed and low latency. However, in such applications, flexible polymer waveguides are required to be bent to meet their stringent space requirements and twisted or stretched when connecting movable parts. Under sharp flexure, the bending or twisting loss dominates the waveguide loss limiting their practical use. In this work therefore, we present a new waveguide design for flexible polymer waveguides with improved bending performance and derive useful layout rules for minimizing twisting losses in such samples. The proposed waveguide structure only requires one additional fabrication step and achieves bending losses below 0.5 dB for a 3 mm bend. In comparison, the conventional waveguide design yields a 2 dB loss under the same bending radius and launch condition. Additionally, useful equations relating the maximum allowed number of twisting turns for low excess loss with sample thickness and width are proposed. Bending and twisting measurements on flexible waveguide samples are presented validating these methods and demonstrating the potential of this technology

High-Speed Data Transmission Over Flexible Multimode Polymer Waveguides Under Flexure

Polymer multimode waveguides on flexible substrates enable the formation of bendable low-cost optical interconnects that can be deployed in a wide range of applications. However, the highly-multimoded nature of such guides in combination with the stress and mode mixing induced due to sample bending raise important concerns about the effect that sample flexure has on their bandwidth performance and potential to support high-speed data transmission. In this work therefore, we present data transmission studies on a 1 m long flexible spiral waveguide when flexure is applied. The flexible polymer sample is bent 180° around a cylindrical mandrel and the loss and frequency response of the waveguide are obtained for radii of curvature down to 4 mm and are compared with the performance obtained when no flexure is applied. The BER performance of the respective optical link is also recorded at data rates up to 40 Gb/s. A flat frequency response up to at least 30 GHz is demonstrated for all bending radii applied and error-free (BER<10-12) data transmission is achieved for all data rates studied up to 40 Gb/s. The results clearly demonstrate that sample flexing does not result in any significant transmission impairments in such links and highlight the strong potential of this technology for use in high-speed board-level interconnections.CAPE OIC Future project, CAPE LEASA Projec

The Hubbard model with smooth boundary conditions

We apply recently developed smooth boundary conditions to the quantum Monte Carlo simulation of the two-dimensional Hubbard model. At half-filling, where there is no sign problem, we show that the thermodynamic limit is reached more rapidly with smooth rather than with periodic or open boundary conditions. Away from half-filling, where ordinarily the simulation cannot be carried out at low temperatures due to the existence of the sign problem, we show that smooth boundary conditions allow us to reach significantly lower temperatures. We examine pairing correlation functions away from half-filling in order to determine the possible existence of a superconducting state. On a $10\times 10$ lattice for $U=4$, at a filling of $\langle n \rangle = 0.87$ and an inverse temperature of $\beta=10$, we did find enhancement of the $d$-wave correlations with respect to the non-interacting case, a possible sign of $d$-wave superconductivity.Comment: 16 pages RevTeX, 9 postscript figures included (Figure 1 will be faxed on request

Bend- and Twist-Insensitive Flexible Multimode Polymer Optical Interconnects

Polymer multimode optical waveguides can enable high-speed short-reach optical interconnection at low cost within high performance electronic systems. The formation of such waveguides on flexible substrates can offer important additional advantages such as light weight, ability to be tightly bent, and reconfigurability which are particularly important in environments where space, weight, and shape conformity are critical, for instance in vehicles and aircraft. The ability of such flexible optical interconnects to be tightly bent and twisted with low excess loss is crucial in enabling their use in systems with limited space and with movable parts. As a result, in this work, we present a new design of such flexible polymer multimode waveguides that achieves improved bending loss performance over the conventional waveguide design. It is experimentally shown that the proposed design achieves a very low excess loss of 0.5 dB for a 3 mm radius bend under a 50 µm MMF launch. In comparison, flexible waveguides with the conventional design exhibit a 2 dB excess loss under the same launch and bend conditions. Additionally, useful rules that associate the twisting loss performance of flexible polymer waveguide samples with their geometric characteristics are derived. It is shown that negligible twisting losses (<0.1 dB for a 50 µm MMF input) can be achieved when the dimensions of the waveguide samples are appropriately selected. The results demonstrate the strong potential of such bend- and twist-insensitive flexible polymer waveguides for use in next-generation vehicles and aircraft

HIGH-LEVEL APPLICATION FRAMEWORK FOR LCLS*

each other easily. Also, many components such as Help, A framework for high level accelerator application Search, Cut, Copy and Paste are seamlessly integrated software is being developed for the Linac Coherent Light through the Eclipse framework. Source (LCLS). The framework is based on plug-in technology developed by an open source project, Eclipse. Many existing functionalities provided by Eclipse are available to high-level applications written within this framework. The framework also contains static data storage configuration and dynamic data connectivity. Because the framework is Eclipse-based, it is highly compatible with any other Eclipse plug-ins. The entire infrastructure of the software framework will be presented. Planned applications and plug-ins based on the framework are also presented

75%-efficiency blue generation from an intracavity PPKTP frequency doubler

We report on a high-efficiency 461 nm blue light conversion from an external cavity-enhanced second-harmonic generation of a 922 nm diode laser with a quasi-phase-matched KTP crystal (PPKTP). By choosing a long crystal (LC=20 mm) and twice looser focusing (w0=43 $\mu$m) than the "optimal" one, thermal lensing effects due to the blue power absorption are minimized while still maintaining near-optimal conversion efficiency. A stable blue power of 234 mW with a net conversion efficiency of eta=75% at an input mode-matched power of 310 mW is obtained. The intra-cavity measurements of the conversion efficiency and temperature tuning bandwidth yield an accurate value d33(461 nm)=15 pm/V for KTP and provide a stringent validation of some recently published linear and thermo-optic dispersion data of KTP