Economic structure, productivity, and infrastructure quality in southern Mexico

There are large and sustained differences in the economic performance of sub-national regions in most countries. The authors examine the economic structure and productivity in Southern Mexico and compare it with the rest of the country. The authors use firm level data from Mexican manufacturing to test the relative importance of firm level characteristics (such as human capital and technology adoption) compared with external characteristics (such as infrastructure quality and regulatory environment) in explaining productivity differentials. The authors find that the economic structure of Southern Mexico is considerably different from the rest of the country, with the economic landscape dominated by micro enterprises and a relative specialization in low productivity activities. This, coupled with low skill levels and fewer skill upgrading opportunities, reduces the performance of Southern firms. Productivity differentials between Southern firms and others, however, only exist for micro enterprises. The econometric analysis shows that while employee training and technology adoption enhance productivity, access to markets by improving transport infrastructure that link urban areas also have important productivity effects.Labor Policies,Economic Theory&Research,Municipal Financial Management,Environmental Economics&Policies,Banks&Banking Reform,Environmental Economics&Policies,Economic Theory&Research,Banks&Banking Reform,Municipal Financial Management,Microfinance

Crystalline optical cavity at 4 K with thermal noise limited instability and ultralow drift

Crystalline optical cavities are the foundation of today's state-of-the-art ultrastable lasers. Building on our previous silicon cavity effort, we now achieve the fundamental thermal noise-limited stability for a 6 cm long silicon cavity cooled to 4 Kelvin, reaching $6.5\times10^{-17}$ from 0.8 to 80 seconds. We also report for the first time a clear linear dependence of the cavity frequency drift on the incident optical power. The lowest fractional frequency drift of $-3\times10^{-19}$/s is attained at a transmitted power of 40 nW, with an extrapolated drift approaching zero in the absence of optical power. These demonstrations provide a promising direction to reach a new performance domain for stable lasers, with stability better than $1\times10^{-17}$ and fractional linear drift below $1\times10^{-19}$/s

VLBI Monitoring of 3C 84 (NGC 1275) in Early Phase of the 2005 Outburst

Multi-epoch Very Long Baseline Interferometry (VLBI) study of the sub-pc scale jet of 3C 84 is presented. We carried out 14-epoch VLBI observations during 2006-2009 with the Japanese VLBI Network (JVN) and the VLBI Exploration of Radio Astrometry (VERA), immediately following the radio outburst that began in 2005. We confirmed that the outburst was associated with the central ~1 pc core, accompanying the emergence of a new component. This is striking evidence of the recurrence of jet activity. The new component became brighter during 2008, in contrast to the constant gamma-ray emission that was observed with the Fermi Gamma-ray Space Telescope during the same time. We found that the projected speed of the new component is 0.23c from 2007/297 (2007 October 24) to 2009/114 (2009 April 24). The direction of movement of this component differs from that of the pre-existing component by ~40 degree. This is the first measurement of kinematics of a sub-pc jet in a gamma-ray active phase. Possible detection of jet deceleration and the jet kinematics in connection with the gamma-ray emission is discussed.Comment: 5 pages, 3 figures. Accepted for publication in PAS

The linear instability of the stratified plane Poiseuille flow

International audienceIn the non stratified case, plane Poiseuille flow is known to be linearly unstable for Reynolds numbers larger than 5572. Above this value, two dimensional waves-known as Tollmien-Schlichting waves-are viscously unstable and can propagate in the flow.We present here the stability analysis of a plane Poiseuille flow which is stably stratified in density along the vertical direction, i.e. orthogonal to the horizontal shear. Density stratification is ubiquitous in nature and we may think here to water flows in submarine canyons, to winds in valleys or to laminar flows in rivers or canals where stratification can be due to temperature or salinity gradients. Our study is based on laboratory experiments, on a linear stability analysis and on direct numerical simulations. This study follows recent investigations of instabilities in stratified rotating or non rotating shear flows: the stratorotational instability [1,2], the stratified boundary layer instability [3] or the stratified Plane Couette flow instability [4] where it is shown that these instabilities belong to a class of instabilities caused by the resonant interaction of Doppler shifted internal gravity waves. A particularity of the present case is that for the Poiseuille flow, Tollmien-Schlichting waves can also interact and possibly resonate with non viscous gravity waves. The experiments are realized in an annular channel having an inner diameter of 1.4 m and a rectangular vertical section of 85 x 200 mm 2. This channel is filled up to a level of 130 mm (position of the free surface) with salt stratified water using the classical double bucket technique. The free surface fluid is then entrained by the side and bottom walls of the canal when this one is set into slow rotation. However, a barrier, placed radially inside the channel, blocks the fluid, prohibiting solid body rotation and resulting in a nearly parabolic horizontal velocity profile. Visualizations and PIV measurements show the appearance of a stationary (versus the laboratory frame) braided pattern of waves above a given threshold that depends on the Reynolds and Froude numbers (Re c ∼ 2000, F r c ∼ 0.5). The comparison with the theoretical threshold and the critical wavenumbers calculated by linear analysis is excellent. Finally, direct numerical simulations permit to complete the description of this instability that can be interpreted as a resonant interaction of boundary trapped waves

Three-terminal resistive switch based on metal/metal oxide redox reactions

A solid-state three-terminal resistive switch based on gate-voltage-tunable reversible oxidation of a thin-film metallic channel is demonstrated. The switch is composed of a cobalt wire placed under a GdOx layer and a Au top electrode. The lateral resistance of the wire changes with the transition between cobalt and cobalt oxide controlled by a voltage applied to the top electrode. The kinetics of the oxidation and reduction process are examined through time- and temperature-dependent transport measurements. It is shown that that reversible voltage induced lateral resistance switching with a ratio of 10 3 can be achieved at room temperature. The reversible non-volatile redox reaction between metal and metal oxide may provide additional degrees of freedom for post-fabrication control of properties of solid-state materials. This type of three-terminal device has potential applications in neuromorphic computing and multilevel data storage, as well as applications that require controlling a relatively large current.National Science Foundation (U.S.) (Grant DMR-1419807

Engineering Blockchain Based Software Systems: Foundations, Survey, and Future Directions

Many scientific and practical areas have shown increasing interest in reaping the benefits of blockchain technology to empower software systems. However, the unique characteristics and requirements associated with Blockchain Based Software (BBS) systems raise new challenges across the development lifecycle that entail an extensive improvement of conventional software engineering. This article presents a systematic literature review of the state-of-the-art in BBS engineering research from a software engineering perspective. We characterize BBS engineering from the theoretical foundations, processes, models, and roles and discuss a rich repertoire of key development activities, principles, challenges, and techniques. The focus and depth of this survey not only gives software engineering practitioners and researchers a consolidated body of knowledge about current BBS development but also underpins a starting point for further research in this field

Graphene Q-switched Yb:KYW planar waveguide laser

A diode-pumped Yb:KYW planar waveguide laser, single-mode Q-switched by evanescent-field interaction with graphene, is demonstrated for the first time. Few-layer graphene grown by chemical vapor deposition is transferred onto the top of a guiding layer, which initiates stable Q-switched operation in a 2.4-cm-long waveguide laser operating near 1027 nm. Average output powers up to 34 mW and pulse durations as short as 349 ns are achieved. The measured output beam profile, clearly exhibiting a single mode, agrees well with the theoretically calculated mode intensity distribution inside the waveguide. As the pump power is increased, the repetition rate and pulse energy increase from 191 to 607 kHz and from 7.4 to 58.6 nJ, respectively, whereas the pulse duration decreases from 2.09 μs to 349 ns