Centrifuge modelling of cone penetration tests in layered soils

Penetration problems are important in many areas of geotechnical engineering, such as the prediction of pile capacity and interpretation of in situ test data. The cone penetration test is a proven method for evaluating soil properties, yet relatively little research has been conducted to understand the effect of soil layering on penetrometer readings. This paper focuses on the penetration of a probe within layered soils and investigates the layered soil effects on both penetration resistance and soil deformation. A series of centrifuge tests was performed in layered configurations of silica sand with varying relative density in a 180° axisymmetric model container. The tests allowed for the use of a half-probe for observation of the induced soil deformation through a poly(methyl methacrylate) window as well as a full-probe for measurement of penetration resistance within the central area of the container. The variations of penetration resistance and soil deformation characteristics as they relate to penetration depth, soil density and soil layering are examined. The results of deformation are also compared with previous experimental data to examine the effect of the axisymmetric condition. The effects of soil layering on both resistance and soil deformation are shown to be dependent on the relative properties between soil layers

Design of an OFDM Physical Layer Encryption Scheme

This paper presents a new encryption scheme implemented at the physical layer of wireless networks employing orthogonal frequency-division multiplexing (OFDM). The new scheme obfuscates the subcarriers by randomly reserving several subcarriers for dummy data and resequences the training symbol by a new secure sequence. Subcarrier obfuscation renders the OFDM transmission more secure and random, whereas training symbol resequencing protects the entire physical layer packet but does not affect the normal functions of synchronization and channel estimation of legitimate users while preventing eavesdroppers from performing these functions. The security analysis shows that the system is robust to various attacks by analyzing the search space using an exhaustive key search. Our scheme is shown to perform better in terms of search space, key rate, and complexity in comparison with other OFDM physical layer encryption schemes. The scheme offers options for users to customize the security level and the key rate according to the hardware resource. Its low complexity nature also makes the scheme suitable for resource-limited devices. Details of practical design considerations are highlighted by applying the approach to an IEEE 802.11 OFDM system case study

Securing Wireless Communications of the Internet of Things from the Physical Layer, An Overview

The security of the Internet of Things (IoT) is receiving considerable interest as the low power constraints and complexity features of many IoT devices are limiting the use of conventional cryptographic techniques. This article provides an overview of recent research efforts on alternative approaches for securing IoT wireless communications at the physical layer, specifically the key topics of key generation and physical layer encryption. These schemes can be implemented and are lightweight, and thus offer practical solutions for providing effective IoT wireless security. Future research to make IoT-based physical layer security more robust and pervasive is also covered

You say you want a data revolution? Taking on food systems accountability

Dramatic improvements in data availability and quality are needed to meet the challenge of monitoring and analyzing food systems, so that appropriate policies and actions to improve human and planetary health can be identified and data-informed accountability mechanisms put in place to strengthen food systems governance. Studying food systems is complex due to diverse actors and interlinking processes that operate on multiple spatial and temporal scales, and their multiple outcomes, which may be subject to hidden feedback mechanisms and tradeoffs. However, descriptive research to characterize food system components and make comparisons across geography, income groups, and population groups is an important foundation. The first part of this article details a series of critical data gaps and limitations that are currently hindering food systems learning and accountability, also comparing these gaps across regions and income groups. The second part of the article introduces the Food Systems Dashboard, a new data visualization tool that aims to improve access to and usage of food systems-related data, thus strengthening the data value chain and better informing policies and actions intended to improve diets, nutrition, livelihoods, and environmental sustainability.1

Methyl CpG Binding Domain Ultra-Sequencing: a novel method for identifying inter-individual and cell-type-specific variation in DNA methylation

Experience-dependent changes in DNA methylation can exert profound effects on neuronal function and behaviour. A single learning event can induce a variety of DNA modifications within the neuronal genome, some of which may be common to all individuals experiencing the event, whereas others may occur in a subset of individuals. Variations in experience-induced DNA methylation may subsequently confer increased vulnerability or resilience to the development of neuropsychiatric disorders. However, the detection of experience-dependent changes in DNA methylation in the brain has been hindered by the interrogation of heterogeneous cell populations, regional differences in epigenetic states and the use of pooled tissue obtained from multiple individuals. Methyl CpG Binding Domain Ultra-Sequencing (MBD Ultra-Seq) overcomes current limitations on genome-wide epigenetic profiling by incorporating fluorescence-activated cell sorting and sample-specific barcoding to examine cell-type-specific CpG methylation in discrete brain regions of individuals. We demonstrate the value of this method by characterizing differences in 5-methylcytosine (5mC) in neurons and non-neurons of the ventromedial prefrontal cortex of individual adult C57BL/6 mice, using as little as 50 ng of genomic DNA per sample. We find that the neuronal methylome is characterized by greater CpG methylation as well as the enrichment of 5mC within intergenic loci. In conclusion, MBD Ultra-Seq is a robust method for detecting DNA methylation in neurons derived from discrete brain regions of individual animals. This protocol will facilitate the detection of experience-dependent changes in DNA methylation in a variety of behavioural paradigms and help identify aberrant experience-induced DNA methylation that may underlie risk and resiliency to neuropsychiatric disease

Discovery of an Ultra-fast X-ray Pulsar in the Supernova Remnant N157B

We present the serendipitous discovery of 16 ms pulsed X-ray emission from the Crab-like supernova remnant N157B in the Large Magellanic Cloud. This is the fastest spinning pulsar associated with a supernova remnant (SNR). Observations with the Rossi X-ray Timing Explorer (RXTE), centered on the field containing SN1987A, reveal an X-ray pulsar with a narrow pulse profile. Archival ASCA X-ray data confirm this detection and locate the pulsar within 1' of the supernova remnant N157B, 14' from SN1987A. The pulsar manifests evidence for glitch(es) between the RXTE and ASCA observations which span 3.5 years; the mean linear spin-down rate is Pdot = 5.126 X 10E-14 s/s. The background subtracted pulsed emission is similar to other Crab-like pulsars with a power law of photon index of ~ 1.6. The characteristic spin-down age (~ 5000 years) is consistent with the previous age estimate of the SNR. The inferred B-field for a rotationally powered pulsar is ~ 1 X 10E12 Gauss. Our result confirms the Crab-like nature of N157B; the pulsar is likely associated with a compact X-ray source revealed by ROSAT HRI observations.Comment: 9 pages with 3 eps figure, LaTex (aas2pp2, psfig). Submitted to the Astrophysical Journal Letter

Structure formation in a colliding flow: The Herschel view of the Draco nebula

The Draco nebula is a high Galactic latitude interstellar cloud likely to have been formed by the collision of a Galactic halo cloud entering the disk of the Milky Way. Such conditions are ideal to study the formation of cold and dense gas in colliding flows of warm gas. We present Herschel-SPIRE observations that reveal the fragmented structure of the interface between the infalling cloud and the Galactic layer. This front is characterized by a Rayleigh-Taylor instability structure. From the determination of the typical length of the periodic structure (2.2 pc) we estimated the gas kinematic viscosity and the turbulence dissipation scale (0.1 pc) that is compatible with that expected if ambipolar diffusion is the main mechanism of energy dissipation in the WNM. The small-scale structures of the nebula are typical of that seen in some molecular clouds. The gas density has a log-normal distribution with an average value of $10^3$ cm$^{-3}$. The size of the structures is 0.1-0.2 pc but this estimate is limited by the resolution of the observations. The mass ranges from 0.2 to 20 M$_{\odot}$ and the distribution of the more massive clumps follows a power law $dN/d\log(M) \sim M^{-1.4}$. We identify a mass-size relation with the same exponent as that found in GMCs ($M\sim L^{2.3}$) but only 15% of the mass of the cloud is in gravitationally bound structures. We conclude that the increase of pressure in the collision is strong enough to trigger the WNM-CNM transition caused by the interplay between turbulence and thermal instability as self-gravity is not dominating the dynamics.Comment: 16 pages, A&A, in pres