Semiconducting-to-metallic photoconductivity crossover and temperature-dependent Drude weight in graphene

We investigated the transient photoconductivity of graphene at various gate-tuned carrier densities by optical-pump terahertz-probe spectroscopy. We demonstrated that graphene exhibits semiconducting positive photoconductivity near zero carrier density, which crosses over to metallic negative photoconductivity at high carrier density. Our observations are accounted for by considering the interplay between photo-induced changes of both the Drude weight and the carrier scattering rate. Notably, we observed multiple sign changes in the temporal photoconductivity dynamics at low carrier density. This behavior reflects the non-monotonic temperature dependence of the Drude weight, a unique property of massless Dirac fermions

Shielding effectiveness of original and modified building materials

This contribution deals with the determination of the shielding effectiveness of building materials used for office, factory and government buildings. Besides the examination of standard materials, measurements were also performed on modified materials, e.g. ferro concrete with enhanced shielding effectiveness due to a changed mixture or structure of the reinforcement. The measurements of original and modified materials were carried out in a fully anechoic room (FAR) according to IEEE 299-1997 from 80 MHz up to 10 GHz

Supply Current Diagnosis in VLSI

This paper presents a technique based upon the power supply current signature (cd) which allows for the testing of mixed-signal systems, in situ. Through experiments with a microprocessor, the cd is shown to contain important information concerning the operational status of the system which may be easily extracted using approaches based on statistical signal detection theory. The fault-detection performance of these techniques is compared to that achieved through auto-regressive modeling of the cd

Nanostructure and crystallography of aberrant columnar vaterite in Corbicula fluminea (Mollusca)

Both the crystallographic and nanostructural organisation of aberrant columnar vaterite occurring in \ud C. fluminea were characterised in detail for the first time using electron microscopic and x-ray \ud powder diffraction techniques. At the millimetre scale, only a confinement of the otherwise \ud randomly oriented c-axis to the growth surface is observed. Domains of one hundred or more \ud individual vaterite columns with common c-axis orientation exist within this disordered material. \ud Each column behaves as a single crystal on the scale of EBSD measurements, but is internally \ud composed of smaller (0.3 – 1.3 μm in dimension) irregularly shaped and slightly misaligned \ud crystalline units. These are in turn partitioned by porous boundaries into rounded nanodomains, up \ud to 600 nm in size. The geometry of the nanodomains and their respective boundaries might suggest \ud formation by the accretion of vesicles. In addition to crystallographic textures, this observation \ud indicates formation under significant biological control with wider implications for possible causes \ud of the condition

The rise of (Chiral) 3D mechanical metamaterials

On the occasion of this special issue, we start by briefly outlining some of the history and future perspectives of the field of 3D metamaterials in general and 3D mechanical metamaterials in particular. Next, in the spirit of a specific example, we present our original numerical as well as experimental results on the phenomenon of acoustical activity, the mechanical counterpart of optical activity. We consider a three-dimensional chiral cubic mechanical metamaterial architecture that is different from the one that we have investigated in recent early experiments. We find even larger linear-polarization rotation angles per metamaterial crystal lattice constant than previously and a slower decrease of the effects towards the bulk lim

AFTER FURTHER REVIEW: AN UPDATE ON MODELING AND DESIGN STRATEGIES FOR AGRICULTURAL DOSE-RESPONSE EXPERIMENTS

Research investigating dose-response relationships is common in agricultural science. This paper is an expansion on previous work by Guo, et al. (2006) motivated by plant nutrition research in horticulture. Plant response to level of nutrient applied is typically sigmoidal, i.e. no response at very low levels, observable response at mid-levels, point-of-diminishing returns and plateau at high levels. Plant scientists need accurate estimates of these response relationships for many reasons, including determining the lower threshold below which plants show deficiency symptoms and the point of diminishing returns, above which excessive doses are economically and environmentally costly. Guo et al. presented models and designs that address these requirements and a simulation study to assess and compare the small-sample behavior of these models and designs. This paper expands on that simulation study. In addition, a simulation study based procedure for exploring designs for experimental scenarios fitting this description is presented. This simulation study approach utilizes simulation based fit statistics in conjunction with various lack-of-fit plots to produce a design robust to multiple candidate models

Training product unit neural networks with genetic algorithms

The training of product neural networks using genetic algorithms is discussed. Two unusual neural network techniques are combined; product units are employed instead of the traditional summing units and genetic algorithms train the network rather than backpropagation. As an example, a neural netork is trained to calculate the optimum width of transistors in a CMOS switch. It is shown how local minima affect the performance of a genetic algorithm, and one method of overcoming this is presented

Hydrogen bonding and charge transport in a protic polymerized ionic liquid

Hydrogen bonding and charge transport in the protic polymerized ionic liquid poly[tris(2-(2-methoxyethoxy)ethyl)ammoniumacryloxypropyl sulfonate] (PAAPS) are studied by combining Fourier transform infrared (FTIR) and broadband dielectric spectroscopy (BDS) in a wide temperature range from 170 to 300 K. While the former enables to determine precisely the formation of hydrogen bonds and other moiety-specific quantized vibrational states, the latter allows for recording the complex conductivity in a spectral range from 10−2 to 10+9  Hz. A pronounced thermal hysteresis is observed for the H-bond network formation in distinct contrast to the reversibility of the effective conductivity measured by BDS. On the basis of this finding and the fact that the conductivity changes with temperature by orders of magnitude, whereas the integrated absorbance of the N–H stretching vibration (being proportional to the number density of protons in the hydrogen bond network) changes only by a factor of 4, it is concluded that charge transport takes place predominantly due to hopping conduction assisted by glassy dynamics (dynamic glass transition assisted hopping) and is not significantly affected by the establishment of H-bonds

Intra-cell dynamics and cyclotron motion without magnetic field

Intra-cell motion endows rich non-trivial phenomena to a wide variety of quantum materials. The most prominent example is a transverse current in the absence of a magnetic field (i.e. the anomalous Hall effect). Here we show that, in addition to a dc Hall effect, anomalous Hall materials possess circulating currents and cyclotron motion without magnetic field. These are generated from the intricate wavefunction dynamics within the unit cell, and correspond to interband transitions (coherences) in much the same way that cyclotron resonances arise from inter-Landau level transitions in magneto-optics. Curiously, anomalous cyclotron motion exhibits an intrinsic decay in time (even in pristine materials) displaying a characteristic power law decay. This reveals an intrinsic dephasing similar to that of inhomogeneous broadening of spinors. Circulating currents can manifest as the emission of circularly polarized light pulses in response to incident linearly polarized (pulsed) electric field, and provide a direct means of interrogating the intra-unit-cell dynamics of quantum materials

“No Matter I’ll Be Selected; in the Next Challenge I Will Be Better!” – Understanding Non-Technical Skill Development in the Gig Economy

While prior research on gig work environments studied necessary technical skills for information systems development (ISD) professionals and how they can be developed, the improvement of non-technical skills (NTS) has been rarely explored. However, to successfully engage in the gig work economy, the need for strong NTS is increasing. Based on an experiential learning theory (ELT) perspective, we explore how ISD professionals engaging in the gig economy develop NTS by following grounded theory methodology. Our results are threefold: first, we identify crucial NTS for gig workers. Second, we uncover how these NTS are developed in different phases of adapting to working on gig economy platforms. Third, we reveal several strategies for thriving in the gig economy. Based on our findings we develop a process model of non-technical skill development and discuss this model in relation to implications for gig economy literature and practice