Split-gate quantum point contacts with tunable channel length

We report on developing split-gate quantum point contacts (QPCs) that have a tunable length for the transport channel. The QPCs were realized in a GaAs/AlGaAs heterostructure with a two- dimensional electron gas (2DEG) below its surface. The conventional design uses 2 gate fingers on the wafer surface which deplete the 2DEG underneath when a negative gate voltage is applied, and this allows for tuning the width of the QPC channel. Our design has 6 gate fingers and this provides additional control over the form of the electrostatic potential that defines the channel. Our study is based on electrostatic simulations and experiments and the results show that we developed QPCs where the effective channel length can be tuned from about 200 nm to 600 nm. Length-tunable QPCs are important for studies of electron many-body effects because these phenomena show a nanoscale dependence on the dimensions of the QPC channel

Creating space for biodiversity by planning swath patterns and field marging using accurate geometry

Potential benefits of field margins or boundary strips include promotion of biodiversity and farm wildlife, maintaining landscape diversity, exploiting pest predators and parasites and enhancing crop pollinator populations. In this paper we propose and demonstrate a method to relocate areas of sub-efficient machine manoeuvring to boundary strips so as to optimise the use of available space. Accordingly, the boundary strips will have variable rather than fixed widths. The method is being tested in co-operation with seven farmers in the Hoeksche Waard within the province of Zuid Holland, The Netherlands. In a preliminary stage of the project, tests were performed to determine the required accuracy of field geometry. The results confirmed that additional data acquisition using accurate measuring devices is required. In response, a local contracting firm equipped a small all-terrain vehicle (quad) with an RTK-GPS receiver and set up a service for field measurement. Protocols were developed for requesting a field measurement and for the measurement procedure itself. Co-ordinate transformation to a metric system and brute force optimization of swath patterns are achieved using an open source geospatial library (osgeo.ogr) and Python scripting. The optimizer basically tests all orientations and relevant intermediate angles of input field boundaries and tries incremental positional shifts until the most efficient swath pattern is found. Inefficient swaths intersecting boundary areas are deleted to create space for field margins. The optimised pattern can be forwarded to an agricultural navigation system. At the time of the conference, the approach will have been tested on several farm fields

Amylose biosynthesis in potato : interaction between substrate availability and GBSSI activity, regulated at the allelic level = [Amylose biosynthese in aardappel : interactie tussen beschikbaar substraat en KGZ activiteit, gereguleerd op allel niveau]

Besides the role of starch as the primary source of calories in both human and animal diet, it is used as raw material for industrial application such as the paper industry, textile industry, chemical industry, and pharmaceutical industry. Starch isolated for industrial applications, is mainly derived from corn. However in Europe a significant proportion of starch is isolated from potato tubers. Starch consists of two glucose polymers, amylose, which is essentially linear and amylopectin, which is highly branched. Industrially important properties, which are responsible for the functional quality of starch, are highly affected by the ratio of amylose to amylopectin. Therefore, different strategies have been applied to obtain starch with altered amylose content. Mutations leading to the selective loss of amylose have been described in many species, including potato. From the synthesis of amylose-free starch in mutants lacking granule-bound starch synthase I (GBSSI) it is clear that GBSSI is responsible for amylose biosynthesis.The goal of this thesis research was to unravel the amylose biosynthesis in potato and to determine the role and regulation of GBSSI in this process. Therefore amylose biosynthesis was studied in vitro and in vivo . GBSSI, like other starch synthases, catalyses the transfer of a glucose residue from ADP-Glc (donor substrate) to the growingα-1,4 linked glucan (acceptor substrate). This reaction can be studied in vitro by the incubation of purified starch granules, containing the active GBSSI, with radiolabelled ADP-Glc. In this thesis we show a new mechanism for amylose biosynthesis, using amylopectin as acceptor substrate. Transfer of chains from amylopectin to amylose was evidenced from pulse-chase experiments performed with starch isolated from Chlamydomonas and higher plants.To alter the amylose content within the plant, different strategies can be applied. Subtle changes in amylose content, can be obtained by classical breeding. These relatively small changes may significantly improve quality as was shown by the effect of GBSSI on amylose content and noodle quality in wheat. The genetics behind amylose content in potato is described in this thesis. Amylose-free potato starch can be obtained by suppression of GBSSI using antisense technology. The effect of allelic composition on antisense inhibition was shown after analysing a large number of transgenics per variety.The allelic composition of a variety can therefore be used as a selection criterion in breeding programs with the aim to obtain cultivars with altered starch composition.</p

A theory on the vertical dispersal of splash-borne pathogen units influenced by arable crop characteristics

An analytical mechanistic model was proposed to study the vertical spread of splash-borne spores in arable crop canopies. Three crop types were considered, with different LAI distributions. The influences of crop characteristics and rain properties on vertical spread were investigated. The LAI affected the amount of rain being intercepted by the canopy and the vertical displacement of splashed spores. Splash dispersal was concentrated in the upper canopy layers in a crop having LAI constant or increasing with height. Splash probabilities were greatest and most spores were intercepted in the layers just beneath the upper layers in a crop having LAI decreasing with height

Coupling of climate models and ice sheet models by surface mass balance gradients: application to the Greenland Ice Sheet

It is notoriously difficult to couple surface mass balance (SMB) results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature, which is often related to surface elevation (&lt;i&gt;H&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt;). In this study, we propose a new strategy to calculate SMB, to allow a direct adjustment of SMB to a change in ice sheet topography and/or a change in climate forcing. This method is based on elevational gradients in the SMB field as computed by a regional climate model. Separate linear relations are derived for ablation and accumulation, using pairs of &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; and SMB within a minimum search radius. The continuously adjusting SMB forcing is consistent with climate model forcing fields, also for initially non-glaciated areas in the peripheral areas of an ice sheet. When applied to an asynchronous coupled ice sheet – climate model setup, this method circumvents traditional temperature lapse rate assumptions. Here we apply it to the Greenland Ice Sheet (GrIS). Experiments using both steady-state forcing and glacial-interglacial forcing result in realistic ice sheet reconstructions

A theory on the vertical dispersal of splash-borne pathogen units influenced by arable crop characteristics

An analytical mechanistic model was proposed to study the vertical spread of splash-borne spores in arable crop canopies. Three crop types were considered, with different LAI distributions. The influences of crop characteristics and rain properties on vertical spread were investigated. The LAI affected the amount of rain being intercepted by the canopy and the vertical displacement of splashed spores. Splash dispersal was concentrated in the upper canopy layers in a crop having LAI constant or increasing with height. Splash probabilities were greatest and most spores were intercepted in the layers just beneath the upper layers in a crop having LAI decreasing with height

Mapping technique of climate fields between GCM's and ice models

Here, we present a mapping method OBLIMAP, which projects and interpolates fields like surface temperature, surface mass balance, and surface height between a geographical based coordinate system of a General Circulation Model (GCM) and a rectangular based Ice Model (IM). We derive an oblique stereographic projection and its inverse, which holds for any area at the Earth's surface, and which can be combined with two different interpolation methods. The first one is suited to interpolate the projected fields of a coarse GCM grid on a fine meshed IM grid. The second one is appropriate for the opposite case. Both grids are allowed to be arbitrary and irregularly spaced. Therefore the OBLIMAP technique is suitable for any GCM-IM combination. After a first scan of the GCM grid coordinates and the specification of the IM grid, fast mapping of various fields is possible. To and fro (GCM-IM-GCM) mapping tests with the Climate Community System Model (CCSM) at T42 resolution (~313 km) and the Regional Atmospheric Climate Model (RACMO) at ~11 km and ~55 km, show average temperature differences of less than 0.1 K with small standard deviations. OBLIMAP, available at GMD, is an accurate, robust and well-documented mapping method for coupling an IM with a GCM or to map state of the art initial and forcing fields available at geographical coordinates to any local IM grid with an optimal centered oblique projection. Currently, the oblique stereographic and the oblique Lambert azimuthal equal-area projections for both the sphere and the ellipsoid are implemented in OBLIMAP

Effects of heatwaves on lake composition derived from satellite observations

As a consequence of the ever-increasing global temperature, not only the air, and surface, but also lakes are warming up. This is expressed by steadily increasing base temperatures, but also in increases in the frequency and intensity of lake heatwaves. Land-based organisms may adapt to a changing climate by migrating to more suitable habitats, but this is usually not an option for lake-dwellers. Because many livelihoods depend on the ecosystem services of lakes, understanding the effects of heatwaves on lake composition form an important input for the assessment of climate change impacts and design of adaptation strategies.Using satellite data of lake temperature and water quality observations, we here investigate the effects of heatwaves on lake composition by studying the relationship between heatwaves and water quality variables of temperature, chlorophyll-a , colored dissolved organic matter, and suspended particulate matter . The latter can be used to infer effects of heat stress on health and populations of phyto- and zooplankton communities and higher aquatic organisms. Satellite-based data sets provided by the Climate Change Initiative of the European Space Agency, CCI-Lakes (https://climate.esa.int/en/projects/lakes/) are used in conjunction with the 2SeaColor model to determine depth-dependent attenuation coefficients and water quality variables.These data are complemented with and compared to data from Copernicus Global Land Services (https://land.copernicus.eu/global/products/). The co-occurrence of heatwaves and changes in lake composition is investigated using statistical tools, and the causality is examined by comparison with biophysical models. The results from this study are discussed in light of previously published projected changes in heatwave frequency and intensity

Public exhibit for demonstrating the quantum of electrical conductance

We present a new robust setup that explains and demonstrates the quantum of electrical conductance for a general audience and which is continuously available in a public space. The setup allows users to manually thin a gold wire of several atoms in diameter while monitoring its conductance in real time. During the experiment, a characteristic step-like conductance decrease due to rearrangements of atoms in the cross-section of the wire is observed. Just before the wire breaks, a contact consisting of a single atom with a characteristic conductance close to the quantum of conductance can be maintained up to several seconds. The setup is operated full-time, needs practically no maintenance and is used on different educational levels

Big Changes in How Students are Tested

For the past decade, school accountability has relied on tests for which the essential format has remained unchanged. Educators are familiar with the yearly testing routine: schools are given curriculum frameworks, teachers use the frameworks to guide instruction, students take one big test at year’s end which relies heavily upon multiple-choice bubble items, and then school leaders wait anxiously to find out whether enough of their students scored at or above proficiency to meet state standards. All this will change with the adoption of Common Core standards. Testing and accountability aren’t going away. Instead, they are developing and expanding in ways that aim to address many of the present shortcomings of state testing routines. Most importantly, these new tests will be computer-based. As such, they will potentially shorten testing time, increase tests’ precision, and provide immediate feedback to students and teachers