Philips (United Kingdom)

Ballistic point contacts, defined in the two-dimensional electron gas of a GaAs-AlGaAs heterostructure, have been studied in zero magnetic field. The conductance changes in quantized steps of ${e}^{2}$/\ensuremath{\pi}\ensuremath{\Elzxh} when the width, controlled by a gate on top of heterojunction, is varied. Up to sixteen steps are observed when the point contact is widened from 0 to 360 nm. An explanation is proposed, which assumes quantized transverse momentum in the point-contact region.

The Vivaldi Aerial is a new member of the class of aperiodic continuously scaled antenna structures and, as such, it has theoretically unlimited instantaneous frequency bandwidth. This aerial has significant gain and linear polarisation and can be made to conform to a constant gain vs. frequency performance. One such design has been made with approximately 10 dBI gain and -20 dB sidelobe level over an instantaneous frequency bandwidth extending from below 2 GHz to above 40 GHz.

Frequency modulated continuous wave (FMCW) radar uses a very low probability of intercept waveform, which is also well suited to make good use of simple solid-state transmitters. FMCW is finding applications in such diverse fields as naval tactical navigation radars, smart ammunition sensors and automotive radars. The paper discusses some features of FMCW radar which are not dealt with in much detail in the generally available literature. In particular, it discusses the effects of noise reflected back from the transmitter to the receiver and the application of moving target indication to FMCW radars. Some of the strengths and weaknesses of FMCW radar are considered. The paper describes how the strengths are utilised in some systems and how the weaknesses can be mitigated. It also discusses a modern implementation of a reflected power canceller, which can be used to suppress the leakage between the transmitter and the receiver, a well known problem with continous wave radars.

Results are presented of an investigation on the origin of the low temperature coefficient of resistance in NiCr thin films. It is shown that this low temperature coefficient is an intrinsic property of the alloy. Besides NiCr a large number of disordered alloys containing transition metals have similar conduction properties, both in bulk and as a thin film. For these materials a correlation has been found between the resistivity and its temperature coefficient. These anomalous conduction properties are probably caused by the very small electron mean free path in these materials. Ergebnisse einer Untersuchung des Ursprungs des niedrigen Temperaturkoeffizienten des Widerstands in dünnen NiCr-Schichten werden mitgeteilt. Es wird gezeigt, daß dieser niedrige Temperaturkoeffizient eine Materialeigenschaft der Legierung ist. Neben NiCr besitzen eine große Zahl von fehlgeordneten Legierungen mit Übergangsmetallen ähnliche Leitfähigkeitseigenschaften, sowohl im Volumen als auch als dünne Schicht. Für diese Materialien wurde ein Zusammenhang zwischen dem Widerstand und seinem Temperaturkoeffizienten gefunden. Diese anomalen Leitfähigkeitseigenschaften werden wahrscheinlich durch die sehr kleine mittlere freie Weglänge der Elektronen in diesen Materialien verursacht.

A model based on Rayleigh–Gans–Debye light‐scattering theory has been developed to describe the light transmission properties of fine‐grained, fully dense, polycrystalline ceramics consisting of birefringent crystals. This model extends light transmission models based on geometrical optics, which are valid only for coarse‐grained microstructures, to smaller crystal sizes. We verify our model by measuring the light transmission properties of fully dense (>99.99%), polycrystalline α‐Al 2 O 3 (PCA) with mean crystal sizes ranging from 60 to 0.3 μm. The remarkable transparency exhibited by PCA samples with small crystal sizes (<2 μm) is well explained by this model.

By means of a detailed x-ray study of a large number of oxides having a spinel structure, it has been established whether they crystallize in the ``normal'' spinel-type structure, XY2O4, or in the ``inversed'' type of structure, Y(XY)O4, discovered by Barth and Posnjak. Certain rules can be derived which are also applicable to more complicated spinels or to solid solutions of different spinel oxides. Madelung constants have been calculated for different spinel types in order to investigate their stability on the basis of an ionic concept of the chemical bond (Born's lattice theory). The experimental results are only partially explainable on this basis. All exceptions to the electrostatic principles can be understood by assuming that Fe3+, Ga3+, In3+, Zn2+, and Cd2+ favor a configuration having the coordination number 4, because of a considerable covalent contribution to the chemical bond for that configuration.

16th International Symposium on Metal - Hydrogen Systems, Guangzhou / China, 28 Oct - 2 Nov 2018 (oral); MH2018: Abstract ID 300

In dynamic magnetic resonance imaging (MRI) studies, the motion kinetics or the contrast variability are often hard to predict, hampering an appropriate choice of the image update rate or the temporal resolution. A constant azimuthal profile spacing (111.246 degrees), based on the Golden Ratio, is investigated as optimal for image reconstruction from an arbitrary number of profiles in radial MRI. The profile order is evaluated and compared with a uniform profile distribution in terms of signal-to-noise ratio (SNR) and artifact level. The favorable characteristics of such a profile order are exemplified in two applications on healthy volunteers. First, an advanced sliding window reconstruction scheme is applied to dynamic cardiac imaging, with a reconstruction window that can be flexibly adjusted according to the extent of cardiac motion that is acceptable. Second, a contrast-enhancing k-space filter is presented that permits reconstructing an arbitrary number of images at arbitrary time points from one raw data set. The filter was utilized to depict the T1-relaxation in the brain after a single inversion prepulse. While a uniform profile distribution with a constant angle increment is optimal for a fixed and predetermined number of profiles, a profile distribution based on the Golden Ratio proved to be an appropriate solution for an arbitrary number of profiles.

Most consumer electronics today contain embedded software. In the early days, developing CE software presented relatively minor challenges, but in the past several years three significant problems have arisen: size and complexity of the software in individual products; the increasing diversity of products and their software; and the need for decreased development time. The question of handling diversity and complexity in embedded software at an increasing production speed becomes an urgent one. The authors present their belief that the answer lies not in hiring more software engineers. They are not readily available, and even if they were, experience shows that larger projects induce larger lead times and often result in greater complexity. Instead, they believe that the answer lies in the use and reuse of software components that work within an explicit software architecture. The Koala model, a component-oriented approach detailed in this article, is their way of handling the diversity of software in consumer electronics. Used for embedded software in TV sets, it allows late binding of reusable components with no additional overhead.

The relations between the electronic conductivity of certain spinels and the arrangement of the cations in the crystal structure (see preceding paper) are studied. Several arguments favor the assumption that Fe3O4 contains both divalent and trivalent iron in the 16-fold position. The transition point in the neighborhood of liquid-air temperature is probably associated with an increased degree of order at low temperature in the distribution of the 8 electrons between the 16 Fe-lattice points per unit cell. The considerably increased conductivity below the transition points shows tetragonal anisotropy when the crystal is cooled in a magnetic field. The possible distributions of the electrons in the crystal at low temperature are discussed. In more complicated spinels, containing other metal atoms as well as iron in both the divalent and the trivalent state, the electronic interchange is more or less inhibited by the foreign metal atoms. The higher values of their resistance in comparison to that of Fe3O4 can be roughly described by an increased activation energy. The investigation of a number of substances with different arrangements of the cations shows that the activation energy (and therefore the electrical resistance) is lowest for those cases in which the electrons can travel, as in Fe3O4, along the Fe of the 16-fold position.

The ongoing longitudinal Adverse Childhood Experiences Study of adults has found significant associations between chronic conditions; quality of life and life expectancy in adulthood; and the trauma and stress associated with adverse childhood experiences, including physical or emotional abuse or neglect, deprivation, or exposure to violence. Less is known about the population-based epidemiology of adverse childhood experiences among US children. Using the 2011-12 National Survey of Children's Health, we assessed the prevalence of adverse childhood experiences and associations between them and factors affecting children's development and lifelong health. After we adjusted for confounding factors, we found lower rates of school engagement and higher rates of chronic disease among children with adverse childhood experiences. Our findings suggest that building resilience-defined in the survey as "staying calm and in control when faced with a challenge," for children ages 6-17-can ameliorate the negative impact of adverse childhood experiences. We found higher rates of school engagement among children with adverse childhood experiences who demonstrated resilience, as well as higher rates of resilience among children with such experiences who received care in a family-centered medical home. We recommend a coordinated effort to fill knowledge gaps and translate existing knowledge about adverse childhood experiences and resilience into national, state, and local policies, with a focus on addressing childhood trauma in health systems as they evolve during ongoing reform.

Abstract In this paper an attempt is made to establish the nature of free charge carriers and of charge carriers bound to centres in p-type NiO, CoO and MnO and in n-type MnO and α-Fe2O3. For free charge carriers, d.c. conductivity, Seebeck coefficient and Hall effect are considered. Effects arising from inhomogeneous conduction and impurity conduction are discussed. Impurity conduction appears to have a strong influence on transport properties in the case of α-Fe2O3, less so in NiO, whereas no influence of this effect has been found in CoO and MnO. It is shown that NiO and CoO do not exhibit the features characteristic of small-polaron conductors but rather can be consistently conceived of as large-polaron band semiconductors. It is suggested that magnetic resistance due to exchange coupling between charge-carrier spin and cation spins plays an important role. The anomalous behaviour of the Hall effect in NiO and α-Fe2O3 is extensively discussed. In contradistinction to NiO, CoO and n-type MnO, free charge carriers in p-type MnO seem to have small-polaron character. For charge carriers bound to centres, dielectric loss, high-frequency conduction and optical absorption are considered. The dielectric loss data relate to Li or Na centres in NiO, CoO and MnO and to Ti, Zr, Sn, Ta, Nb and presumably oxygen vacancy centres in α-Fe2O3. It is concluded from the dependence of dielectric loss on frequency and temperature that bound charge carriers are small polarons. It is shown for the cases of NiO and α-Fe2O3 that apart from small-polaron effects, disorder due to locally varying electric fields determines the nature of dielectric loss. The small-polaron character of bound charge carriers in NiO is corroborated by the behaviour of high-frequency conduction and optical absorption due to centres and also by the magnitude of impurity conduction.

Gives a critical review of idealised two-phase geometrical models. These treatments derive expressions for the resistivity and Hall coefficient of a composite material in terms of the properties of its constituents. The authors show that these models can be applied to the interpretation of transport measurements in polycrystalline films and powder layers. Important distinctions are made depending on whether the depletion layers extend completely or partially through the grains, whether the Debye length is greater or less than the grain size and whether the mean free path is greater or less than the grain size. The authors discuss the theoretical treatment of the Hall effect in percolative systems, as geometrical models neglect percolation. The modulation of Hall coefficient and conductivity by illumination and the adsorption and desorption of ambient gases are also considered.

(1927). VII. Forced oscillations in a circuit with non-linear resistance. (Reception with reactive triode) The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 3, No. 13, pp. 65-80.

We have observed a quantized current in a lateral quantum dot, defined by metal gates in the two-dimensional electron gas (2DEG) of a GaAs/AlGaAs heterostructure. By modulating the tunnel barriers in the 2DEG with two phase-shifted rf signals, and employing the Coulomb blockade of electron tunneling, we produced quantized current plateaus in the current-voltage characteristics at integer multiples of ef, where f is the rf frequency. This demonstrates that an integer number of electrons pass through the quantum dot each rf cycle.

Current management guidelines for the treatment of patients with Parkinson's disease (PD) are limited due to the lack of knowledge of factors that influence health-related quality of life (HRQL). To assess the HRQL of people with PD, and to systematically identify and evaluate those factors (other than disease severity and medication, which could have an impact), we undertook a cross-sectional, randomized selection, multicenter international survey of patients with PD, caregivers, and clinicians. Face-to-face interviews were conducted with subjects in six countries. Disease severity, medication, and other factors hypothesized to influence HRQL were assessed using a combination of specially developed questionnaires and validated instruments including the Parkinson's Disease Questionnaire-39 (HRQL), Hoehn and Yahr Stage (disease severity), and Beck's Depression Inventory (BDI; depression). Multiple linear regression models were used to demonstrate whether the factors investigated contribute significantly to HRQL. The results obtained indicated that Hoehn and Yahr stage and medication explained only 17.3% of the variability in HRQL of patients with PD, although both were significant (R(2) = 0.173, P < 0.05). Other factors increased the explanatory power to adjusted R(2) = 0.597, with BDI being the most significant predictor of variability in HRQL (adjusted R(2) = 0.582; P < 0.001), followed by "Satisfaction with the explanation of the condition at diagnosis" and "Current feelings of optimism" (both P < 0.05). These factors, in addition to disease severity and medication, explain 59.7% of the variability in HRQL across the population. In conclusion, depression (as measured by the BDI) in PD, "satisfaction with the explanation of the condition at diagnosis" and "current feelings of optimism" have a significant impact on HRQL. The completion of this initial analysis is the first step towards developing management guidelines that truly influence the HRQL of patients with PD.

The advantages of using multi-quantum-well or superlattice systems as the absorbers in concentrator solar cells are discussed. By adjusting the quantum-well width, an effective band-gap variation that covers the high-efficiency region of the solar spectrum can be obtained. Higher efficiencies should result from the ability to optimize separately current and voltage generating factors. Suitable structures to ensure good carrier separation and collection and to obtain higher open-circuit voltages are presented using the (AlGa)As/GaAs/(InGa)As system. Efficiencies above existing single-band-gap limits should be achievable, with upper limits in excess of 40%.

Locking down the SARS-CoV-2 spike Many efforts to develop therapies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are focused on the spike (S) protein trimer that binds to the host receptor. Structures of trimeric S protein show its receptor-binding domain in either an up or a down conformation. Toelzer et al. produced SARS-CoV-2 S in insect cells and determined the structure by cryo–electron microscopy. In their dataset, the closed form was predominant and was stabilized by binding linoleic acid, an essential fatty acid. A similar binding pocket appears to be present in previous highly pathogenic coronaviruses, and past studies suggested links between viral infection and fatty acid metabolism. The pocket could be exploited to develop inhibitors that trap S protein in the closed conformation. Science , this issue p. 725

Abstract Worldwide, most sea cucumber fisheries are ineffectively managed, leading to declining stocks and potentially eroding the resilience of fisheries. We analyse trends in catches, fishery status, fishing participation and regulatory measures among 77 sea cucumber fisheries through data from recent fishery reports and fishery managers. Critical gaps in fisheries biology knowledge of even commonly targeted species undermine the expected success of management strategies. Most tropical fisheries are small‐scale, older and typified by numerous (&gt;8) species, whereas temperate fisheries are often emerging, mono‐specific and industrialized. Fisher participation data indicated about 3 million sea cucumber fishers worldwide. Fisher participation rates were significantly related to the average annual yield. permanova analysis showed that over‐exploited and depleted fisheries employed different sets of measures than fisheries with healthier stocks, and a non‐metric multidimensional scaling ordination illustrated that a broad set of regulatory measures typified sustainable fisheries. SIMPER and regression tree analyses identified that the dissimilarity was most related to enforcement capacity, number of species harvested, fleet (vessel) controls, limited entry controls and rotational closures. The national Human Development Index was significantly lower in countries with over‐exploited and depleted fisheries. Where possible, managers should limit the number of fishers and vessel size and establish short lists of permissible commercial species in multispecies fisheries. Our findings emphasize an imperative to support the enforcement capacity in low‐income countries, in which risk of biodiversity loss is exceptionally high. Solutions for greater resilience of sea cucumber stocks must be embedded within those for poverty reduction and alternative livelihood options.

The basic physics underlying the operation and key performance issues of amorphous-silicon thin-film transistors (TFTs) are discussed. The static transistor characteristics are determined by the localized electronic states that occur in the bandgap of the amorphous silicon. The deep states, mostly consisting of Si dangling bonds, determine the threshold voltage, and the conduction band-tail states determine the field-effect mobility. The finite capture and emission times of the deep localized states lead to a dynamic transistor characteristic that can be described by a time-dependent threshold voltage. The transistors also show longer time threshold voltage shifts due to two other distinct mechanisms: charge trapping in the silicon nitride gate insulator and metastable dangling bond state creation in the amorphous silicon. These two mechanisms show characteristically different bias, temperature, and time dependencies of the threshold voltage shift. Illumination of a TFT causes the generation of electron-hole pairs in the space-charge region leading to a steady-state equal flux of electrons and holes and a reduction in the band-bending. In most applications, the photosensitivity should be minimized. The uniformity of large arrays of transistors for display applications is excellent, with variations in the threshold voltage of 0.5-1.0 V.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>