Narrow Results

A novel approach for cascade diode lasers was developed based on type-I quantum wells (QWs). This design adopted the leaky window effect in the GaSb/InAs band alignment for cascade pumping, and exploits the carriers recycling by the cascade pumping and the high optical gain of the type-I QWs. Two-stage cascade lasers were designed and fabricated for 2.45 and 3.0 μm, demonstrating twofold improvement in the internal efficiency. Record continuous-wave (CW) output power of 1.2 W for 2.45 um and 590 mW for 3.0 um were achieved in room temperature (RT), and the devices operate with higher power conversion efficiency at high power level, compared to conventional single-stage diode lasers.

For the complex networks, including scale-free, small-world, local-world and random networks, the global quantitative evaluation of attack-induced cascade is investigated in this paper by introducing the risk assessment, which integrates the probability of occurrence with the damage size of attacks on nodes. It is discovered by simulations, among the several kinds of networks, that the small-world network has the largest risk assessment of attack-induced cascade; the risk assessment of three other networks are all very low and the most protection against attack should be given to the small-world network accordingly. Furthermore, the percentage of the most fragile nodes in the scale-free network is very low, compared with that in the small-world network.

Why does diffusion sometimes show cascade phenomena but at other times is impeded? In addressing this question, we considered a threshold model of diffusion, focusing on the formation of a critical mass, which enables diffusion to be self-sustaining. Performing an agent-based simulation, we found that the diffusion model produces only two outcomes: Almost perfect adoption or relatively few adoptions. In order to explain the difference, we considered the various properties of network structures and found that the manner in which thresholds are arrayed over a network is the most critical factor determining the size of a cascade. On the basis of the results, we derived a threshold arrangement method effective for generation of a critical mass and calculated the size required for perfect adoption.

A diffusion cascade occurs when information spreads from one node to the rest of the network through a succession of diffusion events. So far diffusion phenomena have been mostly considered at a macroscopic scale i.e. by studying all nodes of the network. We give a complementary way to analyse network interactions by considering the problem at different scales. To that purpose, we use the community structure of the network to characterize diffusion between nodes (and between communities) and to identify interactions behaviour patterns.

The spectral distribution of positron created by photon and the spectral distribution of photons radiated from electron in an oriented single crystal of intermediate thickness is calculated at intermediate energies. The energy loss of charged particles as well as photon absorption are taken into account. The used basic probabilities of processes include the action of field of axis as well as the multiple scattering of radiating electron or particles of the created pair (the Landau-Pomeranchuk-Migdal (LPM) effect).

This paper reviews our recent work on the synchronization of excitable systems in a master–slave configuration and when the slave system includes a delayed self-coupling term. Particularly, we address the existence of the so-called anticipated synchronization, i.e. a dynamical regime in which the slave system is able to reproduce in advance the evolution of the master. This is most remarkable since the anticipated synchronization appears even when the excitable spikes are induced by random terms, such as white noise. After providing a short review of the general theory of synchronization as well as the main features of excitable systems, we present numerical and experimental results in coupled excitable systems of the FitzHugh–Nagumo type driven by different types of noise. The experiments have been done in electronic implementations of the model equations. We present the conditions (values of the coupling intensity and delay time) for which the anticipated synchronization regime is a stable one and show that it is possible to increase the anticipation time by using a cascade of several coupled systems. We use a particular limit of the FitzHugh–Nagumo system, as well as a simple excitable model, to give evidence that the physical reason for the existence of anticipated synchronization is the lowering of the excitability threshold of the slave due to the coupling. Finally, we propose a hypothesis for a possible explanation of the zero-lag synchronization observed in some real neuron systems.

A precise characterization of thin-film solar cells is of huge importance for obtaining high open-circuit voltage and low recombination rates from the interfaces or within the bulk of the main materials. Among many electrical characterization techniques, the two- and four-wire probe using the Cascade instrument is of interest since the resistance of the wires and the electrical contacts can be excluded by the additional two wires in four-wire probe configuration. In this paper, both two- and four-point probes configuration are employed to characterize the CIGS chalcogenide thin-film solar cells. The two-wire probe has been used to measure the current–voltage characteristics of the cell which results in a huge internal resistance. Therefore, the four-wire connection is also used to eliminate the load resistance to enhance the characterization’s accuracy. The load resistance in the two-wire probe diminishes the photogenerated current density at smaller voltage ranges. In contrast, the proposed four-wire probe collects more current at higher voltages due to enhanced carrier collection efficiency from contact electrodes. The current conduction mechanism is also identified at every voltage region represented by the value of the ideality factor of that voltage region. It is observed that a longer time given to the charge collection results in increased current density at a higher voltage. According to the results and device characteristics, a novel double-diode model is suggested to extract the saturation current density, shunt and series resistances and ideality factor of the cells. These cells are shown to be efficient in terms of low recombination at the interfaces and with lower series resistance as the quality of the materials is in its most possible conductive form. The measured internal resistance and saturation current density and ideality factor of the two measurement configurations are measured and compared.

Low-noise amplifiers (LNAs) are critical to a wide variety of electronic circuits. In the design phase preceding fabrication, an LNA needs to be designed for a given set of specifications (e.g., gain, noise-figure, power consumption, etc.), which tend to be application-dependent. Typically, LNA design using commercial computer-aided design (CAD) tools can be human-intensive and requires a certain degree of expertise. This paper presents a systematic multi-phase CAD approach for the design of LNAs. In the first phase, a quick pre-analysis of the given LNA specifications is carried out leading to the selection of an appropriate LNA topology. In the second phase, an initial design of the LNA is generated employing an appropriate design procedure. Finally, the initial design is adjusted/fine-tuned so as to meet/exceed the given specifications, where necessary. The advantages of the proposed approach are shown through several practical LNA design examples in 0.18 μm CMOS technology.

Analysis of distributed energy systems (DESs) is more challenging, as multiple energy sources are connected with different loads through power electronics converters. Modeling and simulation become an essential step during the design stage, prior to actual implementation. These DESs comprised numerous converters in various configurations, e.g., parallel and cascade. This paper presents behavioral modeling technique for interconnected converters that can be used to predict dynamics of overall system. First models are developed for two converters in parallel and cascade configuration using direct approach (DA). The model derivation using DA becomes too complex for larger systems. A new transformation-based approach (TBA) is proposed, which, unlike DA, is simple and can easily be extended to model $N$ interconnected converters. In this method, the measured $g$-parameter set is transformed to another domain, equivalent model is computed simply by the addition or multiplication of transformed $g$-parameters and then the equivalent model is transformed back to $g$-parameter set. The modeling techniques are implemented in Matlab/Simulink. The results from DA and TBA are compared, and their close agreement suggests that the new TBA can be used for the analysis of interconnected systems, comprised of multiple parallel and cascade converters.

Cascade-type regulation, where certain enzymes in response to physiological signals modify the activity of other enzymes by covalent modification, is found in many organisms. We study the covalent regulation of glutamine synthetase which is involved in ammonia fixation in the bacterium Escherichia coli. In this paper we pose the question whether this type of regulation of glutamine synthetase has, under certain growth conditions an advantage over other types of regulation, e.g., allosteric regulation. We propose that the relatively slow dynamics of cascade-type regulation has an evolutionary advantage under conditions of fluctuating ammonia concentrations.

The fractal component in the long-term heart rate variability (HRV) in health and in certain heart disease conditions were studied in the framework of dyadic random bounded cascade. The physiology of the fractal component was also proposed and tested in the simulation of HRV in autonomic nervous system blockade. Numerical results suggest the intrinsic mechanism behind HRV is of multiplicative nature and a "failure mechanism" due to the change of the fractal generating mechanism in certain heart diseases and in autonomic blockade.

Banking system crises are complex events that in a short span of time can inflict extensive damage to banks themselves and to the external economy. The crisis literature has so far identified a number of distinct effects or channels that can propagate distress contagiously both directly within the banking network itself and indirectly, between the network and the external economy. These contagious effects, and the potential events that trigger these effects, can explain most aspects of past crises, and are thought to be likely to dominate future financial crises. Since the current international financial regulatory regime based on the Basel III Accord does a good job of ensuring that banks are resilient to such contagion effects taken one at a time, systemic risk theorists increasingly understand that future crises are likely to be dominated by the spillovers between distinct contagion channels. The present paper aims to provide a model for systemic risk that is comprehensive enough to include the important contagion channels identified in the literature. In such a model one can hope to understand the dangerous spillover effects that are expected to dominate future crises. To rein in the number and complexity of the modelling assumptions, two requirements are imposed, neither of which is yet well-known or established in the main stream of systemic risk research. The first, called stock-flow consistency, demands that the financial system follows a rigorous set of rules based on accounting principles. The second requirement, called asset-liability symmetry, implies that every proposed contagion channel has a dual channel obtained by interchanging assets and liabilities, and that these dual channel pairs have a symmetric mathematical representation.

SINGAPORE – A New Way of Looking at Cancer

SINGAPORE – Novel Discovery by NUS Scientists Improves Profiling of AML Patients for Targeted Therapies

SINGAPORE – Red Meat Consumption Linked with Increased Risk of Developing Kidney Failure

SINGAPORE – Thomson Medical and UK-based Cell Therapy Limited Collaborate on Stem Cell Research to Develop Regenerative Medicines

UNITED STATES – New Biomaterial Developed for Injectable Neuronal Control

UNITED STATES – Research Shines Light on Lesser Known Form of Vitamin D in Foods

UNITED STATES – MRIGlobal to Lead International Research Collaboration for Tularemia Vaccine

INDIA – Improving Agricultural Yield and Quality through Tissue Culture Technology

TAIWAN – A Cascade of Protein Aggregation Bombards Mitochondria for Neurodegeneration and Apoptosis under WWOX Deficiency

In this study, we address an issue of stability of global production network by constructing a scheme combining classical Leontieff input–output analysis and modeling of contagion in financial networks. We propose a model of disruptive cascades in global economy with nonlinear effects similar to those in the financial contagion model proposed by Elliott, Golub and Jackson (2014). We apply the model to the analysis of stability of the global input–output sectoral network using the data from the World Input-Output Database (WIOD). We show that this sectoral network appears to be very stable with respect to sectoral shocks. However, by introducing synthetic substructure of economic sectors in the WIOD data we show that this stability is to a significant extent an artifact of working with aggregated data. Namely, we show that the impact of economic shocks may be much more pronounced if an underlying disaggregated network is sufficiently sparse.

Records of physical phenomena, such as turbulence, have been successfully modeled by random multiplicative processes. The present work expands such treatments by considering the effects of memory within the random multiplicative process and its consequences on the multifractal behavior of the measure. The measure-generating multiplicative cascade treated here involves first-order, two-state, Markov multipliers. When the two self-transition Markov probabilities, pii, i = 1,2, are equal, yet different from 0.5, the average occurrence of the multipliers converges to 50% as in the memoryless case. Nevertheless, the Markov memory influences the spread of multipliers. The conservation of measure now relaxes to convergence towards a nontrivial and finite value and the shape of singularity spectrum depends to a great extent on the Markov probabilities. Application of the model to turbulence data indicates an underlying anti-persistent Markov process.

Multi-risk assessment involves the inclusion of hazard and risk interactions within the modeling of the disaster risk chain. These interactions include more than one disastrous event at the same time, cascading events, and how changes in exposure and vulnerability arise over time, including as a result of previous events. At a first glance, multi-risk assessment appears to be a better means of approaching disaster risk reduction actions. However, it is hindered by a lack of knowledge about the fundamental physical processes involved, difficulties in comparing hazards and risks of different types and, especially, the topic of this chapter, barriers within risk governance for the successful implementation of necessary risk mitigation actions. Such barriers include a lack of standardization in terminology, a deficiency in expertise in the range of disciplines that are relevant to multi-risk reduction planning, inadequate resources, and biases and barriers in communication between the relevant public and private actors, as well as between researchers and policy-makers. This chapter details some of the social, institutional and scientific barriers that are associated with the full consideration of multi-risk governance, and provides some suggestions as to how these may be overcome.

The spectral distribution of positron created by photon and the spectral distribution of photons radiated from electron in an oriented single crystal of intermediate thickness is calculated at intermediate energies. The energy loss of charged particles as well as photon absorption are taken into account. The used basic probabilities of processes include the action of field of axis as well as the multiple scattering of radiating electron or particles of the created pair (the Landau-Pomeranchuk-Migdal (LPM) effect).

A novel approach for cascade diode lasers was developed based on type-I quantum wells (QWs). This design adopted the leaky window effect in the GaSb/InAs band alignment for cascade pumping, and exploits the carriers recycling by the cascade pumping and the high optical gain of the type-I QWs. Two-stage cascade lasers were designed and fabricated for 2.45 and 3.0 μm, demonstrating twofold improvement in the internal efficiency. Record continuous-wave (CW) output power of 1.2 W for 2.45 um and 590 mW for 3.0 um were achieved in room temperature (RT), and the devices operate with higher power conversion efficiency at high power level, compared to conventional single-stage diode lasers.