Experimental investigation of bifurcation behavior in nonlinear microwave circuits

We present an experimental technique to study bifurcations in periodically forced nonlinear microwave circuits, including even physically unstable (periodic) steady states. The designer specifies a key node in the circuit being studied (often associated with an active device) and the method synthesizes a voltage waveform to match the waveform at the selected node so that no current flows across the interface. This null condition is maintained while a parameter, such as bias voltage, is varied over a specified range. The addition of the external nulling source is able to stabilize a steady state that would be unstable in the original circuit. Various applications are presented.This work has been funded by the Spanish Government under contract TEC2014-60283-C3-1-R, the European Regional Development Fund (ERDF/FEDER) and the Parliament of Cantabria (12.JP02.64069)

Conceptions of Learning and Teaching and Their Relation to Educational Variables During Teaching Second Language

Background:  People who choose to study a second language like English face an emotional charge that affects directly to the learning process. Regarding the writing production, learners create short compositions about specific topics with instructions based on grammatical structures. Once it is done, learners receive feedback on their work. However, some learners do not want to write any text because the teacher puts more attention to their mistakes rather than their successes. Without taking into account their needs, topics of interest or motivation for carrying out the exercise Contribution:  Therefore, it is set to identify the emotions that are generated by the corrections made to our learners’ written work. Method:  The research was carried on with university students aged between 18 and 25 years old who are attending classes at the center of university language classroom. This research during the April- August 2016 term. Results: It has been found that the emotions (positive and negative) play an important role or have a great impact that causes aversion towards language learning. Therefore, it is necessary that teachers provide adequate feedback for language learning. Conclusion:  Corrections generate aversion towards the learning process. Regarding the feedback students receive from their teachers, it generates emotional charge (positive and negative) which should be followe

Globally Convergent Homotopy Methods for the DC Operating PointProblem

Accurate and efficient computer simulation of a proposed design for an integrated circuit ("chip") is essential because of the difficulty and expense of building prototypes for such devices. The transistors and diodes in such circuits are modeled with nonlinear equations, hence simulation of circuits requires the solution of systems of nonlinear equations involving hundreds or even thousands of variables. This paper discusses the application of probability-one homotopy methods to various systems of nonlinear equations which arise in circuit simulation. The so-called "coercivity conditions" which are required for such methods are proved using concepts from circuit theory. The theoretical claims of global convergence for such methods are substantiated by experiments with a collection of examples which have proved difficult for commercial simulation packages which do not use homotopy methods. Moreover, by careful design of the homotopy equations, the performance of the homotopy methods can be made quite reasonable

Magnetic phase transitions in Gd64Sc36 studied using non-contact ultrasonics

The speed and attenuation of ultrasound propagation can be used to determine material properties and identify phase transitions. Standard ultrasonic contact techniques are not always convenient due to the necessity of using couplant; however, recently reliable non-contact ultrasonic techniques involving electromagnetic generation and detection of ultrasound with electromagnetic acoustic transducers (EMATs) have been developed for use on electrically conducting and/or magnetic materials. We present a detailed study of magnetic phase transitions in a single crystal sample of Gd64Sc36 magnetic alloy using contact and non-contact ultrasonic techniques for two orientations of external magnetic field. Phase diagrams are constructed based on measurements of elastic constant C33, the attenuation and the efficiency of generation when using an EMAT. The EMATs are shown to provide additional information related to the magnetic phase transitions in the studied sample, and results identify a conical helix phase in Gd64Sc36 in the magnetic field orientation

A qualitative study of stakeholders' perspectives on the social network service environment

Over two billion people are using the Internet at present, assisted by the mediating activities of software agents which deal with the diversity and complexity of information. There are, however, ethical issues due to the monitoring-and-surveillance, data mining and autonomous nature of software agents. Considering the context, this study aims to comprehend stakeholders' perspectives on the social network service environment in order to identify the main considerations for the design of software agents in social network services in the near future. Twenty-one stakeholders, belonging to three key stakeholder groups, were recruited using a purposive sampling strategy for unstandardised semi-structured e-mail interviews. The interview data were analysed using a qualitative content analysis method. It was possible to identify three main considerations for the design of software agents in social network services, which were classified into the following categories: comprehensive understanding of users' perception of privacy, user type recognition algorithms for software agent development and existing software agents enhancement

Rapid population decline in migratory shorebirds relying on Yellow Sea tidal mudflats as stopover sites

Migratory animals are threatened by human-induced global change. However, little is known about how stopover habitat, essential for refuelling during migration, affects the population dynamics of migratory species. Using 20 years of continent-wide citizen science data, we assess population trends of ten shorebird taxa that refuel on Yellow Sea tidal mudflats, a threatened ecosystem that has shrunk by >65% in recent decades. Seven of the taxa declined at rates of up to 8% per year. Taxa with the greatest reliance on the Yellow Sea as a stopover site showed the greatest declines, whereas those that stop primarily in other regions had slowly declining or stable populations. Decline rate was unaffected by shared evolutionary history among taxa and was not predicted by migration distance, breeding range size, non-breeding location, generation time or body size. These results suggest that changes in stopover habitat can severely limit migratory populations

Chronic Maternal Depression Is Associated with Reduced Weight Gain in Latino Infants from Birth to 2 Years of Age

BACKGROUND: Latino children are at increased risk for mirconutrient deficiencies and problems of overweight and obesity. Exposures in pregnancy and early postpartum may impact future growth trajectories. OBJECTIVES: To evaluate the relationship between prenatal and postnatal maternal depressive symptoms experienced in pregnancy and infant growth from birth to 2 years of age in a cohort of Latino infants. METHODS: We recruited pregnant Latina mothers at two San Francisco hospitals and followed their healthy infants to 24 months of age. At 6, 12 and 24 months of age, infants were weighed and measured. Maternal depressive symptoms were assessed prenatally and at 4-6 weeks postpartum. Women who had high depressive symptoms at both time periods were defined as having chronic depression. Logistic mixed models were applied to compare growth curves and risk for overweight and underweight based on exposure to maternal depression. RESULTS: We followed 181 infants to 24 months. At 12 and 24 months, respectively, 27.4% and 40.5% were overweight, and 5.6% and 2.2% were underweight. Exposure to chronic maternal depression was associated with underweight (OR = 12.12, 95%CI 1.86-78.78) and with reduced weight gain in the first 2 years of life (Coef = -0.48, 95% CI -0.94-0.01) compared with unexposed infants or infants exposed to episodic depression (depression at one time point). Exposure to chronic depression was also associated with reduced risk for overweight in the first 2 years of life (OR 0.28, 95%CI 0.03-0.92). CONCLUSIONS: Exposure to chronic maternal depression in the pre- and postnatal period was associated with reduced weight gain in the first two years of life and greater risk for failure to thrive, in comparison with unexposed infants or those exposed episodically. The infants of mothers with chronic depression may need additional nutritional monitoring and intervention