Terahertz pulse-driven collective mode in the nematic superconducting state of Ba1−xKxFe2As2

We investigate the collective mode response of the iron-based superconductor Ba1−xKxFe2As2 using intense terahertz (THz) light. In the superconducting state a THz Kerr signal is observed and assigned to nonlinear THz coupling to superconducting degrees of freedom. The polarization dependence of the THz Kerr signal is remarkably sensitive to the coexistence of a nematic order. In the absence of nematic order the C4 symmetric polarization dependence of the THz Kerr signal is consistent with a coupling to the Higgs amplitude mode of the superconducting condensate. In the coexisting nematic and superconducting state the signal becomes purely nematic with a vanishing C4 symmetric component, signaling the emergence of a superconducting collective mode activated by nematicity.

Compact dual-mode microstrip bandpass filter based on slotted square patch resonator

Purpose The purpose of this paper is to present the design of a compact microstrip bandpass filter (BPF) in dual-mode configuration loaded with cross-loop and square ring slots on a square patch resonator for C-band applications. Design/methodology/approach In the proposed design, the dual-mode response for the filter is realized with two transmission zeros (TZs) by the insertion of a perturbation element at the diagonal corner of the square patch resonator with orthogonal feed lines. Such TZs at the edges of the passband result in better selectivity for the proposed BPF. Moreover, the cross-loop and square ring slots are etched on a square patch resonator to obtain a miniaturized BPF. Findings The proposed dual-mode microstrip filter fabricated in RT/duroid 6010 substrate using PCB technology has a measured minimum insertion loss of 1.8 dB and return loss better than 24.5 dB with a fractional bandwidth (FBW) of 6.9%. A compact size of 7.35 × 7.35 mm2 is achieved for the slotted patch resonator-based dual-mode BPF at the center frequency of 4.76 GHz. As compared with the conventional square patch resonator, a size reduction of 61% is achieved with the proposed slotted design. The feasibility of the filter design is confirmed by the good agreement between the measured and simulated responses. The performance of the proposed filter structure is compared with other dual-mode filter works. Originality/value In the proposed work, a compact dual-mode BPF is reported with slotted structures. The conventional square patch resonator is deployed with cross-loop and square ring slots to design a dual-mode filter with a square perturbation element at its diagonal corner. The proposed filter exhibits compact size and favorable performance compared to other dual-mode filter works reported in literature. The aforementioned design of the dual-mode BPF at 4.76 GHz is suitable for applications in the lower part of the C-band.

On the tropospheric response to transient stratospheric momentum torques

An idealised model is used to examine the tropospheric response to sudden stratospheric warmings (SSWs), by imposing transient stratospheric momentum torques tailored to mimic the wave-forcing impulse associated with spontaneously-occurring SSWs. Such an approach enables us to examine both the ∼2-3-week forcing stage of an SSW during which there is anomalous stratospheric wave-activity convergence, as well as the recovery stage during which the wave forcing abates and the stratosphere radiatively recovers over 2-3 months. It is argued that applying a torque is better suited than a heating perturbation for examining the response to SSWs, due to the meridional circulation that is induced to maintain thermal-wind balance (i.e., the ‘Eliassen adjustment’); an easterly torque yields downwelling at high latitudes and equatorward flow below, similar to the wave-induced circulation that occurs during spontaneously-occurring SSWs, whereas a heating perturbation yields qualitatively opposite behavior and thus cannot capture the initial SSW evolution. During the forcing stage, the meridional circulation in response to an impulse comparable to the model’s internal variability is able to penetrate down to the surface and drive easterly-wind anomalies via Coriolis torques acting on the anomalous equatorward flow. During the recovery stage, after which the tropospheric flow has already responded, the meridional circulation associated with the stratosphere’s radiative recovery provides the persistent stratospheric forcing that drives the high-latitude easterly anomalies, which is then augmented by synoptic-wave feedbacks that drive and amplify the annular-mode response. In comparison, planetary waves are found to play a relatively small role.

Exploratory diary study of survey request frequency among research professionals

The survey commons is a global common-pool resource that consists of all populations of potential survey participants that researchers share. As survey research methodology and technology advances, the survey commons has become more accessible and used by an ever-growing variety of professional and non-professional researchers, which creates a climate for potential survey participants of seemingly constant requests to complete various types of questionnaires. Among other factors, the frequency of survey requests likely influences burden, fatigue, and data quality. Yet, few studies have explored the frequency and characteristics of survey requests. In contribution to this growing research area, we conducted an exploratory diary study of survey requests among research professionals for a 1-month period. Participants tracked survey request dates, contact mode, response mode, title, sponsor, host, and completion progress. We observed participants receive a survey request every other day, on average, but only fully completed one-quarter of requests. Marketing surveys were the primary request source, the main contact mode was email, and the main response mode was web-based. While marketing surveys were the most frequently experienced by participants, they also had the lowest completion rate; administrative and academic survey requests had the highest completion rate. Overall, our exploratory diary study told an intriguing story of the quantity and characteristics of survey requests among a select population and adds to growing interests in survey request inquiry.

Signs of the "one-mode" response forces in linear spectral method: comparison of conventional and standard approaches

Two variants of linear-spectral method (LSM) are compared in the paper: the conventional one, prescribed in several foreign standards, and "Standard" one prescribed in the Russian Standard SP 14.13330. "One-component one-mode" responses, obtained by static analysis in the conventional LSM are combined twice: first for different modes but for each single excitation component, then for different excitation components. In the "standard" alternative LSM variant first one chooses the "most dangerous" direction of the one-component excitation for each mode, then one obtains the "one-mode" response for this excitation, and finally these responses are combined. In both cases the combination is performed using the complete quadratic combination (CQC) rule, accounting for the correlation between one-mode responses. "Standard" variant leaves some uncertainty: the "dangerous" direction can be changed for the opposite one. Such a change leads to the sign change in the one-mode response. This is of no importance for the non-correlated responses, which are combined using the SRSS rule. However, for the correlated responses as it is shown in the paper using sample problem the uncertainty in the signs can lead to the incorrect results, and the error can be significant.

Combination of modal responses in linear spectral method: comparison of different formulae for correlation coefficients

Linear-spectral method (LSM) is still the common method for the seismic design analysis. "One-component one-mode" responses, obtained by static analysis in the conventional variant of LSM, are combined twice: first for different modes but for each single excitation component separately, then for the different excitation components. In the alternative LSM variant presented in the Russian code SP 14.13330, first one chooses the "most dangerous" direction of the one-component excitation for each mode; then calculates the "one-mode" response for this excitation, and finally these responses are combined. In both cases the combination is performed using the complete quadratic combination (CQC) rule. Different documents suggest different formulae for the correlation coefficients. In the paper different formulae are compared to each other. The goal is to limit the number of calculated coefficients and decrease the amount of calculations.