Multi-Layer Overlapped Subaperture Algorithm for Extremely-High-Squint High-Resolution Wide-Swath SAR Imaging with Continuously Time-Varying Radar Parameters

Extremely-high-squint (EHS) geometry of the traditional constant-parameter synthetic aperture radar (SAR) induces non-orthogonal wavenumber spectrum and hence the distortion of point spread function (PSF) in focused images. The method invented to overcome this problem is referred to as new-concept parameter-adjusting SAR. It corrects the PSF distortion by adjusting radar parameters, such as carrier frequency and chirp rate, based on instant data acquisition geometry. In this case, the characteristic of signal is quite different from the constant-parameter SAR and therefore, the traditional imaging algorithms cannot be directly applied for parameter-adjusting SAR imaging. However, the existing imaging algorithm for EHS parameter-adjusting SAR suffers from insufficient accuracy if a high-resolution wide-swath (HRWS) performance is required. Thus, this paper proposes a multi-layer overlapped subaperture algorithm (ML-OSA) for EHS HRWS parameter-adjusting SAR imaging with three main contributions: First, a more accurate signal model with time-varying radar parameters in high-squint geometry is derived. Second, phase errors are compensated with much higher accuracy by implementing multiple layers of coarse-to-fine spatially variant filters. Third, the analytical swath limit of the ML-OSA is derived by considering both the residual errors of signal model and phase compensations. The presented approach is validated via both the point- and extended-target computer simulations.

The Relationship Between Stockmarket Development And The Performance of The Nigerian Economy

This paper examined the relationship between stock market development and performance of the Nigerian economy. The analysis scope covered a period of 10 years spanning from 2010-2020. The analytic procedure for the information was econometric. The estimation techniques used are co-integration, Granger Causality and Error Correction to check whether the exchange indices have impacted on the macroeconomic performance of Nigeria.The result showed that the constant parameter is negatively or inversely associated with LGDP.The coefficient of the constant parameter (B0) is –15038.18. This suggests that if all the explanatory variables are held constant, LGDP which is that the explained variable will increase by 15038.18 units. Conclusively, all variables might not have been reasons enough for a change in the Gross domestic product level, but the fact still remains that there is an affinity between them. The study recommends that the central bank of Nigeria (CBN) being the monetary authority should plan and implement policies that bring about an increase flow of investment funds and improves the extent of capitalisation to the economy.

Policy asymmetries and fiscal sustainability: evidence from Nigeria

PurposeThis study examines and compares different specifications of the fiscal policy rule in the fiscal sustainability analysis of Nigeria.Design/methodology/approachThis is methodologically achieved by estimating the baseline constant-parameter and Markov regime switching fiscal models. The asymmetric autoregressive distributed lag fiscal model is also employed to substantiate the differential responses of fiscal authorities to public debt.FindingsThe baseline constant-parameter fiscal model provides mixed results of sustainable and unsustainable fiscal policy. The inconclusiveness is adduced to instability in primary fiscal balance–public debt dynamics. This makes it necessary to capture regime switches in the fiscal policy rule. The Markov switching estimations show a protracted fiscal unsustainable regime that is inconsistent with the intertemporal budget constraint (IBC). The no-Ponzi game and debt stabilizing results of the Markov switching fiscal model further revealed that the transversality and debt stability conditions were not satisfied. Additional findings from the asymmetric autoregressive model estimation show that fiscal consolidation responses vary with contraction and expansion in output and spending, coupled with downturns and upturns in public debt dynamics in both the long and short run. These findings thus confirm the presence of asymmetries in the fiscal policy authorities' reactions to public debt. Further, additional evidences show the violation of the IBC which is exacerbated by the deleterious effect of the pro-cyclical fiscal policy response in boom on the improvement of the primary fiscal balance.Originality/valueThis study deviates from the extant literature by accommodating time variation, periodic switches and fiscal policy asymmetries in the fiscal sustainability analysis of Nigeria.

Specific Resonant Properties of Non-Symmetrical Microwave Antennas

The aircraft avionics modernization process often requires optimization of the aircraft itself. Scale models of aircraft and their antennas are frequently used to solve this problem. Here we present interesting properties of the resonant antennas, which were discovered serendipitously during the measurement process of some microwave antennas’ models as part of an aircraft modernization project. Aircraft microwave antennas are often designed as non-symmetric flat microwave antennas. Due to their thin, low and longitudinally elongated outer profile, they are also called tail antennas. An analysis of the resonant properties of non-symmetric antennas was performed in the band from 1 GHz to 4 GHz. The length of the antenna models ranged from 2 cm to 7 cm. The width of the antennas, together with the thickness of the strip, was always a constant parameter for one measured set of six antennas. In the measurement and subsequent analysis, attention was focused on the first-series resonant frequency (λ/4) of each antenna. During the evaluation of the resonance parameters, the flat microwave antenna models showed specific resonant properties different from those of conventional cylindrical microwave antennas. This article aims to inform professionals about these unknown specific properties of non-symmetrical antennas. The results of experimental measurements are analyzed theoretically and then visually compared using graphs so that the reader can more easily understand the properties observed. These surprising observations open up some new possibilities for the design, implementation, and use of flat microwave antennas, as found in modern aircraft, automobiles, etc.

VARIATION OF THE INTRINSIC ROCK PROPERTIES ON HOEK-BROWN FAILURE CRITERION PARAMETERS

The Hoek-Brown (H-B) criterion is one of the most commonly used rock failure criteria in recent years. This criterion includes a constant parameter called mi which is a fundamental parameter for estimating rock strength. Due to the importance of the mi parameter in the H-B criterion, it is necessary to conduct comprehensive studies on various aspects of the effect of this parameter on the behavior of rocks. Therefore, in this study, using numerical simulation of the Triaxial Compressive Strength (TCS) tests in PFC-2D code, the effects of microscopic properties of different rocks on the H-B parameter mi have been studied. Based on the results of this study, it was found that the effects of micro-parameters on the H-B parameter mi can be different depending on the type of rock, however this parameter has an inverse relationship to the micro-parameters of bond tensile strength and bond fraction of the rocks. Also, the mi parameter increases with an increase in the micro-parameters of the friction coefficient, the friction angle, the particle contact modulus, and the contact stiffness ratio of rocks.