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Junction circulators are internally matched n-port devices where the input signal to a specific port transfer to the adjacent port and isolated from all other ports. Circulators and isolators are used extensively in many communica...
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Junction circulators are internally matched n-port devices where the input signal to a specific port transfer to the adjacent port and isolated from all other ports. Circulators and isolators are used extensively in many communication systems and defense applications. They are used in splitting the forward and reverse signals in radar applications, which facilitates the signal processing and protects the critical system components such as amplifiers. Most of the current design techniques of circulators presented in the literature have no straightforward procedure and embrace many empirical equations. Such techniques provide approximate and iterative solutions, which increase the time and cost of the development process to achieve the required specifications. In this paper, we present a simple circulators design methodology based on a closed-form solution of the stripline Y-junction including the stripline modes. In addition, we criticize the traditional design methodologies and highlight their limitations and shortcomings. We validate the proposed procedure by two designs for the junction circulators based on the stripline technology. The provided closed-form solution is a revolutionary design methodology as it reduces the lengthy approximate expensive trials to a straightforward and systematic cost-effective technique.
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Paleoclimate proxy evidence suggests that the Atlantic meridional overturning circulation (AMOC) was about 1000 m shallower at the Last Glacial Maximum (LGM) compared to the present. Yet it remains unresolved what caused this glac...
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Paleoclimate proxy evidence suggests that the Atlantic meridional overturning circulation (AMOC) was about 1000 m shallower at the Last Glacial Maximum (LGM) compared to the present. Yet it remains unresolved what caused this glacial shoaling of the AMOC, and many climate models instead simulate a deeper AMOC under LGM forcing. While some studies suggest that Southern Ocean surface buoyancy forcing controls the AMOC depth, others have suggested alternatively that North Atlantic surface forcing or interior diabatic mixing plays the dominant role. To investigate the key processes that set the AMOC depth, here we carry out a number of MITgcm ocean-only simulations with surface forcing fields specified from the simulation results of three coupled climate models that span much of the range of glacial AMOC depth changes in phase 3 of the Paleoclimate Model Intercomparison Project (PMIP3). We find that the MITgcm simulations successfully reproduce the changes in AMOC depth between glacial and modern conditions simulated in these three PMIP3 models. By varying the restoring time scale in the surface forcing, we show that the AMOC depth is more strongly constrained by the surface density field than the surface buoyancy flux field. Based on these results, we propose a mechanism by which the surface density fields in the high latitudes of both hemispheres are connected to the AMOC depth. We illustrate the mechanism using MITgcm simulations with idealized surface forcing perturbations as well as an idealized conceptual geometric model. These results suggest that the AMOC depth is largely determined by the surface density fields in both the North Atlantic and the Southern Ocean.
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We characterize the eastern Gulf of Cadiz, proximal to the Strait of Gibraltar, using a multidisciplinary approach that combines oceanographic, morphosedimentary, and stratigraphic studies. Two terraces (upper and lower) were iden...
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We characterize the eastern Gulf of Cadiz, proximal to the Strait of Gibraltar, using a multidisciplinary approach that combines oceanographic, morphosedimentary, and stratigraphic studies. Two terraces (upper and lower) were identified along the middle slope. They are composed of several associated morphologic elements, including two large erosive channels, which allow us to determine a new and more detailed understanding of the Mediterranean Outflow Water (MOW) pathway and its deceleration upon exiting the Strait of Gibraltar. There is evidence for along-slope circulation and additional secondary circulation oblique to the main flow. The present upper core of the MOW flows along the upper terrace and the lower core flows along the lower terrace. However, the lower terrace shows larger and better defined erosive features on the seafloor than does the upper terrace; we attribute this to a denser, deeper, and faster MOW circulation that prevailed during past cold climates. Development of the present features started ca. 3.8-3.9 Ma, but the present morphology was not established until the late Pliocene-early Quaternary (3.2 to older than 2.0 Ma), when the MOW was enhanced, coeval with global cooling, a sea-level fall, and an increase in thermohaline circulation. We propose a direct link between the MOW and the Atlantic Meridional Overturning Circulation and therefore between the MOW and both the Northern Hemisphere and global climate. Our results have enabled a better understanding of a major overflow related to an oceanic gateway, and are of broad interest to geologists, climatologists, oceanographers, and petroleum geologists.
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Future emissions of greenhouse gases into the atmosphere are projected to result in significant circulation changes. One of the most important changes is the widening of the tropical belt, which has great societal impacts. Several...
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Future emissions of greenhouse gases into the atmosphere are projected to result in significant circulation changes. One of the most important changes is the widening of the tropical belt, which has great societal impacts. Several mechanisms (changes in surface temperature, eddy phase speed, tropopause height, and static stability) have been proposed to explain this widening. However, the coupling between these mechanisms has precluded elucidating their relative importance. Here, the abrupt quadrupled-CO2 simulations of phase 5 of the Coupled Model Intercomparison Project (CMIP5) are used to examine the proposed mechanisms. The different time responses of the different mechanisms allow us to disentangle and evaluate them. As suggested by earlier studies, the Hadley cell edge is found to be linked to changes in subtropical baroclinicity. In particular, its poleward shift is accompanied by an increase in subtropical static stability (i.e., a decrease in temperature lapse rate) with increased CO2 concentrations. These subtropical changes also affect the eddy momentum flux, which shifts poleward together with the Hadley cell edge. Transient changes in tropopause height, eddy phase speed, and surface temperature, however, were found not to accompany the poleward shift of the Hadley cell edge. The widening of the Hadley cell, together with the increase in moisture content, accounts for most of the expansion of the dry zone. Eddy moisture fluxes, on the other hand, are found to play a minor role in the expansion of the dry zone.
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Underappreciated data concerning libraries' holdings and circulation over the past century and a half offer insights into the behavior of libraries and their users. Book circulation per public library user indicates an outcome of ...
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Underappreciated data concerning libraries' holdings and circulation over the past century and a half offer insights into the behavior of libraries and their users. Book circulation per public library user indicates an outcome of users' demand for books and libraries' supply of books. From 1856 to 1978, library users borrowed from U.S. public libraries about 15 books per user per year. From 1978 to 2004, about 25% of book circulation shifted to audio-visual circulation. Over about a century and a half, library book circulation per user shows no strong, long-run trend either up or down. This outcome suggests that libraries have adapted to maintain the stability of their operation and that library borrowing practices are well-embedded in popular life.
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Given two graphs G_1 and G_2, one may ask whether or not G_2 is a cover of G_1. Feng and Kwak [Typical circulant double coverings of a circulant graph, Discrete Math. 277 (2004) 73–85] provide a description of typical covers of a...
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Given two graphs G_1 and G_2, one may ask whether or not G_2 is a cover of G_1. Feng and Kwak [Typical circulant double coverings of a circulant graph, Discrete Math. 277 (2004) 73–85] provide a description of typical covers of a circulant graph by another circulant graph, and use other techniques to show that there are no double covers of trivalent circulant graphs. The purpose of this paper is to provide a description of all circulant covers over trivalent circulant graphs.
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Recent global warming caused by humans and the prediction of a reduced Atlantic Ocean meridional overturning circulation in the future has increased interest in the role of the overturning circulation in climate change. A schemati...
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Recent global warming caused by humans and the prediction of a reduced Atlantic Ocean meridional overturning circulation in the future has increased interest in the role of the overturning circulation in climate change. A schematic diagram of the overturn
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The aim of the research was to identify the seasonal variability of correlation between the air motion characteristics and common zonal circulation index (Rossby's Index). Air flow characteristics comprised divergence and vorticit...
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The aim of the research was to identify the seasonal variability of correlation between the air motion characteristics and common zonal circulation index (Rossby's Index). Air flow characteristics comprised divergence and vorticity. The spatial coverage of the research was the so called Euro-Atlantic Region covering parts of North Atlantic and Europe (40W-40E, 35N-75N). Temporal extent was 1971-2000 thus matching the latest WMO normal period. The data used was the components of the wind vector (u - zonal component, v - meridional component) and geopotential heights (hgt) from NCEP/NCAR Reanalysis. The response of the vorticity field is apparent and the greatest variability is noted at 1000 hPa. The mid and upper levels in the troposphere reveal quite homogenous response of vorticity to the macro-scale forcing. The response of the divergence field is also apparent though more complex in the vertical profile of the troposphere. The analysis of correlation was followed by the description of annual as well as seasonal shape of vorticity and divergence fields in the extremes of Rossby Index.
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This paper is concerned with the question: why do coupled general circulation models (CGCM) seem to be biased toward a monostable Atlantic meridional overturning circulation (AMOC)? In particular, the authors investigate whether t...
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This paper is concerned with the question: why do coupled general circulation models (CGCM) seem to be biased toward a monostable Atlantic meridional overturning circulation (AMOC)? In particular, the authors investigate whether the monostable behavior of the CGCMs is caused by a bias of model surface climatology. First observational literature is reviewed, and it is suggested that the AMOC is likely to be bistable in the real world in the past and present. Then the stability of the AMOC in the NCAR Community Climate System Model, version 3 (CCSM3) is studied by comparing the present-day control simulation (without flux adjustment) with a sensitivity experiment with flux adjustment. It is found that the monostable AMOC in the control simulation is altered to a bistable AMOC in the flux-adjustment experiment because a reduction of the surface salinity biases in the tropical and northern North Atlantic leads to a reduction of the bias of freshwater transport in the Atlantic. In particular, the tropical bias associated with the double ITCZ reduces salinity in the upper South Atlantic Ocean and, in turn, the AMOC freshwater export, which tends to overstabilize the AMOC and therefore biases the AMOC from bistable toward monostable state. This conclusion is consistent with a further analysis of the stability indicator of two groups of IPCC Fourth Assessment Report (AR4) CGCMs: one without and the other with flux adjustment. Because the tropical bias is a common feature among all CGCMs without flux adjustment, the authors propose that the surface climate bias, notably the tropical bias in the Atlantic, may contribute significantly to the monostability of AMOC behavior in current CGCMs.
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Liquid biopsy approaches for detection of circulating biomarkers of cancer have been utilized in oncology in many clinical settings from early detection to disease monitoring. Recent approaches have focused on circulating tumor ce...
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Liquid biopsy approaches for detection of circulating biomarkers of cancer have been utilized in oncology in many clinical settings from early detection to disease monitoring. Recent approaches have focused on circulating tumor cells, circulating tumor DNA, and circulating RNAs in a variety of biofluids. However, very little progress has been made in implementing such approaches for detection of brain tumors, despite the tremendous clinical need for earlier and less invasive diagnosis, as well as more accurate assessment of disease status. In this review, we highlight the recent methodological improvements in the field of liquid biopsy technologies specifically for glioblastoma. Although many retrospective and few prospective studies have been conducted to assess the utility of circulating biomarkers for detection of brain tumors, none have yet moved forward to clinical implementation.
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