Fluxon Dynamics of a Long Josephson Junction with Two-gap Superconductors

We investigate the phase dynamics of a long Josephson junction (LJJ) with two-gap superconductors. In this junction, two channels for tunneling between the adjacent superconductor (S) layers as well as one interband channel within each S layer are available for a Cooper pair. Due to the interplay between the conventional and interband Josephson effects, the LJJ can exhibit unusual phase dynamics. Accounting for excitation of a stable 2$\pi$-phase texture arising from the interband Josephson effect, we find that the critical current between the S layers may become both spatially and temporally modulated. The spatial critical current modulation behaves as either a potential well or barrier, depending on the symmetry of superconducting order parameter, and modifies the Josephson vortex trajectories. We find that these changes in phase dynamics result in emission of electromagnetic waves as the Josephson vortex passes through the region of the 2$\pi$-phase texture. We discuss the effects of this radiation emission on the current-voltage characteristics of the junction.Comment: 14 pages, 6 figure

Intelligent Guidance, Navigation and Control of Multi-Agent UASs with Validation and Verification

Following the exponential growth in the usage of unmanned aerial systems (UASs) across the Aerospace Industry, more intelligent and robust guidance, navigation, and control algorithms are vital to cope with increasing levels of mission complexity. Additionally, many unmanned aerial operations require large payloads and long endurance such as extended reconnaissance, large-scale search and rescue and fine resolution terrain mapping. However, the stringent payload of a single agent or small UASs reduces their overall practicality and effectiveness. My research aims to address these inherent limitations of small UASs with a swarm by holding the required formation in order to distribute tasks and payload among multiple UASs. The goal of this research is to overcome the challenges of operating multi-agent systems by developing phasic navigation and guidance algorithms. Aircraft dynamics and their interactions with surrounding agents are highly nonlinear, which makes autonomous formation flight very sensitive to aircraft initial conditions. The phasic navigation algorithms are proposed and consist of hybrid mathematical approaches: Frenet-Serret curvature control, Hungarian algorithm and moving mesh methods. At the first phase, the curvature control allieviates the sensitivity to initial conditions of multi-agent UASs in unstructured environments by matching agents’ heading angle to the united direction. A variation of Hungarian algorithm is implemented with a moving virtual terminal to assign each agent to the formation position. In the second phase of navigation, the moving mesh methods are applied for holding the formation by defining the outer agents’ position for the boundary condition. The significance of the moving mesh methods is a scalability and a inherent intercollision avoidance. Due to the profound difference between the longitudinal and lateral-directional motion of a fixed-wing aircraft, a multi-scale moving point guidance algorithm has been designed to create the separate virtual reference points in the longitudinal and lateral-direction planes for the first time. This method has been shown to greatly reduce tracking oscillations and improve the overall tracking quality and coherency of the formation. Monte Carlo simulations are performed to ensure the stability and robustness of implementing proposed algorithms through an essentially exhaustive search. A broad range of random initial conditions have been used to validate the effectiveness of guidance, navigation, and control algorithms. Another unique contribution of this work is the validation and verification of proposed algorithms by the hardware-in-the-loop testbed and the numerous flight tests. The hardware-in-the-loop testbed is designed to test the avionics and communication before the flight test by simulating onboard 6-degrees of freedom nonlinear equations of motion. Over one hundred flight tests have been conducted using three distinct aircraft platforms between 2016 and 2018 to validate the fundamental building blocks of this architecture. In summary, this dissertation provides a conceptual and practical foundation for guidance, navigation, and control of multi-agent cooperative/collaborative UASs by unique approaches

Atomically Thin Resonant Tunnel Diodes built from Synthetic van der Waals Heterostructures

Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalocogenides: MoS2, MoSe2, and WSe2.The realization of MoS2-WSe2-Graphene and WSe2-MoSe2-Graphene heterostructures leads toresonant tunneling in an atomically thin stack with spectrally narrow room temperature negative differential resistance characteristics

The response of coarse root biomass to long-term CO2 enrichment and nitrogen application in a maturing Pinus taeda stand with a large broadleaved component

Elevated atmospheric CO2 (eCO(2)) typically increases aboveground growth in both growth chamber and free-air carbon enrichment (FACE) studies. Here we report on the impacts of eCO(2) and nitrogen amendment on coarse root biomass and net primary productivity (NPP) at the Duke FACE study, where half of the eight plots in a 30-year-old loblolly pine (Pinus taeda, L.) plantation, including competing naturally regenerated broadleaved species, were subjected to eCO(2) (ambient, aCO(2) plus 200 ppm) for 15-17 years, combined with annual nitrogen amendments (11.2 g N m(-2)) for 6 years. Allometric equations were developed following harvest to estimate coarse root (>2 mm diameter) biomass. Pine root biomass under eCO(2) increased 32%, 1.80 kg m(-2) above the 5.66 kg m(-2) observed in aCO(2), largely accumulating in the top 30 cm of soil. In contrast, eCO(2) increased broadleaved root biomass more than twofold (aCO(2): 0.81, eCO(2): 2.07 kg m(-2)), primarily accumulating in the 30-60 cm soil depth. Combined, pine and broadleaved root biomass increased 3.08 kg m(-2) over aCO(2) of 6.46 kg m(-2), a 48% increase. Elevated CO2 did not increase pine root:shoot ratio (average 0.24) but increased the ratio from 0.57 to 1.12 in broadleaved species. Averaged over the study (1997-2010), eCO(2) increased pine, broadleaved and total coarse root NPP by 49%, 373% and 86% respectively. Nitrogen amendment had smaller effects on any component, singly or interacting with eCO(2). A sustained increase in root NPP under eCO(2) over the study period indicates that soil nutrients were sufficient to maintain root growth response to eCO(2). These responses must be considered in computing coarse root carbon sequestration of the extensive southern pine and similar forests, and in modelling the responses of coarse root biomass of pine-broadleaved forests to CO2 concentration over a range of soil N availability.Peer reviewe

Floating Hem-o-Lok Clips in the Bladder without Stone Formation after Robot-Assisted Laparoscopic Radical Prostatectomy

Hem-o-Lok clips (Weck Surgical Instruments, Teleflex Medical, Durham, NC, USA) are widely used in robot-assisted laparoscopic radical prostatectomy because of their easy application and secure clamping. To date, there have been some reports of intravesical migration of these clips causing urethral erosion, bladder neck contractures, and subsequent calculus formation. We report the first case of bladder migration of Hem-o-Lok clips without stone formation after robot-assisted laparoscopic radical prostatectomy. The Hem-o-Lok clips were found during urethral dilation with a guide wire for bladder neck contracture under cystourethroscopy. The Hem-o-Lok clips were floating in the bladder without stone formation and were removed by a cystoscopic procedure

Isotopic Dependence of GCR Fluence behind Shielding

In this paper we consider the effects of the isotopic composition of the primary galactic cosmic rays (GCR), nuclear fragmentation cross-sections, and isotopic-grid on the solution to transport models used for shielding studies. Satellite measurements are used to describe the isotopic composition of the GCR. For the nuclear interaction data-base and transport solution, we use the quantum multiple-scattering theory of nuclear fragmentation (QMSFRG) and high-charge and energy (HZETRN) transport code, respectively. The QMSFRG model is shown to accurately describe existing fragmentation data including proper description of the odd-even effects as function of the iso-spin dependence on the projectile nucleus. The principle finding of this study is that large errors (+/-100%) will occur in the mass-fluence spectra when comparing transport models that use a complete isotopic-grid (approx.170 ions) to ones that use a reduced isotopic-grid, for example the 59 ion-grid used in the HZETRN code in the past, however less significant errors (<+/-20%) occur in the elemental-fluence spectra. Because a complete isotopic-grid is readily handled on small computer workstations and is needed for several applications studying GCR propagation and scattering, it is recommended that they be used for future GCR studies

Hearing Abilities at Ultra-High Frequency in Patients with Tinnitus

ObjectivesTo compare tinnitus patients who have normal hearing between 250 Hz and 8 kHz with normal controls with regard to the ability of each group to hear extended high-frequency pure tone thresholds.MethodsWe enrolled 18 tinnitus patients, each of whom had a threshold of HL <25 dB and threshold differences of <10 dB between ears at frequencies of 250 and 500 Hz and 1, 2, 4, and 8 kHz. We also enrolled age- and gender-matched normal volunteers (10 ears), for each patient. Extended high frequency pure tone audiometry was performed, and the mean hearing thresholds at 10, 12, 14, and 16 kHz of each tinnitus ear were compared with those of the 10 age- and sex-matched normal ears.ResultsOf the 18 patients with tinnitus, 12 had significantly increased hearing thresholds at more than one of the four high frequencies, compared with the normal group. When we assessed results according to frequency, we found that 8 patients had decreased hearing ability at 10 kHz, 10 at 12 kHz, 8 at 14 kHz, and 4 at 16 kHz.ConclusionSome patients with tinnitus who have normal hearing below 8 kHz have decreased hearing ability at extended high-frequencies. Thus, the proportion of patients with tinnitus who have normal hearing over the entire audible range is smaller than in previous reports

Femoral geometry, bone mineral density, and the risk of hip fracture in premenopausal women: a case control study

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Background The purpose of this study was to determine the relationships among hip geometry, bone mineral density, and the risk of hip fracture in premenopausal women. Methods The participants in this case–control study were 16 premenopausal women with minimal-trauma hip fractures (fracture group) and 80 age-and BMI-adjusted controls. Subjects underwent dual-energy X-ray absorptiometry (DXA) to assess BMD at the proximal femur and to obtain DXA-derived hip geometry measurements. Results The fracture group had a lower mean femoral neck and total hip BMD than the control group (0.721 ± 0.123 vs. 0.899 ± 0.115, p <0.001 for the femoral neck BMD and 0.724 ± 0.120 vs. 0.923 ± 0.116, p <0.001 for the total hip BMD). In addition, participants in the fracture group had a longer hip axis length (HAL; p = 0.007), narrower neck shaft angle (NSA; p = 0.008), smaller cross sectional area (CSA; p < 0.001) and higher cross sectional moment of inertia (CSMI; p = 0.004) than those in control group. After adjusting for BMD, the fracture group still had a significantly longer mean HAL (p = 0.020) and narrower NSA (p = 0.006) than the control group. Conclusions BMD is an important predictor of hip fracture in premenopausal women. Furthermore, HAL and NSA are BMD-independent predictors of hip fracture in premenopausal women. Hip geometry may be clinically useful for identification of premenopausal women for whom active fracture prevention should be considered