Large Spreading Research Articles

Three-dimensional surface gravity waves of a broad bandwidth on deep water

A new nonlinear Schrödinger equation (NLSE) is presented for ocean surface waves. Earlier derivations of NLSEs that describe the evolution of deep-water waves have been limited to a narrow bandwidth, for which the bound waves at second order in wave steepness are described in leading-order approximations. This work generalizes these earlier works to allow for deep-water waves of a broad bandwidth with large directional spreading. The new NLSE permits simple numerical implementations and can be extended in a straightforward manner in order to account for waves on water of finite depth. For the description of second-order waves, this paper proposes a semianalytical approach that can provide accurate and computationally efficient predictions. With a leading-order approximation to the new NLSE, the instability region and energy growth rate of Stokes waves are investigated. Compared with the exact results based on McLean (J. Fluid Mech., vol. 511, 1982, p. 135), predictions by the new NLSE show better agreement than by Trulsen et al. (Phys. Fluids, vol. 12, 2000, pp. 2432–2437). With numerical implementations of the new NLSE, the effects of wave directionality are investigated by examining the evolution of a directionally spread focused wave group. A downward shift of the spectral peak is observed, owing to the asymmetry in the change rate of energy in a more complex manner than that for uniform Stokes waves. Rapid oblique energy transfers near the group at linear focus are observed, likely arising from the instability of uniform Stokes waves appearing in a narrow spectrum subject to oblique sideband disturbances.

Self-Synchronized DS/SS With High Spread Factors for Robust Millimeter-Wave Datalinks

This paper presents direct sequence spread spectrum (DS/SS) datalinks operating at 92-100 GHz with spreading factors up to 100K. Unlike traditional DS/SS datalinks which rely on preamble and cyclic dispreading for synchronization, the reported datalink uses a self-synchronous demodulation scheme, avoiding the large hardware complexity associated with exceptionally large spreading factors, and avoiding the difficulties of synchronizing the long de-spreading codes that are applicable to mm-wave systems. A demonstration link chipset is presented operating at 92-100 GHz with a spreading factor of 104K and a spread bandwidth of 6.0 GHz (baseband bandwidth of 56Kb/s) while consuming a total of 425mW.

Novel approaches to minimize intraoperative bleeding during endoscopic submucosal dissection of a large rectal lateral spreading tumor extended to the dentate line with internal hemorrhoids.

Video 1Endoscopic submucosal dissection (ESD) of large rectal lateral spreading tumors (LSTs) that extend to the dentate line with internal hemorrhoids is a challenging procedure because of the increased risk of bleeding from penetrating and hemorrhoidal vessels and the reduced visual field caused by the dilated venous packages and the narrow anal lumen.This video describes novel technical approaches to minimize the risk of intraoperative bleeding.The described approaches are indicated in large rectal LSTs that extend to the dentate line with large internal hemorrhoids. The described selective-vessel approach is also indicated in any vascularized superficial lesion amenable to endoscopic treatment.ESD was performed in the retroflex view using an Evis Exera II video processor, an H180 gastroscope, an ERBE ICC 200, and CO2 insufflation. As tools, IT-nano, needle knife, hook knife, hemostatic forceps, and a distal cap were used. The lifting solution was a mixture of normal saline, hyaluronic acid, epinephrine, and indigo carmine.A hemicircumferential superficial granular lateral spreading tumor was observed in the lower rectum. Indigo carmine dye spray facilitated the identification of the lesion's margin and demonstrated no ulcer, converging folds, or large nodules. After the submucosal (SM) injection, a shallow mucosal incision was made in the retroflex view using a conventional needle knife, followed by the circumferential incision at the proximal side using an IT-nano. The SM layer was dissected at a superficial level to avoid large SM vessels, thus preventing intraoperative bleeding and maintaining a clean surgical field. Small vessels were selectively coagulated mainly by using the small disc located at the back of the insulated tip as the SM later was superficially dissected. To facilitate precise coagulation, a stepwise dissection technique was used for larger vessels. After identification, the vessel was first exposed by dissecting the surrounding SM layer at the left and right sides using the long blade of IT-nano, with blunt dissection of the surrounding tissue at the vessels' posterior aspect using a Hook knife. Double-vessel sealing using a hemostatic forceps was performed both at the rectal and tumor sides. Lastly, the vessel was transected between sealed segments using the IT-nano, without major bleeding. The circumferential incision was completed at the left side and distally extended to the anal canal where large hemorrhoidal bundles were seen. A needle knife was used to complete the SM dissection and, here, the final cut. En bloc resection was successfully achieved without intraoperative bleeding.The en bloc resected specimen was 85mm in size, and squamous epithelium of the anal canal was observed at the distal margin. Colonoscopy 5 months post-ESD revealed adequate healing, no stenosis and no hemorrhoids.Coagulation and hemostasia should be promptly carried out whenever inadvertent injury to large vessels and subsequent bleeding occurs during lateral exposure, posterior blunt dissection, double coagulation, and transection of vessels.Curative ESD can be achieved in large rectal LSTs that extend to the dentate line with large internal hemorrhoids. Strategies to minimize intraoperative bleeding during ESD should be considered and include the following:•An SM dissection from the proximal tumor margin in the retroflex view to circumvent contact with hemorrhoids.•A differential level of dissection to prevent inadvertent vessel injury-shallow first to avoid large SM vessels and deeper above the muscular layer closer to the dentate line to shut off blood supply by penetrating hemorrhoidal vessels.•Last but not least, a selective approach to vessels to reduce the risk of bleeding, with direct coagulation for small vessels and with lateral exposure, posterior blunt dissection, double-vessel sealing, and transection between sealed segments for larger vessels.

ID: 3525679 SAFETY AND EFFICACY OF HOT VERSUS COLD AVULSION FOR TREATMENT OF RESIDUAL, NON-LIFTING COLONIC POLYPS DURING EMR PROCEDURE

Endoscopic mucosal resection (EMR) is considered the standard practice for removal of large (≥20mm) lateral spreading colorectal lesions. Some lesions fail to lift during submucosal injection which may indicate deep invasion but is frequently due to prior biopsy/snare or tattoo induced fibrosis of otherwise resectable lesions. Recent studies found that using avulsion with biopsy forceps as an adjunct to EMR may effectively treat fibrotic non-lifting areas. Avulsion can be done with electrosurgery (hot) or without (cold). There are insufficient studies comparing the safety and efficacy of both techniques

Coupled SPH-DEM simulations of liquefaction-induced flow failure

A fully Lagrangian particle-based method for coupled fluid-particle interaction is utilized to evaluate flow liquefaction of saturated granular soils overlain by an impermeable crust. The solid particles are modelled as spherical particles using the discrete element method (DEM). The smoothed particle hydrodynamics (SPH) is employed to model the interstitial fluid using an averaged form of Navier-Stokes equations that accounts for the presence of the solid phase. The coupling between SPH and DEM is achieved through local averaging techniques and well-established semi-empirical formulas for fluid-particle interaction. The responses of loose and dense level granular deposits overlain by an impermeable crust to a seismic excitation are first analyzed. The loose deposit exhibited significant pore pressure development and liquefaction while the dense deposit barely showed any considerable buildup of pore pressure and did not liquefy. The formation of a water film was visible at the interface between the top crust and the underlying liquefied soil. When the same deposits were tilted to form an infinite slope, the loose deposit exhibited flow lgiquefaction at the location immediately underneath the impermeable crust and large shear strains accumulated within a thin layer immediately below the crust. Flow liquefaction was marked by dilative behavior at the surface of the liquefied sand and large lateral spreading that continued post-shaking. Void redistribution was observed along the loose deposit in the form of dilation for a thin layer near sand surface and contraction for the deeper depth. The dense sloping deposit did not liquefy and flow liquefaction was not observed.

On the Accuracy of Voluntary Observing Ship’s Records

Abstract A one-to-one comparison of the significant wave height reported by Voluntary Observing Ships (VOS) with the ERA-interim database is performed. A preliminary filtering procedure allows excluding reports affected by the most evident observations’ errors and removing the systematic biases in order to clean up the database. A statistical analysis confirms the previous finding regarding the goodness of the database when analyzing average values, but also highlights a large spreading of the observations. The work identifies critical areas and conditions in which the mismatch between numerical data and observations is more significant. The pattern of the differences reveals a regional consistency with VOS overestimating the significant wave height in marginal and enclosed seas as well as in the western sides of the oceans, while showing good matches in the eastern sides and offshore areas, except in the southern oceans where VOS leads to underestimations. The causes of such differences are finally discussed.

Photodissociation of the methyl radical: the role of nonadiabatic couplings in enhancing the variety of dissociation mechanisms.

The nonadiabatic photodissociation dynamics of the CH3 (and CD3) radical from the 3pz and 3s Rydberg states is investigated by applying a one-dimensional (1D) wave packet model that uses recently calculated ab initio 1D electronic potential-energy curves and nonadiabatic couplings. Calculated predissociation lifetimes are found to be too long as compared to the experimental ones. The 1D dynamical model, however, is able to predict qualitatively and explain the fragmentation mechanisms that produce the hydrogen-fragment translational energy distributions (TED) measured experimentally for the ground vibrational resonance of the 3pz and 3s Rydberg states (CH3(v = 0, 3pz) and CH3(v = 0, 3s)). The CH3(v = 0, 3pz) TED found experimentally displays a rather large energy spreading, while the experimental CH3(v = 0, 3s) TED is remarkably more localized in energy. The present model also predicts a widely spread CH3(v = 0, 3pz) TED, produced by a complex dissociation mechanism which involves predissociation to one dissociative valence state through a nonadiabatic coupling, as well as transfer of population to a second valence state through three conical intersections. Also in agreement with experiment, the model predicts a rather localized CH3(v = 0, 3s) TED because the conical intersections no longer operate in this photodissociation process, and predissociation occurs only into a single valence state. Another complex dissociation mechanism is predicted by the model for initial CH3(v > 0, 3s) and CD3(v > 0, 3s) resonances. In this case the mechanism is gradually activated, as vibrational excitation increases, by the interplay between the two nonadiabatic couplings connecting the 3s and 3px,y Rydberg states with the dissociative 2A1 valence state, and produces complex TEDs with signals from several resonances of both 3s and 3px,y. Thus the present 1D quantum model reveals a rich photodissociation dynamics of methyl, where a variety of complex fragmentation mechanisms is favored by the presence of different nonadiabatic couplings between the electronic states involved.

Regulation of gene transfection by cell size, shape and elongation on micropatterned surfaces.

Gene transfection has been widely studied due to its potential applications in tissue repair and gene therapy. Many studies have focused on designing gene carriers and developing novel transfection techniques. However, the influence of cell size, shape and elongation on gene transfection has rarely been investigated. In this study, poly(vinyl alcohol)-micropatterned surfaces were prepared to precisely manipulate the size, shape and elongation of mesenchymal stem cells, and the influences of these factors on gene transfection were investigated. Cell size showed a significant influence on gene transfection. Elongation could affect the gene transfection of large cells but not small cells. Cells with a large spreading area and high aspect ratio showed high transfection with exogenous plasmid DNA. In particular, the transfection efficiency was the highest in micropatterned cells with a spreading area of 5024 μm2 and an aspect ratio of 8 : 1. In contrast, cell shape had no significant influence on gene transfection. The different influences of cell size, shape and elongation were correlated with their respective impacts on cytoskeletal structures, cellular nanoparticle uptake and DNA synthesis. Cells with a large size and elongated morphology showed well-organized actin filaments with a high cellular modulus, therefore promoting cellular nanoparticle uptake and DNA synthesis. Cells with different shapes showed similarities in actin filament organization, cellular modulus, uptake capacity and DNA synthesis. The results suggest the importance of cell size and elongation in exogenous gene transfection and should provide useful information for gene transfection and gene therapy.

Evaluation of Glycerylphytate Crosslinked Semi- and Interpenetrated Polymer Membranes of Hyaluronic Acid and Chitosan for Tissue Engineering.

In the present study, semi- and interpenetrated polymer network (IPN) systems based on hyaluronic acid (HA) and chitosan using ionic crosslinking of chitosan with a bioactive crosslinker, glycerylphytate (G1Phy), and UV irradiation of methacrylate were developed, characterized and evaluated as potential supports for tissue engineering. Semi- and IPN systems showed significant differences between them regarding composition, morphology, and mechanical properties after physicochemical characterization. Dual crosslinking process of IPN systems enhanced HA retention and mechanical properties, providing also flatter and denser surfaces in comparison to semi-IPN membranes. The biological performance was evaluated on primary human mesenchymal stem cells (hMSCs) and the systems revealed no cytotoxic effect. The excellent biocompatibility of the systems was demonstrated by large spreading areas of hMSCs on hydrogel membrane surfaces. Cell proliferation increased over time for all the systems, being significantly enhanced in the semi-IPN, which suggested that these polymeric membranes could be proposed as an effective promoter system of tissue repair. In this sense, the developed crosslinked biomimetic and biodegradable membranes can provide a stable and amenable environment for hMSCs support and growth with potential applications in the biomedical field.

S0138 Soft Coagulation of the Resection Margin for the Prevention of Residual or Recurrent Adenoma After Endoscopic Mucosal Resection of Large Sessile Colonic Polyps: A Multi-Center, Randomized Controlled Trial

INTRODUCTION: Endoscopic mucosal resection (EMR) of large (≥20 mm) lateral spreading lesions (LSLs) of the colon is effective in decreasing the incidence of colorectal malignancy and avoiding surgery. A drawback of colonic EMR is the adenoma residual/recurrence rate (15-30%) on first surveillance colonoscopy. A single randomized controlled trial (RCT) from Australia showed that prophylactic coagulation of the EMR margin with the tip of a snare (snare tip soft coagulation - STSC) reduced adenoma recurrence. Definitive evidence usually requires at least two RCTs that corroborate the findings. The aim of our study was to confirm the efficacy of STSC to reduce the rate of residual/recurrent adenoma following EMR. METHODS: An RCT comparing standard EMR (control arm) to EMR + STSC (active arm) for the resection of large LSLs at three tertiary referral centers (Mayo Clinic campuses in Jacksonville, FL; Scottsdale, AZ; and Rochester, MN) was performed. Surveillance colonoscopies with photo documentation using standardized near-focus NBI and biopsies were performed at 6 months post resection. The primary endpoint was the presence of residual/recurrent adenoma at the prior EMR site. The protocol was approved by the Institutional Review Board of Mayo Clinic and registered (NCT01789749). RESULTS: A total of 148 patients from the 3 sites (117, FL; 17, AZ; and 14, MN) were randomized: 75 in the control arm and 73 in the active arm. The primary outcome, histologically confirmed residual/recurrence at first follow-up, was available for 114 patients. Median duration to first follow-up was 6.7 months [IQR 6, 8.7]. Except for the variables of prior biopsy and adenoma recurrence, there were no differences between the two groups with regard to other variables, including patient demographics, size and location of lesions, polyp histology, and use of clips (Table 1). Among the 114 patients who had their first follow-up, 27 patients had histologically confirmed residual/recurrence: 20/58 (34%) in the control arm versus 7/56 (12%) in the active arm, unadjusted RR = 0.36 (95% CI 0.17–0.79, P = 0.011) (Table 2). When adjusting for previous biopsy, the use of STSC was associated with a lower rate of residual/recurrent adenoma with adjusted RR = 0.37 (95% CI 0.17–0.83; P = 0.015). CONCLUSION: The use of snare tip soft coagulation as adjuvant treatment to EMR of large lateral spreading lesions significantly reduces the risk of residual or recurrent adenoma at follow-up.Table 1.: EMR versus EMR + STSC for Large Lateral Spreading LesionsTable 2.: Adenoma residual/recurrence among patients who had a first follow-up colonoscopy

A liquefaction case study of gently sloping gravelly soil deposits in the near-fault region of the 2008 Mw7.9 Wenchuan earthquake

The 2008 Mw7.9 Wenchuan earthquake in China caused widespread soil liquefaction and ground failures. A liquefaction case study of gently sloping ground at Yingxiu Town in the near-fault region is presented, which features its relatively thick deposits of sand-gravel mixtures, high soil stiffness, extremely intensive ground motion, large lateral spreading and severe damage of superstructure. The details of ground motion, site condition, field manifestations of liquefaction, subsurface soil profiles and field testing of shear wave velocities are presented. A conceptual binary mixture model is proposed to explain the gravel content effect on the stiffness and liquefaction resistance of gravelly soils. A preliminary liquefaction triggering evaluation method for gravelly soils is proposed by considering the gravel content correction of shear wave velocities based on the existing simplified procedure for typical sandy soils. The failure mechanism of the Baihua Bridge built at this site is explored, and the liquefaction-induced lateral spreading in down-slope direction might aggravate the failure process by imposing a large kinematic load on the piers besides the inertial forces transferred from the superstructure.

Seismic performance of pile group-structure system in liquefiable and non-liquefiable soil from large-scale shake table tests

Observations from previous strong earthquakes reported severe damage of piles installed in different soils, particularly liquefiable saturated sand deposits. This paper examines the seismic performance of pile group-structure system in liquefiable and non-liquefiable sand deposits using large-scale shaking table tests, and discusses the possible failure modes of pile foundation in liquefied site and non-liquefied site. Accelerations and strains of piles, and lateral displacements and accelerations of model soil were recorded. The measured piles’ accelerations and strains were used to calculate their bending moment profiles during the shaking, while the soil dynamic shear strain – shear stress curves were obtained using measured soil accelerations. In addition, characteristics of dynamic responses for liquefied and non-liquefied sites were evaluated by comparing trends of acceleration and lateral displacements of model soil. Furthermore, the failure mode for pile foundations in liquefiable and non-liquefiable site were elucidated from the observed responses of the structure-pile foundation. It was found that (1) the stiffness of liquefied site degraded more significantly (compared to non-liquefies site) due to increase in pore water pressure, but the non-liquefied site experienced higher amplification of acceleration; (2) large lateral spreading did not occur in the liquefiable site experiment due to the horizontal surface of the underlying stable (non-liquefied) soil; (3) profiles of pile bending moment differed for liquefied and non-liquefied sites for the same excitation, which impacted the permanent deformation of the piles. The test results in this study can be used to validate related numerical models.

An Experimental Study on the Way Bottom Widening of Pier Foundations Affects Seismic Resistance

The resistance of a pier to horizontal loads, like seismic loads, is due to the flexural rigidity of its foundations and the horizontal subgrade reaction. In the event of a massive earthquake, the latter becomes very small because of the softening of the ground, while the structure may experience a large inertial force and lateral spreading pressure. Therefore, structures with high seismic resistance are required in areas with high seismicity. When a wide caisson is used as a pier foundation, a rotational resistance moment caused by the vertical subgrade reaction acting on the foundation bottom can be expected. Although this rotational resistance moment increases if the foundation is widened, in design practice the subgrade reaction coefficient is evaluated as being low under such circumstances. Therefore, even if the foundation is widened, the rotational resistance moment does not increase greatly. Rotational resistance commensurate with the increased construction cost due to foundation widening cannot be expected. In the present study, horizontal loading experiments were performed at one pier with a normal foundation and at one with widened at the bottom foundation, and the way that the widening affected the seismic performance was examined. The results show that compared with the normal foundation, the bottom-widened one experienced far less displacement and offered higher earthquake resistance.

Ultrasonic-Driven Spreading of Liquid Solder on Nonwetting Substrates

In this work, the spreading of a solder droplet on a substrate agitated by ultrasonic vibration was recorded by a high-speed camera. The dynamics and physical processes of the spreading, such as corrugate formation and atomization, were investigated. Results showed the solder droplet was able to spread on a nonwetting substrate, and it presented periodic expanding-shrinking spreading characteristics with a periodicity of dozens of acoustic periods. Corrugates formed as a result of the capillary wave propagation on the droplet, and the formation became intensive on a violently vibrating surface. Atomization preferentially occurred at the spreading front during solder expansion, where the liquid solder appeared as a film and burst on the whole droplet with strong vibration. High ultrasonic power resulted in fast spreading and a large spreading diameter. In particular, the solder droplet exhibited fast spreading and a large spreading diameter on the TC4 alloy with high characteristic impedance. The Sn-4Cu solder with large viscosity spread slowly and exhibited a small spreading diameter.

Parallel epidemics, or nearly so: Certainties and uncertainties about SARS-CoV-2 in Italy

Parallel epidemics, or nearly so: Certainties and uncertainties about SARS-CoV-2 in Italy

Biomimetic Bilayer Scaffold as an Incubator to Induce Sequential Chondrogenesis and Osteogenesis of Adipose Derived Stem Cells for Construction of Osteochondral Tissue.

Toward osteochondral tissue construction, the present study introduced a bilayer scaffold to induce sequential chondrogenesis and osteogenesis of stem cells in vitro. Two scaffolds that are both based on poly(l-glutamic acid) (PLGA) and chitosan (CS) were combined to form the bilayer scaffold. The cartilage region was the covalently cross-linked PLGA/CS hydrogel with a tubular pore structure, possessing a swollen network to prevent cellular adhesion, while inducing spontaneous cellular aggregate formation. The bone region was the electrostatically cross-linked PLGA-grafted nano hydroxyapatite (nHA-g-PLGA)/CS scaffold, which supported cellular adhesion and spreading. Human adipose derived stem cells (hASCs) were seeded into the cartilage region and observed to aggregate, formimg multicellular spheroids, which subsequently fused to rod-like aggregates with a larger size. At the same time, hASCs in aggregates crossed the interface and entered the bone region, presenting adhesion and spreading. With the induction of bone morphogenetic protein 2 (BMP-2) and insulin-like growth factor 1 (IGF-1) during the first 14 days and BMP-2 alone during the last 14 days, hASCs aggregates in the cartilage region underwent chondrogenesis, expressing an abundant cartilage matrix including glycosaminoglycans (GAGs) and type II collagen (COL II) at 28 days. The chondrogenic induced hASCs migrated in the bone region turned to osteogenesis at 28 days, which was associated with their large spreading area and the switch of the induce factor. Thus, the present bilayer scaffold induced the different distribution of hASCs, resulting in subsequent chondrogenesis and osteogenesis, realizing osteochondral tissue construction in vitro.

Distortion-Free Sensing of Neural Activity Using Graphene Transistors.

Graphene solution-gated field-effect transistors (g-SGFETs) are promising sensing devices to transduce electrochemical potential signals in an electrolyte bath. However, distortion mechanisms in g-SGFET, which can affect signals of large amplitude or high frequency, have not been evaluated. Here, a detailed characterization and modeling of the harmonic distortion and non-ideal frequency response in g-SGFETs is presented. This accurate description of the input-output relation of the g-SGFETs allows to define the voltage- and frequency-dependent transfer functions, which can be used to correct distortions in the transduced signals. The effect of signal distortion and its subsequent calibration are shown for different types of electrophysiological signals, spanning from large amplitude and low frequency cortical spreading depression events to low amplitude and high frequency action potentials. The thorough description of the distortion mechanisms presented in this article demonstrates that g-SGFETs can be used as distortion-free signal transducers not only for neural sensing, but also for a broader range of applications in which g-SGFET sensors are used.

Tracking COVID-19 by Tracking Infectious Trajectories.

Nowadays, the coronavirus pandemic has and is still causing large numbers of deaths and infected people. Although governments all over the world have taken severe measurements to slow down the virus spreading (e.g., travel restrictions, suspending all sportive, social, and economic activities, quarantines, social distancing, etc.), a lot of persons have died and a lot more are still in danger. Indeed, a recently conducted study [1] has reported that 79% of the confirmed infections in China were caused by undocumented patients who had no symptoms. In the same context, in numerous other countries, since coronavirus takes several days before the emergence of symptoms, it has also been reported that the known number of infections is not representative of the real number of infected people (the actual number is expected to be much higher). That is to say, asymptomatic patients are the main factor behind the large quick spreading of coronavirus and are also the major reason that caused governments to lose control over this critical situation. To contribute to remedying this global pandemic, in this article, we propose an IoTa investigation system that was specifically designed to spot both undocumented patients and infectious places. The goal is to help the authorities to disinfect high-contamination sites and confine persons even if they have no apparent symptoms. The proposed system also allows determining all persons who had close contact with infected or suspected patients. Consequently, rapid isolation of suspicious cases and more efficient control over any pandemic propagation can be achieved.

Analysis of turbulent flow in a channel roughened by two-dimensional ribs: effect of first rib width

This work investigates the turbulent flow in a channel roughened by seven ribs of rectangular cross section disposed transversely. The flow configurations of identical ribs from the first one generate a large eddy spreading along the top of the two first ribs, trapping the flow of the first cavity. The widening of the first rib may solve this problem. Therefore, this flow configuration might be required in building structure applications necessitating regular structures from the first cavity. Streamlines contours indicates that the first rib behaves as a forward facing step when L1 > 5h (L1 is the first rib width), regular structures of the flow occurs from the first cavity. The effect of wider first rib is highlighted by friction and pressure coefficients profiles and those of the turbulent kinetic energy. Its effect also appears in the Darcy friction factor. The viscous and pressure forces applied on the first rib and the 5th pitch roughness indicate that the pressure force is dominant. Darcy friction factor characterizing the flow and pressure drag coefficient evaluated at the 5th pitch roughness remains independent of Reynolds number, while the drag force applied on the first rib increases when Reynolds number augments.

Design and Circuit Modeling of Graphene Plasmonic Nanoantennas

Nanonntennas are critical elements of nanoscale wireless communication technologies with potential to overcome some of the limitations of on-chip interconnects. In this paper, we model the optical response of graphene-based nanoantennas (GNAs) using an equivalent resistive-inductive-capacitive (RLC) circuit by incorporating plasmonic effects that are present in graphene at terahertz (THz) frequencies. The equivalent circuit model is used to estimate the resonance characteristics of the nanoantenna, thereby facilitating geometry and material optimization. Three GNA structures are considered, namely bowtie, circular, and rectangular dimers with vacuum and silicon dioxide dielectric environment. We characterize the radiation efficiency, the Purcell factor, the quality factor, and the resonant frequency of various antennas with respect to the physical properties of the surrounding dielectric media and the graphene sheet. The GNAs are designed for a resonant frequency in the range of 10 – 25 THz with field enhancements around 104 – 105 and radiation efficiency ~5 – 16%. The circuit model is applied to examine the trade-off between the radiation efficiency and the field enhancement in the antenna gap. While bowtie antennas have higher field enhancement due to charge accumulation in their pointed structure, they suffer from low radiation efficiency stemming from the large spreading resistance losses. The circuit model is validated against finite-difference time-domain (FDTD) simulations conducted in Lumerical, and excellent match between the model and numerical results is demonstrated in the THz regime. The circuit models can be readily used in a hierarchical circuit simulator to design and optimize optical nanoantennas for THz communication in high-performance computing systems.