Theoretical Investigation of Intersections of Metal-Insulator-Silicon-Insulator-Metal Waveguides

We theoretically investigate simple, circle-shaped, and diamond-shaped intersections of metal-insulator-silicon-insulator-metal (MISIM) waveguides. Because of the strong light confinement of the hybrid plasmonic waveguides, the simple intersection does not work efficiently. The low efficiency of the simple intersection is improved in the other intersections, and the diamond-shaped intersection is superior to the circle-shaped one. When the footprint of the diamond-shaped intersection is just 1.96 ??m2, its throughput is between -0.68 and -0.78 dB in the wavelength interval between 1.45 and 1.60 ?? m, and its crosstalk is smaller than -18 dB in the interval. This compact, efficient intersection may pave the way to on-chip hybrid networks of photonic and plasmonic devices.ope

Tuning of length-scale and observation-error for radar data assimilation using four dimensional variational (4D-Var) method

The effects of tuning of length-scale and observation-error on heavy rainfall forecasts are investigated. Length scale and observation error are tuned based on observation minus background (O - B) covariances and theoretically expected cost function values, respectively. Tuned length scale and observation error are applied to radar data assimilation using the Four Dimensional Variational (4D-Var) method. Length-scale tuning leads to improved Quantitative Precipitation Forecast (QPF) skill for heavy precipitation, better analyses, and reduced errors of wind, temperature, humidity, and hydrometeor forecasts. The effects of observation-error tuning are not as significant as those of length-scale tuning, and they are limited to improvements in QPF skill. This is because tuned observation errors are close to pre-assumed values. Proper tuning of length-scale and observation-error is essential for radar data assimilation using the 4D-Var method

Compact Silicon Slot Waveguide Intersection Based on Mode Transformation and Multimode Interference

Silicon slot waveguide intersections are necessary for photonic-integrated circuits based on silicon slot waveguides. We theoretically investigate a compact silicon slot waveguide intersection, which consists of mode transformers and a multimode strip waveguide crossing. The mode transformer before the crossing converts the slot waveguide mode into strip waveguide modes with amplitudes and phases appropriate for efficient operation of the crossing, which is based on multimode interference. The reverse conversion happens in the mode transformer after the crossing. The investigated intersection has a throughput of -0.078 dB, a crosstalk of -41 dB, and a footprint of 79.2 mu m(2). Its properties are better than those of previous silicon slot waveguide intersections, and especially its footprint is less than 33% of the previous ones. The intersection may be used for matrix switches based on silicon slot waveguides

Satellite radiance data assimilation for binary tropical cyclone cases over the western North Pacific

A total of three binary tropical cyclone (TC) cases over the Western North Pacific are selected to investigate the effects of satellite radiance data assimilation on analyses and forecasts of binary TCs. Two parallel cycling experiments with a 6 h interval are performed for each binary TC case, and the difference between the two experiments is whether satellite radiance observations are assimilated. Satellite radiance observations are assimilated using the Weather Research and Forecasting Data Assimilation (WRFDA)'s three-dimensional variational (3D-Var) system, which includes the observation operator, quality control procedures, and bias correction algorithm for radiance observations. On average, radiance assimilation results in slight improvements of environmental fields and track forecasts of binary TC cases, but the detailed effects vary with the case. When there is no direct interaction between binary TCs, radiance assimilation leads to better depictions of environmental fields, and finally it results in improved track forecasts. However, positive effects of radiance assimilation on track forecasts can be reduced when there exists a direct interaction between binary TCs and intensities/structures of binary TCs are not represented well. An initialization method (e.g., dynamic initialization) combined with radiance assimilation and/or more advanced DA techniques (e.g., hybrid method) can be considered to overcome these limitations

Initial Nutritional Status and Clinical Outcomes in Patients With Deep Neck Infection

Objectives The current study aims to determine the correlation between nutritional status upon presentation and disease severity, as well as treatment and survival outcomes. Methods Patients who were diagnosed with deep neck infection, underwent at least one surgical drainage/debridement, and had more than 1 week of hospitalization at a tertiary medical center from 2007 to 2015 were retrospectively included. Thereafter, initial serum albumin, C-reactive protein (CRP), and body mass index (BMI) were reviewed. Results A total of 135 patients were included in the final analysis. Accordingly, the proportion of patients with simultaneous mediastinitis (21.0%), necrotizing fasciitis (12.9%), disease extent >1 cervical level (72.6%), mean CRP (22.4 mg/dL), mean length of hospitalization (25.0 days), and mean 1-week follow-up CRP (7.2 mg/dL) was significantly higher in the hypoalbuminemia group (initial serum albumin 1 cervical level (2.12), initial serum CRP over 20 mg/dL (3.79), hospitalization of more than 14 days (4.10), 1-week follow-up CRP over 5 mg/dL (3.78), and increased duration for an over 50% decrease in initial CRP (2.70) (all P<0.05). Although intravascular albumin replenishment decreased the proportion of patients with hypoalbuminemia after 2 weeks (P<0.05), it did not significantly predict better treatment outcomes. Conclusion Among the markers reflecting an individual’s nutritional state, an initial serum albumin of less than 3.0 g/dL was an independent serologic marker predicting increased disease severity and complications in patients with deep neck infection

The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH)

The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) had a Special Observing Period (SOP) that ran from November 16, 2018 to February 15, 2019, a period chosen to span the austral warm season months of greatest operational activity in the Antarctic. Some 2200 additional radiosondes were launched during the 3-month SOP, roughly doubling the routine program, and the network of drifting buoys in the Southern Ocean was enhanced. An evaluation of global model forecasts during the SOP and using its data has confirmed that extratropical Southern Hemisphere forecast skill lags behind that in the Northern Hemisphere with the contrast being greatest between the southern and northern polar regions. Reflecting the application of the SOP data, early results from observing system experiments show that the additional radiosondes

Graphene-based Nanophotonic Modulators for Near-Infrared and Mid-Infrared Applications

Department of Electrical EngineeringGraphene, one of carbon allotropes, which has a two-dimensional hexagonal crystalline structure, has been spotlighted in optoelectronics and photonics since it has extraordinary properties such as zero bandgap, high electron mobility, and electrically-tunable chemical potential. Diverse graphene-based optoelectronic and photonic devices, including optical modulators, optical sensors, and photodetectors, have been investigated up to now. This thesis focuses on graphene-based optical modulators working in the near-infrared (near-IR) and mid-infrared (mid-IR) ranges. In the near-IR range where wavelengths are between 800 nm and 2 ??m, graphene is usually utilized as an active material for optical modulators. Optical signals can be tuned by controlling the chemical potential of graphene because the interband transitions of electrons are allowed or prohibited depending on the chemical potential and photon energy. Due to this tunable absorption by graphene, a variety of graphene-based silicon photonic electroabsorption modulators (EAMs), which can be merged into silicon (Si) photonic integrated circuits, have been proposed and demonstrated. Basically, those modulators are based on the structure in which graphene is placed on the surface of a Si waveguide. Since graphene interacts with the weak evanescent field of a Si waveguide mode, the modulation depths of the previous graphene-based Si waveguide modulators are smaller than 0.16 dB/??m. In order to reduce a device footprint, different methods of integrating graphene with a Si waveguide are essentially required. In this respect, two waveguides are investigated. One is an inverted-rib-type (IRT) Si waveguide, and the other is a metal-insulator-silicon-insulator-metal (MISIM) waveguide. In the case of the former, graphene is placed within the region where the electric field of the IRT Si waveguide mode is mainly confined. In the case of the latter, graphene is placed on the narrow insulator where the electric field of the MISIM waveguide mode is strongly confined. Consequently, both the waveguides can have enhanced light-graphene interaction compared to previous graphene-based waveguides. The EAM based on the IRT Si waveguide is theoretically investigated, and its calculated modulation depth is 0.41 dB/??m. The MISIM waveguide covered with solid-electrolyte-gated graphene is experimentally demonstrated. The measured modulation depth of the MISM waveguide is 0.276 dB/??m. In addition, for a larger electrical bandwidth, the MISIM waveguide covered with double graphene layers is theoretically investigated: its calculated modulation depth and electrical bandwidth are 0.412 dB/??m and 185 GHz, respectively. In the mid-IR range where wavelengths are between 2 ??m and 20 ??m, graphene with an appropriate chemical potential has metallic characteristics such that a graphene plasmon (GP), which is a collective electron oscillation in a graphene layer, exists in the mid-IR range. The electromagnetic wave associated with a graphene plasmon is called a graphene plasmon polariton. Graphene plasmon polaritons have unique properties such as strong field confinement around an ultrathin graphene layer and tunability based on electric gating. Various mid-IR modulators using a GP have been designed and demonstrated. However, those mid-IR GP devices have a difficulty in efficiently exciting a GP and practically using it. To solve this problem, a mid-IR modulator based on grating-assisted coupling between a hybrid plasmonic waveguide mode and a GP is proposed and theoretically investigated. The operation principle of the modulator is that the grating-assisted coupling generates a rejection band in the transmission spectrum of the hybrid plasmonic waveguide. The modulation efficiency of the modulator is estimated to be 25.25 dB. To realize this modulator, it is essential to fabricate a grating with a period of less than 200 nm on a zinc sulfide (ZnS) film used for the modulator and to check if a GP can be really excited by the grating. For the purposes, a dry etching process necessary for making ZnS nanostructures is established and it is used to make various graphene-covered ZnS gratings. It is clearly observed that GPs are effectively excited by the gratings. Finally, a mid-IR perfect absorber based on a metal-insulator-metal (MIM) structure is experimentally investigated to demonstrate the feasibility of the grating-assisted coupling between a GP and an MIM waveguide mode. The absorber has the perfect absorption caused by the magnetic dipole resonance existing in the MIM structure. When the MIM waveguide mode is coupled to the GP around the graphene embedded in the insulator, the magnetic dipole resonance is suppressed, and the perfect absorption disappears. It is observed that the realized absorber has an intensity modulation of 65 %. This work not only indicates the possibility of realizing the theoretically investigated waveguide modulator but also shows the efficient free-space mid-IR modulator.clos