Subwavelength grating metamaterial waveguides and ring resonators on a silicon nitride platform

We propose and demonstrate subwavelength grating (SWG) metamaterial waveguides and ring resonators on a silicon nitride platform for the first time. The SWG waveguide is engineered such that a large overlap of 53% of the Bloch mode with the top cladding material is achieved, demonstrating excellent potential for applications in evanescent field sensing and light amplification. The devices, which have critical dimensions greater than 100 nm, are fabricated using a commercial rapid turn-around silicon nitride prototyping foundry process using electron beam lithography. Experimental characterization of the fabricated device reveals excellent ring resonator internal quality factor (2.11x10^5) and low propagation loss (~1.5 dB/cm) in the C-band, a significant improvement of both parameters compared to silicon based SWG ring resonators. These results demonstrate the promising prospects of SWG metamaterial structures for silicon nitride based photonic integrated circuits.Comment: 12 pages, 7 figures, submitted to Laser & Photonics Reviews for publicatio

Cell-Cell Contact Preserves Cell Viability via Plakoglobin

Control over cell viability is a fundamental property underlying numerous physiological processes. Cell spreading on a substrate was previously demonstrated to be a major factor in determining the viability of individual cells. In multicellular organisms, cell-cell contact is likely to play a significant role in regulating cell vitality, but its function is easily masked by cell-substrate interactions, thus remains incompletely characterized. In this study, we show that suspended immortalized human keratinocyte sheets with persisting intercellular contacts exhibited significant contraction, junctional actin localization, and reinforcement of cell-cell adhesion strength. Further, cells within these sheets remain viable, in contrast to trypsinized cells suspended without either cell-cell or cell-substrate contact, which underwent apoptosis at high rates. Suppression of plakoglobin weakened cell-cell adhesion in cell sheets and suppressed apoptosis in suspended, trypsinized cells. These results demonstrate that cell-cell contact may be a fundamental control mechanism governing cell viability and that the junctional protein plakoglobin is a key regulator of this process. Given the near-ubiquity of plakoglobin in multicellular organisms, these findings could have significant implications for understanding cell adhesion, modeling disease progression, developing therapeutics and improving the viability of tissue engineering protocols

Simulation of the spatial distribution and molecular weight of polymethylmethacrylate fragments in electron beam lithography exposures

We report a three-dimensional (3D) simulation model based on the kinetic transport theory for calculating the distribution of PMMA fragments after an exposure to electron impact. The conditions employed for the modeling were chosen to resemble a typical electron beam lithography exposure. The model accounts for inelastic collisions of electrons in PMMA and resulting random main-chain scissions. We have considered gratings composed of parallel lines distanced by 10\u201350\u2004nm and exposed to electrons with energies of 10\u201360\u2004keV. By the model simulations, we have generated and analyzed the detailed 3D distributions of small PMMA fragments (one to ten monomers) that are soluble at the development stage and thus are responsible for the clearance in the gratings. In terms of the spatial distributions of soluble fragments, we have formulated the criteria that define the total clearance as well as the local grating development and investigated their dependence on the grating period, electron dose, and energy.NRC publication: Ye

Role of platelet activating factor in cardiac dysfunction, apoptosis and nitric oxide synthase mRNA expression in the ischemic-reperfused rabbit heart

Background: The role of platelet activating factor (PAF) and nitric oxide in myocardial ischemia-reperfusion (MIR) injury and the interrelationship of the two mediators is poorly understood. The contribution of PAF to apoptosis during MIR has not been studied. Objectives: To determine the contribution of PAF to ex vivo cardiac dysfunction during the initial 5 h of postischemia reperfusion, to determine the contribution of PAF to inducible nitric oxide synthase (NOS) and endothelial NOS mRNA expression during MIR, and to determine whether PAF contributes to apoptosis during MIR. Methods: Isolated blood-perfused rabbit hearts underwent 30 min of global ischemia and 5 h reperfusion. Animals were divided into four groups, which received either PAF antagonist TCV-309 or vehicle before ischemia, or were sham operated (heart perfusion only), or were control (no heart perfusion). Results: Administration of the PAF antagonist significantly improved myocardial contractility (614 mmHg/s versus 308 mmHg/s, positive dP/dt, P\u3c0.0001) and coronary vascular flow rate (5.5 mL/min versus 3.9 mL/min, P\u3c0.01) during reperfusion compared with untreated animals (values at 5 h reperfusion). Treatment with PAF antagonist significantly increased mRNA expression of endothelial NOS (2.8 versus 1.3 ratio, P\u3c0.05) compared with the untreated group. PAF antagonist reduced procaspase-3 cleavage (66 versus 108 ratio, P\u3c0.05) and DNA fragmentation (8.2 versus 11.0 positive cells per field) compared with untreated animals. Conclusions: PAF antagonism with TCV-309 protected against myocardial contractile depression and coronary vasoconstriction during the initial 5 h reperfusion. PAF may play a role in the regulation of endothelial NOS mRNA expression and contribute to apoptosis during ischemia-reperfusion in the heart