Charles Lin

Bone progenitor dysfunction induces myelodysplasia and secondary leukaemia

Mesenchymal cells contribute to the ‘stroma’ of most normal and malignant tissues, with specific mesenchymal cells participating in the regulatory niches of stem cells. By examining how mesenchymal osteolineage cells modulate haematopoiesis, here we show that deletion of Dicer1 specifically in mouse osteoprogenitors, but not in mature osteoblasts, disrupts the integrity of haematopoiesis. Myelodysplasia resulted and acute myelogenous leukaemia emerged that had acquired several genetic abnormalities while having intact Dicer1. Examining gene expression altered in osteoprogenitors as a result of Dicer1 deletion showed reduced expression of Sbds, the gene mutated in Schwachman–Bodian–Diamond syndrome—a human bone marrow failure and leukaemia pre-disposition condition. Deletion of Sbds in mouse osteoprogenitors induced bone marrow dysfunction with myelodysplasia. Therefore, perturbation of specific mesenchymal subsets of stromal cells can disorder differentiation, proliferation and apoptosis of heterologous cells, and disrupt tissue homeostasis. Furthermore, primary stromal dysfunction can result in secondary neoplastic disease, supporting the concept of niche-induced oncogenesis.

Multilayer Black Phosphorus as a Versatile Mid-Infrared Electro-optic Material.

We investigate the electro-optic properties of black phosphorus (BP) thin films for optical modulation in the mid-infrared frequencies. Our calculation indicates that an applied out-of-plane electric field may lead to red-, blue-, or bidirectional shift in BPs absorption edge. This is due to the interplay between the field-induced quantum-confined Franz-Keldysh effect and the Pauli-blocked Burstein-Moss shift. The relative contribution of the two electro-absorption mechanisms depends on doping range, operating wavelength, and BP film thickness. For proof-of concept, simple modulator configuration with BP overlaid over a silicon nanowire is studied. Simulation results show that operating BP in the quantum-confined Franz-Keldysh regime can improve the maximal attainable absorption as well as power efficiency compared to its graphene counterpart.

Analytical model for metal-insulator-metal mesh waveguide architectures

Metal–insulator–metal (MIM) waveguide mesh structures utilize X-junctions as power distribution elements to create interference and feedback effects, thereby providing rich device functionality. We present a generalized analytical model for MIM mesh structures by incorporating a modified characteristic impedance model for MIM junctions into the scattering matrix formalism. The modified impedance model accounts for metal absorption and provides accurate prediction of plasmonic field distribution at X-junctions in terms of both magnitude and phase. Closed-form expressions for 2×1 and 2×2 MIM mesh architectures as well as MIM stub structures are then obtained and are dependent only on waveguide geometry and junction configuration. The model does not require numerically extracted parameters, and results agree, within a few percent, with those obtained from finite-difference time-domain method for both two-dimensional and three-dimensional waveguide geometries. The capability of the model for efficient design and optimization of junction-based MIM devices is demonstrated through the development of various filter and resonant devices.

Polarization Engineering in Nano-Scale Waveguides Using Lossless Media

A device that achieves controllable rotation of the state of polarization by rotating the orientation of the eigenmodes of a waveguide by 45° is introduced and analyzed. The device can be implemented using lossless materials on the nanoscale and helps circumvent the inherent polarization dependence of photonic devices realized within the silicon-on-insulator platform. We propose and evaluate two novel polarization rotator-based schemes to achieve polarization engineering functions: 1) A multipurpose device, with dimensions on the order of a few wavelengths which can function as a polarization splitter or an arbitrary linear polarization state generator. 2) An energy efficient optical modulator that utilizes eigenmode rotation and epsilon near zero effects to achieve high extinction ratio, polarization insensitive amplitude modulation without the need to sweep the device geometry to match the TE and TM mode attributes. By using indium tin oxide as an example for a tunable material, the proposed modulator provides polarization insensitive operation and can be realized with a modulation bandwidth of 112 GHz, a length of 1800 nm, an energy per bit of 7.5 f.J and an optical bandwidth of 210 nm.

Equivalent circuit model for plasmonic slot waveguides networks

Plasmonic slot waveguide (PSW) provides unique ability to confine the light in few nanometers only. It also allows for near perfect transmission through sharp bends. These features motivate utilizing the PSW in various on chip applications that require nanoscale manipulation of light. The main challenge of using these PSWs are the associated high losses that allow for propagation length of ~10 μm only. However, this constraint plays a minimal rule for circuits designed to have footprint in the order of few micrometers only. Thus, designing PSW with compact size and superior performance is of prime essential. Finite difference time domain (FDTD) is usually utilized for modeling of such networks. This technique is, however, inefficient as it requires very fine grid and carful manipulation of the boundary condition to avoid spurious reflections. In the paper, we present our recent equivalent circuit model that is capable of accurately modeling the various junctions including T and X shapes. This model is highly efficient and allows for obtaining a closed form expression of the response of any network of PSW with accuracy comparable to the FDTD results.

A nonlinear stochastic low-order energy balance climate model

The effects of stochastic forcing on a one-dimensional, energy balance climate model are considered. A linear, stochastic model is reviewed in analogy with the Brownian motion problem from classical statistical mechanics. An analogous nonlinear model is studied and shows different behavior from the linear model. The source of the nonlinearity is the dynamical heat transport. The role of nonlinearity in coupling different temporal and spatial scales of the atmosphere is examined. The Fokker-Planck equation from statistical mechanics is used to obtain a time evolution equation for the probability density function for the climate, and the climatic potential function is calculated. Analytical solutions to the steady-state Fokker-Planck equation are obtained, while the time-dependent solution is obtained numerically. The spread of the energy produced by a stochastic forcing element is found to be characterized by movement mainly from smaller to larger scales. Forced and free variations of climate are also explicitly considered.

The effects of latitudinal asymmetries on baroclinic instability

Abstract Baroclinic instability of zonal flows with different latitudinal structures is examined, using a linear, quasi‐geostrophic two‐level s‐plane model. The flows have different amounts of skew, with respect to the channel centre, at different vertical levels. The results are interpreted in terms of the instability of the baroclinic components of the zonal flows. Because of the presence of latitudinal asymmetries, a spectrum of meridional modes is generated in the perturbation. In general, the meridional spectrum has two peaks: a primary peak at the planetary basic flow scale, and a secondary peak near the radius of deformation. As neutral stability is approached, the latter scale becomes more important, i.e. there is a tendency for more small‐scale structure near neutral stability. The perturbation zonal scale is close to the radius of deformation. The eddy amplitudes and momentum fluxes are also examined. The case that best applies to the atmosphere is also discussed.

Broadband Compact Silicon Wire to Silicon Slot Waveguide Orthogonal Bend

An ultra-compact 90° bend between silicon (Si) wire and silicon slot waveguide (SSW) with a footprint of ~725 nm × 500 nm is experimentally demonstrated on silicon-on-insulator substrate. By achieving momentum matching of the waveguides through an orthogonal junction placement, and maximizing modal overlap through an angled facet, coupling efficiency of ~70% and 3-dB bandwidth of over 500 nm has been achieved. The nominal experimental transmission through cascaded input (Si wire to SSW) and output (SSW to Si wire) orthogonal junctions match closely those obtained from simulations, both in the range from 1270 to 1360 nm and from 1480 to 1590 nm. For slot widths ranging from 30 to 230 nm, our Si wire-SSW bend can achieve coupling efficiency comparable to that of a direct butt-coupler over a 400 nm bandwidth. This compact and wideband waveguide bend serves as an important component to enable dense integration between conventional Si wire and SSW.

Parameterization of meridional energy flux in a one-dimensional climate model

SummaryThe zonally averaged meridional energy transport is parameterized in terms of the zonally averaged temperature gradient and its radiative equilibrium value. Two climate regimes are identified: radiative equilibrium and isothermal climates. The transport and temperature gradient are intermediate between corresponding quantities of these two climates. The parameterization assumes a linear increase of transport as temperature gradient departs from its radiative equilibrium value. The parameterization is formulated using a one-dimensional climate model. Ice-albedo feedback provides the mechanism for climate changes. The parameterization works well for climates associated with seasonal changes.ZusammenfassungDer zonal gemittelte, meridionale Energietransport wird in Abhängigkeit vom zonal gemittelten Temperaturgradienten und seinem Strahlungsgleichgewicht parameterisiert. Zwei Klimaregime können identifiziert werden: Strahlungsgleichgewicht und isothermes Klima. Der Transport und der Temperaturgradient befinden sich zwischen den korrespondierenden Werten dieser zwei Klimate. Die Parameterisierung nimmt eine lineare Zunahme des Transportes mit der Abweichung des Temperaturgradienten vom seinem Strahlungsgleichgewichtswert an. Die Parameterisierung wird unter Verwendung eines eindimensionalen Klimamodelles formuliert. Die Eis-Albedo-Rückkopplung liefert den Mechanismus für Klimadnderungen. Die Parameterisierung funktioniert gut fur Klimate, welche jahreszeitliche Anderungen beinhalten.

Efficient plasmonic integrated circuits

A novel approach that enables long range hybrid plasmonic modes to be supported in asymmetric structures will be discussed. Examining the modal behavior of an asymmetric hybrid plasmonic waveguide (AHPW) reveals that field symmetry on either side of the metal is the only necessary condition for plasmonic structures to support long range propagation. In this talk we shall demonstrate that this field symmetry condition can be satisfied irrespective of asymmetry in waveguide structure, material, or even field profile. The versatility in the choice of parameters allows for long range hybrid plasmonic modes to be achieved in generic structures. Altering the existing limitations of these performance metrics (mode area and propagation losses) can have significant implications on the designs of active devices. As illustrative example, the utility of these waveguide designs is demonstrated when combined with novel material such as ITO to realize optoelectronic components such as filters, modulators and switches with record footprint, performance and insertion losses.