Y. Neve-Oz

Absorbing Frequency-Selective-Surface for the mm-Wave Range

We report on a millimeter-wave (mm-wave) absorber based on the frequency selective surface. It consists of a periodic array of resistive patches on a grounded dielectric layer. By varying the shape of the patches and the distance between them, the device can be tuned to absorb in a given frequency band. We designed and fabricated several devices consisting of square arrays of Nichrome circles or rings. The design was targeted to the mm-wave range, 75-110 GHz. Our measurements of the mm-wave reflection from these devices show good agreement with computer simulations. We discuss the use of our device as a microbolometer array.

Mechanisms of localized activation of the T cell antigen receptor inside clusters.

The T cell antigen receptor (TCR) has been shown to cluster both before and upon engagement with cognate antigens. However, the effect of TCR clustering on its activation remains poorly understood. Here, we used two-color photo-activated localization microscopy (PALM) to visualize individual molecules of TCR and ZAP-70, as a marker of TCR activation and phosphorylation, at the plasma membrane of uniformly activated T cells. Imaging and second-order statistics revealed that ZAP-70 recruitment and TCR activation localized inside TCR clusters. Live cell PALM imaging showed that the extent of localized TCR activation decreased, yet remained significant, with cell spreading. Using dynamic modeling and Monte-Carlo simulations we evaluated possible mechanisms of localized TCR activation. Our simulations indicate that localized TCR activation is the result of long-range cooperative interactions between activated TCRs, or localized activation by Lck and Fyn. Our results demonstrate the role of molecular clustering in cell signaling and activation, and are relevant to studying a wide range of multi-molecular complexes. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.

Magnetic-field tunable photonic stop band in metallodielectric photonic crystals

Abstract We fabricated an artificial crystal consisting of a stack of containers with magnetizable ferromagnetic spheres. In the absence of external magnetic field the particles are in disordered state while in the presence of the field the particles self-assemble in almost a perfect hexagonal order. The degree of order is controlled by magnetic field. We study magnitude and phase of the frequency-dependent mm-wave transmission through the stack as a function of magnetic field. In the ordered state there are well-defined photonic stopbands separated by the regions where transmission is close to unity (“transparency windows”) while in the disordered state these regions mostly disappear. By varying magnetic field we achieve effective tuning of the mm-wave transmission through the stack.

Nanoscale kinetic segregation of TCR and CD45 in engaged microvilli facilitates early T cell activation

T cells have a central function in mounting immune responses. However, mechanisms of their early activation by cognate antigens remain incompletely understood. Here we use live-cell multi-colour single-molecule localization microscopy to study the dynamic separation between TCRs and CD45 glycoprotein phosphatases in early cell contacts under TCR-activating and non-activating conditions. Using atomic force microscopy, we identify these cell contacts with engaged microvilli and characterize their morphology, rigidity and dynamics. Physical modelling and simulations of the imaged cell interfaces quantitatively capture the TCR–CD45 separation. Surprisingly, TCR phosphorylation negatively correlates with TCR–CD45 separation. These data support a refined kinetic-segregation model. First, kinetic-segregation occurs within seconds from TCR activation in engaged microvilli. Second, TCRs should be segregated, yet not removed too far, from CD45 for their optimal and localized activation within clusters. Our combined imaging and computational approach prove an important tool in the study of dynamic protein organization in cell interfaces.T cell activation is critically controlled by T cell receptor (TCR) signalling. Here the authors show, using live cell imaging, atomic force microscopy and modelling simulation, a prompt separation of TCR and CD45 that negatively correlates with TCR activation, supporting a refined kinetic segregation model of TCR signalling.

Resonant transmission of electromagnetic waves through two-dimensional photonic quasicrystals

We present numerical simulations of electromagnetic millimeter-wave propagation in a two-dimensional lattice of dielectric rods arranged in a tenfold Penrose tiling. We find (i) isotropic photonic band gap as expected for quasicrystals and (ii) localized states. We demonstrate that the high frequency edge of the second band gap is characterized by a very small refractive index (fast light). We study the transmission of electromagnetic waves in the frequency range corresponding to fast light and demonstrate that it is related to tunneling through localized states. We use the fast light phenomenon to design a focusing device—a planoconcave lens.

Bragg attenuation length in metallo-dielectric photonic band gap materials

We analyze the ability of the Bragg reflector model to account for the properties of metallo-dielectric photonic crystals. We perform mm-wave transmission measurements on photonic structure consisting of conducting spheres in air and compare our results to the model predictions. In particular, we verify the universal relation between the Bragg attenuation length and the width of the photonic stopband, which is predicted by the Bragg reflector model.

Negative Refraction and Omni Directionality in 2D Photonic Quasicrystal Superstructure

Omni‐directional negative refractive index is a desirable feature that may be hard to achieve by using conventional periodic structures. In 2D periodic photonic crystals, where rotational symmetry is four‐ or six‐ fold, negative refraction index can be achieved but it is highly anisotropic. Another way to achieve negative refraction in 2D arrays is by using photonic crystal superlattices consisting of rods with two different diameters. In this study we employ this method to build a 2D quasicrystal superlattice based on Penrose tiling. The omnidirectionality of the bandgaps that results from the quasicrystalline structure, while the effective negative index results from the superlattice. Together, these two features produce an omnidirectional negative refractive index. We demonstrate this effect by tracing the directions of phase and group velocities in the prism made of the photonic quasicrystal superlattice.

Fast Light and Focusing in 2D Photonic Quasicrystals

We present numerical studies of the electromagnetic wave propagation in a meta- material built from dielectric rods. The rods were arranged in a quasicrystalline lattice based on 10-fold Penrose tiling. We flnd wide isotropic band gaps and localized states, as expected in a quasicrystalline lattice. Our most important flnding is the presence of the band gap edge states that are characterized by a very small refractive index (fast light). We use this phenomenon to design a focusing device | a plano-concave lens.

Photonic crystal superlattice employed as left-handed planoconcave lens

We demonstrate focusing of the microwave radiation by a planoconcave lens based on photonic crystal superlattice. The superlattice consists of dielectric rods of two different diameters. The structural modulation results in a narrow transmission subband inside the band gap. The subband is characterized by a negative refractive index and high transmission efficiency. This negative refractive index arises from the Brillouin zone folding in the lattice with the composite unit cell. The full width at half maximum of the focal spot of our lens is 0.36λ×0.42λ, which is close to the Abbe limit, and the power enhancement is 2.2.

Gp41 dynamically interacts with the TCR in the immune synapse and promotes early T cell activation

The HIV-1 glycoprotein gp41 critically mediates CD4+ T-cell infection by HIV-1 during viral entry, assembly, and release. Although multiple immune-regulatory activities of gp41 have been reported, the underlying mechanisms of these activities remain poorly understood. Here we employed multi-colour single molecule localization microscopy (SMLM) to resolve interactions of gp41 proteins with cellular proteins at the plasma membrane (PM) of fixed and live CD4+ T-cells with resolution of ~20–30 nm. We observed that gp41 clusters dynamically associated with the T cell antigen receptor (TCR) at the immune synapse upon TCR stimulation. This interaction, confirmed by FRET, depended on the virus clone, was reduced by the gp41 ectodomain in tight contacts, and was completely abrogated by mutation of the gp41 transmembrane domain. Strikingly, gp41 preferentially colocalized with phosphorylated TCRs at the PM of activated T-cells and promoted TCR phosphorylation. Gp41 expression also resulted in enhanced CD69 upregulation, and in massive cell death after 24–48 hrs. Our results shed new light on HIV-1 assembly mechanisms at the PM of host T-cells and its impact on TCR stimulation.