Determination of volume and surface scattering from saline iceusing ice sheets with precisely controlled roughness parameters

Experiments were performed at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, NH, to precisely determine the relative contributions of surface and volume scattering from saline ice that has well-known surface roughness characteristics. The ice growth phase of the experiment made use of two 6-ft diameter tanks and a 6-ft diameter mold with known roughness statistical parameters of rms height=0.25 cm and Gaussian correlation (correlation length=2.0 cm). One tank was used for growing a moderately thick saline ice sheet with very smooth surface, and the other was used for growing a thin layer of freshwater ice over the surface mold. The latter resulted in a layer with one statistically known rough boundary and one smooth boundary. Wide-bandwidth, multiple incidence angle backscattering measurements were performed, first on the bare saline ice sheet and then on the same sheet after the thin freshwater ice sheet was placed on top of it. Results indicate that the surface scattering dominates over saline ice volume scattering at all frequencies for low incidence angles for both the very smooth and Gaussian rough surfaces. The significance of volume scattering depends strongly on angle of incidence, frequency, volume scattering albedo, surface roughness, and surface correlation function     

A microwave anechoic chamber for radar-cross section measurement

A microwave anechoic chamber has been developed at the Department of Electrical Engineering, University of Malaya, for monostatic and bistatic radar-cross-section measurements. The structure of the chamber is a quarter-section geodesic dome, with a 12 foot radius, and raised three feet above the floor. An antenna railing system is installed inside the chamber. The antennas can be moved along the rails in the elevation direction, with the microwave beam pointing at the center of the dome where the target is located. This design enables a very large combination of incidence and scattering angles in bistatic measurements. Four transmitting antennas are fixed at different elevation angles next to one of the antenna rails. By using an azimuth-over-elevation positioner as the pedestal for the target, and by positioning the movable antenna along that rail beside those fixed transmitting antennas, monostatic measurements with incidence angles ranging from 0 to 90 degrees can be accomplished. A vector network analyzer is utilized to measure the amplitude and phase of the radar returns. An IEEE-488.2 interface bus is used to control various hardware components, as well as to perform data acquisition. A computer program was written to automate the measurement system. Data are stored in raw format, and processed later with dedicated software, so that different processing methods and parameters can be applied. This paper highlights the design and construction of the microwave anechoic chamber, as well as the measurement-system configuration for scattering-cross-section measurements     

Zr–Zeolite Beta: A New Heterogeneous Catalyst System for the Highly Selective Cascade Transformation of Citral to (±)‐Menthol

Minty green : Zr–zeolite beta (Zr‐beta) directs the one‐pot catalytic cascade transformation of citral to menthols with high diastereoselectivity. The solid catalyst, a bifunctional Ni/Zr‐beta or a composite Zr‐beta–Ni/MCM‐41 system, is easily recovered and reused in this green synthetic method (see figure).

     

A radar backscatter model for forest stands

A Monte Carlo method for calculating the radar backscatter cross-sections from a forest stand is presented in this study. The model for the forest stand consists of two layers: the top layer contains a mixture of randomly orientated dielectric circular disks or small needles representing the leaves of the deciduous trees or coniferous trees respectively, as well as cylindrical-shaped scatterers, representing the branches of the foliage, while the bottom layer consists of randomly distributed vertical cylinders modelling the tree trunks. The phase matrices of the disks and needles are formulated using the generalized Rayleigh-Gans approximation whereas those of the branches and tree trunks are obtained from the infinite-cylinder approximation. The ground is modelled as a Kirchhoff rough surface based on the stationary-phase approximation. The relative contributions from the tree trunks, branches and trunks, leaves and trunks, and the entire forest stand are studied separately. It is found that leaves seem to dominate at higher frequencies while branches at lower frequencies. Effects of various physical and geometrical parameters such as dielectric constants, volume fractions, sizes and orientation distributions of the scatterers in a forested canopy are also studied. Finally, the results from the model are compared with the measured angular distributions of the radar backscattering cross-sections from some field measurements reported in the literature.     

Symplectic Induction and Semisimple Orbits

Symplectic induction was first introduced by Weinstein as thesymplectic analogue of induced representations, and was furtherdeveloped by Guillemin and Sternberg. This paper deals withthe case where the symplectic manifold in question is a semisimplecoadjoint orbit of a Lie group. In this case, the constructionis generalized by adding a smooth mapping, in order to obtainvarious symplectic forms. In particular, when the orbit is elliptic,a study of the complex geometry shows that quantization commuteswith induction. 2000 Mathematics Subject Classification 22F30,53C55, 53D05.     

Comparisons of RZ-OOK and RZ-DPSK in dense OTDM-WDM systems using Q factor models

In view of the differential phase Q (DP-Q) and the traditional Q factor, we compared, using numerical simulations, the performances of the RZ-OOK and RZ-DPSK in dense OTDM-WDM systems. When signal pulse widths and optical filter bandwidths are optimized, there is no upper limit to the WDM channel bit rate (BR) in the purely linear back-to-back configuration. Here, RZ-DPSK performed increasingly better than RZ-OOK in a higher spectral density with Q gain increasing from 3 to 5 dB. In the nonlinear point-to-point configuration, a higher BR leads to increased performance penalties for both the RZ-DPSK and RZ-OOK, while the RZ-DPSK still outperforms RZ-OOK by up to 4 dB. The results obtained correlate with conventional results, indicating the potential of the DP-Q as a performance evaluation tool in numerical simulations.     

Enlarging the Reservoir: High Absorption Coefficient Dyes Enable Synergetic Near Infrared-II Fluorescence Imaging and Near Infrared-I Photothermal Therapy

Although organic materials with near infrared (NIR)-II fluorescence and a photothermal effect have been widely investigated for the accurate diagnosis and treatment of tumors, optimizing the output signals of both remain challenging. Here, a strategy by “enlarging absorption reservoir” to address this issue, since an increase in photon absorption can naturally enhance output signals, is proposed. As a proof-of-concept, a large π-conjugated diketopyrrolopyrrole (DPP) unit is selected to fabricate strong light-absorbing systems. To enhance solid-state fluorescence, highly twisted alkylthiophene–benzobisthiadiazole–alkylthiophene and triphenylamine rotor are introduced to restrict the strong intermolecular π–π interactions. Moreover, the number of DPP units in molecules is engineered to optimize photophysical properties. Results show that TDADT with two DPP units possesses an exceptionally high molar absorptivity of 2.1 × 10⁵ L mol⁻¹ cm⁻¹ at 808 nm, an acceptable NIR-II quantum yield of 0.1% (emission peak at 1270 nm), and a sizeable photothermal conversion efficiency of 60.4%. The excellent photophysical properties of the TDADT nanoparticles are particularly suitable for in vivo NIR-II imaging-guided cancer surgery and NIR-I photothermal therapy. The presented strategy provides a new approach of designing highly efficient NIR-II phototheranostic agents.     

Design and testing of a kinematic package supporting a 32×32array of GaAs MQW modulators flip-chip bonded to a CMOS chip

Innovative approaches to the design and packaging of a high-performance module supporting a 32×32 array of GaAs multiple quantum-well (MQW) modulators flip-chip bonded to a 9×9 mm² complementary metal-oxide-semiconductor (CMOS) chip are described. The module integrates a minilens array, a copper heat spreader, a thermoelectric cooler (TEC) and an aluminum heatsink. The minilens array is aligned and packaged with the chip using a novel six degrees of freedom (DOFs) alignment technique. The kinematic design allows for the manual insertion of the module into a free-space optical system with no need for further adjustments. The chip is mounted directly on a flexible printed circuit board (PCB) using a chip-on-board approach, providing over 200 bond pad connections to the chip. Impedance-controlled lines were operated at 1.0 Gb/s with a crosstalk of 4.0% between nearest neighbor lines. The junction-to-TEC thermal resistance is 0.4°C/W, allowing for the use of a single-stage TEC to regulate the chip at an operating temperature of 40°C under a maximum thermal load of 13.1 W     

Base-functionalized MCM-41 as catalysts for the synthesis of monoglycerides

The mesoporous molecular sieves of the M41S family have little intrinsic catalytic activity. However, it is possible to functionalize the material by grafting organic side chains on the walls. These organic–inorganic hybrid materials maintain the advantages of the inorganic support, notably a high surface area and structural stability at elevated temperature and pressure. Catalysts based on MCM-41 functionalized with either hindered amine bases or free primary amino groups have been evaluated for the facile synthesis of monoglycerides from fatty acids and glycidol. Yields as high as 95% in 8 h have been achieved. The catalysts can be reused several times with little loss of activity.     

Bio-based Poly(hydroxy urethane)s: Synthesis and Pre/Post-Functionalization

New and emerging demand for polyurethane (PU) continues to rise over the years. The harmful isocyanate binding agents and their integrated PU products are at the height of environmental concerns, in particular PU (macro and micro) pollution and their degradation problems. Non-isocyanate poly(hydroxy urethane)s (NIPUs) are sustainable and green alternatives to conventional PUs. Since the introduction of NIPU in 1957, the market value of NIPU and its hybridized materials has increased exponentially in 2019 and is expected to continue to rise in the coming years. The secondary hydroxyl groups of these NIPU′s urethane moiety have revolutionized them by allowing for adequate pre/post functionalization. This minireview highlights different strategies and advances in pre/post-functionalization used in biobased NIPU. We have performed a comprehensive evaluation of the development of new ideas in this field to achieve more efficient synthetic biobased hybridized NIPU processes through selective and kinetic understanding.