Current guidance by leading public health agencies recommends wearing a 3-layer cloth-based face mask with a middle non-woven material insert to reduce the transmission of infectious respiratory viruses like SARS-CoV-2....

Ambient 0.5 Hz hydrogen chloride (HCl) measurements were made in Canadian cities to investigate chlorine activation and constrain the tropospheric chlorine budget. Springtime HCl mixing ratios in a coastal city (St. John’s, NL) were up to 1200 parts per trillion by volume (pptv) with a median of 63 pptv and were consistently elevated during daytime. High time-resolution measurements allowed the attribution of events to general sources, including direct emissions. Most coastal HCl was related to sea-salt aerosol acid displacement (R1) and chlorine activation. Continental urban (Toronto, ON) wintertime HCl mixing ratios reached up to 541 and 172 pptv, with medians of 67 and 11 pptv during two sampling periods characterized by different wind directions. The absence of consistent relationships with NO x , temperature, and wind direction, as well as a lack of diurnal patterns, suggested uncharacterized direct sources of HCl. One period with road salting occurred during sampling, but no relationship to changes in HCl observations was found. The contribution of road salt to the measured HCl may have been masked by larger contributors (such as direct sources of HCl) or perhaps the relationship between HCl and road salt application is not immediate, and thus additional measurements over multiple salting events or between seasons would be required. GEOS-Chem modeled HCl temporal variations in mixing ratios agreed well with coastal measurements only. The measured mixing ratios were underestimated by the model in both locations, but to a greater degree (up to 3 orders of magnitude) in the continental city. The discrepancy between the model and measurements for the continental wintertime city emphasizes the need for a greater understanding of direct sources of HCl and the impact of road salt.

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A Multiport Power Amplifier (MPA) is an amplifying system consisting of two networks, a power divider and a combiner, connected by an array of identical amplifiers (Fig. 1). In the case here submitted both the divider and the combiner are Butler matrices. A signal entering one port of the input matrix is divided in equal parts, phased, and amplified by all the amplifiers and then recombined by the combining matrix at the output port corresponding to that particular input port. In this way the failure of one of the amplifiers no longer causes the total loss of a beam or carrier. Furthermore, for coping with traffic variations it's possible to properly apportion the available RF power among the various beams simply making small adjustments of the low level input signals. Finally, being a signal divided into equal parts by the input matrix, lower power amplifiers operating in linear region are required and intermodulation products can be kept very low.In the framework of ESA (European Space Agency) activities concemig multibeam antenna systems, 4x4 planar and 6x6 Butler matrices in metallic waveguide for Kuband have been built jointly by CSELT and Alenia Spazio (Rome, Italy) and an MPA has been realized in 4x4 configuration using TWTs 111. However, these types of networks can also be used for applications in other fields. In mobile-radio systems, the Butler martix constitutes, owing to its capability of feeding a group of antennas simultaneously, a transmit combining network more efficient and flexible than the common networks employing filters or couplers (Fig. 2)[2].The subject of the present work is the design and implementation of various order Butler matrices and MPAs with thick film microstrip technology for cellular DCS 1800 Base Stations.Using the software Libra [by Eesofl, running on a Hp-730 computer, microstrip Butler networks have been designed to operate over the 1.7-1.9 GHz band. Basic building blocks to obtain networks of any order are the 3x3 and 4x4 matrices in completely planar version. The planar 4x4 matrix has been obtained by substituting the crossover in the center of the general scheme (Fig. 3) with a 0 dB branchline coupler. This seems to be a more reliable solution (Fig. 4) than the commonly used airbridge technique, that produces unwanted couplings between the crossing lines and loss of symmetry of the whole structure. The 3x3 matrix design is more critical owing to the lack of symmetry of this configuration (Fig. 5 ) and a very close phase control is required to achieve signal recombination when two matrices are connected back-to-back.Higher order matrices, specifically 6x6 and 8x8, can be obtained placing two 3x3 or 4x4 building blocks one above the other, so that the inputs of each 3-dB coupler in the output row are coincident with corresponding ports of the upper and lower matrices (see Fig. 6).Computed results show that all types of matrices have very promising electrical performance. Figs. 7 and 8 show typical responses at a recombined output (insertion loss) and at a decoupled output...

Chloramines (NH2Cl, NHCl2, and NCl3) are toxic compounds that can be created during the use of bleach-based disinfectants that contain hypochlorous acid (HOCl) and the hypochlorite ion (OCl-) as their...

Carbon nanotubes (CNTs), with their excellent electronic\ud properties and extremely high aspect ratio, represent an ideal\ud material for building electron sources based on field emission.\ud Fowler-Nordheim equation describes quite successfully\ud the field emission phenomenon, especially for single or isolated\ud tips. However, some complications arise when populations\ud of CNTs are considered, where collective effects and\ud large variability in the emitters features influence the measured\ud I–V characteristics. In this work, the emission properties\ud of multi-walled CNTs grown within ordered anodic alumina\ud templates are investigated. These CNT matrices produce current\ud densities up to some tens of mA/cm2, and the field enhancement\ud factor for collective emission sources can be estimated.\ud Such material can be modelled as an ordered and uniform\ud array of emitters and a simulation of the electrostatic\ud field on the emission tips can be done in order to evaluate the\ud field enhancement factor and its dependence on various geometries.\ud This allows comparing predictions from simulation\ud and experimental measurements, in a direct way

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