Compromises in FIR matched filter design

With duration-limited signals there is the opportunity for perfect matched filtering by a suitable FIR filter, providing the noise can be construed as being supplied through an all-pole coloration filter. The popular matrix solution formulation does not make it obvious just what size the optimal filter length must be, and the signal vector zeropadding mechanism needed for coaxing out the optimal coefficient vector is also unclear. Difficulties are compounded when the filter length allowable for implementation falls short of the optimal length. Worse yet, if it happens that the noise is shaped by a coloration filter which has some zeros (i.e., is MA or ARMA instead of just AR), then any FIR filter can only be an approximation to the ideal IIR matched filter. In either case, decreasing filter length requires compromise strategies that are not at all transparent. We base our analysis approach to the FIR problem setup in terms of (time) correlations and convolutions in which the whitening filter has the central role. It is then easy to see that both "pole-only" and "some-zero" noise cases yield optimal SNR values that are exactly calculatable by a time-domain scalar product. The inevitable degradations of SNR with decreasing FIR filter lengths are, in turn, readily quantifiable. We study several compromise strategies arising from the whitening filter convolution approach and find (albeit with a very limited set of test cases) that they are not attractive when contrasted to the common matrix solution. The matrix solution itself, meanwhile, is shown to demand close attention to zeropadding patterns employed in it if best performance is to be obtained as filter length is reduced. Fortunately, exhaustive zero-padding assessment is a practical proposition, and this is our recommended procedure at this early stage of investigation

A WISE method for designing IIR filters

The problem of designing optimal digital IIR filters with frequency responses approximating arbitrarily chosen complex functions is considered. The real-valued coefficients of the filter's transfer function are obtained by numerical minimization of carefully formulated cost, which is referred here to as the weighted integral of the squared error (WISE) criterion. The WISE criterion linearly combines the WLS criterion that is used in the weighted least squares approach toward filter design and some time-domain components. The WLS part of WISE enforces quality of the frequency response of the designed filter, while the time-domain part of the WISE criterion restricts the positions of the filter's poles to the interior of an origin-centred circle with arbitrary radius. This allows one not only to achieve stability of the filter but also to maintain some safety margins. A great advantage of the proposed approach is that it does not impose any constraints on the optimization problem and the optimal filter can be sought using off-the-shelf optimization procedures. The power of the proposed approach is illustrated with filter design examples that compare favorably with results published in research literature

Classroom design demonstrations for complex IIR filters

An environment for exceptionally fast design of FIR and IIR filter design by pushbutton and easy drag-and-drop manipulations is described. Filter gain and phase credentials are immediately available to the designer, along with the facility to simply sketch the desired filter characteristics. The design flow for a specimen complex FIR and IIR realization of an arbitrary combination of gain and group delay is presented in detail, and a subsequent phase compensation filter also shown. A varied selection of other design examples emphasizes the flexibility and abundance of choice afforder the User

Dynamic matched filtering: animating the action

A simulink-based block diagram modelling environment is described which makes investigation of demanding DSP concepts such as FIR matched filtering easy and fun. Users interact with the experiment to a remarkable degree, watching scope displays while tuning parameter values or moving sliders to effect model changes during run time in a dynamic fashion. Instrumentation for achieved signal-to-noise ratio sits alongside displays advising the experimenter of theoretically optimal SNR for the current parameter settings. A small example problem using a single-pole noise-shaping filter is seen to be very enlightening, especially since a variable-coefficient matched filter block is employed which is self-designing in response to the prevailing pole radius and resonant frequency selection

Quantitative Treatment of Decoherence

We outline different approaches to define and quantify decoherence. We argue that a measure based on a properly defined norm of deviation of the density matrix is appropriate for quantifying decoherence in quantum registers. For a semiconductor double quantum dot qubit, evaluation of this measure is reviewed. For a general class of decoherence processes, including those occurring in semiconductor qubits, we argue that this measure is additive: It scales linearly with the number of qubits.Comment: Revised version, 26 pages, in LaTeX, 3 EPS figure

RAB11FIP5 Expression and Altered Natural Killer Cell Function Are Associated with Induction of HIV Broadly Neutralizing Antibody Responses

HIV-1 broadly neutralizing antibodies (bnAbs) are difficult to induce with vaccines but are generated in ∼50% of HIV-1-infected individuals. Understanding the molecular mechanisms of host control of bnAb induction is critical to vaccine design. Here, we performed a transcriptome analysis of blood mononuclear cells from 47 HIV-1-infected individuals who made bnAbs and 46 HIV-1-infected individuals who did not and identified in bnAb individuals upregulation of RAB11FIP5, encoding a Rab effector protein associated with recycling endosomes. Natural killer (NK) cells had the highest differential expression of RAB11FIP5, which was associated with greater dysregulation of NK cell subsets in bnAb subjects. NK cells from bnAb individuals had a more adaptive/dysfunctional phenotype and exhibited impaired degranulation and cytokine production that correlated with RAB11FIP5 transcript levels. Moreover, RAB11FIP5 overexpression modulated the function of NK cells. These data suggest that NK cells and Rab11 recycling endosomal transport are involved in regulation of HIV-1 bnAb development. Generation of broadly neutralizing antibodies against HIV-1 in humans is linked to the expression of a specific recycling endosome-associated effector in natural killer cells

Breadth of SARS-CoV-2 neutralization and protection induced by a nanoparticle vaccine

Coronavirus vaccines that are highly effective against current and anticipated SARS-CoV-2 variants are needed to control COVID-19. We previously reported a receptor-binding domain (RBD)-sortase A-conjugated ferritin nanoparticle (scNP) vaccine that induced neutralizing antibodies against SARS-CoV-2 and pre-emergent sarbecoviruses and protected non-human primates (NHPs) from SARS-CoV-2 WA-1 infection. Here, we find the RBD-scNP induced neutralizing antibodies in NHPs against pseudoviruses of SARS-CoV and SARS-CoV-2 variants including 614G, Beta, Delta, Omicron BA.1, BA.2, BA.2.12.1, and BA.4/BA.5, and a designed variant with escape mutations, PMS20. Adjuvant studies demonstrate variant neutralization titers are highest with 3M-052-aqueous formulation (AF). Immunization twice with RBD-scNPs protect NHPs from SARS-CoV-2 WA-1, Beta, and Delta variant challenge, and protect mice from challenges of SARS-CoV-2 Beta variant and two other heterologous sarbecoviruses. These results demonstrate the ability of RBD-scNPs to induce broad neutralization of SARS-CoV-2 variants and to protect animals from multiple different SARS-related viruses. Such a vaccine could provide broad immunity to SARS-CoV-2 variants

On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)