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Sheaths ahead of coronal mass ejections (CMEs) are large heliospheric structures that form with CME expansion and propagation. Turbulent and compressed sheaths contribute to the acceleration of particles in the corona and in interplanetary space, but the relation of their internal structures to particle energization is still relatively little studied. In particular, the role of sheaths in accelerating particles when the shock Mach number is low is a significant open problem. This work seeks to provide new insights on the internal structure of CME sheaths with regard to energetic particle enhancements. A good opportunity to achieve this aim was provided by observations of a sheath made by radially aligned spacecraft at 0.8 and $\sim$ 1 AU (Solar Orbiter, Wind, ACE and BepiColombo) on 19-21 April 2020. The sheath was preceded by a weak shock. Energetic ion enhancements occurred at different locations within the sheath structure at Solar Orbiter and L1. Magnetic fluctuation amplitudes at inertial-range scales increased in the sheath relative to the upstream wind. However, when normalised to the local mean field, fluctuation amplitudes did not increase significantly; magnetic compressibility of fluctuation also did not increase. Various substructures were embedded within the sheath at the different spacecraft, including multiple heliospheric current sheet (HCS) crossings and a small-scale flux rope. At L1, the ion flux enhancement was associated with the HCS crossings, while at Solar Orbiter, the enhancement occurred within the rope. Substructures that are swept from the upstream solar wind and compressed in the sheath can act as particularly effective acceleration sites. A possible acceleration mechanism is betatron acceleration associated with the small-scale flux rope and the warped HCS in the sheath., 14 pages, 12 figures; published in Astronomy & Astrophysics, Solar Orbiter First Results (Cruise Phase) special issue

We present the results of experiments on dynamic nuclear polarization and relaxation of 75As in silicon crystals. Experiments are performed in strong magnetic fields of 4.6 T and temperatures below 1 K. At these conditions donor electron spins are fully polarized, and the allowed and forbidden electron spin resonance transitions are well resolved. We demonstrate effective nuclear polarization of 75As nuclei via the Overhauser effect on the time scale of several hundred seconds. Excitation of the forbidden transitions leads to a polarization through the solid effect. The relaxation rate of donor nuclei has strong temperature dependence characteristic of Orbach process.

Efficient manipulation of nuclear spins is important for utilizing them as qubits for quantum computing. In this work we report record high polarizations of ${}^{31}\mathrm{P}$ and $^{29}\mathrm{Si}$ nuclear spins in P-doped silicon in a strong magnetic field (4.6 T) and at temperatures below 1 K. We reached ${}^{31}\mathrm{P}$ nuclear polarization values exceeding $98%$ after 20 min of pumping the high-field electron spin resonance (ESR) line with a very small microwave power of 0.4 $\ensuremath{\mu}\mathrm{W}$. We evaluate that the ratio of the hyperfine-state populations increases by three orders of magnitude after 2 hours of pumping, and an extremely pure nuclear spin state can be created, with less than 0.01 ppb impurities. A negative dynamic nuclear polarization has been observed by pumping the low-field ESR line of ${}^{31}\mathrm{P}$ followed by the flip-flip cross relaxation, the transition which is fully forbidden for isolated donors. We estimate that while pumping the ESR transitions of ${}^{31}\mathrm{P}$ also the nuclei of $^{29}\mathrm{Si}$ get polarized, and polarization exceeding $60%$ has been obtained. We performed measurements of relaxation rates of flip-flop and flip-flip transitions which turned out to be nearly temperature independent. Temperature dependence of the ${}^{31}\mathrm{P}$ nuclear relaxation was studied down to 0.75 K, below which the relaxation time became too long to be measured. We found that the polarization evolution under pumping and during relaxation deviates substantially from a simple exponential function of time. We suggest that the nonexponential polarization dynamics of ${}^{31}\mathrm{P}$ donors is mediated by the orientation of $^{29}\mathrm{Si}$ nuclei, which affect the transition probabilities of the forbidden cross-relaxation processes.

We report on the first ESR study of atomic hydrogen and tritium stabilized in a solid T$_{2}$ and T$_{2}$:H$_{2}$ matrices down to 70$\,$mK. The concentrations of T atoms in pure T$_{2}$ approached $2\times10^{20}$cm$^{-3}$ and record-high concentrations of H atoms $\sim1\times10^{20}$cm$^{-3}$ were reached in T$_{2}$:H$_{2}$ solid mixtures where a fraction of T atoms became converted into H due to the isotopic exchange reaction T+H$_2\rightarrow$TH+H. The maximum concentrations of unpaired T and H atoms was limited by their recombination which becomes enforced by efficient atomic diffusion due to a presence of a large number of vacancies and phonons generated in the matrices by $\beta$-particles. Recombination also appeared in an explosive manner both being stimulated and spontaneously in thick films where sample cooling was insufficient. We suggest that the main mechanism for H and T migration is physical diffusion related to tunneling or hopping to vacant sites in contrast to isotopic chemical reactions which govern diffusion of H and D atoms created in H$_{2}$ and D$_{2}$ matrices by other methods.

A method is presented to synthesize wideband linear-phase FIR filters with a piecewise-polynomial-sinusoidal impulse response. The proposed method is based on merging the earlier synthesis scheme proposed by the authors with the method proposed by Chu and Burrus and by modifying it by using an arbitrary number of separately generated center coefficients instead of only one used in the method by Chu-Burrus. The desired impulse response is created by using a parallel connection of several filter branches and by adding an arbitrary number of center coefficients to form it. The arithmetic complexity of these filters is proportional to the number of branches, the common polynomial order for each branch, the number of separate center coefficients, and the number of complex multipliers. The filter coefficients are optimized by using linear programming. An example shows the benefits of these filters with regard to reducing the number of coefficients as well as the arithmetic complexity.

We demonstrate an efficient control of $^{29}\mathrm{Si}$ nuclear spins for specific lattice sites near $^{31}\mathrm{P}$ donors in silicon at temperatures below 1 K and in a high magnetic field of 4.6 T. Excitation of the forbidden electron-nuclear transitions leads to a pattern of well-resolved holes and peaks in the electron spin resonance (ESR) lines of $^{31}\mathrm{P}$. The pattern originates from dynamic polarization (DNP) of the $^{29}\mathrm{Si}$ nuclear spins near the donors via the solid effect. DNP of $^{29}\mathrm{Si}$ is demonstrated also with the Overhauser effect where the allowed ESR transitions are excited. In this case mostly the remote $^{29}\mathrm{Si}$ nuclei having weak interaction with the donors are polarized, which results in a single hole and a sharp peak pair in the ESR spectrum. Our work shows that the solid effect can be used for initialization of $^{29}\mathrm{Si}$ nuclear spin qubits near the donors.

We introduce a genetic algorithm-based method for structural optimization of multiplicative general parameter (MGP) finite impulse response (FIR) filters. These computationally efficient reduced-rank adaptive filters are robust, suitable for predictive configurations, and they have numerous applications in 50/60 Hz power systems instrumentation. The design process of such filters has three independent stages: Lagrange multipliers-based optimization of the sinusoid-predictive basis filter, genetic algorithm-based search of optimal FIR tap cross-connections and, finally, the online MGP-adaptation phase guided by variations in signal statistics. Thus, our multistage design procedure is a complementary fusion of hard computing (HC) and soft computing (SC) methodologies. Such advantageous fusion (or symbiosis) thinking is emerging among researchers and practicing engineers, and it can potentially lead to competitive combinations of individual HC and SC methods.

We introduce an evolutionary-programming-based method for designing robust and computationally efficient adaptive bandpass filters. These predictive filters are optimized for generating current references in active power filters (APFs). The accuracy (phase/amplitude) of the reference current is crucial in current-injection-type systems, because it directly affects the harmonics reduction ability of the APF. Our digital filtering approach has the following advantages: selective bandpass response, efficient attenuation of specific harmonic components, capability to handle typical frequency alteration, small number of multiplications, and structural simplicity. In addition, practically no prior knowledge of the electricity distribution network and its loading characteristics is needed for designing the current reference generator. In an illustrative example, the total harmonic distortion of an artificial current waveform was reduced from 36.7% to less than 3.7% within the line frequency range 49-51 Hz. The proposed scheme is a combination of the hard-computing (HC)-type multiplicative general parameter method and evolutionary programming that, on the other hand, is a constituent of soft computing (SC). Such open-minded fusion thinking is emerging among researchers and engineers, and it can potentially lead to efficient combinations of HC and SC methodologies*both on the algorithm level and on the system level.

Adaptive filters are often used in signal processing tasks related to line-frequency signals in power distribution systems. In this paper, we discuss a computationally efficient adaptive algorithm for transversal discrete-time filters. The algorithm, which is based on the so-called general parameter method, uses only two dynamically adjusted parameters, each to be added to a block of coefficients of a fixed basis finite-impulse response filter. The parameter updating formula involves running addition of the data samples, causing suppression of certain frequencies. Therefore, the algorithm can be designed to adapt mainly according to the primary input frequency while being tolerant against specific harmonic components. This is advantageous, for instance, when processing 50/60-Hz line-frequency signals. The properties and stability of the algorithm are analyzed.

We report on magnetic resonance studies of high-density atomic hydrogen and deuterium in solid hydrogen matrices at temperatures below 1 K. Average concentrations of H atoms $\ensuremath{\approx}3\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ are obtained in chemical tunneling reactions of isotope exchange with D atoms. The products of these reactions are closely located pairs of H atoms near ${\mathrm{D}}_{2}$ molecules with strong exchange interactions. We discovered a dynamic nuclear polarization effect on H atoms created by pumping the center of the H electron spin resonance spectrum, similar to the Overhauser effect in metals. Our results indicate that H atoms may be arranged inside molecular matrices at separations equivalent to local concentrations of $2.6\ifmmode\times\else\texttimes\fi{}{10}^{21}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$. This opens up a way to build a metallic state of atomic hydrogen at zero pressure.

An in vivo thymus reconstitution assay based on intrathymic injection of hematopoietic progenitors into irradiated chicks was used to determine the number of T-cell progenitors in peripheral blood, paraaortic foci, bone marrow (BM), and spleen during ontogeny. This study allowed us to analyze the regulation of thymus colonization occurring in three waves during embryogenesis. It confirmed that progenitors of the first wave of thymus colonization originate from the paraaortic foci, whereas progenitors of the second and the third waves originate from the BM. The analysis of the number of T-cell progenitors indicates that each wave of thymus colonization is correlated with a peak number of T-cell progenitors in peripheral blood, whereas they are almost absent during the periods defined as refractory for colonization. Moreover, injection of T-cell progenitors into the blood circulation showed that they homed into the thymus without delay during the refractory periods. Thus, thymus colonization kinetics depend mainly on the blood delivery of T-cell progenitors during embryogenesis.

A digital filter design and optimization method for sampling rate alteration of narrow-band signals is presented. The resulting predictive finite-duration impulse-response filters are used to remove the aliasing or imaging frequency components when the sampling rate is changed. The sampling rate can be changed either by an integer factor or a rational factor. A least-squares-based generalization is developed for optimal wide-band noise attenuation.

Additional delay is an unavoidable drawback of conventional filters used frequently in industrial electronics. This delay is particularly harmful if the filtered primary signal is to be used for time-critical feedback or synchronization purposes. Therefore, predictive signal processing methods can offer significant advantages for these real-time applications. Polynomial predictive filters are specified without explicit passbands and stopbands, and they are behaving delaylessly or predictively for smoothly varying signal components. The degree of smoothness of the incoming signal sets the requirements for the applied filtering scheme and its parameters. Smoothness of a signal is a fuzzy and application-specific concept: the degree of smoothness depends on the ratio of the bandwidth of the primary signal and the applied sampling rate, as well as the noise component. In this paper, the authors review the most important polynomial predictive filtering methods and algorithms, their design and implementation techniques, and a collection of successful applications.

The authors describe two adaptive multistage digital filters for 50/60-Hz line-frequency signal processing in zero-crossing detectors and synchronous power systems. These filters combine a median filter with adaptive predictors, either finite-impulse response (FIR)- or infinite-impulse response (IIR)-based, thus making it possible to extract the sinusoidal signals from noise and strong disturbances without phase shifting the primary frequency signal. The median filter is used as a prefilter because it can remove deep commutation notches from the waveform. Adaptation allows the filters to track the exact instantaneous line frequency and avoids the selectivity problem encountered with a fixed filter.

A class of analog continuous-time filters is introduced, having predictive properties for specified narrow-band signal models, such as low-order polynomials or sinusoids. Such filters are designed by using model transfer functions designed in the discrete-time domain. Z-to-s-domain mapping is done using the inverse bilinear transformation. The analog filters are implemented with active-RC structures, using the state-variable structure for biquads and a single-op-amp structure for real poles and zeros. The application examples include a filter for zero-crossing detectors, polynomial predictors for sensor signal smoothing, and an optimized sixth-order ramp-tracking filter for anti-aliasing and anti-imaging in digital signal processor (DSP) systems where high selectivity is required.

We have examined the emigration of chicken thymocytes after intrathymic fluorescein isothiocyanate (FITC) labelling in situ. In this paper we show that in young birds about 0.7% and 0.4% of thymocytes emigrate from the thymus to the blood and the spleen, respectively, per day. This suggests that, as in mammals, most thymocytes die within the thymus. At 3 weeks of age gamma delta and alpha beta T cells leave the thymus in comparable levels to their appearance in the blood. The phenotype of recent emigrants in peripheral tissues is similar to that of mature T cells. Interestingly, recent emigrants contain relatively much higher numbers of CD4+ and fewer CD8+ cells than is observed in peripheral tissues in a steady-state situation.

An improved digital filtering method for line frequency zero-crossing detectors is proposed. The multistage filter efficiently attenuates harmonics, wide-band noise, commutation notches, and other impulsive disturbances without causing any phase shift on the primary sinusoidal waveform. Our novel signal-processing system is a cascade of a median filter and an adaptive sinusoid predictor, followed by up-sampling and interpolation. The three-point median filter effectively removes impulses, and the predictor provides wide-band noise attenuation while compensating for delays in the other processing steps. The predictor adapts to possible line frequency variations within the specified range by changing the set of coefficients, based on an estimate of the instantaneous line frequency. The adaptive approach allows the use of highly selective IIR bandpass predictors.

Two new approaches to the design of predictive FIR filters are presented. First, we discuss the design of predictors and estimators for narrow-band signals based on the interpolated FIR (IFIR) filter approach. The transfer function of the IFIR predictor is of the form H(z)=P(z/sup L/)G(z) where P(z) is a predictor and G(z) is an interpolating estimator. The general-purpose design procedure for efficient IFIR predictors is described, and demonstrated for polynomial predictors. The resulting predictors, optimized for white noise attenuation, have much lower computational complexity than the corresponding direct-form FIR predictors. Secondly, an IIR filter-based implementation of sinusoidal FIR predictors is presented. As an application, a zero-crossing detector for 50 Hz thyristor drives is designed. >

A simple combination of nonlinear and linear digital signal processing methods is proposed for efficient noise reduction in zero crossing detectors. The method is very robust against strong impulsive noise, typically encountered in thyristor power converters, where reliable zero crossing detection is required for firing synchronization. A systematic design procedure is described for the proposed filter-based synchronization method, taking into account the specified line frequency tolerance. The fully digital signal processing approach allows compact implementations, and supports flexible interfacing to digital motor control systems. >

An adaptive, robust, and computationally efficient disturbance reduction method for line-frequency zero-crossing detectors is proposed. Our adaptive system consists of a fixed finite-impulse response filter block and two multiplicative general parameters. The predictive filter is able to handle wide variations in the line frequency without harmfully adapting to the harmonic components.

We present a high magnetic field study of electron spin waves in atomic hydrogen gas compressed to high densities of 10^18 cm^-3 at temperatures ranging from 0.26 to 0.6 K. We observed a variety of spin wave modes caused by the identical spin rotation effect with strong dependence on the spatial profile of the polarizing magnetic field. We demonstrate confinement of these modes in regions of strong magnetic field and manipulate their spatial distribution by changing the position of the field maximum., Comment: 5 pages, 4 figures

The design of sampled-data polynomial estimators for noise reduction in industrial instrumentation applications is discussed. Unlike conventional lowpass filters, an estimator causes no delay on the polynomial-like primary signal. A general purpose design approach is described, incorporating notch frequencies for removal of narrow-band noise components, such as the 50/60 Hz line frequency. A 24-tap FIR estimator is optimized for tachometer signal smoothing in motor control systems. An analog circuit architecture, targeted for silicon CMOS implementation, is described and simulated. >

A VLSI implementation of a linear-phase digital filter for ECG signal processing has been designed. With a sampling rate of 100 Hz, the passband is from 0.5 Hz to 49.5 Hz with 0.5-dB ripple. The filter architecture is based on the use of recursive running-sum blocks, resulting in a very low computational complexity. Module generators have been used in the layout design for high integration density. The circuit has been designed for a 2.0-/spl mu/m double-metal CMOS technology, having about 34000 transistors and a 15.43-mm/sup 2/ chip area. >

We study the output coupling of atoms from a magnetic trap into a linear potential slope of gravity using a weak radio-frequency field. We present a one-dimensional wave-packet model based on a continuous loading of a continuous spectrum of generalised eigenstates to describe the scenario. Analyzing the model, we show how the interference of the classical coupling fields maps to the interference of the resulting atomic streams., Comment: 8 pages, 9 figures, 1 table, 40 references. Submitted for publication

Newton predictors have considerable gain at the higher frequencies, which reduces their applicability to practical signal processing where the narrowband primary signal is often corrupted by additive wideband noise. Two modifications that can be used to extrapolate low-order polynomials have been proposed. In both approaches, the highest order difference of successive input samples, approximating the constant nonzero derivative, is smoothed before it is added to the lower order differences, reducing the undesired noise gain. The linear smoothed Newton (LSN) predictor is extended in this work by including a recursive term in the basic transfer function and cascading the rest of the successive difference paths with appropriately delayed extrapolation filters of corresponding polynomial orders. This leads to computationally efficient IIR predictors with significantly lowered gain at the higher frequencies. The recursive predictor is analyzed in the time and frequency domains and compared to the other predictors. >

Discrete-time computational models of squirrel-cage AC motors are derived and analyzed for the purpose of advanced motor control. The starting point is a continuous-time model defined by a pair of simultaneous complex-coefficient differential equations. Discrete-time models are derived using both the bilinear transformation and the forward-difference approximation. The exact dependence between stability and the minimum sampling rate in the forward-difference approach is shown. The responses of the two discretized models are compared using real-world motor parameters. Using the forward difference method, a more compact implementation is obtained (although a higher sampling rate is required) as compared to the bilinear transformed model of equivalent performance and 2.7 times higher computational complexity. A 16/24-b DSP-ASIC coprocessor prototype implementing the AC motor model is introduced. >

A digital motion control system is presented with primary applications in automatic elevator doors. Digital signal processing methods are used for generating exponential waveforms for the drive motor. The unit keeps track of the actual speed of motion and the corresponding door position. Thus the time consumed by door motion is minimized, and smooth acceleration and deceleration phases are achieved. The proposed algorithm results in an efficient bit-serial application specific IC (ASIC) implementation. >

The well-known noise problem in digital differentiation is addressed by means of using adaptive digital filtering for signal pre-processing. Rapidly responding differentiators with low-noise output can be constructed by using the adaptive filter in a predictor configuration. As the prefilter is adaptive, the approximation is more flexible than polynomial fitting. The recursive least-squares adaptive algorithm is used for prediction.

A flexible method of reducing white noise in measurement signals by means of real-time digital filtering is presented. Compared to the widely used averaging filter, the new approach significantly reduces the delay of the step response of a filter, measured typically al the 50% level of the full step. The optimum filter coefficients are obtained analytically as a function of a single weighting parameter.

Lysinuric protein intolerance (LPI) is characterized by defective cellular transport of the dibasic amino acids, secondary dysfunction of the urea cycle, aversion to dietary protein, failure to thrive, hepatosplenomegaly and osteoporosis. Because several patients have suffered from recurrent respiratory infections and/or severe generalized varicella, and a few have developed systemic lupus, vasculitis or other autoimmune diseases, we have now evaluated the function of patients' immune systems. Serum concentrations of one to three IgG subclasses were decreased in 10 of the 12 patients studied. Antibody titres against diphtheria, tetanus and Haemophilus influenzae (Hib) were below the detection limit of the assay in four, three and eight of the 11 patients examined, respectively. (Re)vaccination of these 11 patients led to satisfactory responses against tetanus, but two patients still failed to develop measurable antibodies against diphtheria, two against Hib and six against one or more of the three serotypes of 23-valent pneumococcus vaccine. The proportions of T cells of all lymphocytes and the proliferative responses of the peripheral blood mononuclear cells were normal. In conclusion, humoral immune responses in some patients with LPI are defective and these patients may benefit from intravenous immunoglobulin therapy.

HEMCAM/gicerin, an immunoglobulin superfamily protein, is involved in homophilic and heterophilic adhesion. It interacts with NOF (neurite outgrowth factor), a molecule of the laminin family. Alternative splicing leads to mRNAs coding for HEMCAM with a short (HEMCAM-s) or a long cytoplasmic tail (HEMCAM-l). To investigate the cellular function of these two variants, we stably transfected murine fibroblasts with either form of HEMCAM. Expression of each isoform of this protein in L cells delayed proliferation and modified their adhesion properties to purified extracellular matrix proteins. Expression of either HEMCAM-s or HEMCAM-l inhibited integrin-dependent adhesion and spreading of fibroblasts to laminin 1, showing that this phenomenon did not depend on the cytoplasmic region. By contrast, L-cell adhesion and spreading to fibronectin depended on the HEMCAM isoform expressed. Flow cytometry and immunoprecipitation studies revealed that the expression of HEMCAM downregulated expression of the laminin-binding integrins (α)3 (β)1, (α)6 (β)1 and (α)7 (β)1, and fibronectin receptor (α)5 (β)1 from the cell surface. Semi-quantitative PCR and northern blot experiments showed that the expression of (α)6 (β)1 integrin modified by HEMCAM occurred at a translation or maturation level. Thus, our data demonstrate that HEMCAM regulates fibroblast adhesion by controlling (β)1 integrin expression. http://www.biologists.com/JCS/movies/jcs1886.html