Longitudinal Density Research Articles

A nonlinear solar magnetic field calibration method for the filter-based magnetograph by the residual network

Context. The method of solar magnetic field calibration for the filter-based magnetograph is normally the linear calibration method under weak-field approximation that cannot generate the strong magnetic field region well due to the magnetic saturation effect. Aims. We try to provide a new method to carry out the nonlinear magnetic calibration with the help of neural networks to obtain more accurate magnetic fields. Methods. We employed the data from Hinode/SP to construct a training, validation and test dataset. The narrow-band Stokes I, Q, U, and V maps at one wavelength point were selected from all the 112 wavelength points observed by SP so as to simulate the single-wavelength observations of the filter-based magnetograph. We used the residual network to model the nonlinear relationship between the Stokes maps and the vector magnetic fields. Results. After an extensive performance analysis, it is found that the trained models could infer the longitudinal magnetic flux density, the transverse magnetic flux density, and the azimuth angle from the narrow-band Stokes maps with a precision comparable to the inversion results using 112 wavelength points. Moreover, the maps that were produced are much cleaner than the inversion results. The method can effectively overcome the magnetic saturation effect and infer the strong magnetic region much better than the linear calibration method. The residual errors of test samples to standard data are mostly about 50 G for both the longitudinal and transverse magnetic flux density. The values are about 100 G with our previous method of multilayer perceptron, indicating that the new method is more accurate in magnetic calibration.

Drawing the Tensile Curve for Pure Metals and Alloys Depending On Crystal Structure and Acoustic Impedance

A new method to predict the stress-strain relation of the pure metals and alloys has been presented in this paper by using the acoustic impedance property. The method involves developing new algorithms that were programmed in a MATLAB code. Also, it compromises the experimental measurement of some physical properties, such as longitudinal wave velocity, density, and crystal structure. The study considered 19-samples, which have been put in three different groups depending on the crystal structure (seven FCC samples, six BCC samples, and six HCB samples). The samples’ crystal structure was examined using the X-ray diffraction method before the samples’ density, and longitudinal wave velocity were experimentally measured. To evaluate the validity of the developed model, a comparison between its prediction for the stress-strain relation and the corresponding curves in the literature was done. The results, also, verified the existence of a relation between pressure transmission coefficient (PrTr) and each of the σu, σy, and modulus of elasticity (E) properties for the metals in the same crystal structure group.

The Wave Origins of Longitudinal Structures in ExoMars Trace Gas Orbiter (TGO) Aerobraking Densities

AbstractThe nature and origins of longitudinal density structures in Mars’ thermosphere between 100 and 120 km altitude, and −30° and −75° latitude around winter solstice (Ls = 70–122°), as measured by the accelerometer on the ExoMars Trace Gas Orbiter (TGO) Mission, are investigated. The methodology consists of deducing the responsible waves by comparing the observed longitude versus local time phase progressions of the structures with those of probable candidate waves in the Mars Climate Database (MCD) climatology. The observed wave‐1, wave‐2, and wave‐3 structures are interpreted as originating mainly from SPW1; (SPW2, S0, DE1); and (SPW3, DE2), respectively, where SPWm denotes a stationary planetary wave with zonal wavenumber s = m, S0 is the zonally symmetric semidiurnal tide, and DE1(DE2) are the eastward‐propagating diurnal tides with s = −1(−2). All of these waves exist in the MCD with amplitudes as large as those observed, although not wholly in the narrow height‐latitude regime accessed by TGO. This disparity between the MCD and TGO amplitude structures is hypothesized to result from the extreme intrusion of the polar‐region eastward winter jet into the thermosphere in the MCD. The winter polar jet blocks poleward expansion of DE1 and DE2 beyond −30° latitude, and also impacts the structures of SPW2, S0 and SPW3 that arise from in situ nonlinear interaction between DE1 and DE2, respectively, with the diurnal migrating tide (DW1).

Focused linearly-polarized-light scattering from a silver nanowire: Experimental characterization of the optical spin-Hall effect

Spin-orbit interactions (SOI) are a set of sub-wavelength optical phenomenon in which spin and spatial degrees of freedom of light are intrinsically coupled. One of the unique example of SOI, spin-Hall effect of light (SHEL) has been an area of extensive research with potential applications in spin controlled photonic devices as well as emerging fields of spinoptics and spintronics. Here, we report our experimental study on SHEL due to forward scattering of focused linearly polarized Gaussian and Hermite-Gaussian ($\textrm{HG}_{10}$) beams from a silver nanowire (AgNW). Spin dependent anti-symmetric intensity patterns are obtained when the polarization of the scattered light is analysed. The corresponding spin-Hall signal is obtained by computing the far-field longitudinal spin density ($s_3$). Furthermore, by comparing the $s_3$ distributions, significant enhancement of the spin-Hall signal is found for $\textrm{HG}_{10}$ beam compared to Gaussian beam. The investigation of the optical fields at the focal plane of the objective lens reveals the generation of longitudinally spinning fields as the primary reason for the effects. The experimental results are corroborated by 3-dimensional numerical simulations. The results lead to better understanding of SOI and can have direct implications on chip-scale spin assisted photonic devices.

Resonant absorption of kink MHD waves in inclined and asymmetric coronal loops

ABSTRACT This paper separately evaluates the effects of inclination and asymmetry of solar coronal loops on the resonant absorption of kink magnetohydrodynamic oscillations. We modelled a typical coronal loop by a straight and axisymmetric cylindrical magnetic flux tube filled with cold plasma. We solved the dispersion relation numerically for different values of the longitudinal mass density stratification. We show that, in inclined and asymmetric loops, the frequencies and their corresponding damping rates of the fundamental and first-overtone modes of kink oscillations are smaller in comparison with semi-circular uninclined loops with the same lengths. The results also indicate that, the period ratio P1/P2, increases with increasing the inclination of the loop, but it decreases less than $2{{\ \rm per\ cent}}$ while imposing the asymmetry to each loop side, up to $9.66{{\ \rm per\ cent}}$ of the loop length. The ratio of each mode frequency to its corresponding damping rate remain unchanged approximately while the inclination or the asymmetry imposed. Hence, we conclude that these ratios are reliable for inferring the physical parameters of coronal loops and coronal medium, regardless of the loop shape or the state of its inclination. In addition, in contrast with the effect of asymmetry, which is not significant on the period ratio P1/P2, when an observed oscillating loop has a smaller apex height, the state of its inclination is an important factor that should be considered, especially when the period ratio P1/P2, is taken into consideration for coronal seismology.

Risk factors for vertebral fractures and bone loss after denosumab discontinuation: A real-world observational study.

Denosumab discontinuation without subsequent bisphosphonates (BPs) is associated with bone loss and multiple vertebral fractures. Identifying risk factors for bone loss and vertebral fractures after denosumab discontinuation. This retrospective study measured the outcome of 219 women with osteoporosis who discontinued denosumab treatment and received subsequent treatment with zoledronate, other BPs or a selective estrogen receptor modulator (SERM), or no therapy. Fracture rate, longitudinal bone mineral density (BMD) changes and bone turnover markers (BTMs) within 2years after denosumab discontinuation were analysed. Linear regression analysis evaluated loss of BMD and age, BMI (kg/m2), denosumab treatment duration, pre-treatment, prior fracture state, baseline T-scores, use of glucocorticoids or aromatase inhibitors and BMD gains under denosumab therapy. 171 women received zoledronate after denosumab discontinuation, 26 had no subsequent treatment and 22 received other therapies (other BPs or a SERM). Zoledronate was associated with the fewest vertebral fractures (hazard ratio 0.16, p=0.02) and all subsequent therapies retained BMD at all sites to some extent. Higher BMD loss was associated with younger age, lower BMI, longer denosumab treatment, lack of prior antiresorptive treatment and BMD gain under denosumab treatment. BTM levels correlated with denosumab treatment duration and bone loss at the total hip, but not the lumbar spine. Compared to no subsequent therapy, zoledronate was associated with fewer vertebral fractures after denosumab. Further, BMD loss depended on denosumab treatment duration, age, prior BP therapy and BMD gain under denosumab therapy, whereas BTM levels were associated with bone loss at the total hip and denosumab treatment duration.

Longitudinal Monostatic Acoustic Effective Bulk Modulus and Effective Density Evaluation of Underground Soil Quality: A Numerical Approach

In this study, we introduce a novel method using longitudinal sound to detect underground soil voids to inspect underwater bed property in terms of effective bulk modulus and effective density of the material properties. The model was simulated in terms of layered material within a monostatic detection configuration. The numerical model demonstrates the feasibility of detecting an underground air void with a spatial resolution of about 0.5 λ and can differentiate a soil firmness of about 5%. The proposed technique can overcome limitations imposed by conventional techniques that use spacing-consuming sonar devices and suffer from low penetration depth and leakage of the transverse sound wave propagating in an underground fluid environment.

Analysis of transmission characteristics of THz waves magnetized at different angles in non-uniform magnetized plasma

When a hypersonic vehicle flies, it will have friction with the atmosphere, ionizing the surrounding air, and producing a plasma sheath containing a large number of free electrons. The plasma sheath will cause the electromagnetic wave to seriously attenuate, which will result in communication interruption and other problems. With the gradual realization of terahertz wave technology, its high penetrability and anti-interference performance provides an important way to solve the blackout problem. Thus, the using of the terahertz wave to solve the blackout problem encountered during vehicle reentry is of great significance to studying the transmission performance of terahertz wave in the plasma sheath. This article refers to the public data of the plasma sheath during the reentry of the RAM vehicle. Considering the asymmetry of the sheath density distribution, a double Gaussian distribution is used to simulate the longitudinal electron density distribution. Based on the SMM algorithm, the article uses the magnetization direction, electron density, external magnetic field strength, collision frequency of the non-uniformly magnetized plasma as variables, and their effects on left-hand and right-hand polarized terahertz wave under normal incidence are studied. The results show that these parameters have obvious effects on the transmission performance of terahertz wave in high-density plasma sheath. The right-hand polarized terahertz wave will produce a power absorption peak near the cyclotron frequency due to cyclotron resonance. Changing the magnetization angle in a certain direction will bring an opposite effect on the transmission rate to left-hand polarized and right-hand polarized terahertz wave. Reducing the magnetization intensity can avoid the absorption peak of the right-hand polarized wave by the plasma to a certain extent. Increasing the magnetization can increase the transmission power of the left-hand polarized wave to a certain extent. Moreover, reducing the collision frequency can narrow the absorption band of the right-hand polarized wave in the plasma and increase the transmission power of left-hand polarized wave. In general, the transmission performance of left-hand polarized terahertz wave in non-uniformly magnetized plasma is better than that of right-hand polarized terahertz wave. These results provide a theoretical basis for investigating the blackout phenomenon. The adjusting of these parameters studied in the article is expected to be able to alleviate the blackout problem to a certain extent.

Bipolar-variant spin angular momentum and its evolution in a tight focusing process

We design and generate the bipolar-variant spin angular momentum (SAM) carried by vector optical field and theoretically investigate the evolution of the bipolar-variant SAM in the tight focusing process. It is found that the longitudinal SAM density annihilates and the purely transverse SAM density appears in the focal plane, and the evolution of the complex singularities of SAM into $V$-point singularities is also studied. We further extend the study to general bipolar-variant SAM, and give the theoretical explanation of the annihilation and appearance of different components of SAM density. We believe the presentation of the bipolar-variant SAM can greatly enrich the study of SAM as well as the singular optics. Meanwhile, the evolution of the bipolar-variant SAM in the focusing process is interesting and important in revealing the focal properties of SAM of the photon, and the purely transverse SAM in the focal plane with a spin axis orthogonal to the propagation direction opens up avenues in optical trapping and manipulation, especially for optically induced rotations.

Non-uniform longitudinal current density induced power saturation in GaAs-based high power diode lasers

The output power of modern 975 nm GaAs-based broad area diode lasers is limited by increasing carrier and photon losses at high bias. We use experiment and one-dimensional calculations on these devices to reveal that higher current densities (and hence higher local recombination rates and higher losses) arise near the front facet due to spatial hole burning and that the non-uniformity is strongly affected by laser geometry, which is more severe for longer resonators and less severe for higher front facet reflectivity. Specifically, we use devices with a segmented p-contact to directly measure the current distribution along the resonator and compare this with laser simulation. Devices with a 6 mm resonator show 29% more current at the front than back, twice as large as the 15% current non-uniformity in devices with a 3 mm resonator. In contrast, increased front facet reflectivity (20% rather than 0.8%) is shown to almost halve the current non-uniformity from 29% to 18% in devices with a 6 mm resonator and reduces power saturation. Although the magnitude of current non-uniformity in experiment and theory is broadly consistent, in experiment, an additional divergence is seen in current flow (and hence recombination rate) near the facets, and earlier power saturation occurs. We discuss the possible saturation mechanisms that are not included in the simulation.

Longitudinal phase space reconstruction for a heavy ion accelerator

At the GSI Helmholtzzentrum f\ur Schwerionenforschung (GSI) in Darmstadt, Germany, a prototype cryomodule (advanced demonstrator) for the superconducting (SC) continuous wave (CW) Helmholtz Linear Accelerator (HELIAC) is under construction. A transport line, comprising quadrupole lenses, rebuncher cavities, beam correctors, and adequate beam instrumentation has been built to deliver the beam from the GSI 1.4 MeV/u High Charge Injector (HLI) to the advanced demonstrator, which offers a test environment for SC CW multigap cavities. In order to achieve proper phase space matching, the beam from the HLI must be characterized in detail. In a dedicated machine experiment the bunch shape has been measured with a nondestructive bunch shape monitor (BSM). Therefore, different bunch projections were obtained by altering the voltage of two rebunchers. These measurements were combined with dedicated beam dynamics simulations using the particle tracking code dynamion. The longitudinal bunch shape and density distribution at the beginning of the matching line are fully characterized by a tomographic reconstruction method based on a non-negative least square minimization approach.

Proton beam defocusing in AWAKE: comparison of simulations and measurements

In 2017, AWAKE demonstrated the seeded self-modulation (SSM) of a 400 GeV proton beam from the Super Proton Synchrotron at CERN. The angular distribution of the protons deflected due to SSM is a quantitative measure of the process, which agrees with simulations by the two-dimensional (axisymmetric) particle-in-cell code LCODE to about 5%. The agreement is achieved in beam population scans at two selected plasma densities and in the scan of longitudinal plasma density gradient. The agreement is reached only in the case of a wide enough simulation box (several plasma wavelengths) that is closer to experimental conditions, but requires more computational power. Therefore, particle-in-cell codes can be used to interpret the SSM physics underlying the experimental data.

Laboratory simulation for single and block supersonic jets

Model experimental studies are presented for the flow field of a single jet, the flow parameters of a block jet, the pressure distribution on the bottom screen, and the parameters of the jet flow from a model nozzle. When expanding into a vacuum and/or a highly rarefied medium, the conditions for reproducing the relative gas pulse value of the full-scale nozzle block section are met. It is shown that when using specific similarity criteria, it is possible to experimentally model the supersonic jet outflow processes of space vehicles on small-sized laboratory vacuum installations, similar to the one created at Novosibirsk State University. Simulation results using spectral density measurements based on the glow excited by a focused electron beam, longitudinal and transverse jet density profiles obtained using modern scanning technology, as well as measurements of bottom pressure near the nozzle block are given. The possibilities and features of each applied registration method are discussed.

In-vivo lung fibrosis staging in a bleomycin-mouse model: a new micro-CT guided densitometric approach

Although increasing used in the preclinical testing of new anti-fibrotic drugs, a thorough validation of micro-computed tomography (CT) in pulmonary fibrosis models has not been performed. Moreover, no attempts have been made so far to define density thresholds to discriminate between aeration levels in lung parenchyma. In the present study, a histogram-based analysis was performed in a mouse model of bleomycin (BLM)-induced pulmonary fibrosis by micro-CT, evaluating longitudinal density changes from 7 to 21 days after BLM challenge, a period representing the progression of fibrosis. Two discriminative densitometric indices (i.e. 40th and 70th percentiles) were extracted from Hounsfield Unit density distributions and selected for lung fibrosis staging. The strong correlation with histological findings (rSpearman = 0.76, p < 0.01) confirmed that variations in 70th percentile could reflect a pathological lung condition and estimate the effect of antifibrotic treatments. This index was therefore used to define lung aeration levels in mice distinguishing in hyper-inflated, normo-, hypo- and non-aerated pulmonary compartments. A retrospective analysis performed on a large cohort of mice confirmed the correlation between the proposed preclinical density thresholds and the histological outcomes (rSpearman = 0.6, p < 0.01), strengthening their suitability for tracking disease progression and evaluating antifibrotic drug candidates.

Numerical investigation of flow characteristics over stepped spillways

Abstract Spillways are constructed to evacuate flood discharge safely so that a flood wave does not overtop the dam body. There are different types of spillways, with the ogee type being the conventional one. A stepped spillway is an example of a nonconventional spillway. The turbulent flow over a stepped spillway was studied numerically by using the Flow-3D package. Different fluid flow characteristics such as longitudinal flow velocity, temperature distribution, density and chemical concentration can be well simulated by Flow-3D. In this study, the influence of slope changes on flow characteristics such as air entrainment, velocity distribution and dynamic pressures distribution over a stepped spillway was modelled by Flow-3D. The results from the numerical model were compared with an experimental study done by others in the literature. Two models of a stepped spillway with different discharge for each model were simulated. The turbulent flow in the experimental model was simulated by the Renormalized Group (RNG) turbulence scheme in the numerical model. A good agreement was achieved between the numerical results and the observed ones, which are exhibited in terms of graphics and statistical tables.

Quantitative MRI using relaxometry in malignant gliomas detects contrast enhancement in peritumoral oedema

Malignant gliomas are primary brain tumours with an infiltrative growth pattern, often with contrast enhancement on magnetic resonance imaging (MRI). However, it is well known that tumour infiltration extends beyond the visible contrast enhancement. The aim of this study was to investigate if there is contrast enhancement not detected visually in the peritumoral oedema of malignant gliomas by using relaxometry with synthetic MRI. 25 patients who had brain tumours with a radiological appearance of malignant glioma were prospectively included. A quantitative MR-sequence measuring longitudinal relaxation (R1), transverse relaxation (R2) and proton density (PD), was added to the standard MRI protocol before surgery. Five patients were excluded, and in 20 patients, synthetic MR images were created from the quantitative scans. Manual regions of interest (ROIs) outlined the visibly contrast-enhancing border of the tumours and the peritumoral area. Contrast enhancement was quantified by subtraction of native images from post GD-images, creating an R1-difference-map. The quantitative R1-difference-maps showed significant contrast enhancement in the peritumoral area (0.047) compared to normal appearing white matter (0.032), p = 0.048. Relaxometry detects contrast enhancement in the peritumoral area of malignant gliomas. This could represent infiltrative tumour growth.

Creation of plasma column with different density gradients to generate terahertz radiation during beam-plasma interaction

The system is described for the preliminary plasma creation in the GOL-PET facility. Currently, after this system was considerably reconstructed, it is based on a high-voltage discharge system with pulsed gas injection. The new system was studied on the subject of whether, with its help, it is possible to create preliminary plasma with different longitudinal and transverse density distributions. The results obtained are presented which seem to be encouraging.

Effect of plasma density gradients on generation of terahertz radiation in magnetized plasma column during relaxation of kiloampere REB inside it

Generation of terahertz radiation in the magnetized plasma column due to the two-stream instability developing in the relativistic electron beam (REB) with a current of 10 kA is studied at the GOL-PET facility. In the first series of the experiments, at the regular transverse plasma density gradients, power of the generated terahertz radiation increased thirty times. At a frequency of the upper-hybrid oscillations (0.2–0.3 THz) and pulse duration of few microseconds, it reached 4 MWs. In the next experiments, when the additional longitudinal density gradients were created in plasma, the radiation power exceeded 10 MWs. These results are described in this paper.

Solar Tides in the Middle and Upper Atmosphere of Mars

AbstractSolar tides are responsible for much of the spatial‐temporal variability of Mars' upper atmosphere (100–∼200 km). However, the tidal spectrum, its latitude versus Ls variability, and its vertical evolution remain uncertain. In this paper, Mars Climate Sounder temperature measurements at 76 km above Mars' areoid are used to construct a multiyear latitude versus Ls climatology of the tidal spectrum. The most important spectral components include the solar‐synchronous (“migrating”) components DW1, SW2, and the solar‐asynchronous (“nonmigrating”) tides DE3, DE2, DE1, SE1, S0, and SW1. The Mars Climate Database (MCD), which provides predictions from the Laboratoire de Météorologie Dynamique Global Climate Model, captures particularly well the amplitudes and key structural features of the solar‐asynchronous tides at 76 km that furthermore underly the large longitudinal structures in density that are observed between 100 and 200 km. Height‐latitude and latitude‐Ls structures of MCD density perturbations are therefore examined between 76 and 172 km and interpreted in terms of mean wind and dissipation effects. In particular, due to the smaller radius and more intense zonal‐mean zonal winds at Mars compared to Earth, Doppler‐shift effects are significantly exaggerated compared to Earth. Evidence is also provided for nonnegligible contributions to density variability from stationary planetary waves which arise from tide‐tide nonlinear interactions. It is moreover shown that MCD captures the salient amplitude and phase characteristics of the ∼±30–60% longitudinal density perturbations measured by the Mars Global Surveyor accelerometer. This, and the excellent MCD‐MCS agreement at 76 km, lends credibility to the ability of MCD to provide new insights into thermosphere density variability at Mars due to vertical coupling by solar tides.

Universality class for a nonequilibrium state of matter: A d=4-ε expansion study of Malthusian flocks.

We show that "Malthusian flocks"-i.e., coherently moving collections of self-propelled entities (such as living creatures) which are being "born" and "dying" during their motion-belong to a new universality class in spatial dimensions d>2. We calculate the universal exponents and scaling laws of this new universality class to O(ε) in a d=4-ε expansion and find these are different from the "canonical" exponents previously conjectured to hold for "immortal" flocks (i.e., those without birth and death) and shown to hold for incompressible flocks with spatial dimensions in the range of 2<d≤4. We also obtain a universal amplitude ratio relating the damping of transverse and longitudinal velocity and density fluctuations in these systems. Furthermore, we find a universal separatrix in real space (r) between two regions in which the equal-time density correlation 〈δρ(r,t)δρ(0,t)〉 has opposite signs. Our expansion should be quite accurate in d=3, allowing precise quantitative comparisons between our theory, simulations, and experiments.