Single Bounce Research Articles

Optical polarization studies of latex beads in aqueous solution: An analog for radar scattering in icy regolith

This study presents low phase angle 0°–5° measurements of polarimetric properties of icy planetary regolith analog materials acquired using the custom-built Multi-Axis- Goniometer-Instrument (MAGI). We present same sense (SC), and opposite sense (OC) backscatter circular polarization coefficients, circular polarization ratio (CPR), and degree linear polarization (DLP) of spherical latex (non-dye) beads of varying sizes and volume concentrations (v/v) in aqueous solutions (λ=0.8μm) in water. We also present measurements of alumina powder in air at λ=1.064μm. Measurements showed that at a low incidence angle (i=0°), backscatter is dominated by surface specular single-bounce scattering, that hides other scattering processes. At high (i=15°) incidence angle, surface single-bounce surface scattering becomes negligible, allowing for the detection of diffuse, dihedral (multiple bounces) scattering. We find that classical Mie alumina particles (2.1μm,4.0μm) enhance subsurface scattering due to a larger void space relative to larger Mie particles (30μm), that cause the radar signal to scatter forward off small imperfections, maintaining the polarization properties of the signal and generating high >1CPR. Latex beads, representing impurities, demonstrate the impact of isotropic and anisotropic scattering on radar signatures. This study also found that the scattering medium’s anisotropy correlates to the size of the beads, while the void space of the medium inversely correlates with the bead size and the volume concentration (v/v) of the beads. Rayleigh beads, due to isotropic scattering from the reduced scattering cross-section and higher transparency relative to larger impurities, generate subsurface single bounce scattering from the sample platform, producing OC≫SC and a low (<0.5)CPR across all v/v. Rayleigh impurities in transparent water-ice simulate single bounce scattering from underlying layers. Conversely, classical and large Mie beads generate anisotropic scattering that intensifies scattering in the forward direction with high CPR, inversely proportional to the volume concentration. This study aids in interpreting radar observations of icy bodies in the solar system, providing insights into the interplay between radar waves and icy regolith compositions.

Relativistic moduli space and critical velocity in kink collisions.

One important tool in the analysis of the collision of kinks and other topological solitons is the reduction of the original field theory to a finite-dimensional system of so-called collective coordinates. Here we study one recent proposal of a collective coordinate model (CCM), the perturbative relativistic moduli space (pRMS), where the amplitudes of the Derrick modes are promoted to collective coordinates. In particular, we analyze the possibility to calculate within the pRMS the critical velocity, i.e., the initial velocity of kinks at which single bounce scattering changes into a multibounce or annihilation collision. We find that for a growing number of Derrick modes the critical velocity of the CCM approaches the full field theory value. In particular, in the case of the ϕ^{4} model we reach a 99% accuracy. We also see this convergence for a wide range of models belonging to the family of the double sine-Gordon and Christ-Lee theories, especially in those cases where the kinks do not reveal a too well-pronounced half-kink inner structure.

A 3-D Semi-Deterministic MIMO Beam Channel Model for Cellular-Assisted Millimeter-Wave Vehicular Communications

The multiple-input multiple-output (MIMO)-based millimeter-wave (mmWave) propagation is envisioned as a key technology to offer greater bandwidths than previously available for vehicular communications. In this paper, we propose a three-dimensional (3-D) semi-deterministic MIMO beam channel model to characterize the fading properties of cellular-assisted mmWave communications. First, we analyze the digital beamforming effects on multipaths and find that beams act like spatial filters. Then, we propose a cluster generation method, which assemblies single-bounce (SB)-based reflection points and surrounding scatterers into a group. On this basis, the SB reflection and scattering propagation mechanisms via clusters are realized by using ray tracing (RT) and propagation-graph (PG) models, respectively. Furthermore, we use the directive scattering model to enhance modeling accuracy regarding scattering components. Based on our proposal, position and beamwidth-based channel statistical properties, including power delay profile (PDP), spatial cross-correlation function (CCF), Doppler power spectrum density (PSD), and additional path loss (PL) are fully investigated considering perfect beam alignment. Numerical results show that our proposal is capable of emulating beam-dependent mmWave channel and narrow beamwidths cause few multipaths and higher PL. Besides, it can capture the non-stationarities for given scenarios, which can be adapted to various communication scenarios by establishing the corresponding digital maps.

PolyX beamline at SOLARIS—Concept and first white beam commissioning results

PolyX is a compact bending magnet beamline under construction at National Synchrotron Radiation Centre SOLARIS, which will be available to users in mid-2023. The beamline is focused on X-ray microimaging and microspectroscopy in the tender/hard (4–15 keV) X-ray energy range. The name PolyX comes from polycapillary X-ray optics that will be extensively used for efficient X-ray focusing and from the possibility of using polychromatic or broadband X-rays to increase the rather low flux from the SOLARIS bending magnet in the hard X-ray energy range. Polycapillary optics will provide focal spots with sizes of 8–200 μm. Single bounce ellipsoidal capillary is expected to provide a ∼2 μm focal spot size. The main experimental techniques at PolyX will be X-ray absorption and phase-contrast imaging and microtomography, micro-X-ray fluorescence imaging and micro-X-ray absorption spectroscopy. This paper presents the concept of PolyX beamline and preliminary “white” beam commissioning results.

In-line monitoring of protein concentration with MIR spectroscopy during UFDF.

Rapid increase of product titers in upstream processes has presented challenges for downstream processing, where purification costs increase linearly with the increase of the product yield. Hence, innovative solutions are becoming increasingly popular. Process Analytical Technology (PAT) tools, such as spectroscopic techniques, are on the rise due to their capacity to provide real-time, precise analytics. This ensures consistent product quality and increased process understanding, as well as process control. Mid-infrared spectroscopy (MIR) has emerged as a highly promising technique within recent years, owing to its ability to monitor several critical process parameters at the same time and unchallenging spectral analysis and data interpretation. For in-line monitoring, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) is a method of choice, as it enables reliable measurements in a liquid environment, even though water absorption bands are present in the region of interest. Here, we present MIR spectroscopy as a monitoring tool of critical process parameters in ultrafiltration/diafiltration (UFDF). MIR spectrometer was integrated in the UFDF process in an in-line fashion through a single-use flow cell containing a single bounce silicon ATR crystal. The results indicate that the one-point calibration algorithm applied to the MIR spectra, predicts highly accurate protein concentrations, as compared with validated offline analytical methods.

Sound speed profile estimation in a thick mud layer from travel time data

The sound speed profile in a surficial mud layer is of importance because it controls what is acoustically illuminated within and below the mud layer. A variety of estimates have been made at the New England Mud Patch (NEMP) with some near-surface sound speed gradients as large as 10 s−1 and larger. Here, single bounce seabed reflection travel time data are used to infer what mud sound speed gradients are and are not plausible near the central NEMP region where the mud thickness is ∼10 m. Time series data were collected on a moored hydrophone from a broadband source with a 1 second repetition rate as the tow ship transited on a radial from the hydrophone to a distance of ∼1 km at a speed of 2 m/s. The water column was essentially isovelocity and grazing angles ranged from 4.5° to 84°. It is known that at the base of the mud, there is a mud-sand transition layer (of order 1 m thick) where sound speed gradients can be large. However, above this layer, the travel time data clearly indicate that a mud 10 s−1 sound speed gradient is too large. [Research supported by ONR Ocean Acoustics Program.]

Position-free multiple-bounce computations for smith microfacet BSDFs

Bidirectional Scattering Distribution Functions (BSDFs) encode how a material reflects or transmits the incoming light. The most commonly used model is the microfacet BSDF. It computes the material response from the microgeometry of the surface assuming a single bounce on specular microfacets. The original model ignores multiple bounces on the microgeometry, resulting in an energy loss, especially for rough materials. In this paper, we present a new method to compute the multiple bounces inside the microgeometry, eliminating this energy loss. Our method relies on a position-free formulation of multiple bounces inside the microgeometry. We use an explicit mathematical definition of the path space that describes single and multiple bounces in a uniform way. We then study the behavior of light on the different vertices and segments in the path space, leading to a reciprocal multiple-bounce description of BSDFs. Furthermore, we present practical, unbiased Monte Carlo estimators to compute multiple scattering. Our method is less noisy than existing algorithms for computing multiple scattering. It is almost noise-free with a very-low sampling rate, from 2 to 4 samples per pixel (spp).

Approximated Backscattered Wave Models of a Lossy Concentric Dielectric Sphere for Fruit Characterization

Approximated models of electromagnetic waves scattered from a sphere with two different dielectric layers were developed and reported in this paper. We proposed that the dielectric properties of a concentric dielectric sphere object, for example, some types of fruit, could be estimated by this model, from some wave components of the backscattered wave. The models were suitable for lossy objects because only a single bounce of the wave was assumed. In terms of first bounce as well as total backscattered wave results, the reported values agreed well with the values calculated by a commercial software. The measurement results verified the calculated wave components. The dielectric properties determination of real fruits was performed and exhibited the potential in fruit characterization. The main advantage of these models is that they can provide the magnitude and phase information of each backscattered wave component, which makes quality monitoring of fruits to be possible.

Nonsingular cosmology from an interacting vacuum

We examine the dynamics of FLRW cosmologies in which the vacuum interacts with a perfect fluid through an energy exchange, exploring nonsingular configurations, including cyclic and bouncing models. We consider two specific choices for the energy transfer. In the first case, the energy transfer is proportional to a linear combination of the vacuum and fluid energy densities which makes the conservation equations exactly integrable. The resulting Friedmann equation can be interpreted as an energy constraint equation with an effective potential for the scale factor that may include an infinite barrier forcing a bounce at small values of the scale factor, as well as a potential well allowing for cycling solutions. In the second case, the energy transfer is a nonlinear combination of the vacuum and fluid energy densities. Nonetheless even in this case the dynamics can be partially integrated, leading to a first integral, reducing the number of degrees of freedom. We show that also in this nonlinear case bouncing and cycling cosmologies may arise. In both cases the structure of the resulting phase space allows for nonsingular orbits with an early accelerated phase around a single bounce, connected via a decelerated matter-dominated era to a late-time accelerated phase dominated by an effective cosmological constant.

Using the Pauli Scattering Mechanisms for Analysis of Polarimetric SAR Images from RADARSAT Constellation and TanDEM-X Missions

This work describes techniques for extraction of information in polarimetric images from RADARSAT constellation mission (RCM) and TanDEM-X (TDX) and TerraSAR-X (TSX) satellites. Using the boundary conditions of Maxwell&#x0027;s equations it is shown how the single bounce and double bounce scattering can be extracted from quad-pol and compact polarimetric (CP) SAR. We develop new equations to calculate the Pauli decomposition from simulated CP data using RCM quad-pol data. The RCM CP option is circular transmit, linear receive (CTLR). We find that using quad-pol data performs better than using CP data for Pauli decomposition, especially extraction of the HV component. Estimation of single bounce and double bounce scattering from RCM CP data is feasible and yields more information about scattering properties than the CP components alone. We show how more information can be extracted from bistatic TSX&#x002F;TDX quad-pol data by estimation of the coherence of the different Pauli components and optimization of the interferometric coherence using ships as detection objects. This is a unique opportunity to use optimized coherence on moving ships for characterizing their structure.

ACE-OT: Polarimetric SAR Data-Based Amplitude Contrast Enhancement Algorithm for Offset Tracking Applications

The use of polarimetric SAR data can improve the performance of persistent scatterer interferometry (PSI). However, its huge potential remains locked for the amplitude information based offset tracking (OT) technology. For example, to the best knowledge of the authors, there is no single example of a polarization based image optimization method that has been developed for OT processing. In this paper, an amplitude contrast enhancement algorithm (ACE) is introduced, which demonstrates the potential of the polarimetric SAR data on the improvement of OT performance. Its core idea is finding the optimal combination of the different scattering mechanisms for each pixel to improve the contrast. Firstly, the orientation of the reflected polarization ellipse is removed, to avoid the influence of the geometric relationship between the antenna and the target, and the properties of the target. Then three similarity parameters are defined to represent the three basic reflection types of the single bounce, the double bounce, and the random reflection. After that, the optimizing equation is constructed with two optimizing vectors. Finally, the optimizing vectors are calculated to obtain the enhanced amplitude image. Three examples of the enhancement are presented with different PolSAR images sets of both full- (Radarsat-2) and dual-polarization (TerraSAR-X and Sentinel-1). The performance of ACE-OT has been compared with another method, the Adaptive Histogram Enhancement (AHE). The impact of the number of polarization channels available on ACE-OT performance has also been studied.

A Novel Non-Stationary 6G UAV Channel Model for Maritime Communications

To achieve space-air-ground-sea integrated communication networks for future sixth generation (6G) communications, unmanned aerial vehicle (UAV) communications applying to maritime scenarios serving as mobile base stations have recently attracted more attentions. The UAV-to-ship channel modeling is the fundamental for the system design, testing, and performance evaluation of UAV communication systems in maritime scenarios. In this paper, a novel non-stationary multi-mobility UAV-to-ship channel model is proposed, consisting of three kinds of components, i.e., the line-of-sight (LoS) component, the single-bounce (SB) components resulting from the fluctuation of sea water, and multi-bounce (MB) components introduced by the waveguide effect over the sea surface. In the proposed model, the UAV as the transmitter (Tx), the ship as the receiver (Rx), and the clusters between the Tx and Rx, can be seen as moving with arbitrary velocities and arbitrary directions. Then, some typical statistical properties of the proposed UAV-to-ship channel model, including the temporal autocorrelation function (ACF), spatial cross-correlation function (CCF), Doppler power spectrum density (PSD), delay PSD, angular PSD, stationary interval, and root mean square (RMS) delay spread, are derived and investigated. Finally, by comparing with the available measurement data, the accuracy of proposed channel model is validated.

Notes on the post-bounce background dynamics in bouncing cosmologies

We investigate the post-bounce background dynamics in a certain class of single bounce scenarios studied in the literature, in which the cosmic bounce is driven by a scalar field with negative exponential potential such as the ekpyrotic potential. We show that those models can actually lead to cyclic evolutions with repeated bounces. These cyclic evolutions, however, do not account for the currently observed late-time accelerated expansion and hence are not cosmologically viable. In this respect we consider a new kind of cyclic model proposed recently and derive some cosmological constraints on this model.

Spectrum of Cuscuton bounce

It has been recently shown that a cosmological bounce model based on Cuscuton gravity does not have any ghosts or curvature instabilities. We explore whether Cuscuton bounce can provide an alternative to inflation for generating near scale-invariant scalar perturbations. While a single field Cuscuton bounce generically produces a strongly blue power spectrum (for a variety of initial/boundary conditions), we demonstrate that scale-invariant entropy modes can be generated in a spectator field that starts in adiabatic vacuum, and is kinetically coupled to the primary field. Furthermore, our solution has no singularity, nor requires an ad hoc matching condition. We also study the generation of tensor modes (or gravitational waves) in Cuscuton bounce and show that while they are stable, similar to other bounce models, the produced spectrum is strongly blue and unobservable.

Hearing the shape of right triangle billiard tables

&lt;p style='text-indent:20px;'&gt;In this paper, we give a positive answer to the problem that whether one can identify the shape of a right triangle billiard table by a single bounce sequence. Moreover, a convenient method to calculate the shape of polygons is given in this paper, too.&lt;/p&gt;

Infrared Analysis of Interfacial Phenomena during Electrochemical Reduction of CO2 over Polycrystalline Copper Electrodes

Using attenuated total reflection (ATR) infrared spectroscopy and ∼10 nm thick, sputtered Cu-films on single bounce Si-ATR-crystals, we have analyzed the electrochemical conversion of CO2 in 0.1 M NaOH/D2O solutions. By using cyclic voltammetry, transitions in the composition of dissolved and surface-adsorbed species could be identified. At a highly negative potential [more negative than −1.2 V (vs RHE)], the formation of OD– and D2 is dominant, resulting in a relatively high concentration of dissolved carbonate, with a maximum IR intensity at ∼1410 cm–1. When the potential is less negative than −1.2 V, spectroscopically resolved interconversion of carbonate (CO32–) to bicarbonate (D)CO3– is evident, explained by a decrease in the local pH. Furthermore, adsorbed carbonate can now be distinguished from dissolved carbonate due to the strongly potential-dependent peak position of adsorbed carbonate ranging from ∼1510 to 1570 cm–1. In the potential range of −1.2 to −0.5 V (vs RHE), using D2O, the recently proposed CO2-dimer-radical-anion was observed, adsorbed on the polycrystalline copper film. We also assign a previously unresolved band at ∼1610 cm–1 to this species. The dimer disproportionates to adsorbed CO and CO32–, the latter being converted to bicarbonate by proton addition. Adsorbed CO is sensitive to a Stark shift, that is, a shift as a function of applied potential. Eventually, CO disappears, and the infrared signature of (dissolved) formate at ∼1590 cm–1 appears at ∼ −0.5 V. We discuss the spectra and chemistry in detail, based on the reference spectra of carbonate, bicarbonate, and formate and using 13CO2 to substantiate the formation of the dimer intermediate. The results are discussed and compared to recent literature on infrared analysis of electrochemical reduction of CO2.

A 3-D Geometry-Based Stochastic Model for Unmanned Aerial Vehicle MIMO Ricean Fading Channels

In this article, we propose a novel 3-D geometry-based stochastic model (GBSM), i.e., a two-cylinder model, for unmanned aerial vehicle (UAV) multiple-input–multiple-output (MIMO) Ricean fading channels. The received signal is a sum of the Line-of-Sight (LoS) component, single-bounced (SB) rays at the UAV side, SB rays at the ground station side, SB rays on the ground, and double-bounced rays. This makes our model adaptable to a wide variety of UAV communication scenarios. More importantly, the proposed UAV model is the first two-cylinder model that considers ground reflections. Moreover, our model has the ability to investigate the impact of some unique UAV-related parameters (e.g., the UAV’s moving direction, UAV’s altitude, and antenna orientation) on channel characteristics in a 3-D nonisotropic propagation environment. From the proposed model, we derive and study some significant statistical properties, including the space-time correlation function (CF), Doppler power spectral density (PSD), envelope level crossing rate (LCR), and average fade duration (AFD). Some numerical results and interesting observations are provided, which can be considered useful guidance for the design of UAV-MIMO communication systems. Finally, the utility of our model is verified by the close agreement between the theoretical results and some example measurement data.

Measurement‐based geometrical characterisation of the vehicle‐to‐vulnerable‐road‐user communication channel

Vehicle-to-vulnerable-road-user (V2VRU) communications have the ability to provide of awareness to both vehicles and vulnerable road users to prevent accidents. An accurate V2VRU channel model in critical accident scenarios is essential to develop a reliable communications system. Therefore, extensive wideband single-input and single-output channel measurement campaigns at 5.2 GHz were carried out in open-field and urban environments. Accident prone scenarios between a vehicle and a cyclist as well as between a vehicle and a pedestrian are considered. In this study, locations of the scatterers in the propagation environment are estimated. The authors propose a method to extract specular multipath components (MPCs) from the estimated time-variant channel impulse response based on the density of neighbouring MPCs. The specular MPCs are then tracked using a novel tracking algorithm based on the multipath component distance approach. Each path is then related to a physical scatterer in the propagation environment by employing a joint delay-Doppler estimation. According to the results, single and double bounce reflections from buildings and parked vehicles are identified in line-of-sight (LoS) situation. In non-LoS(NLoS) situation, scattering from nearby trees as well as reflections from traffic signs and lampposts beneath the trees canopy are identified.

Modeling of 300 GHz Chip-to-Chip Wireless Channels in Metal Enclosures

This paper proposes a two dimensional (2-D) statistical channel model for Terahertz (THz) chip-to-chip wireless communication in desktop size metal enclosures. This model differs from traditional statistical channel models as it models both traveling and resonant waves that exist inside metal enclosures. Based on the cavity environment and the statistical properties of the channel inside the metal cavity, the geometrical model which describes propagation in resonant cavity as a superposition of LoS, single bounced (SB), double bounced (DB), and multi-bounced (MB) rays is proposed. Based on the geometrical model, a parametric reference model is proposed. Furthermore, the path loss model that captures signal strength variation in a resonant cavity is proposed. Frequency correlation functions (FCF) and power delay profiles (PDP) for different possible chip-to-chip communication scenarios are derived and compared with the measured ones. The results show a good agreement between the simulated and measured statistics.

Eternally oscillating zero energy universe

The question of whether the universe is eternal or if it had a singular moment of creation is deeply intriguing. Although different versions of steady state and oscillatory models of eternal universe have been envisaged, empirical evidence suggests a singular moment of creation at the big bang. Here we analyze the oscillatory solutions for the universe in a modified theory of gravity THED (Torsion Hides Extra-Dimension) and evaluate them by fitting Type 1a supernovae redshift data. THED-gravity exactly mimics General Relativity at the kinematical level, while the modifications in its dynamical equations allow the universe to bounce between a minimum size and a maximum size with a zero average energy within each oscillation. The optimally fit oscillatory solutions correspond to a universe with (i) a small matter density requiring little to no dark matter, (ii) a significantly negative spatial curvature, (iii) a tiny negative dark energy. Alternatively, there exists non-oscillating solutions that appear as an ever-expanding universe from a single bounce preceded by a collapse from the infinite past. These ever-expanding solutions provide marginally better fits to the supernova redshift data, but require larger matter densities and positive dark energy along with a positive spatial curvature. A qualitative analysis of CMB power spectrum in the modified theory suggests a significant negative spatial curvature, which is in stark contrast to a near-zero curvature in the standard big bang theory. An independent constraint on the spatial curvature can further shed light on discriminating the ever expanding and oscillatory universe scenarios.