Anisotropic Spectrum Research Articles

Anisotropic plasmons in Au/GaAs(001) structures with gold nanoclusters

The structures Au/GaAs(001) with gold nanoclusters are created by annealing of Au films deposited onto GaAs surface. The samples are diagnosed stepwise by scanning probe microscopy. Using reflectance anisotropy spectroscopy, Au clusters are established to possess plasmons with the in-surface anisotropy. The measured anisotropy spectrum consists of a resonant feature near the energy of 2 eV typical of local plasmons of Au clusters. The results are explained theoretically, and the new spectral feature is assigned to anisotropic plasmons of Au nanoclusters located on GaAs surface.

Two‐Photon Laser‐Written Photoalignment Layers for Patterning Liquid Crystalline Conjugated Polymer Orientation

AbstractSystematic tuning of chemical and physical structure allows fine control over desired electronic and optical properties, including those of conjugated polymer semiconductors. In the case of physical structure, orientation via liquid crystalline alignment allows access to fundamental optical anisotropies and the associated refractive index modification offers great potential for fabrication of photonic structures. In this paper, photoalignment is used to orient the liquid crystalline conjugated polymer poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT), specifically involving two‐photon infrared laser writing of patterns in an azobenzene sulphonic dye (SD1). These patterns are transferred into the overlying film by thermotropic orientation in the nematic melt, then frozen in place by quenching to a room temperature nematic glass. Optimization of laser power and scan speed allows features with linewidths ≤ 1 µm. Photoluminescence (PL) peak anisotropy values reach PLII/PL⊥ = 13 for laser writing, compared with PLII/PL⊥ = 9 for polarized ultraviolet light emitting diode exposure of the same SD1 layer. These two approaches also result in different film microstructures; evidenced by characteristic changes in PL spectra. The anisotropic PL spectra provide information on emissive excited states that complements previous studies on non‐oriented F8BT and related copolymers, also suggesting two emissive states.

Probing dark matter with future CMB measurements

Dark Matter (DM) annihilation and decay during the Dark Ages can affect the cosmic ionization history and leave imprints in the Cosmic Microwave Background (CMB) anisotropy spectra. CMB polarization anisotropy can be sensitive to such energy injection at higher redshifts and help reducing degeneracy with primordial spectral parameters in $\Lambda$CDM and astrophysical ionization processes during reionization. In light of a number of upcoming CMB polarization experiments, such as AdvACTPol, AliCPT, CLASS, Simons Observatory, Simons Array, SPT-3G, we estimate their prospective sensitivity in probing dark matter annihilation and decay signals. We find that future missions have 95\% C.L. projected limits on DM decay and annihilation rates to orders of $\Gamma_\chi (\tau_{\chi}^{-1}) \sim 10^{-27}{\rm{s}}^{-1}$ and $\left<\sigma v \right>/m_{\chi} \sim 10^{-29}{\rm{cm^3s^{-1}GeV^{-1}}}$ respectively, significantly improving the sensitivity to DM from current experimental bounds.

Dark D-brane cosmology: From background evolution to cosmological perturbations

We study the cosmological predictions of the dark D-brane model, in which dark matter resides on a D-brane moving in a higher-dimensional space. By construction, dark matter interacts only gravitationally with the standard model sector in this framework. The dark energy scalar field is associated with the position of the D-brane, and its dynamics is encoded in a Dirac-Born-Infeld action. On the other hand, dark matter is identified with matter on the D-brane, that naturally couples to dark energy \textit{via} a disformal coupling. We analyse the numerical evolution of the cosmological background, highlighting the fact that there are two regimes of interest: one, in which the coupling is positive throughout; and another, in which the coupling is negative at the present. In the latter, there is the enticing possibility of having scenarios in which the coupling is positive for a significant part of the evolution, before decreasing towards negative values. In both cases, the coupling is very small at early times, and only starts to grow during the late matter dominated era. We also derive the equations for the linear cosmological perturbations, an expression for the effective time-dependent gravitational coupling between dark matter particles and present the numerical results for the CMB anisotropy and matter power spectra. This allows for a direct comparison of the predictions for the growth of large scale structure with other disformal quintessence models.

Anisotropic distributions of deuterium–deuterium nuclear fusion products in a compact tokamak

The paper is devoted to calculations of anisotropic spectra of nuclear fusion products in a compact tokamak. The knowledge of these spectra is essential for estimations of the first wall load by neutron radiation and other fast particle fluxes from the plasma, computations of the plasma heating profiles, and correct analysis of experimental data, obtained on the present-day and prospective tokamaks and other controlled fusion devices. Anisotropic analytical S- and L-formulae found earlier for nuclear fusion product distributions are computationally demanding. In this paper improved anisotropic S- and L-algorithms are introduced. The new simplified formulae retain the generality and reduce the calculation time without changing the results. Their application for the calculation of energetic and angular distributions of products of both neutron and proton branches of the deuterium–deuterium nuclear fusion reaction in the neutral beam heated plasma of the Globus-M2 spherical tokamak is described. Notwithstanding the low neutral beam energy, the obtained fusion product spectra are strongly anisotropic and may be observed experimentally.

Statistical learning of NMR tensors from 2D isotropic/anisotropic correlation nuclear magnetic resonance spectra.

Many linear inversion problems involving Fredholm integrals of the first kind are frequently encountered in the field of magnetic resonance. One important application is the direct inversion of a solid-state nuclear magnetic resonance (NMR) spectrum containing multiple overlapping anisotropic subspectra to obtain a distribution of the tensor parameters. Because of the ill-conditioned nature of this inverse problem, we investigate the use of the truncated singular value decomposition and the smooth least absolute shrinkage and selection operator based regularization methods, which (a) stabilize the solution and (b) promote sparsity and smoothness in the solution. We also propose an unambiguous representation for the anisotropy parameters using a piecewise polar coordinate system to minimize rank deficiency in the inversion kernel. To obtain the optimum tensor parameter distribution, we implement the k-fold cross-validation, a statistical learning method, to determine the hyperparameters of the regularized inverse problem. In this article, we provide the details of the linear-inversion method along with numerous illustrative applications on purely anisotropic NMR spectra, both synthetic and experimental two-dimensional spectra correlating the isotropic and anisotropic frequencies.

The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: BAO and RSD measurements from the anisotropic power spectrum of the quasar sample between redshift 0.8 and 2.2

ABSTRACT We measure the clustering of quasars of the final data release (DR16) of eBOSS. The sample contains $343\, 708$ quasars between redshifts 0.8 ≤ z ≤ 2.2 over $4699\, \mathrm{deg}^2$. We calculate the Legendre multipoles (0,2,4) of the anisotropic power spectrum and perform a BAO and a Full-Shape (FS) analysis at the effective redshift zeff = 1.480. The errors include systematic errors that amount to 1/3 of the statistical error. The systematic errors comprise a modelling part studied using a blind N-body mock challenge and observational effects studied with approximate mocks to account for various types of redshift smearing and fibre collisions. For the BAO analysis, we measure the transverse comoving distance DM(zeff)/rdrag = 30.60 ± 0.90 and the Hubble distance DH(zeff)/rdrag = 13.34 ± 0.60. This agrees with the configuration space analysis, and the consensus yields: DM(zeff)/rdrag = 30.69 ± 0.80 and DH(zeff)/rdrag = 13.26 ± 0.55. In the FS analysis, we fit the power spectrum using a model based on Regularised Perturbation Theory, which includes redshift space distortions and the Alcock–Paczynski effect. The results are DM(zeff)/rdrag = 30.68 ± 0.90 and DH(zeff)/rdrag = 13.52 ± 0.51 and we constrain the linear growth rate of structure f(zeff)σ8(zeff) = 0.476 ± 0.047. Our results agree with the configuration space analysis. The consensus analysis of the eBOSS quasar sample yields: DM(zeff)/rdrag = 30.21 ± 0.79, DH(zeff)/rdrag = 3.23 ± 0.47, and f(zeff)σ8(zeff) = 0.462 ± 0.045 and is consistent with a flat ΛCDM cosmological model using Planck results.

Comparative study of structural, optical and magnetic properties of Er3+ doped yttrium gallium borates

The paper presents the results of a comprehensive study of yttrium gallium borate (YGa3(BO3)4) crystals low-doped (0.2 wt%) with erbium (Er3+) ions by in-situ X-ray diffraction (XRD), radioluminescence (RL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) techniques. Structural and elastic properties of YGa3(BO3)4: Er3+ crystals measured by the XRD method in the temperature range from 300 K to 1073 K have revealed the temperature variation of the volume thermal expansion coefficient. The analysis of RL spectra allowed us to assume the existence of the characteristic Er3+-related emission band located in the near-infrared region. The TSL spectra revealed strong peaks at low temperatures due to shallow traps and much less intense bands located above room temperature. Measurements of heat capacity in a wide temperature range allowed us to determine the Debye temperature θD ≈ 332 K. From the detailed analysis of the strongly anisotropic EPR spectra measured in YGa3(BO3)4:Er3+ crystals, the parameters of the spin Hamiltonian of Er3+ ions were determined: g⊥ = 9.34; g∥ = 1.269; A⊥ = 320.9 MHz; A∥ = 47.7 MHz. The temperature dependence of the spin-lattice relaxation rate of Er3+ ions was described well by the Orbach-Aminov process. It was proposed that Er3+ ions reside yttrium ions in YGa3(BO3)4 crystal lattice and are located in a slightly distorted prism made of six oxygen ions.

Cross-correlation of Far-infrared Background Anisotropies and CMB Lensing from Herschel and Planck Satellites

Abstract The cosmic infrared background (CIB) anisotropies and cosmic microwave background (CMB) lensing are powerful measurements for exploring cosmological and astrophysical problems. In this work, we measure the autocorrelation power spectrum of the CIB anisotropies in the Herschel–SPIRE HerMES Large Mode Survey (HeLMS) field, and the cross-power spectrum with the CMB lensing measurements from the Planck satellite. The HeLMS field covers more than 270 deg2, which is much larger than in previous analysis. We use the Herschel Level 1 time stream data to merge the CIB maps at 250, 350, and 500 μm bands, and mask the areas where the flux is greater than or there are no measured data. We obtain the final CIB power spectra at 100 ≤ ℓ ≤ 20,000 by considering several effects, such as beam function, mode coupling, transfer function, and so on. We also calculate the theoretical CIB auto- and cross-power spectra of CIB and CMB lensing by assuming that the CIB emissivity follows a Gaussian distribution in redshift. We find that, for the CIB auto-power spectra, we obtain signal-to-noise ratios (S/Ns) of 15.9, 15.7, and 15.3 at 250, 350, and 500 μm, and for the CIB ⨯ CMB lensing power spectra, S/Ns of 7.5, 7.0, and 6.2 at 250, 350, and 500 μm, respectively. Comparing to previous works, the constraints on the relevant CIB parameters are improved by factors of 2– 5 in this study.

Magnetic Resonance Study of p‐Type 3C SiC Microparticles

The silicon carbide (SiC) 3C polytype microparticles with p‐type conductivity are investigated by X‐band electron paramagnetic resonance (EPR) technique in a wide temperature interval. Morphological and Raman studies show that the mean particle diameter is ≈8 μm, and the SiC polytype is purely 3C. At T = 10 K, the EPR spectrum of the shallow boron acceptor substituting cubic site (BK), with C3V symmetry and anisotropic g‐ and A‐tensors resulting from static Jahn–Teller effect, is observed. At T &gt; 30 K, a continuous transition from static to dynamic Jahn–Teller effect for BK is detected. The temperature‐dependent BK principal g‐values are explained by the transitions between the ground and excited vibronic states of BK. At T = 130–150 K, the BK center is characterized by Td symmetry and isotropic g‐ and A‐tensors. At T = 60–190 K, an additional single EPR Lorentzian line with short spin relaxation times and isotropic g‐value close to BK average g‐value is observed. It was explained by averaging the anisotropic spectrum caused by rapid transitions between the boron ground and excited vibronic states split by Jahn–Teller potential. In addition, the EPR signal from carbon vacancy with characteristic superhyperfine structure is observed at T = 10–298 K.

The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: measurement of the BAO and growth rate of structure of the luminous red galaxy sample from the anisotropic power spectrum between redshifts 0.6 and 1.0

ABSTRACT We analyse the clustering of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey Data Release 16 luminous red galaxy sample (DR16 eBOSS LRG) in combination with the high redshift tail of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey Data Release 12 (DR12 BOSS CMASS). We measure the redshift space distortions (RSD) and also extract the longitudinal and transverse baryonic acoustic oscillation (BAO) scale from the anisotropic power spectrum signal inferred from 377 458 galaxies between redshifts 0.6 and 1.0, with the effective redshift of zeff = 0.698 and effective comoving volume of $2.72\, {\rm Gpc}^3$. After applying reconstruction, we measure the BAO scale and infer DH(zeff)/rdrag = 19.30 ± 0.56 and DM(zeff)/rdrag = 17.86 ± 0.37. When we perform an RSD analysis on the pre-reconstructed catalogue on the monopole, quadrupole, and hexadecapole we find, DH(zeff)/rdrag = 20.18 ± 0.78, DM(zeff)/rdrag = 17.49 ± 0.52 and fσ8(zeff) = 0.454 ± 0.046. We combine both sets of results along with the measurements in configuration space and report the following consensus values: DH(zeff)/rdrag = 19.77 ± 0.47, DM(zeff)/rdrag = 17.65 ± 0.30 and fσ8(zeff) = 0.473 ± 0.044, which are in full agreement with the standard ΛCDM and GR predictions. These results represent the most precise measurements within the redshift range 0.6 ≤ z ≤ 1.0 and are the culmination of more than 8 yr of SDSS observations.

Wave Structure Function and Long-Exposure MTF for Gaussian-Beam Waves Propagating in Anisotropic Maritime Atmospheric Turbulence

The expressions of wave structure function (WSF) and long-exposure modulation transfer function (MTF) for laser beam propagation through non-Kolmogorov turbulence were derived in our previous work. In this paper, based on anisotropic maritime atmospheric non-Kolmogorov spectrum, the new analytic expression of WSF for Gaussian-beam waves propagation through turbulent atmosphere in a horizontal path is derived. Moreover, using this newly derived expression, long-exposure MTF for Gaussian-beam waves is obtained for analyzing the degrading effects in an imaging system. Using the new expressions, WSF and MTF for Gaussian-beam waves propagating in terrestrial and maritime atmospheric turbulence are evaluated. The simulation results show that Gaussian-beam waves propagation through maritime turbulence obtain more degrading effects than terrestrial turbulence due to the humidity and temperature fluctuations. Additionally, the degrading effects under anisotropic turbulence get less loss than that of isotropic turbulence.

Coupling of three intramolecular vibration modes of liquid H2O molecules in the framework of the fluctuation theory of hydrogen bonding.

Vibrational spectra of liquid water contain a wealth of information about its structure and dynamics but there are no generally acknowledged interpretation of their band profiles, unfortunately. We have tried to calculate them taking into account only the coupling of three intramolecular vibrations in the set of H2O molecules with different initial oscillator frequencies and intensities. The matter is that each water molecule forms hydrogen bonds of different strengths; thus the OH stretching band spans several hundreds of wave numbers (the fluctuation theory of hydrogen bonding). This distribution overlaps with the similar band of the first overtone of the HOH bending frequencies thus triggering a Fermi resonance between three vibrations. There were some problems causing some simplifications in previous theoretical modeling of vibrational transitions in condensed water. To solve them we extract the statistical distribution of OH frequencies of H2O molecules directly from the experimental spectra of HOD molecules at the same conditions instead of defining it theoretically. Also the bending overtone is allowed to have non-zero intrinsic intensity when calculating the Fermi resonance. The test calculation of the isotropic component of the Raman spectrum which is most critical for interpretation shows that our algorithm can reproduces the characteristic peculiarities of the experiment. The spectrum consists of three non-Gaussian contours. The overtone of bending vibration, being strengthened by Fermi resonance, makes the greatest contribution to the dominating low-frequency spectrum component that was previously attributed to intermolecular coupling of adjacent OH oscillators by some authors. Further we plan to calculate similar band profiles in the IR and also Raman isotropic and anisotropic spectra of Н2О and D2О molecules within a wide temperature range for their quantitative comparison with experiment.

Theoretical Study of the Anisotropy Spectra of the Valine Zwitterion and Glyceraldehyde.

The electronic absorption (EA), circular dichroism (ECD), and anisotropy spectra of the l-valine zwitterion and d-glyceraldehyde are calculated by time-dependent density functional theory (TDDFT) with the M06-2X and B3LYP functionals. It is found that the absorption and ECD spectra from TDDFT/M06-2X agree well with experimental results measured from the amorphous film of l-valine. Moreover, the calculations reproduce all three major peaks observed in the experimental anisotropy spectra. For d-glyceraldehyde, the TDDFT/M06-2X calculations indicate that the excitation wavelengths of the first excited state of 32 stable conformers distribute from 288 to 322 nm, giving rise to two ECD peaks with opposite signs centered at 288 and 322 nm. The very weak absorption of the first excited state (S1) induces two high peaks in the anisotropy spectra of d-glyceraldehyde, which should be seen in future experimental studies.

Polymorph and anisotropic Raman spectroscopy of Phz-H2ca cocrystals

The nucleation and growth mechanism and polymorph-property correlations in the molecular cocrystal field are widely sought but currently remain unclear. Herein, a new wire-like morphology of phenazine ( Phz )-chloranilic acid ( H2ca) cocrystal (PHC) is demonstrated for the first time, and the self-assembly of Phz and H2ca is controlled to selectively prepare kinetically stable wires and thermodynamically stable plates. Specifically, low precursor concentration is beneficial for one-dimensional (1D) self-assembly along the [010] crystallographic direction, while only supersaturation can trigger 2D self-assembly along the [100] and [010] directions, respectively. This is understandable in terms of the (020) face showing the largest attachment energy ( E att) and the (002) face possessing the smallest surface energy ( E surf). Moreover, anisotropic Raman spectra related to the mode symmetry and atomic displacements in two types of PHCs are revealed, and the same Raman-active vibrational bands of PHC wire and plate show different polarization responses, which is intrinsically ascribed to their different molecular orientations. Overall, this is the first case that morphologies of cocrystal are precisely tuned with comprehensive investigations of their anisotropic vibrational characteristics.

Andreev reflection at the interface of a normal Weyl semimetal and a superconducting type-II Weyl semimetal

We study Andreev reflection at the interface of a time-reversal invariant Weyl semimetal without band tilting in the normal or ferromagnetic state with a type-II Weyl semimetal possessing an overtilted anisotropic energy spectrum in the superconducting state. We find that the Andreev reflection at the normal-superconductor interface is tremendously anisotropic, reflecting the anisotropic energy spectrum of the type-II Weyl semimetal. There is a critical junction direction relative to the band tilting direction which, below it, the Andreev reflection acquires distinct properties without any other counterpart. Further, the conductance of this junction is constant and independent of the energy at subgap energies in two extreme limits of the zero and infinite chemical potentials. We can attribute them to the perfect specular and retro Andreev reflections, respectively. In particular, we find a universal value for the zero-energy conductance independent of the chemical potential on each side of the junction. At the interface of the ferromagnet-superconductor, the Andreev reflection can be switched between the specular and retro regimes by varying the exchange energy. This results in different asymptotic values for conductance at high exchange energies depending on if the junction direction is below or above the critical direction. Moreover, we see that tunneling conductance of the normal-ferromagnet-superconductor junction in the thin barrier limit is independent of the potential barrier strength, while it periodically oscillates in terms of the exchange barrier strength. Furthermore, we find a $\ensuremath{\pi}/4$ phase shift in the periodic oscillation of the conductance of the junctions with directions below and above the critical direction. This highly anisotropic conductance of the junctions studied here can be used as a way, accompanied by the other methods, for detecting the anisotropic spectrum and band-tilting direction of type-II Weyl semimetals.

A rapid distortion theory-based airfoil turbulent inflow noise prediction method

Turbulent inflow (TI) noise is reported as an important source of wind turbine (WT) broadband aeroacoustic noise, coexistent with many other sources (e.g., the airfoil self-noise). This manuscript intends to elucidate the discussion on TI noise by providing an alternative prediction method based on the rapidly distorted anisotropic turbulent velocity energy spectrum. A review on turbulent inflow noise prediction is presented, followed by the discussion on turbulence modeling and the derivation of a modified TI noise prediction expression, which allows a more detailed assessment of wind turbine noise sources. This can contribute for WT blade optimization, once it is implemented in design codes that consider noise as a constraint. Criteria for the turbulent velocity spectrum to be characterized by the rapid distortion theory (RDT) are established, and the validation methodology is carried through comparisons between the novel semi-empirical prediction method and data gathered from recent literature for a flat-plate airfoil with $$3\%$$ relative thickness and a NACA 0008 airfoil. The RDT-modified turbulent inflow noise prediction method shows better agreement with the measured data, when compared to predictions that adopt an isotropic model for the turbulent velocity energy spectrum, a condition only achieved in the absence of the airfoil in the test section of aeroacoustic facilities.

Beam test characterisation of a Plastic Scintillator Prototype for the space-based cosmic ray experiment HERD

The High Energy cosmic-Radiation Detector (HERD) facility is planned to go onboard China's Space Station, planned to be operational starting in around 2025 for about 10 years. The main scientific objectives of HERD are the search for signals of dark matter annihilation products, precise cosmic electron/positron spectrum and measurements of anisotropy up to 10 TeV, precise cosmic ray spectrum and composition measurements up to the knee energy (1 PeV), and high energy γ-ray monitoring and survey. HERD consists of a 3D cubic crystals calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) and scintillating fiber trackers (FIT) and by a Plastic Scintillator Detector (PSD) for γ-ray veto and ion charge measurement. A PSD prototype consisting of a scintillator tile readout by two arrays of SiPMs on opposite sides has been tested with proton and C ion beam at the CNAO (Centro Nazionale Adroterapia Oncologica) in Pavia, (Italy). Preliminary results on charge resolution are presented.

Quantitative examination of a fundamental assumption in small-angle neutron scattering studies of deformed polymer melts

It has long been established that the coherent scattering intensity of neutrons by isotropic mixtures of hydrogenous and deuterated polymers of matching molecular weights is, to the first approximation, proportional to the single-chain structure factor of the polymer chain. The validity of this fundamental relation for equilibrium, undeformed polymer melts is well supported by the extensive experimental and theoretical investigations over the past several decades. The generalization of this relation to the case of nonequilibrium, deformed polymer melts, however, is not a trivial one. Despite its widespread usage in small-angle neutron scattering (SANS) studies of deformed polymer melts, the assumed proportionality between coherent scattering intensity and single-chain structure factor has received very little experimental scrutiny. This work quantitatively examines this issue through spherical harmonic expansion analysis of the anisotropic SANS spectra of deformed polystyrene melts of different levels of deuterium labeling. It is shown that the classical assumption works extremely well over a wide range of scattering wavevectors, where the isotropic component of the SANS spectrum and the leading term of structural anisotropy vary by more than two orders of magnitude.

Measurement of turbulence properties

The aim of the research is to investigate anisotropic turbulence intensities, id est to investigate the distribution of Reynolds stresses and energy spectra in a square cross-section channel, downstream of a semi-active jet turbulence grid generating anisotropic turbulent airflow. In addition to the semi-active jet turbulence grid, another type of turbulence grid was developed and experimentally investigated. This grid contains vertical, flexible strips of aluminum (in this case, there are no perpendicular (horizontal) grid elements), which vibrate at a frequency depending on the velocity of the main airflow. Besides the investigation of the velocity- and turbulence intensity distributions, another main objective of the research is to measure the von Kármán energy spectrum when the turbulence cannot be considered isotropic. This aspiration of ours is justified by the knowledge gap present in the literature in this specific field. Monin has carried out a theoretical study to extend and generalize the von Kármán – Howarth isotropic principal stress equation to the anisotropic regime. The proposed new experimental work aims to provide a solid experimental background for verifying and validating the physical correctness of the Monin equation, which may result in a new theoretical understanding and perception of the major issues and the nature of anisotropic turbulence. Since the anisotropic energy spectra are expected to exhibit different characteristics from the isotropic Kolmogorov spectra, these new experimental results may contribute to the development of new anisotropic and engineering turbulence models that can be used in industrial applications.