TE Spectra Research Articles

Searching for local features in primordial power spectrum using genetic algorithms

ABSTRACTWe present a novel methodology for exploring local features directly in the primordial power spectrum using a genetic algorithm pipeline coupled with a Boltzmann solver and Cosmic Microwave Background data (CMB). After testing the robustness of our pipeline using mock data, we apply it to the latest CMB data, including Planck 2018 and CamSpec PR4. Our model-independent approach provides an analytical reconstruction of the power spectra that best fits the data, with the unsupervised machine learning algorithm exploring a functional space built off simple ‘grammar’ functions. We find significant improvements upon the simple power-law behaviour, by Δχ2 ≲ −21, consistently with more traditional model-based approaches. These best-fits always address both the low-ℓ anomaly in the TT spectrum and the residual high-ℓ oscillations in the TT, TE, and EE spectra. The proposed pipeline provides an adaptable tool for exploring features in the primordial power spectrum in a model-independent way, providing valuable hints to theorists for constructing viable inflationary models that are consistent with the current and upcoming CMB surveys.

Efficient photocatalytic degradation of textile dye pollutants using thermally exfoliated graphitic carbon nitride (TE–g–C3N4)

Graphitic carbon nitride (g–C3N4), an organic photocatalyst was reported to have beneficial properties to be used in wastewater treatment applications. However, g–C3N4, in its bulk form was found to have poor photocatalytic degradation efficiency due to its inherent limitations such as poor specific surface area and fast electron–hole pair recombination rate. In this study, we have tuned the physiochemical properties of bulk g–C3N4 by direct thermal exfoliation (TE–g–C3N4) and examined their photocatalytic degradation efficiency against abundant textile dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB). The degradation efficiencies for MB, MO, and RhB dyes are 92 ± 0.18%, 93 ± 0.31%, and 95 ± 0.4% respectively in 60 min of UV light irradiation. The degradation efficiency increased with an increase in the exfoliation temperature. The prepared catalysts were characterized using FTIR, XRD, FE-SEM, EDAX, BET, and UV-DRS. In BET analysis, TE–g–C3N4 samples showed improved surface area (48.20 m2/g) when compared to the bulk g–C3N4 (5.03 m2/g). Further, the TE–g–C3N4 had 2.98 times higher adsorption efficiency than the bulk ones. The free radicals scavenging studies revealed that the superoxide radicals played an important role in the photodegradation for dyes, when compared to the hydroxyl radical (.OH) and the photo-induced holes (h+), Photoluminescence (PL) emission and electrochemical impedance spectroscopy (EIS) spectra of TE–g–C3N4 indicated a lowered electron–hole pairs’ recombination rate and an increased photo-induced charge transfer respectively. Further, the TE–g–C3N4 were found to have excellent stability for up to 5 cycles with only a minor decrease in the activity from 92% to 86.2%. These findings proved that TE–g–C3N4 was an excellent photocatalyst for the removal and degradation of textile dyes from wastewater.

The Atacama Cosmology Telescope: Galactic Dust Structure and the Cosmic PAH Background in Cross-correlation with WISE

We present a cross-correlation analysis between resolution total intensity and polarization observations from the Atacama Cosmology Telescope (ACT) at 150 and 220 GHz and 15″ mid-infrared photometry from the Wide-field Infrared Survey Explorer (WISE) over 107 12.°5 × 12.°5 patches of sky. We detect a spatially isotropic signal in the WISE×ACT TT cross-power spectrum at 30σ significance that we interpret as the correlation between the cosmic infrared background at ACT frequencies and polycyclic aromatic hydrocarbon (PAH) emission from galaxies in WISE, i.e., the cosmic PAH background. Within the Milky Way, the Galactic dust TT spectra are generally well described by power laws in ℓ over the range 103 < ℓ < 104, but there is evidence both for variability in the power-law index and for non-power-law behavior in some regions. We measure a positive correlation between WISE total intensity and ACT E-mode polarization at 1000 < ℓ ≲ 6000 at >3σ in each of 35 distinct ∼100 deg2 regions of the sky, suggesting that alignment between Galactic density structures and the local magnetic field persists to subparsec physical scales in these regions. The distribution of TE amplitudes in this ℓ range across all 107 regions is biased to positive values, while there is no evidence for such a bias in the TB spectra. This work constitutes the highest-ℓ measurements of the Galactic dust TE spectrum to date and indicates that cross-correlation with high-resolution mid-infrared measurements of dust emission is a promising tool for constraining the spatial statistics of dust emission at millimeter wavelengths.

Deep Ultraviolet BGaN Quantum Dot structures

This research studies boron-containing quantum dot (QD) structures that emit the ultraviolet. Ternary and quaternary lattice-matched structure:, , , , ,, , and and their TE and TM gain spectra, spontaneous emission, spontaneous polarization, and piezoelectric polarization have been examined in these structures. They have high TE and TM spectra under reducing boron content in the QD or barrier layer. The total polarization decreases for the Al-containing systems, which is preferred. Binary systems emit at 199nm, while the quaternary can have a peak wavelength near 235nm. Elongating of the wavelength to 290nm is possible with with high gain at a few boron contents.&#x0D;

Constraints on ΛCDM extensions from the SPT-3G 2018 EE and TE power spectra

We present constraints on extensions to the ΛCDM cosmological model from measurements of the E-mode polarization autopower spectrum and the temperature-E-mode cross-power spectrum of the cosmic microwave background (CMB) made using 2018 SPT-3G data. The extensions considered vary the primordial helium abundance, the effective number of relativistic degrees of freedom, the sum of neutrino masses, the relativistic energy density and mass of a sterile neutrino, and the mean spatial curvature. We do not find clear evidence for any of these extensions, from either the SPT-3G 2018 dataset alone or in combination with baryon acoustic oscillation and Planck data. None of these model extensions significantly relax the tension between Hubble-constant, H0, constraints from the CMB and from distance-ladder measurements using Cepheids and supernovae. The addition of the SPT-3G 2018 data to Planck reduces the square-root of the determinants of the parameter covariance matrices by factors of 1.3–2.0 across these models, signaling a substantial reduction in the allowed parameter volume. We also explore CMB-based constraints on H0 from combined SPT, Planck, and ACT DR4 datasets. While individual experiments see some indications of different H0 values between the TT, TE, and EE spectra, the combined H0 constraints are consistent between the three spectra. For the full combined datasets, we report H0=67.49±0.53 km s−1 Mpc−1, which is the tightest constraint on H0 from CMB power spectra to date and in 4.1σ tension with the most precise distance-ladder-based measurement of H0. The SPT-3G survey is planned to continue through at least 2023, with existing maps of combined 2019 and 2020 data already having ∼3.5×lower noise than the maps used in this analysis.Received 29 March 2021Accepted 18 August 2021DOI:https://doi.org/10.1103/PhysRevD.104.083509© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic microwave backgroundCosmological parametersCosmologyGravitation, Cosmology & Astrophysics

A Detailed Description of the CAMSPEC Likelihood Pipeline and a Reanalysis of the Planck High Frequency Maps

This paper presents a detailed description of the CamSpec likelihood which has been used to analyse Planck temperature and polarization maps of the cosmic microwave background since the first Planck data release. We have created a number of likelihoods using a range of Galactic sky masks and different methods of temperature foreground cleaning. Our most powerful likelihood uses 80 percent of the sky in temperature and polarization. Our results show that the six-parameter LCDM cosmology provides an excellent fit to the Planck data. There is no evidence for statistically significant internal tensions in the Planck TT, TE and EE spectra computed for different frequency combinations. We present evidence that the tendencies for the Planck temperature power spectra to favour a lensing amplitude A_L>1 and positive spatial curvature are caused by statistical fluctuations in the temperature power spectra. Using our statistically most powerful likelihood, we find that the A_L parameter differs from unity at no more than the 2.2 sigma level. We find no evidence for anomalous shifts in cosmological parameters with multipole range. In fact, we show that the combined TTTEEE likelihood over the restricted multipole range 2-800 gives cosmological parameters for the base LCDM cosmology that are very close to those derived from the full multipole range 2-2500. We present revised constraints on a few extensions of the base LCDM cosmology, focussing on the sum of neutrino masses, number of relativistic species and the tensor-scalar ratio. The results presented here show that the Planck data are remarkably consistent between detector-sets, frequencies and sky area. We find no evidence in our analysis that cosmological parameters determined from the CamSpec likelihood are affected to any significant degree by systematic errors in the Planck data (abridged).

The cross correlation of the ABS and ACT maps

One of the most important checks for systematic errors in CMB studies is the cross correlation of maps made by independent experiments. In this paper we report on the cross correlation between maps from the Atacama B-mode Search (ABS) and Atacama Cosmology Telescope (ACT) experiments in both temperature and polarization. These completely different measurements have a clear correlation with each other and with the Planck satellite in both the EE and TE spectra at ℓ<400 over the roughly 0110 deg2 common to all three. The TB, EB, and BB cross spectra are consistent with noise. Exploiting such cross-correlations will be important for future experiments operating in Chile that aim to probe the 30<ℓ<8,000 range.

Effects of noise and linewidth on in vivo analysis of glutamate at 3 T

Magnetic resonance spectroscopy (MRS) can noninvasively detect metabolites in vivo, including glutamate (Glu). However, quantification is known to be affected by the overlaps among metabolite resonance lines and background macromolecule signals. We found that adding a moderate amount of noise or line broadening (2 Hz) caused large variations in concentration of Glu and other metabolites, when determined by LCModel analysis of in vivo short-echo time (TE) spectra. Theses variations were largely attributed to strong spectral baselines in short TE spectra, especially near 2.35 ppm, as well as overlapping metabolite resonance lines. To address this issue, we acquired in vivo data at 3 T using both short-TE and the multiple echo time J-resolved point-resolved spectroscopy (JPRESS) MRS techniques. We found that one-dimensional (1D) JPRESS, by simultaneously fitting the two cross-sections of JPRESS at J = 0 and J = 7.5 Hz, was highly resistant to variations in noise levels and spectral linewidths. Our results demonstrate that LCModel analysis of short-TE data is highly sensitive to variations in noise levels and spectral linewidths and this sensitivity is greatly reduced by 1D JPRESS given its substantially reduced baselines and enhanced spectral resolution.

Joint constraint on primordial gravitational waves and polarization rotation angle with current CMB polarization data

Cosmological CPT violation will rotate the polarized direction of CMB photons, convert partial CMB E mode into B mode and vice versa. It will generate non-zero EB, TB spectra and change the EE, BB, TE spectra. This phenomenon gives us a way to detect the CPT-violation signature from CMB observations, and also provides a new mechanism to produce B mode polarization. In this paper, we perform a global analysis on tensor-to-scalar ratio r and polarization rotation angles based on current CMB datasets with both low ℓ (Planck, BICEP2/Keck Array) and high ℓ (POLARBEAR, SPTpol, ACTPol). Benefited from the high precision of CMB data, we obtain the isotropic rotation angle α¯=0.0∘±0.37∘ at 68% CL, the variance of the anisotropic rotation angles Cα(0)<0.0032rad2, the scale invariant power spectrum Dℓ∈[2,350]αα<4.65×10−5rad2 and r<0.059 at 95% CL. Our result shows that with the polarization rotation effect, the 95% upper limit on r gets tightened by 14%.

Resonance laser ionization spectroscopy of tellurium

Resonance ionization schemes for tellurium are investigated with a resonance ionization laser ion source and Ti:Sapphire lasers for fundamental research applications. We present the first three-step resonance ionization spectra of atomic Te. Several autoionizing Rydberg series converging to the first excited state of Te+ are observed and assigned to 5p3 (2Do3/2) ns and nd configurations. Our results include confirmation and significant expansion of the Rydberg series previously reported as well as observation of three new series. From the series convergence limits the ionization potential of tellurium is revised to be 72,669.006(42)stat(20)sys cm−1.

Polarisation as a tracer of CMB anomalies: Planck results and future forecasts

The lack of power anomaly is an intriguing feature at the largest angular scales of the CMB anisotropy temperature pattern, whose statistical significance is not strong enough to claim any new physics beyond the standard cosmological model. We revisit the former statement by also considering polarisation data. We propose a new one-dimensional estimator which takes jointly into account the information contained in the TT, TE and EE CMB spectra. By employing this estimator on Planck 2015 low-$\ell$ data, we find that a random $\Lambda$CDM realisation is statistically accepted at the level of $3.68 \%$. Even though Planck polarisation contributes a mere $4 \%$ to the total information budget, its use pushes the lower-tail-probability down from the $7.22 \%$ obtained with only temperature data. Forecasts of future CMB polarised measurements, as e.g. the LiteBIRD satellite, can increase the polarisation contribution up to $6$ times with respect to Planck at low-$\ell$. We argue that the large-scale E-mode polarisation may play an important role in analysing CMB temperature anomalies with future mission.

Long TE PRESS and STEAM for measuring the triglyceride glycerol CH2 protons at 3T.

The glycerol methylene proton resonances (4-4.5 parts per million, ppm), which arise from the triglyceride backbone, are relevant to fat composition assessment and can be measured with proton MRS. The purpose of the presented work is to determine long TE (echo time) point resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM) values at 3T to resolve the glycerol resonances from that of overlapping water. The response of the glycerol methylene protons of nine edible oils as a function of PRESS and STEAM TE (mixing time, TM=20ms) was investigated. In addition, high resolution NMR spectra of the oils were acquired at 16.5T. Long TE values where J-coupling losses were lowest were selected, namely a TE of 180ms for PRESS (first echo time 17ms) and a TE of 100ms for STEAM (mixing time 20ms). Oil olefinic (≈5.4ppm) to glycerol ratios were calculated from the long TE spectra and correlated with 16.5T ratios. The two techniques yielded olefinic/glycerol ratios that correlated with 16.5T ratios (R2 =0.79 for PRESS and 0.90 for STEAM). The efficacy of the sequences in resolving the glycerol resonance from that of water was verified in vivo on tibial bone marrow of four healthy volunteers. In addition, the potential for using the glycerol methylene signal normalized to the methyl signal (≈0.9ppm) to assess changes in free fatty acid content was demonstrated by measuring differences in spectra acquired from a triglyceride peanut oil phantom and from a phantom composed of a mixture of peanut oil and free fatty acid oleic acid.

Statistical simulations of the dust foreground to cosmic microwave background polarization (Corrigendum)

The characterization of the dust polarization foreground to the Cosmic Microwave Background (CMB) is a necessary step towards the detection of the B-mode signal associated with primordial gravitational waves. We present a method to simulate maps of polarized dust emission on the sphere, similarly to what is done for the CMB anisotropies. This method builds on the understanding of Galactic polarization stemming from the analysis of Planck data. It relates the dust polarization sky to the structure of the Galactic magnetic field and its coupling with interstellar matter and turbulence. The Galactic magnetic field is modelled as a superposition of a mean uniform field and a random component with a power-law power spectrum of exponent $\alpha_{\rm M}$. The model parameters are constrained to fit the power spectra of dust polarization EE, BB and TE measured using Planck data. We find that the slopes of the E and B power spectra of dust polarization are matched for $\alpha_{\rm M} = -2.5$. The model allows us to compute multiple realizations of the Stokes Q and U maps for different realizations of the random component of the magnetic field, and to quantify the variance of dust polarization spectra for any given sky area outside of the Galactic plane. The simulations reproduce the scaling relation between the dust polarization power and the mean total dust intensity including the observed dispersion around the mean relation. We also propose a method to carry out multi-frequency simulations including the decorrelation measured recently by Planck, using a given covariance matrix of the polarization maps. These simulations are well suited to optimize component separation methods and to quantify the confidence with which the dust and CMB B-modes can be separated in present and future experiments. We also provide an astrophysical perspective on our modeling of the dust polarization spectra.

Transmission spectra in graphene-based octonacci one-dimensional photonic quasicrystals

In this work, we have studied theoretically the optical transmissivity spectra in graphene-based quasiperiodic dielectric multilayers made of SiO2 and TiO2 which are juxtaposed in accordance with the Octonacci sequence, with a graphene monolayer between them. Our results show that all the optical spectra are affected, and their band gaps are slightly displaced for high frequencies. We also show that the properties of fractality and self-similarity of the spectra are maintained for high frequencies. We have also analyzed the influence of the incident angle and the chemical potential, and shown that when one changes the chemical potential, there is not an appreciable difference between TE and TM transmission spectra for angles close to the normal incidence. The absorption is also calculated as a function of the frequency, and is shown that sharp peaks will appear at the edges of the allowed band frequencies when we increase the Octonacci generation number. Our model can be used in the study of polarizing filters based on photonic crystals, in order to perform an angular selectivity in the incident light. Also, it is possible to tune the chemical potential of graphene layers and set up an angular selective filter using these phenomena.

One-dimensional dielectric bi-periodic photonic structures based on ternary photonic crystals

We investigate the transmittivity spectra, fields, and energy distribution of the electromagnetic eigenwaves propagating in a one-dimensional (1D) dielectric photonic crystal [(TiO2/SiO2)NAl2O3]M with two periods formed by unit cells TiO2/SiO2 and (TiO2/SiO2)NAl2O3. Spectra of TE- and TM-modes depend on the geometric parameters of the structure and undergo modifications with the change in the period numbers, layer thicknesses, and incidence angle. Special attention is paid to the applicability of the hybrid effective medium approximation comprising the long-wave approximation and two-dimensional (2 × 2) transfer matrix method. We demonstrate spectral peculiarities of the bi-periodic structure and also show the differences between the band gap spectra of the bi-periodic and ternary 1D dielectric photonic crystals. The presented photonic crystal structure can find its applications in optoelectronics and nanophotonics areas as omnidirectional reflectors, optical ultra-narrow bandpass filters, and antireflection coatings.

Light polarization and color from guided-mode resonance filter

The characteristics of reflected light of a 1-D guided-mode resonance filter (GMRF) are studied in this paper. A triple-layer GMRF is designed by using the finite difference time domain method under non-polarized light illumination. Numerical results show that the reflectance spectra of TE and TM polarizations can be changed by altering the fill factor f of the GMRF. Moreover, by calculating the color of the reflected light with the chromaticity theory, we find that the color of reflected light becomes pure when f is 0.9. The results show that the color and polarization degree of the reflected light of a GMRF are tunable by altering the fill factor.

Statistical simulations of the dust foreground to cosmic microwave background polarization

The characterization of the dust polarization foreground to the cosmic microwave background (CMB) is a necessary step toward the detection of the B-mode signal associated with primordial gravitational waves. We present a method to simulate maps of polarized dust emission on the sphere that is similar to the approach used for CMB anisotropies. This method builds on the understanding of Galactic polarization stemming from the analysis of Planck data. It relates the dust polarization sky to the structure of the Galactic magnetic field and its coupling with interstellar matter and turbulence. The Galactic magnetic field is modeled as a superposition of a mean uniform field and a Gaussian random (turbulent) component with a power-law power spectrum of exponent αM. The integration along the line of sight carried out to compute Stokes maps is approximated by a sum over a small number of emitting layers with different realizations of the random component of the magnetic field. The model parameters are constrained to fit the power spectra of dust polarization EE, BB, and TE measured using Planck data. We find that the slopes of the E and B power spectra of dust polarization are matched for αM = −2.5, an exponent close to that measured for total dust intensity but larger than the Kolmogorov exponent − 11/3. The model allows us to compute multiple realizations of the Stokes Q and U maps for different realizations of the random component of the magnetic field, and to quantify the variance of dust polarization spectra for any given sky area outside of the Galactic plane. The simulations reproduce the scaling relation between the dust polarization power and the mean total dust intensity including the observed dispersion around the mean relation. We also propose a method to carry out multifrequency simulations, including the decorrelation measured recently by Planck, using a given covariance matrix of the polarization maps. These simulations are well suited to optimize component separation methods and to quantify the confidence with which the dust and CMB B-modes can be separated in present and future experiments. We also provide an astrophysical perspective on our phenomenological modeling of the dust polarization spectra.

Application of beam deconvolution technique to power spectrum estimation for CMB measurements

We present two novel methods for the estimation of the angular power spectrum of cosmic microwave background (CMB) anisotropies. We assume an absolute CMB experiment with arbitrary asymmetric beams and arbitrary sky coverage. The methods differ from the earlier ones in that the power spectrum is estimated directly from the time-ordered data, without first compressing the data into a sky map, and they take into account the effect of asymmetric beams. In particular, they correct the beam-induced leakage from temperature to polarization. The methods are applicable to a case where part of the sky has been masked out to remove foreground contamination, leaving a pure CMB signal, but incomplete sky coverage. The first method (deconvolution quadratic maximum likelihood) is derived as the optimal quadratic estimator, which simultaneously yields an unbiased spectrum estimate and minimizes its variance. We successfully apply it to multipoles up to ℓ = 200. The second method is derived as a weak-signal approximation from the first one. It yields an unbiased estimate for the full multipole range, but relaxes the requirement of minimal variance. We validate the methods with simulations for the 70 GHz channel of Planck surveyor, and demonstrate that we are able to correct the beam effects in the TT, EE, BB and TE spectra up to multipole ℓ = 1500. Together, the two methods cover the complete multipole range with no gap in between.

Alleviating the tension at lowℓthrough axion monodromy

There exists some tension on large scales between the Planck data and the LCDM concordance model of the Universe, which has been amplified by the recently claimed discovery of non-zero tensor to scalar ratio $r$. At the same time, the current best-fit value of $r$ suggests large field inflation delta phi>M_p, which requires a UV complete description of inflation. A very promising working example that predicts large tensor modes and can be UV completed is axion monodromy inflation. This realization of inflation naturally produces oscillating features, as consequence of a broken shift symmetry. We analyse a combination of Planck, ACT, SPT, WMAP low l polarization and BICEP2 data, and show a long wavelength feature from a periodic potential can alleviate the tension at low multipoles with an improvement delta chi^2 ~2.5-4 per degree of freedom, depending on the level of foreground subtraction. As with an introduction of running, one expects that any scale dependence should lead to a worsened fit at high multipoles. We show that the logarithmic nature of the axion feature in combination with a tilt n_s~1 allows the fit to be identical to a no feature model at the 2 percent level on scales 100 =< l =<3500, and quite remarkable actually slightly improves the fit at scales l >2000. We also consider possible unremoved dust foregrounds and show that including these hardly changes the best-fit parameters. Our analysis suggests an axion decay constant of f/M_p ~O(.01). We discuss how Planck measurements of the TE and EE spectra can further constrain axion monodromy inflation with such a large feature. A measurement of the large scale structure power spectrum is even more promising, as the effect is much bigger since the tensor modes do not affect the large scales. At the same time, a feature could also lead to a lower sigma8, lifting the tension between CMB and SZ constraints on sigma8.

Broad-band Mach-Zehnder interferometers as high performance refractive index sensors: theory and monolithic implementation.

Broad-band Mach-Zehnder interferometry is analytically described and experimentally demonstrated as an analytical tool capable of high accuracy refractive index measurements over a wide spectral range. Suitable photonic engineering of the interferometer sensing and reference waveguides result in sinusoidal TE and TM spectra with substantially different eigen-frequencies. This allows for the instantaneous deconvolution of multiplexed polarizations and enables large spectral shifts and noise reduction through filtering in the Fourier Transform domain. Due to enhanced sensitivity, optical systems can be designed that employ portable spectrum analyzers with nm range resolution without compromising the sensor analytical capability. Practical detection limits in the 10(-6)-10(-7) RIU range are achievable, including temperature effects. Finally, a proof of concept device is realized on a silicon microphotonic chip that monolithically integrates broad-band light sources and single mode silicon nitride waveguides. Refractive index detection limits rivaling that of ring resonators with externally coupled laser sources are demonstrated. Sensitivities of 20 μm/RIU and spectral shifts in the tens of a pm are obtained.