Explore the vast range of titles available.

The 21-cm absorption profile is detected in the sky-averaged radio spectrum, but is much stronger than predicted, suggesting that the primordial gas might have been cooler than predicted. An absorption profile in the sky As the first stars heated hydrogen in the early Universe, the 21-cm hyperfine line—an astronomical standard that represents the spin-flip transition in the ground state of atomic hydrogen—was altered, causing the hydrogen gas to absorb photons from the microwave background. This should produce an observable absorption signal at frequencies of less than 200 megahertz (MHz). Judd Bowman and colleagues report the observation of an absorption profile centred at a frequency of 78 MHz that is about 19 MHz wide and 0.5 kelvin deep. The profile is generally in line with expectations, although it is deeper than predicted. An accompanying paper by Rennan Barkana suggests that baryons were interacting with cold dark-matter particles in the early Universe, cooling the gas more than had been expected. After stars formed in the early Universe, their ultraviolet light is expected, eventually, to have penetrated the primordial hydrogen gas and altered the excitation state of its 21-centimetre hyperfine line. This alteration would cause the gas to absorb photons from the cosmic microwave background, producing a spectral distortion that should be observable today at radio frequencies of less than 200 megahertz 1 . Here we report the detection of a flattened absorption profile in the sky-averaged radio spectrum, which is centred at a frequency of 78 megahertz and has a best-fitting full-width at half-maximum of 19 megahertz and an amplitude of 0.5 kelvin. The profile is largely consistent with expectations for the 21-centimetre signal induced by early stars; however, the best-fitting amplitude of the profile is more than a factor of two greater than the largest predictions 2 . This discrepancy suggests that either the primordial gas was much colder than expected or the background radiation temperature was hotter than expected. Astrophysical phenomena (such as radiation from stars and stellar remnants) are unlikely to account for this discrepancy; of the proposed extensions to the standard model of cosmology and particle physics, only cooling of the gas as a result of interactions between dark matter and baryons seems to explain the observed amplitude 3 . The low-frequency edge of the observed profile indicates that stars existed and had produced a background of Lyman-α photons by 180 million years after the Big Bang. The high-frequency edge indicates that the gas was heated to above the radiation temperature less than 100 million years later.

The presented paper describes the problem of human health in regions with high level of natural ionizing radiation in various places in the world. The radiation adaptive response biophysical model was presented and calibrated for the special case of constant dose-rate irradiation. The calibration was performed for the data of residents of several high background radiation areas, like Ramsar in Iran, Kerala in India or Yangjiang in China. Studied end-points were: chromosomal aberrations, cancer incidence and cancer mortality. For the case of aberrations, among collected publications about 45% have shown the existence of adaptive response. Average reduction of chromosomal aberrations was ∼ 10%, while for the case of cancer incidence it was ∼ 15% and ∼ 17% for cancer mortality (each taking into account only results showing adaptive response). Results of the other 55% of data regarding chromosomal aberrations have been tested with the LNT (linear no-threshold) hypothesis, but results were inconsistent with the linear model. The conditions for adaptive response occurrence are still unknown, but it is postulated to correlate with the distribution of individual radiosensitivity among members of surveyed populations.

LiteBIRD is a candidate satellite for a strategic large mission of JAXA. With its expected launch in the middle of the 2020s with a H3 rocket, LiteBIRD plans to map the polarization of the cosmic microwave background radiation over the full sky with unprecedented precision. The full success of LiteBIRD is to achieve δ r < 0.001 , where δ r is the total error on the tensor-to-scalar ratio r . The required angular coverage corresponds to 2 ≤ ℓ ≤ 200 , where ℓ is the multipole moment. This allows us to test well-motivated cosmic inflation models. Full-sky surveys for 3 years at a Lagrangian point L2 will be carried out for 15 frequency bands between 34 and 448 GHz with two telescopes to achieve the total sensitivity of 2.5 μ K arcmin with a typical angular resolution of 0.5 ∘ at 150 GHz. Each telescope is equipped with a half-wave plate system for polarization signal modulation and a focal plane filled with polarization-sensitive TES bolometers. A cryogenic system provides a 100 mK base temperature for the focal planes and 2 K and 5 K stages for optical components.

The current best-estimate of the global annual mean radiative forcing (RF) attributable to contrail cirrus is thought to be 3 times larger than the RF from aviation's cumulative CO2 emissions. Here, we simulate the global contrail RF for 2019–2021 using reanalysis weather data and improved engine emission estimates along actual flight trajectories derived from Automatic Dependent Surveillance–Broadcast telemetry. Our 2019 global annual mean contrail net RF (62.1 mW m−2) is 44 % lower than current best estimates for 2018 (111 [33, 189] mW m−2, 95 % confidence interval). Regionally, the contrail net RF is largest over Europe (876 mW m−2) and the USA (414 mW m−2), while the RF values over East Asia (64 mW m−2) and China (62 mW m−2) are close to the global average, because fewer flights in these regions form persistent contrails resulting from lower cruise altitudes and limited ice supersaturated regions in the subtropics due to the Hadley Circulation. Globally, COVID-19 reduced the flight distance flown and contrail net RF in 2020 (−43 % and −56 %, respectively, relative to 2019) and 2021 (−31 % and −49 %, respectively) with significant regional variations. Around 14 % of all flights in 2019 formed a contrail with a net warming effect, yet only 2 % of all flights caused 80 % of the annual contrail energy forcing. The spatiotemporal patterns of the most strongly warming and cooling contrail segments can be attributed to flight scheduling, engine particle number emissions, tropopause height, and background radiation fields. Our contrail RF estimates are most sensitive to corrections applied to the global humidity fields, followed by assumptions on the engine particle number emissions, and are least sensitive to radiative heating effects on the contrail plume and contrail–contrail overlapping. Using this sensitivity analysis, we estimate that the 2019 global contrail net RF could range between 34.8 and 74.8 mW m−2.

In this paper, we investigate a recent proposed model – so called the Tsallis holographic dark energy (THDE) model with consideration of the Hubble and the event future horizon as IR cutoffs. In this case, we consider the non-gravitational and phenomenological interaction between dark sectors. We fit the free parameters of the model using Pantheon Supernovae Type Ia data, Baryon Acoustic Oscillations, Cosmic Microwave Background, Gamma-Ray burst and the the local value of the Hubble constant. We examine the THDE model to check its compatibility with observational data using objective Information Criterion (IC). We find that the THDE models cannot be supported by observational data once the \\[\\Lambda \\]CDM is considered as the referring model. Therefore we re-examine the analysis with the standard holographic dark energy model (HDE) as another reference. Changing the \\[\\Lambda \\]CDM to main standard dark energy model (HDE), we observe the compatibility of the THDE models. Using the Alcock–Paczynski (AP) test we check the deviation of the model compared to \\[\\Lambda \\]CDM and HDE. Surveying the evolution of squared of sound speed \\[v^2_s\\] as an another test we check the stability of the interacting and non-interacting THDE models and we find that while the THDE model with the Hubble horizon as IR cutoff is unstable against the background perturbation, the future event horizon as IR cutoff show stability at the late time. In addition, using the modified version of the CAMB package, we observe the suppressing the CMB spectrum at small K-modes and large scale.

Exposure to medium or high doses of ionizing radiation is a known risk factor for cancer in children. The extent to which low-dose radiation from natural sources contributes to the risk of childhood cancer remains unclear. In a nationwide census-based cohort study, we investigated whether the incidence of childhood cancer was associated with background radiation from terrestrial gamma and cosmic rays. Children < 16 years of age in the Swiss National Censuses in 1990 and 2000 were included. The follow-up period lasted until 2008, and incident cancer cases were identified from the Swiss Childhood Cancer Registry. A radiation model was used to predict dose rates from terrestrial and cosmic radiation at locations of residence. Cox regression models were used to assess associations between cancer risk and dose rates and cumulative dose since birth. Among 2,093,660 children included at census, 1,782 incident cases of cancer were identified including 530 with leukemia, 328 with lymphoma, and 423 with a tumor of the central nervous system (CNS). Hazard ratios for each millisievert increase in cumulative dose of external radiation were 1.03 (95% CI: 1.01, 1.05) for any cancer, 1.04 (95% CI: 1.00, 1.08) for leukemia, 1.01 (95% CI: 0.96, 1.05) for lymphoma, and 1.04 (95% CI: 1.00, 1.08) for CNS tumors. Adjustment for a range of potential confounders had little effect on the results. Our study suggests that background radiation may contribute to the risk of cancer in children, including leukemia and CNS tumors.

This paper reports the results of gamma irradiation experiments and whole genome sequencing (WGS) performed on vegetative cells of two radiation resistant bacterial strains, Metabacillus halosaccharovorans (VITHBRA001) and Bacillus paralicheniformis (VITHBRA024) (D 10 values 2.32 kGy and 1.42 kGy, respectively), inhabiting the top-ranking high background radiation area (HBRA) of Chavara-Neendakara placer deposit (Kerala, India). The present investigation has been carried out in the context that information on strategies of bacteria having mid-range resistance for gamma radiation is inadequate. WGS, annotation, COG and KEGG analyses and manual curation of genes helped us address the possible pathways involved in the major domains of radiation resistance, involving recombination repair, base excision repair, nucleotide excision repair and mismatch repair, and the antioxidant genes, which the candidate could activate to survive under ionizing radiation. Additionally, with the help of these data, we could compare the candidate strains with that of the extremely radiation resistant model bacterium Deinococccus radiodurans , so as to find the commonalities existing in their strategies of resistance on the one hand, and also the rationale behind the difference in D 10 , on the other. Genomic analysis of VITHBRA001 and VITHBRA024 has further helped us ascertain the difference in capability of radiation resistance between the two strains. Significantly, the genes such as uvsE (NER), frnE (protein protection), ppk1 and ppx (non-enzymatic metabolite production) and those for carotenoid biosynthesis, are endogenous to VITHBRA001, but absent in VITHBRA024, which could explain the former’s better radiation resistance. Further, this is the first-time study performed on any bacterial population inhabiting an HBRA. This study also brings forward the two species whose radiation resistance has not been reported thus far, and add to the knowledge on radiation resistant capabilities of the phylum Firmicutes which are abundantly observed in extreme environment.

What are the main findings? * We elucidate the coupling between scan-mirror thermal emission and the instrument’s polarization-dependent response during mirror deflection, quantitatively characterize the resulting interference, and establish a GIIRS-specific scan-mirror thermal-radiation interference model. * Under strongly varying geostationary thermal environments, we establish a nonlinear mapping between the instrument thermal field and the interference term, thereby enabling adaptive modeling and real-time compensation. We elucidate the coupling between scan-mirror thermal emission and the instrument’s polarization-dependent response during mirror deflection, quantitatively characterize the resulting interference, and establish a GIIRS-specific scan-mirror thermal-radiation interference model. Under strongly varying geostationary thermal environments, we establish a nonlinear mapping between the instrument thermal field and the interference term, thereby enabling adaptive modeling and real-time compensation. What are the implications of the main findings? * The correction uses only thermal-field data and scan-mirror angle status data to dynamically model and compensate, in real time, for scan-mirror thermal-radiation interference. * This compensation suppresses biases induced by thermal-environment variability and scan-mirror deflection, significantly improving the continuity, accuracy, and long-term stability of radiometric calibration, thereby providing more reliable inputs for high-precision retrievals. The correction uses only thermal-field data and scan-mirror angle status data to dynamically model and compensate, in real time, for scan-mirror thermal-radiation interference. This compensation suppresses biases induced by thermal-environment variability and scan-mirror deflection, significantly improving the continuity, accuracy, and long-term stability of radiometric calibration, thereby providing more reliable inputs for high-precision retrievals. To meet the growing demand for quantitative remote sensing applications in GIIRS radiometric calibration, this paper proposes a temperature field-driven adaptive scan mirror thermal radiation interference correction method. Based on the on-orbit deep space observation data from the Fengyun-4B satellite, this paper systematically analyzes the thermal radiation interference characteristics caused by scan mirror deflection and constructs the first scan mirror thermal radiation response model suitable for GIIRS. On the basis of this model, this paper further introduces the dynamic variation characteristics of the internal thermal environment of the instrument, enabling adaptive response and compensation for radiation disturbances. This method overcomes the limitations of relying on static calibration parameters and improves the generality and robustness of the model. Independent validation results show that this method effectively suppresses the interference of scan mirror deflection on instrument background radiation and enhances the consistency of the deep space and blackbody spectral diurnal variation time series. After correction, the average system bias of the interference-sensitive channel decreased by 94%, and the standard deviation of radiance bias from 2.5 mW/m[sup.2]·sr·cm[sup.−1] to below 0.5 mW/m[sup.2]·sr·cm[sup.−1]. In the O-B test, the maximum improvement in relative standard deviation reached 0.15 K.