scholarly journals Constraints on the temperature-density relation of the intergalactic medium with non-negligible absorber spatial structure

2021 ◽  
Vol 2103 (1) ◽  
pp. 012028
Author(s):  
K N Telikova ◽  
P S Shternin ◽  
S A Balashev
Keyword(s):  
Spatial Structure ◽  
Intergalactic Medium ◽  
Scale Parameter ◽  
Characteristic Size ◽  
Physical Parameters ◽  
Intergalactic Gas ◽  
Density Relation ◽  
Spatial Size ◽  
First Time ◽  
Photoionization Rate

Abstract We investigate evolution of physical parameters of the intergalactic medium using an analysis of Lya forest lines detected towards distant quasars. We used the enlarged sample of 98 quasars obtained with Keck/HIRES and VLT/UVES. We show that taking into account a finite spatial size of absorbers, regulated by pressure smoothing, significantly affects the inferred thermal parameters of the intergalactic gas, such as the hydrogen photoionization rate and parameters of the temperature-density relation. Using Bayesian framework we constrained for the first time the scale parameter between the Jeans length and characteristic size of the absorbers. We also discuss limitations of the method based on the analysis of the minimal broadending of Lya lines, which stem from the patchy nature of He II reionization.

scholarly journals The Low-redshift Intergalactic Medium

1999 ◽  
Vol 16 (1) ◽  
pp. 95-99 ◽  
Author(s):  
J. Michael Shull ◽  
Steven V. Penton ◽  
John T. Stocke
Keyword(s):  
Galaxy Formation ◽  
Large Scale ◽  
Intergalactic Medium ◽  
Hubble Space Telescope ◽  
Characteristic Size ◽  
Baryon Density ◽  
Frequency Space ◽  
Physical Conditions ◽  
Low Metallicity ◽  
Set Up

AbstractThe low-redshift Lyα forest of absorption lines provides a probe of large-scale baryonic structures in the intergalactic medium, some of which may be remnants of physical conditions set up during the epoch of galaxy formation. We discuss our recent Hubble Space Telescope (HST) observations and interpretation of low-z Lyα clouds toward nearby Seyferts and QSOs, including their frequency, space density, estimated mass, association with galaxies, and contribution to Ωb. Our HST/GHRS detections of ∼ 70 Lyα absorbers with Nhi ≥ 1012·6 cm−2 along 11 sightlines covering pathlength Δ(cz) = 114,000 km s−1 show f (>Nhi) α Nhi−0·63±0·04 and a line frequency dN/dz = 200 ± 40 for Nhi > 1012·6 cm−2 (one every 1500 km s−1 of redshift). A group of strong absorbers toward PKS 2155–304 may be associated with gas (400–800) kpc from four large galaxies, with low metallicity (≤0·003 solar) and D/H ≤ 2 × 10−4. At low-z, we derive a metagalactic ionising radiation field from AGN of J0 = × 10−23 erg cm−2 s−1 Hz−1 sr−1 and a Lyα-forest baryon density Ωb =(0·008 ± 0·004)[J−23N14b100]½ for clouds of characteristic size b = (100 kpc)b100.

IMPROVEMENT OF DOSE ESTIMATION PROCESS USING ARTIFICIAL NEURAL NETWORKS

2018 ◽  
Vol 184 (1) ◽  
pp. 36-43 ◽  
Author(s):  
Gal Amit ◽  
Hanan Datz
Keyword(s):  
Neural Networks ◽  
Support Vector Machine ◽  
Artificial Neural Networks ◽  
Support Vector ◽  
Physical Parameters ◽  
Machine Method ◽  
Algorithm Performance ◽  
Artificial Neural ◽  
First Time ◽  
Automatic Algorithm

Abstract We present here for the first time a fast and reliable automatic algorithm based on artificial neural networks for the anomaly detection of a thermoluminescence dosemeter (TLD) glow curves (GCs), and compare its performance with formerly developed support vector machine method. The GC shape of TLD depends on numerous physical parameters, which may significantly affect it. When integrated into a dosimetry laboratory, this automatic algorithm can classify ‘anomalous’ (having any kind of anomaly) GCs for manual review, and ‘regular’ (acceptable) GCs for automatic analysis. The new algorithm performance is then compared with two kinds of formerly developed support vector machine classifiers—regular and weighted ones—using three different metrics. Results show an impressive accuracy rate of 97% for TLD GCs that are correctly classified to either of the classes.

scholarly journals Detecting shocked intergalactic gas with X-ray and radio observations

2019 ◽  
Vol 627 ◽  
pp. A5 ◽  
Author(s):  
F. Vazza ◽  
S. Ettori ◽  
M. Roncarelli ◽  
M. Angelinelli ◽  
M. Brüggen ◽  
...  
Keyword(s):  
Large Scale ◽  
Intergalactic Medium ◽  
Thermal Emission ◽  
Intergalactic Gas ◽  
Radio Observations ◽  
X Ray ◽  
Large Scale Structures ◽  
Hot Gas ◽  
Scale Structures ◽  
Radio Band

Detecting the thermal and non-thermal emission from the shocked cosmic gas surrounding large-scale structures represents a challenge for observations, as well as a unique window into the physics of the warm-hot intergalactic medium. In this work, we present synthetic radio and X-ray surveys of large cosmological simulations in order to assess the chances of jointly detecting the cosmic web in both frequency ranges. We then propose best observing strategies tailored for existing (LOFAR, MWA, and XMM) or future instruments (SKA-LOW and SKA-MID, Athena, and eROSITA). We find that the most promising targets are the extreme peripheries of galaxy clusters in an early merging stage, where the merger causes the fast compression of warm-hot gas onto the virial region. By taking advantage of a detection in the radio band, future deep X-ray observations will probe this gas in emission, and help us to study plasma conditions in the dynamic warm-hot intergalactic medium with unprecedented detail.

On the Possible Spatial Structures of the β – Amyloid.

2022 ◽  
Vol 7 (1) ◽  
pp. 0-0
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Spatial Structure ◽  
Spatial Models ◽  
Globular Proteins ◽  
Spatial Structures ◽  
Higher Dimensional ◽  
Protein Molecules ◽  
Β Amyloid ◽  
First Time

Spatial models of the β - structures of protein molecules, forming layers of amino acids, in principle, of unlimited length for both antiparallel and parallel conformation have been constructed. It is shown that the simplified flat Pauling models do not reflect the spatial structure of these layers. Using the recently developed theory of higher-dimensional polytopic prismahedrons, models of the volumetric filling of space with amino acid molecules are constructed. The constructed models for the first time mathematically describe the native structures of globular proteins.

scholarly journals Probing the thermal state of the intergalactic medium at z > 5 with the transmission spikes in high-resolution  Ly α forest spectra

2020 ◽  
Vol 494 (4) ◽  
pp. 5091-5109 ◽  
Author(s):  
Prakash Gaikwad ◽  
Michael Rauch ◽  
Martin G Haehnelt ◽  
Ewald Puchwein ◽  
James S Bolton ◽  
...  
Keyword(s):  
High Resolution ◽  
Radiative Transfer ◽  
Intergalactic Medium ◽  
Thermal State ◽  
Neutral Hydrogen ◽  
High Spectral Resolution ◽  
Profile Fitting ◽  
Density Relation ◽  
Width Distribution ◽  
Hydrodynamical Simulations

ABSTRACT We compare a sample of five high-resolution, high S/N  Ly α forest spectra of bright 6 < z < ∼6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z > 5 with those obtained from mock absorption spectra from the Sherwoodand Sherwood–Relics simulation suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile-fitting procedure for the inverted transmitted flux, 1 − F, similar to the widely used Voigt profile fitting of the transmitted flux F at lower redshifts, to characterize the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8  km s−1) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T0 caused by spatial fluctuations in the temperature–density relation.

scholarly journals Constraining the intergalactic medium at z ≈ 9.1 using LOFAR Epoch of Reionization observations

2020 ◽  
Vol 493 (4) ◽  
pp. 4728-4747 ◽  
Author(s):  
R Ghara ◽  
S K Giri ◽  
G Mellema ◽  
B Ciardi ◽  
S Zaroubi ◽  
...  
Keyword(s):  
Large Scale ◽  
Intergalactic Medium ◽  
Volume Fraction ◽  
Characteristic Size ◽  
Gas Temperature ◽  
Spin Temperature ◽  
Simulation Code ◽  
Upper Limits ◽  
Credible Intervals ◽  
Bayesian Inference Framework

ABSTRACT We derive constraints on the thermal and ionization states of the intergalactic medium (IGM) at redshift ≈ 9.1 using new upper limits on the 21-cm power spectrum measured by the LOFAR radio telescope and a prior on the ionized fraction at that redshift estimated from recent cosmic microwave background (CMB) observations. We have used results from the reionization simulation code grizzly and a Bayesian inference framework to constrain the parameters which describe the physical state of the IGM. We find that, if the gas heating remains negligible, an IGM with ionized fraction ≳0.13 and a distribution of the ionized regions with a characteristic size ≳ 8 h−1 comoving megaparsec (Mpc) and a full width at half-maximum (FWHM) ≳16 h−1 Mpc is ruled out. For an IGM with a uniform spin temperature TS ≳ 3 K, no constraints on the ionized component can be computed. If the large-scale fluctuations of the signal are driven by spin temperature fluctuations, an IGM with a volume fraction ≲0.34 of heated regions with a temperature larger than CMB, average gas temperature 7–160 K, and a distribution of the heated regions with characteristic size 3.5–70 h−1 Mpc and FWHM of ≲110 h−1 Mpc is ruled out. These constraints are within the 95 per cent credible intervals. With more stringent future upper limits from LOFAR at multiple redshifts, the constraints will become tighter and will exclude an increasingly large region of the parameter space.

scholarly journals A Boltzmann-Tsallis approach towards cell survival curve in Radiobiology

2019 ◽  
Vol 206 ◽  
pp. 09014
Author(s):  
B.W.Q. Tan ◽  
H.Q. Tan ◽  
A.H. Chan
Keyword(s):  
Statistical Mechanics ◽  
Cell Survival ◽  
Survival Curve ◽  
Phenomenological Approach ◽  
Physical Parameters ◽  
Chain Model ◽  
Nonextensive Statistical Mechanics ◽  
Cell Survival Curve ◽  
New Perspective ◽  
First Time

This paper outlines a phenomenological approach towards cell survival curve at low dose using tools of extensive Statistical Mechanics and nonextensive Statistical Mechanics. An Ising chain model is developed for the cell survival curve and the canonical ensemble formalism based on Boltzmann Gibbs statistic and Tsallis statistic is presented. The resulting cell survival curve shows excellent agreement with the experimental data and the physical parameters from our Tsallis model (N’, q) can be shown to provide clear classification between healthy and cancerous cells. In this paper, we also provides possible biophysical interpretation to the (N’, q) parameters where N’ is representative of the amount of repairable DNA content in the nucleus and q represents the degree of correlation in DNA damage. Overall, this is the first time a Statistical Mechanics approach is used in Radiobiology, and could present a new perspective.

scholarly journals The Intergalactic Medium

1982 ◽  
Vol 97 ◽  
pp. 453-459
Author(s):  
A. C. Fabian ◽  
A. K. Kembhavi
Keyword(s):  
Radio Emission ◽  
Intergalactic Medium ◽  
Radio Sources ◽  
Clusters Of Galaxies ◽  
Intergalactic Gas ◽  
X Ray ◽  
Extended Radio ◽  
X Ray Background ◽  
Ngc 1275 ◽  
Intracluster Gas

The density of intergalactic gas may be an important parameter in the formation of extended radio sources. It may range from ∼ 0.1 particle cm−3 in the centres of some rich clusters of galaxies down to 10−8cm−3 or less in intercluster space. The possible influence of the intracluster gas surrounding NGC 1275 on its radio emission is discussed, and the possibility that a significant fraction of the X-ray background is due to a hot intergalactic medium is explored in some detail.

Pore connectivity across scales and resolutions

2020 ◽  
Author(s):  
Maik Lucas ◽  
Doris Vetterlein ◽  
Hans-Jörg Vogel ◽  
Steffen Schlüter
Keyword(s):  
Characteristic Size ◽  
Small Samples ◽  
Pore Connectivity ◽  
X Ray ◽  
Connection Probability ◽  
Three Samples ◽  
Different Depths ◽  
Pore Types ◽  
First Time ◽  
Joint Evaluation

<p>An important parameter to quantify pore structure and link it to soil functions is connectivity. When quantifying connectivity with X-ray microtomography (X-ray-µCT), one of the major drawbacks is that high resolution can only be achieved in small samples. In these samples, the small pores can be described, but the connectivity of larger pores cannot be quantified reasonably.</p><p>Here we explore changes in pore connectivity with changing sample size covering a range of analyzed pore diameters of more than three orders of magnitude. Soil columns with a diameter of 10 cm were taken in two different depths (0 - 20 cm and 40 - 60 cm) at different sites of an agricultural chronosequence ranging in age from 0 to 24 years. X-ray CT was used for scanning the original columns as well as undisturbed subsamples of 3 and 0.7 cm diameter. This enabled us to detect characteristic traces in certain connectivity metrics on the chronosequence, caused by different pore types and thus different processes. In detail, we determined the connection probability of two random points within the pore system, i.e. the Γ-indicator and the Euler number, χ as a function of minimum pore diameter.</p><p>Our results revealed that scale artifacts in the connectivity functions overlap with characteristic signatures of certain pore types. For the very first time a new method for a joint-Γ-curve was developed that merges information from three samples sizes, as the Γ-indicator gives highly biased information in small samples. In contrast, χ does not require such a scale fusion and is helpful to define characteristic size ranges for pore types. Overall, findings suggest a joint evaluation of both connectivity metrics to identify the contribution of different pore types to the total pore connectivity with Γ and to disentangle different pore types with χ.</p><p>For the samples of the chronosequence such an evaluation revealed that biopores mainly connect pores of diameters between 0.1 and 0.5 mm. However, this was not necessarily coupled with increasing porosity. Tillage, conversely, lead to an increase in porosity due to a shift of pores of diameter >0.05 mm towards pores of diameter >0.20 mm and therefore increased connectivity of pores >0.20 mm.</p><p>The current study is part of the DFG-Project Soil Structure (AOBJ: 628683). </p>

scholarly journals Ostracod Fauna: Eyewitness to Fifty Years of Anthropic Impact in the Gulf of Trieste. A Potential Key to the Future Evolution of Urban Ecosystems

2020 ◽  
Author(s):  
Gianguido Salvi ◽  
Alessandro Acquavita ◽  
Massimo Celio ◽  
Saul Ciriaco ◽  
Stefano Cirilli ◽  
...  
Keyword(s):  
Oxygen Deficiency ◽  
Urban Ecosystems ◽  
Environmental Crisis ◽  
Physical Parameters ◽  
Nitrogen And Phosphorus ◽  
Future Evolution ◽  
Gulf Of Trieste ◽  
Depth Analysis ◽  
First Time

For the first time the distribution and modifications of living ostracod associations present in the Gulf of Trieste (GoT) in relation to the alterations caused by human activity in the last 20 years were investigated. The results were compared with the main chemico-physical parameters (especially nitrogen and phosphorus) measured over the same period, which can lead to a general decrease in environmental quality. For a more in-depth analysis of the changes recorded by ostracods in the last 50 years, a period in which eutrophication and anoxia increased, we revisited the study carried out by Masoli in the GoT in 1967. The results obtained made it possible to verify how over the last 20 years, ostracod assemblages have suffered a decrease both qualitatively and quantitatively. Most of the species recovered show characteristics of opportunism and tolerance to environmentally stressful conditions, high organic matter concentrations and oxygen deficiency. The ostracods analyzed in 1967 showed similar results with few dominant opportunistic species. We verified how ostracods recorded in GoT, similar to Mollusks and Foraminifera, the possible environmental crisis linked to the recurrence of mucilage and hypoxic events documented for the Gulf of Trieste in the last 50 years. Finally, a comparison with the best environmental conditions found in the Marine Nature Reserve of Miramare (MPA) allowed us to emphasize the important role of protected areas to avoid the loss of biodiversity due to urbanization.

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