scholarly journals Laboratory Demonstration of the Local Oscillator Concept for the Event Horizon Imager

2021 ◽  
pp. 2150010
Author(s):  
V. Kudriashov ◽  
M. Martin-Neira ◽  
E. Lia ◽  
J. Michalski ◽  
P. Kant ◽  
...  
Keyword(s):  
Black Hole ◽  
Special Interest ◽  
Integration Time ◽  
Analysis Tool ◽  
Allan Deviation ◽  
Worst Case ◽  
The Third ◽  
Coherent Integration ◽  
Calibration Methods ◽  
Frequency Transfer

Black hole imaging challenges the third-generation space VLBI, the Very Long Baseline Interferometry, to operate on a 500[Formula: see text]GHz band. The coherent integration time needed here is 450[Formula: see text]s though the available space oscillators cannot offer more than 10[Formula: see text]s. Self-calibration methods might solve this issue in an interferometer formed by three antenna/satellite systems, but the need for the third satellite increases the mission costs. A frequency transfer is of special interest to alleviate both performance and cost issues. A concept of two-way optical frequency transfer is examined to investigate its suitability to enable space-to-space interferometry, in particular, to image the “shadows” of black holes from space. The concept, promising on paper, has been demonstrated by tests. The laboratory test set-up is presented and the verification of the temporal stability using standard analysis tool as TimePod has been passed. The resulting Allan Deviation is dominated by the 1/[Formula: see text] phase noise trend since the frequency transfer timescale of interest is shorter than 0.2[Formula: see text]s. This trend continues into longer integration times, as proven by the longest tests spanning over a few hours. The Allan Deviation between derived 103.2[Formula: see text]GHz oscillators is [Formula: see text]/[Formula: see text] within 10[Formula: see text][Formula: see text][Formula: see text]s that degrades twice towards the longest delay of 0.2[Formula: see text]s. The worst case satisfies the requirement with a margin of 11 times. The obtained coherence in the range of 0.997[Formula: see text]0.9998 is beneficial for space VLBI at 557[Formula: see text]GHz. The result is of special interest to future science missions for black hole imaging from space.

The Roman Cemetery at Lankhills: Pre-Roman and Roman Winchester. Part II

2021 ◽  
Author(s):  
Giles Clarke
Keyword(s):  
Special Interest ◽  
Fourth Century ◽  
The Road ◽  
The Third ◽  
The North ◽  
Late Roman

Outside the north gate of Venta Belgarum, Roman Winchester, a great cemetery stretched for 500 yards along the road to Cirencester. Excavations at Lankhills from 1967 to 1972 uncovered 451 graves, many elaborately furnished, at the northern limits of this cemetery, and dating from the fourth century A.D. This book, the second in a two-part study of Venta Belgarum, which forms the third volume of Winchester Studies, describes the excavations of these burials and analyses in detail both the graves and their contents. There are detailed studies and important re-assessments of many categories of object, but it is the information about late Roman burial, religion, and society which is of special interest.

Clusterization of post-communist countries of the Central and Eastern Europe by income inequality level

2021 ◽  
Vol 72 (5) ◽  
pp. 41-52
Author(s):  
T. Cherkashyna
Keyword(s):  
Income Inequality ◽  
Eastern Europe ◽  
Central And Eastern Europe ◽  
National Income ◽  
Analysis Tool ◽  
Tax Rate ◽  
Low Level ◽  
The Third ◽  
High Level ◽  
Communist Countries

Using level of income inequality, the clustering of post-communist countries of the Central and Eastern Europe is carried out by the following indicators: Gini index, share in the national income of the second quintile group, share in the national income of the third quintile group, share in the national income of the fourth quintile group, share in the national income of 10% of the poorest, share in the national income of 20% of the richest.,Сluster analysis (k-means method), in the programming environment Statistica is used as analysis tool and five clusters are obtained. The first cluster includes 8 countries (Albania, Hungary, Poland, Bosnia and Herzegovina, Czech Republic, Сroatia, Russia, Slovakia) is characterized by sufficiently low level of income inequality and can be explained by flow of foreign investment and business transnationalization contributing to the increase of incomes of the main population groups of these countries. The second cluster includes 4 countries (Belarus, Slovenia, Ukraine, Moldova) and is characterized by comparatively low level of income inequality, but high level of property inequality due to heredity, аccumulated wealth та concentration of physical and financial capital by so called «oligarchic clans». The third cluster includes 5 countries (Bulgaria, Montenegro, Macedonia, Romania, Serbia) and is characterized by medium level of income inequality. The fourth and fifth clusters include so called «Baltic tigers» (Latvia, Lihuania, Estonia) and is characterized by high level of income inequality as the result of the occurrence of «excess profits» of financial assets owners. In order to decrease the income inequality in the investigated countries, the following measures are proposed: for the countries of the first cluster to accelerate deconcentration of capital ownership by «spaying» (redemption) of privatized enterprises shares by all categories on preferential terms (so called «ESOP programs»); for the countries of the second cluster to implement progressive tax scale where the tax rate for different groups of population vary depending on the income received and citizens with the lowest incomes (at the level of subsistence minimum or minimum wage) do not pay individual taxes at all; for the countries of the third cluster to cope with «shadow» economy and informal unemployment; for the counties of the fourth and fifth clusters to decrease tax burden on private entrepreneurs and thus stimulate self-employment.

scholarly journals Sensitivity of the lower edge of the pair-instability black hole mass gap to the treatment of time-dependent convection

2020 ◽  
Vol 493 (3) ◽  
pp. 4333-4341 ◽  
Author(s):  
M Renzo ◽  
R J Farmer ◽  
S Justham ◽  
S E de Mink ◽  
Y Götberg ◽  
...  
Keyword(s):  
Black Hole ◽  
Gravitational Wave ◽  
Time Scale ◽  
Turnover Time ◽  
Black Hole Mass ◽  
The Third ◽  
Mass Gap ◽  
Mixing Length Theory ◽  
State Assumption ◽  
Additional Equation

ABSTRACT Gravitational-wave detections are now probing the black hole (BH) mass distribution, including the predicted pair-instability mass gap. These data require robust quantitative predictions, which are challenging to obtain. The most massive BH progenitors experience episodic mass ejections on time-scales shorter than the convective turnover time-scale. This invalidates the steady-state assumption on which the classic mixing length theory relies. We compare the final BH masses computed with two different versions of the stellar evolutionary code $\tt{MESA}$: (i) using the default implementation of Paxton et al. (2018) and (ii) solving an additional equation accounting for the time-scale for convective deceleration. In the second grid, where stronger convection develops during the pulses and carries part of the energy, we find weaker pulses. This leads to lower amounts of mass being ejected and thus higher final BH masses of up to ∼$5\, \mathrm{M}_\odot$. The differences are much smaller for the progenitors that determine the maximum mass of BHs below the gap. This prediction is robust at $M_{\rm BH, max}\simeq 48\, \mathrm{M}_\odot$, at least within the idealized context of this study. This is an encouraging indication that current models are robust enough for comparison with the present-day gravitational-wave detections. However, the large differences between individual models emphasize the importance of improving the treatment of convection in stellar models, especially in the light of the data anticipated from the third generation of gravitational-wave detectors.

scholarly journals Isotropic Gravastar Model in Rastall Gravity

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
G. Abbas ◽  
K. Majeed
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Analytical Solutions ◽  
Thin Shell ◽  
Graphical Analysis ◽  
Stiff Fluid ◽  
Matter Distribution ◽  
The Third ◽  
Schwarzschild Geometry ◽  
Third Phase

In the present paper, we have introduced a new model of gravastar with an isotropic matter distribution in Rastall gravity by the Mazur–Mottola (2004) mechanism. Mazur–Mottola approach is about the construction of gravastar which is predicted as an alternative to black hole. By following this convention, we define gravastar in the form of three phases. The first one is an interior phase which has negative density; the second part consists of thin shell comprising ultrarelativistic stiff fluid for which we have discussed the length, energy, and entropy. By the graphical analysis of entropy, we have shown that our proposed thin shell gravastar model is potentially stable. The third phase of gravastar is defined by the exterior Schwarzschild geometry. For the interior of gravastar, we have found the analytical solutions free from any singularity and the event horizon in the framework of Rastall gravity.

scholarly journals Near-Infrared C2H2 Detection System Based on Single Optical Path Time Division Multiplexing Differential Modulation Technique and Multi-Reflection Chamber

2019 ◽  
Vol 9 (13) ◽  
pp. 2637 ◽  
Author(s):  
Biao Wang ◽  
Hongfei Lu ◽  
Chen Chen ◽  
Lei Chen ◽  
Houquan Lian ◽  
...  
Keyword(s):  
Near Infrared ◽  
Detection System ◽  
Optical Path ◽  
Integration Time ◽  
Allan Deviation ◽  
Differential Modulation ◽  
Time Division Multiplexing ◽  
Detection Range ◽  
Modulation Technique ◽  
Time Division

A time division multiplexing differential modulation technique is proposed to address the interference problem caused by the fluctuation of laser light intensity in the single optical path detection system. Simultaneously, a multi-reflection chamber is designed and manufactured to further improve the system’s precision with an optical path length of 80 m. A near-infrared C2H2 detection system was developed. The absorption peak of the acetylene (C2H2) molecule near 1520 nm was selected as the absorption line. A laser driver is developed, and a lock-in amplifier is used to extract the second harmonic (2f) signal. A good linear relationship existed between C2H2 concentration and the 2f signal, and the correlation coefficient was 0.9997. In the detection range of 10–100 ppmv, the minimum detection limit was 0.3 ppmv, and the precision was 2%. At 50 ppmv, C2H2 and continuous detection for 10 h, the data average was 50.03 ppmv, and the fluctuation was less than ±1.2%. The Allan variance method was adopted to evaluate the long-term characteristic of the system. At 1 s of integration time, the Allan deviation was 0.3 ppmv. When the integration time reached 362 s, the Allan deviation was 0.0018 ppmv, which indicates the good stability of the detection system.

scholarly journals Orbits in a Stäckel Approximation

1999 ◽  
Vol 172 ◽  
pp. 395-396
Author(s):  
V. De Bruyne ◽  
F. Leeuwin ◽  
H. Dejonghe
Keyword(s):  
Black Hole ◽  
Numerical Integration ◽  
Mass Concentration ◽  
Good Representation ◽  
Central Mass ◽  
Good Basis ◽  
The Third ◽  
Integrable Potential ◽  
Building Models ◽  
The Family

Because of their analytical simplicity and regularity, Stäckel potentials are attractive tools for modelling galaxies. The third integral I3 is explicitly known in a Stäckel potential, and can be used as an approximation to the effective third integral, in order to construct three-integral models (cf. Dejonghe, et al., 1996, A&A 306, 363).Moreover, Stäckel potentials turn out to yield good global descriptions for either axisymmetric or triaxial systems without central mass concentration (de Zeeuw 1985, MNRAS 216, 273, de Zeeuw & Lynden-Bell 1985, MNRAS 215, 713), and even for some systems with a black hole included (Sridhar & Touma 1997, MNRAS 292, 657).One long-standing concern though, is that Stäckel potentials form only a very small subspace in the family of all potentials. The main orbit families found by numerical integration in general triaxial potentials are present in a Stäckel potential (Schwarzschild 1981, ApJ 232, 236, de Zeeuw 1985, MNRAS 216, 273), but there is obviously no place in an integrable potential for smaller orbital families or stochastic orbits. However, since regular orbits are the rule rather than the exception, a potential which yields a good representation of those orbits is certainly a good basis for building models.

scholarly journals Joint Acquisition Estimator of Modern GNSS Tiered Signals Using Block Pre-Correlation Processing of Secondary Code

Sensors ◽  
2020 ◽  
Vol 20 (10) ◽  
pp. 2965
Author(s):  
Jiří Svatoň ◽  
František Vejražka
Keyword(s):  
Search Algorithm ◽  
Global Navigation Satellite Systems ◽  
Integration Time ◽  
Zero Padding ◽  
Satellite Systems ◽  
Coherent Integration ◽  
Correlation Processing ◽  
Single Block ◽  
Coherent Integration Time ◽  
Global Navigation Satellite

Objective is a joint primary and secondary code (SC) acquisition estimator of tiered Global Navigation Satellite Systems (GNSS) signals. The estimator is based on the Parallel Code Search algorithm (PCS) combined with the Single-Block-Zero-Padding (SBZP) and the Pre-correlation Coherent Accumulation (PCA). The PCA realizes the extension of the coherent integration time in front of the PCS. However, the PCS with the SBZP and the PCA is affected by a navigation/SC bit transition problem due to its cyclic property of a computed Cross-Ambiguity Function (CAF). This CAF is degraded by diverse parasitic fragments and is not directly applicable for an acquisition. A novel analysis of this mechanism and its impact is presented. Then, the proposed modified SBZP (mSBZP) modified PCA (mPCA) PCS estimator is constructed, which does not degrade the CAF. The mSBZP allows the use of the PCS algorithm in the presence of SC bit transition, while the mPCA decreases the number of PCS algorithm calculations by a factor of SC chip count due to SC pre-correlation processing. The algorithm has the same detection performance in comparison with conventional Double-Block-Zero-Padding (DBZP). However, it allows using the PCS of half-length with longer latency up to a factor of SC chip count.

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