scholarly journals Density Exponent Analysis -- A new vision towards gravitational collapse of molecular clouds

2021 ◽  
Author(s):  
Guang-Xing Li ◽  
Ji-Xuan Zhou
Keyword(s):  
Gravitational Collapse ◽  
Power Law ◽  
Molecular Cloud ◽  
Large Scale ◽  
Density Profiles ◽  
New Formalism ◽  
Interstellar Clouds ◽  
Wide Range ◽  
New Vision ◽  
Using Data

Abstract The evolution of molecular interstellar clouds, during which stars form, is a complex, multi-scale process. The power-law density exponent describes the steepness of density profiles in the log-log space, and it has been used to characterize the density structures of the clouds. Its effectiveness results from the widespread emergence of power-law-like density structures in complex systems that have reached intermediate asymptotic states. However, its usage is usually limited to spherically symmetric systems. Importing the Level-Set Method, we develop a new formalism that generates robust maps of a generalized density exponent kp at every location for complex density distributions. By applying it to a high fidelity, high dynamical range map of the Perseus molecular cloud constructed using data from the Herschel and Planck satellites, we find that the density exponent exhibits a surprisingly wide range of variation (-3.5 < kp < -0.5) Regions at later stages of gravitational collapse are associated with steeper density profiles. Inside a region, gas located in the vicinities of dense structures has very steep density profiles with kp ~ -3, which form because of depletion. This density exponent analysis reveals diverse density structures in a molecular cloud, forming a coherent picture that gravitational collapse and accretion contribute to a continued steepening of the density profile. We expect our method to be effective in studying other power-law-like density structures, including the density structure of granular materials and the Large-Scale Structure of the Universe.

scholarly journals Exploring the Citywide Human Mobility Patterns of Taxi Trips through a Topic-Modeling Analysis

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Hui Xiong ◽  
Kaiqiang Xie ◽  
Lu Ma ◽  
Feng Yuan ◽  
Rui Shen
Keyword(s):  
Power Law ◽  
Traffic Management ◽  
Large Scale ◽  
Latent Dirichlet Allocation ◽  
Topic Model ◽  
Human Mobility ◽  
Mobility Patterns ◽  
Power Law Distribution ◽  
Modeling Analysis ◽  
Wide Range

Understanding human mobility patterns is of great importance for a wide range of applications from social networks to transportation planning. Toward this end, the spatial-temporal information of a large-scale dataset of taxi trips was collected via GPS, from March 10 to 23, 2014, in Beijing. The data contain trips generated by a great portion of taxi vehicles citywide. We revealed that the geographic displacement of those trips follows the power law distribution and the corresponding travel time follows a mixture of the exponential and power law distribution. To identify human mobility patterns, a topic model with the latent Dirichlet allocation (LDA) algorithm was proposed to infer the sixty-five key topics. By measuring the variation of trip displacement over time, we find that the travel distance in the morning rush hour is much shorter than that in the other time. As for daily patterns, it shows that taxi mobility presents weekly regularity both on weekdays and on weekends. Among different days in the same week, mobility patterns on Tuesday and Wednesday are quite similar. By quantifying the trip distance along time, we find that Topic 44 exhibits dominant patterns, which means distance less than 10 km is predominant no matter what time in a day. The findings could be references for travelers to arrange trips and policymakers to formulate sound traffic management policies.

scholarly journals Cloud Collapse and Fragmentation

1989 ◽  
Vol 8 ◽  
pp. 123-126
Author(s):  
A. P. Boss
Keyword(s):  
Power Law ◽  
Thermal Energy ◽  
Initial Density ◽  
Fragmentation Process ◽  
Rapid Phase ◽  
Density Profiles ◽  
Interstellar Clouds ◽  
Spatial Dimensions ◽  
Computer Codes ◽  
Collapse Phase

AbstractInterstellar clouds are thought to undergo a rapid phase of collapse in the process of contracting to form stars. Break-up during this collapse phase is termed fragmentation. Computer codes capable of calculating the hydrodynamics of cloud collapse in three spatial dimensions have been used to study the fragmentation process. Fragmentation into binary or multiple protostellar systems is the preferred outcome of collapse; only very slowly rotating, high thermal energy clouds, or clouds starting from power-law initial density profiles, avoid fragmentation and form single stars.

scholarly journals SMART PANDEMIC MANAGEMENT THROUGH A SMART, RESILIENT AND FLEXIBLE DECISION-MAKING SYSTEM

2020 ◽  
Vol XLIV-4/W3-2020 ◽  
pp. 285-294
Author(s):  
G. Mezzour ◽  
Z. Boudanga ◽  
S. Benhadou
Keyword(s):  
Large Scale ◽  
Business Models ◽  
Global Dynamics ◽  
Digital Twins ◽  
Wide Range ◽  
Decision Making System ◽  
Industrial Ecosystems ◽  
New Vision ◽  
Collaborative Intelligence ◽  
Physical Spaces

Abstract. Over the last few years, the world has seen many social, industrial, and technological revolutions. The latter has enabled a combination of expertise from different fields in order to manage a wide range of multidimensional issues such as integrated societies and industrial ecosystems achievement, urban planning, transport management, sustainable development and environmental protection and currently pandemics management. Super smart society's vision that is driving the 5.0 social revolutions is at the heart of the current situation that requires system resilience, sustainability, proactivity, interoperability and collaborative intelligence between society, economy, and industry. Establishing communication bridges between different entities, of different natures and with different objectives implies solutions that reinforce the development of efficient, dynamic, and communicating business models on a large scale, merging cyber and physical spaces. Through this paper we explored the potential of digital twins for the development of a new vision of world global dynamics under the aegis of a virus whose parameters are still elusive to date.

scholarly journals Finescale Structure of the T–S Relation in the Eastern North Atlantic

2005 ◽  
Vol 35 (8) ◽  
pp. 1437-1454 ◽  
Author(s):  
R. Ferrari ◽  
K. L. Polzin
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Salinity Gradient ◽  
Mesoscale Eddies ◽  
Thermal Dissipation ◽  
Small Scale ◽  
The North ◽  
Wide Range ◽  
Using Data ◽  
Gyre Circulation

Abstract Distributions of temperature (T) and salinity (S) and their relationship in the oceans are the result of a balance between T–S variability generated at the surface by air–sea fluxes and its removal by molecular dissipation. In this paper the role of different motions in setting the cascade of T–S variance to dissipation scales is quantified using data from the North Atlantic Tracer Release Experiment (NATRE). The NATRE observational programs include fine- and microscale measurements and provide a snapshot of T–S variability across a wide range of scales from basin to molecular. It is found that microscale turbulence controls the rate of thermal dissipation in the thermocline. At this level the T–S relation is established through a balance between large-scale advection by the gyre circulation and small-scale turbulence. Further down, at the level of intermediate and Mediterranean waters, mesoscale eddies are the rate-controlling process. The transition between the two regimes is related to the presence of a strong salinity gradient along density surfaces associated with the outflow of Mediterranean waters. Mesoscale eddies stir this gradient and produce a rich filamentation and salinity-compensated temperature inversions: isopycnal stirring and diapycnal mixing are both required to explain the T–S relation at depth.

scholarly journals The rest-frame UV luminosity function at z ≃ 4: a significant contribution of AGNs to the bright end of the galaxy population

2020 ◽  
Vol 494 (2) ◽  
pp. 1771-1783 ◽  
Author(s):  
N J Adams ◽  
R A A Bowler ◽  
M J Jarvis ◽  
B Häußler ◽  
R J McLure ◽  
...  
Keyword(s):  
Power Law ◽  
Luminosity Function ◽  
Large Scale ◽  
Rest Frame ◽  
Galactic Nuclei ◽  
Absolute Magnitude ◽  
Photometric Redshift ◽  
Wide Range ◽  
The Galaxy ◽  
Galaxy Population

ABSTRACT We measure the rest-frame ultraviolet (UV) luminosity function (LF) at z ∼ 4 self-consistently over a wide range in absolute magnitude (−27 ≲ MUV ≲ −20). The LF is measured with 46 904 sources selected using a photometric redshift approach over ∼6 $\, {\rm deg}^2$ of the combined Cosmological Evolution Survey and XMM–Newton Large-Scale Structure fields. We simultaneously fit for both active galactic nuclei (AGNs) and galaxy LFs using a combination of Schechter or double power law (DPL) functions alongside a single power law for the faint-end slope of the AGN LF. We find a lack of evolution in the shape of the bright end of the Lyman-break galaxy (LBG) component when compared to other studies at z ≃ 5 and evolutionary recipes for the UV LF. Regardless of whether the LBG LF is fit with a Schechter function or DPL, AGNs are found to dominate at MUV &lt; −23.5. We measure a steep faint-end slope of the AGN LF with $\alpha _{\mathrm{ AGN}} = -2.09^{+0.35}_{-0.38}$ ($-1.66^{+0.29}_{-0.58}$) when fit alongside a Schechter function (DPL) for the galaxies. Our results suggest that if AGNs are morphologically selected it results in a bias to lower number densities. Only by considering the full galaxy population over the transition region from AGN to LBG domination can an accurate measurement of the total LFs be attained.

The 3D Topology of the Clausius Virial for Two Component Dynamical Models of Elliptical Galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 146-146
Author(s):  
T. Valentinuzzi ◽  
L. Secco ◽  
M. D'Onofrio ◽  
R. Caimmi ◽  
D. Bindoni
Keyword(s):  
Potential Energy ◽  
Power Law ◽  
Large Scale ◽  
Elliptical Galaxies ◽  
Dark Halo ◽  
Dynamical Models ◽  
Density Profiles ◽  
Two Component ◽  
3D Topology ◽  
Scale Length

AbstractAs found in Secco (2000, 2001), the presence of a (non-baryonic) dark halo in large-scale celestial objects, can induce a scale length on the luminous spheroid through the occurrence of an unexpected maximum in the virial potential energy (Clausius Virial, CV). The above mentioned investigations were grounded on two cored power law density profiles, but the same result is shown to hold for more refined and realistic models.

scholarly journals Molecular clouds in galaxies as seen from NIR extinction studies

2006 ◽  
Vol 2 (S237) ◽  
pp. 204-207
Author(s):  
João Alves
Keyword(s):  
Mass Spectrum ◽  
Power Law ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Column Density ◽  
Large Scale ◽  
Near Infrared ◽  
Mass Function ◽  
Core Mass ◽  
Dense Cores

AbstractNear infrared dust extinction mapping is opening a new window on molecular cloud research. Applying a straightforward technique to near infrared large scale data of nearby molecular complexes one can easily construct density maps with dynamic ranges in column density covering, 3σ~ 0.5 < AV< 50 mag or 1021<N<1023 cm−2. These maps are unique in capturing the low column density distribution of gas in molecular cloud complexes, where most of the mass resides, and at the same time allow the identification of dense cores (n~104cm−3) which are the precursors of stars. For example, the application of this technique to the nearby Pipe Nebula complex revealed the presence of 159 dense cores (the largest sample of such object in one single complex) whose mass spectrum presents the first robust evidence for a departure from a single power-law. The form of this mass function is surprisingly similar in shape to the stellar IMF but scaled to a higher mass by a factor of about 3. This suggests that the distribution of stellar birth masses (IMF) is the direct product of the dense core mass function and a uniform star formation efficiency of 30%±10%, and that the stellar IMF may already be fixed during or before the earliest stages of core evolution. We are now extending this technique to extra-galactic mapping of Giant molecular Clouds (GMCs), and although a much less straightforward task, preliminary results indicate that the GMC mass spectrum in M83 and Centaurus A is a power-law characterized by α~−2 unlike CO results which suggest α~−1.

scholarly journals Novel approaches for large-scale two-dimensional hydrodynamic modelling of rivers

2018 ◽  
Vol 40 ◽  
pp. 05040
Author(s):  
Mohamed F.M. Yossef ◽  
J. S. de Jong ◽  
A. Spruyt ◽  
M. Scholten
Keyword(s):  
Large Scale ◽  
Scale Model ◽  
Calibration Data ◽  
Hydrodynamic Modelling ◽  
Two Dimensional ◽  
Data Set ◽  
Wide Range ◽  
Recent Developments ◽  
Model Setup ◽  
Using Data

For decades, the decision-making process for water management in the Netherlands makes full utilisation of state of the art models. For rivers, two-dimensional hydrodynamic models are considered essential for a wide range of questions. Every five years, there is a major model revision that includes software updates, improved physical processes, new modelling strategy, and a new calibration. 2017 marked the setup and calibration of the first river model in the sixth generation of these models. In this paper, we discuss the most recent developments in two-dimensional hydrodynamic modelling of rivers. We give an overview of the process followed to agree on the functional design of the model and address the use of the recently developed Delft3D Flexible Mesh suite. We address, in some details: i) a mesh independent approach for model setup; ii) the utilisation of a new calibration technique, which is automated using data assimilation and includes spatial and discharge dependencies; and iii) the use of a novel operational module to control hydraulic structures. The first river model within the 6th generation of models is that of the Meuse River, where the new approaches are being successfully applied. In conclusion: the mesh independent modelling approach offers great flexibility and facilitates that the same data set can be used for multiple versions of the model (e.g. different grid resolution; or different model extent). The automated calibration approach makes it possible to utilise a comprehensive calibration data set for a large-scale model in a reproducible way. The increased complexity of modelling has become possible over the last decade due to the availability of large datasets and increased computational power. This paper is particularly relevant for modellers and decision makers alike.

Electron microscopy study of reactively sputter-deposited Ti/N films on silicon

1992 ◽  
Vol 50 (2) ◽  
pp. 1362-1363
Author(s):  
V. C. Kannan ◽  
A. K. Singh ◽  
R. B. Irwin ◽  
S. Chittipeddi ◽  
F. D. Nkansah ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Large Scale ◽  
Hexagonal Phase ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Process Conditions ◽  
Tin Films ◽  
Wide Range ◽  
Fcc Phase ◽  
Circuits Vlsi

Titanium nitride (TiN) films have historically been used as diffusion barrier between silicon and aluminum, as an adhesion layer for tungsten deposition and as an interconnect material etc. Recently, the role of TiN films as contact barriers in very large scale silicon integrated circuits (VLSI) has been extensively studied. TiN films have resistivities on the order of 20μ Ω-cm which is much lower than that of titanium (nearly 66μ Ω-cm). Deposited TiN films show resistivities which vary from 20 to 100μ Ω-cm depending upon the type of deposition and process conditions. TiNx is known to have a NaCl type crystal structure for a wide range of compositions. Change in color from metallic luster to gold reflects the stabilization of the TiNx (FCC) phase over the close packed Ti(N) hexagonal phase. It was found that TiN (1:1) ideal composition with the FCC (NaCl-type) structure gives the best electrical property.

THE SOME QUESTIONS OF AUTONOMOUS MOTION AND MANAGEMENT OF LAND-MOBILE ROBOTIC COMPLEXES FOR UKRAINIAN GROUND FORCESE

2019 ◽  
pp. 53-58
Author(s):  
О. Кravchuk ◽  
V. Symonenkov ◽  
I. Symonenkova ◽  
O. Hryhorev
Keyword(s):  
Large Scale ◽  
Armed Forces ◽  
Distributed Information ◽  
Wide Range ◽  
Highly Effective ◽  
Information Management Systems ◽  
Robotic Devices ◽  
Principles And Standards ◽  
And Control ◽  
The Eu

Today, more than forty countries of the world are engaged in the development of military-purpose robots. A number of unique mobile robots with a wide range of capabilities are already being used by combat and intelligence units of the Armed forces of the developed world countries to conduct battlefield intelligence and support tactical groups. At present, the issue of using the latest information technology in the field of military robotics is thoroughly investigated, and the creation of highly effective information management systems in the land-mobile robotic complexes has acquired a new phase associated with the use of distributed information and sensory systems and consists in the transition from application of separate sensors and devices to the construction of modular information subsystems, which provide the availability of various data sources and complex methods of information processing. The purpose of the article is to investigate the ways to increase the autonomy of the land-mobile robotic complexes using in a non-deterministic conditions of modern combat. Relevance of researches is connected with the necessity of creation of highly effective information and control systems in the perspective robotic means for the needs of Land Forces of Ukraine. The development of the Armed Forces of Ukraine management system based on the criteria adopted by the EU and NATO member states is one of the main directions of increasing the effectiveness of the use of forces (forces), which involves achieving the principles and standards necessary for Ukraine to become a member of the EU and NATO. The inherent features of achieving these criteria will be the transition to a reduction of tasks of the combined-arms units and the large-scale use of high-precision weapons and land remote-controlled robotic devices. According to the views of the leading specialists in the field of robotics, the automation of information subsystems and components of the land-mobile robotic complexes can increase safety, reliability, error-tolerance and the effectiveness of the use of robotic means by standardizing the necessary actions with minimal human intervention, that is, a significant increase in the autonomy of the land-mobile robotic complexes for the needs of Land Forces of Ukraine.

Sign in / Sign up

Export Citation Format

Share Document