Cometary evolution and cryovolcanism 1This article is part of a Special issue that honours the work of Dr. Donald M. Hunten FRSC who passed away in December 2010 after a very illustrious career.

2012 ◽  
Vol 90 (8) ◽  
pp. 807-815 ◽  
Author(s):  
Michael J.S. Belton

Recent space observations of cometary nuclei show evidence of internal (cryovolcanic) activity while retaining aspects of their primitive origins. Using discoveries made during the two most recent cometary encounters: EPOXI at 103P/Hartley 2 and Stardust-NExT at 9P/Tempel 1, we test a hypothesis for their physical evolution, which, if true, could provide a unified basis for understanding the relative ages of their surfaces and the causes of a wide range of cometary activity. We show: (i) that the categorization of 103P/Hartley 2 as hyperactive is not a reflection of the extent of activity over the surface of the nucleus for which we find a normal H2O production rate; (ii) that the heterogeneous spatial distribution of CO2 and H2O in the inner comae of 9P/Tempel 1 and 103P/Hartley 2 is best explained by processes associated with cometary activity rather than the presence of primitive compositional heterogeneities in the nucleus; and (iii) that most of the quasi-circular depressions seen on the surface of 9P/Tempel are the result of outburst activity. The apparent absence of circular depressions and large scale layering on 103P/Hartley 2 present a challenge to the evolutionary hypothesis although the small size of its nucleus may ultimately provide an explanation.

Diversity ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 300 ◽  
Author(s):  
Fernando Tuya

Rhodolith seabeds function as ‘ecosystems engineers’, which globally provide a range of ‘ecosystem services’. However, knowledge on the structure, composition and distribution of rhodolith seabeds is still lacking. This Special Issue comprises six articles, addressing specific questions of rhodolith seabeds, and covering a wide range of topics. Two papers provide new large-scale information on the presence, structure and distribution of rhodolith beds at two southern hemisphere areas, in particular continental shelfs off South Africa and Brazil. Another two studies contributed to the discovery on new algal species from rhodolith beds, including Sporolithon franciscanum, a new rhodolith-forming species from Brazil, and the small benthic alga Schizocladia ischiensis. In terms of associated fauna, the taxonomic composition and patterns of abundance of decapod crustaceans are described in another article, including the description of a depth-partitioning in the abundance of juveniles and adults of the crab Nanocassiope melanodactylus. Rhodoliths are often present in fossilized deposits, so we can track changes in their presence with climate fluctuations. High temperatures during the Eocene and widespread oligotrophic conditions are finally connected with low abundances of rhodolith beds at mid and high latitudes, despite a larger presence at equatorial regions.


2014 ◽  
Vol 26 (4) ◽  
pp. 435-435
Author(s):  
Koichi Osuka

As a disaster-prone country, Japan has endured many earthquake disasters. The latest cases include the 1995 Great Hanshin-Awaji earthquake disaster, the 2004 Niigata Chuetsu earthquake, and the 2011 Great East Japan earthquake. Since the 1995 Great Hanshin-Awaji earthquake in particular, many robot researchers have started undertaking the research and development of rescue robots. Their practical applications have a long way to go, so to continue ongoing robot research and development, we should also be aware that comparatively few researchers and engineers are actually engaged in such research and development. Great earthquakes (or tsunami) are both rare and unpredictable, which makes it very difficult to establish research policies for rescue robots intended for specialized use in disaster response. We should also realize that Japan is almost constantly hit by one or another every year – e.g., the typhoons that hit Japan directly every year and themselves triggering other disasters caused by landslides or avalanches due to heavy rainfall. The Japanese populace is so accustomed to such happenings but, nevertheless, few actions have been taken unlike those against large-scale earthquakes. It is often said that an effective disaster response system can only be developed after we have experienced many actual disasters. It then occurs to us that we must first construct disaster response systems – rescue robots, etc. – directly targeting daily natural disasters. Any large-scale disaster response system can be built on such constant efforts. On the other hand, any disaster response system against daily natural disasters could only be developed by locally domiciled researchers and engineers. This makes us feel that it is possible to increase the number of personnel who become involved in disaster response research and development. Based on the above context, this special issue provides a wide range of articles on region-specific disasters and disaster response actions, focusing on their localities and specialties. We sincerely hope that this special issue will help in promoting research and development on rescue robots and putting them to practical use.


2021 ◽  
Vol 9 ◽  
Author(s):  
Alexander H. Weinhart ◽  
Sepp Kipfstuhl ◽  
Maria Hörhold ◽  
Olaf Eisen ◽  
Johannes Freitag

The occurrence of snowpack features has been used in the past to classify environmental regimes on the polar ice sheets. Among these features are thin crusts with high density, which contribute to firn stratigraphy and can have significant impact on firn ventilation as well as on remotely inferred properties like accumulation rate or surface mass balance. The importance of crusts in polar snowpack has been acknowledged, but nonetheless little is known about their large-scale distribution. From snow profiles measured by means of microfocus X-ray computer tomography we created a unique dataset showing the spatial distribution of crusts in snow on the East Antarctic Plateau as well as in northern Greenland including a measure for their local variability. With this method, we are able to find also weak and oblique crusts, to count their frequency of occurrence and to measure the high-resolution density. Crusts are local features with a small spatial extent in the range of tens of meters. From several profiles per sampling site we are able to show a decreasing number of crusts in surface snow along a traverse on the East Antarctic Plateau. Combining samples from Antarctica and Greenland with a wide range of annual accumulation rate, we find a positive correlation (R2 = 0.89) between the logarithmic accumulation rate and crusts per annual layer in surface snow. By counting crusts in two Antarctic firn cores, we can show the preservation of crusts with depth and discuss their temporal variability as well as the sensitivity to accumulation rate. In local applications we test the robustness of crusts as a seasonal proxy in comparison to chemical records like impurities or stable water isotopes. While in regions with high accumulation rates the occurrence of crusts shows signs of seasonality, in low accumulation areas dating of the snowpack should be done using a combination of volumetric and stratigraphic elements. Our data can bring new insights for the study of firn permeability, improving of remote sensing signals or the development of new proxies in snow and firn core research.


2009 ◽  
Vol 4 (3) ◽  
pp. 30-42
Author(s):  
Vladimir Dulin ◽  
Yuriy Kozorezov ◽  
Dmitriy Markovich ◽  
Mikhail Tokarev

This paper is devoted to experimental study of the instantaneous and average flow structure in the pre-mixed propaneair swirling flames using optical noncontact PIV (Particle Image Velocimetry) method in stereoscopic configuration. A visualization of the typical regimes of combustion for the swirling and non-swirling flame in a wide range of Reynolds numbers and equivalence ratios is presented. In addition, boundaries of steady combustion are defined. Measurements of instantaneous velocity fields for typical combustion regimes are performed. Instantaneous velocity fields were used to calculate the spatial distribution of the mean velocity and turbulence kinetic energy component. Interaction of the flame with a large-scale vortex structures is studied. It shows significantly different effects of burning on the turbulent structure of twisted jet. The paper describes algorithms of data processing, in particular, adaptive cross-correlation method of calculating the instantaneous velocity fields based on an analysis of the local particle image concentration. This method allows to effectively filtering out the velocity vector outliers, which appear in areas with low concentration of tracers during gas flows diagnostics, and calculate the spatial distribution of such characteristics as the intensity of turbulent pulsations.


2014 ◽  
Vol 8 (1) ◽  
pp. 154-154
Author(s):  
Mingjin Chu

The Open Civil Engineering Journal, which is one of the most relevant international journals in civil engineering area, wishes to promote the latest researches in engineering structures. This special issue contains 8 invited outstanding articles covering a wide range of topics. We have assembled recent studies in the field of several typical structures, attempting to provide a glimpse into the wide range of engineering problems. It is expected that the special issue will benefit researchers and engineers who are interested in the design of protective structures and stimulate the research interests in this important an d promising area of civil engineering. A brief overview of each article published in this special issue is provided here. In “Experimental Study on Assembled Monolithic Concrete Shear Walls Built with Precast Two-way Hollow Slabs” , Zhijuan Sun et al. present a quasi-static experiment on one reinforced concrete shear wall and two shear walls built with precast two-way hollow slab. Test result shows that the new type of shear walls experienced the loading process from the whole wall to the portioned wall due to the internal and vertical joints of the wall body, which can be applied in practical construction. In “Study on Metering Scheme of Seismic Experiment for Shear Wall Built with Precast Hollow Slab” , Zhijuan Sun et al. present the measuring scheme of shear wall deformation and steel strain. The special mechanical characteristic of the shear wall built with precast two-way hollow slab is the relative deformation of the concrete on both sides of vertical joint. The study shows that the measuring methods of shear wall deformation and relative deformation are reasonable and feasible. In “Experimental Study on Precast Concrete Shear Walls with Different Hollow Slabs” , Qinyan Zhao et al. present a test on two shear walls built with precast two-way hollow slab with different details. The study shows that brittle shear failure can be avoided and the failure behaviors tend to evolve from integral wall to the combination of wall and columns. Also, compressive capacity of walls can be affected by the dimension of transverse holes. In “Test Study on Strength and Permeability Properties of Lime -Fly Ash Loess Under Freeze-Thaw Cycles”, Zhiquan Zhang and Yufen Zhang present a study on the engineering behaviors of lime-fly ash loess using uniaxial compressive test, fast direct shearing test and permeability test. Test data show that uniaxial compressive strength of lime-fly ash loess has good water stability and freeze-thaw stability, and can be applied in permafrost subgrade. In “Unloading Phenomena Characteristics in Brittle Rock Masses by A Large-scale Excavation in Dam Foundation”, Changgen Yan et al. investigate a large-scale excavation around the foundation of the dam. The characteristics of unloading rock masses were described with the acoustic wave velocity monitoring method. The unloading deformation has a direct temporal dependence, and increases quickly during the first 90 days, then with a slower rate from 90 to 180 days, and after that the unloading deformation will be small enough to be neglected In “A Review on Progressive Collapse of Building Structures” , Hao Wang et al. assess the recent studies on the progressive collapse of building structures from experimental study, numerical simulation and theoretical analysis. The design methods to prevent progressive collapse for building structures are also discussed. In “Damage Identification of Continuous Rigid Frame Concrete Bridge”, Shengnan Huang et al. present a large-scale experimental study on safety monitoring methodology for continuous rigid frame concrete bridge. Two load stages and ten different load steps were simulated to test various scenario of long-term loading and different levels of overload. Curva ture mode method was adopted to detect the damage during the exercises. In addition, the Finite-Element Analysis (FEA) was utilized, and the experimental recurring was verified positively through FEA model. In “Corrosion Monitoring Using Embedded Piezoelectric Sensors”, Lei Qin et al. develop a new type of corrosion detection technique for reinforced concrete. The technique used piezoelectric sensors to detect the ultrasonic signals during corrosion. The state of bonding layer of concrete and steel bar could be monitored. It can also detect the initial of corrosion and cracking of bonding layer. I am grateful to all the authors and reviewers for the contribution and support during the course of editing this special issue. Their prompt responses have made it possible for us to publish this special issue on time.


1999 ◽  
Vol 173 ◽  
pp. 381-387
Author(s):  
M. Królikowska ◽  
G. Sitarski ◽  
S. Szutowicz

AbstractThe nongravitational motion of five “erratic” short-period comets is studied on the basis of published astrometric observations. We present the precession models which successfully link all the observed apparitions of the comets: 21P/Giacobini-Zinner, 31P/Schwassmann-Wachmann 2, 32P/Comas Solá, 37P/Forbes, and 43P/Wolf-Harrington. We used the Sekanina's forced precession model of the rotating cometary nucleus to include the nongravitational terms into equations of the comet's motion. Values of six basic parameters (four connected with the rotating comet nucleus and two describing the precession of spin-axis of the nucleus) have been determined along the orbital elements from positional observations of the comets. The solutions were derived with additional assumptions which introduce instantaneous changes of modulus of reactive force,Aand of maximum of cometary activity with respect to perihelion time. The present precession models impose some contraints on sizes and rotational periods of cometary nuclei. According to our solutions the nucleus of 21P/Giacobini-Zinner with oblateness along the spin-axis of about 0.32 (equatorial to polar radius of 1.46) is the most oblate among five investigated comets.


Author(s):  
V. C. Kannan ◽  
A. K. Singh ◽  
R. B. Irwin ◽  
S. Chittipeddi ◽  
F. D. Nkansah ◽  
...  

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.


1995 ◽  
pp. 3-21
Author(s):  
S. S. Kholod

One of the most difficult tasks in large-scale vegetation mapping is the clarification of mechanisms of the internal integration of vegetation cover territorial units. Traditional way of searching such mechanisms is the study of ecological factors controlling the space heterogeneity of vegetation cover. In essence, this is autecological analysis of vegetation. We propose another way of searching the mechanisms of territorial integration of vegetation. It is connected with intracoenotic interrelation, in particular, with the changing role of edificator synusium in a community along the altitudinal gradient. This way of searching is illustrated in the model-plot in subarctic tundra of Central Chukotka. Our further suggestion concerns the way of depicting these mechanisms on large-scale vegetation map. As a model object we chose the catena, that is the landscape formation including all geomorphjc positions of a slope, joint by the process of moving the material down the slope. The process of peneplanation of a mountain system for a long geological time favours to the levelling the lower (accumulative) parts of slopes. The colonization of these parts of the slope by the vegetation variants, corresponding to the lowest part of catena is the result of peneplanation. Vegetation of this part of catena makes a certain biogeocoenotic work which is the levelling of the small infralandscape limits and of the boundaries in vegetation cover. This process we name as the continualization on catena. In this process the variants of vegetation in the lower part of catena are being broken into separate synusiums. This is the process of decumbation of layers described by V. B. Sochava. Up to the slope the edificator power of the shrub synusiums sharply decreases. Moss and herb synusium have "to seek" the habitats similar to those under the shrub canopy. The competition between the synusium arises resulting in arrangement of a certain spatial assemblage of vegetation cover elements. In such assemblage the position of each element is determined by both biotic (interrelation with other coenotic elements) and abiotic (presence of appropriate habitats) factors. Taking into account the biogeocoenotic character of the process of continualization on catena we name such spatial assemblage an exolutionary-biogeocoenotic series. The space within each evolutionary-biogeocoenotic series is divided by ecological barriers into some functional zones. In each of the such zones the struggle between synusiums has its individual expression and direction. In the start zone of catena (extensive pediment) the interrelations of synusiums and layers control the mutual spatial arrangement of these elements at the largest extent. Here, as a rule, there predominate edificator synusiums of low and dwarfshrubs. In the first order limit zone (the bend of pediment to the above part of the slope) one-species herb and moss synusiums, oftenly substituting each other in similar habitats, get prevalence. In the zone of active colonization of slope (denudation slope) the coenotic factor has the least role in the spatial distribution of the vegetation cover elements. In particular, phytocoenotic interactions take place only within separate microcoenoses of herbs, mosses and lichens. In the zone of the attenuation of continualization process (the upper most parts of slope, crests) phytocoenotic interactions are almost absent and the spatial distribution of vegetation cover elements depends exclusively on the abiotic factors. The principal scheme of the distribution of vegetation cover elements and the disposition of functional zones on catena are shown on block-diagram (fig. 1).


Author(s):  
О. Кravchuk ◽  
V. Symonenkov ◽  
I. Symonenkova ◽  
O. Hryhorev

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.


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