scholarly journals Small-scale topographic irregularities on Phobos: image and numerical analyses for MMX mission

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Tomohiro Takemura ◽  
Hideaki Miyamoto ◽  
Ryodo Hemmi ◽  
Takafumi Niihara ◽  
Patrick Michel

AbstractThe mothership of the Martian Moons eXploration (MMX) will perform the first landing and sampling on the surface of Phobos. For the safe landing, the 2.1-m-wide mothership of the MMX should find a smooth surface with at most 40 cm topographic irregularity, however, whose abundance or even existence is not guaranteed based on current knowledge. We studied the highest resolution (a few meters per pixel) images of Phobos for possible topographic irregularities in terms of boulder (positive relief feature) and crater distributions. We find that the spatial number densities of positive relief features and craters can vary significantly, indicating that the surface irregularities vary significantly over the entire surface. We extrapolate the size-frequency distributions of positive relief features to evaluate the surface roughness below the image resolution limit. We find that the probabilities that topographic irregularities are  < 40 cm for the areas of 4 × 4 m and 20 × 20 m are  > 33% and  < 1% for boulder-rich areas and  > 88% and  > 13% for boulder-poor areas, respectively, even for the worst-case estimates. The estimated probabilities largely increase when we reduce the assumed number of positive relief features, which are more realistic cases. These indicate high probabilities of finding a smooth enough place to land on Phobos’ surface safely. Graphical Abstract

2021 ◽  
Author(s):  
Tomohiro Takemura ◽  
Hideaki Miyamoto ◽  
Ryodo Hemmi ◽  
Takafumi Niihara ◽  
Patrick Michel

Abstract The mothership of the Martian Moons eXploration (MMX) will perform the first landing and sampling on the surface of Phobos. For the safe landing, the 2.1 m-wide mothership of the MMX should find a smooth surface with at most 40 cm topographic irregularity, however, whose abundance or even existence is not guaranteed based on current knowledge. We studied the highest resolution images of Phobos for possible topographic irregularities in terms of boulder (positive relief feature) and crater distributions. We find that the spatial number densities of positive relief features and craters can vary significantly; one region has 249/km 2 confirmed positive relief features (and 2,804/km 2 including candidates) and 342/km 2 confirmed craters (1,510/km 2 including candidates) as major negative features. These numbers contrast to another region, where only 46/km 2 positive relief features (260/km 2 including candidates) and 268/km 2 craters (526/km 2 includi ng candidates) exist, indicating that the surface irregularities vary significantly over the entire surface. We extrapolate the size-frequency distributions of positive relief features to evaluate the surface roughness below the image resolution limit. We find that the probabilities that topographic irregularities are <40 cm for the areas of 4 × 4 m and 20 × 20 m are > 65 % and <1 % for boulder-rich areas and >94 % and >41 % for boulder-poor areas, respectively, even for the worst-case estimates. The estimated probabilities largely increase when we reduce the assumed number of positive relief features, which are more realistic cases. These indicate high probabilities of finding a smooth enough place to land on Phobos' surface safely.


Author(s):  
S. J. Krause ◽  
W.W. Adams ◽  
S. Kumar ◽  
T. Reilly ◽  
T. Suziki

Scanning electron microscopy (SEM) of polymers at routine operating voltages of 15 to 25 keV can lead to beam damage and sample image distortion due to charging. Imaging polymer samples with low accelerating voltages (0.1 to 2.0 keV), at or near the “crossover point”, can reduce beam damage, eliminate charging, and improve contrast of surface detail. However, at low voltage, beam brightness is reduced and image resolution is degraded due to chromatic aberration. A new generation of instruments has improved brightness at low voltages, but a typical SEM with a tungsten hairpin filament will have a resolution limit of about 100nm at 1keV. Recently, a new field emission gun (FEG) SEM, the Hitachi S900, was introduced with a reported resolution of 0.8nm at 30keV and 5nm at 1keV. In this research we are reporting the results of imaging coated and uncoated polymer samples at accelerating voltages between 1keV and 30keV in a tungsten hairpin SEM and in the Hitachi S900 FEG SEM.


2007 ◽  
Vol 7 (4) ◽  
pp. 347-359 ◽  
Author(s):  
Gaurav Ameta ◽  
Joseph K. Davidson ◽  
Jami J. Shah

A new mathematical model for representing the geometric variations of lines is extended to include probabilistic representations of one-dimensional (1D) clearance, which arise from positional variations of the axis of a hole, the size of the hole, and a pin-hole assembly. The model is compatible with the ASME/ ANSI/ISO Standards for geometric tolerances. Central to the new model is a Tolerance-Map (T-Map) (Patent No. 69638242), a hypothetical volume of points that models the 3D variations in location and orientation for a segment of a line (the axis), which can arise from tolerances on size, position, orientation, and form. Here, it is extended to model the increases in yield that occur when maximum material condition (MMC) is specified and when tolerances are assigned statistically rather than on a worst-case basis; the statistical method includes the specification of both size and position tolerances on a feature. The frequency distribution of 1D clearance is decomposed into manufacturing bias, i.e., toward certain regions of a Tolerance-Map, and into a geometric bias that can be computed from the geometry of multidimensional T-Maps. Although the probabilistic representation in this paper is built from geometric bias, and it is presumed that manufacturing bias is uniform, the method is robust enough to include manufacturing bias in the future. Geometric bias alone shows a greater likelihood of small clearances than large clearances between an assembled pin and hole. A comparison is made between the effects of choosing the optional material condition MMC and not choosing it with the tolerances that determine the allowable variations in position.


2020 ◽  
Vol 68 (4) ◽  
Author(s):  
Grzegorz Starzynski ◽  
Ryszard Buczkowski ◽  
Bartlomiej Zylinski

AbstractThe aim of the work is to show both the similarities and differences in the formation of deformation-induced roughness in contact compression in the presence of oil and the problem of free surface roughing during uniaxial stretching in a plastic area. The relationships between changes in the roughness are caused by the deformation of the sample and the viscosity of oil at the contact area. It has been shown that normal contact loading with the presence of oil initially leads to an increase in surface roughness, then to its smoothening. The results of the experimental research have been compared with numerical simulation made using FSI (Fluid Structure Interaction) and ABAQUS systems. Using finite element calculations, it was possible to explain the phenomenon of roughness formation on the surface of a smooth steel sample. The changes in the structure of the smooth surface resulting from compression in the presence of oil are caused by the rotation and deformation of surface grains. The roughness of this structure is dependent on the viscosity of oil: the more viscous the liquid is, the rougher texture is formed.


MRS Advances ◽  
2016 ◽  
Vol 1 (31) ◽  
pp. 2237-2245
Author(s):  
Myles Thomas ◽  
Elizabeth Krenek ◽  
Stephen Beaudoin

ABSTRACTUnderstanding particle adhesion is vital to any industry where particulate systems are involved. There are multiple factors that affect the strength of the adhesion force, including the physical properties of the interacting materials and the system conditions. Surface roughness on the particles and the surfaces to which they adhere, including roughness at the nanoscale, is critically important to the adhesion force. The focus of this work is on the capillary force that dominates the adhesion whenever condensed moisture is present. Theoretical capillary forces were calculated for smooth particles adhered to smooth and rough surfaces. Simulations of the classical centrifuge technique used to describe particle adhesion to surfaces were performed based on these forces. A model was developed to describe the adhesion of the particles to the rough surface in terms of the adhesion to a smooth surface and an ‘effective’ contact angle distribution.


2021 ◽  
Vol 22 (2) ◽  
pp. 169-172
Author(s):  
A. R. Ajayi

The study examined the household's decision-making role in small scale goat production in Nsukka Local Government Area of Enugu State, Nigeria. Data for the study were collected from 74 households through the use of interview schedule. Frequency distributions and percentages were used in the data analysis. The findings showed that production of manure for replenishing the lost soil fertility under continuous land use was the most valuable reason for rearing goats in the area. The husbands played a larger decision-making role than their wives for certain aspects (such as goat raising initiation; health care; herd-size; planning for organizing for breedings; and grass cutting) of goat production. Implications of the findings for extension practice were presented.


2019 ◽  
Vol 49 (3) ◽  
pp. 193-200
Author(s):  
N. A. ZABALA ◽  
P. CASTRO ◽  
Walter TUCKART

The purpose of this study is to determinate the influence of surface roughness on the tribological behavior of a lubricated steel against steel tribosystem. Tests were carried out at high pressure and slow sliding speed, in order to simulate at small scale, the contact conditions found in the seal of the threaded joints used in oil & gas casing and tubing strings. Tests were carried out with a simplified block-onring test, varying the surface roughness of rings between 1.3 to 3 m Ra values. A thread compound lubricant containing lead, copper, zinc and graphite was used. During each cycle of test, the normal load was varied linearly between 250 N and 7000 N. An exponential correlation between Ra and Rt roughness values with the wear damage was found and the wear damage of the blocks decreases about 40 percent with the increasing of initial Ra roughness parameter in the movil surface.


Author(s):  
Petra Koucká Knížová ◽  
Jan Laštovička ◽  
Daniel Kouba ◽  
Zbyšek Mošna ◽  
Katerina Podolská ◽  
...  

The ionosphere represents part of the upper atmosphere. Its variability is observed on a wide-scale temporal range from minutes, or even shorter, up to scales of the solar cycle and secular variations of solar energy input. Ionosphere behavior is predominantly determined by solar and geomagnetic forcing. However, the lower-lying atmospheric regions can contribute significantly to the resulting energy budget. The energy transfer between distant atmospheric parts happens due to atmospheric waves that propagate from their source region up to ionospheric heights. Experimental observations show the importance of the involvement of the lower atmosphere in ionospheric variability studies in order to accurately capture small-scale features of the upper atmosphere. In the Part I Coupling, we provide a brief overview of the influence of the lower atmosphere on the ionosphere and summarize the current knowledge. In the Part II Coupling Evidences Within Ionospheric Plasma—Experiments in Midlatitudes, we demonstrate experimental evidence from mid-latitudes, particularly those based on observations by instruments operated by the Institute of Atmospheric Physics, Czech Academy of Sciences. The focus will mainly be on coupling by atmospheric waves.


2018 ◽  
Vol 06 (01) ◽  
pp. 25-31 ◽  
Author(s):  
Junji Yamanaka ◽  
Mai Shirakura ◽  
Chiaya Yamamoto ◽  
Naoto Utsuyama ◽  
Kei Sato ◽  
...  

2006 ◽  
Vol 315-316 ◽  
pp. 852-855 ◽  
Author(s):  
Cheng Yong Wang ◽  
C. Chen ◽  
Yue Xian Song

In order to achieve the smooth surface of diamond, several kinds of mixture oxidizing agents have been used to polish the single crystal diamond by a designed polishing apparatus. The existing of graphite and amorphous carbon has been found in the surface of diamond after polishing. The mechanochemical actions of oxidizing agents and the polishing iron plate have been proved. The mixture of oxidizing agents can decrease the polishing temperature so that the super-smooth surface of single crystal diamond can be achieved at lower temperature. The method provided is benefit not only to simplify polishing device and control the polishing process, but also to improve the removal rate and surface roughness.


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