Design and Simulation of Single Electron Transistor based SRAM and its Memory Controller at Room Temperature

Heterogeneous 3D integration of single electron transistor (SET) circuits with CMOS based circuits is achieved by stacking a SET layer above CMOS IC. Low power and delay efficient circuits can be designed using SET. In this paper, we have designed and simulated 6T SRAM array operating at room temperature and at CMOS comparable voltage. Peripheral circuit like sense amplifier, decoder, write circuit and pre-charge circuit using SET have been designed for optimum performance. The stability of 6T SRAM cell is verified using N-curve method. The designed SET based 8 x 8 bit SRAM is 99.54 % power efficient, 92.19 % faster in write access time and 78.58 % faster in read access time compared to 16 nm CMOS based SRAM. The SRAM is designed to work at CMOS comparable voltage of 800 mV, which can be scaled up to 20 mV with better efficiency. The designed SRAM is tested and verified for variation in process, voltage and temperature. The maximum frequency of operation for the designed SET based SRAM with memory controller is 4 GHz

Evaluating Volatile Induced Surface Features on Vesta and Ceres

This work evaluates volatile induced surface features on Vesta and Ceres, two of the largest asteroids present within the asteroid belt. Both the planetary objects have similar surface acceleration but different regolith nature. Vesta is a relatively dry body whereas Ceres is rich with water ice. Direct measurement of volatiles is challenging due to harsh space conditions. However, when they are mixed with regolith, it produces peculiar landforms due to melting and/or sublimation and affects the overall evolution of a planetary body. Therefore, in this study the surface features which have direct or indirect link to ice and/or volatiles are examined in order to understand the volatile distribution. For this, regional and global scale investigations related to ponded deposits, pit chains and mass wasting analysis were conducted on Vesta and Ceres. In the vicinity of Marcia and Cornelia impact craters of Vesta, two types of pond deposits were observed. Type 1 melt ponds have smooth, shallow deposits (depth <100 m) and are produced from the downslope movement of volatile bearing impact melt material. In contrast, type 2 dust ponds deposit consist of rough surface with ~200 m depth. These deposits are produced from the mobility of granular dust via infrequent high-amplitude seismic diffusivity and/or short-lived volatile outgassing activity. Due to low amounts of volatiles, the dusty material did not achieve kinetic sieving and thus do not attain typical smooth pond morphology. The findings of this study strongly support the hypothesis related to presence of low amounts of volatiles within Vesta’s regolith. To understand the volatile distribution on Ceres, the analysis of pit chains is carried out within three impact craters namely; Occator, Azacca and Urvara. Radial pit chain pattern of Occator is related to subsurface laccolith swelling of volatile rich cryomagmatic material. Linear pit chain clusters at floors of Azacca and Urvara are attributed to seasonal thermal contraction of ice layer present near the surface. Additionally, based on the pit chains depth the depicted average minimum thickness of regolith within Azacca, located at equator is ~200 m. On the contrary, within Occator and Urvara, the localized thickness is 30 m and 800 m, respectively, which is attributed to their distinct subsurface condition. Hence, this investigation favors the presence of ice layer within the subsurface layer and reveals that it is not distributed homogeneously on Ceres. Lastly, the global scale comparative examination of the mass wasting process on Vesta and Ceres shows few common and some distinct characteristics. In general, granular sliding on Vesta and flow-like movements on Ceres are observed as dominant population. Further, slides and slumping features are restricted to mid-latitudes on Ceres which implies ice-rock fractionation at regional scale. Additionally, the volatile concentration also influences the deposit mobility on Vesta and Ceres and is analyzed by estimating height, width and effective coefficient of friction; H/L. The outcome suggests that deposits become immobile at shorter distances on Vesta in comparison to Ceres (avg. distance 4.5 km and 11.2 km, respectively). The difference in morphology and mobility is related to contrast in the amounts of volatiles present within regolith of both the bodies. While comparing the effective coefficient of friction of Vesta and Ceres with planetary objects in outer solar system, the examination shows that lower temperature may have more influence on mobility. Together, all the above-mentioned studies summarize the volatile induced surface landforms and provide evidences related to their distribution on Vesta and Ceres. This work also presents the first-time comparative investigation that reveals the influence of volatile content on the morphological characteristics of Vesta and Ceres

Investigation of Mobility-related Surface Features on Asteroids and their Relation to Volatiles

The identification of regolith material and mass movement processes on icy planetary bodies has grabbed the attention of scientist in the past decades. The well preserved signatures of these materials have been well studied on Moon and Mars. In fact, studies show strong synergy between these physical processes and chemical properties of the planetary objects. With the aim to get better understanding of asteroid surface we plan to analyse mobility related features and establish an inventory

Formation of Ejecta and Dust Pond Deposits on Asteroid Vesta

Dust and melt ponds have been studied on planetary bodies including Eros, Itokawa, and the Moon. However, depending on the nature of the regolith material properties and the location of the planetary body, the formation mechanism of the ponded features varies. On Eros and Itokawa, ponded features are formed from dry regolith materials whereas on the Moon similar features are thought to be produced by ejecta melt. On the surface of Vesta, we have identified type 1, ejecta ponds, and type 2, dust ponds. On Vesta type 1 pond are located in the vicinity of ejecta melt of large impact craters. The material is uniformly distributed across the crater floor producing smooth pond surfaces which have a constant slope and shallow depth. The hosting crater of melt-like ponds has a low raised rim and is located on relatively low elevated regions. Whereas, the type 2 ponds on Vesta reveal an undulating surface that is frequently displaced from the crater center or extends toward the crater wall with an abruptly changing slope. We suggested that for the production of the type 2 ponds, localized seismic diffusion and volatile-induced fluidization may be responsible for Vesta. Due to Vesta's large size (in comparison to Eros and Itokawa), the surface may have experienced local-scale rare high-amplitude seismic diffusion which was sufficient to drift fine material. Similarly, short-lived volatile activities were capable to transfer dusty material on to the surface. Segregation and smoothing of transferred material lack further surface activities, hindering the formation of smooth morphology

Volatile related mass-wasting features on Ceres and Vesta

Various mass wasting features have been identified on Vesta and Ceres with prominent slumping regions, lobate materials, concentric ridges, and curvilinear edges. In this study we present a common classification of these features based on their morphological signatures. Our aim is to relate the mass wasting processes of the two bodies given their different surface compositions but similar environmental conditions

Ponded craters on Vesta

Ponded craters have been predominantly identified on small, dry planetary bodies like (433) Eros and Itokawa. We identified similar features on Vesta, where loose fragmented ponded materials are present on small crater floors. While the morphological details of the ponded features on Vesta and Eros/Itokawa are similar, their production mechanisms may vary, due to differences in gravity or the insolation environment Previous studies conducted on Vesta have provided evidence for volatile outgassing in some regions. In this study, we investigate the morphology of the ponded crater and possible involvement of volatiles outgassing and its interaction with surface material in producing ponded craters on Vesta

Formation of Ejecta and Dust Pond Deposits on Asteroid Vesta

Dust and melt ponds have been studied on planetary bodies including Eros, Itokawa, and the Moon. However, depending on the nature of the regolith material properties and the location of the planetary body, the formation mechanism of the ponded features varies. On Eros and Itokawa, ponded features are formed from dry regolith materials whereas on the Moon similar features are thought to be produced by ejecta melt. On the surface of Vesta, we have identified type 1, ejecta ponds, and type 2, dust ponds. On Vesta type 1 pond are located in the vicinity of ejecta melt of large impact craters. The material is uniformly distributed across the crater floor producing smooth pond surfaces which have a constant slope and shallow depth. The hosting crater of melt-like ponds has a low raised rim and is located on relatively low elevated regions. Whereas, the type 2 ponds on Vesta reveal an undulating surface that is frequently displaced from the crater center or extends toward the crater wall with an abruptly changing slope. We suggested that for the production of the type 2 ponds, localized seismic diffusion and volatile-induced fluidization may be responsible for Vesta. Due to Vesta's large size (in comparison to Eros and Itokawa), the surface may have experienced local-scale rare high-amplitude seismic diffusion which was sufficient to drift fine material. Similarly, short-lived volatile activities were capable to transfer dusty material on to the surface. Segregation and smoothing of transferred material lack further surface activities, hindering the formation of smooth morphology

Ryugu as seen close up by MASCOT

In October 2018, MASCOT landed on the surface of Ryugu to start a campaign of in-situ measurements. Its brief mission was successful, with the onboard camera revealing the surface of this C-type asteroid in unpre- cedented detail. The presence of abundant mm-sized, multi-colored inclusions in one rock suggests a link between Ryugu and carbonaceous chondrites