Ultrashort pulse surface melting and smoothing: The impact of pulse spacing on heat accumulation and structure formation

2021 ◽  
Vol 130 (5) ◽  
pp. 053106
Author(s):  
F. Nyenhuis ◽  
A. Michalowski ◽  
J. L’huillier
Keyword(s):  
Structure Formation ◽  
Ultrashort Pulse ◽  
Surface Melting ◽  
Heat Accumulation ◽  
The Impact ◽  
Pulse Surface ◽  
Pulse Spacing

Greenland land-terminating glaciers velocity trends during the last two decades

2021 ◽  
Author(s):  
Paul Halas ◽  
Jeremie Mouginot ◽  
Basile de Fleurian ◽  
Petra Langebroek
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Limited Area ◽  
Ice Dynamics ◽  
Basal Sliding ◽  
Surface Melt ◽  
Ice Sheet Dynamics ◽  
The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  </p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  </p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  </p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. </p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

scholarly journals Prebiotically-relevant low polyion multivalency can improve functionality of membraneless compartments

2020 ◽  
Author(s):  
Fatma Pir Cakmak ◽  
Saehyun Choi ◽  
McCauley O. Meyer ◽  
Philip C. Bevilacqua ◽  
Christine D. Keating
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Structure Formation ◽  
Rna Structure ◽  
Salt Resistance ◽  
Origins Of Life ◽  
Complex Coacervation ◽  
The Impact ◽  
Local Ph

AbstractMultivalent polyions can undergo complex coacervation, producing membraneless compartments that accumulate ribozymes and enhance catalysis, and offering a mechanism for functional prebiotic compartmentalization in the origins of life. Here, we evaluated the impact of low, prebiotically-relevant polyion multivalency in coacervate performance as functional compartments. As model polyions, we used positively and negatively charged homopeptides with one to 100 residues, and adenosine mono-, di-, and triphosphate nucleotides. Polycation/polyanion pairs were tested for coacervation, and resulting membraneless compartments were analyzed for salt resistance, ability to provide a distinct internal microenvironment (apparent local pH, RNA partitioning), and effect on RNA structure formation. We find that coacervates formed by phase separation of the relatively shorter polyions more effectively generated distinct pH microenvironments, accumulated RNA, and preserved duplexes. Hence, reduced multivalency polyions are not only viable as functional compartments for prebiotic chemistries, but they can offer advantages over higher molecular weight analogues.

scholarly journals Prebiotically-relevant low polyion multivalency can improve functionality of membraneless compartments

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Fatma Pir Cakmak ◽  
Saehyun Choi ◽  
McCauley O. Meyer ◽  
Philip C. Bevilacqua ◽  
Christine D. Keating
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Structure Formation ◽  
Rna Structure ◽  
Functional Performance ◽  
Salt Resistance ◽  
Origins Of Life ◽  
Complex Coacervation ◽  
The Impact ◽  
Local Ph

AbstractMultivalent polyions can undergo complex coacervation, producing membraneless compartments that accumulate ribozymes and enhance catalysis, and offering a mechanism for functional prebiotic compartmentalization in the origins of life. Here, we evaluate the impact of lower, more prebiotically-relevant, polyion multivalency on the functional performance of coacervates as compartments. Positively and negatively charged homopeptides with 1–100 residues and adenosine mono-, di-, and triphosphate nucleotides are used as model polyions. Polycation/polyanion pairs are tested for coacervation, and resulting membraneless compartments are analyzed for salt resistance, ability to provide a distinct internal microenvironment (apparent local pH, RNA partitioning), and effect on RNA structure formation. We find that coacervates formed by phase separation of the shorter polyions more effectively generated distinct pH microenvironments, accumulated RNA, and preserved duplexes than those formed by longer polyions. Hence, coacervates formed by reduced multivalency polyions are not only viable as functional compartments for prebiotic chemistries, they can outperform higher molecular weight analogues.

scholarly journals Effects of debris on ice-surface melting rates: an experimental study

2010 ◽  
Vol 56 (197) ◽  
pp. 384-394 ◽  
Author(s):  
Natalya Reznichenko ◽  
Tim Davies ◽  
James Shulmeister ◽  
Mauri McSaveney
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Interstitial Water ◽  
Geographical Location ◽  
Rock Avalanche ◽  
Surface Melting ◽  
Cold Night ◽  
Ice Surface ◽  
State Radiation ◽  
The Impact

AbstractHere we report a laboratory study of the effects of debris thickness, diurnally cyclic radiation and rainfall on melt rates beneath rock-avalanche debris and sand (representing typical highly permeable supraglacial debris). Under continuous, steady-state radiation, sand cover >50 mm thick delays the onset of ice-surface melting by >12 hours, but subsequent melting matches melt rates of a bare ice surface. Only when diurnal cycles of radiation are imposed does the debris reduce the longterm rate of ice melt beneath it. This is because debris >50 mm thick never reaches a steady-state heat flux, and heat acquired during the light part of the cycle is partially dissipated to the atmosphere during the nocturnal part of the cycle, thereby continuously reducing total heat flux to the ice surface underneath. The thicker the debris, the greater this effect. Rain advects heat from high-permeability supraglacial debris to the ice surface, thereby increasing ablation where thin, highly porous material covers the ice. In contrast, low-permeability rock-avalanche material slows water percolation, and heat transfer through the debris can cease when interstitial water freezes during the cold/night part of the cycle. This frozen interstitial water blocks heat advection to the ice–debris contact during the warm/day part of the cycle, thereby reducing overall ablation. The presence of metre-deep rock-avalanche debris over much of the ablation zone of a glacier can significantly affect the mass balance, and thus the motion, of a glacier. The length and thermal intensity of the diurnal cycle are important controls on ablation, and thus both geographical location and altitude significantly affect the impact of debris on glacial melting rates; the effect of debris cover is magnified at high altitude and in lower latitudes.

scholarly journals Effects of Neglecting PCM Hysteresis While Making Simulation Calculations of a Building Located in Polish Climatic Conditions

2021 ◽  
Vol 11 (19) ◽  
pp. 9166
Author(s):  
Anna Zastawna-Rumin ◽  
Katarzyna Nowak
Keyword(s):  
Surface Temperature ◽  
Phase Change ◽  
Phase Change Materials ◽  
Model Building ◽  
Experimental Tests ◽  
Climatic Conditions ◽  
Heat Accumulation ◽  
Noticeable Effect ◽  
Change Temperature ◽  
The Impact

The use of phase change materials (PCM) in different building applications is a hot topic in today’s research and development activities. Numerous experimental tests confirmed that the hysteresis of the phase change process has a noticeable effect on heat accumulation in PCM. The authors are trying to answer the question of whether the neglecting of hysteresis or the impact of the speed of phase transformation processes reduce the accuracy of the simulation. The analysis was performed for a model building, created to validate the energy calculations. It was also important to conduct simulations for the polish climatic conditions. The calculations were conducted for three variants of materials. In addition, in the case of models containing layers with PCM, calculations were made both taking into account, as well as excluding material hysteresis in the calculations. In the analyzed examples, after taking into account hysteresis in the calculations, the period of time when surface temperature is below the phase change temperature of the materials decreased by 10.6% and 29.4% between 01 June to 30 September, for the options with PCM boards and Dupont boards, respectively. Significant differences in surface temperature were also observed. The effects of neglecting, even relatively small hysteresis, in the calculations are noticeable and can lead to significant errors in the calculation.

scholarly journals Continuum modelling of structure formation of biosilica patterns in diatoms

BMC Materials ◽  
2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Manfred Bobeth ◽  
Arezoo Dianat ◽  
Rafael Gutierrez ◽  
David Werner ◽  
Hongliu Yang ◽  
...  
Keyword(s):  
Phase Separation ◽  
Pattern Formation ◽  
Structure Formation ◽  
Organic Molecules ◽  
Experimental Studies ◽  
Formation Mechanisms ◽  
Phosphate Ions ◽  
High Regularity ◽  
The Impact

Abstract Formation of regularly structured silica valves of various diatom species is a particularly fascinating phenomenon in biomineralization. Intensive investigations have been devoted to elucidate the formation mechanisms of diatom valve structures. Phase-separation of species-specific organic molecules has been proposed to be involved in pattern formation, where the evolving organic molecule structures serve as template for silica formation. In the present work, using a continuum approach, we investigate the conditions under which silica structures of high regularity can develop within a phase separation model. In relation to previously reported in vitro experiments of silica formation, which revealed the important role of phosphate ions in the self-assembly of organic molecules, we propose a model where phase separation is coupled with a chemical reaction. We analyze the impact of the reaction of phosphate ions with organic molecules on the appearing morphology of the organic template. Two- and three-dimensional simulations of the development of regular stationary patterns are presented. The influence of a confined geometry and an interaction of organic molecules with the walls on pattern formation is also addressed. We expect that our approach will be relevant for experimental studies aiming at inducing structure formation under controlled in vitro conditions.

Spatial and temporal temperature distribution of ultrashort pulse induced heat accumulation in glass

2015 ◽  
Author(s):  
Sören Richter ◽  
Fumiya Hashimoto ◽  
Felix Zimmermann ◽  
Yasuyuki Ozeki ◽  
Kazuyoshi Itoh ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Ultrashort Pulse ◽  
Heat Accumulation

CONCRETING AND EARLY HARDENING PROCESSES IN MONOLITHIC REINFORCED CONCRETE STRUCTURES / PROCESAI, VYKSTANTYS BETONAVIMO IR PRADINIO KIETĖJIMO METU GELŽBETONINĖSE MONOLITINĖSE KONSTRUKCIJOSE

2012 ◽  
Vol 4 (2) ◽  
pp. 67-75
Author(s):  
Vigantas Antanas Žiogas ◽  
Svajūnas Juočiūnas ◽  
Violeta Medelienė ◽  
Giedrius Žiogas
Keyword(s):  
Reinforced Concrete ◽  
Structure Formation ◽  
Structural Strength ◽  
Concrete Strength ◽  
Time Moment ◽  
Concrete Structures ◽  
Concrete Mixture ◽  
Industrial Building ◽  
Reinforced Concrete Structures ◽  
The Impact

The exploitation time and reliability of monolithic reinforced concrete structures largely depend on concreting technology and process influence during concreting and early setting stages. Different types of cracks in monolithic reinforced concrete structures appear due to internal and external effects. Cracks appear when the technology of structure concreting is damaged, when formwork is removed during the further setting and structures loaded period. In order to avoid micro and macro cracks in monolithic structures, it is important to measure the particular setting time moment and technological process moment when stresses that exceed the permissible values appear in concrete. The article analyses the processes that appear when horizontal, sloping and vertical monolithic reinforced concrete structures are concreted. The analysis of concrete mixture pressure on formwork is performed. The pressure which is calculated according to different countries’ methodology is different: the smallest pressure is obtained calculating according to the British recommendations, and the largest pressure is obtained according to French CIB recommendations. In Lithuania, it is recommended to follow the German DIN 18218 standard. The balance conditions of concrete mixture concreting on slope surface are described. The main concreting technology parameters and their interaction are analysed; the speed, intensity and time of continuous concreting technology are presented. When the process of continuous concreting is performed, it is necessary to evaluate the interaction and values of parameters properly. Methodical theoretical calculation is presented. Practical solutions for industrial building construction applying the modern sliding formwork technology are presented. The impact of cement type, superplasticizers and temperature over the concrete mixture mobility, changes, fresh concrete structural strength and concrete setting kinetics are analysed. The main characteristics of the initial setting — the beginning of structure formation, when concrete mixture turns into concrete state — is analysed applying the ultrasonic method. The beginning of structure formation influences the regulated time of concrete mixture laying and compaction. The requirements for structural strength (permissible strength limits) and concreting rate (formwork movement) of freshly formed concrete are set when the construction is performed applying the continuous concreting technology method. The analysis is implemented performing the construction of cylindrical sludge tank with slipping formwork. While performing the analysis during concreting, it was stated that the concrete setting kinetics corresponds to the sludge tank concreting rate. The analysis performed after concreting and in 28 days of hardening revealed that there are no surface defects or cracks, and concrete strength exceeds the required sludge tank design strength. Santrauka Monolitinių gelžbetoninių statinių konstrukcijų eksploatacijos trukmė ir patikimumas daugiausia priklauso nuo betonavimo technologijos ir procesų poveikių betonavimo bei pradinio kietėjimo metu. Straipsnyje nagrinėjami procesai, vykstantys betonuojant horizontaliąsias, nuožulniąsias ir vertikaliąsias monolitines gelžbetonines konstrukcijas. Atlikta betono mišinio slėgio į formas analizė. Tiriami pagrindiniai betonavimo technologijos parametrai, analizuojamas jų ryšys, pateikiamas nepertraukiamo betonavimo technologijos betonavimo greitis, intensyvumas, trukmė. Atlikti teoriniai skaičiavimai ir siūlomi praktiniai sprendimai pramoninių statinių statybai, naudojant šiuolaikinę slankiųjų klojinių technologiją. Ištirta cemento tipo, superplastiklių, temperatūros įtaka šviežiai suformuoto betono struktūriniam stipriui ir betono kietėjimo kinetikai. Nustatyti reikalavimai šviežiai suformuoto betono struktūriniam stipriui, betonavimo greičiui (klojinių kėlimui), vykdant statybą nepertraukiamos betonavimo technologijos metodu. Tyrimai pritaikyti vykdant cilindrinio dumblo pūdytuvo statybą slankiaisiais klojiniais.

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