scholarly journals Isothermal Dendritic Growth - A Low Gravity Experiment

1986 ◽  
Vol 87 ◽  
Author(s):  
M. E. Glicksman ◽  
E. Winsa ◽  
R. C. Hahn ◽  
T. A. Lograsso ◽  
E. R. Rubinstein ◽  
...  
Keyword(s):  
Dendritic Growth ◽  
Diffusion Processes ◽  
Free Fall ◽  
Current Approach ◽  
Low Earth Orbit ◽  
Length Scale ◽  
Concentration Gradients ◽  
Volumetric Expansion ◽  
Volumetric Expansion Coefficient ◽  
Orbital Free

AbstractThe growth of dendrites in pure melts and alloys is controlled by diffusion-limited transport of heat and/or solute. The presence of temperature or concentration gradients within a molten phase subject to gravitational forces generally promotes convection, which in turn, modifies the diffusion processes. The vigor of melt convection is controlled by several parameters often expressed as a lumped dimensionless group, the Grashof number Gr = gβΔTℓ3/ν2, where g is the acceleration due to gravity; is the volumetric expansion coefficient; ΔT is the undercooling; ν is the kinematic viscosity; and ℓ is the relevant length scale, e.g., the characteristic diffusion distance. Dendritic growth, by its nature, does not permit independent manipulation of the controlling length scale, ℓ, which is determined by materials properties (e.g. diffusion coefficient or thermal diffusivity) and the undercooling or supersaturation. The reduction of g through orbital free fall is often the only practical way to lower Gr sufficiently to permit careful observation of the morphological and kinetic characteristics of isothermal dendritic growth. Previously conducted ground-based studies and the current approach to performing these studies in low earth orbit will be described.

Dendritic Growth Dynamics: Steady And Oscillatory States

2000 ◽  
Vol 652 ◽  
Author(s):  
J.E. Frei ◽  
M.E. Glicksman ◽  
J.C. LaCombe ◽  
M.B. Koss ◽  
C. Giummarra ◽  
...  
Keyword(s):  
Dendritic Growth ◽  
Space Shuttle ◽  
Function Analysis ◽  
Dynamical Behavior ◽  
Growth Dynamics ◽  
Pivalic Acid ◽  
Side Branch ◽  
Low Earth Orbit ◽  
Video Data ◽  
Growth Speed

ABSTRACTMicrogravity dendritic growth experiments, conducted aboard the space shuttle Columbia (STS-87) in November/December 1997, are analyzed and discussed. In-situ video images now reveal that pivalic acid (PVA) dendrites growing in the diffusion-controlled environment of low-earth orbit exhibit a range of growth behaviors, including steady, transient, and oscillatory states. The observed transient features of the growth process are being studied with the objective of understanding their physical mechanisms. Some transients in the observed growth speed are thought to arise as an intrinsic aspect of the evolving dendritic pattern. Variability in the growth speed observed from a sequence of identical runs at equal supercooling suggests that self-interactions of the dendrite remain important throughout the development of the dendritic pattern. A Greens function analysis of the near-tip diffusion sources contributing to the local field at the tip suggests that strong non-local interactions exist well into the time-dependent side-branch region of real dendrites. Video data obtained at 30 fps allow the first application of discrete Fourier transform methods (Lomb periodograms) to the digitized images of dendritic growths under quiescent microgravity conditions. These observations provide evidence for the appearance of characteristic frequencies in the tip shape and its dynamical behavior. Some of the frequency bands observed coincide closely with the ratio of the dendritic tip growth speed divided by the side branch spacing. Other observed lower frequencies remain as yet unexplained. These data, and their interpretations, are discussed in this paper.

Influence of the Manufacturing Process on the Local Properties of Bronze-Bonded Grinding Tools

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Abdelhamid Bouabid ◽  
Berend Denkena ◽  
Bernd Breidenstein ◽  
Alexander Krödel
Keyword(s):  
Manufacturing Process ◽  
Diffusion Processes ◽  
Initial Mixture ◽  
Mechanical And Thermal Properties ◽  
Concentration Gradients ◽  
Workpiece Material ◽  
Bond Interface ◽  
Local Properties ◽  
Grinding Tool ◽  
Process Behavior

Abstract The process behavior of a grinding tool is defined by the sum of interactions between the active abrasive grains and the workpiece. These interactions depend on the workpiece material, the manipulated parameters of the grinding process, and the tool properties. The tool properties are defined within the tool manufacturing process. In this context, the effects of the abrasive, the bond, and the sinter process on the global properties such as hardness, porosity, and fracture strength of the grinding layer are content of several research works. In contrast to this, the effects on the local properties, which define the grain/bond interface and therefore the process behavior at microscopic scale, have not yet been identified. This paper deals with identifying the influence of the sintering process on the local properties of the grinding layer. This is achieved by investigating the densification as well as the bond microstructure depending on the sintering parameters and on the specification of the initial mixture. As a use case, the bronze bond is considered. The results show that the input parameters have a significant impact on the homogeneity of the grinding layer. Due to the diffusion processes during sintering, there are densification gradients as well as tin concentration gradients in the grinding layer. The local tin concentration gradients imply different local mechanical and thermal properties. For this reason, each abrasive grain has unique interface properties.

scholarly journals STUDIES ON SHELL FORMATION

1961 ◽  
Vol 9 (4) ◽  
pp. 761-771 ◽  
Author(s):  
Norimitsu Watabe ◽  
Karl M. Wilbur
Keyword(s):  
Crystal Growth ◽  
Dendritic Growth ◽  
Three Dimensional ◽  
Outer Part ◽  
Organic Matrix ◽  
Transitional Zone ◽  
Homogeneous State ◽  
Concentration Gradients ◽  
Strong Concentration ◽  
Small Crystals

Details of crystal growth in the calcitostracum of Crassostrea virginica have been studied with the purpose of analyzing the formation of the overlapping rows of oriented tabular crystals characteristic of this part of the shell. Crystal elongation, orientation, and dendritic growth suggest the presence of strong concentration gradients in a thin layer of solution in which crystallization occurs. Formation of the overlapping rows can be explained by three processes observed in the shell: a two-dimensional tree-like dendritic growth in which one set of crystal branchings creeps over an adjacent set of branchings; three-dimensional dendritic growth; and growth by dislocation of crystal surfaces. Multilayers of crystals may thus be formed at one time. This is favored by infrequent secretion of a covering organic matrix which would inhibit crystal growth. The transitional zone covering the outer part of the calcitostracum and the inner part of the prismatic region is generally characterized by aggregates of small crystals with definite orientation. Growth in this zone appears to take place in a relatively homogeneous state of solution without strong concentration gradients. Thin membranes and bands of organic matrix were commonly observed in the transitional zone bordering the prismatic region. The membrane showed a very fine oriented network pattern.

scholarly journals Spatial organization of the Ran pathway by microtubules in mitosis

2016 ◽  
Vol 113 (31) ◽  
pp. 8729-8734 ◽  
Author(s):  
Doogie Oh ◽  
Che-Hang Yu ◽  
Daniel J. Needleman
Keyword(s):  
Signaling Pathways ◽  
Cell Size ◽  
General Feature ◽  
Spatial Organization ◽  
Nuclear Protein ◽  
Soluble Proteins ◽  
Length Scale ◽  
Spectroscopy Technique ◽  
Concentration Gradients ◽  
Distribution Of Components

Concentration gradients of soluble proteins are believed to be responsible for control of morphogenesis of subcellular systems, but the mechanisms that generate the spatial organization of these subcellular gradients remain poorly understood. Here, we use a newly developed multipoint fluorescence fluctuation spectroscopy technique to study the ras-related nuclear protein (Ran) pathway, which forms soluble gradients around chromosomes in mitosis and is thought to spatially regulate microtubule behaviors during spindle assembly. We found that the distribution of components of the Ran pathway that influence microtubule behaviors is determined by their interactions with microtubules, resulting in microtubule nucleators being localized by the microtubules whose formation they stimulate. Modeling and perturbation experiments show that this feedback makes the length of the spindle insensitive to the length scale of the Ran gradient, allows the spindle to assemble outside the peak of the Ran gradient, and explains the scaling of the spindle with cell size. Such feedback between soluble signaling pathways and the mechanics of the cytoskeleton may be a general feature of subcellular organization.

Characterization of electrical charge separation at the interface of two aqueous solutions in the presence of concentration gradients and cation/anion mobility ratio asymmetry

Open Physics ◽  
2005 ◽  
Vol 3 (1) ◽  
Author(s):  
Adrian Cernescu ◽  
Tudor Luchian
Keyword(s):  
Diffusion Processes ◽  
Ionic Mobility ◽  
Electrical Charge ◽  
Diffusion Potential ◽  
Mobility Ratio ◽  
Ionic Diffusion ◽  
Measuring Instruments ◽  
Concentration Gradients ◽  
Diffusion Constants ◽  
Physical Consequences

AbstractPhysical consequences of ionic diffusion processes play a major role on the outcome of electrophysiology experiments due to both their contribution to the ionic transmembrane transport and phenomena taking place at the measuring instruments interface. As most of the time heterogenities in biological media with respect to ionic diffusion constants are disregarded, we intended to look upon the general case of ionic diffusion at the interface of two liquids on which gradients of these diffusion constants no longer can be neglected. We developed a theoretical model for the diffusion potential which emerges at an aqueous interface under gradients of concentration and diffusion constants. The experimental validation of our model was achieved through potential difference measurements of the diffusion potential between two solutions containing sodium chloride (NaCl) and glycerine solutions of various concentrations. Within the studied domain of the electrical charge mobility ratio, we noticed that experimental results are in agreement with the theoretically inferred diffusion potential values. This demonstrates that the resulting relationship for the diffusion potential inferred from our model could be applied for other cases, as well. When the ionic solutions contains an indefinite quantity of glycerine or an unknown substance able to modify diffusion constants of sodium and chloride, it was shown that through measurements of the diffusion potential one can infer the unknown concentration of glycerine and the modified ionic mobility ratio. This, in turn, builds up the foundation for a novel yet simple and efficient analitycal sensing device for quantitative determination in the field.

scholarly journals Thermal Transitions of Cocoa Butter: A Novel Characterization Method by Temperature Modulation

Foods ◽  
2019 ◽  
Vol 8 (10) ◽  
pp. 449 ◽  
Author(s):  
Julia Rocha Gouveia ◽  
Kelly Cristina de Lira Lixandrão ◽  
Lara Basílio Tavares ◽  
Paulo Henrique Lixandrão Fernando ◽  
Guilherme Elias Saltarelli Garcia ◽  
...  
Keyword(s):  
Cocoa Butter ◽  
Expansion Coefficient ◽  
Standard Technique ◽  
Temperature Modulation ◽  
Thermal Transitions ◽  
Scanning Calorimetry ◽  
Volumetric Expansion ◽  
New Information ◽  
Temperature Ramps ◽  
Volumetric Expansion Coefficient

For the first time, the novel experimental technique Temperature Modulated Optical Refractometry (TMOR) was employed for cocoa butter thermal transitions characterization. The average refractive index (NMEAN), the volume (v) change, and the volumetric expansion coefficient ( β q ) as well as the dynamic quantities β ′ and β ″ (real and imaginary volumetric expansion coefficient, respectively) were monitored during cooling and heating and compared to the heat flow curves obtained via the standard technique dynamic scanning calorimetry (DSC). The investigation of these quantities showed that TMOR analysis can yield not only thermal transitions temperatures that are comparable to DSC results, but also some new thermal events that are not detected by DSC. This outcome suggests that TMOR might provide some additional insights on cocoa butter melting and crystallization by means of frequency-dependent measurements due to temperature modulation. This new information that can be accessed during temperature ramps might provide a deeper insight into thermal behavior of fat-based foods, evidencing TMOR value as a tool for thermal transitions investigation.

Production and Characterization of Sugary Cassava Syrup

2013 ◽  
Vol 9 (1) ◽  
pp. 39-44
Author(s):  
Hugo A. L. Souza ◽  
Thaís C. L. Souza ◽  
Alessandra S. Lopes ◽  
Rosinelson S. Pena
Keyword(s):  
Activation Energy ◽  
Manihot Esculenta ◽  
Reducing Sugars ◽  
Sugar Content ◽  
Free Sugar ◽  
Total Sugars ◽  
Volumetric Expansion ◽  
Volumetric Expansion Coefficient ◽  
Newtonian Behavior

AbstractA group of cassava landraces that occur naturally in Amazonia (Manihot esculenta Crantz) are known as mandiocaba or sugary cassava because they have high free sugar content, making them a possible feedstock for the production of syrup. The objective of the study was to evaluate the technological viability of obtaining sugary cassava syrup and to characterize the physical and physicochemical properties of the product. The yield of the syrup (80 °Brix) obtained from the manipueira (liquid obtained by crushing and filtering the cassava) concentration was 262.72 g per plant. The reducing sugars represented 77.26% of total sugars, the density was 1.4210 g cm–3 at 20°C, and the volumetric expansion coefficient was 38.6 m K–1. The Newtonian behavior and activation energy (≥69.65 kJ gmol–1) were similar to that of honey found in the literature.

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