Experimental Studies of the Transitions Between Stationary States in a Bistable Chemical System

1984 ◽  
pp. 70-78 ◽  
Author(s):  
J. C. Roux ◽  
H. Saadaoui ◽  
P. de Kepper ◽  
J. Boissonade
Keyword(s):  
Experimental Studies ◽  
Chemical System ◽  
Stationary States

Oscillations, glow and ignition in carbon monoxide oxidation in an open system. I. Experimental studies of the ignition diagram and the effects of added hydrogen

1985 ◽  
Vol 397 (1812) ◽  
pp. 21-44 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Open System ◽  
Reaction Rate ◽  
Experimental Studies ◽  
Reaction Rates ◽  
Step Change ◽  
Stable Node ◽  
Stationary States ◽  
Show Evidence ◽  
Oxidation Of Carbon Monoxide

The oxidation of carbon monoxide in equimolar mixtures (CO + O 2 ) has been studied in a well-stirred open system (0.5 dm 3 ) at vessel temperatures in the range 700-840 K, and reactant pressures up to 100 Torr ( ca . 13.3 kPa) at a mean residence time of 8.5 s. Stationary states are established and oscillatory states sustained indefinitely in this system. The effect of small quantities of added hydrogen is studied by a carefully controlled, continuous supplement to the principal reactants. Four different modes of reaction (I-IV) have been characterized, and conditions for their occurrence mapped on a reactant pressure-vessel temperature ( p - T a ) ignition diagram. Most boundaries are quite sharp, and some show evidence of hysteresis. Close to the axes, reaction is slow, non-luminous and non-oscillatory (I). Within a first broad promontory (II) reaction is accompanied by steady luminescence. Crossing the boundary is not accompanied by a step change in reaction rate, but there is a change in character from stable node (in I) to stable focus (in II). Auto-oscillatory luminescence occurs in a closed region (III) wholly within the promontory II. The effects of adding hydrogen on all these modes is to increase the reaction rates markedly and to make them non-isothermal; the boundaries between I, II and III are not as greatly affected. However, systems to which more than 0.10% H 2 have been added also display a new mode, of oscillatory ignition. This appears at first in a region (IV) of high temperatures and pressures but as more H 2 is increased its realm expands and it eventually dominates the ignition diagram, invading the region of luminescence and soon obliterating the oscillatory part completely.

scholarly journals Self-Reproduction and Darwinian Evolution in Autocatalytic Chemical Reaction Systems

Life ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 308
Author(s):  
Sandeep Ameta ◽  
Yoshiya J. Matsubara ◽  
Nayan Chakraborty ◽  
Sandeep Krishna ◽  
Shashi Thutupalli
Keyword(s):  
Experimental Evolution ◽  
Experimental Studies ◽  
Theoretical Work ◽  
Living System ◽  
Darwinian Evolution ◽  
Chemical System ◽  
Chemical Systems ◽  
Open Questions ◽  
Scientific Questions ◽  
Emergence Of Life

Understanding the emergence of life from (primitive) abiotic components has arguably been one of the deepest and yet one of the most elusive scientific questions. Notwithstanding the lack of a clear definition for a living system, it is widely argued that heredity (involving self-reproduction) along with compartmentalization and metabolism are key features that contrast living systems from their non-living counterparts. A minimal living system may be viewed as “a self-sustaining chemical system capable of Darwinian evolution”. It has been proposed that autocatalytic sets of chemical reactions (ACSs) could serve as a mechanism to establish chemical compositional identity, heritable self-reproduction, and evolution in a minimal chemical system. Following years of theoretical work, autocatalytic chemical systems have been constructed experimentally using a wide variety of substrates, and most studies, thus far, have focused on the demonstration of chemical self-reproduction under specific conditions. While several recent experimental studies have raised the possibility of carrying out some aspects of experimental evolution using autocatalytic reaction networks, there remain many open challenges. In this review, we start by evaluating theoretical studies of ACSs specifically with a view to establish the conditions required for such chemical systems to exhibit self-reproduction and Darwinian evolution. Then, we follow with an extensive overview of experimental ACS systems and use the theoretically established conditions to critically evaluate these empirical systems for their potential to exhibit Darwinian evolution. We identify various technical and conceptual challenges limiting experimental progress and, finally, conclude with some remarks about open questions.

Mobilization of Residual Oil Under Equilibrium and Nonequilibrium Conditions

1983 ◽  
Vol 23 (05) ◽  
pp. 781-790 ◽  
Author(s):  
Andrew C. Lam ◽  
Robert S. Schechter ◽  
William H. Wade
Keyword(s):  
Mass Transfer ◽  
Oil Recovery ◽  
Chemical Equilibrium ◽  
Capillary Number ◽  
Complex Function ◽  
Experimental Studies ◽  
Marangoni Effect ◽  
Continuous Phase ◽  
Chemical System ◽  
Residual Oil

Abstract A microvisual study of residual oil mobilization that uses a relatively simple chemical system consisting of water, n-propanol, and cyclohexane is presented. Two different classes of experiments were performed to determine the sensitivity of the capillary number required to displace a particular residual oil globule from chemical equilibrium. It was found that under certain circumstances the capillary number required to mobilize the oil drop could be reduced greatly if the displacing phase contained more alcohol than it would in equilibrium with the trapped phase. Experiments clearly demonstrated that spontaneous emulsification by a diffusion and stranding mechanism could not account for the differences between equilibrium and nonequilibrium capillary numbers. Experimental observations did correlate well with the development of interfacial turbulence (Marangoni effect). Variations that, according to theory, tended to enhance the level of interfacial turbulence between the equilibrium and nonequilibrium capillary numbers were observed. The importance of the Marangoni effect relative to laboratory oil recovery experiments is discussed. A second class of experiments consisted of observing, the displacement of residual oil globules that had been increased in volume (swollen) by mass transfer from a continuous phase flowing too slowly to displace the drop. Once the residual oil globule attained equilibrium with the continuous phase, the flooding velocity was increased until the swollen globule was displaced. Surpassingly, slightly swollen globules required a larger capillary, number for [mobilization than the original drop. Thus. the capillary number for swollen residual oil globules goes through a maximum as a function of the degree of volume increase. The precise position of the maximum varies for each globule since mobilization is a complex function of geometry. Introduction The mobilization of residual oil globules by contact with a flowing surfactant-rich solution (microemulsion) is a complex process not fully understood. Most of the complexities arise because the trapped phase and the surfactant solution are not in chemical equilibrium and there is mass transfer from one phase to the other. If the two phases are in equilibrium, then the mechanism ofmobilization appears to be satisfactorily established. An oil globule is displaced when the interfacial tension (IFT) is reduced to an extent that the pressure gradient created by the motion of the continuous phase is sufficient to overcome the capillary forces holding., the globule in place. Several experimental studies have been reported and the concept of a critical capillary number has evolved. The reduction of IFT is considered to be an important factor in the selection of a suitable solution for oil recovery. SPEJ P. 781^

3-D reconstruction and analysis of mammalian mitotic spindle structure

1992 ◽  
Vol 50 (1) ◽  
pp. 578-579
Author(s):  
Kent McDonald ◽  
David Mastronarde ◽  
Rubai Ding ◽  
Eileen O'Toole ◽  
J. Richard McIntosh
Keyword(s):  
Cross Sections ◽  
Mitotic Spindle ◽  
Experimental Studies ◽  
Video Camera ◽  
Three Dimensions ◽  
Mitotic Spindles ◽  
Black And White ◽  
Reconstruction Methods ◽  
Spindle Structure ◽  
Tissue Culture Line

Mammalian spindles are generally large and may contain over a thousand microtubules (MTs). For this reason they are difficult to reconstruct in three dimensions and many researchers have chosen to study the smaller and simpler spindles of lower eukaryotes. Nevertheless, the mammalian spindle is used for many experimental studies and it would be useful to know its detailed structure.We have been using serial cross sections and computer reconstruction methods to analyze MT distributions in mitotic spindles of PtK cells, a mammalian tissue culture line. Images from EM negatives are digtized on a light box by a Dage MTI video camera containing a black and white Saticon tube. The signal is digitized by a Parallax 1280 graphics device in a MicroVax III computer. Microtubules are digitized at a magnification such that each is 10-12 pixels in diameter.

Effects of Attachment Styles on the Experience of Equity in Heterosexual Couples Relationships

2003 ◽  
Vol 50 (4) ◽  
pp. 298-310 ◽  
Author(s):  
Ina Grau ◽  
Jörg Doll
Keyword(s):  
Attachment Theory ◽  
Attachment Style ◽  
Intimate Relationships ◽  
Attachment Styles ◽  
Experimental Studies ◽  
The Other ◽  
Heterosexual Couples ◽  
Secure Attachment ◽  
Dependent Variables ◽  
Equity Ratio

Abstract. Employing one correlational and two experimental studies, this paper examines the influence of attachment styles (secure, anxious, avoidant) on a person’s experience of equity in intimate relationships. While one experimental study employed a priming technique to stimulate the different attachment styles, the other involved vignettes describing fictitious characters with typical attachment styles. As the specific hypotheses about the single equity components have been developed on the basis of the attachment theory, the equity ratio itself and the four equity components (own outcome, own input, partner’s outcome, partner’s input) are analyzed as dependent variables. While partners with a secure attachment style tend to describe their relationship as equitable (i.e., they give and take extensively), partners who feel anxious about their relationship generally see themselves as being in an inequitable, disadvantaged position (i.e., they receive little from their partner). The hypothesis that avoidant partners would feel advantaged as they were less committed was only supported by the correlational study. Against expectations, the results of both experiments indicate that avoidant partners generally see themselves (or see avoidant vignettes) as being treated equitably, but that there is less emotional exchange than is the case with secure partners. Avoidant partners give and take less than secure ones.

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