arXiv subjects

Karo Michaelian

Publications and source records attributed to Karo Michaelian.

13 recordsLinked to original sources

arXiv2025

Abiogenesis on Different Star Types; a Dissipative Photochemical Perspective

From the non-equilibrium thermodynamic perspective of the origin of life as a photochemical dissipative structuring (entropy driven) process, we assess the probability of carbon-based life arising on Earth-like analogues orbiting different main-sequence stellar types (O7 V to M2 V). Using black-body spectra normalized to Earth's solar constant, we calculate surface photon fluxes for an atmosphere like early Archean Earth's in the productive dissipative structuring (P, soft UV-C + UV-B, 205-320 nm) and destructive ionization (D, hard UV-C + EUV, <205 nm) regions. Stationary concentrations of fundamental molecules and times to reach 99% of these are computed for different chemical degradation (e.g., deamination, hydrolysis, oxidation, etc.) rate constants of k = 10^{-7}, 10^{-6}, and 10^{-5} s^{-1}. For a nominal chemical degradation rate constant of k = 10^{-6} s^{-1} (t_{1/2}= 8 days), results show F-, G-, and K-type stars provide the highest stationary concentrations of fundamental molecules and short rise times (weeks to months), while quiescent M-type stars yield extremely low concentrations (~10^{-7} relative to G stars) and require years to reach even these values. Flaring M stars improve stationary concentrations by about an order of magnitude (~10^{-6} relative to G stars) but produce adverse planet surface environments for complex evolution through dissipative structuring. From this non-equilibrium thermodynamic perspective, carbon-based life like Earth's is to be found most probably on F-, G-, and high-mass K-type stars, with intelligent life arising only on G-type stars. Low mass K- and M-dwarfs are highly unlikely to harbor life unless seeded via panspermia. Biosignatures related to the thermodynamic imperative of photon dissipation are proposed.

physics.bio-ph↗

arXiv2020

A Dissipative Photochemical Origin of Life: The UVC Abiogenisis of Adenine

I describe the non-equilibrium thermodynamics and the photochemical mechanisms which may have been involved in the dissipative structuring, proliferation and evolution of the fundamental molecules at the origin of life from simpler and more common precursor molecules under the impressed UVC photon flux of the Archean. Dissipative structuring of the fundamental molecules is evidenced by their strong and broad wavelength absorption bands and rapid radiationless dexcitation in this wavelength region. Proliferation arises from the auto- and cross-catalytic nature of the intermediate products. Evolution towards states of concentration profiles of generally increasing photon disspative efficacy arises since the system has numerous stationary states, due to the non-linearity of the photochemical and chemical reactions with diffusion, which can be reached by amplification of a molecular concentration fluctuation near a bifurcation. An example is given of photochemical dissipative abiogenisis of adenine from the precursors HCN and H$_2$O within a fatty acid vesicle on a hot ocean surface, driven far from equilibrium by the impressed UVC light. The kinetic equations are resolved under different environmental conditions and the results analyzed within the framework of Classical Irreversible Thermodynamic theory.

physics.bio-ph↗

arXiv2019

Properties of cyanobacterial UV-absorbing pigments suggest their evolution was driven by optimizing photon dissipation rather than photoprotection

An ancient repertoire of UV absorbing pigments which survive today in the phylogenetically oldest extant photosynthetic organisms the cyanobacteria point to a direction in evolutionary adaptation of the pigments and their associated biota from largely UVC absorbing pigments in the Archean to pigments covering ever more of the longer wavelength UV and visible in the Phanerozoic.Such a scenario implies selection of photon dissipation rather than photoprotection over the evolutionary history of life.This is consistent with the thermodynamic dissipation theory of the origin and evolution of life which suggests that the most important hallmark of biological evolution has been the covering of Earths surface with organic pigment molecules and water to absorb and dissipate ever more completely the prevailing surface solar spectrum.In this article we compare a set of photophysical photochemical biosynthetic and other germane properties of the two dominant classes of cyanobacterial UV absorbing pigments the mycosporine like amino acids MAAs and scytonemins.Pigment wavelengths of maximum absorption correspond with the time dependence of the prevailing Earth surface solar spectrum and we proffer this as evidence for the selection of photon dissipation rather than photoprotection over the history of life on Earth.

physics.bio-ph↗

arXiv2018

Prebiotic Fatty Acid Vesicles through Photochemical Dissipative Structuring

We describe the photochemical dissipative structuring of fatty acids from CO and CO2 saturated water under the solar UVC and UVA photon potential prevalent at Earth's surface during the Archean. Their association into vesicles and their subsequent association with other fundamental molecules of life such as RNA, DNA and carotenoids to form the first protocells is also suggested to occur through photochemical dissipative structuring. In particular, it is postulated that the first vesicles were formed from conjugated linolenic (C18:3n-3) and parinaric (C18:4n-3) acids which would form vesicles stable at the high temperatures (~85 °C) and the somewhat acidic pH values (6.0-6.5) of the Archean ocean surface, resistant to divalent cation salt flocculation, permeable to ions and small charged molecules, but impermeable to short DNA and RNA, and, most importantly, highly dissipative in the prevailing UVC+UVA regions.

physics.bio-ph↗

arXiv2018

Origin of Information Encoding in Nucleic Acids through a Dissipation-Replication Relation

Ultraviolet light incident on organic material can initiate its spontaneous dissipative structuring into chromophores which can then catalyze their own replication. This may have been the case for one of the most ancient of all chromophores dissipating the Archean UVC photon flux, the nucleic acids. Under the empirically established imperative of increasing entropy production, nucleic acids with affinity to particular amino acids which foment UVC photon dissipation would have been "thermodynamically selected" through this dissipation-replication relation. Indeed, we show here that those amino acids with characteristics most relevant to fomenting UVC photon dissipation are precisely those with greatest affinity to their codons or anticodons. This could provide a physical-chemical mechanism for the accumulation of information in nucleic acids relevant to the dissipation of the externally imposed photon potential. This mechanism could provide a non-equilibrium thermodynamic foundation, based on increasing global entropy production of the biosphere, for the tenants of Darwinian natural selection. We show how this mechanism might have begun operating at the origin of life in the Archean, and how, in fact, it still operates today, albeit indirectly through complex biosynthetic pathways now operating in the visible.

physics.bio-ph↗

arXiv2016

Thermodynamic Explanation for the Cosmic Ubiquity of Organic Pigments

There is increasingly more evidence being accumulated for the occurrence of large amounts of organic material in the cosmos, particularly in the form of aromatic compounds. These molecules can be found on the surface of Earth and Mars, in the atmospheres of the larger planets and on many of their satellites, on asteroids, comets, meteorites, the atmospheres of red giant stars, interstellar nebulae, and in the spiral arms of galaxies. Many of these environments are expected to be of low temperature and pressure, implying that the Gibbs free energy for the formation of these complex molecules should be positive and large, suggesting that their existence could only be attributed to non-equilibrium thermodynamic processes. In this article we first review the evidence for the abundance of these molecules in the cosmos and then describe how the ubiquity can be explained from within the framework of non-equilibrium thermodynamics on the basis of the catalytic properties of these pigment molecules in dissipating photons of the ultraviolet and visible emission spectra of neighboring stars, leading to greater local entropy production. A relation between the maximum wavelength of absorption of these organic pigments and the corresponding stellar photon environment, provides a guide to determining which aromatic compounds are most probable in a given stellar neighborhood, a postulate that can be verified on Earth. It is suggested that at least some of the baryonic dark matter may be associated with these molecules which emit in the extreme infrared with many, but weak, emission lines, thus so far escaping detection. This thermodynamic explanation for the ubiquity of these organic molecules also has relevance to the possibility of life, both as we know it, and as we may not know it, throughout the universe.

astro-ph.EP↗

arXiv2014

Fundamental Molecules of Life are Pigments which Arose and Evolved to Dissipate the Solar Spectrum

The driving force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate. In the upper atmosphere of today, oxygen and ozone derived from life processes are performing the short wavelength UVC and UVB dissipation. On Earth's surface, water and organic pigments in water facilitate the near UV and visible photon dissipation. The first organic pigments probably formed, absorbed, and dissipated at those photochemically active wavelengths in the UVC that could have reached Earth's surface during the Archean. Proliferation of these pigments can be understood as an autocatalytic photochemical process obeying non-equilibrium thermodynamic directives related to increasing solar photon dissipation rate. Under these directives, organic pigments would have evolved over time to increase the global photon dissipation rate by; 1) increasing the ratio of their effective photon cross sections to their physical size, 2) decreasing their electronic excited state life times, 3) quenching non-radiative de-excitation channels (e.g. fluorescence), 4) covering ever more completely the solar spectrum, and 5) dispersing into an ever greater surface area of Earth. From knowledge of the evolution of the spectrum of G-type stars, and considering the most probable history of the transparency of Earths atmosphere, we construct the most probable surface solar spectrum as a function of time and compare this with the history of molecular absorption maxima obtained from the available data in the literature. This comparison supports the thermodynamic dissipation theory for the origin of life, constrains models for Earth's early atmosphere, and sheds some new light on the origin of photosynthesis.

physics.bio-ph↗

arXiv2013

A non-linear irreversible thermodynamic perspective on organic pigment proliferation and biological evolution

The most important thermodynamic work performed by life today is the dissipation of the solar photon flux into heat through organic pigments in water. From this thermodynamic perspective, biological evolution is thus just the dispersal of organic pigments and water throughout Earth's surface, while adjusting the gases of Earth's atmosphere to allow the most intense part of the solar spectrum to penetrate the atmosphere and reach the surface to be intercepted by these pigments. The covalent bonding of atoms in organic pigments provides excited levels compatible with the energies of these photons. Internal conversion through vibrational relaxation to the ground state of these excited molecules when in water leads to rapid dissipation of the solar photons into heat, and this is the major source of entropy production on Earth. A non-linear irreversible thermodynamic analysis shows that the proliferation of organic pigments on Earth is a direct consequence of the pigments catalytic properties in dissipating the solar photon flux. A small part of the energy of the photon goes into the production of more organic pigments and supporting biomass, while most of the energy is dissipated and channeled into the hydrological cycle through the latent heat of vaporization of surface water. By dissipating the surface to atmosphere temperature gradient, the hydrological cycle further increases the entropy production of Earth. This thermodynamic perspective of solar photon dissipation by life has implications to the possibility of finding extra-terrestrial life in our solar system and the Universe.

nlin.AO↗

arXiv2010

Homochirality through Photon-Induced Melting of RNA/DNA: the Thermodynamic Dissipation Theory of the Origin of Life

The homochirality of the molecules of life has been a vexing problem with no generally accepted solution to date. Since a racemic mixture of chiral nucleotides frustrates the extension and replication of RNA and DNA, understanding the origin of homochirality has important implications to the investigation of the origin of life. Here we suggest a novel solution to the homochirality problem based on a recently proposed thermodynamic dissipation theory for the origin of life. Homochirality is suggested to have been incorporated gradually into the emerging life as a result of asymmetric right- over left-handed photon-induced denaturation of RNA/DNA occurring when Archean sea surface temperatures became close to the denaturing temperatures of RNA/DNA. This differential denaturing success would have been promoted by the somewhat right-handed circularly polarized submarine light of the late afternoon when surface water temperatures are highest, and a negative circular dichroism band extending from 220 nm up to 260 nm for small segments of RNA/DNA. A numerical model is presented demonstrating the efficacy of such a mechanism in procuring 100% homochirality of RNA or DNA from an original racemic solution in less than 500 Archean years assuming a photon absorption threshold for replication representing the hydrogen bonding energies between complimentary strands. Because cholesteric D-nucleic acids have greater affinity for L-amino acids due to a positive structural complementarity, and because D-RNA/DNA+L-amino acid complexes also have a negative circular dichroism band between 200 - 300 nm, the homochirality of amino acids can also be explained by the theory.

physics.bio-ph↗

arXiv2007

Negating Negative Heat Capacity in Nanoclusters

It is shown that negative heat capacity in nanoclusters is an artifact of applying equilibrium thermodynamic formalism on a small system trapped out of equilibrium in a particular structural motif representing only part of the energetically available phase space volume. Trapping may occur in either the canonical or microcanonical ensemble, but it is unavoidable in the microcanonical. A more general consequence of trapping is that all macroscopic quantities determined for nanoclusters will depend on the initial conditions.

cond-mat.mtrl-sci↗

arXiv2003

Negative heat capacity of sodium clusters

Heat capacities of Na_N, N = 13, 20, 55, 135, 142, and 147, clusters have been investigated using a many-body Gupta potential and microcanonical molecular dynamics simulations. Negative heat capacities around the cluster melting-like transition have been obtained for N = 135, 142, and 147, but the smaller clusters (N = 13, 20, and 55) do not show this peculiarity. By performing a survey of the cluster potential energy landscape (PEL), it is found that the width of the distribution function of the kinetic energy and the spread of the distribution of potential energy minima (isomers), are useful features to determine the different behavior of the heat capacity as a function of the cluster size. The effect of the range of the interatomic forces is studied by comparing the heat capacities of the Na_55 and Cd_55 clusters. It is shown that by decreasing the range of the many-body interaction, the distribution of isomers characterizing the PEL is modified appropriately to generate a negative heat capacity in the Cd_55 cluster.

physics.atm-clus↗

arXiv2002

Melting of sodium clusters

Thermal stability properties and the melting-like transition of Na_n, n=13-147, clusters are studied through microcanonical molecular dynamics simulations. The metallic bonding in the sodium clusters is mimicked by a many-body Gupta potential based on the second moment approximation of a tight-binding Hamiltonian. The characteristics of the solid-to-liquid transition in the sodium clusters are analyzed by calculating physical quantities like caloric curves, heat capacities, and root-mean-square bond length fluctuations using simulation times of several nanoseconds. Distinct melting mechanisms are obtained for the sodium clusters in the size range investigated. The calculated melting temperatures show an irregular variation with the cluster size, in qualitative agreement with recent experimental results. However, the calculated melting point for the Na_55 cluster is about 40 % lower than the experimental value.

physics.atm-clus↗

arXiv2002

A Non-equilibrium Thermodynamic Framework for the Dynamics and Stability of Ecosystems

The population dynamics and stability of ecosystems of interacting species is studied from the perspective of non-equilibrium thermodynamics by assuming that species, through their biotic and abiotic interactions, are units of entropy production and exchange in an open thermodynamic system with constant external constraints. Within the context of the linear theory of irreversible thermodynamics, such a system will naturally evolve towards a stable stationary state in which the production of entropy within the ecosystem is at a local minimum value. It is shown that this extremal condition leads to equations for the stationary (steady) state population dynamics of interacting species, more general than those of Lotka-Volterra, and to conditions on the parameters of the community interaction matrix guaranteeing ecosystem stability. The paradoxical stability of real complex ecosystems thus has a simple explanation within the proposed framework. Furthermore, it is shown that the second law of thermodynamics constrains the inter- and intra-species interaction coefficients in the sense of maintaining stability during evolution from one stationary state to another. A firm connection is thus established between the second law of thermodynamics and natural selection.

physics.bio-ph↗