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Lars Björn doubts our assertion that 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 global solar photon dissipation. Björn bases his critique on the fact that the albedo of non-biological material can sometimes be lower than that of biological material and concludes that such examples counter our assertion. Our reply to Björn, however, is that albedo (reflection) is only one factor involved in the entropy production through photon dissipation occurring in the interaction of light with material. The other contributions to entropy production, which were listed in our article, are (1) the shift towards the infrared of the emitted spectrum (including a wavelength-dependent emissivity), (2) the diffuse reflection and emission of light into a greater outgoing solid angle, and (3) the heat of photon dissipation inducing evapotranspiration in the pigmented leaf, thereby coupling to the abiotic dissipative processes of the water cycle, which, besides shifting the emitted spectrum even further towards the infrared, promotes pigment production over the entire Earth surface. His analysis, therefore, does not provide a legitimate reason for doubting our assertion that life and evolution are driven by photon dissipation. We remain emphatic in our assertion that the fundamental molecules of life were originally dissipatively structured UV-C pigments arising in response to the thermodynamic imperative of dissipating the prevailing Archean solar spectrum. In the following, we respond to Björn's comment using the same section headings.

Theories on life’s origin generally acknowledge the advantage of a semi-permeable vesicle (protocell) for enhancing the chemical reaction–diffusion processes involved in abiogenesis. However, more and more evidence indicates that the origin of life is concerned with the photo-chemical dissipative structuring of the fundamental molecules under soft UV-C light (245–275 nm). In this paper, we analyze the Mie UV scattering properties of such a vesicle created with long-chain fatty acids. We find that the vesicle could have provided early life with a shield from the faint but destructive hard UV-C ionizing light (180–210 nm) that probably bathed Earth’s surface from before the origin of life and at least until 1200 million years after, until the formation of a protective ozone layer as a result of the evolution of oxygenic photosynthesis.

We have suggested that the abiogenisis of life around the beginning of the Archean may have been an example of microscopic dissipative structuring of UVC pigments (the fundamental molecules of life) under the prevailing surface UV solar spectrum. In a previous article in this series, we have describe the non-equilibrium thermodynamics and the photochemical mechanisms which may have been involved in the dissipative structuring of the purines adenine and hypoxanthine from the common precursor molecules of HCN and water under UVC light. In this article we extend our analysis to include the production of the other two important purines, guanine and xanthine, from these same precursors. The photochemical reactions are presumed to occur within a fatty acid vesicle floating on a hot ocean surface exposed to the prevailing UV light. Reaction-diffusion equations are resolved under different environmental conditions. Significant amounts of adenine (∼10−5 M) and guanine (∼10−6 M) are obtained within only a few months at 80 °C under plausible initial concentrations of HCN and cyanogen (a photochemical product of HCN).

Lars Björn, in his critique of our article, doubts our assertion that at the origin of life the fundamental molecules of life (those in the three domains) were UVC pigments, dissipatively structured under a thermodynamic imperative to absorb and dissipate this UVC light into heat. Björn bases his critique on the suggestion that non-living material can be more photon absorbing than living material. He gives a number of examples in which he shows that the albedo of material devoid of life is lower than that of biotic material and concludes that these examples counter our assertion. However, Björn makes the erroneous assumption that albedo (reflection) is the only important factor related to photon dissipation (entropy production) occurring in the light-pigment interaction in living systems. He ignores the other contributions to entropy production due to the photon interaction which were listed in our article; 1) the shift towards the infrared of the emitted spectrum, 2) the diffuse emission and reflection of light into a greater outgoing solid angle, 3) the coupling of photon-induced evapotranspiration in the pigmented leaf to further photon dissipating processes such as the water cycle, which further allows dissipating biopigments to flourish over all of Earth’s surface. His assumption is therefore incorrect and his analysis does not provide legitimate reason for doubting our assertion that the fundamental molecules of life arose as pigments as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum. In the following, we respond to each critique using the same section headings of Björn’s Comment.

There is little doubt that life’s origin followed from the known physical and chemical laws of Nature. The most general scientific framework incorporating the laws of Nature and applicable to most known processes to good approximation, is that of thermodynamics and its extensions to treat out-of-equilibrium phenomena. The event of the origin of life should therefore also be amenable to such an analysis. In this review paper, I describe the non-equilibrium thermodynamic foundations of the origin of life for the non-expert from the perspective of the “Thermodynamic Dissipation Theory for the Origin of Life” which is founded on Classical Irreversible Thermodynamic theory developed by Lars Onsager, Ilya Prigogine, and coworkers. A Glossary of Thermodynamic Terms can be found at the end of the article to aid the reader.

It has been conjectured that the origin of the fundamental molecules of life, their proliferation over the surface of Earth, and their complexation through time, are examples of photochemical dissipative structuring, dissipative proliferation, and dissipative selection, respectively, arising out of the nonequilibrium conditions created on Earth’s surface by the solar photon spectrum. Here I describe the nonequilibrium thermodynamics and the photochemical mechanisms involved in the synthesis and evolution of the fundamental molecules of life from simpler more common precursor molecules under the long wavelength UVC and UVB solar photons prevailing at Earth’s surface during the Archean. Dissipative structuring through photochemical mechanisms leads to carbon based UVC pigments with peaked conical intersections which endow them with a large photon disipative capacity (broad wavelength absorption and rapid radiationless dexcitation). Dissipative proliferation occurs when the photochemical dissipative structuring becomes autocatalytic. Dissipative selection arises when fluctuations lead the system to new stationary states (corresponding to different molecular concentration profiles) of greater dissipative capacity as predicted by the universal evolution criterion of Classical Irreversible Thermodynamic theory established by Onsager, Glansdorff, and Prigogine. An example of the UV photochemical dissipative structuring, proliferation, and selection of the nucleobase adenine from an aqueous solution of HCN under UVC light is given.

Ultraviolet light incident on organic material can initiate its spontaneous dissipative structuring into chromophores which can 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. Oligos of nucleic acids with affinity to particular amino acids which foment UVC photon dissipation would have been selected through non-equilibrium thermodynamic imperatives which favor entropy production. Indeed, we show here that those amino acids with characteristics most relevant to fomenting UVC photon dissipation are precisely those with greatest chemical affinity to their codons or anticodons. Entropy production could thus provide an explanation for the accumulation of information in nucleic acids relevant to the dissipation of the externally imposed thermodynamic potentials. The accumulation of information in this manner provides a link between evolution and entropy production.

Non-equilibrium thermodynamics is a relevant framework from within which to address formidable difficulties encountered in explaining the origin of life; from molecular synthesis and complexation, enzyme-less proliferation, to evolution (including the acquisition of homochirality and information). From within this framework we have proposed that the origin of life was the origin of the dissipative structuring of organic pigments which became the fundamental molecules of life (e.g. RNA and DNA) proliferated through autocatalytic photochemical reactions under the thermodynamic imperative of dissipating the imposed UVC solar photon flux available at the Archean surface. Here we present experimental evidence demonstrating that the absorption and dissipation of UVC light by synthetic DNA of 25 base pairs (and also natural salmon sperm DNA) over a range of temperatures, including below their melting temperature, leads to denaturing. Since denaturing is a non-trivial step on route to enzyme-less replication, our data suggest the possibility of a dissipative route to DNA replication at the origin of life. Such a dissipation-replication relation provides a simple mechanism for the early accumulation of both homochirality and information. Possible mechanisms of UVC photon-induced denaturing of DNA are discussed.

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., 23 pages, no figures

The response of ecosystems to perturbations is considered from a thermodynamic perspective by acknowl-edging that, as for all macroscopic systems and processes, the dynamics and stability of ecosystems is sub-ject to definite thermodynamic law. For open ecosystems, exchanging energy, work, and mass with the en-vironment, the thermodynamic criteria come from non-equilibrium or irreversible thermodynamics. For ecosystems during periods in which the boundary conditions may be considered as being constant, it is shown that criteria from irreversible thermodynamic theory are sufficient to permit a quantitative prediction of ecosystem response to perturbation. This framework is shown to provide a new perspective on the popula-tion dynamics of real ecosystems.

All irreversible processes arise and persist to produce entropy. Entropy production is not incidental to such processes, but rather the very reason for their origin and persistence. Here we take such a thermodynamic perspective on the origin of life, recognizing that entropy production is not only the vital force of life, but the fundamental link between life in the biosphere today and its origin in the Archean. Today the greatest en-tropy production in the biosphere is due to visible photon absorption and dissipation into heat by organic material in liquid water and the subsequent degradation of the established heat gradient through the water cycle. Following this link back in time to the Archean environment leads to a suggestion for a mechanism for the origin of life based on UV photon absorption and dissipation by RNA and DNA.

Life arose as a non-equilibrium thermodynamic process to dissipate the photon potential generated by the hot Sun and cold outer space. Evidence from the geochemical record of the evolutionary history of life on Earth suggests that life originated in a hot aqueous environment dissipating UV light and evolved later to dissipate visible light. This evidence places constraints on models of solar origin and evolution. The standard solar model seems less compatible with the data than does the pulsar centered solar model.

The dependence of the structural and magnetic properties of Co–Rh alloys at the nanoscale was investigated by exhaustively searching the minimum energy via a symbiotic algorithm on a Gupta potential for particle sizes of 13, 19, and 23 atoms. An unrestricted spd tight-binding Hamiltonian was then used to model the electronic properties. Our results underscore the importance of determining both the geometrical and the chemical configuration. A central result points toward a surface segregation that qualitatively and quantitatively depends on system size, with size effects dominating the surface segregation for small Co–Rh clusters (Rh atoms preferentially occupy surface sites), whereas surface energy dictates the segregation for large Co–Rh nanoparticles (Co segregates to the surface). This might have important consequences for heterogeneous catalysis, where the catalytic activity strongly depends on surface composition.

The structural properties and energy ordering of the lowest lying isomers of bimetallic ( CuAu )n and ( PtPd )n, n=5-22 clusters have been investigated by means of density functional theory (DFT) in the generalized gradient approximation (GGA). The initial cluster geometry optimization is performed by using a genetic algorithm with the many body Gupta potential. This technique provide a distribution of the lowest energy cluster structures, that are further reoptimized using the DFT-GGA methodology. The energy ordering of isomers obtained with the Gupta potential does not agree, in general, with the one obtained using DFT-GGA for the two bimetallic clusters investigated. However, the lowest energy strucutures of the ( CuAu )n nanoalloy show icosahedral patterns in agreement with the results obtained with the model potential. For the ( PtPd )n clusters segregation effects are found, where the Pt atoms are forming the cluster core and the Pd atoms are on the cluster surface, in agreement with previous calculations using the many body Gupta potential.

The caloric and specific heat curves for the bimetallic nanoclusters Au7-xAgx (x=0,3,4,7) are obtained through a statistical determination of the configurational density of states in the evolutive ensemble obtained with a genetic algorithm. The effect of the value of x (the relative concentrations) on the thermodynamics is studied. Three peaks are observed in the specific heat curves for all values of x. This is interpreted as being due to melting, and fragmentation of the cluster into first two, and then into 3 or more parts. A fourth pre-melting peak is observed for Au4Ag3 and is attributed to a new phenomena related to the breaking of the degeneracy of the permutational isomers. The melting transition for the bimetallic clusters is significantly wider than that for the pure clusters. The boiling transition displays a larger specific heat for the bimetallic clusters.

The magnetic properties of free-standing Co n Rh m clusters ( N = n + m ≈ 110 and n ≈ m ) of three different symmetries: cubo-octahedral, icosahedral and HCP, were investigated in the segregated case. The initial geometrical structures constructed at Rh bulk distances were relaxed with a many-body Gupta potential to obtain the cluster geometries and energies. We find that the lowest energy is associated with the HCP structure. The relaxed interatomic distance for all the structures is slightly lower than the Rh bulk distance. The spin-polarized electronic structure and related magnetic properties of these optimized geometries were calculated by solving self-consistently a spd tight-binding Hamiltonian. The magnetic moment of the Rh atoms shows strong dependence on the position and environment, whereas the Co atoms show a smoother dependence. Results are compared with the experimental data and with other theoretical calculations available in the literature.

The magnetic moments of free standing Co N clusters (4≤ N ≤55) were calculated through a self-consistent spd-tight-binding method. The lowest energy geometrical structures of these clusters were obtained by exhaustive global searches on a many-body Gupta potential energy surface using an evolutive algorithm. The relevant structures mainly follow an icosahedral growth pattern with some fcc-type structures at some particular sizes. The calculated magnetic moments demonstrate a decreasing behavior with cluster size with small superimposed oscillations. The calculations are good agreement with the available experimental data. Our results are briefly discussed and compared with other published theoretical results.

Theoretical and experimental information on the shape and morphology of bare and passivated gold clusters is fundamental to predict and understand their electronic, optical, and other physical and chemical properties. An effective theoretical approach to determine the lowest-energy configuration (global minimum) and the structures of low energy isomers (local minima) of clusters is to combine genetic algorithms and many-body potentials (to perform global structural optimizations), and first-principles density functional theory (to confirm the stability and energy ordering of the local minima). The main trend emerging from structural optimizations of bare Au clusters in the size range of 12−212 atoms indicates that many topologically interesting low-symmetry, disordered structures exist with energy near or below the lowest-energy ordered isomer. For example, chiral structures have been obtained as the lowest- energy isomers of bare Au28 and Au55 clusters, whereas in the size-range of 75−212 atoms, defective Marks decahedral structures are nearly degenerate in energy with the ordered symmetrical isomers. For methylthiol-passivated gold nanoclusters (Au28(SCH3)16 and Au38(SCH3)24), density functional structural relaxations have shown that the ligands are not only playing the role of passivating molecules, but their effect is strong enough to distort the metal cluster structure. In this work, a theoretical approach to characterize and quantify chirality in clusters, based on the Hausdorff chirality measure, is described. After calculating the index of chirality in bare and passivated gold clusters, it is found that the thiol monolayer induces or increases the degree of chirality of the metallic core. We also report simulated high- resolution transmission electron microscopy (HRTEM) images which show that defects in decahedral gold nanoclusters, with size between 1−2 nm, can be detected using currently available experimental HRTEM techniques.

A statistical technique to efficiently map out the energy surfaces of nanoclusters and molecules is described. Global energy minimizations are performed to reach of the catchment basins of the lowest energy stationary points. Saddle points are located by using a large value of the iterative energy change as the stopping criterion of a final local relaxation. Minima are derived from saddle points by simply tightening the stopping criterion and continuing the relaxation. A statistical approximation to the widths of the paths in phase space between saddle points and minima is obtained. Application is made to argon clusters of 7 and 38 atoms.

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., Comment: 43 pages, 3 figures

We have modified an analytical model of induced light production by energetic ions interacting in scintillating materials. The original model is based on the distribution of energy deposited by secondary electrons produced along the ion's track. The range of scattered electrons, and thus the energy distribution, depends on a classical impact parameter between the electron and the ion's track. The only adjustable parameter of the model is the quenching density ρq. The modification here presented, consists in proposing a quantum impact parameter that leads to a better fit of the model to the experimental data at low incident ion energies. The light output response of CsI(Tl) detectors to low energy ions (

Ecosystems arise and evolve predominantly through the thermodynamic imperative of dissipating the solar photon flux into heat. Organic pigments coupled to water inside cyanobacteria, algae, and plants provide the dissipative structures for this entropy production. Viruses, bacteria, insects, and animals play the role of diversifiers and nutrient and seed dispersers in favor of the proliferation and dispersal of pigments over Earth’s entire surface. The past few decades has seen an enormous negative human impact on the majority of Earth’s ecosystems, antagonistic to human nominal supportive role in photon dissipation. Discerning whether or not efforts to reverse the damage are having the desired effect requires an accurate measure of ecosystem health. This chapter describes an indicator of global ecosystem health based on the entropy production of the ecosystem as a whole, which recognizes solar photon dissipation as its ultimate thermodynamic function. Thermodynamic justification for using the “red-edge” as an even simpler remotely sensed indicator of ecosystem health is also given.

Formidable difficulties arise when attempting to explain the non-enzymatic replication, proliferation, and the acquisition of homochirality and information content, of RNA and DNA at the beginnings of life. However, new light can be shed on these problems by viewing the origin of life as a non-equilibrium thermodynamic process in which RNA, DNA and other fundamental molecules of life arose as structures to dissipate the prevailing solar spectrum. Here we present experimental results which demonstrate that the absorption and dissipation of UV-C light by DNA at temperatures below their melting temperature leads to complete and reversible denaturing for small synthetic DNA of 25 base pairs (bp), and to partial and reversible denaturing for 48 bp DNA and for large salmon sperm and yeast DNA of average size 100 kbp. This result has direct bearing on the above mentioned problems and thereby opens the door to a possible thermodynamic route to the origin of life.

The controlled assembly of metal nanoparticles into macroscopic materials using DNA oligonucleotides has opened new directions of research in nanoscience and nanotechnology. Here, we describe recent ab initio calculations on structural and electronic properties of the subsystems forming these materials: bare and thiol-passivated gold nanoclusters, gold nanowires and fragments of DNA chains. Our results indicate that gold nanoclusters are distorted dramatically by a passivating methylthiol monolayer, that monatomic gold chains are stable in zigzag geometries and that dry acidic λ-DNA is a good insulator. These results provide useful insights towards the complete understanding, design and proper utilization of hybrid DNA-gold nanostructured materials.

Knowledge of the structure of clusters is essential to predict many of their physical and chemical properties. Using a many-body semiempirical Gupta potential (to perform global minimizations), and first-principles density functional calculations (to confirm the energy ordering of the local minima), we have recently found [Phys. Rev. Lett. 81, 1600 (1998)] that there are many intermediate-size disordered gold nanoclusters with energy near or below the lowest-energy ordered structure. This is especially surprising because we studied ''magic'' cluster sizes, for which very compact-ordered structures exist. Here, we show how the analysis of the local stress can be used to understand the physical origin of this amorphization. We find that the compact ordered structures, which are very stable for pair potentials, are destabilized by the tendency of metallic bonds to contract at the surface, because of the decreased coordination. The amorphization is also favored by the relatively low energy associated to bondlength and coordination disorder in metals. Although these are very general properties of metallic bonding, we find that they are especially important in the case of gold, and we predict some general trends in the tendency of metallic clusters towards amorphous structures. (c) 2000 The American Physical Society.

Gold nanoclusters with disordered and ordered structures are obtained as the lowest-energy configurations of the cluster potential energy surface (PES) by unconstrained dynamical and genetic/symbiotic optimization methods using an n-body Gupta potential and first-principle calculations [Phys. Rev. Lett. 81, 1600 (1998)]. In this paper, we report the distribution of lowest-energy minima which characterize the PES of the Au38 cluster, and a comparison of structural and thermal stability properties among several representative isomers is presented. Coexistence among different cluster isomeric structures is observed at temperatures around 250 K. The structure factor calculated from the most stable (lowest-energy) amorphous-like cluster configuration is in better agreement with the X-ray powder-diffraction experimental measurements than those calculated from ordered structures.

Adenine is one of the four principle bases of nucleic acid, the essential molecule of life and evolution. Apparently, only one configuration of adenine exists in nature giving it unique chemical and biological properties. Using a force field type potential model with parameters fitted to the nucleic acid bases, proteins and other biological molecules (involving the sum of the contributions from bond stretching, bond angle bending, torsional angle twisting, and Coulomb and Lennard–Jones terms) we searched the potential energy surface for other stable isomers of adenine. The search was performed using a genetic algorithm, an efficient and global technique. The most interesting of the lowest energy minima found in the global search were relaxed using quantum-mechanical, semiempirical (PM3), and first principles (Hartree–Fock and density functional theory) methods. These calculations gave similar geometries and energy ordering for the new structures. This work formed part of a larger project to study the binding of nanoclusters of gold to segments of nucleic acid for possible application in the emerging field of nano-electronics. The results could also have implications in mutation and transcription of DNA.

The geometries and binding energies of the most stable isomers of nickel, silver, and gold nanoclusters of size 6, 7, 12, 13, 14, 19, 38, 55, and 75 atoms, predicted with an n-body Gupta potential, are presented. An exhaustive search for low-energy minima on the potential energy surface was carried out using an evolutive ~genetic-symbiotic! algorithm. Our results confirm the existence of disordered global minima for gold clusters of 19, 38, and 55 atoms in size, and disordered low-energy isomers for the 75-atom gold cluster. Disordered structures are also isomers of nickel and silver clusters but they are not among the global minima of these metals. Comparison of the structure factors of the disordered and ordered isomers of gold with published experimental x-ray powder diffraction data suggests that the disordered structures are real. The relation between the form of the n-body potential and the structure of the global minimum is studied, leading to an explanation of why these disordered states were located with the Gupta potential but not with certain other models of the metal bonding. @S0163-1829~99!05524-1#

The lowest energy structures of ${\mathrm{Au}}_{n}$ ( $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}38,55,75$) nanoclusters are obtained by unconstrained dynamical and genetic-symbiotic optimization methods, using a Gupta $n$-body potential. A set of amorphous structures, nearly degenerate in energy, are found as the most stable configurations. Some crystalline or quasicrystalline isomers are also minima of the cluster potential energy surface with similar energy. First principles calculations using density functional theory confirm these results and give different electronic properties for the ordered and disordered gold cluster isomers.

A novel `symbiotic' algorithm, based on the genetic algorithm, is presented for finding the structure and energy distribution of the lowest energy isomers of large clusters and molecules. This approach takes advantage of the strong coupling of nearest neighbor atoms through the fitness function (the binding energy) directing the selection process, due to the short range of the interatomic potential in comparison to the cluster size. Evolving locally in cells and then forming and evolving a symbiosis of the cells is substantially more efficient than employing the genetic algorithm on the full cluster. Application is made to Lennard-Jones clusters of 6, 18, 23, 38 and 55 atoms.

The ground state configuration of a macroscopic quantity of Na and Cl ions is the well-known crystalline, face-centered cubic structure (table salt). However, when the number of ions is reduced to a handful, geometrically quite different and interesting ground state structures occur. Such configurations are realized in the early stages of crystal growth and are important in a growing number of physical applications. This article describes the application of a genetic algorithm to the difficult problem of the determination of the lowest-energy geometrical configurations of few-ion (⩽12) clusters of Na and Cl. The binding energy and the frequencies of vibration determined for these structures are compared to experimental data and to published results of other calculations. The advantages and limitations of the genetic algorithm as a tool for cluster physics are discussed.

Coalescence and fragmentation of equal and unequal liquid-drop pairs are studied using a new experimental technique in which mercury drops collide while sliding on a horizontal glass surface. The limits for coalescence measured as a function of the incident relative velocity and impact parameter are found to be similar to what has been reported for free-moving drops of other liquids, while new correlations are found to occur among the number, size, speed and angular distribution of fragmentation residues. The predictions of various models, including a dynamic theory originally developed for nuclear reactions, and specifically modified by us for macroscopic applications, are compared with the observations.

We derive simple algebraic expressions for the ion-induced light output response of most of the popular scintillation detectors used in nuclear and particle physics. The analytical calculation is based on a model for the energy deposition by secondary electrons scattered along the track of the ion, and the subsequent energy transport to luminescence centers. Predictions are compared with published experimental data for various scintillating materials over a wide range of incident ions and energies.

The publication of “On the Origin of Species” by Darwin in 1859 set the stage for the emergence of a new paradigm. No longer was biology accredited to the whim of an omnipotent mystical being; for the first time the diversity of life was seen as the result of a plausible physical mechanism which led to complex organisms and species from simpler common ancestors. Darwin’s theory assumed a fierce battle for survival of the individual against the hostile biotic and abiotic components of its environment. This fight for survival suggested an implicit metaphysical “will to survive” programmed within each organism, which, together with variability in reproduction, provides sufficient elements for natural selection to drive the evolutionary process. Such a process would lead to ever more apt forms of organisms until reaching what Darwin considered to be a state of “near perfection”. The biosphere, under this paradigm, was considered to be an emergent system, the result of the sum of the many individual or collective struggles for survival.