Evolution: Complexity, uncertainty and innovation

Complexity science provides a general mathematical basis for evolutionary thinking. It makes us face the inherent, irreducible nature of uncertainty and the limits to knowledge and prediction. Complex, evolutionary systems work on the basis of on-going, continuous internal processes of exploration, experimentation and innovation at their underlying levels. This is acted upon by the level above, leading to a selection process on the lower levels and a probing of the stability of the level above. This could either be an organizational level above, or the potential market place. Models aimed at predicting system behaviour therefore consist of assumptions of constraints on the micro-level – and because of inertia or conformity may be approximately true for some unspecified time. However, systems without strong mechanisms of repression and conformity will evolve, innovate and change, creating new emergent structures, capabilities and characteristics. Systems with no individual freedom at their lower levels will have predictable behaviour in the short term – but will not survive in the long term. Creative, innovative, evolving systems, on the other hand, will more probably survive over longer times, but will not have predictable characteristics or behaviour. These minimal mechanisms are all that are required to explain (though not predict) the co-evolutionary processes occurring in markets, organizations, and indeed in emergent, evolutionary communities of practice. Some examples will be presented briefly

Surface Phonons and Other Localized Excitations

The diatomic linear chain of masses coupled by harmonic springs is a textboook model for vibrational normal modes (phonons) in crystals. In addition to propagating acoustic and optic branches, this model is known to support a ``gap mode'' localized at the surface, provided the atom at the surface has light rather than heavy mass. An elementary argument is given which explains this mode and provides values for the frequency and localization length. By reinterpreting this mode in different ways, we obtain the frequency and localization lengths for three other interesting modes: (1) the surface vibrational mode of a light mass impurity at the surface of a monatomic chain; (2) the localized vibrational mode of a stacking fault in a diatomic chain; and (3) the localized vibrational mode of a light mass impurity in a monatomic chain.Comment: 5 pages with 4 embedded postscript figures. This paper will appear in the American Journal of Physic

Optical pumping of the electron spin polarization in bulk CuCl

In CuCl bulk crystal negatively charged excitons (trions $X^-$) can be induced by the resonant optical excitation of extra electrons in conduction band minimum. In the case of light polarization and due to the top valence band structure of CuCl only the electrons with spin antiparallel to the direction of the light propagation contribute to the formation of $X^-$, while the emerging $X^-$ can recombine into both possible electron states, with spin parallel and antiparallel to the direction of light propagation. We propose to use this mechanism for optical electronic spin pumping. We describe the dynamics of pumping in terms of density matrix formalism. The coherent pumping laser pulse propagating through the sample is described by Maxwell wave equation coupled to the density matrix evolution equations. The results of our approximate simple model calculations suggest that spin polarization close to 100% can be achieved in time shorter than 100ps.Comment: new extended version, 7 pages, 4 figure

Multiphoton resonance in a three-level system with nearly degenerate excited states

An analytic study is presented of the efficient multiphoton excitation and strong harmonic generation in three-level systems specified by a pair of nearly degenerate, strongly dipole-coupled excited states. Such systems are physically formed by the three lowest states in, e.g., the hydrogen atom or evenly charged homonuclear diatomic molecular ions under reasonably chosen laser intensities. As a detailed analytic result, we found that the laser pulse of photon energy $2{.}05\text{eV}$, duration $0{.}23\text{ps}$ and intensity $5\cdot 10^{13}\,\frac{\text{W}}{\text{cm}^2}$ is able to produce complete inversion of the initial population in the hydrogen atom through the 5-photon excitation. At the same photon energy, the pulse of duration $0{.}41\text{ps}$ and intensity $3{.}44\cdot 10^{14}\,\frac{\text{W}}{\text{cm}^2}$ was found to produce the same effect in the molecular ion but through the 9-photon excitation. We show that the accompanying scattering of light has very rich spectrum differing substantially from that of the two-level system.Comment: 9 pages, 5 figures,submitted to Phys. Rev. A, comments welcom

Thermally activated breakdown in a simple polymer model

We consider the thermally activated fragmentation of a homopolymer chain. In our simple model the dynamics of the intact chain is a Rouse one until a bond breaks and bond breakdown is considered as a first passage problem over a barrier to an absorbing boundary. Using the framework of the Wilemski-Fixman approximation we calculate activation times of individual bonds for free and grafted chains. We show that these times crucially depend on the length of the chain and the location of the bond yielding a minimum at the free chain ends. Theoretical findings are qualitatively confirmed by Brownian dynamics simulations

Fatalism, Social Support and Mental Health in Four Former Soviet Cultures

Research on social support has identified differences in levels of support between cultures, but has provided only a limited explanation of the role of values or beliefs in accounting for such variations. In this paper we examine the relationship between fatalism and perceived support amongst 2672 respondents in four former Soviet States (Russia, Georgia, Ukraine and Belorussia), with participants drawn from groups of manual workers, managers, civil servants, students and the retired in these four countries. We also examine the consequences of such social support for mental health across these nations. Findings indicate a small but significant moderator effect for fatalism on the relationship between social support and mental health. These results are discussed in the context of the continuing economic and social challenges facing the citizens of these nations

Seismic and gravity investigations on the Malaspina Glacier, Alaska

Seismic reflections obtained from bedrock beneath the Malaspina Glacier along a ten‐mile profile line indicate ice thicknesses ranging from 1130 to 2050 ft. The base of the ice is 700 ft below sea level near the center of the profile and shallows both northward toward the mountains and southward toward the ice margin. Good reflections were obtained with dynamite charges of about one ounce in 26‐ft water‐filled shot holes but only in relatively crevasse‐free areas. Deeper reflections substantiate the inferred sedimentary nature of the subglacial rocks and show geologic structures consistent with the regional pattern. Gravity measurements along the central three miles of the seismic profile line indicate a gentle northwest‐southeast trending subglacial topographic grain. Seismic refraction shots beyond the present margin of the glacier suggest a thickness of unconsolidated proglacial deposits in excess of 500 ft

A New Brown Dwarf Desert? A Scarcity of Wide Ultracool Binaries

We present the results of a deep-imaging search for wide companions to low-mass stars and brown dwarfs using NSFCam on IRTF. We searched a sample of 132 M7-L8 dwarfs to magnitude limits of $J \sim 20.5$ and $K \sim 18.5$, corresponding to secondary-primary mass ratios of $\sim 0.5$. No companions were found with separations between 2{\arcsec} to 31{\arcsec} ($\sim$40 AU to $\sim$1000 AU). This null result implies a wide companion frequency below 2.3% at the 95% confidence level within the sensitivity limits of the survey. Preliminary modeling efforts indicate that we could have detected 85% of companions more massive than $0.05 M_{\odot}$ and 50% above $0.03 M_{\odot}$.Comment: 27 pages, 8 figures, 3 tables: accepted to the Astronomical Journa

Nernst effect, quasiparticles, and d-density waves in cuprates

We examine the possibility that the large Nernst signal observed in the pseudogap regime of hole-doped cuprates originates from quasiparticle transport in a state with d-density wave (DDW) order, proposed by S. Chakravarty et al. [Phys. Rev. B 63, 094503 (2001)]. We find that the Nernst coefficient can be moderately enhanced in magnitude by DDW order, and is generally of negative sign. Thus, the quasiparticles of the DDW state cannot account for the large and positive Nernst signal observed in the pseudogap phase of the cuprates. However, the general considerations outlined in this paper may be of broader relevance, in particular to the recent measurements of Bel et al. in NbSe_2 and CeCoIn_5 [Phys. Rev. Lett. 91, 066602 (2003); ibid. 92, 217002 (2004)].Comment: 9 pages, 3 figures; published versio