Blueprint for a high-performance biomaterial: full-length spider dragline silk genes.

Spider dragline (major ampullate) silk outperforms virtually all other natural and manmade materials in terms of tensile strength and toughness. For this reason, the mass-production of artificial spider silks through transgenic technologies has been a major goal of biomimetics research. Although all known arthropod silk proteins are extremely large (>200 kiloDaltons), recombinant spider silks have been designed from short and incomplete cDNAs, the only available sequences. Here we describe the first full-length spider silk gene sequences and their flanking regions. These genes encode the MaSp1 and MaSp2 proteins that compose the black widow's high-performance dragline silk. Each gene includes a single enormous exon (>9000 base pairs) that translates into a highly repetitive polypeptide. Patterns of variation among sequence repeats at the amino acid and nucleotide levels indicate that the interaction of selection, intergenic recombination, and intragenic recombination governs the evolution of these highly unusual, modular proteins. Phylogenetic footprinting revealed putative regulatory elements in non-coding flanking sequences. Conservation of both upstream and downstream flanking sequences was especially striking between the two paralogous black widow major ampullate silk genes. Because these genes are co-expressed within the same silk gland, there may have been selection for similarity in regulatory regions. Our new data provide complete templates for synthesis of recombinant silk proteins that significantly improve the degree to which artificial silks mimic natural spider dragline fibers

Theoretical And Experimental Studies Of Collision-Induced Electronic Energy Transfer From v=0-3 Of The E(0g+) Ion-Pair State Of Br2: Collisions With He And Ar

Collisions of Br(2), prepared in the E(0(g)(+)) ion-pair (IP) electronic state, with He or Ar result in electronic energy transfer to the D, D(\u27), and beta IP states. These events have been examined in experimental and theoretical investigations. Experimentally, analysis of the wavelength resolved emission spectra reveals the distribution of population in the vibrational levels of the final electronic states and the relative efficiencies of He and Ar collisions in promoting a specific electronic energy transfer channel. Theoretically, semiempirical rare gas-Br(2) potential energy surfaces and diabatic couplings are used in quantum scattering calculations of the state-to-state rate constants for electronic energy transfer and distributions of population in the final electronic state vibrational levels. Agreement between theory and experiment is excellent. Comparison of the results with those obtained for similar processes in the IP excited I(2) molecule points to the general importance of Franck-Condon effects in determining vibrational populations, although this effect is more important for He collisions than for Ar collisions

Generalized Quantum Geometric Tensor in a Non-Hermitian Exciton-Polariton System

In this work, we review two different generalizations of a quantum geometric tensor (QGT) in two-band non-Hermitian systems and apply the formalism to the system of microcavity exciton polaritons. In particular, we extend the existing method of measuring the QGT that uses the pseudospins in photonic and polaritonic systems. We find that both forms of the generalized QGT can be expressed in terms of the exciton-polariton pseudospin components, which can be experimentally measured. We then present the generalized QGT components, i.e. the quantum metric and Berry curvature, for an exemplar non-Hermitian exciton-polariton system. Our simulations of the wave packet dynamics in this exciton-polariton system show that the right-right Berry curvature gives a more accurate description of the anomalous Hall drift.Comment: 2

The thermodynamics and roughening of solid-solid interfaces

The dynamics of sharp interfaces separating two non-hydrostatically stressed solids is analyzed using the idea that the rate of mass transport across the interface is proportional to the thermodynamic potential difference across the interface. The solids are allowed to exchange mass by transforming one solid into the other, thermodynamic relations for the transformation of a mass element are derived and a linear stability analysis of the interface is carried out. The stability is shown to depend on the order of the phase transition occurring at the interface. Numerical simulations are performed in the non-linear regime to investigate the evolution and roughening of the interface. It is shown that even small contrasts in the referential densities of the solids may lead to the formation of finger like structures aligned with the principal direction of the far field stress.Comment: (24 pages, 8 figures; V2: added figures, text revisions

Relationship Between BP (\u3ci\u3eBaculovirus penaei\u3c/i\u3e) Energy Reserves in Larval and Postlarval Pacific White Shrimp \u3ci\u3ePenaeus vannamei\u3c/i\u3e

The relationship between energy reserves of the penaeid shrimp Penaeus vannamei and Baculovirus penaei, or BP, were investigated in a series of experiments using mysis stage or early postlarval shrimp. Pre-exposure and post-exposure levels of protein and triacylgycerol (TAG) were determined. The effect of pre-exposure protein and TAG levels on susceptibility to BP infections was also investigated by starving a group of shrimp immediately prior to BP exposure. There was no consistent relationship between either pre-exposure or post-exposure protein levels and the percent of shrimp developing patent BP infections. There was, however, a significant positive correlation between TAG levels immediately prior to viral exposure and prevalence of infection 72 h later. Experimental reduction of TAG reserves prior to BP exposure delayed the development of a patent infection. In some, but not all, experiments there was a significant reduction in TAG levels of infected compared with uninfected shrimp 72 h post-exposure. The effect of patent BP infections on host TAG levels was subordinate to fluctuations in TAG content associated with the ontogeny of the hepatopancreas. Results of this study support histological observations that shrimp lipid levels can be altered by baculovirus infections. Furthermore, high levels of energy reserves in the form of TAG are associated with increased susceptibility to BP infection in larval and postlarval shrimp

DYNAMIC ANALYSIS OF STABILITY IN HUMAN LOADED WALKING AT DIFFERENT VELOCITIES AND HEIGHTS OF THE CENTER OF MASS, AND POSSIBLE OPTIMAL AREAS IN DIFFERENT MODES OF WALKING

INTRODUCTION: Loaded walking plays an important role in man’s many activities, including sport, such as leisure travel and hill walking. It is known that in loaded walking velocity and height of the body center of mass (COM) are two important factors for the stability of the whole body. This paper investigates which heights and velocities of COM lead to stable loaded and unloaded walking. METHODS: The method was as follows: 1) We considered the whole body as a simple three-segment model, made of two lower limbs (leg-foot) and one upper body (head-trunk-arm, HTA); 2) We recorded motion and ground reaction forces from real subjects walking at self-determined 'slow', 'comfortable', 'fast' speeds and loaded in one of three different ways and different carried ways; 3) We applied dynamic equations to the models; 4) We input the motion and ground reaction forces acquired into the models, and obtained their dynamic response at the body center of mass; 5) From these experiments and simulation, we can analyze possible optimum areas at different velocities and heights of COM. RESULTS: Results confirm that there are different dynamic responses for different modes of walking. In general, taking the stability of the center of mass as our criterion, stability in loaded walking decreases with an increase in the height and velocity of COM. However, a lower height of COM does not always satisfy the criterion of stability. Neither does a greater height of COM always lead to reduced stability. Rather, it is apparent that different modes of loaded walking each have a characteristic height/velocity area, beyond which stability decreases. So it is discovered that a special stability area may exist for a relative walking way. CONCLUSIONS: In fact, for different carried walking ways, there are some suitable areas where optimum stability may be obtained and beyond which the stability of human walking may decrease. For a different height of COM, this paper recommends some relative walking velocity which may be referenced in human leisure, sport and transport activities