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91.
Chen J Sickler JW Fendel P Ippen EP Kärtner FX Wilken T Holzwarth R Hänsch TW 《Optics letters》2008,33(9):959-961
Generation of low-timing-jitter 150 fs pulse trains at 1560 nm with 2 GHz repetition rate is demonstrated by locking a 200 MHz fundamental polarization additive-pulse mode-locked erbium fiber laser to high-finesse external Fabry-Perot cavities. The timing jitter and relative intensity noise of the repetition-rate multiplied pulse train are investigated. 相似文献
92.
Anna G. Scott Diogo Alves Galico Isabel Bogacz Paul H. Oyala Junko Yano Elizaveta A. Suturina Muralee Murugesu Theodor Agapie 《Angewandte Chemie (International ed. in English)》2023,62(49):e202313880
Atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp*4W4Fe13S12 , displaying a Fe13 core with M−M bonds that has precedent only in main group and late metal chemistry. M13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp*4W4Fe13S12 displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements. 相似文献
93.
Kelley P Radlauer MR Yanez AJ Day MW Agapie T 《Dalton transactions (Cambridge, England : 2003)》2012,41(26):8086-8092
Dialuminiummacrocycles based on bisglyoximato moieties were prepared and their coordination chemistry with Fe(II) and Pd(II) was investigated. The bridging aluminium centers were supported by several types of tetradentate diphenoxide diamine ligands. The nature of the ancillary ligands bound to aluminium was found to affect the overall geometry and symmetry of the metallomacrocycles. Enantiopure, chiral diphenoxide ligands based on the (R,R)-trans-1,2-diaminocyclohexane backbone afforded cleanly one metallomacrocycle isomer. The size and electronic properties of remote substituents on aluminium-bound ligands affected the binding mode and electronic properties of the central iron. A structurally characterized iron complex shows trigonal prismatic coordination mode, with phenoxide bridges between iron and aluminium. Increasing the size of the phenoxide substituents led to square bipyramidal coordination at iron. Employing p-NO(2)- instead of p-tBu-substituted phenoxide as supporting ligands for aluminium caused a 0.27 V positive shift of the Fe(III)/Fe(II) reduction potential. These results indicate that the present synthetic approach can be applied to a variety of metallomacrocycles based on bisglyoximato motifs to affect the chemistry at the central metal. 相似文献
94.
Alexandrov NA Marinova KG Gurkov TD Danov KD Kralchevsky PA Stoyanov SD Blijdenstein TB Arnaudov LN Pelan EG Lips A 《Journal of colloid and interface science》2012,376(1):296-306
The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11 mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins. 相似文献
95.
Igor P. Borodin Tatyana I. Borodina Theodor N. Khazanovich 《Macromolecular theory and simulations》2012,21(7):438-447
The loss modulus E″ in elastomer strips stretched by a factor of λ is studied theoretically. A small oscillating deformation is applied to these strips in the transition frequency zone between the glassy and rubbery states. The range of λ under study ranges up to ultimate extensions close to fracture. A model of E″/λ dependence in the transition frequency zone is suggested that considers the possible distortion in the local chain structure in the ultimate extension range. It is found that E″ in the range of moderate and high λ increases owing to the finite extensibility of the chains. However, upon further extension up to ultimate values, E″ decreases and a maximum appears on the E″/λ curves. These features are also confirmed experimentally.
96.
Parthey CG Matveev A Alnis J Bernhardt B Beyer A Holzwarth R Maistrou A Pohl R Predehl K Udem T Wilken T Kolachevsky N Abgrall M Rovera D Salomon C Laurent P Hänsch TW 《Physical review letters》2011,107(20):203001
We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10) Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb. 相似文献
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100.
Theodor Ackermann 《Angewandte Chemie (International ed. in English)》1989,28(8):981-991
The structural transformations that biopolymers undergo in aqueous solution are complex processes, whose mechanisms can only be explained by the coupling of various partial processes. A spectroscopic analysis of the states of the system often requires considerable effort. In many cases, calorimetric studies have proven to be sufficient for a general characterization of the behavior of the system. These measurements provide information on the stability of the initial state and on the cooperativity of the total process. From the thermodynamic parameters of the system, knowledge on the structure-determining influence of the various types of inter- and intramolecular interactions is obtained. This not only applies to solutions of biopolymers and analogous model substances, but also to solutions of biopolymer complexes with low-molecular-weight ligands and to aqueous suspensions of self-aggregating phospholipids. Possibilities and limitations of the calorimetric methods of measurement are demonstrated for typical examples from the numerous polypeptide and polynucleotide systems and the phospholipid bilayer systems that have been studied. In addition, the special problems involved in carrying out measurements on dilute solutions are pointed out. Here, the latest advances made in measuring techniques are readily apparent. 相似文献