Mono‐ and Bis(pyrrolo)tetrathiafulvalene Derivatives Tethered to C60: Synthesis,Photophysical Studies,and Self‐Assembled Monolayers

A series of mono‐ (MPTTF) and bis(pyrrolo)tetrathiafulvalene (BPTTF) derivatives tethered to one or two C₆₀ moieties was synthesized and characterized. The synthetic strategy for these dumbbell‐shaped compounds was based on a 1,3‐dipolar cycloaddition reaction between aldehyde‐functionalized MPTTF/BPTTF derivatives, two different tailor‐made amino acids, and C₆₀. Electronic communication between the MPTTF/BPTTF units and the C₆₀ moieties was studied by a variety of techniques including cyclic voltammetry and absorption spectroscopy. These solution‐based studies indicated no observable electronic communication between the MPTTF/BPTTF units and the C₆₀ moieties. In addition, femtosecond and nanosecond transient absorption spectroscopy revealed, rather surprisingly, that no charge transfer from the MPTTF/BPTTF units to the C₆₀ moieties takes place on excitation of the fullerene moiety. Finally, it was shown that the MPTTF–C₆₀ and C₆₀–BPTTF‐C₆₀ dyad and triad molecules formed self‐assembled monolayers on a Au(111) surface by anchoring to C₆₀.     

A Recovering Beam Search algorithm for the one-machine dynamic total completion time scheduling problem

This paper deals with the one-machine dynamic total completion time scheduling problem. This problem is known to be NP-hard in the strong sense. A polynomial time heuristic algorithm is proposed which applies the recently introduced Recovering Beam Search (RBS) approach. The algorithm is based on a beam search procedure with unitary beam width and includes a recovering subroutine that allows to overcome wrong decisions taken at higher levels of the beam search tree. It is shown that the total number of considered nodes is bounded by n where n is the jobsize. The proposed algorithm is able to solve in very short CPU time problems with up to 500 jobs outperforming the best state of the art heuristics.     

Asymptotic behavior of the Kohn-Sham exchange potential

The Kohn-Sham exchange potential of finite systems is shown to approach different asymptotic limits on nodal surfaces of the energetically highest-occupied orbital than in other regions. This leads to barrier-well structures in the near asymptotic region, which have a strong influence on virtual orbitals and thus on excitation energies. Common approximations for the exchange potential do not exhibit these features. These asymptotic structures, however, can be correctly described by effective exact-exchange methods. Conditions for the presence of an asymptotic barrier well in the full exchange-correlation potential are discussed.     

Use of isothermal microcalorimetry data for the determination of integral molar entropies of adsorption at the gas—solid interface by a quasi-equilibrium procedure

The aim of this paper is to describe the present position in the experimental determination of entropies of adsorption. After pointing out the limitations of the “isosteric” approach and after stressing the fact that the most interesting entropy to know is the integral molar entropy of adsorption, the authors show how the use of isothermal adsorption microcalorimetry, with a special quasi-reversible procedure, allows this entropy to be determined satisfactorily from the thermodynamic point of view.     

Study of double pomeron exchange in pp collisions at √s=31GeV

The reaction pp→ppπ⁺π^? at √s=31GeV was studied at the Split Field Magnet Facility of the CERN-ISR. Selecting events with two leading protons of x>0.9 and a rapidity gap Δy>2 between the protons and both pions a sample of 720 events is obtained representing a cross section of 25±10μb. The mass distribution of the dipion system, x and p_T distributions for the protons are presented and analyzed for the presence of double pomeron exchange.     

The photoelectron spectrum and molecular geometry of bicyclo[2.1.1]hexane

The He(I) photoelectron spectrum of bicyclo[2.1.1]hexane shows excellent correlation with a theoretical spectrum based on the eigenvalues obtained in an ab initio calculation at the theoretical molecular geometry. By contrast, a calculation performed at the experimental geometry exhibits an effect of enhanced ring strain in showing a first ionization energy which is considerably lower than the experimental value. This observation offers experimental support for the recent claim that the published structure for bicyclo [2.1.1]hexane based on electron-diffraction measurements is incorrect. It also accounts for inconsistencies observed in the calculated values of some spin—spin coupling constants for substituted bicyclo[2.1.1]hexanes.     

Comparison between experimental decay of the compound nuclei150Gd and evaporation calculations

The deexcitation of the compound nucleus¹⁵⁰Gd formed by¹⁵⁶O+¹³⁴Ba and⁴⁰Ar+¹¹⁰Pd have been studied. Excitation functions were determined for various exit channels: (HI, × n) withx=3, 4, 5 (HI, pxn) withx=2, 3, 4 (HI, axn) withx=3 and 5. A systematic comparison has been made between these experimental data and the results of evaporation calculation using the ALI CE code. The very good agreement obtained for the total residue cross section disappears completely when a more detailed analysis of the different contributions is performed. Absolute and relative cross sections are not reproduced; excitation functions of each individual channel (HI, 3n), (HI, 4n) etc. ... are not found at the right place in energy. A very preliminary explanation for such a shift towards higher energies is suggested.     

Widely tunable continuous-wave diode-pumped 2-microm Tm-Ho:KYF4 laser

Continuous-wave laser action at approximately 2 microm is demonstrated in a Tm-Ho:KYF4 single crystal at room temperature. Crystal growth, spectroscopic measurements, and laser results are presented. An output power in excess of 250 mW is obtained with a tuning range of 99 nm, the largest ever published, to our knowledge, for Tm-Ho in any crystalline host.