Self-consistent approximation to the polarization propagator

A theorem is presented that characterizes approximate states and truncated operator manifolds associated with self-consistent approximate propagators. This theorem establishes a natural relationship between Hermiticity, stationarity, nonredundance and completeness of operator manifolds, model time evolution, and the vacuum condition. For the case of the polarization propagator we describe algorithms by which we can construct states and manifolds that satisfy this theorem and the vacuum condition.     

The nature of alkanethiol self-assembled monolayer adsorption on sputtered gold substrates

A detailed study of the self-assembly and coverage by 1-nonanethiol of sputtered Au surfaces using molecular resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM) is presented. The monolayer self-assembles on a smooth Au surface composed predominantly of [111] oriented grains. The domains of the alkanethiol monolayer are observed with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. STM imaging shows that the (4 x 2) superlattice structure is observed as a (3 x 2) structure when imaged under noncontact AFM conditions. The 1-nonanethiol molecules reside in the threefold hollow sites of the Au[111] lattice and aligned along its [112] lattice vectors. The self-assembled monolayer (SAM) contains many nonuniformities such as pinholes, domain boundaries, and monatomic depressions which are present in the Au surface prior to SAM adsorption. The detailed observations demonstrate limitations to the application of 1-nonanethiol as a resist in atomic nanolithography experiments to feature sizes of approximately 20 nm.     

Synthesis, crystal structure, and solution stability of Keggin-type heteropolytungstates (NH4)6NiII0.5[alpha-FeIIIO4W11O30NiIIO5(OH2)].nH2O, (NH4)7Zn0.5[alpha-ZnO4W11O30ZnO5(OH2)].nH2O, and (NH4)7NiII0.5[alpha-ZnO4W11O30NiIIO5(OH2)].nH2O (n approximately 18)

Reaction of acidified (pH approximately 7) sodium tungstate solutions with transition metal cations (Fe(3+), Ni(2+), Zn(2+), Co(2+)) leads to the formation of transition-metal-disubstituted Keggin-type heteropolytungstates with 3d-metal ions distributed over three different positions. A detailed investigation of the synthesis conditions confirmed that the complexes could equally be obtained using aqueous solutions of either Na(2)WO(4).2H(2)O (sodium monotungstate) at pH approximately 7, Na(6)[W(7)O(24)]. approximately 14H(2)O (sodium paratungstate A), or Na(10)[H(2)W(12)O(42)].27H(2)O (sodium paratungstate B) as starting materials. Three complexes, (NH(4))(6)Ni(II)(0.5)[alpha-Fe(III)O(4)W(11)O(30)Ni(II)O(5)(OH(2))].18H(2)O, (NH(4))(7)Zn(0.5)[alpha-ZnO(4)W(11)O(30) ZnO(5)(OH(2))].18H(2)O, and (NH(4))(7)Ni(II)(0.5)[alpha-ZnO(4)W(11)O(30)Ni(II)O(5)(OH(2))].18H(2)O were isolated in crystalline form. X-ray single-crystal structure analysis revealed that the solid-state structures of the three compounds consist of four main structural fragments, namely [MO(4)W(11)O(30)M'O(5)(OH(2))](n-) (Keggin-type, alpha-isomer) heteropolytungstates, hexaquo metal cations, [M'(OH(2))(6)](2+), ammonium-water cluster ions, [(NH(4)(+))(8)(OH(2))(12)], and additional ammonium cations and water molecules. The 3d metals occupy the central (tetrahedral, M) and the peripheral (octahedral, M') positions of the Keggin anion, as well as cationic sites (M') outside of the polyoxotungstate framework. UV-vis spectroscopy, solution ((1)H, (183)W) and solid-state ((1)H) NMR, and also chemical analysis data provided evidence that the 3d-metal-disubstituted Keggin anions do not exist in solution but are being formed only during the crystallization process. Investigations in the solid state and in solution were completed by ESR, IR, and Raman measurements.     

Study of the electronic energy band structure of polyethylene using MINDO/3

The electronic structure of polyethylene has been calculated using crystal orbital theory and the latest version (MINDO/3) of the MINDO semi-empirical SCF MO method. The results are in better agreement with the observed photoelectron spectrum than those given by an analogous calculation using MINDO/2, which in turn has been shown superior to treatments based on EHT, CNDO, INDO, or ab initio SCF procedures.     

Fully dispersion-compensated approximately 500 fs pulse transmission over 50 km single-mode fiber

We demonstrate essentially distortionless 50 km fiber transmission for approximately 500 fs pulses, using dispersion-compensating fiber and a programmable pulse shaper as a spectral phase equalizer. This distance is approximately five times longer than previously achieved at similar pulse widths.     

Ultrasensitive second-harmonic generation frequency-resolved optical gating by aperiodically poled LiNbO3 waveguides at 1.5 microm

We retrieve intensity and phase profiles of 280 fs, 50 MHz optical pulses with 124 aJ coupled pulse energy (960 photons) by second-harmonic generation (SHG) frequency-resolved optical gating, using aperiodically poled LiNbO3 waveguides. The strong nonlinear interaction that is due to confinement within the micrometer-sized waveguide structure and the linearly chirped poling period contribute, respectively, to high SHG efficiency and broad phase-matching bandwidth. The achieved sensitivity is 2.7 x 10(-6) mW2, improving on the previous record for self-referenced complete pulse characterization by 5 orders of magnitude.     

Wideband all-order polarization mode dispersion compensation via pulse shaping

We demonstrate the application of ultrafast pulse-shaping techniques for experimental wideband all-order polarization mode dispersion (PMD) compensation, for the first time to our knowledge. PMD is treated as arbitrary variations of state of polarization and phase versus wavelength, in an all-order sense. Consequently, two pulse shapers are implemented in a serial manner to compensate for the polarization and the phase spectra independently. We report compensation of subpicosecond pulses (14 nm bandwidth around 1550 nm) that are anomalously spread to more than 2 ps as a result of PMD. This PMD compensation scheme can potentially be a powerful and cost-effective solution for fiber optic telecommunication networks.     

Ein Beitrag zum Einfluß des Stoffüberganges auf eine erzwungene Konvektion an einer fluiden Phasengrenze

The interfacial-dynamic behaviour of a fluid two-phase-system with mass transfer was investigated under influence of forced convection in the manner of flat jets directed to the interface. The tangential velocities were measured at a characteristic point near to the interface air/water or in the interface itself using a Laser-Doppler-Velocimeter in dependence on the velocities of jets into two phases in both cases with and without transfer of acetone. The variations of velocities due to the interfacial effects are only detectable at small velocities of the jets. They are discussed by model conceptions and compared with the results of a theoretical research of heat transfer in a fluid two-phase-system (Interfacial-dynamic surface renewal model).     

Stability of density solitons formed in nuclear collisions

The effects of three-dimensional motion and the dissipative mechanisms in nuclear matter on the density solitons are investigated. It is seen that while the viscosity of the nuclear fluid does not affect the soliton, transverse motion causes a damping in the soliton during its propagation through the target nucleus.