Highly sensitive laser-based sensor for nanoparticles in air using a dual-ring-mirror setup

One of the most frequently applied techniques to detect nanoparticles in air is analyzing laser light scattering. This technique is very flexible while offering high accuracy and reliability. Yet its functionality highly depends on the sensitivity of the measurement system components. Especially for miniaturized sensor devices with limited space, additional techniques are needed to preserve high intensity of scattered light. In our work we demonstrate a technique using two spherical ring mirrors to identify nanoparticles with diameters below 100 nm in a forward-scattering setup. We succeeded measuring polystyrene particles with diameters of 92 nm with a signal-to-noise-ratio of more than 10.     

Electronically driven phase transitions in a quasi-one-dimensional adsorbate system

A quasi-1D system is prepared using the Pt(110) surface as a template. The electronic surface resonance structure is studied by angle-resolved photoemission spectroscopy for the clean surface as well as for different Bromine coverages. A Fermi surface mapping reveals saddle points at the Fermi level in the interior of the surface Brillouin zone. Correspondingly, a maximum in the static response function χ(q, 0) at the connecting vector q is expected. With 1/2G_x < q < 2/3G_x one observes indeed a 3-fold periodicity around defects and a 2-fold periodicity at low temperature for Θ_Br = 0.5 ML. Cooling of a defect-free c(2×2)-Br/Pt(110) preparation counter-intuitively results in a loss of long-range order. Motivated by DFT calculations this is attributed to an anomalous order-order phase transition into the (2×1) phase accompanied by intense, strongly anisotropic fluctuations within a temperature range of ~200 K. The peculiar behaviour is rationalised in terms of a competition between inter-adsorbate repulsion and an adsorbate triggered 2k_F interaction in the substrate.     

Electron injection into DNA: synthesis and spectroscopic properties of pyrenyl-modified oligonucleotides

The nucleoside 5-(1-pyrenyl)-2'-deoxyuridine (1) was prepared by a Suzuki-Miyaura cross-coupling reaction and subsequently used as a DNA building block in order to prepare a range of modified oligonucleotides using phosphoramidite chemistry. The DNA duplexes contain a pyrenyl group covalently attached to the nucleobase uracil. Upon excitation at 340 nm an intramolecular electron transfer from the pyrenyl group to the uracil moiety takes place which represents an injection of an excess electron into the DNA base stack. Based on the results obtained by steady-state fluorescence and time-resolved pump-probe laser spectroscopy it was possible to show that base-to-base electron transfer can occur from the Py-dU group only to adjacent thymines.     

Non-Fermi liquid regimes in U1−xMxPd2Al3(M=Y,Th)

The temperature-composition (T–x) phase diagram and NFL characteristics in the electrical resistivity ρ(T), specific heat C(T), and magnetic susceptibility χ(T) at low temperatures for the systems U_1−xM_xPd₂Al₃ (M=Y,Th) are described. The T–x phase diagram, the NFL characteristics, and the underlying mechanism for the NFL behavior are distinctly different for M=Y³⁺ and Th⁴⁺, apparently reflecting the difference in valence of the M atom substituents, and suggesting that U is tetravalent in these two systems.     

Modeling the quantum mechanical measurement process

The conceptual background of the quantum measurement problem is discussed with respect to an individual-stochastic interpretation of quantum mechanics in terms of pure states. The derivation of a stochastic dynamics on the pure state space of the system to be measured (starting from the joint system including an environment/measurement apparatus) is sketched. Finally the asymptotic behavior of such a derived stochastic dynamics is discussed: it is argued that usually one cannot expect a measurement-typeasymptotic behavior. Hence measurement-type behavior can only arise during an intermediate period of time and the asymptotic behavior will be thermal.     

Detection of single base mismatches and abasic sites using phenanthridinium as an artificial DNA base and charge donor

Combining the fluorescence properties of phenanthridinium as an artificial DNA base together with DNA-mediated charge transfer processes allows the homogeneous detection of DNA base mismatches and abasic sites.     

Reactivity,Syntheses, and Crystal Structures of Na5[MO2][X] with M = Co+, Ni+, Cu+; X = CO32—, SO42—, SO32—, S2—, and Na25[CuO2]5[SO4]4[S]

Na₅[CuO₂][CO₃], Na₅[CuO₂][SO₃], Na₅[CuO₂][S], and Na₅[CuO₂][SO₄] were obtained as single crystals and powders from reactions of Na₂O, Cu₂O, and Na₂X with X = CO₃^2—, SO₃^2—, S^2—, and SO₄^2—, respectively. A redox reaction between CdO and Co metal occurs in the presence of Na₂O and Na₂X, yielding Na₅[CoO₂][X] with X = CO₃^2— and S^2—. From a mixture of Na₂SO₄, CdO and Na₂O in Ni‐containers we observed the formation of Na₅[NiO₂][S] single crystals. Single crystals of Na₂₅[CuO₂]₅[SO₄]₄[S] can be grown by annealing Na₅[CuO₂][SO₃] at 600 °C, leading to the decomposition of SO₃^2—, yielding SO₄^2— and S^2— at 550 °C. The structures have been determined from single crystal data and powder data. All structures contain the isolated complex [MO₂]^3— in a dumb‐bell like arrangement. The main feature of these compounds is that the anions SO₄^2—, SO₃^2—, CO₃^2— and S^2— are not connected to the transition metal. The formation of Na₅[CuO₂][X] (X = S^2—, SO₄^2—, SO₃^2—, CO₃^2—) has been studied by thermal analysis and in situ X‐ray diffraction techniques. Infrared spectra confirm the presence of SO₄^2—, SO₃^2—, and CO₃^2—, respectively, in the structures.     

Synchronization is enhanced in weighted complex networks

The propensity for synchronization of complex networks with directed and weighted links is considered. We show that a weighting procedure based upon the global structure of network pathways enhances complete synchronization of identical dynamical units in scale-free networks. Furthermore, we numerically show that very similar conditions hold also for phase synchronization of nonidentical chaotic oscillators.     

Femtosecond formation of coupled phonon-plasmon modes in InP: Ultrabroadband THz experiment and quantum kinetic theory

The ultrafast transition of an optical phonon resonance to a coupled phonon-plasmon system is studied. After 10-fs photoexcitation of i-InP, the buildup of coherent beats of the emerging hybrid modes is directly monitored via ultrabroadband THz spectroscopy. The anticrossing is mapped out as a function of time and density. A quantum kinetic theory of microscopic carrier-carrier and carrier-LO-phonon interactions explains the delayed formation of the collective modes. The buildup time is quantitatively reproduced to scale with the oscillation cycle of the upper branch of the coupled resonance.