Synthesen von Heterocyclen, 54. Mitt.: Über umsetzungsprodukte aus Xanthogenamid und Malonsäurederivaten

Zusammenfassung Xanthogenamid reagiert mit Malonsäure und PCl₃ zu 2,4-Dihydroxy-5-acetyl-[1,3-thiazinon-(6)] (IV), mit Malonylchlorid hingegen zu 2-Äthoxy-4-hydroxy-[1,3-thiazinon-(6)] (VII).     

Measurement of frequency differences between visible laser lines up to 170GHz using metal-insulator-metal point contact diodes

Frequency differences of up to 170 GHz between a cw dye laser and a krypton laser at 568 nm were measured by mixing laser and microware radiation with a metalinsulator-metal point contact diode. Beat signals are well above noise and there is still great potential for improvement when better microwave oscillators are used. From the measurements reported it follows that the diode can be used for determining still higher frequency differences of visible laser radiation.     

Indications about the shape of the universe from the Wilkinson microwave anisotropy probe data

It is shown that the recent observations of NASA's Explorer mission, "Wilkinson Microwave Anisotropy Probe," hint that our Universe may possess a nontrivial topology. As an example we discuss the Picard space which is stretched out into an infinitely long horn but with finite volume.     

Exponential decay lifetimes of excitons in individual single-walled carbon nanotubes

The dynamics of excitons in individual semiconducting single-walled carbon nanotubes was studied using time-resolved photoluminescence (PL) spectroscopy. The PL decay from tubes of the same (n,m) type was found to be monoexponential, however, with lifetimes varying between less than 20 and 200 ps from tube to tube. Competition of nonradiative decay of excitons is facilitated by a thermally activated process, most likely a transition to a low-lying optically inactive trap state that is promoted by a low-frequency phonon mode.     

Two photon absorption and coherent control with broadband down-converted light

We experimentally demonstrate two-photon absorption with broadband down-converted light (squeezed vacuum). Although incoherent and exhibiting the statistics of a thermal noise, broadband down-converted light can induce two-photon absorption with the same sharp temporal behavior as femtosecond pulses, while exhibiting the high spectral resolution of the narrow band pump laser. Using pulse-shaping methods, we coherently control two-photon absorption in rubidium, demonstrating spectral and temporal resolutions that are 3-5 orders of magnitude below the actual bandwidth and temporal duration of the light itself. Such properties can be exploited in various applications such as spread-spectrum optical communications, tomography, and nonlinear microscopy.     

Near Optimal Separation Of Tree-Like And General Resolution

We present the best known separation between tree-like and general resolution, improving on the recent exp(n ) separation of [2]. This is done by constructing a natural family of contradictions, of size n, that have O(n)-size resolution refutations, but only exp((n/log n))- size tree-like refutations. This result implies that the most commonly used automated theorem procedures, which produce tree-like resolution refutations, will perform badly on some inputs, while other simple procedures, that produce general resolution refutations, will have polynomial run-time on these very same inputs. We show, furthermore that the gap we present is nearly optimal. Specifically, if S (S _T ) is the minimal size of a (tree-like) refutation, we prove that S _T = exp(O(S log log S/log S)).* This research was supported by Clore Foundation Doctoral Scholarship. Research supported by NSF Award CCR-0098197 and USA–Israel BSF Grant 97-00188. This research was supported by grant number 69/96 of the Israel Science Foundation, founded by the Israel Academy for Sciences and Humanities.     

First results from KamLAND: evidence for reactor antineutrino disappearance

KamLAND has measured the flux of nu;(e)'s from distant nuclear reactors. We find fewer nu;(e) events than expected from standard assumptions about nu;(e) propagation at the 99.95% C.L. In a 162 ton.yr exposure the ratio of the observed inverse beta-decay events to the expected number without nu;(e) disappearance is 0.611+/-0.085(stat)+/-0.041(syst) for nu;(e) energies >3.4 MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the "large mixing angle" region are excluded.     

ChipCheck--a program predicting total hybridization equilibria for DNA binding to small oligonucleotide microarrays

Presented here is the program ChipCheck that allows the computation of total hybridization equilibria for hybridization experiments involving small oligonucleotide arrays. The calculation requires the free energies of binding for all pairs of probes and targets as well as total strand concentrations and probe molecule numbers. ChipCheck has been tested computationally on microarrays with up to 100 spots and 42 target strands (4200 binding equilibria). It arrives at solutions through iterations employing the multidimensional Newton method. While currently running in simulation mode only, an extension of the approach to the exhaustive analysis of chip results is being outlined and may be implemented in the future. The output displays the extent of correct and cross hybridization both graphically and numerically. In principle, calculating total hybridization equilibria allows for eliminating noise from DNA chip results and thus an improvement in sensitivity and accuracy.