Electrooptic effect for cold neutrons in photorefractive materials

First experimental evidence for the existence of an electrooptic effect for cold neutrons in ⁷LiNbO₃ is reported and discussed. The effect is based on the fact that in certain photorefractive crystals a light-induced space-charge field can be generated which causes a modulation of the density via the inverse piezoelectric effect. From such density structures, induced by the internal electric field, cold neutrons can be diffracted. Received: 13 November 1998 / Revised version: 21 December 1998 / Published online: 12 April 1999     

Non-Markovian relaxation in an open quantum system

Non-Markovian dynamics in open quantum systems is characterized by a time-non-locality in the equation of motion valid for the reduced density operator. An expansion of this density matrix equation with respect to Laguerre polynomials is used to tackle the time-non-locality. The applicability and the numerical limitations of the method are discussed in detail. In order to illuminate the characteristics of non-Markovian dynamics the reference example is studied of a single quantum degree of freedom moving in a harmonic potential and being embedded in a heat bath. If interpreted as the photoinduced dynamics of nuclear motion in polyatomic molecules we can suggest two clear signatures of non-Markovian dynamics observable in ultrafast optical experiments, firstly a pronounced and somewhat irregular oscillatory behavior of the vibrational level populations, and secondly a separation of the vibrational wavepacket into a double-structure. Received 12 April 2000 and Received in final form 2 September 2000     

A convenient synthesis of the novel 5H-thieno[2,3-e]-4,1,2-oxathiazepine ring system via an alkoxycarbenium ion intermediate

3-(Methoxymethoxymethyl)-2-thiophenesulfonamides and 3-hydroxymethyl-N-methoxymethyl-2-thiophenesulfonamides have been shown to undergo cyclization when treated under anhydrous acidic conditions to provide the novel 2,3-dihydro-5H-thieno[2,3-e]-4,1,2-oxathiazepine ring system. Incorporation of a primary sulfonamide group into position seven of the molecule provided compounds which inhibit human carbonic anhydrase II.     

High selectivity from configurational match/mismatch in carbon-hydrogen insertion reactions of steroidal diazoacetates catalyzed by chiral dirhodium(II) carboxamidates.

Diazo decomposition of steroidal diazoacetates, where the point of attachment is the 3-position of the steroid A-ring, catalyzed by chiral dirhodium(II) carboxamidates results in products from carbon-hydrogen insertion in high yield and selectivities. Use of S-configured catalysts shows a distinctive preference for insertion into the 3-position to form beta-lactone products. The R-configured catalysts direct insertion preferentially to the equatorial C-H bond at the 2-position. Substituents or functional groups at the 5/6-position prevent C-H insertion from taking place at the 4-position. Even in the best case with the 5/6-positions fully saturated, however, insertion into the 3-position remains competitive with insertion into the 4-position. Corresponding 3-substituted phenyldiazoacetates give only beta-lactone products, and selectivity here is highest with chiral dirhodium(II) prolinate catalysts. A model is presented to explain these results. Overall, this methodology is versatile for functionalization of the steroid A-ring at positions 2 and 3.     

Low-frequency dielectric behavior of hydrated poly(L-proline)II

The dielectric behavior of poly(L -proline) II has been studied by the dc transient method and a contactless pendulum technique. The comparison of measurements performed with and without contacting electrodes shows that the static and low-frequency dielectric behavior are due to bulk phenomena. Both mechanisms are strongly dependent upon the water content of the sample. At low hydration, the static conduction may be attributed to an electronic process. The observed low-frequency relaxation can be characterized by a relaxation time which increases with the water content. This behavior can be explained by an increase in stiffness of the poly(L -proline) chain: two adjacent carbonyl groups of the chain may be hydrogen bonded by two water molecules.     

Diffusivity of gases and main-chain cooperative motions in plasticized poly(vinyl chloride)

Permeability and time-lag measurements for H₂ and CO in poly(vinyl chloride) (PVC) plasticized with tricresyl phosphate show that the apparent diffusion coefficients at first decrease as the plas-ticizer concentration is increased. The diffusion coefficients then increase as the additive concentration is raised above 15 wt %. These changes in the apparent diffusion coefficients can be related to the behavior of a variety of mechanical properties and are attributed to antiplasticization and plasticization effects of low and high concentrations of tricresyl phosphate, respectively. The antiplasticization-plasticization effects reflect altered molecular motions of the polymer. Carbon-13 NMR rotating-frame relaxation rate measurements show directly that the cooperative main-chain molecular motions of PVC are reduced when the additive acts as an antiplasticizer and are increased when the polymer is plasticized. Both the apparent diffusion coefficient and the rotating-frame relaxation rate have a similar dependence on additive concentration. An application of the molecular theory of diffusion of Pace and Datyner accounts qualitatively for the way in which additives alter the average chain interaction energy, cooperative polymer main-chain motions, and the diffusion coefficients of gaseous penetrants.     

Historiographic vices II. Priority chasing

This second essay (Num. I: HM 2, 185–187) argues that the historian may be interested in studying priority controversies but should analyse historically significant events rather than award status.     

Origin of trimuon events in high-energy neutrino interactions

The properties of 76 neutrino-initiated μ^?μ^?μ⁺ events observed in the CDHS detector in the 350 GeV and 400 GeV wide-band beams at the CERN SPS are discussed. For neutrino energies > 30 GeV and muon momenta ? 4.5 GeV, the average trimuon rate is (3.0±0.4)×10^?5 of the single-muon event rate. The data are in agreement with normal charged-current interactions with the additional production of a muon pair by both hadronic and radiative processes. No evidence is found for either heavy-lepton or heavy-quark cascades. Upper limits for these two possibilities are established.