Production properties ofD 0,D +,D *+ andD s + in 230 GeV/cπ − andK −-Cu interactions

We have studied the hadronic production of charmed mesons in the NA 32 experiment at CERN. A special trigger together with a high resolution vertex detector consisting of charge coupled devices and silicon microstrip detectors allowed the selection of very clean samples of charmed mesons. We have collected 852 fully reconstructed decays: 60D _s ⁺ →K ⁺ K ^?π⁺, 543D°→K ^?π⁺ andK ^?π⁺π^?π⁺ as well as 249D ⁺→K ^?π⁺π⁺ (or charge conjugate). 147 mesons out of our \({{D^0 } \mathord{\left/ {\vphantom {{D^0 } {\bar D^0 }}} \right. \kern-0em} {\bar D^0 }}\) sample were produced via chargedD ^* state. For all charmed mesons we determine the total production cross-section and study thex _F andp _t ² distributions.     

Hele Shaw Flows with Time-Dependent Free Boundaries Involving Injection Through Slits

Consider the classical Hele Shaw situation with two parallel planes separated by a narrow gap. Suppose a Newtonian fluid to be injected into this gap through straight-line slits as well as, possibly, at isolated points. We are interested in predicting the plan-view of the resultant expanding blob, or blobs, of fluid. We show that the method of solution developed earlier for dealing with such problems when the injection is only at isolated points can be adapted to yield solutions in this more general situation.     

A reanalysis of branching fractions of charmed mesonsD 0,D + andD s +

We combine highly complementary information on branching fractions of charmed mesonsD ⁰,D ⁺ andD _s ⁺ coming from two experiments both yielding doublecharm samples. The NA 32 experiment provided exclusive branching fractions for channels with at least two charged decay products while a recent Mark III paper provides results on inclusive charm decay properties. The knowledge of channels withK ⁰'s in the former is used to recalculate the charged multiplicity distribution in the latter. We obtain 〈n _ch〉=2.25±0.08 forD ⁰, 〈n _ch〉=1.96±0.08 forD ⁺ and 〈n _ch〉=2.41±0.38 forD _s ⁺ . In turn the knowledge of the charged multiplicity improves the overall normalization of exclusive branching fractions. This reanalysis yields model-independent results for charmed mesons. In particular we obtain branching fractions for 16D _s ⁺ decay channels including $$BF(D_s^ + \to \phi \pi ^ + ) = \left( {4.4\begin{array}{*{20}c} { + 2.3} \\ { - 1.8} \\ \end{array} } \right)\% .$$ .     

DYNGA: a general purpose QM-MM-MD program. I. Application to water

We present a general purpose QM-MM-MD engine (DYNGA) designed to test alternative hybrid Hamiltonians geared towards the treatment of problems of interest in structural biology including the use of experimental data constraints. In this first presentation we use DYNGA to explore the behaviour of a traditional QM-MM approach in the treatment of the water—water interaction. We find the potential energy hypersurface for the water dimer computed with the HF 4–31G*/TIP3P hybrid Hamiltonian tends to be too flat. We also explore the effect of using traditional QM-MM techniques on proton wires and conclude there is a need for improvement, possibly addressed by using polarizable force fields.     

Freezing-off in disc cavities

A semi-quantitative analysis is presented of freezing-off in a disc cavity during the injection moulding of thermoplastics. A criterion is obtained which enables the occurrence of freezing-off to be predicted, at least crudely. The form of the criterion is found to depend on the direction of flow (radially outward or inward) in the disc.     

Lifetimes of charged and neutralD mesons

We have measured the lifetimes of hadronically produced charged and neutralD mesons using silicon microstrip detectors and an active silicon target in the NA32 spectrometer at the CERN SPS. We obtainτ _D± = (10.9± _1.5 ^1.9 )·10^?13s andτ _D ^(?)10 = (4.2±0.5)·10^?13s based on 59 and 90 fully reconstructed decays respectively, giving a ratioτ _D±/τ _D ^(?)10 of 2.6 ±0.5.     

Solid-state laser spectral narrowing using a volumetric photothermal refractive Bragg grating cavity mirror

Dramatic spectral narrowing of two normally broadband lasers, Ti:sapphire and Cr:LiSAF, was achieved by simply replacing the output mirror with a reflective, volumetric Bragg grating recorded in photothermal refractive glass. The output power of each laser was unchanged from that obtained using dielectric coated output mirrors with the same output coupling as the Bragg grating while spectral brightness increased by 3 orders of magnitude.