Prompt K_short production in pp collisions at sqrt(s)=0.9 TeV

The production of K_short mesons in pp collisions at a centre-of-mass energy of 0.9 TeV is studied with the LHCb detector at the Large Hadron Collider. The luminosity of the analysed sample is determined using a novel technique, involving measurements of the beam currents, sizes and positions, and is found to be 6.8 +/- 1.0 microbarn^-1. The differential prompt K_short production cross-section is measured as a function of the K_short transverse momentum and rapidity in the region 0 < pT < 1.6 GeV/c and 2.5 < y < 4.0. The data are found to be in reasonable agreement with previous measurements and generator expectations.Comment: 6+18 pages, 6 figures, updated author lis

In situ synchrotron study of the solution crystallization of ultralong alkanes from dilute solution

The crystallization from dilute solution of two long n-alkanes (C246H494 and C162H326) has been followed in real time using synchrotron X-ray diffraction techniques at the European Synchrotron Radiation Source (ESRF) at Grenoble. The data confirm the existence of minima in crystallization and nucleation rates in C294H590. Further, the ability to record data very rapidly has allowed us to see the minimum in crystallization rate in C162H326 for the first time. Small changes in lattice spacing were seen during and after crystallization in all samples. These indicate that there is some perfectioning of crystals-for example the removal of cilia at the surfaces, etc

Crystallization of hydroxybutyrate oligomers. Part 3. Unfolding transitions followed in real time using SAXS and WAXS

High resolution wide angle X-ray scattering has been used to follow changes in crystallinity and lattice parameter which occur on heating hydroxybutyrate oligomers. These effects can be correlated with changes in crystal thickness detected by small angle X-ray scattering. Melt-grown crystals from oligomers with 24 and 32 repeat units that initially contain once folded chains transform during slow heating to produce extended chain crystals. This chain unfolding occurs via a process of partial melting and recrystallization and is accompanied by an expansion in the crystal lattice of approximately 0.2% in the (110) fold direction. The presence of a benzyl protecting group on one end of the chain does not affect the transformation temperature but reduces the (020) and (110) lattice spacings very slightly, as well as increasing the rate of transformation. In all cases the stable crystal forms display specific crystal thicknesses simply related to the extended chain length, but the intermediate stages of thickening vary between samples

Crystallization of hydroxybutyrate oligomers. Part 2. Growth and thickening of solution grown crystals observed in situ using synchrotron radiation

Synchrotron X-ray radiation has been used in situ to follow the crystallization of a hydroxybutyrate oligomer containing 32 repeat units from dilute solution in propylene carbonate, and to study chain unfolding during heating in oligomers with 24 and 32 repeat units. A discontinuity in growth rate occurs at 36-37˚C for the 32-mer: crystals grown below this temperature contain folded chains, which transform during heating through a process of partial dissolution and re-crystallization to form extended chain crystals. Crystals grown above the transition temperature contain extended chains that do not rearrange during heating. A similar change happens in the 24-mer between 35 and 40˚C. Thermal expansion in the (110) lattice direction (the fold direction) was in the range 5.3 +/- 0.3 x 10-5 nm degreesC, with an additional discontinuous increase in 0.001 nm accompanying chain unfolding

Crystallization of hydroxybutyrate oligomers: 1. morphology and folding

Exact length hydroxybutyrate oligomers containing 24 and 32 repeat units have been prepared and their crystallization behaviour and crystal morphology observed. The oligomers form crystals from dilute solution and from the melt that have similar overall morphologies to crystals of the polymer, poly(hydroxybutyrate). Electron diffraction indicates that the chains are closely perpendicular to the basal planes of the crystals. Wide angle X-ray diffraction suggests that all crystals, no matter what their thickness, have a high degree of crystallinity and the same crystal structure. The crystals have a range of thicknesses, as measured by small angle X-ray diffraction. The most common thicknesses correspond to the extended stem length and to one half or, surprisingly, two thirds of that value. A model is proposed for the non-integer fraction crystals in which half of the chain ends are incorporated in the crystals themselves

A unifying scheme for polymer crystallization based on recent experiments with wider implications for phase transformations

The main stream subject of chain-folded polymer crystn. is linked to the specialty stream of extended-chain crystn., the latter as typified by the crystn. of polyethylene under pressure. This is achieved through some new exptl. material comprising the recognition of thickening growth as a primary growth process of lamellae and of the prominence of metastable phases, specifically of the mobile hexagonal phase in polyethylene. The scheme relies on the consideration of crystal size as a stability detg. factor, namely on m.p. depression, which in general is different for different polymorphs. Under specifiable conditions phase stabilities can invert with size, i.e. a phase which is metastable for infinite size can become the stable one when the phase is sufficiently small. When applying this condition to crystal growth it follows that a crystal in such a situation will appear and grow in a phase that is different from that in its state of ultimate stability, maintaining this state as a metastable one or transforming into the ultimate stable state during growth according to circumstances. The consequences of such deliberations, of potential significance to all phase transformations also beyond polymer crystn., are being developed throughout the pape