Crack propagation in layered plates—an experimental study

The effects of the layer height and the material properties of a layered medium on the propagation mode of a crack are discussed. Crack-propagation velocities and dynamic stress-intensity factors were evaluated during fracture and the corresponding curves were plotted. The medium consisted of two identical external layers and a middle layer of softer or harder material. This layer contained an initial crack which ran parallel to the interfaces of the layers. All phases of the specimens were fabricated from epoxy polymers. After the preparation of the middle layer, the surrounding layers were successively cast along the middle layer's straight boundaries without applying any kind of adhesive. High-speed photography and dynamic caustics were utilized to establish the changes in crack speeds and intensities of the stress field. The influence of geometry and especially of the height of the middle layer and the mechanical properties of the layered material was studied; interesting results were derived.     

Multiphoton ionization of magnesium and calcium atoms by short and intense laser pulses

Single and double ionization of magnesium and calcium atoms following Nd: YAG laser multiphoton excitation at 1064 and 532 nm have been studied by employing pulses of 35 ps and 200 ps duration at intensities of the order of 10¹⁰–2×10¹³ W/cm². The dependence of ion formation on the laser intensity has been measured and the slopes of the linear parts of the log-log plots and the ratios of saturation intensities for two pulse durations have been compared with the predictions of the scaling law. No evidence for a pure direct double ionization process has been obtained.     

Rapid access to the tricyclic spirotetronic core of abyssomicins

[reaction: see text] Abyssomicins, a novel class of polyketide antibiotics, are characterized by an unprecedented spirotetronic tricyclic subunit in their structure. In this letter, a short synthesis of a suitably functionalized tricyclic precursor of abyssomicins is reported. Key steps of the synthesis are (i) the highly stereoselective Al(III)-tethered Diels-Alder reaction and (ii) the tandem Dieckmann cyclization/TBS trapping of the C9 hydroxyl group followed by a regioselective intramolecular epoxide opening for the assembly of the target tricyclic structure.     

Diastereoselective solution and multipin-based combinatorial array synthesis of a novel class of potent phosphinic metalloprotease inhibitors

The solution-phase synthesis and resolution of new phosphinopeptidic building blocks containing a triple bond was realized in high yields and optical purities (units 3 a-d). The absolute configuration of the target compounds was unambiguously established by NMR studies. A post-assembly diversification strategy of these blocks was developed through 1,3-dipolar cycloaddition of a variety of in situ prepared nitrile oxides. This strategy led to the rapid and efficient diastereoselective preparation of a novel class of isoxazole-containing phosphinic peptides (peptides 5 a-i). Solid-phase version of this strategy was efficiently achieved on multipin solid technology, by developing a new protocol for the coupling of P-unprotected dipeptidic blocks with solid supported amino acids in a quantitative and diastereoselective manner. Optimization of dipolar cycloadditions onto pin-embodied phosphinic peptides allowed the convenient preparation of this new class of pseudopeptides. The crude phosphinic peptides (9 a-k) were obtained in high yields and purity as determined by RP-HPLC. Inhibition assays of some of these peptides revealed that they behave as very potent inhibitors of MMPs, outmatching previously reported phosphinic peptides, in terms of potency (K(i) in the range of few nM).     

Products from furans. XV. Synthesis of novel tyramine derivatives via 6-hydroxy-2H-pyran-3(6H)-ones

Furan chemistry was utilized for the synthesis of several novel tyramine derivatives. Thus 2H-pyran-3(6H)-ones were used as keystone intermediates for the preparation of novel α,β-disubstituted tyramine derivatives. Furthermore by the same approach tyramine was derivatized with a molecule of GABA.     

Quantitative angle-resolved SPR imaging of DNA-DNA and DNA-drug kinetics

We demonstrate the quantitative characterization of DNA-DNA and DNA-drug interactions by angle-resolved surface plasmon resonance (SPR) imaging. Combining the angle-scanning capabilities of traditional SPR with the spatial definition capabilities of imaging, we directly measure DNA and drug surface coverages and kinetics simultaneously for multiple patterned spots. We find excellent agreement of DNA-DNA hybridization kinetics and thermodynamics measured by both the imaging system and traditional SPR. Instrument response and sensitivity is further demonstrated by successful measurement of association and dissociation kinetics of actinomycin-D binding to a low-density doubled-stranded DNA binding sequence. Without independent calibration, analysis of angle-resolved SPR imaging data yields 2.9 +/- 0.1 drugs per duplex at saturation coverage, consistent with all available duplex binding sites being occupied.     

Products from furans. V Synthesis of oxygen containing isosteres of sympathomimetic amines via 6-hydroxy-2H-pyran-3(6H)-ones and their cis-platinum(II) complexes

Novel amino analogues of sympathomimetic amines, which contain the pyran ring as a consequence of their common route of preparation, were synthesized. A modified Strecker reaction on tetrahydro-2H-pyran-3-one derivatives yielded α-benzylamino nitriles, which upon subsequent hydrogenation and hydrogenolysis gave the target 1,2-diamines. The prepared diamines were indeed sympathomimetic on the basis of molecular mechanics studies, since they have been found to fulfill earlier considerations on the minimal structural requirements, necessary to attain high affinity to dopamine (DA) receptors. Furthermore the prepared 1,2-diamino compounds were used as ligands for the synthesis of cis-Platinum(II) complexes.     

The effect of traffic shaping in efficiently providing end-to-end performance guarantees

This paper reports new results concerning the capabilities of a family of service disciplines aimed at providing per-connection end-to-end delay (and throughput) guarantees in high-speed networks. This family consists of the class of rate-controlled service disciplines, in which traffic from a connection is reshaped to conform to specific traffic characteristics, at every hop on its path. When used together with a scheduling policy at each node, this reshaping enables the network to provide end-to-end delay guarantees to individual connections. The main advantages of this family of service disciplines are their implementation simplicity and flexibility. On the other hand, because the delay guarantees provided are based on summing worst case delays at each node, it has also been argued that the resulting bounds are very conservative which may more than offset the benefits. In particular, other service disciplines such as those based on Fair Queueing or Generalized Processor Sharing (GPS), have been shown to provide much tighter delay bounds. As a result, these disciplines, although more complex from an implementation point-of-view, have been considered for the purpose of providing end-to-end guarantees in high-speed networks. In this paper, we show that through proper selection of the reshaping to which we subject the traffic of a connection, the penalty incurred by computing end-to-end delay bounds based on worst cases at each node can be alleviated. Specifically, we show how rate-controlled service disciplines can be designed to outperform the Rate Proportional Processor Sharing (RPPS) service discipline. Based on these findings, we believe that rate-controlled service disciplines provide a very powerful and practical solution to the problem of providing end-to-end guarantees in high-speed networks.     

Dynamic thermoelastic effects for half-planes and half-spaces with nearly-planar surfaces

The effects of non-planarity on the dynamic surface temperature changes induced for plane-strain and 3D problems on the nearly-planar surfaces of, respectively, coupled thermoelastic half-planes and half-spaces by surface heat fluxes are treated. The nearly-planar nature of the surfaces allows the problem solutions to be written, following a standard perturbation scheme, as series expansions in a dimensionless surface contour amplitude parameter. The first, or zero-order, terms represent the ideal (planar) surface solutions, while the second, or first-order, terms represent corrections for non-planarity.Because the characteristic thermoelastic time is of O(10^–7)s, large-time asymptotic forms of the exact integral transform solutions can be used. These can be inverted exactly and used in Green's function operations to yield analytic, or integrals of analytic, expressions. Two types of thermal loading for the half-plane and yet a third type of thermal loading for the half-space are considered. Comparison of the zero- and first-order surface temperature changes for each case indicate that non-planarity gives rise for large times to changes in surface regions beyond those predicted by an ideal surface analysis. Moreover, the magnitudes of these changes can be more significant than the ideal surface results.     

Indoor measurements of microclimate variables and ozone in the church of San Vincenzo (Monastery of Bassano Romano — Italy): A pilot study

This experiment describes a way of operation in MMA-CH, Microclimate Multivariate Analysis for Cultural Heritage. It is realised by choosing appropriate meteorological and air composition parameters according to the environment to be investigated, measuring them by appropriate instruments and making acquisition of time series to find out all possible correlations. It is possible to understand how this branch of multivariate analysis could contribute to the “science of conservation” by applying an appropriate microclimatic and air composition monitoring and processing. Microclimate parameters such us air temperature, relative humidity, mixing ratio and air composition parameters such as tropospheric ozone content were monitored during a summer period to assess their impact on the cultural heritage of the Benedictine Monastery dedicated to San Vincenzo Martire (Diocletian's Christians persecution). This marvellous place is settled next to Bassano Romano village, in the Sabatini mountains rural area. The importance of the site is established by the presence of many art treasures, like 2 frescos of '700, 2 frescos of '600 (Caravaggio School) and by a marble statue of Jesus (“The Jesus cross carrying”) which is recently attributed to Michelangelo as the original one.