The influence of specimen geometry on crack tip plasticity

The effect of panel width and thickness on the crack tip plasticity of center-cracked fracture panels of 7075-T6 aluminum alloy was examined. The plastic zone formation was continually monitored photographically during the fracture test and the zone size and shape determined by an image distortion technique. The influence of specimen width and thickness was examined to determine its effect on the plastic zone behavior and the mode (stable tear or pop-in) of initial crack extension. Plastic zone models were then compared with the characteristic plastic zone size parameters measured experimentally and the models evaluated. From these results, the effect of panel thickness and width on the fundamental characteristics of crack tip plasticity and initial crack extension was assessed. The importance and implications of these findings on methods of evaluating material toughness are examined. In addition, the applicability of these zone size models in linear elastic fracture mechanics applications are discussed.     

Failure characteristics during cyclic oxidation of yttria stabilized zirconia thermal barrier coatings deposited via electron beam physical vapor deposition on platinum aluminide and on NiCoCrAlY bond coats with processing modifications for improved performances

In this study, the cyclic oxidation lives of the current state-of-the-art thermal barrier coating (TBC) systems (heavy grit-blasted Pt aluminide and NiCoCrAlY bond coats with EBPVD TBCs) were investigated first, followed by TBC systems that were modified based on the results obtained on the failure of the state-of-the-art TBC systems. The specimens were subjected to cyclic oxidation testing, mostly at 1100 °C, in a bottom-loading furnace in laboratory air. Optical and scanning electron microscopy techniques were used to characterize the as-processed and failed specimens. The state-of-the-art TBC systems with NiCoCrAlY bond coats failed as the result of defects that were identified as TBC defects, transient oxides, surface defects, and reactive element-rich oxide protrusions. On the other hand, the failures of the state-of-the-art TBC systems with Pt aluminide bond coats were due to deformation of the bond coat by a mechanism known as ratcheting. The stored strain energy in the thermally grown oxide (TGO) was also a factor that contributed to the failure of both systems. Most of the modifications performed on the state-of-the-art TBC systems improved their lives to some extent. In the case of NiCoCrAlY systems, elimination or at least minimization of the identified defects was responsible for the improvements, whereas the prevention of the ratcheting type of failure was the main reason for the improvement in lives in the case of Pt aluminide systems. On the other hand, other issues, such as slower growth of the TGO as well as improved TGO/bond coat interfacial toughnesses with some of the modifications, were observed to be contributing factors in the improved lives. Based on the observations on the failure of both the state-of-the-art as well as the modified TBC systems, the surface condition of the bond coats and the morphology of the TBCs close to the TGO were found to have a first-order effect on the failure of TBC systems. The characteristics of the TGO, such as composition, growth rate, and adherence both to the bond coat and the TBC, as well as the characteristics of the bond coats were also observed to have an effect on the failures. Recommendations for future work that should be pursued to better define the conditions necessary for optimized TBC performances are given.     

Triboelectric charging of polymer powders in fluidization andtransport processes

In this paper, we investigated the role of tribocharging in fluidization, flowability, and q/m distribution as functions of particle size distribution (PSD), fluidization time, and transport tubes of different materials. A charge separator was used to determine mass fractions of powder that had positive, zero, and negative charges. For the two acrylic powders tested, one (Sample A) had volume median diameter d₅₀ 18.73 μm while the other (Sample B) had d₅₀ 24.17-μm diameter. During fluidization for 1 h at a relative humidity of 57%, powder B acquired positive charge with charge-to-mass ratio Q/M=0.3 μC/g, and 25% of the powder mass had negative charge with Q/M=-0.36 μC/g. About 35% of the powder mass had particles with nearly zero net charge. Tribocharging during fluidization and transport processes was attributed to particle-particle and particle-wall collisions. Of the total charged particles, about 60% were positively charged while 40% were negatively charged. Each particle may have had patches of charges on its surface, some positive and some negative. The sum total of all patches of charges may yield positive, negative, or essentially neutral polarities on a given particle. For a relatively narrow size distribution of powder, the PSD is often assumed to be conserved during fluidization. A shift in PSD toward larger diameter particles was anticipated because of the possible elutriation of the fine fraction of the powder, but the actual shift was only about 1 μm after 1 h of fluidization. Under identical operational conditions using a fluidized bed, powder pump, transport hose, and corona gun, powder B had nearly twice the mass flow rate of Powder A. Such differences in flowability of powders influence charging and deposition efficiencies in powder coating applications     

Compositional effects on the Type I hot corrosion of β-NiAl alloys

Cast alloys of nominal compositions Ni-36Al, Ni-36Al-5Co, Ni-36Al-5Pt, Ni-36Al-5Co-5Pt, and Ni-36Al-5Cr (at.%) were tested under Type I (900 °C) hot corrosion conditions in order to determine the influence of various elements commonly found in diffusion aluminide coatings on the resistance to this mode of attack. Chromium was found to be the most effective element in conferring hot corrosion resistance, but improvements in performance were also found with the addition of Co and/or Pt. Experimental evidence is presented which suggests that each of these elements increase the hot corrosion resistance of β-NiAl alloys primarily by increasing their ability to rapidly form a thermally grown Al₂O₃ scale and to heal this scale in the event of damage. Potential explanations for this enhanced scale formation and healing capability are discussed.     

Chemically isolated graphene nanoribbons reversibly formed in fluorographene using polymer nanowire masks

We demonstrated the fabrication of graphene nanoribbons (GNRs) as narrow as 35 nm created using scanning probe lithography to deposit a polymer mask(1-3) and then fluorinating the sample to isolate the masked graphene from the surrounding wide band gap fluorographene. The polymer protected the GNR from atmospheric adsorbates while the adjacent fluorographene stably p-doped the GNRs which had electron mobilities of ～2700 cm2/(V·s). Chemical isolation of the GNR enabled resetting the device to nearly pristine graphene.     

Antineoplastic agents. 397: Isolation and structure of sesterstatins 4 and 5 from Hyrtios erecta (the Republic of Maldives)

The wide ranging marine sponge Hyrtios erecta is the source of the spongistatins, a new class of macrocyclic lactone antineoplastic agents. Continuation of a detailed investigation of cancer cell growth inhibitory (P388 lymphocytic leukemia) fractions (trace) from H. erecta has revealed the presence (10(-5) to 10(-7)% yield) of cytotoxic pentacyclic sesterterpenes. Employing P388 leukemia and human tumor cell line-guided bioassay techniques, two new moderate inhibitors of cancer cells were isolated and named sesterstatins 4 (1a, P388 ED50 4.9 micrograms/mL) and 5 (1b, DU-145 prostate GI50 1.9 micrograms/mL). Similar to other sesterterpenes, sesterstatin 5 inhibited growth of a Gram-positive bacterium. High field (500 MHz) 2-D NMR techniques were primarily employed for initial structural assignments, and structural assignments were confirmed by X-ray crystal structure determination of sesterstatin 4 (1a) and 5 (1b).     

Overexpression, purification, and characterization of the cloned metallo-beta-lactamase L1 from Stenotrophomonas maltophilia

OBJECTIVES: The purpose of this study was to assess whether the presence or absence of myocardial viability during dobutamine echocardiography (DE) predicts survival in patients with coronary artery disease (CAD) and severe left ventricular (LV) dysfunction. BACKGROUND: In patients with CAD, the presence of myocardial viability during DE identifies viable myocardium and predicts recovery of LV systolic function after revascularization. However, there is little data on the relation between myocardial viability and clinical outcome in patients with CAD and severe LV dysfunction. METHODS: We studied 318 patients with CAD and a LV ejection fraction (EF) < or =35% who underwent DE and were followed for 18+/-10 months. Patients were classified into four groups. Group I (n=85) consisted of patients who had evidence of myocardial viability and subsequently underwent revascularization. Group II (n=119) consisted of patients with myocardial viability who did not undergo revascularization. Group III (n=30) consisted of patients who did not have myocardial viability and underwent revascularization. Finally, group IV (n=84) patients lacked myocardial viability and did not undergo revascularization. RESULTS: The four groups had similar baseline characteristics and rest LVEF. During follow-up there were 51 deaths (16%). The mortality rate was 6% in group I, 20% in group II, 17% in group III and 20% in group TV (p=0.01, group I vs. other groups). CONCLUSIONS: In patients with CAD and severe LV dysfunction who demonstrated myocardial viability during DE, revascularization improved survival compared with medical therapy.     

Structure-cytotoxic activity relationship for the toad poison bufadienolides

The toad poison bufadienolides including natural and derivatized compounds were tested for their cytotoxic effects on primary liver carcinoma cells PLC/PRF/5 and their structure-cytotoxic activity relationships were studied. For this study, a ligand-binding model was developed by using a pharmacophore mapping program, Distance Comparisons (DISCO). The structural features that are common to the 3D structures of active bufadienolides were identified to provide approach to a 3D QSAR method by using Comparative Molecular Field Analysis (CoMFA) study and to correlate the steric and electrostatic fields of the molecules to their activities. A valuable model which enables prediction of their activities was obtained from the CoMFA analysis, which may be employed for the drug designs of new bufadienolide analogues.     

The effect of observations on Bayesian choice of an autoregressive model

Abstract. We consider the effect, on a Bayes factor, of omitting observations in time‐series models. In particular, we study a Bayes factor for deciding between autoregressive models of different orders. Throughout we use Gibbs sampling to estimate the parameters of the models and the marginal densities. We illustrate the methods using data generated from an autoregressive model and some data on bag snatching in the Hyde Park area of Chicago.