Influence of various process conditions on surface finishes induced by the direct metal deposition laser technique on a Ti–6Al–4V alloy

The direct metal deposition (DMD) with laser is a free-form metal deposition process for manufacturing dense pieces, which allows generating a prototype or small series of near net-shape structures. One of the most critical issues is that produced pieces have a deleterious surface finish which systematically requires post machining steps. This problem has never been fully addressed before.The present work describes investigations on the DMD process, using an Yb-YAG disk laser, and a widely used titanium alloy (Ti–6Al–4V) to understand the influence of the main process parameters on the surface finish quality. The focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish.In order to understand the physical mechanisms responsible for deleterious surface finishes, we have carried out: (1) a precise characterization of the laser beam and the powder stream; (2) a large number of multi-layered walls using different process parameters (P(W), V(m/min), D_m (g/min), Gaussian or uniform beam distribution); (3) a real time fast camera analysis of melt pool dynamics and melt-pool – powder stream coupling; (4) a characterization of wall morphologies versus process parameters using 2D and 3D profilometry.The results confirm that surface degradation depends on two distinct aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters. Last, a simple analytical model was proposed to correlate melt-pool geometries to resulting surface finishes.     

Epoxidized natural rubber/dicarboxylic acid self-vulcanized blends

Curing behaviour as well as mechanical properties of binary blends of epoxidized natural rubber (ENR) and dodecanedioic acid (DA) were investigated for development of self-vulcanizable elastomer blends. Cross-linking reaction at 180 °C of reactive functional rubber containing 25 and 10 mol% epoxide groups was followed by rheology. The properties of the cured materials were studied by dynamic mechanical analysis, stress-strain experiments, and DSC measurements. It was shown that a specific ratio ENR/DA gave rise to optimum mechanical properties. This ratio decreases together with the epoxidation level of the rubber. DSC measurements revealed that the glass transition temperature of the cured material increases nonlinearly at high concentrations of cross-linking agent. By comparing cross-linking with DA and reaction with monofunctional lauric acid, this behaviour was attributed to polar interactions due to free carboxylic groups of pending diacid grafts.     

Coexistence of anti-phospholipid antibodies and endothelial perturbation in systemic lupus erythematosus patients with ongoing prothrombotic state

BACKGROUND: Anti-phospholipid antibodies (aPLs) were associated with an ongoing prothrombotic state in patients with systemic lupus erythematosus (SLE). Because aPLs are able to shift endothelial function toward procoagulant activity in vitro, we investigated the relationship among aPLs, ongoing prothrombotic state, and endothelial perturbation in SLE patients. METHODS AND RESULTS: We measured aPLs, anti-EC antibodies, circulating levels of prothrombin fragment F1 + 2 (F1 + 2), tumor necrosis factor-alpha (TNF-alpha), tissue-type plasminogen activator (TPA), and von Willebrand factor (vWF) in 43 SLE patients and 25 healthy subjects. Patients positive for aPLs (n = 23) had a higher prevalence of anti-EC antibodies (P = .02) and higher levels of F1 + 2 (P = .003) than aPL(-) patients. Endothelial perturbation, defined by elevated plasma levels of both TPA and vWF, was significantly associated with aPL positivity (P = .001). F1 + 2 > 1 nmol/L (mean +/- 2 SD of controls) was detected in all but one patient in whom aPL positivity and endothelial perturbation coexisted and in no aPL(+) patient without endothelial perturbation (P = .0039). F1 + 2 was significantly correlated with vWF (rho = .6, P = .004) and TPA (114 = .70, P = .0006) only in aPL(+) patients. Endothelial perturbation was closely associated with high values of TNF-alpha (P = .0001), anti-phospholipid (P = .001), and anti-EC antibodies (P = .012). In 31 patients without a clinical history of thrombosis followed up for 3 years, aPL(+) patients with endothelial perturbation showed higher F1 + 2 and TNF-alpha values than aPL(+) patients without endothelial dysfunction. CONCLUSIONS: This study shows that in SLE patients, aPL positivity is associated with an ongoing prothrombotic state only in the presence of endothelial perturbation. Our findings also suggest that aPLs and TNF-alpha might cooperate in inducing endothelial perturbation.     

Headache in intracerebral hematomas

OBJECTIVES: We sought to describe the frequency and location of headache in intracerebral hematoma (ICH) and to analyze its clinical and CT predictors by means of multivariate analysis. BACKGROUND: Headache is more common in intracerebral hemorrhage than in ischemic stroke, and its frequency varies with hematoma location, but the pathophysiologic mechanisms of headache associated with ICH are not fully known. METHODS: We examined a cohort of 289 patients with ICH during a 14-month period in a university hospital. Clinical, including the presence and location of headache, and CT features were collected by two neurologists. RESULTS: One hundred and sixty-five (57%) patients with ICH had a headache at the onset of their stroke. Headache was more common in cerebellar and lobar hemorrhages than in deep ones (thalamic, caudate, capsuloputaminal, brainstem). Headache was also more common in women, patients younger than 70 years, those who vomited, and those with meningeal signs, a Glasgow Coma Scale score < 10, a hematoma volume > 10 ml or CT evidence of intraventricular or subarachnoid bleeding, moderate to severe hydrocephalus, or transtentorial herniation or midline shift. In multiple logistic regression analysis, only meningeal signs (odds ratio [OR] = 2.3), cerebellar or lobar location (OR = 2.1), transtentorial herniation (OR = 1.8), and female gender (OR = 1.6) were significant predictors of headache at the onset of ICH. CONCLUSIONS: Hematoma location, meningeal signs, and gender are more predictive of headache than hematoma volume, suggesting that headache is more often related to the activation of an anatomically distributed system in susceptible individuals and to subarachnoid bleeding than to intracranial hypertension.     

A Vapor–Liquid–Solid Mechanism for Growing 3C‐SiC Single‐Domain Layers on 6H‐SiC(0001)

Growing device‐quality 3C‐SiC monocrystalline material is still an issue despite two decades of work dedicated to the subject. Using silicon as the substrate generates too many defects in the layers, owing to lattice mismatch, while it is very difficult to control the initial nucleation on an α‐SiC substrate so that 60° rotated domains are randomly formed. Herein, the elaboration of mono‐orientated 3C‐SiC layers on a 6H‐SiC(0001) on‐axis, Si face substrate using a vapor–liquid–solid mechanism is reported. This non‐conventional approach for growing monocrystalline layers involves feeding a Ge–Si melt by a propane flux at a temperature ranging from 1250 to 1550 °C. We show that, by using this technique, the 3C‐SiC material is almost always obtained on an hexagonal substrate, even if the crystal seed is oriented 8° off‐axis. Using on‐axis 6H‐SiC seeds and optimal growth conditions results in the reproducible deposition of single‐domain 3C‐SiC layers. A mechanism is proposed to clarify some aspects of this process.     

Investing in the Personality Vulnerability Research Program--Current Dividends and Future Growth: Rejoinder to Coyne, Thompson, and Whiffen (2004).

The authors do not see any benefit to J. C. Coyne. R. Thompson, and V. Whiffen's (2004) proposal to draw sharp boundaries between psychodynamic vulnerability theories, research on the onset of syndromal depression, and research with vulnerable, nondepressed populations. These domains have been and remain mutually relevant. Coyne et al. did not bring forward new evidence concerning the 6 issues addressed by D. C. Zuroff. M. Mongrain. and D. A. Santor (2004); consequently, the authors stand by their conclusions. According to Lakatos (as cited in B. Gholson & P. Barker. 1985), scientists justifiably continue to invest in research programs as long as the programs remain progressive. The personality vulnerability program is theoretically and empirically progressive and merits continued investment. Nevertheless, the field would benefit if Coyne et al. articulated a systematic contextualist research program to compete with the personality research program. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the thermochemistry of the rare earth compounds with thep-block elements

A summary is given of the experimental work carried out to determine the heats of formation of the rare earth compounds with a number of elements of thep-block of the periodic table (in particular Al, In, Sn, Pb, As, Sb, and Bi). The experimental methods and the devices constructed to this end are briefly described and commented on. Some results recently obtained in the thermochemical investigation of binary (Pr-Al and Gd-Pb) and ternary (Ce-Ni-Al and La-Sb-Bi) alloys are presented.     

A Cross-Layer Multi-Hop Simulator for IEEE 802.11e

In this work we simulate the ad hoc mode of IEEE 802.11e for routing optimisation. We simulate the behaviour of routing algorithms at the network layer by using a custom-made cross-layer network simulator developed by our team, which simultaneously considers the physical and Medium Access Control (MAC) layers. Although the simulator also supports the infrastructure mode, in this paper we focus on the ad hoc feature which was introduced by the authors. We opted for the simulator approach over the theoretical analysis, but we also present a mathematical model for IEEE 802.11 ad hoc networks. Some initial tests were performed by using a simple routing algorithm (to evaluate the behaviour of the system in terms of selection of the path between a source and a destination, and the correctness of the calculated metrics, which include end-to-end delay, packets lost, packets delivered), but more advanced cross-layer design solutions were also tested. When information from the physical and MAC layers is used as an input to the routing algorithm, improvements are achieved in the performance of the network. Several functions were compared and the algorithm that privileges shorter links accounting with the metric “collision rate” achieves the best results. When compared with a standard routing solution, this cross-layer approach allows to increase the number of packets delivered, while not significantly affecting the end-to-end delay of the packets.