Stress-corrosion behavior of aluminum-lithium alloys in aqueous environments

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing

Effective Dynamics of a Tracer Particle Interacting with an Ideal Bose Gas

We study a system consisting of a heavy quantum particle, called tracer particle, coupled to an ideal gas of light Bose particles, the ratio of masses of the tracer particle and a gas particle being proportional to the gas density. All particles have non-relativistic kinematics. The tracer particle is driven by an external potential and couples to the gas particles through a pair potential. We compare the quantum dynamics of this system to an effective dynamics given by a Newtonian equation of motion for the tracer particle coupled to a classical wave equation for the Bose gas. We quantify the closeness of these two dynamics as the mean-field limit is approached (gas density $\to\infty$). Our estimates allow us to interchange the thermodynamic with the mean-field limit.Comment: 27 pages, typos corrected, a few more explanations adde

Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations

Dynamics of Sound Waves in an Interacting Bose Gas

We consider a non-relativistic quantum gas of $N$ bosonic atoms confined to a box of volume $\Lambda$ in physical space. The atoms interact with each other through a pair potential whose strength is inversely proportional to the density, $\rho=\frac{N}{\Lambda}$, of the gas. We study the time evolution of coherent excitations above the ground state of the gas in a regime of large volume $\Lambda$ and small ratio $\frac{\Lambda}{\rho}$. The initial state of the gas is assumed to be close to a \textit{product state} of one-particle wave functions that are approximately constant throughout the box. The initial one-particle wave function of an excitation is assumed to have a compact support independent of $\Lambda$. We derive an effective non-linear equation for the time evolution of the one-particle wave function of an excitation and establish an explicit error bound tracking the accuracy of the effective non-linear dynamics in terms of the ratio $\frac{\Lambda}{\rho}$. We conclude with a discussion of the dispersion law of low-energy excitations, recovering Bogolyubov's well-known formula for the speed of sound in the gas, and a dynamical instability for attractive two-body potentials.Comment: 42 page

The relative stress-corrosion-cracking susceptibility of candidate aluminum-lithium alloys for aerospace structural applications

The microstructure and tensile properties of two powder metallurgy processed aluminum-lithium alloys were determined. Strength properties of 480 MPa yield and 550 MPa ultimate tensile strength with 5% strain to fracture were attained. Very little reduction in area was observed and fracture characteristics were brittle. The magnesium bearing alloy exhibited the highest strength and ductility, but fracture was intergranular. Recrystallization and grain growth, as well as coarse grain boundary precipitation, occurred in Alloy 2. The fracture morphology of the two alloys differed. Alloy 1 fractured along a plane of maximum shear stress, while Alloy 2 fractured along a plane of maximum tensile stress. It is found that a fixed orientation relationship exists between the shear fracture plane and the rolling direction which suggests that the PM alloys are strongly textured

Laterolateral teleradiography of the skull as a screening method for OSA/OSAS, in patients in orthodontic treatment

Aim: Obstructive sleep apnea syndrome (OSAS) is the most common type of sleep apnea and it is caused by complete or partial obstruction of the upper airway. Adenotonsillar hypertrophy, obesity, cranio-facial anomalies and neuromuscular diseases are the main risk factors for the development of OSAS in the pediatric age. Specially several studies identify the relationship between respiratory disorders in sleep and obesity, and, in particular, between OSAS and obesity, designing a prevalence of OSAS among obese subjects between 14 and 78%. The diagnosis of OSAS in the child is of great importance as it can lead to neurocognitive and behavioral complications, growth retardation, systemic arterial hypertension, pulmonary hypertension, cardiovascular disease and metabolism. The WHO (World Health Organization) has established the new criteria for the classification of Obesity on the basis of BMI and the risk of comorbidities, identifying a moderate risk for underweight subjects, a very low risk for normal weights and an increased risk from severe to severe for overweight and obese individuals respectively. According to that the aim of this study is to evaluate the correlation between obstructive sleep apnea syndrome and cephalometric variables in children considering age and BMI. Materials and methods: Children aged 7–10 years and 11-14 years with no genetic syndrome, previous otorhinolaryngologic or orthodontic therapy treatments are being selected from our Departments of Paediatric Dentistry, University of Palermo, and from the Department of Orthodontics, University of Messina (Italy). All patients so far recruited and visited for orthodontic problems were in mixed or early permanent dentition phase, with the first upper molars fully erupted and presented to the history of several symptoms of Osas, such as recurring episodes of shallow or paused breathing during sleep, waking up frequently to urinate, morning headaches, memory or learning problems and not be able to concentrate or feeling irritable. Dental records and lateral cephalometric radiographs were obtained for all of the patients and than they have been subjected to paediatric, otolaryngology and polysomnography visits. Subject with a positive diagnosis of Osas were studied and they were divided in group based on their BMI. In all groups the inter-molar distance in dental records was measured, and the cephalometric traces have been calculated. As reported by the study by Galeotti et al. the cephalometric measurements analysed are S-PNS, ad1-PNS, and ad2-PNS for the nasopharynx; p-pp and pa for oropharynx; H-H’ for the Hyoid bone; SNA for the maxilla; SNB;ANB and Go-Me for the mandible; S-Go, N-Me and P-A for facial Height; SN for cranial base; SN-MP and PP-MP for the typology, and angle ArGoMe for Growth prevision. At the time that children are still in the way of recruitment the results may not yet be defined; however it is necessary to emphasize the importance of the study, because in the child respiratory disturbances in the sleep, and in particular the OSAS, are often underestimated, despite representing the third place between the threats of health after the smoke and the excess of weight

Stream dynamics between 1 AU and 2 AU: A detailed comparison of observations and theory

A radial alignment of three solar wind stream structures observed by IMP-7 and -8 (at 1.0 AU) and Voyager 1 and 2 (in the range 1.4 to 1.8 AU) in late 1977 is presented. It is demonstrated that several important aspects of the observed dynamical evolution can be both qualitatively and quantitatively described with a single-fluid 2-D MHD numerical model of quasi-steady corotating flow, including accurate prediction of: (1) the formation of a corotating shock pair at 1.75 AU in the case of a simple, quasi-steady stream; (2) the coalescence of the thermodynamic and magnetic structures associated with the compression regions of two neighboring, interacting, corotating streams; and (3) the dynamical destruction of a small (i.e., low velocity-amplitude, short spatial-scale) stream by its overtaking of a slower moving, high-density region associated with a preceding transient flow. The evolution of these flow systems is discussed in terms of the concepts of filtering and entrainment

Simultaneous Bilateral Single-Port Radical Nephrectomies

Results of this study suggest that single-port radical nephrectomy may be a safe and feasible option versus traditional laparoscopic nephrectomy

The Sunyaev-Zeldovich Effect at 1 and 2 mm towards ROSAT Clusters

An observing campaign was devoted to the search for the Sunyaev-Zeldovich (S-Z) effect towards X-ray ROSAT Clusters in the millimetric spectral domain. A double channel (1.2 and 2 {\it mm}) photometer was installed at the focus of the 15m Swedish ESO Submillimeter Telescope (SEST) in Chile in september 1994 and 1995 and observations of the targets S1077, A2744, S295 and RXJ0658-5557 were gathered. Detections were found for A2744 at 1 {\it mm} and in both channels (at 1.2 and 2 {\it mm}) towards RXJ0658-5557. For the first time there is evidence for the S-Z enhancement and both the latter and the decrement were detected on the same source. We discuss astrophysical and systematic effects which could give origin to these signals.Comment: 6 pg Latex file (style file included) including 1 ps figure, XVIth Moriond Astrophysics Meeting "The Anisotropies of the Cosmic Microwave Background", Les Arcs, Savoie-France, March 16-23 199

Notes pour une mise au point:Peintres et photographes italiens de la deuxi\ue8me moiti\ue9 du XIXesi\ue8cle

Catalogo della mostra, Collezioni d'arte e fotografia artistica nell'Italia del Risorgimento, Roma, Museo del Vittoriano-Grenoble, Istituto italiano di cultura. Lo scritto rievoca l'ambivalenza del rapporto tra gli artisti, i pittori, in particolare, e la fotografia nella seconda met\ue0 dell'Ottocento, incerti se accoglierla come un alleato, un utile strumento per la creazione, o un pericoloso rivale