Thermal properties and thermal shock resistance of γ-Y 2Si2O7

Thermal properties, namely, Debye temperature, thermal expansion coefficient, heat capacity, and thermal conductivity of γ-Y 2Si2O7, a high-temperature polymorph of yttrium disilicate, were investigated. The anisotropic thermal expansions of γ-Y2Si2O7 powders were examined using high-temperature X-ray diffractometer from 300 to 1373 K and the volumetric thermal expansion coefficient is (6.68±0.35) × 10-6 K-1. The linear thermal expansion coefficient of polycrystalline γ-Y2Si2O7 determined by push-rod dilatometer is (3.90±0.4) × 10-6 K-1, being very close to that of silicon nitride and silicon carbide. Besides, γ-Y2Si2O7 displays a low-thermal conductivity, with a κ value measured below 3.0 W·(m·K) -1 at the temperatures above 600 K. The calculated minimum thermal conductivity, κmin, was 1.35 W·(m·K) -1. The unique combination of low thermal expansion coefficient and low-thermal conductivity of γ-Y2Si2O7 renders it a very competitive candidate material for high temperature structural components and environmental/thermal-barrier coatings. The thermal shock resistance of γ-Y2Si2O7 was estimated by quenching dense materials in water from various temperatures and the critical temperature difference, ΔTc, was determined to be 300 K.

Kinetics and mechanism of hot corrosion of γ-Y 2Si 2O 7 in thin-film Na 2SO 4 molten salt

γ-Y 2Si 2O 7 is a promising candidate material both for hightemperature structural applications and as an environmental/thermal barrier coating material due to its unique properties such as high melting point, machinability, thermal stability, low linear thermal expansion coefficient (3.9×10 -6/K, 200°-1300°C), and low thermal conductivity (<3.0 W/ṁK above 300°C). The hot corrosion behavior of γ-Y 2Si 2O 7 in thin-film molten Na 2SO 4 at 850°-1000°C for 20 h in flowing air was investigated using a thermogravimetric analyzer (TGA) and a mass spectrometer (MS). γ-Y 2Si 2O 7 exhibited good resistance against Na 2SO 4 molten salt. The kinetic curves were well fitted by a paralinear equation: the linear part was caused by the evaporation of Na2SO4 and the parabolic part came from gas products evolved from the hotcorrosion reaction. A thin silica film formed under the corrosion scale was the key factor for retarding the hot corrosion. The apparent activation energy for the corrosion of γ-Y 2Si 2O 7 in Na 2SO 4 molten salt with flowing air was evaluated to be 255 kJ/mol.

Hot corrosion of γ-Y2Si2O7 in strongly basic Na2CO3 molten salt environment

γ-Y2Si2O7 is a promising candidate both for high temperature structural applications and as thermal barrier coatings due to its unique combination of properties, such as high melting point, good machinability, high thermal stability, low linear thermal expansion coefficient (3.9 × 10-6 K-1, 25-1400 °C) and low thermal conductivity (<3 W/m K above 300 °C). In this work, the hot corrosion behavior of γ-Y2Si2O7 in strongly basic Na2CO3 molten salt at 850-1000 °C for 20 h in flowing air was investigated. In the employed conditions, multi-layer corrosion scales with total thickness less than 90 μm were formed. At 850-900 °C, the outmost layer of the scale was composed of the reprecipitation of Y2O3, the bottom of a Si-rich Na2O·xSiO2 (x > 3.65) melt layer, and the middle of a NaYSiO4 layer. At 1000 °C, the corrosion products turned out to be a mixture of NaY9Si6O26 and Si-rich Na2O·xSiO2 (x > 3.65). In all cases, a thin layer of protective SiO2 formed under the Na2O·xSiO2 melt and protected the bulk material from further corrosion.

Evaluation of Vestibular Function with Visual Feedback Posturography and Motorized Head Impulse Test.

Objectives: To evaluate the applicability of visual feedback posturography (VFP) for quantification of postural control, and to characterize the horizontal angular vestibulo-ocular reflex (AVOR) by use of a novel motorized head impulse test (MHIT). Methods: In VFP, subjects standing on a platform were instructed to move their center of gravity to symmetrically placed peripheral targets as fast and accurately as possible. The active postural control movements were measured in healthy subjects (n = 23), and in patients with vestibular schwannoma (VS) before surgery (n = 49), one month (n = 17), and three months (n = 36) after surgery. In MHIT we recorded head and eye position during motorized head impulses (mean velocity of 170º/s and acceleration of 1 550º/s²) in healthy subjects (n = 22), in patients with VS before surgery (n = 38) and about four months afterwards (n = 27). The gain, asymmetry and latency in MHIT were calculated. Results: The intraclass correlation coefficient for VFP parameters during repeated tests was significant (r = 0.78-0.96; p < 0.01), although two of four VFP parameters improved slightly during five test sessions in controls. At least one VFP parameter was abnormal pre- and postoperatively in almost half the patients, and these abnormal preoperative VFP results correlated significantly with abnormal postoperative results. The mean accuracy in postural control in patients was reduced pre- and postoperatively. A significant side difference with VFP was evident in 10% of patients. In the MHIT, the normal gain was close to unity, the asymmetry in gain was within 10%, and the latency was a mean ± standard deviation 3.4 ± 6.3 milliseconds. Ipsilateral gain or asymmetry in gain was preoperatively abnormal in 71% of patients, whereas it was abnormal in every patient after surgery. Preoperative gain (mean ± 95% confidence interval) was significantly lowered to 0.83 ± 0.08 on the ipsilateral side compared to 0.98 ± 0.06 on the contralateral side. The ipsilateral postoperative mean gain of 0.53 ± 0.05 was significantly different from preoperative gain. Conclusion: The VFP is a repeatable, quantitative method to assess active postural control within individual subjects. The mean postural control in patients with VS was disturbed before and after surgery, although not severely. Side difference in postural control in the VFP was rare. The horizontal AVOR results in healthy subjects and in patients with VS, measured with MHIT, were in agreement with published data achieved using other techniques with head impulse stimuli. The MHIT is a non-invasive method which allows reliable clinical assessment of the horizontal AVOR.

RTK-based GNSS drifters for monitoring in estuaries and rivers: Field experimental results

This paper presents a novel RTK-based GNSS Lagrangian drifter system that is capable of monitoring water velocity, turbulence and dispersion coefficients of river and estuarine. The Lagrangian drifters use the dual-frequency real time kinematic (RTK) technique for both position and velocity estimations. The capsule is designed to meet the requirements such as minimizing height, diameter, minimizing the direct wind drag, positive buoyancy for satellite signal reception and stability, and waterproof housing for electronic components, such as GNSS receiver and computing board. The collected GNSS data are processed with post-processing RTK software. Several experiments have been carried out in two rivers in Brisbane and Sunshine Coast in Queensland. Results show that the high accuracy GNSS-drifters can be used to measure dispersion coefficient resulting from sub-tidal velocity fluctuations in shallow tidal water. In addition, the RTK-GNSS drifters respond well to vertical motion and thus could be applicable to flood monitoring.

Influence of roughness parameters and surface texture on friction during sliding of pure lead over 080 M40 steel

In the present investigation, tests were conducted on a tribological couple made of cylindrical lead pin with spherical tip against 080 M40 steel plates of different textures with varying roughness under both dry and lubricated conditions using an inclined pin-on-plate sliding tester. Surface roughness parameters of the steel plates were measured using optical profilometer. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. It was observed that the coefficient of friction and the formation of transfer layer depend primarily on the surface texture of hard surfaces. A newly formulated non-dimensional hybrid roughness parameter called 'xi' (a product of number of peaks and maximum profile peak height) of the tool surface plays an important role in determining the frictional behaviour of the surfaces studied. The effect of surfaces texture on coefficient of friction was attributed to the variation of plowing component of friction, which in turn depends on the roughness parameter 'xi'.

Design considerations and economics of different shaped surface aeration tanks

This paper deals with the design considerations of surface aeration tanks on two basic issues of oxygen transfer coefficient and power requirements for the surface aeration system. Earlier developed simulation equations for simulating the oxygen transfer coefficient with theoretical power per unit volume have been verified by conducting experiments in geometrically similar but differently shaped and sized square tanks, rectangular tanks of length to width ratio (L/W) of 1.5 and 2 as well as circular tanks. Based on the experimental investigations, new simulation criteria to simulate actual power per unit volume have been proposed. Based on such design considerations, it has been demonstrated that it is economical (in terms of energy saving) to use smaller tanks rather than using a bigger tank to aerate the same volume of water for any shape of tanks. Among the various shapes studied, it has been found that circular tanks are more energy efficient than any other shape.

Peripheral facial palsy : Grading, Etiology, and Melkersson-Rosenthal Syndrome

The objective of this study was to assess the utility of two subjective facial grading systems, to evaluate the etiologic role of human herpesviruses in peripheral facial palsy (FP), and to explore characteristics of Melkersson-Rosenthal syndrome (MRS). Intrarater repeatability and interrater agreement were assessed for Sunnybrook (SFGS) and House-Brackmann facial grading systems (H-B FGS). Eight video-recorded FP patients were graded in two sittings by 26 doctors. Repeatability for SFGS was from good to excellent and agreement between doctors from moderate to excellent by intraclass correlation coefficient and coefficient of repeatability. For H-B FGS, repeatability was from fair to good and agreement from poor to fair by agreement percentage and kappa coefficients. Because SFGS was at least as good in repeatability as H-B FGS and showed more reliable results in agreement between doctors, we encourage the use of SFGS over H-B FGS. Etiologic role of human herpesviruses in peripheral FP was studied by searching DNA of herpes simplex virus (HSV) -1 and -2, varicella-zoster virus (VZV), human herpesvirus (HHV) -6A, -6B, and -7, Epstein-Barr virus (EBV), and cytomegalovirus (CMV) by PCR/microarray methods in cerebrospinal fluid (CSF) of 33 peripheral FP patients and 36 controls. Three patients and five controls had HHV-6 or -7 DNA in CSF. No DNA of HSV-1 or -2, VZV, EBV, or CMV was found. Detecting HHV-7 and dual HHV-6A and -6B DNA in CSF of FP patients is intriguing, but does not allow etiologic conclusions as such. These DNA findings in association with FP and the other diseases that they accompanied require further exploration. MRS is classically defined as a triad of recurrent labial or oro-facial edema, recurrent peripheral FP, and plicated tongue. All three signs are present in the minority of patients. Edema-dominated forms are more common in the literature, while MRS with FP has received little attention. The etiology and true incidence of MRS are unknown. Characteristics of MRS were evaluated at the Departments of Otorhinolaryngology and Dermatology focusing on patients with FP. There were 35 MRS patients, 20 with FP and they were mailed a questionnaire (17 answered) and were clinically examined (14 patients). At the Department of Otorhinolaryngology, every MRS patient had FP and half had the triad form of MRS. Two patients, whose tissue biopsies were taken during an acute edema episode, revealed nonnecrotizing granulomatous findings typical for MRS, the other without persisting edema and with symptoms for less than a year. A peripheral blood DNA was searched for gene mutations leading to UNC-93B protein deficiency predisposing to HSV-1 infections; no gene mutations were found. Edema in most MRS FP patients did not dominate the clinical picture, and no progression of the disease was observed, contrary to existing knowledge. At the Department of Dermatology, two patients had triad MRS and 15 had monosymptomatic granulomatous cheilitis with frequent or persistent edema and typical MRS tissue histology. The clinical picture of MRS varied according to the department where the patient was treated. More studies from otorhinolaryngology departments and on patients with FP would clarify the actual incidence and clinical picture of the syndrome.

Heritability of the network architecture of intrinsic brain functional connectivity

The brain's functional network exhibits many features facilitating functional specialization, integration, and robustness to attack. Using graph theory to characterize brain networks, studies demonstrate their small-world, modular, and "rich-club" properties, with deviations reported in many common neuropathological conditions. Here we estimate the heritability of five widely used graph theoretical metrics (mean clustering coefficient (γ), modularity (Q), rich-club coefficient (ϕnorm), global efficiency (λ), small-worldness (σ)) over a range of connection densities (k=5-25%) in a large cohort of twins (N=592, 84 MZ and 89 DZ twin pairs, 246 single twins, age 23±2.5). We also considered the effects of global signal regression (GSR). We found that the graph metrics were moderately influenced by genetic factors h2 (γ=47-59%, Q=38-59%, ϕnorm=0-29%, λ=52-64%, σ=51-59%) at lower connection densities (≤15%), and when global signal regression was implemented, heritability estimates decreased substantially h2 (γ=0-26%, Q=0-28%, ϕnorm=0%, λ=23-30%, σ=0-27%). Distinct network features were phenotypically correlated (|r|=0.15-0.81), and γ, Q, and λ were found to be influenced by overlapping genetic factors. Our findings suggest that these metrics may be potential endophenotypes for psychiatric disease and suitable for genetic association studies, but that genetic effects must be interpreted with respect to methodological choices.

Vave propagation and bandgaps in a parametrically modulated composite laminate

Wave propagation and its frequency bandgaps in a parametrically modulated composite laminate are reported in this paper. The modulated properties under considerations are due to periodic microstructure, for example honeycomb core sandwich composite, which can be parameterized and homogenized in a suitable scale. Wave equations are derived by assuming a third-order shear deformation theory. Homogenization of the wave equations is carried out in the scale of wavelength. In-plane wave and flexural-shear wave dispersions are obtained for a range of values of a stiffness modulation coefficient (alpha). A clear pattern of stop-bands is observed for alpha >= 4. To validate the band-gap phenomena, we take recourse to time domain response obtained from finite element simulation. As predicted by the proposed analytical technique, a distinct correlation between the chosen frequency band and the simulated wave arrival time and amplitude reduction is found. This promises practical applications of the proposed analytical technique to designing parametrically modulated composite laminate for wave suppression. (C) 2009 Elsevier B.V. All rights reserved.

Fractional damping: Stochastic origin and finite approximations

Fractional-order derivatives appear in various engineering applications including models for viscoelastic damping. Damping behavior of materials, if modeled using linear, constant coefficient differential equations, cannot include the long memory that fractional-order derivatives require. However, sufficiently great rnicrostructural disorder can lead, statistically, to macroscopic behavior well approximated by fractional order derivatives. The idea has appeared in the physics literature, but may interest an engineering audience. This idea in turn leads to an infinite-dimensional system without memory; a routine Galerkin projection on that infinite-dimensional system leads to a finite dimensional system of ordinary differential equations (ODEs) (integer order) that matches the fractional-order behavior over user-specifiable, but finite, frequency ranges. For extreme frequencies (small or large), the approximation is poor. This is unavoidable, and users interested in such extremes or in the fundamental aspects of true fractional derivatives must take note of it. However, mismatch in extreme frequencies outside the range of interest for a particular model of a real material may have little engineering impact.

Influence of magnetic clusters on electrical and magnetic properties of In1-xMnxSb/GaAs dilute magnetic semiconductor grown by liquid phase epitaxy

In1-xMnxSb films have been grown with different Mn doping concentrations (x = 0.0085, 0.018, 0.029 and 0.04) beyond the equilibrium 14 solubility limit by liquid phase epitaxy. We have studied temperature dependent resistivity, the Hall effect, magnetoresistance and magnetization for all compositions. Saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic clusters in the film which has been verified by scanning electron microscopy studies. The anomalous Hall coefficient is found to be negative. Remnant field present on the surface of the clusters seems to affect the anomalous Hall effect at very low fields (below 350 Gauss). In the zero field resistivity, a variable-range hopping conduction mechanism dominates below 3.5 K for all samples above which activated behavior is predominant. The temperature dependence of the magnetization measurement shows a magnetic ordering below 10 K which is consistent with electrical measurements. (c) 2007 Elsevier Ltd. All rights reserved.

Continuous-Flow Surface Aeration Systems

An aeration process in ail activated sludge plant is a continuous-flow system. In this system, there is a steady input flow (flow from the primary clarifier or settling tank with some part from the secondary clarifier or secondary settling tank) and output flow connection to the secondary clarifier or settling tank. The experimental and numerical results obtained through batch systems can not be relied on and applied for the designing of a continuous aeration tank. In order to scale up laboratory results for field application, it is imperative to know the geometric parameters of a continuous system. Geometric parameters have a greater influence on the mass transfer process of surface aeration systems. The present work establishes the optimal geometric configuration of a continuous-flow surface aeration system. It is found that the maintenance of these optimal geometric parameters systems result in maximum aeration efficiency. By maintaining the obtained optimal geometric parameters, further experiments are conducted in continuous-flow surface aerators with three different sizes in order to develop design curves correlating the oxygen transfer coefficient and power number with the rotor speed. The design methodology to implement the presently developed optimal geometric parameters and correlation equations for field application is discussed.

The profile of psychiatric symptoms exacerbated by methamphetamine use

Background Methamphetamine use can produce symptoms almost indistinguishable from schizophrenia. Distinguishing between the two conditions has been hampered by the lack of a validated symptom profile for methamphetamine-induced psychiatric symptoms. We use data from a longitudinal cohort study to examine the profile of psychiatric symptoms that are acutely exacerbated by methamphetamine use. Methods 164 methamphetamine users, who did not meet DSM-IV criteria for a lifetime primary psychotic disorder, were followed monthly for one year to assess the relationship between days of methamphetamine use and symptom severity on the 24-item Brief Psychiatric Rating Scale. Exacerbation of psychiatric symptoms with methamphetamine use was quantified using random coefficient models. The dimensions of symptom exacerbation were examined using principal axis factoring and a latent profile analysis. Results Symptoms exacerbated by methamphetamine loaded on three factors: positive psychotic symptoms (suspiciousness, unusual thought content, hallucinations, bizarre behavior); affective symptoms (depression, suicidality, guilt, hostility, somatic concern, self-neglect); and psychomotor symptoms (tension, excitement, distractibility, motor hyperactivity). Methamphetamine use did not significantly increase negative symptoms. Vulnerability to positive psychotic and affective symptom exacerbation was shared by 28% of participants, and this vulnerability aligned with a past year DSM-IV diagnosis of substance-induced psychosis (38% vs. 22%, _2 (df1) = 3.66, p = 0.056). Conclusion Methamphetamine use produced a symptom profile comprised of positive psychotic and affective symptoms, which aligned with a diagnosis of substance-induced psychosis, with no evidence of a negative syndrome.

Mapping of Average Shear Wave Velocity for Bangalore Region: A Case Study

Mapping the shear wave velocity profile is an important part in seismic hazard and microzonation studies. The shear wave velocity of soil in the city of Bangalore was mapped using the Multichannel Analysis of Surface Wave (MASW) technique. An empirical relationship was found between the Standard Penetration Test (SPT) corrected N value ((N1)60cs) and measured shear wave velocity (Vs). The survey points were selected in such a way that the results represent the entire Bangalore region, covering an area of 220 km2. Fifty-eight 1-D and 20 2-D MASW surveys were performed and their velocity profiles determined. The average shear wave velocity of Bangalore soils was evaluated for depths of 5 m, 10 m, 15 m, 20 m, 25 m and 30 m. The sub-soil classification was made for seismic local site effect evaluation based on average shear wave velocity of 30-m depth (Vs30) of sites using the National Earthquake Hazards Reduction Program (NEHRP) and International Building Code (IBC) classification. Mapping clearly indicates that the depth of soil obtained from MASW closely matches with the soil layers identified in SPT bore holes. Estimation of local site effects for an earthquake requires knowledge of the dynamic properties of soil, which is usually expressed in terms of shear wave velocity. Hence, to make use of abundant SPT data available on many geotechnical projects in Bangalore, an attempt was made to develop a relationship between Vs (m/s) and (N1)60cs. The measured shear wave velocity at 38 locations close to SPT boreholes was used to generate the correlation between the corrected N values and shear wave velocity. A power fit model correlation was developed with a regression coefficient (R2) of 0.84. This relationship between shear wave velocity and corrected SPT N values correlates well with the Japan Road Association equations.