High ΔT Research Articles

Teleseismic P wave spectra from USArray and implications for upper mantle attenuation and scattering

AbstractTeleseismic P wave amplitude spectra from deep earthquakes recorded by USArray are inverted for maps of upper mantle Δt* for multiple frequency bands within 0.08–2 Hz. All frequency bands show high Δt* regions in the southwestern U.S., southern Rocky Mountains, and Appalachian margin. Low Δt* is more common across the cratonic interior. Inversions with narrower frequency bands yield similar patterns, but greater Δt* magnitudes. Even the two standard deviation Δt* magnitude for the widest band is ∼2–7 times greater than predicted by global QS tomography or an anelastic olivine thermal model, suggesting that much of the Δt* signal is nonthermal in origin. Nonthermal contributions are further indicated by only a moderate correlation between Δt* and P travel times. Some geographic variations, such as high Δt* in parts of the cratonic interior with high mantle velocities and low heat flow, demonstrate that the influence of temperature is regionally overwhelmed. Transverse spectra are used to investigate the importance of scattering because they would receive no P energy in the absence of 3‐D heterogeneity or anisotropy. Transverse to vertical (T/Z) spectral ratios for stations with high Δt* are higher and exhibit steeper increases with frequency compared to T/Z spectra for low Δt* stations. The large magnitude of Δt* estimates and the T/Z spectra are consistent with major contributions to Δt* from scattering. A weak positive correlation between intrinsic attenuation and apparent attenuation due to scattering may contribute to Δt* magnitude and the moderate correlation of Δt* with travel times.

A study of the effect of precursors on physical and biological properties of mesoporous bioactive glass

A novel mesoporous bioactive glass (MBG) of composition 64SiO2–26CaO–10P2O5 (mol %) was prepared by hydrothermal method using H3PO4 as a precursor for P2O5. The effect of use of organic triethylphosphate (TEP) and inorganic H3PO4 in MBG synthesis on glass transition temperature (T g), crystallinity, morphology and bioactivity of MBGs was studied. Phase purity determination and structural analysis were done using powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, respectively. XRD revealed that MBG prepared from H3PO4 (MBG-H3PO4) when sintered at 700 °C was partially glassy/amorphous in nature and contained a mixture of crystalline apatite, wollastonite, calcium phosphate and calcium silicate phases. Calcined MBG prepared from TEP (MBG-TEP) contained only wollastonite and calcium silicate phases. Particle size and surface area determined by BET surface area analysis showed higher surface area (310 m2 g−1) for MBG-H3PO4 as compared to MBG-TEP (86 m2 g−1). It also had a smaller particle size (20 nm) and 70 % higher pore volume (0.88 cm3 g−1) for MBG-H3PO4 as compared to MBG-TEP (60 nm particle size and 0.23 cm3 g−1 pore volume). Thermal studies showed that use of H3PO4 decreases T g and increased ΔT (difference between T g and crystallization initiation temperature Tco). Low T g and high ΔT also enhanced bioactivity of MBGs. Bioactivity was determined by immersion in a simulated body fluid for varying time intervals for a maximum period of 14 days. It revealed enhanced bioactivity, as evident by the formation of apatite layer on the surface, for MBG-H3PO4 as compared to MBG-TEP. Scanning electron microscopy and FTIR spectroscopy also supported this observation. Antibacterial studies with Escherichia Coli bacteria, MBG-H3PO4 showed better antibacterial behaviour than MBG-TEP.

Modeling bioaugmentation with nitrifiers in membrane bioreactors.

Bioaugmentation with nitrifiers was studied using two pilot-scale membrane bioreactors, with the purpose of assessing the suitability of state-of-the-art activated sludge models (ASMs) in predicting the efficiency of bioaugmentation as a function of operating conditions. It was demonstrated that the temperature difference between seeding and seeded reactors (ΔT) affects bioaugmentation efficiency. Experimental data were accurately predicted when ΔT was within a range of up to 10 °C at the higher range, and when the temperature was significantly lower in the seeded reactor compared to the seeding one, standard ASMs overestimated the efficiency of bioaugmentation. A modified ASM, capable of accurately representing the behavior of seeded nitrifying biomass in the presence of high ΔT, would require the inclusion of the effect of temperature time gradients on nitrifiers. A simple linear correlation between ΔT and the Arrhenius coefficient was proposed as a preliminary step.

Insights from a thermography-based method suggesting higher carotid inflammation in patients with diabetes mellitus and coronary artery disease

AimDiabetes mellitus (DM) is an independent risk factor for stroke. In a DM population, carotid atheromatosis is a major cause of stroke. The role of carotid plaque inflammation remains conflicting. Microwave radiometry (MWR) is a new non-invasive method allowing in vivo measurement of the temperature of tissues, so reflecting inflammation. The aim of this prospective study was to evaluate the impact of DM on carotid artery inflammation in patients with documented coronary artery disease (CAD). MethodsConsecutive patients (n=300) with significant CAD were evaluated by: (1) ultrasound study of both carotid arteries; and (2) the temperature difference (ΔT) along each carotid artery on MWR. ΔT≥0.90°C was considered high ΔT. Vessel- and patient-based analyses were performed to determine the impact of DM on morphological and functional characteristics of carotid arteries. ResultsOut of 300 patients, 113 (37.7%) had DM. Patients with DM had similar carotid plaque thickness compared with patients without DM in both vessel- and patient-based analyses. In contrast, patients with DM exhibited higher ΔT values in both vessel- and patient-based analyses. On multivariate logistic regression analysis, DM was an independent predictor of high ΔT both unilaterally and bilaterally (OR: 1.66, 95% CI: 1.06–2.58, P=0.03 and OR: 1.96, 95% CI: 1.01–3.81, P=0.05, respectively). ConclusionIn patients with CAD, DM was an independent predictor of local carotid plaque inflammatory activation. Whether or not the assessment of functional plaque characteristics by MWR can be an additional prognostic tool independent of structural factors now needs to be further investigated.

State-of-the-art electrochromic materials based on metallo-supramolecular polymers

Metal ion induced self-assembly of iron(II)-acetate with the rigid ditopic ligand 1,4-bis(2,2′:6′,2′′-terpyridin-4′-yl)benzene results in a metallo-supramolecular coordination polyelectrolyte (Fe-MEPE). Fe-MEPE shows a strong absorption band in the visible region around 590nm, attributed to a metal-to-ligand-charge-transfer (MLCT) transition, which is responsible for the deep blue colour. Large area thin films of high optical quality can be readily fabricated by a dip coating process on transparent conducting electrodes. The Fe-MEPE films have a temperature stability up to 80°C, measured by optical spectroscopy and XAFS (x-ray absorption fine structure). The cathodically coloured Fe-MEPE shows outstanding electrochromic properties and can be reversibly switched from Fe(II) (blue) to Fe(III) (colourless) by applying a potential of 4.1V vs. Li/Li+. A very high optical contrast ΔT of 71% at a wavelength of 590nm and a colouration efficiency of around 525cm2C−1 can be realized. The devices show a long-term stability about 10,000 cycles. Thus, Fe-MEPE is a very promising electrochromic material for future applications of smart windows.

Organic/inorganic-doped aromatic derivative crystals: Growth and properties

Results of a comparative study on the growth from melt by the Bridgman–Stockbarger method of meta-dinitrobenzene (m-DNB) and benzil (Bz) crystals in the same experimental set-up and the same experimental conditions are presented. The incorporation of an inorganic (iodine) dopant in m-DNB was analyzed in the given experimental conditions from the point of view of the solid–liquid interface stability. The limits for a stable growth and the conditions that favor the generation of morphological instability are emphasized. These limits for m-DNB are compatible with those previously determined for Bz, and therefore, even for a high gradient concentration at the growth interface, it is possible to grow m-DNB and Bz crystals in the same experimental conditions characterized by a high ΔT and v. The optical properties were investigated in relation with the dopant incorporation in the crystal in the mentioned experimental conditions. Effects of the dopant (m-DNB/iodine in Bz and iodine in m-DNB) on the optical band gap and optical non-linear properties of the crystals are discussed.

Performance evaluation of the DCMD desalination process under bench scale and large scale module operating conditions

The flux performance of different hydrophobic microporous flat sheet commercial membranes made of poly tetrafluoroethylene (PTFE) and poly propylene (PP) was tested for Red Sea water desalination using the direct contact membrane distillation (DCMD) process, under bench scale (high ΔT) and large scale module (low ΔT) operating conditions. Membranes were characterized for their surface morphology, water contact angle, thickness, porosity, pore size and pore size distribution. The DCMD process performance was optimized using a locally designed and fabricated module aiming to maximize the flux at different levels of operating parameters, mainly feed water and coolant inlet temperatures at different temperature differences across the membrane (ΔT). Water vapor flux of 88.8kg/m2h was obtained using a PTFE membrane at high ΔT (60°C). In addition, the flux performance was compared to the first generation of a new locally synthesized and fabricated membrane made of a different class of polymer under the same conditions. A total salt rejection of 99.99% and boron rejection of 99.41% were achieved under extreme operating conditions. On the other hand, a detailed water characterization revealed that low molecular weight non-ionic molecules (ppb level) were transported with the water vapor molecules through the membrane structure. The membrane which provided the highest flux was then tested under large scale module operating conditions. The average flux of the latter study (low ΔT) was found to be eight times lower than that of the bench scale (high ΔT) operating conditions.

Textural and micro-petrological variations in the eruptive products of the 2006 dome-forming eruption of Merapi volcano, Indonesia: Implications for sub-surface processes

The interplay between magma ascent, degassing and changing magmatic properties are widely recognized as critical factors controlling the style of silicic volcanic eruptions. Microlite textures in samples from the prolonged dome-forming eruption of Merapi in 2006 provide a record of changing magmatic ascent conditions and shallow conduit processes throughout the eruption. Analysis of microlite textural parameters, including measurements of areal number density (NA), mean microlite size, crystal aspect ratio and groundmass crystallinity (φ), combined with the monitoring record and field observations, indicate that magma ascent paths change between continuous ascent at varying rates from a deeper magma storage region, to ascent being temporarily stalled at shallow depths in the latter stages of the eruption, supporting the idea of an ephemeral shallow magma storage region at Merapi. Plagioclase microlite compositions show evidence of decompression-induced degassing, often displaying rims of anorthoclase and more K-rich alkali feldspar (sanidine). Anorthite contents also support the textural data of later erupted magma being temporarily stalled at shallow depths. Crystal size distributions (CSDs) are interpreted to show that both growth-dominated and nucleation-dominated crystallisation regimes existed during the 2006 eruption, resulting from changing conditions of undercooling (ΔT) during variable magma ascent paths. By contrast, microlite textural analysis and feldspar microlite compositions of samples from the fast-growing lava dome of the second phase of the 2010 eruption prior to the cataclysmic events on 5 November indicate faster ascent rates, a crystallisation regime more strongly dominated by nucleation due to high ΔT and interaction of the 2010 magma with more hotter magma from depth.

Crystal and faceted dendrite growth of silicon near (1 0 0)

The crystal growth shape (CGS) and faceted dendrite growth of silicon near (100) are observed by in situ observation. The morphological transformations of the facets and curved orientations on the CGSs under different undercoolings (ΔT) are investigated, and the growth mechanism of the faceted dendrite is clarified. (110) facets with a low growth velocity and (100) curved interface with a relatively high growth velocity are observed on the crystal during the formation of silicon CGS, which shows a perfect foursquare shape dominated by (110) facets. At a relatively high ΔT, a faceted dendrite with a flat tip appears at the (110) facet of CGS. The (100) curved interface disappears with decreasing curvature. With increasing ΔT, both facet and curved interface growth velocities increase linearly, and the rate of curvature decrease increases. A two-dimensional image is developed to elucidate the growth mechanism of silicon 〈110〉 faceted dendrites near (100).

A Power-Generation Test for Oxide-Based Thermoelectric Modules Using p-Type Ca3Co4O9 and n-Type Ca0.9Nd0.1MnO3 Legs

Metal oxides are considered to be promising thermoelectric (TE) materials, especially for high-temperature power-generation applications, because they have many advantages such as low price, light weight, thermal stability, nontoxicity, and high oxidation resistance. For these reasons, oxide-based TE modules were fabricated using p-type pure Ca3Co4O9 and n-type Ca0.9Nd0.1MnO3 legs for power generation at temperatures in excess of 1000 K. This study involved the use of Ag sheets with a Ag paste as electrode materials and alumina plates as a substrate for the modules. The p-type pure Ca3Co4O9 legs were manufactured by spark plasma sintering, and the n-type Ca0.9Nd0.1MnO3 legs were sintered by a conventional process at atmospheric pressure. From a unicouple, a power density as high as 93.2 mW/cm2 under a temperature condition of ΔT = 727 K (Thot = 1175 K) was obtained. This high power density is believed to be a result of the modified contact of the electrode (notch process) and the optimized material properties (the SPS process and a dopant effect) along with the high ΔT obtained in this study (reduced thermal losses because of good packing of thermal insulation). Areas of concern for future research include the following: (1) the measured open-circuit voltage from the present unicouples was only 94.3% of the theoretical voltage, and (2) the internal resistance value was as high as 490% of the theoretical resistance.

Temperature-dependent stability of deep wells in the Cooper Basin

The Cooper-Eromanga Basin is characterised by high heat flow that has been related to the presence of high radiogenic heat-producing granites. Several wells have been drilled in the area to exploit the heat from the fractured granitic rocks of the basement. Drilling through the hot formations in the Cooper Basin (max. temperature ca. 250 °C) with relatively cool drilling fluids induces an almost instantaneous cooling of the wellbore wallrock. Cooling of the hole (the usual case) increases the tensile stresses (and decreases the compressive stresses) at the wellbore wall. The magnitude of the thermal stresses is also dependent on the silica content of the formation. Modelling of the in situ stress tensor and mechanical properties of the wellbore rocks has revealed the time-dependent effect that the borehole collapse pressure has on the stability of the wells. Narrow breakouts form at the time of drilling. Afterwards, the temperature difference (ΔT) decays with time, and as the hole warms up compressive stresses increase and breakouts become enhanced. Therefore, if a high ΔT and a short well exposure time are achieved, it would be possible to inhibit breakout development, drill with a lower mud weight (eventually underbalanced), and, thus, minimise the risk of formation damage.

Impact of type 2 diabetes mellitus on diffuse inflammatory activation of de novo atheromatous lesions: Implications for systemic inflammation

Aims Local coronary and systemic inflammation is pronounced in patients with diabetes mellitus (DM). Intracoronary thermography detects local inflammation and C-reactive protein (CRP) is a marker of systemic inflammation. We investigated whether or not, in patients with DM, thermal heterogeneity of culprit lesions (CLs) correlates with that of non-culprit lesions (NCLs) and with systemic inflammation. Methods We included DM patients who had two angiographically significant lesions and were undergoing percutaneous coronary intervention. We measured the temperature difference (ΔT) between the lesion and proximal vessel wall. Results We included 104 ( n = 208 lesions) patients: 32 ( n = 64 lesions) had DM and 72 ( n = 144 lesions) were non-DM (control group). ΔT was increased in DM in both CLs and NCLs (CLs: DM = 0.12 ± 0.06 °C; no DM = 0.06 ± 0.04 °C; P < 0.01 versus NCLs: DM = 0.13 ± 0.08 °C versus no DM = 0.06 ± 0.05 °C; P < 0.01). Patients with DM had similar ΔT in CLs and NCLs ( P = 0.49). A linear correlation was detected between heat production in all lesions and CRP ( R = 0.45; P < 0.01), which was attributed to the correlation of ΔT in lesions of patients with DM and CRP ( R = 0.32; P < 0.01). In lesions of patients with low CRP, a greater rate of discrepancy was found, as 100% of lesions in patients with DM versus 66.1% of lesions of patients without DM had a high ΔT in one or both lesions ( P < 0.01). Conclusion In patients with DM, local inflammatory activation is diffuse and correlates with systemic inflammation. However, low systemic inflammatory activation does not always predict an increase in local thermal heterogeneity.

Abstract 4912: Thin Fibrous Caps with Excessive Macrophage Infiltration in Culprit Lesions of Patients with Acute Coronary Syndromes are Associated with Increased Local Temperature

Background: Optical coherence tomography (OCT) provides detailed analysis of the morphological characteristics of the culprit lesion (CL) and determines macrophage density within fibrous caps. Intracoronary thermography (ICT) detects the local inflammatory activation of the CL. We investigated the correlation between morphological and functional characteristics of the CL as analysed by OCT and ICT in patients with acute coronary syndromes (ACS). Methods: We studied 31 CL of 31 pts (mean age 61±14 years) with ACS. We measured by ICT the temperature difference between the lesion and the healthy proximal vessel wall (ΔT). Thereafter, we measured the minimal thickness of the fibrous cap (mTFC) at CL by OCT. CL with mTFC ≤65 μm were characterized as thin cap plaques and CL with mTFC &gt;65 μm as thick cap plaques. By OCT, macrophage density in the fibrous cap of the CL was also determined from optical signals. Results: Nineteen CL (61.29%) had increased plaque temperature (ΔT≥0.05°C) and 12 CP (38.7%) had low ΔT (ΔT&lt;0.05°C). All CL (100%, p&lt;0.01) with low ΔT had thick cap (mTFC=98±22 μm). Three CL (15.78%) with high ΔT had thick cap (mTFC=78±9μm, p=0.02), whereas 16 CL with high ΔT (84.2%) had thin cap plaques (mTFC=49±12μm, p=0.02) (Figure ). Among CL with high ΔT, 18 CL (94.7%) had excessive macrophage infiltration in OCT analysis. Only 1 CL with low ΔT(8.3%) had macrophage infiltration of its fibrous cap (p&lt;0.01). Conclusions: CL with thin fibrous cap have increased inflammatory activation. Morphological and functional characteristics of the CL of pts with ACS, evaluated by OCT and ICT, are correlated. Thus, the use of OCT and ICT can provide more information regarding the high-risk plaques.

Abstract 1842: Inflammatory Activation In Patients With Lone Atrial Fibrillation: New Insights By Coronary Sinus Thermography.

Background: In the clinical setting there are conflicting results regarding the role of inflammatory activation in atrial fibrillation (AF). Coronary sinus (CS) thermography assesses myocardial heat production and is correlated with inflammatory states. The purpose of this study was to investigate in patients (pts) with AF whether there is increased CS blood temperature and the correlation of heat production with systemic inflammation. Methods: We included pts with AF and subjects with sinus rhythm (controls). C-reactive protein (CRP) levels were measured in all pts. CS and right atrium (RA) blood temperature measurements were performed by a dedicated 7F thermography catheter. ΔT was calculated by subtracting RA from CS blood temperature. Results: We included 70 pts: 47 with lone AF and 23 controls. We stratified pts with AF into two groups: normotensive (AFN; n=25) and hypertensive (AFH; n=22). Heart rate was similar between the three groups (AFH: 72.91±4.11/min, AFN: 72.84±4.50/min control:72.52±4.19/min, p=0.89). Mean blood temperature was lower in the RA compared with the CS in AFH (37.27±0.52°C vs 37.47±0.54°C, p&lt;0.01), in AFN (37.13±0.53°C vs 37.34±0.54°C, p&lt;0.01), and in controls (37.41±0.69°C vs 37.55±0.68°C, p&lt;0.01). ΔT was greater in AFH, and AFN compared to controls (0.20±0.07°C, 0.20±0.08°C, vs 0.14±0.06°C, p&lt;0.01 for both comparisons). ΔT was similar between AFH and AFN (p=0.95). CRP was higher in AFH and AFN compared to controls (1.72±0.85mg/Dl, 1.69±0.94mg/dL vs 0.98±0.71 mg/dL, p&lt;0.01). CRP was similar between AFH and AFN (p=0.87). Pts with high ΔT (≥0.15°C) had significantly higher CRP compared to pts with low ΔT (1.73±0.95mg/dL vs 1.01±0.57 mg/dL, p=0.01). A correlation between CRP levels with ΔT was observed in AFH and AFN (R=0.58, p&lt;0.01, R=0.44, p=0.02, respectively). Multiple linear regression analysis confirmed that pts with lone AF (b±SE: 0.07±0.02, p=0.01) and pts with hypertension and AF (b±SE: 0.07±0.03, p=0.03) had higher ΔT compared to the control group. Conclusions: Pts with AF have increased myocardial heat production, which is correlated to the systemic inflammation. CS blood temperature measurement may provide significant information for the pathogenesis of AF.

Experimental study of plagioclase rim growth around anorthite seed crystals in rhyodacitic melt

The purpose of this study was to replicate experimentally the growth of new rims around highly anorthitic plagioclase core phenocrysts, analogous to the incorporation of xenocrysts into a silicic magma body through magma mixing. Aniakchak rhyodacite forms the bulk starting composition, and phase-equilibria experiments constrained the pre-eruption magma conditions to be ∼110 MPa and 870-880 °C. The experimental runs were seeded with Great Sitkin anorthite (An 9 1 - 9 5 ) crystals. New rim growth of An 2 8 - 3 8 plagioclase occurred at rates between 3.5 (′0.3) x 10 - 1 0 to 60.6 (′20.0) x 10 - 1 0 cm/s at pressures and temperatures from 50 to 150 MPa and 825 to 880 °C. The values in parentheses are ′1σ standard deviation. Microlite crystallization (An 2 7 - 4 1 ) occurred in all experiments within the plagioclase stability field, and their growth rates varied from 4.4 (′1.3) x 10 - 1 0 to 65.7 (′10.1) x 10 - 1 0 cm/s. The rim and microlite growth rates are similar to one another within each experiment, and microlite number density (N v ) is correlated approximately inversely with rim growth rates. Microlite crystallinities increased from 4.2 to 49.7 vol% as a function of increasing ΔT e f f up to 95 °C. The results indicate growth-dominated crystallization at low ΔT e f f , and nucleation dominated crystallization at high ΔT e f f , in agreement with previous studies. Assuming the experiments apply to nature, the rim growth rates can provide a minimum estimate on how fast magma mixing can occur. Rims that are 10 to 100 μm wide can grow in ∼10 days to 4 months, recording fast mixing timescales as long as eruption occurs shortly after mixing. The growth rate estimates presented here generally agree with those derived from sodic rims growing around anorthite cores after mixing between basalt and andesite prior to the 1996 eruption of Karymsky volcano, Kamchatka.

Measurements of dendrite growth velocities in undercooled pure Ni-melts—some new results

We used a recently developed technique to measure dendrite growth velocities as a function of undercooling in levitated metallic droplets. The data obtained exhibit a low degree of scatter and allow for more accurate comparison with theoretical predictions compared with other measurements. The results for pure Ni-melts and the predictions of the widely used dendrite growth model by Lipton et al. (J. Lipton, W. Kurz and R. Trivedi), Acta Metall., 35 (1987) 957) diverge significantly at low undercoolings in the range ΔT < 80 K, and at high undercoolings ΔT > 200 K. Taking into account laminar fluid flow induced either by forced convection in the bulk liquid or by the volume shrinkage on solidification, reduces the discrepancy at low undercoolings but does not lead to an agreement between experiment and theory. In contrast, the recently developed theoretical approach to the dendrite growth problem by Ben Amar (M. Ben Amar, Phys. Rev. A, 41 (1990) 2080) seems to be able to describe the experimental data in almost the entire undercooling regime accessible to the measurements. However, on the basis of the models and the data available, it is not possible, as yet, to favour one theory over the other.

Isotacticity effect on crystallization and melting in polypropylene fractions: 3. Overall crystallization and melting behaviour

A set of polypropylene (PP) fractions with similar molecular masses and molecular mass distributions but different isotacticities have been investigated and their overall crystallization and crystal melting behaviours determined by differential scanning calorimetry and time resolved small-angle X-ray scattering experiments. The observations indicate that when the supercooling is high ( ΔT > 48 K), only poor and imperfect crystals can form, which are continuously annealed to more perfect crystals upon heating after isothermal crystallization. On the other hand, below ΔT = 48 K, two different crystal morphologies are recognized with their own crystallization kinetics and thermal stabilities. The Avrami treatment for the overall crystallization kinetics of these PP fractions generally reveals a low Avrami exponent ( n) compared with the literature data. The overall crystallization and crystal melting behaviour can be correlated to the crystal morphology change with supercooling, in particular to the ‘cross-hatching’ lamellar phenomenon uniquely observed in the case of PP. The isotacticity effect on the overall crystallization processes and melting behaviour are also focused upon.

2.5 μm GaInAsSb lattice-matched to GaSb by liquid phase epitaxy

GaSb lattice-matched Ga1−xInxAsySb1−y has been grown by liquid phase epitaxy on (100) and (111)B oriented substrates using initial melt supersaturation ΔT varying from 10 to 30 °C, at growth temperatures &amp;gt;600 °C. It is shown that the band-gap cutoff wavelength, measured at room temperature by the electroreflectance method, is ∼2.38 μm for (100) layers whatever ΔT, and increases from 2.38 μm up to 2.51 μm for (111)B oriented layers when ΔT is increased from 15 to 25 °C. Photoluminescence experiments at 2 K confirm the band-gap reduction occurring at high ΔT with the (111)B orientation.

Crystallization history of Obsidian Dome, Inyo Domes, California

Samples obtained by U.S. Department of Energy research drilling at the 600-year-old Obsidian Dome volcano provide the rare opportunity to examine the transition from volcanic (dome) to plutonic (intrusion) textures in a silicic magma system. Textures in the lavas from Obsidian Dome record multiple periods of crystallization initiated in response to changes in undercooling (ΔT) related to variable degassing in the mag-ma. Phenocr)ysts formed first at low ΔT. A drastic increase in ΔT, related to loss of a vapor phase during initial stages of eruption, caused nucleation of microlites. All of the lavas thus contain phenocrysts and microlites. Extrusion and subsequent devitrification of the dry (0.1 wt% H2O) magma crystallized spherulites and fine-grained rhyolite at high ΔT. A granophyric texture, representing crystallization at a moderate ΔT, formed in the intrusions beneath Obsidian Dome. Textures in the intrusion apparently represent crystallization of hydrous (1–2 wt% H2O) rhyolitic magma at shallow depths.

The influence of supercooling on the liquid phase epitaxial growth of inas1−xsbx on (100) GASB substrates

The growth by liquid-phase epitaxy of InAs1−x Sb x (x = 0.08-0.16) on GaSb was accomplished by using melts of constant arsenic concentration x As L = 0.014. The study of the influence of the degree of supercooling ΔT on the crystal growth was investigated. The strong tendency of the In-As-Sb liquid to dissolve the GaSb substrate was resolved by using high ΔT (20-30° C) for layers having a positive lattice-mismatch Δa/a more than 1.5 x 10−3. As positive lattice-mismatch becomes smaller, a larger supersaturation is required to control the substrate dissolution. But owing to the bulk nucleation which restricts the supercooling ΔT at values near 30° C, the growth of epitaxial layers with small lattice-mismatch (until - 5 × 10−4) was achieved only from time to time. It was observed that an increase of ΔT increases the concentration of antimony in the epilayers and hence leads to the lattice-mismatch. The dislocation etch pit density was found to be only dependent on the lattice-mismatch. The thickness of the grown layers is proportional to ΔT xt 1/2 with a factorK = 0.025 μm . °C−2 . s−1/2