Thermal Activation

A new activated carbon has been thermally produced from palm fronds, obtained from palm trees, cultivated widely in desert areas. A (21.75%) yield of Palm Fronds Activated Carbon (PFAC) was obtained from via a physical method. Characterization of PFAC was studied. Welldeveloped porosities verified by SEM were about 14% higher than that of commercial activated carbon. The nature of the product was identified by XRD. The activation process caused both the formation of graphite layers and the increase in bulk density, the graphite layers occurred due to breaking of chemical bonds and carbon burn-off through weak carbon –CO2 oxidation. The development of micro porosity will lead to promising applications for the removal of metal ions, that can be achieved through the surface functional groups of PFAC, detected by FTIR. PFAC is very effective for the adsorption of methylene blue dye from aqueous solutions with great removal (99.5%).

Dynamics in poly(dimethylsi1oxane) (PDMS) melts from Tg + 75 to T, + 175 K have been measured by the fluorescence anisotropy decay of a probe chromophore. The reorientational dynamics of the probe chromophore, 5-(dimethylamino)-1-naphthalenesulfonamide (dansylamide), attached to a trifunctional silane, are characterized in a small molecule solvent, cyclohexanol, and compared to its reorientation in the polymer system. In cyclohexanol, the orientational dynamics obey the Debye-Stokes-Einstein equation with a thermal activation energy equal to that of the cyclohexanol viscosity. In contrast, the rate of reorientation of the probe dispersed in PDMS polymer melts does not reflect the bulk properties of the samples. The local dynamics are exponentially activated, with activation energies that are higher than that of the viscosity of the bulk material. This result is different than conclusions of analogous studies made on carbon-based polymers. Two possible explanations are given based on the unique characteristics of the silicon-oxygen bonds in PDMS.

In this paper, we report the synthesis, structure, transition temperature, upper critical field, critical current density and thermally activated flux flow in CaFFe 0.9 Co 0.1 As superconductor. Superconductivity arises at 23 K by Co substitution at the site of Fe atoms and upper critical field is estimated 102 T by using the Werthamer-Helfand-Hohenberg formula. The flux-flow activation energy (U 0 /kB) varies from 3230 K and 4190 K in the field of 1 T and 9 T respectively. At 2K, the J c is found to be approximately 410 3 A/cm 2 and 0.310 3 A/cm 2 in zero and 6T field, respectively. Transmission electron microscopy analysis shows an amorphous region surrounding around most of the grains which is likely to be present in the form of amorphous and weak link grain boundaries in this compound. It seems that most of the current is hindered by miss aligned grains, amorphous grain boundaries and impurities, which are invariably found between the grains. Presence of the weakly linked granules and their weakly pinned intergranular Josephson vortices are responsible for both low J c and the Arrhenius temperature dependence of resistivity

We consider creep processes in plastically deformed materials as a critical process such as proposed by Zaitsev (Physica A 189 (1992) 411). We give arguments that the low-temperature creep rate necessarily has two di erent modes. During the ÿrst (fast) stage of stress relaxation, dislocations surmount many barriers simultaneously due to their inertia and a low viscosity of the electron liquid. In the second (slow) stage the depinning of dislocations is mostly due to thermal activation. Our experiments on the mechanical relaxation process in lead alloys and zinc are consistent with the proposed mechanism of depinning of dislocations.

We consider creep processes in plastically deformed materials as a critical process such as proposed by Zaitsev (Physica A 189 (1992) 411). We give arguments that the low-temperature creep rate necessarily has two di erent modes. During the ÿrst (fast) stage of stress relaxation, dislocations surmount many barriers simultaneously due to their inertia and a low viscosity of the electron liquid. In the second (slow) stage the depinning of dislocations is mostly due to thermal activation. Our experiments on the mechanical relaxation process in lead alloys and zinc are consistent with the proposed mechanism of depinning of dislocations.

Low-plasma and high-temperature chemical vapor deposition of Si-rich SiO x for concurrently enhancing the carrier tunneling and light emission efficiency is investigated. The O/Si composition ratio of the SiO x film significantly decreases from 2 to 1.2 as the substrate temperature increases from 200 to 400 • C, corresponding to the enhanced precipitation of Si nanocrystals in the Si-rich SiO x . In comparison with stoichiometric SiO 2 , the Si-L 2,3 transition induced kinetic energy loss of the primary electron transmitted through the Si-rich SiO x sample grown at 400 • C is red-shifted by 5 eV. The strongest Si nanocrystal related photoluminescence (PL) can be obtained from the Si-rich SiO x film prepared at a threshold plasma power of 30 W and substrate temperature of 400 • C. In low-plasma and high-temperature deposited samples, the threshold Fowler-Nordheim (F-N) tunneling field and the indium tin oxide (ITO)-SiO x junction potential barrier height of ITO/SiO x /p-Si/Al metal-oxide-semiconductor light emitting diodes (MOSLEDs) are concurrently reduced due to the increasing density of Si nanocrystals precipitated within the SiO x matrix. A thermal activation energy of 0.8 eV was observed for initiating the F-N tunneling process in the MOSLEDs. The electroluminescence (EL) intensity and efficiency of the MOSLEDs are improved by at least 10 dB due to the oxygen deficient plasma enhanced chemical vapor deposition (PECVD) of Si-rich SiO x at low plasma power and high temperatures.

Control of diameter and nitrogen doping in the synthesis of nitrogen doped carbon nanotubes (N-CNTs) can be achieved by careful selection of catalyst, precursor mixture and chemical vapour deposition (CVD) synthesis temperature. A solution of methanol and acetonitrile (20% acetonitrile) was pyrolysed over a Fe/Al/MgO catalyst in a CVD reactor at 850 o C. The product was characterised by TEM, TGA and Raman spectroscopy. N-CNTs with well graphitised morphology, small diameter, and narrow diameter distribution were obtained. Catalyst support and metal particles were removed completely during purification without any change in morphology of the material. Organic solar devices were made from P3HT and the NCNTs synthesized.

Zr -Ti-Al -Ni -Cu bulk metallic glasses have been prepared by copper mould casting and were characterized using neutron and X-ray diffraction and scanning calorimetry in the as-cast glassy state and during crystallization. Depending on chemical composition, the undercooled liquid domain separating the glass transition temperature ðT g Þ from the onset of crystallization ðT x Þ ranges from 82 to 102 K, for a heating rate of 20 K/min. The visco-plastic behaviour of the material has been studied in the supercooled liquid state, between T g and T x ; using constant strain-rate compression tests and strain-rate jump tests. The stress -strain curves display an overshoot at large strain-rate and low temperatures, followed by a constant flow stress up to very large plastic strains. The flow stress is strongly thermally activated. Another characteristic feature of the deformation of the fully amorphous state is the independence of the flow stress on the strain-rate path. The stress -strain curves and their dependence on temperature and strain-rate are first discussed in terms of glass viscosity. It is shown that the data obtained at various temperatures and strain-rates can be scaled on a master curve. The master curve is directly deduced from the stationary strain-rate proposed by Spaepen for homogeneous flow based on the free volume concept. Deformation constitutive laws are then established in the out of equilibrium general case, taking into account the strain induced free volume creation and relaxation. They allow an accurate description of the transients regimes commonly observed such as overshoot, stress oscillations and strain-rate changes. Finally, the hardening resulting from partial crystallization is described by the introduction of a back-stress originating in the undeformability of the crystallites.

Thermally activated surface diffusion has a strong influence on structure widths in atom lithography. We investigate the effects of two barriers to thermally activated atomic diffusion on atom lithography: a thermally activated Ehrlich–Schwoebel (ES) barrier, and pollution from the residual gas in the vacuum system. We performed kinetic Monte Carlo simulations using a one-dimensional surface grid. We find that the ES barrier fails to explain the lack of temperature dependence observed experimentally [W. R. Anderson et al., Phys. Rev. A 59, 2476 (1999)]. The dependencies of the structure width on temperature, vacuum conditions, and beam characteristics can be explained using the pollutant adatom hypothesis. Only the variation of structure width with deposition duration was not entirely reproduced by this model. We attribute this to the one-dimensional nature of our simulations. These results demonstrate that barrier-limited diffusion can play an important role in atom lithography, an...

We simulate the compression of a two-component Lennard-Jones liquid at a variety of constant temperatures using a molecular dynamics algorithm in an isobaricisothermal ensemble. The viscosity of the liquid increases with pressure, undergoing a broadened transition into a structurally arrested, amorphous state. This transition, like the more familiar one induced by cooling, is correlated with a significant increase in icosahedral ordering. In fact, the structure of the final state, as measured by an analysis of the bonding, is essentially the same in the glassy, frozen state whether produced by squeezing or by cooling under pressure. We have computed an effective hard-sphere packing fraction at the transition, defining the transition pressure or temperature by a cutoff in the diffusion constant, analogous to the traditional laboratory definition of the glass transition by an arbitrary, low cutoff in viscosity. The packing fraction at this transition point is not constant, but is consistently higher for runs compressed at higher temperature. We show that this is because the transition point defined by a constant cutoff in the diffusion constant is not the same as the point of structural arrest, at which further changes in pressure induce no further structural changes, but that the two alternate descriptions may be reconciled by using a thermally activated cutoff for the diffusion constant. This enables estimation of the characteristic activation energy for diffusion at the point of structural arrest.

The effect of oxygen impurities and structural imperfections on the coherent on-chain quantum conductance of poly(3-hexylthiophene) is calculated from first principles by solving the scattering problem for molecular structures obtained within density functional theory. It is found that the conductance drops substantially for polymer kinks with curvature radii smaller than 17 Å and rotations in excess of about 60 ı . Oxidation of thiophene group carbon atoms drastically reduces the conductance, whereas the oxidation of the molecular sulfur barely changes the coherent transport properties. Also isomer defects in the coupling along the chain direction are of minor importance for the intrachain transmission.

Activation volumes of the wall-motion and nucleation processes in Co-based multilayer films were characterized from time-resolved domain evolution patterns. These activation volumes were both sensitive to the multilayer structure as well as the film preparation condition. The two activation volumes were generally unequal with each other and the inequality directly influenced on magnetization reversal behavior.

In this study, a pure enzymatic process has been used to impart anti-shrink properties to wool using keratinase and papain applied individually and simultaneously. Both the enzymes have shown to reduce the shrinkage tendency when applied individually, but combined application results in minimum shrinkage. Along with the reduction in shrinkage tendency it is desired to keep the loss in tensile strength to a low level. It is found that the loss in tensile strength could be kept below 10%. The effect of enzyme treatment on other properties like dyeability, wash fastness, light fastness and moisture regain is also studied. SEM study shows that the maximum scale removal is obtained when both the enzymes are applied simultaneously. When the two enzymes are applied individually, papain shows higher efficacy in terms of scale removal than that with keratinase. Infrared spectrophotometric studies using FTIR show that there is no difference in the absorption bands observed in the IR spectra, ...

The ability to integrate carbon nanotubes, especially single-walled carbon nanotubes, seamlessly onto silicon would expand the range of applications considerably. Though direct integration using chemical vapor deposition is the simplest method, the growth of single-walled carbon nanotubes on bare silicon and on ultra-thin oxides is greatly inhibited due to the formation of a non-catalytic silicide. Using x-ray photoelectron spectroscopy, we show that silicide formation occurs on ultra-thin oxides due to thermally activated metal diffusion through the oxide. Silicides affect the growth of single-walled nanotubes more than multi-walled nanotubes due to the increased kinetics at the higher single-walled nanotube growth temperature. We demonstrate that nickel and iron catalysts, when deposited on clean silicon or ultra-thin silicon dioxide layers, begin to form silicides at relatively low temperatures, and that by 900 o C, all of the catalyst has been incorporated into the silicide, rendering it inactive for subsequent single-walled nanotube growth. We further show that a 4 nm silicon dioxide layer is the minimum diffusion barrier thickness which allows for efficient single-walled nanotube growth.

We report magnetic properties and magnetic relaxation phenomena in a sample comprised of nanocrystalline CoFe 2 O 4 ͑ϳ97%͒ϩ␥-Fe 2 O 3 ͑ϳ3%͒ and polymer in potassium silicate ͑as magnetic glass͒ nanoparticle systems in which two very different barrier distributions contributed to the relaxation behavior. We have demonstrated experimentally that only energy barrier distributions and the thermal activation process could not account for a plateau in the viscosity data at low temperatures. Quantum tunneling of magnetization is suggested below ϳ3 K. ͓S0163-1829͑96͒00329-3͔

N-Propargyl imidazole has been synthesized by Knoevenagel condensation of benzaldehyde with propargyl bromide, assisted by microwave irradiation. Two alkaline-promoted clays (Li + -and Cs + -exchanged saponites) have been used as catalysts. The influence of several factors, such as irradiation power, irradiation time and alkaline promoter has been studied. The catalysts were characterized by XRD and chemical analysis. The basicity enhancement is directly connected to the presence of alkaline metal promoters in the saponite structure. In addition, a significant increase in the conversion values has been found when the reaction is activated by microwave irradiation, as compared with thermal activation. The yield to the N-propargyl imidazole shows a maximum for the Cs + -saponite at 750 W in only 5 min of microwave irradiation. This green and solvent-free procedure can be extended to the preparation of other N-substituted heterocycles, which could serve as precursors in the primary route to pharmaceutical compounds of interest.

In glassy materials aging proceeds at large times via thermal activation. We show that this can lead to negative dynamical response functions and novel and well-defined violations of the fluctuationdissipation theorem, in particular, negative fluctuation-dissipation ratios. Our analysis is based on detailed theoretical and numerical results for the activated aging regime of simple kinetically constrained models. The results are relevant to a variety of physical situations such as aging in glass-formers, thermally activated domain growth and granular compaction.

We derive and solve a differential equation satisfied by the probability distribution of the work done on a single biomolecule in a mechanical unzipping experiment. The unzipping is described as a thermally activated escape process in an energy landscape. The Jarzynski equality is recovered as an identity, independent of the pulling protocol. This approach allows one to evaluate easily, by numerical integration, the work distribution, once a few parameters of the energy landscape are known.

Self-supported CVD diamond films having coplanar contacts spaced down to 100 mm have been characterized in the temperature range 300-600 K by electrical measurements in the dark and under illumination at l=220 nm. Up to 600 K the dark conductivity values are smaller than 10-9 S cm-1 and spectrally resolved photocurrent yield measurements in the range 200-800 nm exhibit more than four orders of magnitude discrimination between intrinsic (below 230 nm) and extrinsic (above 230 nm) photoresponses. A thermal activation of the UV photoresponse is also observed, giving an average temperature coefficient for intrinsic photoresponses around 1%/°C.

In situ re#ection high energy electron di!raction (RHEED) has been used to study the time evolution during self-assembled molecular beam epitaxy (MBE) growth of InAs quantum dots on GaAs. Using a special data acquisition technique, two characteristic time constants are determined very precisely: the time t up to the "rst appearance of InAs dots and the time t it takes to complete the 2D}3D transition of all islands. Surprisingly, we "nd that t increases with temperature which disagrees with a thermally activated process. In contrast to this, t behaves Arrhenius-like and an activation energy of E K0.39 eV is determined. Furthermore, the sum t #t does not depend signi"cantly on temperature and corresponds to an InAs coverage of K2.0 monolayers. A second focus of this paper is the study of dissolution of InAs dots after interruption of the As #ux. From the experiments, an activation energy of 3.2 eV for desorption of In located on top of the wetting layer is determined, whereas direct desorption from the wetting layer corresponds to an activation energy of 3.4 eV.

Chlorine is present as an impurity in the UO2 nuclear fuel. 35Cl is activated into 36Cl by thermal neutron capture. In case of interim storage or deep geological disposal of the spent fuel, this isotope is known to be able to contribute significantly to the instant release fraction because of its mobile behavior and its long half life (around 300000 years). It is therefore important to understand its migration behavior within the fuel rod. During reactor operation, chlorine diffusion can be due to thermally activated processes or can be favoured by irradiation defects induced by fission fragments or alpha decay. In order to decouple both phenomena, we performed two distinct experiments to study the effects of thermal annealing on the behaviour of chlorine on one hand and the effects of the irradiation with fission products on the other hand. During in reactor processes, part of the 36Cl may be displaced from its original position, due to recoil or to collisions with fission products...

We applied the molecular electrostatic field of a cluster model of the Si(111) reconstructed crystal surface as a reactivity map for the prediction of preferred adsorption sites of pointlike dipolar molecules. It was found that experimentally located preferred sites are correctly predicted by both molecular electrostatic field maps, as calculated by the semiempirical NDDO molecular orbital method with the AM1 parametrization, and results obtained by ab initio molecular orbital calculations with a split valence-shell basis set. It is thus probable that electrostatic field maps can be applied to other crystalline surfaces for the pictorial representation of reactivity properties, too.

This paper presents a novel pressure swing adsorption process and the development of specifically designed sorbents for the process. It is operated at high temperature (650À800 °C) using the reversible reaction of calcium oxide with CO 2 , i.e., CaO + CO 2 a CaCO 3 . The new process directly stores the reaction heat released from the forward reaction in the sorbent and then releases it for sorbent regeneration under reduced CO 2 partial pressure, so that the need of pure oxygen for oxy-fuel combustion is avoided. Two potential problems of the new process, namely, loss in capacity and slow and unmatched reaction rates of chemicalcontrolled carbonation and calcination, were discussed in detail. Three specifically designed calcium-based sorbents showed stable performance during 92 isothermal carbonationÀcalcination cycles at either 680 or 750 °C. The calcination rate was significantly enhanced by increasing the reaction temperature and the introduction of steam to match the reaction rate of chemical-controlled carbonation. This pressure swing adsorption process could be used for low-cost CO 2 separation using specifically designed sorbents under carefully selected operating conditions.

The problem of metastability due to quantum and thermal fluctuations in a weakly damped sys- tem is treated within Feynman s influence-functional theory. It is shown that quite generally the nonequilibrium density matrix may be written as a single path integral. For a cubic metastable po- tential it has the form of a Feynman propagator with a complex Lagrangian containing second- order derivatives in time and terms noninvariant under time reversal. Dissipative tunneling and thermal activation emerge together as different solutions of the associated Lagrange equations. The low-temperature correction to the exponent of the tunneling rate behaves as T" +' for a spectrum of bath excitations vanishing as co . It is shown, moreover, how this result may be understood in terms of environment-assisted tunneling. Thus the low-temperature behavior of the tunneling rate pro- vides a method to measure the dissipation mechanism in the quantum regime.

We discuss the suppression of Coulomb effects in the low temperature conductance g(T) of small tunnel junctions with increasing dissipation or bare conductance g. The conductance is expressed in terms of the spin correlation function of a classical one dimensional XYmodel with ferromagnetic nearest neighbor plus inverse square interaction. It is shown that at low temperatures the conductance vanishes asymptotically like T 2 instead of exponentially. A Coulomb gap in the sense of a thermally activated contribution to g(T) is present only for bare conductances smaller than gc ~ 1. A simple model for the spin correlation function is compared with experiments.

Zr-V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these getters was investigated by photoelectron spectroscopy using two photon excitation energies of 600 eV (synchrotron light) and 1253.6 eV (Mg K a laboratory source). During the activation by heating from 120 to 320 °C, the adsorbed carbon was transformed to metal carbides and diffused to the subsurface region.

fluctuating magnetic field Shrabani Mondal, L. R. Rahul Biswas, and Bidhan Chandra Bag ∗ Department of Chemistry, University of Massachusetts Boston, Boston, MA 02125 Department of Chemistry, Visva-Bharati, Santiniketan, India, 731235 Abstract It seems to us that a stochastic system must be a nonlinear one to observe the phenomenon, noise induced transition. But in the present paper, we have demonstrated that the phenomenon may be observed even in a linear stochastic process where both deterministic and stochastic parts are linear functions of the relevant phase space variables. The shape of the stationary distribution of particles (which are confined in a harmonic potential) may change on increasing the strength of the applied fluctuating magnetic field. The probability density may vary non monotonically with an increase in the coordinate of a Brownian particle. Thus the distribution of particles may deviate strongly from the Boltzmann one and it is a unique signature of the fluctu...

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A first-principles theory of interfacial segregation of dopants and defects in heterostructures is developed and applied to GaN=AlN superlattices. The results indicate that the equilibrium concentrations of a dopant at two sides of an interface may differ by up to a few orders of magnitude, depending on its chemical identity and charge state, and that these cannot be obtained from calculations for bulk constituents alone. In addition, the presence of an internal electric field in polar heterostructures induces electromigration and accumulation of hydrogen at the appropriate interfaces.

The susceptibility of a thermally co-evaporated CuInGaSe 2 (CIGS) thin-film absorber to humidity and its consequence on composition, morphology, electrical and electronic properties, and device efficiency was investigated. CIGS films on Mo-coated soda lime glass were degraded either in the ambient at ~21 o C and ~21% relative humidity (RH) for a period of several months or in damp heat (DH) at 85 o C and 85% RH briefly for 15-30 min; then the films were processed simultaneously into devices in a batch that included an unexposed control. In addition to severe delamination on some samples of the absorber films, prolonged ambient exposure resulted in numerous "spot" formations that lost CIGS with scale-like disintegration rippling around the spots and showed a significant presence of Na. Exposure in DH for 5 h was able to reproduce the spot formations on the CIGS films. A significant to large decrease of cell efficiency was observed from 14%-16% for the unexposed control to 8%-11% for the CIGS absorber exposed in DH for 15 and 30 min and 1%-4%% for the ambient-degraded CIGS with high series resistance and very low shunt resistance.

Puga geothermal field in NW Himalaya, Ladakh district, Jammu and Kashmir, India, is situated near the junction of the Indian and Asian plates. The thermal activity is attributed to the widespread igneous activity during Upper Cretaceous to late Tertiary age. The study area located at an altitude of 4600 m above mean sea level is characterized by springs with temperatures up to 84 8C that correspond to the boiling point of water at this altitude. In order to image the shallow and deeper parts of the area, wideband (1000-0.001 Hz) magnetotelluric (MT) measurements have been carried out. Five-component MT data were acquired from the E-W-trending, 15-km-long and 1-km-wide Puga valley at 35 locations. The data have been subjected to one-(1D) and two-dimensional (2D) modelling. The results confirm the presence of a shallow conductive region in the area and also indicate the presence of a deep conductive region (5-15 V m) commencing from a depth of about 1.5 to 2.0 km and related to the presence of a geothermal reservoir.

For an inhomogeneous high-Tc superconductor, band-filling dependence of Josephson IcRn product is deduced at T =0 K by means of measurement; this is an extension of the Ambegaokar -Baratoff (AB) theory based on the s-wave theory. The product is given by J obs Rn≡ π 2 ρ△i = ρJiRn, where 0< ρ ≤1 is band filling (or local density), and △i is the intrinsic superconducting true gap and small. When ρ=1, J obs Rn = JiRn is the intrinsic Josephson true product (or the AB product), where Ji is the intrinsic Josephson true current occurring by Cooper pair. When 0< ρ <1, J obs Rn is an average of JiRn over the measurement region and is the effect of measurement. The J obs Rn explains small IcRn values observed by experiments. Furthermore, the intrinsic gap, 8.5< △i <17 meV, is analyzed from IcRn data of Bi2Sr2CaCu2O8+x. d-wave superconductive components do not exist in Bi-2212 crystals.

Distributions of Coulomb blockade peak spacing are reported for large ensembles of both unbroken (magnetic field B = 0) and broken (B ≠ 0) time reversal symmetry in GaAs quantum dots. Both distributions are symmetric and roughly gaussian with a width ~ 2-6% of the average spacing, with broad, non-gaussian tails. The distribution is systematically wider at B = 0 by a factor of ~ 1.2 ± 0.1. No even-odd spacing correlations or bimodal structure in the spacing distribution is found, suggesting an absence of spin-degeneracy. There is no observed correlation between peak spacing and peak height.

We present first-principles density-functional calculations for the adsorption of water on the Ge͑100͒ surface. The dissociation of water molecules into OH and H species is energetically favored over the molecular adsorption, where O forms a bond to the down atom of the Ge dimer, similar to the case of Si͑100͒. However, on Ge͑100͒ the energy barrier for water dissociation is calculated to be ϳ0.49 eV, which is significantly larger than our previous value ͑0.15 eV͒ on Si͑100͒. Since the molecular adsorption on Ge͑100͒ has a relatively smaller adsorption energy of 0.33 eV compared to that ͑0.57 eV͒ on Si͑100͒, adsorbed water molecules on Ge͑100͒ prefer desorption rather than dissociation upon being thermally activated. This result provides an explanation for the experimental observations on Ge͑100͒, where water does not stick easily at room temperature.

Secondary recovery is essential for sustaining oil production once a reservoir's natural drive has depleted. Among the most commonly employed methods are waterflooding and gas injection, both of which aim to maintain reservoir pressure and enhance volumetric sweep. This study presents an in-depth comparative analysis of waterflooding versus gas injection in a mature sandstone reservoir, incorporating reservoir characterization, theoretical principles, and simulation-based performance forecasts. Key factors addressed include reservoir heterogeneity, mobility ratio, displacement efficiency, well patterns, breakthrough behavior, and operational costs. Our results reveal that waterflooding typically provides a more stable displacement front and better areal sweep in moderately heterogeneous sandstone, albeit with higher water-handling requirements. Gas injection, particularly in near-miscible or immiscible modes, can effectively maintain pressure but may suffer from gas override and high GOR production if not carefully managed. The study underscores how geological complexity, fluid properties, and operational constraints guide the choice between these two secondary recovery strategies. It concludes with practical recommendations for optimizing injection processes and highlights scenarios in which each method can offer maximum incremental recovery.

In the study, the thermal fatigue tests on ferrite matrix ductile cast iron were carried out as the specimens were axially constrained completely at room temperature. Then, the topics were studied as follows, the dependence of thermal fatigue life on the peak temperature of thermal cycle, the ordinary serration and the peculiar serration of thermal stress cycle, change of visual fatigue cracks and fracture pattern, the influence of dynamic strain aging, and microstructure change caused by polygonization or by α⇔γtransformation on thermal fatigue. Furthermore, the activation energy for thermal fatigue in Arrhenius equation in each temperature range was investigated and discussed.

In this study, the monosemous effect of thermal plastic strain on the thermal fatigue life is newly found on ferrite ductile cast iron around the alpha phase field. At first, the monosemousness is defined and its meaning described. Next, the monosemousness of thermal fatigue is demonstrated by its conditional equation and its existence is verified by the thermal fatigue test on ferrite ductile cast iron. By doing so, the feature on the thermal fatigue of ferrite ductile cast iron is clarified. Generally, it is considered that fatigue life in ferrite-matrix temperature range can be expressed at least by two or more different Arrhenius equations, namely there are two or more different activation mechanisms to govern the thermal fatigue life corresponding to various ferrite temperature ranges. In this case, for determining the life in any various ferrite temperature ranges, it must have at least four or more unknown quantities. If there is the presence of a general equation which is able to replace above described plural equations, then the life can be determined by simple one variable. Here, by introducing conditional equations, it is verified that the general equation is a Coffin and Manson's equation of low cycle fatigue and whole thermal fatigue life can be determined by a variable of thermal plastic strain occurred in thermal cycle. As a result, the law can apply to describe thermal fatigue phenomenon and predict thermal fatigue life monosemously from cyclic thermal plastic strain on ductile cast iron with ferrite matrix.

Three-dimensional titanium and niobium oxides are superconducting at temperatures considerably lower than layered copper oxides. Therefore it seems worthwhile to study layered titanium and niobium oxides. Layered conducting phases, however, were not known until recently, when the study of the LaTiOx system led to the first layered conducting titanium oxides. Single crystals of isostructural niobium oxides, CaNbO~, SrNbO~ and Sr0.9Lao.lNbO3.4, were prepared with the floating zone melting technique. In common with LaTiO~ they have the following properties. For x-~ 3.4, its layered perovskite-related structure of a known type is derived from the layered highest-T~ (> 1600 K) ferroelectrics LaTiO3.s, CaNbO3.5 and SrNbO3.5. In the range 3.42 < x < 3.50 well ordered intergrowth takes place between the ferroelectric x= 3.5 structure and the x =3.4 structure. This intergrowth was found to be representative of the bulk and the stacking sequence is dependent on x. For x<3.5, magnetic and resistivity measurements were performed between room temperature and 4.2 K. The temperature dependence of the magnetic susceptibility along the layers displays a minimum. Semiconducting behavior was found along and perpendicular to the layers. At low temperatures the resistivity exhibits thermally activated behavior with unexpectedly small activation energies in the meV range. This might indicate that a further lowering of the average titanium and niobium valencies could lead to metallic behavior.

ZnO single crystals, epilayers, and nanostructures often exhibit a variety of narrow emission lines in the spectral range between 3.33 and 3.35 eV which are commonly attributed to deeply bound excitons (Y lines). In this work, we present a comprehensive study of the properties of the deeply bound excitons with particular focus on the Y 0 transition at 3.333 eV. The electronic and optical properties of these centers are compared to those of the shallow impurity related exciton binding centers (I lines). In contrast to the shallow donors in ZnO, the deeply bound exciton complexes exhibit a large discrepancy between the thermal activation energy and localization energy of the excitons and cannot be described by an effective mass approach. The different properties between the shallow and deeply bound excitons are also reflected by an exceptionally small coupling of the deep centers to the lattice phonons and a small splitting between their two electron satellite transitions. Based on a multitude of different experimental results including magnetophotoluminescence, magnetoabsorption, excitation spectroscopy (PLE), time resolved photoluminescence (TRPL), and uniaxial pressure measurements, a qualitative defect model is developed which explains all Y lines as radiative recombinations of excitons bound to extended structural defect complexes. These defect complexes introduce additional donor states in ZnO. Furthermore, the spatially localized character of the defect centers is visualized in contrast to the homogeneous distribution of shallow impurity centers by monochromatic cathodoluminescence imaging. A possible relation between the defect bound excitons and the green luminescence band in ZnO is discussed. The optical properties of the defect transitions are compared to similar luminescence lines related to defect and dislocation bound excitons in other II-VI and III-V semiconductors.

To gain an understanding of the tectono-metamorphic evolution of the Congo Craton in the southern Cameroonian Ntem Complex, alluvial rutile EPMA geochemistry and LA-ICP-MS U-Pb geochronology were carried out, and for the first time, robust rutile ages are obtained in that section of the Congo Craton. Concentrations of Nb vary from 287 to 7074 ppm and those of Zr and Cr from 7 to 592 ppm, and from 75 to 5836 ppm, respectively. These data suggest Minto alluvial rutile was sourced from mainly metapelitic and accessorily metamafic rocks. The Zr-in-rutile thermometer indicates a range of temperatures between 430 and 720 • C, with an average temperature of 613 • C. This suggests that the alluvial rutile rock sources were formed under conditions of amphibolite facies metamorphism. Five alluvial rutile grains yield overlapping and concordant ages of 1974 ±

The DC conductivity and photoconductivity of a-Se0.6Te0.4 is studied in the temperature range from 150 K to 300 K. From the temperature dependence of the dark current, the thermal activation energy of 0.14 eV was obtained. The lux-ampere characteristics at different temperatures and voltages between electrodes show that photocurrent is proportional to the flux of light to the power g. The activation energy of the carriers from dangling-bond levels was obtained from the photocurrent variation with temperature.

In the classical Josephson effect the phase difference across the junction is well defined, and the supercurrent is reduced only weakly by phase diffusion. For mesoscopic junctions with small capacitance the phase undergoes large quantum fluctuations, and the current is also decreased by Coulomb blockade effects. We discuss the behavior of the current-voltage characteristics in a large range of parameters comprising the phase diffusion regime with coherent Josephson current as well as the supercurrent peak due to incoherent Cooper pair tunneling in the Coulomb blockade regime. 1.