Simultaneous DTA-TG Study of Montmorillonite Mechanochemically Treated with Crystal-violet

The mechanochemical solid-state adsorption of the cationic dye crystal violet (CV) by montmorillonite was investigated by XRD and simultaneous DTA-TG. Solid CV was ground with the clay for 5 min and four different varieties of CV mechanochemically treated clay were investigated. X-ray and DTA data were compared with those of CV-montmorillonite obtained from an aqueous suspension. X-ray and DTA studies of a ground mixture and a ground mixture heated at 110°C suggest that the mechanochemical adsorption of organic cations takes place on the external surfaces of the clay. The study of a ground mixture washed with water, and washed with water and acetone reveal that water is essential for the penetration of CV into the interlayer space.This revised version was published online in November 2005 with corrections to the Cover Date.     

Adsorption of alachlor by montmorillonites

The adsorption of the tertiary aromatic amide alachlor by Na-montmorillonite and Al-polyhydroxy-montmorillonite was investigated by DTA, XRD, SEM and Thermo-FTIR Spectroscopy. This molecule is adsorbed into the interlayer space of the montmorillonite, replacing interlayer water. In this organo-clay complex the interlayer water forms hydrogen bonds with N or O atoms of the tertiary amide group. Samples which were aged during six months degraded by hydrolysis to give mainly secondary amide. This reaction was catalysed by Al-polyhydroxy-montmorillonite more than by Na-montmorillonite.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThis research was supported in part under Grand No. HRN5544 GOO2069, US-Israel Cooperative Development Research Program, Human Capacity Development, Bureau for Global Programs, Field Support and Research, USAID, and in part under Grant No. I 195128 12/91, German-Israeli Foundation (GIF) for Scientific Research and Development.     

Ultimate frequency response of GaAs injection lasers

The maximum frequency response attainable in GaAs injection lasers under constraints of limited current density and optical power density is examined in this communication. It is found that under a prescribed current and optical limit, an optimum cavity length exists at which the frequency response attains its maximum. Fundamental frequency limitations under various operating conditions are depicted graphically.     

Infrared study of the thermal transformation of goethite to magnetite in alkali-iodide disks

Synthetic and natural goethites (0.5–1.5 mg) were heated up to 600°C in alkali-halide disks (400 mg). The thermal transformations occurring at different temperatures are found to depend on the preparation of the disks. For mixtures of alkali-halides and goethite not ground during the preparation of the disks, heating at >200°C resulted in protohematite, which persisted up to 600°C. However, disks which were subjected to repeated grinding—pressing cycles before thermal treatments gave rise to protohematite at >200°C, which on further heating at >300°C was transformed to a transitional iron oxide. In CsI disks, the transitional oxide derived from synthetic goethite can be further transformed to maghemite at 500°C; however, almost no maghemite could be obtained from natural goethite. At 600°C, both the transitional oxide and the maghemite resulting from the synthetic goethite in CsI disks were reduced to magnetite. On the other hand, in KI disks, transitional oxides obtained from both synthetic and natural goethites were reduced to magnetite upon re-pressing and gradual heating of the disks at 600°C. In KI disks, magnetite can be formed only if the reduction temperature is reached gradually, whereas in CsI disks magnetite is formed upon direct heating of the disks to 600°C. The iron oxides referred to above, including the transitional oxides resulting from thermal treatments, were studied by IR absorption spectroscopy.     

Classical many-body model for heavy-ion collisions: (III). Ne-Ne and Ca-Ca calculations

The classical many-body model, previously introduced, has been employed to perform numerical calculations of systems consisting of 20 on 20 and 40 on 40 nucleons. Comparison is made with the 800A MeV data of Nagamiya, et al. Microscopic time development of the system and central compressions are displayed for Ca on Ca. Microscopic comparions with the fireball/firestreak models are presented; although qualitative agreement is found, interesting and expected shortcomings in the latter were seen. In particular, the classical many-body model exhibits shear viscosity and incomplete thermalization.     

Thermal study of naphthylammonium- and naphthylazonaphthylammonium-montmorillonite

The blue organo-clay color pigment (OCCP) naphthylazonaphthylammonium-montmorillonite was synthesized from the white naphthylammonium-montmorillonite by treating with NaNO₂, the azo colorant being located in the interlayer space. The following effects on the basal spacing of naphthylazonaphthylammonium-and naphthylammonium-clay were investigated: (1) the amount of naphthylammonium loading the clay, (2) the amount of NaNO₂ used for the staining, (3) aging of the preparation suspension and (4) thermal treatment. Samples were heated at 120, 180, 240, 300 and 360°C and diffracted by X-ray. During aging, some of the dye decomposed. Samples, after one day aging, were investigated by DTA. During the dehydration stage both organo-clays gradually decomposed, the naphthylammonium-clay at 120°C and the OCCP at 180°C. That fraction of organic matter, which did not escape, was air-oxidized at above 200°C and charcoal was obtained. The appearance and size of the DTA exothermic peaks depended on the amount of organic matter, which did not escape and this depended on the total amount of organic matter in the DTA cell. DTA proved that naphthylammonium reacted with NaNO₂ to form OCCP.     

Electrically pumped edge-emitting photonic crystal lasers with angled facets

We demonstrate electrically pumped large-area edge-emitting InGaAsP/InP two-dimensional photonic crystal lasers with angled facets at room temperature. The laser uses a weak index perturbation surface photonic crystal structure to control optical modes in the wafer plane. Measurements of the laser spectra show that the modal selection is due to satisfying the Bragg resonance conditions in both the longitudinal and the transverse directions. The lasing wavelength is tuned lithographically by changing photonic crystal lattice constants. We demonstrate a fine lasing wavelength tuning sensitivity (change of lasing wavelength over change of lattice constant) of 0.08 through the transverse lattice constant tuning.     

Formulating and solving a multi-mode resource-collaboration and constrained scheduling problem (MRCCSP)

The main motivation of this study is to provide, for the first time, a formulation and solution for a class of production scheduling problems (as in cluster tools) characterized mainly by resource collaboration to perform an operation and while allowing batches and considering alternative production methods. We develop a formulation for the new problem and term it a multiple mode per operation, resource collaboration, and constrained scheduling problem (MRCCSP). Some of the important new characteristics we consider are: multiple products (families); multiple orders (jobs) per family; precedence restrictions among the operations that constitute a job; alternative modes for the performance of an operation (each of which needs a set of collaborating resources) may be defined; complementary and exclusive restrictions between operation-modes; batch production is allowed; and setup times may depend on sequence and batch-size. The objective of the MRCCSP is to minimize makespan. We formulate the MRCCSP as a mixed integer linear programming model, and acknowledging the considerable size of the monolithic formulation required, we prescribe a specific method to achieve size reduction. Finally, a customized branch and bound algorithm for optimally solving this problem is proposed and examined experimentally.     

Insulating phases and superfluid-insulator transition of disordered boson chains

Using a strong disorder real-space renormalization group, we study the phase diagram of a fully disordered chain of interacting bosons. Since this approach does not suffer from runaway flows, it allows a direct study of the insulating phases, not accessible in a weak disorder perturbative treatment. We find that the universal properties of the insulating phase are determined by the details and symmetries of the on-site chemical-potential disorder. Three insulating phases are possible: (i) an incompressible Mott glass with a finite superfluid susceptibility, (ii) a random-singlet glass with diverging compressibility and superfluid susceptibility, (iii) a Bose glass with a finite compressibility but diverging superfluid susceptibility. In addition to characterizing the insulating phases, we show that the superfluid-insulator transition is always described by Kosterlitz-Thouless-like flows.