THE SIMULATION AND OPTIMIZATION OF GRADIENT ELUTION HPLC

The movement of a particular component along an HPLC column is studied on the ba-sis of equilibrium equations. Numerical simulation of multi--step gradient elution HPLC isperformed by means o? a personal computer program. The location x, as a fraction of thecolumn length, for a given time t o? each compound is calculated, the velocity and corre-sponding acceleration are given as well. Diagrams for x,dx/dt and d~2x/dt~2 versus t display themovement process of the different components along the HPLC column during gradient elu-tion. The prediction of the retention time and peak width, and the optimization for the multi-step gradient elution HPLC are all based on such simulation and the molecular structure ofthe. components is separated as well.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Increasing the yield from volumetric MRI in patients with epilepsy

Volumetric magnetic resonance imaging has become a routine investigation in the management of patients with chronic partial epilepsy. However, even with the use of reformatted images, an underlying cause for epileps can-not be found in many of these patients. We show that further processing of the data, including three-dimensional reconstruction and quantitative analysis of the volume and complexity of the images in three dimensions, reveals additional positive information in up to 75% of patients. This may be useful for surgical planning, prognostication, and understanding of the structure and development of the human brain.     

Dependence of surface coverage on pore geometry in dispenser cathodes

This paper shows that the surface coverage of Ba/BaO on tungsten is more complete when the activator is supplied via slotted pores rather than circular pores. Both theoretical and experimental evidence is given to support this contention. The effect is primarily a geometrical one, since the surface diffusion in the case of circular pores is two-dimensional, whereas the surface diffusion for slotted pores is linear. The contrast becomes less pronounced as the circular pore size decreases. For dimensions of the order of those found on cathode surfaces (e.g., 10 μ m diameter pores), a hexagonal array of circular pores can be optimized to produce an emitting area of 88% of the total, with a pore open area of about 11%. For slotted pores, the slot widths can be made arbitrarily narrow, consequently, the emitting area approaches 100% while pore evaporation losses are minimized. A slotted-pore cathode should, therefore, be capable of higher and more uniform current density with less barium dispensation. When the pore geometry is controlled, either for round holes or slots, the cathode should be less prone to space-charge-limited slump than those based on random sintered pores     

Investigating the vortex melting phenomenon in BSCCO crystals using magneto-optical imaging technique

Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals of Bi₂Sr₂CaCu₂O₈ (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local melting temperature/field, we have constructed maps of the melting landscape T _m(H, r), viz., the melting temperature (T _m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite effects on the local melting transition.     

Enhanced shape-selective recognition of anion guests through complexation-induced organization of porphyrin hosts

We present a fortuitous discovery of enhanced shape-selective recognition of anion guests that stems from a complexation-induced conformational change in porphyrin hosts upon anion binding. Porphyrin hosts reported here exist in a conformation that is not favorable to guest binding. Anions that bind strongly are those that can induce a conformational change in the host to allow guest binding. Furthermore, guests that mimic the shape of the newly formed pocket bind the strongest.     

Factors affecting the leaching mechanism of Mg bearing oxide impurities in Hydrogen Assisted Magnesiothermic Reduction (HAMR) of TiO2

Titanium production by a direct TiO₂ reduction route which is highly energy-efficient and environment-friendly compared to commercial Kroll's process, known as HAMR (Hydrogen Assisted Magnesiothermic Reduction) process has been developed in recent times to meet the growing global demands of low-cost pure Ti. Removal of the Mg compounds after each reduction and de-oxygenation step in the HAMR process by leaching, is essential to ensure good purity and mechanical properties of the final Ti powder. In this study, we investigate the effects of temperature, particle size, and pH on the dissolution kinetics of Mg from Mg-bearing compounds such as MgO and MgCl₂ that remain after the HAMR Process. We also report the underlying mechanism and rate-controlling steps of Mg removal using HCl in connection with the HAMR process. The dissolution kinetics followed a logarithmic rate kinetic model for diffusion through a porous medium that is commonly used for battery research. Kinetics of leaching were significantly improved using finer particles with 99.96 wt.% Mg removal and corresponding Ti loss of only 1.8 wt. %. The rate of dissolution exhibited a weak dependence with the pH and did not abide by the rate-controlling steps of dissolution of ionic oxides like MgO proposed by previous kinetic models.     

Efficient recovery of rare earth elements from coal based resources: a bioleaching approach

Rare earth element (REE) resources in coal-related materials are vast. Assuming a coal production rate of 600 million short tons per year with an average REE content of 200 ppm, the potential REE resource is 120,000 tons per year, which is similar to the annual global production of REEs. Most of those resources that are associated with coal-related materials are found in association with the gangue or ash-based content from the coal ore. Under normal coal plant operation, the REEs often end up in refuse piles or tailings impoundments. In many cases, these REEs can be recovered at low cost using appropriate coal preparation, heap leaching, solvent extraction and/or selective precipitation, followed by subsequent separation and purification of individual REEs. In the present research, the processing approach uses a natural pyrite stream, which was removed during coal cleaning and used to enhance leaching. Bio-oxidation has been used commercially to accelerate leaching, and this approach has been applied to coal-based materials. The ferric ions generated from bio-oxidation oxidize sulfide minerals such as pyrite, which generates acid. Both acid and ferric ions are helpful for leaching REEs, as well as for removing residual sulfides, thereby preventing future acid mine drainage and related liabilities. It can be seen that, recovery of REEs from coal waste materials can enable coal producers to use untapped REEs resources to produce revenue and extend resource life while simultaneously reducing future environmental issues and costs.     

Musical background not associated with self-perceived hearing performance or speech perception in postlingual cochlear-implant users

In normal-hearing listeners, musical background has been observed to change the sound representation in the auditory system and produce enhanced performance in some speech perception tests. Based on these observations, it has been hypothesized that musical background can influence sound and speech perception, and as an extension also the quality of life, by cochlear-implant users. To test this hypothesis, this study explored musical background [using the Dutch Musical Background Questionnaire (DMBQ)], and self-perceived sound and speech perception and quality of life [using the Nijmegen Cochlear Implant Questionnaire (NCIQ) and the Speech Spatial and Qualities of Hearing Scale (SSQ)] in 98 postlingually deafened adult cochlear-implant recipients. In addition to self-perceived measures, speech perception scores (percentage of phonemes recognized in words presented in quiet) were obtained from patient records. The self-perceived hearing performance was associated with the objective speech perception. Forty-one respondents (44% of 94 respondents) indicated some form of formal musical training. Fifteen respondents (18% of 83 respondents) judged themselves as having musical training, experience, and knowledge. No association was observed between musical background (quantified by DMBQ), and self-perceived hearing-related performance or quality of life (quantified by NCIQ and SSQ), or speech perception in quiet.     

Laser Compton scattering for a linearly polarized laser

Laser Compton light sources are potential candidates for the next generation of high-brightness X or γ-ray sources. When increasing the laser power to obtain intense X-ray laser, nonlinear Compton scattering happens. Nonlinear Compton scattering of linearly polarized laser beam is discussed in this paper. A complete transition probability formula is introduced and the polarization properties of final photons are discussed for different conditions.