Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

Let X(t) be the number of tumor cells at time t, and Pr{X(t) = n} = pn(t) is the density of X. A “birth”, i.e., an increase of one of the total population of cancer cells, can occur either by mutation of a normal cell caused by the action of the carcinogen, consisting of randomly (Poisson) distributed hits, or by reproduction of existing cancer cells. A death of a tumor cell occurs as an additive combination of non-immunological and immunological elements. Once a tumor is initiated by carcinogenic action, it undergoes a birth and death process with infinitesimal birth rate linear and infinitesimal death rate composed of a linear and a nonlinear term, the former due to non-immunological deaths, the latter to immunological feedback. The death rate per tumor cell due to immunological response is proportional to the total number of antigen-producing (tumor) cells; thus, the total death rate is quadratic. Although this assumes a very simple mechanism for the action of immunological feedback, it is nevertheless a first step.

The Mathematical Model

http://www.jlakes.org/config/hpkx/news_category/2015-05-10/1-s2.0-S0883292714002212.pdf

Mine tailings dams: Characteristics, failure, environmental impacts, and remediation

Adsorbents based on montmorillonite for contaminant removal from water: A review

In this study, natural kaolinite, an abundant, low cost, thermally and chemically stable, and easily recyclable material was evaluated for the performance to activate peroxymonosulfate (PMS) by the degradation of atrazine. Based on radical quenching experiments and electron spinning resonance (ESR) spectra, hydroxyl radical ( OH) and sulfate radical (SO4 −) were identified to be the primary reactive species. The effects of catalyst loading, initial reaction pH, PMS dosage, initial atrazine concentration, and the presence of inorganic ions (Cl−, NO3−, HCO3− and H2PO4−) were also investigated in this work. Interestingly, the presence of H2PO4− enhanced the degradation efficiency of atrazine via promoting the decomposition of PMS. The transformation products were detected on a quadrupole time-of-flight liquid chromatography/mass spectrometer (Q-TOF-LC-MS) and the possible degradation pathway of atrazine was proposed. Based on comprehensive characterizations of crystal phase and crystallinity, porosity and pore structure, surface morphology, functional groups, and valence state of specific elements, the catalytic ability of natural kaolinite towards PMS is attributed to the abundant surface-bonded and structural hydroxyl groups. This study provides new insights of PMS activation by natural minerals for the degradation of refractory and deleterious contaminants in wastewater treatment.

Highly efficient activation of peroxymonosulfate by natural negatively-charged kaolinite with abundant hydroxyl groups for the degradation of atrazine

Alteration of swelling clay minerals by acid activation

Frequency- and temperature-dependent complex permittivity or conductivity of a silty clay loam were examined in a broad saturation and porosity range with network analyzer technique (1 MHz-10 GHz, 5 °C-40 °C, coaxial transmission line and open ended coaxial cells). An advanced mixture model based on the well-known Lichtenecker-Rother model (ALRM) was developed and used to parameterize complex permittivity or conductivity at a measurement frequency of 1 GHz under consideration of a dependence of the so-called structure parameter as well as the apparent pore water conductivity on saturation and porosity. The ALRM is compared with frequently applied mixture models: complex refractive index model, Looyenga-Landau-Lifschitz model, Bruggeman-Hanai-Sen model, and Maxwell-Garnet model as well as empirical calibration functions. Comparison of ALRM applied to the investigated frequency and temperature range with sophisticated broadband relaxation models indicates the potential and the limitation to predict the high-frequency electromagnetic material properties.

Experimental Investigations on the Frequency- and Temperature-Dependent Dielectric Material Properties of Soil

Li (super +) , Na (super +) , Ca (super 2+) , Sr (super 2+) , Cu (super 2+) , or Zn (super 2+) -saturated samples of a cis-vacant montmorillonite from Linden, Bavaria, were heated to temperatures between 200-700 degrees C. Half of each heated sample was subsequently autoclaved under steam at 200 degrees C ( approximately 1.5 MPa) to promote rehydroxylation. The smectites were characterized by cation-exchange capacity (CEC), determination of exchangeable cations, infrared (IR) spectroscopy, and thermoanalytical investigations of evolved water in a thermobalance linked with a mass spectrometer. Changes in the montmorillonite structure and dehydroxylation behavior are related to three respective mechanisms: type of the interlayer cation, interlayer cation radius, and the movement of the interlayer cation. The migration of the smaller Li (super +) , Cu (super 2+) , and Zn (super 2+) ions after heating produces a strong reduction of CEC due to the Hofmann-Klemen effect before the initiation of dehydroxylation. Thereafter, the CEC of these smectites remains constant over a large temperature interval during dehydroxylation. After rehydroxylation, Cu (super 2+) and Zn (super 2+) -rich samples release 16-23 meq/100 g of Mg (super 2+) from the structure. No Mg (super 2+) release is observed for the Li (super +) -rich montmorillonite. Also the dehydroxylation behavior after rehydroxylation differs between the Cu (super 2+) , Zn (super 2+) , and Li (super +) -rich samples. The mass curves of the evolved water during thermoanalysis of the rehydroxylated Cu (super 2+) and Zn (super 2+) -rich smectites show a peak doublet between 480-700 degrees C. For the Li (super +) , Na (super +) , Ca (super 2+) , and Sr (super 2+) -rich montmorillonites, the second peak disappeared and a third peak at approximately 760 degrees C developed after rehydroxylation. The resulting structure after rehydroxylation of all samples is celadonite-like.

Dehydroxylation Behavior of Heat-Treated and Steam-Treated Homoionic Cis-Vacant Montmorillonites

Montmorillonites, with the general composition $M_{\rm{x}}^ + \left( {{\rm{S}}{{\rm{i}}_{4 - y}}{\rm{A}}{{\rm{l}}_y}} \right)\left[ {{{\left( {{\rm{Al}},{\rm{F}}{{\rm{e}}^{3 + }}} \right)}_{2 - z}}{{\left( {{\rm{Mg}},{\rm{F}}{{\rm{e}}^{2 + }}} \right)}_z}} \right]{{\rm{O}}_{10}}{\left( {{\rm{OH}}} \right)_2}$
 where x = ξ = 0.2–0.6, x = y+z, and y≪z, vary widely in composition and structure. The commonly used classification into five montmorillonite and two beidellite groups for the solid-solution sequence does not allow an unambiguous classification with respect to structural features and the resulting properties. The smectite structure reveals five features that allow an unambiguous description of a sample: (1) identification as either a dioctahedral or a trioctahedral smectite; (2) layer charge; (3) charge distribution between tetrahedral and octahedral sheets; (4) cation distribution within the octahedral sheet; and (5) Fe content. In addition, the nature of interlayer cations should be given as they influence certain properties of montmorillonites. Analytical methods are now available to measure and determine these structural features. Therefore, a precise classification for montmorillonites requires determination of layer charge and exchangeable cations, analysis of chemical composition, and thermal analysis (to determine the octahedral structure), in addition to X-ray diffraction analysis. A comprehensive classification of montmorillonites based on these parameters is proposed. Ninety-six structural variations (expressed by systematic names) theoretically exist within the montmorillonite-beidellite series. Descriptive names can be used to elucidate the macroscopic properties of the montmorillonite samples in question.

Katja Emmerich

Papers

Alteration of swelling clay minerals by acid activation

Experimental Investigations on the Frequency- and Temperature-Dependent Dielectric Material Properties of Soil

Dehydroxylation Behavior of Heat-Treated and Steam-Treated Homoionic Cis-Vacant Montmorillonites

Clay profiling: the classification of montmorillonites

Alteration of non-swelling clay minerals and magadiite by acid activation.