A test on analytic continuation of thermal imaginary-time data

Some time ago, Cuniberti et al. have proposed a novel method for analytically continuing thermal imaginary-time correlators to real time, which requires no model input and should be applicable with finite-precision data as well. Given that these assertions go against common wisdom, we report on a naive test of the method with an idealized example. We do encounter two problems, which we spell out in detail; this implies that systematic errors are difficult to quantify. On a more positive note, the method is simple to implement and allows for an empirical recipe by which a reasonable qualitative estimate for some transport coefficient may be obtained, if statistical errors of an ultraviolet-subtracted imaginary-time measurement can be reduced to roughly below the per mille level.     

Far infrared (THz) absorption spectra for the quantitative differentiation of calcium carbonate crystal structures: Exemplified in mixtures and in paper coatings

In this paper, far-infrared (FIR) spectroscopic techniques have been employed to detect different calcium carbonate crystal concentrations in powder mixtures. We have compared absorption spectral features of both pure and mixtures of natural ground calcium carbonate (GCC) and synthetic precipitated calcium carbonate (PCC). It is evident that the absorbance data differentiate clearly and unequivocally between calcite and aragonite in the spectral range of 2–18 THz. Also, from the absorbance measurement of two sets of mixtures, we have revealed a linear relationship between the ratio of some selected absorbance peaks of the mixtures and concentration of a particular pigment within the mixture. This innovative technique could be a novel, practicable technique for quality control or for analyzing coating and/or filler pigments and extenders in the paper making and printing industries. Finally, we have proven in the case of paper that, surface roughness and print color play no role as far as the locations and magnitudes of the absorbance spectral features are concerned.     

Unconventional detection methods for microfluidic devices

The direction of modern analytical techniques is to push for lower detection limits, improved selectivity and sensitivity, faster analysis time, higher throughput, and more inexpensive analysis systems with ever-decreasing sample volumes. These very ambitious goals are exacerbated by the need to reduce the overall size of the device and the instrumentation - the quest for functional micrototal analysis systems epitomizes this. Microfluidic devices fabricated in glass, and more recently, in a variety of polymers, brings us a step closer to being able to achieve these stringent goals and to realize the economical fabrication of sophisticated instrumentation. However, this places a significant burden on the detection systems associated with microchip-based analysis systems. There is a need for a universal detector that can efficiently detect sample analytes in real time and with minimal sample manipulation steps, such as lengthy labeling protocols. This review highlights the advances in uncommon or less frequently used detection methods associated with microfluidic devices. As a result, the three most common methods - LIF, electrochemical, and mass spectrometric techniques - are omitted in order to focus on the more esoteric detection methods reported in the literature over the last 2 years.     

Effect of microfibrillated cellulose and fines on the drainage of kraft pulp suspension and paper strength

Different types of microfibrillated cellulose (MFC) and fines suspensions were produced, characterized, and then added to a papermaking pulp suspension. High and medium molar mass cationic polyelectrolytes were used as fixatives. The drainage behavior of the pulp suspensions with additives were evaluated against the strength properties of hand sheets made thereof. The effects of salt concentration, pH, fixative type, dosage and type of fibrillar material on drainage were examined. All the MFC and fines samples produced had clearly different properties due to their dissimilar production methods, and they also introduced specific responses on the measured drainage and paper strength. Generally, the addition of MFC decreased the drainage rate of pulp suspension and increased the strength of paper. However, it was shown that by optimum selection of materials and process conditions an enhancement of the strength properties could be achieved without simultaneously deteriorating the drainage.     

Qualitative and quantitative end-group analysis of a small molecular weight polyester by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used for qualitative and quantitative end-group analysis of a small molecular weight polyester, poly(2-butyl-2-ethyl-1,3-propylene phthalate). The presence of carboxyl-terminated linear and cyclic polyester oligomers was confirmed with the help of simple sample preparation methods. The presence of carboxyl end-groups in the polyester chains was verified through their formation of carboxylate salts with alkali metal cations. Cyclic oligomers were identified through deuterium exchange of the exchangeable protons of the polyester. Various inorganic salts were tested for salt formation of the carboxyl end-groups, but only the alkali metal salts proved effective. The influence of the alkali metal salts on the results of the quantitative end-group analysis was also studied. The relative amounts of differently terminated and cyclic oligomers were calculated when the alkali metal salts were used with different matrices. The results showed that both the salts and the matrices used in sample preparation can have a marked effect on the quantitative results of the end-group analysis. The measurements were carried out using 2,5-dihydroxybenzoic acid (DHB), 1,8, 9-trihydroxyanthracene (dithranol), and 2-(4-hydroxyphenylazo)benzoic acid (HABA) as matrix compounds. Dithranol and HABA repeatably exhibited similar results, and these results differed from those obtained with DHB probably because of the different ionization mechanisms in the MALDI process. Copyright-Copyright 2000 John Wiley & Sons, Ltd.     

Acid strength distributions in the Mo?Al?Si and the Ni?Mo?Al oxide systems determined by ammonia adsorption

Acid strength distributions of Mo–Al–Si and Ni–Mo–Al oxide systems have been found by means of a relationship that gives pK_a values from amounts of ammonia adsorption. Molybdenum is suggested to cause a homogenization in the acid strength distribution of alumina but a heterogenization in silicaalumina, whereas nickel is found to neutralize strong acid sites inherent to molybdenum.

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