On a class of linear stochastic differential games

The solution for a class of stochastic pursuit-evasion differential games between two linear dynamic systems is given. This class includes the classical interception game in Euclidean space. The performance index which is optimized is quadratic, and one of the two players has imperfect (noisy) knowledge of the states of the two systems. The "certainty-equivalence principle' or, equivalently, the technique of separating the estimator and the controller which characterizes the standard stochastic control problem is shown to be applicable to this class of differential games.     

Microribbon‐Like Elastomers for Fabricating Macroporous and Highly Flexible Scaffolds that Support Cell Proliferation in 3D

Hydrogel‐based scaffolds are widely used for culturing cells in three dimensions due to their tissue‐like water content and tunable biochemical and physical properties. Most conventional hydrogels lack the macroporosity desirable for efficient cell proliferation and migration and have limited flexibility when subject to mechanical load. Here microribbon‐like elastomers that, when photocrosslinked, can form macroporous and highly flexible scaffolds that support cell proliferation in 3D are developed. These microribbons are produced by wet‐spinning gelatin solution into microfibers, followed by drying in acetone, which causes asymmetrical collapse of microfibers to form microribbon‐like structures. Gelatin microribbons are then modified using methacrylate anhydride to allow further photocrosslinking into 3D scaffolds. The macroporosity and mechanical properties of the microribbon‐based scaffold may be tuned by varying wet‐spinning rate, drying temperature, choice of drying agent, level of glutaraldehyde crosslinking, and microribbon density. When encapsulated in the microribbon‐based scaffold, human adipose‐derived stromal cells proliferated up to 30‐fold within 3 weeks. Furthermore, microribbons‐based scaffold demonstrate great flexibility and can sustain up to 90% strain and 3 MPa stress without failing. The unique mechanical properties of microribbon‐based scaffolds make them promising tools for engineering shock‐absorbing tissues such as cartilage and intervertebral discs.     

Abbau von UF-Harzen beim TMP- und CTMP-Aufschluss von mitteldichten Faserplatten (MDF)

Thermo-mechanical (TMP) and chemo-thermo-mechanical pulping (CTMP) of UF-bonded MDF induce considerable degradation of the UF-resin in the board and lead to a conspicuous increase in the content of water extractives of the fibres. Moreover, the water extractives of the fibres have a higher pH-value and a lower buffering capacity as well as higher acetate and formate ions content than the extractives of the original board. However, the lignin content seems rather to increase than to decrease. This is possibly due to reaction between lignin and formaldehyde from the resin.     

Use of UF-bonded recycling particle- and fibreboards in MDF-production

The work is related to the use of thermomechanical pulps (TMP) prepared from recycling UF-bonded particle- and fibreboards as a partial substitute for TMP made directly from wood in MDF. The results reveal that TMP from recycling boards show striking differences in their morphological characteristics and chemical properties compared to TMP prepared directly from wood. TMP from recycling boards are of shorter fibre length and higher content of fine fraction. Moreover, their cold water extractives are of higher pH-value and contain appreciably higher amounts of acetate and formate ions. TMP from recycling boards releases also more formaldehyde compared to TMP made directly from wood. Moreover, the results clearly show that TMP from recycling boards can be used up to 30% as a partial substitute for TMP from wood in making UF-bonded MDF without any noteworthy deterioration of the physical-mechanical board properties. Also, the formaldehyde release of the boards made using TMP from recycling boards experiences no negative change. Only small differences were found in the content of formate and acetate ions as well as in the release of volatile acids from MDF made from recycling fibre- and particleboards on the one side and boards directly made from wood on the other side. All the results indicate that chemical interaction seems to take place between the chemically degraded resin in UF-bonded recycling boards and the new binder used in making MDF.     

Chemische Eigenschaften von TMP und CTMP, hergestellt aus Kiefernholz und UF-Harz-gebundenen mitteldichten Faserplatten (MDF)

Thermo-mechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) were prepared from pine wood and from UF-bonded MDF made from pine wood. For preparing TMP pine chips as well as UF-bonded MDF were digested under pressure at 170 °C. Thereafter, the digested chips and MDF were defibrated at 170 °C using a single disc refiner. CTMP was prepared from pine wood with 0.25% NaOH (based on dry wood) under the conditions set forth above. CTMP was also made from MDF under two conditions using 0.15% sodium hydroxide (% based on dry MDF) and a mixture of sodium sulphite (1%) and sodium hydroxide (0.25%). The pulps show distinct differences in their properties: TMP from UF-bonded MDF shows lower extractive content in cold and hot water, lower pH-value and higher buffering capacity towards alkali of the cold water extractives than the CTMP counterpart. Moreover, CTMP prepared by using sodium hydroxide alone as a pulping agent increases the content of formate and acetate ions in the cold water extractives. The use of a mixture of sodium sulfite and sodium hydroxide as a pulping agent decreases, however, significantly the content of formate and acetate ions in the cold water extractives. This may be due to the buffering action of sodium sulfite. In general, CTMP decreases the formaldehyde release of the fibres, as measured by the flask method. In presence of sodium sulfite as a pulping agent for recycled MDF, the formaldehyde release is slashed to almost 30% of its original value. The formaldehyde release of CTMP from UF-bonded boards seems to be in the same range as that of TMP from virgin wood.      

Automated analysis of electrospray ionization fourier transform ion cyclotron resonance mass spectra of natural organic matter

The advent of ultra-high-resolution mass spectrometry has revolutionized the ability of aquatic biogeochemists to examine molecular-level components of complex mixtures of organic matter. The ability to accurately assess the chemical composition, elemental formulas, or both of detected compounds is critical to these studies. Here we build on previous work that uses functional group relationships between compounds to extend elemental formulas of low molecular weight compounds to those of higher molecular weight. We propose an automated compound identification algorithm (CIA) for the analysis of ultra-high-resolution mass spectra of natural organic matter acquired by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. This approach is benchmarked with synthetic data sets of compounds cited in the literature. The sensitivity of our results is examined for different sources of error, and CIA is applied to two previously published data sets. We find that CIA works well for data sets with high mass accuracy (<1 ppm) and can accurately determine the elemental formulas for >95% of all compounds composed of C, H, O, and N. Data with lower mass accuracy must be accompanied with additional knowledge of chemical structure, composition, or both in order to yield accurate elemental formulas.     

Curing of a polysulfide sealant with sodium birnessite

Sodium birnessite (Na₂MnMnO₁₃ · H₂O), a layered manganese(IV) oxide–based phase, gives a liquid polysulfide cure that is too rapid for normal application when added at 10 pph polysulfide. The curing behavior of sodium birnessite added as 5 pph, 4 pph, and as a 5 : 5 pph mixture with an inert natural manganese dioxide was compared with that of a readily available manganese‐based commercial curing agent. The rate of cure at 5 and 4 pph was slower than the commercial agent at 10 pph and led to products with lower tensile strength. The cure with the 5 : 5 pph mixture gave a more rapid reproducible cure than that of the commercial agent, making a product with a higher tensile strength and lower elongation, which indicates better curing and higher crosslinking. The improved performance of sodium birnessite as a curing agent is consistent with the presence of Mn²⁺ in the lattice, creating vacancies in the Mn⁴⁺ O²⁻ lattice and increasing the mobility of Mn⁴⁺ and its transport to the surface of the solid to oxidize the polysulfide. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1177–1181, 2000