Hyperbolic and pseudo-hyperbolic equations in the theory of vibration

Longitudinal vibration of bars is usually considered in mathematical physics in terms of a classicalmodel described by the wave equation under the assumption that the bar is thin and relatively long. Moregeneral theories have been formulated taking into consideration the effect of the lateral motion of a relativelythick bar (beam). The mathematical formulation of these models includes higher-order derivatives in theequation of motion. Rayleigh derived the simplest generalization of the classical model in 1894, by includingthe effects of lateral motion and neglecting the shear stress. Bishop obtained the next generalization of thetheory in 1952. The Rayleigh–Bishop model is described by a fourth-order partial differential equation notcontaining the fourth-order time derivative. He took into account the effects of shear stress. Both Rayleigh’sand Bishop’s theories consider lateral displacement being proportional to the longitudinal strain. The Bishopmodel was generalized by Mindlin and Herrmann. They considered the lateral displacement proportional toan independent function of time and longitudinal coordinate. This result is formulated as a system of twodifferential equations of second order, which could be replaced by a single equation of fourth order resolvedwith respect to the highest order time derivative. To obtain a more general class of equations, the longitudinaland lateral displacements are expressed in the form of a power series expansion in the lateral coordinate. In thispaper, all of the above-mentioned equations are considered in the framework of a general theory of hyperbolicequations, with the aim of classifying the equations into general groups. The solvability of the correspondingproblems is also discussed.     

Ambient‐Dried, 3D‐Printable and Electrically Conducting Cellulose Nanofiber Aerogels by Inclusion of Functional Polymers

This study presents a novel, green, and efficient way of preparing crosslinked aerogels from cellulose nanofibers (CNFs) and alginate using non‐covalent chemistry. This new process can ultimately facilitate the fast, continuous, and large‐scale production of porous, light‐weight materials as it does not require freeze‐drying, supercritical CO₂ drying, or any environmentally harmful crosslinking chemistries. The reported preparation procedure relies solely on the successive freezing, solvent‐exchange, and ambient drying of composite CNF‐alginate gels. The presented findings suggest that a highly‐porous structure can be preserved throughout the process by simply controlling the ionic strength of the gel. Aerogels with tunable densities (23–38 kg m^?3) and compressive moduli (97–275 kPa) can be prepared by using different CNF concentrations. These low‐density networks have a unique combination of formability (using molding or 3D‐printing) and wet‐stability (when ion exchanged to calcium ions). To demonstrate their use in advanced wet applications, the printed aerogels are functionalized with very high loadings of conducting poly(3,4‐ethylenedioxythiophene):tosylate (PEDOT:TOS) polymer by using a novel in situ polymerization approach. In‐depth material characterization reveals that these aerogels have the potential to be used in not only energy storage applications (specific capacitance of 78 F g^?1), but also as mechanical‐strain and humidity sensors.     

Molecular thermodynamics of LNA:LNA base pairs and the hyperstabilizing effect of 5′‐proximal LNA:DNA base pairs

Locked nucleic acids (LNAs) can greatly enhance duplex DNA stability, and are therefore creating opportunities to improve therapeutics, as well as PCR‐based disease and pathogen diagnostics. Realizing the full potential of LNAs will require better understanding of their contributions to duplex stability, and the ability to predict their hydridization thermodynamics. Melting thermodynamics data for a large set of diverse duplexes containing LNAs in one or both strands are presented. Those data reveal that LNAs, when present on both strands, can stabilize a duplex not only through direct interaction with their base‐pair partner, but also through nonlocal hyperstablization effects created by LNA:LNA base pairs and/or specific patterns of oppositely oriented LNA:DNA base pairs. The data are, therefore, used to extend a thermodynamic model previously developed in our lab to permit accurate prediction of melting temperatures for duplexes bearing LNA substitutions within both strands using a classic group‐contribution approach. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2711–2731, 2015     

The Impact of Mine Downscaling on the Free State Goldfields

Mine downscaling is a common international phenomenon; and the deindustrialisation related to mining that occurred in the global north between 1960 and 1990 has been the focus of numerous studies. Mine downscaling in Africa, and more specifically in South Africa, has only risen to prominence in the last two decades. This paper examines the consequences of mine downscaling in the Free State Goldfields of South Africa, against the background of similar impacts in the international arena. Although many of the experiences recorded in the case study mirror the international experience, it is argued that it is probably unrealistic to expect local attempts alone to address mine downscaling, since the magnitude of such downscaling, as described in the paper, is too vast. Subsequently, the paper argues in favour of local partnerships, but with a national strategy for locations that have been affected by the impact of mine downscaling.     

Chemical analysis of environmental samples collected in Iraq: Analysis for the presence of chemical warfare agents

Nineteen samples from the United Nations Special Commission 65 on Iraq (UNSCOM 65) were analyzed for chemical warfare (CW) related compounds using a variety of spectroscopic and chromatographic techniques including multinuclear NMR, GC (phosphorus, sulfur and atomic emission detection), GC/MS (electron impact and chemical ionization), tandem MS, HPLC/ion chromatography, HPLC/thermospray/MS, FTIR, ICP and GFAA. The samples consisted of one piece of cloth, one piece of wood, six waters, six soils, two vegetation samples and two mortar shell crosscut sections. No intact CW agents were detected; however, diethyl phosphoric acid was unambiguously identified in three of the water samples and ethyl phosphoric acid was tentatively identified, at lower levels, in one of the water samples. Diethyl phosphoric acid and ethyl phosphoric acid are degradation products of munitions-grade Tabun (GA), an organophosphorus nerve agent. However, these compounds are also degradation products of the Chemical Weapons Convention (CWC) scheduled compound Amiton as well as many commercially available pesticides.     

Characterization of the recA gene regions of Spiroplasma citri and Spiroplasma melliferum

In previous studies (A. Marais, J. M. Bove, and J. Renaudin, J. Bacteriol. 178:862-870, 1996), we have shown that the recA gene of Spiroplasma citri R8A2 was restricted to the first 390 nucleotides of the N-terminal part. PCR amplification and sequencing studies of five additional strains of S. citri have revealed that these strains had the same organization at the recA region as the R8A2 strain. In contrast to S. citri, Spiroplasma melliferum was found to contain a full-length recA gene. However, in all five S. melliferum strains tested, a TAA stop codon was found within the N-terminal region of the recA reading frame. Our results suggest that S. melliferum, as well as S. citri, is RecA deficient. In agreement with the recA mutant genotype of S. citri and S. melliferum, we have shown that these organisms are highly sensitive to UV irradiation.     

Differential regulation of Raf-1, A-Raf, and B-Raf by oncogenic ras and tyrosine kinases

It has previously been shown that maximal activation of Raf-1 is produced by synergistic signals from oncogenic Ras and activated tyrosine kinases. This synergy arises because Ras-GTP translocates Raf-1 to the plasma membrane where it becomes phosphorylated on tyrosine residues 340 and 341 by membrane-bound tyrosine kinases (Marais, R., Light, Y., Paterson, H. F., and Marshall, C. J. (1995) EMBO J. 14, 3136-3145). We have examined whether the other two members of the Raf family, A-Raf and B-Raf, are regulated in a similar way to Raf-1. A-Raf behaves like Raf-1, being weakly activated by oncogenic Ras more strongly activated by oncogenic Src, and these signals synergize to give maximal activation. B-Raf by contrast is strongly activated by oncogenic Ras alone and is not activated by oncogenic Src. These results show that maximal activation of B-Raf merely requires signals that generate Ras-GTP, whereas activation of Raf-1 and A-Raf requires Ras-GTP together with signals that lead to their tyrosine phosphorylation. B-Raf may therefore be the primary target of oncogenic Ras.     

In vivo and vitro in diagnosis of latex allergy at Groote Schuur Hospital

OBJECTIVE: The aim of this study was to evaluate the diagnostic utility of skin-prick tests, radio-allergosorbent tests (CAP RASTs), basophil histamine release, sulphidoleukotriene release and Western blotting in the diagnosis of latex allergy at Groote Schuur Hospital. DESIGN: Patients with a history suggesting latex hypersensitivity were recruited via staff health and allergy clinics at Groote Schuur Hospital. A clinical assessment was followed by laboratory investigation and skin-prick testing. A control group consisted of laboratory and hospital staff who had regular latex exposure but were asymptomatic. SETTING: Hospital-based cohort at Groote Schuur Hospital. PARTICIPANTS: Twenty-three patients with suspected latex allergy; 10 control subjects exposed to, but not clinically sensitive to, latex. MAIN OUTCOME: Skin-prick testing was more sensitive than in vitro diagnostic tests for the diagnosis of latex allergy. RESULTS: Eighteen of 21 (85.7%) of the patients tested had a positive skin-prick test with a commercial latex solution (Allerbioprick) and 17/21 (80%) tested skin-prick-positive with an in-house glove extract. CAP RASTs were positive in 13/23 patients (56.5%), sulphidoleukotriene release was positive in 10/23 (43%), histamine release assay was positive in 10/23 (45%) and Western blots were positive in 8/23 (34.7%). All patients with only urticaria were Western blot-negative and CAP RAST-negative, suggesting that they have very little circulating latex-specific IgE. Although patients who were Western blot-positive tended to have multi-organ involvement, both patients with anaphylaxis were Western blot-negative. CONCLUSION: Latex allergy is a significant clinical problem at Groote Schuur Hospital. Titrated skin-prick testing performed in a controlled environment can safely and reliably confirm the diagnosis in patients who do not give a history of anaphylaxis. The CAP RAST was the most sensitive in vitro test for latex allergy locally available, but lacks sensitivity in patients presenting with urticaria only.