Thermal models for bobbin tool friction stir welding

This study presents three thermal 3D models for bobbin tool Friction stir welding (FSW) implemented in Comsol and Matlab. The models use thermal pseudo-mechanical (TPM) heat sources and include tool rotation, an analytic shear layer model and ambient heat sinks like the machine and surrounding air. A new transient moving geometry approach has been implemented. It includes the full tool motion along the weld line, while the other two models use fixed geometry with and without moving heat source.The computational effort is small for all three models. The steady state model can be solved in approximately 5 min on a state of the art workstation. Experiments on the FlexiStir experimental welding unit have been carried out to validate the models’ outputs. The predictions of all models are in excellent agreement with each other and the experiment.     

Relating Complex Fluid Composition and Thermophysical Properties with the Advanced Distillation Curve Approach

Complex fluids have long posed a significant challenge in our ability to characterize and model fluid properties. Here, we consider complex fluids to be mixtures with many components that can differ significantly in polarity and polarizability. The penultimate complex fluid is crude oil, although many other fluids such as finished fuels are also highly complex. We have recently introduced a measurement strategy that can simplify these efforts and provides the added potential of linking chemical composition (i.e. analytical) information with physical property information. In addition to chemical characterization, the approach provides the ability to calculate thermodynamic and transport properties for such complex heterogeneous streams. The technique is based on the advanced distillation curve (ADC) metrology, which separates a complex fluid by distillation into fractions that are sampled, and for which thermodynamically consistent temperatures are measured at atmospheric pressure. The collected sample fractions can be analyzed by any method that is appropriate. Analytical methods we have applied include gas chromatography (with flame ionization, mass spectrometric and sulfur chemiluminescence detection), thin‐layer chromatography, FTIR, Karl Fischer coulombic titrimetry, refractometry, corrosivity analysis, neutron activation analysis and cold neutron prompt gamma activation analysis. We have applied this method on product streams such as finished fuels (gasoline, diesel fuels, aviation fuels, rocket propellants), crude oils (including a crude oil made from swine manure) and waste oil streams (used automotive and transformer oils). In this review, we describe the essential features of the ADC metrology with illustrative examples.     

Low-threshold room-temperature operation of injectorless quantum-cascade lasers: influence of doping density

The influence of the doping density in the active sections of InP-based injectorless quantum cascade lasers, emitting at 6.8 mum, is investigated. The doping sheet density is varied in the range 2.5-8.6times10¹⁰ cm^-2. Lasing is observed in the whole range, with a threshold current density as low as 1.2 kA/cm² at 300 K for the smallest doping sheet density of 2.5times10 ¹⁰ cm^-2. Further improvement has been made by additionally increasing the number of periods in the active region from 40 to 60. With the same doping level of 2.5times10¹⁰ cm^-2 record low threshold current densities of 0.73 kA/cm² at 300 K were achieved     

Emulsion-based fluorosensors for potassium featuring improved stability and signal change

A novel kind of potassium optode is presented which is based on the use of lipophilic droplets containing valinomycin and entrapped in a structured hydrogel. A positively charged solvatochromic dye located near the surface of the droplets responds to the valinomycin-assisted extraction of potassium from the sample by dramatic decrease of fluorescence intensity. The dynamic range is from 5 to 100 mM potassium, with negligible cross sensitivity to ionic strength. Cross sensitivity to pH is negligible too in the pH range from 6.5 to 7.3. The effect of interfering lipophilic anions is discussed. Response times within the dynamic range are less than 3 min on going from low to high potassium ion concentrations but about 10 min in the reverse direction. Response is fully reversible with only small drifts in baseline. The measurement uncertainty of determining 5 mM potassium is better than 0.2 mM.     

Ecological behavior of cationic surfactants from fabric softeners in the aquatic environment

The use of cationic surfactants in fabric softeners has reached considerable proportions in the Western industrialized nations during the last 10 years. In the Federal Republic of Germany alone, some 22,000 ton of cationic surfactants were marketed in 1981 for this specific purpose. The considerable share (12%) of total consumption which this class of surfactants accounts for is equivalent to a theoretical wastewater concentration of ca. 5 mg/L. Consequently, it raises questions concerning environmental behavior of this class of substances. The following factors are of substantial importance in this regard: acute and chronic toxicity in the aquatic environment; biodegradability under aerobic and anaerobic conditions; and the possibility of bioaccumulation in the aquatic organisms, particularly in fish. Basically, the ecological behavior of cationic surfactants, like that of distearyl dimethyl ammonium chloride (DSDMAC) and dialkyl imidazolinium salts (DAIC) which are mostly used, is determined markedly by their physicochemical properties, above all their strong adsorption on surfaces, e.g., on clay minerals or on activated sludge, thus leading to their elimination in water treatment plants and water courses. Of far-reaching consequence from the toxicological aspect is the fact that they form neutral salts with the anionic surfactants present in excess in domestic wastewater, thus leading to a considerable decrease in toxicity. Although adsorption and ion-exchange processes are primarily effective in climination of cationic surfactants of the DSDMAC and DAIC types in wastewater treatment, there are significant indications on the basis of experiments that these substances are subject to extensive aerobic biochemical degradation. However, it appears that anaerobic degradation does not take place. Tests conducted so far on the bioaccumulation behavior, particularly on a laboratory scale, indicate that these substances practically do not accumulate in the edible parts of fish and thus no risks are being discerned at present as regards the residue situation.     

Rack-induced metal binding vs. flexibility: Met121His azurin crystal structures at different pH

The rack-induced bonding mechanism of metals to proteins is a useful concept for explaining the generation of metal sites in electron transfer proteins, such as the blue copper proteins, that are designed for rapid electron transfer. The trigonal pyramidal structure imposed by the protein with three strong equatorial ligands (one Cys and two His) provides a favorable geometry for both cuprous and cupric oxidation states. However, the crystal structures of the Met121His mutant of azurin from Alcaligenes denitrificans at pH 6.5 (1.89- and 1.91-A resolutions) and pH 3.5 (2.45-A resolution) show that the preformed metal binding cavity in the protein is more flexible than expected. At high pH (6.5), the Cu site retains the same three equatorial ligands as in the wild-type azurin and adds His121 as a fourth strong ligand, creating a tetrahedral copper site geometry with a green color referred to as 1.5 type. In the low pH (3.5) structure, the protonation of His121 causes a conformational change in residues 117-123, moving His121 away from the copper. The empty coordination site is occupied by an oxygen atom of a nitrate molecule of the buffer solution. This axial ligand is coordinated less strongly, generating a distorted tetrahedral copper geometry with a blue color and spectroscopic properties of a type-1 site. These crystal structures demonstrate that blue copper proteins are flexible enough to permit a range of movement of the Cu atom along the axial direction of the trigonal pyramid.     

Cleavage motifs of the yeast 20S proteasome beta subunits deduced from digests of enolase 1

The 436-amino acid protein enolase 1 from yeast was degraded in vitro by purified wild-type and mutant yeast 20S proteasome particles. Analysis of the cleavage products at different times revealed a processive degradation mechanism and a length distribution of fragments ranging from 3 to 25 amino acids with an average length of 7 to 8 amino acids. Surprisingly, the average fragment length was very similar between wild-type and mutant 20S proteasomes with reduced numbers of active sites. This implies that the fragment length is not influenced by the distance between the active sites, as previously postulated. A detailed analysis of the cleavages also allowed the identification of certain amino acid characteristics in positions flanking the cleavage site that guide the selection of the P1 residues by the three active beta subunits. Because yeast and mammalian proteasomes are highly homologous, similar cleavage motifs might be used by mammalian proteasomes. Therefore, our data provide a basis for predicting proteasomal degradation products from which peptides are sampled by major histocompatibility complex class I molecules for presentation to cytotoxic T cells.     

Criteria for good adjustment to chronic hemodialysis: Nurse-patient differences.

Examined nurse–patient agreement on behaviors and attitudes associated with patient adjustment to chronic hemodialysis treatment. 164 hemodialysis nurses and 79 chronic hemodialysis outpatients completed a patient adjustment to dialysis inventory consisting of 43 behaviors and attitudes reported by nurses in earlier research to be important for adjustment to chronic hemodialysis. Results show that over 60% of nurses and patients showed sufficient agreement on the importance of 33 of 43 behaviors and attitudes for patient adjustment in the areas of compliance with the medical regimen, involvement in treatment, patient–staff interactions, and psychological and social functioning. Nurses and patients disagreed as to whether 9 behaviors and attitudes were at least important, while agreeing that only 1 item was irrelevant. Results also show that significantly more patients than nurses rated 25 out of 43 behaviors and attitudes as crucial. Approximately 50% of these related to interacting with staff, family, and friends. It is suggested that social and psychological criteria for adjustment to hemodialysis treatment should be defined by nurses and patients together. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adsorption Isotherms and Infrared Spectroscopy Study of Nitrogen Condensed in Porous Glasses

Nitrogen has been condensed into Vycor glass and three controlled pore glasses with pore diameters in the nm-range. Adsorption isotherms at 77K have been studied. The induced infrared activity of the N-N stretching vibration has been investigated as function of temperature and filling fraction. Molecules in the first monolayer next to the pore walls can be discriminated from those in the second monolayer, whereas molecules in the center of the pores remain infrared inactive.