Effects of branching upon some surfactant properties of sulfated alcohols

A study was undertaken to determine the surfactant properties of various sulfated alcohols. Most notably, the Krafft point and the ability to emulsify decane were studied. A series of sulfated Guerbet alcohol and Guerbet alcohol alkoxylate sulfates with 16 carbon atoms and an analogous series based upon cetyl alcohol, a linear C₁₆, were studied as hydrophobes.     

Insights into the industrial growth of cyanobacteria from a model of the carbon‐concentrating mechanism

With the advent of modern bioengineering tools, photosynthetic organisms are increasingly being engineered to produce chemicals from CO₂ sources, thereby creating a potential route of sustainable chemical production. Cyanobacteria have evolved a carbon‐concentrating mechanism (CCM) that enables growth at low‐environmental carbon concentrations. However at high‐carbon concentrations these benefits may not outweigh synthesis costs. Here, mass transport and kinetic modeling analyses were performed on two species of cyanobacteria as well as a hypothetical no‐CCM mutant. Modeling results correlated with published experimental data. Three conclusions were drawn from the analysis. Carboxysome geometry was unimportant due to the fast relative rate of diffusion of carbon species. Interspecies variations were largely due to active transporters. The no‐carboxysome cell approaches the wild‐type at 10% CO₂. Therefore, in high CO₂ environments the carboxysome and active bicarbonate transporters provide no benefit and a metabolic advantage could be achieved by eliminating the energy‐intensive CCM proteins. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1269–1277, 2014     

Distribution of large biomass particles in a sand‐biomass fluidized bed: Experiments and modeling

The axial distribution of large biomass particles in bubbling fluidized beds comprised of sand and biomass is investigated in this study. The global and local pressure drop profiles are analyzed in mixtures fluidized at superficial gas velocities ranging from 0.2 to 1 m/s. In addition, the radioactive particle tracking technique is used to track the trajectory of a tracer mimicking the behavior of biomass particles in systems consisting of 2, 8, and 16% of biomass mass ratio. The effects of superficial gas velocity and the mixture composition on the mixing/segregation of the bed components are explored by analyzing the circulatory motion of the active tracer. Contrary to low fluidization velocity (U = 0.36 m/s), biomass circulation and distribution are enhanced at U = 0.64 m/s with increasing the load of biomass particles. The axial profile of volume fraction of biomass along the bed is modeled on the basis of the experimental findings. © 2014 American Institute of Chemical Engineers AIChE J, 60: 869–880, 2014     

In Vacuo Tribological Behavior of Polytetrafluoroethylene (PTFE) and Alumina Nanocomposites: The Importance of Water for Ultralow Wear

Polytetrafluoroethylene (PTFE) is widely regarded as an excellent candidate for solid lubrication in vacuum. However, it is often precluded from many practical applications due to its intrinsically high wear rate. Over the past decade, it has been discovered that small loading fractions of alumina nanofillers can increase the wear resistance of PTFE by three to four orders of magnitude. This dramatic increase in wear resistance has in turn prompted numerous tribological studies to examine the robustness of this performance. In this study, the wear and friction behavior of unfilled PTFE and PTFE and alumina nanocomposites were evaluated under a broad range of vacuum environments from 760 to 4 × 10^?6 Torr. The nanocomposites of PTFE/alumina showed a dramatic increase in wear of over two orders of magnitude at the highest vacuum conditions. There appears to be an optimal vacuum environment around 1–10 Torr, in which these samples achieved the lowest wear rates of approximately 2.5 × 10^?7 mm³/(Nm).     

Body Odors of Parasitized Caterpillars Give Away the Presence of Parasitoid Larvae to Their Primary Hyperparasitoid Enemies

Foraging success of parasitoids depends on the utilization of reliable information on the presence of their often, inconspicuous hosts. These parasitic wasps use herbivore-induced plant volatiles (HIPVs) that provide reliable cues on host presence. However, host searching of hyperparasitoids, a group of parasitoids that parasitize the larvae and pupae of other parasitoids, is more constrained. Their hosts do not feed on plants, and often are even concealed inside the body of the herbivore host. Hyperparasitoids recently have been found to use HIPVs of plants damaged by herbivore hosts in which the parasitoid larvae develop. However, hyperparasitoids that search for these parasitoid larvae may be confronted with healthy and parasitized caterpillars on the same plant, further complicating their host location. In this study, we addressed whether the primary hyperparasitoid Baryscapus galactopus uses caterpillar body odors to discriminate between unparasitized herbivores and herbivores carrying larvae of parasitoid hosts. We show that the hyperparasitoids made faster first contact and spent a longer mounting time with parasitized caterpillars. Moreover, although the three parasitoid hosts conferred different fitness values for the development of B. galactopus, the hyperparasitoids showed similar behavioral responses to caterpillar hosts carrying different primary parasitoid hosts. In addition, a two-chamber olfactometer assay revealed that volatiles emitted by parasitized caterpillars were more attractive to the hyperparasitoids than those emitted by unparasitized caterpillars. Analysis of volatiles revealed that body odors of parasitized caterpillars differ from unparasitized caterpillars, allowing the hyperparasitoids to detect their parasitoid host.     

A Hadamard transform electron ionization time-of-flight mass spectrometer

We describe the first Hadamard transform time-of-flight mass spectrometer (HT-TOFMS) that incorporates an electron (impact) ionization source. This implementation was realized in an existent TOF instrument using commercially available components and simple modifications to the ion source. In the present apparatus, a Hadamard mask is expressed by modulating the ion generation process within the ion source; thus, the present approach differs from previous designs that use external electrostatic devices to modulate a continuous ion stream. The present implementation may be operated in conventional TOF mode at 12.5 kHz and in HT-TOF mode at 20-40 MHz. In Hadamard mode the design can operate using any circulant simplex code, allowing the operator much flexibility for optimizing resolution and mass range and for eliminating nonstochastic fluctuations, e.g., encoding errors and signal hum. We demonstrate typical performance of the HT-TOFMS in standard and reflectron geometries using sequences of three constructions and of varied length, generating HT-TOF mass spectra of molecules that match conventional reference spectra. The auxiliary material includes an electrical schematic for the floating high-speed encoding amplifier, which is also of use in other high-speed electrostatic optics applications, and a list of 537 validated vectors comprising the first row of each circulant simplex sequence (S(n)=3-8219) derived using maximal shift register (n=2(m)-1), quadratic residue (n=4m-3), and twin prime constructions [n=p(p+2)].     

The high response and high efficiency velocity control of a hydraulic injection molding machine using a variable rotational speed electro-hydraulic pump-controlled system

High response and high efficiency velocity control of a hydraulic injection molding machine (HIMM) is requested especially for the process of high-tech industries, such as CD and DVD disks, plastic optical lens, light guide plates, etc. Instead of the hydraulic valve-controlled systems that have the problem of low energy efficiency but have been used widely in today’s HIMMs, the paper develops a high response and high energy efficiency electro-hydraulic pump-controlled system driven by a variable rotational speed AC servo motor for achieving high response and high efficiency velocity control in HIMMs. A constant displacement axial piston pump combined with the AC servo motor is developed in this research as the high response electro-hydraulic pump-controlled system for the HIMMs. For that, the control strategy, signed-distance fuzzy sliding mode control (SD-FSMC) is developed to simplify the fuzzy rule base through the sliding surface for practical applications. The developed high response variable rotational speed electro-hydraulic pump-controlled system controlled by SD-FSMC is implemented and verified experimentally for velocity control with various velocity targets and external loading conditions. Furthermore, the energy efficiencies of different experiments are analyzed and compared precisely by the power quality recorder used to measure the electrical power consumed by the AC servo motor.     

Spiral Tunneling Cracks Induced by Environmental Stress Cracking in LaRC™-TPI Adhesives

Some currently-available formulations of LaRC™-TPI, a thermoplastic polyimide originally developed at NASA-Langley, were found to be highly susceptible to environmental stress cracking when exposed to solvents such as acetone, toluene, diglyme and methyl ethyl ketone. The combination of stress and solvent led to rapid cracking in films and adhesive layers of this material system. Residual cool-down stresses induced when the LaRC-TPI is used as an adhesive or coating led, in the presence of a solvent, to dense “mud crack” patterns which relieve a portion of the stored energy. Because these through-the-thickness cracks are not able to relieve the stored energy in the vicinity of the adherends, additional fractures in the form of curious spiral tunnel cracks initiated and grew inward within each adhesive fragment. Micrographs of the spiral fractures are given, along with a qualitative explanation for the failure process as observed in adhesives and coatings.     

Direct visualization of sliding-induced tribofilm on Au/MoS<Subscript>2</Subscript> nanocomposite coatings by c-AFM

The nanoscale lubrication mechanism of nanocomposite Au/MoS₂ solid lubricant coatings has been studied by conductive atomic force microscopy (c-AFM). A direct visualization of the lubricating process suggests tribomechanical formation of a MoS₂ tribofilm to be a key mechanism. The sliding-induced tribofilm formation was visualized by a reduction in local friction and conductivity in nanoscale AFM images. The tribofilm was found to possess considerable crystallinity and orientation, which was not observed in the as-deposited coatings. The observed mechanism is broadly applicable to a range of nanocomposite metal/MoS₂ coatings.     

Practical considerations for high spatial and temporal resolution dynamic transmission electron microscopy

Although recent years have seen significant advances in the spatial resolution possible in the transmission electron microscope (TEM), the temporal resolution of most microscopes is limited to video rate at best. This lack of temporal resolution means that our understanding of dynamic processes in materials is extremely limited. High temporal resolution in the TEM can be achieved, however, by replacing the normal thermionic or field emission source with a photoemission source. In this case the temporal resolution is limited only by the ability to create a short pulse of photoexcited electrons in the source, and this can be as short as a few femtoseconds. The operation of the photo-emission source and the control of the subsequent pulse of electrons (containing as many as 5 x 10(7) electrons) create significant challenges for a standard microscope column that is designed to operate with a single electron in the column at any one time. In this paper, the generation and control of electron pulses in the TEM to obtain a temporal resolution <10(-6)s will be described and the effect of the pulse duration and current density on the spatial resolution of the instrument will be examined. The potential of these levels of temporal and spatial resolution for the study of dynamic materials processes will also be discussed.