A comprehensive chatter prediction model for face turning operation including tool wear effect

This paper presents a three-dimensional mechanistic frequency domain chatter model for face turning processes, that can account for the effects of tool wear including process damping. New formulations are presented to model the variation in process damping forces along nonlinear tool geometries such as the nose radius. The underlying dynamic force model simulates the variation in the chip cross-sectional area by accounting for the displacements in the axial and radial directions. The model can be used to determine stability boundaries under various cutting conditions and different states of flank wear. Experimental results for different amounts of wear are provided as a validation for the model.     

Multiscale modeling of thermal conductivity of polymer/carbon nanocomposites

Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between nanoparticles and amorphous and crystalline polymer matrices. Bulk thermal conductivities of the nanocomposites were then estimated using an established effective medium approach. To study functionalization, oligomeric ethylene–vinyl alcohol copolymers were chemically bonded to a single wall carbon nanotube. The results, in a poly(ethylene–vinyl acetate) matrix, are similar to those obtained previously for grafted linear hydrocarbon chains. To study the effect of non-covalent functionalization, two types of polyethylene matrices. -- aligned (extended-chain crystalline) vs. amorphous (random coils) were modeled. Both matrices produced the same interfacial thermal resistance values. Finally, functionalization of edges and faces of plate-like graphite nanoparticles was found to be only modestly effective in reducing the interfacial thermal resistance and improving the composite thermal conductivity.     

Results from the Mars Global Surveyor Thermal Emission Spectrometer

The Thermal Emission Spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase, together with about a 35 percent dust component provides the best fit to the spectrum. Qualitative upper limits can be placed on the concentration of carbonates (<10 percent), olivine (<10 percent), clay minerals (<20 percent), and quartz (<5 percent) in the limited regions observed. Limb observations in the northern hemisphere reveal low-lying dust hazes and detached water-ice clouds at altitudes up to 55 kilometers. At an aerocentric longitude of 224 degrees a major dust storm developed in the Noachis Terra region. The south polar cap retreat was similar to that observed by Viking.     

PHASE EQUILIBRIA IN THE H2/CH4 SYSTEM AT TEMPERATURES FROM 92.3 TO 180.0 K AND PRESSURES TO 140 MPa*

Experimental measurements of liquid-vapor phase equilibria in the system H₂/CH₄ are reported for ten temperatures in the range 92.3 to 180 K, and pressures to 140 MPa. The mixture critical line and the pressure-temperature trace of the three-phase region solid-liquid-vapor have been located. The three-phase region and the critical line intersect at T = 91.5 K and P = 147 MPa to form an upper critical end point. Experimental results have been compared with predictions of three equations of state, Peng-Robinson, Reclich-Kwong and Deiters, and with calculations based on statistical mechanical perturbation theory.     

Brain stem reticular formation neuronal correlates of stimulus significance and behavior during discriminative avoidance conditioning in rabbits.

Recorded multiple-unit activity in the reticular formation (RF) of the midbrain and pons in 14 New Zealand white rabbits during discriminative conditioning of locomotor (wheel-running) avoidance behavior, to examine whether discriminative neuronal activity develops in the RF during discriminative avoidance conditioning, and, if so, what its relation is to the activity in the limbic cortical structures and to the behavior. The positive and negative conditional stimuli (CS+ and CS–) were pure tones of different auditory frequency, and the unconditioned stimulus/stimuli (UCS) was a constant-current footshock (1.5–2.5 mA) delivered through the grid floor of the wheel. The pontine, but not the midbrain, sites manifested development during behavioral acquisition, of brief-latency (10–40 msec) discriminative neuronal discharges (i.e., greater discharges to the CS+ than to the CS–). The greatest magnitude of the discriminative discharges in the rostral pontine loci occurred in the 1st conditioning session. The discriminative response in the caudal loci developed more slowly, and it persisted to the criterial stage of training. Both rostral and caudal pontine loci, during the interval from CS onset to UCS onset, manifested a progressive build-up of neuronal firing in anticipation of the behavioral response. (59 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estimation and application of EMG amplitude during dynamiccontractions

The sections above have described an EMG amplitude estimator and an initial application of this estimator to the EMG-torque problem. The amplitude estimator consists of six stages. In the first stage, motion artifact and power-line interference are attenuated. Motion artifact is typically removed with a highpass filter. Elimination of power-line noise is more difficult. Commercial systems tend to use notch filters, accepting the concomitant loss of "true" signal power in exchange for simplicity and robustness. Adaptive methods may be preferable, however, to preserve more "true" signal power. In stage two, the signal is whitened. One fixed whitening technique and two adaptive whitening methods were described. For low-amplitude levels, the adaptive whitening technique that includes adaptive noise cancellation may be necessary. In stage three, multiple EMG channels (all overlying the same muscle) are combined. For most applications, simple gain normalization is all that is required. Stage four rectifies the signal and then applies the power law required to demodulate the signal. In stage six, the inverse of the power law is applied to relinearize the signal. Direct comparison of MAV (first power) to RMS (second power) processing demonstrates little difference between the two. Therefore, unless there is reason to believe that the EMG density departs strongly from that found in the existing studies, RMS and MAV processing are essentially identical. In stage five, the demodulated samples are averaged across all channels and then smoothed (time averaged) to reduce the variance of the amplitude estimate, but at the expense of increasing the bias. For best performance, the window length that best trades off variance and bias error is selected. The advanced EMG processing was next applied to dynamic EMG-torque estimation about the elbow joint. Results showed that improved EMG amplitude estimates led to improved EMG-torque estimates. An initial comparison of different system-identification techniques and model orders was reported. It is expected that these advanced processing and identification algorithms will also improve performance in other EMG applications, including myoelectrically controlled prostheses, biofeedback, and ergonomic assessment.     

Equalization attacks against OFDM: analysis and countermeasures

This paper introduces, investigates, and proposes power‐efficient equalization jamming attacks against the orthogonal frequency division multiplexing (OFDM) and possible countermeasures. Signals known a priori, called pilot tones, are employed in the conventional OFDM‐based systems to estimate the channel response and perform equalization. Attacks against these pilot tones can hamper equalization and degrade target's performance. This paper begins with noise‐based pilot tone jamming and moves onto pilot nulling attack. The paper embraces two mitigation strategies of randomizing the pilot tones. The paper presents mathematical model of effective noise per symbol and simulation results for OFDM systems with conventional and randomized pilot‐tones under such attacks. The paper concludes that the noise‐based pilot tone attacks are power efficient than conventional attacks, and the pilot nulling is capable of doing the most damage, but in the expense of additional channel state information. The paper also claims that the mitigation strategies offer a remedy, but works relatively poorly when no jammer is present. Copyright © 2015 John Wiley & Sons, Ltd.     

The S. cerevisiae nitrogen starvation-induced Yvh1p and Ptp2p phosphatases play a role in control of sporulation

Starvation for nitrogen in the absence of a fermentable carbon source causes diploid Saccharomyces cerevisiae cells to leave vegetative growth, enter meiosis, and sporulate; the former nutritional condition also induces expression of the YVH1 gene that encodes a protein phosphatase. This correlation prompted us to determine whether the Yvh1p phosphatase was a participant in the network that controls the onset of meiosis and sporulation. We found that expression of the IME2 gene, encoding a protein kinase homologue required for meiosis- and sporulation-specific gene expression, is decreased in a yvh1 disrupted strain. We also observed a decrease, albeit a smaller one, in the expression of IME1 which encodes an activator protein required for IME2 expression. Under identical experimental conditions, expression of the MCK1 and IME4 genes (which promote sporulation but do not require Ime1p for expression) was not affected. These results demonstrate the specificity of the yvh1 disruption phenotype. They suggest that decreased steady-state levels of IME1 and IME2 mRNA were not merely the result of non-specific adverse affects on nucleic acid metabolism caused by the yvh1 disruption. Sporulation of a homozygous yvh1 disruption mutant was delayed and less efficient overall compared to an isogenic wild-type strain, a result which correlates with decreased IME1 and IME2 gene expression. We also observed that expression of the PTP2 tyrosine phosphatase gene (a negative regulator of the osmosensing MAP kinase cascade), but not the PTP1 gene (also encoding a tyrosine phosphatase) was induced by nitrogen-starvation. Although disruption of PTP2 alone did not demonstrably affect sporulation or IME2 gene expression, sporulation was decreased more in a yvh1, ptp2 double mutant than in a yvh1 single mutant; it was nearly abolished in the double mutant. These data suggest that the YVH1 and PTP2 encoded phosphatases likely participate in the control network regulating meiosis and sporulation. Expression of YVH1 and PTP2 was not affected by nitrogen source quality (asparagine compared to proline) suggesting that nitrogen starvation-induced YVH1 and PTP2 expression and sensitivity to nitrogen catabolite repression are on two different branches of the nitrogen regulatory network.     

Molecular cloning and functional analysis of a novel macrolide-resistance determinant, mefA, from Streptococcus pyogenes

Several streptococcal strains had an uncharacterized mechanism of macrolide resistance that differed from those that had been reported previously in the literature. This novel mechanism conveyed resistance to 14- and 15-membered macrolides, but not to 16-membered macrolides, lincosamides or analogues of streptogramin B. The gene encoding this phenotype was cloned by standard methods from total genomic digests of Streptococcus pyogenes 02C1064 as a 4.7 kb heterologous insert into the low-copy vector, pACYC177, and expressed in several Escherichia coli K-12 strains. The location of the macrolide-resistance determinant was established by functional analysis of deletion derivatives and sequencing. A search for homologues in the genetic databases confirmed that the gene is a novel one with homology to membrane-associated pump proteins. The macrolide-resistance coding sequence was subcloned into a pET23a vector and expressed from the inducible T7 promoter on the plasmid in E. coli BL21(DE3). Physiological studies of the cloned determinant, which has been named mefA for macrolide efflux, provide evidence for its mechanism of action in host bacteria. E.coli strains containing the cloned determinant maintain lower levels of intracellular erythromycin when this compound is added to the external medium than isogenic clones without mefA. Furthermore, intracellular accumulation of [14C]-erythromycin in the original S. pyogenes strain was always lower than that observed in erythromycin-sensitive strains. This is consistent with a hypothesis that the gene encodes a novel antiporter function which pumps erythromycin out of the cell. The gene appears to be widely distributed in S. pyogenes strains, as demonstrated by primer-specific synthesis using the polymerase chain reaction.     

Effect of air-assisted backwashing on the performance of an anaerobic fixed-bed bioreactor that simultaneously removes nitrate and arsenic from drinking water sources

Contaminant removal from drinking water sources under reducing conditions conducive for the growth of denitrifying, arsenate reducing, and sulfate reducing microbes using a fixed-bed bioreactor may require oxygen-free gas (e.g., N₂ gas) during backwashing. However, the use of air-assisted backwashing has practical advantages, including simpler operation, improved safety, and lower cost. A study was conducted to evaluate whether replacing N₂ gas with air during backwashing would impact performance in a nitrate and arsenic removing anaerobic bioreactor system that consisted of two biologically active carbon reactors in series. Gas-assisted backwashing, comprised of 2 min of gas injection to fluidize the bed and dislodge biomass and solid phase products, was performed in the first reactor (reactor A) every two days. The second reactor (reactor B) was subjected to N₂ gas-assisted backwashing every 3-4 months. Complete removal of 50 mg/L NO₃⁻ was achieved in reactor A before and after the switch from N₂-assisted backwashing (NAB) to air-assisted backwashing (AAB). Substantial sulfate removal was achieved with both backwashing strategies. Prolonged practice of AAB (more than two months), however, diminished sulfate reduction in reactor B somewhat. Arsenic removal in reactor A was impacted slightly by long-term use of AAB, but arsenic removals achieved by the entire system during NAB and AAB periods were not significantly different (p > 0.05) and arsenic concentrations were reduced from approximately 200 μg/L to below 20 μg/L. These results indicate that AAB can be implemented in anaerobic nitrate and arsenic removal systems.