Single state elastoplastic friction models

For control applications involving small displacements and velocities, friction modeling and compensation can be very important. In particular, the modeling of presliding displacement (motion prior to fully developed slip) can play a pivotal role. In this paper, it is shown that existing single-state friction models exhibit a nonphysical drift phenomenon which results from modeling presliding as a combination of elastic and plastic displacement. A new class of single state models is defined in which presliding is elastoplastic: under loading, frictional displacement is first purely elastic and then transitions to plastic. The new model class is demonstrated to substantially reduce drift while preserving the favorable properties of existing models (e.g., dissipativity) and to provide a comparable match to experimental data     

Hepatobiliary and pancreatic mucinous cystadenocarcinomas with mesenchymal stroma: analysis of estrogen receptors/progesterone receptors and expression of tumor-associated antigens

In an attempt to establish a standardized rating system for CT of the paranasal sinuses, the Committee on Rhinology and Paranasal Sinus Disease of the American Academy of Otolaryngology-Head and Neck Surgery instituted a protocol for the review of sinus CT scans at six international sites. Fifty identical scans were rated by four otolaryngologists at each site according to five established sinus CT staging systems. Twenty of 24 reviewers repeated the rating session at least 1 week later to determine intrarater variability. The number of CT scans that could not be classified by a particular rating system ranged from 1.3% to 5.5%. The range of intrarater agreement (kappa = 0.39 to 0.74) exceeded that of interrater agreement (kappa = 0.18 to 0.49). A skewed distribution of CT scans resulted in a system with high rater agreement but poor ability to differentiate among disease states. The use of a numeric rating system to assign a score to each scan produced a comprehensive and disease-sensitive system, but one with low rater agreement. A precise definition of mucosal thickening in terms of millimeters appeared to enhance the raters' ability to assign stage and improve a system's comprehensiveness and reproducibility. On the basis of these findings, recommendations are made for the use of CT rating systems to study clinical outcomes in patients with chronic sinusitis.     

Detection of the local H+ gradients on the internal mitochondrial membrane

Respiration-dependent responses of a pH probe (fluorescein isothiocyanate, FITC), covalently bound to the membrane proteins of mitochondria and submitochondrial particles (SMP) have been studied. A spectral shift indicating FITC deprotonation was observed when respiration was activated in coupled mitochondria. Such a response was increased by valinomycin and reduced by uncoupler. Some FITC deprotonation was detected in the presence of excess of an uncoupler, but the response was smaller and insensitive to valinomycin. FITC deprotonation was also observed in submitochondrial particles after succinate addition. In this case it was not affected by uncoupler. Increase in the buffer concentration was found to (i) decrease the FITC response and (ii) increase the rate of uncoupled respiration in both mitochondria and submitochondrial particles. The results are consistent with the assumption that respiration initiates appearance of local H+ activity gradients on the inner side of the internal mitochondrial membrane during the steady-state H+ pumping. We suggest that the formation of this gradient is due to kinetic barrier to proton transfer from the bulk phase to the respiratory proton pump vicinity.     

Physical design issues for very large ATM switching systems

The authors examine the physical design issues associated with terabit/second switching systems, particularly with regard to the customer access portion of the switch. They determine the physical design requirements in the areas of backplane interconnections, integrated circuit packaging, and circuit board technology and identify areas where existing- or near-future physical design technologies are inadequate to meet the requirements of this application. A new 3D interconnection architecture that solves some of the problems encountered at the backplane level is suggested. It is also suggested that multichip module technology will help meet some of the speed and density requirements at the chip packaging level. Some of the system-level consequences of the proposed model are discussed     

Managed care and open-heart surgery facilities in California

More than 25 percent of hospitals in California that offer open-heart surgery performed fewer than the number recommended by minimum volume guidelines in 1991. This DataWatch examines the characteristics of these hospitals and the patients they treat. The analysis suggests that the market share of these providers has remained constant over recent years, despite substantial growth in managed care. Simple explanations--for example, that these hospitals are serving isolated geographic markets or are hospitals in transition--do not explain the phenomenon. Medicare beneficiaries represent approximately half of the patient volume at these facilities. Health maintenance organizations (HMOs) are more likely to send their enrollees to high-volume facilities.     

Evidence that P2X purinoceptors mediate the excitatory effects of alphabetamethylene-ADP in rat locus coeruleus neurones

Extracellular and whole-cell patch clamp recordings were used to study the excitatory responses elicited by purine nucleotides in pontine slices of the rat brain containing the locus coeruleus (LC). The P2 purinoceptor agonists, alphabeta-methyleneadenosine 5'-triphosphate (alphabetameATP) and adenosine 5'-O-(2-thiodiphosphate) (ADPalphabetaS), and a novel purinoceptor agonist, alphabeta-methyleneadenosine 5'-diphosphate (alphabetameADP), elicited concentration-dependent increases in the spontaneous firing rate over the concentration range (1-300 microM). On vagus nerve or dorsal root preparations alphabetameADP (100 microM) had no agonist activity. In the presence of both alphabetameATP (300 microM), ADPbetaS (300 microM) elicited a further and significant increase in the firing rate of the LC neurones, whilst neither alphabetameATP nor alphabetameADP (300 microM) elicited a further response. The P2 purinoceptor antagonists, suramin (100 microM) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 30 microM), markedly attenuated responses to all three agonists. Whole-cell recording of membrane current showed that, at - 60 mV, alphabetameATP and alphabetameADP (both 100 microM) elicited inward currents of a similar magnitude, whilst the inward currents elicited by a lower concentration of ADPbetaS (30 microM) were larger and faded in the presence of this agonist. In the presence of tetrodotoxin and a combination of other neurotransmission blockers, both alphabetameATP and alphabetameADP still produced inward currents. Based on the known selectivity of the agonists used in this study, there appear to be two distinct P2 purinoceptor types present on neurones in the LC, which correspond to the P2X and P2Y types. The responses elicited by alphabetameADP appear to be mediated through a putative P2X purinoceptor, although further work is required to determine which P2X receptor subtype(s) are involved.