1,720,981 research outputs found
Hard Disk Drive with Voltage Driven Voice Coil Motor
No full textThe paper presents a novel approach for driving a Voice Coil Motor (VCM) in a Hard Disk Drive (HDD), based on an adaptive voltage driver. The adaptation of the driver compensates for the variations of VCM resistance and is performed either during seek operations and track following. As a result, the performance of the proposed driver matches closely that of a standard current driver
Voltage Driven Hard Disk Drive with Voice Coil Model-based Control
No full textIn this paper we describe a new voltage driven head servo-positioning system for hard disk drives (HDDs) called Voice Coil Model-based Control (VCMC). Previous works [1],[2] have shown that the usual current amplifier used in driving the voice coil motor can be replaced by a simpler system, consisting a power voltage amplifier driven by an adaptive, multi-rate, zero-pole pre-filter that cancels out the VCM electrical pole. This fully digital solution can be implemented by using a switching power stage in place of the standard linear high power operational amplifier, with savings in both silicon area and power dissipation. The latter is further reduced with the voltage driver, since there is no need for the shunt resistor, placed in series to the VCM as a current sensor. The major drawback exhibited by a voltage driven HDDs is that the dynamics of the system to be controlled depend on the variations of the VCM coil resistance. Moreover, previous realizations, based on a multi-rate zero-pole pre-filter, did not account for the saturation of the driving power amplifier, causing a performance worsening for seeks with average size span. The drawback related to the dependence on the variations of motor resistance has been partially solved in [2], where the pre-filter is tuned at start-up, using the estimated VCM coil resistance given by an Extended Kalman Filter (EKF). This solution, however, presents a high computational complexity and cannot account for resistance variations when the HDD is in idle mode or during track following operations. During these phases, in fact, signal-to-noise ratio results not to be high enough to guarantee EKF convergence. The solutions proposed in this paper address all these issues. The VCMC is based on a new multi-rate pre-filter, which replicates the behavior of a current loop by using a model of the voice coil motor and its driver, including the saturation of the power stage. The performance obtained, when it is fully tuned, is the same as a current driven HDD during all operational phases. As for the pre-filter tuning, during seek operations, an adaptive algorithm based on a simplified least-square identification procedure, maintains the same performance level of the EKF with a lower computational complexity. Finally, several methods for estimating the value of VCM coil resistance during idle mode and track following operations will be compared. They are all based on the analysis of the information given by position error signal and VCM input. Experimental results, including those related to resistance estimation, will be presented in the final paper, showing that HDD servo-positioning performance obtained with the VCMC matches that obtained with a standard current loop, in both seek and track following operations
Dilutional acidosis : where do the protons come from?
No full textPURPOSE: To investigate the mechanism of acidosis developing after saline infusion (dilutional acidosis or hyperchloremic acidosis). METHODS: We simulated normal extracellular fluid dilution by infusing distilled water, normal saline and lactated Ringer's solution. Simulations were performed either in a closed system or in a system open to alveolar gases using software based on the standard laws of mass action and mass conservation. In vitro experiments diluting human plasma were performed to validate the model. RESULTS: In our computerized model with constant pKs, diluting extracellular fluid modeled as a closed system with distilled water, normal saline or lactated Ringer's solution is not associated with any pH modification, since all its determinants (strong ion difference, CO(2) content and weak acid concentration) decrease at the same degree, maintaining their relative proportions unchanged. Experimental data confirmed the simulation results for normal saline and lactated Ringer's solution, whereas distilled water dilution caused pH to increase. This is due to the increase of carbonic pK induced by the dramatic decrease of ionic strength. Acidosis developed only when the system was open to gases due to the increased CO(2) content, both in its dissociated (bicarbonate) and undissociated form (dissolved CO(2)). CONCLUSIONS: The increase in proton concentration observed after dilution of the extracellular system derives from the reaction of CO(2) hydration, which occurs only when the system is open to the gases. Both Stewart's approach and the traditional approach may account for these results
Effect of aliskiren on (pro)renin receptor expression and activity: in vitro determination of TGF-β, PAI-1 and type I collagen expression and smooth muscle cell migration
No full textThe recent discovery of a specific receptor for renin/prorenin (PRR) has added new interest to the pharmacological actions of aliskiren, the first direct renin inhibitor. In the present study we investigated the effect of aliskiren on PRR expression and activity in cultured human smooth muscle cells (SMCs). Co-incubation of SMCs with angiotensinogen (ANG) (1.5 × 10-7 M) and prorenin (10-8–10-7 M) resulted in an efficient production of angiotensin I, almost completely inhibited by 10-5 M aliskiren (-86.0 ± 14.0%). A 24 h incubation with aliskiren (10-6–10-5 M) resulted in a concentration-dependent reduction of PRR mRNA levels (IC50 4.6 × 10-6 M) and the cell surface expression of PRR (IC50 9.1 × 10-6 M). The lower levels of PRR were associated with a reduced expression of TGF-β, PAI-1 and type I collagen mRNA. The effect of prorenin on SMC migration was also investigated. Prorenin induced SMC migration in a dose-dependent manner, as assessed by Boyden chamber chemotaxis assay. The knockdown of PRR by small interfering RNA completely inhibited the migratory response to prorenin, demonstrating that the chemotactic action of prorenin is mediated by the PRR. Prorenin increased the intracellular levels of both RhoA-GTP (+47.8%) and Rac1-GTP (+36.7%) through PRR. A 24 h incubation with aliskiren (10-6 - 2.5x10-5 M) did not affect SMC migration and RhoA-GTO levels in response to prorenin. In conclusion aliskiren elicits a direct pharmacological action on PRR expression and its signaling pathway in SMCs, affecting gene expression of TGF-β, PAI-1 and type I collagen. However, this action is not sufficient to significantly reduced the chemotactic action of prorenin on SMCs. These results, although obtained from in vitro analysis, may help to better define the pharmacological properties of aliskiren on atherosclerosis.
The present work was supported by a grant from Novartis Farma S.p.A., Origgio, Italy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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