132,843 research outputs found
Initial conditions in the averaging cognitive model
No full textThe initial state parameters s0 and w0 are intricate issues of the averaging cognitive models in Information Integration Theory. Usually they are defined as a measure of prior information (Anderson, 1981; 1982) but there are no general rules to deal with them. In fact, there is no agreement as to their treatment except in specific situations such as linear models where they can be merged with the arbitrary zero inter-response scale C0. We present some considerations on their meaning and usefulness in the Functional Measurement approach, starting from different points of view. Furthermore, we suggest a method to deal with their complexity both within each single trial of a factorial design, and between the overall trials of an experiment
A semi-empirical fluid dynamic model of a vacuum microgripper based on cfd analysis
No full textVacuum microgrippers are devices used to handle and manipulate small objects. Despite their simple working principle and low cost, they show low efficiency in detaching performance, especially when the object to be grasped is very small. In this work, a particular design for vacuum microgrippers with an incorporated automatic release tool is considered. The final goal of this study was to present a numerical model that can supply reliable estimates of the aerodynamic force acting on the release tool and of the air flow rate inside the gripper as a function of geometric parameters and the outlet pressure value. A complete CFD analysis of a simplified model of the device is presented. Grid independence analysis was also performed to define a suitable grid and guarantee a good trade-off between accuracy and computing time. According to Design of Experiments (DOE) techniques, 81 simulations were performed, changing the values of the outlet pressure (p2 ), the body inner diameter (D), the lateral holes’ diameter (d) and the releasing mass length (L). Every design variable could assume three different values. Linear regression, based on the least square method, was employed to determine mass flow rate and lifting force empirical correlations
A new method for monitoring hydration at high altitude by bioimpedance analysis.
No full textOur study evaluated the performance of a graphical method for monitoring the fluid variation at high altitude in seven adult Caucasian male subjects (average age 25 yr, average height 177 cm). The graphical approach is called the Resistance-Reactance (RXc) graph method and is based on standard bioimpedance analysis (tetrapolar, 50 kHz frequency). Measurements were taken at sea level before the expedition, at 5050 m after 1 wk and 3 wk, and again at sea level after descent. Plasma and urine electrolytes, osmolalities, and the free-water clearance were determined by standard methods. All climbers had baseline impedance vectors within the reference 95% tolerance ellipse for the Italian male population. The high altitude dehydration caused a significant lengthening of vectors, which after descent underwent a significant shortening and returned close to the baseline values. Average urine volume increased by 1.4 l.d-1 in the first week and average body weight decreased by 4.4 kg after 3 wk. The RXc graph method could be useful in the planning of the individual climber's appropriate dehydration and fluid intake at altitude since a feedback control of the hydration is allowed without any assumption of body composition
Relationships between firmness of dry-cured hams and breeding values for curing weight loss traits
No full textDry cured ham (DCH) is the most valuable product of the pig industry in Italy. Firmness is an important quality traits affecting slicing. Aim of this study was to investigate the relationship between firmness of DCH (subjective evalution with linear score from 0 to 4) and breeding values (EBV) of pigs for weight loss at the end of curing (WL) and for traits related to the dynamic of weight loss (WLD). Ham weights were recorded at arrival at the ham factory, 15 and 130 day since arrival, and at the end of seasoning (300 days). The dataset included records on left hams from 1602 crossbred heavy pigs (6428 weight records). The dynamic of weight loss was estimated by fitting a nonlinear model (Von Bertallanfy function) and instantaneous rates of weight loss (IS) were determined at different stages of curing (from 10 to 100 d by 10 d steps). Heritability of WL was 25%, whereas heritability of IS ranged from 17 to 30%, with higher values for later curing stages. EBV for WL and IS affected firmness of DCH. High firmness was associated to high EBV for WL and IS
Transition model based on the laminar kinetic energy concept for the prediction of all transition modes
No full textSeparation-induced transition showed to be the weakness of the transition models based on the laminar kinetic energy concept. In fact, these models contemplate only the Tolmien-Schlichting waves, for the natural mode, and the Klebanoff streaks, for the bypass mode. Literature is very poor about the use of these models to cases with the separation-induced mode and in all these works no proofs of the phenomenological agreement between the models and the physics of the flow are spotlighted. A further improvement for the Reynolds-Averaged Navier-Stokes equations in separated and transitional shear layers needs more accurate models to describe the physics behind the phenomena, e.g., the introduction of ad-hoc designed terms for the Kelvin-Helmholtz instability in the transport equations. The objective of this work is to assess a phenomenological and local transition model based on the laminar kinetic energy concept, implemented in a high-order discontinuous Galerkin solver, for the simulation of transitional flows. The prediction capabilities of the model are proved with the simulations of the flow over the ERCOFTAC and UNIGE flat plates, characterized by the bypass and separation-induced mode of transition. The education of the model is not only based on integral coefficients and first-order statistics, but also on the turbulence intensity, laminar and turbulent kinetic energy distributions extracted from finely processed experimental data
Pegylated interferon-associated retinopathy is frequent in hepatitis C virus patients with hypertension and justifies ophthalmologic screening
No full textTreatment with pegylated interferon alpha (PegIFNα) and ribavirin is still regarded as the standard of care for chronic hepatitis C virus (HCV). Retinopathy has been occasionally described but prospective, longitudinal data are lacking. We investigated the frequency and clinical significance of retinopathy during therapy with PegIFNα and ribavirin in 97 consecutive HCV patients. In all, 54 (55.7%) and 43 (44.3%) patients were treated with PegIFNα 2a and PegIFNα 2b, respectively. Ophthalmologic examination was performed before therapy (baseline), at 3 and 6 months (3T and 6T, respectively) of therapy, and 3 months after the end of therapy (3ET). All patients underwent the baseline and 3T examination, 95.9% and 90.7% of patients underwent 6T and 3ET examination, respectively. Overall, 30.9% of patients developed retinopathy, as defined by the presence of cotton wool spots and/or retinal hemorrhages. Variables significantly associated with retinopathy during treatment were age (P = 0.004), metabolic syndrome (P = 0.05), hypertension (P < 0.0001), cryoglobulinemia (P = 0.05), and preexisting intraocular lesions at baseline (P = 0.01). By multivariate analysis, the only variable independently associated with PegIFNα-associated retinopathy was hypertension (hazard ratio [HR] = 4.99, 95% confidence interval [CI] 2.29-10.89). The frequency of retinopathy was significantly higher in hypertensive patients versus those without hypertension at all timepoints (18.5% versus 5.7% at baseline, P = 0.05; 48.1% versus 15.7% at 3T, P = 0.0009; 68.0% versus 19.1% at 6T, P < 0.0001; 32.0% versus 6.2%, P = 0.0005 at 3ET). In one (1.1%) hypertensive patient, who developed bilateral branch retinal vein occlusion at 6T, the therapy was discontinued. A cost analysis showed that screening for PegIFNα-associated retinopathy was cost-effective as compared with thyroid-stimulating hormone screening. Conclusion: Retinopathy is frequent during treatment with PegIFNα and ribavirin, especially in hypertensive patients, who may develop serious complications. Screening for PegIFNα-associated retinopathy should be recommended for HCV patients with hypertension
Sodium regulating hormones at High Altitude: Basal and Post-exercise levels
No full textHigh altitude (HA)-induced diuresis is associated with marked changes in sodium and water regulating hormones, particularly the renin-angiotensin-aldosterone system (RAAS) and atrial natriuretic hormone (ANH). These hormones are also strongly stimulated by physical exercise, which is a major component of daily activity at HA. In spite of the numerous studies in literature, a clear relationship between hormonal changes, HA diuresis, and physical exercise has not yet been established. We therefore evaluated the response of sodium regulating hormones to exhaustive exercise in a group of seven males exposed to prolonged HA hypoxia. The study was divided into four phases: sea level (SL1), after 7 (P1) and after 21 (P2) days at 5050 m (Italian National Research Council Pyramid Laboratory, Nepal), and back at sea level (SL2). At each phase plasma hematocrit (Ht), total body water (TBW), 24-hr sodium excretion (uNa), and urinary volume (uV) were evaluated together with PRA, plasma aldosterone, and ANH, in samples drawn basally from patients in upright position, and at the end of graded step-wise (30 W/2 min) maximal exercise. Levels of uNa and uV were raised at P1 and then declined at P2, with a parallel decrease in TBW and an increase in Ht. Basal PRA and aldosterone levels were suppressed both at P1 and P2 (from 1.9 +/- 0.4 to 0.08 +/- 0.03 and 0.5 +/- 0.1 ng/mL/3 h, and from 7.9 +/- 1.8 to 3.9 +/- 0.4 and 4.5 +/- 0.4 ng/dL, respectively; P < .05). Exhaustive exercise at HA did not induce any significant response in PRA and aldosterone, unlike SL1. Otherwise at P1 ANH levels remained unchanged both basally and during exercise, while at P2 they decreased significantly vs. SL1, both basally and after exercise (from 13.3 +/- 5.7 to 3.5 +/- 1.2 and from 40.2 +/- 10.2 to 17.5 +/- 8.3, respectively; P < .05). Our data show that PRA and aldosterone levels were constantly suppressed at HA and were unresponsive to exercise, whereas the ANH response was significantly stimulated during acute HA exposure, but not during chronic exposure. This suggests that hypoxia-induced chemoreceptor stimulation may cause the natriuretic phenomenon through direct suppression of the RAAS
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