Influence Of Small Variations Research Articles

Математическая модель распределенного проектирования прототипов в машиностроении

Fully functional, full-scale models with characteristics close to those of mass-produced devices are widely employed in mechanical engineering to validate the possibility of implementing a new concept in the actual device. Prototype development and manufacturing is a costly process performed both with a limited time and financial constraints. Therefore, there is a need to create efficient automation tools for process planning in functional prototyping, based on full-scale mathematical models that allow taking into consideration the influence of small variations in technological parameters on the development time and cost. The proposed model employs mathematical programming techniques and ordinary homogeneous differential equations with discontinuous right sides. It takes into account both the limited resources and the distributed nature of the prototyping process. Furthermore, the model potentially allows for application of the automata theory to simulate and analyse the influence of the innovation market fluctuations on the innovation design process. The described modelling capabilities are realized in the software package IDC Requirements Engineering that features both the open PLM platform standards and the concept of digital factories.

Influence of spatial resolution and contrast agent dosage on myocardial T1 relaxation times.

Our aim was to study the influence of small variations in spatial resolution and contrast agent dosage on myocardial T1 relaxation time. Twenty-nine healthy volunteers underwent cardiovascular magnetic resonance at 3T twice, including a modified look-locker inversion recovery (MOLLI) technique-3(3)3(3)5-for T1 mapping. Native T1 was assessed in three spatial resolutions (voxel size 1.4×1.4×6, 1.6×1.6×6, 1.7×1.7×6mm3), and postcontrast T1 after 0.1 and 0.2mmol/kg gadobutrol. Partition coefficient was calculated based on myocardial and blood T1. T1 analysis was done per segment, per slice, and for the whole heart. Native T1 values did not differ with varying spatial resolution per segment (p=0.116-0.980), per slice (basal: p=0.772; middle: p=0.639; apex: p=0.276), and globally (p=0.191). Postcontrast T1 values were significantly lower with higher contrast agent dosage (p<0.001). The global partition coefficient was 0.43±0.3 for 0.2 and 0.1mmol gadobutrol (p=0.079). Related to the tested MOLLI technique at 3T, very small variations in spatial resolution (voxel sizes between 1.4×1.4×6 and 1.7×1.7×6mm3) remained without effect on the native T1 relaxation times. Postcontrast T1 values were naturally shorter with higher contrast agent dosage while the partition coefficient remained constant. Further studies are necessary to test whether these conclusions hold true for larger matrix sizes and in larger cohorts.

Routes of synthesis of nepheline-type polymorphs: An influence of Na-LTA bulk composition on its thermal transformations

In this work we investigated the conditions under which pure basic hexagonal nepheline phase is formed by the zeolite Na-LTA thermal transformation route. The influence of small variations in Na-LTA bulk stoichiometry on the rate and course of the thermal transformation process was examined. The starting materials were three Na-LTA samples with different Na2O: Al2O3: SiO2 ratios: 0.99Na2O: 1.00Al2O3: 2.00 SiO2, 1.05Na2O: 1.06Al2O3: 2.00SiO2 and 1.05Na2O: 1.00Al2O3: 2.05SiO2. Upon heat treatment, the zeolite samples showed different conversion routes. At temperatures above 950°C all three Na-LTA samples transformed into nepheline-type polymorphs. While the Na-LTA sample with the composition close to ideal stoichiometry gave pure basic hexagonal nepheline, the Na-LTA samples containing sodium, aluminum and silica excess formed mixtures of basic hexagonal nepheline and monoclinic trinepheline. The synthesized nepheline-type polymorphs were investigated by X-ray powder diffraction, Raman and NMR spectroscopy.

Properties of Expected Travel Cost Function with Uncertain Travel Time

The paper presents a theoretical analysis of travelers’ scheduling preferences and the resulting form of the expected utility that includes travel time reliability measures. A series of research papers and reports used the mean–standard deviation approach to evaluate policies that improve travel time reliability. Recently, this approach was theoretically substantiated under the conventional assumptions of constant marginal utility of time (MUT) at the origin, two discrete MUT values at the destination, and constant standardized travel time distribution. In this paper, properties of the minimal expected travel cost are investigated with smooth MUTs at the origin and destination of the trip. The influence of small variations in travel time on travel cost is well approximated by a term proportional to the travel time variance and independent of the distribution form of travel time. Two examples of MUT functions are provided: the minimal expected travel cost can be analytically expressed through moments or through a moment generating function of travel time, and conditions are stated guaranteeing that the expected travel cost is exactly additive by independent parts of the trip. These results provide justification in particular for the mean–variance approach to modeling drivers’ decisions under uncertain travel times. This formulation is convenient especially for scheme evaluation in large road networks because it allows the use of conventional network assignment routines by just modifying the volume delay functions to include the travel time variability term.

Robustness of a discrete dynamical process with a given set of attainability

A linear discrete system x (k +1) = A x (k) with a given set of attainability (c, x( N)) ? c 0 is considered. The influence of small variations of problem parameters on the attainability of a required set is investigated. For the control system x (k+1) = Ax (k) + Bu (k), the choice of a controller as a feedback in state u(k) = Kx (k) is studied.

Study of encapsulated T170m sources for their potential use in brachytherapy

High dose-rate (HDR) brachytherapy is currently performed with 192Ir sources, and 60Co has returned recently into clinical use as a source for this kind of cancer treatment. Both radionuclides have mean photon energies high enough to require specific shielded treatment rooms. In recent years, 169Yb has been explored as an alternative for HDR-brachytherapy implants. Although it has mean photon energy lower than 192Ir, it still requires extensive shielding to deliver treatment. An alternative radionuclide for brachytherapy is 170Tm (Z=69) because it has three physical properties adequate for clinical practice: (a) 128.6 day half-life, (b) high specific activity, and (c) mean photon energy of 66.39 keV. The main drawback of this radionuclide is the low photon yield (six photons per 100 electrons emitted). The purpose of this work is to study the dosimetric characteristics of this radionuclide for potential use in HDR-brachytherapy. The authors have assumed a theoretical 170Tm cylindrical source encapsulated with stainless steel and typical dimensions taken from the currently available HDR 192Ir brachytherapy sources. The dose-rate distribution was calculated for this source using the GEANT4 Monte Carlo (MC) code considering both photon and electron 170Tm spectra. The AAPM TG-43 U1 brachytherapy dosimetry parameters were derived. To study general properties of 170Tm encapsulated sources, spherical sources encapsulated with stainless steel and platinum were also studied. Moreover, the influence of small variations in the active core and capsule dimensions on the dosimetric characteristics was assessed. Treatment times required for a 170Tm source were compared to those for 192Ir and 169Yb for the same contained activity. Due to the energetic beta spectrum and the large electron yield, the bremsstrahlung contribution to the dose was of the same order of magnitude as from the emitted gammas and characteristic x rays. Moreover, the electron spectrum contribution to the dose was significant up to 4 mm from the source center compared to the photon contribution. The dose-rate constant lamda of the cylindrical source was 1.23 cGy h(-1) U(-1). The behavior of the radial dose function showed promise for applications in brachytherapy. Due to the electron spectrum, the anisotropy was large for r <6 mm. Variations in manufacturing tolerances did not significantly influence the final dosimetry data when expressed in cGy h(-1) U(-1). For typical capsule dimensions, maximum reference dose rates of about 0.2, 10, and 2 Gy min(-1) would then be obtained for 170Tm, 192Ir, and 169Yb, respectively, resulting in treatment times greater than those for HDR 192Ir brachytherapy. The dosimetric characteristics of source designs exploiting the low photon energy of 170Tm were studied for potential application in HDR-brachytherapy. Dose-rate distributions were obtained for cylindrical and simplified spherical 170Tm source designs (stainless steel and platinum capsule materials) using MC calculations. Despite the high activity of 170Tm, calculated treatment times were much longer than for 192Ir.

Influence of magnetic properties of shields on recording head instability parameters

We report on the origin and the influence of small variations in magnetic properties of magnetically soft Sendust films, used as a bottom shield in magnetoresistive heads, on instability parameters probed by quasi-static measurements. A strong correlation of the shield's magnetic characteristics with the average wafer asymmetry range is found. The variations in magnetic properties are directly connected with local anisotropy effects as revealed by Kerr microscopy. A direct correlation of the domain structures at the shield's surface with microstructure of the film is found. The magnetic domains display a change of magnetics with film growth. The deviations of magnetic properties are due to small structural Sendust changes.

Optimal design of polarizing beam splitters with a birefringent substrate

We present an optimal approach for designing polarizing beam splitters made of a sheet of birefringent material. The polarizing beam splitter is in the form of a transmission diffraction grating with a surface-relief structure of periodic sawtooth shape. We describe the necessary conditions for optimal design and derive the relevant equations for determining the structural parameters of the gratings. We demonstrate how to choose these parameters for a given substrate material to obtain the best result in the designed polarizing beam splitters. The influence of small variations in the parameters on grating performance is also investigated. It is shown that the performance of gratings is quite sensitive to small changes in the structural parameters.

Sem Studies of Co-Cr-Mo Surgical Implant Alloy Corrosion Behavior

The influence of small variations in the composition on the corrosion behavior of Co-Cr-Mo alloys has been studied using scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), and electrochemical measurements. SEM and EDX data were correlated with data from in vitro corrosion measurements involving repassivation and also potentiostatic anodic polarization measurements. Specimens studied included the four alloys shown in Table 1. Corrosion tests were conducted in Hanks' physiological saline solution which has a pH of 7.4 and was held at a temperature of 37°C. Specimens were mechanically polished to a surface finish with 0.05 µm A1203, then exposed to the solution and anodically polarized at a rate of 0.006 v/min. All voltages were measured vs. the saturated calomel electrode (s.c.e.).. Specimens had breakdown potentials near 0.47V vs. s.c.e.

The Influence of Small Variations in the Outlet of a Smooth Brass Tube on the Distribution of Static Pressure When Air is Flowing Through the Tube

The Influence of Small Variations in the Outlet of a Smooth Brass Tube on the Distribution of Static Pressure When Air is Flowing Through the Tube