1,027 research outputs found
Optimization of machinery operation modes from the point of view of their dynamics
This paper presents"strong" "/strong"an analysis and synthesis of optimization methods of machinery dynamic modes. Theoretical studies have shown that in order to find optimum, one must define a differential equation describing the motion of the system, which would ensure the most advantageous dynamic regime determined by the stationary value of the corresponding functional. The definition of this equation must be carried out while machinery construction is taking place, as its physical parameters and layout form the basis of these differential equations. Such approach requires the introduction of certain principles significantly affecting the development of optimization methods justified in this paper. To solve the problem of optimal machinery modes, it is more suitable to perform a separation of complex motion by its dynamic properties Suppose that the complex motion can be devided into the motion of the machinery unit as a whole, to the static displacements of its elements as solid bodies, to the increasing and damping components of motion and to the vibrational component. The findings of the study indicate that the most advantageous machinery dynamic mode is determined by the conditions of the technological process, which would ensure its highest productivity, the lowest energy consumption and other optimal technical and economic indicators. This regime corresponds to the motion of the unit as a whole, that is, to the variation in the quasi-cyclic coordinates. The vector of external forces applied to the machinery is reduced to the initial conditions of its motion; homogeneous differential equations are considered further. The fundamental system of their solutions depends on the initial conditions of motion generated by external systems
Tuning the Polar States of Ferroelectric Films via Surface Charges and Flexoelectricity
Using the self-consistent Landau-Ginzburg-Devonshire approach we simulate and
analyze the spontaneous formation of the domain structure in thin ferroelectric
films covered with the surface screening charge of the specific nature
(Bardeen-type surface states). Hence we consider the competition between the
screening and the domain formation as alternative ways to reduce the
electrostatic energy and reveal unusual peculiarities of distributions of
polarization, electric and elastic fields conditioned by the surface screening
length and the flexocoupling strength. We have established that the critical
thickness of the film and its transition temperature to a paraelectric phase
strongly depend on the Bardeen screening length, while the flexocoupling
affects the polarization rotation and closure domain structure and induces
ribbon-like nano-scale domains in the film depth far from the top open surface.
Hence the joint action of the surface screening (originating from e.g. the
adsorption of ambient ions or surface states) and flexocoupling may remarkably
modify polar and electromechanical properties of thin ferroelectric films.Comment: 33 pages, 5 figure
Defect driven flexo-chemical coupling in thin ferroelectric films
Using Landau-Ginzburg-Devonshire theory, we considered the impact of the
flexoelectro-chemical coupling on the size effects inpolar properties and phase
transitions of thin ferroelectric films with a layer of elastic defects. We
investigated a typical case, when defects fill a thin layer below the top film
surface with a constant concentration creating an additional gradient of
elastic fields. The defective surface of the film is not covered with an
electrode, but instead with an ultra-thin layer of ambient screening charges,
characterized by a surface screening length. This geometry is typical for the
scanning probe piezoelectric force microscopy. Obtained results revealed an
unexpectedly strong effect of the joint action of Vegard stresses and
flexoelectric effect (shortly flexo-chemical coupling) on the ferroelectric
transition temperature, distribution of the spontaneous polarization and
elastic fields, domain wall structure and period in thin PbTiO3 films
containing a layer of elastic defects. A nontrivial result is the
ferroelectricity persisting at film thicknesses below 4 nm, temperatures lower
than 350 K and relatively high surface screening length (~0.1 nm). The origin
of this phenomenon is the re-building of the domain structure in the film
(namely the cross-over from c-domain stripes to a-type closure domains) when
its thickness decreases below 4 nm, conditioned by the flexoelectric coupling
and facilitated by negative Vegard effect. For positive Vegard effect, thicker
films exhibit the appearance of pronounced maxima on the thickness dependence
of the transition temperature, whose position and height can be controlled by
the defect type and concentration. The revealed features may have important
implications for miniaturization of ferroelectric-based devices.Comment: 25 pages, 9 figure
Electron beam test facilities for novel applications
Delivering and tailoring high brightness electron beams for a wide range of novel applications is a challenging task in single pass accelerator test facilities. This paper will review beam dynamics challenges at single pass accelerator test facilities in Europe to generate, transport and tailor low- to medium-energy high brightness electron beams for a range of novel applications
Ability for vegetation and spore formation of <i>Bacillus anthracis</i> strains with different phenotypical properties under soil simulating conditions
Introduction. The study of the ability of Bacillus anthracis strains with different phenotypic properties to spore germination, reproduction and sporulation on a medium based on an aqueous soil extract can help assess the significance of these processes in the formation and maintenance of soil anthrax foci.
Aim. The analysis of individual characteristics of the development of a vegetative culture of anthrax pathogen strains with different phenotypes in a soil medium model.
Materials and methods. On a group of anthrax microbe strains with different plasmid composition and virulence, the possibility of spore germination, reproduction of bacilli and, at least in some of them, productive spore formation on the soil medium was studied.
Results. Three variants of culture development of B. anthracis strains were identified: 1 spores remain intact, not germinating; 2 after germination of spores, bacilli are formed, which multiply with different intensity, passing into involutional forms without spore formation; 3 the passage of a complete physiological cycle "sporebacillusspore". The presence of 2% blood in the soil environment contributed to the germination of spores and reproduction of the culture, but inhibited the process of sporulation during the observation period of 3 days. No correlation was found between a certain phenotype of the studied strains of B. anthracis and the ability to germinate and vegetate on soil media.
Conclusion. The data obtained that only 17% of CFU gives rise to the formation of colonies on the soil medium suggest the heterogeneity of the properties of the population of the studied strains. Isolation of such cultures and their further detailed study will make it possible to identify the most significant complexes of biological properties for the realization of a complete physiological cycle under soil-simulating conditions
Thickness, humidity, and polarization dependent ferroelectric switching and conductivity in Mg doped lithium niobate
Mg doped lithium niobate (Mg:LN) exhibits several advantages over undoped LN such as resistance to photorefraction, lower coercive fields, and p-type conductivity that is particularly pronounced at domain walls and opens up a range of applications, e.g., in domain wall electronics. Engineering of precise domain patterns necessitates well founded knowledge of switching kinetics, which can differ significantly from that of undoped LN. In this work, the role of humidity and sample composition in polarization reversal has been investigated under application of the same voltage waveform. Control over domain sizes has been achieved by varying the sample thickness and initial polarization as well as atmospheric conditions. In addition, local introduction of proton exchanged phases allows for inhibition of domain nucleation or destabilization, which can be utilized to modify domain patterns. Polarization dependent current flow, attributed to charged domain walls and band bending, demonstrates the rectifying ability of Mg: LN in combination with suitable metal electrodes that allow for further tailoring of conductivity. (C) 2015 AIP Publishing LLC
Energy Response and Longitudinal Shower Profiles Measured in CMS HCAL and Comparison With Geant4
The response of the CMS combined electromagnetic and hadron calorimeter to beams of pions with momenta in the range 5-300 GeV/c has been measured in the H2 test beam at CERN. The raw response with the electromagnetic compartment calibrated to electrons and the hadron compartment calibrated to 300 GeV pions may be represented by sigma = (1.2) sqrt{E} oplus (0.095) E. The fraction of energy visible in the calorimeter ranges from 0.72 at 5 GeV to 0.95 at 300 GeV, indicating a substantial nonlinearity. The intrinsic electron to hadron ratios are fit as a function of energy and found to be in the range 1.3-2.7 for the electromagnetic compartment and 1.4-1.8 for the hadronic compartment. The fits are used to correct the non-linearity of the e pi response to 5% over the entire measured range resulting in a substantially improved resolution at low energy. Longitudinal shower profile have been measured in detail and compared to Geant4 models, LHEP-3.7 and QGSP-2.8. At energies below 30 GeV, the data, LHEP and QGSP are in agreement. Above 30 GeV, LHEP gives a more accurate simulation of the longitudinal shower profile
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