166 research outputs found
ANALYSIS OF STEADY-STATE AND DYNAMICAL RADIALLY-SYMMETRIC PROBLEMS OF NONLINEAR VISCOELASTICITY
This thesis treats radially symmetric steady states and radially symmetric motions of nonlinearly elastic and viscoelastic plates and shells subject to dead-load and hydrostatic pressures on their boundaries and with the plate subject to centrifugal force. The plates and shells are described by specializations of the exact (nonlinear) equations of three-dimensional continuum mechanics. The treatment in every case is very general and encompasses large classes of constitutive functions (characterizing the material response).
We first treat the radially symmetric steady states of plates and shells and the radially symmetric steady rotations of plates. We show that the existence, multiplicity, and qualitative behavior of solutions for problems accounting for the live loads due to hydrostatic pressure and centrifugal force depend critically on the material properties of the bodies, physically reasonable refined descriptions of which are given and examined here with great care, and on the nature of boundary conditions.The treatment here, giving new and sharp results, employs several different mathematical tools, ranging from phase-plane analysis to the mathematically more sophisticated direct methods of the Calculus of Variations, fixed-point theorems, and global continuation methods, each of which has different strengths and weaknesses for handling intrinsic difficulties in the mechanics.
We then treat the initial-boundary-value problems for the radially symmetric motions of annular plates and spherical shells that consist of a nonlinearly viscoelastic material of strain-rate type. We discuss a range of physically natural constitutive equations. We first show that when the material is strong in a suitable sense relative to externally applied loads, solutions exist for all time, depend continuously on the data, and consequently are unique. We study the role of the constitutive restrictions and that of the regularity of the data in ensuring the preclusion of a total compression and of an infinite extension for finite time. We then show that when the material is not sufficiently strong then under certain conditions on the (hydrostatic) pressure terms there are globally defined unbounded solutions and there are solutions that blow up in finite time.
The practical importance of these results is that for each problem involving live loads they furnish thresholds in material response delimiting materials for which solutions are ill behaved. A mathematical or numerical study limited to a particular class of materials may dangerously indicate well-behaved solutions when there are other realistic materials for which solutions are ill behaved. Moreover this work furnishes so-called trivial solutions for the subsequent study (not given here) of bifurcation of stable equilibrium configurations from these trivial solutions
Impact of illumination spectrum and eye pigmentation on image quality from a fundus camera using transscleral illumination
Significance: The use of the transscleral illumination approach has the potential to simplify the optical design of fundus cameras. In particular, this approach could allow the use of smaller and cheaper cameras that are easier to use by non-specialists, thereby facilitating a wider spread of eye disease screening programs.
Aim: Our aim was to investigate the suitability of transscleral illumination in a fundus camera system. In particular, we explored the impact of the illumination spectrum and the eye pigmentation on the quality of the image. These factors have never been systematically investigated before in the literature on transscleral illumination.
Approach: A fundus camera was constructed using transscleral illumination. We studied the influence of eye pigmentation and choice of illumination spectra on the image quality for a group of 10 individuals with varied skin pigmentation, ranging from pale white (North-European) to darkest brown (African). The influence of the light source spectrum on the image quality was assessed using wavelength filters.
Results: There was a difference of a factor of 100 in the signal level of retinal images between individuals with low and high skin pigmentation. The image contrast was highest using illumination wavelengths of 500 to 600 nm. The illumination level can be adjusted to obtain high-quality images for highly pigmented eyes while keeping the system eye-safe.
Conclusions: We have demonstrated that a fundus camera with transscleral illumination can provide high-quality images. However, the variations observed in scleral and retinal pigmentation in a practical setting require a system that must be able to adapt illumination and/or exposure to the individual patient.publishedVersio
High-level laser therapy versus scalpel surgery in the treatment of oral lichen planus: a randomized control trial
Objective: To compare the clinical effectiveness of various types of high-level laser therapy (HLLT) toward scalpel excision for the surgical treatment of erosive oral lichen planus (OLP).
Materials and methods: The total number of 128 individuals were enrolled in the study. The 35 did not meet the inclusion criteria due to malignancy signs and presence of diabetes mellitus. In total, 8 were lost to follow-up, and 10 were excluded from the analysis, due to analgesics intake. This way 75 patients with the erosive form of OLP were analyzed in three intervention groups (Er:YAG, n = 19; Nd:YAG, n = 15; Er:YAG + Nd:YAG combination, n = 20) and one control group with scalpel excision (n = 21). The therapy effectiveness has been assessed based on the comparison of salivary interleukin (IL)-1 beta, IL-6 and interferon (IFN)-gamma preoperative levels to 14, 30 days, and 2 years postoperation, as well as pain level and time of epithelization.
Results: All HLLT groups demonstrated a significantly (p > 0.05) higher IL-1 beta, IL-6, IFN gamma and pain level reduction and quicker epithelization toward the control group on the 30th day, except Nd:YAG in case of IFN gamma level. The highest IL-1 beta, IFN gamma and pain level reduction and quicker epithelization on the 30th day was observed in Er:YAG group, followed by Er:YAG + Nd:YAG combination, Nd:YAG respectively. However no significant difference was observed between the HLLT groups with regard to IL-6 level reduction. After a 2-year follow-up, no significant difference was observed between all study groups with regard to all variables.
Conclusion: HLLT yields a superior clinical outcome compared to the scalpel excision for the surgical treatment of oral lichen planus, whereby the Er:YAG has been proposed as the most effective laser type at the end of the first postoperative month.
Clinical relevance: For the surgical treatment of erosive OLP the Er:YAG laser may be a preferable treatment option compared to Nd:YAG and scalpel surgery.
Trial registration: The present trial was registered retrospectively in the German Clinical Trials Register, as a member of WHO international clinical trials registry platform, on the 18.03.2020 with the following number: DRKS00020986
The formation of a risk management system for projects in the field of aquaculture innovative development in the Kaliningrad region: a case study
This article sets out to develop the concept
and the principal scheme of the formation of a
risk management system for innovative economic
development projects in the field of
aquaculture. The research carried out by the
authors helps identify the main problems and
characteristics of risk management projects
for the development of aquaculture in presentday
Russia. The authors outline the status and
features of aquaculture development projects
in the North-western federal district and the
Kaliningrad region. The article formulates
and justifies the concept of “risk management
projects in innovative development of aquaculture
in the region” focusing on the classification
of aquaculture risks in relation to innovative
development projects, which expands
the conceptual framework of risk management
in view of the specific risks relating to economic
development projects in the field of aquaculture.
The authors characterize modern
methods and approaches to risk management
projects and organizations in the context of
their application in the framework of aquaculture
development projects and offer mechanisms
for risk management of aquaculture development
projects, which make it possible to
include risk management activity in the general
context of activities of parent project organizations.
The authors develop the concept
and principal scheme of the formation of risk
management system for innovative development
projects in aquaculture
Paleo-Balkan and Slavic Contributions to the Genetic Pool of Moldavians
Moldova has a rich historical and cultural heritage, which may be reflected in the current genetic makeup of its population.
To date, no comprehensive studies exist about the population genetic structure of modern Moldavians. To bridge this gap
with respect to paternal lineages, we analyzed 37 binary and 17 multiallelic (STRs) polymorphisms on the non-recombining
portion of the Y chromosome in 125 Moldavian males. In addition, 53 Ukrainians from eastern Moldova and 54 Romanians
from the neighboring eastern Romania were typed using the same set of markers. In Moldavians, 19 Y chromosome
haplogroups were identified, the most common being I-M423 (20.8%), R-M17* (17.6%), R-M458 (12.8%), E-v13 (8.8%), RM269*
and R-M412* (both 7.2%). In Romanians, 14 haplogroups were found including I-M423 (40.7%), R-M17* (16.7%), RM405
(7.4%), E-v13 and R-M412* (both 5.6%). In Ukrainians, 13 haplogroups were identified including R-M17 (34.0%), I-M423
(20.8%), R-M269* (9.4%), N-M178, R-M458 and R-M73 (each 5.7%). Our results show that a significant majority of the
Moldavian paternal gene pool belongs to eastern/central European and Balkan/eastern Mediterranean Y lineages.
Phylogenetic and AMOVA analyses based on Y-STR loci also revealed that Moldavians are close to both eastern/central
European and Balkan-Carpathian populations. The data correlate well with historical accounts and geographical location of
the region and thus allow to hypothesize that extant Moldavian paternal genetic lineages arose from extensive recent
admixture between genetically autochthonous populations of the Balkan-Carpathian zone and neighboring Slavic group
Competitive high variance, low volume manufacturing with robot manipulators
Competitive robotized manufacturing of high specter variance, low volume product lines represents market opportunities for manufacturing companies, but cost-efficient production is challenging. In this paper, we present two main industry use cases which represent key challenges to be solved for cost-efficient low-volume, high-variance production. The use cases are found in collaboration with three manufacturing companies. We identify and describe these challenges which include perception and manipulation with shiny/high-reflectivity parts, human-machine interfaces for robot reconfiguration and calibration between simulated and real-world environments. In this paper, we present new methods for meeting these challenges: machine vision for handling sensor data with low quality in robot manipulation, automated robot programming based on CAD-models and automated calibration. Moreover, we implement and demonstrate the methods on the two identified industry use cases for robotized assembly.acceptedVersio
Dual fermion method as a prototype of generic reference-system approach for correlated fermions
We present a purely diagrammatic derivation of the dual fermion scheme [Phys.
Rev. B 77 (2008) 033101]. The derivation makes particularly clear that a
similar scheme can be developed for an arbitrary reference system provided it
has the same interaction term as the original system. Thereby no restrictions
are imposed by the locality of the reference problem or by the nature of the
original problem as a lattice one. We present new arguments in favour of
keeping the dual denominator in the expression for the lattice self-energy
independently of the truncation of the dual interaction. As an example we
present the computational results for the half-filled 2D Hubbard model with the
choice of a plaquette with periodic boundary conditions as a
reference system. We observe that obtained results are in a good agreement with
numerically exact lattice quantum Monte Carlo data
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