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The different methods of displacement monitoring at loading tests of bridges or different structures
Boštjan Kovačič, Rok Kamnik, Andrii Bieliatynskyi, 2016, objavljeni znanstveni prispevek na konferenci

Opis: By measuring the displacements and deformations at different structures we deal in the Faculty of Civil Engineering, transportation Engineering and Architecture in University of Maribor for about 20 years. At that time we measured over 600 structures. Most loading tests of bridges and Viaducts were made. The measurements of movements needed to be as precise and accurate as possible. To do that laboratory test of instruments were made to see which instrument gives us reliable results. Displacements can be determined by geodetic and physical methods, depends of the construction. The use of geodetic methods are still preferable. In the paper the measurements with the total station, the level and rotation level, photogrammetry and solutions on the field by physical methods with inductive transducers are presented. We need to measure displacements as quick as possible but efficiently because we can not repeat the measurements under the same conditions. Also the surveying on the bridge and in the lab with the comparison of methods is presented under the different hard terrain conditions - water beneath the construction, big height of the structure, unapproachability, large span structures.
Ključne besede: bridges, measurements, strain gauge, load test, deformation, strain, signal processing
Objavljeno: 02.08.2017; Ogledov: 679; Prenosov: 251
.pdf Celotno besedilo (3,15 MB)
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Black hole thermodynamics from a variational principle: asymptotically conical backgrounds
Song-ok An, Mirjam Cvetič, Ioannis Papadimitriou, 2016, izvirni znanstveni članek

Opis: The variational problem of gravity theories is directly related to black hole thermodynamics. For asymptotically locally AdS backgrounds it is known that holographic renormalization results in a variational principle in terms of equivalence classes of boundary data under the local asymptotic symmetries of the theory, which automatically leads to finite conserved charges satisfying the first law of thermodynamics. We show that this connection holds well beyond asymptotically AdS black holes. In particular, we formulate the variational problem for N = 2 STU supergravity in four dimensions with boundary conditions corresponding to those obeyed by the so called 'subtracted geometries'. We show that such boundary conditions can be imposed covariantly in terms of a set of asymptotic second class constraints, and we derive the appropriate boundary terms that render the variational problem well posed in two different duality frames of the STU model. This allows us to define finite conserved charges associated with any asymptotic Killing vector and to demonstrate that these charges satisfy the Smarr formula and the first law of thermodynamics. Moreover, by uplifting the theory to five dimensions and then reducing on a 2-sphere, we provide a precise map between the thermodynamic observables of the subtracted geometries and those of the BTZ black hole. Surface terms play a crucial role in this identification.
Ključne besede: M-Theory, Black Holes, String Theory, Gauge-gravity correspondence
Objavljeno: 27.06.2017; Ogledov: 1773; Prenosov: 318
.pdf Celotno besedilo (834,82 KB)
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General U(1) x U(1) F-theory compactifications and beyond: geometry of unHiggsings and novel matter structure
Mirjam Cvetič, Denis Klevers, Hernan Piragua, Washington Taylor, 2015, izvirni znanstveni članek

Opis: We construct the general form of an F-theory compactification with two U(1) factors based on a general elliptically fibered Calabi-Yau manifold with Mordell-Weil group of rank two. This construction produces broad classes of models with diverse matter spectra, including many that are not realized in earlier F-theory constructions with U(1) x U(1) gauge symmetry. Generic U(1) x U(1) models can be related to a Higgsed non-Abelian model with gauge group SU(2) x SU(2) x SU(3), SU(2)(3) x SU(3), or a subgroup thereof. The nonlocal horizontal divisors of the Mordell-Weil group are replaced with local vertical divisors associated with the Cartan generators of non-Abelian gauge groups from Kodaira singularities. We give a global resolution of codimension two singularities of the Abelian model; we identify the full anomaly free matter content, and match it to the unHiggsed non-Abelian model. The non-Abelian Weierstrass model exhibits a new algebraic description of the singularities in the fibration that results in the first explicit construction of matter in the symmetric representation of SU(3). This matter is realized on double point singularities of the discriminant locus. The construction suggests a generalization to U(1)(k) factors with k > 2, which can be studied by Higgsing theories with larger non-Abelian gauge groups.
Ključne besede: F-theory, differential geometry, algebraic geometry, gauge symmetry
Objavljeno: 14.06.2017; Ogledov: 605; Prenosov: 319
.pdf Celotno besedilo (1,36 MB)
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Vertical displacements measuring methods during bridge load tests
Boštjan Kovačič, Ante Marendić, Rok Kamnik, Mikhail Volkov, Vera Roy, 2016, objavljeni znanstveni prispevek na konferenci

Opis: This article introduces the use of the GNSS method for the load testings of bridge structures. We know that there area lot of methods by which you can determine vertical displacement. However, as new bridge constructions are constructed over almost impossible and inaccessible gorges and valleys, the classic measurements method do not allow us to determine vertical displacement so reliably any more or they are very time-consuming. The GNSS method is well known but there are difficulties when determining the altitude component of this method, which is rather questionable. For this purpose, the methods were tested as practical examples in which some difficulties were encountered, so subsequently another test recording was performed of altitude changes using this method.
Ključne besede: bridges, measurements, strain gauge, load test, deformation, strain, signal processing
Objavljeno: 29.08.2016; Ogledov: 941; Prenosov: 369
.pdf Celotno besedilo (1,55 MB)
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Thread gauge calibration for industrial applications
Tadeja Primožič Merkač, Bojan Ačko, 2010, izvirni znanstveni članek

Opis: There are two most commonly used methods for calibration of thread rings, with different measuring uncertainty. The method of mechanical sensing with two balls is mostly used on one-axial measuring machines and on coordinate measuring machines. However, the method of calculating the core diameter of the thread ring combined with the technique of adaptation (in accordance with the method of the smallest squares) is used on the profile scanner. The required tolerances, which are very narrow for adjustable and laboratory thread ring, so the measuring uncertainty may be too high when using the method of mechanical sensing with two balls, and the low quality of some control rings, are the decisive factors for choosing an appropriate method in the industry. This also depends on the laboratoryćs capability of executing a specific method. The measurements of the core diameter of thread rings, which are the main topic of this article, were included into an international inter-comparison in which the main subject was the same thread ring as the one mentioned in this article.
Ključne besede: thread ring gauge, calibration, pitch diameter, measurement uncertainty, dimensional measurements
Objavljeno: 31.05.2012; Ogledov: 1589; Prenosov: 28
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Quasi-distributed long-gauge fiber optic sensor system
Matjaž Linec, Denis Đonlagić, 2009, izvirni znanstveni članek

Opis: This paper presents a quasi-distributed, long-gauge, sensor system for measurement optical path length variation. This system can be directly applied to long gauge strain and/or temperature sensing. The proposed sensor system is comprised of sensing fiber, which is divided into the sensorćs segments separated by semi reflective mirrors made out of standard optical connectors. Short duration radio-frequency modulated optical bursts are launched into the sensing fiber and phase differences among individual reflected bursts are measured to determine the optical path-length variations among neighboring mirrors. Twenty sensing fiber segments were successfully addressed by a single-signal processor, while relying on standard telecommunication PIN diode, and a Fabry Perot laser diode. The resolution of a fiber-length variation better than 5 ìm was demonstrated in practice. Since the long sections of fiber can be employed for constructing individual sensors within the sensor's array, a microstrain resolution can be achieved in practice. The drift of the sensorćs system can be predominantly attributed to the temperature sensitivity of the electronic components, which proved to be below 20 um/°C. The entire system relies on simple and widely-used components that are low-cost.
Ključne besede: fiber optic systems, fiber optics sensors, sensing fiber, long-gauge, strain sensing, temperature sensing, optoelectronics
Objavljeno: 31.05.2012; Ogledov: 1602; Prenosov: 93
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New approach to uncertainty evaluation in the calibration of gauge block comparators
Andrej Godina, Bojan Ačko, Marjan Družovec, 2007, izvirni znanstveni članek

Opis: Gauge blocks (GBs) are being calibrated by two methods: interferometric calibration and calibration by mechanical comparison to reference GB. While interferometric method represents primary level, comparison is more suitable for calibrating industrial GBs because of lower costs and shorter calibration time. Although no significant changes in equipment happened in last decade, improvements in mechanical comparison are on-going. In addition to the uncertainty of the reference GB calibration, uncertainty of the GB comparator is the most important contribution to total uncertainty of the mechanical calibration. The article introduces a new approach for evaluating the uncertainty of GB comparator calibration. The uncertainty budget and results of analytical and experimental evaluation of all contributions are presented. This approach results in lower end-effect uncertainty and a slightly higher length dependent uncertainty, in comparison with the uncertainty evaluation procedure as described in EA document EA-10/02.
Ključne besede: measurements, calibration, measuring uncertainty, gauge block, comparator, CMC, mechanical comparison
Objavljeno: 31.05.2012; Ogledov: 1789; Prenosov: 95
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