Vilnius Gediminas Technical University
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Chimotologiniai transporto priemonių variklių alyvų tyrimai
No full textTransporto priemonių ilgaamžiškumas priklauso ne tik nuo eksploatacijos sąlygų, bet ir nuo degalų bei tepalų kokybės. Naudojant nekokybiškus produktus, didėja išlaidos remontui ir techninei priežiūrai, kartu didėja mechanizuotų darbų bei gaminamos produkcijos savikaina. Todėl iškyla labai svarbus uždavinys racionaliai vartoti turimus degalų ir tepalų išteklius. Darbe pateikti transporto priemonių alyvų chimotologiniai savybių tyrimai. Tyrimų metu paimti nenaudotos ir autobuse dujomis varomame variklyje naudotos alyvos bandiniai. Nustatyti alyvų klampiai, tankiai, pliūpsnio temperatūra ir šarmingumas. Rezultatai išanalizuoti ir palyginti. Pateiktos išvados ir pasiūlymai
Darbų saugos šalmų vertikalių smūginių virpesių tyrimas
No full textDėl darbo procesų atsirandantys virpesiai neigiamai veikia žmogaus sveikatą, todėl norint apsaugoti žmogų nuo susidarančių žalingų virpesių poveikio yra kuriamos įvairios apsaugos priemonės. Straipsnyje pateikiami eksperimentiškai gauti pramoninių apsauginių šalmų dinamikos tyrimų rezultatai
Experimental investigation of dynamic impact of firearm with suppressor
No full textThe internal ballistics processes occur in the tube during firearm firing. They cause tremendous vibratory shock forces and robust sound. The determination of these dynamic parameters is relevant in order to estimate reasonably the firearm ergonomic and noise reduction features. The objective of this study is to improve the reliability of results of measuring firearm suppressor’s dynamic parameters. The analysis of indicators stability is based on assessment of dynamic parameters and setting the correlation during experimental research.An examination of the spread of intensity of firearm with suppressor dynamic vibration and analysis of its signals upon applying the theory of covariance functions are carried out in this paper. The results of measuring the intensity of vibrations in fixed points of firearm and shooter were recorded on the time scale in a form of data arrays (matrixes). The estimates of covariance functions between the arrays of digital results in measuring the intensity of firearm vibrations and the estimates of covariance functions of single arrays were calculated upon changing the quantization interval on the time scale. Software Matlab 7 was applied in the calculation. Finally, basic conclusions are given
Biomechanical evaluation of native acromioclavicular joint ligaments and two reconstruction techniques in the presence of the sternoclavicular joint: A cadaver study
No full textBackground:
Where is over 100 reconstruction techniques described for acromioclavicular (AC) joint reconstruction. Although, it is not clear whether the presence of the sternoclavicular (SC) joint influences the biomechanical properties of native AC ligaments and reconstruction techniques. The purpose of the present study was to investigate the biomechanical properties of native AC joint ligaments and two reconstruction techniques in cadavers with the SC joint still present.
Materials and Methods:
We tested eight fresh-frozen cadaver hemithoraces for superior translation (70 N load) and translation increment after 1000 cycles (loading from 20 to 70 N) in a controlled laboratory study. There were three testing groups created: native ligaments, the single coracoclavicular loop (SCL) technique, and the two coracoclavicular loops (TCL) technique. Superior translation was measured after static loading. Translation increment was calculated as the difference between superior translation after cyclic and static loading.
Results:
Native AC ligaments showed significantly lower translation than the SCL (p = 0.023) and TCL (p = 0.046) groups. The SCL had a significantly lower translation increment than native AC ligaments (p = 0.028). There was no significant difference between reconstruction techniques in terms of translation (p = 0.865) and translation increment (p = 0.113).
Conclusions:
Native AC joint ligaments had better static properties than both reconstruction techniques and worse dynamic biomechanical properties than the SCL technique. The SCL technique appeared to be more secure than the TCL technique. The presence of the SC joint did not have an observable influence on test results.This article is distributed under the terms of the Creative Commons Attribution-Non
Commercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction
and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages
(https://us.sagepub.com/en-us/nam/open-access-at-sage)
Properties of concrete modified with mineral additives
No full textConcrete is the most widely used building material that is obtained by curing the mixture prepared from coarse and fine aggregates, cement and water. The properties of concrete depend on the quality and properties of the aggregates, w/c ratio, the uniformity of compression of the mix. Compressive strength of concrete is one of the most important properties. The present paper analyses the effect of mineral additive content on the properties of concrete. Materials used for the test: Portland cement CEM I 42.5 R, 0/4 fraction sand, 4/16 fraction gravel, mineral additive, polycarboxylatether based superplasticizer and tap water. Concrete mixes of 9 compositions were made by adding 0%, 2.5%, 5%, 7.5% and 10% of mineral additives by weight of cement. The tests revealed that the addition of mineral additives up to 10% increases the compressive strength of concrete. According to the test findings the compressive strength of hardened cement paste containing 10% of mineral additives increased 0.99% compared to the control mix. After 7 and 28 days of curing the ultrasonic pulse velocity in specimens with mineral additives increased 2.6% and 4.1% respectively. With the increase of mineral additives content up to 10%, water absorption of concrete reduces and the predicted freeze-thaw resistance increases
The effect of synthetic zeolite on hardened cement paste microstructure and freeze-thaw durability of concrete
No full textTests were done with synthetic zeolite obtained by synthesizing alumina fluoride production residue,
sodium hydroxide and alumina hydroxide. The synthesis lasted for two hours at 95 C temperature.
The obtained product was a mix of synthetic zeolite of modifications A and X. The binding material
was cement CEM I 42.5R. The test results revealed that substitution of cement with 10% of synthetic zeolite reduces water absorption of hardened cement paste 23.8%; the addition of air entraining admixture
does not change the rate of water absorption. With the increase of zeolite content in concrete with and
without air entraining admixture increases the volume of closed pores from 1.6% to 2.1% and from 4.1% to
7.6% respectively. The open porosity determined by water absorption of concrete with and without air
entraining admixture changes insignificantly. The average distance between pores reduces from
360 lm to 190 lm when part of concrete is replaced by zeolite addition without air entraining admixture
and from 190 lm to 130 lm in the case of using air entraining admixture. The addition of 10% of synthetic zeolite results in reduced content of portlandite and development of hydro aluminate compounds
C3AH6 (cubic crystals) in hardened cement paste. Rose-shaped plates of calcium hydrosulphoaluminates
(mono sulphate form) were also detected. These crystals together with hydroaluminates fill in the pores
of hardened cement paste and thus reduce the open porosity of concrete. Substitution of 10 wt% of
cement with synthetic zeolite addition increases the freeze-thaw resistance of concrete, i.e. reduces
the loss of surface mass after 28 freeze-thaw cycles more than 1.6 times without the air entraining
admixture and up to 3.5 times with air entraining admixture
Architektūros kokybės užtikrinimo priemonės: mokslo straipsnių rinkinys
No full textŠis straipsnių rinkinys it pratęsia dar 2015 metais pradėtą diskusiją architektūros kokybės klausimais, kai buvo išleistas straipsnių rinkinys „Architektūros kokybės kriterijai“. Šių metų rinkinio „Architektūros kokybės užtikrinimo priemonės“ autoriai gvildena svarbius ekspertinio vertinimo, architektūrinės kūrybos, konkursinės veiklos, teritorijų planavimo, kultūros paveldo apsaugos, administravimo ir visuomenės dalyvavimo klausimus. Dalis autorių pristato mokslinės analizės rezultatus, kiti dalijasi savo sopuliais, aptaria profesionalams opias problemas. Manome, kad pristatomo rinkinio straipsniai paskatins architektūros tyrinėtojus ir kūrėjus dar kartą apmąstyti tai, kaip galima būtų pagerinti mūsų kraštovaizdį, miestų architektūrą, kad Lietuva būtų matoma kartu ir kaip moderni valstybė, kurioje veikia kompetentingi architektai ir užsakovai, suvokiantys, kad kokybės negalima pasiekti ignoruojant istoriškai susiklosčiusį mūsų gyvenamosios aplinkos potencialą
Analysis of durability testing of concrete landscaping units
No full textIn recent years the problem of the durability of vibrocompacted concrete products (landscaping elements, paving blocks in particular) has received great attention in Europe. In Easter Europe there are
rather aggressive climate conditions (temperature fluctuations, humidity, precipitation, etc.). Besides,
in winter concrete paving is treated with sodium, calcium, magnesium chloride salts that accelerate
the deterioration of concrete paving block structure. European standard EN 1338:2003+AC:2006 that sets
forth the basic requirements and test methods for concrete paving blocks does not take into account the
performance of concrete products under specific climatic conditions. Therefore, it is important to determine the basic technological factors that influence the quality of vibrocompacted concrete, in particular
freeze-thaw resistance, and to optimize the composition and other technological properties of vibrocompacted concrete. The freeze-thaw resistance of concrete has to be measured by different methods. The
present paper describes the testing of concrete paving blocks, the top layer of which contained different
amounts of cement ranging from 527 to 385 kg/m3
. The cement content in the bottom (support) layer
compositions of all specimens remained the same – 371 kg/m3
. Density, freeze-thaw resistance according
to two different methods, splitting tensile strength and abrasion resistance were measured in the tests
Investigation of symmetric non-spherical particle shapes by applying low-resolution spherical harmonics
No full textThe issue of mathematical modelling of non-spherical shapes of particles is considered. Thus, application of the spherical harmonics (SH) technique in modelling the simplest symmetric star-shaped particles is demonstrated by applying low-resolution functions. The investigation was restricted to a circular cylinder and a rectangular parallelepiped, geometrically primitive, but widespread oblate industrial shapes. The modelling quality was studied by considering selected error norms and the most important integral characteristics of a particle geometry, including the surface area and volume. The presented results discovered new features of the spherical harmonic technique and enhanced understanding of their applicability to describe non-spherical shapes
Communications in Hybrid Arrangements: Case of Australian Construction Project Teams
No full textHybrid team arrangements or partially virtual teams are increasingly being utilised as the structure for construction project teams. However, little research has been conducted on the quality of the communications of these teams. To address the identified research gap, this study adopted a sequential mixed-methods approach. In the first phase, a multidisciplinary literature review identified 7 major indicators of the quality of communications. After conducting 17 interviews with construction experts, the study customised these indicators for the construction context, in form of a list that comprised 12 indicators. Based on the indicators in this list, a questionnaire survey was then designed to elicit construction practitioners’ perceptions on changes in the quality of communications in hybrid team arrangements compared to teams that were fully collocated. Data from the 285 completed questionnaires in Australia then underwent confirmatory factor analysis (CFA). In the findings, the move to hybrid working arrangements was shown to create changes in 10 of the 12 indicators. The identified list of indicators is a significant contribution to the literature, and provides construction practitioners with guidance in assessing the quality of communications in these teams. The findings also shed light on the primary changes in the quality of communications resulting from the increasing use of hybrid team arrangements