18420 research outputs found
Sort by
Kaulaudu morfoloģisks novērtējums pēc dažāda sastāva biokeramikas materiālu implantācijas eksperimenta dzīvnieku žokļa kaulā
No full textKlīniskajā praksē tiek lietoti dažādi kaulaudus aizvietojoši biokeramikas materiāli. Mūsu darba mērķis bija novērtēt žokļu kaulaudu reakciju uz implantēto biokeramikas materiālu, pielietojot morfoloģiskas metodes
Simultaneous RZ-OOK to NRZ-OOK and RZDPSK to NRZ-DPSK Format Conversion in a Silicon Microring Resonator
No full textSimultaneous RZ-OOK to NRZ-OOK and RZ-DPSK to NRZDPSK modulation format conversion in a single silicon microring resonator with free spectral range equal to twice the signal bit rate is experimentally demonstrated for the first time at 41.6 Gb/s. By utilizing an optimized custom-made microring resonator with high coupling coefficient followed by an optical bandpass filter with appropriate bandwidth, good conversion performances for both modulation formats are achieved according to the converted signals eye diagrams and bit-error-rate measurements
Properties of a Composite Prepared Using a Concentrate of Carbon Nanotubes in Polyethylene
No full textResults of an investigation into the properties of polyethylene (PE) with small, no more than 5 wt.%, additions of
multiwall carbon nanotubes (CNTs) are reported. Specimens of the composite were prepared using a concentrate
containing 31.6 wt.% of nanotubes in the polyethylene matrix. The concentrate was fabricated by a patent in situ
polymerization method. Experimental data on the influence of CNT additions on the thermograms of differential
scanning calorimetry, the crystallinity of the polyethylene matrix, and the indices of mechanical properties (yield
stress, strength, elastic modulus, ultimate elongation, and long-term creep) of PE/CNT composite are obtained.
A theoretical analysis of elastic properties of the PE/CNT composite was carried out by using the Mori–Tanaka
theory of an equivalent medium. The calculation results are compared with experimental data
On Optimal Video Transmission over Multiple Paths in Wireless Ad-Hoc Networks
No full textTransmission of video data over MANETs is a
complicated task because of the mobile nodes and limited
throughput. To improve the performance, a video
transmission over several paths is used. However, network
parameters and routing options combined with the most
appropriate video coding schemas must be taken into account
to ensure optimum conditions. In this paper state-of-the-art
practices are surveyed as well as the analyses on how to
combine all the diverse aspects are made. An algorithm to
select optimum coding parameters which ensure “network
friendly” transmission is proposed
Kombinētās saules siltumapgādes sistēmas Latvijā
No full textPromocijas darbā pētīta kombinētās saules siltumapgādes sistēmu efektivitāte, kas ir priekšnoteikums tās lietderīgai izmantošanai Latvijas klimatiskajos apstākļos, tādā veidā palielinot enerģētisko neatkarību, samazinot siltumenerģijas ražošanas procesa negatīvo ietekmi uz vidi, veicinot patērētāju komforta un dzīves kvalitātes paaugstināšanos.
Darba mērķis ir izstrādāt metodiskās nostādnes kombinētās saules siltumapgādes sistēmas efektivitātes noteikšanai Latvijā.
Mērķa sasniegšanai tika izvirzīti sekojoši uzdevumi: izpētīt kombinētās saules siltumapgādes sistēmas funkcionēšanas kartību, identificēt faktorus, kuri ietekmē energoekonomisko rādītāju pārmaiņas, un noteikt kombinēto siltumapgādes sistēmu izmantošanas efektivitāti, lai segtu patērētāju siltuma pieprasījumu ņemot vērā enerģētikas sistēmas attīstību, kā arī noteikt dažādu citu faktoru ietekmi uz optimālo siltumapgādes shēmas izvēli. Izstrādāt un eksperimentāli pārbaudīt Latvijas apstākļiem piemērotu saules enerģijas kombinēto sistēmu, analizēt tās darbības modelēšanas programmā un veikt sistēmas ekonomisko optimizāciju nosakot dažādu pasākumu un tehnisko risinājumu lietderību.
Promocijas darba ietvaros veiktie pētījumi balstīti uz praktisko, pētnieciski eksperimentālo darba pieredzi strādājot Fizikālās Enerģētikas institūta (FEI) Enerģijas resursu laboratorijā. Pētījumu veikšanai tika izmantoti gan FEI laboratorijā uzkrātais apjomīgais datu materiāls par reāliem klimatiskajiem datiem un saules kolektorus raksturojošiem lielumiem, gan autora īstenoto eksperimentālo mērījumu un teorētisko rezultātu apkopojums vienotā metodikā strukturējot to ar matemātiskās modelēšanas iespējām. Promocijas darba zinātniskā novitāte ir kombinētās saules siltumapgādes sistēmas matemātiskā modelēšana, izmantojot eksperimentāli iegūtos datus, tādā veidā aprēķinu metodiku padarot maksimāli precīzu un tuvu reāliem apstākļiem. Promocijas darbā veiktie pētījumi un izstrādātā metodika, kā arī izdarītie secinājumi ir praktiski izmantojami inženieru darbā, projektējot un īstenojot modernizāciju esošajās siltumapgādes sistēmās.
Promocijas darba rezultāti ir ziņoti 13 reizes Starptautiskās Zinātniskās konferencēs un tie atspoguļoti 26 publikācijās. Promocijas darbs sastāv no 5 nodaļām un tā apjoms 118 lappuses, kurās ietverti 47 attēli, 15 tabulas. Darbā izmantoti 89 literatūras avoti
Investigation of Silver Doped Hydroxyapatite
No full textBiomaterials based on calcium phosphate ceramics are used as implants in human/animal body due to their excellent biocompatibility. Silver containing materials have a very broad spectrum of antibacterial activity; therefore silver doped hydroxyapatite can be used in medicine as antibacterial implant material. The aim of this work was to synthesize monophasic and biphasic silver doped hydroxyapatite and evaluate the differences in their physical and antibacterial properties
Strategic Development Directions in Road Construction
No full textTotal road density in Latvia is sufficient but its technical
condition is unsatisfactory and does not meet the safe and
continuous traffic flow requirements. Currently, the road
condition in Latvia is disastrous compared to its neighboring
or the old EU countries. Almost half of the roads with asphalt
surface and one third of the gravel road surface are on the
brink of the collapse. Currently, the road construction industry
is one of the most destroyed sectors in Latvia. Consequently,
the increased attention from the public, politicians, and other
state controlling authorities is paid to this industry sector. The
authors of this study consider that it is important to explore the
history of the development of road construction industry, to
analyze strengths, weaknesses, opportunities and threats of the
road construction and, in accordance with the findings, to
determine the development perspectives of the road
construction industry
Investigation and Upgrading of a Historical Multispan Arch Masonry Bridge
No full textThe aim of this research was the investigation of the properties of clay brick masonry arch bridge materials with a purpose to find the best methods for reconstruction and renovation of the structure. The restoration, reconstruction and upgrading of historical heritage bridges require the careful investigation of materials and causes of damages. In many cases, the use of incorrect composition of joint mortar and clayed brick could lead until an unfavorable result. It is important to ensure the natural water migration in historic masonry could not be interrupted after restoration or reconstruction measures. As an example had been analyzed the results of investigations and upgrading of a historical clayed brick masonry bridge over Venta River in Kuldiga town in Latvia (figure 1). During the long lifetime and pro-active maintenance polity, a bridge had a lot of damages that could influence the further service life. For geometrical data collection was used laser scanning method that ensures enough accurate data for reconstruction design and information for architectural investigation. Three-dimensional scanning of heritage structure by 3D laser scanners allow the further transformation of information into the surface mesh model. Paper presents results of investigation and design of restoration and reconstruction works
Policy Instruments for Managing EU Road Safety Targets: Road Safety Impact Assessment
No full textThe Directive 2008/96/EC of European Parliament and of the Council requires the establishment and implementation of procedures relating to road safety impact assessments, road safety audits, the management of road network safety and safety inspections by the Member States. Directive aims to develop procedures with the aim of increasing safety of road infrastructures. Road Safety Impact Assessment (RSIA) is an initial part of road infrastructure safety management systems. This article describes the scope of RSIA procedures, provides detailed recommendations on qualification of auditors, implementation and execution of procedures for the EU Member States. Road safety should play an important role when routes are being selected and safety awareness should be included in the decision making during the designing/planning stage. RSIA is a very beneficial tool that could increase transparency and availability of information, consequently, it leads all parties concerned to well-informed decisions