18420 research outputs found
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Implementation and Observation of Interactive Distance Teaching
No full textIt is described one inexpensive solution for provision of interactive distance lessons. It is shown the usage of server’s remote control for arranging of shared by teacher and students common session for demonstration of particular software work as well as tools for accompanying the demonstration by video-audio communications between remote teacher and remote auditorium. Students’ considerations regarding implied tools are collected in form of questionnaires and the results are observed
Optimization of Rapeseed Oil Fatty Acid Esterification with Methanol in the Presence of Sulfuric Acid
No full textThe interest in biodiesel production from low cost feedstocks is still increasing. Such feedstocks usually contain large amounts of free fatty acids, which make the currently employed base catalysts inefficient, thereby promoting the use of acid catalysts. Due to the high activity and low cost, sulfuric acid could become the most widely used acid catalyst for biodiesel production. Research undertaken so far using sulfuric acid for esterifi cation of fatty acids has shown that the products obtained fail to meet the requirements of the standard EN 14214. This paper describes a systematic study of rapeseed oil fatty acids esterification in order to obtain a product complying with the standard EN 14214. The influence of sulfuric acid concentrations (0.1-3.0%), methanol molar ratios (1:1-20:1) and reaction time (0-360 min) was evaluated. Finally, a two-stage esterification process was developed, where in optimal conditions esterification yield of 97.8% and ester content of 99.6% were achieved
Anisotropy of Compressive Strength in Porous Alumina Ceramics
No full textAnisotropy of the compressive strength was investigated in porous alumina based
ceramics produced by slip casting method. Aluminium paste was used as pore former similarly as in
the aerated concrete technology. Materials were sintered at 1650°C and 1750°C. The apparent
porosity of the investigated materials was in the range of 54±1% to 60±2%. The compressive
strength of the samples in the directions parallel and perpendicular to the sample expansion
direction was in the range from 3.8±0.3 to 13.0±1.1 MPa and from 6.4±1.3 to 27.0±1.1 MPa,
respectively. The mechanical anisotropy was related with the flattening of the introduced pores. The level of mechanical anisotropy was affected by the initial composition of the slurry and sintering temperature
The Effect of Activator on the Properties of Low-Calcium Alkali-Activated Mortars
No full textPortland cement is the most widely used type of binder in construction materials. World cement production has reached 3780 million tons in 2012. By producing 1 ton of Portland cement 222 kg of CO2 are emitted in the atmosphere that creates serious environmental pollution problems. The possibility to replace Portland cement with alternative binders is a topical issue in the world. According to the results of research made in the last 25 years, alkali activated binder is considered as Portland cement substitute. By using kaolin clay, waste glass, alkali activator and sand it is possible to obtain materials, which are similar to the cement based materials. Properties of the low-calcium alkali – activated mortars (AAMs) were tested in this research with the regard to concentration of activator - alkali solution
Jauni keramikas materiāli un tehnoloģijas
No full textDots pārskats par rezultātiem enerģiju taupošu
tehnoloģiju un relatīvi jaunu keramikas materiālu izstrādi,
izmantojot Latvijas minerālās izejvielas. Parādīts, ka illītu mālu
ķīmiskā apstrāde ievērojami samazina materiāla saķepināšanas
temperatūru un nodrošina augstu spiedes pretestību, salīdzinot
ar tradicionāli iegūtiem keramikas materiāliem.
Mikrobioloģiskā mālu apstrāde maz ietekmē plastisku mālu
plasticitātes/plūstamības izmaiņas. Izstrādāti mullīta-ZrO2
augstas stiprības keramikas materiāli ar illīta mālu piedevu, kā
arī augsttemperatūras, kordierīta un paaugstinātas porainības
keramikas materiāli
Sapropelis un tā izmantošanas iespējas
No full textSapropelis ir ar organiskajām vielām bagāti
nogulumi, kas nogulsnējas ūdenstilpēs. Sapropeļa izplatība un
plašas izmantošanas iespējas padara to par nozīmīgu dabas
resursu, ko var izmantot lauksaimniecībā, dārzkopībā,
mežsaimniecībā, lopkopībā, ķīmijas un celtniecības industrijā,
balneoloģijā un kosmetoloģijā. Kopējie sapropeļa resursi Latvijā
sastāda aptuveni 2 miljardus m3. Šī raksta mērķis ir aplūkot
sapropeļa klasifikāciju, veidošanās apstākļus un izmantošanas
jomas
Sapropeļa kūdras, sapropeļa kokskaidu siltumizolācijas plāksnes un to īpašības
No full textSiltumizolācijas materiāli, kuros par pildvielu
tiktu izmantoti vietējie biomasas produkti, bet par saistvielu
kalpotu dabiskas izcelsmes saistvielas, piemēram, sapropelis,
uzskatāmi par inovatīviem un to pielietošana sekmētu
ekoloģiskās būvniecības nozares attīstību. Šādu risinājumu
izstrāde ir aktuāla, jo Latvijā ir ievērojami sapropeļa resursi,
kuru izmantošanu kavē to nepietiekama izpēte un ekoloģiskās
būvniecības nozares intensīva attīstība. Pētījuma mērķis ir iegūt
sapropeļa-koksnes, kūdras-koksnes siltumizolācijas plāksnes,
noteikt optimālās plātnes sastāva attiecības un raksturot iegūto
plātņu īpašības. Veikto pētījumu rezultātā tika noteiktas
siltumizolācijas materiālu paraugu mehāniskās,
siltumvadītspējas un skaņas izolācijas īpašības un izvērtētas
iespējas tos izmantot ekoloģiskajā būvniecībā, kā arī veikts
salīdzinājums ar šobrīd tirgū esošajiem produktiem
Algorithm for Monitoring Minimum Cost in Fuzzy Dynamic Networks
No full textThe present paper examines the task of minimum
cost flow finding in a fuzzy dynamic network with lower flow
bounds. The distinguishing feature of this problem statement lies
in the fuzzy nature of the network parameters, such as flow
bounds, transmission costs and transit times. The arcs of the
considered network have lower bounds. Another feature of this
task is that fuzzy flow bounds, costs and transit times can vary
depending on the flow departure time. Algorithm, which
implements the solution of considered problem, is proposed