Background: The effect of the antimicrobial agents benzalkonium chloride (BC) and cetylpyridinium chloride (CPC) on the restorative glass ionomer tooth cement (GIC) Fuji IX was investigated. Aim of ...the study: The aim of the study was to determine whether the addition of antimicrobial compounds impairs the physical and mechanical properties of the commercial GIC Fuji IX. Materials and Methods: The concentrations of 1%, 2% and 3% of antimicrobial agentsBC and CPC, by weight of the cement, were added during the mixing phase and different effects were studied. In most samples, there was a slight change in setting time. Samples with 4 mm diameter and 6 mm height were used to measure compressive strength and release. The release of antimicrobial compounds was analysed by UV-visible spectrophotometry at a wavelength of 259 nm for CPC and 214 nm for BC, in deionized water. Results: The obtained results showed that the release takes place through the diffusion mechanism in the first 2-3 hours, and the diffusion coefficients vary depending on the concentration. The values range is from 1.97 x 10-14 -1.78 x 10-12 m2 s-1. Release of antimicrobial compound had ceased after seven days, with total release representing between 2.15 and 4.84% of the initial additive loading. Conclusion: Both compounds have minor effect on the setting time of the GIC. The reduction of compressive strength is not statistically significant. CPC containing cements (1 and 2%), were statistically significantly weaker, than those containing BC (p<0.05).Both antimicrobial compounds have shown constant release from the GIC with values which are directly proportional both to the time and to the concentration.
In the current study, an
artificial neural network
(ANN) and
multiple linear regressions
(MLR) have been used to develop predictive models for the estimation of molecular diffusion coefficients of ...1252 polar and non-polar binary gases at multiple pressures over a wide range of temperatures and substances. The quality and reliability of each method were estimated in terms of the
correlation coefficient
(R),
mean squared errors
(MSE),
root mean squared error
(RMSE), and in terms of
external validation coefficients
(Q2ext).
The comparison between the artificial neural network (ANN) and the multiple linear regressions (MLR) revealed that the neural network models showed a good predicting ability with lower errors (the roots of the mean squared errors in the total database were 0.1400 for ANN1 and 0.1300 for ANN2), and (root mean squared errors in the total databases were 0.5172 for MLR1 and 0.5000 for MLR2).
U ovoj studiji primijenjene su
umjetna neuronska mreža
(ANN) i
model višestruke linearne regresije
(MLR) za razvoj prediktivnih modela za procjenu koeficijenata molekularne difuzije 1252 polarnih i nepolarnih binarnih plinova pri višestrukim tlakovima u širokom rasponu temperatura i tvari. Kvaliteta i pouzdanost svake metode procijenjeni su pomoću
korelacijskog koeficijenta
(R),
srednjih kvadratnih pogrešaka
(MSE),
korijena srednje kvadratne pogreške
(RMSE) te
koeficijenata vanjske validacije
(Q2ext).
Usporedba između umjetne neuronske mreže (ANN) i višestrukih linearnih regresija (MLR) otkrila je da modeli neuronske mreže pokazuju dobru sposobnost predviđanja s nižim pogreškama (korijeni srednjih kvadratnih pogrešaka u ukupnoj bazi podataka bili su 0,1400 za ANN1 i 0 (1300 za ANN2 a pogreške korijena srednje vrijednosti u ukupnim bazama podataka bile su 0,5172 za MLR1 i 0,5000 za MLR2).
Spherical crystallization of drugs is the process of obtaining larger particles by agglomeration during crystallization. The most common techniques used to obtain such particles are spherical ...agglomeration and quasi-emulsion solvent diffusion. Ammonia diffusion systems and crystallo-co-agglomeration are extensions of these techniques. By controlling process parameters during crystallization, such as temperature, stirring rate, type and amount of solvents, or excipient selection, it is possible to control the formation of agglomerates and obtain spherical particles of the desired size, porosity, or hardness. Researchers have reported that the particles produced have improved micromeritic, physical, and mechanical properties, which make them suitable for direct compression. In some cases, when additional excipients are incorporated during spherical crystallization, biopharmaceutical parameters including the bioavailability of drugs can also be tailored.
Sferična kristalizacija je postopek izdelave večjih delcev z aglomeracijo manjših med samo kristalizacijo. Najpogosteje uporabljeni tehniki za izdelavo takšnih delcev sta sferična aglomeracija in kvaziemulzija z difuzijo topila. Sistem z difuzijo amoniaka in kristalo-ko-aglomeracija sta razširitvi teh dveh metod. Z nadzorovanjem procesnih parametrov med kristalizacijo, kot sta temperatura in hitrost mešanja, z izbiro lastnosti in množine topil ter z izbiro pomožnih snovi, lahko vplivamo na nastanek aglomeratov in izdelamo sferične delce želenih velikosti, primerne poroznosti ali trdote. Raziskovalci poročajo, da imajo izdelani delci izboljšane pretočne lastnosti, izboljšane druge fizikalne in mehanske lastnosti zaradi česar so primerni za direktno tabletiranje. V nekaterih primerih lahko ob vgradnji ustreznih pomožnih snovi, ki jih dodamo med procesom sferične kristalizacije, izboljšamo tudi biofarmacevtske lastnosti zdravilnih učinkovin vključno s povečanjem biološke uporabnosti.
Istraživači javnih politika od druge polovice 20. stoljeća sve više analitičke pažnje posvećuju prijenosu javnih politika iz jednog političkog djelokruga u drugi. Pritom se koriste konceptima poput ...difuzije, konvergencije i transfera javnih politika. Transfer javnih politika, najmlaði od navedenih pristupa, dobiva na zamahu nakon druge polovice devedesetih godina prošlog stoljeća te je u posljednjih dvadeset godina izrastao u respektabilan, naveliko citiran i korišten istraživački pristup. Ovaj se rad može shvatiti kao historijat istraživanja prijenosa javnih politika izmeðu političkih djelokruga. Pored pregleda evolucije pristupa ponudit će se i izvorna sistematizacija i demarkacija različitih studija. Rad se zaključuje uvidom kako su studije transfera distinktivne u odnosu na studije konvergencije i difuzije. Odlikuje ih procesni analitički fokus, usmjerenost na razumijevanje djelovanja aktera, kvalitativna metodologija te korištenje malih uzoraka. U radu se zastupa mišljenje kako su studije transfera javnih politika izvrstan heuristički alat jer omogućuju multidimenzionalno istraživanje procesa stvaranja javnih politika.
This work presents the results of the investigation into deuterium retention and thermal release in low activation ferritic-martensitic steel EUROFER and its main components, Fe and Cr, using ion ...implantation, nuclear reaction depth profiling and the thermal desorption spectrometry technique. The samples were exposed to deuterium ECR plasma of 6.5*1024 Dm-2 fluence. Our NRA results show that, at 300 K, most of deuterium is trapped in the near-surface region. A part of the implanted deuterium diffuses into the bulk and is trapped by defects beyond the implantation range. The results of the TDS measurement of the Cr sample confirm the formation of an ordered Cr-hydride phase. / В данной статье приведены результаты исследований по удержанию и термической десорбции дейтерия в железе, хроме и сплаве EOROFER – представляющем новейший материал для фузионного (термоядерного) реактора. Исследования показали следующие результаты: *Удержание дейтерия в хроме намного выше, чем в железе (из-за образования гибридов хрома) *Удержание дейтерия в сплаве EUROFER выше на фактор 2, чем в железе *Выявлена специфиеская структура в концентрационном профиле железа и сплава EUROFER на глубине ~ 4 μm *Высокий уровень диффузии и удержания дейтерия свидетельствует о потенциальном применении Au в качестве диффузионного барьера в фузионном (термоядерном) реакторе. / U ovom radu ispitivano je zadržavanje i termalna desorpcija deuterijuma u gvožđu, hromu i EOROFER-u, leguri koja se razmatra kao najnoviji materijal za buduće fuzione reaktore. Studija je pokazala sledeće rezultate: zadržavanje deuterijuma u hromu je mnogo veće nego u gvožđu (usled formiranja hidrida hroma), zadržavanje deuterijuma u EUROFER-u je za faktor 2 veće nego u gvožđu, primećena je specifična struktura u koncentracionom profilu gvožđa i EUROFER-a na dubini ~ 4 μm, veliki stepen difuznosti i zadržavanja deuterijuma govore o potencijalnoj upotrebi Au kao difuzione barijere u fuzionom reaktoru.
Recent technological advances enabled with use of nanoscale dimensions, opened a lot of room for various investigations, especially with mass transport through nanoporous media and nanochannels. One ...of the fields of research is reproducible fabrication of nanofluidic devices with characteristic size from several hundred down to few nanometers, where precise mass exchange and timing are essential. Accurate prediction of the diffusive transport is needed for rational control of physical phenomena. Another field, which is very important, is diffusion within biological system such as extracellular space, consisting of various fibers and particles, which all together affect diffusion process. Despite the increasing focus on nanofluidics in many of these applications, the laws governing molecular transport through nanoscale fluidic channels and porous media have not been fully understood. As the size of the channels and pores is reduced to the molecule size, classical continuum theories fail to predict even the basic characteristics of fluid transport. In chapter 2 we presented fundamentals of diffusion process and fields of application. As presented in this chapter, mass transport by diffusion is crucial process in biological systems. We have notified the basic nonlinear diffusion equations of mass balance, which are further used in finite element analysis. In chapter 3 we employed molecular dynamics simulations to study the effects of confinement and concentration on diffusive transport of glucose in silica nanochannels. It is found that glucose modifies the electrical properties of nanochannel walls and that, below 5 nm in channel height, glucose diffusion coefficient (diffusivity) is significantly reduced. With increasing concentration, the diffusivity is reduced linearly in the bulk, while it is reduced nonlinearly at the interface. The effective diffusivity reduction is related to the interface thickness, and has an unexpected reduction at low concentrations. Simulation results presented in chapter 3, consistent with the experimental observations, suggest that nanoconfinement is the essential cause of the observed altered fluid diffusive transport, not accounted for by classical theories, because of coupling of confinement and concentration effects. In chapter 4 we presented research of reproducible fabrication of nanofluidic devices with characteristic size from several hundred down to few nanometers, where emerging new material properties and transport phenomena made nanofluidic devices appealing for novel biomedical and industrial applications, including drug delivery, where precise mass exchange and timing are essential. Accurate prediction of the diffusive transport is needed for rational design of nanofluidic components. New transport mechanisms are observed whereby channel surface properties begin to dominate over volume properties. Numerical results are obtained using significantly upgraded PAK-T Finite Element Program, with the experimentally determined dependence of diffusion coefficient on concentration. The agreement between the experimental and numerical results allows using this software as a predictive tool for the rational design of nano-channeled devices for drug delivery, reducing the arduous tasks of production and characterization. As presented in Chapter 3, diffusion in nanospace does not strictly obey to Fick’s law, generally used in macro environment. Deviation from this law is due to surface effects, i.e. due to interaction between transported molecules and bounding surfaces. The continuum methods are not applicable at the nanoscale, therefore molecular dynamics approach remains to be used. Development of computational procedures to couple nanoscale, mesoscale and macroscale would be a desirable direction of research to elucidate mass transport occurring in the NDS devices and to aid the NDS design and optimization. A hierarchical modeling approach, which accounts for interface effects on the diffusion coefficient, is introduced in Chapter 5. The model employs molecular dynamics (MD) for calculation scaling functions to reduce the diffusion coefficient corresponding to “bulk” values. With this reduced diffusion coefficient, modeling is performed using the finite element method (FE) within an incremental iterative scheme. The scaling scheme was validated by predicting experimental glucose diffusion through a nanofluidic membrane with a correlation coefficient of 0.999. Comparison with experiments through a nanofluidic membrane showed interface effects to be crucial. In Chapter 6 we first present a new hierarchical multiscale microstructural model for diffusion within composite materials that incorporates both microstructural geometry and the interaction between diffusing particles and solid surfaces. This model, which couples Molecular Dynamics (MD) and the Finite Element (FE) method, is employed to construct a continuum diffusion model based on a novel numerical homogenization procedure. The procedure is general and robust, and evaluates constitutive material parameters of the continuum model. These parameters include the traditional equivalent bulk diffusion coefficients and the equivalent distances from the solid surface accounting for surface interaction effects. To demonstrate the model’s wide-range of applicability, we examined examples of diffusion of glucose within water through various geometrical/material configurations. The microstructural model, numerical homogenization and continuum model offer a new platform for modeling diffusion within complex composite and biological materials, capable of connecting the molecular and continuum scales.
Najveći deo istraživanja u prošlosti iz oblasti difuzije je obavljen na nivou makro-skale gde fundamentalni zakoni, kao što su Fikov i Darsijev zakon, opisuju kretanje odgovarajuće supstance kroz proizvoljni medijum. Međutim, na kretanje supstance kroz pore složenih mikrostruktura utiču ne samo granične površine solida usled kojih se menjaju putanje supstance, već i hemijska interakcija između supstance i površina solida. Ova interakcija postaje veoma bitna i može znatno uticati na prosečnu brzinu difuzionog procesa u nano-ograničenom prostoru. Stoga, Fikov zakon ne može dovoljno precizno da opiše difuzioni proces pa se površinska interakcija, koja se javlja na molekulskom nivou, mora uzeti u obzir. Jedan od načina da se odrede karakteristike difuzije sa uticajem površina je molekularna dinamika (MD), pomoću koje je moguće odrediti interakciju između supstance i zida na atomskom i molekulskom nivou. Međutim, zbog velikog broja interakcija koje treba da budu uzete u obzir, MD postaje nepraktična čak i za veoma male domene (reda milimetra). Osim metoda molekularne dinamike, razvijen je veliki broj metoda mehanike kontinuma, kao što je metod konačnih elemenata, u cilju izučavanja poroznih sistema. Kod ovih kontinualnih metoda se uzimaju u obzir termodinamičke karakteristike, ali se ipak fizika uticaja površina ostavlja po strani.
Tramadol-loaded interpenetrating polymer network (IPN) alginate-gelatin (AG) microgels (MG) were prepared by the chemical cross-linking technique with glutaraldehyde as cross-linking agent and were ...optimized using response surfaces. A central composite design for 2 factors, at 3 levels each, was employed to evaluate the effect of critical formulation variables, namely the amount of gelatin (X1) and glutaraldehyde (X2), on geometric mean diameter, encapsulation efficiency, diffusion coefficient (D), amount of mucin adsorbed per unit mass (Qe) and 50 % drug release time (t50). Microgels with average particle size in the range of 44.31-102.41 μm were obtained. Drug encapsulation up to 86.5 % was achieved. MGs were characterized by FT-IR spectroscopy to assess formation of the IPN structure and differential scanning calorimetry (DSC) was performed to understand the nature of drug dispersion after encapsulation into IPN microgels. Both equilibrium and dynamic swelling studies were performed in pH 7.4 phosphate buffer. Diffusion coefficients and exponents for water transport were determined using an empirical equation. The mucoadhesive properties of MGs were evaluated in aqueous solution by measuring the mucin adsorbed on MGs. Adsorption isotherms were constructed and fitted with Freundlich and Langmuir equations. In vitro release studies indicated the dependence of drug release on the extent of cross-linking and the amount of gelatin used in preparing IPNs. The release rates were fitted to a power law equation and Higuchi's model to compute the various drug transport parameters, n value ranged from 0.4055 to 0.5754, suggesting that release may vary from Fickian to quasi-Fickian depending upon variation in the formulation composition.
Interpenetrirajući umreženi polimerni (IPN) alginatno-želatinski (AG) mikrogelovi (MG) tramadola pripravljeni su metodom umrežavanja koristeći glutaraldehid kao sredstvo za umrežavanje. Pripravci su optimirani pomoću odzivnih površina. Kompozitini dizajn s dva faktora na tri nivoa upotrijebljen je za procjenu kritičnih formulacijskih varijabli: praćen je utjecaj količine želatine (X1) i glutaraldehida (X2) na prosječnu veličinu čestica, sposobnost kapsuliranja, koeficijent difuzije (D), količinu adsorbiranog mucina po jedinici mase (Qe) i vrijeme potrebno za oslobađanje 50 % lijeka (t50). Dobiveni su mikrogelovi prosječne veličine čestica od 44,31 do 102,41 ?m, a maksimalno postignuto vezanje lijeka bilo je 86,5 %. Mikrogelovi su karakterizirani FT-IR spektroskopijom i diferencijalnom pretražnom kalorimetrijom (DSC). Ravnotežne i dinamičke studije bubrenja provedene su u fosfatnom puferu pH 7,4. Koeficijenti difuzije i eksponenti za transport vode određeni su pomoću empirijske jednadžbe. Mukoadhezivna svojstva MGs evaluirana su u vodenoj otopini mjerenjem adsorpcije mucina na mikrogelove. Konstruirane su adsorpcijske izoterme i uspoređene s Freudlichovim i Langmuirovim jednadžbama. Pokusi in vitro pokazuju da oslobađanje ljekovite tvari ovisi o stupnju umreženja i količini želatine upotrijebljene u pripravi IPN. Vrijednosti oslobađanja uvrštene su u jednadžbu zakona potencije i u Higuchijev model kako bi se izračunali razni parametri prijenosa lijeka; n vrijednosti bile su između 0,4055 i 0,5754, što ukazuje na to da oslobađanje varira od Fickovog do kvazi-Fickovog, ovisno o sastavu pripravka.
This paper will present the results of tests on the diffusion properties of the migrating inhibitor DME and KCR. The tests were done by determining the distribution of concentrations of inhibitors in ...concrete, and then the values of a reliable diffusion coefficient were calculated on the basis of the solution to the reverse-task diffusion equation. Inhibitors have shown very good diffusion properties, which were about 5 rows better than the properties of the inhibitors on the market. Inhibitors DME and KCR were able to quickly penetrate deep into the concrete through the entire thickness of reinforcement concrete cover.
Ovaj rad prikazuje rezultate istraživanja utjecaja perforacija i proreza na difuzivnost vodene pare ekspandiranog polistirena (EPS-a) te utjecaj veličine i broja perforacija i proreza na toplinsku ...vodljivost ploče EPS-a. Istraživanje je provedeno primjenom numeričkih modela (metode kontrolnih volumena), pri čemu je varirana debljina uzorka, razmak proreza te dubina i promjer perforacija. Numeričkim modelom se pokazalo da je moguće dobiti i do 42,18 % bolju difuzivnost vodene pare u odnosu na EPS ploču bez perforacija uz povećanje toplinske vodljivosti od 9, 02 %. Također, iz rezultata ovog istraživanja vidljivo je da efektivni koeficijent difuzije vodene pare ovisi o debljini perforiranih uzoraka EPS-a.
In a number of situations reinforced concrete structures must be protected by barrier materials to prevent contact with aggressive agents. One of the ways to protect concrete structures from ...corrosion is to use protective polymer coatings. Polymers as coating materials are not totally resistant and impermeable to all aggressive agents. Gases, vapors and liquids penetrate into a polymer so that the polymer mass swells and eventually disintegrates. However, the penetration/disintegration progresses at a much lower rate than that in the concrete. Surface coatings are able to reduce considerably the penetration, to slow down the rate of deterioration of concrete cover and to overcome most durability problems associated with external attack. In this article the mechanism of degradation of polymer coatings are analyzed. Methodology and predictive models for the degradation over time caused by aggressive actions of polymer coatings are presented. Proposed models can be applied to design of polymer coatings. Such a design of coatings is presented in a simple form for engineering design purposes.
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