No description available.

Nowadays the ferroelectrics containing of several feroically active sublattices are very attractive, because interactions between these sublattices can caused novel phenomena. Antiferroelectrics, ferrielectrics and multiferoics belong to these materials. In this work new crystalline materials MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se) were investigated, which have ferrielectric and multiferoic properties. The dielectric and electric properties of above mentioned materials have been investigated by broadband dielectric spectroscopy methods, which allows to analyze the collective processes related to order – disorder and displacive phase transitions, ions migration and freezing of dipoles (glassy state) in wide temperature (25 K - 500 K) and frequency (10-5 HZ - 3 GHz) ranges. By substitution or doping it becomes possible to tailor the ferroelectric materials to different properties. In this work is determined that the substitution of 10% Cu ions by Ag ions shifts the phase transition temperature of CuInP2S6 crystal toward lower temperatures while the addition of In ions shifts the phase transitions temperature toward the higher ones. The phase transition temperature difference is about 50 K for mentioned crystals. If the ferroelectric crystal CuInP2S6 is mixed with the antiferroelectric CuCrP2S6 the dipole glass phase occupies the middle of the phase diagram. The distribution of relaxation times has been calculated from the broadband dielectric spectra of dipolar glasses. The... [to full text] / Šiai dienai ypač populiarūs ferroelektrikai susidedantys iš kelių feroiškai aktyvių subgardelių, kurių persitvarkymas fazinio virsmo temperatūroje atskleidžia naujų, dar neaprašytų reiškinių. Prie šių medžiagų priskiriami antiferoelektrikai, ferielektrikai ir multiferoikai. Šiame darbe buvo tiriama nauja medžiagų šeimos MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se ), kurios pasižymi ferielektrinėmis bei multiferoinėmis savybėmis, ir kurių dielektrines ir elektrines savybes galima efektyviai keisti įvedant priemaišas. Minėtų medžiagų dielektrinės ir elektrinės savybės buvo tiriamos dielektrinės spektroskopijos metodais, kurie leidžia tirti kristalų kolektyvinius reiškinius susijusius su tvarkos – netvarkos bei poslinkio tipo faziniais virsmais, jonų migracija bei dipolių užšalimu (stiklėjimu) plačiame dažnių (10-5 Hz iki 3 GHz) bei temperatūrų (25 K iki 500 K) intervaluose. Įvedus 10% Ag jonų vietoj Cu jonų ferielektriniame kristale CuInP2S6 fazinio virsmo temperatūra pasislenka į žemesnias temperatūras, o padidinus indžio koncentraciją fazinio virsmo temperatūra pasislenka į aukštesnes temperatūras. Minėtų kristalų fazinių virsmų temperatūrų skirtumas 50 K. Sumaišius skirtingomis proporcijomis feroelektriką (CuInP2S6) su antiferoelektriku (CuCrP2S6) stebima dipolinio stiklo fazė. Iš dielektrinių matavimų stiklo fazėje buvo paskaičiuota relaksacijos trukmių pasiskirstymo funkcija, kurios aprašymas dvigubos potencialinės duobės modeliu leido susieti mikroskopinius kristalo... [toliau žr. visą tekstą]

No description available.

Kietojo kūno optikos mokslinėje laboratorijoje buvo išmatuoti mūsų išaugintų SbSI, TlInS2 ir TGS kristalų dvejopo lūžio priklausomybė nuo temperatūros. Eksperimentinis dvejopo lūžio priklausomybės nuo temperatūros tyrimas leido nustatyti TGS, TlInS2 ir SbSI kristalų fazinių virsmų temperatūrą. Teoriškai, tankio funkcionalo teorijos metodu (DFT), buvo apskaičiuoti SbSI kristalo lūžio rodikliai paraelektrinėje ir feroelektrinėje fazėse. Taip pat skaičiuotas dvejopas lūžis feroelektrinio fazinio virsmo srityje. Teoriniai dvejopo lūžio skaičiavimų rezultatai palyginti su eksperimentiniais matavimų rezultatais. / In Solid State Science Laboratory we measured birefringence on temperature of grown SbSI, TlInS2 and TGS crystals. The measurement of birefringence helps to evaluate the ferroelectric phase transition of TGS, TlInS2 ir SbSI crystals. Refractive indices of SbSI crystal in paraelectric and ferroelectric phase we investigated by DFT method with program Wien2k. The theoretical results of birefringence were compared with experimental results.

Šiai dienai ypač populiarūs ferroelektrikai susidedantys iš kelių feroiškai aktyvių subgardelių, kurių persitvarkymas fazinio virsmo temperatūroje atskleidžia naujų, dar neaprašytų reiškinių. Prie šių medžiagų priskiriami antiferoelektrikai, ferielektrikai ir multiferoikai. Šiame darbe buvo tiriama nauja medžiagų šeimos MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se ), kurios pasižymi ferielektrinėmis bei multiferoinėmis savybėmis, ir kurių dielektrines ir elektrines savybes galima efektyviai keisti įvedant priemaišas. Minėtų medžiagų dielektrinės ir elektrinės savybės buvo tiriamos dielektrinės spektroskopijos metodais, kurie leidžia tirti kristalų kolektyvinius reiškinius susijusius su tvarkos – netvarkos bei poslinkio tipo faziniais virsmais, jonų migracija bei dipolių užšalimu (stiklėjimu) plačiame dažnių (10-5 Hz iki 3 GHz) bei temperatūrų (25 K iki 500 K) intervaluose. Įvedus 10% Ag jonų vietoj Cu jonų ferielektriniame kristale CuInP2S6 fazinio virsmo temperatūra pasislenka į žemesnias temperatūras, o padidinus indžio koncentraciją fazinio virsmo temperatūra pasislenka į aukštesnes temperatūras. Minėtų kristalų fazinių virsmų temperatūrų skirtumas 50 K. Sumaišius skirtingomis proporcijomis feroelektriką (CuInP2S6) su antiferoelektriku (CuCrP2S6) stebima dipolinio stiklo fazė. Iš dielektrinių matavimų stiklo fazėje buvo paskaičiuota relaksacijos trukmių pasiskirstymo funkcija, kurios aprašymas dvigubos potencialinės duobės modeliu leido susieti mikroskopinius kristalo... [toliau žr. visą tekstą] / Nowadays the ferroelectrics containing of several feroically active sublattices are very attractive, because interactions between these sublattices can caused novel phenomena. Antiferroelectrics, ferrielectrics and multiferoics belong to these materials. In this work new crystalline materials MNP2X6 (M = Cu, Ag; N=In, Cr, Bi; X=S, Se) were investigated, which have ferrielectric and multiferoic properties. The dielectric and electric properties of above mentioned materials have been investigated by broadband dielectric spectroscopy methods, which allows to analyze the collective processes related to order – disorder and displacive phase transitions, ions migration and freezing of dipoles (glassy state) in wide temperature (25 K - 500 K) and frequency (10-5 HZ - 3 GHz) ranges. By substitution or doping it becomes possible to tailor the ferroelectric materials to different properties. In this work is determined that the substitution of 10% Cu ions by Ag ions shifts the phase transition temperature of CuInP2S6 crystal toward lower temperatures while the addition of In ions shifts the phase transitions temperature toward the higher ones. The phase transition temperature difference is about 50 K for mentioned crystals. If the ferroelectric crystal CuInP2S6 is mixed with the antiferroelectric CuCrP2S6 the dipole glass phase occupies the middle of the phase diagram. The distribution of relaxation times has been calculated from the broadband dielectric spectra of dipolar glasses. The... [to full text]

Very specific protein-salt interactions are involved in a multitude of biological phenomena such as protein folding/stability, enzymatic activity, and signal transduction events. In this work, we used two very simple, protein-mimic model biopolymers to obtain a better understanding of specific cation effects operating in aqueous protein environments. The two biopolymers used were Elastin-like Polypeptides (ELPs) and poly(N-isopropylacrylamide) (PNIPAM). ELPs are an especially an ideal model system as these polypeptides can be easily genetically engineered to observe the effect of specific amino acid residues and peptide chain length on these salt interactions. Both of these biopolymers are also highly thermoresponsive as their aqueous solutions undergo a hydrophobic collapse/aggregation induced phase transition process above a lower critical solution temperature (LCST). Thermodynamic measurements of these biopolymers were carried out under various salt solution conditions. Additionally, both of these biopolymers are suitable for making surface specific spectroscopic measurements. Vibrational sum frequeny spectroscopy (VSFS), a non-linear interface sensitive spectroscopic technique, was employed here to investigate biologically relevant cation interactions which occur at peptide/protein surfaces. First, the LCST response of a non-polar ELP and a neutral biopolymer, PNIPAM, was investigated in the presence of 12 different alkali, alkaline-earth metal and transition metal chloride salts. Even though the salt interactions for uncharged proteins are dominated by anions, subtle specific cation effects were also observed. The results followed a direct Hofmeister series for cations. Most alkali cations are excluded from the polar amide regions of proteins. More polarizable cations, however, can solvate the hydrophobic moieties and somewhat counter the salting-out effect of the chloride anion. More charged and hydrated ions like lithium and divalent cations showed a weak interaction to the amide moiety through their hydration shell. The role of acidic amino acid residues in inducing cation specificities was investigated using an aspartate-rich ELP system. Both thermodynamic and spectroscopic data conclusively proved that the negative charge on protein surfaces is the main driving force for cation partitioning and specificity under physiological relevant concentration regimes. Apparent binding constants of carboxylate moieties with cations were determined. This is the first quantitative and thoroughly systematic study of such biologically relevant cation-carboxylate interactions prevalent in enzyme active sites and protein surfaces.

Seed formation consists of two major stages: embryo pattern formation and maturation. During seed maturation, the embryo accumulates storage material, acquires desiccation tolerance, and enters a stage of dormancy. Genetic analyses have identified several master regulators that orchestrate late embryogenesis, including the B3-domain transcription factor FUSCA3 (FUS3). In Arabidopsis, FUS3 has been shown to be a central regulator of hormonal pathways; it positively regulates late embryogenesis by increasing abscisic acid (ABA) level while repressing gibberellin (GA) synthesis. In turn, FUS3 protein level is positively and negatively regulated by ABA and GA, respectively. However, the mechanism of how this regulation occurs has not been well characterized. In this study, FUS3 has been shown to be an unstable protein rapidly degraded by the proteasome through a PEST instablility motif. To further characterize the mechanisms involved in FUS3 homeostasis, FUS3-interacting proteins were identified. The SnRK1 kinase AKIN10 was shown to interact with and phosphorylate FUS3 at its N-terminus. Furthermore, overexpression of AKIN10 delays FUS3 degradation, suggesting AKIN10 positively regulates FUS3 protein accumulation. Overexpression of AKIN10 delays developmental phase transitions, and causes defects in lateral organ development. These defects were partially rescued by the loss-of-function fus3-3 mutation, suggesting FUS3 and AKIN10 genetically interact to regulate these developmental processes. SnRK1/AMPK/Snf1 kinases are regulators of energetic stress responses. Overexpression studies suggest both FUS3 and AKIN10 positively regulate ABA signaling, but differ in sugar responses during germination; AKIN10 mediates glucose sensitivity, while FUS3 regulates osmotic stress responses. Overexpression of AKIN10 and FUS3 results in glucose and osmotic stress hypersensitivities, respectively, both of which are partially dependent on de novo ABA synthesis. Thus, FUS3 and AKIN10 act in overlapping pathways and combine different environmental signals to generate a common ABA-dependent response. In summary, novel mechanisms that regulate FUS3 homeostasis and function were identified. A model explaining the interaction between FUS3 and AKIN10 during embryonic and vegetative development, and the function of these two central developmental regulators in hormonal and stress signaling pathways is discussed.

Seed formation consists of two major stages: embryo pattern formation and maturation. During seed maturation, the embryo accumulates storage material, acquires desiccation tolerance, and enters a stage of dormancy. Genetic analyses have identified several master regulators that orchestrate late embryogenesis, including the B3-domain transcription factor FUSCA3 (FUS3). In Arabidopsis, FUS3 has been shown to be a central regulator of hormonal pathways; it positively regulates late embryogenesis by increasing abscisic acid (ABA) level while repressing gibberellin (GA) synthesis. In turn, FUS3 protein level is positively and negatively regulated by ABA and GA, respectively. However, the mechanism of how this regulation occurs has not been well characterized. In this study, FUS3 has been shown to be an unstable protein rapidly degraded by the proteasome through a PEST instablility motif. To further characterize the mechanisms involved in FUS3 homeostasis, FUS3-interacting proteins were identified. The SnRK1 kinase AKIN10 was shown to interact with and phosphorylate FUS3 at its N-terminus. Furthermore, overexpression of AKIN10 delays FUS3 degradation, suggesting AKIN10 positively regulates FUS3 protein accumulation. Overexpression of AKIN10 delays developmental phase transitions, and causes defects in lateral organ development. These defects were partially rescued by the loss-of-function fus3-3 mutation, suggesting FUS3 and AKIN10 genetically interact to regulate these developmental processes. SnRK1/AMPK/Snf1 kinases are regulators of energetic stress responses. Overexpression studies suggest both FUS3 and AKIN10 positively regulate ABA signaling, but differ in sugar responses during germination; AKIN10 mediates glucose sensitivity, while FUS3 regulates osmotic stress responses. Overexpression of AKIN10 and FUS3 results in glucose and osmotic stress hypersensitivities, respectively, both of which are partially dependent on de novo ABA synthesis. Thus, FUS3 and AKIN10 act in overlapping pathways and combine different environmental signals to generate a common ABA-dependent response. In summary, novel mechanisms that regulate FUS3 homeostasis and function were identified. A model explaining the interaction between FUS3 and AKIN10 during embryonic and vegetative development, and the function of these two central developmental regulators in hormonal and stress signaling pathways is discussed.

Anisotropic molecules confined on a spherical or other curved surface can display coupled positional and orientational orderings, which make possible applications in physics, chemistry, biology, and material science. Therefore, controlling the order of such system has attracted much attention recently. Several distinct conformations of rod-like or chain-like molecules confined on a spherical surface have been predicted, including states such as tennis-ball, rectangle, and cut-and-rotate splay. These conformations have four +1/2 defects and are suggested to dominate over the splay conformation that has two +1 defects. For the purpose of investigating the conformations of 2-fold anisotropic molecules confined on the spherical surface, the author of this thesis utilizes the Onsager model to study the system of rigid rods and conducts Monte Carlo simulations on the bead-bond model to research the system of semiflexible polymer chains. At low surface coverage density, no particular pattern of the molecules would form. However, coupled positional and orientational ordering begins to emerge beyond a transition density. On the basis of the numerical solutions of the Onsager model of rigid rods, the splay conformation is shown to be the only stable state. On the other hand, Monte Carlo simulations on a polymer system indicate that the ordered state always accompanies the tennis-ball symmetry. With comparison to the continuous isotropic-nematic transition of a fluid of hard rods embedded in a flat two-dimensional space, the disorder-order transition for both the system of rigid rods and the system of polymer chains confined on the spherical surface has first-order phase-transition characteristics.

The results of photoluminescence (PL) spectra of TlGaS2 single crystal were reported in the 500-1400 nm wavelength and in the 15-115 K temperature range. Three broad PL bands with an asymmetric Gaussian lineshapes were observed to be centered at 568 nm (A-band), 718 nm (B-band) and 1102 nm (C-band). The shift of the emission band peak energy as well as the change of the half-width of the emission band with temperature and excitation laser intensity were also studied. We analyzed the observed results using the configurational coordinate (CC) model. The powder diffraction patterns of TlInS2 and TlGaS2 crystals were obtained and the diffraction data were indexed using CRYSFIRE computer program packet. TlInS2 has hexagonal system with parameters a = 3.83 and c = 14.88 Ao. TlGaS2 has monoclinic system with parameters a = 9.62, b = 4.01 and c = 7.52 Ao with &amp / #946 / = 96.30o. Our diffraction studies at low temperatures did not reveal any phase transition for TlInS2 as reported in the literature. The specific heat capacities of both TlInS2 and TlGaS2 crystals calculated from Differential Scanning Calorimetry (DSC) measurements at low temperatures are reported in the thesis.