Amorphous Crystallization Research Articles

Assessment of Enamel Remineralisation After Treatment with Four Different Remineralising Agents: A Scanning Electron Microscopy (SEM) Study.

Decades of research has helped to increase our knowledge of dental caries and reduce its prevalence. However, according to World Oral Health report, dental caries still remains a major dental disease. Fluoride therapy has been utilised in a big way to halt caries progression, but has been met with limitations. This has paved the way for the development of newer preventive agents that can function as an adjunct to fluoride or independent of it. The purpose of the present study was to evaluate the ability of Casein Phosphopeptide-Amorphous Calcium Phosphate Fluoride (CPP ACPF), Bioactive Glass (BAG), fluoride enhanced Hydroxyapatite (HA) gel and self-assembling peptide P11-4 to remineralise artificial carious lesions in enamel in vitro using a 30 day pH cycling model through surface microhardness analysis and SEM. Sixty enamel samples were divided into five groups of 12 samples each. The control Group A consisted of intact enamel samples, Group B: CPP-ACPF (Tooth Mousse Plus), Group C: BAG (SHY- NM), Group D: fluoride enhanced HA gel (ReminPro) and Group E: Self-assembling peptide P11-4 (Curodont Protect). All groups excluding the control group were subjected to demineralisation following which four of these groups were remineralised using the four remineralising agents. The treated groups were subjected to pH cycling over a period of 30 days. This was followed by assessment of surface microhardness and SEM for qualitative evaluation of surface changes. The results were analysed by One-Way Analysis Of Variance (ANOVA). Multiple comparisons between groups were performed by paired t-test and post-hoc Tukey test. The results of the study revealed that remineralisation of enamel was the highest in samples of Group E (Self assembling peptide P11-4) followed by Group B (CPP-ACPF), Group C (BAG) and Group D (fluoride enhanced HA gel). There was a significant difference (p<0.05) in the remineralising ability between the self assembling peptide P11-4 group and BAG and fluoride enhanced HA gel group. Although no significant difference was observed between the self assembling peptide P11-4 and CPP-ACPF group, the self assembling peptide P11-4 remineralised the enamel lesions more effectively. SEM photomicrographs of the test groups demonstrated either amorphous crystals or particles scattered on the surface or lines of remineralisation along the prismatic borders. Self assembling peptide P11-4 demonstrated promising results by effectively and significantly remineralising the enamel lesions as compared to other test agents.

Multiple relaxation in uniaxially stretched P(VDF-TrFE) films after crosslinking

Uniaxial stretching has been well reported to be a robust technique to significantly enhance the dielectric performance of poly(vinylidene fluoride) (PVDF) based ferroelectric polymers. That is mostly ascribed to the contribution of the aligned ferroelectric domains located in the crystalline phase in previous investigation. In an effort to give a clear understanding of the relationship between the multiple orientations in different phases and the dielectric performance of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), in this contribution, the films of P(VDF-TrFE) bearing certain internal double bonds are cast from solution followed by crosslinked with benzyl peroxide (BPO). The crosslinked films are stretched at ambient temperature followed by annealed at elevated temperature. By monitoring the shape evolution and the changing of dielectric performances, the orientation and relaxation of polymer chains in amorphous phase and crystal domains have been carefully correlated to the varied dielectric performance under altered electric fields. It has been shown that the orientation of polymer chains in amorphous phase shows great improvement onto the ferroelectric transition and the resultant dielectric properties of these ferroelectric polymers. That might be attributed to the small ferroelectric domains generated in the amorphous phase induced by the extension strength, which exhibits a ferro-to para-electric (F-P) transition temperature at 45 °C. The coupling force among the ferroelectric domains (coupling I) and the aligned polymer chains (coupling II) are responsible for the well maintained shape and extension of the stretched samples at ambient temperature. As annealing temperature increases, the extension is gradually recovered for the weakened coupling forces, so does the enhanced dielectric properties. The work reveals that besides the ferroelectric domains in crystal phase, the ferroelectric grains may be generated in amorphous phase by stretching and lead to great contribution to the dielectric property of the PVDF based ferroelectric polymers.

Facile fabrication of crack-free photonic crystals with enhanced color contrast and low angle dependence

Crack-free amorphous photonic crystals, showing high color visibility and low angle dependence, have been fabricated by simple co-assembly.

Effect of Microstructural Changes during Annealing on Thermoelectromotive Force and Resistivity of Electrodeposited Ni85.8Fe10.6W1.4Cu2.2 Alloy

Ni85.8Fe10.6W1.4Cu2.2 alloy powder containing nanocrystals of an FCC-structured solid solution of iron, tungsten, and copper in nickel embedded in an amorphous matrix was electrodeposited from an ammonia citrate solution. The alloy exhibits thermal stability in the temperature range between 25°C and 150°C. Over the range 150−360°C, the alloy undergoes intense structural relaxation which considerably increases the electron density of states and, hence, its electrical conductivity. Less intense structural relaxation takes place at temperatures between 360°C and 420°C. In the temperature range of 420°C to 460°C, relatively more intense changes in the electron density of states at the Fermi level occur, as induced by the structural relaxation resulting from the stabilization of larger less mobile tungsten atoms and copper atoms. The large decrease in electrical resistivity and the high increase in the electron density of states at the Fermi level in the temperature range 460−520°C are due to amorphous matrix crystallization and FCC-phase crystal grain growth.

Effect of annealing and cobalt content on relaxation and crystallization behavior of zirconium based bulk metallic glasses

The effects of annealing and cobalt content on relaxation and the crystallization process of Zr 64 Ni 10 Al 7 Cu 19 bulk metallic glasses were investigated. β-relaxation occurs during annealing, leading to increased endotherm before crystallization. α-relaxation during high temperature annealing (higher than Tg) affects the crystallization process. The introduction of cobalt leads to an inhomogeneous amorphous structure and two-step crystallization due to the positive mixing enthalpy between cobalt and copper. Non-affine thermal strain arising from low temperature annealing of heterogeneous structure leads to a reduced endotherm phenomenon during relaxation on the DSC curves and a reduction in hardness.

Yield behavior of amorphous alloy based on percolation theory

According to the microstructure of amorphous crystal, the percolation theory, which is a theoretical approach to dealing with the inhomogeneous physical systems or random fractals, is used to describe the plastic flows of amorphous alloys under shear yielding. In order to understand in depth the critical problems about the shear band initiations in amorphous alloys, a percolation model for shear transformations of these alloys is established by combining with the existing free volume model and shear transformation zone model. Taking the binary amorphous alloy Cu25Zr75 for example, the percolation threshold for the shearing instability of the atomic clusters prone to producing plastic flows in the shear transformation zone is calculated when a shear band comes into being. In addition, the size of the above-mentioned cluster is also roughly estimated. The calculated results show that the percolation threshold of the shearing instability is similar to the critical reduced free volume value (xC) of~2.4% for the onset of yielding in amorphous alloy although this threshold is closely related to the dispersity of free volume. The present study may provide a new idea and method of studying the ductile-brittle transition in amorphous alloy.

Synthesis and characterization of hybrid iron oxide silicates for selective removal of arsenic oxyanions from contaminated water

A series of hybrid silicates containing iron oxides was synthesized by adding various amounts of iron into silica on the basis of using post precipitation mechanism from aqueous solutions in order to form hydrated iron oxide species (HFO). The obtained materials were characterized by XRD, SEM, TEM, FTIR, Zeta potential and low temperature nitrogen sorption. XRD analysis confirmed that HFO-Si was amorphous and iron oxide crystals in the silica cannot be detected due to the lower size of HFO, which is the probability of its occupied interstitial positions in the silicate matrix. However, TEM image showed the presence of nano-sized HFO located inside the silicate matrix. The adsorption properties and selective efficiency of the synthesized materials were examined with respect to the removal of As(V) and As(III) species from contaminated water under different experimental conditions and in the presence of competing anions. Increasing iron loading enhanced the arsenic adsorption capacity of HFO-Si; the maximum level of arsenic removal was 300mg As/g HFO-Si after 5 successive loads.

Tunneling magnetoresistance in trilayer structures composed of group-IV-based ferromagnetic semiconductor Ge1−xFex, MgO, and Fe

The group-IV-based ferromagnetic semiconductor Ge1−xFex (GeFe) is one of the most promising materials for efficient spin injectors and detectors for Si and Ge. In this study, we show the first successful observation of the tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) containing a group-IV ferromagnetic semiconductor, that is, in MTJs composed of epitaxially grown Fe/MgO/Ge0.935Fe0.065. We find that the p–d(t2) band in GeFe is mainly responsible for the tunneling transport. Although the obtained TMR ratio is small (∼0.3%), the TMR ratio is expected to be enhanced by suppressing leak current through amorphous crystal domains observed in MgO.

Results of Screening of Apparently Healthy Senior and Geriatric Dogs.

BackgroundThere is a growing interest in health care of elderly dogs; however, scientific information about physical and laboratory examination findings in this age group is limited.ObjectivesTo describe systolic blood pressure (SBP), and results of physical examination and laboratory tests in senior and geriatric dogs that were judged by the owner to be healthy.AnimalsHundred client‐owned dogs.MethodsDogs were prospectively recruited. Owners completed a questionnaire. SBP measurement, physical, orthopedic and neurologic examination, direct fundoscopy and Schirmer tear test were performed. Complete blood count, serum biochemistry, and urinalysis were evaluated.ResultsForty‐one senior and 59 geriatric dogs were included. Mean SBP was 170 ± 38 mmHg, and 53 dogs had SBP > 160 mmHg. Thirty‐nine animals were overweight. A heart murmur was detected in 22, severe calculus in 21 and 1 or more (sub)cutaneous masses in 56 dogs. Thirty‐two dogs had increased serum creatinine, 29 hypophosphatemia, 27 increased ALP, 25 increased ALT, and 23 leukopenia. Crystalluria, mostly amorphous crystals, was commonly detected (62/96). Overt proteinuria and borderline proteinuria were detected in 13 and 18 of 97 dogs, respectively. Four dogs had a positive urine bacterial culture. Frequency of orthopedic problems, frequency of (sub)cutaneous masses, and platelet count were significantly higher in geriatric compared with senior dogs. Body temperature, hematocrit, serum albumin, and serum total thyroxine concentration were significantly lower in geriatric compared with senior dogs.Conclusions and Clinical ImportancePhysical and laboratory abnormalities are common in apparently healthy elderly dogs. Veterinarians play a key role in implementing health screening and improving health care for elderly pets.

The Structural Architecture of an Infectious Mammalian Prion Using Electron Cryomicroscopy.

The structure of the infectious prion protein (PrPSc), which is responsible for Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy, has escaped all attempts at elucidation due to its insolubility and propensity to aggregate. PrPSc replicates by converting the non-infectious, cellular prion protein (PrPC) into the misfolded, infectious conformer through an unknown mechanism. PrPSc and its N-terminally truncated variant, PrP 27–30, aggregate into amorphous aggregates, 2D crystals, and amyloid fibrils. The structure of these infectious conformers is essential to understanding prion replication and the development of structure-based therapeutic interventions. Here we used the repetitive organization inherent to GPI-anchorless PrP 27–30 amyloid fibrils to analyze their structure via electron cryomicroscopy. Fourier-transform analyses of averaged fibril segments indicate a repeating unit of 19.1 Å. 3D reconstructions of these fibrils revealed two distinct protofilaments, and, together with a molecular volume of 18,990 Å3, predicted the height of each PrP 27–30 molecule as ~17.7 Å. Together, the data indicate a four-rung β-solenoid structure as a key feature for the architecture of infectious mammalian prions. Furthermore, they allow to formulate a molecular mechanism for the replication of prions. Knowledge of the prion structure will provide important insights into the self-propagation mechanisms of protein misfolding.

Towards novel Cry toxins with enhanced toxicity/broader: a new chimeric Cry4Ba / Cry1Ac toxin.

Attempts have been made to express or to merge different Cry proteins in order to enhance toxic effects against various insects. Cry1A proteins of Bacillus thuringiensis form a typical bipyramidal parasporal crystal and their protoxins contain a highly conserved C-terminal region. A chimerical gene, called cry(4Ba-1Ac), formed by a fusion of the N-terminus part of cry4Ba and the C-terminus part of cry1Ac, was constructed. Its transformation to an acrystalliferous B. thuringiensis strain showed that it was expressed as a chimerical protein of 116kDa, assembled in spherical to amorphous parasporal crystals. The chimerical gene cry(4Ba-1Ac) was introduced in a B. thuringiensis kurstaki strain. In the generated crystals of the recombinant strain, the presence of Cry(4Ba-1Ac) was evidenced by MALDI-TOF. The recombinant strain showed an important increase of the toxicity against Culex pipiens larvae (LC50=0.84mg l-1±0.08) compared to the wild type strain through the synergistic activity of Cry2Aa with Cry(4Ba-1Ac). The enhancement of toxicity of B. thuringiensis kurstaki expressing Cry(4Ba-1Ac) compared to that expressing the native toxin Cry4Ba, might be related to its a typical crystallization properties. The developed fusion protein could serve as a potent toxin against different pests of mosquitoes and major crop plants.

Bipolar switching in chalcogenide phase change memory.

Phase change materials based on chalcogenides are key enabling technologies for optical storage, such as rewritable CD and DVD, and recently also electrical nonvolatile memory, named phase change memory (PCM). In a PCM, the amorphous or crystalline phase affects the material band structure, hence the device resistance. Although phase transformation is extremely fast and repeatable, the amorphous phase suffers structural relaxation and crystallization at relatively low temperatures, which may affect the temperature stability of PCM state. To improve the time/temperature stability of the PCM, novel operation modes of the device should be identified. Here, we present bipolar switching operation of PCM, which is interpreted by ion migration in the solid state induced by elevated temperature and electric field similar to the bipolar switching in metal oxides. The temperature stability of the high resistance state is demonstrated and explained based on the local depletion of chemical species from the electrode region.

Нанотехнологии в машиностроении

For the production of structural steel with a nanostructure there are used methods combined into five groups – powder metallurgy, amorphous state crystallization, intensive plastic deformation, surface and volumetric thermo-deformation treatment. The last method is the most effective one for products subjected to cyclic loads and destructed because of fatigue. A limited longevity at loads exceeding fatigue strength increases ten times and more. A thermo-deformation working is carried out at the production of cylindrical spiral springs, cylindrical parts – shafts, axles, mill rollers.

Survival of the Fittest: Time-To-Event Modeling of Crystallization of Amorphous Poorly Soluble Drugs

The objective of this study was to gain a quantitative understanding of the link between physicochemical properties and long-term and time-censored amorphous stability of poorly water-soluble drugs using parametric time-to-event modeling. Previously published data on amorphous stability and physicochemical properties of 25 structurally diverse neutral, poorly soluble compounds were used. To describe the general shape of the survival curve (probability of event at time >t), Constant, Gompertz, and Weibull hazard functions and their linear combinations were tested. For a selected Weibull hazard base model, the effect of each physicochemical covariate was investigated, with combined influence of enthalpy of fusion (Hf) and molecular weight (Mr) showing the highest statistical significance. The covariate model was used to simulate survival curves and calculate the median survival time for different values of Hf and Mr. It was found that a decrease in Hf or an increase in Mr contribute to longer survival times. The derived model equation was validated against external data sets consisting of 11 compounds. It showed better predictive ability than a previously published multiple linear regression model incorporating Hf and Mr. The proposed Weibull covariate model may assist in faster and more cost-effective decision making in the pre-formulation phase of drug development, where compound properties and appropriate drug formulation strategies are investigated.

Urinalysis in chinchillas (Chinchilla lanigera).

To evaluate urine variables in chinchillas (Chinchilla lanigera). Evaluation study. Urine samples from 41 chinchillas. Voided urine samples were collected from clinically normal chinchillas that were exhibited during a breeder exposition. Urinalysis was performed within 1 hour after collection. Urine specific gravity (USG) was measured before and after centrifugation with a handheld veterinary refractometer. Urine dipstick analysis and microscopic sedimentation examination were performed on all samples. Additionally, a urine sulfosalicylic acid (SSA) precipitation test and quantitative protein analysis were performed on samples with sufficient volume. 17 of 41 (41%) samples had a USG ≥ 1.050, and USG ranged from 1.014 to > 1.060. The USG before centrifugation did not differ significantly from that after centrifugation. Protein was detected in all urine samples on dipstick analysis. The SSA precipitation test yielded negative results for all samples tested. Results of the quantitative protein analyses were not correlated with the results of the dipstick analyses or SSA tests. The recorded pH for all samples was 8.5, which was the upper limit of detection for the reagent strip. Glucose and ketones were detected in 5 and 6 samples, respectively. Crystals were observed in 28 of 41 (68%) samples; 27 of those samples contained amorphous crystals. Urinalysis results for clinically normal chinchillas were provided. For chinchilla urine samples, measurement of USG by refractometry prior to centrifugation is acceptable and protein concentration should be determined by quantitative protein analysis rather than dipstick analysis or the SSA test.

Mercury species, selenium, metallothioneins and glutathione in two dolphins from the southeastern Brazilian coast: Mercury detoxification and physiological differences in diving capacity

In the present study, the concentration of trace elements, total mercury (Hg) and selenium (Se) and mercury forms (MeHg, Hginorg and HgSe) in the vulnerable coastal dolphins Pontoporia blainvillei and Sotalia guianensis were appraised and compared, using metallothioneins (MT) and glutathione (GSH) as biomarkers for trace element exposure. The trace element concentrations varied between muscle and liver tissues, with liver of all dolphin specimens showing higher Hg and Se concentrations than those found in muscle. Hg, MeHg and Hginorg molar concentrations showed a clear increase with Se molar concentrations in the liver of both dolphins, and Se concentrations were higher than those of Hg on a molar basis. Se plays a relevant role in the detoxification of MeHg in the hepatic tissue of both dolphins, forming Hg-Se amorphous crystals in liver. In contrast, MT were involved in the detoxification process of Hginorg in liver. GSH levels in P. blainvillei and S. guianensis muscle tissue suggest that these dolphins have different diving capacities. Muscle Hg concentrations were associated to this tripeptide, which protects dolphin cells against Hg stress.

Amorphous Phase Formation Analysis of Rapidly Solidified CoCr Droplets

This paper investigates amorphous phase formation and rapid solidification characteristics of a CoCr alloy. High cooling rate and high undercooling-induced rapid solidification of the alloy was achieved by impulse atomization in helium atmosphere. Two atomization experiments were carried out to generate powders of a wide size range from liquid CoCr at two different temperatures. Amorphous fraction and kinetic crystallization properties of impulse atomized powders were systematically quantified by means of differential scanning calorimetry. In addition, different but complementary characterization tools were used to analyze the powders microstructures. The fraction of amorphous phase within the investigated powders is found to be promoted by high cooling rate or smaller powder size. The critical cooling rate for amorphous phase formation, which is influenced by the oxygen content in the melt, is found to be ~3 × 104 K s−1 and corresponds to a 160-µm-diameter powder atomized in helium. Hardness of the powders is found to follow a trend that is described by the Hall–Petch relation when a relatively high fraction of crystalline structures is present and decreases with the fraction of amorphous phase.

Self-biased magnetoelectric effect in (Pb, Zr)TiO3/metglas laminates by annealing method

FeBSiC metglas was annealed at an optimized condition (350°C, 5min) to achieve the mixed phases with pristine amorphous phase and crystallization phase. With such annealed metglas, a self-biased magnetoelectric (ME) laminate of metglas/Pb(Zr, Ti)O3/metglas was fabricated. Without any external magnetic field, the composite exhibits the ME coefficient αE31 of 103mV/(cm Oe) at 1kHz and 15.5V/(cm Oe) at electromechanical resonance frequency. The induced ME voltage shows a good linear relation to the applied AC magnetic field with amplitude as low as 10−7T at 1kHz. It is expected that such self-biased ME composites provide a practical application of economical and compact magnetic sensors.

Investigation of crucial synthesis parameters of rich Al-MTT framework zeolite: Toward more determination for synthesis zone of SSZ-32

Synthesis of zeolite materials using small neutral amines has received more attention recently because of the possibility to produce small crystals and lower price as compared other types of organic structured-directing agents (OSDA). For the first time, a precise synthesis zone of SSZ-32 is reported without seeds. Isobutylamine was applied as an OSDA to synthesize SSZ-32 zeolite (MTT framework). The main synthesis parameters such as rotation speed, synthesis time and Si/Al ratio were carefully investigated. The synthesis process was very sensitive to these studied parameters. The SSZ-32 crystals cannot be synthesized in less than 6 days with rotation speed of 35 rpm in a dynamic crystallization. The Si/Al ratio window was narrow as a ratio higher than 27 yielded to form an amorphous powder and quartz crystals. The smallest crystal size produced using isobutylamine was approximately 200 nm, which will be helpful in the elimination of diffusion limitation in the one-dimensional zeolite.

Dynamics anomaly in high-density amorphous ice between 0.7 and 1.1 GPa

We studied high-density amorphous ices between 0.004 and 1.6 GPa by isobaric in situ volumetry and by subsequent ex situ x-ray diffraction and differential scanning calorimetry at 1 bar. Our observations indicate two processes, namely, relaxation in the amorphous matrix and crystallization, taking place at well-separated time scales. For this reason, we are able to report rate constants of crystallization ${k}_{X}$ and glass-transition temperatures ${T}_{g}$ in an unprecedented pressure range. ${T}_{g}$'s agree within \ifmmode\pm\else\textpm\fi{}3 K with earlier work in the small pressure range where there is overlap. Both ${T}_{g}$ and ${k}_{X}$ show a pressure anomaly between 0.7 and 1.1 GPa, namely, a ${k}_{X}$ minimum and a ${T}_{g}$ maximum. This anomalous pressure dependence suggests a continuous phase transition from high- (HDA) to very-high-density amorphous ice (VHDA) and faster hydrogen bond dynamics in VHDA. We speculate this phenomenology can be rationalized by invoking the crossing of a Widom line between 0.7 and 1.1 GPa emanating from a low-lying HDA-VHDA critical point. Furthermore, we interpret the volumetric relaxation of the amorphous matrix to be accompanied by viscosity change to explain the findings such that the liquid state can be accessed prior to the crystallization temperature ${T}_{X}$ at 0.4 GPa and &gt;0.8 GPa.