Absence Of Pits Research Articles

Comparative effectiveness research of two glass ionomer cements for primary molar fissure sealing

Relevance. A glass ionomer cement (GIC) is the material for primary teeth fissure sealing in children. The research aimed to study the comparative effectiveness of two GIC pit and fissure sealants in primary molars.Materials and methods. Sixty-one children aged 2-5 years (mean 26.99 ± 0.55 months) participated in the study after obtaining the Local Ethical Committee’s permission and the parents’ informed consents. Non-invasive fissure sealing in primary molars was performed according to split-mouth design with two GIC: Fujy-9, GC, Japan (109 teeth, FV-group) and Polyakrilin, TehnoDent, Russia (106 teeth, PV-group). Follow-ups were provided after 6, 12, 18 and 24 months. Complete retention, partial retention or complete loss (%) of the sealants and the frequency (%) of fissure caries development were calculated. The chi-square criterion was used to assess the significance of the differences between the groups at p-value < 0.05.Results. In 6 and 12 months, all the cases demonstrated complete or partial sealant retention and the absence of pit and fissure caries. The following results were found after 24 months: complete GIC retention in 8.6% of molars in FV-group and 1.9% in PV-group, (p < 0.05), partial retention – 78.8% and 79.0% (p > 0.05) respectively, complete loss – 6.7% and 11.4% respectively (p > 0,05). Fissure carious lesions were found only after 18 and 24 months in 2.8% cases in FV-group and 3.8% cases in PV-group, p > 0,05.Conclusions. Both studied GICs for non-invasive primary molar fissure sealing were equally highly effective for pit and fissure caries prevention in children. Annual follow-ups in children are necessary for GIC sealant repair.

Symbiotic embedment structures in Silurian Caryocrinites (Echinodermata, Rhombifera, Hemicosmitida)

AbstractA variety of pits representing symbiotic embedments, sometimes associated with pathological deformation in the host, are known from the skeletons of Paleozoic stalked echinoderms. These structures are well known from multiple genera of crinoids and a limited number of blastozoans but have not previously been described in detail from the skeletons of rhombiferans. This is surprising given the abundance of rhombiferans in certain deposits, the co-occurrence of rhombiferans with frequently infested taxa, including diploporitans, in multiple assemblages, and the morphological similarity between certain rhombiferan taxa and coeval infested crinoids. The common hemicosmitid rhombiferan Caryocrinites Say, 1825 is widespread throughout the middle Silurian of eastern North America and is herein reported to contain symbiotic (potentially parasitic) embedment structures. Specimens were collected from the lower portion of the mudstone lithofacies of the Massie Formation (Wenlock, Sheinwoodian) at the Napoleon quarry of southeastern Indiana, USA. Strong host specificity is indicated by the absence of pits in C. ornatus Say, 1825 and exclusive infestation of a smaller co-occurring species of Caryocrinites. Thecae with embedment structures are consistently smaller than thecae without such structures, with pitted specimens being restricted to a narrow range of thecal heights (20–24 mm). All embedment structures are present only on the proximal portion of thecae, with individual specimens containing between one and 30 pits. No elevated rims or significant swelling were observed on any specimens, and all pits are relatively small (~1 mm in diameter). The presence of symbiotic embedment structures represents an additional example of a crinoid-like aspect to the ecology of Caryocrinites.

Inferring the role of pit membranes in solute transport from solute exclusion studies in living conifer stems.

The functional role of pits between living and dead cells has been inferred from anatomical studies but amassing physiological evidence has been challenging. Centrifugation methods were used to strip water from xylem conduits, permitting a more quantitative gravimetric determination of the water and solid contents of cell walls than is possible by more traditional methods. Quantitative anatomical evidence was used to evaluate the water volume in xylem conduits and the water content of living cells. Quantitative perfusion of stems with polyethylene glycol of different molecular weight was used to determine the solute-free space. We measured the portioning of water and solute-free space among anatomical components in stems and demonstrated that lignin impeded the free movement of solutes with molecular weight >300. Hence, movement of large solutes from living cells to xylem conduits is necessarily confined to pit structures that permit transmembrane solute transport via primary walls without lignin. The functional role of pits was additionally indicated by combining data in this paper with previous studies of unusual osmotic relationships in woody species that lack pits between dead wood fibers and vessels. The absence of pits, combined with the evidence of exclusion of solutes of molecular weight >300, explains the unexpected osmotic properties.

Performance of nitrogen ion-implanted supermartensitic stainless steel in chlorine- and hydrogen-rich environments

Modified supermartensitic stainless steel surfaces were investigated as protective means against deterioration in Cl−- and H+-rich media. Nitrogen plasma immersion ion implantation at the 300–400 °C range produced top nitride-rich layers (with mainly γ′-Fe4N and ε-Fe2-3N, but also with α′N, according to the treatment temperature) followed by underneath expanded martensite cases. The 400 °C nitrided sample presented the best performance in potentiodynamic polarization tests with NaCl electrolyte, featured by 4.3 times increase in the corrosion potential and the absence of pits, attributed to the thickest and continuous ε-phase containing nitride-rich layer. The hydrogen embrittlement was assessed through cathodic hydrogenation tests. Both reference and 400 °C nitrided surfaces disclosed the phenomenon of intensified plastic flow under normal and tangential loadings. A decrease in hardness, elastic modulus and scratch resistance featured a ductile-to-brittle transition on the nitrided surface, possibly due to improved hydrogen trapping by nitride species with subsequent effects in plasticity. In summary, while the nitride layer played an advantageous role in protecting SMSS from chlorine attack, it was susceptible against the hydrogen corrosion.

PREPARATION OF POLY (METHYL METHACRYLATE) THIN FILMS BY SPIN COATING TECHNIQUE FOR OTFT AND WOUND HEALING APPLICATIONS

Thin films of poly (methyl methacrylate) (PMMA) were prepared on cleaned glass slides by using spin coating technique. The prepared films were identified by using FTIR spectrum. Surface morphology of the coated films was studied by using SEM and AFM. Both as grown and annealed films showed smooth and amorphous structure. It also revealed the absence of pits, pin holes and dendritic features in the surface. Both as grown and annealed films showed very low RMS roughness value. The morphology analysis revealed that the prepared film could be used as dielectric layer in thin film transistors and as drug delivery system forwound healing.

Effect of pitting corrosion on similar and dissimilar alloy welded joints

The present study has been carried out to develop an understanding of GTAW process with heterogeneous base and filler metal compositions. Austenitic stainless steel AISI 316L and high-strength low-alloy CrMoV steel were welded using Inconel 625. To ensure weldability, all joints were nondestructively evaluated by dye penetrant and radiographic testing. Pitting as a defect, in next was simulated on weld bead surface through 1.5-mm-deep mechanically drilled holes of 1 mm diameter. Transverse tensile properties in similar and dissimilar cases and microhardness were studied and correlated with microstructures. AISI 316L in all cases has shown acceptable mechanical properties in the absence of pitting, but a drastic decrease has been found in severe pitting case. Subject defect seems to have a marginal impact on UTS and total elongation on CrMoV steel. The weldments of dissimilar joint have shown peak hardness and produced failure region in both pitting and without pitting cases during tensile testing.

Synergistic Erosion–Corrosion Behavior of X-65 Carbon Steel at Various Impingement Angles

A slurry impingement rig containing 6 wt.% SiO2 particles was used to investigate synergistic erosion–corrosion behavior of X-65 carbon steel at various impingement angles. Maximum erosion–corrosion and erosion rates occurred at impingement angles of about 25 deg and 40–55 deg, respectively. The synergy value highly depended on the impingement angle. The formation of patches of porous corrosion product followed by the formation of corrosion pits led to a positive synergy under impingement angle of 25 deg. At higher impingement angles, the absence of pits probably due to the formation of a more durable tribocorrosion layer resulted in a negative synergy.

Corrosion fatigue behavior of a biocompatible ultrafine-grained niobium alloy in simulated body fluid

The present study reports on the corrosion fatigue behavior of ultrafine-grained (UFG) Niobium 2 wt-% Zirconium (NbZr) alloy in simulated body fluid (SBF). The alloy was processed using multipass equal channel angular processing at room temperature, resulting in a favorable combination of high strength and ductility along with superior biocompatibility and excellent corrosion resistance. Electrochemical measurements revealed stable passive behavior in SBF saline solutions, similar to conventional Ti–6Al–4V alloy. High-cycle fatigue tests showed no alteration in the crack initiation behavior due to the SBF environment, and an absence of pitting and corrosion products. More severe test conditions were obtained in the fatigue crack growth experiments in saline environments. Crack growth rates in UFG NbZr were marginally increased in SBF as compared to laboratory air at a constant test frequency of 20 Hz. Upon a 100 fold decrease in the test frequency, slightly higher crack growth rates were observed only in the near-threshold region. Such excellent corrosion and corrosion fatigue properties of UFG NbZr recommend it as an attractive new material for biomedical implants.

Sensing and control in optical drives how to read data from a clear disc

Optical storage devices, such as the compact disc (CD) and digital versatile disc (DVD), are consumer products with control components. In optical storage, data is represented on a plastic disc by the existence or absence of pits, whose reflective characteristics are different from those of the surrounding disc media. Data is read from the disc by reflecting light off the disc to detect these differences. The maximum data transfer rate is directly related to how well the servo systems perform to keep the read/write elements centered over the desired data and at the correct focus.

Basisphenoid and basioccipital pits in microchiropteran bats

We examined 686 skulls of 420 species of microchiropteran bats in 16 families to assess variation in pits in the basisphenoid and basioccipital bones. A total of 26 measurements were used to describe variation in pits, and patterns in the distribution of pits were examined across the families. Pits were absent from 154 species and present in 266 species. While some species had as many as four basisphenoid pits, basioccipital pits, when present, always occurred as a single pair. No species had more than four pits (basisphenoid or basioccipital and basisphenoid) in total. In some families all species either had pits (e.g. Emballonuridae) or none had pits (e.g. Rhinolophidae), but the incidence of pits usually was variable within families. The results of a cluster analysis of families based on the incidence of pits and morphological features of pits bore little resemblance to a recent phylogeny of Microchiroptera. A discriminant function analysis of features of pits of Emballonuridae, Phyllostomidae, Vespertilionidae and Molossidae correctly classified 66% of species to family revealing some continuity in pit structure among related species. There was no evidence of significant sexual dimorphism in the incidence or features of pits. Basisphenoid and basioccipital pits tended to increase in size with skull size. Neither the incidence nor the morphology of basisphenoid nor basioccipital pits was consistently associated with echolocation, diet or foraging behaviour. Pits were present or absent from species using either high-intensity or low-intensity echolocation calls, and the same was true of bats using high or low duty cycle modes of echolocation. Furthermore, the presence or absence of pits did not correspond to the presence or absence of harmonics in echolocation calls. We propose that basisphenoid and basioccipital pits are oscillators in the vocal tract and contribute to the production of non-linear phenomena in vocalizations made by bats. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78, 215–233.

Corrosion Fatigue Crack Initiation in Aluminum Alloys 7075 and 7050

Mechanisms of corrosion fatigue crack initiation by pitting in high-strength, 7000-series aluminum alloys were studied. The alloys used were Al 7075-T7351 (UNSA97075) and Al 7050-T7451 (UNS A7050). Corrosion pits were formed in a 0.6-M sodium chloride (NaCl) solution by the electrochemical reaction between the constituent particles and the surrounding matrix. Depending on whether these particles were cathodic (C-type) or anodic (A-type) relative to the alloy matrix, pits formed as a consequence of matrix or particle dissolution. In the Al 7075 alloy, C-type and A-type particles were present. In the Al 7050 alloy, only C-type particles were present. The C-type particles were identified, using transmission electron microscopic techniques, as Al23CuFe4 in the Al 7075 alloy and Al7Cu2Fe in the Al 7050 alloy. Because these particles tend to cluster parallel to the rolling plane in the rolling direction, significant pit growth from pit coalescence was observed following prolonged exposure to an aerated 0.6 M NaCl solution. The effect of preexisting corrosion pits on fatigue crack initiation was investigated in an ambient air environment (20°C and 42% relative humidity) using blunt-notch fracture mechanics specimens oriented in the short-transverse direction to obtain cracks in the same orientation as those that grow from rivet holes. Results to date indicate that the presence of corrosion pits can significantly shorten the fatigue crack initiation life and decrease the threshold (ΔK/√ρ)th of the alloy by as much as 50%. Post initiation analyses further confirmed that, when corrosion pits were present, fatigue cracks always initiated from these pits. In the absence of pits, fatigue cracks initiated from large inclusions. Identification of constituent particles, mechanism of pit formation and growth, and analyses of fatigue crack initiation kinetics were discussed.

Effect of halide ions on passivation and pitting Corrosion of copper in alkaline solutions

AbstractThe passivity of copper in NaOH and borate buffer solutions containing chloride, bromide and fluoride ions was studied by using cyclic voltammetry and potentiostatic current transient measurements. At scan rates ≥ 20 mVs−1, the addition of halide ions does not nearly affect the cyclic voltammograms in the absence of pitting. But they differ considerably in presence of pitting. The pitting potential was found to depend on the solution pH and decreased linearly with increase of logarithm of halide ion concentration. The current transients in the passivity as well as in the pitting potential regions were analyzed. Before the pitting, i‐time curves were rather similar to those obtained in the plain solutions. At times > 20 seconds, the current varies linearly with the reciprocal of the square root of time indicating diffusional characteristics of the metal corrosion through the passive layer. In presence of pitting, the pitting current versus time relations fit the Engell‐Stolica equation.

Corrosion behaviour of aluminium in the presence of neutrons and gamma radiations

The corrosion of aluminium has been studied employing the irradiation in situ by neutrons from252Cf and gamma radiations from60Co. The effects of irradiation indicated the absence of pitting, suppression of the corrosion rate, i. e., quantitative reduction in corrosion when measured as weight loss as compared with unirradiated specimens. A protective grayish layer had emerged on the specimen surface which was akin to that formed in simulated experimental conditions carried out in presence of hydrogen peroxide. The possible mechanisms of the elimination of pitting and formation of grayish layer on the surface are discussed.

Colpomenia(Endlicher) Derbès et Solier (Phaecphyta) in New Zealand

Abstract Four species of Colpomenia are recorded for New Zealand: C. bullosa, C. sinuosa, C. peregrina, and C. ecuticulata sp.nov. They are distinguished by thallus shape, the shape of the reproductive sori, the presence or absence of a cuticle over the sori, and the presence or absence of pits in the medulla. Their New Zealand distributions are given, with comments on the world distribution of C. sinuosa and C. peregrina.

Critical Potentials for Pitting Corrosion of Ni, Cr‐Ni, Cr‐Fe, and Related Stainless Steels

Critical pitting potentials for the binary Cr‐Fe and Cr‐Ni alloys in become more noble (correspondingly more resistant to pitting) with increasing content, particularly in the region 25–40% and 10–20% Cr, respectively. The potentials for 57.8% Cr‐Fe and pure Cr fall within the transpassive region. Ni containing 3.2% Mo, to the contrary, shows a lower (more active) critical potential; higher per cent Mo‐Ni alloys appear to fall within the transpassive region corroding anodically as plus Ni++ without pitting. Ni alloyed with 15% Cr‐Fe shifts the potential in the noble direction; Mo alloyed with 15% Cr, 13% Ni stainless steel has a similar but even greater effect. At 0°C, 15% Cr, 13% Ni stainless steel exhibits a potential 0.5v more noble than at 25°C, corresponding to greatly increased resistance to pitting. This shift is less pronounced for the stainless steels containing Mo; in fact, at or above 1.5% Mo, the critical potentials at 0°C are below those at 25° C. In , alloyed Mo shifts the potentials slightly in the active direction, contrary to a marked noble shift in . At 0°C the potentials are still more active. These trends correlate with observed pitting for 15% Cr, 13% Ni stainless steel and the similar alloy containing 2.4% Mo in 10% both at 0° and 25°C. Absence of pitting is observed in 10% at 0°C for 15% Cr, 13% Ni stainless steel, but not for the similar alloy containing 2.4% Mo, which pits. The over‐all results are explained on the basis of competitive adsorption at the metal surface and an effect of temperature on the structure of the double layer.

Effect of the Polarity of the III-V Intermetallic Compounds on Etching

For the III-V intermetallic compounds, the <111> directions are polar axes. The shape of etch pits bounded by crystallographic planes and the presence or absence of pits at dislocations are influenced by the effect of the polar axes on the etch rates. Studies of these effects are reported for several etches on InSb, InAs, GaSb, and GaAs. Correlation of these studies with published x-ray investigations shows that these etches reveal dislocations and truncated pyramidal pits only on {111} surfaces that are at the group III end of the polar axis. A difference in the shape of the pits on opposite {100} surfaces was found and is explained by means of the polar axes.

Chemical Factors Affecting Stress Corrosion Cracking of 18–8 Stainless Steels

Transgranular stress corrosion cracking of 18–8 Type 304 specimens in boiling 42% does not depend on rate of stressing (<1 sec to 10 min) nor on small variations in degree of plastic deformation. Cold worked specimens fail in shorter times than annealed, sheared specimens. Addition of to decreases cracking time whereas addition of increases the time. Pre‐exposure of unstressed specimens to slightly decreases cracking times of the same specimens subsequently stressed. Cracks occur along sheared edges of unstressed specimens despite stress relief anneal at 375°C for 2 hr.Cracks propagate along sheared edges of U‐bend specimens at 0.5 to 1 cm/hr through that portion of the specimen cross section in tension, the rate being much slower through the remaining cross section. No induction time for cracks to initiate was observed.Sizeable pits are not necessary for cracking in , but appear to be essential in media like which in absence of pitting is not particularly active in causing cracking. The pitting mechanism produces concentrated low pH metal chlorides within the pit, which like cause immediate cracking. Oxygen is required for pitting of 18–8 by solutions as shown by Uhlig and Morrill, and hence also for stress corrosion cracking as observed by Williams and Eckel, but oxygen is not necessary in or .Cracking can be prevented by cathodic protection at a CD. of 0.03 ma/cm2 or higher. Anodic CD. up to 0.01 ma/cm2 were found to have no effect on cracking tendency, nor did coupling of 18–8 to Pt.

SPECIALIZATION OF VESSELS WITHIN THE XYLEM OF EACH ORGAN IN THE MONOCOTYLEDONEAE

SPECIALIZATION OF VESSELS WITHIN THE XYLEM OF EACH ORGAN IN THE MONOCOTYLEDONEAE

A New Genus of Mexican Snakes Related to Rhadinaea

ONE of the most interesting and surprising results of the recent intensive herpetological explorations of the valley of Cuautlapan, Veracruz, is the present diminutive species. It adds another to the already imposing list of reptilian species known from this small, rich area. For the privilege of describing it, I am indebted to Dr. E. H. Taylor, who secured the specimens and presented me with one. I wish to express appreciation also for the drawing and for advice he has offered. The species appears to be related to both Rhadinaea and Diadophis. It resembles Rhadinaea in having a capitate hemipenis, long recurved teeth, similar characters of the nasal plate (naris pierced in anterior section, bordered below by a ridge), absence of pits on dorsal scales, and certain other features. It approaches Diadophis in color pattern, character of temporals, and tail proportion. It resembles both in having smooth scales in 17 rows, normal colubrid scales on head (except temporals), and a line through the supralabials. From these two genera it differs in numerous characters. From Rhadinaea it differs in its smaller size, short tail, straight spines on hemipenis, temporals 1 + 1, in color pattern, and in the relatively slight enlargement of the posterior teeth. The absence of pits on the dorsal scales, capitate hemipenis, and nearly homogeneous teeth differentiate it from Diadophis. Despite similarity in size, body form, tail proportion and shape of head of this species and various species of Tantilla, the teeth show no relationship whatever between them. Tantilla also lacks a loreal.