Pitch Formation Research Articles

Bridge to M4 (B2M4): An innovative residency application preparation curriculum.

The medical residency application process is daunting, time-consuming, and variable, making mentorship in preparation for this process important. In light of changes to the residency application process due to the COVID-19 pandemic, medical students identified a need to create a formal residency application preparation curriculum. The curriculum focused on reflection, while also furthering professional development and preparing for the nuances of the residency application cycle through structured advising. Bridge to M4 (B2M4) included reflective activities to help guide curriculum vitae (CV) refinement, personal and professional values clarification, residency program exploration, elevator pitch formation, personal statement development, mentor identification, guidance on requesting letters of recommendation, and virtual residency interview preparation. The B2M4 elective first took place in June 2020 with 36 rising fourth year students enrolled. Perceived effectiveness of the curriculum was assessed by having student cohorts evaluate the importance of the CV, personal statement, general preparation, and residency program selection before and after the course. Student feedback was reviewed with content analysis, which highlighted the usefulness of a structured residency preparation course that was rooted in reflection and incorporated faculty mentorship and feedback. This student-driven, innovative curricular design provided students the opportunity to prepare for the residency application process through reflective activities including values clarification, strengths identification, and goal setting. B2M4 demonstrates a process that can be used not only during the Residency Match process, but also throughout graduate medical education and future career decisions.

Humidity-Responsive Photonic Films and Coatings Based on Tuned Cellulose Nanocrystals/Glycerol/Polyethylene Glycol.

It has been extensively reported that cellulose nanocrystals (CNCs) can represent structural colors due to their unique chiral-nematic self-assembly. However, the application of this remarkable structure does need further investigation. It has been challenging to keep the selective reflection band (SRB) resulting from the CNC structure in the visible spectrum. Herein, composition of CNC colloidal suspensions with polyethylene glycol (PEG) and glycerol (Gly) have been studied to develop humidity-responsive sensors in the form of coatings and films. The fabricated samples were characterized for their mechanical properties, optical properties, water uptake capacity, water contact angle, and surface roughness. Additionally, the chemical structure of the samples was studied with FTIR spectroscopy. The produced humidity indicators on microbial glass slides were maintained and tested in a different relative humidity range from 20% to 98% with a different color response from blue to red, respectively. The color change of the humidity sensors was reversible for several cycles. It should be noted that the color change can be detected easily by the naked eye. The water uptake test showed that pure CNC and CNC/Gly had the lowest (34%) and highest (83%) water absorption levels. The mechanical tests for CNC/PEG composites showed the highest tensile strength (40.22 MPa). Moreover, microstructural characterizations confirmed the CNC pitch formation in all the samples. Addition of the fillers increased the CNC pitch, resulting in a mesoporous film formation. These produced humidity sensors are promising candidates in food and drug packaging due to their biodegradability, biocompatibility, and cost-effectiveness.

Effects of Bromination-Dehydrobromination on the Microstructure of Isotropic Pitch Precursors for Carbon Fibers.

In this work, isotropic pitch precursors are synthesized by the bromination-debromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and 13C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by bromination-debromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of bromination-dehydrobromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.

Acceleration of petroleum based mesophase pitch formation by PET (polyethylene terephthalate) additive

To improve mesophase formation in petroleum-based pitch, the PET (polyethylene terephthalate) additive reaction was studied. PFO (pyrolysis fuel oil) was used to prepare the petroleum pitch, and PET was added at a weight ratio of 0.33–1.50%. The chemical structure of PET-added pitch was analyzed by Fourier transform infrared spectroscopy, and the thermal properties were characterized by thermogravimetric analysis and the softening point method. Added PET provides oxygen during the pitch synthesis reaction, and the polycondensation of the pitch was accelerated by oxygen crosslinking. Thus, the softening point and carbonization value increased with the amount of PET added; moreover, the mesophase content increased by more than three times with 0.33wt% PET addition. However, at more than 0.67wt% PET addition, the fluidity rapidly decreased, so the mesophase spheres decreased in size and were independently distributed.

Characterizing the Chemical Composition of Lipophilic Extracts from Acacia mearnsii Wood

The chemical composition of Acacia mearnsii wood extract is described in this paper for the first time. This wood is cultivated in Brazil and has been used to complement the demand for hardwood in the pulp industry. In this study, we performed extractions with acetone (total extracts) and dichloromethane (lipophilic extracts responsible for the pitch formation), with the obtained percentages being 1.68 and 0.68%, respectively. The lipophilic extracts were derivatized and analyzed by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) before and after alkaline hydrolysis. The results showed that 57 compounds were detected in the lipophilic extracts and these are mainly constituted by fatty acids ca. 32.8 mg kg-1 and sterols 26.9 mg kg-1. These chemical classes have always been present in pitch deposits in the pulp industry. Therefore, these results may be used by pulp mills to establish strategies for pitch control and represent an important advance in the knowledge of A. mearnsii.

Lipophilic extractives of the wood and bark from Eucalyptus pellita F. Muell grown in Merauke, Indonesia

Lipophilic extractives in the dichloromethane extract from Eucalyptus pellita wood and bark were identified by GC-MS. Of the various morphological parts, the bark samples contain more extractives than wood samples. The largest extractive content was measured in the bark of the top part. Four groups (i.e., free fatty acids, sterols-steroids, triterpenoids, and other compounds) were detected in all parts. Palmitic, oleic, and linoleic acids as well as β-sitosterol dominated among of the lipophilic extractives. Long chain fatty acids were the major lipophilic groups in heartwood. Sterols-steroids were the major components in the bottom and top part of the bark. Conversely, triterpenoids and short chain-fatty acids were the minor components in bottom and top part of the bark. Very long-chain fatty acids (i.e., docosanoic, lignoceric, and hexacosanoic) were also observed. The concentration of certain lipophilic constituents, e.g., stigmast-4-en-3-one, squalene, glycerol, oleic, linoleic, hexacosanoic, and β-sitosterol, was affected by position within the tree in axial and radial directions. The higher concentration of long chain fatty acids in the heartwood as well as sterols-steroids in the bark seems to be clearly disadvantage as far as pitch formation is concerned.

Application of variable teeth pitch face mill as chatter suppression method for non-rigid technological system

The article describes the results of experimental studies on the effects of variation type for variable teeth pitches on low-rigidity workpiece chatter suppression efficiency in a feed direction and in a direction of the normal to the machined surface. Mill operation performance was identified by comparing the amplitudes of dominant chatter harmonics using constant and variable teeth pitches. The following variable pitch formation variants were studied: alternative, linear rising, and linear rising falling. The angle difference of adjacent teeth pitches ranged from 0 to 10°, from 5 to 8° and from 5 to 10° with interval of 1°. The experiments showed that for all variants, machining dynamics performance resulted from the difference of adjacent pitches corresponding to a half the chatter wavelength along the cutting surface. The alternative nature of a variable teeth pitch is most efficient as it almost completely suppresses the chatters. Theoretical explanations of the results are presented

Supramolecular Nanocomposites: Dual‐Functional Cholesteric Hydroxypropyl Cellulose Esters Chemically Linked to Gold Nanoparticles

AbstractFunctionalization of metal nanoparticles with liquid crystal polymers (LCP) is attractive for the formation of supramolecular structures with unique physical properties. We discovered that the chemical linkage of a liquid crystalline thiolated cellulose ester (HPC‐MTP_80) to gold nanoparticles (AuNP) leads, by control of the supramolecular structure, to a novel concept for functional materials with practical applications. At a critical concentration ratio of only 1.7 mol % HPC‐MTP_80, on average, only single HPC‐MTP_80 functionalized AuNP exist, forming a LC phase. Pure HPC‐MTP_80 forms a cholesteric phase with a pitch in the range of visible light. The slow pitch formation enables usage as a protective sealing material. This property in combination with the temperature dependence of the pitch makes HPC‐MTP_80 a perfect sensor for temperature monitoring of sensitive products like valuable pharmaceutics. Even the presence of very small amounts of functionalized AuNP in the nanocomposite suppress the pitch formation in the range of visible light, providing access for a possible application as a sensitive AuNP detector.

Effect of Albino ophiostoma strains on Eucalyptus nitens extractives

Wood extractives promote pitch formation during pulp and paper manufacturing. To date, this problem has been controlled by extended storage of the chips and/or chemical additives. Biotreatment of the wood prior to pulping provides an alternative that not only decreases the negative impact of the extractives but may also improve the kraft pulping efficiency. This initiative seeks to verify the quantity and chemical composition of Eucalyptus nitens wood extractives following biotreatment with three albino fungi species (Ophiostoma floccosum, Ophiostoma piceae and Ophiostoma piliferum). Eucalyptus nitens wood chips were sprayed with spore suspensions of Ophiostoma piliferum, Ophiostoma piceae and Ophiostoma floccosum albino strains (1 × 108 spore concentration). After 7 and 21 days of fungal treatment, the extractive content was determined via Soxhlet extraction with an 80:20% n-hexane:ethyl acetate solvent mixture. The Ophiostoma floccosum F1A94, Ophiostoma piliferum F2D8 and Ophiostoma piceae F2A68 strains proved to be most capable of bioreduction with reductions of 35,1%, 33,2% and 29,3%, respectively. The chemical composition of the extract was analyzed via gas chromatography coupled with mass spectrometry, which demonstrated that most of the tested strains could reduce the s- sitosterol content.

The effect of styrene–butadiene latex carboxylation on adhesion

Styrene–butadiene latices are widely used as binders in pigmented coatings for the paper and board industry. White pitch deposition, which is one type of surface fouling, is a well-known problem at paper machines using coated broke as a raw material. The main component of white pitch is latex, such as styrene–butadiene. The viscoelastic properties of styrene–butadiene latex have been found to affect on white pitch formation, but the effect of carboxylation has not been studied extensively. Carboxylation has traditionally performed to latices in order to increase colloidal stability, but it has also effect on mechanical properties of the latices.In this paper, we studied the adhesion potential of three styrene–butadiene latices by using a cylindrical probe tack method under dry and aqueous conditions while varying the carboxylation degree of the latex. Adhesion potential was measured using low and high energy surfaces as adherents. The results show that carboxylation influences adhesion potential of latices in both dry and aqueous environments.

Effect of site, species and tree size on the quantitative variation of lipophilic extractives in Eucalyptus woods used for pulping in South Africa

Lipophilic wood extractives have serious negative impacts on both pulping process and quality of produced pulp. This study aimed at identifying suitable wood materials for pulping with respect to their lipophilic extractives contents. The effect of site, species and tree sizes on the amount of lipophilic extractives was evaluated. The lipophilic extractives from selected Eucalyptus species used for pulping in South Africa were quantified using gas chromatography–mass spectrometry. It was revealed by the use of analysis of covariance (ANCOVA) that the quantitative variation of lipophilic extractives in Eucalyptus woods is significantly affected by respective sites and tree species. Principal component analysis (PCA) revealed the correlation of the amount of lipophilic extractives in wood materials with tree species/clones and site soil composition. Thus, high amounts of lipophilic extractives were found in Eucalyptus trees grown at sites with a high composition of clay soil and organic matter. Whereas, Eucalyptus dunnii was found to contain a higher amount of lipophilic extractives than Eucalyptus grandis in all the sampled sites, implying an increased risk of pitch formation during the pulping process.

32 nm Half Pitch Formation with High-Numerical-Aperture Single Exposure

According to the International Technology Roadmap for Semiconductors (ITRS), memory half pitch (hp) will reach 32 and 20 nm by 2012 and 2017, respectively. However, it is difficult to fabricate a sub-40 nm node using single-exposure technology with the currently available 1.35-numerical-aperture (NA) ArF immersion lithography. Although it is expected that either double patterning technology or extreme ultraviolet lithography will enable the realization of 32 nm hp, there are still many problems that need to be solved regarding cost reduction. Thus, the study of high-index fluid immersion technology should be pursued simultaneously. ArF water immersion systems with 1.35 NA have already been introduced for 40-nm-hp production. ArF immersion lithography using high-index materials is currently being studied for next-generation lithography. Currently, many studies are being undertaken in order to increase NA for a high-index fluid and a lens in immersion technology. The combination of LuAG (n = 2.14) and a third-generation fluid could be used to realize 1.55 NA. This combination of 0.25k1 and 32 nm hp can be obtained using single-exposure technology. In order to determine the feasibility of this process and possible process hurdles for this high-NA single-exposure technology, 32 nm hp with a 1:1 line and space pattern is tested. Various illumination conditions are tested to realize 1:1 32 nm hp, and the exposure and development conditions are varied to determine whether this single exposure can provide a processible window. As a result, 32 nm hp could be obtained by single-exposure technology with 1.55 NA.

Comparative study on the chemical composition of lipophilic fractions from three wood tissues of Eucalyptus species by gas chromatography-mass spectrometry analysis

Abstract The chemical compositions of lipophilic fractions from Eucalyptus urograndis and Eucalyptus urophylla cultivated in Brazil and Eucalyptus camaldulensis from Mexico were determined by gas chromatography-mass spectrometry (GC-MS) before and after alkaline hydrolysis followed by derivatization. In all fractions, fatty acids (including small amounts of α-and ω-hydroxy fatty acids) and sterols were the most abundant components followed by smaller amounts of long-chain aliphatic alcohols, phenolic acids, and hydrocarbons. The presence of steroid esters and triacylglycerols in all three species was indirectly confirmed by the increased amount of fatty acids and sterols (manly β-sitosterol) in the hydrolyzed fractions compared with the corresponding nonhydrolyzed fractions. The amount of liphophilic compounds (mainly fatty acids and sterols) identified in hydrolyzed fractions of E. urograndis, E. camaldulensis, and E. urophylla corresponded to 1921, 1915, and 634 mg kg−1 of dry matter, respectively. The lower abundance of fatty acids and sterols in the fractions from E. urophylla indicates that problems related to pitch formation will be less severe for this species than for the other two.

Effect of storage time on the composition and content of wood extractives in Eucalyptus cultivated in Brazil

Lipophilic wood extractives commonly referred to as pitch, cause significant problems for the pulp and paper industries. The reduction of these extractives is an important aspect that concerns industries around the world. In the present work the change in the amount and chemical composition of lipophilic extractives from Eucalyptus spp. stored for 20, 40, 60, 100, 140 and 180 days after harvesting was investigated. The results showed a decrease in extractives content with storage time, with the most significant decrease occurring 60 days after harvesting. In addition, fatty acids and sterols were the main classes of compounds responsible for the significant decrease in extractive content. Data were analyzed by principal component analysis. PC1 explains approximately 99% of the total variance, and β-sitosterol was the major compound responsible for the differentiation. These studies demonstrate that in terms of economical aspects, quality of the pulp and paper and minimization of pitch formation, the best period of wood storage is 60 days.

Characterization of lipophilic wood extractives from clones of Eucalyptus urograndis cultivate in Brazil

The chemical compositions of the lipophilic extractives from four clones of Eucalyptus urograndis cultivated in Brazil were studied by gas chromatography-mass spectrometry (GC-MS) before and after alkaline hydrolysis. The four E. urograndis clones showed similar amounts of dichloromethane soluble (lipophilic) extractives (0.38-0.55% w/w). The major groups of compounds identified in the lipophilic fraction of extractives consisted mainly of fatty acids (mainly palmitic linoleic and oleic acids and small amounts of a- and w-hydroxyacids), steroids (mainly b-sitosterol, b-sitostanol), followed by minor amounts long chain aliphatic alcohols, hydrocarbons and aromatic compounds. The relative abundances of these groups were similar for three of the clones with exception of the clone Ugc, which was shown to have much higher amounts of fatty acids and sterols. The high amounts of extractives found in these clones, and particularly of Ugc, when compared with other Eucalyptus species, suggests an increased risk of pitch formation during bleached pulp production.

Caracterização química do "pitch" em indústria de celulose e papel de Eucalyptus

The chemical analysis of the acetone, chloroform, toluene and methanol extracts of a pitch sample was carried out by IR and GC-MS, leading to the identification of sixty nine compounds, including fatty acids, alcohols and hydrocarbons. Analysis of the acetone extractive of a eucalyptus wood used in Brazil for pulp production was also carried out, resulting in identification of fifty nine compounds, including mainly fatty acids, phenolic compounds, b-sitosterol and other steroids. This analysis showed that pitch formation had a contribution from wood extractives and other sources of contamination. The results obtained and the methodology applied can be used by the pulp industry to develop new methods of pitch control.

Effects of borane–pyridine complex on the mesophase pitch formation from decant oil

Mesophase pitches were prepared by adding 0.5 to 2 wt.% of a borane–pyridine complex to a decant oil in a tubing bomb reactor and heating in a fluidized-sand bath held at 500 °C for 30, 45, and 60 min, respectively. The mesophase pitches were analyzed using thermal gravimetric analysis, X-ray diffraction and polarized-light microscopy. Growth and coalescence of mesophase spheres were hindered, while the crystallinity of mesophase pitches was increased when the materials were heat treated with the boron compound. The addition of the borane–pyridine complex also accelerated the coke formation.

Natural clonal variation of wood extractives in Populus tremuloides

Analysis of the potential genetic variation in quaking aspen (Populus tremuloides Michx.) wood extractives was performed by sampling nine natural clones at breast height. Significant clonal differences were found not only in the levels of total acetone extractives but also in the levels of sterols–triterpenes, steryl esters–waxes, and triglycerides, all of which are known to contribute to pitch formation in pulping and papermaking. In addition, extractive compounds known to elicit toxic effects in aquatic organisms showed statistically significant differences between natural aspen clones. In some cases (e.g., flavonoids), these compounds formed a part of the defense system in the living tree and, thus, were affected in part by the presence of decayed wood.

Different modes of pitch perception and learning-induced neuronal plasticity of the human auditory cortex.

We designed a melody perception experiment involving eight harmonic complex tones of missing fundamental frequencies (hidden auditory object) to study the short-term neuronal plasticity of the auditory cortex. In this experiment, the fundamental frequencies of the complex tones followed the beginning of the virtual melody of the tune “Frère Jacques”. The harmonics of the complex tones were chosen so that the spectral melody had an inverse contour when compared with the virtual one. Evoked magnetic fields were recorded contralaterally to the ear of stimulation from both hemispheres. After a base line measurement, the subjects were exposed repeatedly to the experimental stimuli for 1 hour a day. All subjects reported a sudden change in the perceived melody, indicating possible reorganization of the cortical processes involved in the virtual pitch formation. After this switch in perception, a second measurement was performed. Cortical sources of the evoked gamma-band activity were significantly stronger and located more medially after a switch in perception. Independent Component Analysis revealed enhanced synchronization in the gamma-band frequency range. Comparing the gamma-band activation of both hemispheres, no laterality effects were observed. The results indicate that the primary auditory cortices are involved in the process of virtual pitch perception and that their function is modifiable by laboratory manipulation.

Structural features and formation mechanism of soluble fractions of mesophase pitch derived from 1,2,4,5-tetramethylbenzene methylene-bridged oligomer

A mesophase pitch which has 100 vol.% anisotropic content, low softening point, high solubility and good fluidity was prepared at relatively low temperature from 1,2,4,5-tetramethylbenzene oligomers cross-linked by methylene bridges and subsequent heat treatment. Electron impact mass spectrometry, field desorption mass spectrometry and 1H and 13C nuclear magnetic resonance etc. were used to characterize the structural features of soluble fractions of the mesophase pitch. The results show that the mesophase pitch contains many methyls and some amount of naphthenic groups. The molecules in mesophase pitch appear to have kata-type aromatic skeleton. The mechanism of mesophase pitch formation involves intramolecular reactions, and the occurrence of internal oligomer condensation causes the formation of polyacenes which successively di- and trimerize through adjacent methyls to form long-chain kata-type polyaromatics with naphthenic structures. These structural characteristics favour mesophase with excellent properties.