ECONOMETRICA, Issue 3 2009
Whitney K. Newey
Using many moment conditions can improve efficiency but makes the usual generalized method of moments (GMM) inferences inaccurate. Two-step GMM is biased. Generalized empirical likelihood (GEL) has smaller bias, but the usual standard errors are too small in instrumental variable settings. In this paper we give a new variance estimator for GEL that addresses this problem. It is consistent under the usual asymptotics and, under many weak moment asymptotics, is larger than usual and is consistent. We also show that the Kleibergen (2005) Lagrange multiplier and conditional likelihood ratio statistics are valid under many weak moments. In addition, we introduce a jackknife GMM estimator, but find that GEL is asymptotically more efficient under many weak moments. In Monte Carlo examples we find that t -statistics based on the new variance estimator have nearly correct size in a wide range of cases. [source]

EFFECT OF SURFACTANT GEL AND GUM COMBINATIONS ON DOUGH RHEOLOGICAL CHARACTERISTICS AND QUALITY OF BREAD

JOURNAL OF FOOD QUALITY, Issue 5 2004
M.H. AZIZI
ABSTRACT Sodium stearoyl-2-lactylate (SSL), diacetyl tartaric acid esters of monoglyceride (DATEM), glycerol monostearate (GMS) and distilled glycerol monostearate (DGMS) surfactant gels were made with water. Addition of surfactant gels decreased water absorption by the bread while xanthan, karaya, guar and locust bean gums increased the same. Only DGMS or GMS and gum combinations further improved water absorption. All the gums except for guar along with surfactant gels improved dough stability. Both surfactant gels and gums improved the extensograph dough properties of wheat flour to varying degrees. Alveograph characteristics of wheat flour improved to varying extents with surfactant gels while the gums influenced the viscoelastic properties in differing ways. Different combinations of surfactant gels and gums showed varied influences on rapid visco analyzer characteristics of wheat flour. Both surfactant gels and gums improved the bread making quality. Among surfactants, SSL in combination with gums, and among gums locust bean in combination with surfactant gels improved the bread making quality of wheat flour to a maximum extent. [source]

VISCOELASTIC CHARACTERIZATION OF RICE GEL

JOURNAL OF TEXTURE STUDIES, Issue 4 2003
RASHMI JENA
Rice flour dispersions with 15,25% solids were subjected to microwave heating for 0,75 s and samples were subjected to oscillatory frequency sweep between 0.01,10 Hz. The initial rapid increase in storage modulus (G1) with frequency decreased to a plateau at higher frequencies. An increase in G1 and complex viscosity (,*) with an increase in the time of treatment or concentration of solid indicate the extent of sol-gel transformation. The sensory data on hardness, elasticity and stickiness also followed similar trend. Principal component analysis (PCA) of the sensory results indicate that a minimum treatment time of 45 s is needed to achieve a rice gel with acceptable sensory characteristics. The G' values were modeled (0.936 , r , 0.988, P , .01) by the 4-element spring-dashpot model. [source]

MOISTURE SORPTION CHARACTERISTICS of STARCH GELS.

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2004
PART II: THERMODYNAMIC PROPERTIES
ABSTRACT A thermodynamic approach was used to interpret the experimental adsorption and desorption isotherm data for potato starch gel. Calculation of the thermodynamic properties (differential enthalpy, integral enthalpy, differential entropy and integral entropy) provides an understanding of the properties of water and energy requirements associated with the sorption behavior. Isosteric heats (differential enthalpies) were calculated through direct use of moisture isotherms by applying the Clausius-Clapeyron equation. the differential enthalpy and entropy decreased with increasing moisture content and were adequately characterized by an exponential model. A plot of differential heat versus entropy satisfied the enthalpy-entropy compensation theory. the spreading pressure increased with increasing water activity, and decreased with increasing temperature. the net integral enthalpy increased with moisture content to a maximum value (around the monolayer moisture content) and then decreased. In a reverse manner, the net integral entropy decreased with moisture content to a minimum value and then increased. [source]

MEASUREMENT OF BITING VELOCITIES AT PREDETERMINED AND INDIVIDUAL CROSSHEAD SPEED INSTRUMENTAL IMITATIVE TESTS FOR PREDICTING SENSORY HARDNESS OF GELATIN GELS

JOURNAL OF SENSORY STUDIES, Issue 2 2005
M. FINNEY
ABSTRACT Jaw movements during the act of biting were measured for seven subjects trained in descriptive analysis using an electrognathograph. The effectiveness of instrumental imitative tests performed at predefined and individual crosshead speeds (matching velocities measured in vivo) to predict the perception of hardness in 14 gelatin gels was assessed. For all seven subjects, the perception of hardness was adequately described by imitative instrumental tests performed with dental replicas of individual subjects (0.88 < R < 0.97). For some of the subjects, tests performed at crosshead speeds matching biting speeds improved the instrumental prediction of hardness, suggesting that biting velocity is an important aspect of the perception of hardness in food. [source]

CHARACTERISTICS OF GELLAN GUM BASED FOOD GELS

JOURNAL OF TEXTURE STUDIES, Issue 4 2010
DIPJYOTI SAHA
ABSTRACT Fruit-based gels with gellan gum as the gelling agent was prepared. Textural attributes of the gellan gum gels, formed with different concentrations of the gum (0.5,3.0%) and sugar and/or pineapple juice, were determined employing the methods of large-deformation uniaxial compression and stress relaxation. Fracture stress/energy markedly increases with an increase in the concentration of gellan gum while fracture strain exhibits a marginal effect. The change in these compressive textural parameters is more pronounced for sugar added samples compared with gels without sugar. Marked decay in stress relaxation curves was observed; the extent of relaxation decreases marginally with an increase in gum content up to 2% but shows much lesser values beyond 2% addition. The sugar added samples exhibit lesser relaxation characteristics but higher relaxation times indicating elastic characteristics compared with samples without sugar. Use of gellan gum provides an innovative method for developing fruit juice based gels as a convenience food because of attractive transparent appearance and textural attributes. PRACTICAL APPLICATION The use of hydrocolloids like gellan gum can develop fabricated foods in the form of fruit juice based gels having unique textural properties. These properties can be altered to suit the consumer preference by varying the proportions of gellan gum, fruit juice and sugar. The results in the present investigation arising from compression and relaxation testing thus help in characterizing the developed gels. [source]

OSCILLATING VANE GEOMETRY FOR SOFT SOLID GELS AND FOAMS

JOURNAL OF TEXTURE STUDIES, Issue 6 2002
C. SERVAIS
ABSTRACT Several relationships between the torque and the stress exist for the vane geometry, but only a few equations have been proposed for the relationship between angular displacement and strain. In this study, an expression based on the infinite gap approximation for concentric cylinders is used and well-defined reference data are compared to oscillating vane data to validate the assumptions used. Gelatin gels are used for their property to stick to the wall and carrageenan gels are used to show that wall slip does not occur with oscillating vanes in serrated cup geometries. Shaving foams are used as a model low density, time and shear stable foam, which resists irreversible damage when loaded between serrated parallel plates. Results show that the assumptions used for the determination of stress and strain with the vane provide material viscoelastic properties that are not significantly different from reference values as obtained with concentric cylinders and parallel plates. [source]

ELECTROSTATIC EFFECTS ON PHYSICAL PROPERTIES OF PARTICULATE WHEY PROTEIN ISOLATE GELS

JOURNAL OF TEXTURE STUDIES, Issue 4 2001
MATTHEW K. McGUFFEY
Physical properties of particulate whey protein isolate gels formed under varying electrostatic conditions were investigated using large strain rheological and microstructural techniques. The two treatment ranges evaluated were adjusting pH (5.2-5.8) with no added NaCl and adjusting the NaCl (0.2-0.6 M) at pH 7. Gels (10% protein w/v) were formed by heating at 80C for 30 min. The large strain properties of fracture strain (,f), fracture stress (,f), and a measure of strain hardening (R0.3) were determined using a torsion method. Gel microstructure was evaluated using scanning electron microscopy (SEM) and gel permeability (Bgel). Overlaying ,f and ,f curves for pH and NaCl treatments demonstrated an overlap where gels of equal ,f and ,f could be formed by adjusting pH or NaCl concentration. The high fracture stress (,f, 23 kPa and ,f, 1.86) pair conditions were pH 5.47 and 0.25 M NaCl, pH 7.0. The low fracture stress (,f, 13 kPa and ,f, 1.90) pair conditions were pH 5.68 and 0.6 M NaCl, pH 7.0. The 0.25 M NaCl, pH 7 treatment demonstrated higher R0.3 values than the pH 5.47 treatment. When the sulfhydryl blocker n-ethylmaleimide was added at 2 mM to the 0.25 M NaCl, pH 7 gel treatment, its rheological behavior was NSD (p>0.05) to the pH 5.47 gel treatment, indicating disulfide bond formation regulated strain hardening. Altering surface charge or counterions, and disulfide bonding, was required to produce gels with similar large strain rheological properties. An increase in gel permeability coincided with an increase in pore size as observed by SEM, independent of rheological properties. This demonstrated that at the length scales investigated, microstructure was not linked to changes in large strain rheological properties. [source]

EFFECT OF HEN EGG PRODUCTION AND PROTEIN COMPOSITION ON TEXTURAL PROPERTIES OF EGG ALBUMEN GELS

JOURNAL OF TEXTURE STUDIES, Issue 2 2001
MARIANNE HAMMERSHØJ
The effect of hen age, strain and dietary amino acid intake on the egg albumen gel textural properties was studied in two experiments by textural profile analysis (TPA) and uniaxial compression (UC) tests. In experiment 1, eggs from 4 different hen flocks were heat processed industrially. Egg rejection due to poor albumen gelling was correlated to hen age (r = 0.502), albumen dry matter (r =,0.632), gel hardness of 1st compression (r =,0.765), and gel work of 1st compression (r =,0.740) in TPA. In experiment 2 two hen strains, representing two levels of egg production, were fed diets with supplementation of L-lysine, methionine or both amino acids compared to a control diet. The lysine intake ranged from 818,1272 mg/hen/day and methionine intake from 377,575 mg/hen/day among hen groups, but without significant effect on the albumen gel texture parameters. The hen strains differed significantly in egg production (P<0.001), physical (P<0.001), chemical (P<0.05) and gel textural parameters of egg albumen (P<0.01). Hen age was essential, and correlated to the industrial egg rejection (r = 0.729), albumen dry matter (r =,0.902) and gel stress at fracture (r =,0.884). Albumen gels with high fracture stress values were found to contain a modified form of ovofransferrin. [source]

SENSORY CHARACTERIZATION OF TEXTURE AND FLAVOR OF HIGH VISCOSITY GELS MADE WITH DIFFERENT THICKENERS,

JOURNAL OF TEXTURE STUDIES, Issue 4 2000
NIINA KÄLVIÄINEN
ABSTRACT Four thickeners (pectin, gelatin, starch and gelatin + starch) and two aroma concentrations (1.4 and 0.7 mL aroma / 1 kg candy base) were used for manufacturing high viscosity gel systems, i.e. strawberry candies. The salient texture and flavor attributes of the samples were identified and evaluated by a trained descriptive panel. The thickeners strongly affected texture and flavor attributes of the samples, while the two aroma concentrations did not differentiate between samples. Each thickener used produced its own characteristic texture. The gels with weak and fragile texture had stronger flavor intensities and tart flavor than the gels with strong and cohesive texture. Because of the strong interaction between texture and flavor, the results have major implications for the production of high viscosity gels such as candies. [source]

MECHANICAL PROPERTIES OF TWO-PHASE DISPERSE AGAR/GELATIN MIXED GELS

JOURNAL OF TEXTURE STUDIES, Issue 3 2000
KEIKO FUJII
ABSTRACT Agar/gelatin mixed gels with the same composition but with a different two-phase disperse structure were prepared and their mechanical properties compared. The agar/gelatin mixture was first kept at temperature above the gelling temperature of gelatin but below that of agar and stirred for the selected period, before cooling it below the gelling temperature of gelatin. For the low rupture stress system the agar concentration was 0.7% (w/w), while the gelatin concentration was 4.5% (w/w) to achieve the same rupture stress as the agar gel. The mixing temperatures selected were 20 and 37C. For the high rupture stress system, the agar and gelatin concentration was 2.8 and 10.4% (w/w), respectively, to achieve the same rupture stress. The mixing temperatures selected were 37 and 40C. The both mixed gels prepared by this method consisted of a dispersed phase of agar and a continuous phase of gelatin. The rupture stress of the mixed gels decreased as the content of the dispersed phase increased. The rupture stress had a tendency to be lower as the size of the dispersed particles increased. These results suggest that the interface between the dispersed phase and the continuous phase plays an important role as Griffith's crack, with the rupture of mixed gels occurring from that place. [source]

Allergic contact dermatitis from a hydrogel dressing (Intrasite® Gel) in a patient with scleroderma

CONTACT DERMATITIS, Issue 6 2004
Jung Eun Lee
No abstract is available for this article. [source]

Lubricating Gel as an Aid to Coat the Passage of 6/0 Polyglactin 910 (Vicryl Rapide)

DERMATOLOGIC SURGERY, Issue 11 2008
TANG CHEE LIAN ADV DIPL.
No abstract is available for this article. [source]

Complications from Injectable Polyacrylamide Gel, a New Nonbiodegradable Soft Tissue Filler

DERMATOLOGIC SURGERY, Issue 12p2 2004
Snehal P. Amin
Background. Polyacrylamide gels, containing a hydrogel composed of polyacrylamide and water, are used for soft tissue augmentation and contour correction. There are no reports of significant complications after injection of this material into the face. Objective. We report an inflammatory reaction after injection of polyacrylamide gels for zygomatic facial augmentation. Methods. A retrospective chart review of single case is presented. Results. An inflammatory reaction at the sites of polyacrylamide gels injection was noted at 1 month after initial injection. Despite two ensuing courses of broad-spectrum antibiotics, the patient presented to us with persistent draining nodules. Intralesional steroid injections resulted in prompt resolution and no recurrence. Conclusion. Inflammatory reactions have been noted in patients receiving polyacrylamide gels for breast augmentation. Facial polyacrylamide gels injections may also be associated with an inflammatory reaction that responds to intralesional steroids. With increasing availability of a variety of soft tissue fillers, dermatologists should be aware of this delayed complication from polyacrylamide gels. [source]

Stripping Voltammetry of Cerium(IIl) with a Chemically Modified Carbon Paste Electrode Containing Functionalized Nanoporous Silica Gel

ELECTROANALYSIS, Issue 2 2008
Mehran Javanbakht
Abstract This research introduces the design of an adsorptive stripping voltammetric method for the cerium(III) determination at a carbon paste electrode, chemically modified with dipyridyl-functionalized nanoporous silica gel (DPNSG-CPE). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ,200,mV followed by the electrochemical detection of the Ce(III)/dipyridyl complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (1.0,28,ng mL,1). The precision for seven determinations of 4 and 10,ng mL,1 Ce(III) was 3.2% and 2.5% (relative standard deviation), respectively. The prepared electrode was used for the cerium determination in real samples and very good recovery results were obtained. [source]

Preparation and properties of ,-chitin-whisker-reinforced hyaluronan,gelatin nanocomposite scaffolds

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010
Parintorn Hariraksapitak
Abstract Tissue scaffolds made of naturally derived polymers present poor mechanical properties, which may limit their actual utilization in certain areas where high strength is a key criterion. This study was aimed at developing tissue scaffolds from a 50 : 50 w/w blend of hyaluronan (HA) and gelatin (Gel) that contained different amounts of acid-hydrolyzed ,-chitin whiskers (CWs) by a freeze-drying method. The weight ratios of the CWs to the blend were 0,30%. These scaffolds were characterized for their physical, physicochemical, mechanical, and biological properties. Regardless of the CW content, the average pore size of the scaffolds ranged between 139 and 166 ,m. The incorporation of 2% CWs in the HA,Gel scaffolds increased their tensile strength by about two times compared to those of the other groups of the scaffolds. Although the addition of 20,30% CWs in the scaffolds improved their thermal stability and resistance to biodegradation, the scaffolds with 10% CWs were the best for supporting the proliferation of cultured human osteosarcoma cells (SaOS-2). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

The anesthetic onset and duration of a new lidocaine/prilocaine gel intra-pocket anesthetic (Oraqix®) for periodontal scaling/root planing

JOURNAL OF CLINICAL PERIODONTOLOGY, Issue 5 2001
Johan Friskopp
Abstract Background: A new non-injection anesthetic, lidocaine/prilocaine gel (Oraqix®, AstraZeneca) in a reversible thermosetting system, has been developed to provide local anesthesia for scaling/root planing (SRP). The aim of this study was to determine the anesthetic onset and duration of the gel for SRP in patients with periodontitis. Methods: 30 patients were randomized to either 30 s, 2 min, or 5 min of treatment with the gel prior to SRP of a tooth. The gel was applied to periodontal pockets with a blunt applicator. On completion of the SRP of each tooth (2,3 teeth treated/patient), the patients rated their pain on a 100-mm visual analogue scale (VAS). Results: The median VAS pain score was 7.5 mm in the 30-s group, 28.5 mm in the 2-min group, and 15.5 mm in the 5-min group, with a significant difference between the 30-s and 2-min groups (p=0.03). In 2 patients in the 5-min group, but none in the other groups, the SRP was interrupted due to pain. The mean duration of anesthesia measured as pain on probing were 18.1, 17.3, and 19.9 min in the 30-s, 2-min, and 5-min groups, respectively. There were no reports of numbness of the tongue, lip, or cheek, neither were there any adverse local reactions in the oral mucosa. The gel was easy to apply and did not interfere with the SRP procedure. Conclusion: Oraqix® provides anesthesia after an application time of 30 s, with a mean duration of action of about 17 to 20 min. Zusammenfassung Hintergrund: Eine neues nicht zu injizierendes Anästhetikum, Lidocain/Prilocain Gel (Oraqix®, Astra Zeneca) in einem reversiblen thermischen System, wurde entwickelt, um die lokale Anästhesie für die Wurzelreinigung und -glättung (SRP) zu verbessern. Das Ziel dieser Studie war die Bestimmung des Anästhesieeintrittes und der -dauer durch dieses Gel bei SRP bei Parodontitis-Patienten. Methoden: 30 Patienten wurden zufällig zur 30 Sekunden, 2 Minuten oder 5 Minuten Behandlung mit dem Gel vor der SRP eines Zahnes eingeteilt. Das Gel wurde mit einem stumpfen Applikator in die parodontalen Taschen appliziert. Nach der Vollendung der SRP eines jeden Zahnes (2,3 behandelte Zähne/Patient) beurteilten die Patienten ihre Schmerzen auf einer 100 mm visuellen Analogskala (VAS). Ergebnisse: Der mittlere VAS Score war 7.5 mm in der 30 Sekundengruppen, 28.5 mm in der 2 Minutengruppe und 15.5 mm in der 5 Minutengruppe mit einer signifikanten Differenz zwischen der 30 Sekunden und der 2 Minutengruppe (p=0.03). Bei 2 Patienten in der 5 Minutengruppe, aber keinem in einer anderen Gruppe, wurde das SRP wegen Schmerzen unterbrochen. Die mittlere Dauer der Anästhesie, gemessen als Schmerz auf Sondierung, war 18.1, 17.3 und 19.9 Minuten in der 30 Sekunden, 2 Minuten und 5 Minutengruppe. Es gab keine Berichte über eine Taubheit der Zunge, der Lippen oder der Wangen. Irgendwelche negativen lokalen Reaktionen an der Mukosa wurden nicht beobachtet. Das Gel war leicht zu applizieren und beeinflußte die SRP Prozedur nicht. Zusammenfassung: Oraqix® fördert die Anästhesie nach Applikation von 30 Sekunden mit einer mittleren Dauer von ungefähr 17 bis 20 Minuten. Résumé Un nouvel anesthésique non-injectable, un gel de lidocaine/prilocaine (Oraquix®, AstraZeneca) dans un système thermique réversible a été mis au point afin de créer une anesthésie locale lors du détartrage et du surfaçage radiculaire (SRP). Le but de cette étude a été de déterminer la prise et la durée anesthésique de ce gel pour le SRP chez des patients avec parodontite. 30 patients ont été traités avec ce gel pendant 30 s, 2 min ou 5 min avant le SRP d'une dent. Le gel a été placé dans les poches parodontales avec un applicateur arrondi. A la fin du SRP de chaque dent (2 à 3 dents traitées par patient) les patients ont quantifié leur douleur sur une échelle analogue visuelle de 100 mm (VAS). Le score de douleur VAS moyen était de 7.5 mm dans le groupe de 30 s, 28.5 mm dans le groupe 2 min et de 15.5 min dans celui de 5 min avec une différence significative entre les groupes 30 s et 2 min (p=0.03). Chez 2 patients du groupe 5 min mais chez aucun des 2 autres groupes le SRP a été interrompu à cause de la douleur. La durée moyenne d'anesthésie mesurée en tant que douleur au sondage était respectivement de 18.1, 17.3 et 19.9 min pour les groupes 30 s, 2 min et 5 min. Il n'y a eu aucune plainte d'anesthésie de la langue, des lèvres ou des joues ni aucune réaction locale négative de la muqueuse buccale. Le gel a été facilement appliqué et n'a absolument pas gêné le SRP. L'Oraquix® apporte une anesthésie après un temps d'application de 30 s avec une durée d'action de 17 à 20 min. [source]

Characteristics of Sarcoplasmic Proteins and Their Interaction with Surimi and Kamaboko Gel

JOURNAL OF FOOD SCIENCE, Issue 1 2009
A. Jafarpour
ABSTRACT:, This study examined the effect of adding common carp sarcoplasmic proteins (Sp- P) on the gel characteristics of threadfin bream surimi and kamaboko while maintaining constant moisture and myofibrillar levels. Based on the temperature sweep test, which is involved in heating of surimi gel from 10 to 80 °C to monitor the viscoelastic properties, at temperature range of 40 to 50 °C, the decrease level (depth of valley) in storage modulus (G,) thermograph was in proportion to the concentration of added Sp- P. Storage modulus (G,) showed greater elasticity after adding Sp- P compared with the control without Sp- P. Furthermore, the breaking force and distance and consequently gel strength of the resultant kamaboko were improved significantly (P > 0.05). Thus, added Sp- P did not interfere with myofibrillar proteins during sol,gel transition phase but associated with textural quality enhancement of resultant kamaboko; however, addition of Sp- P from the dark muscle of the carp decreased the whiteness of the resultant surimi. Furthermore, according to the SEM micrographs, the gel strength could not be associated with either the number of polygonal structures/mm2 or the area of the polygonal structures in the kamaboko gel microstructure. [source]

Physicochemical Changes in Alaska Pollock Surimi and Surimi Gel as Affected by Electron Beam

JOURNAL OF FOOD SCIENCE, Issue 1 2004
J. JACZYNSKI
ABSTRACT: Alaska pollock surimi and surimi gels (cooked) were subjected to various doses of electron beam (e-beam). Shear stress of surimi gels increased as the dose increased up to 6 to 8 kGy and then decreased. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed gradual degradation of myosin heavy chain as the dose increased. The degradation was slower for frozen samples. The integrity of actin was slightly affected by high doses (25 kGy). The amount of sulfhydryl groups and the level of surface hydrophobicity of Alaska pollock surimi decreased as the dose increased, suggesting formation of disulfide bonds and hydrophobic interactions. The sulfhydryl groups and hydrophobicity of surimi gels increased as the dose increased up to 6 kGy and then decreased. [source]

Influence of Cooling Rate on Glass Transition Temperature of Sucrose Solutions and Rice Starch Gel

JOURNAL OF FOOD SCIENCE, Issue 6 2003
C.-L. Hsu
ABSTRACT: The study's objectives were to determine the influence of cooling rate through the primary zone of freezing on Tg in sucrose solutions and rice starch gels. The influence of cooling rate, water content, and annealing on Tg were evaluated. Results indicated that the observed Tg values for sucrose solutions were lower after rapid cooling (70% solids: rapid cooling ,66.7°C; slow cooling ,64.6 °C; 30% solids: rapid cooling ,34.6 °C; slow cooling ,33.3 °C). The Tg values of annealed samples are higher than the Tg of both rapidly and slowly cooled samples (70%: ,44.2 °C; 30%: ,32.7 °C). The Tg of the rice starch gel was ,9.0 °C after rapid cooling and ,7.5 °C after slow cooling. [source]

Role of Hydrodynamically Active Biopolymeric Ingredients in Texture Modification and Physical Stabilization of Gel-based Composite Foods

JOURNAL OF FOOD SCIENCE, Issue 3 2002
C.M. Lee
ABSTRACT: Unlike synthetic polymer composites, a large amount of water is required for composite foods and needs to be managed by the use of water-binding (hydrodynamically active) biopolymeric ingredients for texture and physical stabilization. "Hydrodynamic properties" encompass the dynamics of water binding/retention and the distribution between particulates and the matrix, and are responsible for the composite effect. The extent of reinforcement depends on their hydrodynamic and surface properties, volume fraction, size, and shape. Moisture management and the control of texture and physical stability in gel-based composites can be achieved by understanding the interrelationships among the physical parameters governing matrix and dispersed particulates. Such understanding will facilitate the introduction of new composite products with improved texture and storability, as well as improve the functional properties of biopolymeric ingredients through appropriate modification of hydrodynamic properties. [source]

Kinetic Study of Thermally Induced Inulin Gel

JOURNAL OF FOOD SCIENCE, Issue 7 2001
Y. Kim
ABSTRACT: Heated inulin solution undergoes a sol-gel transition during cooling and forms a white smooth gel under optimized conditions. The degree of gel formation is negatively related to hydrolysis of inulin during heating. Heating makes inulin soluble; overheating causes hydrolysis of dissolved inulin into smaller molecules. Using a 2-step model including a solubilization step and a hydrolysis of inulin step, we found that both steps follow pseudo first-order kinetics. Separate studies on initial rates of the solubilization and hydrolysis of inulin steps at constant temperatures show that the solubilization rate of inulin is much faster than that of the hydrolysis of inulin. Gel formation of inulin may be related to the average chain length of inulin after heating. [source]

A Novel Hybrid Method of Sol,Gel and Ultrasonic Atomization Synthesis and Piezoelectric Properties of SrBi4Ti4O15 Ceramics

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008
Zhijun Xu
SrBi4Ti4O15(SBTi) powders were synthesized by a novel hybrid method of sol,gel and ultrasonic atomization. TiO2 particle was used as a starting material to replace other expensive soluble titanium salts. X-ray diffraction results showed that the pure-phase SBTi powders were obtained at 700°C for 2 h, which is much lower than the calcination temperature (800°,850°C) required in solid-state reactions. The ceramics sintered at 1100°C for 1 h exhibited 94.5% of relative density and a piezoelectric coefficient of 21 pC/N. The results showed that this hybrid method could lead to an attractive method for the industrial fabrication of SBTi materials. [source]

Improved Aging Characteristics of NTC Thermistor Thin Films Fabricated by a Hybrid Sol,Gel,MOD Process

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006
Dmitry A. Kukuruznyak
Negative temperature coefficient thermistor oxide thin films with improved aging characteristics are described. Better thermal stability has been achieved by incorporating sol,gel techniques with metallo-organic decomposition methods. A compositional range was identified whereby borosilicate may incorporate into the thermistor oxides, forming nanocomposites showing thermistor electrical characteristics. Thermistor thin films, with composition Ni0.48Co0.24Cu0.6Mn1.68O4·0.22SiO2·0.15B2O3 were deposited onto glass substrates from a solution containing organic transition metal salts, tetraethyl orthosilicate and triethyl borate. Electrical resistance measurements verified characteristic thermistor behavior. Nanocomposite thin films exhibited a factor of four improvement as compared with pure oxides after aging at 150°C for 500 h. [source]

Low-Temperature Synthesis of Fully Crystallized Spherical BaTiO3 Particles by the Gel,Sol Method

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004
Un-Yeon Hwang
The synthesis of spherical BaTiO3 particles was attempted by a new technique, the "gel,sol method," at 45°C. The (Ba,Ti) gel used as a starting material was prepared by aging mixtures of titanyl acylate with a barium acetate aqueous solution ([glacial acetic acid (AcOH)]/[titanium isopropoxide (TIP)] = 4, [barium acetate]/[TIP] = 1) at 45°C for 48 h. Potassium hydroxide (KOH) was used as a catalyst for the formation of BaTiO3. Powder X-ray diffractometry (XRD) results and Fourier-transform infrared (FT-IR) measurements for the (Ba,Ti) gel showed that the gel was amorphous, but the spatial arrangement of barium and titanium in the (Ba,Ti) gel is similar to that in crystalline BaTiO3 particles. Fully crystallized spherical BaTiO3 powder with a particle size of 40,250 nm formed at the very low reaction temperature of 45°C. Scanning electron microscopy images showed that the final particles formed via aggregation of the fine particles that seem to be the primary particles of bulk (Ba,Ti) gel. From the XRD, FT-IR, and Raman spectroscopy analysis, it was found that the crystal structure of the as-prepared particles continuously transformed from cubic to tetragonal as the calcination temperature increased, and high crystalline tetragonal BaTiO3 phase was obtained at 1000°C after 1 h of heat treatment. [source]

Influence of Grafting on the Solution Properties and the Dissociation Behavior of Ionic/Nonionic Grafted Copolymers

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2007
Jens Weber
Abstract A new synthetic approach towards grafted terpolymers based on a poly[(methyl vinyl ether)- alt -(maleic anhydride)] backbone and poly(ethylene glycol) monomethyl ether (MPEG) side chains is presented. Resulting comb polymers with controllable grafting degree still have highly reactive anhydride moieties along the polymer backbone, as proved by IR spectroscopy. Grafting degree depends on the anhydride hydroxide stoichiometric ratio. It is not influenced by the molecular weight of MPEG. An increase in the grafting degree leads to a contraction of the polymer in the solution. Evaluation of potentiometric titration data gave a deeper insight into the dissociation process. The copolymers showed a two-step dissociation behavior. No significant influence of the grafting degree on the acidic strength was observed, whilst there is a strong effect of the grafting degree on the free energy change upon neutralization ,Gel. Grafting leads to a higher change in free energy ,Gel,1 for the first step but to lower ,Gel,2 required for the second step. [source]

A Thermosensitive and Biodegradable Physical Gel with Chemically Crosslinked Nanogels as the Building Block

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2008
Zigang Yang
Abstract A triblock copolymer, poly(ethylene glycol),poly(propylene glycol),poly(ethylene glycol) was end-capped by acryloyl groups using a biodegradable oligolactide as spacer, and such biodegradable amphiphilic macromers could form micelles in water. A nanogel was prepared via polymerizing macromers in a micelle, and a macroscopic physical gelation was found upon heating a concentrated aqueous nanogel suspension. Such a sol,gel transition with a chemically crosslinked nanogel as the building block was thermoreversible. While the hydrogel affords a promising injectable biomaterial; this research reveals new physics of the thermogelling mechanism of amphiphilic block copolymers. [source]

Self-Similar Wave of Swelling/Collapse Phase Transition along Polyelectrolyte Gel

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2004
Andrey Yu.
Abstract Summary: Theoretical analysis of the possibility of collapse/swelling phase transition propagation along a polyelectrolyte gel thread has been performed. A differential equation that determines the time dependence of the degree of swelling of polymer thread under the radial mechanical force has been obtained. It formally coincides with the equation of diffusion of an impurity in a medium with a certain source density that depends on excluded-volume and Coulomb interactions, osmotic pressure of counterions, and entropy of the subchains. Two stationary points of this equation correspond to contracted and swollen states. It has been shown that once activated, the phase transition between these stationary points could propagate along the thread in the form of a wave with positive speed if the initial state is characterized by a higher level of free energy than the final state. The results of numerical calculations illustrating the process of phase transition propagation along polyelectrolyte gel thread show that propagation of the swelling/collapse phase transition takes place in the form of the stepwise self-similar wave with steep front. The sharp boundary between swollen and collapsed zones is observed and does not tend to dissipate as propagation proceeds. [source]

Hierarchical analysis of large-scale two-dimensional gel electrophoresis experiments

PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 10 2003
Amit Rubinfeld
Abstract Large-scale two-dimensional gel experiments have the potential to identify proteins that play an important role in elucidating cell mechanisms and in various stages of drug discovery. Such experiments, typically including hundreds or even thousands of related gels, are notoriously difficult to perform, and analysis of the gel images has until recently been virtually impossible. In this paper we describe a scalable computational model that permits the organization and analysis of a large gel collection. The model is implemented in Compugen's Z4000Ô system. Gels are organized in a hierarchical, multidimensional data structure that allow the user to view a large-scale experiment as a tree of numerous simpler experiments, and carry out the analysis one step at a time. Analyzed sets of gels form processing units that can be combined into higher level units in an iterative framework. The different conditions at the core of the experiment design, termed the dimensions of the experiment, are transformed from a multidimensional structure to a single hierarchy. The higher level comparison is performed with the aid of a synthetic "adaptor" gel image, called a Raw Master Gel (RMG). The RMG allows the inclusion of data from an entire set of gels to be presented as a gel image, thereby enabling the iterative process. Our model includes a flexible experimental design approach that allows the researcher to choose the condition to be analyzed a posteriori. It also enables data reuse, the performing of several different analysis designs on the same experimental data. The stability and reproducibility of a protein can be analyzed by tracking it up or down the hierarchical dimensions of the experiment. [source]

Supramolecular Hydrogels and High-Aspect-Ratio Nanofibers through Charge-Transfer-Induced Alternate Coassembly,

ANGEWANDTE CHEMIE, Issue 25 2010
Venkata Rao
Geliert: Selbstorganisierte Nanofasern aus alternierenden Koaggregaten eines nichtkovalenten Donor-Akzeptor(D-A)-Amphiphils bilden Hydrogele in Wasser (siehe Schema). Mikroskopie und Einkristall-Analytik gaben Einblick in die hierarchische Selbstorganisation , zunächst zu zylindrischen Micellen und, mit steigender D-A-Konzentration, schließlich zu einem Gel , des aus einem Coronen- und einem Viologen-Derivat bestehenden Charge-Transfer(CT)-Amphiphils. [source]