Antibacterial Activity of Hexanol Vapor In Vitro and on the Surface of Vegetables.

Hexanol is a volatile alcohol and a major component of plant essential oils (EOs). However, the antibacterial activity of hexanol vapor has not been well studied. This study aimed to evaluate the antibacterial activity of hexanol. In this study, seven food-related bacteria were exposed to 1-, 2- or 3-hexanol vapor on agar media to evaluate their growth. Additionally, the total viable counts in three vegetables when exposed to 1-hexanol vapor were measured. The results showed that 1-hexanol exhibited antibacterial effects against Gram-negative bacteria but did not affect Gram-positive bacteria. However, compounds 2- and 3-hexanol did not show antimicrobial activity against any bacteria. For the vegetables, exposure to 1-hexanol vapor decreased the total viable bacterial counts in cabbage and carrot and inhibited bacterial growth in eggplants. In cabbage, 1-hexanol vapor at concentrations over 50 ppm decreased the total viable count within 72 h, and 25 ppm of vapor showed bacteriostatic activity for 168 h. However, 1-hexanol vapor also caused discoloration in cabbage. In summary, 1-hexanol has the potential to act as an antibacterial agent, but further studies are required for practical use. Moreover, the study results may help determine the antimicrobial activity of various EOs in the future.

Effect of Air-Particle Abrasion Protocol and Primer on The Topography and Bond Strength of a High-Translucent Zirconia Ceramic.

PURPOSE: To evaluate effect of air-particle abrasion protocol and primer on surface topography and bond strength of resin cement to high-translucent zirconia ceramics. MATERIALS AND METHODS: Two hundred disk-shaped high-translucent zirconia specimens of 5Y-PSZ were prepared. The specimens were assigned to 5 groups in terms of particle type and air-particle abrasion pressure: (1) control, (2) alumina with 0.2 MPa-air pressure [AB-0.2], (3) alumina with 0.4 MPa-air pressure [AB-0.4], (4) glass beads with 0.2 MPa-air pressure [GB-0.2], and (5) glass beads with 0.4 MPa-air pressure [GB-0.4]. Two different primers 1% MDP (Experimental) and MDP-silane primer (Clearfil Ceramic Primer Plus) was also tested. Stainless steel rods were bonded to the 5Y-PSZ specimens with PANAVIA V5. For each group, the tensile bond strength (TBS) was measured after 24-hour water storage (n = 10) and after 5000 thermal-cycling (n = 10) at crosshead speed of 2 mm/min. The data were statistically analyzed using Weibull analysis. Surface roughness (Sa) was measured using a 3D-Laser Scanning Confocal Microscope (n = 5) and analyzed by t-test with Bonferroni correction. Surface topography using scanning electron microscopy (SEM) and surface elemental analysis using energy dispersion spectroscopy (EDX), and cross-section SEM at the interface with composite cement were also investigated. RESULTS: In MDP-silane groups, the highest TBS was observed in AB-0.4 after 24 hours and GB-0.4 after thermal-cycling (p < 0.05). In MDP groups, AB groups resulted in the significantly higher TBS than GB groups (p < 0.05). AB-0.4 group showed the highest Sa value compared to all groups (p < 0.005), meanwhile GB groups did not show different Sa compared to control (p > 0.005). CONCLUSION: Air-abrasion with different particle and blasting pressure can improve bonding to zirconia with proper primer selection. Particularly, glass beads abrasion followed by MDP-silane primer and alumina abrasion followed by MDP primer alone provided stable bond strength of resin cement to high-translucent zirconia after aging. High-translucent zirconia abraded with glass beads achieves a desirable bonding performance without creating surface microcracks which may hinder zirconia's mechanical properties.

UV-Mediated Photofunctionalization of Indirect Restorative Materials Enhances Bonding to a Resin-Based Luting Agent.

PURPOSE: The potential of UV-mediated photofunctionalization to enhance the resin-based luting agent bonding performance to aged materials was investigated. METHODS: Sixty samples of each material were prepared. Yttria-stabilized zirconia (YZr) and Pd-Au alloy (Pd-Au) plates were fabricated and sandblasted. Lithium disilicate glass-ceramic (LDS) was CAD-CAM prepared and ground with #800 SiC paper. Half of the specimens were immersed in machine oil for 24 h to simulate the carbon adsorption. Then, all of the specimens (noncarbon- and carbon-adsorbed) were submitted to UV-mediated photofunctionalization with a 15 W UV-LED (265 nm, 300 mA, 7692 µW/cm2) for 0 (control groups), 5, and 15 min and subjected to contact angle (Ɵ) measurement and bonded using a resin cement (Panavia™ V5, Kuraray Noritake, Japan). The tensile bond strength (TBS) test was performed after 24 h. The Ɵ (°) and TBS (MPa) data were statistically analyzed using two-way ANOVA and Bonferroni correction tests (α = 0.05). RESULTS: In the carbon-adsorbed groups, UV-mediated photofunctionalization for 5 min significantly decreased Ɵ of all materials and increased TBS of YZr, and UV for 15 min significantly increased the TBS of LDS and Pd-Au. In noncarbon-adsorbed groups, UV-photofunctionalization did not significantly change the Ɵ or TBS except YZr specimens UV-photofunctionalized for 15 min. CONCLUSION: UV-mediated photofunctionalization might have removed the adsorbed hydrocarbon molecules from the materials' surfaces and enhanced bond strengths of Panavia™ V5 to YZr, LDS, and Pd-Au. Additionally, UV-mediated photofunctionalization improved the overall TBS of YZr. Further investigation on the optimum conditions of UV photofunctionalization on indirect restorative materials should be conducted.

Evaluation of presumptive identification of Enterobacterales using CHROMagar Orientation medium and rapid biochemical tests.

BACKGROUND: The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is gradually spreading among large-scale laboratories; however, this method is impractical for small-scale laboratories. In laboratories without access to these rapid identification methods, problems related to them remain unsolved. In this study, we aimed to develop a rapid and inexpensive method to presumptively identify Enterobacterales using CHROMagar Orientation medium. METHODS: The algorithm for presumptive identification of Enterobacteriaceae using CHROMagar Orientation medium was based on our previous studies. Modified property tests for indole, lysine decarboxylase, ornithine decarboxylase, and hydrogen sulfide were performed to evaluate the differentiation of the bacterial species. RESULTS: Using the type strains and clinical isolates, it was possible to conduct the property tests at a low cost, within 4 hours. The spot indole test was performed without any nonspecific reactions for the bacteria forming colored colonies. The presumptive identification of bacteria was thereby possible within 24 hours after specimen submission. CONCLUSION: All these results suggest that the rapid presumptive identification of Enterobacterales is possible with this new identification method using CHROMagar Orientation medium. This is therefore a prompt and economical method that can be used in routine laboratory work.

Assessment of Stickiness with Pressure Distribution Sensor Using Offset Magnetic Force.

The quantification of stickiness experienced upon touching a sticky or adhesive substance has attracted intense research attention, particularly for application to haptics, virtual reality, and human-computer interactions. Here, we develop and evaluate a device that quantifies the feeling of stickiness experienced upon touching an adhesive substance. Keeping in mind that a typical pressure distribution sensor can only measure a pressing force, but not a tensile force, in our setup, we apply an offset pressure to a pressure distribution sensor and measure the tensile force generated by an adhesive substance as the difference from the offset pressure. We propose a method of using a magnetic force to generate the offset pressure and develop a measuring device using a magnet that attracts magnetic pin arrays and pin magnets; the feasibility of the method is verified with a first prototype. We develop a second prototype that overcomes the noise problems of the first, arising from the misalignment of the pins owing to the bending of the magnetic force lines at the sensor edges. We also obtain measurement results for actual samples and standard viscosity liquids. Our findings indicate the feasibility of our setup as a suitable device for measuring stickiness.

The effect of different cleaning agents on saliva contamination for bonding performance of zirconia ceramics.

The effects of contamination and cleaning methods on bonding of self-adhesive resin cement to zirconia ceramics were examined. Airborne particle-abraded zirconia (Zpex Smile) specimens were divided into the following four groups: control (con), contaminated with saliva and cleaned with tap water (HS), cleaned with Ivoclean (IC), and cleaned with Multi Etchant (ME). The pretreated specimens were bonded using three self-adhesive resin cements, and tensile bond strengths were measured using a universal testing machine at a crosshead speed of 2 mm/min. Con and IC groups showed significantly higher bond strength than those of HS and ME groups. Separately, the surface chemical composition of the groups was determined using X-ray photoelectron spectroscopy (XPS). XPS revealed that the N/Zr ratio increased in the HS group but decreased in the IC and ME groups. Cleaning agents can improve the adverse effect of saliva contamination on zirconia, but this effect varies depending on the product.

The role of functional phosphoric acid ester monomers in the surface treatment of yttria-stabilized tetragonal zirconia polycrystals.

This study aimed to evaluate the bond strength of a resin cement to yttria-stabilized tetragonal zirconia polycrystals (Y-TZPs) treated with three different phosphate functional monomers containing primers by measuring the water contact angle. Seventy Y-TZP discs were divided into seven experimental groups (n=10), including an untreated (control) group. Specimens were treated with one of the following monomers: MDP (MD), GPDM (GP), and Phenyl-P (PP). After primer application and air drying, half the treated specimens were ultrasonically cleaned in ethanol for 2 min (MD-e, GP-e, and PP-e), and contact angles were measured. The tensile bond strength test was performed after storage for 24 h in 37°C water. The contact angle on the MD-e surface (64°) was significantly higher than that on the Con, GP-e, and PP-e surfaces (51°-52°). The application of the MDP-containing primer resulted in significantly higher bond strength between Y-TZP ceramics and a resin cement.

On the temperature dependence of flammability limits of gases.

Flammability limits of several combustible gases were measured at temperatures from 5 to 100 °C in a 12-l spherical flask basically following ASHRAE method. The measurements were done for methane, propane, isobutane, ethylene, propylene, dimethyl ether, methyl formate, 1,1-difluoroethane, ammonia, and carbon monoxide. As the temperature rises, the lower flammability limits are gradually shifted down and the upper limits are shifted up. Both the limits shift almost linearly to temperature within the range examined. The linear temperature dependence of the lower flammability limits is explained well using a limiting flame temperature concept at the lower concentration limit (LFL)--'White's rule'. The geometric mean of the flammability limits has been found to be relatively constant for many compounds over the temperature range studied (5-100 °C). Based on this fact, the temperature dependence of the upper flammability limit (UFL) can be predicted reasonably using the temperature coefficient calculated for the LFL. However, some compounds such as ethylene and dimethyl ether, in particular, have a more complex temperature dependence.

Flammability limits of olefinic and saturated fluoro-compounds.

Flammability limits were measured for a number of olefinic and saturated fluoro-compounds in a 12l spherical glass vessel. The obtained data together with the ones of previous studies have been analyzed based on the F-number scheme of flammability limits. The flammability limits of these compounds have been found to be explained very well by the present scheme of interpretation. The flammability limits are dependent upon distribution of F atoms in a molecule as well as upon F-substitution rate itself. It has been found that -O-CF(3) group in a molecule conspicuously decreases the flammability of the compound, while -C-CF(3) group does not much. For olefinic compounds, distribution of F atoms around double bonds markedly diminishes the flammability of the molecule.

A study on flammability limits of fuel mixtures.

Flammability limit measurements were made for various binary and ternary mixtures prepared from nine different compounds. The compounds treated are methane, propane, ethylene, propylene, methyl ether, methyl formate, 1,1-difluoroethane, ammonia, and carbon monoxide. The observed values of lower flammability limits of mixtures were found to be in good agreement to the calculated values by Le Chatelier's formula. As for the upper limits, however, some are close to the calculated values but some are not. It has been found that the deviations of the observed values of upper flammability limits from the calculated ones are mostly to lower concentrations. Modification of Le Chatelier's formula was made to better fit to the observed values of upper flammability limits. This procedure reduced the average difference between the observed and calculated values of upper flammability limits to one-third of the initial value.

Burning velocity measurements of nitrogen-containing compounds.

Burning velocity measurements of nitrogen-containing compounds, i.e., ammonia (NH3), methylamine (CH3NH2), ethylamine (C2H5NH2), and propylamine (C3H7NH2), were carried out to assess the flammability of potential natural refrigerants. The spherical-vessel (SV) method was used to measure the burning velocity over a wide range of sample and air concentrations. In addition, flame propagation was directly observed by the schlieren photography method, which showed that the spherical flame model was applicable to flames with a burning velocity higher than approximately 5 cm s(-1). For CH3NH2, the nozzle burner method was also used to confirm the validity of the results obtained by closed vessel methods. We obtained maximum burning velocities (Su0,max) of 7.2, 24.7, 26.9, and 28.3 cm s(-1) for NH3, CH3NH2, C2H5NH2, and C3H7NH2, respectively. It was noted that the burning velocities of NH3 and CH3NH2 were as high as those of the typical hydrofluorocarbon refrigerants difluoromethane (HFC-32, Su0,max=6.7 cm s(-1)) and 1,1-difluoroethane (HFC-152a, Su0,max=23.6 cm s(-1)), respectively. The burning velocities were compared with those of the parent alkanes, and it was found that introducing an NH2 group into hydrocarbon molecules decreases their burning velocity.

Flammability limits of isobutane and its mixtures with various gases.

Flammability limits of isobutane and five kinds of binary mixtures of isobutane were measured by the ASHRAE method. Propane, nitrogen, carbon dioxide, chloroform, and HFC-125 (1,1,1,2,2-pentafluoroethane) were used as the counter part gases in the mixtures. The observed data were analyzed using the equations based on Le Chatelier's formula. The flammability limits of mixtures with propane were well explained by the original Le Chatelier's formula. The flammability limits of mixtures with nitrogen and the ones with carbon dioxide were adequately analyzed by the extended Le Chatelier's formula. It was found that the extended Le Chatelier's formula is also applicable to the flammability limits of mixtures with chloroform and HFC-125.

Extended Le Chatelier's formula for carbon dioxide dilution effect on flammability limits.

Carbon dioxide dilution effect on the flammability limits was measured for various flammable gases. The obtained values were analyzed using the extended Le Chatelier's formula developed in a previous study. As a result, it has been found that the flammability limits of methane, propane, propylene, methyl formate, and 1,1-difluoroethane are adequately explained by the extended Le Chatelier's formula using a common set of parameter values. Ethylene, dimethyl ether, and ammonia behave differently from these compounds. The present result is very consistent with what was obtained in the case of nitrogen dilution.

Measurement and numerical analysis of flammability limits of halogenated hydrocarbons.

Flammability limits measurement was made for a number of halogenated compounds by the ASHRAE method. Most of compounds measured are the ones for which discrepancy was noted between the literature values and predicted values of flammability limits. As a result, it has been found that most of the newly obtained values of flammability limits are not in accordance with the literature values. Numerical analysis was carried out for a set of flammability limits data including the newly obtained ones using a modified analytical method based on F-number scheme. In this method, fitting procedure was done directly to flammability limits themselves instead of fitting to F-number. After the fitting process, the average relative deviation between the observed and calculated values is 9.3% for the lower limits and 14.6% for the upper limits.

Effect of vessel size and shape on experimental flammability limits of gases.

The flammability limits of methane and propane have been measured using cylindrical vessels of various sizes and one spherical vessel. An ac discharge ignition method has been employed. For a cylindrical vessel of small diameter with a large height, the flammability limits are primarily determined by the quenching effect of the wall. For cylindrical vessels of smaller heights, the experimental flammability limits are affected by hot gas accumulation at the vessel ceiling, unburned gas heating, self heating of the incipient flame by the reflection both from walls and ceiling, and the quenching effect of the walls. If the vessel size is large enough so that all these effects become negligible, the experimental values of flammability limits may approach to the values that would be obtained in free space. In order to approach this condition for a cylindrical vessel, it is desirable to use a container at least 30 cm in diameter and 60 cm in height. For comparison purpose, the measurement has also been done using ASHRAE type 12l spherical flask.

Calculation of minimum ignition energy of premixed gases.

The minimum ignition energy of premixed gases has been calculated by using two theoretical expressions and compared with the experimental data. One expression considers the amount of energy that the minimal flame should have, and the other the heat loss from the surface of the minimal flamelet. The former is a cubic function of the quenching distance while the latter is a quadratic function of quenching distance. It has been found that the latter expression gives a better fit to the experimental data than the former, though the discrepancy is considerable even for the latter expression. The calculated widths of the fronts of the minimal flame for various fuels were about one-order of magnitude smaller than the corresponding experimentally determined quenching distances, although no clear correlation relationship between the two quantities was found.

Experimental exploration of discrepancies in F-number correlation of flammability limits.

Flammability limits measurement has been made by ASHRAE method for some 20 kinds of combustible gases and vapors. These compounds have been selected mainly because the literature values of flammability limits are not consistent with the F-number calculated ones [J. Hazard. Mater. A 82 (2001) 113]. As a result, it has been found that the newly obtained values of flammable range are classified into three groups. For the first group of compounds, the present values agree well to the literature values. For the second group, the present values do not agree to the literature values but agree with the calculated ones. For the third group ones, the present values neither agree to the literature values nor to the calculated ones. There are 4, 13, and 6 compounds in the respective groups.

RF number as a new index for assessing combustion hazard of flammable gases.

A new index called RF number has been proposed for assessing the combustion hazard of all sorts of flammable gases and their mixtures. RF number represents the total expectancy of combustion hazard in terms of flammability limits and heat of combustion for each known and unknown compounds. The advantage of RF number over others such as R-index and F-number for classification of combustion hazard has been highlighted.

Theoretical calculation of heat of formation and heat of combustion for several flammable gases.

Heats of formation have been calculated by the Gaussian-2 (G2) and/or G2MP2 method for a number of flammable gases. As a result, it has been found that the calculated heat of formation for compounds containing, such atoms as fluorine and chlorine tends to deviate from the observed values more than calculations for other molecules do. A simple atom additivity correction (AAC) has been found effective to improve the quality of the heat of formation calculation from the G2 and G2MP2 theories for these molecules. The values of heat of formation thus obtained have been used to calculate the heat of combustion and related constants for evaluating the combustion hazard of flammable gases.