Estimation of the survival curve of Listeria monocytogenes during non-isothermal heat treatments

2001 ◽  
Vol 34 (5) ◽  
pp. 383-388 ◽  
Author(s):  
M. Peleg ◽  
C.M. Penchina ◽  
M.B. Cole
Keyword(s):  
Listeria Monocytogenes ◽  
Survival Curve ◽  
Heat Treatments ◽  
Isothermal Heat Treatments

Use of a Modified Gompertz Equation to Predict the Effects of Temperature, pH, and NaCl on the Inactivation of Listeria monocytogenes Scott A Heated in Infant Formula

1996 ◽  
Vol 59 (1) ◽  
pp. 16-23 ◽  
Author(s):  
R. H. LINTON ◽  
W. H. CARTER ◽  
M. D. PIERSON ◽  
C. R. HACKNEY ◽  
J. D. EIFERT
Keyword(s):  
Listeria Monocytogenes ◽  
Infant Formula ◽  
Nonlinear Regression ◽  
Survival Curve ◽  
Interactive Effects ◽  
Parameter Estimates ◽  
Survival Curves ◽  
Gompertz Equation ◽  
Nacl Concentration ◽  
Effects Of Temperature

The heat resistance of Listeria monocytogenes was determined in infant formula for all possible combinations of temperature (50, 55, and 60°C), pH level (5, 6, and 7), and NaCl concentration (0, 2, and 4%). Survival curves were fit using nonlinear regression with a Gompertz equation. The Gompertz equation was flexible enough to fit the three most commonly observed survival curves: linear curves, those with an initial lag region followed by a linear region, and sigmoidal shaped. Parameter estimates obtained by the method of nonlinear least squares were used to describe the effect(s) of different heating treatments on the lag region, death rate, and tailing region of survival curves. These estimates were further used to predict single and interactive effects of temperature, pH, and percentage of NaCl on the log of the surviving fraction (LSF) of bacteria. Interactions among these variables significantly (P ≤ .05) affected the LSF. Generally, increased pH or NaCl concentration lead to an increased LSF, whereas increased time or temperature lead to a decreased LSF. All multiple-factor interactions significantly (P ≤ .05) affected the LSF. The correlation of observed LSF versus predicted LSF (R2 = .92) indicated that the estimated Gompertz equation was in close agreement with the observation. This study demonstrated that the Gompertz equation and nonlinear regression can be used as an effective means to predict survival curve shape and response to heat of L. monocytogenes under many different environmental conditions.

scholarly journals Atomic Level Characterization of the Morphology of Phases in Chromindur Magnetic Alloys

1991 ◽  
Vol 232 ◽  
Author(s):  
M. K Miller ◽  
P. P. Camus ◽  
M. G. Hetherington
Keyword(s):  
Atom Probe ◽  
Heat Treatments ◽  
Miscibility Gap ◽  
Probe Field ◽  
Magnet Alloy ◽  
Two Phases ◽  
Isothermal Heat Treatments ◽  
Field Ion Microscope ◽  
Permanent Magnet Alloy

ABSTRACTThe atom probe field ion microscope has been used to characterize the morphology and determine the compositions of the iron-rich a and chromium-enriched α′ phases produced during isothermal and step cooled heat treatments in a Chromindur II ductile permanent magnet alloy. The good magnetic properties of this material are due to a combination of the composition of the two phases and the isolated nature and size of the ferromagnetic a phase. The morphology of the a phase is produced as a result of the shape of the miscibility gap and the step-cooled heat treatment and is distinctly different from that formed during isothermal heat treatments.

scholarly journals Investigation of the effect of isothermal heat treatments on mechanical properties of thermo-mechanically rolled S700MC steel grade

2020 ◽  
Vol 26 (1) ◽  
pp. 11-16
Author(s):  
Serkan Oktay ◽  
Paolo Emilio Di Nunzio ◽  
Mustafa Kelami Şeşen
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Impact Energy ◽  
Heat Treatments ◽  
Steel Grade ◽  
Secondary Hardening ◽  
Precipitation Kinetics ◽  
High Supersaturation ◽  
Bainitic Structure ◽  
Isothermal Heat Treatments

The effect of isothermal heat treatments (1 hour at 200, 400, 600 and 800°C) on mechanical properties of thermo-mechanically rolled S700MC steel has been investigated by extensive mechanical characterizations. Treatments at 600°C increase yield and tensile strength and decrease impact energy. Below 600°C the steel retains its bainitic structure. Precipitation kinetics simulations indicate that this secondary hardening effect arises from the nucleation of fine (Nb,Ti)C particles, indicating that the bainitic structure is unstable above 600°C due to its high supersaturation with respect to C, Nb and Ti. These results can help to optimize the operating practices for post-weld heat treatments.

Correlation between microstructural evolution during high-pressure torsion and isothermal heat treatment of amorphous Al85Gd8Ni5Co2 alloy

2010 ◽  
Vol 25 (7) ◽  
pp. 1388-1397 ◽  
Author(s):  
Péter Henits ◽  
Ádám Révész ◽  
Erhard Schafler ◽  
Péter J. Szabó ◽  
János L. Lábár ◽  
...  
Keyword(s):  
Heat Treatment ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Thermal Sensitivity ◽  
Heat Treatments ◽  
Isothermal Heat Treatment ◽  
X Ray Diffraction ◽  
Continuous Heat Treatment ◽  
Isothermal Heat Treatments ◽  
Continuous Heat

Al85Gd8Ni5Co2 metallic glass was subjected to partial devitrification by high-pressure torsion, continuous heat treatment, and isothermal annealing. The fully amorphous alloy exhibits a well-defined transition in its first devitrification product during isothermal heat treatments from τm + α-Al phase mixture to primary α-Al by increasing the annealing temperature above 555 K. This thermal sensitivity predestinates the composition to identify the controversial thermal contribution of the plastic deformation in metallic glasses. Thermal stability and structure of the partially devitrified samples were systematically analyzed and compared by calorimetry, x-ray diffraction, and electron microscopy. It seems that the effect of severe deformation cannot be singled out by a simple isothermal heat treatment; i.e., high-pressure torsion acts as a spectrum of heat treatments performed at different annealing temperatures.

Effect of Heat Treatments on Microstructure and Mechanical Properties of Low Carbon Steel Pipes Welded by Induction Process

2014 ◽  
Vol 887-888 ◽  
pp. 1301-1306
Author(s):  
Zakaria Boumerzoug ◽  
Lakhdar Lakhdari
Keyword(s):  
Mechanical Properties ◽  
Isothermal Annealing ◽  
Pipeline Steel ◽  
Low Carbon Steel ◽  
Tensile Tests ◽  
Heat Treatments ◽  
Low Carbon ◽  
Steel Pipes ◽  
Induction Process ◽  
Isothermal Heat Treatments

In this work, the effect of isothermal heat treatments on microstructure evolution and mechanical properties after welding by induction of A37 pipeline steel have been studied by scanning electron microscopy, hardness measurements, and tensile tests. Microstructural evolution in welded joint was identified after isothermal annealing from 200 until 900 °C.

The growth of calcium metasilicate polymorphs from supercooled melts and glasses

1978 ◽  
Vol 42 (323) ◽  
pp. 325-335 ◽  
Author(s):  
R. M. Weston ◽  
P. S. Rogers
Keyword(s):  
Experimental Data ◽  
Crystal Growth ◽  
Amorphous Phase ◽  
Activation Energies ◽  
Heat Treatments ◽  
Temperature Transformation ◽  
Isothermal Heat Treatments ◽  
Transformation Diagrams ◽  
Anionic Groups

SummaryThe morphology of calcium metasilicate produced during the crystallization of glasses and melts of approximately metasilicate composition has been investigated. Both isothermal heat treatments and a dynamic crystal-pulling technique were employed. The crystallization took place by a dendritic or spherulitic mechanism, according to which of the crystal polymorphs is stable under the prevailing conditions. The morphology of the crystals is controlled by the ease with which the anionic groups present in the amorphous phase can be incorporated into the growing crystals. This is reflected in the values of the activation energies of crystal growth found for α-CaSiO3 (160 kJ mol−1) and for β-CaSiO3 (319 to 383 kJ mol−1). The Keith and Padden theory of spherulitic crystallization was verified for the growth of β-CaSiO3 over a range of supercoolings. Time-temperature-transformation diagrams have been constructed from the experimental data.

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