Changes In Physical State Research Articles

Shelf-life Modeling of Bakery Products by Using Oxidation Indices

The aim of this work was to develop a shelf-life prediction model of lipid-containing bakery products. To this purpose (i) the temperature dependence of the oxidation rate of bakery products was modeled, taking into account the changes in lipid physical state; (ii) the acceptance limits were assessed by sensory analysis; and (iii) the relationship between chemical oxidation index and acceptance limit was evaluated. Results highlight that the peroxide number, the changes of which are linearly related to consumer acceptability, is a representative index of the quality depletion of biscuits during their shelf life. In addition, the evolution of peroxides can be predicted by a modified Arrhenius equation accounting for the changes in the physical state of biscuit fat. Knowledge of the relationship between peroxides and sensory acceptability together with the temperature dependence of peroxide formation allows a mathematical model to be set up to simply and quickly calculate the shelf life of biscuits.

Solid molecular dispersions of poorly water-soluble drugs in poly(2-hydroxyethyl methacrylate) hydrogels

The applicability of cross-linked hydrogels in forming solid molecular dispersions to enhance the delivery of poorly soluble drugs has not been fully explored. The purpose of this study is to characterize physicochemical parameters affecting the formation of solid molecular dispersions of poorly water-soluble drugs in poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels and to investigate the effect of storage humidity levels on their physical stability. Samples were prepared by an equilibrium solvent loading process, using diclofenac sodium, piroxicam and naproxen as model drugs. These were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), as well as changes in the physical state during storage under different humidity conditions. The results show that a threshold drug loading level of about 30% exists in these solid molecular dispersions, above which amorphous to crystalline transition may occur. At any given drug loading, the onset of such change in physical state is accelerated at higher relative humidity levels during storage. The presence of hydrogen bonding between the polymer and the drug, as reflected in the observed FTIR band shifts, improves the compatibility between the drug and the polymer. This, together with a decreased mobility in the glassy polymer, helps to retard the crystallization event below the loading threshold. An increase in dissolution rate is also observed from the polymeric solid molecular dispersion as compared with that of the crystalline pure drug. These physicochemical results indicate that solid molecular dispersions based on PHEMA hydrogels can effectively enhance the dissolution and therefore should be potentially useful in improving the oral bioavailability of poorly water-soluble drugs.

Thermodynamic properties of linear polyurethanes based on 1,6-hexamethylenediisocyanate with butane-1,4-diol and hexane-1,6-diol in the temperature range from T → 0 to 460 K

The temperature dependences of the heat capacity of partially crystalline linear polyurethanes based on 1,6-hexamethylenediisocyanate with butane-1,4-diol and hexane-1,6-diol were studied for the first time in a temperature range of 6–460 K by the methods of adiabatic vacuum and dynamic calorimetry. Physical changes in the state of polyurethanes were revealed and characterized; the standard thermodynamic functions, namely, Cp°(T), H°(T)-H°(0), S°(T), and G°(T)-H°(0), were calculated from the obtained experimental data in the temperature range from T → 0 to 460 K for the polymers in the crystalline, glassy, highly elastic, and liquid states. The energies of combustion of the polymers were measured by the bomb calorimetry method, and the standard thermodynamic characteristics of their formation at 298.15 K were calculated. The thermodynamic characteristics of bulk polycondensation of 1,6-hexamethylenediisocyanate with butane-1,4-diol and hexane-1,6-diol to form linear aliphatic polyurethanes-{4,6} and-{6,6} were determined in the range from T → 0 to 350 K at p° = 0.1 MPa. The thermodynamic properties of the polyurethanes under study and polymers of isomeric structure were compared.

Thermal and mechanical fatigue of a PA66/glass fibers composite material

Polymeric matrices are viscoelastic materials and dissipate a part of the mechanical energy in the form of heat when they are submitted to a cyclic strain. During a fatigue test, the temperature of the material can increase and stabilize to some extent. Sometimes it increases until the sample fracture occurs which is called a thermal fracture. When the sample fracture is governed by crack initiation and propagation, it is called a mechanical fracture. The glass transition temperature of the PA66 matrix is not far from the ambient temperature and a temperature increase possibly induces a change of the matrix physical state. So the fatigue behaviour of our material strongly depends on temperature variations. The fatigue tests were carried out with an alternative bending device with a ratio R = −1, at 23 °C, 45% RH and two different frequencies, 2 Hz or 10 Hz. The applied strain varies between 0.0116 and 0.0223. During the test, the surface temperature was measured in the most constrained part of the specimen by an infrared camcorder. For a 10 Hz frequency and although the test temperature is 23 °C, the sample temperature at the surface is much higher and whatever the applied strain, the matrix is in a rubbery state at the material fracture. For a 2 Hz frequency, the PA66 matrix remains in the glassy state. The fatigue failure surface observed by scanning electron microscopy for both kinds of samples will be discussed.

Thermal and mechanical behavior of unsaturated polyesters filled with phase change material

AbstractSamples of commercial unsaturated polyester (UPE) resin, filled with phase‐changeable fillers (PCMs), were prepared, and the thermal and mechanical properties of the cured samples were examined. Fillers chosen were paraffin and Wood's metal. Samples were prepared by making dispersions of these fillers in liquid unsaturated polyester followed by curing with methyl ethyl ketone peroxide (MEKP) and conaphtanate and rigid thermoset samples filled with PCM particles were obtained. The thermal and mechanical behaviors of such a filled composite around the melting points of fillers are very interesting. Effects of varying proportions of PCM on mechanical and thermal properties of final products were examined. The samples show thermal melting behavior without undergoing a change in physical state. Decreases in the maximum working temperature from 75 to 53°C for metal‐filled samples and from 75 to 43°C for paraffin‐filled samples were observed by using dynamic mechanical thermal analysis. Differential scanning calorimetry indicated that heat absorption of paraffin samples were higher than that of metal‐filled samples. For paraffin‐filled samples, heats of fusion were 3.44 cal/g for 10% filled sample and 6.35 cal/g for 20% filled sample. For Wood's metal‐filled samples, heats of fusion were 1.18 cal/g for 10% metal‐filled sample and 1.54 cal/g for 20% metal‐filled sample. Surface hardness was tested with Shormeter D. Surface hardness of metal‐filled composites varied from 86 to 34 shore D at 21°C and 80.6 to 35 shore D at 80°C. For paraffin‐filled samples, surface hardness changed from 86 to 42 shore D at 21°C and from 80.6 to 13 shore D. Morphology of the samples was determined by scanning electron microscopy, of the crack surfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 832–838, 2006

Applying Magnetized Accretion-Ejection Models to Microquasars: A Preliminary Step

We present in this proceeding some aspects of a model that should explain the spectral state changes observed in microquasars. In this model, ejection is assumed to take place only in the innermost disc region where a large scale magnetic field is anchored. Then, in opposite to conventional ADAF models, the accretion energy can be efficiently converted in ejection and not advected inside the horizon. We propose that changes of the disc physical state (e.g. transition from optically thick to optically thin states) can strongly modify the magnetic accretion-ejection structure resulting in the spectral variability. After a short description of our scenario, we give some details concerning the dynamically self-consistent magnetized accretion-ejection model (Ferreira 1997; Casse & Ferreira 2000) used in our computation. We also present some preliminary results of spectral energy distribution.

Measuring temperature

Temperature is a measure of the mean translational kinetic energy associated with the random motion of atoms or molecules within a substance. Heat is the energy transferred between two bodies of differing temperature and flows from the higher temperature body to the lower, until equilibrium is reached. The Farenheit, Celsius and Kelvin scales are three temperature scales in common use. The Farenheit scale separates the freezing and boiling points of water by 180 degrees and the Celsius scale separates the same two fixed points by 100 degrees. The Kelvin thermodynamic scale is defined as the temperature difference between absolute zero and the triple point of water divided by 273.16. Modern thermometers are calibrated to the International Temperature Scale of 1990 (ITS-90), which defines 17 fixed points, of which the triple point of water is the ninth point. A thermometer is a device for estimating the temperature of a substance or body, and commonly utilizes a quantifiable and reproducible change in a physical property of the substance in response to temperature. Thermometers may be classified into contact and non-contact devices. The simplest use a change in physical state or density with temperature. A resistance temperature detector (metal wire) and thermistor utilize a change in electrical resistance, while a thermocouple generates a small emf when placed in a temperature gradient. Non-contact temperature measuring devices include the thermopile, optical pyrometer and radiation thermometer.

Chair massage for carers in an acute cancer hospital

The Chair Massage service considered in this evaluation study was provided to carers, visiting in-patients at a major cancer hospital in the UK. The two-stage evaluation comprised: firstly, a retrospective review of treatment records for the previous 12 months (n=182), and secondly, a prospective study, gathering data by interview and a 'next-day' questionnaire from carers (n=34), during 1 week of service delivery. The study at both stages sought to identify who used the service, post-treatment comments and changes in scores using a Feeling Good Thermometer (Field, T., 2000. Touch Therapy. Churchill Livingstone, London). During the second stage the carers were also asked about their concerns and worries, and to report changes in physical and emotional states using visual scales. Findings included significant improvements in physical and psychological scores; these were retained through to the next day. The next-day questionnaire also reported improved sleep for the majority of carers. A number of concerns and worries were raised at interview, notably anxieties about the patient and uncertainty about the future, family and financial worries. Overall, the service was well evaluated with parents and in particular female carers appearing to gain the most from the intervention.

Is a pyrolitic adiabatic mantle compatible with seismic data?

In this paper, the simplest average physical model of a mantle convecting as a whole (i.e., following an adiabatic temperature gradient) with a single composition (pyrolite with phase transitions) is tested directly against global seismic data, instead of against spherically symmetric seismic models. Constraints from seismic data on average velocities and lower mantle velocity gradients are hard to reconcile with an adiabatic pyrolitic mantle, given the current state of knowledge of elastic and anelastic mineral parameters at high pressure and temperature. This physical model generally gives (a) a stronger baseline offset between upper and lower mantle average travel-time residuals than allowed by the data and (b) an insufficient decrease in velocity with depth in the lower mantle (above 2500 km). We tested 105 upper and 105 lower mantle models that were selected randomly within the mineral parameter uncertainties. Only 2 lower mantle models and 24 upper mantle models yield whole mantle seismic structures that are compatible with global ISC P and S travel times and central frequencies of toroidal and spheroidal fundamental modes with angular order higher than 18. To improve the fit to the seismic data, the physical model would require (a) a lower velocity transition zone composition than dry pyrolite (at least around continents and subduction zones) as well as (b) a gradual change in physical state of the lower mantle that decreases the velocity-depth gradient, e.g., a superadiabatic temperature gradient.

Spontaneous Change of Physical State from Hydrogels to Crystalline Precipitates during Poly‐pseudorotaxane Formation

Spontaneous Change of Physical State from Hydrogels to Crystalline Precipitates during Poly‐pseudorotaxane Formation

A critical evaluation of Raman spectroscopy for the analysis of lipids: Fatty acid methyl esters

The work presented here is aimed at determining the potential and limitations of Raman spectroscopy for fat analysis by carrying out a systematic investigation of C4-C24 FAME. These provide a simple, well-characterized set of compounds in which the effect of making incremental changes can be studied over a wide range of chain lengths and degrees of unsaturation. The effect of temperature on the spectra was investigated over much larger ranges than would normally be encountered in real analytical measurements. It was found that for liquid FAME the best internal standard band was the carbonyl stretching vibration v(C=O), whose position is affected by changes in sample chain length and physical state; in the samples studied here, it was found to lie between 1729 and 1748 cm(-1). Further, molar unsaturation could be correlated with the ratio of the nu(C=O) to either nu(C=C) or delta(H-C=) with R2 > 0.995. Chain length was correlated with the delta(CH2)tw/v(C=O) ratio, (where "tw" indicates twisting) but separate plots for odd- and even-numbered carbon chains were necessary to obtain R2 > 0.99 for liquid samples. Combining the odd- and even-numbered carbon chain data in a single plot reduced the correlation to R2 = 0.94-0.96, depending on the band ratios used. For molal unsaturation the band ratio that correlated linearly with unsaturation (R2 > 0.99) was nu(C=C)/delta(CH2)sc (where "sc" indicates scissoring). Other band ratios show much more complex behavior with changes in chemical and physical structure. This complex behavior results from the fact that the bands do not arise from simple vibrations of small, discrete regions of the molecules but are due to complex motions of large sections of the FAME so that making incremental changes in structure does not necessarily lead to simple incremental changes in spectra.

Activity of membrane-bound NADH-methemoglobin reductase and physical state of lipids in erythrocyte membranes

The activity of membrane-bound NADH-methemoglobin reductase in erythrocytes and the physical state of lipids in erythrocyte membranes under oxidative stress in cells were studied. A decrease of the activity of membrane-bound NADH-methemoglobin reductase and a change of physical state of the lipid bilayer of membranes under oxidative stress were found in erythrocytes in vivo and in vitro.

Temperature dependence of fluid phase endocytosis coincides with membrane properties of pig platelets

In previous studies we have shown that platelets take up low molecular weight molecules from the medium by fluid phase endocytosis, a phenomenon that we previously have used to load trehalose into human platelets, after which we have successfully freeze-dried them. We now extend those findings to a species to be used in animal trials of freeze-dried platelets:pigs. Further, we report results of studies aimed at elucidating the mechanism of the uptake. Temperature dependence of fluid-phase endocytosis was determined in pig platelets, using lucifer yellow carbohydrazide (LY) as a marker. A biphasic curve of marker uptake versus temperature was obtained. The activation energy was significantly higher above 22 °C (18.7±1.8 kcal/mol) than below that critical temperature (7.5±1.5 kcal/mol). The activation energy of fluid phase endocytosis in human platelets was 24.1±1.6 kcal/mol above 15 °C. In order to establish a correlation between the effect of temperature on fluid phase endocytosis and the membrane physical state, Fourier transform infrared spectroscopy (FTIR) and fluorescence anisotropy experiments were conducted. FTIR studies showed that pig platelets exhibit a main membrane phase transition at approximately 12 °C, and two smaller transitions at 26 and 37 °C. Anisotropy experiments performed with 1,6 diphenyl-1,3,5 hexatriene (DPH) complemented FTIR results and showed a major transition at 8 °C and smaller transitions at 26 and 35 °C. In order to investigate the relative roles of known participants in fluid phase endocytosis, the effects of several chemical inhibitors were investigated. LY uptake was unaffected by colchicine, methylamine, and amiloride. However, disruption of specific microdomains in the membrane (rafts) by methyl-β-cyclodextrin reduced uptake of LY by 35%. Treatment with cytochalasin B, which inhibits actin polymerization, reduced the uptake by 25%. We conclude that the inflection point in the LY uptake versus temperature plot at around 22 °C is correlated with changes in membrane physical state, and that optimal LY internalization requires an intact cytoskeleton and intact membrane rafts.

CHEMICAL PHENOMENA VERSUS CHEMICAL REACTIONS: DO STUDENTS MAKE THE CONNECTION?

In this work, we examine whether tenth-grade high school students (N = 197, age 15- 16) as well as first-year university chemistry students (N = 77, age 18-19) can make the connection between chemical reactions and chemical phenomena. We used nineteen physical and chemical phenomena, and asked the students at one stage to distinguish physical from chemical phenomena, and at another stage to state in which cases one or more reactions occur. Students can be categorised into two distinct groups. One group includes those who do not always identify chemical phenomena with reaction(s), while the other group includes those who are successful in that distinction. Further, the students of the first group can be divided into two subgroups: (a) those who perform better in identifying the chemical phenomena; (b) those who perform better in identifying the reactions. A differentiation of chemical changes into natural and man-caused processes seems to be operating, at least with Greek students. On the other hand, students may be intuitively viewing chemical reactions as fairly simple processes, which can be expressed by means of chemical equations. Finally, it might be preferable to group (i) changes of physical state and phase, and (ii) solutions, in a separate category (physicochemical changes). [Chem. Educ. Res. Pract.: 2003, 4, 31-43]

Grounding Social Theory in the Natural Sciences

All social relationships and the coordination of any activity between humans depend upon the transmission, reception, storage and processing units of information measured in bytes. Bytes provide a basis for grounding the study of social relationship and institutions in the natural sciences because their transmission or storage requires changes in energy or physical states. All humans are restricted in their ability to obtain data, information, knowledge, wisdom, or manage complexity, because of their physiological and neurological limits to transact bytes. This introduces an instrumental criterion for investigating, evaluating and designing the informational architecture of organisations and social relationships. Transaction Byte Analysis (TBA) is introduced as a framework to subsume Transaction Cost Economics (TCE). TCE is based on the normative need to economise the social construct of cost while TBA is based on the instrumental need to economise bytes. Human limits in transacting bytes are quantified and used to explain information overload and bounded rationality. Four modes of information and control with their strengths and weaknesses are identified and related to four modes of governing relationships. Unlike TCE and many other theories, TBA accepts that individuals can be either, or both, cooperative/competitive, trusting/suspicious and/or altruistic/selfish. Laws of governance are introduced that provide methods for obtaining reliable results from unreliable components. These provide criteria for evaluating or designing social organisations to reliably achieve their purpose. The utility of TBA as a framework for investigating the form and effectiveness of institutions is illustrated with micro and macro examples.

Physical state changes of membrane lipids in human lung adenocarcinoma A 549 cells and their resistance to cisplatin

The properties of membrane lipids in sensitive A 549 and resistant A 549/DDP cells to cis-dichlorodiammine platinum[II] (cisplatin) were examined by combining different approaches. The results showed that fluorescence intensity (Δ F) of Merocyanine 540 (MC540) was 93.5±21.8 for the sensitive A 549 cells and 49.5±11.2 for the resistive A 549/DDP cells, monitored by flow cytometry, which may indicate that membrane lipid packing of the sensitive A 549 cells were looser than that of the resistant A 549/DDP cells. Diffusion rate of N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-1,2-hexadecanoyl-Sn-glycero-3-phosphatidyl-ethanolamine (NBD-PE) was slower in A 549/DDP cells than in A 549 cells as detected by fluorescence recovery after photobleaching (FRAP) technique. Fatty acid analysis of the membrane lipids showed 21.6, 27.0 and 31.8% increase in the amount of C 18:1, C 18:2 and C 18:3 fatty acid, respectively, in A 549 cells as compared to A 549/DDP cells. The total amount of unsaturated fatty acids in the plasma membrane lipid is 69.13%±2.2% for A 549, and 55.08%±1.8% for A 549/DDP cells, respectively. The resistance to cisplatin in A 549/DDP cells was confirmed by the measurements of the transmembrane influx of Rhodamine-123, cisplatin or Bodipy-cisplatin by fluorescence assay and inductively coupled plasma mass spectrometry (ICP-MS). From the results described previously, it is concluded that changes in the membrane lipids “composition” cause a change in the physical state of the plasma membrane lipids and that this may be associated with the resistance of A 549/DDP cells to cisplatin.

Characterizing ecosystem‐level consequences of biological invasions: the role of ecosystem engineers

Invasions by exotic species represent both threats to ecosystems as well as opportunities to learn more about them. Among the invaders that will have the largest impacts are those that directly modify ecosystems and thus have cascading effects for resident biota. Exotics can affect ecosystems by altering system‐level flows, availability, or quality of nutrients, food, and physical resources (e.g. living space, water, heat or light). The invader‐mediated control of physical resources, typically achieved through the modification of habitats, has received limited attention in invasion biology. This reflects a general trend in ecology, and only recently has the concept of ecosystem engineering been developed to account for the role of species that shape habitats. Plants and animals in terrestrial and aquatic systems can both create and destroy structure. When introduced into ecosystems, these exotic engineers cause physical state changes with effects that ramify throughout the system. Although the consequences of these modifications are varied and complex, insight gained from general ecological principles offers an opportunity to predict what invaders will do upon their integration into systems. Examples from the literature suggest that introduced ecosystem engineers that increase habitat complexity or heterogeneity tend to cause abundances and/or species richness to rise, while those that decrease complexity tend to have the reverse effect. In assessing such patterns, however, it is critical to also consider spatial scales and the life habits of resident organisms. In addition to providing predictive power, recognition of engineering as a major means by which invasive species affect ecosystems provides a unifying theme for invasion biology and offers a chance to consider more fully the general role of species in ecosystems.

Physicochemical, mineralogical, and morphological characteristics of concrete exposed to elevated temperatures

Concrete cubes prepared from ordinary Portland cement (OPC) of known chemical, mineralogical, and physical performance characteristics and fired to various temperature regimes up to 1000 °C in steps of 100 °C for a constant period of 5 h have been studied by using X-ray diffraction (XRD) and DTA/TGA to establish the effect of elevated temperatures on the mineralogical changes occurring in the hydrated phases of concrete. The changes in physical state of concrete were studied by measuring ultrasonic pulse velocity (UPV) and consequent deterioration in the compressive strength with increase in temperature. Scanning electron microscopy (SEM) studies showed distinct morphological changes corresponding to deterioration of concrete exposed to higher temperatures.

Influence of the fluidity of the membrane on the response of microorganisms to environmental stresses.

The aim of this mini-review is to relate membrane physical properties to the adaptation and resistance of microorganisms to environmental stresses. In the first part, the effects of various stresses on the structure and dynamic properties of phospholipid and biological membranes are presented. The compensation of these effects, i.e., change in membrane fluidity, phase transitions, by the active cellular control of the membrane chemical composition, is then described. In this natural process, the change in membrane fluidity is viewed as the detecting "input" signal that initiates the regulation, activating proteic effectors that in turn may influence the chemical composition of the membrane (feedback). This adaptation system allows the maintenance of the physical characteristics of membranes and, thereby, of their functionality. When environmental stresses are extreme and occur abruptly, the regulation process may not compensate for the changes in the membrane physical characteristics. In such cases, important variations in the membrane fluidity and structure may induce cellular damages and cell death. However, the lethal consequences are not systematically observed because protective effects of changes in the membrane physical state on the resistance to stresses are also reported.

気体力学的衝撃波の入射により超流動ヘリウム中に誘起された衝撃波における温度計測実験

Two modes of shock waves propagating in He II, that is, a compression and a thermal shock waves, were investigated by a measurement of temperature and pressure with superconductive temperature sensors and pressure transducers and by visualization. We adopted the experimental method in which a gas dynamic shock wave impinged onto a He II-free surface by a newly developed superfluid shock tube facility. It was found that the temperature sharply drops as a result of compression by a compression shock wave. However, the temperature drop turns to a rise when the phase of liquid helium changes from He II to He I by shock compression. It was also found that in the immediate vicinity of the vapor-He II interface, no thermal shock wave is excited, where a thermal boundary layer with a large temperature gradient in which the physical state changes from supercritical helium to He II via He I is formed with a thickness of several mm. The temperature profile of a thermal shock wave was found to be a single triangular waveform similar to that of a thermal shock wave generated by large heat flux by a planar heater with a long heating time.