Transient Degradation Research Articles

Combination immunotherapy integrating HSP90 inhibitor 17-DMAG reconditions the tumor microenvironment for improved T cell recruitment and anti-tumor efficacy (52.19)

Abstract Deficiencies in MHC Class I antigen presentation by tumor cells is a significant barrier to effective cancer immunotherapy. Therefore, combinational therapies that enhance tumor-associated antigen (TAA) presentation in tumor MHC Class I molecules while coordinately stimulating TAA-specific immunity would be expected to yield a greater clinical benefit. We have previously showed that in vitro treatment of tumor cells with 17-DMAG results in transient (proteasome-dependent) degradation of the EphA2, a TAA that is over expressed in several cancers, accompanied by increased presentation of EphA2 peptides on MHC class I complexes on tumor cells. To further characterize the therapeutic potential of this approach, we assessed the efficacy of a rationally-designed combinational therapy incorporating 17-DMAG and EphA2-targeted immunotherapy in murine tumor models. In vivo administration of 17-DMAG promoted: i) dramatically slowed tumor growth; ii) Enhanced recognition of tumor cells by anti-EphA2 CD8+ T cells; iii) Reduction in the frequency of myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) in the tumor microenvironment, and iv) activation of tumor-associated vascular endothelial cells thereby facilitating Type-1 T cell infiltration. When combined with EphA2-specific active vaccination or the adoptive transfer of EphA2-specific CD8+ T cells, 17-DMAG co-treatment yielded a superior tumor therapeutic regimen that was capable of rendering animals free of disease.

Expansion of bone marrow neutrophils following G-CSF administration in mice results in osteolineage cell apoptosis and mobilization of hematopoietic stem and progenitor cells

Proliferation and differentiation of hematopoietic stem/progenitor cells (HSPC) within bone marrow (BM) niches are regulated by adhesion molecules and cytokines produced by mesenchymal stem/progenitor cells (MPC) and osteoblasts (OB). HSPCs that egresses to peripheral blood are widely used for transplant and granulocyte-colony stimulating factor_(G-CSF) is used clinically to induce mobilization. The mechanisms, through which G-CSF regulates HSPC trafficking however, are not completely understood. Herein we show that G-CSF driven neutrophil expansion alters the BM niche that leads to HSPC mobilization. Alcam−Sca-1+MPC and Alcam+Sca-1− OB are reduced coincident with mobilization, which correlates inversely with BM neutrophil expansion. In mice made neutropenic by the neutrophil specific anti-Ly6G antibody, G-CSF mediated reduction in MPC and OB is attenuated and mobilization reduced without an effect on monocytes/macrophages. Neutrophils, expanded in response to G-CSF induce MPC and OB apoptosis leading to reduced production of BM HSPC retention factors including stromal cell derived factor-1 (SDF-1), stem cell factor (SCF) and vascular cell adhesion molecule-1(VCAM-1). Blockade of neutrophil reactive oxygen species (ROS) attenuates G-CSF mediated MPC and OB apoptosis. These data show that the expansion of BM neutrophils by G-CSF contributes to the transient degradation of retention mechanisms within the BM niche, facilitating enhanced HSPC egress/mobilization.

Study of RF Reliability of GaN HEMTs Using Low-Frequency Noise Spectroscopy

The results of continuous wave short-term RF stress applied at 3 GHz on GaN high electron mobility transistors on silicon substrate are presented. The degradation of the device characteristics for RF overdrive conditions from 3-dB to 8-dB gain saturation is discussed. Output RF power degrades significantly in a short period of time. Both transient and permanent degradation of electronic properties of the device are identified. After high RF gain compression levels, DC characteristics like the threshold voltage and gate leakage current change permanently. Detailed microscopic changes in the electronic structure of the device were studied by performing simultaneous low-frequency noise measurements of gate and drain currents before and after stress. The channel was found to be immune to the whole stress regime with no increase of the Hooge parameter. On the other hand, activation of unstable defects and then an increase of the defect density near the gate metal semiconductor interface were observed from gate noise measurements. A point defect located at around 4.5 nm from the gate metal semiconductor interface with activation energy of 0.9 eV below the AlGaN conduction band edge was determined from random telegraph noise measurements. The role of forward gate biasing as a failure mechanism is also discussed.

Hydrogen PEMFC system for automotive applications

A balance of plant (BOP) system for a 9.5-kWe Nedstack P9.5-75 low-temperature proton exchange membrane fuel cell (FC) stack was tested up to a power of 2 kWe. The system has been designed to act as a range extender for a series hybrid electric vehicle driven under urban duty cycles. Vehicle simulations have estimated that an average gross power requirement of 4 kWe is needed from the FC, whilst simulations of the FC stack and BOP components have allowed for characterisation of transient behaviour and performance degradation. Copyright , Oxford University Press.

Analysis of thermal characteristics and mechanism of degradation of flip-chip high power LEDs

The purpose of this study is to investigate the thermal behavior at the die-attached interfaces of flip-chip GaN high-power light emitting diodes (LEDs) using a combination of theoretical and experimental analyses. The results indicate that contact thermal resistance increased dramatically at the die-attached interfaces with aging time and stress, degrading the luminous flux. The junction temperature and thermal uniformity of the flip-chip structure both strongly depend on the arrangement of gold bumps. Local hot spots effectively reduce light output under high electric and thermal stress, influencing the long-term performance of the LED device. The results were validated using finite element analysis and in experiments using an infrared and an emission microscope. A two-step thermal transient degradation mode was identified under various aging stresses. A simulation further optimized the bump configuration that was associated to yield a low junction temperature and high temperature uniformity of the LED chip. Accordingly, the results are helpful in enhancing the performance and reliability of high-power LEDs.

Epithelial Junction Opener JO-1 Improves Monoclonal Antibody Therapy of Cancer

The efficacy of monoclonal antibodies (mAb) used to treat solid tumors is limited by intercellular junctions which tightly link epithelial tumor cells to each another. In this study, we define a small, recombinant adenovirus serotype 3-derived protein, termed junction opener 1 (JO-1), which binds to the epithelial junction protein desmoglein 2 (DSG2). In mouse xenograft models employing Her2/neu- and EGFR-positive human cancer cell lines, JO-1 mediated cleavage of DSG2 dimers and activated intracellular signaling pathways which reduced E-cadherin expression in tight junctions. Notably, JO-1-triggered changes allowed for increased intratumoral penetration of the anti-Her2/neu mAb trastuzumab (Herceptin) and improved access to its target receptor, Her2/neu, which is partly trapped in tight junctions. This effect translated directly into increased therapeutic efficacy of trastuzumab in mouse xenograft models using breast, gastric, and ovarian cancer cells that were Her2/neu-positive. Furthermore, combining JO-1 with the EGFR-targeting mAb cetuximab (Erbitux) greatly improved therapeutic outcomes in a metastatic model of EGFR-positive lung cancer. A combination of JO-1 with an approach that triggered transient degradation of tumor stroma proteins elicited eradication of tumors. Taken together, our findings offer preclinical proof of concept to employ JO-1 in combination with mAb therapy.

Transient Platinum Oxide Formation and Oxygen Reduction on Carbon-Supported Platinum and Platinum-Alloy Electrocatalysts

Chronoamperometry studies at a fixed potential of 0.9V vs. the reversible hydrogen electrode (RHE) have been performed on three PEM fuel cell catalysts (50 wt.% Pt/C, 30 wt. % PtM1/C and 30 wt. % PtM2/C) on both rotating disk electrodes (RDEs) and membrane electrode assemblies (MEAs), in order to investigate similarities and differences between Pt and Pt-alloy catalysts for transient behavior of the oxygen reduction reaction (ORR). Similar trends of reversible activity degradation were shown for both RDEs and MEAs. Compared to the baseline Pt/C catalyst, alloy catalysts under potential hold were found to have higher oxide coverage and faster oxide-growth rate, with the latter related to their faster transient ORR activity degradation rate. In addition, PtM1/C showed a higher ORR activity than PtM2/C in MEA tests, while the opposite trend was found in RDE tests, which could be attributed to their different transient stability under potential hold.

Repassivation behaviour of stressed aluminium electrodes in aqueous chloride solutions

The combined influence of mechanical stress and chemical environment on the pitting susceptibility of aluminium electrodes was studied by integrating open circuit potential measurements and electrochemical repassivation modelling. The transient degradation of aluminium oxide owing to a tensile stress field and its subsequent repassivation are observed as an abrupt negative potential excursion followed by a slow decay of the corrosion potential back towards its initial value prior to the mechanical loading. Experiments were performed and an electrochemical repassivation model was established to quantitatively describe the dependence of oxide dissolution rate and the reciprocal of cathodic Tafel slope on chloride concentration.

Computational study of local and global ECM degradation and the effects on cell speed and cell–matrix tractions

Cell migration is important to biological processes such as wound healing and cancer invasion. Cell movement involves forming bonds between cell surface receptors and ligands present in the extracellular matrix (ECM) in order to generate the necessary forces on the matrix. For three-dimensional cell migration, partial degradation of the adjacent ECM using matrix metalloproteinases is necessary to create a passage with less motion resistance. Our mathematical model takes into consideration cell–ECM tractions needed to drive cell movement, viscous drag forces, and a transient matrix degradation process. Simulations were performed for global and highly localized matrix degradation processes, where the latter occurred at the cell–ECM interface. It was observed that the higher the speed of the cell boundary, the higher the matrix concentration after localized degradation. The results showed that a greater ECM degradation coefficient was needed for optimal cell migration to occur for the local process and that cell–ECM tractions were larger. The results from this investigation complement those obtained by other studies where it has been shown that cell speed is a biphasic function of ligand and matrix metalloproteinase concentration, and would also be of use for research on wound healing, cancer cell invasion, and tissue engineering.

Regulation of learned vocal behavior by an auditory motor cortical nucleus in juvenile zebra finches

In the process of song learning, songbirds such as the zebra finch shape their initial soft and poorly formed vocalizations (subsong) first into variable plastic songs with a discernable recurring motif and then into highly stereotyped adult songs. A premotor brain area critically involved in plastic and adult song production is the cortical nucleus HVC. One of HVC's primary afferents, the nucleus interface of the nidopallium (NIf), provides a significant source of auditory input to HVC. However, the premotor involvement of NIf has not been extensively studied yet. Here we report that brief and reversible pharmacological inactivation of NIf in juvenile birds leads to transient degradation of plastic song toward subsong, as revealed by spectral and temporal song features. No such song degradation is seen following NIf inactivation in adults. However, in both juveniles and adults NIf inactivation leads to a transient decrease in song stereotypy. Our findings reveal a contribution of NIf to song production in juveniles that agrees with its known role in adults in mediating thalamic drive to downstream vocal motor areas during sleep.

Application of salicylic acid induces antioxidant defense responses in the phloem of Picea abies and inhibits colonization by Ips typographus

The adaptive plasticity of Norway spruce (Picea abies) against attack by Ips typographus depends on systemic acquired resistance which involves salicylic acid (SA), and an antioxidant system both recognized as valuable stress markers in ecophysiological studies. In the presented field experiment, 100mM SA was applied to the bark sections of Norway spruce prior to being attacked by bark beetles, in order to study interactions with antioxidants and its significance for mediating stress-tolerance under natural conditions. SA-treatments significantly elevated the total SA levels over the whole sampling period. Total glutathione (tGSH) and total cysteine (tCys) increased by 167% and 80%, respectively, two weeks after treatment, in comparison with controls. In contrast, SA-treatment caused an initial deterioration in total ascorbic acid (tASC) and enhanced the percentage of dehydroascorbic acid (DHA), but activated tASC levels over later sampling dates. The initial bark beetle attack was characterized by a significant decline in total SA levels, which was accompanied by a transient degradation and oxidation of their ascorbate-glutathione system. This initial reaction was significantly alleviated by SA-application and characterized by 175% higher tGSH contents, when compared to moderately-affected untreated trees. One month after pheromone dispensers were placed on trees, an intensification of ascorbate-glutathione system occurred within moderately-affected bark, but to a greater extent after SA-treatment. Total SA levels within SA-treated moderately-affected trees remained at the control level until June. In contrast, strong attack was characterized by a successive increase in total SA up to 252% following SA-treatment in June, whereas a 110% increase of SA was determined within severely affected control-bark. A strong attack was further characterized by a degradation of tGSH and total phenolics (tPH), a moderate increase in tASC and an oxidation of the ascorbate-glutathione pool within untreated bark. In the SA-treated trees the redox state was unaffected by severe colonization and the degradation of antioxidants was significantly alleviated. In addition, SA-treated bark had significantly less entrance holes and exhibited fewer and shorter maternal galleries than control-bark. From this perspective, exogenous SA was successfully implicated as an activator of systemic acquired resistance in Norway spruce, providing tolerance against the complex interactive effects of bark beetle attack and environmental factors.

Transient degradation of myelin basic protein in the rat hippocampus following acute carbon monoxide poisoning

The neurotoxicity of carbon monoxide (CO) poisoning is a significant clinical problem, but its mechanisms remain unclear. Previous studies of CO-exposed rats showed spatial memory disturbances and degradation of myelin basic protein (MBP) in the brain; however, regional localization of the degradation was not analyzed. In the present study, we histologically determined the foci of CO effects in the hippocampus. Wistar rats were exposed to CO for 60 min (1000 ppm for 40 min + 3000 ppm for 20 min) and returned into room air. For histological evaluation, the animals were sacrificed 90 min, 1, 7 and 14 days after CO exposure and the brain tissue was analyzed with hematoxylin–eosin (HE), Nissl and Gallyas myelin staining as well as immunohistochemistry for MBP and phosphorylated or nonphosphorylated neurofilament. No histological changes were observed on HE, Nissl or Gallyas staining. In contrast, we detected MBP reduction at 90 min after CO exposure in the dentate gyrus and CA3, and the recovery of MBP was observed after 14 days. The immunoreactivity of neurofilament also changed after CO exposure. Nevertheless, water maze test showed no significant effects of CO exposure on spatial memory. Our findings demonstrate that CO poisoning causes transient degradation of MBP and axonal injury in the hippocampus even though the animals showed no neurological disturbances.

Ago-associated human usRNAs and other similar small RNAs

We report the characterization of several subclasses of unusually small RNAs (usRNAs) in human and viral genomes. Prior to our work, two popular, yet incorrect presumptions led to all small RNAs less than 20 bases in length (usRNAs) being thought of as transient degradation products of longer RNAs or as RNAs that cannot be reliably mapped to the genome. In this work, we show that while 100% of usRNAs cannot be mapped reliably to the genomes, ~16% of RNAs as small as 15 bases can be reliably mapped to the genome, corresponding to thousands of new small RNAs. We demonstrate that these 5'-phosphate containing usRNAs are accurately, reproducibly and repeatedly, produced across various tissues, and have very unique biological characteristics, thus contesting the hypothesis that these RNAs can be ignored as transient degradation products. Our observations began with the identification of a Kaposi sarcoma-associated herpesvirus us-K12-1 RNA (17 bases) that is as effective as the K12-1 miRNA in regulating human RAD21, a novel K12-1 target. High-throughput sequencing followed by bioinformatics analysis and molecular profiling reveals a diverse set of human miRNA-derived usRNAs and other non-miRNA-derived usRNAs. Human miRNA-derived usRNAs preferentially match to 5' ends of miRNAs, and are also more likely to associate with the siRNA effector protein Ago2, than Ago1. Many non-miRNA-derived usRNAs associate with Ago proteins and also frequently contain C-rich 3'-specific motifs that are highly position specific, and are overrepresented in comparison to piRNAs and TSSa-RNAs. In summary, our observations suggest that ~ 30% of usRNAs could have evolved to participate in biological processes including gene-silencing.

A temporal analysis of antioxidative defense responses in the phloem of Picea abies after attack by Ips typographus

The temporal gradation of antioxidants was investigated on the phloem tissue of Norway spruce [Picea abies (L.) Karst.] in response to weather conditions and colonization levels of Ips typographus L. (Col., Scolytidae). Two weeks after pheromone dispensers were placed on trees, the initial reaction of Norway spruce to bark beetle attack resulted in moderately lowered levels of total glutathione (tGSH) and total cysteine. Likewise, the total ascorbic acid dropped slightly below the control levels, whereas the concentration of dehydroascorbic acid increased in comparison to the first sampling date. This transient degradation and oxidation of the glutathione and ascorbate system was accompanied by moderately increased concentrations of total phenolics. One month later, the shift in antioxidant balance after moderate attack differed quantitatively from the reaction after massive attack. An intensification of antioxidant defense occurred within moderately affected bark. Total cysteine and tGSH contents were markedly raised, whereas the concentrations of total ascorbic acid and total phenolics were slightly increased by moderate attack. On the other hand, massive bark beetle colonization caused a strong decrease in tGSH and total phenolics, whereas total cysteine and total ascorbic acid values remained at control level. Dependent upon the intensity and the success of the attack, a progressive degradation of antioxidants was determined at later sampling dates, which was accompanied by an obvious oxidation of the ascorbate and glutathione pools. With an unsuccessful defense upon massive attack, the thiols and total phenolics did not reach a new steady state, but deteriorated until the end of the brood beetles' development. In contrast, the dynamic antioxidative response within the moderately affected trees indicated an acclimation stage in the middle of July. It was characterized by a higher accumulation of tGSH, total ascorbic acid and total phenolics as well as a more reduced redox state of glutathione. A sequence of changes in the endogenous levels of antioxidant defense molecules in the bark beetle-affected Norway spruce showed consistency with the general ecophysiological stress-response concept, and provided important avenues for evaluating the role and effectiveness of antioxidants in systemic acquired resistance against the complex interactive effects of bark beetle attack and environmental factors.

Intra-articular injection of tumor necrosis factor-α in the rat: an acute and reversible in vivo model of cartilage proteoglycan degradation

To develop an in vivo model for rapid assessment of cartilage aggrecan degradation and its pharmacological modulation. Tumor necrosis factor-alpha (TNFalpha) was injected intra-articularly (IA) in rat knees and aggrecan degradation was monitored at various times following challenge. Articular cartilage was assessed for aggrecan content by Safranin O staining and by immunohistochemistry for the NITEGE epitope. Synovial fluids (SFs) were analyzed for sulfated glycosaminoglycans (GAGs) using the dimethylmethylene blue dye assay and for aggrecan fragments generated by specific cleavage at aggrecanase-sensitive sites by Western blot analysis with neoepitope antibodies. Indomethacin, dexamethasone, and an aggrecanase inhibitor were evaluated for their ability to modulate TNFalpha-induced proteoglycan degradation in vivo. (1) IA injection of TNFalpha in the knee joint of rats resulted in transient aggrecan degradation and release of aggrecanase-generated aggrecan fragments from the articular cartilage into the SF; (2) a correlation was observed between histologically assessed depletion of aggrecan from the articular cartilage and the appearance of specific neoepitopes in the SF; (3) aggrecan degradation was inhibited by an aggrecanase inhibitor as well as by dexamethasone, but not by the non-steroidal anti-inflammatory drug (NSAID), indomethacin. TNFalpha injection in the knee joints of rats results in rapid transient cartilage proteoglycan degradation, mediated by cleavage at the aggrecanase sites. Biomarker read-out of specific neoepitopes in the SF enables the use of this mechanism-based model for rapid evaluation of aggrecanase-mediated aggrecan degradation in vivo.

New Insight Into NBTI Transient Behavior Observed From Fast-$G_{M}$ Measurements

Fast-I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> measurements have become an important tool to examine MOSFET transient degradation. The threshold voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) extracted from fast-I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> measurements is often used to infer the transient behavior of trapped charges in the gate dielectric and at the interface. In this letter, we show that the peak transconductance (G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> ) can also be extracted reliably in the microsecond time scale. The transient G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> behavior provides additional insights not easily observed from an examination of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> alone. Specifically, transient <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GM</i> results illustrate that an electron trapping/detrapping transient component contributes to the transient behavior observed in the negative bias temperature instability. This electron trapping component has never been reported.

Passive control of liquid water storage and distribution in a PEFC through flow-field design

Liquid water stored in the diffusion media (DM) in a polymer electrolyte fuel cell (PEFC) can dramatically impact steady and transient performance, degradation, and heat transfer. In this study, seven different flow-field designs, with landing-to-channel (L:C) ratio from 1:3 to 2:1, were investigated at dry and fully humidified conditions, using neutron imaging. The results revealed the impact of flow-field geometry on stored liquid overhead is significant. In some cases, the stored water content in the cell can be nearly double that of another design, despite similar performances at low to medium current density. In general, a smaller L:C ratio reduces flooding losses and minimizes the stored water content. Additionally, the channel–DM interface plays a key role. For the same L:C ratio, a reduced number of channel–DM interfaces was shown to reduce flooding and stored liquid water content at steady state. This also suggests that using proper flow-field design can decrease the parasitic power consumption and the stored water content in the cell without any sacrifice from the cell performance. For dryer operating conditions, however, membrane dehydration becomes a dominant effect and a high landing-to-channel ratio flow-field is higher performing.

Influence of Anomeric Configuration on Mechanochemical Degradation of Polysaccharides: Cellulose versus Amylose

Cellulose and amylose are (1-->4)-linked polysaccharides that are used extensively in the textiles, paper, and food and feed industries and are finding increasing use as alternative fuels and so forth. At the molecular level, cellulose and amylose differ only in their anomeric configuration: beta in cellulose, alpha in amylose. During processing and end use, these polymers experience a variety of mechanochemical stresses, many through contact with transient elongational flow fields. Here, we subject solutions of both polysaccharides to extended periods of ultrasonic irradiation, as the cavitational bubble collapse characteristic of ultrasound experiments creates flow fields strictly analogous to those encountered in other transient elongational flow scenarios. With the use of multidetector size-exclusion chromatography, the effects of anomeric configuration on both the limiting molar mass, beyond which polymers do not degrade in transient elongation flow ( M lim), and the rate of degradation have been isolated in these (1-->4)-linked polysaccharides. This effect was found to be pronounced; for example, M lim (cellulose) = 5( M lim (amylose)). Also, while extensive change was observed in molar mass averages, distribution, polydispersity, and size of the analytes during degradation, their structure was found to remain invariant. A modified "path theory" of transient elongational flow degradation was proposed, with the persistence length identified as a parameter which embodies the minimum continuous path length and flexibility requirements of the theory.

An extra-plastidial -glucan, water dikinase from Arabidopsis phosphorylates amylopectin in vitro and is not necessary for transient starch degradation

Starch phosphorylation catalysed by the alpha-glucan, water dikinases (GWD) has profound effects on starch degradation in plants. The Arabidopsis thaliana genome encodes three isoforms of GWD, two of which are localized in the chloroplast and are involved in the degradation of transient starch. The third isoform, termed AtGWD2 (At4g24450), was heterologously expressed and purified and shown to have a substrate preference similar to potato GWD. Analyses of AtGWD2 null mutants did not reveal any differences in growth or starch and sugar levels, when compared to the wild type. Subcellular localization studies in Arabidopsis leaves and in vitro chloroplast import assays indicated that AtGWD2 was not targeted to the chloroplasts. The AtGWD2 promoter showed a highly restricted pattern of activity, both spatially and temporally. High activity was observed in the companion cells of the phloem, with expression appearing just before the onset of senescence. Taken together, these data indicate that, although AtGWD2 is capable of phosphorylating alpha-glucans in vitro, it is not directly involved in transient starch degradation.

Interactive effect of oxygen diffusion and volatiles advection on transient thermal degradation of poly methyl methacrylate (PMMA)

A transient, one-dimensional model has been presented to formulate the substantial role of polymer gasification in the early stages of fire growth. The present model comprises the interaction between the oxygen diffusion and the released volatiles on the rate of polymer gasification, when the polymeric sample is subjected to an external radiative source. The model also includes different mechanisms affecting the degradation process such as in-depth thermal and oxidative decomposition, in-depth absorption of radiation and heat and mass transfer in the both gas and solid phases. The results for two different radiative heat sources (17 and 40 kW m−2) are reported and yielded realistic results, comparing to the published experimental data. It was found that an increase in the oxygen concentration will lead to a considerable decrease in the surface temperature as well as significant increase of gasification rate at 17 kW m−2; nevertheless this effect is less apparent at 40 kW m−2.