Conversion studies in a novel reaction injection molding process for syndiotactic polystyrene

Syndiotactic polystyrene (sPS) has successfully been produced using a novel reaction injection molding (RIM) process and a metallocene catalyst. Previous studies have shown that many of the requirements for a RIM process are achievable. However, problems due to incomplete conversion of monomer have hindered the commercial development of this process. In attempts to overcome this conversion limitation and gain insight into its nature, the effects of the extent of mixing, reaction time, and mold wall temperature were investigated on the monomer conversion and polymer properties. The properties of interest included the sPS fraction, molecular weight, melting point, and stereoregularity of the polymer produced. It was found that this RIM process was not mixing limited. Longer reaction times resulted in an increase in conversion, with no significant change in the polymer properties. Mold wall temperature had the greatest effect on both the conversion and polymer properties. Lower mold wall temperatures resulted in an increase in the conversion. At both of the temperature extremes studied, the polymer properties deteriorated. Infrared spectroscopic analyses of the as-polymerized samples indicated that sPS helical conformations were present. This suggested that the styrene monomer may be entrapped within the helical crystalline structures of sPS, preventing complete monomer conversion during this sPS RIM process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2679–2693, 1998     

Population Growth Rate Responses of Ceriodaphnia dubia to Ternary Mixtures of Specific Acting Chemicals: Pharmacological versus Ecotoxicological Modes of Action

When considering joint toxic apical effects at higher levels of biological organization, such as the growth of populations, the so-called pharmacological mode of action that relies on toxicological mechanistic effects on molecular target sites may not be relevant. Such effects on population growth rate will depend on the extent to which juvenile and adult survival rates and production rates (juvenile developmental rates and reproduction) are affected by toxic exposure and also by the sensitivity of population growth rates to life-history changes. In such cases, the ecotoxicological mode of action, defined as the crucial life-history trait processes and/or xenobiotic-life-history trait interactions underlying a toxicological effect on population growth rate, should be considered. Life-table response experiments with the crustacean Ceriodaphnia dubia exposed to single and ternary mixtures of nine compounds were conducted to test the hypothesis that joint effects on population growth rates could be predicted from the mixture constituent ecotoxicological mode of action. Joint effects of mixtures containing pharmacologically dissimilar compounds (cadmium, λ-cyhalothrin, and chlorpyrifos) that differentially affected life-history traits contributing to population growth rates were accurately predicted by the independent-action concept. Conversely, the concentration-addition concept accurately predicted joint effects of two different mixtures: one containing pharmacologically similar acting pyrethroids that also affected similarly life-history traits, the other one that included pharmacologically dissimilar compounds (3,4-dichloroaniline, sodium bromide, and fenoxycarb) acting mainly on reproduction rates. These results indicate that when assessing combined effects on population growth rate responses, selection of mixture toxicity conceptual models based on the ecotoxicological mode of action of mixture constituents provided more accurate predictions than those based on the pharmacological mode of action.     

anti-Benzo[a]pyrene-7,8-diol-9,10-epoxide Treatment Increases Levels of the Proteins p53 and p21WAF1 in the Human Mammary Carcinoma Cell Line MCF-7

The tumor suppressor p53 is involved in the recognition of DNA damage induced by radiation and chemicals. The effect of polycyclic hydrocarbons on p53 was investigated by treating MCF-7 cells with anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), an ultimate carcinogenic metabolite of benzo[a]pyrene. Western blotting of lysates with antibody mAb1801 showed that B[a]PDE doses of 0.1 to 0.5 μM caused detectable increases in p53 protein. In cells treated with 0.3 μM B[a]PDE, p53 protein levels increased by 2 hours after treatment, reached a maximum between 8 and 24 hours and returned to control value by 120 hours after treatment. Levels of p21^WAF1 protein increased by 8 hours after treatment, reached a maximum by 48 hours and returned to control value by 168 hours after treatment. B[a]PDE-DNA adducts were quantitated by [γ-³³P]ATP postlabeling and separation on reverse-phase HPLC. Adduct levels dropped rapidly between 2 and 24 hrs after treatment (48 to 15 pmol/mg DNA), and subsequently decreased more slowly (12 pmol/mg DNA at 48 hrs to 3 at 168 hrs). By 96 hours after treatment, p53 protein levels were comparable to those from untreated controls, although a low level of B[a]PDE-DNA adducts remained. Cells treated with B[a]PDE also incorporated significantly less [³H]thymidine into DNA than did untreated cells for at least 24 hours after treatment. These results provide preliminary evidence that B[a]PDE-induced DNA damage is recognized by a p53-dependent signal transduction pathway and suggest that cell cycle arrest occurs during the repair of the majority of the B[a]PDE-DNA adducts.     

THE ROLE OF PAH-DNA ADDUCTS IN CAUSING CANCER

This article addresses the evidence for the mechanism of activation of polycyclic aromatic hydrocarbons (PAH) to “ultimate carcinogenic” DNA-binding metabolites in cells and describes how analysis of DNA adducts allowed the determination that the metabolites are dihydrodiol epoxides of PAH. Initially, the PAH-DNA adduct analysis techniques we developed allowed us to establish that the reactive form of PAH that bind to DNA in cells was not the K-region epoxide. Further development of PAH-DNA adduct analysis techniques allowed us to determine that in the case of the very potent carcinogen dibenzo[a,l]pyrene, the reactive metabolite was a diol epoxide with “fjord region” of the molecule. Collaborative studies of DNA adducts in cells from a mouse in which cytochrome P450 1B1 levels were knocked out demonstrated that DB[a,l]P activation to DNA binding intermediates was reduced to undetectable levels demonstrating the great importance of this enzyme in activating fjord region containing PAH.     

Application and evaluation of the method of ellipses for measuring the orientation of long,semi‐flexible fibers

The method of ellipses (MoE) is a common experimental technique utilized to quantitatively determine the orientation state of a population of rigid fibers within a fiber–polymer composite. In this research, the validity of applying the MoE to long, semi‐flexible fiber systems in which the majority of fibers are flexible is discussed. The components of the orientation tensor were first determined for a composite formed by a homogenous, simple shear field. The minimum acceptable image analysis width, or bin width, for the selected geometry was found to be ∼5.5 mm, or 1.4 times the average fiber length. This modified bin width was then used to determine the orientation at multiple percentages of flow within an injection‐molded, center‐gated disc, and compared to orientation values obtained utilizing the traditional, 0.7‐mm bin width. The results show that the traditional, 0.7‐mm bin width is sufficient for analysis of the center‐gated geometry. This fortuitous result is attributed to the axisymmetric nature of the center‐gated geometry, and the highly transverse fiber alignment seen within the samples, especially at moderate to high percentages of flow. In more complex flows, it is expected that the conventional bin width will not apply. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

The experiences of Sudanese unaccompanied minors in foster care.

Sudanese unaccompanied minors were separated from their parents in childhood and lived apart from their families in refugee camps for close to a decade before being resettled in the United States. This phenomenological study examines the refugees’ experiences of living in American foster families after living in peer groups in the camps. Interviews with 18 young adults, 7 years after resettlement, revealed that nearly all of the youth struggled with parental authority initially, and nearly half of them changed placements because of relationship difficulties with their foster parents. Misunderstandings based on cultural differences often exacerbated conflicts. However, 15 of 18 youth currently had a positive relationship with at least 1 foster parent, sometimes with a parent from their second or third placement. Changing foster families is often considered a failure in the child welfare system, but several Sudanese youth reported that having supportive relationships helped them during the acculturation process whether those relationships developed during the first or last placement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reading and arithmetic in adolescents with autism spectrum disorders: Peaks and dips in attainment.

In describing academic attainment in autism spectrum disorders (ASD), results are typically reported at the group mean level. This may mask subgroups of individuals for whom academic achievement is incommensurate with intellectual ability. The authors tested the IQ, literacy, and mathematical abilities of a large group (N = 100) of adolescents (14–16 years old) with ASD. Seventy-three percent of the sample had at least one area of literacy or mathematical achievement that was highly discrepant (approximately 14 standard score points) from full-scale IQ (FSIQ). The authors focused on four subgroups with either word reading (“Reading Peak” and “Reading Dip”) or arithmetic (“Arithmetic Peak” and “Arithmetic Dip”) higher or lower than FSIQ. These subgroups were largely mutually exclusive and were characterized by distinct intellectual profiles. The largest was the “Arithmetic Peak” subgroup of participants, who presented with average intellectual ability alongside superior arithmetic skills and who were predominantly in a mainstream educational setting. Overall, the most pervasive profile was discrepantly poor reading comprehension, which associated with severity of social and communication difficulties. The high rate of uneven academic attainment in ASD has implications for educational practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multilayer PZT 95/5 Antiferroelectric Film Energy Storage Devices with Giant Power Density

A new type of energy storage devices utilizing multilayer Pb(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ films is studied experimentally and numerically. To release the stored energy, the multilayer ferroelectric structures are subjected to adiabatic compression perpendicular to the polarization direction. Obtained results indicate that electrical interference between layers (10–120 layers) during stress wave transit through the structures has an effect on the generated current waveforms, but no impact on the released electric charge. The multilayer films undergo a pressure‐induced phase transition to antiferroelectric phase at 1.7 GPa adiabatic compression and become completely depolarized, releasing surface screening charge with density equal to their remnant polarization. An energy density of 3 J cm^?3 is successfully achieved with giant power density on the order of 2 MW cm^?3, which is four orders of magnitude higher than that of any other type of energy storage device. The outputs of multilayer structures can be precisely controlled by the parameters of the ferroelectric layer and the number of layers. Multilayer film modules with a volume of 0.7 cm³ are capable of producing 2.4 kA current, not achievable in electrochemical capacitors or batteries, which will greatly enhance the miniaturization and integration requirements for emerging high‐power applications.     

Human Endometrial Carcinogenesis Is Associated with Significant Reduction in Long Non-Coding RNA,TERRA

Telomeres are transcribed as long non-coding RNAs called TERRAs (Telomeric repeat containing RNA) that participate in a variety of cellular regulatory functions. High telomerase activity (TA) is associated with endometrial cancer (EC). This study aimed to examine the levels of three TERRAs, transcribed at chromosomes 1q-2q-4q-10q-13q-22q, 16p and 20q in healthy (n = 23) and pathological (n = 24) human endometrium and to examine their association with cellular proliferation, TA and telomere lengths. EC samples demonstrated significantly reduced levels of TERRAs for Chromosome 16p (Ch-16p) (p < 0.002) and Chromosome 20q (Ch-20q) (p = 0.0006), when compared with the postmenopausal samples. No significant correlation was found between TERRA levels and TA but both Ch-16p and Ch-20q TERRA levels negatively correlated with the proliferative marker Ki67 (r = −0.35, p = 0.03 and r = −0.42, p = 0.01 respectively). Evaluation of single telomere length analysis (STELA) at XpYp telomeres demonstrated a significant shortening in EC samples when compared with healthy tissues (p = 0.002). We detected TERRAs in healthy human endometrium and observed altered individual TERRA-specific levels in malignant endometrium. The negative correlation of TERRAs with cellular proliferation along with their significant reduction in EC may suggest a role for TERRAs in carcinogenesis and thus future research should explore TERRAs as potential therapeutic targets in EC.