Polyimides with pendant alkyl groups

The effect on selected polyimide properties when pendant alkyl groups were attached to the polymer backbone was investigated. A series of polymers were prepared using benzophenone tetracarboxylic acid dianhydride (BTDA) and seven different p-alkyl-m,p'-diaminobenzophenone monomers. The alkyl groups varied in length from C(1) (methyl) to C(9) (nonyl). The polyimide prepared from BTDA and m,p'-diaminobenzophenone was included as a control. All polymers were characterized by various chromatographic, spectroscopic, thermal, and mechanical techniques. Increasing the length of the pendant alkyl group resulted in a systematic decrease in glass transition temperature (Tg) for vacuum cured films. A 70 C decrease in Tg to 193 C was observed for the nonyl polymer compared to the Tg for the control. A corresponding systematic increase in Tg indicative of crosslinking, was observed for air cured films. Thermogravimetric analysis revealed a slight sacrifice in thermal stability with increasing alkyl length. No improvement in film toughness was observed

The Tully-Fisher relation of distant field galaxies

We examine the evolution of the Tully-Fisher relation (TFR) using a sample of 89 field spirals, with 0.1 < z < 1, for which we have measured confident rotation velocities (Vrot). By plotting the residuals from the local TFR versus redshift, or alternatively fitting the TFR to our data in several redshift bins, we find evidence that luminous spiral galaxies are increasingly offset from the local TFR with redshift, reaching a brightening of -1.0+-0.5 mag, for a given Vrot, by approximately z = 1. Since selection effects would generally increase the fraction of intrinsically-bright galaxies at higher redshifts, we argue that the observed evolution is probably an upper limit. Previous studies have used an observed correlation between the TFR residuals and Vrot to argue that low mass galaxies have evolved significantly more than those with higher mass. However, we demonstrate that such a correlation may exist purely due to an intrinsic coupling between the Vrot scatter and TFR residuals, acting in combination with the TFR scatter and restrictions on the magnitude range of the data, and therefore it does not necessarily indicate a physical difference in the evolution of galaxies with different Vrot. Finally, if we interpret the luminosity evolution derived from the TFR as due to the evolution of the star formation rate (SFR) in these luminous spiral galaxies, we find that SFR(z) is proportional to (1+z)^(1.7+-1.1), slower than commonly derived for the overall field galaxy population. This suggests that the rapid evolution in the SFR density of the universe observed since approximately z = 1 is not driven by the evolution of the SFR in individual bright spiral galaxies. (Abridged.)Comment: 14 pages, 10 figures, accepted by MNRA

Phonon-induced quadrupolar ordering of the magnetic superconductor TmNi2_2B2_2C

We present synchrotron x-ray diffraction studies revealing that the lattice of thulium borocarbide is distorted below T_Q = 13.5 K at zero field. T_Q increases and the amplitude of the displacements is drastically enhanced, by a factor of 10 at 60 kOe, when a magnetic field is applied along [100]. The distortion occurs at the same wave vector as the antiferromagnetic ordering induced by the a-axis field. A model is presented that accounts for the properties of the quadrupolar phase and explains the peculiar behavior of the antiferromagnetic ordering previously observed in this compound.Comment: submitted to PR

Quiescence: a mechanism for escaping the effects of drug on cell populations

We point out that a simple and generic strategy to lower the risk for extinction consists in the developing a dormant stage in which the organism is unable to multiply but may die. The dormant organism is protected against the poisonous environment. The result is to increase the survival probability of the entire population by introducing a type of zero reproductive fitness. This is possible, because the reservoir of dormant individuals act as a buffer that can cushion fatal fluctuations in the number of births and deaths which without the dormant population would have driven the entire population to extinction.Comment: 18 pages and 9 figure

Synthesis of imide/arylene ether copolymers for adhesives and composite matrices

A series of imide/arylene ether copolymers were prepared from the reaction of an amorphous arylene ether oligomer and a semi-crystalline imide oligomer. These copolymers were thermally characterized and mechanical properties were measured. One block copolymer was endcapped and the molecular weight was controlled to provide a material that displayed good compression moldability and attractive adhesion and composite properties

Power spectrum of mass and activity fluctuations in a sandpile

We consider a directed abelian sandpile on a strip of size $2\times n$, driven by adding a grain randomly at the left boundary after every $T$ time-steps. We establish the exact equivalence of the problem of mass fluctuations in the steady state and the number of zeroes in the ternary-base representation of the position of a random walker on a ring of size $3^n$. We find that while the fluctuations of mass have a power spectrum that varies as $1/f$ for frequencies in the range $3^{-2n} \ll f \ll 1/T$, the activity fluctuations in the same frequency range have a power spectrum that is linear in $f$.Comment: 8 pages, 10 figure

1/z-renormalization of the mean-field behavior of the dipole-coupled singlet-singlet system HoF_3

The two main characteristics of the holmium ions in HoF_3 are that their local electronic properties are dominated by two singlet states lying well below the remaining 4f-levels, and that the classical dipole-coupling is an order of magnitude larger than any other two-ion interactions between the Ho-moments. This combination makes the system particularly suitable for testing refinements of the mean-field theory. There are four Ho-ions per unit cell and the hyperfine coupled electronic and nuclear moments on the Ho-ions order in a ferrimagnetic structure at T_C=0.53 K. The corrections to the mean-field behavior of holmium triflouride, both in the paramagnetic and ferrimagnetic phase, have been calculated to first order in the high-density 1/z-expansion. The effective medium theory, which includes the effects of the single-site fluctuations, leads to a substantially improved description of the magnetic properties of HoF_3, in comparison with that based on the mean-field approximation.Comment: 26pp, plain-TeX, JJ

The life and health challenges of young Malaysian couples: results from a stakeholder consensus and engagement study to support non-communicable disease prevention

BACKGROUND: Malaysia faces burgeoning obesity and diabetes epidemics with a 250% and 88% increase respectively between 1996 and 2006. Identifying the health challenges of young adults in Malaysia, who constitute 27.5 % of the population, is critical for NCD prevention. The aim of the study was two-fold: (1) to achieve consensus amongst stakeholders on the most important challenge impacting the health of young adults, and (2) to engage with stakeholders to formulate a NCD prevention framework.METHODS: The Delphi Technique was utilised to achieve group consensus around the most important life and health challenges that young adults face in Malaysia. Subsequently, the results of the consensus component were shared with the stakeholders in an engagement workshop to obtain input on a NCD prevention framework.RESULTS: We found that life stress was a significant concern. It would seem that the apathy towards pursuing or maintaining a healthy lifestyle among young adults may be significantly influenced by the broader distal determinant of life stress. The high cost of living is suggested to be the main push factor for young working adults towards attaining better financial security to improve their livelihood. In turn, this leads to a more stressful lifestyle with less time to focus on healthier lifestyle choices.CONCLUSIONS: The findings highlight a pivotal barrier to healthier lifestyles. By assisting young adults to cope with daily living coupled with realistic opportunities to make healthier dietary choices, be more active, and less sedentary could assist in the development of NCD health promotion strategies<br/