Molecular separation by thermosensitive hydrogelmembranes

A new method for separation of molecules of different size is presented. The method is a useful addition to conventional separation methods which depend mainly on gel permeation chromatography using size exclusion. In the new method, hydrogel membranes are used which swelling level can be thermally controlled. In this study, a crosslinked poly(N-isopropylacrylamide¿co-butylmethacrylate 95:5mol%) membrane is used and three solutes of distinct molecular size: two dextrans with molecular weights of 150,000 and 4,400 g/mol respectively and uranine with a molecular weight of 376 g/mol. The swelling of the membranes as function of temperature was measured as well as the influence of the swelling level on the permeability of the three solutes. the influence of the swelling level and the solute size on the permeability was as expected from the free-volume theory. Based on these permeability phenomena, separation was performed in a continuous way by varying the membrane swelling at the appropriate time. A linear relationship between inverse membrane hydration and solute diffusion was found for uranine and dextran (MW=4,400), indicating the validity of the free-volume theory

Modelling of the diffusion of carbon dioxide in polyimide matrices by computer simulation

Computer aided molecular modelling is used to visualize the motion of CO2 gas molecules inside a polyimide polymer matrix. The polymers simulated are two 6FDA-bases polyimides, 6FDA-4PDA and 6FDA-44ODA. These polymers have also been synthesized in our laboratory, and thus the simulated properties could directly be compared with “real-world” data. The simulation experiments have been performed using the GROMOS1 package. The polymer boxes were created using the soft-core method, with short (11 segments) chains. This results in highly relaxed and totally amorphous polyimide matrices. The motion of randomly placed CO2 molecules in the boxes during molecular dynamics runs was followed, revealing three types of motion: jumping, continuous- and trapped motion. The calculated diffusivities are unrealistic, but possible shortcomings in our model are given

Magneto-optical Kerr effect in Eu1−xCaxB6Eu_{1-x}Ca_{x}B_{6}

We have measured the magneto-optical Kerr rotation of ferromagnetic $Eu_{1-x}Ca_{x}B_{6}$ with x=0.2 and 0.4, as well as of $YbB_{6}$ serving as the non-magnetic reference material. As previously for $EuB_{6}$, we could identify a feature at 1 $eV$ in the Kerr response which is related with electronic transitions involving the localized 4f electron states. The absence of this feature in the data for $YbB_{6}$ confirms the relevance of the partially occupied 4f states in shaping the magneto-optical features of $Eu$-based hexaborides. Disorder by $Ca$-doping broadens the itinerant charge carrier contribution to the magneto-optical spectra

Solar simulation with a rectangular beam

An existing space simulation test facility was modified by enlarging the solar simulator. Because of the restrictions imposed by existing equipment, the shape of the solar beam was altered from a circular to a rectangular cross section in order to adapt the test facility to test objects of increased size. This modification is described together with the results of preliminary measurements

Carrier-Induced Magnetic Circular Dichloism in the Magnetoresistive Pyrochlore Tl2Mn2O7

Infrared magnetic circular dichloism (MCD), or equivalently magneto-optical Kerr effect, has been measured on the Tl2Mn2O7 pyrochlore, which is well known for exhibiting a large magnetoresistance around the Curie temperature T_C ~ 120 K. A circularly polarized, infrared synchrotron radiation is used as the light source. A pronounced MCD signal is observed exactly at the plasma edge of the reflectivity near and below T_c. However, contrary to the conventional behavior of MCD for ferromagnets, the observed MCD of Tl2Mn2O7 grows with the applied magnetic field, and not scaled with the internal magnetization. It is shown that these results can be basically understood in terms of a classical magnetoplasma resonance. The absence of a magnetization-scaled MCD indicates a weak spin-orbit coupling of the carriers in Tl2Mn2O7. We discuss the present results in terms of the microscopic electronic structures of Tl2Mn2O7.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp

Dorsal root ganglion axon bifurcation tolerates increased cyclic GMP levels: the role of phosphodiesterase 2A and scavenger receptor Npr3

A cyclic GMP (cGMP) signaling pathway, comprising C-type natriuretic peptide (CNP), its guanylate cyclase receptor Npr2, and cGMP-dependent protein kinase I, is critical for the bifurcation of dorsal root ganglion (DRG) and cranial sensory ganglion axons when entering the mouse spinal cord and the hindbrain respectively. However, the identity and functional relevance of phosphodiesterases (PDEs) that degrade cGMP in DRG neurons are not completely understood. Here, we asked whether regulation of the intracellular cGMP concentration by PDEs modulates the branching of sensory axons. Real-time imaging of cGMP with a genetically encoded fluorescent cGMP sensor, RT-PCR screens, in situ hybridization, and immunohistology combined with the analysis of mutant mice identified PDE2A as the major enzyme for the degradation of CNP-induced cGMP in embryonic DRG neurons. Tracking of PDE2A-deficient DRG sensory axons in conjunction with cGMP measurements indicated that axon bifurcation tolerates increased cGMP concentrations. As we found that the natriuretic peptide scavenger receptor Npr3 is expressed by cells associated with dorsal roots but not in DRG neurons itself at early developmental stages, we analyzed axonal branching in the absence of Npr3. In Npr3-deficient mice, the majority of sensory axons showed normal bifurcation, but a small population of axons (13%) was unable to form T-like branches and generated turns in rostral or caudal directions only. Taken together, this study shows that sensory axon bifurcation is insensitive to increases of CNP-induced cGMP levels and Npr3 does not have an important scavenging function in this axonal system

Histone H3 Lysine 27 Methylation Asymmetry on Developmentally-Regulated Promoters Distinguish the First Two Lineages in Mouse Preimplantation Embryos

First lineage specification in the mammalian embryo leads to formation of the inner cell mass (ICM) and trophectoderm (TE), which respectively give rise to embryonic and extraembryonic tissues. We show here that this first differentiation event is accompanied by asymmetric distribution of trimethylated histone H3 lysine 27 (H3K27me3) on promoters of signaling and developmentally-regulated genes in the mouse ICM and TE. A genome-wide survey of promoter occupancy by H3K4me3 and H3K27me3 indicates that both compartments harbor promoters enriched in either modification, and promoters co-enriched in trimethylated H3K4 and H3K27 linked to developmental and signaling functions. The majority of H3K4/K27me3 co-enriched promoters are distinct between the two lineages, primarily due to differences in the distribution of H3K27me3. Derivation of embryonic stem cells leads to significant losses and gains of H3K4/K27me3 co-enriched promoters relative to the ICM, with distinct contributions of (de)methylation events on K4 and K27. Our results show histone trimethylation asymmetry on promoters in the first two developmental lineages, and highlight an epigenetic skewing associated with embryonic stem cell derivation

Who Participates in an Internet-Based Research Program for Mothers of Infants? A Secondary Prevention Research Study Among Low-Income Families

Objective: The objective of this study was to evaluate the participation rates and factors associated with nonparticipation among mothers living in low-income households who were invited to join a parent-education and -support research program delivered via the Internet with professional support. Methods: Four hundred and seventy-seven mothers of infants were contacted via a variety of recruitment methods, including presentations at clinics/classes, direct mailings, print advertisement, and Internet posts. Research staff attempted to contact these mothers by phone, to assess their eligibility, and interest in participation. For those who were eligible but declined participation, we assessed reasons for declining and collected demographic information. Results: Seventy-four percent of those eligible agreed to participate in the program. Statistical tests comparing participants and decliners on demographic variables found no significant differences on mother’s age and marital status. There was a significant difference on baby’s age due to many decliners in the prenatal period. Mothers were an average age of 28 years and most were married (65.6%). Our sample of low-income participants was diverse with a large number of Latina mothers. Approximately half had a high-school diploma or less but 84% reported being moderately or very comfortable using a computer and half had a computer at home