34 research outputs found
Universally diverging Grueneisen parameter and the magnetocaloric effect close to quantum critical points
At a generic quantum critical point, the thermal expansion is more
singular than the specific heat . Consequently, the "Gr\"uneisen ratio'',
\GE=\alpha/c_p, diverges. When scaling applies, \GE \sim T^{-1/(\nu z)} at
the critical pressure , providing a means to measure the scaling
dimension of the most relevant operator that pressure couples to; in the
alternative limit and , \GE \sim \frac{1}{p-p_c} with a
prefactor that is, up to the molar volume, a simple {\it universal} combination
of critical exponents. For a magnetic-field driven transition, similar
relations hold for the magnetocaloric effect .
Finally, we determine the corrections to scaling in a class of metallic quantum
critical points.Comment: 4 pages, 1 figure; general discussion on how the Grueneisen exponent
measures the scaling dimension of the most relevant operator at any QCP is
expande
Kondo engineering : from single Kondo impurity to the Kondo lattice
In the first step, experiments on a single cerium or ytterbium Kondo impurity
reveal the importance of the Kondo temperature by comparison to other type of
couplings like the hyperfine interaction, the crystal field and the intersite
coupling. The extension to a lattice is discussed. Emphasis is given on the
fact that the occupation number of the trivalent configuration may be the
implicit key variable even for the Kondo lattice. Three phase
diagrams are discussed: CeRuSi, CeRhIn and SmS
Challenges in optics for Extremely Large Telescope instrumentation
We describe and summarize the optical challenges for future instrumentation
for Extremely Large Telescopes (ELTs). Knowing the complex instrumental
requirements is crucial for the successful design of 30-60m aperture
telescopes. After all, the success of ELTs will heavily rely on its
instrumentation and this, in turn, will depend on the ability to produce large
and ultra-precise optical components like light-weight mirrors, aspheric
lenses, segmented filters, and large gratings. New materials and manufacturing
processes are currently under study, both at research institutes and in
industry. In the present paper, we report on its progress with particular
emphasize on volume-phase-holographic gratings, photochromic materials,
sintered silicon-carbide mirrors, ion-beam figuring, ultra-precision surfaces,
and free-form optics. All are promising technologies opening new degrees of
freedom to optical designers. New optronic-mechanical systems will enable
efficient use of the very large focal planes. We also provide exploratory
descriptions of "old" and "new" optical technologies together with suggestions
to instrument designers to overcome some of the challenges placed by ELT
instrumentation.Comment: (Proc. OPTICON Key Technology Network Workshop, Rome 20-21 October
2005
Zebrafish Her8a Is Activated by Su(H)-Dependent Notch Signaling and Is Essential for the Inhibition of Neurogenesis
Understanding how diversity of neural cells is generated is one of the main tasks of developmental biology. The Hairy/E(spl) family members are potential targets of Notch signaling, which has been shown to be fundamental to neural cell maintenance, cell fate decisions, and compartment boundary formation. However, their response to Notch signaling and their roles in neurogenesis are still not fully understood. In the present study, we isolated a zebrafish homologue of hairy/E(spl), her8a, and showed this gene is specifically expressed in the developing nervous system. her8a is positively regulated by Su(H)-dependent Notch signaling as revealed by a Notch-defective mutant and injection of variants of the Notch intracellular regulator, Su(H). Morpholino knockdown of Her8a resulted in upregulation of proneural and post-mitotic neuronal markers, indicating that Her8a is essential for the inhibition of neurogenesis. In addition, markers for glial precursors and mature glial cells were down-regulated in Her8a morphants, suggesting Her8a is required for gliogenesis. The role of Her8a and its response to Notch signaling is thus similar to mammalian HES1, however this is the converse of what is seen for the more closely related mammalian family member, HES6. This study not only provides further understanding of how the fundamental signaling pathway, Notch signaling, and its downstream genes mediate neural development and differentiation, but also reveals evolutionary diversity in the role of H/E(spl) genes
Comparative analysis of somitogenesis related genes of the hairy/Enhancer of split class in Fugu and zebrafish
BACKGROUND: Members of a class of bHLH transcription factors, namely the hairy (h), Enhancer of split (E(spl)) and hairy-related with YRPW motif (hey) (h/E(spl)/hey) genes are involved in vertebrate somitogenesis and some of them show cycling expression. By sequence comparison, identified orthologues of cycling somitogenesis genes from higher vertebrates do not show an appropriate expression pattern in zebrafish. The zebrafish genomic sequence is not available yet but the genome of Fugu rubripes was recently published. To allow comparative analysis, the currently known Her proteins from zebrafish were used to screen the genomic sequence database of Fugu rubripes. RESULTS: 20 h/E(spl)/hey-related genes were identified in Fugu, which is twice the number of corresponding zebrafish genes known so far. A novel class of c-Hairy proteins was identified in the genomes of Fugu and Tetraodon. A screen of the human genome database with the Fugu proteins yielded 10 h/E(spl)/hey-related genes. By analysing the upstream sequences of the c-hairy class genes in zebrafish, Fugu and Tetraodon highly similar sequence stretches were identified that harbour Suppressor of hairless paired binding sites (SPS). This motif was also discovered in the upstream sequences of the her1 gene in the examined fish species. Here, the Su(h) sites are separated by longer intervening sequences. CONCLUSIONS: Our study indicates that not all her homologues in zebrafish have been isolated. Comparison to the human genome suggests a selective duplication of h/E(spl) genes in pufferfish or loss of members of these genes during evolution to the human lineage
Optimization of atmospheric plasma treatment of LDPE films: Influence on adhesive properties and ageing behavior
One of the major disadvantages of low density polyethylene (LDPE) films is their poor adhesive properties. Therefore, LDPE films have been treated with atmospheric pressure air plasma in order to improve their surface properties. So as to simulate the possible conditions in an industrial process, the samples have been treated with two different sample distances (6 and 10 mm), and treatment rates between 100 and 1000 mm s-1. The different sample distances are the distance of the sample from the plasma source. The variation of the surface properties and adhesion characteristics of the films were investigated for different aging times after plasma exposure (up to 21 days) using contact angle measurement, atomic force microscopy, weight loss measurements and shear test. Results show that the treatment increases the polar component () and these changes improve adhesive properties of the material. After the twenty-first day, the ageing process causes a decrease of wettability and adhesive properties of the LDPE films (up to 60%).Fombuena Borrás, V.; García Sanoguera, D.; Sánchez Nacher, L.; Balart Gimeno, RA.; Boronat Vitoria, T. (2014). Optimization of atmospheric plasma treatment of LDPE films: Influence on adhesive properties and ageing behavior. Journal of Adhesion Science and Technology. 28(1):97-113. doi:10.1080/01694243.2013.847045S97113281Achilias, D. S., Roupakias, C., Megalokonomos, P., Lappas, A. A., & Antonakou, Ε. V. (2007). Chemical recycling of plastic wastes made from polyethylene (LDPE and HDPE) and polypropylene (PP). Journal of Hazardous Materials, 149(3), 536-542. doi:10.1016/j.jhazmat.2007.06.076Friedman, M., & Walsh, G. (2002). High performance films: Review of new materials and trends. Polymer Engineering & Science, 42(8), 1756-1788. doi:10.1002/pen.11069Wiles, D. M., & Scott, G. (2006). Polyolefins with controlled environmental degradability. Polymer Degradation and Stability, 91(7), 1581-1592. doi:10.1016/j.polymdegradstab.2005.09.010Gao, J., Lei, J., Li, Q., & Ye, S. (2004). Functionalized low-density polyethylene via a novel photografting method and its adhesion properties. Journal of Adhesion Science and Technology, 18(2), 195-203. doi:10.1163/156856104772759403Shenton, M. J., Lovell-Hoare, M. C., & Stevens, G. C. (2001). Adhesion enhancement of polymer surfaces by atmospheric plasma treatment. Journal of Physics D: Applied Physics, 34(18), 2754-2760. doi:10.1088/0022-3727/34/18/307Belgacem, M. N., Salon-Brochier, M. C., Krouit, M., & Bras, J. (2011). Recent Advances in Surface Chemical Modification of Cellulose Fibres. Journal of Adhesion Science and Technology, 25(6-7), 661-684. doi:10.1163/016942410x525867Friedrich, J., Unger, W., & Lippitz, A. (1995). Plasma modification of polymer surfaces. Macromolecular Symposia, 100(1), 111-115. doi:10.1002/masy.19951000118Ladizesky, N. H., & Ward, I. M. (1989). The adhesion behaviour of high modulus polyethylene fibres following plasma and chemical treatment. Journal of Materials Science, 24(10), 3763-3773. doi:10.1007/bf02385768Nardin, M., & Ward, I. M. (1987). Influence of surface treatment on adhesion of polyethylene fibres. Materials Science and Technology, 3(10), 814-826. doi:10.1179/mst.1987.3.10.814Villagra Di Carlo, B., Gottifredi, J. C., & Habert, A. C. (2010). Synthesis and characterization of composite membrane by deposition of acrylic acid plasma polymer onto pre-treated polyethersulfone support. Journal of Materials Science, 46(6), 1850-1856. doi:10.1007/s10853-010-5012-4Matsunaga, M., & Whitney, P. J. (2000). Surface changes brought about by corona discharge treatment of polyethylene film and the effect on subsequent microbial colonisation. Polymer Degradation and Stability, 70(3), 325-332. doi:10.1016/s0141-3910(00)00105-1Novák, I., Pollák, V., & Chodák, I. (2006). Study of Surface Properties of Polyolefins Modified by Corona Discharge Plasma. Plasma Processes and Polymers, 3(4-5), 355-364. doi:10.1002/ppap.200500163Arpagaus, C., Rossi, A., & Rudolf von Rohr, P. (2005). Short-time plasma surface modification of HDPE powder in a Plasma Downer Reactor – process, wettability improvement and ageing effects. Applied Surface Science, 252(5), 1581-1595. doi:10.1016/j.apsusc.2005.02.099Morra, M., Occhiello, E., Marola, R., Garbassi, F., Humphrey, P., & Johnson, D. (1990). On the aging of oxygen plasma-treated polydimethylsiloxane surfaces. Journal of Colloid and Interface Science, 137(1), 11-24. doi:10.1016/0021-9797(90)90038-pKim, K. S., Ryu, C. M., Park, C. S., Sur, G. S., & Park, C. E. (2003). Investigation of crystallinity effects on the surface of oxygen plasma treated low density polyethylene using X-ray photoelectron spectroscopy. Polymer, 44(20), 6287-6295. doi:10.1016/s0032-3861(03)00674-8Kim, S. H., Ha, H. J., Ko, Y. K., Yoon, S. J., Rhee, J. M., Kim, M. S., … Khang, G. (2007). Correlation of proliferation, morphology and biological responses of fibroblasts on LDPE with different surface wettability. Journal of Biomaterials Science, Polymer Edition, 18(5), 609-622. doi:10.1163/156856207780852514Borcia, G., Anderson, C. A., & Brown, N. M. D. (2004). The surface oxidation of selected polymers using an atmospheric pressure air dielectric barrier discharge. Part I. Applied Surface Science, 221(1-4), 203-214. doi:10.1016/s0169-4332(03)00879-1Pascual, M., Calvo, O., Sanchez-Nácher, L., Bonet, M. A., Garcia-Sanoguera, D., & Balart, R. (2009). Optimization of adhesive joints of low density polyethylene (LDPE) composite laminates with polyolefin foam using corona discharge plasma. Journal of Applied Polymer Science, 114(5), 2971-2977. doi:10.1002/app.30906Encinas, N., Díaz-Benito, B., Abenojar, J., & Martínez, M. A. (2010). Extreme durability of wettability changes on polyolefin surfaces by atmospheric pressure plasma torch. Surface and Coatings Technology, 205(2), 396-402. doi:10.1016/j.surfcoat.2010.06.069Takke, V., Behary, N., Perwuelz, A., & Campagne, C. (2009). Studies on the atmospheric air-plasma treatment of PET (polyethylene terephtalate) woven fabrics: Effect of process parameters and of aging. Journal of Applied Polymer Science, 114(1), 348-357. doi:10.1002/app.30618Awaja, F., Gilbert, M., Kelly, G., Fox, B., & Pigram, P. J. (2009). Adhesion of polymers. Progress in Polymer Science, 34(9), 948-968. doi:10.1016/j.progpolymsci.2009.04.007Garcia, D., Sanchez, L., Fenollar, O., Lopez, R., & Balart, R. (2008). Modification of polypropylene surface by CH4–O2 low-pressure plasma to improve wettability. Journal of Materials Science, 43(10), 3466-3473. doi:10.1007/s10853-007-2322-2Guimond, S., & Wertheimer, M. R. (2004). Surface degradation and hydrophobic recovery of polyolefins treated by air corona and nitrogen atmospheric pressure glow discharge. Journal of Applied Polymer Science, 94(3), 1291-1303. doi:10.1002/app.21134Pascual, M., Balart, R., Sánchez, L., Fenollar, O., & Calvo, O. (2008). Study of the aging process of corona discharge plasma effects on low density polyethylene film surface. Journal of Materials Science, 43(14), 4901-4909. doi:10.1007/s10853-008-2712-0Sanchis, R., Fenollar, O., García, D., Sánchez, L., & Balart, R. (2008). Improved adhesion of LDPE films to polyolefin foams for automotive industry using low-pressure plasma. International Journal of Adhesion and Adhesives, 28(8), 445-451. doi:10.1016/j.ijadhadh.2008.04.002Fresnais, J., Chapel, J. P., Benyahia, L., & Poncin-Epaillard, F. (2009). Plasma-Treated Superhydrophobic Polyethylene Surfaces: Fabrication, Wetting and Dewetting Properties. Journal of Adhesion Science and Technology, 23(3), 447-467. doi:10.1163/156856108x370127Abenojar, J., Colera, I., Martínez, M. A., & Velasco, F. (2010). Study by XPS of an Atmospheric Plasma-Torch Treated Glass: Influence on Adhesion. Journal of Adhesion Science and Technology, 24(11-12), 1841-1854. doi:10.1163/016942410x507614Lommatzsch, U., Pasedag, D., Baalmann, A., Ellinghorst, G., & Wagner, H.-E. (2007). Atmospheric Pressure Plasma Jet Treatment of Polyethylene Surfaces for Adhesion Improvement. Plasma Processes and Polymers, 4(S1), S1041-S1045. doi:10.1002/ppap.200732402Balu, B., Berry, A. D., Patel, K. T., Breedveld, V., & Hess, D. W. (2011). Directional Mobility and Adhesion of Water Drops on Patterned Superhydrophobic Surfaces. Journal of Adhesion Science and Technology, 25(6-7), 627-642. doi:10.1163/016942410x525849Bhattacharya, S., Singh, R. K., Mandal, S., Ghosh, A., Bok, S., Korampally, V., … Gangopadhyay, S. (2010). Plasma Modification of Polymer Surfaces and Their Utility in Building Biomedical Microdevices. Journal of Adhesion Science and Technology, 24(15-16), 2707-2739. doi:10.1163/016942410x511105Das, S., Neogi, S., Chainy, G. B. N., & Guha, S. K. (2011). A Novel Two-Step Procedure for Plasma Surface Modification of Low-Density Polyethylene for Improved Drug Adhesion in Intra Uterine Devices (IUDs). Journal of Adhesion Science and Technology, 25(1-3), 151-167. doi:10.1163/016942410x503285Schulz, U., Munzert, P., & Kaiser, N. (2010). Plasma Surface Modification of PMMA for Optical Applications. Journal of Adhesion Science and Technology, 24(7), 1283-1289. doi:10.1163/016942409x12561252292026Silverstein, M. S., Breuer, O., & Dodiuk, H. (1994). Surface modification of UHMWPE fibers. Journal of Applied Polymer Science, 52(12), 1785-1795. doi:10.1002/app.1994.070521213Inagaki, N., Narushim, K., Tuchida, N., & Miyazaki, K. (2004). Surface characterization of plasma-modified poly(ethylene terephthalate) film surfaces. Journal of Polymer Science Part B: Polymer Physics, 42(20), 3727-3740. doi:10.1002/polb.20234Nakamatsu, J., Delgado-Aparicio, L. F., Da Silva, R., & Soberon, F. (1999). Ageing of plasma-treated poly(tetrafluoroethylene) surfaces. Journal of Adhesion Science and Technology, 13(7), 753-761. doi:10.1163/156856199x00983Yun, Y. I., Kim, K. S., Uhm, S.-J., Khatua, B. B., Cho, K., Kim, J. K., & Park, C. E. (2004). Aging behavior of oxygen plasma-treated polypropylene with different crystallinities. Journal of Adhesion Science and Technology, 18(11), 1279-1291. doi:10.1163/1568561041588200Morent, R., De Geyter, N., Leys, C., Gengembre, L., & Payen, E. (2007). Study of the ageing behaviour of polymer films treated with a dielectric barrier discharge in air, helium and argon at medium pressure. Surface and Coatings Technology, 201(18), 7847-7854. doi:10.1016/j.surfcoat.2007.03.018Zhao, B., & Kwon, H. J. (2011). Adhesion of Polymers in Paper Products from the Macroscopic to Molecular Level — An Overview. Journal of Adhesion Science and Technology, 25(6-7), 557-579. doi:10.1163/016942410x52582
Ferroquadrupole ordering and Gamma_5 rattling motion in clathrate compound Ce_3Pd_20Ge_6
Lattice effects in a cerium based clathrate compound Ce_3Pd_20Ge_6 with a
cubic Cr_23C_6-type structure have been investigated by ultrasonic and thermal
expansion measurements. Elastic softenings of (C_11-C_12)/2 and C_44
proportional to the reciprocal temperature 1/T above T_Q1 = 1.25 K are well
described in terms of the quadrupole susceptibility for the ground state
Gamma_8 quartet. A huge softening of 50 % in (C_11-C_12)/2 and a spontaneous
expansion DL/L = 1.9x10^-4 along the [001] direction in particular indicate the
ferroquadrupole ordering of O_2^0 below T_Q1. The elastic anomalies associated
with the antiferromagnetic ordering at T_N2 = 0.75 K and the incommensurate
antiferromagnetic ordering are also found. Notable frequency dependence of C_44
around 10 K is accounted for by the Debye-type dispersion indicating a Gamma_5
rattling motion of an off-center Ce ion along the [111] direction with eight
fractionally occupied positions around the 4a site in a cage. The thermally
activated Gamma_5 rattling motion obeying a relaxation time t = t_0exp(E/k_BT)
with an attempt time t_0 = 3.1x10^-11 sec and an activation energy E = 70 K
dies out with decreasing temperature, and then the off-center tunneling state
of Ce ion in the 4a-site cage will appear at low temperatures.Comment: 11 pages, 15 figures, to be published on Phys. Rev.
Genomewide Expression Analysis in Zebrafish mind bomb Alleles with Pancreas Defects of Different Severity Identifies Putative Notch Responsive Genes
10.1371/journal.pone.0001479PLoS ONE3