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Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm−1 region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined.
We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed
in these distances is an indication of the substitution effect.
It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the
case of o-disubstituted benzenes it is only 80% of the para-substituted shift. 相似文献
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软材料受刺激会发生变形, 该变形会引起相应的功能, 这种材料称为活性软材料(soft active material, SAM). 本综述主要讨论介电高弹聚合物这一类活性软材料. 当介电高弹聚合物薄膜受到厚度方向的电压作用时, 薄膜厚度减小同时面积增大, 可导致超过100{\%}的应变. 介电高弹聚合物作为转换器被广泛应用, 包括柔性机器人、智能光学器件、盲文显示屏、发电机等. 本文综述了建立在连续介质力学和热力学框架内的、并且基于分子理论描述和经验观测的介电高弹聚合物理论. 该理论耦合了大变形和电势, 描述了非线性和非平衡行为, 如力电失稳和黏弹性. 采用该理论能够通过有限元方法模拟实际构型的转换器, 计算力电能量转换的效率, 给出电致大变形的可行途径. 该理论有助于材料和器件设计. 相似文献
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With the advent of medium and large gamma detector arrays, it is now possible to look at nuclear structure at high rotational
forces. The role of pairing correlations and their eventual breakdown, along with the shell effects have showed us the interesting
physics for nuclei at high spins — superdeformation, shape co-existence, yrast traps, alignments and their dramatic effects
on nuclear structure and so on. Nuclear structure studies have recently become even more exciting, due to efforts and possibilities
to reach nuclei far off from the stability valley. Coupling of gamma ray arrays with ‘filters’, like neutron wall, charged
particle detector array, gamma ray total energy and multiplicity castles, conversion electron spectrometers etc gives a great
handle to study nuclei produced online with ‘low’ cross-sections. Recently we studied, nuclei in mass region 80 using an array
of 8 germanium detectors in conjunction with the recoil mass analyser, HIRA at the Nuclear Science Centre and, most unexpectedly
came across the phenomenon of identical bands, with two quasi-particle difference. The discovery of magnetic rotation is another
highlight. Our study of light In nucleus, 107In brought us face to face with the ‘dipole’ bands. I plan to discuss some of
these aspects. There is also an immensely important development — that of the ‘radioactive ion beams’. The availability of
RIB, will probably very dramatically influence our ‘conventional’ concept of nuclear structure. The exotic shapes of these
exotic nuclei and some of their expected properties will also be touched upon. 相似文献
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Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
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La1−x
FeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
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Huawei Li Hong Liu C Eduardo Corrales Jessica R Risner Jeff Forrester Jeffrey R Holt Stefan Heller Albert SB Edge 《BMC neuroscience》2009,10(1):122
Background
Neural differentiation of embryonic stem (ES) cells is usually achieved by induction of ectoderm in embryoid bodies followed by the enrichment of neuronal progenitors using a variety of factors. Obtaining reproducible percentages of neural cells is difficult and the methods are time consuming. 相似文献9.
Rupar PA Cambridge G Winnik MA Manners I 《Journal of the American Chemical Society》2011,133(42):16947-16957
Previous work has established that polyisoprene (PI) coronas in cylindrical block copolymer micelles with a poly(ferrocenyldimethylsilane) (PFS) core can be irreversibly cross-linked by hydrosilylation using (HSiMe(2))(2)O in the presence of Karstedt's catalyst. We now show that treatment of cylindrical PI-b-PFS micelles with Karstedt's catalyst alone, in the absence of any silanes, leads to PI coronal cross-linking through Pt(0)-olefin coordination. The cross-linking can be reversed through the addition of 2-bis(diphenylphosphino)ethane (dppe), a strong bidentate ligand, which removes the platinum from the PI to form Pt(dppe)(2). The Pt(0) cross-linking of PI was studied with self-assembled cylindrical PI-b-PFS block copolymer micelles, where the cross-linking was found to dramatically increase the stability of the micellar structures. The Pt(0)-alkene coordination-induced cross-linking can be used to provide transmission electron microscopy contrast between PI and poly(dimethylsiloxane) (PDMS) corona domains in block comicelles as the process selectively increases the electron density of the PI regions. Moreover, following the assembly of a hierarchical scarf-shaped comicelle consisting of a PFS-b-PDMS platelet template with PI-b-PFS tassels, Pt(0)-induced cross-linking of the PI coronal regions allowed for the selective removal of the PFS-b-PDMS center, leaving behind an unprecedented hollowed-out scarf structure. The addition of Karstedt's catalyst to PI or polybutadiene homopolymer toluene/xylene solutions resulted in the formation of polymer gels which underwent de-gelation upon the addition of dppe. 相似文献
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