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21.
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
22.
The phenomenon of nuclear magnetic resonance (NMR) is widely applied in biomedical and biological science to study structures and dynamics of proteins and their reactions. Despite its impact, NMR is an inherently insensitive phenomenon and has driven the field to construct spectrometers with increasingly higher magnetic fields leading to more detection sensitivity. Here, we are demonstrating that enzymatic reactions can be followed in real-time at millitesla fields, three orders of magnitude lower than the field of state-of-the-art NMR spectrometers. This requires signal-enhancing samples via hyperpolarization. Within seconds, we have enhanced the signals of 2-13C-pyruvate, an important metabolite to probe cancer metabolism, in 22 mM concentrations (up to 10.1% ± 0.1% polarization) and show that such a large signal allows for the real-time detection of enzymatic conversion of pyruvate to lactate at 24 mT. This development paves the pathways for biological studies in portable and affordable NMR systems with a potential for medical diagnostics.We demonstrate that metabolism can be monitored in real-time with magnetic resonance at milli-tesla fields that are 1000 fold lower than state-of-the-art high field spectrometers. 相似文献
23.
The synthesis of diblock copolymer of tert butyl acrylate and methyl methacrylate (PTBA‐b‐PMMA) was prepared by Atom Transfer Radical Polymerization (ATRP). At the outset, macroinitiator of tert butyl acrylate (TBA) was prepared by using N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) ligand, Cuprous Bromide (CuBr) catalyst, and ethyl 2‐bromo isobutyrate (2‐EiBBr) initiator. Immediately after the intake of the utmost TBA in the macroinitiator, the second monomer, methyl methacrylate (MMA) was added to the reaction medium, for further polymerization. In these experiments the compositions of the monomers were varied, although the concentrations of ligand, catalyst and the initiator were kept constant. Subsequently, the diblock copolymers were hydrolyzed, under acidic conditions, using HCl catalyst, to obtain an amphiphilic copolymer. These block copolymers were characterized by NMR, IR, GPC, and DSC techniques. These copolymers will be used in, powder coatings, pigment dispersions, and as compatibilizers in polymer blends. 相似文献
24.
Jagtap S. B. Chikate R. C. Yemul O. S. Ghadage R. S. Kulkarni B. A. 《Journal of Thermal Analysis and Calorimetry》2004,78(1):251-262
Ho(III), Er(III) and Yb(III) complexes of 2-hydroxy-1,4-naphthoquinone-1-oxime derivatives having [ML3(H2O)2] are characterized using spectral and thermal decomposition studies. The thermolytic patterns suggested that they are decomposed
in three distinct stages; 1ststage is related to the loss of two coordinated water molecules while one of the coordinated ligands and remaining two ligands
are lost during subsequent 2nd and 3rd stages of degradation. After the 2nd stage, the structure of these complexes is reorganized reflecting that the structural associations through intermolecular
hydrogen bonding network is essential for thermal stability. The kinetic parameters computed for 2nd step using the non-isothermal procedures of Coats-Redfern are applied to the respective differential thermogravimetric plots
to ascertain the thermal degradation mechanism in air. The order of thermal decomposition reaction is found to be between
1-2 indicating that more than one intermediate might have simultaneously been formed. It also reveals the intermixing of 1st and 3rd stages of decomposition with the predominant 2nd stage leading to more gradual degradation. Energy of activation for 2nd stage of decomposition for these complexes is comparatively lower than those observed earlier for similar types of complexes.
Other spectral data indicate oximino nitrogen and phenolato oxygen as coordination sites of 2-hydroxy-1,4-naphthoquinone monoximates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
This work reports rhodium catalyzed selective hydroformylation of natural olefins like eugenol, estragole, anethole, prenol and isoprenol using biphenyl based Buchwald phosphine ligands (S‐Phos ( L 1 ), t‐Bu XPhos ( L 2 ), Ru‐Phos ( L 3 ), Johnphos ( L 4 ) and DavePhos ( L 5 ). Ru‐Phos ( L 3 ) ligand exhibited high impact on the hydroformylation of eugenol providing high selectivity (90%) of linear aldehyde as major product. In addition, internal natural olefins like anethole and prenol provided moderate to high selectivity (65% and 85% respectively) of branched aldehydes as a major products. The various reaction parameters such as influence of ligands, P/Rh ratio, syngas pressure, temperature, time and solvents have been studied. A high activity and selectivity gained on the way to the linear aldehydes it may be due to the bulky, steric cyclohexyl and isopropoxy groups present in L 3 phosphine ligand. Moreover, this catalytic system was smoothly converting natural olefins into corresponding linear and branched aldehydes with higher selectivity under the mild reaction conditions. 相似文献
26.
A convenient method for the synthesis of phthalides (1–5), involving heteroatom directed lithiation reaction is described. 相似文献
27.
Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
x
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
28.
Measurement of methyl mercury (I) and mercury (II) in fish tissues and sediments by HPLC-ICPMS and HPLC-HGAAS 总被引:1,自引:0,他引:1
A procedure for the extraction and determination of methyl mercury and mercury (II) in fish muscle tissues and sediment samples is presented. The procedure involves extraction with 5% (v/v) 2-mercaptoethanol, separation and determination of mercury species by HPLC-ICPMS using a Perkin-Elmer 3 μm C8 (33 mm × 3 mm) column and a mobile phase 3 containing 0.5% (v/v) 2-mercaptoethanol and 5% (v/v) CH3OH (pH 5.5) at a flow rate 1.5 ml min−1 and a temperature of 25 °C. Calibration curves for methyl mercury (I) and mercury (II) standards were linear in the range of 0-100 μg l−1 (r2 = 0.9990 and r2 = 0.9995 respectively). The lowest measurable mercury was 0.4 μg l−1 which corresponds to 0.01 μg g−1 in fish tissues and sediments. Methyl mercury concentrations measured in biological certified reference materials, NRCC DORM - 2 Dogfish muscle (4.4 ± 0.8 μg g−1), NRCC Dolt - 3 Dogfish liver (1.55 ± 0.09 μg g−1), NIST RM 50 Albacore Tuna (0.89 ± 0.08 μg g−1) and IRMM IMEP-20 Tuna fish (3.6 ± 0.6 μg g−1) were in agreement with the certified value (4.47 ± 0.32 μg g−1, 1.59 ± 0.12 μg g−1, 0.87 ± 0.03 μg g−1, 4.24 ± 0.27 μg g−1 respectively). For the sediment reference material ERM CC 580, a methyl mercury concentration of 0.070 ± 0.002 μg g−1 was measured which corresponds to an extraction efficiency of 92 ± 3% of certified values (0.076 ± 0.04 μg g−1) but within the range of published values (0.040-0.084 μg g−1; mean ± s.d.: 0.073 ± 0.05 μg g−1, n = 40) for this material. The extraction procedure for the fish tissues was also compared against an enzymatic extraction using Protease type XIV that has been previously published and similar results were obtained. The use of HPLC-HGAAS with a Phenomenox 5 μm Luna C18 (250 mm × 4.6 mm) column and a mobile phase containing 0.06 mol l−1 ammonium acetate (Merck Pty Limited, Australia) in 5% (v/v) methanol and 0.1% (w/v) l-cysteine at 25 °C was evaluated as a complementary alternative to HPLC-ICPMS for the measurement of mercury species in fish tissues. The lowest measurable mercury concentration was 2 μg l−1 and this corresponds to 0.1 μg g−1 in fish tissues. Analysis of enzymatic extracts analysed by HPLC-HGAAS and HPLC-ICPMS gave equivalent results. 相似文献
29.
Prakash G. Jagtap Zhiyu Chen Elizabeth Piro Garry J. Southan 《Tetrahedron letters》2009,50(22):2693-2696
Synthesis of potent adenosine A2A and A3 receptor agonist from the modification of adenosine-5′-N-ethylcarboxamide (NECA) has been reported. Diastereoisomer possessing an (R)-3,4-dihydro-2H-pyranyl (DHP) moiety exhibited the highest affinity at the A2A and A3 receptors. The key steps involve the synthesis of (R)-3,4-dihydro-2H-pyran-2-carboxaldehyde (7), which was obtained through the enzyme-catalyzed kinetic resolution of (±)-2-acetoxymethyl-3,4-dihydro-2H-pyran (5). 相似文献
30.
Cs2CO3-catalyzed transamination of primary amines and ethylene carbonate proceeds to form 1,3-disubstituted symmetrical/unsymmetrical ureas in excellent yields. The effect of different reaction parameters such as influences of bases, temperature, and reaction time were investigated for the title reaction. 相似文献