共查询到20条相似文献,搜索用时 15 毫秒
1.
The most prominent peaks in the 12C(6Li, d)16O spectra at energies up to 32 MeV correspond to levels in 16O at 6.910 ± 0.006 MeV (Jπ = 2+), 10.346 ± 0.006 MeV (τCM < 50 keV, Jπ = 4+), 16. 304 ± 0.020 MeV (τCM = 360 ± 40 keV) and 20.88 ± 0.06 MeV (λCM = 720 ± 100 keV). The last two states are probably the higher members of the first rotational band with Jπ = 6+ and 8+, respectively. A comparison with recent theoretical calculations is given. 相似文献
2.
Roberto Laridondo Lui Daniel Rodrigues Blanco Vladimir Pavan Margarido Orlando Moreira Filho 《Micron (Oxford, England : 1993)》2009,40(5-6):552-559
B chromosomes are considered additional and non-essential; they likely originate from A chromosomes and follow a distinct evolution. In fish, approximately half of the Neotropical species with B chromosomes are Characiformes and 35% are Siluriformes. There has been no report of B chromosomes in Auchenipteridae until this moment. B chromosomes found in a population of Parauchenipterus galeatus from the São Francisco River basin in the state of Minas Gerais (Brazil) were small, metacentric, totally heterochromatic and exhibited intra-individual and inter-individual variation. The diploid number was 58 chromosomes (22 metacentric, 16 submetacentric, 12 subtelocentric and 8 acrocentric). The nucleolar organizing regions were simple and the heterochromatin intercalated in the ribosomal sites, characterized by CMA3 and DAPI fluorochromes, was of a GC-rich constitution. The 5S rDNA genes were located in an intercalary position in only one chromosome pair. An hypothesis about the origin of the B chromosomes in P. galeatus and a review on B chromosomes in catfish are also presented in this study. 相似文献
3.
The structural,elastic,and electronic properties of Zr_x Nb_(1-x)C alloys from first principle calculations 下载免费PDF全文
The structural,elastic,electronic,and thermodynamic properties of Zr x Nb1-x C alloys are investigated using the first principles method based on the density functional theory.The results show that the structural properties of Zr x Nb1-x C alloys vary continuously with the increase of Zr composition.The alloy possesses both the highest shear modulus(215 GPa)and a higher bulk modulus(294 GPa),with a Zr composition of 0.21.Meanwhile,the Zr0.21Nb0.79C alloy shows metallic conductivity based on the analysis of the density of states.In addition,the thermodynamic stability of the designed alloys is estimated using the calculated enthalpy of mixing. 相似文献
4.
Comparative cytogenetic analyses were carried out in six species of Brachycephalidae from southeastern Brazil. Barycholos ternetzi, Eleutherodactylus binotatus, Eleutherodactylus guentheri, Eleutherodactylus juipoca, Eleutherodactylus parvus and Eleutherodactylus sp. have 2n=22 karyotypes with a marked variation in the morphology of chromosome pairs 8, 10 and 11, which are of telocentric or metacentric types, resulting in FN=38, 40 and 44. Eleutherodactylus have a single chromosome pair bearing Ag-NOR, i.e. pair 1 in E. binotatus, pair 6 in E. guentheri and E. parvus, and pair 11 in E. juipoca and Eleutherodactylus sp. In contrast, B. ternetzi showed Ag-positive sites in the chromosome pairs 1, 4, 5, 9 and 11, and only one to three labelings per metaphase in each individual. Nevertheless, the main chromosome pair with Ag-NOR in the species seems to be the 11th, like in E. juipoca and Eleutherodactylus sp. The NOR site was confirmed by fluorescence in situ hybridization (FISH) technique in E. binotatus and in B. ternetzi, bearing 1p1p and 9p11p11p Ag-NOR pattern, respectively. All the species exhibited predominantly centromeric C-banding pattern, but interstitial bands have also been observed in some cases. In E. binotatus, there is an indication of geographical difference in the distribution of the interstitial C-bands. The fluorochromes GC-specific chromomycin A(3) (CMA(3)) and AT-specific 4',6-diamidino-2-phenylindole (DAPI), with distamycin A (DA) counterstaining, provided the molecular content of some repetitive regions in the karyotypes of the species. One male of E. binotatus presented an extensive heteromorphism, involving at least five different pairs, probably as a consequence of multiple reciprocal translocations. Such rearrangements might be responsible for the multivalent chain seen in the meiosis of this specimen, as well as in another male, although not exhibiting chromosome heteromorphism. The remaining males and those belonging to the other species have always shown 11 bivalents in diplotene and metaphase I cells. In all male specimens, metaphases II presented 11 chromosomes. Despite the observed discrepancies, the five species of Eleutherodactylus have a great uniformity in the 2n=22 karyotypes, suggesting an assemblage of species from southeastern and southern Brazil, in contrast to northern and northeastern assemblage which is characterized by higher diploid numbers. Undoubtedly, B. ternetzi could be included in that proposed assemblage, due to its karyotypic similarity with the Eleutherodactylus species, as evidenced in the present study. This fact strongly supports the close relationships of both genera, previously inferred on the basis of several characters shared by their species. 相似文献
5.
E. M. Fernández G. Borstel J. M. Soler L. C. Balbás 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):245-248
The ionic and electronic structure of
(Al2O3)n(Ox)
clusters with n
16 and x
= 0,
1, 2 is studied by means of first principles density functional
calculations, norm-conserving pseudopotentials and a numerical
atomic basis set. The equilibrium geometries have been
determined by total energy minimization, starting with several
initial geometries for each cluster size. The trends obtained
for the atomic arrangements (structural isomers, coordination
numbers, disordered versus
ordered structures, etc.) and the electronic properties
(binding energies, Homo-Lumo gap and dipole moments) are
discussed. For most of the oxidized clusters studied here we
find that the Homo-Lumo gap and the magnitude of dipole moment
of isomeric species can vary drastically. 相似文献
6.
7.
Xinguo Li Jianyi Shen Bing Zhong Yi Chen Shaoyi Peng Qin Wang Dong Wu 《Hyperfine Interactions》1992,69(1-4):867-870
The effect of second metal component on the structural characteristic of Fe M UFP catalysts was investigated by in situ Mossbauer
spectroscopy. The incorporation of second metal component hinders, the reduction and carburization of iron containing phase
in the presence of H2 and CO, and the degree of hindrance is in the order of Mg Mn Zn due to the interaction between iron and the second metal
component. Consequently, the formation of light olefinic products is in the order of Fe Mg>Fe−Mn·Fe−Zn catalysts consistent
with the F-T synthesis performance.
This work was supported by the National Natural Science Foundation of China 相似文献
8.
9.
10.
构建了一个ZnO沉积在α-Al2O3(0001)表面生长初期的模型,采用基于密度泛函理论的平面波超软赝势法进行了动力学模拟.发现在400,600和800℃的条件下界面原子有不同的扩散能力,因此温度对ZnO/α-Al2O3(0001)表面界面结构以及ZnO薄膜生长初期模式有决定性的影响.在整个ZnO吸附生长过程中,O原子的扩散系数大于Zn原子的扩散系数,O原子的层间扩散对薄膜的均匀生长起着重要作用.进一步从理论计算上证实了ZnO在蓝宝石(0001)上两种生长模式的存在,400℃左右生长模式主要是Zn螺旋扭曲生长,具有Zn六角平面对称特征,且有利于Zn原子位于最外表面.600℃左右呈现为比较规则的层状生长,且有利于O原子位于最外表面.模拟观察到在ZnO薄膜临近Al2O3基片表面处,Zn的空位缺陷明显多于O的空位缺陷. 相似文献
11.
The scattering of hydrogen, deuterium, and the rare gases from the (111) face of silver has been studied at ultrahigh vacuum. The surfaces were prepared by argon ion bombardment and high temperature annealing. Incident angles between 20° and 65° and surface temperatures between room temperature and 573°K have been investigated. The scattering data exhibit quasi-elastic scattering (He, H2, D2), inelastic scattering (Ne, Ar, Kr), and trapping dominated scattering (Xe). Identification of these scattering regimes correlates with D/kTg and is consistent with similar data from Pt(111) and W(110). The separate effects of microscopic surface roughness and thermal roughening have been identified and thermal attenuation in the elastic regime correlated with dynamical interactions rather than thermal roughening. Trapping and rotational coupling are discussed. Comparison of the data with scattering from epitaxial (111) silver indicates that the epitaxial surfaces are significantly more disordered than the single crystal surfaces. 相似文献
12.
Epitaxial layers of copper were formed on Pt(111) and Pt(553) single crystal surfaces by condensation of copper atoms from the vapor. Surface alloys were formed by diffusing the copper atoms into the platinum substrate at temperatures above 550 K. The activation energy for this process was found to be ~ 120 . These Pt/Cu surfaces were characterized by LEED, AES, and TDS of CO. The copper grows in islands on the Pt(111) surface and one monolayer is completed before another begins. There is an apparent repulsive interaction between the copper atoms and the step sites of the Pt(553) surface which causes a second layer of copper to begin forming before the first layer is complete. Epitaxial copper atoms block CO adsorption sites on the platinum surface without affecting the CO desorption energy. When the copper is alloyed with the platinum however, the energy of desorption of CO from the platinum was reduced by as much as 20 . This reduction in the desorption energy suggests an electronic modification that weakens the Pt-CO bond. 相似文献
13.
14.
E. Barnard N. Coetzee J. A. M. de Villiers D. Reitmann P. van der Merwe 《Zeitschrift für Physik A Hadrons and Nuclei》1971,243(2):121-125
Using time-of-flight methods to discriminate against neutron induced backgrounds, a 40 cm3 Ge(Li) detector was used to observe the γ-rays from the127I(n, n′ γ) reaction. Based on these γ-rays, energy level and decay schemes are derived up to an excitation of 1780 keV in127I. This scheme shows seventeen new levels, whilst the existence of two levels recently determined in Coulomb excitation studies are confirmed. The level scheme is compared with the intermediate coupling unified model predictions. 相似文献
15.
16.
W. HasniA. Boukortt B. BekkoucheS. Kacimi M. DjermouniA. Zaoui 《Physica B: Condensed Matter》2012,407(5):901-906
The ab initio APW+lo method is used to study the cation effect on the electronic structure of CeBO3 (B=Ga, In) compounds. High-pressure structural behavior, magnetic phase stabilities and electronic properties of both materials have been investigated. The observed most stable phases are the orthorhombic (Pnma) and hexagonal (P63cm) for CeGaO3 and CeInO3, respectively. It is shown that the ferromagnetic (FM) state in CeGaO3 is energetically more favorable than the anti-ferromagnetic (AFM) one, unlike CeInO3 where the AFM-III configuration is the lowest in energy. LSDA+U calculation shows that the valence band maximum is located at T point and the conduction band minimum is located at the center of the Brillouin zone, resulting in a wide indirect energy band gap of about 3.6 eV in the ferromagnetic ordering CeGaO3 which is typical of semiconductor with large gap. CeInO3 compound keeps the metallic character using DFT+U calculation. 相似文献
17.
Tarik Ouahrani 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(9):1-11
Local properties of the XSiP2 (X = Be, Mg, Cd, Zn and Hg) compounds are revisited through the partition of static thermodynamic properties under pressure. We pay attention to the metallization that occurs when the investigated compounds undergo a phase transition from chalcopyrite to the NaCl structure. Electron localization function analysis shows that the local valence basin attractors values decrease as a function of pressure. As the pressure increases, the tetragonal distortion (c/a) diminishes while the degree of ionicity enhances. In addition, by means of atom in molecule approach, atomic-like local compressibility and pressures are analyzed. We found that the basins volumes of the investigated compounds in the NaCl phase have lower compressibilities than those in the chalcopyrite phase. According to the predicted core-valence basins, the phosphorus cation is found to be the more affected by the hydrostatic pressure. 相似文献
18.
在水溶液中, 无论是控制一定的pH值(约5及8.5 )把N,N'-二(邻氧乙酸)苄叉乙二胺(H2L3)和三水合硝酸铜混合后回流--直接法, 还是把邻氧乙酸苯甲醛、三水合硝酸铜、乙二胺混合后回流--模板法, H2L3都能与铜离子形成1∶1的单核配合物, 经分离后得到固体配合物. 本文测定了配合物的元素组成、差热曲线、在水溶液中的最大吸收波长及其红外特征吸收峰值, 并据此推断了配合物的可能结构. 结果表明: (1)端基羧酸根离子要与中心Cu(Ⅱ)离子配位只能从轴向配位; (2)在这一类配体中, 芳基醚氧原子对形成稳定的固体Cu(Ⅱ)配合物有重要作用; (3)H2L3和Cu(Ⅱ)形成的配合物是六配位的畸形八面体的构型. 相似文献
19.
20.
V. V. Kamanin A. Kugler Yu. G. Sobolev A. S. Fomichev 《Zeitschrift für Physik A Hadrons and Nuclei》1990,337(1):111-113
In thenatSn+20Ne (164,196 MeV) reactions gamma-ray spectra were observed in coincidence with fast alpha particles forward peaked and with those evaporated into a backward hemisphere. The observed differences in the form of the gamma-ray spectra and in the corresponding yields of high-energy gamma-rays are preliminary related to the time evolution of the deformation of the nuclear systems formed in the heavy ion induced fusion reaction. 相似文献