Rotation Of Nucleus Research Articles

The Halley dust model

The properties of dust ejecta from Comet Halley are studied on the basis of (a) evidence from the comet's past apparitions and (b) analogy with recent, physically similar comets. Specifically discussed are the light curve and spectrum, discrete phenomena in the head, the physical properties of the nucleus (size, albedo, rotation, surface temperature, and morphology), and an interaction between the nucleus and dust atmosphere. Also reviewed are constraints on the size and mass distributions of dust particles, information on submicron-size and submillimeter-size grains from the comet's dust tail and antitail, and the apparent existence of more than one particle type. Similarities between the jet patterns of Halley and the parent comet of the Perseid meteor stream are depicted, and effects of the surface heterogeneity (discrete active regions) on the dust flow are assessed. Current dust models for Halley are summarized and the existence of short-term variations in the dust content in the comet's atmosphere is suggested.

Dynamical Interplay of Pairing and Quadrupole Modes in Transitional Nuclei. III

Using the single j-shell model with the pairing plus quadrupole force, we show that l) the transition from vibrational to rotational excitation structure can be reproduced within the collective model space built up from the J =0- and J =2- coupled nucleon pairs, 2) change of the monopole pair field due to many-quasiparticle excitations does accelerate the transition; this fact indicates the importance of taking explicit account of the cou­ pling between pairing rotation and many-phonon excitations in transitional nuclei.

An extended cranked shape-consistent oscillator model for rotations of triaxial nuclei: Application to 24Mg

The shape-consistent oscillator model is extended to triaxial nuclei. An application to 24Mg shows results similar to those from a variation-after-projection Hartree-Fock calculation with realistic forces. The observed trends of B(E2) values within a band seem to be consistent with self-consistent shape changes but greater experimental accuracy is needed for a more definite conclusion.

Cytochalasin B blocks sperm incorporation but allows activation of the sea urchin egg

Cytochalasin B (CB) (2 × 10 −6 M) prevents the incorporation of sperm into the eggs of Lytechinus pictus and Strongylocentrotus purpuratus as judged by light and transmission electron microscopy (TEM). At lower concentrations of CB (2 × 10 −7 M), sperm are successfully incorporated into the egg, but their migration in the area of the egg cortex is impaired. The site of action of CB on the sperm may be on the initial rotation of the sperm nucleus in the cortex; the subsequent migration is not affected by CB. Although sperm incorporation is prevented at the higher CB concentrations, the eggs become activated—as judged by cortical reaction, increased protein synthesis and increased respiration. These findings raise the concept that egg activation by sperm could result from some pre-fusion event and hence that sperm-egg fusion would not be a prerequisite for the triggering of development. An alternative hypothesis is that fusion occurs between the acrosome process membrane and egg membrane, but since CB has destroyed the integrity of the cortex actin, the fusion bridge is so weak that it cannot be maintained without some contractile or cytoskeletal support by the cortex. The sperm may activate the CB-treated egg in the same manner as pricking with a microelectrode sometimes does.

A quantum-kinetic approach to the theory of nuclear quadrupole relaxation

A generalization of the approach to the magnetic resonance and relaxation problems based on the treating of the lattice as a classical system with random parameters is presented. The main point is taking into account the mutual influence of the spin system and the lattice motions more completely than it conventionally used to be done. The method developed is applied to the problem of the nuclear quadrupole relaxation due to the random rotations of nuclei with I= 3 2 in the case of the axially symmetric electric field gradient. The relaxation time temperature dependence is obtained in the temperature region where the Bayer theory is not valid.

Quantum flow pattern of coherent rotational states

The rotation of a light nucleus is illustrated by the velocity field of a coherent rotational state in Elliott's model. In the rotating system one can see a vortex structure due to non-uniform distribution of V× v. Comparison is made with the results of the cranking model to other authors.

Flow patterns for collective rotations in heavy nuclei

Current and velocity fields for collective rotations are calculated from cranked BCS correlated wave functions for even-even rare earth nuclei. The single-particle Hamiltonian used is that of the Nilsson model. The velocity fields obtained do not yield a spherical inert core, in contrast to the two-fluid model. It is shown that the flow pattern can be represented quite accurately by a superposition of irrotational and rigid flow. The strength of the former can reach up to 60 % — depending on the specific nucleus — in the case without pairing and is usually about 80 % with pairing. Finally several forms for the collective rotational energy are compared. It is found that the classical expression grossly underestimates the correct energies.

Rotation of nuclei around a prolate symmetry axis at very high spin states

Classically one expects that nuclei rotate at very high spins (30≦I≦80) around an oblate symmetry axis. It is shown that strong shell correction energies yield for some nuclei at the end of the rare earth region and in the Pb-region yrast states for a rotation around a prolate symmetry axis. Like for the rotation around an oblate symmetry axis one expects also here yrast traps. The deformation energy surfaces for very high spin states are calculated by the Strutinsky method using a Saxon-Woods potential and by a microscopic method built on constraint Nilsson functions. Both methods agree qualitatively. Yrast traps are studied for these nuclei. It is shown that the MONA (Maximisation of theOverlap ofNuclear wave functions byAlignment) effect prefers at high spin rotation around the symmetry axis of a negative deformed shape at the beginning of the shell and of positive deformation at the end of the shell.

Mitotic cell studies based on in vivo observations. X. Problems on the objectivity of fixation cytology, of genetic information and of the teleonomy in the structure and function of the karyokinetic spindle.

In this report the author has enumerated the differences in interpretations of the mitosis studied both in fixed preparations and in in vivo observations. The author especially maintains the opinion that any movement of chromosomes in mitotic cells should be reinvestigated thoroughly by in vivo observations in the same way as studies on any movement of intracellular organelles, e.g. plastids, mitochondria, rotation of nucleus, streaming of protoplasm, etc.1. Practically all behavior of mitotic cells described in cytology books has scarcely made reference to the genetic back-ground of the mitosis.2. The breakdown of nuclear membrane before spindle formation in higher plants and animals is an impossibility. The nuclear membrane in eukaryotes is predicted and controlled by genes and genetic information which exist as long as the cell lives.3. The participation of centrioles in the formation of spindle fibers and in the chromosome movement in anaphase is also a misinterpretation due to a disregard of genes and genetic information under which centrioles behave as primordia of organelles for cell movement.4. In in vivo observations, the continuous movement of chromosomes in anaphase can be seen objectively in a three dimensional space of living spindles, whereas the same behavior of chromosomes in fixation cytology is made up by animating a series of chromosome images in sectioned plane mitotic cells in fixed preparations under observers' subjective influences.5. The teleonomy and the cause and effect relationship among the behavior of mitotic cells, viz. reversible transformation of nuclear sap proteins, the change of nuclear contour from sphere to spindle-shape, the development of spindle background fibrils, the movement of chromosomes in anaphase by shortening of kinetochore fibers, formation of daughter nuclei, the accumulation of ATP at spindle poles, etc. are practically disregarded of the descriptions on the mitosis in current cytology books.

High spin behavior of nuclei with proton number 40?60

The rapid rotation of even-even nuclei is investigated. The characteristic properties of Zn, Mo, Sn, Te, Xe, Ba, Ce and Nd isotopes for high spin are presented. Microscopic calculations are based on the modified oscillator average potential including the quadrupole axial (ɛ) and nonaxial (γ) deformations. The potential energy surfaces of the nuclei are obtained by the shell correction method. The nuclear shape determined by the potential energy surface as a function of angular momentum is predicted.

On the Rotation of Non-Axial nuclei

The rotational properties of non-axial nuclei are studied by means of the generator coordinate method, and in particular it is shown that using the angular momentum projection technique and assuming the Gaussian overlap approximation for the Hamiltonian and overlap matrix elements, the Hill-Wheeler integral equation may be transformed into an equivalent Schrodinger equation for a non-axial rotator.

Rotations and intrinsic Kπ = 1+ excitations in deformed rare-earth nuclei

The Kπ = 1+ intrinsic excitations in deformed rare-earth nuclei are studied in the framework of the random-phase approximation, which excludes the spurious state (zero-energy excitation) related with the rotation of the whole nucleus. We take the Nilsson-plus-pairing, quadrupole and spin-dependent (magnetic dipole or spin-quadrupole) force model. Cranking-model formulae for the moment of inertia and the collective gyromagnetic ratio are derived as the zero-energy limit of the lowest Kπ = 1+ excitation. They are modified from the usual formulae due to the spin-dependent force. The M1 and E2 transitions from the Kπ = 1+ excited states to the ground state of 170Yb are also calculated. The M1 transition strengths are concentrated almost below 6 MeV, while the E2 ones are scattered even up to 12 MeV. Several levels around 12 MeV show rather strong E2 transitions of ΔN = 2 character.

Nuclear Rotation in Heavy-Ion Scattering

The possibility is discussed that the observed energy dependence of the real part of the optical potential in $^{16}\mathrm{O}$-$^{16}\mathrm{O}$ elastic scattering arises from rotation of nuclei induced by their interaction. An estimate indicates that the effect may have the required magnitude.

Rotation Effects in the Nongravitational Parameters of Comets

The effects of rotation of a cometary nucleus on the character of nongravitational parameters are discussed. It is suggested that the change of a nongravitational acceleration to deceleration (and vice versa) may be related to a precessional motion of the nucleus, or to secular variations in the lag angle coupled with severe orbital modifications.

On the theory of rotation of non-axial nuclei

Rotation of non-axial nuclei is considered in the framework of the model suggested by Krutov (1968). The parameters of the total deformation and non-axiality are calculated for a number of the deformed even-even nuclei with A>or=150 on the basis of the energies of the first 2+ rotational states. The E2 transition probability ratios are calculated for transitions between low-lying rotational levels in the non-axial nuclei. These ratios are compared with experiment (agreement is satisfactory) and with the Davydov-Chaban and Davydov-Filippov model predictions.

Mitotic cell studies based on in vivo observations. I. Differences of mitotic figures between living cells and fixed cells.

In this report the author has enumerated the differences in interpretations of the mitosis studied both in fixed preparations and in in vivo observations. The author especially maintains the opinion that any movement of chromosomes in mitotic cells should be reinvestigated thoroughly by in vivo observations in the same way as studies on any movement of intracellular organelles, e.g. plastids, mitochondria, rotation of nucleus, streaming of protoplasm, etc.1. Practically all behavior of mitotic cells described in cytology books has scarcely made reference to the genetic back-ground of the mitosis.2. The breakdown of nuclear membrane before spindle formation in higher plants and animals is an impossibility. The nuclear membrane in eukaryotes is predicted and controlled by genes and genetic information which exist as long as the cell lives.3. The participation of centrioles in the formation of spindle fibers and in the chromosome movement in anaphase is also a misinterpretation due to a disregard of genes and genetic information under which centrioles behave as primordia of organelles for cell movement.4. In in vivo observations, the continuous movement of chromosomes in anaphase can be seen objectively in a three dimensional space of living spindles, whereas the same behavior of chromosomes in fixation cytology is made up by animating a series of chromosome images in sectioned plane mitotic cells in fixed preparations under observers' subjective influences.5. The teleonomy and the cause and effect relationship among the behavior of mitotic cells, viz. reversible transformation of nuclear sap proteins, the change of nuclear contour from sphere to spindle-shape, the development of spindle background fibrils, the movement of chromosomes in anaphase by shortening of kinetochore fibers, formation of daughter nuclei, the accumulation of ATP at spindle poles, etc. are practically disregarded of the descriptions on the mitosis in current cytology books.

The linked-cluster expansion for the transition amplitude for deuteron stripping reaction: W. F. Junkin and F. Villars. Laboratory for Nuclear Science, M.I.T., Cambridge, Massachusetts

At the Technische Hochschule in Darmstadt the group of Richter and coworkers found in 1983/84 in deformed rare earth nuclei low-lying isovector 1+ states. Such states have been predicted in the generalized Bohr-Mottelson model and in the interacting boson model no. 2 (IBA2). In the generalized Bohr-Mottelson model one allows for proton and neutron quadrupole deformations separately. If one includes only static proton and neutron deformations the generalized Bohr-Mottelson model reduces to the two rotor model. It describes the excitation energy of these states in good agreement with the data but overestimates the magnetic dipole transition probabilities by a factor 5. In the interacting boson model (IBA2) where only the outermost nucleons participate in the excitation the magnetic dipole transition probability is only overestimated by a factor 2. The too large collectivity in both models results from the fact that they concentrate the whole strength of the scissors vibrations into one state. A microscopic description is needed to describe the spreading of the scissors strength over several states. For a microscopic determination of these scissors states one uses the Quasi-particle Random Phase Approximation (QRPA). But this approach has a serious difficulty. Since one rotates for the calculation the nucleus into the intrinsic system the state corresponding to the rotation of the whole nucleus is a spurious state. The usual procedure to remove this spuriosity is to use the Thouless theorem which says that a spurious state created by an operator which commutes with the total hamiltonian (here the total angular momentum, corresponding to a rotation of the whole system) produces the spurious state if applied to the ground state. It says further the energy of this spurious state lies at zero excitation energy (it is degenerate with the ground state) and is orthogonal to all physical states. Thus the usual approach is to vary the quadrupole-quadrupole force strength so that a state lies at zero excitation energy and to identify that with the spuríous state. This procedure assumes that a total angular momentum commutes with a total hamiltonian. But this is not the case since the total hamiltonian contains a deformed Saxon-Woods potential. Thus one has to take care explicitly that the spurious state is removed. This we do in our approach by introducing Lagrange multipliers for each excited states and requesting that these states are orthogonal to the spurious state which is explicitly constructed by applying the total angular momentum operator to the ground state. To reduce the number of free parameters in the hamiltonian we take the Saxon-Woods potential for the deformed nuclei from the literature (with minor adjustments) and determine the proton-proton, neutron-neutron and the proton-neutron quadrupole force constant by requesting that the hamiltonian commutes with the total angular momentum in the (QRPA) ground state. This yields equations fixing all three coupling constants for the quadrupole-quadrupole force allowing even for isospin symmetry violation. The spin-spin force is taken from the Reid soft core potential. A possible spin-quadrupole force has been taken from the work of Soloviev but it turns out that this is not important. The calculation shows that the strength of the scissors vibrations are spread over many states. The main 1+ state at around 3 MeV has an overlap of the order of 14 % of the scissors state. 50% of that state are spread over the physical states up to an excitation energy of 6 MeV. The rest is distributed over higher lying states. The expectation value of the many-body hamiltonian in the scissors vibrational state shows roughly an excitation energy of 7 MeV above the ground state. The results also support the experimental findings that these states are mainly orbital excitations. States are not very collective. Normally only a proton and neutron particle-hole pair are with a large amplitude participating in forming these states. But those protons and neutrons which are excited perform scissors type vibrations.

Stretch Scheme, a Microscopic Description of Rotations in Nuclei

A good angular-momentum wave function containing the maximum possible intrinsic angular momenta leads to rotational spectra. The rotational excitation energies arise from the residual two-body force.Received 9 August 1966DOI:https://doi.org/10.1103/PhysRevLett.17.703©1966 American Physical Society

A mechanism for the formation of twins in evaporated face-centred cubic metal films

Abstract Face-centred cubic metal films that are prepared by evaporation onto sodium chloride contain numerous micro-twins. It is suggested that these twins are formed when two nuclei, which happen to be approximately twins of one another, coalesce and rotate into precisely twin relationship. The rotation takes place in a manner similar to the rotation of nuclei into parallel alignment that was observed by Bassett. It is shown that this mechanism is consistent with the mode of growth of films, and with the size, shape and arrangement of the twins. The mechanism is also able to account for the formation of twins early in film growth, for the rarity of twins of twins, and for the presence of the {112} orientation observed by Gottsche and Kehoe.

Motions in Barred Spiral Galaxies. I. The Nuclei of NGC 1097 and NGC 1365.

view Abstract Citations (84) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Motions in Barred Spiral Galaxies. I. The Nuclei of NGC 1097 and NGC 1365. Burbidge, E. Margaret ; Burbidge, G. R. Abstract The nuclear regions of the barred spirals NGC 1097 and NGC 1365 are shown and described. Spectra of these nuclei have been obtained, and the rotations have been measured from the Ha and [N ii] x 6583 emission lines. The rotation-curve of the nucleus of NGC 1097 is discontinuous in the inner part. The nuclear region in this galaxy consists of a small inner amorphous nucleus and an outer segmented annulus; the cause of the velocity discontinuity may be that the emission lines arise only in the annulus. The rotation-curve of NGC 1365 is linear across the nucleus. The observed rotations of both nuclei are quite large, the velocity difference from one side' to the other amounting to 413 km/sec in NGC 1097 and 431 km/sec in NGC 1365. If rotation alone is present, these, when corrected for orientation, give 549 km/sec across a diameter of about 20" or 1600 pc in NGC 1097 and 808 km/sec across a diameter of about 30" or 3000 pc in NGC 1365. It is stressed that the apparent rotational velocity might contain a component due to expansion in the planes' of the galaxies, whose magnitude could not be measured in objects whose major axes are not unequivocally determined from their geometry. Mass estimates of the nuclei from the rotations are 0.5-1.3 X 1011 `Mo in NGC 1097 and 2.2-3.4 X 1010 Mo in NGC 1365. These correspond to mean densities of >38 Mo/pc3 in NGC 1097 and 7-23 Mo/pc3 in NGC 1365. Publication: The Astrophysical Journal Pub Date: July 1960 DOI: 10.1086/146896 Bibcode: 1960ApJ...132...30B full text sources ADS | data products SIMBAD (2) NED (2) Related Materials (6) Part 2: 1960ApJ...132..654B Part 3: 1960ApJ...132..661B Part 4: 1962ApJ...136..119B Part 5: 1962ApJ...136..704B Part 6: 1964ApJ...140...85B Part 7: 1964ApJ...140...94R