Geometry Of Nucleus Research Articles

Quantum mechanical study of substituted phenoxathiin II: A study of the structure of phenoxathiin diazonium compounds

The structure of phenoxathiin diazonium compounds is studied to deduce the effect exerted by the σ- and π-electron withdrawing properties of the diazonium group on the puckered phenoxathiin nucleus. The study predicts and analyzes the configuration of several yet to be synthesized phenoxathiin diazonium compounds. The ab initio method at the B3LYP/6-31+G(d) basis set level of calculation is employed in this study. The diazonium group is predicted to induce noticeable changes on the geometry of the phenoxathiin nucleus, that are reflected on the puckering angle Φ c of phenoxathiin. The magnitude of the change is found to be dependent on the position of the diazonium group with respect to the sulfur atom of the central heterocyclic ring. Substitution at the 1-position, ortho to the sulfur induces the least flattening effect on the nucleus, while substitution at the 3- position, para to the sulfur induces the highest flattening. Introduction of a second diazonium group enhances these effects. Phenoxathiin-1,9-bis(diazonium) is found to be the most puckered. On the other hand phenoxathiin-3,7-bis(diazonium), phenoxathiin-4,6-bis(diazonium), phenoxathiin-1,4-bis(diazonium), and phenoxathiin-2,3-bis(diazonium) are predicted to be absolutely planar. The inversion barriers for the puckered molecules under study are found to be quite small; ranging between 0.0012 and 0.92 kcal/mol.

Differential diagnosis of breast cancer using quantitative, label-free and molecular vibrational imaging

We present a label-free, chemically-selective, quantitative imaging strategy to identify breast cancer and differentiate its subtypes using coherent anti-Stokes Raman scattering (CARS) microscopy. Human normal breast tissue, benign proliferative, as well as in situ and invasive carcinomas, were imaged ex vivo. Simply by visualizing cellular and tissue features appearing on CARS images, cancerous lesions can be readily separated from normal tissue and benign proliferative lesion. To further distinguish cancer subtypes, quantitative disease-related features, describing the geometry and distribution of cancer cell nuclei, were extracted and applied to a computerized classification system. The results show that in situ carcinoma was successfully distinguished from invasive carcinoma, while invasive ductal carcinoma (IDC) and invasive lobular carcinoma were also distinguished from each other. Furthermore, 80% of intermediate-grade IDC and 85% of high-grade IDC were correctly distinguished from each other. The proposed quantitative CARS imaging method has the potential to enable rapid diagnosis of breast cancer.

Structural dynamics of the nucleus: Basis for Morphology Modulation of Nuclear Calcium Signaling and Gene Transcription

Event Abstract Back to Event Structural dynamics of the nucleus: Basis for Morphology Modulation of Nuclear Calcium Signaling and Gene Transcription Markus Breit1, Hilmar Bading2 and Gillian Queisser1* 1 Bernstein Center Heidelberg/Mannheim and Goethe Center for Scientific Computing, Germany 2 University of Heidelberg, Department of Neurobiology, Germany Neuronal morphology plays an essential role in signal processing in the brain. Individual neurons can undergo use-dependent changes in their shape and connectivity, which affects how intracellular processes are regulated and how signals are transferred from one cell to another in a neuronal network. Calcium is one of the most important intracellular second messengers regulating cellular morphologies and functions. In neurons, intracellular calcium levels are controlled by ion channels in the plasma membrane such as NMDA receptors (NMDARs), voltage-gated calcium channels (VGCCs) and certain α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) as well as by calcium exchange pathways between the cytosol and internal calcium stores including the endoplasmic reticulum and mitochondria. Synaptic activity and the subsequent opening of ligand and/or voltage-gated calcium channels can initiate cytosolic calcium transients which propagate towards the cell soma and enter the nucleus via its nuclear pore complexes (NPCs) embedded in the nuclear envelope. With the help of detailed three-dimensional calcium models and in vivo experiments we recently described the discovery that in hippocampal neurons the morphology of the nucleus affects the calcium dynamics within the nucleus. Here we porpose that nuclear infoldings determine whether a nucleus functions as an integrator or detector of oscillating calcium signals. We outline possible ties between nuclear mophology and transcriptional activity and discuss the importance of extending the approach to whole cell calcium signal modeling in order to understand synapse-to-nucleus communication in healthy and dysfunctional neurons. References Wittmann, M., Queisser, G., Eder, A., Wiegert, J.S., Bengtson, C.P., Hellwig, A., Wittum, G., and Bading, H. (2009) Synaptic Activity Induces Dramatic Changes in the Geometry of the Cell Nucleus: Interplay Between Nuclear Structure, Histone H3 Phosphorylation, and Nuclear Calcium Signaling. The Journal of Neuroscience 29(47):14687-14700 Queisser, G., Wiegert S., and Bading, H. (2011) Structural dynamics of the nucleus: Basis for Morphology Modulation of Nuclear Calcium Signaling and Gene Transcription. Nucleus. DOI: 10.4161/nucl.2.2.15116 Queisser, G., Wittmann, M., Bading, H., and Wittum, G. (2008) Filtering, reconstruction, and measurement of the geometry of nuclei from hippocampal neurons based on confocal microscopy data. Journal of Biomedical Optics 13, 014009. Queisser, G., Wittum, G. (2011) A method to investigate the diffusion properties of nuclear calcium. Biol. Cybern. (to appear) Keywords: Calcium Signaling, detailed 3d-modeling, dysfunctional neurons, Learning and plasticity, morphology modulation, nucleus, synapse-to-nucleus communication Conference: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011, Freiburg, Germany, 4 Oct - 6 Oct, 2011. Presentation Type: Demonstration Topic: learning and plasticity (please use "learning and plasticity" as keyword) Citation: Breit M, Bading H and Queisser G (2011). Structural dynamics of the nucleus: Basis for Morphology Modulation of Nuclear Calcium Signaling and Gene Transcription. Front. Comput. Neurosci. Conference Abstract: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011. doi: 10.3389/conf.fncom.2011.53.00172 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 22 Aug 2011; Published Online: 04 Oct 2011. * Correspondence: Prof. Gillian Queisser, Bernstein Center Heidelberg/Mannheim and Goethe Center for Scientific Computing, Frankfurt am Main, 60325, Germany, gillian.queisser@gcsc.uni-frankfurt.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Markus Breit Hilmar Bading Gillian Queisser Google Markus Breit Hilmar Bading Gillian Queisser Google Scholar Markus Breit Hilmar Bading Gillian Queisser PubMed Markus Breit Hilmar Bading Gillian Queisser Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

On the dust geometry in radio-loud active galactic nuclei

We use photometric and spectroscopic infrared observations obtained with the Spitzer Space Telescope of 12 radio-loud active galactic nuclei (AGN) to investigate the dust geometry. Our approach is to look at the change of the infrared spectral energy distribution (SED) and the strength of the 10 micron silicate feature with jet viewing angle. We find that (i) a combination of three or four blackbodies fits well the infrared SED; (ii) the sources viewed closer to the jet axis appear to have stronger warm (~300 - 800 K) and cold (~150 - 250 K) dust emissions relative to the hot component; and (iii) the silicate features are always in emission and strongly redshifted. We test clumpy torus models and find that (i) they approximate well the mid-infrared part of the SED, but significantly underpredict the fluxes at both near- and far-infrared wavelengths; (ii) they can constrain the dust composition (in our case to that of the standard interstellar medium); (iii) they require relatively large (~10%-20% the speed of light) redward displacements; and (iv) they give robust total mass estimates, but are insensitive to the assumed geometry.

Synaptic Activity Induces Dramatic Changes in the Geometry of the Cell Nucleus: Interplay between Nuclear Structure, Histone H3 Phosphorylation, and Nuclear Calcium Signaling

Synaptic activity initiates many adaptive responses in neurons. Here we report a novel form of structural plasticity in dissociated hippocampal cultures and slice preparations. Using a recently developed algorithm for three-dimensional image reconstruction and quantitative measurements of cell organelles, we found that many nuclei from hippocampal neurons are highly infolded and form unequally sized nuclear compartments. Nuclear infoldings are dynamic structures, which can radically transform the geometry of the nucleus in response to neuronal activity. Action potential bursting causing synaptic NMDA receptor activation dramatically increases the number of infolded nuclei via a process that requires the ERK-MAP kinase pathway and new protein synthesis. In contrast, death-signaling pathways triggered by extrasynaptic NMDA receptors cause a rapid loss of nuclear infoldings. Compared with near-spherical nuclei, infolded nuclei have a larger surface and increased nuclear pore complex immunoreactivity. Nuclear calcium signals evoked by cytosolic calcium transients are larger in small nuclear compartments than in the large compartments of the same nucleus; moreover, small compartments are more efficient in temporally resolving calcium signals induced by trains of action potentials in the theta frequency range (5 Hz). Synaptic activity-induced phosphorylation of histone H3 on serine 10 was more robust in neurons with infolded nuclei compared with neurons with near-spherical nuclei, suggesting a functional link between nuclear geometry and transcriptional regulation. The translation of synaptic activity-induced signaling events into changes in nuclear geometry facilitates the relay of calcium signals to the nucleus, may lead to the formation of nuclear signaling microdomains, and could enhance signal-regulated transcription.

Equivalent Refractive Index of the Human Lens upon Accommodative Response

To experimentally verify the suggestion of Gullstrand (1909), i.e., that the equivalent refractive index of the human lens increases with accommodation. The left eye of five subjects was focused on different accommodation stimuli, while the right eye was imaged with Scheimpflug photography in order to obtain the shape of the lens and cornea during accommodation. The procedure was then repeated, but instead of using the Scheimpflug camera, the accommodative response of the right eye was measured objectively with an aberrometer. The axial length was measured with a Zeiss IOL-master. Combining the results of these measurements made it possible to correct the digital Scheimpflug images for corneal and lenticular refraction, and to simultaneously calculate the equivalent refractive index of the lens for all different accommodative stimuli. Furthermore, a two-compartment model of the lens was constructed, with a nucleus and a cortex. In all five subjects there was no significant change in the equivalent refractive index of the lens as a function of accommodation. The mean equivalent refractive index was 1.435 +/- 0.008. Furthermore, the accommodative response appeared to be lower than the accommodative stimulus (i.e., accommodative lag). It appeared to be possible to model the optical power of the lens, based on the geometry of cortex and nucleus. Based on a refractive index of 1.406 for the nucleus, the mean refractive index of the cortex was 1.381. Gullstrand suggested that there would be an increase in the equivalent refractive index with accommodation; the intra-capsulary mechanism of accommodation. However, we found that the equivalent refractive index of the lens does not change with accommodation when the accommodative lag is taken into account. Furthermore, it appeared to be possible to simulate the accommodative process of a subject with a two-compartment model with constant refractive indices.

Filtering, reconstruction, and measurement of the geometry of nuclei from hippocampal neurons based on confocal microscopy data

The cell nucleus is often considered a spherical structure. However, the visualization of proteins associated with the nuclear envelope in rat hippocampal neurons indicates that the geometry of nuclei is far more complex. The shape of cell nuclei is likely to influence the nucleo-cytoplasmic exchange of macromolecules and ions, in particular calcium, a key regulator of neuronal gene expression. We developed a tool to retrieve the 3-D view of cell nuclei from laser scanning confocal microscopy data. By applying an inertia-based filter, based on a special structure detection mechanism, the signal-to-noise ratio of the image is enhanced, the signal is smoothed, gaps in the membrane are closed, while at the same time the geometric properties, such as diameters of the membrane, are preserved. After segmentation of the image data, the microscopy data are sufficiently processed to extract surface information of the membrane by creating an isosurface with a marching tetrahedra algorithm combined with a modified Dijkstra graph-search algorithm. All methods are tested on artificial data, as well as on real data, which are recorded with a laser scanning confocal microscope. Significant advantages of the inertia-based filter can be observed when comparing it to other state of the art nonlinear diffusion filters. An additional program is written to calculate surface and volume of cell nuclei. These results represent the first step toward establishing a geometry-based model of the-dynamics of cytoplasmic and nuclear calcium.

THE ACCRETION GEOMETRY IN RADIO-LOUD ACTIVE GALAXIES

We review the latest attempts to determine the accretion geometry in radio-loud active galactic nuclei (AGN). These objects, which comprise ~ 10–20% of the AGN population, produce powerful collimated radio jets that can extend thousands of parsecs from the center of the host galaxy. Recent multiwavelength surveys have shown that radio-loudness is more common in low-luminosity AGN than in higher luminosity Seyfert galaxies or quasars. These low-luminosity AGN have small enough accretion rates that they are most likely accreting via a geometrically thick and radiatively inefficient accretion flow. In contrast, X-ray spectroscopic observations of three higher luminosity broad-line radio galaxies (3C 120, 4C+74.26 and PG 1425+267) have found evidence for an untruncated thin disk extending very close to the black hole. These tentative detections indicate that, for this class of radio-loud AGN, the accretion geometry is very similar to their radio-quiet counterparts. These observations suggest that there are three conditions to jet formation that must be satisfied: the presence of a rapidly spinning black hole, an accretion flow with a large H/r ratio, and a favorable magnetic field geometry.

Dipole excitation and geometry of Borromean nuclei

We analyze the Coulomb breakup cross sections of $^{11}\mathrm{Li}$ and $^{6}\mathrm{He}$ nuclei using a three-body model with a density-dependent contact interaction. We show that the concentration of the $B(E1)$ strength near the threshold can be well reproduced with this model. With the help of the calculated $B(E1)$ value, we extract the root-mean-square (rms) distance between the core nucleus and the center-of-mass of two valence neutrons without resorting to the sum rule, which may suffer from unphysical Pauli forbidden transitions. Together with the empirical rms distance between the neutrons obtained from the matter radius study and also from the three-body correlation study in the breakup reaction, we convert these rms distances to the mean opening angle between the valence neutrons from the core nucleus. We find that the obtained mean opening angles in $^{11}\mathrm{Li}$ and $^{6}\mathrm{He}$ agree with the three-body model predictions.

A Long, Hard Look at the Low/Hard State in Accreting Black Holes

We present the first results of coordinated multiwavelength observations of the Galactic black hole GX 339-4 in a canonical low/hard state, obtained during its 2004 outburst. XMM-Newton observed the source for two revolutions, or approximately 280 ks; RXTE monitored the source throughout this long stare. The resulting data offer the best view yet obtained of the inner accretion flow geometry in the low/hard state, which is thought to be analogous to the geometry in low-luminosity active galactic nuclei. The XMM-Newton spectra clearly reveal the presence of a cool accretion disk component and a relativistic Fe K emission line. The results of fits made to both components strongly suggest that a standard thin disk remains at or near to the innermost stable circular orbit, at least in bright phases of the low/hard state. These findings indicate that potential links between the inner disk radius and the onset of a steady compact jet, and the paradigm of a radially recessed disk in the low/hard state, do not hold universally. The results of our observations can best be explained if a standard thin accretion disk fuels a corona that is closely related to, or consistent with, the base of a compact jet. In a brief examination of archival data, we show that Cygnus X-1 supports this picture of the low/hard state. We discuss our results within the context of disk-jet connections and prevailing models for accretion onto black holes.

Comparison of crystal structures of human androgen receptor ligand‐binding domain complexed with various agonists reveals molecular determinants responsible for binding affinity

Androgens exert their effects by binding to the highly specific androgen receptor (AR). In addition to natural potent androgens, AR binds a variety of synthetic agonist or antagonist molecules with different affinities. To identify molecular determinants responsible for this selectivity, we have determined the crystal structure of the human androgen receptor ligand-binding domain (hARLBD) in complex with two natural androgens, testosterone (Testo) and dihydrotestosterone (DHT), and with an androgenic steroid used in sport doping, tetrahydrogestrinone (THG), at 1.64, 1.90, and 1.75 A resolution, respectively. Comparison of these structures first highlights the flexibility of several residues buried in the ligand-binding pocket that can accommodate a variety of ligand structures. As expected, the ligand structure itself (dimension, presence, and position of unsaturated bonds that influence the geometry of the steroidal nucleus or the electronic properties of the neighboring atoms, etc.) determines the number of interactions it can make with the hARLBD. Indeed, THG--which possesses the highest affinity--establishes more van der Waals contacts with the receptor than the other steroids, whereas the geometry of the atoms forming electrostatic interactions at both extremities of the steroid nucleus seems mainly responsible for the higher affinity measured experimentally for DHT over Testo. Moreover, estimation of the ligand-receptor interaction energy through modeling confirms that even minor modifications in ligand structure have a great impact on the strength of these interactions. Our crystallographic data combined with those obtained by modeling will be helpful in the design of novel molecules with stronger affinity for the AR.

Absorbed dose in target cell nuclei and dose conversion coefficient of radon progeny in the human lung

To calculate the absorbed dose in the human lung due to inhaled radon progeny, ICRP focussed on the layers containing the target cells, i.e., the basal and secretory cells. Such an approach did not consider details of the sensitive cells in the layers. The present work uses the microdosimetric approach and determines the absorbed alpha-particle energy in non-spherical nuclei of target cells (basal and secretory cells). The absorbed energy for alpha particles emitted by radon progeny in the human respiratory tract was calculated in basal- and secretory-cell nuclei, assuming conical and ellipsoidal forms for these cells. Distributions of specific energy for different combinations of alpha-particle sources, energies and targets are calculated and shown. The dose conversion coefficient for radon progeny is reduced for about 2 mSv/WLM when conical and ellipsoidal cell nuclei are considered instead of the layers. While changes in the geometry of secretory-cell nuclei do not have significant effects on their absorbed dose, changes from spherical to conical basal-cell nuclei have significantly reduced their absorbed dose from ∼4 to ∼3 mGy/WLM. This is expected because basal cells are situated close to the end of the range of 6 MeV alpha particles. This also underlines the significance of better and more precise information on targets in the T-B tree. A further change in the dose conversion coefficient can be achieved if a different weighting scheme is adopted for the doses for the cells. The results demonstrate the necessity for better information on the target cells for more accurate dosimetry for radon progeny.

Incorporating turn-over in whole body protein retention efficiency in cattle and sheep

AbstractIn pigs the quantification of breakdown and synthesis by powers of body protein led to the estimation of turn-over related protein retention efficiency by the equation kP= {1 + [1 − (P/α)(2/9)Q]−1/6}−1, with α the limit value of whole body protein (P) maturity, so that 0 ≤(P/α)≤1. The factor 2/9 is derived from diffusion attributes indicated by cell and nucleus geometries α and Q represents a scaled transformation of intake, 0 ≤ Q ≤ 1, such that a value of Q = 1 may represent ad libitum intake and Q = 0 the intake at the maintenance requirement. Published observations on finishing steers provide estimates of whole body protein synthesis and breakdown at pre-determined levels of intake in confirmation of the theoretical (2/9)Q power associated with (P/α) inkP. Further confirmation of the (2/9)Q power in cattle follows from satisfactory agreement between an estimate of conventional multiple regression retention efficiency and the turn-over related retention efficiency calculated at the given level of intake, for the mid point of the body mass interval covered by the regression estimate. In addition, a simulation experiment on cattle from the literature gives power estimates of protein breakdown and synthesis in general agreement with those accepted for pigs. Examples on both fine and coarse diets are employed to suggest a general rule for prediction on diets causing submaximal efficiency due to suboptimal intakes.In sheep, evidence derived from estimates of conventional multiple regression efficiencies suggests that the rule (a-b) = (2/9) Q for the calculation ofkPshould be reserved for the description of compensatory growth. Protein retention efficiency for ordinary growth should be described by an adaptation of the rule derived for suboptimal intakes.

Incorporating turn-over in whole body protein retention ef.ciency in pigs

The magnitude of the discrepancy between conventional regression estimates of protein retention efficiency and theoretical estimates of synthesis efficiency indicates a major contribution ascribable to protein turn-over in the generally accepted estimates. As protein turn-over is known to be influenced by diet, feeding level and degree of maturity, this suggests the development of an estimator of protein efficiency that can be adapted for such differences. Therefore, based on generally accepted formulas for growth description, a method of estimating protein retention efficiency was developed which is flexible enough to accommodate different diets, feeding levels and degrees of maturity. Moreover, a formula was derived to convert one type of estimate to the other by regarding constant efficiency as equivalent to variable efficiency at the mid point of the estimation interval. Increase in scientific depth to this descriptive approach is provided by a theoretical consideration of a possible mechanism of hormonal control of protein synthesis and breakdown, ultimately expressed as proportionalities to powers of whole body protein (P). Molecular considerations on cellular synthesis and breakdown indicate a difference between breakdown and synthesis powers equal to (2/9)Q. The factor (2/9) is indicated by an argument based on insulinlike growth factor derived activator diffusion attributes by nucleus and body tissue geometries, whileQis equal to the proportion of nuclei activated by insulin-like growth factor. This proportion is likely to be a function of the concentration of growth factor in the blood. Hence, a linear relationship between intake and blood insulin-like growth factor concentration suggests thatQcan be represented by a scaled transformation of intake, 0 ≤Q≤ 1, such that a value ofQ= 1 represents ad libitum intake on a suitable diet andQ= 0 intake at the maintenance requirement. The quantification of breakdown and synthesis power differences by (2/9)Qleads to kP= {1 + [1 − (P/α)(2/9)Q]−1/6}−1, for turn-over related protein retention efficiency (kP), with α the limit value of P at maturity, so that 0 ≤ (P/α) ≤ 1. Experimental estimates, derived from direct estimates of whole body protein synthesis and breakdown at predetermined levels of intake, are in excellent agreement with the theoretical (2/9)Qin the power associated with (P/α) in kP. Furthermore, conventional multiple regression retention efficiencies satisfactorily approximate the turn-over related retention efficiency that can be calculated at a given level of intake for the mid point of the interval covered by the regression estimates.

Simulation of Precipitation of Compounds from Solid Solution by Joined Finite Difference and Cellular Automaton Methods

The CA method provides an excellent possibility for a lifelike simulation of transformation processes. Using CA method the processes can be displayed on the screen of the computer as a film. CA method is widely used to simulate the transformations controlled by short-range diffusion such as recrystallisation and grain growth. At the simulation of transformations based on long-range diffusion a well-known problem is that the results of simulation depend strongly on the selected nucleus geometry and the neighbourhood of cells. In this paper the influence of neighbourhood will be analysed in the case of simulated precipitation processes. On the one hand, it is verified that an anisotropic (dendritic) structure is formed if there is no strict restriction for the computational algorithm. On the other hand, it is demonstrated that an isotropic phase growth can be obtained by using a special simulation technique based on the joint application of finite difference (FD) and of CA methods.

Kinetics of Two-Phase Electrocrystallization Processes: I. Competitive Growth of Right-Circular Cones

An equation relating the potentiostatic current to the passage of time has been derived for the instantaneous nucleation and charge-transfer-controlled growth of two phases of a crystalline deposit under the restriction that both phases have the same density, molar mass, and ionic forms. The growth geometry of nuclei of each phase is represented by right-circular cones of a unique angle of contact. With the passage of time, the electrocrystallization process is shown to become increasingly dominated by the growth of the phase with the higher outward rate of crystal growth. Unlike the conical model of growth of a single-phase deposit which stipulates the attainment of a steady-state current plateau once the surface of an electrode is completely covered by the lateral growth of the deposit, in the two-phase electrocrystallization processes the attainment of the steady-state current is shown to be prolonged beyond the full coverage of the surface to a time when the phase with the smaller rate of outward growth is fully engulfed by the growth of the other phase. The transients due to the two-phase electrocrystallization reactions are shown to be indistinguishable from those of a single phase only if the rates of outward growth of both phases are set equal to each other. © 2003 The Electrochemical Society. All rights reserved.

Binary methods for the microdosimetric analysis of cell survival data from alpha-particle irradiation.

A new type of alpha-particle irradiator allows survival of each cell to be observed individually along with the size and shape of its nucleus and the positions of the hits it receives. This paper discusses methods of data analysis that can utilize these additional data. Using idealizations of the cell nucleus geometry (i.e., spheres, ellipsoids), the path length (l), energy deposited (e), and specific energy (z) has been determined on a cell-by-cell basis for 772 cells all subjected to the same fluence. Each cell is regarded as a Bernoulli trial with a different probability for success (colony formation). For the survival expectation, A exp(-z/z(o)), the values of A and z(o) are chosen to maximize the likelihood for the observed outcome. Similar results are presented using the alternate functional forms A exp(-e/e(o)) and A exp(-l/l(o)). With these parameter values, the goodness of fit is also evaluated using a chi-square method with variances given by the binary (Bernoulli) methods. A further purpose of the paper is to assess the validity of the microdosimetric computations that would have had to be made if these individual cell-by-cell experimental measurements were not available or were incomplete.

Assessing Formation Scenarios for the Double Nucleus of M31 Using Two-Dimensional Image Decomposition

The double nucleus geometry of M31 is currently best explained by the eccentric disk hypothesis of Tremaine, but whether the eccentric disk resulted from the tidal disruption of an inbounding star cluster, from a nuclear black hole, or from an m = 1 perturbation of a native nuclear disk remains debatable. I perform detailed two-dimensional decomposition of the M31 double nucleus in the Hubble Space Telescope V-band to study the bulge structure and to address competing formation scenarios of the eccentric disk. I deblend the double nucleus (P1 and P2) and the bulge simultaneously using five Sersic and one Nuker components. P1 and P2 appear to be embedded inside an intermediate component (re = 32) that is nearly spherical (q = 0.97 ± 0.02), while the main galaxy bulge is more elliptical (q = 0.81 ± 0.01). The spherical bulge mass (2.8 × 107 M⊙), being coincident with the supermassive black hole mass (3 × 107 M⊙), conjoined with a shallow bulge cusp, is consistent with the scenario that the bulge was scoured by spiraling binary supermassive black holes. In the two-dimensional decomposition the bulge is consistent with being centered near the UV peak of P2, but the exact position is difficult to pinpoint because of dust in the bulge. P1 and P2 are comparable in mass. Within a radius r = 1'' of P2, the relative mass fraction of the nuclear components is M• : Mbulge : P1 : P2 = 4.3 : 1.2 : 1 : 0.7, assuming the luminous components have a common mass-to-light ratio of 5.7. The eccentric disk as a whole (P1 + P2) is massive, M ≈ 2.1 × 107 M⊙, comparable to the black hole and the local bulge mass. As such, the eccentric disk could not have been formed entirely out of stars that were stripped from an inbounding star cluster. Hence, the more favored scenario is that of a disk formed in situ by an m = 1 perturbation caused possibly by the passing of a giant molecular cloud or the passing/accretion of a small globular cluster.

Structural changes without stable intermediate state in inelastic material. Part II. Applications to displacive and diffusional–displacive phase transformations, strain-induced chemical reactions and ductile fracture

Abstract A number of simple examples demonstrate the applicability of the general theory developed in Part I of this paper to various structural changes in solids, namely to displacive and generalized second-order phase transformations, twinning and reorientation of crystal lattice, ductile fracture, and strain-induced chemical reactions. The theory is extended to diffusional-displacive phase transitions. The following problems for elastic and elastoplastic materials are solved analytically: displacive and diffusional–displacive phase transitions in a spherical particle inside the space under external pressure, martensitic phase transition and twinning in ellipsoidal inclusion under applied shear stress, spherical void nucleation, crack propagation in a similar framework to the Dugdale model for a plane stress state. In most cases explicit expressions for the thermodynamic and kinetic conditions for structural changes and the geometric parameters of the nucleus are obtained and analyzed. The following typical cases in the determination of the geometric parameters of nucleus are found: solely from the principle of the minimum of transformation time and the kinetic equation without any constraints or with thermodynamic constraint; from the principle of the minimum of transformation mass and the thermodynamic criterion of structural changes (thermodynamically admissible nucleus); as an interatomic distance. For diffusional–displacive phase transformations, additional variants are related to the necessity to consider the diffusion equation (for the diffusion-controlled transformation) and constraints related to the maximum and minimum possible volume fraction of solute atoms. The nucleation kinetics for various nucleus geometries is compared.

Thermomechanics and kinetics of generalized second-order phase transitions in inelastic materials. Application to ductile fracture

A number of simple examples demonstrate the applicability of the general theory developed in Part I of this paper to various structural changes in solids, namely to displacive and generalized second-order phase transformations, twinning and reorientation of crystal lattice, ductile fracture, and strain-induced chemical reactions. The theory is extended to diffusional-displacive phase transitions. The following problems for elastic and elastoplastic materials are solved analytically: displacive and diffusional–displacive phase transitions in a spherical particle inside the space under external pressure, martensitic phase transition and twinning in ellipsoidal inclusion under applied shear stress, spherical void nucleation, crack propagation in a similar framework to the Dugdale model for a plane stress state. In most cases explicit expressions for the thermodynamic and kinetic conditions for structural changes and the geometric parameters of the nucleus are obtained and analyzed. The following typical cases in the determination of the geometric parameters of nucleus are found: solely from the principle of the minimum of transformation time and the kinetic equation without any constraints or with thermodynamic constraint; from the principle of the minimum of transformation mass and the thermodynamic criterion of structural changes (thermodynamically admissible nucleus); as an interatomic distance. For diffusional–displacive phase transformations, additional variants are related to the necessity to consider the diffusion equation (for the diffusion-controlled transformation) and constraints related to the maximum and minimum possible volume fraction of solute atoms. The nucleation kinetics for various nucleus geometries is compared.