Simple Transitions Research Articles

"Bridge" Texts: The Rhetoric of Persuasion in American Children's Realist and Historical Fiction

Literal come in many styles and may be struc- tures as makeshift as a plank thrown over a stream or as complex as the Golden Gate Bridge. Associated with them in our cultural consciousness are activities and images as diverse as long lines of automobiles at rush hour, terrify- ing car chases during gangster films, or the lone presence of a potential suicide perched precariously atop a high suspension bridge. As symbolic tropes, signify simple transitions, complex challenges, even impossible hurdles. Early in our lives we are warned, Don't cross that bridge till you come to it; politicians speak of bridg- ing the gap between one constituency and another; and media trainers who wish to prepare their clients for a bar- rage of hostile questions by reporters teach them to con- struct bridges as rhetorical strategies for controlling negative traffic.2 Both literal and symbolic abound in books for children. Bridges dot the landscape of children's lit- erature as early as Three Billy-goats Gruff, who suc- ceed in outwitting the great ugly Troll on his archetypal bridge.3 The tradition of rhetorical bridging goes back at least to the nineteenth century, with its use of narrative direct address to the reader and anthropomorphized ani- mals or fantasy figures as ways of dealing with change, disorientation, or death. In fairy tales and Alice in Wonder- land, for example, adult narrators customarily condescend to their protagonists and readers—in parentheses or ex- planatory asides. The goal with such narrative bridges is to mediate the child-reader's experience and soften the blow. These techniques of direct intervention have con- tinued, to some extent, into the present, but they are used much more in fantasy or mixed genres than in the realis- tic, historic, or autobiographical texts that I am consid- ering, in which first-person (immediate or retrospective) narration predominates and the author therefore cannot intercede in her own voice or introduce gratuitously fan-

Geometric transitions, brane dynamics and gauge theories

We consider the interplay between brane constructions and type IIA, IIB or M-theory geometries on Calabi-Yau (CY) and G_2 holonomy manifolds. This is related to N=1 (and N=2) gauge theories in four dimensions. We first discuss simple geometric transitions corresponding to brane set ups involving orthogonal (or parallel) Neveu-Schwarz branes that approach each other. This is related to confinement and Seiberg duality in SQCD. In particular, we argue that in type IIA, a CP^1 of singularities and one unit of Ramond-Ramond (RR) flux is dual to a D6 brane wrapped on a Lens space, describing the UV and IR of N=1 Super-Yang-Mills (SYM), respectively. Also, in the large N_c duality that relates D6 branes on S^3 to an S^2 with RR flux, we implement the presence of $N_f$ flavors of quarks. We then compactify M-theory on T^*(S^3) X S^1)/Z_2 and observe that one phase describes SO(4) SYM in the UV and two others describe confinement. Moreover, we consider compact 7-spaces (CY X S^1)/Z_2. We describe transitions where disconnected S^3's approach and connect each other before they vanish. These effects correspond to non-Abelian Higgs mechanism and confinement. The similar transitions involving S^2 X S^1's are also considered. Finally, we present transitions at finite distance in moduli space, where the first Betti number b_1 of 3-cycles of singularities changes.

State diagrams and sorption isotherms of bacterial suspensions and fermented medium

Physical properties of lactic acid bacteria suspensions were determined by means of state diagrams and sorption isotherms. Differential scanning calorimetry (DSC) was used to establish the thermal transitions of concentrated “fresh” (before freeze-drying) and freeze-dried bacterial suspension equilibrated at different relative humidities. The bacterial cells and the re-suspending medium (fermented culture medium) were studied separately in order to determine each individual effect. No glass transition ( T g) was detected in thermal profiles of washed bacterial cells. Correspondingly, T g curves were similar for fermented medium and bacterial suspension. Simple glass transitions (one heat capacity step) were observed at T g in the case of low moisture samples. For samples containing more than 60.7% water, two steps remained in the glass transition region ( T g1′ and T g2′), even after annealing treatments. Water plasticising effect was well predicted by Gordon–Taylor equation. The invariant point ( C g′, T g′), characteristic of maximally freeze-concentrated samples, was estimated from the intersection of the T g curve and the melting curve T m. A linear relationship was proposed to rapidly predict the T g′ region of complex aqueous solutions, from T g′ values of single solute aqueous solutions. Water sorption properties of fermented medium and bacterial suspension were determined at 25°C and described by the Guggenheim–Anderson–de Boer equation.

On the possibility of investigating the dispersion of the energy bands of a crystal using resonant x-ray emission spectra

It is shown that, when the dispersion of the energy bands of crystals is investigated by resonant x-ray emission (RXE), an ambiguity can arise in the determination of ktr — the transition point in k space — as a result of the characteristic features of the band structure and the value of the matrix elements. It is proposed that calculations of the distribution of partial contributions to interband optical transitions in the Brillouin zone (BZ) be used as a means of obtaining a simplified estimate of ktr. The basic properties of this distribution are examined for lithium hydride, which is a convenient model object having a simple band structure and interband transitions which have been studied in detail. It is shown that the k points of the general position, which form a complex figure in the BZ, make the main contribution to the interband transitions. The contribution of high-symmetry points is much smaller mainly because of their small representativeness. This make it easier to understand the reason for the possible nonmonotonic variation of ktr in RXE measurements of the dispersion of the energy bands of crystals or the sharp changes in the resonance-fluorescence intensity.

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Black-Hole X-Ray Transients: The Effect of Irradiation on Time-Dependent Accretion Disk Structure

Some effects of irradiation on time-dependent accretion-disk models for black hole X-ray novae are presented. Two types of irradiation are considered: direct irradiation from the inner hot disk and indirect irradiation as might be reflected by a corona or chromosphere above the disk. The shadowing effect of the time-dependent evolution of the disk height and consequent blocking of the outer disk by the inner and middle portions of the disk from the direct irradiation is included. The direct irradiation of the disk by inner layers where the soft X-ray flux is generated is found to have only a small effect on the outer disk because of shadowing. Mild indirect irradiation that flattens, but otherwise does not affect the light curve substantially, still has interesting non-linear effects on the structure of the disk as heating and cooling waves propagate. The irradiated disks do not always make simple transitions between the hot and cold states, but can linger at intermediate temperatures or even return temporarily to the hot state, depending on the irradiation and the activity in adjacent portions of the disk.

Recorded magnetization distributions in thin film disk media

The magnetization distributions in recorded transitions in thin film disk media are shown to consist of simple longitudinal magnetization transitions along with flux closure patterns. Together they give rise to the familiar sawtooth patterns but also indicate why arctangent and other approximations used in record theory have proved so successful even when sawteeth are known to be present.

Lecture Notes on Atomic and Molecular Physics

Atomic models radiation and matter wave equations for simple quantum systems perturbation theory and radiative transitions quantum theory of one-electron atoms many-electron atoms molecular structure approximation methods for many-electron systems.

Crystal Structure and Physical Properties of (BEDT-TTF)2BF4Sol0.5 (Sol = 1,1,2-Trichloroethane, 1,2-Dibromoethane, 1,2-Dichroloethane)

Abstract The crystal structures and phase transition nature of (BEDT-TTF)2BF4Sol0.5 (Sol = TCE, DBE, and DCE) are investigated by means of X-ray diffraction, electrical conductivity, ESR, and magnetic susceptibility measurements. As the size of the neutral molecules become smaller (TCE > DBE > DCE), the metal-insulator transition temperature rises (60 K < 100 K < 110 K), showing that their transitions are governed mainly by the structural degrees of freedom. For the DBE and DCE salts, these transitions are simple metal-insulator transitions, whereas the transition of the TCE salt occurs only when the sample is cooled slowly, and the Fermi surfaces survive in the resulting low-temperature phase. For this salt, the anomaly of the interplanar resistivity appears at ca. 160 K for the slow cooling process, and the difference of the ESR line width between the slow and rapid cooling processes is also observed below this temperature. These phenomena are due to the disorder enhanced by the generation of the in-plane superlattice.

New Higgs transitions between dual N = 2 string models

We describe a new kind of transition between topologically distinct N = 2 type II Calabi-Yau vacua through points with enhanced non-abelian gauge symmetries together with fundamental charged matter hyper multiplets. We connect the appearance of matter to the local geometry of the singularity and discuss the relation between the instanton numbers of the Calabi-Yau manifolds taking part in the transition. In a dual heterotic string theory on K3 × T 2 the process corresponds to Higgsing a semi-classical gauge group or equivalently to a variation of the gauge bundle. In special cases the situation reduces to simple conifold transitions in the Coulomb phase of the non-abelian gauge symmetries.

Van der Waals theory of order - disorder transitions

In analogy with the well-known Van der Waals theory for disordered fluid phases we propose a simple analytic expression for the Helmholtz free energy of an ordered crystalline phase. It is based on a free-volume approximation to the entropic contribution due to the hard-core repulsions and a static lattice energy approximation to the contribution of the attractions. In this way we are able to describe in a simple way phase transitions between two disordered phases, between two ordered phases and between an ordered and a disordered phase in systems of any spatial dimensionality.

A scanning calorimetric study of unfolding equilibria in homodimeric chicken gizzard tropomyosins

Using both circular dichroism (CD) and differential scanning calorimetry (DSC), several laboratories find that the thermal unfolding transitions of alpha alpha and beta beta homodimeric coiled coils of rabbit tropomyosin are multistate and display an overall unfolding enthalpy of near 300 kcal (mol dimer)(-1). In contrast, an extant CD study of beta beta and gamma gamma species of chicken gizzard tropomyosin concludes that their unfolding transitions are simple two-state transitions, with much smaller overall enthalpies (98 kcal mol(-1) for beta beta and 162 kcal mol(-1) for gamma gamma). However, these smaller enthalpies have been questioned, because they imply a concentration dependence of the melting temperatures that is far larger than observed by CD. We report here DSC studies of the unfolding of both beta beta and gamma gamma chicken gizzard homodimers. The results show that these transitions are very similar to those in rabbit tropomyosins in that 1) the overall unfolding enthalpy is near 300 kcal mol(-1); 2) the overall delta C(rho) values are significantly positive; 3) the various transitions are multistate, requiring at least two and as many as four domains to fit the DSC data. DSC studies are also reported on these homodimeric species of chicken gizzard tropomyosin with a single interchain disulfide cross-link. These results are also generally similar to those for the correspondingly cross-linked rabbit tropomyosins.

Chemical thermodynamics for earth scientists

Systems and properties the properties of solid minerals aqueous solutions gases, liquid vapours and simple liquid mixtures redox reactions energy and related properties the principles of chemical thermodynamics the thermodynamic properties of simple systems and mixtures phase transitions and phase equilibria the properties of liquid and gaseous water the thermodynamic properties of aqueous electrolytes the thermodynamics of ion exchange reactions the thermodynamic properties of solids electrochemical systems and redox graphical applications of chemical thermodynamics the computer simulation of chemical equilibria.

The molecular biology of carcinogenesis.

Carcinogenesis may result from the action of any one or a combination of chemical, physical, biologic, and/or genetic insults to cells. The process of carcinogenesis may be divided into at least three stages: initiation, promotion, and progression. The first stage of carcinogenesis, initiation, results from an irreversible genetic alteration, most likely one or more simple mutations, transversions, transitions, and/or small deletions in DNA. The reversible stage of promotion does not involve changes in the structure of DNA but rather in the expression of the genome mediated through promoter-receptor interactions. The final irreversible stage of progression is characterized by karyotypic instability and malignant growth. Critical molecular targets during the stages of carcinogenesis include proto-oncogenes, cellular oncogenes, and tumor suppressor genes, alterations in both alleles of the latter being found only in the stage of progression. Although many of these critical target genes have been identified, the ultimate number and characteristics of molecular alterations that define neoplasia have not been elucidated.

Properties of mass‐loading shocks, 2. Magnetohydrodynamics

The one‐dimensional magnetohydrodynamics of shocked flows subjected to significant mass loading are considered. Recent observations at comets Giacobini‐Zinner and Halley suggest that simple nonreacting MHD is an inappropriate description for active cometary bow shocks. The thickness of the observed cometary shock implies that mass loading represents an important dynamical process within the shock itself, thereby requiring that the Rankine‐Hugoniot condition for the mass flux possess a source term. In a formal sense, this renders mass‐loading shocks qualitatively similar to combustion shocks, except that mass loading induces the shocked flow to shear. Nevertheless, a large class of stable shocks exist, identified by means of the Lax conditions appropriate to MHD. Thus mass‐loading shocks represent a new and interesting class of shocks, which, although found frequently in the solar system, both at the head of comets and, under suitable conditions, upsteam of weakly magnetized and nonmagnetized planets, has not been discussed in any detail. Owing to the shearing of the flow, mass‐loading shocks can behave like switch‐on shocks regardless of the magnitude of the plasma beta. Thus the behavior of the magnetic field in mass‐loading shocks is significantly different from that occurring in nonreacting classical MHD shocks. It is demonstrated that there exist two types of mass‐loading fronts for which no classical MHD analogue exists, these being the fast and slow compound mass‐loading shocks. These shocks are characterized by an initial deceleration of the fluid flow to either the fast or the slow magnetosonic speed followed by an isentropic expansion to the final decelerated downstream state. Thus these transitions take the flow from a supersonic to a supersonic, although decelerated, downstream state, unlike shocks which occur in classical MHD or gasdynamics. It is possible that such structures have been observed during the Giotto‐Halley encounter, and a brief discussion of the appropriate Halley parameters is therefore given, together with a short discussion of the determination of the shock normal from observations. A further interesting new form of mass‐loading shock is the “slow‐intermediate” shock, a stable shock which possesses many of the properties of intermediate MHD shocks yet which propagates like a slow mode MHD shock. An important property of mass‐loading shocks is the large parameter regime (compared with classical MHD) which does not admit simple or stable transitions from a given upstream to a downstream state. This suggests that it is often necessary to construct compound structures consisting of shocks, slip waves, rarefactions, and fast and slow compound waves in order to connect given upstream and downstream states. Thus the Riemann problem is significantly different from that of classical MHD.

Differential scanning calorimetric study of frozen sucrose and glycerol solutions

Differential scanning calorimetry (DSC) thermograms have been recorded for sucrose and glycerol solutions as a function of moisture content. Simple second-order transitions were observed at the glass transition for the higher concentration samples which did not form ice. More complicated thermograms were observed from the lower solution concentrations which formed ice. The origin of these transitions in the DSC thermograms from frozen solutions is discussed, together with the methods used to calculate the amount of ice in the freeze-concentrated solutions. The glass-transition temperatures (Tg) and the ice-melting temperatures (Tm) were used to construct the supplemented phase diagrams for both of these solutes. The maximum freeze concentration (C′g) for sucrose is determined to be 81.2% sucrose, and is shown by a novel experimental approach to occur at a temperature (T′g) of –40 °C.

Direct and valence neutron capture by 7Li.

We have measured the cross section for neutron radiative capture by {sup 7}Li at thermal neutron energy as 45.4{plus minus}3.0 mb. We have compared this value, and the available fast-neutron-capture cross-section data on {sup 7}Li, with direct- and valence-capture theory. The mechanism of direct capture involving simple neutron-orbital transitions within a potential well can adequately account for the magnitude of the thermal-neutron-capture cross sections and the shape of the fast-neutron-capture cross sections. We recommend that the capture cross sections from the theoretical calculation, instead of those from a recent measurement, be used for nuclear astrophysics calculations. If the fast-neutron-capture data are normalized at 25 keV to the theoretical value, the magnetic-dipole ({ital M}1) radiation width of the 255-keV {ital p}-wave resonance can be deduced. It is in agreement with the value calculated from a valence theory for {ital M}1 capture, thus lending support for this neutron-capture mechanism as an important one, at least for light nuclei. We also find some evidence from our analysis of the total cross-section data for a possible energy dependence of the potential required to describe the almost pure single-particle {ital s}-wave resonances underlying the {sup 7}Li cross section.

Decay studies of neutron deficient nuclei near the Z=64 subshell: 142Dy, 140,142Tb, 140,142Gd, 140,142Eu, 142Sm, and 142Pm.

The electron-capture and ${\mathrm{\ensuremath{\beta}}}^{+}$-decay branchings (EC/${\mathrm{\ensuremath{\beta}}}^{+}$) and delayed proton decays of A=142 isotopes with 61\ensuremath{\le}Z\ensuremath{\le}66 and A=140 isotopes with 63\ensuremath{\le}Z\ensuremath{\le}65 were investigated with the OASIS facility on-line at the Lawrence Berkeley Laboratory SuperHILAC. Electron capture and positron-decay emission probabilities have been determined for $^{142}\mathrm{Pm}$ and $^{142}\mathrm{Sm}$ decays, and extensive decay schemes have been constructed for $^{142}\mathrm{Eu}^{\mathit{g}}$(2.34\ifmmode\pm\else\textpm\fi{}0.12 s), $^{142}\mathrm{Gd}$(70.2\ifmmode\pm\else\textpm\fi{}0.6 s), $^{140}\mathrm{Eu}$(1.51\ifmmode\pm\else\textpm\fi{}0.02 s), and $^{140}\mathrm{Gd}$(15.8\ifmmode\pm\else\textpm\fi{}0.4 s). Decay schemes for the new isotopes $^{142}\mathrm{Tb}^{\mathit{g}}$(597\ifmmode\pm\else\textpm\fi{}17 ms), $^{142}\mathrm{Tb}^{\mathit{m}}$(303\ifmmode\pm\else\textpm\fi{}17 ms), $^{142}\mathrm{Dy}$(2.3\ifmmode\pm\else\textpm\fi{}0.3 s), $^{140}\mathrm{Eu}^{\mathit{m}}$(125\ifmmode\pm\else\textpm\fi{}2 ms), and $^{140}\mathrm{Tb}$(2.4\ifmmode\pm\else\textpm\fi{}0.2 s) are also presented. We have assigned \ensuremath{\gamma} rays to these isotopes on the basis of \ensuremath{\gamma}\ensuremath{\gamma} and x\ensuremath{\gamma} coincidences, and from half-life determinations. Electron-capture and ${\mathrm{\ensuremath{\beta}}}^{+}$-decay branchings were measured for each decay, and \ensuremath{\beta}-delayed proton branchings were determined for $^{142}\mathrm{Dy}$, $^{142}\mathrm{Tb}$, and $^{140}\mathrm{Tb}$ decays. ${\mathit{Q}}_{\mathrm{EC}}$ values, derived from the measured EC/${\mathrm{\ensuremath{\beta}}}^{+}$ branchings and the level schemes are compared with those from the Wapstra and Audi mass evaluation and the Liran and Zeldes mass calculation. The systematics of the N=77 isomer decays are discussed, and the intense ${0}^{+}$\ensuremath{\rightarrow}${1}^{+}$ and ${1}^{+}$\ensuremath{\rightarrow}${0}^{+}$ ground-state beta decays are compared with shell-model predictions for simple spin-flip transitions.

Voltage-dependent gating of Shaker A-type potassium channels in Drosophila muscle.

The voltage-dependent gating mechanism of A1-type potassium channels coded for by the Shaker locus of Drosophila was studied using macroscopic and single-channel recording techniques on embryonic myotubes in primary culture. From a kinetic analysis of data from single A1 channels, we have concluded that all of the molecular transitions after first opening, including the inactivation transition, are voltage independent and therefore not associated with charge movement through the membrane. In contrast, at least some of the activation transitions leading to first opening are considerably voltage dependent and account for all of the voltage dependence seen in the macroscopic currents. This mechanism is similar in many ways to that of vertebrate neuronal voltage-sensitive sodium channels, and together with the sequence similarities in the S4 region suggests a conserved mechanism for voltage-dependent gating among channels with different selectivities. By testing independent and coupled models for activation and inactivation we have determined that the final opening transition and inactivation are not likely to arise from the independent action of multiple subunits, each with simple gating transitions, but rather come about through their aggregate properties. A partially coupled model accurately reproduces all of the single-channel and macroscopic data. This model will provide a framework on which to organize and understand alterations in gating that occur in Shaker variants and mutants.

The genetic consequences of DNA precursor pool imbalance: sequence analysis of mutations induced by excess thymidine at the hamster aptr locus

To determine the effect of deoxyribonucleoside triphosphate pool imbalances on the accuracy of DNA replication within the cell, we examined the base pair alterations induced by excess intracellular dTTP at the adenine phosphoribosyl transferase ( aprt) locus of CHO cells. The mutations were predominantly simple (C → T) transitions ( 38 44 ) and transversions ( G → T, 5 44 ) explicable by the misincorporation of the DNA precursor supplied in excess (dTTP). Only one small deletion was observed. The context of the mutations is notable as the nucleotide incorporated after the error was usually the nucleotide in excess for the great majority of the transitions but not the transversions. As next nucleotide effects are characteristic of replication complexes having proofreading exocnuclease activity, our data indicate that this mechanism functions within the cell to control the occurrence of some types of replicational errors.