On the predictiveness of single-field inflationary models
NASA Astrophysics Data System (ADS)
Burgess, C. P.; Patil, Subodh P.; Trott, Michael
2014-06-01
We re-examine the predictiveness of single-field inflationary models and discuss how an unknown UV completion can complicate determining inflationary model parameters from observations, even from precision measurements. Besides the usual naturalness issues associated with having a shallow inflationary potential, we describe another issue for inflation, namely, unknown UV physics modifies the running of Standard Model (SM) parameters and thereby introduces uncertainty into the potential inflationary predictions. We illustrate this point using the minimal Higgs Inflationary scenario, which is arguably the most predictive single-field model on the market, because its predictions for A S , r and n s are made using only one new free parameter beyond those measured in particle physics experiments, and run up to the inflationary regime. We find that this issue can already have observable effects. At the same time, this UV-parameter dependence in the Renormalization Group allows Higgs Inflation to occur (in principle) for a slightly larger range of Higgs masses. We comment on the origin of the various UV scales that arise at large field values for the SM Higgs, clarifying cut off scale arguments by further developing the formalism of a non-linear realization of SU L (2) × U(1) in curved space. We discuss the interesting fact that, outside of Higgs Inflation, the effect of a non-minimal coupling to gravity, even in the SM, results in a non-linear EFT for the Higgs sector. Finally, we briefly comment on post BICEP2 attempts to modify the Higgs Inflation scenario.
Geometrical measures of non-Gaussianity generated from single field inflationary models
NASA Astrophysics Data System (ADS)
Junaid, M.; Pogosyan, D.
2015-08-01
We calculate the third-order moments of scalar curvature perturbations in configuration space for different inflationary models. We develop a robust numerical technique to compute the bispectrum for different models that have some features in the inflationary potential. From the bispectrum we evaluate moments analytically in the slow-roll regime while we devise a numerical mechanism to calculate these moments for non-slow-roll single-field inflationary models with a standard kinetic term that are minimally coupled to gravity. With the help of these third-order moments one can directly predict many non-Gaussian and geometrical measures of cosmic microwave background distributions in the configuration space. Thus, we devise a framework to calculate different third-order moments and geometrical measures, e.g. Minkowski functionals or the skeleton statistic, generated by different single-field models of inflation.
Reconstructing single-field inflationary actions from cosmic microwave background radiation data
Gauthier, Christopher S; Akhoury, Ratindranath E-mail: akhoury@umich.edu
2008-07-15
This paper describes a general program for deriving the action of single-field inflation models with non-standard kinetic energy terms using cosmic microwave background radiation power spectrum data. This method assumes that an action depends on a set of undetermined functions, each of which is a function of either the inflaton wavefunction or its time derivative. The scalar, tensor and non-Gaussianity of the curvature perturbation spectrum are used to derive a set of reconstruction equations whose solution set can specify up to three of the undetermined functions. The method is then used to find the undetermined functions in various types of action assuming power law type scalar and tensor spectra. In actions that contain only two unknown functions, the third reconstruction equation implies a consistency relation between the non-Gaussianity, sound speed and slow roll parameters. In particular we focus on reconstructing a generalized Dirac-Born-Infeld action with an unknown potential and warp factor. We find that for realistic scalar and tensor spectra, the reconstructed warp factor and potential are very similar to the theoretically derived result. Furthermore, physical consistency of the reconstructed warp factor and potential imposes strict constraints on the scalar and tensor spectral indices.
Non-Gaussianity and large-scale structure in a two-field inflationary model
Tseliakhovich, Dmitriy; Hirata, Christopher
2010-08-15
Single-field inflationary models predict nearly Gaussian initial conditions, and hence a detection of non-Gaussianity would be a signature of the more complex inflationary scenarios. In this paper we study the effect on the cosmic microwave background and on large-scale structure from primordial non-Gaussianity in a two-field inflationary model in which both the inflaton and curvaton contribute to the density perturbations. We show that in addition to the previously described enhancement of the galaxy bias on large scales, this setup results in large-scale stochasticity. We provide joint constraints on the local non-Gaussianity parameter f-tilde{sub NL} and the ratio {xi} of the amplitude of primordial perturbations due to the inflaton and curvaton using WMAP and Sloan Digital Sky Survey data.
Non-Gaussianity and Large Scale Structure in a two-field Inflationary model
Tseliakhovich, D.; Slosar, A.; Hirata, C.
2010-08-30
Single-field inflationary models predict nearly Gaussian initial conditions, and hence a detection of non-Gaussianity would be a signature of the more complex inflationary scenarios. In this paper we study the effect on the cosmic microwave background and on large-scale structure from primordial non-Gaussianity in a two-field inflationary model in which both the inflaton and curvaton contribute to the density perturbations. We show that in addition to the previously described enhancement of the galaxy bias on large scales, this setup results in large-scale stochasticity. We provide joint constraints on the local non-Gaussianity parameter f*{sub NL} and the ratio {zeta} of the amplitude of primordial perturbations due to the inflaton and curvaton using WMAP and Sloan Digital Sky Survey data.
The inflationary bispectrum with curved field-space
Elliston, Joseph; Tavakol, Reza; Seery, David E-mail: d.seery@sussex.ac.uk
2012-11-01
We compute the covariant three-point function near horizon-crossing for a system of slowly-rolling scalar fields during an inflationary epoch, allowing for an arbitrary field-space metric. We show explicitly how to compute its subsequent evolution using a covariantized version of the separate universe or 'δN' expansion, which must be augmented by terms measuring curvature of the field-space manifold, and give the nonlinear gauge transformation to the comoving curvature perturbation. Nonlinearities induced by the field-space curvature terms are a new and potentially significant source of non-Gaussianity. We show how inflationary models with non-minimal coupling to the spacetime Ricci scalar can be accommodated within this framework. This yields a simple toolkit allowing the bispectrum to be computed in models with non-negligible field-space curvature.
Primordial magnetic fields from the post-inflationary universe
Kobayashi, Takeshi
2014-05-01
We explore cosmological magnetogenesis in the post-inflationary universe, when the inflaton oscillates around its potential minimum and the universe is effectively dominated by cold matter. During this epoch prior to reheating, large-scale magnetic fields can be significantly produced by the cosmological background. By considering magnetogenesis both during and after inflation, we demonstrate that magnetic fields stronger than 10{sup −15} G can be generated on Mpc scales without having strong couplings in the theory, or producing too large electric fields that would dominate the universe.
Can a spectator scalar field enhance inflationary tensor mode?
NASA Astrophysics Data System (ADS)
Fujita, Tomohiro; Yokoyama, Jun'ichi; Yokoyama, Shuichiro
2015-04-01
We consider the possibility of enhancing the inflationary tensor mode by introducing a spectator scalar field with a small sound speed which induces gravitational waves as a second-order effect. We analytically obtain the power spectra of gravitational waves and curvature perturbation induced by the spectator scalar field. We find that the small sound speed amplifies the curvature perturbation much more than the tensor mode and the current observational constraint forces the induced gravitational waves to be negligible compared with those from the vacuum fluctuation during inflation.
Inflationary dynamics of kinetically-coupled gauge fields
Ferreira, Ricardo Z.; Ganc, Jonathan E-mail: ganc@cp3.dias.sdu.dk
2015-04-01
We investigate the inflationary dynamics of two kinetically-coupled massless U(1) gauge fields with time-varying kinetic-term coefficients. Ensuring that the system does not have strongly coupled regimes shrinks the parameter space. Also, we further restrict ourselves to systems that can be quantized using the standard creation, annihilation operator algebra. This second constraint limits us to scenarios where the system can be diagonalized into the sum of two decoupled, massless, vector fields with a varying kinetic-term coefficient. Such a system might be interesting for magnetogenesis because of how the strong coupling problem generalizes. We explore this idea by assuming that one of the gauge fields is the Standard Model U(1) field and that the other dark gauge field has no particles charged under its gauge group. We consider whether it would be possible to transfer a magnetic field from the dark sector, generated perhaps before the coupling was turned on, to the visible sector. We also investigate whether the simple existence of the mixing provides more opportunities to generate magnetic fields. We find that neither possibility works efficiently, consistent with the well-known difficulties in inflationary magnetogenesis.
Effective field theory of dark matter from membrane inflationary paradigm
NASA Astrophysics Data System (ADS)
Choudhury, Sayantan; Dasgupta, Arnab
2016-09-01
In this article, we have studied the cosmological and particle physics constraints on dark matter relic abundance from effective field theory of inflation from tensor-to-scalar ratio (r), in case of Randall-Sundrum single membrane (RSII) paradigm. Using semi-analytical approach we establish a direct connection between the dark matter relic abundance (ΩDMh2) and primordial gravity waves (r), which establishes a precise connection between inflation and generation of dark matter within the framework of effective field theory in RSII membrane. Further assuming the UV completeness of the effective field theory perfectly holds good in the prescribed framework, we have explicitly shown that the membrane tension, σ ≤ O(10-9) Mp4, bulk mass scale M5 ≤ O(0.04 - 0.05) Mp, and cosmological constant Λ˜5 ≥ - O(10-15) Mp5, in RSII membrane plays the most significant role to establish the connection between dark matter and inflation, using which we have studied the features of various mediator mass scale suppressed effective field theory "relevant operators" induced from the localized s, t and u channel interactions in RSII membrane. Taking a completely model independent approach, we have studied an exhaustive list of tree-level Feynman diagrams for dark matter annihilation within the prescribed setup and to check the consistency of the obtained results, further we apply the constraints as obtained from recently observed Planck 2015 data and Planck + BICEP2 + Keck Array joint data sets. Using all of these derived results we have shown that to satisfy the bound on, ΩDMh2 = 0.1199 ± 0.0027, as from Planck 2015 data, it is possible to put further stringent constraint on r within, 0.01 ≤ r ≤ 0.12, for thermally averaged annihilation cross-section of dark matter, < σv > ≈ O(10-28 - 10-27) cm3 / s, which are very useful to constrain various membrane inflationary models.
Effective field theory of weakly coupled inflationary models
Gwyn, Rhiannon; Palma, Gonzalo A.; Sakellariadou, Mairi; Sypsas, Spyros E-mail: gpalmaquilod@ing.uchile.cl E-mail: spyridon.sypsas@kcl.ac.uk
2013-04-01
The application of Effective Field Theory (EFT) methods to inflation has taken a central role in our current understanding of the very early universe. The EFT perspective has been particularly useful in analyzing the self-interactions determining the evolution of co-moving curvature perturbations (Goldstone boson modes) and their influence on low-energy observables. However, the standard EFT formalism, to lowest order in spacetime differential operators, does not provide the most general parametrization of a theory that remains weakly coupled throughout the entire low-energy regime. Here we study the EFT formulation by including spacetime differential operators implying a scale dependence of the Goldstone boson self-interactions and its dispersion relation. These operators are shown to arise naturally from the low-energy interaction of the Goldstone boson with heavy fields that have been integrated out. We find that the EFT then stays weakly coupled all the way up to the cutoff scale at which ultraviolet degrees of freedom become operative. This opens up a regime of new physics where the dispersion relation is dominated by a quadratic dependence on the momentum ω ∼ p{sup 2}. In addition, provided that modes crossed the Hubble scale within this energy range, the predictions of inflationary observables — including non-Gaussian signatures — are significantly affected by the new scales characterizing it.
The behavior of the Higgs field in the new inflationary universe
NASA Technical Reports Server (NTRS)
Guth, Alan H.; Pi, So-Young
1986-01-01
Answers are provided to questions about the standard model of the new inflationary universe (NIU) which have raised concerns about the model's validity. A baby toy problem which consists of the study of a single particle moving in one dimension under the influence of a potential with the form of an upside-down harmonic oscillator is studied, showing that the quantum mechanical wave function at large times is accurately described by classical physics. Then, an exactly soluble toy model for the behavior of the Higgs field in the NIU is described which should provide a reasonable approximation to the behavior of the Higgs field in the NIU. The dynamics of the toy model is described, and calculative results are reviewed which, the authors claim, provide strong evidence that the basic features of the standard picture are correct.
NASA Astrophysics Data System (ADS)
Ijjas, Anna; Steinhardt, Paul J.; Loeb, Abraham
2014-09-01
Classic inflation, the theory described in textbooks, is based on the idea that, beginning from typical initial conditions and assuming a simple inflaton potential with a minimum of fine-tuning, inflation can create exponentially large volumes of space that are generically homogeneous, isotropic and flat, with nearly scale-invariant spectra of density and gravitational wave fluctuations that are adiabatic, Gaussian and have generic predictable properties. In a recent paper, we showed that, in addition to having certain conceptual problems known for decades, classic inflation is for the first time also disfavored by data, specifically the most recent data from WMAP, ACT and Planck2013. Guth, Kaiser and Nomura and Linde have each recently published critiques of our paper, but, as made clear here, we all agree about one thing: the problematic state of classic inflation. Instead, they describe an alternative inflationary paradigm that revises the assumptions and goals of inflation, and perhaps of science generally. Assuming simple inflaton potentials with a single phase of inflation is “not at all realistic”, whereas highly complex potentials with many parameters, tunings, and fields are “very plausible according to recent ideas in high-energy physics” [GKN10-11]. The complex potentials inevitably lead to multiple stages of inflation and a multiverse in which anything can happen [GKN7]. The validity of the postmodern inflationary paradigm cannot be judged on whether it works for typical initial conditions since we do not know what those conditions are [GKN13]. Even if the initial conditions are determined some day they will not affect the validity of inflation; rather, the (yet unknown) measure will then be adjusted such that the observed properties of the universe are likely to emerge from those (yet unknown) initial conditions [GKN14]. The volume measure is rejected in favor of complex measures that are to be (re-)adjusted (a posteriori) to ensure that the
NASA Astrophysics Data System (ADS)
Blau, S. K.; Guth, A. H.
Contents: 1. Introduction. 2. Summary of the standard cosmological model. 3. Problems of the standard cosmological model. 4. The original inflationary universe. 5. Successes of the original inflationary model. 6. Problems of the original inflationary model. 7. The new inflationary universe. 8. Density perturbations in the new inflationary universe. 9. Quantum theory of the new inflationary universe phase transition. 10. Inflation in the minimal SU(5) grand unified theory. 11. False vacuum bubbles and child universes. 12. Conclusion.
Scale and shape dependent non-Gaussianity in the presence of inflationary vector fields
NASA Astrophysics Data System (ADS)
Beltrán Almeida, Juan P.; Rodríguez, Yeinzon; Valenzuela-Toledo, César A.
2014-11-01
We consider cosmological inflationary models in which vector fields play some role in the generation of the primordial curvature perturbation ζ . Such models are interesting because the involved vector fields naturally seed statistical anisotropy in the primordial fluctuations which could eventually leave a measurable imprint on the cosmic microwave background fluctuations. In this article, we estimate the scale and shape dependent effects on the non-Gaussianity (NG) parameters due to the scale dependent statistical anisotropy in the distribution of the fluctuations. For concreteness, we use a power spectrum (PS) of the fluctuations of the quadrupolar form: Pζ(k → )≡Pζ(k )[1 +gζ(k )(n ^ .k ^ )2] , where gζ(k ) is the only quantity which parametrizes the level of statistical anisotropy and n ^ is a unitary vector which points towards the preferred direction. Then, we evaluate the contribution of the running of gζ(k ) on the NG parameters by means of the δ N formalism. We focus specifically on the details for the fNL NG parameter, associated with the bispectrum Bζ, but the structure of higher order NG parameters is straightforward to generalize. Although the level of statistical anisotropy in the power spectrum is severely constrained by recent observations, the importance of statistical anisotropy signals in higher order correlators remains to be determined, this being the main task that we address here. The precise measurement of the shape and scale dependence (or running) of statistical parameters such as the NG parameters and the statistical anisotropy level could provide relevant elements for model building and for the determination of the presence (or nonpresence) of inflationary vector fields and their role in the inflationary mechanism.
Cosmological backreaction for a test field observer in a chaotic inflationary model
Marozzi, Giovanni; Vacca, Gian Paolo; Brandenberger, Robert H. E-mail: vacca@bo.infn.it
2013-02-01
In an inhomogeneous universe, an observer associated with a particular matter field does not necessarily measure the same cosmological evolution as an observer in a homogeneous and isotropic universe. Here we consider, in the context of a chaotic inflationary background model, a class of observers associated with a ''clock field'' for which we use a light test field. We compute the effective expansion rate and fluid equation of state in a gauge invariant way, taking into account the quantum fluctuations of the long wavelength modes, and working up to second order in perturbation theory and in the slow-roll approximation. We find that the effective expansion rate is smaller than what would be measured in the absence of fluctuations. Within the stochastic approach we study the bounds for which the approximations we make are consistent.
NASA Astrophysics Data System (ADS)
Gilmore, James Brian
2010-12-01
General Relativity is the standard framework by which all gravitational systems are analyzed in modern research, and it provides the theme for all the investigations in this thesis. Beyond this common platform, very different gravitating problems are examined here, and several analytical approaches are used to investigate these systems. Effective field theory, a methodological approach prominent in quantum field theory, plays an important role in the analysis of two of the problems in this thesis. In the first instance, an effective field theory for bound gravitational states is used to compute the interaction Lagrangian of a binary system at the second post-Newtonian order. A metric parametrization based on a temporal Kaluza-Klein decomposition is also used. In this effective field theory calculation, the post-Newtonian results for the equations of motion are elegantly reproduced. In the next problem considered, effective field theory is used to investigate the thermodynamics of compactified charged black holes. The relevant thermodynamic quantities are all computed to second order in the perturbation parameter and finite size effects are incorporated through higher order worldline operators. Complete agreement is found with an exact extremal black hole solution constructed with traditional General Relativistic methods. The results indicate that the addition of charge to a compactified black hole may delay the phase transition to a black string. Finally, the third problem examined here concerns the evolution of perturbations at the end of early universe inflation. General Relativity enters this problem through cosmological perturbation theory. It is shown that the coherent oscillations in the inflaton break down at the comoving post-inflationary horizon size, about 14 e-folds after the end of inflation. This is many e-folds before any known constraints, leading to possible implications for the matching problem of inflation, and the generation of stochastic
Effective field theory and non-Gaussianity from general inflationary states
NASA Astrophysics Data System (ADS)
Agarwal, Nishant; Holman, R.; Tolley, Andrew J.; Lin, Jennifer
2013-05-01
We study the effects of non-trivial initial quantum states for inflationary fluctuations within the context of the effective field theory for inflation constructed by Cheung et al. which allows us to discriminate between different initial states in a model-independent way. We develop a Green's function/path integral based formulation that incorporates initial state effects and use it to address questions such as how state-dependent is the consistency relation for the bispectrum, how many e-folds beyond the minimum required to solve the cosmological fine tunings of the big bang are we allowed so that some information from the initial state survives until late times, among others. We find that the so-called consistency condition relating the local limit of the bispectrum and the slow-roll parameter is a state-dependent statement that can be avoided for physically consistent initial states either with or without initial non-Gaussianities.
NASA Astrophysics Data System (ADS)
Kinney, William H.
1996-01-01
Inflationary cosmology is an elegant and straightforward solution to two of the largest puzzles presented by the standard "Big Bang" cosmology: why is the universe so flat, and why is the cosmic microwave background in such excellent thermal equilibrium? However, models of inflation in particle physics typically suffer from the shortcoming that the fundamental energy scale for inflation is driven to nearly the Planck scale by observational constraints. In addition, models of inflation often require the "fine-tuning" of parameters to very small values in order to remain consistent with observation. This thesis investigates inflationary potentials in a general context, and shows that the difficulty of fundamental scales being forced to the Planck scale is in fact characteristic only of scalar field potentials V(phi) dominated near their maxima by terms of order phi^2. It is found that potentials dominated by terms of order phim with m > 2 can satisfy observational constraints at an essentially arbitrary symmetry breaking scale. Potentials characterized by m = 2 and m = 4 are illustrated in the context of several "natural inflation" models, with particular emphasis on questions of fine-tuning and fundamental scale. Natural inflation theories are a class of models in which inflation is driven by a pseudo Nambu-Goldstone boson, which acquires a mass as a result of radiative corrections. Two models characterized by m = 2 are evaluated, in which the potential for inflation is generated by loop effects from a fermion sector which explicitly breaks a global U(1) symmetry. The m = 4 case is implemented in a model with a broken SO(3) symmetry, in which the potential is generated by gauge boson loops. Constraints from the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) measurement of the temperature anisotropy of the cosmic background radiation are used to limit the parameters of the models.
Sensitivity of inflationary predictions to pre-inflationary phases
Bahrami, Sina; Flanagan, Éanna É.
2016-01-15
How sensitive are the predictions of inflation to pre-inflationary conditions when the number of efolds of inflation is not too large? In an attempt to address this question, we consider a simple model where the inflationary era is preceded by an era dominated by a radiation fluid, which is coupled to the inflaton only gravitationally and which extends back to the Planck era. We show that there is a natural generalized Bunch-Davies vacuum state for perturbations to the coupled inflaton-gravity-fluid system at early times. With this choice of initial state the model predicts interesting deviations from the standard power spectrum of single field slow-roll inflation at large scales. However, the deviations are too small to be observable in near future CMB observations.
Inflationary implications of supersymmetry breaking
Borghese, Andrea; Roest, Diederik; Zavala, Ivonne
2013-07-23
We discuss a general bound on the possibility to realise inflation in any minimal supergravity with F-terms. The derivation crucially depends on the sGoldstini, the scalar field directions that are singled out by spontaneous supersymmetry breaking. The resulting bound involves both slow-roll parameters and the geometry of the Kähler manifold of the chiral scalars. We analyse the inflationary implications of this bound, and in particular discuss to what extent the requirements of single field and slow-roll can both be met in F-term inflation.
On the consistency relation of the three-point function in single-field inflation
Cheung, Clifford; Fitzpatrick, A Liam; Kaplan, Jared; Senatore, Leonardo E-mail: fitzpatr@fas.harvard.edu E-mail: senatore@physics.harvard.edu
2008-02-15
The consistency relation for the three-point function of the cosmic microwave background is a very powerful observational signature which is believed to be true for every inflationary model in which there is only one dynamical degree of freedom. Its importance relies on the fact that deviations from it might be detected in next generation experiments, allowing us to rule out all single-field inflationary models. After making more precise the already existing proof of the consistency relation, we use a recently developed effective field theory for inflationary perturbations to provide an alternative and very explicit proof valid at leading non-trivial order in slow roll parameters.
Topics in inflationary cosmologies
Mahajan, S.
1986-04-01
Several aspects of inflationary cosmologies are discussed. An introduction to the standard hot big bang cosmological model is reviewed, and some of the problems associated with it are presented. A short review of the proposals for solving the cosmological conundrums of the big bang model is presented. Old and the new inflationary scenarios are discussed and shown to be unacceptable. Some alternative scenarios especially those using supersymmetry are reviewed briefly. A study is given of inflationary models where the same set of fields that breaks supersymmetry is also responsible for inflation. In these models, the scale of supersymmetry breaking is related to the slope of the potential near the origin and can thus be kept low. It is found that a supersymmetry breaking scale of the order of the weak breaking scale. The cosmology obtained from the simplest of such models is discussed in detail and it is shown that there are no particular problems except a low reheating temperature and a violation of the thermal constraint. A possible solution to the thermal constraint problem is given by introducing a second field, and the role played by this second field in the scenario is discussed. An alternative mechanism for the generation of baryon number within the framework of supergravity inflationary models is studied using the gravitational couplings of the heavy fields with the hidden sector (the sector which breaks supersymmetry). This mechanism is applied to two specific models - one with and one without supersymmetry breaking. The baryon to entropy ratio is found to be dependent on parameters which are model dependent. Finally, the effect of direct coupling between the two sectors on results is related, 88 refs., 6 figs.
Inflationary predictions and moduli masses
NASA Astrophysics Data System (ADS)
Das, Kumar; Dutta, Koushik; Maharana, Anshuman
2015-12-01
A generic feature of inflationary models in supergravity/string constructions is vacuum misalignment for the moduli fields. The associated production of moduli particles leads to an epoch in the post-inflationary history in which the energy density is dominated by cold moduli particles. This modification of the post-inflationary history implies that the preferred range for the number of e-foldings between horizon exit of the modes relevant for CMB observations and the end of inflation (Nk) depends on moduli masses. This in turn implies that the precision CMB observables ns and r are sensitive to moduli masses. We analyse this sensitivity for some representative models of inflation and find the effect to be highly relevant for confronting inflationary models with observations.
Renormalization-group improved inflationary scenarios
NASA Astrophysics Data System (ADS)
Pozdeeva, E. O.; Vernov, S. Yu.
2017-03-01
The possibility to construct an inflationary scenario for renormalization-group improved potentials corresponding to the Higgs sector of quantum field models is investigated. Taking into account quantum corrections to the renormalization-group potential which sums all leading logs of perturbation theory is essential for a successful realization of the inflationary scenario, with very reasonable parameters values. The scalar electrodynamics inflationary scenario thus obtained are seen to be in good agreement with the most recent observational data.
Enhanced Inflationary Trispectrum from a Non-Vacuum Initial State
NASA Astrophysics Data System (ADS)
Agullo, I.; Navarro-Salas, J.; Parker, L.
2015-01-01
We work out the primordial inflationary trispectrum for curvature perturbations in models with standard kinetic terms, when the initial quantum state is not necessarily the Bunch-Davies vacuum state. The presence of initial perturbations enhances the trispectrum amplitude for squeezed configurations, in parallel to the bispectrum enhancement. For those squeezed configurations the trispectrum acquires the so-called local form, with a scale dependent amplitude that can get values larger than the prediction of the so-called Maldacena consistency relation. The enhancement factor could be as large as 106, and could reach the sensitivity of forthcoming observations, even for single-field inflationary models.
Reheating predictions in single field inflation
Cook, Jessica L.; Dimastrogiovanni, Emanuela; Easson, Damien A.; Krauss, Lawrence M. E-mail: emad@asu.edu E-mail: krauss@asu.edu
2015-04-01
Reheating is a transition era after the end of inflation, during which the inflaton is converted into the particles that populate the Universe at later times. No direct cosmological observables are normally traceable to this period of reheating. Indirect bounds can however be derived. One possibility is to consider cosmological evolution for observable CMB scales from the time of Hubble crossing to the present time. Depending upon the model, the duration and final temperature after reheating, as well as its equation of state, may be directly linked to inflationary observables. For single-field inflationary models, if we approximate reheating by a constant equation of state, one can derive relations between the reheating duration (or final temperature), its equation of state parameter, and the scalar power spectrum amplitude and spectral index. While this is a simple approximation, by restricting the equation of state to lie within a broad physically allowed range, one can in turn bracket an allowed range of n{sub s} and r for these models. The added constraints can help break degeneracies between inflation models that otherwise overlap in their predictions for n{sub s} and r.
K-inflationary power spectra at second order
Martin, Jérôme; Vennin, Vincent; Ringeval, Christophe E-mail: christophe.ringeval@uclouvain.be
2013-06-01
Within the class of inflationary models, k-inflation represents the most general single field framework that can be associated with an effective quadratic action for the curvature perturbations and a varying speed of sound. The incoming flow of high-precision cosmological data, such as those from the Planck satellite and small scale Cosmic Microwave Background (CMB) experiments, calls for greater accuracy in the inflationary predictions. In this work, we calculate for the first time the next-to-next-to-leading order scalar and tensor primordial power spectra in k-inflation needed in order to obtain robust constraints on the inflationary theory. The method used is the uniform approximation together with a second order expansion in the Hubble and sound flow functions. Our result is checked in various limits in which it reduces to already known situations.
The Quest for B Modes from Inflationary Gravitational Waves
NASA Astrophysics Data System (ADS)
Kamionkowski, Marc; Kovetz, Ely D.
2016-09-01
The search for the curl component (B mode) in the cosmic microwave background (CMB) polarization induced by inflationary gravitational waves is described. The canonical single-field slow-roll model of inflation is presented, and we explain the quantum production of primordial density perturbations and gravitational waves. It is shown how these gravitational waves then give rise to polarization in the CMB. We then describe the geometric decomposition of the CMB polarization pattern into a curl-free component (E mode) and curl component (B mode) and show explicitly that gravitational waves induce B modes. We discuss the B modes induced by gravitational lensing and by Galactic foregrounds and show how both are distinguished from those induced by inflationary gravitational waves. Issues involved in the experimental pursuit of these B modes are described, and we summarize some of the strategies being pursued. We close with a brief discussion of some other avenues toward detecting/characterizing the inflationary gravitational-wave background.
On soft limits of inflationary correlation functions
NASA Astrophysics Data System (ADS)
Assassi, Valentin; Baumann, Daniel; Green, Daniel
2012-11-01
Soft limits of inflationary correlation functions are both observationally relevant and theoretically robust. Various theorems can be proven about them that are insensitive to detailed model-building assumptions. In this paper, we re-derive several of these theorems in a universal way. Our method makes manifest why soft limits are such an interesting probe of the spectrum of additional light fields during inflation. We illustrate these abstract results with a detailed case study of the soft limits of quasi-single-field inflation.
Curvaton reheating in a logamediate inflationary model
Campo, Sergio del; Herrera, Ramon; Saavedra, Joel; Campuzano, Cuauhtemoc; Rojas, Efrain
2009-12-15
In a logamediate inflationary universe model we introduce the curvaton field in order to bring this inflationary model to an end. In this approach we determine the reheating temperature. We also outline some interesting constraints on the parameters that describe our models. Thus, we give the parameter space in this scenario.
Moduli backreaction on inflationary attractors
NASA Astrophysics Data System (ADS)
Roest, Diederik; Scalisi, Marco; Werkman, Pelle
2016-12-01
We investigate the interplay between moduli dynamics and inflation, focusing on the Kachru-Kallosh-Linde-Trivedi scenario and cosmological α -attractors. General couplings between these sectors can induce a significant backreaction and potentially destroy the inflationary regime; however, we demonstrate that this generically does not happen for α -attractors. Depending on the details of the superpotential, the volume modulus can either be stable during the entire inflationary trajectory or become tachyonic at some point and act as a waterfall field, resulting in a sudden end of inflation. In the latter case there is a universal supersymmetric minimum where the scalars end up, preventing the decompactification scenario. The gravitino mass is independent from the inflationary scale with no fine-tuning of the parameters. The observational predictions conform to the universal value of attractors, fully compatible with the Planck data, with possibly a capped number of e -folds due to the interplay with moduli.
Inflationary buildup of a vector field condensate and its cosmological consequences
Sanchez, Juan C. Bueno; Dimopoulos, Konstantinos E-mail: k.dimopoulos1@lancaster.ac.uk
2014-01-01
Light vector fields during inflation obtain a superhorizon perturbation spectrum when their conformal invariance is appropriately broken. Such perturbations, by means of some suitable mechanism (e.g. the vector curvaton mechanism), can contribute to the curvatue perturbation in the Universe and produce characteristic signals, such as statistical anisotropy, on the microwave sky, most recently surveyed by the Planck satellite mission. The magnitude of such characteristic features crucially depends on the magnitude of the vector condensate generated during inflation. However, in the vast majority of the literature the expectation value of this condensate has so-far been taken as a free parameter, lacking a definite prediction or a physically motivated estimate. In this paper, we study the stochastic evolution of the vector condensate and obtain an estimate for its magnitude. Our study is mainly focused in the supergravity inspired case when the kinetic function and mass of the vector boson is time-varying during inflation, but other cases are also explored such as a parity violating axial theory or a non-minimal coupling between the vector field and gravity. As an example, we apply our findings in the context of the vector curvaton mechanism and contrast our results with current observations.
Constraints on single-field inflation
Pirtskhalava, David; Santoni, Luca; Trincherini, Enrico
2016-06-28
Many alternatives to canonical slow-roll inflation have been proposed over the years, one of the main motivations being to have a model, capable of generating observable values of non-Gaussianity. In this work, we (re-)explore the physical implications of a great majority of such models within a single, effective field theory framework (including novel models with large non-Gaussianity discussed for the first time below). The constraints we apply — both theoretical and experimental — are found to be rather robust, determined to a great extent by just three parameters: the coefficients of the quadratic EFT operators (δN){sup 2} and δNδE, and the slow-roll parameter ε. This allows to significantly limit the majority of single-field alternatives to canonical slow-roll inflation. While the existing data still leaves some room for most of the considered models, the situation would change dramatically if the current upper limit on the tensor-to-scalar ratio decreased down to r<10{sup −2}. Apart from inflationary models driven by plateau-like potentials, the single-field model that would have a chance of surviving this bound is the recently proposed slow-roll inflation with weakly-broken galileon symmetry. In contrast to canonical slow-roll inflation, the latter model can support r<10{sup −2} even if driven by a convex potential, as well as generate observable values for the amplitude of non-Gaussianity.
Constraints on single-field inflation
NASA Astrophysics Data System (ADS)
Pirtskhalava, David; Santoni, Luca; Trincherini, Enrico
2016-06-01
Many alternatives to canonical slow-roll inflation have been proposed over the years, one of the main motivations being to have a model, capable of generating observable values of non-Gaussianity. In this work, we (re-)explore the physical implications of a great majority of such models within a single, effective field theory framework (including novel models with large non-Gaussianity discussed for the first time below). The constraints we apply—both theoretical and experimental—are found to be rather robust, determined to a great extent by just three parameters: the coefficients of the quadratic EFT operators (δN)2 and δNδE, and the slow-roll parameter ɛ. This allows to significantly limit the majority of single-field alternatives to canonical slow-roll inflation. While the existing data still leaves some room for most of the considered models, the situation would change dramatically if the current upper limit on the tensor-to-scalar ratio decreased down to r < 10-2. Apart from inflationary models driven by plateau-like potentials, the single-field model that would have a chance of surviving this bound is the recently proposed slow-roll inflation with weakly-broken galileon symmetry. In contrast to canonical slow-roll inflation, the latter model can support r < 10-2 even if driven by a convex potential, as well as generate observable values for the amplitude of non-Gaussianity.
Recovering the inflationary potential
Turner, Michael S.
1993-08-06
A procedure is developed for the recovery of the inflationary potential owl the interval that affects astrophysical scales. The amplitudes of the scalar and tensor metric perturbations and their power-spectrum indices, which can in principle be inferred from large-angle CBR anisotropy experiments and other cosmological data, determine the value of the inflationary potential and its first two derivatives. From these, the inflationary potential can be reconstructed in a Taylor series and the consistency of the inflationary hypothesis tested. A number of examples are presented, and the effect of observational uncertainties is discussed.
The best inflationary models after Planck
Martin, Jérôme; Vennin, Vincent; Ringeval, Christophe; Trotta, Roberto E-mail: christophe.ringeval@uclouvain.be E-mail: vennin@iap.fr
2014-03-01
We compute the Bayesian evidence and complexity of 193 slow-roll single-field models of inflation using the Planck 2013 Cosmic Microwave Background data, with the aim of establishing which models are favoured from a Bayesian perspective. Our calculations employ a new numerical pipeline interfacing an inflationary effective likelihood with the slow-roll library ASPIC and the nested sampling algorithm MultiNest. The models considered represent a complete and systematic scan of the entire landscape of inflationary scenarios proposed so far. Our analysis singles out the most probable models (from an Occam's razor point of view) that are compatible with Planck data, while ruling out with very strong evidence 34% of the models considered. We identify 26% of the models that are favoured by the Bayesian evidence, corresponding to 15 different potential shapes. If the Bayesian complexity is included in the analysis, only 9% of the models are preferred, corresponding to only 9 different potential shapes. These shapes are all of the plateau type.
Toward the inflationary paradigm: Lectures on inflationary cosmology
Turner, M.S.
1987-02-01
Guth's inflationary Universe scenario has revolutionized our thinking about the very early Universe. The inflationary scenario offers the possibility of explaining a handful of very fundamental cosmological facts - the homogeneity, isotropy, and flatness of the Universe, the origin of density inhomogeneities and the origin of the baryon asymmetry, while at the same time avoiding the monopole problem. It is based upon microphysical events which occurred early (t less than or equal to 10/sup -34/ sec) in the history of the Universe, but well after the planck epoc (t greater than or equal to 10/sup -43/ sec). While Guth's original model was fundamentally flawed, the variant based on the slow-rollover transition proposed by Linde, and Albrecht and Steinhardt (dubbed 'new inflation') appears viable. Although old inflation and the earliest models of new inflation were based upon first order phase transitions associated with spontaneous-symmetry breaking (SSB), it now appears that the inflationary transition is a much more generic phenomenon, being associated with the evolution of a weakly-coupled scalar field which for some reason or other was initially displaced from the minimum of its potential. Models now exist which are based on a wide variety of microphysics: SSB, SUSY/SUGR, compactification of extra dimensions, R/sup 2/ gravity, induced gravity, and some random, weakly-coupled scalar field. While there are several models which successfully implement the inflation, none is particularly compelling and all seem somewhat ad hoc. The common distasteful feature of all the successful models is the necessity of a small dimensionless number in the model - usually in the form of a dimensionless coupling of order 10/sup -15/. All inflationary scenarios rely upon the assumption that vacuum energy was once dynamically very significant, whereas today there exists every evidence that it is not. 133 refs., 17 figs.
Inflationary nonsingular quantum cosmological model
Falciano, Felipe T.; Pinto-Neto, Nelson; Santini, E. Sergio
2007-10-15
A stiff matter-dominated universe modeled by a free massless scalar field minimally coupled to gravity in a Friedmann-Lemaitre-Robertson-Walker (FLRW) geometry is quantized. Generalized complex-width Gaussian superpositions of the solutions of the Wheeler-DeWitt equation are constructed and the Bohm-de Broglie interpretation of quantum cosmology is applied. A planar dynamical system is found in which a diversity of quantum Bohmian trajectories are obtained and discussed. One class of solutions represents nonsingular inflationary models starting at infinity past from flat space-time with Planckian size spacelike hypersurfaces, which inflates without inflaton but due to a quantum cosmological effect, until it makes an analytical graceful exit from this inflationary epoch to a decelerated classical stiff matter expansion phase.
Simple inflationary quintessential model
NASA Astrophysics Data System (ADS)
de Haro, Jaume; Amorós, Jaume; Pan, Supriya
2016-04-01
In the framework of a flat Friedmann-Lemaître-Robertson-Walker geometry, we present a non-geodesically past complete model of our Universe without the big bang singularity at finite cosmic time, describing its evolution starting from its early inflationary era up to the present accelerating phase. We found that a hydrodynamical fluid with nonlinear equation of state could result in such scenario, which after the end of this inflationary stage, suffers a sudden phase transition and enters into the stiff matter dominated era, and the Universe becomes reheated due to a huge amount of particle production. Finally, it asymptotically enters into the de Sitter phase concluding the present accelerated expansion. Using the reconstruction technique, we also show that this background provides an extremely simple inflationary quintessential potential whose inflationary part is given by the well-known 1-dimensional Higgs potential, i.e., a double well inflationary potential, and the quintessential one by an exponential potential that leads to a deflationary regime after this inflation, and it can depict the current cosmic acceleration at late times. Moreover the Higgs potential leads to a power spectrum of the cosmological perturbations which fit well with the latest Planck estimations. Further, we compared our viable potential with some known inflationary quintessential potential, which shows that our quintessential model, that is, the Higgs potential combined with the exponential one, is an improved version of them because it contains an analytic solution that allows us to perform all analytic calculations. Finally, we have shown that the introduction of a nonzero cosmological constant simplifies the potential considerably with an analytic behavior of the background which again permits us to evaluate all the quantities analytically.
Critical constraint on inflationary magnetogenesis
Fujita, Tomohiro; Yokoyama, Shuichiro E-mail: shu@icrr.u-tokyo.ac.jp
2014-03-01
Recently, there are several reports that the cosmic magnetic fields on Mpc scale in void region is larger than ∼ 10{sup −15}G with an uncertainty of a few orders from the current blazar observations. On the other hand, in inflationary magnetogenesis models, additional primordial curvature perturbations are inevitably produced from iso-curvature perturbations due to generated electromagnetic fields. We explore such induced curvature perturbations in a model independent way and obtained a severe upper bound for the energy scale of inflation from the observed cosmic magnetic fields and the observed amplitude of the curvature perturbation , as ρ{sub inf}{sup 1/4} < 300MeV × (B{sub obs}/10{sup −15}G){sup −1} where B{sub obs} is the strength of the magnetic field at present. Therefore, without a dedicated low energy inflation model or an additional amplification of magnetic fields after inflation, inflationary magnetogenesis on Mpc scale is generally incompatible with CMB observations.
Transport equations for the inflationary trispectrum
Anderson, Gemma J.; Seery, David; Mulryne, David J. E-mail: D.Mulryne@qmul.ac.uk
2012-10-01
We use transport techniques to calculate the trispectrum produced in multiple-field inflationary models with canonical kinetic terms. Our method allows the time evolution of the local trispectrum parameters, τ{sub NL} and g{sub NL}, to be tracked throughout the inflationary phase. We illustrate our approach using examples. We give a simplified method to calculate the superhorizon part of the relation between field fluctuations on spatially flat hypersurfaces and the curvature perturbation on uniform density slices, ζ, and obtain its third-order part for the first time. We clarify how the 'backwards' formalism of Yokoyama et al. relates to our analysis and other recent work. We supply explicit formulae which enable each inflationary observable to be computed in any canonical model of interest, using a suitable first-order ODE solver.
Inflationary dynamics in f(𝒢) gravity
NASA Astrophysics Data System (ADS)
Sharif, M.; Ikram, Ayesha
This paper investigates inflationary dynamics for isotropic and homogeneous universe model in the background of f(𝒢) gravity. We construct Hubble-flow functions, slow-roll parameters, amplitude of scalar power spectrum, spectral index and tensor-scalar ratio for a particular form of equation of state which describes quasi-de Sitter expansion. The dynamics of inflationary epoch is analyzed for scalar field as well as fluid cosmology with viable power-law f(𝒢) model. We obtain different potential functions that correspond to chaotic inflation and Starobinsky type models. The graphical behavior of these parameters shows compatible results with observational Planck 2015 data in this gravity.
PLANCK and WMAP constraints on generalised Hubble flow inflationary trajectories
NASA Astrophysics Data System (ADS)
Contaldi, Carlo R.; Horner, Jonathan S.
2014-08-01
We use the Hamilton-Jacobi formalism to constrain the space of possible single field, inflationary Hubble flow trajectories when compared to the WMAP and PLANK satellites Cosmic Microwave Background (CMB) results. This method yields posteriors on the space of Hubble Slow Roll (HSR) parameters that uniquely determine the history of the Hubble parameter during the inflating epoch. The trajectories are used to numerically determine the observable primordial power spectrum and bispectra that can then be compared to observations. Our analysis is used to infer the most likely shape of the inflaton potential V(phi) and also yields a prediction for, Script B, the dimensionless amplitude of the non-Gaussian bispectrum.
PLANCK and WMAP constraints on generalised Hubble flow inflationary trajectories
Contaldi, Carlo R.; Horner, Jonathan S. E-mail: j.horner11@imperial.ac.uk
2014-08-01
We use the Hamilton-Jacobi formalism to constrain the space of possible single field, inflationary Hubble flow trajectories when compared to the WMAP and PLANK satellites Cosmic Microwave Background (CMB) results. This method yields posteriors on the space of Hubble Slow Roll (HSR) parameters that uniquely determine the history of the Hubble parameter during the inflating epoch. The trajectories are used to numerically determine the observable primordial power spectrum and bispectra that can then be compared to observations. Our analysis is used to infer the most likely shape of the inflaton potential V(φ) and also yields a prediction for, B, the dimensionless amplitude of the non-Gaussian bispectrum.
Observational Signatures and Non-Gaussianities ofGeneral Single Field Inflation
Chen, Xingang; Huang, Min-xin; Kachru, Shamit; Shiu, Gary
2006-05-05
We perform a general study of primordial scalar non-Gaussianities in single field inflationary models. We consider models where the inflaton Lagrangian is an arbitrary function of the scalar field and its first derivative, and the sound speed is arbitrary. We find that under reasonable assumptions, the non-Gaussianity is completely determined by 5 parameters. In special limits of the parameter space, one finds distinctive ''shapes'' of the non-Gaussianity. In models with a small sound speed, several of these shapes would become potentially observable in the near future. Different limits of our formulae recover various previously known results.
Quantum inflationary minisuperspace cosmological models
Kim Sangpyo.
1991-01-01
The Wheeler-DeWitt equations for the Friedmann-Robertson-Walker cosmology conformally and minimally coupled to scalar fields with power-lay potential are expanded in the eigenstates of the scalar field parts. The gravitational parts become a diagonal matrix-valued differential equation for a conformal scalar field, and a coupled matrix-valued differential equation for a minimally coupled scalar field. The Cauchy initial value problem is defined with respect to the intrinsic timelike coordinate, and the wavefunctions incorporating initial data are constructed using the product integral formulation. The packetlike wavefunctions around classical turning points are shown possible in the product integral formulation, and the returning wavepackets near the returning point of the classical Friedmann-Robertson-Walker cosmology are constructed. The wavefunctions to the Wheeler-DeWitt equation minimally coupled to the scaler field are constructed by two differential methods, the master equation and the enlarged matrix equation. The spectrum for the wavefunctions regular at the infinite size of universe is found, and these are interpreted as the Hawking-Page spectrum of wormholes connecting two asymptotically Euclidean regions. The quantum Friedmann-Robertson-Walker cosmology is extended to the minimal scalar field with the inflationary potential having a first order phase transition. The Wheeler-DeWitt equation is expanded in the eigenstates of the scalar field, and the gravitational part becomes a coupled matrix-valued differential equation.
Coupling the inflationary sector to matter
NASA Astrophysics Data System (ADS)
Kallosh, Renata; Linde, Andrei; Wrase, Timm
2016-04-01
We describe the coupling of matter fields to an inflationary sector of supergravity, the inflaton Φ and a stabilizer S, in models where the Kähler potential has a flat inflaton direction. Such models include, in particular, advanced versions of the hyperbolic α-attractor models with a flat inflaton direction Kähler potential, providing a good fit to the observational data. If the superpotential is at least quadratic in the matter fields U i , with restricted couplings to the inflaton sector, we prove that under certain conditions: i) The presence of the matter fields does not affect a successful inflationary evolution. ii) There are no tachyons in the matter sector during and after inflation. iii) The matter masses squared are higher than 3 H 2 during inflation. The simplest class of theories satisfying all required conditions is provided by models with a flat direction Kähler potential, and with the inflaton Φ and a stabilizer S belonging to a hidden sector, so that matter fields have no direct coupling to the inflationary sector in the Kähler potential and in the superpotential.
Closed inflationary universe in patch cosmology
Campo, Sergio del Herrera, Ramon Saavedra, Joel Labrana, Pedro
2009-09-15
In this paper, we study closed inflationary universe models using the Gauss-Bonnet Brane. We determine and characterize the existence of a universe with {omega}>1, with an appropriate period of inflation. We have found that this model is less restrictive in comparison with the standard approach where a scalar field is considered. We use recent astronomical observations to constrain the parameters appearing in the model.
Einstein Inflationary Probe (EIP)
NASA Technical Reports Server (NTRS)
Hinshaw, Gary
2004-01-01
I will discuss plans to develop a concept for the Einstein Inflation Probe: a mission to detect gravity waves from inflation via the unique signature they impart to the cosmic microwave background (CMB) polarization. A sensitive CMB polarization satellite may be the only way to probe physics at the grand-unified theory (GUT) scale, exceeding by 12 orders of magnitude the energies studied at the Large Hadron Collider. A detection of gravity waves would represent a remarkable confirmation of the inflationary paradigm and set the energy scale at which inflation occurred when the universe was a fraction of a second old. Even a strong upper limit to the gravity wave amplitude would be significant, ruling out many common models of inflation, and pointing to inflation occurring at much lower energy, if at all. Measuring gravity waves via the CMB polarization will be challenging. We will undertake a comprehensive study to identify the critical scientific requirements for the mission and their derived instrumental performance requirements. At the core of the study will be an assessment of what is scientifically and experimentally optimal within the scope and purpose of the Einstein Inflation Probe.
Higgs vacuum stability and inflationary dynamics after BICEP2 and PLANCK dust polarisation data
Bhattacharya, Kaushik; Chakrabortty, Joydeep; Das, Suratna; Mondal, Tanmoy E-mail: joydeep@iitk.ac.in E-mail: tanmoym@prl.res.in
2014-12-01
If the recent detection of B-mode polarization of the Cosmic Microwave Background by BICEP2 observations, withstand the test of time after the release of recent PLANCK dust polarisation data, then it would surprisingly put the inflationary scale near Grand Unification scale if one considers single-field inflationary models. On the other hand, Large Hadron Collider has observed the elusive Higgs particle whose presently observed mass can lead to electroweak vacuum instability at high scale (∼ O(10{sup 10}) GeV). In this article, we seek for a simple particle physics model which can simultaneously keep the vacuum of the theory stable and yield high-scale inflation successfully. To serve our purpose, we extend the Standard Model of particle physics with a U(1){sub B-L} gauged symmetry which spontaneously breaks down just above the inflationary scale. Such a scenario provides a constrained parameter space where both the issues of vacuum stability and high-scale inflation can be successfully accommodated. The threshold effect on the Higgs quartic coupling due to the presence of the heavy inflaton field plays an important role in keeping the electroweak vacuum stable. Furthermore, this scenario is also capable of reheating the universe at the end of inflation. Though the issues of Dark Matter and Dark Energy, which dominate the late-time evolution of our universe, cannot be addressed within this framework, this model successfully describes the early universe dynamics according to the Big Bang model.
WMAP normalization of inflationary cosmologies
Liddle, Andrew R.; Parkinson, David; Mukherjee, Pia; Leach, Samuel M.
2006-10-15
We use the three-year WMAP observations to determine the normalization of the matter power spectrum in inflationary cosmologies. In this context, the quantity of interest is not the normalization marginalized over all parameters, but rather the normalization as a function of the inflationary parameters n{sub S} and r with marginalization over the remaining cosmological parameters. We compute this normalization and provide an accurate fitting function. The statistical uncertainty in the normalization is 3%, roughly half that achieved by COBE. We use the k-l relation for the standard cosmological model to identify the pivot scale for the WMAP normalization. We also quote the inflationary energy scale corresponding to the WMAP normalization.
Designing and testing inflationary models with Bayesian networks
Price, Layne C.; Peiris, Hiranya V.; Frazer, Jonathan; Easther, Richard E-mail: h.peiris@ucl.ac.uk E-mail: r.easther@auckland.ac.nz
2016-02-01
Even simple inflationary scenarios have many free parameters. Beyond the variables appearing in the inflationary action, these include dynamical initial conditions, the number of fields, and couplings to other sectors. These quantities are often ignored but cosmological observables can depend on the unknown parameters. We use Bayesian networks to account for a large set of inflationary parameters, deriving generative models for the primordial spectra that are conditioned on a hierarchical set of prior probabilities describing the initial conditions, reheating physics, and other free parameters. We use N{sub f}-quadratic inflation as an illustrative example, finding that the number of e-folds N{sub *} between horizon exit for the pivot scale and the end of inflation is typically the most important parameter, even when the number of fields, their masses and initial conditions are unknown, along with possible conditional dependencies between these parameters.
Quantum gravity extension of the inflationary scenario.
Agullo, Ivan; Ashtekar, Abhay; Nelson, William
2012-12-21
Since the standard inflationary paradigm is based on quantum field theory on classical space-times, it excludes the Planck era. Using techniques from loop quantum gravity, the paradigm is extended to a self-consistent theory from the Planck scale to the onset of slow roll inflation, covering some 11 orders of magnitude in energy density and curvature. This preinflationary dynamics also opens a small window for novel effects, e.g., a source for non-Gaussianities, which could extend the reach of cosmological observations to the deep Planck regime of the early Universe.
Quantum Gravity Extension of the Inflationary Scenario
NASA Astrophysics Data System (ADS)
Agullo, Ivan; Ashtekar, Abhay; Nelson, William
2012-12-01
Since the standard inflationary paradigm is based on quantum field theory on classical space-times, it excludes the Planck era. Using techniques from loop quantum gravity, the paradigm is extended to a self-consistent theory from the Planck scale to the onset of slow roll inflation, covering some 11 orders of magnitude in energy density and curvature. This preinflationary dynamics also opens a small window for novel effects, e.g., a source for non-Gaussianities, which could extend the reach of cosmological observations to the deep Planck regime of the early Universe.
NASA Astrophysics Data System (ADS)
Amorós, Jaume; de Haro, Jaume
2016-12-01
The PLANCK collaboration has determined, or greatly constrained, values for the spectral parameters of the CMB radiation, namely the spectral index n s , its running α s , the running of the running β s , using a growing body of measurements of CMB anisotropies by the Planck satellite and other missions. These values do not follow the hierarchy of sizes predicted by single field, slow roll inflationary theory, and are thus difficult to fit for such inflation models. In this work we present first a study of 49 single field, slow roll inflationary potentials in which we assess the likelyhood of these models fitting the spectral parameters to their currently most accurate determination given by the PLANCK collaboration. We check numerically with a MATLAB program the spectral parameters that each model can yield for a very broad, comprehensive list of possible parameter and field values. The comparison of spectral parameter values supported by the models with their determinations by the PLANCK collaboration leads to the conclusion that the data provided by PLANCK2015 TT+lowP and PLANCK2015 TT,TE,EE+lowP taking into account the running of the running disfavours 40 of the 49 models with confidence level at least 92.8 %. Next, we discuss the reliability of the current computations of these spectral parameters. We identify a bias in the method of determination of the spectral parameters by least residue parameter fitting (using MCMC or any other scheme) currently used to reconstruct the power spectrum of scalar perturbations. This bias can explain the observed contradiction between theory and observations. Its removal is computationally costly, but necessary in order to compare the forecasts of single field, slow roll theories with observations.
Bootstrapping from inflationary magnetogenesis to CMB initial conditions
NASA Astrophysics Data System (ADS)
Giovannini, Massimo
2013-10-01
The temperature and polarization anisotropies of the cosmic microwave background are analyzed under the hypothesis that the same inflationary seed accounting for protogalactic magnetism also affects the Einstein-Boltzmann hierarchy whose initial conditions are assigned for typical correlation scales larger than the Hubble radius after matter-radiation equality but before decoupling. Since the primordial gauge spectrum depends on a combination of pivotal parameters of the concordance model, the angular power spectra of the temperature and of the polarization are computed, for the first time, in the presence of a putative large-scale magnetic field of inflationary origin and without supplementary hypotheses.
Particle production and reheating of the inflationary universe
Moss, Ian G.; Graham, Chris
2008-12-15
Thermal field theory is applied to particle production rates in inflationary models, leading to new results for catalyzed or two-stage decay, where massive fields act as decay channels for the production of light fields. A numerical investigation of the Boltzmann equation in an expanding universe shows that the particle distributions produced during small amplitude inflaton oscillations or even alongside slowly moving inflaton fields can thermalize.
Inflationary imprints on dark matter
NASA Astrophysics Data System (ADS)
Nurmi, Sami; Tenkanen, Tommi; Tuominen, Kimmo
2015-11-01
We show that dark matter abundance and the inflationary scale H could be intimately related. Standard Model extensions with Higgs mediated couplings to new physics typically contain extra scalars displaced from vacuum during inflation. If their coupling to Standard Model is weak, they will not thermalize and may easily constitute too much dark matter reminiscent to the moduli problem. As an example we consider Standard Model extended by a Z2 symmetric singlet s coupled to the Standard Model Higgs Φ via λ Φ†Φ s2. Dark matter relic density is generated non-thermally for λ lesssim 10-7. We show that the dark matter yield crucially depends on the inflationary scale. For H~ 1010 GeV we find that the singlet self-coupling and mass should lie in the regime λsgtrsim 10-9 and mslesssim 50 GeV to avoid dark matter overproduction.
Pre-inflationary clues from String Theory?
Kitazawa, N.; Sagnotti, A. E-mail: sagnotti@sns.it
2014-04-01
''Brane supersymmetry breaking'' occurs in String Theory when the only available combinations of D-branes and orientifolds are not mutually BPS and yet do not introduce tree-level tachyon instabilities. It is characterized by the emergence of a steep exponential potential, and thus by the absence of maximally symmetric vacua. The corresponding low-energy supergravity admits intriguing spatially-flat cosmological solutions where a scalar field is forced to climb up toward the steep potential after an initial singularity, and additional milder terms can inject an inflationary phase during the ensuing descent. We show that, in the resulting power spectra of scalar perturbations, an infrared suppression is typically followed by a pre-inflationary peak that reflects the end of the climbing phase and can lie well apart from the approximately scale invariant profile. A first look at WMAP9 raw data shows that, while the χ{sup 2} fits for the low-ℓ CMB angular power spectrum are clearly compatible with an almost scale invariant behavior, they display nonetheless an eye-catching preference for this type of setting within a perturbative string regime.
A scenario for inflationary magnetogenesis without strong coupling problem
Tasinato, Gianmassimo
2015-03-01
Cosmological magnetic fields pervade the entire universe, from small to large scales. Since they apparently extend into the intergalactic medium, it is tantalizing to believe that they have a primordial origin, possibly being produced during inflation. However, finding consistent scenarios for inflationary magnetogenesis is a challenging theoretical problem. The requirements to avoid an excessive production of electromagnetic energy, and to avoid entering a strong coupling regime characterized by large values for the electromagnetic coupling constant, typically allow one to generate only a tiny amplitude of magnetic field during inflation. We propose a scenario for building gauge-invariant models of inflationary magnetogenesis potentially free from these issues. The idea is to derivatively couple a dynamical scalar, not necessarily the inflaton, to fermionic and electromagnetic fields during the inflationary era. Such couplings give additional freedom to control the time-dependence of the electromagnetic coupling constant during inflation. This fact allows us to find conditions to avoid the strong coupling problems that affect many of the existing models of magnetogenesis. We do not need to rely on a particular inflationary set-up for developing our scenario, that might be applied to different realizations of inflation. On the other hand, specific requirements have to be imposed on the dynamics of the scalar derivatively coupled to fermions and electromagnetism, that we are able to satisfy in an explicit realization of our proposal.
A scenario for inflationary magnetogenesis without strong coupling problem
Tasinato, Gianmassimo
2015-03-23
Cosmological magnetic fields pervade the entire universe, from small to large scales. Since they apparently extend into the intergalactic medium, it is tantalizing to believe that they have a primordial origin, possibly being produced during inflation. However, finding consistent scenarios for inflationary magnetogenesis is a challenging theoretical problem. The requirements to avoid an excessive production of electromagnetic energy, and to avoid entering a strong coupling regime characterized by large values for the electromagnetic coupling constant, typically allow one to generate only a tiny amplitude of magnetic field during inflation. We propose a scenario for building gauge-invariant models of inflationary magnetogenesis potentially free from these issues. The idea is to derivatively couple a dynamical scalar, not necessarily the inflaton, to fermionic and electromagnetic fields during the inflationary era. Such couplings give additional freedom to control the time-dependence of the electromagnetic coupling constant during inflation. This fact allows us to find conditions to avoid the strong coupling problems that affect many of the existing models of magnetogenesis. We do not need to rely on a particular inflationary set-up for developing our scenario, that might be applied to different realizations of inflation. On the other hand, specific requirements have to be imposed on the dynamics of the scalar derivatively coupled to fermions and electromagnetism, that we are able to satisfy in an explicit realization of our proposal.
Exploring Inflationary Braneworld Models
Leeper, Emily
2006-11-03
We demonstrate that a two brane system with a bulk scalar field driving power-law inflation on the branes has an instability in the radion. We solve for the resulting trajectory of the brane, and find that the instability can lead to collision. Brane quantities such as the scale factor are shown to be regular at this collision. In addition we describe the system using a low energy expansion. The low energy expansion accurately reproduces the known exact solution, but also identifies an alternative solution for the bulk metric and brane trajectory. This article, and the talk it accompanies are based on work first published in Physical Review D73 043506 (2006000.
Popa, L. A.; Caramete, A.; Mandolesi, N.; Burigana, C.
2009-12-01
We make a more general determination of the inflationary observables in the standard four-dimensional (4D) and five-dimensional (5D) single-field inflationary scenarios by the exact reconstruction of the dynamics of the inflation potential during the observable inflation with a minimal number of assumptions: the computation does not assume the slow-roll approximation and is valid in all regimes if the field is monotonically rolling down its potential. We address higher order effects in the standard and braneworld single-field inflation scenarios by fitting the Hubbble expansion rate and subsequently the inflationary potential directly to WMAP5+SN+BAO and Planck-like simulated data sets. Making use of the Hamilton-Jacobi formalism developed for the 5D single-field inflation model, we compute the scale dependence of the amplitudes of the scalar and tensor perturbations by integrating the exact mode equation. The solutions in 4D and 5D inflation scenarios differ through the dynamics of the background scalar field and the number of e-folds assumed to be compatible with the observational window of inflation. We analyze the implications of the theoretical uncertainty in the determination of the reheating temperature after inflation on the observable predictions of inflation and evaluate its impact on the degeneracy of the standard inflation consistency relation. We find that the detection of tensor perturbations and the theoretical uncertainties in the inflationary observable represents a significant challenge for the future Planck cosmic microwave background measurements: distinguishing between the observational signatures of the standard and braneworld single-field inflation scenarios. This work has been done in the frame of Planck Core Team activities.
Near-field single molecule spectroscopy
Xie, X.S.; Dunn, R.C.
1995-02-01
The high spatial resolution and sensitivity of near-field fluorescence microscopy allows one to study spectroscopic and dynamical properties of individual molecules at room temperature. Time-resolved experiments which probe the dynamical behavior of single molecules are discussed. Ground rules for applying near-field spectroscopy and the effect of the aluminum coated near-field probe on spectroscopic measurements are presented.
Single-layer high field dipole magnets
Vadim V. Kashikhin and Alexander V. Zlobin
2001-07-30
Fermilab is developing high field dipole magnets for post-LHC hadron colliders. Several designs with a nominal field of 10-12 T, coil bore size of 40-50 mm based on both shell-type and block-type coil geometry are currently under consideration. This paper presents a new approach to magnet design, based on simple and robust single-layer coils optimized for the maximum field, good field quality and minimum number of turns.
Inflationary imprints on dark matter
Nurmi, Sami; Tenkanen, Tommi; Tuominen, Kimmo E-mail: tommi.tenkanen@helsinki.fi
2015-11-01
We show that dark matter abundance and the inflationary scale H could be intimately related. Standard Model extensions with Higgs mediated couplings to new physics typically contain extra scalars displaced from vacuum during inflation. If their coupling to Standard Model is weak, they will not thermalize and may easily constitute too much dark matter reminiscent to the moduli problem. As an example we consider Standard Model extended by a Z{sub 2} symmetric singlet s coupled to the Standard Model Higgs Φ via λ Φ{sup †}Φ s{sup 2}. Dark matter relic density is generated non-thermally for λ ∼< 10{sup −7}. We show that the dark matter yield crucially depends on the inflationary scale. For H∼ 10{sup 10} GeV we find that the singlet self-coupling and mass should lie in the regime λ{sub s}∼> 10{sup −9} and m{sub s}∼< 50 GeV to avoid dark matter overproduction.
Modified Chaplygin gas inspired inflationary model in braneworld scenario
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Rani, Shamaila; Mohsaneen, Sidra
2016-05-01
We investigate the modified Chaplygin gas inspired inflationary regime in the brane-world framework in the presence of standard and tachyon scalar fields. We consider the intermediate inflationary scenario and construct the slow-roll parameters, e-folding numbers, spectral index, scalar and tensor power spectra, tensor to scalar ratio for both scalar field models. We develop the ns - N and r - N planes and concluded that ns˜eq96^{+0.5}_{-0.5} and r≤0.0016 for N˜eq60^{+5}_{-5} in both cases of scalar field models as well as for all values of m. These constraints are consistent with observational data such as WMAP7, WMAP9 and Planck data.
Inflationary magnetogenesis without the strong coupling problem
Ferreira, Ricardo J.Z.; Jain, Rajeev Kumar; Sloth, Martin S. E-mail: jain@cp3.dias.sdu.dk
2013-10-01
The simplest gauge invariant models of inflationary magnetogenesis are known to suffer from the problems of either large backreaction or strong coupling, which make it difficult to self-consistently achieve cosmic magnetic fields from inflation with a field strength larger than 10{sup −32}G today on the Mpc scale. Such a strength is insufficient to act as seed for the galactic dynamo effect, which requires a magnetic field larger than 10{sup −20}G. In this paper we analyze simple extensions of the minimal model, which avoid both the strong coupling and back reaction problems, in order to generate sufficiently large magnetic fields on the Mpc scale today. First we study the possibility that the coupling function which breaks the conformal invariance of electromagnetism is non-monotonic with sharp features. Subsequently, we consider the effect of lowering the energy scale of inflation jointly with a scenario of prolonged reheating where the universe is dominated by a stiff fluid for a short period after inflation. In the latter case, a systematic study shows upper bounds for the magnetic field strength today on the Mpc scale of 10{sup −13}G for low scale inflation and 10{sup −25}G for high scale inflation, thus improving on the previous result by 7-19 orders of magnitude. These results are consistent with the strong coupling and backreaction constraints.
Probing Inflationary Cosmology: The Atacama B-Mode Search (ABS)
NASA Astrophysics Data System (ADS)
Essinger-Hileman, Thomas
Observations of the Cosmic Microwave Background (CMB) have provided compelling evidence for the Standard Model of Cosmology and have led to the most precise estimates of cosmological parameters to date. Through its sensitivity to gravitational waves, the CMB provides a glimpse into the state of the universe just 10-35 seconds after the Big Bang and of physics on grand-unification-theory (GUT) energy scales around 1016 GeV, some 13 orders of magnitude above the energies achievable by current terrestrial particle accelerators. A gravitational-wave background (GWB) in the early universe would leave a unique, odd-parity pattern of polarization in the CMB called B modes, the magnitude of which is characterized by the tensor-to-scalar ratio, r. A GWB is generically predicted to exist by inflationary theories, and the current generation of CMB polarization experiments will probe the interesting parameter space of r < 0.05 corresponding to single-field inflationary models at GUT scales. I detail the design and construction of the Atacama B-Mode Search (ABS), which aims to measure the polarization of the CMB at degree angular scales where the primordial B-mode signal is expected to peak. ABS is a 145-GHz polarimeter that will operate from a high-altitude site in the Atacama Desert of Chile, consisting of a 60-cm crossed-Dragone telescope with cryogenic primary and secondary reflectors; an array of 240 feedhorn-coupled, transition-edge-sensor, bolometric polarimeters; and, a continuously-rotating, warm, sapphire half-wave plate (HWP) that will provide modulation of the incoming polarization of light. In this thesis, I describe the optical, mechanical, and cryogenic design of the receiver, including the reflector design, focal-plane layout, HWP design, and free-space lowpass filters. I describe physical-optics modeling of the reflector and feedhorn to validate the optical design. A matrix model that allows the calculation of the Mueller matrix of the anti
Loop Quantum Cosmology: holonomy corrections to inflationary models
Artymowski, Michal; Lalak, Zygmunt; Szulc, Lukasz
2009-01-15
In the recent years the quantization methods of Loop Quantum Gravity have been successfully applied to the homogeneous and isotropic Friedmann-Robertson-Walker space-times. The resulting theory, called Loop Quantum Cosmology (LQC), resolves the Big Bang singularity by replacing it with the Big Bounce. We argue that the LQC holonomy corrections generate also certain corrections to field theoretical inflationary scenarios. These corrections imply that in the LQC the effective sonic horizon becomes infinite at some point after the bounce and that the scale of the inflationary potential implied by the COBE normalisation increases. The evolution of scalar fields immediately after the Bounce becomes modified in an interesting way. We point out that one can use COBE normalisation to establish an upper bound on the quantum of length of LQG. LQC corrections other than the holonomy one are assumed to be subdominant.
Fine-tuning in DBI inflationary mechanism
Chen, Xingang
2008-12-15
We show a model-independent fine-tuning issue in the DBI inflationary mechanism. DBI inflation requires a warp factor h small enough to sufficiently slow down the inflation. On the other hand, the Einstein equation in extra dimensions under the inflationary background deforms the warp space on the IR side. Generically these two locations coincide with each other, spoiling the DBI inflation. The origin and tuning of this 'h problem' is closely related, through the AdS/CFT duality, to those of the well-known '{eta} problem' in the slow-roll inflationary mechanism.
Single cell sequencing: a distinct new field.
Wang, Jian; Song, Yuanlin
2017-12-01
Single cell sequencing (SCS) has become a new approach to study biological heterogeneity. The advancement in technologies for single cell isolation, amplification of genome/transcriptome and next-generation sequencing enables SCS to reveal the inherent properties of a single cell from the large scale of the genome, transcriptome or epigenome at high resolution. Recently, SCS has been widely applied in various clinical and research fields, such as cancer biology and oncology, immunology, microbiology, neurobiology and prenatal diagnosis. In this review, we will discuss the development of SCS methods and focus on the latest clinical and research applications of SCS.
Inflationary potentials from the exact renormalisation group
NASA Astrophysics Data System (ADS)
Grozdanov, Sašo; Kraljić, David; Svanes, Eirik Eik
2016-08-01
We show that an inflationary slow-roll potential can be derived as an IR limit of the non-perturbative exact renormalisation group equation for a scalar field within the mean-field approximation. The result follows without having to specify a Lagrangian in the UV, which we take to be somewhere below the Planck scale to avoid discussing quantum gravity effects. We assume that the theory contains a scalar mode with suppressed coupling to other fields, and that higher derivative couplings are suppressed. In this framework the exact RG equation becomes a one-dimensional Schrödinger equation, which we solve. The effective IR potential is then dominated by the eigen-states of the RG Hamiltonian with the highest eigenvalues. We find that these potentials can generically give rise to slow-roll inflation, which is fully consistent with recent observations. As an example of how the proposed renormalisation group procedure works, we perform an explicit calculation in the ϕ4 theory in an appendix.
Initial conditions for anisotropic extended-type inflationary universes
del Campo, S. )
1992-05-15
Recently, extended-type inflationary universe models have been proposed as an appealing approach for solving most of the cosmological puzzles'' that, in contrast with previous models, do not require a fine-tuning'' for the microphysical parameters present in the effective potential. These scenarios rest on a Brans-Dicke-type theory, where a nonminimal coupling of the form {ital f}({ital cphi}){ital R} is assumed, and it may or may not include a potential for the Brans-Dicke field. In its classical description, different extended inflationary universe scenarios are described, where anisotropy is taken into account. By using the Hartle-Hawking and the Vilenkin boundary conditions for the wave function of the Universe, the probability distributions for the initial states of these extended models in the case of a small anisotropy are determined and discussed.
Surprising phenomena in a rich new class of inflationary models
Vaudrevange, Pascal M.; Podolsky, Dmitry I.; Starkman, Glenn D. E-mail: podolsky@phys.cwru.edu
2010-04-01
We report on a new class of fast-roll inflationary models. In a huge part of its parameter space, inflationary perturbations exhibit quite unusual phenomena such as scalar and tensor modes freezing out at widely different times, as well as scalar modes reentering the horizon during inflation. One specific point in parameter space is characterized by extraordinary behavior of the scalar perturbations. Freeze-out of scalar perturbations as well as particle production at horizon crossing are absent. Also the behavior of the perturbations around this quasi-de Sitter background is dual to a quantum field theory in flat space-time. Finally, the form of the primordial power spectrum is determined by the interaction between different modes of scalar perturbations.
Linde, Andrei
2015-05-05
I describe a simple class of α-attractors, generalizing the single-field GL model of inflation in supergravity. The new class of models is defined for 0<α≲1, providing a good match to the present cosmological data. I also present a generalized version of these models which can describe not only inflation but also dark energy and supersymmetry breaking.
Galilean creation of the inflationary universe
Kobayashi, Tsutomu; Yamaguchi, Masahide; Yokoyama, Jun'ichi E-mail: gucci@phys.titech.ac.jp
2015-07-01
It has been pointed out that the null energy condition can be violated stably in some non-canonical scalar-field theories. This allows us to consider the Galilean Genesis scenario in which the universe starts expanding from Minkowski spacetime and hence is free from the initial singularity. We use this scenario to study the early-time completion of inflation, pushing forward the recent idea of Pirtskhalava et al. We present a generic form of the Lagrangian governing the background and perturbation dynamics in the Genesis phase, the subsequent inflationary phase, and the graceful exit from inflation, as opposed to employing the effective field theory approach. Our Lagrangian belongs to a more general class of scalar-tensor theories than the Horndeski theory and Gleyzes-Langlois-Piazza-Vernizzi generalization, but still has the same number of the propagating degrees of freedom, and thus can avoid Ostrogradski instabilities. We investigate the generation and evolution of primordial perturbations in this scenario and show that one can indeed construct a stable model of inflation preceded by (generalized) Galilean Genesis.
Galilean creation of the inflationary universe
Kobayashi, Tsutomu; Yamaguchi, Masahide; Yokoyama, Jun’ichi
2015-07-13
It has been pointed out that the null energy condition can be violated stably in some non-canonical scalar-field theories. This allows us to consider the Galilean Genesis scenario in which the universe starts expanding from Minkowski spacetime and hence is free from the initial singularity. We use this scenario to study the early-time completion of inflation, pushing forward the recent idea of Pirtskhalava et al. We present a generic form of the Lagrangian governing the background and perturbation dynamics in the Genesis phase, the subsequent inflationary phase, and the graceful exit from inflation, as opposed to employing the effective field theory approach. Our Lagrangian belongs to a more general class of scalar-tensor theories than the Horndeski theory and Gleyzes-Langlois-Piazza-Vernizzi generalization, but still has the same number of the propagating degrees of freedom, and thus can avoid Ostrogradski instabilities. We investigate the generation and evolution of primordial perturbations in this scenario and show that one can indeed construct a stable model of inflation preceded by (generalized) Galilean Genesis.
Loops in inflationary correlation functions
NASA Astrophysics Data System (ADS)
Tanaka, Takahiro; Urakawa, Yuko
2013-12-01
We review the recent progress regarding the loop corrections to the correlation functions in the inflationary universe. A naive perturbation theory predicts that the loop corrections generated during inflation suffer from various infrared (IR) pathologies. Introducing an IR cutoff by hand is neither satisfactory nor enough to fix the problem of a secular growth, which may ruin the predictive power of inflation models if the inflation lasts sufficiently long. We discuss the origin of the IR divergences and explore the regularity conditions of the loop corrections for the adiabatic perturbation, the iso-curvature perturbation, and the tensor perturbation, in turn. These three kinds of perturbations have qualitative differences, but in discussing the IR regularity there is a feature common to all cases, which is the importance of the proper identification of observable quantities. Genuinely, observable quantities should respect the gauge invariance from the view point of a local observer. Interestingly, we find that the requirement of the IR regularity restricts the allowed quantum states.
Single-electron solitons in magnetic field
NASA Astrophysics Data System (ADS)
Rudenko, M.; Svintsov, D.; Filippov, S.; Vyurkov, V.
2016-12-01
Single-electron solitons (or movable polarons) can originate near a metal surface owing to interaction with image charges. Image charges (really, surface charges) appear in response to the `instant' electron density (probability density). Interaction with metal electrodes (as well as any polarization of the environment) much affects a charge qubits functioning. To verify this theory we propose a crucial experiment based on the motion of electrons in a magnetic field in presence of weak and strong polarization.
Inflationary perturbations in bimetric gravity
Cusin, Giulia; Durrer, Ruth; Guarato, Pietro; Motta, Mariele E-mail: ruth.durrer@unige.ch E-mail: mariele.motta@unige.ch
2015-09-01
In this paper we study the generation of primordial perturbations in a cosmological setting of bigravity during inflation. We consider a model of bigravity which can reproduce the ΛCDM background and large scale structure and a simple model of inflation with a single scalar field and a quadratic potential. Reheating is implemented with a toy-model in which the energy density of the inflaton is entirely dissipated into radiation. We present analytic and numerical results for the evolution of primordial perturbations in this cosmological setting. We find that the amplitude of tensor perturbations generated during inflation is sufficiently suppressed to avoid the effects of the tensor instability discovered in refs. [1,2] which develops during the cosmological evolution in the physical sector. We argue that from a pure analysis of the tensor perturbations this bigravity model is compatible with present observations. However, we derive rather stringent limits on inflation from the vector and scalar sectors.
Short distance physics of the inflationary de Sitter universe
Ali, Ahmed Farag; Faizal, Mir; Khalil, Mohammed M. E-mail: f2mir@uwaterloo.ca
2015-09-01
In this work, we investigate inflationary cosmology using scalar field theory deformed by the generalized uncertainty principle (GUP) containing a linear momentum term. Apart from being consistent with the existence of a minimum measurable length scale, this GUP is also consistent with doubly special relativity and hence with the existence of maximum measurable momentum. We use this deformed scalar field theory to analyze the tensor and scalar mode equations in a de Sitter background, and to calculate modifications to the tensor-to-scalar ratio. Finally, we compare our results for the tensor-to-scalar ratio with the Planck data to constrain the minimum length parameter in the GUP.
Inflationary quasiscale-invariant attractors
NASA Astrophysics Data System (ADS)
Rinaldi, Massimiliano; Vanzo, Luciano; Zerbini, Sergio; Venturi, Giovanni
2016-01-01
In a series of recent papers Kallosh, Linde, and collaborators provide a unified description of single-field inflation with several types of potentials ranging from power law to supergravity, in terms of just one parameter α . These so-called α attractors predict a spectral index ns and a tensor-to-scalar ratio r , which are fully compatible with the latest Planck data. The only common feature of all α attractors is a noncanonical kinetic term with a pole, and a potential analytic around the pole. In this paper, starting from the same Einstein frame with a noncanonical scalar kinetic energy, we explore the case of nonanalytic potentials. We find the functional form that corresponds to quasiscale-invariant gravitational models in the Jordan frame characterized by a universal relation between r and ns that fits the observational data but is clearly distinct from the one of the α attractors. It is known that the breaking of the exact classical scale invariance in the Jordan frame can be attributed to one-loop corrections. Therefore we conclude that there exists a class of nonanalytic potentials in the noncanonical Einstein frame that is physically equivalent to a class of models in the Jordan frame, with scale invariance softly broken by one-loop quantum corrections.
Observational signatures of anisotropic inflationary models
Ohashi, Junko; Tsujikawa, Shinji; Soda, Jiro E-mail: jiro@phys.sci.kobe-u.ac.jp
2013-12-01
We study observational signatures of two classes of anisotropic inflationary models in which an inflaton field couples to (i) a vector kinetic term F{sub μν}F{sup μν} and (ii) a two-form kinetic term H{sub μνλ}H{sup μνλ}. We compute the corrections from the anisotropic sources to the power spectrum of gravitational waves as well as the two-point cross correlation between scalar and tensor perturbations. The signs of the anisotropic parameter g{sub *} are different depending on the vector and the two-form models, but the statistical anisotropies generally lead to a suppressed tensor-to-scalar ratio r and a smaller scalar spectral index n{sub s} in both models. In the light of the recent Planck bounds of n{sub s} and r, we place observational constraints on several different inflaton potentials such as those in chaotic and natural inflation in the presence of anisotropic interactions. In the two-form model we also find that there is no cross correlation between scalar and tensor perturbations, while in the vector model the cross correlation does not vanish. The non-linear estimator f{sub NL} of scalar non-Gaussianities in the two-form model is generally smaller than that in the vector model for the same orders of |g{sub *}|, so that the former is easier to be compatible with observational bounds of non-Gaussianities than the latter.
Warm inflationary model in loop quantum cosmology
Herrera, Ramon
2010-06-15
A warm inflationary universe model in loop quantum cosmology is studied. In general we discuss the condition of inflation in this framework. By using a chaotic potential, V({phi}){proportional_to}{phi}{sup 2}, we develop a model where the dissipation coefficient {Gamma}={Gamma}{sub 0}=constant. We use recent astronomical observations for constraining the parameters appearing in our model.
Last stand of single small field inflation
NASA Astrophysics Data System (ADS)
Bramante, Joseph; Lehman, Landon; Martin, Adam; Downes, Sean
2014-07-01
By incorporating both the tensor-to-scalar ratio and the measured value of the spectral index, we set a bound on solo small field inflation of Δϕ/mPl≥1.00√r/0.1 . Unlike previous bounds which require monotonic ɛV, |ηV|<1, and 60 e-folds of inflation, the bound remains valid for nonmonotonic ɛV, |ηV|≳1, and for inflation which occurs only over the eight e-folds which have been observed on the cosmic microwave background. The negative value of the spectral index over the observed eight e-folds is what makes the bound strong; we illustrate this by surveying single field models and finding that for r ≳0.1 and eight e-folds of inflation, there is no simple potential which reproduces observed cosmic microwave background perturbations and remains sub-Planckian. Models that are sub-Planckian after eight e-folds must be patched together with a second epoch of inflation that fills out the remaining ˜50 e-folds. This second, post-cosmic microwave background epoch is characterized by extremely small ɛV and therefore an increasing scalar power spectrum. Using the fact that large power can overabundantly produce primordial black holes, we bound the maximum energy level of the second phase of inflation.
About the isocurvature tension between axion and high scale inflationary models
NASA Astrophysics Data System (ADS)
Estevez, M.; Santillán, O.
2016-07-01
The present work suggests that the isocurvature tension between axion and high energy inflationary scenarios may be avoided by considering a double field inflationary model involving the hidden Peccei-Quinn Higgs and the Standard Model one. Some terms in the lagrangian we propose explicitly violate the Peccei-Quinn symmetry but, at the present era, their effect is completely negligible. The resulting mechanism allows for a large value for the axion constant, of the order f_a˜ M_p, thus the axion isocurvature fluctuations are suppressed even when the scale of inflation H_{inf} is very high, of the order of H_{inf}˜ M_{gut}. This numerical value is typical in Higgs inflationary models. An analysis about topological defect formation in this scenario is also performed, and it is suggested that, under certain assumptions, their effect is not catastrophic from the cosmological point of view.
Simple inflationary quintessential model. II. Power law potentials
NASA Astrophysics Data System (ADS)
de Haro, Jaume; Amorós, Jaume; Pan, Supriya
2016-09-01
The present work is a sequel of our previous work [Phys. Rev. D 93, 084018 (2016)] which depicted a simple version of an inflationary quintessential model whose inflationary stage was described by a Higgs-type potential and the quintessential phase was responsible due to an exponential potential. Additionally, the model predicted a nonsingular universe in past which was geodesically past incomplete. Further, it was also found that the model is in agreement with the Planck 2013 data when running is allowed. But, this model provides a theoretical value of the running which is far smaller than the central value of the best fit in ns , r , αs≡d ns/d l n k parameter space where ns, r , αs respectively denote the spectral index, tensor-to-scalar ratio and the running of the spectral index associated with any inflationary model, and consequently to analyze the viability of the model one has to focus in the two-dimensional marginalized confidence level in the allowed domain of the plane (ns,r ) without taking into account the running. Unfortunately, such analysis shows that this model does not pass this test. However, in this sequel we propose a family of models runs by a single parameter α ∈[0 ,1 ] which proposes another "inflationary quintessential model" where the inflation and the quintessence regimes are respectively described by a power law potential and a cosmological constant. The model is also nonsingular although geodesically past incomplete as in the cited model. Moreover, the present one is found to be more simple compared to the previous model and it is in excellent agreement with the observational data. In fact, we note that, unlike the previous model, a large number of the models of this family with α ∈[0 ,1/2 ) match with both Planck 2013 and Planck 2015 data without allowing the running. Thus, the properties in the current family of models compared to its past companion justify its need for a better cosmological model with the successive
Cosmic inflation in a landscape of heavy-fields
Céspedes, Sebastián; Palma, Gonzalo A. E-mail: gpalmaquilod@ing.uchile.cl
2013-10-01
Heavy isocurvature fields may have a strong influence on the low energy dynamics of curvature perturbations during inflation, as long as the inflationary trajectory becomes non-geodesic in the multi-field target space (the landscape). If fields orthogonal to the inflationary trajectory are sufficiently heavy, one expects a reliable effective field theory describing the low energy dynamics of curvature perturbations, with self-interactions determined by the shape of the inflationary trajectory. Previous work analyzing the role of heavy-fields during inflation have mostly focused in the effects on curvature perturbations due to a single heavy-field. In this article we extend the results of these works by studying models of inflation in which curvature perturbations interact with two heavy-fields. We show that the second heavy-field (orthogonal to both tangent and normal directions of the inflationary trajectory) may significantly affect the evolution of curvature modes. We compute the effective field theory for the low energy curvature perturbations obtained by integrating out the two heavy-fields and show that the presence of the second heavy-field implies the existence of additional self-interactions not accounted for in the single heavy-field case. We conclude that future observations will be able to constrain the number of heavy fields interacting with curvature perturbations.
SU(1,1) Lie algebraic approach for the evolution of the quantum inflationary universe
NASA Astrophysics Data System (ADS)
Choi, Jeong Ryeol
2013-03-01
Quantum behavior of scalar fields and vacuum energy density in the inflationary universe are investigated using SU(1,1) Lie algebraic approach. Wave functions describing the evolution of scalar fields that have been thought to have driven cosmic inflation are identified in several possible quantum states at the early stage of the universe, such as the Fock state, the Glauber coherent state, and the SU(1,1) coherent states. In particular, we focus in this research on two important classes of the SU(1,1) coherent states, which are the so-called even and odd coherent states and the Perelomov coherent state. It is shown in the spatially flat universe driven by a single scalar field that the probability densities in all these states have converged to the origin (ϕ = 0, where ϕ is the scalar field) as time goes by. This outcome implies that the vacuum energy density characterized by the scalar field dissipates with time. The probability density in the matter-dominated era converged more rapidly than that in the radiation-dominated era. Hence, we can confirm that the progress of dissipation for the vacuum energy density became faster as the matter era began after the end of the early dominance of radiation. This consequence is, indeed, in agreement with the results of our previous researches in cosmology (for example, see [Chin. Phys. C 35 (2011) 233] and references there in).
Inflationary magnetogenesis and non-local actions: the conformal anomaly
El-Menoufi, Basem Kamal
2016-02-01
We discuss the possibility of successful magnetogenesis during inflation by employing the one-loop effective action of massless QED. The action is strictly non-local and results from the long distance fluctuations of massless charged particles present at the inflationary scale. Most importantly, it encodes the conformal anomaly of QED which is crucial to avoid the vacuum preservation in classical electromagnetism. In particular, we find a blue spectrum for the magnetic field with spectral index n{sub B} ≅ 2 − α{sub e} where α{sub e} depends on both the number of e-folds during inflation as well as the coefficient of the one-loop beta function. In particular, the sign of the beta function has important bearing on the final result. A low reheating temperature is required for the present day magnetic field to be consistent with the lower bound inferred on the field in the intergalactic medium.
Inflation after COBE: Lectures on inflationary cosmology
Turner, M.S. . Enrico Fermi Inst. Fermi National Accelerator Lab., Batavia, IL )
1992-01-01
In these lectures I review the standard hot big-bang cosmology, emphasizing its successes, its shortcomings, and its major challenge-a detailed understanding of the formation of structure in the Universe. I then discuss the motivations for and the fundamentals of inflationary cosmology, particularly emphasizing the quantum origin of metric (density and gravity-wave) perturbations. Inflation addresses the shortcomings of the standard cosmology and provides the initial data'' for structure formation. I conclude by addressing the implications of inflation for structure formation, evaluating the various cold dark matter models in the light of the recent detection of temperature anisotropies in the cosmic background radiation by COBE. In the near term, the study of structure formation offers a powerful probe of inflation, as well as specific inflationary models.
Inflation after COBE: Lectures on inflationary cosmology
Turner, M.S. |
1992-12-31
In these lectures I review the standard hot big-bang cosmology, emphasizing its successes, its shortcomings, and its major challenge-a detailed understanding of the formation of structure in the Universe. I then discuss the motivations for and the fundamentals of inflationary cosmology, particularly emphasizing the quantum origin of metric (density and gravity-wave) perturbations. Inflation addresses the shortcomings of the standard cosmology and provides the ``initial data`` for structure formation. I conclude by addressing the implications of inflation for structure formation, evaluating the various cold dark matter models in the light of the recent detection of temperature anisotropies in the cosmic background radiation by COBE. In the near term, the study of structure formation offers a powerful probe of inflation, as well as specific inflationary models.
On the initial condition of inflationary fluctuations
Jiang, Hongliang; Wang, Yi; Zhou, Siyi
2016-04-21
It is usually assumed that the inflationary fluctuations start from the Bunch-Davies (BD) vacuum and the iε prescription is used when interactions are calculated. We show that those assumptions can be verified explicitly by calculating the loop corrections to the inflationary two-point and three-point correlation functions. Those loop corrections can be resummed to exponential factors, which suppress non-BD coefficients and behave as the iε factor for the case of the BD initial condition. A new technique of loop chain diagram resummation is developed for this purpose. For the non-BD initial conditions which is setup at finite time and has not fully decayed, explicit correction to the two-point and three-point correlation functions are calculated. Especially, non-Gaussianity in the folded limit is regularized due to the interactions.
Warm-intermediate inflationary universe model
Campo, Sergio del; Herrera, Ramon E-mail: ramon.herrera@ucv.cl
2009-04-15
Warm inflationary universe models in the context of intermediate expansion, between power law and exponential, are studied. General conditions required for these models to be realizable are derived and discussed. This study is done in the weak and strong dissipative regimes. The inflaton potentials considered in this study are negative-power-law and powers of logarithms, respectively. The parameters of our models are constrained from the WMAP three and five year data.
Anisotropic higher derivative gravity and inflationary universe
Kao, W. F.
2006-08-15
Stability analysis of the Kantowski-Sachs type universe in pure higher derivative gravity theory is studied in detail. The nonredundant generalized Friedmann equation of the system is derived by introducing a reduced one-dimensional generalized Kantowski-Sachs type action. Existence and stability of inflationary solution in the presence of higher derivative terms are also studied in detail. Implications to the choice of physical theories are discussed in detail in this paper.
Production of scalar and tensor perturbations in inflationary models
Turner, M.S. NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 )
1993-10-15
Scalar (density) and tensor (gravity-wave) perturbations provide the basis for the fundamental observable consequences of inflation, including CBR anisotropy and the formation of structure in the Universe. These perturbations are nearly scale invariant (Harrison-Zel'dovich spectrum), though a slight deviation from scale invariance ( tilt'') can have significant consequences for both CBR anisotropy and structure formation. In particular, a slightly tilted spectrum of scalar perturbations may improve the agreement of the cold dark matter scenario with the observational data. The amplitude and spectrum of the scalar and tensor perturbations depend upon the shape of the inflationary potential in the small interval where the scalar field responsible for inflation was between about 46 and 54 [ital e]-folds before the end of inflation. By expanding the inflationary potential in a Taylor series over this interval we show that the amplitudes of the perturbations and the power-law slopes of their spectra can be expressed in terms of the value of the potential 50 [ital e]-folds before the end of inflation, [ital V][sub 50], its steepness [ital x][sub 50][equivalent to][ital m][sub Pl][ital V50][sup [prime
Multiple fields in stochastic inflation
Assadullahi, Hooshyar; Firouzjahi, Hassan; Noorbala, Mahdiyar; Vennin, Vincent; Wands, David
2016-06-24
Stochastic effects in multi-field inflationary scenarios are investigated. A hierarchy of diffusion equations is derived, the solutions of which yield moments of the numbers of inflationary e-folds. Solving the resulting partial differential equations in multi-dimensional field space is more challenging than the single-field case. A few tractable examples are discussed, which show that the number of fields is, in general, a critical parameter. When more than two fields are present for instance, the probability to explore arbitrarily large-field regions of the potential, otherwise inaccessible to single-field dynamics, becomes non-zero. In some configurations, this gives rise to an infinite mean number of e-folds, regardless of the initial conditions. Another difference with respect to single-field scenarios is that multi-field stochastic effects can be large even at sub-Planckian energy. This opens interesting new possibilities for probing quantum effects in inflationary dynamics, since the moments of the numbers of e-folds can be used to calculate the distribution of primordial density perturbations in the stochastic-δN formalism.
Inflationary paradigm after Planck 2013
NASA Astrophysics Data System (ADS)
Guth, Alan H.; Kaiser, David I.; Nomura, Yasunori
2014-06-01
Models of cosmic inflation posit an early phase of accelerated expansion of the universe, driven by the dynamics of one or more scalar fields in curved spacetime. Though detailed assumptions about fields and couplings vary across models, inflation makes specific, quantitative predictions for several observable quantities, such as the flatness parameter (Ωk = 1 - Ω) and the spectral tilt of primordial curvature perturbations (ns - 1 = dln PR / dln k), among others-predictions that match the latest observations from the Planck satellite to very good precision. In the light of data from Planck as well as recent theoretical developments in the study of eternal inflation and the multiverse, we address recent criticisms of inflation by Ijjas, Steinhardt, and Loeb. We argue that their conclusions rest on several problematic assumptions, and we conclude that cosmic inflation is on a stronger footing than ever before.
The origin of density fluctuations in the 'new inflationary universe'
NASA Technical Reports Server (NTRS)
Turner, M. S.
1983-01-01
Cosmological mysteries which are not explained by the Big Bang hypothesis but may be approached by a revamped inflationary universe model are discussed. Attention is focused on the isotropy, the large-scale homogeneity, small-scale inhomogeneity, the oldness/flatness of the universe, and the baryon asymmetry. The universe is assumed to start in the lowest energy state, be initially dominated by false vacuum energy, enter a de Sitter phase, and then cross a barrier which is followed by the formation of fluctuation regions that lead to structure. The scalar fields (perturbation regions) experience quantum fluctuations which produce spontaneous symmetry breaking on a large scale. The scalar field value would need to be much greater than the expansion rate during the de Sitter epoch. A supersymmetric (flat) potential which satisfies the requirement, yields fluctuations of the right magnitude, and allows inflation to occur is described.
Spectrum of perturbations in anisotropic inflationary universe with vector hair
Himmetoglu, Burak
2010-03-01
We study both the background evolution and cosmological perturbations of anisotropic inflationary models supported by coupled scalar and vector fields. The models we study preserve the U(1) gauge symmetry associated with the vector field, and therefore do not possess instabilities associated with longitudinal modes (which instead plague some recently proposed models of vector inflation and curvaton). We first intoduce a model in which the background anisotropy slowly decreases during inflation; we then confirm the stability of the background solution by studying the quadratic action for all the perturbations of the model. We then compute the spectrum of the h{sub ×} gravitational wave polarization. The spectrum we find breaks statistical isotropy at the largest scales and reduces to the standard nearly scale invariant form at small scales. We finally discuss the possible relevance of our results to the large scale CMB anomalies.
Inflationary dynamics reconstruction via inverse-scattering theory
NASA Astrophysics Data System (ADS)
Mastache, Jorge; Zago, Fernando; Kosowsky, Arthur
2017-03-01
The evolution of inflationary fluctuations can be recast as an inverse scattering problem. In this context, we employ the Gel'fand-Levitan method from inverse-scattering theory to reconstruct the evolution of both the inflaton field freeze-out horizon and the Hubble parameter during inflation. We demonstrate this reconstruction procedure numerically for a scenario of slow-roll inflation, as well as for a scenario which temporarily departs from slow-roll. The field freeze-out horizon is reconstructed from the accessible primordial scalar power spectrum alone, while the reconstruction of the Hubble parameter requires additional information from the tensor power spectrum. We briefly discuss the application of this technique to more realistic cases incorporating estimates of the primordial power spectra over limited ranges of scales and with specified uncertainties.
Hamilton-Jacobi formalism to warm inflationary scenario
NASA Astrophysics Data System (ADS)
Sayar, K.; Mohammadi, A.; Akhtari, L.; Saaidi, Kh.
2017-01-01
The Hamilton-Jacobi formalism as a powerful method is being utilized to reconsider the warm inflationary scenario, where the scalar field as the main component driving inflation interacts with other fields. Separating the context into strong and weak dissipative regimes, the goal is followed for two popular functions of Γ . Applying slow-rolling approximation, the required perturbation parameters are extracted and, by comparing to the latest Planck data, the free parameters are restricted. The possibility of producing an acceptable inflation is studied where the result shows that for all cases the model could successfully suggest the amplitude of scalar perturbation, scalar spectral index, its running, and the tensor-to-scalar ratio.
Behavior of a Single Langmuir Probe in a Magnetic Field.
ERIC Educational Resources Information Center
Pytlinski, J. T.; And Others
1978-01-01
Describes an experiment to demonstrate the influence of a magnetic field on the behavior of a single Langmuir probe. The experiment introduces the student to magnetically supported plasma and particle behavior in a magnetic field. (GA)
Evolution of perturbations in an inflationary universe
NASA Technical Reports Server (NTRS)
Frieman, J. A.; Will, C. M.
1982-01-01
The evolution of inhomogeneous density perturbations in a model of the very early universe that is dominated for a time by a constant energy density of a false quantum-mechanical vacuum is analyzed. During this period, the universe inflates exponentially and supercools exponentially, until a phase transition back to the true vacuum reheats the matter and radiation. Focus is on the physically measurable, coordinate-independent modes of inhomogeneous perturbations of this model and it is found that all modes either are constant or are exponentially damped during the inflationary era.
Quantum cosmology and the evolution of inflationary spectra
NASA Astrophysics Data System (ADS)
Kamenshchik, Alexander Y.; Tronconi, Alessandro; Venturi, Giovanni
2016-12-01
We illustrate how it is possible to calculate the quantum gravitational effects on the spectra of primordial scalar/tensor perturbations starting from the canonical, Wheeler-De Witt, approach to quantum cosmology. The composite matter-gravity system is analyzed through a Born-Oppenheimer approach in which gravitation is associated with the heavy degrees of freedom and matter (here represented by a scalar field) with the light ones. Once the independent degrees of freedom are identified, the system is canonically quantized and a semiclassical approximation is used for the scale factor. The differential equation governing the dynamics of the primordial spectra with their quantum-gravitational corrections is then obtained and is applied to diverse inflationary evolutions. Finally, the analytical results are compared to observations through a Monte Carlo Markov chain technique and an estimate of the free parameters of our approach is finally presented and the results obtained are compared with previous ones.
Inflationary scenarios in Starobinsky model with higher order corrections
Artymowski, Michał; Lalak, Zygmunt; Lewicki, Marek
2015-06-17
We consider the Starobinsky inflation with a set of higher order corrections parametrised by two real coefficients λ{sub 1} ,λ{sub 2}. In the Einstein frame we have found a potential with the Starobinsky plateau, steep slope and possibly with an additional minimum, local maximum or a saddle point. We have identified three types of inflationary behaviour that may be generated in this model: i) inflation on the plateau, ii) at the local maximum (topological inflation), iii) at the saddle point. We have found limits on parameters λ{sub i} and initial conditions at the Planck scale which enable successful inflation and disable eternal inflation at the plateau. We have checked that the local minimum away from the GR vacuum is stable and that the field cannot leave it neither via quantum tunnelling nor via thermal corrections.
Inflationary scenarios in Starobinsky model with higher order corrections
Artymowski, Michał; Lalak, Zygmunt; Lewicki, Marek E-mail: Zygmunt.Lalak@fuw.edu.pl
2015-06-01
We consider the Starobinsky inflation with a set of higher order corrections parametrised by two real coefficients λ{sub 1} , λ{sub 2}. In the Einstein frame we have found a potential with the Starobinsky plateau, steep slope and possibly with an additional minimum, local maximum or a saddle point. We have identified three types of inflationary behaviour that may be generated in this model: i) inflation on the plateau, ii) at the local maximum (topological inflation), iii) at the saddle point. We have found limits on parameters λ{sub i} and initial conditions at the Planck scale which enable successful inflation and disable eternal inflation at the plateau. We have checked that the local minimum away from the GR vacuum is stable and that the field cannot leave it neither via quantum tunnelling nor via thermal corrections.
Post-inflationary gravitino production revisited
Ellis, John; Garcia, Marcos A.G.; Olive, Keith A.; Nanopoulos, Dimitri V.; Peloso, Marco E-mail: garciagarcia@physics.umn.edu E-mail: olive@physics.umn.edu
2016-03-01
We revisit gravitino production following inflation. As a first step, we review the standard calculation of gravitino production in the thermal plasma formed at the end of post-inflationary reheating when the inflaton has completely decayed. Next we consider gravitino production prior to the completion of reheating, assuming that the inflaton decay products thermalize instantaneously while they are still dilute. We then argue that instantaneous thermalization is in general a good approximation, and also show that the contribution of non-thermal gravitino production via the collisions of inflaton decay products prior to thermalization is relatively small. Our final estimate of the gravitino-to-entropy ratio is approximated well by a standard calculation of gravitino production in the post-inflationary thermal plasma assuming total instantaneous decay and thermalization at a time t ≅ 1.2/Γ{sub φ}. Finally, in light of our calculations, we consider potential implications of upper limits on the gravitino abundance for models of inflation, with particular attention to scenarios for inflaton decays in supersymmetric Starobinsky-like models.
Constraints on tachyon inflationary models with an AdS/CFT correspondence
NASA Astrophysics Data System (ADS)
Bouabdallaoui, Zahra; Errahmani, Ahmed; Bouhmadi-López, Mariam; Ouali, Taoufik
2016-12-01
To study the effect of the anti-de Sitter/conformal field theory correspondence (AdS/CFT) on the primordial inflationary era, we consider a universe filled with a tachyon field in a slow-roll regime. In this context, the background and perturbative parameters characterizing the inflationary era are related to the standard one by correction terms. We show a clear agreement between the theoretical prediction and the observational data for the above-mentioned model. The main results of our work are illustrated for an exponential potential. We show that, for a suitable conformal anomaly coefficient, AdS/CFT correspondence might leave its imprints on the spectrum of the gravitational waves amplitude with a tensor to scalar ratio, r , of the perturbations compatible with Planck data.
Inflationary α -attractors from F (R ) gravity
NASA Astrophysics Data System (ADS)
Odintsov, S. D.; Oikonomou, V. K.
2016-12-01
In this paper, we study some classes of α -attractor models in the Jordan frame, and we find the corresponding F (R ) gravity theory. We study analytically the problem at leading order, and we investigate whether the attractor picture persists in the F (R ) gravity equivalent theory. As we show, if the slow-roll conditions are assumed in the Jordan frame, the spectral index of primordial curvature perturbations and the scalar-to-tensor ratio are identical to the corresponding observational indices of the R2 model, a result which indicates that the attractor property is also found in the corresponding F (R ) gravity theories of the α -attractor models. Moreover, implicit and approximate forms of the F (R ) gravity inflationary attractors are found.
Single-phase-field model of stepped surfaces.
Castro, M; Hernández-Machado, A; Cuerno, R
2009-02-01
We formulate a phase-field description of step dynamics on vicinal surfaces that makes use of a single dynamical field, at variance with previous analogous works in which two coupled fields are employed, namely, a phase-field proper plus the physical adatom concentration. Within an asymptotic sharp interface limit, our formulation is shown to retrieve the standard Burton-Cabrera-Frank model in the general case of asymmetric attachment coefficients (Ehrlich-Schwoebel effect). We confirm our analytical results by means of numerical simulations of our phase-field model. Our present formulation seems particularly well adapted to generalization when additional physical fields are required.
Non-Gaussianities and the stimulated creation of quanta in the inflationary universe
Agullo, Ivan; Parker, Leonard
2011-03-15
Cosmological inflation generates a spectrum of density perturbations that can seed the cosmic structures we observe today. These perturbations are usually computed as the result of the gravitationally induced spontaneous creation of perturbations from an initial vacuum state. In this paper, we compute the perturbations arising from gravitationally induced stimulated creation when perturbations are already present in the initial state. The effect of these initial perturbations is not diluted by inflation and survives to its end, and beyond. We consider a generic statistical density operator {rho} describing an initial mixed state that includes probabilities for nonzero numbers of scalar perturbations to be present at early times during inflation. We analyze the primordial bispectrum for general configurations of the three different momentum vectors in its arguments. We find that the initial presence of quanta can significantly enhance non-Gaussianities in the so-called squeezed limit. Our results show that an observation of non-Gaussianities in the squeezed limit can occur for single-field inflation when the state in the very early inflationary Universe is not the vacuum, but instead contains early-time perturbations. Valuable information about the initial state can then be obtained from observations of those non-Gaussianities.
Electric-field sensing using single diamond spins
NASA Astrophysics Data System (ADS)
Dolde, F.; Fedder, H.; Doherty, M. W.; Nöbauer, T.; Rempp, F.; Balasubramanian, G.; Wolf, T.; Reinhard, F.; Hollenberg, L. C. L.; Jelezko, F.; Wrachtrup, J.
2011-06-01
The ability to sensitively detect individual charges under ambient conditions would benefit a wide range of applications across disciplines. However, most current techniques are limited to low-temperature methods such as single-electron transistors, single-electron electrostatic force microscopy and scanning tunnelling microscopy. Here we introduce a quantum-metrology technique demonstrating precision three-dimensional electric-field measurement using a single nitrogen-vacancy defect centre spin in diamond. An a.c. electric-field sensitivity reaching 202+/-6Vcm-1Hz-1/2 has been achieved. This corresponds to the electric field produced by a single elementary charge located at a distance of ~150nm from our spin sensor with averaging for one second. The analysis of the electronic structure of the defect centre reveals how an applied magnetic field influences the electric-field-sensing properties. We also demonstrate that diamond-defect-centre spins can be switched between electric- and magnetic-field sensing modes and identify suitable parameter ranges for both detector schemes. By combining magnetic- and electric-field sensitivity, nanoscale detection and ambient operation, our study should open up new frontiers in imaging and sensing applications ranging from materials science to bioimaging.
Simple brane-world inflationary models — An update
NASA Astrophysics Data System (ADS)
Okada, Nobuchika; Okada, Satomi
2016-05-01
In the light of the Planck 2015 results, we update simple inflationary models based on the quadratic, quartic, Higgs and Coleman-Weinberg potentials in the context of the Randall-Sundrum brane-world cosmology. Brane-world cosmological effect alters the inflationary predictions of the spectral index (ns) and the tensor-to-scalar ratio (r) from those obtained in the standard cosmology. In particular, the tensor-to-scalar ratio is enhanced in the presence of the 5th dimension. In order to maintain the consistency with the Planck 2015 results for the inflationary predictions in the standard cosmology, we find a lower bound on the five-dimensional Planck mass (M5). On the other hand, the inflationary predictions laying outside of the Planck allowed region can be pushed into the allowed region by the brane-world cosmological effect with a suitable choice of M5.
Consistency of the tachyon warm inflationary universe models
Zhang, Xiao-Min; Zhu, Jian-Yang E-mail: zhujy@bnu.edu.cn
2014-02-01
This study concerns the consistency of the tachyon warm inflationary models. A linear stability analysis is performed to find the slow-roll conditions, characterized by the potential slow-roll (PSR) parameters, for the existence of a tachyon warm inflationary attractor in the system. The PSR parameters in the tachyon warm inflationary models are redefined. Two cases, an exponential potential and an inverse power-law potential, are studied, when the dissipative coefficient Γ = Γ{sub 0} and Γ = Γ(φ), respectively. A crucial condition is obtained for a tachyon warm inflationary model characterized by the Hubble slow-roll (HSR) parameter ε{sub H}, and the condition is extendable to some other inflationary models as well. A proper number of e-folds is obtained in both cases of the tachyon warm inflation, in contrast to existing works. It is also found that a constant dissipative coefficient (Γ = Γ{sub 0}) is usually not a suitable assumption for a warm inflationary model.
Optical singularities in plasmonic fields near single subwavelength holes
NASA Astrophysics Data System (ADS)
de Hoogh, A.; Rotenberg, N.; Kuipers, L.
2014-11-01
We identify phase and polarization singularities in near-field measurements and theoretical modeling of the electric near-field distributions that result from the scattering of surface plasmon polaritons from single subwavelength holes in optically thick gold films. We discuss properties of the singularities, such as their topological charge or the field amplitudes at their locations. We show that it is possible to tune the in-plane field amplitude at the positions of the polarization singularities by three orders of magnitude simply by varying the hole or incident plasmon beam size.
Rojas, Clara
2009-05-15
The phase-integral approximation devised by Froeman and Froeman is used for computing cosmological perturbations in the quadratic chaotic inflationary model. The phase-integral formulas for the scalar and tensor power spectra are explicitly obtained up to fifth order of the phase-integral approximation. We show that the phase integral gives a very good approximation for the shape of the power spectra associated with scalar and tensor perturbations as well as the spectral indices. We find that the accuracy of the phase-integral approximation compares favorably with the numerical results and those obtained using the slow-roll and uniform-approximation methods.
Taming the Runaway Problem of Inflationary Landscapes
Hall, Lawrence J.; Watari, Taizan; Yanagida, T. T.
2006-03-15
A wide variety of vacua, and their cosmological realization, may provide an explanation for the apparently anthropic choices of some parameters of particle physics and cosmology. If the probability on various parameters is weighted by volume, a flat potential for slow-roll inflation is also naturally understood, since the flatter the potential the larger the volume of the sub-universe. However, such inflationary landscapes have a serious problem, predicting an environment that makes it exponentially hard for observers to exist and giving an exponentially small probability for a moderate universe like ours. A general solution to this problem is proposed, and is illustrated in the context of inflaton decay and leptogenesis, leading to an upper bound on the reheating temperature in our sub-universe. In a particular scenario of chaotic inflation and non-thermal leptogenesis, predictions can be made for the size of CP violating phases, the rate of neutrinoless double beta decay and, in the case of theories with gauge-mediated weak scale supersymmetry, for the fundamental scale of supersymmetry breaking.
Modeling Single Particle Transport in Stochastic Magnetic Fields
NASA Astrophysics Data System (ADS)
Hudson, Ben; Fiksel, Gennady; Prager, Stewart
2001-10-01
Single particle transport in a stochastic magnetic field is simulated via code ION and RIO. Developed in collaboration with a group in Novosibirsk, Russia, they simulate both single ion and multiple ion trajectories in a stochastic magnetic field. A sharp decrease in the relative diffusion of ions to magnetic field lines is seen in two gyro-radii regimes. One is explainable from the unbroken flux surfaces near the edge of the plasma. The other is thought to be due to a "gyro-averaging" effect that occurs when the gyro-radius exceeds the radial correlation length of the field lines. The simulations indicate a decrease in expected transport, most strongly as a function of gyro-radius, which will be tested experimentally with the MST neutral beam injector.
Strongly enhanced field-dependent single-molecule electroluminescence
NASA Astrophysics Data System (ADS)
Lee, Tae-Hee; Gonzalez, Jose I.; Dickson, Robert M.
2002-08-01
Individual, strongly electroluminescent Agn molecules (n = 28 atoms) have been electrically written within otherwise nonemissive silver oxide films. Exhibiting characteristic single-molecule behavior, these individual room-temperature molecules exhibit extreme electroluminescence enhancements (>104 vs. bulk and dc excitation on a per molecule basis) when excited with specific ac frequencies. Occurring through field extraction of electrons with subsequent reinjection and radiative recombination, single-molecule electroluminescence is enhanced by a general mechanism that avoids slow bulk material response. Thus, while we detail strong electroluminescence from single, highly fluorescent Agn molecules, this mechanism also yields strong ac-excited electroluminescence from similarly prepared, but otherwise nonemissive, individual Cu nanoclusters.
Single-ion microwave near-field quantum sensor
NASA Astrophysics Data System (ADS)
Wahnschaffe, M.; Hahn, H.; Zarantonello, G.; Dubielzig, T.; Grondkowski, S.; Bautista-Salvador, A.; Kohnen, M.; Ospelkaus, C.
2017-01-01
We develop an intuitive model of 2D microwave near-fields in the unusual regime of centimeter waves localized to tens of microns. Close to an intensity minimum, a simple effective description emerges with five parameters that characterize the strength and spatial orientation of the zero and first order terms of the near-field, as well as the field polarization. Such a field configuration is realized in a microfabricated planar structure with an integrated microwave conductor operating near 1 GHz. We use a single 9 Be+ ion as a high-resolution quantum sensor to measure the field distribution through energy shifts in its hyperfine structure. We find agreement with simulations at the sub-micron and few-degree level. Our findings give a clear and general picture of the basic properties of oscillatory 2D near-fields with applications in quantum information processing, neutral atom trapping and manipulation, chip-scale atomic clocks, and integrated microwave circuits.
Chambers, Alex; Rajantie, Arttu
2008-02-01
If light scalar fields are present at the end of inflation, their nonequilibrium dynamics such as parametric resonance or a phase transition can produce non-Gaussian density perturbations. We show how these perturbations can be calculated using nonlinear lattice field theory simulations and the separate universe approximation. In the massless preheating model, we find that some parameter values are excluded while others lead to acceptable but observable levels of non-Gaussianity. This shows that preheating can be an important factor in assessing the viability of inflationary models.
TOPICAL REVIEW: Organic field-effect transistors using single crystals
NASA Astrophysics Data System (ADS)
Hasegawa, Tatsuo; Takeya, Jun
2009-04-01
Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20-40 cm2 Vs-1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.
Organic field-effect transistors using single crystals.
Hasegawa, Tatsuo; Takeya, Jun
2009-04-01
Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20-40 cm(2) Vs(-1), achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.
Organic field-effect transistors using single crystals
Hasegawa, Tatsuo; Takeya, Jun
2009-01-01
Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for ‘plastic electronics’. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20–40 cm2 Vs−1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps. PMID:27877287
On the divergences of inflationary superhorizon perturbations
Enqvist, K; Nurmi, S; Podolsky, D; Rigopoulos, G I E-mail: sami.nurmi@helsinki.fi E-mail: gerasimos.rigopoulos@helsinki.fi
2008-04-15
We discuss the infrared divergences that appear to plague cosmological perturbation theory. We show that, within the stochastic framework, they are regulated by eternal inflation so that the theory predicts finite fluctuations. Using the {Delta}N formalism to one loop, we demonstrate that the infrared modes can be absorbed into additive constants and the coefficients of the diagrammatic expansion for the connected parts of two-and three-point functions of the curvature perturbation. As a result, the use of any infrared cutoff below the scale of eternal inflation is permitted, provided that the background fields are appropriately redefined. The natural choice for the infrared cutoff would, of course, be the present horizon; other choices manifest themselves in the running of the correlators. We also demonstrate that it is possible to define observables that are renormalization-group-invariant. As an example, we derive a non-perturbative, infrared finite and renormalization point-independent relation between the two-point correlators of the curvature perturbation for the case of the free single field.
Radiation burst from a single {gamma}-photon field
Shakhmuratov, R. N.; Vagizov, F.; Kocharovskaya, O.
2011-10-15
The radiation burst from a single {gamma}-photon field interacting with a dense resonant absorber is studied theoretically and experimentally. This effect was discovered for the fist time by P. Helisto et al.[Phys. Rev. Lett. 66, 2037 (1991)] and it was named the ''gamma echo''. The echo is generated by a 180 Degree-Sign phase shift of the incident radiation field, attained by an abrupt change of the position of the absorber with respect to the radiation source during the coherence time of the photon wave packet. Three distinguishing cases of the gamma echo are considered; i.e., the photon is in exact resonance with the absorber, close to resonance (on the slope of the absorption line), and far from resonance (on the far wings of the resonance line). In resonance the amplitude of the radiation burst is two times larger than the amplitude of the input radiation field just before its phase shift. This burst was explained by Helisto et al. as a result of constructive interference of the coherently scattered field with the phase-shifted input field, both having almost the same amplitude. We found that out of resonance the scattered radiation field acquires an additional component with almost the same amplitude as the amplitude of the incident radiation field. The phase of the additional field depends on the optical thickness of the absorber and resonant detuning. Far from resonance this field interferes destructively with the phase-shifted incident radiation field and radiation quenching is observed. Close to resonance the three fields interfere constructively and the amplitude of the radiation burst is three times larger than the amplitude of the input radiation field.
Large slow roll parameters in single field inflation
Cook, Jessica L.; Krauss, Lawrence M. E-mail: krauss@asu.edu
2016-03-01
We initially consider two simple situations where inflationary slow roll parameters are large and modes no longer freeze out shortly after exiting the horizon, treating both cases analytically. By modes, we refer to the comoving curvature perturbation R. We then consider applications to transient phases where the slow roll parameters can become large, especially in the context of the common 'fast-roll' inflation frequently used as a mechanism to explain the anomalously low scalar power at low l in the CMB. These transient cases we treat numerically. We find when ε, the first slow roll parameter, and only ε is large, modes decay outside the horizon, and when δ, the second slow roll parameter, is large, modes grow outside the horizon. When multiple slow roll parameters are large the behavior in general is more complicated, but we nevertheless show in the 'fast-roll' inflation case, modes grow outside the horizon.
High-scale axions without isocurvature from inflationary dynamics
Kearney, John; Orlofsky, Nicholas; Pierce, Aaron
2016-05-31
Observable primordial tensor modes in the cosmic microwave background (CMB) would point to a high scale of inflation HI. If the scale of Peccei-Quinn (PQ) breaking fa is greater than HI/2π, CMB constraints on isocurvature naively rule out QCD axion dark matter. This assumes the potential of the axion is unmodified during inflation. We revisit models where inflationary dynamics modify the axion potential and discuss how isocurvature bounds can be relaxed. We find that models that rely solely on a larger PQ-breaking scale during inflation fI require either late-time dilution of the axion abundance or highly super-Planckian fI that somehowmore » does not dominate the inflationary energy density. Models that have enhanced explicit breaking of the PQ symmetry during inflation may allow fa close to the Planck scale. Lastly, avoiding disruption of inflationary dynamics provides important limits on the parameter space.« less
High-scale axions without isocurvature from inflationary dynamics
NASA Astrophysics Data System (ADS)
Kearney, John; Orlofsky, Nicholas; Pierce, Aaron
2016-05-01
Observable primordial tensor modes in the cosmic microwave background (CMB) would point to a high scale of inflation HI . If the scale of Peccei-Quinn (PQ) breaking fa is greater than H/I 2 π , CMB constraints on isocurvature naively rule out QCD axion dark matter. This assumes the potential of the axion is unmodified during inflation. We revisit models where inflationary dynamics modify the axion potential and discuss how isocurvature bounds can be relaxed. We find that models that rely solely on a larger PQ-breaking scale during inflation fI require either late-time dilution of the axion abundance or highly super-Planckian fI that somehow does not dominate the inflationary energy density. Models that have enhanced explicit breaking of the PQ symmetry during inflation may allow fa close to the Planck scale. Avoiding disruption of inflationary dynamics provides important limits on the parameter space.
Nonisotropy in the CMB power spectrum in single field inflation
Donoghue, John F.; Dutta, Koushik; Ross, Andreas
2009-07-15
Contaldi et al.[C. R. Contaldi, M. Peloso, L. Kofman, and A. Linde, J. Cosmol. Astropart. Phys. 07 (2003) 002] have suggested that an initial period of kinetic energy domination in single field inflation may explain the lack of CMB power at large angular scales. We note that in this situation it is natural that there also be a spatial gradient in the initial value of the inflaton field, and that this can provide a spatial asymmetry in the observed CMB power spectrum, manifest at low values of l. We investigate the nature of this asymmetry and comment on its relation to possible anomalies at low l.
Single shot line-field optical coherence elastography
NASA Astrophysics Data System (ADS)
Liu, Chih-Hao; Schill, Alexander; Singh, Manmohan; Wu, Chen; Li, Jiasong; Han, Zhaolong; Raghunathan, Raksha; Kazemi, Tina; Nair, Achuth; Hsu, Thomas; Larin, Kirill V.
2016-03-01
Elastic wave imaging optical coherence elastography (EWI-OCE) is an emerging technique that can quantify local biomechanical properties of tissues. However, long acquisition times make this technique unfeasible for clinical use. Here, we demonstrate a noncontact single shot line-field OCE technique using a line-field interferometer and an air-pulse delivery system. The spatial-temporal elastic wave propagation profile was acquired in a single shot and used to quantify the elastic wave group velocity in tissue. Results on tissue-mimicking phantoms and chicken breast muscle agreed well with mechanical compression testing, demonstrating that the presented method can effectively reduce the OCE acquisition time to a few milliseconds in biological application.
Optimal bispectrum constraints on single-field models of inflation
Anderson, Gemma J.; Regan, Donough; Seery, David E-mail: D.Regan@sussex.ac.uk
2014-07-01
We use WMAP 9-year bispectrum data to constrain the free parameters of an 'effective field theory' describing fluctuations in single-field inflation. The Lagrangian of the theory contains a finite number of operators associated with unknown mass scales. Each operator produces a fixed bispectrum shape, which we decompose into partial waves in order to construct a likelihood function. Based on this likelihood we are able to constrain four linearly independent combinations of the mass scales. As an example of our framework we specialize our results to the case of 'Dirac-Born-Infeld' and 'ghost' inflation and obtain the posterior probability for each model, which in Bayesian schemes is a useful tool for model comparison. Our results suggest that DBI-like models with two or more free parameters are disfavoured by the data by comparison with single-parameter models in the same class.
Quantitative annular dark field electron microscopy using single electron signals.
Ishikawa, Ryo; Lupini, Andrew R; Findlay, Scott D; Pennycook, Stephen J
2014-02-01
One of the difficulties in analyzing atomic resolution electron microscope images is that the sample thickness is usually unknown or has to be fitted from parameters that are not precisely known. An accurate measure of thickness, ideally on a column-by-column basis, parameter free, and with single atom accuracy, would be of great value for many applications, such as matching to simulations. Here we propose such a quantification method for annular dark field scanning transmission electron microscopy by using the single electron intensity level of the detector. This method has the advantage that we can routinely quantify annular dark field images operating at both low and high beam currents, and under high dynamic range conditions, which is useful for the quantification of ultra-thin or light-element materials. To facilitate atom counting at the atomic scale we use the mean intensity in an annular dark field image averaged over a primitive cell, with no free parameters to be fitted. To illustrate the potential of our method, we demonstrate counting the number of Al (or N) atoms in a wurtzite-type aluminum nitride single crystal at each primitive cell over the range of 3-99 atoms.
Constraining = 1 supergravity inflationary framework with non-minimal Kähler operators
NASA Astrophysics Data System (ADS)
Choudhury, Sayantan; Mazumdar, Anupam; Pukartas, Ernestas
2014-04-01
In this paper we will illustrate how to constrain unavoidable Kähler corrections for = 1 supergravity (SUGRA) inflation from the recent Planck data. We will show that the non-renormalizable Kähler operators will induce in general non-minimal kinetic term for the inflaton field, and two types of SUGRA corrections in the potential — the Hubble-induced mass ( c H ), and the Hubble-induced A-term ( a H ) correction. The entire SUGRA inflationary framework can now be constrained from (i) the speed of sound, c s , and (ii) from the upper bound on the tensor to scalar ratio, r ⋆. We will illustrate this by considering a heavy scalar degree of freedom at a scale, M s , and a light inflationary field which is responsible for a slow-roll inflation. We will compute the corrections to the kinetic term and the potential for the light field explicitly. As an example, we will consider a visible sector inflationary model of inflation where inflation occurs at the point of inflection, which can match the density perturbations for the cosmic microwave background radiation, and also explain why the universe is filled with the Standard Model degrees of freedom. We will scan the parameter space of the non-renormalizable Kähler operators, which we find them to be order (1), consistent with physical arguments. While the scale of heavy physics is found to be bounded by the tensor-to scalar ratio, and the speed of sound, (1011 ≤ M s ≤ 1016) GeV, for 0 .02 ≤ c s ≤ 1 and 10-22 ≤ r ⋆ ≤ 0 .12.
Field Regulation of Single Molecule Conductivity by a Charged Atom
NASA Astrophysics Data System (ADS)
Wolkow, Robert
2006-03-01
A new concept for a single molecule transistor is demonstrated [1]. A single chargeable atom adjacent to a molecule shifts molecular energy levels into alignment with electrode levels, thereby gating current through the molecule. Seemingly paradoxically, the silicon substrate to which the molecule is covalently attached provides 2, not 1, effective contacts to the molecule. This is achieved because the single charged silicon atom is at a substantially different potential than the remainder of the substrate. Charge localization at one dangling bond is ensured by covalently capping all other surface atoms. Dopant level control and local Fermi level control can change the charge state of that atom. The same configuration is shown to be an effective transducer to an electrical signal of a single molecule detection event. Because the charged atom induced shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature. [1] Paul G. Piva1,Gino A. DiLabio, Jason L. Pitters, Janik Zikovsky, Moh'd Rezeq, Stanislav Dogel, Werner A. Hofer & Robert A. Wolkow, Field regulation of single-molecule conductivity by a charged surface atom, NATURE 435, 658-661 (2005)
Single-point inversion of the coronal magnetic field
Plowman, Joseph
2014-09-01
The Fe XIII 10747 and 10798 Å lines observed in the solar corona are sensitive to the coronal magnetic field in such a way that, in principle, the full vector field at a point on the line of sight can be inferred from their combined polarization signals. This paper presents analytical inversion formulae for the field parameters and analyzes the uncertainty of magnetic field measurements made from such observations, assuming emission dominated by a single region along the line of sight. We consider the case of the current Coronal Multi-channel Polarimeter (CoMP) instrument as well as the future Coronal Solar Magnetism Observatory (COSMO) and Advanced Technology Solar Telescope (ATST) instruments. Uncertainties are estimated with a direct analytic inverse and with a Markov Chain Monte Carlo algorithm. We find that (in effect) two components of the vector field can be recovered with CoMP, and well recovered with COSMO or ATST, but that the third component can only be recovered when the solar magnetic field is strong and optimally oriented.
Relaxation models for single helical reversed field pinch plasmas
NASA Astrophysics Data System (ADS)
Paccagnella, Roberto
2016-09-01
In this paper, a relaxation theory for plasmas where a single dominant mode is present [Bhattacharjee et al., Phys. Rev. Lett. 45, 347 (1980)], is revisited. The solutions of a related eigenvalue problem are numerically calculated and discussed. Although these solutions can reproduce well, the magnetic fields measured in experiments, there is no way within the theory to determine the dominant mode, whose pitch is a free parameter in the model. To find the preferred helical perturbation, a procedure is proposed that minimizes the "distance" of the relaxed state from a state which is constructed as a two region generalization of the Taylor's relaxation model [Taylor, Phys. Rev. Lett. 33, 1139 (1974); Rev. Mod. Phys. 58, 751 (1986)] and that allows current discontinuities. It is found that this comparison is able to predict the observed scaling with the aspect ratio and reversal parameter for the dominant mode in the Single Helical states. The aspect ratio scaling alone is discussed in a previous paper [Paccagnella, Nucl. Fusion 56, 046010 (2016)] in terms of the efficient response of a toroidal shell to specific modes (leaving a sign undetermined), showing that the ideal wall boundary condition, a key ingredient in relaxation theories, is particularly well matched for them. Therefore, the present paper altogether [Paccagnella, Nucl. Fusion 56, 046010 (2016)] can give a new and satisfactory explanation of some robust and reproducible experimental facts observed in the Single Helical Reversed Field Pinch plasmas and never explained before.
[Striate receptive fields mapped with single and bipartite stimuli].
Lazareva, N A; Shevelev, I A; Saltykov, K A; Novikova, R V; Tikhomirov, A S; Sharaev, G A; Tsutskiridze, D Iu; Eĭdeland, P V
2008-01-01
In 22 acute experiments with anesthetized and immobilized adult cats, 364 maps of receptive fields (RF) of 47 striate neurons were obtained by means of single local stimuli flashed at different parts of the visual field, or with additional asynchronous activation of the RF excitatory center with oscillating bar of the optimal orientation. Under bipartite stimulation, considerable and significant decrease in the square and weight of the central excitatory RF zone was revealed in more then 75% of the studied cells. Additional excitatory zones appeared in 54% of cases, or the square and weight of the excitatory zones substantially increased, and inhibitory zones developed in 90% of cases. These effects were correlated with the degree of increase in the background firing during transition from the mode of mapping with single stimulation to that with bipartite stimulation. The mechanism and possible functional role of cooperative excitatory and inhibitory intracortical interactions in organization of receptive fields and detection of features of a visual image are discussed.
On squeezed limits in single-field inflation. Part I
Flauger, Raphael; Green, Daniel; Porto, Rafael A. E-mail: dgreen@stanford.edu
2013-08-01
The n-point correlation functions in single-field inflation obey a set of consistency conditions in the exact squeezed limit which are not present in multi-field models, and thus are powerful tools to distinguish between the two. However, these consistency conditions may be violated for a finite range of scales in single-field models, for example by departures from the Bunch-Davies state. These excited states may be the consequence of interactions during inflation, or may be a remnant of the era that preceded inflation. In this paper we analyze the bispectrum, and show that in the regime of theoretical control the resulting signal in the squeezed limit remains undetectably small in all known models which continuously excite the state. We also show that the signal remains undetectably small if the initial state is related to the Bunch-Davies state by a Bogoliubov transformation and the energy density in the state is small enough so that the usual slow-roll conditions are obeyed. Bogoliubov states that lead to violations of the slow-roll conditions, as well as more general excited states, require more careful treatment and will be discussed in a separate publication.
Hyperspectral Dark Field Optical Microscopy of Single Silver Nanospheres
El-Khoury, Patrick Z.; Joly, Alan G.; Hess, Wayne P.
2016-04-07
We record spectrally (400 nm ≤ λ ≤ 675 nm, Δλ < 4.69 nm) and spatially (diffraction-limited, sampled at 85 nm2/pixel) resolved dark field (DF) scattering from single silver nanospheres of 100 nm in diameter. Hyperspectral DF optical microscopy is achieved by coupling a hyperspectral detector to an optical microscope, whereby spectrally resolved diffraction-limited images of hundreds of silver nanoparticles can be recorded in ~30 seconds. We demonstrate how the centers and edges of individual particles can be localized in 2D to within a single pixel (85 nm2), using a statistical method for examining texture based on a co-occurrence matrix. Subsequently, spatial averaging of the spectral response in a 3x3 pixel area around the particle centers affords ample signal-to-noise to resolve the plasmon resonance of a single silver nanosphere. A close inspection of the scattering spectra of 31 different nanospheres reveals that each particle has its unique (i) relative scattering efficiency, and (ii) plasmon resonance maximum and dephasing time. These observations are suggestive of nanometric structural variations over length scales much finer than the spatial resolution attainable using the all-optical technique described herein.
Subsurface Stress Fields In Single Crystal (Anisotropic) Contacts
NASA Technical Reports Server (NTRS)
Arakere, Nagaraj K.; Knudsen, Erik C.; Duke, Greg; Battista, Gilda; Swanson, Greg
2004-01-01
Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is , presented, for evaluating the subsurface stresses in the elastic half-space, using a complex potential method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis. Effects of crystal orientation on stress response and fatigue life are examined.
Subsurface Stress Fields in Single Crystal (Anisotropic) Contacts
NASA Technical Reports Server (NTRS)
Arakere, Nagaraj K.
2003-01-01
Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and fatigue stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. Techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts are presented in this report. Figure 1 shows typical damper contact locations in a turbine blade. The subsurface stress results are used for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades.
Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts
NASA Technical Reports Server (NTRS)
Arakere, Nagaraj K.; Knudsen, Erik; Swanson, Gregory R.; Duke, Gregory; Ham-Battista, Gilda
2004-01-01
Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and non-crystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves
Conformal consistency relations for single-field inflation
Creminelli, Paolo; Noreña, Jorge; Simonović, Marko E-mail: jorge.norena@gmail.com
2012-07-01
We generalize the single-field consistency relations to capture not only the leading term in the squeezed limit — going as 1/q{sup 3}, where q is the small wavevector — but also the subleading one, going as 1/q{sup 2}. This term, for an (n+1)-point function, is fixed in terms of the variation of the n-point function under a special conformal transformation; this parallels the fact that the 1/q{sup 3} term is related with the scale dependence of the n-point function. For the squeezed limit of the 3-point function, this conformal consistency relation implies that there are no terms going as 1/q{sup 2}. We verify that the squeezed limit of the 4-point function is related to the conformal variation of the 3-point function both in the case of canonical slow-roll inflation and in models with reduced speed of sound. In the second case the conformal consistency conditions capture, at the level of observables, the relation among operators induced by the non-linear realization of Lorentz invariance in the Lagrangian. These results mean that, in any single-field model, primordial correlation functions of ζ are endowed with an SO(4,1) symmetry, with dilations and special conformal transformations non-linearly realized by ζ. We also verify the conformal consistency relations for any n-point function in models with a modulation of the inflaton potential, where the scale dependence is not negligible. Finally, we generalize (some of) the consistency relations involving tensors and soft internal momenta.
Inflationary effect of crude oil prices in Turkey
NASA Astrophysics Data System (ADS)
Berument, Hakan; Taşçı, Hakan
2002-12-01
It is generally acknowledged that changes in oil prices affect economic welfare in ways that are not entirely reflected in transactions in the oil market. In this article, by using the 1990 input-output table, the inflationary effects of crude oil prices are investigated for Turkey. Under fixed nominal wages, profits, interest and rent earnings, the effect of increasing prices of oil on inflation is limited. However, when wages and the other three factors of income (profit, interest and rent) are adjusted to the general price level that includes the oil price increases, the inflationary effect of oil prices becomes significant. Hence, indexation could have very severe effects on an economy when oil prices increase and, in some cases, could even lead to hyperinflation.
High-scale axions without isocurvature from inflationary dynamics
Kearney, John; Orlofsky, Nicholas; Pierce, Aaron
2016-05-31
Observable primordial tensor modes in the cosmic microwave background (CMB) would point to a high scale of inflation H_{I}. If the scale of Peccei-Quinn (PQ) breaking f_{a} is greater than H_{I}/2π, CMB constraints on isocurvature naively rule out QCD axion dark matter. This assumes the potential of the axion is unmodified during inflation. We revisit models where inflationary dynamics modify the axion potential and discuss how isocurvature bounds can be relaxed. We find that models that rely solely on a larger PQ-breaking scale during inflation f_{I} require either late-time dilution of the axion abundance or highly super-Planckian f_{I} that somehow does not dominate the inflationary energy density. Models that have enhanced explicit breaking of the PQ symmetry during inflation may allow f_{a} close to the Planck scale. Lastly, avoiding disruption of inflationary dynamics provides important limits on the parameter space.
Low reheating temperatures in monomial and binomial inflationary models
NASA Astrophysics Data System (ADS)
Rehagen, Thomas; Gelmini, Graciela B.
2015-06-01
We investigate the allowed range of reheating temperature values in light of the Planck 2015 results and the recent joint analysis of Cosmic Microwave Background (CMB) data from the BICEP2/Keck Array and Planck experiments, using monomial and binomial inflationary potentials. While the well studied phi2 inflationary potential is no longer favored by current CMB data, as well as phip with p>2, a phi1 potential and canonical reheating (0wre=) provide a good fit to the CMB measurements. In this last case, we find that the Planck 2015 68% confidence limit upper bound on the spectral index, ns, implies an upper bound on the reheating temperature of Trelesssim 6× 1010 GeV, and excludes instantaneous reheating. The low reheating temperatures allowed by this model open the possibility that dark matter could be produced during the reheating period instead of when the Universe is radiation dominated, which could lead to very different predictions for the relic density and momentum distribution of WIMPs, sterile neutrinos, and axions. We also study binomial inflationary potentials and show the effects of a small departure from a phi1 potential. We find that as a subdominant phi2 term in the potential increases, first instantaneous reheating becomes allowed, and then the lowest possible reheating temperature of Tre=4 MeV is excluded by the Planck 2015 68% confidence limit.
Inflationary Cosmology: Is Our Universe Part of a Multiverse
Guth, Alan
2008-11-06
In 1981, Guth proposed the theory of the inflationary universe, a modification of the Big Bang theory, which is generally accepted by scientists to explain how the universe began. Nevertheless, the Big Bang theory leaves some questions, and the theory of inflation attempts to answer them. Guth states that a repulsive gravitational force generated by an exotic form of matter brought about the expansion of the universe. He postulates that the universe underwent an expansion of astronomical proportions within the first trillionth of a second of its existence, during which the seeds for its large-scale structure were generated. Guth and colleagues have further explored the possibility of mimicking inflation in a hypothetical laboratory, thereby creating a new universe, and they concluded that it might be theoretically possible. If it happened, the new universe would not endanger our own universe. Instead, it would slip through a wormhole, a hypothetical space-time travel shortcut, and rapidly disconnect from our universe. In this talk, Guth will explain the inflationary theory and review the features that make it scientifically plausible. In addition, he will discuss the biggest mystery in cosmology: Why is the value of the cosmological constant, sometimes called the "anti-gravity" effect, so remarkably small compared to theoretical expectations? Guth will explain how the inflationary theory, combined with other ideas from elementary particle physics and cosmology, can provide a possible explanation for this discrepancy.
The field-space metric in spiral inflation and related models
NASA Astrophysics Data System (ADS)
Erlich, Joshua; Olsen, Jackson; Wang, Zhen
2016-09-01
Multi-field inflation models include a variety of scenarios for how inflation proceeds and ends. Models with the same potential but different kinetic terms are common in the literature. We compare spiral inflation and Dante's inferno-type models, which differ only in their field-space metric. We justify a single-field effective description in these models and relate the single-field description to a mass-matrix formalism. We note the effects of the nontrivial field-space metric on inflationary observables, and consequently on the viability of these models. We also note a duality between spiral inflation and Dante's inferno models with different potentials.
Dark energy from primordial inflationary quantum fluctuations.
Ringeval, Christophe; Suyama, Teruaki; Takahashi, Tomo; Yamaguchi, Masahide; Yokoyama, Shuichiro
2010-09-17
We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the Universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.
Single-field consistency relations of large scale structure
Creminelli, Paolo; Noreña, Jorge; Simonović, Marko; Vernizzi, Filippo E-mail: jorge.norena@icc.ub.edu E-mail: filippo.vernizzi@cea.fr
2013-12-01
We derive consistency relations for the late universe (CDM and ΛCDM): relations between an n-point function of the density contrast δ and an (n+1)-point function in the limit in which one of the (n+1) momenta becomes much smaller than the others. These are based on the observation that a long mode, in single-field models of inflation, reduces to a diffeomorphism since its freezing during inflation all the way until the late universe, even when the long mode is inside the horizon (but out of the sound horizon). These results are derived in Newtonian gauge, at first and second order in the small momentum q of the long mode and they are valid non-perturbatively in the short-scale δ. In the non-relativistic limit our results match with [1]. These relations are a consequence of diffeomorphism invariance; they are not satisfied in the presence of extra degrees of freedom during inflation or violation of the Equivalence Principle (extra forces) in the late universe.
Structured dark-field imaging for single nano-particles
NASA Astrophysics Data System (ADS)
Chen, Jian; Gao, Kun; Wang, Zhi-Li; Yun, Wen-Bing; Wu, Zi-Yu
2015-08-01
In this work, we extensively describe and demonstrate the structured dark-field imaging (SDFI). SDFI is a newly proposed x-ray microscopy designed for revealing the fine features below Rayleigh resolution, in which different orders of scattered x-ray photons are collected by changing the numerical aperture of the condenser. Here, the samples of single particles are discussed to extend the scope of the SDFI technique reported in a previous work (Chen J, Gao K, Ge X, et al. 2013 Opt. Lett. 38 2068). In addition, the details of the newly invented algorithm are explained, which is able to calculate the intensity of any pixel on the image plane rapidly and reliably. Project supported by the National Basic Research Program of China (Grant No. 2012CB825800), the Science Fund for Creative Research Groups, the National Natural Science Foundation of China (Grant No. 11321503), the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-YW-N42), and the National Natural Science Foundation of China (Grant Nos. 11475170, 11205157, and 11305173).
Low reheating temperatures in monomial and binomial inflationary models
Rehagen, Thomas; Gelmini, Graciela B. E-mail: gelmini@physics.ucla.edu
2015-06-01
We investigate the allowed range of reheating temperature values in light of the Planck 2015 results and the recent joint analysis of Cosmic Microwave Background (CMB) data from the BICEP2/Keck Array and Planck experiments, using monomial and binomial inflationary potentials. While the well studied φ{sup 2} inflationary potential is no longer favored by current CMB data, as well as φ{sup p} with p>2, a φ{sup 1} potential and canonical reheating (0w{sub re}=) provide a good fit to the CMB measurements. In this last case, we find that the Planck 2015 68% confidence limit upper bound on the spectral index, n{sub s}, implies an upper bound on the reheating temperature of T{sub re}∼< 6× 10{sup 10} GeV, and excludes instantaneous reheating. The low reheating temperatures allowed by this model open the possibility that dark matter could be produced during the reheating period instead of when the Universe is radiation dominated, which could lead to very different predictions for the relic density and momentum distribution of WIMPs, sterile neutrinos, and axions. We also study binomial inflationary potentials and show the effects of a small departure from a φ{sup 1} potential. We find that as a subdominant φ{sup 2} term in the potential increases, first instantaneous reheating becomes allowed, and then the lowest possible reheating temperature of T{sub re}=4 MeV is excluded by the Planck 2015 68% confidence limit.
Low reheating temperatures in monomial and binomial inflationary models
Rehagen, Thomas; Gelmini, Graciela B.
2015-06-23
We investigate the allowed range of reheating temperature values in light of the Planck 2015 results and the recent joint analysis of Cosmic Microwave Background (CMB) data from the BICEP2/Keck Array and Planck experiments, using monomial and binomial inflationary potentials. While the well studied ϕ{sup 2} inflationary potential is no longer favored by current CMB data, as well as ϕ{sup p} with p>2, a ϕ{sup 1} potential and canonical reheating (w{sub re}=0) provide a good fit to the CMB measurements. In this last case, we find that the Planck 2015 68% confidence limit upper bound on the spectral index, n{sub s}, implies an upper bound on the reheating temperature of T{sub re}≲6×10{sup 10} GeV, and excludes instantaneous reheating. The low reheating temperatures allowed by this model open the possibility that dark matter could be produced during the reheating period instead of when the Universe is radiation dominated, which could lead to very different predictions for the relic density and momentum distribution of WIMPs, sterile neutrinos, and axions. We also study binomial inflationary potentials and show the effects of a small departure from a ϕ{sup 1} potential. We find that as a subdominant ϕ{sup 2} term in the potential increases, first instantaneous reheating becomes allowed, and then the lowest possible reheating temperature of T{sub re}=4 MeV is excluded by the Planck 2015 68% confidence limit.
Inflationary cosmology with Chaplygin gas in Palatini formalism
Borowiec, Andrzej; Wojnar, Aneta; Stachowski, Aleksander; Szydłowski, Marek E-mail: aleksander.stachowski@uj.edu.pl E-mail: aneta.wojnar@ift.uni.wroc.pl
2016-01-01
We present a simple generalisation of the ΛCDM model which on the one hand reaches very good agreement with the present day experimental data and provides an internal inflationary mechanism on the other hand. It is based on Palatini modified gravity with quadratic Starobinsky term and generalized Chaplygin gas as a matter source providing, besides a current accelerated expansion, the epoch of endogenous inflation driven by type III freeze singularity. It follows from our statistical analysis that astronomical data favors negative value of the parameter coupling quadratic term into Einstein-Hilbert Lagrangian and as a consequence the bounce instead of initial Big-Bang singularity is preferred.
Gao, Xian; Langlois, David; Mizuno, Shuntaro E-mail: langlois@apc.univ-paris7.fr
2013-10-01
In the context of two-field inflation characterized by a light direction and a heavy direction, we revisit the question of the impact of the massive modes on the power spectrum produced after a turn in the inflationary trajectory. We consider in particular the resonant effect due to the background oscillations following a sharp turn. Working in the mass basis, i.e. in the basis spanned by the eigenvectors of the effective mass matrix for the perturbations, we provide an analytical estimate of the resonant effect, using the in-in formalism. In comparison with earlier estimates, we find the same the spectral dependence but a smaller amplitude. We also compute, again via the in-in formalism, the effect of the direct coupling between the light and heavy modes at the instant of the turn and confirm our previous results obtained via a different method.
Rojas, Clara; Villalba, Victor M.
2007-03-15
The phase-integral approximation devised by Froeman and Froeman, is used for computing cosmological perturbations in the power-law inflationary model. The phase-integral formulas for the scalar and tensor power spectra are explicitly obtained up to ninth-order of the phase-integral approximation. We show that, the phase-integral approximation exactly reproduces the shape of the power spectra for scalar and tensor perturbations as well as the spectral indices. We compare the accuracy of the phase-integral approximation with the results for the power spectrum obtained with the slow-roll and uniform-approximation methods.
The Strength of PIN-PMN-PT Single Crystals under Bending with a Longitudinal Electric Field
2011-04-06
The strength of PIN– PMN – PT single crystals under bending with a longitudinal electric field This article has been downloaded from IOPscience. Please...COVERED 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE The Strength Of PIN- PMN - PT Single Crystals Under Bending With A Longitudinal Electric Field... PMN ? PT ) single crystals was measured using a four point bending apparatus with a longitudinal electric field applied to the bar during bending. The
Second-order reconstruction of the inflationary potential
NASA Technical Reports Server (NTRS)
Liddle, Andrew R.; Turner, Michael S.
1994-01-01
To first order in the deviation from scale invariance the inflationary potential and its first two derivatives can be expressed in terms of the spectral indices of the scalar and tensor perturbations, n and n(sub T), and their contributions to the variance of the quadrupole CBR temperature anisotropy, S and T. In addition, there is a 'consistency relation' between these quantities: n(sub T) = (-1/ 7)(T/S). We derive the second-order expressions for the inflationary potential and its first two derivatives and the first-order expression for its third derivative, in terms, of n, n(sub T), S, T, and dn/d ln gamma. We also obtain the second-order consistency relation, n(sub T) = (-1/7)(T/S)(1 + 0.11(T/S) + 0.15(n-1)). As an example we consider the exponential potential, the only known case where exact analytic solutions for the perturbation spectra exist. We reconstruct the potential via Taylor expansion (with coefficients calculated at both first and second order), and introduce the Pade approximate as a greatly improved alternative.
NASA Astrophysics Data System (ADS)
Das, Suratna; Lochan, Kinjalk; Sahu, Satyabrata; Singh, T. P.
2013-10-01
The inflationary paradigm provides a mechanism to generate the primordial perturbations needed to explain the observed large-scale structures in the Universe. Inflation traces back all the inhomogeneities to quantum fluctuations although the structures look classical today. The squeezing of primordial quantum fluctuations along with the mechanism of decoherence accounts for many aspects of this quantum-to-classical transition, although it remains a matter of debate as to whether this is sufficient to explain the issue of the realization of a single outcome (i.e. the issue of macro-objectification) from a quantum ensemble given that the Universe is a closed system. A similar question of the emergence of classical behavior of macroscopic objects exists also for laboratory systems and apart from decoherence there have been attempts to resolve this issue through continuous spontaneous localization (CSL), which is a stochastic nonlinear modification of the nonrelativistic Schrödinger equation. Recently, Martin et al. have investigated whether a CSL-like mechanism with a constant strength parameter—when the Mukhanov-Sasaki variable is taken as the “collapse operator”—can explain how the primordial quantum perturbations generated during inflation become classical. Within the scope of their assumptions they essentially come to a negative conclusion. In the present work, we generalize their analysis by allowing the CSL strength parameter to depend on physical scales so as to capture the CSL amplification mechanism. We show that such a generalization provides a mechanism for the macro-objectification (i.e. classicalization) of the inflationary quantum perturbations, while also preserving the scale invariance of the power spectrum and the phase coherence of superhorizon perturbation modes in a particular class of these models.
Testing and extending the inflationary consistency relation for tensor modes
NASA Astrophysics Data System (ADS)
Boyle, Latham; Smith, Kendrick M.; Dvorkin, Cora; Turok, Neil
2015-08-01
If observations confirm BICEP2's claim of a tensor-scalar ratio r ≈0.2 on CMB scales, then the inflationary consistency relation nt=-r /8 predicts a small negative value for the tensor spectral index nt. We show that future CMB polarization experiments should be able to confirm this prediction at several sigma. We also show how to properly extend the consistency relation to solar system scales, where the primordial gravitational wave density Ωgw could be measured by proposed experiments such as the Big Bang Observer. This would provide a far more stringent test of the consistency relation and access much more detailed information about the early Universe.
Loop quantum cosmology: from pre-inflationary dynamics to observations
NASA Astrophysics Data System (ADS)
Ashtekar, Abhay; Barrau, Aurélien
2015-12-01
The Planck collaboration has provided us rich information about the early Universe, and a host of new observational missions will soon shed further light on the ‘anomalies’ that appear to exist on the largest angular scales. From a quantum gravity perspective, it is natural to inquire if one can trace back the origin of such puzzling features to Planck scale physics. Loop quantum cosmology provides a promising avenue to explore this issue because of its natural resolution of the big bang singularity. Thanks to advances over the last decade, the theory has matured sufficiently to allow concrete calculations of the phenomenological consequences of its pre-inflationary dynamics. In this article we summarize the current status of the ensuing two-way dialog between quantum gravity and observations.
TOPICAL REVIEW: String cosmology versus standard and inflationary cosmology
NASA Astrophysics Data System (ADS)
Gasperini, M.
2000-06-01
This paper presents a review of the basic, model-independent differences between the pre-big-bang scenario, arising naturally in a string cosmology context, and the standard inflationary scenario. We use an unconventional approach in which the introduction of technical details is avoided as much as possible, trying to focus the reader's attention on the main conceptual aspects of both scenarios. The aim of the paper is not to conclude either in favour of one or other of the scenarios, but to raise questions that are left to the reader's meditation. Warning: the paper does not contain equations, and is not intended as a complete review of all aspects of string cosmology.
Mass spectroscopy of single aerosols from field measurements
Thomson, D.S.; Murphy, D.M.
1995-12-31
We are developing an aircraft instrument for the chemical analysis of individual ambient aerosols in real time. In order to test the laboratory version of this instrument, we participated in a field campaign near the continental divide in Colorado in September, 1993. During this campaign, over 5000 mass spectra of ambient aerosols were collected. Analysis of the negative ion spectra shows that sulfate was the most commonly seen component of smaller particles, while nitrate was more common in larger particles. Organic compounds are present in most particles, and we believe we can distinguish inorganic carbon in some particles. Although numerous distinct classes of particles were observed, indicating external mixtures, almost all of these particle types were themselves mixtures of several compounds. Finally, we note that although the field site experienced distinct polluted and unpolluted episodes, aerosol composition did not correlate with gas phase chemistry.
Analysis of electric field stimulation of single cardiac muscle cells.
Tung, L; Borderies, J R
1992-01-01
Electrical stimulation of cardiac cells by imposed extracellular electric fields results in a transmembrane potential which is highly nonuniform, with one end of the cell depolarized and the other end hyperpolarized along the field direction. To date, the implications of the close proximity of oppositely polarized membranes on excitability have not been explored. In this work we compare the biophysical basis for field stimulation of cells at rest with that for intracellular current injection, using three Luo-Rudy type membrane patches coupled together as a lumped model to represent the cell membrane. Our model shows that cell excitation is a function of the temporal and spatial distribution of ionic currents and transmembrane potential. The extracellular and intracellular forms of stimulation were compared in greater detail for monophasic and symmetric biphasic rectangular pulses, with duration ranging from 0.5 to 10 ms. Strength-duration curves derived for field stimulation show that over a wide range of pulse durations, biphasic waveforms can recruit and activate membrane patches about as effectively as can monophasic waveforms having the same total pulse duration. We find that excitation with biphasic stimulation results from a synergistic, temporal summation of inward currents through the sodium channel in membrane patches at opposite ends of the cell. Furthermore, with both waveform types, a net inward current through the inwardly rectifying potassium channel contributes to initial membrane depolarization. In contrast, models of stimulation by intracellular current injection do not account for the nonuniformity of transmembrane potential and produce substantially different (even contradictory) results for the case of stimulation from rest. PMID:1420884
Creation and recovery of a W(111) single atom gas field ion source.
Pitters, Jason L; Urban, Radovan; Wolkow, Robert A
2012-04-21
Tungsten single atom tips have been prepared from a single crystal W(111) oriented wire using the chemical assisted field evaporation and etching method. Etching to a single atom tip occurs through a symmetric structure and leads to a predictable last atom unlike etching with polycrystalline tips. The single atom tip formation procedure is shown in an atom by atom removal process. Rebuilds of single atom tips occur on the same crystalline axis as the original tip such that ion emission emanates along a fixed direction for all tip rebuilds. This preparation method could be utilized and developed to prepare single atom tips for ion source development.
NASA Astrophysics Data System (ADS)
Rodriguez, Alvar; Singh, Simranjeet; Haque, Firoze; Del Barco, Enrique; Nguyen, Tu; Christou, George
2012-02-01
Dependence of magnetic field and electronic transport of Mn4 Single-molecule magnet in a Single-Electron Transistor A. Rodriguez, S. Singh, F. Haque and E. del Barco Department of Physics, University of Central Florida, 4000 Central Florida Blvd., Orlando, Florida 32816 USA T. Nguyen and G. Christou Department of Chemistry, University of Florida, Gainesville, Florida 32611 USA Abstract We have performed single-electron transport measurements on a series of Mn-based low-nuclearity single-molecule magnets (SMM) observing Coulomb blockade. SMMs with well isolated and low ground spin states, i.e. S = 9/2 (Mn4) and S = 6 (Mn3) were chosen for these studies, such that the ground spin multiplet does not mix with levels of other excited spin states for the magnetic fields (H = 0-8 T) employed in the experiments. Different functionalization groups were employed to change the mechanical, geometrical and transport characteristics of the molecules when deposited from liquid solution on the transistors. Electromigration-broken three-terminal single-electron transistors were used. Results obtained at temperatures down to 240 mK and in the presence of high magnetic fields will be shown.
Single-acquisition wide-field superresolution for telescopes.
Wereley, Steve; Zhang, Yuxing; Khor, Jian-Wei; Snoeyink, Craig
2016-12-10
A simple optical setup is introduced here that is capable of improving the diffraction-limited angular resolution of a telescope at minimal cost to image quality. The system consists of, at minimum, an axicon and a convex lens located in the optical path of the telescope, which can increase the angular resolution by up to 38%. Analytical results for this resolution gain along with the Strehl ratio of this system are presented along with experimental results, which show a 30% improvement in single-acquisition image resolution with a Strehl ratio of 0.07, agreeing well with predicted values. With an ultrashallow axicon, large increases in Strehl ratio are possible, up to and beyond unity making higher angular resolution measurements possible with little cost to image quality or experimental complexity.
Field-induced rectification in rutile single crystals.
NASA Astrophysics Data System (ADS)
Jameson, John R.; Fukuzumi, Yoshiaki; Tsunoda, Koji; Wang, Zheng; Griffin, Peter B.; Nishi, Yoshio
2007-03-01
A previously unknown resistive memory effect is reported in rutile titanium dioxide. Two Pt electrodes were placed on the surface of a rutile crystal, and a large voltage was applied between them. Afterwards, the device allowed current to pass in the direction of the voltage, but not in the other direction. The orientation of this rectification could then be switched by applying a large voltage of opposite sign. The effect was observed with electrodes on the (100) or (110) surfaces, but not the (001) surface. A plausible explanation is the field-induced motion of oxygen vacancies, which the large voltage might cause to pile up under the negative electrode, eliminating a Schottky barrier at that interface, but leaving a Schottky at the positive electrode intact. Parallels are drawn to other memory effects in titanium dioxide.
Case history of the Cormorant field single satellite well
Brommer, J.J.; Fernandinho, C.M.M.S.; Liles, J.R.
1982-01-01
A case history of the development of specifically tailor-made equipment and the experience gained from the installation and production from the first subsea well in the central area of the Cormorant field is presented. Emphasis is placed on development concepts and the equipment uniquely manufactured to meet special needs. A one-year onshore integrated system test of the equipment is described along with the interface problems identified and resolved prior to going offshore. Actual installation and commissioning activities are fully covered including drilling, completion, and production from the well. The study describes the major reasons for the success of the subsea well to date as being extensive onshore testing, detailed planning, and the early involvement of operating personnel.
Quality improvement: single-field sterile scrub, prep, and dwell for laparoscopic hysterectomy.
O'Hanlan, Katherine A; McCutcheon, Stacey Paris; McCutcheon, John G; Charvonia, Beth E
2013-05-01
The vulva and vaginal interior are considered a contaminated surgical area, and current OR guidelines require surgeons who are gloved and gowned at the abdominal field to avoid contact with the urethral catheter, the uterine manipulator, and the introitus or to change their gloves and even regown if contact occurs. It is our belief that the perception of the vaginal field as contaminated reflects a lack of specific standards for the preoperative cleansing of the deeper vagina and a lack of preoperative prep instructions for the combined fields. We developed a comprehensive single-field prep technique designed to improve surgical efficiency and prevent contamination of the sterile field. Combining a methodical scrub, prep, and dwell, this technique allows the entire abdomino-perineovaginal field to be treated as a single sterile field for laparoscopic procedures. Our surgical site infection rate of 1.8% when using this single-field prep technique and the subsequent surgical treatment of the abdominal, vaginal, and perineal fields as a single sterile field is well within reported norms.
Single-shot spatiotemporal measurements of high-field terahertz pulses
van Tilborg, Jeroen; Schroeder, Carl; Toth, Csaba; Geddes, Cameron; Esarey, Eric; Leemans, Wim
2011-06-17
The electric field profiles of broad-bandwidth coherent terahertz (THz) pulses, emitted by laser-wakefield-accelerated electron bunches, are studied. The near-single-cycle THz pulses are measured with two single-shot techniques in the temporal and spatial domains. Spectra of 0-6 THz and peak fields up to {approx_equal} 0.4 MV cm{sup -1} are observed. The measured field substructure demonstrates the manifestation of spatiotemporal coupling at focus, which affects the interpretation of THz radiation as a bunch diagnostic and in high-field pump-probe experiments.
Electric-field-assisted position and orientation control of organic single crystals.
Kotsuki, Kenji; Obata, Seiji; Saiki, Koichiro
2014-12-02
We have investigated the motion of growing pentacene single crystals in solution under various electric fields. The pentacene single crystals in 1,2,4-trichlorobenzene responded to the electric field as if they were positively charged. By optimizing the strength and frequency of an alternating electric field, the pentacene crystals automatically bridged the electrodes on SiO2. The pentacene crystal with a large aspect ratio tended to direct the [1̅10] orientation parallel to the conduction direction, which will be suitable from a viewpoint of anisotropy in mobility. The present result shows a possibility of controlling the position and orientation of organic single crystals by the use of an electric field, which leads to high throughput and low cost industrial manufacturing of the single crystal array from solution.
Chen, Yaofei; Han, Qun; Liu, Tiegen; Lan, Xinwei; Xiao, Hai
2013-10-15
An optical fiber magnetic field sensor based on the single-mode-multimode-single-mode (SMS) structure and magnetic fluid (MF) is proposed and demonstrated. By using a piece of no-core fiber as the multimode waveguide in the SMS structure and MF sealed in a capillary tube as the magnetic sensitive media, which totally immersing the no-core fiber, an all-fiber magnetic sensor was fabricated. Interrogation of the magnetic field strength can be achieved either by measuring the dip wavelength shift of the transmission spectrum or by detecting the transmission loss at a specific wavelength. A demonstration sensor with sensitivities up to 905 pm/mT and 0.748 dB/mT was fabricated and investigated. A theoretical model for the design of the proposed device was developed and numerical simulations were performed.
Bayesian analysis of inflationary features in Planck and SDSS data
NASA Astrophysics Data System (ADS)
Benetti, Micol; Alcaniz, Jailson S.
2016-07-01
We perform a Bayesian analysis to study possible features in the primordial inflationary power spectrum of scalar perturbations. In particular, we analyze the possibility of detecting the imprint of these primordial features in the anisotropy temperature power spectrum of the cosmic microwave background (CMB) and also in the matter power spectrum P (k ) . We use the most recent CMB data provided by the Planck Collaboration and P (k ) measurements from the 11th data release of the Sloan Digital Sky Survey. We focus our analysis on a class of potentials whose features are localized at different intervals of angular scales, corresponding to multipoles in the ranges 10 <ℓ<60 (Oscill-1) and 150 <ℓ<300 (Oscill-2). Our results show that one of the step potentials (Oscill-1) provides a better fit to the CMB data than does the featureless Λ CDM scenario, with moderate Bayesian evidence in favor of the former. Adding the P (k ) data to the analysis weakens the evidence of the Oscill-1 potential relative to the standard model and strengthens the evidence of this latter scenario with respect to the Oscill-2 model.
Inflationary cosmology leading to a soft type singularity
NASA Astrophysics Data System (ADS)
Brevik, I.; Obukhov, V. V.; Timoshkin, A. V.
2016-06-01
A remarkable property of modern cosmology is that it allows for a special case of symmetry, consisting in the possibility of describing the early-time acceleration (inflation) and the late-time acceleration using the same theoretical framework. In this paper, we consider various cosmological models corresponding to a generalized form for the equation of state for the fluid in a flat Friedmann-Robertson-Walker (FRW) universe, emphasizing cases where the so-called type IV singular inflation is encountered in the future. This is a soft (non-crushing) kind of singularity. Parameter values for an inhomogeneous equation of state leading to singular inflation are obtained. We present models for which there are two type IV singularities, the first corresponding to the end of the inflationary era and the second to a late-time event. We also study the correspondence between the theoretical slow-roll parameters leading to type IV singular inflation and the recent results observed by the Planck satellite.
Dynamics of warm Chaplygin gas inflationary models with quartic potential
NASA Astrophysics Data System (ADS)
Jawad, Abdul; Butt, Sadaf; Rani, Shamaila
2016-05-01
Warm inflationary universe models in the context of the generalized Chaplygin gas, the modified Chaplygin gas, and the generalized cosmic Chaplygin gas are being studied. The dissipative coefficient of the form Γ ∝ T, and the weak and the strong dissipative regimes are being considered. We use the quartic potential, λ _{*}φ 4/4, which is ruled out by current data in cold inflation but in our models by analysis it is seen to be in agreement with the WMAP9 and the latest Planck data. In these scenarios, the power spectrum, the spectral index, and the tensor-to-scalar ratio are being examined in the slow-roll approximation. We show the dependence of the tensor-scalar ratio r on the spectral index ns and observe that the range of the tensor-scalar ratio is r<0.05 in the generalized Chaplygin gas, r<0.15 in the modified Chaplygin gas, and r<0.12 in the generalized cosmic Chaplygin gas models. Our results are in agreement with recent observational data like WMAP9 and the latest Planck data.
Dark radiation and inflationary freedom after Planck 2015
NASA Astrophysics Data System (ADS)
Di Valentino, Eleonora; Gariazzo, Stefano; Gerbino, Martina; Giusarma, Elena; Mena, Olga
2016-04-01
The simplest inflationary models predict a primordial power spectrum (PPS) of the curvature fluctuations that can be described by a power-law function that is nearly scale invariant. It has been shown, however, that the low-multipole spectrum of the cosmic microwave background anisotropies may hint at the presence of some features in the shape of the scalar PPS, which could deviate from its canonical power-law form. We study the possible degeneracies of this nonstandard PPS with the active neutrino masses, the effective number of relativistic species, and a sterile neutrino or a thermal axion mass. The limits on these additional parameters are less constraining in a model with a nonstandard PPS when including only the temperature autocorrelation spectrum measurements in the data analyses. The inclusion of the polarization spectra noticeably helps in reducing the degeneracies, leading to results that typically show no deviation from the Λ CDM model with a standard power-law PPS. These findings are robust against changes in the function describing the noncanonical PPS. Albeit current cosmological measurements seem to prefer the simple power-law PPS description, the statistical significance to rule out other possible parametrizations is still very poor. Future cosmological measurements are crucial to improve the present PPS uncertainties.
Renema, J. J.; Rengelink, R. J.; Komen, I.; Wang, Q.; Kes, P.; Aarts, J.; Exter, M. P. van; Dood, M. J. A. de; Gaudio, R.; Hoog, K. P. M. op 't; Zhou, Z.; Fiore, A.; Sahin, D.; Driessen, E. F. C.
2015-03-02
We experimentally investigate the effect of a magnetic field on photon detection in superconducting single-photon detectors (SSPDs). At low fields, the effect of a magnetic field is through the direct modification of the quasiparticle density of states of the superconductor, and magnetic field and bias current are interchangeable, as is expected for homogeneous dirty-limit superconductors. At the field where a first vortex enters the detector, the effect of the magnetic field is reduced, up until the point where the critical current of the detector starts to be determined by flux flow. From this field on, increasing the magnetic field does not alter the detection of photons anymore, whereas it does still change the rate of dark counts. This result points at an intrinsic difference in dark and photon counts, and also shows that no enhancement of the intrinsic detection efficiency of a straight SSPD wire is achievable in a magnetic field.
Single Event Effects (SEE) for Power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)
NASA Technical Reports Server (NTRS)
Lauenstein, Jean-Marie
2011-01-01
Single-event gate rupture (SEGR) continues to be a key failure mode in power MOSFETs. (1) SEGR is complex, making rate prediction difficult SEGR mechanism has two main components: (1) Oxide damage-- Reduces field required for rupture (2) Epilayer response -- Creates transient high field across the oxide.
Quantum teleportation of the angular spectrum of a single-photon field
Walborn, S. P.; Ether, D. S.; Matos Filho, R. L. de; Zagury, N.
2007-09-15
We propose a quantum teleportation scheme for the angular spectrum of a single-photon field, which allows for the transmission of a large amount of information. Our proposal also provides a method to tune the frequencies of spatially entangled fields, which is useful for interactions with stationary qubits.
Optical Field-Strength Polarization of Two-Mode Single-Photon States
ERIC Educational Resources Information Center
Linares, J.; Nistal, M. C.; Barral, D.; Moreno, V.
2010-01-01
We present a quantum analysis of two-mode single-photon states based on the probability distributions of the optical field strength (or position quadrature) in order to describe their quantum polarization characteristics, where polarization is understood as a significative confinement of the optical field-strength values on determined regions of…
NASA Astrophysics Data System (ADS)
Jamonneau, P.; Lesik, M.; Tetienne, J. P.; Alvizu, I.; Mayer, L.; Dréau, A.; Kosen, S.; Roch, J.-F.; Pezzagna, S.; Meijer, J.; Teraji, T.; Kubo, Y.; Bertet, P.; Maze, J. R.; Jacques, V.
2016-01-01
We analyze the impact of electric field and magnetic field fluctuations in the decoherence of the electronic spin associated with a single nitrogen-vacancy (NV) defect in diamond. To this end, we tune the amplitude of a magnetic field in order to engineer spin eigenstates protected either against magnetic noise or against electric noise. The competition between these noise sources is analyzed quantitatively by changing their relative strength through modifications of the host diamond material. This study provides significant insights into the decoherence of the NV electronic spin, which is valuable for quantum metrology and sensing applications.
Trapping and injecting single domain walls in magnetic wire by local fields.
Vázquez, Manuel; Basheed, G A; Infante, Germán; Del Real, Rafael P
2012-01-20
A single domain wall (DW) moves at linearly increasing velocity under an increasing homogeneous drive magnetic field. Present experiments show that the DW is braked and finally trapped at a given position when an additional antiparallel local magnetic field is applied. That position and its velocity are further controlled by suitable tuning of the local field. In turn, the parallel local field of small amplitude does not significantly affect the effective wall speed at long distance, although it generates tail-to-tail and head-to-head pairs of walls moving along opposite directions when that field is strong enough.
Improved field emission stability from single-walled carbon nanotubes chemically attached to silicon
2012-01-01
Here, we demonstrate the simple fabrication of a single-walled carbon nanotube (SWCNT) field emission electrode which shows excellent field emission characteristics and remarkable field emission stability without requiring posttreatment. Chemically functionalized SWCNTs were chemically attached to a silicon substrate. The chemical attachment led to vertical alignment of SWCNTs on the surface. Field emission sweeps and Fowler-Nordheim plots showed that the Si-SWCNT electrodes field emit with a low turn-on electric field of 1.5 V μm−1 and high electric field enhancement factor of 3,965. The Si-SWCNT electrodes were shown to maintain a current density of >740 μA cm−2 for 15 h with negligible change in applied voltage. The results indicate that adhesion strength between the SWCNTs and substrate is a much greater factor in field emission stability than previously reported. PMID:22853557
Single-field sterile-scrub, preparation, and dwell for laparoscopic hysterectomy.
O'Hanlan, Katherine A; McCutcheon, Stacey Paris; McCutcheon, John G; Charvonia, Beth E
2012-01-01
Type VII laparoscopic hysterectomy is classified as a "clean-contaminated" procedure because the surgery involves contact with both the abdominal and vaginal fields. Because the vulva has traditionally been perceived as a separate but contaminated field, operating room guidelines have evolved to require that surgeons gloved and gowned at the abdominal field either avoid contact with the urethral catheter, the uterine manipulator, and the introitus or change their gloves and even re-gown after any contact with those fields. In the belief that the perception of the vaginal field as contaminated stems from inadequate preoperative preparation instructions, we have developed a rigorous abdomino-perineo-vaginal field preparation technique to improve surgical efficiency and prevent surgical site infections. This thorough scrub, preparation, and dwell technique enables the entire abdomino-perineo-vaginal field to be safely treated as a single sterile field while maintaining a low rate of surgical site infection, and should be further investigated in randomized studies.
Bayesian evidence and predictivity of the inflationary paradigm
NASA Astrophysics Data System (ADS)
Gubitosi, Giulia; Lagos, Macarena; Magueijo, João; Allison, Rupert
2016-06-01
In this paper we consider the issue of paradigm evaluation by applying Bayes' theorem along the following nested hierarchy of progressively more complex structures: i) parameter estimation (within a model), ii) model selection and comparison (within a paradigm), iii) paradigm evaluation. In such a hierarchy the Bayesian evidence works both as the posterior's normalization at a given level and as the likelihood function at the next level up. Whilst raising no objections to the standard application of the procedure at the two lowest levels, we argue that it should receive a considerable modification when evaluating paradigms, when testability and fitting data are equally important. By considering toy models we illustrate how models and paradigms that are difficult to falsify are always favoured by the Bayes factor. We argue that the evidence for a paradigm should not only be high for a given dataset, but exceptional with respect to what it would have been, had the data been different. With this motivation we propose a measure which we term predictivity, as well as a prior to be incorporated into the Bayesian framework, penalising unpredictivity as much as not fitting data. We apply this measure to inflation seen as a whole, and to a scenario where a specific inflationary model is hypothetically deemed as the only one viable as a result of information alien to cosmology (e.g. Solar System gravity experiments, or particle physics input). We conclude that cosmic inflation is currently hard to falsify, but that this could change were external/additional information to cosmology to select one of its many models. We also compare this state of affairs to bimetric varying speed of light cosmology.
Basics of quantum field theory of electromagnetic interaction processes in single-layer graphene
NASA Astrophysics Data System (ADS)
Hieu Nguyen, Van
2016-09-01
The content of this work is the study of electromagnetic interaction in single-layer graphene by means of the perturbation theory. The interaction of electromagnetic field with Dirac fermions in single-layer graphene has a peculiarity: Dirac fermions in graphene interact not only with the electromagnetic wave propagating within the graphene sheet, but also with electromagnetic field propagating from a location outside the graphene sheet and illuminating this sheet. The interaction Hamiltonian of the system comprising electromagnetic field and Dirac fermions fields contains the limits at graphene plane of electromagnetic field vector and scalar potentials which can be shortly called boundary electromagnetic field. The study of S-matrix requires knowing the limits at graphene plane of 2-point Green functions of electromagnetic field which also can be shortly called boundary 2-point Green functions of electromagnetic field. As the first example of the application of perturbation theory, the second order terms in the perturbative expansions of boundary 2-point Green functions of electromagnetic field as well as of 2-point Green functions of Dirac fermion fields are explicitly derived. Further extension of the application of perturbation theory is also discussed.
Electric-field-induced domain intersection in BaTiO3 single crystal
NASA Astrophysics Data System (ADS)
He, Ming; Wang, Mengxia; Zhang, Zhihua
2017-03-01
Large-angle convergent beam electron diffraction was used to determine the directions of polarization vectors in a BaTiO3 single crystal. Domain intersections driven by an electric field were investigated by in situ transmission electron microscopy. The dark triangles observed in the domain intersection region can be accounted for by dislocations and the strain field. Domains nucleate at the domain tip depending on the dislocations and strain field to relieve the accumulated stress. Schematic representations of the intersecting domains and the microscopic structure are given, clarifying the special electric-field-induced domain structure.
Single-field inflation and the local ansatz: Distinguishability and consistency
NASA Astrophysics Data System (ADS)
de Putter, Roland; Doré, Olivier; Green, Daniel; Meyers, Joel
2017-03-01
The single-field consistency conditions and the local ansatz have played separate but important roles in characterizing the non-Gaussian signatures of single- and multifield inflation respectively. We explore the precise relationship between these two approaches and their predictions. We demonstrate that the predictions of the single-field consistency conditions can never be satisfied by a general local ansatz with deviations necessarily arising at order (ns-1 )2 . This implies that there is, in principle, a minimum difference between single- and (fully local) multifield inflation in observables sensitive to the squeezed limit such as scale-dependent halo bias. We also explore some potential observational implications of the consistency conditions and its relationship to the local ansatz. In particular, we propose a new scheme to test the consistency relations. In analogy with delensing of the cosmic microwave background, one can deproject the coupling of the long wavelength modes with the short wavelength modes and test for residual anomalous coupling.
Determination of optimal ionic liquid for organic single-crystal field-effect transistors
NASA Astrophysics Data System (ADS)
Ono, S.; Miwa, K.; Seki, S.
2016-02-01
We investigate organic single-crystal field-effect transistors with various ionic liquids as gate dielectric. We find that the mobility of the field-effect transistors for both p-type and n-type organic semiconductors increases with decreasing total capacitance of the ionic liquid. However, it does not depend on the ion species at the interface between the organic semiconductor and the ionic liquid. By choosing an appropriate ionic liquid, a high carrier mobility of 12.4 cm2/V s in rubrene single crystals (p-type) and 0.13 cm2/V s in 7.7.8.8-Tetracyanoquinodimethane single crystals (n-type) are achieved. This study clarifies the influence of ionic liquids on the device performance of organic field-effect transistors and shows a way to maximize carrier mobility at the solid/liquid interface.
Non-Gaussianity in single field models without slow-roll conditions
NASA Astrophysics Data System (ADS)
Noller, Johannes; Magueijo, João
2011-05-01
We investigate non-Gaussianity in general single field models without assuming slow-roll conditions or the exact scale invariance of the scalar power spectrum. The models considered include general single field inflation (e.g. Dirac-Born-Infeld and canonical inflation) as well as bimetric models. We compute the full non-Gaussian amplitude A, its size fNL, its shape, and the running with scale nNG. In doing so we show that observational constraints allow significant violations of slow-roll conditions and we derive explicit bounds on slow-roll parameters for fast-roll single field scenarios. A variety of new observational signatures is found for models respecting these bounds. We also explicitly construct concrete model implementations giving rise to this new phenomenology.
NASA Astrophysics Data System (ADS)
Yoshioka, Katsumasa; Katayama, Ikufumi; Minami, Yasuo; Kitajima, Masahiro; Yoshida, Shoji; Shigekawa, Hidemi; Takeda, Jun
2016-12-01
The ultrafast coherent manipulation of electrons using waveform-controlled laser pulses is a key issue in the development of modern electronics. Developing such an approach for a tunnel junction will provide a new platform for governing ultrafast currents on an even smaller scale, which will be indispensable for the advancement of next-generation quantum nanocircuits and plasmonic devices. Here, we demonstrate that carrier-envelope-phase-controlled single-cycle terahertz electric fields can coherently drive electron tunnelling either from a nanotip to a sample or vice versa. Spatially confined electric fields of more than 10 V nm-1 strongly modulate the potential barrier at a nanogap in a scanning tunnelling microscope (STM) on the subpicosecond timescale and can steer a large number of electrons in an extremely nonlinear regime, which is not possible using a conventional STM. Our results are expected to pave the way for the future development of nanoscale science and technologies.
NASA Astrophysics Data System (ADS)
Thirion, C.; Wernsdorfer, W.; Jamet, M.; Dupuis, V.; Mélinon, P.; Pérez, A.; Mailly, D.
2002-04-01
An improved micro-SQUID technique is presented allowing us to measure the temperature dependence of the magnetisation switching fields of single nanoparticles well above the critical superconducting temperature of the SQUID. Our first measurements on 3 nm cobalt nanoparticle embedded in a niobium matrix are compared to the Néel Brown model describing the magnetisation reversal by thermal activation over a single anisotropy barrier.
Temperature dependence of switching fields of single 3 nm cobalt nanoparticles
NASA Astrophysics Data System (ADS)
Thirion, C.; Wernsdorfer, W.; Jamet, M.; Dupuis, V.; Mélinon, P.; Pérez, A.; Mailly, D.
2002-05-01
We study the temperature dependence of the magnetization switching fields of single nanoparticles with an improved micro-superconducting quantum interference device (SQUID) technique, that allows us to perform measurements independently of the critical superconducting temperature of the SQUID. A simplified Néel-Brown model that describes the magnetization reversal by thermal activation over a single anisotropy barrier is compared to measurements on a 3 nm cobalt nanoparticle embedded in a niobium matrix.
SINGLE CRYSTAL CADMIUM SULFIDE AND CADMIUM SELENIDE INSULATED-GATE FIELD-EFFECT TRIODES.
Insulated-gate field-effect triodes were fabricated on single crystal cadmium sulfide and cadmium selenide . Both bulk crystals and platelets were...used for single crystal samples. Chromium and aluminum were found to make low impedance contacts to cadmium sulfide and cadmium selenide . The...polycrystalline cadmium sulfide and cadmium selenide IGFET’s. The characteristics of the fabricated devices were unstable with respect to time and temperature
Field emission from ZrC films on Si and Mo single emitters and emitter arrays
Xie, T.; Mackie, W.A.; Davis, P.R.
1996-05-01
Field emission from ZrC films deposited on Si and Mo single emitters and field emitter arrays (FEAs) has been studied. For single emitters, the results show dramatic improvements in emitter performance by reducing work functions{emdash}on the order of 1 eV{emdash}and increasing stability. For FEAs, deposition of a ZrC film reduced the operating voltage 30{percent}{endash}50{percent} at an emission current of 1.0 {mu}A/tip and increased the emission stability. {copyright} {ital 1996 American Vacuum Society}
Fast phase manipulation of the single nuclear spin in solids by rotating fields
NASA Astrophysics Data System (ADS)
Shimo-Oka, T.; Tokura, Y.; Suzuki, Y.; Mizuochi, N.
2017-03-01
We propose fast phase gates of single nuclear spins interacting with single electron spins. The gate operation utilizes geometric phase shifts of the electron spin induced by fast and slow rotating fields; the path difference depending on nuclear-spin states enables nuclear phase shifts. The gate time is inversely proportional to the frequency of the slow rotating field. As an example, we use nitrogen-vacancy centers in diamond, and show, in principle, the phase-gate time orders of magnitude to be shorter than previously reported. We also confirmed the robustness of the gate against decoherence and systematic errors.
Measurements of the MHD dynamo in the quasi-single-helicity reversed-field pinch.
Piovesan, P; Craig, D; Marrelli, L; Cappello, S; Martin, P
2004-12-03
The first experimental study of the MHD dynamo in a quasi-single-helicity (QSH) reversed-field pinch toroidal plasma is presented. In QSH plasmas, a dominant wave number appears in the velocity fluctuation spectrum. This velocity component extends throughout the plasma volume and couples with magnetic fluctuations to produce a significant MHD dynamo electric field. The narrowing of the velocity fluctuation spectrum and the single-mode character of the dynamo are features predicted by theory and computation, but only now are observed in experiment.
A single-atom sharp iridium tip as an emitter of gas field ion sources
NASA Astrophysics Data System (ADS)
Kuo, Hong-Shi; Hwang, Ing-Shouh; Fu, Tsu-Yi; Hwang, Ying-Siang; Lu, Yi-Hsien; Lin, Chun-Yueh; Hou, Jin-Long; Tsong, Tien T.
2009-08-01
We report a reliable method for preparing a pure Ir single-atom tip by thermal treatment in oxygen. The atomic structure of the tip apex and its ion emission characteristics are investigated with field ion microscopy. We have shown that the Ir single-atom tip can be a good field ion emitter, capable of emitting a variety of gas ion beams, such as He+, H2+, N2+, and O2+, with high brightness and stability. In addition, this tip can easily be maintained and regenerated in vacuum, ensuring it has sufficient lifetime for practical applications.
Pulsed field actuation of Ni-Mn-Ga ferromagnetic shape memory alloy single crystal
NASA Astrophysics Data System (ADS)
Marioni, M.; Bono, D.; Banful, A. B.; del Rosario, M.; Rodriguez, E.; Peterson, B. W.; Allen, S. M.; O'Handley, R. C.
2003-10-01
Ferromagnetic Shape Memory Alloy Ni-Mn-Ga has twin boundaries in the martensitic phase that move when a suitable magnetic field is applied. In this fashion strains of up to 6% have been observed for static fields in single crystals [1]. Recently 2.5% strain has been demonstrated [2] in Ni-Mn-Ga single crystals for oscillating fields up to frequencies of 75 Hz (150 Hz actuation). This work studies the actuation of single crystals when pulsed fields are applied. Fields in the 0.4-1.5MA/m-range were generated in an air coil with rise times of the order of 1ms and below. The elongation of the samples is measured with a light beam reflected off the tip of the crystal. Single twin boundaries have been observed to advance 0.16 mm during 600 μsec-ong pulses. Actuation has been shown to be possible at least up to frequencies of 1700 Hz.
Longitudinal wave function control in single quantum dots with an applied magnetic field
NASA Astrophysics Data System (ADS)
Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A.; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai
2015-01-01
Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.
Longitudinal wave function control in single quantum dots with an applied magnetic field.
Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai
2015-01-27
Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.
Magnetic-field-induced quantum criticality in a planar ferromagnet with single-ion anisotropy
NASA Astrophysics Data System (ADS)
Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.
2014-08-01
We analyze the effects induced by single-ion anisotropy on quantum criticality in a d-dimensional spin-3/2 planar ferromagnet. To tackle this problem we employ the two-time Green's function method, using the Tyablikov decoupling for exchange interactions and the Anderson-Callen decoupling for single-ion anisotropy. In our analysis the role of non-thermal control parameter which drives the quantum phase transition is played by a longitudinal external magnetic field. We find that the single-ion anisotropy has substantial effects on the structure of the phase diagram close to the quantum critical point.
Gas field ion source current stability for trimer and single atom terminated W(111) tips
Urban, Radovan; Wolkow, Robert A.; Pitters, Jason L.
2012-06-25
Tungsten W(111) oriented trimer-terminated tips as well as single atom tips, fabricated by a gas and field assisted etching and evaporation process, were investigated with a view to scanning ion microscopy and ion beam writing applications. In particular, ion current stability was studied for helium and neon imaging gases. Large ion current fluctuations from individual atomic sites were observed when a trimer-terminated tip was used for the creation of neon ion beam. However, neon ion current was stable when a single atom tip was employed. No such current oscillations were observed for either a trimer or a single atom tip when imaged with helium.
Single-molecule measurements of proteins using carbon nanotube field-effect transistors
NASA Astrophysics Data System (ADS)
Sims, Patrick Craig
Single-walled carbon nanotube (SWCNT) field-effect transistors (FETs) provide a promising platform for investigating proteins at the single-molecule level. Recently, we have demonstrated that SWCNT FETs have sufficient sensitivity and bandwidth to monitor the conformational motions and processivity of an individual T4 lysozyme molecule. This is accomplished by functionalizing a SWCNT FET device with a single protein and measuring the conductance versus time through the device as it is submerged in an electrolyte solution. To generalize this approach for the study of a wide variety of proteins at the single-molecule level, this dissertation investigates the conjugation process to determine and isolate the key parameters involved in functionalizing a SWCNT with a single protein, the physical basis for transducing conformational motion of a protein into an electrical signal, and finally, the general application of the technique to monitor the binary and ternary complex formation of cAMP-dependent protein kinase (PKA).
Single-sided lateral-field and phototransistor-based optoelectronic tweezers
NASA Technical Reports Server (NTRS)
Ohta, Aaron (Inventor); Chiou, Pei-Yu (Inventor); Hsu, Hsan-Yin (Inventor); Jamshidi, Arash (Inventor); Wu, Ming-Chiang (Inventor); Neale, Steven L. (Inventor)
2011-01-01
Described herein are single-sided lateral-field optoelectronic tweezers (LOET) devices which use photosensitive electrode arrays to create optically-induced dielectrophoretic forces in an electric field that is parallel to the plane of the device. In addition, phototransistor-based optoelectronic tweezers (PhOET) devices are described that allow for optoelectronic tweezers (OET) operation in high-conductivity physiological buffer and cell culture media.
Smartphone Microscopy of Parasite Eggs Accumulated into a Single Field of View.
Sowerby, Stephen J; Crump, John A; Johnstone, Maree C; Krause, Kurt L; Hill, Philip C
2016-01-01
A Nokia Lumia 1020 cellular phone (Microsoft Corp., Auckland, New Zealand) was configured to image the ova of Ascaris lumbricoides converged into a single field of view but on different focal planes. The phone was programmed to acquire images at different distances and, using public domain computer software, composite images were created that brought all the eggs into sharp focus. This proof of concept informs a framework for field-deployable, point of care monitoring of soil-transmitted helminths.
Smartphone Microscopy of Parasite Eggs Accumulated into a Single Field of View
Sowerby, Stephen J.; Crump, John A.; Johnstone, Maree C.; Krause, Kurt L.; Hill, Philip C.
2016-01-01
A Nokia Lumia 1020 cellular phone (Microsoft Corp., Auckland, New Zealand) was configured to image the ova of Ascaris lumbricoides converged into a single field of view but on different focal planes. The phone was programmed to acquire images at different distances and, using public domain computer software, composite images were created that brought all the eggs into sharp focus. This proof of concept informs a framework for field-deployable, point of care monitoring of soil-transmitted helminths. PMID:26572870
Design of a surgical robot with dynamic vision field control for Single Port Endoscopic Surgery.
Kobayashi, Yo; Sekiguchi, Yuta; Tomono, Yu; Watanabe, Hiroki; Toyoda, Kazutaka; Konishi, Kozo; Tomikawa, Morimasa; Ieiri, Satoshi; Tanoue, Kazuo; Hashizume, Makoto; Fujie, Masaktsu G
2010-01-01
Recently, a robotic system was developed to assist Single Port Endoscopic Surgery (SPS). However, the existing system required a manual change of vision field, hindering the surgical task and increasing the degrees of freedom (DOFs) of the manipulator. We proposed a surgical robot for SPS with dynamic vision field control, the endoscope view being manipulated by a master controller. The prototype robot consisted of a positioning and sheath manipulator (6 DOF) for vision field control, and dual tool tissue manipulators (gripping: 5DOF, cautery: 3DOF). Feasibility of the robot was demonstrated in vitro. The "cut and vision field control" (using tool manipulators) is suitable for precise cutting tasks in risky areas while a "cut by vision field control" (using a vision field control manipulator) is effective for rapid macro cutting of tissues. A resection task was accomplished using a combination of both methods.
Testing predictions of the quantum landscape multiverse 1: the Starobinsky inflationary potential
NASA Astrophysics Data System (ADS)
Di Valentino, Eleonora; Mersini-Houghton, Laura
2017-03-01
The 2015 Planck data release has placed tight constraints on the allowed class of inflationary models. The current data favors concave downwards inflationary potentials while offering interesting hints on possible deviations from the standard picture of CMB perturbations. We here test the predictions of the theory of the origin of the universe from the landscape multiverse, against the most recent Planck data, for the case of concave downwards inflationary potentials, such as the Starobinsky model of inflation. By considering the quantum entanglement correction of the multiverse, we can place a lower limit on the local `SUSY breaking' scale b > 1.2 × 107 GeV at 95% c.l. from Planck TT+lowTEB. We find that this limit is consistent with the range for b that allows the landscape multiverse to explain a serie of anomalies present in the current data.
NASA Astrophysics Data System (ADS)
Gallagher, John A.; Liu, Tieqi; Lynch, Christopher S.
2013-02-01
The effect of a bias stress induced phase transformation on the large field dielectric loss in [001] cut and poled single crystal stack actuators of (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT, x = 32) was experimentally characterized. Dielectric loss was observed to increase with compressive preload and electric field amplitude. The dielectric loss was determined by measuring the area within electric displacement vs. electric field hysteresis loops and the measured area was expressed in terms of an effective loss tangent. This approach matches the measured area within the hysteresis loop to an equivalent area ellipse in which the electric displacement lags the electric field by an amount, delta, under sinusoidal loading. The results collapse the measured loss as a function of bias stress and electric field amplitude reasonably close to a single curve. The measured dielectric loss behavior was attributed to the compressive stress preload driving a partial phase transformation from rhombohedral to orthorhombic and the electric field driving the reverse phase transformation from the stress induced orthorhombic phase to the zero stress rhombohedral phase. When the compressive bias stress partially or fully drives this phase transformation, the dielectric loss under unipolar electric field loading increases. This work is focused on quasi-static measurements. The large field dielectric loss is anticipated to be a function of frequency and temperature.
Zhou, Jingyu; Tian, Shulin; Yang, Chenglin
2014-01-01
Few researches pay attention to prediction about analog circuits. The few methods lack the correlation with circuit analysis during extracting and calculating features so that FI (fault indicator) calculation often lack rationality, thus affecting prognostic performance. To solve the above problem, this paper proposes a novel prediction method about single components of analog circuits based on complex field modeling. Aiming at the feature that faults of single components hold the largest number in analog circuits, the method starts with circuit structure, analyzes transfer function of circuits, and implements complex field modeling. Then, by an established parameter scanning model related to complex field, it analyzes the relationship between parameter variation and degeneration of single components in the model in order to obtain a more reasonable FI feature set via calculation. According to the obtained FI feature set, it establishes a novel model about degeneration trend of analog circuits' single components. At last, it uses particle filter (PF) to update parameters for the model and predicts remaining useful performance (RUP) of analog circuits' single components. Since calculation about the FI feature set is more reasonable, accuracy of prediction is improved to some extent. Finally, the foregoing conclusions are verified by experiments.
Testing non-standard inflationary models with the cosmic microwave background
NASA Astrophysics Data System (ADS)
Landau, Susana J.
2015-03-01
The emergence of the seeds of cosmic structure from an isotropic and homogeneuous universe has not been clearly explained by the standard version of inflationary models. We review a proposal that attempts to deal with this problem by introducing "the self induced collapse hypothesis". As a consequence of this modification of standard inflationary scenarios, the predicted primordial power spectrum and the CMB spectrum are modified. We show the results of statistical analyses comparing the predictions of these models with recent CMB observations and the matter power spectrum from galaxy surveys.
Non-gaussian inflationary shapes in G{sup 3} theories beyond Horndeski
Fasiello, Matteo; Renaux-Petel, Sébastien E-mail: srenaux@lpthe.jussieu.fr
2014-10-01
We consider the possible signatures of a recently introduced class of healthy theories beyond Horndeski models on higher-order correlators of the inflationary curvature fluctuation. Despite the apparent large number and complexity of the cubic interactions, we show that the leading-order bispectrum generated by the Generalized Horndeski (also called G{sup 3}) interactions can be reduced to a linear combination of two well known k-inflationary shapes. We conjecture that said behavior is not an accident of the cubic order but a consequence dictated by the requirements on the absence of Ostrogradski instability, the general covariance and the linear dispersion relation in these theories.
Is there scale-dependent bias in single-field inflation?
De Putter, Roland; Doré, Olivier; Green, Daniel E-mail: Olivier.P.Dore@jpl.nasa.gov
2015-10-01
Scale-dependent halo bias due to local primordial non-Gaussianity provides a strong test of single-field inflation. While it is universally understood that single-field inflation predicts negligible scale-dependent bias compared to current observational uncertainties, there is still disagreement on the exact level of scale-dependent bias at a level that could strongly impact inferences made from future surveys. In this paper, we clarify this confusion and derive in various ways that there is exactly zero scale-dependent bias in single-field inflation. Much of the current confusion follows from the fact that single-field inflation does predict a mode coupling of matter perturbations at the level of f{sub NL}{sup local}; ≈ −5/3, which naively would lead to scale-dependent bias. However, we show explicitly that this mode coupling cancels out when perturbations are evaluated at a fixed physical scale rather than fixed coordinate scale. Furthermore, we show how the absence of scale-dependent bias can be derived easily in any gauge. This result can then be incorporated into a complete description of the observed galaxy clustering, including the previously studied general relativistic terms, which are important at the same level as scale-dependent bias of order f{sub NL}{sup local} ∼ 1. This description will allow us to draw unbiased conclusions about inflation from future galaxy clustering data.
Electrically controlling single-spin qubits in a continuous microwave field
Laucht, Arne; Muhonen, Juha T.; Mohiyaddin, Fahd A.; Kalra, Rachpon; Dehollain, Juan P.; Freer, Solomon; Hudson, Fay E.; Veldhorst, Menno; Rahman, Rajib; Klimeck, Gerhard; Itoh, Kohei M.; Jamieson, David N.; McCallum, Jeffrey C.; Dzurak, Andrew S.; Morello, Andrea
2015-01-01
Large-scale quantum computers must be built upon quantum bits that are both highly coherent and locally controllable. We demonstrate the quantum control of the electron and the nuclear spin of a single 31P atom in silicon, using a continuous microwave magnetic field together with nanoscale electrostatic gates. The qubits are tuned into resonance with the microwave field by a local change in electric field, which induces a Stark shift of the qubit energies. This method, known as A-gate control, preserves the excellent coherence times and gate fidelities of isolated spins, and can be extended to arbitrarily many qubits without requiring multiple microwave sources. PMID:26601166
Quantum Otto engine of a two-level atom with single-mode fields.
Wang, Jianhui; Wu, Zhaoqi; He, Jizhou
2012-04-01
We establish a quantum Otto engine (QOE) of a two-level atom, which is confined in a one-dimensional (1D) harmonic trap and is coupled to single-mode radiation fields. Besides two adiabatic processes, the QOE cycle consists of two isochoric processes, along one of which the two-level atom as the working substance interacts with a single-mode radiation field. Based on the semigroup approach, we derive the time for completing any adiabatic process and then present a performance analysis of the heat engine model. Furthermore, we generalize the results to the performance optimization for a QOE of a single two-level atom trapped in a 1D power-law potential. Our result shows that the efficiency at maximum power output is dependent on the trap exponent θ but is independent of the energy spectrum index σ.
Quantum Otto engine of a two-level atom with single-mode fields
NASA Astrophysics Data System (ADS)
Wang, Jianhui; Wu, Zhaoqi; He, Jizhou
2012-04-01
We establish a quantum Otto engine (QOE) of a two-level atom, which is confined in a one-dimensional (1D) harmonic trap and is coupled to single-mode radiation fields. Besides two adiabatic processes, the QOE cycle consists of two isochoric processes, along one of which the two-level atom as the working substance interacts with a single-mode radiation field. Based on the semigroup approach, we derive the time for completing any adiabatic process and then present a performance analysis of the heat engine model. Furthermore, we generalize the results to the performance optimization for a QOE of a single two-level atom trapped in a 1D power-law potential. Our result shows that the efficiency at maximum power output is dependent on the trap exponent θ but is independent of the energy spectrum index σ.
Iwasaki, Takayuki; Naruki, Wataru; Tahara, Kosuke; Makino, Toshiharu; Kato, Hiromitsu; Ogura, Masahiko; Takeuchi, Daisuke; Yamasaki, Satoshi; Hatano, Mutsuko
2017-02-28
The electric field inside semiconductor devices is a key physical parameter that determines the properties of the devices. However, techniques based on scanning probe microscopy are limited to sensing at the surface only. Here, we demonstrate the direct sensing of the internal electric field in diamond power devices using single nitrogen-vacancy (NV) centers. The NV center embedded inside the device acts as a nanoscale electric field sensor. We fabricated vertical diamond p-i-n diodes containing the single NV centers. By performing optically detected magnetic resonance measurements under reverse-biased conditions with an applied voltage of up to 150 V, we found a large splitting in the magnetic resonance frequencies. This indicated that the NV center senses the transverse electric field in the space-charge region formed in the i-layer. The experimentally obtained electric field values are in good agreement with those calculated by a device simulator. Furthermore, we demonstrate the sensing of the electric field in different directions by utilizing NV centers with different N-V axes. This direct and quantitative sensing method using an electron spin in a wide-band-gap material provides a way to monitor the electric field in operating semiconductor devices.
Self-Aligned Growth of Organic Semiconductor Single Crystals by Electric Field.
Kotsuki, Kenji; Obata, Seiji; Saiki, Koichiro
2016-01-19
We proposed a novel but facile method for growing organic semiconductor single-crystals via solvent vapor annealing (SVA) under electric field. In the conventional SVA growth process, nuclei of crystals appeared anywhere on the substrate and their crystallographic axes were randomly distributed. We applied electric field during the SVA growth of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) on the SiO2/Si substrate on which a pair of electrodes had been deposited beforehand. Real-time observation of the SVA process revealed that rodlike single crystals grew with their long axes parallel to the electric field and bridged the prepatterned electrodes. As a result, C8-BTBT crystals automatically formed a field effect transistor (FET) structure and the mobility reached 1.9 cm(2)/(V s). Electric-field-assisted SVA proved a promising method for constructing high-mobility single-crystal FETs at the desired position by a low-cost solution process.
Communication: Multiple atomistic force fields in a single enhanced sampling simulation
Hoang Viet, Man; Derreumaux, Philippe; Nguyen, Phuong H.
2015-07-14
The main concerns of biomolecular dynamics simulations are the convergence of the conformational sampling and the dependence of the results on the force fields. While the first issue can be addressed by employing enhanced sampling techniques such as simulated tempering or replica exchange molecular dynamics, repeating these simulations with different force fields is very time consuming. Here, we propose an automatic method that includes different force fields into a single advanced sampling simulation. Conformational sampling using three all-atom force fields is enhanced by simulated tempering and by formulating the weight parameters of the simulated tempering method in terms of the energy fluctuations, the system is able to perform random walk in both temperature and force field spaces. The method is first demonstrated on a 1D system and then validated by the folding of the 10-residue chignolin peptide in explicit water.
Fluorescence modulation in single CdSe quantum dots by moderate applied electric fields
LeBlanc, Sharonda J.; McClanahan, Mason R.; Moyer, Tully; Moyer, Patrick J.; Jones, Marcus
2014-01-21
Single molecule time-resolved fluorescence spectroscopy of CdSe/ZnS core-shell quantum dots (QDs) under the influence of moderate applied electric fields reveals distributed emission from states which are neither fully on nor off and pronounced changes in the excited state decay. The data suggest that a 54 kV/cm applied electric field causes small perturbations to the QD surface charge distribution, effectively increasing the surface trapping probability and resulting in the appearance of gray states. We present simultaneous blinking and fluorescence decay results for two sets of QDs, with and without an applied electric field. Further kinetic modeling analysis suggests that a single trapped charged cannot be responsible for a blinking off event.
Field-effect modulation of Seebeck coefficient in single PbSe nanowires.
Liang, Wenjie; Hochbaum, Allon I; Fardy, Melissa; Rabin, Oded; Zhang, Minjuan; Yang, Peidong
2009-04-01
In this Letter, we present a novel strategy to control the thermoelectric properties of individual PbSe nanowires. Using a field-effect gated device, we were able to tune the Seebeck coefficient of single PbSe nanowires from 64 to 193 microV x K(-1). This direct electrical field control of sigma and S suggests a powerful strategy for optimizing ZT in thermoelectric devices. These results represent the first demonstration of field-effect modulation of the thermoelectric figure of merit in a single semiconductor nanowire. This novel strategy for thermoelectric property modulation could prove especially important in optimizing the thermoelectric properties of semiconductors where reproducible doping is difficult to achieve.
Field emission from a single carbon nanofiber at sub 100 nm gap
NASA Astrophysics Data System (ADS)
Sim, H. S.; Lau, S. P.; Ang, L. K.; You, G. F.; Tanemura, M.; Yamaguchi, K.; Zamri, M.; Yusop, M.
2008-07-01
The authors report the electron field emission from a single carbon nanofiber (CNF) over a range of anode to CNF tip separations of 20-5500nm. Our results show that the field enhancement factor γ is associated with the electrode separation (S). The modified Miller equation is a reasonable empirical model to describe the behavior of γ, which varies with S over a large range of values. The γ approaches to an asymptotic value of 415 or 1 when S is very large or very small as compared to the length of the CNF, respectively. The maximum field emission current sustained by the single CNF without causing damage was estimated to be as high as 15μA.
Inflammable gas mixture detection with a single catalytic sensor based on the electric field effect.
Tong, Ziyuan; Tong, Min-Ming; Meng, Wen; Li, Meng
2014-04-08
This paper introduces a new way to analyze mixtures of inflammable gases with a single catalytic sensor. The analysis technology was based on a new finding that an electric field on the catalytic sensor can change the output sensitivity of the sensor. The analysis of mixed inflammable gases results from processing the output signals obtained by adjusting the electric field parameter of the catalytic sensor. For the signal process, we designed a group of equations based on the heat balance of catalytic sensor expressing the relationship between the output signals and the concentration of gases. With these equations and the outputs of different electric fields, the gas concentration in a mixture could be calculated. In experiments, a mixture of methane, butane and ethane was analyzed by this new method, and the results showed that the concentration of each gas in the mixture could be detected with a single catalytic sensor, and the maximum relative error was less than 5%.
Bowtie nano-aperture as interface between near-fields and a single-mode fiber.
Mivelle, M; Ibrahim, I A; Baida, F; Burr, G W; Nedeljkovic, D; Charraut, D; Rauch, J-Y; Salut, R; Grosjean, T
2010-07-19
We present the development and study of a single bowtie nano-aperture (BNA) at the end of a monomode optical fiber as an interface between near-fields/nano-optical objects and the fiber mode. To optimize energy conversion between BNA and the single fiber mode, the BNA is opened at the apex of a specially designed polymer fiber tip which acts as an efficient mediator (like a horn optical antenna) between the two systems. As a first application, we propose to use our device as polarizing electric-field nanocollector for scanning near-field optical microscopy (SNOM). However, this BNA-on-fiber probe may also find applications in nanolithography, addressing and telecommunications as well as in situ biological and chemical probing and trapping.
Single-molecule imaging of cell surfaces using near-field nanoscopy.
Hinterdorfer, Peter; Garcia-Parajo, Maria F; Dufrêne, Yves F
2012-03-20
Living cells use surface molecules such as receptors and sensors to acquire information about and to respond to their environments. The cell surface machinery regulates many essential cellular processes, including cell adhesion, tissue development, cellular communication, inflammation, tumor metastasis, and microbial infection. These events often involve multimolecular interactions occurring on a nanometer scale and at very high molecular concentrations. Therefore, understanding how single-molecules localize, assemble, and interact on the surface of living cells is an important challenge and a difficult one to address because of the lack of high-resolution single-molecule imaging techniques. In this Account, we show that atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM) provide unprecedented possibilities for mapping the distribution of single molecules on the surfaces of cells with nanometer spatial resolution, thereby shedding new light on their highly sophisticated functions. For single-molecule recognition imaging by AFM, researchers label the tip with specific antibodies or ligands and detect molecular recognition signals on the cell surface using either adhesion force or dynamic recognition force mapping. In single-molecule NSOM, the tip is replaced by an optical fiber with a nanoscale aperture. As a result, topographic and optical images are simultaneously generated, revealing the spatial distribution of fluorescently labeled molecules. Recently, researchers have made remarkable progress in the application of near-field nanoscopy to image the distribution of cell surface molecules. Those results have led to key breakthroughs: deciphering the nanoscale architecture of bacterial cell walls; understanding how cells assemble surface receptors into nanodomains and modulate their functional state; and understanding how different components of the cell membrane (lipids, proteins) assemble and communicate to confer efficient functional
NASA Astrophysics Data System (ADS)
AL-Baradi, Ateyyah M.; Mykhaylyk, Oleksandr O.; Blythe, Harry J.; Geoghegan, Mark
2011-03-01
We consider the effect of applied magnetic fields on the diffusion of single dextran molecules labeled with fluorescein isothiocyanate within a ferrogel [a composite of magnetite nanoparticles in a poly(methacrylic acid) hydrogel] using fluorescence correlation spectroscopy. We show that the mesh size of the ferrogel is controlled by the applied magnetic field, B, and scales as exp ( { - √[4]{{ξ ^3 B^2 /2μ _0 k_B T}}}), where ξ is a correlation length, μ0 the magnetic constant, kB the Boltzmann constant, and T is the absolute temperature. The diffusion coefficient of the dextran can be modeled with a simple Stokes-Einstein law, containing the same scaling behavior with magnetic field as the swelling of the hydrogel. Furthermore, the magnetic field-dependent release of dextran from the hydrogel is also controlled by the same relationship. The samples were characterized by small angle x-ray scattering (SAXS) and magnetometry experiments. Magnetic hysteresis loops from these ferrogels and zero field cooled/field cooled measurements reveal single domain ferromagnetic behavior at room temperature with a similar coercivity for both as-prepared and fully swollen ferrogels, and for increasing magnetic nanoparticle concentration. SAXS experiments, such as the hysteresis loops, show that magnetite does not aggregate in these gels.
Al-Baradi, Ateyyah M; Mykhaylyk, Oleksandr O; Blythe, Harry J; Geoghegan, Mark
2011-03-07
We consider the effect of applied magnetic fields on the diffusion of single dextran molecules labeled with fluorescein isothiocyanate within a ferrogel [a composite of magnetite nanoparticles in a poly(methacrylic acid) hydrogel] using fluorescence correlation spectroscopy. We show that the mesh size of the ferrogel is controlled by the applied magnetic field, B, and scales as exp(-(4)√ξ(3)B(2)/2μ(0)k(B)T), where ξ is a correlation length, μ(0) the magnetic constant, k(B) the Boltzmann constant, and T is the absolute temperature. The diffusion coefficient of the dextran can be modeled with a simple Stokes-Einstein law, containing the same scaling behavior with magnetic field as the swelling of the hydrogel. Furthermore, the magnetic field-dependent release of dextran from the hydrogel is also controlled by the same relationship. The samples were characterized by small angle x-ray scattering (SAXS) and magnetometry experiments. Magnetic hysteresis loops from these ferrogels and zero field cooled∕field cooled measurements reveal single domain ferromagnetic behavior at room temperature with a similar coercivity for both as-prepared and fully swollen ferrogels, and for increasing magnetic nanoparticle concentration. SAXS experiments, such as the hysteresis loops, show that magnetite does not aggregate in these gels.
Vectorial nanoscale mapping of optical antenna fields by single molecule dipoles.
Singh, Anshuman; Calbris, Gaëtan; van Hulst, Niek F
2014-08-13
Optical nanoantennas confine light on the nanoscale, enabling strong light-matter interactions and ultracompact optical devices. Such confined nanovolumes of light have nonzero field components in all directions (x, y, and z). Unfortunately mapping of the actual nanoscale field vectors has so far remained elusive, though antenna hotspots have been explored by several techniques. In this paper, we present a novel method to probe all three components of the local antenna field. To this end a resonant nanoantenna is fabricated at the vertex of a scanning tip. Next, the nanoantenna is deterministically scanned in close proximity to single fluorescent molecules, whose fixed excitation dipole moment reads out the local field vector. With nanometer molecular resolution, we distinctly map x-, y-, and z-field components of the dipole antenna, i.e. a full vectorial mode map, and show good agreement with full 3D FDTD simulations. Moreover, the fluorescence polarization maps the localized coupling, with emission through the longitudinal antenna mode. Finally, the resonant antenna probe is used for single molecule imaging with 40 nm fwhm response function. The total fluorescence enhancement is 7.6 times, while out-of-plane molecules, almost undetectable in far-field, are made visible by the strong antenna z-field with a fluorescence enhancement up to 100 times. Interestingly, the apparent position of molecules shifts up to 20 nm depending on their orientation. The capability to resolve orientational information on the single molecule level makes the scanning resonant antenna an ideal tool for extreme resolution bioimaging.
Direct simulation of single bubble motion under vertical magnetic field: Paths and wakes
NASA Astrophysics Data System (ADS)
Zhang, Jie; Ni, Ming-Jiu
2014-10-01
Motion of single Ar bubbles rising in GaInSn under vertical magnetic fields is studied numerically using a volume-of-fluid method and adaptive mesh refinement technique for two-phase interface treatment; a consistent and conservative scheme calculates induced current density and Lorentz force. Numerical results are compared with published experimental data [C. Zhang, S. Eckert, and G. Gerbeth, "Experimental study of single bubble motion in a liquid metal column exposed to a DC magnetic field," Int. J. Multiphase Flow 31, 824-842 (2005)], where bubble diameters range from 2.5 to 6.4 mm, producing Reynolds numbers that vary between 2000 and 4000. Maximum experimental magnetic field strength was set to 0.3 T because of experimental restrictions, although we increased it to 0.5 T for firm conclusions. Apart from terminal rising velocity comparisons, we focused on variations in bubble motion paths and wake structures under magnetic fields, which cannot be observed experimentally because liquid metal is opaque. Magnetic field effects on bubble trajectory are exerted through vortex structure modification, which reinforced the conjecture that path instability is mainly attributed to wake instability. In bubble motion without magnetic fields, vortex threads in the bubble wake wrap around each other while vortex filaments incline parallel to the field with increasing magnetic intensity. Additionally, high magnetic fields will induce secondary bubble path instabilities, which contribute to the high Reynolds number flow that instabilities develop around the bubble, producing an asymmetrical Lorentz force distribution. This instability vanishes under higher magnetic intensities because flow instability is suppressed. Rising bubble aspect ratios decrease considerably under magnetic fields and may also contribute to smaller vorticities at the bubble surface. A close relationship between fluctuations in rising velocity and shape variations is found.
Chen, Quan; Marble, Andrew E; Colpitts, Bruce G; Balcom, Bruce J
2005-08-01
When fluid saturated porous media are subjected to an applied uniform magnetic field, an internal magnetic field, inside the pore space, is induced due to magnetic susceptibility differences between the pore-filling fluid and the solid matrix. The microscopic distribution of the internal magnetic field, and its gradients, was simulated based on the thin-section pore structure of a sedimentary rock. The simulation results were verified experimentally. We show that the 'decay due to diffusion in internal field' magnetic resonance technique may be applied to measure the pore size distribution in partially saturated porous media. For the first time, we have observed that the internal magnetic field and its gradients in porous rocks have a Lorentzian distribution, with an average gradient value of zero. The Lorentzian distribution of internal magnetic field arises from the large susceptibility contrast and an intrinsic disordered pore structure in these porous media. We confirm that the single exponential magnetic resonance free induction decay commonly observed in fluid saturated porous media arises from a Lorentzian internal field distribution. A linear relationship between the magnetic resonance linewidth, and the product of the susceptibility difference in the porous media and the applied magnetic field, is observed through simulation and experiment.
Electric field effect on (6,0) zigzag single-walled aluminum nitride nanotube.
Baei, Mohammad T; Peyghan, Ali Ahmadi; Moghimi, Masoumeh
2012-09-01
Structural, electronic, and electrical responses of the H-capped (6,0) zigzag single-walled aluminum nitride nanotube was studied under the parallel and transverse electric fields with strengths 0-140 × 10(-4) a.u. by using density functional calculations. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using a locally modified version of the GAMESS electronic structure program. The dipole moments, atomic charge variations, and total energy of the (6,0) zigzag AlNNT show increases with increase in the applied external electric field strengths. The length, tip diameters, electronic spatial extent, and molecular volume of the nanotube do not significantly change with increasing electric field strength. The energy gap of the nanotube decreases with increases of the electric field strength and its reactivity is increased. Increase of the ionization potential, electron affinity, chemical potential, electrophilicity, and HOMO and LUMO in the nanotube with increase of the applied parallel electric field strengths shows that the parallel field has a much stronger interaction with the nanotube with respect to the transverse electric field strengths. Analysis of the parameters indicates that the properties of AlNNTs can be controlled by the proper external electric field.
Gilding the Outcome by Tarnishing the Past: Inflationary Biases in Retrospective Pretests
ERIC Educational Resources Information Center
Taylor, Paul J.; Russ-Eft, Darlene F.; Taylor, Hazel
2009-01-01
We tested for inflationary bias introduced through retrospective pretests by analyzing traditional pretest, retrospective pretest, and posttest evaluation data collected on a first-line supervisory leadership training program, involving 196 supervisors and their subordinates, across 17 organizational settings. Retrospective pretest ratings by both…
Inflationary generalized Chaplygin gas and dark energy in light of the Planck and BICEP2 experiments
NASA Astrophysics Data System (ADS)
Dinda, Bikash R.; Kumar, Sumit; Sen, Anjan A.
2014-10-01
In this work, we study an inflationary scenario in the presence of generalized Chaplygin gas (GCG). We show that in Einstein gravity, GCG is not a suitable candidate for inflation; but in a five-dimensional brane-world scenario, it can work as a viable inflationary model. We calculate the relevant quantities such as ns, r, and As related to the primordial scalar and tensor fluctuations, and using their recent bounds from Planck and BICEP2, we constrain the model parameters as well as the five-dimensional Planck mass. But as a slow-roll inflationary model with a power-law type scalar primordial power spectrum, GCG as an inflationary model cannot resolve the tension between results from BICEP2 and Planck with a concordance ΛCDM Universe. We show that by going beyond the concordance ΛCDM model and incorporating more general dark energy behavior, we may ease this tension. We also obtain the constraints on the ns and r and the GCG model parameters using Planck+WP +BICEP2 data considering the CPL dark energy behavior.
NASA Astrophysics Data System (ADS)
Barseghyan, M. G.
2016-11-01
The intraband optical absorption in GaAs/Ga0.7Al0.3As two-dimensional single quantum ring is investigated. Considering the combined effects of hydrostatic pressure and intense laser field the energy of the ground and few excited states has been found using the effective mass approximation and exact diagonalization technique. The energies of these states and the corresponding threshold energy of the intraband optical transitions are examined as a function of hydrostatic pressure for the different values of the laser field parameter. We also investigated the dependencies of the intraband optical absorption coefficient as a function of incident photon energy for different values of hydrostatic pressure and laser field parameter. It is found that the effects of hydrostatic pressure and intense laser field lead to redshift and blueshift of the intraband optical spectrum respectively.
Field emission of carbon quantum dots synthesized from a single organic solvent.
Liu, Xiahui; Yang, Bingjun; Yang, Juan; Yu, Shengxue; Chen, Jiangtao
2016-11-04
In this paper, a facile synthesis of carbon quantum dots (CQDs) and its field emission performance are reported. The CQDs are prepared from a single N, N-dimethylformamide acting as carbon and nitrogen-doping sources simultaneously. The CQDs are investigated by photoluminescence, transmission electron microscopy and x-ray photoelectron spectroscopy. The CQDs have an average size of 3 nm and are doped with N atoms. CQD dispersion shows strong fluorescence under UV illumination. For the first time, the field emission behavior of CQDs coated on Si substrate is studied. As a candidate of cold cathode, the CQDs display good field emission performance. The CQD emitter reaches the current density of 1.1 mA cm(-2) at 7.0 V μm(-1) and exhibits good long-term emission stability, suggesting promising application in field emission devices.
Comparing Hall Effect and Field Effect Measurements on the Same Single Nanowire.
Hultin, Olof; Otnes, Gaute; Borgström, Magnus T; Björk, Mikael; Samuelson, Lars; Storm, Kristian
2016-01-13
We compare and discuss the two most commonly used electrical characterization techniques for nanowires (NWs). In a novel single-NW device, we combine Hall effect and back-gated and top-gated field effect measurements and quantify the carrier concentrations in a series of sulfur-doped InP NWs. The carrier concentrations from Hall effect and field effect measurements are found to correlate well when using the analysis methods described in this work. This shows that NWs can be accurately characterized with available electrical methods, an important result toward better understanding of semiconductor NW doping.
NASA Astrophysics Data System (ADS)
Wu, Chen-Wu; Shu, Yong-Hua; Xie, Ji-Jia; Jiang, Jian-Zheng; Fan, Jing
2017-02-01
A concept was developed to inversely estimate the near-field temperature as well as the surface heat flux for the transient heat conduction problem with boundary condition of the unknown heat flux. The mathematical formula was derived for the inverse estimation of the near-field temperature and surface heat flux via a single point temperature measurement. The experiments were carried out in a vacuum chamber and the theoretically predicted temperatures were justified in specific positions. The inverse estimation principle was validated and the estimation deviation was evaluated for the present configuration.
A single-step method for RNA isolation from tropical crops in the field
Breitler, J.-C.; Campa, C.; Georget, F.; Bertrand, B.; Etienne, H.
2016-01-01
The RNAzol RT reagent was used to provide pure RNA from human cells. We develop a protocol using RNAzol RT reagent to extract pure RNA from plants tissues and demonstrate that this RNA extraction method works not only at room temperature but also at elevated temperatures and provides the simplest and most effective single-step method to extract pure and undegraded RNA directly from tropical plants in the field. RNA extraction directly in a complex field environment opens up the way for studying gene-environment interactions at transcriptome level to decipher the complex regulatory network involved in multiple-stress responses. PMID:27922073
Triple unification of inflation, dark matter, and dark energy using a single field
Liddle, Andrew R.; Pahud, Cedric; Urena-Lopez, L. Arturo
2008-06-15
We construct an explicit scenario whereby the same material driving inflation in the early universe can comprise dark matter in the present universe, using a simple quadratic potential. Following inflation and preheating, the density of inflaton/dark matter particles is reduced to the observed level by a period of thermal inflation, of a duration already invoked in the literature for other reasons. Within the context of the string landscape, one can further argue for a nonzero vacuum energy of this field, thus unifying inflation, dark matter, and dark energy into a single fundamental field.
Nanoscale magnetic field mapping with a single spin scanning probe magnetometer
Rondin, L.; Tetienne, J.-P.; Spinicelli, P.; Roch, J.-F.; Jacques, V.; Dal Savio, C.; Karrai, K.; Dantelle, G.; Thiaville, A.; Rohart, S.
2012-04-09
We demonstrate quantitative magnetic field mapping with nanoscale resolution, by applying a lock-in technique on the electron spin resonance frequency of a single nitrogen-vacancy defect placed at the apex of an atomic force microscope tip. In addition, we report an all-optical magnetic imaging technique which is sensitive to large off-axis magnetic fields, thus extending the operation range of diamond-based magnetometry. Both techniques are illustrated by using a magnetic hard disk as a test sample. Owing to the non-perturbing and quantitative nature of the magnetic probe, this work should open up numerous perspectives in nanomagnetism and spintronics.
Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields
NASA Astrophysics Data System (ADS)
Noe, G. Timothy; Katayama, Ikufumi; Katsutani, Fumiya; Allred, James J.; Horowitz, Jeffrey A.; Sullivan, David M.; Zhang, Qi; Sekiguchi, Fumiya; Woods, Gary L.; Hoffmann, Matthias C.; Nojiri, Hiroyuki; Takeda, Jun; Kono, Junichiro
2016-12-01
We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.
NASA Astrophysics Data System (ADS)
Liu, Shuhong
The search for low-cost, large area, flexible devices has led to a remarkable increase in the research and development of organic semiconductors. Single-crystal organic field-effect transistors (OFETs) are ideal device structures for studying fundamental science associated with charge transport in organic materials and have demonstrated high mobility and outstanding electrical characteristics. For example, an exceptionally high carrier mobility of 20 cm2/Vs has been demonstrated for rubrene single crystal field effect transistors. However, it remains a technical challenge to integrate single-crystal devices into practical electronic applications. A key difficulty is that organic single-crystal devices are usually fabricated one device at a time by handpicking a single crystal and placing it onto the device substrate. This makes it impossible to mass-produce at high density with reasonable throughput. Therefore, there is a great need for a high-throughput method for depositing large arrays of organic semiconductor single crystals directly onto device structures. In this dissertation, I develop several approaches towards realizing this goal. The first approach is a solution-processing technique, which relies on solvent wetting and de-wetting on substrates with patterned wettability to selectively direct the deposition or removal of organic crystals. The assembly of different organic crystals over centimeter-squared areas on Au, SiO 2 and flexible plastic substrates is demonstrated. By designing line features on the substrate, alignment of needle-like crystals is also achieved. As a demonstration of the potential application of this approach, arrays of organic single crystal FETs are fabricated by patterning organic single crystals directly onto and between transistor source and drain electrodes. Besides organic single crystals, this self-assembly strategy is also applicable for patterning other objects such as metallic nanowires. In the second technique, organic
Magnetic-field-induced diameter-selective synthesis of single-walled carbon nanotubes
NASA Astrophysics Data System (ADS)
Su, Yanjie; Zhang, Yaozhong; Wei, Hao; Zhang, Liling; Zhao, Jiang; Yang, Zhi; Zhang, Yafei
2012-02-01
We report a facile and scalable approach to synthesize single-walled carbon nanotubes (SWNTs) with selected diameter distribution by applying a magnetic field perpendicular to the electric field in the arc plasma region. It is found that this magnetic field-induced diameter-selectivity strategy enables the control of the SWNTs with different diameter distributions in different regions, and the diameter-selective efficiency could be enhanced by modifying the direction of magnetic field. Our results indicate that the motions of the catalysts with different particle sizes, positive carbon ions and electrons are significantly influenced by the magnetic field and electromagnetic force, resulting in the different nucleation and growth processes of SWNTs due to the collective interactions between the magnetic field and arc plasma. This approach would enable a viable route towards the synthesis of SWNTs with desired diameter through the tuning of arc parameters in the arc discharge process.We report a facile and scalable approach to synthesize single-walled carbon nanotubes (SWNTs) with selected diameter distribution by applying a magnetic field perpendicular to the electric field in the arc plasma region. It is found that this magnetic field-induced diameter-selectivity strategy enables the control of the SWNTs with different diameter distributions in different regions, and the diameter-selective efficiency could be enhanced by modifying the direction of magnetic field. Our results indicate that the motions of the catalysts with different particle sizes, positive carbon ions and electrons are significantly influenced by the magnetic field and electromagnetic force, resulting in the different nucleation and growth processes of SWNTs due to the collective interactions between the magnetic field and arc plasma. This approach would enable a viable route towards the synthesis of SWNTs with desired diameter through the tuning of arc parameters in the arc discharge process
NASA Astrophysics Data System (ADS)
Durach, Maxim; Rusina, Anastasia; Kling, Matthias F.; Stockman, Mark I.
2011-08-01
We predict a dynamic metallization effect where an ultrafast (single-cycle) optical pulse with a ≲1V/Å field causes plasmonic metal-like behavior of a dielectric film with a few-nm thickness. This manifests itself in plasmonic oscillations of polarization and a significant population of the conduction band evolving on a ˜1fs time scale. These phenomena are due to a combination of both adiabatic (reversible) and diabatic (for practical purposes irreversible) pathways.
Durach, Maxim; Rusina, Anastasia; Kling, Matthias F; Stockman, Mark I
2011-08-19
We predict a dynamic metallization effect where an ultrafast (single-cycle) optical pulse with a ≲1 V/Å field causes plasmonic metal-like behavior of a dielectric film with a few-nm thickness. This manifests itself in plasmonic oscillations of polarization and a significant population of the conduction band evolving on a ~1 fs time scale. These phenomena are due to a combination of both adiabatic (reversible) and diabatic (for practical purposes irreversible) pathways.
Near-field acoustic characteristics of a single-rotor propfan
NASA Technical Reports Server (NTRS)
Bartel, H. W.; Swift, G.
1989-01-01
The near-field noise characteristics of the SR-7L, an eight-blade, single-rotor, wing-mounted, tractor propfan have been determined. It is found that the noise is dominated by discrete tones, usually at the first order (and occasionally at the second or third order) of the blade-passage frequency. The highest noise levels were noted at conditions of high tip helical speeds and high dynamic pressures.
Phase retrieval from a single near-field diffraction pattern with a large Fresnel number.
Li, Enrong; Liu, Yijin; Liu, Xiaosong; Zhang, Kai; Wang, Zhili; Hong, Youli; Yuan, Qingxi; Huang, Wanxia; Marcelli, Augusto; Zhu, Peiping; Wu, Ziyu
2008-11-01
A new method of phase retrieval from a single near-field diffraction image with a large Fresnel number is presented and discussed. This method requires only the oversampled diffraction pattern without any other information such as the object envelope. Moreover, we show that the combination with a fast computational method is possible when the linear oversampling ratio is an integer. Numerical simulations are also presented, showing that the method works well with noisy data.
ELF-magnetic field induced effects on the bioelectric activity of single neurone cells
NASA Astrophysics Data System (ADS)
Azanza, Maria J.; del Moral, A.
1998-01-01
The membrane bioelectric activity recorded from single neurones is dramatically modified under applied extremely low frequency magnetic fields (ELF-MF) of 50 Hz and 1-15 mT peak intensity. In ≌27% of the neurones studied a firing rhythm is generated for ≌7 mT, which resembles synchronous oscillations activity. The possibility that ELF-MF could generate neuronal networks synchrony firing does exist as an explanatory physical model shows.
NASA Astrophysics Data System (ADS)
Marks, Michael; Kroupa, Pavel
2011-11-01
The galactic field's late-type stellar single and binary populations are calculated on the observationally well-constrained supposition that all stars form as binaries with invariant properties in discrete star formation events. A recently developed tool (Marks, Kroupa & Oh) is used to evolve the binary star distributions in star clusters for a few million years until an equilibrium situation is achieved which has a particular mixture of single and binary stars. On cluster dissolution the population enters the galactic field with these characteristics. The different contributions of single stars and binaries from individual star clusters, which are selected from a power-law-embedded star cluster mass function, are then added up. This gives rise to integrated galactic field binary distribution functions (IGBDFs), resembling a galactic field's stellar content (dynamical population synthesis). It is found that the binary proportion in the galactic field of a galaxy is larger the lower the minimum cluster mass, Mecl, min, the lower the star formation rate, SFR, the steeper the embedded star cluster mass function (described by index β) and the larger the typical size of forming star clusters in the considered galaxy. In particular, period, mass ratio and eccentricity IGBDFs for the Milky Way (MW) are modelled using Mecl, min= 5 M⊙, SFR = 3 M⊙ yr-1 and β= 2 which are justified by observations. For rh≈ 0.1-0.3 pc, the half-mass radius of an embedded cluster, the aforementioned theoretical IGBDFs agree with independently observed distributions, suggesting that the individual discrete star formation events in the MW generally formed compact star clusters. Of all late-type binaries, 50 per cent stem from Mecl≲ 300 M⊙ clusters, while 50 per cent of all single stars were born in Mecl≳ 104 M⊙ clusters. Comparison of the G-dwarf and M-dwarf binary populations indicates that the stars are formed in mass-segregated clusters. In particular, it is pointed out that
Aligned Single Wall Carbon Nanotube Polymer Composites Using an Electric Field
NASA Technical Reports Server (NTRS)
Park, Cheol; Wiklinson, John; Banda, Sumanth; Ounaies, Zoubeida; Wise, Kristopher E.; Sauti, Godfrey; Lillehei, Peter T.; Harrison, Joycelyn S.
2005-01-01
While high shear alignment has been shown to improve the mechanical properties of single wall carbon nanotubes (SWNT)-polymer composites, it is difficult to control and often results in degradation of the electrical and dielectric properties of the composite. Here, we report a novel method to actively align SWNTs in a polymer matrix, which allows for control over the degree of alignment of SWNTs without the side effects of shear alignment. In this process, SWNTs are aligned via field-induced dipolar interactions among the nanotubes under an AC electric field in a liquid matrix followed by immobilization by photopolymerization while maintaining the electric field. Alignment of SWNTs was controlled as a function of magnitude, frequency, and application time of the applied electric field. The degree of SWNT alignment was assessed using optical microscopy and polarized Raman spectroscopy and the morphology of the aligned nanocomposites was investigated by high resolution scanning electron microscopy. The structure of the field induced aligned SWNTs is intrinsically different from that of shear aligned SWNTs. In the present work, SWNTs are not only aligned along the field, but also migrate laterally to form thick, aligned SWNT percolative columns between the electrodes. The actively aligned SWNTs amplify the electrical and dielectric properties in addition to improving the mechanical properties of the composite. All of these properties of the aligned nanocomposites exhibited anisotropic characteristics, which were controllable by tuning the applied field conditions.
Shaped and Feedback-Controlled Excitation of Single Molecules in the Weak-Field Limit
2015-01-01
Coherent control uses tailored femtosecond pulse shapes to influence quantum pathways and drive a light-induced process toward a specific outcome. There has been a long-standing debate whether the absorption properties or the probability for population to remain in an excited state of a molecule can be influenced by the pulse shape, even if only a single photon is absorbed. Most such experiments are performed on many molecules simultaneously, so that ensemble averaging reduces the access to quantum effects. Here, we demonstrate systematic coherent control experiments on the fluorescence intensity of a single molecule in the weak-field limit. We demonstrate that a delay scan of interfering pulses reproduces the excitation spectrum of the molecule upon Fourier transformation, but that the spectral phase of a pulse sequence does not affect the transition probability. We generalize this result to arbitrary pulse shapes by performing the first closed-loop coherent control experiments on a single molecule. PMID:26706166
Magnetic field variations in the umbra of single sunspots during their passage across the solar disk
NASA Astrophysics Data System (ADS)
Zagainova, Iu. S.; Fainshtein, V. G.; Obridko, V. N.; Rudenko, G. V.
2016-12-01
Temporal variations of the maximum ( B max) and average (< B>) magnetic inductions, minimum ( α min) and average (< α>) inclination angles of the field lines to the radial direction from the center of the Sun, and areas of the sunspot umbra S in the umbra of single sunspots during their passage across the solar disk are investigated. The variation of the properties of single sunspots has been considered at different stages of their existence, i.e., during formation, the "quiet" period, and the disappearance stage. It has been found that, for the majority of the selected single sunspots, there is a positive correlation between B max and S and between and S defined at different times during the passage of sunspots across the solar disk. It is shown in this case that the nature of the dependence between the parameters α min and B max, α min and S, as well as between < α> and < B>, < α> and S, can vary from sunspot to sunspot, but for many sunspots the inclination angle of the field lines decreases on average with the growth of the sunspot umbra area and the field strength.
Attentional modulation of MT neurons with single or multiple stimuli in their receptive fields
Lee, Joonyeol; Maunsell, John H.R.
2010-01-01
Descriptions of how attention modulates neuronal responses suggest that the strength of its effects depends on stimulus conditions. Attention to an isolated stimulus in the receptive field of an individual neuron typically produces a moderate enhancement of the cell's response, but neuronal responses are often strongly modulated when attention is shifted between multiple stimuli that lie within the receptive field. However, previous reports have not compared these stimulus effects under equivalent conditions, so differences in task difficulty could have been responsible for much of the difference. Consequently, the quantitative effects of stimulus conditions have remained unknown, and it has not been possible to address the question of whether the differences that have been observed could be explained by a single mechanism. We measured the attentional modulation of the responses of 70 single neurons in area MT of two rhesus monkeys using a task design that kept attention stable across different stimulus configurations. We found that attentional modulation was indeed much stronger when more than one stimulus was within the receptive field. Nevertheless, the broad range of attentional modulations seen across the different conditions could be readily explained by single mechanism. The neurophysiological data from all stimulus conditions were well fit by a model in which attention acts through a response normalization mechanism (Lee and Maunsell, 2009). Collectively, these results validate previous impressions of the effects of stimulus configuration on attentional modulation, and add support to hypothesis that attention modulation depends on a response normalization mechanism. PMID:20181602
NASA Astrophysics Data System (ADS)
Maleknejad, A.; Sheikh-Jabbari, M. M.; Soda, J.
2013-07-01
small field models also have a potential minimum at φ≠0 which the system falls in at the end of inflation. A typical property of small field models is that a sufficient number of e-folds, requires a sub-Planckian inflaton initial value. For this reason they are called small field models. Natural inflation is an example of this type [12]. Hybrid inflation models: These models involve more than one scalar field while inflation is mainly driven by a single inflaton field ϕ. Inflaton starts from a large value rolling down until it reaches a bifurcation point, ϕ=ϕe, after which the field becomes unstable and undergoes a waterfall transition toward its global minimum. Its prime example is the Linde’s hybrid inflation model with the following potential [13] V(ϕ,χ)={λ}/{4}(+{1}/{2}g2ϕ2χ2+{1}/{2}m2ϕ2. During the initial inflationary phase the potential of the hybrid inflation is effectively described by a single field ϕ while inflation ends by a phase transition triggered by the presence of the second scalar field, the waterfall field χ. In other words, when the effective mass squared of a waterfall field becomes negative, the tachyonic instability makes waterfall field roll down toward the true vacuum state and the inflation suddenly ends.Number of e-folds Ne is given as Ne≃{M4}/{4λm2}ln({ϕ0}/{ϕe}), where ϕe={M}/{g} is the critical value of the inflaton below which, due to tachyonic instability, χ=0 becomes unstable and mχ2 gets negative. K-inflation: This is the prime example of models with non-canonical Kinetic term we discuss here. They are described by the action [14] S=∫d4x√{-g}({R}/{2}+P(φ,X)), where φ is a scalar field and X≔-{1}/{2}(. Here, P plays the rule of the effective pressure, while the energy density is given by ρ=2XP-P. Thus, the slow-roll parameter is given as ɛ={3XP}/{2XP-P}. The characteristic feature of these models is that in general they have a non-trivial sound speed cs2 for the propagation of perturbations (cf. our
NASA Astrophysics Data System (ADS)
Kumar, Avshish; Khan, Sunny; Zulfequar, M.; Harsh; Husain, Mushahid
2017-04-01
In this work, high-quality graphene has successfully been synthesized on copper (Cu) coated Silicon (Si) substrate at very large-area by plasma enhanced chemical vapor deposition system. This method is low cost and highly effective for synthesizing graphene relatively at low temperature of 600 °C. Electron microscopy images have shown that surface morphology of the grown samples is quite uniform consisting of single layered graphene (SLG) to few layered graphene (FLG). Raman spectra reveal that graphene has been grown with high-quality having negligible defects and the observation of G and G' peaks is also an indicative of stokes phonon energy shift caused due to laser excitation. Scanning probe microscopy image also depicts the synthesis of single to few layered graphene. The field emission characteristics of as-grown graphene samples were studied in a planar diode configuration at room temperature. The graphene samples were observed to be a good field emitter having low turn-on field, higher field amplification factor and long term emission current stability.
Quantitative 3D electromagnetic field determination of 1D nanostructures from single projection
Phatak, Charudatta; Knoop, Ludvig de; Houdellier, Florent; Gatel, Christophe; Hytch, Martin J.; Masseboeuf, Aurelien
2016-03-10
One-dimensional (1D) nanostructures have been regarded as the most promising building blocks for nanoelectronics and nanocomposite material systems as well as for alternative energy applications. Although they result in confinement of a material, their properties and interactions with other nanostructures are still very much three-dimensional (3D) in nature. In this work, we present a novel method for quantitative determination of the 3D electromagnetic fields in and around 1D nanostructures using a single electron wave phase image, thereby eliminating the cumbersome acquisition of tomographic data. Using symmetry arguments, we have reconstructed the 3D magnetic field of a nickel nanowire as well as the 3D electric field around a carbon nanotube field emitter, from one single projection. The accuracy of quantitative values determined here is shown to be a better fit to the physics at play than the value obtained by conventional analysis. Furthermore the 3D reconstructions can then directly be visualized and used in the design of functional 3D architectures built using 1D nanostructures.
Quantitative 3D electromagnetic field determination of 1D nanostructures from single projection
Phatak, Charudatta; Knoop, Ludvig de; Houdellier, Florent; ...
2016-03-10
One-dimensional (1D) nanostructures have been regarded as the most promising building blocks for nanoelectronics and nanocomposite material systems as well as for alternative energy applications. Although they result in confinement of a material, their properties and interactions with other nanostructures are still very much three-dimensional (3D) in nature. In this work, we present a novel method for quantitative determination of the 3D electromagnetic fields in and around 1D nanostructures using a single electron wave phase image, thereby eliminating the cumbersome acquisition of tomographic data. Using symmetry arguments, we have reconstructed the 3D magnetic field of a nickel nanowire as wellmore » as the 3D electric field around a carbon nanotube field emitter, from one single projection. The accuracy of quantitative values determined here is shown to be a better fit to the physics at play than the value obtained by conventional analysis. Furthermore the 3D reconstructions can then directly be visualized and used in the design of functional 3D architectures built using 1D nanostructures.« less
Quantitative 3D electromagnetic field determination of 1D nanostructures from single projection
Phatak, C.; Knoop, L. de; Houdellier, F.; Gatel, C.; Hÿtch, M. J.; Masseboeuf, A.
2016-05-01
One-dimensional (1D) nanostructures have been regarded as the most promising building blocks for nanoelectronics and nanocomposite material systems as well as for alternative energy applications. Although they result in confinement of a material, their properties and interactions with other nanostructures are still very much three-dimensional (3D) in nature. In this work, we present a novel method for quantitative determination of the 3D electromagnetic fields in and around 1D nanostructures using a single electron wave phase image, thereby eliminating the cumbersome acquisition of tomographic data. Using symmetry arguments, we have reconstructed the 3D magnetic field of a nickel nanowire as well as the 3D electric field around a carbon nanotube field emitter, from one single projection. The accuracy of quantitative values determined here is shown to be a better fit to the physics at play than the value obtained by conventional analysis. Moreover the 3D reconstructions can then directly be visualized and used in the design of functional 3D architectures built using 1D nanostructures.
NASA Astrophysics Data System (ADS)
Fujieda, Tadashi; Okai, Makoto; Tokumoto, Hiroshi
2008-04-01
We investigated the dependence of tip radius on the field emission energy spread of electrons emitted from clean single pentagons in individual multi-walled carbon nanotubes (MWNTs) in a wide range of total emission currents (10-2000 nA). We found that the full width at half maximum of the field emission energy distribution decreases in inverse proportion to the involution of the radius of curvature at a constant total emission current. This is because as the radius of curvature increases, the space between adjoining pentagons becomes wider, and therefore the stochastic Coulomb interactions between electrons emitted from adjoining pentagons become weaker. The full widths at half maximum of the field emission energy distributions of MWNTs with tip radii of 1.8-45.0 nm were 0.38-0.60 eV at a total emission current of 2000 nA.
Growth of carbon nanotube field emitters on single strand carbon fiber: a linear electron source
NASA Astrophysics Data System (ADS)
Kim, Ha Jin; Jong Bae, Min; Kim, Yong C.; Cho, Eun S.; Sohn, Y. C.; Kim, D. Y.; Lee, S. E.; Kang, H. S.; Han, In T.; Kim, Young H.; Patole, Shashikant P.; Yoo, Ji Beom
2011-03-01
The multi-stage effect has been revisited through growing carbon nanotube field emitters on single strand carbon fiber with a thickness of 11 µm. A prepared linear electron source exhibits a turn-on field as low as 0.4 V µm - 1 and an extremely high field enhancement factor of 19 300, when compared with those results from reference nanotube emitters grown on flat silicone wafer; 3.0 V µm - 1 and 2500, respectively. In addition, we introduce a novel method to grow nanotubes uniformly around the circumference of carbon fibers by using direct resistive heating on the continuously feeding carbon threads. These results open up not only a new path for synthesizing nanocomposites, but also offer an excellent linear electron source for special applications such as backlight units for liquid crystal displays and multi-array x-ray sources.
Optical wide field monitor AROMA-W using multiple digital single-lens reflex cameras
NASA Astrophysics Data System (ADS)
Takahashi, Ichiro; Tsunashima, Kosuke; Tatsuhito, Takeda; Saori, Ono; Kazutaka, Yamaoka; Yoshida, Atsumasa
2010-12-01
We have developed and operated the automatic optical observation device Aoyama Gakuin University Robotic Optical Monitor for Astrophysical objects - Wide field (AROMA-W). It covers a large field of view of about 45 degrees W 30 degrees at a time by the multiple digital single-lens reflex cameras, and provides photometric data in four bands with a limiting V magnitude of about 12-13 magnitude (20 seconds, 3 sigma level). The automatic analysis pipeline which can analyze in parallel with observation has been constructed so far. It can draw the light curves of all stars in the field of view of AROMA-W. We are aiming at the simultaneous observation of the transients (e.g., X-ray nova, Supernova, GRB) that MAXI discovered by using the AROMA-W. We report the developmental status, the observational results of AROMA-W and a possibility of the simultaneous observation to the X-ray transients discovered with MAXI.
Effective realization of random magnetic fields in compounds with large single-ion anisotropy
NASA Astrophysics Data System (ADS)
Herbrych, J.; Kokalj, J.
2017-03-01
We show that spin S =1 system with large and random single-ion anisotropy can be at low energies mapped to a S =1 /2 system with random magnetic fields. This is, for example, realized in Ni (Cl1 -xBrx)2-4 SC (NH2)2 compound (DTNX) and therefore it represents a long-sought realization of random local (on-site) magnetic fields in antiferromagnetic systems. We support the mapping by numerical study of S =1 and effective S =1 /2 anisotropic Heisenberg chains and find excellent agreement for static quantities and also for the spin conductivity. Such systems can therefore be used to study the effects of local random magnetic fields on transport properties.
Enhanced electrocaloric cooling in ferroelectric single crystals by electric field reversal
NASA Astrophysics Data System (ADS)
Ma, Yang-Bin; Novak, Nikola; Koruza, Jurij; Yang, Tongqing; Albe, Karsten; Xu, Bai-Xiang
2016-09-01
An improved thermodynamic cycle is validated in ferroelectric single crystals, where the cooling effect of an electrocaloric refrigerant is enhanced by applying a reversed electric field. In contrast to the conventional adiabatic heating or cooling by on-off cycles of the external electric field, applying a reversed field is significantly improving the cooling efficiency, since the variation in configurational entropy is increased. By comparing results from computer simulations using Monte Carlo algorithms and experiments using direct electrocaloric measurements, we show that the electrocaloric cooling efficiency can be enhanced by more than 20% in standard ferroelectrics and also relaxor ferroelectrics, like Pb (Mg1 /3 /Nb2 /3)0.71Ti0.29O3 .
Fabrication and characterization of single-grain organic field-effect transistor of pentacene
NASA Astrophysics Data System (ADS)
Minari, Takeo; Nemoto, Takashi; Isoda, Seiji
2004-07-01
A single-grain pentacene field-effect transistor with ordinary top-contact structure is fabricated, and its electrical properties are characterized at various temperatures. The device exhibits field-effect mobility as high as 2 cm2/V s at 300 K, although mobility is dependent on gate voltage. This value for field-effect mobility is about one order of magnitude higher than that of a polycrystalline device made from the same pentacene film. The activation energy obtained from an Arrhenius plot of mobility is nearly constant with varying gate voltage, whereas the activation energy of the polycrystalline device decreases as gate voltage increases. Such behavior of the activation energy suggests that intrinsic carrier transport in an organic grain can be described by thermally activated hopping of molecular polarons while extrinsic transport across grain boundaries can be described by the trap model.
Electric field dependence of photoluminescence from individual single-walled carbon nanotubes
NASA Astrophysics Data System (ADS)
Yasukochi, S.; Murai, T.; Shimada, T.; Chiashi, S.; Maruyama, S.; Kato, Y. K.
2011-03-01
Using suspended single-walled carbon nanotubes, we investigate electric field effects on photoluminescence. Trenches are fabricated on Si O2 /Si substrates, and Pt is deposited for electrical contacts. Carbon nanotubes are grown by patterned chemical vapor deposition. These devices operate as back-gate field effect transistors, allowing application of electric fields on as-grown ultraclean nanotubes. Individual suspended carbon nanotubes are identified by taking photoluminescence images using a home-built laser-scanning confocal microscope. After determining the chirality by photoluminescence excitation spectra, we measure gate voltage dependence of photoluminescence. We observe quenching of photoluminescence intensity and shifts of emission wavelength as gate voltages are applied. This work is supported by KAKENHI, Mizuho Foundation for the Promotion of Sciences, Research Foundation for Opto-Science and Technology, TEPCO Research Foundation, SCAT, SCOPE, and Photon Frontier Network Program of MEXT, Japan.
The field-space metric in spiral inflation and related models
Erlich, Joshua; Olsen, Jackson; Wang, Zhen
2016-09-22
Multi-field inflation models include a variety of scenarios for how inflation proceeds and ends. Models with the same potential but different kinetic terms are common in the literature. We compare spiral inflation and Dante’s inferno-type models, which differ only in their field-space metric. We justify a single-field effective description in these models and relate the single-field description to a mass-matrix formalism. We note the effects of the nontrivial field-space metric on inflationary observables, and consequently on the viability of these models. We also note a duality between spiral inflation and Dante’s inferno models with different potentials.
Houshyari, Mohammad; Kashi, Amir Shahram Yousefi; Varaki, Sakineh Soleimani; Rakhsha, Afshin; Blookat, Eftekhar Rajab
2015-01-01
Background: The treatment of lymph nodes engaged in breast cancer with radiotherapy leads to improved locoregional control and enhanced survival rates in patients after surgery. The aim of this study was to compare two treatment techniques, namely single anterior posterior (AP) supraclavicular field with plan depth and two anterior and posterior opposed (AP/PA) supraclavicular fields. In the study, we also examined the relationships between the depth of supraclavicular lymph nodes (SCLNs) and the diameter of the wall of the chest and body mass index (BMI). Methods: Forty patients with breast cancer were analyzed using computed tomography (CT) scans. In planning target volume (PTV), the SCLNs and axillary lymph nodes (AXLNs) were contoured, and, with the attention to PTV, supraclavicular (SC) depth was measured. The dosage that reached the aforementioned lymph nodes and the level of hot spots were investigated using two treatment methods, i.e., 1) AP/PA and 2) AP with three-dimensional (3D) planning. Each of these methods was analyzed using the program Isogray for the 6 MV compact accelerator, and the diameter of the wall of the chest was measured using the CT scan at the center of the SC field. Results: Placing the plan such that 95% of the target volume with 95% or greater of the prescribed dose of 50 Gy (V95) had ≥95% concordance in both treatment techniques. According to the PTV, the depth of SCLNs and the diameter of the wall of the chest were 3–7 and 12–21cm, respectively. Regression analysis showed that the mean SC depth (the mean Plan depth) and the mean diameter of the wall of the chest were related directly to BMI (p<0.0001, adjusted R2=0.67) and (p<0.0001, adjusted R2=0.71), respectively. Conclusion: The AP/PA treatment technique was a more suitable choice of treatment than the AP field, especially for overweight and obese breast cancer patients. However, in the AP/PA technique, the use of a single-photon, low energy (6 MV) caused more hot spots
Precision single mode fibre integral field spectroscopy with the RHEA spectrograph
NASA Astrophysics Data System (ADS)
Rains, Adam D.; Ireland, Michael J.; Jovanovic, Nemanja; Feger, Tobias; Bento, Joao; Schwab, Christian; Coutts, David W.; Guyon, Olivier; Arriola, Alexander; Gross, Simon
2016-08-01
The RHEA Spectrograph is a single-mode echelle spectrograph designed to be a replicable and cost effective method of undertaking precision radial velocity measurements. Two versions of RHEA currently exist, one located at the Australian National University in Canberra, Australia (450 - 600nm wavelength range), and another located at the Subaru Telescope in Hawaii, USA (600 - 800 nm wavelength range). Both instruments have a novel fibre feed consisting of an integral field unit injecting light into a 2D grid of single mode fibres. This grid of fibres is then reformatted into a 1D array at the input of the spectrograph (consisting of the science fibres and a reference fibre capable of receiving a white-light or xenon reference source for simultaneous calibration). The use of single mode fibres frees RHEA from the issue of modal noise and significantly reduces the size of the optics used. In addition to increasing the overall light throughput of the system, the integral field unit allows for cutting edge science goals to be achieved when operating behind the 8.2m Subaru Telescope and the SCExAO adaptive optics system. These include, but are not limited to: resolved stellar photospheres; resolved protoplanetary disk structures; resolved Mira shocks, dust and winds; and sub-arcsecond companions. We present details and results of early tests of RHEA@Subaru and progress towards the stated science goals.
Transport studies of quantum dots sensitized single Mn-ZnO nanowire field effect transistors
NASA Astrophysics Data System (ADS)
Sapkota, Keshab R.; Maloney, Francis Scott; Rimal, Gaurab; Poudyal, Uma; Tang, Jinke; Wang, Wenyong
We present opto-electrical transport properties of Mn-CdSe quantum dots (QDs) sensitized single Mn-ZnO nanowire (NW) field effect transistors (FET). The ZnO NWs with 2 atomic % of Mn doping are grown by chemical vapor deposition. The NWs are ferromagnetic at low temperature. The as grown nanowires are transferred to clean SiO2/Si substrate and single nanowire field effect transistors (FET) are fabricated by standard e-beam lithography. Mobility and carrier concentration of Mn-ZnO NWs are estimated from FET device measurement which shows NWs are n-type semiconductors. Pulse laser deposition of Mn-CdSe QDs on the single NW FET significantly increases carrier concentration of the QD-NW system in dark where the QD monolayer conduction is negligibly small. The photoconductivity study of QD sensitized NW FET enlightens the conduction spectrum of QD-NW system and QD to NW carrier transfer mechanism. This work has been supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-10ER46728.
NASA Astrophysics Data System (ADS)
Hermann, Regina; Uhlemann, Margitta; Wendrock, Horst; Gerbeth, Gunter; Büchner, Bernd
2011-03-01
The aim of this work is growth and characterisation of Ti55Nb45 (wt%) single crystals by floating-zone single crystal growth of intermetallic compounds using two-phase radio-frequency (RF) electromagnetic heating. Thereby, the process and, in particular, the flow field in the molten zone is influenced by additional magnetic fields. The growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. It is generally known that the crystallization process stability is enhanced if the crystallization interface is convex. For this, a tailored magnetic two-phase stirrer system has been developed, which enables a controlled influence on the melt ranging from intensive inwards to outwards flows. Since Ti is favourably light, strong and biocompatible, it is one of the few materials that naturally match the requirements for implantation in the human body. Therefore, the magnetic system was applied to crystal growth of Ti alloys. The grown crystals were oriented and cut to cubes with the desired crystallographic orientations [1 0 0] and [1 0 1] normally on a plane. The electron backscatter diffraction (EBSD) technique was applied to clearly determine crystal orientation and to localize grain boundaries. The formation of oxidic nanotubes on Ti surfaces in dependence of the grain orientation was investigated, performed electrochemically by anodic oxidation from fluoride containing electrolyte.
Blumrosen, Gadi; Abazari, Alireza; Golberg, Alexander; Yarmush, Martin L; Toner, Mehmet
2016-09-01
The design of effective electroporation protocols for molecular delivery applications requires the determination of transport parameters including diffusion coefficient, membrane resealing, and critical electric field strength for electroporation. The use of existing technologies to determine these parameters is time-consuming and labor-intensive, and often results in large inconsistencies in parameter estimation due to variations in the protocols and setups. In this work, we suggest using a set of concentric electrodes to screen a full range of electric field strengths in a single test to determine the electroporation-induced transmembrane transport parameters. Using Calcein as a fluorescent probe, we developed analytical methodology to determine the transport parameters based on the electroporation-induced pattern of fluorescence loss from cells. A monolayer of normal human dermal fibroblast (NHDF) cells were pre-loaded with Calcein and electroporated with an applied voltage of 750V with 10 and 50 square pulses with 50μs duration. Using our analytical model, the critical electric field strength for electroporation was found for the 10 and 50 pulses experiments. An inverse correlation between the field strength and the molecular transport time decay constant, and a direct correlation between field strength and the membrane permeability were observed. The results of this work can simplify the development of electroporation-assisted technologies for research and therapies.
Formation of a ''child'' universe in an inflationary cosmological model
Holcomb, K.A.; Park, S.J.; Vishniac, E.T.
1989-02-15
The evolution of a flat, spherically symmetric cosmological model, containing radiation and an inhomogeneous scalar field, is simulated numerically to determine whether the inhomogeneity could cause a ''child'' universe, connected by a wormhole to the external universe, to form. The gravitational and field quantities were computed self-consistently by means of the techniques of numerical relativity. Although we were unable to follow the process to its completion, preliminary indications are that the ''budding'' phenomenon could occur under very general initial conditions, as long as the scalar field is sufficiently inhomogeneous that the wormhole forms before the inflation is damped by the expansion of the background spacetime.
Single trap dynamics in electrolyte-gated Si-nanowire field effect transistors
Pud, S.; Li, J.; Offenhäusser, A.; Vitusevich, S. A.; Gasparyan, F.; Petrychuk, M.
2014-06-21
Liquid-gated silicon nanowire (NW) field effect transistors (FETs) are fabricated and their transport and dynamic properties are investigated experimentally and theoretically. Random telegraph signal (RTS) fluctuations were registered in the nanolength channel FETs and used for the experimental and theoretical analysis of transport properties. The drain current and the carrier interaction processes with a single trap are analyzed using a quantum-mechanical evaluation of carrier distribution in the channel and also a classical evaluation. Both approaches are applied to treat the experimental data and to define an appropriate solution for describing the drain current behavior influenced by single trap resulting in RTS fluctuations in the Si NW FETs. It is shown that quantization and tunneling effects explain the behavior of the electron capture time on the single trap. Based on the experimental data, parameters of the single trap were determined. The trap is located at a distance of about 2 nm from the interface Si/SiO{sub 2} and has a repulsive character. The theory of dynamic processes in liquid-gated Si NW FET put forward here is in good agreement with experimental observations of transport in the structures and highlights the importance of quantization in carrier distribution for analyzing dynamic processes in the nanostructures.
Ambrose, W.P.; Affleck, R.L.; Goodwin, P.M.; Keller, R.A.; Martin, J.C.; Petty, J.T.; Schecker, J.A.; Wu, Ming
1995-12-01
We have developed a near-field scanning optical microscope with the sensitivity to detect single fluorescent molecules. Our microscope is based on scanning a sample under a tapered and metal coated fiber optic probe and has an illumination-aperture diameter as small as 100 nm. The microscope simultaneously acquires a shear force image with a height noise of {approximately} 1 nm. We have used this system to demonstrate the detection of single molecules of Rhodamine-6G on silica. In this paper, we explore the use of NSOM for investigations of biological molecules. We have prepared and imaged double-stranded DNA intercalated with thiazole orange homodimer (TOTO); single chromosomes stained with propidium iodide; and {beta}-phycoerythrin proteins on dry, borosilicate-glass surfaces. At very dilute coverages, isolated fluorescent spots are observed for the un-intercalated TOTO dye and for {beta}-phycoerythrin. These fluorescent spots exhibit-emission intensity fluctuations and abrupt bleaching transitions, similar to the intensity behavior observed previously for single Rhodamine 6G molecules on silica.
DOE and JAEA Field Trial of the Single Chip Shift Register (SCSR)
Newell, Matthew R.
2016-03-23
Los Alamos National Laboratories (LANL) has recently developed a new data acquisition system for multiplicity analysis of neutron detector pulse streams. This new technology, the Single Chip Shift Register (SCSR), places the entire data acquisition system along with the communications hardware onto a single chip. This greatly simplifies the instrument and reduces the size. The SCSR is designed to be mounted into the neutron detector head alongside the instrument amplifiers. The user’s computer connects via USB directly to the neutron detector eliminating the external data acquisition electronics entirely. JAEA, through the INSEP program, asked LANL to demonstrate the functionality of the SCSR in Tokai using the JAEA Epithermal Neutron Multiplicity Counter, ENMC. In late September of 2015 LANL traveled to Tokai to install, demonstrate and uninstall the SCSR in the ENMC. This report documents the results of that field trial.
Near-field imaging of single walled carbon nanotubes emitting in the telecom wavelength range
NASA Astrophysics Data System (ADS)
La China, F.; Caselli, N.; Sarti, F.; Biccari, F.; Torrini, U.; Intonti, F.; Vinattieri, A.; Durán-Valdeiglesias, E.; Alonso Ramos, C.; Le Roux, X.; Balestrieri, M.; Filoramo, A.; Vivien, L.; Gurioli, M.
2016-09-01
Hybrid systems based on carbon nanotubes emitting in the telecom wavelength range and Si-photonic platforms are promising candidates for developing integrated photonic circuits. Here, we consider semiconducting single walled carbon nanotubes (s-SWNTs) emitting around 1300 nm or 1550 nm wavelength. The nanotubes are deposited on quartz substrate for mapping their photoluminescence in hyperspectral near-field microscopy. This method allows for a sub-wavelength resolution in detecting the spatial distribution of the emission of single s-SWNTs at room temperature. Optical signature delocalized over several micrometers is observed, thus denoting the high quality of the produced carbon nanotubes on a wide range of tube diameters. Noteworthy, the presence of both nanotube bundles and distinct s-SWNT chiralities is uncovered.
Non-contact single shot elastography using line field low coherence holography
Liu, Chih-Hao; Schill, Alexander; Wu, Chen; Singh, Manmohan; Larin, Kirill V.
2016-01-01
Optical elastic wave imaging is a powerful technique that can quantify local biomechanical properties of tissues. However, typically long acquisition times make this technique unfeasible for clinical use. Here, we demonstrate non-contact single shot elastographic holography using a line-field interferometer integrated with an air-pulse delivery system. The propagation of the air-pulse induced elastic wave was imaged in real time, and required a single excitation for a line-scan measurement. Results on tissue-mimicking phantoms and chicken breast muscle demonstrated the feasibility of this technique for accurate assessment of tissue biomechanical properties with an acquisition time of a few milliseconds using parallel acquisition. PMID:27570694
NASA Astrophysics Data System (ADS)
Bugoslavsky, Yu. V.; Minakov, A. A.; Vasyurin, S. I.
1996-02-01
Dependence of the remanent magnetization (Mr) anisotropy on the structure and shape of the superconductor and on the magnetizing procedure was studied for a number of high-Tc superconductor ceramics and single crystals. The experiments were done by means of a vibrating-sample magnetometer with a rotatable sample holder. It was found that the main contribution to the anisotropic behavior of Mr is due to the surface screening currents, and therefore the anisotropy is subject to variation when sample shape is changed. The question is resolved, why the effective demagnetization factors for decoupled ceramic samples are different from those calculated in the inscribed-ellipsoid approximation. Influence of inhomogeneous grain magnetization and global bulk currents on the angular dependencies of Mr in ceramic samples is investigated. The evolution of remanence in YBCO single crystals with an increase of the magnetizing field is described within an extended Bean model.
3D position estimation using a single coil and two magnetic field sensors.
Tadayon, P; Staude, G; Felderhoff, T
2015-01-01
This paper presents an algorithm which enables the estimation of relative 3D position of a sensor module with two magnetic sensors with respect to a magnetic field source using a single transmitting coil. Starting with the description of the ambiguity problem caused by using a single coil, a system concept comprising two sensors having a fixed spatial relation to each other is introduced which enables the unique determination of the sensors' position in 3D space. For this purpose, an iterative two-step algorithm is presented: In a first step, the data of one sensor is used to limit the number of possible position solutions. In a second step, the spatial relation between the sensors is used to determine the correct sensor position.
Konik, Robert M.; Sfeir, Matthew Y.; Misewich, James A.
2015-02-17
We demonstrate that a non-perturbative framework for the treatment of the excitations of single walled carbon nanotubes based upon a field theoretic reduction is able to accurately describe experiment observations of the absolute values of excitonic energies. This theoretical framework yields a simple scaling function from which the excitonic energies can be read off. This scaling function is primarily determined by a single parameter, the charge Luttinger parameter of the tube, which is in turn a function of the tube chirality, dielectric environment, and the tube's dimensions, thus expressing disparate influences on the excitonic energies in a unified fashion. As a result, we test this theory explicitly on the data reported in [NanoLetters 5, 2314 (2005)] and [Phys. Rev. B 82, 195424 (2010)] and so demonstrate the method works over a wide range of reported excitonic spectra.
Temperature and Field Induced Strain Measurements in Single Crystal Gd5Si2Ge2
NASA Astrophysics Data System (ADS)
McCall, S. K.; Nersessian, N.; Carman, G. P.; Pecharsky, V. K.; Schlagel, D. L.; Radousky, H. B.
2016-06-01
The first-order magneto-structural transformation that occurs in Gd5Si2Ge2 near room temperature makes it a strong candidate for many energy harvesting applications. Understanding the single crystal properties is crucial for allowing simulations of device performance. In this study, magnetically and thermally induced transformation strains were measured in a single crystal of Gd5Si2.05Ge1.95 as it transforms from a high-temperature monoclinic paramagnet to a lower-temperature orthorhombic ferromagnet. Thermally induced transformation strains of -8500 ppm, +960 ppm and +1800 ppm, and magnetically induced transformation strains of -8500 ppm, +900 ppm and +2300 ppm were measured along the a, b and c axes, respectively. Using experimental data coupled with general thermodynamic considerations, a universal phase diagram was constructed showing the transition from the monoclinic to the orthorhombic phase as a function of temperature and magnetic field.
Electrical coupling of single cardiac rat myocytes to field-effect and bipolar transistors.
Kind, Thomas; Issing, Matthias; Arnold, Rüdiger; Müller, Bernt
2002-12-01
A novel bipolar transistor for extracellular recording the electrical activity of biological cells is presented, and the electrical behavior compared with the field-effect transistor (FET). Electrical coupling is examined between single cells separated from the heart of adults rats (cardiac myocytes) and both types of transistors. To initiate a local extracellular voltage, the cells are periodically stimulated by a patch pipette in voltage clamp and current clamp mode. The local extracellular voltage is measured by the planar integrated electronic sensors: the bipolar and the FET. The small signal transistor currents correspond to the local extracellular voltage. The two types of sensor transistors used here were developed and manufactured in the laboratory of our institute. The manufacturing process and the interfaces between myocytes and transistors are described. The recordings are interpreted by way of simulation based on the point-contact model and the single cardiac myocyte model.
Matlis, Nicholas; Plateau, Guillaume; van Tilborg, Jeroen; Leemans, Wim
2011-06-17
A new single-shot technique based on linear spectral interferometry between a temporally short reader pulse and a temporally long probe pulse is demonstrated for measuring the spatiotemporal phase and amplitude of an optical probe for use as an ultrafast diagnostic. The probe spatiotemporal field information is recovered, with a resolution set by the duration of the reader pulse, by applying a single Fourier transform operation to the interferogram image, without need of any reference data. The technique was used in conjunction with electro-optic sampling to measure waveforms of coherent, ultrashort THz pulses emitted by electron bunches from a laser-plasma accelerator with sub-50fs resolution. The presence of strong spatiotemporal coupling in the THz waveforms and of complex temporal electron-bunch structure was determined.
Konik, Robert M.; Sfeir, Matthew Y.; Misewich, James A.
2015-02-17
We demonstrate that a non-perturbative framework for the treatment of the excitations of single walled carbon nanotubes based upon a field theoretic reduction is able to accurately describe experiment observations of the absolute values of excitonic energies. This theoretical framework yields a simple scaling function from which the excitonic energies can be read off. This scaling function is primarily determined by a single parameter, the charge Luttinger parameter of the tube, which is in turn a function of the tube chirality, dielectric environment, and the tube's dimensions, thus expressing disparate influences on the excitonic energies in a unified fashion. Asmore » a result, we test this theory explicitly on the data reported in [NanoLetters 5, 2314 (2005)] and [Phys. Rev. B 82, 195424 (2010)] and so demonstrate the method works over a wide range of reported excitonic spectra.« less
NASA Astrophysics Data System (ADS)
Konik, Robert M.; Sfeir, Matthew Y.; Misewich, James A.
2015-02-01
We demonstrate that a nonperturbative framework for the treatment of the excitations of single-walled carbon nanotubes based upon a field theoretic reduction is able to accurately describe experiment observations of the absolute values of excitonic energies. This theoretical framework yields a simple scaling function from which the excitonic energies can be read off. This scaling function is primarily determined by a single parameter, the charge Luttinger parameter of the tube, which is in turn a function of the tube chirality, dielectric environment, and the tube's dimensions, thus expressing disparate influences on the excitonic energies in a unified fashion. We test this theory explicitly on the data reported by Dukovic et al. [Nano Lett. 5, 2314 (2005), 10.1021/nl0518122] and Sfeir et al. [Phys. Rev. B 82, 195424 (2010), 10.1103/PhysRevB.82.195424] and so demonstrate the method works over a wide range of reported excitonic spectra.
The cosmological Slavnov-Taylor identity from BRST symmetry in single-field inflation
Binosi, D.; Quadri, A. E-mail: andrea.quadri@mi.infn.it
2016-03-01
The cosmological Slavnov-Taylor (ST) identity of the Einstein-Hilbert action coupled to a single inflaton field is obtained from the Becchi-Rouet-Stora-Tyutin (BRST) symmetry associated with diffeomorphism invariance in the Arnowitt-Deser-Misner (ADM) formalism. The consistency conditions between the correlators of the scalar and tensor modes in the squeezed limit are then derived from the ST identity, together with the softly broken conformal symmetry. Maldacena's original relations connecting the 2- and 3-point correlators at horizon crossing are recovered, as well as the next-to-leading corrections, controlled by the special conformal transformations.
Advances in the field of single-particle cryo-electron microscopy over the last decade.
Frank, Joachim
2017-02-01
In single-particle cryo-electron microscopy (cryo-EM), molecules suspended in a thin aqueous layer are rapidly frozen and imaged at cryogenic temperature in the transmission electron microscope. From the random projection views, a three-dimensional image is reconstructed, enabling the structure of the molecule to be obtained. In this article I discuss technological progress over the past decade, which has, in my own field of study, culminated in the determination of ribosome structure at 2.5-Å resolution. I also discuss likely future improvements in methodology.
A single-channel SQUID magnetometer for measuring magnetic field of human fetal heart
NASA Astrophysics Data System (ADS)
Bachir, Wesam; Grot, Przemyslaw; Dunajski, Zbigniew
2004-07-01
A non-invasive single-channel SQUID magnetometer for fetal magnetocardiography has been developed. The signal is picked-up with a wire wound third order gradiometer. The optimal configuration of the flux transformer is a trade-off between sufficient sensitivity for the magnetic field originated in fetal heart and effective immunity against the ambient magnetic noise. The over all system performance together with the measuring probe and SQUID electronics is described. The balancing of the third order flux transformer is discussed as well as the signal processing of fetal magnetocardiogram recordings.
(AASERT-93) Field-Effect-Controlled, Coulomb-BlocKage Single-Electron Transistor in Silicon.
2007-11-02
imludCigdibei m , f lei reviewingI Ifistrctflnfl iiv thing~ rIUrmg Ol a m"su’e. gi~wr~ng LrIs fl Ifanil fbe data needed, and c~fO atingbl aw~d...AASERT-93) Field-Effect-Controlled, Coulomb -Blockage Single-Electron Transistor in Silicon .61103D 1-. AUTHO-R(S) 3484/TS Professor Dimitri.Antoniadis...limits of X-ray nanolithography for real devices was found. Novel I coulomb -blockade devices have been fabricated using this modified process
Analysis of menisci formed on cones for single field of view parasite egg microscopy.
Cooke, I R; Laing, C J; White, L V; Wakes, S J; Sowerby, S J
2015-02-01
Parasite ova caused to accumulate in a single microscopic field simplifies monitoring soil-transmitted helminthiasis by optical microscopy. Here we demonstrate new egg-accumulating geometries based on annular menisci formed on the surface of a wetted cone. Fluidic features extracted from profile images of the system provided mathematical representations of the meniscus gradient that were compared quantitatively to numerical solutions of an axisymmetric Young-Laplace equation. Our results show that the governing dynamics of these systems is dominated by the surface tension of the fluid. These image analysis and mathematical tools provide simple quantitative methods for system analysis and optimization.
NASA Technical Reports Server (NTRS)
Ng, Tak-kwong (Inventor); Herath, Jeffrey A. (Inventor)
2010-01-01
An integrated system mitigates the effects of a single event upset (SEU) on a reprogrammable field programmable gate array (RFPGA). The system includes (i) a RFPGA having an internal configuration memory, and (ii) a memory for storing a configuration associated with the RFPGA. Logic circuitry programmed into the RFPGA and coupled to the memory reloads a portion of the configuration from the memory into the RFPGA's internal configuration memory at predetermined times. Additional SEU mitigation can be provided by logic circuitry on the RFPGA that monitors and maintains synchronized operation of the RFPGA's digital clock managers.
Revisiting a pre-inflationary radiation era and its effect on the CMB power spectrum
Das, Suratna; Goswami, Gaurav; Rangarajan, Raghavan; Prasad, Jayanti E-mail: gaugo@prl.res.in E-mail: raghavan@prl.res.in
2015-06-01
We revisit the scenario where inflation is preceded by a radiation era by considering that the inflaton too could have been in thermal equilibrium early in the radiation era. Hence we take into account not only the effect of a pre-inflationary era on the inflaton mode functions but also that of a frozen thermal distribution of inflaton quanta. We initially discuss in detail the issues relevant to our scenario of a pre-inflationary radiation dominated era and then obtain the scalar power spectrum for this scenario. We find that the power spectrum is free from infrared divergences. We then use the WMAP and Planck data to determine the constraints on the inflaton comoving 'temperature' and on the duration of inflation. We find that the best fit value of the duration of inflation is less than 1 e-folding more than what is required to solve cosmological problems, while only an upper bound on the inflaton temperature can be obtained.
Can inflationary models of cosmic perturbations evade the secondary oscillation test?
Lewin, Alex; Albrecht, Andreas
2001-07-15
We consider the consequences of an observed cosmic microwave background (CMB) temperature anisotropy spectrum containing no secondary oscillations. While such a spectrum is generally considered to be a robust signature of active structure formation, we show that such a spectrum can be produced by (very unusual) inflationary models or other passive evolution models. However, we show that for all these passive models the characteristic oscillations would show up in other observable spectra. Our work shows that when CMB polarization and matter power spectra are taken into account secondary oscillations are indeed a signature of even these very exotic passive models. We construct a measure of the observability of secondary oscillations in a given experiment, and show that even with foregrounds both the MAP and Planck satellites should be able to distinguish between models with and without oscillations. Thus we conclude that inflationary and other passive models cannot evade the secondary oscillation test.
Inflationary Dilatonic de Sitter Universe from { N} = 4 Super-Yang Mills Theory Perturbed by Scalars
NASA Astrophysics Data System (ADS)
Hurtado, John Quiroga
In this paper a quantum { N} = 4 super-Yang Mills theory perturbed by dilaton-coupled scalars, is considered. The induced effective action for such a theory is calculated on a dilaton-gravitational background using the conformal anomaly found via AdS/CFT correspondence. Considering such an effective action (using the large N method) as a quantum correction to the classical gravity action with cosmological constant we study the effect from dilaton to the scale factor (which corresponds to the inflationary universe without dilaton). It is shown that, depending on the initial conditions for the dilaton, the dilaton may slow down, or accelerate, the inflation process. At late times, the dilaton is decaying exponentially. At the end of this work, we consider the question how the perturbation of the solution for the scale factor affects the stability of the solution for the equations of motion and therefore the stability of the Inflationary Universe, which could be eternal.
The present and future of the most favoured inflationary models after Planck 2015
Escudero, Miguel; Ramírez, Héctor; Boubekeur, Lotfi; Mena, Olga; Giusarma, Elena E-mail: hector.ramirez@ific.uv.es E-mail: elena.giusarma@roma1.infn.it
2016-02-01
The value of the tensor-to-scalar ratio r in the region allowed by the latest Planck 2015 measurements can be associated to a large variety of inflationary models. We discuss here the potential of future Cosmic Microwave Background cosmological observations in disentangling among the possible theoretical scenarios allowed by our analyses of current Planck temperature and polarization data. Rather than focusing only on r, we focus as well on the running of the primordial power spectrum, α{sub s} and the running thereof, β{sub s}. If future cosmological measurements, as those from the COrE mission, confirm the current best-fit value for β{sub s} ∼> 10{sup −2} as the preferred one, it will be possible to rule-out the most favoured inflationary models.
The present and future of the most favoured inflationary models after Planck 2015
NASA Astrophysics Data System (ADS)
Escudero, Miguel; Ramírez, Héctor; Boubekeur, Lotfi; Giusarma, Elena; Mena, Olga
2016-02-01
The value of the tensor-to-scalar ratio r in the region allowed by the latest Planck 2015 measurements can be associated to a large variety of inflationary models. We discuss here the potential of future Cosmic Microwave Background cosmological observations in disentangling among the possible theoretical scenarios allowed by our analyses of current Planck temperature and polarization data. Rather than focusing only on r, we focus as well on the running of the primordial power spectrum, αs and the running thereof, βs. If future cosmological measurements, as those from the COrE mission, confirm the current best-fit value for βs gtrsim 10-2 as the preferred one, it will be possible to rule-out the most favoured inflationary models.
Single field inflation in supergravity with a U(1) gauge symmetry
Heurtier, L.; Khalil, S.; Moursy, A. E-mail: skhalil@zewailcity.edu.eg
2015-10-01
A single field inflation based on a supergravity model with a shift symmetry and U(1) extension of the MSSM is analyzed. We show that one of the real components of the two U(1) charged scalar fields plays the role of inflaton with an effective scalar potential similar to the ''new chaotic inflation'' scenario. Both non-anomalous and anomalous (with Fayet-Iliopoulos term) U(1) are studied. We show that the non-anomalous U(1) scenario is consistent with data of the cosmic microwave background and recent astrophysical measurements. A possible kinetic mixing between U(1) and U(1){sub B−L} is considered in order to allow for natural decay channels of the inflaton, leading to a reheating epoch. Upper limits on the reheating temperature thus turn out to favour an intermediate (∼ O(10{sup 13}) GeV) scale B−L symmetry breaking.
Steep switching characteristics of single-gated feedback field-effect transistors
NASA Astrophysics Data System (ADS)
Kim, Minsuk; Kim, Yoonjoong; Lim, Doohyeok; Woo, Sola; Cho, Kyoungah; Kim, Sangsig
2017-02-01
In this study, we propose newly designed feedback field-effect transistors that utilize the positive feedback of charge carriers in single-gated silicon channels to achieve steep switching behaviors. The band diagram, I-V characteristics, subthreshold swing, and on/off current ratio are analyzed using a commercial device simulator. Our proposed feedback field-effect transistors exhibit subthreshold swings of less than 0.1 mV dec-1, an on/off current ratio of approximately 1011, and an on-current of approximately 10-4 A at room temperature, demonstrating that the switching characteristics are superior to those of other silicon-based devices. In addition, the device parameters that affect the device performance, hysteresis characteristics, and temperature-dependent device characteristics are discussed in detail.
Photon Energy Deposition in Strong-Field Single Ionization of Multielectron Molecules.
Zhang, Wenbin; Li, Zhichao; Lu, Peifen; Gong, Xiaochun; Song, Qiying; Ji, Qinying; Lin, Kang; Ma, Junyang; He, Feng; Zeng, Heping; Wu, Jian
2016-09-02
Molecules exposed to strong laser fields may coherently absorb multiple photons and deposit the energy into electrons and nuclei, triggering the succeeding dynamics as the primary stage of the light-molecule interaction. We experimentally explore the electron-nuclear sharing of the absorbed photon energy in above-threshold multiphoton single ionization of multielectron molecules. Using CO as a prototype, vibrational and orbital resolved electron-nuclear sharing of the photon energy is observed. Different from the simplest one- or two-electron systems, the participation of the multiple orbitals and the coupling of various electronic states in the strong-field ionization and dissociation processes alter the photon energy deposition dynamics of the multielectron molecule. The population of numerous vibrational states of the molecular cation as the energy reservoir in the ionization process plays an important role in photon energy sharing between the emitted electron and the nuclear fragments.
Synthesis of 3D Model of a Magnetic Field-Influenced Body from a Single Image
NASA Technical Reports Server (NTRS)
Wang, Cuilan; Newman, Timothy; Gallagher, Dennis
2006-01-01
A method for recovery of a 3D model of a cloud-like structure that is in motion and deforming but approximately governed by magnetic field properties is described. The method allows recovery of the model from a single intensity image in which the structure's silhouette can be observed. The method exploits envelope theory and a magnetic field model. Given one intensity image and the segmented silhouette in the image, the method proceeds without human intervention to produce the 3D model. In addition to allowing 3D model synthesis, the method's capability to yield a very compact description offers further utility. Application of the method to several real-world images is demonstrated.
Single field inflation in supergravity with a U(1) gauge symmetry
Heurtier, L.; Khalil, S.; Moursy, A.
2015-10-19
A single field inflation based on a supergravity model with a shift symmetry and U(1) extension of the MSSM is analyzed. We show that one of the real components of the two U(1) charged scalar fields plays the role of inflaton with an effective scalar potential similar to the “new chaotic inflation” scenario. Both non-anomalous and anomalous (with Fayet-Iliopoulos term) U(1) are studied. We show that the non-anomalous U(1) scenario is consistent with data of the cosmic microwave background and recent astrophysical measurements. A possible kinetic mixing between U(1) and U(1){sub B−L} is considered in order to allow for natural decay channels of the inflaton, leading to a reheating epoch. Upper limits on the reheating temperature thus turn out to favour an intermediate (∼O(10{sup 13}) GeV) scale B−L symmetry breaking.
Single and multiple light scattering studies of PDLC films in the presence of electric fields
NASA Astrophysics Data System (ADS)
Wu, Wei
Light scattering from Polymer Dispersed Liquid Crystal (PDLC) films is studied in four major respects: the differential scattering cross-section of a single liquid crystal droplet; the total scattering cross-section and film transmittance; multiple scattering effects; and scattering by absorbing droplets (PDLC doped with dichroic dye). The effects of applied electric field, light wavelength and the liquid crystal droplet size on the scattering behavior are examined. PDLC scattering properties under electric field are described by combining the Anomalous Diffraction Approach (ADA) with PDLC electro-optical response theory. Numerical computation results directly demonstrate how the total scattering cross section relates to the incident light wavelength, the droplet size and the applied electric field. Transmittance measurements are used to study the total scattering cross-section. Analyses of the transmittance characteristics show good agreement with the theoretical predictions. PDLC samples with a practical contrast ratio exhibit strong multiple scattering effects. Studies of the single scattering differential cross section provide a foundation for the modeling and experimental work on the multiple scattering effects. Single scattering characteristics of a bipolar droplet director configuration are derived for a highly symmetric situation. The results offer qualitative explanations for some experimental observations, such as the presence of off-normal maxima and breakdown of rotational symmetry in the scattering pattern. As a novel approach, we propose a multiple scattering model for PDLC based on successive order and Monte Carlo methods. This model, along with ADA and electro-optical response theories, was used to calculate the angular distribution of scattered light and electric field switching response. The predictions demonstrate close quantitative agreement with experimental results. Incorporating complex refractive indices to treat dye- doped PDLC
Orientation effect on the giant stress field induced in a single Ni nanowire by mechanical strain
NASA Astrophysics Data System (ADS)
Melilli, G.; Madon, B.; Clochard, M.-C.; Wegrowe, J.-E.
2015-09-01
The change of magnetization (i.e. using the inverse magnetostriction effect) allows to investigate at the nanoscale the effects of thermoelastic and piezoelectric strain of an active track-etched β-PVDF polymer matrix on an electrodeposited single-contacted Ni nanowire (NW). The magnetization state is measured locally by anisotropic magnetoresitance (AMR). The ferromagnetic NW plays thus the role of a mechanical probe that allows the effects of mechanical strain to be characterized and described qualitatively and quantitatively. Due to the inverse magnetostriction, a quasi-disappearance of the AMR signal for a variation of the order of ΔT ≍ 10 K has been evidenced. The coplanarity of the vectors between the magnetization and the magnetic field is broken. A way of studying the effect of the geometry on such a system, is to fabricate oriented polymer templates. Track-etched polymer membranes were thus irradiated at various angles (αirrad) leading, after electrodeposition, to embedded Ni NWs of different orientations. With cylindrical Ni NW oriented normally to the template surface, the induced stress field in a single Ni NW was found 1000 time higher than the bulk stress field (due to thermal expansion measured on the PVDF). This amplification results in three nanoscopic effects: (1) a stress mismatch between the Ni NW and the membrane, (2) a non-negligible role of the surface tension on Ni NW Young modulus, and (3) the possibility of non-linear stress-strain law. When the Ni NWs are tilted from the polymer template surface normality, the induced stress field is reduced and the amplification phenomenon is less important.
Axonal and dendritic density field estimation from incomplete single-slice neuronal reconstructions
van Pelt, Jaap; van Ooyen, Arjen; Uylings, Harry B. M.
2014-01-01
Neuronal information processing in cortical networks critically depends on the organization of synaptic connectivity. Synaptic connections can form when axons and dendrites come in close proximity of each other. The spatial innervation of neuronal arborizations can be described by their axonal and dendritic density fields. Recently we showed that potential locations of synapses between neurons can be estimated from their overlapping axonal and dendritic density fields. However, deriving density fields from single-slice neuronal reconstructions is hampered by incompleteness because of cut branches. Here, we describe a method for recovering the lost axonal and dendritic mass. This so-called completion method is based on an estimation of the mass inside the slice and an extrapolation to the space outside the slice, assuming axial symmetry in the mass distribution. We validated the method using a set of neurons generated with our NETMORPH simulator. The model-generated neurons were artificially sliced and subsequently recovered by the completion method. Depending on slice thickness and arbor extent, branches that have lost their outside parents (orphan branches) may occur inside the slice. Not connected anymore to the contiguous structure of the sliced neuron, orphan branches result in an underestimation of neurite mass. For 300 μm thick slices, however, the validation showed a full recovery of dendritic and an almost full recovery of axonal mass. The completion method was applied to three experimental data sets of reconstructed rat cortical L2/3 pyramidal neurons. The results showed that in 300 μm thick slices intracortical axons lost about 50% and dendrites about 16% of their mass. The completion method can be applied to single-slice reconstructions as long as axial symmetry can be assumed in the mass distribution. This opens up the possibility of using incomplete neuronal reconstructions from open-access data bases to determine population mean mass density fields
NASA Technical Reports Server (NTRS)
Yokoyama, Jun'ichi; Suto, Yasushi
1991-01-01
A phenomenological model to produce isocurvature baryon-number fluctuations is proposed in the framework of inflationary cosmology. The resulting spectrum of density fluctuation is very different from the conventional Harrison-Zel'dovich shape. The model, with the parameters satisfying several requirements from particle physics and cosmology, provides an appropriate initial condition for the minimal baryon isocurvature scenario of galaxy formation discussed by Peebles.
Ferroelectric Single-Crystal Gated Graphene/Hexagonal-BN/Ferroelectric Field-Effect Transistor.
Park, Nahee; Kang, Haeyong; Park, Jeongmin; Lee, Yourack; Yun, Yoojoo; Lee, Jeong-Ho; Lee, Sang-Goo; Lee, Young Hee; Suh, Dongseok
2015-11-24
The effect of a ferroelectric polarization field on the charge transport in a two-dimensional (2D) material was examined using a graphene monolayer on a hexagonal boron nitride (hBN) field-effect transistor (FET) fabricated using a ferroelectric single-crystal substrate, (1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT). In this configuration, the intrinsic properties of graphene were preserved with the use of an hBN flake, and the influence of the polarization field from PMN-PT could be distinguished. During a wide-range gate-voltage (VG) sweep, a sharp inversion of the spontaneous polarization affected the graphene channel conductance asymmetrically as well as an antihysteretic behavior. Additionally, a transition from antihysteresis to normal ferroelectric hysteresis occurred, depending on the V(G) sweep range relative to the ferroelectric coercive field. We developed a model to interpret the complex coupling among antihysteresis, current saturation, and sudden conductance variation in relation with the ferroelectric switching and the polarization-assisted charge trapping, which can be generalized to explain the combination of 2D structured materials with ferroelectrics.
Terahertz probes of magnetic field induced spin reorientation in YFeO{sub 3} single crystal
Lin, Xian; Jiang, Junjie; Ma, Guohong; Jin, Zuanming; Wang, Dongyang; Tian, Zhen; Han, Jiaguang; Cheng, Zhenxiang
2015-03-02
Using the terahertz time-domain spectroscopy, we demonstrate the spin reorientation of a canted antiferromagnetic YFeO{sub 3} single crystal, by evaluating the temperature and magnetic field dependence of resonant frequency and amplitude for the quasi-ferromagnetic (FM) and quasi-antiferromagnetic modes (AFM), a deeper insight into the dynamics of spin reorientation in rare-earth orthoferrites is established. Due to the absence of 4f-electrons in Y ion, the spin reorientation of Fe sublattices can only be induced by the applied magnetic field, rather than temperature. In agreement with the theoretical predication, the frequency of FM mode decreases with magnetic field. In addition, an obvious step of spin reorientation phase transition occurs with a relatively large applied magnetic field of 4 T. By comparison with the family members of RFeO{sub 3} (R = Y{sup 3+} or rare-earth ions), our results suggest that the chosen of R would tailor the dynamical rotation properties of Fe ions, leading to the designable spin switching in the orthoferrite antiferromagnetic systems.
Running spectral index and formation of primordial black hole in single field inflation models
Drees, Manuel; Erfani, Encieh E-mail: erfani@th.physik.uni-bonn.de
2012-01-01
A broad range of single field models of inflation are analyzed in light of all relevant recent cosmological data, checking whether they can lead to the formation of long-lived Primordial Black Holes (PBHs). To that end we calculate the spectral index of the power spectrum of primordial perturbations as well as its first and second derivatives. PBH formation is possible only if the spectral index increases significantly at small scales, i.e. large wave number k. Since current data indicate that the first derivative α{sub S} of the spectral index n{sub S}(k{sub 0}) is negative at the pivot scale k{sub 0}, PBH formation is only possible in the presence of a sizable and positive second derivative (''running of the running'') β{sub S}. Among the three small-field and five large-field models we analyze, only one small-field model, the ''running mass'' model, allows PBH formation, for a narrow range of parameters. We also note that none of the models we analyze can accord for a large and negative value of α{sub S}, which is weakly preferred by current data.
Retrieving three-dimensional displacement fields of mining areas from a single InSAR pair
NASA Astrophysics Data System (ADS)
Li, Zhi Wei; Yang, Ze Fa; Zhu, Jian Jun; Hu, Jun; Wang, Yun Jia; Li, Pei Xian; Chen, Guo Liang
2015-01-01
This paper presents a novel method for retrieving three-dimensional (3-D) displacement fields of mining areas from a single interferometric synthetic aperture radar (InSAR) pair. This method fully exploits the mechanism of mining subsidence, specifically the proportional relationship between the horizontal displacement and horizontal gradient of vertical displacements caused by underground mining. This method overcomes the limitations of conventional InSAR techniques that can only measure one-dimensional (1-D) deformation of mining area along the radar line-of-sight direction. The proposed method is first validated with simulated 3-D displacement fields, which are obtained by the FLAC software. The root mean square errors of the 3-D displacements retrieved by the proposed method are 13.7, 27.6 and 3.6 mm for the West-East, North-South, and Up-Down components, respectively. We then apply the proposed method to estimate the 3-D displacements of the Qianyingzi and the Xuzhou coal mines in China, respectively, each along with two Advanced Land Observing Satellite (ALOS) Phased Array Type L-band Synthetic Aperture Radar images. Results show that the estimated 3-D displacement is highly consistent with that of the field surveying. This demonstrates that the proposed method is an effective approach for retrieving 3-D mining displacement fields and will play an important role in mining-related hazard prevention and environment assessment under limited InSAR acquisitions.
Warm inflation in presence of magnetic fields
Piccinelli, Gabriella; Ayala, Alejandro; Mizher, Ana Julia
2013-07-23
We present preliminary results on the possible effects that primordial magnetic fields can have for a warm inflation scenario, based on global supersymmetry, with a new-inflation-type potential. This work is motivated by two considerations: first, magnetic fields seem to be present in the universe on all scales which rises de possibility that they could also permeate the early universe; second, the recent emergence of inflationary models where the inflaton is not assumed to be isolated but instead it is taken as an interacting field, even during the inflationary expansion. The effects of magnetic fields are included resorting to Schwinger's proper time method.
Thermal gravitational-wave background in the general pre-inflationary scenario
NASA Astrophysics Data System (ADS)
Wang, Kai; Santos, Larissa; Xia, Jun-Qing; Zhao, Wen
2017-01-01
We investigate the primordial gravitational waves (PGWs) in the general scenario where the inflation is preceded by a pre-inflationary stage with the effective equation of state w. Comparing with the results in the usual inflationary models, the power spectrum of PGWs is modified in two aspects: one is the mixture of the perturbation modes caused by he presence of the pre-inflationary period, and the other is the thermal initial state formed at the Planck era of the early Universe. By investigating the observational imprints of these modifications on the B-mode polarization of cosmic microwave background (CMB) radiation, we obtain the constraints on the conformal temperature of the thermal gravitational-wave background T<5.01× 10‑4 Mpc‑1 and a tensor-to-scalar ratio r<0.084 (95% confident level), which follows the bounds on total number of e-folds N>63.5 for the model with w=1/3, and N>65.7 for that with w=1. By taking into account various noises and the foreground radiations, we forecast the detection possibility of the thermal gravitational-wave background by the future CMBPol mission, and find that if r>0.01, the detection is possible as long as T>1.5× 10‑4 Mpc‑1. However, the effect of different w is quite small, and it seems impossible to determine its value from the potential observations of CMBPol mission.
Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies
NASA Astrophysics Data System (ADS)
Ijjas, Anna; Steinhardt, Paul J.
2016-02-01
The results from Planck2015, when combined with earlier observations from the Wilkinson Microwave Anisotropy Probe, Atacama Cosmology Telescope, South Pole Telescope and other experiments, were the first observations to disfavor the ‘classic’ inflationary paradigm. To satisfy the observational constraints, inflationary theorists have been forced to consider plateau-like inflaton potentials that introduce more parameters and more fine-tuning, problematic initial conditions, multiverse-unpredictability issues, and a new ‘unlikeliness problem’. Some propose turning instead to a ‘postmodern’ inflationary paradigm in which the cosmological properties in our observable Universe are only locally valid and set randomly, with completely different properties (and perhaps even different physical laws) existing in most regions outside our horizon. By contrast, the new results are consistent with the simplest versions of ekpyrotic cyclic models in which the Universe is smoothed and flattened during a period of slow contraction followed by a bounce, and another promising bouncing theory, anamorphic cosmology, has been proposed that can produce distinctive predictions.
Testing predictions of the quantum landscape multiverse 2: the exponential inflationary potential
NASA Astrophysics Data System (ADS)
Di Valentino, Eleonora; Mersini-Houghton, Laura
2017-03-01
The 2015 Planck data release tightened the region of the allowed inflationary models. Inflationary models with convex potentials have now been ruled out since they produce a large tensor to scalar ratio. Meanwhile the same data offers interesting hints on possible deviations from the standard picture of CMB perturbations. Here we revisit the predictions of the theory of the origin of the universe from the landscape multiverse for the case of exponential inflation, for two reasons: firstly to check the status of the anomalies associated with this theory, in the light of the recent Planck data; secondly, to search for a counterexample whereby new physics modifications may bring convex inflationary potentials, thought to have been ruled out, back into the region of potentials allowed by data. Using the exponential inflation as an example of convex potentials, we find that the answer to both tests is positive: modifications to the perturbation spectrum and to the Newtonian potential of the universe originating from the quantum entanglement, bring the exponential potential, back within the allowed region of current data; and, the series of anomalies previously predicted in this theory, is still in good agreement with current data. Hence our finding for this convex potential comes at the price of allowing for additional thermal relic particles, equivalently dark radiation, in the early universe.
Malace, Simona P.; Sawatzky, Bradley D.; Gao, Haiyan
2013-09-01
We studied the single-photoelectron detection capabilities of a multianode photomultiplier tube H8500C-03 and its performance in high magnetic field. Our results show that the device can readily resolve signals at the single photoelectron level making it suitable for photon detection in both threshold and ring imaging Cherenkov detectors. We also found that a large longitudinal magnetic field, up to 300 Gauss, induces a change in the relative output of at most 55% for an edge pixel, and of at most 15% for a central pixel. The H8500C-03 signal loss in transverse magnetic fields it is significantly more pronounced than for the longitudinal case. Our studies of single photoelectron reduction in magnetic fields point to the field induced misfocusing of the photoelectron extracted from the photocathode as primary cause of signal loss. With appropriate shielding this PMT could function in high magnetic field environments.
Wang, Feng; Karan, Niladri S.; Minh Nguyen, Hue; ...
2015-09-23
Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results andmore » further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. Finally, this provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap.« less
Wang, Feng; Karan, Niladri S.; Minh Nguyen, Hue; Ghosh, Yagnaseni; Hollingsworth, Jennifer A.; Htoon, Han
2015-09-23
Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results and further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. Finally, this provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap.
Linear magnetoresistance and zero-field anomalies in HfNiSn single crystals
NASA Astrophysics Data System (ADS)
Steinke, Lucia; Kistner-Morris, Jedediah J.; Deng, Haiming; Geschwind, Gayle; Aronson, Meigan C.
The Half-Heusler compound HfNiSn is probably best known as a candidate material for thermoelectric applications, and studies of its properties have mainly focused on polycrystalline samples and thin films. However, magnetotransport studies of HfNiSn show unusual transport properties like linear magnetoresistance (LMR), where single-crystalline samples of HfNiSn exhibit unexpected LMR at very low fields. In this work, we optimized the solution growth of HfNiSn to obtain high-quality single crystals, where electrical transport measurements show that it is a compensated semimetal below ~ 200 K, where the Hall voltage is zero. At higher temperatures, we see a finite Hall contribution from activated excess carriers. In the semimetallic regime, we observe transport anomalies like resistive signals that strongly depend on contact configuration, and LMR below 5 K. Both low-field DC and low frequency AC magntization measurements show pronounced diamagnetic behavior and the onset of paramagnetism below 4 K. High-frequency diamagnetic screening may be attributed to a decreased skin depth with decreased resistance, but this scenario seems unlikely in HfNiSn since the measured resistance increases steeply at the lowest temperatures This research was supported by the Army Research Office.
Single-field consistency relations of large scale structure part II: resummation and redshift space
Creminelli, Paolo; Gleyzes, Jérôme; Vernizzi, Filippo; Simonović, Marko E-mail: jerome.gleyzes@cea.fr E-mail: filippo.vernizzi@cea.fr
2014-02-01
We generalize the recently derived single-field consistency relations of Large Scale Structure in two directions. First, we treat the effect of the long modes (with momentum q) on the short ones (with momentum k) non-perturbatively, by writing resummed consistency relations which do not require k/q⋅δ{sub q} << 1. These relations do not make any assumptions on the short-scales physics and are extended to include (an arbitrary number of) multiple long modes, internal lines with soft momenta and soft loops. We do several checks of these relations in perturbation theory and we verify that the effect of soft modes always cancels out in equal-time correlators. Second, we write the relations directly in redshift space, without assuming the single-stream approximation: not only the long mode affects the short scales as a homogeneous gravitational field, but it also displaces them by its velocity along the line-of-sight. Redshift space consistency relations still vanish when short modes are taken at equal time: an observation of a signal in the squeezed limit would point towards multifield inflation or a violation of the equivalence principle.
Magnetic field of a single muscle fiber. First measurements and a core conductor model.
van Egeraat, J M; Friedman, R N; Wikswo, J P
1990-01-01
We present the first measurements of the magnetic field from a single muscle fiber of the frog gastrocnemius, obtained by using a toroidal pickup coil coupled to a room-temperature, low-noise amplifier. The axial currents associated with the magnetic fields of single fibers were biphasic and had peak-to-peak amplitudes ranging between 50 and 100 nA, depending primarily on the fiber radius. With an intracellular microelectrode, we measured the action potential of the same fiber, which allowed us to determine that the intracellular conductivity of the muscle fiber in the core conductor approximation was 0.20 +/- 0.09 S/m. Similarly, we found that the effective membrane capacitance was 0.030 +/- 0.011 F/m2. These results were not significantly affected by the anisotropic conductivity of the muscle bundle. We demonstrate how our magnetic technique can be used to determine the transmembrane action potential without penetrating the membrane with a microelectrode, thereby offering a reliable, stable, and atraumatic method for studying contracting muscle fibers. PMID:2306511
Modeling of anomalous Wtb interactions in single top quark events using subsidiary fields
NASA Astrophysics Data System (ADS)
Boos, E.; Bunichev, V.; Dudko, L.; Perfilov, M.
2017-01-01
A method to simulate anomalous fermion-boson interactions in Wtb vertex is presented with a minimal set of simulated samples of single top quark events at the LHC energies. In the proposed method, additional subsidiary vector fields corresponding to the Standard Model gauge fields are implemented for each type of the anomalous vertex structure. The method allows to simulate a manifestation of anomalous gauge couplings in two approaches used in experimental analyses either keeping only the linear order contributions in the anomalous couplings or keeping all contributions in numerators and denominators as appeared in matrix elements. For the processes with several anomalous couplings contributing simultaneously to the production and to the decay as well as to various interference terms the method allows to model correctly the dependence of kinematic distributions on anomalous couplings. The method shows how to generate a minimum set of event samples needed for a concrete analysis. All the single top quark production mechanisms, t-, s- and associative tW-channels, are considered. The correctness of the proposed method is demonstrated.
Baker, Kirk R; Woody, Matthew C
2017-03-15
Aircraft measurements made downwind from specific coal fired power plants during the 2013 Southeast Nexus field campaign provide a unique opportunity to evaluate single source photochemical model predictions of both O3 and secondary PM2.5 species. The model did well at predicting downwind plume placement. The model shows similar patterns of an increasing fraction of PM2.5 sulfate ion to the sum of SO2 and PM2.5 sulfate ion by distance from the source compared with ambient based estimates. The model was less consistent in capturing downwind ambient based trends in conversion of NOX to NOY from these sources. Source sensitivity approaches capture near-source O3 titration by fresh NO emissions, in particular subgrid plume treatment. However, capturing this near-source chemical feature did not translate into better downwind peak estimates of single source O3 impacts. The model estimated O3 production from these sources but often was lower than ambient based source production. The downwind transect ambient measurements, in particular secondary PM2.5 and O3, have some level of contribution from other sources which makes direct comparison with model source contribution challenging. Model source attribution results suggest contribution to secondary pollutants from multiple sources even where primary pollutants indicate the presence of a single source.
Florica, Camelia; Costas, Andreea; Boni, Andra Georgia; Negrea, Raluca; Preda, Nicoleta E-mail: encu@infim.ro; Pintilie, Lucian; Enculescu, Ionut E-mail: encu@infim.ro; Ion, Lucian
2015-06-01
High aspect ratio CuO nanowires are synthesized by a simple and scalable method, thermal oxidation in air. The structural, morphological, optical, and electrical properties of the semiconducting nanowires were studied. Au-Ti/CuO nanowire and Pt/CuO nanowire electrical contacts were investigated. A dominant Schottky mechanism was evidenced in the Au-Ti/CuO nanowire junction and an ohmic behavior was observed for the Pt/CuO nanowire junction. The Pt/CuO nanowire/Pt structure allows the measurements of the intrinsic transport properties of the single CuO nanowires. It was found that an activation mechanism describes the behavior at higher temperatures, while a nearest neighbor hopping transport mechanism is characteristic at low temperatures. This was also confirmed by four-probe resistivity measurements on the single CuO nanowires. By changing the metal/semiconductor interface, devices such as Schottky diodes and field effect transistors based on single CuO p-type nanowire semiconductor channel are obtained. These devices are suitable for being used in various electronic circuits where their size related properties can be exploited.
Wang, Dongxing; Zhu, Wenqi; Best, Michael D; Camden, Jon P; Crozier, Kenneth B
2013-10-04
The ability to detect molecules at low concentrations is highly desired for applications that range from basic science to healthcare. Considerable interest also exists for ultrathin materials with high optical absorption, e.g. for microbolometers and thermal emitters. Metal nanostructures present opportunities to achieve both purposes. Metal nanoparticles can generate gigantic field enhancements, sufficient for the Raman spectroscopy of single molecules. Thin layers containing metal nanostructures ("metasurfaces") can achieve near-total power absorption at visible and near-infrared wavelengths. Thus far, however, both aims (i.e. single molecule Raman and total power absorption) have only been achieved using metal nanostructures produced by techniques (high resolution lithography or colloidal synthesis) that are complex and/or difficult to implement over large areas. Here, we demonstrate a metasurface that achieves the near-perfect absorption of visible-wavelength light and enables the Raman spectroscopy of single molecules. Our metasurface is fabricated using thin film depositions, and is of unprecedented (wafer-scale) extent.
Effect of high SARs produced by cell phone like radiofrequency fields on mollusk single neuron.
Partsvania, B; Sulaberidze, T; Shoshiashvili, L
2013-03-01
During exposure to the cell phone electromagnetic field (EMF), some neurons in the brain at areas of peak specific absorption rate (SAR) absorb more electromagnetic energy than is permitted by existing guidelines. The goal of the present work was to investigate the influence of cell phone-like EMF signal on excitability and memory processes in single neurons. A Transverse Electromagnetic Cell (TEM Cell) was used to expose single neurons of mollusk to the EMF. Finite-Difference Time-Domain (FDTD) method was used for modeling the TEM Cell and the EMF interactions with living nerve ganglion and neurons. Neuron electrophysiology was investigated using standard microelectrode technique. SAR deposited into the single neuron was calculated to be 8.2 W/kg with a temperature increment of 1.21°C. After acute exposure, the threshold of firing of action potentials (AP) was significantly decreased (p ≈ 0.001). Time of habituation to stimulation with the intracellular current injection was increased (p ≈ 0.003). These results indicate that acute exposure to EMF at high SARs impairs the ability of neurons to store information.
NASA Technical Reports Server (NTRS)
Larsson, A.; Muttelstein, M.; Arakawa, Y.; Yariv, A.
1986-01-01
Broad-area single-quantum-well graded-index waveguide separate-confinement heterostructure lasers were fabricated by molecular beam epitaxy. A high external quantum efficiency of 79 percent and stable, single-lobed far-field patterns with a beam divergence as narrow as 0.8 deg (1.9 times diffraction limit) for a 100 micron-wide laser were obtained under pulsed conditions.
Relic vector field and CMB large scale anomalies
Chen, Xingang; Wang, Yi E-mail: yw366@cam.ac.uk
2014-10-01
We study the most general effects of relic vector fields on the inflationary background and density perturbations. Such effects are observable if the number of inflationary e-folds is close to the minimum requirement to solve the horizon problem. We show that this can potentially explain two CMB large scale anomalies: the quadrupole-octopole alignment and the quadrupole power suppression. We discuss its effect on the parity anomaly. We also provide analytical template for more detailed data comparison.
Experimental measurement of the near tip strain field in an iron-silicon single crystal
NASA Astrophysics Data System (ADS)
Shield, T. W.; Kim, K.-S.
1994-05-01
EXPERIMENTAL RESULTS are presented for the plastic deformation field near a crack (200 μm wide notch) tip in an iron-3% silicon single crystal. The specimen was loaded in four point bending and the measurements were made at zero load after extensive plastic deformation had occurred. Results are given for a crack on the (011) plane with its tip along the [01|T] direction. The surface deformation field was measured using moire microscopy and a grating on the specimen surface. The in-plane Almansi strain components have been obtained by digitally processing the moire fringes. A well-structured asymptotic field has been found at a distance of 350-500 μm from the notch tip, where the maximum plastic strain is about 9%. The asymptotic field is observed to be composed of many distinct angular sectors. Three (six symmetric) of these sectors are found to have approximately constant strains. In a fourth (two symmetric) sector, the surface strains are approximately 1/ r singular. Between these sectors there are interconnecting transition sectors. The location of the stress state on the yield surface and the active slip systems in each sector are identified by assuming that the plastic strain rates are normal to a Schmid law yield surface. The slip systems identified in this manner show excellent agreement with direct observations of the slip texture on the surface and dislocation etch pits in the interior of the specimen. The experimental strain measurements also show that the constant strain sectors are regions in which unloading occurs. Because of this unloading, the crack tip stress and deformation state is substantially different from an HRR type field which assumes proportional loading. This strong nonproportional loading is thought to be caused by the presence of material anisotropy. The nonproportional loading also provides a large amount of crack tip shielding that is evidence of a toughening mechanism that results from the presence of material anisotropy.
AC field-induced polymer electroluminescence with single wall carbon nanotubes.
Sung, Jinwoo; Choi, Yeon Sik; Kang, Seok Ju; Cho, Sung Hwan; Lee, Tae-Woo; Park, Cheolmin
2011-03-09
We developed a high-performance field-induced polymer electroluminescence (FPEL) device consisting of four stacked layers: a top metal electrode/thin solution-processed nanocomposite film of single wall carbon nanotubes (SWNTs) and a fluorescent polymer/insulator/transparent bottom electrode working under an alternating current (AC) electric field. A small amount of SWNTs that were highly dispersed in the fluorescent polymer matrix by a conjugate block copolymer dispersant significantly enhanced EL, and we were able to realize an SWNT-FPEL device with a light emission of approximately 350 cd/m(2) at an applied voltage of ±25 V and an AC frequency of 300 kHz. The brightness of the SWNT-FPEL device is much greater than those of other AC-based organic or even inorganic ELs that generally require at least a few hundred volts. Light is emitted from our SWNT-FPEL device because of the sequential injection of field-induced holes and then electron carriers through ambipolar carbon nanotubes under an AC field, followed by exciton formation in the conjugated organic layer. Field-induced bipolar charge injection provides great material design freedom for our devices; the energy level does not have to be aligned between the electrode and the emission layer, and the balance of the carrier injected and transported can be altered in contrast to that in conventional organic light-emitting diodes, leading to an extremely cost-effective and unified device architecture that is applicable to all red-green-blue fluorescent polymers.
NASA Astrophysics Data System (ADS)
Stoesser, Anna; von Seggern, Falk; Purohit, Suneeti; Nasr, Babak; Kruk, Robert; Dehm, Simone; Wang, Di; Hahn, Horst; Dasgupta, Subho
2016-10-01
Oxide semiconductors are considered to be one of the forefront candidates for the new generation, high-performance electronics. However, one of the major limitations for oxide electronics is the scarcity of an equally good hole-conducting semiconductor, which can provide identical performance for the p-type metal oxide semiconductor field-effect transistors as compared to their electron conducting counterparts. In this quest, here we present a bulk synthesis method for single crystalline cuprous oxide (Cu2O) nanowires, their chemical and morphological characterization and suitability as active channel material in electrolyte-gated, low-power, field-effect transistors (FETs) for portable and flexible logic circuits. The bulk synthesis method used in the present study includes two steps: namely hydrothermal synthesis of the nanowires and the removal of the surface organic contaminants. The surface treated nanowires are then dispersed on a receiver substrate where the passive electrodes are structured, followed by printing of a composite solid polymer electrolyte (CSPE), chosen as the gate insulator. The characteristic electrical properties of individual nanowire FETs are found to be quite interesting including accumulation-mode operation and field-effect mobility of 0.15 cm2 V-1 s-1.
Independent complexity patterns in single neuron activity induced by static magnetic field.
Spasić, S; Nikolić, Lj; Mutavdžić, D; Saponjić, J
2011-11-01
We applied a combination of fractal analysis and Independent Component Analysis (ICA) method to detect the sources of fractal complexity in snail Br neuron activity induced by static magnetic field of 2.7 mT. The fractal complexity of Br neuron activity was analyzed before (Control), during (MF), and after (AMF) exposure to the static magnetic field in six experimental animals. We estimated the fractal dimension (FD) of electrophysiological signals using Higuchi's algorithm, and empirical FD distributions. By using the Principal Component Analysis (PCA) and FastICA algorithm we determined the number of components, and defined the statistically independent components (ICs) in the fractal complexity of signal waveforms. We have isolated two independent components of the empirical FD distributions for each of three groups of data by using FastICA algorithm. ICs represent the sources of fractal waveforms complexity of Br neuron activity in particular experimental conditions. Our main results have shown that there could be two opposite intrinsic mechanisms in single snail Br neuron response to static magnetic field stimulation. We named identified ICs that correspond to those mechanisms - the component of plasticity and the component of elasticity. We have shown that combination of fractal analysis with ICA method could be very useful for the decomposition and identification of the sources of fractal complexity of bursting neuronal activity waveforms.
Geomagnetic field strength 3.2 billion years ago recorded by single silicate crystals.
Tarduno, John A; Cottrell, Rory D; Watkeys, Michael K; Bauch, Dorothy
2007-04-05
The strength of the Earth's early geomagnetic field is of importance for understanding the evolution of the Earth's deep interior, surface environment and atmosphere. Palaeomagnetic and palaeointensity data from rocks formed near the boundary of the Proterozoic and Archaean eons, some 2.5 Gyr ago, show many hallmarks of the more recent geomagnetic field. Reversals are recorded, palaeosecular variation data indicate a dipole-dominated morphology and available palaeointensity values are similar to those from younger rocks. The picture before 2.8 Gyr ago is much less clear. Rocks of the Archaean Kaapvaal craton (South Africa) are among the best-preserved, but even they have experienced low-grade metamorphism. The variable acquisition of later magnetizations by these rocks is therefore expected, precluding use of conventional palaeointensity methods. Silicate crystals from igneous rocks, however, can contain minute magnetic inclusions capable of preserving Archaean-age magnetizations. Here we use a CO2 laser heating approach and direct-current SQUID magnetometer measurements to obtain palaeodirections and intensities from single silicate crystals that host magnetite inclusions. We find 3.2-Gyr-old field strengths that are within 50 per cent of the present-day value, indicating that a viable magnetosphere sheltered the early Earth's atmosphere from solar wind erosion.
Theoretical investigation of single dopant in core/shell nanocrystal in magnetic field
NASA Astrophysics Data System (ADS)
Talbi, A.; Feddi, E.; Oukerroum, A.; Assaid, E.; Dujardin, F.; Addou, M.
2015-09-01
The control of single dopant or "solitary dopant" in semiconductors constitute a challenge to achieve new range of tunable optoelectronic devices. Knowing that the properties of doped monocrystals are very sensitive to different external perturbations, the aim of this study is to understand the effect of a magnetic field on the ground state energy of an off-center ionized donor in a core/shell quantum dot (CSQD). The binding energies with and without an applied magnetic field are determined by the Ritz variational method taking into account the electron-impurity correlation in the trial wave function deduced from the second-order perturbation. It has been found that the external magnetic field affects strongly the binding energy, and its effect varies as a function of the core radius and the shell thickness. We have shown the existence of a threshold ratio (a / b) crit which represents the limit between the tridimensional and the spherical surface confinement. In addition our analysis demonstrates the important influence of the position of ionized donor in the shell material.
Noninvasive, near-field terahertz imaging of hidden objects using a single-pixel detector
Stantchev, Rayko Ivanov; Sun, Baoqing; Hornett, Sam M.; Hobson, Peter A.; Gibson, Graham M.; Padgett, Miles J.; Hendry, Euan
2016-01-01
Terahertz (THz) imaging can see through otherwise opaque materials. However, because of the long wavelengths of THz radiation (λ = 400 μm at 0.75 THz), far-field THz imaging techniques suffer from low resolution compared to visible wavelengths. We demonstrate noninvasive, near-field THz imaging with subwavelength resolution. We project a time-varying, intense (>100 μJ/cm2) optical pattern onto a silicon wafer, which spatially modulates the transmission of synchronous pulse of THz radiation. An unknown object is placed on the hidden side of the silicon, and the far-field THz transmission corresponding to each mask is recorded by a single-element detector. Knowledge of the patterns and of the corresponding detector signal are combined to give an image of the object. Using this technique, we image a printed circuit board on the underside of a 115-μm-thick silicon wafer with ~100-μm (λ/4) resolution. With subwavelength resolution and the inherent sensitivity to local conductivity, it is possible to detect fissures in the circuitry wiring of a few micrometers in size. THz imaging systems of this type will have other uses too, where noninvasive measurement or imaging of concealed structures is necessary, such as in semiconductor manufacturing or in ex vivo bioimaging. PMID:27386577
NASA Astrophysics Data System (ADS)
Tarduno, J. A.; Cottrell, R. D.
2012-04-01
Pioneering studies of meteorites and recent investigations have presented paleomagnetic data suggesting some parent bodies had dynamos. With this background, meteorites of the Howardite-Eucrite-Diogenite (HED) group of anchondrites, linked to the differentiated asteroid 4 Vesta, represent promising targets for magnetic investigation. Prior studies of HED meteorites have yielded contrasting results. Cisowski [1] reported low paleofields (1-5 μT) from two unbrecciated eucrites, whereas Morden [2] reported paleointensities of up to 37 μT from Thellier analyses of the brecciated Millbillillie eucrite; the latter were interpreted as indicative of a past dynamo. The age of the Millbillillie magnetization might be approximately 3.55 Ga [3] when the meteorite was heated by impact. Fu and Weiss [4-5] have recently reported a study of fusion crust of the Millibillie eucrite, supporting the conclusion that the meteorite preserves an ancient magnetization, but with very low (2-3 μT) paleointensity values. Here we discuss results from Northwest Africa (NWA) 5480, which is a olivine-diogenite (or harzburgite), 57 vol% olivine and 42 vol% orthopyroxene. Olivine is found in bands that have been interpreted as magmatic flow within the Vestan mantle [6-7]. We use single crystal paleointensity analyses [8]. Olivine grains 1-2 mm in size were separated for analyses. We specifically exclude grains with large visible inclusions as these may be multidomain magnetic minerals which relax on relatively short timescales. Magnetic hysteresis measurements suggest that olivine hosts single to pseudo-single domain magnetic inclusions suitable for paleointensity analyses. Thermal demagnetization reveals removal of several scattered magnetizations at low unblocking temperatures, followed by stable decay at higher temperatures. Thellier-Coe paleointensity data suggest a field of approximately 36 μT. These preliminary data, if confirmed, imply a Vestan dynamo because alternative primary magnetic
A strong-field driver in the single-cycle regime based on self-compression in a kagome fibre
Balciunas, T.; Fourcade-Dutin, C.; Fan, G.; Witting, T.; Voronin, A. A.; Zheltikov, A. M.; Gerome, F.; Paulus, G. G.; Baltuska, A.; Benabid, F.
2015-01-01
Over the past decade intense laser fields with a single-cycle duration and even shorter, subcycle multicolour field transients have been generated and applied to drive attosecond phenomena in strong-field physics. Because of their extensive bandwidth, single-cycle fields cannot be emitted or amplified by laser sources directly and, as a rule, are produced by external pulse compression—a combination of nonlinear optical spectral broadening followed up by dispersion compensation. Here we demonstrate a simple robust driver for high-field applications based on this Kagome fibre approach that ensures pulse self-compression down to the ultimate single-cycle limit and provides phase-controlled pulses with up to a 100 μJ energy level, depending on the filling gas, pressure and the waveguide length. PMID:25625549
A strong-field driver in the single-cycle regime based on self-compression in a kagome fibre.
Balciunas, T; Fourcade-Dutin, C; Fan, G; Witting, T; Voronin, A A; Zheltikov, A M; Gerome, F; Paulus, G G; Baltuska, A; Benabid, F
2015-01-27
Over the past decade intense laser fields with a single-cycle duration and even shorter, subcycle multicolour field transients have been generated and applied to drive attosecond phenomena in strong-field physics. Because of their extensive bandwidth, single-cycle fields cannot be emitted or amplified by laser sources directly and, as a rule, are produced by external pulse compression-a combination of nonlinear optical spectral broadening followed up by dispersion compensation. Here we demonstrate a simple robust driver for high-field applications based on this Kagome fibre approach that ensures pulse self-compression down to the ultimate single-cycle limit and provides phase-controlled pulses with up to a 100 μJ energy level, depending on the filling gas, pressure and the waveguide length.
Three-Dimensional Stress Fields and Slip Systems for Single Crystal Superalloy Notched Specimens
NASA Technical Reports Server (NTRS)
Magnan, Shannon M.; Throckmorton, David (Technical Monitor)
2002-01-01
Single crystal superalloys have become increasingly popular for turbine blade and vane applications due to their high strength, and creep and fatigue resistance at elevated temperatures. The crystallographic orientation of a single crystal material greatly affects its material properties, including elastic modulus, shear modulus, and ductility. These directional properties, along with the type of loading and temperature, dictate an anisotropic response in the yield strength, creep resistance, creep rupture ductility, fatigue resistance, etc. A significant amount of research has been conducted to determine the material properties in the <001> orientation, yet the material properties deviating from the <001> orientation have not been assessed for all cases. Based on the desired application and design criteria, a crystal orientation is selected to yield the maximum properties. Currently, single crystal manufacturing is able to control the primary crystallographic orientation within 15 of the target orientation, which is an acceptable deviation to meet both performance and cost guidelines; the secondary orientation is rarely specified. A common experiment is the standard load-controlled tensile test, in which specimens with different orientations can be loaded to observe the material response. The deformation behavior of single-crystal materials under tension and compression is known to be a function of not only material orientation, but also of varying microdeformation (i.e. dislocation) mechanisms. The underlying dislocation motion causes deformation via slip, and affects the activation of specific slip systems based on load and orientation. The slip can be analyzed by observing the visible traces left on the surface of the specimen from the slip activity within the single crystal material. The goal of this thesis was to predict the slip systems activated in three-dimensional stress fields of a notched tensile specimen, as a function of crystal orientation, using
Superelastic rescattering in single ionization of helium in strong laser fields
NASA Astrophysics Data System (ADS)
Li, Zhi-Chao; Jaron-Becker, Agnieszka; He, Feng
2016-10-01
Rescattering is a central process in ultrafast physics, in which an electron, freed from an atom and accelerated by a laser field, loses its energy by producing high-order harmonics or multiple ionization. Here, taking helium as a prototypical atom, we demonstrate numerically superelastic rescattering in single ionization of an atom. In this scenario, the absorption of a high-energy extreme ultraviolet photon leads to emission of one electron and excitation of the second one into its first excited state, forming He+*. A time-delayed midinfrared laser pulse accelerates the freed electron, drives it back to the He+*, and induces the transition of the bound electron to the ground state of the ion. Identification of the superelastic rescattering process in the photoelectron momentum spectra provides a means to determine the photoelectron momentum at the time of rescattering without using any information of the time-delayed probe laser pulse.
García-García, Amanda; Vergaz, Ricardo; Algorri, José F; Zito, Gianluigi; Cacace, Teresa; Marino, Antigone; Otón, José M
2016-01-01
Summary Single-wall carbon nanotubes (SWCNT) are anisotropic nanoparticles that can cause modifications in the electrical and electro-optical properties of liquid crystals. The control of the SWCNT concentration, distribution and reorientation in such self-organized fluids allows for the possibility of tuning the liquid crystal properties. The alignment and reorientation of CNTs are studied in a system where the liquid crystal orientation effect has been isolated. Complementary studies including Raman spectroscopy, microscopic inspection and impedance studies were carried out. The results reveal an ordered reorientation of the CNTs induced by an electric field, which does not alter the orientation of the liquid crystal molecules. Moreover, impedance spectroscopy suggests a nonnegligible anchoring force between the CNTs and the liquid crystal molecules. PMID:27547599
NASA Astrophysics Data System (ADS)
Frassinetti, L.; Brunsell, P. R.; Drake, J. R.
2009-07-01
The interaction of a static resonant magnetic perturbation (RMP) with a tearing mode (TM) is becoming a relevant topic in fusion plasma physics. RMPs can be generated by active coils and then used to affect the properties of TMs and of the corresponding magnetic islands. This paper shows how the feedback system of the EXTRAP T2R reversed field pinch (RFP) can produce a RMP that affects a rotating TM and stimulate the transition to the so-called quasi-single helicity (QSH) regime, a RFP plasma state characterized by a magnetic island surrounded by low magnetic chaos. The application of the RMP can increase the QSH probability up to 10% and enlarge the size of the corresponding island. Part of the experimental results are supported by a theoretical study that models the effect of the active coils on the magnetic island.
Single high dose-large field irradiation in drug resistant non-Hodgkin's lymphoma
Scarantino, C.W.; Greven, K.M.; Buss, D.H.
1988-05-01
Single high dose-large field irradiation (SHD-LFI), also described as half-body irradiation (HBI), has previously been reported as an effective modality for the palliation of symptoms in a number of solid tumors. This report concerns the ability of SHD-LFI to produce palliation of symptoms and/or objective response in patients with drug resistant non-Hodgkin's lymphoma (NHL). From 1981 to 1984, 34 patients with advanced drug resistant NHL were treated with SHD-LFI either to the whole abdomen (24 patients) or to the upper half body (10 patients). Overall, 19 of 23 patients achieved symptomatic improvement, while objective response was noted in 23 of 30 patients. We noted subjective and objective response in all histologies, and duration of response was not significantly different. Our results suggest a beneficial role for the early and judicious use of SHD-LFI in NHL.
NASA Astrophysics Data System (ADS)
Kumar, Avshish; Husain, Mubashshir; Khan, Ayub; Husain, Mushahid
2014-11-01
The effects of dielectric constant and gate insulator thickness on the performance of single wall carbon nanotube field effect transistors (CNTFETs) have been analyzed using a mathematical model based on FETToy simulator. Both the parameters are found to have significant effect on the device performance, particularly the on-current; while the on-current (ION) increases on scaling down the gate oxide thickness, the level of leakage current (IOFF) is not considerably affected. This is an advantage of CNTFET over conventional MOSFETs where the thickness of thin oxide layer causes drastic increase in gate leakage current. Our analysis results show that thinner gate oxide and larger CNT improve the performance of CNTFETs. Therefore, the performance of our simulated CNTFETs using this model has clear lead over those of conventional MOSFETs.
Direct measurement of electrostatic fields using single Teflon nanoparticle attached to AFM tip
2013-01-01
Abstract A single 210-nm Teflon nanoparticle (sTNP) was attached to the vertex of a silicon nitride (Si3N4) atomic force microscope tip and charged via contact electrification. The charged sTNP can then be considered a point charge and used to measure the electrostatic field adjacent to a parallel plate condenser using 30-nm gold/20-nm titanium as electrodes. This technique can provide a measurement resolution of 250/100 nm along the X- and Z-axes, and the minimum electrostatic force can be measured within 50 pN. PACS 07.79.Lh, 81.16.-c, 84.37. + q PMID:24314111
Implications of purely classical gravity for inflationary tensor modes
NASA Astrophysics Data System (ADS)
Ashoorioon, Amjad; Dev, P. S. Bhupal; Mazumdar, Anupam
2014-09-01
We discuss the implications of a purely classical (instead of quantum) theory of gravity for the primordial gravitational wave spectrum generated during inflation. We argue that for a scalar field driven inflation in a classical gravity the amplitude of the gravitational wave will be too small, irrespective of its primordial seed, to be detected in any forthcoming experiments. Therefore, a positive detection of the B-mode polarizations in the Cosmic Microwave Background (CMB) spectrum will naturally confirm the quantum nature of gravity itself. Furthermore there will be no upper limit on the scale of inflation in the case of classical gravity, and a high-scale model of inflation can easily bypass the observational constraints.
A no-scale inflationary model to fit them all
Ellis, John; García, Marcos A.G.; Olive, Keith A.; Nanopoulos, Dimitri V. E-mail: garciagarcia@physics.umn.edu E-mail: olive@physics.umn.edu
2014-08-01
The magnitude of B-mode polarization in the cosmic microwave background as measured by BICEP2 favours models of chaotic inflation with a quadratic m{sup 2} φ{sup 2}/2 potential, whereas data from the Planck satellite favour a small value of the tensor-to-scalar perturbation ratio r that is highly consistent with the Starobinsky R +R{sup 2} model. Reality may lie somewhere between these two scenarios. In this paper we propose a minimal two-field no-scale supergravity model that interpolates between quadratic and Starobinsky-like inflation as limiting cases, while retaining the successful prediction n{sub s} ≅ 0.96.
Srinivasan, Sangeetha; Shetty, Sharan; Natarajan, Viswanathan; Sharma, Tarun; Raman, Rajiv
2016-01-01
Purpose To develop a simplified algorithm to identify and refer diabetic retinopathy (DR) from single-field retinal images specifically for sight-threatening diabetic retinopathy for appropriate care (ii) to determine the agreement and diagnostic accuracy of the algorithm as a pilot study among optometrists versus “gold standard” (retinal specialist grading). Methods The severity of DR was scored based on colour photo using a colour coded algorithm, which included the lesions of DR and number of quadrants involved. A total of 99 participants underwent training followed by evaluation. Data of the 99 participants were analyzed. Fifty posterior pole 45 degree retinal images with all stages of DR were presented. Kappa scores (κ), areas under the receiver operating characteristic curves (AUCs), sensitivity and specificity were determined, with further comparison between working optometrists and optometry students. Results Mean age of the participants was 22 years (range: 19–43 years), 87% being women. Participants correctly identified 91.5% images that required immediate referral (κ) = 0.696), 62.5% of images as requiring review after 6 months (κ = 0.462), and 51.2% of those requiring review after 1 year (κ = 0.532). The sensitivity and specificity of the optometrists were 91% and 78% for immediate referral, 62% and 84% for review after 6 months, and 51% and 95% for review after 1 year, respectively. The AUC was the highest (0.855) for immediate referral, second highest (0.824) for review after 1 year, and 0.727 for review after 6 months criteria. Optometry students performed better than the working optometrists for all grades of referral. Conclusions The diabetic retinopathy algorithm assessed in this work is a simple and a fairly accurate method for appropriate referral based on single-field 45 degree posterior pole retinal images. PMID:27661981
Learning Depth from Single Monocular Images Using Deep Convolutional Neural Fields.
Liu, Fayao; Shen, Chunhua; Lin, Guosheng; Reid, Ian
2016-10-01
In this article, we tackle the problem of depth estimation from single monocular images. Compared with depth estimation using multiple images such as stereo depth perception, depth from monocular images is much more challenging. Prior work typically focuses on exploiting geometric priors or additional sources of information, most using hand-crafted features. Recently, there is mounting evidence that features from deep convolutional neural networks (CNN) set new records for various vision applications. On the other hand, considering the continuous characteristic of the depth values, depth estimation can be naturally formulated as a continuous conditional random field (CRF) learning problem. Therefore, here we present a deep convolutional neural field model for estimating depths from single monocular images, aiming to jointly explore the capacity of deep CNN and continuous CRF. In particular, we propose a deep structured learning scheme which learns the unary and pairwise potentials of continuous CRF in a unified deep CNN framework. We then further propose an equally effective model based on fully convolutional networks and a novel superpixel pooling method, which is about 10 times faster, to speedup the patch-wise convolutions in the deep model. With this more efficient model, we are able to design deeper networks to pursue better performance. Our proposed method can be used for depth estimation of general scenes with no geometric priors nor any extra information injected. In our case, the integral of the partition function can be calculated in a closed form such that we can exactly solve the log-likelihood maximization. Moreover, solving the inference problem for predicting depths of a test image is highly efficient as closed-form solutions exist. Experiments on both indoor and outdoor scene datasets demonstrate that the proposed method outperforms state-of-the-art depth estimation approaches.
NASA Astrophysics Data System (ADS)
Carrey, J.; Hallali, N.
2016-11-01
In the last 10 years, it has been shown in various types of experiments that it is possible to induce biological effects in cells using the torque generated by magnetic nanoparticles submitted to an alternating or a rotating magnetic field. In biological systems, particles are generally found under the form of assemblies because they accumulate at the cell membrane, are internalized inside lysosomes, or are synthesized under the form of beads containing several particles. The torque undergone by assemblies of single-domain magnetic nanoparticles has not been addressed theoretically so far and is the subject of the present article. The results shown in the present article have been obtained using kinetic Monte Carlo simulations, in which thermal activation is taken into account, so the torque undergone by ferromagnetic and superparamagnetic nanoparticles could both be simulated. The first system under study is a single ferromagnetic particle with its easy axis in the plane of the rotating magnetic field. Then, elements adding complexity to the problem are introduced progressively and the properties of the resulting system presented and analyzed: random anisotropy axes, thermal activation, assemblies, and finally magnetic interactions. The most complex studied systems are particularly relevant for applications and are assemblies of interacting superparamagnetic nanoparticles with randomly oriented anisotropy axes. Whenever it is possible, analytical equations describing the torque properties are provided, as well as their domain of validity. Although the properties of an assembly naturally derive from those of single particles, it is shown here that several of them were unexpected and are particularly interesting with regard to the maximization of torque amplitude in biological applications. In particular, it is shown that, in a given range of parameters, the torque of an assembly increases dramatically in the direction perpendicular to the plane of the rotating
Temperature and field induced strain measurements in single crystal Gd5Si2Ge2
McCall, S. K.; Nersessian, N.; Carman, G. P.; ...
2016-03-29
The first-order magneto-structural transformation that occurs in Gd5Si2Ge2 near room temperature makes it a strong candidate for many energy harvesting applications. Understanding the single crystal properties is crucial for allowing simulations of device performance. In this study, magnetically and thermally induced transformation strains were measured in a single crystal of Gd5Si2.05Ge1.95 as it transforms from a high-temperature monoclinic paramagnet to a lower-temperature orthorhombic ferromagnet. Thermally induced transformation strains of –8500 ppm, +960 ppm and +1800 ppm, and magnetically induced transformation strains of –8500 ppm, +900 ppm and +2300 ppm were measured along the a, b and c axes, respectively. Furthermore,more » using experimental data coupled with general thermodynamic considerations, a universal phase diagram was constructed showing the transition from the monoclinic to the orthorhombic phase as a function of temperature and magnetic field.« less
NASA Astrophysics Data System (ADS)
Trifunovic, Luka; Pedrocchi, Fabio L.; Hoffman, Silas; Maletinsky, Patrick; Yacoby, Amir; Loss, Daniel
2015-06-01
Magnetic resonance techniques not only provide powerful imaging tools that have revolutionized medicine, but they have a wide spectrum of applications in other fields of science such as biology, chemistry, neuroscience and physics. However, current state-of-the-art magnetometers are unable to detect a single nuclear spin unless the tip-to-sample separation is made sufficiently small. Here, we demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen-vacancy magnetometer and a target spin, the magnetometer sensitivity is improved dramatically. Using materials and techniques that are already experimentally available, our proposed set-up is sensitive enough to detect a single nuclear spin within ten milliseconds of data acquisition at room temperature. The sensitivity is practically unchanged when the ferromagnet surface to the target spin separation is smaller than the ferromagnet lateral dimensions; typically about a tenth of a micrometre. This scheme further benefits when used for nitrogen-vacancy ensemble measurements, enhancing sensitivity by an additional three orders of magnitude.
Double gate graphene nanoribbon field effect transistor with single halo pocket in channel region
NASA Astrophysics Data System (ADS)
Naderi, Ali
2016-01-01
A new structure for graphene nanoribbon field-effect transistors (GNRFETs) is proposed and investigated using quantum simulation with a nonequilibrium Green's function (NEGF) method. Tunneling leakage current and ambipolar conduction are known effects for MOSFET-like GNRFETs. To minimize these issues a novel structure with a simple change of the GNRFETs by using single halo pocket in the intrinsic channel region, "Single Halo GNRFET (SH-GNRFET)", is proposed. An appropriate halo pocket at source side of channel is used to modify potential distribution of the gate region and weaken band to band tunneling (BTBT). In devices with materials like Si in channel region, doping type of halo and source/drain regions are different. But, here, due to the smaller bandgap of graphene, the mentioned doping types should be the same to reduce BTBT. Simulations have shown that in comparison with conventional GNRFET (C-GNRFET), an SH-GNRFET with appropriately halo doping results in a larger ON current (Ion), smaller OFF current (Ioff), a larger ON-OFF current ratio (Ion/Ioff), superior ambipolar characteristics, a reduced power-delay product and lower delay time.
Villa, Jesús; De la Rosa, Ismael; Miramontes, Gerardo; Quiroga, Juan Antonio
2005-12-01
Recent studies have demonstrated that the phase recovery from a single fringe pattern with closed fringes can be properly performed if the modulo 2pi fringe orientation is estimated. For example, the fringe pattern in quadrature can be efficiently obtained in terms of the orientational phase spatial operator using fast Fourier transformations and a spiral phase spectral operator in the Fourier space. The computation of the modulo 2pi fringe orientation, however, is by far the most difficult task in the global process of phase recovery. For this reason we propose the demodulation of fringe patterns with closed fringes through the computation of the modulo 2pi fringe orientation using an orientational vector-field-regularized estimator. As we will show, the phase recovery from a single pattern can be performed in an efficient manner using this estimator, provided that it requires one to solve locally in the fringe pattern a simple linear system to optimize a regularized cost function. We present simulated and real experiments applying the proposed methodology.
NASA Astrophysics Data System (ADS)
Smith, Helen R.; Baran, Anthony J.; Hesse, Evelyn; Hill, Peter G.; Connolly, Paul J.; Webb, Ann
2016-11-01
A single habit parameterization for the shortwave optical properties of cirrus is presented. The parameterization utilizes a hollow particle geometry, with stepped internal cavities as identified in laboratory and field studies. This particular habit was chosen as both experimental and theoretical results show that the particle exhibits lower asymmetry parameters when compared to solid crystals of the same aspect ratio. The aspect ratio of the particle was varied as a function of maximum dimension, D, in order to adhere to the same physical relationships assumed in the microphysical scheme in a configuration of the Met Office atmosphere-only global model, concerning particle mass, size and effective density. Single scattering properties were then computed using T-Matrix, Ray Tracing with Diffraction on Facets (RTDF) and Ray Tracing (RT) for small, medium, and large size parameters respectively. The scattering properties were integrated over 28 particle size distributions as used in the microphysical scheme. The fits were then parameterized as simple functions of Ice Water Content (IWC) for 6 shortwave bands. The parameterization was implemented into the GA6 configuration of the Met Office Unified Model along with the current operational long-wave parameterization. The GA6 configuration is used to simulate the annual twenty-year short-wave (SW) fluxes at top-of-atmosphere (TOA) and also the temperature and humidity structure of the atmosphere. The parameterization presented here is compared against the current operational model and a more recent habit mixture model.
Locating narrow bipolar events with single-station measurement of low-frequency magnetic fields
NASA Astrophysics Data System (ADS)
Zhang, Hongbo; Lu, Gaopeng; Qie, Xiushu; Jiang, Rubin; Fan, Yanfeng; Tian, Ye; Sun, Zhuling; Liu, Mingyuan; Wang, Zhichao; Liu, Dongxia; Feng, Guili
2016-06-01
We developed a method to locate the narrow bipolar events (NBEs) based on the single-station measurement of low-frequency (LF, 40-500 kHz) magnetic fields. The direction finding of a two-axis magnetic sensor provides the azimuth of NBEs relative to the measurement site; the ionospheric reflection pairs in the lightning sferics are used to determine the range and height. We applied this method to determine the three-dimensional (3D) locations of 1475 NBEs with magnetic signals recorded during the SHandong Artificially Triggered Lightning Experiment (SHATLE) in summer of 2013. The NBE detections are evaluated on a storm basis by comparing with radar observations of reflectivity and lightning data from the World Wide Lightning Location Network (WWLLN) for two mesoscale convective systems (MCSs) of different sizes. As revealed by previous studies, NBEs are predominately produced in the convective regions with relatively strong radar echo (with composite reflectivity ≥30 dBZ), although not all the convections with high reflectivity and active lightning production are in favor of NBE production. The NBEs located by the single-station magnetic method also exhibit the distinct segregation in altitude for positive and negative NBEs, namely positive NBEs are mainly produced between 7 km and 15 km, while negative NBEs are predominantly produced above 14 km. In summary, the results of comparison generally show that the single-station magnetic method can locate NBEs with good reliability, although the accuracy of 3D location remains to be evaluated with the traditional multi-station method based on the time-of-arrival technique. This method can be applied to track the motion of storm convection within 800 km, especially when they move out to ocean beyond the detection range (typically <400 km) of meteorological radars, making it possible to study NBEs in oceanic thunderstorms for which the location with multiple ground-based stations is usually not feasible.
Inflationary tensor fossils in large-scale structure
Dimastrogiovanni, Emanuela; Fasiello, Matteo; Jeong, Donghui; Kamionkowski, Marc E-mail: mrf65@case.edu E-mail: kamion@jhu.edu
2014-12-01
Inflation models make specific predictions for a tensor-scalar-scalar three-point correlation, or bispectrum, between one gravitational-wave (tensor) mode and two density-perturbation (scalar) modes. This tensor-scalar-scalar correlation leads to a local power quadrupole, an apparent departure from statistical isotropy in our Universe, as well as characteristic four-point correlations in the current mass distribution in the Universe. So far, the predictions for these observables have been worked out only for single-clock models in which certain consistency conditions between the tensor-scalar-scalar correlation and tensor and scalar power spectra are satisfied. Here we review the requirements on inflation models for these consistency conditions to be satisfied. We then consider several examples of inflation models, such as non-attractor and solid-inflation models, in which these conditions are put to the test. In solid inflation the simplest consistency conditions are already violated whilst in the non-attractor model we find that, contrary to the standard scenario, the tensor-scalar-scalar correlator probes directly relevant model-dependent information. We work out the predictions for observables in these models. For non-attractor inflation we find an apparent local quadrupolar departure from statistical isotropy in large-scale structure but that this power quadrupole decreases very rapidly at smaller scales. The consistency of the CMB quadrupole with statistical isotropy then constrains the distance scale that corresponds to the transition from the non-attractor to attractor phase of inflation to be larger than the currently observable horizon. Solid inflation predicts clustering fossils signatures in the current galaxy distribution that may be large enough to be detectable with forthcoming, and possibly even current, galaxy surveys.
NASA Astrophysics Data System (ADS)
Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.
2013-08-01
The effects of single-ion anisotropy on quantum criticality in a d-dimensional spin- S planar ferromagnet is explored by means of the two-time Green's function method. We work at the Tyablikov decoupling level for exchange interactions and the Anderson-Callen decoupling level for single-ion anisotropy. In our analysis a longitudinal external magnetic field is used as the non-thermal control parameter and the phase diagram and the quantum critical properties are established for suitable values of the single-ion anisotropy parameter D. We find that the single-ion anisotropy has sensible effects on the structure of the phase diagram close to the quantum critical point. However, for values of the uniaxial crystal-field parameter below a positive threshold, the conventional magnetic-field-induced quantum critical scenario remains unchanged.
Single-taxon field measurements of bacterial gene regulation controlling DMSP fate.
Varaljay, Vanessa A; Robidart, Julie; Preston, Christina M; Gifford, Scott M; Durham, Bryndan P; Burns, Andrew S; Ryan, John P; Marin, Roman; Kiene, Ronald P; Zehr, Jonathan P; Scholin, Christopher A; Moran, Mary Ann
2015-07-01
The 'bacterial switch' is a proposed regulatory point in the global sulfur cycle that routes dimethylsulfoniopropionate (DMSP) to two fundamentally different fates in seawater through genes encoding either the cleavage or demethylation pathway, and affects the flux of volatile sulfur from ocean surface waters to the atmosphere. Yet which ecological or physiological factors might control the bacterial switch remains a topic of considerable debate. Here we report the first field observations of dynamic changes in expression of DMSP pathway genes by a single marine bacterial species in its natural environment. Detection of taxon-specific gene expression in Roseobacter species HTCC2255 during a month-long deployment of an autonomous ocean sensor in Monterey Bay, CA captured in situ regulation of the first gene in each DMSP pathway (dddP and dmdA) that corresponded with shifts in the taxonomy of the phytoplankton community. Expression of the demethylation pathway was relatively greater during a high-DMSP-producing dinoflagellate bloom, and expression of the cleavage pathway was greater in the presence of a mixed diatom and dinoflagellate community [corrected].These field data fit the prevailing hypothesis for bacterial DMSP gene regulation based on bacterial sulfur demand, but also suggest a modification involving oxidative stress response, evidenced as upregulation of catalase via katG, when DMSP is demethylated.
Single-taxon field measurements of bacterial gene regulation controlling DMSP fate
Varaljay, Vanessa A; Robidart, Julie; Preston, Christina M; Gifford, Scott M; Durham, Bryndan P; Burns, Andrew S; Ryan, John P; Marin III, Roman; Kiene, Ronald P; Zehr, Jonathan P; Scholin, Christopher A; Ann Moran, Mary
2015-01-01
The ‘bacterial switch' is a proposed regulatory point in the global sulfur cycle that routes dimethylsulfoniopropionate (DMSP) to two fundamentally different fates in seawater through genes encoding either the cleavage or demethylation pathway, and affects the flux of volatile sulfur from ocean surface waters to the atmosphere. Yet which ecological or physiological factors might control the bacterial switch remains a topic of considerable debate. Here we report the first field observations of dynamic changes in expression of DMSP pathway genes by a single marine bacterial species in its natural environment. Detection of taxon-specific gene expression in Roseobacter species HTCC2255 during a month-long deployment of an autonomous ocean sensor in Monterey Bay, CA captured in situ regulation of the first gene in each DMSP pathway (dddP and dmdA) that corresponded with shifts in the taxonomy of the phytoplankton community. Expression of the cleavage pathway was relatively greater during a high-DMSP-producing dinoflagellate bloom, and expression of the demethylation pathway was greater in the presence of a mixed diatom and dinoflagellate community. These field data fit the prevailing hypothesis for bacterial DMSP gene regulation based on bacterial sulfur demand, but also suggest a modification involving oxidative stress response, evidenced as upregulation of catalase via katG, when DMSP is demethylated. PMID:25700338
Nanoscale Imaging of Local Few-Femtosecond Near-Field Dynamics within a Single Plasmonic Nanoantenna
2015-01-01
The local enhancement of few-cycle laser pulses by plasmonic nanostructures opens up for spatiotemporal control of optical interactions on a nanometer and few-femtosecond scale. However, spatially resolved characterization of few-cycle plasmon dynamics poses a major challenge due to the extreme length and time scales involved. In this Letter, we experimentally demonstrate local variations in the dynamics during the few strongest cycles of plasmon-enhanced fields within individual rice-shaped silver nanoparticles. This was done using 5.5 fs laser pulses in an interferometric time-resolved photoemission electron microscopy setup. The experiments are supported by finite-difference time-domain simulations of similar silver structures. The observed differences in the field dynamics across a single particle do not reflect differences in plasmon resonance frequency or dephasing time. They instead arise from a combination of retardation effects and the coherent superposition between multiple plasmon modes of the particle, inherent to a few-cycle pulse excitation. The ability to detect and predict local variations in the few-femtosecond time evolution of multimode coherent plasmon excitations in rationally synthesized nanoparticles can be used in the tailoring of nanostructures for ultrafast and nonlinear plasmonics. PMID:26375959
Reis, Wieland G.; Tomović, Željko; Weitz, R. Thomas; Krupke, Ralph; Mikhael, Jules
2017-01-01
The potential of single–walled carbon nanotubes (SWCNTs) to outperform silicon in electronic application was finally enabled through selective separation of semiconducting nanotubes from the as-synthesized statistical mix with polymeric dispersants. Such separation methods provide typically high semiconducting purity samples with narrow diameter distribution, i.e. almost single chiralities. But for a wide range of applications high purity mixtures of small and large diameters are sufficient or even required. Here we proof that weak field centrifugation is a diameter independent method for enrichment of semiconducting nanotubes. We show that the non-selective and strong adsorption of polyarylether dispersants on nanostructured carbon surfaces enables simple separation of diverse raw materials with different SWCNT diameter. In addition and for the first time, we demonstrate that increased temperature enables higher purity separation. Furthermore we show that the mode of action behind this electronic enrichment is strongly connected to both colloidal stability and protonation. By giving simple access to electronically sorted SWCNTs of any diameter, the wide dynamic range of weak field centrifugation can provide economical relevance to SWCNTs. PMID:28317942
NASA Astrophysics Data System (ADS)
Reis, Wieland G.; Tomović, Željko; Weitz, R. Thomas; Krupke, Ralph; Mikhael, Jules
2017-03-01
The potential of single–walled carbon nanotubes (SWCNTs) to outperform silicon in electronic application was finally enabled through selective separation of semiconducting nanotubes from the as-synthesized statistical mix with polymeric dispersants. Such separation methods provide typically high semiconducting purity samples with narrow diameter distribution, i.e. almost single chiralities. But for a wide range of applications high purity mixtures of small and large diameters are sufficient or even required. Here we proof that weak field centrifugation is a diameter independent method for enrichment of semiconducting nanotubes. We show that the non-selective and strong adsorption of polyarylether dispersants on nanostructured carbon surfaces enables simple separation of diverse raw materials with different SWCNT diameter. In addition and for the first time, we demonstrate that increased temperature enables higher purity separation. Furthermore we show that the mode of action behind this electronic enrichment is strongly connected to both colloidal stability and protonation. By giving simple access to electronically sorted SWCNTs of any diameter, the wide dynamic range of weak field centrifugation can provide economical relevance to SWCNTs.
Large piezoelectricity in electric-field modified single crystals of SrTiO3
NASA Astrophysics Data System (ADS)
Khanbabaee, B.; Mehner, E.; Richter, C.; Hanzig, J.; Zschornak, M.; Pietsch, U.; Stöcker, H.; Leisegang, T.; Meyer, D. C.; Gorfman, S.
2016-11-01
Defect engineering is an effective and powerful tool to control the existing material properties and produce completely new ones, which are symmetry-forbidden in a defect-free crystal. For example, the application of a static electric field to a single crystal of SrTiO3 forms a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. While it was previously shown that this near-surface phase holds pyroelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO3, this paper reports that the same phase is strongly piezoelectric. We demonstrate the piezoelectricity of this phase through stroboscopic time-resolved X-ray diffraction under alternating electric field and show that the effective piezoelectric coefficient d33 ranges between 60 and 100 pC/N. The possible atomistic origins of the piezoelectric activity are discussed as a coupling between the electrostrictive effect and spontaneous polarization of this near-surface phase.
NASA Astrophysics Data System (ADS)
Li, Jing; Cai, Cong-Bo; Chen, Lin; Chen, Ying; Qu, Xiao-Bo; Cai, Shu-Hui
2015-10-01
In many ultrafast imaging applications, the reduced field-of-view (rFOV) technique is often used to enhance the spatial resolution and field inhomogeneity immunity of the images. The stationary-phase characteristic of the spatiotemporally-encoded (SPEN) method offers an inherent applicability to rFOV imaging. In this study, a flexible rFOV imaging method is presented and the superiority of the SPEN approach in rFOV imaging is demonstrated. The proposed method is validated with phantom and in vivo rat experiments, including cardiac imaging and contrast-enhanced perfusion imaging. For comparison, the echo planar imaging (EPI) experiments with orthogonal RF excitation are also performed. The results show that the signal-to-noise ratios of the images acquired by the proposed method can be higher than those obtained with the rFOV EPI. Moreover, the proposed method shows better performance in the cardiac imaging and perfusion imaging of rat kidney, and it can scan one or more regions of interest (ROIs) with high spatial resolution in a single shot. It might be a favorable solution to ultrafast imaging applications in cases with severe susceptibility heterogeneities, such as cardiac imaging and perfusion imaging. Furthermore, it might be promising in applications with separate ROIs, such as mammary and limb imaging. Project supported by the National Natural Science Foundation of China (Grant Nos. 11474236, 81171331, and U1232212).
Sonnefraud, Yannick; Cuche, Aurélien; Faklaris, Orestis; Boudou, Jean-Paul; Sauvage, Thierry; Roch, Jean-François; Treussart, François; Huant, Serge
2008-03-15
Diamond nanocrystals containing highly photoluminescent color centers are attractive, nonclassical, and near-field light sources. For near-field applications, the size of the nanocrystal is crucial, since it defines the optical resolution. Nitrogen-vacancy (NV) color centers are efficiently created by proton irradiation and annealing of a nanodiamond powder. Using near-field microscopy and photon statistics measurements, we show that nanodiamonds with sizes down to 25 nm can hold a single NV color center with bright and stable photoluminescence.
Water management in a single cell proton exchange membrane fuel cells with a serpentine flow field
NASA Astrophysics Data System (ADS)
Hassan, Nik Suhaimi Mat; Daud, Wan Ramli Wan; Sopian, Kamaruzzaman; Sahari, Jaafar
Gas and water management is the key to achieving good performance from a polymer electrolyte membrane fuel cell (PEMFC) stack. Imbalance between production and evaporation rates can result in either flooding of the electrodes or membrane dehydration, both of which severely limit fuel cell performance. In the present study, a mathematical model was developed to evaluate moisture profiles of hydrogen and air flows in the flow field channels of both the anode and the cathode. For model validation, a single fuel cell was designed with an active area of 200 cm 2. Six humidity sensors were installed in the flow fields of both the anode and the cathode at 457 mm, 1266 mm and 2532 mm from the inlets. The experiment was performed using an Arbin Fuel Cell Test Station. The temperature was varied (25 °C, 40 °C, 50 °C and 60 °C), while hydrogen and air velocities were fixed at 3 L min -1 and 6 L min -1, respectively, during the operation of the single cell. The feed relative humidity at the anode was fixed at 1.0, while the feed relative humidity at the cathode was fixed at 0.005 (dry air). All humidity sensor readings were taken at steady state after 2 h of operation. Model predictions were then compared with experimental results by using the least squares algorithm. The moisture content was found to decrease along the flow field at the anode, but to increase at the cathode. The moisture content profile at the anode was shown to depend on the moisture Peclet number, which decreased with temperature. On the other hand, the moisture profile at the cathode was shown to depend on both the Peclet number and the Damkohler number. The trend of the Peclet number in the cathode followed closely that of the anode. The Damkohler number decreased with temperature, indicating increasing moisture mass transfer with temperature. The moisture profile models were successfully validated by the published data of the estimated overall mass transfer coefficient and moisture effective
Xue, Hai-Bin; Nie, Yi-Hang; Chen, Jingzhe; Ren, Wei
2015-03-15
We study theoretically the full counting statistics of electron transport through a quantum dot weakly coupled to two ferromagnetic leads, in which an effective nuclear-spin magnetic field originating from the configuration of nuclear spins is considered. We demonstrate that the quantum coherence between the two singly-occupied eigenstates and the spin polarization of two ferromagnetic leads play an important role in the formation of super-Poissonian noise. In particular, the orientation and magnitude of the effective field have a significant influence on the variations of the values of high-order cumulants, and the variations of the skewness and kurtosis values are more sensitive to the orientation and magnitude of the effective field than the shot noise. Thus, the high-order cumulants of transport current can be used to qualitatively extract information on the orientation and magnitude of the effective nuclear-spin magnetic field in a single quantum dot. - Highlights: • The effective nuclear-spin magnetic field gives rise to the off-diagonal elements of the reduced density matrix of single QD. • The off-diagonal elements of reduced density matrix of the QD have a significant impact on the high-order current cumulants. • The high-order current cumulants are sensitive to the orientation and magnitude of the effective nuclear-spin magnetic field. • The FCS can be used to detect the orientation and magnitude of the effective nuclear-spin magnetic field in a single QD.
A general theorem on indeterminism in classical particle dynamics: inflationary scenarios
NASA Astrophysics Data System (ADS)
Pérez Laraudogoitia, Jon
2017-01-01
In the study of systems with an infinite number of particles, the results of indeterminism through deterministic collisions have until now usually made use of the temporal symmetry of mechanics. In this paper we take a more general path. This path furnishes proof that (in such systems) indeterminism based on deterministic collisions is rather more common than is suggested in studies published to date. A detailed analysis is made of what are known as inflationary scenarios, an interesting type of very general situations that display indeterminism.
Inflationary cosmology: exploring the universe from the smallest to the largest scales.
Guth, Alan H; Kaiser, David I
2005-02-11
Understanding the behavior of the universe at large depends critically on insights about the smallest units of matter and their fundamental interactions. Inflationary cosmology is a highly successful framework for exploring these interconnections between particle physics and gravitation. Inflation makes several predictions about the present state of the universe-such as its overall shape, large-scale smoothness, and smaller scale structure-which are being tested to unprecedented accuracy by a new generation of astronomical measurements. The agreement between these predictions and the latest observations is extremely promising. Meanwhile, physicists are busy trying to understand inflation's ultimate implications for the nature of matter, energy, and spacetime.
NASA Astrophysics Data System (ADS)
Orlofsky, Nicholas; Pierce, Aaron; Wells, James D.
2017-03-01
The gravitational waves measured at LIGO are presumed here to come from merging primordial black holes. We ask how these primordial black holes could arise through inflationary models while not conflicting with current experiments. Among the approaches that work, we investigate the opportunity for corroboration through experimental probes of gravitational waves at pulsar timing arrays. We provide examples of theories that are already ruled out, theories that will soon be probed, and theories that will not be tested in the foreseeable future. The models that are most strongly constrained are those with a relatively broad primordial power spectrum.
Modelling inflation with a power-law approach to the inflationary plateau
NASA Astrophysics Data System (ADS)
Dimopoulos, Konstantinos; Owen, Charlotte
2016-09-01
A new family of inflationary models is introduced and analyzed. The behavior of the parameters characterizing the models suggest preferred values, which generate the most interesting testable predictions. Results are further improved if late reheating and/or a subsequent period of thermal inflation is taken into account. Specific model realizations consider a sub-Planckian inflaton variation or a potential without fine-tuning of mass scales, based on the Planck and grand unified theory scales. A toy model realization in the context of global and local supersymmetry is examined, and results fitting the Planck observations are determined.
General model of phospholipid bilayers in fluid phase within the single chain mean field theory.
Guo, Yachong; Pogodin, Sergey; Baulin, Vladimir A
2014-05-07
Coarse-grained model for saturated phospholipids: 1,2-didecanoyl-sn-glycero-3-phosphocholine (DCPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and unsaturated phospholipids: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2- dioleoyl-sn-glycero-3-phosphocholine (DOPC) is introduced within the single chain mean field theory. A single set of parameters adjusted for DMPC bilayers gives an adequate description of equilibrium and mechanical properties of a range of saturated lipid molecules that differ only in length of their hydrophobic tails and unsaturated (POPC, DOPC) phospholipids which have double bonds in the tails. A double bond is modeled with a fixed angle of 120°, while the rest of the parameters are kept the same as saturated lipids. The thickness of the bilayer and its hydrophobic core, the compressibility, and the equilibrium area per lipid correspond to experimentally measured values for each lipid, changing linearly with the length of the tail. The model for unsaturated phospholipids also fetches main thermodynamical properties of the bilayers. This model is used for an accurate estimation of the free energies of the compressed or stretched bilayers in stacks or multilayers and gives reasonable estimates for free energies. The proposed model may further be used for studies of mixtures of lipids, small molecule inclusions, interactions of bilayers with embedded proteins.
Spectroscopy of Charge Carriers and Traps in Field-Doped Single Crystal Organic Semiconductors
Zhu, Xiaoyang
2014-12-10
The proposed research aims to achieve quantitative, molecular level understanding of charge carriers and traps in field-doped crystalline organic semiconductors via in situ linear and nonlinear optical spectroscopy, in conjunction with transport measurements and molecular/crystal engineering. Organic semiconductors are emerging as viable materials for low-cost electronics and optoelectronics, such as organic photovoltaics (OPV), organic field effect transistors (OFETs), and organic light emitting diodes (OLEDs). Despite extensive studies spanning many decades, a clear understanding of the nature of charge carriers in organic semiconductors is still lacking. It is generally appreciated that polaron formation and charge carrier trapping are two hallmarks associated with electrical transport in organic semiconductors; the former results from the low dielectric constants and weak intermolecular electronic overlap while the latter can be attributed to the prevalence of structural disorder. These properties have lead to the common observation of low charge carrier mobilities, e.g., in the range of 10-5 - 10-3 cm2/Vs, particularly at low carrier concentrations. However, there is also growing evidence that charge carrier mobility approaching those of inorganic semiconductors and metals can exist in some crystalline organic semiconductors, such as pentacene, tetracene and rubrene. A particularly striking example is single crystal rubrene (Figure 1), in which hole mobilities well above 10 cm2/Vs have been observed in OFETs operating at room temperature. Temperature dependent transport and spectroscopic measurements both revealed evidence of free carriers in rubrene. Outstanding questions are: what are the structural features and physical properties that make rubrene so unique? How do we establish fundamental design principles for the development of other organic semiconductors of high mobility? These questions are critically important but not comprehensive, as the nature of
Effect of carbon substitution on low magnetic field AC losses in MgB 2 single crystals
NASA Astrophysics Data System (ADS)
Ciszek, M.; Rogacki, K.; Karpiński, J.
2011-11-01
The DC magnetization and AC magnetic susceptibilities were measured for MgB2 single crystals, unsubstituted and carbon substituted with the composition of Mg(B0.94C0.06)2. AC magnetic losses were derived from the AC susceptibility data as a function of the AC amplitude and the DC bias magnetic field. From the DC magnetization loops critical current densities were derived as a function of temperature and DC field. Results show that the substitution with carbon decreases critical current densities at low external magnetic fields, in contrast to the well known effect of an increase of the critical current densities at higher magnetic fields.
Critical Number of Fields in Stochastic Inflation.
Vennin, Vincent; Assadullahi, Hooshyar; Firouzjahi, Hassan; Noorbala, Mahdiyar; Wands, David
2017-01-20
Stochastic effects in generic scenarios of inflation with multiple fields are investigated. First passage time techniques are employed to calculate the statistical moments of the number of inflationary e-folds, which give rise to all correlation functions of primordial curvature perturbations through the stochastic δN formalism. The number of fields is a critical parameter. The probability of exploring arbitrarily large-field regions of the potential becomes nonvanishing when more than two fields are driving inflation. The mean number of e-folds can be infinite, depending on the number of fields; for plateau potentials, this occurs even with one field. In such cases, correlation functions of curvature perturbations are infinite. They can, however, be regularized if a reflecting (or absorbing) wall is added at large energy or field value. The results are found to be independent of the exact location of the wall and this procedure is, therefore, well defined for a wide range of cutoffs, above or below the Planck scale. Finally, we show that, contrary to single-field setups, multifield models can yield large stochastic corrections even at sub-Planckian energy, opening interesting prospects for probing quantum effects on cosmological fluctuations.
Critical Number of Fields in Stochastic Inflation
NASA Astrophysics Data System (ADS)
Vennin, Vincent; Assadullahi, Hooshyar; Firouzjahi, Hassan; Noorbala, Mahdiyar; Wands, David
2017-01-01
Stochastic effects in generic scenarios of inflation with multiple fields are investigated. First passage time techniques are employed to calculate the statistical moments of the number of inflationary e -folds, which give rise to all correlation functions of primordial curvature perturbations through the stochastic δ N formalism. The number of fields is a critical parameter. The probability of exploring arbitrarily large-field regions of the potential becomes nonvanishing when more than two fields are driving inflation. The mean number of e -folds can be infinite, depending on the number of fields; for plateau potentials, this occurs even with one field. In such cases, correlation functions of curvature perturbations are infinite. They can, however, be regularized if a reflecting (or absorbing) wall is added at large energy or field value. The results are found to be independent of the exact location of the wall and this procedure is, therefore, well defined for a wide range of cutoffs, above or below the Planck scale. Finally, we show that, contrary to single-field setups, multifield models can yield large stochastic corrections even at sub-Planckian energy, opening interesting prospects for probing quantum effects on cosmological fluctuations.
NASA Astrophysics Data System (ADS)
Zhu, Leqing; Wang, Xun; Wang, Dadong; Wang, Huiyan
2016-10-01
Deep convolutional neural networks (DCNNs) have attracted significant interest in the computer vision community in the recent years and have exhibited high performance in resolving many computer vision problems, such as image classification. We address the pixel-level depth prediction from a single image by combining DCNN and sparse connected conditional random field (CRF). Owing to the invariance properties of DCNNs that make them suitable for high-level tasks, their outputs are generally not localized enough for detailed pixel-level regression. A multiscale DCNN and sparse connected CRF are combined to overcome this localization weakness. We have evaluated our framework using the well-known NYU V2 depth dataset, and the results show that the proposed method can improve the depth prediction accuracy both qualitatively and quantitatively, as compared to previous works. This finding shows the potential use of the proposed method in three-dimensional (3-D) modeling or 3-D video production from the given two-dimensional (2-D) images or 2-D videos.
Modeling comparison of graphene nanoribbon field effect transistors with single vacancy defect
NASA Astrophysics Data System (ADS)
Nazari, Atefeh; Faez, Rahim; Shamloo, Hassan
2016-09-01
In this paper, some important circuit parameters of a monolayer armchair graphene nanoribbon (GNR) field effect transistor (GNRFET) in different structures are studied. Also, these structures are Ideal with no defect, 1SVGNRFET with one single vacancy defect, and 3SVsGNRFET with three SV defects. Moreover, the circuit parameters are extracted based on Semi Classical Top of Barrier Modeling (SCTOBM) method. The I-V characteristics simulations of Ideal GNRFET, 1SVGNRFET and 3SVsGNRFET are used for comparing with SCTOBM method. These simulations are solved with Poisson-Schrodinger equation self-consistently by using Non- Equilibrium Green Function (NEGF) and in the real space approach. The energy band structure of nanoribbon is obtained by using nearest-neighbour interactions within an approximation tight-binding method. The modeling results show that 3SVsGNRFET in comparison to 1SVGNRFET has higher transconductance, cut-off frequency, electron average velocity, mobile charge, and quantum capacitance. Also, 3SVsGNRFET has smaller gate, drain and source capacitances than Ideal GNRFET. Furthermore, Drain-induced barrier lowering (DIBL) and sub-threshold swing (SS) of 3SVsGNRFET are smaller than 1SVGNRFET.
NASA Astrophysics Data System (ADS)
Rajesh, Sharma, Vikash; Puri, Nitin K.; Mulchandani, Ashok; Kotnala, Ravinder K.
2016-12-01
We report a single-walled carbon nanotube (SWNT) field-effect transistor (FET) functionalized with Polyamidoamine (PAMAM) dendrimer with 128 carboxyl groups as anchors for site specific biomolecular immobilization of protein antibody for C-reactive protein (CRP) detection. The FET device was characterized by scanning electron microscopy and current-gate voltage (I-Vg) characteristic studies. A concentration-dependent decrease in the source-drain current was observed in the regime of clinical significance, with a detection limit of ˜85 pM and a high sensitivity of 20% change in current (ΔI/I) per decade CRP concentration, showing SWNT being locally gated by the binding of CRP to antibody (anti-CRP) on the FET device. The low value of the dissociation constant (Kd = 0.31 ± 0.13 μg ml-1) indicated a high affinity of the device towards CRP analyte arising due to high anti-CRP loading with a better probe orientation on the 3-dimensional PAMAM structure.
Setiadi, Agung; Akai-Kasaya, Megumi Saito, Akira; Kuwahara, Yuji
2014-09-01
We fabricated single-walled carbon nanotube (SWNT) field-effect transistor (FET) devices on flattened electrodes, in which there are no height difference between metal electrodes and the substrate. SWNT-FET fabricated using bottom contact technique have some advantages, such that the SWNTs are free from electron irradiation, have direct contact with the desired metal electrodes, and can be functionalized before or after deposition. However, the SWNTs can be bent at the contact point with the metal electrodes leading to a different electrical characteristic of the devices. The number of SWNT direct junctions in short channel length devices is drastically increased by the use of flattened electrodes due to strong attractive interaction between SWNT and the substrate. The flattened electrodes show a better balance between their hole and electron mobility compared to that of the non-flattened electrodes, that is, ambipolar FET characteristic. It is considered that bending of the SWNTs in the non-flattened electrode devices results in a higher Schottky barrier for the electrons.
Nb-doped single crystalline MoS{sub 2} field effect transistor
Das, Saptarshi E-mail: das@anl.gov; Demarteau, Marcellinus; Roelofs, Andreas
2015-04-27
We report on the demonstration of a p-type, single crystalline, few layer MoS{sub 2} field effect transistor (FET) using Niobium (Nb) as the dopant. The doping concentration was extracted and determined to be ∼3 × 10{sup 19}/cm{sup 3}. We also report on bilayer Nb-doped MoS{sub 2} FETs with ambipolar conduction. We found that the current ON-OFF ratio of the Nb-doped MoS{sub 2} FETs changes significantly as a function of the flake thickness. We attribute this experimental observation to bulk-type electrostatic effect in ultra-thin MoS{sub 2} crystals. We provide detailed analytical modeling in support of our claims. Finally, we show that in the presence of heavy doping, even ultra-thin 2D-semiconductors cannot be fully depleted and may behave as a 3D material when used in transistor geometry. Our findings provide important insights into the doping constraints of 2D materials, in general.
Investigation of single- and double-Λ hypernuclei using a beyond-mean-field approach
NASA Astrophysics Data System (ADS)
Cui, Ji-Wei; Zhou, Xian-Rong; Guo, Li-Xin; Schulze, Hans-Josef
2017-02-01
A beyond-mean-field approach consisting of angular momentum projection techniques and generator coordinate method based on Skyrme-Hartree-Fock calculations is employed to investigate single- and double-Λ hypernuclear systems. The density-dependent N Λ interactions derived from the Nijmegen soft-core potentials are used. Rotational energy spectra and electric-quadrupole transition strengths B (E 2 ) of the hypernuclei 13CΛ, 14CΛ Λ, 21Ne21Λ, and 22NeΛ Λ are presented and compared with those of the corresponding core nuclei 12C and 20Ne. The shrinkage effect of the Λ s is demonstrated by the B (E 2 ) values, the charge radii, and the shape deformation β of the nuclear core. It is found that the reduction of the B (E 2 ) values in 13CΛ and 14CΛΛ is mainly caused by the shrinkage of the charge radii of the nuclear cores, while the reduced shape deformations also play important roles; but the contrary is the case in Ne21Λ and 22NeΛΛ. Comparison between this and other theoretical models are made, and the differences between them are illuminated.
Near-field acoustic microbead trapping as remote anchor for single particle manipulation
Hwang, Jae Youn; Cheon, Dong Young; Shin, Hyunjune; Kim, Hyun Bin; Lee, Jungwoo
2015-05-04
We recently proposed an analytical model of a two-dimensional acoustic trapping of polystyrene beads in the ray acoustics regime, where a bead diameter is larger than the wavelength used. As its experimental validation, this paper demonstrates the transverse (or lateral) trapping of individual polystyrene beads in the near field of focused ultrasound. A 100 μm bead is immobilized on the central beam axis by a focused sound beam from a 30 MHz single element lithium niobate transducer, after being laterally displaced through hundreds of micrometers. Maximum displacement, a longest lateral distance at which a trapped bead can be directed towards the central axis, is thus measured over a discrete frequency range from 24 MHz to 36 MHz. The displacement data are found to be between 323.7 μm and 470.2 μm, depending on the transducer's driving frequency and input voltage amplitude. The experimental results are compared with their corresponding model values, and their relative errors lie between 0.9% and 3.9%. The results suggest that this remote maneuvering technique may be employed to manipulate individual cells through solid microbeads, provoking certain cellular reactions to localized mechanical disturbance without direct contact.
Sundberg, Kristy A.; Mitchell, Jude F.; Gawne, Timothy J.
2012-01-01
Many previous studies have demonstrated that changes in selective attention can alter the response magnitude of visual cortical neurons, but there has been little evidence for attention affecting response latency. Small latency differences, though hard to detect, can potentially be of functional importance, and may also give insight into the mechanisms of neuronal computation. We therefore reexamined the effect of attention on the response latency of both single units and the local field potential (LFP) in primate visual cortical area V4. We find that attention does produce small (1–2 ms) but significant reductions in the latency of both the spiking and LFP responses. Though attention, like contrast elevation, reduces response latencies, we find that the two have different effects on the magnitude of the LFP. Contrast elevations increase and attention decreases the magnitude of the initial deflection of the stimulus-evoked LFP. Both contrast elevation and attention increase the magnitude of the spiking response. We speculate that latencies may be reduced at higher contrast because stronger stimulus inputs drive neurons more rapidly to spiking threshold, while attention may reduce latencies by placing neurons in a more depolarized state closer to threshold before stimulus onset. PMID:23136440
Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch
NASA Astrophysics Data System (ADS)
Frassinetti, L.; Brunsell, P. R.; Drake, J. R.; Menmuir, S.; Cecconello, M.
2007-11-01
In recent years, good progress toward a better understanding and control of the plasma performance in reversed-field pinch devices has been made. These improvements consist both of the discovery of spontaneous plasma regimes, termed the quasi single helicity (QSH) regime, in which part of the plasma core is no longer stochastic, and of the development of techniques for active control of plasma instabilities. In this paper, a systematic study of spontaneous QSH in the EXTRAP T2R device [P. R. Brunsell, H. Bergsaker, M. Cecconello et al., Plasma Phys. Control. Fusion 43, 1457 (2001)] is presented. In this device, QSH states can occur spontaneously and it is associated with magnetic and thermal structures. A statistical analysis to determine the most favorable experimental conditions to have a transition to the QSH regime will be presented. The results described here are useful to understand the underlying properties of QSH regimes in view of future applications of the QSH active control in EXTRAP T2R; they are also important to have a comparison with the QSH studied in other devices.
Parasuram, Harilal; Nair, Bipin; D'Angelo, Egidio; Hines, Michael; Naldi, Giovanni; Diwakar, Shyam
2016-01-01
Local Field Potentials (LFPs) are population signals generated by complex spatiotemporal interaction of current sources and dipoles. Mathematical computations of LFPs allow the study of circuit functions and dysfunctions via simulations. This paper introduces LFPsim, a NEURON-based tool for computing population LFP activity and single neuron extracellular potentials. LFPsim was developed to be used on existing cable compartmental neuron and network models. Point source, line source, and RC based filter approximations can be used to compute extracellular activity. As a demonstration of efficient implementation, we showcase LFPs from mathematical models of electrotonically compact cerebellum granule neurons and morphologically complex neurons of the neocortical column. LFPsim reproduced neocortical LFP at 8, 32, and 56 Hz via current injection, in vitro post-synaptic N2a, N2b waves and in vivo T-C waves in cerebellum granular layer. LFPsim also includes a simulation of multi-electrode array of LFPs in network populations to aid computational inference between biophysical activity in neural networks and corresponding multi-unit activity resulting in extracellular and evoked LFP signals. PMID:27445781
Spearhead Nanometric Field-Effect Transistor Sensors for Single-Cell Analysis
Córdoba, Ainara López; Ali, Tayyibah; Shevchuk, Andrew; Takahashi, Yasufumi; Novak, Pavel; Edwards, Christopher; Lab, Max; Gopal, Sahana; Chiappini, Ciro; Anand, Uma; Magnani, Luca; Coombes, R. Charles; Gorelik, Julia; Matsue, Tomokazu; Schuhmann, Wolfgang; Klenerman, David; Sviderskaya, Elena V.; Korchev, Yuri
2016-01-01
Nanometric field-effect-transistor (FET) sensors are made on the tip of spear-shaped dual carbon nanoelectrodes derived from carbon deposition inside double-barrel nanopipettes. The easy fabrication route allows deposition of semiconductors or conducting polymers to comprise the transistor channel. A channel from electrodeposited poly pyrrole (PPy) exhibits high sensitivity toward pH changes. This property is exploited by immobilizing hexokinase on PPy nano-FETs to give rise to a selective ATP biosensor. Extracellular pH and ATP gradients are key biochemical constituents in the microenvironment of living cells; we monitor their real-time changes in relation to cancer cells and cardiomyocytes. The highly localized detection is possible because of the high aspect ratio and the spear-like design of the nano-FET probes. The accurately positioned nano-FET sensors can detect concentration gradients in three-dimensional space, identify biochemical properties of a single living cell, and after cell membrane penetration perform intracellular measurements. PMID:26816294
NASA Astrophysics Data System (ADS)
Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Egler-Lucas, Carolina; Semenov, Sergey N.; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel
2016-02-01
Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0 V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.
NASA Astrophysics Data System (ADS)
Neogy, D.; Paul, P.; Chattopadhyay, K. N.; Bisui, D.
2002-07-01
Magnetic susceptibility measurements on single crystals of dysprosium trifluoromethanesulfonate (DyTFMS) have been carried out from 300 K down to 13 K. The hexagonal crystal structure of DyTFMS renders the crystal uniaxial with the Kramers ion Dy 3+ occupying a site of C 3h symmetry. The principal magnetic susceptibilities, observed by us and the Friedberg group, over the wide range 300 to ˜1.0 K find an excellent theoretical simulation by the crystal field perturbed J-mixed eigenvectors with due consideration of the intermediate coupling effects. No ordering effects were noticed down to ˜13 K indicating the interionic interaction to be predominantly of the dipolar type which is consistent with the discovery of a ferromagnetic transition at T˜0.111 K by the Friedberg group. The g-values derived from other sources are reasonably accounted for. The thermal behavior of quadrupole splitting and that of electronic and nuclear heat capacities is also worked out.
Parasuram, Harilal; Nair, Bipin; D'Angelo, Egidio; Hines, Michael; Naldi, Giovanni; Diwakar, Shyam
2016-01-01
Local Field Potentials (LFPs) are population signals generated by complex spatiotemporal interaction of current sources and dipoles. Mathematical computations of LFPs allow the study of circuit functions and dysfunctions via simulations. This paper introduces LFPsim, a NEURON-based tool for computing population LFP activity and single neuron extracellular potentials. LFPsim was developed to be used on existing cable compartmental neuron and network models. Point source, line source, and RC based filter approximations can be used to compute extracellular activity. As a demonstration of efficient implementation, we showcase LFPs from mathematical models of electrotonically compact cerebellum granule neurons and morphologically complex neurons of the neocortical column. LFPsim reproduced neocortical LFP at 8, 32, and 56 Hz via current injection, in vitro post-synaptic N2a, N2b waves and in vivo T-C waves in cerebellum granular layer. LFPsim also includes a simulation of multi-electrode array of LFPs in network populations to aid computational inference between biophysical activity in neural networks and corresponding multi-unit activity resulting in extracellular and evoked LFP signals.
Single Event Effects Test Results for Advanced Field Programmable Gate Arrays
NASA Technical Reports Server (NTRS)
Allen, Gregory R.; Swift, Gary M.
2006-01-01
Reconfigurable Field Programmable Gate Arrays (FPGAs) from Altera and Actel and an FPGA-based quick-turnApplication Specific Integrated Circuit (ASIC) from Altera were subjected to single-event testing using heavy ions. Both Altera devices (Stratix II and HardCopy II) exhibited a low latchup threshold (below an LET of 3 MeV-cm2/mg) and thus are not recommended for applications in the space radiation environment. The flash-based Actel ProASIC Plus device did not exhibit latchup to an effective LET of 75 MeV-cm2/mg at room temperature. In addition, these tests did not show flash cell charge loss (upset) or retention damage. Upset characterization of the design-level flip-flops yielded an LET threshold below 10 MeV-cm2/mg and a high LET cross section of about lxlO-6 cm2/bit for storing ones and about lxl0-7 cm2/bit for storing zeros . Thus, the ProASIC device may be suitable for critical flight applications with appropriate triple modular redundancy mitigation techniques.
Natural Language Search Interfaces: Health Data Needs Single-Field Variable Search
Smith, Sam; Sufi, Shoaib; Goble, Carole; Buchan, Iain
2016-01-01
Background Data discovery, particularly the discovery of key variables and their inter-relationships, is key to secondary data analysis, and in-turn, the evolving field of data science. Interface designers have presumed that their users are domain experts, and so they have provided complex interfaces to support these “experts.” Such interfaces hark back to a time when searches needed to be accurate first time as there was a high computational cost associated with each search. Our work is part of a governmental research initiative between the medical and social research funding bodies to improve the use of social data in medical research. Objective The cross-disciplinary nature of data science can make no assumptions regarding the domain expertise of a particular scientist, whose interests may intersect multiple domains. Here we consider the common requirement for scientists to seek archived data for secondary analysis. This has more in common with search needs of the “Google generation” than with their single-domain, single-tool forebears. Our study compares a Google-like interface with traditional ways of searching for noncomplex health data in a data archive. Methods Two user interfaces are evaluated for the same set of tasks in extracting data from surveys stored in the UK Data Archive (UKDA). One interface, Web search, is “Google-like,” enabling users to browse, search for, and view metadata about study variables, whereas the other, traditional search, has standard multioption user interface. Results Using a comprehensive set of tasks with 20 volunteers, we found that the Web search interface met data discovery needs and expectations better than the traditional search. A task × interface repeated measures analysis showed a main effect indicating that answers found through the Web search interface were more likely to be correct (F 1,19=37.3, P<.001), with a main effect of task (F 3,57=6.3, P<.001). Further, participants completed the task
NASA Technical Reports Server (NTRS)
Das, M.; Barut, A.; Madenci, E.; Ambur, D. R.
2004-01-01
This study presents a new triangular finite element for modeling thick sandwich panels, subjected to thermo-mechanical loading, based on a {3,2}-order single-layer plate theory. A hybrid energy functional is employed in the derivation of the element because of a C interelement continuity requirement. The single-layer theory is based on five weighted-average field variables arising from the cubic and quadratic representations of the in-plane and transverse displacement fields, respectively. The variations of temperature and distributed loading acting on the top and bottom surfaces are non-uniform. The temperature varies linearly through the thickness.
NASA Astrophysics Data System (ADS)
Abd El-Wahab, N. H.; Salah, Ahmed
2015-08-01
We study the interaction between a single mode electromagnetic field and a three-level Λ-type atom in the presence of a classical homogenous gravitational field when the atom is prepared initially in the momentum eigenstate. The model includes the detuning parameters and the classical homogenous gravitational field. The wave function is calculated by using the Schrödinger equation for a coherent electromagnetic field and an atom is in its excited state. The influence of the detuning parameter and the classical homogenous gravitational field on the temporal behavior of the mean photon number, the normalized second-order correlation function and the normal squeezing is analyzed. The results show that the presence of these parameters has an important effect on these phenomena. The conclusion is reached and some features are given.
Chen, Yan-Cong; Liu, Jun-Liang; Wernsdorfer, Wolfgang; Liu, Dan; Chibotaru, Liviu F; Chen, Xiao-Ming; Tong, Ming-Liang
2017-03-15
An extremely rare non-Kramers holmium(III) single-ion magnet (SIM) is reported to be stabilized in the pentagonal-bipyramidal geometry by a phosphine oxide with a high energy barrier of 237(4) cm(-1) . The suppression of the quantum tunneling of magnetization (QTM) at zero field and the hyperfine structures originating from field-induced QTMs can be observed even from the field-dependent alternating-current magnetic susceptibility in addition to single-crystal hysteresis loops. These dramatic dynamics were attributed to the combination of the favorable crystal-field environment and the hyperfine interactions arising from (165) Ho (I=7/2) with a natural abundance of 100 %.
Burkov, S I; Zolotova, O P; Sorokin, B P
2012-03-01
Paper is presented the results of computer simulation. Effect of the homogeneous dc electric field influence on the propagation of zero and first order Lamb and SH waves in piezoelectric langasite single crystal plates for a lot of cuts and directions have been calculated. Crystalline directions and cuts with maximal and minimal influence of dc electric field have indicated. Effect of hybridization of plate modes has been discussed.
Schlotter, W.F.; Luening, J.; Rick, R.; Chen, K.; Scherz, A.; Eisebitt, S.; Guenther, C.M.; Eberhardt, W.; Hellwig, O.; Stohr, J.; /SLAC, SSRL
2009-04-29
Panoramic full-field imaging is demonstrated by applying spatial multiplexing to Fourier transform holography. Multiple object and reference waves extend the effective field of view for lensless imaging without compromising the spatial resolution. In this way, local regions of interest distributed throughout a sample can be simultaneously imaged with high spatial resolution. A method is proposed for capturing multiple ultrafast images of a sample with a single x-ray pulse.
Dunbar, S.F.; Linggood, R.M.; Doppke, K.P.; Duby, A.; Wang, C.C. )
1990-08-01
Lymphoma of the conjunctiva is rare. It presents in older patients as a mass lesion and usually remains localized. Surgery is limited to biopsy, and radiation therapy is the definitive treatment of choice. The entire conjunctiva is treated. Relatively high doses (approximately 30 Gy) are required for local control, which may lead to cataract formation. Twelve patients with conjunctival lymphoma were treated at the Massachusetts General Hospital between 1979 and 1988. Ten of 12 patients presented with a unilateral lesion; 2 of 12 with bilateral lesions. Two of 12 patients were found to have systemic disease at the time of presentation. One patient developed conjunctival lymphoma 5 years after the diagnosis of generalized disease. Using electron beam, all patients were treated with a single anterior circular field to total doses ranging from 24 Gy to 30 Gy delivered in 8 to 16 fractions over 9 to 20 days. In all cases, the lens was shielded by a specially designed plastic contact lens bearing a 12 mm diameter lead shield. The lens dose was determined at varying depths beneath the shield for 6 MeV and 9 MeV electron beams and ranged from a minimum of 5% to an absolute maximum of 18% of the total dose delivered to the tumor. Local control was maintained in all patients with follow-up to 9 1/2 years. One patient relapsed distantly 3 years after treatment. One of 12 patients died of systemic disease 4 years after treatment of the ocular lesion. Two patients developed cataracts 4 and 5 years after treatment; one had bilateral cataract, although only one eye had been treated. Both patients were over 75 years old. In both cases, the cataracts were felt to be senile cataracts which are ophthalmologically and radiographically distinguishable from radiation induced lesions.
Use of single-well tracer dilution tests to evaluate LNAPL flux at seven field sites.
Mahler, Nicholas; Sale, Tom; Smith, Tim; Lyverse, Mark
2012-01-01
Petroleum liquids, referred to as light non-aqueous phase liquids (LNAPLs), are commonly found beneath petroleum facilities. Concerns with LNAPLs include migration into clean soils, migration beyond property boundaries, and discharges to surface water. Single-well tracer dilution techniques were used to measure LNAPL fluxes through 50 wells at 7 field sites. A hydrophobic tracer was mixed into LNAPL in a well. Intensities of fluorescence associated with the tracer were measured over time using a spectrometer and a fiber optic cable. LNAPL fluxes were estimated using observed changes in the tracer concentrations over time. Measured LNAPL fluxes range from 0.006 to 2.6 m/year with a mean and median of 0.15 and 0.064 m/year, respectively. Measured LNAPL fluxes are two to four orders of magnitude smaller than a common groundwater flux of 30 m/year. Relationships between LNAPL fluxes and possible governing parameters were evaluated. Observed LNAPL fluxes are largely independent of LNAPL thickness in wells. Natural losses of LNAPL through dissolution, evaporation, and subsequent biodegradation, were estimated using a simple mass balance, measured LNAPL fluxes in wells, and an assumed stable LNAPL extent. The mean and median of the calculated loss rates were found to be 24.0 and 5.0 m3/ha/year, respectively. Mean and median losses are similar to values reported by others. Coupling observed LNAPL fluxes to observed rates of natural LNAPL depletion suggests that natural losses of LNAPL may be an important parameter controlling the overall extent of LNAPL bodies.
Single-chain-in-mean-field simulations of weak polyelectrolyte brushes
NASA Astrophysics Data System (ADS)
Léonforte, F.; Welling, U.; Müller, M.
2016-12-01
Structural properties of brushes which are composed of weak acidic and basic polyelectrolytes are studied in the framework of a particle-based approach that implicitly accounts for the solvent quality. Using a semi-grandcanonical partition function in the framework of the Single-Chain-in-Mean-Field (SCMF) algorithm, the weak polyelectrolyte is conceived as a supramolecular mixture of polymers in different dissociation states, which are explicitly treated in the partition function and sampled by the SCMF procedure. One obtains a local expression for the equilibrium acid-base reaction responsible for the regulation of the charged groups that is also incorporated to the SCMF sampling. Coupled to a simultaneous treatment of the electrostatics, the approach is shown to capture the main features of weak polyelectrolyte brushes as a function of the bulk pH in the solution, the salt concentration, and the grafting density. Results are compared to experimental and theoretical works from the literature using coarse-grained representations of poly(acrylic acid) (PAA) and poly(2-vinyl pyridine) (P2VP) polymer-based brushes. As the Born self-energy of ions can be straightforwardly included in the numerical approach, we also study its effect on the local charge regulation mechanism of the brush. We find that its effect becomes significant when the brush is dense and exposed to high salt concentrations. The numerical methodology is then applied (1) to the study of the kinetics of collapse/swelling of a P2VP brush and (2) to the ability of an applied voltage to induce collapse/swelling of a PAA brush in a pH range close to the pKa value of the polymer.
2012-01-01
Background The metals bioavailability in soils is commonly assessed by chemical extractions; however a generally accepted method is not yet established. In this study, the effectiveness of Diffusive Gradients in Thin-films (DGT) technique and single extractions in the assessment of metals bioaccumulation in vegetables, and the influence of soil parameters on phytoavailability were evaluated using multivariate statistics. Soil and plants grown in vegetable gardens from mining-affected rural areas, NW Romania, were collected and analysed. Results Pseudo-total metal content of Cu, Zn and Cd in soil ranged between 17.3-146 mg kg-1, 141–833 mg kg-1 and 0.15-2.05 mg kg-1, respectively, showing enriched contents of these elements. High degrees of metals extractability in 1M HCl and even in 1M NH4Cl were observed. Despite the relatively high total metal concentrations in soil, those found in vegetables were comparable to values typically reported for agricultural crops, probably due to the low concentrations of metals in soil solution (Csoln) and low effective concentrations (CE), assessed by DGT technique. Among the analysed vegetables, the highest metal concentrations were found in carrots roots. By applying multivariate statistics, it was found that CE, Csoln and extraction in 1M NH4Cl, were better predictors for metals bioavailability than the acid extractions applied in this study. Copper transfer to vegetables was strongly influenced by soil organic carbon (OC) and cation exchange capacity (CEC), while pH had a higher influence on Cd transfer from soil to plants. Conclusions The results showed that DGT can be used for general evaluation of the risks associated to soil contamination with Cu, Zn and Cd in field conditions. Although quantitative information on metals transfer from soil to vegetables was not observed. PMID:23079133
Magnetic field asymmetry and high temperature magnetoresistance in single-walled carbon nanotubes
NASA Astrophysics Data System (ADS)
Cobden, David
2006-03-01
The length scales and scattering processes in the one-dimensional electron system in single-walled carbon nanotubes remain only partially understood. Measuring the magnetoresistance, in both linear and nonlinear response, is a way to investigate these processes. In disordered nanotubes with ballistic paths much shorter than the length, we observe magnetoresistance in the metallic regime which at low temperatures resembles the universal fluctuations and weak localization seen in higher dimensional metals. A parabolic magnetoresistance persists at room temperature, indicating a significant role for phase coherence and/or interactions at high temperatures. While the linear resistance of a two-terminal sample must be an even function of magnetic field B by Onsager's principle, the nonlinear resistance need not be. Importantly, the B-asymmetric nonlinear terms can in principle be used to infer the strength of electron-electron interactions in the sample [1]. We have therefore also measured in detail the lowest order B-asymmetric current contributions, with a focus on the B-linear term. This has apparently not been done before in any system. Consistent with general theory, at high temperatures the term is small and has a constant sign independent of Fermi energy. At low temperatures it grows and develops mesoscopic fluctuations. Although these result imply that interactions are involved in the transport, calculations specific to nanotubes are needed in order to extract interaction parameters. This work was done by the authors of Ref [2]. References: [1] E.L. Ivchenko and B. Spivak, Phys. Rev. B 66, 155404 (2002); [2] Jiang Wei, Michael Shimogawa, Zenghui Wang, Iuliana Radu, Robert Dormaier, and David H. Cobden, Phys. Rev. Lett. (Dec. 2005) (cond-mat/0506275).
Numerical simulation of two-dimensional single- and multiple-material flow fields
Lopez, A.R.; Baty, R.S. ); Kashiwa, B.A. )
1992-01-01
Over the last several years, Sandia National Laboratories has had an interest in developing capabilities to predict the flow fields around vehicles entering or exiting the water at a wide range of speeds. Such prediction schemes have numerous engineering applications in the design of weapon systems. For example, such a scheme could be used to predict the forces and moments experienced by an air-launched anti-submarine weapon on water-entry. Furthermore, a water-exit prediction capability could be used to model the complicated surface closure jet resulting from a missile being shot out of the water. The CCICE (Cell-Centered Implicit Continuous-fluid Eulerian) code developed at Los Alamos National Laboratory (LANL) was chosen to provide the fluid dynamics solver for high speed water-entry and water-exit problems. This implicit time-marching, two-dimensional, conservative, finite-volume code solves the multi-material, compressible, inviscid fluid dynamics equations. The incompressible version of the CCICE code, CCMAC (cell-Centered Marker and Cell), was chosen for low speed water- entry and water-exit problems in order to reduce the computational expense. These codes were chosen to take advantage of certain advances in numerical methods for computational fluid dynamics (CFD) that have taken place at LANL. Notable among these advances is the ability to perform implicit, multi-material, compressible flow simulations, with a fully cell-centered data structure. This means that a single set of control volumes are used, on which a discrete form of the conservation laws is satisfied. This is in control to the more classical staggered mesh methods, in which separate control volumes are defined for mass and momentum. 12 refs.
Numerical simulation of two-dimensional single- and multiple-material flow fields
Lopez, A.R.; Baty, R.S.; Kashiwa, B.A.
1992-03-01
Over the last several years, Sandia National Laboratories has had an interest in developing capabilities to predict the flow fields around vehicles entering or exiting the water at a wide range of speeds. Such prediction schemes have numerous engineering applications in the design of weapon systems. For example, such a scheme could be used to predict the forces and moments experienced by an air-launched anti-submarine weapon on water-entry. Furthermore, a water-exit prediction capability could be used to model the complicated surface closure jet resulting from a missile being shot out of the water. The CCICE (Cell-Centered Implicit Continuous-fluid Eulerian) code developed at Los Alamos National Laboratory (LANL) was chosen to provide the fluid dynamics solver for high speed water-entry and water-exit problems. This implicit time-marching, two-dimensional, conservative, finite-volume code solves the multi-material, compressible, inviscid fluid dynamics equations. The incompressible version of the CCICE code, CCMAC (cell-Centered Marker and Cell), was chosen for low speed water- entry and water-exit problems in order to reduce the computational expense. These codes were chosen to take advantage of certain advances in numerical methods for computational fluid dynamics (CFD) that have taken place at LANL. Notable among these advances is the ability to perform implicit, multi-material, compressible flow simulations, with a fully cell-centered data structure. This means that a single set of control volumes are used, on which a discrete form of the conservation laws is satisfied. This is in control to the more classical staggered mesh methods, in which separate control volumes are defined for mass and momentum. 12 refs.
Grantham, K; Wooten, H; Zhao, T; Klein, E
2014-06-01
Purpose: A common practice, in proton therapy, is to deliver a rotating subset of fields from the treatment plan for the daily fractions. This study compares the impact this practice has on the biological effective dose (BED) versus delivering all planned fields daily. Methods: For two scenarios (a phantom with a geometry approximating the anatomy of a prostate treatment with opposing lateral beams, and a clinical 3-field brain treatment), treatment plans were produced in Eclipse (Varian) to simulate delivery of one, two, and three fields per fraction. The RT-Dose file, structure set, and α/β ratios were processed using in-house MATLAB code to return a new RT-Dose file containing the BED (including a proton RBE of 1.1) which was imported back into Eclipse for analysis. Results: For targets and regions of field overlap in the treatment plan, BED is not affected by delivery regimen. In the phantom, BED in the femoral heads showed increased by 20% when a single field was used rather than two fields. In the brain treatment, the minimum BED to the left optic nerve and the pituitary gland increased by 13% and 10% respectively, for a one-field regime compared to three-fields per fraction. Comparing the two-field and threefield regimes, the optic nerve BED was not significantly affected and the minimum pituitary BED was 4% higher for two fields per day. Conclusion: Hypo-fractionation effects, in regions of non-overlap of fields, significantly increase the BED to the involved tissues by as much as 20%. Care should be taken to avoid inadvertently sacrificing plan effectiveness in the interest of reduced treatment time.
Leach, M.J.; Yio, J.J.; Cederwall, R.T.
1997-03-01
The objective analysis method use for deriving Single-Column Model (SCM) forcing fields with ARM data (Leach, et al., 1996) is undergoing continual improvement. Several improvements were identified at the SCM Workshop held at LLNL in April 1996. These include incorporating large-scale analyses in the objective analysis, and time-filtering input data streams.
Magnetic-field-induced quantum criticality in a spin-1 planar ferromagnet with single-ion anisotropy
NASA Astrophysics Data System (ADS)
Mercaldo, Maria Teresa; Rabuffo, Ileana; Decesare, Luigi; Caramicod'Auria, Alvaro
2014-03-01
The effects of single-ion anisotropy on field-induced quantum criticality in spin-1 planar ferromagnet is explored by means of the two-time Green's function method. We work at the Tyablikov decoupling level for exchange interactions and the Anderson-Callen decoupling level for single-ion anisotropy. In our analysis a longitudinal external magnetic field is used as the non-thermal control parameter and the phase diagram and the quantum critical properties are established for suitable values of the single-ion anisotropy parameter. We find that the single-ion anisotropy has sensible effects on the structure of the phase diagram close to the quantum critical point. Indeed, for values of the uniaxial crystal-field parameter above a positive threshold a re-entrant behavior appears for the critical line, while above this value the conventional magnetic-field-induced quantum critical scenario remains unchanged. M. T. Mercaldo, I. Rabuffo, L. De Cesare, A. Caramico D'Auria, Eur. Phys. J. B 86, 340 (2013)
NASA Astrophysics Data System (ADS)
Azanza, María. J.; Calvo, Ana C.; del Moral, A.
2001-05-01
Neurones recruiting and synchronized bioelectric activity recorded from Helix aspersa brain ganglia, under exposure to 50 Hz sinusoidal magnetic fields of 1-15 mT intensity, is reported. We show recruiting responses from single neurones and the synchronization of pairs of neurones activity. Experimental evidence and model theoretical explanation for the spreading of synchronization are presented.
NASA Astrophysics Data System (ADS)
Ban, Yue; Chen, Xi; Li, Chun-Fang
2007-04-01
We investigate the controllable negative and positive group delay in transmission through a single quantum well at the finite longitudinal magnetic fields. It is shown that the magneto-coupling effect between the longitudinal motion component and the transverse Landau orbits plays an important role in the group delay. The group delay depends not only on the width of potential well and the incident energy, but also on the magnetic-field strengthen and the Landau quantum number. The results show that the group delay can be changed from positive to negative by the modulation of the magnetic field. These interesting phenomena may lead to the tunable quantum mechanical delay line.
Pescini, E; Martínez, D S; De Giorgi, M G; Francioso, L; Ficarella, A
2015-12-01
In recent years, single dielectric barrier discharge (SDBD) plasma actuators have gained great interest among all the active flow control devices typically employed in aerospace and turbomachinery applications [1,2]. Compared with the macro SDBDs, the micro single dielectric barrier discharge (MSDBD) actuators showed a higher efficiency in conversion of input electrical power to delivered mechanical power [3,4]. This article provides data regarding the performances of a MSDBD plasma actuator [5,6]. The power dissipation values [5] and the experimental and numerical induced velocity fields [6] are provided. The present data support and enrich the research article entitled "Optimization of micro single dielectric barrier discharge plasma actuator models based on experimental velocity and body force fields" by Pescini et al. [6].
von Diezmann, Alex; Lee, Maurice Y.; Lew, Matthew D.; Moerner, W. E.
2016-01-01
The localization of single fluorescent molecules enables the imaging of molecular structure and dynamics with subdiffraction precision and can be extended to three dimensions using point spread function (PSF) engineering. However, the nanoscale accuracy of localization throughout a 3D single-molecule microscope’s field of view has not yet been rigorously examined. By using regularly spaced subdiffraction apertures filled with fluorescent dyes, we reveal field-dependent aberrations as large as 50–100 nm and show that they can be corrected to less than 25 nm over an extended 3D focal volume. We demonstrate the applicability of this technique for two engineered PSFs, the double-helix PSF and the astigmatic PSF. We expect these results to be broadly applicable to 3D single-molecule tracking and superresolution methods demanding high accuracy. PMID:26973863
NASA Astrophysics Data System (ADS)
Gerbino, Martina; Freese, Katherine; Vagnozzi, Sunny; Lattanzi, Massimiliano; Mena, Olga; Giusarma, Elena; Ho, Shirley
2017-02-01
We study the impact of assumptions about neutrino properties on the estimation of inflationary parameters from cosmological data, with a specific focus on the allowed contours in the ns/r plane, where ns is the scalar spectral index and r is the tensor-to-scalar ratio. We study the following neutrino properties: (i) the total neutrino mass Mν=∑i mi (where the index i =1 , 2, 3 runs over the three neutrino mass eigenstates); (ii) the number of relativistic degrees of freedom Neff at the time of recombination; and (iii) the neutrino hierarchy. Whereas previous literature assumed three degenerate neutrino masses or two massless neutrino species (approximations that clearly do not match neutrino oscillation data), we study the cases of normal and inverted hierarchy. Our basic result is that these three neutrino properties induce <1 σ shift of the probability contours in the ns/r plane with both current or upcoming data. We find that the choice of neutrino hierarchy (normal, inverted, or degenerate) has a negligible impact. However, the minimal cutoff on the total neutrino mass Mν ,min=0 that accompanies previous works using the degenerate hierarchy does introduce biases in the ns/r plane and should be replaced by Mν ,min=0.059 eV as required by oscillation data. Using current cosmic microwave background (CMB) data from Planck and Bicep/Keck, marginalizing over the total neutrino mass Mν and over r can lead to a shift in the mean value of ns of ˜0.3 σ toward lower values. However, once baryon acoustic oscillation measurements are included, the standard contours in the ns/r plane are basically reproduced. Larger shifts of the contours in the ns/r plane (up to 0.8 σ ) arise for nonstandard values of Neff. We also provide forecasts for the future CMB experiments Cosmic Origins Explorer (COrE, satellite) and Stage-IV (ground-based) and show that the incomplete knowledge of neutrino properties, taken into account by a marginalization over Mν, could induce a shift
NASA Astrophysics Data System (ADS)
Ishitobi, Hidekazu; Kobayashi, Taka-aki; Ono, Atsushi; Inouye, Yasushi
2017-03-01
In this study, polymer movement was induced in azo-polymer films by optical near-fields generated in the vicinity of single gold nano particles (GNPs) to visualize near-field distribution with a spatial resolution beyond the diffraction limit of light. A linearly polarized (Ex) laser beam was irradiated into GNPs to excite local surface plasmon resonance that enhanced the near-field around the GNPs. The findings indicated that different GNP diameters (that is, 50 nm and 80 nm) resulted in different deformation patterns on the films. The results were compared with theoretical calculations of near-field distributions, and the observations revealed that the deformation patterns were dependent on the ratio between Ex and Ey wherein each possessed a different field distribution.
Anderson, D.V.; Cohen, R.H.; Ferguson, J.R.; Johnston, B.M.; Sharp, C.B.; Willmann, P.A.
1981-06-30
The single particle orbit code, TIBRO, has been modified extensively to improve the interpolation methods used and to allow use of vector potential fields in the simulation of charged particle orbits on a 3D domain. A 3D cubic B-spline algorithm is used to generate spline coefficients used in the interpolation. Smooth and accurate field representations are obtained. When vector potential fields are used, the 3D cubic spline interpolation formula analytically generates the magnetic field used to push the particles. This field has del.BETA = 0 to computer roundoff. When magnetic induction is used the interpolation allows del.BETA does not equal 0, which can lead to significant nonphysical results. Presently the code assumes quadrupole symmetry, but this is not an essential feature of the code and could be easily removed for other applications. Many details pertaining to this code are given on microfiche accompanying this report.
NASA Astrophysics Data System (ADS)
Anderson, D. V.; Cohen, R. H.; Ferguson, J. R.; Johnston, B. M.; Sharp, C. B.; Willmann, P. A.
1981-06-01
The single particle orbit code, TIBRO, was modified extensively to improve the interpolation methods used and to allow use of vector potential fields in the simulation of charged particle orbits on a 3D domain. A 3D cubic B-spline algorithm is used to generate spline coefficients used in the interpolation. Smooth and accurate field representations are obtained. When vector potential fields are used, the 3D cubic spline interpolation formula analytically generates the magnetic field used to push the particles. This field has del.BETA = 0 to computer roundoff. When magnetic induction is used the interpolation allows del.BETA does not equal 0, which can lead to significant nonphysical results. Presently the code assumes quadrupole symmetry, but this is not an essential feature of the code and could be easily removed for other applications.
Wu, Yupan; Ren, Yukun; Tao, Ye; Hou, Likai; Jiang, Hongyuan
2016-12-06
We propose a simple, inexpensive microfluidic chip for large-scale trapping of single particles and cells based on induced-charge electroosmosis in a rotating electric field (ROT-ICEO). A central floating electrode array, was placed in the center of the gap between four driving electrodes with a quadrature configuration and used to immobilize single particles or cells. Cells were trapped on the electrode array by the interaction between ROT-ICEO flow and buoyancy flow. We experimentally optimized the efficiency of trapping single particles by investigating important parameters like particle or cell density and electric potential. Experimental and numerical results showed good agreement. The operation of the chip was verified by trapping single polystyrene (PS) microspheres with diameters of 5 and 20 μm and single yeast cells. The highest single particle occupancy of 73% was obtained using a floating electrode array with a diameter of 20 μm with an amplitude voltage of 5 V and frequency of 10 kHz for PS microbeads with a 5-μm diameter and density of 800 particles/μL. The ROT-ICEO flow could hold cells against fluid flows with a rate of less than 0.45 μL/min. This novel, simple, robust method to trap single cells has enormous potential in genetic and metabolic engineering.
Effects of quantum gravity on the inflationary parameters and thermodynamics of the early universe
NASA Astrophysics Data System (ADS)
Tawfik, A.; Magdy, H.; Farag Ali, Ahmed
2013-06-01
The effects of generalized uncertainty principle (GUP) on the inflationary dynamics and the thermodynamics of the early universe are studied. Using the GUP approach, the tensorial and scalar density fluctuations in the inflation era are evaluated and compared with the standard case. We find a good agreement with the Wilkinson Microwave Anisotropy Probe data. Assuming that a quantum gas of scalar particles is confined within a thin layer near the apparent horizon of the Friedmann-Lemaitre-Robertson-Walker universe which satisfies the boundary condition, the number and entropy densities and the free energy arising form the quantum states are calculated using the GUP approach. A qualitative estimation for effects of the quantum gravity on all these thermodynamic quantities is introduced.
NASA Astrophysics Data System (ADS)
Fengyun, Yang; Kaige, Wang; Dan, Sun; Wei, Zhao; Hai-qing, Wang; Xin, He; Gui-ren, Wang; Jin-tao, Bai
2016-07-01
The electrodynamic characteristics of single DNA molecules moving within micro-/nano-fluidic channels are important in the design of biomedical chips and bimolecular sensors. In this study, the dynamic properties of λ-DNA molecules transferring along the microchannels driven by the external electrickinetic force were systemically investigated with the single molecule fluorescence imaging technique. The experimental results indicated that the velocity of DNA molecules was strictly dependent on the value of the applied electric field and the diameter of the channel. The larger the external electric field, the larger the velocity, and the more significant deformation of DNA molecules. More meaningfully, it was found that the moving directions of DNA molecules had two completely different directions: (i) along the direction of the external electric field, when the electric field intensity was smaller than a certain threshold value; (ii) opposite to the direction of the external electric field, when the electric field intensity was greater than the threshold electric field intensity. The reversal movement of DNA molecules was mainly determined by the competition between the electrophoresis force and the influence of electro-osmosis flow. These new findings will theoretically guide the practical application of fluidic channel sensors and lab-on-chips for precisely manipulating single DNA molecules. Project supported by the National Natural Science Foundation of China (Grant No. 61378083), the International Cooperation Foundation of the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2011DFA12220), the Major Research Plan of National Natural Science Foundation of China (Grant No. 91123030), and the Natural Science Foundation of Shaanxi Province of China (Grant Nos. 2010JS110 and 2013SZS03-Z01).
Hood, Donald C.; De Cuir, Nicole; Blumberg, Dana M.; Liebmann, Jeffrey M.; Jarukasetphon, Ravivarn; Ritch, Robert; De Moraes, Carlos G.
2016-01-01
Purpose To evaluate a report for glaucoma diagnosis based on a single optical coherence tomography (OCT) protocol. Methods A wide-field (9 × 12 mm) swept-source (SS) OCT scan, encompassing the macula and disc, was obtained on 130 eyes (patients) with or suspected open-angle glaucoma, a mean deviation greater than or equal to −6 dB on a 24-2 visual field (VF), and spherical refractive error between ± 6 diopters (D). The single-page report contained a circumpapillary retinal nerve fiber layer (cpRNFL) thickness plot; retinal ganglion cell layer and retinal nerve fiber layer (RNFL) thickness and probability plots of the macula and optic nerve; and an enface slab image of the optic nerve. A report specialist judged each eye as healthy (H); probably healthy (PH); forced-choice healthy (FC-H); optic neuropathy (ON); probably ON (PON); forced-choice optic neuropathy (FC-ON). Two glaucoma specialists made similar judgments about the presence of glaucomatous damage. The glaucoma specialists had 24-2 and 10-2 VFs, fundus photos, patient chart information, and the single-page report including the report specialist's interpretation. Results The reference standard consisted of 57 eyes judged as glaucomatous (ON or PON) and 45 eyes judged as healthy (H or PH) by both glaucoma specialists. The report specialist identified 56 of the glaucomatous eyes as optic neuropathy (i.e., ON, PON, or FC-ON), and 44 of the healthy eyes as healthy (i.e., H, PH, or FC-H), an accuracy of 98.0%. Conclusions A single-page report based upon a single, wide-field OCT scan has the information needed to diagnose early glaucoma with excellent sensitivity/specificity. Translational Relevance It is possible that screening for glaucoma can be effective with only a single OCT protocol. PMID:27847691
NASA Astrophysics Data System (ADS)
Pian, Qi; Yao, Ruoyang; Intes, Xavier
2016-03-01
Single-pixel imaging based on compressive sensing theory has been a highlighted technique in the biomedical imaging field for many years. This interest has been driven by the possibility of performing microscopic or macroscopic imaging based on low-cost detector arrays, increased SNR (signal-to-noise ratio) in the acquired data sets and the ability to perform high quality image reconstruction with compressed data sets by exploiting signal sparsity. In this work, we present our recent work in implementing this technique to perform time domain fluorescence-labeled investigations in preclinical settings. More precisely, we report on our time-resolved hyperspectral single-pixel camera for fast, wide-field mapping of molecular labels and lifetime-based quantification. The hyperspectral single-pixel camera implements a DMD (Digital micro-mirror device) to generate optical masks for modulating the illumination field before it is delivered onto the sample and focuses the emission light signals into a multi-anode hyperspectral time-resolved PMT (Photomultiplier tube) to acquire spatial, temporal and spectral information enriched 4-D data sets. Fluorescence dyes with lifetime and spectral contrast are embedded in well plates and thin tissues. L-1 norm based regularization or the least square method, is applied to solve the underdetermined inverse problem during image reconstruction. These experimental results prove the possibility of fast, wide-field mapping of fluorescent labels with lifetime and spectral contrast in thin media.
Atalay, Han; Lefrant, Serge
2004-09-01
In this paper, we describe a new method to the selective nanovolume analysing of one isolated single walled carbon nanotube (SWNT). This concept is based on actually available imaging micro-spectrometry systems for working in near-field domain combined with a stigmatic solid immersion lens. This combination of different analytical methods, and modified and configured equipment entitles us to expand the functionality toward a three-dimensional (3D) nanovolume Raman mapping and photoluminescence intensity with a possible discrimination in polarization, as well as photoluminescence decaytime constant mapping with their unique combination. Subsequently, selective spectra can be acquired from the same location on the samples. By spectrally selecting a SWNT, we registered the spatial distribution of the emitted photons in x, y, z vectors to determine the position of a SWNT in the near-field domain. For the SWNTs that are localized with an accuracy better than 18 nm in the x, y and <1 nm in the z directions, we demonstrate an analytical sensitivity close to a single nanotube with unity throughput. This near-field capability is applied to resolve local variations unambiguously in the Raman spectrum along one single SWNT. Finally, in this paper, we report what we believe to be the first evidence of Raman mapping and 3D real optical imaging of carbon nanotubes with near-field resolution.
Emergent Gauge Fields from Curvature in Single Layers of Transition-Metal Dichalcogenides
NASA Astrophysics Data System (ADS)
Ochoa, Héctor; Zarzuela, Ricardo; Tserkovnyak, Yaroslav
2017-01-01
We analyze the electron dynamics in corrugated layers of transition-metal dichalcogenides. Due to the strong spin-orbit coupling, the intrinsic (Gaussian) curvature leads to an emergent gauge field associated with the Berry connection of the spinor wave function. We discuss the gauge field created by topological defects of the lattice, namely, tetragonal and octogonal disclinations and edge dislocations. Ripples and topological disorder induce the same dephasing effects as a random magnetic field, suppressing the weak localization effects. This geometric magnetic field can be detected in an Aharonov-Bohm interferometry experiment by measuring the local density of states in the vicinity of corrugations.
Photon statistics of light fields based on single-photon-counting modules
NASA Astrophysics Data System (ADS)
Li, G.; Zhang, T. C.; Li, Y.; Wang, J. M.
2005-02-01
Single-photon-counting modules (SPCM’s), with their high quantum efficiency, have been widely used to investigate effectively the photon statistics of various light sources, such as the single-photon state and emission light from controlled molecules, atoms, and quantum dots. However, such SPCM’s cannot distinguish the arrivals of one photon and two (or more than two) photons at a moment, which makes measurement correction in real experiments. We analyze the effect of SPCM’s on photon statistics based on the Hanbury-Brown-Twiss configuration when the total efficiency and background are considered, and it shows that the measured second-order degree of coherence and Mandel Q factor for different quantum states, including single-photon states and squeezed vacuum states, are corrected in different forms. A way of determining the squeezing of a squeezed vacuum state based on single-photon detection is presented.
NASA Astrophysics Data System (ADS)
Pascale-Hamri, A.; Perisanu, S.; Derouet, A.; Journet, C.; Vincent, P.; Ayari, A.; Purcell, S. T.
2014-03-01
We present here well-defined Coulomb staircases using an original field-emission experiment on several individual in situ—grown single-wall carbon nanotubes. A unique in situ process was applied nine times to progressively shorten one single-wall carbon nanotube down to ≃10 nm, which increased the oscillations periods from 5.5 to 80 V, the temperature for observable Coulomb staircase to 1100 K and the currents to 1.8 μA. This process led to the brightest electron source ever reported [9×1011 A/(str m2 V)].
Sakai, Masatoshi; Moritoshi, Norifumi; Kuniyoshi, Shigekazu; Yamauchi, Hiroshi; Kudo, Kazuhiro; Masu, Hyuma
2016-04-01
The effect of an applied gate electric field on the charge-order phase in β-(BEDT-TTF)2PF6 single-crystal field-effect transistor structure was observed at around room temperature by technical improvement with respect to sample preparation and electrical measurements. A relatively slight but systematic increase of the electrical conductance induced by the applied gate electric field and its temperature dependence was observed at around the metal-insulator transition temperature (TMI). The temperature dependence of the modulated electrical conductance demonstrated that TMI was shifted toward the lower side by application of a gate electric field, which corresponds to partial dissolution of the charge-order phase. The thickness of the partially dissolved charge order region was estimated to be several score times larger than the charge accumulation region.
A single TLD dose algorithm to satisfy federal standards and typical field conditions
Stanford, N.; McCurdy, D.E. )
1990-06-01
Modern whole-body dosimeters are often required to accurately measure the absorbed dose in a wide range of radiation fields. While programs are commonly developed around the fields tested as part of the National Voluntary Accreditation Program (NVLAP), the actual fields of application may be significantly different. Dose algorithms designed to meet the NVLAP standard, which emphasizes photons and high-energy beta radiation, may not be capable of the beta-energy discrimination necessary for accurate assessment of absorbed dose in the work environment. To address this problem, some processors use one algorithm for NVLAP testing and one or more different algorithms for the work environments. After several years of experience with a multiple algorithm approach, the Dosimetry Services Group of Yankee Atomic Electric Company (YAEC) developed a one-algorithm system for use with a four-element TLD badge using Li2B4O7 and CaSO4 phosphors. The design of the dosimeter allows the measurement of the effective energies of both photon and beta components of the radiation field, resulting in excellent mixed-field capability. The algorithm was successfully tested in all of the NVLAP photon and beta fields, as well as several non-NVLAP fields representative of the work environment. The work environment fields, including low- and medium-energy beta radiation and mixed fields of low-energy photons and beta particles, are often more demanding than the NVLAP fields. This paper discusses the development of the algorithm as well as some results of the system testing including: mixed-field irradiations, angular response, and a unique test to demonstrate the stability of the algorithm. An analysis of the uncertainty of the reported doses under various irradiation conditions is also presented.
A single TLD dose algorithm to satisfy federal standards and typical field conditions.
Stanford, N; McCurdy, D E
1990-06-01
Modern whole-body dosimeters are often required to accurately measure the absorbed dose in a wide range of radiation fields. While programs are commonly developed around the fields tested as part of the National Voluntary Accreditation Program (NVLAP), the actual fields of application may be significantly different. Dose algorithms designed to meet the NVLAP standard, which emphasizes photons and high-energy beta radiation, may not be capable of the beta-energy discrimination necessary for accurate assessment of absorbed dose in the work environment. To address this problem, some processors use one algorithm for NVLAP testing and one or more different algorithms for the work environments. After several years of experience with a multiple algorithm approach, the Dosimetry Services Group of Yankee Atomic Electric Company (YAEC) developed a one-algorithm system for use with a four-element TLD badge using Li2B4O7 and CaSO4 phosphors. The design of the dosimeter allows the measurement of the effective energies of both photon and beta components of the radiation field, resulting in excellent mixed-field capability. The algorithm was successfully tested in all of the NVLAP photon and beta fields, as well as several non-NVLAP fields representative of the work environment. The work environment fields, including low- and medium-energy beta radiation and mixed fields of low-energy photons and beta particles, are often more demanding than the NVLAP fields. This paper discusses the development of the algorithm as well as some results of the system testing including: mixed-field irradiations, angular response, and a unique test to demonstrate the stability of the algorithm. An analysis of the uncertainty of the reported doses under various irradiation conditions is also presented.
Single-Use Sensor Strips for Reliable Field Analysis of Gunshot Residue
2013-10-13
analyzers. From field samples, Gaussian parameters were extracted to build detection model where Bayes decision rule was implemented on Arduino ...GSR Final Report 22 detection model. Bayes decision rule was implemented on Arduino microcontroller and old field samples were run with
Bedard, Claude; Destexhe, Alain
2014-10-01
Neurons generate magnetic fields which can be recorded with macroscopic techniques such as magnetoencephalography. The theory that accounts for the genesis of neuronal magnetic fields involves dendritic cable structures in homogeneous resistive extracellular media. Here we generalize this model by considering dendritic cables in extracellular media with arbitrarily complex electric properties. This method is based on a multiscale mean-field theory where the neuron is considered in interaction with a "mean" extracellular medium (characterized by a specific impedance). We first show that, as expected, the generalized cable equation and the standard cable generate magnetic fields that mostly depend on the axial current in the cable, with a moderate contribution of extracellular currents. Less expected, we also show that the nature of the extracellular and intracellular media influence the axial current, and thus also influence neuronal magnetic fields. We illustrate these properties by numerical simulations and suggest experiments to test these findings.
Liu, Ju; Li, Zhi-Yuan
2014-11-17
One of the simplest models involving the atom-field interaction is the coupling of a single two-level atom with single-mode optical field. Under the rotating wave approximation, this problem is reduced to a form that can be solved exactly. But the approximation is only valid when the two levels are resonant or nearly resonant with the applied electromagnetic radiation. Here we present an analytical solution without the rotating wave approximation and applicable to general atom-field interaction far away from the resonance. We find that there exists remarkable influence of the initial phase of optical field on the Rabi oscillations and Rabi splitting, and this issue cannot be explored in the context of the rotating wave approximation. Due to the retention of the counter-rotating terms, higher-order harmonic appears during the Rabi splitting. The analytical solution suggests a way to regulate and control the quantum dynamics of a two-level atom and allows for exploring more essential features of the atom-field interaction.
Zhang, Junpei; Wang, Xia; Tang, Chaoqun; Zhong, Zhiqiang; Ma, Zongwei; Wang, Shaoliang; Han, Yibo; Han, Jun-Bo Li, Liang
2015-08-28
A bright green photoluminescence (PL) from {sup 4}S{sub 3∕2} → {sup 4}I{sub 15∕2} emission band in Er{sup 3+}:YVO{sub 4} single crystal has been observed with the excitation of an argon laser at 488.0 nm. More than two orders of PL enhancement have been obtained under the effect of magnetic fields, and the enhancement factor f reaches 170 when the applied magnetic field is 7.7 T under the sample temperature of 4.2 K. Unusually, the PL enhancements only happen at some certain magnetic fields (B{sub c}s), and a decrease of sample temperature will lead to the increase of f and decrease of B{sub c}. The results confirm that this PL enhancement originates from the resonance excitation of the electron transitions induced by the cross of the laser energy and the absorption energy modulated by both the magnetic field and temperature. This special PL enhancement in Er{sup 3+}:YVO{sub 4} single crystal can be applied in the calibration of pulsed high magnetic field, detection of material fine energy structures, and modulation of magneto-optical devices.
NASA Astrophysics Data System (ADS)
Pradhan, A. K.; Chen, C.; Wanklyn, B. M.
1995-02-01
We have measured the high-magnetic-field (up to 15 T) transport properties of (BiPb) 2Sr 2Ca 1Cu 2O y (BPSCCO) single crystals and (2223) ceramics. We have extracted the melting line of BPSCCO crystals from the measurements of precise I- V curves when the field is applied parallel to the c-axis and shown that the melting line coincides with the irreversibility line measured by the magnetisation technique. This is explained for the case of weak pinning. The depinning line was found to be 10 to 12 K above the melting line. The observed hump in the magnetoresistance curve above 2 T predicts the depinning of flux from the weak pinning centres when the temperature approaches the depinning temperature. The basic behavior of ceramic BPSCCO, although having a higher Tc, is similar to its single crystal analogue with (2212) phase except for the enhanced depinning line.
Modeling of seismic field in porous medium:Simulation study of single pore and pore ensemble effects
NASA Astrophysics Data System (ADS)
Shatskaya, A. A.; Nemirovich-Danchenko, M. M.; Terre, D. A.
2015-11-01
The article considers the effect of porous media on elastic wave field. Based on numerical modeling, diffraction pattern of the wave propagating through a single pore in carbonates has been produced. Matrix properties (calcite and dolomite) and fluid (water) are modeled based on thin core section image. The qualitative comparison with the available computational data has been performed. Provided that ensemble of pores is involved, the effect of porous medium on seismic field has been studied. For comparison with experimental data the model of porous sintered aluminum Al-6061 has been considered. The processing of numerical modeling results made it possible to estimate average velocities in the model of porous aluminum and compare them with physical modeling data. The provided estimates have indicated qualitative (single pore) and quantitative (ensemble of pores) correlation of simulation and experiment results.
Xiao, Kai; Li, Rongjin; Tao, Jing; Payzant, E Andrew; Ivanov, Ilia N; Puretzky, Alexander A; Hu, Wenping; Geohegan, David B
2009-01-01
This paper describes a simple, vapor-phase route to the synthesis of metastable α-phase copper-phthalocyanine (CuPc) single-crystal nanowires through control of the growth temperature. The influence of the growth temperature on the crystal structures, morphology, and size of the CuPc nanostructures was explored by XRD, optical absorption and Transmission Electron Microscopy (TEM). α-CuPc nanowires were successfully incorporated as active semiconductors in field-effect transistors (FETs). Single nanowire devices exhibited the carrier mobilities and current on/off ratios as high as 0.4 cm2/Vs and > 104, respectively, rendering them useful for organic photovoltaic cells, organic light-emitting diodes, field-effect transistors, memories and gas sensors
Falcucci, G; Chiatti, G; Succi, S; Mohamad, A A; Kuzmin, A
2009-05-01
A nonisotropic tensorial extension of the single-component Shan-Chen pseudopotential Lattice Boltzmann method for nonideal fluids is presented. Direct comparison with experimental data shows that this extension is able to capture relevant features of ferrofluid behavior, such as the deformation and subsequent rupture of a liquid droplet as a function of an externally applied magnetic field. The present model offers an economic lattice-kinetic pathway to the simulation of complex ferrofluid hydrodynamics.
Su, Jiaye; Guo, Hongxia
2011-01-25
The transport of water molecules through nanopores is not only crucial to biological activities but also useful for designing novel nanofluidic devices. Despite considerable effort and progress that has been made, a controllable and unidirectional water flow is still difficult to achieve and the underlying mechanism is far from being understood. In this paper, using molecular dynamics simulations, we systematically investigate the effects of an external electric field on the transport of single-file water molecules through a carbon nanotube (CNT). We find that the orientation of water molecules inside the CNT can be well-tuned by the electric field and is strongly coupled to the water flux. This orientation-induced water flux is energetically due to the asymmetrical water-water interaction along the CNT axis. The wavelike water density profiles are disturbed under strong field strengths. The frequency of flipping for the water dipoles will decrease as the field strength is increased, and the flipping events vanish completely for the relatively large field strengths. Most importantly, a critical field strength E(c) related to the water flux is found. The water flux is increased as E is increased for E ≤ E(c), while it is almost unchanged for E > E(c). Thus, the electric field offers a level of governing for unidirectional water flow, which may have some biological applications and provides a route for designing efficient nanopumps.
Pescini, E.; Martínez, D.S.; De Giorgi, M.G.; Francioso, L.; Ficarella, A.
2015-01-01
In recent years, single dielectric barrier discharge (SDBD) plasma actuators have gained great interest among all the active flow control devices typically employed in aerospace and turbomachinery applications [1,2]. Compared with the macro SDBDs, the micro single dielectric barrier discharge (MSDBD) actuators showed a higher efficiency in conversion of input electrical power to delivered mechanical power [3,4]. This article provides data regarding the performances of a MSDBD plasma actuator [5,6]. The power dissipation values [5] and the experimental and numerical induced velocity fields [6] are provided. The present data support and enrich the research article entitled “Optimization of micro single dielectric barrier discharge plasma actuator models based on experimental velocity and body force fields” by Pescini et al. [6]. PMID:26425667
Excitons and multi-excitons in single CdTe quantum dots probed by near-field spectroscopy
NASA Astrophysics Data System (ADS)
Brun, M.; Huant, S.; Woehl, J. C.; Motte, J.-F.; Marsal, L.; Mariette, H.
2002-03-01
A near-field optical spectroscopy study of a single CdTe/ZnTe quantum dot at low temperatures is presented. While the photoluminescence spectrum at low excitation power reveals only one single sharp peak due to the radiative recombination of excitons (X) in the single dot, several additional sharp peaks appear with increasing excitation density. The dominant features are ascribed to exciton complexes and charged exciton complexes such as negatively charged excitons (X -), neutral (2X and 3X) and negative (2X - and 3X -) biexcitons and triexcitons. Exciton charging arises due to efficient hole trapping by residual acceptors in the barrier material. This partly inhibits the formation of biexcitons and triexcitons. A spectral feature appearing close to the X - peak is tentatively assigned to X 2- negative excitons. This feature is found to shift to the red with increasing power: two possible explanations for this unexpected behaviour are proposed.
Magnetic anisotropy and crystalline electric field effects in RRh{sub 4}B{sub 4} single crystals.
Zhou, H.; Lambert, S. E.; Maple, M. B.; Dunlap, B. D.; Materials Science Division; Univ. of California at San Diego
2009-08-01
Research on polycrystalline RRh{sub 4}B{sub 4} samples has shown that crystalline electric field (CEF) effects play an important role in these compounds. The successful synthesis of single crystal samples of RRh{sub 4}B{sub 4} with R = Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu has provided an opportunity to further investigate CEF effects in these materials. Magnetization and magnetic susceptibility measurements on the RRh{sub 4}B{sub 4} single crystals revealed strong magnetic anisotropy, and the experimental results could be described well by CEF calculations based on the parameters derived from an analysis of experimental data for ErRh{sub 4}B{sub 4} single crystals. The easy directions of magnetization of these compounds are consistent with the signs of the Stevens factor {alpha}J of the CEF Hamiltonian. A strong influence of magnetic anisotropy on superconductivity was also observed.
NASA Astrophysics Data System (ADS)
Ohori, Takahiro; Nagaso, Satoshi; Ohno, Yasuhide; Maehashi, Kenzo; Inoue, Koichi; Matsumoto, Kazuhiko
2010-06-01
We have fabricated nonvolatile memory based on top-gated carbon nanotube field-effect transistors (CNTFETs). Two kinds of insulating films, SiNx and SiO2, were deposited to control the hysteresis characteristics after the removal of water molecules around the single-walled CNT channels. The interface between the SiNx and SiO2 films is expected to act as a charge storage node of nonvolatile memory. The fabricated CNTFET-based memory devices clearly exhibited not only a memory effect but also good retention characteristics for charge storage. Furthermore, single-hole charging and discharging phenomena were clearly observed in the CNTFET-based memory devices by reducing the number of carriers trapped in the interface between the SiNx and SiO2 films. These results indicate that the CNTFET-based nonvolatile memory can be potentially used to realize single-electron memory.
Circular polarization of primordial gravitational waves in string-inspired inflationary cosmology
Satoh, Masaki; Soda, Jiro; Kanno, Sugumi
2008-01-15
We study a mechanism to produce the circular polarization of primordial gravitational waves. The circular polarization is generated during the superinflation driven by the Gauss-Bonnet term in the string-inspired cosmology. The instability in the tensor mode caused by the Gauss-Bonnet term and the parity violation due to the gravitational Chern-Simons term are the essential ingredients of the mechanism. We also discuss detectability of the produced circular polarization of gravitational waves. It turns out that the simple model of single-field inflation contradicts cosmic microwave background (CMB) observations. To circumvent this difficulty, we propose a two-field inflation model. In this two-field model, the circular polarization of gravitational waves is created in the frequency range designed by the big-bang observer (BBO) or the deci-hertz gravitational-wave observatory (DECIGO)
NASA Technical Reports Server (NTRS)
deGroh, H. C.; Li, K.; Li, B. Q.
2002-01-01
A 2-D finite element model is presented for the melt growth of single crystals in a microgravity environment with a superimposed DC magnetic field. The model is developed based on the deforming finite element methodology and is capable of predicting the phenomena of the steady and transient convective flows, heat transfer, solute distribution, and solid-liquid interface morphology associated with the melt growth of single crystals in microgravity with and without an applied magnetic field. Numerical simulations were carried out for a wide range of parameters including idealized microgravity conditions, the synthesized g-jitter and the real g-jitter data taken by on-board accelerometers during space flights. The results reveal that the time varying g-jitter disturbances, although small in magnitude, cause an appreciable convective flow in the liquid pool, which in turn produces detrimental effects during the space processing of single crystal growth. An applied magnetic field of appropriate strength, superimposed on microgravity, can be very effective in suppressing the deleterious effects resulting from the g-jitter disturbances.
Nonadiabatic electron dynamics of single-electron transport in a perpendicular magnetic field
He, JianHong; Guo, HuaZhong; Gao, Jie
2014-04-28
We present results of our investigation into the nonadiabatic electron dynamics of a moving quantum dot assisted by surface acoustic waves (SAWs) in a perpendicular magnetic field. The measurements show the evolution of a quantized acoustoelectric current in a modulated external field, which provides direct information of the energy spectrum and the occupation of the SAW-induced elliptical dynamical quantum dot. By comparing the magnetic field dependence of the spectrum with that of a somewhat symmetric circular dot, we find the appearance of nonadiabatic excitations at low magnetic fields resulting from the anisotropy of the dot. We also detect the transitions between different quantum states of the elliptical dot, achieved by exploiting the interference of two phase-tuned SAWs. Our results demonstrate that the quantum states in an asymmetric dot are fragile and extremely sensitive to their environment.
High Field Magnetization measurements of uranium dioxide single crystals (P08358- E003-PF)
Gofryk, K.; Harrison, N.; Jaime, M.
2014-12-01
Our preliminary high field magnetic measurements of UO_{2 } are consistent with a complex nature of the magnetic ordering in this material, compatible with the previously proposed non-collinear 3-k magnetic structure. Further extensive magnetic studies on well-oriented (<100 > and <111>) UO_{2} crystals are planned to address the puzzling behavior of UO_{2} in both antiferromagnetic and paramagnetic states at high fields.
Experimental Observation of the Nonlinear Response of Single Bubbles to an Applied Acoustic Field
1988-12-31
93 INTRODUCTION Cavitation bubbles in liquids have been of interest to scientists since 175.4. ’. hen Leonhard Euler [l1 first...or can be observed in single bubble oscillations. S REFERENCES 1. L. Euler , Histoire de ’Academic Royale des Sciences et Belles Lettres, Mem. R. 10
Exchange field on the rare earth Sm3+ in a single crystal perovskite SmMnO3
NASA Astrophysics Data System (ADS)
Cheng, J.-G.; Zhou, J.-S.; Goodenough, J. B.; Su, Y. T.; Sui, Y.; Ren, Y.
2011-09-01
Single crystal SmMnO3 has been grown by the floating-zone method. We have measured the magnetization and specific heat in magnetic fields oriented along three principal crystal axes of precisely oriented single crystals. Below TN of the Mn3+-ion array, the magnetic moments of the Sm3+ ions are progressively oriented antiparellel to the weak canted-spin ferromagnetic moment of the antiferromagnetic (AF) Mn3+-ion array due to an internal exchange field Hin ∥ c. On cooling through a compensation temperature Tcomp ≈ 9 K, the dominant moment parallel to c changes from the canted-spin Mn3+ ions to the Sm3+ moments. A spin reversal in an Hc ≥ 1 T changes the magnetic field splitting of the Kramers doublet on the Sm3+ ions from Hin - Hc to Hin + Hc, where Hc is a field applied along the c axis. This change, monitored by the Schottky contribution to the specific heat, creates an abrupt change at Tt = Tcomp ± δ. We have found no evidence that the transition at Tt is first-order despite its abrupt nature.
NASA Astrophysics Data System (ADS)
Oh, Seong-Woo; Lee, Dong-Jin; Park, Min-Kyu; Park, Kyoung Ho; Lee, Joun-Ho; Kim, Byeong Koo; Kim, Hak-Rin
2015-10-01
We demonstrated the effect of the pretilt angle on the viewing angle properties of the single-domain fringe-field switching (FFS) mode, and proposed a method to enhance the viewing angle properties. Firstly, we investigated the origin of the asymmetric viewing angle problems in the field-on and off states by performing a field-induced liquid crystal (LC) reorientation analysis. Because of the asymmetric properties induced by the coupling between the tilting angle of the LC director and the polar component of the electric field, a zero pretilt angle is essential for the symmetric viewing angle properties. Secondly, to eliminate the pretilt angle, which is generally inevitable with the rubbing process, we applied polystyrene (PS) alignment layer which generates an easy axis perpendicular to the rubbing direction. Azimuthal anchoring energy and thermal stability of the PS layer were improved by employing UV-curable reactive mesogen (RM) within the LC cell. The RM-stabilized PS layer preserved the zero pretilt angle with enhanced thermal stability. Finally, by evaluating 2.4 in QVGA single-domain FFS LC cells, we confirmed the improved alignment ability of the RM-stabilized PS layer and the effect of the zero pretilt angle on electro-optical properties such as response time and viewing angle.
Large low-field positive magnetoresistance in nonmagnetic half-Heusler ScPtBi single crystal
NASA Astrophysics Data System (ADS)
Hou, Zhipeng; Wang, Yue; Liu, Enke; Zhang, Hongwei; Wang, Wenhong; Wu, Guangheng
2015-11-01
High-quality nonmagnetic half-Heusler ScPtBi single crystals were synthesized by a Bi self-flux method. This compound was revealed to be a hole-dominated semimetal with a large low-field magnetoresistance up to 240% at 2 K in a magnetic field of 1 T. Magneto-transport measurements demonstrated that the large low-field magnetoresistance effect resulted from the coexistence of field-induced metal-semiconductor transition and weak-antilocalization effect. Moreover, Hall measurements indicated that ScPtBi single crystal showed a high mobility over a wide temperature region even up to room temperature (4050 cm2V-1s-1 at 2 K-2016 cm2V-1s-1 at 300 K). These findings not only suggest the nonmagnetic ScPtBi semimetal a potential material candidate for applications in high-sensitivity magnetic sensors but also are of great significance to comprehensively understand the rare-earth based half-Heusler compounds.
Measuring 10-20 T magnetic fields in single wire explosions using Zeeman splitting
NASA Astrophysics Data System (ADS)
Banasek, J. T.; Engelbrecht, J. T.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.
2016-10-01
We have shown that the Zeeman splitting of the sodium (Na) D-lines at 5890 Å and 5896 Å can be used to measure the magnetic field produced by the current flowing in an exploding wire prior to wire explosion. After wire explosion, the lines in question are either not visible in the strong continuum from the exploding wire plasma, or too broad to measure the magnetic field by methods discussed in this paper. We have determined magnetic fields in the range 10-20 T, which lies between the small field and Paschen-Back regimes for the Na D-lines, over a period of about 70 ns on a 10 kA peak current machine. The Na source is evaporated drops of water with a 0.171 M NaCl solution deposited on the wire. The Na desorbs from the wire as it heats up, and the excited vapor atoms are seen in emission lines. The measured magnetic field, determined by the Zeeman splitting of these emission lines, estimates the average radial location of the emitting Na vapor as a function of time under the assumption the current flows only in the wire during the time of the measurement.
A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies
Islam, Zahirul; Lang, Jonathan C.; Ruff, Jacob P. C.; Ross, Kathryn A.; Gaulin, Bruce D.; Nojiri, Hiroyuki; Matsuda, Yasuhiro H.; Qu Zhe
2009-11-15
We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields ({approx}1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.
NASA Astrophysics Data System (ADS)
Abdikian, Alireza
2016-10-01
Propagation of an electrostatic oscillation by using the linearized quantum hydrodynamic model in conjunction with Maxwell's equations was studied. The dispersion relation of a system of electron plasma in single-walled carbon nanotubes in the presence of an external magnetic field B 0 by considering the exchange-correlation effects in 2D cylindrical geometry is derived here. The uniform static magnetic field is assumed to be normal to the cylindrical surface (Voigt configuration). Distribution of the electrons and ions are considered uniformly over the cylindrical surface of a nanotube. It is found that the external magnetic field has significant impact on the wave in the longer wavelength. The influence of variation in azimuthal index and radius of the nanotube on dispersion relation is also discussed. It is tried to plot some schemes and analyze numerically in different limits of cylindrical and planar geometries. The results can be important in the study of collective phenomena in nanostructures.
A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies.
Islam, Zahirul; Ruff, Jacob P C; Nojiri, Hiroyuki; Matsuda, Yasuhiro H; Ross, Kathryn A; Gaulin, Bruce D; Qu, Zhe; Lang, Jonathan C
2009-11-01
We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields (approximately 1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.
NASA Astrophysics Data System (ADS)
Zhuo, Fangping; Li, Qiang; Li, Yuanyuan; Gao, Jinghan; Yan, Qingfeng; Zhang, Yiling; Xi, Xiaoqing; Chu, Xiangcheng; Cao, Wenwu
2017-02-01
(Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals with composition close to the morphotropic phase boundary had been grown by the flux method. The antiferroelectric-ferroelectric phase switching electric field was 0.8 kV/mm. Temperature-dependent dielectric and polarization versus electric field hysteresis loops revealed that the electric field induced ferroelectric phase could transform back into the antiferroelectric phase at depolarization temperature (145 °C). An enhanced pyroelectric coefficient value of 1.46 μC/cm2/K was obtained at 145 °C, which is several times larger than that of conventional pyroelectric materials. Furthermore, multiple peak pyroelectric responses and an enhanced harvested energy density value of 0.4 J/cm3 were achieved in the PLZST crystal. The enhanced harvested energy density and multiple peak pyroelectric responses make the PLZST crystal a promising candidate for high sensitive temperature sensors and energy conversion technologies.
Kittler, W C; Obruchkov, S; Galvosas, P; Hunter, M W
2014-10-01
Pulsed field gradient nuclear magnetic resonance provides a powerful tool for the measurement of particle diffusion and mobility. When these particles are contained in a porous medium, the diffusive process is influenced by the pore boundaries, and their effect on diffusion measurements provides information about the pore space. The acquisition of the apparent diffusion coefficient and its dependence on time, in the short time limit, reveals the surface to volume ratio of the porous medium, and in the long time limit, its tortuosity. With conventional pulsed field gradient techniques, processes where pore boundaries are evolving on the sub-second time scale cannot be resolved. Using pulsed second order magnetic fields in conjunction with one-dimensional imaging and the pulse sequence Difftrain, this paper presents a proof of concept for the first ever real time single-shot surface to volume NMR measurement.
Chavez-Pirson, A; Chu, S T
1999-01-01
We solve numerically the three-dimensional vector form of Maxwell's equation for the situation of near-field excitation and collection of luminescence from a single quantum dot, using a scanning near-field optical fibre probe with subwavelength resolution. We highlight the importance of polarization-dependent effects in both the near-field excitation and collection processes. Applying a finite-difference time domain method, we calculate the complete vector fields emerging from a realistic probe structure which is in close proximity to a semiconductor surface. We model the photoluminescence from the quantum dot in terms of electric dipoles of different polarization directions, and determine the near-field luminescence images of the dot captured by the same probe. We show that a collimating effect in the high index semiconductor significantly improves the spatial resolution in the excitation-collection mode. We find that the spatial resolution, image shape and collection efficiency of near-field luminescence imaging strongly depend on the polarization direction as represented by the orientation of the radiating electric dipoles inside the quantum dot.
Vera Cruz, C.M.; Leach, J.E.; Ardales, E.Y.; Talag, J.
1996-12-01
The haplotypic variation of Xanthomonas oryzae pv. oryzae in a farmer;s field that had endemic bacterial blight in the Philippines was evaluated at a single time. The genomic structure of the field population was analyzed by repetitive sequence-based polymerase chain reaction with oligonucleotide primers corresponding to interspersed repeated sequences in prokaryotic genomes and restriction fragment length polymorphism (RFLP) with the insertion sequence IS1113. The techniques and specific probes and primers were selected because they grouped consistently into the same lineages a set of 30 selected X. oryzae pv. oryzae strains that represented the four distinct RFLP lineages found in the Philippines did. Strains (155) were systematically collected from a field planted to rice cv. Sinandomeng, which is susceptible to the indigenous pathogen population. Two of the four Philippine lineages, B and C, which included race 2 and races 3 and 9, respectively, were detected in the field. Lineage C was the predominant population (74.8%). The haplotypic diversities of 10 of the 25 blocks were significantly greater than the total haplotypic diversity of the collection in the entire field; however, between individual blocks the haplotypic diversities were not significantly different. Haplo-types from both lineages were distributed randomly across the field. Analysis of genetic diversity at the microgeographic scale provided insights into the finer scale of variation of X. oryzae pv. oryzae, which are useful in designing experiments to study effects of host resistance on the population structure of the bacterial blight pathogen. 46 refs., 4 figs., 2 tabs.
NASA Astrophysics Data System (ADS)
Wang, Xiaoping; Wang, Jinye; Wang, Lijun
2016-05-01
A series of single-layer nano-carbon (SNC) films, diamond films, and diamond/nano-carbon (D/NC) composite films have been prepared on the highly doped silicon substrate by using microwave plasma chemical vapor deposition techniques. The films were characterised by scanning electron microscopy, Raman spectroscopy, and field emission I-V measurements. The experimental results indicated that the field emission maximum current density of D/NC composite films is 11.8-17.8 times that of diamond films. And the field emission current density of D/NC composite films is 2.9-5 times that of SNC films at an electric field of 3.0 V/μm. At the same time, the D/NC composite film exhibits the advantage of improved reproducibility and long term stability (both of the nano-carbon film within the D/NC composite cathode and the SNC cathode were prepared under the same experimental conditions). And for the D/NC composite sample, a high current density of 10 mA/cm2 at an electric field of 3.0 V/μm was obtained. Diamond layer can effectively improve the field emission characteristics of nano-carbon film. The reason may be due to the diamond film acts as the electron acceleration layer.
Single-mode instability of a ferrofluid-mercury interface under a nonuniform magnetic field.
Singh, Chamkor; Das, Arup K; Das, Prasanta K
2016-07-01
This work reports an experimental and a numerical study of the interfacial instability in a mercury-ferrofluid system caused by a spatially nonuniform magnetic field against the action of gravity and interfacial tension. The interface evolution is observed to be continuous till its movement is hindered by a physical boundary. In contrast to the behavior of the ferrofluid interface under uniform field, we noted the instability growth to be monotonic under a field gradient. A steepness in the growth curve is noticed during the later stages of the instability, indicating a high magnitude of the growth velocities. Some unique phenomena, such as similarity of the growth at the initial stage, a slope transition in the growth curve at a later stage, and wrapping and pinning of the interface are observed, both in experiments and simulations.
Spatiotemporal Imaging of the Acoustic Field Emitted by a Single Copper Nanowire.
Jean, Cyril; Belliard, Laurent; Cornelius, Thomas W; Thomas, Olivier; Pennec, Yan; Cassinelli, Marco; Toimil-Molares, Maria Eugenia; Perrin, Bernard
2016-10-12
The monochromatic and geometrically anisotropic acoustic field generated by 400 and 120 nm diameter copper nanowires simply dropped on a 10 μm silicon membrane is investigated in transmission using three-dimensional time-resolved femtosecond pump-probe experiments. Two pump-probe time-resolved experiments are carried out at the same time on both sides of the silicon substrate. In reflection, the first radial breathing mode of the nanowire is excited and detected. In transmission, the longitudinal and shear waves are observed. The longitudinal signal is followed by a monochromatic component associated with the relaxation of the nanowire's first radial breathing mode. Finite difference time domain (FDTD) simulations are performed and accurately reproduce the diffracted field. A shape anisotropy resulting from the large aspect ratio of the nanowire is detected in the acoustic field. The orientation of the underlying nanowires is thus acoustically deduced.
Radu, A.; Kirakosyan, A. A.; Baghramyan, H. M.; Barseghyan, M. G.; Laroze, D.
2014-09-07
The influence of an intense laser field on one-electron states and intraband optical absorption coefficients is investigated in two-dimensional GaAs/Ga{sub 0.7}Al{sub 0.3}As quantum rings. An analytical expression of the effective lateral confining potential induced by the laser field is obtained. The one-electron energy spectrum and wave functions are found using the effective mass approximation and exact diagonalization technique. We have shown that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that only blueshift is obtained with increasing outer radius of the quantum ring.
Nanospectrofluorometry inside single living cell by scanning near-field optical microscopy
NASA Astrophysics Data System (ADS)
Lei, F. H.; Shang, G. Y.; Troyon, M.; Spajer, M.; Morjani, H.; Angiboust, J. F.; Manfait, M.
2001-10-01
Near-field fluorescence spectra with subdiffraction limit spatial resolution have been taken in the proximity of mitochondrial membrane inside breast adenocarcinoma cells (MCF7) treated with the fluorescent dye (JC-1) by using a scanning near-field optical microscope coupled with a confocal laser microspectrofluorometer. The probe-sample distance control is based on a piezoelectric bimorph shear force sensor having a static spring constant k=5 μN/nm and a quality factor Q=40 in a physiological medium of viscosity η=1.0 cp. The sensitivity of the force sensor has been tested by imaging a MCF7 cell surface.
Casimir force for a scalar field in a single brane world
Linares, R.; Morales-Tecotl, H. A.; Pedraza, O.
2010-02-10
Vacuum force is an interesting low energy test for brane worlds due to its dependence on field's modes and its role in submillimeter gravity experiments. In this contribution we obtain the scalar field vacuum force between two parallel plates lying in the brane of a Randall-Sundrum scenario extended by p compact dimensions (RSII-{sub p}). We obtain the force using the Green's function technique and we compare our results with the ones obtained by using the zeta function regularization method. As a result we obtain agreement in the expression for the force independently of the method used, thus we solve a previous discrepancy between the two approaches.
Near-Field Orientation Sensitive Terahertz Micro-Spectroscopy of Single Crystals
NASA Astrophysics Data System (ADS)
Acbas, Gheorghe; Singh, Rohit; Snell, Edward; Markelz, Andrea
2012-02-01
We present spectroscopic imaging studies of molecular crystals. These measurements examine the anisotropy of the intra and inter-molecular vibrational modes of single crystals at terahertz frequencies. The method is based on the technique developed in [1-2] for sub-wavelength resolution time domain terahertz spectroscopy (THz TDS), with added polarization orientation dependent measurements and hydration control. This method allows us to study the spectroscopic properties of small single crystals with sizes down to 20 micrometers. In addition, mapping the spectroscopic information at such small spatial scales allows us to reduce the water absorption and interference artifacts that usually affect protein THz TDS measurements. We show the polarization sensitive terahertz absorption spectra in the (0.3-3THz) range of sucrose, oxalic acid and lysozyme protein crystals. *M. A. Seo, et. al., Opt. Express, 15(19):11781--11789, 09 (2007) *J. R Knab, et. al., App. Phys. Lett.,97, 031115 (2010)
Vibration of a Singly-curved Thin Shell Reflector with a Unidirectional Tension Field
NASA Technical Reports Server (NTRS)
Williams, R. Brett; Klein, Kerry J.; Agnes, Gregory S.
2006-01-01
Increased science requirements for space-based instruments over the past few decades have lead to the increased popularity of deployable space structures constructed from thin, lightweight films. Such structures offer both low mass and the ability to be stowed inside conventional launch vehicles. The analysis in this work pertains to large, singly-curved lightweight deployable reflectors commonly used in radar antennas and space telescopes. These types of systems, which can vary a great deal in size, often have frequency requirement that must be met. This work discusses two missions that utilize this type of aperture technology, and then develops a Rayleigh-Ritz model that predicts the natural frequencies and mode shapes for a (nearly) flat and singly-curved reflector with unidirectional in-plane loading. The results are compared with NASTRAN analyses.
Investigation of a single barrier discharge in submillimeter air gaps. Nonuniform field
NASA Astrophysics Data System (ADS)
Bondarenko, P. N.; Emel'yanov, O. A.; Shemet, M. V.
2014-08-01
Pulse characteristics of single barrier discharges as well as parameters of charges accumulated on the surface of a dielectric under the atmospheric pressure in the "needle-(0.1-2.0)-mm air gap-polymer barrier-plane" system are investigated. It is found experimentally that for the positive polarity of the needle, the voltage for the discharge initiation is higher than in the case of the negative polarity by ˜25-35%. The reversal of the needle polarity from negative to positive increases the amplitude of the discharge current and the accumulated surface charge by ˜1.5-3 times. For the positive polarity of the needle, the discharge is governed by a streamer mechanism, while for the negative polarity, the discharge is initiated by the formation of a single Trichel pulse. The single pulse regime is observed for the discharge current up to a certain electrode gap d CR. For the positive needle and for air gap width d air > d CR ≈ 1.5 mm, a multipulse burst corona is formed, while for the negative needle and d air > d CR ≈ 0.9 mm, a damped sequence of Trichel pulses evolves in the system.
NASA Astrophysics Data System (ADS)
Yan, Hanfei; Li, Li
2014-01-01
The effects of dynamical diffraction in single crystals engender many unique diffraction phenomena that cannot be interpreted by the kinematical-diffraction theory, yet knowledge of them is vital to resolving a vast variety of scientific problems ranging from crystal optics to strain measurements in crystalline specimens. Although the fundamental dynamical-diffraction theory was established decades ago, modeling it remains a challenge in a general case wherein the crystal has complex boundaries and mixed diffraction geometries (Bragg or Laue). Here, we propose a universal approach for modeling x-ray dynamical diffraction from a single crystal with arbitrary shape and strain field that is based on the integral representation of the Takagi-Taupin equations. Using it, we can construct the solution iteratively via a converging series, independent of the diffraction geometry. Moreover, the integral equations offer additional insights into the diffraction physics that are not readily apparent in its differential counterparts. To demonstrate this approach, we studied the dynamical diffraction from a slab of single crystal with both Bragg and Laue diffraction excited on the entrance boundaries, a problem that is difficult to model by other methods. We also explored the mirage effect caused by the presence of a linear strain field and compared it to the Eikonal theory. Lastly, we derived a dynamical-diffraction equation correlating the structural properties of a particle to its far-field Bragg-diffraction pattern, shedding light on how dynamical diffraction affects these kinematical-diffraction-based inverse techniques for reconstructing the shape and the strain field.
Fabrication of graphene field-effect transistor on top of ferroelectric single-crystal substrate
NASA Astrophysics Data System (ADS)
Park, Nahee; Kang, Haeyong; Lee, Yourack; Kim, Jeong-Gyun; Kim, Joong-Gyu; Yun, Yoojoo; Park, Jeongmin; Kim, Taesoo; Kim, Jung Ho; Jin, Youngjo; Shin, Yong Seon; Lee, Young Hee; Suh, Dongseok
2015-03-01
In the analysis of Graphene field-effect transistor, the substrate material which has the direct contact with Graphene layer plays an important in the device performance. In this presentation, we have tested PMN-PT(i.e.(1-x)Pb(Mg1/3Nb2/3) O3-xPbTiO3) substrate as a gate dielectric of Graphene field-effect transistor. Unlike the case of previously used substrates such as silicon oxide or hexagonal Boron-Nitride(h-BN), the PMN-PT substrate can induce giant amount of surface charge that is directly injected to the attached Graphene layer due to its ferroelectric property. And the hysteresis of polarization versus electric field of PMN-PT can cause the device to show the ferroelectric nonvolatile memory operation. We had successfully fabricated Graphene field-effect transistor using the mechanically exfoliated Graphene layer transferred on the PMN-PT(001) substrate. Unlike the case of mechanical exfoliation on the surface of silicon-oxide or the Poly(methyl methacrylate) (PMMA), the weak adhesion properties between graphene and PMNPT required the pretreatment on PMMA before the exfoliation process. The device performance is analyzed in terms of the effect of ferro- and piezo-electric effect of PMNPT substrate.
The magnetic fields at the surface of active single G-K giants
NASA Astrophysics Data System (ADS)
Aurière, M.; Konstantinova-Antova, R.; Charbonnel, C.; Wade, G. A.; Tsvetkova, S.; Petit, P.; Dintrans, B.; Drake, N. A.; Decressin, T.; Lagarde, N.; Donati, J.-F.; Roudier, T.; Lignières, F.; Schröder, K.-P.; Landstreet, J. D.; Lèbre, A.; Weiss, W. W.; Zahn, J.-P.
2015-02-01
Aims: We investigate the magnetic field at the surface of 48 red giants selected as promising for detection of Stokes V Zeeman signatures in their spectral lines. In our sample, 24 stars are identified from the literature as presenting moderate to strong signs of magnetic activity. An additional 7 stars are identified as those in which thermohaline mixing appears not to have occured, which could be due to hosting a strong magnetic field. Finally, we observed 17 additional very bright stars which enable a sensitive search to be performed with the spectropolarimetric technique. Methods: We use the spectropolarimeters Narval and ESPaDOnS to detect circular polarization within the photospheric absorption lines of our targets. We treat the spectropolarimetric data using the least-squares deconvolution method to create high signal-to-noise ratio mean Stokes V profiles. We also measure the classical S-index activity indicator for the Ca ii H&K lines, and the stellar radial velocity. To infer the evolutionary status of our giants and to interpret our results, we use state-of-the-art stellar evolutionary models with predictions of convective turnover times. Results: We unambiguously detect magnetic fields via Zeeman signatures in 29 of the 48 red giants in our sample. Zeeman signatures are found in all but one of the 24 red giants exhibiting signs of activity, as well as 6 out of 17 bright giant stars. However no detections were obtained in the 7 thermohaline deviant giants. The majority of the magnetically detected giants are either in the first dredge up phase or at the beginning of core He burning, i.e. phases when the convective turnover time is at a maximum: this corresponds to a "magnetic strip" for red giants in the Hertzsprung-Russell diagram. A close study of the 16 giants with known rotational periods shows that the measured magnetic field strength is tightly correlated with the rotational properties, namely to the rotational period and to the Rossby number Ro
Huang, D.; Gasiewski, A.; Wiscombe, W.
2010-07-22
Tomographic methods offer great potential for retrieving three-dimensional spatial distributions of cloud liquid water from radiometric observations by passive microwave sensors. Fixed tomographic systems require multiple radiometers, while mobile systems can use just a single radiometer. Part 1 (this paper) examines the results from a limited cloud tomography trial with a single-radiometer airborne system carried out as part of the 2003 AMSR-E validation campaign over Wakasa Bay of the Sea of Japan. During this trial, the Polarimetric Scanning Radiometer (PSR) and Microwave Imaging Radiometer (MIR) aboard the NASA P-3 research aircraft provided a useful dataset for testing the cloud tomography method over a system of low-level clouds. We do tomographic retrievals with a constrained inversion algorithm using three configurations: PSR, MIR, and combined PSR and MIR data. The liquid water paths from the PSR retrieval are consistent with those from the MIR retrieval. The retrieved cloud field based on the combined data appears to be physically plausible and consistent with the cloud image obtained by a cloud radar. We find that some vertically-uniform clouds appear at high altitudes in the retrieved field where the radar shows clear sky. This is likely due to the sub-optimal data collection strategy. This sets the stage for Part 2 of this study that aims to define optimal data collection strategies using observation system simulation experiments.
Sekiguchi, Yuta; Kobayashi, Yo; Watanabe, Hiroki; Tomono, Yu; Noguchi, Takehiko; Takahashi, Yu; Toyoda, Kazutaka; Uemura, Munenori; Ieiri, Satoshi; Ohdaira, Takeshi; Tomikawa, Morimasa; Hashizume, Makoto; Fujie, Masakatsu G
2011-01-01
Recently, robotics systems are focused to assist in Single Port Endoscopic Surgery (SPS). However, the existing system required a manual operation of vision and viewpoint, hindering the surgical task. We proposed a surgical endoscopic robot for SPS with dynamic vision control, the endoscopic view being manipulated by a master controller. The prototype robot consists of a manipulator for vision control, and dual tool tissue manipulators (gripping: 5DOFs, cautery: 3DOFs) can be attached at the tip of sheath manipulator. In particular, this paper focuses on an in vivo experiment. We showed that vision control in the stomach and a cautery task by a cautery tool could be effectively achieved.
NASA Technical Reports Server (NTRS)
Arakere, Nagaraj K.; Magnan, Shannon; Ebrahimi, Fereshteh; Ferroro, Luis
2004-01-01
Metals and their alloys, except for a few intermetallics, are inherently ductile, i.e. plastic deformation precedes fracture in these materials. Therefore, resistance to fracture is directly related to the development of the plastic zone at the crack tip. Recent studies indicate that the fracture toughness of single crystals depends on the crystallographic orientation of the notch as well as the loading direction. In general, the dependence of crack propagation resistance on crystallographic orientation arises from the anisotropy of (i) elastic constants, (ii) plastic deformation (or slip), and (iii) the weakest fracture planes (e.g. cleavage planes). Because of the triaxial stress state at the notch tips, many slip systems that otherwise would not be activated during uniaxial testing, become operational. The plastic zone formation in single crystals has been tackled theoretically by Rice and his co-workers and only limited experimental work has been conducted in this area. The study of the stresses and strains in the vicinity of a FCC single crystal notch tip is of relatively recent origin. We present experimental and numerical investigation of 3D stress fields and evolution of slip sector boundaries near notches in FCC single crystal tension test specimens, and demonstrate that a 3D linear elastic finite element model that includes the effect of material anisotropy is shown to predict active slip planes and sectors accurately. The slip sector boundaries are shown to have complex curved shapes with several slip systems active simultaneously near the notch. Results are presented for surface and mid-plane of the specimens. The results demonstrate that accounting for 3D elastic anisotropy is very important for accurate prediction of slip activation near FCC single crystal notches loaded in tension. Results from the study will help establish guidelines for fatigue damage near single crystal notches.
NASA Astrophysics Data System (ADS)
Kiani, Keivan
2016-12-01
This work deals with the influence of the longitudinal magnetic field on vibrations of inclined single-walled carbon nanotubes (SWCNTs) subjected to an inside fluid flow. Using an equivalent continuum structure model for the SWCNT and a plug-like model for the moving inside fluid flow, the nonlocal longitudinal and transverse equations of motion of magnetically affected SWCNTs are obtained in the context of small deformations. By application of the assumed-mode methodology, the displacements are discretized in terms of vibration mode shapes, and by exploiting generalized Newmark-β scheme, their corresponding time-dependent parameters are determined at each time. In the presence of the longitudinal magnetic field, the effects of the small-scale parameter, fluid flow velocity, and inclination angle on both longitudinal and transverse vibrations of SWCNTs are addressed. The obtained results reveal that the longitudinal magnetic field has fairly no effect on the longitudinal dynamic behavior of the nanostructure. However, maximum values of both transverse displacement and nonlocal bending moment of the fluid-conveying SWCNT would reduce as the strength of the magnetic field grows. Such a fact becomes more highlighted for high levels of the fluid flow velocity. The obtained results indicate that the longitudinal magnetic field can be exploited as an efficient way to control transverse vibrations of SWCNTs conveying fluids.
Richman, Russell; Munroe, Alan James; Siddiqui, Yasmeen
2014-01-01
Electromagnetic fields (EMF) permeate the built environment in different forms and come from a number of sources including electrical wiring and devices, wireless communication, 'energy-efficient' lighting, and appliances. It can be present in the indoor environment directly from indoor sources, or can be transmitted through building materials from outside sources. Scientists have identified it as an indoor environmental pollutant or toxin that has ubiquitously plagued developed nations causing a variety of adverse health effects such as sick-building syndrome symptoms, asthma, diabetes, multiple sclerosis, leukemia, electro-hypersensitivity (EHS), behavior disorders, and more. There is currently no international consensus on guidelines and exposure limits. This paper presents the results of 29 EMF field audits in single family residential dwellings located within an urban neighborhood in Toronto (Canada). The following EMF spectra were evaluated: radio frequency, power frequency electric fields, power frequency magnetic fields and high frequency voltage transients. The field audits were conducted in order to provide initial baseline statistics to be used in future studies and in order to be compared to a low-cost EMF reduction design incorporated within the Renovation2050 research house - located within the test neighborhood. The results show the low-cost reduction strategy to be effective, on average reducing exposure by 80% for high-intensity EMF metrics. Research of this nature has not been conducted with relation to the built environment and can be used to spark an industry movement to design for low-exposure to EMF in a residential context.
Single domain wall manipulation in curved nanowires using a mobile, local, circular field
NASA Astrophysics Data System (ADS)
Shortt, Madeline; Bickel, Jessica; Khan, Mina; Tuominen, Mark; Aidala, Katherine
2014-03-01
Ferromagnetic nanostructures present exciting physics with a range of potential applications in data storage devices, such as magnetoresistive random access memory (MRAM). These proposals require precise control and understanding of domain wall (DW) movement and interactions. We developed a technique that generates a local circular Oersted field at a precise location by applying current through the tip of the atomic force microscope (AFM). We previously used this technique to control DW motion in nanorings. We extend this method to control individual DW movement in curved nanowires by placing the tip near a 180 DW at the vertex of a curved wire and generating a local field. In this way, we can examine the motion of domain walls through regions with different curvature and the effects of pinning. This work was supported in part by NSF DMR-1207924 and the UMass Center for Hierarchical Manufacturing, NSF CMMI-1025020.
Mapping the electrostatic force field of single molecules from high-resolution scanning probe images
Hapala, Prokop; Švec, Martin; Stetsovych, Oleksandr; van der Heijden, Nadine J.; Ondráček, Martin; van der Lit, Joost; Mutombo, Pingo; Swart, Ingmar; Jelínek, Pavel
2016-01-01
How electronic charge is distributed over a molecule determines to a large extent its chemical properties. Here, we demonstrate how the electrostatic force field, originating from the inhomogeneous charge distribution in a molecule, can be measured with submolecular resolution. We exploit the fact that distortions typically observed in high-resolution atomic force microscopy images are for a significant part caused by the electrostatic force acting between charges of the tip and the molecule of interest. By finding a geometrical transformation between two high-resolution AFM images acquired with two different tips, the electrostatic force field or potential over individual molecules and self-assemblies thereof can be reconstructed with submolecular resolution. PMID:27230940
Magnetotransport in single-layer graphene in a large parallel magnetic field
NASA Astrophysics Data System (ADS)
Chiappini, F.; Wiedmann, S.; Titov, M.; Geim, A. K.; Gorbachev, R. V.; Khestanova, E.; Mishchenko, A.; Novoselov, K. S.; Maan, J. C.; Zeitler, U.
2016-08-01
Graphene on hexagonal boron nitride (h-BN) is an atomically flat conducting system that is ideally suited for probing the effect of Zeeman splitting on electron transport. We demonstrate by magnetotransport measurements that a parallel magnetic field up to 30 Tesla does not affect the transport properties of graphene on h-BN even at charge neutrality where such an effect is expected to be maximal. The only magnetoresistance detected at low carrier concentrations is shown to be associated with a small perpendicular component of the field which cannot be fully eliminated in the experiment. Despite the high mobility of charge carriers at low temperatures, we argue that the effects of Zeeman splitting are fully masked by electrostatic potential fluctuations at charge neutrality.
Helgesen, K O; Horsberg, T E
2013-03-01
Sea lice on farmed salmonids are often treated with chemicals. Sensitivity testing of sea lice can reduce the number of treatments by identifying substances the sea lice are susceptible to. This study describes a simpler protocol for field sensitivity testing than today's six-dose bioassay. The protocol, which uses a single dose of the delousing agents deltamethrin, azamethiphos and emamectin benzoate, was developed on four different strains of sea lice and their subsequent generations. A sensitive strain and a strain showing reduced sensitivity were identified for each chemical after performing traditional bioassays and small-scale treatments. The single doses for each chemical were established by modelling dose-response curves from 24-h bioassays on strains with differences in sensitivity. The largest difference between the lower 80% prediction interval for the sensitive strain and the upper 80% prediction interval for the strain showing reduced sensitivity was identified for each delousing agent. The concentration of the chemical and the % mortality corresponding to each of the 80% prediction intervals were subsequently established. To validate the protocol for field use, further studies on both sensitive and resistant strains of sea lice under field conditions are required.
Determination of Flow Orientation of an Optically Active Turbulent Field by Means of a Single Beam
2013-06-18
optically active turbulent field was determined by Fourier transforming the wander of a laser beam propagating in the ocean. A simple physical model... Fourier transform for the situation depicted on the right and on the left, respectively. July 1, 2013 / Vol. 38, No. 13 / OPTICS LETTERS 2185 0146-9592/13...132185-03$15.00/0 © 2013 Optical Society of America to the flow (see top row of Fig. 3). However, the magni- tude of the Fourier transform, in
Hirano, Y.; Koguchi, H.; Yambe, K.; Sakakita, H.; Kiyama, S.
2006-12-15
By applying a small positive pulse ({delta}B{sub ta}) in toroidal magnetic field, the quasi-single helicity (QSH) state can be obtained with a controllable and reproducible manner in a reversed-field pinch (RFP) experiment on the large RFP machine, TPE-RX [Y. Yagi et al., Fusion Eng. Des. 45, 421 (1999)]. The QSH state in RFP is one of the states where the improved confinement can be observed, and is important for development toward the pure single helicity (SH) state. In the SH state, the dynamo-action for sustaining the RFP configuration will be driven by a single helical mode and its harmonics, and the anomalous plasma loss can be avoided which is caused by the multi-helicity dynamo action in ordinary RFPs. In the operating condition presented here, the reversal of toroidal magnetic field (B{sub ta}) is maintained at a shallow value ({approx}-1 mT) for a certain period ({approx}20 ms) after the setting up of the RFP configuration and then the positive {delta}B{sub ta} ((less-or-similar sign)5 mT magnitude and {approx}2 ms width) is applied to the B{sub ta}, which is usually negative during the sustaining phase of RFP. Just after applying the pulse, the m/n=1/6 mode (m and n being the poloidal and toroidal Fourier mode numbers, respectively) grows dominantly and the configuration goes into QSH state. This QSH state can be sustained for a long period (up to {approx}45 ms) almost until the end of discharge by applying a delayed reversal of B{sub ta} with appropriate timing and magnitude. The setting up of the QSH states shows a reproducibility of almost 100% with the same timing corresponding to the applied positive pulse. This observation can confirm the interpretation in the former report [Y. Hirano et al., Phys. Plasmas 12, 112501 (2005)], in which it is claimed that the QSH state is obtained when a small positive pulse in toroidal magnetic field spontaneously appears.
NASA Astrophysics Data System (ADS)
Tarduno, J. A.; Cottrell, R. D.; Smirnov, A. V.
2006-03-01
The basic features of the geomagnetic reversal chronology of the last 160 million years are well established. The relationship between this history and other features of the field, however, has been elusive. The determination of past field strength (paleointensity) is especially challenging. Commonly accepted results have come from analyses of bulk samples of lava. Historic lavas have been shown to faithfully record the past field strength when analyzed using the Thellier double-heating method. Data from older lavas, however, tend to show effects of in situ and laboratory-induced alteration. Here we review an alternative approach. Single plagioclase crystals can contain minute magnetic inclusions, 50-350 nm in size, that are potential high-fidelity field recorders. Thellier experiments using plagioclase feldspars from an historic lava on Hawaii provide a benchmark for the method. Rock magnetic data from older lavas indicate that the feldspars are less susceptible to experimental alteration than bulk samples. This resistance is likely related to the lack of clays. In addition, magnetic minerals are sheltered by the encasing silicate matrix from natural alteration that can otherwise transform the well-defined thermoremanent magnetization into an irresolute chemical remanent magnetization. If there is a relationship between geomagnetic reversal frequency and paleointensity, it should be best expressed during superchrons, intervals with few (or no) reversals. Thellier data sets based on single plagioclase crystals from lavas erupted during the Cretaceous Normal Polarity Superchron (~83-120 million years ago) suggest a strong (>12 × 1022 Am2), stable field, consistent with an inverse relationship between reversal frequency and paleointensity. Superchrons may represent times when the pattern of core-mantle boundary heat flux allows the geodynamo to operate at peak efficiency, as suggested in some numerical models. Thellier data from single plagioclase crystals formed
Nuclear spin-lattice relaxation at field-induced level crossings in a Cr8F8 pivalate single crystal
NASA Astrophysics Data System (ADS)
Yamamoto, Shoji
2016-01-01
We construct a microscopic theory for the proton spin-lattice relaxation-rate 1 / T1 measurements around field-induced level crossings in a single crystal of the trivalent chromium ion wheel complex [Cr8F8(OOCtBu)16] at sufficiently low temperatures [E. Micotti et al., Phys. Rev. B 72 (2005) 020405(R)]. Exactly diagonalizing a well-equipped spin Hamiltonian for the individual clusters and giving further consideration to their possible interactions, we reveal the mechanism of 1 / T1 being single-peaked normally at the first level crossing but double-peaked intriguingly around the second level crossing. We wipe out the doubt about poor crystallization and find out a solution-intramolecular alternating Dzyaloshinsky-Moriya interaction combined with intermolecular coupling of antiferromagnetic character, each of which is so weak as several tens of mK in magnitude.
Lin, Shuang-Yan; Wang, Chao; Zhao, Lang; Wu, Jianfeng; Tang, Jinkui
2015-01-07
Three pairs of homochiral mononuclear lanthanide complexes, with the general formula [LnH4LRRRRRR/SSSSSS(SCN)2](SCN)2·xCH3OH·yH2O(Ln = Dy (R/S-Dy1), Ho (R/S-Ho1) and Er (R/S-Er1)), have been obtained via self-assembly between chiral macrocyclic ligands and the respective thiocyanates, all of which show a saddle-type conformation with seven-coordinated metal ions. Magnetic measurements revealed that the Dy complex shows field-induced single-ion magnet behaviour, which is rarely reported in a seven-coordinated lanthanide-based SIM encapsulated in a macrocyclic ligand. The absolute configuration of all enantiomers was determined by single crystal X-ray crystallography and confirmed by electronic CD and VCD spectra.
NASA Astrophysics Data System (ADS)
Switzer, Eric R.; Watts, Duncan J.
2016-09-01
The B -mode polarization of the cosmic microwave background provides a unique window into tensor perturbations from inflationary gravitational waves. Survey effects complicate the estimation and description of the power spectrum on the largest angular scales. The pixel-space likelihood yields parameter distributions without the power spectrum as an intermediate step, but it does not have the large suite of tests available to power spectral methods. Searches for primordial B -modes must rigorously reject and rule out contamination. Many forms of contamination vary or are uncorrelated across epochs, frequencies, surveys, or other data treatment subsets. The cross power and the power spectrum of the difference of subset maps provide approaches to reject and isolate excess variance. We develop an analogous joint pixel-space likelihood. Contamination not modeled in the likelihood produces parameter-dependent bias and complicates the interpretation of the difference map. We describe a null test that consistently weights the difference map. Excess variance should either be explicitly modeled in the covariance or be removed through reprocessing the data.
Saito, Ryo; Yokoyama, Jun'ichi; Nagata, Ryo E-mail: yokoyama@resceu.s.u-tokyo.ac.jp
2008-06-15
We show a textbook potential for single-field inflation, namely the Coleman-Weinberg model can induce double inflation and formation of primordial black holes (PBHs), because fluctuations that leave the horizon near the end of first inflation are anomalously enhanced at the onset of second inflation when the time-dependent mode turns into a growing mode rather than a decaying mode. The mass of PBHs produced in this mechanism with an appreciable density are distributed at certain intervals depending on the model parameters. We also calculate the effects of non-Gaussian statistics due to higher-order interactions on the abundance of PBHs, which turns out to be small.
Gu, Yaxu; Jie, Wanqi; Li, Linglong; Xu, Yadong; Yang, Yaodong; Ren, Jie; Zha, Gangqiang; Wang, Tao; Xu, Lingyan; He, Yihui; Xi, Shouzhi
2016-09-01
To understand the effects of tellurium (Te) inclusions on the device performance of CdZnTe radiation detectors, the perturbation of the electrical field in and around Te inclusions was studied in CdZnTe single crystals via Kelvin probe force microscopy (KPFM). Te inclusions were proved to act as lower potential centers with respect to surrounding CdZnTe matrix. Based on the KPFM results, the energy band diagram at the Te/CdZnTe interface was established, and the bias-dependent effects of Te inclusion on carrier transportation is discussed.
Li, Shisheng; Liu, Chang; Hou, Peng-Xiang; Sun, Dong-Ming; Cheng, Hui-Ming
2012-11-27
Selective removal of metallic single-walled carbon nanotubes (SWCNTs) and consequent enrichment of semiconducting SWCNTs were achieved through an efficient carbothermic reaction with a NiO thin film at a relatively low temperature of 350 °C. All-SWCNT field effect transistors (FETs) were fabricated with the aid of a patterned NiO mask, in which the as-grown SWCNTs behaving as source/drain electrodes and the remaining semiconducting SWCNTs that survive in the carbothermic reaction as a channel material. The all-SWCNT FETs demonstrate improved current ON/OFF ratios of ∼10(3).
Time-resolved far-field analysis of a high power single emitter laser diode
NASA Technical Reports Server (NTRS)
Cornwell, Donald M., Jr.; Unge, Glenn L.
1992-01-01
A system was developed which is capable of measuring the time-resolved far-field radiation patterns from a high-power semiconductor laser under intensity modulated conditions. Angular steering of the fundamental spatial mode was observed, with pointing variations as large as 0.5 deg, or 7.5 percent of the beamwidth, during the time of the optical pulse. The variations in pointing angle were directly related to gradients in the transverse index profile of the laser, which may oscillate based on lateral spatial hole burning of the gain and carrier density.
Manipulation of a single electron spin in a quantum dot without magnetic field
NASA Astrophysics Data System (ADS)
Bednarek, S.; Pawłowski, J.; Skubis, A.
2012-05-01
In this paper, we propose the construction of a nanodevice performing the spin rotations of an electron confined in an electrostatic quantum dot without the use of a magnetic field. Sinusoidally varying voltage applied in different phases to four gates causes the electron to move along a two-dimensional closed path. The spin-orbit interaction that is present in the structure induces spin rotations. For a properly adjusted AC signal duration, the logical NOT operation or the Hadamard quantum gate can be performed on the electron spin. We perform a simulation of the nanodevice's time evolution.
Mapping nonlinear receptive field structure in primate retina at single cone resolution.
Freeman, Jeremy; Field, Greg D; Li, Peter H; Greschner, Martin; Gunning, Deborah E; Mathieson, Keith; Sher, Alexander; Litke, Alan M; Paninski, Liam; Simoncelli, Eero P; Chichilnisky, E J
2015-10-30
The function of a neural circuit is shaped by the computations performed by its interneurons, which in many cases are not easily accessible to experimental investigation. Here, we elucidate the transformation of visual signals flowing from the input to the output of the primate retina, using a combination of large-scale multi-electrode recordings from an identified ganglion cell type, visual stimulation targeted at individual cone photoreceptors, and a hierarchical computational model. The results reveal nonlinear subunits in the circuity of OFF midget ganglion cells, which subserve high-resolution vision. The model explains light responses to a variety of stimuli more accurately than a linear model, including stimuli targeted to cones within and across subunits. The recovered model components are consistent with known anatomical organization of midget bipolar interneurons. These results reveal the spatial structure of linear and nonlinear encoding, at the resolution of single cells and at the scale of complete circuits.
Verdia-Baguena, C; Gomez, V; Cervera, J; Ramirez, P; Mafe, S
2016-12-21
We demonstrate the electrical rectification and signal averaging of fluctuating signals using a biological nanostructure in aqueous solution: a single protein ion channel inserted in the lipid bilayer characteristic of cell membranes. The conversion of oscillating, zero time-average potentials into directional currents permits charging of a load capacitor to significant steady-state voltages within a few minutes in the case of the outer membrane porin F (OmpF) protein, a bacterial channel of Escherichia coli. The experiments and simulations show signal averaging effects at a more fundamental level than the traditional cell and tissue scales, which are characterized by ensembles of many ion channels operating simultaneously. The results also suggest signal transduction schemes with bio-electronic interfaces and ionic circuits where soft matter nanodiodes can be coupled to conventional electronic elements.
NASA Astrophysics Data System (ADS)
Kartalev, M.; Dryer, M.; Grigorov, K.; Stoimenova, E.
2006-10-01
We propose an approach for estimating the polytropic index in the solar wind. This is an artificially introduced parameter simplifying essentially the gasdynamic or magnetogasdynamic modeling of the interplanetary plasma. The problem in the straightforward utilization of the polytropic equation is to find sufficient homogeneous fragments of the solar wind flow, observed by single spacecraft only, where the application of this polytropic equation is correct. We propose an algorithm for following the plasma data time series to ensure the separation of data segments that belong, with high probability, to the same plasma flow flux tube. A linear regression model between logarithms of plasma density and temperature within such a segment provides an estimate for the polytropic index. Some preliminary applications of the algorithm to real data from spacecraft crossings of different solar wind structures are performed for the Bastille event of 14-16 July 2000.
NASA Technical Reports Server (NTRS)
Jaeck, C. L.
1976-01-01
A model scale flight effects test was conducted in the 40 by 80 foot wind tunnel to investigate the effect of aircraft forward speed on single flow jet noise characteristics. The models tested included a 15.24 cm baseline round convergent nozzle, a 20-lobe and annular nozzle with and without lined ejector shroud, and a 57-tube nozzle with a lined ejector shroud. Nozzle operating conditions covered jet velocities from 412 to 640 m/s at a total temperature of 844 K. Wind tunnel speeds were varied from near zero to 91.5 m/s. Measurements were analyzed to (1) determine apparent jet noise source location including effects of ambient velocity; (2) verify a technique for extrapolating near field jet noise measurements into the far field; (3) determine flight effects in the near and far field for baseline and suppressor nozzles; and (4) establish the wind tunnel as a means of accurately defining flight effects for model nozzles and full scale engines.
Low-field single-sided NMR for one-shot 1D-mapping: Application to membranes
NASA Astrophysics Data System (ADS)
Judeinstein, Patrick; Ferdeghini, Filippo; Oliveira-Silva, Rodrigo; Zanotti, Jean-Marc; Sakellariou, Dimitrios
2017-04-01
Many single-sided permanent magnet NMR systems have been proposed over the years allowing for 1D proton-density profiling, diffusion measurements and relaxometry. In this manuscript we make use of a recently published unilateral magnet for low-field NMR exhibiting an extremely uniform magnetic field gradient with moderate strength and cylindrical symmetry, allowing for a well-defined sweet spot. Combined with a goniometer, our system is used to characterize precisely the uniformity of its gradient and to achieve micrometric precision 1D profiling, as well as spatially localized relaxometry and diffusometry on thick (∼150 μm) membrane samples. Profiling with this magnet did not require repositioning of the samples with respect to the 1D tomograph.
Jaiswal, Manu; Sangeeth, C S Suchand; Wang, Wei; Sun, Ya-Ping; Menon, Reghu
2009-11-01
The electrical and optical response of a field-effect device comprising a network of semiconductor-enriched single-wall carbon nanotubes, gated with sodium chloride solution is investigated. Field-effect is demonstrated in a device that uses facile fabrication techniques along with a small-ion as the gate electrolyte-and this is accomplished as a result of the semiconductor enhancement of the tubes. The optical transparency and electrical resistance of the device are modulated with gate voltage. A time-response study of the modulation of optical transparency and electrical resistance upon application of gate voltage suggests the percolative charge transport in the network. Also the ac response in the network is investigated as a function of frequency and temperature down to 5 K. An empirical relation between onset frequency and temperature is determined.
Hydrogen-deuterium exchange induced by an electric field in α-Al2O3 single crystals
NASA Astrophysics Data System (ADS)
Ramírez, R.; Colera, I.; Gonz&Ález, R.; Savoini, B.; Chen, Y.
Hydrogen and deuterium are observed in α-Al2O3 crystals in the form of OH- and OD- radicals, respectively, which absorb in the infrared region. Infrared-absorption measurements were used to monitor diffusion of deuterons and protons in α-Al2O3 single crystals under the application of a moderate electric field parallel to the crystallographic c-axis, in the temperature range of 973-1333K. A linear dependence of the percent of exchange with both annealing time and applied voltage is observed, indicating that ionic conduction was taking place. The activation energy for the H+ ↔; D+ exchange was determined to be 2.4 eV, less than half the value obtained by pure thermal means, suggesting that under the application of an electric field the deuteron (proton) diffusion mechanism is different.