Extracting science from surveys of our Galaxy

Our knowledge of the Galaxy is being revolutionized by a series of photometric, spectroscopic and astrometric surveys. Already an enormous body of data is available from completed surveys, and data of ever-increasing quality and richness will accrue at least until the end of this decade. To extract science from these surveys, we need a class of models that can give probability density functions in the space of the observables of a survey – we should not attempt to ‘invert’ the data from the space of observables into the physical space of the Galaxy. Currently just one class of model has the required capability, the so-called ‘torus models’. A pilot application of torus models to understand the structure of the Galaxy’s thin and thick discs has already produced two significant results: a major revision of our best estimate of the Sun’s velocity with respect to the local standard of rest, and a successful prediction of the way in which the vertical velocity dispersion in the disc varies with distance from the Galactic plane.     

Managing, profiling and analyzing a library of 2.6 million compounds gathered from 32 chemical providers

Summary The data for 3.8 million compounds from structural databases of 32 providers were gathered and stored in a single chemical database. Duplicates are removed using the IUPAC International Chemical Identifier. After this, 2.6 million compounds remain. Each database and the final one were studied in term of uniqueness, diversity, frameworks, ‘drug-like’ and ‘lead–like’ properties. This study also shows that there are more than 87 000 frameworks in the database. It contains 2.1 million ‘drug-like’ molecules among which, more than one million are ‘lead-like’. This study has been carried out using ‘ScreeningAssistant’, a software dedicated to chemical databases management and screening sets generation. Compounds are stored in a MySQL database and all the operations on this database are carried out by Java code. The druglikeness and leadlikeness are estimated with ‘in–house’ scores using functions to estimate convenience to properties; unicity using the InChI code and diversity using molecular frameworks and fingerprints. The software has been conceived in order to facilitate the update of the database. ‘ScreeningAssistant’ is freely available under the GPL license.     

Droplet velocity and acceleration measurements in dense sprays by laser flow tagging

The feasibility of liquid-phase velocity measurements in dense sprays by 2D laser-based flow tagging is demonstrated. Velocity measurements in dense sprays are difficult with conventional techniques because of the high number densities of droplets, the optical thickness of the medium, and multiple light-scattering effects. The present flow-tagging technique is based on phosphorescent tracer molecules, which are excited by a grid of pulsed ‘write’ laser beams. The motion of the tagged droplet groups can be observed by a CCD camera in this way. In addition, multiple consecutive velocity measurements are performed by ‘droplet-group tracking’. This yields the acceleration along the trajectory of individual groups of droplets in unsteady sprays. Received: 5 June 2000 / Revised version: 28 July 2000 / Published online: 6 September 2000     

Clustering Properties in Turbulent Signals

We consider the telegraph approximation (TA) of turbulent signals by ignoring their amplitude variability and retaining only their ‘zero’-crossing information. We establish a unique relationship between the spectral exponent of a signal and that of its TA, whenever the signal possesses a Gaussian PDF and a spectral shape in which the high-frequency cut-off is sufficiently sharp. The velocity signals in most turbulent flows away from the wall satisfy these conditions adequately, so that the Kolmogorov spectral exponent of −5/3 for the turbulent velocity spectrum corresponds to a −4/3 spectral exponent for its TA. By introducing a new scaling exponent to characterize the tendency of small-scale fluctuations to cluster, we show that the velocity and passive scalar signals display a finite tendency to cluster even in the limit of Re . We advance the notion, on the basis of the properties of the TA, that turbulent processes belong to one of two classes—either the ‘white noise’ type or the ‘Markov-Lorentzian’ type. PACS: 47.27.-i, 47.27.Gs, 47.27.Nz     

Temperature dependence of the sensitivity of a long-range surface plasmon optical sensor

The temperature dependence of the sensitivity of an optical sensor based on long-range surface plasmon resonance (LRSPR) is studied via theoretical modeling. Both the ‘angular interrogation’ and the ‘wavelength interrogation’ modes of operation are studied. In addition, the variation of the full width at half maximum of the LRSPR ‘reflectance dip’ is also studied as a function of temperature, which ultimately determines the temperature dependence of the sensitivity of the sensor when the reflectance is monitored at a fixed incident angle (‘reflectance interrogation’). It is found that while most of the time only the ‘reflectance interrogation’ mode leads to improved sensitivity for the LRSPR sensor compared to a conventional SPR sensor, the temperature stability of the operation of the LRSPR sensor is generally higher than (or at least comparable to) that of the SPR sensor. PACS 73.20.Mf; 07.07.Df     

On the discovery of the Greisen-Zatzepin-Kuzmin cut-off

The recent claim of the ‘5 sigma’ observation of the Greisen-Zatzepin-Kuzmin cut-off by the HiRes group based on their nine years data is a significant step towards the eventual solution of one of the most intriguing questions in physics for more than 40 years. Recent results from Pierre Auger Observatory seem to confirm the statement. However, the word ‘significance’ is used in the mentioned paper in a sense which is not quite obvious. In the present paper we argue that this claim is a little premature.     

Wigner distributions for finite dimensional quantum systems: An algebraic approach

We discuss questions pertaining to the definition of ‘momentum’, ‘momentum space’, ‘phase space’ and ‘Wigner distributions’; for finite dimensional quantum systems. For such systems, where traditional concepts of ‘momenta’ established for continuum situations offer little help, we propose a physically reasonable and mathematically tangible definition and use it for the purpose of setting up Wigner distributions in a purely algebraic manner. It is found that the point of view adopted here is limited to odd dimensional systems only. The mathematical reasons which force this situation are examined in detail     

Against ‘Realism’

We examine the prevalent use of the phrase “local realism” in the context of Bell’s Theorem and associated experiments, with a focus on the question: what exactly is the ‘realism’ in ‘local realism’ supposed to mean? Carefully surveying several possible meanings, we argue that all of them are flawed in one way or another as attempts to point out a second premise (in addition to locality) on which the Bell inequalities rest, and (hence) which might be rejected in the face of empirical data violating the inequalities. We thus suggest that the phrase ‘local realism’ should be banned from future discussions of these issues, and urge physicists to revisit the foundational questions behind Bell’s Theorem.     

Vertically aligned growth of ZnO nanonails by nanoparticle-assisted pulsed-laser ablation deposition

Vertically aligned ZnO nanonails have been successfully grown on annealed sapphire substrates at comparatively high gas pressure using catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD). The growth behavior of the ZnO nanonails has been investigated by variation of the ablation time, which we name ‘isolated particle initiated growth’ and a three-step growth mechanism for ZnO nanonails is proposed. SEM analysis reveals that each of the uniquely shaped ZnO nanonails consists of a so-called hexagonal rod-shaped ‘root’ and a slightly tapered ‘stem’. The well-aligned ZnO nanonails exhibit a strong ultraviolet (UV) emission at around 390 nm under room temperature and only negligible visible emission, which indicates that there is a very low concentration of oxygen vacancies in the highly oriented ZnO nanonails. The as-synthesized nanonail arrays on sapphire substrate could offer novel opportunities for both fundamental research and technological applications. PACS 81.07.Bc; 78.66.Hf; 78.67.Bf; 81.16.Mk     

The gravitational bending of light by stars: a continuing story of curiosity,scepticism, surprise,and fascination

Driven entirely by human curiosity, the effect of the gravitational bending of light has evolved on unforeseen paths, in an interplay between shifts in prevailing paradigms and advance of technology, into the most unusual way to study planet populations. The confirmation of the bending angle predicted by Einstein with the Solar Eclipse measurements from 1919 marked the breakthrough of the theory of General Relativity, but it was not before the detection of the double image of the quasar 0957+561 that ‘gravitational lensing’ really entered the observational era. The observation of a characteristic transient brightening of a star caused by the gravitational deflection of its light by an intervening foreground star, constituting a ‘microlensing event’, required even further advance in technology before it could first emerge in 1993. While it required more patience in waiting before ‘Einstein’s blip’ for the first time revealed the presence of a planet orbiting a star other than the Sun, such detections can now be monitored live, and gravitational microlensing is not only sensitive to masses as low as that of the Moon, but can even reveal planets around stars in galaxies other than the Milky Way.     

Emerging molecular diversity from the intra-molecular Ugi reaction: iterative efficiency in medicinal chemistry

This review details a now established area within the isonitrile multi-component reaction (IMCR) field of study, namely employing bi-functional reagents in the Ugi reaction for the construction of screening sets with the additional element or even possibly ‘metric’ of enhanced ‘iterative efficiency potential’ The concept of ‘iterative efficiency’ will be briefly introduced, coupled with discussion on new synthetic routes to select bi-functional IMCR precursors and their use in the generation of pharmacologically relevant ‘molecular diversity’     

The Evaluation of Atomic Masses

The ensemble of experimental data on the 2830 nuclides which have been observed since the beginning of Nuclear Physics are being evaluated, according to their nature, by different methods and by different groups. The two ‘horizontal’ evaluations in which I am involved: the Atomic Mass Evaluation AME and the NUBASE evaluation belong to the class of ‘static’ nuclear data. In this tutorial lecture I will explain and discuss in detail the philosophy, the strategies and the procedures used in the evaluation of atomic masses. This revised version was published online in July 2006 with corrections to the Cover Date.     

Post-collision interaction effects on the triple-differential cross-section for the ionization of helium by fast positrons

Triple differential cross-sections for the ionization of helium by fast positrons are calculated in a ‘correlated’ first Born approximation supplemented by the inclusion of post-collision interaction effects. The results are analysed with respect to electron-helium experimental data of Jung and coworkers in coplanar asymmetric geometry.     

Studies of polarization/self-depolarization and electret-type effect in AgI

A novel d.c. polarization/self-depolarization study and electret-type effect in AgI are reported. AgI pellets of varying thicknesses, placed between two blocking (graphite) electrodes, were subjected to an external d.c. potential. A state of complete polarization was attained within ∼10 min, irrespective of the sample thickness. At this state, the potential difference, developed across the sample pellet as a result of polarization/accumulation of mobile Ag⁺ ions at the bulk/negative electrode interface, was measured experimentally. The potential difference, obtained immediately after the removal of the external d.c. source, has been referred to as ‘instant peak potential (V_p)’. As soon as the external voltage source is switched off, a process of self-depolarization is initiated due to the chemical/self diffusion of polarized mobile Ag⁺ ions throughout the bulk. ‘V_p’ gives a direct information regarding the extent of mobile ion concentration (n). ‘V_p’ measurements were carried out as a function of temperature and ‘Log V_p vs 1/T’ variation was compared with the ‘Log n vs 1/T’ Arrhenius plot, reported earlier in an entirely independent study. The two variations are almost analogous. This, in turn, supported as an earlier assertion that the abrupt conductivity increase in α-AgI, after β→α-phase transition at ∼147 °C, is predominantly due to the excessive increase in ‘n’. Furthermore, it has also been revealed that the Ag⁺ ions play another unique role which led to the existence of ‘persistent polarization’ states in AgI. These states are identical to the ‘electret-type effects’, observed in a number of dielectric materials. The polarization state persisted for very long time in ‘thermally stimulated polarized’ sample. A detailed investigation of the persistence/retention of polarization in the thermally-stimulated-polarized sample is reported.     

Electron field emission properties of highly dense carbon nanotube arrays

In this paper, we have studied field emission properties of highly dense arrays of multi-walled carbon nanotubes (CNTs) used as cathodes in diode-type field emission devices with a phosphor screen. For the high-density CNT emitters it is demonstrated that the emission sites are located on the CNT-cathode edges, which is direct experimental evidence of the ‘edge effect’. The results of computer simulations (using ‘ANSYS Electromagnetic’ software) are presented to confirm the experimental data and to analyze the effect of patterning on the electric field distribution for high-density CNT arrays. It is shown that selective-area removal of nanotubes in the arrays leads to the formation of additional edges characterized by the high field enhancement factor and enhanced emission from the CNT cathodes. In addition, scanning probe microscopy techniques are employed to examine surface properties of the high-density CNT arrays. For CNT arrays of ‘short’ nanotubes, the work function distribution over the sample surface is detected using a scanning Kelvin microscopy method.     

Schrödinger’s Cat Meets Einstein’s Twins: A Superposition of Different Clock Times

The phenomenon of quantum superposition, which allows a physical system to exist in different states ‘simultaneously’, is one of the most bizarre notions in physics. Here we illustrate an even more bizarre example of it: a superposed state of a physical system consisting of both an ‘older’ version and a ‘younger’ version of that system. This can be accomplished by exploiting the special relativistic effect of time dilation featuring in Einstein’s famous twin paradox.     

Conformal invariance and scalar-tensor theories

A new generalisation of Einstein’s theory is proposed which is invariant under conformal mappings. Two scalar fields are introduced in addition to the metric tensor field, so that two special choices of gauge are available for physical interpretation, the ‘Einstein gauge’ and the ‘atomic gauge’. The theory is not unique but contains two adjustable parameters ζ anda. Witha=1 the theory viewed from the atomic gauge is Brans-Dicke theory (ω=−3/2+ζ/4). Any other choice ofa leads to a creation-field theory. In particular the theory given by the choicea=−3 possesses a cosmological solution satisfying Dirac’s ‘large numbers’ hypothesis.     

On the lyman problem

This paper attempts to answer Lyman's question (1990) on the non-uniqueness in defining the 3D measure of the boundary vorticity-creation rate. Firstly, a straightforward analysis of the vorticity equation introduces a definition of a general vorticity flux-density tensor and its ‘effective’ part. The approach is strictly based on classical field theory and is independent of the constitutive structure of continuous medium. Secondly, the fundamental question posed by Lyman dealing with the ambiguity of the 3D measure of the boundary vorticity-creation rate for incompressible flow is discussed. It is shown that the original 3D measure (for an incompressible Newtonian fluid defined by Panton 1984), which is reminiscent of an analogy to Fourier's law, is in its character ‘effective’ and plays a crucial role in the prognostic vorticity transport equation. The alternative 3D measure proposed by Lyman includes, on the other hand, a ‘non-effective’ part, which plays a role in the local determination of the ‘effective’ measure as well as in a certain diagnostic integral boundary condition.