The politics of physicists' social models

I give an overview of the topic of this dossier, the “applications of (statistical) physics to social sciences at large.” I discuss several examples of simple social models put forward by physicists and examine their interest. I argue that while they may be conceptually useful to correct our intuitive models of social mechanisms, their relevance for real social systems is moot. What is more, since physicists have always needed to ‘tame’ the world inside laboratories to make their models relevant, I suggest that social modeling might be linked to human taming, a smashing political project.     

无机纳米发光材料研究展望:如何走出自己的舒适区?

无机纳米发光材料由于其独特的发光性质,具有广泛的应用前景。本文结合作者的科研经历,展望了无机纳米发光材料未来的发展机遇和挑战,聚焦该领域前沿“痛点”和“冷门”,探讨研究工作如何面向国家重大需求。倡议科学家应走出自己的研究舒适区,树立自己的标签性工作,共同推进无机纳米发光材料研究的可持续发展。     

The Armstrong experiment revisited

When a high-voltage direct-current is applied to two beakers filled with water or polar liquid dielectrica, a horizontal bridge forms between the two beakers. This experiment was first carried out by Lord Armstrong in 1893 and then forgotten until recently. Such bridges are stable by the action of electrohydrodynamic (EHD) forces caused by electric field gradients counteracting gravity. Due to these gradients a permanent pumping of liquid from one beaker into the other is observed. At macroscopic scale several of the properties of a horizontal water bridge can be explained by modern electrohydrodynamics, analyzing the motion of fluids in electric fields. Whereas on the molecular scale water can be described by quantum mechanics, there is a conceptual gap at mesoscopic scale which is bridged by a number of theories including quantum mechanical entanglement and coherent structures in water – theories that we discuss here. Much of the phenomenon is already understood, but even more can still be learned from it, since such “floating” liquid bridges resemble a small high voltage laboratory of their own: The physics of liquids in electric fields of some kV/cm can be studied, even long time experiments like neutron or light scattering are feasible since the bridge is in a steady-state equilibrium and can be kept stable for hours. It is also an electro-chemical reactor where compounds are transported through by the EHD flow, enabling the study of electrochemical reactions under potentials which are otherwise not easily accessible. Last but not least the bridge provides the experimental biologist with the opportunity to expose living organisms such as bacteria to electric fields without killing them, but with a significant influence on their behavior, and possibly, even on their genome.     

Electrodynamics of Magnetoelectric Media and Magnetoelectric Fields

The relationship between magnetoelectricity and electromagnetism is a subject of a strong interest and numerous discussions in microwave and optical wave physics and material sciences. The definition of the energy and momentum of the electromagnetic (EM) field in a magnetoelectric (ME) medium is not a trivial problem. The question of whether electromagnetism and magnetoelectricity can coexist without an extension of Maxwell's theory arises when the effects of EM energy propagation are studied and the group velocity of the waves in an ME medium is considered. The energy balance equation reveals unusual topological structure of fields in ME materials. Together with certain constraints on the constitutive parameters of a medium, definite constraints on the local field structure should be imposed. Analyzing the EM phenomena inside an ME material, the question “what kind of the near fields arising from a sample of such a material can be measured?” should be answered. The visualization of the ME states requires an experimental technique that is based on an effective coupling to the violation of spatial as well as temporal inversion symmetry. To observe the ME energy in a subwavelength region, it is necessary to assume the existence of first-principle near fields—the ME fields. These are non-Maxwellian near fields with specific properties of violation of spatial and temporal inversion symmetry. A particular interest to the ME fields arises in studies of metamaterials with “artificial-atoms” ME elements.     

Complex and biofluids: From Maxwell to nowadays

Complex fluids are the rule in biology and in many industrial applications. Typical examples are blood, cartilage, and polymer solutions. Unlike water (as well as domestic oils, soft clear drinks, and so on), the law(s) describing the behavior of complex fluids are not yet fully established. The complexity arises from strong coupling between microscopic scales (like the motion of a red blood cell in the case of blood, or a polymer molecule for a polymer solution) and the global scale of the flow (say at the scale of a blood artery, or a channel in laboratory experiments). In this issue entitled Complex and Biofluids a large panel of experimental and theoretical problems of complex fluids is exposed. The topics range from dilute polymer solutions, food products, to biology (blood flow, cell and tissue mechanics). One of the earliest model put forward as an attempt to describe a complex fluid was suggested a long time ago by James Clerk Maxwell (in 1867). Other famous scientists, like Einstein (in 1906), and Taylor (in 1932) have made important contributions to the field, but the topic of complex fluids still continues to pose a formidable challenge to science. This field has known during the past decade an unbelievable upsurge of interest in many branches of science (physics, mechanics, chemistry, biology, medical science, mathematics, and so on). Understanding complex fluids is viewed as one of the biggest challenge of the present century. This synthesis will provide a simple introduction to the topic, summarize the main contribution of this issue, and list major open questions in this field. To cite this article: C. Misbah, C. R. Physique 10 (2009).     

What Is “System”: The Information-Theoretic Arguments

The problem of “what is ‘system’?” is in the very foundations of modern quantum mechanics. Here, we point out the interest in this topic in the information-theoretic context. E.g., we point out the possibility to manipulate a pair of mutually non-interacting, non-entangled systems to employ entanglement of the newly defined “(sub)systems” consisting the one and the same composite system. Given the different divisions of a composite system into “subsystems”, the Hamiltonian of the system may generate in general non-equivalent quantum computations. Redefinition of “subsystems” of a composite system may be regarded as a method for avoiding decoherence in the quantum hardware. In principle, all the notions refer to a composite system as simple as the hydrogen atom.     

Water as the fabric of life

Many share the feeling that we are at in the midst of a shift in our perception of water — a shift from the current molecular-level based approach (which focuses on the behaviour of individual or small numbers of molecules) towards a new, systemic view of water. In this new picture, water is perceived as an active substance that responds adaptively to external and internal constraints and signals. These responses can have profound effects on substances immersed in water, and in particular on the functioning of biological constituents, from molecules to living cells. This special volume presents some existing and possible future directions in this trend towards a systemic view of water as an active substance, which plays many essential roles in sustaining life. The work reported here suggests that the notion of water as “life’s solvent” should give way to the new realisation of water as an active “fabric of life”, continuously engaging and interacting with biomolecules in complex and subtle ways.     

Quantitative MRI texture analysis in chronic active multiple sclerosis lesions

ObjectiveRecently, there has been an increasing interest in “chronic enlarging” or “chronic active” multiple sclerosis (MS) lesions that are associated with clinical disability. However, investigation of dynamic lesion volume changes requires longitudinal MRI data from two or more time points. The aim of this study was to investigate the application of texture analysis (TA) on baseline T1-weighted 3D magnetization-prepared rapid acquisition gradient-echo (MPRAGE) images to differentiate chronic active from chronic stable MS lesions.Material and methodsTo identify chronic active lesions as compared to non-enhancing stable lesions, two MPRAGE datasets acquired on a 3 T MRI at baseline and after 12 months follow-up were applied to the Voxel-Guided Morphometry (VGM) algorithm. TA was performed on the baseline MPRAGE images, 36 texture features were extracted for each lesion.ResultsOverall, 374 chronic MS lesions (155 chronic active and 219 chronic stable lesions) from 60 MS patients were included in the final analysis. Multiple texture features including “DISCRETIZED_HISTO_Energy”, “GLCM_Energy”, “GLCM_Contrast” and “GLCM_Dissimilarity” were significantly higher in chronic active as compared to chronic stable lesions. Partial least squares regression yielded an area under the curve of 0.7 to differentiate both lesion types.ConclusionOur results suggest that multiple texture features extracted from MPRAGE images indicate higher intralesional heterogeneity, however they demonstrate only a fair accuracy to differentiate chronic active from chronic stable MS lesions.     

Nanoelectromechanics and single-charge tunneling

The coupling of electronic and mechanical degrees of freedom has important consequences in nanoscale systems, as emphasized in recent theoretical and experimental work. In particular, the electrical properties of composite nanosystems containing elements with quite different abilities to conduct electricity and with different mechanical properties have been found to be strongly affected. Here we briefly review some of our recent work on the nanoelectromechanics of “heteroconducting” and “heteroelastic” Coulomb blockade systems, where single charge tunneling is the dominant conduction mechanism. We examplify nanoelectromechanical effects both in normal and superconducting systems by discussing (i) a self-assembled single-electron tunneling device exhibiting a dynamical instability leading to “shuttling” of electrons by a movable Coulomb dot and (ii) shuttling of Cooper pairs by a movable single-Cooper-pair box.     

Active damping of a micro-cantilever piezo-composite beam

Thick PZT films are of major interest in the actuation of mechanical structures. One of the promising fields deals with active damping. Since it is a dynamic application, hard-PZT type of screen-printed films are suited to this kind of use. Nevertheless, the drop in dielectric, ferroelectric and piezoelectric properties induced by the fabrication process is a serious constraint and it needs to be evaluated. The first section of this paper will present the mechanical system used for the experimental investigations. These investigations look to quantify the electromechanical properties of the films once the deposition process is achieved. The experimental observations highlighting the efficiency of hard-PZT thick films in active damping despite the drop in the electromechanical properties will then be considered. The control strategy used in the experiments can be called pseudo-direct-velocity feedback. Then the constitutive relations of the composites will be needed to derive the roots locus analysis by means of finite element modelling on one hand and through the roots of the partial derivative equations on the other hand. The unconditional stability of the uncollocated system will be demonstrated and its typical asymptotic behavior when the gain tends towards infinity will be explained.     

Transport phenomena of aligned ybco polycrystals near vortex-glass transition temperature in weak magnetic field

Abstract

Transport phenomena of aligned polycrystalline Y₁Ba₂Cu₃O_7?δ samples in weak magnetic fields near the vortex-glass transition temperature T_g have been studied. In YBCO polycrystal a fully superconducting state develops via an “intermediate phase”. The non-ohmic dissipation in this “intermediate phase” is examined in terms of both the thermal activated flux-flow (TAFF) model and vortex-glass transition model. Our experimental results in low magnetic fields can better be explained by a vortex glass transition model rather than a TAFF model. We have reinterpreted the non-ohmic dissipative region below T_c , i.e., the so-called “intermediate phase” in terms of a vortex-glass phase.     

A transformation theory for camouflaging arbitrary heat sources

Camouflage devices have attracted intensive research interest for their significant applications. However, most camouflage devices are specifically designed according to target heat sources. Here, by applying the transformation thermotics approach, we develop a coordinate transformation, and design an unspecific camouflage device which can camouflage arbitrary heat sources into a circular one with an anisotropic shell. We verify the ability of our unspecific camouflage device with both steady and transient simulations. We also find the “apparent negative thermal conductivity” under certain conditions without violating the second law of thermodynamics. To ensure the feasibility, we further put forward the effective medium approximation for sample fabrication, and only two natural materials are required. Our results have relevance to the different applications of infrared misleading, uniform heating, and so on; they may also provide guidance to the research on other diffusive fields, such as magnetostatic and electrostatic fields.     

Angle-resolved photoemission spectroscopy studies of electron-electron interactions in graphene

Graphene is an emergent research topic that has attracted a huge amount of research interest ever since its experimental demonstration as a two-dimensional realization of Dirac fermions in 2005. In subsequent years, the research on graphene has rapidly expanded its field not only due to the new paradigm to study relativistic high energy physics in a condensed matter, but also due to its potential in the application for next generation devices. Most of the novel phenomena observed so far in graphene are attributed to its low-energy excitations, which is described by those of relativistic Dirac fermions. This article reviews recent progress in angle-resolved photoemission spectroscopy studies of electron-electron interactions in graphene.     

Structural phase transitions in isotropic magnetic elastomers

Magnetic elastomers represent a new type of materials that are “soft” matrices with “hard” magnetic granules embedded in them. The elastic forces of the matrix and the magnetic forces acting between granules are comparable in magnitude even under small deformations. As a result, these materials acquire a number of new properties; in particular, their mechanical and/or magnetic characteristics can depend strongly on the polymer matrix filling with magnetic particles and can change under the action of an external magnetic field, pressure, and temperature. To describe the properties of elastomers, we use a model in which the interaction of magnetic granules randomly arranged in space with one another is described in the dipole approximation by the distribution function of dipole fields, while their interaction with the matrix is described phenomenologically. A multitude of deformation, magnetic-field, and temperature effects that are described in this paper and are quite accessible to experimental observation arise within this model.     

Measurement uncertainties of size, shape, and surface measurements using transmission electron microscopy of near-monodisperse, near-spherical nanoparticles

Carbon nanotubes are currently one of the most important materials due to their strong mechanical resistance, light weight, and transport properties. Since the publication of Ijima’s paper on tubular carbon structures (Iijima, Nature 354:56–58, 1991), approximately 80,000 research articles have been published according to the ISI web of science (WOS) database, using “carbon nanotube*” as the search criterion in the search by topic option. In this work, the development and impact of nanoscience and nanotechnology (N&N) and carbon nanotubes on several research areas, journals, specific papers, and emerging research areas are analyzed and discussed. Considering the production of papers in these areas from 1997 to 2012, quantitatively speaking, the People’s Republic of China is emerging as the leading country in N&N and carbon nanotube research, passing the United States of America. WOS data analysis of nanoscience, nanotechnology, and carbon nanotube research in developed and developing countries is discussed, and some ideas for accelerating the progress in these important research areas are proposed.     

Absolute metabolite quantification by in vivo NMR spectroscopy: I. introduction,objectives and activities of a concerted action in biomedical research

By utilizing achievements and results of two previous concerted research projects on magnetic resonance imaging and spectroscopy (MRS), the EU BIOMED 1 Concerted Action on “Cancer and brain disease characterization and therapy assessment by quantitative MRS” was specifically aimed at: 1) developing at a multicentre level harmonized methodologies and protocols for quantitative and reproducible MRS measurements, as a basis for validating these procedures in well controlled clinical and experimental conditions; and 2) providing multicentre critical reviews on the present understanding of the significance of MRS parameters as possible new markers of diagnosis, prognosis and response to therapy. The programme comprised the following main areas of collaborative research and multicentre evaluation: a) development of methods and protocols for quality assessment, calibration and absolute metabolite quantification in in vivo localized, volume-selective MRS; b) design and validation of a new method for assessing localization performance in spectroscopic imaging (MRSI); c) interlaboratory comparison of different methods of signal processing and data analysis, for improving signal quantification in vivo and in vitro MRS spectra; d) quality assessment of high resolution MRS analyses of biological fluids; e) protocol for assembling a pilot data base of MR spectra of tumour extracts for pattern recognition analysis; f) multicentre review on evaluation of the significance of MRS parameters in monitoring lipid metabolism and function in cancer; and g) multicentre review on evaluation of drug pharmacokinetics and metabolism using MRS. The main results and conclusions of four multi-centre trials on items (a), (b) and (c), which involved 24 teams, are reported in the accompanying papers of this series.     

Localized structures in convective experiments

In this work we review localized structures appearing in thermo-convective experiments performed in extended (large “aspect ratio”) fluid layers. After a brief general review (not exhaustive), we focus on some results obtained in pure fluids in a Bénard-Marangoni system with non-homogeneous heating where some structures of this kind appear. The experimental results are compared in reference to the most classical observed in binary mixtures experiments or simulations. In the Bénard-Marangoni experiment we present the stability diagram where localized structures appear and the typical situations where these local mechanisms have been studied experimentally. Some new experimental results are also included. The authors want to honor Prof. H. Brand in his 60th. birthday and to thank him for helpful discussions.     

The Optical Breakdown of Gases and Metal Vapours by Means of Quantum Generators

The studying of electrical breakdown of gaseous, liquid and solid materials has represented hitherto several independent fields of research, with quite elaborated theories and their specific conditions. By the appearance of quantum generators and bright energy sources (by their specific conditions and effects) another time scale of breakdown interval appeared, other frequencies of electromagnetic waves by which the breakdown was made (the data on ∼ 10¹⁷ W/cm² sterrad are not scarce [1]). The extension of the limits within which operate quantum generators (both at the side of long and short waves) made both fields hitherto separated (conditionally said) unite. In this paper we shall consider only some of the basic criteria on the kind of optical breakdown. Since 1963 and since the beginning of first optical breakdowns the field became the topic of numerous world laboratories, of theoretical and practical derivations; later the contradictory results accelerated the development of both, as is usually the case. By the extension of these problems several applicative and nowadays provocative fields, such as: thermonuclear fusion, nuclear bombs, are even when we only “research” stimulated effects in other energy diapasons, for example stimulated effects in gamma domain [2].     

耦合空间的声学研究进展

近年来由于混响室在演艺厅堂工程上的应用,唤发了对耦合空间声场研究的广泛兴趣。本文简短地回顾了马大猷先生对室内声学简正模态理论的贡献,对近代特别是最近15年来室内声学研究在耦合空间方面的发展,做了综述性讨论,包括简正模态分析和模态分解法、统计声学方法、几何声学方法、扩散方程、以及高分辨率实验技术和贝叶斯概率分析在耦合空间研究的应用。值马大猷先生诞辰一百周年之际,以此文缅怀德高望重的声学前辈。