On "jamitons," self-sustained nonlinear traffic waves

"Phantom jams," traffic blockages that arise without apparent cause, have long frustrated transportation scientists. Herein, we draw a novel homology between phantom jams and a related class of self-sustained transonic waves, namely detonations. Through this analogy, we describe the jam structure; favorable agreement with reported measurements from congested highways is observed. Complementary numerical simulations offer insights into the jams' development. Our results identify conditions likely to result in a dangerous concentration of vehicles and thereby lend guidance in traffic control and roadway design.Comment: 6 pages, 4 figure

A myofibrillar protein of insect muscle related to vertebrate titin connects Z band and A band: Purification and molecular characterization of invertebrate mini-titin.

We show that myofibrils of insect flight and leg muscle contain a doublet of polypeptides with apparent molecular weights of 700K (K = 10(3) Mr) (Hmp I) and 600K (Hmp II), respectively. In Locusta migratoria high ionic strength extraction solubilizes only Hmp II, which is readily purified in native form. It probably reflects a proteolytic derivative of the non-extractable Hmp I. On the basis of its viscosity radius and sedimentation coefficient, Hmp II has a molecular weight of 600K and seems to consist of a single polypeptide chain. The highly asymmetric structure of the molecule is confirmed by rotary shadowing. The flexible rods have a uniform diameter of 3–4 nm and an average length of 260 nm. Polyclonal antibodies show cross-reactivity between Hmp II and its putative precursor Hmp I. We discuss the similarities and differences between the larger titin I/titin II of vertebrate sarcomeric muscle and the smaller Hmp I/Hmp II of invertebrate muscle and conclude that the latter may reflect a mini-titin. In line with the smaller length, immunoelectron microscopy locates the insect mini-titin to the I band and a very short portion of the A band only, while vertebrate titin is known to connect the Z band to the M band. Mini-titin has also been purified from several other insects including Drosophila. Immunofluorescence microscopy on frozen sections shows that mini-titin is present in the sarcomeric muscles of various species from different invertebrate phyla. These include Annelida, Nematomorpha, Plathelmintha, Nemertea and Nematoda like Ascaris lumbricoides and Caenorhabditis elegans. This wide-spread occurrence of invertebrate mini-titin is confirmed by immunoblotting experiments

A Variational Monte Carlo Study of the Current Carried by a Quasiparticle

With the use of Gutzwiller-projected variational states, we study the renormalization of the current carried by the quasiparticles in high-temperature superconductors and of the quasiparticle spectral weight. The renormalization coefficients are computed by the variational Monte Carlo technique, under the assumption that quasiparticle excitations may be described by Gutzwiller-projected BCS quasiparticles. We find that the current renormalization coefficient decreases with decreasing doping and tends to zero at zero doping. The quasiparticle spectral weight Z_+ for adding an electron shows an interesting structure in k space, which corresponds to a depression of the occupation number k just outside the Fermi surface. The perturbative corrections to those quantities in the Hubbard model are also discussed.Comment: 9 pages, 9 figure

Axo-glial interdependance in peripheral nerve development

During the development of the peripheral nervous system, axons and myelinating Schwann cells form a unique symbiotic unit, which is realized by a finely tuned network of molecular signals and reciprocal interactions. The importance of this complex interplay becomes evident after injury or in diseases in which aspects of axo-glial interaction are perturbed. This Review focuses on the specific interdependence of axons and Schwann cells in peripheral nerve development that enables axonal outgrowth, Schwann cell lineage progression, radial sorting and, finally, formation and maintenance of the myelin sheath

Vesuvio civil protection exercise MESIMEX: survey on volcanic risk perception.

In October 2006 the European Civil Protection Exercise MESIMEX (Somma Vesuvio Mesimex – Major Emergency SIMulation Exercise) on volcanic risk took place at Vesuvio, promoted by Campania Region and coordinated by the Italian Civil Protection Department. The exercise was focused on the preparedness phase for a major volcanic emergency in the area of Vesuvio. An evacuation of a sample of 1800 inhabitants from the Vesuvio Red Zone was also tested during the drill because the emergency plan ensures the complete evacuation of the population from the higher risk zone before the onset of the eruption. During that event a survey on volcanic risk perception was carried out on the evacuated population in order to compare the results with the ones coming from a previous similar survey, using the same questionnaire, carried out on a wider sample of residents in the Vesuvio Red Zone few months before MESIMEX exercise. The aim was to point out any differences in population’s attitude towards volcanic risk after having received detailed information on the emergency plan and on the hazards and risk related to the reactivation of Vesuvio, and experiencing the exercise. 463 questionnaires were distributed to the population evacuated from the 18 municipalities of the Red Zone and participating to the exercise. Main results in comparing data from MESIMEX survey with the Vesuvio previous one, put in evidence how the general level of Vesuvio residents’ trust remains quite low, indicating that a continuous and effective effort has to be done by both scientific community and Civil Protection Department. Particular attention should be paid in education and outreach activities and in involving people in risk mitigation procedures, also through more frequent exercises

Repetitive titin epitopes with a 42 nm spacing coincide in relative position with known A band striations also identified by major myosin-associated proteins. An immunoelectron-microscopical study on myofibrils.

A direct titin-thick filament interaction in certain regions of the A band is suggested by results using four new monoclonal antibodies specific for titin in immunoelectron microscopy. Antibodies T30, T31 and T32 identify quasi-repeats in the titin molecule characterized by a 42–43 nm repeat spacing. These stripes seem to coincide with striations established by others on negatively stained cryosections of the A band. Antibodies T30 and T32 recognize epitopes matching five or two of the seven striations per half sacromere known to harbor both the myosin-associated C-protein and an 86K (K = 10(3) Mr) protein. Antibody T31 labels two stripes in the P zone, which correspond to the two positions where decoration is seen with 86K protein, but not with C-protein. The single titin epitope defined by antibody T33 is located 55 nm prior to the center of the M band. This position seems to coincide with the M7 striation defined by others on negatively stained A bands. The T33 epitope position proves that the titin molecule, which is known to be anchored at the Z line, also penetrates into the complex architecture of the M band. The titin epitopes described here enable us to begin to correlate known ultrastructural aspects of the interior part of the A band with the disposition of the titin molecule in the sarcomere. They raise the question of whether there is a regular interaction pattern between titin and the thick filaments

A Correction Function Method for Poisson problems with interface jump conditions

In this paper we present a method to treat interface jump conditions for constant coefficients Poisson problems that allows the use of standard “black box” solvers, without compromising accuracy. The basic idea of the new approach is similar to the Ghost Fluid Method (GFM). The GFM relies on corrections applied on nodes located across the interface for discretization stencils that straddle the interface. If the corrections are solution-independent, they can be moved to the right-hand-side (RHS) of the equations, producing a problem with the same linear system as if there were no jumps, only with a different RHS. However, achieving high accuracy is very hard (if not impossible) with the “standard” approaches used to compute the GFM correction terms. In this paper we generalize the GFM correction terms to a correction function, defined on a band around the interface. This function is then shown to be characterized as the solution to a PDE, with appropriate boundary conditions. This PDE can, in principle, be solved to any desired order of accuracy. As an example, we apply this new method to devise a 4th order accurate scheme for the constant coefficients Poisson equation with discontinuities in 2D. This scheme is based on (i) the standard 9-point stencil discretization of the Poisson equation, (ii) a representation of the correction function in terms of bicubics, and (iii) a solution of the correction function PDE by a least squares minimization. Several applications of the method are presented to illustrate its robustness dealing with a variety of interface geometries, its capability to capture sharp discontinuities, and its high convergence rate.National Science Foundation (U.S.) (Grant DMS-0813648)Brazil. Coordenacao de Aperfeicoamento de Pessoal de Nivel SuperiorFulbright Program (Grant BEX 2784/06-8