Thin Ohmic or superconducting strip with an applied ac electric current

The complex impedance, currents, and electric and magnetic fields are calculated as functions of resistivity and frequency or London depth for a long thin strip with applied ac current. Both Ohmic and superconducting strips are considered. While the inductance per unit length of the strip depends on the strip length logarithmically, the sheet current, magnetic field, resistance, and magnetic susceptibility are independent of this length. It is found that the enhancement of resistance by the skin effect in thin Ohmic strips is much weaker (logarithmic) than in thick wires.Comment: 4 pages, 3 figures, for Phys. Rev.

Randomized Dynamical Decoupling Techniques for Coherent Quantum Control

The need for strategies able to accurately manipulate quantum dynamics is ubiquitous in quantum control and quantum information processing. We investigate two scenarios where randomized dynamical decoupling techniques become more advantageous with respect to standard deterministic methods in switching off unwanted dynamical evolution in a closed quantum system: when dealing with decoupling cycles which involve a large number of control actions and/or when seeking long-time quantum information storage. Highly effective hybrid decoupling schemes, which combine deterministic and stochastic features are discussed, as well as the benefits of sequentially implementing a concatenated method, applied at short times, followed by a hybrid protocol, employed at longer times. A quantum register consisting of a chain of spin-1/2 particles interacting via the Heisenberg interaction is used as a model for the analysis throughout.Comment: 7 pages, 2 figures. Replaced with final version. Invited talk delivered at the XXXVI Winter Colloquium on the Physics of Quantum Electronics, Snowbird, Jan 2006. To be published in J. Mod. Optic

DNA-binding transferrin conjugates as functional gene-delivery agents: synthesis by linkage of polylysine or ethidium homodimer to the transferrin carbohydrate moiety

We have previously demonstrated that transferrin-polycation conjugates are efficient carrier molecules for the introduction of genes into eucariotic cells. We describe here a more specific method for conjugation of transferrin with DNA-binding compounds involving attachment at the transferrin carbohydrate moiety. We used the polycation poly(L-lysine) or the DNA intercalator, ethidium homodimer as DNAbinding domains. Successful transferrin-receptor-mediatedd elivery and expression of the Photinus pyralis luciferase gene in K562 cells has been shown with these new transferrin conjugates. The activity of the transferrin-ethidium homodimer (TfEtD) conjugates is low relative to transferrin-polylysine conjugates; probably because of incomplete condensation of the DNA. However, DNA delivery with TfEtD is drastically improved when ternary complexes of the DNA with TfEtD and the DNA condensing agent polylysine are prepared. The gene delivery with the carbohydrate-linked transferrin-polylysine conjugates is equal or superior to described conjugates containing disulfide linkage. The new ligation method facilitates the synthesis of large quantities (>lo0 mg) of conjugates. INTRODUCTION Transferrin-polycation conjugates are efficient carriers for the uptake of DNA into eucariotic cells (I). This gene transfer technique, termed tramferrinfection, is based on receptor-mediated endocytosis of DNA complexed with polycation-transferrin conjugates (2,3). Our initial conjugate synthesis (1) involved the modification of one to two amino groups on the transferrin molecule with the bifunctional reagent succinimidyl34 2-pyridy1dithio)propionate (SPDP), followed by ligation to similarly modified polycations (polylysine or protamine) through the formation of disulfide bonds. Because there are more than 50 lysines on the large (about 80 kDa) transferrin protein, the actual site (or sites) of ligation to the polycation is unknown with this method. In this paper we describe the synthesis of new transferrin conjugates that are ligated with DNA-binding compounds in a specific manner through modification of the transferrin carbohydrate moiety. The conjugates thus obtained are free of any groups derived from chemical linking agents, since the connecting atoms are already present within the starting compounds. The carbohydrate group acts as anatural spacer that puts a 32-atom distance between the transferrin and the DNA binding moiety. This spacer effect may be important for appropriate presentation of the ligand to its receptor. As a DNA-binding compound, the polycation polylysine was used, similar to the use described in ref 1 or to the asialo-orosomucoid conjugates prepared by Wu and Wu (4). We have also prepared a novel type of transferrin conjugate that contains the DNA intercalator ethidium homodimer (5) as the DNAbinding group and demonstrate successful receptormediated gene delivery with these conjugates. EXPERIMENTAL PROCEDURES Human transferrin (iron-free), conalbumin (iron-free), and poly(L-lysine) were obtained from Sigma. Liquid chro- Abbreviations used: FITC, fluorescein ieothiocyenate; TfEtD, traneferrin-ethidium homodimer conjugate; TfpL, traneferrinpolytL- lysine) conjugate; HEPES, 4-(2-hydroxyethyl)-l-piperazineethanesulfonic acid

Acoustics of tachyon Fermi gas

We consider a Fermi gas of free tachyons as a continuous medium and find whether it satisfies the causality condition. There is no stable tachyon matter with the particle density below critical value $n_T$ and the Fermi momentum $k_F<\sqrt{\frac 32}m$ that depends on the tachyon mass $m$. The pressure $P$ and energy density $E$ cannot be arbitrary small, but the situation $P>E$ is not forbidden. Existence of shock waves in tachyon gas is also discussed. At low density $n_T<n<3.45n_T$ the tachyon matter remains stable but no shock wave do survive.Comment: 14 pages, 2 figures (color

Transferrin-polycation conjugates as carriers for DNA uptake into cells.

We have developed a high-efficiency nucleic acid delivery system that uses receptor-mediated endocytosis to carry DNA macromolecules into cells. We accomplished this by conjugating the iron-transport protein transferrin to polycations that bind nucleic acids. Human transferrin, as well as the chicken homologue conalbumin, has been covalently linked to the small DNA-binding protein protamine or to polylysines of various sizes through a disulfide linkage. These modified transferrin molecules maintain their ability to bind their cognate receptor and to mediate efficient iron transport into the cell. The transferrin-polycation molecules form electrophoretically stable complexes with double-stranded DNA, single-stranded DNA, and modified RNA molecules independent of nucleic acid size (from short oligonucleotides to DNA of 21 kilobase pairs). When complexes of transferrin-polycation and a bacterial plasmid DNA containing the gene for Photinus pyralis luciferase are supplied to eukaryotic cells, high-level expression of the luciferase gene occurs, demonstrating transferrin receptor-mediated endocytosis and expression of the imported DNA. We refer to this delivery system as "transferrinfection.

Quantum-Matter-Spacetime : Peter Mittelstaedt's Contributions to Physics and Its Foundations

In a period of over 50 years, Peter Mittelstaedt has made substantial and lasting contributions to several fields in theoretical physics as well as the foundations and philosophy of physics. Here we present an overview of his achievements in physics and its foundations which may serve as a guide to the bibliography (printed in this Festschrift) of his publications. An appraisal of Peter Mittelstaedt's work in the philosophy of physics is given in a separate contribution by B. Falkenburg

Shock waves in superconducting cosmic strings: growth of current

Intrinsic equations of motion of superconducting cosmic string may admit solutions in the shock-wave form that implies discontinuity of the current term \chi. The hypersurface of discontinuity propagates at finite velocity determined by finite increment \Delta \chi =\chi_+ -\chi_-. The current increases \chi_+>\chi_- in stable shocks but transition between spacelike (\chi >0) and timelike (\chi<0) currents is impossible.Comment: 13 pages, 3 figure

On high energy tails in inelastic gases

We study the formation of high energy tails in a one-dimensional kinetic model for granular gases, the so-called Inelastic Maxwell Model. We introduce a time- discretized version of the stochastic process, and show that continuous time implies larger fluctuations of the particles energies. This is due to a statistical relation between the number of inelastic collisions undergone by a particle and its average energy. This feature is responsible for the high energy tails in the model, as shown by computer simulations and by analytical calculations on a linear Lorentz model.Comment: 8 pages, 2 figures, submitted to physica