Pion-Nucleon Scattering in Kadyshevsky Formalism: II Baryon Exchange Sector

In this paper, which is the second part in a series of two, we construct tree level baryon exchange and resonance amplitudes for $\pi N$ / $MB$-scattering in the framework of the Kadyshevsky formalism. We use this formalism to formally implement absolute pair suppression, where we make use of the method of Takahashi and Umezawa. The resulting amplitudes are Lorentz invariant and causal. We continue studying the frame dependence of the Kadyshevsky integral equation using the method of Gross and Jackiw. The invariant amplitudes, including those for meson exchange, are linked to the phase-shifts using the partial wave basis.Comment: 49 page

Spin-mediated dissipation and frequency shifts of a cantilever at milliKelvin temperatures

We measure the dissipation and frequency shift of a magnetically coupled cantilever in the vicinity of a silicon chip, down to $25$ mK. The dissipation and frequency shift originates from the interaction with the unpaired electrons, associated with the dangling bonds in the native oxide layer of the silicon, which form a two dimensional system of electron spins. We approach the sample with a $3.43$ $\mu$m-diameter magnetic particle attached to an ultrasoft cantilever, and measure the frequency shift and quality factor as a function of temperature and the distance. Using a recent theoretical analysis [J. M. de Voogd et al., arXiv:1508.07972 (2015)] of the dynamics of a system consisting of a spin and a magnetic resonator, we are able to fit the data and extract the relaxation time $T_1=0.39\pm0.08$ ms and spin density $\sigma=0.14\pm0.01$ spins per nm$^2$. Our analysis shows that at temperatures $\leq500$ mK magnetic dissipation is an important source of non-contact friction.Comment: 5 pages, 3 figure

Searching for plasticity in dissociated cortical cultures on multi-electrode arrays

We attempted to induce functional plasticity in dense cultures of cortical cells using stimulation through extracellular electrodes embedded in the culture dish substrate (multi-electrode arrays, or MEAs). We looked for plasticity expressed in changes in spontaneous burst patterns, and in array-wide response patterns to electrical stimuli, following several induction protocols related to those used in the literature, as well as some novel ones. Experiments were performed with spontaneous culture-wide bursting suppressed by either distributed electrical stimulation or by elevated extracellular magnesium concentrations as well as with spontaneous bursting untreated. Changes concomitant with induction were no larger in magnitude than changes that occurred spontaneously, except in one novel protocol in which spontaneous bursts were quieted using distributed electrical stimulation

A method for mechanical generation of radio frequency fields in nuclear magnetic resonance force microscopy

We present an innovative method for magnetic resonance force microscopy (MRFM) with ultra-low dissipation, by using the higher modes of the mechanical detector as radio frequency (rf) source. This method allows MRFM on samples without the need to be close to an rf source. Furthermore, since rf sources require currents that give dissipation, our method enables nuclear magnetic resonance experiments at ultra-low temperatures. Removing the need for an on-chip rf source is an important step towards a MRFM which can be widely used in condensed matter physics.Comment: 7 pages, 5 figures, to be submitted to Physical Review Applie

Characterization and transfection properties of lipoplexes stabilized with novel exchangeable polyethylene glycol-lipid conjugates

The positive charge of cationic-lipid/DNA complexes (lipoplexes) renders them highly susceptible to interactions with the biological milieu, leading to aggregation and destabilization, and rapid clearance from the blood circulation. In this study we synthesized and characterized a set of novel amphiphiles, based on N-methyl-4-alkylpyridinium chlorides (SAINTs), to which a PEG moiety is coupled. Plasmids were fully protected in lipoplexes prepared from cationic SAINT-2 lipid and stabilized with SAINT PEGs. Our results demonstrate that SAINT-PEG stabilization is transient, and permits DNA to be released from these lipoplexes. The rate of SAINT PEG transfer from lipoplexes to acceptor liposomes was determined by the nature of the lipid anchor. Increased hydrophobicity, by lengthening the alkyl chain, resulted in a decrease of the rate of DNA release from the lipoplexes. Chain unsaturation had the opposite effect. Similarly, the in vitro transfection potency of lipoplexes containing PEG-SAINT derivatives was sensitive to the length and (un)saturation of the alkyl chain. However, the internalization of SAINT PEG stabilized lipoplexes is determined by their charge, rather than by the concentration of the polymer conjugate. Lipoplexes targeted to cell-surface epithelial glycoprotein 2, by means of a covalently coupled monoclonal antibody, were specifically internalized by cells expressing this antigen. (C) 2003 Elsevier B.V. All rights reserved