Superconducting pipes and levitating magnets

Motivated by a beautiful demonstration of the Faraday's and Lenz's law in which a small neodymium magnet falls slowly through a conducting non-ferromagnetic tube, we consider the dynamics of a magnet falling through a superconducting pipe. Unlike the case of normal conducting pipes, in which the magnet quickly reaches the terminal velocity, inside a superconducting tube the magnet falls freely. On the other hand, to enter the pipe the magnet must overcome a large electromagnetic energy barrier. For sufficiently strong magnets, the barrier is so large that the magnet will not be able to penetrate it and will be suspended over the front edge. We calculate the work that must done to force the magnet to enter a superconducting tube. The calculations show that superconducting pipes are very efficient at screening magnetic fields. For example, the magnetic field of a dipole at the center of a short pipe of radius $a$ and length $L \approx a$ decays, in the axial direction, with a characteristic length $\xi \approx 0.26 a$. The efficient screening of the magnetic field might be useful for shielding highly sensitive superconducting quantum interference devices, SQUIDs. Finally, the motion of the magnet through a superconducting pipe is compared and contrasted to the flow of ions through a trans-membrane channel

Gate stability of GaN-Based HEMTs with P-Type Gate

status: publishe

A multi-methodological study of the (K,Ca)-variety of the zeolite merlinoite

A multi-methodological study of the (K,Ca)-variety of the zeolite merlinoite from Fosso Attici, Sacrofano, Italy was carried out on the basis of electron microprobe analysis in wavelength dispersive mode, singlecrystal X-ray diffraction (at 100 K), Raman and infrared spectroscopy. The chemical formula of the merlinoite from Fosso Attici is (Na0.37K5.69)\u3a3=6.06(Mg0.01Ca1.93Ba0.40)\u3a3=2.34(Fe3+0.02Al10.55Si21.38)\u3a3=31.9O64\u38719.6H2O, compatible with the ideal chemical formula K6Ca2[Al10Si22O64]\u38720H2O. Anisotropic structure refinements confirmed the symmetry and the framework model previously reported (space group Immm, a = 14.066(5),b = 14.111(5), c = 9.943(3) \uc5 at 100 K). Refinement converged with four cationic sites and sixH2Osites; refined bond distances of the framework tetrahedra suggest a highly disordered Si/ Al-distribution. The Raman spectrum of merlinoite (collected between 100 and 4000 cm 121) is dominated by a doublet of bands between 496\u2013422 cm 121, assigned to tetrahedral T\u2013O\u2013T symmetric bending modes. T\u2013O\u2013T antisymmetric stretching is also observed; stretching and bending modes of the H2O molecules are only clearly visiblewhen using a blue laser. The single-crystal near-infrared spectrum shows a very weak band at 6823 cm 121, assigned to the first overtone of the O\u2013H stretching mode, and a band at 5209 cm 121, due to the combination of H2O stretching and bendingmodes.Avery broad and convoluted absorption, extending from 3700 to 3000 cm 121 occurs in the H2O stretching region, while the \u3bd2 bending mode of H2O is found at 1649 cm 121. The powder midinfrared spectrum of merlinoite between 400\u20131300 cm 121 is dominated by tetrahedral T\u2013O\u2013T symmetric and antisymmetric stretches. Raman and Fourier-transform infrared spectroscopy spectra of merlinoite and phillipsite provide a quick identification tool for these zeolites, which are often confused due to their close similarity

Statistical Mechanics of Unbound Two Dimensional Self-Gravitating Systems

We study, using both theory and molecular dynamics simulations, the relaxation dynamics of a microcanonical two dimensional self-gravitating system. After a sufficiently large time, a gravitational cluster of N particles relaxes to the Maxwell-Boltzmann distribution. The time to reach the thermodynamic equilibrium, however, scales with the number of particles. In the thermodynamic limit, $N\to\infty$ at fixed total mass, equilibrium state is never reached and the system becomes trapped in a non-ergodic stationary state. An analytical theory is presented which allows us to quantitatively described this final stationary state, without any adjustable parameters

Chaotic Interaction of Langmuir Solitons and Long Wavelength Radiation

In this work we analyze the interaction of isolated solitary structures and ion-acoustic radiation. If the radiation amplitude is small solitary structures persists, but when the amplitude grows energy transfer towards small spatial scales occurs. We show that transfer is particularly fast when a fixed point of a low dimensional model is destroyed.Comment: LaTex + 4 eps file

Collisionless relaxation in gravitational systems: From violent relaxation to gravothermal collapse

Theory and simulations are used to study collisionless relaxation of a gravitational $N$-body system. It is shown that when the initial one particle distribution function satisfies the virial condition -- potential energy is minus twice the kinetic energy -- the system quickly relaxes to a metastable state described {\it quantitatively} by the Lynden-Bell distribution with a cutoff. If the initial distribution function does not meet the virial requirement, the system undergoes violent oscillations, resulting in a partial evaporation of mass. The leftover particles phase separate into a core-halo structure. The theory presented allows us to quantitatively predict the amount and the distribution of mass left in the central core, without any adjustable parameters. On a longer time scale $\tau_G \sim N$ collisionless relaxation leads to a gravothermal collapse

Separatrix Reconnections in Chaotic Regimes

In this paper we extend the concept of separatrix reconnection into chaotic regimes. We show that even under chaotic conditions one can still understand abrupt jumps of diffusive-like processes in the relevant phase-space in terms of relatively smooth realignments of stable and unstable manifolds of unstable fixed points.Comment: 4 pages, 5 figures, submitted do Phys. Rev. E (1998

POMC and TP53 genetic variability and risk of basal cell carcinoma of skin: Interaction between host and genetic factors.

Background: Basal cell carcinoma (BCC) of the skin is the most common neoplasm among the Caucasian population of the western world. Ultraviolet (UV) radiation-induced p53 activation promotes cutaneous pigmentation by increasing transcriptional activity of pro-opiomelanocortin (POMC) in the skin. Induction of POMC/-melanocyte-stimulating hormone (α-MSH) activates the melanocortin 1 receptor (MC1R), resulting in skin pigmentation. The tumor suppressor p53 is a key player in stress responses that preserve genomic stability, responding to a variety of insults including DNA damage, hypoxia, metabolic stress and oncogene activation. Malfunction of the p53 pathway is an almost universal hallmark of human tumors. Polymorphisms in the gene encoding p53 (TP53) alter its transcriptional activity, which in turn may influence the UV radiation-induced tanning response. Objective: The aim of the present work is to test association between POMC and TP53 genetic variability, the possible interplay with host factors and the risk of basal cell carcinoma of skin. Methods: We covered the variability of the two genes we used 17 tagging polymorphisms in 529 BCC cases and 532 healthy controls. We have also tested the possible interactions between the genetic variants and three known risk factors for BCC: skin complexion, sun effect and skin response to sun exposure. Results: We did not observe any statistically significant association between SNPs in these two genes and BCC risk overall, nor interactions of SNPs with known BCC risk factors. However we found that, in the group of subjects with lower sun exposure, carriers of one copy of the C allele of the TP53 SNP rs12951053 had a decreased risk of BCC (OR = 0.28, 95% CI 0.12-0.62, P= 0.002). Conclusions: We have observed that the interplay of an environmental risk factor and one polymorphism in TP53 gene could modulate the risk of BCC

Nickel (0) complexes as promising chemosensors for detecting the “cork taint” in wine

2,4,6-Trichloroanisole (TCA) is well recognized as one of the most responsible molecules of cork taint, an organoleptic defect of wine which represents a serious problem for wine industries. Up to now, very few examples of TCA-biosensors have been developed and we report herein a promising nickel (0) complex that can be employed as chemosensor for the TCA detection in cork stoppers. Among the three Ni (0) complexes studied in this work, complex Ni(0)(BINAP)(η2-PhCN) (2) showed the best reactivity towards pure TCA affording the oxidative addition product 4 in four hours at room temperature. Compound 4 represents an appealing probe for the indirect quantification of TCA due to the presence of the characteristic UV-adsorption band at 444 nm. Statistical studies on real samples confirmed that the presence of TCA can be detected by employing UV-Visible spectroscopy, as demonstrated by PCA analyses which allowed distinguishing TCA-contaminated samples from non-contaminated ones. Even if the present study has to be considered a preliminary approach for the realization of a chemosensor usable in real systems, the here reported Ni (0)-based sensing procedure represents the first examples of TCA chemical detection

[Ag(PcL)]-Catalysed Domino Approach to 6-Substituted Benzoxazino Isoquinolines

In this paper, we describe a new silver catalysed domino approach to 6-substituted benzoxazino isoquinolines starting from 2-alkynylbenzaldehydes and 1-substituted-(2-aminophenyl)methanols. The strategy is characterized by good reaction yields, and can be performed at room temperature as well as under heating (conventional or dielectric) in different reaction times. Best results have been obtained by using silver complexes of macrocyclic pyridine-containing ligands (PcL) as catalysts. The stereoselectivity of the transformation has been investigated by using chiral reaction partners and chiral catalyst, but unfortunately, modest stereoselectivities has been achieved. On the other hand, this approach represents an alternative synthetic strategy for the preparation of 6-substituted benzoxazino isoquinolines, which are the key scaffold of some compounds endowed of biological activity