Stationary Rotating Strings as Relativistic Particle Mechanics

Stationary rotating strings can be viewed as geodesic motions in appropriate metrics on a two-dimensional space. We obtain all solutions describing stationary rotating strings in flat spacetime as an application. These rotating strings have infinite length with various wiggly shapes. Averaged value of the string energy, the angular momentum and the linear momentum along the string are discussed.Comment: 20pages, 7 figure

Analysis of Imperfections in Practical Continuous-Variable Quantum Key Distribution

As quantum key distribution becomes a mature technology, it appears clearly that some assumptions made in the security proofs cannot be justified in practical implementations. This might open the door to possible side-channel attacks. We examine several discrepancies between theoretical models and experimental setups in the case of continuous-variable quantum key distribution. We study in particular the impact of an imperfect modulation on the security of Gaussian protocols and show that approximating the theoretical Gaussian modulation with a discrete one is sufficient in practice. We also address the issue of properly calibrating the detection setup, and in particular the value of the shot noise. Finally, we consider the influence of phase noise in the preparation stage of the protocol and argue that taking this noise into account can improve the secret key rate because this source of noise is not controlled by the eavesdropper.Comment: 4 figure

Ferromagnetic Properties of ZrZn2_2

The low Curie temperature (T_C approx 28K) and small ordered moment (M_0 approx 0.17 mu_B f.u.^-1) of ZrZn2 make it one of the few examples of a weak itinerant ferromagnet. We report results of susceptibility, magnetization, resistivity and specific heat measurements made on high-quality single crystals of ZrZn2. From magnetization scaling in the vicinity of T_C (0.001<|T-T_C|/T_C<0.08), we obtain the critical exponents beta=0.52+/-0.05 and delta=3.20+/-0.08, and T_C=27.50+/-0.05K. Low-temperature magnetization measurements show that the easy axis is [111]. Resistivity measurements reveal an anomaly at T_C and a non-Fermi liquid temperature dependence rho(T)=rho_0+AT^n, where n=1.67+/-0.02, for 1<T<14K. The specific heat measurements show a mean-field-like anomaly at T_C. We compare our results to various theoretical models.Comment: submitted to PR

Mesoscale observations of Joule heating near an auroral arc and ion-neutral collision frequency in the polar cap E region

We report on the first mesoscale combined ionospheric and thermospheric observations, partly in the vicinity of an auroral arc, from Svalbard in the polar cap on 2 February 2010. The EISCAT Svalbard radar employed a novel scanning mode in order to obtain F and E region ion flows over an annular region centered on the radar. Simultaneously, a colocated Scanning Doppler Imager observed the E region neutral winds and temperatures around 110 km altitude using the 557.7 nm auroral optical emission. Combining the ion and neutral data permits the E region Joule heating to be estimated with an azimuthal spatial resolution of ∼64 km at a radius of ∼163 km from the radar. The spatial distribution of Joule heating shows significant mesoscale variation. The ion-neutral collision frequency is measured in the E region by combining all the data over the entire field of view with only weak aurora present. The estimated ion-neutral collision frequency at ∼113 km altitude is in good agreement with the MSIS atmospheric model

Energy Dependence of Breakup Cross Sections of Halo Nucleus 8B and Effective Interactions

We study the energy dependence of the cross sections for nucleon removal of 8B projectiles. It is shown that the Glauber model calculations with nucleon-nucleon t-matrix reproduce well the energy dependence of the breakup cross sections of 8B. A DWBA model for the breakup cross section is also proposed and results are compared with those of the Glauber model. We show that to obtain an agreement between the DWBA calculations, the Glauber formalism, and the experimental data, it is necessary to modify the energy behavior of the effective interaction. In particular, the breakup potential has a quite different energy dependence than the strong absorption potential.Comment: 13 pages, 4 figure

Observations of diverging field-aligned ion flow with the ESR

We report on observations of a diverging ion flow along the geomagnetic field that is often seen at the EISCAT Svalbard radar. The flow is upward above the peak of the electron density in the F-region and downward below the peak. We estimate that in such events mass transport along the field line is important for the ionization balance, and that the shape of the F-layer and its ion composition should be strongly influenced by it. Diverging flow typically occurs when there are signatures of direct entry of sheath plasma to the ionosphere in the form of intense soft particle precipitation, and we suggest that it is caused by the ionization and ionospheric electron heating associated with this precipitation. On average, 30% of all events with ion upflow also show significant ion downflow below.&lt;br&gt;&lt;br&gt; &lt;b&gt;Key words.&lt;/b&gt;Ionosphere (polar ionosphere; ionization mechanism; plasma temperature and density

Magnetic Field resulting from non-linear electrical transport in single crystals of charge-ordered Pr0.63_{0.63} Ca0.37_{0.37} MnO3_{3}}

In this letter we report that the current induced destabilization of the charge ordered (CO) state in a rare-earth manganite gives rise to regions with ferromagnetic correlation. We did this experiment by measurement of the I-V curves in single crystal of the CO system Pr$_{0.63}$Ca$_{0.37}$MnO$_{3}$ and simultanously measuring the magnetization of the current carrying conductor using a high T$_c$ SQUID working at T = 77K. We have found that the current induced destabilization of the CO state leads to a regime of negative differential resistance which leads to a small enhancement of the magnetization of the sample, indicating ferromagnetically aligned moments.Comment: 4 pages LateX, 4 eps figure

Optical properties of quantum wires: Disorder-scattering in the Lloyd-model

The Lloyd model is extended to the exciton problem in quasi one-dimensional structures to study the interplay between the Coulomb attraction and disorder scattering. Within this model the averaging and resummation of the locator series can be performed analytically. As an application, the optical absorption in quantum box wires is investigated. Without electron-hole interaction, fluctuations in the well-width lead to an asymmetric broadening of the minibands with respect to the lower and upper band-edges.Comment: 7 pages, 6 figure