Absence of the Transition into Abrikosov Vortex State of Two-Dimensional Type-II Superconductor with Weak Pinning

The resistive properties of thin amorphous NbO_{x} films with weak pinning were investigated experimentally above and below the second critical field H_{c2}. As opposed to bulk type II superconductors with weak pinning where a sharp change of resistive properties at the transition into the Abrikosov state is observed at H_{c4}, some percent below H_{c2} (V.A.Marchenko and A.V.Nikulov, 1981), no qualitative change of resistive properties is observed down to a very low magnetic field, H_{c4} < 0.006 H_{c2}, in thin films with weak pinning. The smooth dependencies of the resistivity observed in these films can be described by paraconductivity theory both above and below H_{c2}. This means that the fluctuation superconducting state without phase coherence remains appreciably below H_{c2} in the two-dimensional superconductor with weak pinning. The difference the H_{c4}/H_{c2} values, i.e. position of the transition into the Abrikosov state, in three- and two-dimensional superconductors conforms to the Maki-Takayama result 1971 year according to which the Abrikosov solution 1957 year is valid only for a superconductor with finite dimensions. Because of the fluctuation this solution obtained in the mean field approximation is not valid in a relatively narrow region below H_{c2} for bulk superconductors with real dimensions and much below H_{c2} for thin films with real dimensions. The superconducting state without phase coherence should not be identified with the mythical vortex liquid because the vortex, as a singularity in superconducting state with phase coherence, can not exist without phase coherence.Comment: 4 pages, 4 figure

Spectroscopy of SMC Wolf-Rayet Stars Suggests that Wind-Clumping does not Depend on Ambient Metallicity

The mass-loss rates of hot, massive, luminous stars are considered a decisive parameter in shaping the evolutionary tracks of such stars and influencing the interstellar medium on galactic scales. The small-scale structures (clumps) omnipresent in such winds may reduce empirical estimates of mass-loss rates by an evolutionarily significant factor of >=3. So far, there has been no direct observational evidence that wind-clumping may persist at the same level in environments with a low ambient metallicity, where the wind-driving opacity is reduced. Here we report the results of time-resolved spectroscopy of three presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud, where the ambient metallicity is ~1/5 Z_Sun.We detect numerous small-scale emission peaks moving outwards in the accelerating parts of the stellar winds.The general properties of the moving features, such as their velocity dispersions,emissivities and average accelerations, closely match the corresponding characteristics of small-scale inhomogeneities in the winds of Galactic Wolf-Rayet stars.Comment: 9 pages, 3 figures; accepted by ApJ Letter

Acoustic emissions from in situ compression and indentation experiments on sea ice

We present results from measurement of acoustic emissions (AE) during compression and indentation of natural sea ice in situ. We show that AE amplitudes are associated with load, so that periods of loading and unloading, and cyclic oscillations in loading during indentation, can be determined from AE records as well as from load measurements. We show that AE measured during these experiments obeys Gutenberg-Richter-type scaling laws, implying that the crack distribution within the sea ice is self-similar. We show that b-values, which indicate the ratio of small cracks to large cracks, decrease during loading, tending towards a value around 1 at failure, and increase again when loading is removed. This suggests that AE can be used to measure, non-invasively, damage and healing of natural sea ice. We conclude by discussion practical applications of these results, and opportunities for further development of AE measurement as a tool for understanding cracking in ice

On a systematic approach to defects in classical integrable field theories

We present an inverse scattering approach to defects in classical integrable field theories. Integrability is proved systematically by constructing the generating function of the infinite set of modified integrals of motion. The contribution of the defect to all orders is explicitely identified in terms of a defect matrix. The underlying geometric picture is that those defects correspond to Backlund transformations localized at a given point. A classification of defect matrices as well as the corresponding defect conditions is performed. The method is applied to a collection of well-known integrable models and previous results are recovered (and extended) directly as special cases. Finally, a brief discussion of the classical $r$-matrix approach in this context shows the relation to inhomogeneous lattice models and the need to resort to lattice regularizations of integrable field theories with defects.Comment: 27 pages, no figures. Final version accepted for publication. References added and section 5 amende

The effect of ice rubble on ice-ice sliding

Ice deformation processes in the Arctic can generate ice rubble. Many situations arise where ice fragments of varying size separate sea ice floes. While the shear forces between sea ice floes in direct contact with each other are controlled by ice-ice friction, what is not known is how the slip of the floes is affected by the presence of rubble between the sliding surfaces. We present the result of field experiments undertaken on sea ice in the Barents Sea. A doubledirect-shear experiment was done on floating sea ice in the field, with the addition of rubble ice between the sliding surfaces. This was achieved by pulling a floating ice block through a cut channel of open water 3m long, where broken ice filled the gap between the block and the channel sides. The displacement of the block and the force needed to move the block were measured. The time that the block was held motionless to allow the rubble to consolidate was recorded - this ranged from seconds to several hours. We found that the 'hold time' controls the maximum force needed to move the block. The relation between hold time and force is highly non-linear from which we deduce thermal consolidation is the controlling mechanism

Qualitative features of periodic solutions of KdV

In this paper we prove new qualitative features of solutions of KdV on the circle. The first result says that the Fourier coefficients of a solution of KdV in Sobolev space $H^N,\, N\geq 0$, admit a WKB type expansion up to first order with strongly oscillating phase factors defined in terms of the KdV frequencies. The second result provides estimates for the approximation of such a solution by trigonometric polynomials of sufficiently large degree

Ice properties in ISO 19906's second edition

The second edition of ISO 19906 Arctic Offshore structures was issued in 2019. In this paper, we describe the changes that were made to sections dealing with ice properties and discuss the relationship between them and ice actions. The changes can be divided into five groups: 1) Physical properties (temperature, density and porosity), 2) modulus of elasticity, 3) ice friction, 4) mechanical properties in level ice (uniaxial and multi-axial compressive strength, flexural strength and borehole jack strength), and 5) the keel properties of first-year ridge (Mohr-Coulomb, macro-porosity). The standard is written in such a way so that simple approaches in design guidelines complement more elaborate models. Both currently face at least three challenges, namely, the lack of full-scale data, a complicated physical environment, and a lack of understanding of the deformation mechanisms taking place in the ice

Existence of the Abrikosov vortex state in two-dimensional type-II superconductors without pinning

Theory alternative to the vortex lattice melting theories is advertised. The vortex lattice melting theories are science fiction cond-mat/9811051 because the Abrikosov state is not the vortex lattice with crystalline long-range order. Since the fluctuation correction to the Abrikosov solution is infinite in the thermodynamic limit (K.Maki and H.Takayama, 1972) any fluctuation theory of the mixed state should consider a superconductor with finite sizes. Such nonperturbative theory for the easiest case of two-dimensional superconductor in the lowest Landau level approximation is presented in this work. The thermodynamic averages of the spatial average order parameter and of the Abrikosov parameter $\beta_{a}$ are calculated. It is shown that the position H_{c4} of the transition into the Abrikosov state (i.e. in the mixed state with long-range phase coherence) depends strongly on sizes of two-dimensional superconductor. Fluctuations eliminate the Abrikosov vortex state in a wide region of the mixed state of thin films with real sizes and without pinning disorders, i.e. H_{c4} << H_{c2}. The latter has experimental corroboration in Phys.Rev.Lett. 75, 2586 (1995).Comment: 4 pages, 0 figure

Octupolar order in the multiple spin exchange model on a triangular lattice

We show how a gapless spin liquid with hidden octupolar order arises in an applied magnetic field, in a model applicable to thin films of 3He with competing ferromagnetic and antiferromagnetic (cyclic) exchange interactions. Evidence is also presented for nematic -- i.e., quadrupolar -- correlations bordering on ferromagnetism in the absence of a magnetic field.Comment: 4 pages, 5 figure