On String Tunneling in Power Law Inflationary Universes

We consider the evolution of circular string loops in power law expanding universes represented by a spatially flat Friedman-Robertson-Walker metric with scale factor $a(t)\propto t^p$ where $t$ is the cosmic time and $p\geq 0$. Our main result is the existence of a "magic" power $p_m=3+2\sqrt{2}$. In spacetimes with $p<p_m$ a circular string expands either forever or to a maximal radius and then contracts until it collapses into a point (black hole). For $p>p_m$, however, we find additional types of solutions. They include configurations which contract from a positive initial radius to a minimal one and then expand forever. Their existence we interpret as an indication for the presence of a finite potential barrier. Equivalently the new solutions signal string nucleation and tunneling, phenomena recently shown to occur in de Sitter space.Comment: Latex, 9 pages + 4 figures (not included), NBI-HE-93-5

Summer Transport Estimates of the Kamchatka Current Derived As a Variational Inverse of Hydrophysical and Surface Drifter Data

The quasistationary summer Bering Sea circulation is reconstructed as a variational inverse of the hydrographic and atmospheric climatologies, transport estimates through the Bering Strait, and surface drifter data. Our results indicate the splitting of the Kamchatka Current in the vicinity of the Shirshov Ridge. This branching is in agreement with independent ARGO drifter observations. It was also found, that transport of the Kamchatka Current gradually increases downstream from 14 Sv in the Olyutorsky Gulf to 24 Sv in the Kamchatka Strait, which is twice higher than previous estimates

Summer Transport Estimates of the Kamchatka Current Derived As a Variational Inverse of Hydrophysical and Surface Drifter Data

The quasistationary summer Bering Sea circulation is reconstructed as a variational inverse of the hydrographic and atmospheric climatologies, transport estimates through the Bering Strait, and surface drifter data. Our results indicate the splitting of the Kamchatka Current in the vicinity of the Shirshov Ridge. This branching is in agreement with independent ARGO drifter observations. It was also found, that transport of the Kamchatka Current gradually increases downstream from 14 Sv in the Olyutorsky Gulf to 24 Sv in the Kamchatka Strait, which is twice higher than previous estimates

effect of porosity and cell topology on elastic plastic behavior of cellular structures

Abstract In this work we study the mechanical behavior of Ti6Al4V cellular structures by varying the randomness in the cell topology from regular cubic to completely random and the porosity of the structure. The porosity of the structure is altered by changing the strut thickness and the pore size to obtain a stiffness value between 0.5-12Gpa. The geometrical deviation in the structures from the as-designed values is studied by morphological characterization. The samples are subjected to compression and tensile loading to obtain the stiffness and the elastic-plastic behavior of the samples. Finite element modelling (FEM) is carried out on the as-designed structures for both tensile and compressive loading to study the effect of deviation between the as-designed and as-built structures. FEM is also carried out for as-built regular structures, by introducing the geometrical deviation to match the porosity of the as-built structures. Comparison of FEM and experimental results indicated that the effect of cell topology depends on the porosity values. Simulation results of as-built structures demonstrated the importance of defects in the structure

Properties of cores of the water masses in the Okhotsk Sea

Spatial distribution of depth and water properties (temperature, salinity, dissolved oxygen content) are considered in detail for cores of the Okhotsk Sea water masses: subsurface, intermediate, and deep, on the base of the most comprehensive oceanographic data set

Induced-gravity Inflation and the Density Perturbation Spectrum

Recent experimental determinations of the spectral index describing the scalar mode spectrum of density perturbations encourage comparison with predictions from models of the very early universe. Unlike extended inflation, Induced-gravity Inflation predicts a power spectrum with $0.98 \leq n_s \leq 1.00$, in close agreement with the experimental measurements.Comment: 11pp, no figures. Plain LaTeX. HUTP-94/A011. Revised edition -- Forthcoming in Physics Letters

Interannual variability of thermal state of the cold subsurface layer in the Okhotsk Sea

Long-term variability of the cold subsurface water (CSW) in the Okhotsk Sea is analyzed on the base of all available oceanographic data collected in March through August of 1946-2015 (total 65,742 stations). The Integral Heat Content (IHC) is calculated for each station and average annual IHC anomalies of the cold subsurface water are determined by month and by 2-degree grid. The IHC anomaly series are analyzed using the EOF analysis. Cycles with period of approximately 30 years are revealed in the variations of the subsurface layer heat content. Thus, in the 1946-1950, its temperature decreased, but it grew since 2009-2010 to 2015. The warming of CSW was also observed in the 1951-1964 and 1978-1994, while the cooling was in the 1965-1977 and 1995-2008. Based on this criterion, the CSW thermal condition in certain years is classified as «extremely cold» in 2001, as «cold» in 1949, 1950, 1951, 1958, 1959, 1960, 1966, 1967, 1969, 1973, 1976, 1977, 1978, 1980, 1999, 2000, 2010, 2012, as «normal» in 1946, 1952, 1953, 1954, 1955, 1957, 1961, 1962, 1965, 1970, 1971, 1972, 1975, 1979, 1982, 1983, 1985, 1986, 1988, 1989, 1990, 1993, 1995, 1996, 1998, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2013, 2014, as «warm» in 1948, 1956, 1964, 1968, 1974, 1981, 1984, 1987, 1991, 1992, 1994, 1997, 2015, and as «extremely warm» in 1963. Statistically significant correlation is found between changes of the CSW thermal conditions and long-term variations of atmosphere and ocean climate indices, as well as local patterns of the atmosphere-ice-ocean interaction in the Okhotsk Sea and adjacent onshore and offshore areas of Asia and the Pacific Ocean

Finite Element Thermal Analysis of Metal Parts Additively Manufactured via Selective Laser Melting

In this chapter, a three-dimensional finite element model is developed to simulate the thermal behavior of the molten pool in selective laser melting (SLM) process. Laser-based additive manufacturing (AM) is a near net shape manufacturing process able to produce 3D objects. They are layer-wise built through selective melting of a metal powder bed. The necessary energy is provided by a laser source. The interaction between laser and material occurs within a few microseconds, hence the transient thermal behavior must be taken into account. A calibration procedure is carried out to fit the numerical solution with the experimental data. Once the calibration has corrected the thermal parameters, a dynamic mesh refinement is applied to reduce the computational cost. The scanning strategy adopted by the laser is simulated by a path simulator built using MatLab®, while numerical analysis is carried out using ANSYS®, a commercial finite element software. To improve the performance of the simulation, the two codes interact each other to solve the analysis. Temperature distribution and geometrical feature of the molten pool under different process conditions are investigated. Results from the FE analysis provide guidance for setting up the optimization of process parameters and develop a base for further residual stress analysis

Dynamic Topography of the Bering Sea

A new mean dynamic topography (MDT) for the Bering Sea is presented. The product is obtained by combining historical oceanographic and atmospheric observations with high-resolution model dynamics in the framework of a variational technique. Eighty percent of the ocean data underlying the MDT were obtained during the last 25 years and include hydrographic profiles, surface drifter trajectories, and in situ velocity observations that were combined with National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) atmospheric climatology. The new MDT quantifies surface geostrophic circulation in the Bering Sea with a formal accuracy of 2-4 cm/s. The corresponding sea surface height (SSH) errors are estimated by inverting the Hessian matrix in the subspace spanned by the leading modes of SSH variability observed from satellites. Comparison with similar products based on in situ observations, satellite gravity, and altimetry shows that the new MDT is in better agreement with independent velocity observations by Argo drifters and moorings. Assimilation of the satellite altimetry data referenced to the new MDT allows better reconstruction of regional circulations in the Bering Sea. Comparisons also indicate that MDT estimates derived from the latest Gravity Recovery and Climate Experiment geoid model have more in common with the presented sea surface topography than with the MDTs based on earlier versions of the geoid. The presented MDT will increase the accuracy of calculations of the satellite altimeter absolute heights and geostrophic surface currents and may also contribute to improving the precision in estimating the geoid in the Bering Sea