22,337 research outputs found
A five colour photometry and polarimetry of the zodiacal light - A preliminary report
Five color photometry and polarimetry of the zodiacal ligh
Coherent Description for Hitherto Unexplained Radioactivities by Super- and Hyperdeformed Isomeric States
Recently long-lived high spin super- and hyperdeformed isomeric states with
unusual radioactive decay properties have been discovered. Based on these newly
observed modes of radioactive decay, consistent interpretations are suggested
for previously unexplained phenomena seen in nature. These are the Po halos,
the low-energy enhanced 4.5 MeV alpha-particle group proposed to be due to an
isotope of a superheavy element with Z = 108, and the giant halos.Comment: 8 pages, 2 figures, 1 table, to be published in Int. J. Mod. Phys.
Buckling instability in type-II superconductors with strong pinning
We predict a novel buckling instability in the critical state of thin type-II
superconductors with strong pinning. This elastic instability appears in high
perpendicular magnetic fields and may cause an almost periodic series of flux
jumps visible in the magnetization curve. As an illustration we apply the
obtained criteria to a long rectangular strip.Comment: Submitted to Phys. Rev. Let
Super- and Hyperdeformed Isomeric States and Long-Lived Superheavy Elements
The recent discoveries of the long-lived high spin super- and hyperdeformed
isomeric states and their unusual radioactive decay properties are described.
Based on their existence a consistent interpretation is given to the production
of the long-lived superheavy element with Z = 112, via secondary reactions in
CERN W targets, and to the low energy and very enhanced alpha-particle groups
seen in various actinide fractions separated from the same W target. In
addition, consistent interpretations are suggested for previously unexplained
phenomena seen in nature. These are the Po halos, the low-energy enhanced 4.5
MeV alpha-particle group proposed to be due to an isotope of a superheavy
element with Z = 108, and the giant halos.Comment: 4 pages. Contribution to the 2nd Int. Conf. on the Chemistry and
Physics of the Transactinide Elements (TAN 03) Napa California, November 200
Theory of Type-II Superconductors with Finite London Penetration Depth
Previous continuum theory of type-II superconductors of various shapes with
and without vortex pinning in an applied magnetic field and with transport
current, is generalized to account for a finite London penetration depth
lambda. This extension is particularly important at low inductions B, where the
transition to the Meissner state is now described correctly, and for films with
thickness comparable to or smaller than lambda. The finite width of the surface
layer with screening currents and the correct dc and ac responses in various
geometries follow naturally from an equation of motion for the current density
in which the integral kernel now accounts for finite lambda. New geometries
considered here are thick and thin strips with applied current, and `washers',
i.e. thin film squares with a slot and central hole as used for SQUIDs.Comment: 14 pages, including 15 high-resolution figure
Critical State in Thin Anisotropic Superconductors of Arbitrary Shape
A thin flat superconductor of arbitrary shape and with arbitrary in-plane and
out-of-plane anisotropy of flux-line pinning is considered, in an external
magnetic field normal to its plane.
It is shown that the general three-dimensional critical state problem for
this superconductor reduces to the two-dimensional problem of an infinitely
thin sample of the same shape but with a modified induction dependence of the
critical sheet current. The methods of solving the latter problem are well
known. This finding thus enables one to study the critical states in realistic
samples of high-Tc superconductors with various types of anisotropic flux-line
pinning. As examples, we investigate the critical states of long strips and
rectangular platelets of high-Tc superconductors with pinning either by the
ab-planes or by extended defects aligned with the c-axis.Comment: 13 pages including 13 figure files in the tex
Analytic Solution for the Critical State in Superconducting Elliptic Films
A thin superconductor platelet with elliptic shape in a perpendicular
magnetic field is considered. Using a method originally applied to circular
disks, we obtain an approximate analytic solution for the two-dimensional
critical state of this ellipse. In the limits of the circular disk and the long
strip this solution is exact, i.e. the current density is constant in the
region penetrated by flux. For ellipses with arbitrary axis ratio the obtained
current density is constant to typically 0.001, and the magnetic moment
deviates by less than 0.001 from the exact value. This analytic solution is
thus very accurate. In increasing applied magnetic field, the penetrating flux
fronts are approximately concentric ellipses whose axis ratio b/a < 1 decreases
and shrinks to zero when the flux front reaches the center, the long axis
staying finite in the fully penetrated state. Analytic expressions for these
axes, the sheet current, the magnetic moment, and the perpendicular magnetic
field are presented and discussed. This solution applies also to
superconductors with anisotropic critical current if the anisotropy has a
particular, rather realistic form.Comment: Revtex file and 13 postscript figures, gives 10 pages of text with
figures built i
Broad Absorption Line Variability in Radio-Loud Quasars
We investigate C IV broad absorption line (BAL) variability within a sample
of 46 radio-loud quasars (RLQs), selected from SDSS/FIRST data to include both
core-dominated (39) and lobe-dominated (7) objects. The sample consists
primarily of high-ionization BAL quasars, and a substantial fraction have large
BAL velocities or equivalent widths; their radio luminosities and
radio-loudness values span ~2.5 orders of magnitude. We have obtained 34 new
Hobby-Eberly Telescope (HET) spectra of 28 BAL RLQs to compare to earlier SDSS
data, and we also incorporate archival coverage (primarily dual-epoch SDSS) for
a total set of 78 pairs of equivalent width measurements for 46 BAL RLQs,
probing rest-frame timescales of ~80-6000 d (median 500 d). In general, only
modest changes in the depths of segments of absorption troughs are observed,
akin to those seen in prior studies of BAL RQQs. Also similar to previous
findings for RQQs, the RLQs studied here are more likely to display BAL
variability on longer rest-frame timescales. However, typical values of
|Delta_EW| and |Delta_EW|/ are about 40+/-20% lower for BAL RLQs when
compared with those of a timescale-matched sample of BAL RQQs. Optical
continuum variability is of similar amplitude in BAL RLQs and BAL RQQs; for
both RLQs and RQQs, continuum variability tends to be stronger on longer
timescales. BAL variability in RLQs does not obviously depend upon their radio
luminosities or radio-loudness values, but we do find tentative evidence for
greater fractional BAL variability within lobe-dominated RLQs. Enhanced BAL
variability within more edge-on (lobe-dominated) RLQs supports some geometrical
dependence to the outflow structure.Comment: 27 pages, 16 figures, 6 tables, accepted to MNRAS, full Appendix A at
http://www.macalester.edu/~bmille13/balrlqs.htm
Properties of the Ideal Ginzburg-Landau Vortex Lattice
The magnetization curves M(H) for ideal type-II superconductors and the
maximum, minimum, and saddle point magnetic fields of the vortex lattice are
calculated from Ginzburg-Landau theory for the entire ranges of applied
magnetic fields Hc1 <= H < Hc2 or inductions 0 <= B < Hc2 and Ginzburg-Landau
parameters sqrt(1/2) <= kappa <= 1000. Results for the triangular and square
flux-line lattices are compared with the results of the circular cell
approximation. The exact magnetic field B(x,y) and magnetization M(H, kappa)
are compared with often used approximate expressions, some of which deviate
considerably or have limited validity. Useful limiting expressions and
analytical interpolation formulas are presented.Comment: 11 pages, 8 figure
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