531 research outputs found
Metropolitan Business Cycle Analysis for Lubbock
Abstract. This study develops a business cycle index (BCI) for Lubbock Metropolitan Statistical Area (MSA). The Stock & Watson (1989; 1991; 1993) methodology is used to develop the BCI and assumes that the co-movements of key economic indicators have a single underlying, unobservable factor. This factor is extracted from the indicators and used to calculate an index that represents economic conditions through an econometric approach. The model uses the Kalman filter smoothing approach which smooths across variables and over time. This results in an index that is smoother with less pronounced expansions and recessions. Indicator series used for the study are: establishment employment, unemployment, real retail sales and real wages that begin in 1990 and include complete data through the end of 2015. Results indicate that the Lubbock business cycle has peaks and troughs that occur later than those for the national economy.Keywords. Regional Economics; Business Cycles; Economic Indicators.JEL. R15, E32
Time-Resolved Magnetic Relaxation of a Nanomagnet on Subnanosecond Time Scales
We present a two-current-pulse temporal correlation experiment to study the
intrinsic subnanosecond nonequilibrium magnetic dynamics of a nanomagnet during
and following a pulse excitation. This method is applied to a model
spin-transfer system, a spin valve nanopillar with perpendicular magnetic
anisotropy. Two-pulses separated by a short delay (< 500 ps) are shown to lead
to the same switching probability as a single pulse with a duration that
depends on the delay. This demonstrates a remarkable symmetry between magnetic
excitation and relaxation and provides a direct measurement of the magnetic
relaxation time. The results are consistent with a simple finite temperature
Fokker-Planck macrospin model of the dynamics, suggesting more coherent
magnetization dynamics in this short time nonequilibrium limit than near
equilibrium
Luminescent hyperbolic metasurfaces.
When engineered on scales much smaller than the operating wavelength, metal-semiconductor nanostructures exhibit properties unobtainable in nature. Namely, a uniaxial optical metamaterial described by a hyperbolic dispersion relation can simultaneously behave as a reflective metal and an absorptive or emissive semiconductor for electromagnetic waves with orthogonal linear polarization states. Using an unconventional multilayer architecture, we demonstrate luminescent hyperbolic metasurfaces, wherein distributed semiconducting quantum wells display extreme absorption and emission polarization anisotropy. Through normally incident micro-photoluminescence measurements, we observe absorption anisotropies greater than a factor of 10 and degree-of-linear polarization of emission >0.9. We observe the modification of emission spectra and, by incorporating wavelength-scale gratings, show a controlled reduction of polarization anisotropy. We verify hyperbolic dispersion with numerical simulations that model the metasurface as a composite nanoscale structure and according to the effective medium approximation. Finally, we experimentally demonstrate >350% emission intensity enhancement relative to the bare semiconducting quantum wells
Object-X: The Brightest Mid-IR Point Source in M33
We discuss the nature of the brightest mid-IR point source (which we dub
Object X) in the nearby galaxy M33. Although multi-wavelength data on this
object have existed in the literature for some time, it has not previously been
recognized as the most luminous mid-IR object in M33 because it is entirely
unremarkable in both optical and near-IR light. In the Local Group Galaxies
Survey, Object X is a faint red source visible in VRI and H-alpha but not U or
B. It was easily seen at JHK_s in the 2MASS survey. It is the brightest point
source in all four Spitzer IRAC bands and is also visible in the MIPS 24-micron
band. Its bolometric luminosity is 5x10^5 L_sun. The source is optically
variable on short time scales (tens of days) and is also slightly variable in
the mid-IR, indicating that it is a star. Archival photographic plates (from
1949 and 1991) show no optical source, so the star has been obscured for at
least half a century. Its properties are similar to those of the Galactic OH/IR
star IRC+10420 which has a complex dusty circumstellar structure resulting from
episodic low velocity mass ejections. We propose that Object X is a M>30 M_sun
evolved star obscured in its own dust ejected during episodic mass loss events
over at least half a century. It may emerge from its current ultra-short
evolutionary phase as a hotter post-RSG star analogous to M33 Var A. The
existence and rarity of such objects can be an important probe of a very brief
yet eventful stellar evolutionary phase.Comment: 20 pages, 10 figures. Accepted for publication by Ap
Reorientation of Spin Density Waves in Cr(001) Films induced by Fe(001) Cap Layers
Proximity effects of 20 \AA thin Fe layers on the spin density waves (SDWs)
in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk
Cr we observe a SDW with its wave vector Q pointing along only one {100}
direction which depends dramatically on the film thickness t_{Cr}. For t_{Cr} <
250 \AA the SDW propagates out-of-plane with the spins in the film plane. For
t_{Cr} > 1000 \AA the SDW propagates in the film plane with the spins
out-of-plane perpendicular to the in-plane Fe moments. This reorientation
transition is explained by frustration effects in the antiferromagnetic
interaction between Fe and Cr across the Fe/Cr interface due to steps at the
interface.Comment: 4 pages (RevTeX), 3 figures (EPS
New observations of NGC 1624-2 reveal a complex magnetospheric structure and underlying surface magnetic geometry
NGC 1624-2 is the most strongly magnetized O-type star known. Previous
spectroscopic observations of this object in the ultraviolet provided evidence
that it hosts a large and dense circumstellar magnetosphere. Follow-up
observations obtained with the \textit{Hubble Space Telescope} not only confirm
that previous inference, but also suggest that NGC 1624-2's magnetosphere has a
complex structure. Furthermore, an expanded spectropolarimetric time series
shows a potential departure from a dipolar magnetic field geometry, which could
mean that the strongest field detected at the surface of an O-type star is also
topologically complex. This result raises important questions regarding the
origin and evolution of magnetic fields in massive stars.Comment: 12 pages, 3 figures, accepted for publication by MNRAS (2020 December
1
Effects of epitaxial strain on the growth mechanism of YBa2Cu3O7-x thin films in [YBa2Cu3O7-x / PrBa2Cu3O7-x] superlattices
We report on the growth mechanism of YBa2Cu3O7-x (YBCO). Our study is based
on the analysis of ultrathin, YBa2Cu3O7-x layers in c-axis oriented YBa2Cu3O7-x
/ PrBa2Cu3O7-x superlattices. We have found that the release of epitaxial
strain in very thin YBCO layers triggers a change in the dimensionality of the
growth mode. Ultrathin, epitaxially strained, YBCO layers with thickness below
3 unit cells grow in a block by block two dimensional mode coherent over large
lateral distances. Meanwhile, when thickness increases, and the strain relaxes,
layer growth turns into three dimensional, resulting in rougher layers and
interfaces.Comment: 10 pages + 9 figures, accepted in Phys. Rev.
Magnetic switching in granular FePt layers promoted by near-field laser enhancement
Light-matter interaction at the nanoscale in magnetic materials is a topic of
intense research in view of potential applications in next-generation
high-density magnetic recording. Laser-assisted switching provides a pathway
for overcoming the material constraints of high-anisotropy and high-packing
density media, though much about the dynamics of the switching process remains
unexplored. We use ultrafast small-angle x-ray scattering at an x-ray
free-electron laser to probe the magnetic switching dynamics of FePt
nanoparticles embedded in a carbon matrix following excitation by an optical
femtosecond laser pulse. We observe that the combination of laser excitation
and applied static magnetic field, one order of magnitude smaller than the
coercive field, can overcome the magnetic anisotropy barrier between "up" and
"down" magnetization, enabling magnetization switching. This magnetic switching
is found to be inhomogeneous throughout the material, with some individual FePt
nanoparticles neither switching nor demagnetizing. The origin of this behavior
is identified as the near-field modification of the incident laser radiation
around FePt nanoparticles. The fraction of not-switching nanoparticles is
influenced by the heat flow between FePt and a heat-sink layer
- …