2,159 research outputs found
Learning About the Term Structure and Optimal Rules for Inflation Targeting
n this paper we incorporate the term structure of interest rates in a standard inflation forecast targeting framework. We find that under flexible inflation targeting and uncertainty in the degree of persistence in the economy, allowing for active learning possibilities has effects on the optimal interest rate rule followed by the central bank. For a wide range of possible initial beliefs about the unknown parameter, the dynamically optimal rule is in general more activist, in the sense of responding aggressively to the state of the economy, than the myopic rule for small to moderate deviations of the state variable from its target. On the other hand, for large deviations, the optimal policy is less activist than the myopic and the certainty equivalence policies.
Discovery of Reflection Nebulosity Around Five Vega-like Stars
Coronagraphic optical observations of six Vega-like stars reveal reflection
nebulosities, five of which were previously unknown. The nebulosities
illuminated by HD 4881, HD 23362, HD 23680, HD 26676, and HD 49662 resemble
that of the Pleiades, indicating an interstellar origin for dust grains. The
reflection nebulosity around HD 123160 has a double-arm morphology, but no
disk-like feature is seen as close as 2.5 arcsec from the star in K-band
adaptive optics data. We demonstrate that uniform density dust clouds
surrounding HD 23362, HD 23680 and HD 123160 can account for the observed
12-100 micron spectral energy distributions. For HD 4881, HD 26676, and HD
49662 an additional emission source, such as from a circumstellar disk or
non-equilibrium grain heating, is required to fit the 12-25 micron data. These
results indicate that in some cases, particularly for Vega-like stars located
beyond the Local Bubble (>100 pc), the dust responsible for excess thermal
emission may originate from the interstellar medium rather than from a
planetary debris system.Comment: The Astrophysical Journal, in press for March, 2002 (32 pages, 13
figures
Government Supports United States Exporters
The latest addition to the US law of international trade, the Export Trading Company Act of 1982 (the Act), was passed by Congress with a claim that it will put US exporters on more competitive footing with their foreign counterparts
Government Supports United States Exporters
The latest addition to the US law of international trade, the Export Trading Company Act of 1982 (the Act), was passed by Congress with a claim that it will put US exporters on more competitive footing with their foreign counterparts
Abandoned projects-implication on the strength of exposed steel and concrete in the Southern region of Nigeria
This research is centered on the investigation of the implication of abandonment on the strength of exposed steel and concrete in an abandoned project; as most abandoned project are continued without due consideration to the current strength of the structural members, which may lead to eventual collapse, if the structural members have failed in strength. Six abandoned project sites were investigated: three in Port Harcourt, Rivers state and the other three in Lagos, Lagos state, Nigeria. Thus limiting the investigation to Southern region of Nigeria where the temperature ranges between 23°C and 32°C and precipitation/rainfall ranged between 36mm and 410mm.The Periods of the abandonment ranges from three to thirty-five years. All structural members were cast in-situ. Visual inspections were carried out on site, rebound hammer test was done, concrete samples were cored and steel reinforcement bars were cut from site. Laboratory test and analysis were carried on te cored samples as well as tensile test carried out on the steel samples. Data obtained from both field and laboratory analysis, were analyzed using Excel regression analysis and a model was obtained to help determine the estimated steel strength of exposed steel reinforcement bars after a period of abandonment in the region considered.Keywords: abandonment, concrete, steel, compressive strength, tensile strengt
Exact properties of Frobenius numbers and fraction of the symmetric semigroups in the weak limit for n=3
We generalize and prove a hypothesis by V. Arnold on the parity of Frobenius
number. For the case of symmetric semigroups with three generators of Frobenius
numbers we found an exact formula, which in a sense is the sum of two
Sylvester's formulaes. We prove that the fraction of the symmetric semigroups
is vanishing in the weak limit
Americans are divided on Medicaid work requirements, but it depends on recipients’ circumstances
This week the Biden administration requested a halt to a Trump-era Supreme Court challenge to state Medicaid work requirements. But how do Americans feel about work requirements for Medicaid recipients? In new research, Simon F. Haeder, Steven Sylvester and Timothy H. Callaghan find that while Americans are split in their support or opposition to Medicaid work requirements, public opinion is more nuanced when the public is asked who should be exempted from these requirements
Sub-millimeter images of a dusty Kuiper belt around eta Corvi
We present sub-millimeter and mid-infrared images of the circumstellar disk
around the nearby F2V star eta Corvi. The disk is resolved at 850um with a size
of ~100AU. At 450um the emission is found to be extended at all position
angles, with significant elongation along a position angle of 130+-10deg; at
the highest resolution (9.3") this emission is resolved into two peaks which
are to within the uncertainties offset symmetrically from the star at 100AU
projected separation. Modeling the appearance of emission from a narrow ring in
the sub-mm images shows the observed structure cannot be caused by an edge-on
or face-on axisymmetric ring; the observations are consistent with a ring of
radius 150+-20AU seen at 45+-25deg inclination. More face-on orientations are
possible if the dust distribution includes two clumps similar to Vega; we show
how such a clumpy structure could arise from the migration over 25Myr of a
Neptune mass planet from 80-105AU. The inner 100AU of the system appears
relatively empty of sub-mm emitting dust, indicating that this region may have
been cleared by the formation of planets, but the disk emission spectrum shows
that IRAS detected an additional hot component with a characteristic
temperature of 370+-60K (implying a distance of 1-2AU). At 11.9um we found the
emission to be unresolved with no background sources which could be
contaminating the fluxes measured by IRAS. The age of this star is estimated to
be ~1Gyr. It is very unusual for such an old main sequence star to exhibit
significant mid-IR emission. The proximity of this source makes it a perfect
candidate for further study from optical to mm wavelengths to determine the
distribution of its dust.Comment: 22 pages, 4 figures. Scheduled for publication in ApJ 10 February
2005 issu
The Coronal X-ray Spectrum of the Multiple Weak-Lined T Tauri Star System HD 98800
We present high-resolution X-ray spectra of the multiple (hierarchical
quadruple) weak-lined T Tauri star system HD 98800, obtained with the High
Energy Transmission Gratings Spectrograph (HETGS) aboard the Chandra X-ray
Observatory (CXO). In the zeroth-order CXO/HETGS X-ray image, both principle
binary components of HD 98800 (A and B, separation 0.8'') are detected;
component A was observed to flare during the observation. The infrared excess
(dust disk) component, HD 98800B, is a factor ~4 fainter in X-rays than the
apparently ``diskless'' HD 98800A, in quiescence. The line ratios of He-like
species (e.g., Ne IX, O VII) in the HD 98800A spectrum indicate that the
X-ray-emitting plasma around HD 98800 is in a typical coronal density regime
(log n <~ 11). We conclude that the dominant X-ray-emitting component(s) of HD
98800 is (are) coronally active. The sharp spectral differences between HD
98800 and the classical T Tauri star TW Hya demonstrate the potential utility
of high-resolution X-ray spectroscopy in providing diagnostics of pre-main
sequence accretion processes.Comment: 11 pages, 5 figures; to appear in the Astrophysical Journal (Letters
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