2,920 research outputs found
Dutch corporate liquidity mangement: New evidence on aggregation
In this paper we investigate Dutch corporate liquidity management in general, and target adjustment behaviour in particular. To this purpose, we use a simple error correction model of corporate liquidity holdings applied to firm-level data for the period 1977-1997. We confirm the existence of long-run liquidity targets at the firm level. We also find that changes in liquidity holdings are driven by short-run shocks as well as the urge to converge towards targeted liquidity levels. The rate of target convergence is higher when we include more firm-specific information in the target. This result supports the idea that increased precision in defining liquidity targets associates with a faster observed rate of target convergence. It also suggests that the slow speeds of adjustment obtained in many macro studies on money demand are artefacts of aggregation bias.corporate liquidity demand, precautionary liquidity
Development of sputtered techniques for thrust chambers
Procedures for closing out coolant passages in regeneratively cooled thrust chambers by triode sputtering, using post and hollow Cu-0.15 percent Zr cathodes are described. The effects of aluminum composite filler materials, substrate preparation, sputter cleaning, substrate bias current density and system geometry on closeout layer bond strength and structure are evaluated. High strength closeout layers were sputtered over aluminum fillers. The tensile strength and microstructure of continuously sputtered Cu-0.15 percent Zr deposits were determined. These continuous sputtered deposits were as thick as 0.75 cm. Tensile strengths were consistently twice as great as the strength of the material in wrought form
Characterization of a Quantum Light Source Based on Spontaneous Parametric Down-Conversion
We have built a quantum light source capable of producing different types of
quantum states. The quantum light source is based on entangled state
preparation in the process of spontaneous parametric down-conversion. The
single-photon detection rate of eight-hundred thousand per second demonstrates
that we have created a bright state-of-the-art quantum light source. As a part
of the characterization we measured two-photon quantum interference in a
Hong-Ou-Mandel interferometer.Comment: 33 page
Nanophotonic hybridization of narrow atomic cesium resonances and photonic stop gaps of opaline nanostructures
We study a hybrid system consisting of a narrowband atomic optical resonance
and the long-range periodic order of an opaline photonic nanostructure. To this
end, we have infiltrated atomic cesium vapor in a thin silica opal photonic
crystal. With increasing temperature, the frequencies of the opal's
reflectivity peaks shift down by >20% due to chemical reduction of the silica.
Simultaneously, the photonic bands and gaps shift relative to the fixed
near-infrared cesium D1 transitions. As a result the narrow atomic resonances
with high finesse (f/df=8E5) dramatically change shape from a usual dispersive
shape at the blue edge of a stop gap, to an inverted dispersion lineshape at
the red edge of a stop gap. The lineshape, amplitude, and off-resonance
reflectivity are well modeled with a transfer-matrix model that includes the
dispersion and absorption of Cs hyperfine transitions and the
chemically-reduced opal. An ensemble of atoms in a photonic crystal is an
intriguing hybrid system that features narrow defect-like resonances with a
strong dispersion, with potential applications in slow light, sensing and
optical memory.Comment: 8 pages, 6 figure
FUSE observations of G226-29: First detection of the H_2 quasi-molecular satellite at 1150A
We present new FUV observations of the pulsating DA white dwarf G226-29
obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This ZZ Ceti
star is the brightest one of its class and the coolest white dwarf observed by
FUSE. We report the first detection of the broad quasi-molecular
collision-induced satellite of Ly-beta at 1150 A, an absorption feature that is
due to transitions which take place during close collisions of hydrogen atoms.
The physical interpretation of this feature is based on recent progress of the
line broadening theory of the far wing of Ly-beta. This predicted feature had
never been observed before, even in laboratory spectra.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figure
Observations on White Grubs Affecting Sugar Cane at the Juba Sugar Project, South-Western Somalia, in the 1980s, and Implications for Their Management
The article reports some observations on white grubs affecting sugarcane at the Juba Sugar Project, in South-Western Somalia, in the 1980s, and the implications for their management.Maqaalku wuxuu ka hadlayaa arrimo la xiriira dixiriyaha cad ee waxyeeleeyo qasabka sonkorta ee mashruuca sonkorta ee Jubba. Baaritaankaas waxaa lagu sameeyey koofur-galbeed ee Soomaaliya sannadka 1980.L'articolo riporta alcune osservazioni su larve bianche che colpiscono la canna da zucchero nell'ambito del Juba Sugar Project, svoltosi nel sud-ovest della Somalia negli anni 1980, e le relative implicazioni per la loro gestione
Regularity of higher codimension area minimizing integral currents
This lecture notes are an expanded version of the course given at the
ERC-School on Geometric Measure Theory and Real Analysis, held in Pisa,
September 30th - October 30th 2013. The lectures aim to explain the main steps
of a new proof of the partial regularity of area minimizing integer rectifiable
currents in higher codimension, due originally to F. Almgren, which is
contained in a series of papers in collaboration with C. De Lellis (University
of Zurich).Comment: This text will appear in "Geometric Measure Theory and Real
Analysis", pp. 131--192, Proceedings of the ERC school in Pisa (2013), L.
Ambrosio Ed., Edizioni SNS (CRM Series
A physically motivated and empirically calibrated method to measure effective temperature, metallicity, and Ti abundance of M dwarfs
The ability to perform detailed chemical analysis of Sun-like F-, G-, and
K-type stars is a powerful tool with many applications including studying the
chemical evolution of the Galaxy and constraining planet formation theories.
Unfortunately, complications in modeling cooler stellar atmospheres hinders
similar analysis of M-dwarf stars. Empirically-calibrated methods to measure M
dwarf metallicity from moderate-resolution spectra are currently limited to
measuring overall metallicity and rely on astrophysical abundance correlations
in stellar populations. We present a new, empirical calibration of synthetic M
dwarf spectra that can be used to infer effective temperature, Fe abundance,
and Ti abundance. We obtained high-resolution (R~25,000), Y-band (~1 micron)
spectra of 29 M dwarfs with NIRSPEC on Keck II. Using the PHOENIX stellar
atmosphere modeling code (version 15.5), we generated a grid of synthetic
spectra covering a range of temperatures, metallicities, and
alpha-enhancements. From our observed and synthetic spectra, we measured the
equivalent widths of multiple Fe I and Ti I lines and a temperature-sensitive
index based on the FeH bandhead. We used abundances measured from
widely-separated solar-type companions to empirically calibrate transformations
to the observed indices and equivalent widths that force agreement with the
models. Our calibration achieves precisions in Teff, [Fe/H], and [Ti/Fe] of 60
K, 0.1 dex, and 0.05 dex, respectively and is calibrated for 3200 K < Teff <
4100 K, -0.7 < [Fe/H] < +0.3, and -0.05 < [Ti/Fe] < +0.3. This work is a step
toward detailed chemical analysis of M dwarfs at a similar precision achieved
for FGK stars.Comment: accepted for publication in ApJ, all synthetic spectra available at
http://people.bu.edu/mveyette/phoenix
Propagation on networks: an exact alternative perspective
By generating the specifics of a network structure only when needed
(on-the-fly), we derive a simple stochastic process that exactly models the
time evolution of susceptible-infectious dynamics on finite-size networks. The
small number of dynamical variables of this birth-death Markov process greatly
simplifies analytical calculations. We show how a dual analytical description,
treating large scale epidemics with a Gaussian approximations and small
outbreaks with a branching process, provides an accurate approximation of the
distribution even for rather small networks. The approach also offers important
computational advantages and generalizes to a vast class of systems.Comment: 8 pages, 4 figure
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