6,075 research outputs found
The IT Revolution and the Stock Market.
A new technology or product is often developed by the single entrepreneur. Whether he reaches the initial public offering stage or is acquired by a listed firm, it takes time for the innovator to add value to the stock market. Indeed, the innovation may, at first, reduce the market's value because some firms--usually large or old--will cling to old technologies that have lost their momentum. This paper argues that (a) the market declined in the late 1960s because it felt that the old technologies either had lost their momentum or would give way to IT, and that (b) IT innovators boosted the stock market's value only in the 1980s. If the stock market provides a forecast of future events, then the recent dramatic upswing represents a rosy estimate about growth in future profits for the economy. This translates into a forecast of higher output and productivity growth, holding other things equal (such as capital's share of income).INFORMATION TECHNOLOGY ; STOCK MARKET
Liquid-liquid microreactors for phase transfer catalysis
The research carried out within this thesis studied the hydrodynamics, reaction applications and scale-up of liquid-liquid microreactors. The liquid-liquid flow patterns in microchannels were evaluated in terms of stability, surface-to-volume ratio, achieved throughput and extraction efficiency. The research focused on the optimal flow patterns, the slug and bubbly flow. A liquid-liquid slug flow pressure drop model was developed and validated on examples of water-toluene and water/ethylene glycol-toluene slug flow. The fluidic control over the interfaces in a slug flow microreactor was employed to study a complex system of liquid-liquid phase transfer catalyzed alkylation of phenylacetonitrile. Last, a novel microstructured redispersion reactor was developed and tested on the example of phase transfer catalyzed esterification, allowing for significant increases in yield, process safety and waste reduction compared to the conventional process
Persistence of the laminar regime in a flat plate boundary layer at very high Reynolds number
The influence of microlensing on the shape of the AGN Fe K-alpha line
We study the influence of gravitational microlensing on the AGN Fe K-alpha
line confirming that unexpected enhancements recently detected in the iron line
of some AGNs can be produced by this effect. We use a ray tracing method to
study the influence of microlensing in the emission coming from a compact
accretion disc considering both geometries, Schwarzschild and Kerr.
Thanks to the small dimensions of the region producing the AGN Fe K-alpha
line, the Einstein Ring Radii associated to even very small compact objects
have size comparable to the accretion disc hence producing noticeable changes
in the line profiles. Asymmetrical enhancements contributing differently to the
peaks or to the core of the line are produced by a microlens, off-centered with
respect to the accretion disc.
In the standard configuration of microlensing by a compact object in an
intervening galaxy, we found that the effects on the iron line are two orders
of magnitude larger than those expected in the optical or UV emission lines. In
particular, microlensing can satisfactorily explain the excess in the iron line
emission found very recently in two gravitational lens systems, H 1413+117 and
MG J0414+0534.
Exploring other physical {scenario} for microlensing, we found that compact
objects (of the order of one Solar mass) which belong to {the bulge or the
halo} of the host galaxy can also produce significant changes in the Fe
K line profile of an AGN. However, the optical depth estimated for
this type of microlensing is {very small, , even in a favorable
case.Comment: Astron. Astrophys. accepte
A low-order decomposition of turbulent channel flow via resolvent analysis and convex optimization
We combine resolvent-mode decomposition with techniques from convex
optimization to optimally approximate velocity spectra in a turbulent channel.
The velocity is expressed as a weighted sum of resolvent modes that are
dynamically significant, non-empirical, and scalable with Reynolds number. To
optimally represent DNS data at friction Reynolds number , we determine
the weights of resolvent modes as the solution of a convex optimization
problem. Using only modes per wall-parallel wavenumber pair and temporal
frequency, we obtain close agreement with DNS-spectra, reducing the wall-normal
and temporal resolutions used in the simulation by three orders of magnitude
Integrated photonic building blocks for next-generation astronomical instrumentation II: the multimode to single mode transition
There are numerous advantages to exploiting diffraction-limited
instrumentation at astronomical observatories, which include smaller
footprints, less mechanical and thermal instabilities and high levels of
performance. To realize such instrumentation it is imperative to convert the
atmospheric seeing-limited signal that is captured by the telescope into a
diffraction-limited signal. This process can be achieved photonically by using
a mode reformatting device known as a photonic lantern that performs a
multimode to single-mode transition. With the aim of developing an optimized
integrated photonic lantern, we undertook a systematic parameter scan of
devices fabricated by the femtosecond laser direct-write technique. The devices
were designed for operation around 1.55 {\mu}m. The devices showed (coupling
and transition) losses of less than 5% for F/# 12 injection and the
total device throughput (including substrate absorption) as high as 75-80%.
Such devices show great promise for future use in astronomy.Comment: 12 pages, 9 figure
Point-by-point inscription of apodized fiber Bragg gratings
We demonstrate apodized fiber Bragg gratings inscribed with a point-by-point
technique. We tailor the grating phase and coupling amplitude through precise
control over the longitudinal and transverse position of each laser-inscribed
modification. This method of apodization is facilitated by the
highly-localized, high-contrast modifications generated by focussed IR
femtosecond laser inscription. Our technique provides a simple method for the
design and implementation of point-by-point fiber Bragg gratings with complex
apodization profiles.Comment: 6 pages, 4 figures, article in revie
Multiband processing of multimode light: combining 3D photonic lanterns with waveguide Bragg gratings
The first demonstration of narrowband spectral filtering of multimode light
on a 3D integrated photonic chip using photonic lanterns and waveguide Bragg
gratings is reported. The photonic lanterns with multi-notch waveguide Bragg
gratings were fabricated using the femtosecond direct-write technique in
boro-aluminosilicate glass (Corning, Eagle 2000). Transmission dips of up to 5
dB were measured in both photonic lanterns and reference single-mode waveguides
with 10.4-mm-long gratings. The result demonstrates efficient and symmetrical
performance of each of the gratings in the photonic lantern. Such devices will
be beneficial to space-division multiplexed communication systems as well as
for units for astronomical instrumentation for suppression of the atmospheric
telluric emission from OH lines.Comment: 5 pages, 4 figures, accepted to Laser & Photonics Review
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