10,701 research outputs found
Characterizing the chemical pathways for water formation -- A deep search for hydrogen peroxide
In 2011, hydrogen peroxide (HOOH) was observed for the first time outside the
solar system (Bergman et al., A&A, 2011, 531, L8). This detection appeared a
posteriori quite natural, as HOOH is an intermediate product in the formation
of water on the surface of dust grains. Following up on this detection, we
present a search for HOOH in a diverse sample of sources in different
environments, including low-mass protostars and regions with very high column
densities, such as Infrared Dark Clouds (IRDCs). We do not detect the molecule
in any other source than Oph A, and derive 3 upper limits for the
abundance of HOOH relative to H lower than in Oph A for most sources. This
result sheds a different light on our understanding of the detection of HOOH in
Oph A, and shifts the puzzle to why this source seems to be special. Therefore
we rediscuss the detection of HOOH in Oph A, as well as the implications of the
low abundance of HOOH, and its similarity with the case of O. Our chemical
models show that the production of HOOH is extremely sensitive to the
temperature, and favored only in the range 2030 K. The relatively high
abundance of HOOH observed in Oph A suggests that the bulk of the material lies
at a temperature in the range 2030 K.Comment: 18 pages, 3 figures, invited refereed paper at the Faraday Discussion
16
Squeezed pulsed light from a fiber ring interferometer
Observation of squeezed noise, 5 +/- 0.3 dB below the shot noise level, generated with pulses in a fiber ring interferometer is reported. The interferometric geometry is used to separate the pump pulse from the squeezed vacuum radiation. A portion of the pump is reused as the local oscillator in a homodyne detection. The pump fluctuations are successfully subtracted and shot noise limited performance is achieved at low frequencies (35-85 KHz). A possible utilization of the generated squeezed vacuum in improving a fiber gyro's signal to noise ratio is discussed
Employee Sentiment and Stock Option Compensation
The use of equity-based compensation for employees in the lower ranks of large organizations is a puzzle for standard economic theory: undiversified employees should discount company equity heavily, and any positive incentive effects should be diminished by free rider problems. We analyze whether the popularity of option compensation for rank and file employees may be driven by employee optimism. We develop a model of optimal compensation policy for a firm faced with employees with positive or negative sentiment, and explicitly take into account that current and potential employees are able to purchase equity in the firm through the stock market. We show that employee optimism by itself is insufficient to make equity compensation optimal for the firm. Any behavioral explanation for equity compensation based on employee optimism requires two ingredients: first, employees need be over-optimistic about firm value, and second, firms must be able to extract part of the implied rents even though employees can purchase company equity in the market. Such rent extraction becomes feasible if employees prefer the non-traded compensation options offered by firms to the traded equity offered by the market, or if the traded equity is overvalued. We then provide empirical evidence confirming that firms use broad-based option compensation when boundedly rational employees are likely to be excessively optimistic about company stock, and when employees are likely to have a strict preference for options over stock.
3-Oxabicyclo[3,2,0]hepta-1,4-diene
3-Oxabicyclo[3,2,0]hepta-1,4-diene (3) has been synthesized by partial hydrogenation of 3-oxabicyclo-[3,2,0]hepta-1,4,6-triene (2)
Coleman-Weinberg Mechanism and Interaction of D3-Branes in Type 0 String Theory
The low-energy theory on the world volume of parallel static D3-branes of
type 0 strings is the Yang-Mills theory with six scalar fields in the adjoint
representation. One-loop corrections in this theory induce Coleman-Weinberg
effective potential, which can be interpreted as an interaction energy of
D3-branes. The potential is repulsive at short distances and attractive at
large ones. In the equilibrium, a large number of D3-branes forms a spherical
shell with the radius proportional to the characteristic energy scale of the
world-volume theory.Comment: 5 pages, LaTex, 1 figure; v2: Discussion of the interaction potential
between D3-branes at short distances is modified, version to be published in
Phys. Lett.
How younger students perceive and identify historical significance
Historical significance is a historical thinking concept. Being able to identify
historical significance is viewed as important for understanding change and
continuity in the past, and for understanding the way ‘history’ is constructed by
present society. This article discusses how Swedish students in Grade 5 (age 11
years) perceive and understand historical significance without having received
prior instruction on how to identify historical significance. The results show that
the students see thrilling and exciting events in the past as significant, as well
as the events, inventions, ideas and values that have influenced the present or
changed the course of history in some way. In this paper, I compare students’
answers to definitions of historical significance formulated by Christine Counsell (2004) and Matthew Bradshaw (2006). For the study, 67 students were interviewed
in semi-structured interviews in small groups. They attended six different schools in the middle part of Sweden and came from varying backgrounds. Regardless of their backgrounds or origins, the students see the history culture of the majority, as presented in their history education, as their own
Perturbation Theory for Singular Potentials in Quantum Mechanics
We study perturbation theory in certain quantum mechanics problems in which
the perturbing potential diverges at some points, even though the energy
eigenvalues are smooth functions of the coefficient of the potential. We
discuss some of the unusual techniques which are required to obtain
perturbative expansions of the energies in such cases. These include a
point-splitting prescription for expansions around the Dirichlet (fermionic)
limit of the -function potential, and performing a similarity
transformation to a non-Hermitian potential in the Calogero-Sutherland model.
As an application of the first technique, we study the ground state of the
-function Bose gas near the fermionic limit.Comment: LaTeX, 19 pages, no figure
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