1,449 research outputs found
Combining Sustainable Synthesis of a Versatile Ruthenium Dihydride Complex with Structure Determination Using Group Theory and Spectroscopy
A good-yielding two-step synthesis of RuH2(CO)(PPh3)3 using conventional or microwave-assisted reflux techniques is described for use in undergraduate teaching laboratories. RuH2(CO)(PPh3)3 is synthesized from RuCl3·xH2O, PPh3, and KOH in ethanol in two steps under an inert atmosphere or using a one-pot microwave-assisted reflux to reduce the reaction time to approximately 10 min. This makes this useful compound readily available within an undergraduate laboratory session via efficient and sustainable syntheses, enabling learning outcomes associated with air-sensitive synthesis and application of group theory and spectroscopy to structure determination to be achieved
Counter-propagating entangled photons from a waveguide with periodic nonlinearity
The conditions required for spontaneous parametric down-conversion in a
waveguide with periodic nonlinearity in the presence of an unguided pump field
are established. Control of the periodic nonlinearity and the physical
properties of the waveguide permits the quasi-phase matching equations that
describe counter-propagating guided signal and idler beams to be satisfied. We
compare the tuning curves and spectral properties of such counter-propagating
beams to those for co-propagating beams under typical experimental conditions.
We find that the counter-propagating beams exhibit narrow bandwidth permitting
the generation of quantum states that possess discrete-frequency entanglement.
Such states may be useful for experiments in quantum optics and technologies
that benefit from frequency entanglement.Comment: submitted to Phys. Rev.
Ghrelin is not Related to Hunger or Calories Consumed at Breakfast in Lean and Obese Women
poster abstractBackground: The mechanisms that result in greater caloric intake in obese individuals
are incompletely understood. Ghrelin administration increases ad lib food intake in
humans. We investigated the relationship of ghrelin to calorie consumption and hunger
at breakfast on two separate occasions in lean and obese women.
Methods: 23 lean (BMI 22.3±0.5 kg/m2, 26.5±1.0 yr) and 25 obese (BMI 36.9±0.7 kg/m2,
27.8±1.1 yr) women participated in a noncontiguous 2 day study. The minimum and
maximum days between visits were 6 and 43 days. Participants were given the same
breakfast on both days (turkey sausage, French toast with margarine/syrup, fruit cup,
coffee, tea, diet soda, or water) with portions adjusted to provide 20% of the daily energy
requirement for weight maintenance. Subjects were instructed to eat until full. Hunger
was evaluated on a Satiety Labeled Intensity Magnitude Scale (SLIM) before and after
the meal. Anchors were âgreatest imaginable fullnessâ at 0 and âgreatest imaginable
hungerâ at 100. Blood samples were collected over 120 minutes for measurement of
active ghrelin.
Results: Lean subjects consumed an equivalent number of calories on both days
(380.0±14.6 vs 378.2±14.9 kcal), as did the obese (419.4±16.2 vs 428.8±15.4 kcal). On
average for both days, obese consumed significantly more breakfast calories than lean
(424.1±11.1 vs 379.1±10.3 kcal; P<0.01), but the same percentage of calories provided
(85.7±1.8 vs 86.1±1.7 %kcal). Lean subjects rated hunger before breakfast the same on
both days (69.2±1.6 vs 71.7±1.4), as did the obese (69.8±1.6 vs 69.6±1.8), and there
was no difference between the groups. Lean subjects rated hunger after breakfast the
same on both days (27.8±1.9 vs 30.3±2.4), as did the obese (25.0±1.7 vs 24.3±1.8).
The reduction in hunger score following breakfast was significant for both groups
(P<0.0001), with the obese reporting significantly less hunger/more fullness after
breakfast than the lean (P=0.02). Fasting ghrelin was significantly greater in the lean
than obese women (549.9±58.9 vs 231.0±29.1 pg/ml; P<0.0001). Ghrelin was
significantly reduced at 60 min following breakfast in the lean (375.8±49.2 pg/ml;
P=0.028) but not the obese (212.2±26.4 pg/ml). Ghrelin was not related to hunger score
prior to breakfast, and there was no relationship between reduction in ghrelin and hunger
score in the lean or obese.
Conclusion: Caloric intake (as a percentage provided) and hunger scores before
breakfast on two occasions were the same for both lean and obese women. Fasting
ghrelin was significantly different between lean and obese women but did not predict
hunger score or calories consumed. Our findings do not support a role for ghrelin in
driving food intake at breakfast
Lichenometric dating (lichenometry) and the biology of the lichen genus rhizocarpon:challenges and future directions
Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates
Dispersive properties of quasi-phase-matched optical parametric amplifiers
The dispersive properties of non-degenerate optical parametric amplification
in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary
grating profile are theoretically investigated in the no-pump-depletion limit.
The spectral group delay curve of the amplifier is shown to be univocally
determined by its spectral power gain curve through a Hilbert transform. Such a
constraint has important implications on the propagation of spectrally-narrow
optical pulses through the amplifier. In particular, it is shown that anomalous
transit times, corresponding to superluminal or even negative group velocities,
are possible near local minima of the spectral gain curve. A possible
experimental observation of such effects using a QPM Lithium-Niobate crystal is
suggested.Comment: submitted for publicatio
Electromagnetic Polarization Effects due to Axion Photon Mixing
We investigate the effect of axions on the polarization of electromagnetic
waves as they propagate through astronomical distances. We analyze the change
in the dispersion of the electromagnetic wave due to its mixing with axions. We
find that this leads to a shift in polarization and turns out to be the
dominant effect for a wide range of frequencies. We analyze whether this effect
or the decay of photons into axions can explain the large scale anisotropies
which have been observed in the polarizations of quasars and radio galaxies. We
also comment on the possibility that the axion-photon mixing can explain the
dimming of distant supernovae.Comment: 18 pages, 1 figur
Vector meson production and nucleon resonance analysis in a coupled-channel approach for energies m_N < sqrt(s) < 2 GeV II: photon-induced results
We present a nucleon resonance analysis by simultaneously considering all
pion- and photon-induced experimental data on the final states gamma N, pi N, 2
pi N, eta N, K Lambda, K Sigma, and omega N for energies from the nucleon mass
up to sqrt(s) = 2 GeV. In this analysis we find strong evidence for the
resonances P_{31}(1750), P_{13}(1900), P_{33}(1920), and D_{13}(1950). The
omega N production mechanism is dominated by large P_{11}(1710) and
P_{13}(1900) contributions. In this second part we present the results on the
photoproduction reactions and the electromagnetic properties of the resonances.
The inclusion of all important final states up to sqrt(s) = 2 GeV allows for
estimates on the importance of the individual states for the GDH sum rule.Comment: 41 pages, 26 figures, discussion extended, typos corrected,
references updated, to appear in Phys. Rev.
Imprinting, honeymooning, or maturing: Testing three theories of how interfirm social bonding impacts suppliersâ allocations of resources to business customers
In business markets, does strength of social bonds that a supplier perceives with a specific customer influence the supplierâs allocations of resources relative to other customers? If social bonding does uniquely impact supplier allocation of resources to customers, does the impact vary by relationship duration? Relationship marketing and Homansâ framework for social behavior are the theoretical bases for the study, which uses survey data to examine three alternative models that indicate how suppliersâ perceptions of social bonds with customers influence the suppliersâ allocations of resources over time. Analysis of data from sales and marketing managers confirms that two of these models, the imprinting theory and the maturity theory, are relevant. The findings indicate that relationship managers need to take into account the clear effect that creation of strong social bonds in buyerâseller relationships, as distinct from financial bonds, has on the way in which suppliers allocate resources to those relationships and how relationship duration affects the way in which they do so. The study strengthens the argument, on a strong theoretical base, to adopt a collaborative, as opposed to a transactional, approach to buyerâseller relationships
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