1,084 research outputs found
Chiral Dynamics of Deeply Bound Pionic Atoms
We present and discuss a systematic calculation, based on two-loop chiral
perturbation theory, of the pion-nuclear s-wave optical potential. A proper
treatment of the explicit energy dependence of the off-shell pion self-energy
together with (electromagnetic) gauge invariance of the Klein-Gordon equation
turns out to be crucial. Accurate data for the binding energies and widths of
the 1s and 2p levels in pionic ^{205}Pb and ^{207}Pb are well reproduced, and
the notorious "missing repulsion" in the pion-nuclear s-wave optical potential
is accounted for. The connection with the in-medium change of the pion decay
constant is clarified.Comment: preprint ECT*-02-16, 4 pages, 3 figure
LLC and Partnership Transfer Restrictions Excluded From UCC Article 9 Overrides
The organizational law of limited liability companies (LLCs) and partnerships has always fundamentally embraced an idea known as the “pick-your-partner principle,” under which transfers of a member’s or partner’s ownership interest are restricted by statute, and those restrictions may be tightened or loosened by agreement. In recent years the pick-your-partner principle has interacted in complex and not always practical ways with Article 9 of the Uniform Commercial Code (UCC). Since 2001, UCC §§ 9-406 and 9-408 have overridden a broad range of statutory and agreement-based anti-assignment provisions, subject to complex exceptions that have tended to protect the pick-your-partner principle in many significant respects, while also proving analytically very difficult to handle. Recently, however, in an important step forward, Article 9’s overrides of anti-assignment provisions have been amended to make them simply inapplicable to LLC and partnership interests.
One hopes that these amendments to Article 9’s overrides (hereinafter the “2018 amendments” because they were approved last year) will soon be enacted by the states, but in the meantime, the current overrides will remain on the books in various jurisdictions with all of their existing complexities. Accordingly, this article focuses not only on the 2018 amendments, but also on an analysis of the overrides as they now stand, as applied to LLC and partnership interests. The amendments themselves are quite simple, but the article discusses them only after analyzing the overrides because the amendments are more easily understood against that background
Resilience trinity: safeguarding ecosystem functioning and services across three different time horizons and decision contexts
Ensuring ecosystem resilience is an intuitive approach to safeguard the functioning of ecosystems and hence the future provisioning of ecosystem services (ES). However, resilience is a multi‐faceted concept that is difficult to operationalize. Focusing on resilience mechanisms, such as diversity, network architectures or adaptive capacity, has recently been suggested as means to operationalize resilience. Still, the focus on mechanisms is not specific enough. We suggest a conceptual framework, resilience trinity, to facilitate management based on resilience mechanisms in three distinctive decision contexts and time‐horizons: 1) reactive, when there is an imminent threat to ES resilience and a high pressure to act, 2) adjustive, when the threat is known in general but there is still time to adapt management and 3) provident, when time horizons are very long and the nature of the threats is uncertain, leading to a low willingness to act. Resilience has different interpretations and implications at these different time horizons, which also prevail in different disciplines. Social ecology, ecology and engineering are often implicitly focussing on provident, adjustive or reactive resilience, respectively, but these different notions of resilience and their corresponding social, ecological and economic tradeoffs need to be reconciled. Otherwise, we keep risking unintended consequences of reactive actions, or shying away from provident action because of uncertainties that cannot be reduced. The suggested trinity of time horizons and their decision contexts could help ensuring that longer‐term management actions are not missed while urgent threats to ES are given priority
Spectrum of the excited and baryons in a relativistic chiral quark model
The spectrum of the SU(2) flavor baryons is studied in the frame of a
relativistic chiral quark potential model based on the one-pion and one-gluon
exchange mechanisms.
It is argued that the N* and Delta* resonances strongly coupled to the pi-N
channel are identified with the orbital configurations with
a single valence quark in the excited state (nlj). With the obtained selection
rules based on the "chiral constraint", we show that it is possible to
construct a schematic periodic table of baryon resonances, consistent with the
experimental data and yielding no "missing resonances". A new original method
for the treatment of the center of mass problem is suggested, which is based on
the separation of the three-quark Dirac Hamiltonian into the parts,
corresponding to the Jacobi coordinates. The numerical estimations for the
energy positions of the Nucleon and Delta baryons (up to and including F-wave
resonances), obtained within the field-theoretical framework by using time
ordered perturbation theory, yield an overall good description of the
experimental data at the level of the relativized CQM of S. Capstick and W.
Roberts without any fitting parameters. The Delta(1232) is well reproduced.
However, N g. s. and most of the radially excited baryon resonances (including
Roper) are overestimated. Contrary, the first band of the orbitally excited
baryon resonances with a negative parity are underestimated. At the same time,
the second band of the orbitally excited Delta* states with the negative parity
are mostly overestimated, while the N* states are close to the experimental
boxes. The positive parity baryon resonances with J=5/2, 7/2 are close to the
experimental data.
At higher energies, where the experimental data are poor, we can extend our
model schematically and predict an existence of seven N* and four Delta* new
states with larger spin values.Comment: 19 pages, 6 figures, 2 tables. The results and text have been
updated. arXiv admin note: text overlap with arXiv:1103.366
Entropy production by resonance decays
We investigate entropy production for an expanding system of particles and
resonances with isospin symmetry -- in our case pions and mesons --
within the framework of relativistic kinetic theory. A cascade code to simulate
the kinetic equations is developed and results for entropy production and
particle spectra are presented.Comment: 17 pages, 10 ps-figures included, only change: preprint number adde
Hadron properties in the nuclear medium
The QCD vacuum shows the dynamical breaking of chiral symmetry. In the
hot/dense QCD medium, the chiral order parameter such as is
expected to change as function of temperature and density of the
medium, and its experimental detection is one of the main challenges in modern
hadron physics. In this article, we discuss theoretical expectations for the
in-medium hadron spectra associated with partial restoration of chiral symmetry
and the current status of experiments with an emphasis on the measurements of
properties of mesons produced in near-ground-state nuclei.Comment: 40 pages, submitted to Reviews of Modern Physic
Evolution of trace gases and particles emitted by a chaparral fire in California
Biomass burning (BB) is a major global source of trace gases and particles. Accurately representing the production and evolution of these emissions is an important goal for atmospheric chemical transport models. We measured a suite of gases and aerosols emitted from an 81 hectare prescribed fire in chaparral fuels on the central coast of California, US on 17 November 2009. We also measured physical and chemical changes that occurred in the isolated downwind plume in the first ~4 h after emission. The measurements were carried out onboard a Twin Otter aircraft outfitted with an airborne Fourier transform infrared spectrometer (AFTIR), aerosol mass spectrometer (AMS), single particle soot photometer (SP2), nephelometer, LiCor CO_2 analyzer, a chemiluminescence ozone instrument, and a wing-mounted meteorological probe. Our measurements included: CO_2; CO; NO_x; NH_3; non-methane organic compounds; organic aerosol (OA); inorganic aerosol (nitrate, ammonium, sulfate, and chloride); aerosol light scattering; refractory black carbon (rBC); and ambient temperature, relative humidity, barometric pressure, and three-dimensional wind velocity. The molar ratio of excess O_3 to excess CO in the plume (ΔO_3/ΔCO) increased from −5.13 (±1.13) × 10^(−3) to 10.2 (±2.16) × 10^(−2) in ~4.5 h following smoke emission. Excess acetic and formic acid (normalized to excess CO) increased by factors of 1.73 ± 0.43 and 7.34 ± 3.03 (respectively) over the same time since emission. Based on the rapid decay of C_2H_4 we infer an in-plume average OH concentration of 5.27 (±0.97) × 10^6 molec cm^(−3), consistent with previous studies showing elevated OH concentrations in biomass burning plumes. Ammonium, nitrate, and sulfate all increased over the course of 4 h. The observed ammonium increase was a factor of 3.90 ± 2.93 in about 4 h, but accounted for just ~36% of the gaseous ammonia lost on a molar basis. Some of the gas phase NH_3 loss may have been due to condensation on, or formation of, particles below the AMS detection range. NO_x was converted to PAN and particle nitrate with PAN production being about two times greater than production of observable nitrate in the first ~4 h following emission. The excess aerosol light scattering in the plume (normalized to excess CO_2) increased by a factor of 2.50 ± 0.74 over 4 h. The increase in light scattering was similar to that observed in an earlier study of a biomass burning plume in Mexico where significant secondary formation of OA closely tracked the increase in scattering. In the California plume, however, ΔOA/ΔCO_2 decreased sharply for the first hour and then increased slowly with a net decrease of ~20% over 4 h. The fraction of thickly coated rBC particles increased up to ~85% over the 4 h aging period. Decreasing OA accompanied by increased scattering/particle coating in initial aging may be due to a combination of particle coagulation and evaporation processes. Recondensation of species initially evaporated from the particles may have contributed to the subsequent slow rise in OA. We compare our results to observations from other plume aging studies and suggest that differences in environmental factors such as smoke concentration, oxidant concentration, actinic flux, and RH contribute significantly to the variation in plume evolution observations
The influence of rifle carriage on the kinetics of human gait
The influence that rifle carriage has on human gait has received little attention in the published literature. Rifle carriage has two main effects, to add load to the anterior of the body and to restrict natural arm swing patterns. Kinetic data were collected from 15 male participants, with 10 trials in each of four experimental conditions. The conditions were: walking without a load (used as a control condition); carrying a lightweight rifle
simulator, which restricted arm movements but applied no additional load; wearing a 4.4 kg diving belt, which allowed arms to move freely; carrying a weighted (4.4 kg)
replica SA80 rifle. Walking speed was fixed at 1.5 m/s (+5%) and data were sampled at 400 Hz. Results showed that rifle carriage significantly alters the ground reaction forces produced during walking, the most important effects being an increase in the impact peak and mediolateral forces. This study suggests that these effects are due to the increased range of motion of the body’s centre of mass caused by the impeding of natural arm swing patterns. The subsequent effect on the potential development of injuries in rifle carriers is unknown
In Solidarity
This edition of Next Page is a departure from our usual question and answer format with a featured campus reader. Instead, we asked speakers who participated in the College’s recent Student Solidarity Rally (March 1, 2017) to recommend readings that might further our understanding of the topics on which they spoke
Stochastic optimization of a cold atom experiment using a genetic algorithm
We employ an evolutionary algorithm to automatically optimize different
stages of a cold atom experiment without human intervention. This approach
closes the loop between computer based experimental control systems and
automatic real time analysis and can be applied to a wide range of experimental
situations. The genetic algorithm quickly and reliably converges to the most
performing parameter set independent of the starting population. Especially in
many-dimensional or connected parameter spaces the automatic optimization
outperforms a manual search.Comment: 4 pages, 3 figure
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