7,063 research outputs found
On the origin of the Korteweg-de Vries equation
The Korteweg-de Vries equation has a central place in a model for waves on
shallow water and it is an example of the propagation of weakly dispersive and
weakly nonlinear waves. Its history spans a period of about sixty years,
starting with experiments of Scott Russell in 1834, followed by theoretical
investigations of, among others, Lord Rayleigh and Boussinesq in 1871 and,
finally, Korteweg and De Vries in 1895.
In this essay we compare the work of Boussinesq and Korteweg-de Vries,
stressing essential differences and some interesting connections. Although
there exist a number of articles, reviewing the origin and birth of the
Korteweg-de Vries equations, connections and differences, not generally known,
are reported.Comment: minor corrections; 25 pages, 3 figure
A holistic approach to enhance the use of neglected and underutilized species: the case of Andean grains in Bolivia and Peru
The IFAD-NUS project, implemented over the course of a decade in two phases, represents the first UN-supported global effort on neglected and underutilized species (NUS). This initiative, deployed and tested a holistic and innovative value chain framework using multi-stakeholder, participatory, inter-disciplinary, pro-poor gender- and nutrition-sensitive approaches. The project has been linking aspects often dealt with separately by R&D, such as genetic diversity, selection, cultivation, harvest, value addition, marketing, and final use, with the goal to contribute to conservation, better incomes, and improved nutrition and strengthened livelihood resilience. The project contributed to the greater conservation of Andean grains and their associated indigenous knowledge, through promoting wider use of their diversity by value chain actors, adoption of best cultivation practices, development of improved varieties, dissemination of high quality seed, and capacity development. Reduced drudgery in harvest and postharvest operations, and increased food safety were achieved through technological innovations. Development of innovative food products and inclusion of Andean grains in school meal programs is projected to have had a positive nutrition outcome for targeted communities. Increased income was recorded for all value chain actors, along with strengthened networking skills and self-reliance in marketing. The holistic approach taken in this study is advocated as an effective strategy to enhance the use of other neglected and underutilized species for conservation and livelihood benefits
The views of commerce students regarding "free" higher education in South Arica
At the end of 2015, student protests (demanding âfreeâ higher education) took place at most South African universities. An official answer from the South African government regarding âfree higher educationâ is still being awaited. In the meantime, a zero present increase in university fees for 2016 and an increase of not more than 8% for 2017 was announced. South Africa is known for expensive higher education as tuition fees increase every year. Many students struggle to fund their studies, while government subsidies to higher education institution decrease. The question that remains is: Will it be feasible for South Africa to implement âfree higher educationâ?This study aimed to investigate the perceptions of commerce students at one South African university regarding the feasibility of âfreeâ higher education. A questionnaire was used as research instrument which consisted of Likert-scale statements regarding general ideas about âfree higher educationâ as well as open-ended questions asking students about the definition of âfree higher educationâ and the effects on the South African economy.The results proposed that even though most students were aware of the students protests regarding âfree higher educationâ that took place, not all of them agreed with it. The respondents realised that it is not feasible for South Africa to implement âfree higher educationâ at this moment in time.Despite the views of these commerce students, if âfree higher educationâ were considered as a viable option in South Africa, implementation considerations should be examined. These issues will be discussed in a follow-up study.
Inclusive Quasi-Elastic Charged-Current Neutrino-Nucleus Reactions
The Quasi-Elastic (QE) contribution of the nuclear inclusive electron
scattering model developed in Nucl. Phys. A627 (1997) 543 is extended to the
study of electroweak Charged Current (CC) induced nuclear reactions, at
intermediate energies of interest for future neutrino oscillation experiments.
The model accounts for, among other nuclear effects, long range nuclear (RPA)
correlations, Final State Interaction (FSI) and Coulomb corrections.
Predictions for the inclusive muon capture in C and the reaction
C near threshold are also given. RPA correlations are
shown to play a crucial role and their inclusion leads to one of the best
existing simultaneous description of both processes, with accuracies of the
order of 10-15% per cent for the muon capture rate and even better for the LSND
measurement.Comment: 31 pages and 14 figures, accepted for publication as a regular
article in Physical Review
Spectral Energy Distributions of T Tauri and Herbig Ae Disks: Grain Mineralogy, Parameter Dependences, and Comparison with ISO LWS Observations
We improve upon the radiative, hydrostatic equilibrium models of passive
circumstellar disks constructed by Chiang & Goldreich (1997). New features
include (1) account for a range of particle sizes, (2) employment of
laboratory-based optical constants of representative grain materials, and (3)
numerical solution of the equations of radiative and hydrostatic equilibrium
within the original 2-layer (disk surface + disk interior) approximation. We
explore how the spectral energy distribution (SED) of a face-on disk depends on
grain size distributions, disk geometries and surface densities, and stellar
photospheric temperatures. Observed SEDs of 3 Herbig Ae and 2 T Tauri stars,
including spectra from the Long Wavelength Spectrometer (LWS) aboard the
Infrared Space Observatory (ISO), are fitted with our models. Silicate emission
bands from optically thin, superheated disk surface layers appear in nearly all
systems. Water ice emission bands appear in LWS spectra of 2 of the coolest
stars. Infrared excesses in several sources are consistent with vertical
settling of photospheric grains. While this work furnishes further evidence
that passive reprocessing of starlight by flared disks adequately explains the
origin of infrared-to-millimeter wavelength excesses of young stars, we
emphasize how the SED alone does not provide sufficient information to
constrain particle sizes and disk masses uniquely.Comment: Accepted to ApJ, 35 pages inc. 14 figures, AAS preprin
The yellow hypergiants HR 8752 and rho Cassiopeiae near the evolutionary border of instability
High-resolution near-ultraviolet spectra of the yellow hypergiants HR 8752
and rho Cassiopeiae indicate high effective temperatures placing both stars
near the T_eff border of the ``yellow evolutionary void''. At present, the
temperature of HR 8752 is higher than ever. For this star we found
Teff=7900+-200 K, whereas rho Cassiopeiae has Teff=7300+-200 K. Both, HR 8752
and rho Cassiopeiae have developed strong stellar winds with Vinf ~ 120 km/s
and Vinf ~ 100 km/s, respectively. For HR 8752 we estimate an upper limit for
the spherically symmetric mass-loss of 6.7X10^{-6}M_solar/yr. Over the past
decades two yellow hypergiants appear to have approached an evolutionary phase,
which has never been observed before. We present the first spectroscopic
evidence of the blueward motion of a cool super/hypergiant on the HR diagram.Comment: 13 pages including 3 figures. Accepted for publication in ApJ Letter
Inclusive Muon Capture in Light Nuclei
We study total muon capture rates in light nuclei, taking into account
renormalizations of the nuclear vector and axial vector strengths. We estimate
the influence in the results of uncertainties of the spin-isospin interaction
parameter and nuclear densities. A few of these reactions are theoretical
benchmarks for physics involving searches for neutrino oscillations. New
experiments in muon capture in several targets are suggested, in the light of
some discrepancies with theory, crudeness of some experimental results and
relevance to neutrino physics.Comment: 11 pages, Latex, no figures. Submitted to Phys.Lett.
Does "free" higher education in South Africa make economic sense? Views of commerce students
AbstractStudent protests demanding âfreeâ higher education at South Africa universities in 2015 is a reminder that there are still a lot of unresolved issues regarding the inequalities due to the apartheid era in the higher education system. Some of these issues include insufficient state funding of higher education, the increase of tuition fee and unpaid student debt. Even though âfreeâ higher education sounds appealing, the question is whether implementing âfreeâ higher education would make economic sense in South Africa. The study aimed to investigate the perceptions of commerce students at one South African university regarding the economic feasibility of âfreeâ higher education and how it might affect the South African economy. The research aimed to give a descriptive analysis of the perceptions of commerce students and were empirically investigated by means of a questionnaire, containing both open and closed questions. Gaining understanding into student perceptions can be invaluable, as they are considered the livelihood of higher education institutions.The results show that the respondents do not think that âfreeâ higher education make economic sense in South Africa as the economy is too weak and there is too much corruption and wasteful spending in government. The respondents also indicated that the economy will mostly be negatively affected by âfreeâ higher education in that there will be an increase of the financial burden on the South African economy and tax payer. They also regard other government services to be of greater importance than implementing âfreeâ higher education.The results of this study are not necessarily generalisable beyond the scope of the particular institution, but the findings do create a platform for the continued debate on the importance, economic feasibility and implementation of âfreeâ higher education in South Africa.
Radio Monitoring of the January 11, 1997 Gamma-Ray Burst
We report on a comprehensive radio monitoring program of the bright gamma-ray
burster GRB970111. These VLA observations were made at a frequency of 1.4 GHz
and span a range of post-burst timescales between 28 hours and one month.
Despite extensive sampling at sub-milliJansky sensitivities, no radio source
was detected above 0.5 mJy in the current best error box (~14 arcmin^2) for
GRB970111. A highly unusual radio source, VLA J1528.7+1945, was seen to drop in
flux density by a factor of two in our monitoring period but it lies outside
the error box and thus it is unlikely to be related to GRB970111. Cosmological
fireball models of gamma-ray bursts make predictions of late-time emission
occurring at longer wavelengths. The absence of a flaring or fading radio
counterpart to GRB970111 provides strong constraints on these models.Comment: ApJ Let (accepted
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