575 research outputs found
The galactic antiproton spectrum at high energies: background expectation vs. exotic contributions
A new generation of upcoming space-based experiments will soon start to probe
the spectrum of cosmic ray antiparticles with an unprecedented accuracy and, in
particular, will open up a window to energies much higher than those accessible
so far. It is thus timely to carefully investigate the expected antiparticle
fluxes at high energies. Here, we perform such an analysis for the case of
antiprotons. We consider both standard sources as the collision of other cosmic
rays with interstellar matter, as well as exotic contributions from dark matter
annihilations in the galactic halo. Up to energies well above 100 GeV, we find
that the background flux in antiprotons is almost uniquely determined by the
existing low-energy data on various cosmic ray species; for even higher
energies, however, the uncertainties in the parameters of the underlying
propagation model eventually become significant. We also show that if the dark
matter is composed of particles with masses at the TeV scale, which is
naturally expected in extra-dimensional models as well as in certain parameter
regions of supersymmetric models, the annihilation flux can become comparable
to - or even dominate - the antiproton background at the high energies
considered here.Comment: 17 pages revtex4, 7 figures; minor changes (to match the published
version
Constraints on WIMP Dark Matter from the High Energy PAMELA data
A new calculation of the ratio in cosmic rays is compared to the
recent PAMELA data. The good match up to 100 GeV allows to set constraints on
exotic contributions from thermal WIMP dark matter candidates. We derive
stringent limits on possible enhancements of the WIMP \pbar flux: a =100 GeV (1 TeV) signal cannot be increased by more than a factor 6 (40)
without overrunning PAMELA data. Annihilation through the channel is
also inspected and cross-checked with data. This scenario is
strongly disfavored as it fails to simultaneously reproduce positron and
antiproton measurements.Comment: 5 pages, 5 figures, the bibliography has been updated, minor
modifications have been made in the tex
Host range evaluation and morphological characterization of Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew in Malaysia
A total of 29 isolates of Pseudoperonospora cubensis were collected from various cucurbit farms in West Malaysia. Sporangia of 13 isolates had the ability to germinate at 14°C and were used for host range (pathotype) study using leaf disc assay on a set of twelve cucurbit cultivars. Twelve different pathotypes of P. cubensis were determined and this demonstrated that P. cubensis isolates from cucurbit farms in West Malaysia are highly variable. Based on the host range study, majority of P. cubensis isolates were categorized into medium and high pathogenicity groupings and this fact shows the potential of this pathogen in invading cucurbit fields in the tropical regions. However, the pathotypes could not be differentiated based on morphological characterization of the sporangia and sporangiophores. Therefore, molecular characterization of the 13 isolates of P. cubensis will be useful to study the relationships among them.Key word: Oomycete, differential hosts, compatibility rating, pathogenic variation, sporangial germination
Meningkatkan Hasil Belajar Siswa Pada Perhitungan Bilangan 1-100 Dengan Menggunakan Media Simpoa Di Kelas I SDN Inpres Kautu Kecamatan Tinangkung Kabupaten Banggai Kepulauan
Permasalahan pokok dalam penelitian tindakan kelas ini adalah rendahnya hasil belajar siswa kelas I SDN Inpres Kautu dalam berhitung bilangan 1-100 yang disebabkan karena siswa hanya menggunakan media jari tangan sehingga mendapat kesulitan dalam proses behitung. Tujuan penelitian tindakan kelas ini adalah upaya mendeskripsikan hasil belajar siswa dengan penggunaan media simpoa pada materi berhitung bilangan 1-100 di kelas I SDN Inpres Kautu Kecamatan Tinangkung Kabupaten Banggai Kepulauan. Subjek penelitian ini adalah siswa kelas I SDN Inpres Kautu Kecamatan Tinangkung Kabupaten Banggai Kepulauan sebanyak 30 siswa yang terdiri dari 16 laki-laki dan 14 Perempuan. Jenis penelitian yang digunakan adalah penelitian tindakan kelas (PTK). Pelaksanaan kegiatan penelitian ini dilakukan dengan dua siklus, yang terdiri 4 tahapan yaitu perencanaan, pelaksanaan, observasi, dan refleksi. Dari hasil tes akhir tindakan siklus I didapatkan nilai rata – rata hasil belajar siswa 65,66 dengan ketuntasan klasikal sebesar 60%, sedangkan pada siklus II didapatkan nilai rata – rata hasil belajar siswa 84 dengan ketuntasan klasikal 90%. Berdasarkan tindakan yang dilakukan dapat disimpulkan bahwa dengan menggunakan media simpoa dapat meningkatkan hasil belajar siswa kelas I SDN Inpres Kautu Kecamatan Tinangkung Kabupaten Banggai Kepulauan dalam berhitung bilangan 1-100
Is the Large Magellanic Cloud a Large Microlensing Cloud?
An expression is provided for the self-lensing optical depth of the thin LMC
disk surrounded by a shroud of stars at larger scale heights. The formula is
written in terms of the vertical velocity dispersion of the thin disk
population. If tidal forcing causes 1-5 % of the disk mass to have a height
larger than 6 kpc and 10-15 % to have a height above 3 kpc, then the
self-lensing optical depth of the LMC is , which is
within the observational uncertainties. The shroud may be composed of bright
stars provided they are not in stellar hydrodynamical equilibrium.
Alternatively, the shroud may be built from low mass stars or compact objects,
though then the self-lensing optical depths are overestimates of the true
optical depth by a factor of roughly 3. The distributions of timescales of the
events and their spatial variation across the face of the LMC disk offer
possibilities of identifying the dominant lens population. In propitious
circumstances, an experiment lifetime of less than 5 years is sufficient to
decide between the competing claims of Milky Way halos and LMC lenses. However,
LMC disks can sometimes mimic the microlensing properties of Galactic halos for
many years and then decades of survey work are needed. In this case
observations of parallax or binary caustic events offer the best hope for
current experiments to deduce the lens population. The difficult models to
distinguish are Milky Way halos in which the lens fraction is low (< 10 %) and
fattened LMC disks composed of lenses with a typical mass of low luminosity
stars or greater. A next-generation wide-area microlensing survey, such as the
proposed ``SuperMACHO'' experiment, will be able to distinguish even these
difficult models with just a year or two of data.Comment: 25 pages, 4 figures, The Astrophysical Journal (in press
A new look at the cosmic ray positron fraction
The positron fraction in cosmic rays was found to be a steadily increasing in
function of energy, above 10 GeV. This behaviour contradicts standard
astrophysical mechanisms, in which positrons are secondary particles, produced
in the interactions of primary cosmic rays during the propagation in the
interstellar medium. The observed anomaly in the positron fraction triggered a
lot of excitement, as it could be interpreted as an indirect signature of the
presence of dark matter species in the Galaxy. Alternatively, it could be
produced by nearby astrophysical sources, such as pulsars. Both hypotheses are
probed in this work in light of the latest AMS-02 positron fraction
measurements. The transport of the primary and secondary positrons in the
Galaxy is described using a semi-analytic two-zone model. MicrOMEGAs is used to
model the positron flux generated by dark matter species. The description of
the positron fraction from astrophysical sources is based on the pulsar
observations included in the ATNF catalogue. We find that the mass of the
favoured dark matter candidates is always larger than 500 GeV. The only dark
matter species that fulfils the numerous gamma ray and cosmic microwave
background bounds is a particle annihilating into four leptons through a light
scalar or vector mediator, with a mixture of tau (75%) and electron (25%)
channels, and a mass between 0.5 and 1 TeV. The positron anomaly can also be
explained by a single astrophysical source and a list of five pulsars from the
ATNF catalogue is given. Those results are obtained with the cosmic ray
transport parameters that best fit the B/C ratio. Uncertainties in the
propagation parameters turn out to be very significant. In the WIMP
annihilation cross section to mass plane for instance, they overshadow the
error contours derived from the positron data.Comment: 20 pages, 16 figures, accepted for publication in A&A, corresponds to
published versio
Adipose Stem Cells in Modern-Day Ophthalmology
Stem cells (SCs) have evolved as an interesting and viable factor in ophthalmologic patient care in the past decades. SCs have been classified as either embryonic, mesenchymal, tissue-specific, or induced pluripotent cells. Multiple novel management techniques and clinical trials have been established to date. While available publications are predominantly animal-model-based, significant material is derived from human studies and case-selected scenarios. This possibility of explanting cells from viable tissue to regenerate/repair damaged tissue points to an exciting future of therapeutic options in all fields of medicine, and ophthalmology is surely not left out. Adipose tissue obtained from lipo-aspirates has been shown to produce mesenchymal SCs that are potentially useful in different body parts, including the oculo-visual system. An overview of the anatomy, physiology, and extraction process for adipose-tissue-derived stem cells (ADSC) is important for better understanding the potential therapeutic benefits. This review examines published data on ADSCs in immune-modulatory, therapeutic, and regenerative treatments. We also look at the future of ADSC applications for ophthalmic patient care. The adverse effects of this relatively novel therapy are also discussed
On the observability of the neutrino charge radius
It is shown that the probe-independent charge radius of the neutrino is a
physical observable; as such, it may be extracted from experiment, at least in
principle. This is accomplished by expressing a set of experimental
neutrino-electron cross-sections in terms of the finite charge radius and two
additional gauge- and renormalization-group-invariant quantities, corresponding
to the electroweak effective charge and mixing angle.Comment: 10 pages, 1 figure; a typo in Eq.1 corrected, some comments adde
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