4,508 research outputs found
On Strong Small Loop Transfer Spaces Relative to Subgroups of Fundamental Groups
Let be a subgroup of the fundamental group . By
extending the concept of strong SLT space to a relative version with respect to
, strong -SLT space, first, we investigate the existence of a covering
map for strong -SLT spaces. Moreover, we show that a semicovering map is a
covering map in the presence of strong -SLT property. Second, we present
conditions under which the whisker topology agrees with the lasso topology on
. Also, we study the relationship between open subsets of
and . Finally, we give some
examples to justify the definition and study of strong -SLT spaces.Comment: 16 page
An improved Agrobacterium mediated transformation in tomato using hygromycin as a selective agent
Bacterial wilt is a devastating disease of tomato crop throughout the world. This disease is very dangerous in hot and humid regions, where it spreads with the irrigation water to whole field within days, which resulted in severe decline in yield. Two varieties of tomato were used for developingbacterial wilt resistance. Riogrande responded more efficiently as compared to Roma. Regeneration frequency of 90.6% was achieved when leaf discs were used and 82.5% when hypocotyls were used as explant for tomato cv. Riogrande. While 65.4% regeneration was achieved from hypocotyls and 72.6% regeneration was obtained when leaf discs were used as explant for cv. Roma. Explants were cocultivated with Agrobacterium strain EHA101 containing a binary vector pTCL5, having hygromycin phosphotransferase (HPT) gene which confers resistance to hygromycin and -glucuronidase (GUS) gene in addition to Xa21 gene. Hygromycin (25 mg/l) was used as selectable marker while GUS is areporter gene. Acetosyringone (50 mM) enhanced transformation effeciency. Preselection period of 7 days was found to be indispensable for successful transformation of tomato crop. Transformation efficiency of 24% was observed for Riogrande and 8% for Roma. Molecular analysis of transgenic plants produced was carried out for hygromycin resistance gene. Transgenic plants contained the expected band of 670 bp. PCR analysis confirmed the foreign DNA in to the plant genome
Single-shot determination of spin-polarization for ultrarelativistic electron beams via nonlinear Compton scattering
Impacts of spin-polarization of an ultrarelativistic electron beam head-on
colliding with a strong laser pulse on emitted photon spectra and electron
dynamics have been investigated in the quantum radiation regime. We simulate
photon emissions quantum mechanically and electron dynamics semiclassically via
taking spin-resolved radiation probabilities in the local constant field
approximation. A small ellipticity of the laser field brings about an asymmetry
in angle-resolved photon spectrum, which sensitively relies on the polarization
of the electron beam. The asymmetry is particularly significant in high-energy
photon spectra, and is employed for the polarization detection of a high-energy
electron beam with extraordinary precision, e.g., better than 0.3\% for a
few-GeV electron beam at a density of the scale of cm with
currently available strong laser fields. This method demonstrates for the first
time a way of single-shot determination of polarization for ultrarelativistic
electron beams via nonlinear Compton scattering. A similar method based on the
asymmetry in the electron momentum distribution after the interaction due to
spin-dependent radiation reaction is proposed as well
Polarized positron beams via intense two-color laser pulses
Generation of ultrarelativistic polarized positrons during interaction of an
ultrarelativistic electron beam with a counterpropagating two-color petawatt
laser pulse is investigated theoretically. Our Monte Carlo simulation based on
a semi-classical model, incorporates photon emissions and pair productions,
using spin-resolved quantum probabilities in the local constant field
approximation, and describes the polarization of electrons and positrons for
the pair production and photon emission processes, as well as the classical
spin precession in-between. The main reason of the polarization is shown to be
the spin-asymmetry of the pair production process in strong external fields,
combined with the asymmetry of the two-color laser field. Employing a feasible
scenario, we show that highly polarized positron beams, with a polarization
degree of , can be produced in a femtosecond time scale,
with a small angular divergence, mrad, and high density cm. The laser-driven positron source, along with laser
wakefield acceleration, may pave the way to small scale facilities for high
energy physics studies
Role of non-timber forest products in sustaining forest-based livelihoods and rural households' resilience capacity in and around protected area- a Bangladesh study
People in developing world derive a significant part of their livelihoods
from various forest products, particularly non-timber forest products. This
article attempts to explore the contribution of NTFPs in sustaining
forest-based rural livelihood in and around a protected area of Bangladesh, and
their potential role in enhancing households resilience capacity. Based on
empirical investigation our study revealed that, local communities gather a
substantial amount of NTFPs from national park despite the official
restrictions. 27 percent households of the area received at least some cash
benefit from the collection, processing and selling of NTFPs, and NTFPs
contribute as HHs primary, supplementary and emergency sources of income. NTFPs
also constituted an estimated 19 percent of HHs net annual income, and were the
primary occupation for about 18 percent of the HHs. HHs dependency on nearby
forests for various NTFPs varied vis-a-vis their socio-economic condition as
well as with their location from the park. Based on our case study the article
also offers some clues for improving the situation in PA.Comment: To appear in Journal of Environmental Planning and Management, 201
Effect of explant plant source and acetosyringone concentration on transformation efficiency of wheat cultivars
Gene introduction into crop plants through genetic manipulation is a better alternative to conventional breeding for the improvement of stress tolerance. Agrobacterium-mediated transformation offers precise integration of genes into the genome with enhanced transgene stability. There are a number of factors which influence the rate of genetic transformation. The theme of this study is to exploit the explant source and acetosyringone concentration for the efficient development of Agrobacterium-mediated gene delivery system in wheat cultivars Inqilab 91 and Chakwal 97. Seedlings, mature embryos and calli used as explant sources for transformation in both the cultivars showed positive response. It was further observed that mature embryos produced maximum transformation efficiencies of 40.0 and 36.25% with 37.5 and 31.03% of regeneration frequencies of transgenic plants for Chakwal 97 and Inqilab 91, respectively. Seedlings produced 33.75 and 27.5% while calli produced 26.25 and 22.5% transformation efficiencies for both the cultivars. Acetosyringone concentration is also a limiting factor in transformation experiments especially in the case of cereals crop. Different concentrations of acetosyringone were used at the time of co-cultivation for optimization of the transformation protocol and maximum transformation efficiencies of 52.44 and 47.56% were obtained with 50 μM of acetosyringone from the cultivars Chakwal 97 and Inqilab 91, respectively.Key words: Wheat, agrobacterium, transformation, explant, acetosyringone
Ultrarelativistic polarized positron jets via collision of electron and ultraintense laser beams
Relativistic spin-polarized positron beams are indispensable for future
electron-positron colliders to test modern high-energy physics theory with high
precision. However, present techniques require very large scale facilities for
those experiments.
We put forward a novel efficient way for generating ultrarelativistic
polarized positron beams employing currently available laser fields. For this
purpose the generation of polarized positrons via multiphoton Breit-Wheeler
pair production and the associated spin dynamics in single-shot interaction of
an ultraintense laser pulse with an ultrarelativistic electron beam is
investigated in the quantum radiation-dominated regime. A specifically tailored
small ellipticity of the laser field is shown to promote splitting of the
polarized particles along the minor axis of laser polarization into two
oppositely polarized beams. In spite of radiative de-polarization, a dense
positron beam with up to about 90\% polarization can be generated in tens of
femtoseconds. The method may eventually usher high-energy physics studies into
smaller-scale laser laboratories
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