Estimation of genetic diversity between three Saudi sheep breeds using DNA markers

The genetic variation of Najdi, Harri and Awassi breeds of Saudi sheep prevailing in Raniah province of Makka district were assessed and compared to Sudanese Desert sheep using random amplified polymorphic DNA polymerase cahin reaction (RAPD-PCR) technique. Five primers successfully amplified distinguishable 40  bands with an average of 96% polymorphism revealing that Saudi sheep breeds possess the needed genetic variation required for further genetic improvement. The resulted dendrogram showed that, there are two main separate clades. The Desert sheep is genetically distant and appeared as out-group from the Saudi sheep breeds. The first main clade included all of the Najdi individuals and only two individuals from Harri breed. While, the second main clade comprised two subgroups, the first one included individuals from Harri breed and the second included both Harri and Awassi individuals. The cluster analysis shows that Najdi breed is  genetically different from both Harri and Awassi and that some Harri individuals showed genetic closeness to Awassi. The present study will help to clarify the image of the genetic diversity of these local Saudi sheep breeds in Raniah province and should be followed by further studies using advanced DNA markers and all  available breeds in the kingdom to get the precise estimation of the phylogeny of these local genetic resources.Key words: Dendrogram, biodiversity, Sudanese sheep, random amplified polymorphic DNA (RAPD), Saudi sheep

The nature of localization in graphene under quantum Hall conditions

Particle localization is an essential ingredient in quantum Hall physics [1,2]. In conventional high mobility two-dimensional electron systems Coulomb interactions were shown to compete with disorder and to play a central role in particle localization [3]. Here we address the nature of localization in graphene where the carrier mobility, quantifying the disorder, is two to four orders of magnitude smaller [4,5,6,7,8,9,10]. We image the electronic density of states and the localized state spectrum of a graphene flake in the quantum Hall regime with a scanning single electron transistor [11]. Our microscopic approach provides direct insight into the nature of localization. Surprisingly, despite strong disorder, our findings indicate that localization in graphene is not dominated by single particle physics, but rather by a competition between the underlying disorder potential and the repulsive Coulomb interaction responsible for screening.Comment: 18 pages, including 5 figure

Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2

The linear dispersion relation in graphene[1,2] gives rise to a surprising prediction: the resistivity due to isotropic scatterers (e.g. white-noise disorder[3] or phonons[4-8]) is independent of carrier density n. Here we show that acoustic phonon scattering[4-6] is indeed independent of n, and places an intrinsic limit on the resistivity in graphene of only 30 Ohm at room temperature (RT). At a technologically-relevant carrier density of 10^12 cm^-2, the mean free path for electron-acoustic phonon scattering is >2 microns, and the intrinsic mobility limit is 2x10^5 cm^2/Vs, exceeding the highest known inorganic semiconductor (InSb, ~7.7x10^4 cm^2/Vs[9]) and semiconducting carbon nanotubes (~1x10^5 cm^2/Vs[10]). We also show that extrinsic scattering by surface phonons of the SiO2 substrate[11,12] adds a strong temperature dependent resistivity above ~200 K[8], limiting the RT mobility to ~4x10^4 cm^2/Vs, pointing out the importance of substrate choice for graphene devices[13].Comment: 16 pages, 3 figure

Broken symmetry states and divergent resistance in suspended bilayer graphene

Graphene [1] and its bilayer have generated tremendous excitement in the physics community due to their unique electronic properties [2]. The intrinsic physics of these materials, however, is partially masked by disorder, which can arise from various sources such as ripples [3] or charged impurities [4]. Recent improvements in quality have been achieved by suspending graphene flakes [5,6], yielding samples with very high mobilities and little charge inhomogeneity. Here we report the fabrication of suspended bilayer graphene devices with very little disorder. We observe fully developed quantized Hall states at magnetic fields of 0.2 T, as well as broken symmetry states at intermediate filling factors $\nu = 0$, $\pm 1$, $\pm 2$ and $\pm 3$. The devices exhibit extremely high resistance in the $\nu = 0$ state that grows with magnetic field and scales as magnetic field divided by temperature. This resistance is predominantly affected by the perpendicular component of the applied field, indicating that the broken symmetry states arise from many-body interactions.Comment: 23 pages, including 4 figures and supplementary information; accepted to Nature Physic

Prospective Randomised Controlled Trial of Teaching Medical Students Behavioural Sciences

Background: In the last few decades, medical professionalismcame upas a challenging issue to teach and assess.Objective: To compare the level of understanding of the medical professionalism, medical ethics and human rights among the first year and fifth year medical students at Omdurman Islamic University in Sudan.Methods: Prospective randomised controlled trial. Students were randomized in to four groups during teaching of behavioural sciences which was given at different spectra in the different groups. Responders were 365(91.25%), they were 143(39.2%) first year males, 141(38.6%) first year females split in two groups and 81(22.2%) fifth year mixed male and female.Conceptual understanding of medical ethics, professionalism, human rights and the religion values as part of the university requirement were assessed with a pretested questionnaire.Results: Of the fifth year students 69(86.3%) were able to describe triggering organisational help for patients as an advocacy and 119(83.2%) first year male students were able to identify that availing medical facilities to the disabled and the vulnerable groupsas basic human right. Themajority (>90%) of all students were described well professional integrity and 132(93%) of first year medical students were able mention correctly the differences between the Healer and the professional and 83(58.5%) of fifth year students specified the confidentiality issue in taking informed consent, respectively. However, the students' categorised the regulation of organ transplantation and tissue engineering has human rights followed by Religion Teachings bases.Conclusion: Teaching medical ethics, human rights, professionalism and University requirements to the first year medical students and gains during the practical experience of the clinical clerkship have a considerable impact on the student perception of these subjects. Gains are expected to improve if these issues are integrated in all areas of the curriculum.Key words: Professionalism, Human rights, Medical ethics, medical student

Gate-Controlled Ionization and Screening of Cobalt Adatoms on a Graphene Surface

We describe scanning tunneling spectroscopy (STS) measurements performed on individual cobalt (Co) atoms deposited onto backgated graphene devices. We find that Co adatoms on graphene can be ionized by either the application of a global backgate voltage or by the application of a local electric field from a scanning tunneling microscope (STM) tip. Large screening clouds are observed to form around Co adatoms ionized in this way, and we observe that some intrinsic graphene defects display a similar behavior. Our results provide new insight into charged impurity scattering in graphene, as well as the possibility of using graphene devices as chemical sensors.Comment: 19 pages, 4 figure

The Life-Cycle of Operons

Operons are a major feature of all prokaryotic genomes, but how and why operon structures vary is not well understood. To elucidate the life-cycle of operons, we compared gene order between Escherichia coli K12 and its relatives and identified the recently formed and destroyed operons in E. coli. This allowed us to determine how operons form, how they become closely spaced, and how they die. Our findings suggest that operon evolution may be driven by selection on gene expression patterns. First, both operon creation and operon destruction lead to large changes in gene expression patterns. For example, the removal of lysA and ruvA from ancestral operons that contained essential genes allowed their expression to respond to lysine levels and DNA damage, respectively. Second, some operons have undergone accelerated evolution, with multiple new genes being added during a brief period. Third, although genes within operons are usually closely spaced because of a neutral bias toward deletion and because of selection against large overlaps, genes in highly expressed operons tend to be widely spaced because of regulatory fine-tuning by intervening sequences. Although operon evolution may be adaptive, it need not be optimal: new operons often comprise functionally unrelated genes that were already in proximity before the operon formed

Lepton flavor violation and seesaw symmetries

peer reviewedWhen the standard model is extended with right-handed neutrinos the symmetries of the resulting Lagrangian are enlarged with a new global U(1)R Abelian factor. In the context of minimal seesaw models we analyze the implications of a slightly broken U(1)R symmetry on charged lepton flavor violating decays. We find, depending on the R-charge assignments, models where charged lepton flavor violating rates can be within measurable ranges. In particular, we show that in the resulting models due to the structure of the light neutrino mass matrix muon flavor violating decays are entirely determined by neutrino data (up to a normalization factor) and can be sizable in a wide right-handed neutrino mass range