Conductance of bilayer graphene in the presence of a magnetic field: Effects of disorder

We investigate the electronic transport properties of unbiased and biased bilayer graphene nanoribbon in n-p and n-n junctions subject to a perpendicular magnetic field. Using the non-equilibrium Green's function method and the Landauer-B\"{u}ttiker formalism, the conductance is studied for the cases of clean, on-site, and edge disordered bilayer graphene. We show that the lowest Hall plateau remains unchanged in the presence of disorder, whereas asymmetry destroys both the plateaus and conductance quantization. In addition, we show that disorder induces an enhancement of the conductance in the n-p region in the presence of magnetic fields. Finally, we show that the equilibration of quantum Hall edge states between distinctively doped regions causes Hall plateaus to appear in the regime of complete mode mixing.Comment: 8 pages, 7 figures. Accepted to Phys. Rev.

Irreversibility in response to forces acting on graphene sheets

The amount of rippling in graphene sheets is related to the interactions with the substrate or with the suspending structure. Here, we report on an irreversibility in the response to forces that act on suspended graphene sheets. This may explain why one always observes a ripple structure on suspended graphene. We show that a compression-relaxation mechanism produces static ripples on graphene sheets and determine a peculiar temperature $T_c$, such that for $T<T_c$ the free-energy of the rippled graphene is smaller than that of roughened graphene. We also show that $T_c$ depends on the structural parameters and increases with increasing sample size.Comment: 4 pages, 4 Figure

Stochastic ϕ4−\phi^4-Theory in the Strong Coupling Limit

The stochastic $\phi^4$-theory in $d-$dimensions dynamically develops domain wall structures within which the order parameter is not continuous. We develop a statistical theory for the $\phi^4$-theory driven with a random forcing which is white in time and Gaussian-correlated in space. A master equation is derived for the probability density function (PDF) of the order parameter, when the forcing correlation length is much smaller than the system size, but much larger than the typical width of the domain walls. Moreover, exact expressions for the one-point PDF and all the moments $$ are given. We then investigate the intermittency issue in the strong coupling limit, and derive the tail of the PDF of the increments $\phi(x_2) - \phi(x_1)$. The scaling laws for the structure functions of the increments are obtained through numerical simulations. It is shown that the moments of field increments defined by, $C_b=$, behave as $|x_1-x_2|^{\xi_b}$, where $\xi_b=b$ for $b\leq 1$, and $\xi_b=1$ for $b\geq1$Comment: 22 pages, 6 figures. to appear in Nuclear. Phys.

Dirac Spectrum in Piecewise Constant One-Dimensional Potentials

We study the electronic states of graphene in piecewise constant potentials using the continuum Dirac equation appropriate at low energies, and a transfer matrix method. For superlattice potentials, we identify patterns of induced Dirac points which are present throughout the band structure, and verify for the special case of a particle-hole symmetric potential their presence at zero energy. We also consider the cases of a single trench and a p-n junction embedded in neutral graphene, which are shown to support confined states. An analysis of conductance across these structures demonstrates that these confined states create quantum interference effects which evidence their presence.Comment: 10 pages, 12 figures, additional references adde

Graphene-based modulation-doped superlattice structures

The electronic transport properties of graphene-based superlattice structures are investigated. A graphene-based modulation-doped superlattice structure geometry is proposed and consist of periodically arranged alternate layers: InAs/graphene/GaAs/graphene/GaSb. Undoped graphene/GaAs/graphene structure displays relatively high conductance and enhanced mobilities at elevated temperatures unlike modulation-doped superlattice structure more steady and less sensitive to temperature and robust electrical tunable control on the screening length scale. Thermionic current density exhibits enhanced behaviour due to presence of metallic (graphene) mono-layers in superlattice structure. The proposed superlattice structure might become of great use for new types of wide-band energy gap quantum devices.Comment: 5 figure

Quasiparticle properties of graphene in the presence of disorder

We calculate the quasiparticle properties of chiral two-dimensional Dirac electrons in graphene within the Landau Fermi Liquid scheme based on $GW$ approximation in the presence of disorder. Disorder effects due to charged impurity scattering plays a crucial role in density dependence of quasiparticle quantities. Mode-coupling approach to scattering rate and self-energy in $GW$ approximation for quasiparticle renormalized Fermi velocity and spin-antisymmetric Landau Fermi parameter incorporating the many-body interactions and the disorder effects show reduction of these quantities by 5-15 percent at available experimental charge carrier density region.Comment: 15 pages, 4 figures. To appear in Solid State Communication

Clonal dynamics of BRAF-driven drug resistance in EGFR-mutant lung cancer

Activation of MAPK signaling via BRAF mutations may limit the activity of EGFR inhibitors in EGFR-mutant lung cancer patients. However, the impact of BRAF mutations on the selection and fitness of emerging resistant clones during anti-EGFR therapy remains elusive. We tracked the evolution of subclonal mutations by whole-exome sequencing and performed clonal analyses of individual metastases during therapy. Complementary functional analyses of polyclonal EGFR-mutant cell pools showed a dose-dependent enrichment of BRAF(V600E) and a loss of EGFR inhibitor susceptibility. The clones remain stable and become vulnerable to combined EGFR, RAF, and MEK inhibition. Moreover, only osimertinib/trametinib combination treatment, but not monotherapy with either of these drugs, leads to robust tumor shrinkage in EGFR-driven xenograft models harboring BRAF mutations. These data provide insights into the dynamics of clonal evolution of EGFR-mutant tumors and the therapeutic implications of BRAF(V600E) co-mutations that may facilitate the development of treatment strategies to improve the prognosis of these patients

Study the Pattern of Unusual Attachments of Pronator Teres in Flexor Muscles Group of the Forearm

Background and Objectives: Study of the variations in the muscles, nerves and arteries formation and course is useful for the clinicians during surgery and for differential diagnosis of uncommon clinical conditions. As the arm and forearm are the point of formation of many body structures, variations are not uncommon but variations of Pronator teres (PT) are rare in literature. The role of PT is critical as one of the main flexors and pronators of the elbow joint. We present an unusual case of PT formation found during routine cadaveric dissection. PT is the most lateral muscle of the superficial group muscles of forearm. In pronation, it acts as a medial rotator of radius on ulna. PT has two origins, the humeral head, arises from the medial supracondylar ridge, and from the common flexor tendon which arises from the medial epicondyle of the humerus and the ulnar head which arises from the medial side of the coronoid process of the ulna. Median nerve crosses between these ends. The muscle passes obliquely across the forearm, and ends in a flat tendon, which is inserted at the middle of the lateral surface of the body of the radius. Material and Methods: During routine dissection of a 60 year-old male preserved corpse, whom we had no information from previous diseases, variations were found in PT. Results: There was an abnormal origin of PT and absence of its coronoid attachment. Due to its important relation with median nerve and brachial artery this variation may be important after probable trauma injuries. Furthermore there was a neural variance in this region as too early branching of anterior interosseus branch of median was seen. Conclusion: It is concluded that PT variations may affect the function of upper limb. Knowledge of such variations is important to anatomists, radiologists, anesthesiologists and surgeons in evaluation of unexplained sensory and motor loss after trauma and surgical interventions to the upper limb. The presence of anatomical variations is often used to explain unexpected clinical signs and symptoms and for differential diagnosis of uncommon clinical conditions. In this study Clinical consideration of the present variations has been discussed. The present variation should be considered in the etiology of PT syndrome

Predicting gene expression level in E. coli from mRNA sequence information

The accurate characterization of the translational mechanism is crucial for enhancing our understanding of the relationship between genotype and phenotype. In particular, predicting the impact of the genetic variants on gene expression will allow to optimize specific pathways and functions for engineering new biological systems. In this context, the development of accurate methods for predicting the translation efficiency and/or protein expression from the nucleotide sequence is a key challenge in computational biology. In this work we present PGExpress, a new regression method for predicting the log2-fold-change of the translation efficiency of an mRNA sequence in E. coli. PGExpress algorithm takes as input 12 features corresponding to the predicted RNA secondary structure and anti-Shine-Dalgarno hybridization free energies. The method was trained on a set of 1,772 sequence variants (WT-High)of 137 essential E. coli genes. For each gene, we considered 13 sequence variants of the first 33 nucleotides encoding for the same amino acids followed by the superfolder GFP. Each gene variant is represented sequence blocks that include the Ribosome Binding Site (RBS), the first 33 nucleotides of the coding region (C33), the remaining part of the coding region (CC), and their combinations. Our gradient-boosting-based tool (PGExpress) was trained using a 10-fold gene-based cross-validation procedure on the WT-High dataset. In this test PGExpress achieved a correlation coefficient of 0.60, with a Root Mean Square Error (RMSE)of 1.3. When the regression task is cast as a classification problem, PGExpress reached an overall accuracy of 0.74 a Matthews correlation coefficient 0.48 and an Area Under the Receiver Operating Characteristic Curve (AUC)of 0.81. In the regression task, PGExpress results in better performance than RBSCalculator in the prediction of the log2-fold-change of the translational efficiency and its variation on the WT-High dataset. Finally, we validated our method by performing in-house experiments on five newly generated mRNA sequence variants. The predictions of the expression level of the new variants are in agreement with our experimental results in E. coli