Chiral tunneling in trilayer graphene

We study the effect of chiral-tunneling in Bernal and Rombhohedral stacked trilayer-graphene (3LG). Based on the chirality of the electronic bands, at the K-point, (Rombhohedral) Bernal-3LG exhibits 100% (50%) transparency across a heterojunction. Utilizing this property, we further investigate the effect of electron collimation in 3LG. Due to the difference in the Berry's phase, we show that, Rombhohedral-3LG is a better electron collimator, compared to monolayer and Bernal-bilayer graphene. Since, Bernal-3LG can be decomposed into two separate channels consisting of a monolayer and a modified Bernal-bilayer graphene; the Bernal-3LG is weaker electron collimator, compared to Rombhohedral-3LG.Comment: APL, 2012; http://dx.doi.org/10.1063/1.370375

Multilayer graphene nanoribbon under vertical electric field

We study the effect of vertical electric-field (E-field) on the electronic properties of the multilayer armchair graphene nanoribbon (aGNR). Under E-field, the band structure of a bilayer aGNR undergoes interesting transformations such as change in the electron velocity, sign of the electron effective mass, band gap, the position of the band gap in the momentum space. Depending on the width of the aGNR and the applied E-field, the band gap of the aGNR may either be increased or decreased. When the applied E-field is above a critical value, the band gap of the bilayer aGNR is identical to that of the bilayer graphene, independent of the width. We also show that, for semiconducting multilayer aGNR with more than two layers, the band gap decreases with increasing E-field, resulting in a semiconductor-to-metallic transition. This can be utilized to enhance the performance of a graphene based transistor devices

High magnetoresistance at room temperature in p-i-n graphene nanoribbons due to band-to-band tunneling effects

A large magnetoresistance effect is obtained at room-temperature by using p-i-n armchair-graphene-nanoribbon (GNR) heterostructures. The key advantage is the virtual elimination of thermal currents due to the presence of band gaps in the contacts. The current at B=0T is greatly decreased while the current at B>0T is relatively large due to the band-to-band tunneling effects, resulting in a high magnetoresistance ratio, even at room-temperature. Moreover, we explore the effects of edge-roughness, length, and width of GNR channels on device performance. An increase in edge-roughness and channel length enhances the magnetoresistance ratio while increased channel width can reduce the operating bias.Comment: http://dx.doi.org/10.1063/1.362445

Conductance modulation in graphene nanoribbon under transver-se asymmetric electric potential

We theoretically study the effect of transverse electric potentials on the transport properties of armchair graphene nanoribbons (AGNRs), formed by pairs of asymme-tric gates placed along the side of the ribbon. Single pair and dual pair configurations are considered. We also examine the effect of hollows (spatial regions void of carbon atoms) in the AGNR channels. We find that the use of hollowed AGNRs in the dual pair configuration allows for a significant modulation of the transport gap, when the two pairs have opposite polarity of gate bias. Furthermore, we show that for the dual-gate system, hollowed AGNR channels exhibit the optimal ratio of ON-state to OFF-state conductance, due to the smaller OFF-state conductance compared with spatially homogenous AGNR channels. Our results indicate that transverse gate technology coupled with careful engineering of hollow geometry may lead to possible applications in graphene-based electronic devices.Comment: 14 pages, 6 figure

Development of near isogenic lines (NILS) using backcross method of breeding and simultaneous screening against Karnal bunt disease of wheat

Karnal bunt of wheat caused by Tilletia indica can be a hindrance to wheat trade as the fungal disease is known to affect the quality of the grain. As a breeding strategy, a set of eight near isogenics lines (NILs) and backcross derived recombinant inbred lines (micro-RILs) were developed in the background of PBW 343 and WH542 for Karnal bunt resistance over a period of time. The donor stocks resistant to Karnal bunt used in the study were ALDAN ‘ S’ / IAS 58, CMH 77.308, H567.7I, HD29, HP1531, W485 and their derived lines KBRL 22 and KBRL 57. Effective method for screening to Karnal bunt was standardized and used for identification of resistant lines across many seasons. Some of the identified lines evaluated for yield were found to be equivalent to the high yielding parents and the commercially grown check varieties. These developed lines will serve as a basic material for production of Karnal bunt free wheat

Performance Limits of Monolayer Transition Metal Dichalcogenide Transistors

The performance limits of monolayer transition metal dichalcogenide transistors are examined with a ballistic MOSFET model. Using ab-initio theory, we calculate the band structures of two-dimensional (2D) transition metal dichalco-genide (MX2). We find the lattice structures of monolayer MX2 remain the same as the bulk MX2. Within the ballistic regime, the performances of monolayer MX2 transistors are better compared to the silicon transistors if thin high-{\kappa} gate insulator is used. This makes monolayer MX2 promising 2D materials for future nanoelectronic device applications

Vascular repair in trauma - critical analysis for improving limb salvage.

INTRODUCTION : With continued urbanization over last few decades there has been an alarming and unabated increase in the incidence of traumatic vascular injuries. Between 1-5% of trauma cases involved injury to a major vascular structure which confronts us with the twin problem of haemorrhage on one hand and ischemia on the other hand. The lives and limbs jeoparadised in these critical vascular injuries often belong to young people and their salvage may mean many years of satisfactory function. Though most advances in treatment of vascular injuries has evolved from war surgery it is quite surprising that it was not until 1950s that effective vascular repair was attempted. In an analysed series of 2471 acute arterial wounds from world war-2 end to end anastomosis was accomplished in only three instances. In fact ligation of a artery was the main stay of treatment then and resulted in an amputation rate of about 40%. Reconstruction of the artery was first employed routinely during the Korean war and the amputation rate dramatically dropped to 13%. Further improvement was achieved in Vietnam war largely as a result of further reduction in time lag and availability of expert vascular surgeon these lessons of war time surgery have been applied in peace time injury and restortation of normal blood flow and not merely saving life is prime objective now. AIM OF THE STUDY : This prospective study of vascular injuries in extremities was conducted in Government General Hospital, Chennai during the period from September 2003 to September 2005. The objectives of the study are:- 1) To study the various etiopathological factors involved and modes of clinical presentation. 2) To assess diagnostic difficulties 3) To analyse the factors influencing ultimate result. 4) To compare and contrast injury pattern and results achieved with world literature. 5) Methods to improve limb salvage. CONCLUSION : 65 Patients with arterial injury of extremities were treated during 24 month period. It is significant that 96.1% were in peak of their youth (3rd decade). A marked male preponderance of 98% was noted. Automobile accidents and penetrating injury were predominant causes. Iatrogenic injury occurred in about 4.6% of the patients. About 90% of acute arterial injury endangered the limbs superficial femoral artery, popliteal artery and brachial artery were seen most frequently. Average ischemic time was 16.75 hours with preadmission delay contributing much. ‘Proximity’ was a important clue in our series as almost all cases had injuries or fracture close to the arteries. But nearly ¼ had palpable distal pulses inspite of arterial injury, indicating that absent pulses alone was inadequate to be the sole indication for exploration. Portable doppler velocity meter gave valuable immediate information at the bed side augment the clinical diagnosis. Arterial repair was accomplished with autogenous vein graft in 73.8% patients and end to end anastomosis in 7.6% patients and venous repair done in 15.1% percentage of patient. Associated orthopaedic and nerve injury were responsible for most of the functional impairment and limb losses. A limb salvage rate of Lower Limb 75% and Upper Limb 95% was achieved. There was seven death due to arterial injuries in this series