Synchronous and Asynchronous Mott Transitions in Topological Insulator Ribbons

We address how the nature of linearly dispersing edge states of two dimensional (2D) topological insulators evolves with increasing electron-electron correlation engendered by a Hubbard like on-site repulsion $U$ in finite ribbons of two models of topological band insulators. Using an inhomogeneous cluster slave rotor mean-field method developed here, we show that electronic correlations drive the topologically nontrivial phase into a Mott insulating phase via two different routes. In a synchronous transition, the entire ribbon attains a Mott insulating state at one critical $U$ that depends weakly on the width of the ribbon. In the second, asynchronous route, Mott localization first occurs on the edge layers at a smaller critical value of electronic interaction which then propagates into the bulk as $U$ is further increased until all layers of the ribbon become Mott localized. We show that the kind of Mott transition that takes place is determined by certain properties of the linearly dispersing edge states which characterize the topological resilience to Mott localization.Comment: 4+ pages, 5 figure

Interspecific Hybrid Developed in Epidendrum Orchid from the Cross E. radicans Pav. Ex. Lindl. X E. xanthinum Lindl.

An interspecific Epidendrum hybrid was developed using E. radicans (known as 'fire star orchid', 'ground-rooted orchid') as female parent and E. xanthinum known as 'yellow orchid' as male parent. The selected line (NRCO Epidendrum cross/2005-01) was characterized for morphological and floral traits. Flower size (3.5 cm x 3.4 cm) of selected line was bigger than both parents, with bright saffron-orange colour (RHS 44A). Dorsal sepal size (1.8 cm x 0.6 cm), lateral sepal size (1.9 cm x 0.7 cm), petal size (1.8 cm x 0.6 cm), lip size (2.3 cm x 2 cm) and column size (1.1 cm x 0.2 cm) were bigger than in parents. Shape and fimbriated side lobes of lip with deep cleft of anterior margins was similar to the male parent (E. xanthinum), except colour. The F1progeny of 'NRCO-Epidendrum cross/2005-01' flowered with different red-orange to yellow shades is categorized broadly into three types: Red-orange, Orangeyellow and Yellow. Epidendrums are popularly known as 'Crucifix orchid' and 'Poor man's orchid', have a long flowering period with 2-3 flowerings in a year, and are easy to multiply. These attributes are ideal for popularizing this plant in India as a potted plant as well garden plant

The Barrier Method: A Technique for Calculating Very Long Transition Times

In many dynamical systems there is a large separation of time scales between typical events and "rare" events which can be the cases of interest. Rare-event rates are quite difficult to compute numerically, but they are of considerable practical importance in many fields: for example transition times in chemical physics and extinction times in epidemiology can be very long, but are quite important. We present a very fast numerical technique that can be used to find long transition times (very small rates) in low-dimensional systems, even if they lack detailed balance. We illustrate the method for a bistable non-equilibrium system introduced by Maier and Stein and a two-dimensional (in parameter space) epidemiology model.Comment: 20 pages, 8 figure

Polarization in young open cluster NGC 6823

We present multiwavelength linear polarimetric observations of 104 stars towards the region of young open cluster NGC 6823. The polarization towards NGC 6823 is dominated by foreground dust grains and we found the evidence for the presence of several layers of dust towards the line of sight. The first layer of dust is located approximately within 200 pc towards the cluster, which is much closer to the Sun than the cluster (~ 2.1 kpc). The radial distribution of the position angles for the member stars are found to show a systematic change while the polarization found to reduce towards the outer parts of the cluster and the average position angle of coronal region of the cluster is very close to the inclination of the Galactic parallel (~ 32 degree). The size distribution of the grains within NGC 6823 is similar to those in general interstellar medium. The patchy distribution of foreground dust grains are suggested to be mainly responsible for the both differential reddening and polarization towards NGC 6823. The majority of the observed stars do not show the evidence of intrinsic polarization in their light.Comment: 16 pages, 6 tables, 11 figures, Accepted for publication in MNRA

Helical edge states in multiple topological mass domains

The two-dimensional topological insulating phase has been experimentally discovered in HgTe quantum wells (QWs). The low-energy physics of two-dimensional topological insulators (TIs) is described by the Bernevig-Hughes-Zhang (BHZ) model, where the realization of a topological or a normal insulating phase depends on the Dirac mass being negative or positive, respectively. We solve the BHZ model for a mass domain configuration, analyzing the effects on the edge modes of a finite Dirac mass in the normal insulating region (soft-wall boundary condition). We show that at a boundary between a TI and a normal insulator (NI), the Dirac point of the edge states appearing at the interface strongly depends on the ratio between the Dirac masses in the two regions. We also consider the case of multiple boundaries such as NI/TI/NI, TI/NI/TI and NI/TI/NI/TI.Comment: 11 pages, 15 figure

Helical edge states in multiple topological mass domains

The two-dimensional topological insulating phase has been experimentally discovered in HgTe quantum wells (QWs). The low-energy physics of two-dimensional topological insulators (TIs) is described by the Bernevig-Hughes-Zhang (BHZ) model, where the realization of a topological or a normal insulating phase depends on the Dirac mass being negative or positive, respectively. We solve the BHZ model for a mass domain configuration, analyzing the effects on the edge modes of a finite Dirac mass in the normal insulating region (soft-wall boundary condition). We show that at a boundary between a TI and a normal insulator (NI), the Dirac point of the edge states appearing at the interface strongly depends on the ratio between the Dirac masses in the two regions. We also consider the case of multiple boundaries such as NI/TI/NI, TI/NI/TI and NI/TI/NI/TI.Comment: 11 pages, 15 figure

Bacteria in cancer therapy: a novel experimental strategy

Resistance to conventional anticancer therapies in patients with advanced solid tumors has prompted the need of alternative cancer therapies. Moreover, the success of novel cancer therapies depends on their selectivity for cancer cells with limited toxicity to normal tissues. Several decades after Coley's work a variety of natural and genetically modified non-pathogenic bacterial species are being explored as potential antitumor agents, either to provide direct tumoricidal effects or to deliver tumoricidal molecules. Live, attenuated or genetically modified non-pathogenic bacterial species are capable of multiplying selectively in tumors and inhibiting their growth. Due to their selectivity for tumor tissues, these bacteria and their spores also serve as ideal vectors for delivering therapeutic proteins to tumors. Bacterial toxins too have emerged as promising cancer treatment strategy. The most potential and promising strategy is bacteria based gene-directed enzyme prodrug therapy. Although it has shown successful results in vivo yet further investigation about the targeting mechanisms of the bacteria are required to make it a complete therapeutic approach in cancer treatment

Hairy cell leukemia : experience at a tertiary cancer centre in Northern India

Background : The prognosis of Hairy cell leukemia (HCL) has improved markedly following treatment with cladribine (2- CdA), a nucleoside analogue. We reviewed data on patients with HCL treated in our department. Methods . Between 1995 and 2004, 23 patients with hairy cell leukemia (HCL) were diagnosed Patients median age was 48.5 years (range, 32 to 66 years), there were 18 males and 5 females. The common presenting symptoms were: fatigue (82.6%), fever (34.7%), abdominal discomfort (21.7%), arthralgia/bone pains (13%) and bleeding (17.3%). 22 of 23 (95.6%) patients had enlarged spleen, and hepatomegaly (65%). Lymph node enlargement was present in 17% of patients. Investigations revealedmedian Hb of 7.8g% (5.7 to 12.9 g%), thrombocytopenia (median 55000/cmm) and median WBC count of 3500/cmm (range, 600 to 20,200/cmm). Bicytopenia or pancytopenia was present in 87% and bone marrow fibrosis in 75% of cases. Immunophenotyping studies revealed expression of CD11C (60%), CD25 (60%), FMC7(47.8%), CD23(34.8%), CD103 in 39% of cases. 20 of 23 patients received treatment; two received treatment else where and one patient died of liver failure prior to treatment. 17 of 20 patients were treated with 2-CdA, 2 with interferon alfa (IFN-a) and one patient underwent splenectomy alone. Three patients received 2-CdA as second line therapy for treatment of relapse: this includes . one patient each, treated with IFN- α and splenectomy both and one patient received 2-cdA twice in view of relapse. Results . Following treatment with 2CdA . 95% of patients responded; complete-84.2% and partial response in 10.5%. one (5.2%) patient died of toxicity. Two patients relapsed at a mean follow up of 25 months. The common side effects were febrile episodes (n=10) and grade I-II myelosuppression. One patient died of toxicity to 2-CdA. This patient was a known case of multidrug resistant disseminated tuberculosis. He had severe myelosuppression with fungal sepsis with multiorgan failure and BM Aspirate was positive for AFB. Other infections documented were Pulmonary tuberculosis in 2 and herpes zoster in one patient. The patient who underwent Splenectomy achieved remission but relapsed after 3 years and was salvaged with 2-CdA again. Median time for normalization of blood counts after 2-CdA was 28 days and median time to regress spleen was 41.5 days . Conclusion . Present study confirms good outcome with 2-CdA (cladribine) therapy for patients of hairy cell leukemia

Diversity and Conservation of Rare and Endemic Orchids of North East India -A Review

ABSTRACT Northeast India, a mega-diversity centre, comprises eight states, viz., Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim and Tripura. It occupies 7.7% of India's total geographical area supporting 50% of the flora (ca. 8000 species), of which 31.58% (ca. 2526 species) are endemic. The region is rich in orchids, ferns, oak