Ge growth on ion-irradiated Si self-affine fractal surfaces

We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to study the morphology of ultrathin Ge films eposited on pristine Si(100) and ion-irradiated Si(100) self-affine fractal surfaces. The pristine and the ion-irradiated Si(100) surface have roughness exponents of alpha=0.19+/-0.05 and alpha=0.82+/-0.04 respectively. These measurements were carried out on two halves of the same sample where only one half was ion-irradiated. Following deposition of a thin film of Ge (~6 A) the roughness exponents change to 0.11+/-0.04 and 0.99+/-0.06, respectively. Upon Ge deposition, while the roughness increases by more than an order of magnitude on the pristine surface, a smoothing is observed for the ion-irradiated surface. For the ion-irradiated surface the correlation length xi increases from 32 nm to 137 nm upon Ge deposition. Ge grows on Si surfaces in the Stranski-Krastanov or layer-plus-island mode where islands grow on a wetting layer of about three atomic layers. On the pristine surface the islands are predominantly of square or rectangular shape, while on the ion-irradiated surface the islands are nearly diamond shaped. Changes of adsorption behaviour of deposited atoms depending on the roughness exponent (or the fractal dimension) of the substrate surface are discussed.Comment: 5 pages, 2 figures and 1 tabl

Food Processing in Andhra Pradesh Opportunities and Challenges

There has been diversification of Indian diets away from foodgrains to high value products like milk, meat products, vegetables and fruits. Food-processing industry has been registering good growth since the past few decades and particularly after nineties. The conditions are now ideal for the growth of this industry. The central government has taken some steps to deregulate and encourage the sector after 1991. However, the role of states is vital. The government of Andhra Pradesh released a policy in November 2003. There are no major initiatives in the policy and still can be called a good beginning. As against the robust growth at the All-India level, the growth rate in net value - added in the nineties was almost the same as that in the eighties in the state. Against this background, the study is taken up in the state of Andhra Pradesh with the following objectives 1. To study the opportunities and challenges in processing of rice, fruits and vegetables, oilseeds and livestock products 2. To study the working of contracts between processors and farmers 3. To identify the future areas 4. To recommend suitable policy options The contracts are working, on the whole, well in both oil palm in West Godavari and gherkin in Chittoor district of the state. The firms try to attract with favourable conditions initially, but later tighten them as a part of agribusiness normalization. Therefore caution is needed before a final conclusion can be drawn on the usefulness of contract farming in the state for the farming community. The contracts in oil palm 3 are widespread, covering many farmers and stabilized. The total extent under gherkin is very low. The contracts work through facilitator in gherkin. There are some signs of some mistrust between the facilitator-company and local farmers. The contracts are also evolving gradually to accommodate both parties. The participation of small farmers in oil palm cultivation is almost negligible. On the other hand, in gherkin, participation of small farmers was considerable. The contracts are oral and price is not assured in oil palm. In oil palm gardens, the depletion of ground water level is faster compared to other crops. In the case of gherkin, the processing industry is totally dependent on exports for sustenance, which may not be ideal. The establishment of an independent ministry of food processing and department, enacting of contract farming laws and providing for an efficient arbitration in cases of contract violation, encouraging NGOs participation in food processing sector, formation of product-wise farmers' associations, changing the animal slaughter laws and formation of some more agri-export zones for livestock products are some of the recommendations under institutional aspects. In the case of taxes and subsidies, the recommendations are - exemption from sales tax and market cess and relaxation of duties and taxes on packing material industry. Under research and training, large scale publicity to promote processed foods, undertaking demand driven research by developing processable varieties and required equipment, establishing food processing training centers, developing technology for the tiny food processing units, evolving marketing plan covering the recently emerging super markets, DWCRA bazaars, international markets etc., are some of the suggestions. In case of infrastructure, encouraging some large aseptic packaging units, establishment of a radiation technology plant, encouraging private sector in cold storages, precooling units, pack houses etc., establishment of training courses for service and repair of food processing machinery, formation of expert consultant committee and provision of one incubator are the major suggestions. Other major recommendations are provision of insurance facilities to all horticultural crops and livestock products, taking steps to ensure participation of small farmers in the contract farming, launching of a common brand of mango juice and enactment to regulate the feed industry and nurseries in the state.food processing, Andhra Pradesh, India

Socio-economic Impact of Transgenic Cotton

Agricultural and Food Policy,

A Reaction Diffusion Model Of Pattern Formation In Clustering Of Adatoms On Silicon Surfaces

We study a reaction diffusion model which describes the formation of patterns on surfaces having defects. Through this model, the primary goal is to study the growth process of Ge on Si surface. We consider a two species reaction diffusion process where the reacting species are assumed to diffuse on the two dimensional surface with first order interconversion reaction occuring at various defect sites which we call reaction centers. Two models of defects, namely a ring defect and a point defect are considered separately. As reaction centers are assumed to be strongly localized in space, the proposed reaction-diffusion model is found to be exactly solvable. We use Green's function method to study the dynamics of reaction diffusion processes. Further we explore this model through Monte Carlo (MC) simulations to study the growth processes in the presence of a large number of defects. The first passage time statistics has been studied numerically. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4757592]Microelectronics Research Cente

Neutrino Mixings in SO(10) with Type II Seesaw and theta_{13}

We analyze a class of supersymmetric SO(10) grand unified theories with type II seesaw for neutrino masses, where the contribution to PMNS matrix from the neutrino sector has an exact tri-bi-maximal (TBM) form, dictated by a broken S_4 symmetry. The Higgs fields that determine the fermion masses are two 10 fields and one 126 field, with the latter simultaneously contributing to neutrino as well as charged fermion masses. Fitting charged fermion masses and the CKM mixings lead to corrections to the TBM mixing that determine the final PMNS matrix with the predictions theta_{13} ~ 4-6 degrees and the Dirac CP phase to be between -10 and +15 degrees. We also show correlations between various mixing angles which can be used to test the model.Comment: 16 pages, 4 figures, 2 tables; typos corrected in Eq. (4) and Table I

Leptogenesis with TeV Scale Inverse Seesaw in SO(10)

We discuss leptogenesis within a TeV-scale inverse seesaw model for neutrino masses where the seesaw structure is guaranteed by an SO(10) symmetry. Contrary to the TeV-scale type-I gauged seesaw, the constraints imposed by successful leptogenesis in these models are rather weak and allow for the extra gauge bosons W_R and Z' to be in the LHC accessible range. The key differences in the inverse seesaw compared to the type I case are: (i) decay and inverse decay rates larger than the scatterings involving extra gauge bosons due to the large Yukawa couplings and (ii) the suppression of the washout due to very small lepton number breaking.Comment: References and a few comments added, improved figures; version to be published in PR

Disambiguating Seesaw Models using Invariant Mass Variables at Hadron Colliders

We propose ways to distinguish between different mechanisms behind the collider signals of TeV-scale seesaw models for neutrino masses using kinematic endpoints of invariant mass variables. We particularly focus on two classes of such models widely discussed in literature: (i) Standard Model extended by the addition of singlet neutrinos and (ii) Left-Right Symmetric Models. Relevant scenarios involving the same "smoking-gun" collider signature of dilepton plus dijet with no missing transverse energy differ from one another by their event topology, resulting in distinctive relationships among the kinematic endpoints to be used for discerning them at hadron colliders. These kinematic endpoints are readily translated to the mass parameters of the on-shell particles through simple analytic expressions which can be used for measuring the masses of the new particles. A Monte Carlo simulation with detector effects is conducted to test the viability of the proposed strategy in a realistic environment. Finally, we discuss the future prospects of testing these scenarios at the $\sqrt s=14$ and 100 TeV hadron colliders.Comment: 35 pages, 12 figures, 2 tables; minor changes, accepted for publication in JHE

Quark Seesaw, Vectorlike Fermions and Diphoton Excess

We present a possible interpretation of the recent diphoton excess reported by the $\sqrt s=13$ TeV LHC data in quark seesaw left-right models with vectorlike fermions proposed to solve the strong $CP$ problem without the axion. The gauge singlet real scalar field responsible for the mass of the vectorlike fermions has the right production cross section and diphoton branching ratio to be identifiable with the reported excess at around 750 GeV diphoton invariant mass. Various ways to test this hypothesis as more data accumulates at the LHC are proposed.Comment: 18 pages, 6 figures, 1 table; section on high-scale validity and some discussions and references added, version to appear in JHE