Spin-Charge Separation and Kinetic Energy in the t-J Model

I show that spin-charge separation in 2-D t-J model leads to an increase of kinetic energy. Using a sum rule, I derive an exact expression for the lowest possible KE (E_{bound}) for any state without doubly occupied sites. KE of relevant slave-boson and Schwinger-boson mean-field states -- which exhibit complete spin-charge separation -- are found to be much larger than E_{bound}. Examination of n(k) shows that the large increse in KE is due to excessive depletion of electrons from the bottom of the band (Schwinger boson) and of holes from the top (slave boson). To see whether the excess KE is simply due to poor treatment of the constraints, I solve the constraint problem analytically for the Schwinger boson case in the J = 0 limit. This restores gauge invariance, incorrectly violated in MF theories. The result is a generalized Hartree-Fock state of the Hubbard model, but one that includes spin waves. Even after constraints are imposed correctly, the KE remains much larger than E_{bound}. These results support the notion, advanced earlier [PRB 61, 8663 (2000)] that spin-charge separation in the MF state costs excessive KE, and makes the state unstable toward recombination processes which lead to superconductivity in d = 2 and a Fermi liquid state in higher dimensions.Comment: 13 pages, LateX plus three figures. To appear in Phys Rev B Typos correcte

National Administered Protection Agencies: Their Role in the Post-Uruguay Round World

International Relations/Trade,

NATIONAL ADMINISTERED PROTECTION AGENCIES: THEIR ROLE IN THE POST-URUGUAY ROUND WORLD

This paper reviews the role of national administered protection agencies, whose responsibility is the enforcement of national trade remedy laws. After reviewing four recent trade remedy cases we argue that the role of the national administered protection agencies should be changed. Given the additional responsibilities the WTO has assumed in administering the Agreement on Agriculture, the growth of regional integration agreements and the increasing use of anti-dumping and countervailing duty actions against fairly traded imports, we argue that all trade actions should be taken to the WTO for settlement. The role of the national administered protection agencies should be changed to make them agents for trade liberalization. This would involve them taking on three primary functions: 1) as transparency agents; 2) as investigatory agents; and 3) as advocacy agents.International Relations/Trade,

Economic Performance of Bt Cotton Varieties in Pakistan

Farmers in Pakistan have been growing cotton that contains the first generation of Bt gene since 2002. The cultivation of these varieties, although formally unapproved and unregulated, increased rapidly after 2005. In 2007, nearly 60 percent of the cotton area was under BT varieties. This paper examines the economic performance of Bt cotton in Pakistan based on data collected through a structured questionnaire survey in January-February 2009 in two districts (Bahawalpur and Mirpur Khas). The extent of the impact of Bt cotton on costs of production and yield gains are different across the two districts with their diverse agro-climatic conditions and pest pressures. Seed expenditures increase in both districts, but a decline in the number of bollworm sprays and hence in the expenditure for pesticides is observed and total pesticide control costs (for bollworms and non bollworm pests) declines in both districts. Total production costs decline in Bahawalpur but rise in Mirpur Khas. The yield increases are higher in Mirpur Khas as well, resulting in total revenue and gross margins improving more than in Bahawalpur. The results are similar to other studies of Bt cotton in India and suggest gains for Pakistan from progressing to a regulated national market for Bt cotton technologies.Bt cotton, economic performance, Pakistan, Bahawalpur, Mirpur Khas, Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

ANALYZING THE POTENTIAL FOR INCREASED TRADE IN DAIRY PRODUCTS: A CANADIAN PERSPECTIVE

International Relations/Trade,

Distribution of Benefits and Adoption of Bt Cotton in Pakistan: Ex-ante Analysis

This poster presents the potential impact of Bt cotton adoption in Pakistan. The size and distribution of economic benefits from the commercial adoption of Bt cotton in Pakistan are examined under four hypothetical scenarios. The adjusted economic surplus model is used to measure total benefits and their distribution between producers, consumers and technology innovators. To account for uncertainty in key parameters, the stochastic simulation techniques is applied. The results show that the total net benefits of adopting Bt cotton in Pakistan are large. As a result of increase in production, farmers get considerable benefits despite a decline in price. The share of benefits to innovators is small. The results indicate that the total cost of adopting latest Bt technology to the government of Pakistan is less than the benefits that farmers and consumers of all cotton-textile chain can receive. This is true even if the decline in pesticide expenditure and increase in yield are not very large.Bt cotton, economic surplus model, Pakistan, Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

Schwinger-Boson Mean-Field Theory of Mixed-Spin Antiferromagnet L2BaNiO5L_2BaNiO_5

The Schwinger-boson mean-field theory is used to study the three-dimensional antiferromagnetic ordering and excitations in compounds $L_2BaNiO_5$, a large family of quasi-one-dimensional mixed-spin antiferromagnet. To investigate magnetic properties of these compounds, we introduce a three-dimensional mixed-spin antiferromagnetic Heisenberg model based on experimental results for the crystal structure of $L_2BaNiO_5$. This model can explain the experimental discovery of coexistence of Haldane gap and antiferromagnetic long-range order below N\'{e}el temperature. Properties such as the low-lying excitations, magnetizations of $Ni$ and rare-earth ions, N\'{e}el temperatures of different compounds, and the behavior of Haldane gap below the N\'{e}el temperature are investigated within this model, and the results are in good agreement with neutron scattering experiments.Comment: 12 pages, 6 figure

Journal of Natural Products Discovery (JNPD): Covering Natural Products Research From A New Perspective

Natural products have long been utilized as a source of food, medicine and other commercially important materials and products, and because of this, natural products, from plants, microbes or animals, have been studied extensively in the ever-ending search for new products, particularly new drug candidates. Historically, several ‘block buster’ drugs like the anticancer drugs taxol, vincristine and vinblastine, antibiotics like penicillins and cephalosporins, and the narcotic analgesic morphine were discovered from natural sources, either from plants or microbes. Over the last couple of decades, particularly since the appearance of the ‘open access’ platform, the number of journals that claim to cover research in the area of natural products has mushroomed. However, with the exception of a few reputed journals in this area, most of the other journals have become just a business venture, they charge large sum of money from the authors in the name of so called ‘page charge’, ‘processing charge’ or ‘publication charge’, and publish almost anything and everything without assessing the quality of publications. Most often, all these publications are repetitive, the same findings in a new package or even shamelessly plagiarised from previously published articles and have little or no applied scientific values. Moreover, most of the journals catering for natural products research cover mainly academic research without any tangible outcomes or discoveries that can lead to product development.    Journal of Natural Products Discovery (JNPD), which is the official journal of the Centre for Natural Products Discovery (CNPD) at Liverpool John Moores University (LJMU), will stand out from the crowd because of its product-discovery-focussed approach. The coverage will be focussed more to discoveries of new products or new applications of already known natural products in relation to food, pharmaceuticals, cosmetics and other commercial products. The Centre for Natural Products Discovery (CNPD) was founded within the School of Pharmacy and Biomolecular Sciences at LJMU about three years ago with the aim to facilitate world-class research in natural products discovery impacting on societal, national and global needs. This centre has already organised successfully two international conferences in 2020 and 2021, and the third anniversary conference will be held in March 2022.  A brand-new MSc programme in Natural Products Discovery was launched last year, as a part of the initiatives from CNPD to embed natural products research and to disseminate knowledge at various levels.  Similarly, a monthly research newsletter was also launched a year ago to capture various activities of the centre. Publication of this new journal will further strengthen the activities of the centre and this journal will become one of the main outlets for communicating our research activities to a wider audience using the open access platform, sponsored by the LJMU Library. In this connection, we gratefully acknowledge the outstanding support and assistance that we have received from Ms Catherine Dishman to establish this platform and set up the journal online submission system. We would also like to express our gratitude to our colleague Dr Jose Prieto Garcia (Executive Editor-in-Chief), who worked closely with Catherine, all other colleagues of the CNPD and us to establish this journal, and to make this very first issue possible. This journal is in open access, and there is no charge whatsoever levied to the authors, meaning the publication in this journal is completely free! We hope this journal will grow rapidly as one of the leading journals in the field of natural products research and will attract the finest quality publications from researcher from all over the world

A quantitative model for disruption mitigation in a supply chain

© 2016 Elsevier B.V. In this paper, a three-stage supply chain network, with multiple manufacturing plants, distribution centers and retailers, is considered. For this supply chain system we develop three different approaches, (i) an ideal plan for an infinite planning horizon and an updated plan if there are any changes in the data, (ii) a predictive mitigation planning approach for managing predictive demand changes, which can be predicted in advance by using an appropriate tool, and (iii) a reactive mitigation plan, on a real-time basis, for managing sudden production disruptions, which cannot be predicted in advance. In predictive mitigation planning, we develop a fuzzy inference system (FIS) tool to predict the changes in future demand over the base forecast and the supply chain plan is revised accordingly well in advance. In reactive mitigation planning, we formulate a quantitative model for revising production and distribution plans, over a finite future planning period, while minimizing the total supply chain cost. We also consider a series of sudden disruptions, where a new disruption may or may not affect the recovery plans of earlier disruptions and which consequently require plans to be revised after the occurrence of each disruption on a real-time basis. An efficient heuristic, capable of dealing with sudden production disruptions on a real-time basis, is developed. We compare the heuristic results with those obtained from the LINGO optimization software for a good number of randomly generated test problems. Also, some numerical examples are presented to explain both the usefulness and advantages of the proposed approaches