Magnetic properties of the spin S=1/2S=1/2 Heisenberg chain with hexamer modulation of exchange

We consider the spin-1/2 Heisenberg chain with alternating spin exchange %on even and odd sites in the presence of additional modulation of exchange on odd bonds with period three. We study the ground state magnetic phase diagram of this hexamer spin chain in the limit of very strong antiferromagnetic (AF) exchange on odd bonds using the numerical Lanczos method and bosonization approach. In the limit of strong magnetic field commensurate with the dominating AF exchange, the model is mapped onto an effective $XXZ$ Heisenberg chain in the presence of uniform and spatially modulated fields, which is studied using the standard continuum-limit bosonization approach. In absence of additional hexamer modulation, the model undergoes a quantum phase transition from a gapped string order into the only one gapless L\"uttinger liquid (LL) phase by increasing the magnetic field. In the presence of hexamer modulation, two new gapped phases are identified in the ground state at magnetization equal to 1/3 and 2/3 of the saturation value. These phases reveal themselves also in magnetization curve as plateaus at corresponding values of magnetization. As the result, the magnetic phase diagram of the hexamer chain shows seven different quantum phases, four gapped and three gapless and the system is characterized by six critical fields which mark quantum phase transitions between the ordered gapped and the LL gapless phases.Comment: 21 pages, 5 figures, Journal of Physics: Condensed Matter, 24, 116002, (2012

Dual-band dual linear to circular polarization converter in transmission mode-application to K/Ka-band satellite communications

Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications, the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm ×5.3 mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer.info:eu-repo/semantics/acceptedVersio

Full-wave evaluation of a 40 dBi: Transmit-array for Ka-band SoTM

Transmit-array (TA) antennas have been shown to be a cost-effective solution for the new generation of satellite communications. These antennas are usually composed by thousands of fine-tuned subwavelength unit-cells. Therefore, full-wave evaluations become quite challenging as the required gain increases, constraining the antenna design and optimization. This is aggravated by the fact that, when beam scanning is required, higher gains cannot be obtained by simply scaling a given design. In fact, for a F/D ratio, the maximum gain of the TA is limited by the scanning aberrations. Recently, we have proposed a new phase compensation law for the TA, designated as the bifocal correction, that allows to overcome the usual gain/scanning tradeoff limit. However, due to the lack of computational resources, we were only able to demonstrate this concept for a 40 dBi TA using PO/GO methods. In this communication we present the full-wave performance of this 40 dBi bifocal TA design using a new efficient numerical evaluation method, properly validated with a smaller 30 dBi TA.info:eu-repo/semantics/acceptedVersio

Equivalent dielectric description of transmit-arrays as an efficient and accurate method of analysis

Transmit-arrays (TAs) provide cost-effective solutions for various antenna applications, including satellite and terrestrial communications. Usually, these antennas have electrically large apertures, comprising thousands of fine-tuned subwavelength unit-cells. This makes full-wave simulations demanding in terms of computational resources, constraining the antenna design and optimization. Herein, we present an efficient method for the reduction of the TA's computational complexity that still provides accurate results for the main figures of merit of the antenna. For the chosen example, the simulation was 3 times faster and required 50% less memory. Yet, as the complexity of the problem is further scaled, this method is expected to become even more effective.info:eu-repo/semantics/acceptedVersio

Wide-angle mechanical scanning Transmit-arrays for satellite Ka-band user terminals

The antenna design for broadband satellite communications is particularly challenging, new cost-effective solutions are still needed. An overview of recent contributions from the authors on planar transmit-arrays (TAs) for satellite Kaband user terminals is presented. We tackle several design problems: how to improve the scanning coverage using low cost mechanical beam steering, how to choose the type of unit cells that compose the TA, how to devise a single aperture with high gain that operates simultaneous at two widely separate frequency bands. Different prototypes are used to conduct these studies. All these TAs provide wide beam zenith scanning, [-50º,50º] with less that 3dB of scan loss, good circular polarization performance and low beam distortions. The prototypes have the same aperture size, 195 × 145 mm2, that provide gains up to 29 dBi for 30 GHz.info:eu-repo/semantics/acceptedVersio

Curcumin: A new candidate for melanoma therapy?

Melanoma remains among the most lethal cancers and, in spite of great attempts that have been made to increase the life span of patients with metastatic disease, durable and complete remissions are rare. Plants and plant extracts have long been used to treat a variety of human conditions; however, in many cases, effective doses of herbal remedies are associated with serious adverse effects. Curcumin is a natural polyphenol that shows a variety of pharmacological activities including anti-cancer effects, and only minimal adverse effects have been reported for this phytochemical. The anti-cancer effects of curcumin are the result of its anti-angiogenic, pro-apoptotic and immunomodulatory properties. At the molecular and cellular level, curcumin can blunt epithelial-to-mesenchymal transition and affect many targets that are involved in melanoma initiation and progression (e.g., BCl2, MAPKS, p21 and some microRNAs). However, curcumin has a low oral bioavailability that may limit its maximal benefits. The emergence of tailored formulations of curcumin and new delivery systems such as nanoparticles, liposomes, micelles and phospholipid complexes has led to the enhancement of curcumin bioavailability. Although in vitro and in vivo studies have demonstrated that curcumin and its analogues can be used as novel therapeutic agents in melanoma, curcumin has not yet been tested against melanoma in clinical practice. In this review, we summarized reported anti-melanoma effects of curcumin as well as studies on new curcumin formulations and delivery systems that show increased bioavailability. Such tailored delivery systems could pave the way for enhancement of the anti-melanoma effects of curcumin. © 2016 UIC

Evaluation of Turbulence Models Performance in Predicting Incipient Cavitation in an Enlarged Step-Nozzle

Predictive capability of RANS and LES models to calculate incipient cavitation of water in a step nozzle is assessed. The RANS models namely, Realizable k-?, SST k-? and Reynolds Stress Model did not predict any cavitation, due to the limitation of RANS models to predict the low pressure vortex cores. LES WALE model was able to predict the cavitation by capturing the shear layer instability and vortex shedding. The performance of a barotropic cavitation model and Rayleigh-Plesset-based cavitation models was compared using WALE model. Although the phase change formulation is different in these models, the predicted cavitation and flow field were not significantly different

Design, fabrication and characterization of the first AC-coupled silicon microstrip sensors in India

This paper reports the design, fabrication and characterization of single-sided silicon microstrip sensors with integrated biasing resistors and coupling capacitors, produced for the first time in India. We have first developed a prototype sensor on a four-inch wafer. After finding suitable test procedures for characterizing these AC coupled sensors, we have fine-tuned various process parameters in order to produce sensors with the desired specifications.Comment: 10 pages, 11 figures, 1 table, to appear in JINS

Evaluation of relative suitability of six cultivars of potato to the tomato leafminer, Tuta absoluta (Lep.: Gelechidae)

The tomato leafminer, Tuta absoluta (Meyrick), is an important pest of potato, Solanum tuberosum L., in the world. In this research, life history parameters of this pest were studied on six potato cultivars including: Impala, Agria, Savalan, Florida, Emeraude and Markies. The development time of larvae on Florida and Impala was significantly longer than of that on Markies and Emeraude. The lowest survival rate from egg to adult was observed on Florida (60.48%). The number of eggs laid per female on Florida was significantly lower than on Agria, Savalan, Markies and Emeraude, but no significant difference was found between Impala and Florida. The lowest intrinsic rate of increase (rm) (0.058 day-1) and the lowest finite rate of increase (λ) (1.059 day-1) were recorded on Florida. Moreover, the longest generation time (T) (33.60 days) and the longest doubling time (DT) (11.93 days) was significantly observed on Florida. Therefore, it could be concluded that Florida is the least suitable host to T. absoluta amongst the six tested cultivars of potato. These results could be useful in integrated management programs of T. absoluta in potato fields