Magnetic Field Induced Instabilities In Localized Two-Dimensional Electron Systems

The results of extensive transport studies in localized regime of mesoscopic two-dimensional electron systems (2DES) with varying disorder are presented. A quick overview of previously achieved result is given. The main focus is on the observation of density dependent instabilities manifested by strong resistance oscillations induced by high perpendicular magnetic fields B-perpendicular to. While the amplitude of the oscillations is strongly enhanced with increasing B-perpendicular to, their position in electron density remains unaffected. The temperature dependence of resistivity shows a transition from an activated behaviour at high temperature to a saturated behaviour at low T. In the positions of resistance minima, the T dependence can even become metal-like (d rho/dT > 0). The activation energies obtained from the high T behaviour exhibit a formation of plateaux in connection with the resistance oscillations when analyzed as a function of electron density. We suggest the interplay between a strongly interacting electron phase and the background disorder as a possible explanation for our observation.

Factors affecting localized abundance and distribution of lesser mealworm in earth-floor broiler houses in subtropical Australia.

Factors that influence the localized abundance and distribution of lesser mealworm, Alphitobius diaperinus (Panzer), in litter of two compacted earth-floor broiler houses in subtropical Australia were studied using various experimental manipulations. Numbers of lesser mealworms substantially increased inside caged areas and under uncaged empty feed pans placed in open areas of the houses. These populations were found to be localized and independent of chicken-feed, manure, and high beetle populations that normally occur under existing feed pans. Substantial horizontal movement of larvae to under feed pans was recorded. Placing metal barriers around these pans significantly restricted this movement. In almost all treatments, lesser mealworms typically peaked in numbers during the middle of the flock time. This temporal pattern of abundance also was observed under pans within barriers, where relatively low insect numbers occurred, but it was not observed in uncaged open areas (where chickens had complete access). It is likely that larvae do not establish in open areas, but fluctuate in numbers as they either move to refuges away from chickens or suffer high rates of mortality. In these refuges, larvae peak in numbers and then leave the litter environment to pupate in the earth floor before the end of the flock time. This behavior might be exploited for management of lesser mealworm by targeting applications of control agents.

Hanging drop: An in vitro air toxic exposure model using human lung cells in 2D and 3D structures

Using benzene as a candidate air toxicant and A549 cells as an in vitro cell model, we have developed and validated a hanging drop (HD) air exposure system that mimics an air liquid interface exposure to the lung for periods of 1 h to over 20 days. Dose response curves were highly reproducible for 2D cultures but more variable for 3D cultures. By comparing the HD exposure method with other classically used air exposure systems, we found that the HD exposure method is more sensitive, more reliable and cheaper to run than medium diffusion methods and the CULTEX (R) system. The concentration causing 50% of reduction of cell viability (EC50) for benzene, toluene, p-xylene, m-xylene and o-xylene to A549 cells for 1 h exposure in the HD system were similar to previous in vitro static air exposure. Not only cell viability could be assessed but also sub lethal biological endpoints such as DNA damage and interleukin expressions. An advantage of the HD exposure system is that bioavailability and cell concentrations can be derived from published physicochemical properties using a four compartment mass balance model. The modelled cellular effect concentrations EC50(cell) for 1 h exposure were very similar for benzene, toluene and three xylenes and ranged from 5 to 15 mmol/kg(dry weight) which corresponds to the intracellular concentration of narcotic chemicals in many aquatic species, confirming the high sensitivity of this exposure method. (C) 2013 Elsevier B.V. All rights reserved.

Resistance Minimum in Dilute Magnetic Alloys in the Absence of Impurity Moments

A possible mechanism for the resistance minimum in dilute alloys in which the localized impurity states are non-magnetic is suggested. The fact is considered that what is essential to the Kondo-like behaviour is the interaction of the conduction electron spin s with the internal dynamical degrees of freedom of the impurity centre. The necessary internal dynamical degrees of freedom are provided by the dynamical Jahn-Teller effect associated with the degenerate 3d-orbitals of the transition-metal impurities interacting with the surrounding (octahedral) complex of the nearest-neighbour atoms. The fictitious spin I characterizing certain low-lying vibronic states of the system is shown to couple with the conduction electron spin s via s-d mixing and spin-orbit coupling, giving rise to a singular temperature-dependent exchange-like interaction. The resistivity so calculated is in fair agreement with the experimental results of Cape and Hake for Ti containing 0.2 at% of Fe.

Diffusion of localized optical excitations and trap emission in ruby

Using the critical percolation conductance method the energy-dependent diffusion coefficient associated with thermally assisted transfer of the R1 line excitation between single Cr3+ ions with strain-induced randomness has been calculated in the 4A2 to E(2E) transition energies. For localized states sufficiently far away from the mobility edge the energy transfer is dominated by dipolar interactions, while very close to the mobility edge it is determined by short-range exchange interactions. Using the above energy-dependent diffusion coefficient a macroscopic diffusion equation is solved for the rate of light emission by Cr3+ ion-pair traps to which single-ion excitations are transferred. The dipolar mechanism leads to good agreement with recent measurements of the pair emission rate by Koo et al. (Phys. Rev. Lett., vol.35, p.1669 (1975)) right up to the mobility edge.

Unravelling the self-assembly of hydrogen bonded NDI semiconductors in 2D and 3D

Supramolecular ordering of organic semiconductors is the key factor defining their electrical characteristics. Yet, it is extremely difficult to control, particularly at the interface with metal and dielectric surfaces in semiconducting devices. We have explored the growth of n-type semiconducting films based on hydrogen-bonded monoalkylnaphthalenediimide (NDI-R) from solution and through vapor deposition on both conductive and insulating surfaces. We combined scanning tunneling and atomic force microscopies with X-ray diffraction analysis to characterize, at the submolecular level, the evolution of the NDI-R molecular packing in going from monolayers to thin films. On a conducting (graphite) surface, the first monolayer of NDI-R molecules adsorbs in a flat-lying (face-on) geometry, whereas in subsequent layers the molecules pack edge-on in islands (Stranski–Krastanov-like growth). On SiO2, the NDI-R molecules form into islands comprising edge-on packed molecules (Volmer–Weber mode). Under all the explored conditions, self-complementary H bonding of the imide groups dictates the molecular assembly. The measured electron mobility of the resulting films is similar to that of dialkylated NDI molecules without H bonding. The work emphasizes the importance of H bonding interactions for controlling the ordering of organic semiconductors, and demonstrates a connection between on-surface self-assembly and the structural parameters of thin films used in electronic devices.

A Slotted Aloha joint MAC-cum-Routing protocol for data gathering sensor network applications

In this paper we have proposed and implemented a joint Medium Access Control (MAC) -cum- Routing scheme for environment data gathering sensor networks. The design principle uses node 'battery lifetime' maximization to be traded against a network that is capable of tolerating: A known percentage of combined packet losses due to packet collisions, network synchronization mismatch and channel impairments Significant end-to-end delay of an order of few seconds We have achieved this with a loosely synchronized network of sensor nodes that implement Slotted-Aloha MAC state machine together with route information. The scheme has given encouraging results in terms of energy savings compared to other popular implementations. The overall packet loss is about 12%. The battery life time increase compared to B-MAC varies from a minimum of 30% to about 90% depending on the duty cycle.

A 3D in vitro model reflecting the androgen deprivation state in prostate cancer bone metastasis

In castrate-resistant prostate cancer (CRPC), the prevailing organ for metastasis is bone, where the survival of cancer cells is regulated by the permissive metastatic niche offered by the bone marrow. The tumour microenvironment and cellular interactions with the matrix and bone cells enable metastasis and lead to cancer cells becoming androgen resistant. Hence, 3D models that mimic CRPC in terms of an androgen deprivation state (ADS) are needed to identify the mechanisms for CPRC growth in bone and further develop therapeutic strategies.

Jointly optimal power control and routing for a single cell, dense, ad hoc wireless network

We consider a dense, ad hoc wireless network confined to a small region, such that direct communication is possible between any pair of nodes. The physical communication model is that a receiver decodes the signal from a single transmitter, while treating all other signals as interference. Data packets are sent between source-destination pairs by multihop relaying. We assume that nodes self-organise into a multihop network such that all hops are of length d meters, where d is a design parameter. There is a contention based multiaccess scheme, and it is assumed that every node always has data to send, either originated from it or a transit packet (saturation assumption). In this scenario, we seek to maximize a measure of the transport capacity of the network (measured in bit-meters per second) over power controls (in a fading environment) and over the hop distance d, subject to an average power constraint. We first argue that for a dense collection of nodes confined to a small region, single cell operation is efficient for single user decoding transceivers. Then, operating the dense ad hoc network (described above) as a single cell, we study the optimal hop length and power control that maximizes the transport capacity for a given network power constraint. More specifically, for a fading channel and for a fixed transmission time strategy (akin to the IEEE 802.11 TXOP), we find that there exists an intrinsic aggregate bit rate (Theta(opt) bits per second, depending on the contention mechanism and the channel fading characteristics) carried by the network, when operating at the optimal hop length and power control. The optimal transport capacity is of the form d(opt)((P) over bar (t)) x Theta(opt) with d(opt) scaling as (P) over bar (1/eta)(t), where (P) over bar (t) is the available time average transmit power and eta is the path loss exponent. Under certain conditions on the fading distribution, we then provide a simple characterisation of the optimal operating point.

Localized reversible nanoscale phase separation in Pr0.63Ca0.37MnO3 single crystal using a scanning tunneling microscope tip

We report the destabilization of the charge ordered insulating (COI) state in a localized region of Pr0.63Ca0.37MnO3 single crystal by current injection using a scanning tunneling microscope tip. This leads to controlled phase separation and formation of localized metallic nanoislands in the COI matrix which have been detected by local tunneling conductance mapping. The metallic regions thus created persist even after reducing the injected current to lower values. The original conductance state can be restored by injecting a current of similar magnitude but of opposite polarity. We thus achieve reversible nanoscale phase separation that gives rise to the possibility to "write, read, and erase" nanosized conducting regions in an insulating matrix with high spatial resolution. (c) 2007 American Institute of Physics.

3D extracellular matrix interactions modulate tumour cell growth, invasion and angiogenesis in engineered tumour microenvironments

Interactions between tumour cells and extracellular matrix proteins of the tumour microenvironment play crucial roles in cancer progression. So far, however, there are only a few experimental platforms available that allow us to study these interactions systematically in a mechanically defined three-dimensional (3D) context. Here, we have studied the effect of integrin binding motifs found within common extracellular matrix (ECM) proteins on 3D breast (MCF-7) and prostate (PC-3, LNCaP) cancer cell cultures, and co-cultures with endothelial and mesenchymal stromal cells. For this purpose, matrix metalloproteinase-degradable biohybrid poly(ethylene) glycol-heparin hydrogels were decorated with the peptide motifs RGD, GFOGER (collagen I), or IKVAV (laminin-111). Over 14 days, cancer spheroids of 100-200µm formed. While the morphology of poorly invasive MCF-7 and LNCaP cells was not modulated by any of the peptide motifs, the aggressive PC-3 cells exhibited an invasive morphology when cultured in hydrogels comprising IKVAV and GFOGER motifs compared to RGD motifs or nonfunctionalised controls. PC-3 (but not MCF-7 and LNCaP) cell growth and endothelial cell infiltration were also significantly enhanced in IKVAV and GFOGER presenting gels. Taken together, we have established a 3D culture model that allows for dissecting the effect of biochemical cues on processes relevant to early cancer progression. These findings provide a basis for more mechanistic studies that may further advance our understanding of how ECM modulates cancer cell invasion and how to ultimately interfere with this process.

Providing QoS to Real and Data Applications in WiMAX Mesh Networks

We consider the problem of centralized routing and scheduling for IEEE 802.16 mesh networks so as to provide Quality of Service (QoS) to individual real and interactive data applications. We first obtain an optimal and fair routing and scheduling policy for aggregate demands for different source- destination pairs. We then present scheduling algorithms which provide per flow QoS guarantees while utilizing the network resources efficiently. Our algorithms are also scalable: they do not require per flow processing and queueing and the computational requirements are modest. We have verified our algorithms via extensive simulations.

Handling sectional views in volume-based approach to automatically construct 3D solid from 2D views

This paper presents an algorithm for solid model reconstruction from 2D sectional views based on volume-based approach. None of the existing work in automatic reconstruction from 2D orthographic views have addressed sectional views in detail. It is believed that the volume-based approach is better suited to handle different types of sectional views. The volume-based approach constructs the 3D solid by a boolean combination of elementary solids. The elementary solids are formed by sweep operation on loops identified in the input views. The only adjustment to be made for the presence of sectional views is in the identification of loops that would form the elemental solids. In the algorithm, the conventions of engineering drawing for sectional views, are used to identify the loops correctly. The algorithm is simple and intuitive in nature. Results have been obtained for full sections, offset sections and half sections. Future work will address other types of sectional views such as removed and revolved sections and broken-out sections. (C) 2004 Elsevier Ltd. All rights reserved.

Localized agglutinin staining in muscle capillaries from normal and very old atrophic human muscle using winged bean ( Psophocarpus tetragonolobus ) lectin

The winged bean (Psophocarpus tetragonolobus) agglutinin (total lectin) and its basic (WBA I) and acidic isoform (WBA II) were used to analyze capillaries in sections from human muscle. The microvessels were clearly labeled after incubation with the lectins in both normal muscle and in old muscles with age-related type II atrophy or muscle fiber grouping. Muscle fibers, nerves, and connective tissue remained unstained. The total lectin detected muscle capillaries from all blood group AB0 individuals. The isoform WBA I reacted only with blood vessels in blood group A and B individuals, while the blood vessels in blood group 0 individuals were demonstrated with WBA II. WBA I staining was inhibited by p-nitrophenyl α-galactopyranoside and N-acetylgalactosamine, whereas 2′-fucosyllactose and preincubation with an antibody against type-1 chain H abolished capillary staining with WBA II. The study demonstrates the usefulness of WBA as a marker of capillaries in human muscle.

Localized modes due to impurities in caesium iodide

The nature of the localized modes due to single substitutional impurities in a caesium iodide lattice is investigated using the models of Elliott, Dawber and Maradudin. The infra-red absorption due to U centres and their relation to the lattice spacing is also discussed.