Efficient computation of volume fractions for multi-material cell complexes in a grid by slicing

The paper presents a novel slicing based method for computation of volume fractions in multi-material solids given as a B-rep whose faces are triangulated and shared by either one or two materials. Such objects occur naturally in geoscience applications and the said computation is necessary for property estimation problems and iterative forward modeling. Each facet in the model is cut by the planes delineating the given grid structure or grid cells. The method, instead of classifying the points or cells with respect to the solid, exploits the convexity of triangles and the simple axis-oriented disposition of the cutting surfaces to construct a novel intermediate space enumeration representation called slice-representation, from which both the cell containment test and the volume-fraction computation are done easily. Cartesian and cylindrical grids with uniform and non-uniform spacings have been dealt with in this paper. After slicing, each triangle contributes polygonal facets, with potential elliptical edges, to the grid cells through which it passes. The volume fractions of different materials in a grid cell that is in interaction with the material interfaces are obtained by accumulating the volume contributions computed from each facet in the grid cell. The method is fast, accurate, robust and memory efficient. Examples illustrating the method and performance are included in the paper.

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.

The application of islanded photovoltaic cells and battery storage on the reliability of distribution networks

Renewable energy resources, in particularly PV and battery storage are increasingly becoming part of residential and agriculture premises to manage their electricity consumption. This thesis addresses the tremendous technical, financial and planning challenges for utilities created by these increases, by offering techniques to examine the significance of various renewable resources in electricity network planning. The outcome of this research should assist utilities and customers for adequate planning that can be financially effective.

Synthesis of Diketopyrrolopyrrole Containing Copolymers: A Study of Their Optical and Photovoltaic Properties

The diketopyrrolopyrrole-based copolymers PDPP-BBT and TDPP-BBT were synthesized and used as donor for bulk heterojunction photovoltaic devices. The photophysical properties of these polymers showed absorption in the range 500-600 nm with a maximum peak around 563 nm, while TDPP-BBT showed broadband absorption in the range 620 - 800 nm with a peak around 656 nm. The power conversion efficiencies (PCE) of the polymer solar cells based on these copolymers and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were 0.68% (as cast PDPP-BBT:PCBM), 1.51% (annealed PDPP-BBT:PCBM), 1.57% (as cast TDPPBBT: PCBM), and 2.78% (annealed TDPP-BBT:PCBM), under illumination of AM 1.5 (100 mW/cm2). The higher PCE for TDPP-BBT-based polymer solar cells has been attributed to the low band gap of this copolymer as compared to PDPP-BBT, which increases the numbers of photogenerated excitons and corresponding photocurrent of the device. These results indicate that PDPP-BBT and TDPP-BBT act as excellent electron donors for bulk heterojunction devices.

New insights from a fixed-point analysis of single cell IEEE 802.11 WLANs

We study a fixed-point formalization of the well-known analysis of Bianchi. We provide a significant simplification and generalization of the analysis. In this more general framework, the fixed-point solution and performance measures resulting from it are studied. Uniqueness of the fixed point is established. Simple and general throughput formulas are provided. It is shown that the throughput of any flow will be bounded by the one with the smallest transmission rate. The aggregate throughput is bounded by the reciprocal of the harmonic mean of the transmission rates. In an asymptotic regime with a large number of nodes, explicit formulas for the collision probability, the aggregate attempt rate, and the aggregate throughput are provided. The results from the analysis are compared with ns2 simulations and also with an exact Markov model of the backoff process. It is shown how the saturated network analysis can be used to obtain TCP transfer throughputs in some cases.

Biology and Molecular Markers of Malignant Gonadal Germ Cell Tumors

Germ cell tumors occur both in the gonads of both sexes and in extra-gonadal sites during adoles-cence and early adulthood. Malignant ovarian germ cell tumors are rare neoplasms accounting for less than 5% of all cases of ovarian malignancy. In contrast, testicular cancer is the most common malignancy among young males. Most of patients survive the disease. Prognostic factors of gonadal germ cell tumors include histology, clinical stage, size of the primary tumor and residua, and levels of tumor markers. Germ cell tumors include heterogeneous histological subgroups. The most common subgroup includes germinomas (ovarian dysgerminoma and testicular seminoma); other subgroups are yolk sac tumors, embryonal carcinomas, immature teratomas and mixed tumors. The origin of germ cell tumors is most likely primordial germ cells. Factors behind germ cell tumor development and differentiation are still poorly known. The purpose of this study was to define novel diagnostic and prognostic factors for malignant gonadal germ cell tumors. In addition, the aim was to shed further light into the molecular mechanisms regulating gonadal germ cell tumorigenesis and differentiation by studying the roles of GATA transcription factors, pluripotent factors Oct-3/4 and AP-2γ, and estrogen receptors. This study revealed the prognostic value of CA-125 in malignant ovarian germ cell tumors. In addition advanced age and residual tumor had more adverse outcome. Several novel markers for histological diagnosis were defined. In the fetal development transcription factor GATA-4 was expressed in early fetal gonocytes and in testicular carcinoma precursor cells. In addition, GATA-4 was expressed in both gonadal germinomas, thus it may play a role in the development and differentiation of the germinoma tumor subtype. Pluripotent factors Oct-3/4 and AP-2γ were expressed in dysgerminomas, thus they could be used in the differential diagnosis of the germ cell tumors. Malignant ovarian germ cell tumors expressed estrogen receptors and their co-regulator SNURF. In addition, estrogen receptor expression was up-regulated by estradiol stimulation. Thus, gonadal steroid hormone burst in puberty may play a role in germ cell tumor development in the ovary. This study shed further light in to the molecular pathology of malignant gonadal germ cell tumors. In addition, some novel diagnostic and prognostic factors were defined. This data may be used in the differential diagnosis of germ cell tumor patients.

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.