Optimal opportunistic routing and network coding for bidirectional wireless flows

There is growing interest in recent years in routing methods for wireless networks that leverage the broadcast nature of the wireless medium and the ability of nodes to overhear their neighbors’ transmissions. Such methods include opportunistic routing (OR), which generally choose the next hop on a routing path only after the outcome of the previous transmission is known; and wireless network coding (NC), which linearly combines packets from different flows coexisting in the network. In this paper, we study the potential benefits of forwarding schemes that combine elements from both the OR and NC approaches, when traffic on a bidirectional unicast connection between two nodes is relayed by multiple common neighbors. We present a theoretically optimal scheme that provides a lower bound on the expected number of transmissions required to communicate a packet in both directions as a function of link error probabilities, and demonstrate that this bound can be up to 20% lower than with either OR or NC employed alone even in a small network. Using simulation, we further explore the control overhead in a direct implementation of the scheme with a simple coordination mechanism and show that the optimal bound can be closely approached for a wide range of link error rates.     

Molecular genetic evidence for the conversion hypothesis of the origin of malignant mixed müllerian tumours

The origin of malignant mixed Müllerian tumours (MMMTs) has long been debated, due to the indefinite relationship between epithelial and mesenchymal malignant cells. In order to obtain insight into the clonal relationship between the two components of these tumours, molecular genetic changes were investigated at the level of loss of heterozygosity (LOH) in both cells types. LOH was studied in a series of six cases with 74 polymorphic microsatellite markers mapping to 19 different chromosomes. The epithelial and the mesenchymal neoplastic cells were separately microdissected from formalin-fixed, paraffin-embedded tissue, prior to DNA isolation. LOH was observed for 35 different markers mapping to chromosomes 3, 6, 8, 11, 15, 16, 17, 18, 21, and X. The most frequently involved chromosomes were 17p, 17q, 11q, 15q, and 21q. LOH was observed in five out of six cases and identical alleles were lost in the epithelial and in the mesenchymal cells. No genetic differences were observed between the two cell types for any of the informative markers. Immunohistochemistry (IHC) and TP53 mutation analysis revealed involvement of TP53 in all cases. Mutations were identified in five MMMTs. In four tumours, of which three had a missense mutation, strong nuclear staining for p53 was observed. In the remaining two cases, the mutation resulted in a stop codon, with no nuclear staining for p53 by IHC. The results support a monoclonal origin of MMMTs, with the absence of genetic changes uniquely associated with either of the phenotypes. The latter finding is compatible with current opinion that these neoplasms should be considered as metaplastic carcinomas and supports the conversion hypothesis.     

Ca2+ flux through promiscuous cardiac Na+ channels: slip-mode conductance

The tetrodotoxin-sensitive sodium ion (Na+) channel is opened by cellular depolarization and favors the passage of Na+ over other ions. Activation of the beta-adrenergic receptor or protein kinase A in rat heart cells transformed this Na+ channel into one that is promiscuous with respect to ion selectivity, permitting calcium ions (Ca2+) to permeate as readily as Na+. Similarly, nanomolar concentrations of cardiotonic steroids such as ouabain and digoxin switched the ion selectivity of the Na+ channel to this state of promiscuous permeability called slip-mode conductance. Slip-mode conductance of the Na+ channel can contribute significantly to local and global cardiac Ca2+ signaling and may be a general signaling mechanism in excitable cells.     

Anterior segment sparing to reduce charged particle radiotherapy complications in uveal melanoma

PURPOSE: The purpose of this investigation is to delineate the risk factors in the development of neovascular glaucoma (NVG) after helium-ion irradiation of uveal melanoma patients and to propose treatment technique that may reduce this risk. METHODS AND MATERIALS: 347 uveal melanoma patients were treated with helium-ions using a single-port treatment technique. Using univariate and multivariate statistics, the NVG complication rate was analyzed according to the percent of anterior chamber in the radiation field, tumor size, tumor location, sex, age, dose, and other risk factors. Several University of California San Francisco-Lawrence Berkeley National Laboratory (LBNL) patients in each size category (medium, large, and extralarge) were retrospectively replanned using two ports instead of a single port. By using appropriate polar and azimuthal gaze angles or by treating patients with two ports, the maximum dose to the anterior segment of the eye can often be reduced. Although a larger volume of anterior chamber may receive a lower dose by using two ports than a single port treatment. We hypothesize that this could reduce the level of complications that result from the irradiation of the anterior chamber of the eye. Dose-volume histograms were calculated for the lens, and compared for the single and two-port techniques. RESULTS: NVG developed in 121 (35%) patients. The risk of NVG peaked between 1 and 2.5 years posttreatment. By univariate and multivariate analysis, the percent of lens in the field was strongly correlated with the development of NVG. Other contributing factors were tumor height, history of diabetes, and vitreous hemorrhage. Dose-volume histogram analysis of single-port vs. two-port techniques demonstrate that for some patients in the medium and large category tumor groups, a significant decrease in dose to the structures in the anterior segment of the eye could have been achieved with the use of two ports. CONCLUSION: The development of NVG after helium-ion irradiation is correlated to the amount of lens, anterior chamber in the treatment field, tumor height, proximity to the fovea, history of diabetes, and the development of vitreous hemorrhage. Although the influence of the higher LET deposition of helium-ions is unclear, this study suggests that by reducing the dose to the anterior segment of the eye may reduce the NVG complications. Based on this retrospective analysis of LBNL patients, we have implemented techniques to reduce the amount of the anterior segment receiving a high dose in our new series of patients treated with protons using the cyclotron at the UC Davis Crocker Nuclear Laboratory (CNL).     

The abundance and organization of polypeptides associated with antigens of the Rh blood group system

Twelve murine monoclonal antibodies, which react with human red cells of common Rh phenotype but give weak or negative reactions with Rh null erythrocytes, were used in quantitative binding assays and competitive binding assays to investigate the abundance and organization of polypeptides involved in the expression of antigens of the Rh blood group system. Antibodies of the R6A-type (R6A, BRIC-69, BRIC-207) and the 2D10-type (MB-2D10, LA18.18, LA23.40) recognize related structures and 100,000-200,000 molecules of each antibody bind maximally to erythrocytes of common Rh phenotype. Antibodies of the BRIC-125 type (BRICs 32, 122, 125, 126, 168, 211) recognize structures that are unrelated to those recognized by R6A-type and 2D10-type antibodies and between 10,000 and 50,000 antibody molecules bind maximally to erythrocytes of the common Rh phenotype. The binding of antibodies of the R6A-type and the 2D10-type, but not of antibodies of the BRIC-125-type could be partially inhibited by human anti-D antibodies (polyclonal and monoclonal) and a murine anti-e-like antibody. These results are consistent with evidence (Moore & Green 1987; Avent et al., 1988b) that the Rh blood group antigens are associated with a complex that comprises two groups of related polypeptides of M(r) 30,000 and M(r) 35,000-100,000, respectively, and suggest that there are 1-2 x 10(5) copies of this complex per erythrocyte. The polypeptide recognized by antibodies of the BRIC-125 type is likely to be associated with this complex.