Characterization of optical communication in a leader-follower unmanned underwater vehicle formation

As part of the research to development an optical communication design of a leader-follower formation between unmanned underwater vehicles (UUVs), this paper presents light field characterization and design configuration of the hardware required to allow the use of distance detection between UUVs. The study specifically is targeting communication between remotely operated vehicles (ROVs). As an initial step in this study, the light field produced from a light source mounted on the leader UUV was empirically characterized and modeled. Based on the light field measurements, a photo-detector array for the follower UUV was designed. Evaluation of the communication algorithms to monitor the UUV’s motion was conducted through underwater experiments in the Ocean Engineering Laboratory at the University of New Hampshire. The optimal spectral range was determined based on the calculation of the diffuse attenuation coefficients by using two different light sources and a spectrometer. The range between the leader and the follower vehicles for a specific water type was determined. In addition, the array design and the communication algorithms were modified according to the results from the light field

Evaluation of Detector Array Designs for Optical Communication Between Unmanned Underwater Vehicle

The communication interface is essential for unmanned underwater vehicles (UUVs) to interact with each other or with a stationary target, such as docking station. In this paper, we investigate different optical array designs using a simulator. In addition to the hardware characteristics (e.g., sensitivity of the detectors and noise sources), the environmental conditions affecting the light field underwater were also taken into account. The simulator product is an image of the light field sensed by the detector array. The simulator product provides a signature that allows the UUV to track its position and orientation with respect to a light source. A variety of motion types (i.e., translation in the x, y, z directions including rotation about these axes) were analytically tested and evaluated for different array designs. The results from the simulator are to be validated against empirical measurements conducted in the water tank facilities in the Ocean Engineering Laboratory at the University of New Hampshire. Preliminary results suggest that unique image signatures can be obtained for the relative translational and rotational motion between two platforms

Determination of nonthermal bonding origin of a novel photoexcited lattice instability in SnSe

Interatomic forces that bind materials are largely determined by an often complex interplay between the electronic band-structure and the atomic arrangements to form its equilibrium structure and dynamics. As these forces also determine the phonon dispersion, lattice dynamics measurements are often crucial tools for understanding how materials transform between different structures. This is the case for the mono-chalcogenides which feature a number of lattice instabilities associated with their network of resonant bonds and a large tunability in their functional properties. SnSe hosts a novel lattice instability upon above-bandgap photoexcitation that is distinct from the distortions associated with its high temperature phase transition, demonstrating that photoexcitation can alter the interatomic forces significantly different than thermal excitation. Here we report decisive time-resolved X-ray scattering-based measurements of the nonequlibrium lattice dynamics in SnSe. By fitting interatomic force models to the excited-state dispersion, we determine this instability as being primarily due to changes in the fourth-nearest neighbor bonds that connect bilayers, with relatively little change to the intralayer resonant bonds. In addition to providing critical insight into the nonthermal bonding origin of the instability in SnSe, such measurements will be crucial for understanding and controlling materials properties under non-equilibrium conditions

Friendship as a Political Concept: A Groundwork for Analysis

What kind of a concept is friendship, and what is its connection to politics? Critics sometimes claim that friendship does not have a role to play in the study of politics. Such objections misconstrue the nature of the concept of friendship and its relation to politics. In response, this article proposes three approaches to understanding the concept of friendship: (1) as a ‘family resemblance’ concept, (2) as an instance of an ‘essentially contested’ concept, and (3) as a concept indicating a problématique. The article thus responds to the dismissal of friendship by undertaking the groundwork for understanding what kind of a concept friendship might be, and how it might serve different purposes. In doing so, it opens the way for understanding friendship’s relation to politics

Long-term mortality prediction after operations for type A ascending aortic dissection

<p>Abstract</p> <p>Background</p> <p>There are few long-term mortality prediction studies after acute aortic dissection (AAD) Type A and none were performed using new models such as neural networks (NN) or support vector machines (SVM) which may show a higher discriminatory potency than standard multivariable models.</p> <p>Methods</p> <p>We used 32 risk factors identified by Literature search and previously assessed in short-term outcome investigations. Models were trained (50%) and validated (50%) on 2 random samples from a consecutive 235-patient cohort. NN were run only on patients with complete data for all included variables (N = 211); SVM on the overall group. Discrimination was assessed by receiver operating characteristic area under the curve (AUC) and Gini's coefficients along with classification performance.</p> <p>Results</p> <p>There were 84 deaths (36%) occurring at 564 ± 48 days (95%CI from 470 to 658 days). Patients with complete variables had a slightly lower death rate (60 of 211, 28%). NN classified 44 of 60 (73%) dead patients and 147 of 151 (97%) long-term survivors using 5 covariates: immediate post-operative chronic renal failure, circulatory arrest time, the type of surgery on ascending aorta plus hemi-arch, extracorporeal circulation time and the presence of Marfan habitus. Global accuracies of training and validation NN were excellent with AUC respectively 0.871 and 0.870 but classification errors were high among patients who died. Training SVM, using a larger number of covariates, showed no false negative or false positive cases among 118 randomly selected patients (error = 0%, AUC 1.0) whereas validation SVM, among 117 patients, provided 5 false negative and 11 false positive cases (error = 22%, AUC 0.821, p < 0.01 versus NN results). An html file was produced to adopt and manipulate the selected parameters for practical predictive purposes.</p> <p>Conclusions</p> <p>Both NN and SVM accurately selected a few operative and immediate post-operative factors and the Marfan habitus as long-term mortality predictors in AAD Type A. Although these factors were not new per se, their combination may be used in practice to index death risk post-operatively with good accuracy.</p

LoCuSS: Testing hydrostatic equilibrium in galaxy clusters

We test the assumption of hydrostatic equilibrium in an X-ray luminosity selected sample of 50 galaxy clusters at $0.15<z<0.3$ from the Local Cluster Substructure Survey (LoCuSS). Our weak-lensing measurements of $M_{500}$ control systematic biases to sub-4 per cent, and our hydrostatic measurements of the same achieve excellent agreement between XMM-Newton and Chandra. The mean ratio of X-ray to lensing mass for these 50 clusters is $\beta_{\rm X}=0.95\pm0.05$, and for the 44 clusters also detected by Planck, the mean ratio of Planck mass estimate to LoCuSS lensing mass is $\beta_{\rm P}=0.95\pm0.04$. Based on a careful like-for-like analysis, we find that LoCuSS, the Canadian Cluster Comparison Project (CCCP), and Weighing the Giants (WtG) agree on $\beta_{\rm P}\simeq0.9-0.95$ at $0.15<z<0.3$. This small level of hydrostatic bias disagrees at $\sim5\sigma$ with the level required to reconcile Planck cosmology results from the cosmic microwave background and galaxy cluster counts

What traits are carried on mobile genetic elements, and why?

Although similar to any other organism, prokaryotes can transfer genes vertically from mother cell to daughter cell, they can also exchange certain genes horizontally. Genes can move within and between genomes at fast rates because of mobile genetic elements (MGEs). Although mobile elements are fundamentally self-interested entities, and thus replicate for their own gain, they frequently carry genes beneficial for their hosts and/or the neighbours of their hosts. Many genes that are carried by mobile elements code for traits that are expressed outside of the cell. Such traits are involved in bacterial sociality, such as the production of public goods, which benefit a cell's neighbours, or the production of bacteriocins, which harm a cell's neighbours. In this study we review the patterns that are emerging in the types of genes carried by mobile elements, and discuss the evolutionary and ecological conditions under which mobile elements evolve to carry their peculiar mix of parasitic, beneficial and cooperative genes

Selective Alpha-Particle Mediated Depletion of Tumor Vasculature with Vascular Normalization

BACKGROUND: Abnormal regulation of angiogenesis in tumors results in the formation of vessels that are necessary for tumor growth, but compromised in structure and function. Abnormal tumor vasculature impairs oxygen and drug delivery and results in radiotherapy and chemotherapy resistance, respectively. Alpha particles are extraordinarily potent, short-ranged radiations with geometry uniquely suitable for selectively killing neovasculature. METHODOLOGY AND PRINCIPAL FINDINGS: Actinium-225 ((225)Ac)-E4G10, an alpha-emitting antibody construct reactive with the unengaged form of vascular endothelial cadherin, is capable of potent, selective killing of tumor neovascular endothelium and late endothelial progenitors in bone-marrow and blood. No specific normal-tissue uptake of E4G10 was seen by imaging or post-mortem biodistribution studies in mice. In a mouse-model of prostatic carcinoma, (225)Ac-E4G10 treatment resulted in inhibition of tumor growth, lower serum prostate specific antigen level and markedly prolonged survival, which was further enhanced by subsequent administration of paclitaxel. Immunohistochemistry revealed lower vessel density and enhanced tumor cell apoptosis in (225)Ac-E4G10 treated tumors. Additionally, the residual tumor vasculature appeared normalized as evident by enhanced pericyte coverage following (225)Ac-E4G10 therapy. However, no toxicity was observed in vascularized normal organs following (225)Ac-E4G10 therapy. CONCLUSIONS: The data suggest that alpha-particle immunotherapy to neovasculature, alone or in combination with sequential chemotherapy, is an effective approach to cancer therapy