An estimate of \Omega_m without priors

Using mean relative peculiar velocity measurements for pairs of galaxies, we estimate the cosmological density parameter $\Omega_m$ and the amplitude of density fluctuations $\sigma_8$. Our results suggest that our statistic is a robust and reproducible measure of the mean pairwise velocity and thereby the $\Omega_m$ parameter. We get $\Omega_m = 0.30^{+0.17}_{-0.07}$ and $\sigma_8 = 1.13^{+0.22}_{-0.23}$. These estimates do not depend on prior assumptions on the adiabaticity of the initial density fluctuations, the ionization history, or the values of other cosmological parameters.Comment: 12 pages, 4 figures, slight changes to reflect published versio

Simplest random K-satisfiability problem

We study a simple and exactly solvable model for the generation of random satisfiability problems. These consist of $\gamma N$ random boolean constraints which are to be satisfied simultaneously by $N$ logical variables. In statistical-mechanics language, the considered model can be seen as a diluted p-spin model at zero temperature. While such problems become extraordinarily hard to solve by local search methods in a large region of the parameter space, still at least one solution may be superimposed by construction. The statistical properties of the model can be studied exactly by the replica method and each single instance can be analyzed in polynomial time by a simple global solution method. The geometrical/topological structures responsible for dynamic and static phase transitions as well as for the onset of computational complexity in local search method are thoroughly analyzed. Numerical analysis on very large samples allows for a precise characterization of the critical scaling behaviour.Comment: 14 pages, 5 figures, to appear in Phys. Rev. E (Feb 2001). v2: minor errors and references correcte

Rods progressively escape saturation to drive visual responses in daylight conditions

Rod and cone photoreceptors support vision across large light intensity ranges. Rods, active under dim illumination, are thought to saturate at higher (photopic) irradiances. The extent of rod saturation is not well defined; some studies report rod activity well into the photopic range. Using electrophysiological recordings from retina and dorsal lateral geniculate nucleus of cone-deficient and visually intact mice, we describe stimulus and physiological factors that influence photopic rod-driven responses. We find that rod contrast sensitivity is initially strongly reduced at high irradiances, but progressively recovers to allow responses to moderate contrast stimuli. Surprisingly, rods recover faster at higher light levels. A model of rod phototransduction suggests that phototransduction gain adjustments and bleaching adaptation underlie rod recovery. Consistently, exogenous chromophore reduces rod responses at bright background. Thus, bleaching adaptation renders mouse rods responsive to modest contrast at any irradiance. Paradoxically, raising irradiance across the photopic range increases the robustness of rod responses.Peer reviewe

Measurement of ISR-FSR interference in the processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi- gamma

Charge asymmetry in processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi- gamma is measured using 232 fb-1 of data collected with the BABAR detector at center-of-mass energies near 10.58 GeV. An observable is introduced and shown to be very robust against detector asymmetries while keeping a large sensitivity to the physical charge asymmetry that results from the interference between initial and final state radiation. The asymmetry is determined as afunction of the invariant mass of the final-state tracks from production threshold to a few GeV/c2. It is compared to the expectation from QED for e+ e- --> mu+ mu- gamma and from theoretical models for e+ e- --> pi+ pi- gamma. A clear interference pattern is observed in e+ e- --> pi+ pi- gamma, particularly in the vicinity of the f_2(1270) resonance. The inferred rate of lowest order FSR production is consistent with the QED expectation for e+ e- --> mu+ mu- gamma, and is negligibly small for e+ e- --> pi+ pi- gamma.Comment: 32 pages,29 figures, to be submitted to Phys. Rev.

The ocean sampling day consortium

Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world’s oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits

Sentinel node biopsy for breast cancer: is it already a standard of care? A survey of current practice in an Italian region

BACKGROUND: Although sentinel node biopsy (SNB) is becoming the standard approach for axillary staging in patients with small breast cancer, criteria for patient selection and some technical aspects of the procedure have yet to be clearly defined. The aim of the present survey was therefore to investigate the way in which SNB is used by general surgeons working in the Veneto region, Italy. METHODS: A 29-item questionnaire regarding various aspects of SNB practice was mailed to surgeons in charge of breast surgery in all the 56 surgical centres of the region. RESULTS: The rate of response to the questionnaire was 82.1% (n = 46); 69.6% (n = 32) of the respondents routinely perform SNB in their clinical practice. Most of the interviewed surgeons (93.5%) expressed the belief that the acceptable false negative rate should be ≤5%. However, among the surgeons who perform SNB, only 34.4% performed more than 20 SNB during the learning phase. Indications are limited to tumours of ≤1 cm by 31.2% (n = 10) of respondents, ≤2 cm by 46.9% (n = 15) and ≤3 cm by 21.9% (n = 7). Almost all respondents (93.7%) agreed that a clinically positive axilla is a contraindication to SNB, while opinions differed widely concerning other potential contraindications. In most of the centres considered, SN identification is undertaken on the day before surgery using a subdermal injection of 30–50 MBq of 99mTc-albumin-nanocolloid followed by lymphoscintigraphy. CONCLUSIONS: SNB is currently performed in the majority of hospitals in the Veneto region. However, the training phase and criteria used for patient selection differ from centre to centre. Certified training courses and shared guidelines are therefore highly desirable

A Mouse Model of Pulmonary Metastasis from Spontaneous Osteosarcoma Monitored In Vivo by Luciferase Imaging

BACKGROUND: Osteosarcoma (OSA) is lethal when metastatic after chemotherapy and/or surgical treatment. Thus animal models are necessary to study the OSA metastatic spread and to validate novel therapies able to control the systemic disease. We report the development of a syngeneic (Balb/c) murine OSA model, using a cell line derived from a spontaneous murine tumor. METHODOLOGY: The tumorigenic and metastatic ability of OSA cell lines were assayed after orthotopic injection in mice distal femur. Expression profiling was carried out to characterize the parental and metastatic cell lines. Cells from metastases were propagated and engineered to express Luciferase, in order to follow metastases in vivo. PRINCIPAL FINDINGS: Luciferase bioluminescence allowed to monitor the primary tumor growth and revealed the appearance of spontaneous pulmonary metastases. In vivo assays showed that metastasis is a stable property of metastatic OSA cell lines after both propagation in culture and luciferase trasduction. When compared to parental cell line, both unmodified and genetically marked metastatic cells, showed comparable and stable differential expression of the enpp4, pfn2 and prkcd genes, already associated to the metastatic phenotype in human cancer. CONCLUSIONS: This OSA animal model faithfully recapitulates some of the most important features of the human malignancy, such as lung metastatization. Moreover, the non-invasive imaging allows monitoring the tumor progression in living mice. A great asset of this model is the metastatic phenotype, which is a stable property, not modifiable after genetic manipulation

Collaborative Brain-Computer Interface for Aiding Decision-Making

We look at the possibility of integrating the percepts from multiple non-communicating observers as a means of achieving better joint perception and better group decisions. Our approach involves the combination of a brain-computer interface with human behavioural responses. To test ideas in controlled conditions, we asked observers to perform a simple matching task involving the rapid sequential presentation of pairs of visual patterns and the subsequent decision as whether the two patterns in a pair were the same or different. We recorded the response times of observers as well as a neural feature which predicts incorrect decisions and, thus, indirectly indicates the confidence of the decisions made by the observers. We then built a composite neuro-behavioural feature which optimally combines the two measures. For group decisions, we uses a majority rule and three rules which weigh the decisions of each observer based on response times and our neural and neuro-behavioural features. Results indicate that the integration of behavioural responses and neural features can significantly improve accuracy when compared with the majority rule. An analysis of event-related potentials indicates that substantial differences are present in the proximity of the response for correct and incorrect trials, further corroborating the idea of using hybrids of brain-computer interfaces and traditional strategies for improving decision making

Hydrothermal Alteration of Ultramafic Rocks in Ladon Basin, Mars - Insights From CaSSIS, HiRISE, CRISM, and CTX

The evolution of the Ladon basin has been marked by intense geological activity and the discharge of huge volumes of water from the Martian highlands to the lowlands in the late Noachian and Hesperian. We explore the potential of the ExoMars Trace Gas Orbiter/Color and Stereo Surface Imaging System color image data set for geological interpretation and show that it is particularly effective for geologic mapping in combination with other data sets such as HiRISE, Context, and Compact Reconnaissance Imaging Spectrometer for Mars. The study area displays dark lobate flows of upper Hesperian to early Amazonian age, which were likely extruded from a regional extensional fault network. Spectral analysis suggests that these flows and the underlying rocks are ultramafic. Two distinct altered levels are observed below the lobate flows. The upper, yellow-orange level shows hundreds of structurally controlled narrow ridges reminiscent of ridges of listwanite, a suite of silicified, fracture-controlled silica-carbonate rocks derived from an ultramafic source and from serpentine. In addition to serpentinite, the detected mineral assemblages may include chlorite, carbonates, and talc. Kaolin minerals are detected in the lower, white level, which could have formed by groundwater alteration of plagioclase in the volcanic pile. Volcanism, tectonics, hydrothermal activity, and kaolinization are interpreted to be coeval, with hydrothermal activity and kaolinization controlled by the interactions between the aquifer and the hot, ultramafic lobate flows. Following our interpretations, East Ladon may host the first listwanite ridges described on Mars, involving a hydrothermal system rooted in a Hesperian aquifer and affecting ultramafic rocks from a magmatic source yet to be identified