The effect of load in a contact with boundary lubrication

The effect of the transition load on the wear in a contact with boundary lubrication was investigated. An experimental method was developed for this purpose, and parameters affecting the boundary lubrication under industrial operating conditions were identified. These parameters are the adsorbed boundary film, the contact microgeometry (surface roughness), macrogeometry, and hardness of materials used. It was found that the curve of the tops of the surface protrustion affect the transition load, and thus the boundary lubrication. The transition load also depends on the chemical nature of the contact and its geometrical and mechanical aspects

Imaging Spectropolarimetry with IBIS: Evolution of Bright Points in the Quiet Sun

We present the results from first spectropolarimetric observations of the solar photosphere acquired at the Dunn Solar Telescope with the Interferometric Bidimensional Spectrometer. Full Stokes profiles were measured in the Fe I 630.15 nm and Fe I 630.25 nm lines with high spatial and spectral resolutions for 53 minutes, with a Stokes V noise of 0.003 the continuum intensity level. The dataset allows us to study the evolution of several magnetic features associated with G-band bright points in the quiet Sun. Here we focus on the analysis of three distinct processes, namely the coalescence, fragmentation and cancellation of G-band bright points. Our analysis is based on a SIR inversion of the Stokes I and V profiles of both Fe I lines. The high spatial resolution of the G-band images combined with the inversion results helps to interpret the undergoing physical processes. The appearance (dissolution) of high-contrast G-band bright points is found to be related to the local increase (decrease) of the magnetic filling factor, without appreciable changes in the field strength. The cancellation of opposite-polarity bright points can be the signature of either magnetic reconnection or the emergence/submergence of magnetic loops.Comment: 4 pages, 5 figures, accepted for publication in ApJ Letter

Sensing the impact of COVID-19 restrictions from online reviews: The cases of London and Paris unveiled through text mining

This study aims to understand how the COVID-19 pandemic affected the hotel sector and to identify the current traveler demands. The traveler’s re-views were analyzed based on sentiment analysis and a guest satisfaction model was also proposed, demonstrating a data mining approach within tourism and hospitality research. Given its popularity, TripAdvisor was the chosen platform for collection of hotel reviews in London and Paris. Text data were extracted from reviews made in two time periods, before and during the COVID-19 pan-demic. The sentiment and specific aspects highlighted by travelers were com-pared between each period.info:eu-repo/semantics/acceptedVersio

Lattice Gauge Fixing for Parameter Dependent Covariant Gauges

We propose a non-perturbative procedure to fix generic covariant gauges on the lattice. Varying the gauge parameter, this gauge fixing provides a concrete method to check numerically the gauge dependence of correlators measured on the lattice. The new algorithm turns out to converge with a good efficiency. As a preliminary physical result, we find a sensitive dependence of the gluon propagator on the gauge parameter.Comment: 10 pages (LaTeX2e), 5 eps figure

Is the Cepheus E Outflow driven by a Class 0 Protostar?

New early release observations of the Cepheus E outflow and its embedded source, obtained with the Spitzer Space Telescope, are presented. We show the driving source is detected in all 4 IRAC bands, which suggests that traditional Class 0 classification, although essentially correct, needs to accommodate the new high sensitivity infrared arrays and their ability to detected deeply embedded sources. The IRAC, MIPS 24 and 70 microns new photometric points are consistent with a spectral energy distribution dominated by a cold, dense envelope surrounding the protostar. The Cep E outflow, unlike its more famous cousin the HH 46/47 outflow, displays a very similar morphology in the near and mid-infrared wavelengths, and is detected at 24 microns. The interface between the dense molecular gas (where Cep E lies) and less dense interstellar medium, is well traced by the emission at 8 and 24 microns, and is one of the most exotic features of the new IRAC and MIPS images. IRS observations of the North lobe of the flow confirm that most of the emission is due to the excitation of pure H2 rotational transitions arising from a relatively cold (Tex~700 K) and dense (N{H}~9.6E20 cm-2 molecular gas.Comment: 14 pages (pre-print format), including 6 figures. Published in ApJ Special Spitzer Issue (2004

Evaluating a guest satisfaction model through data mining

Purpose: This paper aims to propose a data mining approach to evaluate a conceptual model in tourism, encompassing a large data set characterized by dimensions grounded on existing literature. Design/methodology/approach: The approach is tested using a guest satisfaction model encompassing nine dimensions. A large data set of 84 k online reviews and 31 features was collected from TripAdvisor. The review score granted was considered a proxy of guest satisfaction and was defined as the target feature to model. A sequence of data understanding and preparation tasks led to a tuned set of 60k reviews and 29 input features which were used for training the data mining model. Finally, the data-based sensitivity analysis was adopted to understand which dimensions most influence guest satisfaction. Findings: Previous user’s experience with the online platform, individual preferences, and hotel prestige were the most relevant dimensions concerning guests’ satisfaction. On the opposite, homogeneous characteristics among the Las Vegas hotels such as the hotel size were found of little relevance to satisfaction. Originality/value: This study intends to set a baseline for an easier adoption of data mining to evaluate conceptual models through a scalable approach, helping to bridge between theory and practice, especially relevant when dealing with Big Data sources such as the social media. Thus, the steps undertaken during the study are detailed to facilitate replication to other models.info:eu-repo/semantics/acceptedVersio

Dermanyssus gallinae in layer farms in Kosovo: a high risk for salmonella prevalence

Background The poultry red mite (PRM), Dermanyssus gallinae (D.g.) is a serious ectoparasitic pest of poultry and potential pathogen vector. The prevalence of D. g. and the prevalence of Salmonella spp. within mites on infested laying poultry farms were investigated in Kosovo. Findings In total, 14 populated layer farms located in the Southern Kosovo were assessed for D. g. presence. Another two farms in this region were investigated 6 months after depopulation. Investigated flocks were all maintained in cages, a common housing system in Kosovo. A total of eight farms were found to be infested with D. g. (50%) at varying levels, including the two depopulated farms. The detection of Salmonella spp. from D. g. was carried out using PCR. Out of the eight layer farms infested with D. g., Salmonella spp. was present in mites on three farms (37.5%). Conclusions This study confirms the high prevalence of D. g. in layer flocks in Kosovo and demonstrates the link between this mite and the presence of Salmonella spp. on infested farms

The X-ray Luminosities of HH Objects

The recent detection of X-ray emission from HH 2 and HH 154 with the Chandra and XMM-Newton satellites (respectively) have opened up an interesting, new observational possibility in the field of Herbig-Haro objects. In order to be able to plan further X-ray observations of other HH objects, it is now of interest to be able to estimate their X-ray luminosities in order to choose which objects to observe. This paper describes a simple, analytic model for predicting the X-ray luminosity of a bow shock from the parameters of the flow (i.e., the size of the bow shock, its velocity, and the pre-shock density). The accuracy of the analytic model is analyzed through a comparison with the predictions obtained from axisymmetric, gasdynamic simulations of the leading working surface of an HH jet. We find that our analytic model reproduces the observed X-ray luminosities of HH 2 and HH 154, and we propose that HH~80/81 is a good candidate for future observations with Chandra.Comment: 10 pages (8 text, 2 figures