10,799 research outputs found
Appraising Forgeability and Surface Cracking in New Generation Cast and Wrought Superalloys
Surface cracking poses a major problem in industrial forging, but the scientific understanding of the phenomenon is hampered by the difficulty of replicating it in a laboratory setting. In this work, a novel laboratory-scale experimental method is presented to investigate forgeability in new generation cast and wrought superalloys. This new approach makes possible appraising the prevalence and severity of surface cracking by mimicking the die chilling effects characteristic of hot die forging. Two high γ′-reinforced alloys are used to explore this methodology. A Gleeble thermo-mechanical simulator is used to conduct hot compression tests following a non-isothermal cycle, with the aim to simulate the cooling of the near-surface regions during the forging process. FEA simulations, sample geometry design, and heat-treatments are used to ensure the correspondence between laboratory and real-scale forging. A wide range of surface cracking results are obtained for different forging temperatures and cooling rates—proving the soundness of the method. Surprisingly, samples heated up to higher initial temperatures typically show more extensive surface cracking. These findings indicate that—along with the local mechanical conditions of the forging—die-chilling effects and forging temperatures are paramount in controlling surface cracking, as they dictate the key variables governing the distribution and kinetics of γ′ formation
Thermophysical properties of functionalized graphene nanoplatelet dispersions for improving efficiency in a wind turbine cooling system
A new generation of heat transfer fluids, nanofluids, can
play a major role in the development of today’s renewable
energies. In the particular case of wind turbines, an undesirable
overheating of electrical and mechanical components can
provoke a noticeable reduction of overall efficiency due to the
temperature is a limiting factor to the electricity generation or
even very expensive repair cost because of an unexpected crash
of generators, or others turbine components. Dispersions of
multiple-layer graphene nanostructures with high thermal
conductivity in conventional working fluids are a promising
type of new heat transfer fluids due to the excellent
performance of nanoadditives in heat transference. Hence,
determining the thermophysical properties of these
nanomaterials under different conditions is the first step and
key issue for analysing and optimizing the dispersions.
Although water-based graphene nanoplatelet nanofluids have
been investigated and some correlations can be found in the
literature, scarce studies were conducted using other industrial
working fluids as base fluids.
The purpose of this study is to carry out a thorough
thermophysical characterization of different loaded samples of
functionalized graphene nanoplatelet dispersions in an
industrial heat transfer fluid, Havoline XLC Pre-mixed 50/50.
Four different nanofluids at mass concentrations (0.25, 0.50,
0.75 and 1.0) wt.% of functionalized graphene nanoplatelets
powder were produced. In order to obtain improved long-term
stabilities, sodium dodecyl benzene sulphonate was added to
the samples at a mass concentration of 0.125 % in relation to
the base fluid without appreciable variations in the pH value.
Stability was assessed through zeta potential and dynamic light
scattering measurements. Tests for determining thermal
conductivity were conducted with a transient hot wire
technique in a wide temperature range. In addition, densities,
dynamic viscosities and specific heat capacities of the samples
were experimentally determined at different temperatures in
order to carry out further studies such as experimental
convective heat transfer coefficients and pressure drops.
Increases in thermal conductivity up to 7.3 % were found with
not very high viscosity rises.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers
Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003
We present an analysis of the pulsation behaviour of the Delta Scuti stars 7
Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the
framework of STEPHI XII campaign during 2003 June--July. 183 hours of high
precision photometry were acquired by using four-channel photometers at three
sites on three continents during 21 days. The light curves and amplitude
spectra were obtained following a classical scheme of multi-channel photometry.
Observations in different filters were also obtained and analyzed. Six and
three frequencies have been unambiguously detected above a 99% confidence level
in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql
respectively. A comparison of observed and theoretical frequencies shows that 7
Aql and 8 Aql may oscillate with p modes of low radial orders, typical among
Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from
n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial
oscillations have to be present in both stars as well. The expected range of
excited modes according to a non adiabatic analysis goes from n=1 to n=6 in
both stars.Comment: 8 pages, 7 fugures, 5 tables, accepted for publication in
Astronomical Journa
Solution of the Bosonic and Algebraic Hamiltonians by using AIM
We apply the notion of asymptotic iteration method (AIM) to determine
eigenvalues of the bosonic Hamiltonians that include a wide class of quantum
optical models. We consider solutions of the Hamiltonians, which are even
polynomials of the fourth order with the respect to Boson operators. We also
demonstrate applicability of the method for obtaining eigenvalues of the simple
Lie algebraic structures. Eigenvalues of the multi-boson Hamiltonians have been
obtained by transforming in the form of the single boson Hamiltonian in the
framework of AIM
Cascade or Direct Speech Translation? A Case Study
Speech translation has been traditionally tackled under a cascade approach, chaining speech recognition and machine translation components to translate from an audio source in a given language into text or speech in a target language. Leveraging on deep learning approaches to natural language processing, recent studies have explored the potential of direct end-to-end neural modelling to perform the speech translation task. Though several benefits may come from end-to-end modelling, such as a reduction in latency and error propagation, the comparative merits of each approach still deserve detailed evaluations and analyses. In this work, we compared state-of-the-art cascade and direct approaches on the under-resourced Basque–Spanish language pair, which features challenging phenomena such as marked differences in morphology and word order. This case study thus complements other studies in the field, which mostly revolve around the English language. We describe and analysed in detail the mintzai-ST corpus, prepared from the sessions of the Basque Parliament, and evaluated the strengths and limitations of cascade and direct speech translation models trained on this corpus, with variants exploiting additional data as well. Our results indicated that, despite significant progress with end-to-end models, which may outperform alternatives in some cases in terms of automated metrics, a cascade approach proved optimal overall in our experiments and manual evaluations. © 2022 by the authors. Licensee MDPI, Basel, Switzerland
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Inverse association between negative symptoms and body mass index in chronic schizophrenia.
BACKGROUND: We investigated whether negative symptoms, such as poor motivation or anhedonia, were associated with higher body mass index (BMI) in stable patients with schizophrenia chronically treated with antipsychotic medication. METHODS: 62 olanzapine- or clozapine-treated patients with illness duration of at least four years were selected from an international multicenter study on the characterization of negative symptoms. All participants completed the Brief Negative Symptom Scale (BNSS) and the Positive and Negative Syndrome Scale (PANSS). Bivariate correlations between BMI and negative symptoms (BNSS) were explored, as well as multiple regression analyses. We further explored the association of two principal component factors of the BNSS and BMI. Subsidiary analyses re-modeled the above using the negative symptoms subscale of the PANSS and the EMSLEY factor for negative symptoms for convergent validity. RESULTS: Lower negative symptoms (BNSS score) were associated with higher BMI (r=-0.31; p=0.015). A multiple regression analysis showed that negative symptoms (BNSS score) and age were significant predictors of BMI (p=0.037). This was mostly driven by the motivation/pleasure factor of the BNSS. Within this second factor, BMI was negatively associated with anhedonia (r=-0.254; p=0.046) and asociality (r=-0.253; p=0.048), but not avolition (r=-0.169; p=0.188). EMSLEY score was positively associated with BNSS (r=0.873, p<0.001), but negatively associated with BMI (r=-0.308; p=0.015). The association between PANSS and BMI did not reach significance (r=-224, p=0.080). CONCLUSIONS: We conclude that lower negative symptoms were associated with higher BMI (assessed using both the BNSS and EMSLEY) in chronic stable schizophrenia patients, mostly due to lower anhedonia and asociality levels
Nature of the spin-glass phase at experimental length scales
We present a massive equilibrium simulation of the three-dimensional Ising
spin glass at low temperatures. The Janus special-purpose computer has allowed
us to equilibrate, using parallel tempering, L=32 lattices down to T=0.64 Tc.
We demonstrate the relevance of equilibrium finite-size simulations to
understand experimental non-equilibrium spin glasses in the thermodynamical
limit by establishing a time-length dictionary. We conclude that
non-equilibrium experiments performed on a time scale of one hour can be
matched with equilibrium results on L=110 lattices. A detailed investigation of
the probability distribution functions of the spin and link overlap, as well as
of their correlation functions, shows that Replica Symmetry Breaking is the
appropriate theoretical framework for the physically relevant length scales.
Besides, we improve over existing methodologies to ensure equilibration in
parallel tempering simulations.Comment: 48 pages, 19 postscript figures, 9 tables. Version accepted for
publication in the Journal of Statistical Mechanic
Phenomenology of the Gauge Boson
Assuming the existence of a gauge boson which couples to ,
we discuss the present experimental constraints on and from and . We also discuss the
discovery potential of at hadron colliders through its decay into pairs. In the scenario where all three charged leptons (and their
neutrinos) mix, lepton flavor nonconservation through becomes possible and
provides another experimental probe into this hypothesis.Comment: 19 pages, LaTeX, including 4 figure
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