Hasil untuk "cond-mat.quant-gas"

Poshadri Chathri, R. Prakash

During pitting corrosion, pits are initiated due to localized chemical or mechanical damage of the protective oxide film. Pits are the leading cause of the initiation of the crack in many types of failure, especially in fatigue. Stainless steels are preferred in view of corrosion resistance; however, they too undergo varying degrees of corrosion and hence, it is important to study the corrosion response in sea water conditions for the better usability of structures in marine, pipping, and oil and natural gas extraction to avoid catastrophic structural failure. In this study, the stochastic pit coordinates are generated using MATLAB. These coordinates are used to generate the pits on dogbone specimen on all faces according to the ASTM G46-21 by using PYTHON scripting incorporated with the ABAQUS. Five sets and four different conditions pits are generated on a tensile specimen and numerical simulations were performed, each with a unique stochastic pit distribution. The results indicated significant variations in failure patterns, with different models failing at distinct locations and exhibiting various displacement responses. The findings highlight the importance of accounting the pit geometry and distribution. From this study, it is found that the maximum strength decreased by 13.84% in set-3 And the maximum displacement by 35.46% in set-5 and the maximum strength decreased by 30.71% in Cond-4 and the maximum displacement by 63.02% in Cond-4 compared with the without pits models. Failure paths were observed in regions with reduced cross-sectional areas and a higher pit density which are consistent with the stress concentration factor.

Emily L. Langford, Haley C. Bergstrom, Sarah N. Lanham et al.

Abstract Langford, EL, Bergstrom, HC, Lanham, S, Eastman, AQ, Best, S, Ma, X, Mason, MR, and Abel, MG. Evaluation of work efficiency in structural firefighters. J Strength Cond Res 37(12): 2457–2466, 2023—To perform occupational tasks safely and effectively, firefighters (FF) must work quickly and consume air provided by the self-contained breathing apparatus (SCBA) efficiently. However, most literature only factors work rate into performance, neglecting the inherent time limitation imposed by the SCBA. The purpose of this article was to (a) evaluate the reliability and variability in a “work efficiency” (WE) performance metric reflective of both work rate and air consumption; (b) explore the relationship between WE and established measures of metabolic strain; and (c) identify fitness, anthropometric, and demographic correlates of WE. About 79 structural FF completed an air consumption drill while breathing through an SCBA. Self-paced work duration and air consumption were entered into the WE equation. A subsample of FF (n = 44) completed another randomized trial while breathing through a portable gas analyzer. Anthropometric and fitness data were collected separately. Correlations were performed between WE vs. fitness, anthropometric, demographic, and metabolic outcomes. Multiple linear regression was used to identify the strongest predictors of WE. WE was reliable (intraclass correlation coefficient = 0.71) and yielded inter-FF variability {0.79 ± 0.25 ([lb·in−2·min]−1) × 104; coefficient of variation = 31.6%}. WE was positively correlated to oxygen consumption (V̇O2) (L·minute−1, mL·kg−1·minute−1) and tidal volume and negatively correlated to V̇E/V̇O2 and respiratory frequency. Height, upper-body endurance, and aerobic endurance were identified as the strongest predictors of WE (adjusted R2 = 0.59, RMSE = 0.16). WE is a reliable and occupationally relevant method to assess FF performance because it accounts for work rate and air consumption. Firefighters may enhance WE through a training intervention focused on improving metabolic tolerance, upper-body endurance, and aerobic endurance.

Todd A. Astorino, Tanner Robson, D. McMillan

Abstract Astorino, TA, Robson, T, and McMillan, DW. Classifying intensity domains from arm cycle ergometry differs versus leg cycling ergometry. J Strength Cond Res 37(11): 2192–2199, 2023—This study compared the distribution of exercise intensity domains in response to progressive leg cycle ergometry (LCE) and arm cycle ergometry (ACE). Seventeen active men and women (age and body fat = 26 ± 7 years and 18 ± 3%) initially performed graded exercise on each modality to assess maximal oxygen uptake (V̇o2max) and peak power output (PPO). Using a randomized crossover design, they subsequently performed moderate intensity continuous exercise consisting of three 15-minute bouts at 20, 40, and 60% PPO on each modality. Gas exchange data (V̇o2, V̇co2, and VE), respiratory exchange ratio, heart rate (HR), blood lactate concentration (BLa), and perceptual responses were acquired. Only 2 subjects were classified in the same intensity domains across modalities, with LCE eliciting more subjects exercising at “vigorous” and “near-maximal” intensities than ACE. Time spent above 70 (22 ± 7 vs. 15 ± 8 minutes, d = 1.03) and 80 %HRmax (15 ± 6 vs. 9 ± 6 minutes, d = 1.04) was significantly greater with LCE vs. ACE. Compared with ACE, LCE revealed significantly higher (p < 0.05) peak (94 ± 6 vs. 88 ± 9 %HRmax, d = 0.81) and mean HR (73 ± 6 vs. 66 ± 6 %HRmax, d = 1.20), V̇o2 (54 ± 5 vs. 50 ± 7 %V̇o2max, d = 0.68), and BLa (5.5 ± 2.0 vs. 4.7 ± 1.5 mM, d = 0.48). The results exhibit that progressive leg cycling at identical intensities elicits a greater cardiometabolic stimulus than ACE.

A.G.Magner, A.I.Sanzhur, S.N.Fedotkin et al.

Level density $\rho(E,N,Z)$ is calculated for the two-component close- and open-shell nuclei with a given energy $E$, and neutron $N$ and proton $Z$ numbers, taking into account pairing effects within the microscopic-macroscopic approach (MMA). These analytical calculations have been carried out by using the semiclassical statistical mean-field approximations beyond the saddle-point method of the Fermi gas model in a low excitation-energies range. The level density $\rho$, obtained as function of the system entropy $S$, depends essentially on the condensation energy $E_{\rm cond}$ through the excitation energy $U$ in super-fluid nuclei. The simplest super-fluid approach, based on the BCS theory, accounts for a smooth temperature dependence of the pairing gap $\Delta$ due to particle number fluctuations. Taking into account the pairing effects in magic or semi-magic nuclei, excited below neutron resonances, one finds a notable pairing phase transition.Pairing correlations sometimes improve significantly the comparison with experimental data.

Lénárd Gulyás Oldal, T. Csizmadia, Z. Filus et al.

The High-Repetition-rate laser-driven Gas-based High-order Harmonic Generation (HR GHHG) beamlines of the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS) have started their operation in the recent years. Both beamlines, one designed for gas-phase targets – the HR GHHG Gas beamline –, and one for condensed-phase samples – the HR GHHG Condensed beamline –, now provide high-flux, extreme ultraviolet (XUV) radiation with pump-probe capabilities at 100 kHz repetition rate. The HR GHHG Cond beamline is equipped with a time-compensated XUV monochromator, allowing for tuning the spectral properties while maintaining short, close to Fourier-limited pulse duration in the femtosecond regime. Cutting-edge experimental end stations are also available, for example a Reaction Microscope and a NanoESCA device. Both beamlines are past their first commissioning user experiments. In this presentation the capabilities along with some recent developments and latest experiments will be presented for these two unique attosecond sources.

G. Bogdanis, Vasiliki J. Mallios, C. Katsikas et al.

Abstract Bogdanis, GC, Mallios, VJ, Katsikas, C, Fouseki, T, Holman, I, Smith, C, and Astorino, TA. Effects of exercise structure and modality on physiological and perceptual responses to exercise. J Strength Cond Res 35(9): 2427–2432, 2021—This study examined the effect of exercise mode and intensity on physiological and perceptual responses to exercise. Twelve active adults (6 men and 6 women, age = 21.7 ± 1.6 years) initially performed incremental testing on the treadmill (TM) and cycle ergometer (CE) to assess maximal oxygen uptake (V̇o2max) and ventilatory threshold (VT). During the next 4 visits in a randomized order, subjects performed 20 minutes of moderate-intensity continuous exercise (MICE) at an intensity 20% below VT on the TM (TMMICE) and cycle ergometer (CEMICE) as well as time-matched high-intensity interval exercise (HIIE; 10 1-minute bouts at workload equal to 20% above VT followed by 1-minute active recovery) on both modes (TMHIIE and CEHIIE). During exercise, gas exchange data, blood lactate concentration, and perceptual responses (rating of perceived exertion, affective valence, and enjoyment) were assessed. Heart rate (p < 0.001) and V̇o2 (p < 0.001) were higher in response to TMHIIE vs. CEHIIE as well as TMMICE vs. CEMICE. Blood lactate concentration was higher (p = 0.003) in response to CEHIIE vs. TMHIIE. The rating of perceived exertion was significantly higher (p < 0.001) in TMMICE compared with CEMICE which showed the most positive affective valence (p = 0.009). Enjoyment was similar across all bouts (p = 0.11). Treadmill-based HIIE leads to higher heart rate and V̇o2 vs. CEHIIE, although there was no difference in affective valence or enjoyment. Practitioners aiming to optimize the cardiorespiratory response to moderate or interval exercise in their clientele should recommend TM running rather than cycling.

V. Bezyazychny, M. Szczerek, M. Timofeev et al.

The paper presents the results of a study on the fretting corrosion effect on strength as per the diagrams of material fatigue of low-cycle and high-cycle loading. An experimental study of the effect of fretting corrosion on fatigue of a titanium alloy VT3-1 showed that, when choosing a particular technological method to increase fatigue resistance of gas turbine engine parts operating under fretting corrosion conditions, it is necessary to take into account the fact that fretting itself is intensive strengthening and at the same time a softening factor affecting the surface layers of the material. Technological methods of surface plastic deformation treatment result in a significant change in the parameters of metal surface layer state, which depends on both the type and duration of treatment. If the power and time parameters of processing are too high, the surface may be re-cold worked and the surface layer of the material almost completely exhausts the reserve of plasticity, as a result dangerous microcracks occur, and the formation of particles of flaking metal emerge. Possible ways using technological methods have been suggested by the authors to improve fretting strength of part surfaces operating under fretting corrosion conditions. Słowa kluczowe: korozja cierna, zmęczenie materiału, wysoka częstotliwość, niska częstotliwość, zwiększanie odporności na zmęczenie, metody odkształcania plastycznego powierzchni. Streszczenie: W artykule przedstawiono wyniki badań wpływu korozji ciernej na wytrzymałość zmęczeniową przy niskiej i wysokiej częstotliwości obciążania. Eksperymentalne badania wpływu korozji ciernej na zmęczenie stopu tytanu VT3-1 wykazały, że wybierając metodę technologicznego zwiększania odporności zmęczeniowej części silników turbogazowych pracujących w warunkach korozji ciernej, należy wziąć pod uwagę fakt, że sam fretting jest czynnikiem wzmacniającym i jednocześnie osłabiającym warstwy wierzchnie materiału. Technologiczne metody powierzchniowej obróbki plastycznej powodują istotną zmianę parametrów stanu warstwy metalu w zależności zarówno od rodzaju, jak i czasu trwania obróbki. Gdy parametry obróbki (moc i czas) są zbyt duże, powierzchnia zostaje poddana obróbce na zimno, warstwa wierzchnia materiału nie jest podatna na odkształcenie plastyczne, wobec czego powstają niebezpieczne mikropęknięcia oraz tworzą się odpryski. Wskazano potencjalne zabiegi technologiczne rekomendowane do zwiększenia odporności elementów maszyn pracujących w warunkach występowania korozji ciernej. * ORCID: 0000-0002-7287-2495. P.A. Solovyov Rybinsk State Aviation Technical University (152934, Rybinsk, Yaroslavl region), Pushkin Street 53, Russia, e-mail: technology@rsatu.ru. ** ORCID: 0000-0002-1049-7853. Łukasiewicz Research Network – Institute for Sustainable Technologies, Pułaskiego 6/10 Street, 26-600 Radom, Poland. *** ORCID: 0000-0003-4480-7220. P.A. Solovyov Rybinsk State Aviation Technical University (152934, Rybinsk, Yaroslavl region), Pushkin Street 53, Russia. **** PJSC “UEC-Saturn”, Rybinsk, Russia. INTRODUCTION The intensity of the effect of metal fatigue strength due to fretting corrosion depends on many factors. However, the number of fretting corrosion cycles becomes the determining factor for aircraft engine parts, since the other factors are regulated in one way or another by the design and operating conditions of real gas turbine engine designs. 8 ISSN 0208-7774 T R I B O L O G I A 2/2020 Analysis of operating conditions and causes of the destruction of disks of GTE low-pressure compressor second stage selected as the object research has shown that this gas turbine engine unit requires scientific substantiated approach to the choice of design and technological measures to ensure the required cyclic durability. Despite the fact that the destruction of disks occurs as per the mechanism of low-cycle fatigue, in this work, an attempt was made to obtain more detailed information about the effect of fretting corrosion on both the low-cycle and high-cycle fatigue of the structural and technological model of the selected object. EXPERIMENTAL STUDY OF EFFECT OF FrETTInG DAMAGES On HIGH-cyclE FATIGuE OF TITAnIuM AllOy VT3-1 When working on the experiment methodology, the following main points were implemented: 1. Ambient temperature θ = 288 К. 2. Displacement amplitude А = 100 μm, frequency f = 30 Hz, contact pressure рн = 5 MPa. 3. The study was carried out on the special specimens made of VT3-1 and L70 alloys. 4. The parameters of the state of the specimen surface layer prior to the experiment corresponded to the technical conditions for disk manufacture applying special finishing operations. 5. The study was accomplished on the single-factor experiment principle using the combined method. Special specimens that were preliminarily damaged by fretting corrosion with different running hours were tested for fatigue prior to destruction of each specimen. 6. The duration of the continuous run for fretting wear of specimens was determined based on a previously obtained fretting wear diagram of this pair of materials for reasons of the reliable achievement of each of the three main stages of the process (adhesion interaction, run-in, steady wear). 7. The influence of the structural and technological stress concentrator in the form of a chamfered circular hole on fatigue of VT3-1 alloy under the simultaneous influence of fretting corrosion was studied. The design of the special specimens made of VT3-1 alloy for conducting comparative tests for high-cycle fatigue is shown in Fig. 1. The design of L70 alloy counter-pieces used to create fretting corrosion damage in laboratory conditions is shown in Fig. 2. The method of conducting the experiment was as follows. Special specimens (Fig. 1) totalling 20 pieces were divided into four structural and technological groups: specimens without a hole and fretting-corrosion damage (the initial state); specimens with a ∅ 3 mm hole without fretting corrosion damages; specimens without a ∅ 3 mm hole with fretting corrosion damages of different run; specimens with a ∅ 3 mm hole, and fretting corrosion damages of a different run. Prior to the experiment all specimens were subjected to recrystallization annealing in the protective atmosphere (Тann = 650 С) and were instrumented with strain gages with a gage length of l = 10 mm. In order to determine the necessary continuous run of specimen fretting wear to reliably achieve each of the 3 main stages of the fretting process, the fretting wear diagram for the specimen pair VT3-1-L70 was taken at the load parameters set above. It is established that the end of the adhesion interaction stage corresponds to N = 5 ⋅ 104 cycles, and the end of the run-in stage and the onset of the stage of steady wear corresponds to N ≈ 105 cycles of interaction. Results of comparative tests for fatigue based on N0 = 5 ⋅ 106 cycles are presented in Table 1. Fig. 1. Outline drawing of the specimen for conducting comparative tests for high-cycle fatigue (Split image A – A is enlarged 5-fold) Rys. 1. Szkic próbki do przeprowadzenia testów porównawczych zmęczenia w wysokiej częstotliwości (fragment A–A jest powiększony 5-krotnie) Fig. 2. Outline drawing of the counter-piece to produce fretting corrosion damages Rys. 2. Szkic przeciwpróbki do badania zużycia w wyniku korozji ciernej Table 1 indicates that fretting-corrosion damages of the surface, including those in conjunction with the structural and technological stress concentrator in the form of a circular chamfered hole, practically do not affect the high-cycle fatigue of the titanium alloy VT3-1. Indeed, comparing the obtained values of σ–1 cond in Groups 1 and 3, it is easy to see that decrease in endurance limit of specimens with fretting wear damage makes 9 ISSN 0208-7774 T R I B O L O G I A 2/2020 Table 1. Specimen fatigue test results Tabela 1. Wyniki testu zmęczeniowego próbki Group No. Specimen No. Conventional endurance limit: σ–1 cond, MPa Average value σ–1 cond, MPa Specimen rupture life Nrupt, tsd cycles

Rodrigo Zacca, Rui Azevedo, R. Peterson Silveira et al.

Abstract Zacca, R, Azevedo, R, Peterson Silveira, R, Vilas-Boas, JP, Pyne, DB, Castro, FAdS, and Fernandes, RJ. Comparison of incremental intermittent and time trial testing in age-group swimmers. J Strength Cond Res 33(3): 801–810, 2019—The aim of this study was to compare physiological and biomechanical characteristics between an incremental intermittent test and a time trial protocol in age-group swimmers. Eleven national level age-group swimmers (6 men and 5 women) performed a 7 × 200-m incremental intermittent protocol (until exhaustion; 30-second rest) and a 400-m test (T400) in front crawl on separate days. Cardiorespiratory variables were measured continuously using a telemetric portable gas analyzer. Swimming speed, stroke rate, stroke length, and stroke index were assessed by video analysis. Physiological (oxygen uptake, heart rate, and lactate concentrations) and biomechanical variables between seventh 200-m step (in which the minimal swimming speed that elicits maximal oxygen uptake—vV[Combining Dot Above]O2max was identified) and T400 (time trial/fixed distance) were compared with a paired student's t test, Pearson's product-moment correlation, Passing-Bablok regression, and Bland-Altman plot analyses. There were high level of agreement and high correlations (r-values ∼0.90; p ⩽ 0.05) for all physiological variables between the seventh 200-m step and T400. Similarly, there were high level of agreements and high correlations (r-values ∼0.90; p ⩽ 0.05) for all biomechanical variables and only trivial bias in swimming speed (0.03 m·s−1; 2%). Primary physiological and biomechanical responses between incremental intermittent and representative time trial protocols were similar, but best practice dictates protocols should not be used interchangeably to minimize errors in prescribing swimming training speeds. The T400 is a valid, useful, and easier to administer test for aerobic power assessment in age-group swimmers.

M. Reggiani, S. Quanz, M. Meyer et al.

We present L′- and J-band high-contrast observations of HD 169142, obtained with the Very Large Telescope/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager, respectively. A source located at 0.″156 ± 0.″032 north of the host star (P.A. = 7.°4 ± 11.°3) appears in the final reduced L′ image. At the distance of the star (∼145 pc), this angular separation corresponds to a physical separation of 22.7 ± 4.7 AU, locating the source within the recently resolved inner cavity of the transition disk. The source has a brightness of L′ = 12.2 ± 0.5 mag, whereas it is not detected in the J band (J >13.8 mag). If its L′ brightness arose solely from the photosphere of a companion and given the J − L′ color constraints, it would correspond to a 28–32 MJupiter object at the age of the star, according to the COND models. Ongoing accretion activity of the star suggests, however, that gas is left in the inner disk cavity from which the companion could also be accreting. In this case, the object could be lower in mass and its luminosity enhanced by the accretion process and by a circumplanetary disk. A lower-mass object is more consistent with the observed cavity width. Finally, the observations enable us to place an upper limit on the L′-band flux of a second companion candidate orbiting in the disk annular gap at ∼50 AU, as suggested by millimeter observations. If the second companion is also confirmed, HD 169142 might be forming a planetary system, with at least two companions opening gaps and possibly interacting with each other.

M. Lilly, K. Cooper, J. Eisenstein et al.

We recently reported [PRL 82, 394 (1999)] large transport anisotropies in a two-dimensional electron gas in high Landau levels. These observations were made utilizing both square and Hall bar sample geometries. Simon recently commented [cond-mat/9903086] that a classical calculation of the current flow in the sample shows a magnification of an underlying anisotropy when using a square sample. In this reply we present more recent data obtained with a very high mobility sample, and reiterate that, with or without magnification, an anisotropic state develops in high Landau levels at very low temperatures.

H. Nami, F. Mohammadkhani, F. Ranjbar

Zhang Yao-we

Seung-Ho Lee, Gilbong Lee, Young-Soo Lee et al.

T. Lourenço, L. Martins, L. S. Tessutti et al.

P. Peeling, Sacha K. Fulton, M. Sim et al.

A. Horsley, K. Macleod, A. Robson et al.

Roohollah Nikooie, R. Gharakhanlo, H. Rajabi et al.

F. Gerbier, S. Foelling, A. Widera et al.

In response to a recent manuscript [cond-mat/0609685] on the analysis of interference patterns produced by ultracold atoms released from an optical lattice, we point out that in the presence of a Bose-Einstein condensate the interference pattern can be strongly modified by interaction effects and the presence of a harmonic trap superimposed on the lattice potential. Our results show that the visibility of the interference pattern is significant only if a sizeable condensate fraction is present in the trap.

Dimitri Hatziavramidis

Fierro, de Candia A, Coniglio

In this paper we study the three-dimensional frustrated lattice gas model in the annealed version, where the disorder is allowed to evolve in time with a suitable kinetic constraint. Although the model does not exhibit any thermodynamic transition it shows a diverging peak at some characteristic time in the dynamical nonlinear susceptibility, similar to the results on the p-spin model in mean field and the Lennard-Jones mixture recently found by Donati et al. (e-print cond-mat/9905433). Comparing these results to those obtained in the model with quenched interactions, we conclude that the critical behavior of the dynamical susceptibility is reminiscent of the thermodynamic transition present in the quenched model, and signaled by the divergence of the static nonlinear susceptibility, suggesting therefore a similar mechanism also in supercooled glass-forming liquids.