Hasil untuk "cond-mat"

G. Marković, D. Dizdar, I. Jukić et al.

B. Kilbride, J. Coleman, J. Fraysse et al.

Alternating current (ac) and direct current (dc) conductivities have been measured in polymer-nanotube composite thin films. This was carried out for a range of concentrations of multiwall nanotubes in two polymer hosts, poly(m-phenylenevinylene-co-2,5-dioctyloxyp-phenylenevinylene) (PmPV) and polyvinylalcohol (PVA). In all cases the dc conductivity σDC was ohmic in the voltage range studied. In general the ac conductivity displayed two distinct regions, a frequency independent region of magnitude σ0 at low frequency and a frequency dependent region at higher frequency. Both σDC and σ0 followed a percolation scaling law of the form σ∝(p−pc)t with pc=0.055% by mass and t=1.36. This extrapolates to a conductivity of 1×10−3 S/m for 100% nanotube content. Such a low value reflects the presence of a thick polymer coating, resulting in poor electrical connection between tubes. This leads to the suggestion that charge transport is controlled by fluctuation induced tunneling. In the high frequency regime the cond...

Katrina A. Rieger, N. P. Birch, Jessica D. Schiffman

J. Gehling

Jean de Dieu Niyigena, I. Ngaruye, J. Nzabanita et al.

Quadratic discriminant analysis is a well-established supervised classification method, which extends the linear the linear discriminant analysis by relaxing the assumption of equal variances across classes. In this study, quadratic discriminant analysis is used to develop a quadratic classification rule based on repeated measurements. We employ a bilinear regression model to assign new observations to predefined populations and approximate the misclassification probability. Through weighted estimators, we estimate unknown mean parameters and derive moments of the quadratic classifier. We then conduct numerical simulations to compare misclassification probabilities using true and estimated mean parameters, as well as probabilities computed through simulation. Our findings suggest that as the distance between groups widens, the misclassification probability curve decreases, indicating that classifying observations is easier in widely separated groups compared to closely clustered ones.

Jarla Thiesbrummel, F. Peña-Camargo, K. Brinkmann et al.

Understanding performance losses in all‐perovskite tandem photovoltaics is crucial to accelerate advancements toward commercialization, especially since these tandem devices generally underperform in comparison to what is expected from isolated layers and single junction devices. Here, the individual sub‐cells in all‐perovskite tandem stacks are selectively characterized to disentangle the various losses. It is found that non‐radiative losses in the high‐gap subcell dominate the overall recombination in the baseline system, as well as in the majority of literature reports. Through a multi‐faceted approach, the open‐circuit voltage (VOC) of the high‐gap perovskite subcell is enhanced by 120 mV. Employing a novel (quasi) lossless indium oxide interconnect, this enables all‐perovskite tandem solar cells with 2.00 V VOC and 23.7% stabilized efficiency. Reducing transport losses as well as imperfect energy‐alignments boosts efficiencies to 25.2% and 27.0% as identified via subcell selective electro‐ and photo‐luminescence. Finally, it is shown how, having improved the VOC, improving the current density of the low‐gap absorber pushes efficiencies even further, reaching 25.9% efficiency stabilized, with an ultimate potential of 30.0% considering the bulk quality of both absorbers measured using photo‐luminescence. These insights not only show an optimization example but also a generalizable evidence‐based optimization strategy utilizing optoelectronic sub‐cell characterization.

M. Beato, N. Datson, L. Anderson et al.

ABSTRACT Beato, M, Datson, N, Anderson, L, Brownlee, T, Coates, A, and Hulton, A. Rationale and practical recommendations for testing protocols in female soccer: A narrative review. J Strength Cond Res XX(X): 000-000, 2023-The aim of this narrative review is to evaluate the presented literature on tests (aerobic, speed, changes of direction [COD], strength, power, jump, and anthropometry) of the varied components of female soccer and to draw attention to the most suitable protocols to allow practitioners to accurately track players' fitness status. The 2 most common field tests used to assess aerobic fitness are the Yo-Yo intermittent test (level 1 and level 2) and the 30-15 intermittent fitness test because of an ability to measure multiple players at once with a soccer-specific intermittent profile. The sprinting performance can be assessed on distances of <30 m; however, longer distances (e.g., 40 m) allow for achieving peak speed (flying sprint test), which can be assessed using global navigation satellite system. Changes-of-direction capacity has been found to be an important component of players testing and training programs, although there is no "gold standard" to assess COD or repeated sprint ability performance in female players. Lower-limb power can be assessed using jump tests that can use force platforms, jump mats, and optoelectronic devices, while maintaining a good reliability. Several in-direct tests are currently available for assessing anthropometry parameters, such as skinfold thickness, hydrodensitometry, and ultrasound. However, dual-energy x-ray absorptiometry is the most valid and reliable method for assessing body composition in team sport athletes, with the addition of bone health that is a key measure in female athletes. In conclusion, the evidence reported in this review will be able to aid practitioners, coaches, and researchers to decide which tests meet the requirements of their environment.

Martin Keller, Eric Lichtenstein, R. Roth et al.

Supplemental Digital Content is Available in the Text. Abstract Keller, M, Lichtenstein, E, Roth, R, and Faude, O. Balance training under fatigue: a randomized controlled trial on the effect of fatigue on adaptations to balance training. J Strength Cond Res 38(2): 297–305, 2024—Balance training is an effective means for injury prevention in sports. However, one can question the existing practice of putting the balance programs at the start of a training session (i.e., train in an unfatigued state) because the occurrence of injuries has been associated with fatigue. Therefore, the aim of this study was to assess the influence of balance training in a fatigued or an unfatigued state on motor performance tested in fatigued and unfatigued conditions. Fifty-two, healthy, active volunteers (28.0 years; 19 women) were randomly allocated to 1 of 3 different training groups. The BALANCE group completed 6 weeks of balance training. The other 2 groups completed the identical balance tasks either before (BALANCE-high-intensity interval training [HIIT]) or after (HIIT-BALANCE) a HIIT session. Thus, these groups trained the balance tasks either in a fatigued or in an unfatigued state. In PRE and POST tests, balance (solid ground, soft mat, wobble board) and jump performance was obtained in fatigued and unfatigued states. Balance training resulted in reduced sway paths in all groups. However, the linear models revealed larger adaptations in BALANCE-HIIT and BALANCE when compared with HIIT-BALANCE (d = 0.22–0.71). These small to moderate effects were—despite some uncertainties—consistent for the “unfatigued” and “fatigued” test conditions. The results of this study revealed for the first time that balance training under fatigue results in diminished adaptations, even when tested in a fatigued state. Therefore, the data indicate that balance training should be implemented at the start of a training session or in an unfatigued state.

L. Baumgartner, R. Reid, C. Dupraz et al.

J. Strathern, A. J. Klar, James B. Hicks et al.

Joseph I. Esformes, T. Bampouras

Donald E. Canfield, D. D. Marais

L. Stal, H. Gemerden, W. Krumbein

N. Stark, C. Jordan

Yuan Xu, B. He

Jeroen van den Brink, Daniel I. Khomskii

In this contribution to the special issue on multiferroics we focus on multiferroicity driven by different forms of charge ordering. We will present the generic mechanisms by which charge ordering can induce ferroelectricity in magnetic systems. There is a number of specific classes of materials for which this is relevant. We will discuss in some detail $(i)$ perovskite manganites of the type (PrCa)MnO$_3$, $(ii)$ the complex and interesting situation in magnetite Fe$_3$O$_4$, $(iii)$ strongly ferroelectric frustrated LuFe$_2$O$_4$, $(iv)$ an example of a quasi one-dimensional organic system. All these are "type-I" multiferroics, in which ferroelectricity and magnetism have different origin and occur at different temperatures. In the second part of this article we discuss "type-II" multiferroics, in which ferroelectricity is completely {\it due to} magnetism, but with charge ordering playing important role, such as $(v)$ the newly-discovered multiferroic Ca$_3$CoMnO$_6$, $(vi)$ possible ferroelectricity in rare earth perovskite nickelates of the type RNiO$_3$, $(vii)$ multiferroic properties of manganites of the type RMn$_2$O$_5$, $(viii)$ of perovskite manganites with magnetic E-type ordering and $(ix)$ of bilayer manganites.

Arne Brataas, A. G. Mal'shukov, Yaroslav Tserkovnyak

We consider Rashba spin-orbit effects on spin transport driven by an electric field in semiconductor quantum wells. We derive spin diffusion equations that are valid when the mean free path and the Rashba spin-orbit interaction vary on length scales larger than the mean free path in the weak spin-orbit coupling limit. From these general diffusion equations, we derive boundary conditions between regions of different spin-orbit couplings. We show that spin injection is feasible when the electric field is perpendicular to the boundary between two regions. When the electric field is parallel to the boundary, spin injection only occurs when the mean free path changes within the boundary, in agreement with the recent work by Tserkovnyak et al. [cond-mat/0610190].

M. Sztyren

The present paper develops the ideas introduced in {\em cond-mat/0312673}. The construction of a hybrid discrete-continuous model of layered superconductors is briefly presented. The model bases on the classic Lawrence-Doniach scenario with admitting, however, long-range interactions between atomic planes. Moreover, apart from Josephson couplings they involve the proximity effects. The range of interactions, K, can, in principle, be arbitrary large. The solutions corresponding to the range K=2 are exposed. The fundamental excitations are understood as deviations from stable ground states.The formulae for energy of those excitations are constructed. The possible shapes of dispersion curves are analysed. For each type of shape the corresponding values of physically measurable quantities like effective maa and bandwidth are expressed by coupling parameters.

Lu Li, J. G. Checkelsky, Seiki Komiya et al.

We report here the supplementary material for Ref. [1]. Using torque magnetometry, we measured the magnetization anisotropy of 7 crystals of $\rm La_{2-x}Sr_xCuO_4$ (LSCO). In optimally-doped cuprates, the bulk susceptibility is dominated by the paramagnetic van-Vleck orbital term $χ_{orb}$ which has a significant anisotropy ($χ^{orb}_c>χ^{orb}_{ab}$) that changes weakly with $T$ (subscripts $c$ and ${ab}$ identify quantities measured with $\bf H||c$ and $\bf H\perp c$, respectively). Moreover, in the lightly-doped regime, the paramagnetic spin susceptibilities $χ^s_c$ and $χ^s_{ab}$ become significantly large below the interval 40-60 K. However, the spin susceptibility is very nearly isotropic (except below 10 K where its anisotropy becomes measurable). Against the large orbital and spin terms, the weak diamagnetic signal is very difficult to resolve using standard bulk magnetometry in lightly-doped cuprates. By contrast, torque magnetometry selectively detects the orbital diamagnetism generated by supercurrents confined to the CuO$_2$ layers while ignoring the large spin contribution when it is isotropic. The orbital van-Vleck contribution is also detected, but as a ``background'' that is $H$-linear to intense fields and only mildly $T$ dependent.

Ulrich

In this article, subrade reaction, the most important variable in designing mat foundations, is reviewed in four landmark buildings in Houston, Ttexas. Broad concepts related to mat foundation analysis using the finite element method are described to explain the related salient soil-structure interaction concepts. A comprenehsive examination is also made of structural considerations in connection with mat foundation design. It is noted that use of a uniform coefficient of subgrade reaction to analyze and design mat foundations is an oversimplification of the soil response and will lead to wrong designs. The coefficient of subradge reaction may vary considerably across a mat. After analysis of bearing capacity, the discrete area method should be used to model mat-soil interaction.