Strain-hardening (the increase of flow stress with plastic strain) is the most important phenomenon in the mechanical behaviour of engineering alloys because it ensures that flow is delocalized, ...enhances tensile ductility and inhibits catastrophic mechanical failure
. Metallic glasses (MGs) lack the crystallinity of conventional engineering alloys, and some of their properties-such as higher yield stress and elastic strain limit
-are greatly improved relative to their crystalline counterparts. MGs can have high fracture toughness and have the highest known 'damage tolerance' (defined as the product of yield stress and fracture toughness)
among all structural materials. However, the use of MGs in structural applications is largely limited by the fact that they show strain-softening instead of strain-hardening; this leads to extreme localization of plastic flow in shear bands, and is associated with early catastrophic failure in tension. Although rejuvenation of an MG (raising its energy to values that are typical of glass formation at a higher cooling rate) lowers its yield stress, which might enable strain-hardening
, it is unclear whether sufficient rejuvenation can be achieved in bulk samples while retaining their glassy structure. Here we show that plastic deformation under triaxial compression at room temperature can rejuvenate bulk MG samples sufficiently to enable strain-hardening through a mechanism that has not been previously observed in the metallic state. This transformed behaviour suppresses shear-banding in bulk samples in normal uniaxial (tensile or compressive) tests, prevents catastrophic failure and leads to higher ultimate flow stress. The rejuvenated MGs are stable at room temperature and show exceptionally efficient strain-hardening, greatly increasing their potential use in structural applications.
The deflection of a 1-GeV proton beam by a bent silicon crystal 1 mm long by an angle of (3.0 ± 0.1) mrad with an efficiency of (32 ± 3)% for end-face capture into the channeling regime has been ...observed for the first time in the presented experiment. The developed crystal deflector makes it possible to increase the beam deflection angle and can be used to produce low-intensity beams at intermediate energies.
An exciton is an electron-hole bound pair in a semiconductor. In the low-density limit, it is a composite Bose quasi-particle, akin to the hydrogen atom. Just as in dilute atomic gases, reducing the ...temperature or increasing the exciton density increases the occupation numbers of the low-energy states leading to quantum degeneracy and eventually to Bose-Einstein condensation (BEC). Because the exciton mass is small-even smaller than the free electron mass-exciton BEC should occur at temperatures of about 1 K, many orders of magnitude higher than for atoms. However, it is in practice difficult to reach BEC conditions, as the temperature of excitons can considerably exceed that of the semiconductor lattice. The search for exciton BEC has concentrated on long-lived excitons: the exciton lifetime against electron-hole recombination therefore should exceed the characteristic timescale for the cooling of initially hot photo-generated excitons. Until now, all experiments on atom condensation were performed on atomic gases confined in the potential traps. Inspired by these experiments, and using specially designed semiconductor nanostructures, we have collected quasi-two-dimensional excitons in an in-plane potential trap. Our photoluminescence measurements show that the quasi-two-dimensional excitons indeed condense at the bottom of the traps, giving rise to a statistically degenerate Bose gas.
We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant ...transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of 10-14 eV. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant β>5.8×108 at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp>3.7×10-16 (5.3×10-16) at a Yukawa length of λ=20 μm (95% C.L.).
The conductance and potential barrier height of a
p-n
-junction created by a pulsed current in a carbon fiber were investigated over a broad temperature range. The voltammetric characteristics of the
...p-n
-junction were obtained. Potential barriers of 53 and 75 meV were found for two opposite directions of potential applied to the
p-n
-junction. The specific resistances of the p- and n-branches ranged from 10
-4
to 10
-5
Ω∙m at temperatures from 300 to 600 K.
The newly inaugurated Research Resource for Complex Physiologic Signals, which was created under the auspices of the National Center for Research Resources of the National Institutes of Health, is ...intended to stimulate current research and new investigations in the study of cardiovascular and other complex biomedical signals. The resource has 3 interdependent components. PhysioBank is a large and growing archive of well-characterized digital recordings of physiological signals and related data for use by the biomedical research community. It currently includes databases of multiparameter cardiopulmonary, neural, and other biomedical signals from healthy subjects and from patients with a variety of conditions with major public health implications, including life-threatening arrhythmias, congestive heart failure, sleep apnea, neurological disorders, and aging. PhysioToolkit is a library of open-source software for physiological signal processing and analysis, the detection of physiologically significant events using both classic techniques and novel methods based on statistical physics and nonlinear dynamics, the interactive display and characterization of signals, the creation of new databases, the simulation of physiological and other signals, the quantitative evaluation and comparison of analysis methods, and the analysis of nonstationary processes. PhysioNet is an on-line forum for the dissemination and exchange of recorded biomedical signals and open-source software for analyzing them. It provides facilities for the cooperative analysis of data and the evaluation of proposed new algorithms. In addition to providing free electronic access to PhysioBank data and PhysioToolkit software via the World Wide Web (http://www.physionet. org), PhysioNet offers services and training via on-line tutorials to assist users with varying levels of expertise.
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•Steroid substrates modulate the interaction of three mitochondrial CYPs with common redox-partner.•Steroids action is isoform-specific: parameters of CYP11A1 – Adx and CYP11B – Adx ...complexes are affected differently.•Intermediates of the multistep reactions, catalyzed by CYP11A1 and CYP11B2 also modulate protein-protein interactions.
Steroidogenesis is strictly regulated at multiple levels, as produced steroid hormones are crucial to maintain physiological functions. Cytochrome P450 enzymes are key players in adrenal steroid hormone biosynthesis and function within short redox-chains in mitochondria and endoplasmic reticulum. However, mechanisms regulating supply of reducing equivalents in the mitochondrial CYP-dependent system are not fully understood. In the present work, we aimed to estimate how the specific steroids, substrates, intermediates and products of multistep reactions modulate protein-protein interactions between adrenodoxin (Adx) and mitochondrial CYP11 s. Using the SPR technology we determined that steroid substrates affect affinity and stability of CYP11s–Adx complexes in an isoform-specific mode. In particular, cholesterol induces a 4-fold increase in the rate of CYP11A1 – Adx complex formation without significant effect on dissociation (koff decreased ∼1.5-fold), overall increasing complex affinity. At the same time steroid substrates decrease the affinity of both CYP11B1 – Adx and CYP11B2 – Adx complexes, predominantly reducing their stability (4–7 fold). This finding reveals differentiation of protein-protein interactions within the mitochondrial pool of CYPs, which have the same electron donor. The regulation of electron supply by the substrates might affect the overall steroid hormones production. Our experimental data provide further insight into protein-protein interactions within CYP-dependent redox chains involved in steroidogenesis.
Theoretical studies of photochemical processes require a description of the energy surfaces of excited electronic states, especially near degeneracies, where transitions between states are most ...likely. Systems relevant to photochemical applications are typically too large for high-level multireference methods, and while time-dependent density functional theory (TDDFT) is efficient, it can fail to provide the required accuracy. A variational, time-independent density functional approach is applied to the twisting of the double bond and pyramidal distortion in ethylene, the quintessential model for photochemical studies. By allowing for symmetry breaking, the calculated energy surfaces exhibit the correct topology around the twisted-pyramidalized conical intersection even when using a semilocal functional approximation, and by including explicit self-interaction correction, the torsional energy curves are in close agreement with published multireference results. The findings of the present work point to the possibility of using a single determinant time-independent density functional approach to simulate nonadiabatic dynamics, even for large systems where multireference methods are impractical and TDDFT is often not accurate enough.
Wide practical application and increasing functional requirements for high-frequency ceramics lead to the active search for novel multicomponent ferrites and their synthesis technique. In this paper, ...a solution-combustion-assisted approach was proposed and realized for the successful production of ultra-magnetically soft LiZnTiMn-ferrite ceramics with advanced electromagnetic performance. Preceramic nanopowders of Li0.28Zn0.16Ti0.41Mn0.10Fe2.05O4 with spinel structure were synthesized via glycine-nitrate combustion at variable Ox/Red ratios (φ = 0.5, 1.0 and 1.5) followed by stabilizing quenching (600 °C, 2 h) and vibrating mill grinding. LiZnTiMn-ferrite-based fine ceramics were produced then using PVA binding (1 wt%), isostatic pressing (400 МPа) and Bi2O3-assisted (0.3 wt%) isothermal sintering (980 °C, 8 h) techniques. As result, a series of LiZnTiMn-ferrite ceramic samples were obtained and their structure was examined in detail using XRD, SEM, EDXS, AAS and ASA methods. It was shown that the Ox/Red ratio of the initial reaction solution is an efficient parameter affecting both crystallite size (26–38 nm) /crystallinity degree (up to 91%) of preceramic LiZnTiMn-ferrite powders and grain size (2.7–9.8 µm) / grain size distribution of resulting fine ceramics. Based on the results of vibration magnetometry it was found that ceramics samples possess the ultra-magnetically soft behavior with Hc = 0.61–0.89 Oe, Mr = 3.62–5.13 emu/g and Ms = 67.23–78.70 emu/g depending on the initial Ox/Red ratio. Besides, results of resonator analysis (100 Hz - 1000 kHz) demonstrate that the dielectric constant of the samples strongly depends on the average grain size and reaches its maximum value (~ 6.4⸱10–4) at 100 Hz for the stoichiometric Ox/Red ratio (φ = 1.0) of reagents, wherein the linewidths of ferromagnetic resonance and resonance of spin waves practically unchanged and are in ranges of 327–344 and 1.43–1.45 Oe, respectively. Thus, it was found that the solution combustion synthesis, adapted for fine ceramics production, provides controlling morphological and structural parameters of the pre-ceramic powders through Ox/Red ratio of initial reagents and as consequence, allows variable magnetic and dielectric characteristics of the resulting ceramic products. Developed ceramic materials can be promising for use as a basis for modern radio-electronic devices of both civil and military use.
•A new approach is proposed to obtain magnetically soft LiZnTiMn ferrite ceramics.•The procedure in based on a solution combustion synthesis followed by sintering.•The Red/Ox ratio affects not only the initial powders, but also the functional properties of ceramic products.•The final ceramics exhibit ultra-soft magnetic behavior.
•A shift in Isfjorden ice cover is linked to decadal trends in heat and salt content.•The fjord has a crucial impact on the local terrestrial climate.•Atlantification and changes in winter convection ...lead to near-surface inflow of AW.
Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord’s climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SSTw/VTw: 0.7 ± 0.1/0.9 ± 0.3 °C 10 yr−1) and summer (SSTS/VTS: 0.7 ± 0.1/0.6 ± 0.1 °C 10 yr−1). Hence, the local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10 yr−1) and summer (0.7 ± 0.1 °C 10 yr−1). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10 yr−1) and summer (0.07 ± 0.05 10 yr−1) suggest increased AW advection as a main reason for Isfjorden’s climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord’s impact on the local terrestrial climate.
In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths corresponding to the winter convection. Tides play a minor role in the variance in the currents, but are important in the side fjords where exchange with the warmer Isfjorden proper occurs in winter. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.
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