An alternative to nickel coatings obtained from a Watts bath could be offered by coatings deposited from solutions based on environmentally-friendly citric acid and its salts. It was found that ...proper selection of the citrate solution concentration (0.3 M), the cathodic current density (5 A/dm2) and hydrodynamic conditions (600 rpm) allows homogeneous nanocrystalline coatings to be obtained, with high current efficiency and characterised by high microhardness (above 600 HV0.05). Furthermore, the properties of nickel coatings deposited in optimal conditions were compared with the characteristics of nickel coatings deposited from the commercially used low-concentrated Watts bath. Based on analysis using scanning and transmission electron microscopy, as well as X-ray diffraction, significant differences in the microstructure of the compared coatings, which determine their functional properties, were shown. Both coatings were homogeneous and adhered well to the steel substrate. However, significant differences can be observed in their surface morphology and structure. Nickel coatings deposited from citrate baths had a compact, globular surface and nanocrystalline microstructure. For coatings obtained from a Watts bath, a surface with visible pyramid-shaped structures was observed. Grains/clusters of grains were visible as a columnar-shape structure, with an average length of about 500–630 nm and a width of about 130–165 nm. In consequence, the microhardness of the nickel coatings obtained from citrate bath (about 618 HV0.05) was more than twice as high as the value for the coatings deposited from a Watts bath (about 261 HV0.05).
•Citrate-based bath as an alternative to commercially used Watts solution was tested.•Plating conditions for obtaining superior nanocrystalline Ni coatings were developed.•Citrate salts in the platting bath causes the significant crystallite size reduction.•The resulting Ni coatings are characterised by high hardness ∼618 HV (Watts bath ∼261 HV).
We study a quantum interacting spin system subject to an external drive and coupled to a thermal bath of vibrational modes, uncorrelated for different spins, serving as a model for dynamic nuclear ...polarization protocols. We show that even when the many-body eigenstates of the system are ergodic, a sufficiently strong coupling to the bath may effectively localize the spins due to many-body quantum Zeno effect. Our results provide an explanation of the breakdown of the thermal mixing regime experimentally observed above 4-5 K in these protocols.
Constant-flux gravity currents of viscoplastic fluid remain axisymmetric when extruded onto a dry horizontal plane. However, if the plane is coated with a shallow layer of water, the current suffers ...a dramatic non-axisymmetric instability in which localized $v$-shaped cuts appear in the outer edge where the viscoplastic fluid is in contact with water. These ‘fractures’ lengthen and guide the subsequent radial outflow, leading to distinctive flower-like patterns. This pattern formation process is illustrated for two viscoplastic materials, an aqueous suspension of Carbopol, and a mixture of water and joint compound (a kaolin-based, commercially available product). The fracturing spreads over the entire upper surface of the current when deeper water baths are used, complicating the extrusion patterns. The instability can be removed entirely when the ambient water layer is replaced by an immiscible liquid of comparable viscosity, indicating that the presence of water at the surface is key to the pattern formation process. We conjecture that the underlying mechanism is the fracture under tension of the viscoplastic material, exacerbated by the ambient water.
Bathing is a routine care procedure that exposes preterm infants to prolonged handling, which could cause stress and potentially disrupt infants' biobehavioral responses. The aim of this double-blind ...randomized crossover trial was to compare the preterm infant's body temperature, heart rate (HR), peripheral capillary oxygen saturation (SpO2), salivary cortisol levels, and sleep-wake states during and after swaddled and conventional tub baths. Forty-three infants born at 32 to 36 weeks postmenstrual age, weighing 2225 g or less, were enrolled in the study. Infants were videotaped before and after each type of baths. The time interval between baths ranged from 24 to 72 hours to allow a washout period. Physiological, hormonal, and behavioral responses were collected at baseline and during recovery from baths. No significant differences in the mean body temperature, HR, SpO2, salivary cortisol levels, and sleep-wake states between the bath types were observed in the baseline or recovery responses during the first 20 minutes after bath. Regardless of bath type, salivary cortisol levels showed a nonstatistical significant increase.
We study entanglement harvested from a quantum field through local interaction with Unruh-DeWitt detectors undergoing linear acceleration. The interactions allow entanglement to be swapped locally ...from the field to the detectors. We find an enhancement in the entanglement harvesting by two detectors with anti-parallel acceleration over those with inertial motion. This enhancement is characterized by the presence of entanglement between two detectors that would otherwise maintain a separable state in the absence of relativistic motion (with the same distance of closest approach in both cases). We also find that entanglement harvesting is degraded for two detectors undergoing parallel acceleration in the same way as for two static, comoving detectors in a de Sitter universe. This degradation is known to be different from that of two inertial detectors in a thermal bath. We comment on the physical origin of the harvested entanglement and present three methods for determining distance between two detectors using properties of the harvested entanglement. Information about the separation is stored nonlocally in the joint state of the accelerated detectors after the interaction; a single detector alone contains none. We also find an example of entanglement sudden death exhibited in parameter space.
The determination of the longitudinal spin Seebeck effect (LSSE) coefficient is currently plagued by a large uncertainty due to the poor reproducibility of the experimental conditions used in its ...measurement. In this work we present a detailed analysis of two different methods used for the determination of the LSSE coefficient. We have performed LSSE experiments in different laboratories, by using different setups and employing both the temperature difference method and the heat flux method. We found that the lack of reproducibility can be mainly attributed to the thermal contact resistance between the sample and the thermal baths which generate the temperature gradient. Due to the variation of the thermal resistance, we found that the scaling of the LSSE voltage to the heat flux through the sample rather than to the temperature difference across the sample greatly reduces the uncertainty. The characteristics of a single YIG/Pt LSSE device obtained with two different setups was (1.143 ± 0.007) 10
Vm/W and (1.101 ± 0.015) 10
Vm/W with the heat flux method and (2.313 ± 0.017) 10
V/K and (4.956 ± 0.005) 10
V/K with the temperature difference method. This shows that systematic errors can be considerably reduced with the heat flux method.
The finite-time dynamics, apart from its fundamental importance in nonequilibrium thermodynamics, is of great significance in designing heat engine cycles. We build an experimental apparatus to test ...the predicted long-time 1/τ scaling of the irreversible entropy generation in the finite-time (τ) thermodynamic process by compressing dry air in a temperature-controlled water bath. We present the first direct experimental validation of the scaling, utilized in many finite-time thermodynamic models at the long-time regime. The experimental data also demonstrate a clear deviation from the scaling at the short-time regime. We show the optimal control scheme to minimize the irreversible entropy generation in finite-time process. Such optimization shall bring new insight to the practical design of heat engine cycles.
Although the Unruh effect can be rigorously considered as well tested as free quantum field theory itself, it would be nice to provide experimental evidence of its existence. This is not easy because ...the linear acceleration needed to reach a temperature 1 K is of order 10^{20} m/s^{2}. Here, we propose a simple experiment reachable under present technology whose result may be directly interpreted in terms of the Unruh thermal bath. Instead of waiting for experimentalists to perform it, we use standard classical electrodynamics to anticipate its output and fulfill our goal.
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