Heat pumps based on magnetocaloric and electrocaloric working bodies-in which entropic phase transitions are driven by changes of magnetic and electric field, respectively-use displaceable fluids to ...establish relatively large temperature spans between loads to be cooled and heat sinks
. However, the performance of prototypes is limited because practical magnetocaloric working bodies driven by permanent magnets
and electrocaloric working bodies driven by voltage
display temperature changes of less than 3 kelvin. Here we show that high-quality multilayer capacitors of PbSc
Ta
O
display large electrocaloric effects over a wide range of starting temperatures when the first-order ferroelectric phase transition is driven supercritically (as verified by Landau theory) above the Curie temperature of 290 kelvin by electric fields of 29.0 volts per micrometre. Changes of temperature in the large central area of the capacitor peak at 5.5 kelvin near room temperature and exceed 3 kelvin for starting temperatures that span 176 kelvin (complete thermalization would reduce these values from 5.5 to 3.3 kelvin and from 176 to 73 kelvin). If magnetocaloric working bodies were to be replaced with multilayer capacitors of PbSc
Ta
O
, then the established design principles behind magnetocaloric heat pumps could be repurposed for better performance without bulky and expensive permanent magnets.
Abstract
Ferroaxial materials that exhibit spontaneous ordering of a rotational structural distortion with an axial vector symmetry have gained growing interest, motivated by recent extensive studies ...on ferroic materials. As in conventional ferroics (e.g., ferroelectrics and ferromagnetics), domain states will be present in the ferroaxial materials. However, the observation of ferroaxial domains is non-trivial due to the nature of the order parameter, which is invariant under both time-reversal and space-inversion operations. Here we propose that NiTiO
3
is an order-disorder type ferroaxial material, and spatially resolve its ferroaxial domains by using linear electrogyration effect: optical rotation in proportion to an applied electric field. To detect small signals of electrogyration (order of 10
−5
deg V
−1
), we adopt a recently developed difference image-sensing technique. Furthermore, the ferroaxial domains are confirmed on nano-scale spatial resolution with a combined use of scanning transmission electron microscopy and convergent-beam electron diffraction. Our success of the domain visualization will promote the study of ferroaxial materials as a new ferroic state of matter.
Competitive cooling with capacitors
Current large-scale cooling devices use vapor compression refrigeration. The efficiency of air conditioners has been optimized, but they can be noisy and rely on ...problematic greenhouse gases. Two groups now present designs for electrocaloric cooling using lead scandium tantalate capacitors that change temperature under an electric field. Y. Wang
et al.
obtained a very large heat flux using only solid materials and a cooling fan to remove heat from their device. Torello
et al.
used fluids for heat transfer, leading to a very large temperature difference between the hot side and the cold side. The new designs demonstrate the potential for devices that might be competitive with vapor compression–based appliances with further optimization.
Science
, this issue p.
129
, p.
125
Two designs for electrocaloric cooling suggest that it may be competitive with vapor compression cooling.
Cooling devices based on caloric materials have emerged as promising candidates to become the next generation of coolers. Several electrocaloric (EC) heat exchangers have been proposed that use different mechanisms and working principles. However, a prototype that demonstrates a competitive temperature span has been missing. We developed a parallel-plate active EC regenerator based on lead scandium tantalate multilayer capacitors. After optimizing the structural design by using finite element modeling for guidance and to considerably improve insulation, we measured a maximum temperature span of 13.0 kelvin. This temperature span breaks a crucial barrier and confirms that EC materials are promising candidates for cooling applications.
The time of propagation (TOP) counter is a novel particle identification device for the Belle II experiment, utilizing the ring imaging Cherenkov technique. It is composed of a 2.7 m long quartz bar ...and 32 micro channel plate photomultiplier tubes (MCP-PMTs) attached on the end of the bar. The MCP-PMT has a typical quantum efficiency of 28%, a photoelectron collection efficiency of about 55%, and a transit time spread (TTS) less than 50 ps for single photon detection. Since the TOP counters are installed in the 1.5 T magnetic field of the Belle II detector, the MCP-PMTs are required to keep those characteristics with gain of more than 510 super(5) in the magnetic field. Therefore, we investigated gain, TTS, and single photon detection efficiency of the MCP-PMTs in the magnetic field and found that they satisfy the requirements. We are starting complete inspections for more than 500 MCP-PMTs, and have inspected up to 87 MCP-PMTs.
We present new numerical results in buckling failure analysis of cracked composite functionally graded plates subjected to uniaxial and biaxial compression loads. An accurate extended 3-node ...triangular plate element in the context of the extended finite element method (XFEM) is developed, integrating the discrete shear gap method (DSG) to eliminate shear-locking. The plate kinematics is based on the Reissner–Mindlin theory, and material properties are assumed to vary through thickness direction, obeying a power law distribution. The developed DSG-XFEM is found to be effective and accurate as it owns many desirable advantages: conveniently representing crack geometry which is independent of the mesh; shear-locking effect is no longer valid; mesh distortion is insensitive and controllable; thin plates is possible; triangular elements are easily generated for problems even with complex geometries; and high accuracy. All these arisen features are demonstrated through numerical examples and the effects of crack-length, material gradation, mesh distortion, inclined angles of cracks, boundary conditions, width-to-thickness ratio, length ratio, etc. on the critical buckling coefficient (CBC) are analyzed. Numerical results reveal that the material gradation, crack-length, thickness, length ratios, etc. have a strong effect on the behavior of CBC. This phenomenon is mainly attributed to the plate stiffness degradation due to the presence of local defects and material composition. Also, the boundary conditions greatly alter the CBC whereas the inclination of cracked angle is found to be insignificant.
With the full data sample of 772×106 BB¯ pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay B¯→D*τ−ν¯τ is studied with the hadronic τ decays τ−→π−ντ and τ−→ρ−ντ. ...The τ polarization Pτ(D*) in two-body hadronic τ decays is measured, as well as the ratio of the branching fractions R(D*)=B(B¯→D*τ−ν¯τ)/B(B¯→D*ℓ−ν¯ℓ), where ℓ− denotes an electron or a muon. Our results, Pτ(D*)=−0.38±0.51(stat)−0.16+0.21(syst) and R(D*)=0.270±0.035(stat)−0.025+0.028(syst), are consistent with the theoretical predictions of the standard model. The polarization values of Pτ(D*)>+0.5 are excluded at the 90% confidence level.
Abstract
Bulk velocities exceed thermal velocities for sufficiently radiation pressure-dominated accretion flows. We model the contribution of bulk Comptonization to the soft X-ray excess in active ...galactic nuclei. Bulk Comptonization is due to both turbulence and the background shear. We calculate spectra both taking into account and not taking into account bulk velocities using scaled data from radiation magnetohydrodynamic shearing box simulations. We characterize our results with temperatures and optical depths to make contact with other warm Comptonization models of the soft excess. We chose our fiducial mass, M = 2 × 106 M⊙, and accretion rate, L/LEdd = 2.5, to correspond to those fit to the super-Eddington narrow-line Seyfert 1 (NLS1) RE1034+396. The temperatures, optical depths and Compton y parameters we find broadly agree with those fit to RE1034+396. The effect of bulk Comptonization is to shift the Wien tail to higher energy and lower the gas temperature, broadening the spectrum. Observations of the soft excess in NLS1s can constrain the properties of disc turbulence if the bulk Comptonization contribution can be separated out from contributions from other physical effects, such as reflection and absorption.
We examine heating and cooling in protostellar disks using three-dimensional radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation ...diffusion approximations. The disk atmosphere is ionized by stellar X-rays, well coupled to magnetic fields, and sustains a turbulent accretion flow driven by magnetorotational instability, while the interior is resistive and magnetically dead. The turbulent layers are heated by absorbing the light from the central star and by dissipating the magnetic fields. They are optically thin to their own radiation and cool inefficiently. The optically thick interior in contrast is heated only weakly, by re-emission from the atmosphere. The interior is colder than a classical viscous model and isothermal. The magnetic fields support an extended atmosphere that absorbs the starlight 1.5 times higher than the hydrostatic viscous model. The disk thickness thus measures not the internal temperature, but the magnetic field strength. Fluctuations in the fields move the starlight-absorbing surface up and down. The height ranges between 13% and 24% of the radius over timescales of several orbits, with implications for infrared variability. The fields are buoyant, so the accretion heating occurs higher in the atmosphere than the stresses. The heating is localized around current sheets, caused by magnetorotational instability at lower elevations and by Parker instability at higher elevations. Gas in the sheets is heated above the stellar irradiation temperature, even though accretion is much less than irradiation power when volume averaged. The hot optically thin current sheets might be detectable through their line emission.
Epilepsy of infancy with migrating focal seizures (EIMFS) is an infantile epileptic encephalopathy characterized by refractory seizures, severe psychomotor delay, and multiple moving epileptic ...discharges. The genetic etiology of EIMFS is relatively homogeneous with the majority of causative mutations found in KCNT1. Currently, gene panel or whole‐exome sequencing is used for testing. To verify the pathogenicity of a variant, co‐segregation of the variant and the disorder in a pedigree is important; hence, de novo mutations that are judged to be deleterious may be considered pathogenic because the patients are isolated. In contrast, in cases from non‐consanguineous families, genes that cause disorders in a recessive manner should remain as potential candidates. Herein, we performed gene panel sequencing of a patient with EIMFS from a non‐consanguineous family, and found a compound heterozygous constellation consisting of a maternally inherited p.Ser399Leu and a de novo p.Arg880Leu in SLC12A5, which encodes the neuronal KCC2 cotransporter. These unique mutations show gene variants that act in a recessive manner may be pathogenic for patients from non‐consanguineous families.
Identification of a novel compound heterozygous constellation (c.1196C>T(;) 2639G>T:p.p.Ser399Leu(;) p.Arg880Leu) in SLC12A5, which consisted of a maternally inherited mutation (p.Ser399Leu) and a de novo mutation (p.Arg880Leu), in a patient with epilepsy of infancy with migrating focal seizures from a non‐consanguineous family.
On increasing the active/total volume ratio of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 multilayer capacitors (MLCs), the electrocaloric temperature change measured using a thermocouple near the centre ...increases, until saturating to reveal the nominally adiabatic limit (|ΔT| ~ 2.7 K for rapid field changes of |ΔE| = 28.8 V µm−1). For all MLCs that we studied, the practice of multiplying the measured temperature change by the total/active heat capacity ratio causes the adiabatic temperature change to be overestimated by a small numerical factor. These findings highlight the challenge associated with quantifying electrocaloric effects in MLCs of the type that are currently being used as working bodies in prototype cooling devices.
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