Gap-like Structures Research Articles

Ohmic vs. conventional heating: Influence of moderate electric fields on properties of potato protein isolate gels

The influence of moderate electric fields (MEF) on thermally induced gelation and network structures of patatin enriched potato protein (PPI) was investigated. PPI solutions with 9 wt% protein (pH 7) and 25 mM NaCl were heated from 25 to 65 °C via OH (3–24 V/cm) or conventional heating (COV) at various come-up (240 s and 1200 s) and holding times (30 s and 600 s). Self-standing gels were produced but less proteins denatured when heated via OH. Further, SDS-PAGE and GPC measurements revealed more native patatin remaining after OH treatment. Scanning electron microscopy showed OH gels to have more gap-like structures and frayed areas than COV treated gels which resulted in lower water holding capacity. On molecular scale, less hydrophobic interactions were measured within the protein network and FTIR trials showed the MEF to affect beta-sheet structures. OH gels further showed lower rigidity and higher flexibility, thus, gelling functionality was affected via OH.Industrial relevance: Ohmic heating (OH) is an advanced heating technology which has gained interest within the last decades as it is a highly energy and time efficient way to heat up foods. Additionally, as OH does not require any fossil energies, OH is considered to be a sustainable heating option for the food processing industry. During OH, electrical current is converted into heat within the food. However, it is not fully understood yet, whether OH influences the food matrix compared to conventional heating and how OH impacts certain ingredients, e.g. globular proteins and their denaturation/ gelation. This study helps to provide knowledge facilitating an implementation of OH into industry processes, serving a more sustainable food production. To evaluate the influence of OH on protein gelation, a patatin enriched potato protein was chosen as this protein offers a high protein functionality and therefore is of high interest for food industry (e.g. to be used as ingredient for plant based foods).

Microstructural Manipulation for Enhanced Average Thermoelectric Performance: A Case Study of Tin Telluride

Achieving a high average figure of merit in a low-cost/toxic compound, tin telluride (SnTe), is crucial for thermoelectric applications. Introducing gap-like structures into the rock–salt matrix once elucidated a large potential; however, the poor quantity and controllability of the planar defects become the drawbacks. Here, we demonstrate, by electron microscopy and X-ray diffraction, that dense planar cationic vacancies can be produced in Sb2Te3(Sn1–xGexTe)8 samples for the first time, leading to an effective targeted solution. On the basis of the optimized lattice matrix, a low room-temperature lattice thermal conductivity of ∼0.7 W m–1 K–1 (25% of pristine SnTe) can be achieved. Additionally, the first-principles calculation result reveals that the value of density-of-state effective mass is increased after manipulating the local cation matrix, resulting in an outstanding power factor of ∼2.5 mW m–1 K–2 at 723 K when x = 0.2. Eventually, a competitive maximum figure of merit ZTmax of ∼1.3 at 723 K and an excellent average ZT value of ∼0.78 at 323–773 K are simultaneously realized in Sb2Te3(Sn0.8Ge0.2Te)8. This pioneered study about manipulating gap-like structures and its effects on the transport properties of SnTe-based materials would also provide a promising alternative for pursuing other high ZTave compounds in the future.

Planetesimal rings as the cause of the Solar System’s planetary architecture

Astronomical observations reveal that protoplanetary disks around young stars commonly have ring- and gap-like structures in their dust distributions. These features are associated with pressure bumps trapping dust particles at specific locations, which simulations show are ideal sites for planetesimal formation. Here we show that our Solar System may have formed from rings of planetesimals—created by pressure bumps—rather than a continuous disk. We model the gaseous disk phase assuming the existence of pressure bumps near the silicate sublimation line (at T ~ 1,400 K), water snowline (at T ~ 170 K) and CO snowline (at T ~ 30 K). Our simulations show that dust piles up at the bumps and forms up to three rings of planetesimals: a narrow ring near 1 au, a wide ring between ~3–4 au and ~10–20 au and a distant ring between ~20 au and ~45 au. We use a series of simulations to follow the evolution of the innermost ring and show how it can explain the orbital structure of the inner Solar System and provides a framework to explain the origins of isotopic signatures of Earth, Mars and different classes of meteorites. The central ring contains enough mass to explain the rapid growth of the giant planets’ cores. The outermost ring is consistent with dynamical models of Solar System evolution proposing that the early Solar System had a primordial planetesimal disk beyond the current orbit of Uranus. The planetary architecture of the Solar System and its isotopic dichotomy can be reproduced using a protoplanetary disk model structured with rings and gaps, as commonly seen in protoplanetary disks around other stars.

Ring structure in the MWC 480 disk revealed by ALMA

Gap-like structures in protoplanetary disks are likely related to planet formation processes. In this paper, we present and analyze high-resolution (0.17′′× 0.11′′) 1.3 mm ALMA continuum observations of the protoplanetary disk around the Herbig Ae star MWC 480. Our observations show for the first time a gap centered at ~74 au with a width of ~23 au, surrounded by a bright ring centered at ~98 au from the central star. Detailed radiative transfer modeling of the ALMA image and the broadband spectral energy distribution is used to constrain the surface density profile and structural parameters of the disk. If the width of the gap corresponds to 4–8 times the Hill radius of a single forming planet, then the putative planet would have a mass of 0.4–3 MJ. We test this prediction by performing global three-dimensional smoothed particle hydrodynamic gas/dust simulations of disks hosting a migrating and accreting planet. We find that the dust emission across the disk is consistent with the presence of an embedded planet with a mass of ~2.3 MJ at an orbital radius of ~78 au. Given the surface density of the best-fit radiative transfer model, the amount of depleted mass in the gap is higher than the mass of the putative planet, which satisfies the basic condition for the formation of such a planet.

Diffusion-advection within dynamic biological gaps driven by structural motion.

To study the significance of advection in the transport of solutes, or particles, within thin biological gaps (channels), we examine theoretically the process driven by stochastic fluid flow caused by random thermal structural motion, and we compare it with transport via diffusion. The model geometry chosen resembles the synaptic cleft; this choice is motivated by the cleft's readily modeled structure, which allows for well-defined mechanical and physical features that control the advection process. Our analysis defines a Péclet-like number, A^{D}, that quantifies the ratio of time scales of advection versus diffusion. Another parameter, A^{M}, is also defined by the analysis that quantifies the full potential extent of advection in the absence of diffusion. These parameters provide a clear and compact description of the interplay among the well-defined structural, geometric, and physical properties vis-a[over ̀]-vis the advection versus diffusion process. For example, it is found that A^{D}∼1/R^{2}, where R is the cleft diameter and hence diffusion distance. This curious, and perhaps unexpected, result follows from the dependence of structural motion that drives fluid flow on R. A^{M}, on the other hand, is directly related (essentially proportional to) the energetic input into structural motion, and thereby to fluid flow, as well as to the mechanical stiffness of the cleftlike structure. Our model analysis thus provides unambiguous insight into the prospect of competition of advection versus diffusion within biological gaplike structures. The importance of the random, versus a regular, nature of structural motion and of the resulting transient nature of advection under random motion is made clear in our analysis. Further, by quantifying the effects of geometric and physical properties on the competition between advection and diffusion, our results clearly demonstrate the important role that metabolic energy (ATP) plays in this competitive process.

Theoretical study of optical conductivity of graphene with magnetic and nonmagnetic adatoms

We present a theoretical study of the optical conductivity of graphene with magnetic and nonmagnetic adatoms. First, by introducing alternating potential in a pure graphene, we demonstrate a gap formation in the density of states and the corresponding optical conductivity. We highlight the distinction between such a gap formation and the so-called Pauli blocking effect. Next, we apply this idea to graphene with adatoms by introducing magnetic interactions between the carrier spins and the spins of the adatoms. Exploring various possible ground-state spin configurations of the adatoms, we find that antiferromagnetic configuration yields the lowest total electronic energy, and is the only configuration that forms a gap. Furthermore, we analyze four different circumstances leading to similar gaplike structures and propose a means to interpret the magneticity and the possible orderings of the adatoms on graphene solely from the optical conductivity data. We apply this analysis to the recently reported experimental data of oxygenated graphene.

Tunneling spectra of break junctions involving Nb3Sn

The electronic gap structure of Nb3Sn was measured by the break-junction (BJ) tunneling technique. The superconducting gap values are estimated to be in the range 2Δ = 4–5.5 meV at T = 4.2 K as follows from the observed distinct conductance peaks. In addition to the superconducting gap structure, we observed reproducible hump-like structures at the biases of about ±20 and ±50 mV. Such a coexistence of gap and hump structures resembles the situation found in the high-Tc copper-oxide superconductors. Above the superconducting critical temperature Tc ∼ 18 K, the humps appear as the only gap-like structures. Their possible origin is discussed in connection to the structural phase transition occurring in Nb3Sn.

Tracing large-scale structures in circumstellar disks with ALMA

Planets are supposed to form in circumstellar disks. The gravitational potential of a planet perturbs the disk and leads to characteristic structures, i.e. spiral waves and gaps, in the disk's density profile. We perform a large-scale parameter study of the observability of these planet-induced structures in circumstellar disks with ALMA. On the basis of HD and MHD simulations, we calculated the disk temperature structure and (sub)mm images of these systems. These were used to derive simulated ALMA images. Because appropriate objects are frequent in Taurus, we focused on a distance of 140pc and a declination of 20{\deg}. The explored range of star-disk-planet configurations consists of 6 HD simulations (including magnetic fields and different planet masses), 9 disk sizes, 15 total disk masses, 6 different central stars, and two different grain size distributions. On almost all scales and in particular down to a scale of a few AU, ALMA is able to trace disk structures induced by planet-disk interaction or by the influence of magnetic fields on the wavelength range between 0.4 and 2.0mm. In most cases, the optimum angular resolution is limited by the sensitivity. However, within the range of typical masses of protoplanetary disks (0.1-0.001Msun) the disk mass has a minor impact on the observability. It is possible to resolve disks down to 2.67e-6Msun and trace gaps induced by a planet with M_p/M_s = 0.001 in disks with 2.67e-4Msun with a signal-to-noise ratio greater than three. The central star has a major impact on the observability of gaps, as well as the considered maximum grainsize of the dust in the disk. In general, it is more likely to trace planet-induced gaps in our MHD models, because gaps are wider in the presence of magnetic fields. We also find that zonal flows resulting from MRI create gap-like structures in the disk's re-emission radiation, which are observable with ALMA.

Single-crystal growth and optical conductivity of SrPt2As2superconductors

SrPt${}_{2}$As${}_{2}$ single crystals with CaBe${}_{2}$Ge${}_{2}$-type structure were synthesized by self-melting technique. X-ray diffraction, transmission electron microscopy, electrical resistivity, magnetic susceptibility, specific heat, and optical spectroscopy measurements were conducted to elucidate the properties of SrPt${}_{2}$As${}_{2}$. SrPt${}_{2}$As${}_{2}$ single crystals undergo a structural phase transition well above room temperature (about 450 K) and become superconducting at 5.18 K. The superconducting and structural phase transition temperatures are reduced by 6$%$ iridium doping. Both the pure SrPt${}_{2}$As${}_{2}$ and the Ir-doped single crystals are demonstrated to be highly metallic with rather high plasma frequencies. In particular, the optical spectroscopy measurement revealed two gaplike suppression structures: a stronger one at high energy near 12 000 cm${}^{\ensuremath{-}1}$ ($\ensuremath{\sim}$1.5 eV), and a less prominent one at lower energy near 3200 cm${}^{\ensuremath{-}1}$ ($\ensuremath{\sim}$0.4 eV) for the pure compound. We elaborate that the former is related to the correlation effect, while the latter could be attributed to the partial energy gap formation associated with structural phase transition.

Disorder effects in pnictides: a tunneling spectroscopy study

We present the synthesis and the tunneling spectroscopy study of superconductingFeSe0.5Te0.5 (Tc = 14 K),SmFeAsO0.85 (Tc = 54 K)and SmFeAsO0.9F0.1 (Tc = 45 K). The samples were characterized by Rietveld refinement of x-ray diffraction patterns andtransport as well as temperature-dependent magnetic measurements. Tunneling experiments onFeSe0.5Te0.5 revealed a singlesuperconducting gap ∼ 1 meV in BCS-like tunneling conductance spectra. InSmFeAsO0.85 andSmFeAsO0.9F0.1, however, more complex spectra were observed, characterized by two gap-like structures at ∼ 4 and ∼ 10 meV. These spectra are qualitatively understood assuming a two-band superconductor with a ‘s ±’ order parameter. We show that, depending on the sign relation between the pairingamplitudes in the two bands, the interband quasiparticle scattering has a crucial effect onthe shape of the tunneling spectra. On the other hand, single-gap spectra found inFeSe0.5Te0.5 are more compatible with a disorder-induced ‘s ’-wave gap, due to the Se–Te substitution.

Proximity effect between an unconventional superconductor and a ferromagnet with spin bandwidth asymmetry

We study the proximity effect within a junction made of an unconventional superconductor (US) and a ferromagnet $(F)$ in the clean limit with high barrier transparency. Superconductivity in the US side is described by an extended Hubbard model with intersite attractive interaction, while metallic ferromagnetism in the $F$ side is assumed to be originated by a relative change in the bandwidths of electrons with opposite spin. The effect of this mass-split mechanism is analyzed in conjunction with the usual Stoner-like one, where one band is rigidly shifted with respect to the other, due to the presence of a constant exchange field. Starting from the numerical solution of the Bogoliubov-de Gennes equations, we show that the two above mentioned mechanisms for ferromagnetism lead to different features as concerns the formation at the interface of dominant and subdominant superconducting components, as well as their propagation in the ferromagnetic side. This considerably affects the opening of gaplike structures in the local density of states for majority and minority spin electrons, leading to distinct effects as one moves toward the half-metallic regime, where the density of the minority carriers becomes vanishing.

Suppression of low-energy Andreev states by a supercurrent inYBa2Cu3O7−δ

We report a coherence-length scale phenomenon related to how the high-Tc order parameter (OP) evolves under a directly-applied supercurrent. Scanning tunneling spectroscopy was performed on current-carrying YBa_2Cu_3O_7-delta thin-film strips at 4.2K. At current levels well below the theoretical depairing limit, the low-energy Andreev states are suppressed by the supercurrent, while the gap-like structures remain unchanged. We rule out the likelihood of various extrinsic effects, and propose instead a model based on phase fluctuations in the d-wave BTK formalism to explain the suppression. Our results suggest that a supercurrent could weaken the local phase coherence while preserving the pairing amplitude. Other possible scenarios which may cause the observed phenomenon are also discussed.

Manipulation of double-stranded DNA by artificial restriction enzyme composed of Ce(IV)/EDTA and PNA

Through the invasion of pseudo-complementary PNA (pePNA) to double-stranded DNA, gap-like structures were formed at predetermined sites in both strands of PBR322 plasmid DNA. These gap-like sites were selectively hydrolyzed by Ce(IV)/EDTA complex, and two designed fragments were obtained. Furthermore, the scission fragment by this artificial restriction enzyme was successfully ligated with foreign DNA.

STM studies of individual Ti impurity atoms in Sr2RuO4

Abstract The unconventional superconductor, Sr2RuO4, was studied with an ultra-low temperature scanning tunneling microscope. Atomic resolution images of the SrO plane were obtained with perturbations caused by Ti impurities substituted for 0.125% of the Ru atoms clearly visible. A complicated gap-like structure in local density of states was measured at all locations on the surface, with some modifications caused by the Ti atoms. The superconducting gap was not clearly visible, possibly due to surface termination effects, but other gap-like structures were found at ∼5 and ∼50 meV .

Different tunneling regimes in La 2−xSr xCuO 4−δ break junctions

Tunneling spectroscopy studies have been performed on differently doped la 2−xSr xCuO 4−δ single crystals by break junction technique. By a fine adjustment of the mechanically controlled spacing between the two fractured electrodes, we were able to investigate highly stable conductance characteristics along the ab-planes in various tunneling regimes. In the weak link regime, Josephson effect was clearly observed with critical current decreasing monotonically with temperature and vanishing below the crystal's T c. By increasing the electrode's distance, in the quasiparticle regime, a well developed zero bias conductance peak and smeared gap-like structures were observed. All these features are consistent with the d-wave model for high T c superconductors.

Angle-resolved Andreev bound states in anisotropicd-wave high-TcYBa2Cu3O7−ysuperconductors

An unusual technique utilizing the two-dimensional junction configuration is introduced to study the pairing symmetry of a ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}y}$ cuprate superconductor. The zero bias conductance peak due to the Andreev bound states was measured for the ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}y}/\mathrm{I}/\mathrm{A}\mathrm{g}$ ramp-edge tunnel junctions with different crystal-interface boundary angles fabricated on the same chip. It was found to develop monotonically as the angle was increased and became a maximum at 45\ifmmode^\circ\else\textdegree\fi{}. Two gaplike structures were also found at the intermediate angle of 30\ifmmode^\circ\else\textdegree\fi{}. The result implies that ${d}_{x2\ensuremath{-}y2}$-wave pairing symmetry predominates in this cuprate.

Interface properties of YBa2Cu3O7-x/I/metaljunctions with native and artificial tunnelling barriers

Tunnelling spectroscopy was used to study interfaceproperties of YBa2Cu3O7-x (YBCO)/artificialbarrier/normal-metal and YBCO/native barrier/normal-metal tunnel junctions. As artificial tunnelling barriers, YBCO + 2% Co and CeO2 thin films were used. The native tunnelbarrier of YBCO was prepared by a surface treatment to create a YBCOlayer with oxygen deficiency. Tunnelling characteristics of thejunctions were obtained as a rule, but the corresponding differentialcharacteristics indicate suppression of the pair potential in YBCO nearthe barrier. Peculiarities like a linear dependence of the differentialconductance versus voltage, smeared gap-like structures, and increaseof the differential conductance close to zero bias voltage for thesejunctions were observed. These phenomena are discussed within themodel of complex structure creation in the tunnel junction as aresult of YBCO degradation near the contact with the metal, as well aspronouncedly inelastic processes in the degraded YBCO.

Observation of gap structures in La 1.85Sr 0.15CuO 4− δ single crystals by tunneling spectroscopy

We studied La 1.85Sr 0.15CuO 4− δ single crystals by tunneling spectroscopy both in planar and in break junction configurations. In the c-axis oriented planar junctions, with natural barriers and evaporated Pb film counterelectrodes, we observed at low-temperature gap-like structures around ±7–10 meV. In the a, b oriented break junctions we found conductance structures at ±15–20 mV, an increasing background at high biases and a conductance peak at zero voltage. The presence of this peak can be interpreted in terms of d-wave component for the order parameter in this material.

TUNNELING CONDUCTANCE OF A NORMAL METAL/INSULATOR/Sr 2RuO 4 JUNCTION

A theory of tunneling conductance spectra for a normal metal/insulator/Sr 2RuO 4 junction is presented. We assume several types of air potentials with triplet symmetries that are promising candidates for Sr 2RuO 4. The calculated conductance spectra show either zero bias peaks of gap-like structures depending on the orientations of the junctions. The existence of residual components in the gap reflects a non-unitary property of the superconducting states. Based on the calculation of a temperature dependence, we verify that a measurement temperature below 100 mK is required to determine the pairing symmetry experimentally.

Theory of Tunneling Conductance for Normal Metal/Insulator/ Triplet Superconductor Junction

Tunneling conductance spectra of normal metal/insulator/triplet superconductor junctions are investigated theoretically. As triplet paring states we select several types of symmetries that are promising candidates for the superconducting states in UPt 3 and in Sr 2 RuO 4 . The calculated conductance spectra are sensitive to the orientation of the junction which reflects the anisotropy of the pairing states. They show either zero-bias conductance peaks or gap-like structures depending on the orientation of the junctions. The existence of a residual density of states, peculiar to nonunitary states, is shown to have a significant influence on the properties of the conductance spectra. Present results serve as a guide for the experimental determination of the symmetry of the pair potentials in UPt 3 and Sr 2 RuO 4 .