Trapped Field Research Articles

Preliminary study of the avifauna of the families Numididae and Phasianidae (Galliformes) of the Bombo-Lumene hunting area and reserve in Kinshasa (DR Congo)

The present study consisted of the identification of Numididae and Phasianidae birds of the Bombo-Lumene Hunting Estate and Reserve with a view to a domestication trial of one or two of their species. It focuses on direct field observations and trapping of birds. The following parameters were targeted in relation to domestication: weight, size, diet of these birds. A total of 468 bird specimens were observed (105) and captured (363) in various habitats. Of the individuals captured, 31 or 8.5% were Numididae and 332 or 91.4% were Phasianidae. The identification revealed five (5) species, three (3) genera, two (2) families and a single order. The species Francolinus afer, Numida meleagris and Francolinus coqui are the richest with respectively 364 individuals, 58 individuals and 42 individuals. On the other hand, the species Guttera pucherani and Francolinus streptophorus are the least rich with three individuals and one individual respectively. As millet farming has already been successfully experimented elsewhere and in the Democratic Republic of Congo, the results obtained from the targeted parameters indicate that among the species identified, only the species Guttera pucherani (Numididae) and Francolinus afer (Phasianidae) are eligible for a domestication trial in the Democratic Republic of Congo.

A novel preform compaction method for fabricating high-performance Y–Ba–Cu–O single-grain bulk superconductor

A novel preform compaction method based on one new type of divisible mould was employed for fabricating single-grain YBCO bulk superconductor, which can complete the preform demoulding process through opening of the mould, rather than pushing the preform out in the regular mould. Thus it has natural superiority on eliminating macro-cracks, which has been proved by the sample surface morphology and the trapped field characterization. In addition, the divisible mould pressed sample exhibits higher levitation force and trapped field properties than the regular mould pressed samples, verifying the potentials of the divisible mould on improving the bulk performance. The optical micrograph results prove the superiority of the divisible mould on eliminating tiny cracks on sample surface. The processing facility and sample reliability brought by the divisible mould should also be emphasized, because the crushing and re-pressing of preform when it presents visible cracks can be omitted and the failed samples with surface cracks will no longer appear. Consequently, the experimental efficiency and stability are both enhanced.

Negative zero‐field‐cooled magnetization and magnetic switching in multiferroic Lu0.5Sc0.5FeO3 ceramics

AbstractIn this study, we have investigated the negative magnetization of Lu0.5Sc0.5FeO3 (LSFO) ceramics in the zero‐field‐cooled (ZFC) mode. The negative magnetization in ZFC measurement appears below the Neél temperature (TN) in LSFO, which is probably caused by the residual negative trapping field in superconducting magnet, and is closely related to the giant coercivity in LSFO. By fitting the high‐temperature paramagnetic data under nominal zero magnetic field, the negative trapping field in superconducting magnet is found to be −3.28 Oe. The giant coercivity is ascribed to the strong uniaxial magnetocrystalline anisotropy in LSFO, which can cause the strong magnetic domain wall pinning effect to limit the nucleation of reversed domains under reverse field. In addition, a switchable magnetization switching is realized in LSFO. The magnetization of LSFO can stably switch between positive and negative values when the applied magnetic field was switched between 0.5 and 3 kOe, which suggests that the LSFO samples are suitable for potential applications in magnetic storage.

Identification of Components of the Aggregation Pheromone of the Guam Strain of Coconut Rhinoceros Beetle, Oryctes rhinoceros, and Determination of Stereochemistry

The coconut rhinoceros beetle, Oryctes rhinoceros (Linnaeus 1758) (Coleoptera: Scarabaeidae: Dynastinae) (CRB), is endemic to tropical Asia where it damages both coconut and oil palm. A new invasion by CRB occurred on Guam in 2007 and eradication attempts failed using commonly applied Oryctes rhinoceros nudivirus (OrNV) isolates. This and subsequent invasive outbreaks were found to have been caused by a previously unrecognized haplotype, CRB-G, which appeared to be tolerant to OrNV. The male-produced aggregation pheromone of the endemic, susceptible strain of O. rhinoceros (CRB-S) was previously identified as ethyl 4-methyloctanoate. Following reports from growers that commercial lures containing this compound were not attractive to CRB-G, the aim of this work was to identify the pheromone of CRB-G. Initial collections of volatiles from virgin male and female CRB-G adults from the Solomon Islands failed to show any male- or female-specific compounds as candidate pheromone components. Only after five months were significant quantities of ethyl 4-methyloctanoate and 4-methyloctanoic acid produced by males but not by females. No other male-specific compounds could be detected, in particular methyl 4-methyloctanoate, 4-methyl-1-octanol, or 4-methyl-1-octyl acetate, compounds identified in volatiles from some other species of Oryctes. Ethyl 4-methyloctanoate elicited a strong electroantennogram response from both male and female CRB-G, but these other compounds, including 4-methyloctanoic acid, did not. The enantiomers of ethyl 4-methyloctanoate and 4-methyloctanoic acid were conveniently prepared by enzymatic resolution of the commercially-available acid, and the enantiomers of the acid, but not the ester, could be separated by gas chromatography on an enantioselective cyclodextrin phase. Using this approach, both ethyl 4-methyloctanoate and 4-methyloctanoic acid produced by male CRB-G were shown to be exclusively the (R)-enantiomers whereas previous reports had suggested male O. rhinoceros produced the (S)-enantiomers. However, re-examination of the ester and acid produced by male CRB-S from Papua New Guinea showed that these were also the (R)-enantiomers. In field trapping experiments carried out in the Solomon Islands, both racemic and ethyl (R)-4-methyloctanoate were highly attractive to both male and female CRB-G beetles. The (S)-enantiomer and the corresponding acids were only weakly attractive. The addition of racemic 4-methyloctanoic acid to ethyl 4-methyloctanoate did significantly increase attractiveness, but the addition of (R)- or (S)-4-methyloctanoic acid to the corresponding ethyl esters did not. Possible reasons for the difference in assignment of configuration of the components of the CRB pheromone are discussed along with the practical implications of these results.

Effects of electric field on pool boiling heat transfer over microstructured surfaces under different liquid subcoolings

• The smooth surface's CHF enhancement by electric field ranges from 15.2% to 22.5%. • Microstructured surfaces’ CHF increment by electric field ranges from −3.9% to 19.2%. • The CHF of PF50-60 is decreased by the electric field at ΔTsub = 25 and 35 K. • The increase of CHF by electric field is closely related to the field trap effect. The uniform electric field is an effective method to improve boiling heat transfer performances, especially via breaking the mushroom bubbles and preventing dry-out; microstructured surfaces remarkably enhance both heat transfer coefficients and critical heat flux in boiling process. In the present study, the coupling effect of a uniform electric field and the microstructured surfaces on pool boiling in FC-72 at the liquid subcoolings (Δ T sub ) of 5 K, 15 K, 25 K, and 35 K was studied. Four kinds of the microstructured surfaces with different sizes of micro-pin-fins were fabricated and tested, and compared with a reference smooth surface. It was found that the critical heat flux (CHF) enhancement of the smooth surface due to the electric field ranges from 15.2% to 22.5% and increases with liquid subcooling. For the microstructured surfaces, the effects of electric field on CHF are closely related to the liquid subcooling and size of micro-pin-fins. For the surfaces with fin width of 30 μm, the increase of CHF due to the electric field is not sensitive to the liquid subcooling; rather, for the surfaces with fin width of 50 μm, the electric field CHF enhancement decreases with the liquid subcooling. The enhancement of CHF due to the electric field can be explained by the competition of a reduction of the Taylor length and the break of the vapor layer (beneficial to the CHF enhancement) and the field trap effect (not conducive to CHF improvement). The field trap effect on the surface with fin width of 50 μm becomes very strong at Δ T sub = 25 and 35 K; as a result, under these two conditions the CHF is reduced under the action of the electric field.

Numerical Study on Ring-shape Superconducting Trapped Field Magnet Based on Circuit Model

The so-called ring-shape superconducting trapped field magnet has been proved as a potential candidate to replace commercial permanent magnets in practical industrial applications on account of its jointless structure. In this paper, a circuit method based on Bean model, E-J power law and Faraday law has been built to investigate the magnetization mechanism of ring-shape magnet. The field dependent critical current of superconducting materials has been taken into consideration for further optimization. The numerical model was verified by both finite element method (FEM) and experiments. Compared with other methods, the circuit-based simulation method has the advantages of high efficiency, fast speed and wide applicability. On basis of this method, the paper also studied characteristics of ring-shape magnets under different working conditions to provide a guideline for the magnet design.

3D-Printed Replica and Porcine Explants for Pre-Clinical Optimization of Endoscopic Tumor Treatment by Magnetic Targeting.

Simple SummaryAnimal models are often needed in cancer research but some research questions may be answered with other models, e.g., 3D replicas of patient-specific data, as these mirror the anatomy in more detail. We, therefore, developed a simple eight-step process to fabricate a 3D replica from computer tomography (CT) data using solely open access software and described the method in detail. For evaluation, we performed experiments regarding endoscopic tumor treatment with magnetic nanoparticles by magnetic hyperthermia and local drug release. For this, the magnetic nanoparticles need to be accumulated at the tumor site via a magnetic field trap. Using the developed eight-step process, we printed a replica of a locally advanced pancreatic cancer and used it to find the best position for the magnetic field trap. In addition, we described a method to hold these magnetic field traps stably in place. The results are highly important for the development of endoscopic tumor treatment with magnetic nanoparticles as the handling and the stable positioning of the magnetic field trap at the stomach wall in close proximity to the pancreatic tumor could be defined and practiced. Finally, the detailed description of the workflow and use of open access software allows for a wide range of possible uses.Background: Animal models have limitations in cancer research, especially regarding anatomy-specific questions. An example is the exact endoscopic placement of magnetic field traps for the targeting of therapeutic nanoparticles. Three-dimensional-printed human replicas may be used to overcome these pitfalls. Methods: We developed a transparent method to fabricate a patient-specific replica, allowing for a broad scope of application. As an example, we then additively manufactured the relevant organs of a patient with locally advanced pancreatic ductal adenocarcinoma. We performed experimental design investigations for a magnetic field trap and explored the best fixation methods on an explanted porcine stomach wall. Results: We describe in detail the eight-step development of a 3D replica from CT data. To guide further users in their decisions, a morphologic box was created. Endoscopies were performed on the replica and the resulting magnetic field was investigated. The best fixation method to hold the magnetic field traps stably in place was the fixation of loops at the stomach wall with endoscopic single-use clips. Conclusions: Using only open access software, the developed method may be used for a variety of cancer-related research questions. A detailed description of the workflow allows one to produce a 3D replica for research or training purposes at low costs.

Reverse chemical ecology guides the screening for Grapholita molesta pheromone synergists.

Pheromone-based management is a leading nonpesticidal strategy among integrated pest management options. Improving the potency of pheromone products by adding synergists would be a practical way to popularize pheromone-based management as well as to reduce pesticide use. Using reverse chemical ecology, synergists for Grapholita molesta sex pheromone were screened. Combined molecular docking and in vitro binding assay led to the determination of four potentially active odorants showing high affinity to G. molesta pheromone binding protein 2 (GmolPBP2). Thereafter, the high affinity between Codlemone and GmolPBP2 was further verified by exploration of GmolPBP2-Codlemone interactions. As the only sex pheromone synergist validated by both laboratory behavioral tests and field trapping, Codlemone was used to optimize commercial sex attractants currently used in G. molesta control. The recommended formulation [(Z)-8-dodecenyl acetate:(E)-8-dodecenyl acetate:Codlemone=95:4:10] was found to trap about five to six times more G. molesta adults than the commercial sex attractant [(Z)-8-dodecenyl acetate:(E)-8-dodecenyl acetate: (Z)-8-dodecenol=95:4:1]. Codlemone is an excellent pheromone synergist that can be potentially sensed by GmolPBP2, which can remarkably improve the potency of G. molesta sex attractants. It is believed that the introduction of reverse chemical ecology would increase the chance of discovering pheromone synergists, promoting the development of more efficacious pheromone products that can be used in controlling G. molesta and beyond. © 2021 Society of Chemical Industry.

Focusing properties of power order space-variant phase modulate Bessel-Gaussian vortex beam

The purpose of this paper is to study the focusing properties of power order space-variant phase modulate the Bessel-Gaussian (BG) vortex beam, which is based on vector diffraction theory. Results show that under different power order of space-variant phase, the modulation of topological charge number and phase parameter have different evolution rules. Specifically, when power order n = 1, the position of the focal pattern will be arbitrarily adjusted on the X-axis by modulating the phase parameter C. Under the condition of n = 2, the focal spot will be expanded along y = -x with the increase of topological charge l. Meanwhile, by modulating C, two opposite phenomena of focal spot separation will be obtained. When n = 3, the increase of l will make the focal spot expand along the positive and negative directions of the Y-axis. Besides, increasing the value of C, the original focal spot intensity will converge to the X-axis, and a new intensity peak will be formed on the X-axis. A series of focal properties have been obtained as the power order space-variant phase introduced. These novel properties have potential applications in many fields such as particle trapping, particle movement and optical modulation related fields.

Stochastic Hopf bifurcations in vacuum optical tweezers

The forces acting on an isotropic microsphere in optical tweezers are effectively conservative. However, reductions in the symmetry of the particle or trapping field can break this condition. Here we theoretically analyze the motion of a particle in a linearly nonconservative optical vacuum trap, concentrating on the case where symmetry is broken by optical birefringence, causing nonconservative coupling between rotational and translational degrees of freedom. Neglecting thermal fluctuations, we first show that the underlying deterministic motion can exhibit a Hopf bifurcation in which the trapping point destabilizes and limit cycles emerge whose amplitude grows with decreasing viscosity. When fluctuations are included, the bifurcation of the underlying deterministic system is expressed as a transition in the statistical description of the motion. For high viscosities, the probability distribution is normal, with a kurtosis of three, and persistent probability currents swirl around the stable trapping point. As the bifurcation is approached, the distribution and currents spread out in phase space. Following the bifurcation, the probability distribution function hollows out, reflecting the underlying limit cycle, and the kurtosis halves abruptly. The system is seen to be a noisy self-sustained oscillator featuring a highly uneven limit cycle. A variety of applications, from autonomous stochastic resonance to synchronization, is discussed.

Modelling higher trapped fields by pulsed field magnetisation of composite bulk MgB2 superconducting rings

The recent results of Hirano et al (2020 Supercond. Sci. Technol. 33 085002) reported a high trapped field of 1.61 T in a composite MgB2 ring comprising copper plates and and a soft iron yoke magnetised by pulsed field magnetisation (PFM). Inspired by these results, an investigation using systematic modelling methods was conducted to investigate the key parameters leading to the success of Hirano et al. Our results indicate that composite structures of MgB2 rings present a viable method of trapping high magnetic fields when magnetised with PFM. Leveraging a finite element method modelling framework with a commercial software package (COMSOL Multiphysics), we have successfully modelled the experimental data with excellent agreement. We have paid careful attention to the assumptions regarding the thermal physics, which enabled the successful and accurate modelling of the experiment. Exploiting the flexibility of computational modelling, we extend our studies to investigate the influence of the constituent elements of the composite bulk on the electromagnetic and thermal behaviour, and discuss in detail how each can enhance the trapped field performance of the bulk. Aided by the models, it is shown how the number of copper layers influences the elongation of the applied pulse, reducing the field penetration and the maximum temperature rise of the bulk. The addition of the iron yoke significantly increases the trapped field, by concentrating flux during and after the pulse.

Modelling of the pulsed field magnetisation of a REBaCuO bulk with a superconducting weld

The Pulsed Field Magnetization (PFM) is a compact and fast method to magnetize superconducting bulks compared to quasi-static magnetization methods like field- or zero-field-cooling. However, the heat generation induced by the strong applied variable magnetic field during the PFM makes high trapped magnetic field harder to achieve. In order to make the REBaCuO bulks easier to magnetize by PFM, superconducting bulks including a superconducting weld are studied by considering the electromagnetic properties of the weld different from those of the bulk body. This artificial grain boundary obtained by superconducting welding method might increase the trapped magnetic flux without increasing the applied magnetic field. In this paper, we are modelling the superconducting weld behavior during PFM using a 3D finite element model with the software COMSOL Multiphysics. The simulations are based on an H-formulation from Maxwell’s equations and the heat diffusion equation. We analyse the impact of the critical current Jc of the weld on the trapped magnetic field.

Magnetic levitation force and trapped field properties of multiseeded YBCO with triangular arrangement of seeds

AbstractAlthough there are studies in literature using different number of seeds with different arrangements, especially line and rectangular, it is seen that there is no detailed study handling the levitation force together with trapped field properties of triangular arrangement of seed in YBCO. Therefore, to further investigate the magnetic properties of seeded YBCO superconductors, we have fabricated cylindrical YBCO (YBa2Cu3O7) superconductors with triangular arrangement of the seeds with different seed distances. Maximum levitation force values were obtained as 39.4 N and 57.1 N, while the maximum guidance force values were obtained as −4.6 N, and −8.7 N, respectively, with single‐seeded and triangular‐seeded samples with seed distance of 14 mm. It was determined that the trapped field, levitation force, and guidance force firstly decreased from the single‐seeded sample to the triangular‐seeded sample with small seed distance and then increased with increasing seed distance. Increased field trapping and levitation force performances in the triangular‐seeded samples with suitable seed distance indicate that the triangular arrangement of seeds is an eligible method to produce larger dimension YBCO samples with bigger shielding current radius and bigger averaged trapped field values.

Attraction of Sitophilus zeamais (Coleoptera: Curculionidae) to Four Host Plants

The maize weevil Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) is an important pest of stored grains, predominantly maize (Zea mays L.), wheat (Triticum L. spp.), rice (Oryza L. spp.), and sorghum (Sorghum bicolor [L.] Moench) (all Poaceae). Weevil infestations occur in the field and weevils are carried to the storage facility after harvest. Infestation also occurs in the grain storage facility. There is no effective field or storage trapping system for control. They are commonly parasitized by Pteromalidae Dalman (Hymenoptera: Chalcidoidea) spp. parasitoids in the Tropics; however, there is no biocontrol use of these Hymenoptera. Therefore, pesticide application and the development of resistant grain are the current control strategies; although, studies have indicated that odors associated with the grain upon which the weevils feed, mate, and oviposit are attractive to the weevil. Host plant produced volatiles and their associations with the maize weevil have not been investigated fully. To better understand the weevil's attraction to crop plants, a study was initiated to investigate the weevil's preference for immature host plants. Weevils that had been reared on 4 types of grain for several generations were presented immature plants of all 4 types of grains in choice tests to determine if they prefer grains of the host plant on which they had been reared. This research demonstrated that immature rice plants have the greatest attraction, and that previous feeding did not influence the weevil's host plant attraction. The isolation of key rice plant semiochemicals will be the focus in the development of an attractant for S. zeamais and may also prove effective for the control of Sitophilus oryzae (L.) (Coleoptera: Curculionidae).

Transparent qubit manipulations with spin-orbit coupled two-electron nanowire quantum dot

We report on the first set of exact orthonormalized states to an ac driven one-dimensional (1D) two-electron nanowire quantum dot with the Rashba–Dresselhaus coexisted spin-orbit coupling (SOC) and the controlled magnetic field orientation and trapping frequency. In the ground state case, it is shown that the spatiotemporal evolutions of probability densities occupying internal spin states and the transfer rates between different spin states can be adjusted by the ac electric field and the intensities of SOC and magnetic field. Effects of the system parameters and initial-state-dependent constants on the mean entanglement are revealed, where the approximately maximal entanglement associated with the stronger SOC and its insensitivity to the initial and parametric perturbations are demonstrated numerically. A novel resonance transition mechanism is found, in which the ladder-like time-evolution process of expected energy and the transition time between two arbitrary exact states are controlled by the ac field strength. Using such maximally entangled exact states to encode qubits can render the qubit control more transparent and robust. The results could be extended to 2D case and to an array of two-electron quantum dots with weak neighboring coupling for quantum information processing.

Complex pulse magnetization process and mechanical properties of spark plasma sintered bulk MgB2

High-density MgB2 bulks with superior mechanical and superconducting properties were fabricated using spark plasma sintering (SPS). The sharp superconducting transition at 37.5 K proved high quality of the superconductors. Critical current density significantly exceeded that of conventionally sintered bulks. Flux pinning diagrams indicated dominance of grain boundary pinning, with peak position at 0.2. SPS bulks showed improved mechanical properties with 8-times higher bending strength compared to dense hot isostatic pressed bulks. Trapped field was measured at 14 K and 20 K, 1 mm above the bulk’s surface, with applied pulse field up to 2 T. A local overheating together with a complex trapped field formation in the MgB2 bulks during pulse-field magnetization were studied to elucidate limitations of Pulse Field Magnetization.

Realization of compact hybrid trapped field magnet above 10 T with 7 T applied field

In this paper, Takahashi et al reported a successful case to reach this goal with a hybrid trapped field magnet (i.e. inner lens and outer cylinder trapped field magnet). The inner lens were cooled from room temperature to about 20 K in zero field cooling followed by applied field (e.g. 7 T) that the flux density will be concentrated to above 10 T. And in the same time the outer trapped field magnet will be field cooled from room temperature to about 20 K in this above 10 T field.

Influence of preforming pressure on the morphology and properties of single-grain Y–Ba–Cu–O superconductors by the 011-type infiltration growth technique

Using the 011-type infiltration growth (011-IG) technique, the influence of preforming pressure on the morphology and superconducting properties of the Y–Ba–Cu–O (YBCO) bulks was investigated. The solid preforms of composition Y2O3 + BaCuO2 (011) containing embedded NdBCO/YBCO/MgO film seed were pressed at different pressures (100 MPa, 200 MPa and 300 MPa). The results indicate that, YBCO single grains can be successfully grown for these pressures. But some macro-defects (such as pores, cracks) were observed on the surface of the samples pressed at 300 MPa. Superconducting property measurements prove that, the 200 MPa pressed sample shows significantly enhanced levitation force and trapped field properties than the 100 MPa pressed sample, indicating that the preforming pressure is a very critical factor for appearance of high bulk performance. While three 300 MPa pressed samples exhibit rather varying properties related to their macro-defects. Magnetization measurements show that, the preforming pressure has no effect on the onset Tc of the samples, and the samples pressed at 200 MPa and 300 MPa display comparable Jc properties, which are both higher than that of 100 MPa pressed sample. Taking into account both of the sample morphology and the bulk property, the preforming pressure of 200 MPa can be considered as an optimum condition for steadily fabricating macro-defect-free YBCO single grains with excellent trapped field and levitation force properties, when a conventional mould for pressing cylindrical pellet is used.

Tetranorsesquiterpenoids as Attractants of Yucca Moths to Yucca Flowers.

The obligate pollination mutualism between Yucca and yucca moths is a classical example of coevolution. Oviposition and active pollination by female yucca moths occur at night when Yucca flowers are open and strongly scented. Thus, floral volatiles have been suggested as key sensory signals attracting yucca moths to their host plants, but no bioactive compounds have yet been identified. In this study, we showed that both sexes of the pollinator moth Tegeticula yuccasella are attracted to the floral scent of the host Yucca filamentosa. Chemical analysis of the floral headspace from six Yucca species in sections Chaenocarpa and Sarcocarpa revealed a set of novel tetranorsesquiterpenoids putatively derived from (E)-4,8-dimethyl-1,3,7-nonatriene. Their structure elucidation was accomplished by NMR analysis of the crude floral scent sample of Yucca treculeana along with GC/MS analysis and confirmed by total synthesis. Since all these volatiles are included in the floral scent of Y. filamentosa, which has been an important model species for understanding the pollination mutualism, we name these compounds filamentolide, filamentol, filamental, and filamentone. Several of these compounds elicited antennal responses in pollinating (Tegeticula) and non-pollinating (Prodoxus) moth species upon stimulation in electrophysiological recordings. In addition, synthetic (Z)-filamentolide attracted significant numbers of both sexes of two associated Prodoxus species in a field trapping experiment. Highly specialized insect-plant interactions, such as obligate pollination mutualisms, are predicted to be maintained through "private channels" dictated by specific compounds. The identification of novel bioactive tetranorsesquiterpenoids is a first step in testing such a hypothesis in the Yucca-yucca moth interaction.

Shared and Distinct Brain Activation During Performance of Working Memory Tasks in Adult Patients With Schizophrenia and Major Depressive Disorder

Using the 011-type infiltration growth (011-IG) technique, the influence of preforming pressure on the morphology and superconducting properties of the Y–Ba–Cu–O (YBCO) bulks was investigated. The solid preforms of composition Y2O3 + BaCuO2 (011) containing embedded NdBCO/YBCO/MgO film seed were pressed at different pressures (100 MPa, 200 MPa and 300 MPa). The results indicate that, YBCO single grains can be successfully grown for these pressures. But some macro-defects (such as pores, cracks) were observed on the surface of the samples pressed at 300 MPa. Superconducting property measurements prove that, the 200 MPa pressed sample shows significantly enhanced levitation force and trapped field properties than the 100 MPa pressed sample, indicating that the preforming pressure is a very critical factor for appearance of high bulk performance. While three 300 MPa pressed samples exhibit rather varying properties related to their macro-defects. Magnetization measurements show that, the preforming pressure has no effect on the onset Tc of the samples, and the samples pressed at 200 MPa and 300 MPa display comparable Jc properties, which are both higher than that of 100 MPa pressed sample. Taking into account both of the sample morphology and the bulk property, the preforming pressure of 200 MPa can be considered as an optimum condition for steadily fabricating macro-defect-free YBCO single grains with excellent trapped field and levitation force properties, when a conventional mould for pressing cylindrical pellet is used.