The dissolution and precipitation behaviours of M
7
C
3
and M
23
C
6
carbides in 8Cr13MoV steel were calculated using Thermo-Calc software. The mechanical properties of carbides were calculated using ...the Vienna Ab-initio Simulation Package. Results showed that M
7
C
3
carbides were ductile and M
23
C
6
carbides were brittle. High holding temperature provided favourable conditions for M
7
C
3
carbides to precipitate and promoted the dissolution of bulky M
23
C
6
carbides. Two heat treatment sequences were designed. During aging treatment, dispersive rodlike nanoscale M
7
C
3
carbides precipitated from matrix, which improved wear resistance and the retention ability of the cutting edge of knives by 56 and 22%, respectively.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Indirect methods to monitor the surface integrity of grinding wheels by acoustic emission (AE) have been proposed, aiming to ensure their optimal performance. However, the time-frequency analysis of ...the content of these signals has not been addressed in the literature. AE signal analysis performed only in the frequency domain makes it impossible to locate faults on the grinding wheel surface during the dressing operation and examine the behavior of the frequencies contained in these signals over time. In this regard, the time-frequency analysis of AE signals during dressing through STFT (short-time Fourier transform) can contribute toward the proposal of new monitoring methodologies, thus reflecting the optimization of the grinding process. This paper proposes an algorithm based on the Kaiser window to adjust the STFT parameters to ensure an appropriate balance between time-frequency resolutions. Besides, this algorithm is used to investigate the characteristic frequencies in the aluminum oxide grinding wheel in dressing operation. The results indicate that the spectral content of the AE signals during dressing follows a uniform behavior, but their amplitude changes depending on the characteristics of topography and sharpness of the grinding wheel cutting edges.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Purpose
To achieve 3D T2w imaging of the prostate with 1‐mm isotropic resolution in less than 3 min.
Methods
We devised and implemented a 3D T2‐prepared multishot balanced steady state free ...precession (T2prep‐bSSFP) acquisition sequence with a variable density undersampled trajectory combined with a total variation regularized iterative SENSE (TV‐SENSE) reconstruction. Prospectively undersampled images of the prostate (acceleration factor R = 3) were acquired in 11 healthy subjects in an institutional review board‐approved study. Image quality metrics (subjective signal‐to‐noise ratio, contrast, sharpness, and overall prostate image quality) were evaluated by 2 radiologists. Scores of the proposed accelerated sequence were compared using the Wilcoxon signed‐rank and Kruskal‐Wallis non‐parametric tests to prostate images acquired using a fully sampled 3D T2prep‐bSSFP acquisition, and with clinical standard 2D and 3D turbo spin echo (TSE) T2w acquisitions. A P‐value < 0.05 was considered significant.
Results
The 3× accelerated 3D T2prep‐bSSFP images required a scan time (min:s) of 2:45, while the fully sampled 3D T2prep‐bSSFP and clinical standard 3D TSE images were acquired in 8:23 and 7:29, respectively. Image quality scores (contrast, sharpness, and overall prostate image quality) of the accelerated 3D T2prep‐bSSFP, fully sampled T2prep‐bSSFP, and clinical standard 3D TSE acquisitions along all 3 spatial dimensions were not significantly different (P > 0.05).
Conclusion
3D T2w images of the prostate with 1‐mm isotropic resolution can be acquired in less than 3 min, with image quality that is comparable to a clinical standard 3D TSE sequence but only takes a third of the acquisition time.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Absolute pitch (AP), the ability of some musicians to precisely identify and name musical tones in isolation, is associated with a number of gross morphological changes in the brain, but the ...fundamental neural mechanisms underlying this ability have not been clear. We presented a series of logarithmic frequency sweeps to age- and sex-matched groups of musicians with or without AP and controls without musical training. We used fMRI and population receptive field (pRF) modeling to measure the responses in the auditory cortex in 61 human subjects. The tuning response of each fMRI voxel was characterized as Gaussian, with independent center frequency and bandwidth parameters. We identified three distinct tonotopic maps, corresponding to primary (A1), rostral (R), and rostral-temporal (RT) regions of auditory cortex. We initially hypothesized that AP abilities might manifest in sharper tuning in the auditory cortex. However, we observed that AP subjects had larger cortical area, with the increased area primarily devoted to broader frequency tuning. We observed anatomically that A1, R and RT were significantly larger in AP musicians than in non-AP musicians or control subjects, which did not differ significantly from each other. The increased cortical area in AP in areas A1 and R were primarily low frequency and broadly tuned, whereas the distribution of responses in area RT did not differ significantly. We conclude that AP abilities are associated with increased early auditory cortical area devoted to broad-frequency tuning and likely exploit increased ensemble encoding.
Absolute pitch (AP), the ability of some musicians to precisely identify and name musical tones in isolation, is associated with a number of gross morphological changes in the brain, but the fundamental neural mechanisms have not been clear. Our study shows that AP musicians have significantly larger volume in early auditory cortex than non-AP musicians and non-musician controls and that this increased volume is primarily devoted to broad-frequency tuning. We conclude that AP musicians are likely able to exploit increased ensemble representations to encode and identify frequency.
Aims.
The response of a protoplanetary disk to luminosity bursts of various durations is studied with the purpose to determine the effect of the bursts on the strength and sustainability of ...gravitational instability in the disk. A special emphasis is paid to the spatial distribution of gas and grown dust (from 1 mm to a few centimetres) during and after the burst.
Methods.
Numerical hydrodynamics simulations were employed to study the dynamics of gas and dust in the thin-disk limit. Dust-to-gas friction, including back reaction and dust growth, were also considered. Bursts of various durations (from 100 yr to 500 yr) were initiated in accordance with a thermally ignited magnetorotational instability. Luminosity curves for constant- and declining-magnitude bursts were adopted to represent two typical limiting cases for FU Orionis-type eruptions.
Results.
The short-term effect of the burst is to reduce the strength of gravitational instability by heating and expanding the disk. The longest bursts with durations comparable to the revolution period of the spiral can completely dissolve the original two-armed spiral pattern in the gas disk by the end of the burst, while the shortest bursts only weaken the spiral pattern. The reaction of grown dust to the burst is somewhat different. The spiral-like initial distribution with deep cavities in the inter-armed regions transforms into a ring-like distribution with deep gaps. This transformation is mostly expressed for the longest-duration bursts. The long-term effect of the burst depends on the initial disk conditions at the onset of the burst. In some cases, vigorous disk fragmentation sets in several thousands of years after the burst, which was absent in the model without the burst. Several clumps with masses in the giant-planet mass range form in the outer disk regions. After the disk fragmentation phase, the spatial distribution of grown dust is characterized by multiple sharp rings located from tens to hundreds of astronomical units. The arrangement and sharpness of the rings depends on the strength of dust turbulent diffusion. The wide-orbit rings are likely formed as the result of dust-rich clump dispersal in the preceding gravitationally unstable phase.
Conclusions.
Luminosity bursts similar in magnitude to FU Orionis-type eruptions can have a profound effect on the dynamics of gas and dust in protoplanetary disks if the burst duration is comparable to, or longer than, the dynamical timescales. In this context, the spatial morphology of the gas-dust disk of V883 Ori, a FU Orionis-like object that is thought to be in the outburst phase for more than a century with an unknown onset date, may be used as test case for the burst models considered in this work. The potential relation of the obtained ring structures to a variety of gaps and rings observed in T Tauri disks remains to be established.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
Sharpness metrics that use the whole frequency spectrum of the image cannot separate the sharpness information from the scene content. The sharpness metrics that use spatial gradients of the edges ...work only for comparisons among versions of the same image. We have developed a content independent, no-reference sharpness metric based on the local frequency spectrum around the image edges. In this approach, we create an edge profile by detecting edge pixels and assigning them to 8×8 pixel blocks. Then we compute sharpness using the average 2D kurtosis of the 8×8 DCT blocks. However, average kurtosis is highly sensitive to asymmetry in the DCT, e.g. different amounts of energy and edges in the x and y directions, therefore causing problems with different content and asymmetric sharpness enhancement. Thus we compensate the kurtosis using spatial edge extent information and the amount of vertical and horizontal energy in the DCT. The results show high correlation with subjective quality for sharpness-enhanced video and high potential to deal with asymmetric enhancement. For compressed, extremely sharpened and noisy video, the metric correlates with subjective scores up to the point where impairments become strongly noticeable in the subjective quality evaluation. The metric can be used by itself as a control variable for high-quality image capture and display systems, high-quality sharpness enhancement algorithms, and as a key component of a more general overall quality metric.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Τhe accuracy of template‐based neuroimaging investigations depends on the template's image quality and representativeness of the individuals under study. Yet a thorough, quantitative investigation of ...how available standardized and study‐specific T1‐weighted templates perform in studies on older adults has not been conducted. The purpose of this work was to construct a high‐quality standardized T1‐weighted template specifically designed for the older adult brain, and systematically compare the new template to several other standardized and study‐specific templates in terms of image quality, performance in spatial normalization of older adult data and detection of small inter‐group morphometric differences, and representativeness of the older adult brain. The new template was constructed with state‐of‐the‐art spatial normalization of high‐quality data from 222 older adults. It was shown that the new template (a) exhibited high image sharpness, (b) provided higher inter‐subject spatial normalization accuracy and (c) allowed detection of smaller inter‐group morphometric differences compared to other standardized templates, (d) had similar performance to that of study‐specific templates constructed with the same methodology, and (e) was highly representative of the older adult brain.
The purpose of this work was to construct a high‐quality standardized T1‐weighted template specifically designed for the older adult brain, and systematically compare the new template to several other standardized and study‐specific templates in terms of image quality, performance in spatial normalization of older adult data and detection of small inter‐group morphometric differences, and representativeness of the older adult brain. The new template was constructed with state‐of‐the‐art spatial normalization of high‐quality data from 222 older adults. It was shown that the new template a) exhibited high image sharpness, b) provided higher inter‐subject spatial normalization accuracy and c) allowed detection of smaller inter‐group morphometric differences compared to other standardized templates, d) had similar performance to that of study‐specific templates constructed with the same methodology, and e) was highly representative of the older adult brain.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A biocompatible Zr
54
Al
17
Co
29
bulk metallic glass (BMG) becomes a potential candidate for medical device materials due to its excellent properties; however, the effort to investigate the material ...performance in medical devices has never been attempted. Surgical blades were developed from Zr
54
Al
17
Co
29
BMG composition using different sizes of plates to address the microstructural variation. Their cutting abilities were investigated using a designed indentation-cutting rig for sharpness tests and compared to commercial carbon steel (CS) blades. While the fully amorphous structure was confirmed in a 2 mm BMG, the presence of nanocrystal phases was implied in the 3 mm BMG. The BMG blades showed extremely higher cutting-edge quality compared to the commercial ones. In addition, the sharpness improvement was shown in 2- and 3-mm BMG blades with the blade sharpness index (BSI) of 0.29 and 0.34 compared to commercial blade BSI of 0.37. The BMG blades also showed good durability indicated by the higher edge resistance from deformation. These phenomena were determined by the absence of grain boundary and dislocation of BMG thus performing a higher elastic strain than the crystalline material to avoid plastic deformation on the extremely small cross-sectional area of the cutting edge during substrate incision.
The significance of NR evaluation of picture sharpness, which is directly related to blur, is covered in this work. Algorithms for evaluating sharpness and blur are currently relied upon edge width, ...local gradients, or energy savings of global or local high frequency content. This research introduces a novel sharpness assessment technique without referring to the original picture and proposes an adaptable structure for LPC calculation in arbitrary fractional sizes. When measured against cutting-edge algorithms, the suggested approach performs admirably. This study concentrates upon the no-reference evaluation of picture sharpness, one of the key factors that determine perceived image quality and one that is influenced by a variety of visual aberrations. Perceptual sharpness measures may be used as design & optimisation criteria for developing picture enhancement, restoration, and compression algorithms as well as auto-focus systems based on visual perception. This extends application spectrum of perceptual sharpness measures over evaluating picture quality. The Local Phase Coherence (LPC) theory, which claims that complex wavelet coefficient phases demonstrate a continuous link throughout scales in the region of sharp image features, including edges and lines, is used in this study to analyse picture sharpness from a different angle. Numerous image distortions which impact perceived sharpness interfere with the LPC relationship, making our measure useful for evaluating sharpness. When used properly, picture sharpening may frequently enhance perceived image quality even more than switching to a high-end camera lens. It is a useful technique for highlighting texture and grabbing the viewer's attention.
Purpose
(1) To investigate the effect of internal localized movement on 3DMR intracranial vessel wall imaging and (2) to develop a novel motion‐compensation approach combining volumetric navigator ...(vNav) and self‐gating (SG) to simultaneously compensate for bulk and localized movements.
Methods
A 3D variable‐flip‐angle turbo spin‐echo (ie, SPACE) sequence was modified to incorporate vNav and SG modules. The SG signals from the center k‐space line are acquired at the beginning of each TR to detect localized motion‐affected TRs. The vNavs from low‐resolution 3D EPI are acquired to identify bulk head motion. Fifteen healthy subjects and 3 stroke patients were recruited in this study. Overall image quality (0‐poor to 4‐excellent) and vessel wall sharpness were compared among the scenarios with and without bulk and/or localized motion and/or the proposed compensation strategies.
Results
Localized motion reduced wall sharpness, which was significantly mitigated by SG (ie, outer boundary of basilar artery: 0.68 ± 0.27 vs 0.86 ± 0.17; P = .037). When motion occurred, the overall image quality and vessel wall sharpness obtained with vNav‐SG SPACE were significantly higher than those obtained with conventional SPACE (ie, basilarartery outer boundary sharpness: 0.73 ± 0.24 vs 0.94 ± 0.24; P = .033), yet comparable to those obtained in motion‐free scans (ie, basilarartery outer boundary sharpness: 0.94 ± 0.24 vs 0.96 ± 0.31; P = .815).
Conclusion
Localized movements can induce considerable artifacts in intracranial vessel wall imaging. The vNav‐SG approach is capable of compensating for both bulk and localized motions.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
You have reached the maximum number of search results that are displayed.
For better performance, the search offers a maximum of 1,000 results per query (or 50 pages if the option 10/page is selected).
Consider using result filters or changing the sort order to explore your results further.
PDF
