578 research outputs found
High flux table-top soft X-ray source driven by sub-2-cycle, CEP stable, 1.85 μm 1 kHz pulses for carbon K-edge spectroscopy
We report on the first table-top high flux source of coherent soft X-ray radiation up to 400 eV, operating at 1 kHz. This source
covers the carbon K-edge with a beam brilliance of (4.3 ± 1.2) × 1015 photons/s/mm2/strad/10% bandwidth and a photon
flux of (1.9 ± 0.1) × 107 photons/s/1% bandwidth. We use this source to demonstrate table-top X-ray near edge fine structure
spectroscopy at the carbon K-edge of a polyimide foil and retrieve the specific absorption features corresponding to the
binding orbitals of the carbon atoms in the foil.Peer ReviewedPostprint (author's final draft
A GPU-accelerated real-time NLMeans algorithm for denoising color video sequences
Abstract. The NLMeans filter, originally proposed by Buades et al., is a very popular filter for the removal of white Gaussian noise, due to its simplicity and excellent performance. The strength of this filter lies in exploiting the repetitive character of structures in images. However, to fully take advantage of the repetitivity a computationally extensive search for similar candidate blocks is indispensable. In previous work, we presented a number of algorithmic acceleration techniques for the NLMeans filter for still grayscale images. In this paper, we go one step further and incorporate both temporal information and color information into the NLMeans algorithm, in order to restore video sequences. Starting from our algorithmic acceleration techniques, we investigate how the NLMeans algorithm can be easily mapped onto recent parallel computing architectures. In particular, we consider the graphical processing unit (GPU), which is available on most recent computers. Our developments lead to a high-quality denoising filter that can process DVD-resolution video sequences in real-time on a mid-range GPU
Evolutionary history of Podarcis tiliguerta on Corsica and Sardinia.
BACKGROUND: Podarcis tiliguerta is a wall lizard endemic to the Mediterranean islands of Corsica and Sardinia. Previous findings of high mtDNA and morphological diversity have led to the suggestion that it may represent a species complex. Here, we analysed mitochondrial and nuclear markers (mtDNA, 3110 bp; 6 nDNA loci, 3961 bp) in P. tiliguerta sampled from thirty-two localities across Corsica and Sardinia. RESULTS: We find much greater intraspecific genetic divergence than between sister species of other Mediterranean island Podarcis, i.e., between P. lilfordi and P. pityusensis. We detected three mtDNA clusters in Corsica (North, South-East and South-West) and either two or three in Sardinia (North vs. South) depending on the clustering method. Only one or two nDNA groups were identified within each main island (again, depending on the method). A Bayesian time-calibrated multispecies coalescent tree was obtained from mtDNA and provided statistical support for a Miocene origin of the species (13.87 Ma, 95% HPD: 18.30-10.77 Ma). The posterior mean divergence time for the Corsican and Sardinian lineages was 12.75 Ma ago (95% HPD: 16.94-9.04 Ma). CONCLUSION: The results support the evolutionary distinctiveness of Corsican and Sardinian populations and also indicate a lack of post-divergence migration despite periods of contact being possible. Further to this, species delimitation analyses of Corsican and Sardinian lineages provided statistical support for their recognition as distinct (sister) taxa. Our results provide new insights into the biogeography of the Mediterranean biodiversity hotspot, and contribute important findings relevant to the systematics and evolution of this speciose lizard genus
Four-dimensional Cone Beam CT Reconstruction and Enhancement using a Temporal Non-Local Means Method
Four-dimensional Cone Beam Computed Tomography (4D-CBCT) has been developed
to provide respiratory phase resolved volumetric imaging in image guided
radiation therapy (IGRT). Inadequate number of projections in each phase bin
results in low quality 4D-CBCT images with obvious streaking artifacts. In this
work, we propose two novel 4D-CBCT algorithms: an iterative reconstruction
algorithm and an enhancement algorithm, utilizing a temporal nonlocal means
(TNLM) method. We define a TNLM energy term for a given set of 4D-CBCT images.
Minimization of this term favors those 4D-CBCT images such that any anatomical
features at one spatial point at one phase can be found in a nearby spatial
point at neighboring phases. 4D-CBCT reconstruction is achieved by minimizing a
total energy containing a data fidelity term and the TNLM energy term. As for
the image enhancement, 4D-CBCT images generated by the FDK algorithm are
enhanced by minimizing the TNLM function while keeping the enhanced images
close to the FDK results. A forward-backward splitting algorithm and a
Gauss-Jacobi iteration method are employed to solve the problems. The
algorithms are implemented on GPU to achieve a high computational efficiency.
The reconstruction algorithm and the enhancement algorithm generate visually
similar 4D-CBCT images, both better than the FDK results. Quantitative
evaluations indicate that, compared with the FDK results, our reconstruction
method improves contrast-to-noise-ratio (CNR) by a factor of 2.56~3.13 and our
enhancement method increases the CNR by 2.75~3.33 times. The enhancement method
also removes over 80% of the streak artifacts from the FDK results. The total
computation time is ~460 sec for the reconstruction algorithm and ~610 sec for
the enhancement algorithm on an NVIDIA Tesla C1060 GPU card.Comment: 20 pages, 3 figures, 2 table
The meaning of aggression varies across culture : testing the measurement invariance of the Refined Aggression Questionnaire in samples from Spain, the US, and Hong Kong
Cultural differences in aggression are still poorly understood. The purpose of this article is to assess whether a tool for measuring aggression has the same meaning across cultures. Analyzing samples from Spain (n=262), US (n=344) and Hong-Kong (n=645), we used confirmatory factor analysis to investigate measurement invariance of the refined version of the Aggression-Questionnaire (Bryant & Smith, 2001). The measurement of aggression was more equivalent between the Chinese and Spanish versions than between these two and the American version. Aggression does not show invariance at the culture level. Cultural variables such as affective autonomy or individualism may influence the meaning of aggression. Aggressive behavior models can be improved by incorporating cultural variable
Slow-spin relaxation of a low-spin S = 1/2 FeIII carborane complex
In this communication, we report the first evidence of slow-spin relaxation of a low-spin FeIII carborane complex. Iron S=1/2 complexes showing such behaviour are specially appealing as qubits candidates because they fulfil some of the main requirements to reach long decoherence times: moderate magnetic anisotropy, small spin, metal element mainly with zero-nuclear spin and furthermore, large versatility to introduce chemical modifications
Publisher's Note: “Attosecond state-resolved carrier motion in quantum materials probed by soft x-ray XANES” [Appl. Phys Rev. 8, 011408 (2021)]
Recent developments in attosecond technology led to table-top x-ray spectroscopy in the soft x-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real-time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, and TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near-edge spectroscopy to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the element- and state-specificity at the transition metal L-edge of the quantum material allows us to unambiguously identify how and where the optical field influences charge carriers. This precision elucidates that the Ti:3d conduction band states are efficiently photo-doped to a density of 1.9 × 1021 cm−3. The light-field induces coherent motion of intra-band carriers across 38% of the first Brillouin zone. Lastly, we describe the prospects with such unambiguous real-time observation of carrier dynamics in specific bonding or anti-bonding states and speculate that such capability will bring unprecedented opportunities toward an engineered approach for designer materials with pre-defined properties and efficiency. Examples are composites of semiconductors and insulators like Si, Ge, SiO2, GaN, BN, and quantum materials like graphene, transition metal dichalcogens, or high-Tc superconductors like NbN or LaBaCuO. Exiting are prospects to scrutinize canonical questions in multi-body physics, such as whether the electrons or lattice trigger phase transitions
GPU-based Low-dose 4DCT Reconstruction via Temporal Non-local Means
Four-dimensional computed tomography (4DCT) has been widely used in cancer
radiotherapy for accurate target delineation and motion measurement for tumors
in thorax and upper abdomen areas. However, 4DCT simulation is associated with
much higher imaging dose than conventional CT simulation, which is a major
concern in its clinical application. Conventionally, each phase of 4DCT is
reconstructed independently using the filtered backprojection (FBP) algorithm.
The basic idea of our new algorithm is that, by utilizing the common
information among different phases, the input information required to
reconstruct image of high quality, and thus the imaging dose, can be reduced.
We proposed a temporal non-local means (TNLM) method to explore the inter-phase
similarity. All phases of the 4DCT images are reconstructed simultaneously by
minimizing a cost function consisting of a data fidelity term and a TNLM
regularization term. We utilized a forward-backward splitting algorithm and a
Gauss-Jacobi iteration method to efficiently solve the minimization problem.
The algorithm was also implemented on graphics processing unit (GPU) to achieve
a high computational speed. Our reconstruction algorithm has been tested on a
digital NCAT thorax phantom in three low dose scenarios. Our new algorithm
generates visually much better CT images containing less image noise and
streaking artifacts compared with the standard FBP algorithm. Quantitative
analysis shows that much higher contrast-to-noise ratio and signal-to-noise
ratio can be obtained using our algorithm. The total reconstruction time for
all 10 phases of a slice ranges from 90 to 140 seconds on an NVIDIA Tesla C1060
GPU card.Comment: 14 pages, 4 figures, and 2 tables, accepted by Med. Phy
First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data
Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of
continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a
fully coherent search, based on matched filtering, which uses the position and rotational parameters
obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto-
noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch
between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have
been developed, allowing a fully coherent search for gravitational waves from known pulsars over a
fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of
11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial
outliers, further studies show no significant evidence for the presence of a gravitational wave signal.
Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of
the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for
the first time. For an additional 3 targets, the median upper limit across the search bands is below the
spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried
out so far
Combinatorial Preconditioners and Multilevel Solvers for Problems in Computer Vision and Image Processing
- …